Ni-mofc catalyst for cracking tar and preparation method and application thereof

Abstract

Ni-MOFC catalyst for cracking tar and its preparation method and application. The present application belongs to the technical field of tar catalytic cracking. The present application is to solve the problem that the catalytic performance of the nickel-based catalyst will decrease seriously during long-term operation, and even cause catalyst deactivation. The method of the present application: taking biomass as the substrate, using two-step carbonization combined with KOH activation to prepare pyrolytic carbon; taking pyrolytic carbon, nickel salt, imidazole and benzene tricarboxylic acid as the substrate for solvothermal reaction, and then pyrolyzing to obtain the catalyst. The obtained catalyst combines the active metal nickel and the carrier in situ, and the nano nickel particles on the inner and outer surfaces of the carrier are uniformly coated as the active center and the support node, the active porous carbon is used as the MOFC carbon base, the interaction between nickel and the carrier is enhanced, the reaction activity and high-temperature anti-inactivation performance of the catalyst are improved, and the catalytic removal of biomass pyrolysis tar is realized. It is suitable for catalytic pyrolysis treatment of tar and resource recovery.

Description

Technical Field

[0001] This invention belongs to the field of tar catalytic cracking technology, specifically relating to a Ni-MOFC catalyst for cracking tar, its preparation method, and its application. Background Technology

[0002] High-efficiency, low-carbon biomass treatment technology has become a major strategic need for the biomass resource utilization industry, and biomass pyrolysis is considered one of the most promising technologies for achieving high-value utilization of biomass. However, biomass pyrolysis produces a mixture of various condensable high-molecular-weight organic compounds—biomass pyrolysis tar. This tar is rich in toxic and harmful organic compounds such as polycyclic aromatic hydrocarbons (PAHs), phenols, pyridines, and furans. Tar byproducts can clog pipelines, corrode equipment, reduce the energy conversion rate of organic matter gasification, and pollute the environment. Its efficient removal has become a bottleneck problem for the industrial application of biomass pyrolysis technology.

[0003] Nickel-based catalytic cracking, which has developed rapidly in recent years, is considered a highly efficient, low-pollution, and sustainable tar removal technology. It significantly lowers the activation energy of the reaction, increases the tar cracking rate, and converts tar pollutants into small-molecule combustible gases under high-temperature conditions (500℃~800℃), reducing tar toxicity and significantly lowering energy consumption and equipment requirements. This represents a cutting-edge direction in biomass pyrolysis tar treatment technology. However, the catalytic performance of nickel-based catalysts deteriorates significantly during long-term operation, even leading to catalyst deactivation and a substantial reduction in catalytic efficiency. The low sintering temperature of metallic nickel makes it prone to sintering at high temperatures, reducing the number of active sites and interfacial activity. Furthermore, the strong affinity between carbocations generated during tar cracking and nickel metal leads to carbon deposition on the catalyst surface. Excessive carbon buildup severely blocks the active sites of the nickel-based catalyst, hindering the synergistic catalytic activity between the metal and the support, and ultimately impeding the efficient tar catalytic cracking reaction. Improving the reactivity of nickel-based catalysts and preparing high-performance, deactivated nickel-based tar cracking catalysts are key to achieving efficient conversion of biomass pyrolysis tar. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a Ni-MOFC catalyst for cracking tar, its preparation method, and its application.

[0005] One objective of this invention is to provide a method for preparing a Ni-MOFC catalyst for cracking tar, the method comprising the following steps:

[0006] S1: Using biomass as a substrate, pyrolytic carbon is prepared by a two-step carbonization process combined with KOH activation;

[0007] S2: Pyrolytic carbon, nickel salt, imidazole and benzoic acid are used as reaction substrates and subjected to a solvothermal reaction. After the reaction is completed, the mixture is filtered, dried and then pyrolyzed to obtain the Ni-MOFC catalyst.

