Exchange of deuterium between gaseous hydrogen and a liquid compound of hydrogen

摘要

PICT:0748991/IV(a)/1 The exchange of the deuterium isotope of hydrogen between gaseous hydrogen and a liquid compound of hydrogen, e.g. water, methanol or cyclohexane, is effected by associating vapour of the liquid with the hydrogen by passing hydrogen in intimate contact with the liquid, passing the mixture over a catalyst for the exchange, and condensing the vapour, the exchange being conducted at a temperature below the boiling point of the liquid at the pressure employed. Depending on whether the hydrogen or the liquid contains deuterium at a concentration in excess of that which it would contain when the liquid vapour-hydrogen system is in isotopic equilibrium, the exchange may be from hydrogen to vapour or vice versa. Catalysts are noble metals of the platinum group, e.g. platinum, palladium, or rhodium, heavy metals, e.g. nickel, zinc, cadmium, copper or cobalt, which may be distributed on porous supports, e.g. platinum on activated carbon, or alumina, or silica gel, or nickel on kieselguhr, chromic, cerium, or thorium oxides, pumice, or alumina. Heavy metal chromites, e.g. of zinc, copper, cadmium, or nickel are also suitable catalysts. Preparations of several catalysts are described in Examples 1-9. Hydrogen is fed by pipe 18 into saturator 10 fed with liquid water from 16 to maintain level 22. The hydrogen bubbles through the water in the saturator, which is packed with glass beads, and the resulting hydrogen-water vapour mixture, which may be in the volume ratio 10:1 to 0.5:1, passes to catalyst chamber 12 containing catalyst 26 between glass wool plugs 28. The vapour mixture then passes to condenser 32 and condensed water is collected in 34 while hydrogen is withdrawn at 36. The process may be carried out at superatmospheric pressure and space velocities of 1000-100,000 are referred to. The saturator 10 and catalyst chamber are enclosed in vapour bath 14 to maintain constant temperature, e.g. benzene at 80 DEG C. Sulphur-containing gases and carbon monoxide should be removed from the reactants to prevent catalyst poisoning. In Fig. 2 (not shown) the saturator and catalyst chamber are enclosed in separate vapour baths and, to prevent deposition of liquid water on the catalyst, the vapour mixture is heated by a coil between the two. Alternatively the catalyst may be heated to a higher temperature than the vapour mixture. Fig. 3 (not shown) discloses a continuous process wherein a number of single exchange units of the above type are connected in a single stage and water is fed from a tank successively through the saturators. Hydrogen enriched with deuterium is fed in overall countercurrent flow to the water successively into the separators and the hydrogen-water vapour mixture is passed from each saturator through a heater and catalyst chamber to the preceding saturator, so that the water in each succeeding saturator becomes enriched with deuterium by exchange with the water vapour in the vapour mixture passing from the next saturator. Impoverished hydrogen is withdrawn from one end and enriched water from the other, part of which may be electrolysed to provide the enriched hydrogen required, while the remainder may be passed to a second stage operating the same as the first and so on. More than one saturator may be provided for each catalyst chamber. Examples 1-10 disclose suitable catalysts and conditions for deuterium exchange between hydrogen and water and Example 11 relates to deuterium exchange between hydrogen and methanol at 56 DEG C. and atmospheric pressure. Deuterium exchange between hydrogen and cyclohexane may be effected at 150 DEG C. and 27 atmospheres and from the cyclohexane hydrogen enriched with deuterium is recovered by decomposition by heat to benzene which is hydrogenated to cyclohexane and reused.ALSO:PICT:0748991/III/1 The exchange of the deuterium isotope of hydrogen between gaseous hydrogen and a liquid compound of hydrogen, e.g. water, methanol or cyclohexane, is effected by associating vapour of the liquid with the hydrogen by passing hydrogen in intimate contact with the liquid, passing the mixture over a catalyst for the exchange, and condensing the vapour, the exchange being conducted at a temperature below the boiling point of the liquid at the pressure employed. Depending on whether the hydrogen or the liquid contains deuterium at a concentration in excess of that which it would contain when the liquid vapour-hydrogen system is in isotopic equilibrium, the exchange may be from hydrogen to vapour or vice versa. Catalysts are noble metals of the platinum group, e.g. platinum, palladium, or rhodium, heavy metals, e.g. nickel, zinc, cadmium, copper, or cobalt, which may be distributed on porous supports, e.g. platinum on activated carbon, or alumnia, or silica gel, or nickel on kieselguhr, chromic, cerium, or thorium oxides, pumice, or alumina. Heavy metal chromites, e.g. of zinc, copper, cadmium, or nickel are also suitable catalysts. Hydrogen is fed by pipe 18 into saturator 10 fed with liquid water from 16 to maintain level 22. The hydrogen bubbles through the water in the saturator, which is packed with glass beads, and the resulting hydrogen-water vapour mixture, which may be in the volumn ratio 10 : 1 to 0.5 : 1, passes to catalyst chamber 12 containing catalyst 26 between glass wool plugs 28. The vapour mixture then passes to condenser 32 and condensed water is collected in 34 while hydrogen is withdrawn at 36. The process may be carried out at superatmospheric pressure and space velocities of 1,000-100,000 are referred to. The saturator 10 and catalyst chamber are enclosed in vapour bath 14 to maintain constant temperature, e.g. benzene at 80 DEG C. Sulphur-containing gases and carbon monoxide should be removed from the reactants to prevent catalyst poisoning. In Fig. 2 (not shown) the saturator and catalyst chamber are enclosed in separate vapour baths and, to prevent deposition of liquid water on the catalyst, the vapour mixture is heated by a coil between the two. Alternatively the catalyst may be heated to a higher temperature than the vapour mixture. Fig. 3 (not shown) discloses a continued process wherein a number of single exchange units of the above type are connected in a single stage and water is fed from a tank successively through the saturators. Hydrogen enriched with deuterium is fed in overall countercurrent flow to the water successively into the separators and the hydrogen-water vapour mixture is passed from each saturator through a heater and catalyst chamber to the preceding saturator, so that the water in each succeeding saturator becomes enriched with deuterium by exchange with the water vapour in the vapour mixture passing from the next saturator. Impoverished hydrogen is withdrawn from one end and enriched water from the other, part of which may be electrolysed to provide the enriched hydrogen required, while the remainder may be passed to a second stage operating the same as the first and so on. More than one saturator may be provided for each catalyst chamber. Examples 1-10 disclose suitable catalysts and conditions for deuterium exchange between hydrogen and water and Example 11 relates to deuterium exchange between hydrogen and methanol at 56 DEG C. and atmospheric pressure. Deuterium exchange between hydrogen and cyclohexane may be effected at 150 DEG C and 27 atmospheres, and from the cyclohexane hydrogen enriched with deuterium is recovered by decomposition by heat to benzene which is hydrogenated to cyclohexane and reused. Catalysts: In the examples: (1) activated coconut charcoal is impregnated with platinum deposited from platinic chloride solution by boiling; (5) activated alumina is impregnated with platinic chloride soluton, reduced in hydrogen, treated with sodium formate, and finally heated on a water bath; (7) a mixture of nickel and chromium nitrates in solution is treated with ammonium carbonate and the precipitate of mixed carbonates is washed, dried, and reduced in hydrogen at 350 DEG C. to form a nickel-chromium catalyst. Other catalysts referred to are palladium on activated coconut charcoal (6) and nickel on a ceria support (8).