CN109867642B

CN109867642B - Method for preparing 5-hydroxymethylfurfural by efficiently catalyzing cellulose with boehmite

Info

Publication number: CN109867642B
Application number: CN201910283819.6A
Authority: CN
Inventors: 苏建辉; 唐喆; 姜瑞雨; 仓辉; 韩粉女; 许琦
Original assignee: Yancheng Institute of Technology
Current assignee: Yancheng Institute of Technology
Priority date: 2019-04-10
Filing date: 2019-04-10
Publication date: 2023-03-24
Anticipated expiration: 2039-04-10
Also published as: CN109867642A

Abstract

The invention discloses a method for preparing 5-hydroxymethylfurfural by using boehmite to efficiently catalyze cellulose, which comprises the steps of adding boehmite and cellulose into a mixed system of ionic liquid, dimethyl sulfoxide and a small amount of water, uniformly stirring, transferring into a conventional glass reactor, stirring at 120-210 ℃ for reaction, adding deionized water into a reaction liquid after the reaction is finished, quenching, centrifuging, and collecting an upper layer liquid to obtain a degradation liquid containing 5-hydroxymethylfurfural. When the method is used for catalyzing cellulose to prepare 5-hydroxymethylfurfural, the method has the characteristics of high-efficiency catalysis (high yield and selectivity of 5-hydroxymethylfurfural), easy separation and reuse of the catalyst, simple operation, low cost (simple equipment and recyclable catalyst and reaction), and the like, can avoid a large number of side reactions, improve the selectivity of the product, reduce the separation cost of the product, and has extremely high application value.

Description

Method for preparing 5-hydroxymethylfurfural from boehmite high-efficiency catalytic cellulose

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a method for preparing 5-hydroxymethylfurfural by efficiently catalyzing cellulose with boehmite.

Background

With the increasing exhaustion of petroleum resources and the increasing demands of people on chemical products, environmental safety and sustainable development requirements, how to produce biomass platform compounds by using renewable, recyclable and clean biological resources to reduce or reduce the dependence of people on fossil energy and protect the environment is an increasingly prominent problem at present. Compared with other biomass platform compounds, 5-Hydroxymethylfurfural (HMF) is considered to be a platform compound with better development prospect, has the capability of synthesizing various fine chemicals, medical precursors, biofuels and high-performance polymers, such as 2, 5-Diformylfuran (DFF), 2, 5-furandicarboxylic acid (FDA), 2, 5-dimethylolfuran (BHMF), 2, 5-Dimethylolfuran (DMF), levulinic Acid (LA) and the like, has very important research and industrial application values, and is a hotspot of current research. Compared with the edible monosaccharide with higher price such as glucose, fructose, xylose and cellulose, the preparation method has the characteristics of inedibility, wide sources, low price and the like, and is a more ideal raw material for preparing HMF. However, because cellulose is a closely packed high molecular compound formed by linking glucose units through beta-1, 4 glycosidic bonds and intermolecular and intramolecular hydrogen bonds, and has the characteristics of high crystallinity, low solubility (water and common organic solvents), difficult degradation and the like, the difficulty of efficiently degrading cellulose to prepare HMF is high, a plurality of technical problems exist, and the method has a great challenge.

