Method for recovering ethylene in preparation process of ethylene-vinyl alcohol copolymer and ethylene-vinyl alcohol copolymer

Abstract

The invention relates to the technical field of ethylene recovery, and discloses a method for recovering ethylene in an ethylene-vinyl alcohol copolymer preparation process and an ethylene-vinyl alcohol copolymer. The method comprises the following steps: sequentially removing monomers and / or polymers, oxygen, carbon monoxide, water and carbon dioxide from a recycled ethylene mixture in the preparation process of the ethylene-vinyl alcohol copolymer to obtain the ethylene-vinyl alcohol copolymer and recycled ethylene. By adopting the method disclosed by the invention, pure recovered ethylene can be obtained, the ethylene yield is improved, the negative influence of harmful gas on polymerization reaction can be reduced, an ethylene-vinyl alcohol copolymer resin product with better quality can be further obtained, and the produced resin material has good chroma and processability; in addition, according to the method, the production cost can be reduced, and pollution to the environment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ethylene recovery, and particularly relates to a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer and an ethylene-vinyl alcohol copolymer. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH), especially the ethylene-vinyl alcohol copolymer with an ethylene content of 20 mol% - 50 mol%, has excellent gas barrier properties, about 10,000 times that of ordinary polyethylene. Coupled with its transparency, processability, solvent resistance and antistatic properties, it is widely used in packaging materials, automotive fuel tanks, oxygen-barrier floor heating pipes, textile materials and medical materials and other fields. Ethylene-vinyl alcohol copolymer is obtained by alcoholysis of ethylene-vinyl acetate copolymer. The high gas barrier property of ethylene-vinyl alcohol copolymer is directly related to its degree of alcoholysis. Under the condition of the same ethylene content, the higher the degree of alcoholysis, the better the gas barrier property. In order to ensure sufficient gas barrier property, usually the degree of alcoholysis of EVOH reaches more than 99%.

[0003] EVOH can be polymerized from ethylene and vinyl acetate by conventional methods such as emulsion polymerization, solution polymerization or suspension polymerization, and then saponified. During the solution polymerization process, usually an alcohol with no more than 4 carbons is used as the solvent, and methanol is preferably used. After the polymerization reaction is completed, ethylene, methanol and unreacted vinyl acetate need to be recycled. Usually, the polymerization reaction pressure is 2.0 - 6.0 MPa, and after the reaction is completed, the polymer enters the flash evaporation system.

[0004] During the flash evaporation process, ethylene is removed in the form of gas phase. Inevitably, a large amount of vinyl acetate and methanol are carried out by ethylene. If it directly enters the ethylene compressor, since vinyl acetate is a polymerization monomer, during the compression process, vinyl acetate and methanol will form a liquid phase precipitation, and the compression process is a process of temperature increase, resulting in the self-polymerization of vinyl acetate, which affects the normal operation of the ethylene compressor. In addition, during the flash evaporation process, the ejected gas-liquid mixture is prone to form a polymer aerosol. The polymer aerosol enters the polymerization kettle with the recycled ethylene and mixes with the product, affecting the product quality. In the actual production process, due to the long-term recycling of ethylene, some harmful gas impurities will inevitably be brought in, mainly the accumulation of harmful gases such as carbon monoxide, oxygen, and carbon dioxide during long-term use. In order to improve the quality of EVOH products, generally, during the recovery and preparation of ethylene and vinyl acetate, purification technologies such as absorbents are used to separate impurities, but this method can only prevent the continuous increase of the impurity concentration in the system, so it can only control the impurity concentration within a certain range, cannot completely remove it, and cannot reduce the content of aerosol. These impurities with fixed concentrations will also directly carry out grafting reactions with the copolymer, having a great negative impact on the properties of the copolymer, including reduced heat resistance, yellowing of the finished product, and difficulty in recycling the ear materials during the processing of the finished product.

