Experimental-based design of oil palm trunk valorization as feed to bioethanol-biochar coproduction process and its exergy-enviro-economic assessment

Abstract

Importance of the work: Managing the very large volume of palm trunks in land clearing and the replanting of palm oil plantations is a costly and difficult. Finding a productive and environmentally friendly way to utilize this biomass is therefore important. Objectives: To design and simulated the valorization of palm trunk as raw materials for producing ethanol and biochar in a self-sustained process. Methods: The process simulation started by separating the trunk sap and the trunk fiber. The trunk sap was fermented to produce bioethanol. The fiber was treated by amylase hydrolysis and fermentation to convert its starch into ethanol. The remaining lignocellulosic material was sent to a pyrolysis unit for biochar production. Laboratory experiments and chemical analyses were conducted to determine palm trunk chemical composition, ethanol yield from sap fermentation and amylase hydrolysate and biochar yield. These experimental data were then used for process design and simulation. Results: The simulation showed that when all production units operated at full capacity, the energy generated from bark combustion and pyrolysis was not enough to meet the plant’s total energy demand. However, the plant model achieved self-sustained energy production by operating the amylase hydrolysis step at 63.77% capacity and sending the rest of fiber to combustion. Operating this plant using the self-sustained conditions was still economically attractive. The ethanol production cost, including plant depreciation, was USD 0.775/L (USD 0.981/kg). The return on investment was 8.36% and the payback period was 11.96 yr. Main findings: Palm trunk valorization for ethanol and biochar production can provide an environmentally friendly and profitable solution for managing the large biomass volume generated during palm oil plantation replanting, and it is more favorable than disposal by natural decay or large-scale burning.