TW202438478A - Process for continuous production of tert-butyl (meth)acrylate - Google Patents

Abstract

Process for continuous production of tert-butyl (meth)acrylate by reaction 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 DEG C to 90 DEG C and an absolute pressure in the range from 0.1 to 20 bar, wherein the two reactants are employed in a molar ratio of isobutene: (meth)acrylic acid in the range from 5 to 60, the gas stream comprising unconverted reactants and tert-butyl (meth)acrylate exiting the reactor is partially 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 obtained and the uncondensed isobutene is recycled into the reactor.

Description

Continuous production method of tert-butyl (meth)acrylate

The present invention relates to a method for continuously producing tert-butyl (meth)acrylate by reacting liquid (meth)acrylic acid with gaseous isobutylene conveyed through the liquid phase in a reactor in the presence of an acidic catalyst at a temperature range of 30°C to 90°C and at an absolute pressure range of 0.1 to 20 bar.

It is to be understood that tert-butyl (meth)acrylate means tert-butyl acrylate (= tert-butyl ester), which is prepared by reaction of acrylic acid with isobutylene, or tert-butyl methacrylate (= tert-butyl ester), which is prepared by reaction of methacrylic acid (= alpha-methacrylic acid) with isobutylene.

The application range of tert-butyl acrylic acid and methacrylic acid [abbreviated as (meth)acrylic acid] is wide. Tert-butyl (meth)acrylate includes, for example, an important raw material for the preparation of polymers, which are used in particular as a component of coatings, adhesives and paint resins.

It is known that tert-butyl (meth)acrylate (TB(M)A for short) can be formed by addition reaction of acrylic acid (AA) or methacrylic acid to isobutylene (IB) under the influence of an acid (e.g. sulfuric acid) as a catalyst. This process is described in particular in WO 2016/156410 A1 (BASF SE) and WO 2002/10110 A2 (BASF AG) and WO 2002/10109 A1 (BASF AG).

The TBA process is described more specifically below with a similar description for the TBMA process. This reaction is an equilibrium reaction. The reaction is carried out continuously in a vertical reactor divided into multiple parts and intermediately cooled, wherein a substantial chemical equilibrium may be obtained at the upper outlet. In such a TBA process, the reaction mixture discharged at the top therefore comprises acrylic acid, TBA, dissolved IB and a catalyst (e.g. sulfuric acid). This reaction mixture is then concentrated under vacuum (e.g. about 60 mbar), thereby preferably achieving evaporation removal of IB, TBA and AA. The TBA and AA obtained in this gas phase are condensed and supplied to post-distillation treatment. Uncondensed IB is circulated to the reactor via a vacuum machine. The problem is that this may be accompanied by the formation and deposition of IB and/or TBA polymers, thereby impairing the operation of the vacuum machine. In particular, part of the liquid high-boiling solvent remaining from the evaporation concentration is also recycled to the reactor.

A disadvantage of this process mode is that the liquid output of the evaporation concentration reactor is heated and the input material (IB) is withdrawn from the equilibrium mixture while the catalyst is concentrated, which leads to a rapid, partial reverse cracking of TBA to form IB. Due to the low pressure, the amount of recycle gas, which comprises predominantly IB, to be recycled to the reactor is very large and the vacuum unit is complex. Scaling up this plant concept far beyond a certain scale (e.g. more than 5 kt/a) is difficult or even impossible, or at least extremely costly, especially from a process engineering point of view. The above applies analogously to the corresponding TBMA process.

The object of the present invention is to provide an improved process for producing TB(M)A with high yield and high purity, which overcomes the above-mentioned disadvantages and is thus more easily scalable.

The inventors have therefore discovered a process for the continuous production of tert-butyl (meth)acrylate by reacting liquid (meth)acrylic acid with gaseous isobutylene conveyed via the liquid phase in a reactor in the presence of an acidic catalyst at a temperature range of 30°C to 90°C and at an absolute pressure range of 0.1 to 20 bar, characterized in that the two reactants are used in a molar ratio of isobutylene:(meth)acrylic acid of 5 to 60, the gas stream leaving the reactor comprising unconverted reactants and tert-butyl (meth)acrylate is partially condensed to obtain tert-butyl (meth)acrylate and unconverted (meth)acrylic acid as a liquid mixture, which are separated by subsequent distillation, wherein tert-butyl (meth)acrylate is obtained, and the uncondensed isobutylene is recycled to the reactor.

Thus, when using acrylic acid as reactant, the process provides the product tert-butyl acrylate (TBA), and when using methacrylic acid as reactant, the process provides the product tert-butyl methacrylate (TBMA).

