Process for preparing polymers

Abstract

The present invention provides a process for preparing a polymer, the process comprising: feeding a feed stream comprising water and a polymer solution to a first stripper, feeding a first stripper lower drain stream comprising polymer and water to a second stripper, feeding the second stripper lower drain stream to a third stripper, and obtaining the polymer from the third stripper lower discharge stream.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0000796, filed on January 3, 2024, which is hereby incorporated by reference herein in its entirety. Technical Field

[0003] The present invention relates to a method for preparing a polymer, in particular to a method for obtaining a polymer from a polymer solution by utilizing a small amount of steam. Background Art

[0004] Solution polymerization is a method of dissolving monomers in a solvent and polymerizing the monomers in a solution state. It is used for free radical polymerization and ionic polymerization. A representative example of polymer preparation by solution polymerization is the preparation of styrene-butadiene copolymers by anionic polymerization of styrene and butadiene. Typically, n-butyl lithium is used as an anionic polymerization initiator and cyclohexane is used as a solvent.

[0005] Since a large amount of solvent is used in the process of preparing polymers by solution polymerization, it is necessary to separate and recover the solvent from the reaction product obtained by solution polymerization to obtain the polymer. Therefore, a steam stripping process using a stripper is applied to obtain a high-purity polymer in the reaction product.

[0006] Typically, during the steam stripping process, a large amount of steam is required, and therefore, energy usage may increase. When the amount of steam fed to the stripping process is insufficient, the amount of solvent remaining in the polymer increases, which has adverse effects on the product, such as causing the polymer to fail to cure or increasing the total volatile organic compounds (tVOC) of the polymer. Summary of the Invention

[0007] Technical issues

[0008] In order to solve the problems mentioned in the background art, an object of the present invention is to provide a method for obtaining a high-purity polymer while reducing the amount of steam in the process.

[0009] Technical Solution

[0010] In one general aspect, a method for preparing a polymer comprises: feeding a feed stream containing water and a polymer solution to a first stripper to obtain a first stripper upper effluent stream containing a solvent and a first stripper lower effluent stream containing a polymer and water; feeding the first stripper lower effluent stream to a second stripper to obtain a second stripper upper effluent stream and a second stripper lower effluent stream, feeding the second stripper upper effluent stream to the first stripper, and feeding the second stripper lower effluent stream to a third stripper; separating the second stripper lower effluent stream into a third stripper upper effluent stream and a third stripper lower effluent stream; supplying a third steam stream containing steam to an ejector, drawing the third stripper upper effluent stream through the ejector to obtain an ejector effluent stream containing the third steam stream and the third stripper upper effluent stream, and supplying a mixed stream obtained by mixing the ejector effluent stream with the second steam stream containing steam to the second stripper; and obtaining a polymer from the third stripper lower effluent stream.

[0011] Beneficial effects

[0012] According to the polymer production method of the present invention, the ejector provided above the third stripper increases the gas generated in the third stripper, thereby improving the stripping efficiency for evaporating the remaining solvent from the polymer in the third stripper even when no steam is supplied to the third stripper. Furthermore, an ejector discharge stream containing a motive fluid used to operate the ejector and a suction fluid drawn by the ejector is fed to the second stripper, and a mixed stream obtained by mixing the ejector discharge stream with a second steam stream containing steam is fed to the second stripper. This allows for smooth dispersion of the polymer present in the liquid phase in the second stripper and improves the mixing efficiency of the polymer and steam, thereby effectively evaporating the remaining solvent from the polymer.

[0013] Therefore, the solvent evaporated by the steam contained in the mixed stream can be contained in the second stripper upper exhaust stream together with the steam and can be fed to the first stripper, and the solvent can also be evaporated in the first stripper by the steam contained in the second stripper upper exhaust stream. That is, since the steam contained in the mixed stream can be used as a heat source to heat the second stripper and the first stripper, it can be expected that the total amount of steam used in the process can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a process diagram illustrating a steam stripping process in a method for preparing a polymer according to an embodiment of the present invention.

[0015] Figures 2 to 4 is a process diagram illustrating a steam stripping process in a method for preparing a polymer according to a comparative example of the present invention. DETAILED DESCRIPTION

[0016] The terms and words used in the description and claims of the present invention should not be interpreted as having general or dictionary meanings, but should be interpreted as having meanings and concepts that satisfy the technical concept of the present invention based on the principle that inventors can appropriately define the concepts of the terms in order to describe their own inventions in the best mode.

[0017] The term "stream" in the present invention may refer to the flow of a fluid in a process, and may also refer to the fluid flowing through the pipeline itself. Specifically, stream may refer to both the fluid flowing through the pipe connecting the respective devices to each other and the fluid flow. In addition, fluid may refer to gas or liquid, and does not exclude the case of a fluid containing a solid component.

[0018] In the present invention, in a device such as a stripper, unless otherwise specified, the "lower part" of the device refers to a point where the height from the uppermost part of the device to the lower position is 80% to 100%, and specifically, it may refer to the lowest part (the bottom of the column). Similarly, unless otherwise specified, the "upper part" of the device refers to a point where the height from the uppermost part of the device to the lower position is 0% to 20%, and specifically, it may refer to the uppermost part (the top of the column).

[0019] In the present invention, in a device such as a stripper, unless otherwise specified, the operating temperature of the device may refer to the temperature of the lower portion of the device. Similarly, unless otherwise specified, the operating pressure of the device may refer to the pressure of the upper portion of the device. Specifically, the operating temperature of the stripper may refer to the temperature in the region from 0 to 20% of the height from the uppermost portion to the lower position of the stripper, and the pressure in the upper portion of the stripper may refer to the pressure in the region from 80 to 100% of the height from the uppermost portion to the lower position of the column.

[0020] The term "crumb" in the present invention is produced by supplying a polymer solution to a stripper and performing a steam stripping process, and may refer to a polymer in the form of droplets from which a solvent is removed by volatilization.

