Application of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to propylene

Abstract

The present invention discloses an application of a zirconium-aluminum-oxygen composite catalyst in the catalytic dehydrogenation of propane to produce propylene. In the zirconium-aluminum-oxygen composite catalyst, zirconium is a highly dispersed zirconium oxide species and alumina composite to form an active phase to promote catalytic dehydrogenation reaction, wherein the mass fraction of zirconium is 2%-20%. Compared with zirconium oxide or alumina, the zirconium-aluminum-oxygen composite catalyst provided by the present invention significantly improves the catalytic activity and product selectivity of propane dehydrogenation reaction, and also shows very excellent reaction stability. The preparation method of the zirconium-aluminum-oxygen composite catalyst includes dissolving a zirconium precursor in a corresponding solvent, adding dropwise to alumina powder and stirring and mixing, and the mixture is evaporated to dryness, calcined and then reduced at high temperature. The method disclosed by the present invention is simple, easy to operate and has strong applicability. In addition, the compounding of a high proportion of alumina components significantly reduces the amount of zirconium component used, greatly reduces the catalyst cost, and reduces the difficulty of catalyst molding and processing, which has very great advantages in economy and practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical catalysis, and specifically relates to application of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene. Background Art

[0002] Propylene is an important basic raw material in the petrochemical industry. Traditionally, it is mainly produced by naphtha cracking or coal-to-olefins routes, which consumes a lot of energy and has large carbon emissions. Propane catalytic dehydrogenation produces propylene exclusively, produces hydrogen as a by-product, has good atom economy, and has a simple process flow and low investment cost. It has developed into the most important oil-based or coal-based alternative route. At present, industrial catalysts for propane dehydrogenation process mainly include platinum-based and chromium oxide-based catalysts. However, platinum resources are very scarce in nature, and chromium is very toxic in the environment. Therefore, it is urgent to develop a catalyst system with both resource and environmental advantages. Zirconium dioxide (ZrO2) has excellent chemical stability and acid and alkali resistance. At the same time, it has a high melting point and low thermal expansion. It is an important temperature-resistant and corrosion-resistant material. It is also the main raw material for artificial drill. It is biocompatible and environmentally friendly. It is very suitable for high-temperature multiphase catalytic reaction processes with harsh working conditions. Recently, researchers have discovered that using zirconium oxide as a substrate, doping some elements such as Y and La with similar ion radius but different valence states to the zirconium ion (Chinese Patent, 2020, Application No.: CN111790370A), or loading some precious metal components with hydrogenation activity such as Ru, Rh, and Cu (Angew. Chem. Int. Ed., 2015, 54, 15880), can create a considerable amount of coordinated unsaturated zirconium cation sites, which, combined with the adjacent oxygen anion sites, jointly promote the activation of the carbon-hydrogen bonds of the propane molecule, thereby realizing the catalytic dehydrogenation of propane to produce propylene.

[0003] Existing research has demonstrated the great application potential of zirconium oxide in propane dehydrogenation reactions, but the rare earth doping, precious metal loading and other processes involved in existing solutions will inevitably bring technical complexity and economic unaffordability. In addition, zirconium dioxide has a low specific surface area and low active site exposure density, which further limits the improvement of its catalytic efficiency. At the same time, compared with metal oxides such as Cr2O3, V2O5, and Ga2O3 that are often reported in propane dehydrogenation reactions, zirconium oxide is very expensive and has poor cost-effectiveness as a catalyst. In addition, it has high chemical and mechanical stability, and is difficult to form and process, so it is not easy to use on a large scale in industry. Summary of the invention

[0004] In view of the above technical difficulties, the present invention provides an application of a zirconium-aluminum-oxygen composite catalyst in the catalytic dehydrogenation of propane to propylene. Compared with zirconium oxide or aluminum oxide, the zirconium-aluminum-oxygen composite catalyst significantly improves the catalytic activity and product selectivity of the propane dehydrogenation reaction, and also shows very excellent reaction stability. The compounding of a high proportion of aluminum oxide components significantly reduces the amount of zirconium components used, reduces the catalyst cost, and reduces the difficulty of catalyst molding and processing, which has advantages in economy and practicality.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0006] The invention discloses an application of a zirconium-aluminum-oxygen composite catalyst in the catalytic dehydrogenation of propane to produce propylene. The zirconium-aluminum-oxygen composite catalyst comprises zirconium oxide and aluminum oxide, wherein zirconium is in the form of highly dispersed zirconium oxide species and is composited with aluminum oxide to form an active phase, and the mass fraction of zirconium is 2%-20%.

