Process for continuously preparing tert-butyl (METH)acrylate

Abstract

A process for continuously preparing tert-butyl (meth)acrylate by conversion of (meth)acrylic acid in the liquid phase in a reactor with gaseous isobutene, which is passed through the liquid phase, in the presence of an acidic catalyst, at a temperature in the range from 30 to 90°C and an absolute pressure in the range from 0.1 to 20 bar, where the two reactants are used in a molar isobutene:(meth)acrylic acid ratio in the range from 5 to 60, the gas stream comprising unconverted reactants and tert-butyl (meth)acrylate that leaves the reactor is partly condensed to obtain tert-butyl (meth)acrylate and unconverted (meth)acrylic acid as a liquid mixture which is separated by subsequent distillation, and wherein the tert-butyl (meth)acrylate is recovered, and the uncondensed isobutene is returned to the reactor.

Description

[0001] Process for the continuous production of tert-butyl (meth)acrylate

[0002] Description

[0003] The invention relates to a process for the continuous production of tert-butyl (meth)acrylate by reacting (meth)acrylic acid in the liquid phase in a reactor with gaseous isobutene, which is passed through the liquid phase, in the presence of an acid catalyst, at a temperature in the range of 30 to 90 °C and an absolute pressure in the range of 0.1 to 20 bar.

[0004] Tert-butyl (meth)acrylate means tert-butyl acrylate (= acrylic acid tert-butyl ester), produced by reacting acrylic acid with isobutene, or tert-butyl methacrylate (= methacrylic acid tert-butyl ester), produced by reacting methacrylic acid (= alpha-methylacrylic acid) with isobutene.

[0005] The tert-butyl esters of acrylic acid and methacrylic acid [abbreviated to (meth)acrylic acid] have a wide range of applications. Tert-butyl (meth)acrylate, for example, is an important starting material for the production of polymers used, among other things, as components of paints, adhesives, and coating resins.

[0006] It is known that tert-butyl (meth)acrylate, abbreviated to TB(M)A, can be produced by an addition reaction of acrylic acid (AS) or methacrylic acid with isobutene (IB) under the influence of an acid (e.g., sulfuric acid) as a catalyst. This process is described in WO 2016 / 156410 A1 (BASF SE) and WO 2002 / 10110 A2 (BASF AG) and WO 2002 / 10109 A1 (BASF AG), among others.

[0007] The TBA process is described in more detail below; the same applies to the TBMA process. The reaction is an equilibrium reaction. The reaction is carried out continuously in a vertical reactor divided into sections and cooled between them, with chemical equilibrium likely being largely achieved at the top outlet. In such a TBA process, the reaction mixture emerging from the top contains acrylic acid, TBA, dissolved IB, and the catalyst (e.g., sulfuric acid). This reaction mixture is then evaporated under vacuum (e.g., approx. 60 mbar), with preferential removal of IB as well as TBA and AS. The TBA and AS obtained in this gas phase are condensed and subjected to distillation. The uncondensed IB is returned to the reactor via vacuum machines.The problem is that polymers of IB and / or TBA can form and deposit, which can impair the operation of the vacuum machines. The liquid high-boiling component remaining after evaporation is also recycled to the reactor.

[0008] An unfavorable effect of this process is that the liquid effluent from the reactor to be evaporated is heated and a feedstock (IB) is withdrawn from the equilibrium mixture, with simultaneous concentration of the catalyst, which leads to rapid, partial decomposition of TBA to form IB. The amount of cycle gas, primarily containing IB, to be returned to the reactor is very large given the low pressure, and the vacuum unit is complex. Scaling up this plant concept significantly beyond a certain size (e.g., over 5 kt / a) is difficult to impossible, or at least extremely costly, particularly from a process engineering perspective. The above statements apply analogously to a corresponding TBMA process.

[0009] The object of the present invention was to provide an improved process for the production of TB(M)A in high yield and purity, which eliminates the above-mentioned disadvantages and can thus be scaled up more easily.

[0010] Accordingly, a process for the continuous production of tert-butyl (meth)acrylate by reacting (meth)acrylic acid in the liquid phase in a reactor with gaseous isobutene, which is passed through the liquid phase, in the presence of an acid catalyst, at a temperature in the range of 30 to 90 °C and an absolute pressure in the range of 0.1 to 20 bar, which is characterized in that the two reactants are used in a molar ratio of isobutene to (meth)acrylic acid in the range of 5 to 60, the gas stream leaving the reactor, containing unreacted reactants and tert-butyl (meth)acrylate, is partially condensed, whereby tert-butyl (meth)acrylate and unreacted (meth)acrylic acid are obtained as a liquid mixture, which is separated by subsequent distillation and whereby the tert-butyl (meth)acrylate is recovered, and the uncondensed isobutene is returned to the reactor.

[0011] When acrylic acid is used as the reactant, the process produces the product tert-butyl acrylate (TBA) and when methacrylic acid is used as the reactant, the product tert-butyl methacrylate (TBMA) is produced.

