JPH09272701A - Method for reaction control and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a peak reaction temperature with ease and with accuracy, in a batch type reactionprocess for the acetylation of cellulose. SOLUTION: This batch type process for producing a cellulose acetate comprises a preceding step of acetylation under reduced pressure, in which cellulose is acetylated under reduced pressure in the presence of an acidic catalyst such as sulfuric acid, while distilling the vapor phase fraction out of the reaction system for acetylation, and a latter step of acetylation in which the acetylation reaction is rendered to further proceed under a pressure higher than in the preceding step of acetylation under reduced pressure, wherein the higher pressure in the latter step is provided e. g. by stopping evacuation. In the two-step batch process, the reaction temperature in the latter step of acetylation is controlled by conducting an operation for the transfer from the preceding step to the latter step according to a procedure in which a rate of distilling out of the reaction system in the preceding step is taken as a criterion for the transfer. The operation for the transfer from the preceding step to the latter step may be conducted by taking, as the criterion, a rate of distilling out of the reaction system in the preceding step which is observed after this rate of distilling has reached a maximum value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the reaction of a cellulose acetylation reaction, which is useful in producing cellulose acetate for use in filter tow for cigarettes, fiber, photographic film, artificial kidney and the like. Regarding

[0002]

2. Description of the Related Art As a typical method for industrially producing cellulose acetate, in the presence of an acid catalyst such as sulfuric acid,
A method of acetylating cellulose with an acetylating agent such as acetic anhydride is known. The acetylation reaction of cellulose is a violent exothermic reaction, and when the reaction temperature, especially the peak temperature (maximum temperature) is high, the depolymerization reaction of cellulose progresses, and the degree of polymerization of cellulose acetate is lowered to deteriorate the quality.
Therefore, in order to maintain the quality of cellulose acetate, it is extremely important to accurately control the reaction temperature in the acetylation reaction.

Japanese Patent Publication No. 2-5761 discloses a method for producing cellulose acetate using cellulose as a raw material, acetic anhydride as an acetylating agent, acetic acid as a solvent, and sulfuric acid as a catalyst.
Characterized in that the reaction product is concentrated by reducing the pressure in the reaction system for the entire period of the acetylation reaction or a part of the period including the initial stage to coagulate the generated vapor and distill it out of the reaction system. A method of making cellulose acetate is disclosed. And, in this publication, when the vapor component distills a certain amount in the course of the reaction, the reduced pressure is broken and the pressure is returned to normal pressure, and if there is some heat radiation, the reaction when the unreacted cellulose is acetylated. It is described that, due to heat, the reaction temperature rises and reaches a peak temperature, and then the temperature falls, and that the peak temperature can be controlled by using the amount of the vapor component distilled as an index.

However, the acetylation reaction step under reduced pressure (vacuum acetylation step) and the acetylation reaction step in which the reaction temperature is raised by increasing the reaction pressure and the reaction heat of the remaining cellulose to further promote the acetylation reaction ( In the case where the post-acetylation step) is continuously carried out by a batch method, the method of increasing the reaction temperature by stopping the depressurization control using the distillation amount of the vapor component as an index as described above Large variations in peak temperature. Therefore, the degree of polymerization of cellulose acetate is not constant and stable quality cannot be obtained.

This is considered to be due to the following reason. That is, since the cellulose used as a raw material usually contains water, in the first half of the reduced pressure acetylation step, in addition to the acetylation reaction of cellulose, the hydrolysis reaction of acetic anhydride by the water proceeds. Therefore, the amount of acetic acid produced in the reaction system varies depending on the water content of the raw material cellulose, and the reaction heat at that time also varies, so the amount of distillate also varies. Also, in the first half of the reduced pressure acetylation process, the reaction temperature rapidly rises and the internal reflux is large, so the system is unstable and the distillate amount (mixture of acetic acid and acetic anhydride) also fluctuates. It's easy to do. Therefore, in the above method, the concentration of unreacted cellulose in the reaction system is often different even if the amount of distillate is the same. If the unreacted cellulose concentration is different, the amount of heat generated in the post acetylation step is also different, and it is considered that the peak temperature is not constant.

