CN109721660B - Method for preparing cellulose acetate by high-temperature acetification process - Google Patents
Method for preparing cellulose acetate by high-temperature acetification process Download PDFInfo
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Abstract
A method for producing cellulose acetate, comprising: mixing cellulose and acetic acid solution at room temperature, and pretreating to obtain a mixture; mixing acetic anhydride and an acetic acid solution, and cooling to obtain mixed acid; adding the mixture into the mixed acid, and adding an acid catalyst to carry out acetification reaction; continuously vacuumizing the reaction system in the temperature rising process to enable acetic acid in the reaction system to be flashed and volatilized, stopping vacuumizing after the temperature of the reaction system reaches the peak acetification temperature, and continuing to react until the acetification reaction process is finished to obtain an acetified product; adding hot water into the acetified product, heating to the peak hydrolysis temperature, maintaining for a period of time, adding magnesium acetate, and continuously maintaining the peak hydrolysis temperature until the hydrolysis reaction is finished; treating the hydrolysate to obtain a cellulose acetate product. The method not only ensures that the addition amount of the acid catalyst is less, but also does not need to adopt chilled brine for cooling after the acetification reaction is finished, thereby greatly reducing the cooling energy consumption and the production cost.
Description
Technical Field
The invention belongs to the technical field of acetate fiber production, and relates to a production method of cellulose acetate.
Background
At present, the industrial production method of cellulose acetate mainly adopts a low-temperature acetification method and a high-temperature acetification method. Because the heat release of the acetification reaction is large, the heat of the system needs to be quickly transferred in a short time, and the low-temperature acetification process needs to pre-cool the reactant mixed acid until part of acetic acid is crystallized and absorb the reaction heat by utilizing the phase change of the reactant mixed acid. The low-temperature method needs to consume a large amount of electric energy in the mixed acid crystallization process, and is not beneficial to energy conservation and environmental protection. The low-temperature method needs to add about 13 percent of sulfuric acid catalyst, and then needs to add corresponding magnesium acetate solution for neutralization, so the material consumption is higher. The traditional high-temperature acetification process (U.S. Pat. No.4,439,605), (U.S. Pat. No.2,923,706), (Canadian Pat. No.565,099), (U.S. Pat. No.3,767,642) and (U.S. Pat. No.2,585,516) consumes about 0.5-1% of catalyst, but the hydrolysis process requires high temperature of about 150 ℃ and high pressure of 4bar, and has high requirements on equipment and operation. In the high-temperature acetification process, the product is yellow due to high hydrolysis temperature, and the whiteness of the product can meet the requirement only by bleaching with hydrogen peroxide in the subsequent process. In contrast, the process developed by the patent does not have the above strict requirements, can well complete the acetification reaction under the condition of lower catalyst concentration, and has better product quality. The method has the advantages that: the mixed acid does not need to be pre-cooled, so that refrigeration equipment and a large amount of electric energy are saved. Compared with the low-temperature process, the consumption of the catalyst is greatly reduced, the magnesium oxide is correspondingly reduced, and the material consumption is reduced. Thirdly, high-temperature high-pressure hydrolysis is not needed, and the requirements on equipment and process operation are reduced. The product does not need hydrogen peroxide for bleaching, the process procedures are reduced, the use of hazardous chemicals is reduced, and the risk is reduced.
Disclosure of Invention
The invention aims to provide a method for producing cellulose acetate, which overcomes the defects of high energy consumption and material consumption in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for producing cellulose acetate, comprising the steps of:
(1) mixing cellulose and acetic acid solution at room temperature, and pretreating to obtain a mixture; mixing acetic anhydride and an acetic acid solution, and then cooling to obtain mixed acid;
(2) adding the mixture into the mixed acid to obtain a reaction mixture, and then adding an acid catalyst accounting for 1.5-3 wt% of the reaction mixture to carry out acetification reaction;
(3) continuously vacuumizing the reaction system in the temperature rising process of the acetification reaction so as to enable acetic acid in the reaction system to be flashed and volatilized, stopping vacuumizing after the temperature of the reaction system reaches the peak acetification temperature, and continuously reacting for a period of time until the acetification reaction process is finished to obtain an acetified product;
(4) adding hot water into the acetified product, heating to the peak hydrolysis temperature at a certain heating rate, maintaining for a period of time, adding magnesium acetate, and continuously maintaining the peak hydrolysis temperature until the hydrolysis reaction is finished;
(5) and treating the hydrolysate to obtain a cellulose acetate product.
