Preparation method of catalyst for preparing isosorbide through sorbitol dehydration

Abstract

The invention discloses a preparation method and application of a catalyst for preparing isosorbide by catalyzing dehydration of sorbitol, acrylonitrile, niobium oxalate and tetraethoxysilane are stirred and dissolved in N, N-dimethylformamide, an Nb2O5-loaded carbon-nitrogen nanofiber white precursor is prepared in an electrostatic spinning mode, the fiber morphology is fixed through roasting in a muffle furnace, and the catalyst is prepared through a hydrothermal method. And carrying out high-temperature annealing in an argon environment to obtain a black material, carrying out alkali washing to remove SiO2 on the surface of the sample, and acidizing with sulfuric acid to obtain a final catalyst sample. The solid acid catalyst which is safe and high in quality activity is prepared in an electrostatic spinning mode, the solid acid catalyst shows high selectivity in the reaction for preparing the isosorbide by catalyzing dehydration of the sorbitol, and a new material is provided for industrial production of the isosorbide.

Description

Technical Field

[0001] This invention belongs to the field of catalysis, specifically relating to a method for preparing a catalyst for the dehydration of sorbitol to isosorbide. Background Technology

[0002] The effective conversion of biomass into renewable energy is considered one of the effective ways to alleviate dependence on fossil fuels. Sorbitol, as an intermediate product in the biomass conversion process, has wide applications in the food, daily chemical, and pharmaceutical industries. Isosorbide is a novel bio-based chemical that can replace many petrochemicals in pharmaceutical synthesis, polymer materials, polymer modification, and electronic information fields. For example, isosorbide, as a monomer or additive, can be used in liquid crystal materials, greatly improving their photoelectric properties; adding isosorbide to polyesters can increase the viscosity of the polyester and improve the glass transition temperature and strength of the polymer. Furthermore, isosorbide, as a drug, has good lipid solubility and can be rapidly absorbed by the human body after oral administration, making it an excellent antihypertensive drug for the treatment of intracranial hypertension.

[0003] Isosorbide can be prepared by dehydrating sorbitol. Sorbitol, the raw material, is widely available and can be obtained from inexpensive biomass resources such as cellulose and glucose. Most reactions involving the dehydration of sorbitol to isosorbide use acidic catalysts. Liquid acids such as sulfuric acid, phosphoric acid, and hydrochloric acid are widely used in sorbitol dehydration due to their low cost. However, using liquid acids as catalysts presents challenges such as difficulty in separating the catalyst from the raw materials and products, and severe equipment corrosion.

[0004] Research on the dehydration of sorbitol to isosorbide in my country is still limited. The main problems are low yield, poor catalyst economics, and difficulties in product separation and purification leading to high production costs, which to some extent restricts its industrial application. Currently, some solid catalysts, such as metal phosphates and molecular sieves, are used to catalyze the dehydration of sorbitol to isosorbide, but these catalysts are mostly used at high reaction temperatures, generating a large amount of byproducts, and the resulting isosorbide yield is unsatisfactory. Compared with various solid acid catalysts, metal oxides are ideal materials to replace traditional liquid acid catalysts, with advantages such as simple and convenient preparation conditions, low raw material prices, and good thermal stability. Given the current state of isosorbide production, developing low-cost, environmentally friendly, efficient, and recyclable solid acid catalysts is of great significance for the utilization of biomass resources. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing isosorbide from sorbitol using a Nb2O5-supported carbon-nitrogen nanofiber solid catalyst under solvent-free and reduced pressure conditions.

[0006] The primary objective of this invention is to provide a method for synthesizing Nb₂O₅-supported carbon and nitrogen nanofiber solid catalysts.

[0007] Another object of the present invention is to provide the application of the above-mentioned Nb2O5-supported carbon-nitrogen nanofiber solid catalyst in the dehydration of sorbitol to prepare isosorbide.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing isosorbide from sorbitol by dehydration, comprising the following steps:

[0010] 1) Polyacrylonitrile (PAN), niobium oxalate, and tetraethyl orthosilicate (TEOS) were dissolved in N,N-dimethylformamide (DMF) at 80°C. The prepared spinning solution was then spun by electrospinning to obtain a white thin film precursor.

[0011] 2) The precursor obtained in step 1) was calcined in an air environment at 250°C for 2 hours in a muffle furnace, and then annealed in an Ar environment at 650°C for 2 hours to obtain a black thin film sample.

