Transesterification process

Abstract

The invention relates to the field of organic synthesis. More specifically, a continuous process is provided for transesterification of a compound comprising at least one C1-4 carboxylic acid ester group in the presence of a C1-4 alcohol and a transesterification catalyst wherein the transesterification step is carried out in at least two subsequent reactors separated by a separation unit. The invention also relates to a method for preparing 1, 4-cyclohexanedicarboxylic acid diethyl ester, which comprises a step of transesterification of dimethyl terephthalate in the presence of ethanol and a step of reduction of diethyl terephthalate.

Description

Technical Field

[0001] The present invention relates to the field of organic synthesis. More specifically, a method for preparing a C 1-4 alcohol and an ester exchange catalyst in the presence of at least one C 1-4 The invention also relates to a method for preparing diethyl 1,4-cyclohexanedicarboxylate, comprising a step of transesterifying dimethyl terephthalate in the presence of ethanol and a step of reducing diethyl terephthalate. Background Art

[0002] There is a great need to obtain compounds containing carboxylate groups, as they represent a very desirable backbone that can be used as such or as a key intermediate for the preparation of more complex compounds in different fields, such as, in particular, perfumery, cosmetics, pharmaceuticals or agrochemicals. In this context, a variety of methods have been developed, such as transesterification. Such reactions can be difficult to implement on a large scale, as they require long reaction times and high energy consumption, and suffer from low productivity.

[0003] As a key reaction for producing valuable compounds, new processes are always needed to improve yield and selectivity and reduce energy consumption.

[0004] The present invention provides a solution to the above mentioned problems by carrying out the transesterification under continuous conditions in at least two continuous reactors separated by a separation unit, wherein the alcohol formed in the process is removed. To the best of our knowledge, there is no report in the prior art about such a continuous process disclosed in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 A schematic process flow diagram illustrating one embodiment of the present invention. Summary of the invention

[0006] Surprisingly, it has now been found that carrying out the transesterification process in conditioned mode in at least two subsequent reactors separated by a separation unit allows more desired product to be produced in a shorter time, thereby reducing energy consumption.

[0007] Therefore, the first object of the present invention is to provide a 1-4 alcohol and an ester exchange catalyst in the presence of at least one C 1-4A continuous process for the transesterification of compounds containing at least one C 1-4 A continuous process for the transesterification of compounds containing carboxylic acid ester groups, wherein the compounds contain at least one C 1-4 The compound containing a carboxylic acid ester group is reacted with C in the presence of an ester exchange catalyst. 1-4 The alcohol is reacted and wherein the transesterification step is performed in at least two subsequent reactors separated by a separation unit.

[0008] For the sake of clarity, it should be understood that by the expression "transesterification", the usual meaning in the art is meant, i.e., the starting materials and the resulting compounds contain at least one carboxylic acid ester group. In other words, transesterification is, for example, from a formula R-COO-R 1 The compound of formula R-COO-R 2 A compound wherein R 1 and R 2 In the method, a compound of the formula HOR is also formed. 1 The alcohol is different from the C 1-4 alcohol.

[0009] The term "comprising at least one C 1-4 The term "compound containing a carboxylate group" is understood to mean a compound containing at least one 1 A compound of the group, wherein R 1 C 1-4 In other words, the 1-4 The compound of the carboxylate group is a compound of the formula:

[0010] R-COO-R 1 (I)

[0011] Where R 1 C 1-4 alkyl, and R is optionally containing one or more C 1-4 The C of the carboxylate group 1-18 Hydrocarbon.

[0012] It is to be understood that by "...hydrocarbyl..." it is meant that the group consists of hydrogen and carbon atoms and may be in the form of an aliphatic hydrocarbon, i.e. a straight or branched saturated hydrocarbon (e.g. an alkyl), a straight or branched unsaturated hydrocarbon (e.g. an alkenyl or alkynyl), a saturated cyclic hydrocarbon (e.g. a cycloalkyl) or an unsaturated cyclic hydrocarbon (e.g. a cycloalkenyl or cycloalkynyl), or in the form of an aromatic hydrocarbon, i.e. an aryl, or also in the form of a mixture of the types of groups mentioned, e.g. unless specifically limited to only one type mentioned, a particular group may contain straight chain alkyl, branched alkenyl (e.g. with one or more carbon-carbon double bonds), (poly)cycloalkyl and aryl moieties. Similarly, in all embodiments of the present invention, when referring to a group in the form of more than one type of topology (e.g. straight chain, cyclic or branched) and / or saturation or unsaturation (e.g. alkyl, aromatic or alkenyl), it also means a group that may contain moieties having any of the topologies or saturation or unsaturation as explained above. Similarly, in all embodiments of the present invention, when referring to a group in one form (e.g., alkyl) of saturation or unsaturation, it is meant that the group can be of any type of topology (e.g., linear, cyclic, or branched) or have several moieties with various topologies.

