JP2001302701A - Preparation method of alkali cellulose and cellulose ether - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation method of an alkali cellulose with very uniform distribution of the alkali and a high bulk density and to charge a large quantity of an alkali cellulose in a smaller reactor in the etherification step by increasing the bulk density of the alkali cellulose and to prepare a cellulose ether with excellent solubility. SOLUTION: A powder pulp obtained by grinding pulp is continuously supplied by a biaxial kneader, mixed with an aqueous alkali solution which is supplied through the same or another inlet simultaneously and continuously, mixed and consolidated in the kneader and discharged continuously through the outlast. The supply of the powder pulp is controlled by a metering feeder to supply a predetermined flow. The supply of the aqueous alkali solution is controlled by a metering pump such that the solution is continuously supplied to give a predetermined alkali concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing alkali cellulose and cellulose ether.

[0002]

2. Description of the Related Art As a method for producing cellulose ether, it has been known that an alkali aqueous solution is prepared by bringing an aqueous alkali solution into contact with highly purified pulp, and an etherification reaction is carried out using an etherifying agent. The final cellulose ether obtained becomes water-soluble by appropriately controlling the degree of substitution.However, there is a water-insoluble portion in it, which lowers the light transmittance of the aqueous solution or becomes a foreign substance, thereby deteriorating its commercial value. May be damaged. This undissolved part
This is caused by the presence of a low-substitution portion having no substituent enough to dissolve in water, and is one of the causes of non-uniform alkali distribution in alkali cellulose. The function of the alkali cellulose is to swell the cellulose and change the crystal structure in the pulp to aid the penetration of the etherifying agent, to catalyze the etherification reaction of the alkylene oxide, to be a reactant for the alkyl halide, etc. Is mentioned. Therefore, the portion where the pulp does not come into contact with the alkaline aqueous solution does not participate in the reaction and becomes undissolved, and the uniformity of the alkali cellulose directly leads to the amount of undissolved portion.

Here, as a method for producing alkali cellulose, pulp is immersed in an aqueous solution of sodium hydroxide to absorb the alkali sufficiently, and then pressurized to a predetermined alkali amount to remove excess alkali. There is. However, the operation is complicated and it is difficult to control the alkali amount to a predetermined value, which is disadvantageous in terms of productivity.

On the other hand, a method in which a predetermined amount of alkali is added to powder obtained by pulverizing pulp and mechanically mixed is easily controlled at a predetermined alkali concentration, and the process can be performed in one step, so that productivity is high. As such a mechanical mixing method, for example, a batch method in which powder pulp and an aqueous sodium hydroxide solution are charged into a twin-screw kneader may be used. Normally, in this kneader type mixer, the larger the mixing volume, the smaller the contact area ratio between the stirring blade and the mixture, the lower the mixing property and the longer it takes to be relatively uniform, and the equipment itself is extremely difficult. The scale becomes large.

In addition, in a mixer having a pro-share type stirring blade and a chopper, if the equipment is large like the above-mentioned kneader, it becomes difficult to apply the share given by the chopper, which causes micro-uniformity and requires large equipment. It is a heavy burden in terms of space and cost. As for this pro-share mixer type, there is a continuous type in addition to the batch type, but the flow between the pulp inlet and the alkali cellulose outlet cannot be completely prevented from flowing back, and uneven portions are discharged. Sometimes.

[0006] In such mechanical mixing, it is difficult to mix a relatively small amount of alkali into the fluffy powdered pulp in a true and uniform manner. Is greater than the immersion method described above.

In order to improve the uniformity of the alkali, it has been considered to increase the volume of the aqueous solution by using a dilute alkaline aqueous solution. However, in the subsequent etherification reaction, water in the system is converted into an etherifying agent. And an undesirable side reaction is caused, and the main reaction efficiency for reacting with cellulose is remarkably reduced. Although it is not impossible to remove water before the reaction, the vapor pressure of the aqueous alkali solution is extremely low as compared with water, which is impractical.

A method of increasing the volume of an alkaline aqueous solution-alcohol mixture using a lower primary alcohol that is compatible with an alkaline aqueous solution is also conceivable. Japanese Patent No. 1325759
However, this lower primary alcohol also causes a side reaction with the etherifying agent, and is premised on removal before the etherification reaction.

