Preparation method of high-molecular-weight cellulose acetate propionate

Abstract

The invention discloses a preparation method of high-molecular-weight cellulose acetate propionate, which comprises the following steps: S1, activation: soaking cellulose in acetic acid to obtain activated cellulose; s2, esterification: mixing the activated cellulose with acetic anhydride, propionic anhydride and an N-alkyl sulfamic acid catalyst, and reacting to obtain cellulose acetate propionate esterification reaction liquid; s3, hydrolysis: adding water into the cellulose acetate propionate esterification reaction solution, and carrying out hydrolysis reaction to obtain a hydrolysis reaction solution; and S4, neutralizing the hydrolysis reaction solution, filtering, and separating to obtain the high-molecular-weight cellulose acetate propionate. According to the method, N-alkyl sulfamic acid is used as a catalyst, degradation in the cellulose esterification process can be effectively reduced, cellulose acetate propionate with the weight-average molecular weight larger than 120,000 is obtained, meanwhile, N-alkyl sulfamic acid is used as the catalyst, generation of gelatinous low-polymerization-degree cellulose ester can be reduced, and the yield of cellulose acetate propionate is increased. The filtering performance of the reaction liquid is obviously improved, and the turbidity value of the product is reduced.

Description

Technical Field

[0001] The invention relates to the field of preparation of cellulose acetate propionate, and in particular to a method for preparing high molecular weight cellulose acetate propionate. Background Art

[0002] Cellulose acetate propionate (CAP for short) is a cellulose mixed ester. Plastics made from CAP are tough, have good dimensional stability, good moldability, and good surface gloss. They are very suitable for making auto parts, tool handles, radio and TV parts, steering wheels, radio transistors, and toys. In addition, CAP can also be used in inks, plastic paints, paper coatings, and other fields. High molecular weight cellulose acetate propionate has a higher melting point and glass transition temperature, and the coatings or plastics prepared from it have higher toughness and mechanical properties.

[0003] In conventional production processes, concentrated sulfuric acid is used as a catalyst. However, sulfuric acid is highly corrosive and severely degrades cellulose during the esterification process, which is not conducive to the preparation of high molecular weight cellulose esters. At the same time, sulfuric acid catalyzes the degradation of cellulose to produce a certain amount of low polymerization degree (DP < 30) cellulose esters. Since low polymerization degree cellulose esters are in a gel-like state in the reaction system, it increases the difficulty of filtering the reaction liquid. Incomplete filtration will cause the product turbidity to be high. In order to prepare high molecular weight cellulose acetate propionate, a low temperature process (below 0°C) is required and high polymerization degree cellulose raw materials are used, which has high production costs.

[0004] Patent CN117720685A uses polyacid-sulfonic acid porous polyionic liquid as a catalyst to prepare cellulose acetate propionate. Polyacid-sulfonic acid porous polyionic liquid is a super solid acid that is green and non-corrosive, can greatly reduce the reaction time, and will not degrade cellulose. After the reaction is completed, the catalyst is easy to separate and can be recycled. The product does not need to be hydrolyzed. The cellulose acetate propionate generated after the reaction has high viscosity and large molecular weight. However, the preparation process of the ionic liquid catalyst is complicated and the production cost is high, which is not conducive to industrial application.

[0005] Patent CN110201724A uses hollow microspheres loaded with heteropolyacid catalysts to prepare high-viscosity cellulose acetate propionate. The organic-inorganic hybrid hollow spheres are prepared by introducing inorganic materials. The inorganic materials realize the morphology control of the catalyst. The polyacid is highly acidic and non-corrosive and will not degrade cellulose. High-viscosity cellulose acetate propionate can be obtained. However, the total degree of substitution of cellulose hydroxyl groups in this method is only 2.4-2.7, which does not meet the complete substitution requirements.

[0006] In summary, the existing disclosed technologies have the following problems: severe corrosion of sulfuric acid catalysts, severe degradation of cellulose during the esterification reaction, and the by-product low-polymerization degree cellulose esters in the reaction system are in a gel state, which makes filtration difficult, affects the turbidity of the product, and is not conducive to the formation of high molecular weight cellulose acetate propionate. The preparation process of ionic liquid catalysts is complicated and the production cost is high. The solid heteropolyacid catalysts catalyze incomplete cellulose esterification. Therefore, it is necessary to find a new preparation method for cellulose acetate propionate, which can prepare high molecular weight cellulose acetate propionate and has low turbidity. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for preparing high molecular weight cellulose acetate propionate.

