Process for manufacture of (METH)acrylates

Abstract

The invention relates to a process for manufacture of (meth)acrylates comprising the following steps: a. Providing an alcohol and an acid, b. Conversion of the alcohol and the acid in presence of a catalyst to the (meth)acrylate, wherein a product mixture stream (1) comprising the (meth)acrylate and at least part of a process water stream (3) are generated, c. Stripping the process water stream (3), in particular with steam (5), in a stripping device (7) having a top end (9), wherein a stripping outlet stream (11) is withdrawn from the top end (9) of the stripping device (7), d. Heating at least part of the product mixture stream (1) in a distillation column (13) with a reboiler (15), e. Feeding at least a part (16) of the stripping outlet stream (11) into the reboiler (15) of the distillation column (13), wherein heat is transferred from the part (16) of the stripping outlet stream (11) to the at least part of the product mixture stream (1). The invention further relates to a device (27) for carrying out the process.

Description

[0001] Process for manufacture of (meth)acrylates

[0002] Description

[0003] The present invention relates to a process for manufacture of (meth)acrylates.

[0004] (Meth)acrylates, also referred to as (meth)acrylic esters, are generally produced by esterification of (meth)acrylic acid with alcohols 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.

[0005] Processes for the production of n-butyl (meth)acrylate are for example described in US 6353130 B1 and US 6472554 B1.

[0006] Alkyl esters of (meth)acrylic acid are well known and are of significance, for example, as starting monomers for the preparation of aqueous polymer dispersions which find use, for example, as adhesives, paints or textile, leather and paper auxiliaries.

[0007] Typically (meth)acrylates are produced by processes comprising an esterification step of esterifying (meth)acrylic acid with a feed alcohol to obtain a crude (meth)acrylate, and purification steps of purifying the crude (meth)acrylate to obtain the target product. In the purification steps distillation and stripping devices are applied, which are operated at an elevated temperature level and therefore require an extensive energy supply. The main energy consumers in those technologies are distillation columns.

[0008] Thus, there is a need for effective processes for preparing (meth)acrylates with a reduced energy consumption.

[0009] US 2013 / 0037404 A1 discloses a process and a distillation system for separating a multi-component feed mixture in a distillation system comprising a first distillation column having a first fired reboiler, and a second distillation column having a second heat-exchange reboiler. A feed mixture is introduced to the first column and separated into at least a first top and a first bottom product. Part of the first bottom product is used for providing heat to the second reboiler. Heat is accordingly transferred between reboilers of two distillation columns without involving a head product for heat exchange.

[0010] US 2013 / 0237726 A1 describes a process for heat integration in the preparation of saturated alcohols, wherein at least one aldehyde is hydrogenated. A discharge is taken off from a zone, where the exothermic hydrogenation occurs, and subjected to distillation to give a fraction enriched in saturated alcohols. A process of acrylate ester formation, in particular, involving a treatment of process water in a stripping unit, is not addressed.

[0011] CN 102040472 A is directed to an energy-saving process for the production of alcohol from fermented liquor.

[0012] It is one object of the present invention to provide an improved process for preparing (meth)acrylates, wherein less energy has to be provided for purification of the (meth)acrylates. The process of the invention shall thus enable a more energy efficient preparation of (meth)acrylates.

[0013] This object is achieved by a process for manufacture of (meth)acrylates comprising the following steps: a. Providing an alcohol and an acid, b. Conversion of the alcohol and the acid in presence of a catalyst to the (meth)acry late, wherein a product mixture stream comprising the (meth)acrylate and at least part of a process water stream are generated, c. Stripping the process water stream, in particular with steam, in a stripping device having a top end, wherein a stripping outlet stream is withdrawn from the top end of the stripping device, d. Heating at least part of the product mixture stream in a distillation column with a reboiler, e. Feeding at least a part of the stripping outlet stream into the reboiler of the distillation column, wherein heat is transferred from the part of the stripping outlet stream to the at least part of the product mixture stream.

[0014] The object is further achieved by a device for carrying out the process for manufacture of (meth)acrylates, wherein the device comprises a conversion vessel, a stripping device with a top end comprising an outlet, a distillation column with a reboiler comprising an inlet and optionally a condenser, wherein the outlet of the top end of the stripping device is arranged in fluidic connection with the inlet of the reboiler of the distillation column, in particular in direct fluidic connection.

[0015] Due to the transfer of heat from the stripping device to the distillation column, a heat integration is realized and the demand for external energy supply is reduced. The vapors of the stripping device are directly used to heat the reboiler of the distillation column. The specific CO2 emission as well as the steam consumption, usually applied as heat energy source, of the process is reduced.

[0016] The process of the invention is used for the preparation of either methacrylates or acrylates, preferably for the preparation of acrylates. The process of the invention may be carried out in a continuous form or a batchwise form, preferably in a continuous form. The alcohol preferably contains 1 to 8 carbon atoms, more preferably 4 to 8 carbon atoms. Preferably, the (meth)acrylate is a Ci-Cs alkyl (meth)acrylate, more preferably a C4-C8 alkyl (meth)acrylate. Preferably, the (meth)acrylate is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-butyl and isobutyl (meth)acrylate and 2-octyl (meth)acrylate. More preferably, the (meth)acrylate is selected from the group consisting of 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate and isobutyl (meth)acrylate. In particular, the (meth)acrylate is selected from n-butyl (meth)acrylate and isobutyl (meth)acrylate. The (meth)acrylate is for example n-butyl (meth)acrylate, in particular n-butyl acrylate.

[0017] According to the invention, the process comprises at least the conversion of the alcohol and the acid as an esterification step and the stripping of the process water stream and the heating of the at least part of the product mixture stream in the distillation column as purification steps. Typically, the process may comprise at least one further purification step such as a catalyst removal step, a wash and neutralization step, an acid separation step, a rectification step, an extraction step, a wash step and / or a finishing step. Preferably, the process comprises at least one purification step, wherein an extraction and / or washing with water is carried out. The extraction and / or washing with water can be carried out for example in the catalyst removal step, the acid separation step, the extraction step and / or the wash and neutralization step. More preferably, the process comprises at least one purification step, wherein an extraction with water is carried out, in particular in the catalyst removal step and / or the extraction step.

[0018] Conversion step

[0019] The acid is preferably (meth)acrylic acid, more preferably acrylic acid. (Meth)acrylic acid can be synthesized via known processes. For example, the (meth)acrylic acid used in the present invention may be obtained by catalytic gas-phase oxidation of propane, propene and acrolein or of isobutane, isobutene and methacrolein with molecular oxygen.

[0020] The terms "(meth)acrylic acid", "(meth)acrylic ester" or "(meth)acrylate" relate to acrylic acid, the corresponding acrylic esters or acrylates and / or to methacrylic acid, the corresponding methacrylic esters or methacrylates, respectively.

[0021] In production of (meth)acrylic acid, crude (meth)acrylic acid can be purified by multistage crystallization or, if required, by chemical treatment with an aldehyde scavenger and distillation. The crude as well as pure or purified (meth)acrylic acid are typically stabilized with a polymerisation inhibitor or polymerisation inhibitor mixture against premature polymerisation of the (meth)acrylic acid.

