Metal modified catalyst for CO2-assisted C5 hydrocarbon aromatization
By modifying ZSM-5 molecular sieve catalyst with Zn, the problem of low selectivity of light aromatics in CO2-assisted C5 hydrocarbon aromatization reaction was solved, and high conversion and high selectivity aromatization effect was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-03-24
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, and specifically to a method for preparing a Zn-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons. Background Technology
[0002] Light aromatic hydrocarbons (BTX) are mainly derived from catalytic reforming and catalytic cracking oils from fossil fuels, with limited production. C5 hydrocarbons, as petrochemical products, are widely available; their aromatization can not only enhance their resource value but also effectively supplement light aromatic hydrocarbons. Alkane aromatization is an endothermic reaction, with product distribution constrained by equilibrium, leading to low alkane conversion rates and catalyst deactivation due to coking. CO2, a major greenhouse gas, acts as a soft oxidant in tandem with alkane dehydrogenation aromatization, consuming the generated H2 and promoting coking oxidation, thus overcoming equilibrium constraints and improving catalytic performance. Furthermore, CO2 can react with catalyst coking via the Boudouard reaction (C + CO2 → 2CO), extending the molecular sieve lifetime. Therefore, the preparation of light aromatic hydrocarbons through the reaction of CO2 and C5 hydrocarbons has promising applications.
[0003] There are currently no reports on CO2-assisted aromatization reactions of C5 hydrocarbons. CO-assisted pentane aromatization is similar to CO2-assisted C5 hydrocarbon aromatization. In this reaction, H-ZSM-5 molecular sieve is used, with a pentane conversion rate close to 100%, ultimately yielding ~80% aromatic products, of which approximately 40% are BTX products. For pentane aromatization, metal-supported modified H-ZSM-5 is typically used, which achieves 100% pentane conversion and approximately 75% aromatic selectivity. For CO2-assisted alkane aromatization, Cu-modified Ga-MFI catalysts and Cu isomorphous substitution ZSM-5 While CO2 assists in improving the performance of propane and cyclohexane, the results are still not ideal. Therefore, these metal-modified molecular sieve methods offer limited improvement in alkane aromatization efficiency.
[0004] Patent CN 116726984 B uses Zn-modified ZSM-5 combined with ZnZrO x When applied to CO2-assisted hexane aromatization, the ZnO inside the molecular sieve channels improved the aromatic selectivity, but it still only reached 34.09%. Therefore, optimizing the Zn active sites for CO2-assisted C5 hydrocarbon dehydrogenation to enhance the activity of molecular sieves in the aromatization of C5 hydrocarbons to produce light aromatics is of great significance. Summary of the Invention
[0005] To address the problem of low selectivity for light aromatics in CO2-assisted C5 hydrocarbon aromatization reactions, this invention provides a metal-modified catalyst for CO2-assisted C5 hydrocarbon aromatization.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons is composed of metal Zn incorporated into a silicon-containing molecular sieve with an MFI topological framework. The Zn is added in situ during the preparation of the silicon-containing molecular sieve with an MFI topological framework. The performance is optimized by changing the structure and content of the active metal component on the molecular sieve.
[0008] Furthermore, the metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons includes silicon-containing molecular sieves with an MFI framework, including any one of ZSM-5, ZSM-11, and Y-type.
[0009] Furthermore, the method for preparing the metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons involves adding the silicon source, aluminum source, zinc source, template agent, mineralizer, and sodium hydroxide for preparing molecular sieves in batches or in one step to the solvent, mixing them evenly, reacting them at a certain temperature for a period of time, and then crystallizing, washing, drying, first calcination, cation exchange, and second calcination to obtain the metal-modified catalyst.
[0010] Furthermore, the molar ratio of silicon source: aluminum source: zinc source: template agent: sodium hydroxide: mineralizer used is 100:(0.1-4):(0.1-4):(0.1-200):(1-8):(10-80). More preferably, the silicon-zinc molar ratio is 30-200:1. Even more preferably, the molar ratio of silicon source to solvent is 1:(30-60).
[0011] Furthermore, the silicon source is one or more of tetraethyl orthosilicate, silica sol, water glass, and silica.
