Method for producing (METH)acrylic acid alkyl ester from (METH)acrylic acid

Abstract

The invention relates to a method for producing (meth)acrylic acid alkyl ester from (meth)acrylic acid, which is present in a gaseous mixture produced by a catalytic gas phase oxidation of at least one C3- / C4 precursor of (meth)acrylic acid, wherein e) the gaseous mixture is depleted of high-boiling components, f) the mixture depleted of high-boiling components is condensed in a separating column having installations which have a separating effect, g) a liquid mixture containing (meth)acrylic acid is guided out of the separating column, and h) the (meth)acrylic acid contained in the liquid mixture is converted into (meth)acrylic acid alkyl ester in an esterification system. The method is characterized in that the separating column is operated such that the temperature profile in the separating column has an inverse sigmoid curve and the liquid mixture guided out of the separating column in step c) is transferred directly into the esterification system without further purifying the obtained (meth)acrylic acid by means of a thermal separating process.

Description

[0001] Process for the production of (meth)acrylic acid alkyl esters starting from (meth)acrylic acid

[0002] The present invention relates to a process and an apparatus for the production of (meth)acrylic acid alkyl esters and the (meth)acrylic acid alkyl esters obtained.

[0003] The term "(Meth)acryl-" is used in this document as a shortened form of "acryl- or methacryl-".

[0004] Alkyl esters of (meth)acrylic acid are generally known and are important, for example, as reactive monoethylene unsaturated monomers for the production of aqueous polymer dispersions via radical aqueous emulsion polymerization, which are used, for example, as adhesives.

[0005] Typically, (meth)acrylic acid alkyl esters are produced by direct, acid-catalyzed reaction (esterification) of (meth)acrylic acid with the corresponding alkanols.

[0006] One route for the large-scale production of (meth)acrylic acid is the heterogeneously catalyzed partial gas-phase oxidation of suitable C3 / C4 precursors (e.g., propylene, acrolein, isobutene, or methacrolein) with molecular oxygen (see, e.g., WO 2010 / 012586 A, US 5,198,578 A, EP 1 710 227 A, EP 1 015410 A, EP 1 484303 A, EP 1 484 308 A, EP 1 484 309 A, US 2004 / 0242826 A, WO 2006 / 136336 A, DE 10 028 582 A, and WO 2007 / 074044 A). However, this process does not yield pure (meth)acrylic acid, but a gas mixture which, in addition to (meth)acrylic acid, contains acetic acid as a by-product, the separation of which from (meth)acrylic acid, especially by rectification, is complex (see, e.g., DE 19814449 A and DE 19814421 A).

[0007] To separate acrylic acid from the product gas mixture of the heterogeneously catalyzed partial gas-phase oxidation of a C3 / C4 precursor compound, a combination of different separation methods is typically employed to achieve a purity suitable for the subsequent use of the acrylic acid in the most economical way possible. The specific combination used depends, among other things, on the type and quantity of components other than acrylic acid contained in the product gas mixture.

[0008] A feature common to essentially all possible combinations of separation processes for separating acrylic acid from the product gas mixture of a heterogeneously catalyzed partial gas phase oxidation of a C3 / C4 precursor compound is that, optionally after direct and / or indirect cooling of the aforementioned product gas mixture, the acrylic acid contained in the product gas mixture is transferred to the condensed, in particular liquid, phase in a basic separation step.

[0009] This can be achieved, for example, by absorption into a suitable solvent (e.g., water, high-boiling organic solvents, aqueous solutions) and / or by partial or essentially complete condensation (e.g., fractional condensation) (see, for example, EP 1 388 533 A, EP 1 388 532 A, EP 1 159 249 A). Acrylic acid separation can also be carried out as described in EP 982 287 A, EP 982 289 A, and EP 982 288 A. Other suitable separation methods are those described in WO 2004 / 063138 A, WO 2008 / 090190 A, WO 2004 / 035514 A, DE25 10 243 625 A, and DE 10 235 847 A.

[0010] On the other hand, the direct esterification of (meth)acrylic acid with alkanols is predominantly carried out in such a way that, due to the equilibrium limitation of the esterification reaction, after continuous distillative removal of the water of reaction, a mixture is obtained that, in addition to the (meth)acrylic acid ester, contains a large proportion of unreacted (meth)acrylic acid and alkanol, as well as heavy byproducts. The separation of the product ester from the reaction mixture represents an unavoidable, extensive separation operation, which is accomplished by rectification (see, e.g., DE 19536178 A, EP-790230 A1) or a combination of extractive and rectification separation steps (DE 199 35 453 A1, EP 4 015 498 A1). Such an esterification process does not require the use of an organic solvent as an azeotropic water carrier.

[0011] However, when using (meth)acrylic acid containing acetic acid (so-called crude (meth)acrylic acid), the corresponding alkyl ester of acetic acid is unavoidably formed as a byproduct during direct esterification, which leads to additional costs due to the unproductive consumption of alkanol.

