Method for preparing lactate by catalyzing directional alcoholysis of cellulose through multifunctional coupling double-salt ionic liquid

Abstract

The invention relates to a method for preparing lactate by catalyzing directional alcoholysis of cellulose by using a multifunctional coupled double-salt ionic liquid, which comprises the following steps: combining a # imgabs0 # acid center and a double Lewis acid center to construct a multifunctional coupled double-salt ionic liquid catalyst, and converting cellulose into lactate by directional catalytic alcoholysis; and the yield of the lactate can reach 60% or above. Compared with an existing preparation method of the lactate, the preparation method provided by the invention has the advantages of high conversion efficiency, low raw material cost, mild reaction conditions, easiness in recycling of the catalyst, high product selectivity and the like, and green industrial production of the lactate can be accelerated.

Description

Technical Field

[0001] The invention belongs to the technical field of green catalytic synthesis of lactic acid esters, and particularly relates to a method for preparing lactic acid esters by catalyzing the directional alcoholysis of cellulose by a multifunctional coupled double salt ionic liquid. Background Art

[0002] As a key intermediate for obtaining high-purity lactic acid by traditional fermentation, lactate has great potential in replacing many petroleum-based organic solvents and chemicals due to its many advantages such as strong solubility, non-volatility, non-toxicity and biodegradability. It has been widely used in food, medicine, synthetic resin coatings, adhesives, printing inks and other industries. At present, lactate is mainly prepared by esterification reaction of lactic acid and corresponding alcohol reagents, which has the disadvantages of high esterification reaction temperature and strong catalyst corrosion. In addition, the production process of raw lactic acid has the disadvantages of long cycle, high solid waste and food waste, which further affects the industrial application of lactate. At present, how to efficiently prepare lactate has become the focus and difficulty of research at home and abroad. Cellulose, as an important component of waste biomass resources, contains the same glucose structural unit as starch and is considered to be an ideal raw material for preparing lactate. Therefore, converting cellulose into lactate by constructing an efficient catalyst system has become a current frontier scientific topic, which has far-reaching significance for the upgrading of upstream (high-purity lactic acid) and downstream (polylactic acid, PLA) industries of lactate and the sustainable development of society.

[0003] The conversion of cellulose to lactate is a continuous multi-step conversion process, which requires cellulose hydrolysis, glucose isomerization, fructose retro-aldol condensation, trisaccharide dehydration, and subsequent alcohol-aldehyde addition, 1,2-hydride anion migration and other steps (Formula 1). Trisaccharides (DHA, GLA) are key intermediates for the preparation of lactate from hexose (glucose, fructose), and hexose (monosaccharides) are the hydrolysis products of cellulose. Therefore, when trisaccharides, hexose monosaccharides, and cellulose are used as raw materials, the dependence on the multifunctionality of the catalyst gradually increases, and the lactate yield gradually decreases.

[0004]

[0005] At present, "SnCl2·2H2O-ZnCl2", "SnCl2·2H2O-AlCl3·6H2O", "HOTf-Sn(OTf)2", "Sm(OTf)3-Bu2SnCl2-InCl3", Zr-SBA-15 and Ga-doped Zn / HNZY catalyst systems have been developed. The efficiency of cellulose alcoholysis conversion is highly dependent on the multifunctionality of the catalyst. Under the action of the "Sm(OTf)3-Bu2SnCl2-InCl3" composite catalyst, the yield of methyl lactate can reach 45%. However, the multifunctionality of the reported cellulose alcoholysis systems is not prominent enough, the synergistic efficiency between active centers is not high, and there are still shortcomings such as high reaction temperature (homogeneous, ≥200℃; heterogeneous, ≥260℃), long reaction time (>4h), and low lactate yield, and the overall catalytic efficiency is not ideal. Through literature research, it was found that cellulose hydrolysis, glucose isomerization and fructose retro-aldol condensation are the key steps in the alcoholysis of cellulose to prepare lactate. Therefore, how to construct a multifunctional coupled catalyst system to convert cellulose into trisaccharide intermediates with high selectivity, improve the coupling efficiency between cellulose hydrolysis, glucose isomerization and fructose retro-aldol condensation, and strengthen the alcoholysis process is a key problem in the process of efficiently catalyzing alcoholysis of cellulose to prepare lactate. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide a method for preparing lactate by directional alcoholysis of cellulose catalyzed by a multifunctional coupled double salt ionic liquid. Acidic (B acid) ionic liquid chloride salt is designed and combined with a metal chloride salt (L1) that has the function of catalyzing glucose isomerization and a metal chloride salt (L2) that has the function of catalyzing fructose retro-aldol condensation to construct a single The double salt ionic liquid catalyst system of the acid center and the double Lewis acid (L1, L2) center couples the catalytic functions of each acid center, strengthens the cellulose alcoholysis process, and improves the lactate yield.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing lactate by directional alcoholysis of cellulose catalyzed by a multifunctional coupled double salt ionic liquid, wherein The acid center and the di-Lewis acid center are combined to construct a multifunctional coupled di-salt ionic liquid catalyst, which can convert cellulose into lactate by directed catalytic alcoholysis.

