Pressure Dependence of Self Diffusion in Some Neat Alkanes and Binary Mixtures

Abstract

The self diffusion coefficients D have been measured for a series of linear and branched alkanes between the melting pressure curve and 450 K at pressures up to 200 MPa. The experiments were performed in a strengthened glass cell by application of the pulsed field gradient technique. — The p, T dependence of the data is described by the rough hard sphere model (Chandler) and by the interacting sphere model (Speedy). — The measurements have been extended to binary mixtures of a long chain alkane (tetradecane) and 4 to 12% w/w methane. The addition of relatively small amounts of the lower alkane enhances significantly the translational mobility and reduces the p. T dependence of the self diffusion coefficients of tetradecane.

Contrasting Friction and Diffusion in Molecularly Thin Confined Films

“…It is intriguingly close to the activation volume obtained some years ago from independent friction measurements [4]. In the bulk, by contrast, the activation volume for diffusion is only 0:2 nm 3 , the size of a fluid molecule (as also confirmed by our own experiments in which the bulk pressure was varied) [11]. This analysis highlights the key conclusion that diffusion appeared to involve cooperative rearrangements of many molecules.…”

Self-Diffusion Coefficients of Methane or Ethane Mixtures with Hydrocarbons at High Pressure by NMR

“…The high-pressure glass capillaries were drawn from Duran 50 glass and glued into the bore of a Cu/Be nipple with Torr Seal, low vapor pressure resin (Varian). This technique originally developed by Yamada (1974), was previously described by Vardag et al (1990).…”

“…Bachl and Lu ¨demann (1986) have measured self-diffusion coefficients in butane, pentane, hexane, decane, trans-2-butene, cis-2-butene, and 2-butyne at temperatures up to 450 K, and pressures up to 200 MPa. Vardag et al (1990) have measured self-diffusion coefficients in methane, butane, pentane, hexane, decane, tetradecane, 2,2,3-trimethylbutane, and a mixture of methane + tetradecane at temperatures up to 450 K, and pressures up to 200 MPa. Vardag et al (1991) have also measured self-diffusion coefficients in melts of n-alkanes with chain lengths between 16 and 154 carbon atoms, in the temperature range from 200 K to 500 K, and pressures up to 600 MPa.…”

Self-Diffusion in Gases and Liquids

“…where D 0 is the diffusion coefficient at very low densities. Equations 2 and 3 have been used to correlate the self-diffusion coefficients of some nonpolar molecules (Vardag et al, 1990(Vardag et al, , 1991Enninghorst et al, 1996). Kushick and Berne (1973) and more recently Straub (1992) used the Weeks-Chandler-Andersen (WCA) (1971) fluid, based on a potential defined later in the paper, as the reference system.…”