Even with these mixers or a vertical mixed phase with a simple stirring blade, a method for improving the uniformity of alkali cellulose by using a large amount of an inert dispersant such as dimethoxyethane or dimethyl ether has been studied. (Japanese Patent Application Laid-Open Nos. 56-16501, 58-10
3501), after the preparation of alkali cellulose, before or after the start of the etherification reaction, it is necessary to remove this dispersant during purification, which complicates the process and increases the cost.

[0010] In addition to the non-uniformity of the alkali, the alkali celluloses produced by these conventional techniques have serious physical defects that they are very fuzzy, fluffy and light in bulk density. This is because the pulp fibers can move relatively freely when the powder pulp and the aqueous alkaline solution are mixed, so that the alkali cellulose after preparation maintains the shape of the pulp fibers as a raw material. When the bulk density per unit weight of the alkali cellulose is low, the amount of the alkali cellulose to be charged in the etherification reaction in the pressure cooker subsequent to the preparation of the alkali cellulose is limited, and the productivity cannot be increased.

[0011]

SUMMARY OF THE INVENTION The present invention provides a process for producing alkali cellulose having a very uniform distribution of alkali in the alkali cellulose and a high bulk density. Also,
By increasing the bulk density of the alkali cellulose, it is possible to produce a large amount of alkali cellulose and a cellulose ether having excellent solubility in a smaller reaction vessel in the etherification reaction step.

[0012]

According to the present invention, powdered pulp obtained by pulverizing pulp is supplied to a twin-screw kneader, and mixed with an alkaline aqueous solution supplied simultaneously from the same supply port or another position. After being mixed and consolidated inside, it is continuously discharged from the discharge port. The supply amount of the powder pulp is controlled by a fixed amount feeder and supplied at a desired flow rate. The supply amount of the alkaline aqueous solution is controlled by a metering pump and supplied so as to have a predetermined alkaline concentration. The supply of the alkaline aqueous solution may be the same as the supply port of the powdered pulp, but it is preferable that the alkali aqueous solution be fed from the supply port immediately after the pulp supply port so that the supply port forms a block and does not block the supply port. Alternatively, the pulp and the required amount of the aqueous alkali solution may be premixed, and the mixture may be continuously supplied to and discharged from the twin-screw kneader. In the premixing, the pulp and the aqueous alkali solution do not necessarily need to be completely and uniformly mixed. For this purpose, for example, a pulp and an alkaline aqueous solution can be continuously supplied to the mixer using the above-mentioned continuous proshare mixer to prepare a premix. Even in this method, since the premix passes through the twin-screw kneader, very uniform and high-density alkali cellulose can be obtained as a result.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The twin-screw kneader used in the present invention preferably comprises two shafts each composed of a screw and a paddle, and two hollow cylinders having a slightly larger radius of rotation than the shafts. Trough (barrel,
Or outer wall). As the paddle, it is preferable to use a combination of a flat paddle for kneading and a helical paddle for kneading and feeding. Screws are used for feeding.

The pulp continuously supplied from the inlet is:
It comes in contact with a continuously supplied alkaline aqueous solution that is fed by a screw. The mixture is mixed and consolidated with the paddles and troughs, and the paddles and paddles providing shear, to achieve uniform dispersion and infiltration of the alkali into the pulp, and is finally discharged from the outlet at the end of the shaft. The mixture during kneading is constantly pushed from behind by another mixture in the narrow space and moves, so that uneven alkaline cellulose in the middle does not mix into the final discharge. When the supply amount is constant, the residence time of the kneader is L, which is the ratio of the shaft rotation speed and the trough length (L) to the paddle diameter (D).
/ D. In addition, the kneading state is the L / D
It is determined by the combination of the internal organ paddle. L / D of about 5 to 13 is usually used.
Too high is not preferable because excessive kneading causes a decrease in the degree of polymerization. Water can be passed through the main body by a jacket, and the internal temperature can be controlled by controlling the heat generated by mixing the alkali and cellulose. In addition, in the presence of oxygen, vacuum or nitrogen replacement can be performed to prevent a decrease in the degree of polymerization of the alkali cellulose. At the same time, when the purpose is to control the degree of polymerization in the presence of oxygen, it has a structure capable of adjusting the amount of oxygen.

