A method of preparing a biochar-based catalyst

Abstract

The application discloses a preparation method of a biochar-based catalyst. The method comprises the following steps: taking agroforestry waste as a basic raw material, crushing, high-temperature pyrolysis and carbonization to form biochar material with a large number of pore structures, nitration and reduction treatment of the biochar to prepare amino-modified modified biochar, impregnation of non-noble metal porphyrin precursors on the surface of the amino-modified modified biochar, high-temperature pyrolysis of the biochar particles loaded with the non-noble metal porphyrin precursors in an N2 atmosphere, removal of metal nanoparticles through acid treatment, and obtaining the biochar-based catalyst with a M-N-C stable structure. The carrier cost of the catalyst is low, the specific surface area of the carrier biochar is large, and the Lewis basic sites on the surface of the biochar can be increased through amino modification. The catalyst structure is M-N-C structure, the M-N-C structure is stable, the structure has relatively high pyrolysis stability, and the durability of the catalyst is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts, in particular to a preparation method of a biochar-based catalyst. BACKGROUND

[0002] γ GVL has a wide range of applications, such as solvent, food additive and liquid fuel, and can also be used to synthesize 1,4-pentanediol and 2-methyltetrahydrofuran and other basic chemical raw materials. In recent years, many researchers have found that GVL has many potential new uses. In the heterogeneous catalytic process of converting levulinic acid (LA) into GVL, there are usually two reaction pathways, which mainly depend on the reaction conditions controlled during the reaction and the catalyst used. As shown in FIG. 1, (1) in an aqueous system, hydrogenation process is easy to occur at a lower temperature, promoting the conversion of LA into 4-hydroxyvaleric acid, which is then dehydrated to form GVL under the action of a catalyst; (2) at a higher temperature, LA is first dehydrated to form angelica lactone, which is hydrogenated to obtain GVL. In fact, hydrogenation and dehydration can occur in either pathway, but the order of the two processes is different under different control conditions. The catalyst of the present application is mainly used to improve the selectivity of the hydrogenation process of pathway (1).

[0003] Chinese patent application CN109985623A proposes a Co / γ-Al2O3 catalyst for hydrogenation of levulinic acid, which applies a carrier γ-Al2O3 to load Co metal element, and has a structure of M-B type. The carrier aluminum hydroxide slurry is prepared by adding a certain amount of high-purity metal aluminum beans and an appropriate amount of n-pentanol into a three-necked flask with a condensation reflux tube, heating to 135℃ until the reaction is initiated, and purging the reaction system with nitrogen before heating. After the reaction is initiated, n-pentanol is continuously added until the aluminum beans are completely reacted, and a mixed solution of n-pentanol and n-pentyloxy aluminum is obtained. The molar ratio of n-pentanol to metal aluminum during synthesis is 3.3:1. The synthesized n-pentyloxy aluminum is heated to 90℃, and deionized water at the same temperature is added under stirring for hydrolysis. After hydrolysis is completed, n-pentanol is separated out, and a pseudo-boehmite slurry is obtained, which has a pH value of 9. In actual application, the cost of the carrier is too high, and the preparation process is complicated. SUMMARY

[0004] The present application aims to provide a preparation method of a biochar-based catalyst, which has a simple preparation process and low cost.

[0005] This invention uses agricultural and forestry waste as the basic raw material. Through crushing and high-temperature pyrolysis carbonization, a biochar material with a large number of pores is formed. The biochar is then subjected to nitration and reduction treatment to produce amino-modified biochar. A non-precious metal porphyrin precursor is then loaded onto the surface of the amino-modified biochar via impregnation. The biochar particles loaded with the non-precious metal porphyrin precursor are then subjected to high-temperature pyrolysis under a N2 atmosphere. After acid treatment, the metal nanoparticles are removed to obtain a biochar-based non-precious metal single-atom catalyst with a stable MNC structure. M is selected from non-precious metals (e.g., Cu, Ni). The core of the MNC structure is the central metal atom (M) and in-plane coordinating atoms (most often N and C), forming a coordination structure as active sites, such as the M-N4 configuration.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a biochar-based catalyst includes the following steps:

