Ionic liquid-modified solid acid catalyst for dehydration of sorbitol to prepare isosorbide, preparation method thereof, and application thereof

Abstract

The present invention belongs to the field of catalytic engineering, and specifically relates to an ionic liquid-modified solid acid catalyst for the dehydration of sorbitol to prepare isosorbide, and its preparation method and application. The ionic liquid-modified solid acid catalyst is modified by an ionic liquid grafting modification method; wherein the ionic liquid is an imidazole ionic liquid; and the solid acid is niobium oxide, tantalum oxide, niobium phosphate, tantalum phosphate, Al2O3, Al2O3-SiO2, etc. The method of the present invention uses an ionic liquid as a modifier to prepare a series of solid acid catalysts. Using sorbitol as a raw material, isosorbide is directly prepared by dehydration reaction under solvent-free and vacuum conditions. The method has the advantages of high isosorbide yield, good selectivity, low catalyst dosage, simple operation and low pollution. The isosorbide yield can reach 96%.

Description

Technical Field

[0001] The invention belongs to the fields of catalytic chemistry and chemical engineering, and particularly relates to an ionic liquid-modified solid acid catalyst for dehydrating sorbitol to prepare isosorbide, a preparation method and an application thereof. Background Art

[0002] Isosorbide is the only saccharide diol that has achieved industrialized production and is widely used in pharmaceuticals, liquid crystal materials, plasticizers, polymers, and other fields. The difficulty in the preparation of isosorbide lies primarily in the violent side reactions during the dehydration process and low selectivity, and the catalyst is key to this reaction. Industrially, this reaction is typically carried out under the action of strong acidic catalysts, including homogeneous catalysts and heterogeneous catalysts. However, homogeneous catalysts are highly corrosive and difficult to separate from the product, while heterogeneous catalysts have low catalytic activity and poor stability. These problems have resulted in difficulties in optimizing the production of isosorbide.

[0003] Solid acids offer advantages such as mild reaction conditions, easy product separation, non-corrosiveness, and reusability. Patent CN114671883A discloses a method for producing isosorbide by dehydrating sorbitol using a niobium-based solid acid catalyst, achieving an isosorbide yield of up to 76%. Patent CN110483678A discloses a series of F-modified polymer-based solid acid catalysts prepared using a hydrothermal synthesis method, achieving isosorbide yields exceeding 80%. To promote the efficient dehydration of sorbitol to isosorbide, the development of highly efficient, highly selective, highly stable, and cost-effective catalysts and their recovery methods are key research priorities.

[0004] Ionic liquids have adjustable structures and can improve the microenvironment of catalytically active sites, providing more acid sites and enabling controlled preparation of catalyst acidic sites. The development of ionic liquid-modified solid acid catalysts offers a new approach for future catalyst development. This invention addresses the issues of intense side reactions and poor selectivity during the preparation of isosorbide by dissolving sorbitol in water using an ionic liquid-modified solid acid catalyst. The catalyst exhibits excellent catalytic activity and easy recovery, and exhibits high catalytic efficiency for the dehydration of sorbitol to produce isosorbide. Summary of the Invention

[0005] In view of the problems and shortcomings in the prior art, the present invention aims to provide an ionic liquid-modified solid acid catalyst for the dehydration of sorbitol to prepare isosorbide, and a preparation method and application thereof.

[0006] Based on the above purpose, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides an ionic liquid-modified solid acid catalyst for dehydrating sorbitol to prepare isosorbide, wherein the catalyst is modified by an ionic liquid grafting modification method; wherein the ionic liquid is any one of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, pyrrolidine, piperidine or a functionalized ionic liquid; and the solid acid is any one of niobium oxide, tantalum oxide, niobium phosphate, tantalum phosphate, Al2O3, and Al2O3-SiO2.

[0008] Preferably, the ionic liquid is an imidazolium ionic liquid.

[0009] More preferably, the imidazolium ionic liquid is 1-butyl-3-methylimidazolium chloride.

[0010] Preferably, the solid acid catalyst is niobium oxide (Nb2O5).

[0011] According to the ionic liquid modified solid acid catalyst, preferably, the amount of the ionic liquid is 0.1 wt% to 10 wt% of the mass of the solid acid catalyst.