Current research indicates that acidic catalysts, both homogeneous and heterogeneous, are beneficial in catalyzing cellulose degradation. However, compared with homogeneous catalysts, heterogeneous catalysis has the advantages of easy catalyst recovery, easy product separation, low corrosivity, easy realization of industrialization and the like, is considered to be a more ideal method for preparing HMF, and is also a development trend and a research hotspot at present. In recent decades, numerous heterogeneous catalysts have been developed and applied to the research of preparing HMF by degrading cellulose, such as metal oxides, zeolite molecular sieves, sulfonated carbon-based materials, doped materials, multifunctional polymers, molten salts, metal-organic framework compounds, resins, and the like. Since metal oxides can provide the necessary acidic sites and are inexpensive and readily available, metal oxides are one of the most studied, and also the most widely and commercially promising heterogeneous catalysts, and are the focus and direction of research. Alumina is one of the commonly used metal oxides, and because of its low cost, it is often used as a catalyst or catalytic carrier to catalyze carbohydrates (glucose, fructose, polysaccharides) to produce HMF in the acquisition aspect. For example, sampath (appl. Catal. A-Gen. 2017; 533. Garcia-Sanchoa (appl. Cat. B-environ. 2017; 206: 617-625; appl. Cat. B-environ. 2014; 152: 1-10) investigated the case of preparing HMF by catalyzing glucose with alumina as a catalyst or catalyst carrier, which also indicates that alumina is a catalyst with good ability of catalyzing sugar water compounds such as glucose, fructose and the like to prepare HMF. However, alumina has poor hydrothermal stability, and is slowly converted into boehmite (gamma-AlOOH) which is a precursor thereof in hot water at 150 ℃. Meanwhile, as HMF is produced by fructose dehydration, water is inevitably added in the process of preparing HMF from carbohydrates. In the process of preparing HMF by cellulose degradation, in addition to water generated in the process, the first part of cellulose degradation is hydrolysis reaction, so that additional water is required to be added. Meanwhile, the temperature of most cellulose degradation reactions is higher than 150 ℃, so the poor hydrothermal stability of the alumina will influence the catalytic performance of the alumina and reduce the catalytic stability. In view of this, takagaki (RSC adv. 2014: 43785-43791) used boehmite, a precursor of alumina (γ -AlOOH), to directly catalyze glucose to prepare HMF in an aqueous phase, obtaining about 18% of the yield of HMF, indicating that γ -AlOOH has the ability to catalyze carbohydrates such as glucose and fructose to prepare HMF. However, to our knowledge, there is no report of the production of HMF by the catalysis of cellulose by γ -AlOOH. Meanwhile, compared with the existing catalyst with cellulose catalytic performance, such as sulfonated carbon-based materials, doped materials, multifunctional polymers, metal organic framework compounds and resins, the gamma-AlOOH catalyst is simple to prepare, low in price and convenient to obtain, and is a more ideal catalyst prepared from HMF.

Reaction solvent selection is another key factor affecting the production of HMF from cellulose. Cellulose is a tightly extruded polymer compound, and is insoluble in common organic solvents and water. Therefore, how to effectively dissolve the cellulose and promote the cellulose to effectively contact with a heterogeneous catalyst is one of the key factors for improving the cellulose degradation efficiency. Compared with other common solvents (ethanol and acetone), the ionic liquid has stronger cellulose dissolving capacity, and the cellulose can be effectively dissolved in the ionic liquid at the temperature of more than 120 ℃. Although the price of the ionic liquid is higher at present, the ionic liquid has strong stability, and can be recycled by simple distillation, ion exchange and extraction, or the use ratio of the ionic liquid is reduced by adding other common reagents, so that the cost is reduced. Therefore, the ionic liquid is still one of the ideal reaction solvents for degrading cellulose at present.

Therefore, the invention discloses a method for preparing HMF by efficiently catalyzing cellulose with boehmite (gamma-AlOOH).

Disclosure of Invention

Compared with edible monosaccharides such as glucose, fructose and xylose with higher price, the cellulose has the characteristics of inedibility, wide source, low price and the like, and is a more ideal raw material for preparing HMF. However, because cellulose is a closely-packed high molecular compound formed by linking glucose units through beta-1, 4 glycosidic bonds and intermolecular hydrogen bonds, and has the characteristics of high crystallinity, low solubility (water and common organic solvents), difficult degradation and the like, the difficulty of efficiently degrading cellulose to prepare HMF is high at present, and a plurality of technical problems exist, so that the method has great challenge. The invention aims to solve the problems that the hydrothermal stability of a common alumina catalyst is not strong, and the complex heterozygosis prepared by other heterogeneous catalysts is not suitable for preparing HMF in a large range, and provides a method for preparing HMF by using boehmite high-efficiency catalytic cellulose.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing 5-hydroxymethylfurfural by using boehmite to efficiently catalyze cellulose comprises the following steps: adding boehmite and cellulose into a mixed system of ionic liquid, dimethyl sulfoxide and water, stirring uniformly, transferring into a reactor, stirring for reaction at 120-210 ℃, adding deionized water into a reaction solution after the reaction is finished, quenching, centrifuging, and collecting an upper layer liquid to obtain a degradation liquid containing 5-hydroxymethylfurfural.

Further, the method for preparing the 5-hydroxymethylfurfural comprises the following steps: adding cellulose into a mixed solution of ionic liquid and dimethyl sulfoxide, stirring until the cellulose is dissolved, adding boehmite and deionized water, stirring uniformly, transferring into a reactor, stirring for reaction at 120-210 ℃, adding deionized water into a reaction solution after the reaction is finished, quenching, centrifuging, and collecting an upper layer liquid to obtain a degradation liquid containing 5-hydroxymethylfurfural.

