A silicon-modified alumina catalyst, a preparation method and application thereof, and a method for preparing ethylene by dehydrating ethanol

Abstract

The present application relates to the technical field of catalyst, in particular to a silicon modified alumina catalyst, a preparation method and application thereof, and a method for preparing ethylene by dehydrating ethanol.The present application places gamma-Al2O3 in a silicon source impregnation solution for impregnation, dries and calcines to obtain a silicon modified alumina catalyst; the impregnation temperature is 20-70 DEG C, and the time is 4-6h.The silicon modified alumina catalyst constructed by the present application has silica modified on the surface and pores of gamma-Al2O3, which significantly prolongs the single cycle operation life of the catalyst.The silicon modified alumina catalyst prepared by the present application can be directly applied to the reaction of preparing ethylene by gas phase dehydration of ethanol, maintains stable ethanol conversion rate and ethylene selectivity in long-term operation, and the prepared ethylene can be directly used as a gas phase raw material for synthesizing aviation kerosene precursor by oligomerization.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a silicon-modified alumina catalyst, its preparation method and application, and a method for producing ethylene from ethanol via dehydration. Background Technology

[0002] Currently, catalytic dehydration of ethanol to ethylene is a preliminary step in the synthesis of aviation kerosene precursors. In existing ethanol gas-phase dehydration processes to ethylene, commonly used solid acid catalysts include zeolite molecular sieves, heteropoly acids, and alumina catalysts. Among these, γ-Al₂O₃ is widely used due to its suitable acidity and high specific surface area. Related technologies have developed catalyst systems using silica-coated alumina supports. This silica-coated structure improves the catalyst's resistance to hydration to some extent. However, in long-term operation, simple external coating is insufficient to fully protect the internal pores of the support, and the catalyst still suffers from limited lifespan. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide a silicon-modified alumina catalyst, its preparation method and application, and a method for producing ethylene from ethanol via dehydration. The silicon-modified alumina catalyst provided by this invention can be directly used for the dehydration of ethanol to produce ethylene, exhibiting a long catalyst life, high ethanol conversion rate, and high selectivity and purity of ethylene.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a silicon-modified alumina catalyst, comprising the following steps: impregnating γ-Al2O3 in a silicon source impregnation solution, drying and then calcining to obtain a silicon-modified alumina catalyst; The immersion temperature is 20~70℃, and the time is 4~6h.

[0005] Preferably, the pore volume of the γ-Al₂O₃ is 0.4~0.8 cm³. 3 / g.

[0006] Preferably, the silicon source in the silicon source impregnation solution includes tetraethyl orthosilicate or methyl orthosilicate, and the solvent includes water, methanol, anhydrous ethanol, n-propanol, isopropanol, or n-butanol. The concentration of the silicon source impregnation solution is 0.4~4.5 mol / L.

[0007] Preferably, the γ-Al2O3 is pre-dried before use.

[0008] Preferably, the calcination holding temperature is 1000~1200℃, the holding time is 4~6h, the calcination atmosphere is nitrogen, and the heating rate to the holding temperature is 2~5℃ / min.

[0009] Preferably, the drying temperature is 80~120℃ and the time is 10~12h.

[0010] The present invention also provides a silicon-modified alumina catalyst prepared by the preparation method described in the above technical solution.

[0011] The present invention also provides the application of the silicon-modified alumina catalyst described in technical solution 7 above in the dehydration of ethanol to ethylene.

[0012] The present invention also provides a method for producing ethylene by dehydrating ethanol, comprising the following steps: subjecting ethanol to a dehydration reaction under a silicon-modified alumina catalyst and a protective atmosphere as described in the above technical solution to obtain ethylene.

[0013] Preferably, the conditions for the dehydration reaction include: a temperature of 350-380°C, a pressure of 1-3 MPa, and a mass hourly space velocity (WHSV) of ethanol of 1-3 h⁻¹. -1 .

