Synthesis method of EVOH

Abstract

The invention discloses a method for synthesizing EVOH, and relates to the technical field of EVOH synthesis. The technical scheme is as follows: S1 puts an adsorbent into a washing solution for washing, places it in a hydrochloric acid solution for soaking, oscillation, filtration, natural cooling to room temperature, and baking; S2 adds it to an organic solvent, and then injects ethylene; S3 mixes vinyl acetate and an initiator, reacts it with an adsorbent, adds a terminator copper acetate to stop the reaction, and obtains a mixed solution containing ethylene-vinyl acetate copolymer, and the mixed solution is filtered to separate the adsorbent, and then desolventizes, removes excess vinyl acetate, and alcoholyzes to obtain a crude EVOH product; S4 washes the crude EVOH product with water, extrude it in a vacuum, and pelletizes it to obtain EVOH after washing. The present invention uses an adsorbent to adsorb ethylene, so that ethylene and vinyl acetate are fully and effectively contacted, thereby controlling the polymerization process, reducing the reaction pressure, and the product EVOH has a narrow molecular weight distribution and a high ethylene content.

Description

Technical Field

[0001] The invention relates to the technical field of EVOH synthesis, in particular to a method for synthesizing EVOH. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is one of the high-barrier polymer materials with the best comprehensive performance at present, and has excellent processing and molding properties. Its downstream applications include packaging materials, automobile fuel tanks, oxygen-barrier floor heating pipes, textiles and medical materials. Ethylene-vinyl acetate copolymer (EVA) is an important precursor for the synthesis of EVOH, and its performance directly affects the barrier properties of EVOH. However, the current synthesis process of EVA requires high temperature and high pressure to enhance the solubility of ethylene in solvents or vinyl acetate monomers, and even requires multi-stage gradient heating and gradual monomer dripping to ensure that ethylene has sufficient polymerization participation. Therefore, the overall preparation process of EVOH is complex and the equipment requirements are high, which has caused a lot of inconvenience to industrial production, and at the same time caused resource waste, which is contrary to the theme of the times, green chemistry. Therefore, it is urgent to simplify the process flow to reduce the burden of industrial production, reduce industrial costs, and promote green chemistry and green production. In addition, if there are too few ethylene repeating units in the EVOH segment, the processing performance will be poor and the product will be difficult to process and mold; and the small number of ethylene repeating units will cause the product to absorb moisture easily, thereby reducing the barrier properties of EVOH.

[0003] Chinese invention patent CN113372477A discloses a control method and synthesis method for EVA synthesis with controllable branching degree, an EVOH resin and its synthesis method, which control its structure based on the response relationship between pressure and structure and the response relationship between the chain transfer constant, solubility and distribution coefficient in the solvent and the structure. Specifically, it includes: (1) controlling the reaction pressure, the pressure of the mixture of ethylene gas and nitrogen or the pressure of pure ethylene gas to achieve the control of the number of branches; (2) setting the type of solvent or the number of solvents according to the solubility of ethylene in the solvent, the solubility of vinyl acetate in the solvent, and the distribution coefficient of ethylene in vinyl acetate and the solvent; (3) setting the ethylene content based on the response relationship between pressure and structure; (4) controlling the initiator, and selecting a suitable initiator according to the different solubility, distribution coefficient and initiation efficiency of different initiators in different solvent systems. This method effectively realizes the control of EVOH branches and the control of ethylene content, but it is highly dependent on the solubility of ethylene in the solution and the solubility of vinyl acetate in the solution. Therefore, this method has high requirements on equipment and strict requirements on the ratio of ethylene, solvent and vinyl acetate.

[0004] Chinese invention patent CN113402647A discloses a control method and synthesis method for synthesizing EVA with controlled release of free radicals, an EVOH resin and its synthesis method. According to the relationship between the kinetic characteristics of the polymerization reaction and the free radical concentration, generation rate, and initiation efficiency, the structure and molecular weight of EVA are controlled by controlling the feeding method, solvent effect, pulse heating, and composite initiator. Specifically, it includes: (1) setting the feeding method and feeding sequence of ethylene and vinyl acetate based on the initiation rate of the initiator to ethylene and vinyl acetate; (2) setting the selection, number, and addition method of the initiator based on the automatic acceleration effect of the free radical polymerization reaction; (3) setting the heating process based on the relationship between the initiator generating free radicals and the temperature. Pulse heating specifically refers to heating to a certain temperature, cooling after staying for a certain time, heating after staying for a certain time, and repeating in sequence to control the temperature and residence time. This method controls the polymerization process by pulse heating, which can achieve the regulation of EVA structure and molecular weight, but this method requires multiple batches of fresh vinyl acetate to increase the solubility of ethylene gas, thereby increasing the participation of ethylene in the reaction process and increasing the proportion of ethylene in the final product; the pulse heating method is also to increase the solubility of ethylene in vinyl acetate at low temperature, and to achieve free radical copolymerization of ethylene and vinyl acetate at low temperature. Therefore, this method is cumbersome to operate and is not conducive to industrial production.

