Process for production of a (METH)acrylate

Abstract

The invention is directed to a process for production of a (meth)acrylate, wherein an alcohol or an alkene, and a (meth)acrylic compound are converted into the (meth)acrylate in presence of a catalyst, wherein the (meth)acrylate is present in a vessel and the vessel contains a gaseous phase and a liquid phase, wherein the liquid phase comprises the (meth)acrylate and optionally the alcohol or the alkene, the (meth)acrylic compound and / or the catalyst, and the gaseous phase comprises less than 0.1 mol.-% of oxygen, based on the total gaseous phase. The invention is further directed to the use of the (meth)acrylate and a system for production thereof.

Description

[0001] 231505

[0002] 1

[0003] Process for production of a (meth)acrylate

[0004] Description

[0005] The invention relates to a process for production of a (meth)acrylate, wherein an alcohol or an alkene, and a (meth)acrylic acid compound are converted into the (meth)acrylate in presence of a catalyst. The (meth)acrylate is present in a vessel, which contains a gaseous phase and a liquid phase comprising the (meth)acrylate.

[0006] (Meth)acrylates, also referred to as (meth)acrylic esters, can be produced for example by esterification of (meth)acrylic acid with alcohols or alkenes, or from (meth)acryl ic acid anhydride and an alcohol, in the presence of esterification catalysts. Such processes are known for example from the articles Acrylic Acid and Derivatives in Kirk- Othmer Encyclopedia of Chemical Technology, Wiley, 2002, https: / / doi.org / 10.1002 / 0471238961.0103182502012105.a01.pub2 and Methacrylic Acid and Derivatives in Kirk- Othmer Encyclopedia of Chemical Technology, Wiley, 2003, https: / / doi.org / 10.1002 / 0471238961.1305200807181519.a01.pub2.

[0007] Further, the (meth)acrylates can be produced by transesterification from a reactant (meth)acrylate, also referred to as starting (meth)acrylate, with an alcohol.

[0008] Polymers and copolymers prepared on the basis of (meth)acrylates in form of polymer dispersions are of significance and in use, for example, as adhesives or paints or as textile, leather and paper auxiliaries.

[0009] It is known that polymerizable compounds such as (meth)acrylates can be easily polymerized, for instance by heat or reaction of light or peroxides. Soiling of apparatuses, blockage of pipes and pumps and fouling of column trays or internals and heat exchanger surfaces are the result of polymer formation. Cleaning of the plants is a complicated procedure which is expensive owing to, for example, the downtimes and is environmentally polluting, for example because of the resulting wastewater from cleaning. The yield and the availability of the plants (time-on-stream) are thus also reduced.

[0010] Since polymerization has to be reduced or prevented for safety and technical reasons when preparing, working up and / or storing (meth) acrylates, there is a constant need for novel, simple and effective methods for reducing the polymerization.

[0011] Typically, polymerization of (meth)acrylates is suppressed by using polymerization inhibitors in combination with oxygen-containing gases as described and recommended in for example US 7700804 B2, EP 2197827 B1 and DE 10 2004 003 733 A1.

[0012] The European Basic Acrylic Monomer Group (EBAM), in the Guidelines for “Safe Handling and Storage of Acrylic Esters”, Third Edition, February 18, 2015, even lists inert gases with less than 5 vol.-% of oxygen as incompatible substance towards acrylic esters as provoking destabilization of the monomers.

[0013] It was an object of the present invention to provide an improved process for stabilization of (meth)acrylates in presence of a gas phase.

[0014] The object is achieved by a process for production of a (meth)acrylate, wherein an alcohol or an alkene, and a (meth)acrylic compound are converted into the (meth)acrylate in presence of a catalyst, wherein the (meth)acrylate is present in a vessel and the vessel contains a gaseous phase and a liquid phase, wherein the liquid phase comprises the (meth)acrylate and optionally the alcohol or the alkene, the (meth)acry I ic compound and / or the catalyst, and the gaseous phase comprises less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

[0015] The invention further relates to the use of the (meth)acrylate produced by the process according to the invention for production of coatings, films, paints, adhesives, plastics, resins, dispersions, rubber, sealants and / or oil drilling fluids.

[0016] The problem is further solved by a system for production of a (meth)acrylate comprising a vessel, wherein an alcohol or an alkene, and a (meth)acrylic compound are converted into the (meth)acrylate in presence of a catalyst, wherein the (meth)acrylate is present in the vessel and the vessel contains a gaseous phase and a liquid phase, wherein the liquid phase comprises the (meth)acrylate and optionally the alcohol or the alkene, the (meth)acrylic compound and / or the catalyst, and the gaseous phase comprises less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

[0017] Preferably, the gaseous phase comprises an inert gas. The gaseous phase comprises for example at least 30 mol.- % or at least 50 mol.-%, preferably at least 85 mol.-%, in particular at least 90 mol.-%, of the inert gas, based on the total gaseous phase. The inert gas is in particular inert towards the (meth)acrylate under the conditions prevailing in the vessel. The inert gas may be for example nitrogen, helium, argon, lower hydrocarbons or their mixtures. Preferably, the inert gas is nitrogen and / or argon. 231505

[0018] 2

[0019] Preferably, the gaseous phase comprises less than 0.05 mol.-%, more preferably less than 0.01 mol.-%, even more preferably less than 0.005 mol.-% of oxygen, even more preferably less than 0.0001 mol.-% of oxygen, based on the total gaseous phase. Preferably, the gaseous phase comprises 0.00 mol.-% to 0.10 mol.-%, more preferably 0.00 mol.-% to 0.05 mol.-%, even more preferably 0.00 mol.-% to 0.01 mol.-%, even more preferably 0.000 mol.-% to 0.005 mol.-% of oxygen, even more preferably 0.0000 mol.-% to 0.0001 mol.-% of oxygen, based on the total gaseous phase. For example, the gaseous phase comprises 0.0001 mol.-% to 0.10 mol.-%, more preferably 0.0001 mol.-% to 0.05 mol.-%, even more preferably 0.0001 mol.-% to 0.01 mol.-%, even more preferably 0.0001 mol.-% to 0.005 mol.-% of oxygen, based on the total gaseous phase, or the gaseous phase comprises 0.001 mol.-% to 0.10 mol.-%, more preferably 0.001 mol.-% to 0.05 mol.-%, even more preferably 0.001 mol.-% to 0.01 mol.-%, even more preferably 0.001 mol.-% to 0.005 mol.-% of oxygen, based on the total gaseous phase. Particularly, oxygen is absent in the gaseous phase.

[0020] By the defined composition of the gaseous phase with highly reduced oxygen content or absence of oxygen, respectively, the (meth)acrylate is stabilized effectively.

[0021] Preferably, the gaseous phase comprises or consists of, based on the total gaseous phase, 50.00 mol.-% to 99.50 mol.-% of the inert gas, 0.00 mol.-% to 1.00 mol.-% of the (meth)acrylate, 0.00 mol.-% to 10.00 mol.-% of the (meth)acrylic compound, 0.50 mol.-% to 30.00 mol.-% of the alcohol or the alkene, 0.00 mol.-% to 10.00 mol.-% of water, 0.00 mol.-% to 1.00 mol.-% of the catalyst, 0.00 mol.-% to 1.00 mol.-% of a polymerization inhibitor and 0.00 mol.-% to 1.00 mol.-% of remainder.

