Solid n-alkanes

The principle of proximity which operates in dimer formation predicts that a solid n-alkane with an odd number, m, of carbons should form m-isomeric dimers while an n-alkane with an even number, n of... 

In Figure 2.2-8 the critical endpoint temperatures for the family 0f CO2 + n-alkanes systems are plotted as a function of the carbon number n. If in a particular binary system the three-phase curve hhg is followed to low temperature then at a certain temperature a solid phase is formed (solid n-alkane or solid C02 at low carbon numbers). This occurs at one unique temperature because we now have four phases in equilibrium in a binary system, so according to the phase rule F= 0. Below this so-called quadruple point temperature the hhg curve is metastable. 

Solubilities of Five Solid n-Alkanes in Supercritical Ethane... 

The n-alkanes are an interesting homologous series because they display great regularity in their behavior. Many of their fluid phase properties, for example, can be correlated with the number of carbon atoms in the molecules ( 1, 2 ). In order to develop general relations for supercritical extraction, therefore, we have stud.ied the solubilities of solid n-alkanes containing 28 to 33 carbon atoms in supercritical ethane. 

Solubilities of heavy hydrocarbons in supercritical fluids depend on the type of solvent (6). Moradinia and Teja (7) showed that the solubilities of solid n-alkanes (n-C2g, n-C Q, n-C ) are about ten times higher in supercritical ethane than in carbon dioxide. Therefore, it is reasonable to search and find an appropriate solvent which can disintegrate and dissolve the carbonaceous deposits from hydrotreating catalysts, resulting in their decoking and regeneration. 

W.B. Nelligan, D.J. LePoire, T.O. Brun R. Kleb (1987). J. Chem. Phys., 87, 2447-2456. Inelastic neutron scattering study of the torsional and CCC bend frequencies in the solid n-alkanes, ethane, hexane. 

The Dill-Flory model may be considered as a more rigorous version of the Hartley model (30). Both models are readily applied to other shapes of micelles, such as rods, discs, bilayers, and vesicles. Also, it follows that diameters of spherical, rodlike, and disclike micelles cannot exceed the total length of two hydrocarbon chains in all-trans conformation. The number of entities in one micelle, i.e. the aggregation number s, is therefore readily estimated for any given chain length r. Assuming equal densities p (= 0.777 g/cm ) for micelles and solid n-alkanes, r may be obtained from the volume v and the constant cross section A (= 2.385 x 10 cm ) of alkane chains ... 

Petroleum is not the only place where alkanes occur naturally. Solid n-alkanes, especially those with relatively long chains, have a waxy constituency and coat the outer surface of many living things where they help prevent the loss of water. Pentacosane [CH3(CH2)23CH3] is present in the waxy outer layer of most insects. Hentriacontane [CH3(CH2)29CH3] is a component of beeswax (see Problem 2.6) as well as the wax that coats the leaves of tobacco, peach trees, pea plants, and numerous others. The C23, C25, C27, C29, and C31 /2-alkanes have been identified in the surface coating of the eggs of honeybee queens. 

LAMs were first observed in the low-frequency Raman spectra of solid n-alkanes as strong, polarised bands with frequency inversely proportional to the chain length [243]. They are due to a symmetrical accordon-like vibration of the extended chain, which can be modelled as an elastic rod of modulus E, length L and density p, with a resultant vibrational frequency Elp)il2L. Therefore, the effect of chain length on frequency is predicted by a simple mechanical model. 

It was discussed elsewhere 16 that in nonionogenic solid/n-alkane - water systems, determinations of zeta potential as a function of the film specific volume may be used for studies of energetic changes. 

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