Method for isolating purified chitosan from reaction mixture (variant)

FIELD: natural substances, chemical technology.

SUBSTANCE: invention relates to a method for preparing chitosan and purification from components of the reaction mixture - low-molecular products of deacetylation and alkali excess. Invention relates to a method for purifying chitosan prepared by solid-state method involving treatment of reaction mass with extractant consisting of 3.3-20.0% of water, 32.2-57.1% of ethyl acetate and 24.6-64.5% of ethanol at the extractant boiling point. Also, invention relates to a method for purifying chitosan prepared by suspension method and involving treatment of the reaction mass with ethyl acetate and the following treatment with extractant consisting of 6.2-25.0% of water, 12.5-62.5% of ethyl acetate and 31.3-62.5% of ethanol at the extractant boiling point.

EFFECT: improved isolating and preparing method.

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The invention relates to the field of chitosan and clearing the components of the reaction mixture of low molecular weight reaction products and excess alkali (sodium hydroxide or other alkali metals). In traditional methods of production of chitosan by dezazetilirovanie chitin with concentrated solutions of sodium hydroxide using 10-20-fold molar excess of NaOH [1]. More environmentally friendly and cost-effective is the solid-state method [2], which requires only a 5-fold molar excess of alkali. However, in this case, the obtained reaction mixture, only 33% consisting of chitosan, and 67% are CH3COONa and excess NaOH. Therefore, purification of chitosan from low molecular weight components of the reaction mixture is an important stage of the technological process of its receipt.

A known method of extraction of chitosan from the reaction mixture by washing with water, in which it is necessary to use a large amount of deionized water 300 to 700 liters per 1 kg of chitosan [1]. The washing water containing alkali, sodium acetate and degradation products of chitin, in the best case, neutralized before discharge into the sewer.

Closer and adopted for the prototype is a method of extraction with alcohol or azeotropic mixture of isopropanol - water [2]. The disadvantage of this method is the low solubility of sodium hydroxide in the extractant and incomplete (to a residual content of more than 1%) the removal of alkali, polluting product and initiating processes leading to loss of chitosan solubility with the long-term storage.

The aim of the proposed method of extraction of chitosan from the reaction mixture is getting a product that does not contain traces of alkali, with ash content less than 1% and not lose solubility during storage.

This goal is achieved by the fact that apply:

the method of purification of chitosan from alkali and sodium acetate, which consists in the extraction of the powdered reaction mass obtained solid way to dezazetilirovanie, an extractive agent consisting of water, ethanol and ethyl acetate, the saponification of which sodium hydroxide is formed ethanol and sodium acetate, extragenomic further, when the boiling point of the extractant 68-74°and the ratio of the components: water - 3,3-20,0%ethyl acetate - 32,2-57,1% and ethanol - 28,6-64,5%;

the method of purification of chitosan from alkali and sodium acetate, which consists in processing wrung the reaction mass obtained suspension method, ethyl acetate, taken in stoichiometric quantity with respect to the content of sodium hydroxide, and subsequent extraction of the formed sodium acetate at the boiling point of the extractant 68-74°and the ratio of its components: water - 6,2-25,0%, ethyl acetate, 12.5 to 62.5 percent and ethanol 31,3-62,5%.

Thus, the reaction mass containing chitosan, alkali and the Etat sodium, extracted with a mixture of ethyl alcohol, ethyl acetate and water, taken in a certain ratio. The proposed method of purification of chitosan is especially useful when conducting dezazetilirovanie chitin solid-state method. But it can be used for isolation of chitosan from the reaction mass obtained traditional suspension method. In this case, when calculating the ratio of components of the extractant should be factored into the amount of water contained in the squeezed reaction mass. Best cleaning results wrung the reaction mass obtained if prior to the extraction process stoichiometric with respect to the remaining alkali amount of ethyl acetate. After extraction, the extractant regenerate, removing the crystallized when cooled sodium acetate and ethanol and the ethyl acetate separated by distillation and re-used for the extraction.

