Method for purifying vinyl acetate

Abstract

The present invention provides a method for purifying vinyl acetate, comprising the steps of: (S1) preparing a reaction mixture comprising vinyl acetate monomer (VAM) and methanol; (S2) supplying the reaction mixture and water to a monomer recovery tower to separate them into an upper stream containing vinyl acetate monomer and a lower stream containing methanol; (S3) condensing the upper stream containing vinyl acetate monomer and then separating it in a decanter into an organic phase, a vinyl acetate monomer-rich layer, and a water layer; and (S4) supplying the organic phase to a monomer purification tower to obtain purified vinyl acetate from the bottom.

Description

Technology Field

[0001] The present invention relates to a method for purifying vinyl acetate, and more specifically, to a purification method for recovering unreacted vinyl acetate monomers generated in the manufacturing process of ethylene vinyl alcohol with high purity. Background Technology

[0002] Ethylene vinyl alcohol (EVOH) is widely used as a protective covering material for metals, paper, wood, etc., and as a packaging material for food, etc., due to its excellent properties such as gas barrier properties, chemical resistance, and mechanical strength.

[0003] Such EVOH can generally be prepared by hydrolyzing polyethylene vinyl acetate, obtained by copolymerizing ethylene monomer and vinyl acetate monomer (VAM), in an alcohol-based solvent such as methanol. In the copolymerization, a significant amount of the monomers remains as unreacted material and must be separated from the EVOH reactor along with the solvent used.

[0004] Generally, in EVOH manufacturing processes, a distillation method using gaseous methanol is used to recover unreacted vinyl acetate monomers from copolymerization solutions. For example, Korean registered patent No. 10-0508071 discloses a process in which a post-copolymerization solution is introduced into the upper part of a distillation column and gaseous methanol is introduced into the lower part thereof, thereby recovering a solution of ethylene-vinyl acetate copolymer with a high boiling point from the lower part of the distillation column and recovering unreacted vinyl acetate monomers and gaseous methanol together from the upper part.

[0005] Since the vinyl acetate monomer recovered from the top of the distillation column contains a large amount of methanol, a process to separate it is required. The vinyl acetate monomer (bp approx. 73°C) and methanol (bp approx. 65°C) form an azeotropic composition, and the separation of the vinyl acetate monomer from the azeotropic composition is carried out by a distillation method utilizing the liquid-liquid phase equilibrium that occurs between the vinyl acetate monomer and water by introducing water. For example, when water is introduced into the upper reflux stream of a distillation column into which an azeotropic mixture of vinyl acetate monomer and methanol is introduced, the vinyl acetate monomer-methanol azeotropic composition is broken by the water, and a VAM-rich stream containing a large amount of vinyl acetate monomer is discharged from the top of the distillation column, while a stream mixed with methanol and water is discharged from the bottom.

[0006] In this case, if a large amount of water is fed into the distillation column, vinyl acetate monomer and methanol can be separated with high purity, but there is a problem with increased energy consumption of the column. On the other hand, if the amount of water fed is small, there are limitations in recovering vinyl acetate monomer with high purity. Prior art literature

[0007] (Patent Document 0001) KR 10-0508071 B The problem to be solved

[0008] The present invention aims to solve the problems mentioned in the background technology of the invention and provides a purification method that can recover vinyl acetate monomer with high purity while minimizing energy consumption during the process of separating unreacted vinyl acetate monomer (VAM) and an azeotropic mixture of methanol generated in the production of ethylene vinyl alcohol. means of solving the problem

[0009] According to one aspect of the present invention for solving the above problem, a method for purifying vinyl acetate is provided, comprising the steps of: (S1) preparing a reaction mixture comprising vinyl acetate monomer (VAM) and methanol; (S2) supplying the reaction mixture and water to a monomer recovery tower to separate them into an upper stream comprising vinyl acetate monomer and a lower stream comprising methanol; (S3) condensing the upper stream comprising vinyl acetate monomer and then separating it in a decanter into an organic phase, a vinyl acetate monomer-rich layer, and a water layer; and (S4) supplying the organic phase to a monomer purification tower to obtain purified vinyl acetate from the bottom.

