Esterification (transesterification) method of (meth) acrylate compound using strongly basic catalyst

Abstract

A process for preparing an alkyl (meth) acrylate product by an esterification (transesterification) reaction of a reaction mixture in a reactor system is disclosed, the reactor system comprises a reaction chamber (1) comprising the reaction mixture comprising a (meth) acrylate starting material and a first alcohol, a feed line, a reboiler, a column having an overhead, a vapor transfer line, a condenser, a return tank, a return line, a distillate removal line and a receiving vessel, the (meth) acrylate starting material is methyl methacrylate, the first alcohol is ethylene glycol or hydroxyethyl methylacrylate, the second alcohol is ethylene glycol or hydroxyethyl methylacrylate, the third alcohol is ethylene glycol or hydroxyethyl methylacrylate, and the fourth alcohol is ethylene glycol or hydroxyethyl methylacrylate, in a reaction chamber at a reaction temperature and a given pressure, in the presence of a strongly basic catalyst, by an esterification (transesterification) reaction to an alkyl (meth) acrylate product and by-products. And wherein the product is ethylene glycol dimethacrylate wherein the strongly basic catalyst comprises one or more compounds selected from the group consisting of calcium oxide (CaO), calcium hydroxide (Ca (OH) 2), lithium hydroxide (LiOH), sodium methoxide (NaOMe), lithium methoxide (LiOMe), lithium tert-butoxide (LiOt-Bu), lithium isopropoxide (LiOIPr), preferably wherein the strongly basic catalyst comprises one or more compounds selected from the group consisting of lithium methoxide (LiOMe), and most preferably wherein the strongly basic catalyst comprises or is lithium methoxide (LiOMe) wherein 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, and wherein 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, and wherein 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 given pressure is repeatedly adjusted to maintain the range of the reaction temperature wherein the repeated adjustment of the given pressure is performed with pressure stages, preferably wherein the difference between two pressure stages is less than 500 mbar, and wherein the given pressure is repeatedly adjusted to maintain the reaction temperature in the range of 70 DEG C to not more than 130 DEG C.

Description

Technical Field

[0001] The present invention relates to the field of discontinuous esterification (transesterification) of (meth)acrylate compounds with alcohols using a strong basic catalyst to produce new target products and subsequently separate the by-product methanol. Background Art

[0002] The production of special methacrylates can be efficiently achieved by transesterification of methyl methacrylate (MMA) and alcohols as starting materials and using catalysts. Titanium (IV) alkoxide catalysts are widely used due to their selectivity and commercial availability. However, titanium (IV) catalysts are easily and irreversibly deactivated by chelated alcohols. In particular, 1,2- or 1,3-difunctional raw materials rapidly deactivate the catalysts.

[0003] For disubstituted 1,3-raw materials, this can be circumvented by using zirconium oxide catalysts with higher selectivity, such as Zr(acac)4, i.e., Zr(C5H7O2)4. However, similar to Ti(IV) alkoxides, Zr(acac)4 catalysts are generally unable to catalyze the reaction of 1,2-difunctional alcohol substrates, such as ethylene glycol, glycerol, 1,2-propylene glycol, or vicinal diols.

[0004] Therefore, the method of choice is to use a strongly basic catalyst whenever the vicinal diol is transesterified with the MMA or contaminants present in the raw materials. These strongly basic catalysts include oxide derivatives of alkali metals and alkaline earth metals or even some transition metal oxides or strongly basic ion exchange resins. All of these catalysts produce an alkoxide of the raw material alcohol, which is transesterified to a methanolate which is released as methanol by proton exchange with another raw material alcohol.

[0005] Among the strongly basic catalysts, calcium oxides and hydroxides are characterized by their safety, approved food suitability and the cheapest raw material cost. However, they are not as fast as another group of catalysts, such as alkoxides. In theory, all alkoxides are easily applicable to catalytic species for the formation of alkoxides. However, only lithium salts have the unique ability to prevent anionic polymerization caused by uncontrolled Michael addition to the double bonds of the methacrylate backbone. All other alkali metals cause thermal runaway due to the fact that the exothermic reaction causes an increase in the reaction rate, which in turn causes further exothermic reactions. This leads to unwanted polymerization, which is why lithium salts are mainly used as esterification (transesterification) catalysts.

[0006] Among lithium salts, lithium amide (LiNH2) is most commonly used for esterification (ester exchange). sValue, LiNH2 basicity is about six orders of magnitude higher than alkoxide. In addition, due to its insolubility in protic media under anhydrous conditions and slow decomposition to release ammonia, LiNH2 has a surprisingly long catalytic life. Like the delayed decomposition and extremely strong basicity of the catalyst, these properties cause some problems in industrial production. Ammonia released from the decomposition reaction of the LiNH2 catalyst can form hard ammonium carbamate solids in the presence of water and carbon dioxide. The formation of such ammonium carbamate solids occurs particularly in or on low-temperature heat exchangers where water can condense. These solids continue to grow until the flow path is completely blocked and needs to be cleaned by maintenance. It is extremely difficult to prevent the presence of carbon dioxide to avoid this process because all esterification (ester exchange) processes involve the use of inhibitors, especially hydroquinone monomethyl ether (HQME). These inhibitors require the presence of oxygen, usually through air or diluted air. Atmospheric carbon dioxide is introduced into the process with air (which is usually purified, dried and diluted if necessary), resulting in the production of the aforementioned carbamate solids.

