Improving bioethanol production – Comparison between extractive and low temperature fermentation

One of the key issues that must be addressed in the biofuel production based on sugarcane industry is the energy consumption of the process. Process energy demand has direct impact on the amount of lignocellulosic material available for use as feedstock for second generation ethanol production. A significant fraction of the energy consumption in bioethanol production occurs in the purification step, since conventional fermentation systems employed in the industry require low substrate concentration and, consequently, produce wine of low (around 8.5 °GL) ethanol content that must be distilled in order to meet product specifications. In this study alternatives to the conventional fermentation processes employed in the industry (low temperature fermentation and vacuum extractive fermentation) were assessed, in the context of a large scale sugarcane autonomous distillery, through computer simulation. Electricity consumption and lignocellulosic material surplus on each case were evaluated. It is shown that the alternative fermentation processes allow a significant reduction on vinasse generation and increases ethanol production when compared with conventional fermentation, but increases electricity consumption (for the extractive fermentation) or steam consumption (for low temperature fermentation); when vinasse concentration is considered in the conventional process, steam consumption in the extractive fermentation is also significantly smaller.