[0008] Further specifying, the biomass in S1 is sewage sludge, biogas residue, peanut shells, walnut shells, corn cobs, or corn stalks.

[0009] Further specifying the process for preparing pyrolytic carbon in S1: after drying the biomass, grind and sieve it, then pre-carbonize it, then add KOH solution and stir to activate it, filter and dry it, then carbonize it a second time, add hydrochloric acid and stir it after carbonization, then wash it with water until it is neutral, and finally dry it.

[0010] Furthermore, the drying temperature is specified as 100–110°C, and the mesh size for grinding and sieving is 100 mesh.

[0011] Further specifying, the pre-carbonization temperature is 300-500℃, the time is 2-4h, the heating rate is 5-10℃ / min, the protective gas is argon or nitrogen, and the flow rate is 50-100mL / min.

[0012] Further specified, the KOH solution concentration is 3-5 mol / L, the mass ratio of pre-carbonized product to KOH is 1:(1-9), the stirring activation temperature is 50-70℃, the time is 1-3h, the drying temperature is 60-70℃, and the time is 10-14h.

[0013] Further specifying, the secondary carbonization temperature is 700-800℃, the time is 1-3h, the heating rate is 5-10℃ / min, the protective gas is argon or nitrogen, and the flow rate is 50-100mL / min.

[0014] Further specify the following: the hydrochloric acid concentration is 1–3 mol / L, the volume is 25–100 mL, the stirring time is 10–14 h, and after washing with water until neutral, the drying temperature is 70–80 °C and the time is 10–14 h.

[0015] Further specifying, the nickel salt in S2 is one of the nickel nitrate, chloride, or sulfate.

[0016] Further specifying, the molar ratio of pyrolytic carbon, nickel salt, imidazole and benzoic acid in S2 is (0.2-1.8):(0.2-1.8):2:2.

[0017] Further specifying, the organic solvent in S2 that is solvothermal is N,N-dimethylformamide (DMF).

[0018] Further specifying, the solvothermal reaction temperature in S2 is 110–130℃, and the reaction time is 20–24h.

[0019] Further specified, the drying temperature in S2 is 160-180℃, and the time is 10-14h.

[0020] Further specified, the protective gas for pyrolysis in S2 is argon, the temperature is 700-900℃, and the reaction time is 2-4h.

[0021] The second objective of this invention is to provide a Ni-MOFC catalyst obtained by the above method.

[0022] The third objective of this invention is to provide an application of the Ni-MOFC catalyst obtained by the above method in high-temperature catalytic cracking of tar.

[0023] Further specifying the specific steps for high-temperature catalytic cracking of tar: Ni-MOFC catalyst, tar, and water vapor are injected into a two-stage catalytic reactor, and catalytic cracking is carried out under argon protection.

[0024] Furthermore, the amount of catalyst is specified as 0.1–1.0 g / mL of tar.

[0025] Furthermore, the mass ratio of water vapor to tar (S / C) is specified to be 1 to 5.

[0026] Furthermore, the argon flow rate is specified as 50–100 mL / min.

[0027] Furthermore, the catalytic cracking temperature is specified as 500–800℃, and the time as 20–60 min.

[0028] The significant advantages of this invention compared to existing technologies are:

[0029] (1) Metal-Organic Framework Carbon (MOFC) materials, through the modification and design of nickel-based catalyst structures, can achieve organic integration of active catalytic metals and supports, increase the number of active sites, and thus improve catalytic performance. MOFs serve as precursors, with their organic components undergoing carbonization and decomposition to form a porous carbon substrate. Ni, a high-boiling-point metal, undergoes in-situ carbothermic reduction, resulting in active metal nanoparticles that act as a connecting framework, uniformly dispersed within the porous carbon substrate. This results in a novel Ni-MOFC catalyst with in-situ uniform metal growth. Compared to traditional supported nickel-based catalysts, Ni-MOFC catalysts organically integrate active nickel and supports in-situ during preparation. The uniformly coated nickel nanoparticles on the inner and outer surfaces of the support serve as both active centers for the catalytic reaction and supporting nodes for the catalyst. This fully utilizes the active sites inside and outside the support, significantly enhancing the interaction between nickel and the support. This has the potential to significantly improve the catalyst's resistance to deactivation and improve the resource utilization efficiency of biomass pyrolysis tar.

