Discontinuous esterification (transesterification) method of (meth) acrylate compound

Abstract

Process strategies and methods for discontinuous esterification (transesterification) of (meth) acrylates are disclosed. The process can produce an alkyl (meth) acrylate product by an esterification (transesterification) reaction of the reaction mixture. The reaction mixture comprises a (meth) acrylate starting material and a first alcohol that is converted to an alkyl (meth) acrylate product and by-products by an esterification (transesterification) reaction in the presence of a catalyst. The esterification (transesterification) reaction is carried out in a reactor system. The reactor system includes a heating and / or cooling system, a reaction chamber containing the reaction mixture, a column having an overhead, a vapor transfer line, a condenser, a return tank, a return line, a distillate transfer line, and a receiving vessel. At least a portion of the by-product is continuously removed by withdrawing the distillate within a major amount of time during the esterification (transesterification) reaction. The pressure is continuously adjusted to maintain the reaction temperature below a predetermined upper limit.

Description

Technical Field

[0001] The present invention relates to the field of discontinuous esterification (transesterification) of (meth)acrylate compounds with alcohols to produce target products with the concomitant separation of by-products. Background Art

[0002] For the discontinuous esterification (transesterification) of (meth) acrylic esters with alcohols, amino alcohols or amines to produce new target products, a heatable reactor with a directly connected tower as a separation system is used. The reactor can be evacuated by a vacuum system. The vacuum can be adjusted as required. The pressure in the reactor system can be freely selected. This means that overpressure in the reactor and tower and condensation system is also possible. The vapor from the tower is condensed and part or all of the stream is discharged into a receiving container. The remaining condensate is used as a return stream for the tower and is returned to the reaction system via the tower reactor (sump).

[0003] In the conventional operating mode, more of the desired (meth)acrylate (e.g. MMA - methyl methacrylate) must be present than the alcohol, amino alcohol or amine before the reaction with the alcohol is started. The reason for this is that the desired (meth)acrylate serves not only as a starting material for the target product to be produced, but also as a boiling aid which limits the reaction temperature, since during the reaction the composition of the reaction mixture changes due to product formation, so that the presence of additional high-boiling components increases the boiling point of the mixture and thus also the overall reactor temperature. Limiting the reaction temperature is important to prevent unintended polymerization of the (meth)acrylate and the target product.

[0004] US 9 776 946 B2 discloses a transesterification reaction of a (meth) acrylic acid lower alkyl ester with another alcohol in an apparatus, wherein a reduced pressure is used to drive the reaction or complete the reaction and remove excess (meth) acrylic acid lower alkyl ester. EP0 906 902 A2, EP 0 683 163 A1 and US 2010 / 274042 A1 disclose similar transesterification of lower (meth) acrylic acid esters with alcohols.

[0005] However, by providing an excess of (meth)acrylate, the reactor volume cannot be fully utilized for the raw materials that will form the target product, which leads to a limited space-time yield. Likewise, larger amounts of the desired (meth)acrylate must be recycled or disposed of as excess, which costs time, energy and money.

[0006] It is therefore an object of the present invention to provide a method which overcomes the above-mentioned problems. Summary of the invention

[0007] The present invention relates to a process for preparing an alkyl (meth)acrylate product by an esterification (transesterification) reaction of a reaction mixture in a reactor system, the reactor system comprising a heating and / or cooling system, a reaction chamber containing the reaction mixture, a column having a column top, one or more vapor transfer lines, a (multi-stage) condenser system, a reflux drum, a reflux line, a distillate transfer line and a receiving vessel,

[0008] wherein the reaction mixture comprises a (meth)acrylate starting material and a first alcohol, amino alcohol or amine, which is converted into a (meth)acrylate alkyl ester or amino ester product and a by-product by an esterification (transesterification) reaction in a reaction chamber at a reaction temperature and a given pressure in the presence of a catalyst,

[0009] wherein at least a portion of the by-products are continuously removed by withdrawing a distillate during a predominant amount of time during the esterification (transesterification) reaction, and

[0010] During the majority of the time during the esterification (transesterification) reaction, the given pressure is continuously adjusted to maintain the reaction temperature below a predetermined upper limit.

[0011] In order to prevent this reaction from exceeding a temperature threshold in the reactor (which would prevent polymerization) without the temperature stabilizing effect of the (meth)acrylate, the pressure in the system is continuously regulated to keep the reaction temperature below a predetermined upper limit. In this method, the pressure is reduced linearly to the target value as the reaction proceeds and the temperature in the reactor naturally rises. This has a positive effect not only on the reduced polymerization tendency, but also on the average reaction rate achieved within the batch time. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A reactor system according to the invention is exemplified, comprising a heating and / or cooling system 12, 12a, a reaction chamber 1, a feed line 13, 13a leading to the reaction chamber 1, a column 2 having a column top 3, a vapor transfer line 4, a (multi-stage) condenser system 5, a reflux drum 6, a reflux line 7 having a mass flow meter 10, a distillate transfer line 8 having a mass flow meter 10, a receiving vessel 9, a recirculation line 11, a distillate withdrawal line 15, 15a and a reaction chamber withdrawal line 14. DETAILED DESCRIPTION OF THE INVENTION

[0014] Unless otherwise specifically defined herein, the relevant terms used in the present invention have the following definitions.

