JPS6344761B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for producing hydroxyalkylalkylcellulose. Hydroxyalkylalkylcelluloses are generally hydroxyethylmethylcellulose (HEMC), hydroxyethylethylcellulose (HEEC), hydroxypropylmethylcellulose (HPMC), hydroxypropylethylcellulose (HPEC), hydroxyethylhydroxypropylmethylcellulose (HEHPMC), hydroxyethylhydroxypropylethylcellulose (HEHPEC) etc. are known. These hydroxyalkylalkylcelluloses are usually produced by reacting alkali cellulose with the corresponding alkylene oxide and alkyl halide. Raw material alkali cellulose is generally prepared by immersing sheet pulp in an aqueous alkali hydroxide solution and then squeezing it, or by spraying an aqueous alkali hydroxide solution onto powdered pulp while stirring.The alkali hydroxide in this alkali cellulose is It acts as a catalyst for alkylene oxide reactions and reacts with alkyl halides in equivalent amounts. Therefore, the etherification efficiency of alkylene oxide and alkyl halide to alkali cellulose is affected by the amount of alkali hydroxide and water in the alkali cellulose, and the molar ratio of alkali hydroxide/cellulose and water/cellulose is It is known that the higher the value, the lower the value. However, in order to obtain the target degree of alkyl group substitution, the alkali hydroxide/cellulose must have a corresponding molar ratio as alkali cellulose because the alkyl halide and the alkali hydroxide are equimolar reactions. be. Knowing this fact, in order to improve the etherification efficiency of alkylene oxide and alkyl halide, it is presumed that the method of reacting alkylene oxide and alkyl halide with alkali cellulose having a small water/cellulose molar ratio is advantageous. be done. Specific methods for preparing alkali cellulose with a small amount of water include a method using a very highly concentrated aqueous alkali hydroxide solution, a method using a combination of an aqueous alkali hydroxide solution and a substantially anhydrous solid alkali hydroxide, and a method that uses a substantially anhydrous solid alkali hydroxide. Possible methods include dehydrating alkali cellulose. However, in the methods of and, the alkali cellulose prepared is heterogeneous, and as a result, the etherification reaction does not proceed uniformly, which has a serious adverse effect on the physical properties of the resulting product. In addition, in the method of
To improve the heterogeneity of alkali cellulose,
There is a method (Japanese Unexamined Patent Publication No. 145901/1983) in which pre-pulverized cellulose is preswollen with an organic solvent, but this method also only slightly improves heterogeneity, and furthermore, alcohols are used as the organic solvent. In this case, since the alkyl halide is consumed in a side reaction with the alcohol used, it is necessary to remove the alcohol from the reaction system prior to the etherification reaction, which is not an advantageous method. In the case of the above method, the alkali cellulose is treated by heating and reducing pressure, but in this case as well, the etherification reaction becomes non-uniform as the water in the alkali cellulose decreases. As described above, it is difficult to proceed with the reaction under alkaline cellulose conditions with a small water/cellulose molar ratio at an advantageous etherification efficiency without impairing the physical properties of the resulting product. The reaction method of alkali cellulose with alkylene oxide and alkyl halide is as follows:
(b) A mixture of the required amount of alkylene oxide and the required amount of alkyl halide corresponding to the target MS degree of substitution (MS) of the hydroxyalkyl group and DS degree of substitution (DS) of the alkyl group is reacted with alkali cellulose. (b) A method of reacting a required amount of alkylene oxide and an alkyl halide in the presence of a large excess of an alkyl halide or a non-reactive organic process inhibitor such as dimethyl ether; (c) A method of reacting a required amount of an alkylene oxide and an alkyl halide. A method is known in which a part of the alkyl is reacted with alkali cellulose, and then a required amount of alkylene oxide and the remaining alkyl halide are reacted. Efficiency is (a) and
