Continuous process for producing n-butyl (METH)acrylate with a catalyst recirculation system

Abstract

The invention relates to a process for continuous production of n-butyl (meth)acrylate by reaction of (meth)acrylic acid with n-butanol in the presence of an acidic catalyst and a polymerisation inhibitor, comprising the steps, according to a first embodiment: • carrying out an esterification within a reactor (A) with a column (B) attached thereto, wherein the components (meth)acrylic acid and n-butanol are used in a molar ratio in the range from 1.0:1.0 to 1.0:2.0, preferably in the range from 1.0:1.1 to 1.0:1.5, and wherein the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar, resulting in a reaction product (6) and a vapour stream at the head of the column (B), • discharging the vapour stream at the head of the column (B), • condensing the vapour stream in a condenser (C), forming an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase, • continuously separating the organic phase from the aqueous phase by means of a phase separator (D), • feeding the resulting reaction product (6) into a rectification column (E), • separating the azeotropes within the rectification column (E): a) water and n-butyl (meth)acrylate, b) n-butanol and n-butyl (meth)acrylate, c) n-butanol and water, d) n-butanol, n-butyl (meth)acrylate and water, wherein the rectification column (E) is operated at a bottom temperature in the range from 80 to 150°C and at a head temperature in the range from 70 to 130°C and at an absolute pressure in the range from 0.2 to 5 bar, preferably in the range from 0.4 to 1.5 bar, • discharging a gas stream enriched by the azeotrope at the head of the rectification column (E), • condensing the gas stream in a condenser (F) to form an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase, • continuously separating the organic phase from the aqueous phase by a phase separator (G), • continuously discharging at least part of the organic phase from the phase separator (G), wherein this discharged part of the organic phase enriched with n-butyl (meth)acrylate represents the raw product stream (15), • discharging a high-boiling bottom product (23) from the bottom of the rectification column (E), wherein the mass flow ratio between the high-boiling bottom product (23) and the (meth)acrylic acid fed to the reactor (A) as reactant is in the range from 0.5 to 5, • feeding a high-boiling sub-stream (7) of the discharged high-boiling bottom product (23) into a mixer (H), wherein the mass flow ratio between the high-boiling sub-stream (7) and the high-boiling bottom product (23) is in the range from 0.01 to 0.50, preferably in the range from 0.05 to 0.08, • feeding a mixture (10) resulting from the mixer (H) into a downstream extraction phase separator (I), • continuously separating the mixture (10) in the extraction phase separator (I) to obtain an organic raffinate (11) and an aqueous extract (12) containing a catalyst, wherein the aqueous extract (12) is at least partially returned to the reactor (A) and / or the rectification column (E), wherein an external water (19) is fed to the mixer (H), wherein the mass flow ratio between the mass flow of the external water (19) and the high-boiling sub-stream (7) of the discharged high-boiling bottom product (23) is in the range from 0.08 to 0.50, preferably in the range from 0.10 to 0.30.

Description

[0001] Continuous process for the production of n-butyl (meth)acrylate with catalyst recycle

[0002] Description

[0003] The present invention relates to a process for the continuous production of n-butyl (meth)acrylate by reacting (meth)acrylic acid with n-butanol in the presence of an acid catalyst and a polymerization inhibitor.

[0004] N-butyl (meth)acrylate is particularly advantageously used in the manufacture of contact lenses or as a crosslinker or adhesion promoter for dispersions which are preferably used as adhesives, coatings, paints, e.g. printing inks, or textile, leather or paper auxiliaries as well as in curable coatings.

[0005] In the esterification of alkanol with acid, typical equilibrium reactions generally occur. These reactions are catalyzed by strong acids and, as typical condensation reactions, lead to the elimination of water of esterification. Typically, removing the water of esterification from the reaction mixture shifts the esterification equilibrium toward the forward reaction, thereby increasing the conversion rates for the target product.

[0006] Acidic catalysts typically used for the esterification reaction include inorganic acids such as sulfuric acid, organic acids such as alkanesulfonic acids, ion exchange resins, and the like.

[0007] The esterification water can be separated by distillation as part of an azeotrope, which typically also includes the target ester. Typically, the esterification reaction proceeds in such a way that the esterification water is continuously removed from the reaction mixture, while the majority of the target ester formed remains in the reaction mixture.

[0008] Examples of esterifications of this type include those in which the esterification water is separated by distillation by adding an organic solvent as an azeotropic entrainer. Excess alkanol can also serve as such an azeotropic entrainer.

[0009] A variant for the production of n-butyl (meth)acrylate consists in separating the esterification water by distillation as a component of a heterogeneous azeotrope of n-butyl (meth)acrylate / n-butanol / water, with the n-butanol and / or the n-butyl (meth)acrylate being at least partially recycled to the esterification as an organic phase.

[0010] A challenge of this process is that the esterification water formed during esterification must be at least partially removed from the process. Furthermore, the removed catalyst portion is typically burned, which, when using sulfuric or sulfonic acids, for example, leads to the formation of undesirable SO X Emissions arise.

[0011] EP 0795 536 A1 (BASF AG) discloses a process for the continuous production of alkyl esters of (meth)acrylic acid with recycling of an acid catalyst into the reaction zone of the reactor. This document explains recycling of the acid catalyst only for the alkyl ester 2-ethylhexyl acrylate (2-EHA). The applicability and transferability of this teaching to the other physical process conditions in the production of n-butyl acrylate and the esterification reaction taking place there, with subsequent, specific purification to the alkyl ester n-butyl acrylate, is not disclosed.

[0012] A process for the continuous production of alkyl (meth)acrylate, in particular n-butyl acrylate, is disclosed in WO 2012 / 026661 A1 (LG Chem, LTD.). In this process, an organic acid catalyst is recycled to the reaction zone of the reactor. However, the recycling is limited to the fact that the mass flow from the bottom outlet of the rectification column is already two-phase. Thus, the mass flow from the bottom outlet of the rectification column already contains an organic and an aqueous phase.

[0013] The objective was therefore to provide a continuous process for the production of n-butyl (meth)acrylate with catalyst recycling to improve the catalyst recovery rate during the production of n-butyl (meth)acrylate using an acidic catalyst. This also reduces the amount of catalyst discharged.

[0014] Another challenge was to minimize the amount of water used during esterification and distillative purification to make the process energy-efficient. This also results in fewer byproducts being formed in the process, as the reaction mixture is exposed to lower temperatures.

[0015] Furthermore, the object was to achieve a higher conversion and a higher yield of n-butyl (meth)acrylate. These objects are achieved according to the invention by claim 1 or alternatively by claim 2. Furthermore, the invention relates to preferred embodiments of the process according to claims 3 to 14.

[0016] In this document, the reference symbols in parentheses are intended to aid reading. The reference symbols in parentheses are not limiting, but merely represent one possible example among several possible implementations.

[0017] The process according to the invention is based on the reactants n-butanol and (meth)acrylic acid. In this document, (meth)acrylic acid refers to a (meth)acrylic acid grade which preferably contains at least 98% by weight, more preferably at least 99.5% by weight, of (meth)acrylic acid, preferably a maximum of 0.2% by weight of water, and preferably a maximum of 0.03% by weight each of acetic acid, propionic acid, and isobutyric acid. Preferably, an n-butanol grade containing at least 99.5% by weight of n-butanol, a maximum of 0.05% by weight of n-butanal, a maximum of 0.02% by weight of dibutyl ether, a maximum of 0.1% by weight of other alcohols, and a maximum of 0.05% by weight of water is used. The color number is preferably a maximum of APHA 5, and the acid number is preferably a maximum of 0.03 mgKOH / g.

