EP3389809A1

EP3389809A1 - Column for thermally treating fluid mixtures

Info

Publication number: EP3389809A1
Application number: EP16819873.7A
Authority: EP
Inventors: Ulrich Hammon; Thomas Walter
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2015-12-18
Filing date: 2016-12-16
Publication date: 2018-10-24
Also published as: DE102015122209A1; CN108367210A; CN108367210B; US20170173492A1; US10493376B2; WO2017103194A1

Abstract

The invention relates to a column (1) for thermally treating fluid mixtures, comprising a vertically aligned cylindrical column body (2) which forms a column cavity (3), a sequence of vertically spaced dual-flow material exchange bases (8) which are mounted in the column cavity (3) and which have openings for the passage of liquid and gas in counter-flow, and at least one gas inlet opening (5) which is arranged below the lowermost base of the sequence of dual-flow material exchange bases (8). The column according to the invention is characterized in that a gas distribution base (9) is arranged between the lowermost base of the sequence of dual-flow material exchange bases (8) and the gas inlet opening (5), said gas distribution base having openings (32) for the vertical passage of gas which can be introduced into the column cavity (3) via the gas inlet opening (5). The openings (32) are designed to cause a uniform distribution of gas over the column cross-section. The invention further relates to a method for thermally treating fluid mixtures in such a column (1).

Description

Column for the thermal treatment of fluid mixtures

The present invention relates to a column for the thermal treatment of fluid mixtures. The column comprises a cylindrical, vertically oriented column body which forms a column cavity. Further, the column has a series of vertically spaced dual-flow mass transfer trays mounted in the column cavity and having openings for the passage of liquid and gas countercurrently. Furthermore, the column comprises at least one gas inlet opening, which is arranged below the lowest of the sequence of dual-flow mass transfer trays. Furthermore, the invention relates to a process for the thermal treatment of fluid mixtures in a column. In separation columns, gaseous (ascending) and liquid (descending) streams are often passed in countercurrent, with at least one of the streams containing in particular a (meth) acrylic monomer. As a result of existing between the streams imbalances takes place a heat and mass transfer, which ultimately causes the desired separation in the separation column (or separation). In this document, such separation processes should be referred to as thermal separation processes.

Examples of and thus element of the expression "thermal separation processes" used in this document are the fractionating condensation (cf., for example, DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1) and the rectification (in both cases the ascending vapor phase is in countercurrent to descending The separation effect is due to the fact that the vapor composition is different in equilibrium from the liquid composition), the absorption (at least one ascending gas is led to at least one descending liquid in the countercurrent, the separation effect is due to the different solubility of the gas components in the Liquid) and desorption (the reversal process for absorption; the gas dissolved in the liquid phase is separated by partial pressure reduction; the partial pressure reduction of the liquid phase dissolved is at least partially conducted by passing a carrier gas through the liquid phase hnet this thermal separation process as stripping; alternatively or additionally (at the same time as a combination), the partial pressure reduction can be effected by lowering the working pressure).

For example, the separation of (meth) acrylic acid or (meth) acrolein from the product gas mixture of the catalytic gas phase oxidation can be carried out in this way. in that the (meth) acrylic acid or the (meth) acrolein is first separated by absorption into a solvent (eg water or an organic solvent) or by fractional condensation of the product gas mixture and the resulting absorbate or condensate is subsequently obtained to obtain more or less less pure (meth) acrylic acid or (meth) acrolein is further fractionated (cf., for example, DE-10332758 A1, DE 10243625 A1, WO 2008/090190 A1, DE 10336386 A1, DE 19924532 A1, DE 19924533 A1, DE 102010001228 A1, WO 2004/035514 A1, EP 1 125912 A2, EP 982289 A2, EP 982287 A1 and DE 10218419 A1). The notation (meth) acrylic monomers in this document is abbreviated to "acrylic monomers and / or methacrylic monomers".

The term acrylic monomers is used in this document to shorten "acrolein, acrylic acid and / or esters of acrylic acid".

The term methacrylic monomers is used in this document to shorten "methacrolein, methacrylic acid and / or esters of methacrylic acid".

In particular, the (meth) acrylic monomers mentioned in this specification are to comprise the following (meth) acrylic esters: hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate, glycidyl methacrylate, methyl acrylate, methyl methacrylate, n-butyl acrylate, isobutyl acrylate, isobutyl Butyl methacrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, N, N-dimethylaminoethyl acrylate and N, N-dimethylaminoethyl methacrylate.

(Meth) acrylic monomers are important starting compounds for the preparation of polymers, e.g. be used as adhesives or as water super absorbent materials in hygiene articles use.

On a large scale, (meth) acrolein and (meth) acrylic acid are predominantly produced by catalytic gas phase oxidation of suitable C3 / C4 precursor compounds (or precursor compounds thereof). In the case of acrolein and acrylic acid, propene and propane are preferably used as such precursor compounds. In the case of methacrylic acid and methacrolein, iso-butene and iso-butane are the preferred precursor compounds.

In addition to propene, propane, isobutene and isobutane, suitable starting materials are other compounds containing 3 or 4 carbon atoms, for example isobutanol, n-propanol or precursor compounds thereof, for example the methyl ether of isobutanol. Acrylic acid can also be produced by gas-phase catalytic oxidation of acrolein. Methacrylic acid can also be produced by gas-phase catalytic oxidation of methacrolein. In the context of such production processes, product gas mixtures are normally obtained, from which the (meth) acrylic acid or the (meth) acrolein must be separated off.

Esters of (meth) acrylic acid are e.g. by direct reaction of (meth) acrylic acid and / or (meth) acrolein with the corresponding alcohols. However, in this case as well, product mixtures are first of which make up the

(Meth) acrylic acid esters must be separated.

