A catalyst for hydroisomerization reaction and its preparation method and application

Abstract

The invention discloses a catalyst for hydroisomerization reaction, the catalyst comprising ZSM-5 molecular sieve and Al 2 O 3 A mixture of supports, wherein the Al 2 O 3 The carrier is loaded with a Pt active component to 2 O 3 A Pt active center is formed on the surface of the carrier, and the distance between the Pt active center and the ZSM-5 molecular sieve is more than 50 nm.

Description

Technical Field

[0001] The invention relates to a catalyst for hydroisomerization reaction and a preparation method and application thereof. Background Art

[0002] In recent years, as society has paid more attention to environmental pollution, the latest National VI standard in my country stipulates that the concentration of olefins and aromatics in gasoline cannot exceed 15% and 35% respectively. The reduction of olefins and aromatics content will inevitably lead to a significant reduction in the octane number of gasoline. Isomerized oil has many advantages such as low sulfur content and no aromatics and olefins. It is an ideal blending component for gasoline oil upgrading. Based on this consideration, the development and optimization of low-sulfur, aromatic-free and olefin-free hydroalkane isomerization technology is more realistic.

[0003] At present, the alkane isomerization catalysts that have been applied in industry are mainly medium-temperature metal / molecular sieve bifunctional catalytic systems. It is generally believed that during the reaction, normal alkanes are preferentially dehydrogenated at the metal active site to generate normal olefins, and normal olefins diffuse to the acidic site of molecular sieve B for isomerization to generate isoolefins. Finally, isoolefins diffuse to the adjacent metal active site for hydrogenation to generate isoalkane. The whole process involves metal active site hydrogenation-dehydrogenation, acidic site isomerization, and intermediate diffusion. The metal active site and the molecular sieve acidic site must have a suitable match to achieve the optimal isomerization rate. For example, the Chinese patent (CN111701616A) provides a hydroisomerization catalyst, which contains two molecular sieves HY and HZSM-5 with different acid strengths, showing a better acid distribution, and through subsequent rare earth element modification, the B acidic site required for alkane isomerization is further increased, and a better active metal-acidic site match is obtained, with better conversion rate and isomerization rate. In addition to having a suitable acid distribution, the close distance between the metal active site and the molecular sieve acid site is also crucial. In the traditional metal / molecular sieve preparation process, most of the metal active centers will fall on the acid sites in the molecular sieve pores, which will cause the olefin intermediates produced by the metal active sites to be restricted by the molecular sieve micropores, slowing down the diffusion rate, making the olefin intermediates inevitably enriched in the pores, aggravating cracking. However, so far, there has been no research on the relationship between the metal active sites and the acid sites. Summary of the invention

[0004] The present invention unexpectedly discovered that the deficiencies in the above-mentioned prior art can be effectively solved by regulating the distance between the metal active site and the molecular sieve. To this end, the present invention provides a catalyst for hydroisomerization reaction and a preparation method and application thereof, aiming to improve the conversion rate of normal alkanes and the selectivity of isomerized products in the isomerization reaction.

[0005] The objectives of the present invention are achieved through the following technical solutions.

[0006] In a first aspect, the present invention provides a catalyst for a hydroisomerization reaction, wherein the catalyst comprises a mixture of a ZSM-5 molecular sieve and an Al2O3 carrier, wherein a Pt active component is loaded on the Al2O3 carrier to form a Pt active center on the surface of the Al2O3 carrier, and the distance between the Pt active center and the ZSM-5 molecular sieve is above 50 nm.

[0007] The mixture of the ZSM-5 molecular sieve and the Al2O3 carrier is mechanically and physically mixed.

[0008] In some embodiments, the distance between the Pt active center and the nearest ZSM-5 molecular sieve is within 1 μm.

[0009] In some embodiments, the specific surface area of ​​Al2O3 is 300-1000 m 2 / g, preferably 800-100 m 2 / g.

[0010] In some embodiments, the mass fraction of the Al2O3 carrier to the catalyst is 0.1-0.9%, preferably 0.3-0.6%.

[0011] In some embodiments, the mass percentage of the Pt active component in the catalyst is 0.01% to 4.0%, preferably 1% to 2%.

