Preparation method of modified activated carbon and application of acidified modified activated carbon in alcoholysis of EVA (Ethylene Vinyl Acetate)

Abstract

The invention discloses a preparation method of modified activated carbon and application of acidified modified activated carbon in EVA alcoholysis, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: S1, carbonizing biomass under an inert gas condition to obtain a silicon oxide / carbon compound; the biomass comprises lignin, cellulose and silicon dioxide; s2, carrying out ball milling and crushing on the silicon oxide / carbon compound, and soaking in an alkaline solution to remove silicon oxide in the silicon oxide / carbon compound, so as to obtain a carbon elementary substance; s3, mixing the elemental carbon and the acidic modified liquid, and acidifying to obtain acidified modified activated carbon; the acidic modified liquid comprises an oxidizing agent, inorganic acid and water. The prepared modified activated carbon can be used for effectively removing impurities in the EVA alcoholysis process, and the application method is simple, low in energy consumption and beneficial to industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and relates to a preparation method of modified activated carbon and the application of acid-modified activated carbon in the alcoholysis of EVA. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a linear crystalline polymer, generally formed by alcoholysis of ethylene-vinyl acetate copolymer (EVA) in the presence of a basic catalyst such as an alkali metal salt. Among them, EVOH with an ethylene structural molar percentage content of 20-80% has excellent barrier properties and is often used in packaging such as food, medical, and fuel tanks, which is closely related to daily life and has a large demand. The residue of alkali metal salts is one of the key factors affecting the quality of EVOH, because alkali metal salts usually cause the EVOH product to turn yellow and increase the ash content, resulting in a decrease in the purity and heat resistance of the product.

[0003] Taking NaOH as an example of the basic catalyst, the generation process and reaction principle of alkali metal salts during the alcoholysis process include: methyl acetate remaining in the alcoholysis solution reacts with sodium hydroxide to form sodium acetate; after the alcoholysis is completed, the alkali metal salts generated during the neutralization process, taking acetic acid as the neutralizing acid, acetic acid reacts with sodium hydroxide to form sodium acetate. The reaction formulas are as follows:

[0004] CH3COOCH3 + NaOH → CH3COONa;

[0005] CH3COOH + NaOH → CH3COONa.

[0006] In current industrial production, generally, the method of repeatedly washing the extruded and granulated EVOH particles with water is used to remove alkali metal salts. This method is simple, but the impurity removal efficiency is low, the washing effect is poor, and a large amount of water resources is wasted. To reduce water consumption, etc., the Chinese patent document with publication number CN 112707986 A discloses a purification method of ethylene-vinyl alcohol copolymer; mainly, continuous water addition and stirring washing are carried out in the semi-molten state of EVOH to reduce the content of impurities such as sodium acetate in the product. Although this method improves the washing efficiency to a certain extent and reduces water consumption, it can only be achieved under high temperature, certain pressure, and long-time washing, which requires high equipment requirements and increases energy consumption at the same time. Summary of the Invention

[0007] To solve the problem of EVOH impurity removal, the present invention provides a preparation method of modified activated carbon and the application of acid-modified activated carbon in the alcoholysis of EVA. By using the prepared modified activated carbon, impurities can be effectively removed during the alcoholysis process of EVA. This application method is simple and has low energy consumption, which is beneficial to industrial production.

[0008] The present invention provides a method for preparing modified activated carbon, comprising the following steps:

[0009] S1, carbonizing biomass under inert gas conditions to obtain a silicon oxide / carbon composite; the components of the biomass include lignin, cellulose and silicon dioxide;

[0010] S2, grinding the silicon oxide / carbon composite by ball milling, and then soaking in an alkaline solution to remove silicon oxide therein, thereby obtaining a single carbon substance;

[0011] S3, mixing the carbon element and the acidic modified liquid and then acidifying to obtain acidified modified activated carbon; the acidic modified liquid contains an oxidant, an inorganic acid and water.

[0012] Preferably, in step S1, before carbonizing, the biomass is also soaked in a low-concentration acid solution, washed to neutrality and then separated, and dried to obtain clean biomass; the concentration of the low-concentration acid solution is 0.01-1 mol / L; the drying temperature is 25-100°C.

[0013] Preferably, in step S1, the carbonization is carried out in a rotary vacuum device; at least one of the following conditions is satisfied: the inert gas flow rate is 10 to 100 mL / min; the rotation speed of the rotary vacuum device is 10 to 200 r / min; and the carbonization time is 0.5 h to 5 h.

[0014] Preferably, in step S2, at least one of the following is satisfied: the average particle size of the silicon oxide / carbon composite after ball milling is 0.05 to 5 μm; the solute of the alkaline solution is one or more of hydroxides, carbonates, bicarbonates and alcoholates of a metal substance, and the metal substance is an alkali metal or an alkaline earth metal; the solute concentration of the alkaline solution is 0.01 to 10 mol / L.

[0015] Preferably, in step S3, the acidification is achieved by shaking in a water bath shaker; at least one of the following is satisfied: the oxidant is one or more of hydrogen peroxide, nitric acid and peracetic acid, with a mass fraction of 1 to 30 wt%; the inorganic acid is one or more of hydrochloric acid, phosphoric acid and nitric acid, with a mass fraction of 1 to 30 wt%; the shaking temperature of the water bath shaker is 25 to 80°C, and the shaking time is 0.5 to 5 h.

[0016] The most common functional groups on the surface of activated carbon are oxygen-containing functional groups, including carboxyl, lactone, phenolic hydroxyl, carbonyl, etc. Among them, carboxyl, phenolic hydroxyl and lactone are acidic functional groups, which can react with alkaline substances and adsorb alkali metal ions.

