A catalyst for converting levulinic acid into 2-methyltetrahydrofuran and its preparation method

Abstract

The invention discloses a catalyst for converting levulinic acid into 2-methyltetrahydrofuran and its preparation method. The preparation of bamboo-based porous adsorbent material and nickel-copper-chromium hydrotalcite is prepared separately, the nickel-copper-chromium hydrotalcite is added to the bamboo-based porous adsorbent material suspension to obtain a catalyst precursor, and the precursor is roasted under 450-550°C for 3-6h. The obtained mixed metal oxide is a catalyst. The present invention composites nickel-copper-chromium hydrotalcite and bamboo-based porous adsorbent material into a catalyst precursor. The larger specific surface area of ​​the bamboo-based porous adsorbent material is evenly distributed on the hydrotalcite, solving the problem of easy agglomeration during the application of the hydrotalcite. The precursor roasting is a catalyst, which has a larger specific surface area and a regular morphology, and its activity performance is better, making it more efficient to convert γ-valerolactone to the downstream product 2-methyltetrahydrofuran.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production, and particularly relates to a catalyst for converting levulinic acid into 2-methyltetrahydrofuran and a preparation method thereof. Background Art

[0002] In recent years, with the depletion of fossil fuels and increasingly severe environmental problems, the search for renewable energy sources to reduce dependence on petroleum-based materials has profound implications for promoting sustainable development. Biomass, as the only renewable carbon energy source, is widely distributed, has a short production cycle, is readily available, and is carbon-neutral, demonstrating great potential as a petroleum alternative. Levulinic acid, a biomass-derived organic acid compound, has attracted considerable attention as a key biomass-based platform compound due to its diverse applications and industrial-scale production. Through sequential metal-catalyzed hydrogenation and acid-catalyzed dehydration steps, levulinic acid can be converted into γ-valerolactone and its derivative fuel molecules. Although γ-valerolactone has demonstrated great potential as a fuel additive, its high water solubility and low octane number limit its further energy applications. 2-Methyltetrahydrofuran, a downstream product of γ-valerolactone, exhibits excellent hydrophobicity and is miscible with gasoline in all proportions, making it a promising biofuel and gasoline additive. The conversion of levulinic acid to 2-methyltetrahydrofuran involves a series of hydrodeoxygenation reactions, which require a bifunctional catalyst with metal sites and acid sites. The use of hydrotalcites (LDHs) as carriers / precursors to target and promote the coupling and collaboration of multi-metal components and "metal-acid" sites is expected to achieve performance improvements in this complex cascade process.

[0003] A mixed metal oxide obtained by calcining an LDHs precursor made from a hydrotalcite-like / bamboo-based porous adsorption material is used to catalyze the conversion of γ-valerolactone to 2-methyltetrahydrofuran. Parameters such as the calcination temperature and interlayer anions influence the catalyst's performance. Chinese patent CN108014798A discloses a method for producing 2-methyltetrahydrofuran by catalytic hydrogenation. Under suitable process conditions, levulinic acid ester is highly selectively hydrogenated using a Cu-based catalyst to produce 2-methyltetrahydrofuran in a single step. However, the actual preparation process for 2-methyltetrahydrofuran is complex and environmentally unfriendly. Furthermore, the conversion of levulinic acid to 2-methyltetrahydrofuran requires very demanding reaction conditions. Even slight variations in these conditions can affect the product, resulting in the formation of 2-methyltetrahydrofuran, 1,4-pentanediol, γ-valerolactone, and other products. Consequently, a 100% conversion of levulinic acid cannot be guaranteed during the preparation process. Therefore, how to develop a hydrotalcite-like bimetallic bifunctional efficient catalytic system suitable for the preparation of 2-methyltetrahydrofuran from levulinic acid and enrich the catalytic system for downstream product conversion is a problem worthy of study. Summary of the Invention

[0004] The present invention aims to provide a catalyst for converting levulinic acid into 2-methyltetrahydrofuran and its preparation method. Hydrotalcites (LDHs) are layered double hydroxides whose main components after calcination are mixed metal oxides. They can be used as catalysts for chemical reactions, but LDHs can agglomerate during use. Therefore, the present invention combines a bamboo-based porous adsorption material with LDHs, which has well-developed pores, a large specific surface area, and strong adsorption properties. The resulting catalyst significantly reduces the agglomeration problem, making the conversion of levulinic acid to 2-methyltetrahydrofuran more efficient.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran comprises the following steps:

[0007] 1) Preparation of bamboo-based porous adsorption materials

[0008] 1-1) Prepare an activator by mixing potassium citrate (C6H5K3O7), anhydrous potassium carbonate (K2CO3), and ammonium bicarbonate (NH4HCO3) in a molar ratio of 1:1:1, with a concentration of 10-15%;

[0009] 1-2) Mix the activator, KOH (2-5%), and distilled water in a ratio of 3-6 mg:1-2 mg:25-35 mL and sonicate for 10-15 minutes to obtain an activator solution.

[0010] 1-3) crushing and drying the bamboo material to obtain bamboo powder, and uniformly mixing the bamboo powder with the activator solution at a ratio of 1 g:3 ± 0.1 mL, allowing to stand for 24-28 hours, and then drying to obtain pretreated bamboo powder;

[0011] 1-4) placing the pretreated bamboo powder in a crucible, heating it to 600-650°C at a rate of 5-10°C / min at room temperature, activating it for 25-30 minutes, cooling it to room temperature, removing it, washing the product with deionized water until neutral, drying it, cooling it, grinding it, and sieving it to obtain a bamboo-based porous adsorption material;

[0012] 2) Preparation of nickel-copper-chromium hydrotalcite

[0013] 2-1) Prepare solution A with a concentration of 2-4 mol / L by mixing Ni(NO3)2·6H2O, Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in a molar ratio of 2:1:1;

[0014] 2-2) Place the three-necked flask in a constant temperature water bath at 60-65°C. Add Solution A and NaOH solution (1 mol / L) dropwise to the flask simultaneously with vigorous stirring using a constant pressure dropping funnel. Control the pH at 6-7. Add dropwise until Solution A is completely reacted.

[0015] 2-3) After the addition is complete, stir and age for 30-35 minutes. The mixed slurry is transferred to a hydrothermal autoclave and placed in an oven at 110-120°C for 6-6.5 hours. The mixture is then removed and washed with deionized water until neutral. The mixture is then dried in an oven at 110-120°C for 3-3.5 hours to obtain a nitrate-intercalated nickel-copper-chromium hydrotalcite.

[0016] 3) Preparation of catalyst precursor (nickel-copper-chromium hydrotalcite / bamboo-based porous adsorption material composite material)

[0017] 3-1) Dissolve the bamboo-based porous adsorbent material in water at a ratio of 0.5-1.5 g:100 mL, and stir magnetically to obtain a suspension of the bamboo-based porous adsorbent material;

[0018] 3-2) Adding nickel-copper-chromium hydrotalcite to a bamboo-based porous adsorbent suspension at a ratio of 8-10 g:100 mL, centrifuging, washing, grinding, and drying the resulting mixture to obtain a catalyst precursor;

[0019] 4) Preparation of catalyst

[0020] The catalyst precursor is heated to 450-550° C. at a rate of 5-8° C. / min, and then calcined for 3-6 hours to obtain a catalyst.

[0021] Compared with the existing method for preparing 2-methyltetrahydrofuran from levulinic acid, the present invention has the following advantages:

[0022] 1. The present invention compounds nickel-copper-chromium hydrotalcite and bamboo-based porous adsorption material. The mixed metal oxide obtained by calcining the precursor is a catalyst, which has a larger specific surface area and regular morphology, better activity, and more efficient conversion of γ-valerolactone to the downstream product 2-methyltetrahydrofuran.

[0023] 2. The present invention constructs an efficient catalytic system. The catalytic effect of the prepared catalyst is not much different from that of the reduced catalyst, and can achieve complete conversion of γ-valerolactone. At the same time, 2-methyltetrahydrofuran has a high selectivity.

[0024] 3. The present invention composites nickel-copper-chromium hydrotalcite and bamboo-based porous adsorption material to prepare a catalyst precursor. The large specific surface area of ​​the bamboo-based porous adsorption material is evenly distributed on the hydrotalcite, solving the problem of easy agglomeration of the hydrotalcite during application.