[0015] As used herein, the term "(meth)acrylate" refers to both (meth)acrylic acid and esters of (meth)acrylic acid. In addition, it refers to both methacrylate and acrylate. Alternatively, it refers to methacrylate or acrylate depending on the respective context. It also refers to methacrylic acid and esters of methacrylic acid. For example, the term "(meth)acrylate compound" or "(meth)acrylate product" refers to (meth)acrylic acid and esters of (meth)acrylic acid, such as alkyl (meth)acrylate.

[0016] Preferred (meth)acrylate products that can be prepared according to the present application are selected from:

[0017] Dimethylaminoethyl methacrylate

[0018] 1,4-Butanediol dimethacrylate

[0019] Ethyl Methacrylate

[0020] Dimethylaminopropyl methacrylate

[0021] Benzyl methacrylate

[0022] Allyl methacrylate

[0023] 2-Ethylhexyl Methacrylate

[0024] Cyclohexyl methacrylate

[0025] Ethylene glycol dimethacrylate

[0026] Butyl diglycol methacrylate

[0027] Triethylene glycol dimethacrylate

[0028] 1,3-Butanediol dimethacrylate

[0029] Trimethylolpropane trimethacrylate

[0030] Ethyl triglycol methacrylate

[0031] 1,6-Hexanediol dimethacrylate

[0032] Polyethylene glycol 200 dimethacrylate (molecular weight = 200 g / mol)

[0033] Methoxy-polyethylene glycol methacrylate (MPEG500, molecular weight = 500 g / mol)

[0034] Methacrylate having an average number of carbon atoms of 17.4

[0035] Isodecyl Methacrylate

[0036] Methacrylate with an average number of 13 carbon atoms (synthetic lauryl methacrylate)

[0037] n-Hexyl Methacrylate

[0038] Methacrylate of a mixture of ethoxylated C16-18 fatty alcohols

[0039] As catalysts, lithium chloride, lithium amide, lithium hydroxide, lithium methoxide, zirconium(IV) acetylacetonate, titanates such as tetraisopropyl orthotitanate, calcium hydroxide and calcium oxide, and combinations thereof may be used.

[0040] As used herein, the term "esterification (transesterification)" or "esterification (transesterification) reaction" refers to both esterification reaction and transesterification reaction. Alternatively, it refers to esterification reaction or transesterification reaction according to the respective context.

[0041] As used herein, the term "reactor system" refers to a reactor in which a chemical reaction of a reaction mixture can occur, and in which the contents of the reactor can undergo a distillation process before and / or during and / or after the chemical reaction process or independently of the chemical reaction. The advantage of such a reactor is that it is not necessary to provide several chambers, one for the reaction to occur and one for the distillation of one or more substances, thereby saving materials, time for transferring substances and saving costs. The reactor system comprises at least an internal and / or external heating and / or cooling system, a reaction chamber, a tower with a tower top, a feed line to the reaction chamber or tower, a vapor transfer line, a (multi-stage) condenser system, a reflux drum, a reflux line, a distillate transfer line and a receiving vessel.

[0042] As used herein, the term "starting material" refers to a raw material, initial material, reagent, feed, reactant or initial reactant that can be used to carry out a chemical reaction, whereby the chemical reaction can produce at least one or more products, which may include side-products or by-products.

[0043] As used herein, the term "heating and / or cooling system" refers to a device capable of heating and, if necessary, cooling a liquid and / or converting a liquid into its vapor or, in other words, gaseous state.

[0044] As used herein, the term "reaction chamber" refers to a container in which a chemical reaction is performed. There are a variety of chambers referred to as such. For example, the size of the reaction chamber ranges from a micro reaction chamber that holds a few microliters, to a reaction chamber of a few milliliters, to a chamber having a volume of several cubic meters. The most important characteristic of each reaction chamber is its tolerance to the reaction conditions.

[0045] As used herein, the term "reaction mixture" refers to a mixture of substances that participate in a reaction. Such a reaction mixture may contain or consist of the following substances:

[0046] - starting materials,

[0047] - starting materials and possible additives, such as auxiliary substances, which may be, for example, catalysts or other reaction accelerators, and / or stabilizers,

[0048] - starting materials and products, including possible by-products,

[0049] - starting materials, additives and products, including possible by-products,

[0050] - products, including possible by-products, and additives,

[0051] - the product itself and additives,

[0052] - products, including possible by-products, or

[0053] - The product itself.

