A post-treatment method for cellulose acetate butyrate

Abstract

This invention relates to a post-processing method for cellulose acetate butyrate, comprising the following steps: a) adding an aqueous solution of an alcohol or ether compound to a precipitate containing cellulose acetate butyrate, separating the upper liquid phase to obtain a crude cellulose acetate butyrate solution; b) dissolving the crude cellulose acetate butyrate solution obtained in step a) in an aqueous solution of a carboxylic acid-functionalized imidazole ionic liquid, and adsorbing it with a chelating resin; c) adding the solution adsorbed by the chelating resin dropwise to a mixed solution containing carboxylic acid, a carboxylic acid-functionalized imidazole ionic liquid, and water for precipitation; d) filtering, washing, and drying the precipitated product to obtain the cellulose acetate butyrate product. This method removes metal ions before precipitation, avoiding the encapsulation of metal ions during precipitation and affecting the turbidity and color of the product. The carboxylic acid-functionalized imidazole ionic liquid is both a good solvent and a good precipitant, which greatly reduces the adhesion and agglomeration during precipitation. The resulting product has uniform particles, high bulk density, less acid encapsulation, and is easy to wash. It greatly reduces the material and energy consumption in the post-processing, reduces the amount of waste acid and wastewater generated, significantly improves production efficiency, and is convenient for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of cellulose ester derivatives, and specifically relates to a post-processing method for cellulose acetate butyrate. Background Technology

[0002] Cellulose acetate butyrate (CAB) is an important cellulose derivative. Due to its excellent leveling properties, color retention, flexibility, and anti-aging properties, it can be used to make plastic sheet bases, films, leveling agents for various coatings, and film-forming substances. It is widely used in film bases, high-end automotive paints, wood coatings, and inks.

[0003] Generally, the production process of CAB includes reaction steps such as activation, esterification, hydrolysis, and neutralization, as well as post-processing steps such as precipitation, filtration, crushing, washing, and drying. Post-processing is a crucial step in product quality control, as its acid content, salt content, particle size, and bulk density directly affect product performance and subsequent use. The traditional post-processing method involves adding CAB to water, dispersing and precipitating the coarse product under high shear, and then obtaining the final product through filtration, crushing, washing, and drying. However, this method suffers from several drawbacks. During precipitation, the product tends to become sticky and agglomerated, forming flocculent or lumpy particles. This can clog equipment and affect its operation. Furthermore, the uneven particle size and bulk density can lead to stickiness and yellowing during crushing. Additionally, precipitation can easily trap acid and inorganic salts, making subsequent washing difficult, resulting in large wastewater volumes, high energy consumption for dilute acid recovery, and product quality that fails to meet usage requirements.

[0004] Patent CN111253616B uses flash evaporation to separate butyric acid and water, resulting in less wastewater and lower energy consumption. However, this method cannot solve problems such as product stickiness and impurity encapsulation during precipitation, and the product bulk density is relatively low, which is not conducive to subsequent product transportation and packaging. Patent CN113831557B uses the method of adding stabilizers to enhance product dispersion, thereby improving product particle size and increasing product bulk density. However, this method introduces new substances, which are prone to encapsulating organic acids, inorganic salts and solvents during granulation, resulting in unqualified products.

[0005] Therefore, it is of great significance to develop a post-processing method for CAB to improve the encapsulation of the product during the granulation process, reduce the amount of wastewater and energy consumption for dilute acid recovery during the precipitation process, improve particle uniformity and product bulk density, and overcome the shortcomings of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to provide a post-treatment method for cellulose acetate butyrate. This method removes metal ions before precipitation and effectively solves the problems of agglomeration and encapsulation of organic acids and inorganic salts during the precipitation process of CAB products by changing the precipitation process. This facilitates subsequent washing, greatly reduces material and energy consumption, significantly improves production efficiency, and is suitable for industrial production.

[0007] To achieve the above-mentioned objectives and technical effects, the technical solution of this invention is as follows:

[0008] A post-treatment method for cellulose acetate butyrate includes the following steps:

[0009] a) Add an aqueous solution of an alcohol or ether compound to the precipitate containing cellulose acetate butyrate, separate the upper liquid phase, and obtain a crude solution of cellulose acetate butyrate.

