Continuous supercritical water gasification of orange peel, sewage sludge, and dairy waste model compounds

An experimental study of the supercritical water gasification (SCWG) of six model compounds (glucose, fructose, xylose, phenol, lactose, and glycine) was carried out individually and in different mixtures in a continuous tubular reactor without using a catalyst to produce hydrogen. Experiments were conducted at 240 bar, temperatures of 600 °C, 700 °C, and 800 °C, and feed concentrations of 5 or 7.5 wt% using a flow rate of 1 L/h. The dry gas produced primarily consisted of H2, CO2, CH4, and CO. The effects of key operating parameters, such as temperature, organic feed concentration, on gas composition and yields were experimentally studied and compared with thermodynamic equilibrium calculations performed by AspenPlus™, using the PSRK equation of state. The experimental results provide new insights, especially for diverse mixtures of model compounds representing high-moisture waste, such as orange peel, sewage sludge, and dairy waste. While numerous SCWG studies focus on individual model compounds, experimental research on multicomponent mixtures in continuous reactors remains extremely limited, particularly with respect to interaction effects among chemically diverse species. Real biomass and waste streams consist of interacting carbohydrates, phenolics, and nitrogen-containing compounds whose combined behavior cannot be inferred from single-compound experiments. This study fills that gap by experimentally demonstrating non-additive behavior and interaction effects in SCWG of representative mixtures, supported by integrated gas- and liquid-phase analysis and mechanistic interpretation consistent with hydrothermal chemistry.