Ni-MOFC catalyst for cracking tar as well as preparation method and application of Ni-MOFC catalyst

Abstract

The invention discloses a Ni-MOFC catalyst for cracking tar as well as a preparation method and application of the Ni-MOFC catalyst. The invention belongs to the technical field of tar catalytic cracking. The invention aims to solve the problems that the catalytic performance of the existing nickel-based catalyst is severely reduced in the long-term operation process, and even the catalyst is inactivated. The method comprises the following steps: taking biomass as a substrate, and preparing pyrolytic carbon by combining two-step carbonization with KOH activation; pyrolytic carbon, nickel salt, imidazole and benzenetricarboxylic acid are used as substrate solvothermal reaction, and then pyrolysis is performed to obtain the catalyst. According to the obtained catalyst, active metal nickel and a carrier are organically combined in situ, nano nickel particles uniformly coating the inner and outer surfaces of the carrier serve as an active center and a supporting node, and active porous carbon serves as an MOFC carbon substrate, so that the interaction between nickel and the carrier is enhanced, and the reaction activity and high-temperature inactivation resistance of the catalyst are improved; the catalytic removal of the biomass pyrolysis tar is realized. The method is suitable for catalytic pyrolysis treatment of tar and resource recovery thereof.

Description

Technical Field

[0001] The invention belongs to the technical field of tar catalytic cracking, and specifically relates to a Ni-MOFC catalyst for cracking tar and a preparation method and application thereof. Background Art

[0002] High-efficiency and low-carbon biomass processing technology has become a major strategic need in the biomass resource industry. Biomass pyrolysis is considered to be one of the most promising technologies for achieving high-value utilization of biomass. However, biomass pyrolysis will produce a mixture of various condensable high-molecular organic matter - biomass pyrolysis tar, which is rich in toxic and harmful organic matter such as polycyclic aromatic hydrocarbons (PAH), phenols, pyridine and furan. Tar by-products 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] The nickel-based catalytic cracking method, which has developed rapidly in recent years, is considered to be an efficient, low-pollution and sustainable tar removal technology. The nickel-based catalytic cracking method greatly reduces the activation energy of the reaction, increases the tar cracking rate, converts tar pollutants into small molecular combustible gases under high temperature conditions (500℃~800℃), reduces the toxicity of tar, significantly reduces the reaction energy consumption and equipment requirements, and represents the frontier direction of the development of biomass pyrolysis tar treatment technology. However, the catalytic performance of nickel-based catalysts will seriously decline during long-term operation, and even cause catalyst deactivation, significantly reducing the catalytic effect. The sintering temperature of metallic nickel is low, which makes metallic nickel easy to sinter at high temperature, resulting in a decrease in the number of active sites of the catalytic metal and a decrease in interfacial activity. In addition, the strong affinity between the carbon cations produced in the tar cracking process and the nickel metal will easily lead to the formation of carbon deposition on the catalyst surface. A large amount of carbon deposition will seriously block the active sites of the nickel-based catalyst, hindering the synergistic catalytic ability between the metal and the carrier, which is not conducive to the efficient tar catalytic cracking reaction. How to improve the reaction activity of nickel-based catalysts and prepare high-performance, deactivation-resistant nickel-based tar cracking catalysts is the key to achieving efficient conversion of biomass pyrolysis tar. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a Ni-MOFC catalyst for cracking tar and a preparation method and application thereof.

[0005] One of the purposes of the present invention is to provide a method for preparing a Ni-MOFC catalyst for cracking tar, the method being carried out according to the following steps:

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

[0007] S2: Use pyrolytic carbon, nickel salt, imidazole and benzenetricarboxylic acid as reaction substrates to carry out solvent thermal reaction. After the reaction is completed, filter and dry, and then carry out pyrolysis to obtain Ni-MOFC catalyst.

[0008] It is further defined that the biomass in S1 is sewage sludge, biogas residue, peanut shells, walnut shells, corn cobs or corn stover.

[0009] It is further defined that the process for preparing pyrolytic carbon in S1 is as follows: the biomass is dried, ground and sieved, and then pre-carbonized, followed by adding KOH solution for stirring and activation, filtered and dried, and then carbonized for the second time, and after carbonization, hydrochloric acid is added, stirred, and then washed with water until neutral, and finally dried.

