Patent Publication Number: US-2022220058-A1

Title: Diester-based material production unit and diester-based material production system including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase entry pursuant to 35 U.S.C. § 371 of International Application No. PCT/KR2020/008664, filed on Jul. 2, 2020, and claims the benefit of and priority to Korean Patent Application No. 10-2019-0080461, filed on Jul. 4, 2019, in the Korean Intellectual Property Office, all of which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein. 
    
    
     TECHNICAL FIELD 
     Technical Field 
     The present invention relates to a diester-based material production unit with an improved reflux system and a diester-based material production system including the same. 
     Background Art 
     Phthalate-based plasticizers had occupied 92% of the world&#39;s plasticizer market by the 20th century (Mustafizur Rahman and Christopher S. Brazel “The plasticizer market: an assessment of traditional plasticizers and research trends to meet new challenges” Progress in Polymer Science 2004, 29, 1223-1248), and are additives used to improve the processability of polyvinyl chloride (hereinafter, referred to as PVC) by imparting flexibility, durability, cold resistance, and the like and lowering viscosity during melting. Phthalate-based plasticizers are introduced into PVC in various contents and used not only for hard products such as rigid pipes, but also for soft products such as food packaging materials, blood bags, and flooring materials since the phthalate-based plasticizers are soft and stretchable. Thus, the phthalate-based plasticizers are more closely related to real life than any other materials and are widely used for materials which come into direct contact with a human body. 
     However, despite the compatibility with PVC and excellent softness imparting properties of phthalate-based plasticizers, there has been controversy over the harmful nature of the phthalate-based plasticizers in that when a PVC product containing a phthalate-based plasticizer is used in real life, the phthalate-based plasticizer can be leaked little by little out of the product and act as a suspected endocrine disruptor (environmental hormone) and a carcinogen to the level of a heavy metal (N R Janjua et al. “Systemic Uptake of Diethyl Phthalate, Dibutyl Phthalate, and Butyl Paraben Following Whole-body Topical Application and Reproductive and Thyroid Hormone Levels in Humans” Environmental Science and Technology 2008, 42, 7522-7527). Particularly, since a report was published in the 1960s in the United States that diethylhexyl phthalate (di-(2-ethylhexyl) phthalate, DEHP), the most used phthalate plasticizer, leaked out of PVC products, global environmental regulations have started to be implemented in addition to various studies on the harmful nature of the phthalate-based plasticizer on human bodies, boosted by increasing interest in environmental hormones in the 1990s. 
     Thus, in order to respond to environmental hormonal problems and environmental regulations due to the leakage of a phthalate-based plasticizer, di(2-ethylhexyl) phthalate in particular, many researchers have been conducting research in order to develop a new non-phthalate-based alternative plasticizer without phthalic anhydride used in the manufacturing of di(2-ethylhexyl) phthalate, and to develop a phthalate-based plasticizer which can replace di(2-ethylhexyl) phthalate and be used for industrial purposes since the leakage of the plasticizer is suppressed even though it is based on phthalate, as well as to develop a leakage suppression technology which suppresses the leakage of phthalate-based plasticizers, thereby significantly reducing risks to human bodies and which meets environmental standards. 
     As such, as diester-based plasticizers, the development of materials which are free from environmental problems and which can replace a di(2-ethylhexyl) phthalate having existing environmental problems is actively underway. In addition, research on developing a diester-based plasticizer with excellent physical properties as well as research on equipment for manufacturing the plasticizer have been actively conducted, and there has been a demand for more efficient, more economical and simpler process designs in terms of process design. 
     Meanwhile, a batch process is being applied in most industrial sites as a process of producing the above diester-based plasticizer. As the batch process, an invention related to a gas-liquid separation system for the reflux of non-reactants and efficient removal of sub-reactants in a reactor (Korean Patent Laid-Open Publication No. 10-2019-0027622) and an invention related to a system integrating facilities of a primary direct esterification reaction and a second trans-esterification reaction in order to simplify facilities of a batch process (Korean Patent Laid-Open Publication No. 10-2019-0027623) have been introduced. However, as a batch process, such inventions have limitations in that there is a limit to the improvement in the amount of reflux or the volume of steam, the productivity is very low, and there is a limit to the technology which can be applied for improvement. 
     In addition, as a continuous process, an invention related to a process configuring a reaction part by connecting two or more reactors in series (Korean Patent Publication No. 10-1663586) has also been introduced. However, there is a limit to improving the overall processability only by controlling the reaction temperature of continuously connected reactors. 
     PRIOR ART DOCUMENT 
     Patent Document 
     (Patent Document 1) Korean Patent Laid-Open Publication No. 10-2019-0027622 
     (Patent Document 2) Korean Patent Laid-Open Publication No. 10-2019-0027623 