[0008] Further, the method specifically includes the following steps:

[0009] (1) The acidic ionic liquid chloride salt and the two metal ion chloride salts are designed and combined in a molar ratio of 1:x:(1-x) to construct a A multifunctional coupled double salt ionic liquid catalyst with acid center and double Lewis acid center, wherein 0<x<1;

[0010] (2) combining 0.30-2.25 mmol of a double salt ionic liquid catalyst with 10-30 mL of an alcohol reagent to construct a cellulose catalytic directional alcoholysis reaction system;

[0011] (3) Add 0.2-4.0 g of cellulose into an alcoholysis catalytic reaction system, and carry out alcoholysis reaction at a temperature of 150-220° C. and a reaction time of 0.5-6 h to prepare lactic acid ester.

[0012] Further, the The acidic ionic liquid chloride salt is an ionic liquid chloride salt whose cation contains a sulfonic acid active center.

[0013] Furthermore, the ionic liquid chloride salt whose cation contains a sulfonic acid active center is an imidazolyl, pyridyl, pyrrolidone, morpholine or quaternary ammonium salt.

[0014] Furthermore, the two metal ion chloride salts are respectively a metal chloride salt having a function of catalyzing glucose isomerization and a metal chloride salt having a function of catalyzing fructose retro-aldol condensation.

[0015] Furthermore, in step (2), the alcohol reagent is a straight-chain fatty alcohol having ≤4 carbon atoms.

[0016] Furthermore, in step (2), the molar percentage of the double salt ionic liquid catalyst relative to the glucose structural unit in the cellulose is 4% to 30%.

[0017] Furthermore, the mass volume ratio of the cellulose to the organic alcohol reagent is (1-20) g:100 mL.

[0018] Furthermore, in step (3), the temperature is 180°C.

[0019] Furthermore, in step (3), the reaction time is 1.0 h.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention is achieved by The acid center catalyzing cellulose hydrolysis function is combined with the diLewis acid (L1, L2) center catalyzing glucose isomerization (L1) and fructose retro-aldol condensation function (L2) to prepare a multifunctional coupled double salt ionic liquid catalyst, which strengthens the directional conversion process of cellulose to lactate and improves the directional conversion efficiency of cellulose. The yield of lactate can reach more than 60%.

[0022] 2. Compared with the existing preparation methods of lactic acid esters, the preparation method provided by the present invention has the advantages of high conversion efficiency, low raw material cost, mild reaction conditions, easy recovery and reuse of catalysts, high product selectivity, etc., which can accelerate the green industrial production of lactic acid esters.

[0023] 3. The reaction system of the multifunctional coupled double salt ionic liquid catalyzing the directional alcoholysis of cellulose in the present invention is mainly realized by the relay catalytic action of the acid active centers in the catalyst. The acid center catalyzes the hydrolysis of cellulose to form glucose, and then the L1 acid center catalyzes the isomerization of glucose to fructose, and the L2 acid center catalyzes the retro-aldol condensation of fructose to form trisaccharides. The trisaccharide is further converted under the synergistic action of the Lewis acid and diLewis acid (L1, L2) centers, realizing the directional conversion process from cellulose to lactate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 H NMR spectrum;

[0025] Figure 2 [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 Electrospray mass spectrometry results;

[0026] Figure 3 Schematic diagram of the reaction process of preparing lactate by catalytic alcoholysis of cellulose;

[0027] Figure 4 Gas chromatogram of the reaction product of Example 1 of the present invention;

[0028] Figure 5 Photo of the reaction residue of Example 1 of the present invention;

[0029] Figure 6 Photo of the reaction solution of Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The method of the present invention is described in detail below in conjunction with specific embodiments and accompanying drawings. Lactate is abbreviated as LA in the present invention.

