WO1991005808A1

WO1991005808A1 - Method for manufacture of chitosan and other products from shells of organisms, especially marine organisms

Info

Publication number: WO1991005808A1
Application number: PCT/FI1990/000247
Authority: WO
Inventors: Henryk Struszczyk; Olli KIVEKÄS
Original assignee: Firextra Oy
Priority date: 1989-10-20
Filing date: 1990-10-19
Publication date: 1991-05-02
Also published as: FI894989A0; NO921464L; FI86068B; FI86068C; NO302661B1; NO921464D0; CA2067788A1

Abstract

The invention relates to a method of manufacture of chitosan and other products, such as chitin and proteins, from the shells of organisms, especially marine organisms, as a result of the reaction stages of deproteinization by alkaline solutions, demineralization by acidic solutions and deacetylation by concentrated alkaline solutions. The method comprises at least two successive stages of said three stages. The chitosan is manufactured so that in the shells of organisms, especially marine organisms, such as crabs or shrimps, are placed in a space in a reactor limited by a wall pervious to reaction liquids but retaining said shells of organisms. Thereafter they are subjected to a continuous action of reaction liquids, especially in a recirculation system flowing through the reactor and said space. After every reaction stage the solid product obtained is optionally washed by water using a continuous flow of water through the reactor to remove the residual reaction liquids. Thereafter the solid end product is optionally dried, preferably in an air flow at a temperature of 40-100 °C.

Description

Method for manufacture of chitosan and other products from shells of organisms, especially marine organisms

The invention relates to a method for manufacture of chitosan and other products, such as chitin and proteins, from shells of organisms, especially marine organisms.

There are methods of manufacturing chitin as well as chitosan, which subject the shells of marine organisms, such as crabs, shrimps or krills, to deproteinization, demineralization and deacetylation in separate reaction systems. The well-known systems of deproteinization processes are carried out by means of diluted agueous solutions of alkaline metal hydroxides or their salts, usually in a temperature ranging from 20 to 120°C for a period of 0.5-24 h or by means of an enzymatic method, in a stirring-disintegrating apparatus or in a tank without stirring. The demineralization process for obtaining chitin in well-known methods is carried out by means of aqueous acidic solutions, also with additives as hydrosulfite or sulfur dioxide, most often at room temperature in mixers or reactors equipped with rotatory mechanisms.

The deacetylation processes of chitin for obtaining chitosan in well-known systems are realized by subjecting the chitin to the action of concentrated aqueous alkaline metal hydroxide solutions, most often sodium hydroxide solution with 40-60 wt% concentration at temperatures of 90-140°C. The deacetylation is carried out in pressure reactors usually equipped with stirrers.

The well-known methods are described in a monography of Chitin, Pergamon Press, 1978; Australian Journal of Biological Science, volume 7, pages 168-178, 1954; Journal of Americal Chemical Society, volume 79, pages 5046-5049, 1957; Nature, volume 180, pages 40-41, 1957; Journal of Organic Chemistry, volume 23, pages 1990-1991, 1958; Norisho Suisan Koshusho Kenkyo Hokoku, volume 11, pages 339-406, 1962; Journal of Organic Chemistry, volume 27, pages 1161-1163, 1962; Methods of Carbohydrate Chemistry, volume 5, pages 403-406, 1965; Chimica Industrie, Genie Chim. , volume 99, pages 1241-1247, 1968; Fishing Technology, volume 11, number 1, pages 50-53, 1974; INFOFISH International, volume 5, pages 31-33, 1987, and also in the conference proceedings of I-IV International Conferences on Chitin/Chitosan in USA, Japan, Italy and Norway at 1978, 1982, 1985 and 1988 as well as in U.S. Patents Nos. 2072771, 2040879, 3533940, 3862122, 3922260, 4066735, 4195175, 4199496, in Japanese Patents Nos. 75,126784 and 78,59700, International Patent Application No. 086/06082 as well as Polish Patent No. 119931.

