Pyrolysis characteristics and kinetic modeling of rice straw with additives of Mg2+

To investigate the effect of Mg2+ on pyrolysis characteristics and kinetics of rice straw, MgO, MgCl2, KCl, NaCl, MgCl2-KCl, MgCl2-NaCl and KCl-MgCl2-NaCl were added into rice straw in a mass ratio of 0.3to 1,respectively.The non-isothermal pyrolysis experiments were carried out in a thermogravimetric analyzer at different heating rates such as 10, 30 and 50℃/min. The results indicated that there was only a weight loss peak during the pyrolysis processes under the roles of NaCl and KCl at three heating rates. A shoulder peak was observed at all pyrolysis processes with Mg2+ additives. Residual of rice straw pyrolysis with MgCl2 was the minimum, it was about 11%. Salts of binary and ternary systems salts can reduce the initial release temperature of volatiles, which indicated that these salts can promote the pyrolysis of rice straw obviously. The comprehensive indexes of pyrolysis under the additives were larger than that of pure rice straw, and there was an appreciable elevation under the roles of mixed salts. In terms of the modeling results, the first step reactions were almost three-dimensional diffusion according to the Jander equation，and the second step reactions were n-order reaction (Fn) . The order of activity for the three kinds of molten salts systems was as follow: ternary> binary> single. It was especially suited for the rice straw pyrolysis process under the roles of molten salts to be described with a two-step reactions model. This research can provide a scientific reference for rice straw pyrolysis in molten salts to produce bio-fuels.