Preparation method of isothermal methanation catalyst
Technical Field
The invention belongs to the technical field of catalysis, and particularly relates to an isothermal methanation catalyst and a preparation method thereof.
Background
In recent years, the consumption proportion of natural gas in China is increasing day by day, the consumption of natural gas in China reaches 3300 billion cubic meters according to the forecast of relevant institutions at the end of 2020, and the supply and demand gaps are serious. Due to the energy characteristics of rich coal, poor oil and less gas in China, the prepared synthetic natural gas not only can produce high-grade clean fuel gas resources, but also can reduce the pollution of coal combustion to the environment, and has great social and economic benefits.
The methanation technology is taken as a core technology for preparing the synthetic natural gas, the circulation multi-section adiabatic fixed bed methanation technology is mainly adopted in the industry at present, the reaction temperature of the technology is high, the heat transfer rate is low, the process flow is complex, the temperature runaway is easily caused by the fault of a circulation compressor, and the requirement on the high temperature resistance of a reactor and a catalyst is strict. Compared with the isothermal fixed bed methanation process, the isothermal fixed bed methanation process has the advantages of high heat exchange efficiency, simple process flow, small number of reactors and the like because water or other liquid is adopted in the reactor as a refrigerant to take away reaction heat. The isothermal bed reactor can effectively avoid the problems of high-temperature sintering or carbon deposition of the catalyst in the fixed bed reactor and the like. However, because the methanation reaction is a strong exothermic reaction, although the isothermal fixed bed reactor can effectively remove the reaction heat, the heat released in the reaction process has higher requirements on the self heat transfer performance of the catalyst, so that the development of the isothermal methanation catalyst which is suitable for the isothermal fixed bed and has good activity, high stability and excellent heat transfer performance is necessary.
Chinese patent CN105195160A describes an isothermal methanation catalyst and a preparation method thereof, the isothermal methanation catalyst takes a composite oxide formed by magnesium, aluminum and silicon as a shaping catalyst carrier, nickel as an active component, and the space velocity is 4000h-1Pressure 2.0Mpa, temperature 400 ℃, inlet gas CO: 3.63% of CO2: the 1.3 percent isothermal fixed bed shows good low-temperature activity, but the patent adopts a strip extrusion molding mode to obtain a carrier, although the carrier has better external surface area and rich pore channels, the strength of the strip extrusion molded catalyst is lower, the activity and the stability of the catalyst are difficult to ensure after long-term use, and the stability of the catalyst is not mentioned in the patent.
At present, the isothermal methanation is more and more emphasized by domestic and foreign scientific research institutes due to short process flow and low energy consumption. One of the key technologies for developing a low-temperature and high-efficiency methanation catalyst as isothermal methanation is an important subject to be solved by researchers at present.
Disclosure of Invention
The purpose of the invention is as follows: provides a preparation method of isothermal methane synthesis catalyst. The problems of poor heat and mass transfer performance, poor stability, poor mechanical strength and the like of the traditional methane synthesis catalyst under the condition of an isothermal fixed bed reactor are solved.
The invention has the main characteristics that:
(1) preparing a modified mesoporous alumina precursor by a hydrothermal treatment process through the synergistic effect of multi-metal components such as Cu, Zn, Ce, Zr, Mo, Mn, La and the like, and then obtaining a carrier with good specific surface area, pore diameter and heat transfer and mass transfer performance through means such as drying, roasting, tabletting and the like;
(2) the bimetallic Ni-Ce is used as an active component, the catalyst has no carbon deposition on the surface and in a pore channel after being used for a long time under the modulation action of phosphotungstic heteropoly acid, and is not sintered and has good stability;
(3) under the condition of a one-stage isothermal non-cyclic reaction process, when the composition of the coke oven gas is 6-10% of CO, the CO is2 2~5%,C2H6 1~4%,H255-60% and the balance of N2Airspeed of 5000-10000 h-1Under the conditions of pressure of 1.5-3.0 MPa and temperature of 250-400 ℃, CO and CO2The conversion rates respectively reach more than 99.0 percent.
