Physicochemical Characterization and Chemical Reactivity of Biochar from Pyrolysis of Dried Distiller's Grains with Solubles (DDGs)

Biomass utilization has attracted great attention for decades, and the dried distiller's grains with solubles (DDGs) is an important source which is the by-product of brewing industries, as fermented from raw biomass such as rice, wheat and sorghum. Currently, there are a few studies on the kinetics and thermodynamics of distiller's grains biomass. Therefore, the physicochemical characterization, kinetic and thermodynamic analyses of DDGs and DDGs-biochar were studied. The characterization results confirmed that DDGs had high volatile matter (81.6%) and higher heating value (21.3 MJ kg(-1)). The pyrolysis kinetics of DDGs and DDGs-biochar at four heating rates of 5, 10, 20 and 40 K min(-1) were investigated by non-isothermal thermogravimetric analysis. The isoconversional method such as Kissinger-Akahira-Sunose (KAS), analysis showed that the effective activation energy varied with the change in the conversion rates. For DDGs, it was 122-159 kJ mol(-1) (alpha: 0.1-0.2), 160 +/- 6.20 kJ mol(-1) (alpha: 0.20-0.75) and 179-194 kJ mol(-1) (alpha > 0.75), corresponded to thermal decomposition of hemicellulose, cellulose and part of lignin, and remaining lignin respectively; as to combustion of DDGs-biochar, it was 152 to 60.1 kJ mol(-1) (alpha: 0.1-0.9) indicated that some of the more complicated structures in DDGs had been carbonized, making as-obtained biochar easier to burn owing to the lower activation energy. The changes in enthalpy, Gibbs free energy and entropy of DDGs and DDGs-biochar were calculated, and the results were helpful to evaluate the conversion efficiency and technical feasibility of DDGs pyrolysis and DDGs-biochar combustion processes.