GB765357A - Improvements in or relating to cyclic process for producing and recovering ammonia and hydrogen chloride from ammonium chloride - Google Patents

Abstract

In a cyclic process for producing ammonia and hydrochloric acid from ammonium chloride by adding ammonium chloride to a melt of a bisulphate in a mixing zone, successively circulating the melt through hydrochloric acid and ammonia stripping zones, recovering hydrochloric acid and ammonia respectively from the vapour stream from the hydrochloric acid and ammonia stripping zones, and returning the stripped melt to the mixing zone, a small amount of phosphoric acid or a soluble inorganic phosphate is added to the circulating melt to precipitate metal impurities, e.g. iron, as phosphate. The concentration of phosphate ion in the melt should be maintained at 0.1 - 10 per cent. and the phosphate or acid may be added intermittently or continuously at any point in the cycle. The preciptated phosphates may be separated by filtering or settling from a sidestream of melt, which is then returned to the cycle. The process and apparatus described are those of Specification 716,754, wherein ammonium chloride is mixed with an alkali metal or ammonium bisulphate melt in amount 0.15-0.75 moles per mole, and the melt is circulated through a hydrogen chloride stripper at 220-270 DEG C., and then through an ammonia stripper at 330-380 DEG C. Suitable phosphates are ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydogen phosphate, and sodium pyrophosphate. Reference is also made to the addition of thermally stable fluid organic media, e.g. trichlorobenzene, for heat transfer, to the melt and to the addition of the ammonium chloride to the melt by slurrying the salt in such a medium.