Process for preparing ester-based compositions

Abstract

The present invention provides a method for preparing an ester-based composition using a continuous reaction system in which a plurality of reactors are connected in series, which can improve heat transfer performance, reactor productivity, and total reactor productivity by controlling operating conditions when preparing an ester-based composition.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2022-0126487, filed on October 4, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present disclosure provides a method for preparing an ester-based composition using a continuous esterification reaction system in which a plurality of reactors are connected in series. Specifically, the present disclosure provides a method that can improve heat transfer performance, reactor productivity, and overall reactor productivity in the manufacture of an ester-based composition. Background Art

[0004] Ester-based compounds generated by the esterification reaction of polycarboxylic acids and alcohols have been widely used as plasticizers.

[0005] The esterification reaction is usually carried out at high temperature in the presence of an esterification catalyst. Therefore, after the reaction is completed, the resulting reaction products include the catalyst, byproducts of catalyst decomposition, unreacted alcohol and unreacted polycarboxylic acid, monoester and reaction impurities. In order to obtain pure ester-based compounds, post-treatment processes such as neutralization, washing, alcohol removal and / or filtration must be performed.

[0006] Therefore, in order to obtain high-purity ester-based compounds, research has been actively conducted in various fields, such as methods for efficiently separating and purifying these by-products in reaction products, methods for suppressing side reactions and catalyst decomposition during esterification reactions, and methods for efficiently designing production facilities or processes.

[0007] Among the methods for suppressing side reactions and catalyst decomposition in esterification reactions, there is a method of removing water produced in the esterification reaction by supplying heat to the reactor using a heat medium. This method uses a reaction system in which multiple reactors are connected in series. In such a system, the performance of supplying heat to each reactor, that is, the heat transfer performance of the reactor, directly affects the esterification reaction rate. Therefore, when multiple reactors with the same heat transfer performance are used to produce ester-based compounds in a continuous process, as the concentration of the raw materials decreases, the reaction rate of the downstream reactor will decrease, and as a result, the heat required to remove water will also decrease. In other words, in the downstream reactor, the available heat transfer performance exceeds the heat actually required for the reaction, leaving idle heat transfer performance. This leads to the problem of reduced heat transfer performance, reactor productivity and total reactor productivity in the production of ester-based compounds. Although various methods for improving the production efficiency and productivity of ester-based compounds by controlling reactor conditions have been proposed, these methods have not yet provided sufficient improvements in terms of effectiveness, economic efficiency and process feasibility. Summary of the invention

[0008] Technical issues

[0009] An object of the present disclosure is to provide a method for preparing an ester-based composition using a continuous esterification reaction system with multiple reactors connected in series, wherein heat transfer performance, reactor productivity, and overall reactor productivity are all improved.

[0010] Technical Solution

[0011] According to the present disclosure, a method for preparing an ester-based composition using a continuous esterification reaction system is provided, in which a total of N reactors from a first reactor to an Nth reactor are connected in series, and the method includes the steps of continuously feeding a raw material comprising a polycarboxylic acid and an alcohol into the continuous esterification reaction system to continuously produce a reaction product, and satisfies the following mathematical formula 1:

[0012] [Mathematical formula 1]

[0013] P1 <P N-1 ≤P N

[0014] Among them, in mathematical formula 1,

[0015] P1 is the pressure of the first reactor (bar),

[0016] P N is the pressure (bar) of the Nth reactor after the first reactor, and

[0017] N is an integer greater than or equal to 3.

[0018] Advantageous Effects of the Invention

[0019] In the method for preparing the ester-based composition according to the present disclosure, the heat transfer performance, the reactor productivity and the total reactor productivity can be improved simultaneously by performing step-by-step pressurization operation on a continuous esterification reaction system in which a plurality of reactors are connected in series. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram showing one example of a continuous esterification reaction system that can be used in the method for preparing an ester-based composition according to the present disclosure.