[0018] Suitable polymerization inhibitors that act as stabilizers can be, for example, N-oxides (nitroxyl or N-oxyl radicals, i.e. compounds that have at least one NO group), such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (HO-TEMPO), 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 2, 2,6,6-tetra-methylpiperidine-N-oxyl, bis(1-oxyl-2,2,6,6-tetramethyl-piperidine-4-yl) sebacate, 4, 4', 4"-tris(2,2,6,6-tetramethyl-piperidine-N-oxyl) phosphite or 3-Oxo-2,2,5,5-tetramethyl-pyrrolidine-N-oxyl; mono- or polyhydric phenols, which may contain one or more alkyl groups, such as alkylphenols, for example o-, m- or p-cresol (methylphenol), 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert-butylphenol, 2-tert-butyl-4-methylphenol, 2,6-tert-butyl-4-methylphenol, 4-tert-butyl-2,6-dimethylphenol or 6-tert-butyl-2,4-dimethylphenol; quinones, such asHydroquinone, hydroquinone monomethyl ether, 2-methylhydroquinone or 2,5-di-tert.-butylhydroquinone; hydroxyphenols, such as pyrocatechol (1,2-dihydroxybenzene) or benzoquinone; aminophenols, such as p-aminophenol; nitrosophenols, such as p-nitrosophenol; alkoxyphenols, such as 2-methoxyphenol (guaiacol, pyrocatechol monomethyl ether), 2-ethoxyphenol, 2-isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-tert.-butyl-4-methoxyphenol; Tocopherols, such as α-tocopherol and 2,3-dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran), aromatic amines, such as N,N-diphenylamine or N-nitrosodiphenylamine; phenylenediamines, such as N,N'-dialkyl-p-phenylenediamine, where the alkyl radicals may be the same or different and each independently consist of 1 to 4 carbon atoms and may be straight-chain or branched, such asN,N'-dimethyl-p-phenylenediamine or N,N'-diethyl-p-phenylenediamine, hydroxylamines such as N,N-diethylhydroxylamine, imines such as methylethylimine or methylene violet, sulfonamides such as N-methyl-4-toluenesulfonamide or N-tert-butyl-4-toluenesulfonamide, oximes such as aldoximes, ketoximes or amidoximes such as diethyl ketoxime, methylethyl ketoxime or salicyladoxime, phosphorus-containing compounds such as triphenylphosphine, triphenyl phosphite, triethyl phosphite, hypophosphorous acid or alkyl esters of phosphorous acids; sulfur-containing compounds such as diphenyl sulfide or phenothiazine; Metal salts, such as copper or manganese, cerium, nickel, chromium salts, for example chlorides, sulfates, salicylates, tosylates, acrylates or acetates, such as copper acetate, copper(II) chloride, copper salicylate, cerium(III) acetate or cerium(III) ethylhexanoate, or mixtures thereof.

[0019] Preferably, at least one compound from the group consisting of hydroquinone, hydroquinone monomethyl ether, phenothiazine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, bis(1-oxyl-2,2,6,6-tetramethyl-piperidine-4-yl) sebacate, 2-tert.-butylphenol, 4-tert.-butylphenol, 2,4-di-tert.-butylphenol, 2-tert.-butyl-4-methylphenol, 6-tert.-butyl-2,4-dimethylphenol, 2,6-di-tert.-butyl-4-methylphenol, 2-methyl-4-tert.-butylphenol, hypophosphorous acid, copper(II) acetate, Copper(I) chloride, copper(II) chloride, copper(II) salicylate and cerium(III) acetate are used.

[0020] Phenothiazine (PTZ) and / or hydroquinone monomethyl ether (MEHQ) are particularly preferably used as polymerization inhibitors.

[0021] PTZ is particularly preferably used as a polymerization inhibitor in esterification and / or distillation.

[0022] The polymerization inhibitor is preferably dissolved in one or more liquid organic compounds. The organic compound is preferably n-butanol and / or n-butyl (meth)acrylate.

[0023] The usual mineral acids and sulfonic acids can be used as esterification catalysts, preferably sulfuric acid, phosphoric acid, alkylsulfonic acids (e.g. methanesulfonic acid, trifluoromethanesulfonic acid) and arylsulfonic acids (e.g. benzene-, p-toluene- or dodecylbenzenesulfonic acid) or mixtures thereof.

[0024] Particularly preferred are sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, m-toluenesulfonic acid, o-toluenesulfonic acid, or mixtures thereof. Very particular preference is given to using p-toluenesulfonic acid as the esterification catalyst.

[0025] The acidic catalyst is, in particular, a homogeneous catalyst. Sulfuric acid, phosphoric acid, alkylsulfonic acids (e.g., methanesulfonic acid, trifluoromethanesulfonic acid), and arylsulfonic acids (e.g., benzenesulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid), or mixtures thereof, more preferably p-toluenesulfonic acid, are preferably used as the acidic catalyst.

[0026] According to the invention, the process for the continuous production of n-butyl (meth)acrylate by reacting (meth)acrylic acid with n-butanol in the presence of an acid catalyst and a polymerization inhibitor comprises the following steps:

[0027] • Carrying out an esterification within a reactor (A) with a column (B) attached thereto, wherein the components (meth)acrylic acid and n-butanol are used in a molar ratio in the range from 1.0:1.0 to 1.0:2.0, preferably in the range from 1.0:1.1 to 1.0:1.5, and wherein the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar, whereby a resulting reaction output (6) and a vapor stream are obtained at the top of the column (B),

[0028] • Discharge of the vapor stream at the top of the column (B),

[0029] • Condensing the vapor stream in a condenser (C), forming an organic phase and an aqueous phase,

[0030] • Continuous separation of the organic phase from the aqueous phase by a phase separator (D),

[0031] • Feeding the resulting reaction effluent (6) into a rectification column (E),

[0032] • Separating the azeotropes within the rectification column (E): a) water and n-butyl (meth)acrylate, b) n-butanol and n-butyl (meth)acrylate, c) n-butanol and water, d) n-butanol, n-butyl (meth)acrylate and water, wherein the rectification column (E) is operated at a bottom temperature in the range of 80 to 150°C and at a temperature at the top in the range of 70 to 130°C and at an absolute pressure in the range of 0.2 to 5 bar,

[0033] • Discharge of a gas stream enriched by the azeotropes at the top of the rectification column (E),

[0034] • Condensing the gas stream in a condenser (F) to form an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase,

[0035] • Continuous separation of the organic phase from the aqueous phase by a phase separator (G),

[0036] • Continuously removing at least part of the organic phase from the phase separator (G), this removed part of the organic phase enriched with n-butyl (meth)acrylate representing the crude product stream (15),

[0037] • Discharging a high-boiling bottom discharge (23) from the bottom of the rectification column (E), wherein the mass flow ratio between the high-boiling bottom discharge (23) and the (meth)acrylic acid (1) fed to the reactor (A) as starting material is in the range from 0.5 to 5,

[0038] • feeding a high-boiling component partial stream (7) of the discharged high-boiling component bottom discharge (23) into a mixer (H), wherein the mass flow ratio between the high-boiling component partial stream (7) and the high-boiling component bottom discharge (23) is in the range from 0.01 to 0.50, preferably in the range from 0.05 to 0.08,

[0039] • Feeding a mixture (10) resulting from the mixer (H) into a downstream extraction phase separator (I),

[0040] • Continuous separation of the mixture (10) in the extraction phase separator (I) to obtain an organic raffinate (11) and a catalyst-containing aqueous extract (12), wherein the aqueous extract (12) is at least partially recycled to the reactor (A) and / or the rectification column (E), wherein an external water (19) is fed to the mixer (H) and the

[0041] Mass flow ratio between the mass flow of the external water (19) and the high-boiling component partial flow (7) of the discharged high-boiling bottom discharge (23) is in the range from 0.08 to 0.50, preferably in the range from 0.10 to 0.30.

