Difunctional solid acid catalyst, preparation and method for preparing HMF from glucose by using difunctional solid acid catalyst

Abstract

The invention discloses a preparation method of a bifunctional solid acid catalyst. The preparation method comprises the following steps: step 1, adding a mixture of X parts of NH4HCO3 and M-X parts of aluminum salt into deionized water; step 2, slowly adding M parts of NH4HCO solution under violent stirring; step 3, after the solution obtained in the step 2 is clear, slowly adding ammonia water until the pH value reaches a preset value; step 4, putting the solid product obtained in the step 3 into a hydrothermal reaction kettle for heating, naturally cooling to room temperature after heating is completed, and centrifuging to obtain a solid product; 5, the solid product is washed with deionized water and then dried in a constant-temperature vacuum environment, the solid acid catalyst Ny (at) gamma-AlOOH is obtained after drying is completed, and y is the molar ratio of NH4HCO3 to aluminum salt in the mixture in the step 1. The preparation method disclosed by the invention has the characteristics of simplicity, high hydrothermal stability, high stability, difficulty in loss of active sites and difficulty in inactivation, and has a good industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of solid acid catalysts, and in particular to a bifunctional solid acid catalyst, a preparation method thereof and a method for using the catalyst to prepare HMF from glucose. Background Art

[0002] Using inorganic salts such as AlCl3, CrCl3, CuCl2 and FeCl3 as LAS, and inorganic acids such as H3PO4, H2SO4 and HCl as BAS to form a homogeneous bifunctional catalytic system for the catalytic preparation of HMF from glucose has been widely studied. However, homogeneous catalytic systems generally have problems such as difficulty in product separation, equipment corrosion, and environmental pollution. Therefore, people prefer to use heterogeneous catalysts, namely solid acid catalysts, because they are easy to separate and reuse, and have positive factors such as environmental friendliness.

[0003] So far, a variety of solid acid catalysts containing LAS and BAS have been developed for the conversion of glucose to HMF. These catalysts include metal organic frameworks (MOFs), zeolites, sulfonated materials, superacids, metal oxides, phosphates, etc. In the process of glucose to HMF catalyzed by these solid acid catalysts, the research focus is mainly on optimizing the ratio of LAS and BAS to improve the yield and selectivity of HMF. However, the reported solid acid catalysts are usually used for the production of HMF in non-aqueous media, such as ionic liquids and polar aprotic solvents. The researchers mainly consider the following points: (1) In aqueous media, the catalyst LAS may undergo hydration, resulting in LAS deactivation, such as γ-Al2O3 and aluminosilicates; (2) In water, the active sites may penetrate into the aqueous phase and be lost, resulting in a decrease in catalyst activity or inactivity, such as sulfate and phosphate supported catalysts; (3) Ionic liquids and aprotic polar solvents such as dimethyl sulfoxide (DMSO) can increase the yield of HMF, stabilize its structure, and prevent side reactions of HMF. However, its industrial application is greatly affected by its major disadvantages such as high cost and high viscosity, as well as its high boiling point affecting the subsequent separation of HMF. Non-aqueous media are not ideal reaction media.

[0004] On the contrary, in the actual production process of HMF, water is an ideal solvent, which provides a clean, economical and environmentally friendly solution. However, since HMF is unstable in water, it is easy to re-hydrolyze to generate by-products such as levulinic acid and formic acid, which reduces the yield and selectivity of HMF. Therefore, a water-organic phase (low-boiling point organic solvent) two-phase system is often used as a reaction solvent for HMF preparation. The generated HMF is extracted from the aqueous phase to the organic phase in time by a low-boiling point organic solvent to prevent HMF from decomposing in the aqueous phase and improve the yield and selectivity of HMF. Therefore, there is currently a lack of bifunctional solid acid catalysts that take into account both LAS and BAS and are stable in water, are not prone to acid site loss, and are easy to prepare. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a bifunctional solid acid catalyst, a preparation method thereof and a method for using the catalyst to produce HMF from glucose, so as to solve the technical problems in the prior art.

