3-25: Increase feedstock availability for second generation ethanol process: Use of extractive and low temperature fermentation

In Brazil, ethanol is produced industrially by yeast fermentation of sugars extracted from sugarcane. In this process yeast cells are submitted to stresses, such as high substrate and product concentration, which has inhibitory effects, and those originated from environmental factors and operating conditions such as temperature. The fermentation is normally conducted under relatively high temperatures (around 33 °C), which increase yeast inhibition by substrate and product. In order to reduce this effect the Brazilian ethanol industry employs low substrate concentration and produce wine of low ethanol content (around 8.5 °GL). However, to be used as biofuel, ethanol concentration must be at least 95 °GL, which significantly increases the process energy consumption, since a larger amount of energy is required in the purification step, as well as producing a large volume of vinasse. In Brazil second generation ethanol will most likely be derived from bagasse and straw. Sugarcane bagasse is used as fuel in cogeneration systems, supplying thermal and electric energy to the plants, while straw is burnt or left in the field. Consequently, reduction on process steam consumption may lead to an increase on the amount of surplus bagasse and straw for second generation ethanol production process. In this work simulations of stand-alone and integrated second generation ethanol production considering alternative configurations for fermentation process were performed with ASPEN Plus™. Results showed that extractive and low temperature fermentation processes increase ethanol production and availability of surplus lignocellulosic material to the second generation ethanol process, simultaneously reducing generation of vinasse.