[0054] As used herein, the term "tower" refers to a device for thermally separating a mixture. In order to avoid heat losses, the tower can be an insulated, preferably cylindrical tube, which can be made of steel, high-alloy stainless steel, glass or plastic in particular. The height of the tower body can depend primarily on the required separation quality; the diameter depends on the volume flow of the mixture to be separated. The tower can be placed between the reaction chamber and the distillation head. The number of separate distillations required for the same separation performance can also be called the "theoretical plate number". On the surface of the tower, the balance between the liquid phase and the gas phase can be continuously rebuilt by condensation and evaporation. Therefore, the proportion of low-boiling components continues to increase toward the top, while higher boiling components flow back to the reaction chamber, the tower kettle. The surface area size of the tower can be greatly increased in various ways by the design of the tower tray (as in the Vigreux tower) or by filling with fillers or structured packing.

[0055] As used herein, the term "feed line" refers to a supply line that feeds a substance or mixture of substances into, for example, a reaction chamber or a column.

[0056] As used herein, the term "condenser system" refers to a unit in which the vapor produced during the distillation process (which may consist of various volatile components of the solution to be separated) can be liquefied by cooling through one or more different cooling liquids.

[0057] As used herein, the term "reflux drum" refers to a vessel into which condensed distillate flows and then the condensed distillate flows back to the column and / or reaction chamber, or is removed from the system.

[0058] As used herein, the term "reflux line" refers to a line that can return distillate from a reflux drum to a column or a reaction chamber.

[0059] As used herein, the term "distillate transfer line" refers to a line that can remove at least a portion of the distillate from the reflux drum and thus remove distillate from the reflux sent to the column or column overhead.

[0060] The term "distillate take-off line" refers to a line by which at least a portion of the distillate can be removed, typically from the reactor system and the distillation system.

[0061] As used herein, the term "starting material" refers to a raw material, initial material, reactant, feed, reactant or initial reactant that can be used to carry out a chemical reaction, whereby the chemical reaction can produce at least one or more products, which may include by-products or by-products.

[0062] As used herein, the term "reaction time" is defined as the duration of time to remove byproducts from the reaction mixture. The reaction time depends greatly on the first alcohol used in the transesterification reaction and can vary between 2 hours and up to 48 hours.

[0063] As used herein, the term "substantial amount of time" means more than 50% of the reaction time, more preferably more than 60% of the reaction time, and most preferably more than 75% of the reaction time.

[0064] As used herein, the term "target value" refers to a value to be achieved in a process. In particular, the target value refers to a specified pressure to be achieved during an esterification (transesterification) reaction.

[0065] As used herein, the term "overhead concentration" refers to the concentration of the overhead distillate. The distillate can be any compound of the reaction mixture or a byproduct or by-product thereof.

[0066] As used herein, the term "vacuum stage" refers to the product generation stage wherein a low pressure or vacuum is applied to the reactor.

[0067] The term "distillation stage" refers to the product formation stage in which materials of the reaction mixture are distilled off.

[0068] As used herein, the term "high boiling point ester" or "high boiling point component" refers to esters having a boiling point above 210°C, such as ethylene glycol dimethacrylate (EGDMA), methacrylates having an average number of 13 C atoms, 1,3-butanediol dimethacrylate (1,3 BDDMA) and 1,4-butanediol dimethacrylate (1,4 BDDMA).

[0069] The term "low-boiling ester" or "low-boiling component" refers to esters having a boiling point below 210°C, such as 2-ethylhexyl methacrylate (EHMA), isodecyl methacrylate (IDMA) and butyl methacrylate (BUMA).

[0070] As used herein, the term "wt %" means percent by weight.

[0071] The problem on which the present invention is based is solved by a process for preparing an alkyl (meth)acrylate product by esterification (transesterification) of a reaction mixture in a reactor system comprising a heating and / or cooling system, a reaction chamber containing the reaction mixture, a column with a column top, a vapor transfer line, a condenser system, a reflux drum, a reflux line, a distillate transfer line and a receiving vessel,

[0072] wherein the reaction mixture comprises a (meth)acrylate starting material and a first alcohol, which are converted into (meth)acrylate alkyl ester products and by-products by an esterification (transesterification) reaction in a reaction chamber at a reaction temperature and a given pressure in the presence of a catalyst,

[0073] wherein at least a portion of the by-products are continuously removed by withdrawing a distillate for a substantial amount of time during the esterification (transesterification) reaction, and

[0074] During the majority of the time during the esterification (transesterification) reaction, the given pressure is continuously adjusted to maintain the reaction temperature below a predetermined upper limit.

[0075] The process according to the invention has the advantage that the tendency to polymerize is reduced and the average reaction rate achieved within the batch time is positively influenced.

