Patent GB-973538-A (GB)
Title: Pressure equalization depressuring in heaterless adsorption
IPC: B01D53/047
Filed: 1962-11-09
Abstract: 973,538. Separation of mixtures. ESSO RESEARCH & ENGINEERING CO. Nov. 9, 1962 [Dec. 18. 1961], No. 42435/62. Heading B1L. In a method of separation of gas mixtures in a heaterless fractionation process comprising adsorption of a key component on a suitable solid adsorbent, and low pressure desorption, an intermediate depressuring step is employed. The adsorption zone is depressured in a flow direction the same as that of the feed to a pressure intermediate the high adsorption pressure and the low desorption pressure and the expanded vapour passed back in a direction opposite to that of the feed. Two adsorber vessels may be connected to a source of hydrocarbon feed and a pressure equalising vessel, each vessel having an outlet into an effluent stream as indicated in Fig. 1, and while one adsorber is on load the other is being desorbed. Feed enters, e.g., adsorber 7 via valve 3 and line 5 at 5-700 p.s.i.g. and at, above or below ambient temperature, and key component becomes adsorbed. Adsorbents include active carbon, alumina, silica gel, glass wool, adsorb. ent cotton and molecular sieves, bone char, fuller's earth, metal oxides and clays. Primary effluent which is now free from key component flows from the adsorber via line 9 and valve 15 and out through line 28. Adsorption of key component in zone 7 is stopped just before any key component breaks through into the primary effluent stream. While zone 7 is on adsorption, zone 8 is on desorption which process can be carried out in two ways: (a) At the beginning of the desorption sequence valves 21 and 23 are opened to bring adsorption zone 8 at high pressure, and pressure equalisation zone 24, at a lower pressure, into communication with each other. When the pressure is the same in both vessels valve 21 is closed. Valve 26 is then opened and adsorption zone 8 is depressured to the low desorption pressure. Some desorption takes place in this step to give part of the secondary effluent. Valve 21 is opened and vapour passes through the adsorbent in adsorption zone 8 from the vessel 24 and forms part of the secondary effluent. Valve 21 is then closed and zone 8 is purged with some primary effluent from line 28. (b) After valve 21 has been opened to allow pressures in 8 and 24 to become equal, valve 26 is opened and the total vapour in 24 and 8 backwashes zone 8. Primary effluent purge is then introduced as indicated above. A special procedure may be followed for the desorption of higher hydrocarbons which are more difficultly desorbable from the adsorbent. The volume of purge gas may be increased by reducing the low desorption pressure or simply by increasing the throughput of purge gas. The product from the adsorption process may be drawn from the equalisation zone, prior to further pressure let down as this is of substantially the same composition as the primary effluent. Comparison is given for the adsorbent capacity decline using the present invention and prior art methods. An example of the separation of hydrogen and methane from C2-C6 compounds is given and reference is made to the separation of hydrogen and methane, air and oxygen, air and argon, air and nitrogen, air and water vapour, and water from inert gas. Specification 850,443 is referred to.