A method for preparing a bifunctional mesoporous solid acid catalyst and its application in the hydrolysis of cellulose to produce glucose.

Abstract

This invention provides a method for preparing a bifunctional mesoporous solid acid catalyst and its application in the hydrolysis of cellulose to produce glucose. Using alkali lignin as the carbon source and sucralose as the chlorine source, the bifunctional mesoporous solid acid catalyst is obtained after high-temperature carbonization and concentrated sulfuric acid sulfonation. This catalyst not only possesses a high density of -SO3H groups, enabling efficient cleavage of cellulose glycosidic bonds, but also exhibits -Cl groups that can form hydrogen bonds with cellulose, enhancing the catalyst's adsorption capacity for cellulose polysaccharides. When the prepared catalyst is used for cellulose hydrolysis, it can efficiently convert cellulose into glucose at a temperature of 150–190 °C for 2–6 h. It exhibits advantages such as high catalytic efficiency, few byproducts, and low corrosiveness to equipment, making it an environmentally friendly solid acid catalyst.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy utilization technology, specifically, it relates to a method for preparing a bifunctional mesoporous solid acid catalyst and its application in the hydrolysis of cellulose to produce glucose. Background Technology

[0002] Biomass, as a renewable energy source, can be directly converted into fuel or used to produce biochemicals and biomaterials. Its efficient utilization can meet the demand for low-carbon energy, reduce environmental pollution, and is also an important means of achieving my country's "dual-carbon" goals. Lignocellulosic biomass is widely distributed and low-cost, possessing enormous development potential. Cellulose, accounting for 40%–55% of the weight of lignocellulosic biomass, is the most abundant renewable carbohydrate in nature, making the targeted conversion of cellulose to produce platform compounds of great significance.

[0003] Cellulose is a high-molecular-weight polymer composed of glucose monosaccharides linked by β-1,4-glycosidic bonds. Hydrolysis can produce glucose, a platform compound, which can be further converted into high-value chemicals such as sorbitol and levulinic acid through hydrogenation and dehydration. Therefore, converting cellulose into glucose via hydrolysis allows for its high-value utilization. During cellulose hydrolysis, achieving high sugar yields depends on highly active and acid-resistant catalysts; however, water-rich environments easily lead to catalyst hydration deactivation and decreased stability.

[0004] In recent years, researchers have developed various catalysts for the hydrolysis of cellulose to produce sugars. Among them, carbon-based solid acids have attracted widespread attention due to their advantages such as strong acid resistance, abundant pore structure, and tunable active sites. Patent [CN108273526A] discloses a sulfonated carbon solid acid catalyst for cellulose hydrolysis, which achieves a microcrystalline cellulose conversion rate of 65.1% and a glucose yield of 41.4% under reaction conditions of 150 °C and 12 h. Patent [CN109759112A] prepared a mesoporous carbon-nitrogen catalyst through calcination and acid modification, achieving a cellulose conversion rate of 82.6% under reaction conditions of 190 °C and 5 h, indicating that pore size control of the catalyst to form more mesopores is beneficial to cellulose conversion. Lignin has advantages such as low cost and high carbon content, making it an excellent carbon source for preparing mesoporous carbon catalysts. Wang et al. prepared a mesoporous sulfonated carbon catalyst for cellulose hydrolysis using alkali lignin as a carbon source, achieving a glucose yield of 42.5% at 180 °C for 7 h [Chemical Physics Letters. 2019, 736: 136808]. However, the catalyst still suffers from low glucose yield and long reaction time, and its synergistic effect in precisely controlling the mesoporous structure and efficiently introducing acidic sites remains insufficient, requiring further research.

[0005] To address the above issues, this invention proposes developing a bifunctional mesoporous solid acid catalyst by controlling the pore structure and acidic sites of the catalyst through processes such as co-carbonization and sulfonation of sucralose and alkali lignin. Furthermore, by utilizing the adsorption and catalytic functions of this catalyst, the degradation of sugars during cellulose hydrolysis is inhibited, enabling the efficient conversion of cellulose into glucose and achieving high-value conversion and utilization of cellulose. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a bifunctional mesoporous solid acid catalyst and its application in catalyzing the hydrolysis of cellulose to produce glucose, thereby achieving efficient glucose production.

[0007] To achieve the above objectives, the technical solution adopted in this invention is as follows: sucralose and alkali lignin are co-carbonized to obtain a mesoporous carbon precursor, which is then sulfonated with concentrated sulfuric acid. The synergistic effect of adsorption groups and sulfonic acid groups is utilized to improve the catalytic effect and promote the efficient conversion of cellulose into glucose.

