GB635910A - An improved manufacture of cyclo-alkadienes - Google Patents

Abstract

Cyclo-alkadienes are recovered from cracked petroleum naphthas containing polymers thereof by fractionally distilling C1-C5 hydrocarbons from the naphtha, heating the bottoms at 300-800 DEG F. to depolymerize the polymers, and distilling off the C5-C8 monomers. Cracking stocks such as naphtha cuts, kerosene or gas oils are cracked under conditions giving high yields of unsaturateds and aromatics, such as 1000-1600 DEG F. and 1-10 atm., with up to 90 mol. per cent of steam. The products are quenched, overhead naphtha vapours and steam condensed, water separated, and the naphtha distillate fractionated to remove C1-C5 hydrocarbons. If higher homologues of cyclopentadiene, such as methyl- and dimethyl-cyclopentadiene and cyclohexadiene are to be recovered, it is desirable also to remove non-aromatic C6-C8 hydrocarbons, with which C6-C8 aromatics may also be separated, preferably using steam or vacuum. The bottoms contain cycloalkadiene polymers and are heated for a short time to produce the monomers, preferably for 0.15-25 secs. at 600-800 DEG F. in the vapour phase or up to 10 hours at 300-600 DEG F. in liquid phase. Pressure is generally atmospheric or slightly above. After quenching, for example, to below 100 DEG F., the monomers are recovered by distillation.