Construction of difunctional carbon-based solid acid catalyst and application of difunctional carbon-based solid acid catalyst in efficiently converting glucose into 5-HMF (5-hydroxymethylfurfural) in two-phase system

Abstract

The invention discloses construction of a bifunctional carbon-based solid acid catalyst and application of the bifunctional carbon-based solid acid catalyst in efficiently converting glucose into 5-HMF (5-hydroxymethylfurfural) in a biphase system. The difunctional carbon-based solid acid catalyst is prepared by taking alkali lignin as a carbon source, potassium chloride as a salt template, and p-toluenesulfonic acid and aluminum nitrate nonahydrate as Browster acid and Lewis acid catalytic active site precursors respectively. The bifunctional carbon-based solid acid catalyst has rich oxygen-containing functional groups, a graded porous structure and a proper ratio of Browster acid active sites to Lewis acid active sites. In addition, the catalyst shows excellent catalytic activity in a two-phase system, can obtain high glucose conversion rate and 5-HMF yield under relatively mild reaction conditions, and has good cycle stability. According to the novel difunctional carbon-based solid acid catalytic reaction system disclosed by the invention, the purpose of efficiently catalyzing conversion of glucose into 5-HMF is achieved.

Description

Technical Field

[0001] The present invention relates to the preparation and application of a bifunctional catalyst, and in particular to the construction of a bifunctional carbon-based solid acid catalyst and the application of the bifunctional carbon-based solid acid catalyst in efficiently converting glucose into 5-HMF in a biphasic system. Background Art

[0002] With the continuous consumption of fossil resources such as petroleum, the use of renewable biomass resources to prepare dyes and chemicals is of great significance to alleviate energy shortages. 5-HMF, as an important biomass-based platform compound, contains highly reactive aldehyde groups, hydroxymethyl groups and furan rings in its structure. It can be synthesized into a variety of high value-added basic chemicals such as 1-hydroxy-2,5-hexanedione, 2,5-furandicarboxylic acid and levulinic acid through chemical reactions such as hydrogenation, oxidation and rehydration.

[0003] At present, the biomass raw materials for preparing 5-HMF include monosaccharides (fructose, glucose), disaccharides (sucrose) and polysaccharides (starch, cellulose, etc.). Among them, 5-HMF can be directly and efficiently obtained by dehydrating fructose, and has high yield and selectivity. However, in comparison, glucose, as the basic component unit of cellulose, has the advantages of low price, wide source and high availability. It has greater research value to use it to replace fructose to prepare 5-HMF. The catalytic conversion of glucose to 5-HMF generally requires two steps: first, glucose is isomerized to fructose through hydrogen transfer under the action of Bronsted or Lewis acid; secondly, fructose removes 3 molecules of water under the action of Bronsted acid to generate 5-HMF. Based on the above reaction pathway, bifunctional catalysts have gradually been developed for glucose conversion to prepare 5-HMF. However, compared with other types of heterogeneous catalyst carriers (mesoporous silica and metal organic frameworks), porous carbon is favored because of its developed pore structure, high specific surface area, rich functional groups and excellent chemical stability. Therefore, if the ratio of active sites between isomerization and dehydration can be rationally adjusted on porous carbon materials so that the rates of the two main reactions can be matched, it will help to improve the yield and selectivity of 5-HMF.

[0004] The reaction solvent is an important component of the catalytic system for the conversion of glucose to 5-HMF, and has a significant effect on the reaction rate, conversion rate and selectivity. It is well known that water, as a cheap and readily available green solvent, is the first choice for the reaction solvent system. However, 5-HMF is unstable in aqueous solution and easily rehydrates to form by-products such as levulinic acid and formic acid. Nowadays, 5-HMF is usually produced in a biphasic reaction system containing an aqueous solution and an organic solvent. The aqueous solution is used as the reaction phase for the catalytic conversion of biomass into 5-HMF. The organic solvent is used as the extraction phase to continuously extract 5-HMF from water to the organic phase, achieving the instant separation of HMF, thereby reducing the occurrence of side reactions and facilitating its subsequent purification and separation. In addition, the addition of inorganic salts to the biphasic reaction system can enhance the immiscibility of the aqueous phase and the organic phase, and significantly improve the distribution coefficient of 5-HMF in the organic phase through the salting-out effect.

