(2024) Chemical Engineering Journal_Use of CO₂ for enhanced carbon recovery in thermochemical processing of fruit peel waste

Kim Y.; Park J.; Lee T.; Moon D.H.; Kwon E.E.

(Elsevier B.V.) Chemical Engineering Journal ISSN: 13858947 Vol.499 Issue. Article No.155908 DOI: 10.1016/j.cej.2024.155908

To address a supply variability associated with biomass, utilization of food waste provides a practical approach to consistently obtain carbon–neutral energy resource. Despite the technical merits of conventional biological process, the inevitable generation of less useful by-products, such as carbon dioxide (CO₂) and sludge, remains a primary constraint. As an alternative, thermochemical process, such as pyrolysis, presents a promising solution for the comprehensive valorisation of food waste. In this study, citrus peel, one of the fruit processing wastes, was used as a model food waste. To enhance the eco-friendliness of the pyrolysis system, CO₂ was introduced as a medium gas given the uncertainty regarding its behaviour as an inert or reactive agent at the pyrolysis temperatures. The pyrolysis approach demonstrated that CO₂ interacts with volatile pyrogenic products, resulting in an increased formation of carbon monoxide (CO). Notably, this enhancement was observed at ≥ 400 °C, suggesting that CO₂′s reactivity is limited at lower temperatures. To maximize the utility of CO₂, the pyrolysis setup was modified by incorporating a heating block at 600 °C and a nickel-based catalyst (Ni/Al2O3). While these adjustments accelerated the thermal cracking of citrus peel, test setup modification led to an aromaticity increase of the resulting pyrogenic products. However, integrating CO₂ into the catalytic pyrolysis created favourable conditions for detoxifying these aromatic compounds and further boosting CO production. Syngas productivity from catalytic pyrolysis in the presence of CO₂ was 35.2 wt%, showing 3.67 times increase over that from conventional pyrolysis. In conclusion, CO₂-assisted catalytic pyrolysis of the citrus peel offers significant technical benefits: it enhances carbon recovery in the form of CO and reduces the formation of undesirable aromatic pyrogenic products. © 2024 Elsevier B.V.

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT) (Grant No. NRF-2023R1A2C3003011 ).