Optionally, in step (1), the cellulose is an acetified grade cellulose selected from the group consisting of specialty pulp grade cellulose or acetified grade wood pulp, derived from wood or cotton linters; and/or the presence of a gas in the gas,
in the step (1), the cellulose has an average length of 0.5-5mm and an average diameter of 10-20 μm; and/or the presence of a gas in the gas,
in the step (1), the mass percent of acetic acid in the acetic acid solution is more than 99 percent, namely pure acetic acid is adopted; and/or the presence of a gas in the gas,
in the step (1), the mass ratio of the cellulose to the pure acetic acid is 100 (20-60), such as 100: 40; and/or the presence of a gas in the gas,
in the step (1), the content of acetic anhydride in the mixed acid may be 30 to 60 wt%, for example, 45 wt%, and the mass ratio of the mixed acid to the cellulose is 5:1 to 8: 1.
Optionally, in step (2), the mixed acid is cooled to-5-15 ℃ before being mixed with the mixture; and/or the presence of a gas in the gas,
in step (2), the reaction mixture has a pH in the range of-1 to 0; and/or the presence of a gas in the gas,
in the step (2), the acidic catalyst is sulfuric acid; or perchloric acid, p-toluenesulfonic acid and methanesulfonic acid are used as the acidic catalyst. Alternatively, in step (3), the peak acetification temperature may be 55-70 ℃, for example 57 ℃; and/or the presence of a gas in the gas,
in the step (3), vacuumizing is carried out in the acetification reaction process, and the absolute pressure is 3-10 kPa; and/or the presence of a gas in the gas,
in the step (3), the concentration of the acetic acid solution obtained by collecting the flash evaporated acetic acid is 95 +/-2 wt%, and the acetic acid solution can be used for continuously preparing a mixed acid solution, which is a recycling way;
optionally, in step (4), the ratio of the mass of the hot water to the mass of the acetified product is 5-10%; and/or the presence of a gas in the gas,
in the step (4), the temperature of the hot water is 70-95 ℃; and/or the presence of a gas in the gas,
in the step (4), the temperature rising speed is 1-1.5 ℃/min; and/or the presence of a gas in the gas,
in the step (4), the peak hydrolysis temperature is 90-100 ℃; and/or the presence of a gas in the gas,
in the step (4), the hydrolysis reaction is carried out under normal pressure, and the advantage of normal pressure is that the hydrolysis equipment is only used under normal pressure, so that the manufacturing cost is low, the operation is simple, and the safety risk is reduced;
in the step (4), acetic acid is recovered by reducing pressure after the hydrolysis reaction process, the concentration of the recovered acetic acid aqueous solution is 65-75%, and the acetic acid aqueous solution can be used as the precipitated acid of the subsequent process and is also a way of recycling;
and/or in the step (4), the mass ratio of the magnesium acetate solution to the acetified product is 2-5%, and the mass fraction of the magnesium acetate solution is 20-25%.
Optionally, in step (4), maintaining the peak hydrolysis temperature for 40-70min before adding magnesium acetate; and/or the presence of a gas in the gas,
in step (4), the time for maintaining the peak hydrolysis temperature after adding magnesium acetate is 30-60 min.
Optionally, in step (5), an excess amount of deionized water is added to the hydrolysate, and the cellulose acetate precipitate is taken and washed with deionized water until the pH value is neutral, and dried to obtain the cellulose acetate product.
Alternatively, the cellulose acetate product has a filter plugging value of 42 ± 10, an acetylation value of 55.4 ± 0.8%, an intrinsic viscosity of 1.45 ± 0.1, and a whiteness b value of 3.0 ± 0.5.
