CN102399203B - Method for preparing 5-hydroxymethylfurfural by degrading carbonhydrate through ionic liquid - Google Patents

Abstract

The invention discloses a method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquids, comprising: adding carbohydrates, ionic liquids and co-catalysts into a reactor, feeding an entrainer, and continuously vacuuming the reaction system , keep the vacuum at 100-500Pa, carry out the catalytic reaction at 120-180°C, and the reaction time is 10-60 minutes; while reacting, place the separator connected to the reactor product outlet in an ice bath to collect the product, so The separator is communicated with the product outlet of the reactor through an insulated connecting pipe, and the separator and the reactor are kept at the same vacuum degree. The present invention couples catalytic reaction and product separation, adopts high-vacuum distillation during the reaction process, and introduces entrainer to make the generated water and 5-HMF leave the reaction system, so as to achieve the purpose of strengthening 5-HMF generation and product separation , effectively solved the problem of difficult separation of 5-HMF.

Description

A method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquid

technical field

The invention belongs to the field of utilization of biomass resources, and in particular relates to a method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with an ionic liquid.

Background technique

In recent years, due to the gradual depletion of fossil energy, the research on the synthesis of chemical substances from biomass to replace gasoline and chemical intermediates has attracted widespread attention. Among these chemicals synthesized from biomass, 5-hydroxymethylfurfural obtained through carbohydrate degradation is an important platform compound. For example, 5-hydroxymethylfurfural can be used to synthesize 2,5-furanddioic acid, 2,5-furandiol, 2,5-dimethylol Tetrahydrofuran, dimethylfuran, and liquid alkanes, etc. (such as patents: US2009124839, US2009156841, etc.). These synthetic products may be important polymer monomers or important fuel substances.

As high molecular carbohydrates are generally polycondensed from glucose or fructose. For example, cellulose is obtained by polycondensation of glucose 1,4-β glycosidic bonds, starch is obtained by polycondensation of glucose 1,4-α and 1,6-α glycosidic bonds, glycogen and inulin are obtained by polycondensation of fructose, and so on. Therefore, glucose and fructose are often selected as the model substances for studying the degradation of carbohydrates into 5-hydroxymethylfurfural.

Through the in-depth investigation of the literature and the research in our laboratory, it is believed that there are three clear conclusions in the research field of carbohydrate degradation into 5-hydroxymethylfurfural: (1) The degradation reaction is generally carried out under acid catalysis, and Lewis acid The catalytic effect is often better than that of Bronsted acid, which is because the protons in Bronsted acid will accelerate the coking of sugar; (2) the aqueous medium is not conducive to the formation of 5-hydroxymethylfurfural, but often leads to the formation of 5-hydroxymethylfurfural (3) It is relatively easy to degrade fructose into 5-hydroxymethylfurfural, but it is very difficult to convert glucose into 5-hydroxymethylfurfural. Glucose isomerizes to fructose before being degraded to 5-HMF.

So far, ionic liquids, especially imidazolium-based ionic liquids, are considered to be one of the most effective catalysts for the degradation of carbohydrates to 5-hydroxymethylfurfural. Such as: Zhao et al. (Zhao et al, Metalchlorides in ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science, 2007, 316 (5831): 1597-1600), the US patent application with application number US20100317879) used CrCl ₂ -[ The EMIM]Cl catalytic system catalyzes the degradation of glucose into 5-hydroxymethylfurfural, and an unprecedented high yield of 69% is obtained; the US patent application with the application number US20090313889 uses a metal complex of N-heterocyclic carbene (N-heterocyclic carbene) Synergistic ionic liquids are used to catalyze carbohydrates. At 70°C, the conversion yields of fructose and glucose into 5-hydroxymethylfurfural are 96% and 82%, respectively. The catalytic system can be recycled by evaporating low boiling point substances. Hu et al. (Hu et al, Efficient conversion of glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl ₄ in an ionic liquid. Green Chem, 2009, 11(11): 1746-1749) adopted SnCl ₄ /[EMIM]BF ₄ catalyzed the degradation of glucose and sugars containing glucose units, and also obtained a 5-HMF yield of more than 60%.

