Method for producing diester compounds

Abstract

The present invention relates to a method for manufacturing diester compounds, and more specifically to the following method for manufacturing diester compounds, which is carried out using a continuous process including a reaction unit, in which a total of n reaction units from the first reaction unit to the nth reaction unit are connected in series, wherein each reaction unit includes a reactor and a layer separator, and the method includes: supplying a feed stream containing dicarboxylic acid and alcohol to the first reactor, esterifying the feed stream to prepare a reaction product, and supplying a lower discharge stream containing the reaction product to the reactor of a subsequent reaction unit (S10); supplying an upper discharge stream of the first reactor to the first layer separator, and refluxing the lower discharge stream containing alcohol from the first layer separator to the first reactor (S20); supplying an upper discharge stream of at least one reactor from the second to the nth reactors to each layer separator, splitting a portion of the lower discharge stream containing alcohol from each layer separator, and refluxing only a portion of the split stream to each reactor (S30).

Description

Technical Field

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0154015, filed on November 17, 2020, which is hereby incorporated by reference in its entirety. Technical Field

[0004] The present invention relates to a method for producing a diester compound, and more particularly, to a method for producing a diester compound that can minimize the size of an apparatus and the amount of energy supplied to a reactor when producing the diester compound using a continuous process. Background Art

[0005] Phthalate plasticizers accounted for 92% of the global plasticizer market until the 20th century. They are additives mainly used to give polyvinyl chloride (PVC) flexibility, durability, cold resistance, etc. and to reduce melt viscosity to improve processability. Therefore, phthalate plasticizers can be introduced into PVC at various levels and are widely used in products ranging from hard products such as hard pipes to soft and stretchable materials such as food packaging materials, blood bags, floor materials, etc., which are closer to real life than other materials and inevitably come into direct contact with the human body.

[0006] Although phthalate plasticizers have compatibility with PVC and excellent softness-imparting properties, when PVC products are used in real life, phthalate plasticizers gradually leak out from PVC products containing phthalate plasticizers. Therefore, there has been controversy over the harmfulness of phthalate plasticizers due to the possibility that phthalate plasticizers may act as endocrine disruptors (environmental hormones) and carcinogens at heavy metal levels. In particular, since di(2-ethylhexyl) phthalate (DEHP), which is the most used in the United States, leaked from PVC products before the 1960s, various studies have been conducted on the harmfulness of phthalate plasticizers to the human body, and attention to environmental hormones increased in the 1990s.

[0007] Therefore, many research groups have conducted research on the development of environmentally friendly plasticizers that can replace di(2-ethylhexyl) phthalate and the process of improving environmentally friendly plasticizers in order to cope with environmental regulations and environmental hormone problems caused by the leakage of phthalic acid diester plasticizers (particularly di(2-ethylhexyl) phthalate).

[0008] Meanwhile, in most industrial fields, a batch process is used as a manufacturing process for diester plasticizers, and a system for refluxing unreacted materials in a reactor and effectively removing side reaction products using a batch process has been developed. However, the manufacture of diester plasticizers using a batch process has limitations in increasing the reflux rate or steam amount, the productivity is very low, and there are also technical limitations applicable to solving the problem. Summary of the invention

[0009] Technical issues

[0010] In order to solve the above problems in the background technology of the present invention, an object of the present invention is to provide a method for producing a diester compound, which can minimize the size of the device and the amount of energy supplied to the reactor when using a continuous process to produce the diester compound as an environmentally friendly plasticizer.

[0011] Technical Solution

[0012] In a general aspect, a method for manufacturing diester compounds is carried out using a continuous process including a reaction section, in which a total of n reaction units from the first reaction unit to the nth reaction unit are connected in series, wherein each reaction unit includes a reactor and a layer separator, and the method includes: supplying a feed stream containing dicarboxylic acid and alcohol to the first reactor, esterifying the feed stream to prepare a reaction product, and supplying a lower discharge stream containing the reaction product to a reactor of a subsequent reaction unit (S10); supplying an upper discharge stream of the first reactor to the first layer separator, and refluxing the lower discharge stream containing alcohol from the first layer separator to the first reactor (S20); supplying an upper discharge stream of at least one reactor from the second to the nth reactors to each layer separator, splitting a portion of the lower discharge stream containing alcohol from each layer separator, and refluxing only a portion of the split stream to each reactor (step S30).

[0013] Beneficial effects

[0014] According to the present invention, when a diester compound is manufactured using a continuous process, by supplying the upper discharge stream of at least one of the 2nd to nth reactors to each layer separator, splitting a portion of the lower discharge stream containing alcohol from each layer separator, and refluxing only a portion of the split stream to each reactor, the excess ratio of alcohol in each reactor can be kept constant, thereby minimizing the size of the device and the amount of energy supplied to the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figures 1 to 8 Each of them is a process flow chart of a method for producing a diester compound according to one embodiment of the present invention.

[0016] Fig. 9 This is a process flow chart of the method for producing a diester compound according to Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0017] Prior to the description, it should be understood that the terms and words used in the specification and the appended claims should not be interpreted as limited to the general and dictionary meanings, but should be interpreted according to the meanings and concepts corresponding to the technical aspects of the present invention based on the principle that the inventor can appropriately define the concept of the terms to best describe the present invention.

[0018] In the present invention, the term "upper" may refer to an area corresponding to a height of more than 50% of the entire height of the device in the container, and the term "lower" may refer to an area corresponding to a height of less than 50% of the entire height of the device and the container.