[0007] The insolubility of LiNH2 has its own challenges and safety aspects in the formation of solids that clog exhaust lines and heat exchangers. Unused or decomposed catalyst floats in the reaction medium as a single particle. Due to polymer formation in the reaction medium, it is preferred to filter out substantially all of the MMA transesterification catalyst particles after the reaction is complete, during the transfer of the crude product from the reactor to the container, and before the final filtration and distillation of the product. This results in agglomeration of high concentrations of lithium amide particles in the combustible mixture. Therefore, replacement, especially storage for disposal, is dangerous and may easily cause fire and / or ammonia release due to the decomposition of the catalyst by atmospheric moisture. In addition, catalyst particles tend to agglomerate in valves, recirculation lines, and especially in nozzles, which therefore do clog and require maintenance.

[0008] Of all the drawbacks of LiNH2, the most serious is the previously admired basicity of this catalyst. The use of LiNH2 as a catalyst results in significant amounts of crude product undergoing multiple Michael addition reactions with the MMA backbone, ultimately yielding non-volatile oligomers. For the distilled product, this means a complete loss of the starting material, which cannot be reused or recycled, and a reduction in the reaction yield. Despite this, these oligomers may be invisible to analytical methods such as gas chromatography (GC). However, their presence reduces the distillation yield. Unfortunately, their presence is difficult to quantify and is usually only quantified by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) or high-pressure liquid chromatography (HPLC).

[0009] In order to overcome the safety issues of filter residues containing LiNH2, maintenance of clogging and cleaning of heat exchangers, the use of lithium methoxide (LiOMe) appears to be very beneficial. LiOMe is an equivalent of the intermediate species released after esterification (transesterification). Therefore, the use of LiOMe will not introduce foreign substances into the process and will be the cleanest catalytic solution.

[0010] Unfortunately, the solubility of lithium alkoxides, especially methoxides, has proven to be a decisive disadvantage for large-scale applications. LiNH2 releases only a portion of its catalytic power over a long period of time, whereas the full catalytic efficiency of lithium alkoxides is immediately available at the start of the reaction. What sounds like a real advantage turns out to be a process engineering problem in production. The initial phase of industrial-scale esterification (transesterification) reactions is impaired by high methanol concentrations in the reactor. Before the methanol can be removed from the reaction system, a distillation unit must first be incorporated to achieve a specified methanol purity. To achieve this, a large part of the condensed methanol is returned to the reaction system to be purified again by distillation to increase the purity. Unfortunately, the presence of high catalysts and high methanol concentrations greatly promotes the formation of Michael addition products, which form methoxyisobutyrates. These not only represent a loss in yield, but are also volatile and enter the end product, where they often result in the material failing to meet the purity specifications.

[0011] US 20200331845 describes a method for preparing dimethylaminoalkyl (meth)acrylate from alkyl (meth)acrylate and dimethylaminoalkanol. It relates to the use of a catalyst system comprising a solution of lithium alcoholate in alcohol in the preparation of dimethylaminoalkyl (meth)acrylate.

[0012] WO2005058862 describes a process for preparing glycerol carbonate methacrylate in the presence of metal chelate catalysts of the metal ion 1,3-diketonate type, in particular zirconium acetylacetonate. Example "V4" from Example 1 shows the large formation of 20% by weight of high boilers with lithium methoxide and how difficult the transesterification reaction with base is.

[0013] US2013172598 describes a method for producing ethylene glycol dimethacrylate using lithium amide (LiNH2) and lithium chloride (LiCl) as catalysts. Comparative Example 2 shows the use of LiOMe as a negative example, which is not suitable for transesterification reactions.

[0014] It is therefore an object of the present invention to provide a process which overcomes the above-mentioned problems when using strongly basic catalysts. Summary of the invention SUMMARY OF THE INVENTION

[0015] The present invention is a method for preparing an alkyl (meth)acrylate product by an esterification (transesterification) reaction of a reaction mixture in a reactor system, wherein the reactor system comprises a reboiler, a reaction chamber containing the reaction mixture, a column having a column top, a vapor transfer line, a condenser, a reflux drum, a reflux line, a distillate withdrawal line and a receiving vessel,

[0016] 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 strong alkaline catalyst,

[0017] 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

[0018] The given pressure is repeatedly adjusted to maintain the reaction temperature range during the major amount of time during the esterification (transesterification) reaction.

[0019] The present invention carries out the reaction at a significantly lower temperature. The reaction temperature in the reactor is kept constant by repeatedly adjusting the pressure in the reaction chamber according to the varying boiling temperature of the reaction mixture. Running the reaction under vacuum or reduced pressure also enables the removal of methanol.