The invention provides a preparation method of an isothermal methanation catalyst, which is characterized in that the catalyst is obtained by the following steps:
(1) preparation of the carrier: calcining pseudo-boehmite in air atmosphere to obtain gamma-Al2O3(ii) a Mixing gamma-Al2O3Adding deionized water into the autoclave lined with polytetrafluoroethylene, uniformly stirring, adding nitric acid to adjust the pH value of the solution, heating and boosting the temperature, and then carrying out hydrothermal treatment; putting the material after the hydrothermal treatment into a high-pressure kettle lined with polytetrafluoroethylene, putting an aqueous solution of one or a mixture of nitrates of Cu, Zn, Ce, Zr, Mo, Mn and La into the high-pressure kettle, controlling the temperature and the pressure, fully mixing and pulping for modification treatment; and drying, roasting and tabletting the modified material to obtain the modified mesoporous alumina carrier.
(2) Preparation of active ingredients: dissolving nitrates of Ni and Ce in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 5.5-6.5 to obtain an impregnation liquid rich in active components;
(3) preparation of the catalyst:
controlling the temperature to be 70-90 ℃, and soaking the mesoporous alumina carrier in the impregnating solution for 1.0-3.0 h in the same volume; and taking out the impregnated catalyst precursor, drying and roasting to obtain the catalyst finished product.
In the step, the molar ratio of Al to Cu to Zn to Ce to Zr to Mo to Mn to La is 1: 0.1-0.5.
In the step, the loading amounts of the active components Ni and Ce are 5-10% and 1-3% of the weight of the catalyst respectively.
In the steps, the roasting temperature is 500-550 ℃, and the roasting time is 3-4 h.
The PH value of the hydrothermal treatment solution in the step is 5.5-6.5.
The hydrothermal treatment temperature in the above steps is 150-200 ℃, and the pressure is 1.0-2.0 MPa.
The hydrothermal treatment time in the above steps is 3-4 h.
In the above steps, the temperature of the carrier modification treatment is 150-200 ℃, and the pressure is 1.0-2.0 MPa.
In the steps, the pulping time of the carrier modification treatment is 20-30 min.
In the above step, the roasting temperature of the carrier is 400-550 ℃, and the roasting time is 4-5 h.
In the above step, the roasting temperature of the catalyst precursor is 300-450 ℃, and the roasting time is 2-3 h.
A typical laboratory preparation procedure of the present invention is as follows:
1) placing pseudo-boehmite into a muffle furnace, roasting for 3-4 h at the temperature of 500-550 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment in an autoclave for 3-4 h under the conditions that the pH value of the solution is 5.5-6.5, the temperature is 150-200 ℃, and the pressure is 1.0-2.0 MPa; 3) adding 7-55 g of one or more oxides of zinc, copper, molybdenum, manganese, lanthanum and cerium into the materials, and pulping for 20-30 min for modification treatment under the conditions that the temperature is 150-200 ℃ and the pressure is 1.0-2.0 MPa; 4) roasting the modified material for 4-5 hours at the temperature of 400-550 ℃; 5) mixing Ni (NO)3)2•6H2O、Ce(NO3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 5.5-6.5 to obtain an impregnation liquid rich in active components; 6) soaking the mesoporous alumina carrier in the impregnating solution for 1.0-3.0 h in the same volume at the temperature of 70-90 ℃; 7) and drying the impregnated catalyst precursor, and roasting at 300-450 ℃ for 2-3 h to obtain a catalyst finished product.
The isothermal bed methane synthesis catalyst prepared by the method is simple in preparation method, beneficial to industrial production and good in activity and stability.
Detailed Description
The process of the present invention is described in detail below with reference to examples, but the examples are only illustrative and are not intended to limit the scope of the present invention.
Example 1
1) 200g of pseudo-boehmite is put into a muffle furnace and is roasted for 4 hours at the temperature of 500 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 4h in an autoclave under the conditions that the pH value of the solution is 5.5, the temperature is 200 ℃ and the pressure is 1.0 MPa; 3) adding 10g of zinc, 5g of copper and 3g of cerium oxide into the materials, and pulping for 20min at the temperature of 150 ℃ and the pressure of 1.0MPa for modification treatment; 4) roasting the modified material for 4 hours at the temperature of 450 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 5.5 to obtain an impregnation solution rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 2.0 hours at the temperature of 75 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 350 ℃ for 2h to obtain a finished catalyst Y-1.