[0012] In the process according to the invention, the addition of acrylic acid (or methacrylic acid) to isobutene is also carried out in a reactor, but with a significantly larger amount [relative to the (meth)acrylic acid used] of gaseous isobutene passed through, which thus acts both as a reactant (educt) and as a stripping gas. The reactor discharge is thus carried out via a gas stream containing isobutene, TB(M)A, and acrylic acid or methacrylic acid, but not the catalyst (e.g., particularly sulfuric acid). A re-cleavage of the TBA or TBMA in the reactor discharge is thus prevented. The stripping gas is then subjected to partial condensation, whereby TB(M)A and acrylic acid or methacrylic acid are obtained in liquid form and are fed for further separation, e.g. analogous to the processes described in WO 2016 / 156410 A1 (BASF SE), WO 2002 / 10110 A2 (BASF AG) or WO 2002 / 10109 A1 (BASF AG).The uncondensed isobutene is recycled, preferably predominantly, particularly completely, e.g., to a level of 75 to 99 wt.%, to the reactor; it can also be referred to as cycle gas and / or stripping gas. Since this process is not a vacuum process like the prior art, the volume flow is significantly lower and the pressure conditions are much less problematic than in the processes for TB(M)A production cited at the beginning and above, which results in significant scale-up opportunities, particularly through simplified upscaling.

[0013] The process according to the invention is carried out in a reactor, which is in particular a cylindrical reactor. More preferably, a reactor is used which is a stirred tank, a bubble column reactor, or a loop reactor.

[0014] The isobutene is fed into the reactor in gaseous form. The isobutene can also be used, for example, in the form of a hydrocarbon gas mixture containing isobutene. In particular, the gas mixture can be a C4 gas mixture containing isobutene, isobutane, butane, 1-butene, and 2-butene.

[0015] The two reactants are used in the reactor in a molar ratio of isobutene to (meth)acrylic acid in the range from 5 to 60, preferably in the range from 8 to 50, more preferably in the range from 10 to 45. A characteristic of the process according to the invention is, among other things, a large molar excess of isobutene used.

[0016] The reaction of the reactants preferably takes place in the absence of a solvent.

[0017] Acidic catalysts used are those that are at least partially soluble in the reaction mixture. Preferred catalysts are strong inorganic or organic acids, such as mineral acids, particularly sulfur- or phosphorus-containing mineral acids, for example sulfuric acid, phosphoric acid, and polyphosphoric acid, preferably sulfuric acid or alkyl- and arylsulfonic acids, such as p-toluenesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, and methanesulfonic acid. Very particular preference is given to sulfuric acid, which is catalytically active under the reaction conditions even in the form of the resulting mono-tert-butyl sulfuric acid. The amount of catalyst is preferably 0.1 to 10 wt. %, preferably 0.5 to 3 wt. %, based in each case on the weight of both reactants [(meth)acrylic acid and isobutene].

[0018] The reaction is preferably carried out in the presence of an inhibitor that inhibits the polymerization of the (meth)acrylic acid and the tert-butyl ester. Particularly suitable inhibitors are hydroquinone, hydroquinone monomethyl ether, p-benzoquinone, p-nitrosophenol, phenothiazine, 4-hydroxy-2,2,6,6-tetramethyl-1-oxypiperidine, and methylene blue. The inhibitors are preferably used in amounts ranging from 200 to 2000 ppm, based on the weight of both reactants [(meth)acrylic acid and isobutene].

[0019] The reactor can advantageously be equipped with internals to improve the mixing of the reaction mixture. Suitable internals are known to those skilled in the art; for example, they can be static mixing elements such as grids, distributor plates, or sieve trays.

[0020] The reactant (meth)acrylic acid is very preferably fed into the reactor in liquid form. The feed can be made directly, e.g., via a dip tube, but it is preferable to provide means that enable uniform distribution and mixing of the reactants. Such means are known to those skilled in the art; for example, they include distributor plates, perforated plates and tubes, nozzles, etc. The gaseous isobutene is preferably fed in via an annular tube with multiple outlet openings. The (meth)acrylic acid is preferably fed in via a nozzle that mixes a gas and a liquid and mixes the reactor contents. It is preferably arranged in the bottom or at the top of the reactor. Suitable nozzles are known to those skilled in the art (jet nozzle, mixing nozzle, two-fluid nozzle, etc.) and are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Vol. B4, 5th Ed., 1992, page 280 ff.

[0021] It has proven advantageous to feed the fresh (meth)acrylic acid into the reactor in a mixture with the predominant, particularly complete, residue from the purifying distillation of the tert-butyl ester. Furthermore, it has proven advantageous to feed the recirculated isobutene resulting from the distillation of the tert-butyl ester predominantly, particularly completely, back into the reactor. When introducing the gaseous isobutene, it is particularly advantageous to feed the isobutene through the aforementioned nozzle together with the (meth)acrylic acid. The nozzle causes automatic suction of the recycled gaseous isobutene. The gas stream leaving the reactor, containing unreacted reactants and tert-butyl (meth)acrylate, is partially condensed, yielding tert-butyl (meth)acrylate and unreacted (meth)acrylic acid as a liquid mixture.

[0022] The uncondensed isobutene is preferably returned predominantly, particularly completely, to the reactor in gaseous form, preferably via the nozzle mentioned.

[0023] The catalyst is preferably fed as a mixture with the (meth)acrylic acid, whereby fresh catalyst or recovered catalyst or a mixture thereof can be used.