[0021] In the following, reference will be made to Figure 1 The present invention is described in more detail to help understanding the present invention.

[0022] The method for preparing a polymer according to an embodiment of the present invention may include: feeding a feed stream comprising water and a polymer solution to a first stripper 100 to obtain a first stripper upper discharge stream comprising a solvent and a first stripper lower discharge stream comprising a polymer and water; supplying the first stripper lower discharge stream to a second stripper 200 to obtain a second stripper upper discharge stream and a second stripper lower discharge stream, supplying the second stripper upper discharge stream to the first stripper 100, and supplying the second stripper lower discharge stream to a third stripper. stripper 300; separating the second stripper lower exhaust stream into a third stripper upper exhaust stream and a third stripper lower exhaust stream in the third stripper 300; supplying a third steam stream containing steam to an ejector, drawing the third stripper upper exhaust stream through the ejector to obtain an ejector exhaust stream containing the third steam stream and the third stripper upper exhaust stream, and supplying a mixed stream obtained by mixing the ejector exhaust stream with the second steam stream 210 containing steam to the second stripper; and obtaining a polymer from the third stripper lower exhaust stream.

[0023] According to an embodiment of the present invention, the polymer solution can be derived from a reaction product produced by feeding a monomer stream and a solvent stream to a reactor and performing a polymerization reaction. Specifically, the reaction product can be obtained by subjecting the monomer to a polymerization reaction in the presence of a solvent in the reactor. The reaction product may contain a polymer formed by the polymerization reaction of the monomer, unreacted monomer, and solvent.

[0024] The monomer may include an aromatic vinyl monomer selected from at least one of styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, isopropenylnaphthalene, 1-vinylnaphthalene, styrene substituted with an alkyl group having 1 to 3 carbon atoms, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, and styrene substituted with a halogen; and a conjugated diene monomer selected from one or more of 1,3-butadiene, 1,4-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, piperylene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and isoprene. As a specific example, the monomer may include styrene and butadiene, and accordingly, the polymer produced by the polymerization reaction may be a styrene-butadiene copolymer.

[0025] The solvent may include a hydrocarbon solvent, specifically one or more of cyclohexane, n-hexane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 1,3-dialkyl-2-imidazolidinone, tetramethylurea, and hexamethylphosphoric acid triamide. As a specific example, the solvent may include cyclohexane. In this case, polymerization of styrene-butadiene copolymer can be effectively performed.

[0026] The polymerization reaction can be carried out by further adding additives such as ion-exchanged water, an initiator, a molecular weight regulator, an activator, or a redox catalyst.

[0027] The initiator may include, for example, one or more selected from n-butyllithium, diisopropylbenzene hydroperoxide, tert-butyl hydroperoxide, isopropylbenzene hydroperoxide, p-menthane hydroperoxide, di-tert-butyl peroxide, tert-butylisopropylphenyl peroxide, acetyl peroxide, isobutyl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanol peroxide, and tert-butylperoxyisobutyrate.

[0028] The reaction product obtained by the solution polymerization reaction of the monomer using a solvent can be transferred to a blowdown tank, for example, so that the solvent contained in the reaction product can be volatilized using the residual heat of the solution polymerization reaction. In this way, a polymer solution having a higher polymer composition than the reaction product can be obtained.

[0029] Therefore, even if the solvent contained in the reaction product volatilizes in the drain tank, a portion of the solvent does not volatilize and remains in the polymer. Therefore, the present invention provides a method for efficiently separating the solvent contained in the polymer solution to obtain a high-purity polymer while reducing the amount of energy used in the method.

[0030] Specifically, there are several methods for separating the solvent from the polymer solution. In the present invention, a steam stripping process can be applied to remove the solvent contained in the polymer solution by volatilizing and solidifying the polymer contained in the polymer solution to obtain the polymer as particles. The steam stripping process can be performed using a multi-stage stripper.

[0031] The method for preparing a polymer according to an embodiment of the present invention may include feeding a feed stream including water and a polymer solution to a first stripper 100 to obtain a first stripper upper effluent stream including a solvent and a first stripper lower effluent stream including a polymer and water.

[0032] Specifically, a feed stream containing a polymer solution and water obtained by mixing the polymer solution with water may be fed to the first stripper 100. As another example, the polymer solution and water may be supplied to the first stripper 100 through separate pipes. The water may be high-temperature water, specifically 90°C to 110°C.

[0033] The polymer solution contained in the feed stream 1 can be heated by the steam introduced into the first stripper 100. Here, the steam introduced into the first stripper 100 can be introduced from the first steam stream 110 described below and / or the second stripper upper discharge stream. Therefore, when the polymer solution is heated, the solvent contained in the polymer solution can evaporate, and the polymer can solidify. In this case, the solidification of the polymer can be carried out by the anti-solvent precipitation mechanism and solvent evaporation. Specifically, the amount of solvent remaining in the polymer is reduced due to the evaporation of the solvent, and the polymer is precipitated in water as the anti-solvent of the polymer, so that the solidification of the polymer can be carried out.

[0034] The high-temperature water supplied to the first stripper 100 can also heat the polymer solution like steam. In addition, water can be used as an anti-solvent and a dispersion medium to disperse the polymer in the liquid phase as much as possible. Therefore, the polymer contained in the polymer solution can be solidified by steam and water, and the solvent and unreacted monomers contained in the polymer solution can be evaporated and discharged from the upper part of the first stripper 100.

[0035] According to an embodiment of the present invention, the first steam stream 110 containing steam can be supplied to the first stripper 100 through a pipeline connected to the first stripper 100. Specifically, the first steam stream 110 can be introduced into the first stripper 100 through a pipeline connected to the lower part of the first stripper 100. More specifically, the first steam stream 110 can be fed as a heat source for heating the first stripper 100, and by this heat source, the temperature of the first stripper 100 can be finely controlled to a desired level. In addition, when the operating temperature of the first stripper 100 is controlled as described above, the stripping efficiency of the process can be maximized, so that the content of total volatile organic compounds (tVOC) in the final product can be reduced. Here, total volatile organic compounds can refer collectively to liquid or gaseous organic compounds that are easily evaporated into the air when the final product is heated, and can include, for example, solvents.

