RU2620551C1 - Method of complex processing of birch wood - Google Patents

Abstract

FIELD: wood industry.

SUBSTANCE: method includes the step of prehydrolysis sawdust at atmospheric pressure with an aqueous solution of 2-3 wt % sulfuric acid at a liquor ratio 8, a temperature of 100°C, duration of 3-5 hours, with vigorous stirring wood delignification stage residue at atmospheric pressure with an aqueous solution containing 30 wt % acetic acid and 4-5 wt % hydrogen peroxide and the catalyst was 2 wt % sulfuric acid at 100°C, liquor ratio of 10-15, the duration of 3.5 hours, with vigorous stirring, acetic acid was distilled off from the spent cooking liquor, dilution of the distillation residue and precipitation of the lignin extraction it with liquor ratio 2 distilled water heated to 90°C, for 10 minutes to obtain a lignin sorbent.

EFFECT: reduced costs.

1 dwg, 3 tbl, 5 ex

Description

The invention relates to the chemical processing of wood, specifically to the production of xylose, cellulose and lignin sorbent from birch wood.

BACKGROUND OF THE INVENTION Methods for processing birch wood are known in the art, including pretreatment of an initial lignocellulosic feedstock to isolate xylose, obtaining cellulose from prehydrolyzed wood, and producing a lignin sorbent.

A known method of separating xylose from wood with a high xylan content (EP 1448801, publ. 08.25.2004), including preliminary grinding of birch wood chips, impregnation with dilute solutions of mineral acids, prehydrolysis of the prepared mass with steam at a temperature of 140-180 ° C for 5-40 minutes, washing and separating the xylose solution from the fibrous lignocellulosic mass. The maximum xylose yield was 78% of the initial hemicellulose content in birch wood, and the cellulose content in the solid residue of lignocellulose was 92.2-93.5% wt.

The disadvantages of this method are associated with the use of high temperatures, pressures, heated steam when processing chips, which requires high energy costs and compliance with increased safety measures, as well as with a limited range of end products (xylose and lignocellulose).

A known method of separating components of lignocellulosic biomass with a high lignin content in order to obtain pure cellulose (US 8603295, publ. 10.12.2013), including preliminary grinding of the biomass, heating at a temperature of 85-100 ° C for 10-60 minutes, treatment with hot steam at 180-200 ° C for 5-15 minutes with or without acid catalyst, xylose evolution (50-90% of the initial content in biomass), delignification of lignocellulose for 0.4-2 hours with a hydromodule 2-10 aqueous solution containing 40-60% ethanol with or without the addition of an acid catalyst, separation of liquor containing dissolved lignin (95-99% of the initial content in the biomass), residual hemicelluloses and extractives, washing and separation of the dispersed cellulose product. The resulting cellulosic product contains from 75 to 95% wt. cellulose, from 4 to 10% hemicelluloses and 5-8% wt. lignin, and can be used to produce bioethanol.

The disadvantages of this method are associated with the use of high temperatures, pressures, hot steam when processing biomass, which requires special equipment, high energy costs and increased safety measures, as well as the limited range of end products (lignin is removed with waste water).

A known method of producing a hydrolyzate of hemicelluloses and a cellulose product with a high content of α-cellulose (US 5139617, publ. 08/18/1992), including prehydrolysis of birch wood chips with sulfur dioxide (0.25% by weight of dry wood) or sulfuric acid (1% by weight of dry wood) in a digester with stirring at a hydromodule 3.5-6, temperature 155 ° C, for 1.5-2.5 hours, separation of the prehydrolyzate and lignocellulose, delignification of lignocellulose for 2.5 h in a solution containing Na ₂ SO ₃ , Na ₂ CO ₃ and anthraquinone, at 175 ° C and a hydromodule of 4.5. The yield of cellulose product obtained was 34.7-39.7% by weight, and the content of α-cellulose in it ranged from 91.7-94.5% by weight.

The disadvantages of this method are associated with the limited range of end products for the separation of birch wood, low yield of cellulosic product (less than 40% wt.), The use of high temperatures and pressures in the processes of prehydrolysis and delignification of birch wood chips.

A known method of producing a lignin sorbent (RU 2471550, publ. 10.01.2013), in which the raw material is a by-product - spent cooking solution for delignification of birch wood. After distilling off the acetic acid, lignin was precipitated by the addition of water. Then, to remove ligno humic and water-soluble substances from lignin, extraction was performed with a 0.4% sodium bicarbonate solution, washing and drying. The output of the sorbent was 76.1% wt.

The disadvantage of this method is the low quality of the sorbent due to incomplete leaching of sodium salts of ligno-humic substances from the pores of the sorbent, which reduce its sorption activity. This disadvantage is due to the use of sodium bicarbonate as an extractant. In addition, its use requires an additional stage of washing the sorbent, which complicates the production process and increases its cost.

