PREPARATION OF ULTRA-PURE SUCCINONITRILE BY COUNTERCURRENT DISTILLATION FOR CRYSTAL-GROWTH

We developed the purification method to produce ultra-pure succinonitr ile by multiple countercurrent distillations. The distillation column used was 25mm in diameter and 110 cm in the packed height with Heli-Pa k(R) packing (0.05 '' x 0.10 '' x 0.10 '', packing factor + 960). Typi cal operational conditions of each stage are as follows: condenser tem perature 65 degrees C, reboiler temperature 160 degrees C, head pressu re 50 m Torr or below, and reflux ratio of 60:1.As the number of disti llation stages increases, the maximum temperature of the freezing curv e increases and the freezing curves became flat. Triple point of our s ample, which is obtained after eight distillation stages, is not appre ciably different from that of a standard NIST specimen. The purity of the SCN prepared in our experiments is estimated at 99.99992% which co rresponds 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 rat e 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 suc cinonitrile at a rate about 1500 g within a week in our distillation c olumn, which is much more faster compared to that obtained by zone ref ining. 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.