阅读说明：本技术 一种以禾本科植物为原料制备木聚糖和高纯木质素的方法 (Method for preparing xylan and high-purity lignin by using gramineous plants as raw materials ) 是由 金贞福 邵金力 于 2020-12-22 设计创作，主要内容包括：本发明公开了一种以禾本科植物为原料制备木聚糖和高纯木质素的方法,包括步骤：(1)预水解：将禾本科植物原料在稀碱液中浸泡0～48小时后进行预水解处理,预水解处理步骤为：控制禾本科植物原料与稀碱液质量比为1∶(2～15),在130～170℃中预水解30～90min,完成后冷却至室温,固液分离；(2)木质素的分离：预水解液用酸液调节pH值至1～3,使木质素沉淀,固液分离出木质素；(3)木聚糖的分离：步骤(2)分离的清液,用碱液调节pH值至6～9,浓缩后滴入10～30倍的乙醇中,使木聚糖沉淀,固液分离出木聚糖。本发明选取禾本科植物为原料,用稀碱液作为预水解液,同时获得木聚糖和高纯度木质素,开创了纤维素、半纤维素和木质素,即“三素”高值化利用的新途径。(The invention discloses a method for preparing xylan and high-purity lignin by using gramineous plants as raw materials, which comprises the following steps: (1) pre-hydrolysis: soaking the gramineous plant raw material in a dilute alkali liquor for 0-48 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw materials to the dilute alkali liquor to be 1: 2-15, carrying out prehydrolysis at 130-170 ℃ for 30-90 min, cooling to room temperature after completion, and carrying out solid-liquid separation; (2) separation of lignin: adjusting the pH value of the prehydrolysis liquid to 1-3 by using acid liquor, precipitating lignin, and carrying out solid-liquid separation to obtain the lignin; (3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid separated in the step (2) to 6-9 by using alkali liquor, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain the xylan. The invention selects gramineous plants as raw materials, uses dilute alkali liquor as prehydrolysis liquid, simultaneously obtains xylan and high-purity lignin, and creates a new way for high-value utilization of cellulose, hemicellulose and lignin, namely 'three elements'.)

1. A method for preparing xylan and high-purity lignin by using gramineous plants as raw materials is characterized by comprising the following steps:

(1) pre-hydrolysis: soaking the gramineous plant raw material in a dilute alkali liquor for 0-48 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw materials to the dilute alkali liquor to be 1: 2-15, carrying out prehydrolysis at 130-170 ℃ for 30-90 min, cooling to room temperature after the prehydrolysis is finished, and carrying out solid-liquid separation on the prehydrolysis liquid and the material sheet; the dilute alkali solution is NaOH or KOH aqueous solution with the mass concentration of 0.1-1.0%;

(2) separation of lignin: adjusting the pH value of the prehydrolysis liquid obtained in the step (1) to 1-3 by using acid liquor to precipitate lignin, and carrying out solid-liquid separation to obtain the lignin;

(3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid obtained after lignin separation in the step (2) to 6-8 by using alkali liquor, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain xylan.

2. The method according to claim 1, wherein in step (1), the graminaceous plant material is bamboo, bamboo processing residues, straw, wheat straw, corn stover, bagasse, reed or miscanthus.

3. The method as claimed in claim 1, wherein in the step (1), the gramineous plant raw material is a dry stock, and the natural water content is 8-12%.

4. The method according to claim 1, wherein in the step (1), the dilute alkali solution is NaOH or KOH aqueous solution with the mass concentration of 0.4-0.8%, the mass ratio of the gramineous plant raw material to the dilute alkali solution in the prehydrolysis treatment is 1: 10-15, and the prehydrolysis temperature is 150-170 ℃.

5. The method according to claim 1, wherein in the step (2), the acid solution is 1-6M hydrochloric acid, sulfuric acid or acetic acid.

6. The method according to claim 1, wherein in the step (2), the solid-liquid separation is performed by centrifugal separation.

7. The method of claim 1, wherein in the step (3), the alkali solution is 1-6M NaOH or KOH aqueous solution.

8. The method according to claim 1, wherein in the step (3), the solid-liquid separation is performed by centrifugal separation.