[0021] [Explanation of Reference Numerals]

[0022] 1 reaction unit

[0023] 1a, 1b, 1n reactors

[0024] 2 Separation unit

[0025] 2a, 2b, 2n separation devices

[0026] 3 Recovery Unit

[0027] 3a, 3b, 3n Unreacted alcohol first recovery device

[0028] 3a', 3b', 3n' unreacted alcohol second recovery device

[0029] 4Pressure control unit

[0030] 4a, 4b, 4n first pressure control device

[0031] 4a', 4b', 4n' second pressure control device

[0032] 4a”, 4b”, 4n” third pressure control device

[0033] 21a, 21b, 21n tower separators

[0034] 22a, 22b, 22n condensers

[0035] 23a, 23b, 23n phase separators

[0036] 100 continuous esterification reaction system DETAILED DESCRIPTION

[0037] In the present disclosure, terms such as "first" and "second" are used to describe various components. These terms are only used to distinguish one component from another.

[0038] In addition, the terms used in this specification are only used to illustrate exemplary embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular includes the plural. In this specification, terms such as "include", "comprise" and "have" indicate the presence of the features, numbers, steps, components or combinations thereof, and do not exclude the possibility of the presence or addition of one or more other features, numbers, steps, components or combinations thereof.

[0039] Unless otherwise specifically stated, "%" or "part(s)" indicating the content is based on weight.

[0040] The present disclosure can be modified in various ways and adopt various forms; therefore, certain embodiments will be described in detail below by way of example. However, this is not intended to limit the present invention to any particular disclosed form, and the present invention should be understood to cover all modifications, equivalents and substitutes that fall within the spirit and scope of the present invention.

[0041] The following is a detailed description of a method for preparing an ester-based composition according to the present disclosure.

[0042] Conventionally, when a continuous reaction system in which a plurality of reactors are connected in series is used to produce an ester-based composition, idle heat transfer performance remains in the downstream reactor, resulting in reduced heat transfer performance, reactor productivity, and overall reactor productivity.

[0043] In the present disclosure, in order to maximize the use of the idle heat transfer performance left in the downstream reactor, in a continuous esterification reaction system, the downstream reactor is pressurized relative to the upstream reactor, thereby increasing the reaction temperature and reactivity, thereby increasing the productivity of each reactor.

[0044] Specifically, the preparation method of the ester-based composition according to the present disclosure is a method for producing an ester-based composition using a continuous esterification reaction system, in which a total of N reactors from a first reactor to an Nth reactor are connected in series, and the method includes the steps of continuously feeding a raw material including a polycarboxylic acid and an alcohol into the continuous esterification reaction system to continuously produce a reaction product, and satisfies the following mathematical formula 1:

[0045] [Mathematical formula 1]

[0046] P1 <P N-1 ≤P N

[0047] Among them, in mathematical formula 1,

[0048] P1 is the pressure of the first reactor (bar),

[0049] P N is the pressure (bar) of the Nth reactor after the first reactor, and

[0050] N is an integer greater than or equal to 3.

[0051] When the downstream reactors are pressurized, the temperature within each pressurized reactor increases, resulting in an increase in the average temperature of the entire reactor. The increase in average reactor temperature increases the esterification reaction rate, thereby increasing the overall reactor productivity.

[0052] In addition, if the pressure increase of the downstream reactor relative to the first reactor exceeds a certain level, the above effect is further enhanced. However, if the pressure of the downstream reactor is too high, the reaction temperature in the reactor may increase so much that the required heat exceeds the heat transfer performance of the reactor, and the amount of heat residue may increase. As a result, side reactions and catalyst decomposition reactions may occur, and the reactivity may actually decrease. Therefore, it is best to control the pressure increase of the downstream reactor to a certain level or below.

[0053] Specifically, the method may also satisfy the following mathematical formula 2:

[0054] [Mathematical formula 2]

[0055] P1+0.01≤P N ≤P1+2

[0056] Among them, in mathematical formula 2, P1, P N and N are as defined above.

[0057] More specifically, the method may also satisfy any one of the following mathematical formulas 2-1 to 2-5:

[0058] [Mathematical formula 2-1]

[0059] P1+0.02≤P N ≤P1+2

[0060] [Mathematical formula 2-2]

[0061] P1+0.05≤P N ≤P1+1.5

[0062] [Mathematical formula 2-3]

[0063] P1+0.06≤P N ≤P1+1.5

[0064] [Mathematical formula 2-4]

[0065] P1+0.1≤P N ≤P1+1

[0066] [Mathematical formula 2-5]

[0067] P1+0.1≤P N ≤P1+0.5

[0068] Among them, in mathematical formulas 2-1 to 2-5, P1, P N and N are as defined above.