Further, the mass ratio of boehmite to cellulose was 0.05:1 to 5:1, preferably 1:1.

further, the mass ratio of the cellulose to the mixed system (ionic liquid, dimethyl sulfoxide and water) is 1:10 to 1:100, preferably 1:60.

further, the mass ratio of the ionic liquid to the dimethyl sulfoxide in the mixed system is 6:0 to 2:4, preferably 4:2.

further, the mass ratio of the ionic liquid to the water in the mixed system is 4:2 to 4:0.5, preferably 4:1.

further, the ionic liquid is 1-butyl-4-methyl imidazole chloride.

Further, the reaction time is 0.5 to 6 hours, preferably 2 hours.

Further, the reaction vessel is a conventional glass reactor.

Further, the boehmite is prepared by the following method: adding an aluminum source and a slow hydrolysis reagent into deionized water, stirring uniformly, then dropwise adding a precipitator, adjusting the pH value of the solution to 9, then transferring the solution into a reaction kettle with a polytetrafluoroethylene lining, reacting the reaction kettle at 100-300 ℃ for 5-60 h, taking out the reaction kettle, naturally cooling to room temperature, collecting reacted solid through centrifugation and washing, and drying the solid at 60-180 ℃ for 8-48 h to obtain the solid catalyst boehmite.

The aluminum source is inorganic aluminum salt and/or aluminum isopropoxide, the slow hydrolysis reagent is ammonium bicarbonate, and the precipitant is ammonia water solution.

Further, the molar ratio of the aluminum source to the slow hydrolysis reagent is 1:2.

further, the inorganic aluminum salt is selected from AlCl ₃ 、Al(NO ₃ ) ₃ 、Al ₂ (SO ₄ ) ₃ 、AlCl ₃ ·6H ₂ O、Al(NO ₃ ) ₃ ·9H ₂ O、Al ₂ (SO ₄ ) ₃ ·16H ₂ One or more of O, wherein Al (NO) ₃ ) ₃ 、Al(NO ₃ ) ₃ ·9H ₂ The O effect is optimal.

Further, the method for extracting and purifying the 5-hydroxymethylfurfural from the degradation liquid containing the 5-hydroxymethylfurfural comprises the following steps: adding ether into a degradation liquid containing 5-hydroxymethylfurfural for primary extraction and separation, standing for layering, adding deionized water into an upper layer liquid, uniformly stirring, adding ether for secondary extraction and separation, extracting and separating for 2-3 times to obtain a 5-hydroxymethylfurfural-ether extract, carrying out reduced pressure distillation on the extract under the condition of ice-water bath, and separating ether to obtain the high-concentration 5-hydroxymethylfurfural.

Advantageous effects

Compared with the prior art, the invention has the following advantages:

(1) The heterogeneous catalyst gamma-AlOOH disclosed by the invention has the characteristics of low price and easiness in obtaining of raw materials, simple preparation method and stable catalyst property, and has a good industrial application prospect.

(2) When the method is used for catalyzing cellulose to prepare HMF, the method has the characteristics of high-efficiency catalysis (high HMF yield and selectivity), easy separation and reuse of the catalyst, simple operation, low cost (simple equipment and recyclable catalyst and reaction), and the like, can avoid a large number of side reactions, improve the product selectivity, reduce the product separation cost, and has extremely high application value.

(3) The method utilizes a direct one-step method to extract the HMF from the mixed solution of the Ionic Liquid (IL), the DMSO and the water, reduces the operation steps, avoids the decomposition of the HMF caused by excessive operation, and improves the extraction efficiency of the HMF; by utilizing the difference of the polarities of the ionic liquid, the DMSO and the HMF, the polarity of water is fully utilized by adding the water first, and the acting force between the DMSO and the ionic liquid and the HMF is reduced; by means of the high extraction capacity of the ether to the HMF, the stability of the HMF can be ensured, and the extraction efficiency of the HMF can be improved; the method realizes the task of extracting the HMF in one step in the high-boiling point strong polar solvent DMSO and the ionic liquid, and can effectively solve the problem of purifying the HMF in the mixed solution of the high-boiling point strong polar solvent DMSO and the ionic liquid at present.

Drawings

FIG. 1 is a schematic flow diagram of a production process of the present invention;

FIG. 2 is an XRD pattern of γ -AlOOH prepared in example 1;

FIG. 3 is a graph showing the effect of the volume fraction of ether in the extractant on the extraction in example 7;

FIG. 4 is a graph showing the effect of the number of extractions on the extraction efficiency in example 8;

FIG. 5 is a graph showing the effect of the solvent on the catalytic effect of example 9;

FIG. 6 is a graph showing the effect of reaction time on catalytic performance in example 10;

FIG. 7 is a graph showing the effect of reaction temperature on the catalytic effect in example 11;

FIG. 8 is a graph showing the effect of the amount of catalyst used on the catalytic performance in example 12;

FIG. 9 is a graph showing the effect of the amount of water added on the catalytic effect in example 13;

FIG. 10 is a graph showing the effect of the number of times the catalyst was recycled on the catalytic effect in example 17.

