Preparation And Reaction Technology Investigation Of The Catalysts For The Combined Reforming Of The Biogas To Syngas

China, as an agricultural giant yields numerous agricultural refuse, such as straw each year. However, the utilization rate of straw is very low and most is incinerated or disregarded. Biogas which is composed of CH4/CO2 with the volume ratio of 2 could be produced by anaerobic fermentation of agriculture wastes. On the basis of the gas composition of biogas, the biogas as a raw material and an appropriate amount of oxygen and steam was added for the combined reforming for the production of synthesis gas. In this way, the biogas could be effectively used and it would not only result in considerable economic and environmental benefits, but such a non-fossil route should have attractive prospects.In this paper, a series of Ni/SBA-15 catalysts with Ni content from 7.5wt% to 15wt% and the modifications were also done with alkali metal(Li, Na, K), alkaline earth metal (Mg, Ca), rare earth metal (La, Ce) and transition metal(Fe, Co, Cu, Mn) were prepared by impregnation method. On the basis of these granular catalysts, Ni/SBA-15/Al2O3/FeCrAl catalysts and M/Ni/SBA-15/Al2O3/FeCrAl (M=Mg, La, Ce) catalysts were also prepared. Finally, their catalytic performances were investigated in a continuous flow fixed-bed micro-reactor under atmospheric pressure. The catalyst structures were also characterized by X-ray diffraction (XRD), N2-adsorption/desorption, transmission electron microscopy (TEM), and H2 temperature programmed reduction (H2-TPR) techniques.The results indicated that the 10%Ni/SBA-15 catalyst exhibited the best catalytic activities for the combined reforming of the biogas to syngas. The optimal molar ratios of oxygen and steam added were both 0.6. Under the reaction conditions that the feed gas molar ratios of CH4/CO2/O2/H2O were 2/1/0.6/0.6, GHSV was 24000 ml·gcat-1·h-1 and the reaction temperature was 800℃, the conversions of CH4 and CO2 were 92.2% and 76.3%, respectively, with 1.35 of H2/CO. The catalytic activities of the catalyst did not obviously decrease after 100 h reaction time on stream. It could be concluded that the prepared molecular sieve SBA-15 obviously showed meso-porous structure and the structure of SBA-15 modified by Ni kept in good condition. The interaction force between active component and carrier was moderate, which promoted the combined reforming.The catalytic activities of 10%Ni/SBA-15 decreased more or less when it was modified by alkali or transition metal. On the whole,3wtMg% was the best choice, the conversions of CH4 and CO2 were 95.6% and 79.3% respectively. The 3%Mg/10%Ni/SBA-15 catalyst showed highly stable activity at 800℃for 130 h. The MgO promoter and NiO could form a solid solution that improved the dispersion of NiO and enhanced the activity.For the 10wt%Ni/SBA-15/Al2O3/FeCrAl catalyst, the CH4 and CO2 conversion was 92.4% and 76.1% respectively, the catalytic activities of which were similar to granular catalyst. The catalytic performance improved in different degree when 10wt%Ni/SBA-15/Al2O3/FeCrAl catalyst was modified by proper amount Mg, La, or Ce promoter. Conclusively,3wt%La promoter was the most suitable and the conversions of CH4 and CO2 were 94.9% and 78.4% respectively at 800℃.