[0017] The present invention provides a method for preparing modified activated carbon. Using biomass as a raw material, it mainly undergoes carbonization, ball milling and pulverization, and alkali washing, and then oxidative acidification to obtain acidified modified activated carbon. In the present invention, after the biomass is carbonized, it undergoes ball milling and pulverization and alkali washing treatment steps. In the process of effectively removing silicon oxide in the carbon material, more carbon layers are exposed, increasing the specific surface area of the carbon material, which helps it to be fully acidified subsequently. After the biomass-based activated carbon is specifically acidified in the present invention, the content of acidic functional groups on the surface of the activated carbon increases, and the surface is acidic, which can achieve a higher adsorption efficiency for alkali metal ions and is beneficial for applications such as the alcoholysis of EVA. In addition, the raw material for preparing the modified activated carbon in the present invention is derived from biomass, which conforms to the concept of current green environmental protection.

[0018] The present invention provides a method for the alcoholysis of EVA, comprising the following steps:

[0019] Mix EVA, a basic catalyst and a solvent and then carry out an alcoholysis reaction to obtain an alcoholysis product;

[0020] Use an activated carbon adsorbent to adsorb and remove impurities from the alcoholysis product to obtain EVOH; the activated carbon adsorbent is the acidified modified activated carbon obtained by the preparation method described above.

[0021] Preferably, the preparation of the EVA comprises: under a protective atmosphere, polymerize vinyl acetate and ethylene in the presence of an initiator to obtain transparent EVA; satisfying at least one of the following: the ratio of the volume of vinyl acetate to the mass of the initiator is (1 - 100) mL : (1 - 100) g; the ethylene pressure is 0.01 - 10 MPa; the temperature of the polymerization is 60 - 100 °C, and the time is 0.5 - 10 h.

[0022] Preferably, the carrying out of the alcoholysis reaction comprises: mix the EVA, a first basic catalyst and a first solvent and then carry out a first-stage alcoholysis, then add a first activated carbon adsorbent under stirring, adsorb for at least 10 min and then raise the temperature, and add a second basic catalyst to carry out a second-stage alcoholysis to obtain an alcoholysis product; the first activated carbon adsorbent is the acidified modified activated carbon obtained by the preparation method described above;

[0023] Satisfying at least one of the following: the first solvent is subjected to dehydration treatment; the first solvent is one or more of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate, tetrahydrofuran, petroleum ether, acetone and hexane; the first basic catalyst and the second basic catalyst are respectively one or more of sodium hydroxide, potassium hydroxide, sodium ethoxide, calcium hydroxide, sodium carbonate and potassium bicarbonate.

[0024] Preferably, at least one of the following conditions is satisfied: the concentrations of the first basic catalyst and the second basic catalyst are respectively 0.01 - 1 mol / L; the temperatures of the first-stage alcoholysis and the second-stage alcoholysis are respectively 40 - 80 °C, and the times are respectively 0.5 - 10 h; the mass ratio of the acidified modified activated carbon to EVA is 1:10 - 100, and the adsorption time is 10 - 60 min.

[0025] Preferably, in the alcoholysis product, a second activated carbon adsorbent is added under stirring. After adsorption for at least 10 min, an acidic organic solution is added and neutralized to neutrality, and then EVOH is obtained by separation; the second activated carbon adsorbent is the acidified modified activated carbon obtained by the preparation method described above.

[0026] At least one of the following conditions is satisfied: the mass ratio of the second activated carbon adsorbent to EVA is 1:10 - 100, and the adsorption time is 10 - 60 min; the concentration of the acidic organic solution is 0.01 - 10 mol / L; the acidic organic solution is one or more of acetic acid solution, boric acid solution and hydrochloric acid solution, and the organic solvent in the acidic organic solution is one or more of ether, methanol, ethanol, tert-butanol, dimethyl carbonate, tetrahydrofuran, petroleum ether, acetone and hexane.

[0027] Compared with the prior art, in the method for alcoholysis of EVA provided by the present invention, the acidified modified activated carbon described above is used to adsorb and remove impurities from the EVA alcoholysis product, thereby obtaining EVOH. In the alcoholysis process of the present invention, the acidified modified activated carbon is used to adsorb alkali metal ions, which is simple and easy to operate, can avoid the stage of repeatedly washing with water, and saves water resources. Moreover, the adsorption process is carried out at the alcoholysis temperature and normal pressure, with low requirements for equipment, and is safe and environmentally friendly. The present invention can improve the yellowness and heat resistance of EVOH while reducing energy consumption, which is beneficial to industrial production.

[0028] Furthermore, the present invention adopts stepwise temperature increase, stepwise addition of basic catalyst, and stepwise addition of acidified modified activated carbon, which can promote the formation of EVOH, avoid the risk that the amount of methyl acetate (the EVA alcoholysis reaction is a reversible reaction, and methyl acetate is the main by-product) increases instantaneously and cannot be discharged from the alcoholysis system in time, and improve the alcoholysis degree of EVOH while removing impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall process of some embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to more clearly understand the technical features, objectives and effects of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0031] The present invention provides a method for preparing modified activated carbon, comprising the following steps:

[0032] S1, carbonizing biomass under inert gas conditions to obtain a silicon oxide / carbon composite; the components of the biomass include lignin, cellulose and silicon dioxide;

[0033] S2, grinding the silicon oxide / carbon composite by ball milling, and then soaking in an alkaline solution to remove silicon oxide therein, thereby obtaining a single carbon substance;

[0034] S3, mixing the carbon element and the acidic modified liquid and then acidifying to obtain acidified modified activated carbon; the acidic modified liquid contains an oxidant, an inorganic acid and water.

[0035] The modified activated carbon prepared by the invention has good adsorption performance, can effectively remove impurities in the process of EVA alcoholysis, etc., and is convenient for application.

[0036] In the embodiment of the present invention, at room temperature, the biomass is preferably soaked with a low concentration hydrochloric acid solution to remove impurities in the biomass; then the biomass is washed with water until neutral, filtered, and dried to obtain clean biomass. The low concentration hydrochloric acid solution may also be other low concentration acid (water) solutions, the solvent is generally deionized water, the concentration may be 0.01 to 1 mol / L, further 0.05 to 0.5 mol / L; the room temperature is generally 15 to 30°C, and the neutral pH range may be 7.0 to 7.5.

