Patent GB-468432-A (GB)
Title: Improvements in and relating to the conversion of hydrocarbons
IPC: C07C15/02
Filed: 1936-10-31
Abstract: In a process for producing cyclic hydrocarbons, useful as motor fuel, from gases consisting wholly or mainly of hydrocarbons having 2--4 carbon atoms, the initial gas is separated into fractions (a and b) of different boiling range, one at least of these fractions (fraction a) containing hydrocarbons of substantially the same polymerization velocity; this fraction (a) is then subjected to polymerization, the liquid polymerization products are removed, the gaseous residue (c) is cracked, the cracking products are mixed with fraction (b), the mixture is polymerized, and the liquid products are removed; alternatively, the gaseous residue (c) is mixed with fraction (b), the mixture is cracked, the cracking products are polymerized, and the liquid products are removed.  If the initial gas does not contain at least about 30 per cent of olefines, it is preferably cracked before it is fractionated.  The plant shown comprises a fractionator 3, a polymerization system 12, 13, a cracking coil 48, and a second polymerization system 71, 72, with cooling and fractionating apparatus between the first polymerization system and the coil 48, and also between the coil 48 and the second polymerization system. The initial gas enters by line 1 and is separated in the fractionator 3 into two fractions, preferably into a liquefied fraction, containing hydrocarbons of 3--4 carbon atoms, and a residual gaseous fraction.  The liquefied fraction is passed to the heating coil 12 and the polymerization coil 13, which is preferably operated at 1050--1150 DEG  F. and a pressure of 200--400 lb. per sq. in.  The products from the coil 3 are cooled and condensed, and the residual gases enter the cracking coil 48, which is preferably operated at 1325--1600 DEG  F. and a pressure of 25--125 lb. per sq. in.  The gaseous fraction from the fractionator 3 may also be fed to the coil 48 by way of the lines p  4, 5 and valves 7, 50.  The products from the coil 48 are cooled and condensed, and the residual gases are passed to the heating coil 71 and polymerization coil 72, which is preferably operated at 15--120 lb. per sq. in.  The gaseous fraction from the fractionator 3 may also be fed directly to the coils 71, 72 by way of line 5 and valve 6.  The products from the coil 72 are cooled and condensed, and residual gases are returned to the line 1 from the final condenser 140 and accumulator 142.  The cooling and condensation system between the coils 12 and 48 comprises an arrester 14 in which the products from the coil 12 are cooled by means of a light distillate supplied through line 15; a separator 16 for tar and heavy hydrocarbons; a condenser 21; a distillate accumulator 23, from which a part of the condensate is withdrawn by pump 27 to serve as reflux in the separator <PICT:0468432/IV/1> 16 and to feed the arrester 14; a fractionator 33 to which distillate is delivered from accumulator 23 through heat-exchanger 31 by pump 28; a reboiler 34, from which the desired product passes through heat-exchanger 31 and cooler 37 into the outlet pipe 38; a condenser 40, and an accumulator 42, from which condensate is returned as reflux to the fractionator 33 by a pump 44.  A similar system is arranged between the coils 48 and 71 and also after the coil 72.  The system between the coils 48 and 71 includes also a compressor 65 and an accumulator 69, from which liquid hydrocarbons produced during the cracking are withdrawn, the gases passing to the coil 71.  The system behind the coil 72 includes an absorber 89 in which aromatic and light hydrocarbons are absorbed in an oil, which is then stripped with steam in a tower 101. The products expelled from the oil in the tower 101 are condensed, and the condensate is collected in a tank 123, to which condensate from the accumulator 69 is also fed and from which the products pass to a fractionator 132 and thence through a reboiler 133 and heat-exchanger 130 to the outlet pipe 38.  Tar and heavy hydrocarbons from the separator 16 and the corresponding separators 54 and 76 are passed through line 19 to a stripping tower 149, the overhead products from which pass through a condenser 155 into an accumulator 157, from which condensate is withdrawn through a line 160 for use in the arrester 14 and the corresponding arresters 51 and 73.  The stripped tar is discharged through the line 153.