A catalyst for enriching aromatic hydrocarbons through carbon cycle and preparation method thereof

Abstract

The present invention provides a carbon cycle rich aromatics catalyst and its preparation method. The catalyst includes a carrier, an active component and nano-scale activated carbon AC, the carrier is a ZSM-5 zeolite molecular sieve, and the pore size distribution is 0.2-0.4nm, the active component is ZnO inside the molecular sieve channel and ZnZrOx dispersed on the outer surface of the molecular sieve; the mass ratio of each substance of the catalyst is 100ZSM5: 6-9ZnO: 6-20ZnZrOx: 1-5AC, Zn modified ZSM5 molecular sieve is subjected to post-processing recrystallization means, the B acid acidity and pores of the ZSM5 molecular sieve are adjusted, and a metal salt is added in an alkaline environment in the later stage of recrystallization to form a metal oxide shell on the surface of the ZSM5 molecular sieve, and the lattice oxygen defects of the metal oxide are used to improve the adsorption capacity and conversion capacity of carbon dioxide. The addition of activated carbon also solves the diffusion problem of the outer surface. The present invention catalyzes the co-conversion reaction of carbon dioxide and light alkanes under milder reaction conditions to obtain higher carbon dioxide, alkane conversion rate and aromatics selectivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing aromatic hydrocarbons, and relates to a catalyst for enriching aromatic hydrocarbons through carbon cycle and a preparation method thereof, and specifically relates to a catalyst for enriching aromatic hydrocarbons through co-conversion of carbon dioxide and light alkanes and a preparation method thereof. Background Art

[0002] With the continuous development of human society, atmospheric carbon emissions have increased by approximately 25%-30%. Excessive carbon dioxide emissions contribute to a range of environmental problems, including global warming, rising sea levels, and increased ocean acidity. Therefore, controlling carbon dioxide emissions has garnered widespread attention worldwide. To address climate change, the Paris Agreement advocates a global green and low-carbon transition, and all countries must take decisive steps. China will enhance its Nationally Determined Contribution (NDC) and adopt more forceful policies and measures.

[0003] CO₂ is one of the most stable chemical molecules. Efficiently converting CO₂ as a raw material into bulk chemicals is both a viable and challenging approach. Olefins, a fundamental chemical process, are used to synthesize polymers such as plastics and rubber. Aromatics, on the other hand, are crucial raw materials in organic chemical industry, widely used in synthetic resins, fibers, dyes, pharmaceuticals, and fragrances. Currently, olefins and aromatics are primarily produced through petrochemical routes such as naphtha catalytic reforming, which presents a carbon-hydrogen imbalance between the raw material and the target product. By coupling CO₂ with hydrogen-rich alkanes, the carbon-hydrogen balance of the reaction can be manipulated, improving the selectivity of the target product while simultaneously converting CO₂ into useful chemical raw materials or products, thereby realizing resource utilization.

[0004] The conversion of CO2 into valuable products is one of the most promising pathways for consuming CO2. For example, CO2 can be used as a chemical feedstock to synthesize oxygenates such as dimethyl carbonate and carboxylic acids at low temperatures. However, these oxygenates are typically fine chemicals, and the demand for these compounds is low, making them insufficient for consuming large amounts of CO2. Considering the large amount of CO2, the valuable chemicals produced by CO2 conversion must be commodity chemicals in order to neutralize CO2 and effectively close the carbon cycle, thereby mitigating the dramatic climate change caused by the "greenhouse effect." It has been demonstrated that the formation of olefins and aromatics can be enhanced by the CO2 oxidative dehydrogenation of alkanes, where CO2 forms acrolein from the hydrogen released by the alkanes and is converted to CO via the water-gas shift (RWGS) reaction. However, due to the high thermal stability of CO2 (ΔGf° = -396 kJ / mol), using CO2 as a direct carbon source to produce commodity chemicals such as olefins and aromatics is a significant challenge. Summary of the Invention

[0005] In order to solve the technical problems of poor hydrothermal stability, weak carbon dioxide adsorption capacity and low conversion rate of existing catalysts, theoretical calculations have shown that low-carbon alkanes and carbon dioxide have a good matching effect on metal active centers and can synergistically catalyze (such as Figure 1 ), therefore, the present invention provides a catalyst for the co-conversion of carbon dioxide and low-carbon alkanes to produce rich aromatics and a preparation method thereof. The prepared catalyst (Zn-modified ZSM-5 molecular sieve) is prepared by post-treatment recrystallization to adjust the B acidity and pores of the ZSM5 molecular sieve, and in the later stage of recrystallization, a metal salt is added in an alkaline environment to form a metal oxide shell on the surface of the ZSM5 molecular sieve. The lattice oxygen defects of the metal oxide are utilized to improve the adsorption and conversion capacity of carbon dioxide. Under relatively mild reaction conditions, it can catalyze the co-conversion reaction of carbon dioxide and low-carbon alkanes to obtain a high carbon dioxide and alkane conversion rate and aromatics selectivity.

