Preparation method and application of catalyst for catalyzing isomerization of n-butane

Abstract

The invention relates to a preparation method of a catalyst for catalyzing isomerization of n-butane, which comprises the following steps: preparing a composite carrier from TiO2 and Al2O3, carrying out coating modification on the composite carrier by using a transition metal oxide, and carrying out loading of active noble metal Pt or Pd and modification and reduction of a chlorinating agent by using an impregnation method. The preparation method comprises the following steps: preparing a composite carrier with an acidic framework from titanium oxide and aluminum oxide through a simple mixing and forming method, then coating and modifying the composite carrier with a transition-state metal oxide, and then simply roasting to obtain the metal oxide with oxygen vacancy and intermediate valence. After being loaded with noble metal, the catalyst can interact to play a role in dispersing active metal, and isomerization of n-butane at active sites is improved. In a fixed bed reaction, a proper amount of catalyst is added into the reaction, so that a good reaction effect is achieved, and reaction results show that the conversion rate of n-butane is 69.2%, the selectivity of isobutane is 98.1%, and the yield of isobutane is 67.9%.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a preparation method and application of a catalyst for catalyzing the isomerization of n-butane. Background Art

[0002] C4 is an organic compound with four carbon atoms, and its main components are n-butane, isobutane, isobutylene, n-butene (1-butene and 2-butene) and butadiene. A large amount of C4 substances are generated in the chemical catalytic section, petroleum refining, natural gas processing, biomass conversion, etc. Their large-scale emissions will not only affect the environment and are not conducive to the strategy of sustainable development, but also waste resources. Therefore, further deep processing of by-product C4 compounds can achieve the circular development of resources and expand downstream industries. Among them, isobutylene is mostly used to react with methanol to generate methyl tert-butyl ether (MTBE) and add it to gasoline to produce high-octane gasoline and improve fuel utilization. N-butene can be used to produce methyl ethyl ketone or dehydrogenate to butadiene. The utilization rate of n-butane is low and it is mostly used for fuel use. If n-butane is converted into isobutane through isomerization reaction, its value can be greatly improved and its utilization rate can be increased. With the development of the global economy, the expansion of the chemical industry, the adjustment of energy structure and the growth of clean energy demand, the application of isobutane energy with high energy density and combustion efficiency will gradually increase. In the chemical industry, isobutane liquid is an important raw material for the production of various chemicals, such as plastics, rubber, fiber, etc. Therefore, the isomerization of n-butane to isobutane is of great significance to the recycling of resources and sustainable development.

[0003] The current isomerization process mainly focuses on low-temperature isomerization and medium-temperature isomerization. The medium-temperature isomerization process has lower requirements on the sulfur content and water content of the raw materials, but has disadvantages such as low activity, high reaction temperature, many cracking products, and low single-pass conversion rate. Compared with the medium-temperature isomerization process, the low-temperature isomerization process can provide higher activity, maximize the conversion of the raw materials, and has the advantages of high liquid yield, high isomerization selectivity, and high single-pass conversion rate. The catalyst is the core of the isomerization process. The existing isomerization catalyst has low activity, poor stability, and low conversion rate. Moreover, chlorine needs to be continuously supplemented during the reaction, which is inconvenient to use and has high cost; therefore, it is urgent to develop an isomerization catalyst with high activity, high stability, and high conversion rate.

