The vacuum distillation process in the Kroll process has been developed to remove residual chlorine from titanium sponge. Despite the efforts to improve the productivity of the process, it takes more than a couple of days to produce desirable quality of the titanium sponge in a commercial scale operation. Though it is important to understand the nature of this process, it is quite difficult because of the complexity of non-linearity in heat transfer and vaporization.The temperature inside the titanium sponge during the distillation process was successfully measured. It revealed that there are two temperature stagnant periods which correspond to the vaporization of Mg and MgCl2, respectively. It was also found that the penetration of the heat to the center of the sponge cake is a very slow process and that it takes more than 30hours.A mathematical model to describe the heat transfer and vaporization kinetic has been developed. The model can regenerate the temperature measurement data successfully. The model calculation results show that topochemical vaporization of Mg and MgCl2 and that the vaporization rate is mainly controlled by the heat transfer in the titanium sponge. The effect of the operation parameters on the process performance was investigated using the model calculation. It indicates that the reduction in the amount of residual Mg and MgCl2 would be effective to reduce the distillation processing time.

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