Comparison of maximum production rates and optimum operating/design parameters in overloaded elution and displacement...

The results of a study of the optimization of the experimental conditions for maximum production rate in overloaded elution and displacement chromatography are discussed. This study is based on the use of the equilibrium-dispersive model of chromatography and the competitive Langmuir isotherms to calculate individual band profiles in the elution and displacement modes, and of a simplex algorithm to optimize the production rate. The operating parameters (sample size, mobile phase velocity, and the displacer concentration in the displacement model) and the column design parameters (column length and average particle diameter) are optimized simultaneously. Binary mixtures having relative concentrations 3:1 and 1:3, and separation factors of 1.2 to 1.8 are investigated. One of our major results is that, in both modes of chromatography, the maximum production rate is achieved at very low values of the retention factors, k', much lower than those used in current practice. In all cases, unless k' exceeds greatly that optimum value, the production rate is higher in overloaded elution than in displacement chromatography. This is particularly true for the extraction of a minor component, which is eluted second.