Design of an optimal process for enhanced production of bioethanol and biodiesel from algae oil via glycerol fermentation

In this paper, we optimize a process that integrates the use of glycerol to produce ethanol via fermentation within the simultaneous production of biodiesel and bioethanol from algae. The process consists of growing the algae, determining the optimal fraction of oil vs. starch, followed by oil extraction, starch liquefaction and saccharification, to sugars, oil transesterification, for which we consider two transesterification technologies (enzymes and alkali) and the fermentation of sugars and glycerol. The advantage of this process is that the dehydration technologies are common for the products of the glucose and glycerol fermentation. Simultaneous optimization and heat integration is performed using Duran and Grossmann's model. The fermentation of glycerol to ethanol increases the production of bioethanol by at least 50%. The energy and water consumptions are competitive with other processes that either sell the glycerol or use it to obtain methanol. However, the price for the biofuels is only competitive if glycerol cannot be sold to the market.