Apple Waste: A Sustainable Source of Carbon Materials and Valuable Compounds

• Published in: ACS sustainable chemistry & engineering Vol. 7; no. 20; pp. 17335 - 17343
• Main Authors: Guardia, Laura, Suárez, Loreto, Querejeta, Nausika, Rodríguez Madrera, Roberto, Suárez, Belén, Centeno, Teresa A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21-10-2019
• Subjects: biocarbon; porous carbon; bioactive compounds; hydrothermal carbonization; apple waste; supercapacitor
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.9b04266

The implementation of sustainable strategies based on the integral valorization of residues is the most efficient way to achieve a profitable circular economy. This comprehensive study highlights the potential of apple waste from juice and cider production as a precursor of porous carbons and provides guidelines to achieve a wide spectrum of physicochemical properties. Hydrothermal carbonization (HTC) of apple bagasse is proposed as a feasible integrated process with zero waste that allows stabilizing this highly pollutant residue in the form of a carbon-enriched solid while extracting valuable compounds in the aqueous phase. The liquid fraction resulting from HTC at 200 °C contains a high total phenolic content and antioxidant activity, the major products being catechol (1,2-dihydroxybenzene) and 5-hydroxymethyl-2-furfural (HMF). The successful upgrading of the solid byproduct into porous carbons provides additional advantage for a more cost-effective waste management. It is reported that a simple one-step activation leads to apple-derived carbons with specific surface areas up to 2000 m2 g–1 and electrochemical capacitances as high as 260–290 F g–1. Their excellent performance as supercapacitor electrodes make them very promising for the storage of electrical energy from renewable sources.