[0019] In the present invention, the term "stream" may refer to the flow of a fluid in a process, or to the fluid itself flowing in a pipe. Specifically, "stream" may refer to the fluid itself, or to the flow of a fluid flowing in a pipe connecting various devices. In addition, a fluid may refer to a gas or a liquid. It is not intended to exclude any situation in which a fluid contains solid contents.

[0020] In the following, reference will be made to Figures 1 to 9 The present invention is described in more detail to help understanding of the present invention.

[0021] According to the present invention, a method for producing a diester compound is provided. Figure 1 and 2 The method for producing a diester compound is carried out using a continuous process including a reaction section, in which a total of n reaction units 10, 20 and n0 from a first reaction unit 10 to an nth reaction unit n0 are connected in series, wherein each reaction unit 10, 20 and n0 includes each reactor 11, 21 and n1 from a first reactor 11 to an nth reactor n1, and each layer separator 14, 24 and n4 from a first layer separator 14 to an nth layer separator n4, the method comprising: supplying a feed stream containing a dicarboxylic acid and an alcohol to the first reactor 11, esterifying the feed stream to obtain a dicarboxylic acid and an alcohol; A reaction product is prepared, and a lower discharge stream containing the reaction product is supplied to a reactor of a rear reaction unit (S10); an upper discharge stream of the first reactor 11 is supplied to a first layer separator, and a lower discharge stream containing alcohol is refluxed from the first layer separator to the first reactor 11 (S20); an upper discharge stream of at least one reactor from the second reactor 21 to the nth reactor n1 is supplied to each layer separator, a portion of the lower discharge stream containing alcohol is split out from each layer separator, and only a portion of the split stream is refluxed to each reactor (step S30).

[0022] According to one embodiment of the present invention, the method of manufacturing a diester compound may be performed using a continuous process including a reaction section in which a total of n reaction units 10, 20, and n0 from the first reaction unit 10 to the nth reaction unit n0 are connected in series.

[0023] Specifically, as known in the prior art, a batch manufacturing process is applied to manufacture diester compounds. However, the use of a batch process to manufacture diester compounds has limitations in terms of the amount of reflux or steam, very low productivity, and also has technical limitations applicable to solving the problem.

[0024] In addition, in order to solve the problem of the above-mentioned batch process, a continuous manufacturing process has been developed in which two or more reactors are connected in series to form a reaction unit in the manufacture of diester compounds. In this case, in order to maintain the excess ratio of alcohol and dicarboxylic acid in the reactor to ensure reactivity, all logistics containing alcohol evaporated from the top of each reactor are refluxed into each reactor. In this case, the amount of dicarboxylic acid decreases towards the rear reactor, but the excess ratio of alcohol increases. Therefore, the shortcoming of the continuous manufacturing process is that the energy consumption required for evaporating excessive alcohol in each reactor increases, and the required device size for processing the alcohol of this excessive evaporation amount inevitably increases, causing the equipment cost to increase.

[0025] Therefore, when the diester compound is manufactured using the continuous process of the present invention, by supplying the upper discharge stream of at least one of the 2nd to nth reactors to each layer separator, splitting a part of the lower discharge stream containing alcohol from each layer separator, and refluxing only a part of the split stream to each reactor, the excess ratio of alcohol in each reactor can be kept constant, thereby minimizing the size of the apparatus and the amount of energy supplied to the reactor.

[0026] In the present invention, the term "excess ratio" may refer to a ratio of alcohol present in excess relative to a molar ratio of dicarboxylic acid and alcohol required for stoichiometry in a reactor in order to ensure reactivity.

[0027] According to one embodiment of the present invention, each reaction unit may include a total of n reactors from the 1st reactor to the nth reactor. As a specific example, each reactor may be a reactor for esterifying dicarboxylic acid and alcohol.

[0028] The esterification reaction may be a reaction in which dicarboxylic acid and alcohol are supplied to a reactor and directly esterified in the presence of a catalyst. Thus, a diester compound and water as a by-product may be produced by the esterification reaction of dicarboxylic acid and alcohol. The operating temperature, operating pressure, time, and type and content of the catalyst for the direct esterification reaction may be directly the conventional conditions used in the prior art, and may also be used after appropriate adjustment according to the process operation if necessary.

[0029] The dicarboxylic acid and the alcohol may be mixed using a premixer and introduced batchwise as a mixture and then supplied to the reactor, or may be introduced batchwise into reactors each provided with separate feed lines.

[0030] The dicarboxylic acid may include, for example, one or more selected from the group consisting of aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid and trimellitic acid, and saturated or unsaturated aliphatic polycarboxylic acids such as adipic acid, sebacic acid, azelaic acid, succinic acid, maleic acid and fumaric acid. As a specific example, the dicarboxylic acid may be terephthalic acid.

[0031] For example, the alcohol can be a monohydric alcohol having 4 to 13, 5 to 12 or 6 to 10 carbon atoms. For example, the monohydric alcohol can include straight or branched alcohols such as n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, n-pentanol, n-hexanol, n-heptanol, n-octanol, 2-ethylhexanol, isooctyl alcohol, isononyl alcohol, n-nonyl alcohol, isodecanol, n-decanol, undecanol and tridecanol, etc. As a specific example, the alcohol can be 2-ethylhexanol.

[0032] Based on the stoichiometry required for the reaction with the dicarboxylic acid, an excess of alcohol may be supplied to the reactor. For example, in the esterification reaction, the molar ratio of the dicarboxylic acid to the alcohol may be 1:2 to 1:10, 1:2 to 1:5, or 1:2 to 1:4.5. Therefore, the molar ratio of the dicarboxylic acid to the alcohol in the feed stream supplied to the first reactor 11 may be 1:2 to 1:10, 1:2 to 1:5, or 1:2 to 1:4.5. When the dicarboxylic acid and the alcohol are supplied as reactants to the first reactor 11 within the molar ratio range, the desired conversion rate can be easily achieved by minimizing the amount of steam used and controlling the forward reaction rate of the esterification reaction.