[0004] The development of high-performance catalysts is the key to the isomerization reaction of n-butane. At present, isomerization catalysts are mainly divided into non-precious metal and precious metal catalysts, and the carriers loaded are generally zirconium-based compounds, molecular sieves, heteropoly acids, etc., but most of the current catalysts have problems such as complex preparation process, high cost, low carrier strength, low performance, etc., and industrialization is difficult. For example, the patent CN104292065A discloses a noble metal-loaded n-butane isomerization reaction using a heteropoly acid skeleton as a carrier, which uses H3PW12O40 and Cs2.5H0.5PW12O40 to load Pd and Pt precious metals, and its conversion rate is still low. The invention patent CN1087660C discloses an application of a molecular sieve catalyst, which uses ZSM-5, ZSM-11, and β-type molecular sieves as raw materials, and then uses a nitric acid compound containing Ti and Zr to mix and roast after acid hydrogenation to obtain a further acid-strengthened carrier, and finally uses a binder and a pore-forming agent to modify the strength and structure of the carrier. The preparation process of this catalyst is relatively complicated, with many parameters to be regulated, and the n-butane conversion rate and isobutane selectivity are low, which is not conducive to large-scale production applications. The invention patent CN117361618A discloses the preparation and application of a zirconium oxide catalyst, wherein a precipitant such as ammonia water is added dropwise to an ammonium salt and a zirconium salt solution, and a monoclinic zirconium oxide with a flower-like morphology is prepared as a catalyst carrier by regulating the raw materials. The preparation method is simple, the isobutane selectivity is acceptable, but the n-butane conversion rate is low, and this method is prepared by a hydrothermal reaction. The hydrothermal method has many instability factors during amplification and production, and the output of one kettle is usually not high, and there is internal pressure, which is dangerous and not conducive to industrial promotion.

[0005] The synergistic coordination of the acidic skeleton center and the active metal center of the bifunctional catalyst can effectively improve the activity of isomerization. The key to the catalytic reaction of n-butane isomerization is to prepare a catalyst with high structural strength, stable and reliable preparation process, low industrial cost and good activity. The present invention uses titanium oxide and aluminum oxide to prepare a composite carrier with an acidic skeleton by a simple mixed molding method, and then the transition metal oxide is coated and modified on the composite carrier. After simple calcination, a metal oxide with oxygen vacancies and an intermediate valence state can be obtained. After loading the precious metal, it can interact with each other to disperse the active metal and improve the isomerization of n-butane at the active site. In the fixed bed reaction, taking an appropriate amount of catalyst into the reaction has a good reaction effect. The reaction results show that the n-butane conversion rate is 69.2%, the isobutane selectivity is 98.1%, and the isobutane yield is 67.9%. Summary of the invention

[0006] The purpose of the present invention is to provide a new method for preparing a catalyst, which can be applied to the isomerization of n-butane.

[0007] A preparation method for a catalyst for catalyzing the isomerization of n-butane, the preparation method comprises the following steps: preparing a composite carrier with TiO2 and Al2O3, coating and modifying the composite carrier with a transition metal oxide, and then loading active precious metals Pt or Pd and a chlorinating agent by an impregnation method, followed by reduction.

[0008] Preferably, the preparation method comprises the following steps: (1) γ-Al2O3 and TiO2 are mixed, hydrochloric acid is added thereto, mixed, extruded, dried, and calcined to obtain a composite carrier; (2) preparing an aqueous solution containing a metal oxide precursor, dispersing it ultrasonically, adding the composite carrier obtained in step (1) thereto, then adding a precipitant to form a hydroxide precipitate to coat the carrier, drying, and heat treating to obtain a modified carrier; (3) Prepare an active precious metal Pt or Pd precursor solution, add a chlorinating agent thereto, and then add the precursor solution to the modified support obtained in step (2), let stand, chlorinate, and reduce.

[0009] Preferably, the metal oxide precursor in step (2) is ZrOCl2.8H2O, CeN3O9.6H2O or H4[Si(W3O 10 )4].xH2O, the amount of the metal oxide precursor is 5%-10% of the mass of the composite carrier; the precipitant is ammonia water, and its added amount is 4% of the mass of the composite carrier.

[0010] Preferably, the drying temperature in step (2) is 120-150°C for 15-24 hours; the heat treatment is carried out in an air atmosphere at a temperature of 400-600°C for 2-3 hours.

[0011] Preferably, the mass ratio of the mixture of γ-Al2O3 and TiO2 in step (1) is (1.8-2.0):(0.6-1); the concentration of the hydrochloric acid is 1%-5%, and the added amount is 10%-50% of the total amount of γ-Al2O3 and TiO2.

[0012] Preferably, the drying temperature in step (1) is 120-150°C for 24 hours, and the calcination is carried out in an air atmosphere at a temperature of 450-500°C for 2 hours to 3 hours.

[0013] Preferably, in step (3), the active precious metal Pt or Pd precursor solution is a solution formed by dissolving chloroplatinic acid or chloropalladic acid in aqua regia, respectively, and the added amount of the precious metals platinum and palladium is 1.5% of the mass of the composite carrier.