[0007] The method for preparing the zirconium-aluminum-oxygen composite catalyst comprises the following steps:

[0008] S1 weighs a zirconium precursor and dissolves it in a solvent with the aid of ultrasound;

[0009] S2: under room temperature stirring, add the solution prepared in S1 dropwise to the alumina powder and mix well;

[0010] S3: putting the uniformly mixed mixture sample into an oven for evaporation;

[0011] S4: Grind the obtained sample, calcine in air atmosphere and then reduce at high temperature to obtain zirconium-aluminum-oxygen composite catalyst.

[0012] The alumina phase is γ phase, the powder particle size is 100-400 mesh, and the specific surface area is 150-400m 2 / g.

[0013] The zirconium precursor is any one of zirconium nitrate or alkoxide.

[0014] The solvent is any one of anhydrous ethanol or deionized water.

[0015] The mass percentage of zirconium precursor in the solution prepared by S1 is 9-11 wt %.

[0016] The drying temperature is 50-100° C. and the drying time is 6-12 hours.

[0017] The calcination temperature is 400-600° C., and the calcination time is 3-8 hours. Furthermore, the calcination atmosphere is 20 vol% O2 / N2, and the total gas flow rate is 10-300 mL / min.

[0018] The reducing atmosphere is 20-80 vol% H2 / N2, the reducing temperature is 400-700°C, and the reducing time is 2-6 hours. Furthermore, the total gas flow rate is 10-300 mL / min.

[0019] The dehydrogenation reaction is carried out in a differential fixed bed reactor at a reaction temperature of 580-620° C., a reaction pressure of 0-0.2 MPa, and a total gas flow rate of 10-300 mL / min.

[0020] Before the dehydrogenation reaction, hydrogen and nitrogen mixed gas was introduced to pretreat the zirconium-aluminum-oxygen composite catalyst, and then -1 The propane mass space velocity is cut into the reaction gas, and the reaction gas composition is propane and nitrogen, wherein nitrogen is the balance gas.

[0021] The beneficial effects of the present invention are:

[0022] Compared with zirconium oxide or aluminum oxide, the zirconium-aluminum-oxygen composite catalyst provided by the present invention significantly improves the catalytic activity and product selectivity of the propane dehydrogenation reaction, and also shows very excellent reaction stability. The highly dispersed zirconium oxide species in the catalyst are compounded with aluminum oxide to form an active phase, which jointly promotes the occurrence of the propane dehydrogenation reaction, while when compounded with other types of oxides (silicon oxide, silicon-aluminum zeolite, etc.), it does not show a promoting effect on the propane catalytic dehydrogenation reaction. The preparation method disclosed in the present invention is simple and easy to operate, and has strong applicability. In addition, the compounding of a high proportion of aluminum oxide components significantly reduces the amount of zirconium components used, greatly reduces the catalyst cost, and at the same time reduces the difficulty of catalyst molding and processing, which has great advantages in economy and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a graph showing the change of propane dehydrogenation reaction rate over time on the catalysts prepared in Example 2 of the present invention and Comparative Example 1.

[0024] Figure 2 It is the X-ray diffraction (XRD) diagram of the catalysts prepared in Example 2, Example 5, Example 6 and Comparative Example 5 of the present invention.

[0025] Figure 3 This is a high-resolution transmission electron microscope (HR-TEM) photograph of the catalyst prepared in Example 6 of the present invention.

[0026] Figure 4 It is a scanning transmission electron microscope (STEM) photograph and EDS element surface scanning distribution diagram of the catalyst prepared in Example 6 of the present invention.

[0027] Figure 5 It is an X-ray photoelectron spectroscopy (XPS) graph of the catalysts prepared in Example 1, Example 2, Example 5 and Example 6 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below through some specific embodiments, but the present invention is not limited to the following embodiments.