[0042] Surprisingly, it was discovered that by supplying an external water source (19) to the mixer (H), a two-phase decomposition of the resulting mixture (10) always occurs after the start-up phase of the plant. This allows for the catalyst to be recycled under all operating conditions in the plant. Furthermore, the water content within the plant, particularly in reactor (A) or in the rectification column (E), can be kept as low as possible. Furthermore, this makes the process more energy-efficient, and fewer secondary components are formed. Furthermore, a higher conversion and a higher yield of n-butyl (meth)acrylate are achieved.

[0043] In an alternative process according to the invention, the following steps are involved for the continuous production of n-butyl (meth)acrylate by reacting (meth)acrylic acid with n-butanol in the presence of an acid catalyst and a polymerization inhibitor:

[0044] • Carrying out an esterification in a reaction zone (E1), wherein the reaction zone (E1) is located in the bottom of a rectification column (E), wherein the components (meth)acrylic acid and n-butanol are used in a molar ratio in the range from 1.0:1.0 to 1.0:2.0, preferably in the range from 1.0:1.1 to 1.0:1.5, and wherein the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar,

[0045] • Separation of the azeotropes formed by the esterification: a) water and n-butyl (meth)acrylate, b) n-butanol and n-butyl (meth)acrylate, c) n-butanol and water, d) n-butanol, n-butyl (meth)acrylate and water, wherein the separation takes place through the rectification column (E), which is operated at a bottom temperature in the range of 80 to 150°C and at a temperature at the top in the range of 70 to 130°C and at an absolute pressure in the range of 0.2 to 5 bar,

[0046] Discharge of a gas stream enriched by the azeotropes at the top of the rectification column (E), condensing the gas stream in a condenser (F) to form an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase,

[0047] • Continuous separation of the organic phase from the aqueous phase by a phase separator (G),

[0048] • Continuously removing at least part of the organic phase from the phase separator (G), this removed part of the organic phase enriched with n-butyl (meth)acrylate representing the crude product stream (15),

[0049] • Discharging a high-boiling bottom discharge (23) from the bottom of the rectification column (E), wherein the mass flow ratio between the high-boiling bottom discharge (23) and the (meth)acrylic acid fed to the reaction zone (E1) as starting material is in the range from 0.05 to 0.5,

[0050] • feeding a high-boiling component partial stream (7) of the discharged high-boiling component bottom discharge (23) into a mixer (H), wherein the mass flow ratio between the high-boiling component partial stream (7) and the high-boiling component bottom discharge (23) is in the range from 0.01 to 1.00, preferably in the range from 0.10 to 0.70,

[0051] • Feeding a mixture (10) resulting from the mixer (H) into a downstream extraction phase separator (I),

[0052] • Continuously separating the mixture (10) in the extraction phase separator (I) to obtain an organic raffinate (11) and a catalyst-containing, aqueous extract (12), wherein the aqueous extract (12) is at least partially recycled to the rectification column (E), wherein an external water (19) is fed to the mixer (H) and the mass flow ratio between the mass flow of the external water (19) and the high-boiling component substream (7) of the discharged high-boiling component bottoms discharge (23) is in the range from 0.08 to 0.50, preferably in the range from 0.10 to 0.30.

[0053] The same technical effects can also be observed in this alternative process according to the invention. Here, too, it was recognized that by supplying external water (19) to the mixer (H), a two-phase decomposition of the resulting mixture (10) always occurs after the start-up phase of the plant. This allows the catalyst to be recycled under all operating conditions occurring in the plant. In addition, the water content within the plant, particularly in the reaction zone (E1) or in the rectification column (E), can be kept as low as possible. Furthermore, the process is more energy-efficient, and fewer secondary components are formed in the process. Furthermore, a higher conversion and a higher yield of n-butyl (meth)acrylate are achieved.

[0054] The term “rectification column” in this document is to be understood as a general term for apparatus in which vapors are generated by the addition of heat, which vapors rise and come into contact with the effluent liquid phase.

[0055] Rectification columns are generally well-known in their design and comprise the usual equipment, such as an evaporator in the bottom, an evaporator in the high-boiler effluent, or a condenser in the low-boiler effluent, with the high-boiler components preferably located in the bottom region and the low-boiler components preferably in the top region of the rectification column. Typically, a portion of the mass flow of the high-boiler effluent is recycled to the bottom region of the rectification column. In principle, however, it is also possible for the bottom region to be heated, for example, by external wall heating of the column in the bottom region and / or for an evaporator to be integrated into the bottom region. Typically, a vapor stream is withdrawn at the top of the rectification column and fed to a condenser. This vapor stream is also commonly referred to as the low-boiler effluent.A portion of the vapor stream condensed in the condenser is returned to the rectification column, while the remaining portion of the condensed vapor stream is discharged as distillate. The reflux ratio describes the ratio between the condensed vapor stream returned to the column and the condensed vapor stream withdrawn as distillate. Typically, a reflux ratio in the range of 10 to 200% is set. In principle, all common column internals can be considered for the rectification column (E), such as trays, packings, and / or random packings. Bubble-cap trays, sieve trays, valve trays, Thormann trays, and / or dual-flow trays are preferred for the trays; rings, spirals, saddles, or braids are preferred for the packings.In addition, the rectification column (E) can also contain other standard control components, such as pressure reducers, flow controllers, or sensors. In principle, several rectification columns can also be connected in series or parallel, which can then act as a single "rectification column" (E).

[0056] In this document, when using acrylic acid, the components are referred to as low boilers if the boiling point at atmospheric pressure is lower than the boiling point of n-butyl acrylate. Similarly, components are referred to as high boilers if the boiling point at atmospheric pressure is greater than or equal to the boiling point of n-butyl acrylate. The boiling point of n-butyl acrylate is 147°C at atmospheric pressure.

[0057] In this document, when using methacrylic acid, the components are referred to as low boilers if the boiling point at atmospheric pressure is lower than the boiling point of n-butyl methacrylate. Similarly, components are referred to as high boilers if the boiling point at atmospheric pressure is greater than or equal to the boiling point of n-butyl methacrylate. The boiling point of n-butyl methacrylate is 163°C at atmospheric pressure.

[0058] In this document, the term "reactor" generally defines a reactor (A) or several interconnected reactors that act as a "reactor" (A). The reactor (A) also includes a reactor heating element for heating the reaction mixture.The reactor heating element is, for example, an immersion heater in the reactor (A), a pipe system comprising pipe coils or half-pipe coils arranged on the outer surface of the reactor and / or within the reactor (A), an electrical heating system arranged on the outer surface of the reactor (A) and / or within the reactor (A), an evaporator located outside the reactor (A), wherein the reaction mixture flows at least partially through the evaporator, or a double-walled embodiment of the reactor outer wall in which a fluid separated from the reaction mixture, such as a liquid, a gas and / or a heating vapor, is tempered and a predetermined heating temperature is thereby set, whereby the reaction mixture in the reactor (A) is heated. In general, several reactor heating elements can be used to heat the reaction mixture in the reactor (A).For example, a double-walled embodiment of the reactor outer wall and an evaporator located outside the reactor (A) can heat the reaction mixture simultaneously or at least partially staggered in time. In addition, the reactor (A) contains a column (B) mounted on it, which preferentially separates water by distillation. The column (B) itself is a distillation column with internal internals. Such internals are trays, such as bubble-cap trays, perforated trays, in particular dual-flow trays, beds, packings, or the like. In a further preferred embodiment, the reactor (A) is integrated into the rectification column (E), so that the esterification can take place in the bottom of the rectification column (E), i.e., in the reaction zone (E1).

[0059] In this document, the term “mass flow ratio” between a real numerical value A1 and a real numerical value B1 is equivalent to the division ratio with A1 in the numerator

[0060] Al and B1 in the denominator. The formula therefore applies: mass flow ratio = — . The term "external water" (19) in this document refers to water which originates from outside the process and is introduced into the process through an inlet on a mixer (H). The external water (19) is preferably demineralized water, particularly preferably fully demineralized water. The external water (19) preferably has a pH in the range from 4.5 to 10.5, particularly preferably in the range from 6.5 to 10.0. The external water (19) preferably contains no or only minor electrolyte components, preferably less than 0.1% by weight of electrolyte components.

