Method for the discontinuous (trans) esterification of (meth) acrylate compounds

Abstract

The present invention discloses a process strategy and a process for the discontinuous (trans) esterification of (meth) acrylic acid esters. This process can prepare alkyl (meth) acrylate products by the (trans) esterification reaction of a reaction mixture. The reaction mixture includes a (meth) acrylate starting material and a first alcohol that are converted into an alkyl (meth) acrylate product and by-products by the (trans) esterification reaction in the presence of a catalyst. The (trans) esterification 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 a column head, a vapor transfer line, a condenser, a reflux tank, a reflux line, a distillate transfer line, and a receiver vessel. For most of the time during the (trans) esterification reaction, at least a portion of the by-products are continuously removed by distillate removal. The pressure is continuously adjusted to keep the reaction temperature below a predetermined upper limit.

Description

Technical Field

[0001] The present invention relates to the field of discontinuous (trans) esterification of (meth) acrylate compounds and alcohols for producing target products, involving the separation of by-products.

[0002] Background of the Invention For the discontinuous (trans) esterification of (meth) acrylic acid esters with alcohols, amino alcohols or amines to produce new target products, a heatable reactor with a column directly connected as a separation system is used. The reactor can be evacuated via a vacuum system. The vacuum can be adjusted as needed. The pressure within the reactor system can be freely selected. This means that overpressure in the reactor, column and condensation system is also possible. The vapors from the column are condensed and a partial or full stream is discharged into a receiver vessel. The remaining condensate is used as the reflux of the column and returned to the reaction system via a column sample.

[0003] In the conventional mode of operation, more of the required (meth) acrylic acid ester (e.g., MMA - methyl methacrylate) than the alcohol, amino alcohol or amine must be present before starting the reaction with the alcohol. The reason for this is that the required (meth) acrylic acid ester is not only used as a starting material for the target product to be produced, but also, due to the change in the composition of the reaction mixture caused by the formation of products during the reaction, it is used as a boiling aid to limit the temperature of the reaction. As a result, the presence of further high - boiling components causes the boiling point of the mixture to rise, and thus the temperature of the entire reactor also rises. Limiting the temperature of the reaction is important to prevent the unintended polymerization of the (meth) acrylic acid ester and the target product.

[0004] U.S. Patent No. 9,776,946 discloses a transesterification reaction of a lower alkyl (meth)acrylate with another alcohol in a plant, using reduced pressure to drive the reaction or to terminate the reaction and remove excess lower alkyl (meth)acrylate. Equivalent transesterifications of lower (meth)acrylates with alcohols are disclosed in European Patent No. 0,906,902, European Patent No. 0,683,163, and U.S. Patent Application Publication No. 2010 / 274,042.

[0005] However, by providing an excess of (meth)acrylic acid ester, the reactor volume cannot be fully utilized for the raw materials to produce the target product, and the space-time yield is limited. Similarly, a larger amount of the required (meth)acrylic acid ester has to be recycled or disposed of in excess, which is time-consuming, energy-consuming, and costly.

[0006] Accordingly, an object of the present invention is to provide a method for overcoming the above-mentioned problems.

[0007] Summary of the Invention The present invention relates to a method for preparing an alkyl (meth)acrylate product by a (trans)esterification 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 head, one or more vapor transfer lines, a (multi-stage) condenser system, a reflux tank, a reflux line, a distillate transfer line, and a receiver vessel, the reaction mixture comprising a (meth)acrylate starting material and a first alcohol, amino alcohol, or amine, which are converted by a (trans)esterification reaction in the presence of a catalyst at a reaction temperature and a given pressure in the reaction chamber into an alkyl or amino (meth)acrylate product and by-products, for most of the time during the (trans)esterification reaction, at least a portion of the by-products are continuously removed by distillate removal, (Trans)esterification reaction over most of the time, a given pressure is constantly adjusted to keep the reaction temperature below a predetermined upper limit.

[0008] To prevent reactions that exceed the temperature threshold in the reactor without the temperature stabilizing effect of the (meth)acrylate ester that prevents polymerization, the pressure in the system is constantly (always) adjusted so that the reaction temperature is maintained below a predetermined upper limit. In this process, the pressure decreases linearly to the target value as the temperature in the reactor naturally rises as the reaction process progresses. This not only has a positive effect on reducing the polymerization tendency, but also has a positive impact on the average reaction rate achieved over the batch time.

