Preparation method of biochar-based catalyst

Abstract

The invention discloses a preparation method of a charcoal-based catalyst. The preparation method comprises the following steps: by taking agricultural and forestry wastes as basic raw materials, carrying out crushing and high-temperature pyrolysis carbonization to form a biochar material with a large number of pore structures, carrying out nitrification and reduction treatment on the biochar to prepare amino-modified biochar, and loading a non-noble metal porphyrin precursor to the surface of the amino-modified biochar by virtue of an impregnation method, so as to obtain the porphyrin-modified biochar. And performing high-temperature pyrolysis on the non-noble metal porphyrin precursor-loaded biochar particles in an N2 atmosphere, and removing metal nanoparticles through acid treatment to obtain the biochar-based catalyst with an 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 number of lewis alkaline sites on the surface of the biochar can be increased through amino modification; the structure of the catalyst is an M-N-C structure, the M-N-C structure is stable, the structure has relatively high pyrolysis stability for the defect of metal loss caused by high-temperature pyrolysis of a common loading body, and the durability of the catalyst is ensured.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a method for preparing a biochar-based catalyst. Background Art

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

[0003] Chinese patent application CN109985623A proposes a Co / γ-Al2O3 catalyst for hydrogenation of levulinic acid, which uses a carrier γ-Al2O3 to load Co metal element, and has an MB structure. Preparation of carrier aluminum hydroxide slurry: A certain amount of high-purity metal aluminum beans and an appropriate amount of n-pentanol are added to a three-necked flask with a condenser reflux tube, heated to 135°C to initiate the reaction, and the reaction system is purged with nitrogen before heating. After the reaction is initiated, n-pentanol is continued to be added until the aluminum beans react completely to obtain a mixture of n-pentanol and n-pentyl aluminum. The molar ratio of n-pentanol to metal aluminum during the synthesis process is 3.3:1. The synthesized n-pentyl aluminum is heated to 90°C, and deionized water at the same temperature is added under stirring for hydrolysis. After the hydrolysis is completed, n-pentanol is separated to obtain a pseudo-boehmite slurry with a pH value of 9. In practical applications, the cost of the carrier is too high and the preparation process is cumbersome. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a biochar-based catalyst, which has a simple preparation process and low cost.

[0005] The present invention uses agricultural and forestry waste as the basic raw material, forms a biochar material with a large number of pore structures by crushing and high-temperature pyrolysis carbonization, performs nitrification and reduction treatment on the biochar to prepare amino-modified biochar, and then loads the non-precious metal porphyrin precursor onto the surface of the amino-modified biochar by an impregnation method, and then performs high-temperature pyrolysis on the biochar particles loaded with the non-precious metal porphyrin precursor under a N2 atmosphere, and then removes the metal nanoparticles by acid treatment to obtain a biochar-based non-precious metal single-atom catalyst with a stable MNC structure. M is selected from non-precious metals (such as: Cu, Ni, etc.). The core of the MNC structure is the central metal atom (M) and the in-plane coordination atoms (N and C in most cases), forming a coordination structure as an active site, such as a site configured by M-N4.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a biochar-based catalyst comprises the following steps: (1) The agricultural and forestry waste is crushed by a crusher and then passed through a 50-100 mesh sieve to obtain biomass powder; (2) carbonizing the biomass powder in a muffle furnace, introducing N2, heating the furnace to 400-600°C at a heating rate of 4.5-5.5°C / min, and maintaining the temperature for 3-3.5 hours to obtain biochar; (3) cooling the biochar at room temperature for 24 to 26 hours, then grinding the biochar with a planetary ball mill, and then sifting through a 200 to 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, and filter to obtain biochar powder B; (5) Dissolve lysine in ethanol as a solvent to obtain a lysine solution with a concentration of 3-4 mol / L, put the lysine solution and biochar powder B in a magnetic stirrer at a mass ratio of 9-10:1, stir in a cold bath magnetic stirrer for 1-2 h, and then filter with a glass container to obtain product A; (6) Drying product A, washing it with deionized water for 3-4 times, and drying it at 45-55°C for 5.5-6.5 h to obtain product B; (7) Product B is placed in a flask, and 3-4 mol / L acetic acid is added to the flask at a solid-liquid mass ratio of 1:15-1:20. The solution is then refluxed at 95-105°C for 4.5-5.5 h to obtain product C. (8) Cooling the product C, collecting the amino-modified biochar by vacuum filtration, and finally drying it at 30-60 °C for 5.5-6.5 h; (9) Add the amino-modified biochar and non-precious metal porphyrin in a mass ratio of 10:1 to 5:1 into a beaker containing 50 mL of N,N-dimethylformamide solution (DMF solution), and then stir magnetically for 30 to 45 minutes to obtain a solid-liquid mixture; (10) The solid-liquid mixture is transferred to a reaction kettle and reacted in a drying oven at 150-180°C for 7-9 hours. After the drying oven is cooled to room temperature naturally, the reaction kettle is taken out and the suspension is poured out; (11) The suspension is filtered to separate the solid, the solid is washed with deionized water for 3-4 times, and dried at 30-60 °C for 10-14 h to obtain a biochar-based non-precious single atom catalyst.