     (Patent Document 3) Korean Patent Laid-Open Publication No. 10-1663586 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     An aspect of the present invention provides a diester-based material production unit and a diester-based material production system including the same, in which a reflux system is applied to the diester-based material production unit applied to a process of continuously producing a diester-based material, the reflux system including a flash drum and improved by selecting an appropriate position of a stream to be refluxed, so that a rheological problem which can occur due to the coexistence of a liquid and a gas in a pipe or a condenser is solved, a coolant usage amount can be greatly reduced even when the amount of reflux is large, and an alcohol to be refluxed can have a temperature maintained to be higher than usual and supplied. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a diester-based material production unit including a reaction device including a reaction vessel in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed and a gas phase discharge line installed at an upper end of the reaction vessel such that vaporized primary alcohol and water are discharged to a column therethrough, the column including a column main body in which the gas-liquid separation of the primary alcohol and the water introduced from the gas phase discharge line is performed, a liquid phase line installed at a lower portion of the column main body such that a liquefied alcohol-rich stream flows into the reaction device, and a gas phase line installed at an upper portion of the column main body and connected to a side portion of a flash drum such that a mixture stream of a gas-phase primary alcohol and water flows out, a heat exchanger installed on the gas phase line of the column to remove heat of the gas phase line, the flash drum having a flash drum main body in which separation of a liquid phase and a gas phase is performed in the mixture stream including the primary alcohol and the water, a flash drum lower line from which the liquid phase including a liquefied primary alcohol is discharged, a flash drum upper line installed to discharge the mixture stream of the gas-phase primary alcohol and the water to a layer separator, a condenser installed on the flash drum upper line to liquefy the mixture of the gas-phase primary alcohol and the water in the line, and the layer separator including a separation tank in which the layer separation of a mixture of the liquefied primary alcohol and the water into an organic layer and an aqueous layer is performed, an organic layer line through which the separated organic layer is discharged, an aqueous layer line through which the separated aqueous layer is discharged. 
     The flash drum lower line of the flash drum of the diester-based material production unit is connected to one or more positions selected from the group consisting of a column main body side upper portion, a column main body side lower portion, and the reaction vessel. 
     The organic layer line of the layer separator of the diester-based material production unit is connected to one or more positions selected from the group consisting of a flash drum main body side portion, the column main body side upper portion, the column main body side lower portion and the reaction vessel. 
     One or more of the flash drum lower line and the organic layer line of the diester-based material production unit are connected to the column main body side upper portion. 
     Advantageous Effects 
     The present invention employs an improved reflux system, and thus, can solve a rheological problem which can occur due to the coexistence of a liquid and a gas in a pipe and a condenser, greatly reduce coolant usage amount even when the amount of reflux is large, and reduce the volume of steam in a reactor by maintaining the temperature of an alcohol to be refluxed to be higher than usual. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a process diagram showing a production unit of a diester-based material according to an embodiment of the present invention; 
         FIG. 2  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention; 
         FIG. 3  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention; 
         FIG. 4  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention; 
         FIG. 5  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention; 
         FIG. 6  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention; and 
         FIG. 7  is a process diagram showing an example of selecting positions of a flash drum lower line and an organic layer line of a diester-based material production unit according to an embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. 
     It will be understood that words or terms used in the description and claims of the present invention shall not be construed as being limited to having the meaning defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having meanings that are consistent with their meanings in the context of the relevant art and the technical idea of the invention, based on the principle that an inventor can properly define the meaning of the words or terms to best explain the invention. 
     A diester-based material production unit according to an embodiment of the present invention includes a reaction device including a reaction vessel in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed and a gas phase discharge line installed at an upper end of the reaction vessel such that vaporized primary alcohol and water are discharged to a column therethrough, a column including a column main body in which the gas-liquid separation of the primary alcohol and the water introduced from the gas phase discharge line is performed, a liquid phase line installed at a lower portion of the column main body such that a liquefied alcohol-rich stream flows into the reaction device, and a gas phase line installed at an upper portion of the column main body and connected to a side portion of a flash drum such that a mixture stream of a gas-phase primary alcohol and water flows out, a heat exchanger installed on the gas phase line of the column to remove heat