KR100493345B1 - Method for Removing by-Products Obtained When Producing Acrylic Acid or Methacrylic Acids - Google Patents

Abstract

A method for removing the low, medium and high boiling point secondary components produced in the preparation of (meth) acrylic acid, comprising adding a low boiling point and a medium boiling point secondary component dissolved in water together with the high boiling point secondary components treated with a solvent. While gaseous low boiling secondary components are burned.

Description

Method for removing by-products obtained when producing acrylic acid or methacrylic acids

The present invention is described in detail with reference to the following examples showing preferred embodiments.

The following description refers to a plant for the production of acrylic acid carried out according to the method described in DE-A-2-136 396, wherein the product containing acrylic acid is 80% by weight of difill (a mixture of diphenyl ether and diphenyl) after synthesis And 20 wt% of dimethylphthalate (DMP). The actual reaction apparatus is consistent with the process shown in FIG. 2, and only the columns / K1 to K4 apparatus are mentioned for simplicity.

From a synthesis section consisting of three cascades of each reactor having two tube bundle reactors acting as an oxidation reactor, a gas stream consisting of the following components (% by weight) is averaged as the reaction product.

Acrylic acid 9.3% CO ₂ 3.2% nitrogen 77.4% Oxygen 3.7% water 3.8%

The description below refers to such a stream of reaction gas, referred to in each case as the following "crude product".

This crude product is mixed as a solvent in a prequench (direct condenser) (K1) with 10 kg of difill / DMP per m ³ of crude product (STP) and then passed through an absorption column (K2) at a gas temperature of about 170 ° C. It was. In addition, additional processes were carried out as described above. A small amount of side stream of solvent is drawn off at the bottom of absorption column (K2) in an amount of 0.5 to 1% by weight pumped through column (K1), T is from 150 ° C to 200 ° C and p is from 500 to 200 mbar Flash evaporation in solvent purification. In this case, the bottom contained a product side stream which was removed as a stream of secondary component 3, while the resulting distillate was a pure solvent. The elemental composition of the stream of this secondary component (3) was as follows on average.

C 68.8% H 4.4% O 23.1% N 1.05% S 2.2%

 In this case, the amounts of nitrogen and sulfur are derived from the process stabilizer used, ie phenothiazine, which is added in the distillation column (K4) and also passed through the absorption column (K2) due to the circulation of the solvent. The stream of secondary component (3) was a solid to viscous material close to black and having a solidification point of about 100 ° C.

The components of the crude product which are not condensed in the absorption column (K2) (inert gas, low boiling organic matter, water, CO, CO _2, etc.) are recycled to the reactor as "recycled gas" and some streams of recycled gas are divided The combustion zone was fed as a stream of secondary component (1). The fractionated stream comprised 90 wt% nitrogen, 4 wt% oxygen, 4 wt% CO and CO ₂ , 1 wt% water and 1 wt% organic components. Some additional stream in the recycled gas was used to strip the low-boiling material from the solvent stream containing acrylic acid in column (K3). This recycled gas stream, enriched with low-boiling constituents, was likewise recycled to the absorption column to reproduce at the end of this absorption column (K2) with some of the recycled gas or with some stream fed to the combustion zone.

The stream of material exiting the absorption column (K2) was stripped in the next step with some stream of recycled gas as described above in the desorption column (K3). The product and solvent stream that were substantially free of low boilers were passed through a distillation column (k4) where the product was removed through the side tubes. At this time, the bottom boiling solvent returned to the absorption column (K2). The low boiling fraction generated in the upper and upper condenser of column K4 was likewise recycled to absorption column K2. All water (product) present in the upper cooling circulator of the absorption column (K2) was extracted with the recycled solvent and then fed to the combustion zone as a stream of secondary components (2). The same applies to some of the streams removed in the recycled gas to produce a stream of secondary components (1).