[0076] The reaction mixture may comprise two or more starting materials and two or more products. Further preferably, the two or more starting materials are a first reactant, a second reactant and one or more optional additional compounds, and wherein the two or more products are a first product, a second product and one or more optional additional products. The reaction mixture may further comprise an additive, such as a reaction promoter, a reaction inhibitor, a buffer, a solvent, a stabilizer, water, a viscosity index improver, a thickener, an antioxidant, a corrosion inhibitor, a dispersant, a high pressure additive, a defoamer, a catalyst or an enzyme. In addition, the reaction may form a by-product, which may also be present in the reaction mixture.

[0077] According to the invention, before starting the reaction, more alcohol (in moles) may be present in the reaction mixture than (meth)acrylate. At the beginning, the ratio of alcohol to (meth)acrylate may be in the range of 1.2:0.8 to 1.0:1.0, preferably in the range of 1.2:0.8 to 1.1:0.9, or in the range of 1.2:0.8 to 1.0:1.0. This ratio relates to the hydroxyl groups present in the alcohol. While the reaction is running, additional amounts of (meth)acrylate may be added to the reaction mixture. During the reaction, the ratio of alcohol to (meth)acrylate may decrease to a range of 1.0:1.0 to 0.7:1.3, preferably a range of 1.0:1.0 to 0.8:1.2.

[0078] The pressure in the system is adjusted continuously or incrementally to keep the reaction temperature below a predetermined upper limit. By adding more alcohol than (meth)acrylate, more boiler volume can be used for product production and the space-time yield of the target product can be increased.

[0079] If the reaction is run conventionally, a temperature threshold will be exceeded in the reactor before the reaction is complete because the reaction temperature will not be adequately regulated by the (meth)acrylate starting material in the presence of more first alcohol, which will prevent polymerization. However, regulating the pressure by applying a vacuum or a substantially lower pressure prevents this process.

[0080] Preferably, the continuous regulation of the given pressure is a continuous linear decrease of the given pressure to the target value.

[0081] This has the advantage that the pressure is reduced in a controlled manner and the target pressure is reached within a predetermined time frame.

[0082] During the esterification (transesterification) reaction, the target value of the reaction temperature is in the range of 90° C. to 145° C., preferably in the range of 100° C. to 135° C., at a pressure in the range of 1300 mbar to 400 mbar (absolute), preferably in the range of 1150 mbar to 600 mbar (absolute). At the end of the reaction phase, the pressure may be reduced to below 600 mbar to 20 mbar (absolute).

[0083] The reactor system may further comprise one or more elements selected from the group consisting of: one or more mass flow meters, a recycle line, a distillate withdrawal line, a reaction chamber withdrawal line and a feed line to a reaction chamber or a column, preferably wherein the feed line is a first feed line, and wherein the reactor system further comprises a second feed line to the reaction chamber or the column, and optionally, additional feed lines to the reaction chamber or the column.

[0084] This has the advantage that substances and / or mixtures can be added to reaction chamber and / or tower via several feed lines. Substances and / or mixtures can be added simultaneously or successively and / or continuously or discontinuously via these feed lines. Different substances and / or mixtures can be added to reaction chamber and / or tower via feed lines. The same substance and / or mixture can also be added to reaction chamber and / or tower via feed lines. In addition, the same substance and / or mixture and different substances and / or mixtures can be added to reaction chamber and / or tower via feed lines. These substances or mixtures can be, for example, starting materials and / or additives for the reaction, such as reaction promoters, reaction inhibitors, buffers, solvents, stabilizers, water, viscosity index improvers, thickeners, antioxidants, corrosion inhibitors, dispersants, high pressure additives, defoamers, catalysts or enzymes.

[0085] Preferably, the reactor comprises the possibility to supply energy by heating and to remove energy by cooling. Preferably, the reactor comprises a mixing device for the reaction chamber. Preferably, the reactor comprises metering devices for solids, liquids and gases, which can be supplied to the reaction chamber, the column, the steam line, the condensation system and the feed line.

[0086] The reactor includes a pressure control system capable of controlling and regulating the pressure in the reactor chamber, column and condensation system.

[0087] Through the reflux line, the distillate can flow back to the column or back to the reaction chamber. The reflux tank stores the reflux of the distillate.

[0088] The first alcohol can be a linear or branched C2-C20 alkanol, a linear or branched C2-C20 alkanediol, an amino alcohol, preferably dimethylaminoethanol and dimethylaminopropanol, an amine, a linear or branched ortho-C2-C20 alkanediol, or preferably ethylene glycol.

[0089] In the process of the present invention, the by-products can also be removed in the form of a mixture of by-products and (meth)acrylate starting material.

[0090] This has the advantage that, in particular at the end of the reaction, the reaction continues to run towards product formation without stagnating.