of the gas phase line, a flash drum having a flash drum main body in which separation of a liquid phase and a gas phase is performed in the mixture stream including the primary alcohol and the water, a flash drum lower line from which the liquid phase including a liquefied primary alcohol is discharged, a flash drum upper line installed to discharge the mixture stream of the gas-phase primary alcohol and the water to the layer separator, a condenser installed on the flash drum upper line to liquefy the mixture of the gas-phase primary alcohol and the water in the line, and a layer separator including a separation tank in which the layer separation of a mixture of the liquefied primary alcohol and the water into an organic layer and an aqueous layer is performed, an organic layer line through which the separated organic layer is discharged, an aqueous layer line through which the separated aqueous layer is discharged. 
     In addition, the flash drum lower line of the flash drum is connected to one or more positions selected from the group consisting of a column main body side upper portion, a column main body side lower portion, and the reaction vessel, the organic layer line of the layer separator of the diester-based material production unit is connected to one or more positions selected from the group consisting of a flash drum main body side portion, the column main body side upper portion, and the column main body side lower portion, and one or more of the flash drum lower line and the organic layer line are connected to the column main body side upper portion. 
     In applying a system which sends gas-phase materials such as an alcohol to be refluxed to an upper portion of a reactor back to the reactor in a typical diester-based material production process, a system which recovers heat by installing a heat exchanger at an upper portion of a column and then sends the recovered heat back to a reactor through further performing liquefaction and layer separation after the liquefaction is generally applied. 
     In this case, in the process of recovering heat from a gas-phase material at the upper portion of the column using the heat exchanger, a portion of a gas phase is liquefied in a line and another portion thereof remains in a gas phase, and thus, a liquid phase and a gas phase coexist in a pipe thereby causing a problem with the flow of a fluid, a problem in which the efficiency of the condenser is greatly deteriorated due to the presence of the liquid phase relatively slow in heat transfer in a line occurs. 
     Accordingly, in the production unit according to an embodiment of the present invention, a liquid phase generated in a line after heat exchange is not immediately introduced into a layer separator but is subjected again to gas-liquid separation through a flash drum, so that a rheological problem of fluid flow in the line can be solved without deteriorating the efficiency of the condenser. In addition, before the layer separation which is performed after liquefaction and cooling through the condenser is performed, some non-reactants can be refluxed to a column and/or a reaction device from the flash drum, and thus, a refluxed non-reactant (e.g., alcohol) can be re-injected into the reactor while the temperature thereof is maintained to be high, so that the reduction in the volume of steam used in the reactor can also be achieved when the amount of reflux is the same. 
     Hereinafter, the diester-based material production unit according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a process diagram showing a production unit  10  of a diester-based material according to an embodiment of the present invention. A facility in which a diester-based material is produced includes a reaction device  11  in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed, a column  12  in which gas-liquid separation is performed by pulling up an alcohol, which is a non-reactant vaporized during a reaction, and water, which is a side-reactant, a heat exchanger  16  for recovering heat of a gas phase line  121  discharged to an upper portion of the column, a flash drum  13  for performing gas-liquid separation of a liquefied primary alcohol and a mixture of a gas-phase primary alcohol and water on a line to return a liquid phase present in the line to the reaction device before layer separation, a condenser  15  for liquefying all of the mixture of the gas-phase primary alcohol and the water before introducing the same into a layer separator, and a layer separator  14  for separating the mixture of the liquefied primary alcohol and the water through layer separation. 
     Specifically, the production unit  10  includes the reaction device  11 , and the reaction device  11  includes a reaction vessel  110  in which an esterification reaction of dicarboxylic acid and a primary alcohol is performed, and a gas phase discharge line  111  installed at an upper end of the reaction vessel  110  through which vaporized primary alcohol and water are discharged to a column. 
     The reaction device  11  can also have a raw material injection line  112 ′ through which dicarboxylic acid and a primary alcohol, which are raw materials, are injected, and a product line  112  for sending a product to a reaction device of the next production unit if a plurality of production units are provided, or to a purification unit when there is a single production unit or when it is the last production unit of a plurality of production units. 
     However, the raw material injection line  112 ′ can have a pre-mixer (not shown) further installed at a front end of an initial production unit to inject raw materials into the pre-mixer, thereby supplying the raw materials to a reaction device, or can supply raw materials by performing line mixing with one raw material input line. Alternatively, raw materials can be supplied through different injection lines for each raw material. The injection method of raw materials is not particularly limited as long as it is a method capable of supplying raw materials into a reaction device. 
