Separation of p-xylene from xylene isomer mixtures within a single stage porous batch cooling crystallizer

Abstract

Crystallization based separation of p-xylene from its isomer mixtures were mostly accomplished in stirring crystallizers, suspension crystallizer and scrapping crystallizer followed by centrifugation. In this work, separation process for p-xylene, where both crystallization and separation of p-xylene in a single batch crystallizer, was performed. Upon cooling, p-xylene, which has the higher melting point than other xylene isomers (o-xylene and m-xylene), crystallizes first. Xylene mixture samples were crystallized at a lower temperature, in a batch cooling crystallizer filled with porous structure made of thin steel wires. Dimethylformamide (DMF, an immiscible solvent with xylene) used as a wash solvent for separation of p-xylene crystals from the mother liquor. The formed p-xylene crystals were seized within porous structure during the wash. DMF which forms single phase with xylene mixture was separated by the addition of water. During the experiments, for a feed xylene mixture sample (80% p-xylene), process parameters such as crystallization time, volume of washing solvent for separation process were tested. The samples at various stages obtained were analyzed using FT-IR and GC-FID. The yield of p-xylene recovered in this process was measured and the results are discussed.