[0033] For example, the catalyst may include one or more selected from the group consisting of acid catalysts such as sulfuric acid, p-toluenesulfonic acid and methanesulfonic acid, alkyl titanate catalysts such as tetraisopropyl titanate, tetrabutyl titanate and tetra-2-ethylhexyl titanate, and organic metal catalysts such as dibutyl tin oxide and butyl tin maleate. As a specific example, an organic titanium compound represented by alkyl titanate can be used as a catalyst. In this way, the reaction time can be shortened by increasing the esterification reaction rate.

[0034] The operating temperature of the reactor may be, for example, in the range of 130 to 250° C., 140 to 240° C., or 150 to 230° C. In this case, the operating temperature of the reactor may individually refer to the operating temperature of the reactor in each of the first to nth reaction units. More specifically, the reactors of each of the first to nth reaction units may be controlled identically or individually within the temperature range.

[0035] The operating pressure of the reactor can be 0 to 4 kg / cm 2 G, 0 to 2 kg / cm 2 G or 0 to 1kg / cm 2 G. In this case, the operating pressure of the reactor may refer to the operating pressure of the reactor in each of the 1st to nth reaction units individually. More specifically, the reactors of each of the 1st to nth reaction units may be controlled identically or individually within the pressure range.

[0036] According to one embodiment of the present invention, the dicarboxylic acid may be terephthalic acid, and the alcohol may be 2-ethylhexanol. Thus, when terephthalic acid and 2-ethylhexanol are introduced into a reactor in the presence of a catalyst and subjected to an esterification reaction, dioctyl terephthalate (DOTP) may be produced as a diester material. Dioctyl terephthalate is a substance widely used as a non-toxic, environmentally friendly plasticizer, and therefore may exhibit excellent compatibility with polymer materials such as PVC, and may have excellent properties such as low volatility and electrical properties.

[0037] According to one embodiment of the present invention, each reaction part is composed of a total of n reaction units connected in series, and can be designed considering the reaction conversion rate controlled, the residence time in each reaction unit, etc., and can also be designed considering the composition of the product to be achieved. For example, n can be 2 to 8, 3 to 7 or 4 to 6. That is, each reaction part can include 2 to 8, 3 to 7 or 4 to 6 reaction units.

[0038] According to one embodiment of the present invention, the reaction units 10, 20, 30, 40 and n0 may further include: columns 12, 22, 32, 42 and n2, wherein the upper discharge stream of the reactor including alcohol and water evaporated during the esterification reaction is received from the reactor 11, 21, 31, 41 and n1 for gas / liquid separation, through which the gas phase is supplied as the upper discharge stream to the layer separators 14, 24, 34, 44 and n4 through the condensers 13, 23, 33, 43 and n3, and the liquid phase is supplied as the lower discharge stream to the reactor 11, 21, 31, 41 and n1; and layer separators 14, 24, 34, 44 and n4, which are configured to separate the water layer and the alcohol layer and reflux only the alcohol to the column and remove water.

[0039] In addition, if Figure 3 As shown, if necessary, the column may be included in the 1st to n-1th reaction units, but may not be included in the nth reaction unit.

[0040] In the reactor, a diester compound as a reaction product of the esterification reaction of dicarboxylic acid and alcohol and water as a byproduct participating in the esterification reaction can be generated. For example, the reaction product of the esterification reaction can include a diester compound, water and unreacted materials.

[0041] In order to improve the forward reaction rate of esterification, water as a by-product should be effectively removed to prevent the reverse reaction and deactivation of the catalyst caused by water. In this regard, as a method for removing water as a by-product, there is a method for evaporating water and discharging. When water evaporates, alcohols with a boiling point higher than water also evaporate due to high reaction temperature. In this case, the evaporated alcohol can be recovered and refluxed back into the reactor to keep a high concentration of reactants in the reactor and remove water.

[0042] Specifically, since the esterification reaction occurs at a temperature higher than the boiling point of alcohol when the esterification reaction is carried out in the reactor, alcohol that evaporates without participating in the reaction may inevitably exist. At the same time, since water is generated as a by-product other than the reaction product (i.e., diester compound), water can be discharged as an upper discharge flow in the reactor while evaporating water and alcohol. The evaporated water and alcohol can be discharged as an upper discharge flow of the reactor and can be supplied to the column.

[0043] In the column, the gas phase alcohol and water introduced from the reactor can be liquefied by the low temperature liquid phase alcohol supplied from the layer separator to the upper part of the column, and most of the gas phase alcohol can be selectively liquefied and discharged as the lower discharge stream in the column. In this case, the lower discharge stream of the column containing the liquid phase alcohol can be reintroduced into the upper part of the reactor, and the liquid phase alcohol can participate in the esterification reaction again.

[0044] Thus, the forward reaction rate can be increased by passing the upper effluent stream of the reactor through the column to prevent water contained in the upper effluent stream of the reactor from being condensed and introduced back into the reactor.

[0045] In addition, alcohol that has evaporated from the reactor can be refluxed into the reactor to maintain an excess ratio of alcohol relative to dicarboxylic acid in the reactor, and water as a by-product of the esterification reaction can be discharged and removed from the reaction system to prevent water from refluxing into the reactor, thereby preventing a decrease in the reaction rate in the reactor and deterioration of catalyst performance.

