CRYSTAL-GROWTH OF THIOUREA ADDUCTS WITH CYCLOHEXANE-METHYLCYCLOPENTANE MIXTURE

The growth kinetics of thiourea adducts formed with the guests of cycl ohexane and methylcyclopentane (MCP) mixtures by adductive crystalliza tion were studied in a batch cooling crystallizer. The effects of the guest concentration on the growth rate and the dissolution rate of add ucts were investigated. The growth rate of true crystal (thiourea) and the inclusion rate of guests were also investigated and compared. The method used to evaluate the crystal growth kinetics from the integral mode batch experiments performed in a cooling crystallizer required t he determination of the first two initial derivatives of supersaturati on and temperature according to time. The orders of the growth for thi ourea adducts with respect to supersaturation were found to be 0.87, 0 .86 and 0.84, and the activation energies of thiourea adducts were det ermined as about 75.3, 68.3 and 60.7 kJ/mol for cyclohexane-thiourea a dduct, cyclohexane-MCP-thiourea adduct, and MCP-thiourea adduct, respe ctively. Furthermore, studies on the composition profile for guest and host in the solution suggest that thiourea adduction is controlled by the integration of thiourea molecules and not by the diffusion of the guest molecules.