Composite catalyst, its preparation method and application

Abstract

This invention discloses a composite catalyst, its preparation method, and its application. The composite catalyst comprises a metal oxide and a carbon-modified molecular sieve. The preparation method of the composite catalyst includes the following steps: (1) the molecular sieve undergoes pre-carbon deposition treatment to obtain a carbon-modified molecular sieve; (2) the metal oxide and the carbon-modified molecular sieve are mixed to obtain the composite catalyst. The composite catalyst provided by this invention is used in the CO / CO2 hydrogenation reaction to produce light aromatics, exhibiting high catalytic activity and high selectivity for light aromatics.

Description

Technical Field

[0001] This invention relates to the field of catalysis, specifically to a composite catalyst and its preparation method, and its application in the preparation of light aromatic hydrocarbons. Background Technology

[0002] Syngas is an important platform for producing chemicals as an alternative to petroleum. It can be derived from natural gas, coal, biomass, etc., and through different catalysts, syngas can be used to produce high-value-added basic chemicals such as oxygenated compounds, C2-C4 hydrocarbons, liquid fuels, and aromatics. Among these, aromatic products, especially BTX (benzene, toluene, and xylene, also known as light aromatics), are raw materials for the synthesis of styrene, polyamide resins, terephthalic acid, etc., and have significant commercial value, attracting widespread attention.

[0003] CN116410044 A discloses a catalyst for preparing aromatics from syngas, comprising an active component and a coating, the coating covering the active component. The active component includes a copper-based metal oxide and a modified HZSM-5 molecular sieve, and the coating includes an alumina-based compound and silicon carbide. This catalyst exhibits high strength and good wear resistance. However, the product of this reaction is heavy aromatics.

[0004] CN110201709A discloses a composite catalyst for the direct production of high-value aromatics from syngas. This catalyst is prepared by mechanically mixing a metal oxide with nano-HZSM-5 molecular sieves or metal-modified nano-HZSM-5 molecular sieves; wherein the metal oxide is at least one of sodium, potassium, iron, and manganese oxides. Using this catalyst enables the coupling of multiple reaction stages, effectively improving the driving force of intermediate reactions, increasing the conversion efficiency of syngas, and reducing the occurrence of side reactions. The CO conversion rate can reach 95%, but the selectivity for aromatics among the organic products is relatively low (<60%).

[0005] Although existing technologies have been studied in the field of CO / CO2 aromatics production, the selectivity for light aromatics (benzene, toluene, xylene, abbreviated as BTX) in the coupled system, which are in high demand, is low. Therefore, further improving the selectivity of BTX is of great significance. Summary of the Invention

[0006] To address the technical problem of low selectivity for light aromatics in the one-step CO / CO2 hydrogenation reaction for producing aromatics in existing technologies, this invention provides a composite catalyst, its preparation method, and its application. The composite catalyst provided by this invention exhibits high catalytic activity and high selectivity for light aromatics in the CO / CO2 hydrogenation reaction.

[0007] The first aspect of the present invention provides a composite catalyst, wherein the catalyst comprises a metal oxide and a carbon-modified molecular sieve.

[0008] Furthermore, in the catalyst, the mass content of the metal oxide is 50-83% based on the mass of the catalyst.

[0009] Furthermore, in the catalyst, the mass content of carbon-modified molecular sieve is 17-50% based on the mass of the catalyst.

[0010] Furthermore, in the carbon-modified molecular sieve, the carbon content is 0.2-8% based on the mass of the carbon-modified molecular sieve, preferably 0.5-5%.

[0011] Furthermore, the metal oxide in the catalyst is selected from MnO. x CrO x Zn a Cr b O x Zn a Zr b O x Zn a Mn b O x Zn a Ce b O x Ce a Zr b O x Ce a Mn b O x At least one of them, preferably MnO x CrO x Zn a Cr b O x Zn a Zr b O x Ce a Zr b O x Ce a Mn b O x At least one of the oxides, wherein the atomic ratio of a to b is 1:(1-100), preferably (2-80), and the x value is independently the total number of oxygen atoms required to satisfy the valence of each element in the metal oxide. The values ​​of a and b may be the same or different in each metal oxide.

[0012] Furthermore, the molecular sieve in the catalyst is selected from at least one of MFI or MEL molecular sieves, preferably at least one of ZSM-5 and ZSM-11. The Si / Al atomic ratio of the molecular sieve is preferably 40 to 300.

