WO2020082427A1

WO2020082427A1 - Method for using poplar bark to produce acetylation-grade dissolving pulp

Info

Publication number: WO2020082427A1
Application number: PCT/CN2018/114525
Authority: WO
Inventors: 吴朝军; 于冬梅; 李荣刚
Original assignee: 齐鲁工业大学
Priority date: 2018-10-22
Filing date: 2018-11-08
Publication date: 2020-04-30
Also published as: US20200173103A1; CN109403115A; BE1026675B1; BE1026675A1; CN109403115B

Abstract

A method for using poplar bark to produce acetylation-grade dissolving pulp: adding a promoter for pre-hydrolysis; Soda/AQ boiling stage I; Soda/AQ boiling stage II; O_PD_QE_PP bleaching; and enzyme co-processing. A high purity and highly reactive poplar bark acetylation-grade dissolving pulp is thus prepared. The chemical products used are clean and environmentally friendly, and the production process is clean.

Description

Method for producing vinegar-grade dissolving pulp by using poplar veneer

Technical field

The invention relates to the technical field of preparation of dissolving pulp, in particular to a method for producing vinegar-grade dissolving pulp using poplar wood veneer.

Background technique

At present, the production of cellulose acetate in the world is nearly 1 million tons, while the annual output of cellulose acetate in China is nearly 400,000 tons, and the annual consumption of vinegar-grade wood dissolving pulp is about 300,000 tons. The vinegar-grade dissolving pulp is mainly used to prepare triacetate fiber Element and cellulose diacetate, the hydroxy groups at the three positions of cellulose glucose unit in the dissolving pulp are almost completely acetylated to obtain cellulose triacetate (degree of substitution> 2.7), and cellulose triacetate is hydrolyzed to obtain Cellulose diacetate (degree of substitution 2.4-2.6), the reaction process is shown in the following formula.

Cellulose triacetate is widely used in film, liquid crystal display polarizing film, reverse osmosis film, etc., while cellulose diacetate is widely used in cigarette filters, plastic products, etc. Cellulose acetate has high requirements on its raw material-acetate grade dissolving pulp, namely high purity and high reactivity. At present, China can only produce vinegar grade cotton pulp, while high purity, high reactivity vinegar Grade wood dissolving pulp mainly depends on import.

At home and abroad, wood is used as the raw material to prepare vinegar-grade dissolving pulp. The process usually adopts pre-hydrolysis + sulfate cooking + ECF bleaching process or acid sulfite cooking + ECF bleaching + cold alkali extraction process. In order to improve the pre-hydrolyzed hemicellulose Removal rate, usually adding inorganic acid or organic acid, which increases the corrosiveness of the equipment. In order to improve the delignification rate, some researchers use the KP method of high sulfidation cooking technology, but the high sulfidation is easy to produce odors such as methyl mercaptan, dimethyl sulfide; in order to reduce the ash content of dissolving pulp, dissolving pulp production enterprises Acid treatment should be carried out after bleaching the pulp, but the low pH value will easily cause acid hydrolysis of some cellulose in the dissolving pulp and reduce the polymerization; in order to increase the α-cellulose content of the vinegar-grade dissolving pulp, some scholars use cold alkali extraction However, this will seriously reduce the reactivity of vinegar grade dissolving pulp and acetic anhydride. Some scholars in Egypt used microwave radiation and high-concentration zinc chloride to treat vinegar grade dissolving pulp to improve its reactivity, but the technology is not yet mature. The United States patent report uses strong acid to treat the vinegar-grade dissolving pulp to improve its purity, but this technology has a high degree of pollution and high cost. Several domestic universities are also conducting research and development of this technology, mainly including South China University of Technology, Beijing Forestry University, Donghua University and other units have made some progress in the research and development of this technology, mainly concentrated in eucalyptus, Acacia Prepare vinegar-grade dissolving pulp from wood and pine.

As a wood processing residue, poplar veneer is cheap and has sufficient raw materials. It is reported that the annual production of wood processing residues in China is about 50 million tons. Poplar veneer as a type of wood processing residue has a comprehensive cellulose content of about 82 %, Of which the content of α-cellulose is about 44%. If poplar wood veneer is used as a raw material to produce highly reactive vinegar grade dissolving pulp, it will be of great benefit to the development of vinegar grade dissolving pulp raw materials. However, there is no record of making vinegar grade dissolving pulp using poplar veneer at home and abroad.

