RU2087483C1 - Method of preparing chitosan - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: chitosan is used as sorbent and is prepared by grinding natural chitin - containing stock, decalcination with 1.5% hydrochloric acid solution and deproteinazation with 1-5% hydrochloric acid solution and also by washing and deaacylation with 46-47% sodium hydroxide solution. Chitin-containing stock is ground to obtain at least 90% particles having from (+5) to (0.5) fractions. Prior to washing operation, three cycles of deproteination and decalcination are carried out alternately. Each subsequent cycle of the alternating stages is carried out at temperature higher than that in the preceding stage. EFFECT: more efficient preparation method. 6 cl

Description

 The present invention relates to chemical technology for producing sorbents based on chitosan.

A known method of producing chitosan, including decalcification with a 3.5% solution of hydrochloric acid at a ratio of Т Ж 1 4 and a temperature of 20 ^o C, fat removal by extraction in ethyl acetate at a temperature of 30 ^o C, deproteinization with a 3.5% caustic sodium 24 hours at t 25 ^o C, deacylation with 50% NaOH at t 80-96 ^o C for 15-30 minutes, washing and drying at 80 ^o C [1]
The disadvantage of this method is the low degree of deacetylation of 56-70% NaOH, which indicates a low quality product. The resulting chitosan has a high content of mineral impurities. The process runs periodically, so the performance of the process is low.

 The product yield in the method of 70% of chitin. In a known manner it is impossible to obtain high molecular weight chitosan.

To eliminate these drawbacks, a method for producing chitosan is proposed, including grinding chitin-containing raw materials, deproteinization with a 1-5% solution of sodium hydroxide, decalcification with a 1-5% solution of hydrochloric acid, deacetylation with a 46-47% solution of sodium hydroxide at a temperature of 80- 85 ^o C, wherein the grinding is carried out to obtain not less than 90% of the particles fractions ^{(+5) o C (-0,5)} , before the deacetylation is carried further, respectively, the additional step of deproteinization and decalcification, deproteinization first step are 1-3 AC and the first stage of decalcification are 0.5-1.5 hours, the second stage of deproteinization is 1-3 hours, the second stage of decalcification is 0.5-1.5 hours, the third stage of deproteinization is 1-3 hours, decalcification -0, 5-1.5 hours

The steps are carried out without intermediate washes, i.e. reduced water consumption. In addition, the process is semi-continuous, which allows to increase productivity. All stages of decalcification are carried out at a temperature of 35-55 ^o C, and deproteinization at a temperature of 60-85 ^o C.

 The main task in performing all these operations is to preserve the intact (if possible) multi-link chitin molecule with a maximum degree of deacetylation (at least 70% of acetyl groups replaced by hydrogen).

After each stage of the process, the mother liquor is removed and the solid phase is thoroughly washed with drinking water to a pH of 6-7. The water consumption in this case reaches 180 m ³ per ton of chitosan.

 The alkali necessary for the process is prepared by dissolving solid caustic soda in water.

 The stages of deproteinization (removal of protein), decalcification (removal of calcium carbonate) and deacetylation (replacement of acetyl groups) are carried out either in one reactor or by loading the filtered solid phase into other devices. The process is carried out periodically.

 The present invention allows the removal of protein and calcium carbonate from the shell by deproteinization and decalcification in several stages under milder conditions. First, a portion of the protein is removed with an alkaline solution, then decalcification, these steps are repeated two more times without intermediate washing steps. The finished chitin, which is obtained after the above steps, is subjected to deacetylation with a 46-47% sodium hydroxide solution. Sodium hydroxide can be obtained by the method of diaphragm electrolysis or membrane method. Diaphragm electrolysis conditions are standard.

The deacetylation reaction time is 4 hours, the process temperature: 1 hour 82-83 ^o C, 1.5 hours 88-90 ^o C, 1.5 hours 82-83 ^o C. After this time, the mixture in the apparatus is diluted with drinking water by half and the mother liquor is sucked off. Chitosan is washed with drinking water to pH 7, filtered by centrifuge and dried to a water content of not more than 10%
The diluted alkali solution is subjected to evaporation at a vacuum of 680-720 mm Hg. to a concentration of 50% and again returned to the cycle.

Example. As chitin-containing raw materials, 42 kg of carapace of carapace are taken, crushed in a ball mill to obtain 90% of particles of fraction (+5) - (- 0.5). The crushed shell in an amount of 40 kg is loaded into a 4% sodium hydroxide solution taken in an amount of 270 liters preheated to 63 ^° C. The reaction mass is stirred for 1 hour 30 minutes, maintaining the indicated temperature. After the process, the mother liquor is removed into the spent alkaline solution collector. 270 l of a 1.5% hydrochloric acid solution are loaded into the apparatus, heated to 35 ^° C and kept under stirring for 1 hour. The mother liquor is removed into the spent acid solution collector and 240 liters of a 4% sodium hydroxide solution are charged. Heated to a temperature of 75 ^o C and kept under stirring for 2 hours. The mother liquor is removed and 240 L of 3% hydrochloric acid is charged, heated to 40 ^o C and kept under stirring for 1 hour 30 minutes? The mother liquor is removed and 240 L of a 4% sodium hydroxide solution is charged.

