A kinetic study of the fast micro-pyrolysis of hybrid poplar

Hybrid poplar from the clone DN34 was studied to determine the rate of production of bio-oil species with respect to time during the fast pyrolysis process. 300-660 ug samples were pyrolyzed using a micropyrolzer at 500 °C at very high heating rates and very short vapor residence times. Individual poplar samples were run in triplicate at discrete time points ranging from 1 to 20 s in the micropyrolzer. Several bio-oil compounds from each individual sample were analyzed using GC/MS. Select bio-oil compounds, derived from the hemicellulose, cellulose, and lignin fractions of the wood, were used to determine their rates of production from thermal degradation of the biomass. These rates were quantified using standards to determine the weight percent relative to the original raw biomass with respect to time. Pyrolysis kinetic reaction models were fit to this experimental data in order to determine suitability of each model. A first order exponential decay model for degradation of the solid biomass was fit against the data along with a six-step consecutive degradation model previously developed by our group. The experimental data suggests that compounds derived from the hemicellulose are produced at faster rates than that of the lignin or cellulose fractions of the wood, consistent with prior data from thermogravimetric analysis (TGA). When applying the first order exponential decay model, the reaction rates calculated did prove that holocellulose compounds reaction rates were approximately twice that of the lignin compounds reaction rate but did not provide the best fit. The six-step degradation model provided a better fit to all of the biooil compounds and char data, and the stoichiometric parameters derived from the model fit showed that the first three reactions involved mostly the hemicellulose derived compounds while reaction steps 4-6 released cellulose- and lignin-derived compounds.