[0022] In one embodiment, the acid, which is converted into the (meth)acrylate, is (meth)acrylic acid or 3-hydroxypropionic acid, in particular 3-hydroxypropionic acid. The acid can be converted directly or indirectly into the (meth)acrylate. Alkyl acrylates can be produced from 3-hydroxypropionic acid, as described, for example, in WO 2019 / 034577 A1. The acid according to the invention can be 3-hydroxypropionic acid and then the resulting 3-hydroxypropionic ester can be dehydrated to the corresponding alkyl acrylate in the same step or a subsequent step, in particular in the same step. Alternatively, 3-hydroxypropionic acid can first be dehydrated in a first step or in a first reaction, respectively, and then the resulting acrylic acid can be esterified with the alcohol in a subsequent step or subsequent reaction, respectively. In particular, 3-hydroxypropionic acid is converted under dehydrating and esterifying conditions in the presence of the alcohol to form the (meth)acrylate. One possible route for preparation of 3- hydroxypropionic acid proceeds via glucose through fermentation, wherein the glucose is obtained from renewable raw materials, for example corn. The preparation of 3-hydroxypropionic acid by fermentation is described for example in WO 2012 / 074818 A2. The 3-hydroxypropionic acid used is preferably biobased 3-hydroxypropionic acid that has been prepared from renewable raw materials, in particular by fermentation. Through the use of 3-hydroxypropionic acid, it is possible to prepare a virtually acetate-free (meth)acrylate.

[0023] For the process according to the invention, alcohols containing 1 to 8 carbon atoms are preferably used in the conversion step, for example, Ci-Cs-alkanols such as methanol, ethanol, 2-ethylhexanol, n-butanol, isobutanol or 2- octanol. The alcohol is more preferably 2-ethylhexanol, n-butanol or isobutanol, even more preferably n-butanol or isobutanol, for example n-butanol.

[0024] The molar ratio of the acid to the alcohol in the reaction mixture to be converted in the conversion step is typically in the range from 1 :0.7 to 1 :2.0, preferably from 1 :0.7 to 1 :1.7, particularly preferably from 1 :0.7 to 1 :1.3.

[0025] The conversion is carried out in presence of the catalyst. Preference is given to an acidic catalyst, especially a strongly acidic catalyst. In one embodiment the acidic catalyst is a heterogeneous catalyst having an acidic surface such as an acidic ion exchanger or a zeolite. Preferably, the catalyst is a mineral acid, more preferably a sulfonic acid, in particular 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, o-toluenesulfonic acid or dodecylbenzenesulfonic acid; and mixtures thereof. In particular, the catalyst is sulfuric acid or pTSA. The catalyst content usually is in a range from 0.1 wt.-% to 20.0 wt.-%, preferably from 0.1 wt.-% to 15.0 wt.-%, more preferably from 0.5 to 10.0 wt.-% and even more preferably from 0.8 wt.-% to 5.0 wt.-%, based on the total reaction mixture.

[0026] Unless otherwise stated, the parts, percentages and ppm data given herein relate to parts by weight, % by weight and ppm by weight. Here and throughout the specification, the terms "wt.-%" and "% by weight" are used synonymously.

[0027] The conversion is preferably carried out at a conversion temperature in a range from 70°C to 160°C, more preferably from 90°C to 140°C. Further, the conversion is preferably carried out at a conversion absolute pressure in a range from 100 hPa to 1020 hPa, more preferably from 200 hPa to 800 hPa, even more preferably from 250 hPa to 700 hPa. The conversion can be carried out in one or more than one reaction regions. In the case of more than one reaction regions, the conversion temperature is preferably set in such a way that it rises along the cascade.

[0028] The residence time of the reactants, i.e. the acid and the alcohol, in the conversion step, in particular in the conversion vessel, is preferably 0.5 to 20.0 hours, more preferably 2.0 to 8.0 hours. The residence time is understood to mean the time for which the bottoms draw volume resides in the liquid volume of the conversion vessel.

[0029] Heat can be supplied to the conversion via internal and / or external heat exchangers of conventional design and / or via jacket heating. A usual heat transfer medium is steam. The heat is preferably supplied via external circulation evaporators with natural or forced circulation. A thorough mixing of the reaction mixture is preferably effected in a known manner, for example by stirring, pumped circulation or natural circulation.

[0030] The conversion can be performed in conversion vessels such as reactors and / or columns. Preferably, the conversion is carried out in a reaction zone comprising one or more reaction regions, for example a reactor cascade of two to four, preferably two to three reactors. In the embodiment of the invention having a plurality of reaction regions, it is advantageous to cascade these. If more than one reaction region is created within one and the same reactor, e.g. by the use of separating sheets of metal, the number of reaction regions can also be greater than 4.

[0031] The conversion is preferably carried out in presence of at least one polymerisation inhibitor or inhibitor mixture, also referred to as stabilizers.

[0032] Suitable polymerisation inhibitors include alkylphenols, for example o-, 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-tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-butyl-2,6-dimethylphenol, or 2, 2'-methy lene-bis-(6-tert- butyl-4-methylphenol), hydroxyphenols, for example hydroquinone, 2-methylhydroquinone, 2,5-di-tert- butylhydroquinone, catechol (1,2-dihydroxybenzene) or benzoquinone, aminophenols, such as para-aminophenol, nitrosophenols, such as para-nitrosophenol, alkoxyphenols, for example 2-methoxyphenol (guaiacol, pyrocatechol monomethyl ether), 2-ethoxy phenol, 2-isopropoxy phenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-tert-butyl-4-methoxyphenol, tocopherols, such as e.g. alpha-tocopherol and 2,3-dihydro-2,2-dimethyl-7- hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran), N-oxyls such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N- oxyl, 4-oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 2,2, 6,6- tetramethyl-piperidine-N-oxyl, 4,4',4"-tris (2,2,6,6-tetramethyl-piperidine-N-oxyl) phosphite or 3-oxo-2,2, 5,5- tetramethyl-pyrrolidine-N-oxyl, aromatic amines or phenylenediamines, such as N, N-diphenylamine, N- nitrosodiphenylamine, N, N'-dialkyl-para-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, hydroxylamines, such as N, N-diethylhydroxylamine, phosphorus-containing compounds, such as triphenylphosphine, triphenylphosphite, hypophosphorous acid or triethylphosphite, sulfur-containing compounds, such as diphenyl sulfide or phenothiazine, optionally in combination with metal salts, such as the chlorides, dithiocarbamates, sulfates, salicylates or acetates of copper, manganese, cerium, nickel or chromium. Mixtures of polymerisation inhibitors can also be used. Typically, one or more, for example two or three, of the aforementioned polymerisation inhibitors are used. Preference is given to using one or two of the aforementioned polymerisation inhibitors. Phenothiazine, methylene blue, hydroquinone, hydroquinone monomethyl ether, alkyl-substituted phenols or N-oxyl compounds or mixtures are more preferably used. The at least one polymerisation inhibitor or inhibitor mixture comprises in particular phenothiazine and / or 4- hydroxy-2, 2, 6, 6-tetramethy I -p i peridi ne-N-oxy I .

[0033] Preferably, the water resulting from esterification is removed from the conversion, in particular from the conversion vessel, by rectification as part of a mixture comprising the water and the alcohol.

[0034] The conversion vessels, in particular reactors or reaction regions, are preferably equipped with at least one distillation unit, advantageously with one common distillation unit. In this case, a reflux from the common distillation unit is preferably passed into a first reaction region.

[0035] The product mixture stream is generated in the conversion step and comprises typically the (meth)acrylate and optionally unconverted alcohol, unconverted acid, byproducts which are boiling at a lower temperature than the (meth)acrylate such as alkyl acetate or dialkyl ether, the catalyst and / or oxyesters which are boiling at a higher temperature than the (meth)acrylate and formed by Michael addition.

