CS272877B1 - Method of xylans preparation from lignocellulosic materials - Google Patents

Abstract

The purpose of the invention is to improve the method of preparation of xylan from lignocellulosic materials. This purpose is achieved by subjecting the lignocellulosic material to the action of a 3 to 10 % by weight aqueous solution of hydroxide of alkaline metal and hydrogen peroxide, whereas the mass ratio of lignocellulosic material : aqueous solution of hydroxide of alkaline metal : hydrogen peroxide is 1 : 10 to 25 : 0.01 to 0.25, at 40 to 80 degrees C for 1 to 4 hours. After separation of the extract the lignocellulosic residue is extracted with 5 to 15 times the weight of the amount of 5 to 10 % by weight of aqueous solution of hydroxide of alkaline metals, at 20 to 30 degrees C for 1 to 4 hours. Xylan is precipitated from the alkaline extract and dried. This method of preparation of xylans from lignocellulosic materials can be used in the cellulose-paper, chemical, textile and pharmaceutical industries.

Description

Method of preparing xylans from lignocellulosic materials (57) The purpose of the solution is to improve the process of preparing xylans from lignocellulosic materials. This is achieved by impregnating the lignocellulosic material with 3 to 10 wt. aqueous alkali metal hydroxide solution and hydrogen peroxide, wherein the weight ratio of lignocellulosic material: aqueous alkali metal hydroxide solution: hydrogen peroxide is 1: 10 to 25: 0.01 to 0.25 at 40 to 80 ° C for 1 to 4 hours. After separation of the extract, the lignocellulosic residue is extracted with 5 to 15 times by weight of 5 to 10% by weight. with an aqueous solution of an alkali metal hydroxide at 20-30 ° C for 1-4 hours, the xylanes are precipitated and dried from the alkali extract. The process for preparing xylans from lignocellulosic materials has utility in the pulp, paper, chemical, textile and pharmaceutical industries).

(13) B1 Int. Cl. ⁵

OJ C 08 B 37/14 C 07 H 1/08 t

CS 272 877 B1

The invention relates to a process for the preparation of xylans from ligno-cellulosic materials.

D-xylan-type hemicelluloses with a different content of L-arabinose and uronic acids (predominantly 4-O-methyl-D-glucuronic acid) are found in the cell walls of the wood and fiber tissues of plants (wood, grass, cereals) in amounts of approximately 15 to 35

The prior art methods of isolating xylans from lignocellulosic materials include often complex techniques and energy-intensive operations (different types of thermal pretreatment, multi-stage extraction, use of nitrogen atmosphere), with delignification largely performed by chlorine compounds, which is not appropriate from an environmental point of view [τ. E. Timell: Adv. Carbohydr. Chem. 19, 255 0964); CS AO 195 527; CS AO 231,686; CS AO 244 59l] · The disadvantage of the procedures is the technical, economic and energy demands. Obtained hemicelluloses often have a significantly reduced molecular weight and oemic purity, and their purification is disadvantageous from an economic point of view.

The above-mentioned disadvantages are substantially eliminated by the process for preparing xylanes from the ligno-cellulosic materials of the invention, which consists in that 3 to 10 wt. an aqueous alkali metal hydroxide solution and hydrogen peroxide, wherein the weight ratio of lignocellulosic material: aqueous alkali metal hydroxide solution to hydrogen peroxide is 1: 10 to 25: 0.01 to 0.25 at 40 to 80 ° C for 1 to 4 hours, after separation of the extract, the ligno-cellulosic residue is extracted with 5 to 15 times by weight of 5 to 10% by weight. aqueous alkali metal hydroxide solution at 20-30 ° C for 1-4 hours, the xylanes precipitated and dried from the alkali extract.

An advantage of the proposed process for the preparation of xylans from lignocellulosic materials over the prior art is that it allows simple processes to obtain xylanes of relatively high purity and molecular weight in a yield of 50-90% of the D-xylan-type hemicelluloses present in the flood. The process does not burden the waste water with chlorine compounds or other toxic degradation products, it is not machinery intensive. a more violent advantage is that the extraction residue, i.e.. ligno-cellulosic material is suitable for feeding and preparation of feed biomass and the like.

Example 1

A suspension of 100 g of air-dry beech sawdust in 2 L of 3 wt. % aqueous sodium hydroxide solution containing 37 ml of 30 wt. The aqueous hydrogen peroxide solution was heated to 50 ° C with stirring and maintained at that temperature for 2 hours. The extract is then filtered through a glass cloth and added to the sawdust extraction residue successively over a period of 1 hour to wash 115 wt. aqueous sodium hydroxide solution. From the combined extracts, xylan is obtained in a yield of 20.5% by weight by precipitation with two to three times the volume of ethyl alcohol. (based on flood sawdust) with a content of 93% by weight. xylose in the proportion of neutral saccharides and with an average molecular weight Sw = 11 900.

Example 2

The procedure was as in Example 1 except that 115 wt. aqueous potassium hydroxide solution containing 7 ml of 30 wt. aqueous hydrogen peroxide solution, 70 ° C for 1 hour. Xylan was obtained in a yield of 19% by weight (wood), with a content of 95% by weight. xylose in the proportion of neutral saccharides and Bw = 13,000.

Example 3

The procedure was as in Example 1 except that 4 wt. aqueous potassium hydroxide solution containing 85 ml of 30% by weight of potassium hydroxide; % aqueous hydrogen peroxide solution, at 70 ° C for 1 hour and for washing with 5 wt. aqueous potassium hydroxide solution for 2 hours. The xylan was obtained in a yield of 17.5% by weight. (wood), containing by weight 92% xylose and with Bw = 12 500,

Example 4

The procedure is as in Example 1 except that the starting material is used

CS 272 877 B1 is an air-dry corn spindle which is extracted with 2.5 l of a 10% by weight aqueous potassium hydroxide solution which contains 3.5 ml of 30% by weight. of an aqueous solution of hydrogen peroxide at 80 ° C for 1 hour. 10% w / w is used to wash the fibrous residue. aqueous potassium hydroxide solution. Xylan was obtained in a yield of 26% by weight. (based on lignocellulosic material) with a content by weight of 91%. xylosis and arabinose, in a molar ratio of 100: 16 and fc = 18,000.

Example 5

The procedure is as in Example 1, except that chopped wheat straw is used as the starting material and is extracted with 10 wt. aqueous sodium hydroxide solution containing 17 ml of 30 wt. aqueous hydrogen peroxide solution at 40 ° C for 4 hours, and the extraction residue was washed with 10 wt. aqueous sodium hydroxide solution. 20% by weight of xylan is obtained. (on straw) with a content of 93% by weight. xylosis and arabinose, in a molar ratio of 100: 12 and fflw = 23,100.

The invention can be widely used in the production of xylans, which are used as auxiliaries in the manufacture of paper, tablet formulations, in cosmetics, in the textile and chemical industries.

Claims (1)

OBJECT OF THE INVENTION Process for preparing xylans from lignocellulosic materials, characterized in that 3 to 10 wt. an aqueous alkali metal hydroxide solution and hydrogen peroxide, wherein the weight ratio of lignocellulosic material: aqueous alkali metal hydroxide: hydrogen peroxide solution is 1: 10 to 25: 0.01 to 0.25 at 40 to 80 ° C for 1 to 4 hours, after separation of the extract, the lignocellulose residue is extracted with 5 to 15 times by weight of 5 to 10% by weight. aqueous alkali metal hydroxide solution at 20-30 ° C for 1-4 hours, the xylanes precipitated and dried from the alkali extract.