Due to the adoption of the scheme, the invention has the beneficial effects that:
firstly, the addition amount of an acidic catalyst (such as sulfuric acid) required by the acetification reaction of the invention accounts for 0.5-3 wt% of the amount of a reaction mixture, so that the addition amount of the acidic catalyst is less, subsequent products do not need to be bleached by hydrogen peroxide, the working procedures are reduced, and the explosion risk is reduced;
secondly, the peak value hydrolysis temperature of the invention is 90-100 ℃, the hydrolysis reaction is carried out under normal pressure, high-pressure hydrolysis is not needed, and the requirements on equipment and operation are reduced;
thirdly, the acetic acid is recovered under reduced pressure in the high-temperature acetification process, and the concentration of the obtained acetic acid is about 95 wt%; the acetic acid is recovered by reducing the pressure after the hydrolysis process, and the concentration of the obtained acetic acid is about 70 wt%, so that the method can realize the recycling of the acetic acid.
Fourthly, the invention can take away a large amount of heat emitted by the reaction by decompressing and recovering the acetic acid, and the recovered acetic acid has higher concentration and can realize cyclic utilization, so that the refrigeration of brine is not needed, the use of an industrial refrigerator with higher price is avoided, and the power consumption and the cost of the refrigerator are greatly reduced;
fifthly, compared with the low-temperature acetification method, the usage amount of the sulfuric acid and the magnesium acetate of the invention is reduced by 70-90 wt%, thus greatly saving the cost of raw materials. The method can reduce the use amount of sulfuric acid, simultaneously, the product does not need hydrogen peroxide for bleaching, the color of the product can meet the requirement, compared with other processes, the method reduces the bleaching procedures, avoids the use of explosive substances, namely hydrogen peroxide, and reduces the production cost and the safety risk.
Detailed Description
The invention provides a production method of cellulose acetate, which comprises the following steps:
(1) stirring and mixing cellulose and acetic acid solution at room temperature for 30-40min, and pretreating to obtain a mixture; mixing acetic anhydride and an acetic acid solution, and then cooling to obtain mixed acid;
(2) adding the mixture into mixed acid to obtain a reaction mixture, and then adding an acid catalyst accounting for 0.5-3 wt% of the reaction mixture to carry out an acetification reaction;
(3) the acetification reaction generates heat, so that the temperature of the reaction system is gradually increased. Continuously vacuumizing the reaction system in the temperature rising process of the acetification reaction so as to continuously flash and volatilize the acetic acid in the reaction system. Stopping vacuumizing when the temperature of the acetification reaction system reaches the peak acetification temperature, and continuously reacting for a period of time until the acetification reaction process is finished (such as 10-20min) to obtain an acetified product;
(4) adding hot water into the acetified product, heating to the peak hydrolysis temperature at a certain heating rate, maintaining for a period of time, adding magnesium acetate, and continuously maintaining the peak hydrolysis temperature until the hydrolysis reaction is finished;
(5) and treating the hydrolysate to obtain a cellulose acetate product.
Wherein, in the step (1), the cellulose is acetified cellulose, is selected from special pulp-grade cellulose or acetified wood pulp, and is derived from wood or cotton linters.
In the step (1), the cellulose is ground and pulverized in advance before being mixed with acetic acid so that the cellulose has an average particle diameter of 0.5 to 5mm in length and 10 to 20 μm in diameter.
In the step (1), the mass percent of acetic acid in the acetic acid solution which is stirred and mixed with the cellulose is more than 99 percent, namely pure acetic acid is adopted. The purpose of stirring and mixing the acetic acid solution is to enhance the reaction activity of the cellulose in the acetification reaction process.
In step (1), the mass ratio of cellulose to acetic acid may be 100 (20-60), for example 100: 40. The acetic acid solution plays a role in activation and dissolution.
In the step (1), the content of acetic anhydride in the mixed acid can be 30-60 wt%, preferably 45 wt%, and the mass ratio of the mixed acid to the cellulose is 5:1-8: 1.
In step (2), the mixed acid is cooled to-5-15 ℃ before being mixed with the mixture.
In step (2), the acidic catalyst is sulfuric acid.
In step (3), the peak acetification temperature can be made between 55 and 70 ℃, preferably 57 to 67 ℃ by controlling the reaction mass and reaction conditions.
In the step (3), vacuumizing is carried out in the acetification reaction process, and the absolute pressure is 3-10 kPa. Through the vacuum pumping, the acetic acid in the reaction system can be continuously flashed and volatilized, and then the volatilized acetic acid is collected, so that the cyclic utilization of the acetic acid is realized.
In the step (3), the concentration of the acetic acid solution obtained after collecting the flash evaporated acetic acid is 95 +/-2 wt%. The acetic acid solution may be recycled to step (2).
