GB900374A - Combined steam cracker and butene dehydrogenation light ends - Google Patents

Abstract

<FORM:0900374/IV (b)/1> Hydrocarbons are separately recovered from the light ends from a steam cracker operated to produce olefins and diolefins and a butene dehydrogenation unit employing two or more reactors, one or more of which is in stream while one is being regenerated, by combining the two streams, compressing to above 150 p.s.i.g. and passing to an absorption/fractionation system to recover the separate components. A naphtha or gas oil, e.g. boiling in the range 350-700 DEG F. is supplied with steam to furnace 2 operated at 1300-1500 DEG F., 0-50 p.s.i.g. with residence times of 0.05-1 second. The effluent is quenched to 400-600 DEG F. with heavy oil supplied through line 4 and passed to distillation tower 6 where tar, quench oil, and gas oil are separated from light ends recovered overhead. These are cooled to 75-125 DEG F. and C6- materials passed to compressor 14 and heavier materials removed through line 15. A butane/butene feed containing 70-95% mol butenes is heated in furnace 18 and contacted with catalyst in one of reactors 22 and 29, the other being on regeneration. Using calcium nickel phosphate as catalyst the feed is mixed with steam and passed at 1,000-1,400 DEG F. into the reactor with a butene gas rate of 75-200 v/v/hr. and a steam rate of 1,400-4,000 v/v/hr. and a pressure of 15-30 p.s.i.a. Using chromia alumina the temperature may be 1,000-1,200 DEG F. at 1-15 p.s.i.a. with a WHSV of 0.5-1.5 wt./hr./wt. On switching reactors from on stream to regeneration the effluent rate fluctuates, the fluctuation being diminished by combining with the steam cracker light ends before passing to the compressor 14. Steam if present is condensed out in separator 33. The combined stream cooled to 75-125 DEG F. and in separator 39 C3- are taken overhead through line 40 while heavier materials pass with material in line 15 to naphtha splitter 42 where C6+ materials are removed as bottoms while the overhead is caustic treated to remove sulphur compounds and CO2 and passed to absorber de-ethaniser 47.C3- compounds in line 40 are treated with diethanolamine for removal of H2S and CO2 in tower 48 and with a caustic wash in tower 53 before passing to absorber de-ethaniser 47. Here the vapours are treated with a C5 lean oil obtaining a C2- stream overhead. This is washed with sponge oil in tower 59 to remove traces of C5 lean oil. C2-product is recovered in line 60. The C3+ material from the bottom of tower 47 is fractionated in tower 62 to obtain C5 products as bottoms, part being used as the C5 lean oil in tower 47. The overhead is split in tower 69 into C3 overhead and C4 bottoms which latter passes to butadiene extraction. Generally in the combined light ends the C4/C3 ratio will be 0.7-2:1 and the butene dehydrogenation effluent will be 5-50% by volume of the steam cracker light ends. The debutaniser 62 can be operated at less than 140 p.s.i.g., i.e. lower than a conventional steam cracker debutaniser.