[0036] Specifically, the temperature of the first steam stream 110 may be 120° C. to 280° C., and the pressure of the first steam stream 110 may be 2 bar to 100 bar. When the temperature and pressure of the first steam stream 110 are within the above ranges, the stripping efficiency performed in the first stripper 100 may be maximized.

[0037] According to an embodiment of the present invention, the operating temperature of the first stripper 100 can be 5°C or higher than the glass transition temperature (Tg) of the polymer, and can be 10°C or higher than the azeotropic point of the solvent and water. Specifically, when the operating temperature of the first stripper 100 is 5°C or higher than the glass transition temperature of the polymer, the amorphous part of the polymer can move easily. Therefore, the solvent remaining in the polymer can diffuse in the liquid phase, which makes the solvent evaporate easily. When the operating temperature of the first stripper 100 is 10°C or higher than the azeotropic point of the solvent and water, it can be an appropriate temperature level for fully volatilizing the solvent present in the polymer solution. Here, the azeotropic point of the solvent and water can refer to the boiling point of the azeotropic mixture containing water and solvent.

[0038] According to the present invention, the operating temperature of the first stripper 100 may be 85° C. to 95° C., particularly 85° C. to 90° C. When the operating temperature of the first stripper 100 is lower than 80° C., the stripping efficiency of the first stripper 100 for evaporating the remaining solvent in the polymer and separating the polymer and the solvent may decrease rapidly, and polymer agglomerates called mats may be formed in water, and thus the steam stripping process may not be able to be operated. When the operating temperature of the first stripper 100 exceeds 95° C., the amount of heat to be supplied to the first stripper 100 may increase excessively, which may not be preferable in terms of energy.

[0039] By heating the first stripper 100 with steam and high-temperature water, a gaseous first stripper upper effluent stream containing a solvent and a liquid first stripper lower effluent stream containing a polymer and water can be obtained. Specifically, the first stripper lower effluent stream may contain solidified polymer, and the solidified polymer may be transferred by water. The first stripper upper effluent stream may also contain steam (water vapor) and unreacted monomers.

[0040] The first stripper top discharge stream may be cooled by the condenser 10 and then introduced into the purification process 20. In the purification process 20, the solvent and unreacted monomers contained in the cooled first stripper top discharge stream may be separated and recovered. The solvent and unreacted monomers recovered in the purification process 20 may be used as raw materials for the above-mentioned polymerization reaction.

[0041] The method for preparing a polymer according to an embodiment of the present invention may include supplying the first stripper lower exhaust stream to the second stripper 200 to obtain a second stripper upper exhaust stream and a second stripper lower exhaust stream, supplying the second stripper upper exhaust stream to the first stripper 100, and supplying the second stripper lower exhaust stream to the third stripper 300.

[0042] Specifically, the first stripper lower exhaust stream containing polymer and water may be fed to the second stripper 200 and heated by steam. In this case, the steam used in the second stripper 200 may be introduced from the mixed stream described below.

[0043] The solvent and unreacted monomers that are not volatilized in the first stripper 100 may be included in the first stripper lower effluent stream. Therefore, the solvent and unreacted monomers contained in the first stripper lower effluent stream may be further evaporated by the steam in the second stripper 200 and separated into the upper portion of the second stripper 200. Thus, a gaseous second stripper upper effluent stream containing volatilized solvent and unreacted monomers and a liquid-phase second stripper lower effluent stream containing polymer and water may be obtained in the second stripper 200.

[0044] Specifically, the content of the polymer in the lower discharge stream of the second stripper can be higher than the content of the polymer in the lower discharge stream of the first stripper. That is, by removing as much unreacted monomer and solvent as possible, the lower discharge stream of the second stripper can be fed to the third stripper 300 as a stream having a higher content of polymer.

[0045] The second stripper upper exhaust stream may be fed to the first stripper 100 and may contain steam in addition to the solvent and unreacted monomers. As described above, the steam contained in the second stripper upper exhaust stream may be used as a heat source to heat the first stripper 100.

[0046] According to an embodiment of the present invention, the first stripper 100 and the second stripper 200 may be operated while satisfying the following Expressions 1 and 2.

[0047] [Expression 1]

[0048] P2-P1≥0.2bar

[0049] [Expression 2]

[0050] 1.8bar≥P1≥1.1bar

[0051] In Expressions 1 and 2, P1 is the operating pressure of the first stripper 100, and P2 is the operating pressure of the second stripper 200. Specifically, the second stripper 200 may be operated at an operating pressure of 0.2 bar or more, 0.2 bar to 0.8 bar, or 0.2 bar to 0.5 bar higher than the operating pressure of the first stripper 100. The first stripper 100 and the second stripper 200 are operated while satisfying Expression 1, so that the second stripper upper exhaust stream can be fed to the first stripper 100 without a separate compressor.

[0052] Specifically, when Expression 1 is satisfied, the second stripper upper exhaust stream can be sufficiently supplied to the first stripper 100 due to the difference in operating pressure between the first stripper 100 and the second stripper 200. Therefore, it may not be necessary to provide the second stripper 200 with a separate device, such as an ejector, to feed the second stripper upper exhaust stream to the first stripper 100. Since the ejector is not provided above the second stripper 200, additional use of steam for feeding to operate the ejector can be avoided, which is also preferable in terms of economic feasibility, such as the device cost of the ejector and the process facility cost.