[0037] In an embodiment of the present invention, the biomass (mainly composed of lignin, cellulose, silicon dioxide SiO2, etc.) includes one or more of lignocellulose such as straw and trees, waste materials from agricultural product processing industry, agricultural and forestry wastes, and livestock and poultry manure. In some embodiments, the cellulose content in the biomass is 30-40wt%, the lignin content is 12-29wt%, and the silicon dioxide content is 10-20wt%. The present invention uses biomass as a preparation raw material, which is more environmentally friendly. The ratio of the mass of the biomass to the volume of the low-concentration acid solution can be 1:1000-1:10 (g / mL); the soaking time of the low-concentration acid solution can be 0.5-5h; the drying temperature of the washed biomass can be 25-100°C, such as 40-60°C, and the drying time can be 0.5-12h.

[0038] In the embodiments of the present invention, this clean biomass can be placed in equipment such as a rotary vacuum furnace and carbonized (also known as pyrolysis) under the protection of an inert gas to obtain a silicon dioxide / carbon composite (denoted as SiO2 / C composite). When carbonizing, the inert gas used includes one or more of nitrogen (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), etc., generally under nitrogen conditions. The flow rate of the inert gas can be 10 - 100 mL / min, further 20 - 50 mL / min. The rotation speed of the rotary vacuum furnace can be 10 - 200 r / min, for example 50 - 100 r / min; the carbonization time can be 0.5 h - 5 h, preferably 3 - 5 h, to obtain the SiO2 / C composite.

[0039] In the embodiments of the present invention, this composite is ball-milled and pulverized, and then soaked in an alkaline solution to remove SiO2 therein, obtaining elemental carbon. After the biomass in the embodiments of the present invention is carbonized and undergoes the steps of ball-milling and pulverizing and alkali washing, during the process of effectively removing SiO2 from the carbon material, more carbon layers can be exposed, increasing the specific surface area of the carbon material, which helps its subsequent full acidification, etc.

[0040] In some embodiments of the present invention, the ball-milling and pulverizing is carried out using a ball mill, the rotation speed can be 100 - 1000 r / min, and the ball-milling time is preferably 0.5 h - 5 h; the average particle size of the SiO2 / C composite after ball-milling can be 0.05 - 5 μm. The solvent of the alkaline solution can be one or more of polar solvents such as deionized water, methanol, and ethanol, generally an aqueous solution; its basic solute preferably includes one or more of hydroxides, carbonates, and bicarbonates of sodium and potassium, hydroxides, carbonates, and bicarbonates of calcium and magnesium, sodium methoxide, potassium ethoxide, potassium tert-butoxide, etc., and the concentration can be 0.01 - 10 mol / L, further 0.5 - 2 mol / L. The soaking time of the alkaline solution can be 0.5 - 12 h; the mass ratio of the SiO2 / C composite to the volume of the alkaline solution is preferably 1:100 - 1:10 (g / mL).

[0041] In the embodiments of the present invention, the obtained elemental carbon and the acid-modifying solution can be placed in a polyethylene bottle, oscillated in a water bath shaker, filtered, and dried to obtain acid-modified activated carbon; the acid-modifying solution contains an oxidant, an inorganic acid, and water, which can increase the content of acidic oxygen-containing functional groups on the surface of the activated carbon, making the surface acidic and facilitating the adsorption of alkali metal ions, etc.

[0042] Preferably, in the acidic modified liquid, the oxidant is one or more of hydrogen peroxide, nitric acid and peracetic acid, with a mass fraction of 1 to 30 wt%, and further is hydrogen peroxide; the inorganic acid is one or more of hydrochloric acid, phosphoric acid and nitric acid, with a mass fraction of 1 to 30 wt%, and further is phosphoric acid. For example, the acidic modified liquid of some embodiments is composed of 30 wt% hydrogen peroxide aqueous solution and 30 wt% phosphoric acid water.

[0043] The acidification described in the specific embodiment of the present invention is achieved by oscillating in a water bath shaker; the above-mentioned apparatuses should be clean processing equipment commonly used in the art. Among them, the ratio of the mass of the carbon single substance to the volume of the acidic modified liquid can be 1:1000-1:10 (g / mL), and can further be 1:20, 1:30, etc. The oscillation temperature of the water bath shaker is preferably 25-80°C, more preferably 40-60°C; the oscillation time can be 0.5-5h, such as 1h, 2h, 4h, 5h, etc. After filtration, the solid phase can be dried at 100°C to obtain acidified modified activated carbon and retain it. In addition, the various solvents, solutes, biomass, etc. involved are all commercially available.

[0044] The most common functional groups on the surface of activated carbon are oxygen-containing functional groups, including carboxyl, lactone, phenolic hydroxyl, carbonyl, etc., among which carboxyl, phenolic hydroxyl and lactone are acidic functional groups; the functional group structure of the surface of activated carbon is shown below.

[0045]

[0046] The acidified modified activated carbon (hereinafter referred to as acidified activated carbon or acid activated carbon) prepared in the embodiment of the present invention has an acidic surface (pH 2-6), has a large number of acidic functional groups, and a specific surface area (S BET ) can be 1280~1400m 2 / g.

[0047] The present invention provides a method for alcoholysis of EVA, comprising the following steps:

[0048] The EVA, the alkaline catalyst and the solvent are mixed and then subjected to alcoholysis reaction to obtain an alcoholysis product;

[0049] The alcoholysis product is adsorbed and impurized by an activated carbon adsorbent to obtain EVOH; the activated carbon adsorbent is the acidified modified activated carbon obtained by the preparation method described above.

[0050] The embodiment of the present invention is simple in preparing acid modified activated carbon and using it as a purification method for activated carbon to adsorb alkali metal ions during alcoholysis, which reduces the ash content in EVOH, improves the stability of EVOH and reduces energy consumption, etc., and is conducive to industrial production.

[0051] See alsoFigure 1 , Figure 1 is a schematic diagram of the overall reaction process of some embodiments of the present invention. The overall embodiments of the present invention may include three steps: ① preparing acidified (modified) activated carbon; ② preparing EVA by free radical solution polymerization; ③ alcoholyzing EVA to prepare EVOH copolymer.

