Straight alkanes

Aviation gasoline consists primarily of straight and branched alkanes and cycloalkanes. Aromatic hydrocarbons are limited to 20 to 25% of the total mixture because they produce smoke when burned. A maximum of 5% alkenes is allowed in JP-4. The approximate distribution by chemical class is 32% straight alkanes, 31% branched alkanes, 16% cycloalkanes, and 21% aromatic hydrocarbons. 

The results presented in this paper provide a simple explanation for the compensation effect. Neopentane (C-(CH3)4) is chosen as a specific example since neopentane can only adsorb via one of the methyl groups, and therefore its adsorption can be approximated by CH3 adsorption, which has been considered in this paper. Other, more straight alkanes like n-hexane can adsorb in a variety of geometries, which complicates the picture. 

Both types of anti-knock are more effective in paraffinic fuels then in olefinic or aromatic fuels, and can even promote knock when added to some alcohols. In Fig. 7.9 the response of some pure hydrocarbons to the addition of 3ml/US gal of tetra-ethyl lead is shown, in terms of Performance Number. Almost all the alkanes lie on a steeper line than the alkenes. The exceptions are low octane number alkenes, which are largely straight alkane chains, and a few highly-branched alkanes (which also have high sensitivity, see Section 7.2.3). Notwithstanding the subtleties of lead additives, a broad explanation in chemical kinetic terms is that the antiknock acts to increase radical termination rates and, consequently, has proportionately less effect in those fuels where the termination rates are already high. 

Alkane sulfonates are mainly produced by two methods, i.e. the process of sulfochlorination and the process of sulfoxidation. In both processes, a radical chain reaction takes place and therefore the alkane starting material must be free from branched compounds, olefines and aromatics because such compounds will act as chain-stoppers in the chain reactions. Highly pure straight alkanes of paraffin fractions from 13 to 18 carbon atoms are used, with an optimum in the range of 14-17 carbons in the chain. 

However, some authors have stressed the difficulties associated with the determination of the molecular area, especially for non-spherical molecules such as straight alkanes. To avoid the problems derived from the molecular area, Dorris and Gray [26] considered the adsorption characteristics of single methylene groups in the n-alkane probes. By defining the increment in free energy of adsorption per - CH2- unit ... 

For branched alkanes, the alkoxy radical dissociation rate coefficients are higher than for the straight alkanes, and these reactions compete more effectively with isomerization, so that the dominant products become carbonyls. For example, from n-hexane, carbonyls constitute 10% of the products and hydroxycarbonyls 57%, while for 2,2,4-trimethylpentane the carbonyls constitute 50-55% of the products and the hydroxycarbonyls 25-30% (Atkinson et al., 2008). 

Paraffins consist mainly of straight chain alkanes, with a very small proportion of isoalkanes and cycloalkanes. Their freezing point is generally between 30°C and 70°C, the average molecular weight being around 350. When present, aromatics appear only in trace quantities. 

Fig. 8.22 Schetnatic structure of the zeolite silicalite showing the straight and zig-zag chaimels. (Figure adapted fron Smit B and JI Siepmann 2994. Simulating the Adsorption of Alkanes in Zeolites. Science 264 1118-1120.)...

Isomerization (rearrangement) of hydrocarbons is of substantial practical importance. Straight-chain alkanes obtained from petroleum... 

Unbranched alkanes are sometimes referred to as straight chain alkanes but as we 11 see m Chapter 3 their chains are not straight but instead tend to adopt the zigzag shape portrayed m the bond line formulas introduced m Section 1 7... 

ALKYLATION OF ALIPHATIC COMPOUNDS The first reported alkylation of branched-chain alkanes by ethylene, over aluminum chloride (69), made it possible to alkylate alkanes (except methane and ethane) with straight chain or branched alkenes. 

Mote stable catalysts ate obtained by using fluorinated graphite or fluorinated alumina as backbones, and Lewis acid halides, such as SbF, TaF, and NbF, which have a relatively low vapor pressure. These Lewis acids ate attached to the fluorinated soHd supports through fluorine bridging. They show high reactivity in Friedel-Crafts type reactions including the isomerization of straight-chain alkanes such as / -hexane. 

Open-chain saturated hydrocarbons have the generic names alkanes and paraffins. In this article, terms such as hexanes, heptanes, and octanes are synonymous with C, C, and Cg alkanes, respectively, and do not refer to the straight chains of 6 carbons, 7 carbons, and 8 carbons, as defined in the lUPAC system. 

About 2% of benzene consumed in 1988 was used for the manufacture of straight-chain or branched-chain detergent alkylate. Linear alkane sulfonates (LAS) are widely used as household and laundry detergents. 

The straight-chain hydrocarbons represent just one group of straight-chain hydrocarbons, the saturated hydrocarbons known as the alkanes. There are other series of hydrocarbons that are unsaturated one of those is important in the study of hazardous materials. Additionally, the first hydrocarbon in another series is the only hydrocarbon important in that series. Each of these hydrocarbon series are briefly described below. 

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