[0024] Since the addition of (meth)acrylic acid to isobutene is highly exothermic, it is advisable to temperature-control the reactor to adjust the reaction temperature. Temperature control of the reactor is preferably achieved by one or more internal heat exchangers, one or more external heat exchangers, or by means of one or more external liquid circuits.

[0025] The reaction is carried out at a temperature in the range of 30 to 90 °C and an absolute pressure in the range of 0.1 to 20 bar, preferably at a temperature in the range of 35 to 85 °C and an absolute pressure in the range of 0.2 to 15 bar, more preferably at a temperature in the range of 40 to 80 °C and an absolute pressure in the range of 0.5 to 13 bar.

[0026] The liquid mixture resulting from the partial condensation of the gas stream leaving the reactor contains a high proportion, e.g., > 30 wt.% (based on the mixture), of the desired tert-butyl ester. It also contains unreacted (meth)acrylic acid, inhibitor, and other minor by-products. The mixture contains only very small amounts of isobutene oligomerization product, particularly < 2 wt.% (based on the mixture).

[0027] Figure 1 shows schematically a preferred embodiment of the method according to the invention in an overall overview.

[0028] It shows the interconnection of the units 'Reactor A', 'Condensation B', 'Condensation C', 'Low-boiling distillation D', 'Pure distillation E' and 'Residue distillation F'.

[0029] For comparison, Figure 2 shows a schematic embodiment of the TB(M)A process according to the state of the art.

[0030] It shows the interconnection of the units "Reactor A", "Condensation B", "Condensation C", "Low-boiler distillation D", "Pure distillation E", and "Residue distillation F". Preferred embodiments of the process according to the invention follow, with particular, exemplary reference to the designations (in parentheses) in Figure 1.

[0031] Condensation (B; C):

[0032] The vapors (4) can be condensed in a conventional manner, for example in condensers (B, C) of conventional design. Preferably, two series-connected condensers are used, in particular plate or tube-bundle condensers, with the second condenser (C) operating at a lower cooling temperature. Generally, the temperature difference is approximately 30 to 50 °C, with the cooling temperature of the first condenser (B) being in the range of approximately 10 to 35 °C. This enables rapid distillation and condensation and suppresses the formation of polymers.

[0033] The uncondensed vapors (5) are preferably predominantly fed, preferably to 80 to 99.9 wt. %, to reactor (A) (7), and the remainder of the uncondensed vapors (6) is discharged. The uncondensed vapors (5) preferably contain > 75 wt.% isobutene, < 23 wt.% inert compounds, and < 2 wt.% residue.

[0034] In order to further reduce polymer formation, an inhibitor which is soluble in the target ester [= TB(M)A] is preferably introduced into the condenser, here into the second condenser (C). The inhibitor used is preferably a mixture of phenothiazine (PTZ) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (4-HT), which is expediently introduced, for example, as a solution in the target ester, for example in an amount of 0.02 to 0.15 kg of 4-HT and 0.5 to 1.5 kg of PTZ in 100 l of target ester, preferably in the top region of the condenser, here in the top region of a vertically arranged second condenser (C). The inhibitor solution is preferably applied in such an amount that the inhibitor concentration in the combined condensates (8) is approximately in the range from 100 ppm to 500 ppm. The inhibitor is introduced in the usual way, preferably by spraying the inhibitor solution.In addition, in order to reduce polymer formation, it has proven advantageous to introduce and in particular to inject at least five times the weight of distillate, based on the weight of vapor, into the condenser, here into the first condenser (B), preferably in the head region of a vertically arranged condenser (B).

[0035] Low-boiling distillation (D)

[0036] To obtain the target ester from the combined condensates of condensation (B) and (C), the condensate (8) is separated into an overhead product (10) and a bottom product (11) in a distillation unit (D), e.g., a conventional distillation unit consisting of an evaporator, column, and condenser. The distillation temperature (bottom temperature) is generally in the range of 40 to 90 °C. The pressure is selected accordingly depending on the product, i.e., TBA or TBMA: preferably, the pressure is the same for both target esters.

[0037] The top product (10) contains the low-boiling components, such as tertiary butyl acetate, tertiary butanol, and diisobutene. It may also contain up to 40 wt.%, based on the top product, of the target ester. The bottom product essentially comprises the target ester and (meth)acrylic acid.

[0038] Conventional columns with random packing or directional packing, or with bubble-cap, valve, or sieve trays, are suitable. However, a tray column with 30 to 50 dual-flow trays is preferred. The feed to the distillation column is generally in the middle section.

[0039] The condensation of the low-boiling components takes place in the usual way. Condensation preferably takes place in two condensers connected in series, for example, tube-bundle condensers. The cooling temperature of the second condenser is preferably about 30 to 50 °C lower, while the first condenser is operated at a cooling temperature of preferably about 10 to 35 °C. The condensates are combined and partially used as column reflux. The remainder of the condensate (10) is discharged. The uncondensed vapors (9) are preferably predominantly, particularly completely, returned to the reactor (A).

[0040] The uncondensed vapors (9) preferably contain > 85 wt.% isobutene, < 2 wt.% inert compounds and < 13 wt.% residue.