[0005] The present invention prepares a bifunctional carbon-based solid acid catalyst through subsequent impregnation and calcination, and applies the catalyst to the reaction of efficiently catalyzing the conversion of glucose into fructose in a biphasic system. Summary of the invention

[0006] In view of the many limitations of current heterogeneous catalysts, such as complex preparation process, low catalytic activity and poor cyclic stability, the purpose of the present invention is to provide a method for preparing a bifunctional carbon-based solid acid catalyst and its application in efficiently converting glucose into 5-HMF in a two-phase system. The bifunctional carbon-based solid acid catalyst has the structural characteristics of a porous carbon support and can provide a suitable ratio of Bronsted and Lewis acid active sites, exhibiting excellent catalytic activity in a two-phase system, and can efficiently convert glucose into 5-HMF under relatively mild reaction conditions.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] Step 1: Mix the alkali lignin and potassium chloride thoroughly in a mortar.

[0009] Step 2: Heat the mixture obtained in step 1 in a tube furnace 2 Carbonization is carried out under atmosphere, including two processes: pre-carbonization and high-temperature carbonization.

[0010] Step 3: Wash and dry the carbonized product obtained in step 2 to obtain porous carbon.

[0011] Step 4: Add the porous carbon obtained in step 3, p-toluenesulfonic acid and aluminum nitrate nonahydrate into a mixed solution of water and ethanol, and stir at room temperature for 12 hours.

[0012] Step 5: Dry the mixed solution obtained in step 4 in an oven at 65°C for 24 hours.

[0013] Step 6: Heat the dried product obtained in step 5 in a tube furnace 2 The carbonization is carried out under atmosphere to prepare a bifunctional carbon-based solid acid catalyst.

[0014] The masses of the alkali lignin and potassium chloride in step 1 are 3.0 g and 0.75 g respectively.

[0015] The pre-carbonization process in step 2 is as follows: the temperature is increased from room temperature to 300° C. at a heating rate of 3° C. / min and maintained for 1 hour.

[0016] The high temperature carbonization process in step 2 is as follows: the temperature is increased from 300° C. to 700° C. at a heating rate of 1° C. / min and maintained for 2 hours.

[0017] The washing in step 3 is firstly done with diluted HCl and then with deionized water.

[0018] The mass ratios of the porous carbon, p-toluenesulfonic acid and aluminum nitrate nonahydrate in the step 4 are 1:0.5:0.2 respectively.

[0019] The volume of the mixed solution of water and ethanol in step 4 is 18 mL, and the volume ratio of water to ethanol is 1:1.

[0020] The carbonization process in step six is ​​as follows: the temperature is increased from room temperature to 300° C. at a heating rate of 3° C. / min and maintained for 2 h.

[0021] The present invention also provides the use of the bifunctional carbon-based solid acid catalyst in the efficient conversion of glucose into 5-HMF in a biphasic system. The specific process is: 0.2g of glucose, 0-0.3g of catalyst, 16mL of water and a mixed solution of methyl isobutyl ketone are weighed and added into a 30mL high-pressure reactor in sequence, and N 2 The mixture was purged and pressurized to 1.5 MPa, and then reacted at 170° C. with a stirring speed of 600 rpm for 0-3.0 h to prepare 5-HMF.