[0020] Surprisingly, it has been found that if the reaction is carried out at such significantly lower temperatures, the formation of methoxyisobutyrate can be avoided despite the use of strongly basic catalysts such as LiOMe and despite the presence of high concentrations of methanol.

[0021] Furthermore, at sufficiently low temperatures, there is no loss of activity of the strongly basic catalyst, since the catalyst is active at room temperature. Filtration of the process liquid is greatly improved, resulting in significantly fewer filters requiring replacement and cleaning. Furthermore, the color of the crude product (i.e., the product before filtration and distillation) improves from amber brown to light yellow, indicating improved product purity. The distillation of this new process material runs significantly longer, with a smaller increase in vapor pressure on the wiped film evaporator for the same product amount, since there is less clogging of the walls and waste pipes.

[0022] Another advantage of the present invention is that by regulating the temperature via pressure regulation, thereby avoiding exceeding a temperature threshold in the reactor before the end of the reaction, less excess (meth)acrylate starting material is required in the reaction chamber for reaction temperature control. Reducing the excess of (meth)acrylate starting material makes it possible to increase the amount of the first alcohol instead. In this way, the reaction chamber volume can be utilized more efficiently in terms of space-time yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The reactor system according to the present invention is illustrated, and the reactor system includes a reboiler 12, a reaction chamber 1, a column 2 having a column top 3, a vapor transfer line 4, a condenser 5, a reflux drum 6, a reflux line 7, a distillate withdrawal line 8 having a mass flow meter 10, a receiving vessel 9 and a recycle line 11. DETAILED DESCRIPTION OF THE INVENTION

[0025] Unless otherwise specifically defined herein, the relevant terms used in the present invention have the following definitions.

[0026] 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 a reboiler, a reaction chamber, a tower with a tower top, a feed line to the reaction chamber or tower, a vapor transfer line, a condenser, a reflux drum, a reflux line, a distillate withdrawal line and a receiving vessel.

[0027] 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.

[0028] 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" refers to (meth)acrylic acid and esters of (meth)acrylic acid, such as alkyl (meth)acrylate.

[0029] 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.

[0030] As used herein, the term "reboiler" refers to a device used to heat a liquid and / or convert a liquid to its vapor or, in other words, gaseous state.

[0031] 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.

[0032] 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:

[0033] - starting materials,

[0034] - starting materials and possible additives such as auxiliary substances, which may be, for example, catalysts or other reaction accelerators,

[0035] - starting materials and products, including possible by-products,

[0036] - starting materials, additives and products, including possible by-products,

[0037] - products, including possible by-products, and additives,

[0038] - the product itself and additives,

[0039] - products, including possible by-products, or

[0040] - The product itself.

[0041] 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 reactor (sump). The surface area size of the tower can be greatly increased in various ways by the design of the tray (as in the Vigreux tower) or by filling with fillers or structured packing.

[0042] 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.

[0043] As used herein, the term "condenser" 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.

[0044] 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.

[0045] 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.

[0046] As used herein, the term "distillate take-off line" refers to a line that can remove at least a portion of the distillate from a reflux drum, or generally from a reactor system or a distillation system.

[0047] As used herein, the term "pressure level" refers to a pressure drop or pressure increase at a defined pressure value. The difference between two pressure levels may be, for example, less than 1000 mbar, less than 500 mbar, less than 100 mbar, less than 50 mbar or less than 10 mbar.

[0048] As used herein, the term "recipe control" refers to a control system that can automatically control certain processes (such as pressure regulation) after evaluating certain data, such as the temperature of the reaction chamber.

[0049] As used herein, the term "wt %" means percent by weight.

[0050] As used herein, the term "sparkler filter" refers to a filter in which unfiltered liquid is fed into the filter under positive pressure. The liquid reaches the openings on the sides of the filter plates. Suspended particles are trapped on the filter media mounted on the filter plates. The clean filtrate flows out of the peripheral holes of the plates, into the tank and out of the bottom outlet. Filtration in a sparkling filter is performed until the holding capacity of the filter cake is reached or until the flow rate of the filtrate becomes too slow.

[0051] The problem to which the present invention relates is solved by a method 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 reboiler, a reaction chamber containing the reaction mixture, a column having a column top, a vapor transfer line, a condenser, a reflux drum, a reflux line, a distillate withdrawal line and a receiving container, the reaction mixture comprising a (meth)acrylate starting material and a first alcohol, which are converted into an alkyl (meth)acrylate product and by-products by an esterification (transesterification) reaction in the presence of a strong basic catalyst at a reaction temperature and a given pressure in the reaction chamber, wherein at least a portion of the by-products is continuously removed by withdrawing a distillate during a major amount of time during the esterification (transesterification) reaction, and wherein during a major amount of time during the esterification (transesterification) reaction, the given pressure is repeatedly adjusted to maintain a range of the reaction temperature.