[0031] 1. A method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid

[0032] Example 1

[0033] A method for preparing lactate by directional alcoholysis of cellulose catalyzed by a multifunctional coupled double salt ionic liquid, comprising the following steps:

[0034] 1) 8.21g (0.1mol) N-methylimidazole and 13.7043g (0.1mol) 1,4-butane sultone were placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50℃ for 72h. After the reaction, a white zwitterionic intermediate was obtained. After extraction, washing and purification with ethyl acetate, an equimolar amount of hydrochloric acid was added, and the reaction was continued at 80℃ for 24h to prepare a light yellow ionic liquid [C4H8SO3Hmim]Cl. 5mmol mol SnCl4·5H2O and 5mmol mol SnCl2·2H2O were added to 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, and the reaction was continued at 80℃ for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , and H NMR spectroscopy ( 1 H-NMR, CD3OD as NMR solvent) to verify its cationic structure (see Figure 1 ), and electrospray ionization mass spectrometry (negative ion mode, methanol dissolution) to analyze its anions (see Figure 2 ).exist Figure 1 middle( 1 HNMR, ppm), the single peak at δ = 8.97 is the hydrogen at the 1 position of the imidazole ring (NCHN), the single peak at δ = 7.66 is the hydrogen at the 2 position of the imidazole ring (NCH), the single peak at δ = 7.59 is the hydrogen at the 3 position of the imidazole ring (NCH), the single peak at δ = 3.98 is the hydrogen of the methyl (4 position) on the imidazole ring (NCH3), the triple peak at δ = 4.31 is the hydrogen at the 5 position of the alkyl group connected to the imidazole ring (NCH2), the multiple peaks at δ = 2.09 and δ = 1.82 are the hydrogen at the 6th and 7th positions of the alkyl group connected to the imidazole ring (CH2), and the triple peak at δ = 2.90 is the hydrogen at the 8th position of the alkyl group connected to the sulfonic group (SCH2). The area comparison of the peaks at each location is 1:1:1:3:2:2:2:2, indicating that the prepared double salt ion cation is consistent with the target ionic liquid. In addition, Figure 2 The peaks at m / z 225.7 and 296.6 in [SnCl5] － and [SnCl3] － The presence of further verifies that the prepared ionic liquid is the target double salt ionic liquid.

[0035] 2) Add 20 mL of anhydrous ethanol and 1.0 mmol [C4H8SO3Hmim] [SnCl5] to a 50 mL reactor. 0.5 [SnCl3] 0.5After adding 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the apparatus was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0036] Example 2

[0037] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [FeCl4] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmolSnCl4·5H2O and 5mmolFeCl3 are added successively and the reaction is continued at 80°C for 24h to obtain a yellow ionic liquid [C4H8SO3Hmim][SnCl5] 0.5 [FeCl4] 0.5 .

[0038] 2) Add 20 mL of anhydrous ethanol and 1.0 mmol [C4H8SO3Hmim] [SnCl5] to a 50 mL reactor. 0.5 [FeCl4] 0.5 After adding 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the apparatus was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0039] Example 3

[0040] 1) The catalyst used in this example is [C4H8SO3Hmim][InCl4] 0.5 [FeCl4] 0.5 The preparation method of ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol ionic liquid [C4H8SO3Hmim]Cl, 5mmolInCl3 and 5mmolFeCl3 are added successively and the reaction is continued at 80°C for 24h to obtain yellow ionic liquid [C4H8SO3Hmim][InCl4] 0.5 [FeCl4] 0.5 .

[0041] 2) Add 20 mL of anhydrous ethanol and 1.0 mmol [C4H8SO3Hmim] [InCl4] to a 50 mL reactor. 0.5 [FeCl4] 0.5After adding 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0042] Example 4

[0043] 1) The catalyst used in this example is [C4H8SO3Hmim][CrCl4] 0.5 [SnCl3] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmol CrCl3·6H2O and 5mmol mol SnCl2·2H2O are added successively and the reaction is continued at 80°C for 24h to obtain a dark green ionic liquid [C4H8SO3Hmim][CrCl4] 0.5 [SnCl3] 0.5 .

