Comparative Study of Modified Simulated Moving Bed Systems at Optimal Conditions for the Separation of Ternary Mixtures of Xylene Isomers

In this paper, separation of a ternary mixture based on simulated moving bed (SMB) technology is studied. The conventional four-zone SMB system for binary separation was modified into different configurations to facilitate simultaneous collection of all three components. The performances of these systems were compared at optimal conditions based on multiobjective optimization for an industrial-scale separation of C8 aromatics. Simultaneous recovery of p-xylene, ethylbenzene, and mixtures of o- and m-xylene with the highest possible purities are considered. The effect of a reflux stream addition containing one of the components is also investigated. It was observed that, as the separation becomes more difficult, the five-zone SMB performs better than the modified four-zone SMB for ternary separation, while at the same time consuming a lesser amount of desorbent. Efficacies in overall performances of the different modified SMB configurations are discussed. Rigorous multiobjective optimization is performed using a nontraditional optimization technique based on an adaptation of a genetic algorithm, elitist nondominated sorting genetic algorithm with jumping genes.