Research On Biomass Gasification Catalysts For Hydrogen Production

To develop catalysts for hydrogen production from biomass used in solid heat-carrier system and free-fall reactor, Ni catalysts supported on natural mineral (olivine and dolomite) are prepared and studied. In the first stage, operation conditions and preparation parameters are determined by using benzene as the model compound. The catalyst obtains the best catalytic performance on the operation conditions of 800℃ and S/C ratio 1.0 when prepared at the following conditions: the support is calcined at 900℃ for 3h, pH value of impregnant solution is 11-12, the NiO/olivine(dolomite) is calcined at 1100℃(900℃) for 3h and the loading of La is 3%. In the comparison of olivine from different quarries, the olivine from Hubei Yichang gets the best general catalytic performance. The prepared catalyst obtains the 100% conversion of benzene in the 500min catalytic test with its activity keeping steady during the reaction.Apricot stones are chosen as the typical biomass in the following experiments for their high lignin content. The comparison of olivine and dolomite is made by using they as the down-stream catalysts for the gasification of apricot stones. Reaction temperature, S/B (steam/biomass) ratio, particle size of catalysts and biomass, and calcination of the catalyst, etc. have been studied. The results show that the catalytic activities of calcined olivine and dolomite are higher than the natural ones. With calcined dolomite, a H2 potential yield of 130.9 gH2/kg Biomass (daf), which is 86.1% of the stoichiometric yield (152 gH2/kg biomass (daf.)) is obtained at 850℃ and S/B ratio 0.8, and that with calcined olivine at 800℃ and S/B ratio 0.8 is 67.7gH2/kg biomass (daf), 44.5 % of the stoichiometric yield. The calcined dolomite becomes very friable and the calcined olivine, on the contrary, kept its good resisting attrition after calcination and reaction.XRD analysis of olivine and dolomite before and after calcination includes that calcination of catalysts causes the disappearance of (Mg,Fe)SiO3 phase and the formation of Fe2O3 for olivine and eliminates CO2 and forms CaO-MaO for dolomite, which may be the reason for the difference of the activity. Four olivines are compared by XRF to analysized their chemical composition. It is found that their difference in catalytic performance may result from their difference in MgO and Fe2O3 content. The HY olivine has the highest MgO and Fe2O3 content so it gets the best catalytic performance while the SN olivine showed the relatively worst. The catalysts are also analysised by TEM and SEM. The results show that the interaction between Ni and support is proper so that the prepared catalysts show good catalytic performance duringreaction and there are no losing and agglomeration of Ni. Carbon formation of catalyst is analyzed by TG. The results show that the type of carbon formed on the surface of NiO/olivine is graphite carbon while the one on NiO/dolomite vests in two types: the precursor of carbide and the graphite carbon. The carbon formation on the surface of NiO/olivine and NiO/dolomite are 0.025% and 1.7%, respectively.