[0006] The present invention provides a method for preparing a bifunctional solid acid catalyst, comprising the following steps:

[0007] Step 1: Add X parts of NH4HCO3 and MX parts of aluminum salt mixture into deionized water;

[0008] Step 2: Slowly add M parts of NH4HCO solution under vigorous stirring;

[0009] Step 3: After the solution obtained in step 2 becomes clear, slowly add ammonia water until the pH value reaches a preset value;

[0010] Step 4: placing the product obtained in step 3 into a hydrothermal reactor for heating, cooling it naturally to room temperature after heating, and centrifuging to obtain a solid product;

[0011] Step 5: After washing the solid product with deionized water, the solid product is dried under a constant temperature vacuum environment. After drying, a solid acid catalyst N is obtained. y @γ-AlOOH, wherein y is the molar ratio of NH4HCO3 to aluminum salt in the mixture of step 1.

[0012] Furthermore, the range of y is 0 / 15 to 15 / 0.

[0013] Furthermore, the y is 4 / 11.

[0014] Furthermore, the aluminum salt is an inorganic aluminum salt and / or aluminum isopropoxide.

[0015] Furthermore, the aluminum salt is one or more of: AlCl3, Al(NO3)3, Al2(SO4)3, AlCl3·6H2O, Al(NO3)3·9H2O, Al2(SO4)3·16H2O.

[0016] Furthermore, the aluminum salt is: Al(NO3)3 or / and Al(NO3)3·9H2O.

[0017] Furthermore, the preset value of the pH value in step 3 is in the range of 8-12.

[0018] Furthermore, the preset value is: 9.

[0019] The invention also provides a bifunctional solid acid catalyst prepared by a method for preparing the bifunctional solid acid catalyst.

[0020] The present invention also provides a method for preparing a bifunctional solid acid catalyst and application of the bifunctional solid acid catalyst prepared in preparing HMF from glucose.

[0021] Furthermore, the specific steps of applying glucose to produce HMF include:

[0022] First, a solid acid catalyst and glucose are added to a biphasic solution or a NaCl solution containing the corresponding biphasic solution, and then stirred for reaction under high temperature conditions. After the reaction is completed, the mixture is cooled to room temperature, and the liquid is collected by centrifugation to obtain a degradation solution containing HMF.

[0023] Furthermore, the catalyst loading range of the solid acid catalyst on the substrate glucose is 10% to 100%.

[0024] Furthermore, the catalyst loading amount of the solid acid catalyst on the substrate glucose is 30%.

[0025] Furthermore, the concentration range of glucose is: 0.5 gL -1 ~40gL -1 .

[0026] Furthermore, the concentration of glucose is: 10 g / L -1 .

[0027] Furthermore, the temperature range of the high temperature condition is: 110°C to 170°C; the reaction time range is: 0.5h to 12h.

[0028] Furthermore, the temperature of the high temperature condition is: 140°C; and the reaction time is: 3h.

[0029] Furthermore, the biphasic solution is: n-butanol-water-NaCl, n-pentanol-water-NaCl, tetrahydrofuran (THF)-water-NaCl or methyl isobutyl ketone (MIBK)-water-NaCl.

[0030] Beneficial effects of the present invention:

[0031] The bifunctional solid catalyst disclosed in the present invention has a good ratio of BAS to LAS, a simple preparation method, strong hydrothermal stability, strong stability - the active sites are not easy to lose and deactivate, and has good industrial application prospects.

[0032] When the method of the present invention is used to catalyze glucose to prepare HMF, the method has the characteristics of low temperature, high efficiency, high HMF yield and selectivity, easy separation and reusability of the catalyst, low energy consumption, etc., can avoid the generation of a large number of side reactions, improve product selectivity, reduce product separation costs, and has extremely high application value.

