Optimization of a free-fall reactor for the production of fast pyrolysis bio-oil

► A novel, 1kg/h free-fall reactor is designed for bio-oil production. ► We investigated and modeled yields from the biomass fast pyrolysis reactor. ► Response surface methodology was used to identify optimal conditions for bio-oil. ► We examined heater temperature, gas flow rate, biomass particle size and feed rate. ► Liquid yields greater than 70wt.% were achieved with minimal sweep gas flow. A central composite design of experiments was performed to optimize a free-fall reactor for the production of bio-oil from red oak biomass. The effects of four experimental variables including heater set-point temperature, biomass particle size, sweep gas flow rate and biomass feed rate were studied. Heater set-point temperature ranged from 450 to 650°C, average biomass particle size from 200 to 600μm, sweep gas flow rate from 1 to 5sL/min and biomass feed rate from 1 to 2kg/h. Optimal operating conditions yielding over 70wt.% bio-oil were identified at a heater set-point temperature of 575°C, while feeding red oak biomass sized less than 300μm at 2kg/h into the 0.021m diameter, 1.8m tall reactor. Sweep gas flow rate did not have significant effect on bio-oil yield over the range tested.