[0061] Para-toluenesulfonic acid is preferably used as the acidic esterification catalyst, i.e., acidic catalyst. Its content in the reaction zone (E1) or in the reactor (A), based on the reaction mixture present therein, is advantageously 0.1-10.0 wt. %, preferably 0.1-6.0 wt. %. Other organic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, and / or sulfuric acid can also be used. Their amount is equimolar to that of para-toluenesulfonic acid. Corresponding mixtures are also possible. The content of catalytically active acid in the bottom of the rectification column (E), based on the mixture present therein, can advantageously be between 2.5 and 50.0 wt. % para-toluenesulfonic acid, or an equimolar amount of another organic sulfonic acid and / or sulfuric acid.

[0062] In a preferred embodiment of the process, the resulting mixture (10) from the mixer (H) has a temperature in the range of 20 to 100°C, preferably in the range of 70 to 95°C, at the outlet of the mixer (H). This results in the advantage that neither the aqueous nor the organic phase needs to be heated during the further course of the process, thus saving energy.

[0063] In a preferred embodiment of the process, the high-boiling bottom product (23) has a water concentration of less than 10 wt. %, preferably less than 5 wt. %. This results in the advantage that less water needs to be distilled off in the rectification column (E) and thus less energy is consumed to heat the rectification column (E), which also results in fewer secondary components being formed.

[0064] In a preferred embodiment of the process, a partial stream of the aqueous extract is recycled to the reactor (A) or the reaction zone (E1), wherein the mass flow ratio between the partial stream of the aqueous extract and the total mass flow of the aqueous extract (12) is in the range from 0.1 to 1.0, preferably in the range from 0.8 to 1.0. This results in the advantage that the catalyst can be recycled efficiently without increasing the water content in the plant. In a preferred embodiment of the process, such a mass flow of the external water (19) is added to the high-boiling component substream (7) of the discharged high-boiling component bottoms discharge (23) in the mixer (H) that a phase ratio between the aqueous extract (12) to be obtained and the organic raffinate (11) to be obtained in the range from 0.08 to 0.5 kg / kg, preferably from 0.1 to 0.3 kg / kg, is achieved.This has the advantage that a two-phase decomposition of the two phases is ensured, as little catalyst as possible has to be removed from the process and the water content is kept as low as possible during esterification and distillation.

[0065] A mass flow ratio of 0.5 kg / kg or less between the mass flow of the external water (19) and the high-boiling component substream (7) of the discharged high-boiling component bottom effluent (23) is sufficient for the successful recycling of the acid catalyst, and the energy requirement of the process, particularly for the evaporation of water, is reduced compared to the use of larger amounts of water. A mass flow ratio of at least 0.08 kg / kg between the mass flow of the external water (19) and the high-boiling component substream (7) of the discharged high-boiling component bottom effluent (23) serves to ensure effective extraction and phase separation in the extraction phase separator (I).

[0066] In a preferred embodiment of the process, at least a partial stream of the organic raffinate (11) is fed to a cleavage reactor (J). In particular, the cleavage reactor (J) is arranged downstream of the mixer (H) and the extraction phase separator (I). This results in the advantage that the organic components after phase separation, i.e. the organic raffinate (11), are fed to the cleavage reactor (J), whereby the bottom mixture in the cleavage reactor (J), which is discharged via line 21, is anhydrous and thus less corrosive. Furthermore, this arrangement avoids the recirculation of by-products formed in the cleavage reactor (J) with the extract into the reactor (A) or into the reaction zone (E1).The phase separation in the extraction phase separator (I) is also improved by this arrangement, among other things because the viscosity of the continuous phase, i.e. the organic raffinate (11), is lower and the density difference between the two phases, i.e. the organic raffinate (11) and the aqueous extract (12), is higher compared to an extraction downstream of the cleavage reactor (J).

[0067] In a preferred embodiment of the process, a partial stream of the organic raffinate (11) is fed to a cleavage reactor (J), the mass flow ratio between the partial stream of the organic raffinate (11) and the total mass flow of the organic raffinate being in the range from 0.1 to 1.0, preferably in the range from 0.95 to 1.0. This results in the advantage that the high boilers can be cleaved and the cleavage products such as (meth)acrylic acid and n-butanol can be reused as reactants in the process.

[0068] In a preferred embodiment of the process, the esterification takes place at a temperature in the range of 90 to 130°C, preferably in the range of 95 to 105°C, and at an absolute pressure in the range of 0.8 to 2.0 bar, preferably in the range of 1.0 to 1.5 bar. This results in the advantage that the conversion is kept as high as possible and the formation of secondary components as low as possible.

[0069] In a preferred embodiment of the process, a substream (8) of the high-boiling bottom effluent (23) is fed to the cleavage reactor (J) at a mass flow ratio to the high-boiling substream (7) of the high-boiling bottom effluent (23) in the range from 0.0 to 10.0, preferably in the range from 0.1 to 1.0. This results in the advantage that sufficient catalyst is present for the cleavage reaction in the cleavage reactor (J).

[0070] In a preferred embodiment of the process, a partial stream (9) of the high-boiling bottom effluent (23) is fed to the reactor (A) at a mass flow ratio to the total high-boiling bottom effluent (23) in the range from 0.1 to 0.99, preferably in the range from 0.85 to 0.95. This results in the advantage that the catalyst is recycled and reused.

[0071] In a preferred embodiment of the process, the high-boiling component bottom product (23) has a water content in the range from 0.1 to 10.0 wt. %, more preferably from 0.1 to less than 10.0 wt. %, more preferably from 0.1 to less than 5 wt. %, in particular from 0.1 to 4.5 wt. %. This results in the advantage that not too much water is present in the process, thus requiring less energy and resulting in fewer secondary components. At the same time, however, a single-phase removal of the high-boiling component bottom product (23) and then, after addition of water in the mixer (H), a two-phase decomposition of the resulting mixture (10) is ensured.

[0072] In a preferred embodiment of the process, the high-boiling component bottom effluent (23) has a content of oligomers and / or polymers in the range from 1 to 80 wt. %, more preferably from 10 to 65 wt. %, in particular from 20 to 60 wt. %. Oligomers and / or polymers are understood to mean molecules with a mass-average molar mass of more than 1000 g / mol. A content of oligomers and / or polymers of 80 wt. % or less in the high-boiling component bottom effluent (23) results in the advantage of a lower viscosity, so that the subsequent phase separation in the extraction phase separator (I) is improved. The mass flow ratio between the mass flow of the external water (19) and the high-boiling component partial stream (7) of the discharged high-boiling component bottom effluent (23) can be further reduced.

[0073] In a preferred embodiment of the process, the high-boiling bottom product (23) has a catalyst content in the range of 0.1 to 10.0 wt. %. This results in the advantage that not too much catalyst needs to be removed, thus allowing the process to be more energy-efficient and less catalyst to be used in the process.

[0074] In a preferred embodiment of the process, the acidic catalyst contains p-toluenesulfonic acid in a range of 0 to 100 wt. %, preferably in the range of 80 to 100 wt. %, particularly preferably in the range of 95 to 100 wt. %. This results in the advantage that the esterification proceeds very efficiently because this catalyst exhibits high selectivity, high reactivity, and a long lifetime in this process.

[0075] In a further embodiment of the process, the high-boiling bottom product (23) is single-phase. In this case, the external water (19) is added to the mixer (H) in such an amount that the resulting mixture (10) is two-phase.

[0076] In a further embodiment of the process, a partial stream of the organic phase (14) from the phase separator (G) is recycled to the rectification column (E) at a reflux ratio based on the organic phase in the range from 0.1 to 1.0, and a partial stream of the aqueous phase (16) from the phase separator (G) is recycled to the rectification column (E) at a reflux ratio based on the aqueous phase in the range from 1 to 10. This results in the advantage that less organic phase has to be discharged from the process or less aqueous phase has to be separated, and both the esterification and the separation in the rectification column (E) are energy-efficient. In addition, fewer secondary components are formed.