[0046] Meanwhile, the gas phase water in the column and the unliquefied gas phase alcohol can be discharged as the upper discharge stream of the column, and the upper discharge stream of the column can be supplied to the layer separator through a condenser. Specifically, in the layer separator or before introducing the layer separator, it is necessary to liquefy the gas phase alcohol and water. Therefore, a condenser is set in any region of the pipeline where the upper discharge stream of the column is transported to the layer separator, and the heat of the gas phase alcohol and water can be removed through the condenser and the gas phase alcohol and water are liquefied and then introduced into the layer separator.

[0047] The layer separation in the layer separator can utilize the density difference between alcohol and water to carry out.As a specific example, because the density of alcohol is lower than water, an alcohol layer can be formed on the top of the layer separator, and an aqueous layer can be formed on the bottom of the layer separator.Like this, after separating the aqueous layer and the alcohol layer in the layer separator, only alcohol can be selectively separated from the alcohol layer and refluxed into the post by the pipeline connected to the top of the post.In addition, water can be removed by the external row pipeline that discharges water from the aqueous layer, or can be recycled by various approaches.

[0048] Since the alcohol whose temperature is reduced by condensation in the column flows back into the reactor, the internal temperature of the reactor may be reduced. Therefore, heat can be supplied to the reactor alone by the energy of supplying high-pressure steam or high-temperature steam to maintain the internal temperature of the reactor. Since high-pressure steam has an equilibrium temperature (high temperature) under high pressure, heat can be supplied to the reactor by supplying high-pressure steam.

[0049] The reaction product in the reactor can be separated from the lower discharge flow of the reactor, and the lower discharge flow of each reactor from the 1st reaction unit to the n-1th reaction unit can be supplied to the reactor of the rear reaction unit of each reaction unit. In addition, the lower discharge flow in the reactor of the nth reaction unit as the last reaction unit can be separated, refined and made into a product. Specifically, the lower discharge flow of each reactor in the n-1th reactor of the 1st reactor as the reactor of the 1st reaction unit can be supplied to the respective rear reaction units as the corresponding reaction units, and the lower discharge flow in the nth reactor as the reactor of the last reaction unit (nth reaction unit) can be separated, refined and made into a product.

[0050] For example, Figure 4As shown, when a reaction section including four reaction units connected in series is used to produce a diester compound, the lower discharge flow of the first reactor 11 as the reactor of the first reaction unit 10 can be supplied to the second reactor 21 as the reactor of the second reaction unit 20, the lower discharge flow of the second reactor 21 can be supplied to the third reactor 31 as the reactor of the third reaction unit 30, the lower discharge flow of the third reactor 31 can be supplied to the fourth reactor 41 as the reactor of the fourth reaction unit 40, and the lower discharge flow of the fourth reactor 41 as the reactor of the fourth reaction unit 40 can be separated, refined and made into a product.

[0051] According to one embodiment of the present invention, the lower part of each reactor may be provided with a lower external discharge pipeline to transport the lower discharge streams of the reactors of the reaction units 10, 20, 30, 40 and n0 to the reactor of the rear reaction unit or to transport the lower discharge streams for subsequent separation and refining processes. In addition, the lower external discharge pipeline may be provided with a pump (not shown).

[0052] The diester compound contained in the lower discharge stream of the nth reactor as the reactor of the last reaction unit can be refined using methods known in the art. For example, when an organic titanium compound is used as a catalyst for esterification, water is added to the obtained diester compound to deactivate the catalyst, and the residual unreacted alcohol is removed by evaporation by distilling the lower discharge stream with water vapor. In addition, the residual dicarboxylic acid can be neutralized by treating with an alkaline material. In addition, the solid can be removed by filtration to obtain a high-purity diester compound.

[0053] According to one embodiment of the present invention, a method for manufacturing a diester compound may include: supplying a feed stream containing a dicarboxylic acid and an alcohol to a first reactor 11, esterifying the feed stream to prepare a reaction product, and supplying a lower discharge stream containing the reaction product to a reactor of a rear reaction unit (S10); supplying an upper discharge stream of the first reactor 11 to a first layer separator, and refluxing the lower discharge stream containing alcohol from the first layer separator to the first reactor 11 (S20); supplying an upper discharge stream of at least one reactor from the second to nth reactors to each layer separator, splitting a portion of the lower discharge stream containing alcohol from each layer separator, and refluxing only a portion of the split stream to each reactor (step S30).

[0054] According to one embodiment of the present invention, the upper exhaust stream containing alcohol and water can be supplied from each reactor to columns 12, 22, 32, 42 and n2 for gas / liquid separation, and after the gas phase is condensed through condensers 13, 23, 33, 43 and n3, the gas phase can be supplied as the upper exhaust stream to layer separators 14, 24, 34, 44 and n4, and the liquid phase can be supplied as the lower exhaust stream to each reactor.

[0055] According to one embodiment of the present invention, the upper exhaust stream containing alcohol and water can be supplied from the 1st to n-1th reactors to a column for gas / liquid separation, the gas phase can be condensed and supplied to a layer separator as the upper exhaust stream, and the liquid phase can be supplied to each reactor as a lower exhaust stream.

[0056] According to one embodiment of the present invention, a water layer and an alcohol layer can be separated in a layer separator, and only the lower discharge stream containing alcohol can be supplied to the upper part of the column to pass through the column and then refluxed to each reactor. Then, water can be removed or recycled through various routes.