On the other hand, if the acetylation reactor is made an adiabatic system and the amounts and temperatures of the input materials, the acetylating agent, the reaction solvent and the catalyst are strictly controlled, the theoretical peak temperature of the reaction can be stabilized. You can However, in the case of industrial production, a large amount of equipment is required in order to make the acetylation reactor a complete adiabatic system and to precisely control the amount and temperature of the acetylating agent, etc. Takes.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a reaction control method capable of simply and accurately controlling the reaction temperature of the acetylation reaction when carrying out the batch acetylation reaction step of cellulose, and the reaction. It is to provide a control device. Another object of the present invention, when producing a cellulose acetate by performing the vacuum acetylation step and the post-acetylation step in a batch manner, a reaction control method capable of simply suppressing the variation of the peak temperature in the post-acetylation step, And to provide a reaction control device. Still another object of the present invention is to provide a method for producing cellulose acetate, which gives a stable quality of cellulose acetate.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the distillate in the reduced pressure acetylation step can be used for the transfer operation from the reduced pressure acetylation step to the post acetylation step. It was found that the peak temperature in the post acetylation step can be precisely controlled by using the distillation rate as an index, and the present invention was completed.

That is, the present invention is conducted in the presence of an acidic catalyst,
Decompression acetylation step of acetylating cellulose under reduced pressure while distilling the gas phase components of the reaction system out of the reaction system, and acetylation after further proceeding the acetylation reaction under a higher pressure than this reduced pressure acetylation step. A method for producing a cellulose acetate in a batch method by controlling the reaction temperature of the post-acetylation step, which comprises a step,
Provided is a reaction control method in which the operation of shifting from the reduced-pressure acetylation step to the post-acetylation step is performed by using the distillation rate of the distillate in the reduced-pressure acetylation step as an index.

The present invention also includes a reduced pressure acetylation step of acetylating cellulose under reduced pressure while distilling gas phase components of the reaction system out of the reaction system in the presence of an acidic catalyst; A device for controlling the reaction in the cellulose acetate production step including a post-acetylation step of further advancing the acetylation reaction under a high pressure, the acetylation reactor, and a depressurizing means for depressurizing the reaction system. A condensing means for condensing the distillate distilled from the reaction system, a measuring means for measuring the distilling rate of the distillate in the reduced pressure acetylation step, and a reduced pressure acetylation based on the measurement value by the measuring means. Provided is a reaction control device having a pressure adjusting means for relatively increasing the pressure in the post-acetylation step rather than the step. The present invention further relates to a method for producing cellulose acetate, the reaction of which is controlled by the control method as described above.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view showing an example of the reaction control device of the present invention. This reaction control device is an acetylation reactor 1 for acetylating cellulose with an acetylating agent under stirring.
A vacuum pump 2 for reducing the pressure of the reaction system, a condenser 3 for condensing the distillate distilled from the reaction system, and a flow rate for measuring the distillation rate of the distillate condensed by the condenser 3. It has 4 in total.

The acetylation reactor 1 is provided with a raw material supply line 5 for supplying raw materials and a gas extraction line 6 for introducing gas in the gas phase portion of the reaction system to the condenser 3. A valve 9 for releasing the reduced pressure of the reaction system is attached to the gas extraction line 6. Capacitor 3
Is equipped with a distillate withdrawal line 7 for withdrawing the condensed distillate, and in the middle of this distillate withdrawal line 7,
The flow meter 4 is attached. Also, the capacitor 3
Is provided with a decompression line 8 communicating with the vacuum pump 2, and the decompression line 8 is provided with an intake line 12 having a valve 11 for adjusting the pressure of the reaction system.

