Benzene Research Octane Number

The cumene product is 99.9 wt % pure, and the heavy aromatics, which have a research octane number (RON) of 109, can either be used as high octane gasoline-blending components or combiaed with additional benzene and sent to a transalkylation section of the plant where DIPB is converted to cumene. The overall yields of cumene for this process are typically 97—98 wt % with transalkylation and 94—96 wt % without transalkylation. 

A tank containing 1500 m3 of naphtha is to be blended with two other hydrocarbon streams to meet the specifications for gasoline. The final product must have a minimum research octane number (RON) of 95, a maximum Reid Vapor Pressure (RVP) of 0.6 bar, a maximum benzene content of 2% vol and maximum total aromatics of 25% vol. The properties and costs of the three streams are given in the Table 3.5. 

In view of these considerations, a large amount of effort is reported in the scientific press on the development of a process to produce benzene from n-hexane by combined cyclization and dehydrogenation. w-Hexane has a low Research octane number of only 24.8 and can be separated in fair purities from virgin naphthas by simple distillation. Recently, an announcement was made of a process in the laboratory stage for aromatiza-tion of n-hexane (16). The process utilizes a chromia-alumina catalyst at 900° F., atmospheric pressure, and a liquid space velocity of about one volume of liquid per volume of catalyst per hour. The liquid product contains about 36% benzene with 64% of hexane plus olefin. The catalyst was shown to be regenerable with a mixture of air and nitrogen. The tests were made on a unit of the fixed-bed type, but it was indicated that the fluid technique probably could be used. If commercial application of this or similar processes can be achieved economically, it could be of immense help in relieving the benzene short-age. 

Since the work described above was completed, 23 additional hydrocarbons have been brought to cool-flame combustion in the same apparatus (19). Any paraffin, cycloparaffin, or olefin having a research octane number not to exceed 90 may be brought to cool-flame combustion by such a procedure. Aromatic hydrocarbons for the most part do not fall within the indicated range, but n-butyl benzene yields a cool flame with much smoke and soot formation. 

Several patents discuss the use of Raman spectroscopy to determine the properties of finished products.93 94 For reformulated gasoline, some of these properties include sulfur, olefin, benzene, volatile organic carbon (VOC), nitrogen oxides (NOx), aromatic contents, total air pollutants (TAPs), Reid Vapor Pressure (RVP), distillation properties, motor and research octane numbers, and drivability. For the octane numbers, the accuracy of the Raman method was limited by errors in the reference method. 

Figure 6.9.1 Research octane numbers (ROMs) of hydrocarbons of different chain length and molecular structure (naphthenes cyclopentane, cyclohexane, methylcyclohexane, 1,3 dimethylcyclohexane, and 1,3,5-trimethylcyclohexane aromatics benzene, toluene, and m-xylene).

In Fig. 23, spectra of two different grades of U.S. gasoline are shown, de Bakker and Fredericks [90] demonstrated that it was possible to perform a variety of petroleum property measurements, including research octane number (RON), motor octane number (MON), density, benzene content, and flexible volatile index (FVI), using fiber-optical FT-Raman spectroscopy coupled with partial least-squares analysis to reduce sample fluorescence. The potential for on-line measurement of these properties was mentioned by both Cooper et al. [89] and de Bakker and Fredericks [90], Cooper et al. [89,92,93] compared Raman spectroscopy to both mid-IR and near-IR for the measurement of several parameters in fuel mixtures including aromatic concentrations, octane number, and vapor pressures. Cooper et al. similarly utilized partial least squares to accomplish the data analysis. In this series of articles. Cooper et al. described their attempts to quantify mid-IR, near-... 

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. 

Octane number is measured by research. The octane number of hexane is 24.9, branched alkane wobutane is 101.3 and 2,3,4-trimethylpentane is 102.5, in aromatic compounds benzene is 106, toluene is 110 [28,29]. These compounds having high octane numbers are used for blending agents to gasoline. 

One of the advantages of GC-MS over an IR spectroscopic analyzer is the ability to measure distillation characteristics as well as predict other properties. There are several other materials that can be directly measured and reported. These include benzene, total aromatics, oxygenates, certain sulfur compounds and additives. The properties that can be predicted include (among others) cetane number and index, research and motor octanes, refractive index, distillation properties, aniline point, cloud point, pour point, volatility, flash point, density, conductivity, and viscosity [57]. 

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