[0014] The silicon-modified alumina catalyst constructed in this invention, with silicon species (silicon dioxide) modified on the surface and channels of γ-Al2O3, significantly extends the catalyst's single-cycle operating life. The silicon-modified alumina catalyst prepared in this invention can be directly applied to the gas-phase dehydration of ethanol to ethylene. During long-term operation, it maintains stable ethanol conversion and ethylene selectivity, significantly enhancing the catalyst's resistance to deactivation and operating life, increasing catalyst life by approximately three times. This reduces the overall production cost of large-scale ethylene production (by approximately 25-30%), resulting in high ethanol conversion, high ethylene selectivity and purity. The prepared ethylene can be directly used as a gas-phase feedstock for downstream oligomerization to synthesize aviation kerosene precursors.

[0015] As shown in the test results of the examples, the single-cycle operating life of the silicon-modified alumina catalyst prepared by the present invention is extended to 10-12 months (about 3 times that of traditional pure γ-Al2O3), the catalyst has good stability, high ethanol conversion rate (≥98%), high ethylene selectivity (≥97.8%), and high purity (≥96%). The prepared ethylene can be directly used as a gaseous feedstock for downstream oligomerization to form aviation kerosene precursors. Detailed Implementation

[0016] This invention provides a method for preparing a silicon-modified alumina catalyst, comprising the following steps: impregnating γ-Al2O3 in a silicon source impregnation solution, drying and then calcining to obtain a silicon-modified alumina catalyst; the impregnation temperature is 20~70℃ and the time is 4~6h.

[0017] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0018] In this invention, the pore volume of the γ-Al₂O₃ can be 0.4~0.8 cm³.3 / g, and can also be 0.5~0.7cm 3 / g, which can be specifically 0.6cm 3 / g; the γ-Al2O3 can be industrial-grade pure γ-Al2O3. In this invention, the γ-Al2O3 can be pre-dried before use; the pre-drying temperature can be 100~140℃, or 110~130℃, specifically 120℃; the pre-drying time can be 2~4h, or 2.5~3.5h, specifically 3h; the purpose of the pre-drying is to remove physically adsorbed moisture on the surface and in the pores.

[0019] In this invention, the silicon source in the silicon source impregnation solution may include tetraethyl orthosilicate (TEOS) or methyl orthosilicate (TMOS); the solvent in the silicon source impregnation solution may include water, methanol, anhydrous ethanol, n-propanol, isopropanol, or n-butanol; the concentration of the silicon source impregnation solution may be 0.4~4.5 mol / L, or 1~4 mol / L, or further 2~3 mol / L. In this invention, the concentration of the silicon source impregnation solution can be calculated based on the mass fraction of SiO2 in the silicon-modified alumina catalyst and the pore volume of the γ-Al2O3 support, to determine the amount of silicon source added, and the concentration of the silicon source impregnation solution can be calculated and prepared accordingly.

[0020] In this invention, the impregnation temperature is 20~70℃, which can be 30~65℃, 40~60℃, or even 50~60℃; the impregnation time is 4~6h, which can be 4.5~5.5h, specifically 5h; the impregnation can be carried out under sealed conditions. Under the above conditions, the silicon species can fully and uniformly penetrate into the interior and surface of the γ-Al2O3 channels.

[0021] In this invention, the drying temperature can be 80~120℃, or 90~110℃, specifically 100℃; the drying time can be 10~12h, or 10.5~11.5h, specifically 11h. Under the above conditions, this invention enables the slow evaporation and removal of solvents from the system.

[0022] In this invention, the holding temperature for calcination can be 1000~1200℃, or 1050~1150℃, specifically 1100℃; the holding time for calcination can be 4~6h, or 4.5~5.5h, specifically 5h; the atmosphere for calcination is nitrogen; the heating rate to the holding temperature can be 2~5℃ / min, or 3~4℃ / min; and the process after calcination includes cooling to room temperature.

[0023] This invention also provides a silicon-modified alumina catalyst prepared by the method described above. In this invention, the mass fraction of SiO2 in the silicon-modified alumina catalyst can be 2-8%.

[0024] This invention also provides the application of the silicon-modified alumina catalyst described in the above-mentioned technical solution in the dehydration of ethanol to ethylene. In this invention, the ethanol can be anhydrous ethanol (purity above 99.9%). The silicon-modified alumina catalyst prepared by this invention is used to catalyze the production of ethylene from ethanol and has a long catalyst lifetime.

