Preparation and application of difunctional solid acid catalyst AlPO4-SnO2

Abstract

The invention discloses a method for selectively catalyzing cellulose into levulinic acid by using a bifunctional solid acid catalyst AlPO4-SnO2, and belongs to the field of biomass resource utilization. A high-pressure reaction kettle is adopted as a reaction container, cellulose powder and a difunctional solid acid catalyst AlPO4-SnO2 are added into the reaction container according to a certain mass ratio, then a certain amount of water is added, and a degradation reaction of cellulose is carried out under a hydrothermal condition, so that high-yield levulinic acid can be obtained. The method has the advantages that the aluminum phosphate loaded tin oxide solid acid catalyst AlPO4-SnO2 simultaneously has Bronsted acid and Lewis acid, when the catalyst is used for preparing levulinic acid through catalytic conversion of cellulose under the hydrothermal condition, the reaction temperature can be reduced, the selectivity of levulinic acid can be improved, and the catalyst has good reusability and is easy for industrial production.

Description

Technical Field

[0001] The invention relates to the synthesis of aluminum phosphate-supported tin oxide solid acid catalyst AlPO4-SnO2 and its application in catalytic conversion of cellulose to levulinic acid, belonging to the field of biomass resource utilization. Background Art

[0002] The molecular structure of levulinic acid has functional groups such as carboxyl and carbonyl, and has high reactivity. It can be converted into bio-liquid fuels and various high-value chemicals. It is an important platform compound. Cellulose is a renewable biomass resource with a wide range of sources and low cost. The solid acid-catalyzed degradation of cellulose is a reaction in which cellulose is initially hydrolyzed under hydrothermal conditions to produce monosaccharides such as hexose and pentose, and then undergoes an isomerization-dehydration cascade conversion reaction through intermediate products such as glucose and 5-hydroxymethylfurfural (HMF) to obtain the levulinic acid product.

[0003] In the field of acid catalysis, solid acids have the advantages of easy separation, reusability, and simple operation. The bifunctional solid acid catalyst composed of metal oxides and zeolite molecular sieves not only connects different reactions in series, but also improves the catalytic activity through the synergistic effect of B acid and L acid. It is widely used in catalytic cracking, isomerization, transesterification and other fields. Aluminum phosphate molecular sieves are composed of Al-O tetrahedrons and PO tetrahedrons, which are strictly alternating. The overall skeleton is electrically neutral and has a regular pore structure. The surface phosphate provides B-rich B acid sites. SnO2 has a mixed oxidation state (Sn 2+ / Sn 4+ ) and there are sufficient oxygen vacancies, which is a typical acidic oxide, providing L acid sites. AlPO4 was coupled with SnO2 to prepare aluminum phosphate-supported tin oxide solid acid catalyst AlPO4-SnO2, providing a new B / L acid bifunctional solid acid catalyst. The catalyst was used for the catalytic conversion of cellulose to levulinic acid under hydrothermal conditions, which can reduce the reaction temperature and improve the selectivity of levulinic acid. The catalyst has good reusability and is easy to industrialize. Summary of the invention

[0004] The present invention aims to provide a method for selectively catalyzing cellulose into levulinic acid using a bifunctional solid acid catalyst AlPO4-SnO2.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A high-pressure reactor is used as a reaction container, cellulose powder and a catalyst are added to the reaction container according to a certain mass ratio, and then a certain amount of water is added, and the cellulose degradation reaction is carried out under magnetic stirring and a certain temperature. After the reaction is completed, the system is cooled to room temperature, and the solid residue and the liquid product are separated. The solid residue is dried and weighed, and the cellulose conversion rate is calculated. The filtrate is fixed to a fixed volume, and the product analysis is performed to calculate the levulinic acid yield.

[0006] In the method for selectively catalyzing cellulose to levulinic acid, the B acid in the bifunctional catalyst is AlPO4, and the L acid is SnO2.

[0007] In the method for selectively catalyzing cellulose to levulinic acid, the mass ratio of cellulose to catalyst is 0.6-3.

[0008] In the method for selectively catalyzing cellulose to levulinic acid, the solid-liquid mass ratio of cellulose to solvent water is 1:500-5:500.

[0009] The method for selectively catalyzing cellulose to levulinic acid has a reaction temperature of 180-200°C.

[0010] The method for selectively catalyzing cellulose to levulinic acid has a reaction time of 4 to 5 hours.

[0011] The method for selectively catalyzing cellulose to levulinic acid comprises a solid-liquid separation method of vacuum filtration.

[0012] The method for selectively catalyzing cellulose to levulinic acid, the method for product analysis is high performance liquid chromatography, a series of standard solutions of cellulose degradation products such as glucose, 5-hydroxymethylfurfural and levulinic acid are prepared, a standard curve of peak area and concentration is drawn, and then the filtrate of the degradation reaction is sampled and analyzed, the concentration of each product is calculated, and the reaction yield of each product is further calculated.

[0013] The amount of cellulose used was 0.5 g, the amount of catalyst used was 0.5 g, the volume of solvent water was 50 ml, and the reaction was carried out at 190 °C for 4 h. The yield of levulinic acid reached 42.4%.