[0033] Using a two-phase solvent composed of water and an organic solvent as a reaction medium can not only extract HMF from water to the organic phase in a timely manner, stabilize HMF, prevent its decomposition, and improve HMF yield and selectivity. Secondly, since the selected organic solvent has a lower boiling point and a lower saturated vapor pressure, it is convenient for subsequent HMF separation and purification, obtains high-purity HMF, and reduces the cost of HMF separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0035] Figure 1 It is a schematic diagram of a flow chart of a specific embodiment of the present invention;

[0036] Figure 2 The XRD diagrams of the products prepared at different molar ratios of NH4HCO3 / Al(NO3)3·9H2O in Example 1 of the specific embodiment of the present invention;

[0037] Figure 3 XRD diagrams of products prepared at different pH values ​​in Example 2 of a specific embodiment of the present invention;

[0038] Figure 4 N is obtained in Example 3 of the specific embodiment of the present invention. y @XRD pattern of γ-AlOOH;

[0039] Figure 5 N is obtained in Example 3 of the specific embodiment of the present invention. y @FT-IR image of γ-AlOOH;

[0040] Figure 6 N is obtained in Example 3 of the specific embodiment of the present invention. y @Pyridine infrared image of γ-AlOOH;

[0041] Figure 7 The specific embodiment of the present invention is a diagram showing the effect of the solvent on the catalytic effect in Example 5;

[0042] Figure 8 The reaction time and HMF yield at different reaction temperatures in Example 6 of the specific embodiment of the present invention;

[0043] Fig. 9 This is an influence diagram of product distribution at different reaction times at 140° C. in Example 6 of a specific embodiment of the present invention;

[0044] Fig.10 This is a graph showing the effect of the loading amount of the catalyst on the substrate glucose on the catalytic effect in Example 7 of a specific embodiment of the present invention;

[0045] Fig.11 This is a graph showing the effect of substrate glucose concentration on catalytic effect in Example 8 of a specific embodiment of the present invention;

[0046] Fig.12 It is a diagram of the catalyst acid potential loss in Example 9 of a specific embodiment of the present invention;

[0047] Fig.13 This is a graph showing the effect of the number of cycles on the catalytic effect in Example 9 of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0049] The present invention is further illustrated below in conjunction with specific embodiments. Those skilled in the art should understand that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and modifications to various equivalent forms of the present invention fall within the scope defined by the appended claims of this application.

[0050] like Figure 1 As shown, the present invention provides a method for preparing a bifunctional solid acid catalyst, comprising the following steps:

[0051] Step 1: Add X parts of NH4HCO3 and MX parts of aluminum salt mixture into deionized water;

[0052] The aluminum salt is an inorganic aluminum salt and / or aluminum isopropoxide. The aluminum salt may specifically be one or more of: AlCl3, Al(NO3)3, Al2(SO4)3, AlCl3·6H2O, Al(NO3)3·9H2O, Al2(SO4)3·16H2O. The preferred aluminum salt is: Al(NO3)3 or / and Al(NO3)3·9H2O.

[0053] Step 2: Slowly add M parts of NH4HCO solution under vigorous stirring;

[0054] Step 3: After the solution obtained in step 2 is clear, slowly add ammonia water until the pH value reaches a preset value, the preset value range is: 8-12, and the preferred preset value is: 9;

[0055] Step 4: placing the product obtained in step 3 into a hydrothermal reactor for heating, cooling it naturally to room temperature after heating, and centrifuging to obtain a solid product;

[0056] Step 5: After washing the solid product with deionized water, the solid product is dried under a constant temperature vacuum environment. After drying, a solid acid catalyst N is obtained. y @γ-AlOOH, wherein y is the molar ratio of NH4HCO3 to aluminum salt in the mixture of step 1, and the range of y is 0 / 15 to 15 / 0, and preferably y is 4 / 11.