Summary of the invention

In order to solve the above technical gap that no poplar board skin is used to prepare vinegar grade dissolving pulp, the present application discloses a method for producing vinegar grade dissolving pulp using poplar wood board skin.

Pre-hydrolysis technology with added additives selectively removes hemicellulose in poplar wood bark materials while selectively protecting cellulose and swells fiber cells, then using staged cooking to selectively remove lignin and hemicellulose , Controlling the depolymerization of cellulose, the slurry is oxygen delignified by hydrogen peroxide / chlorine dioxide bleaching with chelating agent / hot alkali extraction with hydrogen peroxide / hydrogen peroxide bleaching (O _P D _Q E _P P) Remove the remaining lignin and hemicellulose, improve the whiteness of the pulp and adjust the degree of polymerization of the dissolving pulp, and perform biological enzyme synergistic treatment on the pulp after bleaching to further increase its vinegar reaction value (PV value) and reduce ash content And dichloromethane (DCM) extract content. After treatment with this process, the purity and reactivity of the vinegar-grade dissolving pulp are improved.

The present invention is obtained through the following steps:

A method for producing vinegar-grade dissolving pulp using poplar board skin includes the following steps:

(1) Adding auxiliary agent for pre-hydrolysis: liquid ratio 1: (4 ～ 10), adding amount of hydrolysis auxiliary agent is 0.1 ～ 2.0% of dry matter mass of poplar wood veneer, hydrolysis temperature 80 ～ 170 ℃, holding time 10 ～ 180 minutes The hydrolysis aid is a mixture obtained by mixing sodium borate, magnesium sulfate, nonylphenol polyoxyethylene ether phosphate and tetrasodium iminodisuccinate according to a mass ratio of 1: 1: 1: 1;

(2) Soda / AQ cooking stage Ⅰ;

(3) Soda / AQ cooking section Ⅱ;

(4) O _P D _Q E _P P bleaching;

(5) Enzyme synergistic treatment: pulp concentration 2 ～ 10%, temperature 30-50 ℃, treatment time 60min, pH = 4.0 ～ 7.0, dosage of polyaspartic acid is 0.01% -1.0% of absolute dry pulp quality, OP- 13 The dosage is 0.001-0.01% of the mass of the absolute dry pulp, the dosage of OP-15 is 0.001-0.01% of the mass of the absolute dry pulp, the dosage of the endo-cellulase is 0.1 ～ 0.6IU / gpulp, and the dosage of the xylanase is 2 ～ 4XU / gpulp, the dosage of pectinase is 0.1 ～ 10IU / gpulp.

The preferred Soda / AQ cooking stage I process conditions are: the amount of alkali used as Na ₂ O is 5-15% of the quality of the absolute dry pulp, the liquid ratio is 1: (3-8), and the amount of magnesium hydroxide is the quality of the absolute dry pulp 0.5%, the dosage of sodium sulfite is 1.0 ～ 10.0% of the mass of the absolute dry pulp, the dosage of AQ is 0.05% of the mass of the absolute dry pulp, the temperature is 80 ～ 120 ℃, and the holding time is 10 ～ 180 minutes.

The preferred Soda / AQ cooking stage II process conditions are: the amount of alkali used as Na ₂ O is 5-25% of the quality of the dry pulp, the amount of magnesium hydroxide is 0.5% of the quality of the dry pulp, and the amount of sodium sulfite is the quality of the dry pulp 1.0 to 10.0%, liquid ratio 1: (3 to 10), AQ dosage is 0.05% of the quality of absolute dry pulp, temperature 140 to 180 ℃, holding time 10 to 240 minutes.

Preferably O _{_P} D _Q E _{P P} bleaching conditions were: O _P bleaching oxygen pressure of 0.4 ~ 0.6Mpa, pulp consistency 10%, MgSO ₄ in an amount of mass of dry pulp 0.6%, NaOH in an amount of dry pulp mass 1.0 ～ 3.0%, the dosage of H ₂ O ₂ is 0.5 ～ 3.0% of the quality of absolute dry pulp, the temperature is 70 ～ 110 ℃, and the temperature is kept for 60min.