[0041] To prevent polymer formation in the first condenser and in the column, a solution of an inhibitor in the target ester is preferably applied to the first condenser. The inhibitor used is preferably a mixture of PTZ and 4-HT, which is expediently introduced as a solution in the target ester, e.g., in an amount of 0.02 to 0.15 kg of 4-HT and 0.5 to 1.5 kg of PTZ in 100 l of the target ester, preferably in the top region of a vertically arranged second condenser. The inhibitor solution is applied in such an amount that the inhibitor concentration in the combined condensates is approximately in the range of 100 ppm to 500 ppm.

[0042] Pure distillation (E)

[0043] The target ester is obtained from the bottom product (11) of the low-boiling distillation (D) in a distillation unit, preferably of conventional design (evaporator, column, and condenser), in a purity of preferably at least 99.5% by weight. The resulting bottom product (13) generally contains at least 70% by weight of (meth)acrylic acid and is preferably predominantly, particularly completely, recycled to the reactor (A). The distillation temperature is generally in the range from 50 to 100°C. The pressure is selected according to the target ester to be distilled. Purification is preferably carried out using a conventional tray column, for example a column with 30 to 50 dual-flow trays, and feed in the middle column region. The pure target ester is separated off at the top. The condensation of the target ester is preferably carried out in two condensers arranged in series, in particular in tube-bundle condensers.The temperature of the coolant in the second condenser is preferably about 30 to 50°C lower than that of the first condenser, where the coolant preferably has a temperature in the range of about 10 to 35°C. The combined condensates are used partly as column reflux and partly to stabilize the column top and the condenser, here the first condenser, i.e. to prevent polymerization in the column top and in the condenser, here the first condenser. The other part of the target ester is obtained as a product of value (12). To prevent polymerization in the condenser, here particularly in the second condenser, a solution of an inhibitor is introduced into the target ester. Preference is given to using a solution of, for example, 0.5 to 2% by weight of hydroquinone monoethyl ether (MEHQ), the amount of inhibitor introduced preferably being chosen such that the inhibitor content of the combined condensates is 10 to 20 ppm.To prevent polymerization in the first condenser, a portion (preferably about 5 to 10 times the weight of the discharged target ester, based on the weight of vapor) of the combined, stabilized condensates is introduced into the vapor pipe. The condensates are preferably introduced by injecting them into the vapor pipe above the column in the opposite direction to the gas flow and / or in the region of the condenser inlet in the same direction as the gas flow. Polymerization in the column is suppressed, on the one hand, by the reflux of the condensate, which contains, for example, 10 to 20 ppm of inhibitor. On the other hand, a solution of another inhibitor in the target ester is preferably applied to a tray in the upper column section. A solution of PTZ and 4-HT in the target ester is preferably used, e.g.0.5 to 1.5 kg of PTZ and 0.05 to 0.15 kg of 4-HT in 100 l of target ester, the amount preferably being such that the inhibitor content in the rectifier section is 50 ppm to 500 ppm. Furthermore, a solution of MEHQ in the target ester, e.g., 15 to 30 g of MEHQ in 100 l of target ester, is preferably introduced into the column hood or into the vapor tube above the column and / or into the upper condenser hood.

[0044] This is conveniently and advantageously achieved by injection through a nozzle installed centrally in the upper column head, in the vapor tube, or in the upper condenser head. If desired, oxygen-containing gas, such as air, can be injected into the distillation unit for further stabilization. These measures make it possible to prevent polymer formation in the condensers, the vapor tubes, and the column. The resulting target ester (12) is of high purity and generally has the following composition: tertiary-butyl (meth)acrylate 99.5 to 99.9 wt.% tertiary-butyl acetate 0.001 to 0.01 wt.% tertiary-butyl propionate 0.02 to 0.03 wt.% tertiary-butanol 0.001 to 0.01 wt.% (Meth)acrylic acid 0.005 to 0.02 wt.% Inhibitor (MEHQ) 0.001 to 0.002 wt.% Rest 0.072 to 0.428 wt.%

[0045] Residue distillation (F)

[0046] Preferably, the liquid reaction mixture (14) from the reactor (A) is separated as a discharged partial stream in a distillation (F). The distillation, preferably continuous, can be carried out at the same pressure as the reactor pressure. The temperature depends on the particular desired product (i.e., TBA or TBMA); it is generally selected such that the target ester is cleaved back and only a small proportion of the target ester, e.g., less than 5% by weight of the target ester (based on the bottoms amount), remains in the bottoms. The resulting gaseous isobutene is preferably predominantly, particularly completely, recycled to the reactor (15). The resulting bottoms (16) essentially comprise the acidic catalyst, the residual (i.e., unreacted) (meth)acrylic acid, and high-boiling constituents [i.e., by-products with a boiling point higher than TB(M)A at the same pressure], in particular polymeric (meth)acrylic compounds.

[0047] The bottoms of the residue distillation (16), e.g. 10 to 90 wt.% of the bottoms (16), in particular the predominant part of the bottoms (16), e.g. 75 to 90 wt.% of the bottoms (16), is fed to the reactor (A) (18), the rest of the bottoms is discharged (17).

[0048] The distillation can be carried out in conventional devices. However, devices that allow rapid distillation are preferably used, for example, film evaporators, thin-film evaporators, or spiral-tube evaporators. Suitable film evaporators are known to the person skilled in the art; see, for example, Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. B3, 2-21 to 2-24 and 3-1 to 3-25, 1988.