9. The method according to claim 1, comprising the steps of:

(1) pre-hydrolysis: soaking a gramineae raw material with natural water content of 8-12% in a dilute alkali liquor for 12-36 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw material to the dilute alkali liquor to be 1: 10-15, carrying out prehydrolysis at the temperature of 150-170 ℃ for 60-90 min, cooling to room temperature after the prehydrolysis is finished, and carrying out solid-liquid separation on the prehydrolysis liquid and the material sheet; the dilute alkali solution is a NaOH aqueous solution with the mass concentration of 0.4-0.8%;

(2) separation of lignin: adjusting the pH value of the prehydrolysis liquid obtained in the step (1) to 2 by using 4M hydrochloric acid to precipitate lignin, and carrying out solid-liquid separation to obtain the lignin;

(3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid obtained after lignin separation in the step (2) to 7 by using a 4M NaOH aqueous solution, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain the xylan.

Technical Field

The invention relates to the technical field of dissolving pulp preparation, in particular to a method for preparing xylan and high-purity lignin by using gramineous plants as raw materials.

Background

The preparation of dissolving pulp has two technological processes, prehydrolysis sulfate process and acid sulfite process. Generally, raw materials with high hemicellulose content and high resin content must be cooked by a prehydrolysis sulfate process to obtain an acceptable pulp, and raw materials with low hemicellulose content can be cooked by an acid sulfite process. The prehydrolysis sulfate process has strong adaptability to raw materials compared with the sulfite process, the produced dissolving pulp has high alpha-cellulose content, the black liquor alkali recovery rate is high, the environmental pollution is small, and the advantages of the sulfate process and the sulfite process are integrated. Therefore, most enterprises produce dissolving pulp by using the prehydrolysis sulfate process. The prehydrolysis sulfate process includes two stages, prehydrolysis and sulfate cooking, in which acid, water and steam are usually subjected to the prehydrolysis treatment. Water prehydrolysis, long heating time, high steam consumption, low production efficiency, large amount of waste liquid after hydrolysis and difficult treatment; if acid prehydrolysis is adopted, more hemicellulose can be removed, the operation temperature is low, but the temperature and time are not easy to control, especially the pH value of reaction waste liquid is low, the equipment is seriously corroded, the waste liquid after hydrolysis is difficult to treat, and cellulose can undergo acid hydrolysis in an acid solution to crack cellulose macromolecules, so that the pulp yield is reduced. Many enterprises use steam for prehydrolysis, but most of hydrolysate after prehydrolysis is still adsorbed in the material sheet and neutralized by a certain amount of cold white liquid in the subsequent process, the neutralized waste liquid and the waste liquid after prehydrolysis are subjected to alkali recovery, and the steam prehydrolysis easily generates hydrolysis nonuniformity, so that xylan, ash and the like are not easily removed. These problems are more prominent in gramineous plants, which have higher xylan and ash contents than wood.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for preparing xylan and high-purity lignin by using gramineous plants as raw materials, and solves the technical problem of designing a simple and pollution-free prehydrolysis method.

The method for preparing xylan and high-purity lignin by using gramineous plants as raw materials comprises the following steps:

(1) pre-hydrolysis: soaking the gramineous plant raw material in a dilute alkali liquor for 0-48 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw material to the dilute alkali liquor to be 1: 2-15, carrying out prehydrolysis at 130-170 ℃ for 30-90 min, cooling to room temperature after the prehydrolysis is finished, carrying out solid-liquid separation on the prehydrolysis liquid and material sheets, and enabling the material sheets to enter a sulfate cooking process; the dilute alkali solution is NaOH or KOH aqueous solution with the mass concentration of 0.1-1.0%;

(2) separation of lignin: adjusting the pH value of the prehydrolysis liquid obtained in the step (1) to 1-3 by using acid liquor to precipitate lignin, and carrying out solid-liquid separation to obtain the lignin;

(3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid obtained after lignin separation in the step (2) to 6-8 by using alkali liquor, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain xylan.

