In Reply to: Unleaded Petrol Diffusion Coefficient in Polyethylene posted by Ali Hussein on July 16, 2004 at 00:44:35:

Dear Ali,

The use of the average diffusion coefficient of a BTEX compound, for example based on the respective volume fractions of the different molecules in the mixture, we would not advice. In any case, the experimental method and theoretical assumptions with regard to the diffusion coefficients that you have acquired, are very essential in whether they will be of any use for the determination of the diffusivity of a mixture. If the figures are Fickian diffusion coefficients, they will be rather worthless for the determination of the diffusivity of a BTEX mixture. For mixtures, the free volume theory and related definition of diffusivities - although not perfect - is recommended to solve this diffusion problem. This theory will also allow you to incorporate the counter diffusion of water.

For petrol simulation you could use a BTEX mixture, at least the solubility might be more or less resembled.

However, taking the previous remarks on diffusion into account, we would recommend you just to carry out the test with real petrol or a standard simulant for petrol like indolene. Please do not hesitate to contact us for more information!

Diffusion in Polymers

: Hi Forum

: I am a research student working on the diffusion of Petrol through plastic water pipes. I have been looking for diffusion coefficients of petrol in Polyethylene pipes without much success. Can averaging diffusion coefficients of BTEX compounds be used as a guide? Could you please advise me on the above

: Many thanks

: Ali

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