[0006] The technical solutions of the present invention are as follows:

[0007] A catalyst for the carbon cycle to enrich aromatics is a molecular sieve metal oxide composite bifunctional (B / L acid synergistic catalysis + lattice oxygen vacancy of metal oxide) catalytic system, comprising a carrier, an active component and nano-scale activated carbon AC. The carrier is a ZSM-5 zeolite molecular sieve with a pore size distribution of 0.2-0.4 nm. The active component is ZnO inside the molecular sieve pores and ZnZrO dispersed on the outer surface of the molecular sieve. x ; The mass ratio of each material in the catalyst is 100ZSM5:6-9ZnO:6-20ZnZrOx:1-5AC.

[0008] The present invention provides a preparation method of the catalyst, which comprises the following steps: adding Zn-modified ZSM-5 molecular sieve to an organic alkaline solution, stirring evenly, transferring the mixture to a crystallization kettle, performing a recrystallization reaction, opening the kettle after the recrystallization reaction, adding zinc salt, zirconium salt and nano-grade activated carbon, stirring for 4-8 hours, and filtering the solid matter, drying, and calcining the solid matter to obtain a carbon cycle catalyst for rich production of aromatic hydrocarbons (molecular sieve metal oxide composite bifunctional catalyst).

[0009] The organic alkali solution is selected from at least one of TMAOH solution, TEAOH solution, TPAOH solution, TBAOH solution, n-butylamine solution and ethylenediamine solution.

[0010] The concentration of the organic alkali solution is 0.1 to 4.0 mol / L; the mass ratio of the organic alkali solution to the Zn-modified ZSM-5 molecular sieve is 2 to 10:1.

[0011] The conditions of the recrystallization reaction are: temperature of 150° C. to 200° C., and time of 12 to 48 hours.

[0012] The zinc salt is one or more of zinc chloride, zinc nitrate, zinc sulfate and zinc acetate; the zirconium salt is one or more of zirconium nitrate, zirconium citrate and zirconium n-propoxide; the amount of the zinc salt added is 1-5% of the mass of the Zn-modified ZSM-5 molecular sieve based on the weight of Zn; the amount of the zirconium salt added is 5-15% of the mass of the Zn-modified ZSM-5 molecular sieve based on the weight of Zr.

[0013] The addition amount of nano-scale activated carbon AC is 1-3% of the mass of the Zn-modified ZSM-5 molecular sieve.

[0014] The preparation method of Zn-modified ZSM-5 molecular sieve comprises the following steps:

[0015] Preparation of S1 impregnation solution: Add zinc salt to deionized water. The amount of deionized water added is the same as the amount of ZSM-5 molecular sieve added. The amount of zinc salt added is 1-10% of the weight of Zn based on the weight of ZSM-5 molecular sieve. This solution is recorded as one part, and the impregnation solution is 3-5 parts of this solution.

[0016] S2: Slowly add ZSM-5 zeolite to the impregnation solution, and place the mixed solution in a water bath, set the temperature to 50-80°C, stir for 4-8 hours, and filter the solid obtained by drying and calcining to obtain Zn-modified ZSM-5 molecular sieve.

[0017] The zinc salt is one or more of zinc chloride, zinc nitrate, zinc sulfate and zinc acetate.

[0018] The drying temperature is 100-110° C., the roasting temperature is 540-550° C., and the roasting time is 4-6 hours.

[0019] The present invention also provides application of the catalyst in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons.

[0020] Compared with existing modification technologies, the beneficial effects of this application include:

[0021] The catalyst of the present invention is suitable for the co-conversion of low-carbon alkanes and carbon dioxide: (1) This patent adopts the steps of recrystallization of zinc-modified ZSM-5 molecular sieve (such as zinc salt solution impregnated ZSM-5 molecular sieve) and modification of zinc salt, zirconium salt and nano-scale activated carbon. Compared with zinc-modified ZSM-5 molecular sieve, it has a higher specific surface area and perfect mesoporous composite pores, and has more superior diffusion performance, which can improve the conversion rate of alkanes and carbon dioxide, as well as the rapid diffusion of product aromatics, and avoid the deep reaction of product aromatics to reduce selectivity. (2) The alkaline environment provided by the recrystallized ammonium salt solution is fully utilized to modify the metal solid solution on the outer surface of the catalyst, which not only saves production costs, but also the lattice oxygen defect sites of the metal solid solution interact strongly with carbon dioxide molecules, thereby improving the conversion rate of carbon dioxide. In addition, the addition of activated carbon in the modification process plays a role in pore formation, and the diffusion problem of the outer surface is also well solved. Therefore, the molecular sieve metal oxide composite bifunctional catalytic system shows high carbon dioxide, alkane conversion rate and aromatics selectivity in the reaction of co-conversion of carbon dioxide and low-carbon alkanes to produce rich aromatics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the reaction pathway for the co-conversion of light alkanes with carbon dioxide for theoretical calculation prediction;

[0023] Figure 2 TEM images of sample ZP-Zn6 of comparative example 1 and sample ZM-Zn6-ZnZrOx-3 of example 3. DETAILED DESCRIPTION

[0024] Comparative Example 1

[0025] 10g of calcined and dehydrated ZSM-5 molecular sieve was loaded with 6% Zn using the four-fold impregnation method: 8.12g of zinc acetate dihydrate was added to 40g of deionized water, stirred thoroughly, and then 10g of ZSM-5 was added. The mixture was placed in a water bath set to 60°C and stirred for 6 hours. The resulting solid was dried in a 110°C oven for 8 hours and then calcined in a muffle furnace at 550°C for 5 hours to obtain Zn-modified ZSM-5 molecular sieve ZP-Zn6.

[0026] Example 1

[0027] 50g of a 1.2mol / L n-butylamine solution was placed in a reactor, followed by the addition of 5g of the ZP-Zn6 sample. After shaking, the reactor was placed in a 170°C oven for 24 hours. The reactor was then opened and 0.34g of zinc acetate dihydrate (2% Zn), 1.41g of zirconium nitrate pentahydrate (6% Zr), and 0.05g of nano-activated carbon were added, followed by stirring at 25°C for 6 hours. The resulting solid was then filtered and dried in a 110°C oven for 8 hours, followed by calcination in a muffle furnace at 550°C for 5 hours, yielding the molecular sieve metal oxide composite catalyst ZM-Zn6-ZnZrOx-1.

[0028] Example 2

[0029] 50g of a 1.5mol / L TPAOH solution was placed in a reactor, and 5g of the ZP-Zn6 sample was added. After shaking, the reactor was placed in an oven at 180°C for 24 hours. The reactor was then opened and 0.68g of zinc acetate dihydrate (4% Zn), 2.82g of zirconium nitrate pentahydrate (12% Zr), and 0.08g of nano-activated carbon were added. The mixture was stirred at 25°C for 6 hours. The resulting solid was dried in a 110°C oven for 8 hours and then calcined in a muffle furnace at 550°C for 5 hours to obtain the molecular sieve metal oxide composite catalyst ZM-Zn6-ZnZrOx-2.

[0030] Example 3

[0031] 50g of a 1.5mol / L TPAOH solution was placed in a reactor, and 5g of the ZP-Zn6 sample was added. After shaking, the reactor was placed in an oven at 180°C for 24 hours. The reactor was then opened and 0.85g of zinc acetate dihydrate (5% Zn), 3.54g of zirconium nitrate pentahydrate (15% Zr), and 0.15g of nano-activated carbon were added. The mixture was stirred at 25°C for 6 hours. The resulting solid was dried in a 110°C oven for 8 hours and then calcined in a muffle furnace at 550°C for 5 hours to obtain the molecular sieve metal oxide composite catalyst ZM-Zn6-ZnZrOx-3.

[0032] Example 4

[0033] In a fixed bed reactor, 500 ° C, WHSV = 0.5h -1 , n-hexane / N2=50:50 (v / v), the experimental data after stable operation for 24 hours are shown in Table 1:

[0034] Table 1 Catalytic results of catalysts

[0035] catalyst ZP-Zn6 ZM-Zn6-ZnZrOx-1 ZM-Zn6-ZnZrOx-2 ZM-Zn6-ZnZrOx-3 <![CDATA[CO2 / n - hexane (% vol)]]> 0.46 0.46 0.46 0.46 n-Hexane conversion rate (%) 96.11 98.32 98.12 98.55 <![CDATA[CO2 conversion rate (%)]]> 11.95 20.03 22.11 23.78 Aromatic selectivity (%) 24.64 32.47 33.09 34.09

[0036] It can be seen from the reaction data that compared with the ZP-Zn6 catalyst prepared by the traditional method, the catalyst prepared by the patented method has better catalytic activity. The conversion rate of n-hexane is not significantly improved, but the conversion rate of carbon dioxide and the selectivity of the product aromatics are significantly improved.

