RU2472768C2 - Method of producing acrylic acid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: conducting heterogeneously catalysed gas-phase partial oxidation of at least one corresponding starting compound with three carbon atoms on catalysts in a solid aggregative state at high temperature with molecular oxygen enables to obtain a gaseous mixture of products containing acrylic acid, water vapour and secondary components; if necessary, temperature of said mixture is lowered by direct and/or indirect cooling, after which said mixture is fed into a condensation column equipped with efficiently separating elements, wherein said mixture rises by itself along said column with simultaneous flow of fractional condensation. Through a first side outlet, which lies above the point of feeding the gaseous mixture of reaction products into the condensation column, crude acrylic acid poor in water and secondary components is output from the condensation column as the end product; through a second liquid phase outlet lying above the first side outlet, acid water containing acrylic acid and secondary components is output from the condensation column; a residual gaseous mixture containing secondary components which boil at a lower temperature than water is output from the top part of the condensation column; still liquor which contains acrylic acid, as well as byproducts and secondary components which boil at higher temperature than acrylic acid are output the bottom of the condensation column; part of the amount of the collected acid water as it is and/or after cooling is returned into the condensation column as reflux, and crude acrylic acid is optionally subjected to additional treatment using at least another thermal separation method, and, if necessary, part of the amount of collected acid water is added to acrylic acid before additional crystallisation treatment, where acrylic acid contained in at least part of the amount acid water which is not returned into the condensation column is transferred from the acid water to an organic solvent through extraction carried out by said solvent, which is accompanied by formation of an organic extract containing acrylic acid, from which acrylic acid is further separated by stripping thereof with a first stripping gas, wherein the first stripping gas containing acrylic acid is returned into the condensation column, and/or acrylic acid contained in the first stripping gas is transferred into an aqueous solution of a metal hydroxide or the formed first stripping gas which contains acrylic acid is used as a second stripping gas in order to strip acrylic acid contained in the still liquor output from the condensation column, and wherein the formed second stripping gas containing acrylic acid is returned into the condensation column and/or acrylic acid contained in the second stripping gas is transferred into an aqueous solution of a metal hydroxide.

EFFECT: improved method.

21 cl, 6 ex

Description

The present invention relates to a method for producing acrylic acid, according to which, at an elevated temperature of a heterogeneously catalyzed gas-phase partial oxidation by molecular oxygen of at least one corresponding starting compound with three carbon atoms on solid state catalysts, a gas mixture of products containing acrylic is obtained acid, water vapor and side components, the temperature of this mixture, if necessary, reduce the put direct and / or indirect cooling, after which the said mixture is sent to a condensation column equipped with effectively separating elements, along which it independently rises while fractional condensation flows simultaneously, moreover, through the first side extraction located above the place of supply of the reaction gas mixture to the condensation column, crude acrylic acid, depleted in water and by-products, is withdrawn from the condensation column as a target product through the above Acid lateral extraction of the second (preferably lateral) extraction of the liquid phase from the condensation column leads to acidic water containing side components and acidic components, residual gas mixture containing side components that boil at atmospheric pressure at a lower temperature than water is removed from the top of the condensation column , bottoms containing acrylic acid are withdrawn from the bottom of the condensation column, as well as by-products and by-products that boil at atmospheric pressure at At a lower temperature than acrylic acid, a partial amount of acidic water taken as such and / or after cooling is returned to the condensation column as reflux, and the crude acrylic acid is subjected to additional purification by at least one other thermal separation method, if necessary.

Acrylic acid is an important intermediate, used, for example, to obtain polymer dispersions (if necessary also in the form of esters of acrylic acid with alkanols), as well as water-superabsorbing polymers.

Acrylic acid can be obtained, in particular, by carrying out at a higher temperature a heterogeneously catalyzed gas-phase partial oxidation of the corresponding starting compounds with three carbon atoms by molecular oxygen on solid state catalysts, and under these starting compounds primarily mean chemical compounds that can formally be obtained by reduction of acrylic acid (known starting compounds of this type are for example, propane, propylene, acrolein, propionic aldehyde and propionic acid, but they also mean, for example, compounds such as glycerin, acrylic acid from which can be obtained, for example, by heterogeneously catalyzed oxidative dehydration in the gas phase; see, for example , European patent application EP A 1710227, as well as international applications WO 06/114506 and WO 06/092272).

In this case, the aforementioned source gases are usually diluted with inert gases, for example, such as nitrogen, carbon dioxide, saturated hydrocarbons and / or water vapor, after which they are passed at elevated temperatures and, if necessary, at elevated pressure, in a mixture with molecular oxygen them through catalysts based on mixed metal oxides (for example, transition metals), subjecting oxidatively to a gas mixture of reaction products containing acrylic acid, water, as well as undesirable side effects products, for example, such as furfural, benzaldehyde, acetone, formaldehyde, maleic anhydride and the like, from which it is then necessary to isolate acrylic acid (to indicate by-products that are different from water vapor, inert dilution gases, as well as polymerization inhibitors usually added during implementation Acrylic acid recovery processes according to the present invention use the generic term “side components”).

In a heterogeneously catalyzed gas-phase partial oxidation of propionic aldehyde and / or propionic acid with molecular oxygen, at least partial oxidative dehydrogenation occurs.

From German patent applications DE A 19924533 and DE A 19924532, international application WO 01/77056, German patent applications DE A 10156016, DE A 10243625, DE A 10223058 and DE A 10235847, international applications WO 2004/035514 and WO 00 / 53560, as well as from German patent application DE A 10332758, methods are known for producing acrylic acid of the type indicated at the beginning of the description, according to which the main extraction of crude acrylic acid is carried out by fractional condensation of a gas mixture of heterogeneous catalyzed gas-phase partial oxidation products. The term "crude acrylic acid" is used to emphasize the fact that the first side selection does not mean pure acrylic acid, but a mixture in which, in addition to acrylic acid (its content in terms of the total weight, as a rule, is more than 50 or 60% of the mass., most often more than 70 or 80% of the mass., in many cases more than 90% of the mass. and often more than 95% of the mass or higher) there are water and side components, for example, such as lower aldehydes (for example, furfural , acrolein, benzaldehyde), lower carbon isloty (e.g., acetic acid, propionic acid, formic acid) and so on. In any case, the total content of water and side components in crude acrylic acid is less than the content of acrylic acid itself in it than in a gas mixture of products of gas-phase partial oxidation, and therefore it can be said that crude acrylic acid is depleted in the sum of these components compared with the specified gas mixture, although some of them may be present in crude acrylic acid in a relatively higher concentration.

The degree of purity of the crude acrylic acid emitted by the above methods is sometimes already high enough to be used for certain purposes, for example, to obtain etherification products or for the synthesis of polymers by radical polymerization. However, in many cases, the isolated crude acrylic acid is subjected to processing by at least one other thermal separation method to isolate more pure acrylic acid from it, which has a higher acrylic acid content (% by weight) compared to crude acrylic acid, and therefore , meets the requirements for the degree of purity used in the relevant field of acrylic acid.

At the same time, thermal separation methods are understood to mean processes in accordance with which, when energy is supplied or removed (usually thermal), at least a two-phase system is physically formed, and due to the temperature and concentration gradient existing between the phases, heat transfer and mass transfer take place, which ultimately determines the necessary separation and extraction.

Thermal separation methods are often implemented in distillation columns with effectively separating built-in elements, and at least the two material phases indicated above move in these columns, as a rule, towards each other (countercurrent). In many cases, one of the two material phases is a gaseous phase that moves in the distillation column, usually from the bottom up, while the other is a liquid phase that moves in the distillation column, usually from top to bottom. However, in principle, at least two material phases can be liquid (for example, in the case of extraction), respectively solid and liquid (for example, in the case of crystallization), or respectively, solid and gaseous (for example, in the case of adsorption).

An example of the practical embodiment of thermal separation methods, when at least one of the two material phases is liquid and the other is gaseous, is a rectification, according to which the vapor phase rising in the distillation column moves towards the descending liquid phase, as well as the reverse absorption process of desorption, in according to which the gas dissolved in the liquid phase is removed from it by reducing the pressure above the liquid phase, increasing its temperature and / or passing through it the gas phase, moreover, the latter case, desorption is also called steaming. In addition, the methods of thermal separation include absorption, according to which the gas rising in the distillation column moves, as a rule, in countercurrent with respect to at least one liquid descending absorbent, as well as fractional condensation of the gas mixture, which is accompanied by the formation of gas and liquid phases . A particularly suitable thermal separation method used for additional purification of crude acrylic acid is additional crystallization purification (crystallization).

A disadvantage of the known methods for the main separation of crude acrylic acid by fractional condensation of a gas mixture of products of a heterogeneously catalyzed gas-phase partial oxidation of at least one starting compound with three carbon atoms is the additional formation of so-called acidic water, in which acrylic acid and side components are present. The water content in acidic water, as a rule, is more than or equal to 50 wt. -%, often more than or equal to 60 wt. -%, in many cases, more than or equal to 70% of the mass. and often more than or equal to 80 wt. -%, moreover, under water, as a rule, is meant reaction water, as well as dilution water (water vapor used for the implementation of gas-phase partial oxidation as an inert dilution gas).

In addition to water, acidic by-products are present in acidic water, such as propionic acid, acetic acid and formic acid, as well as acrylic acid, and therefore the pH value of acidic water is less than 7 (the total content of acidic by-products which differ from acrylic acid in calculated on the mass of acidic water, as a rule, is less than or equal to 10% of the mass., in particular less than or equal to 5% of the mass.).

The content of acrylic acid in acidic water is usually in the range from 4 or 5% of the mass. up to 15% of the mass. and often makes up about 10% of the mass. The disadvantage of the methods for the main separation of acrylic acid from a gas mixture of products of heterogeneously catalyzed gas-phase partial oxidation, recommended in the above-cited prior art, is that all acid water containing acrylic acid not returned to the distillation column is sent to combustion (see, first of all, German applications for patent DE A 10243625 and DE A 10332758, as well as international application WO 2004/035514).

This circumstance should be considered as a disadvantage, since the burning of acidic water causes, for example, a decrease in the yield of acrylic acid as the target product.

Based on the aforementioned prior art, the present invention was based on the task of proposing an improved method for the production of acrylic acid, primarily characterized in that it allows for increased yields of acrylic acid without significantly reducing its purity.

The specified task according to the invention is solved by a method for producing acrylic acid, according to which by means of a heterogeneously catalyzed gas-phase partial oxidation by molecular oxygen of at least one corresponding starting compound with three carbon atoms on a solid state of aggregation, the catalysts obtain a gas mixture of products, containing acrylic acid, water vapor and side components, the temperature of the mixture when not the cost is reduced by direct cooling (i.e. cooling realized by direct contact with the coolant) and / or indirect cooling, after which the mixture is sent to a condensation column equipped with effectively separating elements, along which it independently rises while fractional condensation flows, moreover through the first side sampling, located above the feed point of the gas mixture of the reaction products into the condensation column, from the condensation column to lead-depleted water and secondary components crude acrylic acid as the target product, through the first side located above the second selected sampling of the liquid phase withdrawn from the condensing column containing the acrylic acid and the secondary components acidic water (preferably a second selection side; in this case, all embodiments of the method primarily relate specifically to lateral extraction of acidic water), the residual gas mixture containing side components that are boiled at atmospheric pressure at a lower temperature than water is withdrawn from the top of the condensation column, bottoms are removed from the cubic condensation column a liquid containing acrylic acid, as well as by-products and by-products boiling at a higher temperature than acrylic acid, a partial amount of acid water taken as t Acic and / or after cooling is returned to the condensation column as reflux, and the crude acrylic acid, if necessary, is subjected to further purification by at least one other thermal separation method, characterized in that the acrylic acid contained at least in part is not returned to the condensation column acidic water, is converted into an organic solvent by extraction carried out by this solvent, accompanied by the formation of acrylic acid-containing organic e a extract from which acrylic acid is subsequently isolated by at least one thermal separation method, the recovered acrylic acid being returned to a condensation column, sent for further purification of the crude acrylic acid and / or transferred to an aqueous metal hydroxide solution.

According to the invention, preferably at least 25% by weight, preferably at least 50% by weight, even better at least 75% by weight. and preferably, the entire amount of acidic water not returned to the condensation column is subjected to extraction and further processing according to the invention.

In order to realize the extraction required according to the invention, in principle, any known extraction equipment suitable for liquid extraction by liquid can be used. Such equipment should provide the ability to form a large phase interface and a fine distribution of the corresponding droplets in the continuous phase, as well as the ability to quickly and as completely as possible phase separation after the mass transfer.

In the simplest embodiment, a mixer (for example, a container with a stirrer or a static mixer) can be used as an extraction device in combination with a separator (for example, a settling tank). However, in principle, you can use any commonly used mixers. Examples of suitable mixers are disk mixers, paddle mixers, paddle mixers, frame mixers, plane paddle mixers, anchor mixers, propeller mixers, spiral mixers and multi-position impulse countercurrent mixers. Agitators can also be multi-tier, i.e. several mixing elements can be located on the same axis one above the other. Preferred is the use of bunker blade mixers. In principle, any conventional tank can be used as a settling tank. A horizontal settling tank is preferred. Such an extraction device can be operated continuously or periodically, and in the latter case, it is possible to refuse to use a settling tank and to carry out phase separation in a vessel with a mixer. The substance to be extracted passes into its absorbing phase in the mixer, while the separation of the corresponding phases by gravity occurs in the separator. In the case of a continuous mode, the efficiency of the separation of the product entering into the settling tank into the heavy and light phases can be improved by using built-in elements arranged transversely to the direction of flow. Furthermore, any commonly used built-in elements, for example perforated sheets, plates, nozzles and / or bulk materials, are suitable in principle. Preferred bulk materials are rings, spirals, saddles, Raschig rings, Intos rings, Poll rings, Burl saddles, Intalox saddles, Top-Pak materials and so on or wicker materials. Perforated sheets in combination with bulk materials are particularly preferred. A typical residence time in a settling tank is from 0.05 to 2 hours.

Several units connected to each other, including a mixer and a separator, form a cascade. The nodes of the cascade can be connected to each other to operate in countercurrent, forward flow or cross current mode.

The extraction carried out according to the invention from a production and technical point of view is expediently carried out in an extraction column equipped with effectively separating built-in elements. A relatively heavier phase is introduced into the extraction column from above, while a relatively lighter phase enters from below. These phases move countercurrently in the extraction column. Extraction columns are in principle similar to columns used for countercurrent distillation (rectification). Thus, extraction columns suitable for carrying out the extraction process of the invention may have a known design and comprise conventional built-in elements.

Extraction columns may be potentially suitable that operate with or without energy. Extraction columns with built-in elements in the form of nozzles (primarily structured, respectively ordered) and / or bulk materials can function with or without energy. Preferred bulk materials are rings, spirals, saddles, Raschig rings, Intos rings, Poll rings, Burl saddles, Intalox saddles, Top Pak materials and the like. Nozzles particularly suitable for extraction columns to be used according to the invention are, for example, products from Julius Montz GmbH (D-40705 Hilden), in particular such as the nozzle Montz-Pak B1-350. Preferably, perforated structured nozzles of special sheet steel are used. Packed columns with ordered packing are known to those skilled in the art and are described, for example, in Chem. - Ing. Tech., 58 (1986), Nr. 1, pp. 19-31, as well as in Technischen Rundschau Sulzer, 2/1979, p. 49 and the following (Gebruder Sulzer Aktiengesellschaft, CH-Winterthur). In addition, extraction columns with integrated plate-shaped elements are also suitable, with columns with pulsating mesh plates and columns equipped with cross-current mesh plates being distinguished. In the case of columns with pulsating mesh plates, both phases pass through through holes made in the plates, which, as a rule, have a round shape. The lighter phase during pulsation with an upward stroke passes through the openings of the mesh plate in the direction from the bottom up, the heavier phase during pulsation with an upward stroke passes through the corresponding holes in the direction from top to bottom. The Carr column also functions in a similar way, but in this case there is no pulsation of the liquid, and the mesh plates alternately move up and down. Pulsating mesh tray extraction columns are preferred. In contrast to similar columns, in the case of columns equipped with cross-flow mesh trays, the continuous phase flows from one tray to another through drain pipes, while the dispersed phase passes through the openings of the grid trays due to the density difference (the designations of mass transfer trays used in the present description are similar given in German patent application DE A 10332758).

For acid acid extraction according to the invention, as a rule, from 1 to 10 theoretical plates are sufficient. According to the invention, a theoretical plate (or theoretical stage) in the most general case means a unit volume of a distillation column with built-in elements providing efficient separation by thermal separation, which helps to concentrate the substance in accordance with thermodynamic equilibrium. Thus, the term “theoretical plate” is equally applicable to both extraction columns with mass transfer plates and extraction columns with nozzles and / or packed bodies.

