GB742365A - Improvements in or relating to process for segregation of c dienes - Google Patents

Abstract

C5 diolefines are separated from a cracked petroleum distillate fraction containing appreciable amounts of isoprene together with piperylene and cyclodiolefines including cyclopentadiene, by heating said fraction in the liquid phase in a first thermal soaking zone, under such conditions of temperature and pressure and for such a time that at least half but not all of the cyclopentadiene is dimerized without substantially polymerizing or copolymerizing the isoprene and piperylene, distilling an isoprene-rich distillate from the heat-soaked fraction, heating the bottoms product in the liquid phase in a second thermal soaking zone under more severe conditions and for such a time that the dimerization of the cyclopentadiene is substantially completed, and distilling the piperylene from the cyclopentadiene dimer. The bottoms product from the isoprene distillation may be blended with a C5-C7 hydrocarbon stream, obtained from severely cracked petroleum oils and containing methylcyclopentadiene, before passing to the second thermal soaking zone. Preferably the initial cracked petroleum fraction is kept in the first thermal soaking zone for 4 to 12 hours at a temperature of 180 DEG to 220 DEG F. and a pressure of 50-120 p.s.i.g., whereby 80 to 90 per cent of the cyclopentadiene is dimerized. The isoprene may be distilled from the heat soaked fraction at a bottoms temperature between 230-270 DEG F., an overhead temperature of 130 DEG to 150 DEG F. and a pressure of 15-30 p.s.i.g. in a tower containing 30 to 50 plates. The bottoms product is preferably maintained at 200 DEG to 260 DEG F. for 6 to 20 hrs. in the second thermal soaking zone, the pressure being sufficient to maintain liquid phase. The piperylene may be distilled off at a bottoms temperature of 270 DEG to 310 DEG F., an overhead temperature of 160-210 DEG F. and a pressure of 5 to 20 p.s.i.g. in a tower containing 20 to 30 plates. The piperylene-rich stream may be subjected to thermal dimerization at 250 DEG to 400 DEG F. for 6 to 24 hours, or polymerized, e.g. with aluminium chloride catalyst, whereafter benzene may be separated. Alternatively piperylene monomer may be obtained by further fractionation and extractive distillation with aqueous acetone, furfural or dimethyl sulpholone. Data is given illustrating the improvement in isoprene recovery over a process without partial dimerization of cyclopentadiene.