[0022] More preferably, the gaseous phase comprises or consists of, based on the total gaseous phase, 85.00 mol.-% to 99.40 mol.-% of the inert gas, 0.00 mol.-% to 1.00 mol.-% of the (meth)acrylate, 0.00 mol.-% to 2.00 mol.-% of the (meth)acrylic compound, 0.50 mol.-% to 14.00 mol.-% of the alcohol or the alkene, 0.10 mol.-% to 10.00 mol.-% of water, 0.00 mol.-% to 1.00 mol.-% of the catalyst, 0.00 mol.-% to 1.00 mol.-% of a polymerization inhibitor and 0.00 mol.-% to 1.00 mol.-% of remainder.

[0023] Preferably, a stream of the inert gas is added to the gaseous phase and / or the liquid phase in the vessel, in particular continuously. The stream of the inert gas is preferably added to the gaseous phase and / or the liquid phase at a flow rate in a range from 20 L / min to 300 L / min. More preferably, the stream of the inert gas is added to the gaseous phase and / or the liquid phase in the vessel during conversion and / or purification of the (meth)acrylate.

[0024] The alcohol comprises preferably 1 to 22, more preferably 1 to 20, carbon atoms. The alcohol can be a mixture of alcohols comprising 10 to 20 carbon atoms, preferably 13 to 15 carbon atoms. The alcohol is preferably selected from the group consisting of methanol, ethanol, propanol, n-pentanol, 1 -methyl butanol, glycerin, isopropyliden glycerin, butanol such as tert-butanol, n-butanol or 2-methyl butanol; n-hexanol, cyclohexanol, 2-ethylhexanol, 2- hydroxyethanol, n-heptanol, n-octanol, 2-octanol, n-nonanol, n-decanol, n-undecanol, dodecanol such as n- dodecanol, n-tridecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, octadecan-1 -ol, docosan-1-ol, isodecanol, isotridecanol and 1-(2-hydroxyethyl)-2-imidazolidinone. In particular, the alcohol is selected from the group consisting of methanol, butanol, in particular tert-butanol or n-butanol, cyclohexanol, 2-ethylhexanol, 2-hydroxyethanol, dodecanol, octadecan-1 -ol, docosan-1-ol, isodecanol, isotridecanol, behenyl polyethylene glycol, stearyl polyethylene glycol and 1-(2-hydroxyethyl)-2-imidazolidinone, and mixtures thereof. More preferably, the alcohol is selected from the group consisting of tert-butanol, cyclohexanol and methanol.

[0025] The alkene is preferably isobutene.

[0026] Here and throughout the specification, the term “(meth)acryl” includes both acryl and / or methacryl groups. Hence, for example the term “(meth)acrylate” includes acrylate and / or methacrylate and the term “(meth)acrylic acid” includes acrylic acid and / or methacrylic acid.

[0027] Preferably, the (meth)acrylic compound is a reactant (meth)acrylate, (meth)acrylic acid, or (meth)acrylic acid anhydride, in particular a reactant (meth)acrylate or (meth)acrylic acid, for example (meth)acrylic acid. The reactant (meth)acrylate is different from the (meth)acrylate which is produced by the inventive process. The (meth)acrylate can be produced by the inventive process from the reactant (meth)acrylate. More preferably the (meth)acrylic compound is a reactant methacrylate, methacrylic acid, or methacrylic acid anhydride, in particular a reactant methacrylate or methacrylic acid, for example methacrylic acid. 231505

[0028] 3

[0029] In many cases, the (meth)acrylate is formed by conversion of the alcohol, or alternatively the alkene, with (meth)acrylic acid. In another embodiment, the alcohol and the reactant (meth)acrylate are converted into the (meth)acrylate by means of transesterification. The reactant (meth)acrylate is preferably methyl (meth)acrylate or ethyl (meth)acrylate. In case of transesterification, the alcohol comprises preferably at least one more carbon atom than the alcohol constituents in the reactant (meth)acrylate.

[0030] The (meth)acrylate is preferably a Ci-C22-alkyl (meth)acrylate, more preferably a Ci-C2o-alkyl (meth)acrylate.

[0031] The prefixes Cn-Cmused in connection with compounds or molecular moieties each indicate a range for the number of possible carbon atoms that a molecular moiety or a compound can have. The term Ci-Cnalkyl denominates a group of linear, branched or cyclic saturated hydrocarbon radicals having from 1 to n carbon atoms. The term C1-C22 alkyl denominates a group of linear, branched or cyclic saturated hydrocarbon radicals with 1 to 22 carbon atoms.

[0032] The (meth)acrylate can be a Cie-C22-alkyl (meth)acrylate, which in turn is for example a Cie-Cis-alkyl (meth)acrylate with an alkyl chain of 16 to 18 carbon atoms, in particular of 16 and / or 18 carbon atoms. The Cie-Cis-alkyl (meth)acrylate is, in particular, octadecan-1 -yl (meth)acrylate and / or hexadecan-1 -yl (meth)acrylate, especially octadecan- 1-y I (meth)acrylate or a mixture of octadecan-1 -yl (meth)acrylate and hexadecan-1 -yl (meth)acrylate. The Cie-C22-alkyl (meth)acrylate can consist of octadecan-1 -yl (meth)acrylate. Stearyl (meth)acrylate is an abbreviation for stearyl acrylate and / or stearyl methacrylate. Stearyl (meth)acrylate is understood to be a Cis-alkyl (meth)acrylate with an alkyl chain having 18 carbon atoms. Stearyl (meth)acrylate can be produced for example by esterification as described in JP 2007 / 001886 A or by transesterification as described in DE 2317226 A1.

[0033] Preferably, the (meth)acrylate is a methacrylate. More preferably, the (meth)acrylate, in particular the methacrylate, is chosen from the group consisting of tert-butyl methacrylate (tBMA), cyclohexyl methacrylate (CHMA), 2-ethylhexyl methacrylate (EHMA), n-butyl methacrylate (nBMA), 2-hydroxyethyl methacrylate (HEMA), lauryl methacrylate (also referred to as dodecyl methacrylate), stearyl methacrylate, behenyl methacrylate (comprising C18, C20 and C22-alkyl methacrylates), isodecyl methacrylate, isotridecyl methacrylate, ureido methacrylate, behenyl polyethyleneglycol methacrylate (BEPEGMA), stearyl polyethyleneglycol methacrylate (SPEGMA) and methyl methacrylate (MMA) and mixtures thereof; for example chosen from the group consisting of tert-butyl methacrylate (tBMA), cyclohexyl methacrylate (CHMA), 2-ethylhexyl methacrylate (EHMA), 2-hydroxyethyl methacrylate (HEMA), lauryl methacrylate (also referred to as dodecy methacrylate), stearyl methacrylate, behenyl methacrylate (comprising Cis, C20 and C22- alkyl methacrylates), isodecyl methacrylate, isotridecyl methacrylate, ureido methacrylate, behenyl polyethyleneglycol methacrylate (BEPEGMA), stearyl polyethyleneglycol methacrylate (SPEGMA) and methyl methacrylate (MMA) and mixtures thereof; preferably from tert-butyl methacrylate (tBMA), cyclohexyl methacrylate (CHMA) and / or methyl methacrylate (MMA).

[0034] Preferably, the liquid phase comprises a polymerization inhibitor.

[0035] Examples of useful polymerization inhibitors include in general phenolic compounds, amines such as aromatic amines, phenylenediamines and hydroxyl amines; nitro compounds, phosphorus or sulfur compounds, N-oxyls and inorganic salts, and also optionally mixtures thereof. Preference is given to polymerization inhibitors such as phenothiazine, N-oxyls and phenolic compounds.

