JP2000212201A - Production of cellulose acetate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a low-viscosity cellulose acetate by preparing two catalyst solutions prepared by diluting sulfuric acid with acetic acid and having the same or different concentrations, adding the first portion to the reaction system at the start of an acetylation reaction and adding the second portion to the system when the degree of substitution of a cellulose acetate as the reaction intermediate exceeds a specified value. SOLUTION: The second portion is added to the reaction system when the degree of substitution of a cellulose acetate as the reaction intermediate exceeds 1.8. The amounts of sulfuric acid added in the first and second stages are desirably 0.5-5 pts.wt. and 0.01-2.0 pts.wt., respectively per 100 pts.wt. starting cellulose. The ratio between the first and second portions added is desirably 80/20 to 50/50 in terms of a ratio between the weights of the sulfuric acid added. It is desirable that sulfuric acid used in the first and second addition is in the form of a 1-5 wt.% acetic acid solution. It is desirable that the amounts of acetic anhydride and acetic acid added in the acetylation step are 200-400 pts.wt. and 300-600 pts.wt. per 100 pts.wt. cellulose. It is desirable that the acetylation reaction is performed in a vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing low-viscosity cellulose acetate.

[0002]

2. Description of the Related Art Cellulose acetate is used in various applications such as filter tow for tobacco, fiber, photographic film and artificial kidney.
When applied to these uses, it is desirable that the viscosity of the cellulose acetate solution is low from the viewpoint of ease of handling and molding. Factors controlling viscosity in the production of cellulose acetate include acetylation temperature, acetylation time, amount of catalyst, ripening temperature, ripening time, and the like, and the viscosity of cellulose acetate can be adjusted by appropriately combining these factors. it can.

However, all control factors have advantages and disadvantages, and it is difficult to stably produce low-viscosity cellulose acetate using only a combination of these factors. For example, when trying to obtain a low-viscosity cellulose acetate by increasing the acetylation temperature, it is difficult to control the depolymerization rate and it is difficult to obtain a stable product, and the method for obtaining a low-viscosity cellulose acetate by increasing the acetylation time is stable. Products are easy to obtain, but there is a problem with productivity. Further, when trying to obtain low-viscosity cellulose acetate by increasing the amount of catalytic sulfuric acid, which is a strong acid, it becomes difficult to control the rate of depolymerization, and it is also difficult to obtain a stable product. Furthermore, since the saponification reaction and the depolymerization reaction proceed simultaneously in the aging step, it is very difficult to determine conditions that simultaneously satisfy both the degree of acetylation and the degree of polymerization (viscosity).

An object of the present invention is to provide a method capable of stably producing low-viscosity cellulose acetate in order to meet the above demand.

[0005]

The present inventors have focused on the acetylation reaction as a viscosity control factor, and have disclosed a catalyst solution disclosed in Japanese Patent Application Laid-Open No. 3-205401 proposed as a technique for improving the acetylation reaction. The technology for controlling the rate of acetylation by multi-stage split addition of phenol was further improved, and the research was repeated to solve the above problems. As a result, in the acetylation step, a catalyst solution obtained by diluting sulfuric acid into acetic acid is added in two stages, and the acetylation reaction is controlled by optimizing the time of the second stage addition,
The present inventors have found that cellulose acetate having a low viscosity can be stably obtained, and have completed the present invention.

That is, the present invention relates to a method for producing cellulose acetate, which comprises an acetylation step using a catalyst solution obtained by diluting sulfuric acid into acetic acid.
Provided is a method for producing cellulose acetate, wherein a stage is added at the start of an acetylation reaction, and a stage is added at a stage where the degree of substitution of cellulose acetate as a reaction intermediate exceeds 1.8.