[0091] When carrying out the process according to the invention, one preferred option is to compensate at least a portion of the withdrawn (meth)acrylate starting material and / or first alcohol by adding further amounts of (meth)acrylate starting material and / or first alcohol to the reaction mixture in the reaction chamber, preferably via a feed line to the reaction chamber or the column, so that the filling level of the reaction chamber is kept constant.

[0092] The filling level of the reaction chamber is kept constant by using, for example, an inflow controller for MMA and / or alcohol. The feed of the reactants is regulated (e.g., control valves and mass flow measurement). During the reaction, byproducts (e.g., methanol) are taken out of the reaction chamber via a tower. Therefore, if no additional reactants are fed, the reaction chamber filling level will continue to decline. The filling level controller now controls and regulates the feed of one or more reactants. The output signal from the filling level controller serves as the target value of the inflow controller, which then regulates the mass flow to be metered. In this way, individual streams of components or several components in a single stream can be metered into the reactor. Based on the mass meter, the feed flow rate can be 3.5 to 0.01 times the amount taken out. Preferably, the feed flow rate is 2.5 to 0.1 times the amount taken out, more preferably 1.75 to 0.25 times.

[0093] This has the advantage that the available volume in the reactor chamber is used for the esterification (transesterification) reaction, which increases the space-time yield. Preferably, the additional alcohol, amino alcohol or amine starting material is added to the maximum reactor filling level in order to use the maximum volume of the reactor for the esterification (transesterification) reaction and to increase the space-time yield even further. This has the further advantage that, since a maximum utilized heat transfer area is provided, an optimal heat transfer from the outer wall to the reaction wall into the reaction medium is achieved. Further preferably, the reactor filling level remains constant during the esterification (transesterification) process.

[0094] When carrying out the process according to the invention, a further preferred option is to keep the by-product concentration at the top of the column constant. This has the advantage that the separation of the compounds in the reactor system is optimal and thus reduces the loss of, for example, MMA from the system.

[0095] refer to Figure 1 , illustrating that the amount of reflux 7 sent to the top 3 can be controlled via the filling level in the reflux drum 6. If more distillate accumulates from the condenser system 5, the reflux amount will increase if the filling level in the reflux drum 6 is increased. If no distillate is taken out of the system via the distillate transfer line 8, all condensate obtained from the condenser system 5 is fed to the column via the reflux drum 6 and the reflux line 7. In the process step of transesterification, it is preferred that the controller ensures that there is always a distillate transfer via the transfer line 8 to the receiving container 9. This is achieved by calculating the reflux ratio (v = reflux flow in the reflux line 7 / distillate transfer in the line 8). The distillate transfer stream 8 is adjusted so that the reflux ratio (v) is always within the range of a maximum of 15 and a minimum of 0.33. The transfer stream 8 can be freely selected between the specified limits defined by the reflux ratio (v). However, this is preferably set in a manner that a constant top concentration of methanol in the top 3 can be maintained. The concentration in the column top 3 is determined using a flow meter 10 in the stream 7 or 8 .

[0096] This concentration should be maintained between 78 mol % (MeOH) and 62 mol % (MeOH), preferably between 74 mol % (MeOH) and 68 mol % (MeOH). If the methanol concentration in the top 3 increases, the transfer stream 8 increases; if the methanol concentration in the top 3 decreases, the transfer stream 8 decreases.

[0097] Byproduct concentration can be measured by online measurement. For example, refractive index and / or density can be measured. The tower top can be adjusted to take out by concentration measurement so that the tower top concentration remains constant during the reaction. When MMA is used as starting material, byproducts (which are methanol) accumulate during the reaction and are continuously separated by distillation via the connected tower. If the methanol concentration in the tower top remains constant within a determined range of 78 to 62 mol %, preferably 74 to 68 mol %, then the separation from the reactor and therefore the MMA loss from the system is optimal. However, the minimum take-out is always maintained so that the reaction process remains to be continued, even if only low conversion is present at the end of the reaction.

[0098] According to the invention, the concentration measured at the top of the column can be used to influence the withdrawal amount by calculation and regulation. The return flow rate back to the column can be controlled by the filling level of the distillate collecting tank. If no material is withdrawn from the system, the resulting distillate is completely returned to the column as reflux. Calculations in the process control system can ensure that the maximum and minimum reflux ratios are maintained, regardless of what the concentration measurement at the top of the column indicates.

[0099] The calculation scheme can be as follows:

[0100] a) Concentration measurement (tower top),

[0101] b) control of concentration (to set point),

[0102] c) The controller output is converted to the discharge volume flow rate,

[0103] d) Discharge volume flow limitations, including maximum and minimum reflux ratios (range is 15 max, 0.33 min), and

[0104] e) Set points for fume hood controllers.