[0052] In the embodiments of the present invention, an activated carbon adsorbent is mainly used to remove impurities from the product of alcoholyzed EVA. The activated carbon adsorbent is the acidified modified activated carbon obtained by the preparation method described above. Exemplarily, the preparation method described above includes: using biomass as the preparation raw material, removing impurities with hydrochloric acid, washing with water until neutral, and carbonizing under N2 protection to obtain SiO2 / C composite; then ball-milling and pulverizing the SiO2 / C composite, removing SiO2 by alkali washing, and washing until neutral to obtain carbon element C; finally, acidifying with an acidic modification solution containing an oxidant and an inorganic acid to obtain acidic activated carbon. The specific method for preparing the acidified activated carbon is as described above and will not be elaborated here one by one.

[0053] Meanwhile, in the embodiments of the present invention, the EVA is prepared by free radical solution polymerization, including: carrying out free radical polymerization on vinyl acetate (VAc) and ethylene in the presence of an initiator (such as azobisisobutyronitrile AIBN) to obtain an EVA copolymer.

[0054] The preparation of EVA by free radical solution polymerization may include: under the protection of high-purity N2, mixing VAc, initiator, and solvent in a certain proportion, transferring the clarified solution into a reaction kettle with a polytetrafluoroethylene lining, filling ethylene at a certain pressure, waiting for the pressure to stabilize, starting the circulation pump to heat, when reaching the target polymerization temperature, starting timing, after polymerizing for a period of time, taking out the material while it is hot, drying it in vacuum at 60°C for 24 h to remove volatile components, obtaining a transparent EVA copolymer for later use; the molecular weight of this EVA is 50,000 - 150,000, and the vinyl molar content is 20 - 40%.

[0055] In a preferred specific embodiment, the reaction apparatuses involved, including the reaction kettle lining, etc., must be clean, dry, and flushed with nitrogen; VAc is distilled under reduced pressure to remove the polymerization inhibitor and stored in a sealed manner at 10°C; the initiator is purified by recrystallization, dried in vacuum, protected from light, and stored in a sealed manner at 10°C. The solvent needs to be dehydrated by molecular sieve.

[0056] Among them, the initiator is an organic or inorganic substance such as azo or peroxide, including one or several of azobisisobutyronitrile (AIBN), azobisisoheptonitrile (ABVN), benzoyl peroxide (BPO), diethylhexyl peroxydicarbonate (EHP), potassium persulfate, ammonium persulfate, hydroperoxide, etc., and preferably AIBN. The solvents include one or several of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate (DMC), tetrahydrofuran, petroleum ether, acetone, hexane, etc., and preferably anhydrous methanol. The volume ratio of vinyl acetate to the mass of the initiator is preferably (1-100) mL:(1-100) g; preferably, the ratio of VAc:initiator:solvent (V:m:V) is 1-100:1-100:1-100, where V represents volume in mL and m represents mass in g. The ethylene pressure is preferably 0.01-10 MPa; the polymerization temperature is preferably 60-100 °C, and the polymerization time can be 0.5-10 h, for example, 2-8 h. In addition, the ethylene, VAc, solvent, and initiator involved are all commercially available.

[0057] In the embodiment of the present invention, EVA is alcoholyzed under the action of a basic catalyst, and the acidic activated carbon adsorbs alkali metal ions during the alcoholysis process, and an EVOH copolymer and a by-product methyl acetate can be obtained. The principle of the acidic activated carbon adsorbing alkali metal ions includes:

[0058]

[0059] The embodiment of the present invention further combines segmented alcoholysis and the addition of acidified activated carbon. The alcoholysis reaction preferably includes: after mixing the EVA, the first basic catalyst, and the first solvent, the first-stage alcoholysis is carried out, then the first activated carbon adsorbent (the acidified modified activated carbon mentioned above) is added under stirring, after adsorbing for at least 10 min, the temperature is raised, and the second basic catalyst is added for the second-stage alcoholysis to obtain an alcoholysis product; then, the second activated carbon adsorbent (the acidified modified activated carbon mentioned above) is added under stirring, after adsorbing for at least 10 min, an acidic organic solution is added to neutralize to neutrality, and EVOH is obtained by separation.

[0060] The preparation of EVOH by segmented alcoholysis of EVA in the preferred embodiment of the present invention may include: mixing the previously obtained EVA, the first alkaline catalyst, and the first solvent in a certain proportion in a three-necked flask, stirring and mixing evenly, and performing the first-stage alcoholysis at a certain temperature. Then, under stirring, add the acidified modified activated carbon obtained above and adsorb for a period of time. Continue to raise the temperature to a higher alcoholysis temperature than the first stage, and then add the second alkaline catalyst solution to perform the second-stage alcoholysis. After reacting for a certain time, under stirring, add the acidified modified activated carbon obtained above and adsorb for a period of time. A certain concentration of acidic organic solution can be dropped into the obtained mixed solution. The organic solvent can be the same as or different from the first solvent used in the alcoholysis. Neutralize the reactants until pH = 7, filter while it is hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with absolute ethanol to remove the excess water. It is preferably dried overnight in a vacuum at 100 °C to obtain the final product EVOH, which is reserved for later use.

[0061] In the specific embodiment of the present invention, the reaction apparatuses involved, including the reaction flask, Buchner funnel, etc., must be clean, dry, and flushed with nitrogen; the solvent needs to be dehydrated. Among them, the first solvent includes one or several of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate (DMC), tetrahydrofuran, petroleum ether, acetone, hexane, etc. The first alkaline catalyst and the second alkaline catalyst can be the same or different, preferably the same, and include one or several of sodium hydroxide, potassium hydroxide, sodium ethoxide, calcium hydroxide, sodium carbonate, potassium bicarbonate, etc.; "first" and "second" are mainly used to distinguish the order.

