Effects of different seedings on the crystallization of M-and p-CNB

Abstract

Crystallization has been used for the separation of chloronitrobenzenes (CNBs), which are isomeric substances (0-, m-, and p-CNB) and important intermediates in chemical production. Effects of seeding including m-CNB, p-CNB, and KY zeolite were reported. In the experiments, a liquid mixture of m- and p-CNB was cooled to its crystallization temperature, and the precipitate composition was analyzed by gas chromatography. The result showed that after adding different particle sizes of m- and p-CNB seeds, 20/40 and 12/14 mesh, into the crystallizer, the precipitates below the eutectic compositions are rich in p-CNB and above the eutectic compositions are rich in m-CNB. The eutectic composition changed from 62.90 to 65.0 wt% p-CNB. There was no significant change in the phase diagram for the different m- and p-CNB particle sizes. However, the crystallization temperature was shifted from higher to lower due to the presence of foreign particles may induce the nucleation step, which, in turn, changed the metastable zone.