Detailed Description

The invention is further illustrated by the following examples. The percentages in the following examples are by mass unless otherwise specified. The reagents or instruments used are not indicated by manufacturers, and are regarded as conventional products which can be purchased in the market.

Example 1

At 800 rpm40 mL of 0.75 mol/L NH were added under magnetic stirring ₄ HCO ₃ The solution was slowly added to 10 mL of 1.5 mol/L Al (NO) ₃ ) ₃ In solution. After the solution becomes clear and transparent, 25 percent of concentrated ammonia water solution is slowly dropped into the solution, and the pH value is adjusted to 9. After the mixture becomes uniform mixed solution, the mixture is transferred into a 100 mL reaction kettle with a polytetrafluoroethylene lining and reacts for 12 hours at 150 ℃. And when the reaction time reaches the set time, taking out the reaction kettle. Naturally cooling to room temperature, opening the reaction kettle, and separating and washing the catalyst to obtain a solid product. Finally, the solid product is dried for 12 h at 150 ℃, and the solid catalyst gamma-AlOOH is obtained. This solid catalyst was subjected to XRD analysis. As shown in FIG. 2, it can be seen from FIG. 2 that all diffraction peaks of the sample are consistent with those of the orthorhombic γ -AlOOH (JCPDS 021-1307) marker, while no diffraction peaks of other substances are observed, indicating that the synthesized sample is a high-purity γ -AlOOH.

0.1 g of cellulose was added to a mixed solution of 4.0 g of ionic liquid 1-butyl-4-methylchloroimidazole (BmimCl) and 2.0 g of dimethyl sulfoxide (DMSO) under magnetic stirring at 800 rpm, and stirred until the cellulose was completely dissolved to form a uniform reaction solution. Then 0.1 g of catalyst gamma-AlOOH and 1.0 g of deionized water are added into the reaction solution, after the mixture is uniformly stirred, the reaction system is transferred into a 160 ℃ oil bath crucible, and the mixture reacts for 2 hours under the magnetic stirring of 800 r/min. Immediately after the reaction, 20 mL of cold deionized water was added to the reaction mixture to quench it. Separating with centrifuge at 10000 rpm for 5min, and collecting upper layer liquid to obtain degradation liquid containing HMF. Taking out a little of the degradation liquid, diluting the degradation liquid by 200 times by using deionized water, analyzing products in the degradation liquid by using high performance liquid chromatography, and calculating to obtain that the yield of HMF of the reaction is 58.4%, the selectivity of HMF is 60% and the conversion rate of cellulose is 97%.

20 mL of diethyl ether was added to the degraded solution obtained by the above centrifugal separation for extraction and separation. Standing for 10 min, and taking out the upper layer liquid. Then, 20 mL of deionized water was added to the supernatant, and after stirring the mixture to be uniform, 10 mL of diethyl ether was added to the uniform to conduct extraction separation. After standing for 10 min, the upper solution was taken out. This process was repeated two more times and the upper liquid was removed to give the final ether-HMF extract solution. Meanwhile, all the lower layer liquid in the process is collected and subjected to rotary distillation at 80 ℃, and the ionic liquid and DMSO are recovered. Then, the ether-HMF extract solution is subjected to distillation under reduced pressure in an ice-water bath, and the ether solution (used as an extractant for the next time) is recovered to obtain HMF with high concentration. A small amount of HMF is taken, diluted by 20 mL of deionized water, and the content of the HMF is analyzed by high performance liquid chromatography, so that the purity of the HMF is 94% and the extraction rate is 59%.

Example 2

The preparation method of gamma-AlOOH is the same as that of example 1. The procedure for preparing HMF by cellulose degradation was also the same as in example 1.