Example 2
1) 200g of pseudo-boehmite is put into a muffle furnace and roasted for 3h under the air atmosphere and the temperature of the muffle furnace is 550 ℃, so that gamma-Al is obtained2O3(ii) a 2) 100g of gamma-Al2O3In an autoclave, under the conditions of pH 6.0, temperature 150 ℃ and pressure 2.0MPaCarrying out hydrothermal treatment for 3 h; 3) adding 10g of zinc and 5g of cerium oxide into the materials, and pulping for 25min at the temperature of 200 ℃ and the pressure of 2.0MPa for modification treatment; 4) roasting the modified material for 4 hours at the temperature of 500 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 6.0 to obtain an impregnation liquid rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 1.0h at the temperature of 80 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 400 ℃ for 2h to obtain a finished catalyst Y-2.
Example 3
1) 200g of pseudo-boehmite is put into a muffle furnace and roasted for 3.5h under the air atmosphere and the temperature of the muffle furnace is 520 ℃, thus obtaining gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 6.5, the temperature is 180 ℃ and the pressure is 1.5 MPa; 3) adding oxides of 10g of zinc, 8g of copper and 3g of manganese into the materials, and pulping for 30min at the temperature of 180 ℃ and the pressure of 1.5MPa for modification treatment; 4) roasting the modified material for 4 hours at the temperature of 550 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 5.5 to obtain an impregnation solution rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 1.0h at the temperature of 90 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 450 ℃ for 2h to obtain a finished catalyst Y-3.
Example 4
1) 200g of pseudo-boehmite is put into a muffle furnace and is roasted for 4 hours at the temperature of 500 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 6.0, the temperature is 180 ℃ and the pressure is 1.5 MPa; 3) adding 10g of zinc, 8g of copper and 3g of molybdenum oxide into the above materials, and pulping at 180 ℃ and 1.5MPaPerforming modification treatment for 20 min; 4) roasting the modified material for 4 hours at the temperature of 550 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 5.5 to obtain an impregnation solution rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 1.0h at the temperature of 85 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 350 ℃ for 3h to obtain a finished catalyst Y-4.
Example 5
1) 200g of pseudo-boehmite is put into a muffle furnace and is roasted for 4 hours at the temperature of 500 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in an autoclave under the conditions that the pH value of the solution is 6.5, the temperature is 200 ℃ and the pressure is 1.5 MPa; 3) adding 10g of zinc, 8g of copper and 3g of cerium oxide into the materials, and pulping for 20min at the temperature of 200 ℃ and the pressure of 1.5MPa for modification treatment; 4) roasting the modified material for 4.5 hours at the temperature of 500 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 6.5 to obtain an impregnation solution rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 3.0 hours at the temperature of 75 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 450 ℃ for 3h to obtain a finished catalyst Y-5.
Example 6
1) 200g of pseudo-boehmite is put into a muffle furnace and is roasted for 3 hours at the temperature of 500 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 6.0, the temperature is 150 ℃ and the pressure is 2.0 MPa; 3) adding oxides of 10g of zinc, 5g of copper and 3g of lanthanum into the materials, and pulping for 30min at the temperature of 150 ℃ and the pressure of 2.0MPa for modification treatment; 4) roasting the modified material for 5 hours at the temperature of 450 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 6.0 to obtain an impregnation liquid rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 1.5h at the temperature of 85 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 400 ℃ for 2h to obtain a finished catalyst Y-6.
Example 7
1) 200g of pseudo-boehmite is put into a muffle furnace and roasted for 3.5h under the air atmosphere and the temperature of the muffle furnace is 550 ℃, thus obtaining gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 6.5, the temperature is 150 ℃ and the pressure is 2.0 MPa; 3) adding 10g of zinc and 5g of copper oxide into the materials, and pulping for 25min at the temperature of 150 ℃ and the pressure of 2.0MPa for modification treatment; 4) roasting the modified material for 5 hours at the temperature of 450 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 6.0 to obtain an impregnation liquid rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 2.5 hours at the temperature of 80 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 430 ℃ for 3h to obtain a finished catalyst Y-7.
Example 8
1) 200g of pseudo-boehmite is put into a muffle furnace and is roasted for 4 hours at the temperature of 500 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 5.5, the temperature is 190 ℃ and the pressure is 1.8 MPa; 3) adding 10g of zinc and 5g of copper oxide into the materials, and pulping for 25min at the temperature of 150 ℃ and the pressure of 2.0MPa for modification treatment; 4) roasting the modified material for 5 hours at the temperature of 450 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to the pH value of 6.5 to obtain the product rich in phosphorusAn impregnation fluid of the sexual component; 6) soaking a mesoporous alumina carrier in the impregnating solution for 2.5 hours at the temperature of 80 ℃ in the same volume; 7) and drying the impregnated catalyst precursor, and roasting at 400 ℃ for 2.5 hours to obtain a finished catalyst Y-8.
