Alcoholysis method of EVA

Abstract

The present invention discloses a method for alcoholysis of EVA, which relates to the technical field of EVA. The technical solution is as follows: S1 Soak the alkaline anion exchange resin in deionized water for swelling; S2 Wash the alkaline anion exchange resin in deionized water; S3 Pack the washed alkaline anion exchange resin in a chromatography column and wash it with a hydrochloric acid solution; S4 Wash the eluted alkaline anion exchange resin with deionized water until neutral, and then wash it with a sodium hydroxide solution to obtain the activated alkaline anion exchange resin; S5 Pass the EVA solution through the activated alkaline anion exchange resin chromatography column to obtain crude EVOH; S6 The crude EVOH after alcoholysis is washed with water and dried under vacuum, then enters the extrusion equipment, and is granulated and washed to obtain EVOH resin. The present invention solves the problems of introducing metal impurities by the NaOH catalyst, complex post-treatment process and environmental pollution, and reduces the preparation difficulty and cost of EVOH.

Description

Technical Field

[0001] The present invention relates to the technical field of EVA, and specifically relates to a method for alcoholysis of EVA. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a polymer material with special properties and is a crystalline polymer with a chain structure. EVOH combines the good processability of ethylene polymers and the extremely high gas barrier property of vinyl alcohol polymers, and is a new type of high-barrier material. On the one hand, the gas barrier property of EVOH is ten thousand times that of the commonly used product PE of the same kind, so it can effectively extend the shelf life and fragrance retention period of food; on the other hand, it has excellent physical properties, such as good transparency, gloss, mechanical properties, etc., is easy to mold and process, and can be made into products of various shapes and sizes. In addition, EVOH does not contain chlorine elements and dioxins, waste materials can be recycled, and carbon dioxide and water are generated during incineration, belonging to excellent packaging materials, and thus are widely used in packaging materials, the automotive field, the medical field, etc.

[0003] Conventional methods for preparing EVOH are generally prepared by alcoholysis reaction of ethylene-vinyl acetate copolymer (EVA). Traditional alcoholysis reactions usually use NaOH as a catalyst, but this method has many deficiencies: 1) Metal ion residues: NaOH catalyst may introduce metal ions during the reaction process, and these ions are difficult to remove, which will affect the purity and performance of the product; 2) Complicated post-treatment: When using NaOH as a catalyst, complex subsequent treatment steps are required, such as neutralizing, washing, and drying the EVOH product, increasing the production cost and process complexity; 3) Environmental pollution: Waste water, waste gas, and waste residue may be generated during the use and subsequent treatment of NaOH catalyst, causing certain pollution to the environment. Therefore, finding a catalyst to replace NaOH to overcome the above deficiencies has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, provide a method for alcoholysis of EVA, use an alkaline anion exchange resin as a catalyst, solve the problems that the NaOH catalyst may introduce metal impurities, the post-treatment process is complicated, and it may cause environmental pollution, the process is simple and environmentally friendly, and greatly reduces the preparation difficulty and preparation cost of EVOH.

[0005] The technical solution of the present invention is as follows:

[0006] A method for alcoholysis of EVA, comprising the following steps:

[0007] S1 Soak the alkaline anion exchange resin in deionized water for swelling;

[0008] S2 Wash the swollen alkaline anion exchange resin in deionized water;

[0009] S3 Pack the washed alkaline anion exchange resin into a chromatography column and elute it with a 1 - 6 mol / L hydrochloric acid solution until there are no impurities such as Fe 3+ , Cu 2+ , Mg 2+ in the eluate, which macroscopically shows a colorless solution; at this time, the fixed cation of the alkaline anion exchange resin is still the quaternary ammonium group, and the anion group has been changed to Cl - ;

