Patent GB-951455-A (GB)
Abstract: 951,455. Separating gases by zeolites. AEROJET-GENERAL CORPORATION. June 9, 1960 [Sept. 25, 1959], No. 20391/60. Heading B1L. A component is separated from a gaseous mixture by contacting said mixture with a natural or synthetic zeolite having molecular pores through which all the molecules of the mixture will pass into the molecular cavities and being such that molecules of said component pass through said cavities, collecting said component, and removing adsorbed components from said zeolite, e.g. by heat treatment or evacuation. The invention is described in relation to the recovery of oxygen from air, but the invention can be applied to separation of carbon dioxide and air and removal of helium from natural gas. The preferred zeolite in the recovery of oxygen from air is a zeolite of formula 0.96 + 0.04 Na 2 0. Al 2 O 3 .- 1.92 + 0.09 SiO 2  in which 75% of the sodium ions have been replaced by calcium ions: this material has an effective pore size of 5A and further details are supplied: the unexchanged form can be employed if subjected to strong heat treatment. An alternative zeolite has the formula 0À83Œ0À05 Na 2 O. Al 2 O 3. -2À48 Œ 0.03 SiO 2  and an effective pore size of 13A. In Fig. 1 a laboratory apparatus for producing oxygen from air is shown ; a glass column 2 is packed with <SP>1</SP>/ 16  inch pellets of zeolite supported on sintered glass disc 13. A tube 43 is connected to a vacuum pump, tube 41 is in communication with the atmosphere and tube 7 is provided for the removal of oxygen. A piston 17 operated by eccentric 21 and motor 25 can be moved in the column between the extreme positions shown. When the piston is in the position shown by broken lines the tap 11 is closed. The piston is lowered and when it falls below the level of a port opening 4, cock 37 is opened to the vacuum line 43 to desorb nitrogen from a preceding cycle. When the piston reaches the point shown in full lines cock 37 is turned to admit air to the column. When the piston is about to reach port 4, cock 37 is closed to both air and vacuum lines and cock 11 is opened. As the piston rises, air is forced into the bed and oxygen passes out of line 7. The cycle is then repeated. Figs. 2-4 (not shown) illustrate a similar cycle in which desorption of nitrogen is achieved by heating to about 400 ‹F. and air is admitted under compression. Fig. 5 shows a system comprising three adsorbent units 71, 73, 75 in each of which the above cycle is operated and each of which is in a different phase of the cycle so as to provide a continuous supply of oxygen. In the various valve positions shown, unit 71 is being evacuated by pump 101 while to unit 73 is passed air from a dryer 83 under atmospheric pressure through lines 123 and 97. The air is first filtered (in 79) and from the dryer another portion of the air is pumped under pressure by blower 85 to unit 75 from which at the same time oxygen escapes to storage. The valves are solenoid-controlled and programmed to ensure proper functioning of the apparatus. The units 71, 73, 75 may each comprise a plurality of beds: in Fig. 6 an arrangement of six such beds is shown, the valve positions corresponding to the illustrated phase of bed 71 in Fig. 5. The Specification also mentions a process in which zeolite moves in a closed circuit, into one point of which air is admitted to flow in countercurrent thereto, oxygen being removed continuously at another point and nitrogen at another by application of heat.