Combustion of the stream of secondary components to be removed was carried out in a burner of the flame evaporable burner type as shown in FIG. 1. Each stream of material was in contact with each other in the chlorine chamber and the feed of this material stream was carried out through a concentric annular outlet. In addition to the stream of secondary components to be removed, support gas (preferably natural gas), combustion air and atomizing air must also be added.

Thus, the waste heat section of the combustion chamber was constructed in such a way that, for the production of high pressure steam, first of all the hot exhaust gas was used and then used to superheat this steam under a pressure of 21 bar. After using the hot exhaust gases in the second of the two stages involved in preheating the stream of secondary component 1 to be removed, for combustion they are heated after combustion air and then as a second stage, They energized the first of two stages involved in preheating the stream of secondary component (1). The rest of the energy was used to produce low pressure steam depending on the plant settings. This meant that the energy recovered from the plant could be measured in terms of the amount of steam produced. In this plant two experiments were carried out according to the method of the invention, and the stream of secondary components (3) was removed externally in the first experiment and burned with the remaining secondary components in the second experiment.

Experiment 1

In each case, on the basis of the crude product,

Gaseous stream of secondary component (1) 38.5% v / v,

3.7% w / w of the liquid aqueous stream of the secondary component (2),

0.3% w / w organic stream as liquid pool of secondary component (3)

The residue having the composition of was removed by burning the gaseous and aqueous liquid streams (1) and (2) and removing the stream of component (3) to the outside until there was no residue.

The temperature at the end of the combustion chamber during combustion was about 904 ° C. It was found that there was a 22.4% increase in high pressure steam generation compared to the blank experiments performed using the support gas instead of the stream of secondary components to be removed.

Experiment 2

In each case, on the basis of the crude product,

Gaseous stream of secondary component (1) 38.50% v / v,

3.7% w / w of the liquid aqueous stream of the secondary component (2),

Organic stream such as liquid pool of secondary component (3) 0.4% w / w

The residue having a composition of was removed by supplying all three components to the burner system described above. Therefore, in this case the stream of secondary component 3 is also combusted with the rest of the stream and in the burner system a nozzle with an additional annular feed gap was used.

It was found that the steam generation increased by 24.6% compared to the blank experiment (combustion with only support gas).

Thus, this experiment has shown that the process of the present invention provides a removal method that ensures that there are no residues of secondary component streams produced in the production of acrylic acid.

The present invention relates to a method for removing the low, medium and high boiling secondary components produced in the preparation of (meth) acrylic acid.

Acrylic acid is an important basic chemical. It is particularly suitable for use as monomer for preparing polymers due to the highly reactive double bonds and acid functionality. Most acrylic acid monomers produced are esterified prior to polymerization, ie with adhesives, dispersants or brighteners. Only a small amount of the acrylic acid monomers produced are polymerized directly, ie directly into the "high absorbent". In the direct polymerization of acrylic acid, high purity monomers are typically required, while the purity requirements of acrylic acid are not very high if they are esterified prior to polymerization.

It is well known that acrylic acid can be prepared in two steps via acrolein by heterogeneously catalyzed gas phase oxidation of propene using oxygen molecules on a catalyst present in the solid state in the temperature range of 200 ° C. to 400 ° C. (E.g. DE-A-1 962 431, DE-A-2 943 707, DE-C-1 205 502, EP-A-0 257 565, EP-A-0 253 409, DE-A-2 251 364, EP-A-0 117 146, GB-B-1 450 986 and EP-A-0 293 224). In this case, oxide multicomponent catalysts are used, for example catalysts based on oxides of molybdenum, chromium, vanadium or tellurium elements.