[0005] TW200420585A provides a method for cleaning and recycling ethylene using a cleaning agent. In this method, the gas phase of the ethylene-vinyl acetate polymerization reaction is connected to an impurity removal tower and the gas phase is washed with the solvent used in the polymerization reaction, and then recycled back to the reaction system, thereby removing the impurities generated by the reaction. However, this method cannot completely wash away the impurities, and a small amount of insoluble substances can still have an adverse impact on the product quality.

[0006] At present, the domestic production process of ethylene-vinyl alcohol copolymer is in its infancy, and the recovery of ethylene plays an important role in the maturity of its process. There is relatively little research on the ethylene recovery process for the production of ethylene-vinyl alcohol copolymer in China, and it is impossible to produce high-quality ethylene-vinyl alcohol copolymer products using the existing ethylene recovery process. Therefore, there is an urgent need for a method that can completely solve the problem of impurities in the recycled ethylene. Summary of the Invention

[0007] The object of the present invention is to overcome the defect that the ethylene recovery process for the production of ethylene-vinyl alcohol copolymer in the prior art cannot produce high-quality ethylene-vinyl alcohol copolymer products, and the defect that the ethylene recovery process for the production of ethylene-vinyl alcohol copolymer in the prior art cannot completely solve the problem of impurities in the recycled ethylene. The present invention provides a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer and an ethylene-vinyl alcohol copolymer. The method provided by the present invention can obtain pure recycled ethylene, improve the ethylene yield, reduce the negative impact of harmful gases on the polymerization reaction, and further obtain ethylene-vinyl alcohol copolymer resin products with better quality.

[0008] To achieve the above object, the first aspect of the present invention provides a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer, wherein the method includes: sequentially performing treatment for removing monomers and / or polymers, oxygen, carbon monoxide, water, and carbon dioxide on the recycled ethylene mixture during the preparation of ethylene-vinyl alcohol copolymer to obtain ethylene-vinyl alcohol copolymer and recycled ethylene.

[0009] The second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the method described above.

[0010] Through the above technical solutions, the present invention has the following beneficial effects:

[0011] (1) By using the method of the present invention, the recycled ethylene mixture in the preparation process of ethylene-vinyl alcohol copolymer is successively removed of monomers and / or polymers, oxygen, carbon monoxide, water and carbon dioxide, so as to obtain pure recycled ethylene, improving the ethylene yield; moreover, it can also reduce the negative impact of harmful gases on the polymerization reaction, and further obtain an ethylene-vinyl alcohol copolymer resin product with better quality. The produced resin material has good chromaticity and processing performance; in addition, the method of the present invention can reduce the production cost and environmental pollution.

[0012] (2) The present invention further preferably adopts a design of parallel operation of two towers, which can greatly facilitate operations such as tower switching, maintenance, and regeneration during continuous production.

[0013] (3) The present invention further uses renewable removing agents (cleaning agents, deoxidizers, copper oxide and / or NiO, 3A molecular sieve, spherical adsorbent), which have excellent economy and simplicity of operation. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of a device for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer provided by the present invention.

[0015] Description of the Reference Numerals

[0016] I - Cleaning Tower; II - Deoxygenation Tower; III - CO Removal Tower; IV - Drying Tower; V - CO 2 Removal Tower;

[0017] 1 - Ethylene; 2 - Cleaning Agent; 3 - Liquid Recovery; 4 - Recovery by Ethylene Compressor. Detailed Embodiments

[0018] As mentioned above, the first aspect of the present invention provides a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer, wherein the method includes: successively performing treatments for removing monomers and / or polymers, oxygen, carbon monoxide, water and carbon dioxide on the recycled ethylene mixture in the preparation process of ethylene-vinyl alcohol copolymer to obtain ethylene-vinyl alcohol copolymer and recycled ethylene.

