阅读说明：本技术 一种碱性四氢糠醇从核桃壳中分级沉降提取低分子量木质素的方法 (Method for extracting low-molecular-weight lignin from walnut shells through fractional precipitation by using alkaline tetrahydrofurfuryl alcohol ) 是由 徐建 左宗涛 王标 李新龙 耿繁辉 张楷 徐霞 于 2021-06-08 设计创作，主要内容包括：本发明涉及一种碱性四氢糠醇从核桃壳中分级沉降提取低分子量木质素的方法,包括如下步骤：1)核桃壳经过粉碎、过筛、水洗、烘干后得到核桃壳粉末,按一定固液比加入碱性四氢糠醇,在一定温度下预处理一段时间后得到混合浆液,混合浆液减压抽滤后得滤液；2)向滤液中加水并调节pH＝6后第一次离心,沉降物经干燥得木质素级分I；3)将离心后得到的上清液pH调至4,再经第二次离心、干燥后得木质素级分II；4)将离心后得到的上清液pH调至2,再经第三次离心、干燥后得木质素级分III。本发明利用碱性四氢糠醇从核桃壳中高效提取木质素,再通过酸析法进行分级分离,最终获得低分子量、分布均一、高反应活性的木质素。(The invention relates to a method for extracting low-molecular-weight lignin from walnut shells by fractional precipitation with alkaline tetrahydrofurfuryl alcohol, which comprises the following steps: 1) crushing, sieving, washing and drying walnut shells to obtain walnut shell powder, adding alkaline tetrahydrofurfuryl alcohol according to a certain solid-to-liquid ratio, pretreating for a period of time at a certain temperature to obtain mixed slurry, and performing vacuum filtration on the mixed slurry to obtain filtrate; 2) adding water into the filtrate, adjusting the pH value to 6, centrifuging for the first time, and drying the sediment to obtain a lignin fraction I; 3) regulating the pH value of the supernatant obtained after centrifugation to 4, and then carrying out secondary centrifugation and drying to obtain a lignin fraction II; 4) and adjusting the pH value of the supernatant obtained after centrifugation to 2, and then carrying out third centrifugation and drying to obtain a lignin fraction III. According to the method, alkaline tetrahydrofurfuryl alcohol is used for efficiently extracting lignin from walnut shells, and then the lignin is subjected to fractional separation by an acid precipitation method, so that the lignin with low molecular weight, uniform distribution and high reaction activity is finally obtained.)

1. The method for extracting the low-molecular-weight lignin from the walnut shells by fractional sedimentation with alkaline tetrahydrofurfuryl alcohol is characterized by comprising the following steps:

1) crushing, sieving, washing and drying walnut shells to obtain walnut shell powder, adding alkaline tetrahydrofurfuryl alcohol into the walnut shell powder according to a certain solid-to-liquid ratio, pretreating for a period of time at a certain temperature to obtain mixed slurry, and performing reduced pressure suction filtration on the mixed slurry to obtain filtrate;

2) adding water into the filtrate, adjusting the pH value to 6, centrifuging for the first time, and drying the sediment to obtain a lignin fraction I;

3) adjusting the pH value of the supernatant obtained after the centrifugation in the step 2) to 4, and then carrying out secondary centrifugation and drying to obtain a lignin fraction II;

4) adjusting the pH value of the supernatant obtained after the centrifugation in the step 3) to 2, and then carrying out third centrifugation and drying to obtain a lignin fraction III.

2. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 1, characterized in that: in the step 1), adding the walnut shell powder into alkaline tetrahydrofurfuryl alcohol according to the solid-to-liquid ratio of 1:4-6g/ml, pretreating at the temperature of 130-.

3. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 1, characterized in that: in the step 1), adding alkaline tetrahydrofurfuryl alcohol into the walnut shell powder according to the solid-to-liquid ratio of 1:5g/ml, pretreating for 90min at 135 ℃ to obtain mixed slurry, and carrying out reduced pressure suction filtration on the mixed slurry through non-woven fabrics to obtain filtrate.

4. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 1, characterized in that: in the step 1), the particle size of the walnut shell powder is 10-100 meshes.

5. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 1, characterized in that: in the step 2), the filter residue obtained in the step 1) is washed by adding distilled water, washing liquid and filtrate are mixed and then added with water, and the mixture is centrifuged for the first time after the pH value is adjusted to 6.

6. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 5, characterized in that: and carrying out enzymolysis treatment on the washed filter residue.

7. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 1, characterized in that: in the step 1), the alkaline tetrahydrofurfuryl alcohol is obtained by adding a certain amount of alkali into a tetrahydrofurfuryl alcohol solvent and mixing.

8. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 7, characterized in that: the tetrahydrofurfuryl alcohol solvent in the alkaline tetrahydrofurfuryl alcohol is prepared by taking biomass as a raw material.

9. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 7, characterized in that: the alkali in the alkaline tetrahydrofurfuryl alcohol is sodium hydroxide.

10. The method of fractional precipitation extraction of low molecular weight lignin from walnut shells by alkaline tetrahydrofurfuryl alcohol according to claim 9, characterized in that: the addition amount of the alkali in the alkaline tetrahydrofurfuryl alcohol is 1-10% w/w.

Technical Field

The invention relates to the technical field of biomass pretreatment and comprehensive utilization of agricultural wastes, in particular to a method for extracting low-molecular-weight lignin from walnut shells by fractional sedimentation with alkaline tetrahydrofurfuryl alcohol.

Background

The problem of sustainable development of energy due to the gradual exhaustion of petrochemical resources and the environmental problems of greenhouse effect, air pollution and the like caused by the use of the petrochemical resources have led people to look at renewable biomass resources which can realize carbon neutralization and are used as chemical raw materials, in particular, lignocellulose which does not have competitive relationship with food crops, such as agricultural wastes including corn straws, wheat straws, cotton straws, bagasse and the like, or plants which can grow in severe environment, such as miscanthus, switchgrass and the like. However, lignocellulose is difficult to convert due to its complex structure. Some degree of pretreatment is required to loosen the structure of the lignocellulose to improve the conversion efficiency. Research on pretreatment is currently focused on improving the fractionation ability of cellulose, hemicellulose and lignin, increasing the efficiency of enzymatic hydrolysis of cellulose and hemicellulose to produce sugars, reducing the use cost of enzymes, and improving the efficiency of conversion of the resulting sugars to ethanol and other compounds. In addition, a large amount of lignin is generated in the process, and a large amount of lignin is also generated in the paper and pulp industry. Most of the lignin is used as fuel for combustion, and only less than 2% of the lignin is used for other production purposes. Therefore, while improving the grading capacity of cellulose, hemicellulose and lignin, how to better utilize lignin has great significance for improving the economic benefit of the biorefinery industry and enhancing the market competitiveness of the biorefinery industry.

The walnut shell is mainly used as a filter material and a polishing material, and the utilization of higher value of the walnut shell is less. Walnut shells, a type of lignocellulose, are composed primarily of cellulose, hemicellulose, and lignin, and although lignocellulosic biomass has long been considered a sustainable resource for the production of biofuels and other chemicals by saccharification and fermentation, the conversion of cellulose before it is not treated is very low, primarily due to the complexity of its structure. The structure of lignocellulose is extraordinarily complex, most typically hydrogen bond linkage between cellulose and hemicellulose, and lignin-carbohydrate complex (LCC) formed by connecting lignin and hemicellulose through chemical bonds such as ether bond, acetal bond, ester bond, carbon-carbon bond, etc., and the ubiquitous structure often causes the separation and utilization of lignocellulose.

In previous researches, it is found that the acidified tetrahydrofurfuryl alcohol has a good effect on the pretreatment of lignocellulose, but the dissolution rate of lignin and the purity, molecular weight and dispersity of the lignin still need to be improved.

In view of the above, there is a need to provide a method for extracting low molecular weight lignin from walnut shells by fractional precipitation, which provides a basis for high value utilization.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provides a method for extracting low-molecular-weight lignin from walnut shells by fractional sedimentation through alkaline tetrahydrofurfuryl alcohol.