[0029] In the propane dehydrogenation performance test of the catalyst in the embodiment, the product was analyzed online by gas chromatograph, and the reaction conversion rate and selectivity were calculated by normalization method based on the contents of alkanes and olefins in the dehydrogenation product.

[0030] Example 1

[0031] S1: calcining pseudo-boehmite powder in a muffle furnace, heating the temperature from room temperature to 600°C at a rate of 1°C / min, maintaining the temperature for 2h, and finally cooling the temperature to room temperature to obtain γ-Al2O3;

[0032] S2 Take 28 mg Zr(NO3)4·5H2O and add it to 300 μL anhydrous ethanol, sonicate for 5-10 min to obtain a clear, colorless solution;

[0033] S3: adding the above solution dropwise to the dried alumina powder, and stirring at room temperature and 400 r / min for 2 h;

[0034] S4 The stirred mixture was dried in an oven at 50°C for 10-12h and ground to obtain a white powder;

[0035] S5: placing the obtained white powder in a calcining furnace, in a calcining atmosphere of 20 vol% O2 / N2, with a total gas flow rate of 50 mL / min, increasing the temperature to 500°C at 5°C / min, and calcining at 500°C for 4 h;

[0036] S6 was introduced with 20 vol% H2 / N2 mixed gas, with a total gas flow rate of 40 mL / min, and heated to 590°C at 10°C / min for 2 h of reduction treatment, and was labeled as 2% Zr-Al2O3;

[0037] S7: 200 mg of the above catalyst was loaded into a fixed bed differential reactor, and a C3H8 / N2 reaction mixture with a volume ratio of 8 / 42 was introduced. The total gas flow rate was controlled at 50 mL / min. The evaluation results after 6 hours of propane dehydrogenation reaction are shown in Table 1.

[0038] Example 2

[0039] The preparation and reaction were carried out using the method of Example 1, except that in step S2, the amount of zirconium nitrate pentahydrate used was 98 mg, the amount of ethanol used was 1 mL, the stirring time in S3 was 2.5 h, the drying temperature in S4 was 80° C., the sample was marked as 5% Zr-Al2O3, and the performance evaluation results are shown in Table 1.

[0040] Example 3

[0041] The preparation and reaction were carried out using the method of Example 1, except that the solvent in step S2 was deionized water, and the amount used was 2 mL, the amount of zirconium nitrate pentahydrate used was 98 mg, the stirring time in S3 was 2.5 h, the drying temperature in S4 was 100° C., the sample was labeled 5% Zr-Al2O3-deionized water, and the performance evaluation results are shown in Table 1.

[0042] Example 4

[0043] The preparation and reaction were carried out using the method of Example 1, except that zirconium nitrate pentahydrate was replaced with tetrabutyl zirconium oxide in step S2, the amount of ethanol used was 4 mL, the sample was marked as 5% Zr-Al2O3-tetrabutyl zirconium oxide, and the performance evaluation results are shown in Table 1.

[0044] Example 5

[0045] The preparation and reaction were carried out using the method of Example 1, except that in step S2, the amount of zirconium nitrate pentahydrate used was 188 mg, the amount of ethanol used was 2 mL, the stirring time in S3 was 3 h, the drying temperature in S4 was 80° C., the sample was marked as 10% Zr-Al2O3, and the performance evaluation results are shown in Table 1.

[0046] Example 6

[0047] The preparation and reaction were carried out using the method of Example 1, except that in step S2, the amount of zirconium nitrate pentahydrate used was 418 mg, the amount of ethanol used was 4 mL, the stirring time in S3 was 4 h, the drying temperature in S4 was 90° C., the sample was marked as 20% Zr-Al2O3, and the performance evaluation results are shown in Table 1.

[0048] Table 1. Performance of propane dehydrogenation reaction on catalysts of series examples

[0049]

[0050] Comparative Example 1 (not according to the present invention)

[0051] 200 mg of m-ZrO2 (Alfa) was weighed and loaded into a fixed-bed differential reactor. Before the reaction, 20 vol% H2 / N2 was introduced at a total gas flow rate of 40 mL / min. The temperature was raised to 590°C at 10°C / min. The reaction mixture was pre-reduced at 590°C for 2 h. Then, a C3H8 / N2 reaction mixture with a volume ratio of 8 / 42 was introduced. The total gas flow rate was controlled at 50 mL / min. The evaluation results of the propane dehydrogenation reaction for 6 h are shown in Table 2.