[0010] S4 After washing the eluted alkaline anion exchange resin with deionized water until it is neutral, then elute it with a 1 - 10 mol / L sodium hydroxide solution to obtain the activated alkaline anion exchange resin; at this time, the fixed cation of the alkaline anion exchange resin is the quaternary ammonium group, and the anion group has become OH - again after being eluted with the sodium hydroxide solution; during the entire elution process of steps S3 and S4, first use the hydrochloric acid solution to wash away the residual metal ions, wash with deionized water until neutral, and then use the sodium hydroxide solution to wash until the anion group of the alkaline anion exchange resin becomes OH - again; during the elution process of the sodium hydroxide solution, Cl - is continuously washed off. Essentially, the eluate is a mixed solution of sodium hydroxide and sodium chloride, and the anion on the alkaline anion exchange resin can be judged whether it has been completely replaced by OH - by titrating Cl - or detecting the pH of the eluate;

[0011] S5 Pass the EVA solution through the activated alkaline anion exchange resin chromatography column to carry out the alcoholysis reaction of EVA to obtain crude EVOH;

[0012] S6 The crude EVOH after alcoholysis is washed with water, vacuum dried, then enters the extrusion equipment, and finally obtained EVOH resin after pelletizing and cleaning.

[0013] Preferably, in step S1, the alkaline anion exchange resin is 201×7MBFC, D201 or LH - 400Cl alkaline anion exchange resin; the soaking and swelling time is 6 - 12 h. Among them, the fixed cation group of the 201×7MBFC alkaline anion exchange resin is the quaternary ammonium group, which can adsorb and exchange anions with negative charges, and the exchange anion group is OH - , used to capture acidic substances and acidic ions; the fixed cation groups of D201 and LH - 400Cl alkaline anion exchange resins are the quaternary ammonium groups, which can adsorb and exchange anions with negative charges, and the exchange anion group is Cl -, which is used to capture acidic substances and acidic ions.

[0014] Preferably, in step S5, the concentration of the EVA solution is 4-25 wt.%.

[0015] Preferably, in step S5, the alcoholysis reaction temperature is 40-70 °C, and the flow rate of the EVA solution in the activated alkaline anion exchange resin chromatography column is 1-80 mL / h.

[0016] Preferably, in step S5, the EVA solution is passed through three activated alkaline anion exchange resin chromatography columns in sequence, and a continuous stirred tank reactor with stirring and heating functions is arranged between the chromatography columns.

[0017] Preferably, it further includes step S7, and the used alkaline anion exchange resin in step S5 is activated in sequence with a good solvent, deionized water and a sodium hydroxide solution to restore its catalytic activity and retain it for repeated use; if the alkaline anion exchange resin used in step S5 is a newly used one, steps S1-S4 need to be carried out, and if the alkaline anion exchange resin used in step S5 is the one treated by step S7, steps S1-S4 are not carried out and it is directly used in step S5.

[0018] Preferably, in step S7, the good solvent is tetrahydrofuran or N,N-dimethylformamide.

[0019] Preferably, in step S7, the concentration of the sodium hydroxide solution is 1-10 mol / L.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The surface of the alkaline anion exchange resin of the present invention is provided with alkaline anion exchange groups, which can change the charge state and reaction activity of the reactants, thereby reducing the activation energy of the reaction and accelerating the reaction efficiency, so as to realize the alcoholysis reaction of EVA. Among them, the alkaline anion exchange groups are mainly quaternary ammonium groups, which dissociate OH - in water and show strong alkalinity, and can adsorb and combine with anions in the solution to produce anion exchange. And after the present invention uses the alkaline anion exchange resin to replace the NaOH catalyst, no metal ions are introduced and no post-treatment is required, which not only simplifies the EVA alcoholysis process, but also reduces the solvent usage and pure water usage in the post-treatment process, being green, environmentally friendly, economical and applicable.

[0022] 2. After the alkaline anion exchange resin of the present invention is used up, it can be activated, recycled and reused, greatly reducing the production cost. Specific embodiments

[0023] To enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0024] Example 1

[0025] The alcoholysis method of EVA in this example includes the following steps:

[0026] S1 Take 20 parts of 201×7MBFC alkaline anion exchange resin and soak it in sufficient deionized water for 10 h to swell.