[0053] That is, according to the present invention, the second stripper 200 is operated at an operating pressure higher than the operating pressure of the first stripper 100 by 0.2 bar or more, so that the second stripper upper exhaust stream can be fed to the first stripper 100 without a separate device and without additionally using energy for a separate device. The condition for controlling the operating pressure according to Expression 1 may be affected by the operating temperatures of the first stripper 100 and the second stripper 200.

[0054] The operating pressure of the first stripper 100 may be 1.1 bar to 1.8 bar, specifically, 1.1 bar to 1.5 bar. Specifically, when the operating pressure of the first stripper 100 is less than 1.1 bar, the stripping efficiency may be reduced due to the low operating pressure of the first stripper 100. In this case, in order to increase the stripping efficiency of the first stripper 100, the amount of steam fed to the first stripper 100 may be increased; however, entrainment may occur due to the excessive volume flow rate of the gas in the upper exhaust stream of the first stripper, which may cause fouling in the condenser 10. When the operating pressure of the first stripper 100 exceeds 1.8 bar, energy use may increase to meet these operating conditions, and the operating temperature of the first stripper 100 may also be excessively increased due to the high temperature, resulting in problems such as local polymer chain scission.

[0055] The method of preparing a polymer according to an embodiment of the present invention may include separating the second stripper lower exhaust stream into a third stripper upper exhaust stream and a third stripper lower exhaust stream in the third stripper 300 .

[0056] As described above, the second stripper lower effluent stream may contain water and solidified polymer, and may also contain solvent remaining in the solidified polymer. Therefore, in the third stripper 300, the second stripper lower effluent stream may be heated to cause gas-liquid separation into a gas-phase third stripper upper effluent stream containing unreacted monomers and solvent and a liquid-phase third stripper lower effluent stream containing water and polymer.

[0057] Specifically, the heating of the second stripper lower exhaust stream in the third stripper 300 can be performed by the pressure difference between the second stripper 200 and the third stripper 300. More specifically, since the operating pressure of the second stripper 200 is higher than the operating pressure of the third stripper 300, when the second stripper lower exhaust stream is supplied to the third stripper 300, the second stripper lower exhaust stream can be heated in the third stripper 300 using the waste heat generated by the pressure drop.

[0058] The third stripper 300 can be used to uniformly transfer the third stripper lower effluent stream containing the solidified polymer to the dehydration process 40 following the third stripper 300. To this end, it is preferable not to feed steam to the third stripper 300. For example, when steam is supplied to the third stripper 300, the mixing efficiency of the third stripper 300 is reduced by the steam, so that the polymer present in the water can be transferred in a state of being unevenly mixed with the water and contained in the third stripper lower effluent stream. In this case, due to the uneven mixing of water and polymer contained in the third stripper lower effluent stream, hunting problems may occur in the dehydration process 40, and the quality of the final product may be deteriorated. Therefore, it may be preferable to use the residual heat generated by the pressure difference between the second stripper and the third stripper without introducing steam to separate the second stripper lower effluent stream into the third stripper upper effluent stream and the third stripper lower effluent stream in the third stripper 300.

[0059] According to one embodiment of the present invention, no steam is introduced into the third stripper 300. The temperature and pressure of the steam may be 120°C to 280°C and 2 bar to 100 bar, respectively. Specifically, the steam is in the gas phase and can be distinguished from the water contained in the lower discharge stream of the third stripper based on its state of matter. The water contained in the lower discharge stream of the third stripper is in the liquid phase and may have a temperature of 90°C to 110°C.

[0060] The operating pressure of the third stripper 300 may be 0.9 bar to 1.0 bar. Specifically, when the operating pressure of the third stripper 300 is less than 0.9 bar, intermittent inflow of external air (oxygen) may occur due to the vacuum atmosphere in the third stripper 300, which may cause discoloration of the polymer. When the operating pressure of the third stripper 300 exceeds 1.0 bar, the third stripper lower exhaust stream is introduced into the dehydration process 40 at high temperature and high pressure. Therefore, heat loss due to superheated steam may occur in the dehydration process 40. Specifically, the dehydration process 40 can be performed under pressure conditions similar to the operating pressure of the third stripper 300 (approximately 0.9 bar to 1.0 bar). When the high-pressure and high-temperature third stripper lower exhaust stream is introduced into the dehydration process 40, waste heat is generated due to the pressure difference, and superheated steam is generated due to the waste heat, which may cause heat loss.

[0061] A method for preparing a polymer according to an embodiment of the present invention may include: supplying a third steam stream containing steam to an ejector; drawing a third stripper upper exhaust stream through the ejector to obtain an ejector exhaust stream containing a third steam stream and the third stripper upper exhaust stream; and supplying a mixed stream obtained by mixing the ejector exhaust stream with a second steam stream 210 containing steam to a second stripper 200.

[0062] Specifically, the ejector 30 is a device that uses the pressure energy of a high-pressure motive fluid to draw and move the drawn fluid, and can be disposed above the third stripper 300. Thus, the ejector 30 is disposed above the third stripper 300, so that the gas volatilized to the upper portion of the third stripper 300 can be included in the third stripper upper portion exhaust stream and drawn into the ejector 30. More specifically, since the gas generated in the third stripper 300 can be increased by the ejector 30, the stripping efficiency of the third stripper 300 can be increased without newly supplying steam to the third stripper 300.

[0063] The third steam stream 310 can be used as a motive fluid to operate the ejector 30. In addition, the third steam stream 310 as the motive fluid and the third stripper upper exhaust stream as the suction fluid are mixed in the ejector 30, so that the third stripper upper exhaust stream can be heated by the third steam stream 310, and it is possible to ensure fluidity upward to the second stripper 200 or the first stripper 100. The flow rate of the third steam stream 310 can be controlled to maintain the operating pressure of the third stripper 300 at 0.9 bar to 1.0 bar.

[0064] In other words, the third steam stream 310 is supplied to the ejector 30 , and the ejector 30 draws the third stripper upper stream, so that an ejector exhaust stream including the third stripper upper exhaust stream and the third steam stream 310 may be obtained.