[0014] Preferably, the chlorinating agent in step (3) is HCl, AlCl3, PCl3, PCl5 or C2HCl3O2; the amount of the chlorinating agent added is 5% to 25% of the mass of the composite carrier; the chlorination temperature is 100°C and the time is 18h; the reduction in step (3) is carried out under hydrogen-argon conditions, wherein the hydrogen accounts for 10%, the reduction temperature is 400°C, and the time is 3h.

[0015] Preferably, the standing time in step (3) is 10 hours.

[0016] The invention discloses an application of a catalyst for catalyzing the isomerization of normal butane. The catalyst is used for the isomerization reaction of normal butane to prepare isobutane.

[0017] Advantages of the present invention: The isomerization bifunctional catalyst prepared by the present invention has a large number of uniformly dispersed metal active centers and synergistic acid centers. The catalyst fully maintains the single substance form of the active metal and has good dispersibility on the carrier. The preparation method has a simple process, mild conditions, low cost, and is easy to realize industrialization: the obtained catalyst is stable and can be used for the isomerization reaction of normal alkanes, making the reaction easy to carry out without additional chlorine supplementation, and has the characteristics of high catalytic activity, high liquid yield, high isomerization selectivity, and high single-pass conversion rate. DETAILED DESCRIPTION

[0018] In order to clearly demonstrate the technical content, characteristics and effects of the present invention, the present invention will be described more precisely and comprehensively through the following embodiments, but they should not be construed as limiting the practicable scope of the present invention.

[0019] Example 1 A method for preparing a catalyst for catalyzing the isomerization of n-butane, the method comprising the following steps: (1) γ-Al2O3 and TiO2 were mixed in a mass ratio of 2:1, 1% hydrochloric acid was added thereto, and the amount of hydrochloric acid added was 20% of the total amount of γ-Al2O3 and TiO2, mixed, extruded, dried at 140°C for 24 hours, and calcined at 470°C for 3 hours in an air atmosphere to obtain a composite carrier; (2) preparing an aqueous solution containing ZrOCl2.8H2O, dispersing it by ultrasonic, adding the composite carrier obtained in step (1) thereto, wherein the amount of ZrOCl2.8H2O added is 5% of the mass of the composite carrier; then adding 4% of the mass of the composite carrier with ammonia water to form a hydroxide precipitate to wrap the carrier, drying at 120°C for 24h, and then heat treating at 500°C in air atmosphere for 2h to obtain a modified carrier; (3) Dissolve chloropalladic acid in aqua regia to obtain a chloropalladic acid solution, take a chloropalladic acid solution with a palladium content of 1.5% by weight of the composite support, and then add a C2HCl3O2 chlorinating agent of 10% by weight of the composite support to obtain a mixed solution; add the mixed solution to the modified support obtained in step (2), let it stand for 10 hours, chlorinate at 100°C for 18 hours, and reduce at 400°C for 3 hours under hydrogen and argon conditions, wherein the hydrogen content is 10%.

[0020] Example 2 The metal oxide precursor is CeN3O9.6H2O, and the rest is the same as in Example 1.

[0021] Example 3 The added amount of ZrOCl2.8H2O is 10% of the mass of the composite carrier, and the rest is the same as in Example 1.

[0022] Example 4 A method for preparing a catalyst for catalyzing the isomerization of n-butane, the method comprising the following steps: (1) γ-Al2O3 and TiO2 were mixed in a mass ratio of 1.8:0.6, 5% hydrochloric acid was added thereto, and the amount of hydrochloric acid added was 10% of the total amount of γ-Al2O3 and TiO2, mixed, extruded, dried at 120°C for 24 hours, and calcined at 450°C in an air atmosphere for 2 hours to obtain a composite carrier; (2) Prepare a solution containing H4[Si(W3O 10 )4].xH2O aqueous solution, ultrasonic dispersion, add the composite carrier obtained in step (1) thereto, the H4[Si(W3O 10 )4]. The amount of xH2O added is 5% of the weight of the composite carrier; then 4% of the weight of the composite carrier is added with ammonia water to form a hydroxide precipitate to wrap the carrier, which is dried at 120°C for 15h, and then heat-treated in an air atmosphere at 400°C for 3h to obtain a modified carrier; (3) Dissolve chloroplatinic acid in aqua regia to obtain a chloropalladic acid solution, take a chloropalladic acid solution with a platinum content of 1.5% by weight of the composite support, and then add HCl chlorinating agent of 5% by weight of the composite support to obtain a mixed solution; add the mixed solution to the modified support obtained in step (2), let it stand for 10 hours, chlorinate at 100°C for 18 hours, and reduce at 400°C for 3 hours under hydrogen and argon conditions, wherein the hydrogen content is 10%.

