Patent GB-501287-A (GB)
Title: Process for the recovery of oxygen from gaseous mixtures
IPC: C01B13/02
Filed: 1937-08-23
Abstract: 501,287. Oxygen. WARNE, K. C., WOOLCOCK, J. W., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. Aug. 23, 1937, No. 23118. [Class 90] Oxygen is obtained from gas mixtures by the use, in association with at least one aqueous medium, of a complex cobaltous salt forming a relatively unstable peroxo compound, i.e. one that is decomposed to form the original cobaltous salt and free oxygen by the action of aqueous ammonia or other complex-forming radicle without increased temperature or pressure, the change from absorption to regeneration or vice versa being effected by a change in the concentration of ammonia or other complex-forming radicle in the aqueous medium and /or a change in the partial pressure of oxygen above the medium. Temperature variations may be used to assist the process, but appreciable oxidation to the cobaltic state must be avoided: the maximum temperature is about 35‹ C. To ensure that the reaction goes to completion in both directions, the complex cobaltous salt or the peroxo salt, or both, should be present mainly in the solid phase and should possess a low solubility in the aqueous medium or be made so by the addition of a salt having the same acid radicle as the complex cobaltous salt. Such addition also assists in preventing undesirable oxidation to the cobaltic state. The preferred salt is cobaltous hexammine perchlorate, with aqueous ammonia containing dissolved ammonium perchlorate as the aqueous medium. Excess ammonia or other complex-forming radicle in the aqueous medium prevents decomposition of the cobaltous salt or peroxo compound. Increase of the concentration of complexforming radicle in the aqueous medium for regeneration may be effected in any suitable manner, e.g. (1) by physical transfer of medium, using in the absorption stage one. relatively poor'in complex-forming radicle and replacing it in the regeneration stage by one relatively rich in such radicle. The presence of polyhydric alcohols, e.g. ethylene glycol, increases the rate of regeneration. If desired, the medium may contain a buffer for the complex radicle, which reduces the net change of concentration of the radicle when it is added to /or withdrawn from the medium. Suitable buffer compounds for ammonia are ammonium salts of weak acids, and bodies which form loose compounds with ammonia which are partly hydrolysed in aqueous solution. (2) A single aqueous medium may be used in which case ammonia or other complex-forming radicle may be added to or removed from the medium as a gas, or a hydrolysable ammonium salt may be present which, on hydrolysis, favoured by increase in temperature, forms an insoluble or unionized or volatile acid and free ammonia. Ammonium borate is such a soluble salt, or lithium metaborate octahydrate may be used with an ammonium salt of a strong acid, e.g. ammonium sulphate. At low temperatures, lithium metaborate is present in the solid phase and the ammonia concentration is low. On solution of the lithium salt, ammonium borate is formed and hydrolysed. (3) Salts which form ammonia or other complex-forming radicle on heating, or a basic ammonium salt of which the concentration in solution changes rapidly with temperature may also be used. If desired, a number of aqueous media may be used in both absorption and regeneration stages. According to an example, the aqueous medium consisted of a mixture of 61 pts. of cobaltous perchlorate hexahydrate with a solution containing 39 pts. ammonium perchlorate, 17À14 pts. ammonia and 400 pts. water. Cobaltous hexammine perchlorate was precipitated. The suspension was placed in vessel 1 and carbon dioxide-free air blown through pipe 3. The undissolved gases passed through pipe 4, any free ammonia being scrubbed out. The contents were stirred and prevented from rising above 30‹ C. by cooling coil 7. The liquid only was withdrawn through porous bottom 8 and' pumped to vessel 10. The peroxo compound left in vessel 1 was regenerated by the addition of 39 pts. ammonium perchlorate, 27À2 pts. ammonia and 400 pts. water from tank 11. The evolved oxygen was collected via pipe 14 and freed from ammonia in a scrubber 24. During regeneration, heat was absorbed, and the liquid was maintained just below 30‹ C. On completion, the liquid was returned to vessel 11. The cycle was then repeated by transferring the liquid from tank 10 to vessel 1 and again passing air through. In each cycle, 2À4 pts. of oxygen were obtained from 20À9 pts. of air. .Excess ammonia was removed from weak liquor in tank 10, which gradually becomes stronger, by heating in still 19. The ammonia evolved being transferred to tank 11, the liquor which gradually becomes weaker owing to transfer of ammonia during the cycle. Additional ammonia is added to tank 11 when necessary.