[0008] A method for preparing high molecular weight cellulose acetate propionate comprises the following steps:

[0009] S1. Activation: soaking cellulose in acetic acid to obtain activated cellulose;

[0010] S2, esterification: mixing activated cellulose with acetic anhydride, propionic anhydride, and N-alkylaminosulfonic acid catalyst to react to obtain cellulose acetate propionate esterification reaction liquid;

[0011] S3, hydrolysis: adding water to the cellulose acetate propionate esterification reaction liquid to carry out a hydrolysis reaction to obtain a hydrolysis reaction liquid;

[0012] S4. The hydrolysis reaction liquid is neutralized and then filtered to separate high molecular weight cellulose acetate propionate.

[0013] As a preferred embodiment of the present invention, in step S1, the cellulose is selected from one or more of refined cotton, cotton pulp, and wood pulp;

[0014] Preferably, in step S1, the amount of acetic acid used is 5-10 times the mass of cellulose, and the soaking time is 1-10 hours.

[0015] Preferably, the mass ratio of cellulose: acetic anhydride: propionic anhydride: N-alkylaminosulfonic acid catalyst is 1: (0.2-2): (2-5): (0.01-0.3);

[0016] Preferably, the N-alkylaminosulfonic acid catalyst is one or more of N-isopropylaminosulfonic acid, N-tert-butylaminosulfonic acid, and N-cyclohexylaminosulfonic acid.

[0017] Preferably, in step S2, the esterification reaction temperature is 30-60° C., and the reaction time is 3-10 h.

[0018] Preferably, in step S3, the amount of water used is 0.5-2 times the mass of cellulose.

[0019] Preferably, in step S3, the hydrolysis reaction temperature is 70-120° C. and the reaction time is 2-20 h.

[0020] Preferably, a neutralizing agent is added in step S4 for neutralization, and the neutralizing agent is selected from one or more of sodium acetate, potassium acetate, calcium acetate, and magnesium acetate;

[0021] Preferably, the amount of the neutralizing agent is 1-1.5 times the molar amount of the N-alkylaminosulfonic acid catalyst;

[0022] Preferably, the neutralization time is 10-60 min.

[0023] After the neutralization reaction is completed, the sulfonate precipitate is filtered to obtain a clear reaction solution; then the clear reaction solution is added to 10-20 times the mass of water to precipitate crude cellulose acetate propionate, which is filtered and washed with water to neutrality, and dried at 100-120° C. for 2-5 hours to obtain a high molecular weight cellulose acetate propionate product.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) The esterification reaction uses N-alkylaminosulfonic acid as a catalyst. The amino group in N-alkylaminosulfonic acid is easy to form hydrogen bonds with the hydroxyl group of cellulose, which promotes the catalyst to penetrate into the internal crystallization area of ​​cellulose and accelerates the esterification reaction. The alkyl group in N-alkylaminosulfonic acid has a certain steric hindrance, which can inhibit the sulfonic acid catalyst from contacting the glycosidic bond of cellulose, effectively reducing the degradation of cellulose, thereby obtaining a high molecular weight cellulose acetate propionate product; due to the reduction of cellulose degradation, the formation of gel-like low-polymerization degree cellulose ester is avoided, thereby improving the filtration performance of the reaction liquid and reducing the turbidity value of the product.

[0026] (2) The problem of serious equipment corrosion caused by the use of concentrated sulfuric acid as a catalyst in the existing process can be avoided; since N-alkylaminosulfonic acid is a monobasic acid, the problem of low thermal stability of the product caused by the formation of cellulose sulfate when catalyzed by sulfuric acid can be avoided.

[0027] (3) The catalyst preparation process is simple and the raw material price is low, which effectively reduces the production cost. The method is suitable for industrial production. DETAILED DESCRIPTION

[0028] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0029] The main raw material information in the present invention is as follows:

[0030] Acetic acid (Aladdin, 99.5%), propionic anhydride (Aladdin, 99.5%), acetic anhydride (Aladdin, 99.5%), concentrated sulfuric acid (Aladdin, 98%), sodium acetate (Aladdin, 99%), potassium acetate (Aladdin, 99%), calcium acetate (Aladdin, 99%), magnesium acetate (Aladdin, 99%), refined cotton (Hubei Jinhanjiang Company), cotton pulp (Buckeye Company, USA), wood pulp (Buckeye Company, USA)

[0031] N-isopropylaminosulfonic acid (Sigma-Aldrich, 98%), N-tert-butylaminosulfonic acid (Sigma-Aldrich, 98%), N-cyclohexylaminosulfonic acid (Aladdin, 98%), aminosulfonic acid (Aladdin, 98%).

[0032] Unless otherwise specified, other raw materials and reagents can be purchased from commercial sources.