[0036] The term low boiler (relative to the (meth)acrylate in question) or low boiling component is understood to be a substance whose boiling point is lower than the boiling point of the (meth)acrylate in question. The term high boiler (relative to the (meth)acrylate in question) or heavy-end impurity is understood to be a substance whose boiling point is higher than the boiling point of the (meth)acrylate in question. For example, the boiling point at standard pressure is 147°C for n-butyl acrylate and under standard pressure, the low boilers have generally a boiling point in a range from - 6°C to 145°C, in particular from 50 to 145°C, and the high boilers in a range from 149°C to 371°C.

[0037] The product mixture stream is preferably withdrawn from the conversion vessel, more preferably below or at the bottom of the at least one distillation unit. The at least part of the product mixture stream, which is heated in the distillation column, is typically depleted by at least one separation step in content of the (meth)acrylate compared to the product mixture stream leaving the conversion step.

[0038] The at least one distillation unit can be placed directly atop the conversion vessel. Placing the at least one distillation unit directly on top offers the advantage of conveying vapors formed in the conversion vessel directly without additional pipelines into the at least one distillation unit and the liquid effluxing from the at least one distillation unit directly into the conversion vessel. In particular, the reaction water is removed from the conversion and the reaction equilibrium is not limiting for the reaction progress. However, a separate arrangement of the conversion vessel and the at least one distillation unit is also possible, with corresponding pipelines for feeding of vapors into the at least one distillation unit and for efflux of liquid flowing through the at least one distillation unit into the conversion vessel.

[0039] The at least one distillation unit preferably has conventional internals. Suitable column internals are all conventional internals, for example trays, random packings and / or structured packings.

[0040] The term packing means solid or hollow bodies of predetermined size, shape and configuration, which are used as column internals to provide an enlarged surface area for the liquid to allow improved mass transfer at the liquid-vapor interface during countercurrent flow of two phases. The packing can be random or structured.

[0041] Random packings are understood to be packings wherein individual members do not have any particular orientation relative to each other or to the column axis. Random packings comprise small, hollow structures with large surface area per unit volume that are loaded at random into a column. Structured packing elements are made up of a multiplicity of individual layers of packing elements, such as metal sheets, expanded metals or wire fabrics, which are disposed vertically to one another in a regular structure and are usually held together in a composite by attachments such as metal wires, thin metal rods or metal sheet strips. Usually, the structured packing elements have a geometric structuring, for example in the form of folds or circular holes, in particular of from about 4 mm to 6 mm in diameter.

[0042] Among the trays, bubble trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred; among the random packings, those comprising rings, coils, saddles, Raschig, Intos or Pall rings, barrel or Intalox saddles, Top-Pak or braids are preferred. In general, the at least one distillation unit comprises 5 to 30, preferably 10 to 20, theoretical plates to achieve a desirable degree of separation.

[0043] Structured packing layers may have an internal geometry which varies over its height. A structured packing is preferred in which the structured packing has one or more structured packing elements having a surface area density of at least 100 m2 / m3, preferably at least 200 m2 / m3, more preferably at least 300 m2 / m3. In one embodiment, the structured packing has a surface area density of about 250 m2 / m3to 350 m2 / m3, and includes a plurality of corrugated plates disposed in parallel relation. The surface area density denotes the surface area of the structured packing per unit volume of the structured packing and is expressed in terms of m2 / m3of the volume occupied by the packing. The structured packing elements preferably have a total height of at least 6 m, preferably at least 8 m.

[0044] The absolute pressure at the top of the at least one distillation unit is preferably in a range from 100 hPa to 5000 hPa, particularly from 100 hPa to 2000 hPa, more particularly from 200 hPa to 800 hPa (from 0.1 to 5.0 bar, particularly from 0.1 to 2.0 bar, more particularly from 0.2 to 0.8 bar). The top of a column is usually understood as that part of the column, which is located above a highest theoretical plate. The bottom of a column is usually understood as that part of the column, which is located beneath a lowest theoretical plate.

[0045] Water formed during the conversion, generating at least part of the process water stream, is preferably removed from the conversion via the at least one distillation unit, in particular together with low-boiling component and / or with solvents which form an azeotrope with water and have a boiling point at normal pressure of up to 130°C.

[0046] Usually, the at least one distillation unit is supplemented by an associated condenser and separation vessel. Preferably, the water is condensed in the condenser. Further preferably, no extraneous solvent is used in the conversion.

[0047] The condensate decomposes into a water phase and an organic phase, in particular comprising by-products of the conversion. Preferably, the separation into the water phase and the organic phase is affected by means of the separation vessel. The water phase particularly forms at least part of the process water stream.

[0048] At least part of the water phase obtained in the separation vessel of the at least one distillation unit, which typically comprises water and the alcohol, with or without traces of further components, is preferably discharged, in particular via a waste water treatment unit. At least part of the water phase is fed to the stripping device as at least part of the process water stream and then to the waste water treatment unit. A remaining portion of the water phase can be recycled.

[0049] The organic phase obtained in the separation vessel of the at least one distillation unit typically comprises the alcohol and optionally alkyl acetate, the (meth)acrylate and / or dialkyl ether. Usually, the organic phase is partly, preferably to an extent of 5 wt.-% to 40 wt.-% referring to the total organic phase, removed and partly re-cycled as reflux to the conversion, preferably to the at least one distillation unit, in particular in combination with fresh alcohol. Before at least part of the organic phase is disposed of, the alcohol comprised in the organic phase can be separated off by extraction with water.

[0050] Catalyst removal step

[0051] In a preferred embodiment, the catalyst is separated from the product mixture stream generated in the conversion, in particular by extraction with water. Preferably, the product mixture stream withdrawn from the conversion step and comprising the (meth)acrylate, the alcohol, the acid, in particular (meth)acrylic acid, low boilers such as acetate ester, polymerisation inhibitors, the catalyst and heavy boilers such as oxyesters, is fed into a catalyst separation unit. In the catalyst removal step typically a catalyst extraction water stream is formed, which usually comprises water, the catalyst and the acid. The catalyst extraction water stream can for example be recycled to the conversion step, disposed of and / or combined with an alkaline aqueous phase resulting from a wash and neutralization step, in particular for the purpose of back-extraction. The catalyst extraction water stream is preferably at least partly fed to the stripping device as part of the process water stream.

[0052] The product mixture stream withdrawn from the catalyst removal step typically comprises the (meth)acrylate, heavy boilers and the alcohol, in particular part of the unconverted alcohol.

[0053] Wash and neutralization step

[0054] In a preferred embodiment, in particular when the (meth)acrylate is n-butyl (meth)acrylate, the process comprises a wash and neutralization step. Preferably, at least part of the catalyst is removed from the product mixture stream in the catalyst removal step before the remaining part of the product mixture stream is subjected to the wash and neutralization wash step. In the wash and neutralization step part of the product mixture stream, in particular withdrawn from the catalyst removal step, is contacted with an aqueous alkaline solution, which preferably comprises sodium hydroxide and / or potassium hydroxide, in particular in a concentration in a range from 1 wt.-% to 50 wt.-%, more preferably from 5 wt.-% to 15 wt.-%, referring to the total aqueous alkaline solution. Preferably a wash unit is applied.

[0055] The remaining part of the product mixture stream, which is withdrawn from the wash and neutralization step, can be referred to as crude (meth)acrylate and preferably consists to more than 90 wt.-% of the (meth)acrylate.

[0056] The used aqueous alkaline solution, which is withdrawn from the wash and neutralization step, in particular the wash unit, can be fed to the stripping device as part of the process water stream and then for example be disposed of. Alternatively, at least part of the used aqueous alkaline solution can be acidified, for example by addition of sulfuric acid, and submitted to an acid separation step. The used aqueous alkaline solution is preferably acidified to a pH value of 2 or lower.

