Unified kinetic model for torrefaction-pyrolysis

Thermochemical conversion is a promising pathway to renewable fuels. Torrefaction is the low temperature conversion to a primarily solid fuel, and pyrolysis is a higher temperature process that produces mainly a liquid bio-oil product. Though these processes are both thermal degradation routes in an inert atmosphere, they are often presented as different processes. A novel six stage consecutive model is proposed to describe a unified view of torrefaction and pyrolysis. The reactions lump chemical species formation in the six reaction stages and represent decomposition of cellulose, hemicellulose, and lignin. Activation energies of 104, 129, 154, 217, 256, and 285 kJ/mol were found through modeling of 32 unique gas-phase species fragments and weight loss dynamics for degradation from 260 to 425 °C. It is demonstrated that there is a unified process that occurs, and can describe the degradation of the structural components in biomass. These dynamics yield important insight into the thermal degradation mechanism such as the chemical product detachment dynamics, and the influence of process severity.