Cyclohexane dehydrogenation catalyst as well as preparation method and application thereof

Abstract

The present invention discloses a cyclohexane dehydrogenation catalyst, which comprises a carrier alumina, an active component Pt and a modification auxiliary agent In, and the catalyst comprises, by weight, 0.1-3% of Pt, 0.1-5% of In, and the balance of the carrier alumina. Meanwhile, the invention also discloses a preparation method and application of the catalyst. The catalyst has the characteristics of high metal dispersity, high activity, thermal stability and excellent service life, and when the catalyst is used for continuously catalyzing cyclohexane dehydrogenation to prepare benzene, the cyclohexane conversion rate is greater than 98%, the benzene selectivity of the product is greater than 99.5%, and the hydrogen purity is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of dehydrogenation catalysts, and particularly relates to a cyclohexane dehydrogenation catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Hydrogen energy is widely used in fields such as aerospace, civil use, transportation, construction industry, energy storage, etc., and will become the mainstream direction of global energy development, playing an important role in the energy transformation system.

[0003] The storage and transportation of hydrogen is one of the bottleneck problems in the use of hydrogen energy. Currently, the storage methods of hydrogen studied more are generally divided into high-pressure hydrogen storage, liquid hydrogen storage, solid hydrogen storage and organic liquid hydrogen storage. The organic liquid hydrogen storage technology is a form in which, under specific conditions, by means of the reversible hydrogenation-dehydrogenation reaction between unsaturated aromatic hydrocarbons such as benzene, toluene and naphthalene and their corresponding organic hydrides such as cyclohexane, methylcyclohexane and decalin, the organic matter in the unsaturated state reacts with hydrogen to generate a hydrogenation product, thereby storing hydrogen in the hydrogenation product. In the hydrogen release stage, hydrogen is released through a catalytic dehydrogenation reaction to achieve the purpose of hydrogen energy utilization. Pradhan et al. verified the superiority and feasibility of the organic hydride hydrogen storage process through energy balance calculations in aspects such as the value of energy transmission and consumption and CO 2 emissions.

[0004] In the organic liquid hydrogen storage cycle process, the hydrogenation technology is relatively mature. How to achieve efficient dehydrogenation is crucial, and the corresponding dehydrogenation catalyst is one of the key problems in the application of the liquid organic hydride hydrogen storage technology. Organic liquid hydrogen storage is a strongly endothermic and highly reversible reaction. High temperature and low pressure are beneficial to the reaction. Finding a suitable catalyst is the key to improving the dehydrogenation efficiency. The commonly used dehydrogenation catalysts are supported metal catalysts, and the active components include Pt, Pd, Rh, Ni, Co, etc., and the carriers are Al 2 O 3 , SiO 2 , TiO 2 , activated carbon and molecular sieves, etc. Currently, Pt / Al 2 O 3 is often used as a dehydrogenation catalyst in the organic liquid hydrogen storage technology and is obtained by a traditional impregnation method or precipitation method. Pt / Al 2 O 3 , as a catalyst with good selectivity and high conversion rate, is the most commonly used catalytic system in the dehydrogenation reaction of cyclohexane. However, due to Al 2 O 3The presence of a relatively large number of acidic sites leads to the easy aggregation of Pt particles into larger particles, and the catalyst is prone to coking deposition and deactivation. In addition, the extensive use of precious metals is also not conducive to reducing the process cost. Therefore, the research and development of highly efficient catalysts is crucial for the large-scale promotion of new organic liquid hydrogen storage systems. Summary of the Invention

[0005] Aiming at the defects of the prior art, the present invention provides a cyclohexane dehydrogenation catalyst, a preparation method thereof, and an application thereof. The catalyst has the advantages of high activity, good thermal stability, and excellent service life.

[0006] A cyclohexane dehydrogenation catalyst, which is composed of a carrier alumina, an active component Pt, and a modifying assistant In. The weight of the catalyst is recorded as 100%. The contents of each component are as follows: Pt 0.1 - 3%, In 0.1 - 5%, and the balance is the carrier alumina.