In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:

a method for extracting low molecular weight lignin from walnut shells by fractional precipitation with alkaline tetrahydrofurfuryl alcohol comprises the following steps:

1) crushing, sieving, washing and drying walnut shells to obtain walnut shell powder, adding alkaline tetrahydrofurfuryl alcohol into the walnut shell powder according to a certain solid-to-liquid ratio, pretreating for a period of time at a certain temperature to obtain mixed slurry, and performing reduced pressure suction filtration on the mixed slurry to obtain filtrate;

2) adding water into the filtrate, adjusting the pH value to 6, centrifuging for the first time, and drying the sediment to obtain a lignin fraction I;

3) adjusting the pH value of the supernatant obtained after the centrifugation in the step 2) to 4, and then carrying out secondary centrifugation and drying to obtain a lignin fraction II;

4) adjusting the pH value of the supernatant obtained after the centrifugation in the step 3) to 2, and then carrying out third centrifugation and drying to obtain a lignin fraction III.

Further, the method for extracting the low molecular weight lignin from the walnut shells by fractional sedimentation comprises the step 1) of adding the walnut shell powder into the alkaline tetrahydrofurfuryl alcohol according to the solid-to-liquid ratio of 1:4-6g/ml, pretreating at the temperature of 130-140 ℃ for 80-100min to obtain mixed slurry, and carrying out reduced pressure suction filtration on the mixed slurry through non-woven fabrics to obtain filtrate.

Further, the method for extracting the low molecular weight lignin from the walnut shells by fractional sedimentation with the alkaline tetrahydrofurfuryl alcohol comprises the following step 1), adding the walnut shell powder into the alkaline tetrahydrofurfuryl alcohol according to the solid-to-liquid ratio of 1:5g/ml, pretreating for 90min at 135 ℃ to obtain mixed slurry, and carrying out vacuum filtration on the mixed slurry through non-woven fabrics to obtain filtrate.

Further, in the method for extracting the low molecular weight lignin from the walnut shells by fractional precipitation with the alkaline tetrahydrofurfuryl alcohol, in the step 1), the particle size of the walnut shell powder is 10-100 meshes.

Further, in the method for extracting low molecular weight lignin from walnut shells by fractional precipitation with alkaline tetrahydrofurfuryl alcohol as described above, in step 1), the alkaline tetrahydrofurfuryl alcohol is obtained by adding a certain amount of alkali into a tetrahydrofurfuryl alcohol solvent and mixing.

Further, as mentioned above, the method for extracting low molecular weight lignin from walnut shells by fractional precipitation with alkaline tetrahydrofurfuryl alcohol comprises the steps of 2), washing the filter residue obtained in the step 1) with distilled water, mixing the washing solution with the filtrate, adding water, adjusting the pH value to 6, and then performing primary centrifugation.

Further, in the method for extracting the low-molecular-weight lignin from the walnut shells by fractional precipitation by using the alkaline tetrahydrofurfuryl alcohol, the washed filter residue is subjected to enzymolysis treatment.

Further, the method for extracting the low molecular weight lignin from the walnut shells by fractional sedimentation with the alkaline tetrahydrofurfuryl alcohol as described above is characterized in that the tetrahydrofurfuryl alcohol solvent in the alkaline tetrahydrofurfuryl alcohol is prepared by taking biomass as a raw material.

Further, the method for extracting the low molecular weight lignin from the walnut shells by fractional sedimentation by using the alkaline tetrahydrofurfuryl alcohol as described above, wherein the alkali in the alkaline tetrahydrofurfuryl alcohol is sodium hydroxide.

Further, the method for extracting the low molecular weight lignin from the walnut shells by fractional sedimentation by using the alkaline tetrahydrofurfuryl alcohol as described above is characterized in that the addition amount of the alkali in the alkaline tetrahydrofurfuryl alcohol is 1-10% w/w.

The invention has the beneficial effects that:

1. the method utilizes the alkaline tetrahydrofurfuryl alcohol to carry out the fractional sedimentation extraction of the lignin on the walnut shells with high lignin content, compact structure and hard texture, has relatively mild treatment conditions, simple steps and high extraction efficiency, and can obtain the organic solvent lignin with high purity, low molecular weight and low dispersity coefficient by grades.

