(436b) Modeling of Multicomponent Sorption of Acetone-Butanol-Ethanol in a Fixed-Bed Adsorber Using the General Rate Model

Butanol production via fermentation is gaining renewed interest in recent years due to its various applications as raw material in the production of butyl carboxylates, as an industrial solvent, and as an alternative biofuel due its high energy density and heat of vaporization closer to that of gasoline. Biobutanol is being produced on a large scale using fermentation processes based on various renewable feedstocks such as corn, sugar beets, and agro-wastes. Compared to bioethanol, biobutanol is less volatile, less corrosive, and has higher energy content. It can be blended with gasoline without any modifications to the automotive engine. Biobutanol can become economically viable if the upstream feedstock costs are reduced, yields increased, and downstream separation costs are reduced. In the fermentation processes, the end product concentration of butanol is only about 20 g/L due to product inhibition at high concentrations. The high normal boiling point of butanol relative to water makes distillation process complex and energy intensive. Separation and recovery strategies using various resin sorbents in fixed-bed columns have been studied as more efficient alternatives. This is due to the high product selectivity of the resins and the feasibility of continuous mode of operation in fixed-beds. Mathematical modeling of sorption dynamics provides the ability to understand the effects of different operational parameters on the separation process. The aim of this research is to implement a general rate model of the multicomponent sorption process using COMSOL Multiphysics^® software and to evaluate the impact of process variables on multicomponent separations. The PDEs representing mass balance in the liquid phase and the solid phase along with axial dispersion, external mass transfer, and intraparticle mass transfer effects for multicomponent sorption of acetone, butanol, and ethanol in the product stream were developed and solved in the coefficient form PDE interface available in COMSOL Multiphysics^® software. The breakthrough profiles of weakly adsorbed components show roll over effect and their outlet concentrations are about 50% greater than inlet feed concentrations. The results show that the operational conditions need to be selected appropriately to achieve good separation between the three components. The effects of feed flow rate, initial concentration, and bed length on fixed-bed breakthrough curves including roll-over effects will be presented.