Then, this device has a measurement value R of the flow meter 4.
And a predetermined reference value Rs are compared with each other, and when the comparison result is R ≦ Rs, there is provided control means 10 for giving a release signal to the valve 9 for releasing the depressurization of the reaction system. Therefore, when the distillation rate of the distillate becomes less than or equal to a preset reference value (that is, when the threshold value is reached),
The reduced pressure of the reaction system can be automatically released. The control means 10 includes a flow meter 4 having a flow sensor, and a differentiating circuit for differentiating the flow rate data detected by the flow meter at predetermined time intervals to obtain differential data corresponding to the distilling speed. , A comparing circuit for comparing the differential data (measured value R) by this differentiating circuit and the reference value Rs, and from the comparing circuit to the drive circuit of the decompression releasing means (valve 9) when the differential data reaches the reference value. And a control circuit for giving a decompression release signal. More specifically, for example, the flow rate (flow velocity) measured by a flow meter by a computer is integrated every moment, and this is converted into a distillation rate from the amount distilled for one minute, for example (measurement value R). When this value becomes equal to or lower than the reference value Rs, a bit for releasing the reduced pressure is generated. The control means 10 is composed of a generation circuit for generating this bit and a control circuit for giving a pressure reduction release signal to the drive circuit of the pressure reduction release means (valve 9) in response to the bit generated by the circuit. You may.

As the acetylation reactor 1, a reactor usually used for producing cellulose acetate can be used. Preferred acetylation reactors include kneading reactors such as kneaders (eg twin screw kneaders). Further, as the vacuum pump 2 and the condenser 3, conventional ones can be used. The flow meter 4 is not particularly limited as long as it can measure the distillate rate of the distillate, and for example, a mass flow meter such as a micro motion flow meter, a positive flow meter, or the like can be used. A preferable flow meter includes a mass type flow meter that does not require squeezing of piping and is unlikely to be blocked by foreign matter mixed in by entrainment of droplets. The distillate removal line 7
It is preferable to provide a defoamer on the upstream side of the flow meter 4 in order to prevent air bubbles from entering the flow meter 4.

The valve 9 may be any stop valve (shutoff valve) that shuts off the line as long as it can release the depressurization of the reaction system.
Alternatively, since the pressure of the reaction system is set to atmospheric pressure, a switching valve or the like that can ventilate the reactor and the outside can be used. As the valve, various valves such as a solenoid valve, a piston type, a diaphragm type, and a bellows type can be used.

Instead of the vacuum pump 2, other depressurizing means such as an ejector or an aspirator may be used. Further, the flow meter 4 may be any means capable of measuring the distillation rate of the distillate, and may be a flow meter for measuring the distillation rate of the distillate gas. In this case, the flow meter is attached to the gas extraction line 6. Further, the distillation rate of the distillate gas is determined by the pressures P1 and P2 at two arbitrary positions in the distillate gas flow path.
It can also be expressed by the pressure difference ΔP (= P1−P2).
For example, as the distillation rate of the distillate gas, the pressure of the reactor (P
1) and the pressure (P2) at the inlet of the condenser 3 (or at a predetermined location of the gas extraction line 6), ΔP (= P1)
-P2) can be adopted. The pressure difference ΔP can be measured by, for example, a differential pressure gauge. Further, the pressure difference ΔP can also be obtained by calculating the difference between the measurement values of the two pressure gauges installed at the two places.

The valve 9 does not necessarily need to be able to release the depressurization of the reaction system, and may be a pressure adjusting valve or the like capable of adjusting the degree of pressure increase according to the degree of opening / closing. Further, instead of the valve, other pressure adjusting means such as a cock may be used. The preferable pressure adjusting means includes a pressure adjusting means capable of releasing the reduced pressure of the reaction system. The valve 9 may be attached at any position where the pressure of the reaction system can be adjusted,
In addition to the above, the valve 9 may be attached to the decompression line 8, for example.

The control means 10 is not always necessary. Even without the control means 10, the operator can increase the pressure of the reaction system based on the measured value of the flow meter 4 by operating the pressure adjusting means such as the valve.

According to the above reaction control device, the measuring means for measuring the distilling rate of the distillate and the pressure adjusting means for increasing the pressure of the reaction system based on the value measured by the measuring means are provided. The pressure of the reaction system, and thus the reaction temperature, can be controlled by using the distillation rate of the distillate as an index.

