Process for preparation of C4 to C12 esters of (meth) acrylates

Abstract

The invention relates to a method for producing C4-C12 alkyl (meth) acrylates, in which a tetraC4-C12 alkyl titanate is produced in a first step and subsequently used together with isopropyl-alcohol-coordinated titanium (IV) as a catalyst mixture for producing the C4-C12 alkyl (meth) acrylates.

Description

Technical Field

[0001] The present invention relates to a process for preparing C4-C 12 alkyl (meth)acrylates, in which in a first step tetra-C4-C 12 alkyl titanates are prepared and subsequently used together with titanium(IV) coordinated with isopropoxide as a catalyst mixture for preparing C4-C 12 alkyl (meth)acrylates. Background Art

[0002] DE 100 26 644 A1 describes the preparation of esters of unsaturated carboxylic acids by transesterification with C4-C 20 alcohols in the presence of a transesterification catalyst comprising 2,2,6,6-tetraalkyl-1-oxyl-piperidin-4-yl.

[0003] The transesterification catalyst described in DE 100 26 644 A1 is expensive in its preparation, making the process overall costly.

[0004] DE 102 00 171 A1 describes a process for the continuous preparation of higher (meth)acrylate esters by reaction of methyl (meth)acrylate with C2-C 12 alcohols. Purification of the product is carried out by means of distillation and subsequent transfer of the obtained distillation column bottoms to an evaporator. Pure tetraalkyl titanates are used as catalysts.

[0005] EP 1 583 733 B1 describes a process for the continuous preparation of higher (meth)acrylate esters by reaction of methyl (meth)acrylate with higher alcohols in the presence of a catalyst. Pure tetraalkyl titanates are used as catalysts.

[0006] The processes described in DE 102 00 171 A1 and EP 1 583 733 B1 are already well-suited for the preparation of (meth)acrylates. However, these processes are costly because high-purity tetraalkyl titanate catalysts must be used. Summary of the Invention

[0007] Object

[0008] Accordingly, there is a need for a process for preparing C4-C 12 alkyl (meth)acrylates that has none or only to a reduced extent the disadvantages of the processes described in the prior art. In particular, the process should be capable of being carried out simply and inexpensively.

[0009] Solution

[0010] The object is achieved by a process for preparing C4-C 12A method for alkyl esters is implemented, wherein the method comprises the following steps a) to d):

[0011] a) Reacting tetraisopropyl titanate with a C4-C 12 alcohol to obtain a first mixture comprising isopropanol and tetra-C4-C titanate 12 alkyl ester,

[0012] b) Distilling the first mixture obtained in step a) to obtain a first overhead stream comprising isopropanol and a first bottoms stream comprising tetra-C4-C 12 alkyl ester,

[0013] c) Reacting a C1-C2 alkyl (meth)acrylate with a C4-C 12 alcohol in the presence of a catalyst mixture, the catalyst mixture comprising the tetra-C4-C titanate obtained in the first bottoms stream in step b) and 0.02 to 30% by weight of titanium(IV) coordinated with isopropoxide radicals relative to the total weight of the catalyst mixture, the second mixture comprising tetra-C4-C 12 alkyl ester, C4-C 12 alkyl (meth)acrylate, C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, C4-C 12 alcohol and C1-C2 alcohol, 12 alcohol and C1-C2 alcohol,

[0014] d) Separating the C4-C 12 alkyl (meth)acrylate from the second mixture.

[0015] Another subject of the present invention is a method for preparing a C4-C 12 alkyl (meth)acrylate, wherein the method comprises the following steps c) and d):

[0016] c) Reacting a C1-C2 alkyl (meth)acrylate with a C4-C 12 alcohol in the presence of a catalyst mixture, the catalyst mixture comprising the tetra-C4-C titanate obtained in the first bottoms stream in step b) and 0.02 to 30% by weight of titanium(IV) coordinated with isopropoxide radicals relative to the total weight of the catalyst mixture, the second mixture comprising tetra-C4-C 12 alkyl ester, C4-C 12 alkyl (meth)acrylate, C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, C4-C 12 alkyl (meth)acrylate, C4-C 12 alcohol and C1-C2 alcohol,

[0017] d) Separating the C4-C12 Alkyl esters.

[0018] Unexpectedly, it has been found that in the process of the present invention, a catalyst mixture containing titanium(IV) coordinated with isopropoxide in addition to tetra-C4-C 12 alkyl esters can be used without adversely affecting the reaction of C1-C2 alkyl (meth)acrylates with C4-C 12 alcohols. In particular, it has been unexpectedly found that the isopropanol formed in the reaction does not adversely affect the reaction.

[0019] Using the catalyst mixture makes the process according to the present invention particularly inexpensive. Particularly advantageously, in a preferred embodiment of the process according to the present invention, the first bottom stream can be used as the catalyst mixture. Since the first bottom stream that can be used as the catalyst mixture in the process according to the present invention can also contain 0.02 to 30% by weight of titanium(IV) coordinated with isopropoxide, the preparation of the catalyst mixture is less costly, so that time and cost in the preparation can also be saved.

[0020] In addition, titanium(IV) coordinated with isopropoxide has a smaller mass than tetra-C4-C 12 alkyl esters. Therefore, the catalyst mixture according to the present invention is lighter than pure tetra-C4-C 12 alkyl esters, which, for example, makes the transportation of the catalyst mixture according to the present invention simpler and thus less costly.

[0021] The catalyst mixture according to the present invention allows the use of a smaller amount of catalyst by weight while maintaining the reaction rate unchanged compared to using pure tetra-C4-C 12 alkyl esters. When the amount of the catalyst mixture is the same as that of pure tetra-C4-C 12 alkyl esters, the reaction rate is increased compared to pure tetra-C4-C 12 alkyl esters.

[0022] In addition, the process according to the present invention is particularly environmentally friendly because the by-products formed can be recycled and / or sent to the process for preparing the reactants used.

[0023] The process according to the present invention will be explained in detail below.

[0024] In step a) of the process according to the present invention, tetra-isopropyl titanate is reacted with C4-C 12 alcohols to obtain a first mixture containing isopropanol and tetra-C4-C 12 alkyl esters.

[0025] Tetra-isopropyl titanate is also known as tetra-isopropyl orthotitanate or tetra-isopropoxide.

[0026] Within the scope of the present invention, the term "C4-C 12 alcohol" includes not only exactly one C4-C 12 alcohol, but also mixtures formed from two or more C4-C 12 alcohols. Preferably according to the present invention is exactly one C4-C 12 alcohol.

