Valorization of cocoa's mucilage waste to ethanol and subsequent direct catalytic conversion into ethylene

Abstract

BACKGROUND: The identification of new resources for producing biofuels and chemical-based products is crucial for processes sustainability. This study presents a valorization route to produce ethanol and ethylene using cocoa’s mucilage juice (MJ) residue from cocoa’s farms of variety “Arriba” (AC). The processing parameters to maximize the ethanol production and subsequent selectively conversion into ethylene were determined. The ethanol production has been carried out by investigating the effect of three parameters such as the temperature of fermentation, the initial fermentation pH, and the addition of (NH4)2SO4 as an N source in presence of free Saccharomyces cerevisiae NCYC 366. Consecutively, the selectivity of ethanol-ethylene conversion using a zeolite-based ZSM-5 catalyst was evaluated at different temperatures and ethanol concentrations. RESULTS: During the ethanol production, the best sugar conversion was reached at 30 ºC, adjusting the initial pH to 5 and without nitrogen source, resulting in 86.83% of sugars conversion, the maximum ethanol concentration of 68.65 g·L-1, and maximum ethanol production rate of 2.03 g·L-1 ·h-1 after 168 hours of fermentation. On the other hand, ethylene was produced using ZSM-5 based zeolite catalyst with > 99.9 % of efficiency in the temperature range between 240 ºC to 300 ºC. In addition, selectively ethylene formation was found at 240 ºC and 30 g·L-1 of ethanol. CONCLUSIONS: The approach hereby presented shows the valorization of MJ waste of AC variety to produce ethanol and ethylene with minimum processing inputs costs, demonstrating a successful route to convert a farm residue into a bio-based product with enhanced marketability.