Preferably O _{_P} D _Q E _{P P} bleaching conditions were: Q _D bleaching reaction time 10 to 120 minutes, T = 30 ± 2 ℃, pulp consistency 2 ~ 8%, pH = 1 ~ 3, the amount of sodium chlorite It is 0.2-6.0% of the quality of the absolutely dry pulp, and the amount of IDS is 0.01-1.0% of the quality of the absolutely dry pulp.

Preferably O _{_P} D _Q E _{P P} bleaching conditions were: reaction time Ep Extraction Technology of 30 ~ 180min, MgSO ₄ in an amount of 0.5% of absolute dry mass of pulp, NaOH in an amount of 0.5-5.0% absolute dry pulp mass. The dosage of H ₂ O ₂ is 1.0-5.0% of the mass of the absolutely dry pulp, the dosage of IDS is 0.01-1.0% of the mass of the absolutely dry pulp, the pulp concentration is 8%, and the temperature is 70-95 ° C.

Preferably O _{_P} D _Q E _{P P} bleaching conditions: P bleaching reaction time of 60 ~ 180min, MgSO ₄ in an amount of dry pulp mass to 0.5%, NaOH in an amount of dry pulp mass to 0.4%, NaAC amount of must. The dry pulp quality is 0.4%, the H ₂ O ₂ dosage is 1.0-5.0% of the absolute dry pulp quality, the pulp concentration is 10%, and the temperature is 80-95 ° C.

In summary, by adding additives during the pre-hydrolysis of poplar veneer to selectively remove hemicellulose in poplar veneer, and then using Soda / AQ staged cooking with added additives to remove lignin as much as possible to protect cellulose, after cooking slurry was O _{_P} D _Q E _{P P} bleaching lignin removal and further adjusting the degree of polymerization of pulp is dissolved, and finally, to further improve the collaborative process with an enzyme purity of dissolving pulp and dissolving pulp adjust reactivity, A high-purity and highly reactive poplar board vinegar-grade dissolving pulp is obtained.

The beneficial effects of the invention:

(1) Firstly, the hemicellulose in poplar wood veneer can be selectively dissolved by means of pre-hydrolysis with the aid of additives, and finally the enzyme synergistic treatment can be used to further improve the purity and vinegar reaction value of the poplar wood veneer pulp. Stage cooking and O _P D _Q E _P P bleaching, prepared high-purity and highly reactive poplar veneer vinegar-grade dissolving pulp;

(2) The process of the present invention is used to treat poplar wood veneer, the chemicals used are clean and environmentally friendly, and the production process is clean.

BRIEF DESCRIPTION

Figure 1 is a flow chart of the process of producing vinegar-grade dissolving pulp from poplar board skin.

detailed description

In order to better understand the present invention, it will be further described below with specific examples.

In the following examples, the hydrolysis assistant is sodium borate, magnesium sulfate, nonylphenol polyoxyethylene ether phosphate and tetrasodium iminodisuccinate in a mass ratio of 1: 1: 1: 1.

The percentage content of the materials used in each process stage is the percentage of the absolute dry pulp quality.

Example 1:

Additive-assisted pre-hydrolysis-additive-assisted Soda / AQ staged cooking-O _P Q _D EpP-enzyme synergistic process for processing poplar wood veneer raw materials: take 500 g of poplar wood veneer sheet from a certain factory, 10-30 mm long The pentose content was 24.3% and the α-cellulose content was 43.0%.

The pre-hydrolysis process conditions for controlling the addition of additives are: liquid ratio 1: 6, additives 0.4%, maximum temperature 160 ° C, holding time 60 minutes, polypentose content after hydrolysis is 8.6%, and hydrolysis yield is 80%;

The process conditions of Soda / AQ cooking stage I are: 5% alkaline, 1: 4 liquid ratio, 0.5% magnesium hydroxide, 5.0% sodium sulfite, 0.05% AQ dosage, Tmax = 100 ℃ ± 2 ℃, holding time 60 minutes;

Soda / AQ cooking stage II process conditions are: the amount of alkali used is 18%, magnesium hydroxide 0.5%, sodium sulfite 3.0%, the liquid ratio is 1: 7, the AQ dosage is 0.05%, the maximum temperature is 160 ℃, and the holding time is 120 minutes;

The oxygen pressure of the O _P bleaching is 0.5Mpa, the slurry concentration is 10%, MgSO ₄ 0.6%, NaOH 2.0%, H ₂ O ₂ 1.0%, the temperature is 95 ° C, and the temperature is kept for 60 minutes;