The process according to the invention therefore also involves carrying out the addition of acrylic acid (or methacrylic acid) to isobutene in the reactor, but using significantly larger amounts (based on the (meth)acrylic acid used) of gaseous isobutene which is conveyed and thus serves simultaneously as reactant and as stripping gas. The reactor output is therefore carried out here via a gas stream which comprises isobutene, TB(M)A and acrylic acid/methacrylic acid but no catalyst, such as, in particular, sulfuric acid. Retrocleavage of TBA or TBMA in the reactor output is thus prevented. The stripping gas is then partially condensed, TB(M)A and acrylic acid/methacrylic acid being obtained in liquid form and being sent to a further separation, for example in a manner analogous to the processes described in WO 2016/156410 A1 (BASF SE), WO 2002/10110 A2 (BASF SE) or WO 2002/10109 A1 (BASF SE). Uncondensed isobutene is preferably predominantly, in particular completely, for example in an amount of 75% to 99% by weight, recycled to the reactor; it may also be referred to as circulating gas and/or stripping gas. Since the process is not a vacuum process as described in the prior art, the volume flows are significantly smaller and the pressure conditions are much less problematic than in the process for producing TB(M)A cited above and at the beginning, thus leading to important plant expansion possibilities, in particular by simplified upgrading.

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

Isobutene is introduced into the reactor in gaseous form. Isobutene can also be used, for example, in the form of a hydrocarbon gas mixture comprising isobutene. The gas mixture can in particular be a C4 gas mixture comprising isobutene, isobutane, butane, 1-butene and 2-butene.

The molar ratio of isobutylene:(meth)acrylic acid of the two reactants used in the reactor is in the range of 5 to 60, preferably in the range of 8 to 50, more preferably in the range of 10 to 45. Therefore, the main feature of the method according to the present invention is the use of a large molar excess of isobutylene.

The reaction of the reactants is preferably carried out in the absence of a solvent.

The acidic catalyst used is at least partially soluble in the reaction mixture. Preferred catalysts are strong inorganic or organic acids, such as mineral acids, in particular sulfur- or phosphorus-containing mineral acids, for example sulfuric acid, phosphoric acid and polyphosphoric acid, preferably sulfuric acid or alkylsulfonic acids and arylsulfonic acids, such as p-toluene, benzene, dodecylbenzene and methanesulfonic acid. Very particularly preferred is sulfuric acid, which under the reaction conditions is also catalytically active in the form of the resulting mono-tert-butyl sulfate.

The amount of catalyst is preferably 0.1% to 10% by weight, preferably 0.5% to 3% by weight, based in each case on the weight of the two reactants [(meth)acrylic acid and isobutylene].

The reaction is preferably carried out in the presence of an inhibitor for inhibiting the polymerization of (meth)acrylic acid and tert-butyl ester. Particularly suitable inhibitors are hydroquinone, hydroquinone monomethyl ether, p-benzoquinone, p-nitrosophenol, phenothiazine, , 4-hydroxy-2,2,6,6-tetramethyl-1-oxy-piperidine and methylene blue. The amount of the inhibitor used is preferably in the range of 200-2000 ppm based on the weight of the two reactants [(meth)acrylic acid and isobutylene].

The reactor may advantageously be equipped with internal components to improve the mixing of the reaction mixture. Suitable internal components are known to those skilled in the art and include, for example, static mixing elements such as grids, distributor plates or sieve plates.

The reactant (meth)acrylic acid is very preferably introduced into the reactor in liquid form. The introduction can be carried out directly, for example via a dip tube, but preferably an apparatus is used which allows a uniform distribution and mixing of the reactants. Such apparatus are known to the person skilled in the art and include, for example, distribution plates, perforated plates and pipes, nozzles, etc. The gaseous isobutylene is preferably introduced via an annular pipe with a plurality of outlet openings. The (meth)acrylic acid is preferably introduced via a nozzle which achieves mixing of the gas and liquid as well as mixing of the reactor contents. It is preferably arranged at the bottom or at the top of the reactor. Suitable nozzles are known to the person skilled in the art (injection nozzles, mixing nozzles, two-fluid nozzles, etc.) and are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Volume B4, 5th Edition, 1992, pages 280 et seq.

It has proven to be advantageous to introduce a mixture of fresh (meth)acrylic acid and the residues of the last distillation of tert-butyl ester to the reactor in the main part, in particular in the entirety. It has also proven to be advantageous to reintroduce a main part, in particular in the entirety, of the retro-isobutene obtained in the distillation of tert-butyl ester into the reactor. With regard to the introduction of gaseous isobutene, it is particularly advantageous to introduce isobutene together with the (meth)acrylic acid via the above-mentioned nozzle. The nozzle automatically draws in the circulating gaseous isobutene.

The gas stream leaving the reactor comprising unreacted reactants and tert-butyl (meth)acrylate is partially condensed to obtain tert-butyl (meth)acrylate and unreacted (meth)acrylic acid as a liquid mixture.

Uncondensed isobutene is preferably circulated predominantly, in particular entirely, in gaseous form into the reactor, preferably via the aforementioned nozzle.

The catalyst is preferably introduced in a mixture with (meth)acrylic acid, whereby fresh catalyst or recycled catalyst or a mixture thereof can be used.

Since the addition of (meth)acrylic acid to isobutylene is highly exothermic, it is advantageous to temperature control the reactor to adjust the reaction temperature. The temperature control of the reactor is preferably carried out via one or more internal heat exchangers or via one or more external heat exchangers or using one or more external liquid loops.