[0044] 2) Add 20 mL of anhydrous ethanol and 1.0 mmol [C4H8SO3Hmim] [CrCl4] to a 50 mL reactor. 0.5 [SnCl3] 0.5 After adding 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the apparatus was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1.0 h. After the reaction was completed, the mixture was cooled with tap water.

[0045] Example 5

[0046] 1) The catalyst used in this example is [C4H8SO3Hmim][ZnCl3] 0.5 [LaCl4] 0.5 The preparation method of ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol ionic liquid [C4H8SO3Hmim]Cl, 5mmol ZnCl2 and 5mmol LaCl3·xH2O are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][ZnCl3] 0.5 [LaCl4] 0.5 .

[0047] 2) Add 1.0mmol [C4H8SO3Hmim] [ZnCl3] to a 50mL reactor 0.5 [LaCl4] 0.5, 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1.0 h. After the reaction was completed, the mixture was cooled with tap water.

[0048] Example 6

[0049] 1) The catalyst used in this example is [C4H8SO3Hmim][InCl4] 0.5 [SnCl3] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmolInCl3 and 5mmolSnCl2·2H2O are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][InCl4] 0.5 [SnCl3] 0.5 .

[0050] 2) Add 20 mL of anhydrous ethanol and 1.0 mmol [C4H8SO3Hmim] [InCl4] to a 50 mL reactor. 0.5 [SnCl3] 0.5 After adding 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the apparatus was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0051] Example 7

[0052] 1) The catalyst used in this example is [C4H8SO3Hmim][CrCl4] 0.5 [InCl4] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmolCrCl3·6H2O and 5mmolInCl3 are added successively and the reaction is continued at 80°C for 24h to obtain a dark green ionic liquid [C4H8SO3Hmim][CrCl4] 0.5 [InCl4] 0.5 .

[0053] 2) Add 1.0mmol [C4H8SO3Hmim] [CrCl4] to a 50mL reactor 0.5 [InCl4] 0.5, 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0054] Example 8

[0055] 1) The catalyst used in this example is [C4H8SO3Hmim][ZnCl3] 0.5 [InCl4] 0.5 The preparation method of ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol ionic liquid [C4H8SO3Hmim]Cl, 5mmol ZnCl2 and 5mmol InCl3 are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][ZnCl3] 0.5 [InCl4] 0.5 .

[0056] 2) Add 1.215 g microcrystalline cellulose (7.5 mmol glucose structural unit), 1.0 mmol [C4H8SO3Hmim][ZnCl3] 0.5 [InCl4] 0.5 After adding 20 mL of anhydrous ethanol, fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0057] Example 9

[0058] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [InCl4] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmolSnCl4·5H2O and 5mmolInCl3 are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.5 [InCl4] 0.5 .

[0059] 2) Add 1.215 g microcrystalline cellulose (7.5 mmol glucose structural unit), 1.0 mmol [C4H8SO3Hmim][SnCl5] to a 50 mL reactor. 0.5 [InCl4] 0.5After adding 20 mL of anhydrous ethanol, fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0060] Example 10

[0061] 1) The catalyst used in this example is [C4H8SO3Hmim][CrCl4] 0.5 [SnCl5] 0.5 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 5mmolCrCl3·6H2O and 5mmolSnCl4·5H2O are added successively and the reaction is continued at 80°C for 24h to obtain a dark green ionic liquid [C4H8SO3Hmim][CrCl4] 0.5 [SnCl5] 0.5 .

[0062] 2) Add 1.0mmol [C4H8SO3Hmim] [CrCl4] to a 50mL reactor 0.5 [SnCl5] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0063] Embodiment 11

[0064] 1) The catalyst used in this example is [C4H8SO3HPy][SnCl5] 0.5 [SnCl3] 0.5 The preparation method is as follows: 7.91g (0.1mol) pyridine and 13.7043g (0.1mol) 1,4-butane sultone are placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50°C for 72h. After the reaction, a white zwitterionic intermediate is obtained. After extraction, washing and purification with ethyl acetate, an equimolar amount of hydrochloric acid is added, and the reaction is continued at 80°C for 24h to prepare a light yellow ionic liquid [C4H8SO3HPy]Cl. 5mmol SnCl4·5H2O and 5mmol SnCl2·2H2O are added to 10mmol ionic liquid [C4H8SO3HPy]Cl successively, and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3HPy][SnCl5] 0.5 [SnCl3] 0.5 .