[0007] Preferably, the ratio H / D of the half-peak width H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier is 0.6 - 1.5.

[0008] The preparation method of the cyclohexane dehydrogenation catalyst includes the following steps: (1) Modifying the carrier with an assistant: Dissolve the precursor of the modifying assistant in water to obtain a solution containing the assistant, then impregnate the solution containing the assistant on the carrier, adsorb at room temperature for 6 - 24 h, adjust the pH of the system to 7 - 10 with an alkali metal solution, continue to adsorb for 6 - 12 h, and obtain the modified carrier after drying, roasting, and natural cooling. (2) Loading the active component: Take chloroplatinic acid and dissolve it in water to obtain solution A; weigh a water-soluble amide ligand and dissolve it in water to obtain solution B; while stirring solution A, drop solution B into it, and continue to stir for 0.5 - 3 h after dropping to obtain solution C; impregnate solution C on the modified carrier obtained in step (1), age at a constant temperature under a closed condition, filter, wash the filtered solid with deionized water until the conductivity of the filtrate is less than 500 S / m, and dry to obtain the catalyst precursor. (3) Reduction: First roast the catalyst precursor obtained in step (2) in an air atmosphere, and then roast it in a mixed atmosphere of N 2 and H 2 to complete one-step staged roasting, and then cool it naturally to obtain the catalyst.

[0009] Preferably, the water-soluble amide ligand is any one of urea, iminodicarbonic diamide, carbonic diamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylpropionamide, cyanoacetamide, propionamide, isobutyramide, formamide, or N,N-dimethylglycinamide; The molar ratio of the water-soluble amide ligand to Pt is (0.5 - 5):1; The concentration of the solution B is 5 - 20 wt%, and the dropping rate of the solution B is (0.01 - 0.1) mol amide / 1 mol Pt.

[0010] Preferably, the conditions for the constant-temperature aging are aging at 90 - 150 °C for 4 - 24 h.

[0011] Preferably, the conditions for the drying in step (2) are drying at 60 - 150 °C until the solution contains 1 - 15% based on the weight of the modified carrier.

[0012] Preferably, the one-step sectional roasting in step (3) is specifically as follows: First, in an air atmosphere, heat up at a heating rate of 1 - 5 °C / min to 200 - 300 °C and roast for 2 - 8 h, and the volumetric air velocity of the air is 1 - 10 h -1 ; then in a mixed atmosphere of N 2 and H 2 , heat up at a heating rate of 1 - 5 °C / min to 350 - 550 °C and roast for 2 - 8 h, and the volume ratio of N 2 and H 2 is (1 - 5):(1 - 5), and the volumetric air velocity of the mixed atmosphere is 1 - 5 h -1 .

[0013] Preferably, the precursor of the modification assistant is indium nitrate or indium nitrate hydrate; the alkali metal solution is an aqueous solution of the corresponding carbonate or hydroxide of the alkali metal, the concentration of the alkali metal solution is 5 - 20 wt%, and the alkali metal is lithium, sodium, or potassium.

[0014] Preferably, in step (1), the conditions for the drying are drying at 60 - 150 °C for 6 - 18 h; the conditions for the roasting in step (1) are heating up at a heating rate of 1 - 5 °C / min to 400 - 900 °C and roasting for 2 - 10 h.

[0015] Use of the cyclohexane dehydrogenation catalyst in continuously catalyzing cyclohexane dehydrogenation to prepare benzene, specifically: filling the catalyst into a fixed-bed reactor to form a catalyst bed layer, then flash-vaporizing cyclohexane and introducing it into the fixed-bed reactor, and carrying out a gas-solid two-phase continuous catalytic dehydrogenation reaction under the conditions of no carrier gas, 280-350 °C, and atmospheric pressure. The reaction mixture gas is condensed by a condenser, and hydrogen gas and liquid product benzene are obtained after flash separation and liquid removal. Among them, the mass space velocity of the cyclohexane is 0.2-1.5 h -1 .