In step (4), hot water is added in order to allow the acetified product to undergo hydrolysis reaction.
In step (4), the temperature of the hot water is 70 to 95 ℃, preferably 85 to 95 ℃. In the step (3), the flash evaporation volatilization of the acetic acid can take away a large amount of heat released in the acetification reaction process, so that cooling is not needed after the acetification reaction is finished, for example, the cooling is not needed by using frozen brine, and the power consumption of a refrigerator can be greatly reduced. The resulting acetified product can be directly mixed with hot water without cooling.
In the step (4), the temperature rise rate is 1-1.5 ℃/min. After the acetified product is mixed with hot water and reaches 50 + -3 ℃, the mixed system needs to be slowly heated. For example, the temperature may be raised to the peak hydrolysis temperature within 40 min.
In step (4), the peak hydrolysis temperature is 90 to 100 ℃, preferably 95 to 100 ℃. The peak hydrolysis temperature is the temperature that is most favorable for the hydrolysis reaction to proceed.
In the step (4), the hydrolysis reaction is carried out under normal pressure, and the hydrolysis reaction can be carried out under normal pressure or reduced pressure without high-pressure hydrolysis, so that the requirement on the operation of equipment is lower, and the safer production is favorably realized.
In step (4), acetic acid is recovered by reducing pressure during the hydrolysis reaction to obtain a concentration of about 65 to 75% acetic acid.
In the step (4), the mass ratio of the magnesium acetate solution to the acetified product is 2-5%, and the magnesium acetate refers to the magnesium acetate solution.
In step (4), the time for maintaining the peak hydrolysis temperature before adding the magnesium acetate may be 40-70 min.
In step (4), the time for maintaining the peak hydrolysis temperature after adding magnesium acetate is 30-40 min. The time to maintain the peak hydrolysis temperature after the addition of the magnesium acetate is less than or equal to the time to maintain the peak hydrolysis temperature before the addition of the magnesium acetate.
In the step (5), the step of treating the hydrolysate comprises: adding excessive deionized water into the hydrolysate to precipitate cellulose acetate, collecting the precipitate of cellulose acetate, washing with deionized water until pH is neutral, and drying at 120 deg.C for 8 hr to obtain cellulose acetate product.
In the step (5), the filtration clogging value of the cellulose acetate product is 42. + -. 10, the acetylation value is 55.4. + -. 0.8%, and the intrinsic viscosity is 1.45. + -. 0.1.
The filter blockage value test method comprises the following steps: the vinegar tablets were dissolved in acetone to prepare a 9.5% strength solution, and then the slurry was filtered with a filter paper under 1.5 atmospheres, according to the filtration amount.
The acetylation value = 6000 × degree of substitution/(162 +42 × degree of substitution), and the degree of substitution is obtained by acid-base titration.
Intrinsic viscosity: dissolving the vinegar slices in acetone to prepare a 0.25% solution, and testing by using an Ubbelohde viscometer.
Whiteness: and testing the color b value by using a spectrocolorimeter.
The present invention will be further described with reference to the following examples.