[0012] The second aspect of the present invention provides a method for preparing the ionic liquid-modified solid acid catalyst described in the first aspect, comprising the following steps:

[0013] (1) adding the ionic liquid to a solvent and stirring to dissolve the ionic liquid to obtain a solution with a concentration of 0.01 to 10 mol / L;

[0014] (2) adding a solid acid catalyst to the solution obtained in step (1) and stirring to react, and filtering to obtain a product after the reaction is completed;

[0015] (3) adding an acid solution to the product obtained in step (2) for acidification, and removing the solvent to obtain the ionic liquid-modified solid acid catalyst.

[0016] According to the preparation method, preferably, the reaction temperature in step (2) is 20 to 80° C., and the reaction time is 1 to 4 hours.

[0017] According to the preparation method, preferably, the acid solution in step (3) is an inorganic acid solution.

[0018] More preferably, the inorganic acid is any one of sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid.

[0019] More preferably, the inorganic acid is sulfuric acid or phosphoric acid.

[0020] A third aspect of the present invention provides use of the ionic liquid-modified solid acid catalyst described in the first aspect in the dehydration of sorbitol to produce isosorbide. The specific operating steps of using the ionic liquid-modified solid acid catalyst in the dehydration reaction of sorbitol to produce isosorbide are as follows: after a sorbitol solution is subjected to high-temperature negative pressure dehydration or solid sorbitol is heated to melt, the ionic liquid-modified solid acid catalyst is added to the sorbitol to carry out a dehydration reaction to produce isosorbide.

[0021] According to the application, preferably, the amount of the ionic liquid-modified solid acid catalyst is 0.1wt% to 20wt% of the mass of sorbitol; the dehydration reaction temperature is 130°C to 200°C; the dehydration reaction pressure is from atmospheric pressure to -0.1MPa; and the reaction time is 1h to 6h.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The method of the present invention uses ionic liquids as modifiers to prepare a series of solid acid catalysts. Using sorbitol as the raw material, isosorbide is prepared directly through a solvent-free, vacuum-based dehydration reaction. The method exhibits the advantages of high isosorbide yield, good selectivity, simple operation, and minimal pollution, with an isosorbide yield of up to 96%. The modifiers contain various functional groups capable of forming specific binding sites with reactant and intermediate molecules, further facilitating diffusion and mass transfer of reactants and products on the catalyst surface.

[0024] The method provided by the present invention uses an ionic liquid in an amount ranging from 0.1% to 10% by weight of the catalyst. This small amount does not decompose during the reaction, and the catalyst can be easily reused. The catalyst dosage ranges from 0.1% to 20% by weight of the solid sorbitol, significantly reducing catalyst usage compared to existing preparation methods and saving costs.

[0025] The catalyst used in the present invention is an ionic liquid-modified solid acid catalyst. The ionic liquid and the solid acid each have good catalytic performance for the sorbitol dehydration reaction. After the two are combined and modified, they are more conducive to the diffusion and mass transfer of reactants and products. In addition, the combination of the two can effectively avoid carbon accumulation on the surface of the solid acid catalyst and improve the long-term stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the pyridine infrared spectrum of the ionic liquid-modified niobium oxide solid acid prepared in Example 1 of the present invention;

[0027] Figure 2 This is the pyridine infrared spectrum of the ionic liquid-modified tantalum oxide solid acid prepared in Example 2 of the present invention;

[0028] Figure 3This is the pyridine infrared spectrum of the ionic liquid-modified niobium phosphate solid acid prepared in Example 3 of the present invention;

[0029] Figure 4 This is the pyridine infrared spectrum of the ionic liquid-modified tantalum phosphate solid acid prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] 1. Preparation of ionic liquid modified solid acid catalyst

[0032] Example 1

[0033] This embodiment provides an ionic liquid-modified solid acid catalyst for dehydrating sorbitol to prepare isosorbide. The solid acid catalyst is modified by an ionic liquid grafting modification method. The ionic liquid is 1-butyl-3-methylimidazolium chloride; the solid acid is niobium oxide; and the amount of 1-butyl-3-methylimidazolium chloride used is 0.5 wt% of the mass of the niobium oxide.