[0025] The present invention also provides a method for producing ethylene by dehydrating ethanol, comprising the following steps: subjecting ethanol to a dehydration reaction under a silicon-modified alumina catalyst and a protective atmosphere as described in the above technical solution to obtain ethylene.

[0026] In this invention, the ethanol can be anhydrous ethanol (purity 99.9% or higher).

[0027] In this invention, the conditions for the dehydration reaction may include: a temperature of 350-380°C, or 360-370°C; a pressure of 1-3 MPa, or 1.5-2.5 MPa, specifically 2 MPa; and a mass hourly space velocity (HSV) of ethanol of 1-3 h⁻¹. -1 It can also be 1.5~2.5h. -1 The dehydration can be carried out in a fixed-bed reactor; the dehydration can be carried out under a protective atmosphere, which may include nitrogen, argon or helium.

[0028] In this invention, the specific operation of ethanol dehydration to ethylene in a fixed-bed reactor may include the following steps: placing a silicon-modified alumina catalyst in the isothermal reaction section of the fixed-bed reactor, purging the system with a protective atmosphere (such as nitrogen) to replace the internal air, starting the heating system at atmospheric pressure to raise the reactor bed temperature and stabilize the dehydration temperature, continuously feeding ethanol into the preheater using a metering pump to completely vaporize it, and then having the vaporized ethanol enter the fixed-bed reactor, contact the silicon-modified alumina catalyst bed, and undergo a gas-phase dehydration reaction.

[0029] After the dehydration is completed, the present invention also includes ethylene separation and collection. The specific operation may include: introducing the mixed gas (containing ethylene gas, unreacted ethanol, water vapor generated by the reaction and a small amount of by-products) from the outlet of the fixed bed reactor into the condensation separation system. After gas-liquid separation, the liquid phase products (water and unreacted ethanol) are discharged from the bottom and enter the subsequent recovery unit; high-purity gaseous ethylene is collected from the top and can be directly used as gaseous feedstock for downstream oligomerization into aviation kerosene precursor.

[0030] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1 (1) Preparation of silicon-modified alumina catalyst: Industrial-grade pure γ-Al2O3 was dried at 110℃ for 3 h to obtain dried γ-Al2O3. The amount of tetraethyl orthosilicate was calculated based on the mass fraction of SiO2 in the final silicon-modified alumina catalyst being 5%. Tetraethyl orthosilicate was dissolved in anhydrous ethanol to prepare a silicon source impregnation solution with a tetraethyl orthosilicate molar concentration of 1.35 mol / L. According to the principle of equal volume impregnation, the ratio of the dried γ-Al2O3 support to the silicon source impregnation solution was 1 g: 0.65 mL. The silicon source impregnation solution was added to the dried γ-Al2O3 and stirred in a sealed container at 40℃ for 5 h. Then, it was dried again at 100℃ for 12 h and calcined at 1000℃ for 5 h under a nitrogen atmosphere with a heating rate of 3℃ / min to obtain the silicon-modified γ-Al2O3 catalyst (SiO2 content of 5 wt%).

[0032] (2) Application of catalyst: The silicon-modified alumina catalyst was packed into the isothermal reaction section of the fixed-bed reactor. Under the conditions of 360℃, system pressure of 2MPa, and nitrogen atmosphere, anhydrous ethanol (purity above 99.9%) was used as the raw material, and the feed mass hourly space velocity (WHSV) of ethanol was controlled at 2.0 h⁻¹. -1 A continuous catalytic dehydration reaction is carried out.

[0033] Experimental results: The initial ethanol conversion rate was 99.2%, the ethylene selectivity was 98.5%, and the ethylene purity was ≥97.71%. After 10 months of continuous and stable operation, the ethylene purity remained above 97%.

[0034] Example 2 High silicon ratio and high temperature and high air velocity operating conditions.

[0035] The only difference from Example 1 is that the concentration of the silicon source impregnation solution is 2.16 mol / L; the calcination heating rate is 5℃ / min, and the calcination is carried out at a constant temperature of 1000℃ for 4h; thus, a silicon-modified γ-Al2O3 catalyst (SiO2 content is 8wt%) is obtained.

[0036] The dehydration temperature was 380℃, the system pressure was 2MPa, the ethanol was anhydrous ethanol (purity ≥ 99.9%), and the WHSV was 3.0h. -1 .

