Metathesis unit pretreatment process with formation of octene

A process for converting an olefinic C4 stream comprising isobutene, butene-1 and butadiene to propylene and octenes, comprising:

• a) subjecting the olefinic C4 stream to a selective hydrogenation step, in the presence of a catalyst, to remove butadiene by partial hydrogenation to butene and to convert butene-1 to butene-2, to thereby obtain a partially hydrogenated effluent stream;
• b) separating the partially hydrogenated effluent stream, by distillation, into an overhead fraction containing butene-1 and hydrocarbon compounds boiling at lower temperatures than butene-1, and a bottom fraction containing compounds boiling at higher temperatures than butene-1;
• c) feeding at least a portion of the overhead fraction from step (b) as a dimerization reactor feed to a dimerization reactor, and subjecting the dimerization reactor feed, in the presence of a dimerization catalyst, to a dimerization step to form a dimerization reactor product;
• d) separating at least a portion of the dimerization reactor product to form an octene-rich liquid and a C4-rich vapor stream;
• e) feeding the octene-rich liquid from step (d) to the distillation of step (b), and removing a bottoms product from the distillation of step (b), containing substantially all of the octene from the octene-rich liquid;
• f) removing a mid-cut product comprising butene-2 from the distillation of step (b), from a point intermediate from where the overhead and the bottom fractions are taken;
• and
• g) subjecting the mid-cut product to metathesis with ethylene, in the presence of a metathesis catalyst, to obtain a metathesis reactor product including propylene.