The separation columns in which these separation processes are carried out contain separating internals. These pursue in the thermal separation process the purpose of increasing the surface area for the separation in the separation column causing heat and mass transfer ("the exchange surface").

As such internals come e.g. Packings, packing and / or trays, which are also referred to as mass transfer trays, into consideration. Often, the separation columns used are those which contain at least one sequence of mass transfer trays, at least as part of the separating internals.

Mass transfer trays pursue the purpose of providing areas in the separation column in the form of liquid layers which form on them, with substantially closed liquid phases. The surface of the rising in the liquid layer and thereby distributing in the liquid phase vapor or gas flow is then the relevant exchange surface. A succession of mass transfer trays is understood to mean a succession (one after the other) of at least two superimposed in the separation column, generally identically constructed (i.e., identical), mass transfer trays. Advantageously in terms of application technology, the clear distance between two mass transfer beds directly following one another in such a series (series) of mass transfer trays is made uniform (i.e., the mass transfer trays are arranged equidistantly one above the other in the separation column).

The simplest embodiment of a mass transfer tray is the so-called Regensiebboden. This is a plate or plate segments assembled into a plate, which are used for the ascending gas or vapor phase (the Terms "gaseous" and "vaporous" are used interchangeably in this document) and substantially planar passage openings, eg round holes and / or slots, distributed over the plate (cf., for example, DE 10230219 A1, EP 1279429 A1, US Pat. No. 3,988,213) and EP 1029573 A1). Exceeding openings (eg at least one downcomer (at least one drain segment)) do not have rain screen bottoms. As a result of this absence of downcomers, both the gas ascending in the separating column (the vapor rising in the separating column) and the liquid descending in the separating column have to flow oppositely in temporal change through the (same) passage openings (through the open cross sections of the passages ) move. This is also referred to as the "dual-flow" of rising gas and descending liquid through the passage openings, which is why the term "dual-flow tray" or "dual-flow tray" is used herein for such media trays. The cross section of the passages of a dual-flow tray is adapted in a conventional manner its load. If it is too small, the ascending gas flows through the passage openings at such a high speed that the liquid descending in the separation column is entrained substantially without separation effect. If the cross-section of the passages is too large, ascending gas and descending liquid move past each other substantially without replacement, and the mass transfer tray runs the risk of running dry.

That is, the separating effective working area of a Regensiebbodens (dual-flow floor) has two limits. A minimum limit speed of the ascending gas must be given so that a certain liquid layer is held on the rain sieve bottom, in order to enable a segregation work of the rain sieve bottom. The upper limit of the velocity of the rising gas is determined by the flood point, when the gas velocity leads to congestion of the liquid on the Regensiebboden and their rain is prevented.

The longest extent of the passage openings of a technical dual-flow tray (= longest direct connecting line of two points lying on the outline of the cross section of the passage opening) is typically 10 to 80 mm (cf., for example, DE 10156988 A1). Normally, the passages within a rain screen bottom are identical (ie, they all have the same geometric shape and cross section (cross sectional area)). From an application point of view, the circumferential line of its cross-sectional areas is circular. That is, preferred passages of Regensiebböden are circular holes. The relative arrangement of the passage openings of a rain screen floor advantageously follows a strict triangular division (cf., for example, DE 10230219 A1). Of course the passages can also be designed differently within one and the same Regensiebbodens, z. B. vary over the Regensiebboden.

In terms of application technology, a sequence of rain sieve bottoms in a separation column comprises identical (identical) rain sieve trays, which are preferably arranged equidistantly one above the other.

However, according to DE 10156988 A1, it is also possible to use sequences of rain sieve bottoms in separation columns whose cross-section (preferably circular) within a dual-flow tray is uniform but varies within the sequence (for example decreases from bottom to top).

In general, each dual-flow bottom of a corresponding bottom sequence concludes flush with the wall of the separation column. But there are also variants in which there is a gap between column wall and floor, which is only partially interrupted by bridges. In addition to the actual passage openings, a rain sieve bottom usually still has at most openings which serve to fasten the floor to support rings or the like (cf., for example, DE 10159823 A1). In the normal working area of a succession of rain screen floors, the rain falls in the

Separating column descending liquid in drops from dual-flow soil to dual-flow soil, that is, the gas phase rising between the dual-flow trays is penetrated by a divided liquid phase. The falling on the respective bottom Regensiebboden drops are partially sprayed on impact. The gas stream flowing through the passage openings bubbles through the liquid layer formed on the surface of the floor, whereby an intensive mass and heat exchange takes place between the liquid and the gas.

Depending on the liquid and gas load, rain sieve trays with column diameters of> 2 m tend to cause small unequal distributions of liquids to swell so that the liquid holdup of a floor can fluctuate over a large area or a rotating wave can form, which, on the one hand, results in the mechanical stability of the liquid On the other hand, the separation effect is reduced, since the liquid distribution under these conditions is then greatly different in time and place. To avoid such instationarities, it has therefore proved to be advantageous to distribute flow breakers in the form of vertical plates on the bottom cross-section, which prevent or at least greatly reduce the swirling of the liquid within the column body. The height of the sheets should correspond approximately to the height of the forming liquid spouting layer. This is about 20 cm under normal loads. The peripheral line of the cross section of a separation column is usually circular. This applies in a corresponding manner to the associated mass transfer trays. For the purposes of this document usable dual-flow trays are described for example in Technical Progress Reports, Vol. 61, Basics of Dimensioning of Column Trays, pages 198 to 21 1, Verlag Theodor Steinkopf, Dresden (1967) and in DE 10230219 A1. In the case of large diameter columns, it has been found that there is a deterioration of the separating effect between the gas introduced below and the liquid dripping from above.

