N-pentane diffusion

In mixtures with n-hexane for which the influence of intermolecular repulsive forces appear to be stronger, we find that n-pentane diffusivity is enhanced. This is most likely due to higher repulsive forces between n-pen-tane/n-hexane molecules residing in adjacent pore positions than between... 

Figure A3.6.13. Density dependence of die photolytic cage effect of iodine in compressed liquid n-pentane (circles), n-hexane (triangles), and n-heptane (squares) [38], The solid curves represent calculations using the diffusion model [37], the dotted and dashed curves are from static caging models using Camahan-Starling packing fractions and calculated radial distribution fiinctions, respectively [38],...

C. In their first series of experiments, six data sets were obtained for (H) and (u), employing six solvent mixtures, each exhibiting different diffusivities for the two solutes. This served two purposes as not only were there six different data sets with which the dispersion equations could be tested, but the coefficients in those equations supported by the data sets could be subsequently correlated with solute diffusivity. The solvents employed were approximately 5%v/v ethyl acetate in n-pentane, n-hexane, n-heptane, -octane, -nonane and n-decane. The solutes used were benzyl acetate and hexamethylbenzene. The diffusivity of each solute in each solvent mixture was determined in the manner of Katz et al. [3] and the values obtained are included... 

This increase in activity was attributed to a lower diffusion resistance of the aluminum-deficient zeolites, which resulted from the removal of amorphous material from the zeolite channels. However, the hydroisomerization of n-pentane... 

If the addition of pentane occurs at 60-70% conversion, two influences result an increase in pressure due to the arranged loss of soluble styrene with increasing conversion, and a decrease in pressure because of increasing diffusion of pentane into the beads. The equilibrium pressure for the quaternary system styrene-polystyrene-isopentane-n-pentane has been calculated by Wolfahrt [27] for different conversions, temperatures and //-/isopentane ratios using a thermodynamic sorption model based on chain-of-rotators equation-of-state. 

Kinnear and Knox [106, 172] studied the oxidation of n-pentane at low conversions at 290 °C and found the acetone, a major product, was particularly sensitive to the nature of the reactor surface (Fig. 21) and that the ratio of the yields of the other products to acetone varies linearly with pentane concentration (Fig. 22). Addition of inert gas showed that this ratio is also directly proportional to the diffusion time for the pentylperoxy radicals (Fig. 23). 

Fig. 23. The variation with diffusion time of the ratio of product yield/acetone yield at a constant n-pentane pressure of 10 torr. , pent-2-ene 2-methyltetrahydrofuran , 2,4-dimethyloxetan , pent-l-ene. (From ref. 106.)...

The intracrystalline diffusivities of llZSM-5 zeolite were directly measured for several hydrocarbons at higher temperatures (373-773 K) by the constant volume method. High silicious HZSM-5 zeolite, which has no activity for reactions, was used as the adsorbent. Aromatics benzene, xylene-isomers ortho-, meta- and para-xylene) and toluene, and paraffins n-hexane, n-pentane, p-octane and iso-octane, were used as adsorbates. Intracrystalline diffusivities of aromatics markedly depended on the minimum size of the aromatics and that of paraffins depended on the carbon number (molecular weight of the paraffins). A method was developed for predicting diffusivity in terras of pore diameter and molecular properties of hydrocarbons. This method was found to well represent the experimental results. 

Table 8 also summarizes the activation energies, a> which do not exhibit any apparent dependence on the chain length. This behavior was also stated by Eic and Ruthven [54,55], who found an increasing activation energy for the diffusion of paraffins in silicalite-1 up to n-hexane and a leveling off for carbon numbers greater than six. For n-pentane, these authors determined... 

Fig. 8 FR spectra of methane (a), ethane (b), propane (c), n-butane (d), n-pentane (e) and n-hexane (f) in sUicalite-l (cf. [65]). (n.o) indicate the experimental in-phase and out-of-phase KSqm characteristic functions, respectively. A single diffusion process model was used to fit the data in (1), while the non-isothermal diffusion model was used to fit the data in (2) except (f, 2) which was fitted using the two independent diffusion processes model. Solid lines denote the theoretical overall characteristic functions, and dash and dash-dot lines denote the theoretical diffusion processes occurring in the straight channels (dash) and the sinusoidal channels (dash-dot). Note 1 Torr= 133.33 Pa...

Around a value of the gas-phase fraction of 2-methylpentane of about 0.83, the influence of the acid sites on the n-hexane diffusivity is not dominant anymore in comparison to the pore occupation of slow-diffusing 2-methyl-pentane. Figure 14 shows the dependence of the diffusivities of both components versus the concentration of adsorbed 2-methylpentane in terms of molecules per unit cell. The diffusivities of n-hexane in silicalite-1 and H-ZSM-5 become nearly equal when the concentration of 2-methylpentane reaches approximately 2.75 molecules per unit cell. For 2-methylpentane we And that the self-diffusivity in silicalite-1 becomes very close to the value in H-ZSM-5 at the same loading. 

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