[0030] (2) KOH decomposes at high temperatures (>600℃) to generate key active species such as metallic potassium (K) and potassium oxide (K2O), which form active porous structures with gaseous products generated by carbon material etching. At the same time, it significantly increases the specific surface area of ​​pyrolytic carbon and generates an ordered carbon structure. Active porous carbon provides a more active carbon substrate in the synthesis of MOFC ligands, enhances the catalytic performance of Ni-MOFC catalyst, and improves the reaction activity of Ni-MOFC catalyst.

[0031] (3) The organic ligands of the Ni-MOFC catalyst are a binary mixed rigid ligand of imidazole (C3H4N2) and tricresylcarboxylic acid (H3BTC). The rigid ligands contain strong conjugated structures, aromatic rings, or rigid cyclic structures. These structures enable the ligands to maintain a stable geometric configuration around the metal center and form a stable three-dimensional framework structure. The resulting MOFC material has high crystallinity, and the catalyst has high thermal stability, structural stability, and large porosity. The imidazole ligand can form a very stable coordination bond with the metal center due to its nitrogen atom, and the strong electron-donating ability of the imidazole ring can enhance the catalytic activity of the metal center. It can also effectively create ordered metal sites in the MOF and provide more tar adsorption and catalytic active sites in the pore structure. The tricresylcarboxylic acid (carboxylic acid ligand) contains metal-oxygen bonds, which further ensures the stability of the MOFC catalyst in the high-temperature catalytic tar reaction and further optimizes the pore characteristics of the catalyst, greatly improving the activity and stability of the nickel-based catalyst. Attached Figure Description

[0032] Figure 1 The X-ray diffraction patterns of the activated pyrolytic carbon AC, Ni-MOF and Ni-MOFC catalysts in Example 1 are shown below.

[0033] Figure 2 The image shows a scanning electron microscope (SEM) image of the Ni-MOFC catalyst obtained in Example 1; where a) and b) represent different magnifications.

[0034] Figure 3 The image shows the energy spectrum of the Ni-MOFC catalyst obtained in Example 1. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0037] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0038] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0039] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0040] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] Example 1:

[0043] (1) Preparation of pyrolytic carbon: 250g of sewage sludge was dried at 105℃ for 24h and then ground through a 100-mesh sieve. Under an argon atmosphere of 50mL / min, the temperature was increased to 500℃ at a heating rate of 5℃ / min, and pre-carbonized at 500℃ for 3h. Then, 4M KOH solution was used, with the mass ratio of the pre-carbonized product to KOH in the KOH solution being 1:6, and the mixture was stirred and activated at 60℃ for 2h. After activation, the mixture was filtered and then dried at 65℃ for 12h. Next, the temperature was increased to 700℃ at a protective argon flow rate of 50mL / min and a heating rate of 5℃ / min, and carbonized again at 700℃ for 2h. After carbonization, 50mL of 2M hydrochloric acid solution was added and stirred for acid washing for 12h. The mixture was then filtered through a 0.22μm aqueous filter membrane, washed with water until the pH of the supernatant was 7, and finally dried at 75℃ for 12h to obtain pyrolytic carbon AC.

[0044] (2) Preparation of Ni-MOFC catalyst: 0.3 g of pyrolytic carbon, 7.27 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 3.4045 g of imidazole (C3H4N2) and 10.5075 g of tricresylbenzene (H3BTC) were used as reaction substrates and dissolved in 80 mL of N,N-dimethylformamide (DMF). The reaction was carried out in a high-temperature and high-pressure reactor at 120 °C for 24 h. The mixture was then vacuum filtered through a 0.22 μm organic membrane and dried at 170 °C for 12 h to obtain Ni-MOF. Finally, Ni-MOF was pyrolyzed at 800 °C for 3 h under an argon atmosphere to obtain Ni-MOFC catalyst.

