Patent GB-1059974-A (GB)
Title: Process for separating gaseous mixtures using zeolitic molecular sieves
IPC: B01D53/04
Filed: 1963-09-02
Abstract: <PICT:1059974/C4-C5/1> A gas mixture containing molecules capable of being internally absorbed on a zeolitic molecular sieve and other molecules, is separated by feeding the mixture to a bed of zeolitic molecular sieve at a first pressure and temperature, purging the bed at the first pressure and temperature to remove non-internally absorbed molecules, depressurizing the bed to remove a portion of the purge gas and the other molecules and further depressurizing to remove the internally absorbed molecules.  The feed step is terminated while the leading adsorption front lies within the bed while the purge step is continued until the purge gas in the effluent stream constitutes at least 5 vol. per cent but less than 8 bed volumes after the purge gas has reached equilibrium.  The separation of straight chain paraffins from a hydrocarbon stream having an end point of up to 700 DEG  F., e.g. C8 to C22 streams, is achieved using a 5A DEG  Ca zeolite A.  The gas stream is heated to 600 DEG  to 850 DEG  F. and passed to adsorption zone A through conduit 10 at 15 to 150 p.s.i.a., the effluent leaving through conduit 12 where it may be recovered.  When the adsorption front of the normal paraffins has reached a predetermined position within the bed, the valves 11 and 13 are closed and a purge gas which may or may not be internally adsorbed on the sieve is passed co-currently through the bed using conduits 14 and 16.  The purge gas may be methane, isopentane or isohexane, but is preferably a normal paraffin of at least four C atoms, e.g. butane, pentane or hexane. The purge gas content of the effluent stream may be recovered by knock-out drum 40 or fractionater 41 and recycled to the bed. The bed is then depressurized to preferably atmospheric pressure either co- or counter-currently by opening valves 21 or 23 respectively and the purge gas recovered from the effluent. Further depressurization to sub-atmospheric through valve 25 and compressor 43 may be either co-current or counter current thus removing normal paraffins.  After final depressurization, a purge steam, e.g. a n-pentane or n-hexane, may be passed into the bed via valve 31 and the normal paraffins in the effluent recovered as above.  The bed may then be repressurized counter-currently to the initial adsorption temperature and pressure using e.g. branched chain butane, pentane, hexane or heptane, or N2 alternatively, normal paraffins of at least 4 C atoms may be fed in to 1 atom and then feed stock co-currently.  Specific examples comparing the method of the invention with processes without co-current purges are disclosed together with a continuous process using three beds.  Various critical factors in the operation of the process are also discussed, such as the relation between bed loading and bed pressure and the volume of purge gas necessary.  Several natural zeolitic molecular sieves are specified as well as the synthetic zeolites A, D, L, R, S, T, X and Y.  Specific mixtures separated are (i) n-C8-17 + aromatic, cyclic and branched chain hydrocarbons, (ii) n-C9-17 + other hydrocarbons, sulphur and nitrogen.ALSO:A gas mixture containing molecules capable of being internally absorbed on a zeolitic molecular sieve and other molecules, is separated by feeding the mixture to a bed of zeolitic molecular sieve at a first pressure and temperature, purging the bed at the first pressure and temperature to remove non-internally absorbed molecules, depressurizing the bed to remove a portion of the purge gas and the other molecules and further depressurizing to remove the internally absorbed molecules.  The process may be adapted to the separation of n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol and n-decanol from their isomeric forms.