Lignocellulose thermal pretreatment and its effect on fuel properties and composition of the condensable products (tar precursors) from char devolatilization for coal substitution in gasification application

To establish the potential of thermally pretreated biomass as fuel for coal replacement in applications such as gasification, the fuel properties (higher heating value, elemental and proximate analyses) and the composition of char devolatilization products were analyzed and compared to those of sub-bituminous coal. Samples of pine, bamboo, corn cob and corn stover were pretreated at 250, 300, 350 and 400 °C with a hold time of 30 min. The devolatilization experiments were done in a Thermogravimetric analyzer, while captured volatiles were analyzed by thermal desorption/gas chromatography–mass spectrometry. The results showed that an increase in pretreatment temperature consistently decreased the oxygen and volatile matter contents of the char, while its fixed carbon content and the higher heating values increased, with a more drastic evolution from 300 °C onwards. Analysis of the char devolatilization products confirmed a major modification of the polysaccharides structure, as only traces of depolymerisation products were observed following pretreatment at 350 °C. Devolatilization of chars pretreated at 350 and 400 °C resulted in the evolution of the tar precursors, especially the phenolics, at similar and lower amounts, respectively, in comparison to coal devolatilization. Overall, a pretreatment temperature of at least 350 °C would be recommended for sub-bituminous coal substitution in gasification, while 400 °C could be considered for biomass species with high lignin content.