The reaction time of Q _D bleaching process is 60 minutes, T = 30 ± 2 ℃, pulp concentration 4.0%, pH = 1.5, sodium chlorite dosage 3.0%, IDS dosage 0.05%;

The reaction time of Ep extraction process is 90 min., MgSO ₄ 0.5%, NaOH 3.0%, H ₂ O ₂ 2.0%, IDS dosage 0.05%, slurry concentration 8%, temperature 85 ℃;

The reaction time of P bleaching is 120min., MgSO ₄ 0.5%, NaOH 0.4%, NaAC 0.4%, H ₂ O ₂ 3.0%, slurry concentration 10%, temperature 90 ℃;

The enzyme synergistic treatment conditions are: pulp concentration 5%, temperature 40 ℃, treatment time 60min, pH = 5.0, polyaspartic acid dosage 0.05%, OP-13 dosage 0.005%, OP-15 dosage 0.005%, The dosage of endocellulase is 0.2IU / gpulp, the dosage of xylanase is 3XU / gpulp, and the dosage of pectinase is 3IU / gpulp.

The α-cellulose content of the vinegar-grade dissolving pulp of poplar board skin was 97%, polypentose was 2.6%, degree of polymerization was 1250, whiteness was 89% ISO, ash content was 0.01%, DCM extract content was 0.03%, vinegar Chemical reaction value (PV value) 800.

The detection indexes of vinegar-grade dissolving pulp of poplar board skin are better, and can be used to produce high-grade cellulose acetate products.

Example 2:

Additive-assisted pre-hydrolysis-additive-assisted Soda / AQ staged cooking-O _P Q _D EpP-enzyme synergistic process for the processing of poplar wood veneer raw materials, the polypentose content of the poplar wood veneer taken was 22.3%, α-fiber The element content is 45.0%, and the process conditions are the same as in Example 1. The α-cellulose content of the vinegar-grade dissolving pulp of poplar board skin was 97%, polypentose 2.2%, degree of polymerization 1280, whiteness 90% ISO, ash content 0.01%, DCM extract content 0.02%, vinegar Chemical reaction value (PV value) 820.

Example 3:

Add prehydrolysis aid - adding additives Soda / AQ cooking segment -O _P Q _D EpP- enzyme synergistic skin treatment process raw wood Yang, Yang wood skin, taken in Example 1. Only the pre-hydrolysis holding time is changed to 120 minutes, the content of polypentose after hydrolysis is 8.5%, the yield of hydrolysis is 79%, and other processes remain unchanged. Finally, the α-cellulose content of the vinegar-grade dissolving pulp of poplar veneer was 97%, polypentose 2.2%, degree of polymerization 1200, whiteness 89% ISO, ash content 0.01%, DCM extract content 0.02%, Vinegar reaction value (PV value) 780.

Example 4:

Add prehydrolysis aid - adding additives Soda / AQ cooking segment -O _P Q _D EpP- enzyme synergistic skin treatment process raw wood Yang, Yang wood skin, taken in Example 1. Only the cooking liquid ratio of Soda / AQ cooking section II is changed to 1: 4, other processes remain unchanged. The resulting alpha-cellulose content of poplar board vinegar-grade dissolving pulp is 97%, polypentose 2.5%, degree of polymerization 1060, whiteness 90% ISO, ash content 0.01%, DCM extract content 0.02%, Vinegar reaction value (PV value) 730.

Example 5:

Adding additives Soda / AQ cooking segment -O _P Q _D EpP- enzyme synergistic skin treatment process raw wood Yang, Yang wood skin, taken in Example 1. The auxiliary additives added in the step are pre-hydrolyzed and removed, the liquid ratio is 1: 6, and other processes are the same as those in Example 1. The alpha-cellulose content of the vinegar-grade dissolving pulp of poplar board skin was 95%, polypentose was 3.6%, polymerization degree was 1200, whiteness was 88% ISO, ash content was 0.015%, and DCM extract content was 0.025%. Vinegar reaction value (PV value) 680.