[0057] Acid separation step

[0058] In a further preferred embodiment, the process of the invention comprises an acid separation step, in particular downstream of the catalyst removal step and the wash and neutralization step. In a preferred embodiment, the used aqueous alkaline solution from the wash and neutralization step is fed into an acid separation unit comprising an acid separation column.

[0059] In the acid separation step the acid contained in the used aqueous alkaline solution is preferably back-extracted, in particular with an extracting agent comprising the alcohol and the (meth)acrylate. The acid separation step is preferably performed at a temperature in a range from 15°C to 50°C, in particular from 20°C to 30°C. A mass ratio between the extracting agent and the used aqueous alkaline solution fed to the acid separation step, respectively, is preferably in a range from 0.1 to 1.0, more preferably from 0.4 to 0.7. In the acid separation step typically a phase separation is performed. The resulting organic phase from the acid separation step can be recycled to the conversion step. Typically, part of the alcohol is extracted from the extracting agent into the resulting aqueous phase in the acid separation step. The resulting aqueous phase from the acid separation step is preferably fed to the stripping device as part of the process water stream.

[0060] Rectification

[0061] At least part of the product mixture stream, in particular the part which is withdrawn from the wash and neutralization step, is purified by rectification. The term rectification is to be understood as a general term for processes in which vapors produced by supplying heat rise and are in contact with downward-flowing liquid phase.

[0062] Part of the product mixture stream, in particular the crude (meth)acrylate stream, is preferably fed into a low boiler column, which might be a dividing wall column. The part of the product mixture stream is more preferably fed into the side of the low boiler column, in particular to the upper half of the low boiler column. The low boiler column preferably comprises a rectifying section disposed above the feed point of the part of the product mixture stream, e.g. the crude (meth)acrylate, and a stripping section disposed below the feed point. The feed stream to the low boiler column typically contains the (meth)acrylate as main component, in particular to more than 90 wt.-%, referring to the total feed stream to the low boiler column, as well as the alcohol and optionally ester such as acetate ester and other low boilers. When the alcohol is for example n-butanol, the crude (meth)acrylate stream comprises in particular the (meth)acrylate, dibutyl ether, butylacetate, n-butanol and low boilers.

[0063] In the low boiler column, the part of the product mixture stream fed thereto, is preferably separated into a lower boiler fraction containing components boiling at a lower temperature than the (meth)acrylate; and a further remaining part of the product mixture stream, also referred to as purified (meth)acrylate, in particular comprising the (meth)acrylate and components boiling at a higher temperature than the (meth)acrylate, for example oxyesters. The low-boiler fraction typically comprises water, the alcohol, alkyl acetate, dialkyl ether and the (meth)acrylate. Water can be separated from the low-boiler fraction and fed to the stripping device.

[0064] Part of the low-boiler fraction can be recycled to the low boiler column, preferably with a reflux ration from 3 to 20, more preferably from 5 to 10, and another part of the low-boiler fraction can be recycled to the conversion. In particular, at least part of the low-boiler fraction is fed to the distillation column of the present invention.

[0065] Part of the product mixture stream, in particular the purified (meth)acrylate, is preferably taken off from the low boiler column, in particular as bottom stream. Generally, the product mixture stream withdrawn from the low boiler column, in particular the purified (meth)acrylate, has a purity of at least 95 wt.-% (meth)acrylate content based on the total part of the product mixture stream, which is taken off from the low boiler column, in particular the total purified (meth)acrylate.

[0066] In a preferred embodiment, the low boiler fraction is withdrawn from the top of the low boiler column. At least part of the low boiler fraction, in particular at least part of the organic phase of the low boiler fraction, is preferably fed into the distillation column according to step d. of the present invention. Preferably, the low boiler fraction is the part of the product mixture stream, which is heated in the distillation column in step d.

[0067] Preferably, the rectifying section of the low boiler column comprises at least 5 theoretical plates, for example 8 to 25 theoretical plates. Further preferably, the number of theoretical plates in the rectifying section of the low boiler column is smaller than in the stripping section.

[0068] In particular, the low boiler column comprises a total number of theoretical plates in the range from 16 to 70. Preferably, the side feed point for the crude (meth)acrylate stream is arranged at a theoretical plate in the region commencing at least 4 theoretical plates above the bottom most theoretical plate and ending at least 5 theoretical plates below the uppermost theoretical plate.

[0069] The low boiler column can be built as one single column or be split in two columns, which are connected in series.

[0070] The low boiler column typically comprises an evaporator and optionally a condenser, a phase separator vessel and separation internals. The separation internals of the low boiler column may in principle be all standard internals, for example trays, structured packing elements and / or random packing elements. Among the trays, preference is given to bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays; among the random packing elements, preference is given to those comprising rings, helices, saddles, Raschig, Intos or Pall rings, Berl or Intalox saddles, or braids.

[0071] More preferably, the rectifying section of the low boiler column comprises one or more structured packing elements as specified above.

[0072] Heat can be supplied to the low boiler column via internal and / or external heat exchangers of conventional design and / or via jacket heating, wherein the heat transfer medium used is advantageously steam. The heat is preferably supplied via external circulation evaporators with natural or forced circulation.

[0073] In general, the absolute pressure is in a range from 50 hPa to 300 hPa, preferably from 120 hPa to 200 hPa, measured at the top of the low boiler column. The temperature is preferably in a range from 80°C to 160°C, more preferably from 100°C to 120°C, measured at the bottom of the low boiler column. A polymerisation inhibitor solution is typically added to the low boiler column and / or the purified (meth)acrylate. With regard to polymerisation inhibitors suitable and preferred ones for this purpose, reference is made to the general observations made above in relation to suitable and preferred polymerisation inhibitors.

[0074] Finishing column

[0075] Optionally, the process according to the invention involves a finishing step, wherein a finishing column is applied. In a preferred embodiment, part of the product mixture stream, in particular withdrawn from the low boiler column, is introduced into the finishing column. In the finishing column, the (meth)acrylate is particularly separated from components boiling at a higher temperature than the (meth)acrylate.

[0076] In a more preferred embodiment, the part of the product mixture stream, also referred to as the purified (meth)acrylate, is withdrawn from the bottom of the low boiler column, and introduced into the finishing column, in particular to the lower half of the finishing column. In particular pure (meth)acrylate is withdrawn from the finishing column, preferably as top stream, and preferably condensed. The pure (meth)acrylate comprises preferably at least 99.0 wt.-%, more preferably at least 99.5 wt.-%, even more preferably at least 99.7 wt.-%, of the (meth)acrylate, referring to the total pure (meth)acrylate. Preferably, a polymerisation inhibitor is added to the finishing column and / or to the pure (meth)acrylate, for example hydroquinone monoethyl ether (HQME). The pure (meth)acrylate can comprise 10 to 20 weight ppm of HQME, referring to the total pure (meth)acrylate.

[0077] A bottom stream from the finishing column generally comprises the (meth)acrylate and high boilers such as oxyesters. The bottom stream from the finishing column can be subjected to a high boiler treatment unit for cracking, in particular for cleavage of the oxyesters. The cracking is preferably performed at a cracking temperature in a range from 140°C to 260°C, more preferably from 150°C to 200°C, at an absolute pressure in a range from 400 hPa to 900 hPa and in presence of a cracking catalyst such as mineral acids, for example sulfuric acid or phosphoric acid, or organic acids, for example methanesulfonic acid or p-toluenesulfonic acid. Cracking products such as the alcohol and the (meth)acrylate and the acid can be recycled to the conversion step.