[0012] 3) Treat the sample with an appropriate amount of 1M NaOH at 40℃ for 24 hours.

[0013] 4) The catalyst and sulfuric acid were acidified at a mass ratio of 1:16 using 2M H2SO4 at 60°C for 3 hours to obtain the final product.

[0014] 5) Sorbitol dehydration reaction steps: First, add sorbitol to the reactor and mix it evenly with the catalyst. Heat to a certain reaction temperature and react for a period of time under solvent-free and reduced pressure conditions. Then cool to room temperature, add water to dissolve the reaction product, and separate the catalyst and isosorbitol.

[0015] Furthermore, the volume-to-mass ratio of polyacrylonitrile, niobium oxalate, tetraethyl orthosilicate and N,N-dimethylformamide in step 1) is (600-800) mg: (800-1200) mg: (1.5-2) mL: (8.5-10) mL.

[0016] Furthermore, the electrospinning conditions described in step 1) are as follows: a solution flow rate of 0.08–0.016 ml / min, a spinning voltage of 12–17 kV, a spinning distance of 15–20 cm, an ambient humidity of 40%–50%, an ambient temperature of approximately 20–30 °C, and the use of a 0.4–0.7 mm needle.

[0017] Furthermore, the precursor treatment method in step 2) is to calcine it in an air environment at 250°C for 2 hours, and then anneal it in an Ar / NH3 environment at 650-850°C for 2-6 hours to obtain a black thin film sample.

[0018] Furthermore, the sample acidification process in step 4) involves acidifying the sample with 1–3 M H₂SO₄ at a mass ratio of 1:16 at 60°C for 3 hours to obtain the final product.

[0019] Furthermore, in step 5), the reaction temperature is 130–150°C, the reaction time is 1–5 h, the stirring speed is 200–400 r / min, the catalyst dosage is 5–20% of the raw material mass, and a negative pressure is maintained during the reaction.

[0020] Any of the above methods can be used to prepare Nb2O5-supported carbon-nitrogen nanofiber solid catalysts.

[0021] The above-described Nb2O5-supported carbon-nitrogen nanofiber solid catalyst is used in the dehydration of sorbitol to prepare isosorbide.

[0022] The reaction sample was analyzed using nuclear magnetic resonance spectroscopy. 1 H-NMR and DMSO were used as internal standards in 10% D2O to calculate product selectivity, yield, and reactant conversion.

[0023] The beneficial effects of this invention are:

[0024] A Nb₂O₅-supported carbon-nitrogen nanofiber solid catalyst was prepared by electrospinning to catalyze the dehydration of sorbitol to isosorbitol. The reaction was carried out under solvent-free, reduced pressure conditions, achieving an isosorbitol yield of over 80%. This method offers advantages such as mild reaction conditions, high catalytic efficiency, easy catalyst separation, and high reactivity due to its high metal quality, making it highly practical and economical. Attached Figure Description

[0025] Figure 1 The reaction route for the dehydration of sorbitol to isosorbide using the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst prepared in this embodiment is shown.

[0026] Figure 2 SEM image of the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst prepared in this embodiment catalyzing the dehydration of sorbitol to isosorbide.

[0027] Figure 3 TEM image of the dehydration of sorbitol to isosorbide catalyzed by the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst prepared in this embodiment.

[0028] Figure 4 The XRD pattern of the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst prepared in this embodiment for the dehydration of sorbitol to isosorbide.

[0029] Figure 5The Nb₂O₅-supported carbon-nitrogen nanofiber solid catalyst prepared in this embodiment is used for the catalytic dehydration of sorbitol to isosorbide. 1 1H-NMR analysis spectrum. Detailed Implementation Plan

[0030] A method for preparing isosorbide from sorbitol by dehydration, comprising the following steps:

[0031] 1) Polyacrylonitrile (PAN), niobium oxalate, and tetraethyl orthosilicate (TEOS) were added to N,N-dimethylformamide (DMF) and dissolved by stirring at 80°C to prepare a spinning solution. Then, this spinning solution was spun by electrospinning to obtain a white, thin-film precursor.

[0032] 2) The precursor obtained in step 1) was calcined in an air environment at 250°C for 2 hours, and then annealed in an Ar environment at 650°C for 2 hours to obtain a black thin film sample.

[0033] 3) Place the sample in an appropriate amount of 1M NaOH and treat it with alkali at 40℃ for 24 hours.