The well-known methods of manufacture of chitosan and other products from the shells of marine organisms require the using of several apparatuses equipped with stirrers and also requiring the transport of solid substances between particular technological process stages. The technological process is of long duration resulting at the same time in augmentation of production costs and in occupational health risk from the chemical substances used. Moreover, the chemical processes realized by the well-known methods, in spite of the use of stirring, do not create possibilities to obtain products with homogenous properties because of the heterogenous character of above processes.

The object of this invention is to provide a method for manufacture of chitosan and other products, such as chitin and proteins, from the shells of organisms, especially of marine type, in a single apparatus, by deproteinization using alkaline solutions, demineralization using acidic solutions, as well as by deacetylation using concentrated alkaline solutions.

In accordance with a preferred embodiment of the method of the invention the manufacture of chitosan and other products from the shells of organisms, especially marine organisms, by deproteinization, demineralization and deacetylation, is characterized in that the shells of organisms, especially marine organisms, such as crabs or shrimps, are subjected to the continuous action of reaction liquids in a single apparatus of perforated type or equipped with perforated divisions, especially in a circulation system, whereby the reaction liquids flow through a reactor with a flow rate of 0.5-10000 volume parts per 1 weight part of solid product and 1 hour, whereby after each reaction stage the solid product obtained is optionally washed with water using a continuous system flowing through the reactor with a flow rate of 1-20000 volume parts per 1 weight part of solid product and l hour in order to remove the residual reaction liquids, whereafter the chitosan obtained in a solid form is eventually dried, preferably in air- flow conditions at a temperature of 40-100°C.

According to a preferred embodiment of the invention, the manufacture of chitosan and other products is characterized in that the deproteinization is carried out by using alkaline solutions, especially aqueous alkaline metal hydroxide solutions or their salts, such as sodium hydroxide or sodium carbonate, having a concentration of 0.1-10 wt%, at a temperature not lower than 10°C for a time necessary to complete the removal of proteins, the demineralization is carried out either before or after the deproteinization stage by using aqueous acidic solutions, expecially inorganic acids, such as hydrochloric or sulfuric acids having a concentration of 0.1-20 wt% for a time necessary to dissolve the inorganic compounds, such as calcium and magnesium derivatives, at a temperature not lower than 10°C, especially 20-100°C, whereafter the deacetylation is carried out by using concentrated alkaline solutions, especially aqueous alkaline metal hydroxide solutions or their salts, such as sodium or potassium hydroxides or their salts, having a concentration of 20-60 wt%, for a time ranging from 30 minutes to 25 hours at a temperature ranging from 60 to 140°C.

The proteins from the alkaline solutions are recovered by reduction the pH to 3-6 by means of organic or inorganic acids, such as acetic, hydrochloric or sulfuric acids, especially having a concentration of 1-10 wt%. The chitin obtained after demineralization is purified and optionally dried.

The fundamental advantage of the method according to the invention is the realization of all the processes, starting fromdeproteinizationthroughdemineralization finally to deacetylation, including the purification as well, in a single apparatus, in which the substrate in a form of shells of organisms such as crabs, shrimps, krills or insects, constitutes a stationary phase whereas the reaction liquids as well as the washing water are acting in a continuous movement enhancing at the same time the effectivity of the processes by reduction of the time of an individual operation as well as by reduction of the concentration of the reagents used in comparison to well-known methods. Application of a closed circulation system reduces considerably the consumption of the reaction liquids.

The advantage of the method according to the invention is the use of the continuous flow system of liquids without a necessity for stirring, which is difficult or even impossible to realize in a case of raw materials used in the form of shells of marine organisms. Due to the flow of the reaction liquids the deproteinization, demineralization and deacetylation related to the production of proteins, chitin and chitosan, are facilitated.