[0014] Compared with the prior art, the present invention has the following significant advantages: Provided is a novel B / L acid bifunctional solid acid catalyst, which is used for catalytic conversion of aqueous phase cellulose to produce levulinic acid. The catalyst is resistant to high temperatures, has a high cellulose conversion rate, and has high selectivity for a single product, levulinic acid. It can be used for catalytic degradation of cellulose, and the catalyst has good reusability and is easy for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1UV-visible diffuse reflectance absorption spectra of AlPO4-SnO2(20%) (a) and AlPO4(b) Figure 2 SEM-Mapping spectrum of AlPO4-SnO2(20%) DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to these specific embodiments.

[0017] Example 1 Effects of different catalysts on cellulose conversion and levulinic acid yield (1) The cellulose raw material is microcrystalline cellulose without any pretreatment operation.

[0018] (2) Catalysts include no catalyst, AlPO4, Al2O3-SnO2, and AlPO4-SnO2 (the SnO2 loading is the same, all 30%) (3) Preparation of AlPO4-SnO2 catalyst: AlCl3·6H2O and (NH3)2PO4 were dissolved in deionized water to prepare a mixed solution with a concentration of 0.5 mol / L of AlCl3·6H2O and (NH4)2HPO4. The pH value of the solution was adjusted to acidic using 0.5 mol / L hydrochloric acid. Ammonia water was added dropwise to the acidified solution. The white precipitate was obtained by filtration under reduced pressure. The precipitate was washed with deionized water and dried. The obtained white solid was fully ground and calcined in a muffle furnace at a calcination temperature of 550°C for 3 h to obtain AlPO4 white solid. A certain amount of SnCl4·5H2O solution was weighed, and 2.0 g of the previously prepared aluminum phosphate carrier was added to the clear and transparent solution. The solution was stirred at room temperature for 12 h. The water was removed by rotary evaporation. The obtained solid was dried to constant weight at 110°C in a constant temperature drying oven. The dried solid was placed in a muffle furnace for calcination at a temperature of 550°C for 5 h. After calcination, the negative solid acid catalyst AlPO4-SnO2 was obtained. The catalyst was characterized by UV-Vis diffuse reflectance absorption spectroscopy ( Figure 1 ) and SEM-Mapping ( Figure 2 ) as shown. Figure 1 The AlPO4 sample has only a weak absorption peak between 200-300 nm, while the sample AlPO4-SnO2 (20%) loaded with SnO2 has a strong absorption peak between 200-300 nm, which proves that SnO2 and AlPO4 are successfully combined together. Figure 2 O, Al, P and Sn elements were all detected in the sample, and the Sn element was evenly dispersed on the aluminum phosphate carrier.

[0019] (4) At 190℃, 50 ml of water was used as solvent, 0.3 g of cellulose was used, and the cellulose degradation reaction was carried out for 2 h with no catalyst, AlPO4, Al2O3-SnO2, and AlPO4-SnO2 as catalysts. The results of the degradation reaction with AlPO4 and Al2O3-SnO2 as catalysts did not increase the conversion rate and product yield significantly compared with the condition without catalyst, while AlPO4-SnO2 as catalyst showed good catalytic activity, as shown in Table 1.

[0020] Table 1 Conversion rate of levulinic acid and cellulose on different catalysts catalyst Levulinic acid yield Cellulose conversion rate blank 0 7% <![CDATA[AlPO4]]> 0 12% <![CDATA[Al2O3-SnO2]]> 0 14% <![CDATA[AlPO4-SnO2]]> 33.27% 90.02% Example 2 Effect of Tin Oxide Loading on Cellulose Conversion and Levulinic Acid Yield The preparation method of cellulose raw material and catalyst is the same as that in Example 1.

[0021] As can be seen from Table 2, as the tin oxide loading increases, the conversion rate also increases. When the tin oxide loading is 20%, the yield of levulinic acid is the highest, reaching 43.1%, and the catalytic activity is the best. The yield of levulinic acid on the solid acid catalyst with a loading of 30% and 40% decreases slightly.

[0022] Table 2 Effect of tin oxide loading on cellulose conversion and levulinic acid yield <![CDATA[SnO2 loading]]> Levulinic acid yield Cellulose conversion rate 10% 9.10% 60% 20% 43.1% 85.60% 30% 33.27% 90.02% 40% 33.23% 95% Example 3 Effect of reaction temperature on cellulose conversion and levulinic acid yield The cellulose raw material is the same as in Example 1. The catalyst preparation method is the same as in Example 1, and the loading amount of SnO2 is 30%. The reaction of cellulose to levulinic acid is the same as in Example 1. The reaction temperature is 160°C, 170°C, 180°C, 190°C, and 200°C. The results are shown in Table 3. When the temperature is between 160°C and 180°C, the reaction product is mainly glucose, and the yield of levulinic acid is very low. When the temperature is raised to 190°C, the reaction product is mainly levulinic acid, reaching 40.1%. When the temperature is further raised to 200°C, the cellulose conversion rate increases, and the yield of levulinic acid decreases to 34.4%. 190°C is the optimal reaction temperature.