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

The liquid mixture from the partial condensation of the gas stream leaving the reactor contains a high proportion, for example ≥30% by weight (based on the mixture), of the desired tert-butyl ester. It also contains unconverted (meth)acrylic acid, inhibitors and other minor by-products. The mixture contains only very small amounts of isobutene oligomerization products, in particular <2% by weight (based on the mixture).

The following contains a preferred configuration of the method according to the invention, with particular reference to the description of FIG. 1 (in brackets). Condensation (B; C):

The condensation of the vapor (4) can be carried out in a conventional manner, for example in condensers (B, C) of conventional design. Preferably, two condensers are used in series, in particular plate or tube bundle condensers, wherein the second condenser (C) is operated at a lower cooling temperature. The temperature difference is generally about 30° C. to 50° C., wherein the cooling temperature of the first condenser (B) is in the range of about 10° C. to 35° C. This allows rapid distillation and condensation and suppresses the formation of polymers.

Preferably, the uncondensed steam (5) is mainly supplied to the reactor (A) (7), preferably 80 wt% to 99.9 wt%, and the remaining uncondensed steam (6) is discharged. The uncondensed steam (5) preferably contains ≥ 75 wt% of isobutylene, ≤ 23 wt% of inert compounds and ≤ 2 wt% of the remainder.

In order to further reduce polymer formation, an inhibitor soluble in the target ester [=TB(M)A] is preferably introduced into the condenser, currently into the second condenser (C). The inhibitor used is preferably phenothiazine A mixture of (PTZ) and 4-hydroxy-2,2,6,6-tetramethylpiperidinyl N-oxyl (4-HT), which is advantageously introduced, for example, as a solution in the target ester, for example in an amount of 0.02 to 0.15 kg 4-HT and 0.5 to 1.5 kg PTZ in 100 liters of the target ester, preferably in the top region of the condenser, in the present case in the vertically arranged second condenser (C). The amount of inhibitor solution used is preferably such that the inhibitor concentration in the combined condensate (8) is, for example, in the range of 100 ppm to 500 ppm. The introduction of the inhibitor is carried out in the customary manner, preferably by introducing the inhibitor solution by injection. It has also proven to be advantageous for reducing polymer formation if at least five parts by weight of the distillate, based on the parts by weight of the vapor, are introduced and injected, in particular, into the condenser, currently into the first condenser (B), preferably into the top region of the vertically arranged condenser (B) into the low-boiling solvent distillation (D).

In order to obtain the target ester from the combined condensate of condensation (B) and (C), the condensate (8) is separated into a top product (10) and a bottom product (11) in a distillation unit (D), for example, a conventional distillation apparatus comprising an evaporator, a column and a condenser. The distillation temperature (bottom temperature) is usually in the range of 40°C to 90°C. The pressure is appropriately selected according to the product, i.e., TBA or TBMA, and preferably the same pressure for the two target esters.

The top product (10) comprises low-boiling solvent components such as tert-butyl acetate, tert-butyl alcohol and diisobutylene. It may also comprise up to 40% by weight of the target ester, based on the top product. The bottom product substantially comprises the target ester and (meth)acrylic acid. The desired tower includes conventional towers comprising random packings or structured packings or having bubble caps, valves or sieve trays. However, a plate tower having 30 to 50 dual-flow trays is preferably used. The feeding of the distillation tower is usually carried out in the central region.

The condensation of the low-boiling solvent components is carried out in a conventional manner. The condensation is preferably carried out in two condensers connected in series, for example tube bundle condensers. The cooling temperature of the second condenser is preferably about 30° C. to 50° C. lower, the first condenser is preferably operated at a cooling temperature of about 10° C. to 35° C. The condensates are combined and partly used as column reflux. The remaining condensate (10) is discharged. The uncondensed vapor (9) is preferably recycled mainly, in particular completely, to the reactor (A).

The uncondensed vapor (9) preferably contains ≥ 85 wt % of isobutylene, ≤ 2 wt % of inert compounds and ≤ 13 wt % of the remainder.

In order to prevent the formation of polymers in the first condenser and the column, a solution of the inhibitor in the target ester is preferably introduced into the first condenser. The inhibitor used is preferably a mixture of PTZ and 4-HT, which is advantageously introduced as a solution in the target ester, for example in an amount of 0.02 to 0.15 kg 4-HT and 0.5 to 1.5 kg PTZ per 100 liters of target ester, preferably in the top area of the vertically arranged second condenser. The amount of inhibitor solution is such that the inhibitor concentration in the combined condensate is, for example, in the range of 100 ppm to 500 ppm. Final distillation (E)

The target ester is obtained from the bottom product (11) of the distillation (D) from the low-boiling solvent in a distillation apparatus (evaporator, column and condenser) of preferably conventional design with a purity of preferably at least 99.5% by weight. The bottom product (13) obtained usually contains at least 70% by weight of (meth)acrylic acid and is preferably mainly, especially completely, recycled to the reactor (A). The distillation temperature is generally 50° C. to 100° C. The pressure is selected depending on the target ester to be distilled.