A method for controlling the cellulose acetylation reaction in the cellulose acetate production process using the above reaction control device will be described below. This cellulose acetate production step is higher than the reduced pressure acetylation step of acetylating the cellulose under reduced pressure while distilling the gas phase component of the reaction system out of the reaction system in the presence of an acidic catalyst, and the reduced pressure acetylation step. And a post-acetylation step of further advancing the acetylation reaction under pressure.

In the reduced-pressure acetylation step, a predetermined amount of cellulose, an acetylating agent and a reaction solvent are charged into the acetylation reactor 1 through the raw material supply line 5, the reaction system is decompressed by the vacuum pump 2, and the valve 11 is preselected. Set to the pressure of. And
A predetermined amount of acidic catalyst is added to the acetylation reactor 1 to start the reaction.

The cellulose, acetylating agent, reaction solvent and acidic catalyst used in the reaction may be those commonly used in the production of cellulose acetate. For example, as pulp, various pulps such as sulfite dissolving pulp (eg, softwood pulp, wood pulp such as hardwood pulp),
It is possible to use, for example, cotton linter, acetic anhydride as an acetylating agent, acetic acid as a reaction solvent, and sulfuric acid as an acidic catalyst. A sulfuric acid-acetic acid solution may be used as the catalyst solution. It is preferable to use cellulose that has been pretreated and activated with acetic acid or the like. The pretreatment activation can be performed, for example, by treating the cellulose by spraying acetic acid or hydrous acetic acid, dipping in acetic acid or hydrous acetic acid, and the amount of acetic acid used is 10 to 100 parts by weight of cellulose. 1
00 parts by weight, preferably 20 to 80 parts by weight, more preferably 25 to 50 parts by weight.

The amounts of cellulose, acetylating agent, reaction solvent and acidic catalyst used can be appropriately set within the range not impairing the reaction. For example, the amount of the acetylating agent used is 200 to 400 parts by weight (for example, 220 to 350 parts by weight) with respect to 100 parts by weight of cellulose.
Parts by weight), preferably about 230 to 300 parts by weight,
The amount of the reaction solvent used is, for example, when acetic acid is used, as a total amount including acetic acid for pretreatment and acetic acid for catalyst dilution,
300-800 parts by weight (eg 350-700 parts by weight)
About 400 to 600 parts by weight, and the amount of the acidic catalyst used is about 0.4 to 10 parts by weight, preferably 0.5.
˜5 parts by weight, more preferably about 0.6 to 2 parts by weight.

The degree of vacuum of the reaction system may be any pressure as long as it can bring the reaction system to a boiling state, and can be appropriately set according to the reaction temperature. For example, the degree of vacuum is 40 to 150 Torr, preferably about 45 to 100 Torr. The addition of the acidic catalyst may be carried out at one time, but may be carried out multiple times (for example, 2 to 5
Times, preferably about twice). When the acidic catalyst is dividedly added, it is often easy to control the reaction.

After the reaction starts, the temperature in the reaction system rises due to the heat of reaction, and the reaction system becomes a boiling state. After the reaction temperature reaches the maximum value, it gradually decreases as acetic anhydride is consumed. The vapor (mixed vapor of acetic anhydride and acetic acid) having a composition according to the composition of the liquid phase component in the reactor reaches the condenser 3 through the gas extraction line 6. The condensate (distillate) condensed in the condenser 3 is drawn from the distillate draw line 7. At this time, the flow rate meter 4 measures the distillation rate of the distillate. The distillation rate of the distillate can also be obtained as the amount of distillate per unit time by measuring the amount of distillate with time.

The reaction temperature of the acetylation reaction can be selected within a range in which the acetylation reaction is not impaired and side reactions can be suppressed.
To 90 ° C, preferably about 30 to 80 ° C. Among them, the reaction temperature in the reduced pressure acetylation step is, for example, 20 to 70.
C., preferably about 30 to 65.degree.