[0008] (1) After crushing agricultural and forestry waste in a pulverizer, it is passed through a 50-100 mesh sieve to obtain biomass powder;

[0009] (2) Carbonize the biomass powder in a muffle furnace, introduce N2, heat it to 400-600°C at a heating rate of 4.5-5.5°C / min, and maintain the temperature for 3-3.5 hours to obtain biochar;

[0010] (3) The biochar was cooled and allowed to stand at room temperature for 24-26 h, then ground with a planetary ball mill, and then passed through a 200-300 mesh sieve to obtain biochar powder A;

[0011] (4) Add biochar powder A to hypochlorous acid with a concentration of 3~4 mol / L at a solid-liquid mass ratio of 1:6-1:10, stir magnetically for 30~50 min, filter, and obtain biochar powder B;

[0012] (5) Dissolve lysine in ethanol to obtain a lysine solution with a concentration of 3-4 mol / L. Put the lysine solution and biochar powder B into a magnetic stirrer at a mass ratio of 9-10:1 and perform cold bath magnetic stirring for 1-2 h. Then filter the mixture in a glass container to obtain product A.

[0013] (6) Dry product A, wash it with deionized water 3-4 times, and then dry it at 45-55℃ for 5.5-6.5 h to obtain product B;

[0014] (7) Place product B into a flask, add acetic acid with a concentration of 3-4 mol / L at a solid-liquid mass ratio of 1:15-1:20, and then reflux the solution at a temperature of 95-105℃ for 4.5-5.5 h to obtain product C;

[0015] (8) Cool product C, collect amino-modified biochar by vacuum filtration, and finally dry it at 30~60℃ for 5.5~6.5h;

[0016] (9) Add amino-modified biochar and non-precious metal porphyrin in a mass ratio of 10:1 to 5:1 to a beaker containing 50 mL of N,N-dimethylformamide solution (DMF solution), and then stir magnetically for 30 to 45 min to obtain a solid-liquid mixture;

[0017] (10) Transfer the solid-liquid mixture to a reaction vessel and react it in a drying oven at 150~180 ℃ for 7~9 h. After the drying oven naturally cools to room temperature, remove the reaction vessel and pour out the suspension.

[0018] (11) The suspension is filtered to separate the solid, the solid is washed with deionized water 3-4 times, and dried at 30-60 °C for 10-14 h to obtain a biochar-based non-noble single-atom catalyst.

[0019] Furthermore, the agricultural and forestry waste mentioned includes straw, plant debris, weeds, fallen leaves, fruit shells, vines, branches, etc.

[0020] Furthermore, the non-noble metal porphyrin is Cu porphyrin, Ni porphyrin, etc.

[0021] Furthermore, the biochar-based catalyst is used for the hydrogenation of levulinic acid to prepare γ-valerolactone.

[0022] This invention employs the above technical solution to prepare biochar from agricultural and forestry waste. After amino-modification of the biochar, a non-precious metal porphyrin precursor is loaded onto the surface of the biochar. The biochar particles loaded with the non-precious metal porphyrin are then subjected to high-temperature pyrolysis under a N2 atmosphere. Following acid treatment, metal nanoparticles are removed to obtain a biochar-based non-precious metal single-atom catalyst with a stable MNC structure. This invention has the following advantages:

[0023] 1. In the preparation of biochar, a planetary ball mill is used for grinding to increase the specific surface area of ​​biochar. By modifying the biochar with amino groups, the covalent bonds formed by the amino groups of biochar and the hydroxyl groups of porphyrin are used to improve the adhesion between biochar and porphyrin, reduce the effects of metal loss and metal thermal accumulation, and disperse the active metal sites on the biochar carrier.

