Patent GB-890555-A (GB)
Title: Process for the separation of normal olefins from normal paraffins
IPC: C07C7/13
Filed: 1960-10-24
Abstract: Normal olefins are separated from mixtures also containing normal paraffins by selective adsorption of the former on a molecular sieve followed by desorption with an eluent containing a normal saturated compound with a higher number of carbon atoms per molecule than the highest molecular weight adsorbed compound.  In particular normal olefins are separated from normal paraffins containing the same number of carbon atoms and desorbed with a normal paraffin containing one or two more carbon atoms using a 5  sodium calcium alumino silicate which may be supported with a clay binder and may be in powder or pellet form.  The feed may for example be a C2-C6 hydrocarbon mixture which may also contain nonnormal hydrocarbons, e.g. isoparaffins and cyclic hydrocarbons and is preferably a gaseous mixture, e.g. obtained by catalytic or thermal cracking from which methane and lighter components, CO2 and H2S have been removed, or obtained by pyrolysis of ethane or propane.  In a preferred embodiment the eluent also contains isoparaffins, e.g. in a volume ratio to normal paraffins between 3:2 and 1:4 such as the effluent from isomerizing n-butane, an alkylation process isobutane recycle stream, a C4 fraction from a catalytic reforming process, or a mixture of normal and isopentanes.  During the desorption normal paraffins in the eluent are separated from isoparaffins, the product being a mixture of isoparaffins and n-olefins which may be passed to an alkylation process or, if the olefin is propylene, a process for the production of di-isopropyl ether. On passing the feed through the sieve again after desorption, the mixture of unadsorbed materials and displaced desorbent is preferably fractionated to recover the desorbent which may be re-used.  Between adsorption and desorption the sieve may be purged with an inert gas or a mixture containing both the normal olefins and paraffins of the feed mixture but having a higher ratio of olefin to paraffin than in the feed, e.g. the product recovered as effluent in the desorption.  The amount of purge may be 1-15 times the volume of void spaces in the adsorbent. Although liquid phase operations may be used, vapour phase is preferred with the pressure remaining constant throughout all operations at sub-atmospheric to 705 atmospheres absolute and temperature varying by less than 55 DEG C. in the range-10 DEG  to 315 DEG C. Space velocity of the feed or eluent may be 0,1-40 volumes per volume of adsorbent per hour.  Fixed or moving beds of adsorbent may be employed as may be fluidized bed or dilute phase operation. Flow diagrams (not shown) indicate a method of achieving pseudo continuous operation and illustrate integrated processes in which some products are recirculated as eluents.ALSO:Normal olefins are separated from mixtures also containing normal paraffins by selective adsorption of the former on a moleculat sieve followed by desorption with an eluent containing a normal saturated compound with a higher number of carbon atoms per molecule than the highest molecular weight adsorbed compound.  In particular normal olefins are separated from normal paraffins containing the same number of carbon atoms and desorbed with a normal paraffin containing one or two more carbon atoms using a 5<\>fA sodium calcium alumino silicate which may be supported with a clay binder and may be in powder or pellet form. The feed may, for example, be a C2-C6 hydrocarbon mixture which may also contain nonnormal hydrocarbons, e.g. isoparaffins and cyclic hydrocarbons and is preferably a gaseous mixture, e.g. obtained by catalytic or thermal cracking from which methane and lighter components, CO2 and H2S have been removed, or obtained by pyrolysis of ethane or propane.  In a preferred embodiment the eluent also contains isoparaffins, e.g. in a volume ratio to normal paraffins between 3 : 2 and 1 : 4 such as the effluent from isomerising n-butane, an alkylation process isobutane recycle stream, a C4 fraction from a catalytic reforming process, or a mixture of normal and isopentanes.  During the desorption normal paraffins in the eluent are separated from isoparaffins, the product being a mixture of isoparaffins and n-olefins which may be passed to an alkylation process or, if the olefin is propylene, a process for the production of di-isopropyl ether.  On passing the feed through the sieve again after desorption, the mixture of unadsorbed materials and displaced desorbent is preferably fractionated to recover the desorbent which may be re-used.  Between adsorption and desorption the sieve may be purged with an inert gas or a mixture containing both the normal olefins and paraffins of the feed mixture but having a higher ratio of olefin to paraffin than in the feed, e.g. the product recovered as effluent in the desorption.  The amount of purge may be 1-15 times the volume of void spaces in the adsorbent.  Although liquid phase operations may be used, vapour phase is preferred with the pressure remaining constant throughout all operations at sub-atmospheric to 705 atmospheres absolute and temperature varying by less than 55 DEG C. in the range -10 DEG C.-315 DEG C.  Space velocity of the feed or eluent may be 0.1-40 volumes per volume of adsorbent per hour.