Patent GB-718219-A (GB)
Title: Improvements in or relating to the separation of aromatic hydrocarbons from mixturesthereof with non-aromatic hydrocarbons
IPC: C07C7/12
Filed: 1952-08-01
Abstract: Aromatic hydrocarbons are recovered from mixtures with non-aromatic of the same boiling range by passing a first hydrocarbon feed mixture boiling within the gasoline and kerosene range, containing a first aromatic and a non-aromatic hydrocarbon through a bed of a porous adsorbent under conditions to adsorb preferentially said first aromatic, passing a second feed boiling within the gasoline and kerosene range and comprising a second aromatic of different boiling point from the first, alone or together with non-aromatics of different boiling points from those of the first mixture, through said bed under conditions to adsorb preferentially said second aromatic whereby the first aromatic is desorbed and recovered admixed with the hydrocarbons of the second feed, resuming flow of the first mixture whereby the second aromatic is recovered admixed with non-aromatics of the first feed, separately recovering aromatics from these mixtures by fractional distillation, and repeating the sequence of steps.  The aromatics include benzene, toluene, xylenes, ethyl- and propyl-benzene, homologues thereof, e.g. durene, naphthalene and other condensed ring aromatics.  These are preferably separated from mixtures with paraffins and/or naphthenes but olefins may be present. Preferred feeds are benzene with C6-C7 saturateds, and xylenes with C9 saturateds.  The second feed may be of higher or lower boiling point and, when it consists of aromatics only, is preferably at least 95 per cent pure, either a single compound or a group of isomers. Particularly when aromatics only are used as second feed, it may be desirable to treat the adsorbent first with the second feed, then desorb this with the first feed, and so on.  The preferred adsorbent is silica gel of 28-250 mesh.  Other sizes may be used, and such adsorbents as activated carbons, e.g. 28-65 mesh, and activated alumina. Temperatures are about 32-250 DEG , preferably 38-120 DEG F., and contact times 15 minutes-2 hours or more.  A bed of length: diameter ratio between 2 : 1 and 200 : 1 is suitable.  The volume ratio of adsorbent: feed stream is from 0.3 : 1 to 14 : 1, and it is preferred to continue the feed until the adsorbent is substantially saturated.  Down-flow is preferred, and the bed may be divided by baffles.  After changeover of feed, a small slop cut may be taken off prior to collection of effluent.  Preferably, continuous operation is effected with a plurality of adsorption zones, each connected in sequence alternately to the two feeds, the effluents being collected alternately in two tanks and fractionated to recover the pure aromatics.  This operation is described using a benzene-hexanes feed, and a xylene-C9 saturateds feed.  More than two feeds may be used; thus the xylene feed may be followed by a durene feed.  Examples use silica gel as adsorbent and describe: (1) charging a mixture of 50 per cent xylenes together with C9 paraffins, naphthenes, and some olefins obtained by hydroforming, following with 10 per cent benzene admixed with hexanes, heptanes, and C6 naphthenes, and so on, and recovering benzene and xylenes from the effluents; (2) charging with impure xylenes, following with 10 per cent benzene and C6 saturateds, and so on; (3) using pure xylenes or mixed C8 aromatics for first charging, followed by 6 per cent benzene with hexanes, heptanes, and some C6 naphthenes, then pure xylenes; (4) using a 20 per cent benzene mixture alternately with xylenes as in (3); (5) first charging with toluene, then feeding a 330-450 DEG  F. cracked naphtha containing 38 per cent C9-C11 aromatics and 30 per cent olefins, followed by toluene, and recovering a 90 per cent aromatic concentrate after removal of toluene.ALSO:Aromatic hydrocarbons are recovered from mixtures with non-aromatic hydrocarbons of the same boiling range by passing a first hydrocarbon feed mixture boiling within the gasoline and kerosene range, containing a first aromatic and a non-aromatic hydrocarbon through a bed of a porous adsorbent under conditions to adsorb preferentially said first aromatic, passing a second feed boiling within the gasoline and kerosene range and comprising a second aromatic of different boiling point from the first, alone or together with non-aromatics of different boiling points from those of the first mixture, through said bed under conditions to adsorb preferentially said second aromatic whereby the first aromatic is desorbed and recovered admixed with the hydrocarbons of the second feed, resuming flow of the first mixture whereby the second aromatic is recovered admixed with non-aromatics of the first feed, separately recovering aromatics from these mixtures by fractional distillation, and repeating the sequence of steps. The aromatics are preferably separated from mixtures with paraffins and/or naphthenes but olefins may be present.  Preferred feeds are benzene with C6-C7 saturateds and xylenes with C9 saturateds.  The second feed may be of higher or lower boiling point and, when it consists of aromatics only, is preferably at least 95 per cent. pure, either a single compound or a group of isomers. Particularly when aromatics only are used as second feed, it may be desirable to treat the adsorbent first with the second feed, then adsorb this with the first feed, and so on. The preferred adsorbent is silica gel of 28-250 mesh.  Other sizes may be used, and such adsorbents as activated carbons, e.g. 28-65 mesh, and activated alumina.  Temperatures are about 32-250, preferably 38-120 DEG  F. and contact times 15 mins.-2 hours or more. A bed of length: diameter ratio between 2 : 1 and 200 : 1 is suitable.  The volume ratio of adsorbent feed stream is from 0.3 : 1 to 14 : 1, and it is preferred to continue the feed until the adsorbent is substantially saturated. Downflow is preferred, and the bed may be divided by baffles.  After changeover of feed, a small slop cut may be taken off prior to collection of effluent. Preferably, continuous operation is effected with a plurality of adsorption zones, each connected in sequence alternately to the two feeds, the effluents being collected alternately in two tanks and fractionated to recover the pure aromatics.  This operation is described using a benzenehexanes feed, and a xylene C9 saturateds feed.  More than two feeds may be used; thus the xylene feed may be followed by a durene feed.  Examples use silica gel as adsorbent and describe: (1) charging a mixture of 50 per cent. xylenes together with C9 paraffins, naphththenes and some olefins obtained by hydroforming, following with 10 per cent. benzene admixed with hexanes, heptanes and C6 naphthenes, and so on, recovering benzene and xylenes from the effluents; (2) charging with impure xylenes, following with 10 per cent. benzene and C6 saturateds, and so on; (3) using pure xylenes or mixed C8 aromatics for first charging, followed by 6 per cent. benzene with hexanes, heptanes and some C6 naphthenes, then pure xylenes; (4) using a 20 per cent. benzene mixture alternately with xylenes as in (3); (5) first charging with toluene, then feeding a 330-450 DEG  F. cracked naphtha containing 38 per cent. C9-C11 aromatics and 30 per cent. olefins, followed by toluene and recovering a 90 per cent. aromatic concentrate after removal of toluene.