Method for acquiring lignin with high phenolic hydroxyl group content from residues after hemicelluloses degradation conversion

Abstract

The invention discloses a method for acquiring lignin with a high phenolic hydroxyl group content from residues after hemicelluloses degradation conversion. The method comprises the following steps: uniformly mixing water, a polar aprotic solvent of a low melting point and a small amount of an alkali so as to obtain an extraction agent, mixing the extraction agent with lignocelluloses formed afterxylooligosaccharide and xylose are extracted or furfural is prepared, increasing the temperature to 150-180 DEG C, conducting a heat-preservation reaction to extract for 90-180 minutes, rapidly decreasing the temperature to 40 DEG C or lower after the reaction is completed, conducting filtration so as to obtain filtrate, washing filter residues twice to three times by using a same type of the polar aprotic solvent which is free of water or alkali and has a same low melting point, completely combining collected filtrate, recycling an organic solvent through distillation, adding 2-3 times of the volume of water into a residual water phase, adjusting the pH value of the solution to 2.0-3.0 by using sulfuric acid, leaving the solution to stand for 2-4 hours to enable lignin to settle down, and conducting filtration, washing and drying on the product, so as to obtain the lignin. By adopting the method, the extraction rate of the lignin in the residues is up to 75% or greater, the loss rateof cellulose in the residues is less than 17%, and high extraction selectivity is achieved for the lignin.

Description

technical field [0001] The invention belongs to the technical field of biochemical industry, and in particular relates to a method for obtaining lignin with high phenolic hydroxyl content from xylooligosaccharide / xylose extraction residue or furfural residue. Background technique [0002] Lignin is a macromolecular amorphous phenolic natural polymer, which can be divided into three basic structural units according to the position and content of methoxy groups in lignin: syringyl lignin, guaiacyl lignin and p-hydroxyl phenyl lignin. Since lignin is rich in active groups such as: phenolic hydroxyl group, carboxyl group, methoxyl group, etc., a variety of chemical reactions can occur, so lignin and its chemically modified products can be used in the fields of polymer materials, among which the content of phenolic hydroxyl group The level is directly related to its reactivity and is an important indicator for its application in the field of polymer materials. [0003] At prese...

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Problems solved by technology

During this process, there is a risk of excessive supply of protons, leading to the degradation of hemicellulose, cellulose as well

Polar aprotic solvents are a class of organic solvents that do not self-deliver protons, reducing the risk of excessive proton supply. However, current research focuses on γ-valerolactone, γ-valerolactone, γ- - Polar aprotic solvents with high boiling points such as butyrolactone and dioxane, but these solvents are not very selective for the depolymerization and dissolution of lignin and cellulose, so it is not conducive to improving the purity of lignin

[0004] In order to solve the above drawbacks, currently the extracted lignin generally needs to be chemically modified to increase the phenolic hydroxyl content of lignin, such as phenolization modification, catalytic reduction, demethylation, ultrasonic and electrochemical methods, but These reactions add to the complexity and cost of the process, so increasing the phenolic hydroxyl content of lignin during extraction is of great value

[0005] Furfural, xylose, and xylo-oligosaccharides are typical hemicellulose degradation products. my country is the main producer of furfural, xylose, and xylo-oligosaccharides. The huge amount of residue is rich in lignin and cellulose, but at present it is mainly used as a raw material for the preparation of fuel or activated carbon, and the lignin resources are not fully utilized.

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