[0013] The term "optionally" should be understood as meaning that the R group may or may not contain a functional group. The term "one or more" should be understood as meaning that the R group may or may not contain a functional group. 1-4 Carboxylate groups.

[0014] The term "C 1-4 "Alcohol" is understood to mean the formula R 2 OH alcohol, where R 2 C 1-4 Alkyl. C 1-4 The alcohol contains only one hydroxyl group and no other functional groups; i.e., C 1-4 Alcohol is a monohydric alcohol. 1-4 The alcohol is not glycerol or a fatty alcohol.

[0015] The term "alkyl" is understood to include both branched and straight chain alkyl groups.

[0016] The term "separation unit" is to be understood as any device which allows the separation of molecules from a reaction mixture comprising a plurality of molecules, in particular the separation of molecules having different boiling points. Non-limiting examples of suitable separation units may include distillation columns, rectification units, membranes, pervaporation units, adsorption units, absorption units.

[0017] According to one embodiment of the present invention, the 1-4The carboxylate group of the compound is not a fatty acid ester, a monoglyceride, a diglyceride or a triglyceride.

[0018] According to one embodiment of the present invention, the 1-4 The compound of the carboxylic acid ester group is a diester compound. In particular, the diester is a compound of the formula:

[0019] R 1 -OOC-R'-COO-R 1 (II)

[0020] Two of the R 1 Independently of each other, C 1-4 alkyl, and R' is optionally containing one or more C 1-4 The C of the carboxylate group 1-18 Hydrocarbon.

[0021] According to any embodiment of the present invention, R 1 Can be C 1-3 Alkyl, in particular methyl or ethyl, more in particular methyl. In other words, the carboxylate group can be C 1-3 The alcohol formed / released in the method of the present invention may be C 1-3 Alcohols, especially C 1-2 Carboxylate groups and C 1-2 Alcohols, even more particularly C1 carboxylic acid ester groups and methanol. In particular, the alcohol formed / released in the process of the invention is not glycerol or ethylene glycol.

[0022] According to any embodiment of the present invention, R may be optionally comprised of one or more C 1-4 The C of the carboxylate group 1-16 In particular, R may be a hydrocarbon group optionally containing one or more C 1-4 The C of the carboxylate group 1-14 In particular, R may be a hydrocarbon group optionally containing one or more C 1-4 The C of the carboxylate group 1-12 In particular, R may be a hydrocarbon group optionally containing one or more C 1-4 The C of the carboxylate group 1-10 In particular, R may be a hydrocarbon group optionally containing one or more C 1-4 The C of the carboxylate group 1-8 In particular, R may be C 1-8 Alkyl, C 3-8 Cycloalkyl, C 2-8 alkenyl or phenyl; each group is optionally substituted with one or more C 1-4 In particular, R may be C 1-6 Alkyl, C 3-6 Cycloalkyl, C2-6 alkenyl or phenyl; each group is optionally substituted with one or more C 1-4 In particular, R may be C 1-6 Alkyl, C 3-6 Cycloalkyl, C 2-6 alkenyl or phenyl; each group is optionally substituted with one or two C 1-4 In particular, R may be C 1-6 Alkyl, C 3-6 Cycloalkyl, C 2-6 alkenyl or phenyl, optionally substituted with a C 1-4 Even more particularly, R may be C 1-6 Alkyl, C 5-6 Cycloalkyl, C 2-6 alkenyl or phenyl, optionally substituted with a C 1-4 Carboxylate groups.