If an extraction column is used to implement the method of the invention, it is advisable to supply a relatively heavier phase to the column by means of a distribution manifold located in its upper part, which ensures the most uniform distribution of this phase over the entire cross section of the column. The introduction of a relatively lighter phase into the column from a production and technical point of view is also expedient through the distribution manifold located at the bottom of the column. Accordingly, the lighter phase inside the column rises, while the heavier phase drops. If the lighter phase is dispersed (i.e., it is in the form of droplets), phase separation occurs at the top of the column, while in the case of dispersion of a heavier phase, phase separation occurs in the column cube. In both cases, the optimum diameter (largest longitudinal size) of the droplets is in the range of 1 to 10 mm, preferably 2 to 5 mm.

According to the invention, the extracting agent preferably has a higher boiling point compared to acrylic acid (respectively, at atmospheric pressure), since this, as a rule, facilitates the subsequent isolation of acrylic acid from the organic extract.

In this regard, it is highly likely that in accordance with the extraction carried out according to the invention, the organic solvent to be used as an extracting agent will have a significantly higher viscosity than water. In such a case, according to the invention, it is preferable that the organic extracting agent entering the extraction column be in the form of a dispersed phase, and acidic water in the form of a continuous phase [this promotes, for example, acceleration of mass transfer between both phases and allows to use more to achieve the same result. short columns; in addition, the extraction column made of special steel and the corresponding built-in elements are better wetted by the continuous aqueous phase, and the transport of the substance to be extracted from the continuous phase to the dispersed phase causes the latter to stabilize (its slight tendency to coalescence)]. In the case of using an organic extracting agent having a higher specific gravity than acidic water, this means that the extracting agent is fed and dispersed to the top of the column, and the resulting droplets of the extracting agent are lowered along the column. In the opposite case, that is, when using an extracting agent with a lower specific gravity than acidic water, the extracting agent is dispersed in the bottom of the column, and the resulting extractant droplets rise in the column. In the case of using extraction columns of the above types equipped with built-in elements in the form of nozzles, packed bodies and / or plates, the undispersed continuous phase should well wet such built-in elements, since otherwise the droplets of the dispersed phase will usually drain over their surface.

In the simplest embodiment, the organic extracting agent is fed through pipes, usually provided with round through holes located above the cross section of the column and extending along each of the corresponding lengths of the cross section of the extraction column, usually in the form of a circular cylinder, and the pipes usually have the same cross section ( a collection of such pipes is also called a distribution manifold). In the case of supplying the organic extracting agent to the top of the column, the round through holes face downwards, while when the extracting agent is fed into the cube of the column, the round through holes face up. The diameter (largest transverse dimension) of said through holes is usually from 1 to 10 mm, preferably from 3 to 6 mm, in many cases from 2 to 5 mm. Moreover, in a simple embodiment, the extracting agent can flow into the pipes of the distribution manifold and flow out of them through the through holes.

In principle, for the extraction of acidic water carried out according to the invention, stirring columns or centrifugal extractors can also be used. The use of columns with stirring allows for a good mutual phase contact. In a suitable production and technical embodiment, all the mixers of such a column are located on a common shaft. The column pipe at the walls is expediently equipped with stator rings. The shaft located, as a rule, in the middle, is typically equipped with working bodies, the design of which allows the stirrer to rotate between two corresponding stator rings. Such stirred columns include, for example, a column with rotating disks, a column with asymmetric rotating disks, a column of a Kuni design, or a QVF type extractor with mixing bodies. Centrifugal force is needed to mix and separate countercurrent phases moving in centrifugal extractors. The latter also contributes to the qualitative separation of the product of purification / extract in the event that both phases are prone to the formation of a stable emulsion. Examples of this type of apparatus are the Podbielnak extractor or the Westfalia separator.

An extraction device suitable for implementing the method of the invention is preferably made of 1.4571 steel. Other devices are also made from similar steel, which are designed to separate acrylic acid from a gas mixture of reaction products of heterogeneously catalyzed gas-phase partial oxidation.

The driving force for the separation of the extract and the purification product is the difference between the specific gravities (g / cm ³ ) of both liquid phases. The higher the specified difference, the more efficient the separation of phases occurs and an emulsion is formed to a lesser extent.

Thus, for the implementation of the extraction according to the invention, an organic solvent is preferably used whose specific gravity (kg / m ³ ) differs from the specific gravity of water (kg / m ³ ) ≥25 kg / m ³ , preferably ≥50 kg / m ³ (at used for pressure and temperature extraction). Moreover, the specified difference in the values of specific gravity, as a rule, ≤250, respectively ≤150 kg / m ³ .

In addition, in a favorable embodiment of the method of the invention, the dynamic viscosity of the organic extracting agent under extraction conditions is ≤100 mPa · s, preferably ≤50 mPa · s. In this case, the dynamic viscosity, as a rule, is ≥1 MPa · s. According to the invention, in a particularly favorable embodiment, the dynamic viscosity of the extracting agent is in the range from 2 to 10 MPa · s.

In addition, in accordance with the method of the invention, a relatively high surface tension at the interface between two fluid phases is preferable.

In view of the foregoing, extracting agents according to the invention suitable for the extraction of acidic water are, in particular, organic liquids whose boiling point at normal pressure (1 atmosphere) exceeds 150 ° C, respectively 160 ° C. Examples of such extractants are middle oil fractions of paraffin distillation, diphenyl ether, diphenyl or mixtures of these liquids, for example, such as a mixture containing from 70 to 75% of the mass. diphenyl ether and from 25 to 30% of the mass. diphenyl. It is also beneficial to use a mixture containing from 70 to 75% of the mass. diphenyl ether and from 25 to 30% of the mass. diphenyl, to which is added from 0.1 to 25% of the mass. o-dimethyl phthalate.

According to the invention, particularly preferred organic solvents used for the extraction of acidic water are esters of aliphatic or aromatic monocarboxylic or dicarboxylic acids (especially with two esterified carboxyl groups), the alcohol component of which contains 1-8 carbon atoms, while the acid component contains 5-20 carbon atoms. In a preferred embodiment, the alcohol component used for esterification contains only two or one hydroxyl group. Particularly preferred alcohol components are monoatomic (with one hydroxyl group) or diatomic (with two hydroxyl groups) alkanols. The amount of carbon atoms contained in the alcohol component (especially in the case of monatomic or diatomic alkanols) is preferably from 1 to 6, particularly preferably from 1 to 4, and even more preferably one or two. Aliphatic or aromatic monocarboxylic or dicarboxylic acids preferably contain from 5 to 15 carbon atoms, preferably from 5 to 10 carbon atoms, and particularly preferably from 6 to 8 carbon atoms (in this case, first of all, it is an esterification of acids with alkanols with 1-4 carbon atoms, respectively with one or two carbon atoms, including up to diesters). More preferred acid components of the corresponding esters are dicarboxylic acids (especially if both carboxyl groups are esterified) than monocarboxylic acids. According to the invention, even more preferred acidic components of the corresponding esters include phthalic acid, isophthalic acid, terephthalic acid and adipic acid. The latter primarily relates to dialkyl esters (alkyl with 1-8 carbon atoms, preferably with 1-6 carbon atoms, even more preferably with 1-4 carbon atoms, even better with one or two carbon atoms). Accordingly, the extraction agents, the most suitable for realization of the inventive process are dimethyl phthalate, diethyl phthalate (e.g., Palatinol ^® BASF company A Aktiengesellschaft), dimethyl isophthalate, diethyl isophthalate, dimethyl terephthalate, dietiltereftalat, dimethyl adipate and diethyl adipate.

Other esters suitable for performing acidic water extraction of the invention are phosphoric acid esters, such as, for example, tributyl phosphate or tricresyl phosphate. In this case, the corresponding crescent residues are derivatives of ortho-cresil, meta-cresil or para-cresil. In addition, extraction agents suitable for performing the acid water extraction proposed in the invention are esters based on acrylic acid and branched or unbranched monohydroxy alkanols with 6-12 carbon atoms (for example, 2-propylheptyl acrylate or 2-ethylhexyl acrylate), as well as complex monoesters and diesters based on maleic acid and monatomic alkanols with 4-10 carbon atoms. According to the invention, preferred of the above extracting agents are compounds whose boiling point at normal pressure exceeds 150 ° C, 160 ° C, 170 ° C, 180 ° C or 190 ° C.

Acid water to be extracted, in addition to acrylic acid and water, usually contains acetic acid as another component (in quantitative terms, acetic acid, as a rule, is the third component of acidic water). Depending on the conditions of partial oxidation (such as a catalyst, the content of water vapor in the mixture of reaction gases, process temperature), acidic water may contain up to 10 wt.%, Respectively, up to 5 wt. (often from 2 to 8% of the mass.) or more acetic acid. The mass ratio between the acrylic acid contained in acidic water and acetic acid is most often about 2: 1. The content of other acidic by-products that may be present in acidic water is usually much lower. In accordance with this, preferred according to the invention are extracting agents, mainly absorbing acrylic acid than acetic acid. Such extracting agents include, in particular, phthalic acid diethyl ester.

Also preferred according to the invention are extracting agents which, under extraction conditions, do not interact with water and have only insignificant solubility in water. Particularly high resistance to hydrolysis is characterized, for example, phthalic acid diethyl ester. Another advantage of phthalic acid diethyl ester is the relatively high boiling point of this compound at normal (atmospheric) pressure, which is ≥200 ° C, preferably ≥225 ° C and even better ≥250 ° C for the extractants (organic solvents) preferably used according to the invention .

In addition, phthalic acid diethyl ether has a relatively low solubility in water, which leads to a reduction in losses of this extractant. The temperature of the acidic water generated during the fractional condensation of the reaction product gas mixture according to the invention is typically from 50 to 80 ° C., preferably from 60 to 70 ° C. It is this temperature that the second (preferably lateral) selection of the liquid phase usually has (the lower the temperature, the less the need for a polymerization inhibitor, and in favorable cases there is no need for separate addition of the polymerization inhibitor to acidic water, extracting agent, purification product and / or extract) . In this regard, in an expediently industrial-technical aspect, the extraction is also performed in the above temperature range. Thus, the acidic water directed to the extraction device, which is preferably an extraction column (particularly preferably a packed column, preferably filled with a Montz-Pak B1-350 nozzle), according to the invention preferably has a temperature which advantageously corresponds to the above temperature range. Acidic water is preferably introduced into the lower part of the extraction column, while a relatively heavier extracting agent (preferably diethyl phthalate) is fed into its upper part. The temperature of the extractant sent to the extraction column usually does not differ too much from the temperature of the acidic water supplied to it. Typically, the difference in the respective temperatures is ≥0 and ≤20 ° C, preferably ≥0 and ≤15 ° C, and in many cases ≥0 and ≤10 ° C. According to the invention, the typical pressure of the acidic water taken from the condensation column at the point of extraction is more than 1 to 1.5 bar, often 2 bar. Acidic water taken from the condensation column is pumped to the extraction column. In this case, the discharge pressure can be, for example, from 2 to 6 bar. According to the invention, the working pressure in the extraction column is set so that there is no need to use an additional pump for transporting the organic extract to the first stripping column. In principle, acidic water extraction can also be carried out at higher or lower temperatures, as well as at higher or lower pressures. When starting the extraction column in the industrial-technical relation, it is advisable to first fill it with acidic water, and then proceed to supply, as indicated above, the organic extracting agent, preferably in the form of drops, to the top of the extraction column. The supply of acidic water (preferably a continuous phase) to the extraction column can, in principle, be carried out directly through the corresponding column fitting. In principle, acidic water can also be introduced into the extraction column through a feed pipe with one or more through holes in its walls (the diameter of the through holes in a typical case is from 5 to 10 mm).

As indicated above, in the industrial-technical relation it is advisable to use an extraction column made of special steel. Typical wall thickness is 5 to 20 mm. Such an extraction column is usually provided with external thermal insulation.

According to the method of the invention, the ratio V between the organic extracting agent stream (E, kg / h) directed to the extraction column and the acidic water stream (S, kg / h), i.e. the ratio E: S, can be in the range from 0.05: 1 to 20: 1, preferably from 0.1: 1 to 10: 1, preferably from 0.8: 1 to 1.2: 1, and in a particularly preferred embodiment, it is 1: 1.

Acidic acid-depleted (extracted) acidic water is usually sent for disposal (e.g., incineration or recycling in a sewage treatment plant). According to the invention, it is typically withdrawn from the top of the extraction column as a refined product, while the acrylic acid-containing organic extract is typically withdrawn from the extraction column from below.

The separation of acrylic acid from an organic extract, the selection temperature of which from the extraction column mainly corresponds to the temperature of the supply of acidic water to the extraction column, can in principle be carried out using different methods of thermal separation, as well as a combination of similar methods.

One suitable option for the isolation of acrylic acid is crystallization. In this case, the crystallization method recommended in German patent applications DE A 19838845 and DE A 102005015637 can be used. The advantage of the crystallization separation method is the possibility of more precise crystallization in comparison with other methods of thermal separation. That is, the composition of the crystals formed is largely independent (in the ideal case, does not depend at all) on the composition of the liquid phase (liquid extract). The difference between the fuzzy thermal separation method and the above method is that the composition of the resulting phase using a concentrated target product differs sharply from the composition of the mixture to be separated. Thus, in the case of using the clear separation method to obtain a pure target product, it is sufficient to establish thermodynamic equilibrium once, while in the case of using fuzzy thermal separation methods, it is necessary to realize thermodynamic equilibrium several times in a row. Particularly suitable crystallization methods according to the invention in order to isolate acrylic acid from the extract are suspension crystallization and layer crystallization.

According to the invention, the extraction of acrylic acid from the extract is even more preferably carried out by desorption, which primarily relates to the case when a compound is used as the extracting agent, the boiling point of which at normal pressure is at least 60 ° C, preferably at least 80 ° C and even more preferably at least 100 ° C exceeds the corresponding boiling point of acrylic acid, which is 141 ° C. For the implementation of desorption usually use a column with effectively separating the built-in elements. As the latter, in principle, any known effectively separating built-in elements can be used. These primarily include plates, nozzles and / or bulk materials. Preferred mass transfer plates are cap plates, mesh plates, for example forced, respectively, failed mesh plates (double-flow plates), valve plates and / or Torman plates (respectively Torman ^® plates). Preferred bulk materials are rings, spirals, saddles, Raschig rings, Intos rings, Poll rings, Burl saddles, Intalox saddles, Top-Pak materials, etc., or woven materials. Even more preferred are dual-flow trays and / or Torman trays. Preferred Torman plates are corresponding single-threaded plates. In the case of double-threaded plates and Torman plates, the former are even more preferably used in the lower part of the desorption unit, while the latter in its upper part. A sufficient number of theoretical plates used in the desorption unit, as a rule, is from 5 to 10. The implementation of desorption can, in principle, be facilitated solely by reducing the pressure. From a manufacturing and technical point of view, it is even more preferable to lower the partial pressure of acrylic acid to be stripped by dilution with a gas that is not able to condense under stripping conditions (the boiling point of the stripping gas at atmospheric pressure is preferably at least 50 ° C lower than the boiling point of water) and mostly inert with respect to chemical changes. Thus, it is even more preferable to separate acrylic acid from the extracted phase by stripping it with gas. That is, as a result of passing gas through an acrylic acid extract, the latter passes into the gas. The driving force of this process is the higher vapor pressure of the acrylic acid extracted from the extract compared to its partial pressure in the gas, which causes the transition of acrylic acid from the extract to gas. For the purpose of steaming, the extract preferably moves in the opposite direction to the flow of the stripping gas (i.e. countercurrent). Therefore, the extract is preferably introduced into the upper part of the stripping column, and the stripping gas into its lower part. In an even more preferred embodiment, the residual gas discharged from the top of the condensation column (respectively, the residual gas mixture), a partial amount of this residual gas, the composition of which is similar to or different from the total residual gas, or a gas that is in composition corresponds to one or more inert components of the residual gas (for example, water vapor, nitrogen, carbon dioxide and / or air). According to the invention, the advantage of the preferred use of the residual gas mixture as stripping gas is due to the fact that in this case, on the one hand, there is no need to prepare additional stripping gas (which would further need to be subjected to additional utilization), and on the other hand, that in this case a stripping gas is used, which does not contain components different from those that are characteristic of the general process of separation of acrylic acid from gases minutes the reaction mixture products of the partial oxidation. The residual gas, as a rule, mainly consists of inert diluent gases used to partially oxidize the starting compounds with three carbon atoms to acrylic acid (such inert gases during partial oxidation remain mostly chemically unchanged), as well as from water vapor, which is usually formed during partial oxidation as a by-product, and if necessary added as a dilution gas, and carbon oxides resulting from undesired complete oxidation that occurs a side reaction (frequently a partial amount of the residual gas having a composition identical with that of the total residual gas mixture is also recycled as a diluent gas in the partial oxidation step, herein called a partial amount of the circulating gas partial oxidation, a gas circulation circuit, respectively). The residual gas sometimes contains insignificant amounts of molecular oxygen, which remains unspent at the stage of partial oxidation (its presence is preferred, allowing, for example, to reduce the undesired formation of the polymer), unconverted starting compounds with three carbon atoms and / or unconverted intermediate. At the same time, inert dilution gases (for example, nitrogen, carbon dioxide, water and / or saturated hydrocarbons, etc.) shared at the stage of partial oxidation are useful on the one hand, since they are capable of absorbing the reaction heat released at the stage of partial oxidation, and on the other hand, they, as a rule, simultaneously ensure the safety of heterogeneously catalyzed gas-phase partial oxidation of the starting compounds with three carbon atoms, because due to their presence in the mixture and reaction gases, the composition of the latter is outside the explosive range or in a reliably controlled part of the explosive range (see, for example, German patent applications DE A 19740253, DE A 19740252, DE A 10243625 and DE A 10332758, as well as international application WO 2004/035514) .