[0005] In summary, enhancing the participation of ethylene gas in the reaction system and the ease of operation of the actual reaction are of great significance to improving the batch stability of EVOH. Summary of the invention

[0006] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art, to provide a method for synthesizing EVOH, to increase the concentration of ethylene in the reaction system by adsorbing ethylene through a porous adsorbent, to promote sufficient and effective contact between ethylene and vinyl acetate, and then to control the polymerization process, to reduce the reaction pressure, and the final product EVOH has a narrow molecular weight distribution and a high ethylene content, and the product stability and product quality are significantly improved.

[0007] The technical solution of the present invention is:

[0008] The synthesis method of EVOH comprises the following steps:

[0009] S1: washing the adsorbent in a washing liquid, then soaking the adsorbent in a hydrochloric acid solution, shaking, filtering, naturally cooling to room temperature, and baking for later use; wherein the adsorbent is silica gel, activated carbon or Y-type zeolite molecular sieve;

[0010] S2: adding the adsorbent treated in step S1 to an organic solvent, and then injecting ethylene, and after mixing, the ethylene is uniformly adsorbed on the adsorbent;

[0011] S3: vinyl acetate and an initiator are mixed, and the mixture is mixed with an adsorbent having ethylene adsorbed thereon for reaction, and a terminator, copper acetate, is added to stop the reaction, and the pressure is released to discharge the ethylene to obtain a mixed solution containing ethylene-vinyl acetate copolymer. The mixed solution is filtered to separate the adsorbent, and then subjected to desolventization, removal of excess vinyl acetate, and alcoholysis to obtain a crude EVOH product.

[0012] The crude EVOH obtained in S4 is washed with water, vacuum dried, and then enters the extrusion equipment, and then pelletized and washed to obtain EVOH;

[0013] In parts by weight, the added amount of vinyl acetate is 100 parts, the added amount of organic solvent is 15-40 parts, the added amount of initiator is 0.01-0.3 parts, and the added amount of adsorbent is 10-50 parts; the added amount of terminator is 500-1500ppm of the mass of ethylene-vinyl acetate copolymer.

[0014] Adsorption refers to the phenomenon that molecules (gas or liquid), atoms or ions gather on the surface of solid materials. The binding of molecules to the active sites of the surface involves physical, chemical or van der Waals interactions. In the polymerization reaction, the adsorbent can capture ethylene and generate a new active free radical, preventing the chain reaction of the polymerization reaction. The synthesis method of the present invention is based on the porous microstructure of the adsorbent, which has a very large specific surface area. The adsorbent captures ethylene, increases the contact area between ethylene gas and vinyl acetate, forms a local active reaction domain of ethylene-vinyl acetate free radical copolymerization, and increases the participation of ethylene gas in the reaction polymerization system; at the same time, the adsorbent can realize the controllable release of ethylene gas, realize the high concentration of ethylene gas in the reaction system and the timely replenishment after the reaction, ensure the conversion rate of ethylene gas, and realize the synthesis of EVOH products with high batch repetition rate and high ethylene conversion rate.

[0015] Preferably, in step S1, the washing solution comprises a surfactant and a weak acid.

[0016] Preferably, the surfactant is sodium vinyl sulfonate, sodium dodecylbenzene sulfonate or disodium lauryl sulfosuccinate; and the weak acid is a 3-8 wt.% hydrochloric acid solution.

[0017] Preferably, in step S1, the pH of the washing solution is 5-6.

[0018] Preferably, in step S1, the adsorbent is soaked in a 3-8wt.% hydrochloric acid solution at room temperature for 1-5h, shaken at 80-100°C for 4-8h, and baked at 50-80°C for standby use.

[0019] Preferably, in step S2, the mixing temperature of the ethylene and the adsorbent is 40-80°C, and the mixing time is 2-10 hours.

[0020] Preferably, in step S2, the ethylene pressure is 1-3 MPa.

[0021] Preferably, in step S2, the organic solvent is methanol, ethanol or isopropanol.

[0022] Preferably, in step S3, the initiator is azobisisobutyronitrile, azobisisoheptanenitrile or dimethyl azobisisobutyrate.