[0034] The preparation method of the ionic liquid-modified solid acid catalyst comprises the following steps: (1) adding 1-butyl-3-methylimidazolium chloride into a solvent and stirring and dissolving the mixture to obtain a solution with a concentration of 0.5 mol / L;

[0035] (2) adding 3 g of niobium oxide to 30 mL of the solution obtained in step (1) and stirring the mixture at 60° C. for 2 h. After the reaction, filtering the mixture to obtain the product;

[0036] (3) adding sulfuric acid to the product obtained in step (2) for acidification, and removing the solvent to obtain an ionic liquid-modified niobium oxide catalyst.

[0037] Example 2

[0038] This embodiment provides an ionic liquid-modified solid acid catalyst for dehydrating sorbitol to prepare isosorbide. The solid acid catalyst is modified by an ionic liquid grafting modification method. The ionic liquid is 1-butyl-3-methylimidazolium chloride; the solid acid is tantalum oxide; and the amount of 1-butyl-3-methylimidazolium chloride used is 0.5 wt% of the mass of the tantalum oxide.

[0039] The preparation method of the ionic liquid-modified solid acid catalyst comprises the following steps: (1) adding 1-butyl-3-methylimidazolium chloride into a solvent and stirring and dissolving the mixture to obtain a solution with a concentration of 0.5 mol / L;

[0040] (2) adding 3 g of tantalum oxide to 30 mL of the solution obtained in step (1) and stirring the mixture at 60° C. for 2 h. After the reaction, filtering the mixture to obtain the product;

[0041] (3) adding sulfuric acid to the product obtained in step (2) for acidification, and removing the solvent to obtain an ionic liquid-modified tantalum oxide solid acid catalyst.

[0042] Example 3

[0043] This embodiment provides an ionic liquid-modified solid acid catalyst for the dehydration of sorbitol to prepare isosorbide, wherein the solid acid catalyst is modified by an ionic liquid grafting modification method; wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride; the solid acid is niobium phosphate, and the amount of 1-butyl-3-methylimidazolium chloride is 0.5 wt% of the mass of the niobium phosphate.

[0044] The preparation method of the ionic liquid-modified solid acid catalyst comprises the following steps: (1) adding 1-butyl-3-methylimidazolium chloride into a solvent and stirring and dissolving the mixture to obtain a solution with a concentration of 0.5 mol / L;

[0045] (2) adding 3 g of niobium phosphate to 30 mL of the solution obtained in step (1) and stirring the mixture at 60° C. for 2 h. After the reaction, filtering the mixture to obtain the product;

[0046] (3) adding sulfuric acid to the product obtained in step (2) for acidification, and removing the solvent to obtain an ionic liquid-modified niobium phosphate solid acid catalyst.

[0047] Example 4

[0048] This embodiment provides an ionic liquid-modified solid acid catalyst for dehydrating sorbitol to prepare isosorbide, wherein the solid acid catalyst is modified by an ionic liquid grafting modification method; wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride; the solid acid is tantalum phosphate, and the amount of 1-butyl-3-methylimidazolium chloride is 0.5 wt% of the mass of the tantalum phosphate.

[0049] The preparation method of the ionic liquid-modified solid acid catalyst comprises the following steps: (1) adding 1-butyl-3-methylimidazolium chloride into a solvent and stirring and dissolving the mixture to obtain a solution with a concentration of 0.5 mol / L;

[0050] (2) adding 3 g of tantalum phosphate to 30 mL of the solution obtained in step (1) and stirring the mixture at 60° C. for 2 h. After the reaction, filtering the mixture to obtain the product;

[0051] (3) adding sulfuric acid to the product obtained in step (2) for acidification, and removing the solvent to obtain an ionic liquid-modified tantalum phosphate solid acid catalyst.

[0052] Example 5

[0053] The contents of an ionic liquid-modified solid acid catalyst for dehydration of sorbitol to prepare isosorbide are substantially the same as those of Example 1, except that phosphoric acid is used for acidification.

[0054] Example 6

[0055] The contents of an ionic liquid-modified solid acid catalyst for dehydration of sorbitol to prepare isosorbide are substantially the same as those of Example 2, except that phosphoric acid is used for acidification.

[0056] Example 7

[0057] The contents of an ionic liquid-modified solid acid catalyst for dehydration of sorbitol to prepare isosorbide are substantially the same as those of Example 3, except that phosphoric acid is used for acidification.

