JPS62179503A - Production of chitosan - Google Patents

Abstract

PURPOSE:To produce a high-MW chitosan having a low content of a component insoluble in an aqueous acetic acid, by heating and deacetylating an alkali- impreganted chitosan obtained by soaking chitin in a concentrated aqueous alkali solution and removing excess aqueous alkali solution. CONSTITUTION:1pt.wt. chitin of a water content <=70wt%, obtained by treating the shells of crabs, lobsters, etc. with dilute hydrochloric, etc. to remove Ca from them, treating the product with a dilute alkali solution to remove proteins and other impurities and water-washing and drying it, is soaked in 5-20pts.wt. concentrated aqueous alkali (e.g., a NaOH solution of a concentration of 35-60wt%) at 20-50 deg.C for 5-60min, and the mixture is separated into an alkali-impreganted chitin containing 0.5-2.5pts.wt. (in terms of solid matter) alkali per pt. wt. chitin and excess aqueous alkali solution. this alkali- impregnated chitin is deacetylated by heating at 45-110 deg.C for 1-10hr, and the crude chitosan is washed with water, neutralized and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an improvement in a method for producing chitosan by deacetylating chitin contained in the shells of crabs, shrimps, etc., for example.

[Prior art]

Conventionally, chitosan has been produced by decalcifying and deproteinizing a natural product containing chitin, followed by deacetylation at high temperature in a highly concentrated alkaline aqueous solution.

However, according to this method, the polymer main chain of chitin or chitosan is cleaved, making it difficult to produce high-molecular-weight chitosan.

The aim is to eliminate this drawback, for example.

[A method for deacetylating chitin in a 30-50% by weight aqueous alkaline solution at a reaction temperature of 60°C or lower.”
(Unexamined Japanese Patent Publication No. 50-126784) Or, "a method of adding an aqueous alkali solution of 30 to 50% by weight, which is 2 to 7 times the amount of chitin, mixing in a kneader etc., and then reacting at 40 to 80°C" ( (U.S. Pat. No. 4,195,175) etc. have been proposed, but in the former method,
The amount of alkaline aqueous solution must be 10 to 30 times that of chitin, and the deacetylation reaction must be carried out at a low temperature (below 60°C) to prevent the molecular weight of chitosan from decreasing, so the reaction time is limited. It has the disadvantage of being long,
In addition, the latter method has the drawbacks that the reaction is non-uniform, resulting in a large amount of insoluble matter in the acetic acid aqueous solution, the lower molecular weight of chitosan, making it impossible to obtain chitosan with a high molecular weight, and the reaction time being long. Ta.

〔the purpose〕

An object of the present invention is to provide an industrially advantageous method for producing chitosan, which has a small amount of insoluble components in an acetic acid aqueous solution and can obtain high molecular weight chitosan in high yield.

〔composition〕

According to the present invention, after immersing chitin in a 35 to 60% by weight concentrated alkaline aqueous solution, the chitin is soaked with excess so that the chitin is impregnated with an alkaline content of 0.5 to 2.5 parts by weight per 1 part by weight of chitin. A method for producing chitosan is provided, which comprises removing an aqueous alkali solution and heating the resulting alkali-impregnated chitin to 45 to 110'C to deacetylate it.

As a result of intensive studies on a method for producing chitosan by deacetylation of chitin, the present inventors found that chitin was impregnated with an alkali content of 0.5 to 2.5 parts by weight per 1 part by weight of chitin. It was discovered that deacetylation at a temperature of 45 to 110° C. can yield high molecular weight chitosan with few insoluble components in an acetic acid aqueous solution in a short period of time, and the present invention was completed based on this finding.

In the present invention, chitin is used as a raw material.

For example, crab or shrimp shells are treated with dilute hydrochloric acid to remove calcium, then treated with dilute alkaline solution to remove proteins and other impurities, and washed with water.

Either dry chitin or semi-dry chitin in the form of powder or cubes can be used. In the case of semi-dry chitin, it is desirable that the water content is 70% by weight or less.

Furthermore, examples of the alkaline aqueous solution used in the dipping step of the present invention include sodium hydroxide.

A 35 to 60% by weight aqueous solution, preferably a 37 to 55% by weight aqueous solution of potassium hydroxide or lithium hydroxide can be mentioned.