[0012] Alkyl acetates as companions of (meth)acrylic acid alkyl esters continue to prove problematic in many applications of (meth)acrylic acid alkyl esters, as they are not radically polymerizable and are relatively volatile.

[0013] In the production of aqueous polymer dispersions containing alkyl(meth)acrylates, one would obtain, for example, aqueous polymer dispersions containing free alkyl acetate. Due to the generally good solubility of alkyl acetates in the polymer particles dispersed in the aqueous polymer dispersion, subsequent removal of alkyl acetate, e.g., by stripping with air or steam, is difficult and costly. On the other hand, the partial pressure of alkyl acetate in aqueous polymer dispersions containing alkyl acetate is high enough to result in workplace concentrations of alkyl acetate in the atmosphere surrounding the processing area of ​​the polymer dispersion that are not entirely harmless. Therefore, polymerizers generally require essentially alkyl acetate-free alkyl(meth)acrylate as the starting material for their polymerizations.

[0014] The high separation efficiency (i.e., either a large reflux ratio and / or a large number of theoretical separation stages) required for both the rectification of alkyl(meth)acrylates and alkyl acetates, especially in the presence of alkanol and water, and the rectification of acetic acid from (meth)acrylic acid can only be avoided in a known manner by performing the rectification with reduced separation efficiency in a less precise manner. The disadvantage of such a less precise rectification is that some of the desired product, which is obtained in essentially pure form, is lost as a component of the mixture; that is, the yield of the desired product is reduced.At the same time, shifting the acetic acid separation from the (meth)acrylic acid level to the alkyl (meth)acrylate level would be desirable, since (meth)acrylic acid consists of monomers that are significantly more polymerizable than the corresponding alkyl esters. The polymerizability of (meth)acrylic acid necessitates regular flushing shutdowns during conventional rectification purification (WO 2017 / 025391 A), resulting in reduced plant uptime and significant organizational effort. Therefore, a crystallizative acetic acid separation at the (meth)acrylic acid level is often considered necessary to solve this problem (see, e.g., WO 1999 / 014181 A). However, a disadvantage of this solution is the substantial investment required in a crystallization plant. On the other hand, the separation of acetic acid at the alkyl(meth)acrylate level has been improved with regard to loss of valuable product and equipment costs (see WO 2000 / 27788 A).

[0015] The object of the present invention was to provide an improved process for the production of alkyl acrylates starting from (meth)acrylic acid and a corresponding apparatus. The process was intended to be particularly easy to carry out technically and economically, and not to adversely affect the product quality.

[0016] The problem is solved by a process for the production of (meth)acrylic acid alkyl esters starting from (meth)acrylic acid, which is present in a gaseous mixture generated by catalytic gas-phase oxidation of at least one C3 / C4 precursor of (meth)acrylic acid, wherein a) the gaseous mixture is depleted of heavy boiling elements, b) the mixture depleted of heavy boiling elements is condensed in a separation column with separation-effective internals, c) a liquid mixture containing the (meth)acrylic acid is removed from the separation column, and d) the (meth)acrylic acid contained in the liquid mixture is reacted to form (meth)acrylic acid alkyl esters in an esterification plant, characterized in that the separation column is operated such that the temperature profile in the separation column has an inverse sigmoidal shape, and the liquid mixture removed in step c)The (meth)acrylic acid contained in the product is transferred directly to the esterification plant without further purification by a thermal separation process.

[0017] The temperature profile according to the invention, or its course, is inversely sigmoidal and can be essentially described by the function where n = soil number, c = soil with the greatest temperature change, and a, b, d, g = adjustment constants. This means that initially the temperature decreases only slowly (the curve is flat) and then gradually begins to fall until a sharp or exponential drop in temperature occurs (the curve is very steep). Subsequently, the rate of decrease slows again, and the temperature continues to fall only slowly (the curve is flat). In summary, the shape of the inverse sigmoidal curve is flat in the upper part, steep in the middle, and flat again in the lower part. The shape of an inverse sigmoidal curve is shown in Figure 1 with reference to Examples 1 to 4 according to the invention.

[0018] The temperature profile according to the invention in the separation column or in a separation column section cannot be set by a conventional ratio control of the column reflux, e.g., in relation to the (meth)acrylic acid flow rate in the reaction gas. The temperature profile according to the invention is very sensitive. It is influenced, among other things, by the reaction gas temperature, the acrylic acid concentration in the reaction gas, the reflux temperature, and the reflux composition. The temperature profile is preferably set by measuring the temperature in the separation column, e.g., using a temperature sensor. The temperature measurement is preferably taken, or the temperature sensor is preferably located, where the inverse sigmoidal shape of the temperature profile exhibits the steepest or exponential drop (steep curve), i.e., where the temperature change is greatest. For this purpose, a temperature setpoint is preferably defined.If the measured temperature (actual temperature) is above the setpoint, the reflux rate in the separation column is increased; if the measured temperature (actual temperature) is below the setpoint, the reflux rate in the separation column is reduced. Such a setup is shown in detail in Figure 2. The inverse sigmoidal temperature profile according to the invention preferably extends from the sampling plate of the liquid (meth)acrylic acid-containing mixture to the plate onto which the reflux is added.