In the present invention, the term "catalyst solution obtained by diluting sulfuric acid into acetic acid" refers to a solution obtained by diluting sulfuric acid as a catalyst into acetic acid as a reaction solvent, and separately adding sulfuric acid and acetic acid to a reaction system. Includes sulfuric acid diluted with acetic acid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing cellulose acetate of the present invention is characterized by an acetylation step using a catalyst solution obtained by diluting sulfuric acid into acetic acid. The processing of a general production process of cellulose acetate can be applied. Hereinafter, the method for producing cellulose acetate of the present invention will be described step by step.

First, acetic acid is added to cellulose such as wood pulp, which is a raw material, to activate pretreatment. The amount of acetic acid used in this pretreatment activation is preferably 10 to 500 parts by weight based on 100 parts by weight of cellulose. Also,
The pretreatment activation is preferably performed under closed and stirred conditions, for 20 minutes.
Perform at ６０60 ° C. for 0.1 to 3 hours.

Next, a treatment in an acetylation step is performed. In this acetylation step, acetic anhydride as an acetylation reactant, acetic acid as a reaction solvent, and sulfuric acid as a catalyst are added. The catalyst solution obtained by diluting sulfuric acid into acetic acid is divided into two parts and added in two stages. I do. Note that acetic anhydride and acetic acid are usually added before adding the catalyst solution.

The first stage catalyst solution is added at the start of the acetylation reaction. The amount of sulfuric acid added in the first stage is based on the raw material cellulose 1
The amount is preferably 0.5 to 5 parts by weight, particularly preferably 0.8 to 4 parts by weight with respect to 00 parts by weight.

The catalyst solution of the second stage is added after the start of the acetylation reaction, when the degree of substitution of the cellulose acetate as a reaction intermediate exceeds 1.8, preferably when it exceeds 2.0. The acetylation reaction has non-uniformity in the progress of the reaction derived from the solid-liquid phase reaction, and the reaction proceeds non-uniformly as a reaction mechanism.
Accordingly, in the reaction system, the reaction proceeds in a state in which the reaction is delayed and coexisted in the cellulose acetate solution dissolved in the solvent acetic acid with a portion still in a fiber state. However, when the average degree of substitution of cellulose acetate exceeds 1.8,
Although a semi-fibrous material or fibrous material still remains in the reaction system, the amount thereof is small, and most of the material is in a liquid phase state. When the second stage catalyst solution is added in such a state, the catalyst is uniformly diffused in the liquid phase, so that the depolymerization of cellulose acetate proceeds uniformly. Depolymerization of a small amount of cellulose acetate in the state of a semi-fibrous material or fibrous material is delayed as compared with the liquid phase portion, but the effect on viscosity is negligible.
Therefore, by adding the second stage catalyst solution at the stage when the average degree of substitution of cellulose acetate in the reaction process exceeds 1.8, that is, when the reaction system is almost in a liquid phase, the depolymerization reaction can be uniformly performed. It is possible to proceed, and it is possible to stably obtain cellulose acetate having a desired low viscosity.

The amount of sulfuric acid added in the second stage is preferably 0.01 to 2.0 parts by weight, particularly preferably 0.05 to 1.0 part by weight, based on 100 parts by weight of the raw material cellulose.

It is preferable that the weight ratio of the sulfuric acid in the first and second stages is 80:20 to 50:50 in terms of the weight ratio of sulfuric acid, since the effect of divided addition is high. In addition, sulfuric acid is the first stage and 2
It is preferable to add as a 1 to 5% by weight acetic acid solution also at the stage of addition.

The addition ratio of the first-stage and second-stage catalyst solutions can be more easily adjusted by fixing the amount of the first-stage catalyst solution and changing the amount of the second-stage catalyst solution. Viscosity can be controlled.

The amount of acetic anhydride and acetic acid added in the acetylation step is preferably 200 to 400 parts by weight, particularly preferably 250 to 400 parts by weight, based on 100 parts by weight of cellulose.
400 parts by weight, and acetic acid is preferably 300 to 600 parts by weight.
Parts by weight, particularly preferably 350 to 500 parts by weight.