[0069] In addition, in mathematical formulas 1 and 2, the pressure (P1) of the first reactor can be 1 bar to 4 bar. More specifically, P1 can be at least 1 bar, or 1.1 bar, or 1.2 bar, or 1.24 bar, and up to 4 bar, or 3 bar, or 2 bar, or 1.5 bar, or 1.3 bar, or 1.28 bar, or 1.26 bar. When P1 is controlled within this range, process feasibility and reactor productivity are better.

[0070] In addition, in Mathematical Formulas 1 and 2, N is the number of reactors in the reaction system. Specifically, N is 3 or more, or 4 or more, and 20 or less, or 10 or less, or 8 or less, or 5 or less, expressed as an integer.

[0071] In the method according to the present disclosure, the pressure in each reactor can be adjusted by controlling the amount of inert gas introduced into the reactor so as to meet the above pressure conditions. In addition, the pressure in each reactor can be controlled by adjusting the amount of uncondensed gas (including inert gas) and water discharged as a result of the reaction.

[0072] For example, increasing the amount of inert gas introduced into the reactor or decreasing the amount of uncondensed gases and water vented can increase the pressure within the reactor.

[0073] The amount of inert gas, uncondensed gas and water can be adjusted by a pressure control device of a pressure control unit provided in the continuous esterification reaction system. This will be described in detail below in the description of the continuous esterification reaction system.

[0074] Meanwhile, in the method according to the present disclosure, the raw material for producing the ester-based composition is prepared by mixing polycarboxylic acid and alcohol. Therefore, the method of the present disclosure may further include a step of mixing polycarboxylic acid and alcohol before feeding the raw material.

[0075] The mixing of the polycarboxylic acid and the alcohol can be carried out by conventional methods. Before feeding them into the reactor, they can be homogenized using a stirrer or other mixing device to avoid uneven esterification reaction due to different positions in the reactor.

[0076] Among the raw materials, the polycarboxylic acid may be an aliphatic or aromatic carboxylic acid having 2 or more, specifically 2 to 4, carboxyl (—COOH) groups in the molecule, or an anhydride of the polycarboxylic acid.

[0077] Specifically, the polycarboxylic acid may be an aliphatic carboxylic acid having 2 to 20 carbon atoms or an aromatic carboxylic acid having 6 to 20 carbon atoms. For example, the polycarboxylic acid may be at least one selected from adipic acid, azelaic acid, phthalic acid, isophthalic acid, terephthalic acid, citric acid, trimellitic acid and anhydrides thereof, but is not limited thereto. Preferably, the polycarboxylic acid may be at least one selected from phthalic acid, isophthalic acid, terephthalic acid and anhydrides and derivatives thereof, more preferably terephthalic acid or anhydrides thereof.

[0078] The alcohol may be a straight or branched aliphatic alcohol having 1 to 20 carbon atoms, or 4 to 20 carbon atoms, or 5 to 15 carbon atoms. Specifically, it may be at least one selected from butanol, hexanol, 2-ethylhexanol, isononanol, isodecanol, and propylheptanol.

[0079] In one example, the method of preparing an ester-based composition of the present disclosure may be a method of preparing dioctyl terephthalate (di-2-ethylhexyl terephthalate, DOTP) using terephthalic acid as a polycarboxylic acid and 2-ethylhexanol as an alcohol.

[0080] In addition, an esterification reaction catalyst may be added during the preparation of the raw materials.

[0081] The esterification catalyst can be fed into the mixture of the polycarboxylic acid and the alcohol, or fed into the polycarboxylic acid or the alcohol separately before mixing them. The esterification catalyst can also be fed directly into the reactor.