     In addition, the production unit  10  includes the column  12 , and the column  12  connected to the reaction device  11  through the gas phase discharge line  111  includes a column main body  120  in which the gas-liquid separation of the primary alcohol and the water introduced from the gas phase discharge line  111  is performed, a liquid phase line  122  installed at a lower portion of the column main body  120  such that a liquefied alcohol-rich stream flows into the reaction device, and a gas phase line  121  installed at an upper portion of the column main body  120  and connected to a side portion of the flash drum  13  such that a mixture stream of the gas-phase primary alcohol and the water flows out. 
     In the reaction device  11 , an esterification reaction is performed in the reaction vessel  110 , and the reaction can be performed at a temperature of about 150° C. to 230° C. by having dicarboxylic acid and a primary alcohol as raw materials. The dicarboxylic acid, which is a raw material, can include one or more selected from the group consisting of terephthalic acid, phthalic acid, isophthalic acid, and cyclohexane dicarboxylic acid, and the primary alcohol which is another raw material can have 3 to 10 carbon atoms. 
     When the raw materials are used to perform an esterification reaction, the reaction temperature of the esterification reaction can be higher than the boiling point of the primary alcohol having 3 to 10 carbon atoms applied as a raw material, so that the vaporization of the primary alcohol inevitably occurs during the reaction. In addition, due to the evaporation of the primary alcohol, a problem in which reactants are continuously decreased in a reaction vessel occurs. Therefore, the reaction is performed by injecting an excess amount of the primary alcohol above an equivalent ratio in theory. 
     Accordingly, the molar ratio of the dicarboxylic acid and the primary alcohol in a reaction part (particularly a first reaction part in a production system to be described later) can be 1:2 to 1:5, and can be to prevent energy loss due to unnecessary reflux caused by the injection of an excessive amount of alcohol and can be determined in consideration of the excess amount of alcohol required in terms of achieving the conversion rate of the reaction and controlling the minimum residence time. The molar ratio can preferably be 1:2 to 1:4, and in order to optimally reflect the above, a molar ratio of 1:2.5 to 1:4 can be applied. 
     In addition, the esterification reaction generates water as a side-reactant, but the generation of water, on the contrary, can accelerate a reverse reaction and become the cause to interfere with the achievement of a target conversion rate, and thus, it can also be important to remove the water from a reaction vessel. 
     That is, gas-phase water generated during the reaction should be removed in the reaction device  11 , and inevitably, the operation to re-liquefy the vaporized primary alcohol and return the re-liquefied primary alcohol to the reactor is essential. Accordingly, the column  12  is installed at an upper portion of the reaction device  11 . 
     In the column  12 , the gas-liquid separation of the vaporized primary alcohol and the water is performed. The mixture of the gas-phase primary alcohol and the water is introduced to a lower portion of the column main body  120  of the column  12  from the gas phase discharge line  111  at the upper portion of the reaction vessel  110 , and the introduced gas-phase mixture ascends in the column main body  120  of the column  12  and comes in contact with a liquid-phase primary alcohol descending from a side upper portion of the column  12 , so that the primary alcohol and the water are separated into the lower portion of the column main body  120  and the upper portion of the column main body  120 , respectively. Here, the liquid-phase primary alcohol descending from an upper portion of the column  12  can be supplied from a flash drum  13  at a rear end or from a layer separator  14 . 
     The primary alcohol and the water vaporized in the reaction device  11  are primarily separated through the gas-liquid separation in the column  12 , and the liquefied primary alcohol is supplied back to the reactor  110  through the liquid phase line  122 , and thus, can participate in the reaction. In addition, a mixture gas of water still in gas phase and unseparated primary alcohol is discharged through the gas phase line  121  at the upper portion of the column. At this time, the temperature of an internal gas phase mixture stream discharged through the gas phase line  121  can be about 130° C. to 180° C. Although a portion of the primary alcohol is liquefied and returned to the reactor, the primary alcohol can still be excessive, and thus, the weight ratio of the primary alcohol to the water can be about 1 or more. 
     The production unit  10  includes a heat exchanger  16  for recovering the heat of the gas phase line  121  of the column and transferring the same to another place which needs heat supply in the process, and the heat exchanger  16  is installed on the gas phase line  121  of the column  12 . The mixture stream of the gas-phase water and primary alcohol discharged through the gas phase line  121  from the column should be eventually liquefied such that the primary alcohol is refluxed and the water is removed, which is a stream from which heat should be removed. However, when heat is removed by only a condenser, energy loss is large. Therefore, it is preferable to perform an operation of transferring the heat of the mixture stream in the gas phase line to another place in the process through the heat exchanger  16  and removing the heat. 