[0023] Preferably, in step S3, the mixed solution is filtered by vacuum filtration or pressure filtration.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention introduces an adsorbent into the reaction system so that ethylene is adsorbed on the adsorbent. During the reaction, the concentration of ethylene adsorbed on the adsorbent is higher than that of the surrounding environment, thereby forming an active center for a local polymerization reaction. This directional polymerization method greatly improves the reaction efficiency, makes the reaction more controllable, reduces the reaction pressure, and the synthesized EVOH has the characteristics of high ethylene content and narrow molecular weight distribution. In addition, the synthesis method of the present invention has mild conditions and is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the HNMR graph of the EVOH particles synthesized in Example 1 of the present invention.

[0027] Figure 2 It is the DSC graph of the EVOH particles synthesized in Example 1 of the present invention.

[0028] Figure 3 It is the GPC chart of EVOH particles synthesized in Example 1 of the present invention.

[0029] Figure 4 This is the HNMR graph of the EVOH particles synthesized in Example 2 of the present invention.

[0030] Figure 5 It is the DSC graph of EVOH particles synthesized in Example 2 of the present invention.

[0031] Figure 6 This is the GPC chart of the EVOH particles synthesized in Example 2 of the present invention.

[0032] Figure 7 This is the HNMR graph of the EVOH particles synthesized in Example 3 of the present invention.

[0033] Figure 8 It is the DSC graph of EVOH particles synthesized in Example 3 of the present invention.

[0034] Fig. 9This is the GPC chart of the EVOH particles synthesized in Example 3 of the present invention. DETAILED DESCRIPTION

[0035] In order to enable persons skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0036] In the following examples, the added amount of each component "part" refers to the weight part.

[0037] Example 1

[0038] The synthesis method of EVOH of the present embodiment comprises the following steps:

[0039] S1: Take 20 parts of Y-type zeolite molecular sieve particles and put them into 200 parts of washing liquid for washing to remove surface impurities, wherein the washing liquid is composed of 0.1wt.% sodium dodecyl sulfate and 5wt.% hydrochloric acid solution, and the pH of the washing liquid is 5.5; then soak the Y-type zeolite molecular sieve particles in 5wt.% hydrochloric acid solution at room temperature for 2 hours, place them in a high-temperature cyclotron oscillator at 80°C for 4 hours, filter the washing liquid, cool it naturally to room temperature, and then place it in a vacuum oven and bake it at 80°C for 5 hours for use;

[0040] S2 Check the air tightness of the reactor, replace the air with nitrogen three times, preheat the reactor to 80°C, replace the air with nitrogen once, add 20 parts of Y-type zeolite molecular sieve particles treated in step S1 and 15 parts of methanol to the feed port of the reactor, introduce 3MPa ethylene, and stir for 2h to make the ethylene evenly adsorbed on the Y-type zeolite molecular sieve particles;

[0041] S3 adds 100 parts of vinyl acetate and 0.1 parts of azobisisobutyronitrile under pressure, raises the temperature to 60°C, reacts for 4 hours under stirring, maintains the pressure at 3MPa, and cools to 28°C; then adds 1000ppm (based on the mass of ethylene-vinyl acetate copolymer) of terminator copper acetate, stirs for 2 hours, releases the pressure to exhaust the residual ethylene, and obtains a mixed solution containing ethylene-vinyl acetate copolymer. The mixed solution is filtered under pressure to separate Y-type zeolite molecular sieve particles, and then the excess vinyl acetate and methanol are distilled under reduced pressure to obtain ethylene-vinyl acetate copolymer (EVA), and the EVA is alcoholyzed to obtain crude EVOH;

[0042] The crude EVOH obtained in S4 is washed with water and vacuum dried before entering the extrusion equipment, and then pelletized and cleaned to obtain EVOH particles.

[0043] The HNMR, DSC and GPC diagrams of EVOH particles are shown in Figure 1. Figure 1-3 As shown, the M of the synthesized EVOH particles w =77.9k,M n=41.4k, PDI=1.87, ethylene content is 31.5mol%.

