Conversion and syngas production of toluene as a biomass tar model compound in chemical looping reforming

•Tar removal and produce syngas (CO + H2) by using chemical looping reforming method.•Three oxygen carriers were compared for the CLR of toluene, and the effects of operation parameters were evaluated.•Oxygen carrier exhibited a dual-function of oxidation-catalysis for the CLR of toluene.•The 4Ni2Fe oxygen carrier has higher reactivity and stronger carbon deposition resistance.•The stable performance of the 4Ni2Fe oxygen carrier during long time operation is discussed. The removal of tar is a main challenge for biomass gasification. In this paper, toluene was used as a tar model compound, and 6Ni, 4Ni2Cu and 4Ni2Fe were used as oxygen carriers (OCs). The chemical looping reforming (CLR) of toluene was studied at different temperatures and different steam/carbon molar ratios (S/C). Experimental results showed that the metal OC plays a dual-function of oxidation-catalysis for CLR of toluene. When using 6Ni, 4Ni2Cu and 4Ni2Fe as OC, the toluene conversions were 93.07%, 87.18% and 94.44%, respectively, at the S/C of 2.0 and the reaction temperature of 900 °C, and the syngas yields were 3.19 Nm3/kg, 3.10 Nm3/kg and 3.26 Nm3/kg, respectively. Meanwhile, 4Ni2Fe has the best carbon deposition resistance among the three OCs. The stable performance of 4Ni2Fe with high reactivity was demonstrated during 10 cyclic experiments with the temperature of 900 °C and at the S/C of 2.0. After 10 cycles, SEM-EDX and XRD results indicated that the 4Ni2Fe has satisfactory stability and regeneration performance. These results fully demonstrate that, among the three OCs, the 4Ni2Fe is the most ideal OC in the CLR of toluene.