[0019]

[0020] ​The inventors of the present invention have found that: in the current production process of ethylene-vinyl alcohol copolymer, the utilization rate of ethylene in a single-pass reaction is less than 30%. During the resin degassing process, a large amount of recycled ethylene mixture will be removed, and since the removed recycled ethylene mixture contains a large amount of harmful impurity gases, it affects the polymerization reaction, resulting in the quality of the produced ethylene-vinyl alcohol copolymer product not meeting the standards and being unable to be recycled. The inventors of the present invention have proposed an ethylene refining process to solve the problem of the adverse effects caused by the currently discovered harmful gas substances. This process sequentially removes monomers and / or polymers, oxygen, carbon monoxide, water, and carbon dioxide according to a specific refining sequence, and can obtain pure recycled ethylene, improving the ethylene yield; moreover, it can also reduce the negative impact of harmful gases on the polymerization reaction, and further obtain an ethylene-vinyl alcohol copolymer resin product with better quality. The produced resin material has good chromaticity and processing performance.

[0021] Furthermore, preferably, the refining process proposed by the present invention has a specific sequence. It must first pass through Scrubber I to remove the polymerization monomers and / or polymers in the recycled ethylene mixture, and then pass through Deoxygenation Tower II, Carbon Monoxide Removal Tower III, Drying Tower IV, and Carbon Dioxide Removal Tower V, and finally enter the ethylene compressor 4 for recycling. The function of Scrubber I is to remove the polymerization monomers and / or polymers to prevent them from affecting the subsequent refining process. Since the principle of carbon monoxide removal is to oxidize carbon monoxide to carbon dioxide, Carbon Dioxide Removal Tower V must be placed at the end.

[0022] According to the present invention, the recycled ethylene mixture in the preparation process of ethylene-vinyl alcohol copolymer is contacted with a cleaning agent to remove the monomers and polymers in the gas-liquid mixture; wherein, the cleaning agent is an alcohol solvent. Preferably, the alcohol solvent is an alcohol with C 1 -C 4 and more preferably one or more of methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol. In addition, in the present invention, the monomers in the gas-liquid mixture are removed, where the monomers refer to vinyl acetate that is not completely reacted during the reaction process; the polymers in the gas-liquid mixture are removed, where the polymers refer to polyethylene-vinyl acetate copolymer.

[0023] According to the present invention, the ethylene after removing the monomers and / or polymers in the gas-liquid mixture is contacted with an oxygen scavenger for oxygen removal treatment; preferably, the oxygen scavenger is selected from one or more of noble metal oxygen scavengers, nickel-based oxygen scavengers, and their alloy oxygen scavengers; more preferably, the oxygen scavenger includes but is not limited to noble metals such as palladium and platinum and their alloys, Ni-Cr 2 O 3 、Ni-Al 2 O 3 ,MnO, Fe / Al 2 O 3, Fe-Mo / Al 2 O 3 , one or more of Co-Mo / C, more preferably MnO, Ni-Cr 2 O 3 , Ni-Al 2 O 3 one or more of them.

[0024] According to the present invention, ethylene after removing monomers and / or polymers and oxygen in the gas-liquid mixture is contacted with copper oxide and / or NiO for CO removal treatment.

[0025] According to the present invention, ethylene after removing monomers and / or polymers, oxygen, and carbon monoxide in the gas-liquid mixture is contacted with 3A molecular sieve for drying treatment to remove the water. In the present invention, the chemical formula of the 3A molecular sieve is: 2 / 3K 2 O1 3 ·Na 22 O·Al 2 O 3 ·2SiO 2· ·4.5H 2 O.

[0026] According to the present invention, ethylene after removing monomers and / or polymers, oxygen, carbon monoxide, and water in the gas-liquid mixture is contacted with a spherical adsorbent for CO 2 removal treatment to obtain ethylene-vinyl alcohol copolymer and recycled ethylene; preferably, the spherical adsorbent is one or more of CaO / CaZrO 3 , X-type molecular sieve, Y-type molecular sieve, β-type molecular sieve, and ZSM-type molecular sieve.