[0057] As mentioned above, in the conventional method of continuously manufacturing diester compounds known in the art, all logistics including the alcohol evaporated from each reactor are refluxed in each reactor to keep the excess ratio of alcohol relative to dicarboxylic acid in the reactor to ensure reactivity. In this case, the amount of reactant decreases towards the rear reactor, but the excess ratio of alcohol increases. Therefore, the shortcoming of the process of continuously manufacturing diester compounds is that the energy consumption required for evaporating excessive alcohol in each reactor increases, and the required device size for processing the alcohol of this excessive evaporation amount inevitably increases, causing the equipment cost to increase.

[0058] In this regard, according to the present invention, by supplying all of the upper effluent stream of the first reactor 11 to the first layer separator, recirculating all of the lower effluent stream containing alcohol from the first layer separator to the first reactor 11, supplying the upper effluent stream of at least one of the second reactor 21 to the nth reactor n1 to each layer separator, splitting a portion of the lower effluent stream containing alcohol from each layer separator, and recirculating only a portion of the split stream to each reactor, the excess ratio of alcohol in each reactor can be kept constant, thereby minimizing the size of the device and the amount of energy supplied to the reactor.

[0059] In step (S30), after a portion of the lower discharge stream containing alcohol is split into each layer separator and only a portion of the split stream is refluxed into each reactor, the molar ratio of dicarboxylic acid and alcohol in each reactor may be 1:2 to 1:10, 1:2 to 1:5 or 1:2 to 1:4.5. That is, as described above, only a portion of the split stream may be refluxed from the layer separator instead of refluxing all of the lower discharge stream containing alcohol into each reactor. In this case, only a portion of the split stream may be refluxed so that the molar ratio of dicarboxylic acid and alcohol in each reactor falls within the above range.

[0060] In this case, the excess ratio of alcohol to dicarboxylic acid contained in the feed stream can be kept constant without any increase toward the rear reactor. Therefore, it is possible to easily achieve a desired conversion rate in the nth reactor n1 as the last reactor while minimizing the amount of steam supplied to each reactor.

[0061] According to one embodiment of the present invention, the at least one reactor may be, for example, a reactor having a conversion rate of 50 to 99% among the second to nth reactors, but the present invention is not limited thereto.

[0062] In addition, the ratio of the flow rate of the lower discharge stream of the layer separator that is not refluxed into each reactor to the flow rate of the lower discharge stream containing the entire alcohol of the layer separator of each reactor (draw-off rate) can be adjusted according to the reaction conditions such as the temperature and pressure of the reactor, the residence time of the reactants, and the conversion rate of the reactor from which the feed stream starts to be discharged in the second to nth reactors. In addition, the energy usage in the process can be minimized compared to when no draw-off is performed.

[0063] According to one embodiment of the present invention, for example, step (S30) may include: splitting a portion of the lower discharge stream containing alcohol by each layer separator from the second reactor 21 to the reactor with a conversion rate of 50 to 99% in the nth reactor n1 to the nth reactor, and refluxing only a portion of the split stream to each reactor. For example, Figure 8 As shown, after the lower discharge stream of the first layer separator 14 passes through the first column 12, all of the lower discharge stream of the first layer separator 14 can be refluxed to the first reactor 11, and a part of the lower discharge stream containing alcohol can be separated from each layer separator 24, 34 and 44 in each reactor from the second reactor 21 to the fourth reactor 41 with a conversion rate of 50 to 99%, and only a part of the separated stream can be refluxed to each reactor. In this case, only a part of the separated stream of each layer separator 24, 34 and 44 can be refluxed to each reactor, and the remaining stream can be discharged to the outside.

[0064] The reactors from the second reactor 21 to the n-th reactor n1 in which the conversion rate reaches 50% to 99% may be changed according to the initiation conditions of the esterification reaction, but are not limited to the second reactor 21 .

[0065] Specifically, when the conversion rate is greater than or equal to 50% at the time point (i.e., the discharge time point) when a part of the lower discharge stream containing alcohol is separated from each layer separator and only a part of the separated stream is refluxed into each reactor, it is easy to achieve the desired conversion rate in the nth reactor as the last reactor. At the same time, the conversion rate is less than or equal to 99% at the time point when a part of the lower discharge stream containing alcohol is separated from each layer separator and only a part of the separated stream is refluxed into each reactor, which can reduce the steam usage of the whole process, which can effectively reduce the energy usage.

[0066] According to one embodiment of the present invention, in step (S30), a part of the lower discharge stream containing alcohol can be split out from each layer separator, and only a part of the stream split out can be refluxed into each reactor, and the remaining stream of the lower discharge stream in each layer separator can be recycled as a feed stream. In addition, when all lower discharge streams containing alcohol can be discharged from the layer separator, all lower discharge streams of the layer separator can be recycled as a feed stream.

[0067] According to one embodiment of the present invention, if necessary, devices such as a distillation tower, a condenser, a reboiler, a valve, a pump, a separator and a mixer may be further installed in the method for producing a diester compound.

[0068] As described above, the method for manufacturing diester compounds of the present invention has been described and illustrated with reference to the accompanying drawings. However, the above description and the illustration of the accompanying drawings are provided only for describing and illustrating the core components for understanding the present invention. Therefore, in addition to the processes and devices described and illustrated herein, processes and devices that are not described or illustrated in any separate manner can be appropriately applied and used to implement the method for manufacturing diester compounds of the present invention.

[0069] Hereinafter, the present invention will be described in more detail with reference to its embodiments. However, it is obvious to those skilled in the art that the following embodiments are given for the purpose of illustrating the present invention, and various modifications and changes can be made without departing from the technical spirit and scope of the present invention, but are not actually intended to limit the scope of the present invention.