[0036] Examples of N-oxyls (understood as nitroxyl or N-oxyl radicals, i.e. compounds containing at least one N-0 group) include 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine N-oxyl, 4-acetoxy-2, 2,6,6- tetramethylpiperidine N-oxyl, 2,2,6,6-tetramethylpiperidine N-oxyl or 3-oxo-2,2,5,5-tetramethylpyrrolidine N-oxyl.

[0037] Examples of phenolic compounds include alkylphenols, for example 0-, m- or p-cresol (methylphenol), 2-tert-butyl-4- methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tertbutylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol or 2,2'-methylenebis(6-tert-butyl-4- methylphenol), 4,4'-oxybiphenol, 3,4-methylenedioxyphenol (sesamol), 3,4-dimethylphenol, hydroquinone, catechol (1 ,2-dihydroxybenzene), 2-(T-methylcyclohex-T-yl)-4,6-dimethylphenol, 2- or 4-(1 '-phenyleth-1 '-yl)phenol, 2-tert- butyl-6-methylphenol, 2,4,6-tris-tert-butylphenol, 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, 4-tert-butylphenol, nonylphenol, octylphenol, 2,6-dimethylphenol, bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol S, 3,3',5,5'-tetrabromobisphenol A, 2,6-di-tert-butyl-p-cresol, methy 3,5-di-tert-butyl-4-hydroxybenzoate, 4-tert- butylcatechol, 2-hydroxybenzyl alcohol, 2-methoxy-4-methylphenol, 2,3,6-trimethylphenol, 2,4,5-trimethylphenol, 2,4,6-trimethylphenol, 2-isopropylphenol, 4-isopropylphenol, 6-isopropyl-m-cresol, n-octadecyl [beta]-(3,5-di-tert- buty l-4-hydroxyphenyl) propion ate, 1 , 1 , 3-tris(2-methy l-4-hyd roxy-5-tert-buty I pheny l)bu tane, 1 ,3,5-trimethyl-2,4,6- tris(3, 5-d i-tert-buty l-4-hyd roxy benzyl) benzene, 1 , 3, 5-tris(3, 5-d i-tert-buty l-4-hyd roxy benzyl) isocyanurate, 1,3,5- tris(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl isocyanurate, 1 ,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert- butylbenzyl) isocyanurate or pentaerythrityl tetrakis[[beta]-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,6-di-tert- butyl-4-dimethylamino-methylphenol, 6-sec-butyl-2,4-dinitrophenol, octadecyl 3-(3',5'-di-tert-butyl-4'- hydroxyphenyl)propionate, hexadecyl 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate, octyl 3-(3',5'-di-tert-butyl-4'- hydroxyphenyljpropionate, 3-thia-1 ,5-pentanediol bis[(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate], 4,8-dioxa-1 , 11- undecanediol bis[(3",5'-di-tert-butyl-4'-hydroxyphenyl)propionate], 4, 8-dioxa-1, 11 -undecanediol bis[(3'-tert-butyl-4'- hydroxy-5'-methylphenyl)propionate], 1 ,9-nonanediol bis[(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate], 1 ,7- heptanediamine-bis[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionamide], 1 ,1-methanediamine-bis[3-(3',5'-di-tert- 231505

[0038] 4 butyl-4'-hydroxyphenyl)propionamide], 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionic hydrazide, 3-(3',5'-di-methyl-4'- hyd roxy phenyl) propion ic hydrazide, bis(3-tert-bu tyl-5-ethy l-2-hyd roxy phen- 1 -yl)methane, bis(3, 5-d i-tert-butyl-4- hydroxyphen-1-yl)methane, bis 3-(T-methylcyclohex-T-yl)-5-methyl-2-hydroxyphen-1-yl]methane, bis(3-tert-butyl-2- hydroxy-5-methylphen-1-yl)methane, 1,1-bis(5-tert-butyl-4-hydroxy-2-methylphen-1-yl)ethane, bis(5-tert-butyl-4- hydroxy-2-methylphen-1-yl) sulfide, bis(3-tert-butyl-2-hydroxy-5-methylphen-1 -yl) sulfide, 1 , 1-bis(3,4-dimethyl-2- hydroxyphen-1-yl)-2-methylpropane, 1, 1-bis(5-tert-butyl-3-methyl-2-hydroxyphen-1 -yl)butane, 1 ,3,5-tris[1 '-(3",5'-di- tert-buty l-4"-hydroxy phen- 1 "-y I) meth-1 '-yl]-2, 4, 6-tri methyl benzene, 1 , 1 , 4-tris(5'-tert-buty l-4’-hydroxy-2’-methy lphen-l’- yl)butane, aminophenols such as para-aminophenol, nitrosophenols such as para-nitrosophenol, p-nitroso-o-cresol, alkoxyphenols, for example 2-methoxyphenol (guajacol, catechol monomethyl ether), 2-ethoxyphenol, 2- isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-tert-butyl-4-methoxyphenol, 3,5- di-tert-butyl-4-hydroxyanisole, 3-hydroxy-4-methoxybenzyl alcohol, 2,5-dimethoxy-4-hydroxybenzyl alcohol (syringa alcohol), 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy-3-ethoxybenzaldehyde (ethylvanillin), 3-hydroxy-4- methoxybenzaldehyde (isovanillin), 1-(4-hydroxy-3-methoxyphenyl)ethanone (acetovanillone), eugenol, dihydroeugenol, isoeugenol, tocopherols such as [alpha]-, [beta]-, [gamma]-, [delta]- and [epsilon]-tocopherol, tocol, alpha]-tocopherolhydroquinone and also 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7- lydroxycoumaran), quinones and hydroquinones such as hydroquinone, 2,5-di-tert-butylhydroquinone, 2-methyl-p- lydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone and 4-methylcatechol,

[0039] Aromatic amines are, for example, N,N-diphenylamine; phenylenediamines are, for example, N, N'-dialkyl-para- phenylenediamine, where the alkyl radicals may each independently contain from 1 to 4 carbon atoms and may be linear or branched, for example, N,N'-di-sec-butyl-para-phenylenediamine; hydroxylamines are, for example, N,N- diethylhydroxylamine; phosphorus compounds are, for example, triphenylphosphine, triphenyl phosphite or triethyl phosphite, sulfur compounds are, for example, diphenyl sulfide and inorganic salts are, for example, the chloride, dithiocarbamate, sulfate, salicylate or acetate salts of copper, manganese, cerium, nickel or chromium.

[0040] Preference is given to phenothiazine, p-aminophenol, p-nitrosophenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di- tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, hydroquinone and / or hydroquinone monomethyl ether, N,N'-di-sec.-butyl-para-phenylenediamine and also manganese(ll) acetate, cerium(lll) carbonate or cerium(lll) acetate; particular preference is given to phenothiazine, p-aminophenol, p-nitrosophenol, 2-tert- butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, hydroquinone and / or hydroquinone monomethyl ether, cerium(lll) acetate and / or manganese(ll) acetate.