As a result of the flow of alkaline solution in the deproteinization process, a dissolution of proteins present as a residue on the shells will take place.

In a method according to the invention, the rate of removal of the proteins is 2-3 times faster than in a conventional periodical method. At the same time it is possible to use alkaline solutions having lower concentration for removing of proteins, or to use a lower temperature in carrying out the process.

Deproteinization in a method according to the invention allows to obtain the proteins without their superfluous degradation and having homogenous properties.

The demineralization in a method according to the invention by means of the flow of an acid solution, resulting in the removal of calcium compounds from the shells, takes place where these compounds are existing in the shells in a form of insoluble carbonates and their removal takes place through conversion of these carbonates to suitable soluble salts. The method according to the invention increases the effectivity of demineralization process by the order of 2-4 times in comparison to well-known methods, as a result of a better penetration of the demineralizing liquids causing the acceleration of reaction, which leads firstly to the reduction of process time and secondly to decreased energy consumption. The method according to the invention allows to obtain chitin characterized by minimal content of ash, being below 0.5-1.0 wt%. The deacetylation process as a ^• result of treatmet with alkaline solutions having a high concentration ranging from 20 to 60 wt% causes a deacetylation reaction of acetylamino groups of chitin to amine groups in chitosan. The process is carried out in order to obtain a product with homogenous properties and being soluble in an aqueous acetic acid solution.

A method according to the invention ensures a 2-3 times increment in effectivity of a deacetylation process as a result of better mass exchange caused by the continuous flow of the deacetylating solution and also by the augmentation of the deacetylation rate. It is possible to obtain chitosan with correct properties as early as after 4 hours of deacetylation process by using 30-50 wt% concentrated sodium hydroxide solution at a temperature of 90-100°C.

An advantage of a method according to the invention is also a possibility for effective purification of the products, resulting from a continuous washing flow using water, especially in a circulation system. A possibility of drying of chitin or chitosan in a reactor by a pressurized air at higher temperature is also an advantage afforded by the method.

A method according to the invention allows to reduce the production cost at least 1.5-2 times, based on a lower consumption of energy as well as chemicals and also on a lower cost of labour.

The chitosan, chitin and proteins obtained by the method according to the invention are applied to the chemical industry, agriculture, medicine, pharmaceutical and cosmetic industry, paper industry, waste water treatment etc. A method for manufacture of chitosan and other products from the shells of organisms, especially marine, is realized in an installation shown schematically in the accompanying drawings, where

Fig. 1 shows the installation having a reactor equipped with a perforated basket, and

Fig. 2 shows an installation having a reactor equipped with perforated divisions.

The installation in Fig. 1 contains a reactor 1 in a form of a tank having a heating jacket 4, the reactor being equipped with an immersed perforated basket 2 in which the shells 3 are located. The reactor 1 is joined to a draining or outlet pipe 5 located in the reactor outside the basket and being of a controllable depth of immersion. The pipe is connected through a pump 6 and through subsequent valves 7 and 9 to an inlet or conveying pipe 10 leading back to the reactor into the basket and having its outlet end near the bottom of the basket. A draining and supply pipe is connected through a valve 8 to the outlet pipe 5 from the reactor 1 and to the inlet pipe 10 leading to the reactor, the junction point being between the valves 7 and 9. A branch supply pipe containing a valve 11 is connected to the pipe 10 between the valve 9 and the reactor.