[0070] Example

[0071] Examples 1-1 to 1-4

[0072] according to Figure 4The process flow diagram shown uses the commercially available process simulation program ASPEN PLUS (AspenTech) to simulate the process of manufacturing dioctyl terephthalate (DOTP).

[0073] Specifically, a feed stream containing terephthalic acid (TPA) and 2-ethylhexanol (2-EH) in a molar ratio of 1:2 to 4.5 is supplied to the first reactor 11 as the reactor of the first reaction unit 10, and esterification is performed in the presence of a catalyst, all of the lower discharge stream containing alcohol of the layer separator 14 is refluxed to the reactor 11, and water is removed from the upper discharge stream evaporated in the first reactor 11 using the column 12, the condenser 13 and the layer separator 14. In addition, the lower discharge stream containing the reaction product is supplied from the first reactor 11 to the second reactor 21 as the reactor of the second reaction unit 20.

[0074] As in the operation flow in the first reaction unit 10, a continuous stirred tank reactor (CSTR) is operated through the second reaction unit 20, the third reaction unit 30 and the fourth reaction unit 40, and the lower discharge stream of the fourth reactor 41 which is the last reactor of the fourth reaction unit 40 is separated and purified to obtain dioctyl terephthalate.

[0075] In this case, a part of the lower discharge stream containing alcohol is separated from the layer separator in the fourth reactor 41 of the fourth reaction unit 40, and only a part of the separated stream is supplied to the upper part of the fourth column 42 and passes through the fourth column 42. Thereafter, the partially separated stream is refluxed to the fourth reactor 41, while the remaining part of the lower discharge stream of the layer separator is not refluxed to the fourth reactor 41 and is discharged to the outside to be recycled as a feed stream of the first reactor 11.

[0076] In particular, Figure 5 As shown, in the case of Example 1-4, the upper discharge stream evaporated in the fourth reactor 41 is not supplied to the column of the fourth reaction unit 40, and the lower discharge stream containing all alcohol is discharged from the layer separator 44 using the condenser 43 and the layer separator 44. Then, the feed stream of the first reactor 11 is recycled, and water is removed.

[0077] Table 1 below lists the final conversion rate according to the evacuation rate, which is the ratio of the flow rate of the lower effluent stream of the layer separator discharged to the outside without being refluxed to the fourth reactor 41, and the steam usage used in the entire process. In this case, the steam usage is expressed by a relative amount with respect to the steam usage (100.0%) measured in Comparative Example 1 below.

[0078] Examples 2-1 to 2-6

[0079] according to Figure 6 The process flow diagram shown uses the commercially available process simulation program ASPEN PLUS (AspenTech) to simulate the process of manufacturing dioctyl terephthalate (DOTP).

[0080] Specifically, a feed stream containing terephthalic acid (TPA) and 2-ethylhexanol (2-EH) in a molar ratio of 1:2 to 4.5 is supplied to the first reactor 11 as the reactor of the first reaction unit 10, and esterification is performed in the presence of a catalyst, all of the lower discharge stream containing alcohol of the layer separator 14 is refluxed to the reactor 11, and water is removed from the upper discharge stream evaporated in the first reactor 11 using the column 12, the condenser 13 and the layer separator 14. In addition, the lower discharge stream containing the reaction product is supplied from the first reactor 11 to the second reactor 21 as the reactor of the second reaction unit 20.

[0081] As in the operation flow in the first reaction unit 10, a continuous stirred tank reactor (CSTR) is operated through the second reaction unit 20, the third reaction unit 30 and the fourth reaction unit 40, and the lower discharge stream of the fourth reactor 41 which is the last reactor of the fourth reaction unit 40 is separated and purified to obtain dioctyl terephthalate.

[0082] In this case, a part of the lower discharge stream containing alcohol is separated from the layer separator in the third reactor 31 of the third reaction unit 30, and only a part of the separated stream is supplied to the upper part of the third column 32 and passes through the third column. Thereafter, the partially separated stream is refluxed to the third reactor 31, while the remaining part of the lower discharge stream of the layer separator is not refluxed to the third reactor 31 and is discharged to the outside and recycled as a feed stream of the first reactor 11.

[0083] Table 2 below lists the final conversion rate according to the evacuation rate, which is the ratio of the flow rate of the lower effluent stream of the layer separator discharged to the outside without being refluxed to the third reactor 31, and the steam usage used in the entire process. In this case, the steam usage is expressed by a relative amount relative to the steam usage (100.0%) measured in Comparative Example 1 below.

[0084] Examples 3-1 to 3-4

[0085] according to Figure 7 The process flow diagram shown uses the commercially available process simulation program ASPEN PLUS (AspenTech) to simulate the process of manufacturing dioctyl terephthalate (DOTP).

[0086] Specifically, a feed stream containing terephthalic acid (TPA) and 2-ethylhexanol (2-EH) in a molar ratio of 1:2 to 4.5 is supplied to the first reactor 11 as the reactor of the first reaction unit 10, and esterification is performed in the presence of a catalyst, all of the lower discharge stream containing alcohol of the layer separator 14 is refluxed to the reactor 11, and water is removed from the upper discharge stream evaporated in the first reactor 11 using the column 12, the condenser 13 and the layer separator 14. In addition, the lower discharge stream containing the reaction product is supplied from the first reactor 11 to the second reactor 21 as the reactor of the second reaction unit 20.

[0087] As in the operation flow in the first reaction unit 10, a continuous stirred tank reactor (CSTR) is operated through the second reaction unit 20, the third reaction unit 30 and the fourth reaction unit 40, and the lower discharge stream of the fourth reactor 41 which is the last reactor of the fourth reaction unit 40 is separated and purified to obtain dioctyl terephthalate.

