Optimizing carrot pulp waste valorization via thermochemical conversion using carbon dioxide

Abstract

This study proposes an environmentally sustainable approach for converting food waste into fuels and chemicals, especially focusing on syngas production. The carbon-negative aspect of the pyrolysis process was achieved by employing CO2 as the reaction medium. Carrot pulp waste (CPW) was used as an exemplary food waste in this work. In the single-stage pyrolysis of CPW, the presence of CO2 led to improved syngas generation. The introduction of CO2, rather than N2 carrier gas, resulted in substantial increase of CO formation at temperatures ≥ 400 °C, with a decrease in bio-oil production. This phenomenon was due to the chemical reactions between CO2 and the volatile organic compounds (VOCs) produced during the pyrolysis of CPW. Specifically, CO2 played a mechanistic role by providing an extra oxygen source for CO production and participating in the oxidative thermal cracking of VOCs. In-depth analysis of multi-stage pyrolysis verified the mechanistic role of CO2, particularly at temperatures ≥ 190 °C. However, CO2-induced reactions influenced the molecular size of the VOCs. To boost the CO2-induced reactions for additional syngas formation, a nickel-based catalyst was introduced during the pyrolysis of CPW, which effectively expedited the homogeneous reactions initiated by CO2, thereby indicating its potential to accelerate and optimize food waste valorization.