The final distillation is preferably carried out using a conventional plate column, for example a column with 30 to 50 dual-flow plates and a feed in the central column region. The pure target ester is separated at the top of the column. The condensation of the target ester is preferably carried out in two condensers arranged in series, in particular in a tube bundle condenser. The coolant temperature of the second condenser is preferably about 30°C to 50°C lower than the coolant temperature of the first condenser, wherein the coolant preferably has a temperature in the range of about 10°C to 35°C. The combined condensate is used partly as column reflux and partly for stabilizing the top of the column and the condenser (currently the first condenser), i.e., for avoiding polymerization in the top of the column and the condenser (currently the first condenser). Another part of the target ester is obtained as a valuable product (12). In order to avoid polymerization in the condenser (in particular in the second condenser), a solution of an inhibitor in the target ester is introduced. Preferably, for example, a solution of 0.5% by weight to 2% by weight of hydroquinone monoethyl ether (MEHQ) is used, wherein the amount of inhibitor introduced is preferably selected so that the inhibitor content of the combined condensate is 10 to 20 ppm. In order to avoid polymerization in the first condenser, a part of the combined stable condensate (preferably about 5 to 10 times the weight of the target ester discharged in terms of the weight of the vapor) is introduced into the vapor pipe. The introduction of the condensate is preferably achieved by countercurrent injection to the gas flow into the steam pipe above the column and/or cocurrent injection to the gas flow into the condenser inlet area. The polymerization in the column is firstly inhibited by refluxing the condensate, which contains, for example, 10 to 20 ppm of inhibitor. In addition, a solution of another inhibitor in the target ester is preferably introduced onto the trays in the upper region of the column. Preferably, a solution of PTZ and 4-HT in the target ester is used, for example 0.5 to 1.5 kg PTZ and 0.05 to 0.15 kg 4-HT in 100 liters of target ester, wherein the amounts are preferably measured so that the inhibitor content in the rectification stage is 50 ppm to 500 ppm. It is further preferred to introduce a solution of MEHQ in the target ester, for example 15 to 30 g MEHQ in 100 liters of target ester, into the column cover or into the vapor pipe above the column and/or into the upper condenser cover.

This is suitably and advantageously achieved by spraying through a nozzle mounted in the center of the upper column hood or the vapor pipe or the upper condenser hood. For further stabilization, an oxygen-containing gas, such as air, can be blown into the distillation apparatus if necessary. These measures can prevent the formation of polymers in the condenser, vapor pipe and column.

The obtained target ester (12) has high purity and generally has the following composition: tert-butyl (meth)acrylate 99.5% to 99.9% by weight tert-butyl acetate 0.001% to 0.01% by weight tert-butyl propionate 0.02% to 0.03% by weight tert-butyl alcohol 0.001% to 0.01% by weight (meth)acrylic acid 0.005% to 0.02% by weight inhibitor (MEHQ) 0.001% to 0.002% by weight the rest 0.072% to 0.428% by weight residue distillation (F)

The liquid reaction mixture (14) from the reactor (A) is preferably separated in a distillation (F) as a withdrawn substream. Preferably, the continuous distillation can be carried out at the same pressure as the reactor pressure. The temperature depends on the desired product (i.e. TBA or TBMA) and is generally selected so that the target ester undergoes reverse cleavage and only a small portion of the target ester, for example less than 5% by weight of the target ester (based on the bottoms), remains in the bottoms product. The gaseous isobutene obtained is preferably recycled mainly, in particular completely, to the reactor (15). The obtained bottom product (16) mainly comprises the acidic catalyst, the remaining (i.e., unconverted) (meth)acrylic acid and high boiling point components [i.e., by-products having a boiling point higher than that of TB(M)A at the same pressure], in particular, polymerized (meth)acrylic acid compounds.

The bottom product from the residue distillation (16), for example 10% to 90% by weight of the bottom product (16), in particular a major part of the bottom product (16), for example 75% to 90% by weight, is supplied to the reactor (A) (18), while the rest of the bottom product is discharged (17).

The distillation can be carried out in conventional apparatuses. However, it is preferred to use apparatuses which allow rapid distillation, such as film evaporators, thin film evaporators or spiral tube evaporators. Suitable film evaporators are known to those skilled in the art, see for example Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume B3, 2-21 to 2-24 and 3-1 to 3-25, 1988.

The condensation of the vapors can be carried out in a conventional manner, for example in a condenser of conventional design. Preferably, two condensers are used in series, in particular plate or tube bundle condensers, wherein the second condenser is preferably operated at a lower cooling temperature. This temperature difference is generally about 30°C to 50°C, wherein the cooling temperature of the first condenser is preferably in the range of about 10°C to 35°C. This allows rapid distillation and condensation and inhibits polymer formation. In order to further reduce the formation of polymers, an inhibitor dissolved in the target ester is introduced into the condenser (currently the second condenser). The inhibitor used is preferably a mixture of PTZ and 4-HT, which is advantageously introduced as a solution, for example in an amount of 0.02 to 0.15 kg 4-HT and 0.5 to 1.5 kg PTZ per 100 liters of target ester, preferably in the top region of the condenser, in the present case the top region of the second condenser arranged vertically. The amount of inhibitor solution used is such that the inhibitor concentration in the combined condensate is, for example, in the range of 100 ppm to 500 ppm.