Brief Description of the Drawings

[0009]

Figure 1

[0010] Detailed Description of the Invention Unless otherwise specifically defined herein, the related terms used in the present invention have the following definitions.

[0011] As used herein, the term "(meth)acrylate" refers to both (meth)acrylic acid and (meth)acrylic acid esters. Further, it refers to both methacrylates and acrylates. Or, it refers to methacrylate or acrylate depending on the respective context. It also refers to methacrylic acid and methacrylic acid esters. For example, the terms "(meth)acrylate compound" or "(meth)acrylate product" refer to (meth)acrylic acid and (meth)acrylic acid esters, such as alkyl (meth)acrylates.

[0012] Preferred (meth)acrylate products that can be prepared in accordance with this application are selected from the group consisting of: Dimethylaminoethyl methacrylate 1,4-Butanediol dimethacrylate Ethyl methacrylate Dimethylaminopropyl methacrylate Benzyl methacrylate Allyl methacrylate 2-Ethylhexyl methacrylate Cyclohexyl methacrylate Ethylene glycol dimethacrylate Butyl diglycol methacrylate Triethylene glycol dimethacrylate 1,3-Butanediol dimethacrylate Trimethylolpropane trimethacrylate Ethyl triglycol methacrylate 1,6-Hexanediol dimethacrylate Polyethylene glycol 200 dimethacrylate (molecular weight = 200 g / mol) Methoxypolyethylene glycol methacrylate (MPEG500, molecular weight = 500 g / mol) Methacrylic acid ester with an average carbon number of 17.4 Isodecyl methacrylate Methacrylic acid ester with an average carbon number of 13 (synthetic lauryl methacrylate) n-Hexyl methacrylate Methacrylic acid esters of mixtures of ethoxylated C16-18 aliphatic alcohols

[0013] As catalysts, lithium chloride, lithium amide, lithium hydroxide, lithium methoxide, zirconium(IV) acetylacetonate, titanates such as tetra-isopropyl orthotitanate, calcium hydroxide, and calcium oxide, and combinations of the above can be used.

[0014] As used herein, the term "(trans)esterification" or "(trans)esterification reaction" refers to both esterification reactions and transesterification reactions. Or, it refers to either an esterification reaction or a transesterification reaction depending on the respective context.

[0015] As used herein, the term "reactor system" refers to a reactor in which a chemical reaction of a reaction mixture can occur, and the contents of the reactor can be subjected to a distillation process before and / or during and / or after the course of the chemical reaction and / or independently of the chemical reaction. The advantage of such a reactor is that there is no need to provide several chambers for the reaction to occur and for the substance(s) to be distilled, thus saving materials, time for the transfer of substances, and costs. The reactor system comprises at least an internal and / or external heating and / or cooling system, a reaction chamber, a column with a column head, a feed line to the reaction chamber or column, a vapor transfer line, a (multi-stage) condenser system, a reflux tank, a reflux line, a distillate transfer line, and a receiver vessel.

[0016] As used herein, the term "starting material" refers to a raw material, initial material, educt, feedstock, reactant, or initial reactant that can be used to undergo a chemical reaction, whereby the chemical reaction can result in at least a product(s), which may include by-products or co-products.

[0017] As used herein, the term "heating and / or cooling system" refers to a device that can heat a liquid, cool it if necessary, and / or convert the liquid to its vapor or, in other words, its gaseous state.

[0018] As used herein, the term "reaction chamber" refers to a vessel in which a chemical reaction is carried out. In itself, a wide variety of chambers are referred to. For example, the size of the reaction chamber ranges from a micro reaction chamber holding a few microliters to a reaction chamber for a few milliliters to a chamber having a volume of several cubic meters. The most important feature of each reaction chamber is its resistance to reaction conditions.

[0019] As used herein, the term "reaction mixture" refers to a mixture of substances involved in a reaction. Such a reaction mixture can - starting material(s), - starting material(s) and possible additive(s) (e.g., a catalyst or other reaction promoter, and / or an auxiliary substance which may be a stabilizer(s)), - product(s) containing starting material(s) and possible by-product(s), - product(s) containing starting material(s), additive(s) and possible by-product(s), - product(s) containing possible by-product(s) and additive(s), - product(s) alone and additive(s), - product(s) containing possible by-product(s), or - product(s) only and can include or consist of.