[0027] According to the present invention, relative to 400 - 2000 kg / h of recycled ethylene mixture, the dosage of the cleaning agent is 100 - 5000 Kg / h, the dosage of the deoxidizer is 1000 - 5000 Kg, the dosage of copper oxide or NiO is 1000 - 5000 Kg, the dosage of 3A molecular sieve is 1000 - 5000 Kg, and the dosage of the spherical adsorbent is 1000 - 5000 Kg; preferably, relative to 1500 - 2000 kg / h of recycled ethylene mixture, the dosage of the cleaning agent is 3000 - 4000 Kg / h, the dosage of the deoxidizer is 3500 - 5000 Kg / h, the dosage of copper oxide or NiO is 3000 - 4500 Kg, the dosage of 3A molecular sieve is 3500 - 4600 Kg, and the dosage of the spherical adsorbent is 3000 - 5000 Kg.

[0028] The described method is carried out in a device for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer. The device includes a scrubbing tower I, a deoxidation tower II, a CO removal tower III, a drying tower IV, and a CO removal 2 tower V, which are connected in sequence.

[0029] According to the present invention, the scrubbing tower I is filled with a cleaning agent, the deoxidation tower II is filled with a deoxidizer, the CO removal tower III is filled with copper oxide and / or NiO, the drying tower IV is filled with 3A molecular sieve, and the CO removal 2 tower V is filled with a spherical adsorbent.

[0030] According to the present invention, preferably, the deoxidation tower II, the CO removal tower III, the drying tower IV, and the CO removal 2 tower V are all arranged in parallel with two towers. When one tower is in use, the other tower is in a regeneration or standby state. This can greatly facilitate operations such as tower switching, maintenance, and regeneration during continuous production.

[0031] Specifically, according to the present invention, a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer provided by the present invention includes:

[0032] (1) The recycled ethylene mixture during the preparation of ethylene-vinyl alcohol copolymer enters the scrubbing tower I through a pipeline and contacts with the cleaning agent to remove monomers and / or polymers in the gas-liquid mixture;

[0033] (2) The ethylene gas after being scrubbed in step (1) enters the deoxidation tower II through a pipeline and contacts with the deoxidizer for deoxidation treatment;

[0034] (3) The ethylene gas after step (2) enters the CO removal tower III through a pipeline and contacts with copper oxide or NiO for CO removal treatment;

[0035] (4) The ethylene gas after step (3) enters the drying tower IV through a pipeline and contacts with 3A molecular sieve for drying treatment;

[0036] (5) The ethylene gas after step (4) enters the CO removal 2 tower V through a pipeline and contacts with the spherical adsorbent for CO removal 2 treatment to obtain ethylene-vinyl alcohol copolymer and recycled ethylene, and the recycled ethylene enters an ethylene compressor for recycling.

[0037] According to a particularly preferred embodiment of the present invention, as Figure 1 shown, a method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer provided by the present invention includes:

[0038] (1) After the recycled ethylene mixture in the preparation process of ethylene-vinyl alcohol copolymer is removed from the polymer, it enters the washing tower I, where monomers and / or polymers in the gas-liquid mixture are washed off with the help of a cleaning agent to prevent the monomers from affecting the purification effect in the subsequent purification process; the cleaning agent is preferably methanol;

[0039] (2) The ethylene gas after washing enters the deoxygenation tower II. The deoxygenation tower II is a packed tower. The ethylene deoxygenation tower adopts a two-tower operation, and the two deoxygenation towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state; the deoxidizer filled in it is a reducing agent, including MnO, Ni-Cr 2 O 3 and Ni-Al 2 O 3 one or more of them;

[0040] (3) After deoxygenation treatment, the ethylene gas enters the CO removal tower III through a pipeline. The CO removal tower III is also a packed tower and adopts a two-tower operation. The two CO removal towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state; the CO removal agent is preferably copper oxide or NiO;

[0041] (4) The recycled ethylene gas then enters the drying tower IV, and the packing is 3A molecular sieve to remove trace moisture in it; the drying tower IV is also a packed tower and adopts a two-tower operation. The two drying towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0042] (5) The recycled ethylene gas from which water has been removed enters the carbon dioxide removal tower V through a pipeline. The packing is a spherical adsorbent. The carbon dioxide removal also selects a packed tower and adopts a two-tower operation. The two carbon dioxide removal towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0043] (6) Finally, the purified recycled ethylene enters the ethylene compressor for recycling.