It was found that there was no difference in case (b), and the rate was actually lower in case (c). That is, in these reaction methods, no higher etherification efficiency of alkylene oxide can be obtained. The present inventors completed the present invention as a result of intensive research in view of such technical problems, and this is a method for producing hydroxyalkylcellulose by reacting alkylene oxide and alkyl halide with alkali cellulose. In alkali cellulose, the content of alkali hydroxide is 2.0 or more in molar ratio of alkali hydroxide to anhydroglucose units, and an amount of alkyl halide corresponding to 1/2 or less of the content of alkali hydroxide in molar ratio to cellulose. and an amount of alkylene oxide necessary for the reaction to perform the first stage reaction, and then add the remaining amount of alkyl halide to conduct the second stage reaction. The present invention relates to a method for producing hydroxyalkylalkylcellulose in which the degree of DS substitution of alkyl groups per glucose unit is greater than 1.3. According to the method of this invention, compared to the conventional simultaneous one-stage etherification reaction in which the entire amount of alkylene oxide and alkyl halide is reacted with alkali cellulose at the same time, the mole of alkali hydroxide/cellulose for alkali cellulose, which is the main raw material, is The effect is that the etherification efficiency of alkylene oxide can be significantly improved without changing the water/cellulose molar ratio. Furthermore, it was confirmed that the method of the present invention significantly improves the viscosity stability against cellulases and the like when the produced hydroxyalkylalkylcellulose is made into an aqueous solution. The present invention will be explained in detail below. The alkali cellulose used in the present invention may be obtained by soaking pulp in an aqueous alkali hydroxide solution and then pressing it, or by mixing a powdered pulp with an aqueous alkali hydroxide solution. Alkaline cellulose prepared to have a small water/cellulose molar ratio can also be used. However, in order to have an effect sufficient to compensate for the negative effect on productivity caused by dividing the reaction into two stages in the present invention, the ether efficiency of alkylene oxide must be 1.1 times or more compared to that in the reaction by mixed addition. This requires that the content of alkali hydroxide in the starting material alkali cellulose be 2.0 in molar ratio of alkali hydroxide to anhydroglucose units.
By adopting the above method, it is necessary to make the hydroxyalkylcellulose finally obtained so that the degree of DS substitution of the alkyl group per anhydroglucose unit is greater than 1.3. In the first-stage etherification reaction, the alkylene oxide/cellulose molar ratio can be used within any range of equivalents or more required for the reaction. Also this one
The reaction in the second stage is preferably carried out at a temperature of 30°C to 70°C for a period of 0.5 to 5 hours. At temperatures below 30°C, the reaction rate of alkylene oxide is extremely slow and it takes a long time to complete the reaction, which is not reasonable.
Furthermore, at temperatures of 70° C. or higher, the reaction rate of alkylene oxide is extremely high, making it difficult to proceed with the reaction uniformly and making it difficult to remove the heat of reaction. The reaction time depends on the amount of alkylene oxide used, but if it is less than 0.5 hours, the reaction of alkylene oxide may not be completed, and if it is more than 5 hours, it is not industrially reasonable. During the first stage alkylene oxide reaction, it is possible to coexist a non-reactive organic process inhibitor in order to remove the reaction heat or to avoid the explosive range of the alkylene oxide. It is preferable to use the non-reactive organic process inhibitor in an amount of 20 times or less based on the weight of cellulose. If it is used in excess, the reaction rate of alkylene oxide will decrease and it will take a long time to complete the reaction, and it will also lead to a decrease in industrial productivity, so it is not advantageous to use it in excess. . When a non-reactive organic process inhibitor is used, the reaction temperature can be higher than when a non-reactive organic process inhibitor is used. Note that dimethyl ether or lower aliphatic alcohol is suitable as the non-reactive organic process inhibitor. When a lower aliphatic alcohol is used, it must be removed from the reaction system prior to the second-stage alkyl halide reaction. This is because lower aliphatic alcohols react with alkyl halides to produce side reaction products, which adversely affect the efficiency of etherification of alkyl halides. Although the first stage reaction has been described above on the assumption that no alkyl halide is present, an alkyl halide may be present in this reaction.
