In response to a request, I wrote an article for Oil & Gas Journal in 1985 on future unleaded compositions, optimizing blends, using generalized blending equations (www.gasolineblendingplus.com; OGJ, Mar. 18, 1985, p. 99). I assumed 75% regular and 25% premium. In addition, I chose to add a case with 25% subregular, 50% regular, and 25% premium, with (R+M)/2 ratings of 82, 87, and 92. The subregular composition was 57% cat-cracked, 39% light straight run, 4% butane. Essentially, the same octane would have been obtained by replacing full boiling cat-cracked with heavy cat-cracked to increase miles per gallon.
The desirability of adding a subregular has increased since then through introduction of automatic spark retard to avert knock. The control-knock intensity is so light that typical motorists will not notice it unless the spark retard is insufficient to prevent noticeable knock. With the spark-retard feature, switching to a lower octane gasoline is unlikely to result in noticeable knock, but acceleration will be slower due to the spark retard. This effect has been documented in a Coordinating Research Council Study (CRC Report 597). However, I believe the slower acceleration would go unnoticed by most motorists, even with an 82 (R+M)/2 gasoline. Furthermore, the lower cost might overshadow a noticeable increase in acceleration time or occasional noticeable knock. The market for a subregular could be quite large.
In the 1985 study, introduction of the subregular gasoline allowed a decrease in reforming severity from 101 to 96. If high-severity reforming is necessary to provide sufficient hydrogen, it may be feasible to take advantage of the economics by purchasing full-boiling straight run and using it along with heavy reformate to provide a high-mileage “economy-grade” gasoline.
Refineries appear to be operating more and more in a cash-cow mode. This should not foreclose being alert to profit opportunities due to changing conditions. Addition of an economy grade gasoline is one possibility. Other opportunities exist within the refinery. One opportunity is the higher price for diesel.
A possible response to the higher diesel price is dedication of the 300-400° F. straight-run cut to diesel. Current economics might favor separation of hydrocarbon types to maximize the cetane of the 300-400° F. cut. My most recent OGJ article, “Calculating high cetane 300-400° F. cut for diesel,” estimates 53 cetane number after extracting aromatics (OGJ, Feb. 8, 2010, p. 46).
William E. Morris
Consultant
Wilmington, Del.
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