High-polymerization-degree cellulose extraction method based on alkali / hydrated acidic deep-eutectic solvent

Abstract

The invention belongs to the technical field of cellulose extraction, and particularly relates to a high-polymerization-degree cellulose extraction method based on an alkali / hydrated acidic deep-eutectic solvent. Comprising the steps that bamboo residues obtained after extrusion and tearing are mixed with alkali liquor, the mixture is added into a normal-pressure reaction kettle to be subjected to a cooking reaction, solid-liquid separation is conducted after the reaction is completed, bamboo residues obtained after alkali pretreatment are obtained, and air drying is conducted; mixing the bamboo residues subjected to alkali treatment, a deep-eutectic solvent and water, and adding the mixture into a normal-pressure reaction kettle for reaction; after the reaction is finished, carrying out solid-liquid separation to obtain crude slurry, and washing the crude slurry with a washing solution; and finally, screening by using a pulp screening machine to obtain fine pulp. According to the method disclosed by the invention, the effective separation of lignocellulose is realized at normal pressure and low temperature by utilizing the excellent performance of the acidic eutectic solvent in the aspect of removing lignin and hemicellulose, so that the cooking energy consumption and the acid consumption are obviously reduced, and the requirements on reaction equipment are reduced. In addition, the eutectic solvent and the washing liquid can be recycled, so that the burden of subsequent pollution treatment is reduced, and the method has both economic and environmental feasibility.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cellulose extraction, and particularly relates to a high-polymerization-degree cellulose extraction method based on alkali / hydrated acidic deep eutectic solvent. BACKGROUND

[0002] Cellulose is the most abundant renewable resource on earth and is the most widely distributed natural polymer material in the world, and has important uses in pulp and papermaking, regenerated cellulose, food, packaging, and pharmaceutical industries. With the overexploitation of petrochemical resources and the increasing environmental problems, renewable resources have become the focus of many researchers. Among them, high-polymerization-degree cellulose plays an important role in cellulose film and regenerated cellulose material fields, and patent CN108070109A shows that high-polymerization-degree cellulose can effectively improve the processing performance and mechanical properties of cellulose materials.

[0003] Traditional cellulose separation methods are mainly based on sulfite or caustic soda methods. These technologies not only have high energy consumption, but also produce toxic and harmful waste liquid and waste gas, causing great pressure on the ecological environment. In addition, the cellulose produced by these technologies has a low degree of polymerization (<900) due to harsh reaction conditions. In addition, traditional processes are mainly based on wood raw materials, and the growth cycle of wood is relatively long, and overexploitation is not conducive to environmental protection. In this regard, bamboo has become a reliable substitute for wood due to its short growth cycle and strong sustainable regeneration ability. However, traditional bamboo cellulose extraction processes often require harsh reaction conditions (such as high temperature and high pressure), which requires a large amount of energy input in the production process. Therefore, it is urgent to break through the bottleneck of traditional technology and find an environmentally friendly, efficient, and operable high-polymerization-degree cellulose extraction process.

[0004] In recent years, deep eutectic solvents (DESs) have attracted widespread attention as a new type of green organic solvent. Deep eutectic solvents (DES) are eutectic mixtures formed by hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA) through hydrogen bond interactions. These solvents have many advantages, including simple synthesis, high stability, good biocompatibility, great design flexibility, and recyclability. Therefore, the introduction of acidic deep eutectic solvents is expected to achieve cellulose extraction under mild conditions, which not only reduces production costs, but also meets the concept of green development. Patent CN104631175A uses biological and chemical methods to treat jute biomass to prepare cellulose with high degree of polymerization under mild conditions, but the overall process is complex, and the efficiency of the enzyme treatment used is low, which limits its industrialization. Therefore, developing an alkali / hydrated acidic deep eutectic solvent-based high-polymerization-degree cellulose extraction method is still a problem that needs to be solved. SUMMARY

[0005] The application aims to provide a high-polymerization-degree cellulose extraction method based on alkali / hydrated acidic deep eutectic solvent, and solve the problems of high energy consumption, strict equipment requirements, large chemical consumption and low polymerization degree in the current cellulose extraction process.