[0052] In a preferred embodiment of the invention, the (meth)acrylate starting material is methyl methacrylate, the first alcohol is ethylene glycol or hydroxyethyl methacrylate, and wherein the product is ethylene glycol dimethacrylate.

[0053] According to the present invention, the strongly basic catalyst preferably comprises one or more compounds selected from alkali metal oxides, alkaline earth metal oxides, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal alkoxides, alkaline earth metal alkoxides, alkali metal amides and alkaline earth metal amides.

[0054] More preferably, the strongly basic catalyst used in the method of the present invention comprises one or more compounds selected from calcium oxide (CaO), calcium hydroxide (Ca(OH)2), lithium hydroxide (LiOH), sodium methoxide (NaOMe), lithium methoxide (LiOMe), lithium tert-butoxide (LiOt-Bu), lithium isopropoxide (LiOiPr) and lithium amide (LiNH2), preferably wherein the strongly basic catalyst comprises one or more compounds selected from lithium methoxide (LiOMe) and lithium amide (LiNH2), and most preferably wherein the strongly basic catalyst comprises or is lithium methoxide (LiOMe).

[0055] The process according to the invention has the advantage that catalysts which were previously unsuitable or poorly suitable for esterification (transesterification) reactions can now be used effectively in esterification (transesterification) processes, which leads to accelerated reaction rates and increased space-time yields.

[0056] The reactor system may further comprise one or more elements selected from the group consisting of one or more mass flow meters, a recirculation 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 a reaction chamber or a column, and optionally, additional feed lines to a reaction chamber or a column.

[0057] Preferably, the feed line is the first feed line, and the reactor system includes a second feed line leading to a reaction chamber or tower, and optionally, another feed line leading to a reaction chamber or tower. This has the advantage that substances and / or mixtures can be added to a 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 a reaction chamber and / or tower via feed lines. The same substance and / or mixture can also be added to a 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 a 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.

[0058] Through the reflux line, the distillate can flow back to the column or back into the reaction chamber. The reflux tank stores the reflux of the distillate.

[0059] The first alcohol may be a linear C2-C6 alkanol, a linear C2-C6 alkanediol, a linear ortho-C2-C6 alkanediol, or preferably ethylene glycol.

[0060] 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.

[0061] 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.

[0062] When carrying out the process according to the invention, one preferred option is to compensate at least a portion of the converted (meth)acrylate starting material by adding a further amount of (meth)acrylate starting material to the reaction mixture, preferably via a feed line to the reaction chamber or column.

[0063] When carrying out the process according to the invention, a further preferred option is to compensate at least a portion of the converted (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.

[0064] 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 (meth)acrylate 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 an optimal heat transfer from the outer wall to the reaction wall into the reaction medium is achieved, since a maximum utilized heat transfer area is provided. Further preferably, the reactor filling level remains constant during the esterification (transesterification) process.

[0065] Preferably, the esterification (transesterification) reaction is carried out in the presence of an inhibitor.

[0066] This has the advantage that polymerization is inhibited and the space-time yield is increased. In addition, the product can be purer. The polymerization inhibitor (inhibitor) HQME can be present in the range of 1 ppm to 1000 ppm, preferably 10 to 1000 ppm, more preferably 10 to 500 ppm, most preferably 50 to 100 ppm, wherein ppm is by weight. The inhibitor Tempol or any derivative thereof can be present in the range of 0.1 ppm to 1000 ppm, more preferably 1 to 500 ppm, most preferably 10 to 100 ppm, wherein ppm is by weight.

[0067] As inhibitors, p-phenylenediamine, phenothiazine and hydroxylamines such as N,N-bis(2-hydroxypropyl)hydroxylamine (HPHA) and N,N-diethylhydroxylamine (DEHA) can be used. The most preferred inhibitors are hydroquinone (HQ), its methyl ether HQME and 2,2,6,6-tetramethylpiperidinyloxy (TEMPO), or its derivatives such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) and any derivatives of this hydroxyl functionalization such as methacrylate of 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy.

[0068] Preferably, the esterification (transesterification) reaction is carried out with the introduction of oxygen into the reaction mixture.

[0069] 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.

[0070] Preferably, the repeated adjustment of a given pressure is performed using pressure stages, preferably wherein the difference between two pressure stages is less than 500 mbar, preferably less than 100 mbar, more preferably less than 50 mbar, even more preferably less than 10 mbar.

[0071] This has the advantage that the pressure can be adjusted in steps, which can gradually adjust the pressure. In addition, by means of pressure steps, it is possible to adjust the pressure in the reaction according to the conditions in the reactor. The lower the pressure level, the more sensitive the reaction can be.

[0072] The pressure reduction facilitates the separation of by-products.

