Microbial oil and biodiesel production in an integrated sugarcane biorefinery: Techno-economic and life cycle assessment

Abstract

Biodiesel and bioethanol play an important role as renewable liquid fuels. Bagasse, a by-product from the bioethanol industry, can generate a “sugarcane bagasse hemicellulose hydrolysate” (SCBH) that contains fermentable sugars, mainly xylose. Oleaginous yeasts (eg., Rhodotorula toruloides) can grow in SCBH, producing microbial oil (MO), a source of triacylglycerol for biodiesel production. The integration of bioethanol and biodiesel (from MO) production may be a promising approach in order to exploit synergies between bioethanol and biodiesel processes within a biorefinery. This integration may improve the economic and environmental performance of both processes. This work presents the techno-economic-environmental analysis of the integrated production of first-generation bioethanol, bioelectricity, and biodiesel in a Brazilian sugarcane biorefinery, where MO from the yeast R. toruloides feeds the biodiesel unit. The biorefinery, processing 4.0 million t of sugarcane per harvest, produces 71.7 m3/h of bioethanol, 2.55 m3/h of biodiesel (that can replace 75.6% of the diesel demand in the field), and 86.3 MW of surplus bioelectricity. A life cycle assessment shows that the integrated biorefinery had a lower environmental impact than the first-generation bioethanol plant. The integrated process exhibits a positive economic performance (net present value of approx. 110 million of dollars and internal rate of return of about 14.5% per year, higher than the minimum acceptable rate of return, assumed as 11% per year), indicating that this is a feasible industrial option. Sensitivity analysis shows that R&D should mainly focus on the MO bioreactor operation.