[0006] The application is implemented by the following technical scheme:

[0007] A high-polymerization-degree cellulose extraction method based on alkali / hydrated acidic deep eutectic solvent, comprising the following steps:

[0008] (1) The lignocellulose raw material is subjected to extrusion tearing and dust removal treatment, the bamboo residue obtained after extrusion tearing is mixed with alkali liquor and added into a normal-pressure reaction kettle for cooking reaction, and after the reaction is completed, the mixture is subjected to solid-liquid separation to obtain alkali pretreated residue, which is washed and naturally air-dried;

[0009] (2) The alkali treated residue, deep eutectic solvent and water are mixed and subjected to cooking reaction, and after the cooking is completed, a mixture is obtained;

[0010] (3) The mixture is subjected to solid-liquid separation to obtain crude pulp, and the crude pulp is washed with a washing liquid;

[0011] (4) The washed crude pulp is screened using a screen pulp machine to obtain pulp residue and fine pulp.

[0012] Further, the lignocellulose raw material in step (1) is bamboo.

[0013] Further, the alkali liquor in step (1) is sodium hydroxide solution, and the concentration is 1.4-2.5wt%.

[0014] Further, the solid-liquid ratio of the lignocellulose raw material to the alkali liquor in step (1) is 1:(4-8), and the cooking temperature is controlled to be 70-90℃ and the cooking time is controlled to be 1-2h during the cooking reaction.

[0015] Further, the deep eutectic solvent in step (2) is a mixture of benzyltriethylammonium chloride and formic acid, and the molar ratio of the two components is 1:(3-6).

[0016] Further, the solid-liquid ratio of the lignocellulose raw material to the deep eutectic solvent in step (2) is 1:(5-10), and the cooking temperature is controlled to be 100-130℃ and the cooking time is controlled to be 0.5-2h during the cooking reaction.

[0017] Further, the proportion of water in step (2) is 10-50% of the total mass of the liquid.

[0018] Further, the washing liquid in step (3) is ethanol or water.

[0019] Further, the screen gap of the screen plate of the screening machine in step (4) is 0.1-0.25 mm.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] 1. The present application utilizes the excellent performance of the acidic eutectic solvent in removing lignin and hemicellulose, and realizes effective separation of lignocellulose at normal pressure and low temperature, thereby significantly reducing the cooking energy consumption and acid consumption, and reducing the requirements for reaction equipment.

[0022] 2. The low-cost, non-toxic and recyclable eutectic solvent used in the high-polymerization cellulose extraction method provided by the present application reduces the amount of chemicals used and the subsequent pollution treatment burden, and is economical and environmentally friendly.

[0023] 3. The pulping method provided by the present application has relatively low requirements for equipment, and the cooking reaction can be completed in a normal pressure reaction kettle.

[0024] 4. The high-polymerization cellulose extraction method provided by the present application significantly reduces the required temperature and time of cooking, and greatly reduces the energy consumption demand. DETAILED DESCRIPTION

[0025] In order to further explain the present application, the following specific examples are combined for illustration.

[0026] Example 1

[0027] A high-polymerization cellulose extraction method based on an alkali / hydrated acidic eutectic solvent, comprising the following steps:

[0028] (1) The extruded and torn bamboo residue is washed with clean water to remove the surface dirt, and after being air-dried in an indoor environment for 5 days, the moisture content is measured and placed in a sealed bag for standby;

[0029] (2) A certain mass of bamboo residue is mixed with 2.5wt% of lye according to a solid-liquid ratio of 1:5 (g / mL), and the mixture is added to a normal pressure reaction kettle for reaction, the reaction temperature is 70℃, the reaction time is 1h, after the reaction is completed, solid-liquid separation is performed, the bamboo residue after reaction is washed and dried for 3 days;

[0030] (3) Benzyltriethylammonium chloride and formic acid were mixed in a molar ratio of 1:5 to form a homogeneous transparent liquid eutectic solvent at 25°C by magnetic stirring. 20.00 g of alkali-treated bamboo residue (absolute dry), 16 g of water, and 144 g of eutectic solvent were weighed and mixed and added to a normal-pressure reaction kettle for cooking reaction. The cooking time was 70 min, and the cooking temperature was 120°C. After the completion of cooking, 100 mL of washing liquid (water) was added to dilute the solid-liquid mixture, and then a 200-mesh pulp bag was used to filter the mixture to obtain eutectic solvent and coarse pulp, respectively. The coarse pulp was washed again with 300 mL of washing liquid (water).

