Activated Carbons Produced from Hydrothermally Carbonized Prickly Pear Seed Waste

Abstract

The agro-sector generates organic waste of various kinds, which potentially could be used to prepare functional materials, lessen environmental problems, and enhance circularity. In this context, the hypothesis that was put forward in this work is that prickly pear seed waste from the Tunisian agro-food industry could be used to prepare activated carbons. The prickly pear seed waste was first hydrothermally carbonized and the resulting hydrochar was activated in CO2 at 800 °C. The yield of the hydrothermal carbonization process is of importance, and it was the highest at intermediate dwell times and temperatures, which was ascribed to the re-precipitation of hydrochar particles on the heat-treated biomass. The hydrochars and activated carbons were characterized with scanning electron microscopy, thermogravimetry, Raman spectroscopy, and N2 and CO2 adsorption/desorption analyses. The activated carbons had micro- (<2 nm) and mesopores (2–50 nm), and specific surface areas and total pore volumes of about 400 m2 −1 and 0.21 cm3 g−1. The study showed that the prickly pear seed waste could be effectively transformed into both hydrochars and activated carbons and that is advisable to optimize the hydrothermal process for the mass yield. A life cycle analysis was performed to assess the environmental impact of the production of typical activated carbons using the approach of this study. Further studies could be focused on enhancing the properties of the activated carbons by further optimization of the activation process.