[0065] Afterwards, a mixed stream can be obtained by mixing the ejector discharge stream with a second steam stream 210 containing steam, and the mixed stream can be supplied to the second stripper 200. When the ejector discharge stream is mixed with the second steam stream 210, the steam contained in the ejector discharge stream and the steam contained in the second steam stream 210 are mixed together and introduced into the second stripper 200, so that the dispersion of the polymer in the liquid phase present in the second stripper 200 can be smoothly carried out. Thus, the mixing efficiency between the polymer and the steam is maximized, so that the remaining solvent in the polymer can be evaporated more efficiently. Therefore, the effect of solvent volatilization (i.e., the stripping performed in the second stripper 200) can be maximized.

[0066] Reference Figure 3In the related art, the second steam stream 210 containing steam is not mixed with the ejector exhaust stream, and the second steam stream 210 is supplied to the second stripper 200 via a separate pipeline connected to the lower portion of the second stripper 200. In this case, the second stripper 200 must be equipped with separate devices, such as nozzles and distributors, which is not preferable from the perspective of economic feasibility, such as process facility costs and equipment costs. In addition, when the second steam stream 210 and the ejector exhaust stream are respectively supplied to the lower portion of the second stripper 200 via separate pipelines, the second steam stream 210 and the ejector exhaust stream may mix in the liquid phase in the second stripper 200. In this case, the high-temperature heat source is introduced into two parts of the second stripper 200, causing imbalance (uneven distribution) in material transfer and heat transfer, and the temperature of the polymer in the second stripper 200 is uneven, resulting in uneven quality of the final product.

[0067] Therefore, according to the present invention, the second steam flow 210 is mixed with the ejector exhaust flow in the gas phase, so that the mixed flow obtained by mixing the second steam flow 210 with the ejector exhaust flow can be formed into a uniform heat source through rapid heat transfer and material transfer, and the mixed flow can be supplied to the second stripper 200, thereby improving the thermal mixing efficiency and stripping efficiency of the second stripper 200.

[0068] The solvent evaporated by the steam contained in the mixed stream can be included in the second stripper upper exhaust stream together with the steam and can be supplied to the first stripper 100, and the solvent can also be evaporated in the first stripper 100 by the steam contained in the second stripper upper exhaust stream. That is, since the steam contained in the mixed stream can be used as a heat source for evaporating the solvent in the second stripper 200 and the first stripper 100, it can be expected that the total amount of steam used in the process will be reduced.

[0069] Typically, the ejector 30 is a device with fixed operating conditions, and the flow rate of the third steam stream 310, which serves as the motive fluid of the ejector 30, can be fed to the ejector 30 at a constant rate without fluctuation. Therefore, when the amount of steam fed to the first stripper 100 and the second stripper 200 is controlled according to process conditions, it may be difficult to control the amount of steam through the third steam stream 310. Therefore, the steam is supplemented with the second steam stream 210, making it possible to flexibly handle the steam feed in the process, thereby preventing a decrease in the stripping efficiency of the process due to process control oscillation.

[0070] The temperature of the second steam flow 210 may be 120°C to 280°C, and the pressure of the second steam flow 210 may be 2 bar to 100 bar. The temperature of the third steam flow 310 may be 140°C to 280°C, and the pressure of the third steam flow 310 may be 4 bar to 100 bar. Specifically, the pressure of the third steam flow 310 is preferably higher than the pressures of the second steam flow 210 and the first steam flow 110. Thus, the third steam flow 310, as a high-pressure motive fluid, can improve the suction efficiency of the ejector 30.

[0071] According to an embodiment of the present invention, the mass flow rate of the second steam flow 210 may be 0.15 to 0.40 or 0.29 to 0.33 relative to the total mass flow rate of the first steam flow 110, the second steam flow 210, and the third steam flow 310. Here, since the third steam flow 310 is used as the motive fluid of the ejector 30 as described above, it may be necessary to ensure that the flow rate of the third steam flow 310 is above a certain level in order to operate the ejector 30.

[0072] Specifically, when the mass flow rate of the second steam stream 210 is 0.40 or less relative to the total mass flow rate of the first to third steam streams, when the ejector 30 is provided above the second stripper 200, the design and manufacture of the ejector 30 can be facilitated. In addition, since the mass flow rate of the second steam stream 210 is not excessively high, it is possible to prevent the performance of the ejector 30 for supplying the third stripper upper exhaust stream to the second stripper 200 from being deteriorated. In the case where the mass flow rate of the second steam stream 210 is 0.15 or more relative to the total mass flow rate of the first to third steam streams, the second steam stream 210 can easily control the temperature of each of the second steam stream 210 and the first stripper 100 when the yield of the product in the process changes.

[0073] The method for preparing a polymer according to an embodiment of the present invention may include obtaining a polymer from a lower exhaust stream of the third stripper.

[0074] Specifically, in the method for preparing a polymer according to the present invention, the step of obtaining the polymer from the third stripper lower effluent stream may include supplying the third stripper lower effluent stream to a dehydration process and dehydrating the third stripper lower effluent stream to obtain the polymer.

[0075] More specifically, the third stripper lower exhaust stream can minimize the content of solvent and unreacted monomers by the stripping process performed on the third stripper 300 in the first stripper 100. In addition, the content of the polymer in the third stripper lower exhaust stream can be higher than the content of the polymer in the second stripper lower exhaust stream.

[0076] The third stripper lower effluent stream may be introduced into the dehydration process 40. The dehydration process 40 may be a process for obtaining a high-purity polymer by solid-liquid separation of liquid water and the solid polymer contained in the third stripper lower effluent stream. Specifically, in the present invention, the dehydration process 40 may be performed in an open system, and the third stripper lower effluent stream may be dehydrated by filtration.