[0024] 2. This invention improves the amino-modification process. First, the biochar is acidified by replacing the concentrated sulfuric acid solution commonly used for acidification with the weaker acid hypochlorous acid. Then, the safer amino acid (lysine) is used to replace the mixture of concentrated sulfuric acid and concentrated nitric acid commonly used for amino-modification. After washing with deionized water, the biochar is washed and activated again with acetic acid, which improves the loading rate and adhesion of the porphyrin in the next step.

[0025] 3. Compared with existing methods for preparing levulinic acid catalysts, this method can effectively save on the cost of the original catalyst loading material (such as SiO₂). 2、 Al2O3, etc.), and the basic raw materials for this method are relatively easy to obtain.

[0026] 4. Unlike existing catalyst supports, biochar with a MNC structure exhibits high catalytic stability, preventing the loss of active metals involved in the hydrogenation of levulinic acid due to pyrolysis and the accumulation of metals due to thermal stress. Biochar-based catalysts with an MNC structure also possess high catalytic activity from non-precious metal nitrogen atoms and a high specific surface area due to the porous structure of biochar.

[0027] 5. The catalyst of this invention has a lower cost support, a larger specific surface area of ​​biochar support, and can increase Lewis basic sites on the surface of biochar through amino modification. Moreover, the preparation process is simpler than that of γ-Al2O3.

[0028] 6. The catalyst structure of the present invention is an MNC structure. The MNC structure is stable and has relatively high pyrolysis stability, which is a defect caused by metal loss due to high temperature pyrolysis of conventional supports, thus ensuring the durability of the catalyst. Attached Figure Description

[0029] Figure 1 The reaction pathway for the conversion of LA to GVL.

[0030] Figure 2 This is the structural formula for a metalloporphyrin.

[0031] Figure 3 It is an MNC structure.

[0032] Figure 4 This is a schematic diagram of the process flow for biochar-based non-precious metal single-atom catalysts. Detailed Implementation Example 1

[0033] A method for preparing a biochar-based catalyst includes the following steps:

[0034] (1) After the agricultural and forestry waste is crushed by a crusher, it is passed through an 80-mesh sieve to obtain biomass powder;

[0035] (2) The biomass powder was carbonized in a muffle furnace, N2 was introduced, the temperature was raised to 500°C at a heating rate of 5°C / min, and the temperature was maintained for 3.2h to obtain biochar;

[0036] (3) Cool and stand at room temperature for 25 h, then grind the biochar with a planetary ball mill, and then pass it through a 250-mesh sieve to obtain biochar powder A;

[0037] (4) Add biochar powder A to hypochlorous acid with a concentration of 3.5 mol / L at a solid-liquid mass ratio of 1:8, stir magnetically for 40 min, filter, and obtain biochar powder B;

[0038] (5) Lysine was dissolved in ethanol to obtain a lysine solution with a concentration of 3.5 mol / L. The lysine solution and biochar powder B were placed in a magnetic stirrer at a mass ratio of 9.5:1 and stirred magnetically in a cold bath for 1.5 h. Then the mixture was filtered through a glass container to obtain product A.

[0039] (6) Dry product A, wash it three times with deionized water, and then dry it at 50°C for 6 hours to obtain product B;

[0040] (7) Place product B into a flask, add acetic acid with a concentration of 3.5 mol / L at a solid-liquid mass ratio of 1:18, and then reflux the solution at 100℃ for 5 h to obtain product C;

[0041] (8) Cool product C, collect amino-modified biochar by vacuum filtration, and finally dry it at 45°C for 6 hours;

[0042] (9) Add amino-modified biochar and Cu porphyrin to a beaker containing 50 mL of DMF solution at a mass ratio of 17.5:1, and then stir magnetically for 40 min to obtain a solid-liquid mixture;

[0043] (10) Transfer the solid-liquid mixture to a reaction vessel and react in a drying oven at 175°C for 8 hours. After the drying oven has cooled to room temperature, remove the reaction vessel and pour out the suspension.

