Patent GB-896133-A (GB)
Title: Process for the continuous separation of a hydrocarbon mixture by distillation
IPC: C10G7/00
Filed: 1959-10-05
Abstract: <PICT:0896133/III/1> A process for the continuous separation of a hydrocarbon mixture comprises distilling the mixture in a primary distillation column, partly condensing the primary top product, separating the partly condensed product into condensate and gas, distilling at least part of the condensate in a second column, partly condensing the top product from the second column, separating this condensate into liquid and gas, and recycling this gas so as to combine it with the primary top product at a point where the top product has not yet been separated into condensate and gas.  The condensate from the top product of the second column may be passed to one or more additional columns so arranged and operated that each is fed with a quantity of condensate derived from the partly condensed top product of a preceding column and that the gases remaining after partial condensation of the top product of each of the columns are recycled and combined with the primary top product at a point where the primary top product has not yet been separated into condensate and gas.  The recycling of the gases as described reduces the volume of gaseous by-products, and the same effect is achieved if a part of the bottom product from the secondary column or from an additional column is recycled and combined with the primary top product.  As shown, a desulphurized hydrocarbon oil with a relatively high content of normally gaseous components is fed by line 1 to a primary column 2 operated at about atmospheric pressure and at such a temperature that the portion boiling above 165 DEG C. can be withdrawn through line 4 while the fraction boiling below that temperature passes as a top product through the line 3 and a cooler 5, where only partial condensation occurs, to an accumulator 6, which is maintained at 45 DEG C. and a pressure of 1,1 atm.  The gases from accumulator 6 pass through line 8, compressor 9, line 10 and cooler 11 to an accumulator 12 to which liquid from the accumulator 6 is also delivered by line 7, the provision of separate paths for liquid and gases from the accumulator 6 to the accumulator 12 serving to reduce the work of compression.  The accumulator 12 is maintained at 40 DEG C. and 5 atm. pressure, and from it liquid is passed by line 13 to secondary column 14, operated at 12 atm. pressure, where it is separated into a butane-free gasoline as bottom product and a fraction containing butane and lower boiling components as top product.  The bottom product is withdrawn by line 15 to a column 16 where it is separated into light gasoline discharged through line 17 and heavy gasoline (naphtha), discharged through line 18. The top product from the secondary column 14 passes through line 19 and cooler 20 to an accumulator 21 maintained at 45 DEG C. and 12 atm. pressure.  Some of the liquid from accumulator 21 is returned as reflux to the column 14 and the remainder is passed through line 22 to a column 23, operated at a pressure of 24 atm., where C4 hydrocarbons are separated from lower boiling components.  The C4 hydrocarbons are discharged through line 25 and the lower-boiling components pass through line 26 and cooler 27 to an accumulator 28, maintained at 45 DEG C. and 24 atm. pressure, where liquid propane separates and is partly withdrawn through line 29 and partly returned as reflux to the column 23. The uncondensed gases from the accumulators 21 and 28 are recycled to the accumulator 12 through lines 31, 32 and 33, and gaseous products are removed from the system only through the line 34. The loss of gas may be further reduced by recycling naphtha from line 18 through line 35 to line 3.  If the cutting point in column 2 is changed, e.g. to 185 DEG C., the quantity of naphtha recycled through line 35 is preferably adjusted so that the quantity withdrawn from the system through line 18 remains substantially constant.  Specification 837,401 is referred to.