The distillation rate of the distillate increases with an increase in the reaction temperature, and after reaching the maximum value, gradually decreases. When the acidic catalyst is dividedly added, the distillate rate of the distillate may exhibit a plurality of maximum values as the reaction progresses. For example, when the acidic catalyst is added in two divided portions, it usually shows two maximum values. After the distillation rate of the distillate reaches the maximum value, at a time point when it falls below a predetermined value (reference value) (that is, when it reaches a threshold value), the control means 10
In response to the release signal given by, the valve 9 shuts off the gas extraction line 6 and the depressurization of the reaction system is released, and the depressurized acetylation step shifts to the post-acetylation step. In the case where the reaction is automatically controlled in the case where the distillation rate has one or more local maximum values as described above, the control means provided with the differentiating circuit is provided with the differential data from the differentiating circuit, Moreover, a peak detection circuit for detecting the peak of the differential data, a counter circuit for counting the peaks from this peak detection circuit, a memory circuit in which a predetermined reference count number is set, and a count number from the counter circuit Reaches the reference count number set in the memory circuit,
A logic circuit is provided for giving differential data from the differentiating circuit to the comparing circuit and for giving a depressurizing release signal from the comparing circuit to the drive circuit of the depressurizing releasing means (valve 9) when the differential data reaches the reference value Rs. It can be configured with a control circuit. More specifically, for example, when the catalyst is added in two portions, a certain time has elapsed after the second addition of the catalyst, the outflow amount reaches a certain value, and R ≦ Rs is detected twice ( For example, a bit for releasing the decompression may be set at the time when the check is continuously performed at intervals of 15 seconds.

It should be noted that, without using the control means 10, the operator reads the measured value of the flow meter 4, and when the measured value falls below the reference value, the valve 9 is operated and the gas extraction line 6 is connected. You may block it.

The distillate rate of the distillate, which is an index for releasing the reduced pressure of the reaction system, varies depending on the peak temperature desired in the post-acetylation step, but usually 2 to 15 parts by weight when 100 parts by weight of raw material cellulose is used. / Min, preferably 4 to 12 parts by weight / minute, more preferably about 5 to 10 parts by weight / minute.

The transfer operation from the reduced pressure acetylation step to the post acetylation step may be carried out by releasing the reduced pressure of the reaction system as described above, but it may also be carried out by relaxing the degree of vacuum.
When the transfer operation is performed by releasing the reduced pressure of the reaction system, the post acetylation step may be performed in a closed system, or may be performed in an open system under atmospheric pressure. The peak temperature in the post-acetylation step can be appropriately set depending on the desired degree of polymerization of cellulose acetate and the like, but is usually 40 to 90 ° C, preferably 50 to 80 ° C.
It is a degree.

When the depressurization of the reaction system is released, the pressure in the system rises, so the reaction temperature again rises due to the reaction heat due to the acetylation reaction of unreacted cellulose, and if there is some heat radiation, after reaching the peak temperature. , The temperature drops.

As described above, since the operation of shifting from the reduced-pressure acetylation step to the post-acetylation step is performed by using the distillate rate of the distillate in the reduced-pressure acetylation step as an index, the flow meter 4 can be used to simplify the transition timing. Can be determined. Further, it is possible that the variation of the peak temperature in the post-acetylation step depending on the reaction heat amount of the residual cellulose can be made extremely small, probably because the distillation rate of the distillate has a close correspondence with the cellulose concentration in the reaction system. Therefore, it is possible to suppress a decrease in the degree of polymerization due to depolymerization of cellulose acetate that tends to occur when the reaction temperature is high, and to obtain a stable quality of cellulose acetate.

The depressurization of the reaction system is preferably performed by using the distillation rate after the distillation rate reaches the maximum value as an index. When the distillation rate has a plurality of maximum values,
It is preferable to stop the pressure reduction control of the reaction system using the distillation rate after reaching the final maximum value as an index. When the decompression control stop time is set based on the distillation rate after reaching the maximum value, after the distillation rate reaches the maximum value, the hydrolysis reaction of acetic anhydride due to the water content in the cellulose has already ended. However, almost only the acetylation reaction of cellulose is proceeding, and since the system is stabilized, because the correspondence relationship between the distillation rate and the cellulose concentration in the reaction system shows a closer relationship, It is possible to remarkably suppress the variation of the peak temperature in the post-acetylation step.