In the case of using in the desorption (stripping) column as effectively separating the built-in elements of the double-flow plates, the diameter of the through holes made therein, as a rule, is from 8 to 50 mm, preferably from 10 to 35 mm. The diameter of the holes in the direction from top to bottom preferably decreases. The distance between the plates (usually the same) is often from 300 to 800 mm, in many cases from 400 to 600 mm and most often 500 mm. As indicated above, the desorption unit is usually made of austenitic steel, preferably steel 1.4571 (according to DIN EN 10020).

The extract to be steamed is introduced into the upper part of the desorption column, preferably on its uppermost (theoretical) plate. In the production and technical sense, it is advisable to preheat the extract to a temperature, typically from 80 to 120 ° C, often about 100 ° C. In a preferred embodiment, heat is additionally supplied to the cube of the stripping (desorption) column, for which an internal and / or external indirect heat exchanger of a conventional design is used (for example, Robert's evaporator, forced-circulation shell-and-tube heat exchanger, forced-circulation shell-and-tube heat exchanger, plate heat exchanger, etc. ; see, for example, European patent application EP A 854129) and / or a double-wall heating system (preferably used as a heat transfer medium Acquiring the step of partial oxidation of steam). The cube of the stripping column is preferably heated by means of an external circulation evaporator with natural or forced circulation. Particularly preferably used are external forced circulation evaporators (especially expansion evaporators). It is possible to use several series-connected or parallel-connected evaporators (a typical cube temperature is from 145 to 165 ° C, most often around 155 ° C).

The stripping inert gas, unable to condense under conditions of desorption, is preferably introduced directly into the cube of the desorption unit. The supply of a stripping inert gas from an external heat exchanger, in which the required amount of heat from the bottom liquid taken from the column is supplied to said gas, is preferably carried out on one of the bottom (theoretical) plates of the desorption column, preferably between the 2nd and 4th lower theoretical plates or below. The extracting agent formed in the bottom of the desorption column, preferably not containing acrylic acid, is preferably returned to the top of the acid water extraction column.

Since the extracting agent returned from the stripping column to the extraction column usually has a higher temperature than the temperature of the extract formed in the extraction column, the extract sent from the extraction column to the stripping column and the extracting agent returned from the stripping column for extraction are expediently pass through a conventional heat exchanger indirect (shell-and-tube or plate) heat exchanger, in which they heat extract and cooling of the extractant (in connection with the return of the extracting agent to the extraction column, if necessary, in the cube of the stripping column, it is preferable to perform the required active inhibition of the polymerization occurring in the extraction and stripping columns, which, if molecular oxygen is present in the stripping gas, can be performed, for example, by p-methoxyphenol and / or phenothiazine). After that, the extracting agent is usually subjected to additional cooling in an indirect heat exchanger, for example, by means of water as a refrigerant to the temperature of use of the extractant in the acid water extraction unit. From the stripping column is usually removed from 0.01 to 1% of the mass. bottoms liquid (in terms of the flow of extractant returned from the bottom of the stripping column for extraction), and after the above water cooling, the stream of the returned extracting agent is usually supplemented with an appropriate amount of fresh extracting agent. The bottom liquid removed from the system can be disposed of (for example, burned together with the residual gas) or rectified, followed by introduction into a fresh extracting agent.

The temperature of the stripping gas supplied to the stripping column is preferably at least substantially the temperature of the bottoms liquid in the stripping column, the difference between the respective temperatures, as a rule, not exceeding 30 ° C, better not exceeding 20 ° C. If residual gas is used as stripping gas, the indicated temperature difference can be achieved, for example, by compressing the gas to a higher pressure. Such compression can preferably be carried out together with the gas of the circulation circuit to a pressure suitable also for returning the residual gas to the stage of partial oxidation of the starting compounds with three carbon atoms (a centrifugal compressor is usually used for compression). Typically, such compression is carried out to a pressure of from 2 to 4 bar, most often from 2.5 to 3.5 bar (typical compression pressure in the case of using only residual gas is more than 1 and ≤1.5 bar).

In a typical case, the flow rate of stripping gas necessary for the release of acrylic acid by stripping one kilogram of extract is from 1.5 to 2.5 nm ³ . Typical acrylic acid content in the stripping gas (in the upper part of the stripping column) is from 2 to 6% of the mass.

The heat supply to the cube of the stripping column as the flow rate of the used stripping gas increases, in principle, can be reduced. The advantage of separating acrylic acid from the extract by stripping by means of a usually non-condensable stripping gas and an inert stripping gas is, in particular, that this is a particularly efficient technology, which simultaneously requires low energy and hardware costs. In addition, the advantage of this technology in comparison with, for example, crystallization or distillation of acrylic acid from the extract is due to the absence of the formation of an additional liquid phase with an increased concentration of acrylic acid, which would require additional costs for inhibition of polymerization.

The above advantages are not least due to the fact that the stripping gas containing stripped acrylic acid, especially if residual gas was used for steaming, can be returned to the condensation column, which is used for fractional condensation of a gas mixture of partial oxidation reaction products. Advantageously, the return stripping gas is introduced into the condensation column below the first side extraction. The return stripping gas is preferably introduced directly into the bottom volume of the condensation column. In principle, it can be introduced directly into the still liquid.

Thus, one embodiment of the method of the invention is that acrylic acid is contained in at least a partial amount (at least 25% by weight, preferably at least 50% by weight, preferably at least in 75% by weight or in total) of acidic water not returned to the condensation column, by extraction with an organic solvent, is transferred to this solvent to obtain an organic extract containing acrylic acid, the acrylic acid from which is isolated by evaporation Nia stripping gas, the stripped comprising acrylic acid stripping gas is recycled into the condensation column. The stripped acrylic acid contained in the stripping gas can, in principle, be returned to the condensation column also in a condensed state. Such condensed acrylic acid can also be sent for further purification after combining it with crude acrylic acid taken from the condensation column.

In an even more preferred embodiment of the method according to the invention, a stripping gas containing stripped acrylic acid (at least a partial amount of stripped acrylic acid, respectively) can be used for the acrylic acid stripping in the second stripping column, which is also contained in bottoms liquid taken from the condensation column , before supplying the latter for disposal (and only after that return the stripping gas to the condensation column). According to the invention, the stripping acrylic acid-containing stripping gas of this second stripping stage is preferably subjected to an additional (countercurrent) distillation as described in international application WO 2004/035514 and German patent application DE A 10332758 (but using the residual gas directly as stripping gas), and only then return to the condensation column.

The cubic volume of the condensation column used in the process of the invention (respectively, in the most general case of the column equipped with effectively separating built-in elements) is the space inside the condensing column below the lowest effective separating built-in element (built-in elements, for example, in the form of plates, nozzles and nozzles bodies allow to increase the boundary surface between the phases moving in the distillation column countercurrent).

The so-called bottoms liquid accumulates in the still volume, primarily containing components whose boiling point at normal (atmospheric) pressure exceeds the boiling point of acrylic acid. We are talking about by-products whose boiling point exceeds the boiling point of acrylic acid, for example, such as maleic anhydride, about by-products, such as phenothiazine, added as polymerization inhibitors, as well as by-products that are formed during fractional condensation of the stream gaseous products of partial oxidation from the components of this stream. Such by-products primarily include products of undesired radical polymerization of acrylic acid, which are formed despite the inhibition of such polymerization. High-molecular compounds, which are formed as a result of the condensation reaction of various components of a gas mixture of partial oxidation products, also belong to them. Such high molecular weight compounds include, not least, Michael adducts, which are formed due to Michael's reversible addition of acrylic acid to itself, as well as to the resulting dimers of acrylic acid (the so-called diacrylic acid), respectively, of acrylic acid oligomers (in the present description, the term “Acrylic acid oligomers” are always used to refer to the corresponding Michael adducts, and not the oligomers resulting from the radical polymerization of acrylic acid lots). Due to the effect of elevated temperature while removing the resulting acrylic acid [for example, by “steaming” it with a preferably (chemically) inert and non-condensable gas under appropriate conditions], Michael coupling may be reversible. Monomer acrylic acid itself, which is present in a small amount, is also a component of the bottom liquid of the condensation column, which makes it expedient to separate it by steaming. Since the bottom liquid of the condensation column also contains by-products, which at normal pressure boil at a temperature only slightly higher than the boiling point of acrylic acid (for example, benzaldehyde, furfural and maleic anhydride), an additional countercurrent (i.e., with counter-reflux) rectification containing acrylic the acid of the stripping gas of this second stage of stripping (for example, before it returns to the condensation column), which in an expedient variant e is carried out in the same column, which causes increase in purity acrylic acid comprising second stripping gas.

The return of the first stripping gas containing and stripped acrylic acid and / or the second stripping gas to the condensation column does not have to be carried out directly.

On the contrary, there is also the possibility of at least partially or completely mixing the stripping acrylic acid containing the first stripping gas and / or the second stripping gas with the gas mixture of the reaction products and then supplying the resulting gas mixture to the condensation column.

The combination of these gas streams can be carried out before, during and / or after, if necessary, realized direct and / or indirect cooling of the gas mixture of gas-phase partial oxidation products.

To avoid confusion, the acrylic acid-containing stripping gas (stripping gas) is referred to in the following description as “the first stripping acrylic acid gas”, while the stripping gas containing preferably rectified acrylic acid (gas sold in the bottoms condensation column) is called “ the second gas containing stripped acrylic acid "(respectively, the stripping of the extract is called" the first steaming ", while the distillation steaming is called" the second about parivaniem ", and so on). The pressure of the first gas stripping the extract at the outlet of the corresponding stripping system, as a rule, is from 1.5 to 3.5 bar, most often from 2 to 3 bar, for example 2.5 bar. The temperature of the first stripping gas is usually about 10 ° C lower than the temperature that the extract entering the first stripping column has. The typical temperature of the first gas containing stripped acrylic acid is from 65 to 95 ° C, most often from 75 to 95 ° C, or 85 ° C.

In order to carry out a second stripping (including rectification of the stripping gas), in principle, any columns with effectively separating built-in elements can be used, such as nozzles, packing bodies and / or plates. In principle, you can also use columns with rotating packing elements (the so-called rotational columns), providing spray reflux with the formation of drops. According to the invention, it is preferable to use a second stripping column provided only with trays and / or nozzles. In this case, double-flow trays are preferably used, and in a particularly preferred embodiment, the stripping column contains exclusively double-flow trays as effectively separating the built-in elements.

In accordance with the present invention, double-threaded plates mean plates provided with single simple passage places (holes, slots, and the like). The gas rising inside the second stripping column and the dropping phlegm pass through each of these passage passages in countercurrent. The cross section of the passageways in a known manner is brought into line with the load on the second stripping column. If the cross section is too small, the gas rising inside the stripping column passes through the passageways with such a high speed that it captures the downward reflux mainly without the separation effect. If the cross section of the passageways is too large, the rising gas and the downward reflux pass by each other mainly without mass transfer, which leads to the risk of operating the plates in a dry mode. Double-flow trays usually do not have drain pipes connecting them to adjacent trays. Each of the double-flow trays can obviously be flush adjacent to the inner wall of the second stripping column. It can also be connected to the inner walls of the column by means of jumpers. When the load on the second stripping column is reduced, double-flow trays, in contrast to hydraulically sealed cross-flow trays, operate in a dry mode.

In an advantageous embodiment, a double-flow tray stripper used to perform a second steam (including rectification) may include up to sixty double-flow trays. The D: U ratio for such a plate (D means gas-permeable part of the total area of the plate, U means the total area of the plate) is preferably in the range from 10 to 20%, preferably from 10 to 15%.

The passages of the double-flow plates are preferably round holes having the same diameter for the same plate. The latter expediently ranges from 10 to 30 mm The diameter of the holes for the plates located in the upper part of the column is preferably from 10 to 20 mm, respectively from 10 to 15 mm, while for the plates located in the lower part of the column, it is preferably from 20 to 30 mm. In addition, the round openings of the individual double-flow plates are evenly ordered, preferably in accordance with strict triangular gradation (see German patent application DE A 10230219). The burrs resulting from the cutting of through holes in the double-flow plates of the second stripping column are preferably facing downward. Double-flow plates of the second stripper are usually at the same distance from each other. A typical distance between two-threaded plates is 300 to 500 mm. According to the invention, a distance between the plates of 400 mm is also advantageous. In an expedient embodiment, the supply of the still-to-be-boiled bottoms liquid (which before this can be used for direct cooling of the gas mixture of the products of partial oxidation and / or into which the fraction of heavy boiling products taken at the bottom of the condensation column can be added) is carried out between the fourth and tenth two-threaded plates of the second stripping columns (counting from below). The temperature of the cube of the second stripping column is maintained in the preferred range from 150 to 190 ° C, preferably from 160 to 180 ° C. The working pressure in the second stripping column is usually from 1 to 3 bar, most often from 1.5 to 2.5 bar.

The energy supply to the second stripping column is preferably carried out by means of a forced-expansion shell-and-tube evaporator located outside this column, into which, for the purpose of overheating, the bottoms liquid taken from the second stripping column is returned to the same column (see German patent application DE A 10332758) . In principle, a pure forced circulation evaporator or a natural circulation evaporator, such as Robert’s evaporator, which can also be mounted inside a second stripper, can also be used for this purpose.

The second stripping column (as well as the condensation column, as well as the first stripping column) in the production and technical respect, it is advisable to provide external thermal insulation.

Phlegm can be obtained by direct and / or indirect cooling. According to the invention, direct cooling is preferably used to obtain reflux. For this purpose, in the simplest version, the gas passed through the last (theoretical) plate is sent to the quenching device, which is integrated (seated on the effectively separating part) into the second stripping column, for example, above the fireplace plate, regardless of the effectively separating the built-in elements of the second stripping column. In principle, the quenching device may also be located outside the second stripping column. As such a quenching device, any devices known to the prior art (for example, scrubbers, Venturi scrubbers, bubble columns or other apparatus with irrigated surfaces) can be used, preferably using Venturi scrubbers or irrigation chillers. Suitable direct-flow devices (e.g., diffuser with reflective plates) are preferred. For the purpose of indirect cooling, quenching fluid is usually passed through a (indirect) heat exchanger. However, any commonly used heat exchangers are suitable. It is preferable to use shell-and-tube heat exchangers, plate heat exchangers and air coolers. Suitable cooling media are air (in the case of using an air cooler) and coolants, especially water, for example surface water (in the case of using other types of cooling devices). As a quenching liquid (in the following description also called “quenching liquid 0"), it is advisable to use a partial amount of condensate formed during quenching in the production and technical sense. Another partial amount of condensate formed during quenching, mainly in the form of reflux, is returned to the uppermost (theoretical) plate of the second stripping column (in this case, a small partial amount of condensate can also be taken, sent to the bottoms liquid taken from the condensation column and combined with this stream; part of the resulting mixture can be used as the quenching liquid 1 discussed below; another part of this mixture forms a stream feeding the second stripping column, moreover a relatively small residual amount of this mixture is combined with the remaining partial amount of condensate, and the resulting mixture is used as part of the reflux directed to the uppermost (theoretical) plate of the second stripping column, and part of the quenching liquid 0). Typically, the temperature of the quenching liquid 0 immediately before it is used for quenching is about 40 ° C, while the temperature of the reflux returned to the column is typically about 80 ° C. The mass ratio of the returned reflux to the second stripping liquid column (in some cases also low boiling liquid) fed into the cube is typically ≥2. The ratio is often from 2 to 10, preferably from 4 to 8.

The second stripping column, like all other apparatuses into which the liquid phases enter with any significant acrylic acid content, should obviously be operated with the simultaneous use of polymerization inhibitors. As the latter, in principle, any polymerization inhibitors known in the art and suitable for a similar purpose can be used.

Examples of suitable polymerization inhibitors are phenothiazine and p-methoxyphenol. Often use a combination of these inhibitors. In a suitable embodiment, they are used in the form of a solution in pure acrylic acid. Para-methoxyphenol is preferably added as a melt.