DE-C-2 136 396 discloses that acrylic acid can be separated from the reaction gas obtained in the catalytic oxidation of propene or acrolein by countercurrent absorption with a mixture of 75% by weight diphenyl ether and 25% by weight diphenyl. . DE-A-2 449 780 describes a method for cooling a hot reaction gas by partially evaporating the solvent in a direct condenser (quenching unit) prior to backflow absorption. A problem arising from this and other processes is the generation of solid materials in the device, which degrades the usability of the device. As mentioned in DE-A-4 308 087, the amount of such solid materials is reduced by adding a polar solvent, such as dimethylphthalate, in an amount of 0.1 to 25% by weight in a relatively nonpolar solvent mixture of diphenyl ether and diphenyl (difill). You can.

In addition to the absorption of the above-mentioned reaction products containing acrylic acid into high boiling solutions (mixtures), there are methods of other principles. The method differs from other methods in that acrylic acid is absorbed in the high boiling point solution (mixture) as possible in the anhydride state. A separate process step removes water from the process. Another method completely condenses acrylic acid and water produced during catalytic oxidation. In this case, an aqueous solution of acrylic acid is produced, via a distillation step using an agent capable of producing an azeotrope with acrylic acid (DE-C-3 429 391, JP-A-1 124 766, JP-A-7 118 766, JP-A-7 118 966, JP-A-7 118 968 and JP-A-7 241 885), through the extraction step (DE-A-2 164 767, JP-A-5 8140 039 and JP -A-4 8091 013) which may be further purified. EP-A-0 551 111 discloses an aqueous solution obtained by contacting water with acrylic acid and by-products prepared by catalytic gas phase oxidation in water in a absorption tower, such as a polar low-boiler such as water or acetic acid. And distillation in the presence of a solvent capable of producing an azeotrope. DE-C-2 323 328 describes the separation of acrylic acid from an aqueous eluate prepared in the esterification of acrylic acid or acrylic acid aqueous solution, as produced in the oxidation of propene or acrolein, in the preparation of acrylic acid by extraction with a specific mixture of organic solvents. It is described.

Common facts about all methods used industrially in the production of acrylic acid or methacrylic acid are that any low, medium and high boiling fractions produced are not suitable for the removal of undesirable secondary components and thus material streams to be removed. It contains. Such three or more material streams would add significant cost to the process.

It is therefore an object of the present invention to provide a removal method that solves the by-product problem associated with (meth) acrylic acid production with economical and ecologically optimal effects.

The inventors have surprisingly found that this problem is caused by burning a gaseous low-boiling material with an aqueous liquid stream of a material comprising a water soluble low- and / or medium-boiling material, and optionally burning the high-boiling material with them. I finally knew it could be solved.

Accordingly, the present invention burns the gaseous secondary component 1 which is easily volatilized, and the high boiling point secondary component 3 in which the low boiling point and the intermediate boiling point secondary component 2 dissolved in water are optionally treated with a low viscosity solvent. And the combustion is advantageously carried out in a combustion chamber equipped with one or more support gas burners, nozzle burners or multifuel burners, for example flame evaporable burners. The present invention relates to a method for removing low boiling point, medium boiling point and high boiling point secondary components.

In one embodiment, the present invention

(a) catalytic gas phase oxidation of propene or isobutene and / or acrolein or methacrolein,

(b) absorption of the reaction product produced in step (a) into the high boiling solvent, and

(c) acrylic acid or methacrylic acid is prepared by separation of acrylic acid or methacrylic acid from the added solvent of step (b) by distillation and / or extraction,

A portion of the solvent is evaporated prior to absorption in step (b), and some of the residual liquid solvent is optionally removed as high boiling secondary component 3 after further solvent evaporation,

The non-absorbed reaction product remaining after absorption of the reaction product of step (b) is cooled down, and optionally the aqueous concentrate obtained after the subsequent extraction as secondary component 2 and at least a portion of the gas stream obtained is secondary It is related with the method characterized by removing as component (1).

Preferred embodiments of the invention are defined in the sub-claims. Other preferred features are shown in FIGS. 1 and 2 and described below.

In the drawings,

1 is a diagram illustrating a flame evaporative burner which is preferably used when carrying out the process of the invention.

