Combustion kinetics of pine sawdust biochar Data smoothing and isoconversional kinetic analysis

摘要

The combustion kinetics of biochar derived from fast pyrolysis of pine sawdust was investigated by using nonisothermal thermogravimetric analysis under air atmosphere at different heating rates. The experimental conversion (alpha-T) curves contain some experimental errors, and the corresponding derivative conversion (d alpha/dT-T) curves have many fluctuations. Two strategies of obtaining the smooth d alpha/dT-T curves were used based on the robust locally weighted scatterplot smoothing method coupled with the corrected AIC smoothing parameter selection method. In the strategy of firstly smoothing alpha-T data and then differentiating smoothed alpha-T data, although the smoothed alpha-T data are relatively smooth, the d alpha/dT-T curves obtained from the differentiation of the smoothed alpha-T data have fluctuations. In the strategy of firstly differentiating alpha-T data and then smoothing d alpha/dT-T data, the obtained d alpha/dT-T curves with the optimal smoothing parameters are smooth enough, which indicates that the second strategy is effective. The isoconversional kinetic analysis of the smoothed d alpha/dT-T curves was performed by using the Friedman differential isoconversional method. The effective activation energies of biochar combustion were obtained and found to significantly vary with the conversion degree (from about 150 to 250 kJ mol(-1) in the range of conversion degree from 0.05 to 0.95).