Ethanol production. A process-based mathematical model

Two ethanol production models were developed as a function of microbial growth, metabolism, and the chemical and physical processes occurring in a fermentation system. The first equation, which considered a monosaccharide as the substrate, fit measured data well (R²>0.98). This function considered lag time through a microbial population increase component and fit all physical boundary conditions. Because of the theoretical basis for the equation and the excellent fit to measured data, it was concluded that the model fully explained the fermentative conversion of a monosaccharide to ethanol. The upper boundary condition for the monosaccharide substrate equation was modified to include effects of the chemical and physical processes that convert starch and/or cellulose to a sugar. This starch-based equation also closely fit measured data reported in the literature. The four coefficients in the general starch equation were related to carbohydrate concentration, percent saccharification, and temperature. A physical explanation was given for each coefficient. Independent verification of the second model using 18 data sets reported in the literature predicted measured results with an R² value of 0.89 and was highly significant (α=0.001).