(178f) General Design and Splitting Strategies for Non-Ideal Displacement Chromatography for the Separation of Complex Mixtures

Displacement chromatography has wide potential applications for the separation and purification of metal ions, chemicals, biochemicals, and pharmaceuticals. Displacement chromatography in the constant-pattern state can simultaneously concentrate and separate mixtures, leading to higher sorbent productivity, higher product concentration, and lower solvent usage than elution chromatography. Applications of displacement chromatography at commercial scales, however, are few because of two major barriers. The yields of high-purity products are poor if the design variables are inappropriate for the feed composition or the material properties; the loading fraction, the displacer concentration, and the linear velocity to reach the constant pattern state depend on the specific feed composition and the adsorption/mass transfer properties of the adsorbent, the displacer, the presaturant, or the solutes in the feed mixture. Optimization of such systems is even more challenging; optimal separation of a ternary mixture would already involve 20 parameters. A trial and error approach for design and optimization is impractical, and this challenge is the first barrier. Furthermore, if both a minority component and a majority component in a complex mixture need to be recovered as pure products with high yields, sorbent productivity is significantly reduced. This limitation is the second barrier.

In this study, a constant-pattern design and optimization method was developed to overcome the first barrier. Theoretical analysis and strategic combinations of dimensionless groups were developed to reduce the multi-dimensional parameter space into two dimensions. Systematic rate model simulations were used to find the general boundary between the transient region and the constant pattern region. The design and optimization method based on the boundary can be used to find the loading and operating parameters to achieve high yields of high purity products without any trial and error. To overcome the second barrier, general splitting strategies for various separation goals were developed for complex mixtures. Examples for rare earth purification showed that by dividing the separation tasks in multiple zones, sorbent productivities were increased by two or three orders of magnitude compared to those of single-column designs.