Influence of feedstock pretreatment on biomass pyrolysis kinetics

In order to investigate the influence of pretreatment methods such as water and acid wash on biomass pyrolysis kinetics, rice straw was selected as biomass feedstock, deionized water, hydrochloric acid, sulfuric acid and phosphoric acid, whose weight fraction were 3%, 7% and 10%, respectively, and deionized water were used to wash rice straw, and the thermal decomposition behaviors and comprehensive index of rice straw pyrolysis were analyzed through thermogravimetric analysis method. The thermo-kinetics software and multiple non-linear curve fitting method were adopted to calculate the kinetic parameters, and the model of pyrolysis kinetics was speculated. The results showed that water and acid wash can make TG and DTG curves of rice straw pyrolysis shift to higher temperature section, and the maximum weight loss rate and temperature increased. The impacts of the concentration of hydrochloric acid and phosphoric acid were negligible, but that of sulfuric acid was significant which became obvious with the increasing concentration. Acid wash was in favor of the emission of volatile matters contained in rice straw, and can eliminate the K salt, the ability order of three acid was as follows: hydrochloric acid, sulfuric acid and phosphoric acid. The thermal comprehensive characteristic index of pyrolysis decreased after rice straw was pretreated, and changed with the acid concentration. The two-step continuous model can descript the pyrolysis process of pretreated rice straw. Rice straw washed by deionized water and phosphoric acid tended to occur an n-dimensional nucleation/nucleus growth reaction according to Avrami/Erofeev, and that washed by hydrochloric acid and sulfuric acid washing tended to occur an n-order reaction.