The introduction of the inhibitor is carried out in a conventional manner, preferably by injecting the inhibitor solution. In addition, it has been found to be advantageous for reducing polymer formation if at least five parts by weight of the distillate (crude ester) are introduced, based on the parts by weight of the vapor, in particular into the condenser (currently into the first condenser), preferably into the top region of the vertically arranged condenser.

In a particularly preferred embodiment, condensation can be avoided and the resulting vapors can be recycled directly to the reactor (A) (15). The pressure in the residue distillation (F) is then equal to the pressure in the reactor.

All reported pressures are absolute pressures.

All reported ppm values are by weight (ppmw). Examples and Comparative Examples

The following method embodiments are simulated by thermodynamic simulation. The embodiments are performed using Aspen Plus® software (Aspen), which can be found at https://www.aspentech.com. Aspen is a broad simulation software package for modeling, simulation and optimization of industrial chemical processes and plants. Aspen has an extensive model database for basic operational modeling and a material database for the physical properties of many different substances. Aspen calculates the properties of mixtures from the physical data of pure substances using different thermodynamic models. Comparative Examples

The thermodynamic simulation of the entire plant was performed using Aspen as shown in Figure 2, and the following results were obtained:

Reactor A is supplied with isobutylene at a mass flow rate of 479 kg/h via pipeline 1, with catalytic sulfuric acid at a mass flow rate of 2 kg/h via pipeline 2, and with acrylic acid at a mass flow rate of 605 kg/h via pipeline 3.

Reactor A is supplied with a steam recycle stream from the condensation stage C at a mass flow rate of 343 kg/h via pipeline 7, a steam recycle stream from the low-boiling solvent distillation D at a mass flow rate of 21 kg/h via pipeline 9, a liquid recycle stream from the final distillation E at a mass flow rate of 320 kg/h via pipeline 13, and a liquid recycle stream from the residue distillation F at a mass flow rate of 2256 kg/h via pipeline 18.

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

Low-boiling solvents and non-condensable components are discharged from the process in the vapor phase from reactor A via line 6 at a mass flow rate of 9 kg/h.

The vapor phase has the following composition: Isobutylene: 50.10 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 0.10 wt% Diisobutylene: 0.04 wt% Triisobutylene: < 0.01 wt% Unknown component: 0.01 wt% Sulfuric acid: < 0.01 wt% Inert component 49.71 wt%

The liquid phase is conveyed from reactor A via line 19 to the residue distillation F at a mass flow rate of 4016 kg/h.

The liquid phase has the following composition: Isobutylene: 6.70 wt% Acrylic acid: 26.70 wt% Diacrylic acid: 2.00 wt% Tert-butyl acrylate: 48.09 wt% Diisobutylene: 0.88 wt% Triisobutylene: 4.53 wt% Sulfuric acid: 2.03 wt% Unknown components: 9.06 wt% Inert components < 0.01 wt%

The liquid phase is transferred from condensates B and C to the low boiling solvent distillation D via pipeline 8 at a mass flow rate of 1378 kg/h.

The liquid phase has the following composition: Isobutylene: 1.14 wt% Acrylic acid: 19.74 wt% Diacrylic acid: 0.02 wt% Tert-butyl acrylate: 71.19 wt% Diisobutylene: 1.74 wt% Triisobutylene: 5.10 wt% Sulfuric acid: < 0.01 wt% Unknown components: 1.05 wt% Inert components < 0.01 wt%

The vapor phase is conveyed from condensate C via line 7 to reactor A at a mass flow rate of 343 kg/h.

The vapor phase has the following composition: Isobutylene: 95.62 wt% Acrylic acid: 0.07 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 2.73 wt% Diisobutylene: 1.16 wt% Triisobutylene: 0.05 wt% Sulfuric acid: < 0.01 wt% Unknown components: 0.20 wt% Inert components: 0.15 wt%

The liquid phase is transferred from the low-boiling solvent distillate D to the high-purity distillate E from the bottom of the column via a pipeline 11 at a mass flow rate of 1351 kg/h.

The liquid phase has the following composition: Isobutylene: < 0.01 wt% Acrylic acid: 20.11 wt% Diacrylic acid: 0.02 wt% Tert-butyl acrylate: 73.12 wt% Diisobutylene: 0.71 wt% Triisobutylene: 5.20 wt% Sulfuric acid: < 0.01 wt% Unknown components: 0.81 wt% Inert components < 0.01 wt%

From the low boiling solvent distillation D downstream of the condenser, the low boiling solvent is discharged in a liquid phase through a pipe 10 at a mass flow rate of 19 kg/h.