[0027] S2 Take the swollen 201×7MBFC alkaline anion exchange resin and wash it in deionized water to remove surface and soluble impurities.

[0028] S3 Pack the washed 201×7MBFC alkaline anion exchange resin into a chromatography column and wash it with 1 mol / L hydrochloric acid solution at a flow rate of 4 mL / min until there are no impurities such as Fe 3+ , Cu 2+ , Mg 2+ in the eluent, macroscopically showing a colorless solution.

[0029] S4 After washing the washed 201×7MBFC alkaline anion exchange resin with deionized water until it is neutral, then wash it with 1 mol / L sodium hydroxide solution at a flow rate of 4 mL / min to obtain the activated 201×7MBFC alkaline anion exchange resin, and the anion is exchanged into OH - ;

[0030] S5 Pack the activated 201×7MBFC alkaline anion exchange resin into three chromatography columns A, B, and C. The inner diameter of the chromatography column is 26 mm and the height is 20 cm, and it is equipped with a heat preservation layer with a temperature of 50°C. Pump the methanol solution of EVA with a concentration of 25 wt.% from bottom to top for washing at a feeding rate of 24 mL / h, and pass through the three chromatography columns in sequence to carry out the alcoholysis reaction of EVA; a continuous stirred tank reactor (CSTR) with stirring and heating functions is arranged between the chromatography columns to remove the by-product methyl acetate generated by the methanol transesterification reaction during the reaction. The overflow volume of the CSTR is 500 mL, the top is open and equipped with a condensation recovery device, the heating temperature is 60°C, and the stirring rate is 200 rpm. After the EVA solution is catalytically alcoholyzed by the 201×7MBFC alkaline anion exchange resin three times, the degree of alcoholysis can reach 99.5% to obtain the crude EVOH.

[0031] The crude EVOH product after alcoholysis of S6 is washed with water and dried under vacuum, then enters the extrusion equipment, and after pelletizing and cleaning, the EVOH resin is obtained. No obvious yellowing or other color impurities are found in the EVOH resin;

[0032] S7 First, use tetrahydrofuran to dissolve and remove the residual basic anion exchange resin in the chromatography column, and then wash it with deionized water and 1mol / L sodium hydroxide solution to remove the acetate ions in the basic anion exchange resin. The flow rate of the sodium hydroxide solution is 4mL / min; the finally obtained basic anion exchange resin can be used again as the alcoholysis catalyst of EVA, and it is applied to the alcoholysis of EVA in step S5. The alcoholysis degree of EVA is 99.6%, indicating that the basic anion exchange resin can be recycled and reused without affecting the EVA alcoholysis reaction, reducing the production cost and saving the solvent.

[0033] Example 2

[0034] The alcoholysis method of EVA in this example includes the following steps:

[0035] S1 Take 20 parts of D201 basic anion exchange resin and soak it in sufficient deionized water for 12h to swell;

[0036] S2 Take the swollen D201 basic anion exchange resin and wash it in deionized water to remove surface and soluble impurities;

[0037] S3 Pack the washed D201 basic anion exchange resin in a chromatography column and wash it with 6mol / L hydrochloric acid solution. The washing flow rate of the hydrochloric acid solution is 4mL / min until there are no Fe 3+ , Cu 2+ , Mg 2+ and other impurities, which macroscopically show a colorless solution;

[0038] S4 After washing the washed D201 basic anion exchange resin with deionized water to neutrality, then wash it with 10mol / L sodium hydroxide solution. The washing flow rate of the sodium hydroxide solution is 4mL / min to obtain the activated D201 basic anion exchange resin, and the anion is exchanged into OH - ;