[0041] The polymerization inhibitor is in particular phenothiazine (PTZ), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1 -oxyl (HO- TEMPO), 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO), N,N'-di(butan-2-yl)benzene-1,4-diamine (Kerobit, BPD), hydroquinone, hydroquinone monomethyl ether, 2,6-di-tert-butyl-4-hydroxytoluene (BHT), 4- methoxyphenol (MeHQ), p-benzoquinone, p-nitrosophenol, methylene blue, metal salts; in particular salts of manganese, copper or cerium; or mixtures thereof. Preferably, the polymerization inhibitor is selected from phenothiazine (PTZ), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1 -oxyl (HO-TEMPO), 4-oxo-2,2,6,6-tetramethyl-1- piperidinyloxy (4-oxo-TEMPO), N,N'-di(butan-2-yl)benzene-1,4-diamine (Kerobit, BPD), hydroquinone monomethyl ether, 2,6-di-tert-butyl-4-hydroxytoluene (BHT), 4-methoxyphenol (MeHQ), p-benzoquinone, p-nitrosophenol, methylene blue, metal salts; in particular salts of manganese, copper or cerium; or mixtures thereof. In particular, the polymerization inhibitor is selected from phenothiazine (PTZ), 4-methoxyphenol (MeHQ), N,N'-di(butan-2-yl)benzene- 1 ,4-diamine (Kerobit BPD), HO-TEMPO, metal salts; such as salts of manganese, copper or cerium, in particular copper; or mixtures thereof. In a preferred embodiment, the polymerization inhibitor is phenothiazine (PTZ), 4- methoxyphenol (MeHQ), N,N'-di(butan-2-yl)benzene-1 ,4-diamine (Kerobit BPD) and / or HO-TEMPO.

[0042] Further, the polymerization inhibitor can be for example a mixture of phenothiazine (PTZ) and 4-hydroxy-2, 2,6,6- tetramethylpiperidine- 1 -oxyl (HO-Tempo).

[0043] Preferably, the concentration of the polymerization inhibitor in the liquid phase is in a range from 0.0001 wt.-% to 1 .0000 wt.-%, more preferably from 0.0005 wt.-% to 0.1000 wt.-%, even more preferably from 0.0005 wt.-% to 0.0500 wt.-%, even more preferably from 0.0050 wt.-% to 0.0500 wt.-%, based on the total liquid phase.

[0044] The polymerization inhibitor may be added individually or as a mixture, in liquid form or in dissolved form in a suitable solvent. The polymerization inhibitors may, for example, be added in a suitable formulation at any desired point to the vessel, to an external cooling circuit and / or to a suitable recycle stream. When a mixture of a plurality of polymerization inhibitors is used, these may be fed independently at different metering points or at the same metering point. When a mixture of a plurality of polymerization inhibitor is used, these may be dissolved independently in different solvents or together in the same solvent. Particular preference is given to spraying the dissolved polymerization inhibitor or a mixture thereof onto any condenser surfaces, column internals and / or column lid.

[0045] In a preferred embodiment, the catalyst is chosen from a group consisting of sulfuric acid; phosphoric acid; alkyl sulfonic acid such as methanesulfonic acid or trifluoromethanesulfonic acid; aryl sulfonic acid such as benzenesulfonic acid, p-toluenesulfonic acid (pTSA), m-toluenesulfonic acid, o-toluenesulfonic acid or dodecylbenzenesulfonic acid, tripotassium phosphate, sodium methoxide, magnesium methoxide, magnesium oxide, combinations of magnesium oxide with lithium hydroxide, calcium oxide, combinations of calcium oxide with lithium 231505

[0046] 5 hydroxide, dibutyltin oxide, zirconium acetylacetonate and titanates such as tetramethyl, tetraethyl, tetraisopropyl, tetrapropyl, tetraisobutyl and tetrabutyl titanate; and mixtures thereof. For example, the catalyst is chosen from a group consisting of sulfuric acid; phosphoric acid; alkyl sulfonic acid such as methanesulfonic acid or trifluoromethanesulfonic acid; aryl sulfonic acid such as benzenesulfonic acid, p-toluenesulfonic acid (pTSA), m- toluenesulfonic acid, o-toluenesulfonic acid or dodecylbenzenesulfonic acid, tripotassium phosphate, sodium methoxide, magnesium methoxide, magnesium oxide, combinations of magnesium oxide with lithium hydroxide, calcium oxide, combinations of calcium oxide with lithium hydroxide, dibutyltin oxide, zirconium acetylacetonate and titanates such as tetraethyl, tetraisopropyl, tetrapropyl, tetraisobutyl and tetrabutyl titanate; and mixtures thereof; or the catalyst is chosen from a group consisting of sulfuric acid; phosphoric acid; alkyl sulfonic acid such as methanesulfonic acid or trifluoromethanesulfonic acid; aryl sulfonic acid such as benzenesulfonic acid, p- toluenesulfonic acid (pTSA), m-toluenesulfonic acid, o-toluenesulfonic acid or dodecylbenzenesulfonic acid, tripotassium phosphate, sodium methoxide, magnesium methoxide, magnesium oxide, combinations of magnesium oxide with lithium hydroxide, calcium oxide, combinations of calcium oxide with lithium hydroxide, dibutyltin oxide, zirconium acetylacetonate; and mixtures thereof.

[0047] More generally, preferred catalysts, in particular in case of tB(M)A production, are strong inorganic or organic acids, such as mineral acids, particularly sulfur- or phosphorus-containing mineral acids, for example sulfuric acid, phosphoric acid and polyphosphoric acid, preferably sulfuric acid or alkylsulfonic and arylsulfonic acids, such as p- toluene-, benzene-, dodecylbenzene- and methanesulfonic acid. Very particular preference is given to sulfuric acid. Sulfuric acid is under the reaction conditions also catalytically active in the form of the resulting sulfuric acid mono- tert-butyl ester.

[0048] In case of transesterification, the catalyst is preferably chosen from the group consisting of titanium alcoholates whose alkyl groups are preferably Ci-C4-alkyl radicals, such as tetramethyl, tetraethyl, tetraisopropyl, tetrapropyl, tetraisobutyl and tetrabutyl titanate; titanium phenolates, metal chelate compounds of, for example, hafnium, titanium, zirconium or calcium; alkali metal and magnesium alcoholates, organic tin compounds and calcium or lithium compounds, for example oxides, hydroxides, carbonates or halides thereof. The catalyst is for example titanium tetraisopropylate or butylate.

[0049] Preferably, the liquid phase comprises at least 20 wt.-%, more preferably at least 50 wt.-%, of the (meth)acrylate, based on the total liquid phase. The liquid phase additionally typically comprises the alcohol or the alkene, the (meth)acrylic compound, the catalyst, the polymerization inhibitor and optionally minor byproducts or impurities also referred to as remainder. The liquid phase preferably comprises only very small amounts of oligomerization products, particularly less than 2 wt.-%, based on the total liquid phase.

[0050] More preferably, the liquid phase comprises or consists of, based on the total liquid phase, 20.000 wt.-% to 99.900 wt.-% of the (meth)acrylate, 0.010 wt.-% to 50.000 wt.-% of the (meth)acrylic compound, 0.050 wt.-% to 60.000 wt.-% of the alcohol or the alkene, 0.000 wt.-% to 20.000 wt.-% of water, 0.010 wt.-% to 20.000 wt.-% of the catalyst, 0.001 wt.-% to 5.000 wt.-% of the polymerization inhibitor and 0.001 wt.-% to 5.000 wt.-% of remainder.

[0051] Even more preferably, the liquid phase comprises or consists of, based on the total liquid phase, 50.000 wt.-% to 99.900 wt.-% of the (meth)acrylate, 0.010 wt.-% to 30.000 wt.-% of the (meth)acrylic compound, 0.050 wt.-% to 40.000 wt.-% of the alcohol or the alkene, 0.000 wt.-% to 20.000 wt.-% of water, 0.010 wt.-% to 10.000 wt.-% of the catalyst, 0.001 wt.-% to 5.000 wt.-% of the polymerization inhibitor and 0.001 wt.-% to 5.000 wt.-% of remainder.

[0052] Preferably, the liquid phase comprises less than 5 wt-ppm, more preferably less than 1 wt-ppm, of dissolved oxygen, based on the total liquid phase.