Although imidazole-based ionic liquids are considered to be the most effective catalyst/solvent for degrading glucose into 5-hydroxymethylfurfural, how to separate the product-hydroxymethylfurfural product from the ionic liquid reaction medium is rarely mentioned. It is also one of the important reasons hindering its industrialized production. It has been reported in the literature that simple solvent extraction can be used to achieve this purpose, such as Amarasekara et al. (Amarasekara, Mechanism of the dehydration of D-fructose to 5-hydroxymethylfurfural in dimethyl sulfoxide at 150degrees C: an NMR study. Carbohydr Res, 2008, 343 (18) : 3021-3024) After the reaction of catalyzing the dehydration of glucose and fructose to generate 5-hydroxymethylfurfural in ionic liquid is completed, a certain amount of water and ether are added to the reaction medium, and extracted three times at room temperature to separate 5-hydroxymethylfurfural base furfural, and then remove other low-boiling impurities at 100°C, so as to realize the reuse of ionic liquid and catalyst. Moreau et al, Dehydration of fructose and sucrose into 5-hydroxymethylfurfural in the presence of 1-H-3-methyl imidazolium chlorideacting both as solvent and catalyst. Mol Catal A: Chem, 2006, 253 (1-2): 165 -169) Using [HMIM]Cl as a catalyst and solvent to catalyze the dehydration of fructose and sucrose to generate 5-hydroxymethylfurfural, which is extracted completely by ether in batches or continuously. Continuous extraction with ether for 8h. After the ionic liquid was reused 5 times, the yield of 5-hydroxymethylfurfural was still 82%. Although bibliographical reports can adopt the method for low-boiling point organic solvent extraction to separate 5-hydroxymethylfurfural from ionic liquid reaction medium, yet these methods have obvious defects: (1) at first, this method needs a large amount of circulating solvents, and for To alleviate the disadvantages of high viscosity of ionic liquids and to facilitate stratification, an aqueous phase must be added during extraction, which makes the extraction process very complicated; (2) secondly, experiments have shown that the separation of 5-hydroxymethylfurfural between the ionic liquid phase and the organic phase It takes a very long time to balance, so that its industrial application prospect is not good; (3) the extraction rate is low, and multiple extractions are often needed to achieve a satisfactory yield; (4) after the extraction is completed, there are also 5-hydroxymethylfurfural and The problem of secondary separation of extraction organic solvents.

Contents of the invention

The invention provides a method for preparing 5-hydroxymethylfurfural (5-HMF) by degrading carbohydrates with an ionic liquid. The reaction-vacuum distillation coupling method based on entrainer enhancement is adopted to promote the degradation of carbohydrates and simultaneously obtain high yield and high yield. The pure 5-hydroxymethylfurfural crystal product solves the problem that the product is difficult to separate in the prior art.

A method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquids, comprising:

Add carbohydrates, ionic liquids and cocatalysts to the reactor, and feed entrainer, while continuously evacuating the reaction system to keep the vacuum at 100-500Pa, and carry out catalytic reaction at 120-180°C, and the reaction time is 10- 60 minutes; while reacting, the separator connected to the reactor product outlet was placed in an ice bath to collect the product, and the separator was communicated with the reactor product outlet through an insulation connecting pipe, and the separator Keep the same vacuum as the reactor;

Wherein, the carbohydrate is monosaccharide, disaccharide or polysaccharide, the ionic liquid is imidazolium chloride type ionic liquid, the co-catalyst is metal salt or metal oxide, and the entrainer is nitrogen, One of inert gas, carbon dioxide, C ₁ -C ₈ alkanes, acetone, and methyl isobutyl ketone; in terms of mass percentage, the amount of the carbohydrate is 1%-10% of the amount of the ionic liquid .

The collected product was characterized by ¹ H-MR and ¹³ C-MR spectra, and confirmed to be 5-hydroxymethylfurfural.

In a preferred technical solution, the monosaccharide is fructose or glucose, the disaccharide is sucrose or maltose, and the polysaccharide is cellulose or starch.