[0010] It is further defined that the drying temperature is 100-110° C. and the mesh size of the ground and sieved material is 100 meshes.

[0011] It is further defined that the pre-carbonization temperature is 300-500°C, the time is 2-4h, the heating rate is 5-10°C / min, the protective gas is argon or nitrogen, and the flow rate is 50-100mL / min.

[0012] It is further specified that the concentration of KOH solution 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°C, the time is 1-3h, and the drying temperature is 60-70°C, and the time is 10-14h.

[0013] It is further defined that the secondary carbonization temperature is 700-800°C, the time is 1-3h, the heating rate is 5-10°C / min, the protective gas is argon or nitrogen, and the flow rate is 50-100mL / min.

[0014] It is further defined that the concentration of hydrochloric acid is 1-3 mol / L, the volume is 25-100 mL, the stirring time is 10-14 h, and after washing with water to neutrality, the drying temperature is 70-80° C. and the time is 10-14 h.

[0015] It is further defined that the nickel salt in S2 is one of nickel nitrate, chloride or sulfate.

[0016] It is further defined that the molar ratio of pyrolytic carbon, nickel salt, imidazole and trimesic acid in S2 is (0.2-1.8):(0.2-1.8):2:2.

[0017] It is further defined that the organic solvent for the solvothermal reaction in S2 is N,N-dimethylformamide (DMF).

[0018] It is further defined that the solvent thermal reaction temperature in S2 is 110-130° C., and the reaction time is 20-24 h.

[0019] It is further defined that the drying temperature in S2 is 160-180° C. and the drying time is 10-14 h.

[0020] It is further defined that the protective gas for the pyrolysis in S2 is argon, the temperature is 700-900° C., and the reaction time is 2-4 hours.

[0021] A second object of the present invention is to provide a Ni-MOFC catalyst obtained by the above method.

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

[0023] It is further defined 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.

[0024] It is further defined that the amount of the catalyst is 0.1 to 1.0 g / mL of tar.

[0025] It is further defined that the mass ratio of water vapor to tar (S / C) is 1-5.

[0026] It is further defined that the argon gas flow rate is 50 to 100 mL / min.

[0027] It is further defined that the catalytic cracking temperature is 500-800°C and the time is 20-60 minutes.

[0028] Compared with the prior art, the present invention has the following significant effects:

[0029] (1) Metal Organic Framework Carbon (MOFC) can improve the catalytic performance by modifying the structure of nickel-based catalysts to achieve organic bonding between active catalytic metals and carriers, increase the number of active sites, and thus improve the catalytic performance. MOF is used as a precursor, and the organic components in the structure are carbonized and decomposed to form a porous carbon substrate, while Ni, as a metal with a high boiling point, is subjected to in-situ carbon thermal reduction to form active metal nanoparticles that are uniformly dispersed in the porous carbon substrate as a connecting skeleton, i.e., a new type of Ni-MOFC catalyst with in-situ uniform growth of metal. Compared with traditional supported nickel-based catalysts, Ni-MOFC catalysts organically bond active metal nickel and carriers in situ during the preparation process. The nano-nickel particles uniformly coated on the inner and outer surfaces of the carrier are both active centers of the catalytic reaction and supporting nodes of the catalyst, making full use of the active sites inside and outside the carrier, greatly enhancing the interaction between nickel and the carrier, and having the potential to significantly improve the anti-deactivation performance of the catalyst, thereby improving the resource utilization efficiency of biomass pyrolysis tar.

[0030] (2) KOH will decompose at high temperature (>600℃) to produce key active species such as metallic potassium (K) and potassium oxide (K2O), which will etch with carbon materials to generate gaseous products to form an active porous structure. At the same time, it will significantly increase the specific surface area of ​​pyrolytic carbon and generate an ordered carbon structure. The active porous carbon provides a more active carbon substrate in the MOFC ligand synthesis process, enhances the catalytic performance of the Ni-MOFC catalyst, and improves the reaction activity of the Ni-MOFC catalyst.