[0058] Example 8

[0059] The contents of an ionic liquid-modified solid acid catalyst for dehydration of sorbitol to prepare isosorbide are substantially the same as those of Example 4, except that phosphoric acid is used for acidification.

[0060] Comparative Example 1

[0061] The contents of a catalyst for dehydrating sorbitol to prepare isosorbide are substantially the same as those of Example 1, except that no niobium oxide solid acid catalyst is added.

[0062] Comparative Example 2

[0063] The contents of a catalyst for dehydrating sorbitol to prepare isosorbide are substantially the same as those in Example 1, except that 1-butyl-3-methylimidazolium chloride is not added.

[0064] Comparative Example 3

[0065] The contents of a catalyst for dehydrating sorbitol to prepare isosorbide are substantially the same as those of Example 2, except that 1-butyl-3-methylimidazolium chloride is not added.

[0066] Comparative Example 4

[0067] The contents of a catalyst for dehydrating sorbitol to prepare isosorbide are substantially the same as those in Example 3, except that 1-butyl-3-methylimidazolium chloride is not added.

[0068] The ionic liquid modified solid acid catalysts prepared in Examples 1 to 4 were subjected to pyridine infrared testing, and the results are shown in FIG. Figures 1 to 4 As shown by Figures 1 to 4It can be found that the characteristic vibration peaks of pyridine adsorbed on Lewis acid sites are detected at 1448cm-1, 1575cm-1 and 1608cm-1, among which 1448cm-1 and 1608cm-1 are strong Lewis acid sites; 1540cm-1 and 1635cm-1 are strong Lewis acid sites. The characteristic vibration peak of the acid site is at 1490cm-1, which is Lewis acid and It can be seen that there are more Lewis acid sites in the catalyst than Acid sites. Even after vacuum desorption at the reaction temperature (200°C) for 25 minutes, the catalyst's Lewis acid sites remain sufficiently stable. Calculated B / L values ​​for different catalysts under pyridine desorption conditions at 200°C are shown in Table 1.

[0069] Table 1 Acid properties of [BMIM] modified solid acid catalysts

[0070]

[0071]

[0072] Note: -1 means sulfuric acid acidification, -2 means phosphoric acid acidification.

[0073] As shown in Table 1, the acid property characterization results show that sulfuric acid modification can significantly increase the total acid content of the catalyst, and the B acid ratio is higher, indicating that ionic liquid modification and acid modification mainly affect the B acid property of the catalyst. For different solid acids, the total acid content is significantly different from BAS / LAS and is higher than that of the unmodified catalyst, fully demonstrating the effectiveness of ionic liquid modification. The ionic liquid used in the present invention is liquid and cannot be quantitatively or qualitatively evaluated for its acid property by acid characterization. However, the total acid content of the catalyst without ionic liquid modification is significantly reduced.

[0074] 2. Preparation of Isosorbide by Dehydration of Sorbitol

[0075] 1. Experiment on catalytic preparation of isosorbide using solid sorbitol as raw material

[0076] The catalysts prepared in Examples 1-8 and Comparative Examples 1-4 were used to dehydrate solid sorbitol to produce isosorbide. The specific steps were as follows: 30 g of sorbitol was heated in a reactor until melted, 2 g of the catalyst prepared in Examples 1-8 or Comparative Examples 1-4 was added thereto, and the reaction was continued at 5 kPa and 170°C for 5 hours. Samples were then collected and analyzed by high-performance liquid chromatography. The results are shown in Table 2.

[0077] Table 2 Chromatographic analysis results

[0078]

[0079] Note: -1 means sulfuric acid acidification, -2 means phosphoric acid acidification.

[0080] As can be seen from Table 2, the catalytic effect is best when [BMIM] / Nb2O5 is used as the catalyst, with sorbitol completely converted to an isosorbide yield of 96%, with 1,4-sorbitol being the primary byproduct. In the other examples acidified by sulfuric acid, the isosorbide yields were all above 80%, while the 1,4-sorbitol content was slightly higher than that of the niobium oxide system. However, the solid acid catalyst acidified by phosphoric acid performed slightly worse, likely due to the relatively low total acid content on the catalyst surface. Compared to the comparative example, the performance of the solid acid catalyst acidified by sulfuric acid without ionic liquid modification was significantly reduced, indicating that ionic liquid modification can improve catalyst activity.