[0082] Examples of esterification catalysts include organometallic catalysts, organic sulfonic acids, acid catalysts, or mixtures thereof. Specifically, examples include tetraalkyl titanates, such as tetraisopropyl titanate, tetra-n-butyl titanate (TnBT), tetraoctyl titanate, butyltin maleate, etc. as organometallic catalysts; organic sulfonic acids, such as p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, or butanesulfonic acid; and acid catalysts, such as formic acid, nitric acid, acetic acid, hydrochloric acid, phosphoric acid, and sulfuric acid. Any one of these catalysts or a mixture of two or more thereof may be used.

[0083] The amounts of the polycarboxylic acid, alcohol and esterification catalyst used in the present disclosure are not particularly limited and may be appropriately determined according to the properties and uses of the ester-based composition to be prepared.

[0084] In one example, in the method of preparing dioctyl terephthalate using terephthalic acid and 2-ethylhexanol, a polycarboxylic acid corresponding to terephthalic acid and an alcohol corresponding to 2-ethylhexanol may be fed in a molar ratio of 1:2 to 1:4 or 1:3 to 1:3.5.

[0085] In addition, based on the total weight of the alcohol, the feed amount of the catalyst may be about 100 to about 2000 ppm, more specifically 100 ppm or more, or 200 ppm or more, or 300 ppm or more, or 500 ppm or more, and 2000 ppm or less, or 1500 ppm or less, or 1000 ppm or less, or 700 ppm or less. When the feed is in the above range, the maximum reaction efficiency can be achieved relative to the feed amount.

[0086] The esterification reaction conditions of the polycarboxylic acid and the alcohol are not particularly limited either, but for example, it can be carried out at a temperature of 180°C to 260°C.

[0087] When a raw material including a polycarboxylic acid and an alcohol, optionally including an esterification catalyst, is continuously fed to the first reactor of the continuous esterification reaction system, an esterification reaction occurs in the first reactor. The resulting reaction product is sequentially transferred to each subsequent reactor in series after the first reactor. When the reaction product is introduced into the subsequent reactor, the esterification reaction occurs in the same manner as in the first reactor.

[0088] Since the reaction feedstocks continuously pass through multiple reactors connected in series, the entire process can be optimized by independently adjusting the process variables of each reactor, thereby maximizing the efficiency of the final manufacturing process.

[0089] Specifically, in the method according to the present disclosure, by utilizing a pressure control unit provided in a continuous esterification reaction system to control the pressurization conditions of each reactor to meet the above conditions, the heat transfer performance of each reactor can be fully utilized to improve the reactor productivity and the total reactor productivity.

[0090] Meanwhile, the continuous esterification reaction system used in the method according to the present disclosure has a structure in which N reactors from the first reactor to the Nth reactor are connected in series.

[0091] Figure 1 is a schematic diagram showing one example of a continuous esterification reaction system that can be used in the method for preparing the ester-based composition of the present disclosure. Figure 1 These are merely examples for explaining the present disclosure; they are not intended to limit the present disclosure.

[0092] See also Figure 1 , the continuous esterification reaction system 10 comprises: a reaction unit 1, wherein N reactors connected in series perform esterification reaction on raw materials including polycarboxylic acid and alcohol; a separation unit 2, which comprises a separation device for separating unreacted alcohol from the reaction product introduced from the reactor of the reaction unit; a recovery unit 3, which comprises a recovery device for returning the unreacted alcohol separated in the separation device of the separation unit to the reactor of the reaction unit; a pressure control unit 4, which comprises a pressure control device for controlling the pressure in the reactor of the reaction unit. Here, N is an integer greater than 3, more specifically an integer greater than 3, or an integer greater than 4, and an integer less than 20, or an integer less than 10, or an integer less than 8, or an integer less than 5.

[0093] In the continuous esterification reaction system, the reaction unit 1 includes N reactors 1a, 1b, ... 1n connected in series in such a manner that the esterification reaction proceeds sequentially, where "n" is a letter label corresponding to the integer N. Therefore, when the raw materials including the polycarboxylic acid and the alcohol and the optional esterification catalyst are continuously fed to the first reactor 1a of the reaction unit 1, the esterification reaction occurs in the first reactor 1a. The resulting reaction products are then transferred sequentially to each subsequent reactor connected in series, specifically from the second reactor 1b to the Nth reactor 1n. The reaction products are transported through a transport line (e.g., a pipeline) connecting each pair of reactors. For example, as Figure 1As shown, the first reactor and the second reactor are connected by a reaction product transfer line located at the bottom of the first reactor, and the reaction product in the first reactor is transferred through the transfer line. When the reaction product flows into the subsequent reactor, the esterification reaction is carried out therein in the same manner as in the first reactor.