[0057] The invention also provides a bifunctional solid acid catalyst prepared by a method for preparing the bifunctional solid acid catalyst.

[0058] The present invention also provides a method for preparing a bifunctional solid acid catalyst and an application of the prepared bifunctional solid acid catalyst in preparing HMF from glucose, the specific steps comprising:

[0059] First, a solid acid catalyst and glucose are added to a biphasic solution or a NaCl solution containing a corresponding biphasic solution, and then stirred for reaction under high temperature conditions. After the reaction is completed, the mixture is cooled to room temperature and the liquid is collected by centrifugation to obtain a degradation solution containing HMF.

[0060] The catalyst loading range of the solid acid catalyst on the substrate glucose is: 10% to 100%, preferably: 30%; the concentration range of glucose is: 0.5 g / L -1 ~40gL -1 , preferably: 10gL -1The temperature range of the high temperature condition is: 110°C to 170°C, preferably: 140°C; the reaction time range is: 0.5h to 12h, preferably: 3h; the biphasic solution is: n-butanol-water-NaCl, n-pentanol-water-NaCl, tetrahydrofuran (THF)-water-NaCl or methyl isobutyl ketone (MIBK)-water-NaCl.

[0061] The present invention is described below by way of examples:

[0062] Embodiment 1:

[0063] The effect of the reaction conditions NH4HCO3 / Al(NO3)3·9H2O molar ratio on the preparation of γ-AlOOH and AACH was investigated. The process is as follows:

[0064] 15mmol Al(NO3)3·9H2O was dissolved in 50mL deionized water. Subsequently, a certain amount of NH4HCO3 was slowly added under vigorous stirring to control the molar ratio of NH4HCO3 / Al(NO3)3·9H2O. After a clear solution was formed, 25% ammonia water was slowly added until the pH value reached 9. Then, the resulting solution was transferred to a 100ml polytetrafluoroethylene-lined hydrothermal reactor, sealed, and heated at 110°C for 12 hours, then naturally cooled to room temperature, the solid product was collected by centrifugation, washed three times with deionized water, and vacuum dried at 80°C for 24 hours to obtain γ-AlOOH. The product was characterized by XRD to investigate the effect of the molar ratio of NH4HCO3 / Al(NO3)3·9H2O on the product.

[0065] like Figure 2 As shown, it can be found that the molar ratio of NH4HCO3 / Al(NO3)3·9H2O has a significant effect on the product structure. When the molar ratio of the two is higher than 4:1, AACH is easily generated; on the contrary, when the molar ratio is lower than 4:1, γ-AlOOH is easily generated. Considering that γ-AlOOH is mainly prepared, the preferred molar ratio is 2:1.

[0066] Embodiment 2:

[0067] The effect of the molar ratio of the reaction conditions pH value on the preparation of γ-AlOOH and AACH was investigated, and the process is as follows:

[0068] 15mmol Al(NO3)3·9H2O was dissolved in 50mL deionized water. Subsequently, 30mmol NH4HCO3 was slowly added under vigorous stirring. After a clear solution was formed, 25% ammonia water was slowly added until the pH value reached 8-12. Then, the resulting solution was transferred to a 100ml polytetrafluoroethylene-lined hydrothermal reactor, sealed, and heated at 110°C for 12 hours, then naturally cooled to room temperature, the solid product was collected by centrifugation, washed three times with deionized water, and vacuum dried at 80°C for 24h to obtain γ-AlOOH. The product was characterized by XRD, and the effect of the molar ratio of pH value on the product was investigated.

[0069] like Figure 3 As shown, it can be found that the pH value has a significant effect on the product structure. The higher the pH value, the more favorable it is for the formation of AACH. Considering that this process is to prepare γ-AlOOH, the preferred pH value is 9.

