This study develops a dynamic model of a continuous acetone butanol ethanol (ABE) fermentation process combined with ex situ butanol recovery (termed "ESBR-by-adsorption system") using a mixed sugar media and recombinant strain. The previously constructed ABE cofermentation kinetic model from fed-batch experiments is extended to the continuous ESBR-by-adsorption system for the purpose of supporting future optimization and control research. Critical fermentation model parameters identified by a sensitivity analysis are fitted to lab-scale experimental data of the ESBR-by-adsorption system using glucose/xylose mixtures. The developed model is validated under various operating conditions, and it is demonstrated that the model can reliably predict the complex dynamics of the ESBR-by-adsorption system including the cofermentation kinetics of glucose and xylose. Using the model, productivity and economics of the continuous biobutanol production are assessed after optimizing the cyclic steady state corresponding to several feed concentration levels. It is shown that, compared to the glucose-based ESBR-by-adsorption system, the glucose/xylose-based ESBR-by-adsorption system gives 1.21-fold improved butanol productivity and 1.67-fold reduced sugar feed cost.