[0078] The finishing column preferably comprises separation internals. Useful column internals include in principle all common internals, for example trays, structured packings and / or random packings. The finishing column preferably comprises dual flow trays. In general, the finishing column comprises 5 to 15 theoretical plates.

[0079] The absolute pressure measured at the top of the finishing column is preferably in a range from 10 hPa to 200 hPa, more preferably from 40 hPa to 200 hPa, even more preferably from 90 hPa to 125 hPa. The temperature measured at the bottom of the finishing column is preferably in a range from 80°C to 120°C, more preferably from 100°C to Distillation column

[0080] At least part of the product mixture stream from the conversion is fed, preferably continuously, to the distillation column. In a preferred embodiment a residual part of the product mixture stream comprising less than 80 wt.-% of the (meth)acrylate, for example the low boiler fraction from the low boiler column, is fed to the distillation column.

[0081] In an alternative embodiment the distillation column can be the low boiler column or another column applied in the process for manufacture of the (meth)acrylates. However, preferably the distillation column is a distillation column in which the low boiler fraction from the low boiler column is fed. More preferably 50 wt.-% to 100 wt.-%, even more preferably 80 wt.-% to 100 wt.-%, of the low boiler fraction from the low boiler column is heated in the distillation column. In particular, the organic phase of the low boiler fraction from the low boiler column is heated in the distillation column.

[0082] The distillation column is preferably operated at a temperature in a range from 70°C to 120°C, more preferably in a range from 80°C to 110°C, measured at the bottom of the distillation column. The absolute pressure measured at the top of the distillation column is preferably in a range from 50 hPa to 500 hPa absolute, more preferably from 100 hPa to 250 hPa absolute.

[0083] The distillation column is preferably operated at an absolute pressure of at least 30 hPa higher than the low boiler column pressure. The operating absolute pressure in the distillation column is preferably at least 40 hPa higher than the finishing column absolute pressure, measured in each case at the top of the finishing column, the low boiler column and the distillation column, respectively. While for example the alcohol and for example acetic ester have similar boiling points at the low boiler column absolute pressure, the relative boiling points change to a significant degree, as the pressure to which the low boiler fraction is exposed to in the distillation column is changed.

[0084] Preferably, the at least part of the product mixture stream is heated to a distillation temperature in a range from 70°C to 120°C, more preferably in a range from 80°C to 110°C, in the reboiler of the distillation column. The at least part of the product mixture stream is heated in the distillation column by means of the stripping outlet stream. In one embodiment, the at least part of the product mixture stream is additionally heated by means of auxiliary steam in the reboiler of the distillation column.

[0085] Preferably, the distillation column is operated at an absolute distillation pressure in a range from 50 hPa to 1000 hPa, more preferably from 100 hPa to 800 hPa (from 0.05 bar to 1 .00 bar, more preferably from 0.1 bar to 0.8 bar).

[0086] The distillation column can comprise separation internals such as trays, random packing and / or structured packing.

[0087] The separation internals ensure intimate contact between liquid and vapor in the column. With regard to separation- active internals suitable and preferred for this purpose, reference is made to the general observations stated above. In particular, the distillation column comprises a structured packing.

[0088] Step d. of the process of the invention comprises heating part of the product mixture stream in the distillation column with the reboiler. Preferably, at least part of the (meth)acrylate is separated off from the product mixture stream, for example in the low boiler column, before this part of the product mixture stream is fed to the distillation column and heated in the distillation column.

[0089] Preferably, the at least part of the product mixture stream which is fed to the distillation column, in particular at least part of the low boiler fraction from the low boiler column, comprises less than 80 wt.-%, more preferably less than 70 wt.-%, even more preferably less than 65 wt.-%, of the (meth)acrylate, referring to the total part of the product mixture stream which is fed to the distillation column. More preferably, the at least part of the product mixture stream which is fed to the distillation column, in particular at least part of the low boiler fraction from the low boiler column, comprises 10 wt.-% to 80 wt.-%, more preferably 20 wt.-% to 70 wt.-%, even more preferably 25 wt.-% to 65 wt.-%, of the (meth)acrylate, referring to the total part of the product mixture stream which is fed to the distillation column.

[0090] The at least part of the product mixture stream entering the distillation column comprises preferably water, the alcohol, the (meth)acrylate, acetate ester and ether, for example water, n-butanol, n-butyl(meth)acrylate, butyl acetate and dibutyl ether. More preferably, the at least part of the product mixture stream entering the distillation column comprises 1 wt.-% to 20 wt.-% of water, 25 wt.-% to 60 wt.-% of the alcohol, 20 wt.-% to 70 wt.-% of the (meth)acrylate, 0.1 wt.-% to 10 wt.-% of acetate ester and 0.1 wt.-% to 5 wt.-% of ether, for example 3 wt.-% to 15 wt.-% of water, 30 wt.-% to 55 wt.-% of n-butanol, 30 wt.-% to 65 wt.-% of n-buty I (meth)acry late, 0.5 wt.-% to 8 wt.-% of butyl acetate and 0.5 wt.-% to 3 wt.-% of dibutyl ether, referring to the total part of the product mixture stream entering the distillation column.

[0091] In the distillation column a top fraction, which is in particular withdrawn at the top of the distillation column, is separated from a bottom fraction, which is in particular withdrawn at the bottom of the distillation column. The top fraction typically comprises a higher concentration regarding the alcohol than the bottom fraction. Preferably the top fraction comprises a lower concentration regarding the (meth)acrylate than the bottom fraction. The top fraction consists preferably to less than 40 wt.-%, more preferably less than 20 wt.-%, even more preferably less than 10 wt.- %, of the (meth)acrylate, referring to the total top fraction. The bottom fraction consists preferably to more than 40 wt.-%, more preferably more than 50 wt.-%, even more preferably more than 60 wt.-%, of the (meth)acrylate, referring to the total bottom fraction. In a preferred embodiment the top fraction is at least partially recycled from the distillation column to the conversion step.

[0092] The alcohol from the top fraction is preferably at least partly recycled directly or indirectly from the distillation column to the conversion step. The top fraction can be for example fed to an extraction step, which is described in further detail below. The top fraction can be used as an extracting agent for back-extraction of the acid after the wash and neutralization step. The bottom fraction from the distillation column can be discharged of or fed to the acid separation step for example.

[0093] In a preferred embodiment, the product mixture stream, here also referred to as crude (meth)acrylate, is introduced into the side of the low boiler column and the low boiler column has a rectifying section disposed above the feed point of the product mixture stream and a stripping section disposed below the feed point. A purified product mixture stream comprising the at least part of the (meth)acrylate, is preferably withdrawn from the low boiler column and a low boiler fraction is preferably withdrawn from the top of the low boiler column, wherein at least part of the low boiler fraction is fed to the distillation column.

[0094] Extraction step

[0095] In a preferred embodiment the process comprises an extraction step, wherein the alcohol is extracted from at least part of the product mixture stream, in particular from at least part of the organic phase of the product mixture stream, with water. Before being removed or discharged, the alcohol can be separated from part of the organic phase obtained from the product mixture stream, in particular by extraction for example in an extraction unit.

[0096] A resulting extraction water stream, comprising water and the alcohol, is preferably conducted to the stripping device, in particular as part of the process water stream. The organic phase subjected to the extraction step can be conducted from the distillation column to the extraction step. Accordingly, the organic phase from the at least one distillation unit is preferably fed to the extraction unit. In a preferred embodiment, the top fraction from the distillation column is submitted to the extraction step, in particular fed to the extraction unit. Further the organic phase from the condensate of the at least one distillation unit at the conversion vessel can be fed to the extraction step.