[0023] Example 5 A method for preparing a catalyst for catalyzing the isomerization of n-butane, the method comprising the following steps: (1) γ-Al2O3 and TiO2 were mixed in a mass ratio of 1.9:0.8, and hydrochloric acid with a concentration of 1% was added thereto, wherein the amount of hydrochloric acid added was 50% of the total amount of γ-Al2O3 and TiO2, mixed, extruded, dried at 150°C for 24 hours, and calcined at 500°C for 3 hours in an air atmosphere to obtain a composite carrier; (2) preparing an aqueous solution containing ZrOCl2.8H2O, dispersing it by ultrasonic, adding the composite carrier obtained in step (1) thereto, wherein the amount of ZrOCl2.8H2O added is 5% of the mass of the composite carrier; then adding 4% of the mass of the composite carrier with ammonia water to form a hydroxide precipitate to wrap the carrier, drying at 150°C for 15 hours, and then heat treating at 600°C in an air atmosphere for 2 hours to obtain a modified carrier; (3) Dissolve chloroplatinic acid in aqua regia to obtain a chloropalladium acid solution, take a chloropalladium acid solution with a platinum content of 1.5% by weight of the composite support, and then add an AlCl3 chlorinating agent of 25% by weight of the composite support to obtain a mixed solution; add the mixed solution to the modified support obtained in step (2), let it stand for 10 hours, chlorinate at 100°C for 18 hours, and reduce at 400°C for 3 hours under hydrogen and argon conditions, wherein the hydrogen content is 10%.

[0024] Example 6 A method for preparing a catalyst for catalyzing the isomerization of n-butane, the method comprising the following steps: (1) γ-Al2O3 and TiO2 were mixed in a mass ratio of 1.8:1, 3% hydrochloric acid was added thereto, and the amount of hydrochloric acid added was 30% of the total amount of γ-Al2O3 and TiO2, mixed, extruded, dried at 150°C for 24 hours, and calcined at 500°C for 2.5 hours in an air atmosphere to obtain a composite carrier; (2) preparing an aqueous solution containing ZrOCl2.8H2O, dispersing it by ultrasonic, adding the composite carrier obtained in step (1) thereto, wherein the amount of ZrOCl2.8H2O added is 5% of the mass of the composite carrier; then adding 4% of the mass of the composite carrier with ammonia water to form a hydroxide precipitate to wrap the carrier, drying at 150°C for 15h, and then heat treating at 600°C in air atmosphere for 3h to obtain a modified carrier; (3) Dissolve chloroplatinic acid in aqua regia to obtain a chloropalladium acid solution, take a chloropalladium acid solution with a platinum content of 1.5% by weight of the composite carrier, and then add a PCl3 chlorinating agent of 20% by weight of the composite carrier to obtain a mixed solution; add the mixed solution to the modified carrier obtained in step (2), let it stand for 10 hours, chlorinate at 100°C for 18 hours, and reduce at 400°C for 3 hours under hydrogen and argon conditions, wherein the hydrogen content is 10%.

[0025] Comparative Example 1 (No coating modification of the composite carrier) A method for preparing a catalyst for catalyzing the isomerization of n-butane, the method comprising the following steps: 1) γ-Al2O3 and TiO2 were mixed in a mass ratio of 2:1, and hydrochloric acid with a concentration of 1.5%, which was 20% of the total amount of γ-Al2O3 and TiO2, was added thereto, and dried at 120°C for 12 hours. The water content was measured to be less than 1%, thereby obtaining a composite carrier; (3) Dissolve chloroplatinic acid in aqua regia to obtain a chloropalladium acid solution, take a chloropalladium acid solution with a platinum content of 1.5% by weight of the composite carrier, and then add a C2HCl3O2 chlorinating agent of 10% by weight of the composite carrier to obtain a mixed solution; add the mixed solution to the composite carrier obtained in step (1), let it stand for 10 hours, chlorinate at 100°C for 18 hours, and reduce at 400°C for 3 hours under hydrogen-argon conditions, wherein the hydrogen content is 10%.