[0049] The vapors can be condensed in the usual way, for example in condensers of conventional design. Preferably, two condensers connected in series are used, in particular plate or tube bundle condensers, with the second condenser preferably being operated at a lower cooling temperature. In general, the temperature difference is about 30 to 50 °C, with the cooling temperature of the first condenser preferably being in the range of about 10 to 35 °C. In this way, rapid distillation and condensation are enabled and polymer formation is suppressed. To reduce polymer formation even further, an inhibitor dissolved in the target ester is introduced into the condenser, in this case the second condenser. The inhibitor used is preferably a mixture of PTZ and 4-HT, which is expediently provided as a solution, e.g.in an amount of 0.02 to 0.15 kg of 4-HT and 0.5 to 1.5 kg of PTZ in 100 l of target ester, preferably in the top region of the condenser, here in the top region of a vertically arranged second condenser. The inhibitor solution is applied in such an amount that the inhibitor concentration in the combined condensates is approximately in the range of 100 ppm to 500 ppm.

[0050] The inhibitor is introduced in the usual way; preferably, the inhibitor solution is sprayed in. Furthermore, to reduce polymer formation, it has proven advantageous to introduce, and in particular to spray, at least five times the weight of distillate (crude ester), based on the weight of vapor, into the condenser, here into the first condenser, preferably in the top region of a vertically arranged condenser.

[0051] In a particularly preferred embodiment, condensation can be omitted, and the resulting vapors are fed directly back into the reactor (A) (15). The pressure in the residue distillation (F) is then equal to the pressure in the reactor.

[0052] All pressure specifications refer to absolute pressure.

[0053] All ppm values ​​refer to weight (wt. ppm).

[0054] Examples and comparison example

[0055] The following process examples are modeled using thermodynamic simulations. The software used for this purpose is Aspen Plus® (Aspen), which can be found at https: / / www.aspentech.com. Aspen is a comprehensive simulation software used for modeling, simulating, and optimizing chemical processes and plants in industry. Aspen has extensive model databases for modeling basic operations as well as material databases for the material properties of many different substances. Aspen calculates the properties of mixtures using various thermodynamic models from the material data of the pure substances.

[0056] Comparison example

[0057] A thermodynamic simulation of the entire plant according to Fig. 2 is carried out by Aspen and provides the following results: Isobutene with a mass flow of 479 kg / h is fed to a reactor A through a line 1, the catalyst sulfuric acid through a line 2 with a mass flow of 2 kg / h and acrylic acid through a line 3 with a mass flow of 605 kg / h.

[0058] A vaporous recycle stream from the condensation stage C is fed to reactor A via line 7 with a mass flow of 343 kg / h, a vaporous recycle stream from the low-boiling distillation D is fed via line 9 with a mass flow of 21 kg / h, a liquid recycle stream from the pure distillation E is fed via line 13 with a mass flow of 320 kg / h and a liquid recycle stream from the residue distillation F is fed via line 18 with a mass flow of 2256 kg / h.

[0059] The reaction in reactor A is carried out at a temperature of 16-32 °C, an absolute pressure of 1200 mbar and a residence time of 4 hours.

[0060] From a reactor A, low-boiling components and non-condensable components are discharged from the process as a vapor phase through a line 6 with a mass flow of 9 kg / h.

[0061] The vapor phase has the following composition:

[0062] Isobutene: 50.10 wt.%

[0063] Acrylic acid: < 0.01 wt.%

[0064] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 0.10 wt.%

[0065] Diisobutene: 0.04 wt.%

[0066] Triisobutene: < 0.01 wt.%

[0067] Unknown: 0.01 wt%

[0068] Sulfuric acid: < 0.01 wt.%

[0069] Inert 49.71 wt.%

[0070] From a reactor A, a liquid phase is passed through a line 19 with a mass flow of 4016 kg / h to the residue distillation F.

[0071] The liquid phase has the following composition:

[0072] Isobutene: 6.70 wt%

[0073] Acrylic acid: 26.70 wt%

[0074] Diacrylic acid: 2.00 wt.% tert.-Butyl acrylate: 48.09 wt.%

[0075] Diisobutene: 0.88 wt.%

[0076] Triisobutene: 4.53 wt%

[0077] Sulfuric acid: 2.03 wt% Unknown: 9.06 wt%

[0078] Inert < 0.01 wt.%

[0079] From a condensation B and C, a liquid phase is passed through a line 8 with a mass flow of 1378 kg / h to the low-boiling distillation D.

[0080] The liquid phase has the following composition:

[0081] Isobutene: 1.14 wt.%

[0082] Acrylic acid: 19.74 wt%

[0083] Diacrylic acid: 0.02 wt.% tert.-Butyl acrylate: 71.19 wt.%

[0084] Diisobutene: 1.74 wt.%

[0085] Triisobutene: 5.10 wt.%

[0086] Sulfuric acid: < 0.01 wt.%

[0087] Unknown: 1.05 wt%

[0088] Inert < 0.01 wt.%

[0089] From a condensation C, a vapor phase is passed through a line 7 with a mass flow of 343 kg / h to reactor A.

