Regulation of the elemental distribution in biomass by the torrefaction pretreatment using different atmospheres and its influence on the subsequent pyrolysis behaviors

Abstract

In this work, four types of torrefaction atmosphere (N2, 14% O2, CO2, and NH3) were employed during torrefaction pretreatment to regular the element distribution of biomass, then the effect of torrefaction pretreatment on subsequent pyrolysis behaviors was investigated. After torrefaction pretreatment, the content of carbon increased, while the content of oxygen sharply decreased. CO2 atmosphere resulted in highest content of carbon, and NH3 atmosphere resulted in lowest content of oxygen and highest content of nitrogen. The residual mass in TG curve increased after torrefaction pretreatment, resulting in lower mass loss rate at the DTG peaks. Meanwhile, the release amounts of H2O, CH4, CO2, and CO were highly related to the element distribution in torrefied biomass. As the increase of torrefaction temperature, the contents of ketones and acids decreased, while the content of phenols increased. Compared to other three types of torrefaction atmospheres (N2, CO2, and 14%O2), NH3 atmosphere resulted in lowest content of acids because of the Maillard reactions where majority of carbonyl group in the biomass was replaced by the NH2*/NH* radicals. Thus, some nitrogen-containing components was detected after the NH3 torrefaction pretreatment because of the incorporation of nitrogen element in torrefied biomass.