The core of the invention is to select the gramineae plants with lignin-polysaccharide complex and unique structure of ester bond taking ferulic acid and p-coumaric acid as bridge as raw materials, and dilute alkali liquor is used as prehydrolysis liquid to obtain xylan and high-purity lignin at the same time, thus opening a new way for high-value utilization of cellulose, hemicellulose and lignin, namely 'three elements'.

The lignin-polysaccharide complex in the superfine structure of the fiber cell wall of the gramineous plant comprises a benzyl ether bond, a phenyl glycoside bond, a hemiacetal and an acetal bond which are arranged on needle wood and broad wood, and also has a unique structure of an ester bond taking ferulic acid and p-coumaric acid as a bridge, and the ester bond saponification reaction in alkali liquor is degraded, so that the separation of lignin and hemicellulose is improved, and the hemicellulose is smoothly removed. This is an inherent factor in the selection of graminaceous plants as raw materials and also a reason for the selection of dilute alkali solutions as prehydrolysis solutions.

The hemicellulose of Gramineae plant is mainly xylan, which usually contains acetyl on main chain, and if prehydrolysis is carried out with water, the hydrolysate is acidic (pH 3.5-5.5), and in order to neutralize acid liquor, a certain amount of alkali liquor is added to neutralize for 30min at 70-80 deg.C. However, the pH value of the pre-hydrolyzed solution is neutral by using the dilute alkali solution for pretreatment, and the neutralization is not needed, which is also the reason for selecting the dilute alkali solution as the pre-hydrolyzed solution.

Dilute alkali solution is used as prehydrolysis liquid, and xylan and lignin can be extracted simultaneously. Adjusting the pH value of the prehydrolysis liquid to 1-3 by using acid to precipitate lignin, centrifugally separating, drying, sealing and packaging to obtain the lignin, wherein the purity of the lignin prepared by using the method reaches 95-100%, and the lignin is rich in phenolic hydroxyl groups; concentrating the supernatant after lignin precipitation, dripping into ethanol to precipitate xylan, centrifuging, drying, sealing and packaging.

Preferably, in the step (1), the gramineous plant raw material is bamboo, bamboo processing residues, straw, wheat straw, corn stalks, bagasse, reed or awn stalks and the like.

The hard raw materials such as bamboo, bamboo processing residues, Chinese silvergrass stalks and the like are soaked in a dilute alkali liquor for one day before prehydrolysis, so that the yield of lignin and xylan can be improved. The non-hard materials may also be prehydrolyzed directly without soaking.

Preferably, in the step (1), the gramineous plant raw material is a dry stock, and the natural water content is 8-12%.

Preferably, in the step (1), the dilute alkali solution is NaOH or KOH aqueous solution with the mass concentration of 0.4-0.8%, the mass ratio of the gramineous plant raw materials to the dilute alkali solution is 1: 10-15 during the prehydrolysis treatment, and the prehydrolysis temperature is 150-170 ℃, preferably 160 ℃.

Preferably, in the step (2), the acid solution is 1-6M (mol/L), preferably 3-5M, and more preferably 4M hydrochloric acid, sulfuric acid or acetic acid.

Preferably, in the step (2), the solid-liquid separation is performed by centrifugal separation.

Preferably, in the step (3), the alkali solution is 1-6M, preferably 3-5M, and more preferably 4M NaOH or KOH aqueous solution.

Preferably, in the step (3), the solid-liquid separation is performed by centrifugal separation.

Some preferred embodiments of the present invention specifically include the steps of:

(1) pre-hydrolysis: soaking a gramineae raw material with natural water content of 8-12% in a dilute alkali liquor for 12-36 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw material to the dilute alkali liquor to be 1: 10-15, carrying out prehydrolysis at the temperature of 150-170 ℃ for 60-90 min, cooling to room temperature after the prehydrolysis is finished, and carrying out solid-liquid separation on the prehydrolysis liquid and the material sheet; the dilute alkali solution is a NaOH aqueous solution with the mass concentration of 0.4-0.8%;

(2) separation of lignin: adjusting the pH value of the prehydrolysis liquid obtained in the step (1) to 2 by using 4M hydrochloric acid to precipitate lignin, and carrying out solid-liquid separation to obtain the lignin;

(3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid obtained after lignin separation in the step (2) to 7 by using a 4M NaOH aqueous solution, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain the xylan.

