Modeling, analysis and control of ethylene glycol reactive distillation column

The dynamic behavior and control of an ethylene glycol reactive distillation column were studied. A detailed tray-by-tray model that explicitly includes the vapor-phase balances is derived and compared with a conventional model that ignores the vapor holdup. The steady-state variation of the product purity (the key output to be controlled) with respect to reboiler hear duty was studied identifying a region of output multiplicity with three branches corresponding to different conversion and product selectivity. Further analysis of the process on the steady-state branch with high conversion and selectivity reveals a transition from minimum phase behavior at moderate purity to nonminimum phase behavior at high purity. The nonminimum phase behavior was analyzed and addressed in the design of a nonlinear inversion-based controller that performs well with stability in the high purity region.