[0012] Furthermore, the zinc source is one or more of zinc chloride, zinc nitrate, and zinc acetate;
[0013] Furthermore, the aluminum source is one or more of aluminum chloride and aluminum nitrate;
[0014] Furthermore, the template agent is one or more selected from ethylenediamine, n-butylamine, tetrapropylammonium hydroxide, and ethylene glycol;
[0015] Furthermore, the mineralizing agent is one or more of ammonium fluoride and urea;
[0016] Furthermore, the solvent is one or more of water and ethanol;
[0017] Further, the preferred molar ratio of tetraethyl orthosilicate: aluminum nitrate: zinc nitrate: tetrapropylammonium hydroxide: ethylenediamine: water: sodium hydroxide: urea is 100:2.5:1.25:35:63:3600:4.65:62.
[0018] Furthermore, the reaction temperature after uniform mixing is 30-100℃.
[0019] Furthermore, the reaction time after uniform mixing is 10-300 minutes.
[0020] Furthermore, the crystallization step involves raising the temperature in an oven from room temperature to 150-180°C at a rate of 0.25-100°C / min, and maintaining the temperature at 150-180°C for 24-72 hours.
[0021] Furthermore, the drying temperature is 80-120℃, and the time is 6-24 hours. The cation exchange is performed using ammonium nitrate (NH4NO3) solution to obtain an NH4-type catalyst.
[0022] Furthermore, the temperature for the first and second roasting is 300-550℃, and the time is 4-12 hours.
[0023] The metal-modified catalyst described herein can be used in CO2-assisted aromatization reactions of C5 hydrocarbons, wherein the C5 hydrocarbons include any one of pentane, isopentane, n-pentene, and isopentene.
[0024] Furthermore, CO2 and C5 hydrocarbons are co-fed as reactants at a molar ratio of 0.01-50:1, with a C5 hydrocarbon mass hourly space velocity (HHSV) of 1-20 h⁻¹. -1 For CO2, nitrogen is selected as the carrier gas for feeding, with CO2 accounting for 5-100% of the nitrogen by volume, and the reaction temperature is 300-600℃.
[0025] Furthermore, the CO2-assisted aromatization reaction of C5 hydrocarbons is carried out in a fixed-bed reactor. 0.1-10g of metal-modified molecular sieves are placed in the fixed-bed reactor and first reduced at 400-600℃ for 0.5-10h under H2 atmosphere. Then, the mixture of CO2 and C5 hydrocarbons is switched to carry out the aromatization reaction.
[0026] Conventional H-ZSM-5 catalysts are aluminum-rich, resulting in numerous strong acid sites that facilitate alkane cracking, reduce aromatization efficiency, and promote surface alkylation of light aromatics. Introducing active metal Zn into the molecular sieve synthesis process can increase the number of aromatization sites, enhance the aromatization reaction, and improve the selectivity of light aromatics.
[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0028] The Zn-ZSM-5 catalyst used in this invention exhibits superior activity in CO2-assisted C5 hydrocarbon aromatization tests, at a pentane mass hourly space velocity (WHSV) of 1.6 h⁻¹. -1 At atmospheric pressure, with a pentane to CO2 feed molar ratio of 1:4, 100% pentane conversion and over 90% light aromatic selectivity were achieved, proving that it is a Zn-modified ZSM-5 catalyst with both high conversion and high light aromatic selectivity.
[0029] The catalyst Zn-ZSM-5 prepared by introducing Zn active sites in this invention has a simple process, high reproducibility, and can be produced on a large scale. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 SEM image of molecular sieve catalyst in Example 1.
[0032] Figure 2 XRD patterns of molecular sieve catalysts in Examples 1-2 and Comparative Examples 1-2.
[0033] Figure 3 UV-vis images of the molecular sieve catalysts of Examples 1-3 and Comparative Examples 1-5.
[0034] Figure 4 The graph shows a comparison of the CO2-assisted pentane aromatization performance of molecular sieve catalysts in Examples 1-3 and Comparative Examples 1-5. Detailed Implementation
[0035] The present invention will be further described in detail below with reference to specific examples and accompanying drawings. These examples will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. Furthermore, it is noted that for those skilled in the art, the optimal data in this invention are only applicable to this invention, and reasonable adjustments and improvements made without departing from the concept of the invention are all within the scope of protection of this invention.