[0105] A further preferred option of the process according to the invention is that the energy input into the reactor chamber is controlled via the total amount of distillate produced.

[0106] According to the invention, the energy input into the reactor 1 is realized via the heating system 12, 12a of the reactor. The system can be heated, for example, by steam, a hot oil system, electricity, etc.

[0107] The required heat output (energy input to the reactor) is usually adjusted so that certain parameters (total distillate occurring in the condenser system 5, pressure drop across the column 2 and reactor temperature) are not exceeded during the process. The main control variable for the energy input is usually the amount of the distillate stream occurring in the condenser 5 or the reflux drum 6. This should remain constant throughout the reaction. The amount of distillate produced should be selected so that for the column 2, an F factor in the range of 0.5 to 3.0 Pa^(1 / 2), preferably in the range of 1.0 to 2.0 Pa^(1 / 2) is achieved. If the pressure loss in the column rises above a preset value in the range of 10 to 4 mbar / m of packing, preferably in the range of 6.5 to 4 mbar / m of packing, the energy input via the heating and / or cooling system 12, 12a should be reduced to such an extent that this value can be maintained. If the temperature of the reaction chamber or the reaction chamber wall rises above a preset value of 150°C to 185°C, preferably 160°C to 170°C, the energy input should be adjusted so that this value can be maintained. This energy input strategy ensures that the loads on column 2 and reactor 1 do not exceed their system limits, but the system is always at its upper operating limit and is therefore optimally utilized.

[0108] The energy input to the reactor can be controlled by the total amount of distillate produced. The measured amount of distillate can be corrected by possible level fluctuations of the condenser. The mass flow rate of the vapor flowing from the tower into the condenser can be kept constant. However, the distillate flowing from the tower into the condenser may be limited by two parameters. If the wall temperature at the heat transfer location is higher than a critical value, the amount of energy flowing into the reactor can be adjusted downward so as not to exceed this critical temperature. The critical temperature is usually in the range of 150°C to 185°C, preferably 160°C to 170°C. This is important because otherwise the operating time of the reactor is reduced and the polymerization tendency of the product is reduced. The pressure difference across the tower (including the steam line) can also be measured continuously. If the pressure loss rises above a critical value (which can be defined as or in the range of 10 mbar / m to 4 mbar / m for structured packing, preferably in the range of 6.5 mbar / m to 4 mbar / m for structured packing), the amount of energy entering the reactor is also adjusted downward. This prevents foam from entering the tower, which causes a sharp drop in operating time and performance. In any case, due to these two interventions, it is still possible to operate with high-performance energy input throughout the entire reaction time, because if limitations due to pressure differences or wall temperatures occur in certain process sections, the system intervenes in a self-protective manner. That is, only in small process sections or process time phases, the intervention that reduces performance is carried out, and the system can be operated at full capacity (can be operated at full power) for the rest of the time. This also leads to an increase in the space-time yield.

[0109] In a still further preferred option of the process of the invention, the end point of the esterification (transesterification) reaction is determined by the by-product concentration at the top of the column, the temperature at the top of the column and the reactor temperature.

[0110] If the reaction is complete, this point can be reliably detected so that the next process step, the vacuum phase or the distillation phase, can be started. If the methanol concentration in the column top 3 reaches 5 mol %, preferably 3 mol %, more preferably 2 mol %, the vacuum or distillation phase is started.

[0111] As described above, the end point of the esterification (transesterification) reaction can be determined by a combination of values ​​regarding the top concentration and / or temperature and the reactor temperature. This has the advantage that the risk of polymerization can be limited and an increase in the concentration of secondary components (based on side reactions) can be prevented.

[0112] In normal operating mode, only the reactor temperature is used to detect endpoint.

[0113] According to a preferred option of the process according to the invention, the removal of by-products is stopped when the end of the vacuum phase is reached.

[0114] As an alternative, in the case of low-boiling esters, the end point of the vacuum stage is determined by the pressure and temperature profile of the column, and when the end point of the vacuum stage is reached, the removal of by-products is stopped.

[0115] The end of the low-boiling ester production process can be confirmed by identifying a characteristic temperature profile. Temperature sensors can be installed at different heights in tower 2. These can be located at (a) the top of the tower, (b) after the first 1 / 3 of the tower packing, (c) after the second 1 / 3 of the tower packing, and (d) at the bottom of the tower. The end of the process can be defined in such a way that sensors (c), (b) and (d) must have almost the same temperature. If this is the case, the temperature can be recorded in (a). The recorded temperature in (a) can then be subtracted from the temperature (d). If the temperature (a) has now increased by 1 / 3 of the calculated value, the end point of the process has been reached.