[0044] Example 2

[0045] The synthesis method of EVOH of the present embodiment comprises the following steps:

[0046] S1: 30 parts of activated carbon are washed in 300 parts of a washing solution to remove surface impurities, wherein the washing solution is composed of 0.3wt.% sodium vinyl sulfonate and 8wt.% hydrochloric acid solution, and the pH of the washing solution is 5; then, the activated carbon is soaked in the 8wt.% hydrochloric acid solution at room temperature for 5 hours, and then oscillated in a high-temperature cyclotron oscillator at 100°C for 6 hours, the washing solution is filtered, cooled naturally to room temperature, and then placed in a vacuum oven, baked at 70°C for 6 hours for use;

[0047] S2 Check the air tightness of the reactor, replace with nitrogen 3 times, preheat the reactor to 60°C, replace with nitrogen once, add 50 parts of activated carbon treated in step S1 and 25 parts of ethanol to the feed port of the reactor, pass 2MPa ethylene, stir for 5h, so that ethylene is evenly adsorbed on the activated carbon;

[0048] S3 adds 100 parts of vinyl acetate and 0.3 parts of azobisisoheptanenitrile under pressure, raises the temperature to 70°C, reacts for 4 hours under stirring, maintains the pressure at 2MPa, and cools to 25°C; then adds 1500ppm (based on the mass of ethylene-vinyl acetate copolymer) of terminator copper acetate, stirs for 1 hour, releases the pressure to exhaust the residual ethylene, and obtains a mixed solution containing ethylene-vinyl acetate copolymer. After the mixed solution is vacuum filtered to separate the activated carbon, the excess vinyl acetate and ethanol are removed by reduced pressure distillation to obtain ethylene-vinyl acetate copolymer (EVA), and the EVA is alcoholyzed to obtain crude EVOH;

[0049] The crude EVOH obtained in S4 is washed with water and vacuum dried before entering the extrusion equipment, and then pelletized and cleaned to obtain EVOH particles.

[0050] The HNMR, DSC and GPC diagrams of EVOH particles are shown in Figure 1. Figure 4-6 As shown, the M of the synthesized EVOH particles w =72.9k,M n =41.4k, PDI=1.76, ethylene content is 33.7mol%.

[0051] Example 3

[0052] The synthesis method of EVOH of the present embodiment comprises the following steps:

[0053] S1 Take 50 parts of silica gel MS001 and put them into 400 parts of washing liquid to remove surface impurities, wherein the washing liquid is composed of 0.2wt.% disodium lauryl sulfosuccinate and 3wt.% hydrochloric acid solution, and the pH of the washing liquid is 6; then soak the silica gel MS001 in 3wt.% hydrochloric acid solution at room temperature for 1 hour, oscillate it in a high-temperature gyroscopic oscillator at 90°C for 8 hours, filter the washing liquid, cool it naturally to room temperature, and then put it in a vacuum oven and bake it at 50°C for 8 hours for use;

[0054] S2 Check the air tightness of the reactor, replace the air with nitrogen three times, preheat the reactor to 40°C, replace the air with nitrogen once, add 10 parts of silica gel MS001 treated in step S1 and 40 parts of isopropanol to the feed port of the reactor, introduce 1MPa ethylene, and stir for 10 hours to make the ethylene evenly adsorbed on the silica gel MS001;

[0055] S3, under pressure, adds 100 parts of vinyl acetate and 0.01 parts of dimethyl azobisisobutyrate, raises the temperature to 65°C, reacts under stirring for 3.5 hours, maintains the pressure at 1MPa, and cools to 30°C; then adds 500ppm (based on the mass of ethylene-vinyl acetate copolymer) of terminator copper acetate, stirs for 1.5 hours, releases the pressure to exhaust the residual ethylene, and obtains a mixed solution containing ethylene-vinyl acetate copolymer, the mixed solution is filtered under pressure to separate silica gel MS001, and then the excess vinyl acetate and isopropanol are distilled under reduced pressure to obtain ethylene-vinyl acetate copolymer (EVA), and the EVA is alcoholyzed to obtain crude EVOH;

[0056] The crude EVOH obtained in S4 is washed with water and vacuum dried before entering the extrusion equipment, and then pelletized and cleaned to obtain EVOH particles.

[0057] The HNMR, DSC and GPC diagrams of EVOH particles are shown in Figure 1. Figure 7-9 As shown, the M of the synthesized EVOH particles w =87.9k,M n =45.5k, PDI=1.93, ethylene content is 30.54mol%.

[0058] Comparative Example 1

[0059] The synthesis method of EVOH of Comparative Example 1 comprises the following steps:

[0060] S1 Check the air tightness of the reactor, replace the atmosphere with nitrogen three times, preheat the reactor to 80°C, replace the atmosphere with nitrogen once, add 15 parts of methanol to the reactor feed port, introduce 4MPa ethylene, and stir for 2h;

[0061] S2 adds 100 parts of vinyl acetate and 0.1 parts of azobisisobutyronitrile under pressure, raises the temperature to 60°C, reacts for 4 hours under stirring, maintains the pressure at 4MPa, and cools to 28°C; then adds 1000ppm (based on the mass of ethylene-vinyl acetate copolymer) of terminator copper acetate, stirs for 2 hours to obtain a mixed solution containing ethylene-vinyl acetate copolymer, releases the pressure to flash off to remove excess ethylene, and then removes excess vinyl acetate and methanol by reduced pressure distillation to obtain ethylene-vinyl acetate copolymer (EVA), and alcoholizes EVA to obtain crude EVOH;

[0062] The crude EVOH obtained in S3 is washed with water and vacuum dried before entering the extrusion equipment, and then pelletized and cleaned to obtain EVOH particles.