According to a particularly suitable embodiment, inhibition of polymerization in the quenching circuit 0 and the second stripping column can be carried out by supplying to the quenching circuit 0 a partial amount of bottoms liquid withdrawn from the condensation column containing polymerization inhibitors and, if necessary, a fraction of heavy boiling products. Inhibited in this way, the quenching fluid 0 typically contains, for example, from 0.01 to 0.1% of the mass. p-methoxyphenol and from 0.01 to 0.5% of the mass. phenothiazine. The polymerization is further inhibited by molecular oxygen, typically present in the first acrylic acid-containing gas used as the stripping gas in the second stripping column.

A partial amount of liquid formed in the cube of the second stripping column is continuously withdrawn and disposed of. The fluid state of such a volatile residue, if necessary, is ensured by the addition of an organic solvent, for example methanol. Instead of methanol, you can also use other hydrophilic organic liquids, for example, such as ethanol, liquids recommended in international application WO 2004/035514, as well as mixtures thereof. The second stripping column stream withdrawn from the cube in terms of the flow of bottoms liquid supplied to it from the condensation column is in the approximate range of 10 or 20% of the mass. up to 30% of the mass. It is advisable to divert the output stream from the production stream from the material stream exiting in an overheated state from an expansion evaporator with forced circulation, which supplies the second stripping column with energy. The specified stream is subjected to deaeration and, for example, in a diluted state with methanol is directed, for example, to the burning of industrial waste.

The second gas taken from the quenching circuit 0, which is cooled to a temperature, typically from 70 to 90 ° C, can be returned to the condensation column (it should be noted that, in a typical case, in the second stripping column, from 1 up to 10 nm ^{3 of the} first gas containing stripped acrylic acid in terms of 1 kg of bottoms liquid supplied from the condensation column; the liquid in the bottom of the second stripper column is usually in a boiling state). The acrylic acid content in the second gas containing stripped acrylic acid is typically 15 to 20% by weight. The acrylic acid contained in this gas can, in principle, be returned to the condensation column also in a condensed state. The corresponding condensate of acrylic acid can also be combined with crude acrylic acid taken from the condensation column and sent for further purification of acrylic acid. According to the invention, acrylic acid is returned to the condensation column, preferably in the form of a component of a second gas containing stripped acrylic acid, that is, in gaseous form (in principle, the return of acrylic acid can also be carried out in partially condensed form).

The second gas containing the stripped acrylic acid returned to the condensation column is preferably introduced below the first side extraction (all of the above applies equally to the return of the first gas containing the stripped acrylic acid to the condensation column), although in principle it can also be introduced into the direct cooling circuit of the product gas mixture gas phase partial oxidation. From a production and technical point of view, it is advisable to return the second gas containing stripped acrylic acid to the bottom part of the condensation column. At the same time, it can be introduced directly into the still liquid or into the space between the mirror of the still liquid and the first (theoretical) plate of the condensation column. The bottom part of the condensation column is preferably equipped with a droplet separator (for example, a centrifugal droplet separator), which prevents the entrainment of droplets of the bottom liquid by the rising gas. In addition, the bottom part can be separated from the lowest effectively separating the built-in element by the first fireplace type plate.

The residence time of the bottoms liquid in the second stripping column supplied to it from the condensation column (if necessary including the selected fraction of heavy boiling products) should usually be from 0.5 to 4 hours (for the final boiling point side component to be unloaded). Obviously, it is possible to meter acrylic acid oligomer cleavage catalysts recommended for example in WO 2004/035514 into the bottom of the second stripping column.

The cube second stripping column is obviously possible to add as auxiliaries such as Komad ^® 313 company Mol (Hungary), and / or dispersing agent (known for example from European patent application EP-A-1062197 and / or US patent application US A 3271296), as well as, for example, such as tertiary amines (in particular, trimethylamine, triethylamine, N, N, N ', N'-tetramethyl-1,6-hexanediamine and pentamethyldiethylenetriamine), which reduce pollution by providing the necessary energy for indirect heat exchangers and contributing to an increase in the yield of acrylic acid. The amount of the respective additives may be from 0.1 to 10% of the mass. in terms of still liquid of the second stripping column. Since such additives are preferably low boiling substances or they form low boiling substances with acrylic acid, they are not subject to steaming.

The advantages achieved through the use of the above-described variants of the method proposed in the invention are due, in particular, to the fact that their implementation allows to increase the yield of acrylic acid without significantly reducing the purity of crude acrylic acid removed through the first side selection. This is not least true of the above-mentioned steaming option, in accordance with which the residual gas of the condensation column is used for steaming.

At the same time, the degree of purity of both the first and the second gas containing stripped acrylic acid, determined by the content of side components in them, which interfere with the subsequent use of acrylic acid, for example, to produce water-superabsorbing polymers, is already quite sufficient for acrylic acid contained in the corresponding total or a partial amount of the first and / or second gases, it was possible to directly transfer from the gas phase of the first or second gas containing stripped acrylic acid to water metal hydroxide solution (e.g., alkali metal hydroxide and / or alkaline earth metal hydroxide, especially NaOH, KOH, Ca (OH) ₂ and / or Mg (OH) _2), e.g., in full accordance with the technique described in international patent application WO 2003/095410, and in the case of transfer, for example, into an aqueous solution of caustic soda, the resulting aqueous solution of sodium acrylate can be used, for example, for the direct production of water-superabsorbing polymers by appropriate radical polymerization (see also international application WO 2003/014172).

This is not least due to the fact that by-products, such as formaldehyde and formic acid, usually preferably remain in the aqueous phase of acidic water. The first or second gas containing stripped acrylic acid freed from acrylic acid, for example, by countercurrent washing with an aqueous solution of caustic soda (or an aqueous solution of the other metal hydroxide indicated above) in a column containing effectively separating the built-in elements (plates, packing bodies and / or nozzles ), then can be returned to the steaming of the extract and / or sent for burning.

In a typical case, a gas mixture containing acrylic acid gas mixture of products of a heterogeneously catalyzed gas-phase partial oxidation of the starting compounds with three carbon atoms with molecular oxygen on solid state aggregates can have, for example, the following composition (primarily if, as the starting compound with three atoms carbon use propylene):

from 1 to 30% of the mass. acrylic acid from 0.05 to 10% of the mass. molecular oxygen from 1 to 30% of the mass. water more than 0 to 5% of the mass. acetic acid more than 0 to 3% of the mass. propionic acid more than 0 to 1% of the mass. maleic acid and / or maleic anhydride from 0 to 2% of the mass. acrolein from 0 to 1% of the mass. formaldehyde more than 0 to 1% of the mass. furfural more than 0 to 0.5% of the mass. benzaldehyde from 0 to 1% of the mass. propylene the rest (up to 100% of the mass.) mainly inert gases, for example, such as nitrogen, carbon monoxide, carbon dioxide, methane and / or propane.

The gas mixture of the reaction products usually contains ≥0.005 mol.%, Most often ≥0.03 mol.% Furfural (in terms of the amount of acrylic acid contained in it). At the same time, the relative content of furfural, as a rule, ≤3 mol.%.

Partial oxidation gas phase can be carried out by methods known in the art. For example, gas-phase partial oxidation of propylene can be carried out in two successively carried out oxidation stages, as described in European patent applications EP A 700714 and EP A700893. Partial gas-phase oxidation can obviously also be carried out as proposed in German patent applications DE A 19740253 and DE A 19740252.

Partial gas phase oxidation of propylene is preferred, as described in German patent application DE A 10148566, since in this case fewer side components are formed. In this case, polyethylene grade propylene or chemically pure propylene can be used as a source of propylene according to German patent application DE A 10232748. When propane is used as a starting compound with three carbon atoms, partial oxidation can be carried out as described in German patent application DE A 10245585.

Gas phase partial oxidation can in principle also be carried out as described in US patent application US 2006/0161019, international applications WO 2006/092410, WO 2006/002703, WO 2006/002713 and WO 2005/113127, German patent application DE A 102004021763, European patent application EP A 1611076, international patent application WO 2005/108342, European patent applications EP A 1656335, EP A 1656335, EP A 1682478 and EP A 1682477, German patent applications Nr.10 2006054214.2 and Nr.10 2006024901.1, European patent applications EP A 1611080 and EP A 1734030, German patent applications Nr.10 2006000996.7, 10 2005062026.4 and 10 2005062010.8, as well as in international patent applications t Nr. PCT / EP 2006/065416, PCT / EP 2006/067784 and PCT / EP 2006/067080.

The temperature of the gas mixture of the reaction products of gas-phase partial oxidation is often from 150 to 350 ° C, in many cases from 200 to 300 ° C, sometimes up to 500 ° C.

In a technically feasible embodiment, the hot gas mixture of the reaction products is cooled by direct cooling in a quenching device 1, usually to a temperature of from 100 to 180 ° C, and then, in accordance with a technically preferred embodiment, together with the quenching liquid used 1 for the purpose of fractional condensation, they are preferably sent to the lower section of the condensation column containing effectively separating the built-in elements (preferably to the lowest Example, a bottom part of this column).

The condensation column can in principle be equipped with any known built-in elements, in particular plates, nozzles and / or nozzle bodies. In this case, the preferred plates are cap, mesh, valve and / or dual-flow plates. The total number of plates in a plate condensation column is typically from 20 to 100, often from 20 to 80, preferably from 50 to 80.

According to the invention, a condensation column recommended in German patent applications DE A 10243625, DE A 19924532 and DE A 10243625 is preferred, which, as effectively separating the built-in elements, contains (from bottom to top) first double-flow trays and then hydraulically sealed cross-flow trays (e.g. Thormann ^® plates). The number of double-flow trays can be from 5 to 60, often from 25 to 45, while the number of hydraulically sealed trays with cross current is from 5 to 60, often from 30 to 50. In the case of the formation of acidic water according to the invention ( the acrylic acid content in phlegm is typically ≤15% wt., respectively, in some cases ≤10% wt.) valve plates are preferably used as effectively separating embedded elements (see German patent applications DE A 19924532 and DE A 10243625) . In principle, you can also use other well-known effectively separating built-in elements (in the most general case, separate zones of the condensation column instead of being located one above the other in the same column, obviously, can also be completely identical in the form of smaller smaller columns connected in series to each other, in connection with which both the term "condensation column" used in the present description in individual cases, and the term "column" used in the general case, serve as also to indicate the indicated sequences of the corresponding smaller columns).

As the quenching device 1, any device designed for a similar purpose and known from the prior art can be used (for example, scrubbers, Venturi scrubbers, bubble columns or other apparatus with irrigated surfaces), preferably using Venturi scrubbers or irrigation chillers.

For the purpose of indirect cooling or heating, the quenching liquid 1 is preferably, but not necessarily, passed through a heat exchanger, which primarily relates to the start-up stage. Suitable are any conventional heat exchangers. Shell and tube heat exchangers, plate heat exchangers and air coolers are preferred. Suitable coolants include air (in the case of using an appropriate air cooler) and coolants, especially water (in the case of using other types of cooling devices).

As the quenching liquid 1, it is possible to use, for example, bottoms liquid taken from the cube of the condensation column (if necessary combined with condensate discharged from the quenching circuit 0), a fraction of heavy boiling products, discharged through lateral extraction located near the cube, or a mixture of the specified bottoms liquid and the specified fraction heavy boiling products, which primarily relates to the case if the bottom part and the lowest (theoretical) plate (the lowest effectively separating the built-in element) are separated for yz other chimney tray. If necessary, only part of the quenching liquid condensation column taken from the cube is passed through the heat exchangers indicated above. The temperature of the quenching liquid 1 at the inlet to the quenching device 1 is suitable, as a rule, from 90 to 120 ° С.

The place of introduction into the condensation column of a quenched (or otherwise cooled, as well as non-cooled) gas mixture of products of catalytic gas-phase partial oxidation (according to the invention, preferably in a mixture with quenching liquid used for direct cooling 1) is preferably located in its bottom volume, preferably equipped with an integrated centrifugal a droplet separator and, as a rule, separated from the lowest effectively separating the built-in element by the first fireplace-type plate ( in this case, from a production and technical point of view, it is advisable to continuously send a fraction of heavy boiling products through the corresponding connecting pipe or overflow pipe into the cube of the condensation column). In accordance with the preferred embodiment (which is considered below as the only one applicable without limitation, the variant) by the indicated plate is meant the first plate of the first series of double-flow plates located expediently at equal distances from each other. The fireplace-type plate simultaneously serves as a storage plate, with which continuous condensate is collected (fractions of heavy boiling products), then sent as part of the quenching liquid 1 to the quenching device 1 or cube. The first series of double-threaded plates ends with a second fireplace-type plate (catch plate). Crude acrylic acid, the purity of which is preferably ≥90% wt., Respectively ≥95% wt., Is continuously taken from this second trap plate through the first side selection in the form of a medium boiling fraction.

In accordance with a suitable option, the specified crude acrylic acid is sent for additional distillation (distillation) and / or crystallization treatment, and at least part of the bottoms and / or mother liquors resulting from the corresponding distillation (rectification) and / or crystallization are returned to condensation column, introducing them in a place below the first side selection, but above the first catching plate. Said recirculation is preferably carried out while recovering heat. Namely, the cold mother liquor to be returned is passed through one or more series-connected indirect heat exchangers (for example, spiral heat exchangers) in order to cool the crude acrylic acid to be further crystallized from the condensation column and sent to the heat exchanger from its opposite side. Thereby, heating of the mother liquor is simultaneously provided. For this purpose, preferably two series-connected plate heat exchangers are used.

In an expedient embodiment, the crude acrylic acid selected as a medium boiling fraction is sent to crystallization for additional purification. Appropriate crystallization methods are, in principle, not subject to any restrictions. Crystallization can be performed in continuous or batch, single-stage or multi-stage mode to any degree of purity.

If necessary, it is preferable to add water to the raw acrylic acid to be crystallized to be purified before crystallization. In this case, acrylic acid usually contains up to 20 wt.% Or up to 10 wt.%, In most cases up to 5 wt. amount of acrylic acid). With an increased content of aldehydes or other side components in acrylic acid, the addition of water should be discarded, since aldehydes can take on the function of water. According to the invention, the addition of water in the form of acidic water is even more preferred. In this case, the yield of pure acrylic acid increases.

It was unexpectedly found that even with the preliminary addition of acidic water to crude acrylic acid (such an action simultaneously provides an increase in the yield of acrylic acid), the most stringent requirements regarding the purity of acrylic acid sufficient to carry out its esterification, for example, to obtain n-butyl acrylate, 2 -ethylhexyl acrylate, methyl acrylate or ethyl acrylate (the degree of purity of acrylic acid should be 98% by mass), can be satisfied due to the implementation of the unity This crystallization operation. In a suitable embodiment, such an operation is performed in the form of suspension crystallization, similar to that described in column 10 of German patent application DE A 19924532, respectively, in example 1 of German patent application DE A 10223058 (for example, in a crystallizer with cooling disks described in international application WO 2006 / 111565). The crystals of acrylic acid formed as a result of suspension crystallization have a shape from cubes to rectangular parallelepipeds. The ratio (L: D) of the length (L) of the respective crystals to the thickness (D) is usually in the range from 1: 1 to 6: 1, preferably from 1: 1 to 4: 1, particularly preferably from 1.5: 1 to 3 5: 1. The thickness (D) of the crystals is usually from 20 to 600 microns, often from 50 to 300 microns. The length (L) of the crystals usually corresponds to an interval of from 50 to 1500 microns, often from 200 to 800 microns. Separation of the suspended crystallizate from the residual mother liquor (in the case of acrylic acid suitable for esterification) can be carried out in a centrifuge (for example, a two-stage or three-stage pulsating centrifuge), and in a preferred embodiment, the crystals separated in the centrifuge are washed with molten pure crystallizate. In the case of separating the suspended crystallizate from the residual mother liquor in a washing column, for example a melt washing column, sold, for example, in accordance with international application WO 01/77056, German patent applications DE A 10156016 and DE A 10223058, international applications WO 2006 / 111565, WO 04/35514, WO 03/41833, WO 02/09839 and WO 03/41832, by German patent application DE A 10036881 or international applications WO 02/55469 and WO 03/78378, acrylic acid can be isolated by a single crystallization operation suitable even for superabsorbents (ste Shade its purity is ≥99,7% wt., respectively ≥99,9% wt.), i.e. acrylic acid, suitable for receiving water or other superabsorbent polyacrylates. In accordance with a suitable option, in such a case, the entire amount of the selected mother liquor is returned to the condensation column.