However, in that case, the amount of alkyl halide is an amount equivalent to 50% or less of the total amount of alkyl halide consumed in the reaction, that is, 1/2 or less of the molar ratio of alkali hydroxide/cellulose in the alkali cellulose (especially desirable). (1/3 or less) in an alkyl halide/cellulose molar ratio. This is because if the amount of coexisting alkyl halide becomes too large, the object of the present invention, which is to improve the efficiency of etherification of alkylene oxide, cannot be achieved. Furthermore, this 1
When an alkyl halide coexists in the etherification reaction in the second step, the alkyl halide acts as a heat transfer medium, resulting in the effect that reaction control becomes easier. The reaction of the alkyl halide in the second stage is carried out by charging the alkyl halide all at once or continuously over a period of 1 to 6 hours under internal temperature conditions of 10°C to 80°C after the completion of the first stage reaction. During the reaction of alkyl halides, it is possible to coexist a non-reactive organic process inhibitor to remove the reaction heat, or it is also possible to use a large excess of the alkyl halide as an etherification agent. be. The non-reactive organic process inhibitor or excess alkyl halide is preferably used in an amount of 20 times or less based on the weight of cellulose. It is not advantageous to use too much because using more than that will lead to a decrease in productivity. The alkylene oxide and alkyl halide used in the reaction are not limited to one type each, and two or more types may be used in combination. After the second stage reaction is completed, the desired hydroxyalkylalkylcellulose is obtained by purification using a known method. The method of the present invention is carried out under the conditions described above, and the improvement in the etherification efficiency of alkylene oxide by this method is improved as the molar ratio of alkali hydroxide/cellulose in the alkali cellulose increases. The more alkyl halides are present, the more noticeable it is, and furthermore,
In the case of alkylene oxide, which has a lower reactivity with alkali cellulose, specifically, in the case of propylene oxide, which has a lower reactivity, than in the case of ethylene oxide, which has a high reactivity,
The effect is remarkable. The attached drawing shows the change in etherification efficiency of alkylene oxide as the molar ratio of alkali hydroxide/cellulose in alkali cellulose changes in the case of hydroxypropyl methylcellulose, using the case where the molar ratio of propylene oxide/cellulose is 1.40 as an example. In particular, a case using a two-stage reaction according to the present invention and a case using a known simultaneous one-stage reaction for comparison are shown. However, in this case, a 50% aqueous sodium hydroxide solution was used to prepare the alkali cellulose. Curve, and 〓 ... Method of the present invention Curve, ... Known simultaneous one-step reaction As can be seen from the drawing, for example, when the molar ratio of sodium hydroxide/cellulose is 5.0, in the case of the known simultaneous one-step reaction hydroxypropyl group in
MS=0.23, etherification efficiency 16.0%, whereas in the case of the method of the present invention, MS=0.33, etherification efficiency 23.5%, and the mole of propylene oxide/cellulose to make the hydroxypropyl group MS 0.23. The ratio may be 0.88, and the etherification efficiency at that time will be 26.0%. In general, cellulose derivatives are subject to biological degradation, especially the enzyme cellulase (i.e. β-1,4-
glucan 4-glucanohydrolase) between the unsubstituted anhydroglucose units.
