Ethanol production from sugarcane under very-high-gravity (VGH) fermentation conditions: experimental study and kinetic modeling

There is a great tendency to work in very-high-gravity (VHG) fermentation in Brazil, where sugarcane is used for the production of ethanol, mainly in greenfield mills. Ethanol content in wine of 8 to 9^oGL is obtained in the current process of ethanol production, which results in the disposal of 10 to 12 L of vinasse per L of ethanol produced. The VHG fermentation aims to obtain high ethanol content wines that results in an increase of up to 15^oGL and reduces the effluent generation by up to 5 L of vinasse / L ethanol produced. Bearing this in mind, in this work several experimental tests were developed to obtain validated operating protocols for the determination of operating parameters of a VHG fermentation technology as well as a detailed kinetic model of the process. A first set of batch cultures with an industrial yeast strain and operating from 24 to 36^oC was used to estimate kinetic parameters of a mechanistic model that describes the kinetics as a function of temperature. Whereas a multi-parameter optimization is not a trivial procedure, a hybrid stochastic-deterministic method was used to find optimum values for the parameters that produce the best fit between the experimental observation and the simulated response. The kinetic model was then validated with a second set of experimental data from several cycles of VHG fed-batch fermentation with cell recycle. The experimental and simulated results were further used for determining and validating the process parameters for VHG fermentation scale-up purposes.