A mesoporous silica-based composite material with phosphotungstic acid and titanium oxide simultaneously immobilized and a cellulose hydrolysis method thereof

Abstract

This invention discloses a mesoporous silica-based composite material with phosphotungstic acid simultaneously immobilized with titanium oxide and its cellulose hydrolysis method, belonging to the field of biomass catalytic conversion technology. This invention aims to solve the problems of easy desorption of active components, low catalytic efficiency, and poor cycle stability in existing solid acid catalysts during cellulose hydrolysis. This method uses an ionic liquid as the reaction medium and a titanium-silicon-supported phosphotungstic acid composite material with a two-dimensional hexagonal ordered mesoporous structure prepared by a one-step hydrothermal synthesis as the solid acid catalyst, catalyzing the hydrolysis of cellulose to reduce sugars in the presence of water. This invention achieves highly efficient cellulose conversion through the synergistic catalytic effect of the two acid sites combined with the good solubility of cellulose in the ionic liquid. The catalyst exhibits excellent recyclability, the process conditions are well-defined, it meets the requirements of green chemistry, and it is applicable to the field of biomass resource utilization.

Description

Technical Field

[0001] This invention relates to the field of biomass catalytic conversion technology, specifically to a mesoporous silica-based composite material with phosphotungstic acid simultaneously immobilized titanium oxide and its method in cellulose hydrolysis, which is particularly suitable for the efficient catalytic hydrolysis of cellulose to prepare reducing sugars in ionic liquid systems, and belongs to the field of biomass resource utilization technology. Background Technology

[0002] Cellulose is the most abundant renewable organic carbon resource in nature. Catalytically converting it into high-value-added platform compounds such as glucose and 5-hydroxymethylfurfural (5-HMF) is of great significance in alleviating the depletion of fossil resources and environmental pollution. Cellulose is composed of glucose units linked by β-1,4-glycosidic bonds, and the key to its hydrolysis is the breaking of these glycosidic bonds.

[0003] Traditional cellulose hydrolysis often uses liquid inorganic acids (such as dilute sulfuric acid and hydrochloric acid) as catalysts. While these catalysts offer good catalytic performance, they suffer from drawbacks such as difficulty in catalyst recovery, environmental pollution from reaction waste, and equipment corrosion. Solid acid catalysts can overcome these problems, but cellulose is insoluble in water and common organic solvents, resulting in low efficiency in solid-solid catalytic reactions between solid acids and cellulose. In recent years, ionic liquids (such as [BMIm]Cl) have demonstrated excellent solubility for cellulose, enabling the transformation of solid-solid catalysis into liquid-solid catalysis and significantly improving reaction efficiency.

[0004] Polyoxometalates (POMs), especially Keggin-type phosphotungstic acid (H3PW) 12 O 40 Phosphotungstic acid (PTA) exhibits strong Brønsted acidity, making it an excellent acid catalyst. However, its direct application in cellulose hydrolysis presents challenges such as easy solubility in the reaction system, difficulty in recovery, and small specific surface area. Supporting PTA on mesoporous materials can address these issues. However, existing supported polyacid catalysts for cellulose hydrolysis suffer from problems such as easy desolvation of polyacids, poor accessibility of active sites, insufficient catalyst cycle stability, and a lack of process optimization for ionic liquid systems.

[0005] Therefore, developing a composite catalyst and its dedicated hydrolysis process for the efficient and stable catalysis of cellulose hydrolysis in ionic liquid systems is of significant application value. Summary of the Invention

[0006] Purpose of the invention This invention aims to overcome the shortcomings of existing technologies and provide a method for the hydrolysis of cellulose using a mesoporous silica-based composite material with phosphotungstic acid simultaneously immobilized with titanium oxide. This method uses an ionic liquid as a solvent and a bifunctionalized mesoporous titanium silica-supported phosphotungstic acid composite material as a catalyst. By optimizing the hydrolysis reaction conditions, it achieves efficient conversion of cellulose and high yield of reducing sugars, and the catalyst exhibits good recyclability.

