A systematic simulation and optimization of an industrial-scale p-xylene simulated moving bed process

Abstract

Abstract This work presents a detailed study for the systematic analysis, simulation and optimization of an industrial-scale simulated moving bed process with Ba/K-exchanged faujasite-type zeolite as adsorbent for separating p -xylene from the C 8 aromatic mixture. The adsorption equilibrium of C 8 aromatic isomers and p -diethylbenzene on the commercial adsorbent were determined experimentally, while the lumped mass transfer coefficients were estimated through pulse experimental results. A generic mathematic model incorporating the fixed model, node model as well as dead volume model was developed to implement a numerical simulation of an industrial-scale p -xylene simulated moving bed process. Moreover, the accuracy of mathematic model was validated by industrial data. Furthermore, a dynamic optimization framework, with state of the art Sequential Quadratic programming optimization algorithm, was firstly proposed to obtain the optimal operating conditions for an existing industrial simulated moving bed unit. Optimization results reflect that the desorbent consumption of p -diethylbenzene was favorable to be selected as objective function to be minimized, which could achieve 3.12% increase in SMB unit productivity and 8.66% decrease in desorbent consumption for seven zone p -xylene simulated moving bed process. Two-level optimization procedure was also constructed to get the maximum feed throughput with a desired minimized desorbent consumption. Under the optimal operating conditions, the productivity increases by 16.63% while the PDEB consumption decreases by 18.85% for seven zone p -xylene simulated moving bed process. Eight zone p -xylene simulated moving bed process as a new operating mode, which was also analyzed, emulated and optimized through numerical calculation. Results show that the eight zone operation could achieve a much higher productivity and the desorbent consumption of p -diethylbenzene was almost the same in comparison with seven zone operation.