[0019] Preferably, a temperature measurement is performed in the section of the column with the greatest temperature change, and the reflux rate is controlled as a function of the measured temperature (actual temperature). As preferably described above, the temperature profile is controlled by increasing the reflux rate when the temperature setpoint is exceeded and decreasing it when the temperature setpoint is undershot.

[0020] The reflux rate in the separation column can preferably be adjusted via the amount of reflux at the top of the column or at a position above the steep temperature drop above the side outlet from which the liquid mixture, the crude acrylic acid, is drawn off. The reflux into the separation column is preferably obtained by condensing the low-boiling components of the reaction gas and consists essentially of water. Alternatively, water or other low-boiling components can also be used as reflux. The condensation of the low-boiling components is preferably carried out by cooling following the (meth)acrylic acid condensation according to the invention, either in a separation column section located above the column or in a separate separation column.

[0021] Separation columns and separating internals are known to those skilled in the art and can be found in textbooks on process engineering, particularly on thermal separation (for example, M. Baerns et al., Technische Chemie, 2006, WILEY-VCH, Weinheim). In the context of the present invention, a separation column is preferably understood to be an apparatus for the thermal separation of mixtures. Examples include rectification columns, absorption columns, and condensation columns, with condensation columns being preferred. The column body is typically designed as a cylindrical tube insulated to prevent heat loss. For the evaporation of the mixture to be separated, or a portion thereof, the lower end of the column can include an evaporator, or an evaporator can be implemented as an external apparatus adjacent to the column.Almost all conceivable heat sources can be used for evaporation, such as hot water, electricity, microwaves, or waste heat from other processes or other process steps within the present process. For condensation of the mixture to be separated, or a portion thereof, the column can include a condenser at the top, or the condenser can be implemented as an external unit adjacent to the column. Various operating media can be used for cooling in the condenser, such as water, refrigerants, air, or even media to be heated from other processes or other parts of the present process. To improve heat and mass transfer within the column, the column body can contain internals such as screens, bubble caps, or valve trays, packing materials such as Raschig rings, or structured packings.Experts know that (horizontal) separating elements in such columns are generally referred to as trays. In principle, columns with rotating inserts, so-called rotary columns, can also be used, which spray the reflux liquid in droplets.

[0022] In the context of the present invention, dual-flow trays and cross-flow trays are preferably used as separating internals. Dual-flow trays as such are known to those skilled in the art. In the context of the present invention, these are horizontal internals that are installed in the column at specific intervals and have openings through which vapor and liquids can pass in counterflow. These openings can be, for example, holes or slots, the opening ratio being adjustable via the number of openings. Typically, dual-flow trays do not have a drain pipe connecting them to the next tray. Naturally, each dual-flow tray can be flush with the walls of the rectification column, but can also be connected to it via webs.

[0023] Crossflow trays are also known to those skilled in the art. In the context of the present invention, these are horizontal internals installed at specific intervals in the column, in which liquid is fed onto the tray at one side, flows over the tray, and comes into contact with the rising gas. The liquid then flows to a discharge chute, is collected there, and fed to the tray below. Crossflow trays can, for example, contain sieve holes, movable valves, bells, or tunnels.

[0024] Preferably, dual-flow trays and / or cross-flow trays are used as separation-effective internals in the separation column according to the invention. Furthermore, the separation column can include additional inlets and / or outlets, for example at the top, to, for example, withdraw lighter components and / or recycle components. The operating pressure prevailing in the separation column is preferably 0 to 5 bar, more preferably 0 to 3 bar, and even more preferably 0 to 1.6 bar.

[0025] The liquid mixture removed from the separation column in step c) is commonly referred to as crude acrylic acid. Crude acrylic streams obtained during the purification of acrylic acid are well known to those skilled in the art. It is also known to those skilled in the art that such a crude acrylic acid stream typically does not represent a pure product, but rather contains acrylic acid as its largest component, as well as (small) amounts of other components, such as water, lower aldehydes (e.g., furfurals, acrolein, benzaldehyde), lower carboxylic acids (e.g., acetic acid, propionic acid), and diacrylic acid.

[0026] Preferably, the thermal separation processes for purifying the (meth)acrylic acid contained in the liquid mixture are adsorptive, extractive, desorptive, distillative, stripping, rectifying, azeotropic distillative, azeotropic rectifying and crystallizing processes.

