Separation of m-xylene from the mixed xylenes by distillative freezing

Xylenes have very broad applications in chemical industries. The mixed xylenes produced mainly consist of p-xylene (PX), m-xylene (MX), o-xylene (OX), and ethylbenzene (EB). Due to their similar molecular structures, these isomers have close boiling points, making them difficult to separate from each other by distillation. A new separation technique, called distillative freezing (DF), was applied to separate PX from a liquid mixture of 10% MX and 90% PX. In principle, the DF process is operated at a triple point condition, in which the liquid mixture is simultaneously vaporized and crystallized due to the three-phase equilibrium. Thus, DF is a distillative crystallization technology, which combines distillation and crystallization to produce pure crystals. DF was applied to separate and produce MX crystals from the mixed xylene mixtures containing MX, PX, OX, and EB. When the DF experiments are performed based on the simulated adiabatic DF operation, MX crystals can be produced and the purity of MX crystals can reach 99∼99.5% for the mixed xylene mixtures of MX, PX, OX, and EB. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).