Example 6:

Add prehydrolysis aid - adding additives Soda / AQ cooking segment -O _P Q _D EpP- enzyme synergistic skin treatment process raw wood Yang, Yang wood skin, taken in Example 1. Combine the two-stage cooking of steps (2) and (3) into one-stage cooking. Add two-step cooking with alkali, magnesium hydroxide, sodium sulfite, AQ at a time, liquid ratio 1: 6, Tmax = 100 ℃ ± 2 ℃, keep warm 60 minutes; 160 ° C for 120 minutes, other processes are the same as in Example 1. The alpha-cellulose content of the vinegar-grade dissolving pulp of poplar veneer was 96%, polypentose 2.7%, degree of polymerization 1000, whiteness 89% ISO, ash content 0.01%, DCM extract content 0.02%, Vinegar reaction value (PV value) 700.

The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the examples. Any other changes, modifications, combinations, substitutions, and simplifications made without departing from the spirit and principles of the present invention All of them should be equivalent replacement methods, which are all included in the protection scope of the present invention.

Claims

A method for producing vinegar-grade dissolving pulp using poplar board skin, which is characterized by comprising the following steps:

(1) Adding auxiliary agent for pre-hydrolysis: liquid ratio 1: (4 ～ 10), adding amount of hydrolysis auxiliary agent is 0.1 ～ 2.0% of dry matter mass of poplar wood veneer, hydrolysis temperature 80 ～ 170 ℃, holding time 10 ～ 180 minutes The hydrolysis aid is a mixture obtained by mixing sodium borate, magnesium sulfate, nonylphenol polyoxyethylene ether phosphate and tetrasodium iminodisuccinate according to a mass ratio of 1: 1: 1: 1;

(2) Soda / AQ cooking stage Ⅰ;

(3) Soda / AQ cooking section Ⅱ;

(4) O P D Q E P P bleaching;

(5) Enzyme synergistic treatment: pulp concentration 2 ～ 10%, temperature 30-50 ℃, treatment time 60min, pH = 4.0 ～ 7.0, dosage of polyaspartic acid is 0.01% -1.0% of absolute dry pulp quality, OP- 13 The dosage is 0.001-0.01% of the mass of the absolute dry pulp, the dosage of OP-15 is 0.001-0.01% of the mass of the absolute dry pulp, the dosage of the endo-cellulase is 0.1 ～ 0.6IU / gpulp, and the dosage of the xylanase is 2 ～ 4XU / gpulp, the dosage of pectinase is 0.1 ～ 10IU / gpulp.
The method according to claim 1, characterized in that the Soda / AQ cooking stage I process conditions are: the amount of alkali used as Na 2 O is 5 to 15% of the quality of the absolute dry pulp, and the liquid ratio is 1: (3 to 8) , The dosage of magnesium hydroxide is 0.5% of the mass of the absolute dry pulp, the dosage of sodium sulfite is 1.0-10.0% of the mass of the absolute dry pulp, the dosage of AQ is 0.05% of the mass of the absolute dry pulp, the temperature is 80 ～ 120 ℃, and the holding time is 10 ～ 180 minutes .
The method according to claim 1, characterized in that the Soda / AQ cooking II process conditions are: the amount of alkali used as Na 2 O is 5-25% of the quality of the dry pulp, and the amount of magnesium hydroxide is the quality of the dry pulp 0.5%, the dosage of sodium sulfite is 1.0 ～ 10.0% of the mass of the absolute dry pulp, the liquid ratio is 1: (3 ～ 10), the dosage of AQ is 0.05% of the mass of the absolute dry pulp, the temperature is 140 ～ 180 ℃, and the holding time is 10 ～ 240 minutes .
The method according to claim 1, characterized in that the O P D Q E P P bleaching conditions were: O P bleaching oxygen pressure of 0.4 ~ 0.6Mpa, pulp consistency 10%, MgSO 4 in an amount of dry pulp mass 0.6%, the dosage of NaOH is 1.0 ～ 3.0% of the mass of the absolute dry pulp, the dosage of H 2 O 2 is 0.5 ～ 3.0% of the mass of the absolute dry pulp, the temperature is 70 ～ 110 ℃, and the temperature is kept for 60min.
The method according to claim 1, characterized in that the O P D Q E P P bleaching conditions were: Q D bleaching reaction time 10 to 120 minutes, T = 30 ± 2 ℃, 2 to 8% pulp consistency, pH = 1 ~ 3, the dosage of sodium chlorite is 0.2-6.0% of the quality of the dry pulp, and the dosage of IDS is 0.01-1.0% of the quality of the dry pulp.
The method according to claim 1, characterized in that the O P D Q E P P bleaching conditions were: reaction time Ep Extraction Technology of 30 ~ 180min, MgSO 4 in an amount of mass of dry pulp 0.5%, NaOH amount It is 0.5-5.0% of the quality of the absolute dry pulp, the dosage of H 2 O 2 is 1.0-5.0% of the quality of the absolute dry pulp, the dosage of IDS is 0.01 ～ 1.0% of the quality of the absolute dry pulp, the concentration of the pulp is 8%, and the temperature is 70 ～ 95 ℃ .
The method according to claim 1, characterized in that the O P D Q E P P bleaching conditions:. P bleaching reaction time of 60 ~ 180min, MgSO 4 in an amount of mass of dry pulp 0.5%, NaOH absolute amount of The dry pulp mass is 0.4%, the amount of NaAC is 0.4% of the mass of the dry pulp, the amount of H 2 O 2 is 1.0-5.0% of the mass of the dry pulp, the pulp concentration is 10%, and the temperature is 80-95 ° C.
The method according to claim 1, characterized by comprising the following steps:

(1) Add auxiliary agent to pre-hydrolyze: liquid ratio is 1: 6, the amount of auxiliary agent is 0.4% of the quality of absolute dry pulp, the temperature is 160 ℃, and the holding time is 60 minutes;

(2) Soda / AQ cooking stage I: the amount of alkali used is 5% of the quality of the dry pulp, the liquid ratio is 1: 4, the amount of magnesium hydroxide is 0.5% of the quality of the dry pulp, and the amount of sodium sulfite is 5.0 of the quality of the dry pulp %, AQ dosage is 0.05% of absolute dry pulp quality, Tmax = 100 ℃ ± 2 ℃, holding time 60 minutes;

(3) Soda / AQ cooking section II: the amount of alkali used is 18% of the quality of the dry pulp, the amount of magnesium hydroxide is 0.5% of the quality of the dry pulp, the amount of sodium sulfite is 3.0% of the quality of the dry pulp, the liquid ratio is 1: 7. The dosage of AQ is 0.05% of the quality of absolute dry pulp, the maximum temperature is 160 ℃, and the holding time is 120 minutes;

(4) O P D Q E P P bleaching O P bleaching oxygen pressure is 0.5Mpa, pulp concentration is 10%, the dosage of MgSO 4 is 0.6% of the quality of the absolute dry pulp, the dosage of NaOH is 2.0% of the quality of the absolute dry pulp, H The amount of 2 O 2 is 1.0% of the quality of the absolute dry pulp, the temperature is 95 ℃, and the temperature is kept for 60 minutes; the reaction time of the Q D bleaching process is 60 minutes, T = 30 ± 2 ℃, the pulp concentration is 4.0%, pH = 1.5, sodium chlorite in an amount of 3.0% absolute dry pulp mass, IDS dry pulp in an amount of 0.05% by mass; reaction time Ep extraction process 90min, MgSO 4 in an amount of 0.5% of absolute dry mass of pulp, NaOH dry pulp mass in an amount of 3.0%, the amount of H 2 O 2 is 2.0% of the quality of the dry pulp, the amount of IDS is 0.05% of the quality of the dry pulp, the pulp concentration is 8%, the temperature is 85 ° C; the reaction time of P bleaching is 120min., The amount of MgSO 4 is 0.5% of the quality of absolute dry pulp, 0.4% of the quality of NaOH, 0.4% of the quality of NaAC, 3.0% of the quality of H 2 O 2 , 10% of the concentration of pulp, temperature 90 ℃;

(5) Enzyme synergistic treatment: pulp concentration 5%, temperature 40 ℃, treatment time 60min, pH = 5.0, the dosage of polyaspartic acid is 0.05% of the quality of the dry pulp, and the dosage of OP-13 is 0.005 of the quality of the dry pulp %, The dosage of OP-15 is 0.005% of the quality of absolute dry pulp, the dosage of endo-cellulase is 0.2IU / gpulp, the dosage of xylanase is 3XU / gpulp, and the dosage of pectinase is 3IU / gpulp.
The method according to claim 1, wherein the length of the poplar board used in step (1) is 10-30 mm, the polypentose content is 22.3-24.3%, and the α-cellulose content is 43.0-45.0%.