[0026] Comparative Example 2 In step (3), no chlorinating agent is added and no chlorination is performed. The other steps are the same as those in Example 1.

[0027] The catalyst obtained in the examples and comparative examples was added to a fixed bed reactor. 5 g of the catalyst was taken. The reaction tube was fixed with inert materials up and down to make the catalyst bed temperature most uniform. The reaction temperature was set to 130° C., the hydrogen pressure was 2.0 MPa, the volume ratio of hydrogen to normal alkane was 0.5, and the volume space velocity was 0.6. -h After a period of reaction, the reaction liquid was taken and tested in gas chromatography. The reaction results are shown in Table 1: .

Claims

1. A method for preparing a catalyst for catalytic isomerization of n-butane, characterized in that: The preparation method comprises the following steps: preparing a composite carrier with TiO2 and Al2O3, coating and modifying the composite carrier with a transition metal oxide, and then loading active precious metals Pt or Pd and a chlorinating agent through an impregnation method, followed by reduction.

2. The method for preparing a catalyst for catalytic isomerization of n-butane according to claim 1, characterized in that: The preparation method comprises the following steps: (1) γ-Al2O3 and TiO2 are mixed, hydrochloric acid is added thereto, mixed, extruded, dried, and calcined to obtain a composite carrier; (2) preparing an aqueous solution containing a metal oxide precursor, dispersing it ultrasonically, adding the composite carrier obtained in step (1) thereto, then adding a precipitant to form a hydroxide precipitate to coat the carrier, drying, and heat treating to obtain a modified carrier; (3) Prepare an active precious metal Pt or Pd precursor solution, add a chlorinating agent thereto, and then add the precursor solution to the modified support obtained in step (2), let stand, chlorinate, and reduce.

3. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 2, characterized in that: The metal oxide precursor in step (2) is ZrOCl2.8H2O, CeN3O9.6H2O or H4[Si(W3O 10 )4].xH2O, the amount of the metal oxide precursor is 5%-10% of the mass of the composite carrier; the precipitant is ammonia water, and its added amount is 4% of the mass of the composite carrier.

4. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 3, characterized in that: The drying temperature in step (2) is 120-150°C for 15-24 hours; the heat treatment is carried out in an air atmosphere at a temperature of 400-600°C for 2-3 hours.

5. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 2, characterized in that: The mass ratio of the γ-Al2O3 and TiO2 mixed in step (1) is (1.8-2.0): (0.6-1); the concentration of the hydrochloric acid is 1%-5%, and the added amount is 10%-50% of the total amount of γ-Al2O3 and TiO2.

6. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 5, characterized in that: The drying temperature in step (1) is 120-150°C for 24 hours, and the calcination is carried out in an air atmosphere at a temperature of 450-500°C for 2 hours to 3 hours.

7. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 2, characterized in that: In step (3), the active precious metal Pt or Pd precursor solution is a solution formed by dissolving chloroplatinic acid or chloropalladic acid in aqua regia, respectively. The amount of the precious metal platinum and palladium added is 1.5% of the mass of the composite carrier.

8. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 2, characterized in that: The chlorinating agent in step (3) is HCl, AlCl3, PCl3, PCl5 or C2HCl3O2; the amount of the chlorinating agent added is 5% to 25% of the mass of the composite carrier; the chlorination temperature is 100°C and the time is 18h; the reduction in step (3) is carried out under hydrogen-argon conditions, wherein the hydrogen accounts for 10%, the reduction temperature is 400°C, and the time is 3h.

9. The method for preparing a catalyst for catalyzing the isomerization of n-butane according to claim 8, characterized in that: The standing time in step (3) is 10 hours.

10. An application of a catalyst for catalyzing the isomerization of n-butane, characterized in that: The catalyst is used for the isomerization reaction of n-butane to prepare isobutane, and the catalyst is prepared according to the preparation method of claim 1.