[0010] Additionally, the lower stream of the monomer recovery tower is supplied to a methanol separation tower to separate it into an upper stream of methanol and a lower stream of water, and the water recovered from the bottom of the methanol separation tower can be supplied to the decanter along with supplementary water.

[0011] The total flow rate of the supplementary water and recovered water can be controlled to a range of 60 to 100 weight percent, specifically 60 to 80 weight percent, of the flow rate of the reaction mixture supplied to the monomer recovery tower. Effects of the invention

[0012] According to the present invention, when recovering unreacted vinyl acetate monomer generated in the manufacturing process of ethylene vinyl alcohol (EVOH), the purity is increased by applying a monomer purification tower, and the energy consumption of the entire process can be minimized by supplying an optimal amount of makeup water and water recovered from the tower through a decanter. Brief explanation of the drawing

[0013] FIGS. 1 and 2 schematically illustrate the purification process of vinyl acetate monomer (VAM) according to one embodiment (Examples 1 and 2) of the present invention. Figure 3 schematically illustrates the vinyl acetate monomer purification process applied in Comparative Examples 1 to 4. Figure 4 is a graph showing the energy consumption when the amount of water input is changed according to Example 3. Specific details for implementing the invention

[0014] Terms and words used in the description and claims of the present invention shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0015] As used herein, the terms 'include' or 'contain' refer to specifying a particular characteristic, area, integer, step, action, element, or component, and do not exclude the addition of other particular characteristic, area, integer, step, action, element, or component.

[0016] Unless otherwise specified, the term 'upper' as used herein refers to a point at a height of 0 to 5 percent downward from the top of the device, and specifically may refer to the top (top of the tower). Additionally, the term 'lower' refers to a point at a height of 95 to 100 percent downward from the top of the device, and specifically may refer to the bottom (bottom of the tower).

[0017] As used herein, the term 'stream' may refer to the flow of fluid within a process, and may also refer to the fluid itself flowing within the piping. Specifically, the stream may simultaneously refer to the fluid itself flowing within the piping connecting each device and the flow of the fluid. Additionally, the fluid may include one or more components of gas, liquid, and solid.

[0019] One embodiment of the present invention relates to a purification method for recovering unreacted vinyl acetate monomer (VAM) generated in the manufacturing process of ethylene vinyl alcohol (EVOH) with high purity.

[0020] The purification method of the present invention will be described in detail below with reference to the attached drawings.

[0021] FIGS. 1 and 2 schematically illustrate a method for purifying vinyl acetate monomer according to one embodiment of the present invention. The purification method of the present invention can be performed using a system comprising a monomer recovery tower (100), a decanter (20, 30), a monomer purification tower (200), and a methanol separation tower (300).

[0022] A method for purifying vinyl acetate monomer according to one embodiment of the present invention first prepares a reaction mixture comprising vinyl acetate monomer (VAM) and methanol (S1).

[0023] The above reaction mixture of vinyl acetate monomer and methanol is an azeotropic mixture recovered from the EVOH manufacturing process. The reaction mixture can be prepared by introducing a solution of copolymerization of ethylene monomer and vinyl acetate monomer into the top of a distillation column and methanol into the bottom of a distillation column, discharging a solution of the ethylene-vinyl acetate copolymer with a high boiling point from the bottom of the distillation column, and then recovering the unreacted vinyl acetate monomer and gaseous methanol together from the top of the distillation column.

[0024] In the above reaction mixture, vinyl acetate monomer and methanol may be included in a weight ratio of 1:0.1 to 0.1:1, specifically 1:0.4 to 1:1, or 1:0.5 to 1:0.8 (e.g., 63% by weight of vinyl acetate monomer and 37% by weight of methanol), but are not particularly limited thereto. In order to reuse the vinyl acetate monomer contained in the above reaction mixture for the production of EVOH, a process of separating it from methanol and purifying it to a high purity is required. However, since the vinyl acetate monomer contained in the above reaction mixture has a boiling point of about 73°C and the boiling point of methanol is about 65°C, and these two components form an azeotropic composition, it is difficult to separate them from each other by simple distillation. This mixture of vinyl acetate monomer and methanol can be separated by contacting it with water as an azeotropic agent due to differences in solubility and specific gravity.