[0012] In some embodiments, the Pt active center is a Pt nanoparticle, and the size of the Pt nanoparticle is 1.0-10 nm.

[0013] In a second aspect, the present invention provides a method for preparing a catalyst for a hydroisomerization reaction, comprising first preparing an Al2O3 carrier from a Pt active component and Al2O3, and then grinding the Al2O3 carrier and a ZSM-5 molecular sieve in a mortar to obtain a mixture.

[0014] In some embodiments, the preparation of the Al2O3 carrier from the Pt active component and Al2O3 comprises mixing an acidified solution of Al2O3 with a chloroplatinic acid solution for precipitation, filtering, and drying.

[0015] In some embodiments, the grinding time of grinding the Al2O3 carrier and the ZSM-5 molecular sieve in a mortar is 0.1-10 min, preferably 2-5 min.

[0016] In some embodiments, the pH of the acidified solution of Al2O3 is 1-6.

[0017] In some embodiments, the preparation of the Al2O3 carrier from the Pt active component and Al2O3 further comprises subjecting the dried product to high temperature treatment under an atmosphere of H2, O2, N2 or Ar.

[0018] In some embodiments, the high temperature treatment conditions are as follows: the treatment temperature is 150-600° C., and the treatment time is 0.5-10 h.

[0019] In some embodiments, the acidified solution of Al2O3 is prepared by adding acid to a suspension formed by dispersing Al2O3 in water, and the mass ratio of water to alumina in the suspension is 50-500:1, preferably 150-250:1.

[0020] In some embodiments, the acidic solution is at least one selected from hydrochloric acid, acetic acid, and nitric acid, preferably hydrochloric acid.

[0021] In a third aspect, the present invention provides an application of a catalyst for a hydroisomerization reaction, which is used for the isomerization reaction of C6~C8 normal alkanes.

[0022] In some embodiments, the alkane isomerization reaction temperature is 200-370°C.

[0023] In some embodiments, the alkane isomerization reaction pressure is 0.1-3.0 MPa.

[0024] In some embodiments, the molar ratio of hydrogen to normal alkane in the alkane isomerization reaction is 2.0 to 9.0:1.

[0025] In some embodiments, the mass space velocity of the alkane in the alkane isomerization reaction is 1.5 to 6.0 h -1 .

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The catalyst for hydroisomerization reaction provided by the present invention avoids the close contact of the metal active sites on the micropore acid sites of the molecular sieve in the traditional synthesis process by controlling the Pt active center to be away from the acid active center of the molecular sieve in the range of 50 nm-1 μm, effectively reduces the enrichment of olefin intermediates in the micropore channels of the ZSM-5 molecular sieve during the reaction, and weakens the cracking reaction path.

[0028] (2) The present invention selectively deposits Pt nanoparticles on an alumina carrier and uses physical grinding and mixing to achieve separation of Pt metal active centers and ZSM-5 molecular sieve acid centers at the micro-nano level, thereby avoiding the enrichment of olefin intermediates in the micropores of the molecular sieve. The alkane conversion rate and isomerization product selectivity are excellent. At the same time, the preparation method of the catalyst of the present invention is simple and easy to industrialize.

[0029] Reference numerals

[0030] Figure 1 This is a spherical aberration scanning transmission electron microscopy image of the catalyst for hydroisomerization reaction obtained in Example 1. DETAILED DESCRIPTION

[0031] In order to make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments and drawings. These embodiments are only for illustration and are not intended to limit the application scope of the present invention.

[0032] The relevant parameters of the ZSM-5 molecular sieve used in the examples and comparative examples are as follows: SiO2 / Al2O3=40, specific surface area (S BET ) = 520 m 2 / g, pore volume = 0.12 cm 3 / g, average pore size = 0.52 nm; alumina is γ crystalline, with a total porosity of 85%, a pore size of 500 nm, and macropores accounting for 85% of the total porosity.