[0007] Technical solution To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A mesoporous silica-based composite material with phosphotungstic acid simultaneously immobilized titanium oxide and its application in cellulose hydrolysis, wherein the mesoporous silica-based composite material with phosphotungstic acid simultaneously immobilized titanium oxide (H3PW) 12 O 40 Ti-OMS is a solid acid catalyst that uses an ionic liquid as the reaction medium to catalyze the hydrolysis of cellulose to reduce sugars in the presence of water. The specific steps include: (1) Preparation of reaction system: Microcrystalline cellulose was dissolved in ionic liquid by heating to form a homogeneous solution; mesoporous H3PW was added. 12 O 40 -Ti-OMS composite catalyst and deionized water were mixed evenly to obtain the reaction system; (2) Hydrolysis reaction: The reaction system obtained in step (1) is heated to the reaction temperature under stirring to carry out the hydrolysis reaction; (3) Product separation: After the reaction is completed, deionized water is added to the reaction system to quench the reaction, centrifuge to separate, collect the supernatant, and obtain a hydrolysis product solution containing reducing sugar and 5-hydroxymethylfurfural; (4) Catalyst recovery: The solid residue obtained by centrifugation in step (3) is washed, dried, and activated by calcination and then reused.

[0008] Further, the ionic liquid in step (1) is 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), and the mass ratio of the ionic liquid to microcrystalline cellulose is 10-30:1.

[0009] Furthermore, the dissolution temperature of the microcrystalline cellulose in step (1) is 90-110°C.

[0010] Furthermore, the mesoporous H3PW described in step (1) 12 O 40 -Ti-OMS composite catalyst H3PW 12 O 40 The load capacity is 6-10%, and the titanium-silicon molar ratio is 0.02-0.08:1.

[0011] Furthermore, the mesoporous H3PW described in step (1) 12 O 40 The mass ratio of Ti-OMS composite catalyst to microcrystalline cellulose is 0.1-0.4:1.

[0012] Further, the volume ratio of deionized water to ionic liquid in step (1) is 0.05-0.15:1.

[0013] Furthermore, the hydrolysis reaction temperature in step (2) is 120-150°C, and the reaction time is 2-6 hours.

[0014] Furthermore, the calcination activation temperature in step (4) is 300-400°C, and the calcination time is 8-12 hours.

[0015] Furthermore, the mesoporous H3PW 12 O 40 The Ti-OMS composite catalyst is a titanium-silicon supported phosphotungstic acid catalyst with a two-dimensional hexagonal ordered mesoporous structure prepared by a one-step hydrothermal synthesis method. Its average pore size is 6-9 nm and its specific surface area is 730-910 m² / g.

[0016] Beneficial effects Compared with the prior art, the present invention has the following significant advantages: High cellulose conversion rate: This invention uses mesoporous H3PW 12 O 40 The Ti-OMS composite catalyst, under optimized reaction conditions (140°C, 4 h, catalyst dosage 0.02 g / 0.1 g cellulose), achieved a cellulose conversion rate of over 99% and a total reducing sugar yield of up to 67%, significantly superior to pure H3PW. 12 O 40 Single-component supported catalysts and materials without supported polyacids.

[0017] Dual-acid site synergistic catalysis: The composite catalyst of this invention contains both tetracoordinated titanium (Lewis acid) and phosphotungstic acid (Brønsted acid). The synergistic effect of the dual acid sites enhances the protonation and hydrolytic breaking efficiency of the β-1,4-glycosidic bond of cellulose. At the same time, the ionic liquid medium further promotes the dissolution of cellulose and the interfacial contact of the catalyst, realizing a highly efficient liquid-solid catalytic process.

[0018] The catalyst exhibits good stability and is recyclable: the composite catalyst used in this invention has a stable structure in ionic liquid systems, and the active components are not easily dissolved. After calcination regeneration, the recovered catalyst can be recycled five times without a significant decrease in cellulose conversion rate and reducing sugar yield, demonstrating excellent reusability and industrial application potential.

[0019] The process conditions have been clearly optimized: This invention has optimized key process parameters such as catalyst type, polyacid loading, catalyst dosage, reaction temperature, and reaction time through a single-factor experimental system, and established the optimal reaction conditions, providing reliable technical parameters for industrial production.

[0020] The reaction mechanism is clear: This invention elucidates the hydrolysis mechanism of cellulose in an ionic liquid / composite catalyst system: the ionic liquid destroys the crystalline structure of cellulose, the catalyst synergistically catalyzes the cleavage of glycosidic bonds at the two acid sites to generate glucose, and some glucose is further isomerized to fructose and dehydrated to generate 5-HMF, providing theoretical guidance for subsequent process optimization and catalyst design.