[0027] Within the scope of the present invention, the term "C4-C 12 alcohol" is understood to mean an alcohol having 4 to 12 carbon atoms in the alkyl residue. The alkyl residue can be cyclic or straight-chain, and can equally well be a branched group. The alkyl residue having 4 to 12 carbon atoms can also be substituted by heteroatoms within the alkyl residue. C4-C 12 alcohol is also understood within the scope of the present invention to mean an alcohol having an aromatic group in the alkyl residue, where such C4-C 12 alcohol then has a total of 4 to 12 carbon atoms in the alkyl residue and the aromatic group. Examples of such C4-C 12 alcohols having an aromatic group in the alkyl residue are benzyl alcohol. Other examples of C4-C 12 alcohols are n-butanol, tert-butanol, isobutanol, pentanol, cyclohexanol, hexanol, heptanol, octanol, isooctanol, isodecanol, 2-ethylhexanol, isoborneol, benzyl alcohol, tetrahydrofurfuryl alcohol, 3,3,4-trimethyl-cyclohexanol, phenylethanol, tert-butylaminoethanol, diethylaminoethanol, triethylene glycol ethyl ether (Ethylentriglycol), triethylene glycol methyl ether (Methylentriglycol), diethylene glycol butyl ether, and acetone glycerol.

[0028] Preferably, the C4-C 12 alcohol in step a) is selected from the group consisting of n-butanol, isobutanol, 2-ethylhexanol, tert-butanol, isodecanol, and cyclohexanol.

[0029] Particularly preferably, the C4-C 12 alcohol in step a) is selected from the group consisting of n-butanol, isobutanol, and 2-ethylhexanol.

[0030] For example, the weight ratio of tetra-isopropyl titanate to C4-C 12 alcohol in step a) is in the range of 1:2 to 2:1.

[0031] C4-C 12 alcohol usually contains residual water. "Residual water" is understood to mean water in the range of 0.005 to 0.05% by weight relative to the total weight of the C4-C 12 alcohol.

[0032] Thus, the reaction in step a) can be carried out in the presence of residual water.

[0033] In the reaction in step a), the isopropoxide groups from tetraisopropyl titanate are replaced by the alkoxide groups of C4-C 12 alcohols, and isopropanol and tetra-C4-C 12 alkyl titanates are formed here. This reaction is also referred to as the transesterification of tetraisopropyl titanate or the ligand exchange of tetraisopropyl titanate. This reaction itself is known.

[0034] Tetra-C4-C 12 alkyl titanates are formed here. "Tetra-C4-C 12 alkyl titanates" are understood to be titanium(IV) coordinated by four C4-C 12 alkoxide groups. Examples of such tetra-C4-C 12 alkyl titanates are tetra-isobutyl titanate and tetra-2-ethylhexyl titanate.

[0035] It goes without saying that the C4-C 12 alkoxide groups coordinated to titanium(IV) are the C4-C 12 alkoxide groups of the C4-C 12 alcohols that undergo the reaction.

[0036] If, for example, isobutanol is used as the C4-C 12 alcohol, then tetra-isobutyl titanate and isopropanol are formed in the reaction in step a). That is, the first mixture obtained then contains isopropanol and tetra-isobutyl titanate as the tetra-C4-C 12 alkyl titanate.

[0037] If, for example, 2-ethylhexanol is used as the C4-C 12 alcohol, then tetra-2-ethylhexyl titanate and isopropanol are formed in the reaction in step a). That is, the first mixture obtained then contains isopropanol and tetra-2-ethylhexyl titanate as the tetra-C4-C 12 alkyl titanate.

[0038] Therefore, the first mixture contains isopropanol and tetra-C4-C 12 alkyl titanates.

[0039] Those skilled in the art are aware that the reaction in step a) (transesterification or ligand exchange) generally proceeds step by step. For example, in the reaction in step a), tetra-C4-C 12 alkyl titanate-triisopropoxide is first formed, followed by bis-C4-C 12 alkyl titanate-diisopropoxide, then tri-C4-C 12 alkyl titanate-isopropoxide, and finally tetra-C4-C 12 alkyl titanate.

[0040] Thus, the first mixture obtained in step a) generally contains at least one additional compound selected from the group consisting of tetraisopropyl titanate, C4-C 12 alkyl ester-triisopropyl titanate, di-C4-C 12 alkyl ester-diisopropyl titanate, and tri-C4-C 12 alkyl ester-isopropyl titanate.

[0041] Within the scope of the present invention, the compounds tetraisopropyl titanate, C4-C 12 alkyl ester-triisopropyl titanate, di-C4-C 12 alkyl ester-diisopropyl titanate, and tri-C4-C 12 alkyl ester-isopropyl titanate are also referred to as isopropoxide-coordinated titanium(IV).

[0042] Thus, within the scope of the present invention, the term "isopropoxide-coordinated titanium(IV)" is understood to mean a compound containing at least one isopropoxide ligand on a titanium(IV) complex. Isopropoxide-coordinated titanium(IV) may have only isopropoxide ligands on the titanium(IV), or may have a mixture formed by isopropoxide ligands and C4-C 12 alkoxide ligands. Within the scope of the present invention, the term "isopropoxide-coordinated titanium(IV)" includes not only exactly one isopropoxide-coordinated titanium(IV), but also mixtures formed by two or more isopropoxide-coordinated titanium(IV).

[0043] In addition, the first mixture obtained in step a) may further contain yet additional components, such as C4-C 12 alcohols.

[0044] The reaction in step a) is generally carried out at a temperature in the range of 80 °C to 120 °C. The pressure in the reaction in step a) is, for example, in the range of 0.1 bar to 1 bar.

[0045] The reaction in step a) can be carried out in a reactor known to those skilled in the art for transesterification and / or ligand exchange. Preferred is a reactor with a vapor outlet and a distillation column. Such reactors are known per se.

[0046] In step b), the first mixture obtained in step a) is distilled to obtain a first overhead stream containing isopropanol and a first bottoms stream containing tetra-C4-C 12 alkyl titanate.

[0047] The distillation in step b) can be carried out according to methods known to those skilled in the art. For example, the first mixture obtained in step a) can be transferred to a distillation column and / or a rectification column and distilled there. It is also possible and preferred according to the present invention to carry out the distillation in step b) in the same reactor as in step a).

[0048] Particularly preferably, the distillation in step b) is carried out simultaneously with the reaction in step a).

[0049] Therefore, the following method is also preferred, in which the distillation in step b) is carried out simultaneously with the reaction in step a).

