Isohexane molecules

Table 2 shows the adsorbed concentrations of the pure components. At a partial pressure of 6.6 kPa the amount of n-hexane is just slightly higher than that of isohexane in silicalite-1, while the linear alkane is obviously adsorbed more strongly than 2-methylpentane in H-ZSM-5 due to the stronger interaction with the acid sites. The maximum loading of each component has been measured by a separate adsorption study. The sorption capacity of n-hexane (7 molecules per unit cell), in agreement with earlier studies [48,59-61] exceeds that of 2-methylpentane (4 molecules per unit cell). The latter value equals the number of channel intersections in the MFI pore system per unit cell. Indeed, the sorption of isohexane molecules at... 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

Figure 2 shows the results of isohexane cracking on MCM-41 and HZSM-5 as examples of mesoporous silica and acidic catalysts. On all the catalysts, products mainly composed of C2 to C4 components as cracking products and C6 components as isomerization products, and the products of possible secondary reactions were not appreciably observed probably because of low conversion level. Since the amount of C2 component was very close to that of C4 components, it is considered that isohexane is cracked in two modes giving C2+C4 and two C3 molecules. In the case of MCM-41, cracking of isohexane proceeded above 598 K, and temperature dependence was not so large below 723 K, but very large above it, as shown in Fig. 2a. On the other hand, HZSM-5 gave smooth temperature dependence as shown in Fig. 2b. Another significant difference between MCM-41 and HZSM-5 was the distribution of cracking products The ratio of C3/C4 was much larger on HZSM-5 than on MCM-41.

Isomerization—A refining process which alters the fundamental arrangement of atoms in the molecule, Used to convert normal butane into isobutane, as alkylation process feedstock, and normal pentane and hexane into isopentane and isohexane, high-octane gasoline components,... 

In our work, only > l% of the propylene formed in the flow system reacted with another molecule of methane to form isobutane. Also, based upon the results of acid quenching and analysis of hydrocarbons, only traces of isopentane and isohexanes were present in the acid. No hydrogen or hydrocarbons above C5 could be detected in the product. 

Of further interest is the fact thot ii-butyl chloride reacts in the presence of excess ethane, also at 40 C, to form butylenes %) and some isobutane (15%)(eq. 6a). These products lead to the conclusion that rearrangement of the "free" trivalent carbenium ion is more rapid than hydride abstraction from another n-butyl chloride molecule. The t-butyl carbenium ion thus formed, being too weak an acid to abstract a hydride, deprotonotes to form butylene products. No isohexane alkylation products are formed (eq. 6). 

Now in the prefix meth- Figure 7.20 od of naming things the molecule in Figure 6.12 (p. 119) would he called isohexane because there are six carhon atoms total and it s the first rearrangement you can create heyond having all six carbons in a row. In the lUPAC system the molecule in Figure 6.12 is called 2-methylpentane. The... 

ZSM-5 is the one in the middle, the one with an n-hexane molecule sitting comfortably inside its ten-membered ring. A hexane with a methyl branch would also fit. The n-hexane, but not the isohexane, would fit into the pores of Erionite, the zeolite with the eight-membered ring at the left. Both hexanes... 

The loading of n-hexane in mixtures is somewhat higher than it is expected to be if it were proportional to its partial pressure (Fig. 12). On the contrary, the 2-methylpentane loading is somewhat lower. This points to preferential adsorption of -hexane over isohexane in their mixtures in H-ZSM-5 than in silicalite-1. In earlier experimental [50] and CBMC simulation studies [44] of n-hexane/isohexane mixtures in silicalite-1, a slight preferential adsorption of the linear alkane over the branched one has been found. The most prominent explanation for this preference is the molecular siting of these two hydrocarbon molecules. Whereas -hexane exhibits no clear preference for a position in the micropore system of MFI zeolite, the branched isomer is preferentially located at the channel intersections due to entropic reasons [44]. Consequently, 2-methylpentane will be pushed out from silicalite-1 by -hexane. These effects are even stronger for H-ZSM-5, most likely due to the stronger... 

Effect on Gasoline Properties. The isomerization of a paraffin rearranges the molecule without changing the density. There is a large increment in the octane number of the gasoline, upon paraffin isomerization. For example, in the case of ra-hexane, there is an increase of more than 60 octane numbers when isomerized to any isohexanes (see Table 1). 

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