[0070] Embodiment 3:

[0071] Investigate the reaction conditions y to N y @γ-AlOOH structure and acid sites, namely LAS and BAS, were used to prepare N by finely controlling the ratio of NH4HCO3 to Al(NO3)3·9H2O. y @γ-AlOOH, the specific process is as follows:

[0072] A mixture containing 15-X mmol aluminum salt and X mmol NH4HCO3 was added to 50 mL of deionized water. Subsequently, 15 mmol NH4HCO3 was gradually added under vigorous stirring. The remaining reaction steps were consistent with the steps for synthesizing γ-AlOOH in Examples 1 and 2. Finally, vacuum drying was performed at 80°C for 24 h to obtain N y @γ-AlOOH. Where y is the molar ratio of NH4HCO3 to Al(NO3)3·9H2O in the initial 15mmol mixture of 15-X mmol aluminum salt and X mmol NH4HCO3. y @γ-AlOOH was characterized by XRD and IR, and the acidic sites were obtained by pyridine IR. The total acid content of the catalyst was determined by acid-base titration.

[0073] like Figure 4 , 5 As shown, the y value is N y @γ-AlOOH has a significant effect on the structure. When y = 0 / 15 and 2 / 13, the catalyst N y @γ-AlOOH has the structure of γ-AlOOH. But as the value of y increases, N y@AACH structure begins to appear in the structure of γ-AlOOH. When y=7 / 8, catalyst N y @γ-AlOOH main structure begins to change to AACH. When y = 15 / 0, catalyst N y @γ-AlOOH completely turns into AACH.

[0074] like Figure 6 As shown, N is determined by pyridine y @γ-AlOOH acidic site, Table 1 below is the determination of N by pyridine y @The table of acid position of γ-AlOOH and total acid content by acid-base titration:

[0075]

[0076]

[0077] Table 1

[0078] From Table 1, it can be found that as the y value increases, BAS continues to increase. When y = 7 / 8, the ratio of BAS to LAS reaches the maximum, reaching 0.24. Subsequently, as the y value increases, the ratio of BAS to LAS slowly decreases. When y = 9 / 6 and 15 / 0, the ratio of BAS to LAS drops to 0.20 and 0.16. However, the total acid content and LAS continue to decrease as the y value increases. When y is greater than 4 / 11, the strength of LAS drops below 100umol pyridine / g.

[0079] Embodiment 4:

[0080] Investigate different N y @γ-AlOOH catalyzes glucose to produce HMF and determines the best catalyst. y @γ-AlOOH preparation method is the same as that in Example 3. Different N y The process of preparing HMF from glucose catalyzed by @γ-AlOOH is as follows:

[0081] 100 mg of glucose was added to 20 mL of a biphasic solution of n-butanol-water-20% NaCl, wherein the volume ratio of water to n-butanol was 1:2. After the glucose was completely dissolved, 30 mg of catalyst N was added to the solution. y @γ-AlOOH, stirred at 140 ° C for 3 hours. Then, the reactor was quickly cooled to room temperature with ice water. Centrifuged at 10,000 rpm for 10 minutes to separate the solid and liquid. The dilution including the organic phase and the aqueous phase was used to analyze the distribution and content of the reaction products.

[0082]

[0083] Table 2

[0084] As shown in Table 2, N y The corresponding table of the amount of HMF produced from glucose catalyzed by @γ-AlOOH is shown in Table 2. y @γ-AlOOH catalyzes the production of HMF from glucose. It is found that when y = 4 / 11, that is, the catalyst N 4 / 11 @γ-AlOOH has the best catalytic effect, and can obtain up to 73.8% HMF yield and selectivity. Therefore, the best catalyst in this example is: N 4 / 11 @γ-AlOO.

[0085] Embodiment 5:

[0086] N 4 / 11 The preparation method of @γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of converting glucose to produce HMF is also the same as that of Example 4, except that the reaction solvent is changed to a single-phase solvent: dimethyl sulfoxide (DMSO) dimethylformamide (DMF) and water, a biphasic solvent: n-butanol (1-butanol)-water n-pentanol (1-hexanol)-water methyl isobutyl ketone (MIBK)-water tetrahydrofuran (THF)-water and its corresponding 20% ​​NaCl solution, to investigate the effect of the reaction solvent on the catalytic production of HMF from glucose.