[0008] The primary objective of this invention is to provide a method for preparing a bifunctional mesoporous solid acid catalyst; the secondary objective is to provide an application of this catalyst for the hydrolysis of cellulose to prepare glucose.

[0009] In a first aspect, the present invention provides a bifunctional mesoporous solid acid catalyst. The preparation method of the bifunctional mesoporous solid acid catalyst includes the following steps: S1, adding sucralose and alkali lignin in a mass ratio of 1:1-3 to a beaker containing a certain amount of deionized water, and rapidly stirring to obtain a homogeneous mixture; S2, heating and stirring the homogeneous mixture obtained in step S1 to evaporate the water, obtaining a dry black solid chlorine-doped alkali lignin; S3, carbonizing the chlorine-doped alkali lignin obtained in step S2 in a fixed-bed reactor under a nitrogen atmosphere at 600-800 °C, and then acid-washing, washing, filtering, and drying the resulting solid to obtain a mesoporous carbon precursor; S4, placing the mesoporous carbon precursor obtained in step S3 and a certain amount of 98% concentrated sulfuric acid solution into a three-necked flask, heating and stirring at 120-160 °C, and then filtering, washing, and drying to obtain the bifunctional mesoporous solid acid catalyst. The preferred process conditions for this catalyst preparation method are as follows:

[0010] In step S1, the preferred mass ratio of sucralose to alkali lignin is 1:2, the liquid-solid ratio of deionized water to alkali lignin is 20 mL: 1 g, the oil bath temperature is 40 ℃, and the time is 2 h.

[0011] In step S2, the heating temperature is 80~105 ℃.

[0012] In step S3, the carbonization reaction conditions are: heating from room temperature to 700 ℃ at a heating rate of 5 ℃ / min and holding for 60 min;

[0013] The pickling solution used is a 0.1-1 mol / L hydrochloric acid solution, and the washing solution used is deionized water; the drying temperature is 105 ℃.

[0014] In step S4, the solid-liquid ratio between the mesoporous carbon precursor and the 98% concentrated sulfuric acid solution is 1 g: 20 mL, the preferred heating temperature is 140 °C, the heating time is 4 h, and the washing solution is deionized water at 80 °C.

[0015] In a second aspect, the present invention provides a method for preparing glucose by hydrolyzing cellulose using a bifunctional mesoporous solid acid catalyst, comprising the following steps: under a nitrogen atmosphere, the catalyst, cellulose raw material and deionized water are thoroughly mixed in a certain proportion, heated to 150~190 °C and stirred, and after reacting for 2~6 h, glucose product is obtained.

[0016] Preferably, the mass ratio between the catalyst and the cellulose raw material is 1:1, and the solid-liquid ratio between the cellulose raw material and deionized water is 1 g: 20 mL.

[0017] Preferably, the optimal temperature for cellulose hydrolysis is 170 °C, and the optimal reaction time is 4 h.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] First, the catalyst provided by this invention employs a co-carbonization-sulfonation process of alkali lignin and sucralose to form an ordered mesoporous structure, which is beneficial for substrate diffusion and mass transfer during the reaction.

[0020] Secondly, the addition of sucralose introduces chlorine groups into the catalyst, which enhances the catalyst's adsorption capacity for cellulose. The sulfonation process introduces sulfonic acid groups, which promote the breaking of β-1,4-glycosidic bonds in cellulose, resulting in efficient hydrolysis of cellulose and thus obtaining a high glucose yield. Attached Figure Description

[0021] Figure 1 The SEM characterization results are for the catalysts prepared in Examples 2 and 4. Figure 2 The results are FTIR test results for the catalysts prepared in Examples 1-4. Detailed Implementation

[0022] To more clearly illustrate the present invention, the following description, in conjunction with embodiments, will further elaborate on the invention. The content described below is merely a partial embodiment of the present invention, and those skilled in the art should understand that the following description is for illustrative purposes only and is not intended to limit the scope of protection of the present invention.

[0023] The method for calculating the cellulose conversion rate of the present invention is as follows:

[0024]

[0025] The method for calculating glucose yield in this invention is as follows:

[0026]

[0027] The chemical bonds and functional groups of the catalyst were analyzed using the Nicolet iS spectrometer from Thermo Fisher Scientific. 2 mg of catalyst was uniformly dispersed in 120 mg KBr, directly compressed into a tablet, and the sample was measured at 4000 cm⁻¹. -1 ~400 cm -1 Fourier transform infrared spectroscopy within the wavelength range, with 32 scans and a resolution of 4 cm⁻¹. -1 .

