Carbon-silicon composite catalyst, preparation method thereof and application of carbon-silicon composite catalyst in preparation of aromatic hydrocarbons through catalytic pyrolysis of kitchen waste

Abstract

The application discloses a carbon-silicon composite catalyst, a preparation method thereof and application of the catalyst in preparation of aromatic hydrocarbons through catalytic pyrolysis of kitchen waste, and belongs to the technical field of solid waste resource utilization and catalytic conversion. The catalyst takes ZSM-5@SBA-15 core-shell structure composite molecular sieve as a carrier, loads nano NiO active components, and coats N-doped carbon layers on the surface. The catalyst is prepared through hydrothermal synthesis of the core-shell carrier, impregnation of the metal loading, and calcination of the carbon layer in an inert atmosphere. The pretreated kitchen waste is mixed with the catalyst, and catalytic pyrolysis is carried out in an inert atmosphere at normal pressure, so that bio-oil rich in aromatic hydrocarbons (BTX) can be prepared with high selectivity. The content of the aromatic hydrocarbons in the obtained bio-oil is greater than or equal to 72%, and the content of BTX in the total aromatic hydrocarbons is greater than or equal to 58%, so that high-quality raw materials can be provided for subsequent preparation of bio-jet fuel components and fine chemicals. The application has simple process, environmental and economic benefits, and wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and catalytic conversion, and in particular to a carbon-silicon composite catalyst, its preparation method, and its application in the catalytic pyrolysis of kitchen waste to produce aromatics. Background Technology

[0002] With the acceleration of urbanization, the amount of food waste generated has increased dramatically. Food waste is characterized by high moisture content, high oil and salt content, and easy biodegradability. Traditional treatment methods (such as landfill and incineration) easily cause secondary pollution. Pyrolysis technology, as an environmentally friendly method that can achieve energy recovery, has received widespread attention. However, the direct pyrolysis products of food waste are complex in composition, including bio-oil, pyrolysis gas, and coke. Among them, bio-oil has high oxygen content, strong acidity, and low calorific value, making it difficult to use directly as fuel or chemical raw material, thus limiting its application value.

[0003] Aromatic hydrocarbons (such as benzene, toluene, and xylene, abbreviated as BTX) are important basic chemical raw materials and key components of bio-jet fuel. As a green alternative to traditional aviation fuel, bio-jet fuel must meet stringent aviation fuel standards for its aromatic hydrocarbon content to ensure engine sealing and energy density. Therefore, developing technologies to directionally convert waste such as kitchen waste into aromatic hydrocarbon components can provide high-value raw materials for subsequent bio-jet fuel production, possessing significant strategic importance and promising industrial prospects.

[0004] In existing technologies, commonly used catalysts include molecular sieves (such as HZSM-5). However, the pyrolysis of food waste generates a large number of oxygen-containing compounds (such as fatty acids and alcohols) and nitrogen-containing compounds. Although ordinary molecular sieve catalysts have a certain aromatization ability, they have the following problems: 1) Poor resistance to carbon deposition, the micropores are easily blocked by coke and deactivated, and the activity usually decreases significantly after a long period of operation; 2) Insufficient tolerance to oxygen-containing and nitrogen-containing compounds, resulting in low selectivity for target products; 3) Alkali metals (such as Na and K) in food waste can easily poison the catalyst, further shortening the catalyst life.

[0005] Therefore, developing a highly active, selective, carbon-resistant, and stable catalyst to achieve the efficient and targeted conversion of food waste into aromatic components, and providing stable and sustainable aromatic component raw materials for industries such as bio-aviation fuel and fine chemicals, is of great significance for the high-value utilization of food waste and the development of green aviation fuel. Summary of the Invention

[0006] The purpose of this invention is to provide a carbon-silicon composite catalyst, its preparation method, and its application in the catalytic pyrolysis of food waste to produce aromatics, so as to solve the problems in the background art and achieve efficient and high-value conversion of food waste.

[0007] To achieve the above objectives, the present invention provides a carbon-silicon composite catalyst, comprising a core-shell structured composite molecular sieve support, an active metal oxide, and an N-doped carbon layer; the core-shell structured composite molecular sieve support is ZSM-5@SBA-15, with a microporous ZSM-5 molecular sieve core and a mesoporous SBA-15 shell; the active metal oxide is nano-NiO, supported on the core-shell structured composite molecular sieve support; the N-doped carbon layer coats the outer surface of the NiO / core-shell structured composite molecular sieve support material and partially exposes the active sites of the nano-NiO.

