A generalizable and robust kinetic model for predicting sustainable hydrogen production by supercritical water gasification of food waste

The conversion of food waste into hydrogen-rich gas using supercritical water gasification (SCWG) technology is very attractive. Developing a generalizable kinetic model describing the conversion of food waste into hydrogen is a prerequisite for reactor optimization design. This paper investigated the product evolution characteristics of food waste in supercritical water (SCW) under various operating parameters, namely pressure of 25 MPa, reaction temperature of 600–700 °C, residence time of 3–15 min, and concentration of 2–5 wt%. The results showed that increasing the reaction temperature and extending the residence time were beneficial in increasing carbon gasification efficiency (CE) and hydrogen gasification efficiency (HE). The maximum CE and HE can reach 78.65% and 78.88%, respectively. The gasification reaction pathway and kinetic model were established by the lumped parameter method to reveal reaction mechanism. The kinetic model developed quantitatively describes the gas products (H₂, CO, CH₄, and CO₂) and exhibits robust predictive abilities (R²: 0.91). Further, the generalization capability of the model was proved by predicting other work (R²: 0.90 and 0.88). The activation energies for the hydrolysis of food waste to chain intermediate organic products (Int 1) and cyclic intermediate organic products (Int 2) were 88.86 kJ/mol and 93.36 kJ/mol, respectively. The analyzed gas product generation and consumption pathways suggested that accelerated decomposition of intermediates (especially Int 2) may be the key to increased gas yield. This work may provide insights into the conversion behavior of food waste in supercritical water from a reaction kinetics perspective.