The advantage of the proposed method of purification of chitosan is the lack of alkali and discharge the wash water. In addition, the practical elimination of water usage that causes the crystallization of the polymer, and the more amorphous and porous chitosan provide a high rate of dissolution and reactivity of chitosan, including sorption and sulfation [3]. Diffraction patterns of chitosan, purified by pre the proposed method (see curve 1 in the figure), and chitosan, purified by washing with water (curve 2), confirm the most amorphous of the first.

The technical result achieved by the application of the inventive method the selection of the pure chitosan is a complete transformation of an excess of sodium hydroxide in sodium acetate and removal of the last content in the finished product less than 1%, as well as maintaining a high level of reactivity and solubility of the polymer during storage.

Examples

Table 1 presents the composition of two species of the reaction mass of:

1 is obtained by solid-state technology from a mixture of caustic soda 50% and chitin 50% (5:1 mol/mol)

2 is obtained by suspension technology from a mixture of caustic soda 22,7%, chitin 7.8% and water 69,5% (14,8:1:100 mol/mol).

The reaction mass may contain an antioxidant, bleach or other additives that are acceptable for the process and introduce, if necessary.

The method of purification of chitosan illustrated by the examples presented in table 2.

Thus, the proposed method of purification of chitosan from low molecular weight components (NaOH, CH3COONa)remaining in the reaction mass after the process of dezazetilirovanie, allows you to:

- clear chitosan to a residual ash content of less than 1%;

- to obtain a chitosan containing no alkali;

- save rastvorimosti with long-term (>2 years) storage;

to obtain chitosan with more porous and amorphous structure, especially when using solid-state technology to dezazetilirovanie chitin;

to obtain sodium acetate as an additional commercial product.

Bibliography

1. Muzzarelli R.A.A. Chitin. Oxford-N.Y.-Toronto-Sydney-Paris-Frankfurt: Pergamon Press. 1977. 309 p.

2. A.C. 1760749 A1 / Enikolopov NS, galbraikh PS, Rogovin SZ, Vikhoreva GA and other Way of chitosan. 1989.

3. Stolboushkin P.P. preparation, structure and properties of low molecular weight sulfated aminopolysaccharide. Diss. c.ch.s. - M.: Moscow state technical University n.a. An Kosygin. - 2003. - S.

Table 2
# exampleno reaction massThe composition of the extractant,.%*The time of extraction, hCharacterization of chitosanOutput acetate NaThe consumption of acetate by saponification
EthanolThe ethyl acetateWaterThe ash content of chitosan, %The content of NaOH in the chitosan, %The solubility of chitosan after storage for 2 years %The output of chitosan
kg/kg reaction mass% of theorykg/kg of the reaction mixture.% of theorykg/kg reaction mass% of theory
1128,657,114,380,401000,37198,01,101160,875106,6
2140,040,020,0100,901000,37097,61,051110,870105,6
3164,532,23,3248,10-0,400105,50,951000,866105,2
4**262,512,525,080,501000,12699,20,90597,60,902+0,05101,3
5**231,362,56,2249,90- was 0.138108,60,81of 87.30,902+0,05101,3
*Excluding regeneration flow rate of the extractant is 6 kg/kg reaction mass.
**Before extraction to the reaction mass 2 added ethyl acetate in the amount of 0,902 kg/kg

1. The method of purification of chitosan from alkali and sodium acetate, characterized in that it includes the extraction of the powdered reaction mass obtained solid-state method, the extractant consisting of 3,3-20,0% water, 32,2-57,1% ethyl acetate and 28.6-64,5% ethanol, at the boiling point of the extractant.

2. The method of purification of chitosan from alkali and sodium acetate, characterized in that it includes processing wrung the reaction mass obtained suspension method, ethyl acetate, taken in stoichiometric quantity with respect to the content of alkali and subsequent extraction with an extractant consisting of a 6.2-25,0% water, 12.5 to 62.5% of ethyl acetate and 31.3-62.5% of ethanol, at the boiling point of the extractant.



 

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