The acetylation reaction can be performed under normal pressure or reduced pressure. Next, the acetylation conditions will be described separately for normal pressure and reduced pressure.

(When the acetylation reaction is carried out at normal pressure) The first stage catalyst is added while stirring a mixture of cellulose, acetic anhydride and acetic acid. It is desirable to raise the temperature to a predetermined temperature of 85 ° C. (preferably 35 to 70 ° C.) and hold the temperature at the same temperature for 3 to 90 minutes. The second stage catalyst is added at a predetermined point in the way.

(When the acetylation reaction is performed under reduced pressure) While the mixture of cellulose, acetic anhydride and acetic acid is stirred, the reaction system is reduced to 5.3 to 20 kPa, preferably 6 to 12 kPa, The catalyst is added to start the acetylation reaction. The mixed vapor of acetic acid and acetic anhydride that evaporates is condensed in a condenser and distilled out of the reaction system, and the same reduced pressure is maintained (the temperature is 5 ° C.).
(The temperature is kept at about 0 to 65 ° C.) The acetylation reaction is continued, a second-stage catalyst is added at a predetermined time on the way, and the reaction is further continued under reduced pressure. When a predetermined amount of the mixture of acetic acid and acetic anhydride has been distilled off or when the condensate of the mixture has hardly distilled off, the pressure of the reaction system is gradually returned to normal pressure over about 5 minutes.
The reaction is continued at 0-80 ° C for 1-60 minutes. In the present invention, the acetylation reaction is desirably performed under reduced pressure. The advantage of performing the acetylation reaction under reduced pressure is that the heat of the acetylation reaction is removed by the latent heat of vaporization of the mixture of acetic acid and acetic anhydride, thereby facilitating the control of the reaction temperature and having an energy saving effect.

Next, a saponification / aging process is performed. In this saponification and aging treatment, the catalyst sulfuric acid in the primary cellulose acetate (cellulose triacetate) producing system is completely or partially neutralized, the temperature in the reaction system is set to 125 to 170 ° C.
Hold for minutes to 6 hours to obtain secondary cellulose acetate (cellulose diacetate) having a desired degree of acetylation.

Next, the secondary cellulose acetate (cellulose diacetate) reaction mixture is put into a dilute aqueous acetic acid solution, collected as a precipitate, washed, purified, and dried to obtain a product.

The cellulose acetate obtained by the production method of the present invention has a 6% by weight viscosity measured by the following method, preferably less than 100 mPa · s.

(Measurement method) Dry sample in Erlenmeyer flask
Then, 39 g of an aqueous solution of 00 g and 95% acetone was added, and the mixture was sealed and stirred for about 1.5 hours. Thereafter, the mixture is shaken for about 1 hour with a rotary shaker to completely dissolve. The obtained 6 wt / vol% solution was transferred to the marked line of a predetermined Ostwald viscometer, and 25 ± 1.
Heat at ℃ for about 15 minutes. The flow time between the timing marks is measured, and the 6% viscosity is calculated by the following equation. 6% viscosity (mPa · s) = flowing time (s) × viscometer coefficient The viscometer coefficient is obtained by measuring the flowing time by the same operation as above using a viscometer calibration standard solution, and using the following equation.

[0024]

(Equation 1)

[0025]

The present invention will now be described in more detail with reference to the following Examples, which by no means limit the scope of the present invention. In the examples, “parts” means “parts by weight” and “%” means “% by weight”. The physical properties of cellulose acetate were measured by the following methods.