[0044] The second aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the method described above.

[0045] According to the present invention, the chromaticity of the ethylene-vinyl alcohol copolymer is 1-15, and the molecular weight distribution index is 1-4; preferably, the chromaticity of the ethylene-vinyl alcohol copolymer is 3-12, and the molecular weight distribution index is 1.2-2; more preferably, the chromaticity of the ethylene-vinyl alcohol copolymer is 9-11, and the molecular weight distribution index is 1.6-1.9.

[0046] According to the present invention, the content of ethylene in the ethylene-vinyl alcohol copolymer is 20 mol%-50 mol%.

[0047] The present invention will be described in detail below with reference to embodiments.

[0048] In the following examples and comparative examples:

[0049] The chromaticity parameters were measured by a resin chromaticity meter according to the test method for the yellow index of plastics GB / T 2409-1980.

[0050] The molecular weight distribution index was measured by high-temperature gel permeation chromatography. Among them, high-temperature gel permeation chromatography was carried out using a high-temperature gel permeation chromatograph with the model number GPC-220, which was purchased from Agilent Technologies, Inc., USA.

[0051] The ethylene-vinyl alcohol copolymers were commercially available products with the grades of EW3801 and EW3201.

[0052] Example 1

[0053] This example is to illustrate the use of the device of the present invention to recover ethylene and prepare and purify the products produced from the recovered ethylene.

[0054] (1) The recycled ethylene mixture in the preparation process of the ethylene-vinyl alcohol copolymer was removed from the polymer and then entered the washing tower I. With the help of the cleaning agent, the monomers in the gas-liquid mixture were washed away to prevent the monomers from affecting the purification effect in the subsequent purification process.

[0055] (2) The ethylene gas after washing entered the deoxygenation tower II. The ethylene deoxygenation tower adopted a two-column operation, and the two deoxygenation towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state.

[0056] (3) After the deoxygenation treatment, the recovered ethylene gas entered the CO removal tower III through a pipeline. The CO removal tower III also selected a packed tower and adopted a two-column operation. The two CO removal towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state.

[0057] (4) The recovered ethylene gas then entered the drying tower IV. The packing was 3A molecular sieve to remove the trace moisture in it. The drying tower IV also selected a packed tower and adopted a two-column operation. The two drying towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state.

[0058] (5) The recovered ethylene gas from which the water had been removed entered the carbon dioxide removal tower V through a pipeline. The packing was a spherical adsorbent. The carbon dioxide removal also selected a packed tower and adopted a two-column operation. The two carbon dioxide removal towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state.

[0059] (6) Finally, the purified recovered ethylene entered the ethylene compressor for recycling; in addition, ethylene-vinyl alcohol copolymer was prepared.

[0060] Among them, the specific components and dosages of the cleaning agent, deoxidizer, copper oxide or NiO, 3A molecular sieve, and spherical adsorbent used are shown in Table 1;

[0061] The composition of the recycled ethylene mixture before purification and the composition of the recovered ethylene after purification are shown in Table 2;

[0062] The chromaticity, molecular weight distribution index of the product produced from the unpurified recovered ethylene, and the characterization of the product produced from the purified recovered ethylene are shown in Table 3.

[0063] Examples 2 - 3

[0064] Ethylene was recovered and the product produced from the purified recovered ethylene was prepared in the same manner as in Example 1, except that:

[0065] The specific components and dosages of the cleaning agent, deoxidizer, copper oxide or NiO, 3A molecular sieve, and spherical adsorbent used are shown in Table 1;

[0066] The composition of the recycled ethylene mixture before purification and the composition of the recovered ethylene after purification are shown in Table 2;

[0067] The chromaticity, molecular weight distribution index of the product produced from the unpurified recovered ethylene, and the characterization of the product produced from the purified recovered ethylene are shown in Table 3.

[0068] Comparative Example 1

[0069] Ethylene was recovered and the product produced from the purified recovered ethylene was prepared in the same manner as in Example 1, except that: Instead of using the method of the present invention, the recycled ethylene mixture was directly used.