[0016] Advantages of the present invention: (1) During the preparation of the catalyst of the present invention, by controlling the hydrolysis precipitation rate of the amide ligand through a constant-temperature aging process, the particle size of the active metal of the catalyst can be effectively regulated, the metal dispersion can be increased, the interaction force between the active metal and the carrier can be promoted, and the aggregation tendency of the active metal can be reduced; (2) After the catalyst is dried and maintained in a state containing a certain amount of solvent, it is calcined and reduced in one step by stages. The water vapor generated during the first-stage calcination plays the role of Passivation the strong acidic sites of the catalyst, and the hydrogen chloride gas generated during the second-stage calcination adjusts the platinum dispersion, and the hydrothermal passivation and activation are completed in one step; (3) During the loading process of the promoter In, the pH is adjusted by an alkali metal solution. The alkali metal salt reacts with indium nitrate to form a complex, and In 3+ will be reduced to a lower-valent indium compound or metallic indium, enhancing the metal-support interaction force. The completely reduced In atoms in InO 3 form Pt 2 In 3 intermetallic compounds, dispersing the aggregates of Pt into smaller clusters and increasing the dispersion. In addition, the electron transfer from In atoms to Pt atoms through the Pt-In bond leads to electron accumulation, promoting the desorption of cyclohexene; (4) A carrier with a special pore structure is selected to increase the hydrogen spillover and product diffusion desorption during the reaction process, significantly reduce the carbon deposition C / H ratio, and reduce the probability of carbon deposition; (5) The catalyst prepared by the present invention has high metal dispersion, and has the characteristics of high activity, good thermal stability and long service life. The cyclohexane conversion rate > 98%, the product benzene selectivity > 99.5%, and the hydrogen purity is high. Specific embodiments

[0017] Example 1 1. A cyclohexane dehydrogenation catalyst, which is composed of a carrier alumina, an active component Pt, and a modifying assistant In. Taking the weight of the catalyst as 100%, the contents of each component are as follows: Pt 0.5%, In 1%, and the balance is the carrier alumina. Among them, the ratio H / D of the half-peak width H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier is 1.0. The catalyst is denoted as S1.

[0018] 2. A preparation method of the cyclohexane dehydrogenation catalyst according to claim 1, comprising the following steps: (1) Modifying the carrier with the assistant: Dissolve indium nitrate in water to obtain a solution containing the assistant, then immerse the solution containing the assistant on the carrier alumina, adsorb at room temperature for 12 h, adjust the pH of the system to 8 with 10 wt% potassium hydroxide solution, continue to adsorb for 8 h, dry at 120 °C for 12 h, heat up to 600 °C at a rate of 2 °C / min and calcine for 4 h, and obtain the modified carrier after natural cooling; (2) Loading the active component: Take chloroplatinic acid and dissolve it in water to obtain solution A; weigh urea according to the molar ratio of amide ligand to Pt of 2:1, dissolve it in water to obtain a 10% urea solution, denoted as solution B; under the stirring state of solution A, add solution B dropwise into solution B at a rate of 0.05 mol amide / 1 mol Pt, and continue to stir for 1 h after the dropping is completed to obtain solution C; immerse solution C on the modified carrier obtained in step (1), age at a constant temperature of 120 °C for 12 h under closed conditions, filter, wash the filtered solid with deionized water until the conductivity of the filtrate is 480 S / m, and dry at 100 °C until it contains 8% of the solution based on the weight of the modified carrier to obtain the catalyst precursor; (3) Reduction: Place the catalyst precursor obtained in step (2) in a tubular furnace. First, under an air atmosphere, heat up to 280 °C at a rate of 2 °C / min and calcine for 5 h, and the volume space velocity of air is 5 h -1 ; then under a mixed atmosphere of N 2 and H 2 , heat up to 450 °C at a rate of 2 °C / min and calcine for 4 h, the volume ratio of N 2 and H 2 is 1:1, and the total volume space velocity of N 2 and H 2 is 2.5 h -1 , complete one-step sectional calcination, and obtain the catalyst after natural cooling.