[0027] Crystallizative separation processes can be carried out in the manner described in documents DE-A 102008041573, DE-A 102008040799 and WO 2007 / 074044 A as well as DE-A 102007029053.

[0028] Non-crystallizing separation processes are generally thermal separation processes in which gaseous (ascending) and liquid (descending) streams, or two liquid streams, are fed countercurrently into separation columns containing separating internals. Due to the gradients between the streams, heat and mass exchange occurs, ultimately resulting in the desired separation effect in the column. Examples of such non-crystallizing thermal separation processes include rectification, azeotropic rectification, extraction, desorption, stripping, distillation, azeotropic distillation, and adsorption. Such thermal separation processes (e.g.,All thermal separation processes described in WO 2011 / 000808 A2, DE-A 10 10336386, DE-A 19924532, DE-A 19924533, and DE-A 102007004960 are preferably carried out according to the invention in devices that comply with the recommendations of US 6441228 B2 and US 6966973 B2.

[0029] The term “thermal separation processes” is intended to express that heat must be added to or removed from the system to achieve the desired separation effect (see DE-A 10 2008 041573 and DE-A 10 2008 8040799).

[0030] Furthermore, the heterogeneously catalyzed partial gas-phase oxidation process for the production of acrylic acid can be carried out in a manner known per se, as described in the prior art. If the cesium precursor compound is, for example, propylene and / or acrolein, the heterogeneously catalyzed partial gas-phase oxidation can be carried out, for example, as described in WO 2005 / 042459 A, WO 2005 / 047224 A and WO 2005 / 047226 A.

[0031] If the Ca precursor compound is, for example, propane, the heterogeneously catalyzed partial gas-phase oxidation for the production of acrylic acid can be carried out, for example, as described in documents EP-A 608 838, DE-A 198 35 247, DE-A 102 45 585 and DE-A 102 46 119.

[0032] If the calcium precursor compound is, for example, glycerol, the heterogeneously catalyzed partial gas-phase oxidation for the production of acrylic acid can be carried out, for example, as described in documents WO 2007 / 090991 A, WO 2006 / 114506 A, WO 2005 / 073160 A, WO 2006 / 114506 A, WO 2006 / 092272 A or WO 2005 / 073160 A.

[0033] The esterification of (meth)acrylic acid as such is known to those skilled in the art and can be found in various forms in the prior art. For example, the acid-catalyzed esterification of acrylic acid with n-butanol to n-butyl acrylate is described in EP 4 015 498 A1 or EP 1 129 061 A1.

[0034] The continuous production of n-butyl acrylate is carried out by reacting acrylic acid with n-butanol in a solvent-free phase at elevated temperature and with the addition of acid, particularly sulfuric acid, as an acidic esterification catalyst. The acrylic acid, n-butanol, and esterification catalyst are fed into a reaction zone. During the residence time in the reaction zone, the water formed, as a component of an n-butanol-containing mixture, is separated from the reaction mixture in a first rectification unit placed on top of the reaction zone. The resulting distillate is separated into an n-butanol-containing organic phase and a water-containing aqueous phase, and the organic phase is recycled to the first rectification unit. The aqueous phase is optionally removed entirely or partially (e.g., a proportion of 50 to 100 wt.%, particularly 80 to 100 wt.%, most especially 95 to 100 wt.%, and in particular, entirely, i.e., 100 wt.%).-%), is fed to a stripping unit. The reaction mixture containing n-butyl acrylate, which is drawn off from the reaction zone, is subjected to pre-purification. In a first pre-purification stage, the majority of the esterification catalyst is extracted by water washing. In a second pre-purification stage, the acidic components are neutralized and extracted with an aqueous alkali solution by reactive extraction. Optionally, in a third pre-purification stage, residual salts and aqueous foreign phase components can be extracted with water from the organic reaction residue mixture remaining after the second pre-purification stage. The remaining organic first reaction residue mixture is fed into a separation zone comprising a further rectification unit, and the n-butyl acrylate formed is separated in this zone by feeding the remaining first reaction residue mixture to a second rectification unit.In this process, the remaining first reaction mixture is rectified into a low-boiling product containing n-butyl acrylate and components that boil more easily than n-butyl acrylate, and into a second reaction mixture comprising n-butyl acrylate and components that boil more heavily than n-butyl acrylate. The low-boiling product is preferably fed into a further rectification unit, in which the low-boiling components are distilled off and the bottoms product is recycled (see EP 4 015 498 A1). The second reaction mixture is fed into a third rectification unit, in which the n-butyl acrylate is separated from the components that boil more heavily than n-butyl acrylate.

[0035] It was surprisingly found that the process according to the invention, with its advantageous temperature profile in the separation column, offers an advantage over the prior art in that crude (meth)acrylic acid can be taken directly from the separation column after removal of the high-boiling components and fed to the esterification process, without the need for complex additional purification of the crude (meth)acrylic acid and / or the resulting (meth)acrylic acid alkyl ester. This reduces the equipment requirements and saves costs.