[0052] Comparative Example 2 (not according to the present invention)

[0053] S1 Take 98 mg of Zr(NO3)4·5H2O and add it to 1 mL of anhydrous ethanol, and sonicate for 5-10 min to obtain a clear, colorless solution;

[0054] S2: Add the above solution dropwise into 400 mg of dried SiO2 and stir at room temperature and 400 r / min for 2.5 h;

[0055] S4 The stirred mixture was dried in an oven at 80°C for 10-12h and ground to obtain a white powder;

[0056] S5 places the obtained white powder in a calcination furnace, raises the temperature to 500°C at 5°C / min in a calcination atmosphere of 20 vol% O2 / N2 and a total gas flow rate of 50 mL / min, and calcines at 500°C for 4 hours to obtain a white powder, which is marked as 5% Zr-SiO2.

[0057] S6: 200 mg of the above catalyst was loaded into a fixed bed differential reactor. Before the reaction, 20 vol% H2 / N2 was introduced, the total gas flow rate was 40 mL / min, and the temperature was increased to 590°C at 10°C / min. The reaction mixture was pre-reduced at 590°C for 2 h, and then a C3H8 / N2 reaction mixture with a volume ratio of 8 / 42 was introduced. The total gas flow rate was controlled at 50 mL / min. The evaluation results after 6 h of propane dehydrogenation reaction are shown in Table 2.

[0058] Comparative Example 3 (not according to the present invention)

[0059] The preparation and reaction were carried out in the same manner as in Comparative Example 2, except that the SiO2 used in S2 was replaced by Silicalite-1 zeolite molecular sieve, labeled as 5% Zr-Silicalite-1. The performance evaluation results are shown in Table 2.

[0060] Comparative Example 4 (not according to the present invention)

[0061] The preparation and reaction were carried out in the same manner as in Comparative Example 2, except that the SiO2 used in S2 was replaced with Beta zeolite molecular sieve, marked as 5% Zr-Beta. The performance evaluation results are shown in Table 2.

[0062] Comparative Example 5 (not according to the present invention)

[0063] S1: calcining pseudo-boehmite powder in a muffle furnace, heating the temperature from room temperature to 600°C at a rate of 1°C / min, maintaining the temperature for 2h, and finally cooling the temperature to room temperature to obtain γ-Al2O3;

[0064] S2 Weigh 200 mg of γ-Al2O3 powder and load it into a fixed bed differential reactor. Before the reaction, introduce 20 vol% H2 / N2 with a total gas flow rate of 40 mL / min. The temperature is raised to 590°C at 10°C / min. Pre-reduction is performed at 590°C for 2 h. Then, a C3H8 / N2 reaction mixture with a volume ratio of 8 / 42 is introduced. The total gas flow rate is controlled at 50 mL / min. The evaluation results of the propane dehydrogenation reaction for 6 h are shown in Table 2.

[0065] Table 2. Performance of propane dehydrogenation reaction on catalysts of a series of comparative examples

[0066]

