FCC gasoline

Table 10.10 is an evaluation of the improvement resulting from the addition of alkylate and ethers to an FCC gasoline. 

Sweetening of the FCC gasoline is usually sufficient to meet its sulfur specifications. However, in areas where reformulated gasoline is marketed, sulfur specifications in the gasoline may require more treatment. The mercaptans in the LPG need to be extracted to protect the downstream processes, such as alkylation. Sulfur increases acid consumption and produces undesirable by-products. 

Desulfurization of FCC feedstocks reduces the sulfur content of FCC products and SOX emissions. In the United States, road diesel sulfur can be 500 ppm (0.05 wt%). In some European countries, for example in Sweden, the sulfur of road diesel is 50 ppm or less. In California, the gasoline sulfur is required to be less than 40 ppm. The EPA s complex model uses sulfur as a controlling parameter to reduce toxic emissions. With hydroprocessed FCC feeds, about 5% of feed sulfur is in the FCC gasoline. For non-hydroprocessed feeds, the FCC gasoline sulfur is typically 10% of the feed sulfur. 

When using ZSM-5, there is almost an even trade-off between FCC gasoline volume and LPG yield. For a one-number increase in the research octane of FCC gasoline, there is a 1 vol% to 1.5 vol% decrease in the gasoline and almost a corresponding increase in the LPG. This again depends on feed quality, operating parameters, and base octane. 

Engelhard Corporation, Reduced Unit Cell Size Catalysts Offer Improved Octane for FCC Gasoline, The Catalvst Report, Tl-762. 

In the previous examples, the feed characterizing correlations in Chapter 2 are used to determine composition of the feedstock. The results show that the feedstock is predominantly paraffinic (i.e., 61.6% paraffins. 19.9% naphthenes, and 18.5% aromatics). Paraffinic feedstocks normally yield the most gasoline with the least octane. This confirms the relatively high FCC gasoline yield and low octane observed in the test run. This is the kind of information that should be included in the report. Of course, the effects of other factors, such as catalyst and operating parameters, will also affect the yield structure and will be discussed. 

FCC gasoline has always been the most valuable product of a cat cracker unit. FCC gasoline accounts for about 35 vol% of the total U.S. gasoline pool. Historically, the FCC has been run for maximum gasoline yield with the highest octane. 

The key components affecting FCC gasoline quality are octane, benzene, and sulfur and are discussed in the following sections. 

FCC gasoline contains 0.5 to 1.3 vol% benzene. Since it accounts for about 35 vol% of the gasoline pool, it is important to know what affects the cat cracker gasoline benzene levels. The benzene content in the FCC gasoline can be reduced by ... 

FCCU Feed Sulfur, wt% Figure 6-7. FCC gasoline sulfur yield [4],... 

FCCU FEEDSTOCK SULFUR (wt%) Figure 6-8. Hydrotreating reduces FCC gasoline sulfur [4],... 

The fresh catalyst s chemical properties also influence the FCC gasoline octane. Gasoline octane is increased by ... 

These non-linear equations can be embedded into the refinery s linear program (LP) to achieve compliance and optimize the gasoline blend. The key FCC gasoline components that influence RFG are ... 

The sulfur compounds in FCC gasoline consist of C -C mercaptan and various thiophenes. 

FCC feed hydrotreating Gasoline end point reduction FCC gasoline hydrotreating Catalyst additives Bio-catalytic desulfurization... 

For nonhydrotreated feed, the gasoline sulfur level is about 10% of the feed sulfur level. For hydrotreated feed, it is about 5%. For example, if the sulfur content of a nonhydrotreated feed is 1.0 r (10,000 ppm), the sulfur in FCC gasoline will be 1,000 ppm. Assuming 80% desulfurization, feed to the FCC unit will contain 0.2% (2000 ppm) sulfur, resulting in FCC gasoline containing 100 ppm sulfur. Sulfur compounds that survive the hydrotreater are in the heav fraction and tend to end up in the LCO, decanted oil, and coke. 

Caustic extraction can remove mercaptan sulfur in light fractions, but not higher carbon number mercaptans or other types of sulfur molecules that are in the FCC gasoline. 

Catalyst additives can reduce FCC gasoline sulfur by about 15%. They work by converting mercaptan, thiophene, etc., to H S. A secondary benefit of the additives is an approximate 10% reduction in the LCO sulfur. 

The benzene content of FCC gasoline is typically in the range of 0.6 vol /i to 1.3 vol%. CAAA s Simple Model requires RFC to have a maximum of 1 vol% benzene. In California, the basic requirement is also 1 vol% however, if refiners are to comply with averaging provisions, the maximum is 0.8 vol%. Operationally, the benzene content of FCC gasoline can be reduced by reducing catalyst-oil contact time and catalyst-to-oil ratio. Lower reactor temperature, lower rates of hydrogen transfer, and an octane catalyst will also reduce benzene levels. 

In 1990, U.S. gasoline contained about 10 vol% olefins, the majority of which emanate from FCC gasoUne. FCC gasoline has 25 vol% to 35 vol% olefins. Of these olefins, Cg-C olefins account for about 85% of the total pool. For non-RFG gasoline, as with sulfur, the regulation allows the maximum olefin content to be 125% of the 1990 baseline values. 

Further developments in the effectiveness of the FCC gasoline sulfur reduction additives will allow a number of refiners to meet the required reduction in gasoline sulfur without undertaking costly capital projects. Additionally, improvements in the CO promoter additives will reduce NO emissions when the promoter is used. Finally, other... 

Baco, F., Debuisschert, Q. Marchal, N., et al., Prime G+ process, desulfurization of FCC gasoline with minimized octane loss, in Fifth International Conference on Refinery Processing, AICHE 2002 Spring National Meeting. 2002. New Orleans, LA, March 11-14. 180-188. 

Shih, S. S. Owens, P. J. Palit, S., and Tryjankowski, D. A., Mobil s OCTGainprocess FCC gasoline desulfurization XE desulfurization reaches a new performance level, in NPRA 1999 Annual Meeting. 1999, March 21-23. AM-99-30. 

Figure 11 SCD chromatogram of catalytic cracked (FCC) gasoline, demonstrating the selectivity for sulfur compounds. (A) SCD response (B) FID response. (Reprinted from American Laboratory 23(3) 117, 1991. Copyright 1991 by International Scientific Communications, Inc.)...

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