2. The pretreatment method is simple and convenient, and the tetrahydrofurfuryl alcohol in the alkaline tetrahydrofurfuryl alcohol can be produced by taking biomass as a raw material, and is cheap and easy to obtain; the pretreatment temperature is relatively low, and the energy consumption is saved.

Of course, it is not necessary for any one product that embodies the invention to achieve all of the above advantages simultaneously.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic flow chart of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A method for extracting low molecular weight lignin from walnut shells by fractional precipitation with alkaline tetrahydrofurfuryl alcohol comprises the following steps:

1) crushing, sieving, washing and drying walnut shells to obtain walnut shell powder, adding alkaline tetrahydrofurfuryl alcohol into the walnut shell powder according to a certain solid-to-liquid ratio, pretreating for a period of time at a certain temperature to obtain mixed slurry, and performing reduced pressure suction filtration on the mixed slurry to obtain filtrate;

2) adding water into the filtrate, adjusting the pH value to 6, centrifuging for the first time, and drying the sediment to obtain a lignin fraction I; in addition, the filter residue can be washed by adding distilled water according to the requirement, the washing liquid and the filtrate are mixed and then added with water, the first centrifugation is carried out after the pH value is adjusted to be 6, and the filter residue is subjected to enzymolysis treatment after washing;

3) adjusting the pH value of the supernatant obtained after the centrifugation in the step 2) to 4, and then carrying out secondary centrifugation and drying to obtain a lignin fraction II;

4) adjusting the pH value of the supernatant obtained after the centrifugation in the step 3) to 2, and then carrying out third centrifugation and drying to obtain a lignin fraction III.

The invention mainly aims at the walnut shells with higher lignin content and adopts alkaline tetrahydrofurfuryl alcohol for pretreatment, thereby removing a large amount of lignin and partial hemicellulose, and in addition, partial hemicellulose also has degradation reaction and peeling reaction under the alkaline condition. After the reaction is finished, performing continuous gradient pH sedimentation on the black liquor rich in lignin, separating out lignin with different molecular weights in a grading way, and then centrifuging, washing and drying to obtain a series of lignin products with high purity, low dispersibility and different molecular weights.

The specific embodiment of the invention is as follows:

example 1

After crushing, sieving, washing and drying the walnut shells, taking 400g as a raw material for biomass pretreatment, dividing the raw material into 4 parts, and respectively transferring the 4 parts into 1000mL blue-cap bottles according to the proportion of 1:5, adding 500ml of 5 percent alkaline tetrahydrofurfuryl alcohol solution (w/w) respectively, and then putting the mixture into a sterilizing pot for reaction at the reaction temperature of 135 ℃ for 90 min. After the pretreatment, after the non-woven fabric is subjected to vacuum filtration, 1000ml of filtrate is taken out to be put in a beaker, 3 times of water is added to dilute the organic solvent, then, the pH value is slowly adjusted to 6, a part of lignin (lignin fraction II) is settled out, the filtrate is collected and adjusted to pH 4, the other part of lignin (lignin fraction II) is settled out, the filtrate is collected, the pH value is adjusted to 2, the last part of lignin (lignin fraction III) is settled out, and after centrifugation and drying, the lignin is subjected to component analysis and GPC molecular weight determination (an apparatus: Agilent-1260 II high performance liquid chromatograph; the analysis conditions are that a chromatographic column is MIXED-D and 300 x 7.5mm, a mobile phase is chromatographic grade tetrahydrofuran, a column temperature is 40 ℃, a detector is a RID detector and a sample rate is 20 mu L, and a flow rate is 0.5 mL/min).

The purity of lignin was analyzed to be 95.23%, the relative number average molecular weight of lignin was 2124 and the weight average molecular weight was 3048, and the dispersion coefficient PDI was 1.43.