[0025] Referring to FIG. 1, the reaction mixture and water are supplied to a monomer recovery tower (100) as a feed (1) to separate them into an upper stream (110) containing vinyl acetate monomer and a lower stream (120) containing methanol (S2).

[0026] The monomer recovery tower (100) described above corresponds to a distillation tower capable of separating vinyl acetate monomer and residual methanol by azeotropic distillation using water, and can be designed with materials, sizes, and operating methods commonly applied in the field without any particular limitations. For example, the reaction mixture supplied to the tower is heated by heat provided by a reheater connected to the bottom of the tower, and the generated steam is moved to the top of the tower and discharged, and the discharged steam can be partially or completely condensed in a condenser attached to the top of the tower. Meanwhile, a portion of the condensate can be recirculated back to the tower.

[0027] In one embodiment of the present invention, the monomer recovery tower (100) may be operated at a pressure of 0.5 to 1.5 bar, for example, 1 bar, at a temperature of 60 to 100°C, for example, 60 to 85°C, and under these conditions, the azeotropic mixture of the methanol-vinyl acetate monomer is broken by water and a new azeotropic mixture of water-vinyl acetate monomer is formed, and the methanol moves to the bottom of the recovery tower (100) by water, which has a high specific gravity and high solubility in water, and the vinyl acetate monomer moves to the top of the recovery tower (100) in the form of an azeotropic mixture with water and can be separated.

[0028] The stream (110) separated at the top of the monomer recovery tower (100) may contain 70 to 90 weight% vinyl acetate monomer, 2 to 10 weight% water, and 5 to 20 weight% unseparated MeOH based on total weight.

[0029] In addition, the stream (120) separated at the bottom of the monomer recovery tower (100) may contain 20 to 40 weight percent of methanol and 60 to 80 weight percent of water based on the total weight. Furthermore, the bottom stream (120) may contain some unseparated vinyl acetate monomer and impurities such as acetaldehyde, methyl acetate, etc.

[0031] Next, the upper stream (110) of the monomer recovery tower (100) is partially or completely condensed in a condenser connected to the top of the recovery tower and then passes through a decanter (20) (S3).

[0032] The condensation temperature of the upper stream (110) may be in the range of 35 to 45°C, for example, 38 to 42°C, and the stream condensed to the temperature range may be separated into a water layer (21) and an organic phase vinyl acetate monomer-rich layer (22) as it passes through a decanter (20).

[0033] The above decanter (20) is a device for separating immiscible fluids using gravity or centrifugal force based on density differences, such that a relatively lighter liquid can be separated into the upper part of the decanter and a relatively heavier liquid into the lower part of the decanter. The aqueous layer (21) separated in the above decanter (20) is recirculated to the monomer recovery tower (100), and the vinyl acetate monomer-rich layer (22) can be transferred to a subsequent purification tower.

[0034] The vinyl acetate monomer-rich layer (22) may contain 80 to 95 weight percent, e.g. 85 to 95 weight percent, of vinyl acetate monomer based on total weight. In addition, the vinyl acetate monomer-rich layer (22) may contain trace amounts of methanol and water in addition to vinyl acetate monomer.

[0035] Meanwhile, the stream (120) containing separated methanol at the bottom of the monomer recovery tower (100) can be supplied to the methanol separation tower (300).

[0036] The methanol separation tower (300) is a distillation tower capable of separating methanol from water by boiling and condensing the stream (120), and can be designed with materials, sizes, and operating methods commonly applied in the field, with no particular limitations.