[0036] Example 1
[0037] The formulation of tetraethyl orthosilicate:aluminum nitrate:zinc nitrate:tetrapropylammonium hydroxide:ethylenediamine:sodium hydroxide:urea in a molar ratio of 100:2.5:1.25:35:63:4.65:62 was used for synthesis (the preferred molar ratio of tetraethyl orthosilicate to water was 100:3600, but more or less was acceptable). Specifically, 5.6 g of tetraethyl orthosilicate (TEOS) was dissolved in 9.69 g of tetrapropylammonium hydroxide (20 wt.% TPAOH) to prepare mixed solution #1; 1 g of ethylenediamine (EDA) was dissolved in 3.5 mL of deionized water, and then 0.2 g of zinc nitrate (Zn(NO3)2) was added under vigorous stirring, and the reaction was carried out at room temperature for 60 minutes to prepare mixed solution #2; 0.05 g of sodium hydroxide (NaOH) and 1 0.126 g of urea (N2H4CNO) and 0.126 g of aluminum nitrate (Al(NO3)3) were dissolved in 6 mL of deionized water and stirred vigorously at room temperature for 60 minutes to prepare mixed solution #3. Solution #2 was added to solution #1 and stirred vigorously at 80 °C for at least 3 hours. Then solution #3 was added to the mixture and stirred until homogeneous. The solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and further placed in a programmed temperature oven for crystallization. The temperature in the oven was increased from room temperature to 180 °C at a rate of 15 °C / h and maintained at 180 °C for 48 hours. After the crystallization reaction was completed, the autoclave was removed and cooled. The obtained crystals were collected by filtration (washed several times with deionized water to remove the mother liquor) and dried overnight in an oven at 90 °C. The crystals were calcined in air at 550 °C for 5 hours to remove the template agent TPAOH.
[0038] Na-type 2Zn-ZSM-5-80 (i.e., 10 g) was dispersed in 1 M ammonium nitrate (NH4NO3) solution (i.e., 100 mL) under vigorous stirring via cation exchange (the steps were repeated at least three times). After 6 hours, it was converted to NH4-type 2Zn-ZSM-5-80. Finally, NH4-type 2Zn-ZSM-5-80 was converted to H-type 2Zn-ZSM-5-80 by a simple calcination step of calcining in air at 550°C for 5 hours.
[0039] Example 2
[0040] The implementation steps are similar to those in Example 1, except that the zinc source is 0.1g of zinc nitrate, and the final product is H-type 1Zn-ZSM-5-80.
[0041] Example 3
[0042] The implementation steps are similar to those in Example 1, except that the zinc source is 0.04g of zinc nitrate, and the final product is H-type 0.4Zn-ZSM-5-80.
[0043] Comparative Example 1
[0044] The steps are similar to those in Example 1, except that the aluminum nitrate is 0g, and the final product is H-type 2Zn-MFI.
[0045] Comparative Example 2
[0046] The steps are similar to those in Example 1, except that the zinc source is 0g of zinc nitrate and the aluminum source is 0.252g of aluminum nitrate, ultimately yielding H-type ZSM-5-40.
[0047] Comparative Example 3
[0048] The steps are similar to those in Example 1, except that the zinc source is 0g of zinc nitrate, and H-type ZSM-5-80 is finally obtained.
[0049] Comparative Example 4
[0050] The steps are similar to those in Example 2, except that the zinc source is 0g of zinc nitrate and the aluminum nitrate source is 0.063g, and H-type ZSM-5-120 is finally obtained.
[0051] Comparative Example 5
[0052] The steps were similar to those in Comparative Example 3, except that after obtaining H-type ZSM-5-80, Zn-ZSM-5-80-IE was obtained by ion exchange three times with 1M zinc nitrate solution at 80℃.
[0053] Characterization and performance testing
[0054] Example 1 was characterized by transmission electron microscopy (SEM), and the results are shown in [Figure number missing]. Figure 1 The molecular sieves are around 600 nm in size, have a uniform morphology, and a rough outer surface.
[0055] The ZSM-5 catalysts prepared in Examples 1-2 and Comparative Examples 1 and 3 were characterized by XRD, and the results are shown in the figure. Figure 2 .Depend on Figure 2 It can be seen that the preparation methods in the embodiments and comparative examples of this invention can all yield pure-phase, high-density ZSM-5 molecular sieves, without the characteristic diffraction peaks of ZnO, indicating that Zn species are highly dispersed on the catalyst surface. The XRD diffraction peak intensity of the Zn-MFI sample prepared using Comparative Example 1 is reduced, but no ZnO diffraction peaks are observed, indicating that Zn species are highly dispersed on the catalyst surface. Comparative Example 3 shows characteristic diffraction peaks consistent with typical H-ZSM-5-80.