2 shows a flow sheet for acrylic acid production.

In the present disclosure, the terms high-boiling, medium-boiling, low-boiling and corresponding adjective terms refer to compounds having a higher boiling point than acrylic or methacrylic acid (high-boiling) or acrylic or methacrylic. Compounds having a boiling point approximately equal to acid (medium-boiling material) or compounds having lower boiling points (low boiling point) are shown.

Gas phase low-boiling secondary components comprising gaseous secondary components (a) and liquid phase components (b) boiling at low temperature (room temperature) produced during acid production are substantially inert gases such as nitrogen, water, carbon monoxide and carbon dioxide. In addition, among the substances to be removed, low-boiling fractions, preferably ducts which are not converted in the preparation of acrolein, acetaldehyde, propane, propene, formaldehyde, formic acid and / or (meth) acrylic acid, are included. This stream 1 is advantageously combusted in the combustion chamber. Such combustion chambers may be assigned to the (meth) acrylic acid production plant alone or may be operated in conjunction with other devices. An example of a flame evaporable burner which is preferably used is shown in FIG. 1 and will be described in more detail below.

The low or medium boiling point secondary component (2) dissolved in water and to be removed is preferably 0.1 to 10% by weight acetic acid, maleic acid, in each case based on 100% by weight of the secondary component (2) 0.01 to 5 wt%, fumaric acid 0.01 to 8 wt%, formaldehyde 0.2 to 4 wt% and / or formic acid, propionic acid, benzaldehyde, diacrylic acid, hydroxypropionic acid, benzoic acid and / or diphenyl ether (when used as solvent, 0.1 to 10% by weight and preferably 5% by weight of other organic materials such as residues thereof). These secondary components mainly contain acetic acid, maleic acid and formaldehyde. This stream of secondary components 2 is added and preferably injected as an aqueous stream of material during the step involving combustion of the low boiling secondary components 1. In one advantageous embodiment of the invention, the injection process is carried out via a concentric multi-fuel nozzle, as is known in the art. This aqueous stream containing the secondary component 2 is advantageously preconcentrated as possible, for example by evaporation. To this end, the heat generated in the production process can be usefully used to improve energy-utilization. Suitable devices include commercial evaporators.

The high boiling secondary component (3) mainly contains polymers of acrylic or methacrylic acid, unconsumed production stabilizers such as phenothiazine or p-nitrosophenol, inhibitors such as methylene blue and / or thermal decomposition products thereof do.

This stream of solid, solid-boiling material 3 is advantageously pretreated first, because of its physicochemical properties, which makes it difficult to handle. The solidification point is generally too high to pump this stream of material at normal ambient temperature. Blending with a solvent having a low viscosity at ambient temperature (typically 0.5 · 10 ⁻³ to 2 · 10 ⁻³ Pa · s) and preferably having a high boiling point of 100 ° C. to 250 ° C. is capable of pumping the mixture The solidification point can be dropped to such a range. In this connection, acetone, dimethyl formamide (DMF) or alcohols, in particular C ₃ -C ₁₀ diols and / or triols, for example pentane diols, hexane diols, glycerol, glycols, dimethyl glycol, monomethyl glycol, Monoethyl glycol, diethyl glycol or mixtures thereof gave particularly good results. A stream of secondary components (3) treated with this low viscosity diluent can be fed to the combustion process of the present invention, and this feed is carried out separately from the remaining streams of secondary components (1) and (2). Preferably, the secondary components (2) and (3) are injected separately. On the one hand, the high-boiling secondary components 3 can be sent to industrial incinerators, such as decentral in-situ incinerators, after suitable purification, which are comparable to heated heavy oils in their combustion characteristics, or they may be subjected to any other treatment. Can be supplied to the plant.