[0031] (3) The organic ligands of the Ni-MOFC catalyst are binary mixed rigid ligands of imidazole (C3H4N2) and benzenetricarboxylic acid (H3BTC). The rigid ligands contain strong conjugated structures, aromatic rings or rigid ring 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 supply ability of the imidazole ring can enhance the catalytic activity of the metal center, and can effectively create ordered metal sites in MOF, and provide more tar adsorption and catalytic active sites in the pore structure. The benzenetricarboxylic acid (carboxylic acid ligand) contains a ligand with a metal-oxygen bond, 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 X-ray diffraction patterns of activated pyrolytic carbon AC, Ni-MOF and Ni-MOFC catalysts in Example 1;

[0033] Figure 2 This is a scanning electron microscope image of the Ni-MOFC catalyst obtained in Example 1; wherein a) and b) represent different magnifications;

[0034] Figure 3 This is the energy spectrum of the Ni-MOFC catalyst obtained in Example 1. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

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

[0038] When equivalent, concentration or other value or parameter is represented by the range limited by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the scope is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the scope is intended to include its end value and all integers and fractions within the scope. In the present application specification and claims, range limitation can be combined and / or interchanged, if these ranges are not otherwise stated, include all sub-ranges contained therein.

[0039] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0040] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0041] The endpoints and any values ​​of the ranges disclosed in the 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0042] Embodiment 1:

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

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

[0045] The X-ray diffraction patterns of the pyrolysis 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 the diffraction peaks of the carbon-based AC are retained in both Ni-MOF and Ni-MOFC, and the peak intensities of Ni and NiO in Ni-MOFC are both larger than those in Ni-MOF, and the crystal phase purity of the catalyst active components is purer, that is, the Ni-MOFC catalyst was successfully synthesized based on the highly active AC.

[0046] The scanning electron microscopy image of the Ni-MOFC catalyst obtained in step (2) is as follows: Figure 2 As shown, from Figure 2 It can be seen that the surface structure of the catalyst is rough and porous, with obvious pore structure, which can to some extent explain that the porosity and specific surface area of ​​the catalyst prepared in this embodiment are both high, and the catalyst has a high specific surface area and active site distribution. Figure 3 As shown, from Figure 3It can be seen that the active metal nickel and the carrier in the Ni-MOFC catalyst of the present invention are organically combined in situ during the preparation process, and the active nano-nickel particles uniformly coated on the inner and outer surfaces of the carrier substrate serve as both the active center of the catalytic reaction and the supporting nodes of the catalyst, making full use of the active sites inside and outside the catalyst, enhancing the interaction between nickel and the carrier, and improving the performance and anti-deactivation ability of the catalyst.

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

[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 pyrolysis gas were: CO, CH4, H2 and CO accounting for 5.2%, 1.9%, 77.2%, 15.7% respectively, and the content of tar not participating in the reaction was 11.25%.

[0049] Embodiment 2:

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

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

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

[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 pyrolysis gas were: CO, CH4, H2 and CO accounting for 2.4%, 1.2%, 87.5%, 8.9% respectively, and the content of tar not participating in the reaction was 7.32%.

[0054] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing a Ni-MOFC catalyst for cracking tar, characterized in that: The method: S1: Using biomass as substrate, pyrolytic carbon was prepared by two-step carbonization combined with KOH activation; S2: Use pyrolytic carbon, nickel salt, imidazole and benzenetricarboxylic acid as reaction substrates to carry out solvent thermal reaction. After the reaction is completed, filter and dry, and then carry out pyrolysis to obtain Ni-MOFC catalyst.

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

3. The method according to claim 1, characterized in that The process of preparing pyrolytic carbon in S1 is as follows: the biomass is dried, ground and sieved, and then pre-carbonized, followed by adding KOH solution for stirring and activation, filtering and drying, and then secondary carbonization, and after carbonization, hydrochloric acid is added, stirred, and 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°C, the time is 2-4h, the heating rate is 5-10°C / min, the concentration of KOH solution is 3-5mol / L, the mass ratio of pre-carbonization product to KOH is 1:(1-9), the stirring activation temperature is 50-70°C, the time is 1-3h, the secondary carbonization temperature is 700-800°C, the time is 1-3h, and the heating rate is 5-10°C / min.

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

2.

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

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

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

9. The use 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 use according to claim 9, characterized in that: The amount of catalyst is 0.1-1.0 g / mL tar, the mass ratio of water vapor to tar is 1-5, the catalytic cracking temperature is 500-800° C., and the time is 20-60 min.

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