GB800730A - Process for enrichment of water in deuterium oxide - Google Patents

Abstract

Water is enriched in deuterium by contacting water and hydrogen in the presence of a supported catalyst. The catalyst is nickel, cobalt, iron, ruthenium, rhodium, palladium, osmium, iridium, platinum, molybdenum, tungsten, or rhenium, or a sulphide of rhenium, molybdenum or tungsten supported on a carbon or refractory oxide base. The catalyst metal or compound may be deposited in amount 0.05-9 per cent on the carrier, e.g. activated carbon, charcoal, or alumina, and may be converted to granules or pellets. Various specific catalysts are: molybdenum or tungsten sulphide on a support, nickel on Cr2O3 (chromia), palladium on carbon or alumina, platinum on carbon, silica, or activated alumina, ruthenium or osmium on carbon, nickel, cobalt, or iron on kieselguhr, and rhenium sulphide (Re2S7) on charcoal. The exchange may be effected at 0-100 DEG C. and up to 500 atms., but preferred conditions are 25-100 DEG C. and atmospheric to 300 atms. pressure. Various apparatus (Figs. 1-4, not shown) are described. In the first apparatus liquid water and H2 are contacted in countercurrent in a single catalyst tower, and part of the enriched water is withdrawn as product, while the remainder is converted to H2 in an electrolytic cell, a water gas-coke reaction, or a methane-water catalytic reaction, and is returned to the tower. In a second apparatus liquid water or water vapour and H2 are contacted in concurrent in a single catalyst tower and the enriched water is withdrawn as product; the use of water vapour requires the provision of a stripper for the mixture withdrawn from the tower. A cascade apparatus may be made up of a number of the above concurrent contact catalyst towers connected in series with liquid water entering each tower from the preceding tower and flowing thence to the succeeding tower, while H2 enters each tower from the succeeding tower and flows thence to the preceding tower; water leaving the last column of the cascade is part withdrawn as product and part converted to H2 and returned to the last tower. Alternatively, a cascade of concurrent contact catalyst towers may be provided for exchange between water vapour and H2, in which each tower has a stripper in the entrance and exit thereto. Each stripper is a bubble cap plate tower in which the mixture of H2 and water vapour flows countercurrent to a stream of water; the water fed to the stripper coming from the preceding stripper and flowing to the succeeding stripper, while the water from the last stripper is partly converted to H2, which is passed back through the last stripper, where it is saturated with water vapour, to the last catalyst tower, and thence through the next-to-last stripper, and next-to-last catalyst tower, and so on. Towers in cascades may be connected to other than their nearest neighbours. A number of cascades of decreasing size may be connected in series with part of the enriched water from one cascade passing to the succeeding cascade, and part being converted to H2 which, with the H2 from the succeeding cascade, is fed back to the cascade. An experimental apparatus (Figs. 13, 14, not shown) is described for con- or counter-current contact of water and H2 for evaluating the effectiveness of catalysts. Catalysts.-Nickel, iron or cobalt on kieselguhr catalysts are prepared by impregnating kieselguhr with a solution of the metal nitrate, precipitating the oxide with excess Na2CO3 solution, washing with distilled water, and reducing with H2 at 350-450 DEG C. Platinum catalysts are prepared by impregnating charcoal or activated alumina carrier with platinum chloride solution (hexachloroplatinic acid), precipitating platinum with sodium formate or hydrazine hydrochloride, washing with distilled water and drying. Nickel on Cr2O3 catalysts are prepared by precipitating nickel carbonate and chromium hydroxide from a solution of the two nitrates with Na2CO3 solution, washing the precipitate, drying at 105-120 DEG C., calcining at 350-400 DEG C., pelleting, if desired, and reducing in H2 at 250 DEG C. rising to 350-375 DEG C. These nickel catalysts may be stabilized against spontaneous oxidation by passing N2 into the catalyst, or impregnating the catalyst with water and allowing slow oxidation to take place while the water evaporates. The nickel catalyst may be regenerated by passing H2 over at 100 DEG C. Apparatus is also described (not shown) for static evaluation of the effectiveness of the catalysts without using flowing water. Molybdenum or tungsten sulphide catalyst is precipitated on a support by adding dilute HCl or H2SO7 to an aqueous solution of ammonium thiomolybdate or ammonium thiotungstate, washing the product, drying, and heating in H2 to 100-200 DEG C., when the final composition is between MOS2 and MOS3 or WS2 and WS3.ALSO:Platinum catalysts are prepared by impregnating a charcoal or activated alumina carrier with platinum chloride solution (hexa-chloroplatinic acid), precipitating platinum with sodium formate or hydrazine hydrochloride, washing with distilled water, and drying.