[0013] Furthermore, the specific surface area of ​​the carbon-modified molecular sieve is 300–500 m². 2 / g.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned composite catalyst, comprising the following steps:

[0015] (1) Molecular sieves are pre-carbonized to obtain carbon-modified molecular sieves;

[0016] (2) The metal oxide and the carbon-modified molecular sieve are mixed to obtain the composite catalyst.

[0017] Further, the pre-carbonization treatment process in step (1) includes: heating the molecular sieve in an atmosphere containing organic gas; wherein the heating treatment conditions include: treating at 300-450°C for 0.5-8 hours, preferably 0.5-4 hours.

[0018] Further, the organic gas in step (1) is selected from at least one of methanol, ethanol, ethylene, propylene, butene, isobutene, ethane, propane, n-butane, and isobutane, preferably at least one of methanol, ethanol, ethylene, propylene, isobutene, ethane, and propane; the volume content of the organic gas in the atmosphere containing organic gas is 1% to 10%.

[0019] Further, the molecular sieves in step (1) are selected from at least one of MFI or MEL molecular sieves, preferably at least one of ZSM-5 and ZSM-11.

[0020] Furthermore, the metal oxide described in step (2) can be commercially available or prepared using existing methods. The preparation method can employ conventional techniques in the art, such as precipitation, which involves contacting a metal salt solution with a precipitant to precipitate the metal.

[0021] Furthermore, in step (2), the mixing method of the metal oxide and carbon-modified molecular sieve adopts conventional methods in the art, preferably physical mixing.

[0022] Further, in step (2), the mass ratio of the metal oxide and the carbon-modified molecular sieve is (1-5):1.

[0023] A third aspect of the present invention provides the application of the above-mentioned catalyst in the preparation of light aromatic hydrocarbons.

[0024] Furthermore, the reaction for preparing light aromatics includes a reaction involving the hydrogenation of carbon monoxide to prepare light aromatics.

[0025] Furthermore, the reaction for preparing light aromatics includes the reaction of hydrogenating carbon dioxide to prepare light aromatics.

[0026] Furthermore, the reaction for preparing light aromatics by hydrogenation of carbon monoxide includes: reacting a mixture of carbon monoxide and hydrogen as raw material with the catalyst to prepare light aromatics. Preferably, the light aromatics are aromatics with 6-8 carbon atoms, more preferably including at least one of benzene, toluene, and xylene.

[0027] Furthermore, the operating conditions for the reaction of preparing light aromatics by hydrogenation of carbon monoxide include: a reaction temperature of 350–450°C, preferably 370–420°C; and / or a reaction pressure of 1–10 MPa, preferably 2–8 MPa; and / or a volume hourly space velocity of 100–10000 h⁻¹. -1 Preferably 300-8000h -1 ; and / or, the molar ratio of hydrogen to carbon monoxide is 0.4 to 5, preferably 0.5 to 3.

[0028] Furthermore, the reaction for preparing light aromatics by hydrogenation of carbon dioxide includes: reacting a mixture of carbon dioxide and hydrogen as raw material with the catalyst to obtain light aromatics. Preferably, the light aromatics are aromatics with 6-8 carbon atoms.

[0029] Furthermore, the operating conditions for the reaction of hydrogenating carbon dioxide to prepare light aromatics include: a reaction temperature of 300–450°C, preferably 320–400°C; and / or a reaction pressure of 1–10 MPa, preferably 2–8 MPa; and / or a volume hourly space velocity of 100–10000 h⁻¹. -1 Preferably 300-8000h -1 ; and / or, the molar ratio of hydrogen to carbon dioxide is 2 to 7, preferably 2 to 5.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The inventors discovered through research that using carbon-modified molecular sieves as one component of a composite catalyst can, on the one hand, pre-coke the molecular sieve channels and cages, shortening the induction period of the reaction; on the other hand, it can carbon-cover the outer surface of the molecular sieve, appropriately shielding the acidic sites on the outer surface. Combined with the other component, metal oxides, this can effectively suppress the alkylation side reactions of light aromatic hydrocarbons while improving activity and reducing C9... + Selectivity of aromatic hydrocarbons.