In the process of preparing 5-hydroxymethylfurfural, the ratio of the ionic liquid to DMSO in the reaction solvent was kept constant, the reaction solvent (ionic liquid and DMSO) was increased to 9.0 g, and the influence of the reactant concentration on the catalytic effect was examined. The specific process is as follows: 0.1 g of cellulose was added to a mixed solution of 6.0 g of ionic liquid 1-butyl-4-methylchloroimidazole (BmimCl) and 3.0 g of dimethyl sulfoxide (DMSO) under magnetic stirring at 800 rpm, and stirred until the cellulose was completely dissolved to form a uniform reaction solution. Then, 0.1 g of catalyst γ -AlOOH and 1.0 g of deionized water were added to the reaction solution. After the mixture is stirred uniformly, the reaction system is transferred to a 160 ℃ oil bath crucible and reacts for 2 hours under the magnetic stirring of 800 r/min. Immediately after the reaction, 20 mL of cold deionized water was added to the reaction mixture to quench it. Separating with centrifuge at 10000 rpm for 5min, and collecting upper layer liquid to obtain degradation liquid containing HMF. Taking out a little of the degradation liquid, diluting the degradation liquid by 200 times by using deionized water, analyzing products in the degradation liquid by using high performance liquid chromatography, and calculating to obtain that the yield of HMF of the reaction is 60.3%, the selectivity of HMF is 61.4% and the conversion rate of cellulose is 98%.

Example 3

In the process of preparing 5-hydroxymethylfurfural, the ratio of the ionic liquid to DMSO in the reaction solvent is kept unchanged, the reaction solvent (the ionic liquid and the DMSO) is reduced to 3.0 g, and the influence of the concentration of reactants on the catalytic effect is examined. The specific process is as follows: 0.1 g of cellulose was added to a mixed solution of 2.0 g of ionic liquid 1-butyl-4-methylchloroimidazole (BmimCl) and 1.0 g of dimethyl sulfoxide (DMSO) under magnetic stirring at 800 rpm, and stirred until the cellulose was completely dissolved to form a uniform reaction solution. Then, 0.1 g of catalyst γ -AlOOH and 1.0 g of deionized water were added to the reaction solution. After the mixture is stirred uniformly, the reaction system is transferred to a 160 ℃ oil bath crucible and reacts for 2 hours under the magnetic stirring of 800 r/min. Immediately after the reaction, 20 mL of cold deionized water was added to the reaction mixture to quench it. And separating for 5min at 10000 r/min by using a centrifuge, and collecting the upper liquid to obtain the degradation liquid containing the HMF. Taking out a little of the degradation liquid, diluting the degradation liquid by 200 times by using deionized water, analyzing products in the degradation liquid by using a high performance liquid chromatography, and calculating to obtain that the yield of HMF of the reaction is 50.3%, the selectivity of HMF is 54.1% and the conversion rate of cellulose is 93%.

It can be seen from examples 1-3 that the reaction solvent content has little effect on the yield and selectivity of HMF when the mixed reaction solvent content of ionic liquid and DMSO is not less than 6.0 g, i.e., the cellulose content is not more than 1.7%. However, once the reaction solution content is less than 6.0 g, i.e., the glucose content is greater than 1.7%, the reaction solvent content has a great effect on the yield and selectivity of HMF. The lower the amount of reaction solvent, the lower the HMF yield and selectivity, which may be related to the solubility of cellulose in the ionic liquid, the lower the amount of reaction solvent, the lower the ionic liquid content, the lower the amount of dissolved cellulose, and the lower the chance of contact of cellulose with the catalyst, the poorer the catalytic effect.

Example 4

The preparation method and preparation conditions of gamma-AlOOH, the experimental process for preparing HMF by degrading cellulose and the addition amount of raw materials are completely the same as in example 1. Only the HMF extraction method is changed, and the influence of no water addition on the extraction result is examined. The specific process is as follows: and adding 20 mL of diethyl ether into the upper-layer degradation liquid obtained after centrifugal separation for extraction and separation. Standing for 10 min, and taking out the upper layer liquid. Then, 20 mL of diethyl ether was added directly to the supernatant to conduct extraction separation. Standing for 10 min, and taking out the upper solution. This process was repeated 2 times, and the upper solution was taken out to obtain an extract of ether-HMF. Then, the ether-HMF extract was subjected to distillation under reduced pressure in an ice-water bath, and the ether solution (used as an extractant for the next time) was recovered to obtain HMF with high concentration. A small amount of HMF is taken, diluted by 20 mL of deionized water, and the content of the HMF is analyzed by high performance liquid chromatography, so that the purity of the HMF is calculated to be 19%, and the extraction rate is 42%. This experiment shows that the addition of water has a great influence on the extraction result, and it is difficult to separate the reaction solvent (ionic liquid and DMSO mixed solution) from the HMF without adding water, and thus it is difficult to achieve the separation and purification.