The liquid phase has the following composition: Isobutylene: 3.68 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 5.01 wt% Diisobutylene: 70.48 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: 20.78 wt% Inert components < 0.01 wt%

The vapor phase is conveyed from the low-boiling solvent distillation D downstream of the condenser to the reactor A via line 9 at a mass flow rate of 21 kg/h.

The vapor phase has the following composition: Isobutylene: 73.69 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 0.07 wt% Diisobutylene: 5.73 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: 1.20 wt% Inert components 19.27 wt%

The pure product tert-butyl acrylate from the high-purity distillation E is discharged in the liquid phase via the pipeline 12 at a mass flow rate of 1000 kg/h.

The liquid phase has the following composition: Isobutylene: 0.03 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 99.84 wt% Diisobutylene: 0.02 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown component: 0.06 wt% Inert component < 0.01 wt%

The liquid phase is circulated from the final distillation E to the reactor A via the pipeline 13 at a mass flow rate of 320 kg/h from the bottom of the column.

The liquid phase has the following composition: Isobutylene: 1.43 wt% Acrylic acid: 76.71 wt% Diacrylic acid: 1.30 wt% Tert-butyl acrylate: 1.20 wt% Diisobutylene: < 0.01 wt% Triisobutylene: 17.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: 2.32 wt% Inert components < 0.01 wt%

The liquid phase was circulated from the residue distillation F to the reactor A via the pipeline 18 at a mass flow rate of 2256 kg/h, and the high-boiling solvent was discharged from the process via the pipeline 17 at a mass flow rate of 63 kg/h.

The liquid phase has the following composition: Isobutylene: 2.65 wt% Acrylic acid: 41.95 wt% Diacrylic acid: 3.46 wt% Tert-butyl acrylate: 29.54 wt% Diisobutylene: 0.29 wt% Triisobutylene: 4.70 wt% Sulfuric acid: 3.52 wt% Unknown components: 13.88 wt% Inert components < 0.01 wt%

Embodiment 1

Thermodynamic simulation of the entire plant shown in Figure 1 was performed using Aspen, and the following results were obtained:

Reactor A was supplied with isobutylene via line 1 at a mass flow rate of 455 kg/h, with catalytic sulfuric acid via line 2 at a mass flow rate of 7 kg/h and with acrylic acid via line 3 at a mass flow rate of 598 kg/h.

Reactor A is supplied with a steam recycle flow from the condensation stage C at a mass flow rate of 31521 kg/h via pipeline 7, a steam recycle flow from the low-boiling solvent distillation D at a mass flow rate of 561 kg/h via pipeline 9, a liquid recycle flow from the final distillation E at a mass flow rate of 481 kg/h via pipeline 13, a steam recycle flow from the residue distillation F at a mass flow rate of 5 kg/h via pipeline 15, and a liquid recycle flow from the residue distillation F at a mass flow rate of 11 kg/h via pipeline 18.

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

The vapor phase is conveyed from reactor A to condenser B via line 4 at a mass flow rate of 33580 kg/h.

The vapor phase has the following composition: Isobutylene: 82.43 wt% Acrylic acid: 1.37 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 3.19 wt% Diisobutylene: 0.12 wt% Triisobutylene:      < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: 0.05 wt% Inert components 12.81 wt%

The liquid phase is conveyed from reactor A via line 14 to the residue distillation F at a mass flow rate of 60 kg/h.

The liquid phase has the following composition: Isobutylene: 3.93 wt% Acrylic acid: 30.18 wt% Diacrylic acid: 30.86 wt% Tert-butyl acrylate: 16.75 wt% Diisobutylene: 0.17 wt% Triisobutylene: 0.10 wt% Sulfuric acid: 15.00 wt% Unknown components: 3.00 wt% Inert components < 0.01 wt%

The liquid phase is transferred from condensates B and C to the low boiling solvent distillation D via pipeline 8 at a mass flow rate of 2054 kg/h.

The liquid phase has the following composition: Isobutylene: 26.26 wt% Acrylic acid: 22.11 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 49.47 wt% Diisobutylene: 1.27 wt% Triisobutylene: 0.03 wt% Sulfuric acid: < 0.01 wt% Unknown components: 0.83 wt% Inert components < 0.01 wt%

The vapor phase is transferred from condenser C to reactor A via pipe 7 at a mass flow rate of 31521 kg/h, and the low-boiling solvent is discharged via pipe 6 at a mass flow rate of 5 kg/h.

The vapor phase has the following composition: Isobutylene: 86.08 wt% Acrylic acid: 0.02 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 0.18 wt% Diisobutylene: 0.04 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: < 0.01 wt% Inert components 13.64 wt%

The liquid phase is transferred from the low boiling solvent distillation D to the final distillation E from the bottom of the column via the pipeline 11 at a mass flow rate of 1481 kg/h.