[0090] The vapor phase has the following composition:

[0091] Isobutene: 95.62 wt.%

[0092] Acrylic acid: 0.07 wt%

[0093] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 2.73 wt.%

[0094] Diisobutene: 1.16 wt.%

[0095] Triisobutene: 0.05 wt.%

[0096] Sulfuric acid: < 0.01 wt.%

[0097] Unknown: 0.20 wt%

[0098] Inert 0.15 wt.%

[0099] From a low-boiling distillation D, a liquid phase from the column bottom is passed through a line 11 with a mass flow of 1351 kg / h to the pure distillation E.

[0100] The liquid phase has the following composition:

[0101] Isobutene: < 0.01 wt.%

[0102] Acrylic acid: 20.11 wt%

[0103] Diacrylic acid: 0.02 wt.% tert.-Butyl acrylate: 73.12 wt.%

[0104] Diisobutene: 0.71 wt% Triisobutene: 5.20 wt%

[0105] Sulfuric acid: < 0.01 wt.%

[0106] Unknown: 0.81 wt%

[0107] Inert < 0.01 wt.%

[0108] From a low-boiling distillation D, the low-boiling components are discharged from the process as a liquid phase through a line 10 with a mass flow of 19 kg / h after the condenser.

[0109] The liquid phase has the following composition:

[0110] Isobutene: 3.68 wt%

[0111] Acrylic acid: < 0.01 wt.%

[0112] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 5.01 wt.%

[0113] Diisobutene: 70.48 wt.%

[0114] Triisobutene: < 0.01 wt.%

[0115] Sulfuric acid: < 0.01 wt.%

[0116] Unknown: 20.78 wt%

[0117] Inert < 0.01 wt.%

[0118] From a low-boiling distillation D, a vaporous phase is passed through a line 9 with a mass flow of 21 kg / h to reactor A after the condenser.

[0119] The vapor phase has the following composition:

[0120] Isobutene: 73.69 wt%

[0121] Acrylic acid: < 0.01 wt.%

[0122] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 0.07 wt.%

[0123] Diisobutene: 5.73 wt%

[0124] Triisobutene: < 0.01 wt.%

[0125] Sulfuric acid: < 0.01 wt.%

[0126] Unknown: 1.20 wt.%

[0127] Inert 19.27 wt.%

[0128] From a pure distillation E, a liquid phase is discharged from the process through a line 12 with a mass flow of 1000 kg / h, the pure product tert-butyl acrylate.

[0129] The liquid phase has the following composition:

[0130] Isobutene: 0.03 wt.%

[0131] Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% tert-butyl acrylate: 99.84 wt% Diisobutene: 0.02 wt%

[0132] Triisobutene: < 0.01 wt.%

[0133] Sulfuric acid: < 0.01 wt% Unknown: 0.06 wt%

[0134] Inert < 0.01 wt.%

[0135] From a pure distillation E, a liquid phase from the column bottom is returned to reactor A through a line 13 with a mass flow of 320 kg / h.

[0136] The liquid phase has the following composition:

[0137] Isobutene: 1.43 wt.%

[0138] Acrylic acid: 76.71 wt%

[0139] Diacrylic acid: 1.30 wt.% tert.-Butyl acrylate: 1.20 wt.%

[0140] Diisobutene: < 0.01 wt.%

[0141] Triisobutene: 17.01 wt%

[0142] Sulfuric acid: < 0.01 wt.%

[0143] Unknown: 2.32 wt%

[0144] Inert < 0.01 wt.%

[0145] From a residue distillation F, a liquid phase is returned to reactor A through a line 18 with a mass flow of 2256 kg / h and the high boilers are discharged from the process through a line 17 with a mass flow of 63 kg / h.

[0146] The liquid phase has the following composition:

[0147] Isobutene: 2.65 wt%

[0148] Acrylic acid: 41.95 wt.%

[0149] Diacrylic acid: 3.46 wt.% tert.-Butyl acrylate: 29.54 wt.%

[0150] Diisobutene: 0.29 wt.%

[0151] Triisobutene: 4.70 wt.%

[0152] Sulfuric acid: 3.52 wt.%

[0153] Unknown: 13.88 wt%

[0154] Inert < 0.01 wt.% Example 1

[0155] A thermodynamic simulation of the entire system according to Fig. 1 is carried out by Aspen and provides the following results:

[0156] Isobutene with a mass flow of 455 kg / h is fed to a reactor A through a line 1, the catalyst sulfuric acid through a line 2 with a mass flow of 7 kg / h and acrylic acid through a line 3 with a mass flow of 598 kg / h.

[0157] A vaporous recycle stream from the condensation stage C is fed via line 7 with a mass flow of 31521 kg / h, a vaporous recycle stream from the low-boiling distillation D is fed via line 9 with a mass flow of 561 kg / h, a liquid recycle stream from the pure distillation E is fed via lines 13 with a mass flow of 481 kg / h, a vaporous recycle stream from the residue distillation F is fed via lines 15 with a mass flow of 5 kg / h to reactor A and a liquid recycle stream from the residue distillation F is fed via line 18 with a mass flow of 11 kg / h to reactor A.

[0158] The reaction in reactor A is carried out at a temperature of 50 °C, an absolute pressure of 1000 mbar and a residence time of 2 hours.

