FCC Process Role in Propylene Demands

It is widely recognized that naphtha steam crackers are the largest current source of propylene. The yield of propylene from a naphtha cracker is approximately half the yield of ethylene because ethylene has historically averaged a higher market price than propylene. Ethylene producers have primary built naphtha crackers to meet their ethylene demands and recovered propylene as a by-product. The availability of ethane at standard gas prices has attracted a large buildup of ethane-based steam cracker capacity, which produces very little propylene. As a result of buildup of ethane-based crackers, the propylene production rate from steam crackers is anticipated to fall, though the demand for propylene is expected to increase relative to the demand for ethylene. These market dynamics, if proven true, will result is a growing gap between propylene demands and propylene supplied from steam crackers, placing more emphasis and creating more opportunity for fluid catalytic cracking unit (FCC) units. The second largest source of propylene supplied for petrochemical application is from FCC units. The primary function of FCC units has typically been to produce gasoline. However, refiners have been taking advantage of the opportunity to produce and recover more propylene from FCC units by increasing the reaction severity via riser temperature, adding shape-selective catalyst, and installing propylene recovery units (PRUs). In this article propylene production methods are reviewed and comparisons between the methods are made.