[0039] S5 Fill the activated D201 alkaline anion exchange resin into three chromatography columns A, B, and C. The inner diameter of the chromatography column is 26 mm, the height is 20 cm, and it is equipped with a thermal insulation layer with a temperature of 70 °C. Feed and wash the methanol solution of EVA with a concentration of 12 wt.% from bottom to top at a feed rate of 80 mL / h, passing through the three chromatography columns in sequence to carry out the alcoholysis reaction of EVA; a continuous stirred tank reactor (CSTR) with stirring and heating functions is arranged between the chromatography columns to remove the by-product methyl acetate generated by the methanol transesterification reaction during the reaction. The overflow volume of the CSTR is 500 mL, the top is open and equipped with a condensation recovery device, the heating temperature is 60 °C, and the stirring rate is 200 rpm. After the EVA solution undergoes alcoholysis catalyzed by the D201 alkaline anion exchange resin three times, the degree of alcoholysis can reach 99.2% to obtain the crude EVOH product;

[0040] S6 Wash the crude EVOH product after alcoholysis with water and then dry it under vacuum, and then enter the extrusion equipment. After pelletizing and cleaning, the EVOH resin is obtained, and no obvious yellowing or other color impurities are found in the EVOH resin;

[0041] S7 First, use tetrahydrofuran to dissolve and remove the residual alkaline anion exchange resin in the chromatography column, and then wash it with deionized water and 10 mol / L sodium hydroxide solution to remove the acetate ions in the alkaline anion exchange resin. The flow rate of the sodium hydroxide solution is 4 mL / min; the finally obtained alkaline anion exchange resin can be used again as an alcoholysis catalyst for EVA, and it is applied to participate in the alcoholysis of EVA in step S5. The degree of alcoholysis of EVA is 99.3%, indicating that the alkaline anion exchange resin can be recycled and reused without affecting the EVA alcoholysis reaction, reducing the production cost and saving the solvent.

[0042] Example 3

[0043] The alcoholysis method of EVA in this example includes the following steps:

[0044] S1 Take 20 parts of LH-400CL alkaline anion exchange resin and soak it in sufficient deionized water for 6 h to swell;

[0045] S2 Take the swollen LH-400CL alkaline anion exchange resin and wash it in deionized water to remove surface and soluble impurities;

[0046] S3 Load the washed LH-400CL alkaline anion exchange resin into the chromatography column and wash it with 3 mol / L hydrochloric acid solution at a washing flow rate of 4 mL / min until there are no Fe 3+ , Cu 2+ , Mg 2+ and other impurities, which macroscopically show a colorless solution;

[0047] After washing the leached LH-400CL basic anion exchange resin with deionized water until neutral, it was then leached with a 5 mol / L sodium hydroxide solution at a leaching flow rate of 4 mL / min to obtain the activated LH-400CL basic anion exchange resin, and the anion was exchanged into OH - ;

[0048] S5 The activated LH-400CL basic anion exchange resin was filled into three chromatography columns A, B, and C. The inner diameter of the chromatography column was 26 mm, the height was 20 cm, and it had a heat-insulating layer with a temperature of 40 °C. A methanol solution of EVA with a concentration of 4 wt.% was fed and washed from bottom to top at a feeding rate of 1 mL / h, passing through the three chromatography columns in sequence to carry out the alcoholysis reaction of EVA; A continuous stirred tank reactor (CSTR) with stirring and heating functions was set between the chromatography columns to remove the by-product methyl acetate generated by the methanol transesterification reaction during the reaction. The overflow volume of the CSTR was 500 mL, the top was open and equipped with a condensation recovery device, the heating temperature was 60 °C, and the stirring rate was 200 rpm. After the EVA solution was catalytically alcoholyzed by the LH-400CL basic anion exchange resin three times, the degree of alcoholysis could reach 99.4% to obtain crude EVOH;

[0049] S6 The crude EVOH after alcoholysis was washed with water and dried under vacuum, then entered the extrusion equipment, and after pelletizing and cleaning, EVOH resin was obtained. No obvious yellowing or other color impurities were found in the EVOH resin;