In the preferred technical scheme, the amount of the substance of the promoter is 3%-10% of the amount of the glucose (or fructose) unit substance in the carbohydrate, that is: when the carbohydrate is fructose or glucose, the The amount of the substance of the promoter is 3%-10% of the amount of the substance of the carbohydrate; when the carbohydrate is sucrose, the amount of the substance of the promoter is the glucose unit and 3%-10% of the amount of the total substance of fructose unit; when the carbohydrate is maltose, cellulose or starch, the amount of the substance of the promoter is the amount of the substance of the glucose unit in the carbohydrate 3%-10%.

In the preferred technical scheme, the imidazole chloride type ionic liquid is hexylmethylimidazole chloride [HexMIM]Cl or octylmethylimidazole chloride [OMIM]Cl, most preferably octyl chloride with a higher boiling point Methylimidazole [OMIM] Cl.

In a preferred technical solution, the metal salt is metal chloride or metal nitrate. For the degradation of carbohydrates containing fructose units, the metal salt is further preferably AlCl ₃ , FeCl ₃ , IrCl ₃ , AuCl ₃ or (NH ₄ ) ₂ Ce(NO ₃ ) ₆ , and other methods described in literature and patents can also be used. Disclosed similar substances; for the degradation of carbohydrates containing glucose units, the metal salt is further preferably CrCl ₂ , CrCl ₃ , SnCl ₄ , TiCl ₄ or Zr(NO ₃ ) ₄ , which can also be used as reported in the literature of other substances.

In a preferred technical solution, the metal oxide is ZrO ₂ , and other substances reported in literature can also be used.

In the present invention, the entraining agent must have good thermal stability and do not participate in the system reaction. Therefore, the entraining agent can also be selected from other polar or non-polar ones that have good thermal stability and do not participate in the system reaction. aggressive gaseous solvents. The entrainer is preferably nitrogen, which is cheap and easy to obtain.

In the preferred technical scheme, the collected product can also be post-treated, such as: crystallize the collected product at -5°C to 4°C to obtain 5-hydroxymethylfurfural crystals, or spray-dry the collected product 5-Hydroxymethylfurfural powder was obtained.

In the present invention, carbohydrates are used as raw materials, imidazole chloride-type ionic liquids are used as reaction solvents and catalysts, and metal salts or metal oxides are added as catalytic assistants to form a catalytic system, and catalytic reactions are carried out in reactors to generate product 5 -HMF. The reactor and the separator are communicated and connected to the high vacuum oil pump, and the system is in a high vacuum state by starting the high vacuum oil pump, and the catalytic reaction is carried out under high vacuum conditions. Under high vacuum conditions, the water and 5-HMF formed by the reaction are evaporated and condensed in a separator placed in an ice bath. In addition, the entrainer gas is passed into the imidazolium chloride-type ionic liquid to promote the evaporation of 5-HMF and water, thereby achieving the purpose of strengthening the reaction and product separation. That is, the present invention uses high-vacuum distillation during the reaction process and the introduction of entrainer to make the generated water and 5-HMF leave the reaction system, so as to achieve the purpose of strengthening the formation of 5-HMF and product separation.

In the present invention, when fructose is used as raw material, the recovery rate of 5-HMF reaches 95%; when glucose is used as raw material, the recovery rate of 5-HMF reaches 88%. This data is the most ideal experimental result about carbohydrate degradation to 5-HMF reported in the literature and patents we know so far. Moreover, the invention has the advantages of short reaction time and simple device. More importantly, when previous documents and patents reported higher 5-HMF yields, no effective method was proposed to separate the 5-HMF product from the reaction medium; and the present invention combines the catalytic reaction with the product The separation phase is coupled, and the separation of 5-HMF is effectively solved by a simple method of high vacuum distillation and gas entrainment.

Description of drawings

Fig. 1 is a schematic diagram of a reaction device used in the method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquids of the present invention.

FIG. 2 is the ¹ H-NMR spectrum of the product prepared in Example 1.

FIG. 3 is the ¹³ C-NMR spectrum of the product prepared in Example 1.

Detailed ways

The present invention will be described in detail below in conjunction with the embodiments and accompanying drawings, but the present invention is not limited thereto.

