Thermochemical conversion of grape marc into carbon-negative syngas

Abstract

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.