[0044] (11) The suspension was filtered to separate the solid, the solid was washed three times with deionized water, and dried at 45°C for 12 hours to obtain a biochar-based non-noble single-atom catalyst. Example 2

[0045] A method for preparing a biochar-based catalyst includes the following steps:

[0046] (1) After crushing agricultural and forestry waste in a pulverizer, it is passed through a 50-mesh sieve to obtain biomass powder;

[0047] (2) The biomass powder is carbonized in a muffle furnace, N2 is introduced, the temperature is raised to 400°C at a heating rate of 4.5°C / min, and the temperature is maintained for 3.5h to obtain biochar;

[0048] (3) Cool and stand at room temperature for 24 h, then grind the biochar with a planetary ball mill, and then pass it through a 200-mesh sieve to obtain biochar powder A;

[0049] (4) Add biochar powder A to hypochlorous acid with a concentration of 3 mol / L at a solid-liquid mass ratio of 1:6, stir magnetically for 30 min, filter, and obtain biochar powder B;

[0050] (5) Dissolve lysine in ethanol to obtain a lysine solution with a concentration of 3 mol / L. Put the lysine solution and biochar powder B into a magnetic stirrer at a mass ratio of 9:1 and perform cold bath magnetic stirring for 1-h. Then filter the mixture in a glass container to obtain product A.

[0051] (6) Dry product A, wash it three times with deionized water, and then dry it at 45°C for 6.5 h to obtain product B;

[0052] (7) Place product B into a flask, add acetic acid with a concentration of 3 mol / L at a solid-liquid mass ratio of 1:15, and then reflux the solution at 95°C for 5.5 h to obtain product C;

[0053] (8) Cool product C, collect amino-modified biochar by vacuum filtration, and finally dry it at 30°C for 6.5 h;

[0054] (9) Add amino-modified biochar and Ni porphyrin to a beaker containing 50 mL DMF solution at a mass ratio of 10:1, and then stir magnetically for 30 min to obtain a solid-liquid mixture;

[0055] (10) Transfer the solid-liquid mixture to a reaction vessel and react in a drying oven at 150°C for 9 hours. After the drying oven has cooled to room temperature, remove the reaction vessel and pour out the suspension.

[0056] (11) The suspension was filtered to separate the solid, the solid was washed three times with deionized water, and dried at 30°C for 14 hours to obtain a biochar-based non-noble single-atom catalyst. Example 3

[0057] A method for preparing a biochar-based catalyst includes the following steps:

[0058] (1) After crushing agricultural and forestry waste in a pulverizer, it is passed through a 100-mesh sieve to obtain biomass powder;

[0059] (2) The biomass powder is carbonized in a muffle furnace, N2 is introduced, the temperature is raised to 600°C at a heating rate of 5.5°C / min, and the temperature is maintained for 3 hours to obtain biochar;

[0060] (3) Cool and stand at room temperature for 26 h, then grind the biochar with a planetary ball mill and pass it through a 300-mesh sieve to obtain biochar powder A;

[0061] (4) Add biochar powder A to hypochlorous acid with a concentration of 4 mol / L at a solid-liquid mass ratio of 1:10, stir magnetically for 50 min, filter, and obtain biochar powder B;

[0062] (5) Dissolve lysine in ethanol to obtain a lysine solution with a concentration of 4 mol / L. Put the lysine solution and biochar powder B into a magnetic stirrer at a mass ratio of 10:1 and perform cold bath magnetic stirring for 2 hours. Then filter the mixture in a glass container to obtain product A.

[0063] (6) Dry product A, wash it 4 times with deionized water, and then dry it at 55°C for 5.5 h to obtain product B;

[0064] (7) Place product B into a flask, add acetic acid with a concentration of 4 mol / L at a solid-liquid mass ratio of 1:20, and then reflux the solution at 105℃ for 4.5 h to obtain product C;

[0065] (8) Cool product C, collect amino-modified biochar by vacuum filtration, and finally dry it at 60°C for 5.5 h;

[0066] (9) Add amino-modified biochar and Cu porphyrin to a beaker containing 50 mL DMF solution at a mass ratio of 5:1, and then stir magnetically for 45 min to obtain a solid-liquid mixture;

[0067] (10) Transfer the solid-liquid mixture to a reaction vessel and react in a drying oven at 180°C for 7 hours. After the drying oven has cooled to room temperature, remove the reaction vessel and pour out the suspension.