[0037] In one embodiment of the present invention, the methanol separation tower (300) may be operated at a pressure of 0.5 to 1.5 bar, for example, 1 bar, at an atmospheric pressure of 80 to 100°C, for example, 90 to 100°C, and under these conditions, low-boiling point methanol may be separated into an upper stream (310). Subsequently, the upper stream of methanol may be partially or completely condensed in a condenser and then recovered as a discharge stream, and a portion of the condensed methanol may be fed back into the tower. Meanwhile, water, which has a higher boiling point than methanol, may be separated into a lower stream (320) of the methanol separation tower (300), and a portion may be reheated and fed back into the methanol separation tower (300), while the remainder may be recovered as process water (321).

[0038] The water recovered from the bottom of the methanol separation tower (300) can be combined with the transfer line of the water layer separated in the decanter (20) and supplied to the monomer recovery tower (100). Additionally, supplementary water can be added to the transfer stream (321) of the recovered water.

[0040] Afterwards, the vinyl acetate monomer-rich stream (22), which is the organic phase separated in the decanter (20), can be fed to a monomer purification tower (200) to obtain purified vinyl acetate monomer at the bottom (S4).

[0041] The monomer purification tower (200) described above corresponds to a distillation tower capable of separating vinyl acetate monomers with high purity by re-boiling and condensing a vinyl acetate monomer-rich stream, and can be designed with materials, sizes, and operating methods commonly applied in the field, such as the monomer recovery tower (100) described above, without any particular limitations.

[0042] In one embodiment of the present invention, the monomer purification tower (200) can be operated at a pressure of 0.5 to 1.5 bar, for example, at an atmospheric pressure of 1 bar, and at a temperature of 60 to 80°C, for example, 70 to 80°C. Under these conditions, components with a lower boiling point than vinyl acetate monomer are separated into an upper stream (210), and vinyl acetate monomer is separated into a lower stream (220) to obtain high-purity vinyl acetate monomer.

[0043] Additionally, the upper stream (210) of the monomer purification tower (200) may contain vinyl acetate monomer, methanol, and water, which may be partially or completely condensed in a condenser connected to the top of the purification tower (200) and then passed through a decanter (30) to be separated into an organic layer (31) and a water layer (32) of vinyl acetate monomer, and the water layer (32) may be supplied to the monomer recovery tower (100) and the organic layer (31) may be supplied to the purification tower (200).

[0045] FIG. 2 illustrates another embodiment of the method for purifying vinyl acetate according to the present invention, illustrating a case in which makeup water and water recovered from the bottom of a methanol separation tower (300) are supplied to a decanter (20), and said makeup water and recovered water are supplied back to a monomer recovery tower (100) via the decanter (20).

[0046] That is, in one embodiment of the present invention, unlike the conventional method, the input location of the supplementary water is changed to a decanter (20) rather than the upper reflux stream of the distillation tower, and through this, the effect of minimizing energy consumption while controlling the amount of water used to obtain high purity by separating vinyl acetate monomer from the reaction mixture of vinyl acetate monomer and methanol to an optimal level can be achieved.

[0047] In one embodiment of the present invention, the total flow rate of the supplementary water and the recovered water may be in the range of 60 to 100 weight%, specifically 60 to 80 weight%, of the flow rate of the reaction mixture supplied to the monomer recovery tower (100). When the above flow rate range is satisfied, it has the effect of minimizing energy consumption in the purification process while increasing the efficiency of separating vinyl acetate monomer from the reaction mixture with high purity.

[0048] Specifically, if the total flow rate of the supplementary water and recovered water is less than 60% by weight of the reaction mixture flow rate, it may be difficult to supply enough water for the separation of the reaction mixture, resulting in reduced separation efficiency or difficulty in the separation itself. On the other hand, if the total flow rate of the supplementary water and recovered water exceeds 100% by weight of the reaction mixture flow rate, while the separation efficiency of unreacted vinyl acetate monomer and methanol may be increased as the amount of water input increases, there is a problem of excessively increasing operating costs due to increased energy consumption.