[0159] From a reactor A, a vapor phase is passed through a line 4 with a mass flow of 33580 kg / h to condensation B.

[0160] The vapor phase has the following composition:

[0161] Isobutene: 82.43 wt%

[0162] Acrylic acid: 1.37 wt.%

[0163] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 3.19 wt.% Diisobutene: 0.12 wt.%

[0164] Triisobutene: < 0.01 wt.%

[0165] Sulfuric acid: < 0.01 wt% Unknown: 0.05 wt%

[0166] Inert 12.81 wt.%

[0167] From a reactor A, a liquid phase is passed through a line 14 with a mass flow of 60 kg / h to the residue distillation F.

[0168] The liquid phase has the following composition: Isobutene: 3.93 wt.%

[0169] Acrylic acid: 30.18 wt%

[0170] Diacrylic acid: 30.86 wt.% tert.-Butyl acrylate: 16.75 wt.%

[0171] Diisobutene: 0.17 wt.%

[0172] Triisobutene: 0.10 wt.%

[0173] Sulfuric acid: 15.00 wt.%

[0174] Unknown: 3.00 wt%

[0175] Inert < 0.01 wt.%

[0176] From a condensation B and C, a liquid phase is passed through a line 8 with a mass flow of 2054 kg / h to the low-boiling distillation D.

[0177] The liquid phase has the following composition:

[0178] Isobutene: 26.26 wt%

[0179] Acrylic acid: 22.11 wt%

[0180] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 49.47 wt.%

[0181] Diisobutene: 1.27 wt.%

[0182] Triisobutene: 0.03 wt.%

[0183] Sulfuric acid: < 0.01 wt.%

[0184] Unknown: 0.83 wt%

[0185] Inert < 0.01 wt.%

[0186] From a condensation C, a vaporous phase is passed through a line 7 with a mass flow of 31521 kg / h to reactor A and the low boilers are discharged from the process through a line 6 with a mass flow of 5 kg / h.

[0187] The vapor phase has the following composition:

[0188] Isobutene: 86.08 wt%

[0189] Acrylic acid: 0.02 wt.%

[0190] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 0.18 wt.%

[0191] Diisobutene: 0.04 wt.%

[0192] Triisobutene: < 0.01 wt.%

[0193] Sulfuric acid: < 0.01 wt.%

[0194] Unknown: < 0.01 wt%

[0195] Inert 13.64 wt.% From a low-boiling distillation D, a liquid phase from the column bottom is passed through a line 11 with a mass flow of 1481 kg / h to the pure distillation E.

[0196] The liquid phase has the following composition:

[0197] Isobutene: < 0.01 wt.%

[0198] Acrylic acid: 29.66 wt%

[0199] Diacrylic acid: 1.00 wt.% tert.-Butyl acrylate: 68.10 wt.%

[0200] Diisobutene: 0.02 wt.%

[0201] Triisobutene: 0.04 wt.%

[0202] Sulfuric acid: < 0.01 wt.%

[0203] Unknown: 1.15 wt.%

[0204] Inert < 0.01 wt.%

[0205] From a low-boiling distillation D, the low-boiling components are discharged from the process as a liquid phase through a line 10 with a mass flow of 12 kg / h after the condenser.

[0206] The liquid phase has the following composition:

[0207] Isobutene: 9.09 wt%

[0208] Acrylic acid: < 0.01 wt.%

[0209] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 37.02 wt.%

[0210] Diisobutene: 53.83 wt%

[0211] Triisobutene: < 0.01 wt.%

[0212] Sulfuric acid: < 0.01 wt.%

[0213] Unknown: < 0.01 wt%

[0214] Inert < 0.01 wt.%

[0215] From a low-boiling distillation D, a vaporous phase is passed through a line 9 with a mass flow of 561 kg / h to reactor A after the condenser.

[0216] The vapor phase has the following composition:

[0217] Isobutene: 95.96 wt%

[0218] Acrylic acid: < 0.01 wt.%

[0219] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 0.51 wt.%

[0220] Diisobutene: 3.47 wt%

[0221] Triisobutene: < 0.01 wt.%

[0222] Sulphuric acid: < 0.01 wt% Unknown: < 0.01 wt%

[0223] Inert 0.01 wt.%

[0224] From a pure distillation E, a liquid phase is discharged from the process through a line 12 with a mass flow of 1000 kg / h, the pure product tert-butyl acrylate.

[0225] The liquid phase has the following composition:

[0226] Isobutene: < 0.01 wt.%

[0227] Acrylic acid: < 0.01 wt.%

[0228] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: 99.90 wt.%

[0229] Diisobutene: 0.03 wt.%

[0230] Triisobutene: < 0.01 wt.%

[0231] Sulfuric acid: < 0.01 wt.%

[0232] Inert < 0.01 wt.%

[0233] From a pure distillation E, a liquid phase from the column bottom is returned to reactor A through a line 13 with a mass flow of 481 kg / h.

