Acid-promoted hydrothermal on Chinese herbal residue toward upgradation and denitrogenation capabilities

Chinese herbal residue (CHR) is an association of renewable resource and hazardous waste , and high nitrogen content and low energy density are two primary obstacles to its efficient and clean thermal utilization. In this paper, acid-promoted hydrothermal was employed to probe the feasibility on CHR toward enhanced solid biofuel concerning upgradation and denitrogenation. A more excellent hydrothermal promoter (H 2 SO 4 ) was demonstrated to upgrade and denitrogenate CHR with better energy (1.125) and nitrogen densities (0.586) at optimal conditions (160 °C, 0.5 N H 2 SO 4 ), which could be attributed to the improved removal of oxygen, amino and ash during acid-promoted hydrothermal. Compared to raw feedstock or the conventional hydrochar , the acid-promoted hydrochar had enhanced compositional characteristics with higher heating value (21.00 kJ·mol −1 ), lower nitrogen (1.44 wt%) and ash (11.03 wt%) contents, thus showing more stable combustion flame with a higher comprehensive combustion index of 4.861 × 10 −8 , a higher combustion stability index of 4979.342, lower combustion alkali index of 0.026, and less nitrogen gaseous pollutant emission. Thus, acid-promoted hydrothermal would be a promising way to convert CHR into much cleaner and higher-grade solid biofuel.