[0070] Specifically, the recycled ethylene mixture in the preparation process of ethylene - vinyl alcohol copolymer was removed from the polymer and then entered the ethylene press for recycled production.

[0071] The composition of the recycled ethylene mixture before purification and the composition of the recovered ethylene after purification are shown in Table 2;

[0072] The chromaticity, molecular weight distribution index of the product produced from the unpurified recovered ethylene, and the characterization of the product produced from the purified recovered ethylene are shown in Table 3.

[0073] Comparative Example 2

[0074] Ethylene was recovered and the product produced from the purified recovered ethylene was prepared in the same manner as in Example 1, except that: Instead of using the method of the present invention, only the scrubbing tower was used.

[0075] (1) After removing ethylene from the ethylene-vinyl alcohol copolymer preparation process, the ethylene enters the scrubbing tower I, where monomers in the gas-liquid mixture are washed off with the help of a cleaning agent to prevent the monomers from affecting the purification effect during the subsequent purification process;

[0076] (2) The ethylene gas after scrubbing directly enters the ethylene compressor for reuse.

[0077] The specific components and dosages of the cleaning agent used are shown in Table 1;

[0078] The composition of the recycled ethylene mixture before purification and the composition of the recycled ethylene after purification are shown in Table 2;

[0079] The color, molecular weight distribution index of the product produced from the unpurified recycled ethylene and the characterization of the product produced from the purified recycled ethylene are shown in Table 3.

[0080] Comparative Example 3

[0081] Ethylene was recovered and the product was prepared from the purified recycled ethylene in the same manner as in Example 1, except that: no scrubbing tower was used.

[0082] (1) After removing ethylene from the ethylene-vinyl alcohol copolymer preparation process, the ethylene enters the deoxygenation tower II. The ethylene deoxygenation tower uses a two-tower operation, and the two deoxygenation towers are operated in parallel. When one tower is in use, the other tower is in a regeneration or standby state;

[0083] (2) After deoxygenation treatment, the recycled ethylene gas enters the CO removal tower III through a pipeline. The CO removal tower III also selects a packed tower and uses a two-tower operation. The two CO removal towers are operated in parallel. When one tower is in use, the other tower is in a regeneration or standby state;

[0084] (3) The recycled ethylene gas then enters the drying tower IV, with 3A molecular sieve as the packing to remove trace moisture therein; the drying tower IV also selects a packed tower and uses a two-tower operation. The two drying towers are operated in parallel. When one tower is in use, the other tower is in a regeneration or standby state;

[0085] (4) The recycled ethylene gas from which water has been removed enters the carbon dioxide removal tower V through a pipeline, with spherical adsorbent as the packing. The carbon dioxide removal also selects a packed tower and uses a two-tower operation. The two carbon dioxide removal towers are operated in parallel. When one tower is in use, the other tower is in a regeneration or standby state;

[0086] (5) Finally, the purified recycled ethylene enters the ethylene compressor for recycling; in addition, the ethylene-vinyl alcohol copolymer is prepared.

[0087] The specific components and dosages of the deoxidizer, copper oxide or NiO, 3A molecular sieve, and spherical adsorbent used are shown in Table 1;

[0088] The composition of the recycled ethylene mixture before purification and the recovered ethylene after purification are shown in Table 2;

[0089] The color, molecular weight distribution index of the product produced from the unpurified recovered ethylene and the characterization of the product produced from the purified recovered ethylene are shown in Table 3.