[0088] In this case, a part of the lower discharge stream containing alcohol is separated from the layer separator in the second reactor 21 of the second reaction unit 20, and only a part of the separated stream is supplied to the upper part of the second column 22 and passes through the second column. Thereafter, the partially separated stream is refluxed to the second reactor 21, while the remaining part of the lower discharge stream of the layer separator is not refluxed to the second reactor 21 and is discharged to the outside and recycled as a feed stream of the first reactor 11.

[0089] Table 3 below lists the final conversion rate according to the evacuation rate, which is the ratio of the flow rate of the lower effluent stream of the layer separator discharged to the outside without being refluxed to the second reactor 21, and the steam usage used in the entire process. In this case, the steam usage is expressed by a relative amount relative to the steam usage (100.0%) measured in Comparative Example 1 below.

[0090] Examples 4-1 to 4-4

[0091] according to Figure 8 The process flow diagram shown uses the commercially available process simulation program ASPEN PLUS (AspenTech) to simulate the process of manufacturing dioctyl terephthalate (DOTP).

[0092] Specifically, a feed stream containing terephthalic acid (TPA) and 2-ethylhexanol (2-EH) in a molar ratio of 1:2 to 4.5 is supplied to the first reactor 11 as the reactor of the first reaction unit 10, and esterification is performed in the presence of a catalyst, all of the lower discharge stream containing alcohol of the layer separator 14 is refluxed to the reactor 11, and water is removed from the upper discharge stream evaporated in the first reactor 11 using the column 12, the condenser 13 and the layer separator 14. In addition, the lower discharge stream containing the reaction product is supplied from the first reactor 11 to the second reactor 21 as the reactor of the second reaction unit 20.

[0093] As in the operation flow in the first reaction unit 10, a continuous stirred tank reactor (CSTR) is operated through the second reaction unit 20, the third reaction unit 30 and the fourth reaction unit 40, and the lower discharge stream of the fourth reactor 41 which is the last reactor of the fourth reaction unit 40 is separated and purified to obtain dioctyl terephthalate.

[0094] In this case, each layer separator in each reactor from the second reactor 21 of the second reaction unit 20 to the fourth reactor 41 of the fourth reaction unit 40 separates a part of the lower discharge stream containing alcohol, and only a part of the separated stream is supplied to the upper part of each column and passes through the column. Thereafter, the partially separated stream is refluxed to the reactor, and the remaining part of the lower discharge stream of the layer separator is not refluxed to the reactor but discharged to the outside and recycled as a feed stream of the first reactor 11.

[0095] The following Table 4 lists the final conversion rate according to the evacuation rate, which is the ratio of the flow rate of the lower effluent stream of the layer separator discharged to the outside without being refluxed to each reactor to the flow rate of all the lower effluent streams containing alcohol of the layer separator of each reactor, and the steam usage used in the whole process. In this case, the steam usage is expressed by a relative amount relative to the steam usage (100.0%) measured in the following Comparative Example 1.

[0096] Comparative Example 1

[0097] according to Fig. 9 The process flow diagram shown uses the commercially available process simulation program ASPEN PLUS (AspenTech) to simulate the process of manufacturing dioctyl terephthalate (DOTP).

[0098] Specifically, a feed stream containing terephthalic acid (TPA) and 2-ethylhexanol (2-EH) in a molar ratio of 1:2 to 4.5 is supplied to the first reactor 11 as the reactor of the first reaction unit 10, and esterification is performed in the presence of a catalyst, all of the lower discharge stream containing alcohol of the layer separator 14 is refluxed to the reactor 11, and water is removed from the upper discharge stream evaporated in the first reactor 11 using the column 12, the condenser 13 and the layer separator 14. In addition, the lower discharge stream containing the reaction product is supplied from the first reactor 11 to the second reactor 21 as the reactor of the second reaction unit 20.

[0099] As in the operation flow in the first reaction unit 10, a continuous stirred tank reactor (CSTR) is operated through the second reaction unit 20, the third reaction unit 30 and the fourth reaction unit 40, and the lower discharge stream of the fourth reactor 41 which is the last reactor of the fourth reaction unit 40 is separated and purified to obtain dioctyl terephthalate.

[0100] The final conversion rate and the amount of steam used in the whole process are listed in the following Table 4. In this case, the amount of steam used is expressed by a relative amount relative to the amount of steam used in the examples (100.0%).

[0101] [Table 1]

[0102]

[0103] [Table 2]

[0104]

[0105] [Table 3]

[0106]

[0107] [Table 4]

[0108]

[0109] *Exhaust rate: The ratio of the flow rate of the lower exhaust stream of the layer separator that is discharged to the outside without being refluxed to each reactor to the flow rate of all the lower exhaust streams containing alcohol of the layer separator of each reactor.

[0110] Referring to Tables 1 to 4, it can be seen that the total amount of energy used in the entire process is reduced because all of the lower exhaust streams containing alcohol are refluxed from the layer separators of each of the 1st to 4th reactors in all the cases of the examples, and the amount of steam is reduced as compared to 100.0% of the steam amount in the case of Comparative Example 1 in which no external exhaust is performed.

[0111] Specifically, referring to Examples 1-1 to 1-4 listed in Table 1 and Examples 2-1 to 2-4 listed in Table 2, it can be seen that even if the effluent rate increases, the final conversion rate does not change because the conversion rate in the rear reactor (the 3rd to 4th reactor) has been guaranteed. That is, it can be seen that in the case of Examples 1-1 to 1-4, even if the effluent rate reaches 100%, the final conversion rate is maintained at 99%; in the case of Examples 2-1 to 2-4, even if the effluent rate reaches 78%, the final conversion rate is maintained at 99%. In addition, it can be seen that compared with Comparative Example 1, the steam consumption is reduced to 93% under the condition that the final conversion rate is maintained at 99%.

