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Cat naphtha sulfur management: undercut or not?

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


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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