[0116] As a reaction endpoint detection, it is important to detect the end of the entire process (which can also be the end of the vacuum phase). This has the advantage that the final purity can be guaranteed when the vacuum phase is completed. In addition, detecting the reaction endpoint has the further advantage that the vacuum phase does not last too long and the risk of polymerization is reduced. Demand-based identification generally increases the space-time yield.

[0117] Preferably, the esterification (transesterification) reaction is carried out in the presence of a polymerization inhibitor. This can be fed into the system as a solid and / or as a solution of one or more components of the reaction mixture into any point in the system.

[0118] This has the advantage that polymerization is suppressed and the space-time yield is increased. In addition, the product can be purer.

[0119] As inhibitors, p-phenylenediamine, phenothiazines and hydroxylamines such as N,N-bis(2-hydroxypropyl)hydroxylamine (HPHA) and N,N-diethylhydroxylamine (DEHA) can be used.

[0120] The most preferred inhibitors or stabilizers are hydroquinone (HQ), its methyl ether HQME and 2,2,6,6-tetramethylpiperidinyloxy (TEMPO), or derivatives thereof such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (hydroxy-TEMPOL) and any derivatives of this hydroxy functionalization such as methacrylate of 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy.

[0121] The polymerization inhibitor hydroquinone methyl ether (HQME) may be present in the range of 1 ppm to 2000 ppm, preferably 10 to 1000 ppm, more preferably 10 to 500 ppm, and most preferably 50 to 100 ppm. The polymerization inhibitor 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) or any derivative thereof may be present in the range of 0.1 ppm to 1000 ppm, more preferably 1 ppm to 500 ppm, and most preferably 10 ppm to 100 ppm, wherein ppm is by weight.

[0122] Preferably, the esterification (transesterification) reaction is carried out with the introduction of oxygen into the reaction mixture.

[0123] This has the advantage of stabilizing the reaction and accelerating the reaction rate.

[0124] In addition to oxygen, air can also be introduced into the reaction to accelerate the reaction process. Oxygen can be introduced continuously or discontinuously, preferably continuously.

[0125] In the method according to the present invention, the (meth)acrylate starting material may contain methyl (meth)acrylate and the by-product may contain methanol, or the (meth)acrylate starting material may contain ethyl (meth)acrylate and the by-product may contain ethanol, or the (meth)acrylate starting material may contain n-butyl (meth)acrylate and the by-product may contain butanol, or the (meth)acrylate starting material may contain (meth)acrylic acid and the by-product may contain water, preferably the (meth)acrylate starting material contains methyl (meth)acrylate and the by-product contains methanol.

[0126] The whole method sequence:

[0127] The overall process of the esterification (transesterification) process can be characterized by a specific sequence of sub-steps. These depend on the product to be manufactured and can vary depending on the product.

[0128] Basically, the following steps can be carried out in the esterification (transesterification) process:

[0129] Filling and feeding the reactor with reactants,

[0130] Add stabilizers,

[0131] Optionally, dehydrating the mixture,

[0132] Adding catalyst,

[0133] Heating the reactor contents,

[0134] Separation of by-products (e.g. methanol) during the reaction to the target product under regulated pressure and temperature,

[0135] Optionally, adding reactants during the reaction phase,

[0136] further reducing the pressure to separate the excess starting material and transfer it to the feed for the next reaction batch,

[0137] Detecting the endpoint of the process,

[0138] Regulate pressure and temperature in subsequent process steps.

[0139] Further advantages, details and features of the invention will become apparent hereinafter from the embodiments explained. DETAILED DESCRIPTION Example

[0140] Example 1: Preparation of EHMA (2-ethylhexyl methacrylate)

[0141] exist Figure 1 2-Ethylhexyl methacrylate (EHMA) is produced in the reaction system shown in FIG.

[0142] 2.26 kg of MMA (methyl methacrylate) are placed in a stirred reactor 1 and heated to 100° C. after adding 2.62 kg of 2-ethylhexanol, 8 g of catalyst (ethylhexyl titanate) and stabilizer (4-hydroxy-TEMPO, hydroquinone monomethyl ether). Reactor 1 is continuously flushed with air. The pressure is maintained at 1.05 bar. Once the heating is complete and the temperature of the stirred reactor 1 is above 100° C., the energy supply is adjusted to accumulate a constant amount of distillate at the top of the column condenser 5.

[0143] All condensate obtained is returned from 6 via (7) to the top 3 of the column. As soon as the temperature of the top 3 has fallen below 70° C., low boilers (methanol) begin to be separated from the system via line 8 into a receiving container 9. The concentration of low boilers in the discharge stream 8 is determined by a mass flow meter 10. The discharge stream is adjusted so that the low boiler concentration (methanol) is between 68 mol % and 72 mol %. MMA is added to the reactor via feed line 13 in a manner corresponding to the withdrawal amount, so that the level in reactor 1 is maintained. Alternatively or additionally, MMA may have been added to the column 2 reactor via feed line 13a in a manner corresponding to the withdrawal amount, so that the level in reactor 1 is maintained. The amount added during the reaction time is 7.3 kg. The temperature in reactor 1 is kept constant at 125° C. by the pressure in the reaction system.