[0094] In addition, in the reaction unit, an inert gas is fed into the lower part of each reactor to control the pressure inside the reactor. In addition to being a means of regulating the reactor pressure, the inert gas can also suppress side reactions by forming an inert atmosphere inside the reactor during the esterification reaction.

[0095] The inert gas is fed into the interior of the reactor through an inert gas inlet line connected to the lower portion of the reactor, and is discharged to a separation unit together with a reaction product (reaction by-product) through a reaction product discharge line connected to the upper portion of the reactor.

[0096] As the inert gas, nitrogen gas or the like can be used.

[0097] In addition, the supply amount of the inert gas satisfies the pressure condition in the reactor, and the supply amount can be controlled by the pressure control device described below.

[0098] In addition, in the continuous esterification reaction system, the separation unit 2 is connected to the reaction unit 1, more specifically, to the reactor of the reaction unit, and includes separation devices 2a, 2b, 2n for separating unreacted alcohol from the reaction product flowing out of the reactor. Specifically, each separation device 2a, 2b, 2n may include: tower separators 21a, 21b, 21n, in which the reaction product introduced from the reactor of the reaction unit is subjected to gas-liquid separation; condensers 22a, 22b, 22n, which condense the gaseous substances separated and discharged in the tower separator, convert them into liquid phase, and discharge uncondensed gas (including inert gas); and phase separators 23a, 23b, 23n, which separate the substances converted into liquid phase in the condenser into an organic layer and an aqueous layer.

[0099] In the separation unit, each separation device can be connected one-to-one to each reactor in the reaction unit, or one separation device can be connected to more than two reactors. For example, if there are five reactors in the reaction unit, one separation device can be connected to each of the first to third reactors, and a second separation device can be connected to the fourth and fifth reactors. Therefore, if there are N reactors, the separation unit may include 1 to N separation devices, where N is defined as above.

[0100] In addition, in the continuous esterification reaction system, the recovery unit 3 includes a first unreacted alcohol recovery device 3a, 3b, 3n, which is used to collect the liquid containing unreacted alcohol separated by gas-liquid separation in the tower separator 21a, 21b, 21n of the separation device in the separation unit 2, and then send it back to the reactor 1a, 1b, 1n, and may also include a second unreacted alcohol recovery device 3a', 3b', 3n', which is used to collect the organic layer containing unreacted alcohol separated by the phase separator 23a, 23b, 23n, and send it back to the top of the tower separator 21a, 21b, 21n. Each first or second unreacted alcohol recovery device can take various forms, such as a storage tank or a recovery pipeline.

[0101] In addition, in the continuous esterification reaction system, the pressure control unit 4 controls the pressure in each reactor of the reaction unit so as to satisfy the above-mentioned pressure conditions.

[0102] Specifically, the pressure control unit may include a first pressure control device 4a, 4b, 4n located in the inert gas inlet pipeline connected to the lower part of each reactor, which adjusts the pressure in the reactor by controlling the amount of inert gas continuously flowing into the lower part of each reactor. In addition, the pressure control unit may include a second pressure control device 4a', 4b', 4n' located in the uncondensed gas discharge pipeline, which is connected to the top of the condenser in the separation device of the separation unit, and adjusts the reactor pressure by controlling the amount of uncondensed gas discharged from the separation unit. In addition, the pressure control unit 4 may include a third pressure control device 4a", 4b", 4n", which is located in the discharge line of the water layer separated by gravity separation in the phase separator 23a, and adjusts the reactor pressure by controlling the amount of water discharged. Therefore, the tower separator, condenser and phase separator in the separation unit connected to each reactor have the same pressure as this reactor.

[0103] Each pressure control device in the pressure control unit 4 may be, for example, a control valve, but is not limited thereto.

