Preparation of ultra-pure succinonitrile by countercurrent distillation for crystal growth

Abstract

We developed the purification method to produce ultra-pure succinonitrile by multiple countercurrent distillations. The distillation column used was 25mm in diameter and 110 cm in the packed height with Heli-Pak(R) packing (0.05 " x 0.10 " x 0.10 ", packing factor + 960). Typical operational conditions of each stage are as follows: condenser temperature 65 degrees C, reboiler temperature 160 degrees C, head pressure 50 m Torr or below, and reflux ratio of 60:1. As the number of distillation stages increases, the maximum temperature of the freezing curve increases and the freezing curves became flat. Triple point of our sample, which is obtained after eight distillation stages, is not appreciably different from that of a standard NIST specimen. The purity of the SCN prepared in our experiments is estimated at 99.99992% which corresponds to a melting range (T-1-T-s) of 1.2 mK. To ensure the purity of our purified SCN for the purpose of crystal growth, the growth rate and the tip radius of dendrite were measured at various supercooling. It was found that there was no discrepancy in data between ours and Glicksman's within measurement errors. We could prepare ultra-pure succinonitrile at a rate about 1500 g within a week in our distillation column, which is much more faster compared to that obtained by zone refining. Furthermore, since the scale-up method of distillation unit is well developed, it is possible that a much larger amount of ultra pure SCN can be produced in a short time.