[0023] According to any embodiment of the present invention, R' may be C 1-16 In particular, R' may be C 1-14 In particular, R' may be C 1-12 In particular, R' may be C 1-10 In particular, R' may be C 1-8 In particular, R' may be C 1-8 Alkanediyl, C 3-8 Cycloalkanediyl, C 2-8 In particular, R' may be C 1-6 Alkanediyl, C 3-6 Cycloalkanediyl, C 2-6 In particular, R' may be C 1-6 Alkanediyl, C 5-6 Cycloalkanediyl, C 2-6 Even more particularly, R' may be 1,4-phenylene.

[0024] According to any embodiment of the present invention, the C 1-4 The alcohol can be C 2-3 Alcohol, preferably ethanol.

[0025] According to any embodiment of the present invention, from the 1-4 The compound of carboxylic acid ester (i.e., formula R 1 The boiling point of the alcohol released by the compound with OH is higher than that of the C 1-4 Alcohol (i.e., formula R 2 In particular, the C 1-4 Alcohol (i.e., formula R 2OH) and the boiling point of the compound containing at least one C 1-4 The compound of carboxylic acid ester (i.e., formula R 1 The difference between the boiling points of the alcohols released by the compounds containing OH) is 10 to 30°C, in particular 10 to 20°C, even more in particular 12 to 18°C.

[0026] According to any embodiment of the present invention, the 1-4 The compound of the carboxylate group is dimethyl terephthalate or dimethyl 1,4-cyclohexanedicarboxylate.

[0027] According to any embodiment of the present invention, from the 1-4 The alcohol released from the carboxylate group of the compound is completely or partially removed in a separation unit and C 1-4 In particular, the C 1-4 The alcohol was the same, that is, ethanol was added to each reactor.

[0028] According to any embodiment of the present invention, the reactor used in the inventive method can be any reactor that is applicable to continuous method (process).The reactor can be the same or different.The non-limiting example of suitable reactor can include plug flow reactor, continuous stirred tank reactor, laminar flow reactor, loop reactor, microreactor, the reactor that is divided into multiple sections and their combination.Especially, the reactor can be plug flow reactor, continuous stirred tank reactor and their combination.

[0029] According to any embodiment of the present invention, the continuous process is carried out in two reactors. The residence time in each reactor depends on the type of reactor. The residence time can be 0.01 hour to 100 hours, particularly 0.2 hour to 20 hours.

[0030] According to any embodiment of the present invention, the separation unit can be a distillation column. The distillation column used in the process of the present invention can be any distillation column suitable for a continuous process. The distillation column can include plates or trays or packing. A person skilled in the art can select and determine the size of the distillation column based on the melting and boiling points of the starting and final products.

[0031] According to any embodiment of the present invention, the distillation can be carried out at atmospheric pressure or at reduced pressure, in particular at a pressure below 200×10 5 Pa (200 bar), for example, at 5×10 5 Pa to 100×10 5 Pa (5 to 100 bar).

[0032] According to any embodiment of the present invention, the method of the present invention comprises:

[0033] a) in a first reactor, in the presence of a transesterification catalyst, 1-4 Carboxylate compounds with C 1-4 Alcohol undergoes transesterification reaction;

[0034] b) the reaction mixture of step a) is then distilled in a distillation column, wherein the liberated alcohol is completely or partially removed; and

[0035] c) The reaction mixture is then passed into a second reactor, where C 1-4 alcohol.

[0036] According to any embodiment of the present invention, in step a) and step c) the C 1-4 The alcohol is the same.

[0037] According to any embodiment of the present invention, the second reactor is followed by at least one separation unit, wherein the unreacted or partially reacted 1-4 Compounds with carboxylic acid ester groups, released alcohol, excess added C 1-4 The alcohol and the transesterification catalyst are removed. In particular, the second reactor is followed by two separation units. The separation units are distillation columns.

[0038] According to any embodiment of the present invention, the transesterification catalyst is a Lewis acid, a Bronsted acid, or a base, in particular a Lewis acid. Specific and non-limiting examples of transesterification catalysts can be selected from the group consisting of: an organotin compound or an organotitanium compound, an organotin compound formed in situ by reaction of a dialkyltin oxide with an acid of the ester being transesterified, preferably a dialkyltin derivative such as the oxide (C4H9)2SnO, (C8H 17 )2SnO, dicarboxylates such as dibutyltin dilaurate, dioctyltin dicarboxylate and mixtures thereof.