The action of the above installation is as following: a suitable amount of shells 3 is introduced into the perforated basket 2 and the basket is inserted into the reactor 1. The deproteinization liquid is introduced into the reactor 1 after opening of the valves 8 and 9, and after closing of the valve 8 and opening of the valve 7 and starting of the pump 6, the removal of proteins will be carried on by recirculating the reaction liquid through the pipes 5 and 10 optionally by heating the reactor simultaneously. The inlet end of the pipe is located close to the liquid surface of the reactor during the recirculating. The valve 9 is closed after the deproteinization is completed, whereafter the valve 8 is opened, and the pipe 5 is lowered deeper into the reactor 1 taking away the proteinaceous solution into a suitable tank. Next the valve 9 is opened and washing water is introduced through the valve 8 and valve 9, and after closing of the valve 8 the purification process is carried on. The purification process can be carried on also with a continuous flow of the washing water through the valve 11. The liquid can be recirculated also partly by taking of the liquid through the valve 8 only partly. After the purification and water removal the demineralization as well as the deacetylation liquids are introduced in turn followed by an application of suitable water purification operations.

The installation in Fig. 2 contains a reactor 1 in the form of a tank equipped with a horizontal perforated division or partition 2 restricting the area of the shells 3 to the upper part of the reactor. The area outside the shells below the partition 2 is joined to a valve 5 at the bottom of the reactor and to a draining pipe 6 having a pump 7. In the direction of flow, the pump is followed by a system of valves 8, 9 and 10, where the valve 9 has the same function as the valve 8 in Fig.9, being situated in a supply and drainage line joined to the recirculation line at the junction point between the valves 8 and 10. The pump 7 is joined through the valves 8 and 10 to the reactor 1, where the shells 3 are located, through a conveying pipe 11 to which is connected a supply branch pipe having a valve 12. The outlet of the pipe 11 is located above the shells 3 in the reactor. The action of the installation shown in Fig. 2 is analogous to the installation in Fig. 1. The well-known methods for manufacture of chitosan and other products from the shells up to now have comprised a stationary system for recovery of proteins, chitin and chitosan, as described for example in US. Pat. No. 4,199,496. The following processes as

- deproteinization

- demineralization - deacetylation

have always been realized in stationary conditions in separate apparatuses. Penetration rate by reaction liquid media, reaction effectivity as well as properties of products obtained have been low in these conventional methods. The new method for manufacture of chitosan and other products as chitin and proteins according to the present invention, utilizes the continuous action of reacting liquid media penetrating solid wastes with much higher effectivity of reactions of deproteinization, demineralization as well as deacetylation. In addition, the processes of chitosan, chitin and proteins manufacture need to be realized only in one single apparatus where the shells are placed in the beginning and the citosan is removed in the end of the process series.

The action of reaction media in the new system is better than in well-known methods. In the following table is presented some comparative data between the older method and the method of the present invention. Table Comparison of optimal conditions for processing of shells '

Process Optimal conditions Well-known methods New method

1. Deproteinization NaOH cone. 0,5% NaOH cone. 0,5% temp, about 100°C te p.max. 40-60°C or higher

2. Demineralization HC1 cone. 5-10% HC1 cane. 5-10% time 10-16h time max. 4-6 h

3. Deacetylation NaOH cone. 40-60% NaOH cone. 40-60% min. 100-140°C, max. 100-110 °C preferably high without pressure min. 10-20h max. 4-8h

The chitin and chitosan obtained according to the new method is more homogenous in properties in comparison to products obtained by well-known methods . The ash content in chitosan obtained by new method is lower than 1% , usually 0. 1-0.5% , whereas the level of 1% of ash is possible to be obtained by well-known methods us ing the drastic conditions mainly in a demineralization stage, taking usually 10-16h in comparison to max. 4-6h in the new method.

The invention is explained further in the following examples which do not restrict the scope of claims .

