Chemical looping gasification of benzene as a biomass tar model compound using hematite modified by Ni as an oxygen carrier

The effective removal of tar is a major challenge for biomass gasification. Schemes based on chemical looping gasification (CLG) offer a promising alternative for converting biomass into syngas with low tar content. The present work examined the influence of a Ni-modified oxygen carrier (OC) on the benzene conversion rate, hydrogen yield, carbon deposition rate, and yield of combustible gas products under various experimental conditions in the CLG of benzene as a model biomass tar compound. After modification, the NiFe2O4 OC exhibited good catalytic and oxidation performance. With the increase in reaction temperature and Ni loading, the hydrogen yield, benzene conversion rate, and carbon deposition rate all increased gradually. With the increase of weight hourly space velocity (WHSV), the benzene conversion rate decreased from 89.75% to 81.1%. which indicated that the oxidation capacity of the OC to benzene decreased. Meanwhile, the addition of steam significantly eliminated the carbon deposition, which decreased to 2.62% at an S/C ratio of 1.48. During the long-term experiment, the oxidation activity and catalytic activity of the OC each exhibit a slight decreased, which was possibly due to the sintering and agglomeration of the OC. Finally, the cracking mechanism of the tar model compound benzene was proposed.