Example 1
A method for producing cellulose acetate, comprising the steps of:
(1) mixing 10kg of acetified cellulose and 4kg of pure acetic acid with the concentration of more than 99% at room temperature for 30min to enhance the reaction activity of the mixture and obtain a mixture; mixing acetic anhydride with pure acetic acid with the concentration of more than 99% and then cooling to obtain mixed acid, wherein the content of the acetic anhydride is 41 wt%; the average length of the acetified cellulose is 0.5-5mm, and the average diameter is 10-20 μm;
(2) cooling 56kg of mixed acid to 5 ℃, adding the mixture to the cooled mixed acid to obtain a reaction mixture, and adding 0.3kg of an acidic catalyst (sulfuric acid) accounting for 3% of the mass of the cellulose to perform an acetification reaction, wherein the pH is-0.58 measured after adding the sulfuric acid;
(3) the heat is released during the acetification reaction, so that the temperature of the acetification reaction system is gradually increased and is increased to the peak acetification temperature (57 ℃) within 30 min. Continuously vacuumizing the reaction system in the temperature rising process, wherein the absolute pressure is 4.7kPa, so that acetic acid in the reaction system is flashed and volatilized, stopping vacuumizing after the temperature of the reaction system reaches the peak acetification temperature (57 ℃) and continuing to react for 10min until the acetification reaction process is finished, so as to obtain an acetified product; 2.1kg of acetic acid volatilized by flash evaporation is collected in the process, and the concentration of the obtained acetic acid solution is 95 wt%;
(4) adding 4kg of hot water into the acetified product, wherein the mass ratio of the hot water to the acetified product is 5.7%, starting to heat from 50 ℃, heating to the peak hydrolysis temperature (95 ℃) for 40min and maintaining for 50min, then adding 1.6kg of magnesium acetate, wherein the mass ratio of the magnesium acetate solution to the acetified product is 2.3%, and continuing to maintain the peak hydrolysis temperature (95 ℃) for 40min until the hydrolysis reaction is finished; after the hydrolysis reaction is finished, 2.4kg of acetic acid aqueous solution is recovered under reduced pressure, wherein the reduced pressure is 14 kPa;
(5) and treating the hydrolysate by the following method: adding excessive deionized water into the hydrolysate to precipitate the acetate sheets to obtain cellulose acetate precipitate; taking cellulose acetate precipitate, washing the precipitate with deionized water until the pH value is neutral, and drying the precipitate for 8 hours at 120 ℃ to obtain a cellulose acetate product;
the cellulose acetate product of this example was found to have a filtration blockage value of 42, an acetylation value of 55.4%, an intrinsic viscosity of 1.42, and a whiteness of 3.1.
Example 2
(1) Adding 8kg of pure acetic acid with the concentration of more than 99% into 20kg of ground acetified wood pulp cellulose, and stirring and pretreating at room temperature for 30min to enhance the reaction activity;
(2) 113kg of a mixture of acetic anhydride and acetic acid (mixed acid) is cooled to 4.5 ℃ in a reaction vessel, wherein the mass ratio of the acetic anhydride is 45%;
(3) adding the pretreated wood pulp into the cooled mixed acid, and then starting to add 0.6kg of catalyst sulfuric acid, wherein the dosage of the sulfuric acid is 3 percent of the mass of the cellulose, the pH value of the system is-0.32, and the reaction starts. After the reaction starts, the system releases heat to cause the temperature of the system to rise to 57 ℃ within 30min, a vacuum pump is started to pump vacuum when the temperature rises, the absolute pressure is 5.5kPa, and acetic acid in the reaction system is flashed and volatilized. Stopping the vacuum pump after the temperature reaches 57 ℃, continuing to react for 13min, ending the acetification reaction, and collecting 4.8kg of flash evaporated acetic acid in the process, wherein the concentration of the obtained acetic acid solution is 95.8 wt%;
(4) adding 7.6kg of hot water accounting for 5.2% of the mass of the acetified product, heating from about 50 ℃, heating to 95 ℃ within about 40min, maintaining the temperature at 95 ℃ for about 50min, adding 4kg of magnesium acetate solution, keeping the mass ratio of the magnesium acetate solution to the acetified product at 2.8%, continuing to maintain the temperature at 95 ℃ for about 40min, and ending the reaction. Recovering acetic acid from the hydrolysate under reduced pressure by using a vacuum pump, wherein the absolute pressure is 12kPa, pumping for 14min, recovering about 5.6kg of acetic acid aqueous solution, and the concentration of the acetic acid solution is 66%; after pumping out, adding a large amount of deionized water product vinegar tablets into the reaction product, beginning to precipitate, continuously washing the vinegar tablet particles with deionized water, and detecting the washing water until the washing water is neutral; drying the product vinegar tablet at 120 ℃ for 8h, and detecting;
(5) the obtained product has the filtration blockage value of 40.8, acetylation value of 55.0%, intrinsic viscosity of 1.40 and whiteness of 2.7.