[0037] Example 5

[0038] The samples were characterized by TEM, with the comparative example ZP-Zn6 and the sample ZM-Zn6-ZnZrOx-3 from Example 3 as examples. The TEM results are shown in the figure. The results show that the sample ZM-Zn6-ZnZrOx-3 contains two distinct phases: a metal oxide and a zeolite crystalline phase, with the metal oxide located on the outer surface of the molecular sieve.

[0039] Example 6

[0040] The specific surface area and pore volume and other structural properties of the catalyst were characterized by N2 physical adsorption and desorption, as shown in Table 2. Usually, the loading of oxides on the external surface will lead to blockage of the molecular sieve pores. However, the recrystallization of this patent and the addition of pore-forming activated carbon during the oxide deposition process not only do not lead to blockage of the molecular sieve pores, but to a certain extent, repair the decrease in surface area caused by the early loading of zinc. In addition, due to the introduction of oxides, a certain amount of mesopores are introduced, so the catalyst prepared by this patent has rich meso-micro composite pores.

[0041] Table 2 Structural properties of catalysts

[0042]

Claims

1. A carbon cycle catalyst for enriching aromatics in the co-conversion of carbon dioxide and light alkanes to enrich aromatics, characterized by: The catalyst is a molecular sieve metal oxide composite bifunctional catalytic system, including a carrier, an active component and nano-scale activated carbon AC. The carrier is a ZSM-5 zeolite molecular sieve with a pore size distribution of 0.2-0.4 nm. The active component is ZnO inside the molecular sieve pores and ZnZrO dispersed on the outer surface of the molecular sieve. x The mass ratio of each substance in the catalyst is 100ZSM-5: 6-9ZnO: 6-20ZnZrOx: 1-5AC. The preparation method of the catalyst comprises the following steps: adding Zn-modified ZSM-5 molecular sieve to an organic alkaline solution, stirring evenly, transferring the mixture to a crystallization kettle, performing a recrystallization reaction, opening the kettle after the recrystallization reaction, adding zinc salt, zirconium salt and nano-grade activated carbon, stirring for 4-8 hours, and filtering the solid matter, drying, and calcining the solid matter to obtain a carbon cycle catalyst for rich production of aromatics.

2. Use of a catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The organic alkali solution is selected from at least one of TMAOH solution, TEAOH solution, TPAOH solution, TBAOH solution, n-butylamine solution and ethylenediamine solution; the concentration of the organic alkali solution is 0.1-4.0 mol / L.

3. Use of a catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The mass ratio of the organic base solution to the Zn-modified ZSM-5 molecular sieve is 2-10:

1.

4. Use of a catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The conditions of the recrystallization reaction are: temperature of 150° C. to 200° C. and time of 12 to 48 hours.

5. Use of the catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The zinc salt is one or more of zinc chloride, zinc nitrate, zinc sulfate and zinc acetate; the zirconium salt is one or more of zirconium nitrate, zirconium citrate and zirconium n-propoxide; the amount of the zinc salt added is 1-5% of the mass of the Zn-modified ZSM-5 molecular sieve based on the weight of Zn; the amount of the zirconium salt added is 5-15% of the mass of the Zn-modified ZSM-5 molecular sieve based on the weight of Zr.

6. Use of a catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The addition amount of nano-scale activated carbon AC is 1-3% of the mass of Zn-modified ZSM-5 molecular sieve.

7. Use of the catalyst for enriching aromatic hydrocarbons through carbon cycle according to claim 1 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The preparation method of Zn-modified ZSM-5 molecular sieve comprises the following steps: S1 Preparation of impregnation solution: Add zinc salt to deionized water. The amount of deionized water added is the same as the amount of ZSM-5 molecular sieve added. The amount of zinc salt added is 1-10% of the weight of Zn based on the weight of ZSM-5 molecular sieve. This solution is recorded as one part, and the impregnation solution is 3-5 parts of this solution. S2 Slowly add ZSM-5 zeolite to the impregnation solution, and place the mixture in a water bath, set the temperature to 50-80°C, stir for 4-8 hours, and filter the solid obtained by drying and calcining to obtain Zn-modified ZSM-5 molecular sieve.

8. Use of a catalyst for enriching aromatic hydrocarbons in carbon cycle according to claim 1 or 7 in co-conversion of carbon dioxide and light alkanes to enrich aromatic hydrocarbons, characterized in that: The drying temperature is 100-110° C., the roasting temperature is 540-550° C., and the roasting time is 4-6 hours.

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