     Meanwhile, when heat is removed from a stream in the gas phase line  121  as described above, liquefaction can occur, in which case a phenomenon in which a liquid and a gas coexist within the line can occur. However, when a gas and a liquid coexist in a pipe, a rheological problem can occur therein, and there is also a problem in which cooling efficiency is considerably lowered due to the presence of a liquid phase in removing residual heat through the condenser afterwards. 
     Therefore, in the present invention, the flash drum  13  is introduced to solve the above problem. Since the primary alcohol liquefied by the heat exchanger  16  can be immediately recirculated through the flash drum  13  before passing through the condenser  15 , the rheological problem in the pipe or the problem of the efficiency deterioration of the condenser cannot occur. 
     The flash drum  13  connected to the column  12  through the gas phase line  121  has a flash drum main body  130  in which the mixture stream including partially liquefied primary alcohol and water by the heat exchanger  16  is subjected to gas-liquid separation, a flash drum lower line  132  through which a liquid phase including the liquefied primary alcohol is discharged, and a flash drum upper line  131  installed to discharge a mixture stream of the gas-phase primary alcohol and the water to the layer separator  14 . 
     The flash drum  13  can perform the gas-liquid separation inside the flash drum main body  130 , and can return a large amount of primary alcohol to the reactor through simple equipment and treatment. At this time, the liquefied primary alcohol can be recovered to the reaction system through the reaction device  11  or the column  12  through the flash drum lower line  132 . Since the temperature of the primary alcohol recovered from the flash drum  13  is higher than that by condensation and cooling, even if the primary alcohol is recovered to the reactor, it is possible to minimize the temperature change in the reaction system. Also, since a portion of the primary alcohol is primarily separated, the amount of cooling water used in the condenser can be greatly reduced, and thus, the energy saving effect obtained through the introduction of the flash drum  13  can be significant. 
     In addition, the production unit  10  includes the layer separator  14 . The layer separator  14  connected to the flash drum  13  through the flash drum upper line  131  includes a separation tank  140  in which a gas phase discharged from the upper portion of the flash drum is liquefied to perform layer separation into an organic layer and an aqueous layer, an organic layer line  141  from which the separated organic layer is discharged, and an aqueous layer line  142  from which the separated aqueous layer is discharged. 
     Furthermore, the production unit  10  includes a condenser  15  for performing cooling and condensing such that a stream flowing through the flash drum upper line  131  of the flash drum  13  is liquefied before being introduced into the layer separator  14 , and the condenser  15  is installed on the flash drum upper line  131 . The liquefied liquid-phase primary alcohol and water are separated into an organic layer of the primary alcohol and an aqueous layer of the water in the separation tank  140  of the layer separator  14 . 
     The primary alcohol in the organic layer can be recirculated to the flash drum  13 , column  12 , or the reaction device  11  through the organic layer line  141 , and the temperature of a primary alcohol stream in the organic layer line can be about 40° C. to about 95° C. Typically, reflux is achieved only through the layer separator  14  without the recirculation of a primary alcohol by the flash drum  13 , so that when the recirculated primary alcohol is introduced into a reaction system, the reaction temperature is lowered, and thus, additional steam supply to the reactor is required. However, in the present invention, since the temperature of the primary alcohol recirculated from the flash drum  13  is relatively high, an effect of energy saving can be additionally expected. 
     In addition, the water in the aqueous layer is discharged from the separation tank  14  through the aqueous layer line  142 . At this time, the discharged water can be used to produce steam through an additional separation facility as generated water in the process and there is no particular limitation to the utilization of the water after being removed from the reaction device. 
     The production unit  10  according to one embodiment of the present invention includes a flash drum lower line  132  of the flash drum  13  and the organic layer line  141  of the layer separator  14  as lines for subjecting a primary alcohol to reflux, that is, recirculation. In returning the primary alcohol to the reaction device  11 , the recirculation lines can be connected at various positions. The flash drum lower line  132  is connected to one or more positions selected from the group consisting of a side upper portion of the column main body  120 , a side lower portion of the column main body  120 , and the reaction vessel  110 , and the organic layer line  141  is connected to one or more positions selected from the group consisting of a side portion of the flash drum main body  130 , the side upper portion of the column body main  120 , the side lower portion of the column main body  120 , and a reaction vessel  110 . 
     At this time, any one of the flash drum lower line  132  and the organic layer line  141  is necessarily to be connected to the side upper portion of the column main body  120  of the column  12 . This is because gas-liquid separation can be performed only when a gas phase ascends in a lower portion and a liquid phase descends in an upper portion of the column main body  120  of the column  12 . 
       FIG. 2  to  FIG. 7  show an example of connecting a line such that the flash drum lower line  132  and the organic layer line  141  are finally introduced into the reaction device  11 . 
