阅读说明：本技术 一种冷冻预处理协同秸秆碳基固体酸水解纤维素的方法 (Method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid ) 是由 陆佳 刘伟 王欣 周闯 苏小红 范超 王玉鹏 秦国辉 孙丽 于 2019-11-13 设计创作，主要内容包括：本发明涉及一种冷冻预处理协同秸秆碳基固体酸水解纤维素的方法,属于纤维素水解方法技术领域。为解决固体酸催化纤维素水解效率低的问题,本发明提供了一种冷冻预处理协同秸秆碳基固体酸水解纤维素的方法,首先纤维素在-18～-30℃的环境下进行冷冻预处理,经盐酸再生得到低结晶度的再生纤维素,然后以农作物秸秆经碳化、磺化处理得到的秸秆碳基固体酸为催化剂对再生纤维素进行水解,将纤维素高效转化为还原糖。本发明经预处理得到的纤维素结晶度降低,能够有效的增加纤维素与催化剂的接触面积,同时本发明制备的秸秆碳基固体酸表面酸量高,催化活性强,能显著提高纤维素的水解效率。将本发明应用于北方寒冷地区,还能进一步节约预处理成本。(The invention relates to a method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid, and belongs to the technical field of cellulose hydrolysis methods. In order to solve the problem of low hydrolysis efficiency of solid acid catalytic cellulose, the invention provides a method for hydrolyzing cellulose by freezing pretreatment and straw carbon-based solid acid. The crystallinity of the cellulose obtained by pretreatment is reduced, the contact area of the cellulose and a catalyst can be effectively increased, and meanwhile, the straw carbon-based solid acid prepared by the method has high surface acid content and strong catalytic activity, and can remarkably improve the hydrolysis efficiency of the cellulose. The method is applied to northern cold regions, and can further save the pretreatment cost.)

1. A method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid is characterized by comprising the following steps:

step one, freezing pretreatment and regeneration:

uniformly mixing cellulose and a sodium hydroxide solution according to a certain mass volume ratio, freezing the mixture for 24 hours at the temperature of between 18 ℃ below zero and 30 ℃ below zero, taking the mixture out, naturally thawing the mixture in a room temperature environment, and stirring the mixture;

preparing a hydrochloric acid solution with the same molar volume as the sodium hydroxide solution, mixing the obtained unfrozen solution with the hydrochloric acid solution to make the mixed solution neutral, wherein white floccule generated in the mixed solution is regenerated cellulose;

step two, preparing the straw carbon-based solid acid:

drying, crushing and sieving straws to obtain straw powder, carbonizing the straw powder under the protection of nitrogen to obtain black powder, grinding the black powder, adding the ground black powder into concentrated sulfuric acid according to a certain solid-liquid ratio to perform sulfonation reaction, filtering a mixed system obtained by the reaction, collecting solids, and cleaning the mixed system until no SO can be detected in a cleaning solution₄ ^2-Drying to obtain straw carbon-based solid acid;

step three, hydrolyzing cellulose:

and (3) adding the carbon-based solid acid of the straw obtained in the step two into the mixed solution obtained in the step one, uniformly mixing, hydrolyzing at a certain temperature, and performing solid-liquid separation after the hydrolysis reaction is finished to obtain hydrolysate containing reducing sugar.

2. The method for hydrolyzing cellulose by using freezing pretreatment cooperated straw carbon-based solid acid according to claim 1, wherein the mass volume ratio of the cellulose to a sodium hydroxide solution in the first step is 0.01-0.08 g: 1 mL; the mass concentration of the sodium hydroxide solution is 1-9%.

3. The method for hydrolyzing the cellulose by the freezing pretreatment cooperated with the straw carbon-based solid acid according to the claim 1 or 2, wherein the straw in the second step is crop straw including corn straw, soybean straw, rice straw, wheat straw or sorghum straw, and the sieving is 100-mesh.

4. The method for hydrolyzing cellulose by freezing pretreatment and straw carbon-based solid acid according to claim 3, wherein the straw powder carbonization treatment conditions in the second step are that the temperature is increased to 300-450 ℃ at a temperature rise rate of 5 ℃/min, and the temperature is kept for 2-5 h.