1 shows the intersection of burners which are preferably used in carrying out the process of the present invention, which is a flame evaporable burner. The required part of this burner is indicated by the reference sign. In this case reference numbers (1) to (5) are the following conduits: conduits for wastewater (1), conduits (2) for spray steam to wastewater, liquid or gaseous (e.g., natural gas and / or ) CO) supplemental fuel conduit (3), secondary component (2) stream conduit (4) and support gas conduit (5), such as natural gas. Combustion air is introduced through conduit (6). A stream of secondary components (1) is separately applied to the combustion air to avoid explosion. The liquid component is injected into the combustion chamber via the nozzle 7. Reference numerals 8 to 9 represent swirl rings, which serve as guides of air. Reference numeral 10 represents a flame retardant insulating material. The nozzle 7 may be a known concentric multi-fuel nozzle, which exhibits a plurality of central annular feed gaps suitable for feeding the stream of secondary components 2, which stream of secondary components. And also steam off the remaining ingredients mentioned above. Thus, all components except the combustion air and the stream of secondary components 1 pass through this nozzle. In addition, when attempting to inject a stream (handling form) of the secondary component 3, the nozzle 7 must have an additional central annular feed gap.

In practice, combustion takes place in a combustion chamber (not shown) at an adiabatic combustion temperature of 800 ° C to 1200 ° C, preferably 800 ° C to 1000 ° C. In FIG. 1, the start of the combustion chamber is indicated by the flame retardant insulating material 10 to the left of the nozzle 7. The combustion chamber is advantageously only associated with a (meth) acrylic acid production plant or operated in conjunction with other plants. The energy released here can be recovered in a waste heat section away from the combustion chamber, for example in the form of high pressure heavy air. The combustion gas advantageously passes through the waste heat section in such a way that the temperature gradually decreases upwards. Thus, the gas typically reaches a waste heat section at a combustion temperature of 850 ° C. to 1000 ° C., preferably approximately 860 ° C., which is then sent to a heat exchanger that serves to dissipate some of its energy to cool and recover energy. Lose. At this time, the outlet temperature of the waste heat section is approximately 200 ° C. The aqueous stream of material containing the injected secondary component (2) makes a positive or negative contribution to the energy yield in the combustion chamber depending on the content of the combustible material contained, because, among other things, the evaporation enthalpy of water is in the form of energy. This is because the furnace must be supplied during the system. Also for this reason it is advantageous to preconcentrate this stream as far as possible. Waste heat generated during combustion is advantageously used for the generation of steam, such as steam.

Acrylic acid or methacrylic acid is typically the catalytic gas phase oxidation of propene or isobutene and / or acrolein or methacrolein, followed by absorption of the reaction product resulting from oxidation into low boiling solvents, preferably water or high boiling solvents. And then separated by acrylic or methacrylic acid by distillation and / or extraction. On the other hand, it is also possible to condense a gaseous reaction product containing water, which is produced during oxidation, to obtain an aqueous solution of acrylic acid or methacrylic acid, of which acrylic acid or methacrylic acid is separated by distillation and / or extraction. It is possible.

In a preferred embodiment, the invention relates to the process of steps (a) to (c) as defined above. Each of these steps for acrylic acid is described below. Unless stated otherwise, they apply similarly to methacrylic acid. Included in FIG. 2 is a suitable flow sheet representing steps (a) to (c) and also a stream of secondary components (1) to (3) to be removed. Reference numerals 11 to 22 in FIG. 2 denote process steps, numerals 30 to 48 denote conduits, and K1 to K4 denote different columns / apparatus.

<Step a>

Step (a) involves producing acrylic acid in a one- or two-stage catalytic gas phase reaction of molecular oxygen with propene and / or acrolein. In the case of methacrylic acid, the gas phase reaction of molecular oxygen with isobutene and / or methacrolein occurs in a similar manner. The gas phase reaction can take place by known methods, in particular by the methods described in the above references. Advantageously, the process is carried out in a temperature range of 200 ° C to 500 ° C. The heterogeneous catalyst used is preferably an oxide multicomponent catalyst based on an oxide of molybdenum, chromium, vanadium or tellurium. Furthermore, (1) condensation of propionaldehyde with formaldehyde (in the presence of a secondary amine acting as a catalyst) produces methacrolein, and (2) as a two step by oxidation of methacrolein to methacrylic acid Methacrylic acid can also be manufactured.