[0062] In the first-stage alcoholysis, the molar ratio of the first alkaline catalyst to the mass of EVA is preferably 1:10 - 1:100 (mol:g), and the first alkaline catalyst is added in the form of a solution, and the concentration can be 0.01 - 1 mol / L; after the addition of the first alkaline catalyst solution, the alcoholysis temperature is preferably 40 - 80 °C, more preferably 40 - 60 °C, and the alcoholysis time can be 0.5 - 10 h. The temperature of the first-stage alcoholysis is relatively low. Adding a part of the alkaline catalyst solution such as sodium hydroxide is to avoid the excessive contact of EVA with too much sodium hydroxide and the overly violent alcoholysis reaction, so that the by-product methyl acetate cannot be discharged in large quantities. Adding the acidified modified activated carbon at this stage, the mass ratio of it to EVA can be 1:100 - 1:10, such as 1:100, 1:10, 1:20, etc.; the adsorption time can be 10 - 60 min, and further 20 - 30 min.

[0063] In the second-stage alcoholysis, the molar ratio of the second basic catalyst to the mass of EVA is preferably 1:10 to 1:100. The second basic catalyst is added in the form of a solution, and the concentration can be 0.01 to 1 mol / L. After the addition of the second basic catalyst solution, the alcoholysis temperature is higher than that of the first-stage alcoholysis, preferably 40 to 80°C, more preferably 70 to 80°C, and the alcoholysis time can be 0.5 to 10 h. The slightly higher temperature in the second-stage alcoholysis (a significant amount of EVA has been consumed in the first stage) will appropriately increase the alcoholysis rate and degree of alcoholysis.

[0064] The second activated carbon adsorbent is also the acid-modified activated carbon described above, and its addition amount can be the same as or different from that of the first activated carbon adsorbent. The mass ratio of the second activated carbon adsorbent to EVA can be 1:100 to 1:10, and the adsorption time is preferably 10 to 60 min, further 20 to 30 min. The concentration of the acidic organic solution can be 0.01 to 10 mol / L. The acidic reagents include organic acids and inorganic acids, preferably one or more of acetic acid, boric acid, hydrochloric acid, etc. The organic solvents include one or more of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate (DMC), tetrahydrofuran, petroleum ether, acetone, hexane, etc. For example, 1 mol / L acetic acid methanol solution is added to neutralize the reactants to neutral. The solvents, acidic reagents, absolute ethanol, basic catalysts, etc. involved are all commercially available and are not particularly limited.

[0065] In the preferred embodiment of the present invention, alcoholysis is carried out by stepwise heating, stepwise adding a basic catalyst, and stepwise adding the activated carbon adsorbent, which can promote the formation of EVOH, improve the degree of alcoholysis of EVOH and the impurity removal effect, etc. Experiments show that the yellowness index of EVOH purified in the examples of this application is lower than 9, its yellowness is improved, and it has good heat resistance. The examples of this application can omit the stage of repeated washing with water, saving water resources, and the adsorption process is carried out at the alcoholysis temperature and atmospheric pressure, with low equipment requirements, low energy consumption, safety and reliability, and in line with the environmental protection concept.

[0066] In order to further illustrate the present invention, the following describes the present invention in detail with reference to examples. In the examples, all the original reagents and materials are commercially available, and the experimental methods without specific experimental conditions are the conventional methods and conditions well known in the art.

[0067] Example 1

[0068] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean corn stalks; the corn stalks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C complex; the complex was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C complex with an average particle size of 2μm, 10g of the complex was taken and placed in 100mL 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 therein to obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C., filtered, and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0069] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V-ml: mg: V-ml, the same as in the following examples), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene; after the pressure stabilized, the circulation pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer (molecular weight 93691, ethylene molar fraction 32%), which was retained (the large amount of EVA prepared was separately alcoholyzed later).

[0070] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask, stirred and mixed, and the first alcoholysis was carried out at 60°C for 2h, then 0.2g of the acid-modified activated carbon was added under stirring, adsorbed for 30min, and the temperature was continued to rise to 70°C, and 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis. After reacting for 2h, 0.2g of the acid-modified activated carbon was added under stirring, adsorbed for 30min; then 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until the pH was 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0071] Example 2

[0072] At room temperature, 100g of rice husks were soaked in 1L of 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean rice husks; the rice husks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C composite; the composite was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C composite with an average particle size of 2μm, 10g of the composite was taken and placed in 100mL of 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 therein to obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60°C, filtered, and dried at 100°C for 5 h to obtain acidified modified activated carbon, which is retained.

[0073] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0074] Put 20g EVA and 200mL 1mol / L NaOH methanol solution in a three-necked flask, stir and mix, and perform the first alcoholysis at 60℃ for 2h. Then, add 0.2g acid modified activated carbon under stirring, adsorb for 30min, continue to heat to 70℃, add 200mL 1mol / L NaOH methanol solution for the second alcoholysis, react for 2h, add 0.2g acid modified activated carbon under stirring, adsorb for 30min; add 1mol / L acetic acid methanol solution to the mixed solution, neutralize the reactant until pH = 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100℃ overnight to obtain the final product EVOH.

[0075] Example 3

[0076] At room temperature, 100g of wheat husks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean wheat husks; the wheat husks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C composite; the composite was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C composite with an average particle size of 2μm, 10g of the composite was taken and soaked in 100mL 0.5mol / L sodium hydroxide aqueous solution for 1h to remove SiO2 and obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle. The acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution. Deionized water is added thereto to make up to 500 mL. 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C. The mixture is filtered and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0077] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0078] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask and stirred and mixed. The first alcoholysis was carried out at 60°C for 2h. Then, 0.2g of the acid-modified activated carbon was added under stirring and adsorbed for 30min. The temperature was further raised to 70°C, and 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis. After 2h of reaction, 0.2g of the acid-modified activated carbon was added under stirring and adsorbed for 30min. 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until the pH was 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0079] Example 4

[0080] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100℃ for 5h to obtain clean corn stalks; the corn stalks were then placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C complex; the complex was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C complex with an average particle size of 2μm, 10g of the complex was taken and soaked in 100mL 0.5mol / L sodium hydroxide aqueous solution for 1h to remove SiO2 and obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle. The acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution. Deionized water is added thereto to make up to 500 mL. 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C. The mixture is filtered and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0081] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0082] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask, stirred and mixed, and the first alcoholysis was carried out at 60°C for 2h, then 0.4g of the acid modified activated carbon was added under stirring, adsorbed for 30min, and the temperature was continued to rise to 70°C, 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis, after 2h of reaction, 0.2g of the acid modified activated carbon was added under stirring, adsorbed for 30min; 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until pH = 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0083] Example 5

[0084] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean corn stalks; the corn stalks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C complex; the complex was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C complex with an average particle size of 2μm, 10g of the complex was taken and placed in 100mL 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 therein to obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60°C, filtered, and dried at 100°C for 5 h to obtain acidified modified activated carbon, which is retained.

