KR20240033400A - Method for purifying vinyl acetate - Google Patents

Abstract

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

Description

Method for purifying vinyl acetate {METHOD FOR PURIFYING VINYL ACETATE}

The present invention relates to a method for purifying vinyl acetate, and more specifically, to a method for recovering unreacted vinyl acetate monomers generated in the production process of ethylene vinyl alcohol with high purity.

Ethylene vinyl alcohol (EVOH) has excellent properties such as gas barrier properties, chemical resistance, and mechanical strength, and is widely used as a coating material to protect metal, paper, wood, etc., and as a packaging material for food.

Such EVOH can be generally produced by hydrolyzing polyethylene vinyl acetate obtained by copolymerization of ethylene monomer and vinyl acetate monomer (VAM) in an alcohol-based solvent such as methanol. In this copolymerization, a significant amount of the monomers remain unreacted and must be separated in the EVOH reactor along with the solvent used.

Generally, in the EVOH production process, a distillation method using gaseous methanol is used to recover unreacted vinyl acetate monomer from the copolymerization solution. For example, in Domestic Patent No. 10-0508071, a post-copolymerization solution is introduced into the upper part of the distillation tower and gaseous methanol is introduced into the lower part, a solution of ethylene-vinyl acetate copolymer with a high boiling point is recovered from the lower part of the distillation tower, and the upper part of the distillation tower is recovered. A process for recovering unreacted vinyl acetate monomer and gaseous methanol together is disclosed.

Since the vinyl acetate monomer recovered from the top of the distillation column contains a large amount of methanol, a process of separating it is necessary. The vinyl acetate monomer (b.p. about 73°C) and methanol (b.p. about 65°C) form an azeotropic composition, and the separation of the vinyl acetate monomer from the azeotropic composition occurs between the vinyl acetate monomer and water by adding water. It is performed using a distillation method using liquid-liquid phase equilibrium. 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 azeotrope of vinyl acetate monomer-methanol is broken due to the water, resulting in a large number of vinyl acetate monomers (VAM) at the top of the distillation column. -rich) stream is discharged, and a mixed stream of methanol and water is discharged from the bottom.

At this time, if the amount of water input to the distillation column is large, vinyl acetate monomer and methanol can be separated with high purity, but there is a problem that the energy consumption of the column increases. On the other hand, when the amount of water input is small, there is a limit to recovering vinyl acetate monomer with high purity.

KR 10-0508071 B

The present invention is intended to solve the problems mentioned in the technology behind the invention, minimizing energy consumption in the process of separating the azeotropic mixture of unreacted vinyl acetate monomer (VAM) and methanol generated in the production of ethylene vinyl alcohol. The aim is to provide a purification method that can recover vinyl acetate monomer with high purity.

According to one aspect of the present invention for solving the above problem, (S1) preparing a reaction mixture containing vinyl acetate monomer (VAM) and methanol, (S2) combining the reaction mixture and water with the monomer. Supplying to a recovery tower and separating into an upper stream containing vinyl acetate monomer and a lower stream containing methanol, (S3) condensing the upper stream containing vinyl acetate monomer to produce a vinyl acetate monomer-rich organic phase in a decanter. A method for purifying vinyl acetate is provided, comprising the steps of separating the organic phase into an aqueous layer and a water layer, and (S4) feeding the organic phase to a monomer purification tower to obtain purified vinyl acetate from the bottom.

Additionally, the bottom stream of the monomer recovery tower is supplied to the 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 make-up water. there is.

The total flow rate of the make-up water and recovered water may be adjusted to 60 to 100% by weight, specifically 60 to 80% by weight, of the flow rate of the reaction mixture supplied to the monomer recovery tower.

According to the present invention, when recovering unreacted vinyl acetate monomer generated in the production process of ethylene vinyl alcohol (EVOH), purity is increased by applying a monomer purification tower, and makeup water is supplied through a decanter. By supplying the water recovered from the tower in an optimal amount, energy consumption throughout the process can be minimized.