[0036] According to the invention, a high-boiling component or compound is understood to have a higher boiling point than (meth)acrylic acid. According to the invention, a low-boiling component or compound is understood to have a lower boiling point than (meth)acrylic acid.

[0037] Preferably, the liquid mixture extracted in step c) contains 2500 to 4500 ppm, more preferably 2600 to 4100 ppm, further preferably 2700 to 3700 ppm, and especially preferably 2800 to 3500 ppm, based on the total amount of liquid mixture, of diacrylic acid.

[0038] Preferably, the liquid mixture extracted in step c) contains 1 to 3 wt.%, preferably 1.2 to 2.7 wt.%, more preferably 1.4 to 2.5 wt.%, particularly preferably 1.6 to 2.3 wt.%, especially preferably 1.8 to 2.0 wt.%, in each case based on the total amount of liquid mixture, water.

[0039] Preferably, the liquid mixture extracted in step c) contains 200 to 325 ppm, preferably 210 to 310 ppm, more preferably 220 to 300 ppm, particularly preferably 230 to 290 ppm, and especially preferably 240 to 280 ppm, in each case based on the total amount of liquid mixture, furfural.

[0040] Preferably, the liquid mixture extracted in step c) contains at most 100 ppm, preferably at most 50 ppm, more preferably at most 25 ppm, especially preferably at most 20 ppm, and particularly preferably at most 15 ppm, in each case based on the total amount of liquid mixture, maleic anhydride.

[0041] Preferably, the mass ratio of acetic acid to water in the liquid mixture extracted in step c) is 0.05 to 0.5, more preferably 0.1 to 0.4, more preferably 0.15 to 0.3 ppm, and especially preferably 0.15 to 0.25.

[0042] Preferably, the separation column is operated with temperature-dependent reflux, resulting in an inverse sigmoidal temperature profile. The ratio of water in the reflux (kg / h) to the product of the product gas mixture (t / h) and the product gas mixture temperature (°C) is preferably between 0.453 and 0.490, more preferably between 0.455 and 0.485, and most preferably between 0.457 and 0.480. The separation column is preferably operated at a reflux temperature of 50 to 85 °C, more preferably between 53 and 80 °C, more preferably between 57 and 75 °C, and most preferably between 60 and 70 °C. The reflux temperature refers to the temperature of the reflux fluid.

[0043] Preferably, the removal of the heavy elements in step a) takes place at higher temperatures than the temperature of the liquid mixture discharged from the separation column in step c). The removal of the heavy elements can be carried out in the same separation column as the condensation of the (meth)acrylic acid, or it can be carried out in a separate separation column.

[0044] Preferably, the number of trays for heavy-boiling reduction is at least 10, more preferably at least 12, and particularly preferably at least 15. More preferably, the number of trays for heavy-boiling reduction is from 10 to 35, more preferably from 12 to 32, more preferably from 15 to 30, and particularly preferably from 17 to 27. The trays for heavy-boiling reduction are the trays (separation-effective internals) in the distillation column on which the removal of the heavy-boiling components takes place in step a).

[0045] Preferably, the number of trays between the point of extraction of the liquid mixture from the separation column of step c) and the temperature measurement or the temperature sensor for adjusting the reflux rate is at least 10, preferably at least 12, more preferably at least 15 trays, and also preferably between 10 and 40 trays, more preferably between 15 and 35 trays and particularly preferably between 20 and 30 trays.

[0046] Preferably, the number of trays between the temperature measurement or temperature sensor for adjusting the reflux rate and the tray to which the reflux is added is at least 10, preferably at least 12, more preferably at least 15 trays, and also preferably 10 to 50 trays, more preferably 15 to 45 trays, particularly preferably 20 to 40 trays, and especially preferably 25 to 35 trays.

[0047] Preferably, the (meth)acrylic acid is reacted with an alkanol in step d) under acid catalysis.

[0048] Preferably, the acid used as a catalyst is a sulfur-containing mineral acid, a phosphorus-containing mineral acid, an organic sulfonic acid, or a mixture thereof.

[0049] Preferably, the (meth)acrylic acid alkyl ester is n-butyl acrylate. The (meth)acrylic acid is preferably reacted with n-butanol in step d).

[0050] Preferably, the reaction of (meth)acrylic acid in step c) is carried out at a temperature in the range of 70 to 160 °C, preferably 80 to 130 °C, more preferably 110 to 125 °C, and at an absolute pressure in the range of 300 to 1500 mbar, preferably 400 to 700 mbar, more preferably 500 to 600 mbar. Preferably, the liquid mixture withdrawn in step c) has a temperature of 85 to 120 °C, more preferably 90 to 115 °C, more preferably 95 to 110 °C, and particularly preferably 100 to 105 °C.

