Valorization of orange peels in a biorefinery loop: recovery of limonene and production of volatile fatty acids and activated carbon
Fabio Rizzioli, Vittoria Benedetti, Francesco Patuzzi, Marco Baratieri, David Bolzonella, Federico Battısta
Abstract
Abstract Orange peels (OPs) were valorized in a lab-scale biorefinery loop for the recovery of limonene and the subsequent production of volatile fatty acids (VFAs) and activated carbon (AC). Solid/liquid extraction of limonene was optimized using n -hexane at 85 °C with an OPs-to-solvent ratio of 2:1, allowing for a limonene recovery yield of 1.20% w/w. Then, post-extraction OPs were used for the production of both VFAs and AC. For VFA production, a hydraulic retention time (HRT) of 5 days and a total solid (TS) inlet content of 10% w/w were adopted leading to a VFA yield of about 43% gVFAs/gTS. Adsorption tests revealed that, among all the solid matrixes tested, only powdered activated carbon (PAC) was able to discriminate no-VFA compounds and allowed for VFA purification. For AC production, post-extraction OPs were firstly converted into biochar through slow pyrolysis at 550 °C for 1 h and then physically activated with CO 2 at 880 °C for 1 h. Extraction did not appreciably affect OP properties, while pyrolysis increased the carbon content (from 43 to 83%) and the heating value (from 17 to 29 MJ/kg) of the material. Physical activation of OP biochar increased its surface area by almost ten times, from 40 to 326 m 2 /g, proving the effectiveness of the treatment.