Increase the value of steam-cracker pyrolysis gasoline (pygas) using conversion, distillation and selective hydrogenation processes. Pygas, the C5–C9 fraction issuing from steam crackers, is a potential source of products such as dicyclopentadiene (DCPD), isoprene, cyclopentane, benzene, toluene and xylenes (BTX).
To produce DCPD and isoprene, pygas is depentanized and the C5 fraction is processed thermally to dimerize cyclopentadiene to DCPD, which separates easily (1) from the C5s via distillation. Isoprene can be recovered by extractive distillation and distillation. The remaining C5s and the C6–C9 cut are fed to the first-stage catalytic hydrogenation unit (2) where olefins and diolefins are eliminated. The C5s are recycled to the steam cracker or an isomerization unit. Sulfur and nitrogen compounds are removed in the second-stage hydrogenation units (3). The BTX cut is ideal for processing in an aromatics complex.