C. W. Nofsinger Company has recently annotmced that it will license (in North America) a new crystallization process developed by Tsukishima Kikai Company (TSK). This process is claimed to recover ultrahigh purity para-xylene from mixed xylenes. It is a countercurrent cooling crystallization (CCCC) process; the crystalline slurry and the mother liquor flow countercurrently to each other. This process uses multistage crystallizers followed by a purification column in which para-xylene is collected as a melt.
In this Review, SRI examines the economics of the TSK process coupled with isomerization and rerun sections. We also determine, on the same basis, its competitive economic position relative to the existing Parex� process developed by UOP.
The integrated CCCC process has a higher utility cost than does the Parex�/Isomar� process previously evaluated in PEP Reports 25B1 and 182. We conclude that this new process, although more economical than the conventional crystallization routes, has not yet overcome the inherent disadvantage of crystallization. The eutectic mixture that is formed limits the recovery of para-xylene to 65% and thus necessitates a large recycle.