Figures 1 and 2 schematically show the purification process of vinyl acetate monomer (VAM) according to an embodiment of the present invention (Examples 1 and 2), respectively.
Figure 3 schematically shows the vinyl acetate monomer purification process applied in Comparative Examples 1 to 4.
Figure 4 is a graph showing energy consumption when the amount of water input is changed according to Example 3.

Terms or words used in the description and claims of the present invention should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately use the concepts of terms to explain his invention in the best way. Based on the principle of definability, it must be interpreted with meaning and concept consistent with the technical idea of the present invention.

As used herein, the meaning of 'comprising' or 'containing' specifies a specific characteristic, area, integer, step, operation, element, or ingredient, and the addition of another specific characteristic, area, integer, step, operation, element, or ingredient. It is not excluded.

As used herein, the term 'top' refers to a point of 0 to 5% height from the top of the device, unless otherwise specified, and may specifically mean the top (top). Additionally, the term 'bottom' refers to a point at a height of 95 to 100% from the top of the device, and may specifically mean the bottom (bottom of the tower).

The term 'stream' used herein may refer to the flow of fluid within a process, or may also refer to the fluid itself flowing within a pipe. Specifically, the stream may refer to both the fluid itself and the flow of the fluid flowing within the pipes connecting each device. Additionally, the fluid may include any one or more of gas, liquid, and solid.

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

Hereinafter, the purification method of the present invention will be described in detail with reference to the attached drawings.

1 and 2 schematically show a method for purifying vinyl acetate monomer according to an embodiment of the present invention. The purification method of the present invention includes a monomer recovery tower (100), a decanter (20, 30), and a monomer purification tower (200). ) and a methanol separation tower (300).

In the method for purifying vinyl acetate monomer according to an embodiment of the present invention, a reaction mixture containing vinyl acetate monomer (VAM) and methanol is first prepared (S1).

The reaction mixture of vinyl acetate monomer and methanol is an azeotropic mixture recovered in the EVOH production process. In EVOH production, the reaction mixture is a copolymerization solution of ethylene monomer and vinyl acetate monomer and introduced into the top of the distillation column, and methanol is added to the bottom of the distillation column. By introducing a solution of ethylene-vinyl acetate copolymer with a high boiling point from the bottom of the distillation tower, unreacted vinyl acetate monomer and gaseous methanol can be recovered together from the top of the distillation tower.

In the reaction mixture, vinyl acetate monomer and methanol are present 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 vinyl acetate monomer and methanol). 37% by weight), but is not particularly limited thereto. In order to reuse the vinyl acetate monomer contained in the reaction mixture again for the production of EVOH, it is necessary to separate it from methanol and purify it to high purity. However, the boiling point of the vinyl acetate monomer contained in the reaction mixture is about 73°C, and the boiling point of methanol is about 65°C. Since these two components form an azeotropic composition, it is difficult to separate them from each other by simple distillation. difficult. This mixture of vinyl acetate monomer/methanol can be separated by differences in solubility and specific gravity by contacting it with water as an azeotrope.

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

The monomer recovery tower 100 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, and can be designed with special There are no limits. For example, the reaction mixture supplied to the tower is heated by heat provided from a reboiler connected to the bottom of the tower, the generated vapor moves to the top of the tower and is discharged, and the discharged vapor is partially discharged from a condenser attached to the top of the tower. Or it can be completely condensed. Meanwhile, part of the condensate can be recycled back to the tower.

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

The stream 110 separated at the top of the monomer recovery tower 100 will contain 70 to 90% by weight of vinyl acetate monomer, 2 to 10% by weight of water, and 5 to 20% by weight of MeOH that was not separated, based on the total weight. You can.

