Effect of Vacuum on Lignocellulosic Biomass Flash Pyrolysis in a Conical Spouted Bed Reactor

The continuous flash pyrolysis of lignocellulosic biomass under atmospheric and vacuum conditions (0.25 atm) has been studied in a bench-scale plant provided with a conical spouted bed reactor. A previous kinetic study has been carried out in thermobalance, and the kinetic data have been fitted to a three parallel and independent reaction model by deconvolution of the differential thermogravimetry (DTG) curve. The influence of vacuum on product yields, compositions, and properties has been carried in a bench-scale plant at 400 and 500 degrees C. Vacuum operation in a conical spouted bed is advantageous for biomass pyrolysis because of the reduction in the N-2 mass flow rate required for the spouted bed regime. Consequently, the energy requirements for heating Nz and the problems related to the condensation of the outlet stream are significantly reduced. The yields obtained and the composition of the bio-oil provide evidence that the vacuum operation does not affect the good gas-solid contact and the excellent performance of the conical spouted bed reactor for lignocellulosic biomass flash pyrolysis. High bio-oil yields are obtained, 77% at 500 degrees C and under 0.25 atm. Vacuum leads to a slightly heavier and less oxygenated bio-oil and a char fraction with improved surface characteristics.