       FIG. 2  illustrates that the flash drum lower line  132  is connected to the side upper portion of the column main body  120  of the column  12  and the organic layer line  141  is connected to the side portion of the flash drum main body  130  of the flash drum  13 .  FIG. 3  illustrates that while the connection of the flash drum lower line  132  is the same, the organic layer line  141  is configured to be connected to the flash drum lower line  132  rather than the side portion of the flash drum main body such that a primary alcohol is recirculated though a line connection.  FIG. 4  also illustrates that the connection of the flash drum lower line  132  is the same and the organic layer line  141  is connected to the side lower portion of the column main body  120  of the column  12 . 
     In addition,  FIG. 5  illustrates that the connection to the side upper portion of the column main body  120  of the column  12  is achieved through the organic layer line  141  of the layer separator  14  and the flash drum lower line  132  is connected to the side lower portion of the column main body  120 .  FIG. 6  and  FIG. 7  illustrate examples in which the flash drum lower line  132  and the organic layer line  141  are connected to the side upper portion of the column main body  120  and the reaction vessel  110 , respectively. 
     As described above, in  FIGS. 2 to 7 , it can be confirmed that either one of the flash drum lower line  132  and the organic layer line  141  is necessarily connected to the side upper portion of the column main body  120  of the column  12 . As described above, it is only necessary to have a line connected to the side upper portion of the column main body  120  of the column  12 . However, it can be appropriately configured in consideration of the fact that the organic layer line  141  of the layer separator  14  has a low stream temperature, so that the effect cannot be great in terms of the volume of steam supplied from the reaction device  11  to the reaction vessel, and when introduced into the side lower portion of the column main body  120 , it can be difficult to expect an improvement in gas-liquid separation efficiency in the column  12 . 
     A shown in  FIGS. 2 to 4 , it is preferable that the flash drum lower line  132  and the organic layer line  141  are connected. 
     According to an embodiment of the present invention, provided are a reaction part in which two or more of the above-described diester-based material production unit are connected in series, and a purification unit for purifying a reaction product discharged from the reaction part. 
     The above-described production unit of a diester-based material can be one reactor constituting a portion of the ‘reaction part’ in view of the entire process. In the present invention, in a continuous process of producing a diester-based material, it is preferable that two or more of the production unit are connected, preferably 3 to 6 or 3 to 5. 
     When two or more of the production unit  10  are connected, a product produced in the reaction device  11  can be discharged through the product line  112  and moved to the next production unit. “ . . . ” represented in  FIGS. 1 to 8  can be interpreted as an expression that two or more production units can be coupled. 
     Specifically, the continuous process of producing a diester-based material can include a first production system including a first reaction part in which a direct esterification reaction is performed and a first purification unit in which a product of the first reaction part is purified, and a second production system including a second reaction part in which a trans-esterification reaction with a diester generated is performed through an additional injection of alcohol, and a second purification unit in which a product of the second reaction part is purified. Furthermore, a wastewater treatment unit or a mixed alcohol separation unit can be included. 
     The production unit according to an embodiment of the present invention can particularly relate to the first reaction part in the first production system in which a direct esterification reaction is performed. However, even if the first purification unit, the second reaction unit, and the second purification unit at a rear end are not connected together, a reaction process is not particularly limited as long as it is a process in which an alcohol is included as a reactant and water is generated as a by-product in order to reduce the volume of steam and the amount of reflux in the reactor. 
     EXAMPLES 
     Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. 
     In the following Examples and Comparative Examples, a process system according to the method of continuous production of a diester-based material, the method according to the present invention, has been simulated by using CONTINUOUS MODELER in a commercial process simulation program ASPEN PLUS. 
     Experimental Example 1 
     In performing simulation using the above program, the simulation has been performed by the process illustrated in  FIG. 2 , wherein four same production units are coupled, dicarboxylic acid was terephthalic acid and a primary alcohol was 2-ethylhexanol as raw materials, and the molar ratio of the two raw materials was set to 1:3. The temperature of an organic layer including the primary alcohol discharged through the organic layer line  141  was set to 40° C., and the connection position of the flash drum lower line  132  and the organic layer line  141  was varied as shown in Table 1 below. The amount of coolant consumed in the condenser  15  and the total flow rate of a steam flowing in the gas phase line  121  of the column  12  were identified, and values in Table 1 below are relative % assuming that Comparative Example 1-1 is 100%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Flash drum 
                 Organic 
                 Amount of 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 lower line 
                 layer line 
                 Coolant 
                 Column gas phase 
                 heat recovered 
               
