Assesment of alternative routes for sugarcane-based ethanol recovery: exergy and economic analysis

Abstract

The aim of this thesis was to develop a methodological approach that can systematically guide process simulation for better understanding of bioethanol production process. In the present work, the ethanol production process was studied combining liquid-liquid extraction (LLE), non-conventional process, with extractive distillation system. The designed process was based on an autonomous distillery that crushs 500 tons of cane per hour. The commercial process simulator Aspen Plus® V.8.2 was used as a computer-aided tool. In this work, isoamilic alcohol, n-octanol, n-dodecanol and oleic acid were evaluated as solvent extraction for LLE and monoethylene glycol was used as entrainer in the extractive distillation column. The results of the environmental impact of a standard distillery applying renewability analysis showed that the conventional distillation process provides worse environmental performance. Distillation with use of a reboiler as heat source has better environmental performance than other two cases. In addition, the economic evaluation showed that distillation with use of a reboiler achieved the value of US$ 115 million with respect to ethanol selling. This finding is approximately 9% and 12% higher than achieved for standard process and distillation with mechanical vapor recompression scheme. In sequence, it was carried the simulation of an alternative route combining liquid-liquid extraction-distillation system to evaluate the process downstream and its environment impact. The results have shown that among the candidates under investigation: isoamilic alcohol, n-octanol, n-dodecanol and oleic acid, the hybrid system with dodecanol reached 37.57 % reduction of liquid waste emissions when compared to conventional process. At the same time, using the concepts of exergy and renewability index, LLE with oleic acid and conventional process were considered to provide the worst environmental performance when compared to extraction system with dodecanol. The analysis of optimal entrainer agent feeding flow into the extractor column showed that LLE with oleic acid required a solvent feeding flow of 2.40e+6 kg/h which represent an increasing of 83% in solvent consumption when compared to isoamilic alcohol system the lowest solvent feeding flow (4.06e+5 kg/h). The hybrid system with dodecanol reached 35.6 m3 of anhydrous ethanol per hour .This value is close to standard process production which is 38.8 m3 of anhydrous ethanol per hour.