[0051] The invention further relates to (meth)acrylic acid alkyls obtained or produced by the process according to the invention.

[0052] Preferably, the (meth)acrylic acid alkyl ester is n-butyl acrylate obtained by acid-catalyzed reaction of (meth)acrylic acid with n-butanol.

[0053] Furthermore, the invention relates to a plant for the production of (meth)acrylic acid alkyl esters starting from (meth)acrylic acid, comprising

[0054] - a separation column,

[0055] - an esterification plant, and

[0056] - a first line directly connecting the separation column and the esterification plant, characterized in that the first line is connected to a crude acrylic acid withdrawal point of the separation column.

[0057] Preferably, at least one temperature sensor is arranged in the separation column, configured to measure the temperature within the column. The temperature sensor is preferably positioned where the inverse sigmoidal temperature profile in the separation column exhibits a steep or exponential drop (steep curve). Preferably, the reflux rate in or to the separation column is controlled based on this measured temperature. For this purpose, a temperature setpoint is preferably defined. If the measured temperature is above the setpoint, the reflux rate in the separation column is increased; if the measured temperature is below the setpoint, the reflux rate in the separation column is reduced. Such a setup is shown in detail in Figure 2. The reflux rate is preferably controlled by a suitable control unit, which, for example, controls the opening degree of a valve.

[0058] Figure 2 shows a schematic representation of an exemplary system according to a preferred embodiment. Details not essential to the invention and already well known to those skilled in the art have been omitted.

[0059] 100 column

[0060] 101 Synthesis gas stream in column

[0061] 102 Crude acrylic acid stream in esterification

[0062] 103 Reflux fluid flow

[0063] 104 Esterification plant

[0064] 105 Temperature sensor

[0065] 106 Column tray. An acrylic acid-containing synthesis gas stream 101, e.g., from a reactor for the heterogeneously catalyzed partial gas-phase oxidation of propene, is introduced into column 100. In column 100, which has separating internals 106, e.g., column trays, the acrylic acid is purified, and a crude acrylic acid stream 102, which still contains impurities, is withdrawn and fed into the esterification unit 104 without further purification. The temperature in the column is measured by a temperature sensor 105, and the reflux liquid flow rate 103, i.e., the reflux quantity, into column 100 is adjusted depending on the measured temperature.

[0066] Below the extraction point of the crude acrylic acid stream 102, the removal of the heavy elements takes place; between the extraction point of the crude acrylic acid stream 102 and the addition point of the reflux liquid stream 103, the acrylic acid condensation takes place.

[0067] The features disclosed for the process shall also be deemed disclosed for the plant, mutatis mutandis, and vice versa.

[0068] Examples

[0069] Example 1 (according to the invention)

[0070] The procedure is as described in Example 1 of EP 4 015 498 A1.

[0071] The starting material for the esterification is an acrylic acid produced by the heterogeneously catalyzed partial gas-phase oxidation of propene with molecular oxygen. The process for the preparation of the acrylic acid is shown in Figure 3.

[0072] A product gas mixture was obtained from a heterogeneously catalyzed gas-phase partial oxidation of polymer-grade propylene. Mass flow rate, temperature, and composition are given in Table 1.

[0073] The product gas mixture is cooled to the temperature Tq specified in Table 1 in a co-current spray cooler K, into which a mass flow of 171 t / h of sump liquid is fed.

[0074] The mixture (101 in Fig. 2) is then fed to the separation column (100 in Fig. 2). The separation column has an inner diameter of 7.4 m and features separation-effective internals in the form of different trays. Trays 1 to 37 of the separation column are dual-flow trays. Trays 38 to 75 are single-flow Thormann trays.

[0075] A liquid mixture (102 in Fig. 2), the so-called crude acrylic acid, was drawn from a side outlet on tray 22 of the distillation column and fed directly to the esterification unit (104 in Fig. 2) without further thermal purification. The composition of the drawn crude acrylic acid is shown in Table 2. The temperature profile according to the invention on trays 22 to 75 was adjusted to the target value Tsoii by measuring the temperature on tray 46 (105 in Fig. 2) of the distillation column and changing the reflux rate (103 in Fig. 2). The temperature profile present in the column is shown in Figure 1. The respective operating conditions are shown in Table 3.

[0076] Trays 1 to 21, i.e., below the side outlet, are used for the removal of heavy substances from the gas phase. 4193 kg / h of the sump liquid are diverted to the residue column R for this purpose. The temperature on tray 10 is 102.5°C.

[0077] Above tray 75 is a collection tray and the sour water condensation stage (trays 76 to 85). For this, a partial stream (570 t / h) of the sour water drawn off at the collection tray via a side outlet is cooled by indirect heat exchange and returned to the trays, resulting in a gas temperature of 32°C at the column outlet.