[0032] 2. When the catalyst of this invention is applied to the reaction of CO hydrogenation or CO2 hydrogenation to prepare light aromatics, it can significantly improve the activity and the selectivity of BTX in aromatics without reducing the total aromatics selectivity. Detailed Implementation

[0033] The technical solution of the present invention will be further illustrated below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] In this paper, the post-reaction components were separated and quantitatively analyzed by gas chromatography. The formulas for calculating CO conversion, aromatic selectivity, and alkane selectivity in the reaction of carbon monoxide and hydrogen to produce aromatics are as follows:

[0035] CO conversion rate (%) = CO conversion amount / CO feed amount × 100%, in molar quantity;

[0036] Aromatic selectivity (%) = (number of moles of aromatics produced / total number of moles of organic products) × 100%;

[0037] BTX / Aromatics (%) = Number of moles of BTX produced / Number of moles of aromatics produced × 100%.

[0038] In this paper, the post-reaction components were separated and quantitatively analyzed by gas chromatography. The formulas for calculating CO2 conversion, aromatic selectivity, and alkane selectivity in the reaction of carbon dioxide and hydrogen to produce aromatics are as follows:

[0039] CO2 conversion rate = CO2 conversion amount / CO2 feed amount × 100%, in terms of amount of substance;

[0040] Aromatic selectivity (%) = (number of moles of aromatics produced / total number of moles of organic products) × 100%;

[0041] BTX / Aromatics (%) = Number of moles of BTX produced / Number of moles of aromatics produced × 100%.

[0042] In this paper, thermogravimetric analysis (TGA) was used to detect carbon species in the catalyst. TG was performed by heating to 800℃ at a rate of 10℃ / min and an air flow rate of 100 mL / min.

[0043]

Example 1

[0044] Cr₂O₃ catalyst was prepared by precipitation method. 0.5 mol of chromium nitrate was dissolved in 1000 mL of distilled water, and 1.5 mol of sodium hydroxide was dissolved in 1000 mL of water. The two aqueous solutions were co-precipitated under parallel flow, aged at 80 °C for 2 h, filtered, dried at 100 °C overnight, and calcined in air at 500 °C for 1 h to obtain Cr₂O₃.

[0045] ZSM-5 molecular sieves were purchased from the catalyst factory of Nankai University, with a silicon-to-aluminum atomic ratio of 100.

[0046] ZSM-5 molecular sieve was first treated with nitrogen at 400℃ for 1 hour, followed by the introduction of an organic gas mixture of ethylene and nitrogen (nethylene:nnitrogen = 2:98) at 400℃ for 1 hour. Then, nitrogen was introduced for purging and cooling to obtain carbon-modified molecular sieve C / ZSM-5. The specific surface area of ​​carbon-modified molecular sieve C / ZSM-5 is 358 m². 2 / g. The carbon content in the carbon-modified molecular sieve C / ZSM-5 is 1.5% by mass.

[0047] A composite catalyst was obtained by grinding and mixing 1.0 g of Cr2O3 oxide and 1.0 g of carbon-modified molecular sieve C / ZSM-5. The mass ratio of the metal oxide to the carbon-modified molecular sieve C / ZSM-5 was 50:50.

[0048]

Example 2

[0049] ZnZr was prepared by precipitation method 10 O x Catalyst. Weigh 0.5 mol of zirconium nitrate and 0.05 mol of zinc nitrate, dissolve them in 1000 mL of distilled water, then dissolve 2.1 mol of sodium hydroxide in 1000 mL of water. Co-precipitate the two aqueous solutions under co-current flow, age at 80 °C for 2 h, filter, dry at 100 °C overnight, and calcine in air at 500 °C for 1 h to obtain ZnZr. 10 O x .

[0050] The ZSM-5 molecular sieve and its carbon modification are the same as in Example 1.

[0051] Add 1.0g of ZnZr 10 O x The composite catalyst was obtained by grinding and mixing 1.0 g of carbon-modified molecular sieve C / ZSM-5. The mass ratio of metal oxide to carbon-modified molecular sieve C / ZSM-5 was 50:50.

[0052]

Example 3

[0053] Cr2O3 is the same as in Example 1.

[0054] The ZSM-5 molecular sieve and its carbon modification are the same as in Example 1.

[0055] A composite catalyst was obtained by grinding and mixing 2.0 g of Cr2O3 oxide and 1.0 g of carbon-modified molecular sieve C / ZSM-5. The mass ratio of the metal oxide to the carbon-modified molecular sieve C / ZSM-5 was 67:33.

[0056]

Example 4

[0057] Cr2O3 is the same as in Example 1.

[0058] ZSM-5 is the same as in Example 1.