[0039] The transesterification catalyst may be added to the reaction medium of the process of the present invention in a wide range of concentrations. As non-limiting examples, the concentrations of the transesterification catalyst in the reaction medium may be exemplified relative to the reaction medium comprising at least one C 1-4 The amount of the compound of the carboxylic acid ester ranges from about 0.001 to about 5 mol % acid concentration, preferably relative to the at least one C 1-4 The amount of the compound of the carboxylic acid ester ranges from 0.02 to about 0.5 mol % acid concentration. As known to those skilled in the art, the optimal concentration of the transesterification catalyst depends on the nature of the catalyst, the presence of at least one C 1-4The properties of carboxylic acid ester compounds, C 1-4 The nature of the alcohol, the reaction temperature and the process flow.

[0040] C 1-4 The alcohol can be added to the reaction medium of the process of the invention in a wide range of concentrations. As non-limiting examples, the concentrations of alcohols in the reaction medium of the process of the invention can be cited relative to the reaction medium comprising at least one C 1-4 The amount of the carboxylic acid ester compound ranges from about 2 to about 20 equivalents of C 1-4 Alcohol value, preferably relative to a content of at least one C 1-4 The amount of the carboxylic acid ester compound is at least 5 equivalents of C 1-4 Alcohol value. As known to those skilled in the art, C 1-4 The optimum concentration of alcohol depends on the nature of the alcohol, including at least one C 1-4 The nature of the carboxylic acid ester compound, the nature of the ester exchange catalyst, the reaction temperature and the process flow.

[0041] According to any embodiment of the present invention, C is added to each reactor in the process of the present invention. 1-4 Alcohol, in particular, the same C 1-4 alcohol.

[0042] According to any embodiment of the present invention, the method of the present invention is carried out at a temperature of 20° C. to 250° C. Specifically, the temperature is in the range of 70° C. to 200° C. Of course, those skilled in the art can also select the preferred temperature according to the melting point and boiling point of the starting product and the final product and the desired reaction or conversion time.

[0043] The method of the present invention can be used in 0.1×10 5 Pa to 100×10 5 Pa (0.1 to 100 bar), and if necessary, even at a higher pressure. Likewise, those skilled in the art will be able to determine the catalyst loading and the amount of the catalyst containing at least one C 1-4 The pressure can be adjusted by using carboxylic acid ester compounds. As an example, 1 to 50×10 5 Typical pressures are Pa (1 to 50 bar).

[0044] The process of the present invention may be carried out under an inert atmosphere such as nitrogen and / or argon.

[0045] The process of the present invention can be carried out in the presence or absence of a solvent. When a solvent is required or used for practical reasons, any solvent of the type of reaction at the present time can be used for the purposes of the present invention. The choice of solvent depends on the 1-4The nature of the compound of the carboxylate group and / or of the catalyst and the person skilled in the art is fully capable of selecting the most suitable solvent in each case in order to optimize the reaction.

[0046] According to any embodiment of the present invention, C 1-4 Both the alcohol and the transesterification catalyst are recycled.

[0047] In the method of the present invention, for a plurality of C 1-4 Compounds of carboxylic acid esters, involving the formation of monoester exchange compounds as intermediates; such intermediates may be present in the final reaction mixture at a certain level and can be recovered in the process of the present invention. In addition, unreacted starting materials can also be recovered in the process of the present invention.

[0048] The second object of the present invention is to produce a fragrance product, a cosmetic product or a pharmaceutical product using the above method, in particular a fragrance product. In particular, the fragrance product can be diethyl 1,4-cyclohexanedicarboxylate.

[0049] Another object of the present invention is a method for preparing diethyl 1,4-cyclohexanedicarboxylate, comprising the following steps:

[0050] a) transesterification of dimethyl terephthalate in the presence of ethanol to give diethyl terephthalate as defined above; and

[0051] b) Reduction of the diethyl terephthalate obtained in step a).