[0067] From the reaction data in Table 1 and Table 2, it can be seen that the propane conversion activity and product selectivity of the zirconium-aluminum-oxygen composite catalyst disclosed in the present invention are significantly better than those of the zirconium oxide and aluminum oxide control samples (Comparative Examples 1 and 5). Taking the catalyst of Example 2 as an example, the propylene production rate based on zirconium is 3.6 mmol g Zr -1 min -1 , which is nearly two orders of magnitude higher than the propylene production rate on m-ZrO2 (Comparative Example 1). Figure 1 The results further show that the catalytic reaction rate on the catalyst gradually increases with the reaction time. Unlike the gradual deactivation trend of the m-ZrO2 catalyst, the catalyst has excellent reaction stability. A careful analysis of the data in Table 1 shows that when the zirconium content in the zirconium-aluminum-oxygen composite catalyst reaches 5%, the propane conversion rate reaches 12.3% and the propylene selectivity is close to 83%. When the zirconium content increases to 20%, the propane conversion rate increases slightly and the propylene selectivity increases to 89%. Figure 2 The XRD spectrum shows that until the zirconium content increases to 20%, there is no characteristic diffraction peak attributable to bulk zirconium oxide or metallic zirconium in the composite catalyst. The HR-TEM image of the 20% Zr-Al2O3 catalyst ( Figure 3 ) further confirmed that there was no obvious nanoscale zirconium species in the composite catalyst, and the STEM combined with EDS elemental surface scanning results ( Figure 4 ) shows that zirconium species are highly uniformly distributed in the alumina matrix, and the XPS spectrum results ( Figure 5 ) further proves that zirconium exists in the form of zirconium oxide species. These results together reveal that zirconium in the composite catalyst exists in the form of highly dispersed zirconium oxide species in alumina. Correlating reaction data and structural information, highly dispersed zirconium oxide species and alumina composite constitute an active phase, which jointly promotes the occurrence of propane dehydrogenation reaction, while when composited with other types of oxides (silicon oxide, pure silicon molecular sieve, silicon aluminum β molecular sieve, etc.), it does not show a promoting effect on the catalytic dehydrogenation reaction of propane (Comparative Examples 2-4).

Claims

1. Application of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to propylene, characterized in that: The zirconium-aluminum-oxygen composite catalyst comprises zirconium oxide and aluminum oxide, wherein zirconium is in the form of highly dispersed zirconium oxide species and is composited with aluminum oxide to form an active phase, and the mass fraction of zirconium is 2%-20%; the zirconium-aluminum-oxygen composite catalyst is prepared by high-temperature reduction; the reaction gas composition is propane and nitrogen, wherein nitrogen is the balance gas.

2. The use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to propylene as claimed in claim 1, characterized in that: The method for preparing the zirconium-aluminum-oxygen composite catalyst comprises the following steps: S1 weighs the zirconium precursor and dissolves it in the solvent with the aid of ultrasound; S2: Add the solution prepared in S1 dropwise to the alumina powder under stirring at room temperature and mix well; S3 putting the uniformly mixed mixture sample into an oven for evaporation; S4 The obtained sample was ground, calcined in air atmosphere and then reduced at high temperature to obtain a zirconium-aluminum-oxygen composite catalyst.

3. Use of a zirconium-aluminum-oxygen composite catalyst as claimed in claim 1 or 2 in catalytic dehydrogenation of propane to produce propylene, characterized in that: The alumina phase is γ phase, the powder particle size is 100-400 mesh, and the specific surface area is 150-400 m 2 / g.

4. The use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to propylene as claimed in claim 2, characterized in that: S1 The zirconium precursor is zirconium nitrate or alkoxide.

5. The use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to propylene as claimed in claim 2, characterized in that: The solvent in S1 is anhydrous ethanol or deionized water.

6. Use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene as claimed in claim 2, characterized in that: The mass percentage of zirconium precursor in the solution prepared by S1 is 9-11wt%.

7. Use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene as claimed in claim 2, characterized in that: In S4, the calcination temperature is 400~600℃ and the calcination time is 3~8h.

8. The use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene as claimed in claim 2, characterized in that: The reducing atmosphere in S4 is 20~80vol% H2 / N2, the reducing temperature is 400~700℃, and the reducing time is 2~6h.

9. Use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene as claimed in claim 1, characterized in that: The catalytic dehydrogenation of propane to produce propylene is carried out in a differential fixed bed reactor at a reaction temperature of 580-620°C, a reaction pressure of 0-0.2 MPa, and a total gas flow rate of 10-300 mL / min.

10. Use of a zirconium-aluminum-oxygen composite catalyst in catalytic dehydrogenation of propane to produce propylene as claimed in claim 1, characterized in that: Before the catalytic dehydrogenation of propane to propylene, hydrogen and nitrogen mixed gas was introduced to pretreat the zirconium-aluminum-oxygen composite catalyst, and then -1 The propane mass space velocity is cut into the reaction gas.

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