| This thesis presents new methods for the dynamic analysis of heterogeneous azeotropic distillation, thereby extending the methodology for steady-state analysis. It concentrates on the dehydration of secbutanol with disecbutylether, a system with two partially-miscible binary pairs. This system requires more accurate methods for distinguishing between vapor-liquid and vapor-liquid-liquid phase distributions at equilibrium. A new algorithm is introduced to overcome difficulties with high-index differential/algebraic equations and phase stability analysis.; Extensive parameterization with respect to the aqueous reflux ratio has been carried out for the ARCO SBA-II tower. Using the steady-state model developed by Kovach (1986), singularities are observed as the second liquid phase is introduced on the trays and regions of steady-state multiplicity are demonstrated. Furthermore, a critical aqueous reflex ratio, in the vicinity of which two liquid phases are introduced on most of the trays, varies only slightly with the number of trays in the tower. The model predicts that the product purities and recoveries remain high using one-third of the trays in the industrial SBA-II tower.; Phase diagrams for the ethanol-benzene-water and secbutanol-disecbutylether-water systems have been generated at various temperatures and pressures. Unlike the ethanol-benzene-water system, the secbutanol-disecbutylether-water system has two VLL regions connected by a vapor envelope. As the temperature decreases, the vapor envelope shrinks and the two VLL regions approach each other in two thin strips. More reliable and accurate methods for phase stability analysis are introduced to properly detect the formation of the second liquid phase.; The model for the dynamic simulation of heterogeneous azeotropic distillation towers is solved with a new algorithm capable of generating consistent initializations for a system of index-1 differential/algebraic equations. A novel branch-switching algorithm has been implemented which locates the real bifurcation point at the intersection of solution branches having different phase distributions. The latter algorithm uses the tangent-plane criterion (Michelsen, 1982) to detect the addition and deletion of phases as the integration proceeds.; The algorithm for the dynamic simulation of heterogeneous azeotropic distillation towers performs well for several test cases. Open-loop responses for a shortened 12-tray tower, to dehydrate secbutanol, in response to changes in the reboiler duty, aqueous reflux ratio, and the feed flow rate, have been studied extensively. The tower is less sensitive to these changes than predicted by the steady-state simulations. The tower responds to changes in the aqueous reflux ratio like a first-order system and to changes in the reboiler duty like a second-order system. The temperature front is confirmed to be located between trays with different phase distributions. A limited comparison with the experimental dynamic response to a decrease in the feed flow rate is favorable. |