[0234] The liquid phase has the following composition:

[0235] Isobutene: < 0.01 wt.%

[0236] Acrylic acid: 91.23 wt.%

[0237] Diacrylic acid: 3.08 wt.% tert.-Butyl acrylate: 2.00 wt.%

[0238] Diisobutene: < 0.01 wt.%

[0239] Triisobutene: 0.12 wt.%

[0240] Sulfuric acid: < 0.01 wt.%

[0241] Unknown: 3.53 wt%

[0242] Inert < 0.01 wt.%

[0243] From a residue distillation F, a liquid phase is returned to reactor A through a line 18 with a mass flow of 11 kg / h and the high boilers are discharged from the process through a line 17 with a mass flow of 44 kg / h.

[0244] The liquid phase has the following composition:

[0245] Isobutene: 3.49 wt%

[0246] Acrylic acid: 43.00 wt.%

[0247] Diacrylic acid: 33.57 wt.% tert.-Butyl acrylate: < 0.01 wt.%

[0248] Diisobutene: 0.17 wt% Triisobutene: 0.11 wt%

[0249] Sulfuric acid: 16.37 wt%

[0250] Unknown: 3.27 wt%

[0251] Inert < 0.01 wt.%

[0252] From a residue distillation F, a vaporous phase is returned to reactor A through a line 15 with a mass flow of 5 kg / h.

[0253] The vapor phase has the following composition:

[0254] Isobutene: 95.28 wt%

[0255] Acrylic acid: 3.08 wt%

[0256] Diacrylic acid: < 0.01 wt.% tert.-Butyl acrylate: < 0.01 wt.%

[0257] Diisobutene: 0.18 wt.%

[0258] Triisobutene: < 0.01 wt.%

[0259] Sulfuric acid: < 0.01 wt.%

[0260] Unknown: 0.08 wt%

[0261] Inert 1.34 wt.%

[0262] In the example according to the invention, the specific low boiler discharge is 0.012 kg of low boilers per kg of tert-butyl acrylate and the specific high boiler discharge is 0.044 kg per kg of tert-butyl acrylate.

[0263] In the comparative example, the specific low-boiling component discharge is 0.019 kg of low-boiling components per kg of tert-butyl acrylate and the specific high-boiling component discharge is 0.063 kg per kg of tert-butyl acrylate.

[0264] In the example according to the invention, the low boiler discharge is 37% lower and the high boiler discharge is 30% lower than in the comparative example.

[0265] Due to the lower specific discharges of low boilers and high boilers, the process according to the invention is significantly more economical than the conventional process.

[0266] The concentration of the polymerizable component tert-butyl acrylate in the recycle gas (line 5) is 3.72 wt.% in the comparative example and only 0.18 wt.% in the inventive example. This significantly reduces the risk of polymerization in the recycle gas blower, which is warm at operating temperature.

Claims

Patent claims 1. A process for the continuous production of tert-butyl (meth)acrylate by reacting (meth)acrylic acid in the liquid phase in a reactor with gaseous isobutene, which is passed through the liquid phase, in the presence of an acid catalyst, at a temperature in the range of 30 to 90 °C and an absolute pressure in the range of 0.1 to 20 bar, characterized in that the two reactants are used in a molar ratio of isobutene to (meth)acrylic acid in the range of 5 to 60, the gas stream leaving the reactor, containing unreacted reactants and tert-butyl (meth)acrylate, is partially condensed, whereby tert-butyl (meth)acrylate and unreacted (meth)acrylic acid are obtained as a liquid mixture, which is separated by subsequent distillation and whereby the tert-butyl (meth)acrylate is recovered, and the uncondensed isobutene is recycled to the reactor becomes.

2. Process according to the preceding claim, characterized in that the reactor is a stirred tank, a bubble column reactor or a loop reactor.

3. Process according to one of the preceding claims, characterized in that the reactants are used in a molar ratio of isobutene : (meth)acrylic acid in the range from 8 to 50.

4. Process according to one of the preceding claims 1 to 2, characterized in that the reactants are used in a molar ratio of isobutene : (meth)acrylic acid in the range from 10 to 45.

5. Process according to one of the preceding claims, characterized in that the reaction is carried out at a temperature in the range from 35 to 85 °C and an absolute pressure in the range from 0.2 to 15 bar.

6. Process according to one of the preceding claims 1 to 4, characterized in that the reaction is carried out at a temperature in the range from 40 to 80 °C and an absolute pressure in the range from 0.5 to 13 bar.

7. Process according to one of the preceding claims, characterized in that the (meth)acrylic acid obtained after the partial condensation of the gas stream from the liquid Mixture obtained by distillative separation is returned to the reactor. Process according to one of the preceding claims, characterized in that the temperature of the reactor is controlled by one or more internal heat exchangers or by one or more external heat exchangers or by means of one or more external liquid circuits. Process according to one of the preceding claims, characterized in that the catalyst is a sulfur- or phosphorus-containing mineral acid, alkylsulfonic acid or arylsulfonic acid. Process according to the preceding claim, characterized in that the catalyst is sulfuric acid. Process according to one of the preceding claims, characterized in that the isobutene is used in the form of a hydrocarbon gas mixture comprising isobutene.Process according to the preceding claim, characterized in that the gas mixture is a C4 gas mixture containing isobutene, isobutane, butane, 1-butene, and 2-butene. Process according to one of the preceding claims, characterized in that high-boiling by-products are discharged from the liquid reaction mixture in the reactor via the bottom of a distillation of a discharged partial stream of the liquid reaction mixture.

Images