[0050] Therefore, steps a) and b) are preferably carried out simultaneously. Therefore, it is preferred that the reaction of titanium tetraisopropyl ester with C4-C 12 alcohols is carried out simultaneously with the distillation of the first mixture. This embodiment is particularly advantageous because thereby the reaction equilibrium in step a) is shifted towards tetra-C4-C 12 alkyl titanates.

[0051] A first top product stream is obtained in the distillation in step b). The first top product stream contains isopropanol. If the first mixture contains C4-C 12 alcohols, then in step b) this mixture is usually also included in the first top product stream.

[0052] In addition, a first bottom product stream is also obtained. Within the scope of the present invention, the "bottom product stream" is understood not only as the bottom product continuously withdrawn from the reactor, but also as, for example, the bottom product that remains in the reactor as a distillation product in a discontinuous mode of operation and is only removed from the reactor at a subsequent point in time.

[0053] Isopropanol has a lower boiling point than tetra-C4-C 12 alkyl titanates. Therefore, the first bottom product stream is also referred to as a high-boiling residue.

[0054] In addition to tetra-C4-C 12 alkyl titanates, the first bottom product stream preferably further contains titanium(IV) coordinated with isopropoxide. The above-described embodiment applies to the term "titanium(IV) coordinated with isopropoxide". Based on the total weight of the first bottom product stream, the first bottom product stream contains, for example, in the range of 0.02 to 30% by weight, preferably in the range of 3 to 15% by weight, and particularly preferably in the range of 5 to 10% by weight of titanium(IV) coordinated with isopropoxide.

[0055] Therefore, the following method is also preferred, in which, based on the total weight of the first bottom product stream, the first bottom product stream obtained in step b) further contains 0.02 to 30% by weight of titanium(IV) coordinated with isopropoxide.

[0056] The first bottom product stream obtained in step b) can preferably be used as the catalyst mixture in step c).

[0057] Therefore, the following method is also preferred, in which the first bottom product stream obtained in step b) is used as the catalyst mixture in step c).

[0058] In step c) of the process according to the invention, the C1-C2 alkyl (meth)acrylate is reacted with a C4-C 12 alcohol in the presence of a catalyst mixture to obtain a second mixture.

[0059] Within the scope of the present invention, the "C1-C2 alkyl (meth)acrylate" is understood not only as exactly one C1-C2 alkyl (meth)acrylate, but also as a mixture formed from two or more C1-C2 alkyl (meth)acrylates. Within the scope of the present invention, the term "C1-C2 alkyl (meth)acrylate" includes not only C1-C2 alkyl methacrylates, but also C1-C2 alkyl acrylates. The "C1-C2 alkyl (meth)acrylate" is understood as an alkyl (meth)acrylate having 1 or 2 carbon atoms in the alkyl residue. Within the scope of the present invention, the term "(meth)acrylic acid" includes not only acrylic acid but also methacrylic acid.

[0060] For example, the C1-C2 alkyl (meth)acrylate is selected from the group consisting of methyl (meth)acrylate and ethyl (meth)acrylate. The C1-C2 alkyl (meth)acrylate is particularly preferably methyl (meth)acrylate.

[0061] Accordingly, a process according to the invention is also preferred, in which the C1-C2 alkyl (meth)acrylate is methyl (meth)acrylate.

[0062] The embodiments and preferences previously described for the C4-C 12 alcohol in step a) correspondingly apply to the C4-C 12 alcohol. Particularly preferably, the C4-C 12 alcohol reacted in step c) is the same C4-C 12 alcohol that has already reacted in step a).

[0063] Accordingly, preferably according to the invention, the C4-C 12 alcohol in step c) is selected from the group consisting of n-butanol, isobutanol and 2-ethylhexanol.

[0064] Accordingly, a process according to the invention is also preferred, in which the C4-C 12 alcohol in steps a) and c) is selected from the group consisting of n-butanol, isobutanol and 2-ethylhexanol.

[0065] The catalyst mixture comprises a tetra-C4-C 12 alkyl titanate obtained in the first bottoms stream in step b) and 0.02 to 30% by weight of isopropoxide-coordinated titanium(IV) relative to the total weight of the catalyst mixture.

[0066] The catalyst mixture preferably contains tetra-C4-C 12 alkyl esters obtained in the first bottoms stream in step b) and titanium(IV) coordinated with isopropoxide in an amount of 3 to 15% by weight, particularly preferably 5 to 10% by weight, based on the total weight of the catalyst mixture.

[0067] Based on the total weight of the catalyst mixture, the catalyst mixture contains, for example, 70 to 99.98% by weight, preferably 85 to 97% by weight, particularly preferably 90 to 95% by weight of tetra-C4-C 12 alkyl esters.

[0068] The titanium(IV) coordinated with isopropoxide and tetra-C4-C 12 alkyl esters contained in the catalyst mixture preferably add up to 100% by weight.

[0069] Particularly preferably, the catalyst mixture consists of tetra-C4-C 12 alkyl esters obtained in the first bottoms stream in step b) and titanium(IV) coordinated with isopropoxide in an amount of 0.02 to 30% by weight, based on the total weight of the catalyst mixture.

[0070] It goes without saying that the weight percentages of titanium(IV) coordinated with isopropoxide and tetra-C4-C 12 alkyl esters in the first bottoms stream relate to the weight percentages before the reaction in step c) has occurred. Those skilled in the art are aware that the reaction in step c) may change the weight percentages, in particular, for example, by transesterification of the catalyst mixture. Transesterification of the catalyst mixture is also referred to as ligand exchange in the catalyst mixture.

[0071] For example, in the reaction in step c), the molar ratio of C1-C2 alkyl (meth)acrylate to C4-C 12 alcohol is in the range of 2:1 to 1:2.

[0072] (The molar ratio of C1-C2 alkyl (meth)acrylate to C4-C 12 alcohol relates to the molar ratio before the reaction. Those skilled in the art are aware that the molar ratio may change during the reaction.)

[0073] Based on the total weight of the C1-C2 alkyl (meth)acrylate in step c), a catalyst mixture in the range of 0.2 to 0.5% by weight is generally used.

[0074] The reaction in step c) can be carried out in any reactor. The reaction can be carried out continuously, and discontinuous reactions are equally possible. The reaction in step c) is preferably carried out continuously. In this regard, "continuously" is understood to mean that the C1-C2 alkyl (meth)acrylate and the C4-C 12 alcohol are continuously fed into the reactor, while at the same time a second mixture is continuously withdrawn from the reactor.

[0075] The reaction in step c) can be carried out, for example, at a temperature in the range from 80 °C to 160 °C, preferably in the range from 110 °C to 135 °C.