[0010] b) Dissolve the crude cellulose acetate butyrate solution obtained in step a) in an aqueous solution of carboxylic acid-functionalized imidazole ionic liquid and adsorb it through a chelating resin;

[0011] c) The solution after adsorption by the chelating resin is added dropwise to a mixed solution containing carboxylic acid, carboxylic acid-functionalized imidazole ionic liquid and water for precipitation;

[0012] d) The product obtained from precipitation is filtered, washed, and dried to obtain cellulose acetate butyrate product.

[0013] In the method of the present invention, the precipitate containing cellulose acetate butyrate, based on its total amount of 100%, contains 13-35 wt.% cellulose acetate butyrate, 60-85 wt.% butyric acid, 0.5-10 wt.% acetic acid, 0.5-1.5 wt.% water, and 0.1-1 wt.% metal ions.

[0014] In the method of the present invention, the alcohol or ether compound in step a) is selected from alkyl alcohols and alkyl ethers, preferably one or more of methanol, ethanol, propanol, isopropanol, butanol, methyl ether, methyl ethyl ether, diethyl ether, propyl ether, and methyl tert-butyl ether.

[0015] In the method of the present invention, in the aqueous solution of alcohol / ether compound in step a), the mass concentration of alcohol or ether compound is 10-30 wt.%, and the mass ratio of aqueous solution to precipitate is 0.5-1.5:1.

[0016] In the method of this invention, the chelating resin in step b) is selected from one or more of aminocarboxylic acid resins, aminophosphate resins, thiourea resins, and mixed-bed resins, preferably D402, D403, D412, and MP64. In addition to selectively adsorbing magnesium, iron, calcium, etc., the selected chelating resin is also alkaline, which can further remove acidic substances, thereby reducing the organic acids and inorganic salts in cellulose acetate butyrate at the source.

[0017] In the method of this invention, the structure of the carboxylic acid-functionalized imidazole ionic liquid described in steps b) and c) is as follows: In the cation, R is selected from C1-C8 alkyl groups, and n is 1-5; in the anion... Selected from BF4- Cl-, Br - PF6 - One of them. This ionic liquid can dissolve both cellulose acetate butyrate and water, allowing for the full release of impurities in the product. At the same time, the alkyl chain increases the hydrophobicity of the ionic liquid. This ionic liquid contains both hydrophilic and hydrophobic ends, which can prevent the product from precipitating too quickly, encapsulating impurities, and causing the precipitates to clump together with uneven particle size. In addition, the ionic liquid has an extremely low saturated vapor pressure, which facilitates separation and reuse.

[0018] In the method of this invention, the carboxylic acid-functionalized imidazole ionic liquid catalyst can be synthesized by any method known to those skilled in the art for synthesizing ionic liquids with similar structures. The ionic liquid used in this invention is synthesized according to the method described in patent CN112062663B.

[0019] In the method of the present invention, the concentration of the ionic liquid in the carboxylic acid-functionalized imidazole ionic liquid aqueous solution in step b) is 70 wt.%-95 wt.%, and the ratio of the precipitate to the carboxylic acid-functionalized imidazole ionic liquid aqueous solution is 1:0.3-1:3.

[0020] In the method of the present invention, the adsorption rate of the chelating resin in step b) is 1-6 BV / h, preferably 2-4 BV / h, where BV represents the resin bed volume.

[0021] In the method of the present invention, the carboxylic acid in the mixed solution in step c) is selected from formic acid, acetic acid, propionic acid, and butyric acid, and the mixed solution contains 10-20 wt.% carboxylic acid, 5-15 wt.% ionic liquid, and 65-85 wt.% water.

[0022] In the method of the present invention, the mass ratio of the chelating resin adsorption solution to the mixed solution in step c) is 1:0.5-1:2.

[0023] In the method of the present invention, in step c), the equipment used for precipitation is a precipitation kettle or a kneader.

[0024] In the method of the present invention, the number of washing cycles in step d) is 2-5 times, the washing temperature is 20-60℃, the drying temperature is 50-80℃, the pressure is 3-10 kPaA, and the drying time is 4-8 hours.

