Effect of Pressure and Hot Vapor Residence Time on the Fast Pyrolysis of Biomass: Experiments and Modeling
P.S. Marathe, Roel J. M. Westerhof, Sascha R.A. Kersten
Abstract
Pyrolysis of acid-leached bagasse (515 °C) and pinewood (485 °C) has been carried out in the pressure range from 5 × 10<sup>-3</sup> to 100 kPa in a screen-heater, designed for nearly isothermal operation and rapid quenching of reaction products. At the lowest pressure, i.e., by maximizing the escape rate of products away from the hot reaction zone, 73% of the poly-C<sub>6</sub>-sugars in bagasse were recovered in the liquid product as C<sub>6</sub>-anhydrosugars (C<sub>6</sub>aS) with degree of polymerization between 1 and 6 (DP<sub>1</sub> to DP<sub>6</sub>). A mathematical model, including reactions and mass transfer, was able to predict the measured decrease in the total yield of C<sub>6</sub>aS and the shift to lighter C<sub>6</sub>aS in the DP-distribution as a function of increasing pressure. The effect of the hot vapor residence time on the DP-distribution of the C<sub>6</sub>aS was investigated by pyrolyzing pinewood in a fluidized bed. At identical pressure (50 kPa) and temperature (485 °C) the total yield of C<sub>6</sub>aS was the same for the screen-heater and fluidized bed while the DP-distribution shifted to DP<sub>1</sub> as a result of the higher hot vapor residence time in the fluidized bed, which could be described by assuming first order kinetics for all possible cracking reactions of C<sub>6</sub>aS in the vapor phase.