Enhanced decomposition of biomass tar using low concentration copper doped hematite in direct chemical looping process

Abstract

Biomass tar is an unavoidable side product in the biomass direct chemical looping process. It is necessary to eliminate tar as it may cause operational problems, such as fouling and blocking in the downstream equipment. Innovative in-situ tar removal through oxidation and catalysis of oxygen carrier is attractive because it can decrease the decomposition temperature and simplify the process components. This work studied the decomposition enhancement of biomass tar (toluene as tar compound) using low concentration copper-doped hematite. Both experiments and simulations were conducted to investigate the effect of copper concentration on toluene conversion. The main finding was that low concentration (1–3 mol%) of copper-doped hematite could significantly enhance the tar conversion, which was elevated by up to 200% and 142% at 600 and 700 °C, respectively; whereas the copper concentration played an insignificant role, thus 1% copper-doped one was recommended for practical application. Furthermore, this result was partially supported by comparing oxygen vacancy formation energy in density functional theory calculations.