Example 1

12.16 weight parts of Norwegian shrimp shells containing 1.0 wt% of moisture and 0.88 wt% of nitrogen, and 400 volume parts of 2.5% aqueous sodium hydroxide solution were introduced into the reactor shown in Fig. 1. Deproteinization was carried out at a temperature of 30°C and for a period of 1.5 h in the circulation system using a flow rate of 4934 volume parts per 1 weight part of shells and 1 hour, whereafter the alkaline solution containing dissolved

Z o proteins with a red colour, d^ = 1.154 g/cirr and pΗ = 11.6, was continuously taken away. Next the shrimp shells were continuously washed by water with a flow rate of 6000 volume parts per 1 weight part of shells and 1 hour, whereafter 350 volume parts of 10% aqueous hydrochloric acid solution was introduced into the installation. The demineralization was carried out using a continuous flow of hydrochloric acid solution with a flow rate of 5000 volume parts per 1 weight part of shells and 1 hour at a temperature of 40°C for a period of 2 h, then the excess of hydrochloric acid solution was washed off at a temperature of 20- 30°C using a water flow rate of 500 volume parts per 1 weight part of chitin and 1 hour to obtain a neutral reaction of eluate, whereafter the chitin was dried at a temperature of 90°C.

3.1 weight parts of chitin in a solid form with a light yellow colour was obtained. The product was characterized by a water retention value (WRV) of 87.6%, nitrogen content of 5.5 wt%, ash content of 0.28 wt%. The chitin was not soluble in 4% aqueous acetic acid solution. IR studies showed the absorption band at the frequency of 1650 cm^"1 characteristic for amide groups.

2.5 weight parts of chitin obtained was introduced in a reactor shown in Fig. 1 and on it 200 volume parts of 35% aqueous sodium hydroxide solution was poured. The deacetylation was carried on using a continuous flow with a flow rate of 15 volume parts per 1 weight part of chitin and 1 hour at a temperature of 75°C for 20 h. Next the excess of sodium hydroxide solution was washed off continuously at a temperature of 20- 30°C using a flow rate of 500 volume parts per 1 weight part of chitin and 1 hour to obtain a neutral reaction. After the removal of water, the product was dried by pressurized air at a temperature of 70°C.

2.1 weight parts of chitosan with a white colour was obtained. The product was characterized by the WRV of 95.5%, average molecular weight M_w of 205000, deacetylation degree of 69.5% and nitrogen content of 6.9 wt%. IR studies showed the absorption band at the frequency of 1570 cm^-1 characteristic for amine groups.

Example 2

27.72 weight parts of Norwegian shrimp shells containing 1 wt% of moisture and 0.88 wt% of nitrogen and 800 volume parts of 5 wt% aqueous sodium hydroxide solution were introduced into the reactor as in Example 1. The deproteinization was carried on at a temperature of 60°C for 1 h in a circulation system having a flow rate of 2480 volume parts per 1 weight part of shells and 1 hour, whereafter the alkaline solution of proteins with red colour, d^ = 1.143 g/cπr⁵, pH = 11.7, was drained out.

The protein solution was treated on continuous stirring by 5% hydrochloric acid solution to obtain pH = 4.0. 0.6 weight parts of proteins with a light red colour, containing 1.83 wt% nitrogen, characterized by the presence of aspartic acid, glutamic acid, alanine, glycine, tyrosine, fenylalanine, lysine, arinine, threonine, serine, isoleucine and leucine was obtained.

Next the shells were continuously washed by water with a flow rate of 9000 volume parts per 1 weight part of shells and 1 hour. Subsequently, 600 volume parts of 10% aqueous sulfuric acid solution was introduced into the reactor. Demineralization was carried out by means of a continuous flow with a flow rate of 1210 volume parts per 1 weight part of shells and 1 hour at a temperature of 40°C for 2 h, whereafter the excess of sulfuric acid solution was washed out at a temperature 20-30°C using a flow rate of 1200 volume parts per 1 weight part of chitin and 1 hour to obtain a neutral pH of eluate. Next 500 volume parts of 30% aqueous potassium hydroxide solution containing 1.5 wt% of potassium carbonate and 0.5 wt% of sodium carbonate was introduced. Deacetylation was carried out at a temperature of 100-105°C for a period of 4 h using a flow rate of 7200 volume parts per 1 weight part of chitin and 1 hour and then, after purification, the product was dried by pressurized air at a temperature of 100°C.