[0085] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0086] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask and stirred and mixed. The first alcoholysis was carried out at 60°C for 2h. Then, 0.2g of the acid-modified activated carbon was added under stirring and adsorbed for 30min. The temperature was further raised to 70°C, and 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis. After 2h of reaction, 0.4g of the acid-modified activated carbon was added under stirring and adsorbed for 30min. 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until the pH was 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0087] Example 6

[0088] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed to neutrality, filtered, and dried at 100℃ for 5h to obtain clean corn stalks; the corn stalks were then placed in a rotary vacuum furnace for carbonization under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain SiO2 / C composites. The composites were ball milled for 3h at a ball mill speed of 800r / min to obtain SiO2 / C composites with an average particle size of 2μm, and 10g of the composites were placed in 100mL 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 and obtain carbon. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C., filtered, and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0089] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0090] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask, stirred and mixed, and the first alcoholysis was carried out at 60°C for 2h. Then, 0.4g of the acid-modified activated carbon was added under stirring, adsorbed for 30min, and the temperature was continued to rise to 70°C, and 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis, and the reaction was reacted for 2h. 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until the pH was 7; the filtrate was filtered while hot, and the filtrate was transferred to cold water, filtered, and the filter cake was washed three times with anhydrous ethanol to remove excess water, and vacuum dried at 100°C overnight to obtain the final product EVOH.

[0091] Example 7

[0092] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean corn stalks; the corn stalks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C complex; the complex was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C complex with an average particle size of 2μm, 10g of the complex was taken and placed in 100mL 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 therein to obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C., filtered, and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0093] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0094] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask, stirred and mixed, and the first alcoholysis was carried out at 60°C for 2h, then 0.4g of the acid modified activated carbon was added under stirring, adsorbed for 60min, and the temperature was continued to rise to 70°C, and 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis. After reacting for 2h, 0.2g of the acid modified activated carbon was added under stirring, and adsorbed for 30min; 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until the pH was 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0095] Example 8

[0096] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100°C for 5h to obtain clean corn stalks; the corn stalks were placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions, the rotary vacuum furnace speed was 50r / min, and the carbonization time was 5h to obtain a SiO2 / C complex; the complex was ball-milled for 3h at a ball-milling speed of 800r / min to obtain a SiO2 / C complex with an average particle size of 2μm, 10g of the complex was taken and placed in 100mL 0.5mol / L sodium hydroxide aqueous solution and soaked for 1h to remove SiO2 therein to obtain a carbon element. The carbon single substance and the acidic modified liquid are placed in a polyethylene bottle, the acidic modified liquid consists of 10 mL of a 30 wt% hydrogen peroxide aqueous solution and 10 mL of a 30 wt% phosphoric acid aqueous solution, deionized water is added thereto to 500 mL, 25 g of the carbon single substance and 500 mL of the acidic modified solution are placed on a water bath shaker and shaken for 2 h at a shaking temperature of 60° C., filtered, and dried at 100° C. for 5 h to obtain acidified modified activated carbon, which is retained.

[0097] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0098] 20g EVA and 200mL 1mol / L NaOH methanol solution were placed in a three-necked flask, stirred and mixed, and the first alcoholysis was carried out at 60°C for 2h, then 0.4g of the acid modified activated carbon was added under stirring, adsorbed for 30min, and the temperature was continued to rise to 70°C, 200mL 1mol / L NaOH methanol solution was added for the second alcoholysis, after 2h of reaction, 0.2g of the acid modified activated carbon was added under stirring, adsorbed for 60min; 1mol / L acetic acid methanol solution was added dropwise to the mixed solution to neutralize the reactants until pH = 7. Filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100°C overnight to obtain the final product EVOH.

[0099] Comparative Example 1

[0100] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0101] Put 20g EVA and 200mL 1mol / L NaOH methanol solution in a three-necked flask, stir and mix, and carry out the first alcoholysis at 60℃ for 2h; continue to heat to 70℃, add 200mL 1mol / L NaOH methanol solution for the second alcoholysis, and react for 2h. Then drop 1mol / L acetic acid methanol solution into the mixed solution to neutralize the reactants until the pH is 7; filter while hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with anhydrous ethanol to remove excess water, and vacuum dry it at 100℃ overnight to obtain the final product EVOH.

[0102] Comparative Example 2

[0103] At room temperature, 100g corn stalks were soaked in 1L 0.5mol / L hydrochloric acid solution for 1h to remove impurities in the biomass, washed until neutral, filtered, and dried at 100℃ for 5h to obtain clean corn stalks; the corn stalks were then placed in a rotary vacuum furnace and carbonized under 50mL / min nitrogen conditions. The speed of the rotary vacuum furnace was 50r / min and the carbonization time was 5h to obtain SiO2 / C complex; 10g of the complex was soaked in 100mL 0.5mol / L sodium hydroxide aqueous solution for 1h to remove SiO2 and obtain carbon single substance for retention.

[0104] Under the protection of high-purity N2, VAc, AIBN and anhydrous methanol were mixed in a ratio of 30:10:50 (V:m:V), and the clarified solution was transferred into a reactor with a polytetrafluoroethylene liner and filled with 3MPa of ethylene. After the pressure stabilized, the circulating pump was turned on for heating, the polymerization temperature was 60°C, and after polymerization for 2h, the material was taken out while hot, and vacuum dried at 60°C for 24h to remove volatiles to obtain a transparent EVA elastomer for retention.