[0052] In other words, another object of the present invention is a method for preparing diethyl 1,4-cyclohexanedicarboxylate, comprising the following steps:

[0053] a) transesterification as defined above, wherein dimethyl terephthalate is reacted with ethanol in the presence of a transesterification catalyst to obtain diethyl terephthalate; and

[0054] b) Reduction of the diethyl terephthalate obtained in step a).

[0055] According to any embodiment of the invention, the reduction is a hydrogenation using molecular H2 and a hydrogenation catalyst. The hydrogenation catalyst may be a metal in elemental metal form, in particular palladium or ruthenium in elemental metal form.

[0056] According to any one of the above embodiments of the present invention, the palladium (Pd) or ruthenium (Ru) is supported on a support material.

[0057] For the sake of clarity, support material refers to a material on which the metal can be deposited and which is inert to the substrate (diethyl terephthalate).

[0058] According to any of the above embodiments of the present invention, specific and non-limiting examples of support materials are carbon, silica or alumina. Such supports are well known to those skilled in the art.

[0059] Supported palladium (Pd) or ruthenium (Ru) catalysts are known compounds and are commercially available. Those skilled in the art can select the preferred metal species based on the deposition method of the metal on the support, the proportion of the metal on the support material, the form (powder, granular, pelletized, extrudate, foam ...) and the surface area of ​​the support. Specifically, the hydrogenation catalyst is ruthenium supported on alumina.

[0060] According to any of the above embodiments of the invention, the amount of metal relative to the support may be from 0.05% to 25% w / w, or even from 0.4% to 6% w / w, relative to the weight of the support used.

[0061] The hydrogenation catalyst can be added to the reaction medium of the process of the present invention in a wide range of concentrations. As non-limiting examples, metal concentration values ​​of 0.001 mol% to 1 mol% relative to the total amount of diethyl terephthalate can be cited. Preferably, the metal concentration is 0.02 mol% to 1 mol%, or even 0.04 mol% to 1 mol%. It goes without saying that, as known to those skilled in the art, the optimum concentration of the metal will depend on the nature of the metal, whether the process is intermittent or continuous operation, the temperature and H2 pressure used in the process, and the required reaction time.

[0062] The hydrogenation catalyst can be recycled at the end of the process of the invention. In other words, the hydrogenation catalyst can be recovered at the end of the process of the invention and used multiple times in the process of the invention.

[0063] According to any of the above embodiments of the present invention, molecular hydrogen can be used alone or mixed with an inert gas. Specific and non-limiting examples of such inert gases are nitrogen or argon. When molecular hydrogen is used in combination with an inert gas, the volume ratio of H2 / inert gas is 1 / 1 to 0.01 / 1, and more preferably the ratio is 0.05 / 1.

[0064] Molecular hydrogen can be added to the reaction medium of the inventive method with a large range of ratios relative to substrate. As non-limiting example, the molecular hydrogen ratio value of 100mol% to 5000mol% can be enumerated relative to the amount of diethyl terephthalate. Even more preferably, the molecular hydrogen concentration is 300mol% to 2000mol% relative to the amount of diethyl terephthalate. Of course, those skilled in the art can regulate the pressure or flow (for example, in a continuous process) of molecular hydrogen to obtain this concentration range according to whether the method is intermittent or continuous. Those skilled in the art can also regulate the concentration of molecular hydrogen according to the dilution of catalyst loading and diethyl terephthalate in a solvent.

[0065] The reduction can be carried out batchwise or continuously. According to a particular embodiment of the invention, the reduction is carried out continuously, since this can increase the productivity.

[0066] The reduction can be carried out in the presence or absence of a solvent. When a solvent is required or used for practical reasons, any solvent of the type of reaction at the time may be used for the purposes of the present invention. Non-limiting examples include C 6-12 Aromatic solvents such as toluene, 1,3-diisopropylbenzene, p-cymene, cumene, pseudocumene, benzyl acetate, xylene or mixtures thereof, C 3-16 Alkanes such as hexadecane, ether solvents such as tetrahydrofuran, butyl ether, methyltetrahydrofuran or mixtures thereof, esters such as ethyl acetate or diethyl cyclohexanedicarboxylate (reaction product), the latter being preferred solvents. The choice of solvent depends on the hydrogenation catalyst, and those skilled in the art are fully capable of selecting the most convenient solvent in each case to optimize the reaction.