[0087]

[0088] Table 3

[0089] As shown in Table 3, the effect of adding 20% ​​NaCl on the catalytic effect is compared. Figure 7 As shown in Table 3, the separation coefficient is: HMF in the organic phase divided by HMF in the aqueous phase. It can be found that DMSO has the best effect among the single-phase solvents, and the HMF yield and selectivity both reach 80.3%. In the biphasic solvents, it can be found that due to the salt-out effect, all biphasic solvents have a significant increase in HMF yield after adding 20% ​​NaCl. Among all biphasic solvents, n-butanol-water-20% NaCl has the best effect, and the HMF yield and selectivity reach 73.8%.

[0090] Due to the high boiling point and strong polarity of DMSO, HMF is difficult to separate from DMSO in the subsequent separation and purification process. Therefore, the best solvent in this embodiment is preferably a biphasic solvent of n-butanol-water-20% NaCl.

[0091] Embodiment 6:

[0092] N 4 / 11The preparation method of @γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of converting glucose to produce HMF is the same as that of Example 4, except that the reaction temperature is adjusted to 110°C to 170°C and the reaction time is adjusted to 0.5h to 12h. The effects of reaction temperature and reaction time on the catalytic production of HMF from glucose are investigated.

[0093] like Figure 8 As shown, it can be concluded that the optimal reaction temperature and reaction time for this process are 140℃ and 3h.

[0094] Embodiment 7:

[0095] N 4 / 11 The preparation method of @γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of converting glucose to produce HMF is the same as that of Example 4, except that the loading amount of the catalyst on the substrate glucose is adjusted to 10% to 100%. The effect of the loading amount of the catalyst on the catalytic production of HMF from glucose is investigated.

[0096] like Fig.10 As shown, it can be found that when the catalyst loading is 30%, the catalytic effect is the best.

[0097] Embodiment 8:

[0098] N 4 / 11 The preparation method of γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of converting glucose to produce HMF is the same as that of Example 4, except that the concentration of the substrate glucose is adjusted to 0.5-40 g / L -1 The effect of substrate glucose concentration on the catalytic production of HMF from glucose was investigated.

[0099] like Fig.11 As shown, it can be found that when the substrate concentration is not higher than 10gL -1 When the glucose concentration is 10 g / L -1 , the HMF yield was still 67%. -1 When the concentration increases to 20 g / L -1 and 40gL -1 When , the yield of HMF dropped rapidly to 51% and 23%.

[0100] Considering that too low a substrate concentration will increase industrial operating costs, the optimal substrate concentration in this embodiment is preferably 10 g / L -1 .

[0101] Embodiment 9:

[0102] N 4 / 11The preparation method of @γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of glucose conversion to produce HMF is the same as that of Example 4, and the effects of catalyst acid site loss and catalyst reuse on the production of HMF from glucose are investigated. The experimental process of catalyst acid site loss is as follows:

[0103] After a 2-hour glucose degradation experiment at 140 °C, N 4 / 11 @γ-AlOOH is filtered out, and then no N is added 4 / 11 @γ-AlOOH catalyst was used to carry out the reaction for another 4 hours.

[0104] like Fig.12 As shown, it can be concluded that N 4 / 11 @No acid sites in γ-AlOOH are leached and lost, N 4 / 11 @γ-AlOOH acidic site is stable.

[0105] The catalyst repeated experimental process is as follows:

[0106] After the reaction is completed, the catalyst N is recovered by filtration. 4 / 11 @γ-AlOOH, after washing with water and ethanol, was dried in vacuum at 60 °C overnight and used as the catalyst for the next reaction.