[0022] Compared with the prior art, the present invention has the following advantages and effects: the bifunctional carbon-based solid acid catalyst prepared by the present invention has abundant oxygen-containing functional groups, hierarchical porous structure, and suitable ratio of Bronsted and Lewis acid active sites. In addition, it exhibits excellent catalytic activity in a two-phase system, can efficiently realize the conversion of glucose into 5-HMF under relatively mild reaction conditions, and has good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 X-ray diffraction pattern of the bifunctional carbon-based solid acid catalyst obtained in Example 1.

[0024] Figure 2 Pyridine adsorption infrared spectrum of the bifunctional carbon-based solid acid catalyst obtained in Example 1.

[0025] Figure 3 Infrared spectrum of the bifunctional carbon-based solid acid catalyst obtained in Example 1.

[0026] Figure 4 Scanning electron micrograph of the bifunctional carbon-based solid acid catalyst obtained in Example 1.

[0027] Figure 5 The relationship between reaction time and catalytic effect in Example 2.

[0028] Figure 6 The relationship between the catalyst loading and the catalytic effect in Example 3.

[0029] Figure 7 The relationship between the number of catalyst cycles and the catalytic effect in Example 4. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the claims attached to the application.

[0031] Example 1

[0032] Usually, 3.0 g of alkali lignin and 0.75 g of potassium chloride are thoroughly mixed and then heated in a tube furnace. 2 Carbonization under atmosphere, including pre-carbonization (30-300°C, 3°C / min, maintained at 300°C for 1h) and high-temperature carbonization (300-700°C, 1°C / min, maintained at 700°C for 2h). The carbonized product was washed and dried to obtain porous carbon. Afterwards, 1.2g of porous carbon, p-toluenesulfonic acid and aluminum nitrate nonahydrate were added to 18mL of a mixed solution of water and ethanol in a certain mass ratio and stirred at room temperature for 12h. The mixed solution was then dried in an oven at 65°C for 24h, and carbonized at a specified temperature for 2h in a tubular furnace under N2 atmosphere to prepare a bifunctional carbon-based solid acid catalyst. Figure 1 As shown, the bifunctional carbon-based solid acid catalyst exhibits a partially graphitized structure; Figure 2 As shown, the bifunctional carbon-based solid acid catalyst has both Bronsted and Lewis acid active sites; Figure 3As shown, the bifunctional carbon-based solid acid catalyst was successfully introduced with sulfonic acid groups; Figure 4 As shown, the bifunctional carbon-based solid acid catalyst exhibits an irregular and rough surface structure formed by the aggregation of carbon particles.

[0033] Example 2

[0034] 0.2 g of glucose, 0.2 g of the bifunctional carbon-based solid acid catalyst obtained in Example 1, and 16 mL of a mixed solution of water and methyl isobutyl ketone were weighed and added to a 30 mL autoclave in sequence. 2 Purge and pressurize to 1.5Mpa. Then react the mixture at 170°C with a stirring speed of 600rpm for 0.5-3.0h. After the reaction, the high-pressure reactor is quickly cooled to room temperature, and the catalyst is separated, rinsed, and dried for a cycle experiment. Finally, the content of 5-HMF in the filtrate is detected by high performance liquid chromatography, and the yield of 5-HMF is further calculated. Figure 5 As shown, when the reaction time is 1.0 h, the glucose conversion rate and 5-HMF yield can reach 98.4% and 60.2%, respectively.

[0035] Example 3

[0036] 0.2 g of glucose, 0-0.3 g of the bifunctional carbon-based solid acid catalyst obtained in Example 1, and 16 mL of a mixed solution of water and methyl isobutyl ketone were weighed and added to a 30 mL autoclave in sequence. 2 Purge and pressurize to 1.5Mpa. Then, the mixture was reacted at 170°C with a stirring speed of 600rpm for 1.0h. After the reaction, the high-pressure reactor was quickly cooled to room temperature, and the catalyst was separated, rinsed, and dried for a cycle experiment. Finally, the content of 5-HMF in the filtrate was detected by high performance liquid chromatography, and the yield of 5-HMF was further calculated. Figure 6 As shown, when the catalyst loading is 0.75 mg·mg -1 When , the glucose conversion rate and 5-HMF yield can reach 96.6% and 61.1% respectively.