[0020] As used herein, the term "column" refers to an apparatus for the thermal separation of mixtures. To avoid heat loss, the column can be an insulated, preferably cylindrical tube, which can be made especially of steel, high-alloy stainless steel, glass or plastic. The height of the column body can be determined mainly by the required separation quality; the diameter depending on the volume flow rate of the mixture to be separated. The column can be arranged between the reaction chamber and the distillation head. The number of individual distillations required for the same separation performance can also be called the "number of theoretical plates". At the surface of the column, the equilibrium between the liquid phase and the gas phase can be continuously re-established by condensation and evaporation. As a result, the proportion of low-boiling components continues to increase towards the top, while the high-boiling components flow countercurrent to the reaction chamber, the sample. The size of the surface area of the column can be significantly increased in various ways, by the design of trays such as a Vigreux column, or by filling with packing or structured packing.

[0021] As used herein, the term "feed line" refers to a supply line for feeding a substance or a mixture of substances, for example, to a reaction chamber or a column.

[0022] As used herein, the term "condenser system" refers to a unit in which the vapors generated during distillation, which can consist of various volatile components of the solution to be separated, can be liquefied by cooling with one or more different coolant liquids.

[0023] As used herein, the term "reflux tank" refers to a container into which the condensed distillate flows, and then the distillate either flows countercurrent to the column and / or the reaction chamber or is removed from the system.

[0024] As used herein, the term "reflux line" refers to a line through which the distillate from the reflux tank can be fed to the column or the reaction chamber.

[0025] 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 tank and thus divert the distillate from the reflux to the column or column head.

[0026] The term "distillate removal line" generally refers to a line that can remove at least a portion of the distillate from the reactor system and the distillation system.

[0027] As used herein, the term "starting material" refers to a raw material, initial material, educt, feedstock, reactant or initial reactant that can be used to undergo a chemical reaction, whereby the chemical reaction can result in at least a product(s), which may include by-products or co-products.

[0028] As used herein, the term "reaction time" is defined as the period during which by-products are removed from the reaction mixture. The reaction time is strongly dependent on the first alcohol used in the transesterification reaction and can vary from 2 hours to a maximum of 48 hours.

[0029] As used herein, the term "majority of the time" means more than 50% of the reaction time, more preferably more than 60%, and most preferably more than 75% of the reaction time.

[0030] As used herein, the term "target value" refers to a value to be achieved within a process. In particular, the target value refers to a specific pressure to be reached during the (trans)esterification reaction.

[0031] As used herein, the term "column head concentration" refers to the concentration of the distillate within the column head. The distillate can be any compound of the reaction mixture or its by-products or co-products.

[0032] As used herein, the term "vacuum phase" refers to the phase of product production in which a low pressure or vacuum is applied to the reactor.

[0033] The term "distillation phase" refers to the phase of production of the product in which the substances of the reaction mixture are distilled.

[0034] As used herein, the term "high-boiling ester" or "high-boiling component" refers to esters having a boiling point of 210 °C or higher, such as ethylene glycol dimethyl acrylate (EGDMA), methacrylates having an average of 13 carbon atoms, 1,3-butanediol dimethacrylate (1,3 BDDMA), and 1,4-butanediol dimethacrylate (1,4 BDDMA).

[0035] The term "low-boiling ester" or "low-boiling component" refers to esters having a boiling point of less than 210 °C, such as 2-ethylhexyl methacrylate (EHMA), isodecyl methacrylate (IDMA), and butyl methacrylate (BUMA).

[0036] As used herein, the term "wt%" refers to weight percent.

[0037] The problem underlying the present invention is solved by a method for preparing an alkyl (meth)acrylate product by a (trans)esterification 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 head, a vapor transfer line, a condenser system, a reflux tank, a reflux line, a distillate transfer line, and a receiver vessel, The reaction mixture contains a (meth)acrylate starting material and a first alcohol, which are converted by a (trans)esterification reaction in the presence of a catalyst at a reaction temperature and a given pressure in the reaction chamber into an alkyl (meth)acrylate product and by-products, Over most of the time during the (trans)esterification reaction, at least a portion of the by-products are continuously removed by distillate removal, (Trans)esterification reaction, for most of the time, a given pressure is constantly adjusted to keep the reaction temperature below a predetermined upper limit.