According to the preferred embodiment shown in FIG. 2, the compression 11 of the gas circulated from the conduit 30, consisting essentially of nitrogen, carbon oxides and unconverted ducts, is carried out and supplied by the conduit 46. Then, propene from conduit 31 and air from conduit 32 are fed to the reactor, where heterogeneously catalyzed oxidation (synthesis) 12 takes place to produce acrylic acid.

However, in step (a) acrolein and / or propene, vapor, carbon monoxide and carbon dioxide, nitrogen, oxygen, acetic acid, propionic acid, formaldehyde, additionally not purely acrylic acid, but substantially converted as acrylic acid and secondary components A gaseous mixture is obtained which may contain aldehydes and maleic anhydride. In particular, the reaction product mixture is typically in weight percent based on the total reaction mixture, up to 1% propene and up to 1% acrolein, up to 2% propane, up to 20% steam, up to 15% carbon oxide, up to 90% nitrogen , Up to 5% oxygen, up to 2% acetic acid, up to 2% propionic acid, up to 1% formaldehyde, up to 2% aldehyde and up to 0.5% maleic anhydride.

<Step b>

In step (b), some of the acrylic acid and secondary components are separated from the reaction gas by absorption in a high boiling solvent. All high boiling point solvents capable of absorbing acrylic acid, especially those having a boiling point above 160 ° C., are suitable for this purpose. Particularly suitable are those commercially available such as mixtures of diphenyl ether and biphenyl, for example a mixture of 75% by weight diphenyl ether and 25% by weight biphenyl (called "difill").

Advantageously, as shown in FIG. 2, the hot reaction gas obtained from step (a) after synthesis 12 is fed via conduit 47 to a quenching apparatus or directly to condenser K1, where Cool by partial evaporation (13) of solvent prior to absorption. Venturi scrubbers, bubble-cap columns or spray condensers are particularly suitable for this purpose. In this case, the high boiling secondary component in the reaction gas from step (a) is condensed into an unevaporated solvent (condensation and partial evaporation in FIG. 2 are indicated by reference number 13). Moreover, partial evaporation of the solvent constitutes a purification step for the solvent. In a preferred embodiment of the present invention, a partial stream of unevaporated solvent, preferably 1 to 10% of the material stream fed to the absorption column is removed from the condenser K1 and enters a solvent purification (not shown). . The solvent is distilled off completely. Distillation of the solvent serves to avoid increasing the amount of unwanted material present in the solvent. The high boiling secondary components, which contain mainly the unclear acrylic acid polymer and decomposition products of the stabilizers used, remain as a residue and are removed as secondary components 3 by conduits 33.

Absorption 14 takes place in countercurrent absorption column K2, which is preferably equipped with a sieve, valve or dual flow tray, in which the lowering action of the (unevaporated) solvent takes place. The gaseous reaction product and optionally evaporated solvent pass upwards to enter column K2 and subsequently cooled to absorption temperature. In the absorption zone of column K2, both the medium and high boiling components present in the acrylic acid are almost completely removed from the stream of residual gas.

As shown in FIG. 2 as the acid water quench 15, the remaining non-absorbed reaction gas of step (a) is condensed to reduce the low-boiling secondary components, in particular water, formaldehyde and acetic acid. Cool to separate condensable parts. Therefore, this condensate is called product below. The residual gas stream, referred to as the recycled gas below, contains mainly nitrogen, carbon oxides and unconverted ducts. Preferably, this is partially recycled to the reaction stage as a diluent gas. The recycled gas exits absorption column K2 as overhead by conduit 34. Here, the stream is preferably divided in a ratio of 3: 1 to 1: 3, in particular in a ratio of 1: 1, depending on the device design, a portion of which is via conduit 30 for synthesis 12 via a gas compressor. Is recycled to the reactor, and the remaining part of the stream is removed by conduit 35 in the form of a gaseous stream of secondary component 1 to be removed. The product constitutes a secondary component (2) which is to be dissolved in water and removed. This includes the water produced in step (a) and also water soluble low and medium boiling point components such as acetic acid, formaldehyde and maleic acid and the like.