[0037] Experimental results: The initial ethanol conversion rate was 99.5%, the ethylene selectivity was 97.8%, and the ethylene purity was ≥97.31%. After 11 months of continuous operation, the catalyst activity remained stable, the by-product formation rate was less than 3%, and the catalyst crystal form maintained the γ-Al2O3 structure.

[0038] Example 3 Low silicon ratio and low temperature and low air velocity operating conditions.

[0039] The only difference from Example 1 is that the concentration of the silicon source impregnation solution is 0.54 mol / L; the second drying is carried out at 80°C for 10 h; the calcination heating rate is 2°C / min, and the constant temperature calcination is carried out at 1000°C for 6 h; thus, a silicon-modified γ-Al2O3 catalyst (SiO2 content is 2 wt%) is obtained.

[0040] The dehydration temperature was 350℃, the ethanol was anhydrous ethanol (purity ≥ 99.9%), and the WHSV was 1.0h. -1 .

[0041] Experimental results: The initial ethanol conversion rate was 98.0%, the ethylene selectivity was 98.8%, and the ethylene purity was ≥96.82%. After 8 months of continuous operation, the ethanol conversion rate decreased to 95%, and the service life was still significantly extended compared to the unmodified catalyst.

[0042] Comparative Example 1 Industrial-grade pure γ-Al2O3 was used directly as the catalyst.

[0043] The application conditions for the catalyst are the same as in Example 1.

[0044] Experimental results: The initial ethanol conversion rate was 98.5%, and the ethylene selectivity was 98.0%. After three months of continuous operation, the ethanol conversion rate rapidly decreased to below 70%, and the ethylene selectivity dropped to 85%. Characterization of the deactivated catalyst confirmed that most of the γ-Al2O3 had undergone hydration phase transition, transforming into non-catalytically active boehmite and gibbsite phases.

[0045] Comparative Example 2 Commercially available large-particle-size pure γ-Al2O3 (particle size 3~5mm) was directly used as the catalyst.

[0046] The application conditions for the catalyst are the same as in Example 1.

[0047] The initial ethanol conversion rate was 97.2%, and the ethylene selectivity was 96.8%. After 2.5 months of continuous operation, the ethanol conversion rate dropped below 65%, and the ethylene selectivity decreased to 82%. Characterization of the deactivated catalyst confirmed that most of the γ-Al2O3 had undergone a hydration phase transition, transforming into non-catalytically active pseudoboehmite and boehmite phases.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-modified alumina catalyst, comprising the following steps: γ-Al2O3 was impregnated in a silicon source impregnation solution, dried, and then calcined to obtain a silicon-modified alumina catalyst. The immersion temperature is 20~70℃, and the time is 4~6h.

2. The preparation method according to claim 1, characterized in that, The pore volume of the γ-Al₂O₃ is 0.4~0.8 cm⁻¹. 3 / g.

3. The preparation method according to claim 1, characterized in that, The silicon source in the silicon source impregnation solution includes tetraethyl orthosilicate or methyl orthosilicate, and the solvent includes one or more of water, methanol, anhydrous ethanol, n-propanol, isopropanol, or n-butanol. The concentration of the silicon source impregnation solution is 0.4~4.5 mol / L.

4. The preparation method according to claim 1, characterized in that, The γ-Al2O3 is pre-dried before use.

5. The preparation method according to claim 1, characterized in that, The calcination temperature is 1000~1200℃, the holding time is 4~6h, and the calcination atmosphere is nitrogen; the heating rate to the holding temperature is 2~5℃ / min.

6. The preparation method according to claim 1, characterized in that, The drying temperature is 80~120℃, and the time is 10~12h.

7. The silicon-modified alumina catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the silicon-modified alumina catalyst according to claim 7 in the dehydration of ethanol to ethylene.

9. A method for producing ethylene by dehydrating ethanol, comprising the following steps: Ethylene is obtained by dehydrating ethanol under the silicon-modified alumina catalyst described in claim 7 and under a protective atmosphere.

10. The method according to claim 9, characterized in that, The conditions for the dehydration reaction include: a temperature of 350-380℃, a pressure of 1-3 MPa, and a mass hourly space velocity (WHSV) of ethanol of 1-3 h⁻¹. -1 .