CN111100323A

CN111100323A - Ethylene recovery method in EVOH production process

Info

Publication number: CN111100323A
Application number: CN201811256685.0A
Authority: CN
Inventors: 汪清泉; 窦玉芹; 胡腊梅; 何灵芝; 王文
Original assignee: Chongqing Chuanwei Technology Co ltd; China Petroleum and Chemical Corp; Sinopec Chongqing Chuanwei Chemical Co Ltd
Current assignee: Chongqing Chuanwei Technology Co ltd; China Petroleum and Chemical Corp; Sinopec Chongqing Chuanwei Chemical Co Ltd
Priority date: 2018-10-26
Filing date: 2018-10-26
Publication date: 2020-05-05

Abstract

The invention belongs to the technical field of separation realized by using a rectification method, and particularly relates to an ethylene recovery method in an EVOH (ethylene-vinyl alcohol) production process. The method can obviously reduce the purge amount of the ethylene gas. The method can obviously improve the recovery rate of the ethylene and reduce the production cost.

Description

Ethylene recovery method in EVOH production process

Technical Field

The invention belongs to the technical field of separation realized by using a rectification method, and particularly relates to an ethylene recovery method in an EVOH (ethylene-vinyl alcohol) production process.

Background

Ethylene-vinyl alcohol copolymer (EVOH for short), especially ethylene-vinyl alcohol copolymer with 20 mol% -50 mol% of ethylene content, has excellent gas barrier property which is about 10,000 times of common polyethylene, and has transparency, processability, solvent resistance and antistatic property, so that the ethylene-vinyl alcohol copolymer can be widely applied to the fields of packaging materials, automobile fuel tanks, oxygen-resistant floor heating pipes, textile materials, medical materials and the like. The ethylene-vinyl alcohol copolymer is obtained by alcoholysis of an ethylene-vinyl acetate copolymer, the high gas barrier property of the ethylene-vinyl alcohol copolymer is directly related to the alcoholysis degree of the ethylene-vinyl alcohol copolymer, the higher the alcoholysis degree is, the better the gas barrier property is under the same ethylene content condition, and in order to ensure the sufficient gas barrier property, the alcoholysis degree of EVOH is usually more than 99%.

EVOH is prepared from ethylene and vinyl acetate by emulsion, solution or suspension polymerization and saponification. In the solution polymerization process, an alcohol having not more than 4 carbons is usually used as a solvent, and methanol is preferably used. After the polymerization reaction is finished, ethylene, methanol and unreacted vinyl acetate need to be recycled, the polymerization reaction pressure is usually 2.0-6.0MPa, and the polymer enters a flash evaporation system after the reaction is finished. The ethylene is removed in a gas phase form in the flash evaporation process, the ethylene inevitably carries a large amount of vinyl acetate and methanol, if the ethylene directly enters an ethylene compressor, the vinyl acetate is a polymerization monomer, the vinyl acetate and the methanol can form a liquid phase to be separated out in the compression process, and the compression process is a temperature rise process, so that the self polymerization of the vinyl acetate influences the normal operation of the ethylene compressor, and therefore, the vinyl acetate in the ethylene must be effectively removed before the ethylene enters the compressor.

In the actual production process, due to the long-term recycling use of ethylene, part of gas impurities, mainly the accumulation of inert gases such as nitrogen, ethane and the like, are inevitably brought in. Therefore, in order to ensure long-term stable operation of the production, it is necessary to discharge a part of the gas as purge gas of the production. Venting of the purge gas can increase the environmental pressure and operating costs of the production operation.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for recovering ethylene in EVOH production process, which can effectively recover ethylene in purge gas.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the ethylene recovery method in the EVOH production process, the solvent of the solution polymerization reaction comprises an alcohol solvent or vinyl acetate.

The inventors have surprisingly found that the solvent of the solution polymerization reaction, including an alcoholic solvent or vinyl acetate, allows for efficient recovery of ethylene from the purge gas.