[0078] A further partial flow of the acid water is returned to bottom 75. The flow rate is variable in order to adjust the inverse sigmoidal temperature profile according to the invention.

[0079] The residual gas extracted at the top of the condensation column is partially recycled as dilution gas (recycled gas) into the gas-phase partial oxidation process and partially fed as stripping gas to the desorber and the residue column. The remaining residual gas stream is fed to the exhaust gas aftertreatment system, with the flow rate adjusted to maintain an absolute pressure of 1.2 bar at the column head.

[0080] The difference between the condensed and recirculated acid water is fed to the countercurrent extraction column E. The packing section of the column (MontzPak B1-350) has a diameter of 1.3 m and a height of 19.5 m. The acid water is fed below the packing section, while the extraction solvent Palatinol® A is fed countercurrently above the packing section at a mass ratio of 0.97 and a temperature of 66°C.

[0081] The acid-depleted water, extracted from the head of the extraction column and reduced in acrylic acid, is thermally utilized.

[0082] The extraction solvent, enriched with acrylic acid and taken from the bottom of the extraction column, is fed to the top tray of desorber D. Desorber D contains 5 dual-flow trays in the lower section, followed by 15 single-flow cross-flow trays, and has an inner diameter of 2 m.

[0083] Below the bottom tray, 10.7 t / h of compressed residual gas at a temperature of 162°C is fed to desorber D in countercurrent flow with the enriched extraction solvent. The desorber's bottom contents are heated to 162°C by heat exchange. For this purpose, a stream of 88 t / h of bottom contents is heated and returned to the desorber on tray 5. The loaded stripping gas is discharged from the top of the desorber, mixed with 20.2 t / h of compressed residual gas at a temperature of 162°C, and fed to the residue column R below the first tray. This column has an inner diameter of 2.4 m and features 50 dual-flow trays. The bottom liquid for the condensation column is fed onto tray 8.

[0084] The sump liquid is heated to 162°C by a forced-circulation evaporator. The mass flow rate through the forced-circulation evaporator is 550 t / h. A residue stream of 914 kg / h is discharged and sent for thermal treatment.

[0085] A gas mixture is extracted from the head of the residue column R, fed to the direct circulation evaporator and mixed there with reaction gas and bottom contents.

[0086] A spray cooler is located at the top of the residue column R. A flow rate of 99 t / h is taken from the collecting tray located above the last dual-flow tray, indirectly cooled, and then sprayed into the gas stream, resulting in a liquid temperature of 69°C. A partial flow rate of 4000 kg / h of the liquid from the collecting tray is returned as reflux to tray 50 of the residue column.

[0087] N-butyl acrylate conforming to specifications with a purity >99.5 wt% was successfully produced. The butanol content was not elevated within the measurement accuracy (+ / - 0.5%).

[0088] Example 2 (according to the invention)

[0089] The procedure is the same as in Example 1. The temperature of the synthesis gas mixture from the gas-phase oxidation of propene, which is fed into the condensation column, is higher. The composition of the extracted crude acrylic acid is shown in Table 1.

[0090] To maintain the inverse sigmoidal temperature profile according to the invention, the reflux or reflux rate was increased. The temperature profile present in the column is shown in Figure 1. The operating conditions are shown in Table 2. The temperature on tray 10 is 103.8°C.

[0091] N-butyl acrylate conforming to specifications with a purity >99.5 wt% was successfully produced. The butanol content was not elevated within the measurement accuracy (+ / - 0.5%).

[0092] Example 3 (according to the invention)

[0093] The procedure is the same as in Example 1. The amount of gas recycled from the process into the synthesis is higher. The composition of the extracted crude acrylic acid is shown in Table 1. To maintain the inverse sigmoidal temperature profile according to the invention, the reflux or reflux rate was increased. The temperature profile present in the column is shown in Figure 1. The operating conditions are shown in Table 2. The temperature on tray 10 is 102.8°C.

[0094] N-butyl acrylate conforming to specifications with a purity >99.5 wt.% was produced. The butanol content was not elevated within the measurement accuracy (+ / -0.5%).

[0095] Example 4 (according to the invention)

[0096] The procedure is the same as in Example 1. The temperature of the reflux or reflux liquid in the condensation column is lower. The composition of the extracted crude acrylic acid is shown in Table 1.

[0097] To maintain the inverse sigmoidal temperature profile according to the invention, the reflux or reflux rate was reduced. The temperature profile present in the column is shown in Figure 1. The operating conditions are shown in Table 2. The temperature on tray 10 is 102.5°C.

[0098] N-butyl acrylate conforming to specifications with a purity >99.5 wt% was successfully produced. The butanol content was not elevated within the measurement accuracy (+ / - 0.5%).

[0099] Example 5 (comparative example)

[0100] The procedure is the same as in Example 1. The reflux temperature is increased. This results in losses of acrylic acid. The propene input number is significantly increased (Table 2). The composition of the extracted crude acrylic acid is shown in Table 1.