[0053] In one embodiment, the liquid phase comprises, based on the total liquid phase, less than 50.00 wt-%, preferably less than 30 wt-% of the (meth)acrylate.

[0054] Preferably, the liquid phase in the vessel has a temperature of 50°C or more, more preferably 70°C or more. In particular, for example during conversion, the liquid phase in the vessel has a temperature in the range from 50°C to 115°C, more preferably from 50°C to 90°C, even more preferably from 70°C to 90°C. An absolute pressure in the vessel is preferably in the range from 100 hPa to 20000 hPa, more preferably from 200 hPa to 15000 hPa, even more preferably from 500 hPa to 13000 hPa. 231505

[0055] 6

[0056] The gaseous phase is in contact with the liquid phase, in particular in direct contact, in the vessel. The liquid phase is preferably at least partly a continuous phase. The gaseous phase is preferably a continuous phase and / or a dispersed phase. The liquid phase can be flushed, in particular continuously, with the gaseous phase.

[0057] Preferably, in the vessel the conversion to the (meth)acrylate is carried out and / or the (meth)acrylate is purified, in particular by condensation, distillation and / or extraction, more preferably by condensation and / or distillation. In the conversion, in particular, the alcohol or the alkene, and the (meth)acrylic compound are converted into the (meth)acrylate in presence of the catalyst. The (meth)acrylate can be formed by conversion of the alcohol, or alternatively of the alkene, with (meth)acrylic acid. In another embodiment, the alcohol and the reactant (meth)acrylate can be converted into the (meth)acrylate by means of transesterification. By purification, typically the content of the (meth)acrylate is increased. A distillation typically results in a top product and a bottom product. A conventional distillation unit typically comprises an evaporator, a column and a condenser. Further details of examples for possible distillation steps are described below.

[0058] Further, the (meth)acrylate can be stored in the vessel, for example temporarily during the purification process and / or long-term after the purification process.

[0059] Preferably, the vessel is a reactor, a column, a collection vessel, a buffer container and / or a storage tank. The gaseous phase can be present, and in particular in contact with liquid phase and thus the (meth)acrylate, during synthesis, purification, storage and / or transport of the (meth)acrylate.

[0060] In one embodiment, the vessel is a reactor, for example a cylindrical reactor, preferably a stirred tank, a bubble column reactor or a loop reactor. The reactor may advantageously be fitted with internals to improve commixing of the liquid phase. Suitable internals are known to those skilled in the art and include for example static mixing elements, such as gratings, distributor plates and / or sieve trays.

[0061] It is advantageous to effect temperature control of the reactor to adjust the reaction temperature. The temperature control of the reactor is preferably effected via one or more internal heat exchangers or via one or more external heat exchangers or using one or more external liquid circuits. Heat exchangers are for example tubular or plate heat exchangers. The gaseous phase can be passed along heat exchanger surfaces.

[0062] The liquid phase can be introduced to the reactor directly, for example via an immersion tube, or by means which allow uniform distribution and commixing. Such means are known to those skilled in the art and include for example distributor plates, perforated plates and pipes, nozzles etc. Suitable nozzles are known to those skilled in the art (jet nozzle, mixing nozzle, two-fluid nozzle etc.) and are described for example in Ullmann's Encyclopedia of Industrial Chemistry, vol. B4, 5th ed., 1992, pages 280 ff.

[0063] A residence time of the (meth)acrylate in the vessel, is generally in a range from 20 minutes to 12 hours, preferably from 20 minutes to 4 hours, more preferably from 20 minutes to 2.5 hours.

[0064] In one embodiment, the vessel is a column, wherein preferably the liquid phase is metered into. Further, the column can be attached to the reactor. The column may be a distillation, rectification or reaction column or a column for fractional condensation. The column can comprise separating internals installed and at least one means of condensation in the top region.

[0065] Useful separating internals are in principle any common internals, in particular trays, structured packings and / or random packings. Among the trays, preference is given to bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays, and among the random packings, preference is given to those comprising rings, spirals, saddles, Raschig, Intos or Pall rings, barrels or Intalox saddles, Top-Pak, etc. or braids.

[0066] Typically, the total number of theoretical plates in the column is from 2 to 100, preferably from 10 to 80, more preferably from 3 to 80 and even more preferably from 10 to 80. In case the column is directly attached to a reactor, the total number of theoretical plates in the column is preferably from 2 to 20, more preferably from 3 to 10.

[0067] In the case of a column, the pressure is generally in a range from 40 hPa to 1200 hPa. Within the column, the pressure drop per tray is preferably in a range from 1.5 hPa to 5.0 hPa per tray. The reflux at which the column is operated may be, for example, from 100:1 to 1 :100, preferably from 50:1 to 1:50, even more preferably from 20:1 to 1 :20 and even more preferably from 10:1 to 1 :10, but may also be zero (no reflux).

[0068] In general, a column has at least two removal means for product streams, customarily one at the top and one at the bottom, and also optionally one or more sidestream takeoffs. For example, the product may be removed from the column via the top and / or at least one sidestream takeoff. In the latter case, the removal may be in liquid or gaseous form. Preference is given to removing via a sidestream takeoff. 231505

[0069] 7

[0070] Preferably, the gaseous phase is, in particular continuously, metered into the vessel. The amounts of gaseous phase metered into the vessel is not limited in accordance with the invention. It is advantageously from 0.004 to 2.500 times the amount of the liquid phase being present or metered into the vessel (based in each case on the weight), preferably from 0.004 to 1 .000 times, more preferably from 0.08 to 0.50 times and most preferably from 0.1 to 0.5 times.

[0071] At least part of the gaseous phase, for example the inert gas, is preferably metered to the vessel at at least one feed point, more preferably into the bottom and more preferably into the bottom circuit of the vessel, even more preferably to a circulation evaporator at the column. The gaseous phase may be fed in via any desired devices, for example tubes, slits, nozzles or valves mounted in the vessel wall on the sides or in the center, preferably via those metering devices which allow a uniform distribution of the gaseous phase, in particular over the surface of the separating internals. The orifices in the devices may be, for example / holes, slits, valves and / or nozzles, preferably holes.

[0072] The polymerization inhibitor may be metered into the vessel with the liquid phase and / or be introduced additionally into the vessel, for example using a recycle stream.

[0073] Preferably, the process according to the invention comprises the following steps: a. a conversion step, wherein the alcohol or the alkene, and the (meth)acrylic compound are converted into the (meth)acrylate and the (meth)acrylate is obtained in a crude product solution and b. at least one purification step, wherein the crude product solution is purified, in particular by condensation, distillation and / or extraction, for example by condensation and / or distillation, wherein a purified product solution comprising the (meth)acrylate is obtained.

[0074] Preferably, step a. and / or step b. are carried out in the vessel. In particular, step a. is carried out in a first vessel and step b. is carried out in at least one second vessel and the first vessel and the at least one second vessel each comprise a gaseous phase comprising less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

[0075] The liquid phase can be the crude product solution and / or the purified product solution. In particular, the crude production solution is a first liquid phase and / or the purified production solution is a second liquid phase. The first liquid phase and the second liquid phase can have same or different compositions, preferably different compositions. Typically, the purified product solution has a higher content of the (meth)acrylate than the crude product solution, referring to the respective solution.

[0076] Between the process steps, for example between the conversion step and the at least one purification step, and / or between different purification steps, the liquid phase can be conveyed into a buffer container. The vessel can be for example the buffer container. A discharge from the buffer container can be recycled for example into the conversion step. The buffer container can be heated. A residence time of the (meth)acrylate in the buffer container is generally in a range from 0.5 to 1.5 hours.