[0038] The method according to the invention has the advantage that the polymerization tendency is reduced and the average reaction rate achieved over the batch time is positively affected.

[0039] The reaction mixture may contain two or more starting materials and two or more products. More preferably, the two or more starting materials are a first educt, a second educt, and optionally one or more further compounds, and the two or more products are a first product, a second product, and optionally one or more further products. The reaction mixture may further contain additives 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. Furthermore, by-products may be formed by the reaction, which may also be present in the reaction mixture.

[0040] According to the invention, more alcohol (in moles) than (meth)acrylic acid ester may be present in the reaction mixture before starting the reaction. Initially, the ratio of alcohol to (meth)acrylic acid ester 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 refers to the hydroxyl groups present in the alcohol. During the progress of the reaction, an additional amount of (meth)acrylic acid ester can be added to the reaction mixture. During the course of the reaction, the ratio of alcohol to (meth)acrylic acid ester can be reduced to the range of 1.0:1.0 to 0.7:1.3, preferably to the range of 1.0:1.0 to 0.8:1.2.

[0041] The pressure within the system is constantly or stepwise adjusted to keep the reaction temperature below a predetermined upper limit. By adding more alcohol than (meth)acrylic acid ester, more boil-up volume can be used for the production of the product, and the space-time yield of the target product can be increased.

[0042] When the reaction is carried out as usual, due to the presence of more of the first alcohol, the reaction temperature cannot be adequately adjusted by the (meth)acrylate starting material, and polymerization is hindered, so that the temperature threshold is exceeded in the reactor before the end of the reaction. However, the adjustment of the pressure by applying a vacuum or a fairly low pressure hinders this process.

[0043] Preferably, the continuous adjustment of a given pressure is a constant linear decrease to the target value of the given pressure.

[0044] This has the advantage that the pressure is reduced in a controlled manner and reaches the target pressure within a predetermined time frame.

[0045] During the (trans)esterification 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 pressure), preferably in the range of 1150 mbar to 600 mbar (absolute pressure). At the end of the reaction phase, the pressure may be reduced to less than 600 mbar to 20 mbar (absolute pressure).

[0046] The reactor system may further comprise one or more elements selected from the group of one or more mass flow meters, recycle lines, distillate removal lines, reaction chamber removal lines, and feed lines to the reaction chamber or column, preferably the feed line is the first feed line, and the reactor system further comprises a second feed line to the reaction chamber or column, and optionally, a further feed line to the reaction chamber or column.

[0047] This has the advantage that substances and / or mixtures can be added to the reaction chamber and / or column via several feed lines. The substances and / or mixtures can be added via these feed lines simultaneously or sequentially and / or continuously or discontinuously. Different substances and / or mixtures can be added to the reaction chamber and / or column via the feed lines. Also, the same substances and / or mixtures can be added to the reaction chamber and / or column via the feed lines. Furthermore, the same substances and / or mixtures as well as different substances and / or mixtures can be added to the reaction chamber and / or column via the feed lines. These substances or mixtures can be, for example, starting materials and / or reaction accelerators used in the reaction, reaction inhibitors, buffers, solvents, stabilizers, water, viscosity index improvers, thickeners, antioxidants, corrosion inhibitors, dispersants, high-pressure additives, defoamers, catalysts or enzymes and other additives.

[0048] Preferably, the reactor includes the possibility of supplying energy by heating and removing energy by cooling. Preferably, the reactor is equipped with mixing equipment for the reaction chamber. Preferably, the reactor includes input means for solids, liquids and gases that can be provided to the reaction chamber, column, vapor line, condensation system and feed line.

[0049] The reactor is equipped with a pressure control system that can control and adjust the pressure within the reactor chamber, column and condensation system.

[0050] Via the reflux line, the distillate can flow back to the column or the reaction chamber. The reflux tank stores the reflux of the distillate.

[0051] The first alcohol can be a straight-chain or branched C2-C20 alkanol, a straight-chain or branched C2-C20 alkanediol, an amino alcohol, preferably dimethylaminoethanol and dimethylaminopropanol, an amine straight-chain or branched vicinal C2-C20 alkanediol, or preferably ethylene glycol.