[0065] 2) Add 1.215 g microcrystalline cellulose (7.5 mmol glucose structural unit), 1.0 mmol [C4H8SO3HPy][SnCl5] 0.5 [SnCl3] 0.5 After adding 20 mL of anhydrous ethanol, fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0066] Example 12

[0067] 1) The catalyst used in this example is [C4H8SO3HNmp][SnCl5] 0.5 [SnCl3] 0.5 The preparation method is as follows: 9.9131g (0.1mol) N-methylpyrrolidone and 13.7043g (0.1mol) 1,4-butane sultone are placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50°C for 72h. After the reaction, a white zwitterionic intermediate is obtained. After extraction, washing and purification with ethyl acetate, an equimolar amount of hydrochloric acid is added, and the reaction is continued at 80°C for 24h to prepare a light yellow ionic liquid [C4H8SO3HNmp]Cl. 5mmol SnCl4·5H2O and 5mmolSnCl2·2H2O are added to 10mmol ionic liquid [C4H8SO3HNmp]Cl successively, and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3HNmp][SnCl5] 0.5 [SnCl3] 0.5 .

[0068] 2) Add 1.215 g microcrystalline cellulose (7.5 mmol glucose structural unit), 1.0 mmol [C4H8SO3HNmp][SnCl5] 0.5 [SnCl3] 0.5 After adding 20 mL of anhydrous ethanol, fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0069] Example 13

[0070] 1) The catalyst used in this example is [C4H8SO3HNmm][SnCl5] 0.5 [SnCl3] 0.5The preparation method is as follows: 10.115g (0.1mol) N-methylmorpholine and 13.7043g (0.1mol) 1,4-butane sultone are placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50°C for 72h. After the reaction is completed, a white zwitterionic intermediate is obtained, which is extracted, washed and purified with ethyl acetate, and then an equimolar amount of hydrochloric acid is added. The reaction is continued at 80°C for 24h to prepare a light yellow ionic liquid [C4H8SO3HNmm]Cl. 5mmol SnCl4·5H2O and 5mmol SnCl2·2H2O are added to 10mmol ionic liquid [C4H8SO3HNmm]Cl (0.01mol) and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3HNmm][SnCl5] 0.5 [SnCl3] 0.5 .

[0071] 2) Add 1.0mmol [C4H8SO3HNmm][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0072] Embodiment 14

[0073] 1) The catalyst used in this example is [C4H8SO3HNte][SnCl5] 0.5 [SnCl3] 0.5 The preparation method is as follows: 10.119g (0.1mol) of triethylamine and 13.7043g (0.1mol) of 1,4-butane sultone are placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50°C for 72h. After the reaction is completed, a white zwitterionic intermediate is obtained, which is extracted, washed and purified with ethyl acetate, and then an equimolar amount of hydrochloric acid is added. The reaction is continued at 80°C for 24h to prepare a light yellow ionic liquid [C4H8SO3HNte]Cl. 5mmol SnCl4·5H2O and 5mmolSnCl2·2H2O are added to 10mmol of the ionic liquid [C4H8SO3HNte]Cl, and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3HNte][SnCl5] 0.5 [SnCl3] 0.5 .

[0074] 2) Add 1.0mmol [C4H8SO3HNte][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0075] Embodiment 15

[0076] 1) The catalyst used in this example is [C3H6SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 The preparation method is as follows: 8.21g (0.1mol) n-methylimidazole and 12.2143g (0.1mol) 1,3-propane sultone are placed in a 50mL round-bottom flask and reacted in an oil bath at 30-50°C for 72h. After the reaction, a white zwitterionic intermediate is obtained. After extraction, washing and purification with ethyl acetate, an equimolar amount of hydrochloric acid is added, and the reaction is continued at 80°C for 24h to prepare a light yellow ionic liquid [C3H6SO3Hmim]Cl. 5mmol SnCl4·5H2O and 5mmolSnCl2·2H2O are added to 10mmol ionic liquid [C3H6SO3Hmim]Cl successively, and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C3H6SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 .