[0008] Preferably, the silicon-aluminum molar ratio of the ZSM-5 molecular sieve is 25-50; the NiO loading is 3-8 wt% of the total catalyst mass; and the thickness of the N-doped carbon layer is 2-10 nm.

[0009] Preferably, the nitrogen source of the N-doped carbon layer is at least one of melamine and 1-butyl-3-methylimidazolium chloride.

[0010] This invention also provides a method for preparing a carbon-silicon composite catalyst, comprising the following steps: S1. Preparation of core-shell support: ZSM-5 molecular sieve was dispersed in an acidic aqueous solution containing template agent P123, and tetraethyl orthosilicate was added as a silicon source. After hydrothermal reaction, it was calcined to obtain ZSM-5@SBA-15 core-shell molecular sieve. S2. Metal support: The ZSM-5@SBA-15 support was immersed in an ethanol solution of nickel nitrate, dried, and then calcined in air for the first time to obtain NiO / ZSM-5@SBA-15. S3, N-doped carbon layer coating: NiO / ZSM-5@SBA-15 was dispersed in an ethanol-water mixed solution containing nitrogen precursor, and after stirring and adsorption, the solvent was evaporated and then calcined for the second time under an inert atmosphere to form an N-doped carbon layer in situ, thus obtaining a carbon-silicon composite catalyst.

[0011] Preferably, in step S1, the hydrothermal reaction temperature is 90~110℃ and the reaction time is 40~56h; the calcination temperature is 540~560℃ and the calcination time is 5~7h; the acidic aqueous solution is a 1.6M HCl solution, and the ratio of ZSM-5 molecular sieve to acidic aqueous solution is 5g:120mL.

[0012] Preferably, in step S2, the first calcination temperature is 430~470℃ and the calcination time is 3~5h; the impregnation is ultrasonic-assisted impregnation, the ultrasonic time is 1~1.5h, after impregnation, it is left to stand for 10~14h, the evaporation temperature is 75~85℃, and the drying temperature is 95~105℃.

[0013] Preferably, in step S3, the volume ratio of the ethanol-water mixed solution is 1:1; the second calcination temperature is 550~650℃, the heating rate is 3~7℃ / min, and the calcination time is 1.5~2.5h; the inert atmosphere is a nitrogen atmosphere.

[0014] This invention also provides the application of carbon-silicon composite catalysts in the catalytic pyrolysis of food waste to produce aromatics, including the following steps: Pretreated kitchen waste is mixed with a carbon-silicon composite catalyst and placed in an atmospheric pressure pyrolysis reactor. Under an inert atmosphere, the mixture is heated to 500-650°C at a heating rate of 10-20°C / min to carry out a catalytic pyrolysis reaction. After holding the reaction at this temperature for 25-35 minutes, the liquid product is condensed and collected to obtain bio-oil rich in aromatic components.

[0015] Preferably, the mass ratio of the kitchen waste to the carbon-silicon composite catalyst is 1:(0.1~0.5).

[0016] Preferably, the inert atmosphere is N2 atmosphere, and the flow rate is 80~120mL / min.

[0017] Therefore, the carbon-silicon composite catalyst, its preparation method, and its application in the catalytic pyrolysis of kitchen waste to produce aromatics, as described in this invention, have the following beneficial effects: (1) The catalyst of the present invention adopts a ZSM-5@SBA-15 core-shell hierarchical porous structure. The mesoporous SBA-15 shell realizes the pre-cracking and rapid diffusion of long-chain macromolecular oxygen-containing compounds, while the microporous ZSM-5 core provides sufficient aromatization acidic sites, forming a "pre-cracking-aromatization" hierarchical catalytic system. At the same time, the nano-NiO active component promotes the dehydrogenation reaction and significantly improves the aromatic hydrocarbon generation efficiency.

[0018] (2) The N-doped carbon layer coated on the surface of the catalyst of the present invention can physically block alkali metal ions, protect acidic active sites, and avoid catalyst poisoning; at the same time, the N-doped carbon layer and NiO particles work together to consume carbon deposits through reverse water-gas shift reaction or dry reforming reaction, and inhibit carbon deposit formation.