The bond is hydrolytically cleaved. When an aqueous solution thickened by a water-soluble cellulose derivative undergoes hydrolytic cleavage, its viscosity decreases and its value as a thickener is lost. The rate of this viscosity reduction is derived from the enzyme concentration and the number and distribution of unsubstituted anhydroglucose units present in the cellulose derivative. In other words, the lower the content of unsubstituted anhydroglucose units, the higher the viscosity stability. The hydroxyalkylalkylcellulose produced by the method of the present invention not only has the advantage of improved etherification efficiency of alkylene oxide as described above, but also surprisingly has resistance to biodegradation by cellulases, that is, stable viscosity. It was found that the performance improved. This is because by reacting alkylene oxide in the presence of many activated hydroxyl groups of anhydroglucose in alkali cellulose, substitution of hydroxyalkyl groups is performed relatively uniformly, and by introducing hydroxyalkyl groups. This is thought to be due to the fact that by reacting an alkyl halide while the structure of cellulose is further disrupted, the introduction of alkyl groups is performed more uniformly, resulting in a decrease in the content of unsubstituted anhydroglucose units. It will be done. Next, a specific example will be given. Example 1 [Manufacture of hydroxypropyl methyl cellulose (HPMC)] Sheet cellulose was immersed in a 50% aqueous sodium hydroxide solution, compressed and cut to obtain NaOH/cellulose (molar ratio: MR) = 5.00, H ₂ O/cellulose ( An alkali cellulose with MR)=11.1 was obtained. This alkali cellulose equivalent to 4.0 kg of cellulose weight was charged into a pressurized reactor with an internal volume of 80 kg, and sufficient N ₂
After substitution, propylene oxide (PO) 2.00Kg
Charge [PO/cellulose (MR) = 1.40],
The reaction was carried out for 3 hours while stirring at a reaction temperature of 30°C to 60°C. Then, once cooled to 25℃, methyl chloride
6.60Kg [CH ₃ Cl/cellulose (MR) = 5.29] was charged and reacted at 35°C to 80°C for 5 hours. After washing and purifying with hot water, the degree of substitution of the obtained hydroxypropyl methylcellulose was hydroxypropyl group MS = 0.33, methoxy group DS = 2.00, and the etherification efficiency was 23.5% for propylene oxide and 40.0% for methyl chloride. Ta. Note that in the above, MR indicates a molar ratio. Same below. Example 2 The amount of propylene oxide charged was 1.26Kg [P.
O./Cellulose (MR) = 0.88], and all other operations were performed in the same manner as in the previous example. The degree of substitution of the obtained hydroxypropyl methylcellulose is hydroxypropyl group MS = 0.23, methoxy group DS = 1.99
and the etherification efficiency is propylene oxide
26.0% and methyl chloride 39.8%. Comparative Example 1 The same alkali cellulose as in Example 1, equivalent to cellulose weight 4.0 kg, was charged into a pressurized reactor with an internal volume of 80, and after sufficient _N2 substitution, 2.00 kg of propylene oxide and 6.60 kg of methyl chloride were charged.
The reaction was carried out at 30°C to 80°C for 7 hours. The degree of substitution of hydroxypropyl methylcellulose obtained after washing and purification with hot water is hydroxypropyl group MS = 0.23,
Methoxy group DS = 1.99, etherification efficiency is 16.0% for propylene oxide, methyl chloride
It was 39.8%. As a result, the etherification efficiency of propylene oxide in Example 2 was 1.63 times that of Comparative Example 1. Example 3 [Manufacture of HPMC] 10.0 kg of powdered cellulose was charged into an internally stirred pressurized reactor with an internal volume of 130 mm, and after sufficient _nitrogen substitution, 12.5 kg of a 50% aqueous sodium hydroxide solution was added dropwise while stirring. NaOH/cellulose (MR)
= 2.00 and H ₂ O/cellulose (MR) = 4.4, an alkali cellulose was prepared. Next, propylene oxide 1.50Kg [PO/cellulose (MR) = 0.42]
was charged and reacted at 30°C to 60°C for 3 hours. Then, 6.90Kg of methyl chloride at 50℃~80℃
[CH ₃ Cl/cellulose (MR) = 2.15] was continuously charged over 4 hours, and the reaction was completed 5 hours after the start of methyl chloride charging. After washing and purifying with hot water, the degree of substitution of the obtained hydroxypropyl methylcellulose is hydroxypropyl group MS =
0.20, methoxy group DS = 1.34, and the etherification efficiency was 48.3% for propylene oxide and 67.0% for methyl chloride. Comparative Example 2 Alkaline cellulose was prepared under the same conditions as in Example 3, and then 1.50 kg of propylene oxide and 6.90 kg of methyl chloride were charged and reacted at 30°C to 80°C for 7 hours. The degree of substitution of the obtained hydroxypropyl methyl cellulose is determined by the hydroxypropyl group MS
= 0.18, methoxy group DS = 1.33, and the etherification efficiency was 44.0% for propylene oxide and 66.5% for methyl chloride. As a result, the etherification efficiency of propylene oxide in Example 3 was lower than that in Comparative Example 3.