5. The method for hydrolyzing cellulose by using the freezing pretreatment cooperated with the straw carbon-based solid acid according to claim 4, wherein the solid-to-liquid ratio of the black powder to concentrated sulfuric acid in the second step is 1 g: 10-20 mL.

6. The method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid according to claim 5, wherein the sulfonation reaction condition in the second step is reaction at 70-200 ℃ for 2-8 h.

7. The method for hydrolyzing cellulose by using the freezing pretreatment cooperated with the straw carbon-based solid acid according to claim 6, wherein the washing in the second step is washing by using hot water at 80 ℃, and the drying temperature is 80 ℃.

8. The method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid in cooperation with the straw carbon-based solid acid according to claim 7, wherein the mass ratio of the adding amount of the straw carbon-based solid acid to the total cellulose in the mixed solution in the third step is 1-3: 1.

9. The method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid according to claim 8, wherein the hydrolysis reaction in the third step is performed under the condition of stirring speed of 1000r/min and at the temperature of 140-200 ℃ for 30-180 min.

Technical Field

The invention belongs to the technical field of cellulose hydrolysis methods, and particularly relates to a method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid.

Background

Today, where conventional energy sources are increasingly in short supply, biomass can receive a wide range of attention. Plants produce millions of tons of cellulose each year through photosynthesis, and cellulose is formed by connecting numerous glucose units through glycosidic bonds and hydrogen bonds. Under certain conditions, cellulose can be converted into saccharides through hydrolysis, and the saccharides are taken as a platform to be further produced into liquid fuel and a series of basic platform compounds with high added values, such as fuel ethanol, 5-hydroxymethylfurfural, levulinic acid, polyhydric alcohol and the like through chemical conversion or biological catalysis. Therefore, the conversion of cellulose to sugars is a key link in our exploitation of biomass, the "sugar mine". At present, cellulose hydrolysis mainly comprises biological enzyme hydrolysis and liquid acid hydrolysis, and the two methods have the common problems of difficult separation of products and catalysts, complex catalyst recycling process and the like.

The heterogeneous catalyst is an important method for solving the problem of separation of the catalyst from the product, and therefore, in recent years, the development of a carbon-based solid acid catalyst has attracted attention. The original researchers utilized the carbon-containing compounds such as polycyclic aromatic hydrocarbon, glucose and microcrystalline cellulose to prepare the novel amorphous carbon-based solid acid catalytic hydrolysis cellulose containing high-density sulfonic acid groups, and higher reducing sugar yield is obtained, but the preparation cost of the carbon-based solid acid is higher.

Then, the research of the carbon-based solid acid taking the biomass as the raw material is carried out successively, the Wanluol of southern university and the like disclose the straw carbon-based solid acid prepared by the one-step solvothermal method, the straw is reacted with concentrated sulfuric acid at the temperature of 200 ℃ for 12 hours, and the surface acid concentration of the obtained straw carbon-based solid acid is only 1.01 mmol/g^-1The industrialization requirement of cellulose hydrolysis cannot be met.

Meanwhile, in the practical application process, because of the influence of intramolecular and intermolecular hydrogen bonds, the glycosidic bond of the cellulose is enclosed in the crystal region structure, and the contact of the glycosidic bond with the catalyst is hindered, so that the efficiency of catalyzing the hydrolysis of the cellulose by the solid acid is lower.

Disclosure of Invention

In order to solve the problem of low hydrolysis efficiency of solid acid catalytic cellulose, the invention provides a method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid.