[0025] The cellulose acetate butyrate particles obtained by the method of the present invention have an average particle size (D50) of 200-500 μm, a particle size distribution coefficient of 0.2-0.4, a bulk density of 0.5-0.7 g / ml, an acid value of <200 ppm (calculated as acetic acid), a metal ion content of <30 ppm, a color of <50 Hazen, and a turbidity of <30 ppm NTU.

[0026] Compared with the prior art, the positive effects of the present invention are as follows:

[0027] (1) The post-treatment method of cellulose acetate butyrate of the present invention can effectively solve the problem of organic acid and inorganic salt being wrapped in the product during the precipitation process, and the resulting product has good color and low turbidity.

[0028] (2) The precipitation method in this invention can precisely control the product forming state during the precipitation process, avoid the product becoming sticky during precipitation, and the resulting product particles are uniform and have a moderate bulk density.

[0029] (3) The product obtained by the method of the present invention is easy to wash, generates less waste, greatly reduces material and energy consumption in the post-processing process, reduces production costs, and significantly improves production efficiency.

[0030] (4) In this invention, the precipitate is first mixed with alkyl alcohol and alkyl ether to separate most of the acid and salt in the precipitate. Then, the resulting crude cellulose acetate butyrate solution is fully dissolved in an ionic liquid aqueous solution. The chelating resin is used to coordinate and selectively adsorb metal ions, thereby reducing the amount of inorganic salts that are easily wrapped and removing metal ions such as magnesium and iron that affect the turbidity and color of the product. The adsorbed crude CAB solution is then added dropwise to a mixed solution of carboxylic acid, ionic liquid and water. This mixed solution system can fully dissolve CAB, acid and salt, and avoid CAB from precipitating too quickly and wrapping organic matter and inorganic salts, as well as avoid the product from agglomerating due to untimely dispersion, which would cause difficulties in subsequent washing, large product particle size and poor product performance. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0032] The main sources of raw materials are as follows:

[0033]

[0034]

[0035] Test method:

[0036] Particle size testing: Bettersize2600 laser particle size analyzer (dry method), Dandong Bettersize Instruments Co., Ltd.

[0037] Acid value test: Using acid-base titration, weigh 10.0 g of dry sample and dissolve it in 200 mL of acetone and 20 mL of water. After the sample is completely dissolved, add 50 mL of water and shake well to allow the cellulose ester to precipitate in a small amount. Add 3 drops of methyl red indicator solution and titrate with 0.01 mol / L NaOH solution until the solution reaches the lemon yellow endpoint. Acid value % = {[(AB)*C×0.06] / W}×100 (where A = volume of sodium hydroxide solution consumed in titrating the sample, mL; B = volume of sodium hydroxide solution consumed in titrating the blank sample, mL; C = concentration of sodium hydroxide solution; W = sample mass, g).

[0038] Metal ion content test: The metal content was analyzed using a Varian 710ES inductively coupled plasma atomic emission spectrometer with a plasma gas flow rate of 15 ml / min and an atomizing gas pressure of 200 kPa.

[0039] Colorimetric test: The sample was dissolved in butyl acetate to prepare a 20 wt.% butyl acetate solution, and the colorimetric test was performed using a LANGE LICO620 colorimeter.

[0040] Turbidity test: The sample was dissolved in butyl acetate to prepare a 20 wt.% butyl acetate solution, and the turbidity was tested using a HACH TL2300 turbidity meter.

[0041] Bulk density test: The bulk density of the powder was tested using the HMK Test LABULK 0335 tap density meter.

[0042] Key raw material indicators for the example:

[0043] Precipitation solution: The composition of the precipitation solution by mass percentage is 13-35 wt.% cellulose acetate butyrate, 60-85 wt.% butyric acid, 0.5-10 wt.% acetic acid, 0.5-1.5 wt.% water, and 0.1-1 wt.% metal ions.

