Thermochemical conversion of grape marc into carbon-negative syngas

The massive generation of waste from the food industry requires sustainable management strategies to mitigate its contribution to greenhouse gas emissions. Therefore, this study explored a sustainable approach by valorizing food waste into energy through pyrolysis. Grape marc (GM), a byproduct of the wine industry, was selected as the model (carbon) substrate. To ensure sustainability, CO₂ was introduced as the reactive pyrolysis medium. During the pyrolysis of GM, interactions between CO₂ and the volatiles released from GM resulted in increased production of carbon-negative CO and simultaneous suppression of pyrogenic oil formation. The increase in carbon-negative CO production attributed to CO₂ was observed at temperatures ≥370 °C, which indicates the slow CO₂ reaction kinetics. To further improve the carbon-negative syngas yield, the experimental setup was modified to supply additional heat energy and incorporate a nickel catalyst into the pyrolysis process. These modifications enhanced the reactivity of CO₂, leading to an increased formation of carbon-negative syngas. Optimization experiments were then conducted to identify the ideal conditions for catalytic pyrolysis by varying temperatures and CO₂ concentrations. Optimization at 700 °C and 80 vol% CO₂ maximized carbon-negative syngas yield, achieving a CO₂ mitigation potential of 845.8 million tons, surpassing conventional pyrolysis by 7.0 times. This highlights the viability of valorizing food waste through CO₂-assisted pyrolysis as a sustainable strategy for reducing greenhouse gas emissions and producing carbon-negative syngas.