The better embodiment of the invention comprises the following steps:

(1) pre-hydrolysis: soaking a gramineae raw material with natural water content of 8-12% in a dilute alkali liquor for 12-36 hours, and then carrying out pre-hydrolysis treatment, wherein the pre-hydrolysis treatment comprises the following steps: controlling the mass ratio of the gramineous plant raw material to the dilute alkali liquor to be 1: 10, carrying out prehydrolysis at 160 ℃ for 90min, cooling to room temperature after the prehydrolysis is finished, and carrying out solid-liquid separation on the prehydrolysis liquid and the tablets; the dilute alkali solution is a NaOH aqueous solution with the mass concentration of 0.5%;

(2) separation of lignin: adjusting the pH value of the prehydrolysis liquid obtained in the step (1) to 2 by using 4M hydrochloric acid to precipitate lignin, and carrying out solid-liquid separation to obtain the lignin;

(3) and (3) separating xylan: and (3) regulating the pH value of the clear liquid obtained after lignin separation in the step (2) to 7 by using a 4M NaOH aqueous solution, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, and carrying out solid-liquid separation to obtain the xylan.

The positive progress effects of the invention are as follows:

the core of the invention is to select the gramineae plants with lignin-polysaccharide complex and unique structure of ester bond taking ferulic acid and p-coumaric acid as bridge as raw materials, and dilute alkali liquor is used as prehydrolysis liquid to obtain xylan and high-purity lignin at the same time, thus opening a new way for high-value utilization of cellulose, hemicellulose and lignin, namely 'three elements'.

The invention promotes the removal of xylan, ash and part of lignin on the premise that cellulose is less degraded; simultaneously separating xylan and lignin from the prehydrolysis liquid; alkali is not required to be added for neutralization before cooking, and simultaneously, the raw materials are impregnated, so that subsequent cooking is favorably and smoothly carried out; easy operation and less working procedures, and achieves the purposes of energy conservation, emission reduction, consumption reduction and clean production.

Detailed Description

The present invention will be further described with reference to the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.

Examples 1 to 8

Example 1 the preparation procedure was:

preparing materials: drying bamboo chips as raw materials to natural water content of 8% -12%, and soaking in 0.5% NaOH water solution for one day;

pre-hydrolysis: adding 1 part by weight of bamboo chips and 10 parts of 0.5% NaOH aqueous solution into a reaction kettle, pretreating for 90 minutes at 160 ℃, cooling to room temperature after the pretreatment is finished, and sieving by a 60-mesh sieve to separate prehydrolysis liquid and tablets;

separation of lignin: adjusting pH of the prehydrolysis solution to 2 with 4M hydrochloric acid to precipitate lignin, centrifuging, drying, and sealing and packaging to obtain refined lignin with yield of 6.5%;

and (3) separating xylan: centrifuging the supernatant, adjusting pH to 7 with 4M NaOH, concentrating, dripping into 10-30 times of ethanol to precipitate xylan, centrifuging, drying, and sealing and packaging to obtain refined xylan with yield of 4.2%; and (5) distilling and recovering the ethanol, and recycling.

Examples 2-8 the preparation process was as in example 1, with the prehydrolysis parameters adjusted, and table 1 below shows the prehydrolysis parameters such as lye concentration, solid-to-liquid ratio, temperature, time, etc. and xylan and lignin yields for examples 1-8.

TABLE 1 prehydrolysis parameters and xylan and lignin yields for examples 1-8

Note: in the table, the alkali is sodium hydroxide (NaOH), xylan (g) and lignin (g) are based on 50g of raw materials, and the pH value is the pH value of prehydrolyzed liquid.

The core idea of the invention is to select the gramineae plants with the lignin-polysaccharide complex body with the unique structure of the ester bond taking ferulic acid and p-coumaric acid as bridges as raw materials, and use dilute alkali liquor as prehydrolysis liquid to obtain xylan and high-purity lignin at the same time, thereby opening a new way for high-value utilization of cellulose, hemicellulose and lignin, namely 'three elements'.