The present invention is therefore based on the object of specifying a column and a method for the thermal treatment of fluid mixtures, in which the separation effect is improved.

This object is achieved by a column having the features of claim 1 and a method having the features of claim 13. Advantageous embodiments and further developments emerge from the dependent claims.

The column according to the invention is thus characterized in that between the lowest of the sequence of dual-flow mass transfer trays and the gas inlet opening a gas distribution tray is arranged, which has openings for a vertical passage of gas, which is introduced via the gas inlet opening in the column cavity, wherein the Openings are formed to bring about a gas equal distribution over the column cross-section. According to the invention, it has been found that the deterioration of the separation effect in conventional columns with dual-flow mass transfer trays, especially in large diameter columns, is caused by the inhomogeneous distribution of the introduced gas over the cross-sectional area of the column below the lowermost dual-flow mass transfer tray , In particular, there are inhomogeneities with regard to the pressure distribution of the gas over the cross-sectional area of the column. In many cases the gas pressure is higher outside than in the middle. This has the disadvantage that through the outer openings of the bottom dual-flow mass transfer tray a larger amount of gas flows upwards than through the openings in the region of the center of the dual-flow mass transfer tray. This uneven gas flow up through the openings of the dual-flow Mass transfer soil has the consequence that the separation effect of the column deteriorates.

The spatial terms "top", "bottom", "horizontal" and "vertical", unless explicitly stated otherwise, refer to the orientation of the column during operation.

The inventive arrangement of a gas distribution tray between the bottom dual-flow mass transfer tray and the gas inlet opening causes between the gas distribution tray and the bottom dual-flow mass transfer tray, especially immediately below the bottom dual-flow mass transfer tray, a gas uniform distribution over the column cross-section results. This in turn has the consequence that in each case substantially the same amount of gas flows through openings of equal size in the bottom dual-flow mass transfer tray. This gas equal distribution is also continued to higher arranged dual-flow mass transfer trays, so that overall a gas uniform distribution over the column cross section in the range of dual-flow mass transfer trays is achieved. This in turn has the effect of an improved separation effect between the rising gas and the descending liquid.

According to one embodiment of the column according to the invention, the gas inlet opening and the gas distribution floor are formed such that the dynamic pressure of the gas flowing into the column cavity is 1/6 to 1/10, in particular 1/7 to 1/10, of the pressure loss of the gas distribution floor. In particular, the dynamic pressure of the gas entering the column cavity is 1/6 to 1/10 of the dry pressure loss of the gas distribution tray.

In this document, the dynamic pressure of the gas flowing into the column cavity is understood in particular to mean the dynamic pressure at the gas inlet opening.

Under the dry pressure loss of a soil is understood in this document, the pressure loss without liquid supply to the soil. The pressure loss that a gas distribution tray must apply to ensure a uniform gas distribution depends in particular on the extent of the inhomogeneities in front of the gas distribution tray. The dry pressure drop of the gas distribution tray must be sufficiently large in order to bring about a gas equal distribution over the column cross-section. In particular, the dry pressure loss is relevant, since a soil that is not uniformly flown tends to gas the one horizontal side to let through and on another horizontal side raining the liquid through, without the gas comes into contact with the liquid. Therefore, if the non-uniform flow of the soil results in separation of the gas and liquid passage areas, the dry pressure drop of the soil means that it must be able to smooth the flow again, ie to remove the separation of the gas and liquid passage areas , According to the invention, it has been found that, for the homogeneous gas distribution, the pressure loss of the gas distribution tray should be in the range of 6 to 10 times, in particular 7 to 10 times, the dynamic pressure of the gas at the gas inlet opening, ie in particular in the inflow nozzle. This also applies if the gas distribution tray is not a dual-flow mass transfer tray. For example, if the dynamic pressure at the gas inlet opening about 240 Pa or 2.4 mbar, the pressure drop of the flow straightener, ie the gas distribution tray should be at least 14 mbar, in particular at least 17 mbar.

According to one embodiment of the column according to the invention, the openings of the gas distribution floor over the cross section are arranged uniformly distributed. For example, the centers of the openings of the gas distribution floor are arranged on at least two concentric circles. Preferably, the gas distribution floor per square meter from 0.2 to 1 opening. This ensures that a particularly good gas uniform distribution over the column cross-section is brought about.

According to one embodiment of the column according to the invention, the proportion of the opening area formed by the openings of the gas distribution tray to the cross-sectional inner surface of the column is in a range of 10% to 20%.

According to one embodiment of the column according to the invention, the proportion of the opening area formed by the openings of at least the bottom of the sequence of dual-flow mass transfer trays to the cross-sectional inner surface of the column is greater than this proportion of the gas distribution tray. The proportion is in particular in a range of 14% to 20%. The dry pressure loss of this lowest of the sequence of dual-flow mass transfer soils is z. B. in a range of 0.5 to 1, 0 mbar.