[0105] Put 20 g of EVA and 200 mL of 1 mol / L NaOH methanol solution into a three-necked flask, stir and mix evenly, and carry out the first-stage alcoholysis at 60 °C for 2 h. Then, with stirring, add 0.2 g of activated carbon (not acidified, oxidized, ball-milled), adsorb for 30 min, continue to heat up to 70 °C, add 200 mL of 1 mol / L NaOH methanol solution for the second-stage alcoholysis. After reacting for 2 h, with stirring, add 0.2 g of activated carbon (not acidified, oxidized, ball-milled), and adsorb for 30 min. Dropwise add 1 mol / L acetic acid methanol solution to the mixed solution to neutralize the reactants until pH = 7; filter while it is hot, transfer the filtrate to cold water, filter, take the filter cake and wash it three times with absolute ethanol to remove the excess water, and vacuum dry at 100 °C overnight to obtain the final product EVOH.

[0106] The following are the main processing conditions of the examples;

[0107] Table 1 Data comparison

[0108]

[0109]

[0110] Note 1: The test objects of n(-COOH), n(-CO-), n(-OH), and total acid amount are all the acidified and modified activated carbon before adsorption (five parallel samples were made during the test to obtain five groups of data). n(-COOH): The amount of -COOH substance on the carbon surface per unit mass, mol / g; n(-CO-): The amount of -CO- substance on the carbon surface per unit mass, mol / g; n(-OH): The amount of -OH substance on the carbon surface per unit mass, mol / g; Total acid amount: The total amount of acidic functional groups on the carbon surface per unit mass, mol / g.

[0111] The following are the test parameters of the modified activated carbon and the comparison of the test results of the final product EVOH:

[0112] Table 2 Data comparison of modified activated carbon

[0113]

[0114]

[0115] Note 2: The BET test object is the acidified and modified activated carbon before adsorption;

[0116] Note 3: The test objects of thermogravimetry, ICP, yellowness index, and oxygen transmission coefficient are all EVOH polymers. S BET : The total area possessed by the material per unit mass, with the unit of m 2 / g; V total: The total pore volume of the porous solid per unit mass, with the unit of m 3 / g; V misro : The micropore area of the material per unit mass, with the unit of m 2 / g; Pore size: The average pore diameter of the porous body, with the unit of nm.

[0117] Yellowness index: Characterizes the degree of yellowness of a white sample; Thermogravimetry: The sample is under the control of a certain temperature program (heating / cooling / constant temperature), and the change process of the sample's mass with temperature or time is observed to determine the thermal stability and oxidation stability of the material in different atmospheres; Oxygen permeability coefficient (P g ): Under constant temperature and unit pressure difference, at the stable permeation time, the volume of gas permeating through the sample per unit thickness and unit area per unit time, with the unit of cm 3 ·20um / cm 2 ·s·Pa. Residual amount of Na element % (ICP): The detection object is the filtrate after alcohol washing.

[0118] Note 4: The main components of the attached biomass are provided later.

[0119] The main components of the biomass involved are lignin, cellulose, silica, etc., which are commercially available lignocelluloses such as straw and trees. The specific components are as follows.

[0120] Table 3 Main components of biomass

[0121] Experiment Serial Number Cellulose Content % Hemicellulose Content % Lignin Content % Silica Content % Other Content % Corn Stalk 34 29 12 12 13 Rice Husk 30 20 20 20 10 Wheat Husk 40 14 29 10 7

[0122] In addition, the pH of the modified activated carbon is 2 - 6; The test method is as follows.

[0123] Surface acidity test characterization: Quantitative analysis of the content of acidic functional groups by beohm titration. Qualitative and quantitative analysis of the oxides is carried out according to the possibility of different strengths of bases reacting with acidic surface oxides. Accurately weigh 3 samples of 1g of activated carbon and put them into a 200mL conical flask. Add 25mL of standard solutions of NaOH, Na2CO3, and NaHCO3 with a concentration of 0.05mol / L respectively. After stirring for 24h, filter and wash thoroughly with distilled water, and collect all the filtrates. Using methyl red as the end point indicator, titrate the unreacted alkali solution in the filtrate with a 0.05mol / L HCl standard solution to obtain the reaction amount of the alkali solution, and thus calculate the content of acidic functional groups on the surface of the activated carbon.

[0124] The content n (mol / g) of acidic functional groups in the activated carbon per unit mass reacting with each standard alkali solution is calculated according to formulas (1) - (6).

[0125] n NaOH =(C NaOH×V NaOH -C HCl ×V HCl ) / m (1)

[0126] n Na2CO3 =(2C Na2CO3 ×V Na2CO3 -C HCl ×V HCl ) / m (2)

[0127] n NaHCO3 =(C NaHCO3 ×V NaHCO3 -C HCl ×V HCl ) / m (3)

[0128] where: V HCl is the volume (mL) of the standard hydrochloric acid solution used in the titration; m is the mass (g) of the sample.

[0129] From the difference between n NaOH , n Na2CO3 and n NaHCO3 , the ratios of carboxyl group, weak acid and phenolic hydroxyl group can be calculated.

[0130] n RCOOH =n NaHCO3 (4)

[0131] n RCOOCOR =n Na2CO3 -n NaHCO3 (5)

[0132] n ArOH =n NaOH -n Na2CO3 (6)

[0133] According to the above table, after the biomass-based activated carbon is oxidized and acidified, the content of surface acidic functional groups increases, the surface becomes acidic, and the specific surface area increases, which can improve the adsorption efficiency of alkali metal ions, etc. Among them, impurities (mainly sodium ion content) will greatly affect the thermal stability, yellowness and oxygen barrier property of the EVOH finished product. Example 8 can be compared with Example 6. The sodium ion content in the final filtrate of Example 8 is lower, the thermal stability is better, the yellowness index is lower, and the oxygen permeation coefficient is lower. Therefore, Example 8 is superior to Example 6.