[0021] Environmentally friendly: This invention uses a recyclable solid acid catalyst to replace the traditional liquid acid, avoiding pollution from reaction waste liquid and equipment corrosion; the ionic liquid medium can be reused, and the catalyst has excellent cycle performance, which meets the requirements of green chemistry and sustainable development. Attached Figure Description

[0022] Figure 1 shows the mesoporous H3PW in an embodiment of the present invention. 12 O 40 -Ti-OMS composite catalyst recycling performance diagram. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The scope of protection of the present invention is not limited to the following embodiments. All equivalent transformations made based on the technical solutions of the present invention fall within the scope of protection of the present invention.

[0024] The mesoporous H3PW used in this invention 12 O 40 -Ti-OMS composite catalyst as described above, "a mesoporous H3PW 12 O 40 The Ti-OMS composite catalyst was prepared using a method that utilizes commercially available microcrystalline cellulose and [BMIm]Cl with a purity ≥99%.

[0025] Example 1 A mesoporous silica-based composite material with phosphotungstic acid-supported titanium oxide and its application in cellulose hydrolysis, the specific steps of which are as follows: (1) Preparation of reaction system: Dissolve 0.1 g microcrystalline cellulose in 2.0 g [BMIm]Cl ionic liquid at 100°C to form an amber homogeneous solution; add 0.02 g 0.5PW-Ti(0.05)-OMS composite catalyst and 0.15 mL deionized water, mix well to obtain the reaction system.

[0026] (2) Hydrolysis reaction: The reaction system obtained in step (1) is heated to 140°C under stirring and kept at that temperature for 4 hours.

[0027] (3) Product separation: After the reaction is completed, 5 mL of deionized water is added to the reaction system to quench the reaction, and the mixture is centrifuged multiple times. The supernatant is collected and diluted to 25 mL with deionized water. The total reducing sugar content is determined by DNS method and the 5-hydroxymethylfurfural (5-HMF) content is determined by high performance liquid chromatography (HPLC).

[0028] (4) Catalyst recovery: The solid residue (including catalyst and unreacted cellulose) obtained by centrifugation in step (3) is dried in a vacuum drying oven. After recording the mass, it is calcined in a muffle furnace at 350°C for 10 hours to remove cellulose and attached products, and a regenerated catalyst is obtained.

[0029] The results showed that the cellulose conversion rate in this embodiment was >99%, the total reducing sugar yield was 67.0%, and the 5-HMF yield was 19.1%.

[0030] Example 2 The results were basically the same as in Example 1, except that the catalyst in step (1) was changed to 0.5PW-OMS (without Ti). The cellulose conversion rate was 84.6%, the total reducing sugar yield was 58.4%, and the 5-HMF yield was 16.6%.

[0031] Example 3 The process is basically the same as in Example 1, except that the catalyst in step (1) is changed to Ti(0.05)-OMS (without H3PW). 12 O 40 The cellulose conversion rate was measured to be 66.7%, the total reducing sugar yield was 42.1%, and the 5-HMF yield was 12.0%.

[0032] Example 4 The process is basically the same as in Example 1, except that the catalyst in step (1) is replaced with pure H3PW. 12 O 40 The cellulose conversion rate was measured to be 83.2%, the total reducing sugar yield was 57.0%, and the 5-HMF yield was 16.3%.

[0033] Example 5 The results were basically the same as in Example 1, except that the catalyst in step (1) was changed to 0.5PWs-Ti(0.05)-OMS (addition of polyacids later). The cellulose conversion rate was 81.2%, the total reducing sugar yield was 48.6%, and the 5-HMF yield was 13.7%.

[0034] Example 6 The results were basically the same as in Example 1, except that the amount of catalyst 0.5PW-Ti(0.05)-OMS in step (1) was changed to 0.01 g. The cellulose conversion rate was 87.3%, the total reducing sugar yield was 55.4%, and the 5-HMF yield was 17.2%.

[0035] Example 7 The results were basically the same as in Example 1, except that the amount of catalyst 0.5PW-Ti(0.05)-OMS in step (1) was changed to 0.03 g. The cellulose conversion rate was >99%, the total reducing sugar yield was 58.9%, and the 5-HMF yield was 15.8%.

[0036] Example 8 The reaction was basically the same as in Example 1, except that the reaction temperature in step (2) was changed to 130°C. The cellulose conversion rate was 89.7%, the total reducing sugar yield was 58.2%, and the 5-HMF yield was 15.3%.

[0037] Example 9 The reaction was basically the same as in Example 1, except that the reaction temperature in step (2) was changed to 150°C. The cellulose conversion rate was >99%, the total reducing sugar yield was 58.5%, and the 5-HMF yield was 18.7%.

