GB807803A - Improvements in or relating to a method of extracting deuterium from hydrogen-containing gases - Google Patents

Abstract

Deuterium is extracted from hydrogen-containing gases by subjecting the gases to a countercurrent catalytic exchange with liquid ammonia to transfer the major part of the deuterium content to the ammonia, distilling the deuterium enriched ammonia into two fractions and withdrawing the fraction having the higher deuterium content. A catalyst, which may be dissolved in liquid ammonia, may be used, e.g. potassium amide. The catalyst may be formed in situ by using a solution of an alkali metal in liquid ammonia, which solution also contains a salt of a metal, such as iron or titanium, capable of existing in more than one state of oxidation, e.g. ferric sulphate. Alternatively, a solid catalyst, e.g. chromium, platinum, nickel, palladium or vanadium, which may be on a carrier may be used. Ammonia may be evaporated into the gas before exchange. As described, ammonia synthesis gas (N2 + H2) is passed through a converter containing a nickel catalyst to convert CO and CO2 to CH4. The purified gas, after heat exchange with effluent gases, is passed through an ammonia producer where 10 per cent of the gases are converted to NH3, which, after cooling, is condensed and separated. The remaining gases are passed to the base of a first catalytic exchange tower where they are scrubbed with liquid NH3 containing KNH2. The ammonia condensed from the gases is passed to the upper part of the tower. The gases pass from the scrubber to the ammonia plant. The deuterium-enriched NH3 from the first exchange tower passes to a second catalytic exchange tower where it is used to scrub N2 + H2 gases produced by decomposing part of the liquid NH3 leaving the second tower. Residual gases from the second tower are passed back to the base of the first tower. The remaining liquid NH3 from the second tower is reduced to atmospheric pressure and the KNH2 is recovered for return to the first tower feed. The liquid NH3 passes to the distillation column whence NH3 of the same isotopic ratio as that supplied to the scrubber is recovered above and deuterium-enriched liquid ammonia is recovered below. The distillation column is below ambient temperature and is provided with a separate vapour recompression system equipped with two indirect heat exchangers to provide partial condensation of the top fraction for reflux, and partial boil up of the bottom fraction. The deuterium-rich fraction may be burned to form heavy water.