[0104] In the continuous esterification reaction system having the above structure, when the esterification reaction occurs in the first reactor 1a of the reaction unit, an ester compound is produced as a result. In addition to the ester compound, the reaction product also includes unreacted raw materials and water. As the reaction product containing the ester compound and the unreacted raw materials is sequentially transferred to each subsequent reactor after the first reactor 1a, such as the second reactor 1b, the esterification reaction is repeated. Therefore, as the esterification reaction is carried out in these subsequent reactors, the ester compound content in the reaction product increases, while the content of the unreacted raw materials decreases, and only the ester compound remains in the final reactor. At the same time, under the heat and pressure inside the first reactor 1a, the reaction product including the unreacted raw materials (such as unreacted alcohol and water) is discharged to the first separation device 2a through the reaction product discharge line at the top of the first reactor 1a. When the reaction product is introduced into the tower separator 21a in the first separation device 2a through the reaction product discharge line, gas-liquid separation occurs in the tower separator, a separated liquid is produced, and it is returned to the first reactor 1a through the recovery line 3a as the tower separator bottom recovery device. The gaseous substance is discharged to the condenser 22a through the discharge line at the top of the tower separator 21a. The liquid mainly includes unreacted alcohol and may also include a small amount of low-boiling ester compounds escaping from the reactor in a vapor state. Therefore, the liquid returned to the first reactor can be reused in the esterification reaction. The gaseous substance can also include uncondensed alcohol and water. In the condenser 22a, the gaseous substance discharged from the tower separator 21a is cooled into a liquid phase, and uncondensed gases including inert gases are discharged at the same time. The liquid substance condensed by the condenser 22a is sent to the phase separator 23a through the discharge line of the condenser. In the phase separator 23a, the liquid substance introduced from the condenser 22a is separated into an organic layer and a water layer under the action of gravity. The separated organic layer (mainly including unreacted alcohol) is sent back to the top of the tower separator 21a through the recovery line 3a', and the water layer is discharged to the outside.

[0105] In addition, the continuous esterification reaction system may further include one or more neutralization vessels for neutralizing the ester-based composition produced by the reactor, and one or more purification tanks for further refining the composition. The neutralization vessel or the purification tank may be connected to the last (nth) reactor in the series-connected reactors.

[0106] In one example, if a purification tank is additionally included, once the esterification reaction in the reaction unit is completed, the reaction product including the ester compound from the last reactor flows into the neutralization vessel or the purification tank, and the unreacted alcohol remaining in the reaction product can be separated and removed, thereby producing a purified ester compound.

[0107] The purification tank may include a separation tower or a flash evaporator. If a separation tower is included, the final composition ratio of the produced composition may vary depending on the number of stages in the separation tower. Therefore, it is best to determine the number of separation tower stages in consideration of the composition ratio and characteristics of the composition to be produced. If a flash evaporator is included, it is best to operate under vacuum conditions in order to effectively remove unreacted alcohol from the thermal reaction product.

[0108] Furthermore, in the purification tank, the unreacted alcohol separated can be returned to one or more reactors in the reaction unit and reused in the continuous esterification reaction.

[0109] In addition, the continuous esterification reaction system may also include devices commonly used in process design, such as a mixing device for mixing polycarboxylic acid and alcohol, a decanter, a heat exchanger, a reboiler and a pump. These devices may be appropriately arranged according to their intended use.

[0110] As described above, in the method for preparing an ester-based composition according to the present disclosure, by continuously feeding raw materials including polycarboxylic acids and alcohols into a continuous esterification reaction system, a reaction product can be continuously produced, and at the same time, by controlling the pressurization conditions in each reactor to meet the above conditions through a pressure control unit included in the reaction system, the heat transfer performance of each reactor can be maximized, and the reactor productivity and the overall reactor productivity can be improved.

[0111] Below, preferred embodiments are given to help understand the present disclosure. However, these embodiments are only used to make it easier to understand the present disclosure and do not limit its subject matter in any way.

[0112] In the following examples and comparative examples, a continuous esterification reaction system in which four reactors were connected in series was simulated using Aspen Plus process simulation program.