[0044] Example 1

[0045] 1 kg of cellulose acetate butyrate precipitate (13 wt.% cellulose acetate butyrate, 85 wt.% butyric acid, 0.5 wt.% acetic acid, 1.0 wt.% water, 0.5 wt.% metal ions) was mixed with 20 wt.% ethanol aqueous solution at a mass ratio of 1:1 and stirred until homogeneous. After standing for 30 min, the upper liquid phase was separated to remove most of the acid and salt in the system, yielding a crude cellulose acetate butyrate solution. Then, the crude cellulose acetate butyrate solution was dissolved in 80 wt.% 1-carboxymethyl-3-methylimidazolium chloride ionic liquid aqueous solution at a mass ratio of 1:1, and adsorbed onto a D402 chelating resin at an adsorption rate of 3 BV / h. The adsorbed... The solution was added dropwise at a mass ratio of 1:0.7 to a precipitation vessel containing a mixed solution of 10 wt.% acetic acid, 5 wt.% 1-carboxymethyl-3-methylimidazolium chloride ionic liquid, and 85% water for precipitation. The product obtained after precipitation was filtered, washed three times with water at 25°C (each time the water volume was three times the solid volume), and dried at 60°C and 3 kPa for 4 hours to obtain cellulose acetate butyrate product. The average particle size (D50) of the obtained cellulose acetate butyrate particles was 300 μm, the particle size distribution coefficient was 0.25, the bulk density was 0.55 g / ml, the acid value was 180 ppm (calculated as acetic acid), the metal ion content was 20 ppm, the color was 44 Hazen, and the turbidity was 8 NTU.

[0046] Example 2

[0047] One kg of cellulose acetate butyrate precipitate (cellulose acetate butyrate 35 wt.%, butyric acid 64 wt.%, acetic acid 0.4 wt.%, water 0.5 wt.%, metal ions 0.1 wt.%) was mixed with 30 wt.% methyl tert-butyl ether aqueous solution at a mass ratio of 1.5:1. The mixture was allowed to stand for 30 min, and the upper liquid phase was separated to remove most of the acid and salts, yielding a crude cellulose acetate butyrate solution. This crude solution was then dissolved in 95 wt.% 1-carboxymethyl-3-methylimidazolium tetrafluoroborate ionic liquid aqueous solution at a mass ratio of 1:0.3, and adsorbed onto a D403 chelating resin at an adsorption rate of 1 BV / h. The solution was added dropwise at a mass ratio of 1:0.5 to a precipitation vessel containing a mixed solution of 20 wt.% butyric acid, 15 wt.% 1-carboxymethyl-3-methylimidazolium tetrafluoroborate ionic liquid, and 65% water for precipitation. The precipitated product was filtered, washed twice with water at 60°C (each time the water volume was 3 times the solid volume), and dried at 80°C and 10 kPa for 8 hours to obtain cellulose acetate butyrate product. The average particle size (D50) of the obtained cellulose acetate butyrate particles was 200 μm, the particle size distribution coefficient was 0.30, the bulk density was 0.65 g / ml, the acid value was 150 ppm (calculated as acetic acid), the metal ion content was 23 ppm, the color was 35 Hazen, and the turbidity was 12 NTU.

[0048] Example 3

[0049] One kg of cellulose acetate butyrate precipitate (cellulose acetate butyrate 25.4 wt.%, butyric acid 73.5 wt.%, acetic acid 0.5 wt.%, water 0.5 wt.%, metal ions 0.1 wt.%) was mixed with a 10 wt.% aqueous ethanol solution at a mass ratio of 1:1 and stirred until homogeneous. The mixture was allowed to stand for 30 min, and the supernatant was separated to remove most of the acid and salts, yielding a crude cellulose acetate butyrate solution. This crude solution was then dissolved in a 70 wt.% aqueous solution of 1-carboxyethyl-3-methylimidazolium bromide ionic liquid at a mass ratio of 1:1, and adsorbed onto an MP64 chelating resin at an adsorption rate of 6 BV / h. The adsorbed solution was then... The solution was added dropwise at a mass ratio of 1:2 to a kneader containing a mixed solution of 15 wt.% acetic acid, 15 wt.% 1-carboxyethyl-3-methylimidazolium bromide ionic liquid and 70 wt.% water for precipitation. The precipitated product was filtered, washed 5 times with water at 20°C (each time the water volume was 3 times the solid volume), and dried at 50°C and 3 kPaA for 6 hours to obtain cellulose acetate butyrate product. The average particle size (D50) of the obtained cellulose acetate butyrate particles was 320 μm, the particle size distribution coefficient was 0.26, the bulk density was 0.63 g / ml, the acid value was 140 ppm (calculated as acetic acid), the metal ion content was 15 ppm, the color was 32 Hazen, and the turbidity was 13 NTU.

