PEP Review 80-1-2
Recycle C4s for Ethylene Production
Published: January 1981
Stone & Webster Engineering Corporation have patented a process to increase ethylene yields in liquid-feedstock-based steam crackers by recycling C4s through hydrogenation and isomerization to n-butane. Our evaluation of the process indicates that, under conditions at the U.S. Gulf Coast, the process is not economically viable, because the savings in naphtha feedstock consumption fail to compensate for the loss in C4 by-product values plus the additional processing costs for the C4 recycle. In fact, even if the unsaturated C4s were charged to the recycle system at the cost of fuel, n-butane produced in the recycle process for use in ethylene production would have a transfer price (production cost + 25%/yr ROI before taxes) higher than its market price. We have not examined the economics of the process for conditions in Japan and Western Europe.