[0090] Comparative Example 4

[0091] Ethylene was recovered and the product produced from the purified recovered ethylene was prepared in the same manner as in Example 1, except that:

[0092] The positions of the deoxidation tower (II), the CO removal tower (III), the drying tower (IV) and the CO removal 2 tower (V) were adjusted. Specifically:

[0093] (1) After the ethylene was removed from the polymer, it entered the washing tower I, and with the help of the cleaning agent, the monomers in the gas-liquid mixture were washed away to prevent the monomers from affecting the purification effect in the subsequent purification process;

[0094] (2) The recovered ethylene gas after washing then entered the drying tower IV, with 3A molecular sieve as the packing, to remove the trace moisture therein; The drying tower IV also selected a packed tower and adopted a two-tower operation. The two drying towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state;

[0095] (3) The ethylene gas after drying entered the deoxygenation tower II. The ethylene deoxygenation tower adopted a two-tower operation. The two deoxygenation towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state;

[0096] (4) After the deoxygenation treatment, the recovered ethylene gas entered the CO removal tower III through a pipeline. The CO removal tower III also selected a packed tower and adopted a two-tower operation. The two CO removal towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state;

[0097] (5) The recovered ethylene gas after CO removal entered the carbon dioxide removal tower V through a pipeline, with spherical adsorbent as the packing. The carbon dioxide removal also selected a packed tower and adopted a two-tower operation. The two carbon dioxide removal towers were operated in parallel. When one tower was in use, the other tower was in a regeneration or standby state;

[0098] (6) Finally, the purified recovered ethylene entered the ethylene compressor for recycling; In addition, ethylene-vinyl alcohol copolymer was prepared.

[0099] Among them, the specific components and dosages of the cleaning agent, deoxidizer, copper oxide or NiO, 3A molecular sieve and spherical adsorbent used are shown in Table 1;

[0100] The composition of the recycled ethylene mixture before purification and the recovered ethylene composition after purification are shown in Table 2;

[0101] The colority, molecular weight distribution index of the products produced from the recovered ethylene without purification and the characterization of the products produced from the purified recovered ethylene are shown in Table 3.

[0102] Comparative Example 5

[0103] Ethylene was recovered and the product produced from the purified recovered ethylene was prepared in the same manner as in Example 1, except that:

[0104] The positions of the deoxidation tower (II), the decarbonization tower (III), the drying tower (IV) and the decarbonization 2 tower (V) were adjusted. Specifically:

[0105] (1) After ethylene is removed from the polymer, it enters the washing tower I, and with the help of the cleaning agent, the monomers in the gas-liquid mixture are washed away to prevent the monomers from affecting the purification effect in the subsequent purification process;

[0106] (2) The recovered ethylene gas after washing enters the decarbonization tower V through a pipeline. The packing is spherical adsorbent. The decarbonization also selects a packed tower and adopts a two-tower operation. The two decarbonization towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0107] (3) The ethylene gas after drying enters the deoxidation tower II. The ethylene deoxidation tower adopts a two-tower operation. The two deoxidation towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0108] (4) After the deoxidation treatment, the recovered ethylene gas enters the decarbonization tower III through a pipeline. The decarbonization tower III also selects a packed tower and adopts a two-tower operation. The two decarbonization towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0109] (5) The recovered ethylene gas after decarbonization enters the drying tower IV through a pipeline. The packing is 3A molecular sieve to remove the trace moisture therein; the drying tower IV also selects a packed tower and adopts a two-tower operation. The two drying towers are operated in parallel. When one is in use, the other tower is in a regeneration or standby state;

[0110] (6) Finally, the purified recovered ethylene enters the ethylene compressor for recycling; in addition, ethylene-vinyl alcohol copolymer is prepared.

[0111] Among them, the specific components and dosages of the cleaning agent, deoxidizer, copper oxide or NiO, 3A molecular sieve and spherical adsorbent used are shown in Table 1;

[0112] The composition of the recycled ethylene mixture before purification and the recovered ethylene composition after purification are shown in Table 2;

[0113] The characterization of the products produced from the unpurified recovered ethylene and the products produced from the purified recovered ethylene, such as chromaticity and molecular weight distribution index, are shown in Table 3.

[0114] Table 1

[0115]

[0116]

[0117] Table 2

[0118]

[0119]

[0120] Remark *: The deoxidizer has poor effect and the regeneration effect becomes worse, affecting the continuous process production.

[0121] Table 3

[0122]

[0123] Remark: * indicates the products prepared by the purification and recovery process of this example or comparative example.