[0056] Figure 3 The UV-Vis spectra of the molecular sieve catalysts prepared in Examples 1-3 and Comparative Examples 1, 3 and 5 are shown. Figure 2 The peaks at 260 nm, 300 nm, and 370 nm correspond to ZnOH species, ZnO clusters, and large-grained ZnO species, respectively. Figure 3 Examples 1-3 show that with increasing Zn content, the number of ZnOH species increases, while no ZnO clusters or large-grained ZnO species are observed, indicating that zinc species exist in a highly dispersed state. Figure 3 Comparative Examples 1 and 5 show that only ZnOH species appeared in Zn-MFI. The Zn-ZSM-5-80-IE catalyst prepared by the ion exchange method mainly exhibited the characteristic peak of ZnOH at 260 nm, indicating that the zinc species existed in a highly dispersed state. Figure 3 Comparative Example 3 shows that none of the above three peaks appeared on the H-ZSM-5-80 molecular sieve, which is consistent with the characteristics of H-ZSM-5-80.
[0057] The catalytic performance of 0.2 g catalysts obtained from Examples 1-2 and Comparative Examples 1-5, sieved to 40-60 mesh, was evaluated after reduction with 100% H2 at 550 °C for 2 h. The fixed-bed reaction temperature was 500 °C, the reaction pressure was 100 kPa, the pentane liquid injection rate was 0.5 mL / h, the CO2:N2 ratio was 2:3, and the space velocity was 6000 mL / g. cat / h, the molar ratio of pentane to CO2 feed is 1:4.
[0058] Pentane aromatization was carried out in a fixed-bed microreactor using eight catalysts from Examples 1-3 and Comparative Examples 1-5. The final product was analyzed online by gas chromatography, and the activity was as follows: Figure 4 As shown.
[0059] When the catalyst was from Example 1, the pentane conversion rate was 100%, the CO2 conversion rate was 6.0%, the aromatics selectivity was 91.3%, and the BTX selectivity among the aromatics was 90.3% (of which benzene accounted for 38.6%, toluene for 40.7%, and xylene for 11.0%). When the catalyst was from Example 2, the pentane conversion rate was 96.7%, the CO2 conversion rate was 9.6%, the aromatics selectivity was 85.0%, and the BTX selectivity among the aromatics was 82.4% (of which benzene accounted for 26.8%, toluene for 32.7%, and xylene for 22.9%). When the catalyst was Example 3, the pentane conversion rate was 97.9%, the CO2 conversion rate was 8.7%, the aromatics selectivity was 81.1%, and the BTX selectivity among the aromatics was 75.7% (of which benzene accounted for 24.1%, toluene for 30.2%, and xylene for 21.4%). When the catalyst was Comparative Example 1, the pentane conversion rate was 54.8%, the CO2 conversion rate was 8.8%, the aromatics selectivity was 39.0%, and the BTX selectivity among the aromatics was 35.2% (of which benzene accounted for 9.0%, toluene for 15.8%, and xylene for 10.4%). When the catalyst was Comparative Example 2, the pentane conversion rate was 88.3%, the CO2 conversion rate was 7.2%, the aromatics selectivity was 41.2%, and the BTX selectivity among aromatics was 38.3% (of which benzene accounted for 7.5%, toluene for 18.0%, and xylene for 12.8%). When the catalyst was Comparative Example 3, the pentane conversion rate was 82.7%, the CO2 conversion rate was 5.9%, the aromatics selectivity was 41.1%, and the BTX selectivity among aromatics was 39.4% (of which benzene accounted for 10.6%, toluene for 20.5%, and xylene for 8.3%). When the catalyst was Comparative Example 4, the pentane conversion rate was 64.0%, the CO2 conversion rate was 5.2%, the aromatic selectivity was 31.6%, and the BTX selectivity among the aromatics was 30.4% (of which benzene accounted for 9.6%, toluene accounted for 14.4%, and xylene accounted for 6.4%). When the catalyst was Comparative Example 5, the pentane conversion rate was 91.6%, the CO2 conversion rate was 8.2%, the aromatic selectivity was 79.3%, and the BTX selectivity among the aromatics was 76.4% (of which benzene accounted for 26.6%, toluene accounted for 31.2%, and xylene accounted for 18.6%).