Example 5

The preparation method and preparation conditions of gamma-AlOOH, the experimental process for preparing HMF by cellulose degradation and the raw material addition are completely the same as in example 1. Except that the HMF extraction process was changed to a two-step separation extraction process. The specific process is as follows: collecting supernatant, distilling at 150 deg.C under reduced pressure, and separating ionic liquid to obtain degradation solution of DMSO-water-HMF. And (3) carrying out water-ether extraction separation on the collected degradation liquid, firstly adding 10 mL of ether into the degradation liquid, fully mixing, standing for 10 min, and taking out the upper layer liquid. Then, 20 mL of deionized water was added to the supernatant, and after stirring was carried out, 10 mL of diethyl ether was added to the homogeneous solution to carry out extraction separation. Standing for 10 min, and taking out the upper solution. This process was repeated 2 more times and the upper liquid was taken out to obtain the final ether-HMF extract. Then, the ether-HMF extract was subjected to distillation under reduced pressure in an ice-water bath, and the ether solution (used as an extractant for the next time) was recovered to obtain HMF with high concentration. A small amount of HMF is taken, diluted by 20 mL of deionized water, and the content of the HMF is analyzed by high performance liquid chromatography, so that the purity of the HMF is calculated to be 98%, and the extraction rate is 45%.

In comparison with example 1, it can be seen that although the purity of HMF is higher in the two-stage extraction, the extraction rate is significantly reduced, and the overall effect is not as good as that of one-stage extraction separation.

Example 6

The preparation method and preparation conditions of gamma-AlOOH, the experimental process for preparing HMF by degrading cellulose and the addition amount of raw materials are completely the same as in example 1. The effect of the type of HMF extractant on the extraction results was examined using toluene, acetone (Acetone), ethyl acetate, methyl isopropyl ketone, tetrahydrofuran (THF), and petroleum ether as the extractants, respectively, and the extraction procedure was the same as in example 1. The extraction results are shown in table 1, and it can be seen from table 1 that diethyl ether has the best extraction effect as an extractant.

TABLE 1 Effect of different extractants on HMF extraction results

	Toluene	Acetone (II)	Ethyl acetate	Methyl isopropyl ketone	Tetrahydrofuran (THF)	Petroleum ether	Ether (A)
								HMF purity (%)	32	58	65	85	86	76	94
HMF extraction (%)	5	18	6	35	20	8	59

Example 7

The preparation method and preparation conditions of gamma-AlOOH, the experimental process for preparing HMF by degrading cellulose and the addition amount of raw materials are completely the same as in example 1. The experimental procedure of example 1 was the same as that of example 1, and the extraction results are shown in FIG. 3, in which the effect of the percentage by volume of ether in the extractant from the second time on the extraction results was examined under the condition that the amount of ether added in the first time was kept constant, that is, 10 mL of ether was added to the supernatant liquid after the centrifugation, and the effect of the percentage by volume of ether in the extractant from the second time was examined, while the effect of the volume fractions of ether of 30 mL and water were respectively 17%, 20%, 33%, 50%, 67% and 80% on the extraction results was examined. As can be seen from fig. 3, when the volume fraction of diethyl ether is 33%, i.e. the volume ratio of diethyl ether/water is 1:2, the extraction effect is best.

Example 8

The preparation method and preparation conditions of gamma-AlOOH, the experimental process for preparing HMF by degrading cellulose and the addition amount of raw materials are completely the same as in example 1. The effect of the number of extractions (1, 2, 3, 4, 5, 6 and 7) on the extraction effect was examined, and the results are shown in FIG. 4, which is the same as example 1. As can be seen from FIG. 4, the extraction efficiency was the best when the number of extractions was 4.

Example 9

The preparation method and preparation conditions of gamma-AlOOH are the same as in example 1. The experimental process for preparing HMF by cellulose degradation is the same as that in example 1, the reaction solvent is changed, and the influence of the change of the reaction solvent on the catalytic effect is examined. The experimental results are shown in fig. 5, IL is an ionic liquid; DMSO is twoMethyl sulfoxide; DMF is N' N-dimethylformamide; THF is tetrahydrofuran; acetone is Acetone; x _IL Refers to the mass fraction of the ionic liquid in the mixed solvent. From fig. 5, it can be seen that the mass ratio of the ionic liquid to the DMSO mixed solution as the solvent is 4:2, the catalytic effect is best.