[0077] 2) Add 1.0mmol [C3H6SO3Hmim] [SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0078] Example 16

[0079] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.1 [SnCl3] 0.9The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl (0.01mol), 1mmol SnCl4·5H2O and 9mmol SnCl2·2H2O are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.1 [SnCl3] 0.9 .

[0080] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.1 [SnCl3] 0.9 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0081] Embodiment 17

[0082] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.3 [SnCl3] 0.7 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 3mmolSnCl4·5H2O and 7mmolSnCl2·2H2O are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.3 [SnCl3] 0.7 .

[0083] 2) Add 1mmol [C4H8SO3Hmim] [SnCl5] to a 50mL reactor 0.3 [SnCl3] 0.7 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0084] Embodiment 18

[0085] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.7 [SnCl3] 0.3The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 7mmolSnCl4·5H2O and 3mmolSnCl2·2H2O are successively added and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.7 [SnCl3] 0.3 .

[0086] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.7 [SnCl3] 0.3 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0087] Embodiment 19

[0088] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.9 [SnCl3] 0.1 The preparation method of the ionic liquid [C4H8SO3Hmim]Cl is shown in Example 1. To 10mmol of the ionic liquid [C4H8SO3Hmim]Cl, 9mmolSnCl4·5H2O and 1mmolSnCl2·2H2O are added successively and the reaction is continued at 80°C for 24h to obtain a colorless and transparent ionic liquid [C4H8SO3Hmim][SnCl5] 0.9 [SnCl3] 0.1

[0089] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.9 [SnCl3] 0.1 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 180°C at a stirring rate of 600 rpm and maintain for 1 hour. After the reaction is completed, cool with tap water.

[0090] Embodiment 20

[0091] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0092] 2) Add 1mmol [C4H8SO3Hmim][SnCl3] to a 50mL reactor 0.5 [SnCl5] 0.5 , 20 mL of methanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0093] Embodiment 21

[0094] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0095] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl3] to a 50mL reactor 0.5 [SnCl5] 0.5 , 20 mL of propanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the apparatus was fixed and the air in the autoclave was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 h. After the reaction was completed, the mixture was cooled with tap water.

[0096] Embodiment 22

[0097] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0098] 2) Add 1mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of n-butanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0099] Embodiment 23

[0100] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0101] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 10 mL of ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the apparatus was fixed and the air in the autoclave was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 h. After the reaction was completed, the mixture was cooled with tap water.

[0102] Embodiment 24

[0103] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0104] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 30 mL of ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 180°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0105] Embodiment 25

[0106] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0107] 2) Add 1mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 150°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0108] Embodiment 26

[0109] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0110] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 160°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0111] Embodiment 27

[0112] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0113] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0114] Embodiment 28

[0115] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0116] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 220°C at a stirring rate of 600 rpm and maintained for 1 hour. After the reaction was completed, the mixture was cooled with tap water.

[0117] Embodiment 29

[0118] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0119] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 0.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0120] Embodiment 30

[0121] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0122] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0123] Embodiment 31

[0124] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 5.

[0125] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 200°C at a stirring rate of 600 rpm and maintain for 2 hours. After the reaction is completed, cool with tap water.

[0126] Embodiment 32

[0127] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0128] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 6 hours. After the reaction was completed, the mixture was cooled with tap water.

[0129] Embodiment 33

[0130] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0131] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 0.2 g of microcrystalline cellulose (1 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 200°C at a stirring rate of 600 rpm and maintain for 1.5 h. After the reaction is completed, cool with tap water.

[0132] Embodiment 34

[0133] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0134] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.62 g of microcrystalline cellulose (10 mmol of glucose structural unit), the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0135] Embodiment 35

[0136] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0137] 2) Add 1.0mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 4.0 g of microcrystalline cellulose (24.7 mmol of glucose structural unit), fix the device and replace the air in the kettle with N2 three times, heat to 200°C at a stirring rate of 600 rpm and maintain for 1.5 h. After the reaction is completed, cool with tap water.