5.35 weight parts of chitosan with a light yellow colour was obtained. The chitosan was characterized by nitrogen content of 5.9 wt%, WRV of 73.4%, M_w = 169060, deacetylation degree of 73.4% and a good solubility in a 4% aqueous acetic acid solution. IR studies showed the absorption band at the frequency of 1560 cm^"1 characteristic of amine groups.

Example 3

21.49 weight parts of Norwegian shrimp shells with properties as in Example 1 and 900 volume parts of 1% aqueous sodium hydroxide solution was introduced into the reactor shown in Fig. 1. Deproteinization at a temperature of 50°C for 1.5 h in a circulation system using a flow rate of 9800 volume parts per 1 weight part of shells and 1 hour was carried on, whereafter the proteins containing solution with a red colour, a = 1.112 g/cm-³, pH = 12.05 was drained out. Next the product obtained was washed by water using a flow rate of 4200 volume parts per 1 weight part of shells and 1 hour, whereafter 700 volume parts of 10% aqueous hydrochloric acid solution were introduced. Demineralization at a temperature of 20-23°C for 280 minutes using a flow rate of 10 volume parts per l weight part of shells and 1 hour was carried out. Next the excess of hydrochloric acid solution was washed out with water at room temperature using a flow rate of 1000 volume parts per 1 weight part of chitin and 1 hour. After the water had drained out, 600 volume parts of 50% aqueous sodium hydroxide solution were introduced into the reactor and the deacetylation was carried out using continuous circulation at a temperature of 110-120°C for 330 minutes using a flow rate of 2400 volume parts per 1 weight part of chitin and 1 hour. The product obtained after the washing was dried at a temperature of 80°C.

3.3 weight parts of chitosan with white colour characterized by WRV of 87.6%, nitrogen content of 6.2%, M_w of 75690, deacetylation degree of 78.2%, ash content of 0.93 wt% and very good solubility in 4% aqueous acetic acid solution was obtained. IR studies showed the absorption band at the frequence of 1580 cm"¹ characteristic of amine groups.

Example 4

31.73 weight parts of Norwegian shrimp shells with properties as in Example 1 and 800 volume parts of 5% aqueous sodium hydroxide solution were introduced into the reactor presented in Fig. 1. Deproteinization at a temperature of 50°C for 2 h with a flow rate of 7560 volume parts per 1 weight part of shells and 1 hour was carried on, whereafter the alkaline solution contai .ni.ng protei.ns wi.th a red colour, d 2^0 = 1.159 g/cm³, pH = 11.7 was taken off. Next the product was washed continuously by water to obtain a pH of 7 using a flow rate of 1150 volume parts per 1 weight part of shells and 1 hour, whereafter the water was taken out from the reactor.

Demineralization was carried out by means of 800 volume parts of 10% aqueous hydrochloric acid solution for 2 h at a temperature of 40°C using a flow rate of 125 volume parts per 1 weight part of shells and 1 hour. Next the excess of hydrochloric acid solution was washed out by water with a flow rate of 15200 volume parts per 1 weight part of chitin and 1 hour to obtain a pH of 7.0. After water had drained out, 600 volume parts of 40% aqueous sodium hydroxide solution was introduced into the reactor and the deacetylation at a temperature of 90°C for 6 h as well as at a temperature of 100°C for next 1 h was carried on. The product obtained after purification was dried at a temperature of 90°C.

6.3 weight parts of chitosan with a white colour characterized by deacetylation degree of 85.8%, ash contents of 0.83 wt%, nitrogen contents of 6.1 wt%, WRV of 106.6%, M_w of 184800 and a good solubility in 4% aqueous acetic acid solution was obtained. IR studies showed the absorption band at the frequency of 1560 cm^"1 characteristic of amine groups.

