Research Of Steam Reforming Catalysts For Hydrogen Production From Biomass Tar

The main objective of this paper is to study catalysts for biomass gasification tar removal. With attapulgite as catalyst carrier,steam reforming of apricot stone pyrolysis tar was carried out over Ni-Fe/Attapulgite and Ni-Fe-Al/Attapulgite catalysts prepared by coprecipitation and adsorption method.The two kinds of catalysts were investigated at lower temperature and higher temperature,respectively.The association among the structure of catalyst,reaction temperature and catalytic activity was explored.Silica sand,natural dolomite,NiO/olivine, NiO/olivine and commercial Ni-based catalyst Z409 were also tested for comparison.It is shown that the Ni-Fe/Attapulgite calcined at 600℃has excellent low temperature activity and anticoke ability.It is very suitable for steam reforming of tar in downstream fixed-bed reactor.A 92.1%carbon conversion to gas can be obtained at 500℃,tar weight space velocity of 0.63 h^-1,and S/C molar ratios of 4.3.The product gas contains 69.1vol.%H₂, 0.5 vol.%CH4,3.5 vol.%CO,and 26.8 vol.%CO2.No obvious deactivation of the catalyst was observed during 5h sequential test.Under the same conditions,the catalytic activity of the Z409 catalyst decreased significantly after 90min reaction.Higher specific surface areas (146.9 m²/g) and suitable pore distribution of the Ni-Fe/Attapulgite catalyst play a key role for its higher activity at low temperature.However,this effect decreases when reaction temperature increases.The effect of calcination temperature on catalyst activity is severe, both catalytic activity and catalyst lifetime decreased with the calcination temperature increased from 600 to 800℃.The optimal calcination temperature is 600℃for Ni-Fe/Atta catalyst at lower temperature use.It has shown that the 22%～28wt.%of NiO is the optimum amount;Fe addition improved the catalytic activity of the catalyst,whereas the effect of K addition is little;the catalyst is favorable to be used under S/C(steam to carbon ratio) 1.5-3.5 and WHSV not higher than 0.63 h^-1.In order to improve the high temperature stability of Ni-Fe/Attapulgite catalyst, aluminium was introduced into the catalyst.The experimental results of steam reforming of apricot stone pyrolysis tar showed that the Ni-Fe-Al/Attapulgite calcined at 900℃has better stability and activity than that of Ni-Fe/Attapulgite at higher reaction temperature.This kind of catalyst is suitable for in situ catalytic craking of tar in biomass gasifier.The catalytic activity of Ni-Fe-Al/Attapulgite catalyst at 800℃was almost the same as that of Z409 catalyst,although its NiO content(10.5wt%) is much lower than that of Z409.The product gas contains 68.0vol.%H₂,0.6 vol.%CH₄,11.3 vol.%CO,and 20.0 vol.%CO₂.The catalyst obtains the best catalytic performance when it is calcined at 900℃for 3h.XRD diagrams of Ni-Fe-Al/Attapulgite calcined at 900℃showed a coexistence structure of spinel(NiAl₂O₄) and NiO crystal.It is important to keep a reasonable proportion of NiO to NiAl₂O₄ for achieving low temperature reducible ability and stable activity.TG curves reflected that the Ni-Fe-Al/Attapulgite catalyst after reaction has an obvious weight gain peak.