On the application of chiral amplification via adsorption

Abstract

Chiral amplification is a known phenomenon in crystallization. Recent atomistic simulations have shown that amplification can also occur in equilibrium processes when a mixtures of chiral molecules adsorb in metal-substituted zeolites that are not chiral by themselves. In this article we investigate how this process could be exploited for enantiopurification and separation in a pressure-swing adsorption process. For this purpose, we develop a mathematical model that reproduces the main features of the full-atom simulations and allows us to study the impact of several parameters on the enantioselectivity on a macroscopic scale. Besides numerical solutions of this model, we provide some analytic results which suggests that the enantioselective materials prohibit a phase transition as a function of temperature. Below a certain critical temperature, the enantiomeric content of the adsorbed phase becomes a discontinuous function of the enantiomeric gas content. This has the following consequences: (i) the adsorbed phase in racemic conditions becomes unstable, (ii) a sudden increase in efficiency of the purification process, and (iii) the possibility to not only purify but also fully separate chiral mixtures using a parallel batch process in which both lines use an input that is enriched with opposite enantiomer.