RU2065447C1 - Method of chitosan preparing - Google Patents

Abstract

FIELD: biotechnology. SUBSTANCE: crayfishes Gammarus were used as parental raw which were treated with diluted aqueous sodium hydroxide solution by two stages. At the first stage 0.1N aqueous sodium hydroxide solution is used and at the second stage 3 wt.-% aqueous sodium hydroxide solution is used. Then raw is treated with diluted solution of hydrochloric acid followed by washing. Obtained chitosan is subjected for deacetylation with 50 wt. -% sodium hydroxide solution at 120-130 C for 1-2 hr. EFFECT: improved method of chitosan preparing.

Description

 The invention relates to the field of polymer-analogous transformations of natural macromolecular compounds, namely deacetylation of chitin-poly-N-acetyl-D-glucosamine, and can be used in the chemical, textile, paper, food industry and medicine.

A known method for producing chitosan- (1-4) -2 amino-2 deoxy-V-D-glucon consists in deacetylation of chitin with hydrazine hydrate at 120-150 ^o C for 2-4 hours in vacuum (USSR AS N 730695 C 08 B 37/08).

 The disadvantage of this method is the use of extremely expensive reagents.

 There is also known a method for producing chitosan, in which the chitin feed is suspended in an organic solvent miscible with water, the suspension is treated with an aqueous-alkaline solution at elevated temperature to deacetylate the chitin and the chitosan formed as a result of the reaction is isolated (PCT mz 90/04608, publ. 3.05 .90, C 08 B 37/08).

 The disadvantage of this method is that obtaining a suspension requires additional costs for the double treatment of chitin, as well as the use of an additional organic solvent.

 Closest to the features of the proposed technology is the method of producing chitosan according to the classical method, which is a series of sequential operations: raw material deproteination, demineralization of chitin purification, deacetylation of chitosan purification. Deproteinization is carried out by treating chitin-containing raw materials with a weak alkaline solution, then they are demineralized in a weakly acid hydrochloric acid solution, the purity of the raw materials from protein and mineral salts is achieved by varying the time. The isolated chitin is decolorized with hydrogen peroxide and washed with methanol; deacetylation is carried out with sodium hydroxide. The obtained chitosan is washed with water and then with methanol (Gamzazade A. I. Sklyar A. I. Rogozhin S. V. "Some Features of the Production of Chitosan" Navy. Volume (A) XXYII, 1985, p.6).

 The method described above allows you to get chitosan with a degree of deacetylation of 70-85% and good viscosity characteristics of its solution. Along with this, a significant drawback is the length of the process of isolation of chitin from the protein-mineral complex and the use of marine crustaceans that are not available in many regions as raw materials. It is also of little use that toxic and inaccessible methanol is used as a solvent for pigments. Chitosan obtained by this method does not have a sufficiently high degree of deacetylation, which significantly limits its use.

 The basis of the invention is the task of obtaining chitosan from the local feedstock of the Gamarus crustacean, less degraded and with a high degree of deacetylation.

The problem is solved by the fact that a method for producing chitosan is proposed, including deproteinization and demineralization of the raw materials in order to obtain chitin, washing chitin with methanol until the pigment is completely removed, and chitin deacetylation, in which according to the invention, the Gamarus crustacean is used as a starting material, which is subjected to deproteination in two stages by alkaline treatment of 3% wt. NaOH solution for one hour, and deacetylation of chitin obtained from Gamarus is carried out 50% wt. aqueous NaOH solution at a temperature of 120-130 ^o C for 1-2 hours.

 The method is as follows.

 Gamarus, purified from mechanical impurities and washed with tap water, is subjected to deproteination in two stages.

Stage I: a hamarous is placed in a glass cylinder equipped with a stirrer and poured into 0.1N. NaOH solution, while observing the vanine modulus 1:15. The processing of hamarussa with alkali is carried out for one hour at a temperature of 25 ^o C with constant stirring. After a period of time (1 hour) the raw materials are filtered and squeezed. Then carry out the second stage of deproteination.

Stage II: strained and squeezed raw materials are poured with a 15-fold excess of 3% wt. NaOH solution, incubated for 1 hour at a temperature of 25 ^o C with constant stirring.