[0097] In a preferred embodiment part of the extracted alcohol is returned from the extraction step to the conversion, in particular after being separated from the water in the stripping device. The remaining organic phase from the extraction step is preferably discharged.

[0098] Stripping step

[0099] The process water stream is stripped in the stripping device, in particular with steam. In a preferred embodiment collected waste water from the process for manufacture of the (meth)acrylate is stripped in the stripping device. The process water stream comprises preferably the reaction water, optionally the extraction water stream, optionally the catalyst extraction water stream and / or optionally the used aqueous alkaline solution. The stripping device is preferably a waste water stripper. Preferably the stripped process water stream, more preferably the stripped collected waste water stream, is conducted from the stripping device to a waste water treatment unit.

[0100] The stripping device can comprise for example a heatable stirred reactor which is combined with a column or the stripping device can comprise a column which is operated in counter-current mode. In particular, the process water stream, preferably the collected waste water, is fed to the top end of the stripping device and the steam is fed in counter-current to a bottom end of the stripping device.

[0101] The stripping device preferably comprises or is a stripping column. The stripping device can be heated for example directly by steam and / or indirectly for example with a double-jacket heater.

[0102] Preferably organic compounds, in particular the alcohol, are separated from the process water stream by contacting the process water with steam in the stripping device, in particular in counter-current mode. The alcohol separated from the process water stream can be recycled to the conversion.

[0103] In particular the steam enters the stripping device at a bottom of the stripping device and ascends in the process water stream, which is collected in the bottom of the stripping device. The stripping device is preferably heated by the steam, which ascends in the process water stream, only. More preferably, the stripping device, in particular the bottom of the stripping device, has no, in particular indirect or additional, evaporator.

[0104] The stripping device typically comprises at least two stripping inlets, a first stripping inlet for feeding the process water stream and a second stripping inlet, in particular a gas inlet, for feeding the steam into the interior of the stripping device, where it is contacted and mixed with the process water stream. In comparison, a distillation column typically has only one inlet for feeding the liquid to be distilled.

[0105] The process water stream is preferably fed at the top to the stripping device, in particular to the stripping column. In a preferred embodiment the process water stream is stripped in countercurrent mode with steam in the stripping device. For this purpose steam, for example with a mass ratio between the process water stream and the steam stream submitted to the stripping device from 0.001 to 0.100 t / m3, in particular from 0.005 to 0.050 t / m3, is preferably fed to the stripping device.

[0106] Preferably, the stripping outlet stream comprises the alcohol in a concentration in a range from 0.5 wt.-% to 50.0 wt.- %, in particular from 4.0 wt.-% to 40.0 wt.-%, more particularly from 10.0 wt.-% to 35.0 wt.-%, based on the total stripping outlet stream. The stripping outlet stream comprises more preferably 50.0 wt.-% to 95.0 wt.-% of water, 4.0 wt.-% to 40.0 wt.-% of the alcohol, 0 wt.-% to 5.0 wt.-% of alkyl acetate and 0.1 wt.-% to 10.0 wt.-% of the (meth)acry late, even more preferably 60.0 wt.-% to 80.0 wt.-% of water, 10.0 wt.-% to 35.0 wt.-% of the alcohol, 0 wt.-% to 3.0 wt.-% of alkyl acetate and 0.5 wt.-% to 5.0 wt.-% of the (meth)acrylate, based on the total stripping outlet stream respectively. The stripping outlet stream is in particular a gas stream.

[0107] The process water stream typically stems from reaction water formed during conversion to the (meth)acrylate and / or water used in the wash and neutralization step and / or water used in the catalyst removal step and / or water used in alcohol extraction step. Preferably, at least part of the process water stream is formed as reaction water during the conversion to the (meth)acrylate.

[0108] More preferably the process water stream is collected from reaction water formed during the conversion to the (meth)acrylate, water used in the wash and neutralization step, water used in the catalyst removal step and water used in the alcohol extraction step. The process water stream, which enters the stripping column, in particular the combined process water stream from different sources, preferably comprises from 85.00 wt.-% to 99.00 wt.-% of water, from 0.50 wt.-% to 15.00 wt.-% of the alcohol, from 0.00 wt.-% to 2.00 wt.-% of alkyl acetate and from 0.01 wt.-% to 5 wt.-% of the (meth)acrylate, even more preferably from 90.000 wt.-% to 98.000 wt.-% of water, from 1 .000 wt.-% to 7.000 wt.-% of the alcohol, from 0.001 wt.-% to 1 .000 wt.-% of alkyl acetate and from 0.050 wt.-% to 2.000 wt.-% of the (meth)acrylate, based on the total process water stream entering the stripping column. The process water stream, which enters the stripping column, in particular the combined process water stream from different sources, can further comprise sodium butyl sulfate sodium sulfate and sodium acrylate, in particular in an accumulated concentration of less than 2.000 wt.-%, based on the total process water stream entering the stripping column.

[0109] Preferably, a mass ratio between the process water stream introduced into the stripping device and the produced (meth)acrylate, in particular the pure (meth)acrylate stream leaving the finishing column as target product, is in a range from 0.2 to 3, more preferably from 0.8 to 1 .5. Due to these amounts of water, which are processed during production of the (meth)acrylate, the heat from the applied stripping unit can be reused very advantageously.

[0110] Preferably, the stripping device is operated at an absolute stripping pressure in a range from 1200 hPa to 5000 hPa, more preferably from 1800 hPa to 3000 hPa, for example at 2000 hPa (from 1,2 bar to 5 bar, more preferably from 1,8 bar to 3 bar, for example at 2 bar). The absolute stripping pressure is measured at the top of the stripping device.

[0111] Preferably, the stripping outlet stream is withdrawn from the top end of the stripping device with an outlet temperature in a range from 100°C to 150°C, more preferably from 110°C to 125°C for example with 117°C.

[0112] According to the invention, at least a part of the stripping outlet stream or the complete stripping outlet stream, is fed as heat transfer medium into the reboiler of the distillation column. Preferably, the reboiler of the distillation column comprises an indirect heat exchanger and the stripping outlet stream is passed through the indirect heat exchanger. Preferred as indirect heat exchanger are shell tube evaporators, natural circulation evaporators and forced circulation evaporators. The reboiler can be arranged internally in or externally at the distillation column, preferably internally. More preferably, the reboiler is a Robert type reboiler.

[0113] The thermal coupling of the distillation column with the stripping device is in particular preferred, as the released heat flow at the stripping device corresponds to the required heat flow at the distillation column. Further, the temperature levels, the stripping device and the distillation column are operated at, are suitable to each other.

[0114] Preferably, an optionally remaining part of the stripping outlet stream is cooled in a condenser together with the part of the stripping outlet stream withdrawn from the reboiler of the distillation column.

[0115] Preferably, the part of the stripping outlet stream withdrawn from the reboiler of the distillation column is collected in a collection vessel before being fed to the condenser.

[0116] The device for carrying out the process according to the invention preferably further comprises a collection vessel and optionally a pump, wherein the collection vessel and optionally the pump are arranged in fluidic connection between the reboiler of the distillation column and the condenser. Preferably, the part of the stripping outlet stream is conveyed from the reboiler of the distillation column to the condenser by the pump.

[0117] Embodiments of the invention are illustrated in the figures and further described in the following examples.

[0118] The figures show:

[0119] Figure 1 a schematic view of an embodiment of a process for manufacture of (meth)acrylates and

[0120] Figure 2 a part of a device for heat transfer between a stripping device and a distillation column.