Example 3
(1) Adding 10kg of pure acetic acid with the concentration of more than 99% into 20kg of ground acetified cellulose, and stirring and pretreating at room temperature for 40min to enhance the reaction activity;
(2) cooling 120kg of mixture of acetic anhydride and acetic acid (mixed acid) to 7 ℃ in a reaction vessel, wherein the ratio of the acetic anhydride is 40%;
(3) adding the pretreated wood pulp into the cooled mixed acid, and then starting to add 0.4kg of catalyst sulfuric acid, wherein the dosage of the sulfuric acid is 2 percent of the mass of the cellulose, the pH value of the system is-0.14, and the reaction starts. After the reaction starts, the system releases heat to cause the temperature of the system to rise to 55 ℃ within 36min, a vacuum pump is started to pump vacuum at absolute pressure of 6.7kPa while the temperature rises, and acetic acid in the reaction system is flashed and volatilized. Stopping the vacuum pump after the temperature reaches 55 ℃, continuing to react for 15min, ending the acetification reaction, and collecting 5.3kg of flash evaporated and volatilized acetic acid in the process, wherein the concentration of the obtained acetic acid solution is 97.8 wt%;
(4) adding 8.9kg of hot water accounting for 5.9 percent of the mass of the acetified product into the acetified product, starting heating from about 52 ℃, heating to 99 ℃ within about 44min, maintaining the 99 ℃ for about 47 minutes, then adding 3.5kg of magnesium acetate solution, keeping the mass ratio of the magnesium acetate solution to the acetified product at 2.3 percent, continuing to maintain the 99 ℃ for about 36 minutes, and then finishing the reaction. And (3) decompressing and recovering acetic acid in the hydrolysate by using a vacuum pump, wherein the absolute pressure is 10kPa, pumping is carried out for 15min, and the recovered acetic acid aqueous solution is about 6.8kg, and the concentration of the acetic acid solution is 67%. Adding a large amount of deionized water product into the reaction product, precipitating, washing the vinegar tablet particles with deionized water, and detecting the washing water until the solution is neutral; drying the product vinegar tablet at 120 ℃ for 8h, and detecting;
(5) the obtained product has the filtration blockage value of 39, the acetylation value of 55.8 percent, the intrinsic viscosity of 1.46 and the whiteness of 2.5.
Example 4
(1) Adding 9kg of pure acetic acid with the concentration of more than 99% into 20kg of ground and ground acetified cellulose, and stirring and pretreating at room temperature for 60min to enhance the reaction activity;
(2) 118kg of a mixture of acetic anhydride and acetic acid (mixed acid) is cooled to 12 ℃ in a reaction vessel, wherein the proportion of the acetic anhydride is 47 percent;
(3) adding the pretreated wood pulp into the cooled mixed acid, and then starting to add 0.3kg of catalyst sulfuric acid, wherein the dosage of the sulfuric acid is 1.5 percent of the mass of the cellulose, the pH value of the system is-0.06, and the reaction starts. After the reaction starts, the system releases heat to cause the temperature of the system to rise to 58 ℃ within 40min, a vacuum pump is started to pump vacuum at the same time of temperature rise, the absolute pressure is 7.4kPa, and acetic acid in the reaction system is flashed and volatilized. Stopping the vacuum pump after the temperature reaches 58 ℃, continuing to react for 10min, ending the acetification reaction, and collecting 6.5kg of flash evaporated and volatilized acetic acid in the process, wherein the concentration of the obtained acetic acid solution is 96.2 wt%;
(4) adding 9.1kg of hot water accounting for 6.2 percent of the mass of the acetified product into the acetified product, starting heating from about 53 ℃, heating to 91 ℃ within about 38min, maintaining the 91 ℃ for about 52min, then adding 3.1kg of magnesium acetate solution, keeping the mass ratio of the magnesium acetate solution to the acetified product at 2.1 percent, continuing to maintain the 91 ℃ for about 44min, and then finishing the reaction. And (3) decompressing and recovering acetic acid in the hydrolysate by using a vacuum pump, wherein the absolute pressure is 15kPa, pumping is carried out for 11min, and the recovered acetic acid aqueous solution is about 7.0kg, and the concentration of the acetic acid solution is 72%. Adding a large amount of deionized water product into the reaction product, precipitating, washing the vinegar tablet particles with deionized water, and detecting the washing water until the solution is neutral; drying the product vinegar tablet at 120 ℃ for 8h, and detecting;
(5) the obtained product has the filtration blockage value of 45, the acetylation value of 55.3%, the intrinsic viscosity of 1.44 and the whiteness of 3.2.