[0059] ZSM-5 molecular sieve was first treated with nitrogen at 400℃ for 1 hour, followed by the introduction of an organic gas mixture of ethylene and nitrogen (nethylene:nnitrogen = 5:95) at 400℃ for 1 hour. Then, nitrogen was introduced for purging and cooling to obtain carbon-modified molecular sieve C / ZSM-5. The specific surface area of ​​the carbon-modified molecular sieve was 332 m². 2 / g. The carbon content of the carbon-modified molecular sieve C / ZSM-5 is 2.4% by mass.

[0060] A composite catalyst was obtained by grinding and mixing 1.0 g of Cr2O3 oxide and 1.0 g of carbon-modified molecular sieve C / ZSM-5. The mass ratio of the metal oxide to the carbon-modified molecular sieve C / ZSM-5 was 50:50.

[0061]

Example 5

[0062] Cr2O3 is the same as in Example 1.

[0063] ZSM-5 is the same as in Example 1.

[0064] ZSM-5 molecular sieve was first treated with nitrogen at 400℃ for 1 hour, followed by the introduction of an organic gas mixture of methanol and nitrogen (n-methanol:n-nitrogen = 10:90) at 400℃ for 1 hour. Then, nitrogen was introduced for purging and cooling to obtain carbon-modified molecular sieve C / ZSM-5. The specific surface area of ​​carbon-modified molecular sieve C / ZSM-5 is 295 m². 2 / g. The carbon content of the carbon-modified molecular sieve C / ZSM-5 is 3.0% by mass.

[0065] A composite catalyst was obtained by grinding and mixing 1.0 g of Cr2O3 oxide and 1.0 g of carbon-modified molecular sieve C / ZSM-5. The mass ratio of the metal oxide to the carbon-modified molecular sieve was 50:50.

[0066] Comparative Example 1

[0067] Cr2O3 is the same as in Example 1.

[0068] ZSM-5 molecular sieve is the same as in Example 1.

[0069] A composite catalyst was obtained by grinding and mixing 1.0 g of Cr2O3 oxide and 1.0 g of ZSM-5 molecular sieve. The mass ratio of metal oxide to molecular sieve was 50:50.

[0070] Comparative Example 2

[0071] Cr2O3 is the same as in Example 1.

[0072] ZSM-5 molecular sieve is the same as in Example 1.

[0073] 1.0 g of Cr₂O₃ oxide and 1.0 g of ZSM-5 molecular sieve were ground and mixed, and an organic gas mixture of ethylene and nitrogen (nethylene:nnitrogen = 2:98) was introduced. The mixture was treated at 400 °C for 1 h to complete the pre-coking treatment and obtain the catalyst. The carbon content in the catalyst was 2.3% by mass.

[0074] Comparative Example 3

[0075] The Cr2O3 oxide is the same as in Example 1.

[0076] ZSM-5 molecular sieve is the same as in Example 1.

[0077] The Cr2O3 oxide was first treated with nitrogen at 400℃ for 1 hour, then a mixture of organic gases of ethylene and nitrogen (nethylene:nnitrogen = 2:98) was introduced and treated at 400℃ for 1 hour. Finally, nitrogen was introduced to purge and cool down to obtain the pre-coked metal oxide C / Cr2O3.

[0078] A composite catalyst was obtained by grinding and mixing 1.0 g of pre-coated metal oxide C / Cr2O3 and 1.0 g of ZSM-5 molecular sieve. The mass ratio of pre-coated metal oxide C / Cr2O3 to ZSM-5 molecular sieve was 50:50. The carbon content of the pre-coated metal oxide C / Cr2O3 was 1.2% by mass.

[0079] [Application Test 1]

[0080] The catalysts described in Examples 1-5 and Comparative Examples 1-3 were used in evaluation tests for the hydrogenation of carbon monoxide to produce light aromatics. The specific process is as follows:

[0081] The catalyst was granulated to 20-40 mesh and packed into a quartz reaction tube with an inner diameter of 6 mm. Before the reaction, it was reduced with hydrogen at 400℃ for 2 hours. After the reduction was complete, hydrogen and carbon monoxide (n hydrogen:n carbon monoxide = 50:50) were introduced into the reaction tube and allowed to react in the catalytic bed. The reaction temperature was 400℃, the reaction system pressure was 5 MPa, and the gas hourly space velocity was 2000 h⁻¹. -1 The synthesis of aromatics from syngas was carried out under the specified conditions. The activity evaluation results are shown in Table 2.

