Food waste supercritical water gasification for combustible gas production: product distribution, conversion pathways, kinetic characteristics

Supercritical water gasification (SCWG) of food waste to produce combustible gas is highly promising. The existing work has focused on the evolution of gas products under various operating parameters, with limited consideration of the reaction mechanism. This work comprehensively investigated the product distribution, conversion pathways, and kinetic mechanisms of food waste gasification in supercritical water (SCW). The results indicated that increasing temperature, reaction time, and decreasing feedstock concentration can enhance the production of gas. There was no significant change in the pressure range of 23–31 MPa for gas products and liquid products. The carbon gasification efficiency (CE) and hydrogen gasification efficiency (HE) can reach 82.61 % and 78.21 % by parameter optimization (temperature of 650 °C, pressure of 25 MPa, concentration of 2 wt%, reaction time of 30 min). The reaction pathways of food waste in SCW were summarized to be mainly through the hydrolysis of food waste, degradation of chain and cyclic hydrocarbons, and conversion between gaseous products. The correlation between the experimental data and the reaction limit was analyzed through a comparative analysis of the experimental results with the thermodynamic equilibrium results to provide the direction of regulation of total gasification. The classical deceleration model indicates that the reaction rate of the process is maximum at the initial moment and then decreases with increasing reaction time. The rapid gasification of chain hydrocarbons and the slow degradation of cyclic hydrocarbons caused the food waste SCWG to exhibit a fast and then slow deceleration process. The activation energy of food waste SCWG was calculated as 194.30 kJ/mol. This work may be of great value in understanding the response process of food waste SCWG.