Example 5

32.5 weight parts of milled crab shells characterized by nitrogen contents of 0.7 wt%, and 800 volume parts of 5% aqueous hydrochloric acid solution were introduced into the reactor presented in Fig. 2. Demineralization at a temperature of 70° for 90 minutes using a flow rate of 1580 volume parts per 1 weight part of shells and 1 hour was carried out, whereafter the acid solution was taken off and the residues were continuously washed by water with a flow rate of 5050 volume parts per 1 weight part of shells and 1 hour. After the water had been taken off 600 volume parts of 0.5% aqueous potassium hydroxide solution were introduced into the reactor and the deproteinization was carried out at a temperature of 50°C for 4 h using a flow rate of 4580 volume parts per 1 weight part of shells and 1 hour. Next the alkaline solution containing proteins with a red colour, d 2«0 = 1.112 g/cm³, pH = 12.06, was taken off from the reactor, and immediately thereafter 500 volume parts of 60% aqueous potassium hydroxide solution were introduced obtaining a 57.5% aqueous potassium hydroxide solution as a result. Deacetylation was carried on at a temperature of 130°C for 3 h. The alkaline solution was next taken off from the reactor and the product obtained was purified and dried at a temperature of

80°C.

4.5 weight parts of chitosan with light red colour characterized by deacetylation degree of 75%, ash contents of 0.35 wt%, nitrogen contes of 7.4 wt%, WRV of 115% and a good solubility in 4% acetic acid solution was obtained. IR studies showed the absorption band at the frequency of 1570 cm"¹ characteristic of amine groups.

A prolongated deacetylation realized in the above conditions for the next 14 h allowed to obtain 4 weight parts of chitosan with a light red colour characterized by WRV of 120%, deacetylation degree of 92.5%, ash contents of 0.32 wt%, nitrogen contents of 7.9 wt% and a very good solubility in 4% aqueous acetic acid solution.

Claims

Claims :

1. Method of manufacture of chitosan and other products, such as chitin and proteins, from the shells of organisms, especially marine organisms, as a result of the reaction stages of deproteinization by alkaline solutions, demineralization by acidic solutions and deacetylation by concentrated alkaline solutions, the method comprising at least two successive stages of said three stages, characterized in that the shells of organisms, especially marine organisms, such as crabs or shrimps, are placed in a space in a reactor limited by a wall pervious to reaction liquids but retaining said shells of organisms, whereafter they are subjected to a continuous action of reaction liquids, especially in a recirculation system, flowing through the reactor and said space, and that after every reaction stage the solid product obtained is optionally washed by water using a continuous flow of water through the reactor to remove the residual reaction liquids, whereafter the solid end product is optionally dried, preferably in an air flow at a temperature of 40-100°C.

2. The method as claimed in claim 1, characterized in that the deproteinization is carried out by the use of alkaline solutions, especially aqueous alkaline metal hydroxide solutions or their salts, such as sodium hydroxide or sodium carbonate, at a concentration of 0.1-10 wt% at a tempreature of not lower than 10°C for a period of time necessary to complete the removal of proteins, the demineralization is carried out before or after deproteinization, using aqueous acid solutions, especially inorganic acids such as hydrochloric or sulfuric at a concentration of 0.1-20 wt% for a time necessary to dissolve the inorganic compounds such as calcium and magnesium derivatives, at a temperature not lower than 10°C, especially 20-100°C, whereas the deacetylation is carried out using concentrated aqueous alkaline metal hydroxide solutions or their salts at a concentration of 20-60 wt% and for a time ranging from 30 minutes to 24 hours at a temperature of 60- 140°C.

3. The method as claimed in claims 1 or 2, characterized in that the proteins are separated from the alkaline deproteinizing solutions by reduction of the pH of the solution to a level of pH in the range of 3-6 by an organic or inorganic acid solution, such as acetic, hydrochloric or sulfuric acid, especially at a concentration of 1-10 wt%, whereafter the chitin obtained after demineralization is purified and optionally dried.