[0025] 4. The preparation process of the catalyst of the present invention omits the step of reducing the hydrotalcite-like substance, making the preparation process simpler. The catalyst prepared by the present invention is used to catalyze the selective hydrogenation process of γ-valerolactone and can promote the efficient progress of the same reaction. DETAILED DESCRIPTION Example 1

[0026] A method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran comprises the following steps:

[0027] 1) Preparation of bamboo-based porous adsorption materials

[0028] 1-1) Potassium citrate, anhydrous potassium carbonate, and ammonium bicarbonate are prepared in a molar ratio of 1:1:1 to prepare an activator with a concentration of 10%;

[0029] 1-2) Mix the activator, KOH (2%), and distilled water in a ratio of 3 mg:1 mg:25 mL and sonicate for 10 minutes to obtain an activator solution.

[0030] 1-3) crushing and drying the bamboo material to obtain bamboo powder, and uniformly mixing the bamboo powder with the activator solution at a ratio of 1 g:3 mL, allowing to stand for 24 hours, and then drying to obtain pretreated bamboo powder;

[0031] 1-4) placing the pretreated bamboo powder in a crucible, heating it to 600°C at a rate of 5°C / min at room temperature, activating it for 30 minutes, cooling it to room temperature, and then removing it. The product is washed with deionized water until neutral, then dried, cooled, ground, and finely sieved to obtain a bamboo-based porous adsorption material;

[0032] 2) Preparation of nickel-copper-chromium hydrotalcite

[0033] 2-1) Prepare solution A with a concentration of 2 mol / L by mixing Ni(NO3)2·6H2O, Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in a molar ratio of 2:1:1;

[0034] 2-2) Place the three-necked flask in a constant-temperature water bath at 60°C. Add Solution A and NaOH solution (1 mol / L) dropwise to the flask concurrently with strong stirring using a constant-pressure dropping funnel. Control the pH to 6. Add dropwise until Solution A is completely reacted.

[0035] 2-3) After the addition is complete, the mixture is aged for 30 minutes, and then transferred to a hydrothermal kettle, placed in an oven at 110°C for 6.5 hours, removed, washed with deionized water until neutral, and dried in an oven at 110°C for 3.5 hours to obtain a nitrate-intercalated nickel-copper-chromium hydrotalcite.

[0036] 3) Preparation of catalyst precursor

[0037] 3-1) Dissolve the bamboo-based porous adsorbent material in water at a ratio of 0.5 g:100 mL, and stir the mixture magnetically to obtain a suspension of the bamboo-based porous adsorbent material;

[0038] 3-2) Adding nickel-copper-chromium hydrotalcite to a bamboo-based porous adsorbent suspension at a ratio of 8 g:100 mL, centrifuging the resulting mixture, washing, grinding, and drying to obtain a catalyst precursor;

[0039] 4) Preparation of catalyst

[0040] The catalyst precursor was heated to 450° C. at a rate of 5° C. / min and then calcined for 6 h to obtain a catalyst. Example 2

[0041] A method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran comprises the following steps:

[0042] 1) Preparation of bamboo-based porous adsorption materials

[0043] 1-1) Potassium citrate, anhydrous potassium carbonate, and ammonium bicarbonate are prepared in a molar ratio of 1:1:1 to prepare an activator with a concentration of 15%;

[0044] 1-2) Mix the activator, KOH (5%), and distilled water in a ratio of 6 mg:2 mg:35 mL and sonicate for 15 minutes to obtain an activator solution.

[0045] 1-3) crushing and drying the bamboo material to obtain bamboo powder, uniformly mixing the bamboo powder with the activator solution at a ratio of 1 g:3 mL, standing for 28 hours, and then drying to obtain pretreated bamboo powder;

[0046] 1-4) placing the pretreated bamboo powder in a crucible, heating it to 650°C at a rate of 10°C / min at room temperature, activating it for 25 minutes, cooling it to room temperature, and then removing it. The product is washed with deionized water until neutral, then dried, cooled, ground, and finely sieved to obtain a bamboo-based porous adsorption material;

[0047] 2) Preparation of nickel-copper-chromium hydrotalcite

[0048] 2-1) Prepare solution A with a concentration of 4 mol / L by mixing Ni(NO3)2·6H2O, Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in a molar ratio of 2:1:1;

[0049] 2-2) Place the three-necked flask in a constant-temperature water bath at 65°C. Add Solution A and NaOH solution (1 mol / L) dropwise to the flask concurrently with strong stirring using a constant-pressure dropping funnel. Control the pH at 7. Add dropwise until Solution A is completely reacted.