Example 10

The preparation method and preparation conditions of gamma-AlOOH are the same as in example 1. The experimental process for preparing HMF by cellulose degradation is also the same as in example 1, except that the reaction time of the catalytic reaction is adjusted (0.5 h to 6 h), and the influence of the reaction time on the catalytic effect is examined. The results of the experiment are shown in FIG. 6. From FIG. 6, it can be seen that the catalytic reaction time is 2 h, and the catalytic effect is the best.

Example 11

The preparation method and preparation conditions of gamma-AlOOH are the same as in example 1. The experimental process for preparing HMF by cellulose degradation is the same as that of example 1, except that the reaction temperature of the catalytic reaction is adjusted (120 ℃ to 210 ℃), and the influence of the reaction temperature on the catalytic effect is examined. The results of the experiment are shown in FIG. 7. It can be seen from FIG. 7 that the reaction temperature is 160 ℃ and the catalytic effect is the best.

Example 12

The preparation method and preparation conditions of gamma-AlOOH are the same as in example 1. The experimental procedure for preparing HMF by degrading cellulose is also the same as in example 1, except that the amount of the catalyst (0.05 g to 0.2 g) is adjusted and the influence of the amount of the catalyst on the catalytic effect is examined. The results of the experiment are shown in FIG. 8. It can be seen from FIG. 8 that the catalyst is used in an amount of 0.1 g, which is the most effective.

Example 13

The preparation method and preparation conditions of gamma-AlOOH are the same as in example 1. The procedure of the cellulose degradation HMF test was also the same as in example 1 except that the amount of water added was varied (0 to 4 mL) and the effect of the amount of water added on the catalytic effect was examined. The results of the experiment are shown in FIG. 9. As can be seen from FIG. 9, the catalytic effect was the best when the amount of water added was 1.0 mL.

Example 14

Gamma-AlOOH preparation method and preparation process As in example 1, the preparation of different gamma-A by modulating the aluminum sourcelOOH, each with Al ₂ (SO ₄ ) ₃ 、AlCl ₃ And Al (i-OPr) ₃ Replace the original Al (NO) ₃ ) ₃ Gamma-AlOOH is prepared, and the prepared gamma-AlOOH is used as a catalyst to catalyze the hydrolysis of cellulose to prepare HMF, and the process for preparing the HMF by degrading the cellulose is the same as that of the example 1. The results of the specific experiments are shown in table 2.

TABLE 2 preparation of HMF by degradation of cellulose catalyzed by gamma-AlOOH prepared from different aluminum sources

Aluminum source	Al ₂ (SO ₄ ) ₃	AlCl ₃	Al(i-OPr) ₃	Al(NO ₃ ) ₃
					HMF（%）	35.6	48.6	20	58.4
HMF selectivity (%)	45	54	34	60
					Cellulose conversion (%)	79	89	59	97

As can be seen from Table 2, the gamma-AlOOH prepared by using an inorganic aluminum source as a raw material has better catalytic effect than the gamma-AlOOH prepared by using an organic aluminum source as a raw material. In the inorganic aluminum source, al (NO) is used ₃ ) ₃ The gamma-AlOOH prepared by the method as an aluminum source has the best catalytic effect.

Example 15

The preparation method and the preparation process of the gamma-AlOOH are the same as those of the example 1, except that the preparation temperature of the gamma-AlOOH catalyst is adjusted, the original preparation temperature is adjusted to any one of 100 ℃,130 ℃, 140 ℃, 150 ℃, 160 ℃, 180 ℃ or 200 ℃ at 150 ℃, and the prepared gamma-AlOOH is used as the catalyst to catalyze the cellulose degradation to prepare the HMF. The HMF preparation process by cellulose degradation is the same as in example 1. The results are shown in Table 3. From Table 3, it can be seen that the catalytic effect of the prepared gamma-AlOOH is the best when the preparation temperature is 150 ℃.

TABLE 3 preparation of HMF by catalyzing cellulose degradation with gamma-AlOOH prepared at different temperatures

Preparation temperature (. Degree. C.)	100	130	150	160	180	200
							HMF（%）	44.3	52.5	58.4	55.6	50.2	46.8
HMF selectivity (%)	53	56	60	59	55	54
							Cellulose conversion (%)	83	93	97	95	92	87

Example 16

The preparation method and the preparation process of the gamma-AlOOH are the same as those in example 1, except that the preparation time of the gamma-AlOOH catalyst is adjusted, the original preparation time is adjusted to be 12 h to be any one of 2 h, 6h, 12 h, 18 h, 24 h, 36 h or 48h, and the prepared gamma-AlOOH catalyst is used for catalyzing cellulose degradation to prepare HMF. The HMF preparation process by cellulose degradation is the same as in example 1. The results are shown in Table 4. From Table 4, it can be seen that the prepared gamma-AlOOH has the best catalytic effect when the preparation time is 12 hours.