Inhomogeneities with regard to the pressure distribution of the gas over the cross-sectional area of a column are compensated particularly effectively if the gas uniform distribution over the column cross-section takes place as completely as possible below the gas distribution tray. As explained, such inhomogeneities lead to problems. In many cases, the gas pressure in the edge region is higher than in the middle, in particular if the gas is fed to the side of the column body. This has the disadvantage that through the outer openings of the bottom dual-flow mass transfer tray a larger amount of gas flows upwards than through the openings in the middle of the dual-flow mass transfer tray. Conversely, if the gas is supplied centrally to the column body, that is to say in the middle, the gas pressure in the edge region is lower than in the middle. This has the disadvantage that a smaller amount of gas flows upwards through the outer openings of the lowermost dual-flow mass transfer tray than through the openings in the region of the center of the dual-flow mass transfer tray. This uneven gas flow upward through the openings of the dual-flow mass transfer tray has the consequence that the separation effect of the column deteriorates. These problems also occur to a lesser extent when the flow resistance of the gas in the vertical passage through the gas distribution tray is too low compared to the flow resistance in the vertical passage through the lowermost dual-flow mass transfer tray. In that case, the gas equal distribution would in some cases take place below the lowest dual-flow mass transfer soil. However, since liquid flows down through its openings, instead of the illustrated inhomogeneities, resulting in a poor separation effect, albeit to a lesser extent, than completely without gas distribution floor.

The ratio of the flow resistances can be controlled, for example, via the opening conditions of both trays.

According to a preferred embodiment of the column according to the invention, therefore, the proportion of the opening area formed by the openings of at least the bottom of the sequence of dual-flow mass transfer trays to the internal cross-sectional area of the column is at least 1.13 times greater, generally at least 1.16 times larger. preferably at least 1.20 times greater, more preferably at least 1.25 times greater, eg at least 1, 30 times larger, especially at least 1, 35 times larger than this proportion of the gas distribution tray. Preferably, the two trays are designed such that the pressure loss of the gas distribution tray, in particular the dry pressure loss of the gas distribution tray, is at least 20%, preferably at least 50%, in particular at least 150%, preferably at least 200%, particularly preferably at least 300%, e.g. is at least 400% of the pressure loss of the bottom dual-flow mass transfer tray, in particular the dry pressure drop of the bottom dual-flow mass transfer tray, the sequence of dual-flow mass transfer trays.

The person skilled in the art can selectively select or set the opening areas and the relative pressure losses of the gas distribution floor and the lowermost dual-flow mass transfer tray according to the process conditions to be expected. So For example, the pressure of the gas entering the column through the gas inlet can be subject to fluctuations, for example if the process operation in an upstream part of the installation is impaired. Then, in addition to the spatial inhomogeneities mentioned in the remaining sections of the description, temporal inhomogeneities can also arise in the column, which can lead to an additional deterioration of the separation effect of the column. It is advantageous to achieve gas equalization not only spatially but also in time. The temporal gas equal distribution should be as complete as possible already under the gas distribution floor and only to the smallest possible extent only under the lowest dual-flow mass transfer tray. In particular, if only very small pressure fluctuations of the gas entering the column through the gas inlet opening are to be expected, it may be sufficient if the pressure loss of the gas distribution tray is at least 20% of the pressure loss of the lowermost dual-flow mass transfer tray, in particular the dry pressure loss of the lowermost dual-flow Mass transfer bed, which is the result of dual-flow mass transfer trays. Small spatial and temporal inhomogeneities are thereby already sufficiently compensated. In particular, when greater pressure fluctuations of the gas entering the column through the gas inlet opening are to be expected, it may be necessary for the pressure loss of the gas distribution tray to be higher than the pressure loss of the lowermost dual-flow mass transfer tray. For example, the pressure loss of the gas distribution tray may then be required to be at least 400% of the pressure loss of the bottom dual-flow mass transfer tray, particularly the dry pressure drop of the bottom dual-flow mass transfer tray, the sequence of dual-flow mass transfer trays.

In general, the two trays are designed so that the pressure loss of the gas distribution tray, in particular the dry pressure loss of the gas distribution tray, is at most 5000% (e.g., 400% to 5000%), preferably at most 3000%.

(eg 300% to 3000%), in particular at most 2000% (eg 200% to 2000%), preferably at most 1000% (eg 150% to 1000%) of the pressure loss of the lowermost dual-flow mass transfer tray, in particular the dry pressure loss of the bottom dual-flow mass transfer tray, which is the sequence of dual-flow mass transfer trays. High pressure losses increase the energy expenditure. According to one embodiment of the column according to the invention, the gas inlet opening is aligned in the column such that gas entering the column cavity forms a horizontal vortex. With such a design of the gas inlet opening, the risk of an inhomogeneous gas distribution over the horizontal cross section of the column is particularly great. If, for example, the gas flows tangentially into the column cavity, the gas pressure is usually higher in the outer region than in the Center. This inhomogeneous pressure distribution is compensated by the inventive arrangement of the gas distribution tray, so that there is a uniform gas pressure distribution below the lowermost dual-flow mass transfer tray. In a further embodiment of the column according to the invention, a liquid outlet is arranged above the gas distribution tray or in the gas distribution tray, which has a feed for liquid from an upper collecting surface of the gas distribution tray and a discharge into an area below the gas distribution tray. The gas distribution floor may thus be in particular a mass transfer floor with forced liquid guidance. This liquid withdrawal prevents liquid from flowing down through the same openings through which the gas flows upwards. Thus, the gas distribution tray is not a dual-flow tray as the liquid does not flow down through the same openings through which the gas flows. In this way, it is achieved that the gas flows up in a controlled manner through the gas distribution tray, the gas passage, the pressure loss achieved by the gas distribution tray and the resulting equal distribution of the gas pressure above the gas distribution tray due to the size, geometry and arrangement of the openings in the gas distribution tray is determined for the gas flowing upwards.

Advantageously, a collecting basin for the liquid flowing through the liquid withdrawal can be arranged between the inlet and the outlet of the liquid withdrawal, so that the liquid collecting in the collecting basin provides a hydraulic seal. This hydraulic seal prevents a bypass for the rising gas from being formed. The rising gas can not flow up through the liquid withdrawal past the openings of the gas distribution tray.