[0007] Furthermore, the agricultural and forestry wastes are straw, stumps, weeds, fallen leaves, fruit shells, vines, branches and the like.

[0008] Furthermore, the non-precious metal porphyrin is Cu porphyrin, Ni porphyrin and the like.

[0009] Furthermore, the biochar-based catalyst is used for hydrogenation of levulinic acid to prepare γ-valerolactone.

[0010] The present invention adopts the above technical scheme, uses agricultural and forestry waste to prepare biochar, and after amino modification of the biochar, loads the non-precious metal porphyrin precursor onto the surface of the biochar, and then pyrolyzes the biochar particles loaded with non-precious metal porphyrin at high temperature under N2 atmosphere, removes the metal nanoparticles by acid treatment, and obtains a biochar-based non-precious metal single-atom catalyst with a stable MNC structure. The present invention has the following advantages: 1. In the preparation of biochar, a planetary ball mill is used for grinding to increase the specific surface area of ​​the biochar. By modifying the amino group of the biochar, the amide bond covalent bond formed by the amino group of the biochar and the hydroxyl group of the porphyrin is used to improve the adhesion between the biochar and the porphyrin, reduce the effect of metal loss and metal thermal aggregation, and disperse the active metal sites on the biochar carrier.

[0011] 2. The present invention improves the amino modification process. First, weaker hypochlorous acid is used to replace the concentrated sulfuric acid solution commonly used for acidification to acidify the biochar, and then a safer amino acid (lysine) is used to replace the concentrated sulfuric acid and concentrated nitric acid mixture commonly used for amino modification. After washing with deionized water, it is washed again with acetic acid and activated to increase the loading rate and adhesion degree for the next step of loading porphyrin.

[0012] 3. Compared with the existing preparation method of levulinic acid catalyst, this method can effectively save the cost of the original catalyst support (such as SiO 2、 Al2O3, etc.), and the basic raw materials of this method are relatively easy to obtain.

[0013] 4. Unlike existing catalyst supports, biochar with MNC structure has high catalytic stability, which can prevent the loss of active metals that catalyze the hydrogenation of levulinic acid and the thermal aggregation of metals due to pyrolysis. MNC structured biochar-based catalysts also have high catalytic activity of non-precious metal nitrogen atoms and high specific surface area brought by the porous structure of biochar.

[0014] 5. The cost of the carrier of the catalyst of the present invention is lower, the specific surface area of ​​the carrier biochar is larger, and the Lewis basic sites on the surface of the biochar can be increased after amino modification, and the preparation process is simpler than that of γ-Al2O3.

[0015] 6. The catalyst structure of the present invention is an MNC structure. The MNC structure is stable. With respect to the defect that high-temperature pyrolysis of a conventional carrier causes metal loss, the present structure has relatively high pyrolysis stability, thus ensuring the durability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The reaction pathway for the conversion of LA to GVL.

[0017] Figure 2 It is the structural formula of metalloporphyrin.

[0018] Figure 3 It is an MNC structure.