[0049] As described above, in the present invention, the purity of unreacted vinyl acetate monomers generated during the EVOH manufacturing process is increased by applying a monomer purification tower, and the energy consumption of the entire process can be minimized by supplying an optimal amount of makeup water and water recovered from the tower through a decanter.

[0051] The present invention will be described in more detail below through examples. However, the following examples are intended to illustrate the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, and the scope of the present invention is not limited only to these examples.

[0052] Example 1: Method for purifying vinyl acetate monomer using a monomer purification tower

[0053] According to the process shown in Fig. 1, vinyl acetate monomer (VAM) was purified from a reaction mixture containing vinyl acetate monomer and methanol.

[0054] First, a reaction mixture containing vinyl acetate monomer (63 kg / hr) and methanol (37 kg / hr) was supplied to a monomer recovery tower (100) along with water (100 kg / hr). At this time, the amount of water supplied included water recovered from another tower in a subsequent step and supplementary water.

[0055] The above monomer recovery tower (100) was operated under conditions of atmospheric pressure (1 bar) and 75°C to separate into an upper stream (110) containing vinyl acetate monomer and a lower stream (120) containing methanol.

[0056] The vinyl acetate monomer-containing upper stream was cooled to 40°C in a condenser connected to the top of the monomer recovery tower (100), and then passed through a decanter (20) to separate the liquid into a water layer (21) and an organic phase vinyl acetate monomer-rich layer (22).

[0057] Meanwhile, the methanol-containing stream (120) separated from the bottom of the monomer recovery tower (100) was supplied to the methanol separation tower (300), and the methanol separation tower (300) was operated under conditions of atmospheric pressure (1 bar) and 100°C to separate the upper stream (310) of methanol and the lower stream (320) of water. At this time, the water recovered from the bottom of the methanol separation tower (300) was combined with the moving stream (321) of the water layer separated in the decanter (20) and supplied back to the monomer recovery tower (100), and additionally, supplementary water was supplied to the moving stream (321) of the recovered water.

[0058] The organic phase (vinyl acetate monomer-rich stream) separated in the above decanter (20) is fed to a monomer purification tower (200) and operated under conditions of atmospheric pressure (1 bar) and 73°C to separate it into an upper stream (210) of components with a lower boiling point than vinyl acetate monomer and a lower stream (220) of vinyl acetate monomer.

[0060] Comparative Examples 1 to 4: Method for purifying vinyl acetate monomer without applying a monomer purification tower

[0061] As shown in FIG. 3, vinyl acetate monomer was separated from the reaction mixture by performing the same process as in Example 1, except that the amount of water supplied to the monomer recovery tower (100) was changed without using the monomer purification tower (200).

[0063] Table 1 below shows the amount of water input and energy consumption applied to Example 1 and Comparative Examples 1 to 4.

[0064]

[0065] As can be seen in Table 1 above, Example 1 obtained vinyl acetate monomer with higher purity compared to Comparative Example 1, which had the same amount of water input, by additionally applying a monomer purification tower. In the case of Comparative Example 1, approximately 10% higher energy consumption is required to obtain the same purity as Example 1.

[0066] Meanwhile, Comparative Examples 2 to 4 improved the purity of the finally separated vinyl acetate monomer by increasing the amount of water input under conditions without a monomer purification tower, but energy consumption increased as the amount of water input increased. Specifically, in the case of Comparative Examples 3 and 4, which obtained vinyl acetate monomer of the same purity as Example 1, it can be confirmed that energy consumption increased significantly as the amount of water input increased two to three times compared to Example 1.

[0068] Example 2: Method for purifying vinyl acetate monomer by changing the water input position to a decanter

[0069] As shown in FIG. 2, vinyl acetate monomer was obtained by performing the same process as in Example 1, except that makeup water and water recovered from the bottom of the methanol separation tower (300) were supplied to the decanter (20), and said makeup water and recovered water were supplied back to the monomer recovery tower (100) via the decanter (20).

[0070] Table 2 below shows the energy consumption of Example 1 and Example 2.