[0033] Comparative Example 1: Pt / ZSM-5-A

[0034] Pt was directly loaded on the ZSM-5 molecular sieve using the equal volume impregnation method. The specific method is as follows: 4 mg Pt 5 mL of 1.5-1.5% Pt(NH3)4(NO3)2 solution was added to a 20 mL beaker, stirred for 10 min, and then 2 g of ZSM-5 molecular sieve was added. The mixture was stirred at room temperature for 24 h, dried in an oven at 80 °C for 12 h, and then treated in air at 500 °C for 4 h to obtain a Pt / ZSM-5-A catalyst. The percentage of Pt nanoparticles in the catalyst was 1 wt%, and the Pt nanoparticles were located on the surface of the ZSM-5 molecular sieve.

[0035] Comparative Example 2: Pt / ZSM-5 + Al2O3-B

[0036] Measure 4 mg Pt5 mL of Pt(NH3)4(NO3)2 solution with a concentration of 100 μg / mL was added to a 20 mL beaker, stirred for 10 min, and then 2 g of ZSM-5 molecular sieve was added. The mixture was stirred at room temperature for 24 h, dried in an oven at 80 °C for 12 h, and then treated in air at 500 °C for 4 h to obtain a Pt / ZSM-5 catalyst, in which the percentage of Pt nanoparticles was 1 wt%. Subsequently, 1 g of Pt / ZSM-5 was taken out and ground with 1 g of Al2O3 carrier in a mortar for 3 min to obtain Pt / ZSM-5+Al2O3-B. The percentage of Pt nanoparticles in the catalyst was 0.5 wt%, and the Pt nanoparticles were located on the surface of the ZSM-5 molecular sieve.

[0037] Example 1: Pt / Al2O3+ ZSM-5-C

[0038] 2 g of Al2O3 carrier was added to 100 g of deionized water. After stirring for 30 min, 0.1 mol / L hydrochloric acid was slowly dripped in to adjust the pH to 3. Stirring was continued for 1 h. Then, 20 mL of 1 mg Pt / mL H2PtCl6∙6H2O solution, stirred for 3 h, filtered and washed with 1.5 L deionized water, the filter cake was dried in an oven at 80 ℃ for 12 h, and then treated in air at 500 ℃ for 4 h to obtain a Pt / Al2O3 sample with a Pt nanoparticle content of 1 wt%. Then 1g of the Pt / Al2O3 sample was taken out and ground with 1g of ZSM-5 molecular sieve in a mortar for 3 min to obtain a Pt / Al2O3+ZSM-5-C catalyst. The Pt nanoparticle content in the catalyst was 0.5 wt%, and the Pt nanoparticles were located on the surface of the Al2O3 carrier.

[0039] Example 2: Pt / Al2O3+ ZSM-5-D

[0040] 2 g of Al2O3 carrier was added to 100 g of deionized water. After stirring for 30 min, 0.1 mol / L hydrochloric acid was slowly dripped in to adjust the pH to 3. Stirring was continued for 1 h. Then, 20 mL of 1 mg Pt / mL H2PtCl6∙6H2O solution was stirred for 3 h, filtered and washed with 1.5 L deionized water, and the filter cake was dried in an oven at 80 ℃ for 12 h, and then treated in air at 500 ℃ for 4 h to obtain a Pt / Al2O3 sample with a Pt nanoparticle content of 1 wt%. Subsequently, 1 g of the Pt / Al2O3 sample was taken out and ground with 1 g of ZSM-5 molecular sieve in a mortar for 1 min to obtain a Pt / Al2O3+ZSM-5-D catalyst with a Pt nanoparticle content of 0.5 wt%.

[0041] Example 3: Pt / Al2O3+ ZSM-5-E

[0042] 2 g of Al2O3 carrier was added to 100 g of deionized water. After stirring for 30 min, 0.1 mol / L hydrochloric acid was slowly dripped in to adjust the pH to 5. Stirring was continued for 1 h. Then, 20 mL of 1 mg Pt / mL H2PtCl6∙6H2O solution was stirred for 3 h, filtered and washed with 1.5 L deionized water, and the filter cake was dried in an oven at 80 ℃ for 12 h, and then treated in air at 500 ℃ for 4 h to obtain a Pt / Al2O3 sample with a Pt nanoparticle content of 1 wt%. Subsequently, 1 g of the Pt / Al2O3 sample was taken out and ground with 1 g of ZSM-5 molecular sieve in a mortar for 3 min to obtain a Pt / Al2O3+ZSM-5-E catalyst with a Pt nanoparticle content of 0.5 wt%.