[0113] Example 1

[0114] like Figure 1 As shown, a continuous reaction system connected in series by four reactors is adopted to produce an ester-based composition. As reaction raw materials, terephthalic acid and 2-ethylhexanol are used in a molar ratio of 1:3.4. Tetra-n-butyl titanate (TnBT) is used as a catalyst for esterification, and its consumption is 500ppm relative to the gross weight of 2-ethylhexanol. When these reaction raw materials are fed to the first reactor in the series reactor, the resulting reaction product is fed to subsequent reactors in sequence. By controlling the amount of nitrogen fed to each reactor by a pressure control device, the amount of uncondensed gas discharged from the top of the condenser, and the amount of water discharged after gravity separation in a phase separator, the pressure in each reactor is set to the conditions shown in Table 1 below.

[0115] Examples 2 to 4 and Comparative Examples 1 to 3

[0116] An ester-based composition was produced in the same manner as in Example 1, except that the pressure in each reactor was set to the conditions shown in Table 1 below.

[0117] Experimental example

[0118] When the ester-based compositions were produced according to the above-described Examples and Comparative Examples, increases in average reactor temperature, heat transfer performance, reactor productivity, and total reactor productivity were evaluated as follows.

[0119] (1) Average reactor temperature increase (unit: °C)

[0120] From the simulation results obtained using the Aspen Plus process simulation program, the temperature of each reactor when producing the ester-based composition in each example or comparative example was obtained. The temperature values ​​of all reactors were added together and then divided by the number of reactors to obtain the average reactor temperature (° C.). The increase in the average reactor temperature was calculated according to the following mathematical formula 3:

[0121] [Mathematical formula 3]

[0122] (Average reactor temperature increase, °C) = Ta – Tb

[0123] In mathematical formula 3,

[0124] Ta is the average reactor temperature (° C.) in each Example or Comparative Example, which is obtained by adding the temperatures of all reactors (derived by Aspen Plus simulation) and dividing by the total number of reactors,

[0125] Tb is the average reactor temperature (° C.) in Comparative Example 1, which is obtained by adding the temperatures of all reactors (obtained by Aspen Plus simulation of Comparative Example 1) and dividing by the total number of reactors.

[0126] (2) Heat transfer performance ratio of each reactor (%)

[0127] According to the following mathematical formula 4, the heat transfer performance (MJ / h·℃·m 3 ), and the heat transfer performance ratio of each reactor was calculated as a percentage relative to the heat transfer performance of the first reactor (n=1, reactor #1).

[0128] [Mathematical formula 4]

[0129] (Reactor heat transfer performance, MJ / h·℃·m 3 )=A1 / (A2×A3)

[0130] Among them, in mathematical formula 4,

[0131] A1 is the heat energy Q (MJ / h, megajoule / hour) transferred from the heating facility to the fluid in the reactor,

[0132] A2 is the logarithmic mean temperature difference (LMTD, °C) between the heating facility and the reactor, and

[0133] A3 is the liquid volume of the reactor (m 3 ).

[0134] (3) Reactor productivity ratio of each reactor (%)

[0135] The productivity of each reactor (kg / hr·m 3 ), and the reactor productivity ratio (%) of each reactor was determined by expressing its productivity as a percentage relative to the productivity of the first reactor (n=1, reactor #1).

[0136] [Mathematical formula 5]

[0137] (Reactor productivity, kg / hr·m 3 )=P / V

[0138] Among them, in mathematical formula 5,

[0139] P is the amount of reaction product produced in each reactor (kg / hr), simulated using the Aspen Plus process simulation program, and

[0140] V is the liquid volume of the reactor (m 3 ).

[0141] (4) Average reactor productivity (%) and total reactor productivity (%)

[0142] After adding the reactor productivity ratios of all reactors calculated in (3) above, the total was divided by the number of reactors to calculate the average reactor productivity as a percentage. The average reactor productivity was then expressed as a percentage relative to the average reactor productivity of Comparative Example 1.

[0143] [Table 1]

[0144]

[0145]

[0146] In Examples 1 and 2, in a continuous esterification reaction system with four reactors connected in series, the pressure of the downstream reactor is increased to a certain extent relative to the first reactor, and all downstream reactors have the same increased pressure. In Examples 3 and 4, the reaction pressure is increased sequentially from the first reactor to the last reactor.

