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

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.