Comprehensive utilization of agricultural wastes by combined wet torrefaction and pyrolysis

Wet torrefaction (WT) is promising to convert moist biomass into hydrophobic fuel with higher heating value and energy density. The current study investigated the comprehensive utilization of biomass with combined wet torrefaction and pyrolysis. Characterizations of both torrefied solid and liquid were achieved to understand the evolution of physicochemical properties during WT. The composition analysis showed that the torrefied liquid was a promising candidate for furfural and organic acid production, and could affect the WT solid properties as well. Torrefied solid products with less reactive ash, larger surface area, and higher crystallinity were obtained. And the AAEM removal by WT could be enhanced with corncob due to its hemicellulose abundance. Followed by WT, techniques including TGA, py-GC/MS and py-in-situ DRIFT were used for pyrolysis investigation of torrefied solids. It was found that WT could change the activation energy of cellulose decomposition mainly due to the removal of AAEMs. The energy required for levoglucosan production could be mildly reduced, resulted from enlarged pore structure and better cellulose accessibility. Because of the removal of reactive AAEMs and enhanced product transportation, levoglucosan yield reached 55 wt% based on cellulose content, even with some inert AAEMs left in torrefied solids. The yields of phenols without methoxyl groups were also enhanced by WT. The perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) analysis of the in-situ DRIFT results further proved that WT could significantly change the pyrolysis pathway of cellulose from dehydration and condensation to hydrogen bond dissociation and glycosidic bond cleavage. •An integrated process including wet torrefaction and pyrolysis of biomass was investigated.•Hemicellulose component strongly decomposed with wet torrefaction between 170 and 190 °C.•Liquid rich in furfural and acetic acid was generated from wet torrefaction process.•Pyrolysis of torrefied biomass generated more sugars and simple phenols.•Pyrolytic decomposition pathways of cellulose changed after wet torrefaction.