The reaction device as shown in Figure 1, comprises: three-necked flask reactor 3 and two-necked flask separator 8, and three-necked flask reactor 3 is built-in magnetic stirrer 2, and is provided with entrainer inlet 4, and three-necked flask reactor 3 is placed in In the oil bath tank 1; the two-necked flask separator 8 is provided with an interface 7, connected to a high vacuum oil pump, and the two-necked flask separator 8 is placed in the ice bath tank 9; the three-necked flask reactor 3 is provided with a first connection port 5, and the two-necked flask separator 8 is provided with a second connection port 10, the first connection port 5 and the second connection port 10 are communicated through a connecting pipe, and a heat preservation jacket 6 is provided on the periphery of the connecting pipe.

In the above reaction device, the three-necked flask reactor 3 and the two-necked flask separator 8 are communicated and connected to a high vacuum oil pump, and the system is in a high vacuum state by starting the high vacuum oil pump, and the catalytic reaction is carried out under high vacuum conditions. Under high vacuum conditions, the water and 5-HMF produced by the reaction will be evaporated and condensed in the two-necked flask separator 8 placed in an ice bath. In addition, the entrainer gas is passed into the interior of the ionic liquid through the entrainer inlet 4 to promote the evaporation of 5-HMF and water, thereby achieving the purpose of strengthening the reaction and product separation. After the reaction, a yellow oily liquid can be collected in the two-necked flask separator 8, and the light yellow 5-HMF crystal can be obtained by further crystallization in a refrigerator (4° C.); the powder of 5-HMF can also be obtained by spray drying.

Example 1:

Adopt reaction unit as shown in Figure 1, a kind of ionic liquid degradation carbohydrate prepares the method for 5-hydroxymethylfurfural (5-HMF) as follows:

Weigh 20 g of [OMIM]Cl and place it in reactor 3 of a three-necked flask, and raise the temperature of the oil bath to 180°C. Weigh 2 g of fructose and 0.065 g of IrCl ₃ ·(1-2)H ₂ O (approximately 7 mol% of the amount of fructose), and quickly add them into the reactor 3 of the three-necked flask. Nitrogen gas was introduced as an entrainer, and the high vacuum oil pump was started to continuously evacuate the reaction system, maintaining the vacuum degree at 300Pa-500Pa, and the reaction was terminated after 10 minutes. The product deposited in the connecting pipe and the two-necked flask separator 8 and the product remaining in the three-necked flask reactor 3 were collected, and the absolute mass of the product was calculated by HPLC.

The product was characterized by ¹ H-NMR and ¹³ C-NMR, as shown in Fig. 2 and Fig. 3 respectively, and it was determined that the product was 5-hydroxymethylfurfural (5-HMF) through comparative literature analysis. The specific instructions are as follows:

¹ H NMR (400MHz, CDCl ₃ , 29°C): δ=9.56 (s, 1H _a ), 7.21 (d, J=3.5Hz, 1H _b ), 6.51 (d, J=3.5Hz, 1H _c ), 4.71 (s, 2H _d ), 2.73 (s, 1H _e ). It was confirmed as 5-HMF by control.

¹³ C NMR (101MHz, CDCl ₃ , 29°C): δ _C = 177.40 (1C _a ), 160.42 (1C _b ), 152.12 (1C _c ), 122.68 (1C _d ), 109.90 (1C _e ), 57.62 (1 _C f). Confirmed as 5-HMF by control.

Examples 2-16

Take the same method and process as Example 1 to prepare 5-hydroxymethylfurfural, the difference is only in the reaction substrate and reaction conditions.

In Examples 2-16, the ionic liquid is [OMIM]Cl, the entrainer is nitrogen, n-hexane or methyl isobutyl ketone organic vapor, and the vacuum degree of the reaction system is maintained at 300-500Pa.

When the carbohydrate is fructose, the raw material ratio is: 2g carbohydrate and 0.065g IrCl ₃ ·(1-2)H ₂ O dissolved in 20g [OMIM]Cl.

When the carbohydrate is glucose, sucrose, α-starch or cellulose, the raw material ratio is: 2g carbohydrate and 0.049g CrCl ₃ ·6H ₂ O are dissolved in 20g [OMIM]Cl.

The reaction substrate, entrainer, reaction temperature and reaction time taken by each embodiment are listed in Table 2.

Comparative example D1～D6

In comparative examples D1-D6, the ionic liquids were all [OMIM]Cl, no entrainer was introduced, and the reaction was carried out under normal pressure.