[0019] (3) The present invention adopts the preparation process of "loading metal first and then coating carbon layer", which can effectively limit the migration and aggregation of nano NiO particles in the high temperature process, so that they always maintain the nano size and ensure the stability of catalytic activity. At the same time, by adjusting parameters such as NiO loading, N doped carbon layer thickness, and ZSM-5 silicon-aluminum ratio, the acidity and catalytic performance of the catalyst can be flexibly controlled to adapt to different working conditions.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1This is a comparison chart of the recyclability of the catalyst prepared in Example 1 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0024] The raw materials used in the following examples are all commercially available conventional raw materials. Among them, P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer), tetraethyl orthosilicate, nickel nitrate (Ni(NO3)2·6H2O), melamine, 1-butyl-3-methylimidazolium chloride, and hydrochloric acid are all analytical grade. The kitchen waste is taken from the kitchen of urban catering establishments and is used after removing impurities such as bones and plastics.

[0025] Example 1 This embodiment provides a carbon-silicon composite catalyst, its preparation method, and its application, as detailed below: 1) Preparation of carbon-silicon composite catalysts: S1. Preparation of core-shell support: Take 5g of HZSM-5 molecular sieve (Si / Al=38) and add it to 120mL of 1.6MHCl solution containing 4g of P123. Stir at 40℃ for 2h to uniformly disperse the HZSM-5 molecular sieve. Slowly add 9mL of tetraethyl orthosilicate and continue stirring at 40℃ for 24h. Transfer the mixed solution to a hydrothermal reactor and crystallize at 100℃ for 48h. After the reaction is completed, filter, wash with deionized water until neutral, dry at 100℃ for 12h, and then place in a muffle furnace and calcine at 550℃ for 6h to remove the template agent P123, and obtain ZSM-5@SBA-15 core-shell support.

[0026] S2. Metal support: Take 2g of the above ZSM-5@SBA-15 core-shell support and add it to 20mL of ethanol solution containing 0.3g Ni(NO3)2·6H2O. Impregnate with ultrasound for 1h and let stand at room temperature for 12h. Evaporate the solvent at 80℃ and dry at 100℃ for 12h. Then place it in a muffle furnace and calcine in air atmosphere at 450℃ for 4h to obtain NiO / ZSM-5@SBA-15 intermediate (NiO loading is about 5wt% of the total mass of the catalyst).

[0027] S3, N-doped carbon layer coating: Take 1g of melamine and dissolve it in 50mL of a mixed solution of ethanol:water = 1:1 (volume ratio). Add 1.5g of the above NiO / ZSM-5@SBA-15 intermediate and reflux and stir at 80℃ for 6h. Evaporate the solvent to obtain a solid product. Place the solid product in a tube furnace, introduce N2 gas (flow rate 100mL / min), heat to 600℃ at a heating rate of 5℃ / min, calcine for 2h, and naturally cool to room temperature to obtain NiO@NC / ZSM-5@SBA-15 carbon silicon composite catalyst (N-doped carbon layer thickness is about 5nm).

[0028] 2) Application of catalysts: After removing impurities from the kitchen waste, it was dried to a moisture content of ≤10wt% and pulverized to a particle size of ≤2mm. 10g of the pretreated kitchen waste was mixed evenly with 3g of the carbon-silicon composite catalyst prepared in the example and placed in a fixed-bed pyrolysis reactor. N2 gas was introduced at a flow rate of 100mL / min and heated to 600℃ at a heating rate of 15℃ / min. The reaction was held at this temperature for 30min. The volatiles from the pyrolysis were condensed using a condenser, and the liquid product was collected to obtain a bio-oil rich in aromatics.

[0029] Cyclic stability tests were conducted on the catalyst. After each reaction, the catalyst was removed from the reactor and calcined at 600℃ for 2 hours under N2 atmosphere to remove surface carbon. The catalytic pyrolysis experiment was then repeated, and the aromatic selectivity after each cycle was recorded.

[0030] The results are as follows Figure 1 As shown, after five cycles, the aromatic selectivity was 66%, the carbon deposit increased to 8%, and no obvious poisoning was observed.

[0031] Example 2 The difference between this embodiment and Example 1 is that the NiO loading is adjusted to 8wt%, the nitrogen source of the N-doped carbon layer is changed to 1-butyl-3-methylimidazolium chloride, and the rest of the preparation steps and application conditions are the same as in Example 1.

[0032] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that after the catalyst was cycled 5 times, the aromatic selectivity was 63%, and the carbon deposition was 10% of the catalyst mass, which was slightly higher than in Example 1. This was mainly due to the excessively high NiO loading, which led to a slight increase in carbon deposition.

[0033] Example 3 The difference between this embodiment and Example 1 is that the silicon-to-aluminum ratio (Si / Al) of the ZSM-5 molecular sieve is 25, the thickness of the N-doped carbon layer is adjusted to 2 nm, and the remaining preparation steps and application conditions are the same as in Example 1.