[0077] In a further embodiment of the process, the acid catalyst is present in a concentration ranging from 0.1 to 10 wt.% in the reaction zone (E1) of the rectification column (E) or in the resulting reaction effluent from the reactor (A). This results in the advantage that not too much catalyst needs to be removed, thus making the process more energy-efficient and allowing less catalyst to be used in the process.

[0078] In a further embodiment of the process, a partial stream of the aqueous extract (12) is fed to the reactor (A) in a mass flow ratio to the total high-boiling bottoms discharge (23) in the range from 0.01 to 0.50, preferably in the range from 0.01 to 0.30.

[0079] The invention is explained in more detail below with reference to the drawings. The drawings are to be understood as schematic representations. They do not represent a limitation of the invention, for example, with regard to specific dimensions or design variants. They show:

[0080] Fig. 1: A first embodiment of a process according to the invention for the continuous production of n-butyl (meth)acrylate, in which a reactor A with a downstream rectification column E is used. A catalyst-containing aqueous extract is recycled to reactor A and / or to the rectification column E.

[0081] Fig. 2: A second embodiment of a process according to the invention for the continuous production of n-butyl (meth)acrylate, in which a reaction zone E1 is integrated in the bottom region of a rectification column E. A catalyst-containing aqueous extract is recycled to the rectification column E.

[0082] Fig. 3: A third embodiment of a process for the continuous production of n-butyl (meth)acrylate as a comparative example, in which a reactor A is used with a downstream rectification column E. In this case, no catalyst-containing aqueous extract is recycled to reactor A and / or to rectification column E.

[0083] List of reference symbols used:

[0084] 1 line for supplying the reactant stream

[0085] 2 residual vapors from condenser C

[0086] 3 Line for the return of the organic phase from the liquid-liquid phase separator D

[0087] 4 Line for discharging the organic phase from the liquid-liquid phase separator D

[0088] 5 Line for supplying the aqueous phase from the liquid-liquid phase separator D to the liquid-liquid phase separator G

[0089] 6 Line for feeding the resulting reaction product into the rectification column E

[0090] 7 Line for the partial flow of the high-boiling bottom discharge 23 to the mixer H or heavy-boiling partial flow of the high-boiling bottom discharge 23 to the mixer H

[0091] 8 Line for the partial stream of the high-boiler bottom effluent 23 to the fission reactor J or partial stream of the high-boiler bottom effluent 23 to the fission reactor J 9 Line for the return of a partial stream of the high-boiler bottom effluent 23 to the reactor A or partial stream of the high-boiler bottom effluent 23 to the reactor A

[0092] 10 Resulting mixture from mixer H

[0093] 11 Line for supplying organic raffinate from the extraction phase separator I to the cleavage reactor J or organic raffinate

[0094] 12 Line for returning the aqueous extract from the extraction phase separator I to the reactor or to the rectification column E or aqueous extract

[0095] 13 Residual vapors from condenser F

[0096] 14 Line for the return of the organic phase from the liquid-liquid phase separator G to the rectification column E or organic phase from the liquid-liquid phase separator G

[0097] 15 Line for discharging a partial stream of the organic phase from the phase separator G or crude product stream

[0098] 16 Line for returning the aqueous phase from the liquid-liquid phase separator G to the rectification column E or aqueous phase from the liquid-liquid phase separator G

[0099] 17 Line for discharging a partial stream of the aqueous phase from the liquid-liquid phase separator G

[0100] 19 Line for supplying external water to mixer H or external water

[0101] 21 Line for discharging the high boiler bottoms discharge from the cleavage reactor J

[0102] 22 Line for the discharge of the low-boiling components from the cleavage reactor J

[0103] 23 Line for the high-boiling bottom discharge of the rectification column E or high-boiling bottom discharge of the rectification column E

[0104] 24 Line for supplying the polymerization inhibitor stream to the condenser C

[0105] 25 Line for supplying the polymerization inhibitor stream to the condenser F

[0106] A reactor

[0107] B pillar

[0108] C capacitor

[0109] D Phase separator

[0110] E rectification column

[0111] E1 reactor integrated into the rectification column

[0112] F capacitor

[0113] G Phase separator

[0114] H mixer

[0115] I Extraction phase separator

[0116] J Fission reactor Fig. 1 shows schematically a process flow diagram of a process engineering process according to a first embodiment of the process according to the invention, in which an external water 19 is added to a mixer H.

[0117] A reactant mass stream comprising n-butanol, acrylic acid, PTZ, and p-toluenesulfonic acid as an esterification catalyst is fed to a reactor A through a line 1. A column B arranged above reactor A separates a vapor mixture flowing from reactor A through its separating internals. A downstream condenser C, which may optionally be supplemented by an aftercooler, at least partially condenses the vapor stream resulting from column B. A solution of the polymerization inhibitor PTZ is added to condenser C through a line 24. The uncondensed portion from condenser C contains low-boiling impurities and is withdrawn in vapor form via a line 2.

[0118] The condensed vapor stream flows as condensate into a liquid-liquid phase separator D. There, the condensate separates into an aqueous and an organic phase. The aqueous phase, which contains primarily water, is conducted through a line 5 from the liquid-liquid phase separator D to a liquid-liquid phase separator G.

[0119] From the lower part of reactor A, a resulting reaction effluent, which contains, among other things, n-butyl acrylate, unreacted reactants and higher-boiling impurities, is withdrawn through a line 6 and fed to a rectification column E with separation-effective internals. In the rectification column E, among other things, water, n-butyl acrylate and alcohol are separated. The vapors emerging from the column are fed to a condenser F, which can optionally be supplemented by an aftercooler, where they are partially condensed. A solution of the polymerization inhibitor PTZ is added to the condenser F via a line 25. The uncondensed portion from the condenser F contains low-boiling impurities and is withdrawn in vapor form through a line 13, whereas the resulting condensate flows into the liquid-liquid phase separator G. There, the condensate separates into an aqueous and an organic phase.

[0120] An organic phase, which mainly contains n-butyl acrylate and n-butanol, is partially recycled as reflux through a line 14 to the rectification column E, and the remainder is discharged through a line 15 for further processing. The aqueous phase, which mainly contains water, is partially recycled as reflux through a line 16 to the rectification column E, and the remainder is discharged through a line 17 for further processing.

[0121] From the lower part of the rectification column E, mainly higher-boiling impurities and the catalyst used are withdrawn through a line 23 and fed through the downstream lines 7, 8 and 9 to the cleavage reactor J, to the mixer H and back to the reactor A. In the mixer H, external water 19 is added as an extraction agent, with the resulting mixture being fed through a line 10 to an extraction phase separator I.

[0122] In the extraction phase separator I, the resulting mixture separates into an organic raffinate and a catalyst-containing aqueous extract. The aqueous extract, which contains mainly water, is returned to reactor A via line 12. The organic raffinate is fed at least partially through line 11 to a cleavage reactor J for further processing. The high-boiling bottom product is also fed at least partially through line 8 to the cleavage reactor J for further processing. The bottom product of cleavage reactor J is discharged from the process via line 21, whereas the gaseous substances are withdrawn at the top of cleavage reactor J via line 22. The gaseous substances can then be condensed and finally returned to reactor A.

[0123] Fig. 2 shows schematically a process flow diagram of a process according to a second, alternative embodiment of the process according to the invention, in which an external water 19 is added to a mixer H, wherein in this embodiment, in comparison to the first embodiment, the reaction zone E1 is integrated into the bottom of the rectification column E.

[0124] Fig. 3 shows a schematic process flow diagram of a process engineering process as a comparative example, wherein, in comparison to the first embodiment, no mixer H and no extraction phase separator I are present, whereby no recirculation of the aqueous extract from the extraction phase separator I to the reactor A is possible.