[0073] Preferably, the esterification (transesterification) reaction is started at a pressure in the range of 0.1 bar to 5.0 bar, preferably 0.1 bar to 4.0 bar, more preferably 0.1 bar to 3.0 bar, even more preferably 0.1 bar to 2.0 bar, most preferably 0.5 bar to 1.5 bar, for example 1 bar, or wherein the esterification (transesterification) reaction is started at a pressure above 1.0 bar and the reaction process is ended at a pressure below 1.0 bar. If the formation of by-products increases significantly at elevated temperatures, it is advisable to end the reaction at a pressure below standard pressure, i.e. standard pressure can be defined as 1 bar, so as to reduce the reaction temperature above the boiling temperature of the reactants in a targeted manner.

[0074] Preferably, the repeated adjustment of the given pressure is performed continuously.

[0075] This has the advantage that the pressure can be controlled and regulated when the reaction temperature is below the boiling temperature. Reactor shutdowns due to boiling of the reaction mixture can be prevented.

[0076] As the boiling temperature of the reaction mixture changes during the esterification (transesterification) reaction, the esterification (transesterification) reaction is preferably carried out while repeatedly adjusting the pressure according to the boiling temperature of the reaction mixture. The adjustment of the pressure level can also be automatically affected by recipe control.

[0077] This has the advantage that the reaction conditions remain more or less constant for the majority of the time or for the entire time of the esterification (transesterification) reaction and that the reaction conditions are maintained at the optimum reaction temperature. This has the further advantage that the reaction proceeds at an optimum rate and polymerization and other side effects, such as the formation of undesirable by-products (including in particular Michael addition of the corresponding alcoholate as nucleophile to the methacrylic acid derivative) are reduced to a minimum.

[0078] In the present invention, the given pressure is repeatedly adjusted to keep the reaction temperature in the range of usually 70° C. to not more than 130° C. Preferably, the given pressure is repeatedly adjusted to keep the reaction temperature in the range of 80° C. to not more than 125° C., more preferably in the range of 90° C. to not more than 120° C.

[0079] The starting material comprises (meth) acrylate and a first alcohol. 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 optionally one or more additional compounds, and wherein the two or more products are a first product, a second product and optionally one or more additional products.

[0080] The reaction mixture may further contain additives such as reaction accelerators, reaction inhibitors, buffers, solvents, stabilizers, water, viscosity index improvers, thickeners, antioxidants, corrosion inhibitors, dispersants, high pressure additives, defoamers, catalysts or enzymes.

[0081] Preferably, the catalyst is a strongly basic catalyst. The stabilizer comprises, for example, HQME, phenothiazine (PTZ), Tempol or hydroxytempol. In addition, at least an alcohol, for example a second alcohol, is formed as a by-product. Further by-products may be formed by the reaction, which are then also present in the reaction mixture.

[0082] As mentioned above, another advantage of the present invention is that less excess (meth)acrylate starting material is required in the reaction chamber for reaction temperature control. When carrying out the method according to the present invention, the ratio of the first alcohol to the (meth)acrylate starting material before the reaction begins can be in the range of 1:1 to 1:5. The ratio is preferably in the range of 1:1 to 1:2, more preferably in the range of 1:1.1 to 1:1.5, and most preferably in the range of 1:1.1 to 1:1.3, for example 1:1.2.

[0083] The pressure change in the reaction chamber is carried out by actively changing the gas space or the liquid-filled space. The gas used for pressure regulation can be oxygen, nitrogen, ethylene oxide or isobutylene or a mixture thereof. It is also possible to increase the pressure by liquid, but it limits the reactor volume, which is therefore disadvantageous. Therefore, it has been shown that using gas is preferred. Due to the need to always supply air to the reaction to achieve stabilization, this gas is most preferably an oxygen-containing gas, such as air or dilution air. If the reactant is also a gas, it has been shown that this reactant is particularly preferably mixed with oxygen or an oxygen-containing gas.

[0084] Preferably, the reboiler is an internal or external heating coil, a heating jacket, an internal heat exchanger or an external heat exchanger.

[0085] The following examples are intended to explain and illustrate the principles of the present invention to those skilled in the art, and to show how the present invention may be applied in practice. DETAILED DESCRIPTION Example

[0086] Comparative Example 1

[0087] Generating EGDMA using lithium amide (LiNH2) as a catalyst

[0088] 4263 kg of hydroxyethyl methacrylate (HEMA), 4234 kg of methyl methacrylate (MMA) were combined with 0.183 kg of HQME as an inhibitor and 8 kg of lithium amide as a catalyst in a stirred tank reactor, which was a stirred reaction vessel in reactor 1, equipped with a stirrer, a feed line 13, a reboiler 12, a distillation column 2 and a condenser 5, and stirred while passing air. In order to stabilize the column 2, a total of 22.68 kg / hour of MMA containing 0.1% by weight of hydroquinone monomethyl ether and 0.01% by weight of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in dissolved form was introduced into the column runback. Reactor 1 was heated until a distillate stream was obtained, wherein the column was initially operated at total reflux at a distillate flow rate of 40.8 kg / min. Once the methanol concentration at the top of the column increased to 75% by weight, a methanol / MMA mixture was removed until the concentration was maintained at 75% by weight, or at least 1.63 kg / min was removed. The MMA reserve in the reactor was replenished by metering an equal portion of MMA relative to each portion of methanol / MMA mixture removed. A total of 3039 kg of MMA was thus introduced during the reaction, and once this total amount was obtained, no replacement was performed. No additional catalyst dosage was added except for the initial amount. The reaction temperature increased to approximately 132° C. during the reaction. When the amount of residual HEMA was less than 0.8% by weight, the reaction was completed, with MMA not being part of the integration, with a good constant total time of 20 hours. Once the reaction was complete, excess MMA was removed under reduced pressure, with the pressure gradually reduced to 0.042 bar. When no more MMA was distilled out or the concentration of ethylene glycol dimethacrylate (EGDMA) in the distillate exceeded a threshold value of 35% by weight, the vacuum was broken. The kettle contents containing the catalyst and ethylene glycol dimethacrylate were freed of the catalyst by means of a sparkler filter.

