Abstract: Producing light olefins from a contaminated liquid hydrocarbon feed by means of thermal cracking of, which process comprises the steps of supplying the feed (6) to the inlet (7) of a membrane unit (1) provided with a polysiloxane membrane (10), and removing from the permeate side (9) a permeate (14) and from the retentate side (8) a retentate (12); supplying the permeate (14) to the inlet of a cracking furnace (2), allowing the permeate to crack in the coils (15, 16) of the cracking furnace (2) in the presence of steam (17) at elevated temperature and removing from the cracking furnace (2) a cracked stream (19) which is enriched in light olefins; quenching (22, 24) the cracked stream; supplying the cooled cracked stream to a fractionation column (3); supplying the retentate (12) to the fractionation column (3); and removing from the fractionation column (3); a gaseous stream (30), a side stream of fuel oil components (45) and a bottom stream (50).

Abstract: A method of distilling a crude oil and a contaminated liquid stream in an atmospheric distillation column (2) comprising the steps of (a) heating (13, 15) the crude oil at atmospheric pressure and introducing the heated crude oil into the inlet section (10) of the column (2); (b) removing from bottom a residue (19), removing from the top an overhead (20) and removing from the rectification section (7) at least one side stream (26, 28); (c) cooling (13) one of the side streams (28) and introducing the cooled side stream (29) into the rectification section (7) and partly condensing (21) the overhead (20) and introducing the condensed fraction (24) into the upper end of the distillation column (2); (d) supplying the contaminated liquid stream (40) to a membrane unit (3) provided with a suitable membrane (33), and removing a permeate (37) and a retentate (36); and (e) introducing the permeate (37) into the rectification section (7) and adding the retentate (36) to the crude oil (11) upstream of the furnace (1).