| There is a large amount of low-concentration methane with a concentration of0.5-3%in the mine ventilation.The low concentration of this part of methane is extremely difficult to directly use and is discharged into the atmosphere,which intensifies the greenhouse effect.The catalytic combustion technology of low-concentration methane is of great significance for mitigating the greenhouse effect and the energy crisis.At present,in the utilization of low-concentration methane in mine exhaust air,the emerging mine exhaust air catalytic oxidation gas turbine has been tested for power generation by catalytically oxidizing low-concentration methane.Application,the core of this technology lies in the need to develop high-efficiency catalysts that meet the utilization pressure conditions of mine exhaust gas turbines.At present,noble metal catalysts are widely used in them because of their high comprehensive activity,but they are expensive,and catalyst experimental research is often carried out.Press down to proceed.Therefore,the development of a non-precious metal catalyst with excellent comprehensive activity instead of precious metals is used in the high-pressure and complex environment of mine exhaust gas turbines,which has very high engineering application value.In this paper,a series of Mn-Ce-Cu catalysts with different Mn/Ce ratios are prepared by impregnation.Through experimental research and theoretical analysis,the effect of the synergy between different metals on the catalytic combustion characteristics of methane is explored,and then the pressure is experimentally studied on the catalyst activity and stability.Finally,the changes in the catalytic reaction zone of low-concentration methane under pressure are studied,and the kinetic equation is established.The results are compared with the results under normal pressure,and the changes in the surface covering species under pressure are found to affect the methane combustion reaction order.And the impact of speed control steps.The main research results are as follows:(1)Obtain the optimal loading ratio of Mn-Ce-Cu/Al2O3 catalyst and its optimal reaction conditions,and discuss the reasons for the regulation of Cu-based catalyst by Mn/Ce promoter:(1)The experiment obtained the best ratio of Mn:Ce:Cu=7:3:10;(2)It is concluded that the best calcination temperature of 7Mn-3Ce-10Cu/Al2O3 catalyst is600?,the best reaction space velocity is 25000 ml/(g·h),and the best reaction pressure is 0.7MPa.(3)Co-doping of Mn and Ce can generate metal oxides such as Mn O2,Mn2O3,Ce O2,Cu Mn2O4,which are beneficial to increase the activity,and can inhibit the generation of Cu Al2O4,which is more conducive to the conversion of lattice oxygen to surface oxygen.(4)When the calcination temperature is lower than 500?,the active metal load is uneven.When the calcination temperature reaches 800?,the active sites will agglomerate or sinter.When the calcination temperature is 600?,it is more favorable for Cu O,Ce O2,Mn O2 and other metal oxides.The active species are conducive to the activity,and the firing temperature is too high to cause the formation of metaaluminate oxide,which is not conducive to the activity.(2)Obtain the influence law of Mn-Ce-Cu catalyst low-concentration methane catalytic reaction characteristics under pressure conditions:(1)The overall activity of0.7MPa is significantly higher than the catalytic activity of 0.1MPa,and the increase is up to 20%;(2)With the reaction With the decrease of oxygen content(oxygen enrichment-hypoxia),the methane conversion rate and reaction rate show a downward trend as a whole;from the perspective of each zone,as the pressure increases,the methane conversion rate and reaction rate show an overall trend A substantial upward trend.(3)When the reaction temperature is 450?,the activities of both normal pressure and under pressure show a trend of increasing first and then decreasing and tending to be stable with the progress of time;when the optimal reaction temperature is 475?,the conversion rate under normal pressure Keep it at about 80%.When the pressure is0.7MPa,it basically stays at 100%.(4)After the reaction,agglomeration and sintering occurred on the surface of the catalyst,and the microporous structure on the catalyst surface became less,which affected the adsorption of reactant gas on the active sites of the catalyst surface,and the agglomeration phenomenon was more slight after the pressure reaction;The pressure reaction makes it easier for the lattice oxygen to be converted into surface oxygen and adsorbed oxygen that are more easily used by the reactants during the catalytic reaction,making it easier for the metal elements to maintain a lower valence state and facilitate the progress of the catalytic reaction.(3)Obtain the kinetic equation of the low-concentration methane catalytic reaction of Mn-Ce-Cu catalyst under normal pressure and under pressure,and discuss the influence of pressure on the change of the catalytic reaction surface coverage species and the reaction rate control steps:(1)Oxygen-enriched combustion zone(O2/CH4>2)is only affected by the partial pressure of methane;in the lean oxygen combustion zone(0.1<O2/CH4<2),it is also affected by the partial pressure of methane and oxygen;in the anoxic combustion zone(0<O2/CH4<0.1),it is only affected by the partial pressure of oxygen;under pressure,the partition limit value of O2/CH4 is larger and shifted,indicating that the pressure is easier to adapt to the catalytic combustion of low-concentration methane.(2)The reaction kinetic equations of three reaction kinetic intervals under normal pressure 0.1MPa and under pressure 0.7MPa are established,which facilitates calculation and directly obtains various reaction parameters in each interval,and provides theoretical calculation basis for engineering applications.(3)The coverage rate of adsorbed oxygen on the catalyst surface corresponding to the three reaction kinetic regions is obviously different,the apparent activation energy is reduced,and the reaction order is different.As the oxygen partial pressure decreases,the relevant steps of the catalytic reaction are all caused by the reaction of CH4 and O2 The transition is the adsorption process of O2 on the catalyst surface.(4)The methane conversion rate and reaction rate under pressure are higher than normal pressure.This is because the methane reaction order?under pressure is greater than the reaction order?of normal pressure methane,so the high pressure makes it easier for methane to adsorb on the surface of active components.,Which increases the reaction rate. |
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