[0068] (11) The suspension was filtered to separate the solid, the solid was washed with deionized water 4 times, and dried at 60 °C for 10 h to obtain a biochar-based non-noble single-atom catalyst. Example 4

[0069] Application of biochar-based catalysts in the hydrogenation of levulinic acid to γ-valerol

[0070] The hydrogenation of levulinic acid to γ-valerolactone was carried out in a 100 ml reactor with 50-100 ml of isopropanol solution as the reaction solution. The mass ratio of levulinic acid to biochar-based catalyst was 50:3. The reactor was purged five times with N2 under standard atmospheric pressure and heated to a predetermined temperature of 150-200 °C with magnetic stirring at 400-600 rpm. Results showed that the conversion rate of levulinic acid was 95.0-99.0%, with a selectivity of 96.0-99.0% for γ-valerolactone.

Claims

1. A method for preparing a biochar-based catalyst, characterized in that, Includes the following steps: (1) After crushing agricultural and forestry waste in a pulverizer, it is passed through a 50-100 mesh sieve to obtain biomass powder; (2) The biomass powder is placed in a muffle furnace, N2 is introduced, the temperature is raised to 400~600℃ and maintained at this temperature for 3~3.5h to obtain biochar; (3) After cooling the biochar, grind it with a planetary ball mill and then pass it through a 200-300 mesh sieve to obtain biochar powder A; (4) Add biochar powder A to hypochlorous acid with a concentration of 3~4 mol / L at a solid-liquid mass ratio of 1:6-1:10, stir magnetically for 30~50 min, filter, and obtain biochar powder B; (5) A lysine solution with a concentration of 3-4 mol / L and biochar powder B are placed in a magnetic stirrer at a mass ratio of 9-10:1 and stirred magnetically in a cold bath for 1-2 h. Then the mixture is filtered to obtain product A. (6) After drying and washing product A, it is dried again to obtain product B; (7) Place product B into a flask, add acetic acid with a concentration of 3-4 mol / L at a solid-liquid mass ratio of 1:15-1:20, and then reflux the solution at a temperature of 95-105℃ for 4.5-5.5 h to obtain product C; (8) Cool product C, collect amino-modified biochar by vacuum filtration, and dry it; (9) Add amino-modified biochar and non-precious metal porphyrin to a beaker containing N,N-dimethylformamide solution at a mass ratio of 10:1 to 5:1, and then stir magnetically for 30 to 45 minutes to obtain a solid-liquid mixture; (10) Transfer the solid-liquid mixture to a reaction vessel and react it in a drying oven at 150~180℃ for 7~9h. After the drying oven naturally cools to room temperature, remove the reaction vessel and pour out the suspension. (11) The suspension is filtered to separate the solid, washed and dried to obtain a biochar-based non-noble single-atom catalyst.

2. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (1), the agricultural and forestry wastes are straw, plant debris, weeds, fallen leaves, fruit shells, vines or branches.

3. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (2), the heating rate is 4.5~5.5℃ / min.

4. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (3), the cooling is performed by allowing the water to stand at room temperature for 24 to 26 hours.

5. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (6), the washing is done by washing with deionized water 3-4 times, and the drying is done at 45-55℃ for 5.5-6.5 h.

6. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (8), the drying is carried out at 30~60℃ for 5.5~6.5h.

7. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (9), the non-noble metal porphyrin is Cu porphyrin or Ni porphyrin.

8. The method for preparing a biochar-based catalyst according to claim 1, characterized in that, In step (11), the washing and drying process involves washing the solid with deionized water 3-4 times and then drying it at 30-60 ℃ for 10-14 hours.

9. The application of the biochar-based catalyst obtained by the preparation method according to any one of claims 1 to 8 in the hydrogenation of levulinic acid to prepare γ-valerol.

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