Even if the distillate rate of the distillate is measured instead of the distillate rate of the distillate and the measured value is used as an index, the operation of shifting from the reduced-pressure acetylation step to the post-acetylation step is performed. Good. Even when the distillation rate of the distillation gas is used as an index, the variation in the peak temperature in the post-acetylation step can be reduced. As described above, as the distillation rate of the distillate gas, the pressure difference ΔP (= P1 −P2) between the pressures P1 and P2 at any two points in the distillate gas flow path, for example, the pressure of the reactor (P1 ) And the pressure (P2) at the inlet of the condenser 3 can be used.

After the reaction temperature reaches the peak temperature for a predetermined time, a reaction terminator is added to the reaction mixture to stop the reaction. The reaction terminator may be any one as long as it does not adversely affect the operability and quality of the separation operation of cellulose acetate and can deactivate the acidic catalyst, and examples thereof include basic compounds [for example, alkali metal salts (potassium and sodium. Salt, etc.), alkaline earth metal salt (calcium salt, magnesium salt such as magnesium acetate, strontium salt,
Barium salt etc.)] can be used. The average degree of acetylation of the obtained cellulose acetate (cellulose triacetate) is usually 58 to 62.5%, preferably 60 to 62.5.
%, More preferably about 61 to 62.5% (particularly 6
1.5 to 62.5%), and the viscosity average degree of polymerization is usually 200 to 400 (for example, 200 to 350), preferably 250 to 350, and more preferably 270 to 350 (for example, 290 to 350). , 270 to 350 (for example, 270 to 330). When methylene chloride / methanol (91: 9, volume%) was used as a solvent, 6% by weight of cellulose acetate was used.
The solution viscosity is, for example, about 60 to 100 cps, preferably 65 to 95 cps, and particularly about 70 to 90 cps.
The obtained cellulose acetate can be purified by a conventional purification means such as precipitation and washing, after being hydrolyzed as necessary to adjust the degree of acetyl group substitution.

[0036]

In the reaction control method of the present invention, since the operation of shifting from the reduced pressure acetylation step to the post acetylation step is performed by using the distillation rate of the distillate in the reduced pressure acetylation step as an index, The reaction temperature can be controlled easily and accurately. In addition, variations in peak temperature in the post acetylation step can be easily suppressed. Further, in the reaction control device of the present invention,
Based on the measurement value of the measuring means for measuring the distillation rate of the distillate in the reduced pressure acetylation step, the pressure of the reaction system can be adjusted by the pressure adjusting means, so that the reaction temperature in the post acetylation step can be easily and accurately determined. You can control. According to the method for producing cellulose acetate of the present invention, the reaction can be controlled as described above, and cellulose acetate of stable quality can be obtained.

[0037]

EXAMPLES The present invention will be described in more detail below with reference to examples. Unless otherwise specified, "part" and "%"
Means “parts by weight” and “% by weight”, respectively. Example Cellulose acetate was produced from cellulose using the reaction control device of FIG. As a raw material for cellulose, 100 parts of sulfite-dissolved pulp was crushed into fluff, and 4
Pretreatment was activated by adding 0 part of acetic acid and treating at about 40 ° C. for 20 minutes. Acetification reactor (biaxial kneader) 1
To the above, while stirring, the pretreated activated cellulose was charged, and 270 parts of acetic anhydride and 330 parts of acetic acid were charged. The inside of the reactor 1 was depressurized by the vacuum pump 2 and the degree of vacuum was controlled to 75 Torr. Into the reactor 1, 28 parts of a 3% sulfuric acid-acetic acid solution was added as a catalyst solution to start the reaction. The reaction temperature was raised by the heat of reaction generated by the acetylation of cellulose, and after reaching about 59 ° C., which almost corresponds to the boiling point, became almost constant. About 5 minutes after the catalyst solution was added, the mixed vapor of acetic acid and acetic anhydride was condensed by the condenser 3 and started to distill. Then, about 8 minutes after the catalyst solution was added, 6 parts of the same catalyst solution as above was further added. The distillate rate of the distillate was measured by the flow meter 4, and its change with time is shown in FIG. The reaction time means the time elapsed after the first catalyst solution was added.