 After processing, the deproteinated feed is washed with distilled water to a neutral medium (pH 7).

 After that, the raw materials are purified from mineral components using 0.6N. hydrochloric acid solution, for which deproteinated raw materials are placed in a glass cylinder and poured with an acid solution and incubated for 1 hour at M. at 1:15. Then the solution is separated from the precipitate by filtration and washing with water to pH 7.

 The chitin thus obtained is washed with ethanol and acetone until discoloration and dried in vacuo.

 The yield of chitin is 95% of theoretical.

 The next step is to get chitosan.

 Dry, crushed chitin is poured into a three-necked pyrex glass flask equipped with a stirrer, reflux condenser and bubbler. Nitrogen (60 bubbles per minute) was passed through for 10 minutes.

After that, 50% wt. an aqueous NaOH solution having a temperature of 80 ^{° C.} in a ratio by weight of 1:15.

After 10 minutes, the flask was lowered into a heated oil bath, where the temperature of 120-130 ^o C was maintained by a temperature regulator for 1-2 hours. After processing (after this time), the system is rapidly cooled, the contents of the flask are filtered and washed with distilled water to pH 7 by phenolphthalein. For final purification, the obtained chitosan is washed with ethanol and acetone, and dried in air. The yield of chitosan in chitin is 82% of theoretical.

 Example 1

400 g of a hamarous are placed in a glass cylinder with a capacity of 10 l, and 6 l of tap water are poured, stirred for 1 hour, then the hammar is separated from the solution by filtering and the raw material is squeezed out. After this, the squeezed raw material is poured into 6 l of 0.1N. NaOH solution and stirred for one hour, after which the raw material is squeezed and poured again 6 l of 3% wt. NaOH solution, add 18 g of surfactant to the solution, mix for 1 hour, then separate from the solution and wash with distilled water to pH 7. The pressed raw material is poured into 6 L of 0.6N. HCl solution and demineralized with stirring for 1 hour, the resulting substance is separated from the solution and washed with distilled water to pH 7, without drying, washed with ethanol and acetone until discoloration. The result is 30 g of chitin, which is 95% of the theoretical content in hamarus. 30 g of dry powdered chitin are poured into a three-necked pyrex glass flask equipped with a stirrer, reflux condenser and bubbler. Nitrogen is passed for 10 minutes, then 450 g of 50% wt. Are added to the flask through a filter. an aqueous NaOH solution having a temperature of 80 ^o C. After 10 minutes, the flask was lowered into a heated oil bath, where the temperature was maintained at 130 ^o C. for 1 hour. After processing, the reaction system was quickly cooled, the contents of the flask were transferred to the filter and washed with distilled water to pH 7 for phenolphthalein. The obtained chitosan is washed with ethanol and acetone, dried in air. Chitin yield of 18 g of chitin (82% of theoretical); deacetylation degree 94-98%. Characteristic viscosity of a solution of chitin in 2% acetic acid (η) 25.0.
Example 2
Getting lead according to example 1, but 30 g of chitin is treated with 450 g of 50% wt. NaOH solution at a temperature of 120 ^o C for 2 hours. The yield of chitosan is 82%; the degree of deacetylation is 95%; The characteristic viscosity of a solution of chitin in 2% acetic acid (η) is 25.5.
The main advantage of the invention is the ease of disposal of mineral protein waste, the production of chitazan with a high degree of deacetylation and degree of polymerization, which ensures its widespread use.

Claims (1)

A method of producing chitosan, including treating the shell of a crustacean first with a dilute aqueous solution of sodium hydroxide, then with a dilute aqueous solution of hydrochloric acid, washing the treated raw materials with subsequent deacetylation of the chitin obtained with an alkaline reagent in an inert atmosphere, characterized in that the Gamarus crustacean is used as the starting material processing of the feedstock with a dilute aqueous solution of sodium hydroxide is carried out in two stages, while in the first stage using 0.1N sodium hydroxide solution, and the second stage using a 3 wt.% aqueous solution of caustic soda and deacetylation of chitin is carried out with 50 wt.% aqueous solution of caustic soda at 120 130 ^o C for 1-2 hours