Effect of surface scraping on chiral symmetry in seeded cooling crystallization of sodium chlorate

Abstract

We report, for the first time, that the number of nuclei with opposite handedness to seed is directly related to the amount of scraping generated between baffle edge and wall surface in an oscillatory baffled crystalliser (OBC) and reaches an asymptotical maximum of 43.4%, when primary nucleation events due to scraping dominate over secondary nucleation by seeding in a daylong operation. The 6.6% shortfall to the theoretical symmetry of 50% : 50% of dextrorotatory to laevorotatory crystals could be a quantitative indication of the remaining effect of secondary nucleation. We examine the effect of scraping durations at a fixed seeding time and the effect of seeding times at a fixed oscillation period on chiral symmetry. Based on our experimental data, the rate of primary nucleation events due to scraping and the rate of secondary nucleation due to seeding are evaluated. We show that the relative importance of primary to secondary nucleation in seeded cooling crystallisation of sodium chlorate can be varied by the amount of scrapping in the OBC.