In the case of dry chitin, the amount of alkaline aqueous solution used is sufficient to soak the chitin, and in the case of semi-dry chitin, it is necessary to make sure that the alkali concentration at the time of soaking is 37 to 55% by weight. , generally 5 parts per part by weight of chitin.
It is preferable to set the amount to 20 parts by weight.

The dipping step in the present invention is usually carried out at a temperature of 20 to 50°C for 5 to 60 minutes, but when semi-dried chitin is used, the alkali is diluted with water and generates heat, so it is carried out under cooling. It is also desirable to stir occasionally so that the alkali concentration during dipping becomes more uniform.

In the present invention, the soaked chitin is then treated with a solid-liquid separator such as a press or a centrifugal filter to reduce the alkaline content in solid terms to 0.00% per part by weight of chitin.
The chitin impregnated in an amount of 5 to 2.5 parts by weight, preferably 1.0 to 2.0 parts by weight, is separated from the excess alkaline aqueous solution.

In the present invention, by limiting the alkaline content impregnated into chitin to the above-described specific range, it is possible to suppress lowering of the molecular weight of chitin or chitosan, and to prevent the formation of insolubilized components in an aqueous acetic acid solution. If the amount of alkali impregnated in solid terms is less than 0.5 parts by weight based on the weight of chitin I, the deacetylation reaction in the next step will be delayed, resulting in a decrease in the yield of chitosan. If the amount is exceeded, the molecular weight of chitin or chitosan will be lowered, making it impossible to obtain high molecular weight chitosan.

In the present invention, as the alkali-impregnated chitin is separated, surplus alkaline aqueous solution is recovered, but unlike the one subjected to the deacetylation process, this aqueous solution does not contain the alkali acetate salt produced as a by-product of the reaction. Therefore, it can be directly recycled to the soaking process without purification.

Next, in the present invention, the alkali-impregnated chitin obtained in the separation step is charged into a reaction vessel, and after nitrogen substitution,
After transferring the reactor into a constant temperature chamber, a deacetylation step is carried out. This deacetylation step.

At a temperature of 45 to 110°C, preferably 50 to 100°C1
It is appropriate to carry out the treatment for ~10 hours. When the temperature is lower than 45°C, a long time is required for deacetylation, and when the temperature exceeds 110°C, the molecular weight of chitin or chitosan is significantly lowered. After deacetylation, the unpurified chitosan is washed with water, neutralized, and dried to obtain chitosan, which is the object of the present invention.

Since the chitosan obtained in the present invention has a high molecular weight and high purity, it can be used as a flocculant, a cosmetic base material, a film, etc.

〔effect〕

The present invention has the above-described structure, and in particular, chitin impregnated with a specific proportion of alkali is deacetylated at a reaction temperature of 45 to 110°C. can be obtained in high yield, and the alkaline aqueous solution recovered in the solid-liquid separation process can be directly recycled to the soaking process without being purified, making it an industrially extremely advantageous method for producing chitosan. I can do it.

〔Example〕

Next, the present invention will be explained in more detail with reference to the following examples.

The degree of deacetylation was calculated by quantifying free amino groups by a colloid titration method using methylene blue as an indicator and a 1/400 normal polyvinyl potassium sulfate aqueous solution. To determine the viscosity, prepare a 0.4% chitosan-acetic acid aqueous solution,
The tl was determined at 20° C. using a B-type viscometer (rotor No. 31, rotation speed: 30 rpm).

Example 1 Red snow crab shells crushed into pieces of 10 mm or less were first treated with 1N hydrochloric acid at 25° C. for 2 hours to decalcify them. After washing with water, add to 4% caustic soda aqueous solution at 75-85℃
Deproteinization was performed by heat treatment for 2 hours, followed by washing with water.
It was semi-dried to obtain chitin with a moisture content of 50%. This semi-dried chitin tooK was added to 430 g of 48% caustic soda while maintaining the temperature at 30 to 40°C. Thereafter, the mixture was stirred occasionally and left at the same temperature for 30 minutes. Excess caustic soda aqueous solution was separated using a centrifugal filter, and 185 g of a chitin cake containing 1.2 times as much solid caustic soda as chitin was placed in an IQ stainless steel container and replaced with nitrogen. This container was transferred into a 100° C. thermostat. The temperature inside the container reached 80°C in 1 hour, and then the temperature inside the thermostat was set to 80°C.

It was left still for another 3 hours. After cooling, 40 g of flaky chitosan was obtained by washing with water, neutralizing, and drying. The degree of deacetylation of this chitosan is 87%, and the viscosity is 1300 cp (0.4%
aqueous solution, 20°C).

