Diffusion alkanes

Courtney S H, Kim S K, Canonica S and Fleming G R 1986 Rotational diffusion of stiibene in alkane and alcohol solutions J. Chem. See. Faraday Trans. 2 82 2065-72... 

Sun Y-P and Saltiel J 1989 Application of the Kramers equation to stiibene photoisomerization in / -alkanes using translational diffusion coefficients to define microviscosity J. Phys. Chem. 93 8310-16... 

Matthews-Akgerman The free-volume approach of Hildebrand was shown to be valid for binary, dilute liquid paraffin mixtures (as well as self-diffusion), consisting of solutes from Cg to Cig and solvents of Cg and C o- The term they referred to as the diffusion volume was simply correlated with the critical volume, as = 0.308 V. We can infer from Table 5-15 that this is approximately related to the volume at the melting point as = 0.945 V, . Their correlation was vahd for diffusion of linear alkanes at temperatures up to 300°C and pressures up to 3.45 MPa. Matthews et al. and Erkey and Akger-man completea similar studies of diffusion of alkanes, restricted to /1-hexadecane and /i-octane, respectively, as the solvents. 

Asfour-Dullien developed a relation for predicting alkane diffusivities at moderate concentrations that employs ... 

Although reaction 6 is essentially a diffusion-controlled process for all kinds of substituents, the small differences observed in the rate constants through the series alkane-, amino- and alkoxy-sulfonyl chlorides have been attributed to the increased importance of polar effects to the transition state11. 

These reactions had similar rate constants, 4 x 109 dm3 mol-1 second-1, which approached the diffusion-controlled limit. Thus, for 10-2 M concentration of added ligand the half-life of Cr(CO)5 would be 17 nseconds. Interest in these experiments has been reawakened by the recent reports of photoactivation of alkanes by metal carbonyl species 34). 

The hydroisomerization of heavy linear alkanes is of a great interest in petroleum industry. Indeed, the transformation of long chain n-alkanes into branched alkanes allows to improve the low temperature performances of diesel or lubricating oils [1-3]. On bifunctional Pt-exchanged zeolite catalysts, n-CK, transformed into monobranched isomers, multibranched isomers and cracking products [4], The HBEA zeolite based catalyst was more selective for isomerization than those containing MCM-22 or HZSM-5 zeolites [4], This was explained on one hand by a rapid diffusion of the reaction intermediates inside the large HBEA channels, and on the other hand by the very small crystallites size of this zeolite (0.02 pm). 

The analysis of the literature data shows that zeolites modified with nobel metals are among perspective catalysts for this process. The main drawbacks related to these catalysts are rather low efficiency and selectivity. The low efficiency is connected with intracrystalline diffusion limitations in zeolitic porous system. Thus, the effectiveness factor for transformation of n-alkanes over mordenite calculated basing on Thiele model pointed that only 30% of zeolitic pore system are involved in the catalytic reaction [1], On the other hand, lower selectivity in the case of longer alkanes is due to their easier cracking in comparison to shorter alkanes. 

The sulfoxidation of alkanes occurs with heat evolution. This is the basis for rate of oscillation of rapid sulfoxidation at a relatively high pressure when the feedback arises between reaction rate, diffusion of reactants into liquid phase, and heat evolution [27],... 

Macek [27] examined the flammability limits for premixed fuel-air systems and small diffusion flames under natural convection conditions, and computed the equilibrium flame temperature for these flame systems. Data were considered for the alkanes and alcohols at their measured premixed lower flammability limits, and at their measured... 

The alcohols are intermediates in the formation of ketones. Isomerization of the products is not observed. Hydroxylation at the 2-position is favored over that at the 3-position, and the latter is preferred over hydroxylation at the 4-position. Solubility and concentration in the reaction medium, intrazeolite diffusion of the reactants, steric hindrance at the reactive carbon center, and C-H bond strength influence the reactivity and H202 selectivity (Table XXIV). The advantage of the large-pore Ti-beta over TS-1 in the oxidation of bulky alkane molecules is shown by the results in Table XXV. 

Only large-pore zeolites exhibit sufficient activity and selectivity for the alkylation reaction. Chu and Chester (119) found ZSM-5, a typical medium-pore zeolite, to be inactive under typical alkylation conditions. This observation was explained by diffusion limitations in the pores. Corma et al. (126) tested HZSM-5 and HMCM-22 samples at 323 K, finding that the ZSM-5 exhibited a very low activity with a rapid and complete deactivation and produced mainly dimethyl-hexanes and dimethylhexenes. The authors claimed that alkylation takes place mainly at the external surface of the zeolite, whereas dimerization, which is less sterically demanding, proceeds within the pore system. Weitkamp and Jacobs (170) found ZSM-5 and ZSM-11 to be active at temperatures above 423 K. The product distribution was very different from that of a typical alkylate it contained much more cracked products trimethylpentanes were absent and considerable amounts of monomethyl isomers, n-alkanes, and cyclic hydrocarbons were present. This behavior was explained by steric restrictions that prevented the formation of highly branched carbenium ions. Reactions with the less branched or non-branched carbenium ions require higher activation energies, so that higher temperatures are necessary. 

Reactions of 0 with Alkanes. Bohme and Fehsenfeld (16), working in the gas phase, have shown that 0 reacts with simple alkanes by abstracting a hydrogen atom, and except for methane the efficiency of this reaction is quite high. Even in the case of methane, the reaction occurs with a reaction probability of 0.08. Surface reactions between alkanes and surface 0 ions follow a similar pathway. As indicated by a disappearance of the 0 signal, stoichiometric reactions occur at temperatures sufficient to allow the diffusion of the alkane across the surface (17). For example, most of the 0" on Mo/Si02 reacts with CH in a period of 10 min at 77K ( 2). Thus, hydrogen atom abstraction does not appear to be an activated process. 

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