[0107] like Fig.13 As shown, it can be concluded that N 4 / 11 @γ-AlOOH exhibited excellent catalytic performance with no apparent activity loss. Even after five consecutive runs, the yield of HMF reached about 61.5% and the glucose conversion was 94.2%, which can be attributed to its excellent hydrothermal stability.

[0108] Embodiment 10:

[0109] N 4 / 11 The preparation method of @γ-AlOOH is the same as that of Examples 2 and 3. The experimental process of converting glucose to produce HMF is the same as that of Example 4, except that the reaction substrate is adjusted from glucose to one of fructose, cellulose, starch, and inulin, and other conditions remain unchanged, to investigate the use range of the catalyst.

[0110]

[0111] Table 4

[0112] As shown in Table 4, N 4 / 11 @γ-AlOOH catalyzes the production of HMF from different carbohydrates. 4 / 11 @γ-AlOOH catalyst has a wide range of applications. It is not only suitable for catalyzing monosaccharides (fructose and glucose), but also for catalyzing polysaccharides (starch and inulin). It is also suitable for catalyzing oligosaccharides (cellulose) to produce HMF.

[0113] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for preparing a bifunctional solid acid catalyst, characterized in that: The steps include: Step 1: Add X parts of NH4HCO3 and MX parts of aluminum salt mixture into deionized water; Step 2: Slowly add M parts of NH4HCO solution under vigorous stirring; Step 3: After the solution obtained in step 2 becomes clear, slowly add ammonia water until the pH value reaches a preset value; Step 4: placing the product obtained in step 3 into a hydrothermal reactor for heating, cooling it naturally to room temperature after heating, and centrifuging to obtain a solid product; Step 5: After washing the solid product with deionized water, the solid product is dried under a constant temperature vacuum environment. After drying, a solid acid catalyst N is obtained. y @γ-AlOOH, wherein y is the molar ratio of NH4HCO3 to aluminum salt in the mixture of step 1.

2. The method for preparing a bifunctional solid acid catalyst according to claim 1, characterized in that: The range of y is 0 / 15 to 15 / 0.

3. The method for preparing a bifunctional solid acid catalyst according to claim 1, characterized in that: The preset value of the pH value in step 3 is in the range of 8-12.

4. A bifunctional solid acid catalyst prepared by the method for preparing a bifunctional solid acid catalyst as claimed in any one of claims 1 to 3.

5. Use of the bifunctional solid acid catalyst as claimed in claim 4 in the preparation of HMF from glucose.

6. Use of the bifunctional solid acid catalyst as claimed in claim 5 in the preparation of HMF from glucose, characterized in that: The specific steps of applying glucose to produce HMF include: First, a solid acid catalyst and glucose are added to a biphasic solution or a NaCl solution containing the corresponding biphasic solution, and then stirred for reaction under high temperature conditions. After the reaction is completed, the mixture is cooled to room temperature, and the liquid is collected by centrifugation to obtain a degradation solution containing HMF.

7. Use of the bifunctional solid acid catalyst as claimed in claim 6 in the preparation of HMF from glucose, characterized in that: The catalyst loading range of the solid acid catalyst on the substrate glucose is 10% to 100%.

8. Use of the bifunctional solid acid catalyst as claimed in claim 6 in the preparation of HMF from glucose, characterized in that: The concentration range of glucose is: 0.5gL -1 ~40gL -1 .

9. Use of the bifunctional solid acid catalyst as claimed in claim 6 in the preparation of HMF from glucose, characterized in that: The temperature range of the high temperature condition is: 110°C to 170°C; the reaction time range is: 0.5h to 12h.

10. Use of the bifunctional solid acid catalyst according to claim 6 in the preparation of HMF from glucose, characterized in that: The biphasic solution is: n-butanol-water-NaCl, n-pentanol-water-NaCl, tetrahydrofuran-water-NaCl or methyl isobutyl ketone-water-NaCl.

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