Effective Energy-Conserving Separation Technology---Distillative Freezing Process(I)

Separation and purification step in a chemical manufacturing process is generally very energy-consuming and, in the production of high purity chemicals, often dictate the overall economic feasibility of a process. Cheng and his coworkers1-8 introduced a new separation technique, called distillative freezing (DF), to separate the mixture of the volatile compounds. The DF process is operated at triple point condition, in which the liquid mixture is simultaneously vaporized and solidified due to the three-phase equilibrium. It results in the formation of pure solid, and liquid phase and vapor phase of mixtures. The process is continued until the liquid phase is completely eliminated and only the pure solid crystals remain in the feed. The low-pressure vapor formed in the process is condensed and removed. 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). These isomers are separated by solvent extraction, distillation and fractional crystallization. Due to the structure similarities and the close boiling temperatures among these isomers, it is very costly to separate and purify theses isomers. The objective of this research is to investigate the feasibility of the DF process in separating a mixture to produce PX with purity greater 99.0%.

Project ID:PB9501-0160
External Project ID:NSC95-2623-7182-003-ET