[0034] 4) The final product is obtained by acidifying the catalyst and sulfuric acid at a mass ratio of 1:16 with 2M H2SO4 at 60℃ for 3 hours.

[0035] 5) Sorbitol dehydration reaction steps: First, add sorbitol to the reactor and mix it evenly with the catalyst. Heat to a certain reaction temperature and react for a period of time under reduced pressure and solvent-free conditions. Then cool to room temperature, add water to dissolve the reaction product, and separate the catalyst and isosorbitol.

[0036] Preferably, the volume-to-mass ratio of polyacrylonitrile, niobium oxalate, tetraethyl orthosilicate and N,N-dimethylformamide in step 1) is (600-800) mg: (800-1200) mg: (1.5-2) mL: (8.5-10) mL.

[0037] Preferably, the electrospinning conditions in step 1) are as follows: solution flow rate of 0.08–0.016 ml / min, spinning voltage of 12–17 kV, spinning distance of 15–20 cm, ambient humidity of 40%–50%, ambient temperature of approximately 20–30 °C, and the use of needles with a diameter of 0.4–0.7 mm.

[0038] Preferably, the reaction temperature in step 5) is 130-150℃, the reaction time is 1-5h, the stirring speed is 200-400r / min, the catalyst dosage is 5-20% of the raw material mass, and a negative pressure is maintained during the reaction.

[0039] Any of the above methods can be used to prepare Nb2O5-supported carbon-nitrogen nanofiber solid catalysts.

[0040] The above-described Nb2O5-supported carbon-nitrogen nanofiber solid catalyst is used in the dehydration of sorbitol to prepare isosorbide.

[0041] Example 1

[0042] The preparation of Nb2O5-supported carbon and nitrogen nanofiber solid catalysts includes the following steps:

[0043] (1) Dissolve 0.6g PAN in 8.5mL DMF until the solution becomes transparent, then add 1g niobate oxalate and 1.5mL TEOS and stir at 60℃ until the solution becomes an orange-yellow transparent solution. Put the prepared solution into a 10mL syringe and spin it under the following conditions: solution flow rate 0.013ml / min, spinning voltage 15kv, spinning distance 15cm, ambient humidity 40%-50%, ambient temperature around 25℃, and a 0.55mm needle to obtain a white thin film precursor.

[0044] (2) The 0.9612g white film precursor was pre-oxidized in air at 250℃ for 2h at a heating rate of 5℃ / min to obtain 0.7534g yellowish-brown fibrous intermediate.

[0045] (3) 0.7534 g of the yellowish-brown fibrous intermediate was annealed at 650 °C for 2 h in an argon (Ar) atmosphere at a heating rate of 5 °C / min. Then, the SiO2 template in the catalyst was removed by maintaining the temperature at 40 °C for 24 h with an appropriate amount (30 ml) of 1 M NaOH. Finally, 0.4682 g of the sample was acidified in 7.5 ml of 2 M H2SO4 at 60 °C for 3 h, and the catalyst was then ground to obtain the final product.

[0046] The steps for the dehydration of sorbitol to isosorbide using Nb2O5-supported carbon-nitrogen nanofiber solid catalyst are as follows:

[0047] (1) First, add 0.25g of sorbitol and 0.05g of catalyst to the flask, heat to 130℃, turn on the vacuum water pump to reduce the pressure of the reaction apparatus to 3000Pa, react for 3 hours, and stir at 200r / min. After the reaction is complete, add an appropriate amount of water to the reaction flask to cool the reaction solution, and rinse the reactor with a small amount of deionized water, then pour the rinsed solution into the reaction flask. After all soluble substances in the reaction flask have dissolved, separate the catalyst by vacuum filtration. 1 The reaction solution was analyzed by ¹H-NMR. The conversion rate of sorbitol was >99%, and the yield of isosorbide was 74.13%.

[0048] The chemical reactions involved are as follows Figure 1As shown.

[0049] The following is a further performance test of the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst prepared in the above examples.

[0050] Figure 2 The image shows a low-magnification SEM image of a Nb2O5-supported carbon-nitrogen nanofiber solid catalyst, revealing that the sample is a fibrous material with a rough surface.

[0051] Figure 3 The high-resolution TEM image shows a carbon-nitrogen nanofiber solid catalyst supported on Nb2O5. It was observed that the sample had no obvious metal lattice and the supported Nb2O5 had an amorphous structure.

