Patent GB-867848-A (GB)
Title: Improvements in or relating to the concentration of deuterium
IPC: C01B4/00
Filed: 1958-03-10
Abstract: A process of concentrating D by isotopic exchange between two immiscible molecular species each containing H comprises passing a stream of the first species, from which D is to <PICT:0867848/III/1> <PICT:0867848/III/2> be extracted, through only the first of a system of three towers in countercurrent to the second species, circulating the second species also through the second and third towers operating at different temperatures and constituting a dual temperature isotopic exchange system, and circulatitng as a countercurrent through the second and third towers a further stream of the first species.  When the species, from which the D is to be extracted, contains a smaller, or larger, atomic concentration of D the first tower is at the same temperature as the cooler or hotter respectively of the dual temperature towers.  The process may be used for exchanging D between H2 and H2O, NH3, H2S or mercaptan, or between H2S and NH3 or H2O.  In the latter case the H2O may contain alcohol, acetone, or glycol.  For exchange between H2 and liquid NH3 the first two columns may be at -40 DEG  to -25 DEG C., while the third column may be at 80-110 DEG C., and the NH3 may contain 0.1-1% potassium amide catalyst.  The specific example refers to pressures of 250 and 255 atmospheres.  NH3 synthesis gas (N2 + H2) is cooled in heat-exchanger 11 and cooler 12, scrubbed in first tower 13 with liquid NH3, and withdrawn through 11.  The NH3 from the bottom of 13 is passed to the top of cold tower 14 whence it is withdrawn through heat-exchanger 17 and expansion valve to gas separator 18 from which separated gas is compressed in 19 and returned to the feed to tower 13.  The liquid NH3 enters evaporator 20, whence half is evaporated, and the remaining liquid is transferred through pump 22, compressor 23, heat-exchanger 24, and steam heater 25 to hot tower 15.  The NH3 from 15 is returned through pump 26, heat-exchangers 24, 17, and cooler 28 to cold tower 14.  Synthesis gas from cold tower 14 is heated in heat-exchangers 29, 30, circulation compressor 16, heat-exchanger 34 and steam heater 32 before entering hot tower 15. The gas passes through bath of NH3 heated by steam coils 33, leaves the top of tower 15, and is cooled before re-entering tower 14 by passage through heat-exchangers 31, 35, 30, evaporator 20, heat-exchanger 29 and cooler 41, each having associated separators 34, 36, 37, 39, 40, 42 from which separated liquid NH3 is returned to the feed to tower 15.  The enriched NH3 evaporated from 20 is fed to the first column 21 of a distillation system containing nine columns 21, and 44-51.  Vapour from the top of column 21 is compressed in 52 and used as the heating medium for reboilers 53-57 and liquid NH3 collecting in the reboilers is pumped through a common main to the top of column 21 or to the dual temperature columns at compressor 23 as lean return.  Part of the liquid leaving 21 is evaporated in reboiler 53 and returned and part is passed as reflux into column 44, whence overhead is returned to column 21 through compressor 61. Columns 45, 46 are arranged in the same way as columns 21 and 44. Columns 21, 44-49 operate on cascade, but 47-49 are not relatively reduced in diameter and operate on the same reflux rate.  The small amount of remaining liquid from column 49 is mixed with H2O and passed into column 50 where NH3 and H2O are separated after establishment of isotopic exchange equilibrium.  NH3 from the top of column 50 is compressed in 66, condensed in 67 and part returned as reflux to 50 and part to column 49.  The D-enriched water from column 50 is transferred to column 51 and separated into heavy water product and a reject fraction which is returned to the feed to 50.  The enriched NH3 may be subjected to further dual temperature enrichment. Specification 803,274 is referred to.