(1) Degree of acetylation Degree of substitution of cellulose acetate in the course of the reaction (DS) The degree of substitution means the average number of substituted hydroxyl groups per glucose residue and was determined from the measured value of the degree of acetylation. . The degree of acetylation was measured according to the method for measuring the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). In the case of the normal pressure method, a reaction mixture in the middle of the reaction was taken out, and a large excess of an aqueous solution of magnesium acetate was added with vigorous stirring to separate flaky cellulose acetate.
Then, it was sufficiently washed with water, taken out, and dried. In the case of the depressurization method, since sampling is difficult during the process, a large excess of an aqueous magnesium acetate solution was added while vigorously stirring the entire reaction mixture to separate flaky cellulose acetate.
Then, it was sufficiently washed with water, taken out, and dried. This operation was performed for each condition and time, and the DS transition was simulated, and the DS at the time of adding the catalyst was determined. 1.9 g of the dried cellulose acetate obtained by the above operation was precisely weighed and dissolved in 150 ml of a mixed solvent of acetone and dimethylsulfoxide (volume ratio: 4: 1). Saponified at 200C for 2 hours.
Phenolphthalein was added as an indicator and excess sodium hydroxide was titrated with 1N sulfuric acid. Further, a blank test was performed in the same manner as described above, and the degree of acetylation was calculated from the following equation. Degree of acetylation (%) = [6.5 × (BA) × F] / W [A: titration of 1N sulfuric acid in sample (ml), B: titration of 1N sulfuric acid in blank test (ml) ), F: concentration factor of 1N sulfuric acid, W: weight of sample (g)] Using the acetylation degree value measured by the above method, the substitution degree (DS) was calculated from the following equation. Degree of substitution (DS) = (degree of acetylation × 162) / (6005-degree of acetylation × 42).

Degree of acetylation of cellulose diacetate Approximately 0.52 g of a pulverized sample was collected in a weighing bottle, and was placed at 105 ± 5 ° C.
, And allowed to cool in a desiccator for about 40 minutes. This was precisely weighed and transferred to a flask, and the empty weighing bottle was precisely weighed again, and the difference in weight was taken as the sample weight. Next, about 2 ml of ethanol was added to wet well, and then 50 ml of acetone was added and stirred for about 30 minutes to completely dissolve. Next, 50 ml of a 0.2 mol / L sodium hydroxide solution was added with stirring, the mixture was stirred until a white precipitate was formed, and the mixture was allowed to stand for about 3 hours. With stirring again, 50 ml of a 0.2 mol / L hydrochloric acid solution was added, and the mixture was allowed to stand for 15 minutes or more. A phenolphthalein solution was added as an indicator, and titration was performed with a 0.2 mol / L sodium hydroxide normal solution until the solution became light red (Aml).
At the same time, a blank test was performed (Bml). The degree of acetylation was calculated by the following equation.

[0028]

(Equation 2)

(2) 6% by weight viscosity Measured and calculated by the above method.

Example 1 A pulp for dissolving kraft method, which is a cellulose raw material, was pulverized into a fluff and dried to a water content of about 6%. 31 parts of glacial acetic acid was added to 100 parts of the dried fluff pulp, and the pretreatment was activated for 1 hour. The pretreated activated cellulose was charged into a stirring acetylation reactor, and a mixed solution of 270 parts of acetic anhydride as an acetylation reagent and 330 parts of acetic acid as a reaction solvent was simultaneously charged. Then, the first stage catalyst solution (3%
30 parts of sulfuric acid (acetic acid solution) was added over 0.5 minutes to start the reaction. The time at which the addition of the catalyst solution was started was set to 0 minute, and was set as a reference time thereafter. Since the temperature of the reaction system rapidly increased and reached 55 ° C. after about 5 minutes, the temperature was adjusted to a constant temperature thereafter. At 20 minutes (DS = 2.32)
Was added 10 parts of a second stage catalyst solution. Thereafter, at 60 minutes, 11 parts of a 24% aqueous solution of magnesium acetate was added and mixed to completely neutralize the sulfuric acid in the reaction system and to reduce the amount of magnesium acetate to excess. 71 parts of water at 60 ° C. was added to the completely neutralized reaction mixture, and the mixture was stirred and mixed. The reaction mixture was transferred to an autoclave and heated for 150 minutes by external heating.
° C. After maintaining at 150 ° C. for 30 minutes, the mixture was hydrolyzed to 100 ° C. in about 20 minutes by external cooling to obtain a reaction mixture containing cellulose diacetate. A dilute acetic acid aqueous solution was added to the obtained reaction mixture while vigorously stirring to separate flaky cellulose diacetate, and then sufficiently washed with water, taken out, and dried to produce a product.