Comparative example:
(1) adding 8kg of pure acetic acid with the concentration of more than 99% into 20kg of ground and ground acetified cellulose, and stirring and pretreating at room temperature for 40min to enhance the reaction activity;
(2) cooling 110kg of mixture of acetic anhydride and acetic acid (mixed acid) to-18 ℃ in a reaction vessel, wherein the proportion of the acetic anhydride is 45%;
(3) adding the pretreated wood pulp into the cooled mixed acid, and then starting to add 2.6kg of catalyst sulfuric acid, wherein the dosage of the sulfuric acid is 1.5 percent of the mass of the cellulose, the pH value of the system is-0.62, and the reaction starts. The system exothermicity after the reaction is started leads to the temperature of the system rising to 47 ℃ within 28min, and the cooling medium circulation of the jacket of the acetification reactor needs to be started to take away the exothermic heat of the reaction when the temperature rises. After the peak temperature is reached, the reaction is continued for 20min, and the acetification reaction is finished.
(4) Adding 9.1kg of hot water into the acetified product, wherein the hot water accounts for 4.6 percent of the mass ratio of the acetified product, starting heating from about 40 ℃, heating to 82 ℃ within about 48min, maintaining the 82 ℃ for about 100min, then adding 9.0kg of magnesium acetate solution, the mass ratio of the magnesium acetate solution to the acetified product is 6.0 percent, and stirring for 5min to finish the reaction. Adding a large amount of deionized water product into the reaction product, precipitating, washing the vinegar tablet particles with deionized water, and detecting the washing water until the solution is neutral; drying the product vinegar tablet at 120 ℃ for 8h, and detecting;
(5) the obtained product has the filtration blockage value of 35, the acetylation value of 55.7%, the intrinsic viscosity of 1.50 and the whiteness of 3.9.
The comparison example shows that the mixed acid needs to be cooled to-18 ℃, the whiteness of the vinegar slices is low, a large amount of electric energy needs to be consumed, and the energy consumption is high; the consumption of the wood pulp catalyst concentrated sulfuric acid and magnesium acetate with the same quality is greatly increased, and the consumption is larger.
According to the production method of the cellulose acetate, the method of high-temperature acetification and reduced-pressure acetic acid recovery is adopted, so that the addition amount of an acid catalyst is small, and after the acetification reaction is finished, the cooling by using chilled brine is not needed, so that the cooling energy consumption is greatly reduced; 3% sulfuric acid catalyst is used, and subsequent products need to be bleached by hydrogen peroxide, so that the working procedures are reduced, and the explosion risk is reduced; the hydrolysis temperature is 95 ℃, high-pressure hydrolysis is not needed, and the requirements on equipment and operation are reduced.
The foregoing description of the embodiments is provided to facilitate the understanding and appreciation of the invention by those skilled in the art; it will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty; therefore, the present invention is not limited to the embodiments described herein, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (12)
1. A method for producing cellulose acetate, characterized in that it comprises the following steps:
(1) mixing cellulose and acetic acid solution at room temperature, and pretreating to obtain a mixture; mixing acetic anhydride and an acetic acid solution, and then cooling to obtain mixed acid;
(2) adding the mixture into the mixed acid to obtain a reaction mixture, and then adding an acidic catalyst to carry out an acetification reaction, wherein the dosage of the acidic catalyst is 0.5-3 wt% of the mass of the cellulose;
(3) continuously vacuumizing the reaction system in the temperature rising process of the acetification reaction so as to enable acetic acid in the reaction system to be flashed and volatilized, stopping vacuumizing after the temperature of the reaction system reaches the peak acetification temperature, and continuing to react until the acetification reaction process is finished to obtain an acetified product;
(4) adding hot water into the acetified product, heating to the peak hydrolysis temperature, maintaining the peak hydrolysis temperature, adding magnesium acetate, and continuously maintaining the peak hydrolysis temperature until the hydrolysis reaction is finished, wherein the peak hydrolysis temperature is 90-100 ℃, and the hydrolysis reaction is carried out under normal pressure;
(5) and treating the hydrolysate to obtain a cellulose acetate product.
2. The production method according to claim 1, characterized in that: in the step (1), the cellulose is acetified-grade cellulose; and/or the presence of a gas in the gas,
in the step (1), the cellulose has an average length of 0.5-5mm and an average diameter of 10-20 μm; and/or the presence of a gas in the gas,
in the step (1), the mass percent of acetic acid in the acetic acid solution is more than 99 percent; and/or the presence of a gas in the gas,
in the step (1), the mass ratio of the cellulose to the acetic acid is 100 (20-60); and/or the presence of a gas in the gas,
in the step (1), the content of acetic anhydride in the mixed acid is 30-60 wt%, and the mass ratio of the mixed acid to the fibers is 5:1-8: 1.