               
                   
                 Connection 
                 Connection 
                 usage 
                 line flow rate 
                 from heat 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 position 
                 position 
                 amount 
                 1st 
                 2nd 
                 3rd 
                 exchanger 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 — 
                 Column main 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Example 1-1 
                   
                 body side upper 
               
               
                   
                   
                 portion 
               
               
                 Example 1-1 
                 Column main 
                 Drum main body 
                 61 
                 155 
                 138 
                 170 
                 263 
               
               
                   
                 body side upper 
                 side portion 
               
               
                   
                 portion 
               
               
                 Example 1-2 
                 Column main 
                 Column main 
                 63 
                 142 
                 124 
                 158 
                 250 
               
               
                   
                 body side upper 
                 body side upper 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 1-3 
                 Column main 
                 Column main 
                 63 
                 145 
                 127 
                 161 
                 252 
               
               
                   
                 body side upper 
                 body side lower 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 1-4 
                 Column main 
                 Column main 
                 65 
                 148 
                 131 
                 188 
                 330 
               
               
                   
                 body side lower 
                 body side upper 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 1-5 
                 Reaction vessel 
                 Column main 
                 64 
                 200 
                 184 
                 222 
                 353 
               
               
                   
                   
                 body side upper 
               
               
                   
                   
                 portion 
               
               
                 Example 1-6 
                 Column main 
                 Reaction vessel 
                 63 
                 169 
                 153 
                 189 
                 288 
               
               
                   
                 body side upper 
               
               
                   