[0050] 2-3) After the addition is complete, the mixture is allowed to stand and age for 35 minutes. The mixed slurry is transferred to a hydrothermal kettle and placed in an oven at 110-120°C for 6-6.5 hours. The mixture is then removed and washed with deionized water until neutral. The mixture is then dried in an oven at 110-120°C for 3-3.5 hours to obtain a nitrate-intercalated nickel-copper-chromium hydrotalcite.

[0051] 3) Preparation of catalyst precursor (nickel-copper-chromium hydrotalcite / bamboo-based porous adsorption material composite material)

[0052] 3-1) Dissolve the bamboo-based porous adsorbent material in water at a ratio of 1.5 g:100 mL, and stir the mixture magnetically to obtain a suspension of the bamboo-based porous adsorbent material;

[0053] 3-2) Adding nickel-copper-chromium hydrotalcite to a bamboo-based porous adsorbent suspension at a ratio of 10 g:100 mL, centrifuging the resulting mixture, washing, grinding, and drying to obtain a catalyst precursor;

[0054] 4) Preparation of catalyst

[0055] The catalyst precursor was heated to 550° C. at a rate of 8° C. / min and then calcined for 3 h to obtain a catalyst. Example 3

[0056] A method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran comprises the following steps:

[0057] 1) Preparation of bamboo-based porous adsorption materials

[0058] 1-1) Potassium citrate, anhydrous potassium carbonate, and ammonium bicarbonate are prepared in a molar ratio of 1:1:1 to prepare an activator with a concentration of 12.5%;

[0059] 1-2) Mix the activator, KOH (3.5%), and distilled water in a ratio of 4.5 mg:1.5 mg:30 mL and sonicate for 12 minutes to obtain an activator solution.

[0060] 1-3) crushing and drying the bamboo material to obtain bamboo powder, and uniformly mixing the bamboo powder with the activator solution at a ratio of 1 g:3 mL, allowing to stand for 24 hours, and then drying to obtain pretreated bamboo powder;

[0061] 1-4) placing the pretreated bamboo powder in a crucible, heating it to 625°C at a rate of 7.5°C / min at room temperature, activating it for 28 minutes, cooling it to room temperature, removing it, washing the product with deionized water until neutral, drying it, cooling it, grinding it, and sieving it to obtain a bamboo-based porous adsorption material;

[0062] 2) Preparation of nickel-copper-chromium hydrotalcite

[0063] 2-1) Prepare solution A with a concentration of 3 mol / L by mixing Ni(NO3)2·6H2O, Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in a molar ratio of 2:1:1;

[0064] 2-2) Place the three-necked flask in a constant-temperature water bath at 60°C. Add Solution A and NaOH solution (1 mol / L) dropwise to the flask concurrently with strong stirring using a constant-pressure dropping funnel. Control the pH at 6.5. Add dropwise until Solution A is completely reacted.

[0065] 2-3) After the addition is complete, the mixture is aged for 30 minutes, and then transferred to a hydrothermal kettle, placed in an oven at 115°C for 6 hours, removed, washed with deionized water until neutral, and dried in an oven at 115°C for 3 hours to obtain a nitrate-intercalated nickel-copper-chromium hydrotalcite.

[0066] 3) Preparation of catalyst precursor (nickel-copper-chromium hydrotalcite / bamboo-based porous adsorption material composite material)

[0067] 3-1) Dissolve the bamboo-based porous adsorbent material in water at a ratio of 1 g:100 mL and stir evenly with a magnetic stirrer to obtain a bamboo-based porous adsorbent material suspension;

[0068] 3-2) Adding nickel-copper-chromium hydrotalcite to a bamboo-based porous adsorbent suspension at a ratio of 9 g:100 mL, centrifuging the resulting mixture, washing, grinding, and drying to obtain a catalyst precursor;

[0069] 4) Preparation of catalyst

[0070] The catalyst precursor was heated to 500° C. at a rate of 6° C. / min and then calcined for 4.5 h to obtain a catalyst. Example 4

[0071] The catalyst prepared in Example 3 was used to catalyze the conversion of levulinic acid into 2-methyltetrahydrofuran.