3. The production method according to claim 2, characterized in that: in step (1), the cellulose is selected from specialty pulp grade cellulose or acetified grade wood pulp; and/or the presence of a gas in the gas,
in the step (1), the mass ratio of the cellulose to the acetic acid is 100 (20-60); and/or the presence of a gas in the gas,
the content of acetic anhydride in the mixed acid is 30-60 wt%.
4. The production method according to claim 1, characterized in that:
in the step (2), the mixed acid is cooled to-5-15 ℃ before being mixed with the mixture; and/or the presence of a gas in the gas,
in the step (2), the pH value of the mixed acid and the catalyst mixture is between-1 and 0; and/or the presence of a gas in the gas,
in the step (2), the acidic catalyst is concentrated sulfuric acid.
5. The production method according to claim 1, characterized in that: in the step (3), the peak acetification temperature is 55-70 ℃; and/or the presence of a gas in the gas,
in the step (3), vacuumizing and absolute pressure are performed in the acetification reaction process, and the vacuum degree is 3-10 kPa; and/or the presence of a gas in the gas,
in the step (3), collecting flash evaporated acetic acid to obtain an acetic acid solution with the concentration of 95 +/-2 wt%; and/or the presence of a gas in the gas,
in the step (3), the collected acetic acid volatilized by flash evaporation is recycled to the step (2).
6. The production method according to claim 1, characterized in that: in the step (4), the mass ratio of the hot water to the acetified product is 5-10%; and/or the presence of a gas in the gas,
in the step (4), the temperature of the hot water is 70-95 ℃; and/or the presence of a gas in the gas,
in the step (4), the temperature rising speed is 1-1.5 ℃/min; and/or the presence of a gas in the gas,
in the step (4), acetic acid is recovered by reducing pressure after the hydrolysis reaction process, and the concentration of the recovered acetic acid aqueous solution is 65-75%; and/or the presence of a gas in the gas,
in the step (4), the mass ratio of the magnesium acetate to the acetified product is 2-5%.
7. The production method according to claim 1, characterized in that:
in step (4), the time to maintain the peak hydrolysis temperature after the addition of magnesium acetate is less than or equal to the time to maintain the peak hydrolysis temperature before the addition of magnesium acetate.
8. The production method according to claim 7, characterized in that: in step (4), the time for maintaining the peak hydrolysis temperature before adding the magnesium acetate is 40-70 min; and/or the presence of a gas in the gas,
in step (4), the time for maintaining the peak hydrolysis temperature after adding magnesium acetate is 30-60 min.
9. The production method according to claim 6, characterized in that:
in the step (4), after the acetified product is mixed with hot water and reaches 50. + -. 5 ℃, the temperature of the mixed system is slowly raised.
10. The production method according to claim 9, characterized in that:
in step (4), the temperature is raised to the peak hydrolysis temperature within 30-50 min.
11. The production method according to claim 1, characterized in that: in the step (5), an excessive amount of deionized water is added into the hydrolysate, and the cellulose acetate precipitate is taken and washed by deionized water until the pH value is neutral, and is dried to obtain the cellulose acetate product.
12. The production method according to claim 1, characterized in that: the filtration blockage value of the cellulose acetate product is 42 +/-10, the acetylation value is 55.4 +/-0.8%, the intrinsic viscosity is 1.45 +/-0.1, and the whiteness b value is 3.0 +/-0.5.
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| CN111253616B (en) * | 2020-03-02 | 2022-07-12 | 万华化学集团股份有限公司 | Method and device for precipitating cellulose acetate butyrate |
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| US4439605A (en) * | 1981-11-30 | 1984-03-27 | Daicel Chemical Industries, Ltd. | Process for producing cellulose acetate |
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| US5869646A (en) * | 1996-02-08 | 1999-02-09 | Daicel Chemical Industries, Ltd. | Method and apparatus for acetylating cellulose |
| CN1075513C (en) * | 1999-09-08 | 2001-11-28 | 中国科学院广州化学研究所 | Process for preparing acetyl cellulose by gas-solid reaction |
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