[0121] Figure 1 shows a schematic view of an embodiment of a process for manufacture of (meth)acrylates. An alcohol stream 35, an acid stream 37 and a catalyst stream 39 are fed to a conversion vessel 41, which is equipped with a distillation unit 43. Alcohol and acid are converted to the (meth)acrylate. A product mixture stream 1 comprising the (meth)acrylate and part of a process water stream 3 are generated. The process water stream 3 is stripped with steam 5 in a stripping device 7, where a stripping outlet stream 11 is withdrawn. After several purification steps a residual part 45 of the product mixture stream 1 is heated in a distillation column 13.

[0122] In the conversion vessel 41 water is formed during esterification, which is removed via the distillation unit 43, condensed and separated from an organic phase in a phase separator 47. The process water stream 3 still comprises residual amounts of low-boiling components such as the alcohol, which are stripped off in the stripping device 7. The product mixture stream 1 is conducted from the conversion vessel 41 to a catalyst separation unit 49, where in this embodiment, the catalyst is removed from the product mixture stream 1 by extraction with water. The catalyst separation unit 49 is followed by a wash unit 51, where part of the product mixture stream 1 is contacted with caustic wash water 52. From the wash unit 51 wash water is conducted to the stripping device 7 as part of the process water stream 3. The stripping device 7 is connected to a waste water treatment unit 63.

[0123] In an acid separation unit 53 part of the product mixture stream 1, which left the catalyst separation unit 49 and passed the wash unit 51 is contacted with water to recycle the acid into the conversion vessel 41. Here, the separation of the acid is effectuated by extraction.

[0124] The remaining part of the product mixture stream 1 is fed into a purification unit 55, which comprises a low boiler column 57 and a finishing column 59. The residual part 45 of the product mixture stream 1 is led from the low boiler column 57 to the distillation column 13 and the product (meth)acrylate is withdrawn from the finishing column 59. From a top stream resulting from the distillation column 13 alcohol can be removed in an extraction unit 60 by extraction with water to be recycled into the conversion vessel 41. A high boiler fraction resulting from the purification unit 55 is conducted to a high boiler treatment unit 61 and partly recycled into the conversion vessel 41.

[0125] Heat can be transferred from the stripping device 7 to the distillation column 13 by means of the stripping outlet stream 11 .

[0126] Figure 2 shows a part of a device 27 for heat transfer between a stripping device 7 and a distillation column 13. The device 27 comprises a conversion vessel 41 (not shown in figure 2), a stripping device 7 with a top end 9 comprising an outlet 31 and a distillation column 13 with a reboiler 15 comprising an inlet 33. The device 27 further comprises a condenser 21 . The outlet 31 of the top end 9 of the stripping device 7 is arranged in direct fluidic connection with the inlet 33 of the reboiler 15 of the distillation column 13. The device 27 further comprises a collection vessel 23 and a pump 25. The collection vessel 23 and the pump 25 are arranged in fluidic connection between the reboiler 15 of the distillation column 13 and the condenser 21.

[0127] By conversion of an alcohol with an acid in presence of a catalyst a product mixture stream 1 comprising a (meth)acrylate and a part of a process water stream 3 are generated. The part of the process water stream 3 is formed as reaction water during conversion to the (meth)acrylate.

[0128] The process water stream 3 is stripped with steam 5 in the stripping device 7. The stripping device 7 has the top end 9, where a stripping outlet stream 11 is withdrawn from the stripping device 7. The product mixture stream 1 can be subjected to one or more purification steps and a remaining part of the product mixture stream 1, so at least part of the product mixture stream 1, is heated in the distillation column 13. The distillation column 13 is heated by means of the reboiler 15.

[0129] A part 16 of the stripping outlet stream 11 is fed into the reboiler 15 of the distillation column 13. The reboiler 15 of the distillation column 13 comprises an indirect heat exchanger 17 and the stripping outlet stream 11 is passed more precisely through the indirect heat exchanger 17. Hereby heat is transferred from the part 16 of the stripping outlet stream 11 to the at least part of the product mixture stream 1, which is fed to the distillation column 13.

[0130] A remaining part 19 of the stripping outlet stream 11 is cooled in the condenser 21 together with the part 16 of the stripping outlet stream 11, which was sent to and is then withdrawn from the reboiler 15 of the distillation column 13. Before being fed to the condenser 21 the part 16 of the stripping outlet stream 11, which is withdrawn from the reboiler 15 of the distillation column 13, is collected in the collection vessel 23. The part 16 of the stripping outlet stream 11 is conveyed from the reboiler 15 of the distillation column 13 to the condenser 21 by the pump 25.

[0131] Examples and comparative examples

[0132] The following examples of a process for preparing n-butyl acrylate are illustrated by thermodynamic simulations. For this purpose, the software Aspen Plus® (Aspen) can be used. Aspen is a comprehensive simulation software used to model, simulate and optimize 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.

[0133] In a production plant for continuous preparation of n-butyl acrylate, comprising a reactor cascade comprising three reactors with external circulation evaporators and an attached distillation unit for separating off the water of esterification, n-butyl acrylate is synthesized from acrylic acid and butanol using sulfuric acid as catalyst. The applied feed ratio of butanol to acrylic acid is 0.93 kg / kg. The sulfuric acid is adjusted to a constant concentration of 1 .9 wt.-% by weight at the outlet of the third reactor. The residence time in the conversion step is 2 hours.

[0134] The product mixture stream withdrawn from the conversion is submitted to a catalyst removal step, wherein a major part of the sulfuric acid is separated from the product mixture stream by continuous extraction with water in a mixersettler apparatus comprising a phase separator. The organic phase from the phase separator is fed to a wash and neutralization step. Also a mixer-settler apparatus and phase separator are applied, and an aqueous sodium hydroxide solution comprising 6 wt.-% of sodium hydroxide, referring to the total aqueous sodium hydroxide solution, is added.

[0135] The organic phase from the wash and neutralization step is submitted to a two step rectification, wherein a low boiler column and a finishing column are applied in series. In a first step a low boiler fraction is withdrawn from the top of the low boiler column and the organic phase of the low boiler fraction is fed to a distillation column comprising a reboiler. The low boiler column comprises an evaporator, a condenser, a phase separator and dual flow trays and is operated at a bottom temperature between 100°C and 110°C, a top temperature between 60°C and 70°C and a top absolute pressure of 120 hPa. The low boiler fraction from the low boiler column, which is introduced into the distillation column, comprises, referring to the total low boiler fraction: water 5.7 wt.-% n-butanol 32.2 wt.-% n-butyl acrylate 60.4 wt.-% residuals 1.7 wt.-%.

[0136] The distillation column is operated at a bottom temperature between 85°C and 95°C, a top temperature between 50°C and 60°C and a top absolute pressure of 160 hPa. The reboiler is supplied with an energy amount of 54.3 kW / (t / h), referring to the amount of n-butyl acrylate produced per hour.

[0137] The remaining product mixture stream is withdrawn from the bottom of the low boiler column and fed to the side of the finishing column. In a second step the product n-butyl acrylate is withdrawn from the top of the finishing column. The finishing column comprises dual flow trays and is operated at a bottom temperature of 116°C, a top temperature between 80°C and 85°C and a top absolute pressure of 110 hPa.

[0138] A resulting process water stream comprising the water of esterification and water used in the catalyst removal step and the wash and neutralization step is stripped in a stripping column with steam.