Example 2 Chitin 1 with 50% water content obtained by the same method as Example 1
00g was added to 430g of a 48% caustic soda aqueous solution while maintaining the temperature at 30-40°C. Then sometimes.

The mixture was stirred and left at the same temperature for 30 minutes. Chitin cake 283 containing twice as much solid caustic soda as chitin, obtained by separating excess caustic soda aqueous solution using a centrifugal filter.
g was placed in an IQ stainless steel container. After performing nitrogen substitution, it was placed in a thermostat at 120°C. The temperature inside the reaction vessel reached 100° C. in 1 hour, and then the temperature inside the thermostat was set to 100° C., and the mixture was allowed to stand still for another 1 hour. After cooling,
By washing with water, neutralizing, and drying, 40 g of flaky chitosan was obtained. The degree of deacetylation of this chitosan is 88%, and the viscosity is 1
000 cp (0.4% aqueous solution, 20°C).

Example 3 50 g of dry chitin obtained in the same manner as in Example 1 was
It was added to 400 g of 0% caustic soda aqueous solution and left standing at 30° C. for 30 minutes. It was obtained by separating excess caustic soda aqueous solution using a centrifugal filter. 300 g of chitin cake containing twice as much solid caustic soda as chitin was placed in an IQ stainless steel container. After nitrogen substitution, 100
It was placed in a thermostat at ℃. The temperature inside the reaction vessel reached 90°C in 80 minutes, and then the temperature inside the thermostat was set at 90°C, and the reaction vessel was allowed to stand still for another 2 hours. After cooling, 41 g of flaky chitosan was obtained by washing with water, neutralizing, and drying. The degree of deacetylation of this chitosan is 86%, and the viscosity is 1200 cp (0,
4% aqueous solution, 20°C).

Example 4 50g of dry chitin obtained in the same manner as Example 1 was
It was added to 300 g of 0% caustic soda aqueous solution and left standing at 40° C. for 30 minutes. Excess caustic soda aqueous solution was separated using a centrifugal filter, and 200 G of chitin cake containing twice as much solid caustic soda as the obtained chitin was placed in an IQ stainless steel container. After performing nitrogen substitution, it was placed in a thermostat at 80°C. The temperature inside the reaction vessel reached 60℃ in 40 minutes.
After that, the temperature in the incubator was set to 60° C., and the temperature was left still for another 7 hours. After cooling, the mixture was washed with water, neutralized, and dried to obtain 40 g of chitosan flakes. The degree of deacetylation of this chitosan is 86%, and the viscosity is 1400 cρ (0.4%
aqueous solution, 20°C).

The concentration of the aqueous caustic soda solution separated in Examples 1 to 4 was adjusted with solid caustic soda as necessary, and the experiments were repeated under the same conditions.

In each case, no accumulation of sodium acetate was observed in the deacetylation reaction, and similar results were obtained, confirming that the 1-separated caustic soda can be recycled.

Comparative Example 1 Chitin 1 with 50% water content obtained by the same method as Example 1
00g and 647g of a 46% caustic soda aqueous solution were charged into an IQ stainless steel reactor. After performing nitrogen substitution,
The reaction was carried out at 85° C. for 3 hours while stirring. After cooling, the contents were taken out, washed with water, neutralized, and dried to obtain 40 g of flaky chitosan. The degree of deacetylation of this chitosan is 86%, and the viscosity is 200 cp (0.4% aqueous solution, 20°C)
Met.

Comparative Example 2 Dry chitin sog and 5 obtained by the same method as Example 1
200 g of 0% caustic soda aqueous solution was charged into an IQ kneader. After nitrogen substitution, the reaction was carried out at 60°C for 7 hours. After cooling, 43 g of flaky chitosan was obtained by washing with water, neutralizing, and drying. This chitosan contained many insoluble components in the acetic acid aqueous solution, and the degree of deacetylation was 70%.

Claims (1)

[Claims] (1) After immersing chitin in a concentrated aqueous alkaline solution of 35 to 60% by weight, excess alkaline aqueous solution is added so that the chitin is impregnated with 0.5 to 2.5 parts by weight of solid alkaline content per 1 part by weight of chitin. A method for producing chitosan, which comprises removing and heating the obtained alkali-impregnated chitin to 45 to 110°C to deacetylate it.