[0089] result:

[0090] In this example, 6486 kg of EGDMA crude product were obtained, which contained 92.4% by weight of EGDMA, 0.8% by weight of HEMA, 0.8% by weight of MMA, 0.4% by weight of diethylene glycol dimethacrylate, 0.24% by weight of Michael addition product of EGDMA and methanol, 1.8% by weight of Michael addition product of EGDMA and HEMA, which after distillation gave 98.2% by weight of EGDMA, 0.8% by weight of HEMA, 0.7% by weight of MMA, 0.2% by weight of diethylene glycol dimethacrylate.

[0091] Comparative Example 2

[0092] Generation of EGDMA using lithium methoxide (LiOMe) as a catalyst

[0093] 4263 kg of HEMA, 4234 kg of methyl methacrylate (MMA) were combined with 0.183 kg of HQME as inhibitor and 13.6 kg of lithium methoxide as catalyst in a stirred tank reactor, which was a stirred reaction vessel in reactor 1, equipped with a stirrer, feed line 13, reboiler 12, distillation column 2 and condenser 5, and stirred while passing air. In order to stabilize the column 2, a total of 22.68 kg / hour of MMA containing 0.1% by weight of hydroquinone monomethyl ether and 0.01% by weight of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in dissolved form was introduced into the column reflux. Reactor 1 was heated until a distillate stream was obtained, wherein the column was initially operated at total reflux at a distillate flow rate of 40.8 kg / min. Once the methanol concentration at the top of the column increased to 75% by weight, a methanol / MMA mixture was removed until the concentration was maintained at 75% by weight, or at least 1.63 kg / min was removed. The MMA reserve in reactor 1 is replenished by metering an equal portion of MMA relative to each portion of methanol / MMA mixture taken out. A total of 3039 kg of MMA is therefore introduced during the reaction, and once this total amount is obtained, no replacement is performed. No additional catalyst dosage is added except for the initial amount. The reaction temperature rises to about 132° C. during the reaction. When the amount of residual HEMA is less than 0.8% by weight, the reaction is completed, wherein MMA is not part of the integral, with a good constant total time of 20 hours. Once completed, excess MMA is taken out under reduced pressure, wherein the pressure is gradually reduced to 0.042 bar. When no more MMA is distilled out or the EGDMA concentration in the distillate exceeds a threshold value of 35% by weight, the vacuum is destroyed. The kettle contents comprising catalyst and ethylene glycol dimethacrylate are decatalyzed by means of a sparkler filter.

[0094] result:

[0095] This gave 6486 kg of crude EGDMA: it contained 87.5% by weight of EGDMA, 0.93% by weight of HEMA, 0.6% by weight of MMA, 0.4% by weight of diethylene glycol dimethacrylate, 2.73% by weight of Michael addition products of EGDMA and methanol, 5.15% by weight of Michael addition products of EGDMA and HEMA, which after distillation gave 96.2% by weight of EGDMA, 0.9% by weight of HEMA, 0.44% by weight of MMA, 0.16% by weight of diethylene glycol dimethacrylate, 2.0% by weight of Michael addition products of EGDMA and methanol.

[0096] Comparative Example 3

[0097] Generation of EGDMA using LiNH2 as a catalyst

[0098] 2038 kg of ethylene glycol, 4927 kg of methyl methacrylate (MMA) are combined with 0.183 kg of HQME as inhibitor and 8.165 kg of lithium amide as catalyst in a stirred tank reactor, which is a stirred reaction vessel in reactor 1, equipped with a stirrer, feed line 13, reboiler 12, distillation column 2 and condenser 5, and stirred while passing air. In order to stabilize the column 2, a total of 22.68 kg / hour of MMA containing 0.1% by weight of hydroquinone monomethyl ether and 0.01% by weight of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in dissolved form is introduced into the column reflux. Reactor 1 is heated until a distillate stream is obtained, wherein the column is initially operated at total reflux at a distillate flow rate of 40.8 kg / min. Once the methanol concentration at the top 3 of the column has increased to 75% by weight, a methanol / MMA mixture is withdrawn until this concentration is maintained at 75% by weight, or at least 1.63 kg / min is withdrawn. The MMA reserve in reactor 1 is replenished by metering an equal portion of MMA relative to each portion of methanol / MMA mixture taken out. A total of 3039 kg of MMA is therefore introduced during the reaction, and once this total amount is obtained, no replacement is performed. No additional catalyst dosage is added except the initial amount. The reaction temperature rises to about 132 ° C during the reaction. When the amount of residual HEMA is less than 0.8% by weight, the reaction is completed, wherein MMA is not part of the integral, with a good constant total time of 22 hours. Once completed, excess MMA is taken out under reduced pressure, wherein the pressure is gradually reduced to 0.042 bar. When no more MMA is distilled out or the EGDMA concentration in the distillate exceeds a threshold value of 35% by weight, the vacuum is destroyed. The kettle contents comprising catalyst and ethylene glycol dimethacrylate are decatalyzed by means of a sparkler filter.