[0028] The surface morphology of the catalyst was observed using a Hitachi SU8600 scanning electron microscope. During the test, the test voltage was 3 kV, the working distance was 8.2 mm, and the magnification was 500~2000 times.

[0029] The pore size of the catalyst was analyzed using a JW-BK132F specific surface area and pore size analyzer from Beijing Jingwei Gaobo Co., Ltd. Prior to analysis, the catalyst was pretreated in a vacuum environment at 105 °C for 300 min, followed by nitrogen adsorption-desorption experiments at -196 °C.

[0030] The content of sulfonic acid groups (-SO3H) in the catalyst was determined by acid-base titration. 0.100 g of catalyst was accurately weighed into a beaker, and 30 mL of 2 mol / L NaCl solution was added. The mixture was then sonicated at room temperature for 60 min to release H2O from the catalyst. + and Na in the solution + Fully allow ion exchange to occur. Filter the solution, add 2-3 drops of phenolphthalein indicator to the filtrate, and titrate with 0.01 mol / L NaOH solution. When the solution changes from colorless to light red, record the volume V of NaOH solution consumed. The content of sulfonic acid groups in the catalyst can then be calculated as follows:

[0031]

[0032] Example 1

[0033] The preparation method of the bifunctional mesoporous solid acid catalyst includes the following steps: 6 g of alkali lignin, 2 g of sucralose, and 120 mL of deionized water are added sequentially to a beaker. The mixture is stirred at 40 °C for 2 h in an oil bath to obtain a homogeneous mixture. After stirring, the homogeneous mixture is heated in an oil bath at 105 °C to evaporate the water, yielding a dry black solid chlorine-doped alkali lignin. The chlorine-doped alkali lignin is then placed in a fixed-bed reactor and heated to 700 °C under a nitrogen atmosphere, held for 60 min. The resulting solid is washed with 30 mL of 0.2 mol / L hydrochloric acid solution, followed by washing with deionized water and filtration until neutral. The solid is then dried at 105 °C for 12 h to obtain a mesoporous carbon precursor. 3 g of mesoporous carbon precursor and 60 mL of 98% concentrated sulfuric acid solution were added to a three-necked flask and stirred in an oil bath at 140 °C for 4 h. After heating, the mixture was cooled to room temperature, washed with deionized water at 80 °C until neutral, and dried at 105 °C for 12 h to obtain a bifunctional mesoporous solid acid catalyst (CB3-Cl-SO3H).

[0034] The cellulose hydrolysis method includes the following steps: 2 g of eutectic solvent cellulose (from the research group's patent CN117683244A) and 2 g of catalyst are mixed with 40 mL of deionized water in a 100 mL high-pressure reactor. The air in the reactor is replaced with nitrogen, and the reaction is carried out at 170 °C for 4 h. After the hydrolysis reaction is completed, the mixture is naturally cooled to room temperature, and the liquid and solid are separated by vacuum filtration.

[0035] Example 2

[0036] The mass of sucralose in Example 1 was replaced with 3 g to obtain the catalyst CB2-Cl-SO3H, and everything else was the same as in Example 1.

[0037] Example 3

[0038] The mass of sucralose in Example 1 was replaced with 6 g to obtain the catalyst CB1-Cl-SO3H, and everything else was the same as in Example 1.

[0039] Example 4

[0040] The mass of sucralose in Example 1 was replaced with 0 g to obtain catalyst CB-SO3H, otherwise it was the same as in Example 1.

[0041] The hydrolysis results of Examples 1-4 are shown in Table 1:

[0042] Table 1 Sucralose Addition Amount

[0043]

[0044] Comparing the pore size and cellulose hydrolysis performance of the catalysts prepared in Examples 1-3, it was found that the catalyst in Example 2 had a larger average pore size and higher cellulose hydrolysis conversion and glucose yield. Comparing the -SO3H content and cellulose hydrolysis performance of the catalysts prepared in Examples 3 and 4, it was found that the catalyst with higher -SO3H content had better catalytic performance and higher cellulose conversion and glucose yield. Combined with SEM (… Figure 1 ) and FTIR ( Figure 2 Characterization results showed that the addition of sucralose increased the catalyst pore size; the S=O characteristic peak corresponding to the -SO3H group was stronger, indicating a higher -SO3H content and stronger catalyst acidity; the characteristic peak of C-Cl indicated that Cl was successfully introduced, and the adsorption between the catalyst and cellulose through hydrogen bonding was enhanced. In Example 2, the catalyst CB2-Cl-SO3H prepared with a sucralose and alkali lignin mass ratio of 1:2 showed good catalytic performance, with a cellulose conversion rate of 77.89% and a glucose yield of 58.92%.