[0076] In the reaction in step c), a second top stream and a second bottom stream are preferably obtained.

[0077] The second top stream contains the C1-C2 alkyl (meth)acrylate, the C1-C2 alcohol and isopropanol. The second bottom stream comprises the second mixture. The second bottom stream preferably consists of the second mixture.

[0078] Accordingly, the following method is also preferred, in which a second top stream and a second bottom stream are obtained in the reaction in step c), the second top stream containing the C1-C2 alkyl (meth)acrylate, the C1-C2 alcohol and isopropanol, and the second bottom stream comprising the second mixture.

[0079] The second top stream and the second bottom stream are generally formed by distillation during the reaction in step c). The reactor in which the reaction in step c) is carried out can include a vapor outlet leading to a first distillation column. The first distillation column is also referred to as an azeotropic distillation column. Such reactors are known per se and are described, for example, in EP 1 583 733 and DE 10 200 171. Thus, the distillation during the reaction in step c) is preferably carried out in the first distillation column.

[0080] The second top stream can be at least partially removed from the reaction in step c). This is particularly advantageous since it can shift the reaction equilibrium of the reaction in step c) towards the second mixture.

[0081] The second top stream obtained can be at least partially returned to step c). In particular, a portion of the second top stream can be condensed in the first distillation column and thus returned to step c).

[0082] Furthermore, it is possible and according to the invention preferred to send the second top stream at least partially to a process for preparing a C1 to C2 alkyl (meth)acrylate, in particular methyl (meth)acrylate.

[0083] Therefore, the following method is also preferred, in which the obtained second top product stream is guided back to step c) and / or sent to a process for preparing C1-C2 alkyl (meth)acrylates.

[0084] Processes for preparing C1-C2 alkyl (meth)acrylates, in particular methyl (meth)acrylate, are known per se to those skilled in the art. These esters are generally prepared by means of various processes starting from C2, C3 or C4 building blocks.

[0085] In one of these processes (C4 process), MMA is obtained by the reaction of oxidizing isobutene or tert-butanol to methacrolein (MAL) with air oxygen in the gas phase over a heterogeneous catalyst and then oxidative esterification of methacrolein in the presence of methanol. This process developed by ASAHI is described in particular in documents US 5,969,178 and US 7,012,039.

[0086] Another commercially widely used process is based on acetone as the base material and is mostly referred to as the C3 process or the ACH-sulfonic acid process. Here, acetone reacts with hydrogen cyanide (HCN) to form the key intermediate acetone cyanohydrin (ACH). This intermediate is separated and used in subsequent process steps for preparing methacrylic acid (MAS) and MMA. Such processes are described, for example, in US 4,529,816.

[0087] WO 2014 / 170223 describes a very efficient process in which propionaldehyde is obtained from a C2 fraction in a first stage and reacted with formaldehyde to form methacrolein in a second stage. This can then in turn be oxidatively esterified to MMA in the presence of a special metal or metal oxide catalyst and methanol. This process is also referred to as the C2 process.

[0088] Preferably, at least part of the second top product stream obtained in step c) is sent to a process for preparing C1-C2 alkyl (meth)acrylates, which is a process for preparing methyl (meth)acrylate. More preferably, the process for preparing C1-C2 alkyl (meth)acrylates is selected from the group consisting of the C3 process and the C4 process. This process is known per se.

[0089] Therefore, according to the invention, it is preferred that at least part of the second top product stream obtained in step c) is sent to a process for preparing C1-C2 alkyl (meth)acrylates, wherein the process for preparing C1-C2 alkyl (meth)acrylates is selected from the group consisting of the C3 process and the C4 process.

[0090] If at least a part of the second top stream obtained in step c) is sent to a process for preparing a C1-C2 alkyl (meth)acrylate, the second top stream is generally mixed with a further stream comprising a C1-C2 alkyl (meth)acrylate, wherein the further stream is part of a process for preparing a C1-C2 alkyl (meth)acrylate, to obtain a mixed stream comprising at least a part of the second top stream and the further stream. The obtained mixed stream is then used in a process for preparing a C1-C2 alkyl (meth)acrylate to prepare a C1-C2 alkyl (meth)acrylate.

[0091] As described above, the second top stream contains isopropanol. For example, based on the total weight of the C1-C2 alkyl (meth)acrylate prepared in the process for preparing a C1-C2 alkyl (meth)acrylate, the second top stream contains up to 60 weight ppm, preferably up to 25 weight ppm of isopropanol.

[0092] Therefore, a method is also preferred in which the second top stream is sent to a process for preparing a C1-C2 alkyl (meth)acrylate, wherein the process for preparing a C1-C2 alkyl (meth)acrylate is carried out in a C1-C2 alkyl (meth)acrylate plant, and based on the total weight of the C1-C2 alkyl (meth)acrylate produced in the C1-C2 alkyl (meth)acrylate plant, the second top stream contains up to 60 weight ppm of isopropanol.

[0093] Unexpectedly, it has been found that although isopropanol is contained in the second top stream, a C1-C2 alkyl (meth)acrylate containing only a lower proportion of isopropyl (meth)acrylate can be prepared.

[0094] Accordingly, another subject of the present invention is also a process for preparing a C4-C 12 alkyl (meth)acrylate, wherein the process comprises the following steps:

[0095] a) reacting tetraisopropyl titanate with a C4-C 12 alcohol to obtain a first mixture comprising isopropanol and tetra-C4-C 12 alkyl titanate,

[0096] b) distilling the first mixture obtained in step a) to obtain a first top stream comprising isopropanol and a first bottom stream comprising tetra-C4-C 12 alkyl titanate,

[0097] c) reacting a C1-C2 alkyl (meth)acrylate with a C4-C 12React with an alcohol to obtain a second overhead stream and a second bottoms stream, wherein the catalyst mixture comprises tetra-C4-C 12 alkyl esters obtained in the first bottoms stream in step b) and 0.02 to 30% by weight of isopropoxide-coordinated titanium(IV) relative to the total weight of the catalyst mixture. The second overhead stream comprises C1-C2 alkyl (meth)acrylates, C1-C2 alcohols, and isopropanol. The second bottoms stream comprises a second mixture, which second mixture comprises tetra-C4-C 12 alkyl esters, C4-C 12 alkyl (meth)acrylates, C1-C2 alkyl (meth)acrylates, isopropyl (meth)acrylate, C4-C 12 alcohols, and C1-C2 alcohols.

[0098] d) Separate C4-C 12 alkyl (meth)acrylates from the second mixture.

