Optimization of a Six-Zone Simulated-Moving-Bed Chromatographic Process

Abstract

Using strong cation-exchange simulated-moving-bed (SMB) chromatography, a nitrogen−phosphate−potassium (NPK) fertilizer is produced in a cost-effective manner. The SMB process, operated in a nontraditional way, is divided into production and regeneration sections, for exclusion of undesirable ions, and is composed of six zones, including two wash-water zones. This paper addresses modeling, simulation, and optimization studies on this ion-exchange SMB process, based on experimental data obtained both from a pilot plant and an industrial plant. Model parameters that are initialized by empirical equations are identified, comparing the simulation results with the experimental data. Through sensitivity analysis of the model parameters, their effects on the process performance are examined. The simulation results show good agreement with in situ experimental data obtained in both the pilot- and industrial-scale plants. The objectives of this study are to optimize the SMB process in terms of (i) maximization of productivity in the production section and (ii) minimization of wash-water consumption, thereby resulting in (i) an increase in profit and (ii) a reduction in the overall operating cost in the downstream processing, respectively. The two objectives are sequentially treated within the framework of a multilevel optimization procedure (MLOP), which includes two pre-optimization levels, a productivity maximization level, and a desorbent (or wash-water) consumption minimization level. In this optimization study, it is demonstrated that wash-water consumption can be reduced by 5% at a 5% higher productivity.