Catalytic fast pyrolysis of rice husk: Effect of coupling leaching with torrefaction pretreatment

The effect of coupling leaching with torrefaction pretreatment process on bio-oil production from catalytic fast pyrolysis using ZSM-5 zeolite catalyst was evaluated by Py-GC/MS. During coupling leaching with torrefaction pretreatment, the fuel characteristics and structural characteristics of rice husk samples were changed, which were evaluated using proximate, ultimate, and calorific analyses, Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD) techniques. The experimental results of catalytic fast pyrolysis indicated that coupling leaching with torrefaction pretreatment further improved the relative contents of BTX (benzene, toluene and xylene) compounds in bio-oil compared to that of raw rice husk sample. It was mainly ascribed to the effective removal of metallic species during leaching process. In addition, the selective removal of hemicellulose fraction and the increasing lignin fraction and changes in the structure of lignin (cleavage of ether linkages and demethoxylation) during torrefaction process also plays positive roles. Severe torrefaction process resulted in the cross-linking and charring of sample, thus reducing the formation of BTX compounds. Thus, coupling leaching with middle torrefaction pretreatment process was the optimum pretreatment conditions for catalytic fast pyrolysis of rice husk samples.