[0072] After levulinic acid and the catalyst are evenly mixed, they are added to a reactor, and hydrogen is introduced into the reactor with a hydrogen pressure of 2-3 MPa. The reaction temperature is controlled at 190-210° C. and the reaction time is 4-7 hours.

[0073] Under the above reaction conditions, levulinic acid has high activity in the process of catalytic conversion to 2-methyltetrahydrofuran, and levulinic acid has high selectivity for 2-methyltetrahydrofuran, with a selectivity of approximately 85-90%.

Claims

1. A method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran, comprising the following steps: 1) Preparation of bamboo-based porous adsorption materials 1-1) Potassium citrate, anhydrous potassium carbonate, and ammonium bicarbonate are prepared into an activator in a molar ratio of 1:1:1; 1-2) Mixing the activator, KOH, and water and then ultrasonically treating the mixture to obtain an activator solution; 1-3) crushing and drying the bamboo material to obtain bamboo powder, uniformly mixing the bamboo powder with an activator solution, allowing the mixture to stand and then drying to obtain pretreated bamboo powder; 1-4) placing the pretreated bamboo powder in a crucible, activating it at 600-650° C. for 25-30 minutes, cooling it to room temperature, removing it, washing it to neutrality, drying it, cooling it, grinding it, and sieving it to obtain a bamboo-based porous adsorption material; 2) Preparation of nickel-copper-chromium hydrotalcite 2-1) Prepare solution A by mixing Ni(NO3)2·6H2O, Cu(NO3)2·3H2O and Cr(NO3)3·9H2O in a molar ratio of 2:1:1; 2-2) Place the three-necked flask in a constant temperature water bath at 60-65°C. Add Solution A and NaOH solution dropwise to the flask in parallel with vigorous stirring using a constant pressure dropping funnel. Control the pH to 6-7. Add solution dropwise until Solution A is completely reacted. 2-3) After the addition is complete, the mixture is stirred and aged for 30-35 minutes. The mixed slurry is transferred to a hydrothermal kettle for primary drying, washed to neutrality, and secondary drying to obtain a nitrate-intercalated nickel-copper-chromium hydrotalcite. 3) Preparation of catalyst precursor 3-1) dissolving the bamboo-based porous adsorbent material in water and stirring the mixture uniformly with a magnetic stirrer to obtain a bamboo-based porous adsorbent material suspension; 3-2) adding the nickel-copper-chromium hydrotalcite to a suspension of a bamboo-based porous adsorbent material, centrifuging the resulting mixture, washing, grinding, and drying to obtain a catalyst precursor; 4) Preparation of catalyst The catalyst precursor is calcined at 450-550° C. for 3-6 hours to obtain a catalyst.

2. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 1), the concentration of the activator is 10-15%, the concentration of KOH is 2-5%, the mixing ratio of the activator, KOH, and water is 3-6 mg:1-2 mg:25-35 mL, and the ultrasonic treatment time is 10-15 min.

3. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 1), the mixing ratio of the bamboo powder and the activator solution is 1 g: 3 ± 0.1 mL.

4. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 1), the crucible is heated to 600-650° C. at a rate of 5-10° C. / min.

5. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 2), the concentration of the solution A is 2-4 mol / L, and the concentration of the NaOH solution is 1 mol / L.

6. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 2), the primary drying is performed in an oven at 110-120° C. for 6-6.5 hours and then the product is taken out. The secondary drying is performed in an oven at 110-120° C. for 3-3.5 hours.

7. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, characterized in that: In step 3-1), the ratio of the bamboo-based porous adsorption material to water is 0.5-1.5 g:100 mL.

8. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 3-1), the ratio of nickel-copper-chromium hydrotalcite to bamboo-based porous adsorption material suspension is 8-10 g:100 mL.

9. The method for preparing a catalyst for converting levulinic acid into 2-methyltetrahydrofuran according to claim 1, wherein: In step 4), the temperature is raised to 450-550°C at a rate of 5-8°C / min.

10. The catalyst obtained according to the preparation method according to any one of claims 1 to 9.