Comparative example 1

After crushing, sieving, washing and drying the walnut shells, taking 400g as a raw material for biomass pretreatment, dividing the raw material into 4 parts, and respectively transferring the 4 parts into 1000mL blue-cap bottles according to the proportion of 1:5, adding 500ml of 5 percent alkaline tetrahydrofurfuryl alcohol solution (w/w) respectively, and then putting the mixture into a sterilizing pot for reaction at the reaction temperature of 135 ℃ for 90 min. After the pretreatment, the filtrate is subjected to vacuum filtration by non-woven fabrics, 1000mL of the filtrate is taken out and put into a beaker, water with the volume of 3 times is added to dilute the organic solvent, the pH is slowly adjusted to 2, the lignin is completely settled out, and after centrifugation and drying, the lignin is subjected to component analysis and GPC molecular weight determination (an instrument: Agilent-1260 II high performance liquid chromatograph; the analysis conditions are that a chromatographic column is MIXED-D and 300 x 7.5mm, a mobile phase is chromatographic grade tetrahydrofuran, the column temperature is 40 ℃, a detector is a RID detector and 40 ℃, the sample injection amount is 20 mu L, and the flow rate is 0.5 mL/min).

The purity of the lignin was analyzed to be 90.66%, the relative number average molecular weight of the lignin was 1458 and the weight average molecular weight was 3215, and the dispersion coefficient PDI was 2.20.

Comparative example 2

After crushing, sieving, washing and drying the walnut shells, taking 400g as a raw material for biomass pretreatment, dividing the raw material into 4 parts, and respectively transferring the 4 parts into 1000mL blue-cap bottles according to the proportion of 1:5, adding 500ml of 5 percent alkaline tetrahydrofurfuryl alcohol solution (w/w) respectively, and then putting the mixture into a sterilizing pot for reaction at the reaction temperature of 135 ℃ for 90 min. After the pretreatment, the filtrate was subjected to suction filtration under reduced pressure through a nonwoven fabric, 1000mL of the filtrate was taken out into a beaker, and 3 times the volume of water was added to dilute the organic solvent, then the pH was slowly adjusted to 6, a part of the lignin (lignin fraction I) was precipitated, and after centrifugation and drying, the lignin was subjected to component analysis and GPC molecular weight measurement (instrument: Agilent-1260 II high performance liquid chromatograph; analytical conditions are: MIXED-D, 300X 7.5mm for a chromatographic column; chromatographic grade tetrahydrofuran for a mobile phase; 40 ℃ for a column temperature; RID detector, 40 ℃ for a sample introduction: 20. mu.L; and a flow rate: 0.5 mL/min).

The purity of the lignin was 95.96%, the relative number average molecular weight of the lignin was 1548 and the weight average molecular weight was 3985, and the dispersion coefficient PDI was 2.59.

Comparative example 3

After crushing, sieving, washing and drying the walnut shells, taking 400g as a raw material for biomass pretreatment, dividing the raw material into 4 parts, and respectively transferring the 4 parts into 1000mL blue-cap bottles according to the proportion of 1:5, adding 500ml of 5 percent alkaline tetrahydrofurfuryl alcohol (w/w) respectively, and then putting the mixture into a sterilizing pot for reaction at the reaction temperature of 135 ℃ for 90 min. After the pretreatment, the solution was subjected to suction filtration through a nonwoven fabric under reduced pressure, 1000ml of the filtrate was taken out into a beaker, and 3 times the volume of water was added to dilute the organic solvent, then the pH was slowly adjusted to 6, a part of the lignin was precipitated, the filtrate was collected and adjusted to pH 4, and a part of the lignin (lignin fraction II) was precipitated again. After centrifugation and drying, the lignin was subjected to component analysis and GPC molecular weight measurement (instrument: Agilent-1260 II high performance liquid chromatograph; analysis conditions: chromatographic column: MIXED-D, 300X 7.5 mm; mobile phase: chromatographic grade tetrahydrofuran; column temperature: 40 ℃; detector: RID detector; 40 ℃; sample introduction: 20. mu.L; flow rate: 0.5 mL/min).

The purity of lignin was 94.95%, the relative number average molecular weight of lignin was 2373 and the weight average molecular weight was 3608, and the dispersion coefficient PDI was 1.52.

By comparing example 1 with comparative examples 1 to 3, it can be seen that the "black liquor" rich in lignin is subjected to continuous gradient pH sedimentation, lignin with different molecular weights is separated out in a grading manner, and then a series of lignin products with high purity, low dispersibility and different molecular weights are obtained by centrifugation, washing and drying.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.