[0043] Example 4: Pt / Al2O3+ ZSM-5-F

[0044] 2 g of Al2O3 carrier was added to 100 g of deionized water. After stirring for 30 min, 0.1 mol / L hydrochloric acid was slowly dripped in to adjust the pH to 3. Stirring was continued for 1 h. Then, 20 mL of 1 mg Pt / mL H2PtCl6∙6H2O solution, stirred for 3 h, filtered and washed with 1.5 L deionized water, the filter cake was dried in an oven at 80 ℃ for 12 h, and then treated with H2 at 500 ℃ for 4 h to obtain a Pt / Al2O3 sample with a Pt nanoparticle content of 1 wt%. Subsequently, 1 g of the Pt / Al2O3 sample was taken out and ground with 1 g of ZSM-5 molecular sieve in a mortar for 3 min to obtain a Pt / Al2O3+ ZSM-5-F catalyst with a Pt nanoparticle content of 0.5 wt%.

[0045] Example 5: Pt / Al2O3+ ZSM-5-G

[0046] 2 g of Al2O3 carrier was added to 100 g of deionized water. After stirring for 30 min, 0.1 mol / L hydrochloric acid was slowly dripped in to adjust the pH to 3. Stirring was continued for 1 h. Then, 40 mL of 1 mg Pt / mL H2PtCl6∙6H2O solution, stirred for 3 h, filtered and washed with 1.5 L deionized water, the filter cake was dried in an oven at 80 ℃ for 12 h, and then treated with H2 at 500 ℃ for 4 h to obtain a Pt / Al2O3 sample with a Pt nanoparticle content of 2 wt%. Subsequently, 1 g of the Pt / Al2O3 sample was taken out and ground with 1 g of ZSM-5 molecular sieve in a mortar for 3 min to obtain a Pt / Al2O3+ZSM-5-G catalyst with a Pt nanoparticle content of 1.0 wt%.

[0047] Example 6: Catalyst Evaluation

[0048] The catalysts prepared in Examples 1-5 and Comparative Examples 1-2 were pressed into tablets, sieved through 20-40 meshes, and 0.3 g of the catalyst was placed in a fixed bed reactor. The temperature was raised from room temperature to 450°C at a rate of 10°C / min under a hydrogen atmosphere. After reduction for 2 h, the temperature was lowered to the reaction temperature and the catalyst was evaluated. The reaction products were analyzed using an Agilent 7890B gas chromatograph. The results can be obtained from the following formula:

[0049] Conversion rate = 1 - (amount of isohexane in reactants / amount of n-hexane in feed) × 100%;

[0050] Isomer selectivity = (amount of isohexane in product / product) × 100%;

[0051] Isomer yield = conversion rate × isomer selectivity × 100%

[0052] The catalyst evaluation conditions were as follows: temperature 240 °C, pressure 1.5 MPa, molar ratio of hydrogen to n-hexane 6.0, and mass space velocity of n-hexane 4.5 h -1 The evaluation results of each catalyst are shown in Table 1.

[0053] Table 1 Catalyst evaluation results

[0054]

[0055] The catalyst used in the present invention has excellent n-hexane isomerization performance. From the performance results of Comparative Example 1, Comparative Example 2 and Example 1 in Table 1, it can be seen that in Comparative Example 1, no alumina carrier is added during the catalyst preparation process, but the Pt active center is directly located on the molecular sieve using the existing technology. Although Comparative Example 2 contains alumina, the Pt active center is still directly located on the molecular sieve, and the alumina and the molecular sieve are physically mixed. Therefore, the distance between the Pt in Comparative Example 1 and Comparative Example 2 and the molecular sieve is both less than 50nm at the atomic level. In the embodiment, the Pt active metal is selectively located on the alumina carrier, away from the metal active center and the molecular sieve acid center, which is beneficial to the n-hexane isomerization process, and the isomer yield has been significantly improved; on the other hand, it can be seen from the catalyst performance evaluation results of Examples 1-5 that by controlling the conditions such as the loading amount of metal Pt, pH value, grinding time and subsequent calcination atmosphere type, the activity of the catalyst can be effectively improved, and the isomer yield can reach up to 70.8%.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the substantial technical content of the present invention. The substantial technical content of the present invention is broadly defined in the scope of the claims of the application. Any technical entity or method completed by others, if it is exactly the same as that defined in the scope of the claims of the application or an equivalent variation, will be deemed to be included in the scope of the claims.