[0067] The temperature at which the reduction can be carried out is 90° C. to 300° C. For a continuous process, it is more preferably 100° C. to 200° C. Of course, those skilled in the art can also select the preferred temperature based on the melting and boiling points of the starting and final products and the desired reaction or conversion time.

[0068] Reduction can be performed at 0.1×10 5 Pa to 100×10 5 Pa (0.1 to 100 bar) or higher pressure (if necessary). Likewise, those skilled in the art will be able to adjust the pressure according to the catalyst loading and the desired reaction or conversion time. As an example, 1 to 50×10 5 Typical pressures are Pa (1 to 50 bar).

[0069] According to any of the above embodiments of the present invention, the reduction is carried out in a fixed bed reactor.

[0070] According to any of the above embodiments of the present invention, the reduction is performed in the absence of a transesterification catalyst.

[0071] Another object of the present invention is a method for preparing diethyl 1,4-cyclohexanedicarboxylate, comprising the following steps:

[0072] a) reduction of dimethyl terephthalate; and

[0073] b) transesterification of the dimethyl 1,4-cyclohexanedicarboxylate obtained in step a) in the presence of ethanol as defined above to obtain diethyl 1,4-cyclohexanedicarboxylate.

[0074] The typical manner of implementing the method of the present invention is reported below by way of examples in conjunction with the accompanying drawings. DETAILED DESCRIPTION

[0075] Example

[0076] The present invention will now be described in further detail by the following examples, wherein abbreviations have their usual meanings in the art and temperatures are expressed in degrees Celsius (°C). The accompanying drawings are for illustrative purposes only, and the present invention should not be construed as being limited to the precise arrangement and components of the apparatus shown in the drawings. In addition, those skilled in the art are fully aware that other equipment components not shown in the drawings may be required to implement the method of the present invention, such as, for example, a vacuum pump, a sensor for measuring temperature or pressure, a valve, etc. ...

[0077] Example 1

[0078] Preparation of diethyl 1,4-cyclohexanedicarboxylate according to the continuous process of the present invention

[0079] Into a 4,000 gallon (about 15 cubic meters) pressure reactor R-1 equipped with an agitator and a heating system, 450 kg of molten dimethyl terephthalate (DMT), 45 kg of a circulating solution of a tin transesterification catalyst in diethyl terephthalate (DET) (from the bottom of C-3) (wherein the catalyst concentration is 2 mol%), 70 kg of a circulating mixture of dimethyl terephthalate, methyl ethyl terephthalate (MET) and diethyl terephthalate from the top of C-3, and 520 kg of circulating ethanol from the top of C-2 (purity is about 90%) were introduced in a steady mode. The temperature in R-1 was set to 150° C., the pressure to 6 bar, and the liquid level in the reactor was controlled to provide an average residence time of 6 hours.

[0080] The product is continuously taken out from R-1 and a methanol-rich distillate is removed in a distillation column C-1 at a rate of 70 kg / hour. The residue from C-1 is continuously introduced into a reactor R-2 similar in design to R-1 and under similar conditions (pressure, temperature, residence time) together with 120 kg / hour of fresh ethanol. The reaction mixture leaving R-2 is distilled in the column C-2 to produce 520 kg / hour of recycled ethanol (to be returned to R-1), and the residue from C-2 is separated in the column C-3, where 99.3% pure diethyl terephthalate is removed as a side line at a rate of 512 kg / hour, and the top fraction is recycled to R-1 at a rate of 70 kg / hour and the residue at a rate of 45 kg / hour.

[0081] Diethyl terephthalate is hydrogenated continuously at 55 bar and 120° C. in a trickle bed catalytic reactor R-3 over a supported noble metal catalyst, with about 75% of the reaction mixture returned to the top of the reactor to avoid undesirably high temperatures due to the hydrogenation exotherm. The 530 kg / hour effluent containing about 90% of diethyl 1,4-cyclohexanedicarboxylate (DECC), 6% of unreacted starting materials and 4% of hydrogenation by-products is distilled in a C-4 column to obtain 465 kg / hour of diethyl 1,4-cyclohexanedicarboxylate as a side stream, and 35 kg / hour of diethyl terephthalate recovered from the bottom, which are sent to the recycle feed of the reactor R-3.

