Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Glucose, the main product of the hydrolysis of the cellulosic fraction of sugar cane bagasse, may be the input to numerous processes, including the production of 2nd generation (2G) bioethanol. However, 2G-bioethanol is not economically competitive yet. The reduction of enzyme costs is a major issue for the feasibility of the 2G-biochemical route, via the enzymatic hydrolysis of biomass, but it must be complemented by the optimization of the operational policy of the industrial reactor. The use of fed-batch reactors is one common choice for this process, aiming at minimum costs – or maximum yields and productivities. The optimization problem for fed-batch reactors usually consists in determining substrate feeding profiles, in order to maximize some performance index. This is a singular arc problem of optimal control, because the performance index and the system dynamics are both linear with respect to the control variable (the trajectory of substrate feed flow). Here, Michaelis-Menten kinetic models with product inhibition were applied for the dynamic modeling of a fed-bath reactor and two feeding policies were simulated and validated using bench-scale reactors. The first one (substrate feeding) was defined using optimal control theory. The second policy was defined in order to sustain a constant rate of glucose production, adding enzyme and substrate simultaneously during the reaction course. The methodology allowed evaluation of the best operational mode of the reactor. Fed-batch mode was less sensitive to enzyme prices than successive batches. Process intensification in a fed-batch reactor led to glucose concentrations greater than 200 g/L.