Hexane isomers

Tbe partial results are shown in Figure 2-6.2.1. Tbe ranges of ignitable concentrations are superimposed on a spark ignition energy curve for bexane in air calculated from data in [56]. Both data sets are assumed to be characteristic ofn-hexane, unbiased by the presence of methylcyclopentane or hexane isomers (dimethylbutanes and methylpentanes). 

The neurotoxicity of pure M-hexane (99%) has been compared to mixed hexanes (a mixture containing the -hexane isomers 2-methylpentane, 3-methylpentane, cyclohexane, methyl cyclopentane, and 2,3-dimethyl butane with approximately 1% -hexane) (IRDC 1981). The mixture was intended to be more representative of products used commercially. In this experiment, groups of Sprague-Dawley rats were exposed to -hexane alone (500 ppm), mixed hexanes (494 ppm) or -hexane plus mixed hexanes (992 ppm) daily for 6 months, 22 hours a day. No deaths occurred as a result of treatment. 

Indirect evidence for an effect of co-exposure to acetone on /2-hexane metabolism in humans has been described (Cardona et al. 1996). In this study, the relationship between free and total 2,5-hexanedione (2,5-hexanedione and 4,5-dihydroxy-2-hexanone, See Section 2.7) in urine and workplace air concentrations of /2-hexane, hexane isomers, acetone, and toluene was analyzed in a group of 87 workers. Median /2-hexane concentrations were 47 mg/m3 (range, 4-652 mg/m3 [13 ppm range, 1-185 ppm]) and median acetone concentrations (only 70 of the 87 workers were exposed) were 109 mg/m3 (range,... 

The increase in hydrogen pressure should suppress both benzene and methylcyclopentane formation. Equilibrium composition for the five hexane isomers, methylcyclopentane, and benzene in sixfold hydrogen excess consists of nearly 100% of benzene at about 400°C (673 K) at 3 atm and at about 600°C (873 K) at 20 atm. Cyclohexane and unsaturated products should be present in concentrations between 10" and 10" mole %. In fact, less cyclohexane and more unsaturated products are observed (30). 

H2/CO2 H2/light hydrocarbons, Hj/n-butane. Xylene isomers, Hexane isomers ... 

Methanol/MTBE, Hexane isomers. Xylene isomers... 

Problem 4.26 Assign numbers, ranging from (1) for lowest to (3) for highest, to the boiling points of the following hexane isomers 2,2-dimelhylbutane, 3-methylpentane. and n-hexane. Do not consult any tables for data. <... 

Equilibria. The equilibrium distributions of butane, pentane, and hexane isomers have been experimentally determined (5, 16) and are diagrammed in Figure 2. In each case, lower temperatures favor the more highly branched structures. At the approximately 200° F. temperature usually employed for isomerization, the butane equilibrium mixture contains about 75% isobutane. That for pentane contains about 85% isopentane.. In the case of hexane, the equilibrium product contains about 50% neohexane and has a Motor octane rating of about 82. In all cases, of course, the yield of the desired isomers can be increased by fractionation and recycle. 

June et al. investigated the sorption and spatial distribution of butane and three hexane isomers within the pores of silicalite, using a Metropolis MC method (87) and MD simulations (85). Perturbations of conformation as a result of confinement within the pore were also reported. Heats of adsorption and Henry s law coefficients were found to be in good agreement with experimental values for butane (48-51 kJ/mol) (142,148,150,163-165) and n-hexane (70-71 kJ/mol) (163, 166, 167). The heats of sorption of the other two hexane isomers, 2- and 3-methylpentane, were predicted to be 5 kJ/mol lower than that of n-hexane. 

The presence of other hexane isomers and a typical hexane isomer distribution of 26% 2,3-dimethylbutane, 28% 2-methylpentane, 14% 3-methylpentane, 32% n-hexane, far from equilibrium, indicate that the 1-propyl cation (although significantly delocalized with protonated cyclopropane nature) is also involved in alkylation. It yields n-hexane and 2-methylpentane through primary or secondary C—H bond insertion, respectively (Scheme 5.3). 