Commercially available examples of the twin-screw continuous kneader include:
KRC Kneader manufactured by Kurimoto Tekkosho Co., Ltd. may be mentioned. In addition,
The kneading apparatus of the present invention is not limited to what is generally referred to as a kneading apparatus, but may be a mixer, a kneading extruder, or the like as long as the object, action, and effect of the present invention can be substantially achieved. It is natural to include.

The alkaline aqueous solution used is preferably selected from aqueous solutions of sodium hydroxide or potassium hydroxide, but sodium hydroxide is particularly preferred for economic reasons, and its concentration is usually 30 to 60% by weight. ,
Consider the subsequent etherification reaction and handling of the aqueous solution.
It is desirable to be around weight%.

In the present invention, the uniformity of alkali can be basically improved without using a lower primary alcohol or other inert solvent, but the use in a system using these solvents in combination is not possible. Of course, the combination system can also be applied to improve alkali uniformity and bulk density of alkali cellulose. Further, since the present invention is a continuous manufacturing method, the apparatus main body can be made smaller than in a batch type, which is advantageous in terms of space.

A cellulose ether can be produced by a known method using the alkali cellulose obtained by the above production method as a raw material. As a reaction method, a batch method and a continuous method are considered. Since the method for producing alkali cellulose of the present invention is a continuous method, a continuous reaction method is preferable, but there is no problem with a batch method. In the case of a batch type, the alkali cellulose discharged from the twin-screw kneader is stored in a buffer tank, or may be directly charged into an etherification reaction vessel, but is stored in a buffer tank to shorten the occupation time of the etherification reaction vessel. Later, the productivity is higher when the reaction vessel is charged in a short time. The buffer tank is desirably a vacuum or an oxygen-free atmosphere by nitrogen substitution in order to suppress a decrease in the degree of polymerization.

Cellulose ethers obtained using alkali cellulose as a starting material include methyl cellulose,
Ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HP
C), and further, hydroxyethylmethylcellulose (HEMC), hydroxypropylmethylcellulose (HPMC), and carboxymethylcellulose (CMC), which are mixed cellulose ethers. Examples of the etherifying agent include alkyl halides such as methyl chloride and ethyl chloride, alkylene oxides such as ethylene oxide and propylene oxide, and monochloroacetic acid.

[0020]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. (Example 1) Powdered pulp (water: 3.0% by weight) obtained by pulverizing high-purity dissolved pulp derived from wood was twin-screw kneader (KRC kneader S1, type, paddle diameter 25 mmφ, trough length 255 mm, L /D=10.2, internal volume 0.12 liter, rotation speed 100rpm, manufactured by Kurimoto Iron Works)
min, and at the same time, a 49% by weight aqueous sodium hydroxide solution was injected from an inlet provided near the pulp supply port.
A fixed amount was supplied at 7 g / min. Cold water at 20 ° C. was circulated through the jacket. The system was set to a nitrogen atmosphere in order to suppress a decrease in the degree of polymerization. Of the alkali cellulose obtained by continuous operation for about 30 minutes, 585.0 g was charged into a 5-liter pressure vessel with a pro-share internal stirring,
After reducing the pressure to 97 kPa, the pressure was returned to the atmospheric pressure with nitrogen, and the pressure was reduced again to -97 kPa. 52.5 g of propylene oxide and subsequently 212.6 g of methyl chloride were charged and reacted for 2 hours so that the internal temperature became 60 ° C., and then the temperature was raised and maintained at 90 ° C. for 30 minutes to complete the etherification reaction. The reaction was washed with hot water and dried, and the resulting HP
Table 1 shows the physical properties of MC. Alkaline cellulose not used for the reaction was poured into a 100 cc cup without giving any vibration, and its bulk density was measured to be 0.33 g.
/ Ml. In addition, the bulk density including the following Examples and Comparative Examples was measured with a powder tester manufactured by Hosokawa Micron Corporation.