[0050] S7 First, N,N-dimethylformamide was used to dissolve and remove the residual basic anion exchange resin in the chromatography column, and then deionized water and a 5 mol / L sodium hydroxide solution were used to wash and remove the acetate ions in the basic anion exchange resin at a flow rate of 4 mL / min for the sodium hydroxide solution; The finally obtained basic anion exchange resin could be reused as a catalyst for the alcoholysis of EVA, and it was applied to participate in the alcoholysis of EVA in step S5. The degree of alcoholysis of EVA was 99.3%, indicating that the basic anion exchange resin could be recycled and reused without affecting the alcoholysis reaction of EVA, reducing the production cost and saving the solvent.

[0051] Comparative Example 1

[0052] The difference from Example 1 was that step S3 was not carried out.

[0053] Finally, in step S5, the degree of alcoholysis of EVA was 98.2%; there were red and yellow color impurities in the EVOH resin obtained in step S6, and after analysis, they were Fe 3+ 、Cu 2+Precipitation color of metal ions in alkaline solution; in step S7, the alcoholysis degree of EVA is 98.5%, and there are also red and yellow color impurities in the EVOH resin.

[0054] Comparative Example 2

[0055] The difference from Example 1 is that step S4 is not carried out, and in step S7, the basic anion exchange resin is only washed with good solvent and deionized water, without using sodium hydroxide solution to wash the basic anion exchange resin.

[0056] Finally, in step S5, the alcoholysis degree of EVA is 65.2%, and no red, yellow or other color impurities are found in the EVOH resin; in step S7, the alcoholysis degree of EVA is 34%, and no red, yellow or other color impurities are found in the EVOH resin. This is because all anions of the basic anion exchange resin are OH - Only when it has strong alkalinity, and in Comparative Example 2, since the basic anion exchange resin is not rinsed with sodium hydroxide solution, some negative ions of the basic anion exchange resin are Cl - At this time, the basic anion exchange resin is weakly basic or weakly acidic, resulting in weak alcoholysis catalytic activity.

[0057] Comparative Example 3

[0058] The difference from Example 1 is that in step S5, only two chromatographic columns A and B are set, and a CSTR is set between the two chromatographic columns.

[0059] Finally, in step S5, the alcoholysis degree of EVA is 98.2%, and no obvious red, yellow or other color impurities are found in the EVOH resin; in step S7, the finally obtained basic anion exchange resin is applied to participate in the alcoholysis of EVA in step S5. Similarly, only through two chromatographic columns and a CSTR, the alcoholysis degree of EVA is 98.4%, and no obvious red, yellow or other color impurities are found in the EVOH resin. It shows that most of the EVA alcoholysis reaction is basically completed in the two basic anion exchange resin chromatographic columns, and the third basic anion exchange resin chromatographic column can play a role in further improving the alcoholysis degree of EVA.

[0060] Comparative Example 4

[0061] The difference from Example 1 is that in step S3, the concentration of the hydrochloric acid solution is 0.01 mol / L.

[0062] In the final step S5, the alcoholysis degree of EVA is 99.4%, and there are red and yellow color impurities in the EVOH resin; in step S7, the alcoholysis degree of EVA is 99.2%, and there are also red and yellow color impurities in the EVOH resin. This is because when the concentration of the hydrochloric acid solution is too low, it may cause the inability to remove the Fe and Cu element impurities present in the basic anion exchange resin for a long time. These element impurities will produce colored precipitates during the sodium hydroxide washing, and these colored precipitates are the reasons for the red and yellow color impurities in the EVOH resin.

[0063] Comparative Example 5

[0064] The difference from Example 1 is that in step S4, the concentration of the sodium hydroxide solution is 0.02 mol / L.