[0050] Example 4

[0051] 1 kg of cellulose acetate butyrate precipitate (13 wt.% cellulose acetate butyrate, 74.5 wt.% butyric acid, 10 wt.% acetic acid, 1.5 wt.% water, 1 wt.% metal ions) was mixed with 10 wt.% diethyl ether aqueous solution at a mass ratio of 0.5:1. The mixture was allowed to stand for 30 min, and the upper liquid phase was separated to remove most of the acid and salts, yielding a crude cellulose acetate butyrate solution. This crude solution was then dissolved in 70 wt.% 1-carboxymethyl-3-propylimidazolium tetrafluoroborate ionic liquid aqueous solution at a mass ratio of 1:3, and adsorbed onto a D412 chelating resin at an adsorption rate of 5 BV / h. The adsorbed solution was then... The solution was added dropwise at a mass ratio of 1:2 to a kneader containing a mixed solution of 20 wt.% acetic acid, 10 wt.% 1-acetic acid-3-methylimidazolium ionic liquid and 70 wt.% water for precipitation. The precipitated product was filtered, washed four times with water at 25°C (each time the water volume was 3 times the solid volume), and dried at 60°C and 5 kPaA for 6 hours to obtain cellulose acetate butyrate product. The average particle size (D50) of the obtained cellulose acetate butyrate particles was 310 μm, the particle size distribution coefficient was 0.23, the bulk density was 0.65 g / ml, the acid value was 190 ppm (calculated as acetic acid), the metal ion content was 18 ppm, the color was 38 Hazen, and the turbidity was 17 NTU.

[0052] Comparative Example 1

[0053] One kg of cellulose acetate butyrate precipitate (24 wt.% cellulose acetate butyrate, 71 wt.% butyric acid, 3.2 wt.% acetic acid, 1.2 wt.% water, and 0.6 wt.% metal ions) was mixed with a 20 wt.% aqueous ethanol solution at a mass ratio of 1:1 and stirred until homogeneous. The mixture was allowed to stand for 30 min, and the supernatant was separated to remove most of the acid and salts, yielding a crude cellulose acetate butyrate solution. This crude cellulose acetate butyrate solution was then dissolved in an 80 wt.% aqueous solution of 1-ethyl-3-methylimidazolium chloride ion solution at a mass ratio of 1:1, and adsorbed onto a D402 chelating resin at an adsorption rate of 3B. V / h; The adsorbed solution was added dropwise at a mass ratio of 1:0.7 to a precipitation vessel containing a mixed solution of 10 wt.% butyric acid, 5 wt.% 1-ethyl-3-methylimidazolium chloride ion liquid and 85% water for precipitation; The product obtained by precipitation was filtered, washed three times with water at 25°C (each time the amount of water was three times the volume of the solid), and dried at 60°C and 3 kPaA for 4 hours to obtain cellulose acetate butyrate product. The obtained cellulose acetate butyrate product agglomerated into lumps during precipitation, with a bulk density of 0.41 g / ml, an acid value of 3743 ppm (calculated as acetic acid), a metal ion content of 50 ppm, a color of 144 Hazen, and a turbidity of 28 NTU.