Claims

1. A method for preparing a catalyst for hydroisomerization reaction, characterized in that: The method comprises first preparing an Al2O3 carrier from a Pt active component and Al2O3, and then grinding the Al2O3 carrier and a ZSM-5 molecular sieve in a mortar to obtain a mixture; The preparation of the Al2O3 carrier from the Pt active component and Al2O3 includes mixing an acidified solution of Al2O3 with a chloroplatinic acid solution for precipitation, filtering, and drying; the pH of the acidified solution of Al2O3 is 1 to 3; The preparation of the Al2O3 carrier from the Pt active component and Al2O3 also includes subjecting the dried product to high temperature treatment in air; The grinding time of grinding the Al2O3 carrier and the ZSM-5 molecular sieve in a mortar is 0.1-10 minutes.

2. The method for preparing a catalyst for hydroisomerization reaction according to claim 1, characterized in that: The grinding time of grinding the Al2O3 carrier and the ZSM-5 molecular sieve in a mortar is 2-5 minutes.

3. The method for preparing a catalyst for hydroisomerization reaction according to claim 1, characterized in that: The acidified solution of Al2O3 is prepared by adding acid to a suspension formed by dispersing Al2O3 in water, wherein the mass ratio of water to alumina in the suspension is 50-500:

1.

4. The method for preparing a catalyst for hydroisomerization reaction according to claim 3, characterized in that: The mass ratio of water to aluminum oxide in the suspension is 150-250:

1.

5. The method for preparing a catalyst for hydroisomerization reaction according to any one of claims 1 to 4, characterized in that: The conditions of the high temperature treatment are as follows: the treatment temperature is 150-600° C., and the treatment time is 0.5-10 h.

6. A catalyst for hydroisomerization reaction, prepared by the preparation method according to any one of claims 1 to 5.

7. The catalyst for hydroisomerization reaction according to claim 6, characterized in that The catalyst comprises a mixture of a ZSM-5 molecular sieve and an Al2O3 carrier, wherein the Al2O3 carrier is loaded with a Pt active component to form a Pt active center on the surface of the Al2O3 carrier, and the distance between the Pt active center and the ZSM-5 molecular sieve is more than 50 nm.

8. The catalyst for hydroisomerization reaction according to claim 7, characterized in that The distance between the Pt active center and the nearest ZSM-5 molecular sieve is within 1 μm.

9. The catalyst for hydroisomerization reaction according to claim 7 or 8, characterized in that: The specific surface area of ​​Al2O3 is 300-1000m 2 / g; and / or the mass fraction of the Al2O3 carrier in the catalyst is 0.1 to 0.9%.

10. The catalyst for hydroisomerization reaction according to claim 9, characterized in that: The specific surface area of ​​Al2O3 is 800-1000m 2 / g; and / or the mass fraction of the Al2O3 carrier in the catalyst is 0.3-0.6%.

11. The catalyst for hydroisomerization reaction according to claim 7 or 8, characterized in that: The mass percentage of the Pt active component in the catalyst is 0.01% to 4.0%, and / or the Pt active center is a Pt nanoparticle, and the size of the Pt nanoparticle is 1.0 to 10 nm.

12. The catalyst for hydroisomerization reaction according to claim 11, characterized in that: The mass percentage of the Pt active component in the catalyst is 1% to 2%.

13. Use of the catalyst for hydroisomerization reaction according to any one of claims 6 to 12 in the isomerization reaction of C6 to C8 normal alkanes.

14. The use according to claim 13, characterized in that The isomerization temperature of the normal alkane is 200-370°C; and / or the pressure of the hydroisomerization of the normal alkane is 0.1-3.0 MPa; and / or the molar ratio of hydrogen to normal alkane in the hydroisomerization of the normal alkane is 2.0-9.0:1; and / or the mass space velocity of the alkane in the hydroisomerization of the normal alkane is 1.5-6.0 h -1 .

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