(Comparative Example 1) The same powdered pulp 3 as in Example 1
00g was charged into a 5-liter pro-share mixer with chopper, main stirring 200rpm, chopper 1500
rpm, jacket 20 ° C, nitrogen atmosphere 381.3
g of 49% by weight aqueous sodium hydroxide solution was supplied for 10 minutes, and the mixture was further stirred for 10 minutes and then discharged. HPMC was obtained in the same manner as in Example 1 by using 585.0 g of the alkali cellulose. The properties are shown in Table 1. The bulk density of the alkali cellulose was measured in the same manner as in Example 1, and the result was 0.15 g / ml.

Example 2 Water content of powdered pulp obtained from wood pulp having a lower degree of polymerization than that used in Example 1
0% by weight) to produce alkali cellulose in the same manner as in Example 1. However, the supply amount of the 49% by weight aqueous sodium hydroxide solution was 20.5 g / min. Of the alkali cellulose obtained by continuous operation for about 30 minutes, 78
6.8 g was charged into a 5-liter pressure vessel with a pro-share internal stirring, and the pressure was reduced to -97 kPa, then returned to atmospheric pressure with nitrogen, and further reduced to -97 kPa. 343.7 g of methyl chloride was charged and reacted for 2 hours so that the internal temperature became 60 ° C., and then the temperature was raised and maintained at 90 ° C. for 30 minutes to complete the etherification reaction. The reaction product was washed with hot water and dried, and the physical properties of the obtained MC are shown in Table 1.
The bulk density of the alkali cellulose was measured in the same manner as in Example 1, and the result was 0.35 g / ml.

(Comparative Example 2) Powdered pulp 3 same as in Example 2
00g was charged into a 5-liter pro-share mixer with chopper, main stirring 200rpm, chopper 1500
rpm, jacket 20 ° C, 615.9 under nitrogen atmosphere
g of a 49% by weight aqueous sodium hydroxide solution was supplied for 10 minutes, and the mixture was further stirred for 10 minutes and then discharged. Using 786.8 g of the alkali cellulose, MC was obtained in the same manner as in Example 2. The properties are shown in Table 1. The bulk density of the alkali cellulose was measured in the same manner as in Example 1, and the result was 0.17 g / ml.

[0024]

[Table 1]

In Table 1, "2% by weight viscosity" means that a sample is dispersed in hot water which is a 2% by weight aqueous solution for 30 minutes, then stirred and dissolved in a 5 ° C bath for 1 hour, and the temperature is adjusted to 20 ° C. It was measured with a Brookfield-type rotational viscometer. “Methoxyl group substitution amount” or “hydroxypropoxyl group substitution amount” was measured based on the Japanese Pharmacopoeia. The “transparency at 5 ° C. dissolved” is 20% of the aqueous solution dissolved at 2% by weight and 5 ° C.
It is the transmittance | permeability of white light in ° C, and made 100% of pure water. “30 ° C. dissolved light transmittance” is the transmittance of white light at 30 ° C. of an aqueous solution dissolved at 2% by weight and 30 ° C., and 100% pure water. “Undissolved at 5 ° C.” means that 20 g of a sample was dissolved at a concentration of 0.5% by weight at 5 ° C.
Filter with a 00 mesh (38 μm opening) filter,
The amount of the filter residue was measured, and the weight% in 20 g of the sample was determined.
Expressed as

[0026]

The alkali cellulose obtained by the production method of the present invention has a very uniform distribution of alkali in the alkali cellulose, and the alkali cellulose is used to produce cellulose ethers such as methyl cellulose (MC). In this case, a material having extremely excellent solubility can be obtained. In addition, the alkali cellulose obtained by the production method of the present invention has a high bulk density, and in a subsequent etherification reaction step, a large amount of alkali cellulose can be charged into a smaller reaction vessel, and the productivity is high.

Claims (3)

[Claims] 1. A method for continuously producing alkali cellulose by supplying pulp and an aqueous alkali solution to a twin-screw kneader. 2. The supply of the pulp and the aqueous alkali solution,
The method for producing alkali cellulose according to claim 1, which is a supply of a mixture of pulp and an aqueous alkali cellulose solution. 3. A method for producing cellulose ether, comprising reacting an alkali cellulose obtained by the method according to claim 1 with an etherifying agent.