As shown in FIG. 2, the distillation rate of the distillate rapidly increased from about 5 minutes to about 6 minutes after the initial addition of the catalyst solution, and reached its maximum value. Diminished. Then, by the second addition of the catalyst solution, the distillation rate again increased, reached the maximum value, and then decreased. About 15 minutes after the first addition of the catalyst solution, the distillation rate of the distillate was 7.2 parts / minute with respect to 100 parts of the raw material cellulose. At this point, the valve 9 was operated, the gas extraction line 6 was shut off to make the reaction system a closed system, and the reduced pressure acetylation step was transferred to the post-acetylation step. After shutting off the gas extraction line 6, the reaction temperature rises and the peak temperature (6
7 ° C) was reached. About 1 minute after reaching the peak temperature, 2
The reaction was stopped by adding 11 parts of a 4% aqueous magnesium acetate solution. The obtained cellulose acetate (cellulose triacetate) was transferred to another reactor and hydrolyzed to obtain cellulose acetate (cellulose diacetate) having a desired degree of acetyl group substitution.

The above batch reaction operation was repeated 103 times, and the distillation rate of the distillate was changed to the raw material cellulose 1 each time.
When it reached 7.2 parts / min with respect to 00 parts, the valve 9 was closed to make the inside of the reactor a closed system. Then, when the average value of the peak temperatures and the standard deviation of the peak temperatures of the reaction in each case were obtained, the average value of the peak temperatures was 67.2.
(° C), the standard deviation of the peak temperature was 0.34 (° C).

Comparative Example In the transition operation from the reduced-pressure acetylation step to the post-acetylation step, the valve 9 was operated and the gas extraction line 6 was shut off when the amount of distillate reached 170 parts by weight. A batch reaction was carried out in the same manner as in Example except that the reaction system was a closed system. Repeating the batch reaction operation 120 times,
In each case, the valve 9 was closed when the outflow amount of the distillate reached 170 parts by weight with respect to 100 parts by weight of the raw material cellulose, and the inside of the reactor was closed. Then, when the average value of the peak temperatures of the reactions and the standard deviation of the peak temperatures in each batch reaction were determined, the average value of the peak temperatures was 68.0.
(° C.), standard deviation was 1.02 (° C.). As a result of analyzing these data, when the peak temperature of the acetylation reaction was increased by 1 ° C. with respect to the reference temperature, the viscosity of a 6% by weight solution of the obtained cellulose ester (cellulose diacetate) was decreased by 8 cps, and It was found that the viscosity of a 6 wt% solution of cellulose acetate (cellulose diacetate) increased by 8 cps when the temperature was lowered by 1 ° C. with respect to the reference temperature. The 6 wt% solution viscosity was measured by dissolving 3 g of absolutely dry cellulose acetate (cellulose diacetate) cotton in 50 ml of 95 wt% acetone aqueous solution and using an Ostwald viscous tube.

As is clear from these results, by performing the operation of shifting from the reduced pressure acetylation step to the post-acetylation step by using the distillation rate of the distillate in the reduced pressure acetylation step as an index,
Compared with the case where the outflow amount of the distillate was used as an index, the variation in the peak temperature in the post-acetylation step could be made extremely small, and a stable quality cellulose ester was obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a reaction control device of the present invention.

FIG. 2 is a view showing a change with time of a distillation rate of a distillate in Example 1.