Example 2 After treating in the same manner as in Example 1, the first stage catalyst (3
30% sulfuric acid and acetic acid solution) was added over 0.5 minutes to start the reaction. The reaction was carried out under the same temperature conditions, and at 12 minutes (DS = 1.89), 10 parts of the second stage catalyst solution was added. Then, at 60 minutes, 11 parts of a 24% aqueous solution of magnesium acetate was added and mixed to completely neutralize sulfuric acid in the reaction system and to reduce the amount of magnesium acetate in excess. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 1 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

Comparative Example 1 After treating in the same manner as in Example 1, 30 parts of the first stage catalyst solution (3% sulfuric acid acetic acid solution) was added over 0.5 minutes to start the reaction. The reaction was carried out under the same temperature conditions, and at 10 minutes (DS = 1.69), 10 parts of the second stage catalyst solution was added. Then, at 60 minutes, 11 parts of a 24% aqueous solution of magnesium acetate was added and mixed to completely neutralize sulfuric acid in the reaction system and to reduce the amount of magnesium acetate in excess. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 1 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

Comparative Example 2 After treating in the same manner as in Example 1, 40 parts of a catalyst solution (3% sulfuric acid / acetic acid solution) was added over 0.5 minutes to start the reaction. The reaction was carried out under the same temperature conditions. Then, at 60 minutes, 11 parts of a 24% aqueous magnesium acetate solution was added and mixed.
Sulfuric acid in the system was completely neutralized, and the system was adjusted to excess magnesium acetate. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 1 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

[0034]

[Table 1]

As shown in the table, a low-viscosity cellulose diacetate was stably obtained by adjusting the addition time of the second stage catalyst solution according to the present invention.

Example 3 100 parts of the dissolving pulp produced by the Kraft method, which is a cellulose raw material, was pulverized into a fluff and activated by pretreatment with 31 parts of acetic acid. The pretreated activated cellulose is charged into a stirring acetylation reactor, and acetic anhydride 270, which is an acetylation reaction agent, is charged.
And a mixed solution of 330 parts of acetic acid as a reaction solvent. After reducing the pressure in the reactor and controlling the degree of vacuum to 8.7 kPa, the first stage catalyst solution (3% sulfuric acid acetic acid solution)
30 parts were added over 2 minutes to start the reaction. The time at which the addition of the catalyst solution was started was set to 0 minute, and was set as a reference time thereafter. The temperature of the reaction system rapidly increased, and after reaching about 56 ° C., which was the boiling point of the mixture of acetic acid and vinegar-free, about 4 minutes later, the temperature became constant and the distillation of the acid started. The reaction was allowed to proceed while the generated vapor mixture of acetic anhydride and acetic acid was condensed by a condenser and distilled out of the reaction system. 11 minutes (DS =
2.07), 28 parts of the second stage catalyst solution were added. At 27 minutes (15 minutes after the vacuum control in the acetylation reactor was stopped after a predetermined amount of acid was distilled off), the reaction temperature reached a peak of about 66 ° C. At this time, the reaction was stopped by adding 17 parts of a 24% aqueous solution of magnesium acetate as a reaction terminator, and the amount of magnesium acetate was reduced to excess. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. The reaction mixture was transferred to an autoclave and brought to 150 ° C. over 60 minutes by external heating. After holding at 150 ° C. for 30 minutes, hydrolysis was performed by external cooling to 100 ° C. in about 20 minutes,
A reaction mixture containing cellulose diacetate was obtained. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