Crystallization can also be performed as fractional crystallization with a falling film recommended in European patent application EP A 616998. Such a process may include, for example, two, three or more (for example, two to four) cleaning operations (suitable falling film crystallizers may contain, for example, from 1000 to 1400 crystallization tubes with a length of 10 to 15 m and an outer diameter of 50 up to 100 mm). Uterine liquor released at a higher cleaning stage can be returned to one of the previous cleaning stages. The mother liquor released in the first purification step is preferably completely returned to the condensation column. In another embodiment, to return to one of the previous purification steps, the mother liquors of the individual purification steps can also be returned to the condensation column as a combination thereof. The pure product of the penultimate cleaning step can be sent to the last cleaning step in whole or in part. In the case of a partial feed, the remaining amount of said pure product is usually mixed with the pure product of the last purification step to obtain a usable final product.

In an advantageous embodiment of the present invention, a partial amount of crude acrylic acid, taken at the place of the condensation column, located above the first side selection, is fed to a two-flow plate located below its corresponding trap plate. If necessary, as a rule, mother liquor to be returned to the condensation column is also fed to said plate. Before feeding, the mother liquor is usually heated in accordance with the above method of heat recovery to a temperature that practically corresponds to the temperature of selection of crude acrylic acid.

Another partial amount of crude acrylic acid, taken at the site of the condensation column, located above the first side extraction, is heated by 10-15 ° C, preferably by indirect heat exchange, and returned to the condensation column above the collection point, preferably immediately below the first double-flow plate next to it. Such a technical measure favorably affects the content of acetic acid in the selected crude acrylic acid.

Above the second trap plate, a second series of double-flow trays is arranged, suitably at the same distance from each other, followed by hydraulically sealed mass transfer trays with transverse current (for example, Torman trays or modified Torman trays according to German patent application DE A 10243625), which, in an expedient embodiment, are also at the same distance from each other. The uppermost double-flow plate, if necessary, is made in the form of a distribution plate. That is, it is equipped, for example, with a drain trough with a winding overflow.

The first bottom Torman plate has a design that is expedient from a production and technical point of view, according to which the liquid flows from it through six drain pipes in the form of corresponding pipes. These pipes are hydraulically sealed with respect to the gas volume below the double-flow plate. In the industrial and technical respect, it is expedient to reduce the headroom of the six drain pipes in the direction of flow of the plate with cross current. The hydraulic seal of the openings for idle discharge is preferably provided with a reflective plate. The drain pipes are evenly distributed, preferably in the second half, particularly preferably in the last third of the cross section of the plate (opposite to the entrance to the plate).

The hydraulic seal is implemented in a shutter with an inclined overflow device (inclination angle 45 °).

A series of mass transfer plates with transverse current completes the third fireplace-type plate (trap plate).

Above the third collecting plate are preferably double-flow valve plates. The principle of operation of valve plates, as well as valve plates used according to the invention, are described, for example, in Technische Fortschrittsberichte, Volume 61, Grundlagen der Dimensionierung von Kolonnenboden, S. 96-138. The main feature of such valve plates is that they allow pairs to pass through the corresponding hole at a flow rate that can be varied over a wide range. According to the invention, ballast plates are preferably used. We are talking about plates, in the openings of which there are cells with openings closed by loads. According to the invention, W12 valves from Stahl (Germany, Wierheim) are particularly preferred. In the volume of the valve disc, predominant condensation of water occurs, as well as less volatile components compared to water. The resulting condensate is acidic water.

Acid water is continuously discharged from the third catching plate through the second side extraction. Part of the selected acidic water is returned to the condensation column to the uppermost transverse mass transfer plate. The other part of the acidic water taken is cooled by indirect heat exchange and, after a suitable crushing into droplets, is also returned to the condensation column. In this case, one chilled partial amount of acidic water (with a temperature of 15 to 25 ° C, preferably 20 to 25 ° C) is returned to the uppermost valve plate of the condensation column, while another chilled partial amount (with a temperature of 20 to 35 ° C, preferably from 25 to 30 ° C) is returned to the valve plate located approximately in the middle between the third catch plate and the uppermost valve plate. Acrylic acid contained in the selected residual amount of acidic water can be isolated by the method of the invention.

Partial cooling of acidic water, which can be accomplished by means of one or more series-connected indirect heat exchangers, is ensured by the fact that the corresponding partial amount of acidic water is passed through a device for evaporating the starting compound with three carbon atoms (for example, through a propylene evaporator), in which the specified starting the compound in order to implement a heterogeneously catalyzed gas-phase oxidation is transferred to the gas phase.

More volatile than water, the components are removed from the top of the condensation column as residual gas (respectively, the residual gas mixture) and are usually at least partially returned to the gas-phase partial oxidation step as a dilution gas (circulating gas). In order to prevent condensation of the residual gas mixture in the compressor of the circulation circuit, it is subjected to preliminary overheating in an indirect heat exchanger. A portion of the residual gas mixture that cannot be returned to the circulation loop is usually sent to combustion. As indicated above, a portion (preferably compressed) of the residual gas mixture in a preferred embodiment of the invention is used as stripping gas to separate acrylic acid from the extract and from the bottoms liquid of the condensation column. Partial oxidation gas phase is preferably carried out using an excess of molecular oxygen, and therefore, in the case of using the residual gas mixture as such a stripping gas, the residual gas mixture and, therefore, the first and second stripping gases contain molecular oxygen.

In order to inhibit polymerization, a solution of p-methoxyphenol in acrylic acid or (preferably according to the invention) a melt of p-methoxyphenol and, if necessary (in both cases) an additional solution of phenothiazine in acrylic acid is supplied to the uppermost hydraulically sealed mass transfer plate with a transverse current. In this case, pure acrylic acid, obtained as a result of additional purification of crude acrylic acid taken from the condensation column, is preferably used as a solvent. So, for example, you can use obtained from additional crystallization purification of pure acrylic acid (pure target product). The appropriate solution is also advisable to use to stabilize the pure target product.

Approximately in the middle of the column section with hydraulically sealed mass transfer plates with a transverse current, a solution of phenothiazine in a pure target product is additionally introduced.

The formation of acidic water can in principle be realized, for example, also after the first condensation column (see German patent application DE A 10235847). In such a case, from a gas stream of boiling compounds escaping from the upper part of the first condensation column, it is advisable by direct cooling in a volume that does not contain built-in elements (a similar volume can also be mounted inside the condensation column to form acidic water; in this case, quenching the volume without built-in elements is usually separated from the topmost effectively separating built-in element inside the condensation column, for example, by means of a fireplace plate th type) or connected in series with the integrated screen elements (second column) via the quench fluid is condensed 2 mainly water. The resulting condensate is also acidic water. Part of the acidic water is expediently returned to the upper part of the first condensation column in order to increase its separation ability. Another part of the acidic water is subjected to indirect cooling in an external heat exchanger and used as quenching liquid 2, and acrylic acid can also be extracted from the residual amount of acidic water according to the invention. The components of the flow of boiling compounds, the volatility of which exceeds the volatility of water, also form a residual gas, which is usually at least partially returned to the stage of gas-phase partial oxidation as the gas of the circulation circuit, respectively, used as the stripping gas.

In accordance with a preferred embodiment of the method of the invention, double-flow trays are conveniently located along the condensation column to a level corresponding to the cross section of the column, starting from which (towards the top of the column) the acrylic acid content in reflux is ≤90% by mass .

As indicated above, in accordance with the preferred fractional condensation option under consideration, the number of double-flow trays is typically from 25 to 45. The D: U ratio indicated above in a suitable embodiment of the double-flow tray is from 12 to 25%. In this case, the passage points of the double-flow plates are preferably round holes of a standard diameter. Suitable hole diameter is from 10 to 20 mm. The diameter of the holes along the condensation column in the direction from top to bottom, if necessary, may decrease or increase, and / or the number of holes may decrease or increase (for example, all holes may have a standard diameter of 14 mm, but the D: U ratio in the direction from top to bottom may increase with 17.4% to 18.3%). However, a variant of the design of double-flow plates is also possible, according to which they all have the same number of holes. In addition, the round holes for each of the individual double-flow plates are evenly ordered, preferably in accordance with a strictly triangular gradation (see German patent application DE A 10230219).

In addition, the burrs remaining after cutting through holes in the double-flow plates of the condensation column are preferably facing down, thereby reducing undesired polymer formation.

According to the invention, it is advisable if the number of double-flow plates used in the condensation column corresponds to about 10 to 15 theoretical stages.

As indicated above, the number of hydraulically sealed cross-flow mass transfer trays located after a series of double-flow trays in the preferred condensation column according to the invention is typically from 30 to 50. Such mass transfer trays are characterized by a D: U ratio, which is suitably from 5 to 25%, preferably from 10 to 20% (as indicated above, the ratio D: U generally means the percentage of the passage cross section of the plate to its total cross sectional, preferably shared for mass transfer trays crossflow suitable ratio D: U is generally in the above range).

According to the invention, single-flow transverse mass transfer trays are preferably used.

The number of hydraulically sealed cross-flow plates in a preferred embodiment of fractional condensation of the product gas mixture is typically calculated so that it corresponds to a number of theoretical stages of about 10 to 30, most often 25.

Both hydraulically sealed cross-flow trays and, if necessary, shared valve trays have at least one drain port. Plates of both types can have both single-threaded and multi-threaded, for example, two-threaded, design. At the same time, single-threaded plates may also have more than one drain pipe. The valve manifold inlets are also typically equipped with a hydraulic seal.

The polymerization inhibition of the quenching system 1 for a gas mixture of products of partial gas-phase oxidation can be carried out both by means of polymerization inhibitors contained in the bottoms used for quenching (from the condensation column) and by polymerization inhibitors contained in the fraction of heavy boiling products used for quenching (from the condensation column )

The advantage of the method proposed in the invention is that it allows to provide an increased yield of crude acrylic acid, basically having the same degree of purity. Any embodiments of the present invention primarily relate to a gaseous mixture of reaction products resulting from the (preferably two-stage) heterogeneous partial oxidation of propylene to acrylic acid. The preferred embodiment of the method according to the invention described above in no way limits its overall feasibility.

In conclusion, it should be noted once again that both the first and second stripping gases preferably contain molecular oxygen.

In addition, it should be noted that in accordance with the method of the invention, a liquid absorbent different from reflux is introduced into the condensation column through a feed place located between the first side extraction and the second side extraction, if necessary, whose boiling point T _S at atmospheric pressure is higher or equal to the boiling point T _{W of} water at atmospheric pressure. In principle, it is possible to use the technology described, for example, in European patent application EP A 1818324. Suitable absorbents are, in particular, high-boiling organic liquids. Examples of suitable absorbents are organic liquids recommended in German patent application DE A 10336386 and the prior art cited therein for use as absorbents. In addition, obviously, absorbents recommended in the European patent application EP A 1818324 can also be used.

So, for example, suitable absorbents are high boiling (inert) liquid hydrophobic organic liquids given in European patent application EP A 722926, as well as in German patent applications DE A 4436243 and DE A 10336386 (in particular, dimethyl phthalate, diethyl phthalate and / or diphenyl). This is, for example, liquids whose boiling point at normal (atmospheric) pressure exceeds the boiling point of acrylic acid, with at least 70% of the mass. the molecules that make up such liquids do not contain polar groups with an external effect, and therefore, for example, are not able to form hydrogen bonds. Examples of such absorbents are mixtures of diphenyl ether (from 70 to 75% by weight) with diphenyl (from 25 to 30% by weight) called Diphyl ^® , as well as mixtures containing from 70 to 75% by weight. diphenyl ether, from 25 to 30% of the mass. diphenyl and from 0.1 to 25% of the mass. dimethyl phthalate (in terms of a mixture of diphenyl ether with diphenyl).

As such absorbents, obviously, you can also use aqueous liquids. Examples of suitable aqueous liquids are compounds recommended in European patent application EP A 1818324. Such absorbents, in particular, include water. As a similar aqueous absorbent, obviously, it is also possible to use the extracted aqueous phase remaining after acidic water extraction according to the invention.

The purpose of adding the above absorbents is to deliberately reduce the amount of certain side components typically found in crude acrylic acid discharged from the condensation column through a first side extraction. Therefore, in a favorable embodiment, the absorbent used itself does not contain such side components, in any case, their content should be extremely small, and the complete absence of such components is preferable.

In the case of using an aqueous absorbent, it is advantageous, for example, that the mass amount of the individual side components contained in them is less than in the corresponding acidic water.

The supply of an aqueous absorbent (e.g. water) is particularly advantageous, in particular with the aim of reducing the aldehyde content having a boiling point comparable with acrylic acid (primarily furfural) in crude acrylic acid discharged from the condensation column through a first side extraction. In principle, a mixture of aqueous and organic liquids can also be used as a similar absorbent. Such a mixture, in principle, can also be multiphase.

In a preferred embodiment, the absorbent can be fed to the condensation column at a location that is at the same level with the reflux site. A mixture of these two streams can also be fed to the condensation column.

The temperature of the absorbent supplied to the condensation column can vary widely. It can be either higher or lower than the reflux temperature. The temperature of the absorbent often differs from the reflux temperature by an amount of ± 20 ° C. Phlegm and absorbent preferably have the same temperature.

If the crude acrylic acid taken through the first side extraction contains a shared absorbent, it is isolated from the crude acrylic acid, usually by the additional crystallization treatment described above. Otherwise, the shared absorbent will usually end up in the bottom liquid removed from the condensation column, and after separation, it can be reused as the absorbent in accordance with the technology described above.

In a suitable embodiment, the mass flow of the absorbent fed to the condensation column in terms of acrylic acid (which is a component of the mass flow of the reaction product gas mixture fed into the condensation column) is from 0 to 30%.

In the technical and industrial respect, it is advisable to supply the absorbent to the upper third of the condensation column between the first side extraction and the second side extraction.

The crystallization treatment carried out according to the present invention (especially the additional crystallization treatment in accordance with paragraphs 16-20 below), instead of using crude acrylic acid obtained according to the present invention for processing, can be used to process crude acrylic acid obtained in accordance with German DE patent application A 10336386. The specified additional crystallization purification, obviously, can also be used for any mixture of these two types of crude acrylic th acid. Such crystallization purification is resorted to, for example, in the case of parallel implementation of the isolation technology proposed in the invention and isolation technology according to DE A 10336386: the purpose of crystallization purification is to isolate acrylic acid from a gas mixture of products (if necessary, simultaneously carried out) of heterogeneously catalyzed partial gas-phase oxidation of the starting materials compounds with three carbon atoms. In a situation where it is necessary to temporarily stop the fractional condensation proposed in the invention in order to separate acrylic acid, however, the flow of crude acrylic acid obtained according to DE A 10336386 for the corresponding additional crystallization treatment is continued, a partial mass flow (mass flow in terms of the flow directed to additional crystallization treatment crude acrylic acid) would be from 5 to 30%, in typical cases from 10 to 20% (the recovered crystallizate should still satisfy the requirements aniyam specification); the stream of residual amount of mother liquor is usually returned to crystallization (mixed with a mass stream of crude acrylic acid), mother liquor resulting from the isolation of crystallizate from a suspension of crystallized acrylic acid is temporarily stored in a storage tank (feeding to the storage tank can be carried out continuously or cyclically ) and after restarting the fractional condensation, they are gradually returned to fractional condensation in a mixture with the mother liquor formed according to the invention (corresponding the mass flow is more than 0 to 20%, preferably more than 0 to 10% in terms of the mass flow returned to the fractional condensation of the mother liquor formed according to the invention). Moreover, the selection from the storage tank can be carried out continuously or cyclically. Typically, such a selection is carried out in such a way that the formed crystallizate meets the requirements of the specification (the design capacity of the crystallization unit is usually higher than the design capacity of the crude acrylic acid production unit; additional crystallization treatment can also be carried out for a short time with a capacity exceeding the design capacity of the crystallization unit).

Thus, the present invention is carried out primarily in accordance with the following options.

1. A method of producing acrylic acid, according to which, by means of a heterogeneously catalyzed gas-phase partial oxidation by molecular oxygen of at least one corresponding starting compound with three carbon atoms on solid state catalysts, a gas mixture of products containing acrylic acid is obtained, water vapor and side components, the temperature of this mixture, if necessary, is reduced by direct and / or indirect cooling then the specified mixture is sent to a condensation column equipped with effectively separating elements, along which it independently rises while fractional condensation flows simultaneously, and through the first side extraction, which is higher than the feed of the reaction gas mixture into the condensation column, depleted of water from the condensation column and by-products, crude acrylic acid as a target product, through a second (above preferably lateral) the selection of the liquid phase from the condensation column removes acid water containing acid and side components, the residual gas mixture containing side components boiling at a lower temperature than water is removed from the top of the condensation column, bottoms are removed from the bottom of the condensation column, containing acrylic acid, as well as by-products and by-products boiling at a higher temperature than acrylic acid, a partial amount of acid water withdrawn as such and / or after cooling is returned to the condensation column as reflux, and the crude acrylic acid, if necessary, is subjected to further purification by at least one other thermal separation method, characterized in that the acrylic acid contained in at least a partial amount of acid not returned to the condensation column water, is converted into an organic solvent by extraction carried out by this solvent, accompanied by the formation of an acrylic acid-containing organic a extract from which acrylic acid is subsequently isolated by at least one thermal separation method, the recovered acrylic acid being returned to a condensation column, sent for further purification of the crude acrylic acid and / or transferred to an aqueous metal hydroxide solution.

