Zone Melting of Benzene Containing Iodine

Abstract

The low-temperature zone melting method was applied to the separation of iodine from benzene in order to investigate the similarity between multipass zone melting and fractional distillation. The experimental conditions were as follows: the initial concentration of the iodine was 0.5 mass%; zone travel rate was 0.91 cm/h; the number of zone passes were 1, 5, and 40 and the temperatures of the molten zone and the ambient air were 13°C and -10°C, respectively.
The respective values of the effective distribution coefficients of iodine obtained from the results after 1 and 40 zone passes were 0.53 and 0.55. On the other hand, the equilibrium distribution coefficient determined from the freezing points of dilute solutions of iodine in benzene was found to be 0.25.
After 40 zone passes the concentration of iodine near the top of the specimen was reduced to 1.11 × 10^-4 mass%. The iodine distribution in the column after 40 zone passes was found to correspond to tha t after the fractional distillation of 14 stages, which was in agreement with the value estimated by the Pfann's theory. Moreover, the concept of the number of theoretical stages in the zone melting was represented by the xs(solid) -y1(liquid) diagram which resembles the xi (liquid) -yv( v apor) diagram in the fractional distillation. From these results the analogy between multipass zone melting and fractional distillation was explained in view of the phase equilibrium.