[0037] Example 4

[0038] 0.2 g of glucose, 0.15 g of the bifunctional carbon-based solid acid catalyst obtained in Example 1, and 16 mL of a mixed solution of water and methyl isobutyl ketone were weighed and added to a 30 mL autoclave in sequence. 2Purge and pressurize to 1.5Mpa. Then, the mixture was reacted at 170°C with a stirring speed of 600rpm for 1.0h. After the reaction, the high-pressure reactor was quickly cooled to room temperature, and the catalyst was separated, rinsed, and dried for a cycle experiment. Finally, the content of 5-HMF in the filtrate was detected by high performance liquid chromatography, and the yield of 5-HMF was further calculated. Figure 7 As shown, after the catalyst was cycled five times, it still had a high catalytic activity, and the glucose conversion rate and 5-HMF yield could reach 40.0% and 31.0%, respectively.

[0039] This bifunctional carbon-based solid acid catalyst not only has the structural characteristics of a porous carbon support, but also provides a suitable ratio of Bronsted and Lewis acid active sites. It exhibits excellent catalytic activity in a two-phase system and can efficiently convert glucose into 5-HMF under relatively mild reaction conditions.

[0040] Finally, it should be noted that the above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novelties disclosed herein.

Claims

1. A method for preparing a bifunctional carbon-based solid acid catalyst, characterized in that: The following steps are involved: Step 1: Mix alkali lignin and potassium chloride thoroughly in a mortar. Step 2: Carbonizing the mixture obtained in step 1 in a tube furnace under N2 atmosphere, including two processes: pre-carbonization and high-temperature carbonization. Step 3: Wash and dry the carbonized product obtained in step 2 to obtain porous carbon. Step 4: Add the porous carbon obtained in step 3, p-toluenesulfonic acid and aluminum nitrate nonahydrate into a mixed solution of water and ethanol, and stir at room temperature for 12 hours. Step 5: Dry the mixed solution obtained in step 4 in an oven at 65°C for 24 hours. Step 6: Carbonize the dried product obtained in step 5 in a tubular furnace under a N2 atmosphere to prepare a bifunctional carbon-based solid acid catalyst.

2. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The masses of the alkali lignin and potassium chloride in the step 1 are 3.0 g and 0.75 g respectively.

3. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The pre-carbonization process in step 2 is as follows: the temperature is increased from room temperature to 300° C. at a heating rate of 3° C. / min and maintained for 1 hour.

4. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The high temperature carbonization process in step 2 is as follows: the temperature is increased from 300° C. to 700° C. at a heating rate of 1° C. / min and maintained for 2 hours.

5. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The washing in step 3 is firstly done with diluted HCl and then with deionized water.

6. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The mass ratios of the porous carbon, p-toluenesulfonic acid and aluminum nitrate nonahydrate in the step 4 are 1:0.5:0.2 respectively.

7. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The volume of the mixed solution of water and ethanol in step 4 is 18 mL, and the volume ratio of water to ethanol is 1:

1.

8. The method for preparing a bifunctional carbon-based solid acid catalyst according to claim 1, characterized in that: The carbonization process in step six is ​​as follows: the temperature is increased from room temperature to 300° C. at a heating rate of 3° C. / min and maintained for 2 h.

9. The bifunctional carbon-based solid acid catalyst obtained by the preparation method according to claim 1 and its use in efficiently converting glucose into 5-HMF in a two-phase system, characterized in that: 0.2 g of glucose, 0-0.3 g of catalyst, 16 mL of water and a mixed solution of methyl isobutyl ketone were weighed and added to a 30 mL autoclave, purged with N2 and pressurized to 1.5 MPa. The mixture was then reacted at 170° C. with a stirring speed of 600 rpm for 0.5-3.0 h to prepare 5-HMF.

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