[0138] Embodiment 36

[0139] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0140] 2) Add 0.3mmol[C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0141] Embodiment 37

[0142] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0143] 2) Add 0.75mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0144] Embodiment 38

[0145] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0146] 2) Add 1.125mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0147] Embodiment 39

[0148] 1) The catalyst used in this example is [C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 , the preparation method is shown in Example 1.

[0149] 2) Add 2.25mmol [C4H8SO3Hmim][SnCl5] to a 50mL reactor 0.5 [SnCl3] 0.5 , 20 mL of anhydrous ethanol and 1.215 g of microcrystalline cellulose (7.5 mmol of glucose structural unit) were added, the device was fixed and the air in the kettle was replaced with N2 three times, and the mixture was heated to 200°C at a stirring rate of 600 rpm and maintained for 1.5 h. After the reaction was completed, the mixture was cooled with tap water.

[0150] 2. Sample Analysis

[0151] After the reaction, the unreacted cellulose was separated by suction filtration, washed three times with anhydrous ethanol, dried, weighed, and the conversion rate was calculated. The filtrates after suction filtration were combined, and then the unreacted ethanol was recovered by rotary evaporator at 40°C. Lactate, ionic liquid catalyst and unreacted glucose derivatives existed in the form of black viscous liquid. Finally, ethyl acetate (5×5mL) was used to extract and separate small molecular products such as lactate in the viscous liquid, and the ethyl acetate extractant was combined and fixed with ethyl acetate. The viscous liquid (ionic liquid catalyst and unreacted glucose derivative) extracted with ethyl acetate can be directly used to evaluate the catalyst reusability performance. After the fixed volume, the test solution was filtered through a 0.22μm microporous filter membrane and analyzed by gas chromatograph (Shimadzu GC-2010Pro), and the external standard method was used for quantification. When analyzing the yield of lactate, an SK-1 chromatographic column (30m×0.25mm, 0.25μm) was used, and N2 was used as the carrier gas. The temperature program was: 60°C for 1 min, then raised to 180°C at a rate of 30°C / min, and then maintained for 3 min. The sample inlet temperature was 260°C, and the split ratio was 20:1.

[0152] During the sample analysis process, the lactate yield (Y LA , mol%) and the corresponding selectivity (S LA ,%). The calculation formula is as shown in 1-3.

[0153]

[0154] Where W F and W R are the weight of cellulose before and after reaction (g); M LA and M G are the molar number of lactate produced during the reaction and the original molar number of glucose structural units, respectively.

[0155] Table 1 shows the effects of different catalyst compositions on the performance of directional catalytic alcoholysis of cellulose in Examples 1 to 19.

[0156]

[0157] From Table 1, we can see that the double salt ionic liquid The composition of the acid center and the di-Lewis acid center (L1, L2) has a great influence on its performance in catalyzing the alcoholysis of cellulose to prepare lactate. When the cation remains unchanged, by regulating the anion of the catalyst (Examples 1-10), [SnCl5] － (L1) and [SnCl3] － (L2) Combination (Example 1) and [InCl4] － (L1) and [SnCl3] － (L2) combination (Example 6) has a better catalytic effect, indicating that [SnCl5] － and [InCl4] － The ability to catalyze the isomerization of glucose can be compared with [SnCl3] － The ability to catalyze the retro-aldol condensation of fructose has a good synergistic catalytic effect, and together realizes the catalytic conversion process of cellulose to lactate. In addition, by comparing the molecular structure of the cations in the catalyst, it is found that the basic skeleton structure of the cations in the ionic liquid has no obvious effect on the directional conversion of cellulose (Example 1 and Examples 11-15), indicating that the basic skeleton structure of the cations in the catalyst does not participate in the catalytic process during the catalytic alcoholysis of cellulose. At the same time, the study found that in addition to the composition of the anions (L1, L2) in the catalyst having a greater influence on the catalytic alcoholysis of cellulose, the proportion of anions also has a significant effect on its directional catalytic performance (Example 1 and Examples 16-19). For example, [C4H8SO3Hmim][SnCl5] x [SnCl3] 1-x (0<x<1) is a catalyst, when [SnCl5]－ (L1) and [SnCl3] － When the ratio of (L2) is 1:1 ([C4H8SO3Hmim][SnCl5] 0.5 [SnCl3] 0.5 ), the catalytic effect is the best. This shows that the constructed double salt ionic liquid There is an optimal combination and optimal ratio of acid centers and di-Lewis acid centers (L1, L2).