In order to further improve the recovery rate of ethylene, the alcohol solvent comprises alcohols with 1-4 carbon atoms, including methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol.

In order to further improve the recovery rate of ethylene, the alcohol solvent is methanol.

To further increase ethylene recovery, the second solvent comprises dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, or vinyl acetate.

In order to further improve the ethylene recovery rate, the second solvent is vinyl acetate.

In order to further improve the recovery rate of ethylene, the flow rate of the solvent for the solution polymerization reaction is 100-500 kg/h.

In order to further improve the recovery rate of ethylene, the flow ratio of discharged ethylene purge gas to raw material ethylene in the production process is 1:2-1: 30.

The invention has the beneficial effects that:

the method can obviously improve the recovery rate of the ethylene, and the recovery rate of the ethylene can reach 30.5 to 90.2 percent.

The method of the invention recovers the ethylene and reduces the production cost.

Drawings

Fig. 1 is a schematic structural view of an apparatus used in example 1, in which 1 is a feed pipe, 3 is a discharge pipe, 2 is a flash pump, 4 is a shell-and-tube condenser, 5 is a gas-liquid separator, 6 is a centrifugal compressor, 7 is an ethylene inlet line, 8 is a circulating ethylene line, 9 is an ethylene purge gas line, 10 is an

absorption tower

10, 11 is an ethylene

purge gas line

11, 12 is a solvent line, and 13 is an absorbent line;

fig. 2 is a schematic structural view of an apparatus used in comparative example 1, in which 1 is a feed pipe, 3 is a discharge pipe, 2 is a flash pump, 4 is a shell and tube condenser, 5 is a gas-liquid separator, 6 is a centrifugal compressor, 7 is an ethylene inlet line, 8 is a circulating ethylene line, and 9 is an ethylene purge line.

Detailed Description

The examples are given for the purpose of better illustration of the invention and are not intended to be exhaustive

The invention is limited only to the examples presented. Therefore, those skilled in the art should make insubstantial modifications and adaptations to the embodiments of the present invention in light of the above teachings and remain within the scope of the invention.

The following measurements of ethylene content and nitrogen content were carried out by analysis with a chromatograph.

Example 1

The device comprises a flash pump 2, a tube-type condenser 4, a gas-liquid separator 5 and a centrifugal compressor, wherein the flash pump 2 is simultaneously connected with a feeding pipeline 1 and a discharging pipeline 3, the tube-type condenser 4 is communicated with the flash pump 2, the tube-type condenser 4 is communicated with the gas-liquid separator 5, the gas-liquid separator 5 is also respectively communicated with the flash tank 2 and the centrifugal compressor 6, and the gas-liquid separator 5 is also connected with an ethylene inlet pipeline 7; the centrifugal compressor 6 is also connected with a circulating ethylene pipeline 8 and an ethylene purge gas pipeline 9, the ethylene purge gas pipeline 9 is communicated with an absorption tower 10, and the absorption tower 10 is provided with an ethylene purge gas pipeline 11, a solvent pipeline 12 and an absorbent pipeline 13;

the specific method comprises the following steps:

the method comprises the steps of enabling materials in a polymerization kettle of an EVOH production device to enter a flash tank 2 through a feeding pipeline 1, reducing pressure in the flash tank 2 to carry out flash evaporation, enabling flash evaporation pressure to be 0.4MPa, condensing the materials to 10 ℃ through a tubular condenser 4, enabling the materials to enter a gas-liquid separator 5 to be mixed with fresh ethylene entering through an ethylene inlet pipeline 7, enabling the mixed gas alkene to enter a centrifugal compressor 6 to carry out ethylene compression, enabling the compressed pressure to be 5.0MPa and the compressed flow to be 800kg/h, enabling the flow of ethylene to enter an absorption tower 10 to carry out ethylene absorption by controlling the flow of an ethylene purge gas pipeline 9 to be 20kg/h, enabling an absorbent adopted by an absorbent pipeline 13 to be methanol and enabling the absorbent flow to be 300kg/h, discharging the absorbed ethylene gas from a No. 11 pipeline, and directly adding a solvent coming out of a solvent pipeline 12 into the polymerization kettle.

