Patent ID: 7157533

Claim:
A process for obtaining, from a fluid catalytically cracked initial C5 fraction, a final C5 fraction which is enriched with isoprene and purified and usable to form a medium for the selective polymerization of isoprene in the presence of a catalytic system based on a conjugated diene, a rare earth salt of an organic phosphoric acid suspended in a saturated inert hydrocarbon solvent, an alkylaluminum of formula AlR 3 or HAlR 2 in which Al represents an aluminium atom, H represents a hydrogen atom and the radicals R, which may be identical or different, and straight-chain or branched, represent hydrocarbon groups having from 1 to 8 carbon atoms, and an alkylaluminum halide, said process comprising: a catalytic hydrogenation reaction of said initial C5 fraction by means of a palladium-based catalyst, which produces an intermediate C5 fraction comprising n-pentenes in a mass ratio which is less than 0.1%, and methyl butenes, a dehydrogenation reaction which is applied to the intermediate C5 fraction, comprising methyl butenes, and which produces said final C5 fraction, and purification of said final C5 fraction thus obtained to obtain said purified final C5 fraction which is essentially free of disubstituted alkynes, true alkynes and cyclopentadiene.