Patent GB-582495-A (GB)
Title: Improvements relating to the catalytic isomerization of paraffinic hydrocarbons
IPC: C07C5/27
Filed: 1943-03-11
Abstract: Normal paraffins of at least four carbon atoms are isomerized by contacting in the vapour phase with a Friedel-Crafts' type catalyst sorbed in a porous carrier and in the presence of a halogen-containing promoter, the temperature of the reaction zone and the amount of catalyst being correlated with the activity of the catalyst so as to maintain a substantially constant conversion of between 20 and 80 per cent.  Thus, in isomerizing butane using a catalyst of partially dehydrated bauxite containing 8-12 per cent of aluminium chloride at about 300 DEG  F., with a feed containing 6 per cent of hydrogen chloride, a throughput of about 2-3 v./v./hr. gives a conversion of 40-50 per cent.  After 100-150 hrs. of operation, the activity of the catalyst would drop until conversion was about 30 per cent.  To prevent this, the feed may be passed through a pick-up drum of heated aluminium chloride, and the temperature lowered, e.g. to 275 DEG  F., to prevent the conversion exceeding 50 per cent.  When it falls below this, the temperature may be increased gradually up to 300 DEG  or even 400 DEG  F.  Alternatively, reaction may be commenced at 200-250 DEG  F. and small amounts of catalyst introduced with the feed, the temperature at the same time being gradually raised, e.g. to 325-340 DEG  F.  A further variation is to add with the feed more than sufficient aluminium chloride to saturate the porous carrier, the temperature being decreased to prevent excessive activity. The amount of promoter may be varied, but is preferably kept constant.  The catalyst is prepared by impregnating the carrier of the siliceous, aluminous or other type, generally preheated to dehydrate, with halide, preferably in such amount that it is tenaciously held, the excess halide being removed if desired by heating the mass above the isomerization temperature in an inert gas stream.  The feed may be a single paraffin from butane to heptane or higher or a mixture such as field butanes or casinghead gasoline.  It is purified with concentrated sulphuric or chlor- or fluor-sulphonic acid, and with caustic alkali.  The feed rate is preferably kept constant at about 0.2-3 liquid vols./vol./hr. and the temperature is about 150-400 DEG  F. with a pressure up to about 350 lbs./sq. in. For butane isomerization, the vapours, with 2-8 per cent of hydrogen chloride, may be passed upwards at a rate of 0.5-2 liquid vols. butane/vol./hr. and at 150-300 lbs./sq. in. through a bed of 12 per cent AlCl3 on a dehydrated bauxite at about 200 DEG  F.  Conversion is maintained constant by addition of .005-.04 per cent by weight of AlCl3 to the butane, and gradual increase of temperature to about 375 DEG  F.  For pentane, the temperatures are 150 DEG  and 225 DEG  F., pressure 50-100 lbs./sq. in., throughput 0.75-2.5 vols./vol./hr., and AlCl3 addition .02-.04 per cent.  In an example, dehydrated "Porocel" (Registered Trade Mark) impregnated with AlCl3 is heated at 250 DEG F. and used for butane isomerization.  Conversion is kept at 40-50 per cent by adding AlCl3 from a pick-up drum after the 120th hour and gradually raising the temperature to about 300 DEG  F.  With the addition of large amounts of AlCl3 after 200 hours, it is necessary to drop the temperature to 260 DEG  F.  The Specification as open to inspection under Sect. 91 comprises also the variation of the reaction temperature or amount of catalyst alone.  Further examples describe the isomerization of butane while gradually increasing the temperature.  When this expedient alone fails to maintain the conversion, additional AlCl3 may be taken up by the feed.  This subject-matter does not appear in the Specification as accepted.