[0031] (4) The coarse pulp was screened using a flat vibrating screen with a screen gap of 0.15 mm to obtain fine pulp.

[0032] The calculated yield of fine pulp was 42.98%, the degree of polymerization of cellulose was 1426, the content of a-cellulose was 85.09%, the length-weighted average length of fibers was 1.17 mm, and the area ratio of fine fibers was 2.36%.

[0033] Example 2

[0034] A high-polymerization-degree cellulose extraction method based on alkali / water acid eutectic solvent, comprising the following steps:

[0035] (1) The extruded and torn bamboo residue was washed with clean water to remove the surface sand, and then dried in the indoor environment for 5 days. The moisture content was measured and the residue was placed in a sealed bag for later use.

[0036] (2) A certain amount of bamboo residue was mixed with 2.5 wt% of lye at a solid-liquid ratio of 1:5 (g / mL). The mixture was added to a normal-pressure reaction kettle for reaction. The reaction temperature was 70°C, and the reaction time was 1 h. After the reaction was completed, the solid and liquid were separated, the bamboo residue after reaction was washed, and then dried for 3 days.

[0037] (3) Benzyltriethylammonium chloride and formic acid were mixed in a molar ratio of 1:5 to form a homogeneous transparent liquid eutectic solvent at 25°C by magnetic stirring. 20.00 g of alkali-treated bamboo residue (absolute dry), 16 g of water, and 144 g of eutectic solvent were weighed and mixed and added to a normal-pressure reaction kettle for cooking reaction. The cooking time was 70 min, and the cooking temperature was 120°C. After the completion of cooking, 100 mL of washing liquid (water) was added to dilute the solid-liquid mixture, and then a 200-mesh pulp bag was used to filter the mixture to obtain eutectic solvent and coarse pulp, respectively. The coarse pulp was washed again with 300 mL of washing liquid (water).

[0038] (4) The coarse pulp was screened using a flat vibrating screen with a screen gap of 0.15 mm to obtain fine pulp.

[0039] The calculated fine pulp yield is 43.22%, the cellulose polymerization degree is 1500, the a-cellulose content is 86.84%, the fiber length weighted average length is 1.30 mm, and the fine fiber area ratio is 1.29%.

[0040] Example 3

[0041] A high-polymerization-degree cellulose extraction method based on alkali / hydrated acid deep eutectic solvent, comprising the following steps:

[0042] (1) The extruded and torn bamboo residues are washed with clean water to remove the surface sand, dried in an indoor environment for 5 days, and then measured for moisture content and placed in a sealed bag for standby;

[0043] (2) A certain mass of bamboo residues is mixed with 2.5wt% alkali solution at a solid-liquid ratio of 1:5 (g / mL), the mixture is added to a normal-pressure reaction kettle for reaction, the reaction temperature is 70°C, the reaction time is 1h, after the reaction is completed, solid-liquid separation is performed, the reacted bamboo residues are washed and dried for 3 days;

[0044] (3) Benzyltriethylammonium chloride and formic acid are mixed at a molar ratio of 1:5 to form a uniform transparent liquid deep eutectic solvent at 25°C, 20.00g of alkali-treated bamboo residues (bone-dry), 64g of water, and 96g of deep eutectic solvent are weighed, mixed, and added to a normal-pressure reaction kettle for cooking reaction, the cooking time is 70min, the cooking temperature is 120°C, after the cooking is completed, 100mL of washing liquid (water) is added to dilute the solid-liquid mixture, then a 200-mesh pulp bag is used to filter the mixture to obtain the deep eutectic solvent and the crude pulp, and the crude pulp is washed again with 300mL of washing liquid (water);

[0045] (4) The crude pulp is screened using a flat vibrating screen with a screen gap of 0.15mm to obtain the fine pulp.