The closest to the invention in terms of technological essence and the achieved result is a method of producing xylose and cellulose for chemical processing (RU 2512339, publ. 11/27/2012), including prehydrolysis of crushed birch wood with sulfur dioxide in an autoclave at a temperature of 140-145 ° C, liquid module 1 , 7-2.5 and a duration of 0.8-1.5 hours, separation of the dissolved hemicellulose hydrolyzate from solid pre-hydrolyzed biomass, sulphate cooking of pre-hydrolyzed birch wood at a temperature of 170 ° C for 2.25 hours.

The disadvantages of this method are the low yield of xylose (43.6-44.0% of its initial content in birch wood), the low yield of cellulose (35.7% of the mass of the original birch wood chips), the use of toxic sulfur dioxide at the stage of prehydrolysis of ground birch, which provides for special sealing of production equipment, effective ventilation of the room, individual respiratory protection, the use of heated steam, high temperatures and pressures at the stages of prehydrolysis and cooking, which requires special equipment, high energy costs and compliance with increased safety measures, as well as the limited range of target products.

The objective of the invention is to develop a simple, environmentally friendly and economical method of processing birch wood with obtaining an expanded assortment of valuable chemical products.

The technical result of the invention:

- the assortment of valuable chemical products was expanded due to the additional production of a lignin sorbent from the spent cooking solution of catalytic oxidative delignification of wood;

- increased economic efficiency by simplifying the method and increasing the assortment of obtained chemical products;

- simplified stages of prehydrolysis and delignification of birch wood due to their implementation at atmospheric pressure and low temperature;

- increased yield and quality of the lignin sorbent by replacing sodium bicarbonate with distilled water;

- increased yield of xylose and cellulose.

The technical result is achieved by the fact that in the method of complex processing of birch wood, including prehydrolysis of sawdust of birch wood to obtain xylose and delignification of prehydrolyzed wood to produce cellulose, according to the invention, the stage of prehydrolysis of sawdust is carried out at atmospheric pressure with an aqueous solution of 2-3% wt. sulfuric acid, with stirring, hydromodule 8, a temperature of 100 ° C, for 3-5 hours, and the stage of delignification of the wood residue is carried out at a temperature of 100 ° C and atmospheric pressure with an aqueous solution containing 30% wt. acetic acid, 4-5% wt. hydrogen peroxide and 2% wt. sulfuric acid, with stirring, a hydromodule 10-15, for 3.5 hours, while acetic acid is distilled off from the spent cooking solution, the bottom residue is diluted with a five-fold volume of water, then the precipitated lignin is extracted with distilled water at a temperature of 90 ° C for 10 minutes to obtain a lignin sorbent.

In contrast to the prototype in the present invention, prehydrolysis of birch wood is carried out at atmospheric pressure of 740-760 mm Hg (in the prototype 2710 mm Hg), a low temperature of 100 ° C (in the prototype 140-145 ° C), using a catalyst of 2-3% sulfuric acid (in the prototype sulfur dioxide). Subsequent oxidative delignification of the resulting wood residue is carried out at atmospheric pressure (in the prototype 5940 mm Hg), a temperature of 100 ° C (in the prototype 170 ° C) with an aqueous solution containing 30% wt. acetic acid, 4-5% wt. hydrogen peroxide and a catalyst of 2% wt. sulfuric acid (in the prototype sulfate cooking). In addition, in the present invention, a lignin sorbent is additionally obtained from the spent cooking liquor of catalytic oxidative delignification (in the prototype, lignin is removed with waste water).

In known methods for producing xylose from birch wood (EP 1448801, US 8603295, US 5139617), including the stage of prehydrolysis of wood with dilute solutions of mineral acids, use elevated temperatures and pressures, treatment with direct steam. In the known method for producing cellulose (RU 2490384), aspen raw materials are used aspen softwood chips, and cooking is carried out at a temperature of 90-98 ° C, atmospheric pressure, vigorous stirring in a mixture containing 25.2-26.7% wt. acetic acid, 3.9-5.6% wt., hydrogen peroxide, in the presence of sulfuric acid catalyst 2% by weight of wood chips. In the proposed method, birch wood is used, which is characterized by the presence of significant amounts of hemicelluloses and high density, which complicates the process of obtaining a cellulosic product. In the pulp and paper industry, birch wood for pulp is practically not used. Thanks to these distinguishing features, it was possible to:

- to expand the range of valuable chemical products due to the additional production of lignin sorbent released from the spent cooking solution of catalytic oxidative delignification of wood;

- to increase economic efficiency by simplifying the method and increasing the assortment of obtained chemical products;

- to simplify the method by carrying out the stages of prehydrolysis and delignification of birch wood at atmospheric pressure and low temperature;

- increase the yield of xylose to 77.1% wt. (in the prototype 44.0% wt.) and cellulose product up to 45.0% wt. (in the prototype 35.7% wt.);

- increase the yield of lignin sorbent to 85.6% wt. (in the patent RU 2471550 - 76.1% wt.) and its quality: adsorption 12 - up to 43.2%, adsorption on methylene blue - up to 92.0 mg / g, adsorption on gelatin - up to 223.5 mg / g (in the patent RU 2471550 - 39.0%, 89.6 mg / g, 183.0 mg / g, respectively).

