Patent GB-989073-A (GB)
Title: Adsorption separation process
IPC: B01D53/047
Filed: 1961-09-14
Abstract: 989,073. Molecular sieve separation process. UNION CARBIDE CORPORATION. Sept. 14, 1961 [Sept. 16, 1960; Oct. 5, 1960], No.32933/61. Heading B1L. A feed fluid gaseous or liquid stream containing an admixture of impurity and product fluid is purified by introducing the stream into the inlet end of an adsorption zone, which contains a bed of particulate zeolitic molecular sieve, at an increased pressure, thereby adsorbing impurity in the sieve and trapping a part of the feed fluid stream in the voids of the sieve. An impurity adsorption front is established during this adsorption step, which advances to a predetermined location within the adsorption zone, whereupon the introduction of the feed fluid stream is terminated. The product fluid trapped in the voids is removed by a cocurrent depressurizing step during which time the pressure in the adsorption zone decreases and the impurity adsorption front moves to the discharge end of the adsorption zone. The impurity is then removed from the adsorbent by any known desorption method. The desorbed adsorption zone is then repressurized to the initial higher pressure. When the repressurization stream has an impurity partial pressure not higher than that permissible in the product, repressurization is countercurrent to the adsorption flow direction. When the impurity partial pressure of the repressurization stream is greater than this, the repressurization flow direction should be cocurrent to the adsorption flow direction. Up to four adsorption zones may be used in the process, the successive-adsorption, cocurrent depressurizing, desorption and repressurizing steps being carried out consecutively in each zone. The adsorption zones may comprise one or two beds of molecular sieve. Referring now to Fig. 3, the feed gas stream at a first higher pressure is directed through heat exchanger 11, and passed into bed A. The effluent which is purified prdouct gas is passed through conduit 17 to storage. Adsorption is continued in bed A until breakthrough point is reached, when the flow to bed A is shut off and redirected to bed B. Valves 18 and 28 are opened cocurrently depressurizing bed A, the effluent from bed A is passed, via conduit 26, to bed D which thus functions as an unused portion of bed A into which the impurity adsorption front now moves. The effluent from adsorption bed D is a purified product at a lower pressure than the adsorption step pressure and is directed through conduits 30 and 31 to repressurize adsorption bed C, which had previously completed a desorption step. When the pressure between beds C and D equalizes, passaeg of gas between them is terminated and bed C is further repressurized by passing feed gas together with the effluent from bed D (via reservoir 34) through thermocompressor 40 to bed C. The pressure in bed A which is still connected to bed D is also decreased by this method, thus completing the cocurrent depressurizing step for bed A. At this point, bed D is vented via conduit 44 to atmospheric pressure. When the pressure in bed D approaches atmospheric, bed A is desorbed at a yet lower pressure through conduit 41, eductor 48 and conduit 49. The eductor 48 at the same time evacuates and desorbs bed D to a subatmospheric pressure through conduit 29 and 49. When adsorbent beds A and D are finally desorbed, the feed gas stream is directed to bed C. Meanwhile adsorbent bed A is being repressurized and adsorbent bed B is being cocurrently depressurized and desorbed. In this method the adsorbent bed D is used to provide the unused molecular sieve capacity required during the cocurrent depressurization stroke for each of the adsorbent beds A, B and C thereby completing for each bed the adsorption zone.