The liquid withdrawal can in particular comprise a siphon-like tube in which the collecting basin is formed. This siphon-like tube provides in a simple way a hydraulic closure for the rising gas.

According to a further embodiment, the inlet of the liquid withdrawal comprises an opening in the upper collecting surface of the gas distribution tray. From this opening, a drain pipe extends downwards. The catch basin may in this case be formed as a collecting cup, which is arranged below the lower opening of the drain pipe, wherein the drain pipe passes through a surface of the collecting cup, which is formed by the upper edge of the collecting cup, and wherein the upper edge of the collecting cup above the lower edge of the lower opening of the drain pipe is arranged. The area formed by the upper edge of the collecting cup is only an imaginary surface. It coincides in particular with the liquid surface when the collecting cup is filled with liquid. Thus, when the collecting cup is filled with liquid, the drain tube dips into the liquid in the collecting cup, thus providing the hydraulic seal.

In order for the liquid accumulating on the collecting surface of the gas distribution tray to drain off via the liquid withdrawal, the collecting surface may have a slope in the direction of the inlet for the liquid withdrawal. For example, a groove may be provided in the collecting surface, which has a slope and opens into the inlet of the liquid withdrawal.

According to a further embodiment of the column according to the invention, the gas distribution floor is a chimney tray with a chimney with a cover. In particular, the chimney tray comprises several chimneys which provide the openings of the gas distribution floor for the passage of gas from the bottom to the top. The hoods of the chimneys prevent the top down raining liquid from passing down through the chimneys. Instead, the liquid falling down from above collects on the collecting surface of the chimney tray. From there, as described above, it is led down through the liquid withdrawal into the area below the gas distribution tray.

The clear distance between two directly within the column according to the invention immediately successive dual-flow mass transfer trays is in particular not more than 700 mm, preferably not more than 600 mm or not more than 500 mm. In terms of application, the clear distance within the floor sequence is 300 to 500 mm. As a rule, the ground clearance should not be less than 250 mm.

The height of the column body is, for example, greater than 5 m, in particular greater than 10 m. However, it is also possible that the height of the column body exceeds 30 m or 40 m.

Between the dual-flow mass transfer trays further separation-effective internals can be arranged. Due to the separating internals, the separation of substances in the separation column is improved. These further installations can be provided, for example, in the form of packages, in particular structured or ordered packages, and / or fillings. Among the beds, those having rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles, Top-Pak etc. are preferred. For example, for the extraction columns to be used according to the invention particularly suitable packages are z. B. packs of Julius Montz GmbH in D-40705 Hilden, such. For example, the pack Montz-Pak B1 -350. Preferably used perforated structured packings made of stainless steel sheets. Packing columns with ordered packs are known in the art and z. In Chem.-Ing.Tech. 58 (1986) No. 1, pp. 19-31 as well as in the Technical Review Sulzer 2/1979, p. 49 et seq. Of the Brothers Sulzer Aktiengesellschaft in CH-Winterthur.

The invention further relates to a thermal separation process between at least one gas rising in a column as described above and at least one liquid descending in the column. The invention thus relates to a process for the thermal treatment of fluid mixtures in a column having a cylindrical, vertically oriented column body which forms a column cavity in which a sequence of vertically spaced dual-flow mass transfer trays is mounted, with at least one gas inlet opening, positioned below the bottom of the series of dual-flow mass transfer trays, and having a gas distribution tray disposed between the bottom of the series of dual-flow mass transfer trays and the gas inlet opening having openings for vertical passage of gas. In the process according to the invention, liquid is introduced into an upper region of the column and this liquid rises in the column. Furthermore, gas is introduced through the gas inlet opening into the column cavity. This gas flows up through the openings of the gas distribution tray, resulting in a pressure drop, wherein the openings are formed so that a gas equal distribution over the column cross-section is brought about. Since the process according to the invention can be carried out in particular with the column described above, it also has the same advantages as this column.

In the method according to the invention, the dynamic pressure of the gas flowing into the column cavity is in particular 1/6 to 1/10, preferably 1/7 to 1/10, of the pressure loss, in particular of the dry pressure loss, of the gas distribution tray.

In the method according to the invention, the ascending gas and / or the descending liquid contains in particular (meth) acrylic monomers.

The thermal separation process according to the invention can be, for example, a fractional condensation process for separating acrylic acid from a product gas mixture containing acrylic acid of a heterogeneously catalyzed gas phase partial oxidation a C3 precursor compound (especially propene and / or propane) of acrylic acid with molecular oxygen to acrylic acid.

Exemplary embodiments of the column according to the invention and exemplary embodiments of the method according to the invention are explained below with reference to the drawings.

FIG. 1 shows a schematic view of a column according to an embodiment of the invention,

FIG. 2 shows a cross section of the column shown in FIG. 1 in the region of the gas inlet,

FIG. 3 shows a cross-section of the column shown in FIG. 1 in the area of the gas distribution floor.

Figure 4 shows a section of a cross section of the gas distribution tray shown in Figure 3 and Figure 5 shows schematically a cross section of the lower portion of another embodiment of the column.

The embodiment described below relates to a separation column 1, as z. B. in a process of fractional condensation for the separation of acrylic acid from an acrylic acid-containing product gas mixture of a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (in particular propene and / or propane) of acrylic acid is used with molecular oxygen to acrylic acid. In Fig. 1, the known separation column 1 is shown schematically. It comprises a cylindrical column body 2 whose axis is vertically aligned. The column body 2 is essentially a hollow cylinder. That is, the column body 2 forms a column cavity 3. The column body 2 is made of stainless steel. Outwardly, the separation column 1 is normally thermally insulated in a conventional manner. The height of the separation column 1 is 40 m. The inner diameter of the column body 2 is continuously 7.4 m.