Additionally, the stream 120 separated from the bottom of the monomer recovery tower 100 may contain 20 to 40% by weight of methanol and 60 to 80% by weight of water based on the total weight. In addition, the bottom stream 120 may contain some impurities such as unseparated vinyl acetate monomer, acetalhehyde, and methyl acetate.

Subsequently, 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 the decanter 20 (S3).

The condensation temperature of the upper stream 110 may be in the range of 35 to 45 ℃, for example, 38 to 42 ℃, and the stream condensed in the above temperature range passes through the decanter 20 and passes through the aqueous layer 21 of water and the vinyl organic phase. Liquid-liquid separation can be achieved with an acetate monomer-rich layer (22).

The decanter 20 is a device for separating immiscible fluids using gravity or centrifugal force due to density differences. Relatively light liquids can be separated into the upper part of the decanter, and relatively heavy liquids can be separated into the lower part of the decanter. there is. The aqueous layer 21 separated in the decanter 20 is re-supplied to the monomer recovery tower 100, and the vinyl acetate monomer-rich layer 22 can be moved to the subsequent purification tower.

The vinyl acetate monomer-rich layer 22 may include 80 to 95% by weight of vinyl acetate monomer, for example, 85 to 95% by weight, based on the total weight. Additionally, the vinyl acetate monomer-rich layer 22 may contain trace amounts of methanol and water in addition to vinyl acetate monomer.

Meanwhile, the stream 120 containing methanol separated at the bottom of the monomer recovery tower 100 may be supplied to the methanol separation tower 300.

The methanol separation tower 300 corresponds to 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, and can be designed with special materials, sizes, and operation methods. There are no limits.

In one embodiment of the present invention, the methanol separation tower 300 may be operated at a temperature of 80 to 100°C, for example, 90 to 100°C, at a pressure of 0.5 to 1.5 bar, for example, 1 bar, and under these conditions, the low boiling point The methanol can be separated as an overhead stream (310). Thereafter, the top stream of methanol can be partially or completely condensed in a condenser and then recovered as an exhaust stream, and a portion of the condensed methanol can be fed back into the tower. Meanwhile, water with a higher boiling point than methanol can be separated into the lower stream 320 of the methanol separation tower 300, and then some of it is reheated and re-supplied into the methanol separation tower 300, and the remainder is process water 321. It can be recovered.

The water recovered from the bottom of the methanol separation tower (300) may be combined with the moving line of the water layer separated in the decanter (20) and supplied to the monomer recovery tower (100). Make-up water may also be added to the recovered water moving stream 321.

Thereafter, the vinyl acetate monomer-rich stream 22, which is the organic phase separated in the decanter 20, can be supplied to the monomer purification tower 200 to obtain purified vinyl acetate monomer at the bottom (S4).

The monomer purification tower 200 corresponds to a distillation tower capable of separating vinyl acetate monomer with high purity by boiling and condensing the vinyl acetate monomer-rich stream, and is commonly used in the field like the monomer recovery tower 100 described above. It can be designed with the applied material, size, and operation method, and there are no special restrictions.

In one embodiment of the present invention, the monomer purification tower 200 may be operated at a temperature of 60 to 80°C, for example, 70 to 80°C, at a pressure of 0.5 to 1.5 bar, for example, 1 bar, and under these conditions, vinyl Components with a lower boiling point than the acetate monomer are separated into the upper stream 210, and the vinyl acetate monomer is separated into the lower stream 220 to obtain high purity vinyl acetate monomer.

Additionally, the top stream 210 of the monomer purification tower 200 may include vinyl acetate monomer, methanol, and water, and is partially or completely condensed in a condenser connected to the top of the purification tower 200. Passing through the decanter 30, the vinyl acetate monomer can be separated into an organic layer 31 and an aqueous layer 32, where the aqueous layer 32 is transferred to the monomer recovery tower 100, and the organic layer 31 is transferred to the purification tower 200. ) can be resupplied.