2. The method according to claim 1, characterized in that the starting compound with three carbon atoms is propylene, acrolein or a mixture of propylene with acrolein.

3. The method according to claim 1 or 2, characterized in that the acrylic acid contained in at least 25% of the mass. non-returnable acidic water to the condensation column is transferred to an organic solvent by extraction carried out by this solvent, accompanied by the formation of an acrylic acid-containing organic extract, from which acrylic acid is subsequently isolated by at least one thermal separation method, the recovered acrylic acid being returned to the condensation column, sent for additional purification of crude acrylic acid and / or transferred to an aqueous solution of metal hydroxide.

4. The method according to one of claims 1 to 3, characterized in that the extraction of acrylic acid from acidic water is carried out in an extraction column, which contains nozzles and / or mesh plates as effectively separating built-in elements.

5. The method according to claim 4, characterized in that an organic solvent is supplied to the upper part of the extraction column, and acidic water is introduced into its cube zone, the organic solvent falling in the form of a phase dispersed in a continuous acidic aqueous phase, or characterized in that the upper part of the extraction column is supplied with acidic water, and an organic solvent is introduced into the zone of its cube, and the organic solvent rises in the form of a phase dispersed in a continuous acidic aqueous phase.

6. The method according to one of claims 1 to 5, characterized in that the organic solvent contains at least one ester based on an aliphatic or aromatic monocarboxylic acid with 5-20 carbon atoms and an alcohol with 1-8 carbon atoms.

7. The method according to one of claims 1 to 5, characterized in that the organic solvent contains at least one diester based on an aliphatic or aromatic monocarboxylic acid with 5-20 carbon atoms and an alcohol with 1-8 carbon atoms.

8. The method according to one of claims 1 to 5 or claim 7, characterized in that the organic solvent is dimethyl phthalate, diethyl phthalate, dimethyl isophthalate, diethyl isophthalate, dimethyl terephthalate and / or diethyl terephthalate.

9. The method according to one of claims 1 to 8, characterized in that the boiling point of the organic solvent at atmospheric pressure is ≥200 ° C.

10. The method according to one of claims 1 to 9, characterized in that acrylic acid is isolated from the organic extract by stripping it with a first stripping gas, wherein the first stripping gas containing stripped acrylic acid is returned to the condensation column and / or stripped acrylic acid, contained in the first stripping gas is transferred into an aqueous solution of a metal hydroxide.

11. The method according to one of claims 1 to 9, characterized in that acrylic acid is isolated from the organic extract by stripping with the first stripping gas, wherein the first stripping gas containing the stripped acrylic acid is used as the second stripping gas for the purpose of stripping the acrylic acid contained in the bottoms liquid discharged from the condensation column, and wherein the second stripping gas resulting from this, which contains stripped acrylic acid, is returned to the condensation column and / or discharge The acrylic acid contained in the second stripping gas is transferred to an aqueous solution of a metal hydroxide.

12. The method according to claim 11, characterized in that the stripping of bottom liquid from the condensation column is carried out in a stripping column equipped with effectively separating built-in elements, the temperature in the cube of which is from 150 to 190 ° C.

13. The method according to claim 11 or 12, characterized in that before returning the second stripping gas containing the stripped acrylic acid to the condensation column and / or transfer the stripped acrylic acid contained in the second stripping gas to an aqueous solution of metal hydroxide, the second the stripping gas is subjected to countercurrent distillation.

14. The method according to one of paragraphs.10-13, characterized in that the first stripping gas using air, nitrogen, carbon dioxide and / or water vapor.

15. The method according to one of claims 10 to 13, characterized in that the residual gas mixture is used as the first stripping gas.

16. The method according to one of claims 1 to 15, characterized in that the crude acrylic acid is subjected to additional crystallization treatment.

17. The method according to clause 16, characterized in that in the crude acrylic acid before additional crystallization treatment add a partial amount of acidic water not returned to the condensation column.

18. The method according to p. 16 or 17, characterized in that the additional crystallization purification of crude acrylic acid or its mixture with acidic water is carried out by suspension crystallization.

19. The method according to p. 18, characterized in that a wash column is used to separate the mother liquor remaining after suspension crystallization and the suspension crystallization formed during suspension crystallization.

20. The method according to one of paragraphs.17-19, characterized in that after its implementation, radical polymerization is performed, in accordance with which the molten acrylate crystallizate and / or its metal salt are copolymerized.

21. The method according to one of paragraphs.10, 11 or 13, characterized in that after its implementation, radical polymerization is performed, according to which acrylic acid is copolymerized, converted into an aqueous solution of a metal hydroxide from the first and / or second stripping gas containing acrylic acid.

22. The method according to one of claims 1 to 21, characterized in that a partial amount of the residual gas mixture as the gas of the circulation loop is returned to the gas-phase partial oxidation.

23. The method according to one of claims 1 to 22, characterized in that, under extraction conditions, the specific gravity of the organic solvent is ≥25 kg / m ³ different from the specific gravity of water.

24. The method according to one of claims 1 to 23, characterized in that the aqueous metal hydroxide solution contains dissolved sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ) and / or magnesium hydroxide (Mg (OH) ₂ ).

25. The method according to one of claims 1 to 24, characterized in that a liquid absorbent is supplied to the condensation column between the first lateral extraction and the second lateral extraction, whose boiling point T _S at atmospheric pressure is higher than or equal to the boiling temperature T _{W of} water at atmospheric pressure .

Preliminary applications for US patent No. 60/886771 from 01/26/07 and No. 60/988619 from 11/16/07 are incorporated into this description by reference. In relation to the above technical solutions, numerous changes and deviations from the present invention are possible. Thus, it should be borne in mind that the invention in accordance with the following formula may differ from the above description.

Examples and comparative example

Example 1 (stationary mode)

In three parallel operating lines consisting of dual reactors, two-stage heterogeneously catalyzed gas-phase partial oxidation of propylene of the chemically pure grade, a combined gas mixture of reaction products of the following composition is obtained having a temperature of 270 ° C and a pressure of 1.5 bar:

10.3141% of the mass. acrylic acid 0.2609% of the mass. acetic acid 4.6513% of the mass. water 0.0251% of the mass. formic acid 0.0851% of the mass. formaldehyde 0.1052% of the mass. acrolein 0.0024% of the mass. propionic acid 0.0028% of the mass. furfural 0.0012% of the mass. allyl acrylate 0.0013% of the mass. allyl formate 0.0032% of the mass. benzaldehyde 0.1151% of the mass. maleic anhydride 0.0096% of the mass. benzoic acid 0.0126% of the mass. phthalic anhydride 2.0334% of the mass. carbon dioxide 0.6604% of the mass. carbon monoxide 0.6259% of the mass. propane 0.1459% of the mass. propylene 2,3772% of the mass. oxygen and 78.5670% of the mass. nitrogen

The mixture of reaction gases entering each of the three lines of the reactors is, respectively, a mixture of gas from the circulation loop and propylene of the “chemically pure” grade, into which primary air is then dosed. Mixing is carried out in appropriate mixers.

Between the reactors of the first and second stages, respectively, secondary air is supplied.

The number of starting reagents entering the first stage in accordance with the operating mode of each of the lines of reactors is:

A) gas circulating circuit 25339 kg / h,

chemically pure propylene 3481 kg / h,

air 17791 kg / h;

B) gas circulation circuit 38341 kg / h,

chemically pure propylene 4035 kg / h,

air 19561 kg / h;

C) gas circulating circuit 30874 kg / h,

chemically pure propylene 4689 kg / h,

air 23936 kg / h;

The composition of the three resulting reaction gas streams:

A) 10.2909% of the mass. oxygen 1.2926% of the mass. carbon dioxide 0.4136% of the mass. carbon monoxide 0.6533% of the mass. propane 7.2976% of the mass. propylene 1.5383% of the mass. water and 78.2693% of the mass. nitrogen C) 8.9782% of the mass. oxygen 1.4660% of the mass. carbon dioxide 0.4710% of the mass. carbon monoxide 0.6744% of the mass. propane 6.3907% of the mass. propylene 1.6626% of the mass. water and 80.0789% of the mass. nitrogen C) 10.6981% of the mass. oxygen 1.2357% of the mass. carbon dioxide 0.3948% of the mass. carbon monoxide 0.6500% of the mass. propane 7.6922% of the mass. propylene 1.4968% of the mass. water and 77.5992% of the mass. nitrogen

The gas mixture of the reaction products (177,184 kg / h) is cooled to a temperature of 107.3 ° C by direct cooling in a once-through irrigation cooler (quenching unit 1).

The liquid to be used for direct cooling of the gas mixture of the reaction products (quenching liquid 1) is a partial amount of mixture 1, including cubic liquid taken from the cube of the condensation column described below and a small amount (251 kg / h) of condensate taken from the quenching circuit 0.

Mixture 1 with a temperature of 104.9 ° C has the following composition:

The quench cooler of irrigation circuit 1 in order to direct cooling is supplied 458 ^m3 / h of the gas mixture of the reaction products having a temperature above. 3137 kg / h is fed into the second stripping column and 1195 kg / h into the quenching circuit 0 to inhibit the unwanted polymerization of the quenching liquid 0 and reflux directed to the uppermost plate of the second stripping column.

The mixture resulting from direct cooling, consisting of a gas mixture of reaction products cooled to 107.3 ° C and an unevaporated quenching liquid 1, as such is sent to the cube of the condensation column. The pressure in the cubic volume and the quenching unit 1 is 1.50 bar.

The inner diameter of the condensation column in the area of the plates of Torman is 6.5 m, in the remaining parts of the column is 6.0 m.

3137 kg / h of mixture 1 is fed into a second stripping column, which contains 50 double-flow plates as effectively separating the built-in elements. The second stripping column is similar to a condensation column provided with external thermal insulation. The internal diameter of the second stripping column in the area of the dual-flow trays is 2.4 m. The double-flow trays are located in the second stripping column at equal distances from each other (400 mm). The D: U ratio (see above) for all plates is 12%. The diameter of the holes of the first eight double-flow plates (in the direction from the bottom up) is 14 mm (the holes are strictly in accordance with the triangular gradation; the distance between the centers of the neighboring holes is 26 mm); the hole diameter of all subsequent double-flow plates is also 14 mm (the holes are also located strictly in accordance with the triangular gradation; the distance between the centers of adjacent holes is 25 mm).

3137 kg / h of mixture 1 with a temperature of 105.2 ° C enters the first eight bottom two-flow plates.

Energy is supplied to the second stripping column by means of a forced expansion shell-and-tube heat exchanger with forced circulation (see Grundoperationen chemischer Verfahrens-technik, 4th edition, Steinkopff, Dresden, 1974, p. 434). 271650 kg / h are sent to the evaporator of the second stripping column of bottoms liquid taken from the cube with a temperature of 151.7 ° C and a pressure of 1.655 bar, which has the following composition:

As a heat carrier, water vapor is passed through a zigzag-shaped space with corresponding reflective partitions surrounding the heat exchanger tubes at a pressure of 16 bar. When passing through the pipes of the heat exchanger, the bottoms liquid is heated, and 270,900 kg / h of the total amount of bottoms liquid passed through the heat exchanger with a temperature of 158.6 ° C is returned to the cube of the second stripping column. 750 kg / h of the total amount of bottoms liquid passed through the heat exchanger is removed, deaerated, diluted with methanol and sent to the burning of industrial waste.

In addition, 17424 kg / h, discharged from the upper part of the first stripper, containing acrylic acid of a gas with a temperature of 82.2 ° C and a pressure of about 2.50 bar, is supplied to the cube of the second stripping column, which has the following composition:

3.3977% of the mass. acrylic acid 1.1198% of the mass. acetic acid 4.1030% of the mass. water 0.0622% of the mass. formic acid 0.0321% of the mass. formaldehyde 0.1181% of the mass. acrolein 0.0030% of the mass. propionic acid 0,0006% of the mass. furfural 0.0139% of the mass. allyl formate 0.0247% of the mass. phthalic acid diethyl ester 2.5667% of the mass. oxygen 2.1951% of the mass. carbon dioxide 0.7129% of the mass. carbon monoxide 0.6756% of the mass. propane 0.1575% of the mass. propylene and 84.8133% of the mass. nitrogen

25831 kg / h of the second gas containing acrylic acid (temperature 96.7 ° C, pressure 1.58 bar) are discharged from the upper part of the second stripping column, which is cooled to a temperature of 80.9 by direct cooling in a countercurrent irrigation cooler (quenching unit 0) ° C and partially condensed.

20755 kg / h remaining after direct cooling of the gas mixture of the following composition with a pressure of 1.58 bar is returned to the still part of the condensation column (supply of still bottom liquid over the mirror):

18.5793% of the mass. acrylic acid 0.9849% of the mass. acetic acid 3.6185% of the mass. water 0.0571% of the mass. formic acid 0.0271% of the mass. formaldehyde 0.1006% of the mass. acrolein 0.0099% of the mass. propionic acid 0,0436% of the mass. furfural 0,0003% of the mass. allyl acrylate 0.0117% of the mass. allyl formate 0.0053% of the mass. benzaldehyde 0.0642% of the mass. maleic anhydride 0.0001% of the mass. benzoic acid 0.0001% of the mass. diacrylic acid 0.0001% of the mass. p-methoxyphenol 2.1548% of the mass. oxygen 1.8428% of the mass. carbon dioxide 0.5985% of the mass. carbon monoxide 0.5672% of the mass. propane 0.1322% of the mass. propylene and 71,2018% of the mass. nitrogen

As quenching liquid 0, 32956 kg / h of a mixture consisting of 1195 kg / h of mixture 1 and 37761 kg / h of condensate formed in quenching unit 0 as a result of direct cooling are used (for this, the indicated partial amount of the mixture is cooled with water in an indirect spiral-type heat exchanger from 80.9 to 40.1 ° C). 6020 kg / h of the specified mixture with a temperature of 80.9 ° C as reflux is sent to the uppermost plate of the second stripping column.

The mixture has the following composition:

A centrifugal droplet separator is mounted in the cubic volume of the condensation column, which prevents droplets from dropping from the cubic column into its upper part.

As indicated above, the bottom volume of the condensation column at the level of 7.80 m (all levels are counted from the bottom of the bottom) is completed by the first catching plate (storage plate; fireplace type plate with sixteen almost evenly distributed conventional fireplaces with a diameter of 600 mm, height 1 m).

The storage plate has double walls with an inward angle of inclination of 2 ° and is equipped with a central outlet valve and an outlet fitting (nominal diameter of about 200). The free gas section is about 30%.

The fraction of heavy boiling products (88579 kg / h) from the specified first trap plate enters the bottom volume below it.

The fraction of heavy boiling products with a temperature of 99.8 ° C and a pressure of about 1.50 bar has the following composition:

94.6665% of the mass. acrylic acid 0.5402% of the mass. acetic acid 1.3577% of the mass. water 0.0160% of the mass. formic acid 0.0014% of the mass. formaldehyde 0.0071% of the mass. acrolein 0.0577% of the mass. propionic acid 0.3814% of the mass. furfural 0.0023% of the mass. allyl acrylate 0.0010% of the mass. allyl formate 0.1279% of the mass. benzaldehyde 2.1925% of the mass. maleic anhydride 0.0051% of the mass. benzoic acid 0.0046% of the mass. phthalic anhydride 0.6008% of the mass. diacrylic acid 0.0061% of the mass. phenothiazine 0.0314% of the mass. p-methoxyphenol and 0,0002% of the mass. oxygen

The temperature of the cube is 104.9 ° C, the pressure above the liquid level is 1.51 bar.

At a level of 2.0 m from the first catching plate is the first two-line plate of fifteen such plates. Similar double-flow plates (the number of holes in each of them is 33678) are at the same distance from each other, which is 380 mm. The same through circular holes have a diameter of 14 mm, with the remaining burrs after felling, facing down the distillation column. The centers of the holes are strictly ordered according to the triangular gradation. The distance between the centers of the two nearest holes is 24.5 mm.

The fifteenth double-flow plate serves as a distribution plate. Accordingly, at the walls of the column between the second catching plate and the fifteenth two-line plate there are two insertion pipes (conditional passage about 150) with 45 outlet openings with a diameter of 15 mm in each insertion pipe.

From the point above the insertion tubes, crude acrylic acid and mother liquor are returned to the condensation column.

The first series of double-flow plates is completed by a second catching plate (storage plate; fireplace-type plate with sixteen almost evenly distributed conventional fireplaces with a height of about 1.70 m with an outlet fitting (nominal passage of about 250) with a central shutter and a free gas section of about 30%), which 1.50 m above the last double-threaded plate.

