Cat naphtha sulfur management: undercut or not?

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02.01.2001 | Sloley, A. W., CH2M, Bellingham, Washington

Several processing options can create a high-sulfur heavy cat naphtha that concentrates FCC sulfur into one stream

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New U.S. regulations will place intense investment and economic pressures on refinery processing to meet tighter sulfur specifications for gasoline.¹ Fluid catalytic cracking (FCC) unit naphtha (cat naphtha) is the major contributor to gasoline sulfur. Approximately 90%, or even more, of current gasoline sulfur originates from cat naphtha. Efforts to reduce cat-naphtha-sulfur content include:

Pretreat the FCC feed to remove sulfur
Increase sulfur conversion to hydrogen sulfide inside the FCC
Post treat FCC product to remove sulfur.^2-10

Where is the sulfur? Since the 1940s, refiners have known that the bulk of the sulfur concentrates in the heavy end of the cat naphtha.^{11 - 14} Undercutting FCC naphtha is an obvious way to reduce sulfur content. Undercutting includes both dropping naphtha down to light cycle oil (LCO) and taking a separate heavy-naphtha product.

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