In a preferred embodiment of the invention, it contains acrylic acid, high and medium boiling point secondary components and also a small amount of low boiling secondary components through conduit 37 from the absorption zone of column K2 used in step (b). The solvent stream is run off and desorbed by low boiling point component stripping (16) and low boiling point component washing (17). This is advantageously carried out in the desorption column K3, as shown in FIG. 2, preferably packed into a sieve, valve or double-flow tray or alternatively in the presence of a so-called stripping gas. Material or ordered packing can be created. The stripping gas used may be any inert gas or gas mixture, preferably using a gas mixture of air and nitrogen or some streams of recycled gas described in (a). During desorption (16) and (17), the majority of the low-boiling material is stripped from the added solvent of some of the recycled gas which has flowed out before step (a) by conduit 38, and via conduit 39 Is recycled to column K2.

Little low-boiling material and solvent stream containing acrylic acid will flow out of the bottom of the desorption column (K3) via conduit (41) and will be fed to the column (K4) for distillation.

<Step c>

In the step (c) process, acrylic acid is separated from the solvent together with the final residue of the mid-boiling component and also of the low boiling secondary component. This separation takes place by distillation, and basically any distillation column for the purpose of distillation can be used. To this end, advantageously, a column having a sieve tray, a double flow tray or a metal crossflow sieve tray or a valve tray is used. In FIG. 2, distillation is shown in several process steps: solvent mixture distillation 19, medium boiling component distillation 20, low boiling component distillation 21, and partial condensation 22. All these steps are carried out in column K4. In the portion indicating distillation column K4, acrylic acid is distilled without intermediate boiling secondary components such as solvent and maleic anhydride (step 21). In order to reduce the low boiling fraction in acrylic acid, acrylic acid is advantageously flowed out of the column K4 through the side pipe 42. This acrylic acid is crude acrylic acid. In the stripping portion of column K4, intermediate boiling component distillation 20 and solvent mixture distillation 19 take place. The solvent that flows out from the bottom of column K4 is recycled to column K2 through conduit 43.

At this time, the low-boiling-rich stream at the top of column K4 exits through conduit 44 after condensation 22 has been carried out. However, as shown in FIG. 2, it is advantageous to recycle the adsorption column (K2) and work up again without discarding since this stream still contains acrylic acid.

The product from conduit 36, which may still contain dissolved acrylic acid prior to removal in the process of the present invention, is preferably a small amount of solvent with little acrylic acid from the bottom of the distillation column K4 from the conduit 40. Extract to some stream. In this product extraction 18, a portion of the acrylic acid is extracted into the solvent and then recovered from the product. The product also avoids increasing levels of these components in solvent circulation by extracting polar intermediate boiling components from the solvent stream. The product remaining after extraction is removed as a secondary component (2) stream via conduit (45). Upon acid extraction the solvent in which acrylic acid is dissolved is returned to solvent stream 43 via conduit 48.