[0077] A residence time of the (meth)acrylate in the storage tank is generally at least 24 hours. The storage tank can be transported.

[0078] The process according to the present invention, in particular the conversion step, can be carried out batchwise, as semi-batch or in a continuous manner. Preferably, the process is carried out continuously.

[0079] The liquid phase according to the present invention is preferably the crude product solution, the purified product solution and / or any mixture which is transformed into the crude product solution or the purified product solution, respectively.

[0080] The conversion step is typically carried out in one or more reactors. During conversion, the liquid phase is preferably mixed, for example by stirring, pumped circulation or natural circulation. For the at least one purification step, typically at least one or more columns are applied.

[0081] In a preferred embodiment, the crude product solution is purified by a condensation step and at least one distillation step, preferably two distillation steps, for example a low-boiler distillation step and optionally a final distillation step. A distillation step typically results in a top product and a bottom product. A conventional distillation unit typically comprises an evaporator, a column and a condenser.

[0082] The (meth)acrylate can be withdrawn from the conversion step for example in a gaseous form and be subjected to a condensation step, followed by at least one distillation step, preferably two distillation steps, for example the low- boiler distillation step and the final distillation step. 231505

[0083] 8

[0084] Low-boiler distillation

[0085] In one distillation step, in particular in the low-boiler distillation step, the distillation temperature at the bottom of the column is generally in a range from 40°C to 90°C. The pressure is selected as appropriate according to the product, for example tBA or tBMA. The vessel can be for example the column applied in the low-boiler distillation.

[0086] Here, the top product typically comprises low-boiling constituents, such as for example in case of tBA or tBMA, tertbutyl acetate, tert-butanol and diisobutene. The top product may also comprise up to 40 wt.-%, based on the total top product, of the (meth)acrylate. The bottoms product typically comprises substantially the (meth)acrylate and the (meth)acrylic compound such as (meth)acrylic acid.

[0087] A column applied in the low-boiler distillation step preferably has 30 to 50 dual-flow trays. The feed to the column is generally effected in the central region. Preferably, the inert gas is fed to the bottom of the column. The condensation of the low-boiling components can be effected in customary fashion. The condensation is preferably effected in two serially connected condensers, for example tube bundle condensers. The cooling temperature of the second condenser is preferably about 30°C to 50°C lower than the first condenser and the first condenser is operated with a cooling temperature of the coolant of preferably from 10°C to 35°C. Preferably, the condensates are combined and partly employed as column reflux. The remaining condensate is preferably discharged. Uncondensed vapors can be at least partly recycled to the conversion step. Uncondensed vapors comprise at least 85 wt.-% of the alcohol or the alkene, for example in case of tB(M)A at least 85 wt.-% of isobutene, and less than 2 wt.-% of the inert gas and a remainder of less than 13 wt.-%, based on the total uncondensed vapors.

[0088] To prevent polymer formation in the condensers and in the column, it is preferable to introduce a solution of the polymerization inhibitor in the (meth)acrylate into the first and / or second condenser. The polymerization inhibitor employed is for example a mixture of PTZ and HO-Tempo.

[0089] Final distillation

[0090] The bottom product of the low-boiler distillation is preferable fed to a final distillation step in a customary distillation unit with evaporator, column and condenser. The vessel can be for example the column applied in the final distillation. In the final distillation step, the (meth)acrylate is preferably obtained in a purity of at least 99.5 wt.-%, also referred to as purified product solution, in particular as top product. The bottom product resulting from the final distillation step generally comprises at least 70 wt.-% of the (meth)acrylic compound such as (meth)acrylic acid and is preferably at least partly recycled to the conversion step.

[0091] The distillation temperature in the final distillation step is generally in the range from 50°C to 100°C, measured at the bottom of the column. The pressure is selected according to the (meth)acrylate to be distilled. The final distillation is preferably carried out using a conventional tray column, for example a column having 30 to 50 dual-flow trays and a feed in the central column region. The (meth)acrylate is preferably separated overhead. The condensation of the (meth)acrylate is preferably carried out in two serially arranged condensers, in particular in tube bundle condensers. The temperature of the coolant of the second condenser is preferably about 30°C to 50°C lower than that of the first condenser where the coolant preferably has a temperature in the range from about 10°C to 35°C. The combined condensates are used preferably partially as column reflux and partially for stabilizing the column head and the condenser, in particular the first condenser, i.e. for avoiding polymerization in the column head and in the condenser, in particular the first condenser.

[0092] The other portion of the combined condensates, in particular the (meth)acrylate, is preferably obtained as value product, also referred to as purified product solution. To avoid polymerization in the condenser, particularly in the second condenser, typically a solution of the polymerization inhibitor in the (meth)acrylate is introduced. Here, the polymerization inhibitor is for example MEHQ. It is preferable to employ a solution of for example 0.5 wt.-% to 2.0 wt.- % of the polymerization inhibitor. The concentration of the polymerization inhibitor in the purified product solution is preferably in a range from 10 wt-ppm to 20 wt-ppm, referring to the total purified product solution. The concentration of the polymerization inhibitor in the liquid phase in the column is preferably in a range from 50 wt.-ppm to 500 wt- ppm, referring to the total liquid phase in the column.

[0093] Residue distillation

[0094] In the case where the (meth)acrylate is withdrawn from the conversion step in a gaseous form, a liquid reaction mixture from the reactor is preferably separated in a residue distillation as a discharged substream. The vessel can be for example the apparatus applied in the residue distillation. The, preferably continuous, residue distillation may be carried out at identical pressure to the reactor pressure. The temperature for the residue distillation depends on the desired product and is generally selected such that retrodeavage of the (meth)acrylate occurs and only a small proportion of the (meth)acrylate, for example less than 5 wt-% of the (meth)acrylate, based on the total liquid reaction mixture, remains in the bottoms product. The resulting gaseous educt, for example isobutene, is preferably predominantly, in particular entirely, recycled to the reactor. The resulting bottoms product from the residue distillation comprises essentially the catalyst, the (meth)acrylic compound such as (meth)acrylic acid and high-boiling constituents, which are byproducts having a boiling point higher than the (meth)acrylate at identical pressure, in 231505

[0095] 9 particular polymeric (meth)acrylic compounds. The bottom product from the residue distillation is preferably at least partly recycled to the conversion while the remaining bottoms product is discharged.

[0096] The residue distillation may be performed in customary apparatuses. However, it is preferable to employ apparatuses which allow rapid distillation, for example 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 Ed., vol. B3, 2-21 to 2-24 and 3-1 to 3-25, 1988. Condensation of the vapors may be carried out in customary fashion, for example in condensers of conventional design. It is preferable to employ two serially connected condensers, in particular plate or tube bundle condensers, wherein the second condenser is preferably operated at a lower cooling temperature. The temperature difference is generally in a range from 30°C to 50°C, wherein the cooling temperature of the coolant of the first condenser is preferably in the range from 10°C to 35°C. This allows rapid distillation and condensation and inhibits polymer formation. To reduce polymer formation even further, the polymerization inhibitor dissolved in the (meth)acrylate is preferably introduced into the condenser, presently the second condenser. The polymerization inhibitor employed is for example a mixture of PTZ and HO- Tempo. The inhibitor solution is employed preferably in an amount such that the concentration of the polymerization inhibitor in the combined condensates is for instance in the range from 100 wt.-ppm to 500 wt.-ppm.

[0097] In a particularly preferred embodiment a condensation can be eschewed and the resulting vapors are directly recycled into the conversion. The pressure in the residue distillation is then equal to the pressure in the reactor.

