Ethylene from Citrus Wastes: An Environmental and Financial Perspective

Biomass-derived ethylene has the potential to displace relatively high market value products, while also contributing to sustainability objectives. The production of bioethylene from agricultural residues such as citrus wastes (CWs) can have both environmental and financial benefits. Citrus wastes are main byproduct of juice factories, with  worldwide production exceeding  30 million tonnes per year and an annual growth rate of 14%. Currently, a majority  of CWs are sent to landfill. The disposal of CWs is costly and also creates environmental concerns due to the high organic content of CWs. In this work, we introduced a pathway to convert CW to bioethylene. The pathway is based on hydrolysis of the carbohydratesin CWs to sugar, fermentation of sugar to ethanol, and then catalytic conversion of ethanol to ethylene. The remaining compounds from the process are anaerobically digested to biomethane, which is utilized as a source of energy for the entire pathway of CW toethylene. The pathway is integrated and energy self-sufficient. The production cost of ethylene from CW is mainly dependent on the plant capacity and CW cost. In Florida, with  CW processed at 3.5 million tonne/year, the production cost of ethylene from CW ranges from 680 to 1700 USD/tonne at CW cost of 20 and 40 USD/tonne, respectively. The life cycle GHG emission of production of ethylene from CW include CW transportation, ethanol production and final conversion of ethanol to ethylene. Our results show that life cycle GHG emission of CW-derived ethylene is substantially lower than fossil based ethylene.