Raw material ratio also satisfies:

When the carbohydrate is fructose, the raw material ratio is: 2g carbohydrate and 0.065g IrCl ₃ ·(1-2)H ₂ O dissolved in 20g [OMIM]Cl.

When the carbohydrate is glucose, sucrose, α-starch or cellulose, the raw material ratio is: 2g carbohydrate and 0.049g CrCl ₃ ·6H ₂ O are dissolved in 20g [OMIM]Cl.

The reaction yields and recovery results of the product 5-HMF obtained in Examples 1-16 and Comparative Examples D1-D6 are listed in Table 2.

In table 2, the reaction yield of 5-HMF refers to the actual yield of this step chemical reaction that carbohydrate is degraded into 5-HMF, by calculating the molar number of the 5-HMF distilled out and the residual 5-HMF in the reaction solution The sum of the number of moles accounts for the percentage of the number of moles of 5-HMF that the carbohydrate added before the reaction can theoretically generate, and obtains, that is:

In table 2, the rate of recovery of 5-HMF refers to the percentage of the total 5-HMF quality that the quality of the 5-HMF that distills out from reaction system accounts for reaction generation, and its calculation method is:

As can be seen from Table 2, take the method of the present invention (embodiment 1～16) to prepare 5-hydroxymethylfurfural, when taking fructose as raw material, the reaction yield of 5-HMF can reach 95.1%, simultaneously, 5-HMF The highest recovery rate of 5-HMF can reach 95%; when glucose is used as raw material, the highest reaction yield of 5-HMF can reach 71.8%, and at the same time, the highest recovery rate of 5-HMF can reach more than 88%. And in contrast example (comparison example D1～D6), although when using fructose as substrate, the reaction yield of 5-HMF also can reach 90%, but because there is not the technology of entrainment distillation, the generated 5-HMF can only Stay in the reaction system, but can not be separated (the recovery of 5-HMF is zero).

Table 2 Reaction recovery experiment of carbohydrates in ionic liquid reaction system

It can be seen that the present invention couples the catalytic reaction and product separation, adopts high vacuum distillation in the reaction process, and the introduction of entrainer makes the generated moisture and 5-HMF leave the reaction system, thereby achieving the strengthening of 5-HMF generation and product The purpose of separation effectively solves the difficult problem of separation of 5-HMF.

Claims (5)

1. A method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquid, is characterized in that, comprising: Add carbohydrates, ionic liquids and cocatalysts to the reactor, and feed entrainer, while continuously evacuating the reaction system to keep the vacuum at 100-500Pa, and carry out catalytic reaction at 120-180°C, and the reaction time is 10- 60 minutes; while reacting, the separator connected to the reactor product outlet was placed in an ice bath to collect the product, and the separator was communicated with the reactor product outlet through an insulation connecting pipe, and the separator Keep the same vacuum as the reactor; Wherein, the carbohydrate is monosaccharide, disaccharide or polysaccharide, the monosaccharide is fructose or glucose, the disaccharide is sucrose or maltose, and the polysaccharide is cellulose or starch; The ionic liquid is hexylmethylimidazole chloride or octylmethylimidazole chloride, the cocatalyst is a metal salt or metal oxide, and the entrainer is nitrogen, C ₁ -C ₈ alkanes, One of methyl isobutyl ketone; in terms of mass percentage, the amount of the carbohydrate is 1%-10% of the amount of the ionic liquid. 2. the method for preparing 5-hydroxymethylfurfural by ionic liquid degradation carbohydrate as claimed in claim 1 is characterized in that, described ionic liquid is octylmethylimidazole chloride. 3. the method for preparing 5-hydroxymethylfurfural by ionic liquid degradation carbohydrate as claimed in claim 1 is characterized in that, described metal salt is metal chloride or metal nitrate. 4 . The method for preparing 5-hydroxymethylfurfural by degrading carbohydrates with ionic liquids according to claim 1 , wherein the metal oxide is ZrO ₂ . 5. the method for preparing 5-hydroxymethylfurfural by ionic liquid degradation carbohydrate as claimed in claim 1, is characterized in that, described entrainer is nitrogen.

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