It was 1.10 times the value of . Example 4 [Manufacture of HEMC] Alkaline cellulose was prepared under the same conditions as in Example 1, and 8.00 kg of dimethyl ether (DME) was added.
[DME/cellulose (weight ratio: WR) = 2.00] was charged, and ethylene oxide (EO) 1.20Kg [E.
O./Cellulose (MR) = 1.10] and 30℃
The reaction was carried out at ~70°C for 3 hours. Dimethyl ether was used to remove the heat of reaction and to avoid the explosive range of ethylene oxide. Then, cool it to 40℃ and add methyl chloride.
8.73Kg [CH ₃ Cl/cellulose (MR) = 7.00] was charged and reacted at 50°C to 80°C for 5 hours. The degree of substitution of the obtained hydroxyethyl methyl cellulose is hydroxyethyl group MS = 0.46, methoxy group DS =
2.02, and the etherification efficiency was 42.0% for ethylene oxide and 40.4% for methyl chloride. Comparative Example 3 Alkaline cellulose was charged under the same conditions as in Example 1, 6.60 kg of methyl chloride and 1.20 kg of ethylene oxide were charged, and the mixture was reacted at 30°C to 80°C for 6 hours. The degree of substitution of the obtained hydroxyethyl methyl cellulose is hydroxyethyl group MS = 0.39,
Methoxy group DS = 2.00, etherification efficiency is 35.0% for ethylene oxide, methyl chloride
It was 40.0%. Viscosity Stability The following viscosity stability test was conducted on each of the hydroxypropyl methylcelluloses (HPMC) obtained in Example 1, Example 2, and Comparative Example 1, and the results were as shown in Table 1. Viscosity stability test: 2% of sample (HPMC)
Cellulase "A3" (manufactured by Amano Pharmaceutical) was added to the aqueous solution at a pH of 7.5 and a temperature of 20°C at 20 ppm based on the solution, and the viscosity was measured after 20 minutes (viscosity after decomposition). ”
The viscosity before addition (viscosity before decomposition) was compared.
However, the viscosity was measured using a B-type viscometer in all cases.

[Table] Viscosity after decomposition
(Note) Viscosity retention rate:

Claims (1)

[Claims] 1. A method for producing hydroxyalkyl cellulose by reacting alkylene oxide and alkyl halide with alkali cellulose, comprising:
In alkali cellulose, the content of alkali hydroxide is 2.0 or more in molar ratio of alkali hydroxide to anhydroglucose units, and an amount of alkyl halide corresponding to 1/2 or less of the content of alkali hydroxide in molar ratio to cellulose. and an amount of alkylene oxide necessary for the reaction to perform the first stage reaction, and then add the remaining amount of alkyl halide to conduct the second stage reaction. A method for producing hydroxyalkylcellulose, wherein the degree of DS substitution of alkyl groups per glucose unit is greater than 1.3. 2. A hydroxyl compound having a DS degree of substitution of an alkyl group of more than 1.3 per anhydroglucose unit according to claim 1, wherein the first stage reaction is carried out in the absence of an alkyl halide. A method for producing alkyl cellulose. 3. The alkylene oxide is either propylene oxide or ethylene oxide, or both, and the degree of DS substitution of the alkyl group per anhydroglucose unit according to claim 1 is greater than 1.3. Method for producing hydroxyalkyl cellulose. 4. The degree of DS substitution of the alkyl group per anhydroglucose unit according to claim 1, characterized in that the halogenated alkyl is either chloromethyl or chloroethyl, or both.
1.3 A method for producing hydroxyalkylcellulose greater than 3.