[0054] Comparative Example 2

[0055] One kg of cellulose acetate butyrate precipitate (cellulose acetate butyrate 25 wt.%, butyric acid 68.6 wt.%, acetic acid 5 wt.%, water 1.0 wt.%, metal ions 0.4 wt.%) was mixed with a 20 wt.% aqueous ethanol solution at a mass ratio of 1:1 and stirred until homogeneous. The mixture was allowed to stand for 30 min, and the supernatant was separated to remove most of the acid and salts, yielding a crude cellulose acetate butyrate solution. This crude solution was then dissolved in an 80 wt.% aqueous butyric acid solution at a mass ratio of 1:1 and adsorbed onto a D403 chelating resin at an adsorption rate of 3 BV / h. The solution was added dropwise at a mass ratio of 1:1 to a precipitation vessel containing a mixed solution of 15 wt.% acetic acid and 85% water for precipitation. The product obtained from precipitation was filtered, washed three times with water at 25°C (each time the water volume was three times the solid volume), and dried at 60°C and 3 kPa for 4 hours to obtain cellulose acetate butyrate product. The average particle size (D50) of the obtained cellulose acetate butyrate particles was 1100 μm, the particle size distribution coefficient was 0.35, the bulk density was 0.45 g / ml, the acid value was 5520 ppm (calculated as acetic acid), the metal ion content was 100 ppm, the color was 159 Hazen, and the turbidity was 35 NTU.

Claims

1. A post-treatment method for cellulose acetate butyrate, comprising the following steps: a) Add an aqueous solution of an alcohol or ether compound to the precipitate containing cellulose acetate butyrate, separate the upper liquid phase, and obtain a crude solution of cellulose acetate butyrate. b) Dissolve the crude cellulose acetate butyrate solution obtained in step a) in an aqueous solution of carboxylic acid-functionalized imidazole ionic liquid and adsorb it through a chelating resin; c) The solution after adsorption by the chelating resin is added dropwise to a mixed solution containing carboxylic acid, carboxylic acid-functionalized imidazole ionic liquid and water for precipitation; d) The product obtained from precipitation is filtered, washed, and dried to obtain cellulose acetate butyrate product. The precipitate containing cellulose acetate butyrate, based on its total amount (100%), contains 13-35 wt.% cellulose acetate butyrate, 60-85 wt.% butyric acid, 0.5-10 wt.% acetic acid, 0.5-1.5 wt.% water, and 0.1-1 wt.% metal ions. The structure of the carboxylic acid-functionalized imidazole ionic liquid described in steps b) and c) is as follows: In the cation, R is selected from C1-C8 alkyl groups, and n is 1-5; in the anion... Selected from BF4 - Cl - ,Br - PF6 - One of the following: In step b), the concentration of the ionic liquid in the carboxylic acid-functionalized imidazole ionic liquid aqueous solution is 70 wt.%-95 wt.%, and the ratio of the precipitate to the carboxylic acid-functionalized imidazole ionic liquid aqueous solution is 1:0.3-1:3; The chelating resin in step b) is selected from one or more of aminocarboxylic acid resin, aminophosphate resin, thiourea resin, and mixed bed resin; In step c), the mixed solution contains 10-20 wt.% carboxylic acid, 5-15 wt.% ionic liquid, and 65-85 wt.% water.

2. The post-processing method as described in claim 1, characterized in that, The alcohol or ether compound mentioned in step a) is selected from alkyl alcohols and alkyl ethers; and / or, in the aqueous solution of the alcohol / ether compound mentioned in step a), the mass concentration of the alcohol or ether compound is 10-30 wt.%, and the mass ratio of the aqueous solution to the precipitate is 0.5-1.5:

1.

3. The post-processing method according to claim 2, characterized in that, The alcohol or ether compound mentioned in step a) is selected from one or more of methanol, ethanol, propanol, isopropanol, butanol, methyl ether, methyl ethyl ether, ethyl ether, propyl ether, and methyl tert-butyl ether.

4. The post-processing method according to any one of claims 1-3, characterized in that, The chelating resin in step b) is selected from D402, D403, D412, and MP64.

5. The post-processing method according to any one of claims 1-3, characterized in that, The carboxylic acid in the mixed solution described in step c) is selected from one of formic acid, acetic acid, propionic acid, and butyric acid.

6. The post-processing method according to any one of claims 1-3, characterized in that, The mass ratio of the chelating resin adsorption solution to the mixed solution in step c) is 1:0.5-1:

2.

7. The post-processing method according to any one of claims 1-3, characterized in that, The number of washing cycles in step d) is 2-5 times, the washing temperature is 20-60℃, the drying temperature is 50-80℃, the pressure is 3-10 kPaA, and the drying time is 4-8 hours.

8. Cellulose acetate butyrate obtained by the post-processing method according to any one of claims 1-7.

Images