Pentane, Research Octane Number

The isomerization process is utilized to convert light paraffins such as butane, pentane, and hexane into higher-octane isoparaffins. Isoparaffins have higher octane numbers than normal paraffins of the same carbon number. For example, n-pentane has a research octane number of about 61, and isopentane has an octane number of approximately 92. 

The temperature of isomerization controls equilibrium isomer composition, and thereby product octane. Figure 4.8 is a plot of isopentane in the C5 product as a function of temperature. The data are from pilot plant runs with three types of commercial UOP isomerization catalysts. The feedstock was a 50/50 mixture of normal pentane and normal hexane, containing about 6% cyclics. The 1-8 and I-80 catalysts are very active at a low temperature, where equilibrium isopentane content is highest. The acid functions in 1-8 and 1-80 are chlorided aluminas. The zeolitic catalyst, HS-10 , requires relatively high temperatures of operation. The LPI-100 catalyst contains sulfated zirconia as the acid function and falls in the middle of the temperature range (12). Due to the equilibrium constraints, a lower temperature operation yields a higher octane product. The 1-8 and 1-80 catalysts yielded Research Octane Numbers of 82-84, as compared to 80-82 for LPI-100 catalyst and 78-80 for HS-10. 

Table 7.2 Research Octane Number (RON) of pentanes and hexanes...

For resin/BF3 catalyst, the above process variables also affect alkylate quality. However, with the resin/ BF3 catalyst, the surface area of resin in addition to the functional group of the resin, may also play an important role in directing alkylation. Some results illustrating the effect of the resin s surface area on alkylate quality are shown in Table III. clearly, increasing the resin s surface area improves the alkylate quality both in terms of the fraction of trimethyl-pentanes in the C5+ alkylate and the clear research octane number (RON) of the C5+ alkylate. 

Alkylate product has a high concentration of 2,2,4-trimethyl pentane, the standard for the 100 rating of the octane number scale. Other compounds in the alkylate are higher or lower in octane number, but the lower octane number materials predominate so that alkylate has a Research octane number in the range of 92 to 99. Developments are under way to slant the reactions in favor of the higher-octane materials. Random samples of alkylate quality reported in the literature are summarized in Table 15.10. 

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