The liquid phase has the following composition: Isobutylene: < 0.01 wt% Acrylic acid: 29.66 wt% Diacrylic acid: 1.00 wt% Tert-butyl acrylate: 68.10 wt% Diisobutylene: 0.02 wt% Triisobutylene: 0.04 wt% Sulfuric acid: < 0.01 wt% Unknown components: 1.15 wt% Inert components < 0.01 wt%

From the low boiling solvent distillation D downstream of the condenser, the low boiling solvent is discharged in a liquid phase through a pipe 10 at a mass flow rate of 12 kg/h.

The liquid phase has the following composition: Isobutylene: 9.09 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 37.02 wt% Diisobutylene: 53.83 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown component: < 0.01 wt% Inert component < 0.01 wt%

The vapor phase is conveyed from the low-boiling solvent distillation D downstream of the condenser to the reactor A via line 9 at a mass flow rate of 561 kg/h.

The vapor phase has the following composition: Isobutylene: 95.96 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 0.51 wt% Diisobutylene: 3.47 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: < 0.01 wt% Inert components 0.01 wt%

The pure product tert-butyl acrylate from the high-purity distillation E is discharged in the liquid phase via the pipeline 12 at a mass flow rate of 1000 kg/h.

The liquid phase has the following composition: Isobutylene: < 0.01 wt% Acrylic acid: < 0.01 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: 99.90 wt% Diisobutylene: 0.03 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Inert components < 0.01 wt%

The liquid phase is transferred from the final distillation E to the reactor A via the pipeline 13 at a mass flow rate of 481 kg/h from the bottom of the column.

The liquid phase has the following composition: Isobutylene: < 0.01 wt% Acrylic acid: 91.23 wt% Diacrylic acid: 3.08 wt% Tert-butyl acrylate: 2.00 wt% Diisobutylene: < 0.01 wt% Triisobutylene: 0.12 wt% Sulfuric acid: < 0.01 wt% Unknown components: 3.53 wt% Inert components < 0.01 wt%

The liquid phase was circulated from the residue distillation F to the reactor A via the pipe 18 at a mass flow rate of 11 kg/h, and the high-boiling solvent was discharged from the reactor via the pipe 17 at a mass flow rate of 44 kg/h.

The liquid phase has the following composition: Isobutylene: 3.49 wt% Acrylic acid: 43.00 wt% Diacrylic acid: 33.57 wt% Tert-butyl acrylate: < 0.01 wt% Diisobutylene: 0.17 wt% Triisobutylene: 0.11 wt% Sulfuric acid: 16.37 wt% Unknown components: 3.27 wt% Inert components < 0.01 wt%

The vapor phase is conveyed from the residue distillation F via line 15 to the reactor A at a mass flow rate of 5 kg/h.

The vapor phase has the following composition: Isobutylene: 95.28 wt% Acrylic acid: 3.08 wt% Diacrylic acid: < 0.01 wt% Tert-butyl acrylate: < 0.01 wt% Diisobutylene: 0.18 wt% Triisobutylene: < 0.01 wt% Sulfuric acid: < 0.01 wt% Unknown components: 0.08 wt% Inert components 1.34 wt%

In this embodiment of the present invention, the specific low boiling solvent yield is 0.012 kg of low boiling solvent per kg of tert-butyl acrylate, and the specific high boiling solvent yield is 0.044 kg per kg of tert-butyl acrylate.

In the comparative example, the specific low boiling solvent yield is 0.019 kg of low boiling solvent per kg of tert-butyl acrylate, and the specific high boiling solvent yield is 0.063 kg per kg of tert-butyl acrylate.

In the embodiment of the present invention, the yield of low-boiling solvent is 37% lower than that of the comparative embodiment, and the yield of high-boiling solvent is 30% lower.

Due to the low specific yield of the low boiling solvent and the high boiling solvent, the method of the present invention is significantly more economical than the conventional method.

The concentration of the polymerizable component tert-butyl acrylate present in the circulating gas (line 5) was 3.72% by weight in the comparative example, but only 0.18% by weight in the example of the present invention. This significantly reduces the risk of polymerization in the relatively warm circulating gas blower at operating temperature.

1: TB(M)A feed 2: Isobutylene feed 3: Catalyst feed 4: Steam from reactor A is used to condense B and C 5: Uncondensed steam from condensation C 6: Uncondensed steam from condensation C is discharged 7: Uncondensed steam from condensation C is circulated into reactor A 8: Condensate from condensation B and condensation C 9: Uncondensed steam from low boiling solvent distillation D is circulated into reactor A 10: Residual condensate from low boiling solvent distillation D is discharged 11: Bottom product of low boiling solvent distillation D 12: Process product TB(M)A from the final distillation E 13: Bottom product from the final distillation E is circulated into reactor A 14: Reaction mixture from reactor A 15: Distillate and/or steam from residue distillation F is recycled to reactor A 16: Bottoms from residue distillation F 17: Discharge of bottoms from residue distillation F 18: Bottoms from residue distillation F is recycled to reactor A A: Reactor B: Condensation C: Condensation D: Low boiling solvent distillation E: Final distillation F: Residue distillation Figure 2 1: TB(M)A feed 2: Isobutylene feed 3: Catalyst feed 4: Distillate from residue distillation F is used for condensation in B and C 6: Discharge the uncondensed steam from reactor A 7: Circulate the uncondensed steam from condensation C to reactor A 8: Condensate from condensation B and condensation C 9: Circulate the uncondensed steam from low-boiling solvent distillation D to reactor A 10: Discharge the residual condensate from low-boiling solvent distillation D 11: The bottom product of low-boiling solvent distillation D 12: Process product TB(M)A from the last distillation E 13: Circulate the bottom product from the last distillation E to reactor A 16: The bottom product from the residue distillation F 17: Discharge the bottom product of the residue distillation F 18: Recycling of the bottom product of the residue distillation A: Reactor B: Condensation C: Condensation D: Low boiling solvent distillation E: Final distillation F: Residue distillation