[0139] Example 1

[0140] The stripping outlet stream of 0.14 t / t (referring to the amount of n-butyl acrylate produced per hour), which is withdrawn from the stripping column operated at 1050 hPa, is disposed of and comprises 69.02 wt.-% of water, 27.65 wt.-% of butanol, 2.18 wt.-% of n-butyl acrylate, 1.06 wt.-% of butyl acetate and 0.03 wt.-% of di-n-butyl ether, referring to the total process water stream after stripping. 54.3 kW / (t / h), referring to the amount of n-butyl acrylate produced per hour, are supplied to the reboiler of the distillation column from an external auxiliary steam source.

[0141] The process water stream of 0.92 t / t (referring to the amount of n-butyl acrylate produced per hour) is depleted regarding the alcohol in the stripping column to a butanol content of 2 ppm, referring to the mass of the total process water stream after stripping. The process water stream obtained from the stripping device comprises 96.40 wt.-% of water, 2 ppm of butanol, 0.60 wt.-% of sodium butyl sulfate, 2.80 wt.-% of sodium sulfate and 0.19 wt.-% of sodium acrylate, referring to the total process water stream after stripping.

[0142] Example 2 The process corresponds to that of example 1, but 93 wt.-%, corresponding to 0.13 t / t (referring to the amount of n- butyl acrylate produced per hour), of the stripping outlet stream, which is withdrawn from the stripping column operated at 2000 hPa, is fed into the reboiler of the distillation column for heat transfer from the stripping outlet stream to the low boiler fraction from the low boiler column as part of the product mixture stream obtained during conversion. The gaseous stripping outlet stream obtained from the stripping device comprises 70.71 wt.-% of water, 26.17 wt.-% of butanol, 2.04 wt.-% of n-butyl acrylate, 1.00 wt.-% of butyl acetate and 0.03 wt.-% of di-n-butyl ether, referring to the total process water stream after stripping. Energy supply to the reboiler of the distillation column from external auxiliary sources is dispensable and thus 54.3 kW / (t / h), referring to the amount of n-butyl acrylate produced per hour, are saved in the overall process. The process water stream is depleted regarding the alcohol to a butanol content of less than 1 ppm, referring to the mass of the total process water stream after stripping. This corresponds to a reduction of the remaining alcohol content in the stripping outlet stream by about 80 % compared to example 1. The process water stream obtained from the stripping device comprises 96.45 wt.-% of water, less than 1 ppm of butanol, 0.59 wt.-% of sodium butyl sulfate, 2.76 wt.-% of sodium sulfate and 0.19 wt.-% of sodium acrylate, referring to the total process water stream after stripping.

[0143] List of reference numerals

[0144] I product mixture stream

[0145] 3 process water stream

[0146] 5 steam

[0147] 7 stripping device

[0148] 9 top end

[0149] I I stripping outlet stream

[0150] 13 distillation column

[0151] 15 reboiler

[0152] 16 part of the stripping outlet stream

[0153] 17 indirect heat exchanger

[0154] 19 remaining part

[0155] 21 condenser

[0156] 23 collection vessel

[0157] 25 pump

[0158] 27 device

[0159] 31 outlet

[0160] 33 inlet

[0161] 35 alcohol stream

[0162] 37 acid stream

[0163] 39 catalyst stream

[0164] 41 conversion vessel

[0165] 43 distillation unit

[0166] 45 residual part

[0167] 47 phase separator

[0168] 49 catalyst separation unit

[0169] 51 wash unit

[0170] 52 caustic wash water

[0171] 53 acid separation unit

[0172] 55 purification unit

[0173] 57 low boiler column

[0174] 59 finishing column

[0175] 60 extraction unit

[0176] 61 high boiler treatment unit

[0177] 63 waste water treatment unit

Claims

Claims1. Process for manufacture of (meth)acrylates comprising the following steps: a. Providing an alcohol and an acid, b. Conversion of the alcohol and the acid in presence of a catalyst to the (meth)acrylate, wherein a product mixture stream (1) comprising the (meth)acrylate and at least part of a process water stream (3) are generated, c. Stripping the process water stream (3), in particular with steam (5), in a stripping device (7) having a top end (9), wherein a stripping outlet stream (11) is withdrawn from the top end (9) of the stripping device (7), d. Heating at least part of the product mixture stream (1) in a distillation column (13) with a reboiler (15), e. Feeding at least a part (16) of the stripping outlet stream (11) into the reboiler (15) of the distillation column (13), wherein heat is transferred from the part (16) of the stripping outlet stream (11) to the at least part of the product mixture stream (1).

2. Process according to claim 1, wherein the reboiler (15) of the distillation column (13) comprises an indirect heat exchanger (17) and the stripping outlet stream (11) is passed through the indirect heat exchanger (17).

3. Process according to claim 1 or 2, wherein a remaining part (19) of the stripping outlet stream (11) is cooled in a condenser (21) together with the part (16) of the stripping outlet stream (11) withdrawn from the reboiler (15) of the distillation column (13).

4. Process according to claim 3, wherein the part (16) of the stripping outlet stream (11) withdrawn from the reboiler (15) of the distillation column (13) is collected in a collection vessel (23) before being fed to the condenser (21).

5. Process according to claim 3 or 4, wherein the part (16) of the stripping outlet stream (11) is conveyed from the reboiler (15) of the distillation column (13) to the condenser (21) by a pump (25).

6. Process according to any of claims 1 to 5, wherein the stripping outlet stream (11) comprises the alcohol in a concentration in a range from 0.5 wt.-% to 50 wt.-%, in particular from 4 wt.-% to 40 wt.-%, more particularly from 10 wt.-% to 35 wt.-%, based on the total stripping outlet stream (11).

7. Process according to any of claims 1 to 6, wherein at least part of the process water stream (3) is formed as reaction water during the conversion to the (meth)acrylate.

8. Process according to any of claims 1 to 7, wherein the stripping device (7) is operated at an absolute stripping pressure in a range from 1500 hPa to 5000 hPa, preferably from 2000 hPa to 5000 hPa.

9. Process according to any of claims 1 to 8, wherein the distillation column (13) is operated at an absolute distillation pressure in a range from 50 hPa to 1000 hPa.

10. Process according to any of claims 1 to 9, wherein the stripping outlet stream (11) is withdrawn from the top end (9) of the stripping device (7) with an outlet temperature in a range from 100°C to 150°C.11 . Process according to any of claims 1 to 10, wherein the at least part of the product mixture stream (1) is heated to a distillation temperature in a range from 70°C to 120°C in the reboiler (15) of the distillation column (13).

12. Process according to any of claims 1 to 11, wherein the acid is (meth)acrylic acid and the alcohol contains 1 to 8 carbon atoms and preferably the (meth)acrylate is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-butyl and iso-butyl (meth)acrylate and 2-octyl (meth)acrylate.

13. Process according to any of claims 1 to 12, wherein the catalyst is a mineral acid or a sulfonic acid, in particular the catalyst is chosen from the 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, o-toluenesulfonic acid or dodecylbenzenesulfonic acid; and mixtures thereof.

14. Device (27) for carrying out the process according to any of claims 1 to 13, comprising a conversion vessel (41), a stripping device (7) with a top end (9) comprising an outlet (31), a distillation column (13) with a reboiler (15) comprising an inlet (33) and optionally a condenser (21), wherein the outlet (31) of the top end (9) of the stripping device (7) is arranged in fluidic connection with the inlet (33) of the reboiler (15) of the distillation column (13), in particular in direct fluidic connection.

15. Device (27) according to claim 14 further comprising a collection vessel (23) and optionally a pump (25), wherein the collection vessel (23) and optionally the pump (25) are arranged in fluidic connection between the reboiler

Images