Figure 2 shows another embodiment of the method for purifying vinyl acetate according to the present invention, in which makeup water and water recovered from the bottom of the methanol separation tower 300 are supplied to the decanter 20, and the makeup water is supplied to the decanter 20. The example illustrates the case where water and recovered water are supplied back to the monomer recovery tower (100) through the decanter (20).

That is, in one embodiment of the present invention, unlike the conventional method, the input location of the make-up water was changed to the decanter 20 rather than the upper reflux stream of the distillation tower, and through this, vinyl acetate monomer was extracted from the reaction mixture of vinyl acetate monomer and methanol. The effect of minimizing energy consumption can be realized while controlling the amount of water consumed to obtain high purity through separation to an optimal level.

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

Specifically, if the total flow rate of the make-up water and recovered water is less than 60% by weight of the reaction mixture flow rate, the water consumed for separation of the reaction mixture may not be sufficiently supplied, and separation efficiency may be reduced or separation itself may be difficult. On the other hand, when the total flow rate of the make-up water and recovered water exceeds 100% by weight of the reaction mixture flow rate, the separation efficiency of unreacted vinyl acetate monomer and methanol can be increased as the water input amount increases, but energy consumption increases. There is a problem of excessive increase in operating costs.

As described above, in the present invention, purity is increased by applying a monomer purification tower when recovering unreacted vinyl acetate monomer generated in the EVOH manufacturing process, and makeup water and water recovered from the tower are purified through a decanter. By supplying the optimal amount, energy consumption throughout the process can be minimized.

Hereinafter, the present invention will be described in more detail 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 to these alone.

Example 1: Method for purifying vinyl acetate monomer using monomer purification tower

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

First, a reaction mixture containing vinyl acetate monomer (63 kg/hr) and methanol (37 kg/hr) was supplied to the monomer recovery tower (100) along with water (100 kg/hr). At this time, the input amount of water includes water recovered from other towers and make-up water in a later step.

The monomer recovery tower 100 was operated at normal pressure (1 bar) and 75° C. to separate an upper stream 110 containing vinyl acetate monomer and a lower stream 120 containing methanol.

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

Meanwhile, the methanol-containing stream 120 separated from the bottom of the monomer recovery tower 100 is supplied to the methanol separation tower 300, and the methanol separation tower 300 is operated under the conditions of normal pressure (1 bar) and 100°C. It was operated and separated into an upper stream of methanol (310) and a lower stream of water (320). At this time, the water recovered from the lower part 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 the recovered water was further transferred. Make-up water was supplied to stream 321.

The organic phase (vinyl acetate monomer-rich stream) separated in the decanter 20 is supplied to the monomer purification tower 200, and operated under conditions of normal pressure (1 bar) and 73° C. to produce an upper stream of components with a lower boiling point than the vinyl acetate monomer ( 210) and a bottom stream of vinyl acetate monomer (220).

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

As shown in FIG. 3, the same process as Example 1 was performed except for changing the amount of water supplied to the monomer recovery tower 100 without using the monomer purification tower 200, to obtain water from the reaction mixture. Vinyl acetate monomer was isolated.

Table 1 below shows the water input and energy consumption applied in Example 1 and Comparative Examples 1 to 4.

As can be seen in Table 1, Example 1 was obtained by separating vinyl acetate monomer of higher purity than Comparative Example 1 with the same water input amount by additionally applying a monomer purification tower. In the case of Comparative Example 1, a high energy usage of about 10% is required to obtain the same purity as Example 1.

Meanwhile, Comparative Examples 2 to 4 improved the purity of the finally separated vinyl acetate monomer by increasing the water input amount in the absence of a monomer purification tower, but energy consumption increased as the water input amount increased. Specifically, in the case of Comparative Examples 3 and 4, in which vinyl acetate monomer of the same purity as Example 1 was obtained, it can be seen that the energy consumption increased significantly as the water input amount was increased by 2 to 3 times compared to Example 1.