                 portion 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1 above, it can be confirmed that the gas phase line of the column, that is the flow rate of an upper portion was increased due to the installation of a flash drum, which means that the capacity of the column can be divided with the flash drum. It can be seen that the cooling efficiency was greatly increased by recirculating the liquid phase once in the flash drum before flowing to the condenser. 
     In addition, in the cases of Examples 1-1 to 1-6, although the amount of reflux was relatively large when compared to Comparative Examples, it can be confirmed that the coolant usage amount was greatly reduced despite the large amount of reflux. 
     Accordingly, it can be confirmed that the amount of heat which can be recovered from the heat exchanger was also increased by 2 to 3 times. 
     From the above, it can be confirmed that the production unit according to the present invention is an innovative process which can reduce energy loss of the entire process by increasing the amount of heat which can be recovered as well as increasing cooling efficiency by installing a flash drum. 
     Experimental Example 2 
     In performing simulation using the above program, the simulation has been performed by the process illustrated in  FIG. 2 , wherein four same production units are coupled, dicarboxylic acid was terephthalic acid and a primary alcohol was 2-ethylhexanol as raw materials, and the molar ratio of the two raw materials was set to 1:2.5. The temperature of an organic layer including the primary alcohol discharged through the organic layer line  141  was set to 95° C., and the connection position of the flash drum lower line  132  and the organic layer line  141  was varied as shown in Table 2 below. The amount of coolant consumed in the condenser  15  and the total flow rate of a steam flowing in the gas phase line  121  of the column  12  were identified, and values in Table 2 below are relative % assuming that Comparative Example 2-1 is 100%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Flash drum 
                 Organic 
                 Amount of 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 lower line 
                 layer line 
                 Coolant 
                 Column gas phase 
                 heat recovered 
               
               
                   
                 Connection 
                 Connection 
                 usage 
                 line flow rate 
                 from heat 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 position 
                 position 
                 amount 
                 1st 
                 2nd 
                 3rd 
                 exchanger 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 — 
                 Column main 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Example 2-1 
                   
                 body side upper 
               
               
                   
                   
                 portion 
               
               
                 Example 2-1 
                 Column main 
                 Drum main body 
                 60 
                 127 
                 130 
                 143 
                 224 
               
               
                   
                 body side upper 
                 side portion 
               
               
                   
                 portion 
               
               
                 Example 2-2 
                 Column main 
                 Column main 
                 64 
                 125 
                 106 
                 137 
                 217 
               
               
                   
                 body side upper 
                 body side upper 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 2-3 
                 Column main 
                 Column main 
                 64 
                 127 
                 109 
                 141 
                 219 
               
               
                   
                 body side upper 
                 body side lower 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 2-4 
                 Column main 
                 Column main 
                 60 
                 131 
                 114 
                 165 
                 269 
               
               
                   
                 body side lower 
                 body side upper 
               
               
                   
                 portion 
                 portion 
               
               
                 Example 2-5 
                 Reaction vessel 
                 Column main 
                 59 
                 182 
                 166 
                 190 
                 303 
               
               
                   
                   
                 body side upper 
               
               
                   
                   
                 portion 
               
               
                 Example 2-6 
                 Column main 
                 Reaction vessel 
                 65 
                 147 
                 131 
                 171 
                 260 
               
               
                   
                 body side upper 
               
               
                   
                 portion 
               
               
                   
               
            
           
         
       
     
     Referring to Table 2 above, it can be confirmed that the gas phase line of the column, that is the flow rate of an upper portion was increased due to the installation of a flash drum, which means that the capacity of the column can be divided with the flash drum. It can be seen that the cooling efficiency was greatly increased by recirculating the liquid phase once in the flash drum before flowing to the condenser. 
     In addition, in the cases of Examples 2-1 to 2-6, although the amount of reflux was relatively large when compared to Comparative Examples, it can be confirmed that the coolant usage amount was greatly reduced despite the large amount of reflux. Accordingly, it can be confirmed that the amount of heat which can be recovered from the heat exchanger was also increased by 2 to 3 times. 
     From the above, it can be confirmed that the production unit according to the present invention is an innovative process which can reduce energy loss of the entire process by increasing the amount of heat which can be recovered as well as increasing cooling efficiency by installing a flash drum. 
     
       
         
           
               
             
               
                   
               
               
                 [Description of the Reference Numerals or Symbols] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 10: Production unit 
                 11: Reaction device 
               
               
                   
                 110: Reaction vessel 
                 111: Gas phase discharge line 
               
               
                   
                 112: Product line 
                 112′: Raw material injection line 
               
               
                   
                 12: Column 
                 120: Column main body 
               
               
                   
                 121: Gas phase line 
                 122: Liquid phase line 
               
               
                   
                 13: Flash drum 
                 130: Flash drum main body 
               
               
                   
                 131: Flash drum upper line 
                 132: Flash drum lower line 
               
               
                   
                 14: Layer separator 
                 140: Separation tank 
               
               
                   
                 141: Organic layer line 
                 142: Aqueous layer line 
               
               
                   
                 15: Condenser 
                 16: Heat exchanger