[0052] In the process according to the invention, the by-products can also be removed in the form of a mixture of the by-products and the (meth)acrylate starting material.

[0053] This has the advantage, especially at the end of the reaction, that the reaction continues to proceed in the direction of product formation and does not come to a stop.

[0054] When carrying out the process according to the invention, it is preferably a selected option to keep the filling level of the reaction chamber constant by replenishing at least part of the withdrawn (meth)acrylate starting material and / or the first alcohol by adding a further amount of (meth)acrylate starting material and / or the first alcohol to the reaction mixture in the reaction chamber via a feed line.

[0055] The filling level of the reaction chamber is kept constant, for example, by using an inflow control for MMA and / or alcohol. The feed of the educts is regulated (for example, control valves and mass flow measurement). During the reaction, by-products (for example, methanol) are withdrawn from the reaction chamber via a column. Thus, if no additional educt is fed, the filling level of the reaction chamber continuously decreases. Here, the filling level control controls and regulates the feed of the educt(s). The output signal from the filling level control acts as a target value for the inflow control, and the inflow control then regulates the metered mass flow. In this way, the individual flows of the components or several components in a single stream can be fed into the reactor. The feed stream can be from 3.5 times to 0.01 times the removal based on mass. Preferably, the feed flow rate is from 2.5 times to 0.1 times the removal, more preferably from 1.75 times to 0.25 times.

[0056] This has the advantage that the available volume within the reactor chamber is used for the (trans)esterification reaction, increasing the space-time yield. Preferably, further 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 (trans)esterification reaction and to further increase the space-time yield. This has the further advantage that optimal heat transfer from the outer wall to the reaction wall to the reaction medium is achieved since the maximum available heat transfer area is provided. More preferably, the filling level of the reactor is kept constant during the (trans)esterification process.

[0057] When implementing the method according to the invention, it is a further preferred option that the concentration of by-products within the column head is kept constant. This has the advantage that the separation of compounds in the reactor system is optimal and thus losses of e.g. MMA from the system are reduced.

[0058] Referring to FIG. 1, it is shown that the reflux rate (7) to the column head (3) can be controlled via the filling level in the reflux tank (6). When more distillate accumulates from the condenser system (5), as the filling level in the reflux tank (6) rises, the reflux rate increases. If no distillate is withdrawn from the system via the distillate transfer line (8), all the condensate obtained from the condenser system (5) is fed to the column via the reflux tank (6) and the reflux line (7). In the process steps of the transesterification, it is preferable for the controller to ensure that there is always a transfer of distillate to the receiver vessel (9) via the transfer line (8). This is done from the calculation of the reflux ratio (v = reflux flow in the reflux line (7) / distillate transfer in the line (8)). The distillate transfer flow (8) is adjusted such that the reflux ratio (v) is always within the range of a maximum of 15 and a minimum of 0.33. The transfer flow (8) can be freely selected between the specified limits defined by the reflux ratio (v). However, it is preferably set such that the column top concentration of methanol in the column head (3) can be kept constant. The concentration at the top of the column (3) is determined using the flow meter (10) of the flow (7) or (8).

[0059] The concentration should be maintained at 78 mol% (MeOH) to 62 mol% (MeOH), preferably 74 mol% (MeOH) to 68 mol% (MeOH). When the concentration of methanol in the column head (3) increases, the transfer flow (8) increases; when the concentration of methanol in the column head (3) decreases, the transfer flow (8) decreases.

[0060] The by-product concentration can be determined by measurements that can be performed online. For example, the refractive index and / or density can be measured. The removal of the column head can be adjusted by concentration measurement so that the column head concentration remains constant over the course of the reaction. When using MMA as a starting material, the by-product that is methanol accumulates during the reaction and is continuously separated by distillation through a connected column. When the concentration of methanol in the column head is kept constant within a determined range of 78 to 62 mol%, preferably 74 to 68 mol%, the separation from the reactor and thus the loss of MMA from the system is optimal. However, even when there is only low conversion at the end of the reaction, a minimum amount of removal always keeps the reaction process going.

[0061] According to the present invention, the concentration measured at the top of the column can act on the amount withdrawn via calculation and regulation. The reflux to the column can be controlled by the filling level of the distillate collection tank. If nothing is withdrawn from the system, the distillate obtained is completely returned to the column as reflux. The 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.