[0098] In case of transesterification, preferably either essentially the reactant (meth)acrylate can be separated and then the catalyst can be separated by distillation (catalyst separation), or the catalyst is separated by distillation first (catalyst separation), and then essentially the reactant (meth)acrylate is separated from the crude product solution of the transesterification. Constituents from the crude product solution, which have a lower boiling point than the (meth)acrylate, are preferably separated by distillation (separation of constituents at low boiling point), and the (meth)acrylate is then preferably purified by distillation (purification by distillation).

[0099] In one preferred embodiment, the a (meth)acrylate is tert-butyl (meth)acrylate (tB(M)A). tert-Butyl (meth)acrylate is to be understood as meaning tert-butyl acrylate (acrylic acid tert- butyl ester), in particular produced by reaction of acrylic acid with isobutene, or tert-butyl methacrylate (methacrylic acid tert-butyl ester), in particular produced by reaction of methacrylic acid (alpha- methylacrylic acid) with isobutene.

[0100] The tert-butyl esters of acrylic acid and methacrylic acid are used in a wide range of applications. (Meth)acrylic acid tert-butyl esters include for example important starting materials for producing polymers which are used inter alia as a constituent of coatings, adhesives and paint resins.

[0101] It is known that tert-butyl (meth)acrylate may be formed by an addition reaction of acrylic acid (AA) or methacrylic acid to isobutene (IB) under the influence of an acid, for example sulfuric acid, as catalyst. This process is described inter alia in WO 2016 / 156410 A1, WO 2002 / 10110 A2 and WO 2002 / 10109 A1.

[0102] The tBA process is more particularly described below with analogous description applying to the tBMA process. The process thus provides the product tert-butyl acrylate (tBA) when using the reactant acrylic acid and the product tertbutyl methacrylate (tBMA) when using the reactant methacrylic acid.

[0103] The reaction is an equilibrium reaction. The reaction is preferably performed continuously in a vertical reactor divided into sections and intermediately cooled wherein substantial chemical equilibrium is likely obtained at the upper outlet. In such a tBA process the reaction mixture discharged at the top typically comprises acrylic acid, tBA, dissolved IB and the catalyst such as sulfuric acid. This reaction mixture is then preferably concentrated under vacuum, at for example about 60 mbar absolute, thus more preferably effecting evaporative removal of IB and tBA and AA. The tBA and AA obtained in this gas phase are preferably condensed and supplied to a distillative workup. The uncondensed IB is preferably recycled to the reactor via vacuum machines.

[0104] Further, tert-butyl (meth)acrylate can be produced by reaction of (meth)acrylic acid in the liquid phase in a reactor with gaseous isobutene which is passed through the liquid portion in the presence of an acidic catalyst, wherein 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. Preferably, during reaction the temperature is in the range from 30°C to 90°C and the absolute pressure is in the range from 100 hPa to 20000 hPa. The two reactants are preferably employed in a molar ratio of isobutene to (meth)acrylic acid in the range from 5 to 60. The addition of acrylic acid (or methacrylic acid) onto isobutene can be performed in a reactor with a large amount, based on employed (meth) aery I ic acid, of passed- through gaseous isobutene which thus functions both as a reactant and as stripping gas. The stripping gas is then preferably subjected to a partial condensation, wherein tB(M)A and (meth)acrylic acid are obtained in liquid form and sent for further separation, for example analogously to the processes described in WO 2016 / 156410 A1 , WO 2002 / 10110 A2 or WO 2002 / 10109 A1. The uncondensed isobutene can be recycled into the reactor; it may also be referred to as recycle gas and / or stripping gas. 231505

[0105] 10

[0106] The liquid phase according to the present invention can be the reaction mixture in or discharged from the reactor, the concentrated reaction mixture, the liquid portion and / or the liquid mixture.

[0107] The isobutene is preferably introduced into the reactor in gaseous form. The isobutene may also be employed for example in the form of a hydrocarbon gas mixture comprising isobutene. The gas mixture may particularly be a C4- gas mixture comprising isobutene, isobutane, butane, 1- butene and 2-butene.

[0108] The inert gas is preferably metered into the vessel, in particular into the column, via the bottom of the vessel, for example together with a reflux stream of one of the reactants such as isobutene.

[0109] Isobutene and the (meth)acrylic acid are preferably employed in a molar ratio of isobutene to (meth)acrylic acid, which is lower than 1, for example in the range from 0.2 to 0.8, more preferably in the range from 0.4 to 0.7.

[0110] The reaction of isobutene and the (meth)acrylic acid is preferably carried out in the absence of a solvent. Acidic catalysts employed for the reaction of isobutene and the (meth)acrylic acid can be homogenous catalysts or heterogenous catalysts. The acidic catalysts are preferably those that are at least partially soluble in the reaction mixture. The catalyst is preferably introduced as a mixture with the (meth)acrylic acid, wherein fresh catalyst or recovered catalyst or a mixture thereof may be used.

[0111] In the case where the (meth)acrylate is tB(M)A, the purified product solution preferably has the following composition, based on the total purified product solution:

[0112] 99.500 wt.-% to 99.900 wt.-% of tertiary-butyl (meth)acrylate, 0.001 wt.-% to 0.010 wt.-% of tertiary-butyl acetate, 0.020 wt.-% to 0.030 wt.-% of tertiary-butyl propionate, 0.001 wt.-% to 0.010 wt.-% of tertiary-butanol, 0.010 wt.-% to 0.020 wt.-% of (meth)acrylic acid, 0.001 wt.-% to 0.002 wt.-% of the polymerization inhibitor, in particular MEHQ, and 0.050 wt.-% to 0.428 wt.-% of remainder.

[0113] All reported pressures refer to absolute pressures. All reported ppm values refer to weight (ppmw). The terms “wt.-%” and “% by weight” are used synonymously.

[0114] The invention is explained in more detail by the following examples and comparative examples.

[0115] Examples and comparative examples

[0116] One parameter for the tendency of a monomer solution to polymerize is the inhibition period (IP). This factor depends in particular on the surrounding gaseous phase. To measure the IP of inventive and comparative examples the so- called grill test was used. Gas chromatography (GO) vials with a volume of 1 .5 mL were filled with liquid phase and gaseous phase. Directly after preparing the samples, the vials were fixed in a mounting of a drying oven (Nabertherm TR 60 / S with rotary drive) at a defined temperature. With about 12 cycles per minute of the rotary drive, the time until solidification and thus polymerization, the inhibition period (IP) was measured. Therefore, the progress of polymerization was monitored with a video camera for a subsequent evaluation and determination of the IP. When polymerizing the transparent liquid was converted into a solid material. The samples underwent a reduction in volume and the solid material, in most cases a white solid material, became visible. The start of the polymerization and thus the IP was detected optically. Values are given as a mean of the quintuple determination.

[0117] Where applicable, defined amounts of polymerization inhibitor were added. For measurements under inert atmosphere an argon stream was passed through the samples for 90 seconds before closing them.

[0118] Liquid phases of various compositions were exposed to elevated temperatures in presence of different gaseous phases. Stability of the liquid phase was observed over time at hand of visual inspection of the samples with regard to solidification of the sample.

[0119] In all samples the concentration of the (meth)acrylate was more than 99 wt.-% in the liquid phase, based on the total liquid phase. As the (meth)acrylate nBMA, nBA, tBMA or tBA was applied, respectively. As gaseous phase either air, containing 20 vol.-% oxygen and 80 vol.-% nitrogen, or an inert gas, containing 100 vol.-% of argon, was applied.