[0046] The calculated fine pulp yield is 57.49%, the cellulose polymerization degree is 1465, the a-cellulose content is 84.98%, the fiber length weighted average length is 2.13mm, and the fine fiber area ratio is 1.09%.

[0047] Example 4

[0048] A high-polymerization-degree cellulose extraction method based on alkali / hydrated acid deep eutectic solvent, comprising the following steps:

[0049] (1) The extruded and torn bamboo residues are washed with clean water to remove the surface sand, dried in an indoor environment for 5 days, and then measured for moisture content and placed in a sealed bag for standby;

[0050] (2) Take a certain mass of bamboo residue and 2.5wt% of lye according to the solid-liquid ratio 1:5(g / mL) to mix, the mixture is added to the atmospheric reaction kettle for reaction, the reaction temperature is 70℃, the reaction time is 1h, after the reaction, the solid-liquid separation, wash the bamboo residue after reaction, air dry for 3 days;

[0051] (3) Benzyltriethylammonium chloride and formic acid are mixed in a molar ratio of 1:5 to form a homogeneous transparent liquid eutectic solvent at 25℃, 20.00g of alkali treated bamboo residue (absolute dry), 80g of water and 80g of eutectic solvent are weighed respectively, mixed and added to the atmospheric reaction kettle for cooking reaction, the cooking time is 70min, the cooking temperature is 120℃, after the cooking is completed, 100mL of washing liquid (water) is added to dilute the solid-liquid mixture, then the mixture is filtered using a 200 mesh pulp bag to obtain eutectic solvent and crude pulp, and the crude pulp is washed again with 300mL of washing liquid (water);

[0052] (4) The crude pulp is screened using a flat vibrating screen with a screen gap of 0.15mm to obtain fine pulp.

[0053] The calculation shows that the fine pulp yield is 56.41%, the cellulose polymerization degree is 1553, the α-cellulose content is 89.22%, the fiber length weighted average length is 1.90mm, and the fine fiber area ratio is 0.81%.

[0054] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent, characterized in that: The steps include: (1) The lignocellulose raw material is subjected to extrusion, tearing and dust removal treatment, and the bamboo residue obtained after the extrusion and tearing is mixed with alkali solution and added into a normal pressure reactor for steaming reaction. After the reaction is completed, the mixture is separated into solid and liquid to obtain the residue after alkali pretreatment, which is washed and naturally air-dried; (2) mixing the alkali-treated residue, a deep eutectic solvent, and water and performing a steam cooking reaction to obtain a mixture; (3) performing solid-liquid separation on the mixture to obtain a crude pulp, and washing the crude pulp with a washing liquid; (4) Use a pulp screening machine to screen the washed coarse pulp to obtain pulp residue and fine pulp respectively.

2. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The lignocellulose raw material described in step (1) is bamboo.

3. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The alkali solution described in step (1) is a sodium hydroxide solution with a concentration of 1.4 to 2.5 wt%.

4. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The solid-liquid ratio of the lignocellulose raw material to the alkali solution in step (1) is 1:(4-8), and the cooking temperature is controlled to be 70-90° C. during the cooking reaction, and the cooking time is 1-2 hours.

5. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The deep eutectic solvent described in step (2) is a mixture of benzyltriethylammonium chloride and formic acid, and the molar ratio of the two components is 1:(3-6).

6. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The solid-to-liquid ratio of the lignocellulosic raw material to the low eutectic solvent in step (2) is 1:(5-10), and the cooking temperature is controlled to be 100-130° C. during the cooking reaction, and the cooking time is 0.5-2 h.

7. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The proportion of water in step (2) is 10 to 50% of the total mass of the liquid.

8. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The washing liquid described in step (3) is ethanol or water.

9. The method for extracting high-polymerization cellulose based on an alkali / hydrated acidic deep eutectic solvent according to claim 1, characterized in that: The screen plate sieve gap of the pulp screening machine described in step (4) is 0.1 to 0.25 mm.