Effect of thermo-lime and hot-water pretreatment on the thermal-decomposition characteristics and structure of Spartina alterniflora

The thermal-decomposition characteristics and kinetics of Spartina alterniflora (smooth cordgrass; SC) pretreated with thermo-lime and hot water were investigated by thermogravimetric analysis. Results showed that pretreatment changed the thermal-decomposition behavior of pretreated biomass, as shown in the change of the volatile-matter yield, the thermal-decomposition temperature for a given conversion and the mass-loss rate, because of the breakage of lignocellulosic structure. The activation energy of SC ranged from 40.8 to 55.8 kJ mol−1 for conversion ratios between 0.15 and 0.8. Pretreatment increased the activation energy of thermal-decomposition reaction, indicating the increment of the thermal stability of biomass. Compared with thermo-lime pretreatment, hot-water pretreatment increased the volatile-matter yield, activation energy, and mass-loss rate of the sample. Structure changes were further investigated by X-ray and Fourier-transform infrared (FTIR) spectroscopy analysis to determine the effect of pretreatment on thermal decomposition. FTIR analyses revealed the depolymerization of lignocellulosic structure and the disruption of carboxyl carbons attached to the lignin side chain. X-ray and FTIR results also showed that thermo-lime and hot-water pretreatment broke the crystalline structure of cellulose by disrupting hydrogen bonding and removing amorphous matter. Compared with hot water, thermo-lime pretreatment resulted in many modifications of lignocellulosic structure and composition. Furthermore, structure breakage and composition removal changed thermal-decomposition characteristics of pretreated samples.