[0077] According to the present invention, the water contained in feed stream 1 can be obtained from the water separated from the polymer by dehydrating the third stripper lower effluent stream in the dehydration process 40. When the third stripper lower effluent stream is dehydrated in the dehydration process 40, a large amount of water can be separated from the polymer. In this case, the water can be high-temperature water of approximately 100°C, and the high-temperature water is recycled to the first stripper 100 and reused, thereby reducing the amount of steam used as a heat source during the steam stripping process. In other words, the water separated from the polymer in the dehydration process 40 can be mixed with the polymer solution and included in feed stream 1.

[0078] The mass flow rate of water included in the feed stream 1 may be 11 to 15 times, specifically 11 to 13 times, the mass flow rate of the polymer included in the feed stream 1. Here, the water included in the feed stream 1 may include water separated from the polymer in the dehydration process 40.

[0079] Specifically, when the mass flow rate of water in feed stream 1 is less than 11 times the mass flow rate of the polymer in feed stream 1, the low amount of water prevents the polymer from dispersing in the liquid phase and may aggregate as polymer agglomerates, making it difficult to operate the steam stripping process. When the mass flow rate of water in feed stream 1 is greater than 15 times the mass flow rate of the polymer in feed stream 1, as the mass flow rate of water in feed stream 1 increases excessively, the pressure difference between the second stripper 200 and the third stripper 300 may cause an excessive increase in waste heat generated in the third stripper 300. Consequently, the ejector 30 provided above the third stripper 300 may have difficulty extracting the excess waste heat in the form of steam, potentially leading to an increase in the operating pressure of the third stripper 300. Furthermore, the size of the apparatus for circulating the water separated from the polymer in the dehydration process 40 to the first stripper 100 would need to increase, which may not be preferable in terms of economic feasibility, such as process facility costs and equipment costs.

[0080] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are provided to illustrate the present invention. It will be apparent to those skilled in the art that various modifications and variations may be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0081] Example

[0082] Example 1

[0083] according to Figure 1 The process flow shown is for polymer preparation process.

[0084] Specifically, a polymerization reaction is performed in a reactor using styrene and butadiene as monomers and cyclohexane as a solvent to produce a reaction product. Thereafter, the reaction product is heated in a drain tank to obtain a reaction product in which the solvent is partially evaporated as a polymer solution. The polymer solution contains a styrene-butadiene copolymer as a polymer, cyclohexane, and unreacted monomers.

[0085] A feed stream containing a polymer solution and water is fed to the first stripper 100. Specifically, the feed stream contains styrene-butadiene copolymer (flow rate: 10 tons / hour), cyclohexane (flow rate: 35 tons / hour), unreacted monomer (flow rate: 0.01 tons / hour), and water (temperature: 100°C, flow rate: 120 tons / hour). In the first stripper 100, steam is used to heat the feed stream, and a first stripper upper effluent stream containing steam and solvent and a first stripper lower effluent stream containing polymer and water are obtained. At this time, the operating temperature of the first stripper 100 is 85°C, and the operating pressure of the first stripper 100 is 1.2 bar.

[0086] The first stripper upper exhaust stream is cooled by the condenser 10 and then introduced into the purification process 20. The first stripper lower exhaust stream is supplied to the second stripper 200.

[0087] In the second stripper 200, the first stripper lower exhaust stream is heated with steam to obtain a second stripper upper exhaust stream containing steam and solvent and a second stripper lower exhaust stream containing polymer and water. At this time, the operating temperature of the second stripper 200 is 112° C., and the operating pressure of the second stripper 200 is 1.5 bar.

[0088] The second stripper upper exhaust stream is supplied to the first stripper 100 , and the second stripper lower exhaust stream is supplied to the third stripper 300 .

[0089] In the third stripper 300, the second stripper lower exhaust stream is heated to obtain a third stripper upper exhaust stream containing a solvent and a third stripper lower exhaust stream containing a polymer and water. At this time, the operating pressure of the third stripper 300 is 1 bar.

[0090] The third steam stream 310 (flow rate: 8 tons / hour, temperature: 220 ° C., pressure: 13 bar) containing steam and the third stripper upper discharge stream are fed to the ejector 30 to obtain an ejector discharge stream. The mixed stream obtained by mixing the ejector discharge stream with the second steam stream 210 (flow rate: 4 tons / hour, temperature: 200 ° C., pressure: 11 bar) containing steam is supplied to the second stripper 200.

[0091] The lower effluent stream from the third stripper is fed to a dehydration process 40 and dehydrated to separate the water contained in the upper effluent stream from the third stripper from the polymer. The water separated from the polymer is then circulated to the first stripper 100 as a recycle stream 41 and, specifically, is included in the feed stream. The polymer dehydrated in the dehydration process 40 is obtained as a high-purity polymer as a final product.

[0092] As a result, in Example 1, a total of 12 tons / hour of steam was used, the tVOC content in the final product was 10 ppm based on 1 part by weight of the final product, and the change in the tVOC content in the final product over one month (the difference between the highest and lowest tVOC contents in the final product measured for one month) was approximately 0.1% based on 10 ppm. Here, the tVOC content in the final product may refer to the content of the solvent and unreacted monomers contained in the finally obtained polymer, and it can be understood that since the tVOC content in the final product was low, steam stripping was effectively performed in the process.

[0093] Example 2

[0094] In Example 2, a polymer was prepared by the same process flow as in Example 1, except that the flow rate of the second steam stream was controlled to 3.7 tons / hour, the first steam stream 110 was fed through a pipeline connected to the first stripper, the flow rate of the first steam stream was controlled to 0.3 tons / hour, the temperature of the first steam stream was controlled to 200° C., and the pressure of the first steam stream was controlled to 11 bar.

[0095] As a result, in Example 2, a total of 12 tons / hour of steam was used, the tVOC content in the final product was 10 ppm based on a total of 1 part by weight of the final product, and the change in the tVOC content in the final product per month was about 0.01% based on 10 ppm.