[0101] The temperature profile in the condensation column did not exhibit the inverse sigmoidal curve according to the invention. The temperature profile present in the column is shown in Figure 1. The operating conditions are shown in Table 2. The temperature on tray 10 is 102.7°C.

[0102] N-butyl acrylate conforming to specifications with a purity >99.5 wt% was successfully produced. The butanol content was not elevated within the measurement accuracy (+ / - 0.5%).

[0103] Example 6 (comparative example)

[0104] The procedure is as in Example 1. The reflux temperature is lower. The acrylic acid content in the liquid gas mixture withdrawn from the side outlet (the crude acrylic acid) was reduced. The composition of the withdrawn crude acrylic acid is shown in Table 1. The temperature profile in the condensation column did not exhibit the inverse sigmoidal curve according to the invention. The temperature profile present in the column is shown in Figure 1. The operating conditions are shown in Table 2. The temperature on tray 10 is 102.4°C. It was not possible to produce n-butyl acrylate according to specifications with a purity >99.5 wt%.

[0105] Table 1: Reaction gas

[0106] Comparative example

[0107] Table 2: Composition of crude acrylic acid

[0108] Comparative example

[0109] Table 3: Operating conditions of the column ) Comparative example *) Unit Ratio = Amount of propene used [kg] / Amount of acrylic acid obtained [kg] **) Synthesis gas temperature = Temperature at which the synthesis gas leaves the reactor

Claims

Patent claims 1. A process for the production of (meth)acrylic acid alkyl esters starting from (meth)acrylic acid present in a gaseous mixture generated by catalytic gas-phase oxidation of at least one C3 / C4 precursor of (meth)acrylic acid, wherein a) the gaseous mixture is depleted of heavy-boiling components, b) the mixture depleted of heavy-boiling components is condensed in a separation column with separation-effective internals, c) a liquid mixture containing the (meth)acrylic acid is discharged from the separation column, and d) the (meth)acrylic acid contained in the liquid mixture is reacted to form (meth)acrylic acid alkyl esters in an esterification plant, characterized in that the separation column is operated such that the temperature profile in the separation column has an inverse sigmoidal shape, and the liquid mixture discharged in step c) is removed without further purification of the contained (meth)acrylic acid by a thermal separation process.is transferred directly to the esterification plant.

2. Method according to claim 1, characterized in that a temperature measurement is carried out in the area of ​​the separation column with the greatest temperature change and the reflux quantity is controlled depending on the temperature measured there.

3. Method according to claim 1 or 2, characterized in that the liquid mixture extracted in step c) contains 2500 to 4500 ppm diacrylic acid.

4. Method according to one of claims 1 to 3, characterized in that the liquid mixture extracted in step c) contains 1 to 3 wt.% water, based on the total amount of liquid mixture.

5. Method according to one of claims 1 to 4, characterized in that the liquid mixture extracted in step c) contains 1 to 3 wt.% water, in each case based on the total amount of liquid mixture.

6. Method according to any one of claims 1 to 5, characterized in that the mass ratio of acetic acid to water in the liquid mixture extracted in step c) is from 0.05 to 0.

5.

7. Method according to one of claims 1 to 6, characterized in that the separation column is operated with a ratio of water in reflux in kg / h to the product of product gas mixture in t / h and product gas mixture temperature in °C between 0.453 and 0.

490.

8. Method according to one of claims 1 to 7, characterized in that the separation column is operated with a reflux temperature of 50 to 85 °C.

9. A method according to any one of claims 1 to 8, characterized in that the (meth)acrylic acid is reacted with an alkanol in step c) in an acid-catalyzed reaction.

10. Method according to any one of claims 1 to 9, characterized in that the (meth)acrylic acid realkyl ester is n-butyl acrylate, wherein the (meth)acrylic acid is reacted with n-butanol in step c).

11. Method according to one of claims 1 to 10, characterized in that the reaction of (meth)acrylic acid in step c) is carried out at a temperature in the range of 70 to 160 °C and an absolute pressure in the range of 300 to 1500 mbar.

12. Method according to any one of claims 1 to 11, characterized in that the liquid mixture extracted in step c) has a temperature of 85 to 120 °C.

13. (Meth)acrylic acid alkyl esters obtained by a process according to any one of claims 1 to 12.

14. (Meth)acrylic acid alkyl ester according to claim 13, wherein the (meth)acrylic acid alkyl ester is n-butylacrylate obtained by acid-catalyzed reaction of (meth)acrylic acid with n-butanol.

15. Plant for the production of (meth)acrylic acid alkyl esters starting from (meth)acrylic acid, comprising - a separation column, - an esterification plant, and - a first line directly connecting the separation column and the esterification plant, characterized in that the first line is connected to a withdrawal point for a liquid mixture of the separation column.

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