(601e) Analysis of the Dynamic Phenomena in Liquid Chromatography Systems With Reactions in the Mobile Phase

Reactions in liquid chromatography systems have many important applications. One can estimate the reaction rate constants for irreversible reactions, or the reaction stoichiometry and equilibrium constants for reversible reactions. For large-scale production using a reversible reaction, if the products are well separated from each other in a chromatography column, one can obtain purified products and achieve a higher conversion than the equilibrium conversion in a batch reactor. Additives (ligands or complexants) can be added to the mobile phase to enhance solute separation if a sorbent does not have sufficient selectivity for the solutes. Proteins and polymers can aggregate in chromatography systems and result in either multiple peaks or merged broad peaks in elution chromatography or multiple breakthroughs and plateaus in capture chromatography. The number of peaks, peak retention times, and the relative peak areas in elution and the number of plateaus in capture may depend on sample concentration, sample size, temperature, linear velocity, and column length.  In this study, the adsorption/separation dynamic phenomena of six typical reactions are analyzed using dimensionless groups and rate model simulations.

The results provide overall guidelines for understanding, design, and optimization of chromatography systems with reactions. One can design experiments to find out whether reactions occur, whether the reactions are reversible or irreversible, and whether the reactions are first order or higher order. One can also determine the rate constants of an irreversible reaction from the peak areas as a function of the residence time. One can find the equilibrium constants and reaction stoichiometry from the peak ratios at different sample concentrations. For large scale production using a chromatography reactor, a reversible reaction can reach 100% conversion if the reaction rate is relatively large compared to the convection rate, and if the loading pulse size is sufficiently small to ensure the separation of  the product bands. High purity products can be obtained if the  diffusion rate is large and the axial dispersion rate is small relative to the convection rate. For reversibly aggregating systems, if the reactions reach equilibrium, one can separate the various aggregates by increasing the convection rate relative to the reaction rates. This separation can be achieved by increasing the sample concentration or the linear velocity of the mobile phase, or by reducing the temperature or the column length.  One can merge multiple plateaus and increase the dynamic binding capacity in capture chromatography by increasing the reaction rate relative to the convection rate. For ligand-assisted separation, if the ligand concentration is sufficiently large and if the complexed solutes do not adsorb, then the overall selectivity is the ratio of the sorbent selectivity to the ligand selectivity, leading to a separation even if the sorbent has no selectivity. The sorbent selectivity should be opposite to that of the complexant selectivity to have synergistic effects on separation.