[0019] Example 2 The content of In is 0.1%, and the others are the same as in Example 1. The obtained catalyst is denoted as S2.

[0020] Example 3 The content of In is 5%, and the others are the same as in Example 1. The obtained catalyst is denoted as S3.

[0021] Example 4 The content of Pt is 0.1%, and the others are the same as in Example 1. The obtained catalyst is denoted as S4.

[0022] Example 5 The content of Pt is 3%, and the others are the same as in Example 1. The obtained catalyst is denoted as S5.

[0023] Example 6 The ratio H / D of the full width at half maximum H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier alumina is 1.5, and the others are the same as in Example 1. The obtained catalyst is denoted as S6.

[0024] Example 7 In step (2), the amide ligand used is N,N-dimethylformamide, and the others are the same as in Example 1. The obtained catalyst is denoted as S7.

[0025] Example 8 In step (2), the molar ratio of the urea ligand to the active component Pt is 0.5:1, and the others are the same as in Example 1. The preparation method is the same as in Example 1. The obtained catalyst is denoted as S8.

[0026] Example 9 The temperature of isothermal aging is 150 °C, and the others are the same as in Example 1. The obtained catalyst is denoted as S9.

[0027] Example 10 In step (2), it is dried until the solution contains 15% based on the weight of the modified carrier, and the others are the same as in Example 1. The obtained catalyst is denoted as S10.

[0028] Example 11 In step (3), the temperature of air calcination is 200 °C, and the others are the same as in Example 1. The obtained catalyst is denoted as S11.

[0029] Example 12 In step (3), under a mixed atmosphere, the calcination temperature is 550 °C, and the others are the same as in Example 1. The obtained catalyst is denoted as S12.

[0030] Example 13 1. A cyclohexane dehydrogenation catalyst, which is composed of a carrier alumina, an active component Pt, and a modifying assistant In. The weight of the catalyst is recorded as 100%, and the contents of each component are as follows: Pt 1.5%, In 2%, and the balance is the carrier alumina; wherein, the ratio H / D of the half-peak width H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier is 0.6; the catalyst is denoted as S13.

[0031] 2. A preparation method of the cyclohexane dehydrogenation catalyst according to claim 1, comprising the following steps: (1) Modifying the carrier with the assistant: Dissolve indium nitrate in water to obtain an assistant-containing solution, then impregnate the assistant-containing solution on the carrier alumina, adsorb at room temperature for 6 h, adjust the pH of the system to 10 with a 5 wt% sodium hydroxide solution, continue to adsorb for 12 h, dry at 60 °C for 18 h, heat up to 400 °C at a rate of 1 °C / min for calcination for 10 h, and naturally cool to obtain a modified carrier; (2) Loading the active component: Take chloroplatinic acid and dissolve it in water to obtain solution A; weigh diethyl carbonate according to the molar ratio of amide ligand to Pt of 5:1, dissolve it in water to obtain a 5% diethyl carbonate solution, denoted as solution B; under stirring of solution A, add solution B dropwise into solution B at a rate of 0.01 mol amide / 1 mol Pt, and continue to stir for 0.5 h after dropping to obtain solution C; immerse solution C on the modified carrier obtained in step (1), age at a constant temperature of 90 °C for 24 h under a closed condition, filter, wash the filtered solid with deionized water until the conductivity of the filtrate is 450 S / m, and dry at 60 °C until it contains 10% of the solution based on the weight of the modified carrier to obtain a catalyst precursor; (3) Reduction: Place the catalyst precursor obtained in step (2) in a tubular furnace, first heat up to 200 °C at a rate of 1 °C / min for calcination for 8 h in an air atmosphere, and the volume space velocity of air is 10 h -1 ; then in a mixed atmosphere of N 2 and H 2 , heat up to 350 °C at a rate of 1 °C / min for calcination for 8 h, and the volume ratio of N 2 and H 2 is 1:1, and the total volume space velocity of N 2 and H 2 is 5 h -1 , complete one-step sectional calcination, and naturally cool to obtain the catalyst.