[0062] The calculation scheme may be as follows: a) Measurement of the concentration (at the top of the column), b) Control of the concentration (to the setpoint), c) Conversion of the controller output to the draw-off volumetric flow rate, d) Limitation of the draw-off volumetric flow rate, including the maximum and minimum reflux ratios (in the range of maximum 15, minimum 0.33), and e) The setpoint of the fume hood controller.

[0063] A further preferred option of the method of the present invention is that the energy input to the reactor chamber is controlled by the total amount of distillate produced.

[0064] According to the present invention, the energy input to the reactor (1) is realized via the heating system (12, 12a) of the reactor. The system can be heated, for example, via steam, a hot oil system, electricity, etc.

[0065] The required heat output (energy input to the reactor) is typically adjusted so as not to exceed certain parameters (total distillate generated in the condenser system (5), pressure drop across the entire column (2), and reactor temperature) during the process. The main control variable for the energy input is typically the amount of the distillation stream generated in the condenser (5) or the reflux tank (6). This should be kept constant throughout the reaction. The amount of distillate produced should be selected such that an F-factor within the range of 0.5 to 3.0 Pa 1 / 2 for the column (2), preferably within the range of 1.0 to 2.0 Pa 1 / 2 is achieved. The energy input via the heating and / or cooling system (12, 12a) should only be reduced to the extent that this value can be maintained when the pressure loss within the column rises above a preset value within the range of 10 to 4 mbar / m of packing, preferably within the range of 6.5 to 4 mbar / m of packing. When the temperature of the reaction chamber or the walls of the reaction chamber rises above a preset value of 150°C to 185°C, preferably 160°C to 170°C, the energy input should be adjusted so as to maintain this value. This strategy for the energy input can ensure that the column (2) and the reactor (1) are not loaded beyond their system limits while the system is always at its upper operating limit, and thus is optimally utilized.

[0066] The energy input to the reactor can be controlled by the total amount of distillate produced. The measured amount of distillate can be corrected for possible level fluctuations in the condenser. The mass flow rate of vapor flowing from the column to the condenser can be kept constant. However, the distillate flowing from the column to the condenser can be restricted by two parameters. When the wall temperature at the heat transfer location exceeds 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 typically in the range of 150 °C to 185 °C, preferably in the range of 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 column including the vapor line can also be continuously measured. When the pressure loss rises above a critical value (which can be defined as being in the range of 10 mbar / m to 4 mbar / m, preferably in the range of 6.5 mbar / m to 4 mbar / m for structured packings, or being within that range), the amount of energy entering the reactor is also adjusted downward. This prevents foams that would lead to a significant reduction in operating time and performance from entering the column. However, due to these two situation-dependent interventions, a high-performance energy input can still operate over the complete reaction time. This is because when a restriction due to the pressure difference or the wall temperature occurs in a specific process section, the system intervenes self-regulatingly. That is, the intervention that reduces performance is only carried out in small process sections or process time phases. The remaining time during which the system can operate at full capacity can operate at full power. This also results in an increase in the space-time yield.

[0067] In a further preferred option of the method according to the invention, the endpoint of the (trans)esterification reaction is determined by the concentration of by-products in the column head, the temperature in the column head and the reactor temperature.

[0068] When the reaction is complete, this point can be reliably detected and the next process step, vacuum phase, or distillation phase can be initiated. The vacuum or distillation phase starts when the concentration of methanol in the column head (3) reaches 5 mol%, preferably 3 mol%, more preferably 2 mol%.

[0069] As described above, the endpoint of the (trans)esterification reaction can be determined by a combination of values regarding the column head 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.

[0070] In the conventional operating mode, the endpoint was detected using only the reactor temperature.

[0071] According to a preferred option of the method of the present invention, the removal of by-products is stopped when the end of the vacuum phase is reached.

[0072] Alternatively, the endpoint of the vacuum phase in the case of low-boiling esters is determined from the column pressure and temperature profile, and the removal of by-products is stopped when the end of the vacuum phase is reached.