[0033] Molecular weight test method: weigh 0.04g (accurate to 0.0001g) of sample and add it to a 4ml sample bottle, add tetrahydrofuran with a disposable dropper to dilute the sample to a concentration of 0.5-1%, filter through a 0.45μm nylon filter membrane, and use Agilent1260 for GPC analysis. The instrument is equipped with 1260ALS automatic sampler, 1260TCC column oven, 1260RID differential detector; column temperature: 35℃; flow rate: 1.0ml / min; time: 40min; injection volume: 20μl.

[0034] [Example 1]

[0035] Prepare cellulose acetate propionate as follows:

[0036] (1) Weigh 100 g of wood pulp and place it in a beaker. Add 500 g of acetic acid, mix well, and soak for 1 hour to obtain activated cellulose for later use.

[0037] (2) 20 g of acetic anhydride, 480 g of propionic anhydride, 1 g of N-isopropylaminosulfonic acid, and the above-mentioned activated cellulose were added to a jacketed glass kettle in sequence, the temperature was controlled at 60° C. with stirring, and the temperature was kept for 3 hours to obtain an esterification reaction liquid.

[0038] (3) Add 50 g of water to the esterification reaction solution under stirring, maintain the hydrolysis reaction temperature at 70° C., and the hydrolysis reaction time for 20 h to obtain a hydrolysis reaction solution.

[0039] (4) 0.62 g of sodium acetate was added to the hydrolysis reaction solution, and the reaction was neutralized for 10 min. The solid was removed by filtration, and the clear liquid of the reaction solution was added to 11.6 kg of water to precipitate a white solid. The solid was filtered and washed with water until neutral, and dried at 100° C. for 5 hours to obtain a cellulose acetate propionate product.

[0040] The weight average molecular weight of cellulose acetate propionate prepared in this example is Mw=13.5×10 4 .

[0041] [Example 2]

[0042] Prepare cellulose acetate propionate as follows:

[0043] (1) Weigh 100 g of refined cotton and place it in a beaker. Add 900 g of acetic acid, mix well, and soak for 6 hours to obtain activated cellulose for later use.

[0044] (2) 50 g of acetic anhydride, 350 g of propionic anhydride, 12 g of N-tert-butylaminosulfonic acid, and the above-mentioned activated cellulose were added to a jacketed glass kettle in sequence, the temperature was controlled at 50° C. with stirring, and the temperature was kept at 50° C. for 8 hours to obtain an esterification reaction liquid.

[0045] (3) Add 200 g of water to the esterification reaction solution under stirring, maintain the hydrolysis reaction temperature at 120° C., and the hydrolysis reaction time for 2 h to obtain a hydrolysis reaction solution.

[0046] (4) Add 9.5 g of potassium acetate to the hydrolysis reaction solution, neutralize for 20 min, filter to remove solids, add the clear reaction solution to 23.5 kg of water, precipitate white solids, filter, wash with water until neutral, and dry at 105° C. for 4 hours to obtain cellulose acetate propionate product.

[0047] The weight average molecular weight of cellulose acetate propionate prepared in this example is Mw=15.2×10 4 .

[0048] [Example 3]

[0049] Prepare cellulose acetate propionate as follows:

[0050] (1) Weigh 100 g of cotton pulp and place it in a beaker. Add 700 g of acetic acid, mix well, and soak for 10 hours to obtain activated cellulose for later use.

[0051] (2) 200 g of acetic anhydride, 200 g of propionic anhydride, 30 g of N-cyclohexylaminosulfonic acid, and the above-mentioned activated cellulose were sequentially added into a jacketed glass kettle, the temperature was controlled at 30° C. with stirring, and the temperature was kept for 10 hours to obtain an esterification reaction liquid.

[0052] (3) 120 g of water was added to the esterification reaction solution under stirring, and the hydrolysis reaction temperature was maintained at 100° C. and the hydrolysis reaction time was 5 h to obtain a hydrolysis reaction solution.

[0053] (4) 19.7 g of calcium acetate was added to the hydrolysis reaction solution, and the reaction was neutralized for 60 min. The solid was filtered out, and the clear liquid of the reaction solution was added to 26.6 kg of water to precipitate a white solid. The solid was filtered out, washed with water until neutral, and dried at 110° C. for 3 hours to obtain a cellulose acetate propionate product.

[0054] The weight average molecular weight of cellulose acetate propionate prepared in this example is Mw=17.6×10 4 .

[0055] [Comparative Example 1]

[0056] (1) Weigh 100 g of wood pulp and place it in a beaker. Add 500 g of acetic acid, mix well, and soak for 1 hour to obtain activated cellulose for later use.

