Separation of Nonaromatic C6 Compounds from Naphtha Cracking Raffinate by Adductive Crystallization

The separation of the nonaromatic raffinate found in naphtha crackers was studied using adductive crystallization with thiourea. Experimental results of the separation of cyclohexane from nonaromatic raffinate and on the separation capacity of three binary mixtures—methyl cyclopentane (MCP)-cyclobexane, MCP-n-hexane and cyclohexane-n-hexane—are presented in this study. Structure, habit and shape of adduct crystals were investigated to examine the adduction mechanism by SEM and X-ray diffraction. Separation factors as high as 92 and extent of separation up to 0.78 were observed for one adduction stage, and the separation by one stage is approximately 5.6 to 19.2 times greater than the maximum separation that could be obtained by one theoretical distillation stage. The tendency for adduction in thiourea was found to be cyclohexane > MCP >> n-hexane. Cyclohexane of a purity of 99.9 wt.% was obtained by 4-stage adductions from nonaromatic raffinate.