[0125] Examples

[0126] The following process examples are modeled using thermodynamic simulations. The software used for this purpose is Aspen Plus® (Aspen), which can be found at http: / / www.aspentech.com (accessed on July 15, 2022). Aspen is a comprehensive simulation software used for modeling, simulating, and optimizing chemical processes and plants in industry. Aspen has extensive model databases for modeling basic operations as well as material databases for the material properties of many different substances. Aspen calculates the properties of mixtures using various thermodynamic models from the material data of the pure substances.

[0127] Comparison example 1

[0128] A thermodynamic simulation of the entire system according to Fig. 3 is carried out by Aspen and provides the following results:

[0129] A reactant stream is fed through a line 1 to a reactor A with a mass flow of 1000 kg / h, the reactant stream being a mixture with the following composition: n-Butanol: 582.2 kg / h

[0130] Acrylic acid: 413.9 kg / h p-toluenesulfonic acid: 3.9 kg / h.

[0131] A column B, located above reactor A, separates a vapor mixture flowing from reactor A through its separating internals. A downstream condenser C at least partially condenses the vapor stream resulting from column B.

[0132] A solution of the polymerization inhibitor is fed through line 24 to a condenser C at a mass flow rate of 2 kg / h, the solution of the polymerization inhibitor having the following composition: n-butyl acrylate: 98 wt% phenothiazine: 2 wt%.

[0133] The non-condensed portion from the condenser C contains low-boiling impurities and is withdrawn in vapor form via a line 2.

[0134] The esterification is carried out in reactor A at a temperature of 105°C, a pressure of 470 mbar and a residence time of 2 h.

[0135] From a liquid-liquid phase separator D downstream of the condenser C, 27 kg / h of the organic phase are withdrawn through a line 4 as organic distillate and 798 kg / h are returned to column B through a line 3 as reflux.

[0136] The organic phase as organic distillate has the following composition: Water: 19.6 wt.% n-Butanol: 77.3 wt.% n-Butylacrylate: 1.5 wt.%

[0137] Acrylic acid: < 0.01 wt.% n-Butyl acetate: 1.2 wt.%

[0138] Phenothiazine: < 0.01 wt%

[0139] Unknown: 0.4 wt%.

[0140] From the liquid-liquid phase separator D, 145 kg / h of the aqueous phase are fed through a line 5 to a liquid-liquid phase separator G. The aqueous phase has the following composition:

[0141] Water: 94.0 wt% n-Butanol: 5.9 wt%

[0142] Unknown: 0.1 wt%.

[0143] At the lower part of reactor A, a resulting reaction effluent with a mass flow of 1415 kg / h with the following composition is withdrawn through line 6 and added to a rectification column E: Water: 0.2 wt.% n-Butanol: 10.2 wt.% n-Butyl acrylate: 68.0 wt.%

[0144] Acrylic acid: 5.0 wt.% n-Butyl acetate: < 0.1 wt.% pT oluenesulfonic acid: 1.6 wt.%

[0145] Phenothiazine: 0.1 wt%

[0146] Unknown: 14.8 wt%.

[0147] In a rectification column E equipped with 13 theoretical stages, water, n-butanol, and n-butyl acrylate are withdrawn in vapor form via the top of the rectification column E, condensed in a condenser F, and then fed to a liquid-liquid phase separator G. In the top region of the column, the pressure is 1059 mbar and the temperature is 95°C.

[0148] A solution of the polymerization inhibitor is fed through line 25 to a condenser F at a mass flow rate of 2 kg / h. The polymerization inhibitor solution has the following composition: n-Butyl acrylate: 98 wt.% Phenothiazine: 2 wt.%. From the liquid-liquid phase separator G, 803 kg / h of the organic phase is withdrawn through line 15 as organic distillate for further purification. A partial stream with a mass flow rate of 365 kg / h is returned to the rectification column E via line 14 as reflux.

[0149] The organic phase has the following composition:

[0150] Water: 2.7 wt% n-Butanol: 16.8 wt% n-Butyl acrylate: 80.3 wt%

[0151] Acrylic acid: < 0.01 wt% n-Butyl acetate: 0.1 wt%

[0152] Phenothiazine: < 0.01 wt%

[0153] Unknown: 0.1 wt%.

[0154] From the liquid-liquid phase separator G, 83 kg / h of the aqueous phase is withdrawn as aqueous distillate through line 17. A partial stream with a mass flow of 724 kg / h of the aqueous phase is returned to the rectification column E through line 16 as reflux.

[0155] The aqueous phase has the following composition:

[0156] Water: 96.7 wt% n-Butanol: 2.0 wt% n-Butyl acrylate: 1.3 wt%

[0157] Unknown: < 0.1 wt%.

[0158] At the lower part of the rectification column E, a partial stream of the high-boiling bottom effluent 23 with a mass flow of 53 kg / h is passed through a line 8 to a cleavage reactor J, and a partial stream of the high-boiling bottom effluent 23 with a mass flow of 585 kg / h is passed through a line 9 back to reactor A. The vapor mixture produced in the cleavage reactor J is discharged through a line 22, whereas the bottom mixture is discharged through a line 21.

[0159] The high boiler bottom discharge 23 has the following composition:

[0160] Water: 3.1 wt% n-Butanol: 4.3 wt% n-Butylacrylate: 21.4 wt%

[0161] Acrylic acid: 11.1 wt% p-toluenesulfonic acid 3.4 wt% Phenothiazine: 0.2 wt%

[0162] Unknown: 56.5 wt%.

[0163] A content of oligomers and / or polymers is included in the unknowns.

[0164] Example 1

[0165] In this Example 1, an embodiment of the process for producing n-butyl (meth)acrylate according to the invention shown in Fig. 1 is simulated using the Aspen software. The simulation yields the following results:

[0166] A reactant stream is fed through line 1 to a reactor A with a mass flow of 1000 kg / h, the reactant stream having the following composition: n-Butanol: 584.3 kg / h

[0167] Acrylic acid: 414.4 kg / h p-toluenesulfonic acid: 1.3 kg / h.

[0168] The esterification in reactor A is carried out at a temperature of 105 °C, an absolute pressure of 470 mbar and a residence time of 2 hours.

[0169] A column B, located above reactor A, separates a vapor mixture flowing from reactor A through its separating internals. A downstream condenser C at least partially condenses the vapor stream resulting from column B.

[0170] A solution of the polymerization inhibitor is fed through line 24 to the condenser C at a mass flow rate of 2 kg / h, the solution of the polymerization inhibitor having the following composition: n-butyl acrylate: 98 wt% phenothiazine: 2 wt%.

[0171] The non-condensed portion from the condenser C contains low-boiling impurities and is withdrawn in vapor form via a line 2.

[0172] From a liquid-liquid phase separator D downstream of the condenser C, 27 kg / h of the organic phase are withdrawn through a line 4 as organic distillate and 934 kg / h are returned to column B through a line 3 as reflux.

[0173] The organic phase has the following composition:

[0174] Water: 19.6 wt% n-Butanol: 76.9 wt% n-Butyl acrylate: 1.7 wt% Acrylic acid: < 0.01 wt% n-Butyl acetate: 1.4 wt%

[0175] Phenothiazine: < 0.01 wt%

[0176] Unknown: 0.4 wt%.

[0177] From the liquid-liquid phase separator D, an aqueous phase with a mass flow of 155 kg / h is led through line 5 to a liquid-liquid phase separator G.

[0178] The aqueous phase has the following composition:

[0179] Water: 94.0 wt% n-Butanol: 5.9 wt%

[0180] Unknown: 0.1 wt%.