Example 4 After the same treatment as in Example 3, 11 minutes later (DS = 2.
07), 19 parts of a second-stage catalyst solution (3% sulfuric acid / acetic acid solution) was added. At 27 minutes (15 minutes after the vacuum control in the acetylation reactor was stopped after a predetermined amount of acid was distilled off), the reaction temperature reached a peak of about 66 ° C. At this time, 14 parts of a 24% aqueous magnesium acetate solution as a reaction terminator was added and mixed to completely neutralize sulfuric acid in the reaction system to stop the reaction, and to reduce the amount of magnesium acetate to excess. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 3 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

Example 5 After the same treatment as in Example 3, 11 minutes later (DS = 2.
07), 9 parts of a second-stage catalyst solution (3% sulfuric acid / acetic acid solution) was added. At 27 minutes (15 minutes after the vacuum control in the acetylation reactor was stopped after a predetermined amount of acid was distilled off), the reaction temperature reached a peak of about 66 ° C. At this time, 11 parts of a 24% aqueous magnesium acetate solution as a reaction terminator was added and mixed to completely neutralize sulfuric acid in the reaction system to stop the reaction, and to reduce the amount of magnesium acetate to excess. To the completely neutralized reaction mixture, 71 parts of water at 60 ° C was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 3 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

Comparative Example 3 After the same treatment as in Example 3, 8 minutes later (DS = 1.7)
To 0), 9 parts of the second stage catalyst solution (3% sulfuric acid / acetic acid solution) was added. At 27 minutes (15 minutes after the vacuum control in the acetylation reactor was stopped after a predetermined amount of acid was distilled off), the reaction temperature reached a peak of about 66 ° C. At this time, 11 parts of a 24% aqueous magnesium acetate solution as a reaction terminator was added and mixed.
The sulfuric acid in the reaction system was completely neutralized to stop the reaction, and the reaction was adjusted to an excess of magnesium acetate. 6 in the fully neutralized reaction mixture
71 parts of water at 0 ° C. was added and mixed with stirring. Hydrolysis was performed in the same manner as in Example 3 to obtain a reaction mixture containing cellulose diacetate. The obtained reaction mixture was subjected to the same post-treatment as in Example 1 to obtain a product.

[0040]

[Table 2]

As shown in the table, low viscosity cellulose diacetate was stably obtained by adjusting the addition time of the second stage catalyst solution according to the present invention.

[0042]

According to the present invention, low viscosity, especially 6% by weight
Cellulose acetate having a solution viscosity of less than 100 mPa · s can be stably produced. Therefore, when forming into a fiber, a film, or the like using the cellulose acetate solution, handling and forming operations are facilitated.

Claims (5)

[Claims] 1. A method for producing cellulose acetate comprising an acetylation step using a catalyst solution obtained by diluting sulfuric acid into acetic acid, wherein a catalyst solution obtained by diluting sulfuric acid into acetic acid is divided into two parts, and a first stage is added at the start of the acetylation reaction. And adding the second stage at a stage where the degree of substitution of the cellulose acetate as a reaction intermediate exceeds 1.8. 2. The addition ratio of the first and second stage catalyst solutions is as follows:
The weight ratio of sulfuric acid is 80:20 to 50:50.
The method for producing cellulose acetate according to the above. 3. The method for producing cellulose acetate according to claim 1, wherein the addition amount of the first-stage catalyst solution is fixed, and the desired viscosity is controlled by changing the addition amount of the second-stage catalyst solution. . 4. The method for producing cellulose acetate according to claim 1, wherein the acetylation reaction is performed under reduced pressure. 5. A viscosity at 25 ° C. of a solution obtained by dissolving cellulose acetate produced by the production method according to claim 1 in a 95% by volume aqueous solution of acetone so as to be 6% by weight. Is less than 100 mPa · s. The process for producing cellulose acetate according to claim 1, wherein