Techno-economic-environmental analysis of a microbial oil production integrated into a bioethanol sugarcane biorefinery

Abstract

Biodiesel and bioethanol play an important role as renewable liquid fuels. The production of these biofuels generates low-value by-products, such as sugarcane bagasse (usually used for heat generation). This bagasse can be processed to produce a sugarcane bagasse hemicellulose hydrolysate (SCBH) that contains fermentable sugars, mainly xylose. Oleaginous yeasts (eg., Rhodotorula toruloides) can grow in this SCBH producing microbial oil (MO) which can be used as raw material for biodiesel production. This strategy arises as a promising approach to exploit a synergy between bioethanol and biodiesel production processes within a biorefinery. Since techno-economic-environmental analysis (TEEA) can identify bottlenecks, providing insights concerning feasibility and sustainability of processes, in this work TEEA was applied to a study case consisting of a MO production from SCBH integrated into a first-generation (1G) bioethanol plant. The 1G section of the plant – processing 4x10 6 t of sugarcane per season (240 days) - produces bioethanol and bioelectricity generating a surplus bagasse, which is sent to the MO production. Net present value and internal rate of return were chosen as the economic metrics and global warming potential as environmental one for evaluating the process options simulations. The main result of this study had the plant producing74. 8 m 3 /h of bioethanol, 2.8 t/h of MO, and 89.3 MW of bioelectricity. The integrated process exhibited a positive economic performance (net present value equals to US$34. 5x10 6 and internal rate of return of 12.4%) indicating that the microbial oil production from sugarcane is feasible. From the environmental perspective, a decrease of 13% in GHG emissions was obtained.