Less information is available about the cracking of alkanes. Three sources [212,232,233] confirm that, in the series of straight-chain alkanes, the rate increases with the molecular weight. The data could be correlated by the Taft equation when the molecule was divided into the reaction centre and such substituents as R—CH2—CH3 [125]. The reactivity of hexane isomers was studied at 550°C on an A1203—Si02— Zr02... 

Ridgway, J. A., Schoen, W., "Hexane Isomer Equilibrium, "Abstracts of... 

Branched-chain alkanes do not exhibit the same smooth gradation of physical properties as do the continuous-chain alkanes. Usually there is too great a variation in molecular structure for regularities to be apparent. Nevertheless, in any one set of isomeric hydrocarbons, volatility increases with increased branching. This can be seen from the data in Table 4-2, which lists the physical properties of the five hexane isomers. The most striking feature of the data is the 19° difference between the boiling points of hexane and 2,2-dimethylbutane. 

Figure 5.12. Distribution of hexane isomers versus reaction time at 20°C.

Here H, I, B, MC, and P are n-hexane, hexane isomers, benzene, methyl-... 

Hexane isomers (C6H14) are produced by two-tower distillation of straight-run gasoline that has been distilled from crude oil or natural gas liquids. 

Let us exemplify the effectiveness of the idea of tree in equilibrium thermodynamic modeling again by isomerization, using the calculations of transformations of three hexane isomers h-hexane (ay), 2-methylpen-tane (x2), and 3-methylpentane (x3) at T = 600 K and P = 0.1 MPa. Graphical interpretation of the analysis is presented in Figure 6a and b. 

The decreasing selectivity for C3 products, but also for C4 and C5 products, indicates that the cracking reaction is more deactivated than the other reactions of the network. The decrease of the paraffin/olefin ratio with the coke content illustrates that the hydrogen transfer reactions, which play an important role in the production of paraffins, are less deactivated. The same can be concluded for the isomerisation reactions leading to the hexane isomers. 

Pending a complete kinetic analysis of the reaction network, the deactivation effect of coke is quantified here by way of example for two types of reactions only the coking reaction itself, and the formation of the hexane isomers. 

The hexane isomers are primary products of n-hexane cracking, so that the partial pressures determing the deactivation effect of coke on these reactions are related to the n-hexane conversion. Hence, the effect of coke on the isomerisation rate of n-hexane is rigorously quantified, provided that the alkane isomers are not significantly involved in further reactions, however. 

Deactivation functions deactivation functions are shown in Table 4. 

The parameters a do not differ significantly, so that the rates of formation of the various isomers equally deactivate, except the 2,2-di-Me-butazie formation. Where the corresponding carbcnium ion of all other hexane isomers is tertiary, that for 2,2-di-Me-butane is secondary, and thus its formation is kinetically much less favored. This explains the low concentration of 2,2-di-Me-butane in the reaction mixture at the conversions shown in Table 3b, and implies that its formation needs a stronger acid site. Since coke is preferentially formed on the stronger acid sites, the formation of this hexane isomer will be more deactivated by the coke formation. 

Figure 5. Diffusion coefficients in HZSM-5 for hexane isomers (at 500°C) and...

Hexanes are a colorless, very volatile liquid with a faint, peculiar odor. It is rarely sold as n-hexane but usually admixed with hexane isomers simply called hexanes , but marketed as hexane . Hexane has a boiling point of 69 Celsius, and a melting point of-100 Celsius. It is insoluble in water, but miscible with alcohol, chloroform, and ether. Hexane is a major component of gasoline, and can be distilled from the gasoline using a multiple-path distillation apparatus. Hexane is obtained commercially from petroleum, and is a widely available commercial chemical. 

Although diffusivity is often important in zeolite catalysis, other factors may also be crucial in determining shape selectivity. Recent work by Post 15a), for example, has shown that the shape selectivity behavior observed for the relative cracking rates of hexane isomers over H-ZSM 5 zeolite (see Section VIII) could not be understood on the basis of their measured diffusivities. Spatial restrictions imposed on transition-state species formed within the zeolite pores provide a possible explanation for the observed results. 

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