[0099] result:

[0100] This gave 6486 kg of crude EGDMA: It contained 92.5% by weight of EGDMA, 1.22% by weight of HEMA, 0.46% by weight of MMA, 0.04% by weight of diethylene glycol dimethacrylate, 0.14% by weight of Michael addition products of EGDMA and methanol, 2.17% by weight of Michael addition products of EGDMA and HEMA, which after distillation gave 98.2% by weight of EGDMA, 0.99% by weight of HEMA, 0.41% by weight of MMA, 0.05% by weight of diethylene glycol dimethacrylate, 0.19% by weight of Michael addition products of EGDMA and methanol. Example 1

[0101] EGDMA production using LiOMe as catalyst and pressure regulation

[0102] 4264 kg HEMA, 4235 kg MMA, 0.183 kg HQME as inhibitor and 13.6 kg lithium methoxide as catalyst were mixed. Figure 1 Combined in a stirred tank reactor, which is a stirred reaction vessel in reactor 1, equipped with a stirrer, feed line 13, reboiler 12, distillation column 2 and condenser 5, and stirred while passing air. In order to stabilize the column, a total of 22.68 kg / h of MMA containing 0.1% by weight of hydroquinone monomethyl ether and 0.01% by weight of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in dissolved form was introduced into the column reflux. The reactor was heated until a distillate stream was obtained, wherein the column was initially operated at total reflux at a distillate flow rate of 40.8 kg / min. The reactor pressure was reduced by 0.007 bar whenever the reactor temperature was less than 0.5°C from the target set point of 100°C. If the temperature was not more than 0.5°C from the target set point 2 minutes after the pressure reduction was completed, the pressure reduction was repeated. Once the temperature has been reduced, if the reactor temperature is more than 1°C from the target set point, the pressure is increased. Once the methanol concentration at the top of the tower increases to 75% by weight, take out the methanol / MMA mixture until the concentration is maintained at 75% by weight, or take out at least 1.63 kg / min. By metering an equal portion of MMA relative to each portion of methanol / MMA mixture taken out, the MMA reserve in the reactor is supplemented. Therefore, a total of 3039 kg of MMA is introduced during the reaction, and once this total amount is obtained, it is no longer replaced. No additional catalyst dosage is added except the initial amount. The reaction temperature is well maintained at 100 ° C during the reaction, and the end pressure is 0.525 bar. The reaction is completed while completing the reference batch in Comparative Example 2 under a total time of 20 hours. Once the reaction is completed, take out excess MMA under reduced pressure, wherein the pressure is gradually reduced to 0.042 bar. When no longer distilling out MMA or the EGDMA concentration in the distillate exceeds the threshold value of 35% by weight, the vacuum is destroyed. The kettle contents comprising catalyst and ethylene glycol dimethacrylate are removed by means of a sparkler filter.

[0103] result:

[0104] This gave 6486 kg of crude EGDMA: It contained 95.1% by weight of EGDMA, 1.5% by weight of HEMA, 0.33% by weight of MMA, 0.4% by weight of diethylene glycol dimethacrylate, 0.3% by weight of Michael addition products of EGDMA and methanol, 1.7% by weight of Michael addition products of EGDMA and HEMA, which after distillation gave 98.18% by weight of EGDMA, 0.28% by weight of MMA, 1.22% by weight of HEMA, 0.13% by weight of diethylene glycol dimethacrylate and 0.13% by weight of Michael addition products of EGDMA and methanol. Example 2