[0112] However, referring to Examples 2-5 and 2-6 listed in Table 2, even if the effluent rate is a very high 88% or more, the steam usage is reduced and the final conversion rate is reduced. Therefore, there are disadvantages such as a reduction in product basic units and a decrease in product specifications.

[0113] In addition, the case where the discharge is performed in the first reactor is not shown in the table. However, it was confirmed that when the discharge is performed in the first reactor, the effect of ensuring the reactivity is poor because the excess ratio of alcohol to dicarboxylic acid in the reactor is maintained. Therefore, it was confirmed that the reactivity can be reduced because the excess ratio of alcohol to dicarboxylic acid in all reactors in this process is reduced, so there is a problem of reduced final conversion rate. In this case, the conversion rate in the first reactor is, for example, less than 50%, but the present invention is not limited to this.

[0114] Meanwhile, referring to Examples 3-1 to 3-4 listed in Table 3, it can be seen that when the efflux is performed in the second reactor, the excess ratio of alcohol in the subsequent reactors (the third to fourth reactors) changes, which has an impact on the final conversion rate. That is, it can be seen that in the case of Examples 3-1 to 3-4, even if the efflux rate is 34%, the final conversion rate is maintained at 99%; even if the efflux rate is 45%, the final conversion rate is reduced to 98%. As a result, it can be seen that, compared with Comparative Example 1, under the condition that the final conversion rate is maintained at 99%, the steam consumption is reduced to 93%.

[0115] In addition, referring to Table 4, it can be seen that in the case of Examples 4-1 to 4-4 in which all the exhaust was performed in the 2nd to 4th reactors, compared with Comparative Example 1, the steam consumption was reduced to 93% under the condition that the final conversion rate was maintained at 99%.

[0116] Therefore, according to the present invention, it is confirmed that by supplying the upper effluent stream of at least one of the 2nd to nth reactors to each layer separator, splitting a part of the lower effluent stream containing alcohol from each layer separator to reflux a part of the lower effluent stream, and discharging the remaining part of the lower effluent stream (wherein the effluent rate is adjusted according to reaction conditions such as the temperature and pressure of the reactor, the residence time of the reactants, etc.), the total energy usage in the process is reduced compared with Comparative Example 1 where no effluent is performed.

Claims

1. A method for producing a diester compound, which is carried out using a continuous process including a reaction section in which a total of n reaction units from a first reaction unit to an nth reaction unit are connected in series, in, Each reaction unit includes a reactor and a layer separator, and The method includes: Step S10: supplying a feed stream containing dicarboxylic acid and alcohol to the first reactor of the first reaction unit, esterifying the feed stream to prepare a reaction product, and supplying a lower discharge stream containing the reaction product to a reactor of a subsequent reaction unit; Step S20: supplying the upper discharge stream of the first reactor to the first layer separator of the first reaction unit, and refluxing the lower discharge stream containing alcohol from the first layer separator to the first reactor; and Step S30: supplying the upper discharge stream of at least one of the second to nth reactors to each layer separator, splitting a portion of the lower discharge stream containing alcohol from each layer separator, and refluxing only a portion of the split stream to each reactor, wherein the at least one reactor is a reactor having a conversion rate of 50% to 99% among the second reactor to the nth reactor, The step S30 comprises: supplying the upper discharge stream of each reactor from the reactor having a conversion rate of 50 to 99% among the second to nth reactors to any one of the third to nth reactors to each layer separator, splitting a part of the lower discharge stream containing alcohol from each layer separator, and refluxing only a part of the split stream to each reactor, wherein the molar ratio of the dicarboxylic acid to the alcohol in the feed stream is from 1:2 to 1:10, and Wherein, in step S30, after only a part of the split stream is refluxed into each reactor, the molar ratio of the dicarboxylic acid to the alcohol in each reactor is 1:2 to 1:

10.

2. The method of claim 1, wherein: An upper effluent stream containing alcohol and water is supplied from each reactor to a column for gas / liquid separation, a gas phase is condensed as an upper effluent stream and supplied to the layer separator, and a liquid phase is supplied as a lower effluent stream to each reactor.

3. The method of claim 1, wherein: The upper effluent stream containing alcohol and water is supplied from the 1st to n-1th reactors to the column for gas / liquid separation, the gas phase is condensed into the upper effluent stream and supplied to the layer separator, and the liquid phase is supplied as the lower effluent stream to each reactor.

4. The method according to claim 2 or 3, wherein: The layer is separated into a water layer and an alcohol layer in the layer separator, and the lower discharge stream containing the alcohol is supplied to the upper part of the column to pass through the column, and then refluxed to each reactor.

5. The method of claim 1, wherein: Step S30 comprises: in each reactor from the second to the nth reactors in which the conversion rate reaches 50% to 99%, a part of the lower discharge flow containing alcohol is split from each layer separator in these reactors, and only the split flow is refluxed to each reactor.

6. The method of claim 1, wherein: In step S30, a part of the lower discharge stream containing alcohol is separated from each layer separator, and only a part of the separated stream is refluxed to each reactor, and The remainder of the lower effluent stream in each layer separator is recycled as a feed stream.

7. The method of claim 1, wherein: n is 2 to 8.

8. The method of claim 1, wherein: The dicarboxylic acid includes terephthalic acid, and the alcohol includes 2-ethylhexanol.

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