[0032] Example 14 1. A cyclohexane dehydrogenation catalyst, which is composed of a carrier alumina, an active component Pt, and a modified promoter In. The weight of the catalyst is recorded as 100%, and the contents of each component are as follows: Pt 1%, In 1.5%, and the balance is carrier alumina; wherein, the ratio H / D of the half-peak width H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier is 1.0; the catalyst is denoted as S14.

[0033] 2. A preparation method of the cyclohexane dehydrogenation catalyst according to claim 1, comprising the following steps: (1) Modifying the carrier with the promoter: Dissolve indium nitrate in water to obtain a promoter-containing solution, then impregnate the promoter-containing solution on the carrier alumina, adsorb at room temperature for 24 h, adjust the pH of the system to 7 with 20 wt% sodium carbonate solution, continue to adsorb for 6 h, dry at 150 °C for 6 h, calcine at a rate of 5 °C / min to 900 °C for 2 h, and naturally cool to obtain a modified carrier; (2) Loading the active component: Take chloroplatinic acid and dissolve it in water to obtain solution A; weigh propionamide according to the molar ratio of amide ligand to Pt of 2:1, dissolve it in water to obtain a 10% propionamide solution, denoted as solution B; under stirring of solution A, add solution B dropwise into solution B at a rate of 0.1 mol amide / 1 mol Pt, and continue to stir for 3 h after dropping to obtain solution C; impregnate solution C on the modified carrier obtained in step (1), age at a constant temperature of 140 °C for 4 h under closed conditions, filter, wash the filtered solid with deionized water until the conductivity of the filtrate is 400 S / m, and dry at 150 °C until it contains 1% of the solution based on the weight of the modified carrier to obtain a catalyst precursor; (3) Reduction: Place the catalyst precursor obtained in step (2) in a tubular furnace, first calcine at a rate of 5 °C / min to 300 °C for 2 h in an air atmosphere, and the volume space velocity of air is 1 h -1 ; then in a mixed atmosphere of N 2 and H 2 , calcine at a rate of 5 °C / min to 500 °C for 2 h, the volume ratio of N 2 and H 2 is 1:1, and the total volume space velocity of N 2 and H 2 is 1 h -1 , complete one-step sectional calcination, and naturally cool to obtain the catalyst.

[0034] Comparative Example 1 The ratio H / D of the half-peak width H to the average micropore diameter D obtained from the adsorption distribution curve of the carrier alumina is 0.2, and the others are the same as in Example 1. The obtained catalyst is denoted as D1.

[0035] Comparative Example 2 In step (2), there was no constant-temperature aging, and the other conditions were the same as in Example 1. The obtained catalyst was denoted as D2.

[0036] Comparative Example 3 In step (2), it was dried at 100 °C until there was no solvent state, that is, dried to constant weight. The other conditions were the same as in Example 1. The obtained catalyst was denoted as D3.

[0037] Comparative Example 4 In step (1), the pH was not adjusted, and the co-adsorption was carried out for 20 h. The other conditions were the same as in Example 1. The obtained catalyst was denoted as D4.

[0038] Performance detection The above catalysts were filled into a fixed-bed reactor to form a catalyst bed layer. Then, cyclohexane was flash-vaporized and introduced into the fixed-bed reactor. Under the conditions of no carrier gas, 280 - 350 °C, and atmospheric pressure, a gas-solid two-phase continuous catalytic dehydrogenation reaction was carried out. The reaction mixture gas was condensed by a condenser, and hydrogen and liquid product benzene were obtained after flash separation and liquid removal. Among them, the mass space velocity of the cyclohexane was 0.2 - 1.5 h -1 , and the reaction was carried out for 4300 h. The other reaction conditions and results are shown in Table 1; Table 1 Reaction conditions and reaction results

Claims

1. A cyclohexane dehydrogenation catalyst, characterized in that: The catalyst is composed of carrier alumina, active component Pt and modification aid In. The weight of the catalyst is 100%, and the content of each component is as follows: Pt 0.1-3%, In 0.1-5%, and the balance is carrier alumina.