[0099] e) Mix the second overhead stream obtained in step c) with an additional stream comprising C1-C2 alkyl (meth)acrylates, wherein the additional stream is part of a process for preparing C1-C2 alkyl (meth)acrylates, thereby obtaining a mixed stream comprising at least a portion of the second overhead stream and the additional stream.

[0100] f) React the mixed stream obtained in step e) in a process for preparing C1-C2 alkyl (meth)acrylates to obtain C1-C2 alkyl (meth)acrylates.

[0101] Additionally, the reaction in step c) of the process according to the invention can be carried out in the presence of at least one polymerization inhibitor. Suitable polymerization inhibitors are known to those skilled in the art and are, for example, hydroquinone monomethyl ether used in combination with oxygen, and hydroquinone used in combination with oxygen and / or tempol.

[0102] In the reaction of C1-C2 alkyl (meth)acrylates with C4-C 12 alcohols in the presence of the catalyst mixture, C4-C 12 alkyl (meth)acrylates are formed. At the same time, C1-C2 alcohols are formed. This reaction is also known as transesterification and is itself known to those skilled in the art. Isopropoxide-coordinated titanium(IV) comprised in the catalyst mixture also forms isopropyl (meth)acrylate.

[0103] The C1-C2 alcohol formed is generally selected from the group consisting of methanol and ethanol. It is clear to those skilled in the art that when methyl (meth)acrylate is used as the C1-C2 alkyl (meth)acrylate, methanol is generally formed as the C1-C2 alcohol. When ethyl (meth)acrylate is used as the C1-C2 alkyl (meth)acrylate, ethanol is generally formed as the C1-C2 alcohol.

[0104] Therefore, the second mixture obtained in step c) contains tetra C4-C 12 alkyl ester, C4-C 12 alkyl (meth)acrylate, C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, C4-C 12 alcohol and C1-C2 alcohol.

[0105] The C1-C2 alkyl (meth)acrylate contained in the second mixture is generally the unreacted C1-C2 alkyl (meth)acrylate. Similarly, C4-C 12 alcohol is the unreacted C4-C 12 alcohol.

[0106] For example, the second mixture contains

[0107] 0.01 to 1% by weight of tetra C4-C 12 alkyl ester,

[0108] 50 to 80% by weight of C4-C 12 alkyl (meth)acrylate,

[0109] 10 to 30% by weight of C1-C2 alkyl (meth)acrylate,

[0110] 0.005 to 0.05% by weight of isopropyl (meth)acrylate,

[0111] 5 to 25% by weight of C4-C 12 alcohol, and

[0112] 0.1 to 2% by weight of C1-C2 alcohol,

[0113] each based on the total weight of the second mixture.

[0114] In step d), the C4-C 12 alkyl (meth)acrylate is separated from the second mixture.

[0115] The C4-C 12 alkyl (meth)acrylate can be separated from the second mixture by methods known to those skilled in the art. Preferably, the C4-C 12 alkyl (meth)acrylate is separated from the second mixture by distillation.

[0116] For example, step d) includes the following step d1):

[0117] d1) Distilling the second mixture to obtain a third overhead stream and a third bottoms stream, the third overhead stream comprising a C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, a C1-C2 alcohol, and a C4-C 12 alcohol, and the third bottoms stream comprising tetra-C4-C 12 alkyl titanate and a C4-C 12 alkyl (meth)acrylate.

[0118] Accordingly, the following method is also preferred, wherein step d) includes the following step d1):

[0119] d1) Distilling the second mixture to obtain a third overhead stream and a third bottoms stream, the third overhead stream comprising a C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, a C1-C2 alcohol, and a C4-C 12 alcohol, and the third bottoms stream comprising tetra-C4-C 12 alkyl titanate and a C4-C 12 alkyl (meth)acrylate.

[0120] The distillation in step d1) is carried out, for example, in a second distillation column. The components of the third overhead stream have a lower boiling point than the C4-C 12 alkyl (meth)acrylate and are separated therefrom. Accordingly, the second distillation column is also referred to as a low boilers distillation column. 12 alkyl (meth)acrylate.

[0121] The second mixture is generally transferred, preferably continuously, to the second distillation column after step c) and distilled therein according to step d1).

[0122] The distillation in step d1) is generally carried out at a temperature in the range from 70 to 150 °C.

[0123] The distillation in step d1) is preferably carried out under reduced pressure, in particular at a pressure in the range from 5 mbar to 200 mbar.

[0124] The third overhead stream obtained in step d1) can, for example, be fed back to step c) of the process according to the invention. Thereby, the C1-C2 alkyl (meth)acrylate comprised in the third overhead stream and the C4-C 12 alcohol comprised in the third overhead stream can react according to step c), so that resources can be saved and the overall conversion of the process according to the invention can be carried out substantially completely.

[0125] It is also possible that at least part of the third top stream is sent to a process for preparing a C1-C2 alkyl (meth)acrylate.

[0126] Therefore, the following process according to the invention is also preferred, in which the third top stream is directed back to step c) and / or sent to a process for preparing a C1-C2 alkyl (meth)acrylate.

[0127] Preferably, the third top stream is directed back to step c) of the process according to the invention.

[0128] The third bottom stream obtained in step d1) preferably contains more than 98% by weight of a C4-C 12 alkyl (meth)acrylate.

[0129] If the reaction in step c) is carried out in the presence of at least one polymerization inhibitor, the third bottom stream generally also contains said at least one polymerization inhibitor.

[0130] Therefore, preferably, the third bottom stream contains a C4-C 12 alkyl (meth)acrylate, tetra-C4-C 12 alkyl titanate and said at least one polymerization inhibitor. In addition, the third bottom stream may for example contain titanium dioxide (TiO2), which may be formed in the reaction of tetra-C4-C 12 alkyl titanate with water. In addition, the C1-C2 alkyl (meth)acrylate and / or the C4-C 12 alkyl (meth)acrylate may react with each other to obtain a poly(alkyl (meth)acrylate). Therefore, the third bottom stream may additionally contain a poly(alkyl (meth)acrylate).

[0131] According to the invention, it is preferred that the following step d2) is carried out after step d1):

[0132] d2) Distilling the third bottom stream obtained in step d1) to obtain a fourth top stream containing a C4-C 12 alkyl (meth)acrylate and a fourth bottom stream containing tetra-C4-C 12 alkyl titanate.