[0045] Example 5

[0046] The carbonization temperature in Example 2 was replaced with 600 °C instead of 700 °C, and everything else was the same as in Example 2.

[0047] Example 6

[0048] The carbonization temperature in Example 2 was replaced with 800 °C instead of 700 °C, and everything else was the same as in Example 2.

[0049] Example 7

[0050] The carbonization time in Example 2 was replaced with 30 min instead of 60 min, and everything else was the same as in Example 2.

[0051] Example 8

[0052] The carbonization time in Example 2 was changed from 60 min to 90 min, and everything else was the same as in Example 2.

[0053] The results of hydrolysis experiments 5-8 in Example 2 are shown in Table 2:

[0054] Table 2 Different carbonization conditions

[0055]

[0056] Comparing the catalysts prepared in Examples 6-8 and their SO3H content and cellulose hydrolysis performance, it was found that the catalyst in Example 6 had a higher SO3H content, resulting in higher cellulose conversion and glucose yield. Comparing the catalyst pore size and cellulose hydrolysis performance in Examples 5 and 8, it was found that the catalyst in Example 8 had a larger average pore size, resulting in higher cellulose hydrolysis conversion and glucose yield. In Example 2, the catalyst had the largest average pore size and the highest SO3H content, yielding the highest cellulose conversion (77.89%) and the highest glucose yield (58.92%).

[0057] Example 9

[0058] The amount of catalyst used in Example 2 was replaced with 0.67 g instead of 2 g, and everything else was the same as in Example 2.

[0059] Example 10

[0060] The amount of catalyst used in Example 2 was replaced with 1 g instead of 2 g, and everything else was the same as in Example 2.

[0061] Example 11

[0062] The amount of catalyst used in Example 2 was replaced with 4 g instead of 2 g, and everything else was the same as in Example 2.

[0063] The results of hydrolysis experiments 9-11 in Example 2 are shown in Table 3:

[0064] Table 3 Catalyst Usage

[0065]

[0066] As can be seen from the data in the table, when the mass ratio of catalyst to cellulose was 1:1 in Example 2, the glucose yield was the highest at 58.92%, and the cellulose conversion rate was 77.89%.

[0067] Example 12

[0068] The reaction temperature in Example 2 was replaced with 160 °C instead of 170 °C, and everything else was the same as in Example 2.

[0069] Example 13

[0070] The reaction temperature in Example 2 was replaced with 180 °C instead of 170 °C, and everything else was the same as in Example 2.

[0071] Example 14

[0072] The reaction time in Example 2 was changed from 4 h to 2 h, and everything else was the same as in Example 2.

[0073] Example 15

[0074] The reaction time in Example 2 was changed from 4 h to 3 h, and everything else was the same as in Example 2.

[0075] Example 16

[0076] The reaction time in Example 2 was changed from 4 h to 5 h, and everything else was the same as in Example 2.

[0077] The results of hydrolysis experiments 12-16 in Example 2 are shown in Table 4:

[0078] Table 4 Different reaction conditions

[0079]

[0080] By comparing the hydrolysis performance of the catalysts in Examples 2 and 12-16 under different conditions, in Example 2, a higher cellulose conversion rate (77.89%) and a higher glucose yield (58.92%) were obtained at a reaction temperature of 170 °C and a reaction time of 4 h. This is because when the reaction temperature is too low, cellulose hydrolysis is incomplete; as the reaction temperature increases, the cellulose conversion rate increases. Extending the reaction time can improve the cellulose conversion rate and significantly increase the glucose yield, but the glucose yield decreases after 4 h, indicating that glucose undergoes further degradation.

[0081] Comparative Example 1

[0082] Example 2 in the patent application with publication number CN109806899A serves as a comparative example of the present invention.

[0083] (1) Preparation of hydrolysis catalyst

[0084] First, aminoguanidine hydrochloride and silica were dissolved in water at a mass ratio of 1:3. The solution was then heated and stirred at 80 °C to evaporate the water, yielding solid particles. These particles were ground and heated to 500 °C at a nitrogen atmosphere at a rate of 5 °C / min, held for 1 h, to obtain a brownish-yellow solid powder. The brownish-yellow solid powder was immersed in a 5% HF solution to remove SiO2, filtered, and washed repeatedly with deionized water until clean with hydrofluoric acid. The solid was then dried in an oven at 80 °C for 12 h to obtain a mesoporous carbonitriding material. The prepared carbonitriding material was immersed in 7 mol / L hydrochloric acid for 24 h, filtered, and washed repeatedly with deionized water until clean with hydrochloric acid. Finally, it was dried in an oven at 80 °C for 12 h to obtain a carbon-based mesoporous solid acid catalyst.

