Vaez, S. / Karimi, K. / Mirmohamadsadeghi, S. / Jeihanipour, A. (2021)

Process Safety and Environmental Protection, 2021, 152, 513-526

Abstract

Orange wastes, including peel and pulp, were used as a biorefinery feedstock to produce pectin, ethanol, and biogas. The orange wastes were subjected to dilute acid treatment with sulfuric acid (1% w/v) at 94, 100, 140, and 180 °C for 60, 30, and 0 min. The sulfuric acid treatment was performed for pectin extraction, sugars hydrolysis, and lignocellulose pretreatment. The pectin was extracted from the hydrolysate, the liquor was used to produce ethanol, and the pretreated solid was anaerobically digested to produce biogas. The highest pectin extraction yield was 24.7 % (w/w) from orange peel and 23.7 % (w/w) from pulp, which was obtained from the supernatants of treatment at 94 °C for 60 min. Fourier transfer infrared spectrometer results confirmed the similar characteristics of the extracted pectin to a commercial product. The galacturonic acid content (an indicator of pectin purity) of pectin extracted from orange peel was 70.2 % and from orange pulp was 69.9 %, at the optimum conditions. The pectin obtained from the acid treatment at 94 °C for 60 min had a degree of esterification higher than 69 %, whereas it was less than 45 % for that obtained after treatment at 140 °C for 30 min. The maximum ethanol yields of 81.5 % (from peel) and 82.9 % (from pulp) were achieved from the hydrolysate of the acid treatment at 140 °C for 30 min. The highest methane yields were 176.8 mL/g volatile solids (from the untreated peel) and 191.8 mL/g volatile solids (from the untreated pulp). Overall, the maximum total product value was 2,472.9 USD/t orange wastes, which was achieved from dilute acid treatment at 94 °C for 60 min. At the optimal conditions for high production of pectin, without any enzyme consumption, 244 kg of pectin, 26.5 L of ethanol, and 36 m3 of methane were produced from 1 t of orange wastes.

Download