Example 9
1) 200g of pseudo-boehmite is put into a muffle furnace, and is roasted for 3h at the temperature of 530 ℃ in the air atmosphere to obtain gamma-Al2O3(ii) a 2) 100g of gamma-Al2O3Carrying out hydrothermal treatment for 3h in a high-pressure kettle under the conditions that the pH value of the solution is 6.0, the temperature is 190 ℃ and the pressure is 1.8 MPa; 3) adding 15g of zinc oxide into the materials, and pulping for 25min at the temperature of 150 ℃ and the pressure of 2.0MPa for modification treatment; 4) roasting the modified material for 5 hours at the temperature of 450 ℃; 5) 30g of Ni (NO)3)2•6H2O and 10gCe (NO)3)2•6H2Dissolving O in water, and adding 0.02-0.1 mol/L phosphotungstic heteropoly acid to a pH value of 6.0 to obtain an impregnation liquid rich in active components; 6) soaking a mesoporous alumina carrier in the impregnating solution for 2 hours at the temperature of 85 ℃ in equal volume; 7) and drying the impregnated catalyst precursor, and roasting at 430 ℃ for 2h to obtain a finished catalyst Y-9.
Comparative example 1
1) Carrying out heat treatment on 100g of pseudo-boehmite at 500 ℃, and tabletting to obtain an alumina carrier; 2) immersing the carrier in Ni (NO) at 75 deg.C3)2And Ce (NO)3)2•6H2O solution for 2 h; 3) and taking out the impregnated catalyst precursor, drying, and roasting at 450 ℃ for 2h to obtain a catalyst finished product D-1 with Ni and Ce loading amounts of 8% and 2% respectively.
Comparative example 2
1) Dissolving 100g of pseudo-boehmite in water to prepare suspension; 2) at 70 deg.C, adding a certain amount of Ni (NO)3)2、Ce(NO3)2•6H2Adding O into the solution, and fully mixing; 3) then the mixed solution is evaporated to dryness, roasted at 550 ℃ and extruded to obtain N, Ce comparative catalyst D-2 with the load of 7% and 3% respectively.
Comparative example 3
1)Dissolving 100g of pseudo-boehmite in water to prepare a suspension, and adding 1: 1, preparing aluminum sol from dilute nitric acid; 2) at 80 deg.C, adding a certain amount of Ni (NO)3)2、Ce(NO3)2•6H2Adding O into the sol, and fully mixing; 3) then evaporating the mixed solution to dryness, roasting at 600 ℃ and tabletting to obtain a comparative catalyst D-3 with Ni and Ce loading amounts of 5% and 5% respectively.
Evaluation of catalyst Performance
The examples Y-1 to Y-9 and the comparative examples D-1 to D-3 were packed in an isothermal bed reactor at a temperature of 300 ℃, a pressure of 3.0MPa and a space velocity of 10000h-1,H2Samples were taken at 72h and 200h for analysis at/CO = 3.
Specific data are shown in table 1 below.
TABLE 1 comparison of catalyst Performance between examples and comparative examples
As can be seen from the reaction data in the table, the catalysts Y-1-Y-9 prepared by the method show good CO conversion rate and CO conversion rate after 72 hours and 300 hours2The conversion rate performance and the stability are ensured; while the comparative examples D-1, D-2 and D-3 show good conversion rate performance in 72h, the conversion rate and the selectivity are greatly reduced after 300h reaction, which proves that the catalyst has poor stability in long-time operation under the condition of an isothermal bed.
Meanwhile, after the catalysts Y-1-Y-9 prepared by the method are removed after running for 300 hours, the phenomena of surface and internal blockage or carbon deposition are not found through SEM (scanning electron microscope) detection, and carbon deposition of different degrees appears in comparative examples D-1, D-2 and D-3, which may be the reason that the activity and selectivity of the later comparative examples are reduced in different degrees.
In addition, the comparative example had a powdering phenomenon at 300h of operation, and the reduction in mechanical strength was significant.