[0085] (2) Cellulose hydrolysis

[0086] 0.1 g of cellulose and 10 mL of water were added to a reaction vessel and allowed to soak for 2 h. Then, 0.4 g of a carbon-based mesoporous solid acid catalyst was added, and the reaction was carried out at 180 °C for 6 h. After the hydrolysis reaction was completed, the mixture was allowed to cool naturally to room temperature. The liquid and solid were separated by vacuum filtration, and the glucose in the liquid product was determined by high performance liquid chromatography. The results showed that the cellulose conversion rate was 82.5%, and the glucose yield was 36.2%.

[0087] Examples 2 and 1 show that Example 2 achieved a glucose yield of 58.92%, demonstrating a higher glucose yield. Furthermore, Comparative Example 1 uses a hard template method for pore creation, requiring the introduction of SiO2 as a template agent followed by HF etching to remove the template and form a mesoporous structure. This step is not only highly hazardous but also highly corrosive to equipment and poses an environmental pollution risk. In contrast, Example 2 utilizes in-situ self-activation pore creation through co-carbonization of sucralose and alkali lignin, eliminating the need for additional template agents and subsequent etching steps, making the process safer and more environmentally friendly.

[0088] As can be seen from the above examples, this invention obtains a bifunctional mesoporous solid acid catalyst through the co-carbonization-sulfonation process of sucralose and alkali lignin. This effectively improves the pore size and -SO3H content of the catalyst. -SO3H can catalyze the cleavage of glycosidic bonds in cellulose, and -Cl, as an adsorption group, enhances the catalyst's adsorption capacity for cellulose, thereby enhancing the catalyst's effect. The cellulose conversion rate is 77.89%, and the glucose yield is 58.92%, achieving the goal of efficiently converting cellulose into glucose.

[0089] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A bifunctional mesoporous solid acid catalyst, characterized in that, The preparation method of the bifunctional mesoporous solid acid catalyst includes the following steps: Step S1: Add a certain mass of sucralose and alkali lignin to a beaker containing a certain amount of deionized water, and stir rapidly at 40 °C for 2 h to obtain a homogeneous mixture; Step S2: The homogeneous mixture obtained in step S1 is heated and stirred at 80~105 °C to evaporate the water and obtain a dry black solid chlorine-doped alkali lignin. Step S3: The chlorine-doped alkali lignin obtained in step S2 is subjected to carbonization reaction in a fixed-bed reactor at a temperature of 600-800 °C under a nitrogen atmosphere. The resulting solid is then acid-washed, washed, filtered, and dried to obtain a mesoporous carbon precursor. Step S4: Place the mesoporous carbon precursor obtained in step S3 and a certain amount of 98% concentrated sulfuric acid solution into a three-necked flask, heat and stir, filter, wash and dry to obtain a bifunctional mesoporous solid acid catalyst.

2. The method for preparing the bifunctional mesoporous solid acid catalyst according to claim 1, characterized in that: In step S1, the mass ratio of sucralose to alkali lignin is 1:1~3, and the liquid-solid ratio between alkali lignin and deionized water is 1g:20mL.

3. The method for preparing the bifunctional mesoporous solid acid catalyst according to claim 1, characterized in that: In step S3, the filtrate is washed with 0.1-1 mol / L hydrochloric acid solution and then washed with deionized water until the filtrate is neutral.

4. The method for preparing the bifunctional mesoporous solid acid catalyst according to claim 1, characterized in that: In step S4, the solid-liquid ratio between the mesoporous carbon precursor and the 98% concentrated sulfuric acid solution is 1 g: 20 mL, the heating temperature is 120~160 ℃, the heating time is 4 h, and the washing solution is deionized water at 80 ℃.

5. A method for preparing glucose by hydrolyzing cellulose using the bifunctional mesoporous solid acid catalyst according to claim 1, characterized in that, Includes the following steps: The catalyst, cellulose raw material, and deionized water are thoroughly mixed in a certain proportion, heated to 150~190 ℃ and stirred, and the cellulose hydrolysis reaction is carried out in a nitrogen atmosphere. After 2~6 h of reaction, glucose product is obtained.

6. The method for preparing glucose by hydrolyzing cellulose using a bifunctional mesoporous solid acid catalyst according to claim 5, characterized in that: in, The cellulose raw material is eutectic solvent cellulose separated from corn stalks using a eutectic solvent. The mass ratio between the catalyst and the cellulose raw material is 1:1~3, and the solid-liquid ratio between the cellulose raw material and deionized water is 1g:20mL.

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