[0081] 2. Experiment on catalytic preparation of isosorbide using sorbitol solution as raw material

[0082] The catalysts prepared in Examples 1-8 and Comparative Examples 1-4 were used to dehydrate a 37 wt% sorbitol solution to produce isosorbide. The specific steps were as follows: the sorbitol solution was added to a reactor, heated to 110°C, vacuumed with a water pump to a negative pressure of -0.9 MPa, and after sufficient water removal, the catalyst was added and the reaction was continued. Specifically, 100 g of a 37 wt% sorbitol solution was added and reacted. After dehydration at 110°C and -0.9 MPa for 2 hours, 5 g of the catalyst prepared in Examples 1-8 or Comparative Examples 1-4 was added and reacted at 170°C for 5 hours. Samples were then taken for HPLC analysis. The results are shown in Table 3.

[0083] Table 3 Chromatographic analysis results

[0084]

[0085] Note: -1 means sulfuric acid acidification, -2 means phosphoric acid acidification.

[0086] Using sorbitol solution as the reactant, the yield of isosorbide decreased by approximately 10%, while the yield of sulfuric acid-treated niobium oxide modified with ionic liquid decreased to 83%, likely due to excess water inhibiting the dehydration reaction. Comparing Example 1 with Comparative Example 2, it was found that ionic liquid modification still helped improve product yield.

[0087] 3. Repeatability Experiment

[0088] The catalyst prepared in Example 1 was recovered and the experiment was repeated five times. Samples were taken for HPLC analysis. The results are shown in Table 4. After filtration and washing, the catalyst was reused directly and still exhibited good catalytic performance. The yield of isosorbide reached 91.8% after five repetitions, and the corresponding yield of 1,4-anhydrosorbitol increased slightly.

[0089] Table 4 Effect of cycle number on the dehydration of sorbitol to prepare isosorbide

[0090]

Claims

1. An ionic liquid-modified solid acid catalyst for dehydration of sorbitol to isosorbide, characterized in that: The solid acid catalyst is modified by an ionic liquid grafting modification method; wherein the ionic liquid is 1-butyl-3-methylimidazolium chloride; and the solid acid catalyst is niobium oxide, tantalum oxide, niobium phosphate, or tantalum phosphate; The ionic liquid modified solid acid catalyst is prepared by the following method: (1) Add the ionic liquid to the solvent and stir to dissolve it to obtain a solution with a concentration of 0.01 to 10 mol / L; (2) adding a solid acid catalyst to the solution obtained in step (1), stirring and reacting, and filtering after the reaction to obtain a product; (3) Adding an acid solution to the product obtained in step (2) for acidification, and removing the solvent to obtain the ionic liquid-modified solid acid catalyst.

2. The ionic liquid-modified solid acid catalyst according to claim 1, wherein The amount of the ionic liquid used is 0.1 wt% to 10 wt% of the mass of the solid acid catalyst.

3. The ionic liquid-modified solid acid catalyst according to claim 1, characterized in that The reaction temperature in step (2) is 20-80° C., and the reaction time is 1-4 h.

4. The ionic liquid-modified solid acid catalyst according to claim 1, characterized in that The acid solution in step (3) is an inorganic acid solution.

5. The ionic liquid-modified solid acid catalyst according to claim 4, characterized in that The inorganic acid is any one of sulfuric acid, phosphoric acid, hydrochloric acid and nitric acid.

6. Use of the ionic liquid-modified solid acid catalyst according to any one of claims 1 to 5 in the dehydration of sorbitol to produce isosorbide.

7. The use according to claim 6, characterized in that The specific operation steps are: after the sorbitol solution is dehydrated at high temperature and negative pressure or solid sorbitol is heated to melt, a solid acid catalyst modified by an ionic liquid is added to the sorbitol to carry out a dehydration reaction to prepare isosorbide.

8. The use according to claim 7, characterized in that The amount of the ionic liquid-modified solid acid catalyst is 0.1 wt% to 20 wt% of the mass of sorbitol; the dehydration reaction temperature is 130° C. to 200° C.; the dehydration reaction pressure is from normal pressure to -0.1 MPa; and the reaction time is 1 hour to 6 hours.

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