[0096] In Example 2, it was confirmed that since the first steam stream was additionally supplied to the first stripper unlike Example 1, the temperature of the first stripper was most easily controlled, and therefore, the monthly variation in the tVOC content in the final product was lowest.

[0097] Example 3

[0098] In Example 3, a polymer was prepared by the same process as in Example 2, except that the operating pressure of the first stripper was controlled to 1.0 bar, and the flow rate of the third steam flow was controlled to 9 tons / hour.

[0099] As a result, in Example 3, when the flow rate of the third steam stream was increased compared to Example 2 while maintaining the operating temperature of the first stripper at 85° C., fouling occurred in the condenser due to entrainment caused by the excessive volumetric flow rate of the gas in the upper exhaust stream of the first stripper, and thus the process was not operated for a long time.

[0100] Example 4

[0101] In Example 4, a polymer was prepared by the same process as in Example 2, except that the operating pressure of the first stripper was controlled to 1.9 bar, and the operating temperature of the first stripper was set to 96°C.

[0102] As a result, in Example 4, the first stripper was operated at a high temperature, and thus problems with product quality such as local polymer chain scission and polymer discoloration occurred.

[0103] Example 5

[0104] In Example 5, a polymer was prepared by the same process as in Example 2, except that the flow rate of the third steam stream was controlled to 7 tons / hour, and the operating temperature of the first stripper was controlled to 82°C.

[0105] As a result, in Example 5, the stripping efficiency of the first stripper rapidly decreased, and the steam stripping process was not operated due to the occurrence of polymer agglomerates.

[0106] Specifically, these problems occur because the operating temperature of the first stripper should be 5°C or higher than the glass transition temperature of the polymer (78°C) so that the solvent in the first stripper can actively diffuse and suitable conditions for evaporating the solvent can be created. In addition, this is because the operating temperature of the first stripper should be 10°C or higher than the azeotropic point (73°C) of the solvent (cyclohexane) and water to reach a temperature level that can fully evaporate the solvent.

[0107] Comparative Example

[0108] Comparative Example 1

[0109] according to Figure 2 The process flow shown performs a polymer preparation process.

[0110] Specifically, a polymer solution was obtained using the same method as in Example 1. A feed stream containing the polymer solution and water was fed to the first stripper 100. Specifically, styrene-butadiene copolymer (flow rate: 10 tons / hour), cyclohexane (flow rate: 35 tons / hour) and water (temperature: 100° C., flow rate: 120 tons / hour) were included in the feed stream.

[0111] A first steam stream 110 containing steam (10 tons / hour) is supplied to the first stripper 100 via a pipeline connected to the first stripper 100. In the first stripper 100, the feed stream is heated using steam, and a first stripper upper effluent stream containing steam and solvent and a first stripper lower effluent stream containing polymer and water are obtained. At this time, the operating temperature of the first stripper 100 is 92° C., and the operating pressure of the first stripper 100 is 1.2 bar. The first stripper lower effluent stream is supplied to the second stripper 200.

[0112] A second steam stream 210 containing steam (10 tons / hour) is supplied to the second stripper 200 via a pipeline connected to the second stripper 200. In the second stripper 200, the steam is used to heat the first stripper lower exhaust stream, and a second stripper upper exhaust stream containing steam and solvent and a second stripper lower exhaust stream containing polymer and water are obtained. At this time, the operating temperature of the second stripper 200 is 112°C, and the operating pressure of the second stripper 200 is 1.5 bar. The second stripper lower exhaust stream is fed to the third stripper 300.

[0113] In the third stripper 300, the second stripper lower exhaust stream is heated to obtain a third stripper upper exhaust stream containing a solvent and a third stripper lower exhaust stream containing a polymer and water. At this time, the operating pressure of the third stripper 300 is 1 bar.

[0114] The third stripper upper exhaust stream is mixed with the above-mentioned first stripper upper exhaust stream and second stripper upper exhaust stream and cooled as a mixed stream by passing through a condenser 10 , and then the cooled mixed stream is introduced into the purification process 20 .

[0115] The third stripper lower effluent stream is fed to a dehydration process 40 and dehydrated to separate the water contained in the third stripper lower effluent stream from the polymer. The water separated from the polymer is thereby circulated to the first stripper 100 as a recycle stream 41 and, specifically, is contained in the feed stream. The polymer dehydrated in the dehydration process 40 is obtained as a high-purity polymer as a final product.

[0116] As a result, in Comparative Example 1, a total of 20 tons / hour of steam was used, the tVOC content in the final product was 10 ppm based on a total of 1 part by weight of the final product, and the monthly change in the tVOC content in the final product was about 3% based on 10 ppm.

[0117] In Comparative Example 1, it was confirmed that the total amount of steam used increased compared to Example 1, and the variation in the tVOC content in the final product per month also significantly increased.

[0118] Comparative Example 2

[0119] In Comparative Example 2, a polymer was prepared by the same process as in Example 1, except that the second steam stream was not fed and the flow rate of the third steam stream was 12 tons / hour.

[0120] As a result, in Comparative Example 2, a total of 12 tons / hour of steam was used, the tVOC content in the final product was 10 ppm based on a total of 1 part by weight of the final product, and the monthly change in the tVOC content in the final product was about 1% based on 10 ppm.

[0121] In Comparative Example 2 in which the second steam flow was not provided unlike Example 1, it was difficult to control the operating temperature of the first stripper, and it was confirmed that the variation in the tVOC content in the final product per month increased compared to Example 1.

[0122] Comparative Example 3

[0123] according to Figure 3 The process flow shown performs a polymer preparation process.

[0124] In Comparative Example 3, a polymer was prepared by the same process flow as Example 2, except that the second steam stream was not mixed with the ejector discharge stream and the second steam stream was directly supplied to the second stripper through a line connected to the second stripper.