[0071]

[0072] As can be seen in Table 2 above, in Example 2, the purity of the vinyl acetate monomer was improved compared to Example 1 by changing the input position of the water recovered from the methanol separation column and the replenishment water to a decanter, and the energy consumption in the monomer purification column was significantly reduced.

[0074] Example 3: Method for purifying vinyl acetate monomer according to changes in water input amount

[0075] In Example 2, the amount of water supplied to the monomer recovery tower (100) through the decanter (20) (the sum of the water recovered from the methanol separation tower (300) and the supplementary water) was varied from 50 to 150 kg / hr based on the flow rate (100 kg / hr) of the reaction mixture, and the energy consumed throughout the purification process was measured. The results are shown in FIG. 4.

[0076] From FIG. 4, it can be seen that when the total flow rate of the supplementary water supplied to the decanter (20) and the recovered water is in the range of 0.6 to 1, more specifically 0.6 to 0.8, relative to the flow rate (100 kg / hr) of the reaction mixture supplied to the monomer recovery tower, the total energy consumption during the purification process is low. In particular, when the total flow rate of water relative to the reaction mixture (100 kg / hr) is 70 kg / hr, the total energy consumption is minimized.

[0077] This is a result of the increase in total energy consumption caused by a rise in the temperature of the stream moving to the bottom of the tower as the water input increases. In other words, as the water input increases, the temperature difference between the top and bottom of the monomer recovery tower widens, leading to energy consumption due to the increased load on the reheater required to raise the temperature at the bottom of the tower. Explanation of the symbols

[0078] 1: Feed stream 20, 30: Decanter 21, 22, 31, 32: Layers separated in the decanter 100: Monomer recovery tower 110: Upper stream separated in the monomer recovery tower 120: Downstream separated in the monomer recovery tower 200: Monomer purification tower 210: Upper stream separated from the monomer purification tower 220: Downstream separated from the monomer purification tower 300: Methanol separation column 310: Top stream separated in the methanol separation tower 320, 321: Downstream separated in the methanol separation tower

Claims

Claim 1 (S1) a step of preparing a reaction mixture comprising vinyl acetate monomer (VAM) and methanol; (S2) a step of supplying the reaction mixture and water to a monomer recovery tower to separate them into an upper stream containing vinyl acetate monomer and a lower stream containing methanol; (S3) a step of condensing the upper stream containing vinyl acetate monomer and then separating it in a decanter into an organic phase, a vinyl acetate monomer-rich layer, and a water layer; and (S4) a step of supplying the organic phase to a monomer purification tower to obtain purified vinyl acetate from the bottom, comprising a method for purifying vinyl acetate. Claim 2 A method for purifying vinyl acetate according to claim 1, wherein the reaction mixture comprises vinyl acetate monomer and methanol in a weight ratio of 1:0.1 to 0.1:

1. Claim 3 A method for purifying vinyl acetate according to claim 1, wherein the lower stream of the monomer recovery tower is supplied to a methanol separation tower to separate it into an upper stream of methanol and a lower stream of water, and water is recovered from the bottom of the methanol separation tower and supplied to a decanter. Claim 4 A method for purifying vinyl acetate according to claim 3, wherein makeup water and recovered water are supplied to the decanter, and the total flow rate of the makeup water and recovered water is 60 to 100 weight percent of the flow rate of the reaction mixture supplied to the monomer recovery tower. Claim 5 A method for purifying vinyl acetate according to claim 4, wherein the total flow rate of the supplementary water and recovered water is 60 to 80 weight percent of the flow rate of the reaction mixture supplied to the monomer recovery tower. Claim 6 A method for purifying vinyl acetate according to claim 4, wherein the makeup water and the recovered water are mixed at the front of the decanter and supplied to one or more of the recovery tower, separation tower, and purification tower. Claim 7 A method for purifying vinyl acetate according to claim 1, wherein the upper stream of the monomer purification tower is fed back to the monomer recovery tower. Claim 8 In claim 1, the monomer recovery tower, methanol separation tower, and monomer purification tower are a method for purifying vinyl acetate operated at a pressure of 0.5 to 1.5 bar.

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