Reforming of tar model compounds over sustainable and low-cost biochar: Special focus on spontaneous gasification reactivity and tar reforming kinetics for reformer design

Abstract In this study, the spontaneous gasification and catalytic activity of wood char were experimentally evaluated in simulated sorption enhanced gasification (SEG) environments with toluene and naphthalene as tar model compounds. Besides, CaO was used as a reference catalyst for the comparison purpose since CaO is a commonly used sorbent in the SEG process. A model of gasification reactivity during reforming of tar model compounds over wood char was developed in this work based on the reactivity at 20 % carbon conversion adopting the Extended Random Pore Model, where the pre-exponential factor, activation energy, and structural parameter were calculated to be 1.65·1010 min-1, 265.8 kJ mol-1, and 127, respectively. During the catalytic activity investigation, hydrogen was found to inhibit tar-reforming performance over CaO while the impact of hydrogen was insignificant over wood char. The results showed that spontaneous gasification during tar surrogates reforming led to mass loss, pore collapse, and inorganics agglomeration, which contributed to the catalytic deactivation of wood char. By considering gasification-caused deactivation, the carbon conversion was then used as a variable to modify the kinetic equations of the tar surrogates reforming. The activation energy and pre-exponential factor of naphthalene reforming (and toluene reforming) over wood char were calculated with the values of 422.5 kJ mol-1 and 2.92·1022 m3 kg-1 h-1 (284.8 kJ mol-1 and 1.90·1015 m3 kg-1 h-1), respectively, whereas the values for CaO were 126.9 kJ mol-1 and 6.79·104 m3 kg-1 h-1 (254.5 kJ mol-1 and 6.73·1011 m3 kg-1 h-1), respectively. The kinetic models developed in this study were later used for designing a tar reformer integrated with the SEG process.