[0045] The X-ray diffraction patterns of the pyrolytic carbon AC obtained in step (1), the Ni-MOF in step (2), and the Ni-MOFC catalyst obtained in step (2) are as follows: Figure 1 As shown, from Figure 1 It can be seen that both Ni-MOF and Ni-MOFC retain the diffraction peaks of carbon-based AC. Compared with Ni-MOF, the Ni and NiO peak intensities are greater in Ni-MOFC, indicating that the crystal phase purity of the active catalyst component is higher. Thus, Ni-MOFC catalyst was successfully synthesized based on highly active AC.

[0046] The scanning electron microscope image of the Ni-MOFC catalyst obtained in step (2) is shown below. Figure 2 As shown, from Figure 2 As can be seen, the catalyst surface has a rough and porous structure with obvious pores, which to some extent indicates that the catalyst prepared in this embodiment has high porosity and specific surface area, and possesses a high specific surface area and a good distribution of active sites. The energy dispersive spectroscopy (EDS) spectrum is shown below. Figure 3 As shown, from Figure 3As can be seen, in the Ni-MOFC catalyst of this invention, the active metal nickel and the support are organically combined in situ during the preparation process. The active nano-nickel particles uniformly coated on the inner and outer surfaces of the support substrate serve as both active centers for the catalytic reaction and support nodes for the catalyst. This fully utilizes the active sites inside and outside the catalyst, enhances the interaction between nickel and the support, and improves the performance and deactivation resistance of the catalyst.

[0047] (3) High-temperature catalytic cracking of tar: 0.5g of the prepared Ni-MOFC catalyst was loaded into a pre-aerated two-stage catalytic reactor. 2mL of tar and 6mL of water vapor were injected into the catalytic reactor at rates of 0.1mL / min and 0.3mL / min, respectively. Argon gas was used as a protective gas at 100mL / min. Catalytic cracking was carried out at 700℃ for 20min. Unreacted tar was collected with 50mL of dichloromethane. The gas was dried and collected into a 5L gas collection bag.

[0048] After the reaction, the total yield of pyrolysis gas was determined by GC / GC-MS to be 1857 mL / g tar. The components of the pyrolysis gas were: CO, CH4, H2 and CO accounted for 5.2%, 1.9%, 77.2% and 15.7% respectively, and the content of unreacted tar was 11.25%.

[0049] Example 2:

[0050] (1) Preparation of activated pyrolytic carbon: 250g of sewage sludge was dried at 105℃ for 24h and then ground through a 100-mesh sieve. Under an argon atmosphere of 50mL / min, the temperature was increased to 300℃ at a heating rate of 10℃ / min, and pre-carbonized at 300℃ for 3h. Then, 4M KOH solution was used with a mass ratio of 1:9 of pre-carbonized product to KOH solution, and the mixture was stirred and activated at 60℃ for 2h. After activation, the mixture was filtered and then dried at 65℃ for 12h. The temperature was increased to 800℃ at a protective argon flow rate of 50mL / min and a heating rate of 5℃ / min, and carbonized again at 800℃ for 2h. 50mL of 2M hydrochloric acid solution was added and stirred for acid washing for 12h. The mixture was then filtered through a 0.22μm aqueous filter membrane, washed with water until the pH of the supernatant was 7, and finally dried at 75℃ for 12h to obtain activated pyrolytic carbon.

