Patent ID: 7214841

Claim:
A process for the production of propylene from a C 4 olefin stream containing n-butenes, isobutylene and paraffins comprising the steps of: a. passing said C 4 olefin stream in contact with a metathesis catalyst whereby autometathesis occurs including the reaction of isobutylene with n-butenes and an autometathesis product is produced containing ethylene and propylene and heavier olefins including unreacted isobutylene and paraffins; b. fractionating said autometathesis product to remove an ethylene stream leaving a deethyleneized stream of said propylene and said heavier olefins and paraffins; c. fractionating said deethyleneized stream to remove propylene product leaving a depropyleneized stream of said heavier olefins and paraffins; d. processing said depropyleneized stream to remove isobutylene leaving a remaining C 4 and heavier olefins stream also containing paraffins; e. purging a portion of said remaining C 4 and heavier olefins stream to limit paraffin buildup; f. admixing the remaining portion of said remaining C 4 and heavier olefins stream with a quantity of ethylene sufficient for conventional metathesis wherein said quantity of ethylene comprises said removed ethylene stream and an amount of external fresh ethylene selected such that the molar ratio of said external fresh ethylene to the n-butenes in said C 4 olefin stream is from zero to 0.8; and g. passing said admixture in contact with a metathesis catalyst and reacting at least a portion of the C 4 and heavier olefins stream with ethylene to produce a metathesis product containing additional propylene.