[Explanation of symbols]

 1 ... Acetation reactor 2 ... Vacuum pump 3 ... Condenser 4 ... Flow meter 9 ... Valve 10 ... Control means

Claims (14)

[Claims] 1. A reduced pressure acetylation step of acetylating cellulose under reduced pressure while distilling gas phase components of the reaction system out of the reaction system in the presence of an acidic catalyst, and a pressure higher than this reduced pressure acetylation step. A method for producing cellulose acetate in a batch process by controlling the reaction temperature of the post-acetylation step, which comprises a post-acetylation step of further advancing the acetylation reaction in A reaction control method, wherein the transfer operation to the step is performed by using the distillation rate of the distillate in the reduced pressure acetylation step as an index. 2. The method according to claim 1, wherein when the distillation rate of the distillate under a constant pressure in the reduced pressure acetylation step becomes equal to or lower than a reference value, the reduced pressure acetylation step is transferred to the post acetylation step. Reaction control method. 3. The reduced pressure acetylation step is transferred to the post-acetylation step by releasing the reduced pressure of the reaction system using the distillation rate of the distillate under a constant pressure in the reduced pressure acetylation step as an index. 1. The reaction control method according to 1. 4. When the distillation rate of the distillate under a constant pressure in the reduced pressure acetylation step reaches a maximum value and then becomes equal to or lower than a reference value, the reduced acetylation step to the post acetylation step is performed. The reaction control method according to claim 1, wherein the transfer is performed. 5. The reaction control method according to claim 1, wherein the acidic catalyst is added in a plurality of divided portions in the reduced pressure acetylation step. 6. When the distillation rate of the distillate under a constant pressure in the reduced pressure acetylation step has a plurality of maximum values, after the distillation rate reaches the final maximum value, the reduced pressure acetylation step is performed. The reaction control method according to claim 1, wherein the reaction is transferred to the post-acetylation step. 7. The vacuum acetylation step is performed at a vacuum degree of 40 to 150 To.
The reaction control method according to claim 1, which is carried out by rr. 8. The standard value of the distillation rate is cellulose 1
The reaction control method according to claim 2, wherein when 100 parts by weight is used, the amount is 2 to 15 parts by weight / minute. 9. The reaction control method according to claim 1, wherein the post-acetylation step is performed in a closed system or a release system in which the reduced pressure is released. 10. A peak temperature of 40 to 40 in the post-acetylation step.
The reaction control method according to claim 1, wherein the reaction is performed at 90 ° C. 11. A vacuum acetylation step is vacuumized using a total of 0.4 to 10 parts by weight of an acetating agent, 200 to 400 parts by weight, a reaction solvent of 300 to 800 parts by weight, and an acidic catalyst, relative to 100 parts by weight of cellulose. 45 to 100 Torr, temperature 20 to
When the distillation rate of the distillate reaches a maximum value at 70 ° C., and thereafter, the distillation rate becomes less than or equal to a reference value in the range of 4 to 12 parts by weight per 100 parts by weight of cellulose. 2. The reaction control method according to claim 1, wherein the reduced pressure is released to shift from the reduced pressure acetylation step to the post-acetylation step. 12. A reduced pressure acetylation step of acetylating cellulose under reduced pressure while distilling gas phase components of the reaction system out of the reaction system in the presence of an acidic catalyst, and a pressure higher than this reduced pressure acetylation step. A method for producing cellulose acetate in a batch process by controlling the reaction temperature of the post-acetylation step, which comprises a post-acetylation step of further advancing the acetylation reaction in A method for producing cellulose acetate, wherein the operation of shifting to the step is performed by using the distillation rate of the distillate in the reduced pressure acetylation step as an index. 13. A reduced pressure acetylation step of acetylating cellulose under reduced pressure while distilling gas phase components of the reaction system out of the reaction system in the presence of an acidic catalyst, and a pressure higher than this reduced pressure acetylation step. In the device for controlling the reaction in the cellulose acetate production step including the acetylation step after further advancing the acetylation reaction, an acetylation reactor, a decompression means for reducing the pressure of the reaction system, and a reaction system Condensing means for condensing the distillate to be distilled, measuring means for measuring the distilling rate of the distillate in the reduced pressure acetylation step, and based on the measurement value by the measuring means, after the reduced pressure acetylation step A reaction control device having a pressure adjusting means for relatively increasing the pressure in the acetylation step. 14. The measured value R of the distillation rate measured by the measuring means is compared with a reference value Rs, and when the comparison result is R ≦ Rs, a release signal for releasing the reduced pressure in the reduced pressure acetylation step is applied. 14. A control means provided to the adjusting means.
The reaction control device described.