[0120] Different polymerization inhibitors were added to the liquid phase to further prevent polymerization of the (meth)acrylate. The liquid phase either contained phenothiazine (PTZ), 4-methoxyphenol (MeHQ), N,N'-di(butan-2- yl)benzene-1,4-diamine (Kerobit BPD) or HO-TEMPO or was free of a polymerization inhibitor, and was stored at 100°C or 120°C, respectively. The achieved inhibition periods under the described conditions are summarized in tables 1, 2, 3 and 4. Each data point is the arithmetic mean of a quintuple sample set. All polymerization inhibitors were present in the liquid phase in a concentration of 10 wt-ppm, based on the total liquid phase. 231505

[0121] 11

[0122] Table 1

[0123] Table 2 Table 3

[0124] Table 4

[0125] An improved stability in presence of an inert gaseous phase was observed.

Claims

23150512Claims1 . A process for production of a (meth)acrylate, wherein an alcohol or an alkene, and a (meth)acrylic compound are converted into the (meth)acrylate in presence of a catalyst, wherein the (meth)acrylate is present in a vessel and the vessel contains a gaseous phase and a liquid phase, wherein the liquid phase comprises the (meth)acrylate and optionally the alcohol or the alkene, the (meth)acrylic compound and / or the catalyst, and the gaseous phase comprises less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

2. Process according to claim 1, wherein the liquid phase in the vessel has a temperature of 50°C or more, preferably 70°C or more.

3. Process according to claim 1 or 2, wherein the (meth)acrylic compound is a reactant (meth)acrylate, (meth)acrylic acid, or (meth)acrylic acid anhydride.

4. Process according to any of claims 1 to 3, wherein the (meth)acrylate is a methacrylate.

5. Process according to claim 4, wherein the methacrylate is chosen from the group consisting of tert-butyl methacrylate (tBMA), cyclohexyl methacrylate (CHMA), 2-ethylhexyl methacrylate (EHMA), n-butyl methacrylate (nBMA), 2-hydroxyethyl methacrylate (HEMA), lauryl methacrylate, stearyl methacrylate, behenyl methacrylate, isodecyl methacrylate, isotridecyl methacrylate, ureido methacrylate, behenyl polyethyleneglycol methacrylate (BEPEGMA), stearyl polyethyleneglycol methacrylate (SPEGMA) and methyl methacrylate (MMA), preferably tert-butyl methacrylate (tBMA), cyclohexyl methacrylate (CHMA) and methyl methacrylate (MMA).

6. Process according to any of claims 1 to 5, wherein in the vessel the conversion to the (meth)acrylate is carried out and / or the (meth)acrylate is purified, in particular by distillation and / or extraction.

7. Process according to any of claims 1 to 6, wherein the vessel is a reactor, a column, a collection vessel, a buffer container and / or a storage tank.

8. Process according to any of claims 1 to 7, wherein the liquid phase comprises a polymerization inhibitor, in particular phenothiazine (PTZ), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1 -oxyl (HO-TEMPO), 4-oxo-2, 2,6,6- tetramethyl-1 -piperidinyloxy (4-oxo-TEMPO), N,N'-di(butan-2-yl)benzene-1 ,4-diamine (Kerobit BPD), hydroquinone, hydroquinone monomethyl ether, 2,6-di-tert-butyl-4-hydroxytoluene (BHT), 4-methoxyphenol (MeHQ), p-benzoquinone, p-nitrosophenol, methylene blue, metal salts; in particular salts of manganese, copper or cerium; or mixtures thereof.

9. Process according to any of claims 1 to 8, wherein the liquid phase comprises at least 20 wt.-% of the (meth)acrylate, based on the total liquid phase.

10. Process according to any of claims 1 to 9, wherein the liquid phase comprises, based on the total liquid phase, 20.000 wt.-% to 99.900 wt.-% of the (meth)acrylate,0.010 wt.-% to 50.000 wt.-% of the (meth)acrylic compound, 0.050 wt.-% to 60.000 wt.-% of the alcohol or the alkene, 0.000 wt.-% to 20.000 wt.-% of water, 0.010 wt.-% to 20.000 wt.-% of the catalyst, 0.001 wt.-% to 5.000 wt.-% of the polymerization inhibitor and 0.001 wt.-% to 5.000 wt.-% of remainder.

11. Process according to any of claims 1 to 10, wherein the liquid phase comprises less than 5 wt.-ppm, preferably less than 1 wt.-ppm, of dissolved oxygen, based on the total liquid phase.

12. Process according to any of claims 1 to 11 , wherein the gaseous phase comprises at least 85 mol.-% of an inert gas, in particular nitrogen and / or argon, based on the total gaseous phase.

13. Process according to any of claims 1 to 12, wherein the gaseous phase comprises, based on the total gaseous phase,85.00 mol.-% to 99.40 mol.-% of an inert gas, 0.00 mol.-% to 1.00 mol.-% of the (meth)acrylate, 0.00 mol.-% to 2.00 mol.-% of the (meth)acrylic compound,231505130.50 mol.-% to 14.00 mol.-% of the alcohol or the alkene,0.10 mol.-% to 10.00 mol.-% of water,0.00 mol.-% to 1.00 mol.-% of the catalyst,0.00 mol.-% to 1.00 mol.-% of the polymerization inhibitor and0.00 mol.-% to 1.00 mol.-% of remainder.

14. Process according to any of claims 1 to 13, wherein a stream of the inert gas is added to the gaseous phase in the vessel, in particular continuously.

15. Process according to any of claims 1 to 14, wherein the catalyst is chosen from a group consisting of sulfuric acid; phosphoric acid; alkyl sulfonic acid such as methanesulfonic acid or trifluoromethanesulfonic acid; aryl sulfonic acid such as benzenesulfonic acid, p-toluenesulfonic acid (pTSA), m-toluenesulfonic acid, o- toluenesulfonic acid or dodecylbenzenesulfonic acid; tripotassium phosphate, sodium methoxide, magnesium methoxide, magnesium oxide, combinations of magnesium oxide with lithium hydroxide, calcium oxide, combinations of calcium oxide with lithium hydroxide, dibutyltin oxide, zirconium acetyl acetonate and titanates such as tetramethyl, tetraethyl, tetraisopropyl, tetrapropyl, tetraisobutyl and tetrabutyl titanate; and mixtures thereof.

16. Process according to any of claims 1 to 15, comprising the following steps: a. a conversion step, wherein the alcohol or the alkene, and the (meth)acrylic compound are converted into the (meth)acrylate and the (meth)acrylate is obtained in a crude product solution and b. at least one purification step, wherein the crude product solution is purified, in particular by condensation, distillation and / or extraction, wherein a purified product solution comprising the (meth)acrylate is obtained, wherein step a. is carried out in a first vessel and step b. is carried out in at least one second vessel and the first vessel and the at least one second vessel each comprise the gaseous phase comprising less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

17. Process according to any of claims 1 to 16, wherein the process is carried out continuously.

18. Use of the (meth)acrylate produced by the process according to any of claims 1 to 17 for production of coatings, films, paints, adhesives, plastics, resins, dispersions, rubber, sealants and / or oil drilling fluids.

19. System for production of a (meth)acrylate comprising a vessel, wherein an alcohol or an alkene, and a (meth)acrylic compound are converted into the (meth)acrylate in presence of a catalyst, wherein the (meth)acrylate is present in the vessel and the vessel contains a gaseous phase and a liquid phase, wherein the liquid phase comprises the (meth)acrylate and optionally the alcohol or the alkene, the (meth)acrylic compound and / or the catalyst, and the gaseous phase comprises less than 0.1 mol.-% of oxygen, based on the total gaseous phase.

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