Production of an upgraded bio-oil with minimal water content by catalytic pyrolysis: Optimisation and comparison of CaO and MgO performances

Abstract

Pyrolysis of forest residues using CaO and MgO catalysts was carried out in an induction heating reactor, to produce an upgraded bio-oil with increased higher heating value (HHV). Optimisation with central composite design (CCD) included temperature (444−656 °C) and catalyst concentration (1.7–58.3 wt.%). A fractional condensation system with the first condenser heated to 40 °C was used to collect an organic-rich oil. The optimum HHV of the oil was 26.9 MJ/kg (560.0 °C and 33.8 wt.% catalyst) at 19.4 wt.% yield with MgO and 26.4 MJ/kg (550.0 °C and 30.0 wt.% catalyst) at 18.9 wt.% yield with CaO (based on a desirability function used to obtain significant oil yield). The combination of water-gas shift reaction (WGSR) catalysed by CaO and the fractional condensation system resulted in water content of the oil at the optimum of only 7.8 wt.%. Absorption of CO2 by CaO, together with significant H2 production (400 % increase compared to non-catalytic case) allowed the production of a gas calorific value of 13.7 MJ/kg compared to 5.2 MJ/kg without catalyst.