The technical scheme of the invention is as follows:

a method for hydrolyzing cellulose by using freezing pretreatment and straw carbon-based solid acid comprises the following steps:

step one, freezing pretreatment and regeneration:

uniformly mixing cellulose and a sodium hydroxide solution according to a certain mass volume ratio, freezing the mixture for 24 hours at the temperature of between 18 ℃ below zero and 30 ℃ below zero, taking the mixture out, naturally thawing the mixture in a room temperature environment, and stirring the mixture;

preparing a hydrochloric acid solution with the same molar volume as the sodium hydroxide solution, mixing the obtained unfrozen solution with the hydrochloric acid solution to make the mixed solution neutral, wherein white floccule generated in the mixed solution is regenerated cellulose;

step two, preparing the straw carbon-based solid acid:

drying, pulverizing and sieving straw to obtainThe method comprises the steps of carbonizing straw powder under the protection of nitrogen to obtain black powder, grinding the black powder, adding the ground black powder into concentrated sulfuric acid according to a certain solid-liquid ratio for sulfonation reaction, performing suction filtration on a mixed system obtained by the reaction, collecting solids, cleaning the solids until SO cannot be detected in a cleaning solution₄ ^2-Drying to obtain straw carbon-based solid acid;

step three, hydrolyzing cellulose:

and (3) adding the carbon-based solid acid of the straw obtained in the step two into the mixed solution obtained in the step one, uniformly mixing, hydrolyzing at a certain temperature, and performing solid-liquid separation after the hydrolysis reaction is finished to obtain hydrolysate containing reducing sugar.

Further, the mass-to-volume ratio of the cellulose to the sodium hydroxide solution in the first step is 0.01-0.08 g: 1 mL; the mass concentration of the sodium hydroxide solution is 1-9%.

Further, the straws in the second step are crop straws comprising corn straws, soybean straws, rice straws, wheat straws or sorghum straws, and the sieving is a 100-mesh sieve.

And further, the carbonization treatment condition of the straw powder in the second step is to heat the straw powder to 300-450 ℃ at a heating rate of 5 ℃/min and keep the temperature for 2-5 h.

Further, the solid-to-liquid ratio of the black powder to the concentrated sulfuric acid in the second step is 1 g: 10-20 mL.

Further, the sulfonation reaction condition in the second step is reaction for 2-8 hours at 70-200 ℃.

Further, in the second step, the cleaning is performed by using hot water at 80 ℃, and the drying temperature is 80 ℃.

Further, the mass ratio of the adding amount of the carbon-based solid acid in the straw to the total cellulose in the mixed solution in the third step is 1-3: 1.

Further, the hydrolysis reaction in the third step is carried out for 30-180 min at 140-200 ℃ under the stirring speed of 1000 r/min.

The invention has the beneficial effects that:

the method for hydrolyzing the cellulose by the freezing pretreatment and straw carbon-based solid acid provided by the invention has the advantages that the freezing pretreatment is carried out on the cellulose under the low-temperature environment of-18 to-30 ℃, the crystallinity of the regenerated cellulose is reduced, the contact area of the cellulose and a catalyst can be effectively increased, and the hydrolysis efficiency of the cellulose is improved.

The carbon-based solid acid prepared by the invention takes the straws of crops such as corn and the like as raw materials, has large yield, low cost and simple preparation process, and develops a new way for utilizing the high added value of the straws. The carbon-based solid acid prepared by the method contains various active groups on the surface, and the total acid amount can reach 5.58 mmol/g at most^-1The catalyst has strong catalytic activity and high thermal stability, and has good catalytic effect for cellulose hydrolysis. When the carbon-based solid acid of the straw prepared by the method is used for cellulose hydrolysis, the yield of reducing sugar reaches 15.2-48.9%, and the conversion rate of cellulose reaches 25.1% -65.1%.

The method for hydrolyzing the cellulose by the freezing pretreatment and the straw carbon-based solid acid is applied to northern cold regions, can utilize the natural low-temperature cold environment of the cold regions as the reaction condition, saves the pretreatment cost, and is a new green and low-energy-consumption auxiliary pretreatment technology for improving the straw carbon-based solid acid hydrolysis efficiency.

Drawings

FIG. 1 is a process flow diagram of a method for hydrolyzing cellulose by freezing pretreatment and straw carbon-based solid acid;

FIG. 2 is a comparative XRD pattern of dried raw material cellulose used in example 7 and regenerated cellulose obtained after the freezing pretreatment;

FIG. 3 is an XRD pattern of the straw carbon-based solid acid prepared in example 5;

FIG. 4 is a FT-IR diagram of the carbon-based solid acid from straw prepared in example 5.

Detailed Description

The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.