[0181] At the lower part of reactor A, a liquid mixture with a mass flow of 1422 kg / h is withdrawn through line 6 with the following composition and

[0182] Rectification column E:

[0183] Water: 0.2 wt% n-Butanol: 10.2 wt% n-Butyl acrylate: 68.0 wt%

[0184] Acrylic acid: 5.0 wt.% n-Butyl acetate: 0.0 to 0.1 wt.% pT oluenesulfonic acid 1.6 wt.%

[0185] Phenothiazine 0.2 wt.%

[0186] Unknowns: 14.7 to 14.8 wt%.

[0187] In a rectification column E equipped with 13 theoretical stages, water, n-butanol, and n-butyl acrylate are withdrawn in vapor form via the top of the rectification column E, condensed in a condenser F, and then fed to a liquid-liquid phase separator G. In the top region of the rectification column E, the absolute pressure is 1059 mbar and the temperature is 95 °C.

[0188] A solution of the polymerization inhibitor is fed through line 25 to a condenser F at a mass flow rate of 2 kg / h. The polymerization inhibitor solution has the following composition: n-Butyl acrylate: 98 wt.% Phenothiazine: 2 wt.%. From the liquid-liquid phase separator G, the organic phase is withdrawn as organic distillate at a mass flow rate of 807 kg / h through line 15 for further purification. A partial stream with a mass flow rate of 367 kg / h is returned to the rectification column E as reflux through line 14.

[0189] The organic phase has the following composition:

[0190] Water: 2.6 wt% n-Butanol: 16.7 wt% n-Butyl acrylate: 80.5 wt%

[0191] Acrylic acid: < 0.01 wt% n-Butyl acetate: 0.1 wt%

[0192] Phenothiazine: < 0.01 wt%

[0193] Unknown: 0.1 wt%.

[0194] From the liquid-liquid phase separator G, a mass flow of 101 kg / h of the aqueous phase is withdrawn as aqueous distillate through line 17 for further purification. A partial stream with a mass flow of 728 kg / h is returned to the rectification column E through line 16 as reflux.

[0195] At the lower part of the rectification column E, a partial stream is fed through a line 7 with a

[0196] Mass flow of 49 kg / h to mixer H, a partial flow with a mass flow of 24 kg / h through a line 8 to a fission reactor J and a partial flow with a mass flow of 588 kg / h through a line 9 back to reactor A.

[0197] The liquid mixture has the following composition:

[0198] Water: 3.1 wt% n-Butanol: 4.3 wt% n-Butylacrylate: 21.7 wt%

[0199] Acrylic acid: 11.1 wt% p-toluenesulfonic acid 3.4 wt%

[0200] Phenothiazine: 0.4 wt%

[0201] Unknown: 56.0 wt%.

[0202] The content of oligomers and / or polymers is included in the unknowns.

[0203] In the mixer H, the partial stream from the rectification column E, which contains the catalyst and higher-boiling impurities, is mixed through line 7 with a mass flow consisting of external water 19, resulting in a phase ratio of 0.2 kg / kg, the phase ratio being determined by the ratio between the value of the addition of the mass flow of the external water 19 to the mass flow of the aqueous phase of the partial stream 7 and the value of the mass flow of the organic phase of the partial stream 7. The mixture resulting from the mixer H is then fed through a line 10 to an extraction phase separator I.

[0204] Through line 11, 45 kg / h of the organic raffinate is discharged as an organic mixture from the extraction phase separator I and added to the cleavage reactor J for further purification. The vapor mixture produced in the cleavage reactor J is discharged through line 22, whereas the bottoms mixture is discharged through line 21.

[0205] The organic raffinate has the following composition:

[0206] Water: 1.9 wt% n-Butanol: 4.6 wt% n-Butylacrylate: 23.8 wt%

[0207] Acrylic acid: 9.0 wt% pT oluenesulfonic acid < 0.05 wt%

[0208] Phenothiazine: 0.2 wt.%

[0209] Unknown: 60.5 wt%.

[0210] The content of oligomers and / or polymers is included in the unknowns.

[0211] From the extraction phase separator I, the aqueous extract is fed back to reactor A through a line 12 at a mass flow rate of 15 kg / h.

[0212] The aqueous extract has the following composition:

[0213] Water: 71.4 wt% n-Butanol: 0.6 wt% n-Butylacrylate: 0.9 wt%

[0214] Acrylic acid: 10.1 wt% pT oluenesulfonic acid 11.5 wt%

[0215] Phenothiazine: 0.7 wt%

[0216] Unknown: 4.8 wt%.

[0217] In summary, the two examples show that with the same catalyst concentration in reactor A, the following results:

[0218] The catalyst-containing reactant stream, which is fed to reactor A via line 1, has a lower catalyst concentration in inventive example 1 than in comparative example 1. Thus, in inventive example 1, a mass flow of 1.3 kg / h of new catalyst is fed to line 1, whereas in comparative example 1, a mass flow of 3.9 kg / h of new catalyst is fed to line 1. This is due to the fact that in inventive example 1, the aqueous extract 12 is returned to reactor A at a mass flow of 15 kg / h, the catalyst concentration being 11.5 wt. %.In Example 1, phase decomposition occurs because the phase ratio between the external water 19 and the high-boiler substream 7 of the high-boiler bottoms discharge 23 at the outlet of mixer H is 0.2 kg / kg, whereas in Comparative Example 1, no external water 19 is added and the water concentration in the high-boiler bottoms discharge 23 is also only 0.03 kg / kg. Thus, no phase decomposition occurs in Comparative Example 1, which also means that no catalyst can be recycled to reactor A.

[0219] Thus, in Example 1 according to the invention, 66.7% of the catalyst quantity is saved.

[0220] Furthermore, the influence of the arrangement of a fission reactor J in the process was investigated experimentally.

[0221] Example 2

[0222] In Example 2, the cleavage reactor J was connected downstream of the mixer H and the extraction phase separator I, analogously to Example 1. A high-boiling component substream 7 of the high-boiling component bottom effluent 23 from the bottom of the rectification column E was fed to the mixer H. The viscosity of the organic raffinate 11, which was withdrawn from the extraction phase separator I and fed to the cleavage reactor J, was 0.7 mPas. External water 19 was used in the mixer H, with a mass flow ratio between the mass flow of the external water 19 and the high-boiling component substream 7 of the discharged high-boiling component bottom effluent 23 in a range of 0.13 to 0.34 kg / kg. The separation time in the extraction phase separator I was 60 s, and the density difference was 100 kg / m 3 .

[0223] Example 3

[0224] In Example 3, the cleavage reactor J was connected upstream of the mixer H, and a partial stream 8 (analogous to Fig. 3) of the high-boiler bottoms effluent 23 from the bottom of the rectification column E was first fed to the cleavage reactor J. The high-boiler bottoms effluent 21 from the cleavage reactor J was then fed to the mixer H, which was followed by the extraction phase separator I. The viscosity of the organic raffinate 11, which was taken from the extraction phase separator I here, was 30 mPas. External water 19 with a mass flow ratio between the mass flow of the external water 19 and the high-boiler bottoms effluent 21 from the cleavage reactor J of 1 kg / kg was used in the mixer H. The separation time in the extraction phase separator I was 240 to 300 s, and the density difference was 12 kg / m 3 small amount.