[0147] On the other hand, in Comparative Example 1, in the continuous esterification reaction system with 4 reactors connected in series, the pressures of all reactors are the same; in Comparative Example 2, the reaction pressures decrease successively; in Comparative Example 3, the pressure of the second reactor increases relative to the first reactor, but the subsequent reactors return to the same pressure as the first reactor.

[0148] In Comparative Example 1, the heat transfer performance of the second to fourth reactors, except for the first reactor, was 55% to 69%, indicating that there was still idle heat transfer performance. In contrast, in Examples 1 to 4, the pressure of the downstream reactors increased, the heat transfer performance of each reactor increased, and the productivity also increased. This improvement became more obvious as the pressure increase became larger. In addition, in Example 5, the pressure continued to increase from one reactor to the next, and the heat transfer performance of each reactor was almost 100% utilized, so the total reactor productivity was the highest.

[0149] Meanwhile, in Comparative Example 2, the reactor pressure decreased toward the downstream reactor, and the heat transfer performance ratio and productivity decreased in each stage compared to Comparative Example 1. In Comparative Example 3, the second reactor with increased pressure exhibited enhanced heat transfer performance and productivity relative to the first reactor, but these values ​​decreased again in the third and fourth reactors where the pressure was decreased back to the pressure of the first reactor.

[0150] From the above results, it can be seen that the step-by-step pressure increase operation of the continuous esterification reaction system with multiple reactors connected in series can improve the heat transfer performance of each reactor, and improve the reactor productivity and the total reactor productivity.

Claims

1. A method for preparing an ester-based composition using a continuous esterification reaction system, in which a total of N reactors from a first reactor to an Nth reactor are connected in series, the method comprising the steps of continuously feeding a raw material comprising a polycarboxylic acid and an alcohol into the continuous esterification reaction system to continuously produce a reaction product, and satisfies the following mathematical formula 1: [Mathematical formula 1] P1 <P N-1 ≤P N in, In mathematical formula 1, P1 is the pressure of the first reactor (bar), P N is the pressure (bar) of the Nth reactor after the first reactor, and N is an integer greater than or equal to 3.

2. The method for preparing an ester-based composition according to claim 1, which satisfies the following mathematical formula 2: [Mathematical formula 2] P1+0.01≤P N ≤P1+2 in, In mathematical formula 2, P1, P N and N as defined in claim 1.

3. The method for preparing an ester-based composition according to claim 2, wherein: P1 is 1 bar to 4 bar.

4. The method for preparing an ester-based composition according to claim 1, wherein: N is an integer of 3 to 20.

5. The method for preparing an ester-based composition according to claim 1, wherein The polycarboxylic acid is at least one selected from phthalic acid, isophthalic acid, terephthalic acid, their anhydrides and derivatives thereof.

6. The method for preparing an ester-based composition according to claim 1, wherein: The alcohol is an aliphatic alcohol having 1 to 20 carbon atoms.

7. The method for preparing an ester-based composition according to claim 1, wherein: The raw materials also include an esterification catalyst.

8. The method for preparing an ester-based composition according to claim 1, wherein The continuous esterification reaction system comprises: A reaction unit, wherein N reactors are connected in series, and the N reactors carry out an esterification reaction of a feedstock comprising a polycarboxylic acid and an alcohol; a separation unit including a separation device that separates unreacted alcohol from a reaction product flowing from a reactor of the reaction unit; a recovery unit, comprising a recovery device for returning unreacted alcohol separated in the separation device of the separation unit to the reactor of the reaction unit; and A pressure control unit comprises a pressure control device for adjusting the pressure in a reactor of a reaction unit.

9. The method for preparing an ester-based composition according to claim 8, wherein: The separation device comprises: a tower separator in which a reaction product flowing from a reactor of a reaction unit is subjected to gas-liquid separation; a condenser that condenses the gaseous substances separated and discharged after the gas-liquid separation in the tower separator into a liquid phase, and discharges uncondensed gas at the same time; and A phase separator that separates the substance converted into the liquid phase in the condenser into an organic layer and an aqueous layer.

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