[0133] Therefore, the following process according to the invention is also preferred, in which the following step d2) is carried out after step d1):

[0134] d2) Distilling the third bottom stream obtained in step d1) to obtain a fourth top stream containing a C4-C 12 alkyl (meth)acrylate and a fourth bottom stream containing tetra-C4-C 12 alkyl titanate.

[0135] The distillation in step d2) is carried out, for example, in a third distillation column. The (meth)acrylic acid C4-C 12 alkyl ester is obtained in the top stream of the fourth column. The components of the bottom stream of the fourth column have a higher boiling point than the (meth)acrylic acid C4-C 12 alkyl ester and are separated therefrom. Therefore, the third distillation column is also referred to as a high-boiler distillation column. 12

[0136]

[0136] The bottom stream of the third column obtained in step d1) is usually continuously transferred to the third distillation column and distilled there according to step d2).

[0137] The distillation in step d2) is usually carried out at a temperature in the range of 70 to 150 °C.

[0138] The distillation in step d2) is preferably carried out under reduced pressure, in particular at a pressure in the range of 5 mbar to 200 mbar.

[0139] The distillation in step d2) can include thin-film evaporation. Suitable thin-film evaporators are known per se and are selected, for example, from the group consisting of falling-film evaporators, thin-layer evaporators and short-path evaporators.

[0140] The bottom stream of the fourth column obtained in step d2) contains tetra-C4-C 12 alkyl titanate. Preferably, the bottom stream of the fourth column is led back to step c). This makes the process according to the invention particularly economical.

[0141] Therefore, the following process is also preferred, in which the bottom stream of the fourth column is led back to step c).

[0142] It can be purified before the bottom stream of the fourth column is led back to step c), for example, in a vacuum evaporation stage. Such vacuum evaporation stages are known per se and are, for example, thin-film evaporators such as falling-film evaporators, thin-layer evaporators and / or short-path evaporators.

[0143] In the vacuum evaporation stage, the residual (meth)acrylic acid C4-C 12 alkyl ester contained in the bottom stream of the fourth column can also be removed therefrom, which further increases the yield of the (meth)acrylic acid C4-C 12 alkyl ester.

[0144] The (meth)acrylic acid C4-C 12 alkyl ester is separated off in step d). Particularly preferably, the (meth)acrylic acid C4-C 12 alkyl ester is obtained in the top stream of the fourth column in step d2).

[0145] “(meth)acrylic acid C4-C 12The "alkyl ester" is understood to be an alkyl ester of (meth)acrylic acid having 4 to 12 carbon atoms in the alkyl residue. The alkyl residue can be cyclic or straight-chain, and can also be a branched group. The alkyl residue having 4 to 12 carbon atoms can also be substituted by heteroatoms within the alkyl residue.

[0146] For example, C4-C 12 alkyl esters of (meth)acrylic acid are selected from the group consisting of n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, isodecyl (meth)acrylate, and lauryl (meth)acrylate.

[0147] It goes without saying that the alkyl residue having 4 to 12 carbon atoms is derived from the C4-C 12 alcohol that reacts in step c).

[0148] Thus, if, for example, isobutanol reacts as the C4-C 12 alcohol in step c), the resulting C4-C 12 alkyl ester of (meth)acrylic acid is isobutyl (meth)acrylate. Correspondingly, when cyclohexanol reacts as the C4-C 12 alcohol, the resulting C4-C 12 alkyl ester of (meth)acrylic acid is, for example, cyclohexyl (meth)acrylate.

[0149] Steps a) to d) can be carried out discontinuously or continuously. Within the scope of the present invention, "discontinuous" is understood to mean that the method according to the present invention is interrupted between at least two of steps a) to d). For example, the method according to the present invention can be interrupted between steps b) and c). The first bottoms stream obtained in step b) can, for example, be canned and only subsequently fed to the reaction in step c).

[0150] If steps a) to d) are carried out discontinuously, the method according to the present invention is also referred to as a batch process or a batch method.

[0151] Preferably, steps a) to d) are carried out continuously.

[0152] Therefore, the following method according to the present invention is also preferred, in which steps a) to d) are carried out continuously.

[0153] Within the scope of the present invention, "continuous" is understood to mean that steps a) to d) are carried out without interruption. Within the scope of the present invention, semi-continuous implementation also falls within the scope of the term "continuous". For example, it is possible to carry out steps a) and b) in a batch reactor, but directly transfer the first bottoms stream therefrom to step c). Within the scope of the present invention, this mode of implementation also falls within the scope of the term "continuous".

[0154] Especially in the case of continuously implementing the method according to the present invention, all reactants are continuously fed to the respective different method steps, while all products or product mixtures are continuously withdrawn from the method steps and optionally transferred to the next method step.

[0155] The method according to the present invention will be explained in detail below with the aid of examples, without limiting the method according to the present invention to these examples. Description of the Drawings

[0156] List of Reference Numerals:

[0157] 1a Reactor

[0158] 1b Azeotropic Column

[0159] 2 Low-Boiling Column

[0160] 3 High-Boiling Column

[0161] 4 C3 High-Boiling Column

[0162] 5 C3 Esterification Reactor

[0163] 6 C3 Extraction Reactor

[0164] 7 C3 Low-Boiling Column

[0165] 8 C3 Purification Unit

[0166] 9 C4 Methacrylic Acid Purification Unit

[0167] 10 C4 Esterification Reactor

[0168] 11 C4 Methacrylic Acid Recovery Unit

[0169] 12 C4 Dehydration Unit

[0170] 13 C4 Purification Unit

[0171] 14 C4 Methanol Recovery Unit

[0172] 101 Methyl Methacrylate (MMA) Stream

[0173] 102 n-Butanol Stream

[0174] 103 Catalyst Mixture Stream

[0175] 104 Second Top Stream

[0176] 105 Second Bottom Stream

[0177] 106 Third Top Stream

[0178] 107 Third Bottom Stream

[0179] 108 Fourth top tower stream

[0180] 109 Fourth bottom tower stream

[0181] 110 Methacrylamide stream

[0182] 111 Methanol

[0183] 112 Steam

[0184] 113 C3 - First top tower stream

[0185] 114 C3 - First bottom tower stream

[0186] 115 C3 - Second top tower stream

[0187] 116 C3 - Second bottom tower stream

[0188] 117 C3 - Third top tower stream

[0189] 118 C3 - Third bottom tower stream

[0190] 119 C3 - Fourth top tower stream

[0191] 120 C3 - Fourth bottom tower stream

[0192] 121 C3 - Fifth top tower stream (MMA)

