Abstract: Manufacture of propylene and ethylene in a FCC unit. Each FCC riser comprises an acceleration zone, a lift stream feed nozzle, a main hydrocarbon stock feed nozzle, and an olefinic naphtha feed nozzle. Mixed FCC catalyst comprising at least 2 percent by weight pentasil zeolite and at least 10 percent by weight Y-zeolite is injected at the bottom of each FCC riser. Olefinic naptha is injected through the olefinic feed nozzle, main hydrocarbon stock is injected through the main hydrocarbon stock feed nozzle and lift stream is injected through the lift stream feed nozzle. Lift stream comprises olefinic C4 hydrocarbon stream and optionally steam and/or a fuel gas. Olefinic C4 hydrocarbon steam is cracked in the acceleration zone at 600 to 800° C., 0.8 to 5 kg/cm2 (gauge) pressure, WHSV 0.2 to 100 hr up 1 and vapour residence time 0.2 to 5 seconds.

Abstract: A fluid catalytic cracking (FCC) process for manufacturing propylene and ethylene in increased yield. The process comprises cracking an olefinic naphtha stream and main hydrocarbon stock in combination with an olefinic C4 hydrocarbon stream in different zones of one or more risers of an FCC unit. Each FCC riser comprises an acceleration zone at the lower portion thereof, a lift stream feed nozzle at the bottom of the acceleration zone, a main hydrocarbon stock feed nozzle above the acceleration zone and an olefinic naphtha feed nozzle at a location along the acceleration zone between the lift stream feed nozzle and main hydrocarbon stock feed nozzle. The cracking is carried out on a mixed FCC catalyst comprising at least 2 percent by weight pentasil zeolite and at least 10 percent by weight Y-zeolite.