[0060] Depend on Figure 4It is known that H-ZSM-5 generally has low efficiency in CO2-assisted pentane to light aromatics conversion. Using this method to synthesize Zn isomorphously substituted Zn-MFI for CO2-assisted pentane to light aromatics conversion yields mostly olefins, as Zn provides active sites for pentane dehydrogenation but lacks active sites for olefin aromatization. Furthermore, using this method to synthesize Zn isomorphically substituted Zn-ZSM-5, the catalyst's aromatization ability increases due to the presence of Al sites (olefin aromatization active sites), coupled with the pentane dehydrogenation function of Zn sites, significantly improving the catalyst's efficiency in CO2-assisted pentane to light aromatics conversion. After optimization, the 2Zn-ZSM-5-80 catalyst exhibits the optimal efficiency in CO2-assisted pentane to light aromatics conversion when Si / Zn is 40 and Si / Al is 80.
[0061]
Claims
1. A metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons, characterized in that: A metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons is composed of metal Zn incorporated into a silicon-containing molecular sieve with an MFI topological framework, wherein the Zn is added in situ during the preparation of the silicon-containing molecular sieve with an MFI topological framework.
2. The metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons according to claim 1, characterized in that, The molecular sieve with the MFI framework includes any one of ZSM-5, ZSM-11, and Y-type.
3. The method for preparing the metal-modified catalyst for CO2-assisted aromatization of C5 hydrocarbons according to claim 1 or 2, characterized in that: The silicon source, aluminum source, zinc source, template agent, mineralizer, and sodium hydroxide for preparing molecular sieves are added to the solvent in batches or in one step and mixed evenly. The mixture is then reacted at a certain temperature for a period of time. After crystallization, washing, drying, first calcination, cation exchange, and second calcination, the metal-modified catalyst is obtained.
4. The preparation method according to claim 3, characterized in that, The molar ratio of silicon source, aluminum source, zinc source, template agent, sodium hydroxide, and mineralizer used is 100:(0.1-4):(0.1-4):(0.1-200):(1-8):(10-80); further, the silicon-zinc molar ratio is 30-200:
1.
5. The preparation method according to claim 3, characterized in that, The molar ratio of silicon source to solvent is 1:(30-60).
6. The preparation method according to claim 3, characterized in that, The silicon source is one or more of tetraethyl orthosilicate, silica sol, water glass, and silica; the zinc source is one or more of zinc chloride, zinc nitrate, and zinc acetate; the template agent is one or more of ethylenediamine, n-butylamine, tetrapropylammonium hydroxide, and ethylene glycol; the mineralizing agent is one or more of ammonium fluoride and urea; and the solvent is one or more of water and ethanol.
7. The preparation method according to claim 3, characterized in that, Seed crystals can be added during the preparation process. Seed crystals are prepared by mixing tetraethyl orthosilicate and tetrapropylammonium hydroxide in a mass ratio of 1:1, hydrolyzing at 30-60°C for 2-6 hours, and then aging at 60-100°C for 96 hours.
8. The method according to claim 3, characterized in that, The reaction temperature for uniform mixing is 30-100℃; the reaction time for uniform mixing is 10-300 minutes; the crystallization step involves raising the temperature in an oven from room temperature to 150-180℃ at a rate of 0.25-100℃ / min and maintaining it at 150-180℃ for 24-72 hours; the drying temperature is 80-120℃ for 6-24 hours; and the two calcinations are both at 300-550℃ for 4-12 hours.
9. The application of the metal-modified catalyst according to claim 1 or 2 in CO2-assisted aromatization of C5 hydrocarbons, characterized in that: The C5 hydrocarbons include any one of pentane, isopentane, n-pentene, and isopentene.
10. The application according to claim 9, characterized in that: CO2-assisted aromatization of C5 hydrocarbons is carried out in a fixed-bed reactor. 0.1-10g of metal-modified molecular sieves are placed in the fixed-bed reactor and first reduced at 400-600℃ for 0.5-10h under H2 atmosphere. Then, the mixture of CO2 and C5 hydrocarbons is switched to carry out the aromatization reaction. CO2 and C5 hydrocarbons are co-fed as reactants at a molar ratio of 0.01-50:1, with a mass hourly space velocity (WHSV) of 1-20 h⁻¹ for the C5 hydrocarbons. -1 For CO2, nitrogen is selected as the carrier gas for feeding, and the volume percentage of CO2 in nitrogen is 5-100%, and the reaction temperature is 300-600℃. Especially when the molar ratio of pentane to CO2 feed is 1:4, it has a 100% pentane conversion rate and more than 90% selectivity for light aromatics.