[0057] (2) 20 g of acetic anhydride, 480 g of propionic anhydride, 1 g of concentrated sulfuric acid (98 wt%), and the above-mentioned activated cellulose were added to a jacketed glass kettle in sequence, the temperature was controlled at 60° C. with stirring, and the temperature was kept for 3 hours to obtain an esterification reaction liquid.

[0058] (3) Add 50 g of water to the esterification reaction solution under stirring, maintain the hydrolysis reaction temperature at 70° C., and the hydrolysis reaction time for 20 h to obtain a hydrolysis reaction solution.

[0059] (4) 0.86 g of sodium acetate was added to the hydrolysis reaction solution, and the reaction was neutralized for 10 min. The solid was filtered out, and the clear liquid of the reaction solution was added to 11.6 kg of water to precipitate a white solid. The solid was filtered out, washed with water until neutral, and dried at 100° C. for 5 hours to obtain a cellulose acetate propionate product.

[0060] The weight average molecular weight of cellulose acetate propionate prepared in this comparative example is Mw=4.3×10 4 .

[0061] [Comparative Example 2]

[0062] (1) Weigh 100 g of wood pulp and place it in a beaker. Add 500 g of acetic acid, mix well, and soak for 1 hour to obtain activated cellulose for later use.

[0063] (2) 20 g of acetic anhydride, 480 g of propionic anhydride, 1 g of aminosulfonic acid, and the above-mentioned activated cellulose were added to a jacketed glass kettle in sequence, the temperature was controlled at 60° C. with stirring, and the temperature was kept for 3 hours to obtain an esterification reaction liquid.

[0064] (3) Add 50 g of water to the esterification reaction solution under stirring, maintain the hydrolysis reaction temperature at 70° C., and the hydrolysis reaction time for 20 h to obtain a hydrolysis reaction solution.

[0065] (4) 0.89 g of sodium acetate was added to the hydrolysis reaction solution, and the reaction was neutralized for 10 min. The solid was filtered out, and the clear liquid of the reaction solution was added to 11.6 kg of water to precipitate a white solid. The solid was filtered out, washed with water until neutral, and dried at 100° C. for 5 hours to obtain a cellulose acetate propionate product.

[0066] The weight average molecular weight of cellulose acetate propionate prepared in this comparative example is Mw=6.7×10 4 .

Claims

1. A method for preparing high molecular weight cellulose acetate propionate, characterized in that: The following steps are involved: S1. Activation: soaking cellulose in acetic acid to obtain activated cellulose; S2, esterification: mixing activated cellulose with acetic anhydride, propionic anhydride, and N-alkylaminosulfonic acid catalyst to react to obtain cellulose acetate propionate esterification reaction liquid; S3, hydrolysis: adding water to the cellulose acetate propionate esterification reaction liquid to carry out a hydrolysis reaction to obtain a hydrolysis reaction liquid; S4. The hydrolysis reaction liquid is neutralized and then filtered to separate high molecular weight cellulose acetate propionate.

2. The preparation method according to claim 1, characterized in that: In step S1, the cellulose is selected from one or more of refined cotton, cotton pulp, and wood pulp; Preferably, in step S1, the amount of acetic acid used is 5-10 times the mass of cellulose, and the soaking time is 1-10 hours.

3. The preparation method according to claim 1 or 2, characterized in that: The mass ratio of cellulose: acetic anhydride: propionic anhydride: N-alkylaminosulfonic acid catalyst is 1: (0.2-2): (2-5): (0.01-0.3).

4. The preparation method according to any one of claims 1 to 3, characterized in that: The N-alkylaminosulfonic acid catalyst is one or more of N-isopropylaminosulfonic acid, N-tert-butylaminosulfonic acid, and N-cyclohexylaminosulfonic acid.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S2, the esterification reaction temperature is 30-60°C, and the reaction time is 3-10h.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step S3, the amount of water used is 0.5-2 times the mass of cellulose; Preferably, in step S3, the hydrolysis reaction temperature is 70-120° C. and the reaction time is 2-20 h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S4, a neutralizing agent is added for neutralization, wherein the neutralizing agent is selected from one or more of sodium acetate, potassium acetate, calcium acetate, and magnesium acetate; Preferably, the amount of the neutralizing agent is 1-1.5 times the molar amount of the N-alkylaminosulfonic acid catalyst; Preferably, the neutralization time is 10-60 min.

8. The preparation method according to any one of claims 1 to 7, characterized in that: After the neutralization reaction is completed, the sulfonate precipitate is filtered to obtain a clear reaction solution; then the clear reaction solution is added to 10-20 times the mass of water to precipitate crude cellulose acetate propionate, which is filtered and washed with water until neutral, and dried at 100-120° C. for 2-5 hours to obtain a cellulose acetate propionate product.