[0019] Figure 4 Schematic diagram of the process flow of biochar-based non-precious metal single-atom catalysts. DETAILED DESCRIPTION Example 1

[0020] A method for preparing a biochar-based catalyst comprises the following steps: (1) The agricultural and forestry waste is crushed by a crusher and passed through an 80-mesh sieve to obtain biomass powder; (2) carbonizing the biomass powder in a muffle furnace, introducing N2, heating the furnace to 500°C at a heating rate of 5°C / min, and maintaining the temperature for 3.2 hours to obtain biochar; (3) Cool and stand at room temperature for 25 h, then grind the biochar with a planetary ball mill and pass it through a 250-mesh sieve to obtain biochar powder A; (4) Add biochar powder A to 3.5 mol / L hypochlorous acid at a solid-liquid mass ratio of 1:8, stir magnetically for 40 min, and filter to obtain biochar powder B; (5) Dissolving lysine in ethanol as a solvent to obtain a lysine solution with a concentration of 3.5 mol / L, placing the lysine solution and biochar powder B in a magnetic stirrer at a mass ratio of 9.5:1, performing cold bath magnetic stirring for 1.5 h, and then filtering with a glass container to obtain product A; (6) Drying product A, washing it with deionized water three times, and drying it at 50 °C for 6 h to obtain product B; (7) Product B was placed in a flask, and 3.5 mol / L acetic acid was added to the flask at a solid-liquid mass ratio of 1:18. The solution was then refluxed at 100 °C for 5 h to obtain product C. (8) Cooling the product C, collecting the amino-modified biochar by vacuum filtration, and finally drying it at 45 °C for 6 h; (9) Add the amino-modified biochar and Cu porphyrin in a mass ratio of 17.5:1 into a beaker containing 50 mL of DMF solution, and then stir magnetically for 40 min to obtain a solid-liquid mixture; (10) The solid-liquid mixture is transferred to a reaction kettle and reacted in a drying oven at 175°C for 8 hours. After the drying oven cools down to room temperature naturally, the reaction kettle is taken out and the suspension is poured out; (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 h to obtain a biochar-based non-precious single atom catalyst. Example 2

[0021] A method for preparing a biochar-based catalyst comprises the following steps: (1) The agricultural and forestry waste is crushed by a crusher and passed through a 50-mesh sieve to obtain biomass powder; (2) carbonizing the biomass powder in a muffle furnace, introducing N2, heating the furnace to 400°C at a heating rate of 4.5°C / min, and maintaining the temperature for 3.5 hours to obtain biochar; (3) Cool and stand at room temperature for 24 h, then grind the biochar with a planetary ball mill and pass it through a 200-mesh sieve to obtain biochar powder A; (4) Add biochar powder A to 3 mol / L hypochlorous acid at a solid-liquid mass ratio of 1:6, stir magnetically for 30 min, and filter to obtain biochar powder B; (5) dissolving lysine in ethanol as a solvent to obtain a lysine solution with a concentration of 3 mol / L, placing the lysine solution and biochar powder B in a magnetic stirrer at a mass ratio of 9:1, performing cold bath magnetic stirring for 1 h, and then filtering with a glass container to obtain product A; (6) Product A was dried, washed with deionized water three times, and then dried at 45 °C for 6.5 h to obtain product B; (7) Product B was placed in a flask, and 3 mol / L acetic acid was added to the flask at a solid-liquid mass ratio of 1:15. The solution was then refluxed at 95 °C for 5.5 h to obtain product C. (8) Cooling the product C, collecting the amino-modified biochar by vacuum filtration, and finally drying it at 30 °C for 6.5 h; (9) Add the amino-modified biochar and Ni-porphyrin in a mass ratio of 10:1 into a beaker containing 50 mL of DMF solution, and then stir magnetically for 30 min to obtain a solid-liquid mixture; (10) The solid-liquid mixture was transferred to a reaction kettle and reacted in a drying oven at 150° C. for 9 h. After the drying oven naturally cooled to room temperature, the reaction kettle was taken out and the suspension was poured out; (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 h to obtain a biochar-based non-precious single atom catalyst. Example 3