[0065] In the final step S5, the alcoholysis degree of EVA is 54.2%, and there are no red, yellow or other color impurities in the EVOH resin; in step S7, the alcoholysis degree of EVA is 22.7%, and there are also no red, yellow or other color impurities in the EVOH resin. This is because when the concentration of the sodium hydroxide solution is too low, the sodium hydroxide solution elution of the basic anion exchange resin within a certain period of time may cause the Cl - in the basic anion exchange resin cannot be completely replaced by OH - , which may cause the basic anion exchange resin not to have extreme strong alkalinity, thus affecting the alcoholysis degree.

[0066] Comparative Example 6

[0067] The difference from Example 1 is that in step S5, the methanol solution of EVA is replaced by an isopropanol solution of EVA, and the temperature of the insulation layer is 80 °C.

[0068] In the final step S5, the alcoholysis degree of EVA is 99.6%, and the EVOH resin shows yellow color impurities; in step S7, the alcoholysis degree of EVA is 99.3%, and the EVOH resin also shows yellow color impurities. This is because the alcoholysis reaction temperature is too high and the alcoholysis rate is too fast, and the alcoholysis may be completed in the early stage of the basic anion exchange resin chromatography column. Under the condition of continuous high-temperature insulation in the middle section, the EVOH resin is oxidized, which leads to its yellowing phenomenon.

[0069] Comparative Example 7

[0070] The difference from Example 1 is that in step S7, the concentration of the sodium hydroxide solution is 0.02 mol / L.

[0071] In the final step S5, the alcoholysis degree of EVA is 99.5%, and no red or yellow color impurities appear in the EVOH resin; in step S7, the alcoholysis degree of EVA is 32.7%, and no red or yellow color impurities appear in the EVOH resin either. This is because when the concentration of the sodium hydroxide solution is too low, activating the alkaline anion exchange resin may cause Cl - not to be completely replaced by OH - , which may result in the alkaline anion exchange resin not having extreme strong alkalinity, thus affecting the alcoholysis degree.

Claims

1. A method for alcoholysis of EVA, characterized in that: The following steps are involved: S1: soaking and swelling the alkaline anion exchange resin in deionized water; S2 washing the swollen basic anion exchange resin in deionized water; S3: loading the washed alkaline anion exchange resin into a chromatography column and eluting it with a 1-6 mol / L hydrochloric acid solution; S4: washing the washed alkaline anion exchange resin with deionized water until it is neutral, and then washing it with a 1-10 mol / L sodium hydroxide solution to obtain an activated alkaline anion exchange resin; S5: passing the EVA solution through three activated alkaline anion exchange resin chromatography columns in sequence, and a continuous stirring reactor with stirring and heating functions is arranged between the chromatography columns to make the EVA undergo alcoholysis reaction at a temperature of 40-70° C. to obtain a crude EVOH product; S6 The crude EVOH after alcoholysis is washed with water and vacuum dried before entering the extrusion equipment, and then pelletized and cleaned to obtain EVOH resin; In S7, a good solvent, deionized water and sodium hydroxide solution are used in sequence to activate the alkaline anion exchange resin used in step S5, to restore its catalytic activity, and to retain it for repeated use. The concentration of the sodium hydroxide solution is 1-10 mol / L. If the alkaline anion exchange resin used in step S5 is used for the first time, steps S1-S4 need to be performed. If the alkaline anion exchange resin used in step S5 is treated in step S7, steps S1-S4 are not performed and it is directly used in step S5.

2. The alcoholysis method of EVA as claimed in claim 1, characterized in that In step S1, the alkaline anion exchange resin is 201×7MBFC, D201 or LH-400Cl alkaline anion exchange resin; and the soaking and swelling time is 6-12 hours.

3. The alcoholysis method of EVA as claimed in claim 1, characterized in that, In step S5, the concentration of the EVA solution is 4-25wt.%.

4. The alcoholysis method of EVA as claimed in claim 1, characterized in that, In step S5, the flow rate of the EVA solution in the activated alkaline anion exchange resin chromatography column is 1-80 mL / h.

5. The alcoholysis method of EVA as claimed in claim 1, characterized in that, In step S7, the good solvent is tetrahydrofuran or N,N-dimethylformamide.