[0158] It should be noted that the conversion of cellulose to lactate requires multiple steps of reaction, so the final lactate yield is not very high. In addition, there are many competitive reactions (side reactions) in the reaction process (see Figure 3 For example, cellulose is catalytically hydrolyzed to form glucose, glucose is isomerized to form fructose, and fructose is catalytically dehydrated, alcoholized, and other steps to form levulinic acid esters, and the chromatogram of the reaction product clearly has a chromatographic peak corresponding to levulinic acid esters (see Figure 4 ), further confirming the occurrence of this side reaction. At the same time, humin is also an inevitable by-product (black or dark brown) in the field of biomass catalytic conversion, which can be seen from the color of the residue after the reaction (see Figure 5 ) and the color of the reaction solution (see Figure 6 ) for confirmation.

[0159] Table 2 shows the effects of different alcohol reagents and dosages on the directional catalytic alcoholysis of cellulose in Examples 20 to 24 and Example 1

[0160]

[0161]

[0162] As can be seen from Table 2, the constructed double salt ionic liquid catalyst can catalyze the alcoholysis of cellulose in different alcohol reagents to prepare the corresponding lactic acid ester (Example 1 and Examples 20-22). In addition, by comparing Examples 23 and 24, it is found that the volume of the solvent also has a significant effect on the alcoholysis efficiency of cellulose, but overall, the experimental results are still within an acceptable range. This shows that the constructed double salt ionic liquid catalyst has a good application range in the preparation of lactic acid ester.

[0163] Table 3 shows the effects of process parameters of Examples 25 to 39 and Example 1 on directional catalytic alcoholysis of cellulose

[0164]

[0165] As can be seen from Table 3, the process parameters of the catalytic reaction, such as the amount of catalyst, the amount of substrate, the reaction temperature, the reaction time, etc., have a significant effect on the efficiency of the directional catalytic conversion of cellulose (Example 1 and Examples 25 to 39). Under the optimized reaction conditions (Example 30), efficient conversion of cellulose to lactate can be achieved, with a lactate yield of more than 60% and a selectivity of nearly 66%, which is significantly better than the known cellulose catalytic alcoholysis system.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing lactic acid ester by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid, characterized in that: By The acid center and the di-Lewis acid center are combined to construct a multifunctional coupled di-salt ionic liquid catalyst, which can convert cellulose into lactate by directed catalytic alcoholysis.

2. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 1, characterized in that: The specific steps include: (1) The acidic ionic liquid chloride salt and the two metal ion chloride salts are designed and combined in a molar ratio of 1:x:(1-x) to construct a A multifunctional coupled double salt ionic liquid catalyst with acid center and double Lewis acid center, wherein 0<x<1; (2) combining 0.30-2.25 mmol of a double salt ionic liquid catalyst with 10-30 mL of an alcohol reagent to construct a cellulose catalytic directional alcoholysis reaction system; (3) Add 0.2-4.0 g of cellulose into an alcoholysis catalytic reaction system, and carry out alcoholysis reaction at a temperature of 150-220° C. and a reaction time of 0.5-6 h to prepare lactic acid ester.

3. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: Said The acidic ionic liquid chloride salt is an ionic liquid chloride salt whose cation contains a sulfonic acid active center.

4. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 3, characterized in that: The cation containing the ionic liquid chloride salt of the sulfonic acid active center is imidazolyl, pyridyl, pyrrolidone, morpholine or quaternary ammonium salt.

5. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: The two metal ion chloride salts are respectively a metal chloride salt having a function of catalyzing glucose isomerization and a metal chloride salt having a function of catalyzing fructose retro-aldol condensation.

6. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: In step (2), the alcohol reagent is a straight-chain fatty alcohol having 4 or less carbon atoms.

7. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: In step (2), the molar percentage of the double salt ionic liquid catalyst relative to the glucose structural unit in the cellulose is 4% to 30%.

8. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: The mass volume ratio of the cellulose to the organic alcohol reagent is (1-20) g:100 mL.

9. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: In step (3), the temperature is 180°C.

10. The method for preparing lactate by directional alcoholysis of cellulose catalyzed by multifunctional coupled double salt ionic liquid according to claim 2, characterized in that: In step (3), the reaction time is 1.0 h.

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