The ethylene content and the nitrogen content of the ethylene gas discharged from the ethylene purge line 9 and the line 11 were measured, and the results are shown in Table 1, and the ethylene recovery rate was calculated in accordance with the method of (ethylene amount in line 9-ethylene amount in line 11)/ethylene amount in line 9 x 100%.

Examples 2 to 7

Examples 2 to 7 were conducted in the same manner as in example 1 except that the parameters shown in Table 1 were set, and the ethylene content and the nitrogen content in the ethylene gas discharged from the ethylene purge line 9 and the ethylene gas discharged from the line No. 11 were measured, and the results were shown in Table 1, and the ethylene recovery rate was calculated according to the formulas, which were conducted in the same manner as in example 1.

TABLE 1 Performance test

Remarking: above- -indicates no detection.

Comparative example 1

The device comprises a flash pump 2, a tube-type condenser 4, a gas-liquid separator 5 and a centrifugal compressor, wherein the flash pump 2 is simultaneously connected with a feeding pipeline 1 and a discharging pipeline 3, the tube-type condenser 4 is communicated with the flash pump 2, the tube-type condenser 4 is communicated with the gas-liquid separator 5, the gas-liquid separator 5 is also respectively communicated with the flash tank 2 and the centrifugal compressor 6, and the gas-liquid separator 5 is also connected with an ethylene inlet pipeline 7; the centrifugal compressor 6 is also connected with a circulating ethylene pipeline 8 and an ethylene purge gas pipeline 9;

the specific method comprises the following steps:

the materials in a polymerization kettle of an EVOH production device enter a flash tank 2 through a feeding pipeline 1, the materials are decompressed in the flash tank 2 for flash evaporation, the flash evaporation pressure is 0.4MPa, the materials are condensed to 10 ℃ through a tubular condenser 4 and then enter a gas-liquid separator 5 to be mixed with fresh ethylene entering through an ethylene inlet pipeline 7, the mixed gas olefin enters a centrifugal compressor 6 for ethylene compression, the compressed pressure is 5.0MPa, the compressed flow is 800kg/h, and the ethylene gas is discharged from an ethylene purge gas pipeline 9.

The ethylene content and the nitrogen content in the ethylene gas discharged from the ethylene purge line 9 were measured, and the results are shown in table 1, and the ethylene recovery rate was calculated according to the formula; the detection method was the same as in example 1.

As can be seen from table 1, the ethylene content in the ethylene purge gas treated in examples 1 to 7 was significantly reduced and the ethylene recovery rate was significantly improved, as compared to comparative example 1.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

The method for recovering ethylene in the EVOH production process is characterized by comprising the following steps: the solvent for ethylene washing includes an alcohol solvent or a second solvent.
2. The method for recovering ethylene in the production of EVOH according to claim 1, wherein the alcohol solvent comprises alcohols having 1-4 carbon atoms, including methanol, ethanol, propanol, ethylene glycol, n-butanol and t-butanol.
3. The method for recovering ethylene in the production of EVOH according to claim 2, wherein the alcohol solvent is methanol.
4. The method for recovering ethylene in the production of EVOH as recited in claim 1, 2 or 3, wherein the second solvent includes dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone or vinyl acetate.
5. The method for recovering ethylene in the production of EVOH according to claim 4, wherein the second solvent is vinyl acetate.
6. The method for recovering ethylene in the production of EVOH as recited in claim 1, 2, 3, 4 or 5, wherein the flow rate of the washing solvent is 100-500 kg/h.
7. The method for recovering ethylene in the production of EVOH according to claim 1, 2, 3, 4, 5 or 6, wherein the flow ratio of discharged purge gas of ethylene to raw material ethylene in the production process is 1:2 to 1: 30.