Example 2: Method for purifying vinyl acetate monomer by changing the water input location to a decanter

As shown in FIG. 2, make-up water and water recovered from the bottom of the methanol separation tower 300 are supplied to the decanter 20, and the make-up water and recovered water pass through the decanter 20. Vinyl acetate monomer was obtained by performing the same process as in Example 1, except that it was supplied to the monomer recovery tower (100) again.

Table 2 below shows the energy consumption of Examples 1 and 2.

As can be seen in Table 2, in Example 2, the purity of the vinyl acetate monomer was improved compared to Example 1 by changing the input location of the water recovered from the methanol separation tower and the make-up water to a decanter, and the purity of the vinyl acetate monomer was improved compared to Example 1, and monomer purification Energy use in the tower has been significantly reduced.

Example 3: Method for purifying vinyl acetate monomer according to change in water input amount

In Example 2, the amount of water supplied to the monomer recovery tower 100 through the decanter 20 (the combined amount of water recovered from the methanol separation tower 300 and make-up water) was calculated based on the flow rate of the reaction mixture (100 kg/hr). While varying from 50 to 150 kg/hr, the amount of energy consumed throughout the purification process was measured. The results are shown in Figure 4.

From Figure 4, the total flow rate of the make-up water and recovered water supplied to the decanter 20 is in the range of 0.6 to 1, more specifically 0.6 to 0.8, compared to the flow rate of the reaction mixture (100 kg/hr) supplied to the monomer recovery tower. When , it can be seen that the total energy usage during the purification process is low. In particular, when the total flow rate of water based on the reaction mixture (100 kg/hr) was 70 kg/hr, the total energy consumption was minimal.

This is the result of an increase in the temperature of the stream moving to the bottom of the tower as the water input increases, resulting in an increase in total energy usage. In other words, as the amount of water input increases, the temperature difference between the top and bottom of the monomer recovery tower increases, and energy consumption is accompanied by an increase in the load of the reboiler to raise the temperature of the bottom of the tower.

1: Feed Stream
20, 30: Decanter
21, 22, 31, 32: Separated layers in decanter
100: Monomer recovery tower
110: Top stream separated from monomer recovery tower
120: Bottom stream separated from monomer recovery tower
200: Monomer purification tower
210: Top stream separated from monomer purification tower
220: Bottom stream separated from monomer purification tower
300: Methanol separation tower
310: Top stream separated in methanol separation tower
320, 321: Bottom stream separated in methanol separation tower

Claims (8)

(S1) preparing a reaction mixture containing 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 the vinyl acetate monomer and then separating it into a vinyl acetate monomer-rich layer as an organic phase and an aqueous layer of water in a decanter, and
(S4) A method for purifying vinyl acetate, comprising the step of supplying the organic phase to a monomer purification tower to obtain purified vinyl acetate from the bottom. According to paragraph 1,
The reaction mixture includes vinyl acetate monomer and methanol in a weight ratio of 1:0.1 to 0.1:1. According to paragraph 1,
The bottom 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,
A method for purifying vinyl acetate in which water is recovered from the bottom of the methanol separation tower and supplied to a decanter. According to paragraph 3,
Makeup water and the recovered water are supplied to the decanter,
A method for purifying vinyl acetate, wherein the total flow rate of the makeup water and recovered water is 60 to 100% by weight of the flow rate of the reaction mixture supplied to the monomer recovery tower. According to paragraph 4,
A method for purifying vinyl acetate, wherein the total flow rate of the makeup water and recovered water is 60 to 80% by weight of the flow rate of the reaction mixture supplied to the monomer recovery tower. According to paragraph 4,
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. According to paragraph 1,
A method for purifying vinyl acetate, wherein the upper stream of the monomer purification tower is fed back to the monomer recovery tower. According to paragraph 1,
A method for purifying vinyl acetate in which the monomer recovery tower, methanol separation tower, and monomer purification tower are operated at a pressure of 0.5 to 1.5 bar.