TABLE 4 preparation of HMF by catalyzing cellulose degradation with gamma-AlOOH prepared at different times

Preparation time (h)	2	6	12	18	24	36	48
								HMF（%）	11.3	40.3	58.4	57.3	56.3	54.6	52.6
HMF selectivity (%)	25	49	60	60	59	57	56
								Cellulose conversion (%)	45	82	97	96	95	95	94

Example 17

The catalyst is recycled and used repeatedly. The dried solid residue after centrifugation in example 1 was used as the catalyst for the next cellulose degradation to prepare HMF experiments. The specific process is as follows: in experimental example 1, the residue obtained by first using γ -AlOOH was obtained by centrifugal separation, washed with deionized water, ethanol and γ -valerolactone, and then surface unreacted cellulose and residual reactants (such as glucose, fructose, HMF, etc.) were removed, and dried in a vacuum drying oven at 100 ℃ to obtain solid residue, which was used as a catalyst in the next experiment, and a catalytic cycle experiment was performed to examine the stability of the catalyst, and the experimental procedure for preparing cellulose by hydrolysis was the same as in experimental example 1. The catalytic results are shown in FIG. 10. As can be seen from fig. 10, the catalyst γ -AlOOH has good catalytic stability, the catalytic efficiency of the catalyst is not greatly changed after 5 times of repeated use, and the HMF yield and the cellulose conversion rate are 47.8% and 91%, respectively.

The protection of the present invention is not limited to the above embodiments. Variations and advantages that may occur to those skilled in the art may be incorporated into the invention without departing from the spirit and scope of the inventive concept and the scope of the appended claims is intended to be protected.

Claims

1. Preparation of 5-hydroxymethyl bran from boehmite high-efficiency catalysis celluloseThe method for preparing the aldehyde is characterized by comprising the steps of adding boehmite and cellulose into a mixed system of an ionic liquid, dimethyl sulfoxide and water, uniformly stirring, transferring the mixture into a reactor, stirring and reacting at 120-210 ℃, adding deionized water into a reaction solution after the reaction is finished, quenching, centrifuging, and collecting an upper-layer liquid to obtain a degradation liquid containing 5-hydroxymethylfurfural, wherein the mass ratio of the boehmite to the cellulose is 0.05:1 to 5:1, the mass ratio of the cellulose to the mixed system is 1:10 to 1:100, the mass ratio of the ionic liquid to the dimethyl sulfoxide in the mixed system is 6:0 to 2:4, the mass ratio of the ionic liquid to the water in the mixed system is 4:2 to 4:0.5, the reaction time is 0.5h to 6h, and the boehmite is prepared by the following method: adding an aluminum source and a slow hydrolysis reagent into deionized water, stirring uniformly, then dropwise adding a precipitator, adjusting the pH value of the solution to 9, then transferring the solution into a reaction kettle with a polytetrafluoroethylene lining, reacting the reaction kettle at 100-300 ℃ for 5-60h, taking out the reaction kettle, naturally cooling to room temperature, collecting reacted solid through centrifugation and washing, and drying the solid at 60-180 ℃ for 8-48h to obtain the solid catalyst boehmite; the aluminum source is inorganic aluminum salt and/or aluminum isopropoxide, the slow hydrolysis reagent is ammonium bicarbonate, the precipitant is an ammonia water solution, and the molar ratio of the aluminum source to the slow hydrolysis reagent is 1:2, the inorganic aluminum salt is selected from AlCl ₃ 、Al(NO ₃ ) ₃ 、Al ₂ (SO ₄ ) ₃ 、AlCl ₃ ·6H ₂ O、Al(NO ₃ ) ₃ ·9H ₂ O、Al ₂ (SO ₄ ) ₃ ·16H ₂ One or more of O; the method also comprises the step of extracting and purifying the 5-hydroxymethylfurfural from the degradation liquid containing the 5-hydroxymethylfurfural, and specifically comprises the following steps: adding ether into the degradation liquid containing 5-hydroxymethylfurfural for primary extraction and separation, and standing for layering to obtain an upper layer liquid; adding deionized water into the upper layer liquid, stirring uniformly, adding diethyl ether for extraction separation again, extracting and separating for 2-3 times to obtain 5-hydroxymethylfurfural-diethyl ether extract, distilling the extract under reduced pressure under the condition of ice water bath, and separating diethyl ether to obtain the final product.