[0134] In the examples of the present invention, a specific activated carbon adsorbent is used to remove impurities and purify the EVA alcoholysis product, which improves the yellowness and heat resistance of the EVOH, reduces energy consumption at the same time, can avoid the stage of repeated washing with water, and saves water resources, etc. Further, by using stepwise temperature-rising alcoholysis and stepwise addition of the activated carbon adsorbent, the alcoholysis degree of the EVOH is improved while removing impurities.

[0135] The foregoing description of specific exemplary embodiments of the present invention is for purposes of illustration and exemplification. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many modifications and variations are possible in light of the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the invention and its practical applications, so that those skilled in the art can implement and utilize the various different exemplary embodiments of the invention, as well as various different selections and modifications. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A preparation method of modified activated carbon, characterized in that, The following steps are involved: S1, carbonizing biomass under inert gas conditions to obtain a silicon oxide / carbon composite; the components of the biomass include lignin, cellulose and silicon dioxide; S2, grinding the silicon oxide / carbon composite by ball milling, and then soaking in an alkaline solution to remove silicon oxide therein, thereby obtaining a single carbon substance; S3, mixing the carbon element and the acidic modified liquid and then acidifying to obtain acidified modified activated carbon; The acidic modifying liquid comprises an oxidant, an inorganic acid and water.

2. The preparation method according to claim 1, characterized in that, In step S1, before the biomass is carbonized, it is also soaked in a low-concentration acid solution, washed to neutrality and then separated, and dried to obtain clean biomass; the concentration of the low-concentration acid solution is 0.01-1 mol / L; the drying temperature is 25-100°C.

3. The preparation method according to claim 2, wherein In step S1, the carbonization is carried out in a rotary vacuum device; at least one of the following conditions is met: the inert gas flow rate is 10 to 100 mL / min; the rotation speed of the rotary vacuum device is 10 to 200 r / min; and the carbonization time is 0.5 h to 5 h.

4. The preparation method according to claim 3, characterized in that, In step S2, at least one of the following conditions is satisfied: the average particle size of the silicon oxide / carbon composite after ball milling is 0.05 to 5 μm; the solute of the alkaline solution is one or more of hydroxides, carbonates, bicarbonates and alcoholates of a metal substance, and the metal substance is an alkali metal or an alkaline earth metal; and the solute concentration of the alkaline solution is 0.01 to 10 mol / L.

5. The preparation method according to claim 4, characterized in that, In step S3, the acidification is achieved by shaking in a water bath shaker; at least one of the following is satisfied: the oxidant is one or more of hydrogen peroxide, nitric acid and peracetic acid, with a mass fraction of 1 to 30 wt%; the inorganic acid is one or more of hydrochloric acid, phosphoric acid and nitric acid, with a mass fraction of 1 to 30 wt%; the shaking temperature of the water bath shaker is 25 to 80°C, and the shaking time is 0.5 to 5 h.

6. A method for the alcoholysis of EVA, characterized in that, The following steps are involved: The EVA, the alkaline catalyst and the solvent are mixed and then subjected to alcoholysis reaction to obtain an alcoholysis product; The alcoholysis product is adsorbed and impurized by an activated carbon adsorbent to obtain EVOH; the activated carbon adsorbent is an acidified modified activated carbon obtained by the preparation method according to any one of claims 1 to 5.

7. The method for alcoholysis of EVA according to claim 6, characterized in that, The preparation of the EVA comprises: polymerizing vinyl acetate and ethylene in the presence of an initiator under a protective atmosphere to obtain transparent EVA; satisfying at least one of the following conditions: the ratio of the volume of the vinyl acetate to the mass of the initiator is (1-100) mL: (1-100) g; the ethylene pressure is 0.01-10 MPa; the polymerization temperature is 60-100° C., and the polymerization time is 0.5-10 h.

8. The method for alcoholysis of EVA according to claim 6, wherein, The alcoholysis reaction comprises: the EVA, the first alkaline catalyst and the first solvent are mixed to perform a first stage alcoholysis, then a first activated carbon adsorbent is added under stirring, the temperature is raised after adsorption for at least 10 minutes, and a second alkaline catalyst is added to perform a second stage alcoholysis to obtain an alcoholysis product; the first activated carbon adsorbent is an acidified modified activated carbon obtained by the preparation method according to any one of claims 1 to 5; Meet at least one of the following: the first solvent is dehydrated; the first solvent is one or more of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate, tetrahydrofuran, petroleum ether, acetone and hexane; the first basic catalyst and the second basic catalyst are each one or more of sodium hydroxide, potassium hydroxide, sodium ethoxide, calcium hydroxide, sodium carbonate and potassium bicarbonate.

9. The method for alcoholysis of EVA according to claim 8, characterized in that, Meet at least one of the following: the concentrations of the first basic catalyst and the second basic catalyst are each 0.01 - 1 mol / L; the temperatures of the first-stage alcoholysis and the second-stage alcoholysis are each 40 - 80 °C, and the times are each 0.5 - 10 h; the mass ratio of the acid-modified activated carbon to EVA is 1:10 - 100, and the adsorption time is 10 - 60 min.

10. The method for alcoholysis of EVA according to claim 6, characterized in that, In the alcoholysis product, a second activated carbon adsorbent is added under stirring. After adsorption for at least 10 min, an acidic organic solution is added and neutralized to neutrality, and EVOH is obtained by separation; the second activated carbon adsorbent is the acid-modified activated carbon obtained by the preparation method according to any one of claims 1 - 5. Meet at least one of the following: the mass ratio of the second activated carbon adsorbent to EVA is 1:10 - 100, and the adsorption time is 10 - 60 min; the concentration of the acidic organic solution is 0.01 - 10 mol / L; the acidic organic solution is one or more of acetic acid solution, boric acid solution and hydrochloric acid solution, and the organic solvent in the acidic organic solution is one or more of diethyl ether, methanol, ethanol, tert-butanol, dimethyl carbonate, tetrahydrofuran, petroleum ether, acetone and hexane.

Images