Diffusion of monoaromates in LDPE/HDPE
Thread by Kurt Overgaard on 14 Sep 2009 at 11:40:06
Dear Platform,

I'm looking for diffusion coefficients in order to determine diffusion of monoaromate gases - xylenes and ethylbenzene - into water pipes made of LDPE and HDPE.

How do I calculate the effect of temperature and permeant concentration?

May somebody assist me?

Regards
Kurt Overgaard

Comment by Composite Analytica on 22 Sep 2009 at 11:04:36  | |responses: 2|
Dear Kurt,

The diffusivity of Xylenes and Ethyl Benzene into LDPE and HDPE can be extracted from available reference data. Temperature dependency can be estimated using Arrhenius Law. Below we list some of the diffusvities. However, note that with regard to pollution of potable water pipelines, the thermodynamics (resulting in a certain solubility of the chemicals in the polymer, giving rise to an actual drive force for diffusion, swellling or stress cracks) is just as - or even more - important than the actual diffusion coefficient.

Diffusion coefficients (theoretical minimum figures while obtained at 1% of actual vapour pressure):

temperature: 23 degrees Celsius,
system pressure: 1 bar
partial pressure: 1% of actual vapour pressure (chemical activity approaches 0):

Toluene - LDPE: 1 E-12 m2/s (@ 1% of vapour pressure)
Xylene - LDPE: 1 E-12 m2/s (@ 1% of vapour pressure)
Toluene - HDPE: 3E-13 m2/s (@ 1% of vapour pressure)
Xylene - HDPE: 5E-13 m2/s (@ 1% of vapour pressure)

Kind Regards,
Sijmon
Composite Analytica

Comment by Kurt Overgaard on 22 Sep 2009 at 11:36:23  | |responses: 1|
Dear Sijmon,

Thank you very much for your reply - and the remarks on the importance of thermodynamics with regard to pollution of potable water pipelines.

Now I'm on track again!

Kind Regards
Kurt

Comment by Composite Analytica on 22 Sep 2009 at 11:42:04  | |responses: 0|
Dear Kurt:

Good to hear! Good luck with the project!

;-)

Sijmon