From the indicated second trap plate at a pressure of 1.48 bar, crude acrylic acid with a temperature of 97.1 ° C, which has the following composition, is continuously taken as the first side selection.

96.7716% of the mass. acrylic acid 0.8253% of the mass. acetic acid 1.6640% of the mass. water 0.0213% of the mass. formic acid 0.0018% of the mass. formaldehyde 0.0070% of the mass. acrolein 0.0681% of the mass. propionic acid 0.1642% of the mass. furfural 0.0027% of the mass. allyl acrylate 0.0012% of the mass. allyl formate 0.0164% of the mass. benzaldehyde 0.1052% of the mass. maleic anhydride 0.3278% of the mass. diacrylic acid 0.0050% of the mass. phenothiazine 0.0180% of the mass. p-methoxyphenol and 0,0002% of the mass. oxygen

18474 kg / h of crude acrylic acid, taken from the second catching plate, together with 72716 kg / h of mother liquor, formed during the additional crystallization treatment of the selected crude acrylic acid and heated in the indirect heat exchanger, the selected crude acrylic acid and steam to be used as a heat carrier 90 ° C, is returned to the condensation column through the above-mentioned insertion pipes to a two-flow plate located directly under the second catching plate.

89303 kg / h of crude acrylic acid, taken from the second catching plate, is subjected to indirect heat exchange to multi-stage cooling to a temperature of 29 ° C (in particular, with heat recovery of the above mother liquor to be returned to the condensation column) and, if necessary, sent to intermediate storage into the appropriate tank. Then, 1204 kg / h of acidic water taken from the second side selection of the condensation column is added to the cooled crude acrylic acid.

Acidic water has the following composition:

10.7677% of the mass. acrylic acid 6.4390% of the mass. acetic acid 79.5610% of the mass. water 0.7038% of the mass. formic acid 2.4712% of the mass. formaldehyde 0.0132% of the mass. acrolein 0.0082% of the mass. propionic acid 0.0013% of the mass. furfural 0,0331% of the mass. allyl formate 0.0001% of the mass. p-methoxyphenol and 0.0013% of the mass. oxygen

The resulting mixture by repeated indirect heat transfer (countercurrent cooling brine, which is a mixture of 25 to 35% by weight of glycol and from 65 to 75% by weight of water) is cooled to 16 ° C and sent to two or three concurrently operating crystallizers with cooling disks ( see international application WO 2006/111565). We are talking about the respective tanks, each of which at the same distance from each other, amounting to 30 ± 1 cm, contains 24 successively suspended rubbed round cooling plates with a diameter of 3.3 m (inside each plate there is a cooling medium, which is a mixture of water and glycol with a glycol content of 25 to 35% by weight.). In this case, the corresponding cooling medium moves through the corresponding crystallizer from one cooling disk to the other cooling disk located above it in countercurrent with respect to the crystallizing mixture. The corresponding cooling medium is passed through the cooling plates of the corresponding mold in the form of two parallel flows. One stream is passed through even cooling plates, while the other stream is passed through odd cooling plates (plate numbering starts from one and corresponds to the direction of flow). The total flow rate of the cooling medium through each mold is from 180 to 220 t / h (from 90 to 110 t / h per stream). The pressure loss for each cooling disc is 60 to 100 mbar. The temperature of the cooling medium at the inlet is from +2.5 to + 3 ° С. The temperature of the cooling medium at the outlet is 2.5 ° C higher than its inlet temperature. The thickness of the cooling planes made of special steel is 4 mm. The heat transfer coefficient of the brine is in the approximate range from 1500 to 2500 W / (m ² · K). The values of the heat transfer coefficient in most cases lie in the range from 380 to 420 W / (m ² · K). The specific cooling capacity is 1.5 ± 0.2 kW / m ^{2 of the} cooling surface. The wiping of the cooling plates prevents the formation of a layer of crystals. The moistened crude acrylic acid is continuously passed through appropriate crystals with overflow control by means of a pump. In this case, a single-phase moistened crude acrylic acid (residence time 2.5 hours) is condensed to a two-phase suspension containing acrylic acid crystals as a solid phase, with a temperature of 7 to 8.5 ° C and a solids content of about 25% of the mass . The specific gravity of the suspension usually corresponds to an interval from 1110 to 1115 kg / m ³ . The rotation speed of the wiper blades is from 5 to 6 rpm The drive shaft passed through the centers of the cooling disks is equipped with a gland seal washed with water (gland packing in the form of a Teflon or graphite cord, the flow rate of wash water from several liters to several tens of liters per hour for each seal).

A hollow profile (in the simplest version, for example, a tube to be welded) heated by means of a second heat carrier (for example, also a water / glycol mixture) to a temperature exceeding the crystallization temperature and, in most cases, is in the range from 8 to 20 ° C, preferably from 10 to 14 ° C. In this case, the second heat carrier forms parallel heating flows.

In addition, the wiper blades in the radial direction are preferably segmented (four segments). The specific clamping force of the cleaners in the mounted state, acting perpendicular to the cooled plane, is from 3 to 5 N / cm of the length of the active wiping edge. High-molecular-weight polyethylene or ultra-high-molecular-weight polyethylene grades, such as Multilene ^® PE 1000, are used as the material for cooling plate cleaners. For example, in addition to the cleaners, the shaft also rotates the blades for better mixing, between each two, and also before the first and last cooling discs, respectively, it is advisable to have two symmetrically ordered blades.

A pipe adjoins the rear side of the corresponding crystallizer in the direction of movement of the suspension (preferably after the last cooling disk) (it is expediently immersed in the suspension; in another embodiment, the suspension through the overflow device can flow into the collector with a mixer, from where it is sent to the wash columns), which suspension in order to separate the mother liquor from the suspended crystallizate is sent to the hydraulic columns for washing with a melt, described in the European patent application nt EP A 1272453 and EP A 1448283, international application WO 03/041833, European patent application EP A 1305097, as well as in German patent applications DE A 10156016, DE A 102005018702 and DE A 10223058. The diameter of the wash columns is 1.4 m. The suspension of crystals in the washing columns is carried out by means of a centrifugal pump (such as a tunnel wheel), and the flow rate of the suspension is preferably controlled by varying the speed of the pump. The flow in the pump control line is also made in the form of a circulation circuit with a control valve. The slurry flow rate used to control the wash column in the control line is usually from 5 to 60 t / h, in most cases from 8 to 30 t / h. If the flow rate of the liquid contained in the suspension supplied to the wash column is sufficient for transporting the crystalline layer, the corresponding wash column can sometimes be operated without using a control flow. The ratio of the pressure drop providing transport, to the pressure drop providing flushing, is usually from 1.1: 1 to 3: 1, in most cases from 1.2: 1 to 1.8: 1. The frequency of rotation of the knife in most cases is from 5 to 10 rpm. The temperature in the melt circuit is usually from 13 to 16 ° C. The control of the filtration front is carried out according to the German patent application DE A 102005018702 by means of two results of measuring the pressure drop across sections of a layer of variable length that are comparable to each other. The washing front is controlled by measuring the temperature in the crystalline layer.

The total height of the crystalline layer, depending on the nature of the regulation, is from 250 to 1500 mm, in most cases from 600 to 1100 mm. The flushing front is typically located above the knife by a value ranging from 100 to 200 mm. A centrifugal pump with washing the shaft seal on the melt side (double contact sealing ring with a sealing medium cooled to a temperature of 15 to 30 ° C (water / glycol mixture) or a pump with an electromagnetic coupling and an intensive flushing bearing system is suitable as a melt circulation pump) ) The volume of the melt circulating in the corresponding circuit is from 10 to 15 m ³ / h per ton of purified crystallizate removed by a knife. Depending on the purpose of acrylic acid and the column design, the melt is stabilized in the circulation loop by means of p-methoxyphenol, used in a concentration of from 200 to 300 or from 40 to 70 wt. parts per million, or phenothiazine used in a concentration of from 100 to 300 wt. ppm. Air or lean air (a mixture of nitrogen with air containing less than 6 vol.% oxygen) is additionally supplied to the melt circulation circuit, the excess of which (the part that does not dissolve in the wash melt) is separated by a gas separator before the wash melt enters the wash column . As a result, the content of dissolved oxygen in the molten pure product is from 5 to 40 wt. parts per million ^- .

[a) In order to obtain acrylic acid suitable for esterification, the selection of the corresponding suspension crystallizate can be carried out not in a melt column, but by means of a centrifuge (for example, a two-stage or three-stage pulsating centrifuge). Suitable are sieves with a mesh size of 150 to 300 μm, suitable centrifugal acceleration is from 500 to 900 g, in most cases from 600 to 800 g, a suitable number of strokes per minute is from 40 to 80.

For washing one kilogram of crystals recovered in the second or third stage of the centrifuge, preferably 0.15 to 0.3 kg of washing liquid is used. The temperature of the washing liquid is from 15 to 30 ° C., preferably from 20 to 30 ° C. To prevent the formation of deposits, the channel for discharging solids from the centrifuge is washed with a washing liquid thermostatically controlled in the temperature range from 15 to 30 ° C. The washing and washing liquids are preferably centrifuged and washed molten crystallizate. In order to prevent the formation of deposits and crystalline crusts, the centrifuge body, the suspension supply pipe and the washing liquid supply pipe are expediently thermostated in the temperature range from 15 to 40 ° C. It is advisable to inert the working volume of the centrifuge by means of nitrogen or a mixture of air and nitrogen. The shaft seal is purged with gas (for example, nitrogen or a mixture of air and nitrogen) or washed with water.

b) Alternatively, for slurry crystallization, layer-by-layer crystallization technology (for example, falling-film crystallization according to European patent application EP A 616998 or crystallization in a continuous through-flow pipe) with two, three or more (for example, from two to four) cleaning steps. Instead of returning the mother liquor from the subsequent purification step to the previous one, it can also be returned together to the condensation column.]

From the melt circulation circuits stabilized by adding a solution (104 kg / h) of p-methoxyphenol (3 kg / h) at a temperature of 25 ° C and a pressure of 1.1 bar in a pure acrylic acid melt taken from the circulation circuits (101 kg / h ) with a temperature of 25 ° C, 17894 kg / h of pure acrylic acid are taken (temperature 14 ° C, pressure 1.5 bar), which has the following composition:

99.7334% of the mass. acrylic acid 0.2091% of the mass. acetic acid 0.0180% of the mass. water 0.0230% of the mass. propionic acid 0.0001% of the mass. furfural <0.0001% of the mass. benzaldehyde 0.0001% of the mass. maleic anhydride 0,0002% of the mass. diacrylic acid 0.0150% of the mass. p-methoxyphenol and 0.001% of the mass. oxygen

Acrylic acid of the above composition is excellently suited for the production of polysodium acrylate-based superabsorbers.

To prepare a solution of inhibitor 1 having a temperature of 25 ° C, 5 kg / h of phenothiazine are dissolved in 352 kg / h of the above heated pure acrylic acid. To prepare an inhibitor 2 solution having a temperature of 25 ° C., 19 kg / h of p-methoxyphenol is dissolved in 30 kg / h of the inhibitor 1 solution.

17439 kg / h of pure acrylic acid stabilized by p-methoxyphenol with a temperature of 25 ° C and a pressure of 1.5 bar is continuously fed into the storage tank.

The mother liquor separated in the wash columns is first sent to a heated collector, from which it enters the storage tank. 72716 kg / h of mother liquor from this tank, heated to 90 ° C using the above heat recovery system, together with 18474 kg / h of crude acrylic acid taken from the second collecting tray are returned to the condensation column to the fifteenth bottom two-flow tray. Such a return uterine liquor has the following composition:

94.6188% of the mass. acrylic acid 1.0690% of the mass. acetic acid 3.3562% of the mass. water 0,0378% of the mass. formic acid 0.0431% of the mass. formaldehyde 0.0088% of the mass. acrolein 0.0782% of the mass. propionic acid 0.2016% of the mass. furfural 0.0034% of the mass. allyl acrylate 0.0021% of the mass. allyl formate 0,0202% of the mass. benzaldehyde 0.1292% of the mass. maleic anhydride 0.4025% of the mass. diacrylic acid 0.0061% of the mass. phenothiazine 0.0227% of the mass. p-methoxyphenol and 0,0003% of the mass. oxygen

In the condensation column above the second trap plate at a distance of 2.9 m from it is the first of 21 double-flow trays of the type described above (hole diameter 14 mm, number of holes 32020, the distance between the centers of two adjacent holes 24.5 mm), which are on the same a distance of 380 mm from each other.

At a level 800 mm higher than the level of the last double-flow plate, the conical expansion of the condensation column begins. The conical expansion is completed at a distance of 500 mm from the last double-flow plate (the inner diameter of the column at this point is 6.50 m).

At the indicated level (1.50 m above the last two-line plate), a series of 28 ordinary single-line Torman plates at the same distance from each other (500 mm) begins. The first bottom plate of Torman has a design in accordance with which the liquid flows from it through six drain pipes in the form of pipes. The pipes are hydraulically sealed relative to the gas space below the double-flow plate. The slide height of the six drain pipes decreases in the direction of flow of the plate with cross current. The hydraulic seal is equipped with idle holes with reflective plates. Drain pipes are evenly distributed in the last third of the cross section of the plate (from the opposite side from the supply side). The hydraulic seal is realized by a shutter with an inclined overflow device (inclination angle 45 °).

In addition, the Torman plates have a design in accordance with which, due to the placement of injection slots in their casings in grooves sequentially located in the transverse flow direction, a corresponding counter fluid flow is formed.

The D: U ratio (see above) for Torman plates is 14%. The ratio of the area of the fireplace to the area of the output section of the slots is 0.8. The height of the fireplace and the height of the drain pipe are respectively 40 mm. The gap of the caps (the distance between the lower edge of the slot and the plate) is 10 mm. The height of the slots is 15 mm. The angle between the expanding slot and the longitudinal edge of the casing is 30 degrees. The maximum length of the longitudinal edge of the casing is 800 mm. In the inner marginal zones of the column, the length of the casing is reduced to 200 mm, which is due to the need to bring its configuration in accordance with the curvature of the column. The distance between two housings located on one line in the direction of flow is 66 mm. The flow area of the drain pipe is 1.5% of the plate cross-sectional area. The distance between the two lower longitudinal edges of the casing is 64 mm.

At the level corresponding to the topmost plate of Torman, the conical narrowing of the distillation column begins again. The narrowing is completed at a level 700 mm above the topmost plate of Torman (the diameter of the column at this point is again 6.00 m).

At a height of 1.70 m above the top plate of Torman there is a third catching plate (storage plate, fireplace-type plate with sixteen almost evenly distributed conventional fireplaces with a height of 1.50 m).

535506 kg / h of acidic water with a temperature of 65.1 ° C and a pressure of about 1.24 bar are discharged from the third catching plate as a second side extraction.

Acidic water has the following composition:

10.7677% of the mass. acrylic acid 6.4390% of the mass. acetic acid 79.5610% of the mass. water 0.7038% of the mass. formic acid 2.4712% of the mass. formaldehyde 0.0132% of the mass. acrolein 0.0082% of the mass. propionic acid 0.0013% of the mass. furfural 0,0331% of the mass. allyl formate 0.0001% of the mass. p-methoxyphenol and 0.0013% of the mass. oxygen

25537 kg / h of selected acidic water with a temperature of 65.1 ° C together with the inhibitor solution 2 is returned to the topmost plate of Torman.

329 kg / h of a solution of inhibitor 1 with a temperature of 25 ° C is returned to the nineteenth bottom plate of Torman.

316 kg / h of selected acidic water is sent for combustion.

310 m ³ / h of selected acidic water with a temperature of 29.1 ° C is returned to the valve plate described below, the sixth bottom (acidic water is cooled by multi-stage indirect heat exchange).

194011 kg / h of selected acidic water with a temperature of 23 ° C is returned to the uppermost valve plate described below (it is cooled together with the above amount of acidic water by multi-stage indirect heat exchange; cooling from 29.1 to 23 ° C in the last stage is carried out separately at simultaneous heat recovery (liquid chemically pure propylene is used as a cooling agent and vaporized propylene gas is then used to form a mixture of reaction gases intended A gas-phase partial oxidation)).

1204 kg / h of selected acidic water, as described above, is added to the crude acrylic acid to be further crystallized.

6010 kg / h of selected acidic water is sent to the extraction column for the purpose of subsequent extraction according to the invention.

At the level of 2300 mm above the third catching plate in the condensation column at the same distances from each other (500 mm) are eleven double-flow valve plates. The height of the respective drain pipes is from 18 to 35 mm (for upper plates it is greater than for lower ones). The D: U ratio (see above) is 14.8%, the total flow area of the drain pipes of two valve plates in series is about 10% of the cross-sectional area of the column. As valves use valves W12 company Stahl (Germany, Wirnheim).

