Biomass chemical-looping gasification coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier

Abstract Bio-syngas generation with flexible H2 to CO ratios via biomass chemical-looping gasification (CLG) coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier (OC) was proposed in the present work. The presence of NiFe2O4 OC promotes biomass conversion, especially bio-char conversion at elevated temperature stage. Addition steam and/or CO2 into the carrying gas increased the weight loss rates of biomass. Up to 5.88 wt%/min and 4.97 wt%/min of the maximum weight loss rates were achieved during biomass conversion with NiFe2O4 OC in CO2 and steam flows in a TGA reactor, respectively. With NiFe2O4 as an oxygen carrier, an optimal lattice oxygen/biomass mass ratio is 0.51 giving the highest syngas yield of 0.77 m3/kgbiomass in the absence of steam or CO2 at 850 °C. Steam/biomass mass ratio of 2.25 gave the maximum carbon conversion of 92.53% and syngas yield of 1.38 m3/kgbiomass suggesting that steam addition significantly improves the biomass conversion and the syngas yield. Introducing a fraction of CO2 into steam could reduce the steam consumption as well as enhance the carbon conversion in biomass gasification step. NiFe2O4 OC serves as an effective catalyst for tars cracking in biomass-CLG. The tars content in the syngas generated in biomass-CLG with NiFe2O4 is 2.83 g/m3, which is much lower than that (14.25 g/m3) in biomass gasification with inert ZrO2. The productivities of H2 and CO are 211 ml/gOC and 101 ml/gOC in water- and CO2-splitting steps. The proposed approach can potentially be applied for providing bio-syngas with flexible H2 to CO ratios from 1:1 to 2.2:1 for purpose of various synthesis processes such as Fischer-Tropsch, acetic acid, and oxo-synthesis.