[0034] According to the test results, the yield of liquid product in this embodiment was 30%, and the aromatic content in the bio-oil was 72%, of which BTX accounted for 58% of the total aromatic content.

[0035] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that after five cycles of catalyst recycling, the aromatic selectivity was 64%, and the catalyst exhibited good resistance to carbon buildup and poisoning.

[0036] Example 4 The difference between this embodiment and Example 1 is that the silicon-to-aluminum ratio (Si / Al) of the ZSM-5 molecular sieve is 50, the thickness of the N-doped carbon layer is adjusted to 10 nm, and the remaining preparation steps and application conditions are the same as in Example 1.

[0037] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that the aromatic selectivity was 65% after the catalyst was recycled 5 times.

[0038] Comparative Example 1 This comparative example uses pure HZSM-5 molecular sieve as a catalyst, as detailed below: The catalyst was a commercially available HZSM-5 molecular sieve (Si / Al=38) without any modification. The specific application conditions were exactly the same as in Example 1, namely, the pretreatment method of kitchen waste, the amount of catalyst, the pyrolysis temperature, the holding time, and the N2 flow rate were all the same as in Example 1.

[0039] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that after one use, the surface carbon content of the catalyst was 12.8% of the catalyst mass, the pores were severely blocked, the catalyst was completely deactivated, and it could not be recycled.

[0040] Comparative Example 2 This comparative example provides a NiO / ZSM-5 catalyst without an SBA-15 mesoporous shell and an N-doped carbon layer. The specific preparation and application are as follows: 1) Catalyst preparation: Take 2g of HZSM-5 molecular sieve (Si / Al=38), add it to 20mL of ethanol solution containing 0.3g Ni(NO3)2·6H2O, impregnate with ultrasound for 1h, and let stand at room temperature for 12h; evaporate the solvent at 80℃, dry at 100℃ for 12h, and calcine in air atmosphere at 450℃ for 4h to obtain NiO / ZSM-5 catalyst (NiO loading of about 5wt%).

[0041] 2) Catalyst application: The application conditions are exactly the same as in Example 1.

[0042] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that after the catalyst was cycled three times, the aromatic selectivity decreased to 28%, mainly due to alkali metal poisoning and severe carbon buildup, which led to rapid deactivation of the catalyst.

[0043] Comparative Example 3 This comparative example uses ZSM-5@SBA-15 core-shell molecular sieve as a catalyst, without NiO active component and N-doped carbon layer. The specific preparation and application are as follows: 1) Catalyst preparation: The ZSM-5@SBA-15 core-shell support prepared in step S1 of Example 1 was used as the catalyst, but NiO loading and carbon layer coating were not performed.

[0044] 2) Catalyst application: The application conditions are exactly the same as in Example 1.

[0045] Cyclic stability tests were conducted using the same method as in Example 1. The results showed that after the catalyst was cycled twice, the aromatic selectivity decreased to 35%, mainly because the lack of NiO active component to improve aromatization efficiency and the absence of carbon layer protection made the catalyst prone to carbon deposition and poisoning.

[0046] The catalytic pyrolysis performance of Examples 1-4 and Comparative Examples 1-3 was tested, and the results are shown in Table 1 below.

[0047] Table 1: Comparison Results of Catalytic Pyrolysis Performance

[0048] The results showed that the aromatic hydrocarbon content in Examples 1-4 all reached over 72%, and the BTX content was over 58%, which was much higher than the 35% in Comparative Example 1 and the 50% in Comparative Example 2. This demonstrates that the synergistic effect of the ZSM-5@SBA-15 core-shell structure and the NiO active component significantly improved the aromatization efficiency.

[0049] The carbon deposition in Examples 1-4 was only 3.5~4.2 wt%, far lower than 12.8 wt% in Comparative Example 1 and 8.5 wt% in Comparative Example 2. Comparing Example 1 with Comparative Example 3 (carbon deposition 6.1 wt%), it can be seen that the presence of the N-doped carbon layer reduced the carbon deposition by about 40%, proving that the N-doped carbon layer effectively inhibited carbon deposition through physical barrier and chemical synergy.

[0050] After five cycles, the aromatic selectivity of the present invention remained at 63-66%, while that of Comparative Example 2 dropped to 28% after three cycles; this demonstrates that the N-doped carbon layer effectively protects the active sites of the catalyst and significantly extends the catalyst lifetime.