[0125] As a result, in Comparative Example 3, a total of 12 tons / hour of steam was used, the tVOC content in the final product was 37 ppm based on a total of 1 part by weight of the final product, and the monthly change in the tVOC content in the final product was about 2.6% based on 37 ppm.

[0126] In Comparative Example 3, the second steam stream is directly fed to the second stripper without being mixed with the ejector exhaust stream, and imbalance (maldistribution) of material transfer and heat transfer occurs in the second stripper 200, resulting in difficulty in controlling the operating temperature of the first stripper and causing deterioration and unevenness in the quality of the final product.

[0127] Comparative Example 4

[0128] according to Figure 4The process flow shown performs a polymer preparation process.

[0129] In Comparative Example 4, a polymer was prepared by the same process flow as in Example 2, except that no ejector was provided above the third stripper 300, the third steam stream 310 was supplied to the third stripper 300 instead of the ejector, a mixture of the second stripper upper exhaust stream and the second steam stream 210 was supplied to the second stripper 200, the flow rate of the first steam stream 110 was 1 ton / hour, the flow rate of the second steam stream 210 was 7 tons / hour, and the flow rate of the third steam stream 310 was 8 tons / hour.

[0130] Therefore, in Comparative Example 4, maintaining the operating temperature of the first stripper 100 at 85°C required an additional 4 tons / hour of steam compared to Example 3. Furthermore, since there was no ejector above the third stripper 300, the overpressure in the third stripper 300 was not relieved. Furthermore, since the piping for moving the third stripper's upper exhaust stream connected the upper portion of the third stripper 300 to the lower portion of the second stripper 200, the pressure in the third stripper was naturally 1.8 bar. Consequently, the operating temperature of the third stripper increased to 117°C. Consequently, the lower exhaust stream from the third stripper was introduced into the dehydration process 40 at high temperature and pressure, generating waste heat due to the temperature difference. However, since the dehydration process 40 was conducted in an open system, recovering the superheated steam generated by this waste heat was difficult, resulting in heat loss within the dehydration process 40. Furthermore, a white plume phenomenon occurred, where the superheated steam condensed from the cold outside air, resulting in a white fog that obscured vision and made it impossible to operate in the dehydration process 40.

[0131] [Detailed description of main components]

[0132] 10: Condenser

[0133] 20: Purification process

[0134] 100: First stripper

[0135] 200: Second stripper

[0136] 300: The third stripper

[0137] 110: First steam flow

[0138] 120: Second steam flow

[0139] 130: Third steam flow

[0140] 30: Injector

[0141] 40: Dehydration process

[0142] 41: Circular Flow

Claims

1. A method for preparing a polymer, the method comprising: feeding a feed stream comprising water and a polymer solution to a first stripper to obtain a first stripper upper effluent stream comprising a solvent and a first stripper lower effluent stream comprising the polymer and water; feeding the first stripper lower effluent stream to a second stripper to obtain a second stripper upper effluent stream and a second stripper lower effluent stream, feeding the second stripper upper effluent stream to the first stripper, and feeding the second stripper lower effluent stream to a third stripper; separating the second stripper lower exhaust stream into a third stripper upper exhaust stream and a third stripper lower exhaust stream; supplying a third steam stream containing steam to an ejector, drawing the third stripper upper exhaust stream through the ejector to obtain an ejector exhaust stream containing the third steam stream and the third stripper upper exhaust stream, and supplying a mixed stream obtained by mixing the ejector exhaust stream with a second steam stream containing steam to the second stripper; and The polymer is obtained from the lower discharge stream of the third stripper.

2. The method according to claim 1, wherein The second stripper upper exhaust stream and the third stripper upper exhaust stream contain the solvent, and The second stripper lower effluent stream and the third stripper lower effluent stream contain the polymer and water.

3. The method according to claim 1, wherein A first steam stream comprising steam is fed to the first stripper through a line connected to the first stripper.

4. The method according to claim 3, wherein: The mass flow rate of the second steam flow is 0.15 to 0.40 relative to the total mass flow rate of the first steam flow, the second steam flow, and the third steam flow.

5. The method according to claim 1, wherein The operating temperature of the first stripper is more than 5° C. higher than the glass transition temperature (Tg) of the polymer and more than 10° C. higher than the azeotropic point of the solvent and water.

6. The method according to claim 5, wherein: The operating temperature of the first stripper is 85°C to 95°C.

7. The method according to claim 1, wherein The following expressions 1 and 2 are satisfied: [Expression 1] P2-P1≥0.2bar [Expression 2] 1.8bar≥P1≥1.1bar Wherein, P1 is the operating pressure of the first stripper, and P2 is the operating pressure of the second stripper.

8. The method according to claim 1, wherein The step of obtaining the polymer from the third stripper lower effluent stream includes feeding the third stripper lower effluent stream to a dehydration process and dehydrating the third stripper lower effluent stream to obtain the polymer.

9. The method according to claim 8, wherein The water contained in the feed stream comes from the water separated from the polymer by dehydrating the third stripper lower exhaust stream in the dehydration step, and The mass flow rate of water contained in the feed stream is 11 to 15 times the mass flow rate of the polymer contained in the feed stream.

10. The method according to claim 1, wherein The polymer solution is derived from a reaction product produced by feeding a monomer stream and a solvent stream into a reactor and performing a polymerization reaction, and The polymer solution contains the polymer and the solvent.

11. The method according to claim 1, wherein The solvent includes one or more selected from the group consisting of cyclohexane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 1,3-dialkyl-2-imidazolidinone, tetramethylurea and hexamethylphosphoric acid triamide.

12. The method of claim 1, wherein the polymer comprises styrene-butadiene copolymer.

13. The method according to claim 1, wherein no steam is introduced into the third stripper, and The temperature and pressure of the steam are 120° C. to 280° C. and 2 bar to 100 bar, respectively.

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