In the vertical direction, the separation column 1 is subdivided into three regions: the upper region A is referred to as the column head. At the top of the column an inlet 4 is provided, via which a liquid is introduced into the column cavity 3 can. Further, an exhaust pipe 13 is formed at the top for removing the gaseous mixture.

Below the column head a region B is formed. In this area, the fractional condensation is carried out. In the area B, a sequence of vertically spaced dual-flow trays 8 is fixed in the column cavity 3. These dual-flow trays 8 are used for mass transfer. These are thus mass transfer trays. They have a plurality of openings for the passage of liquid and gas in countercurrent.

The openings of the dual-flow trays 8 are circular and have a uniform diameter of 14 mm, with the burr in the separation column pointing downwards. The aperture ratio, d. H. the proportion of the opening area formed by the openings to the cross-sectional inner surface of the column 1 or of the dual-flow tray 8 is 19.75%. The arrangement of the centers of the circular openings follows a strict triangular division. The nearest distance between two circle centers is 30 mm.

With such a geometry of the openings, the pressure loss of the dual-flow trays 8 is so low that the inhomogeneous gas pressure distribution which arises when the gas flows in via the gas inlet opening 5 can not be compensated. The dry pressure loss of the dual-flow trays 8 of the present embodiment is 4 mbar for each of the trays 8. In the region B, a discharge line 7 is also arranged, is taken over which Rohacryl- acid.

Below the region B, the bottom of the column is formed in region C. At the bottom of the column is a gas inlet opening 5 for the tangential introduction of gas into the column cavity 3. The gas inlet is shown in detail in Figure 2. The gas enters tangentially into the column cavity 3 via the gas inlet opening 5 and forms a horizontal vortex 14 there. Since the diameter of the column 1 is relatively large, it may happen in this case that the gas pressure in the outer area is greater than in the middle of Column cavity 3.

Referring again to FIG. 1, a drain 6 for the bottoms liquid is also located in the bottom of the column. The pumped liquid can be supplied to a spraying device (quench), for example. In the spraying apparatus, gas is supplied to the sprayed liquid. The gas then enters the column 1 via the gas inlet opening 5. According to the invention, below the lowermost dual-flow tray 8, but above the gas inlet opening 5, ie between the lowermost dual-flow tray 8 and the gas inlet opening 5, a gas distribution tray 9 designed as a chimney tray is arranged. The gas distribution tray 9 has in the chimneys 1 1 openings for a vertical passage of gas, which was introduced via the gas inlet opening 5 in the column cavity 3. The size, the geometry and the number of these openings are designed so that a gas equal distribution over the column cross-section below the bottom dual-flow tray 8 is brought about.

A gas uniform distribution is understood in this document to mean that the dynamic pressure of the gas flowing into the column cavity 3 is 1/6 to 1/10 of the pressure loss, in particular of the dry pressure loss, of the gas distribution base 9. In this case, the pressure loss of the gas distribution tray 9 is sufficiently large to bring about a gas equal distribution over the column cross-section. For example, if the dynamic pressure at the gas inlet opening about 2.4 mbar, the dry pressure drop of the gas distribution tray 9 z. B. 17 mbar.

Furthermore, the gas distribution tray 9 has a liquid discharge 15. About this liquid withdrawal, the collecting at the gas distribution tray 9 liquid is passed into the column bottom.

Details of the gas distribution tray are explained with reference to FIGS. 3 and 4. The gas distribution tray 9 has a diameter of 7.4 m, so that it can be fixed horizontally in the column interior 3 to the column body 2. Furthermore, the gas distribution floor 9 comprises a total of twelve chimneys 12, which form openings 23 for the vertical passage of gas upwards. The openings 23 have a circular circumference and a diameter of 810 mm. The opening ratio, ie the proportion of the area formed by the openings 23 on the total area of the gas distribution floor 9 is thus 14.38%. Since the opening ratio of the lowermost dual-flow tray 8 is 19.75%, it is 1.37 times greater than that of the gas distribution tray 9. The openings 23 are distributed over the gas distribution tray 9 so that the centers of eight openings 23 are arranged uniformly distributed on a first outer to the column body 2 concentric circular ring and the centers of four openings 23 are arranged uniformly distributed on an inner annulus, which is also concentric with the outer annulus and to the column body 2. Two adjacent openings 23 on the outer circular ring form an opening 23 on the inner circular ring an isosceles triangle, so that a total of four isosceles triangles are formed. The openings 23 are thus arranged uniformly distributed over the cross section of the gas distribution tray 9. At the openings 23 extends from a collecting surface 18 of the gas distribution tray 9 each have a cylindrical body or fireplace body 19 upwards. Above the chimney body 19 is vertically spaced a cover 20 which completely spans the opening 23 and in the horizontal direction over the chimney body 19 passes. The cover 20 prevents the drops of liquid 22 falling down from above from passing through the opening 23 through the gas distribution base 9.