[0193] 122 C3 - Fifth bottom tower stream

[0194] 123 Water

[0195] 124 C4 - First top tower stream

[0196] 125 C4 - First bottom tower stream

[0197] 126 C4 - Product stream

[0198] 127 C4 - Second top tower stream

[0199] 128 C4 - Second bottom tower stream

[0200] 129 C4 - Third top tower stream

[0201] 130 C4 - Third bottom tower stream

[0202] 131 C4 - Fourth top tower stream

[0203] 132 C4 - Fourth bottom tower stream

[0204] 133 C4 - Fifth top tower stream

[0205] 134 C4 - Bottom Material Flow of the Fifth Tower

[0206] 135 Methacrylic Acid

[0207] 136 Sulfuric Acid

[0208] Figure 1 Schematically shows the equipment for synthesizing n - butyl methacrylate. The methyl methacrylate (MMA) feed stream 101 and the catalyst mixture feed stream 103 are sent to the reactor 1a with an azeotropic tower 1b. The methyl methacrylate (MMA) feed stream 101 may include MMA led back from the low - boiling tower 2. The n - butanol feed stream 102 is sent to the reactor 1a via the azeotropic tower 1b. In the reactor 1a, methyl methacrylate (MMA) 101 reacts with n - butanol 102 in the presence of the catalyst mixture 103. The obtained second overhead stream 104 is separated via the azeotropic tower 1b, and the second bottom stream 105 including the second mixture is transferred to the low - boiling tower 2. The third overhead stream 106 is separated in the low - boiling tower, and the third bottom stream 107 is transferred to the high - boiling tower 3. There, n - butyl methacrylate is separated as the fourth overhead stream 108. The fourth bottom stream 109 containing the catalyst mixture 103 can be at least partially led back to the reactor 1a.

[0209] Figure 2 Shows a part of the equipment for preparing C3 methyl methacrylate. The methacrylamide feed stream 110, methanol 111, steam 112, sulfuric acid 136 and the second overhead stream 104 from the equipment according to Figure 1 are sent to the C3 esterification reactor 5 and made to react. Here, the C3 first overhead stream 113 and the C3 first bottom stream 114 are obtained. The C3 first bottom stream 113 is transferred to the C3 high - boiling tower 4 and distilled there to obtain the C3 second overhead stream 115 and the C3 second bottom stream 116. The C3 second overhead stream 115 is transferred to the C3 extraction reactor 6. Water 123 is added thereto and the C3 third overhead stream is obtained, and the third overhead stream is transferred to the C3 low - boiling tower 7. The C3 third bottom stream 118 is also obtained. It is led back to the C3 esterification reactor 5. In the C3 low - boiling tower 7, the low - boiling substances are separated as the C3 fourth overhead stream 119 and partially led back to the C3 esterification reactor 5. The obtained C3 fourth bottom stream is transferred to the C3 purification device 8, where methyl methacrylate (MMA) 121 is obtained as the C3 fifth overhead stream. The C3 fifth bottom stream 122 can be at least partially led back to the C3 esterification reactor 5.

[0210] Figure 3Shows a part of the C4 methyl methacrylate production equipment. In the C4 methacrylic acid purification device 9, the methacrylic acid 135 is purified to obtain the C4 first top stream 124 and the C4 first bottom stream 125. At least part of the C4 first top stream 124 is transferred to the C4 esterification reactor 10 and mixed with the second top stream 104 from the equipment according to Figure 1 In the esterification reactor 10, the C4 product stream 126 is obtained. It is transferred to the C4 methacrylic acid recovery device 11. There, the C4 second top stream 127 and the C4 second bottom stream 128 are obtained. The C4 second bottom stream 128 is led back to the C4 methacrylic acid purification device 9, and the C4 second top stream 127 is transferred to the C4 dehydration device 12. There, the C4 third bottom stream 130 and the C4 third top stream 129 are obtained. The C4 third bottom stream 130 is transferred to the C4 purification device 13 to obtain the C4 fourth top stream 131 containing methyl methacrylate and the C4 fourth bottom stream 132. It can be led back to the C4 methacrylic acid recovery device 11. A part of the C4 second top stream can be transferred to the C4 methanol recovery device 14. Detailed Description of the Invention

[0211] Examples

[0212] Examples 1 and 2: Simulation of the Preparation of n-Butyl Methacrylate

[0213] The synthesis of n-butyl methacrylate was simulated. Figure 1 The device shown in was used as the basis for the simulation. The parameters of the reactor 1a with the azeotrope column 1b, the low-boiling column 2 and the high-boiling column 3 are given in Table 1.

[0214] The reaction material streams used and their compositions are given in Table 2. n-Butanol was used as the C4-C 12 alcohol, and methyl methacrylate was used as the C1-C2 alkyl (meth)acrylate. The catalyst mixture contains tetra-n-butyl titanate and tetra-isopropyl titanate. Table 3 gives the obtained intermediate product streams and product streams.

[0215] Table 1

[0216]

[0217] Table 2

[0218]

[0219] Table 3

[0220] Unit Example 1 Example 2 Second Top Product Stream 104 kg / h 1277 593 Methanol wt% 78.6 78.6 Methyl Methacrylate wt% 21.3 21.3 Isopropyl Alcohol wt ppm 1057 529 Isopropyl Methacrylate wt ppm 0 0 n-Butanol wt ppm 2 2 n-Butyl Methacrylate wt ppm 2 2 Second Bottom Product Stream (Second Mixture) 105 kg / h 7285 3384 Methanol wt% 0.7 0.7 Methyl Methacrylate wt% 18.9 18.9 Isopropyl Alcohol wt ppm 23 12 Isopropyl Methacrylate wt ppm 144 72 n-Butanol wt% 12.2 12.2 n-Butyl Methacrylate wt% 67.7 67.7 Catalyst Mixture wt% 0.4 0.4 Third Top Product Stream 106 kg / h 2345 1090 Methanol wt% 2.1 2.1 Methyl Methacrylate wt% 38.0 38.0 Isopropyl Alcohol wt ppm 73 36 Isopropyl Methacrylate wt ppm 444 222 n-Butanol wt% 38.0 38.0 n-Butyl Methacrylate wt% 1.1 1.1 Fourth Top Product Stream 108 kg / h 4453 2069 n-Butyl Methacrylate wt% 99.99 99.99 n-Butanol wt ppm 15 15 Isopropyl Methacrylate wt ppm 2 2

[0221] Example 3: Simulation - Redirecting the Second Top Product Stream Back into the C3 Process

[0222] In the simulation, the second top stream obtained in Example 1 was directed back into the C3 process for the preparation of methyl methacrylate. Figure 2 The apparatus shown in was used as the basis for the simulation. The parameters of the individual reactors and columns are given in Table 4.