The invention is illustrated in the figure, which shows a diagram of the integrated processing of birch wood into chemical products (see drawing). The method is confirmed by specific examples.

Example 1. 10 g of air-dried sawdust of birch fraction 2-5 mm were placed in a three-neck round-bottom flask made of heat-resistant glass with a volume of 500 ml, equipped with a stirrer, reflux condenser and thermometer. Then poured 80 ml of an aqueous solution of 2% wt. sulfuric acid. The hydrolysis of wood hemicelluloses was carried out at atmospheric pressure, a temperature of 100 ° C, for 4 hours, with a stirring intensity of 14 r / s. After a predetermined time, the resulting hydrolyzate was cooled to room temperature, filtered on a Buchner funnel on a paper filter under vacuum, poured into a bottle, closed with a ground lid and analyzed on a VARIAN-450 gas chromatograph. The hydrolyzate sample was previously derivatized according to the method of [Ruiz-Matute A.I., Hernandez-Hernandez O., Rodriguez-Sanchez S., Sanz M.L., Martinez-Castro I. Derivatization of carbohydrates for GC and GC-MS analyses J. Chromatogr. B. - 2011. - V. 879. - P. 1226-1240.] With the formation of trimethylsilyl derivatives. The yield of xylose was 57.3% wt. from the initial content of hemicelluloses in birch (see table 1). The wood residue was dried in an oven at a temperature of 103 ° C. Wood conversion was determined by the weight method with an accuracy of ± 2-3%.

Then, oxidative delignification of the wood residue was carried out in a glass reactor equipped with a mechanical stirrer and reflux condenser. The delignification solution was prepared from a mixture of glacial acetic acid, the content of which was 30% wt., Hydrogen peroxide 5% wt. and distilled water. As the catalyst used sulfuric acid in an amount of 2% by weight of wood residue. The wood residue was added to the reactor with the reaction solution in the amount remaining after the prehydrolysis step and delignified at 100 ° С, hydromodule 15 and duration of 3.5 hours. The solid cellulose product was separated from the cooking solution by filtration on a Buchner funnel, washed until neutral washing water, dried in a drying cabinet SNOL-3,5 at a temperature of 103 ± 2 ° C until a constant weight was achieved and analyzed. The mass of the sample was considered constant if the difference between two successive weighings carried out after 6 hours of drying did not exceed 0.1% of the mass of the test sample. The yield of cellulose product amounted to 45.0% by weight of the air-dry wood residue after prehydrolysis, and the content of cellulose in it was 88.3%, residual hemicellulose was 8.8% wt. and lignin -1.2% wt. (see tab. 2).

In order to isolate lignin from the spent cooking liquor, acetic acid was distilled off on a rotary evaporator at a temperature of 50 ° C. A five-fold volume of water was added to the bottom residue and lignin was precipitated. To obtain a lignin sorbent, precipitated lignin with a moisture content of 75-80% was treated with hydromodule 2 for 10 minutes with hot distilled water heated to 90 ° C. Then the lignin sorbent was separated from the solution by filtration and dried in air. The output of the lignin sorbent was 76.6% wt.

Examples 2-5. Carried out analogously to example 1. The differences are in the parameters of the processes of preliminary hydrolysis (duration, concentration of H ₂ SO ₄ ) and delignification (concentration of H ₂ O ₂ , hydromodule).

The effect of the concentration of sulfuric acid catalyst and the duration of the prehydrolysis stage of birch wood on the xylose yield and the content of the main components in the wood residue (temperature 100 ° C, water module 8)

Thus, a simple, environmentally friendly and economical method of complex processing of birch wood with the production of xylose, cellulose and lignin sorbent is proposed.

Claims (1)

A method of complex processing of birch wood, including prehydrolysis of sawdust of birch wood to obtain xylose and delignification of prehydrolyzed wood to obtain cellulose, characterized in that the stage of prehydrolysis of sawdust is carried out at atmospheric pressure with an aqueous solution of 2-3 wt.% Sulfuric acid, with stirring, hydromodule 8 at a temperature of 100 ° C for 3-5 hours, and the stage of delignification of the wood residue is carried out at a temperature of 100 ° C and atmospheric pressure with an aqueous solution containing 30 wt.% acetic acid oty, 4-5 wt.% hydrogen peroxide and 2 wt.% sulfuric acid, with stirring, a hydromodule 10-15, for 3.5 hours, while acetic acid is distilled from the spent cooking solution, the bottom residue is diluted with five times the volume of water, then the precipitated lignin is extracted with distilled water at a temperature of 90 ° C, for 10 minutes to obtain a lignin sorbent.

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