[0124] From the results in Tables 1 - 3, it can be seen that the ethylene recovery rates of Examples 1 - 3 of the present invention are above 50%, the molecular weight distribution indexes of the prepared ethylene-vinyl alcohol copolymers are lower, and the chromaticity has also decreased significantly, showing significantly better effects.

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer, characterized in that, the method includes: subjecting the recycled ethylene mixture during the preparation of ethylene-vinyl alcohol copolymer to treatment for removing monomers and / or polymers, oxygen, carbon monoxide, water and carbon dioxide in sequence, to obtain ethylene-vinyl alcohol copolymer and recovered ethylene.

2. The method according to claim 1, wherein, contacting the recycled ethylene mixture with a cleaning agent to remove monomers and polymers in the gas-liquid mixture; preferably, the cleaning agent is an alcohol solvent; Preferably, the alcohol solvent is an alcohol having C 1 -C 4 , and more preferably one or more of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol.

3. The method according to claim 1, wherein, contacting the ethylene after removing monomers and / or polymers in the gas-liquid mixture with an oxygen scavenger to remove oxygen; preferably, the oxygen scavenger is selected from one or more of noble metal oxygen scavengers, nickel-based oxygen scavengers and their alloy oxygen scavengers; More preferably, the deoxidizer includes, but is not limited to, noble metals such as palladium and platinum and their alloys, Ni-Cr 2 O 3 , Ni-Al 2 O 3 , MnO, Fe / Al 2 O 3 , Fe-Mo / Al 2 O 3 and Co-Mo / C, and more preferably one or more of MnO, Ni-Cr 2 O 3 and Ni-Al 2 O 3 .

4. The method according to claim 1, wherein, contacting the ethylene after removing monomers and / or polymers in the gas-liquid mixture and after removing the oxygen with copper oxide and / or NiO to remove CO.

5. The method according to claim 1, wherein, contacting the ethylene after removing monomers and / or polymers in the gas-liquid mixture, after removing the oxygen and after removing the carbon monoxide with 3A molecular sieve for drying treatment to remove the water.

6. The method according to claim 1, wherein, The ethylene from which monomers and / or polymers in the gas-liquid mixture have been removed, oxygen has been removed, carbon monoxide has been removed, and water has been removed is contacted with a spherical adsorbent for CO removal 2 treatment to obtain ethylene-vinyl alcohol copolymer and recycled ethylene; Preferably, the spherical adsorbent is one or more of CaO / CaZrO 3 , X-type molecular sieve, Y-type molecular sieve, β-type molecular sieve, and ZSM-type molecular sieve.

7. The method according to any one of claims 1-6, wherein, relative to 400-2000 kg / h of the recycled ethylene mixture, the dosage of the cleaning agent is 100-5000 Kg / h, the dosage of the oxygen scavenger is 1000-5000 Kg, the dosage of the copper oxide and / or NiO is 1000-5000 Kg, the dosage of the 3A molecular sieve is 1000-5000 Kg, and the dosage of the spherical adsorbent is 1000-5000 Kg.

8. The method according to any one of claims 1-7, wherein, The described method is carried out in a device for recovering ethylene during the preparation of ethylene-vinyl alcohol copolymer. The device includes a washing tower (I), a deoxidation tower (II), a CO removal tower (III), a drying tower (IV), and a CO removal tower (V) which are connected in sequence. 2 tower (V).

9. The method according to claim 8, wherein, The deoxidation tower (II), the CO removal tower (III), the drying tower (IV), and the CO removal 2 tower (V) are all arranged in parallel with two towers.

10. An ethylene-vinyl alcohol copolymer prepared by the method according to any one of claims 1-9.

11. The ethylene-vinyl alcohol copolymer according to claim 10, wherein, the chromaticity of the ethylene-vinyl alcohol copolymer is 1-15, and the molecular weight distribution index is 1-4; preferably, the chromaticity of the ethylene-vinyl alcohol copolymer is 3-12, and the molecular weight distribution index is 1.2-2; and / or, the content of ethylene in the ethylene-vinyl alcohol copolymer is 20 mol%-50 mol%.

Images