[0051] Therefore, this invention provides a carbon-silicon composite catalyst, its preparation method, and its application in the catalytic pyrolysis of food waste to produce aromatics. Through the synergistic effect of the ZSM-5@SBA-15 core-shell support, nano-NiO active component, and N-doped carbon layer, it significantly improves the selectivity and yield of aromatics from the catalytic pyrolysis of food waste. It also possesses excellent resistance to carbon deposition, alkali metal poisoning, and cycle stability, with overall performance far superior to existing traditional catalysts. The raw materials used are all commercially available conventional products, readily available and low in cost. The preparation process employs conventional techniques such as hydrothermal synthesis, ultrasonic impregnation, and calcination, requiring no complex equipment or harsh reaction conditions. The process steps are simple, highly controllable, and suitable for large-scale industrial production, enabling the batch preparation of the catalyst.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A carbon-silicon composite catalyst, characterized in that: It consists of a core-shell composite molecular sieve support, an active metal oxide, and an N-doped carbon layer. The core-shell composite molecular sieve support is ZSM-5@SBA-15, with a microporous ZSM-5 molecular sieve core and a mesoporous SBA-15 shell. The active metal oxide is nano-NiO, which is loaded on the core-shell composite molecular sieve support. The N-doped carbon layer coats the outer surface of the NiO / core-shell composite molecular sieve support material and partially exposes the active sites of nano-NiO.

2. The carbon-silicon composite catalyst according to claim 1, characterized in that: The ZSM-5 molecular sieve has a silicon-to-aluminum molar ratio of 25-50; the NiO loading is 3-8 wt% of the total catalyst mass; and the thickness of the N-doped carbon layer is 2-10 nm.

3. The carbon-silicon composite catalyst according to claim 1, characterized in that: The nitrogen source for the N-doped carbon layer is at least one of melamine and 1-butyl-3-methylimidazolium chloride.

4. A method for preparing a carbon-silicon composite catalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of core-shell carrier: ZSM-5 molecular sieve was dispersed in an acidic aqueous solution containing template agent P123, tetraethyl orthosilicate was added as a silicon source, and after hydrothermal reaction, it was calcined to obtain ZSM-5@SBA-15 core-shell molecular sieve. S2. Metal support: The ZSM-5@SBA-15 support was immersed in an ethanol solution of nickel nitrate, dried, and then calcined in air for the first time to obtain NiO / ZSM-5@SBA-15. S3, N-doped carbon layer coating: NiO / ZSM-5@SBA-15 was dispersed in an ethanol-water mixed solution containing nitrogen precursor, and after stirring and adsorption, the solvent was evaporated and then calcined for the second time under an inert atmosphere to form an N-doped carbon layer in situ, thus obtaining a carbon-silicon composite catalyst.

5. The preparation method according to claim 4, characterized in that: In S1, the hydrothermal reaction temperature is 90~110℃ and the reaction time is 40~56h; the calcination temperature is 540~560℃ and the calcination time is 5~7h; the acidic aqueous solution is a 1.6M HCl solution, and the ratio of ZSM-5 molecular sieve to acidic aqueous solution is 5g:120mL.

6. The preparation method according to claim 4, characterized in that: In step S2, the first calcination temperature is 430~470℃ and the calcination time is 3~5h; the impregnation is ultrasonic-assisted impregnation, the ultrasonic time is 1~1.5h, after impregnation, it is left to stand for 10~14h, the evaporation temperature is 75~85℃, and the drying temperature is 95~105℃.

7. The preparation method according to claim 4, characterized in that: In step S3, the volume ratio of the ethanol-water mixed solution is 1:1; the second calcination temperature is 550~650℃, the heating rate is 3~7℃ / min, and the calcination time is 1.5~2.5h; the inert atmosphere is nitrogen atmosphere.

8. The application of a carbon-silicon composite catalyst as described in any one of claims 1-3 in the catalytic pyrolysis of kitchen waste to produce aromatics, characterized in that, Includes the following steps: Pretreated kitchen waste is mixed with a carbon-silicon composite catalyst and placed in an atmospheric pressure pyrolysis reactor. Under an inert atmosphere, the mixture is heated to 500-650°C at a heating rate of 10-20°C / min to carry out a catalytic pyrolysis reaction. After holding the reaction at this temperature for 25-35 minutes, the liquid product is condensed and collected to obtain bio-oil rich in aromatic components.

9. The application according to claim 8, characterized in that: The mass ratio of kitchen waste to carbon-silicon composite catalyst is 1:(0.1~0.5).

10. The application according to claim 8, characterized in that: The inert atmosphere is N2 atmosphere, and the flow rate is 80~120mL / min.

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