[0073] The end of the process in the production of low-boiling esters can be identified by identifying a characteristic temperature profile. Temperature sensors can be installed at different heights within the column (2). These can be arranged at (a) the top of the column, (b) the rear of the first 1 / 3 of the column packing, (c) the rear of the second 1 / 3 of the column packing, and (d) the bottom of the column. The end of the process can be defined such that sensors (c), (b), and (d) must have approximately the same temperature. In this case, the temperature can be recorded at (a). Then, the recorded temperature at (a) can be subtracted from the temperature at (d). If the temperature at (a) increases by 1 / 3 of the calculated value here, the end of the process has been reached.

[0074] For 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 ends. Furthermore, detecting the endpoint of the reaction has the additional advantage that the vacuum phase does not last too long and the risk of polymerization is reduced. Needle-based recognition increases the overall space-time yield.

[0075] Preferably, the (trans)esterification reaction is carried out in the presence of a polymerization inhibitor. This can enter the system as a solid and / or can be fed into the system anywhere as a solution of one or more components of the reaction mixture.

[0076] This has the advantages of inhibiting polymerization and increasing the space-time yield. Furthermore, the product can be made purer.

[0077] As inhibitors, p-phenylenediamines, phenothiazine, and hydroxylamines such as N,N-bis(2-hydroxypropyl)hydroxylamine (HPHA) and N,N-diethylhydroxylamine (DEHA) can be used.

[0078] The most preferred inhibitors or stabilizers are hydroquinone (HQ), its methyl ether HQME and 2,2,6,6-tetramethylpiperidinyl oxyl (TEMPO), or derivatives thereof such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyl oxyl (hydroxy-TEMPOL) and any derivatives of this that functionalize the hydroxy group such as methacrylic acid esters of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl oxyl.

[0079] The polymerization inhibitor hydroquinone methyl ether (HQME) can 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-tetramethylpiperidinyl oxyl (TEMPO) or any of its derivatives can be present in the range of 0.1 ppm to 1000 ppm by weight ppm, more preferably 1 ppm to 500 ppm, and most preferably 10 ppm to 100 ppm.

[0080] Preferably, the (trans)esterification reaction is carried out using the introduction of oxygen into the reaction mixture.

[0081] This has the advantage that the reaction is stabilized and the reaction rate is increased.

[0082] In addition to oxygen, air can also be introduced into the reaction to increase the rate of the reaction process. Oxygen may be introduced continuously or discontinuously, and preferably oxygen is introduced continuously.

[0083] In the method according to the 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.

[0084] Order of the whole process: The overall process of the (trans)esterification process can be characterized by a specific series of sub-steps. These are determined by the product to be manufactured and can vary depending on the product.

[0085] Basically, the following steps can be carried out in a (trans)esterification process: · Filling and feeding of reactants in the reactor, · Addition of stabilizers, · Optionally, dehydration of the mixture, · Addition of catalysts, · Heating of the reactor contents, · Separation of by-products (e.g., methanol) during the reaction to the target product under adjusted pressure and temperature, · Optionally, addition of reactants during the reaction phase, · Lowering the pressure further for separation of excess starting materials and transferring it to the feedstock for the next reaction batch, · Detection of the end point of the process, · Adjustment of pressure and temperature for the next process step.

[0086] Further advantages, details and features of the present invention will become apparent from the examples described below.

Examples

[0087] Example 1: Preparation of EHMA (2-ethylhexyl methacrylate) In the reaction system shown in Figure 1, 2-ethylhexyl methacrylate (EHMA) was produced.

[0088] 2.26 kg of MMA (methyl methacrylate) was placed in a stirred reactor (1), 2.62 kg of 2-ethylhexanol was added, and then 8 g of catalyst (ethylhexyl titanate) and stabilizers (4-hydroxy-TEMPO, hydroquinone monomethyl ether) were heated to 100 °C. Air was continuously flowed through the reactor (1). The pressure maintenance was set at 1.05 bar. When the heating was completed and the temperature of the stirred reactor (1) exceeded 100 °C, the energy supply was adjusted so that a certain amount of distillate accumulated at the top of the column condenser (5).

[0089] All of the obtained condensates were returned to the top of column (3) via (6) to (7). When the temperature at the top of column (3) dropped below 70 °C, the low boiler (methanol) began to be separated from the system and into the receiver vessel (9) via line (8). The concentration of the low boiler in the discharge stream (8) was determined by a mass flow meter (10). The draw-off flow was adjusted so that the low boiler concentration (methanol) was between 68 mol% and 72 mol%. Equivalent to the withdrawal, MMA was added to the reactor via feed line (13) to maintain the level in reactor (1). Alternatively or additionally, equivalent to the withdrawal, MMA could be added to the column (2) reactor via feed line (13a) to maintain the level in reactor (1). The amount added over the reaction time was 7.3 kg. The temperature in reactor (1) was kept constant at 125 °C by the pressure in the reaction system.