[FIG. 1] shows in schematic form an overview of a preferred configuration of the method according to the present invention. FIG. 1 shows the interconnection of the units "reactor A", "condensation B", "condensation C", "low boiling solvent distillation D", "final distillation E" and "residue distillation F". [FIG. 2] For comparison, FIG. 2 shows in schematic form the configuration of the TB(M)A method according to the prior art. FIG. 2 shows the interconnection of the units "reactor A", "condensation B", "condensation C", "low boiling solvent distillation D", "final distillation E" and "residue distillation F".

1: TB(M)A feed

2: Isobutylene feed

3: Catalyst feed

4: Steam from reactor A is used to condense B and C

5: Uncondensed steam from condensation C

6: Exhaust the uncondensed steam from condensation C

7: Uncondensed steam from condenser C is circulated into reactor A

8: Condensate from condensation B and condensation C

9: The uncondensed steam from the low-boiling solvent distillation D is circulated into the reactor A

10: Discharge the residual condensate from the low boiling solvent distillation D

11: Bottom product of low boiling solvent distillation D

12: Process product TB(M)A from the final distillation E

13: The bottom product from the final distillation E is recycled into reactor A

14: Reaction mixture from reactor A

15: Distillate and/or steam from residue distillation F is recycled to reactor A

16: Bottoms from Residue Distillation F

17: Discharge the bottom product of the residual distillation F

18: The bottom product of the residue distillation F is circulated into the reactor A

A: Reactor

B: Condensation

C: Condensation

D: Distillation with low boiling solvent

E: Final distillation

F: Residue distillation

Claims (13)

A method for continuously producing tert-butyl (meth)acrylate by reacting liquid (meth)acrylic acid with gaseous isobutylene conveyed via the liquid phase in a reactor in the presence of an acidic catalyst at a temperature range of 30°C to 90°C and a pressure range of 0.1 to 20 bar absolute, wherein the two reactants are used in a molar ratio of isobutylene:(meth)acrylic acid of 5 to 60, partially condensing the gas stream leaving the reactor comprising unconverted reactants and tert-butyl (meth)acrylate to obtain tert-butyl (meth)acrylate and unconverted (meth)acrylic acid as a liquid mixture, which are separated by subsequent distillation to obtain tert-butyl (meth)acrylate, and recycling the uncondensed isobutylene to the reactor. A method as claimed in any of the preceding claims, wherein the reactor is a stirred tank, a bubble column reactor or a loop flow reactor. A method as claimed in any of the preceding claims, wherein the reactant used is an isobutylene:(meth)acrylic acid molar ratio in the range of 8 to 50. A method as claimed in any one of claims 1 to 2, wherein the reactant used is isobutylene:(meth)acrylic acid in a molar ratio ranging from 10 to 45. The method of any of the preceding claims, wherein the reaction is carried out at a temperature in the range of 35°C to 85°C and at a pressure in the range of 0.2 to 15 bar absolute. The method of any one of claims 1 to 4, wherein the reaction is carried out at a temperature in the range of 40°C to 80°C and an absolute pressure in the range of 0.5 to 13 bar. A method as claimed in any of the preceding claims, wherein the (meth)acrylic acid obtained by distillation separation of the liquid mixture after the gas stream is partially condensed is recycled to the reactor. A method as in any of the preceding claims, wherein the temperature of the reactor is controlled via one or more internal heat exchangers or via one or more external heat exchangers or using one or more external liquid loops. A method as claimed in any preceding claim, wherein the catalyst is a sulfur or phosphorus containing inorganic acid, an alkyl sulfonic acid or an aryl sulfonic acid. The method of any of the preceding claims, wherein the catalyst is sulfuric acid. A process as claimed in any of the preceding claims, wherein the isobutylene is used in the form of a hydrocarbon mixture comprising isobutylene. A method as claimed in any of the preceding claims, wherein the gas mixture is a C4 gas mixture comprising isobutylene, isobutane, butane, 1-butene and 2-butene. A process as claimed in any preceding claim, wherein high boiling point by-products are removed from the liquid reaction mixture in the reactor via the bottoms product of distillation of the liquid reaction mixture removal substream.