2. The cyclohexane dehydrogenation catalyst according to claim 1, characterized in that: The ratio H / D of the half-peak width H to the average micropore diameter D obtained in the adsorption distribution curve of the carrier is 0.6-1.

5.

3. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 1, characterized in that: The following steps are involved: (1) Additive modified carrier: The precursor of the modified auxiliary agent is dissolved in water to obtain an auxiliary agent solution, and then the auxiliary agent solution is impregnated on the carrier, adsorbed at room temperature for 6-24 hours, the pH of the system is adjusted to 7-10 with an alkali metal solution, and the adsorption is continued for 6-12 hours. After drying, roasting, and natural cooling, a modified carrier is obtained; (2) Loading active components: Take chloroplatinic acid and dissolve it in water to obtain solution A; weigh a water-soluble amide ligand and dissolve it in water to obtain solution B; add solution B dropwise to solution A while stirring, and continue stirring for 0.5-3 hours after the addition is complete to obtain solution C; impregnate solution C on the modified carrier obtained in step (1), age at a constant temperature under closed conditions, filter, wash the filtered solid with deionized water until the conductivity of the filtrate is less than 500 S / m, and dry it to obtain a catalyst precursor; (3) Restore: The catalyst precursor obtained in step (2) is first calcined in an air atmosphere, and then calcined in a mixed atmosphere of N2 and H2 to complete a one-step staged calcination reduction, and then naturally cooled to obtain the catalyst.

4. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 3, characterized in that: The water-soluble amide ligand is any one of urea, iminodicarbonic acid diamide, carbonic acid diamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylpropionamide, cyanoacetamide, propionamide, isobutyramide, formamide, or N,N-dimethylglycinamide; The molar ratio of the water-soluble amide ligand to Pt is (0.5-5):1; The concentration of the solution B is 5-20 wt %, and the dropping rate of the solution B is (0.01-0.1) mol amide / 1 mol Pt.

5. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 4, characterized in that: The constant temperature aging condition is aging at 90-150° C. for 4-24 hours.

6. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 5, characterized in that: The drying condition in step (2) is drying at 60-150° C. until the solution contains 1-15% based on the weight of the modified carrier.

7. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 6, characterized in that: The step (3) of the one-step calcination is as follows: first, in an air atmosphere, the temperature is raised to 200-300°C at a heating rate of 1-5°C / min and calcined for 2-8h, with the air volume space velocity of 1-10h -1 Then, in a mixed atmosphere of N2 and H2, the temperature was raised to 350-550℃ at a heating rate of 1-5℃ / min and calcined for 2-8h. The volume ratio of N2 and H2 was (1-5): (1-5) and the volume space velocity of the mixed atmosphere was 1-5h -1 .

8. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 3, characterized in that: The precursor of the modification aid is indium nitrate or indium nitrate hydrate; the alkali metal solution is an aqueous solution of carbonate or hydroxide corresponding to the alkali metal, the concentration of the alkali metal solution is 5-20wt%, and the alkali metal is lithium, sodium or potassium.

9. The method for preparing the cyclohexane dehydrogenation catalyst according to claim 3, characterized in that: In step (1), the drying condition is drying at 60-150°C for 6-18h; the calcination condition in step (1) is heating at a heating rate of 1-5°C / min to 400-900°C and calcining for 2-10h.

10. Use of the cyclohexane dehydrogenation catalyst according to claim 1 in the continuous catalytic dehydrogenation of cyclohexane to prepare benzene, characterized in that: The application is as follows: the catalyst is loaded into a fixed bed reactor to form a catalyst bed, and then cyclohexane is flash vaporized and introduced into the fixed bed reactor, and a gas-solid two-phase continuous catalytic dehydrogenation reaction is carried out under the conditions of no carrier gas, 280-350° C., and normal pressure, and the reaction mixture is condensed by a condenser, flashed and separated, and liquid is removed to obtain hydrogen and liquid product benzene, wherein the mass space velocity of the cyclohexane is 0.2-1.5h -1 .

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