[0051] (2) Preparation of Ni-MOFC catalyst: 0.45 g of pyrolytic carbon, 10.905 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 5.1068 g of imidazole (C3H4N2) and 15.7613 g of tricresylbenzene (H3BTC) were used as reaction substrates and dissolved in 120 mL of N,N-dimethylformamide (DMF). The reaction was carried out in a high-temperature and high-pressure reactor at 120 °C for 24 h of solvothermal reaction. Then, the mixture was vacuum filtered through a 0.22 μm organic membrane and dried at 170 °C for 12 h to obtain Ni-MOF. Finally, Ni-MOF was pyrolyzed at 800 °C for 3 h under an argon atmosphere to obtain Ni-MOFC catalyst.

[0052] (3) High-temperature catalytic cracking of tar: 0.5g of the prepared Ni-MOFC catalyst was loaded into a pre-aerated two-stage catalytic reactor. 2mL of tar and 6mL of water vapor were injected into the catalytic reactor at rates of 0.1mL / min and 0.3mL / min, respectively. Argon gas was used as a protective gas at 100mL / min. Catalytic cracking was carried out at 800℃ for 20min. Unreacted tar was collected with 50mL of dichloromethane. The gas was dried and collected into a 5L gas collection bag.

[0053] After the reaction, the total yield of pyrolysis gas was determined by GC / GC-MS to be 2376 mL / g tar. The components of the pyrolysis gas were: CO, CH4, H2 and CO accounting for 2.4%, 1.2%, 87.5%, 8.9%, and the content of unreacted tar was 7.32%.

[0054] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a Ni-MOFC catalyst for cracking tar, characterized in that, The method described: S1: Using biomass as a substrate, pyrolytic carbon is prepared by a two-step carbonization process combined with KOH activation; S2: Pyrolytic carbon, nickel salt, imidazole and benzoic acid are used as reaction substrates and subjected to a solvothermal reaction. After the reaction is completed, the mixture is filtered, dried and then pyrolyzed to obtain the Ni-MOFC catalyst.

2. The method according to claim 1, characterized in that, The biomass in S1 consists of sewage sludge, biogas residue, peanut shells, walnut shells, corn cobs, or corn stalks.

3. The method according to claim 1, characterized in that, The process of preparing pyrolytic carbon in S1 is as follows: after drying the biomass, it is ground and sieved, then pre-carbonized, then KOH solution is added and stirred to activate it, filtered and dried, then carbonized a second time, then hydrochloric acid is added and stirred, then washed with water until neutral, and finally dried.

4. The method according to claim 3, characterized in that, The pre-carbonization temperature is 300–500℃, the time is 2–4 h, the heating rate is 5–10℃ / min, the KOH solution concentration is 3–5 mol / L, the mass ratio of pre-carbonization product to KOH is 1:(1–9), the stirring activation temperature is 50–70℃, the time is 1–3 h, the secondary carbonization temperature is 700–800℃, the time is 1–3 h, and the heating rate is 5–10℃ / min.

5. The method according to claim 1, characterized in that, In S2, the nickel salt is one of the nickel nitrate, chloride or sulfate. The molar ratio of pyrolytic carbon, nickel salt, imidazole and benzoic acid is (0.2-1.8):(0.2-1.8):2:

2.

6. The method according to claim 1, characterized in that, The solvothermal reaction temperature in S2 is 110–130℃, and the reaction time is 20–24 h. The protective gas for pyrolysis is argon, the temperature is 700–900℃, and the reaction time is 2–4 h.

7. The Ni-MOFC catalyst obtained by the method according to any one of claims 1 to 6.

8. The application of the Ni-MOFC catalyst according to claim 7 in high-temperature catalytic cracking of tar.

9. The application according to claim 8, characterized in that, The specific steps of high-temperature catalytic cracking of tar are as follows: Ni-MOFC catalyst, tar and water vapor are injected into a two-stage catalytic reactor, and catalytic cracking is carried out under argon protection.

10. The application according to claim 9, characterized in that, The amount of catalyst was 0.1–1.0 g / mL of tar, the mass ratio of water vapor to tar was 1–5, the catalytic cracking temperature was 500–800℃, and the time was 20–60 min.

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