Claims

Patent claims 1. A process for the continuous production of n-butyl (meth)acrylate by reacting (meth)acrylic acid with n-butanol in the presence of an acid catalyst and a polymerization inhibitor, comprising the steps: • Carrying out an esterification within a reactor (A) with a column (B) attached thereto, wherein the components (meth)acrylic acid and n-butanol are used in a molar ratio in the range from 1.0:1.0 to 1.0:2.0, preferably in the range from 1.0:1.1 to 1.0:1.5, and wherein the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar, whereby a resulting reaction output (6) and a vapor stream are obtained at the top of the column (B), • Discharge of the vapor stream at the top of the column (B), • Condensing the vapor stream in a condenser (C), forming an organic phase and an aqueous phase, • Continuous separation of the organic phase from the aqueous phase by a phase separator (D), • Feeding the resulting reaction effluent (6) into a rectification column (E), • Separating the azeotropes within the rectification column (E): a) water and n-butyl (meth)acrylate, b) n-butanol and n-butyl (meth)acrylate, c) n-butanol and water, d) n-butanol, n-butyl (meth)acrylate and water, wherein the rectification column (E) is operated at a bottom temperature in the range of 80 to 150°C and at a temperature at the top in the range of 70 to 130°C and at an absolute pressure in the range of 0.2 to 5 bar, • Discharge of a gas stream enriched by the azeotropes at the top of the rectification column (E), Condensing the gas stream in a condenser (F) to form an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase, • Continuous separation of the organic phase from the aqueous phase by a phase separator (G), • Continuously removing at least part of the organic phase from the phase separator (G), this removed part of the organic phase enriched with n-butyl (meth)acrylate representing the crude product stream (15), • Discharging a high-boiling bottom effluent (23) from the bottom of the rectification column (E), wherein the mass flow ratio between the high-boiling bottom effluent (23) and the (meth)acrylic acid fed to the reactor (A) as starting material is in the range from 0.5 to 5, • feeding a high-boiling component partial stream (7) of the discharged high-boiling component bottom discharge (23) into a mixer (H), wherein the mass flow ratio between the high-boiling component partial stream (7) and the high-boiling component bottom discharge (23) is in the range from 0.01 to 0.50, preferably in the range from 0.05 to 0.08, • Feeding a mixture (10) resulting from the mixer (H) into a downstream extraction phase separator (I), • Continuous separation of the mixture (10) in the extraction phase separator (I) to obtain an organic raffinate (11) and a catalyst-containing, aqueous extract (12), wherein the aqueous extract (12) is at least partially recycled to the reactor (A) and / or the rectification column (E), characterized in that an external water (19) is fed to the mixer (H), wherein the mass flow ratio between the mass flow of the external water (19) and the high-boiling component partial stream (7) of the discharged high-boiling component bottoms discharge (23) is in the range from 0.08 to 0.50, preferably in the range from 0.10 to 0.

30.

2. A process for the continuous production of n-butyl (meth)acrylate by reacting (meth)acrylic acid with n-butanol in the presence of an acid catalyst and a polymerization inhibitor, comprising the steps: • Carrying out an esterification in a reaction zone (E1), wherein the reaction zone (E1) is located in the bottom of a rectification column (E), wherein the components (meth)acrylic acid and n-butanol are used in a molar ratio in the range from 1.0:1.0 to 1.0:2.0, preferably in the range from 1.0:1.1 to 1.0:1.5, and wherein the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar, • Separating the azeotropes formed by the esterification: a) water and n-butyl (meth)acrylate, b) n-butanol and n-butyl (meth)acrylate, c) n-butanol and water, d) n-butanol, n-butyl (meth)acrylate and water, wherein the separation also takes place by the rectification column (E), which is operated at a bottom temperature in the range of 80 to 150°C and at a temperature at the top in the range of 70 to 130°C and at an absolute pressure in the range of 0.2 to 5 bar, preferably in the range of 0.4 to 1.5 bar, • Discharge of a gas stream enriched by the azeotropes at the top of the rectification column (E), • Condensing the gas stream in a condenser (F) to form an organic phase enriched with n-butyl (meth)acrylate and an aqueous phase, • Continuous separation of the organic phase from the aqueous phase by a phase separator (G), • Continuously removing at least part of the organic phase from the phase separator (G), this removed part of the organic phase enriched with n-butyl (meth)acrylate representing the crude product stream (15), • Discharging a high-boiling bottom discharge (23) from the bottom of the rectification column (E), wherein the mass flow ratio between the high-boiling bottom discharge (23) and the (meth)acrylic acid fed to the reaction zone (E1) as starting material is in the range from 0.05 to 0.5, • feeding a high-boiling component partial stream (7) of the discharged high-boiling component bottom discharge (23) into a mixer (H), wherein the mass flow ratio between the high-boiling component partial stream (7) and the high-boiling component bottom discharge (23) is in the range from 0.01 to 1.00, preferably in the range from 0.10 to 0.70, • Feeding a mixture (10) resulting from the mixer (H) into a downstream extraction phase separator (I), • Continuously separating the mixture (10) in the extraction phase separator (I) to obtain an organic raffinate (11) and a catalyst-containing, aqueous extract (12), wherein the aqueous extract (12) is at least partially recycled to the rectification column (E), characterized in that an external water (19) is fed to the mixer (H), wherein the mass flow ratio between the mass flow of the external water (19) and the high-boiling component substream (7) of the discharged high-boiling component bottoms discharge (23) is in the range from 0.08 to 0.50, preferably in the range from 0.10 to 0.

30.

3. The process according to claim 1 or 2, wherein the resulting mixture (10) from the mixer (H) has a temperature in the range of 20 to 100°C, preferably in the range of 70 to 95°C, at the outlet of the mixer (H).

4. Process according to one of claims 1 to 3, wherein a partial stream of the aqueous extract is returned to the reactor (A) or the reaction zone (E1), wherein the mass flow ratio between the partial stream of the aqueous extract and the total mass flow of the aqueous extract (12) is in the range from 0.1 to 1.0, preferably in the range from 0.8 to 1.

0.

5. The process according to any one of claims 1 to 4, wherein such a mass flow of the external water (19) is added to the high-boiling component substream (7) of the discharged high-boiling bottom product (23) in the mixer (H) that a phase ratio between the aqueous extract (12) to be obtained and the organic raffinate (11) to be obtained in the range from 0.08 to 0.5 kg / kg, preferably in the range from 0.1 to 0.3 kg / kg, is achieved.

6. The process according to any one of claims 1 to 5, wherein a partial stream of the organic raffinate (11) is fed to a cleavage reactor (J), wherein the mass flow ratio between the partial stream of the organic raffinate (11) and the total mass flow of the organic raffinate is in the range from 0.1 to 1.0, preferably in the range from 0.95 to 1.

0.

7. The process according to claim 6, wherein a partial stream (8) of the high-boiling bottom effluent (23) is fed to the cleavage reactor (J) in a mass flow ratio to the high-boiling partial stream (7) of the high-boiling bottom effluent (23) in the range from 0.0 to 10.0, preferably in the range from 0.1 to 1.

0.

8. The process according to any one of claims 1 to 7, wherein the high-boiling bottom product (23) has a water content in the range of 0.1 to 10.0 wt.%.

9. Process according to one of claims 1 to 8, wherein the high-boiling bottom product (23) has a catalyst content in the range from 0.1 to 10.0 wt.%.

10. The process according to any one of claims 1 to 9, wherein the acid catalyst contains p-toluenesulfonic acid in the range from 0 to 100% by weight, preferably in the range from 80 to 100% by weight, particularly preferably in the range from 95 to 100% by weight.

11. Process according to one of claims 1 to 10, wherein the high boiler bottom discharge (23) is single-phase.

12. The process according to any one of claims 1 to 11, wherein a partial stream of the organic phase (14) from the phase separator (G) is recycled to the rectification column (E) at a reflux ratio based on the organic phase in the range from 0.1 to 1.0 and a partial stream of the aqueous phase (16) from the phase separator (G) is recycled to the rectification column (E) at a reflux ratio based on the aqueous phase in the range from 1 to 10.

13. The process according to any one of claims 1 to 12, wherein the acid catalyst is present in a concentration in the range from 0.1 to 10.0 wt.% in the reaction zone (E1) of the rectification column (E) or in the resulting reaction effluent from the reactor (A).

14. The process according to claim 1 or any one of claims 3 to 13, wherein a partial flow of the aqueous extract (12) is fed to the reactor (A) in a mass flow ratio to the total High boiler bottom discharge (23) in the range from 0.01 to 0.50, preferably in the range from 0.01 to 0.30.

Images