Study On The Stability Of Ni-based Catalysts For SNG

SNG is a process often based on coal as raw material,producing synthesis gas by coal gasification,making the required natural gas from the methanation of synthesis gas.The core technology of SNG is the gasification of coal and methanation.As methanation is the key technology of SNG,the development of domestic independent intellectual property methanation catalyst which has good performance is one of the core problems of methanation.Ni based catalyst is the most popular catalyst used at home and abroad at present.This paper mainly studied the effects of process conditions,preparation methods and dopants on the performance of the nickel based methanation catalysts,obtained following conclusions:1.The methanation catalyst 20%Ni/Al₂O₃ was prepared by solid state gridding method.The effects of reaction pressure,feed ratio?H₂:CO?,space velocity,and temperature on the activity and stability of the catalyst were studied.It was found that with the increase of pressure and feed ratio?H₂:CO?,the stability of the catalyst is enhanced;with the increase of space velocity,the stability of the catalyst decreased;elevated reaction temperature can make the carbon deposited on the surface of the catalyst transfer to a more stable form,thereby enhancing the stability of the catalyst.2.Four different preparation methods?that is solid-state gridding,impregnation,deposit-precipitation and coprecipitation?of 20%Ni2.35%La₂O₃/Al₂O₃ were studied for their different methanation performance.The catalysts prepared by solid-state gridding and impregnation had better stability at 350?,3.0MPa,24000h^-1,while the catalysts prepared by deposit-precipitation and co-precipitation had poor stability and deactivated rapidly,all the catalysts deactivated because of the gum deposited on the metal surface.Besides,the catalysts prepared by solid-state gridding and impregnation had better reduction performance while the catalyst prepared by co-precipitation had quite poor reduction performance.Last but not the least,the solid-state gridding preparation was simple and had no solvent pollution which was environmental friendly.3.A systematic investigation was studied on the effects of different dopants on the performance of methanation catalysts.?1?The L₈?2⁷?orthogonal experimental method was used when studying the effect of La₂O₃,ZrO₂,MnO₂ which was impregnated on the support to modify the stability of the support thus improving the stability of the catalysts.The results showed that the addition of MnO₂ was unfavorable to the stability of the catalyst,ZrO₂ had no significant effect on the stability of the catalyst,La₂O₃ could improve the catalyst's stability.Besides,the best way of adding dopants was adding La₂O₃ separately.?2?Different kinds of doptants?ZrO₂,CeO₂,BaO,K₂O?were added to 20%Ni2.35%La₂O₃/Al₂O₃ to improve the stability of the catalyst.It was found that different types of dopants had no significant effect on the activity and selectivity of the catalysts,but greatly influenced it's resistance of carbon deposition and stability.Under the condition of 0.1MPa,350?,2400h^-1,the carbon resistance was:ZrO₂>CeO₂>BaO>None>K₂O.The stability tests were carried out under 3.0MPa,350?,24000h^-1 and it was found that the stability order was ZrO₂>CeO₂>BaO>None>K₂O,which was in coincidence with the carbon resistance of the catalysts.Besides,as the amount of carbon deposited on the surface of catalyst increased they intended to change into a more stable form.?3?The influence of CeO₂ contents on the stability of the catalyst was studied and the optimum adding amount was 2%.