In the middle of the gas distribution tray 9, a liquid discharge 15 is arranged. The liquid outlet 15 comprises a circular opening from which a drainage pipe 17 extends downwards. Via the outlet pipe 17, liquid which accumulates on the collecting surface 18 of the gas distribution tray 9 can drain downwards. For this purpose, the collecting surface 18 may be formed inclined in the direction of the drain pipe 17. Below the drain pipe 17 is a collecting cup 16, which forms a catch basin for liquid. The lower edge 31 of the lower opening of the drainage pipe 17 is arranged vertically spaced from the bottom 33 of the collecting cup 16. Further, the upper edge 30 of the collecting cup 16 above the lower edge 31 of the drain pipe 17 is arranged. Liquid, which flows down through the discharge pipe 17 into the collecting cup 16, collects there, so that the liquid level rises up to the upper edge 30 of the collecting cup 16. Thereafter, the liquid passes from the collecting cup 16 via the upper edge 30 and then passes into the bottom of the column. In this state, the drain pipe 17 immersed in the liquid, which is located in the collecting cup 16. The drain pipe 17 thus passes through an imaginary surface of the collecting cup 16, which is formed by the upper edge 30 of the collecting cup 16. In this way, a hydraulic seal is provided which prevents gas rising from below from passing through the opening of the discharge pipe 17 upwards through the gas distribution tray 9. It is thus ensured that the gas 21 rising upwards rises only through the openings 23 of the chimneys 12 upwards. FIG. 5 schematically shows another example of the liquid withdrawal 15 with the hydraulic seal:

In this case, the gas distribution tray 9 has no liquid discharge 15 in the middle. This liquid discharge 15 is rather formed in the column body 2. For this purpose, in the column body 2 immediately above the collecting surface 18 of the gas distributor lungsbodens 9 an inlet 24 is provided. Adjoining the inlet 24 is a tube 25, which merges into a siphon-like tube 26. Thereafter, the tube opens at a sequence 27 back into the column cavity 3 below the gas distribution tray 9. In this way, liquid 28, which accumulates on the collecting surface 18 of the gas distribution tray 9, be discharged via the liquid outlet 15 and fed to the column bottom. The inlet 24 is arranged below the upper edge of the chimney body 19, so that no liquid 28 overflows over the chimney body 19 and can pass down through the openings 23.

In the following, an embodiment of the method according to the invention will be described, which is carried out with the above-described separation column 1 of one of the embodiments. The process is a thermal separation process between at least one gas rising in the separation column 1 and at least one liquid descending in the separation column 1. In particular, the ascending gas and / or the descending liquid contains (meth) acrylic monomers. In the separation process, a fractional condensation is carried out to separate acrylic acid from a product gas mixture containing acrylic acid a heterogeneously catalyzed gas phase partial oxidation of a C3 precursor compound (especially propene and / or propane) of acrylic acid with molecular oxygen to acrylic acid in a separation column 1 containing separating internals, as they has been described above. In the method, the dynamic pressure of the gas flowing into the column cavity 3 is 1/6 to 1/10, preferably 1/7 to 1/10, of the pressure loss of the gas distribution tray 9. The method is otherwise carried out as described in DE 19924532 A1, DE 10243625 A1 and WO 2008/090190 A1.

The term "C3 precursor" of acrylic acid is taken to mean those chemical compounds which are obtainable formally by reduction of acrylic acid. Known C3 precursors of acrylic acid are, for example, propane, propene and acrolein. But also compounds such as glycerol, propionaldehyde, propionic acid or 3-hydroxypropionic acid are among these C3 precursors count. From them, the heterogeneously catalyzed gas phase partial oxidation with molecular oxygen is at least partially an oxidative dehydrogenation. In the relevant heterogeneously catalyzed gas phase partial oxidations said C3 precursors of acrylic acid, usually diluted with inert gases such as molecular nitrogen, CO, C02, inert hydrocarbons and / or water vapor, im Passed mixture with molecular oxygen at elevated temperatures and optionally elevated pressure via transition metal mixed oxide catalysts and oxidatively converted into an acrylic acid containing product gas mixture. Typically, the acrylic acid containing product gas mixture of a heterogeneously catalyzed gas phase partial oxidation of C3 precursors (eg propene) of acrylic acid with molecular oxygen to solid state catalysts, based on the total amount of (indicated in) specified constituents, the following contents :

From 1 to 30% by weight of acrylic acid,

From 0.05 to 10% by weight of molecular oxygen,

From 1 to 30% by weight of water,

0 to 5% by weight of acetic acid,

0 to 3% by weight of propionic acid,

0 to 1% by weight of maleic acid and / or maleic anhydride,

0 to 2% by weight of acrolein,

0 to 1% by weight of formaldehyde,

0 to 1% by weight furfural,

0 to 0.5% by weight of benzaldehyde,

0 to 1% by weight of propene, and

as residual amount of inert gases, e.g. Nitrogen, carbon monoxide, carbon dioxide, methane and / or propane. The partial gas phase oxidation itself can be carried out as described in the prior art. On the basis of propene, the partial gas phase oxidation may e.g. in two consecutive oxidation steps, e.g. in EP 700 714 A1 and in EP 700 893 A1. Of course, however, the gas phase partial oxidations cited in DE 19740253 A1 and in DE 19740252 A1 can also be used.

In general, the temperature of the product gas mixture leaving the partial gas phase oxidation is 150 to 350 ° C., frequently 200 to 300 ° C. By direct and / or indirect cooling, the hot product gas mixture is expediently first cooled to a temperature of 100 to 180 ° C, before it is conducted for the purpose of fractional condensation in the region C (the bottom) of the separation column 1. The pressure prevailing in the separation column 1 operating pressure is usually 0.5 to 5 bar, often 0.5 to 3 bar and often 1 to 2 bar. LIST OF REFERENCE NUMBERS

1 column, separation column

2 column body

3 column cavity

4 inlet

5 gas inlet opening

6 expiration

7 sampling line

8 mass transfer trays

9 gas distribution floor

1 1 fluid drain

12 fireplaces

13 deduction

14 horizontal swirls

15 fluid drain

16 collecting cup

17 drain pipe

18 collection area

19 cylindrical body; fireplace body

20 cover

21 gas

22 drops of liquid

23 gas passage opening

24 inlet

25 drainpipe

26 siphon-like trained tube

27 process

28 liquid

29 fluid level

30 upper edge of the collecting cup

31 lower edge of the lower opening of the drain pipe

32 openings

33 bottom of the collecting cup

Claims

claims:

Column (1) for the thermal treatment of fluid mixtures with

a cylindrical, vertically oriented column body (2) forming a column cavity (3),

a series of vertically spaced dual-flow mass transfer trays (8) mounted in the column cavity (3) and having openings for countercurrent flow of liquid and gas, and

at least one gas inlet opening (5), which is arranged below the lowest of the sequence of dual-flow mass transfer trays (8),

characterized in that

between the bottom of the sequence of dual-flow mass transfer trays (8) and the gas inlet (5) a gas distribution tray (9) is arranged, which has openings (32) for a vertical passage of gas through the gas inlet opening (5) in the Column cavity (3) can be introduced,

wherein the openings (32) are formed to bring about a gas uniform distribution over the column cross-section.

Column (1) according to claim 1, characterized in that the gas inlet opening (5) and the gas distribution bottom (9) are formed so that the dynamic pressure of the gas flowing into the column cavity (3) 1/6 to 1/10 of the pressure loss of Gas distribution floor (9) is.

Column (1) according to one of the preceding claims, characterized in that the openings (32) of the gas distribution tray (9) are arranged uniformly distributed over the cross section.

Column (1) according to one of the preceding claims, characterized in that the gas distribution tray (9) per square meter has 0.2 to 1 opening (32).

Column (1) according to one of the preceding claims, characterized in that the proportion of the opening area formed by the openings (32) of the gas distribution tray (9) to the cross-sectional inner surface of the column (1) is in a range of 10% to 20%.

6. Column (1) according to one of the preceding claims, characterized in that the proportion of the openings formed by the openings of at least the lowest of the sequence of dual-flow mass transfer trays (8) to the transverse Section surface of the column (1) is greater than this proportion of the gas distribution tray (9).

Column (1) according to one of the preceding claims, characterized in that the proportion of the opening area formed by the openings of at least the bottom of the sequence of dual-flow mass transfer trays (8) to the cross-sectional inner surface of the column (1) is at least 1.13 times greater than this proportion of the gas distribution floor (9) is.

Column (1) according to one of the preceding claims, characterized in that the pressure loss of the gas distribution tray (9) is at least 20% of the pressure loss of the bottom dual-flow mass transfer tray of the sequence of dual-flow mass transfer trays.

Column (1) according to one of claims 6 to 9, characterized in that the proportion of the opening area formed by the openings of at least the bottom of the sequence of dual-flow mass transfer trays (8) to the cross-sectional inner surface of the column (1) in a range of 14 % to 20%.

Column (1) according to one of the preceding claims, characterized in that the gas inlet opening (5) is aligned in the column (1) such that gas entering the column cavity (3) forms a horizontal vortex (14)

Column (1) according to one of the preceding claims, characterized in that above the gas distribution tray (9) or in the gas distribution tray (9) there is arranged a liquid outlet (15) which has a feed for liquid from an upper collecting surface (18) of the gas distribution tray (15). 9) and a drain in an area below the gas distribution tray (9).

Column (1) according to Claim 1 1, characterized in that a collecting basin for the liquid flowing through the liquid withdrawal (15) is arranged between the inlet and the outlet of the liquid withdrawal (15), so that the liquid collecting in the collecting basin forms a hydraulic seal provides.

Column (1) according to one of claims 1 1 or 12, characterized in that the liquid withdrawal (15) comprises a siphon-like tube (26) in which the collecting basin is formed. 14. A column (1) according to any one of claims 1 1 or 12, characterized in that the inlet of the liquid withdrawal (15) comprises an opening in the upper collecting surface (18) of the gas distribution tray (9) from which a drain pipe (17) extends downwardly and that the catch basin is formed as a collecting cup (16) which is disposed below the lower opening of the drain pipe (17), wherein the drain pipe (17) passes through an area of the collecting cup (16), of the upper edge (30) of the collecting cup (16) is formed, and wherein the upper edge (30) of the collecting cup (16) above the lower edge (31) of the lower opening of the discharge pipe (17) is arranged, so that in the collecting cup (16) accumulating liquid forms the hydraulic seal.

Column (1) according to one of the preceding claims, characterized in that the gas distribution tray (9) is a chimney tray with a chimney (12) with a cover (20).

Process for the thermal treatment of fluid mixtures in a column (1) having a cylindrical, vertically oriented column body (2) which forms a column cavity (3) in which a sequence of vertically spaced dual-flow mass transfer trays (8) is mounted, with at least one gas inlet opening (5) arranged below the lowest of the sequence of dual-flow mass transfer trays (8) and with one between the lowest of the sequence of dual-flow mass transfer trays (8) and the gas inlet opening (5) Gas distribution tray (9) having openings (32) for vertical passage of gas, in which

Liquid is introduced into an upper region of the column (1) and this liquid in the column (1) descends and

Gas is introduced through the gas inlet opening (5) into the column cavity (3) and the gas flows upwards through the openings (32) of the gas distribution tray (9) resulting in a pressure drop, wherein the openings (32) are formed so that a gas uniform distribution over the column cross-section is brought about.

A method according to claim 16, characterized in that the dynamic pressure of the gas flowing into the column cavity (3) is 1/6 to 1/10 of the pressure loss of the gas distribution tray (9).

18. The method according to claim 16 or 17, characterized in that the rising gas and / or the descending liquid contains (meth) acrylic monomers.