Uncovering Structure-Reactivity Relationships In Pyrolysis And Gasification Of Biomass With Varying Severity Of Torrefaction

Lignocellulosic biomass is the widely available source of renewable organic carbon that can be used as a potential alternative to fossil fuel for the production of chemicals,liquid fuels,power and heat.The objective of this study is to establish the structure-reactivity relationships in pyrolysis and gasification of biomass with varying severity of torrefaction.Biomass materials were torrefied in a bench scale tubular reactor with varying torrefaction temperature(220-300 ?).The structural alterations in torrefied biomass and its derived biochar were characterized by solid-state nuclear magnetic resonance spectroscopy(NMR)and Raman spectroscopy,respectively.The effect of torrefaction severity,as well as the resulting structural changes in biomass,upon subsequent pyrolysis and gasification reactivity were systematically studied.The experimental results showed that the pyrolysis reactivity of pine was promoted by torrefaction,whereas the gasification reactivity of biochar derived from biomass was reduced by torrefaction.The results were mainly attributed to the severe degradation,polycondensation and carbonization of hemicellulose and lignin fractions during torrefaction of pine.The pyrolysis and gasification reactivity of torrefied pine was a strong linear function of its aromaticity or H/C molar ratio.Therefore,H/C molar ratio and aromaticity of pine were good indicators to quantitatively assess the structural alterations of pine during torrefaction and their impacts on the reactivity of subsequent pyrolysis and gasification.These findings provide a simple and efficient method to predict the pyrolysis and gasification reactivity of biomass with varying severity of torrefaction.For pyrolysis reactivity of xylans and corncobs,torrefaction pretreatment showed a promoting effect at low temperatures.However,when the torrifaction temperature exceeds 260 ?,torrefaction plays a suppressive role.The gasification reactivity of biochar derived from ylan and corncob still showed a strong linear relationship with the H/C olar ratio of torrefied samples.In addition,for cellulose and sludge samples,torrefaction has an inhibitory effect on pyrolytic reactivity because it contains little or no hemicellulose and lignin.