[0223] The reaction feed streams used and their compositions are given in Table 5, and the product streams obtained are given in Table 6.

[0224] Table 4

[0225]

[0226] Table 5

[0227]

[0228] Table 6

[0229]

[0230] Example 4: Simulation - Redirecting the Second Top Product Stream Back into the C4 Process

[0231] In the simulation, the second top stream obtained in Example 2 was directed back into the C4 process for the preparation of methyl methacrylate. Figure 3 The apparatus shown in was used as the basis for the simulation. The parameters of the individual reactors and columns are given in Table 7.

[0232] The reaction feed streams used and their compositions are given in Table 8, and the product streams obtained are given in Table 9.

[0233] Table 7

[0234]

[0235] Table 8

[0236]

[0237] Table 9

[0238]

[0239] Comparative Example 5: Reaction Time of Pure Tetraethylhexyl Titanate Catalyst

[0240] A total of 200 g of 2-ethylhexanol and methyl methacrylate (MMA) were mixed in a stoichiometric ratio of 1:1. 0.5 g of tetraethylhexyl titanate was added to this mixture as a catalyst.

[0241] The obtained mixture was divided into 12 boxes, each box containing 10 g of the mixture. These boxes were simultaneously placed in a hot bath at 130 °C. After the times given in Table 10, one box was taken out of the hot bath, cooled in an ice bath and the mass ratio of each component was determined by means of GC (calibrated column).

[0242] The mass ratios of the individual components are given in Table 10, the % given being % by weight.

[0243] Table 10

[0244]

[0245] Example 6: Reaction Time of the Catalyst Mixture

[0246] A total of 200 g of 2-ethylhexanol and methyl methacrylate (MMA) were mixed in a stoichiometric ratio of 1:1. To this mixture was added a mixture of 0.35 g of tetraethylhexyl titanate and 0.15 g of tetra-isopropyl titanate as the catalyst mixture.

[0247] The obtained mixture was divided into 12 boxes, each box containing 10 g of the mixture. These boxes were simultaneously placed in a hot bath at 130 °C. After the times given in Table 11, one box was taken out of the hot bath, cooled in an ice bath and the mass ratio of each component was determined by means of GC (calibrated column).

[0248] The mass ratios of the individual components are given in Table 11, the % given being % by weight.

[0249] Table 11

[0250]

[0251] In Figure 4 the change in the ratio of 2-ethylhexyl methacrylate over time is plotted for Comparative Example 5 and Example 6. It can clearly be seen that the reaction in Example 6 according to the invention proceeds faster than in Comparative Example 5.

Claims

1. A method for preparing a C4-C 12 alkyl (meth)acrylate, wherein the method comprises the following steps a) to d): a) Reacting tetraisopropyl titanate with a C4-C 12 alcohol to obtain a first mixture comprising isopropanol and tetra C4-C 12 alkyl titanate, b) Distilling the first mixture obtained in step a) to obtain a first overhead stream comprising isopropanol and a first bottom stream comprising tetra C4-C 12 alkyl titanate, c) Reacting a C1-C2 alkyl (meth)acrylate with a C4-C 12 alcohol in the presence of a catalyst mixture, the catalyst mixture comprising the tetra C4-C 12 alkyl titanate obtained in the first bottom stream in step b) and titanium(IV) coordinated with isopropoxide in an amount of 0.02 to 30% by weight based on the total weight of the catalyst mixture, the second mixture comprising tetra C4-C 12 alkyl titanate, C4-C 12 alkyl (meth)acrylate, C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, C4-C 12 alcohol and C1-C2 alcohol, d) Separating the C4-C 12 alkyl (meth)acrylate from the second mixture.

2. The method according to claim 1, characterized in that, In step c), a second top stream and a second bottom stream are obtained in the reaction, the second top stream comprising a C1-C2 alkyl (meth)acrylate, a C1-C2 alcohol and isopropanol, and the second bottom stream comprising the second mixture.

3. The method according to claim 2, characterized in that, The obtained second top stream is directed back to step c) and / or sent to a process for preparing a C1-C2 alkyl (meth)acrylate.

4. The method according to claim 2 or 3, characterized in that, The second top stream is sent to a process for preparing a C1-C2 alkyl (meth)acrylate, wherein the process for preparing a C1-C2 alkyl (meth)acrylate is carried out in a C1-C2 alkyl (meth)acrylate plant, and the second top stream comprises up to 60 weight ppm of isopropanol, based on the total weight of the C1-C2 alkyl (meth)acrylate produced in the C1-C2 alkyl (meth)acrylate plant.

5. The method according to any one of claims 1 to 4, characterized in that, Based on the total weight of the first bottom stream, the first bottom stream obtained in step b) further comprises 0.02 to 30 weight % of titanium(IV) coordinated with isopropoxide.

6. The method according to claim 5, characterized in that, The first bottom stream obtained in step b) is used as a catalyst mixture in step c).

7. The method according to any one of claims 1 to 6, characterized in that, C4-C in steps a) and c) 12 The alcohol is selected from the group consisting of n-butanol, isobutanol, and 2-ethylhexanol.

8. The method according to any one of claims 1 to 7, characterized in that, Steps a) to d) are carried out continuously.

9. The method according to any one of claims 1 to 8, characterized in that, Step d) comprises the following step d1): d1) Distill the second mixture to obtain a third top stream and a third bottom stream, the third top stream comprising a C1-C2 alkyl (meth)acrylate, isopropyl (meth)acrylate, a C1-C2 alcohol, and a C4-C 12 alcohol, and the third bottom stream comprising a tetra-C4-C 12 alkyl titanate and a C4-C 12 alkyl (meth)acrylate.

10. The method according to claim 9, wherein, The third top stream is directed back to step c) and / or sent to a process for preparing a C1-C2 alkyl (meth)acrylate.

11. The method according to claim 9 or 10, wherein, Following step d1), the following step d2) is carried out: d2) Distill the third bottoms stream obtained in step d1) to obtain a fourth overhead stream comprising (meth)acrylic acid C4-C 12 alkyl esters and a fourth bottoms stream comprising tetra C4-C 12 alkyl titanates.

12. The method according to claim 11, wherein, The fourth bottom stream is directed back to step c).

13. The method according to any one of claims 1 to 12, wherein, The distillation in step b) is carried out simultaneously with the reaction in step a).

14. The method according to any one of claims 1 to 12, wherein, The C1-C2 alkyl (meth)acrylate is methyl (meth)acrylate.

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