Enthalpy changes during pyrolysis of biomass: Interpretation of intraparticle gas sampling

Abstract

The results of birch wood pyrolysis are presented providing details on the gas, liquid and char mass production rates as a function of temperature from 25 °C to 500 °C. Quantitative measurements, using a Kr tracer, were taken from the center of a sphere sample enabling insight into the product gas formation profiles over the same temperature range. A unique calculation methodology was developed to combine data from TG measurements, quantitative GC measurements of the gaseous chemical species and ultimate analysis of the char product enabling the elucidation of the energetics of the pyrolysis process as a function of temperature. Precise calculations based on the measurements of gas, liquid and char production rates demonstrated the pyrolysis of birch wood transitions from endothermic to exothermic conditions at 280 °C. The reactions maintain an exothermic character until 480 °C then return to an endothermic nature at 500 °C. Changes in gas, char and liquid elemental compositions, plotted as a Van Krevelen diagram, indicated as temperature increases char and liquids trend toward lower O/C and H/C ratios. However, the gaseous H/C decreased slightly from 1.7 to 1.45 yet the O/C increased dramatically from 0.3 to 2.0.