GB679905A - Improved adsorption process - Google Patents

Abstract

<PICT:0679905/III/1> <PICT:0679905/III/2> In a cyclic process for the separation of a gaseous or liquid mixture of a less readily adsorbed component A and a more readily adsorbed component B, with or without a component of intermediate adsorbability, by means of a fluidized or moving bed of a solid adsorbent wherein the unadsorbed component A is removed and the component B is desorbed from the adsorbent which is recycled, the component B is partially desorbed from the total adsorbent and completely desorbed from a minor portion of the adsorbent in a clean-up desorption zone, the partially desorbed adsorbent being returned to the adsorption zone and the completely desorbed adsorbent being employed to scrub the fluid stream of component A, and optionally thereafter being returned to the main body of the adsorbent. As shown in Fig. 1, a gaseous mixture of C1, C2 and C3 hydrocarbons from line 2 enters the column 1 which may contain a plurality of fluidized beds of solid adsorbent, or the latter may gravitate from top to bottom of the tower. In the adsorption section above line 2, C2 and C3 components are adsorbed and the adsorbent moves downwards to a rectification zone between pipes 2 and 5 where it is contacted with an upflowing stream of desorbed C2 and C3 components which release any adsorbed C1 components and are themselves readsorbed. A C2 product stream may be withdrawn at 23. The adsorbent is then heated by heater 6 to 450-550 DEG F to partially release the C3 components which are withdrawn at 5, and then passes to a partial desorption zone below the heater. This zone is fed with steam from a clean-up desorption zone 9 and the partially desorbed adsorbent is entrained in a stream of lift gas withdrawn through pipe 11 and recycled through pipe 13, a cooler 14 and pipe 15 to the adsorption zone. 10-40 per cent by weight of the adsorbent is withdrawn through pipe 8 and completely desorbed in vessel 9 by steam entering at 16, the completely desorbed adsorbent being recycled through lines 17, 18, 20 to a tail gas scrubber 21. The scrubbed C1 components are withdrawn at 22, a portion being employed as lift gas for the completely desorbed adsorbent. The adsorbent from vessel 21 may be returned to the main adsorber through line 4. If a pure C2 fraction is desired instead of withdrawal thereof through pipe 23, the adsorbent containing C2 and C3 fractions is withdrawn at 28 and passed to a side stream scrubber 31 where it is scrubbed with the completely desorbed adsorbent from a stripper 9 and pipe 25, the adsorbent returning through pipe 29 and the product withdrawn at 34, a portion being used as lift gas as before. For the separation of two liquid components A and B, such as isooctane (A) and heptane (B), or methyl cyclohexane (A) and toluene (B) using a liquid C for stripping such as pentane and/or hexane and charcoal or silica gel adsorbent respectively, the apparatus of Fig. 2 is employed, the A and B fractions entering at 2, the B fraction being adsorbed in section 3 and passing to a rectification section 4 where it meets an upflow of desorbed fraction B and stripping liquid C. The solid adsorbent passes down through line 7 to a partial desorber 8, the partially desorbed solid being mainly withdrawn into line 11 for recycling and partially passed to a clean-up desorber 13 through line 12, heated by coil 14. The wash liquid C enters at 15, washes the B fraction from the adsorbent and passes through line 9 to the partial desorber 8 and thence to the rectification section 4 through line 10, a portion comprising components B and C being withdrawn as product for separation of the B and C components by distillation. The totally desorbed adsorbent from desorber 13 is passed by line 19 to contact the unadsorbed A component in a clean-up adsorption section 5. The A and C fraction is withdrawn at 20 and the components separated by distillation. Activated charcoal or silica gel may be used as adsorbent in either apparatus and preferably a portion of the activated charcoal is withdrawn from the clean-up desorption zone and passed to a high temperature regeneration zone where it is treated with steam, flue gas or carbon dioxide at 700-1600 DEG F.