9-08: Techno-economic and environmental assessment of on-site enzyme production in sugarcane plants for second generation ethanol production

In the second generation ethanol production, cellulose is converted to glucose using cellulase enzymes; however, enzyme contribution on ethanol costs and environmental impacts has been pointed out as a concerning issue for the techno-economic and environmental viability of cellulosic ethanol. The use of lower enzyme loading or its recycling could significantly decrease enzyme contribution on ethanol costs and environmental impacts, though these alternatives are still under development. Other alternative would be an on-site enzyme production, reducing enzyme costs/impacts related to purification and transportation operations.

In this work, the inclusion of on-site cellulase production in an integrated 1^st and 2^nd generation sugarcane ethanol production process was evaluated and compared with an alternative scenario purchasing commercial enzyme. Economic and environmental impacts on 1^st and 2^nd ethanol production were assessed. Process simulations developed on Aspen Plus^® were used to provide data regarding technical aspects, input and output streams, energy requirements and equipment that were used for the economic analysis and for modelling the life cycle inventory. Results showed that on-site enzyme production may be an attractive alternative from technical, economic and environmental point of view. However, reducing enzyme requirement or its recycle would also be very interesting in order to achieve better environmental and economic results. Studies on enzyme production at this development stage are of the utmost importance, since there are no established technological routes to obtain cellulases; and the costs of enzyme considering a full scale sugarcane biorefinery, such as the designed scenario for second generation biofuels production, are highly uncertain.