[0144] If the pressure in the reaction system reaches 600 mbar, it is maintained at 600 mbar regardless of the temperature in the reactor 1 .

[0145] If the top temperature measured in 3 reaches a value of 85° C., the receiving vessel 9 is emptied via the distillate discharge line 15. The resulting distillate from 8 is then collected in 9. This is then used for the subsequent production in 1.

[0146] If the temperature of the heating steam in 12 exceeds 155° C. or if the pressure difference in the column 2 increases to more than 40 mbar, the energy input into the heating system 2 is limited.

[0147] By adjusting the withdrawal stream 8, the ratio measured across 10 between 7 and 8 is maintained in the range between 15 and 0.33.

[0148] If the reactor 1 reaches a temperature of 132° C., the system pressure is further reduced to a final pressure of less than 20 mbar. The temperature in the reactor 1 is kept constant at 110° C. by the energy input in 2. The pressure reduction in the reaction system is carried out so that the total amount of distillate (totaled from the output 8 and the reflux 7) remains constant.

[0149] Any distillate obtained at the top of the column condenser 5 is then transferred to a receiving vessel 9 .

[0150] If the MMA content in reactor 1 drops below 1 mol %, it is cooled via 2 to less than 60° C. and then evacuated via 14 for further processing.

Claims

1. A process for preparing an alkyl (meth)acrylate product by an esterification (transesterification) reaction of a reaction mixture in a reactor system, the reactor system comprising a heating and / or cooling system (12, 12a), a reaction chamber (1) containing the reaction mixture, a column (2) having a column top (3), a feed line (13) to the reaction chamber (1) and / or a feed line (13a) to the column (2), a vapor transfer line (4), a condenser system (5), a reflux drum (6), a reflux line (7), a distillate transfer line (8) and a receiving vessel (9), wherein the reaction mixture comprises a (meth)acrylate starting material and a first alcohol, which are converted into (meth)acrylate alkyl ester products and by-products by an esterification (transesterification) reaction in a reaction chamber at a reaction temperature and a given pressure in the presence of a catalyst and other additives, wherein at least a portion of the by-products are removed continuously or incrementally by withdrawing a distillate for a substantial amount of time during the esterification (transesterification) reaction, and wherein during the major amount of time during the esterification (transesterification) reaction, the given pressure is adjusted continuously or incrementally to maintain the reaction temperature below a predetermined upper limit, and wherein during the esterification (transesterification) reaction, the target value of the reaction temperature is in the range of 90° C. to 145° C. at a pressure in the range of 1300 mbar to 400 mbar (absolute), and wherein at least a portion of the converted (meth)acrylate starting material and / or first alcohol is compensated by adding a further amount of (meth)acrylate starting material and / or first alcohol to the reaction mixture in the reaction chamber (1) via a feed line (13, 13, a) to the reaction chamber (1) and / or the column (2) so that the filling level of the reaction chamber (1) is kept constant.

2. The process according to claim 1, wherein during the esterification (transesterification) reaction, the target value of the reaction temperature is in the range of 100°C to 135°C at a pressure in the range of 1150 mbar to 600 mbar (absolute).

3. The process according to one or more of the preceding claims, wherein at the end of the reaction phase the pressure is reduced to below 600 mbar to 20 mbar (absolute).

4. The method according to claim 1, wherein the continuous regulation of the given pressure is a continuous linear reduction of the given pressure to a target value.

5. The process according to one or more of the preceding claims, wherein the by-products are removed in the form of a mixture of the by-products and the (meth)acrylate starting material.

6. The process according to one or more of the preceding claims, wherein the concentration of by-products at the top of the column is kept constant.

7. The method according to one or more of the preceding claims, wherein the energy input into the reaction chamber is controlled by the total amount of distillate produced.

8. The process according to one or more of the preceding claims, wherein the end point of the esterification (transesterification) reaction is determined by the by-product concentration at the top of the column and / or the reactor temperature and / or the temperature at the top of the column.

9. The method according to one or more of the preceding claims, wherein when the end of the vacuum phase is reached, the removal of by-products is stopped, wherein - in the case of high-boiling esters, the end of the vacuum stage is determined by the collapse of the distillate volume, or - In the case of low-boiling esters, the end point of the vacuum stage is determined by the pressure and temperature profile of the column.

10. The process according to one or more of the preceding claims, wherein the esterification (transesterification) reaction is carried out in the presence of a polymerization inhibitor.

11. The process according to one or more of the preceding claims, wherein the esterification (transesterification) reaction is carried out with introduction of oxygen into the reaction mixture.

Images