The pressure at the top of the column is 1.17 bar. 170121 kg / h of residual gas with a temperature of 31 ° C, which has the following composition, is removed from the upper part of the column:

0.1946% of the mass. acrylic acid 0.1246% of the mass. acetic acid 2.3031% of the mass. water 0.0062% of the mass. formic acid 0.1212% of the mass. acrolein 0,0002% of the mass. propionic acid 0.0001% of the mass. furfural 0.0027% of the mass. allyl formate 2.3427% of the mass. carbon dioxide 0.7609% of the mass. carbon monoxide 0.7211% of the mass. propane 0.1681% of the mass. propylene 2.7387% of the mass. oxygen and 90.5158% of the mass. nitrogen

The residual gas is heated in an indirect heat exchanger to 38 ° C, after which 110880 kg / h of the specified residual gas is compressed by means of a gas compressor for the circulation circuit to 2.9 bar, and the temperature rises to about 160 ° C. 94553 kg / h of compressed residual gas is returned to the gas-phase partial oxidation as the gas circuit. 16327 kg / h of compressed residual gas is sent to the first stripping column to steam off the extract of the acid water extraction unit, while 59241 kg / h of residual gas is sent to combustion.

The extraction column designed for the extraction of acidic water, as effectively separating the built-in elements, contains perforated structured nozzles of the Montz-Pak B1-350 type, arranged one above the other, with an active total height of 10 m (the height of the nozzle elements is 200 mm, the nozzle is made of special sheet steel 1.4571).

The inner diameter of the extraction column, regardless of the type of nozzles used, is 800 mm. The height of the extraction column is 14 m. The product Palatinol ^® A is used as the extractant. The bottom and top of the extraction column are expanded to a diameter of 1100 mm, which contributes to a more efficient separation of the phases in the cube and reduces the entrainment of the extracting agent to the top of the column. In addition, as an auxiliary agent used to reduce coalescence, in the upper part of the column there is a bulk layer of polymer filler particles (for example, polyethylene or Teflon).

The supply of 6010 kg / h of acidic water to be extracted with a temperature of 65.1 ° C. is carried out below the lowest nozzle of the extraction column through the corresponding through holes of the distribution manifold, the diameter of which is 8 mm. A mixture of about 25 kg / h of fresh Palatinol ^® A product and 5987 kg / h of the return from the first stripping column and the extraction agent stripped therein at a temperature of 50 ° C. is fed above the topmost nozzle of the extraction column.

The returned extracting agent has the following composition:

≤0.5% of the mass. acrylic acid ≤0.03% of the mass. acetic acid ≤0.02% of the mass. water ≤0.001% of the mass. formic acid ≤0.0035% of the mass. acrolein ≤0,0005% of the mass. propionic acid ≤0.001% of the mass. furfural ≤0.001% of the mass. allyl formate 0.03% of the mass. p-methoxyphenol 0.0001% of the mass. oxygen and ≥99.5% of the mass. Palatinol ^® A

The specific gravity of acidic water is 967.5 kg / m ³ . The extracting agent is also fed through the corresponding through holes with a diameter of 4 mm distribution manifold.

Acidic water forms a continuous phase, while the extracting agent forms a dispersed phase in the form of droplets (droplet diameter is from 2 to 5 mm) rising in the aqueous phase.

From the top of the extraction column 4930 kg / h of purification product (temperature of about 57.6 ° C) are selected, which has the following composition:

1.7618% of the mass. acrylic acid 4.3046% of the mass. acetic acid 90.1197% of the mass. water 0.6446% of the mass. formic acid 2.8993% of the mass. formaldehyde and 0.27% of the mass. Palatinol ^® A

Together with the residual gas to be burned, it is sent for combustion.

7090 kg / h of extract with a temperature of about 64.5 ° C., which has the following composition, are selected from the cube of the extraction column.

8.1556% of the mass. acrylic acid 2.4838% of the mass. acetic acid 4.7901% of the mass. water 0.1490% of the mass. formic acid 0.0788% of the mass. formaldehyde 0.0140% of the mass. acrolein 0.0073% of the mass. propionic acid 0.0014% of the mass. furfural 0.0282% of the mass. allyl formate 0.0192% of the mass. p-methoxyphenol and 84.2726% of the mass. Palatinol ^® A

The entire amount of extract is sent to the top of the first stripping column. The extract is subjected to preliminary indirect heating to a temperature of 95 ° C in a plate heat exchanger. In this case, 5987 kg / h of bottoms liquid taken from the first stripping column are used as a heat carrier. As effectively separating the built-in elements, the first stripping column contains five dual-flow trays and fifteen Torman trays. Similarly to the extraction column, the first stripping column is provided with external thermal insulation. The inner diameter of the first stripping column at the level of all plates is 1.5 m

The height of the first stripping column is 14.5 m. The five lowest trays are double-flow trays located at a distance of 500 mm from each other. The D: U ratio (see above) for all double-flow plates is 18%. The diameter of the holes for all double-flow plates is 14 mm (the holes are located strictly in accordance with the triangular gradation). Above the highest double-threaded plate are fifteen single-threaded Torman plates, which are at the same distance from each other (500 mm). Torman plates have a design in accordance with which, due to the placement of injection slots in their casings in grooves, sequentially located in the direction of the transverse flow, a corresponding counter flow of liquid is formed. The D: U ratio (see above) is 14%.

Above the last plate is a bulk layer of 400 mm high Polla rings made of metal (rings 25 × 25) used as a droplet eliminator.

13000 nm ³ / h of compressed residual gas with a pressure of about 2.9 bar and a temperature of about 160 ° C, which rises countercurrently with respect to the extract flowing down along the stripper column, are fed into the first stripping column below the lowest double-flow tray.

From the upper part of the first stripping column, 17424 kg / h of the first gas containing acrylic acid with a temperature of 82.2 ° C are withdrawn, which is sent to the second stripping column. The temperature in the cube of the first stripping column is about 155 ° C. From the cube of the first stripping column, 49311 kg / h of bottoms are continuously withdrawn. 5987 kg / h of the first bottoms column taken from the cube is cooled to 50 ° C by a two-stage indirect heat exchange (the first stage is realized in a plate heat exchanger by allowing the heat of countercurrent cooling to be recovered by the extract) and returned to the top of the extraction column. 43324 kg / h of bottoms liquid taken from the first stripping column is heated to 160 ° C in an external expansion heat exchanger with forced circulation and returned to the first stripping column.

Comparative example

The example is performed similarly to the previous example. However, the acidic water extracted in accordance with Example 1 is not subjected to extraction, but is burned in accordance with the prior art.

The extraction column and the first stripping column are absent. An appropriate amount of compressed residual gas is used for stripping the bottoms liquid taken from the condensation column. Through the first side extraction, a stream of crude acrylic acid (87307 kg / h) containing 96.863% of the mass is discharged. acrylic acid.

The amount of pure acrylic acid sent to the storage tank is 16,994 kg / h. The degree of purity of the corresponding acrylic acid is 99.736% of the mass.

Example 2

In a water-thermostatic vessel with an internal volume of 1.3 l, equipped with a jacket and a two-stage three-blade stirrer, at 50 ° C, 498 g of acidic water without an inhibitor with a temperature of 50 ° C was loaded, which had the following composition:

2.19% of the mass. formaldehyde 82.00% of the mass. water 4.01% of the mass. acetic acid 11.09% of the mass. acrylic acid 0.69% of the mass. formic acid and 0.01% of the mass. diacrylic acid

Then, 499 g of dimethyl phthalate was added with stirring, the temperature of which was also 50 ° C. The resulting mixture was stirred for 10 minutes at a constant temperature (50 ° C) and a stirrer speed of 250 rpm. After the mixer was turned off, the mixture was kept at 50 ° С, and after a short time the phases were separated. The mass of the organic phase was 565 g, the weight of the aqueous phase was 432 g. According to the results of a gas chromatographic analysis of the aqueous phase, it contained 20.26 g of acrylic acid and 13.0 g of acetic acid.

Example 3

A glass extraction column was used to extract the acrylic acid of acidic water. Acidic water not containing polymerization inhibitors had the following composition:

2.36% of the mass. formaldehyde 83.12% of the mass. water 3.98% of the mass. acetic acid 9.70% of the mass. acrylic acid 0.68% of the mass. formic acid and 0.01% of the mass. diacrylic acid

The extraction column was thermostatically controlled by means of water passing through its jacket at a temperature of 60 ° C. As an effectively separating built-in elements, the extraction column contained structured packing bodies made of special sheet steel 1.4404 (perforated nozzle type B1-350 from Montz). The inner diameter of the extraction column in its nozzle-filled portion was 40 mm. 10 kg / h of an aqueous solution with a temperature of 60 ° C. was fed into the cube of the column. 10 kg / h of diethyl phthalate used as the dispersed phase with a droplet size of 4 to 5 mm (temperature 60 ° C) were counter-fed to the upper part of the extraction column. The aqueous purification product withdrawn from the top of the column contained 0.8% of the mass. acrylic acid and 2.9% of the mass. acetic acid. Thus, the content of acrylic acid in acidic water was able to increase to 93.3% of the mass. (in terms of its initial mass amount), and the content of acetic acid up to 41% of the mass. The purification product was present 0.2% of the mass. dissolved diethyl phthalate.

Example 4

Example 3 was repeated. As the extracting agent and the dispersed phase, 27.5 kg / h of dimethyl phthalate (temperature 60 ° C., droplet size 4 to 5 mm) was supplied to the top of the extraction column. Acidic water with a temperature of 60 ° C, simultaneously supplied to the cube of the column as a continuous phase (27.5 kg / h), had the following composition:

2.77% of the mass. formaldehyde 82.82% of the mass. water 4.02% of the mass. acetic acid 9.53% of the mass. acrylic acid 0.63% of the mass. formic acid and 0.05% of the mass. diacrylic acid

Leaving from the top of the extraction column, the aqueous purification product contained 0.2% of the mass. acrylic acid and 2.4% of the mass. acetic acid. Thus, the content of acrylic acid in acidic water could be increased to 98.3% of the mass. (in terms of its initial mass amount), and the content of acetic acid up to 51.5% of the mass. The purification product contained 0.9% of the mass. dissolved dimethyl phthalate.

Example 5

The example was carried out analogously to example 1. In addition to reflux (acidic water) together with it and at the same temperature, 1000 kg / h of water was supplied to the condensation column as an additional absorbent. As a result, the content of furfural in the crude acrylic acid discharged from the second trap plate of the condensation column as the first side selection decreased from 0.1642% of the mass. (example 1) to 0.1225% of the mass.

Example 6

The example was carried out analogously to example 1. In addition to phlegm (acidic water) together with it and at the same temperature, 5000 kg / h of water was supplied to the condensation column as an additional absorbent. As a result, the content of furfural in the crude acrylic acid discharged from the second trap plate of the condensation column as the first side selection decreased from 0.1642% of the mass. (example 1) to 0.1125% of the mass.

Claims (21)

1. A method of producing acrylic acid, according to which, by means of a heterogeneously catalyzed gas-phase partial oxidation by molecular oxygen of at least one corresponding starting compound with three carbon atoms on solid state catalysts, a gas mixture of products containing acrylic acid is obtained, water vapor and side components, the temperature of this mixture, if necessary, is reduced by direct and / or indirect cooling then the specified mixture is sent to a condensation column equipped with effectively separating elements, along which it independently rises while fractional condensation flows simultaneously, and through the first lateral extraction, which is higher than the supply of the reaction gas mixture into the condensation column, depleted of water from the condensation column and by-products, crude acrylic acid as a target product, through a second selection above the first side selection the liquid phase contains acidic water containing acrylic acid and side components from the condensation column, residual gas mixture containing side components boiling at a lower temperature than water is removed from the top of the condensation column, bottoms containing acrylic acid are removed from the cube of the condensation column, as well as by-products and by-products boiling at a higher temperature than acrylic acid, a partial amount of acidic water taken as such and / or after cooling The reactions are returned to the condensation column as reflux, and the crude acrylic acid, if necessary, is subjected to further purification by at least one other thermal separation method, and, if necessary, a partial amount of selected acid water is added to the crude acrylic acid before further crystallization treatment, characterized in that acrylic the acid contained in at least a partial amount of acidic water not returned to the condensation column is converted from acidic water to organic a solvent by extraction by this solvent followed by the formation of an acrylic acid-containing organic extract, from which acrylic acid is subsequently isolated by stripping it with a first stripping gas, the first stripping gas containing acrylic acid being returned to the condensation column and / or acrylic acid, contained in the first stripping gas is transferred to an aqueous solution of metal hydroxide or the resulting first stripping gas containing acrylic acid is used as a second stripping gas to vaporize the acrylic acid contained in the bottoms liquid discharged from the condensation column, and the resulting second stripping gas containing acrylic acid is returned to the condensation column and / or acrylic acid contained in the second stripping gas, transferred to an aqueous solution of metal hydroxide. 2. The method according to claim 1, characterized in that the starting compound with three carbon atoms is propylene, acrolein or a mixture of propylene with acrolein. 3. The method according to claim 1, characterized in that the acrylic acid contained in at least 25 wt.% Non-returnable acidic water in the condensation column is converted into an organic solvent by extraction carried out by this solvent, accompanied by the formation of an organic extract containing acrylic acid from which acrylic acid is subsequently isolated by stripping it with a first stripping gas, the first stripping gas containing acrylic acid being returned to the condensation column and / or acrylic to the slot contained in the first stripping gas is transferred to an aqueous solution of metal hydroxide, or the resulting first stripping gas containing acrylic acid is used as the second stripping gas to vaporize the acrylic acid contained in the bottoms liquid withdrawn from the condensation column, and thus formed the second stripping gas containing acrylic acid is returned to the condensation column and / or the acrylic acid contained in the second stripping gas is transferred to an aqueous solution Op metal hydroxide. 4. The method according to claim 1, characterized in that the extraction of acrylic acid from acidic water is carried out in an extraction column, which contains nozzles and / or mesh plates as effectively separating the built-in elements. 5. The method according to claim 4, characterized in that an organic solvent is fed into the upper part of the extraction column, and acidic water is fed into the cube zone, the organic solvent falling in the form of a phase dispersed in a continuous acidic aqueous phase, or characterized in that acidic water is fed into the top of the extraction column, and an organic solvent is fed into the cube zone, and the organic solvent rises in the form of a phase dispersed in a continuous acidic aqueous phase. 6. The method according to claim 1, characterized in that the organic solvent contains at least one ester based on aliphatic or aromatic monocarboxylic acid with 5-20 carbon atoms and alcohol with 1-8 carbon atoms. 7. The method according to claim 1, characterized in that the organic solvent contains at least one diester based on aliphatic or aromatic dicarboxylic acid with 5-20 carbon atoms and alcohol with 1-8 carbon atoms. 8. The method according to claim 1, characterized in that the organic solvent is dimethyl phthalate, diethyl phthalate, dimethyl isophthalate, diethyl isophthalate, dimethyl terephthalate and / or diethyl terephthalate. 9. The method according to claim 1, characterized in that the boiling point of the organic solvent at atmospheric pressure is ≥200 ° C. 10. The method according to claim 1, characterized in that the stripping of bottoms liquid withdrawn from the condensation column is carried out in a stripping column equipped with effectively separating built-in elements, the temperature in the cube of which is from 150 to 190 ° C. 11. The method according to claim 1, characterized in that before returning the second stripping gas containing acrylic acid to the condensation column and / or transferring the acrylic acid contained in the second stripping gas to an aqueous solution of metal hydroxide, a second stripping gas containing boiled acrylic acid is subjected to counter-current rectification. 12. The method according to claim 1, characterized in that the first stripping gas using air, nitrogen, carbon dioxide and / or water vapor. 13. The method according to claim 1, characterized in that the residual gas mixture is used as the first stripping gas. 14. The method according to claim 1, characterized in that the crude acrylic acid is subjected to additional crystallization treatment. 15. The method according to claim 1, characterized in that a partial amount of acidic water that is not returned to the condensation column is added to the crude acrylic acid before further crystallization treatment. 16. The method according to 14, characterized in that the additional crystallization purification of crude acrylic acid or its mixture with acidic water is carried out by suspension crystallization. 17. The method according to clause 16, characterized in that a wash column is used to separate the mother liquor remaining after suspension crystallization and suspension suspension formed during suspension crystallization. 18. The method according to claim 1, characterized in that a partial amount of the residual gas mixture as the gas of the circulation loop is returned to the gas-phase partial oxidation. 19. The method according to claim 1, characterized in that under extraction conditions the specific gravity of the organic solvent is ≥25 kg / m ³ different from the specific gravity of water. 20. The method according to claim 1, characterized in that the aqueous metal hydroxide solution contains dissolved sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ) and / or magnesium hydroxide (Mg (OH) ₂ ) 21. The method according to one of claims 1 to 20, characterized in that a liquid absorbent is supplied to the condensation column between the first lateral extraction and the second lateral extraction, whose boiling point T _s at atmospheric pressure is higher than or equal to the boiling temperature T _{w of} water at atmospheric pressure .