Cost analysis of subcritical water pretreatment of sugarcane straw and bagasse for second-generation bioethanol production: a case study in a sugarcane mill

The value of lignocellulose residues for green technologies has been growing, but biomass pretreatment is still an economic challenge. In this case study, a cost analysis of subcritical water pretreatment (SCWP) of sugarcane by-products for ethanol production was conducted. The proposed industrial scheme is attached to a Brazilian sugarcane mill, which generates a surplus of bagasse. Seven scenarios were simulated to address the prospects of the implementation of the process in the mill. The fermentation of sugarcane bagasse hydrolysate with Scheffersomyces stipitis upgraded the ethanol yield. The fixed capital investment of the industrial process was approximately US$27 million and 35% of this was associated with the SCWP. The highest ethanol yield was obtained for the process operated with hydrolysate from sugarcane bagasse (6740.5 kg ethanol day(-1)), which is associated with the high hemicellulose content in the bagasse composition compared with straw. The cost difference revealed that the fixed capital investment and utilities were the largest expenses for process implementation and operation. The simulated process reached 5.45 US$ L-1 as the lowest cost of manufacturing. However, this cost is approximately 10-fold higher than the market price for ethanol in Brazil. In conclusion, the SCWP of sugarcane straw and bagasse demands significant technical improvement before scaling up to the industrial scale for bioethanol production. (c) 2021 Society of Chemical Industry and John Wiley & Sons, Ltd