[0038] Example 10 The reaction was basically the same as in Example 1, except that the reaction time in step (2) was changed to 3 hours. The cellulose conversion rate was 94.2%, the total reducing sugar yield was 59.3%, and the 5-HMF yield was 17.8%.

[0039] Example 11 The reaction was basically the same as in Example 1, except that the reaction time in step (2) was changed to 5 hours. The cellulose conversion rate was >99%, the total reducing sugar yield was 59.6%, and the 5-HMF yield was 20.4%.

[0040] Example 12 (Performance Test for Repeated Use) The catalyst recovered and regenerated in Example 1 was repeatedly subjected to the cellulose hydrolysis reaction and recycled a total of 5 times.

[0041] First cycle: Cellulose conversion >99%, total reducing sugar yield 66.5%, 5-HMF yield 18.9%; Second cycle: Cellulose conversion >99%, total reducing sugar yield 65.8%, 5-HMF yield 18.2%; Third cycle: Cellulose conversion rate >99%, total reducing sugar yield 65.1%, 5-HMF yield 18.0%; Fourth cycle: cellulose conversion rate 98.5%, total reducing sugar yield 64.3%, 5-HMF yield 17.5%; Fifth cycle: cellulose conversion rate 98.2%, total reducing sugar yield 64.0%, 5-HMF yield 17.2%.

[0042] The above results indicate that the mesoporous H3PW used in this invention... 12 O 40 The Ti-OMS composite catalyst exhibits excellent catalytic activity and cycling stability in the cellulose hydrolysis reaction. After five cycles, the cellulose conversion rate and reducing sugar yield remain at a high level, and the catalyst shows no obvious deactivation.

[0043] This invention is not limited to the specific embodiments described above. Those skilled in the art can make various modifications or variations within the scope of the essence of this invention, and these modifications or variations should also be considered within the scope of protection of this invention.

Claims

1. A method for applying a mesoporous silica-based composite material with phosphotungstic acid-simultaneously immobilized titanium oxide in cellulose hydrolysis, characterized in that, Mesoporous H3PW 12 O 40 The Ti-OMS composite catalyst is a solid acid catalyst that uses an ionic liquid as the reaction medium to catalyze the hydrolysis of cellulose to reduce sugars in the presence of water. The process includes the following steps: (1) Preparation of reaction system: Microcrystalline cellulose was dissolved in ionic liquid by heating to form a homogeneous solution; mesoporous H3PW was added. 12 O 40 -Ti-OMS composite catalyst and deionized water were mixed evenly to obtain the reaction system; (2) Hydrolysis reaction: The reaction system obtained in step (1) is heated to the reaction temperature under stirring to carry out the hydrolysis reaction; (3) Product separation: After the reaction is completed, deionized water is added to the reaction system to quench the reaction, centrifuge to separate, collect the supernatant, and obtain a hydrolysis product solution containing reducing sugar and 5-hydroxymethylfurfural; (4) Catalyst recovery: The solid residue obtained by centrifugation in step (3) is washed, dried, and activated by calcination and then reused.

2. The application method according to claim 1, characterized in that, The ionic liquid mentioned in step (1) is 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), and the mass ratio of the ionic liquid to microcrystalline cellulose is 10-30:

1.

3. The application method according to claim 1, characterized in that, The dissolution temperature of the microcrystalline cellulose in step (1) is 90-110°C.

4. The application method according to claim 1, characterized in that, The mesoporous H3PW described in step (1) 12 O 40 H3PW in Ti-OMS composite catalyst 12 O 40 The load capacity is 6-10%, and the titanium-silicon molar ratio is 0.02-0.08:

1.

5. The application method according to claim 1, characterized in that, The mesoporous H3PW described in step (1) 12 O 40 The mass ratio of Ti-OMS composite catalyst to microcrystalline cellulose is 0.1-0.4:

1.

6. The application method according to claim 1, characterized in that, The volume ratio of deionized water to ionic liquid in step (1) is 0.05-0.15:

1.

7. The application method according to claim 1, characterized in that, The hydrolysis reaction in step (2) is carried out at a temperature of 120-150°C for 2-6 hours.

8. The application method according to claim 1, characterized in that, The calcination activation temperature in step (4) is 300-400°C, and the calcination time is 8-12 hours.

9. The application method according to claim 1, characterized in that, The mesoporous H3PW 12 O 40 The Ti-OMS composite catalyst is a titanium-silicon supported phosphotungstic acid catalyst with a two-dimensional hexagonal ordered mesoporous structure prepared by a one-step hydrothermal synthesis method. Its average pore size is 6-9 nm and its specific surface area is 730-910 m² / g.

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