[0023] Table 3 Effect of reaction temperature on cellulose conversion and levulinic acid yield temperature Levulinic acid yield Cellulose conversion rate 160 2.25% 27% 170 9.84% 47.17% 180 12.11% 51.83% 190 33.27% 90.02% 200 34.39% 91% Example 4 Effect of reaction time on cellulose conversion and levulinic acid yield The results are shown in Table 4. The cellulose raw material is the same as in Example 1. The catalyst is the same as in Example 2. The reaction of cellulose to levulinic acid is the same as in Example 1. The reaction time is 1h, 2h, 3h, 4h, and 5h. The results are shown in Table 4. As time goes by, the cellulose conversion rate gradually increases. When the time is 4 h, the yield of levulinic acid reaches 41.9%. When the reaction time is 5 h, the yield of levulinic acid also decreases by 6.6%. 4 h is the optimal reaction time.

[0024] Table 4 Effect of reaction time on cellulose conversion and levulinic acid yield Example 5 Effect of Catalyst Amount on Cellulose Conversion and Levulinic Acid Yield The cellulose raw material is the same as in Example 1. The catalyst is the same as in Example 2. The reaction of cellulose to levulinic acid is the same as in Example 1. The results are shown in Table 5. When the amount of cellulose is 0.3 g, when the amount of catalyst increases from 0.1 g to 0.3 g, the cellulose conversion rate increases accordingly, and it is easier to convert into levulinic acid. The yield of levulinic acid reaches the maximum at a catalyst dosage of 0.3 g, which is 41.9%. When the amount of catalyst continues to increase, the conversion rate of cellulose and the yield of levulinic acid both decrease slightly. When the amount of cellulose is 0.3 g, the best amount of catalyst is 0.3 g.

[0025] Table 5 Effect of catalyst dosage on cellulose conversion and levulinic acid yield Catalyst dosage Levulinic acid yield Cellulose conversion rate 0.1g 16.29% 80.40% 0.2g 30.10% 88.40% 0.3g 41.99% 89.96% 0.4g 41% 87.50% 0.5g 41.10% 86.90% Example 5 Effect of solid-liquid ratio on cellulose conversion and levulinic acid yield The cellulose raw material is the same as in Example 1. The catalyst is the same as in Example 2. The reaction of cellulose to levulinic acid is the same as in Example 1. The solvent water is 50 mL, and the solid-liquid ratio is 1:500, 2:500, 3:500, 4:500, and 5:500. The results are shown in Table 6. As the amount of cellulose increases, the total yield of the reaction and the yield of levulinic acid also increase. When the ratio of cellulose to water is 3:500, the yield of levulinic acid reaches 41.9%. After that, as the amount of cellulose increases, the yield of levulinic acid no longer changes significantly.

[0026] Table 6 Effect of catalyst dosage on cellulose conversion and levulinic acid yield Solid-liquid ratio Levulinic acid yield Cellulose conversion rate 1:500 15.12% 99.60% 2:500 31.33% 91.55% 3:500 41.99% 89.96% 4:500 42.89% 85.80% 5:500 46.84% 85%

Claims

1. A method for selectively catalyzing cellulose to levulinic acid using a bifunctional solid acid catalyst AlPO4-SnO2, characterized in that: A high-pressure reactor is used as a reaction container, cellulose powder and a catalyst are added to the reaction container according to a certain mass ratio, and then a certain amount of water is added, and the cellulose degradation reaction is carried out under magnetic stirring and a certain temperature. After the reaction is completed, the system is cooled to room temperature, and the solid residue and the liquid product are separated. The solid residue is dried and weighed, and the cellulose conversion rate is calculated. The filtrate is fixed to a fixed volume, and the product analysis is performed to calculate the levulinic acid yield.

2. The method according to claim 1, characterized in that The B acid in the bifunctional catalyst is AlPO4 and the L acid is SnO2.

3. The method according to claim 1, characterized in that The mass ratio of cellulose to catalyst is 0.6-3.

4. The method according to claim 1, characterized in that The solid-liquid mass ratio of cellulose and solvent water in the reaction system is 1:500-5:

500.

5. The method according to claim 1, characterized in that The reaction temperature is 180~200℃.

6. The method according to claim 1, characterized in that The reaction time is 4~5h.

7. The method according to claim 1, characterized in that The solid-liquid separation method is vacuum filtration.

8. The method according to claim 1, characterized in that The product analysis method is high performance liquid chromatography. A series of standard solutions of cellulose degradation products such as glucose, 5-hydroxymethylfurfural, and levulinic acid are prepared, and a standard curve of peak area and concentration is drawn. The filtrate of the degradation reaction is then sampled and analyzed, and the concentration of each product is calculated, and the reaction yield of each product is further calculated.

9. The method according to claim 1, characterized in that The amount of cellulose used was 0.5 g, the amount of catalyst used was 0.5 g, the volume of solvent water was 50 ml, and the reaction was carried out at 190 °C for 4 h. The yield of levulinic acid reached 42.4%.

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