[0022] A method for preparing a biochar-based catalyst comprises the following steps: (1) The agricultural and forestry waste is crushed by a crusher and passed through a 100-mesh sieve to obtain biomass powder; (2) carbonizing the biomass powder in a muffle furnace, introducing N2, heating the furnace to 600°C at a heating rate of 5.5°C / min, and maintaining the temperature for 3 hours to obtain biochar; (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; (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, and filter to obtain biochar powder B; (5) Using ethanol as a solvent to dissolve lysine to obtain a lysine solution with a concentration of 4 mol / L, the lysine solution and biochar powder B were placed in a magnetic stirrer at a mass ratio of 10:1, and magnetically stirred in a cold bath for 2 h, and then filtered using a glass container to obtain product A; (6) Product A was dried, washed with deionized water 4 times, and dried at 55°C for 5.5 h to obtain product B; (7) Product B was placed in a flask, and 4 mol / L acetic acid was added to the flask at a solid-liquid mass ratio of 1:20. The solution was then refluxed at 105 °C for 4.5 h to obtain product C. (8) Cooling the product C, collecting the amino-modified biochar by vacuum filtration, and finally drying it at 60 °C for 5.5 h; (9) Add the amino-modified biochar and Cu porphyrin in a mass ratio of 5:1 into a beaker containing 50 mL of DMF solution, and then stir magnetically for 45 min to obtain a solid-liquid mixture; (10) The solid-liquid mixture is transferred to a reaction kettle and reacted in a drying oven at 180°C for 7 hours. After the drying oven cools down to room temperature naturally, the reaction kettle is taken out and the suspension is poured out; (11) The suspension was filtered to separate the solid, the solid was washed with deionized water for 4 times, and dried at 60 °C for 10 h to obtain a biochar-based non-precious single atom catalyst. Example 4

[0023] Application of biochar-based catalyst in hydrogenation of levulinic acid to γ-valerolactone The hydrogenation reaction of levulinic acid to γ-valerolactone was carried out in a 100 ml reactor. The reaction liquid was 50 ml~100 ml of isopropanol solution, and the mass ratio of levulinic acid to biochar-based catalyst was 50:3. The reactor was purged with N2 for 5 times under standard atmospheric pressure, heated to a predetermined temperature of 150~200 ℃, and magnetically stirred at 400~600rpm. Results: The conversion rate of levulinic acid was 95.0~99.0%, of which the selectivity of γ-valerolactone was 96.0~99.0%.

Claims

1. A method for preparing a biochar-based catalyst, characterized in that: The following steps are involved: (1) The agricultural and forestry waste is crushed by a crusher and then passed through a 50-100 mesh sieve to obtain biomass powder; (2) placing the biomass powder in a muffle furnace, introducing N2, heating the furnace to 400-600°C and maintaining the temperature for 3-3.5 hours to obtain biochar; (3) After cooling the biochar, grinding it with a planetary ball mill, and then passing 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, and filter to obtain biochar powder B; (5) Place a lysine solution with a concentration of 3-4 mol / L and biochar powder B in a mass ratio of 9-10:1 into a magnetic stirrer, stir in a cold bath for 1-2 h, and then filter to obtain product A; (6) Drying and washing product A, and then drying again to obtain product B; (7) Product B is placed in a flask, and 3-4 mol / L acetic acid is added to the flask at a solid-liquid mass ratio of 1:15-1:

20. The solution is then refluxed at 95-105°C for 4.5-5.5 h to obtain product C. (8) cooling the product C, collecting the amino-modified biochar by vacuum filtration, and drying it; (9) Adding the amino-modified biochar and the non-precious metal porphyrin in a mass ratio of 10:1 to 5:1 into a beaker containing N,N-dimethylformamide solution, and then magnetically stirring for 30 to 45 minutes to obtain a solid-liquid mixture; (10) The solid-liquid mixture is transferred to a reaction kettle and reacted in a drying oven at 150-180° C. for 7-9 hours. After the drying oven cools down to room temperature naturally, the reaction kettle is taken out and the suspension is poured out; (11) The suspension is filtered to separate the solid, which is then washed and dried to obtain a biochar-based non-precious 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 waste is straw, stumps, 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°C / 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 standing and cooling 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 performed by washing with deionized water for 3-4 times, and the drying is performed at 45-55° C. 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 performed at 30-60° C. for 5.5-6.5 h.

7. The method for preparing a biochar-based catalyst according to claim 1, characterized in that: In step (9), the non-precious 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 are washing the solid with deionized water for 3-4 times and then drying at 30-60°C for 10-14h.

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

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