Mechanistic insights and kinetics of torrefaction of pine wood biomasses using solid-state NMR

Abstract

The purpose of this study is to investigate the potential use of torrefied biomass of the genus Pinus, in the form of wood bark (CC), chips (CV) and wood pellets (PP), as substitutes for metallurgical coke to reduce the high CO2 emissions from the use of metallurgical coke in blast furnaces. Thermogravimetric analysis were used to optimize the torrefaction temperature (250 °C or 290 °C), residence time (30 or 60 min) under inert atmosphere. All of the torrefied biomasses were analyzed to determine physical and chemical characteristics (proximate analyses, ultimate analyses, higher calorific value (HHV), Fourier transform infrared spectroscopy (FTIR) and ss-NMR. The composition of condensable and non-condensable gases formed during torrefaction process were also measured. The results showed that the two most promising biomasses were CV and PP torrefied at a temperature of 290 °C at a residence time of 30 min. The kinetics of torrefaction was analyzed by solid state ss-NMR characterization of the torrefied biomass at different time reactions and temperature (250–290 °C) under inert atmosphere, and followed a pseudo-first order kinetic model. The kinetics of evolution of ss-NMR signals related to C-1 of cellulose; C-4 of cellulose in ordered cellulose; C-4 of cellulose in disordered/amorphous cellulose; C-6 of cellulose, and carbon atoms of methoxyl groups in lignins, at different temperatures were used to estimate the activation energy, and values in the range 11–25 kJ mol−1 were obtained.