[0105] EGDMA production using LiOMe as catalyst and pressure regulation

[0106] 2038 kg of ethylene glycol, 4927 kg of MMA were combined with 0.183 kg of HQME as inhibitor and 13.6 kg of lithium methoxide as catalyst in a stirred tank reactor, which was a stirred reaction vessel in reactor 1, equipped with a stirrer, feed line 13, reboiler 12, distillation column 2 and condenser 5, and stirred while passing air. In order to stabilize this column 2, a total of 22.68 kg / hour of MMA containing 0.1% by weight of hydroquinone monomethyl ether and 0.01% by weight of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl in dissolved form was introduced into the column reflux. Reactor 1 was heated until a distillate stream was obtained, wherein column 2 was initially operated at total reflux at a distillate flow rate of 40.8 kg / min. The reactor pressure was reduced by 0.007 bar whenever the reactor temperature was less than 0.5°C from the target set point of 100°C. If the temperature is not more than 0.5°C from the target set point 2 minutes after the pressure reduction is completed, the pressure reduction is repeated. Once the temperature has been reduced, if the reactor temperature is more than 1°C from the target set point, the pressure is increased. Once the methanol concentration at the top of the tower increases to 75% by weight, the methanol / MMA mixture is taken out until the concentration is maintained at 75% by weight, or at least 1.63 kg / min is taken out. The MMA reserve in the reactor is supplemented by metering an equal portion of MMA relative to each portion of methanol / MMA mixture taken out. Therefore, a total of 3039 kg of MMA is introduced during the reaction, and once this total amount is obtained, it is no longer replaced. No additional catalyst dosage is added except the initial amount. The reaction temperature is well maintained at 100°C during the reaction, and the end pressure is 0.511 bar. The reaction is completed at the same time as the reference batch in Comparative Example 3 is completed at a total time of 22 hours. Once the reaction is completed, excess MMA is taken out under reduced pressure, wherein the pressure is gradually reduced to 0.042 bar. When no more MMA is distilled out or the EGDMA concentration in the distillate exceeds the threshold value of 35% by weight, the vacuum is destroyed. The contents of the kettle comprising catalyst and ethylene glycol dimethacrylate were freed from the catalyst by means of a sparkler filter.

[0107] result:

[0108] This gave 6486 kg of crude EGDMA: It contained 95.0% by weight of EGDMA, 1.6% by weight of HEMA, 0.41% by weight of MMA, 0.04% by weight of diethylene glycol dimethacrylate, 0.1% by weight of Michael addition products of EGDMA and methanol, 1.5% by weight of Michael addition products of EGDMA and HEMA, which after distillation gave 98.08% by weight of EGDMA, 0.28% by weight of MMA, 1.32% by weight of HEMA, 0.13% by weight of diethylene glycol dimethacrylate and 0.13% by weight of Michael addition products of EGDMA and methanol.

[0109] Thus, it has been demonstrated that the above-mentioned safety issues of LiNH2 are overcome by using lithium alkoxides, preferably lithium methoxide (LiOMe). Surprisingly, the disadvantage of LiOMe providing immediate catalytic efficiency at the beginning of the reaction, which leads to, for example, high methanol concentrations in the reactor, can be successfully suppressed by a selected reduction in the constant reaction temperature (optionally combined with an additional stepwise reduction in pressure). With reference to Comparative Example 2 and Examples 1 and 2, at a reduction in the reaction temperature of up to 32°C, the yield of the product EGDMA after distillation can be significantly increased by 1.28% by weight, thereby obtaining 97.54% by weight up to 98.18% by weight of EGDMA after distillation.

Claims

1. A method 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 reaction chamber (1) containing the reaction mixture, a feed line (13), a reboiler (12), a column (2) having a column top (3), a vapor transfer line (4), a condenser (5), a reflux drum (6), a reflux line (7), a distillate withdrawal line (8) and a receiving vessel (9), 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 strong alkaline catalyst, wherein the (meth)acrylate starting material is methyl methacrylate, the first alcohol is ethylene glycol or hydroxyethyl methacrylate, and wherein the product is ethylene glycol dimethacrylate, wherein the strong alkaline catalyst comprises one or more compounds selected from calcium oxide (CaO), calcium hydroxide (Ca(OH)2), lithium hydroxide (LiOH), sodium methoxide (NaOMe), lithium methoxide (LiOMe), lithium tert-butoxide (LiOt-Bu), lithium isopropoxide (LiOiPr), preferably wherein the strong alkaline catalyst comprises one or more compounds selected from lithium methoxide (LiOMe), and most preferably wherein the strong alkaline catalyst comprises or is lithium methoxide (LiOMe), 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 The given pressure is repeatedly adjusted to maintain the reaction temperature range during the main amount of time during the esterification (transesterification) reaction. wherein the repeated adjustment of a given pressure is performed using pressure stages, preferably wherein the difference between two pressure stages is less than 500 mbar, preferably less than 100 mbar, more preferably less than 50 mbar, even more preferably less than 10 mbar, and The given pressure is repeatedly adjusted to keep the reaction temperature in the range of 70°C to not more than 130°C, preferably in the range of 80°C to not more than 125°C, more preferably in the range of 90°C to not more than 120°C.

2. 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.

3. The process according to one or more of the preceding claims, wherein at least a portion of the converted (meth)acrylate starting material is compensated by adding a further amount of (meth)acrylate starting material to the reaction mixture, preferably via a feed line to the reaction chamber or column.

4. 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. 5 . The process according to claim 1 , wherein the esterification (transesterification) reaction is carried out with introduction of oxygen into the reaction mixture.

6. Method according to one or more of the preceding claims, wherein the repeated adjustment of the given pressure is performed continuously.

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