It is particularly advantageous to preconcentrate the product stream from conduit 45 as far as possible before removal. This can be done, for example, using waste heat which is removed by cooling the reaction gas in column K2 for the purpose of concentrating the product and separating the steam. This steam can be passed to the incinerator plant described above, for example, via a gaseous stream of secondary component 1. Residual products, in particular with large amounts of combustible materials, can obtain large amounts of recoverable energy, especially in the form of high pressure steam. The recovery of this energy can be carried out in the plant, for example, by distilling acrylic acid in column K4 or in solvent distillation, and also to operate a compressor for air and / or recycled gas by the steam turbine. It is particularly advantageous when used in

The crude acrylic acid obtained in step (c) is in each case based on the crude acrylic acid, acrylic acid, preferably 98 to 99.8% by weight, in particular 98.5 to 99.7% by weight and impurities such as acetic acid, aldehyde and maleic anhydride 0.2 to 2 % By weight, in particular 0.5 to 1.5% by weight. Such acrylic acid can be used for esterification, optionally without further purification, unless the demand for its purity is very high. Further separation of the secondary components of the crude acid thus separated can optionally be carried out according to the quality of acrylic acid required, if necessary, crystallization, distillation or other suitable separation methods. The acrylic acid thus obtained can be subjected to further further treatment or to further chemical reactions such as esterification.

Claims (12)

By burning the gaseous low boiling secondary component 1 and supplying the low boiling point or the intermediate boiling secondary component 2 dissolved in water to the step including the combustion of the secondary component 1, the low boiling secondary component A method of removing secondary components formed in the production of (meth) acrylic acid, characterized by having a lower boiling point than (meth) acrylic acid and having the intermediate boiling point secondary component having approximately the same boiling point as (meth) acrylic acid. 2. The process according to claim 1, wherein the low or medium boiling secondary component dissolved in water is fed to the step comprising combustion of the secondary component (1) together with the high boiling secondary component (3) treated with a low viscosity solvent. Thereby allowing the high boiling secondary component to have a higher boiling point than (meth) acrylic acid. The process according to claim 1, wherein the low boiling secondary component (1) contains a compound selected from the group consisting of carbon monoxide, carbon dioxide, nitrogen, ducts which are not converted in the preparation of (meth) acrylic acid and mixtures thereof. The process according to claim 1, wherein the secondary component (2) contains a compound selected from the group consisting of acetic acid, maleic acid, fumaric acid, formaldehyde, organic substances and mixtures thereof. The process according to claim 1, wherein the high boiling secondary component (3) contains an acrylic acid polymer or a methacrylic acid polymer. The method of claim 1 wherein the combustion is carried out in a combustion chamber using a support gas burner or a multi-fuel burner. The process of claim 1 wherein the combustion is carried out at a temperature of 800 ° C. to 1000 ° C. 7. The method of claim 1, further comprising supplying a gas selected from the group consisting of natural gas, air, and mixtures thereof to the combustion zone. 2. The catalytic gas phase oxidation (12) of a compound according to claim 1, wherein the acrylic or methacrylic acid is selected from the group consisting of propene, isobutene, (meth) acrolein, and mixtures thereof; It is prepared by absorption 14 into a high boiling solvent, or condensation of the reaction gas obtained during oxidation, and separation by distillation (19, 20, 21, 22) or extraction of the resulting acrylic or methacrylic acid. How to. The method according to any one of claims 1 to 9, (a) catalytic gas phase oxidation of a compound selected from the group consisting of propene, isobutene, (meth) acrolein and mixtures thereof (12), (b) absorption (14) of the reaction product produced in step (a) into a solvent, and (c) acrylic acid or methacrylic acid is prepared by separation of acrylic acid or methacrylic acid from the added solvent of step (b) by extraction or distillation, Some of the solvent is evaporated (13) prior to absorption (14) in step (b), some of the residual liquid solvent is removed as the high boiling secondary component (3), In step (b) the non-absorbed reaction product remaining after absorption 14 of the reaction product is cooled 15, the resulting aqueous concentrate is removed as secondary component 2 and at least a portion of the resulting gas stream is removed. Removing as tea component (1). Process according to claim 10, characterized in that some of the residual liquid solvent is removed as the high boiling secondary component (3) after solvent evaporation. Process according to claim 10, characterized in that the obtained aqueous concentrate is removed as secondary component (2) after subsequent extraction.