Octane number blending

Most of the octane blending values reported ia the Hterature use a slight variation on this theoretically sound approach. The composition and octane of the base fuel are assumed to be fixed and the second component is assumed to be added. Using the same nomenclature, the blending octane number (BON) of component 2 is defined as... 

The advantage of this definition is that it does not depend on measuting the tangent of the response curve, although the variation ia the value of the blending octane number is greater. Typically, BONs are measured at an 80/20 mixture. This technique is also usehil when trying to measure the octane of a compound such as butane or methanol that is difficult or impossible to measure ia its pure state. 

The octane number R + M jT) of such reformates is typically in the range of 88.9—94.5, depending on severity of the reforming operation. Toluene itself has a blending octane number of 103—106, which, as shown in Table 19, is exceeded only by oxygenated compounds such as methyl tert-huty ether, ethanol, and methanol. 

Table 19. Blending Octane Number, (R + for Selected Components in Unleaded Gasoline...

The data in Table IV and Figure 1 indicate that most of the paraffin concentration reduction took place in the Ce to Ce range and involved monomethyl paraffins. The blending octane numbers for 2-methyl and 3-methyl hexanes are reported as 40 to 56 by ASTM ( ) and are lower than the blending numbers for light (Cs to C ) olefins and Ce to Cii aromatics. Thus, reduction in concentration of these branched paraffins is expected to improve the research octane number of the gasoline. 

An arbitrary mixture of hydrocarbons is compared to a mixture of these two compounds, with its octane number that equal to the appropriate mixture of these standard compounds. Some molecules and their octane ratings are indicated in Table 2-6. Aromatics have a high octane number (toluene is 120), and some compounds such as tetraethyl lead have a strong octane enhancement when added to other mixtures (blending octane number). Oxygenates such as ethanol and ethers (MTBE) have fairly high octane numbers and supposedly produce less pollution, either alone or blended with hydrocarbons. 

The process data are summarized in Table XI. The operation was conducted at a pressure of 250 pounds per square inch and a temperature of 934° F. The depentanized liquid product was fractionated into three cuts called preaviation, aviation, and postaviation blending agents. The yields of these three products were 22.8, 33.5, and 12.6 volume %, respectively. The aviation blending agent had an F-3 blending octane number (1-C) of 100 and an F-4 blending index number (3-C) of 216. The clear research oc-... 

The boiling point, refractive index, and density of the olefin derivative of any paraffin were shown, by use of Table III, to stand in the onier of their olefin type. Table X contains the engine data of the olefin derivatives of 2-methylpentane and 3-methylpentane, recorded in the order of their olefin type. No consistent relations between octane numbers or critical compression ratios are obvious—but the blending octane numbers of these branched olefins, as measured by both the research and Motor methods, do generally stand in the order of their type. Two olefins of type III form exceptions, the exceptions being in one case too high and in the other case too low. 

The blending octane number of benzene is the lowest for any aromatic hydrocarbon thus far measured. When measured by either the Research or Motor method it seems to form another case where the first member of an homologous series is anomalous. 

Traditionally, solid acidic catalysts are applied in industry for the oligomerization of butenes and are still studied. MTS-type aluminosilicates,522 a NiCsNaY zeolite,523 and a silica-alumina containing 13% alumina524 proved to be active and selective catalysts. Moreover, deactivation rates of these catalysts are also favorable. Sulfated zirconia promoted with Fe and Mn was active and selective to yield primarily dimethylbutene isomers under supercritical conditions.525 A small amount of water improved productivity and decreased deactivation. A study showed that the blending octane number of Cg hydrocarbons is directly linked to the number of allylic hydrogens in the molecules.526... 

Kobayashi used molecular dimensions directly (101-4). For paraffins he defined an unstability factor which was a measure of approach to a sphere. A fair correlation was obtained between his factor and blending octane number. The calculated factors indicated the observed rise in knock rating with centralization of the double bond in a straight-chain olefin. Gaylor (69) applied Kobayashi s method to aromatics and compared calculations with both clear and blending octane numbers. It is difficult to select molecular dimensions of a flexible molecule representative of its configuration during reaction. 

The published values of blending octane numbers from the API project... 

Fig. 7.7. Non-linear blending of octane number and the definition of blending octane number as used in the API-45 project, illustrated schematically. Mixtures of fuels may show either positive or negative deviations from linearity (solid curves). The blending octane number of a hydrocarbon tabulated in Refs. [10] and [13] is obtained by extrapolation from the ON of the base fuel through the measured octane number of a mixture containing 20% of the hydrocarbon to the righthand axis, as shown.

The FCC produces roughly 2.5 wt% on feed of tertiary amylenes. They are also readily etherified on cationic resins into TAME. The octane numbers for TAME are somewhat lower than for MTBE RON =112, MON = 99. In blends one finds that part of the MTBE may be substituted by TAME without penalty on the blend octane numbers. Again, full recovery and etherification of the tertiary amylenes would yield a total TAME product representing less than 3.5% of the gasoline pool. 

Heavy aromatics formed in the octafiner also have excellent octane number blending values and are generally returned to the refinery gasoline pool. The stream consists entirely of Co and Cio alkylbenzenes. Blending octane numbers (I) of these compounds range from 118 to 170. The Co fraction contains approximately 50 vol % pseudocumene and 20 vol % mesitylene. 

The differentiation between additives and secondary fuels is arbitrary. Synthetic materials, like alkaly tes, act as secondary fuels of a high-blending octane number. They are usually added in quantities above 5% by weight of the blend. A substance is classified as an additive if less than 5% of it is present in the fuel and as a secondary fuel if the quantity varies between 5% and 50%. 

Table 4. Octane and Blending Octane Numbers by Research Method...

Cetane number Diesel Index Blending octane number (Motor method) Character- ization Factor Boiling- point gravity number ... 

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