Patent GB-812680-A (GB)
Title: Improvements in or relating to separation of hydrocarbons with molecular sieves
Filed: 1957-11-04
Abstract: A molecular sieve adsorbent known as a molecular template comprises a resin or gel, such as polystyrene or silica gel, formed in the presence of the material it is subsequently desired to adsorb, e.g. esters or hydrocarbons, and for which it subsequently shows selectivity.  The adsorbent may be used in a fixed or fluidized bed. A sodium aluminosilicate for use as a molecular sieve adsorbent is prepared by reaction of a sodium silicate having a high ratio of sodium to silica, e.g. sodium metasilicate, is reacted with a sodium aluminate having a sodium to alumina ratio of 1 : 1 to 3 : 1, the amounts being such that the ratio of silica to alumina is at least 3 : 1 and preferably between 4 : 1 and 10 : 1.  The sodium aluminate is added to the sodium metasilicate solution at ambient temperature with stirring and the paste obtained heated at 180-215 DEG  F. for a time which may be as long as 200 hours or more to ensure the crystals have the desired pore size, e.g. about 13  .  The sodium aluminosilicate is then filtered, washed, dried and activated in a calcining zone at 700-900 DEG  F.ALSO:Aromatic hydrocarbons or mixtures of aromatic and olefinic hydrocarbons are separated from hydrocarbon mixtures containing them using molecular sieves by passing the hydrocarbon feed through two separate zones containing molecular sieves for a time at least sufficient to desorb from the first zone all hydrocarbons, other than olefines and aromatics, initially adsorbed in said first zone, discontinuing the flow of hydrocarbons, desorbing the adsorbed hydrocarbons from said first zone then repeating the operation with a reversed direction of flow of hydrocarbon feed.  The sieves used preferably have pore sizes of 8-15   and particularly useful are those having a pore size of about 13  .  They may be of the alumino-silicate type such as a natural or synthetic zeolite, or the molecular template type, i.e. a resin or gel, such as a polystyrene or silica gel formed in the presence of the hydrocarbon it is subsequently desired to adsorb.  The preparation of a particular sodium aluminosilicate is described (see Group III).  The adsorption is preferably performed in the vapour phase.  Useful conditions are 100-500 DEG  F. and feed rates of 0.1-10 volumes of liquid feed per volume of sieve per hour.  Desorption may be accomplished (1) by purging with an unreactive gas or vapour at 450-750 DEG  F.; (2) by evacuation at temperatures about the same as or above that used for adsorption; (3) by displacement with an aromatic hydrocarbon of different boiling point from the adsorbed material and from which it can be subsequently separated by distillation; (4) steaming followed by dehydration at relatively low temperatures. When separating aromatics alone the feed flow is continued until all non-aromatics are desorbed from the first zone (with reference to hydrocarbon flow) whereupon the aromatics are desorbed from this zone; when separating aromatics and olefines the flow is continued until olefines appear in the effluent from the second zone and aromatics and olefines then desorbed from the first.