The reaction mixture is stirred at t 82 ^o C for 3 hours, the mother liquor is removed and 240 l of a 3% hydrochloric acid solution are charged. The reaction mixture was stirred at t 45 ^o C for 2 hours. The mother liquor is removed and the wash water is supplied and washed until the pH of the wash water is 7. To the resulting wet chitin containing moisture up to 80% 200 l of a 52% alkali hydroxide solution are added, and a 46% sodium hydroxide solution is formed in the reaction mixture. Deacetylation is carried out at t 84 ^o C for 4 hours. The resulting chitosan is washed with water. Flushing is carried out with steam condensate.

 The mother liquor after the deacetylation stage contains 32% NaOH, it is strengthened to 52%, for example, by evaporation and again sent for reuse or to obtain sodium hypochlorite, or for hydrolysis of soap fats, or at a water purification and neutralization station as a reagent, this solution can be sent to glass production.

 Protein is isolated from the mother liquor from the deproteinization step and sent for mixing with the mother liquor from the decalcification step. After mixing, we obtain a solution and bring it to pH 7 with its further use for dissolving salt in chlorine production or in soap making.

The resulting chitosan is characterized by the following characteristics:
basic substance content 99.98%
impurities 0,020 (in terms of dry matter)
non-combustible residue of 0.015%
heavy metals, including iron 0.005%
degree of deacetylation 78%
the yield of the target product 96% of the obtained chitin
viscosity of 1% chitosan in a 1% solution of acetic acid 1.1 Pa
The obtained chitosan can be used as an adsorbent in the deodorization of gas mixtures containing methyl mercaptan and other acid gases. The resulting chitosan is used to isolate heavy metals, such as mercury and cadmium, from industrial waste.

 The decalcification process is carried out within 1-5% hydrochloric acid solution; below 1% it is impractical to use solutions, since the reaction volumes increase sharply, and above 5% the process is rapid, foaming occurs, which degrades the characteristics of the method. At a time of less than 0.5 hours, stoichiometry does not completely reaction, more than 2 hours to carry out the process does not make sense, because the process is completed, it is no longer possible to wash out calcium from the particles.

At temperatures below 35 ^o C will not be completely removed calcium, which must be extracted completely at this stage. Above 55 ^o C, heat costs unnecessarily increase.

 Stages of deproteinization.

 At a solution concentration below 1% sodium hydroxide, large reaction volumes will be involved.

 When the content of sodium hydroxide in the solution is higher than 5%, the protein that is present in the chitin-containing raw material is ground, and the deproteinization process does not occur.

 If the process takes less than 1 hour, then the reaction does not pass completely, and above 3 hours it is impractical because of the end of the reaction.

At temperatures below 60 ^o C the reaction rate is low, and above 85 ^o C the process becomes dangerous, because can destroy the chitosan chain.

 Stage of deacetylation.

 At a concentration below 46%, the degree of deacetylation drops sharply, and with an increase above 47%, the chitosan chain breaks.

In the temperature range of 80-85 ^o C, the chitosan chain remains intact.

 Thus, chitosan with a high degree of deacetylation, with a high molecular weight and good sorption properties was obtained.

 Literature.

 [1] Brzeski M. "Bouleten Morski Institut Rubacki", Gdynia, 1985, vol. 14, N 3-4, p. 57-60.

Claims (6)

1. A method of producing chitosan, including grinding natural chitin-containing raw materials, decalcification with 1 5% hydrochloric acid solution, deproteinization with 1 5% sodium hydroxide solution, washing and deacetylation with 46 47% sodium hydroxide solution at 80 85 ^o C and separation chitosan from the mother liquor, characterized in that the chitin-containing raw material is ground to obtain at least 90% of the particles of the fraction (+5) (-0.5), after which three cycles of alternating stages of deproteinization and decalcification are carried out before washing, with deproteinization The reaction is carried out at 60 - 85 ^o C for 1 3 hours, decalcification at 35 55 ^o C for 0.5 2 hours, and each subsequent cycle from alternating stages is carried out at a higher temperature than the previous one.  2. The method according to claim 1, characterized in that the mother liquor from the deacetylation step is concentrated and fed to the deacetylation step.  3. The method according to claim 1, characterized in that the mother liquor from the deacetylation step is sent for chlorination to produce sodium hypochlorite.  4. The method according to claim 1, characterized in that the mother liquor from the deacetylation step is fed to the stage of fat hydrolysis in soap manufacture.  5. The method according to claim 1, characterized in that the mother liquor from the deacetylation step is fed to the etching of aluminum products.  6. The method according to claim 1, characterized in that the mother liquor from the deacetylation stage serves to neutralize and treat wastewater.