[0090] When the pressure in the reaction system reached 600 mbar, this was maintained at 600 mbar regardless of the temperature in reactor (1).

[0091] When the top temperature of the column measured at (3) reached a value of 85 °C, the receiver vessel (9) was emptied via the distillate discharge line (15). Then, the distillate obtained from (8) was collected in (9). Then, this was used in the next production in (1).

[0092] When the heating steam temperature in (12) exceeded 155 °C, or when the differential pressure in column (2) increased by more than 40 mbar, the energy input to the heating system (2) was throttled.

[0093] Between (7) and (8), the ratio measured over (10) was maintained within the range of 15 to 0.33 by adjusting the draw-off flow (8).

[0094] When the reactor (1) reached a temperature of 132 °C, the system pressure was further reduced to a final pressure of less than 20 mbar. The temperature in the reactor (1) was kept constant at 110 °C by the energy input in (2). The reduction of the pressure in the reaction system was carried out such that the total amount of distillate (total amount from outlet (8) and reflux (7)) remained constant.

[0095] Subsequently, all the distillate obtained at the top of the column condenser (5) was transferred to the receiver vessel (9).

[0096] When the MMA content in the reactor (1) dropped below 1 mol%, it was cooled via (2) to below 60 °C and then emptied via (14) for further processing.

Claims

1. A method for preparing an alkyl (meth)acrylate product by a (trans)esterification 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 head (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 tank (6), a reflux line (7), a distillate transfer line (8), and a receiver vessel (9), The reacting mixture is A (meth)acrylate starting material and a first alcohol are converted to the alkyl (meth)acrylate product and by-product by the (trans)esterification reaction at a reaction temperature and a given pressure in the reaction chamber in the presence of a catalyst and other additives, For most of the time during the (trans)esterification reaction, at least a portion of the by-products is removed continuously or stepwise by distillate removal. For most of the time during the (trans)esterification reaction, the given pressure is continuously or incrementally adjusted to maintain the reaction temperature below a predetermined upper limit. During the (trans)esterification reaction, the target reaction temperature is within the range of 90°C to 145°C at a pressure within the range of 1300 mbar to 400 mbar (absolute pressure). A method wherein the packing level of the reaction chamber (1) is kept constant by adding a further amount of the (meth)acrylate starting material and / or the first alcohol to the reaction mixture in the reaction chamber (1) and / or the column (2) via the feed lines (13, 13a) to supplement at least a portion of the converted (meth)acrylate starting material and / or the first alcohol.

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

3. The method according to claim 1 or 2, wherein at the end of the reaction phase, the pressure is reduced to less than 600 mbar to 20 mbar (absolute pressure).

4. The method according to claim 1 or 2, wherein the continuous adjustment of the given pressure is a constant linear decrease of the given pressure toward a target value.

5. The method according to claim 1 or 2, wherein the by-product is removed in the form of a mixture of the by-product and the (meth)acrylate starting material.

6. The method according to claim 1 or 2, wherein the concentration of the by-product in the column head is kept constant.

7. The method according to claim 1 or 2, wherein the energy input into the reaction chamber is controlled by the total amount of distillate produced.

8. The method according to claim 1 or 2, wherein the endpoint of the (trans)esterification reaction is determined via the concentration of the byproduct in the column head and / or the temperature of the reaction chamber and / or the temperature of the top of the column.

9. The removal of the by-product is stopped when the end of the vacuum phase is reached. - In the case of high-boiling point esters, the endpoint of the vacuum phase is determined by the volume drop of the distillate, or - In the case of low-boiling point esters, the endpoint of the vacuum phase is determined from the pressure and temperature profile of the column. The method according to claim 1 or 2.

10. The method according to claim 1 or 2, wherein the (trans)esterification reaction is carried out in the presence of a polymerization inhibitor.

11. The method according to claim 1 or 2, wherein the (trans)esterification reaction is carried out by introducing oxygen into the reaction mixture.

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