[0082] [Application Test 2]

[0083] The catalysts described in Example 1 and Comparative Example 1 were used in the evaluation test of the reaction of carbon dioxide hydrogenation to produce light aromatics. The specific process is as follows:

[0084] The catalyst was granulated to 20-40 mesh and packed into a quartz reaction tube with an inner diameter of 6 mm. Before the reaction, it was reduced with hydrogen at 400℃ for 3 hours. After the reduction was complete, hydrogen and carbon dioxide (nhydrogen:ncarbon dioxide = 67.5:22.5) were introduced into the reaction tube and allowed to react in the catalytic bed. The reaction temperature was 370℃, the reaction system pressure was 5 MPa, and the gas hourly space velocity was 2000 h2. -1 The synthesis of aromatics from syngas was carried out under the specified conditions. The activity evaluation results are shown in Table 3.

[0085] Table 1. Physicochemical properties of each embodiment and comparative example.

[0086]

[0087] Table 2 Catalytic performance results of each example and comparative example.

[0088]

[0089] Table 3 Catalytic performance results of Example 1 and Comparative Example 1

[0090]

Claims

1. A composite catalyst, characterized in that, The catalyst comprises metal oxides and carbon-modified molecular sieves.

2. The composite catalyst according to claim 1, characterized in that, The metal oxide in the catalyst is selected from MnO. x CrO x Zn a Cr b O x Zn a Zr b O x Zn a Mn b O x Zn a Ce b O x Ce a Zr b O x Ce a Mn b O x At least one of them, preferably MnO x CrO x Zn a Cr b O x Zn a Zr b O x Ce a Zr b O x Ce a Mn b O x At least one of the oxides, wherein the atomic ratio of a to b is 1:(1 to 100), and the x value is independently the total number of oxygen atoms required to satisfy the valence of each element in the metal oxide.

3. The composite catalyst according to claim 1, characterized in that, In the carbon-modified molecular sieve, the carbon content is 0.2-8% by mass, preferably 0.5-5%, based on the mass of the carbon-modified molecular sieve. And / or, the molecules in the catalyst are screened from at least one of MFI or MEL molecular sieves, preferably at least one of ZSM-5 and ZSM-11; And / or, the Si / Al atomic ratio of the molecular sieve is 40 to 300; And / or, the specific surface area of ​​the carbon-modified molecular sieve is 300–500 m². 2 / g.

4. The composite catalyst according to claim 1, characterized in that, In the catalyst, the mass content of the metal oxide is 50-83% based on the mass of the catalyst. And / or, in the catalyst, the mass content of carbon-modified molecular sieve is 17-50% based on the mass of the catalyst.

5. A method for preparing the composite catalyst according to any one of claims 1-4, comprising the following steps: (1) Molecular sieves are pre-carbonized to obtain carbon-modified molecular sieves; (2) The metal oxide and the carbon-modified molecular sieve are mixed to obtain the catalyst.

6. The preparation method according to claim 5, characterized in that, The pre-carbon deposition treatment process in step (1) includes: heating the molecular sieve in an atmosphere containing organic gas; wherein the heating treatment conditions include: treating at 300-450°C for 0.5-8 hours, preferably 0.5-4 hours.

7. The preparation method according to claim 5, characterized in that, The organic gas in step (1) is selected from at least one of methanol, ethanol, ethylene, propylene, butene, isobutene, ethane, propane, n-butane, and isobutane, preferably at least one of methanol, ethanol, ethylene, propylene, isobutene, ethane, and propane; the volume content of the organic gas in the atmosphere containing organic gas is 1% to 10%. And / or, the molecular sieves in step (1) are selected from at least one of MFI or MEL molecular sieves, preferably at least one of ZSM-5 and ZSM-11. And / or, in step (2), the mass ratio of the metal oxide and the carbon-modified molecular sieve is (1-5):

1.

8. The application of the composite catalyst according to any one of claims 1-4 or the composite catalyst obtained by the preparation method according to any one of claims 5-7 in the preparation of light aromatic hydrocarbons.

9. The application according to claim 8, characterized in that, The reaction for preparing light aromatics includes the reaction of hydrogenating carbon monoxide to prepare light aromatics.

10. The application according to claim 8, characterized in that, The reaction for preparing light aromatics includes the reaction of hydrogenating carbon dioxide to prepare light aromatics.

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