Method of recovering acid values from dilute streams and improved alkylene oxide process using same

摘要

It has been found practical to upgrade streams containing relatively small concentrations (about 1 to 3 weight percent) of hydrochloric acid or other strong mineral acid by multi-stage electrodialysis. This discovery has remarkable implications for the whole chemical industry, particularly in view of the increasing importance of ecological considerations. Moreover, it has further been discovered that, at least in some instances, such multi-stage electrodialysis is applicable even to streams containing small amounts of organic impurities that might be expected to foul the membranes of the electrodialytic cells. One such stream is the output of the chlorinator in the production of propylene oxide from propylene via propylene chlorohydrin, a process of substantial importance in the chemical industry and one that in its form before the instant invention has been particularly beset with ecological problems. Electrodialysis of the chlorinator output yields dilute hydrochloric acid which may be upgraded by subsequent distillation and a saponifier-input stream that can be saponified with little more than half of the caustic or lime previously required. With the instant invention, the aforementioned problems are very largely overcome, and similar benefits are to be expected from the use of the instant invention in its broader aspects to upgrade various other chemical processes that yield waste streams of dilute, strongly ionized acids.