[0052] Figure 4 The image shows the XRD pattern of the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst, further demonstrating that the supported Nb2O5 has an amorphous structure.

[0053] Example 2

[0054] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that the amount of TEOS used in step (1) was 2 ml.

[0055] Example 3

[0056] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that the amount of TEOS used in step (1) was 1 ml.

[0057] Example 4

[0058] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that the amount of niobium oxalate used in step (1) was 0.8 g.

[0059] Example 5

[0060] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that the amount of niobium oxalate used in step (1) was 1.2g.

[0061] Example 6

[0062] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that sulfuric acid with a concentration of 1 M H2SO4 was used in step (3).

[0063] Example 7

[0064] The preparation of Nb2O5 supported carbon and nitrogen nanofiber solid catalyst was carried out in the same manner as in Example 1, except that the concentration of NaOH used in step (3) was 3M.

[0065] Example 8

[0066] The dehydration of sorbitol to isosorbide was catalyzed by Nb2O5-supported carbon-nitrogen nanofiber solid catalyst. Except for the reaction temperature of 150°C in step (1), all other operations were the same as in Example 1.

[0067] Example 9

[0068] The dehydration of sorbitol to isosorbide was catalyzed by Nb2O5-supported carbon-nitrogen nanofiber solid catalyst. Except for the reaction temperature of 140°C in step (1), all other operations were the same as in Example 1.

[0069] Table 1

[0070]

[0071] The invention and several embodiments thereof have been described above by way of example and not limitation. Other alternative embodiments will be apparent to those skilled in the art upon reading this specification, and these embodiments are also within the scope of the invention.

Claims

1. A method for producing a catalyst for the dehydration of sorbitol to isosorbide, characterized by, Includes the following steps: 1) Polyacrylonitrile (PAN), niobium oxalate, and tetraethyl orthosilicate (TEOS) were dissolved in N,N-dimethylformamide (DMF) at 80°C. The prepared spinning solution was then spun by electrospinning to obtain a white thin film precursor. 2) The precursor obtained in step 1) was calcined in an air environment at 250°C for 2 hours in a muffle furnace, and then annealed in an Ar environment at 650°C for 2 hours to obtain a black thin film sample. 3) Treat the sample with an appropriate amount of 1M NaOH at 40℃ for 24 hours. 4) The final product is obtained by acidifying with 2M H2SO4 at 60℃ for 3 hours at a mass ratio of 1:

16. 5) Sorbitol dehydration reaction steps: First, add sorbitol to the reactor and mix it evenly with the catalyst. Heat to a certain reaction temperature and react for a period of time under solvent-free and reduced pressure conditions. Then cool to room temperature, add water to dissolve the reaction product, and separate the catalyst and isosorbitol.

2. The method of claim 1, wherein, The volume-to-mass ratio of polyacrylonitrile, niobium oxalate, tetraethyl orthosilicate and N,N-dimethylformamide in step 1) is (600-800) mg: (800-1200) mg: (1.5-2) ml: (8.5-10) ml.

3. The method according to claim 1, characterized in that, The electrospinning conditions described in step 1) are as follows: solution flow rate of 0.08–0.016 ml / min, spinning voltage of 12–17 kV, spinning distance of 15–20 cm, ambient humidity of 40%–50%, ambient temperature of approximately 20–30 °C, and the use of needles with a diameter of 0.4–0.7 mm.

4. The method according to claim 1, characterized in that, Step 2) The precursor treatment method is to calcine it in an air environment at 250°C for 2 hours, and then anneal it in an Ar / NH3 environment at 650-850°C for 2-6 hours to obtain a black thin film sample.

5. The method according to claim 1, characterized in that, Step 4) The sample acidification process is as follows: acidification with 1-3M H2SO4 at 60℃ for 3 hours at a mass ratio of 1:16 to obtain the final product.

6. The method according to claim 1, characterized in that, Step 5) The reaction temperature is 130-150℃, the reaction time is 1-5h, the stirring speed is 200-400r / min, the catalyst dosage is 5-20% of the raw material mass, and a negative pressure is maintained during the reaction.

7. The Nb2O5 supported carbon-nitrogen nanofiber solid catalyst prepared by any of the methods of claims 1 to 5.

8. The application of the Nb2O5-supported carbon-nitrogen nanofiber solid catalyst of claim 6 in the dehydration of sorbitol to prepare isosorbide.

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