[0063] M of EVOH particles w =84.4k,M n =42.8k, PDI=1.97, and ethylene content is 18.5mol%. Compared with Example 1, Comparative Example 1 does not use an adsorbent, so that the ethylene content in the synthesized EVOH is low.

[0064] Comparative Example 2

[0065] The difference from Embodiment 1 is that step S1 is not performed.

[0066] The M of synthesized EVOH particles w =72.6k,M n =37.23k, PDI=1.95, and ethylene content of 26.3mol%. Compared with Example 1, Comparative Example 2 did not pretreat the adsorbent, resulting in a decrease in the ethylene content of the synthesized EVOH and a broadening of the molecular weight distribution.

[0067] Comparative Example 3

[0068] The difference from Example 1 is that in step S1, the washing liquid consists of 0.1 wt.% sodium dodecyl sulfate, and the pH of the washing liquid is 7.4.

[0069] The M of synthesized EVOH particles w =62.7 k, M n =32.3 k, PDI=1.94, and ethylene content is 23.7 mol%. Compared with Example 1, in Comparative Example 3, when the adsorbent is pretreated with a weakly alkaline washing solution, the molecular weight distribution of EVOH becomes broadened and the ethylene content decreases.

Claims

1. A method for synthesizing EVOH, characterized in that: The following steps are involved: S1: washing the adsorbent in a washing liquid, then soaking the adsorbent in a hydrochloric acid solution, shaking, filtering, naturally cooling to room temperature, and baking for later use; wherein the adsorbent is silica gel, activated carbon or Y-type zeolite molecular sieve; S2: adding the adsorbent treated in step S1 to an organic solvent, and then injecting ethylene, and after mixing, the ethylene is uniformly adsorbed on the adsorbent; S3: vinyl acetate and an initiator are mixed, and the mixture is mixed with an adsorbent having ethylene adsorbed thereon for reaction, and a terminator, copper acetate, is added to stop the reaction, and the pressure is released to discharge the ethylene to obtain a mixed solution containing ethylene-vinyl acetate copolymer. The mixed solution is filtered to separate the adsorbent, and then subjected to desolventization, removal of excess vinyl acetate, and alcoholysis to obtain a crude EVOH product. The crude EVOH obtained in S4 is washed with water, vacuum dried, and then enters the extrusion equipment, and then pelletized and washed to obtain EVOH; In parts by weight, the amount of vinyl acetate added is 100 parts, the amount of organic solvent added is 15-40 parts, the amount of initiator added is 0.01-0.3 parts, and the amount of adsorbent added is 10-50 parts; the amount of terminator added is 500-1500ppm of the mass of ethylene-vinyl acetate copolymer; In step S1, the pH of the washing solution is 5-6.

2. The method for synthesizing EVOH according to claim 1, characterized in that: In step S1, the washing solution includes a surfactant and a weak acid.

3. The method for synthesizing EVOH according to claim 2, characterized in that: The surfactant is sodium vinyl sulfonate, sodium dodecylbenzene sulfonate or disodium lauryl sulfosuccinate; and the weak acid is a 3-8wt.% hydrochloric acid solution.

4. The method for synthesizing EVOH according to claim 1, characterized in that: In step S1, the adsorbent is immersed in a 3-8 wt.% hydrochloric acid solution at room temperature for 1-5 hours, shaken at 80-100°C for 4-8 hours, and baked at 50-80°C for standby use.

5. The method for synthesizing EVOH according to claim 1, characterized in that: In step S2, the mixing temperature of the ethylene and the adsorbent is 40-80°C, and the mixing time is 2-10 hours.

6. The method for synthesizing EVOH according to claim 1, characterized in that: In step S2, the ethylene pressure is 1-3 MPa.

7. The method for synthesizing EVOH according to claim 1, characterized in that: In step S2, the organic solvent is methanol, ethanol or isopropanol.

8. The method for synthesizing EVOH according to claim 1, characterized in that: In step S3, the initiator is azobisisobutyronitrile, azobisisoheptanenitrile or dimethyl azobisisobutyrate.

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