[0082] Example 2

[0083] Preparation of diethyl 1,4-cyclohexanedicarboxylate according to the method of the present invention

[0084] The hydrogenation of diethyl terephthalate was carried out analogously to Example 1, but instead of continuous hydrogenation in a fixed bed reactor, diethyl terephthalate was hydrogenated in an autoclave at 70 bar / 140° C. for 12 hours. The reaction mixture contained 99.0% of 1,4-cyclohexanedicarboxylic acid ester, less than 0.05% of unreacted diethyl terephthalate and 1.0% of by-products.

[0085] Example 3

[0086] Preparation of diethyl terephthalate (Comparative Example)

[0087] 21,000 kg of dimethyl terephthalate flakes and 0.2 mol% of a soluble tin catalyst were loaded into a 10,000 gallon (37.5 cubic meter) rated pressure reactor equipped with a heating system, agitator, and a distillation column. After the heating was turned on, the dimethyl terephthalate melted within 18 hours. After that, the pressure was set to 3 bar and 4,000 kg of ethanol was pumped in. As the reaction byproduct methanol was distilled out (steam flowed to the heater at about 500 kg / hour), more fresh ethanol was added, so the distillate composition was gradually enriched with ethanol. After 90 hours, the reaction mixture contained (excluding ethanol and methanol) 91% of diethyl terephthalate, and about 11,000 kg of alcohol byproducts (about 50% each of methanol and ethanol) were distilled out. After distilling the remaining material in the reactor using a separate distiller, about 17,000 kg of pure diethyl terephthalate can be obtained, which is equivalent to a production rate of 157 kg per hour (including melting and reaction time, but excluding addition and preparation time, etc.).

Claims

1. A kind of 1-4 alcohol and an ester exchange catalyst in the presence of at least one C 1-4 A continuous process for the transesterification of compounds having carboxylic acid ester groups, wherein the transesterification step is carried out in at least two subsequent reactors separated by a separation unit.

2. The continuous process according to claim 1, wherein in the separation unit a mixture containing at least one C 1-4 The alcohol released from the carboxylic acid ester group of the compound is completely or partially removed and C 1-4 Alcohol was added to each reactor.

3. The continuous process according to any one of claims 1 to 2, wherein the continuous process is carried out in two reactors.

4. The continuous process according to any one of claims 1 to 3, wherein the second reactor is followed by one or two separation units.

5. The continuous process according to any one of claims 1 to 4, wherein the separation unit is a distillation column.

6. The continuous process according to any one of claims 1 to 5, wherein the transesterification catalyst is a Lewis acid, a Bronsted acid, or a base.

7. The continuous process according to any one of claims 1 to 6, wherein the transesterification catalyst is selected from the group consisting of an organotin compound or an organotitanium compound, an organotin compound formed in situ by reaction of a dialkyltin oxide with an acid of the ester to be transesterified, (C4H9)2SnO, (C8H 17 )2SnO, dibutyltin dilaurate, dioctyltin dicarboxylate and mixtures thereof.

8. The continuous process according to any one of claims 1 to 7, wherein the at least one C 1-4 The compounds of the carboxylate group are diester compounds.

9. The continuous process according to any one of claims 1 to 8, wherein the carboxylate group is a C1 carboxylate group.

10. The continuous process according to any one of claims 1 to 9, wherein the at least one C 1-4 The compound with carboxylate group is dimethyl terephthalate.

11. The continuous process according to any one of claims 1 to 10, wherein the alcohol is C 2-3 Alcohol, preferably ethanol.

12. A method for preparing diethyl 1,4-cyclohexanedicarboxylate, comprising the following steps: a) transesterification of dimethyl terephthalate as defined in claims 1 to 11 in the presence of ethanol to give diethyl terephthalate; as well as b) Reduction of the diethyl terephthalate obtained in step a).

13. The method according to claim 12, wherein the reduction is carried out under continuous conditions.

14. The process according to any one of claims 12 to 13, wherein the reduction is a hydrogenation using molecular H2 and a hydrogenation catalyst.

15. The process according to any one of claims 12 to 14, wherein the hydrogenation catalyst is selected from the group consisting of supported Ru or Pd metals, more preferably ruthenium supported on alumina.

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