Diffusivity of Hydrogen gas through an Acrylic based Polymer. 1

[thermcool]

Hello All,
I am trying to calculate the loss of hydrogen gas by diffusion through the wall of acrylic container (Grade: Polymethyl Metha-Acrylate) stored at atmospheric pressure and temperature.

To explain my question further:
Actually, i am doing some research work on the cost efficient storage of hydrogen at low pressures. Due to the smaller molecular size of the hydrogen the issues like diffusivity in case of hydrogen storage is a major issue. At this time, i am using a small laboratory scale acrylic container (diameter 150 mm, height 550 mm and wall thickness 3 mm). I have done some research using Ficks law of diffusion through polymers for my calculations. I will greatly appreciate if someone could provide me with any relevant information in this regard like diffusivity coefficient for acrylic materials, fibre reinforced plastics (FRP), non metalic composite etc.

 

[Demon3]

There is a lot of work done on such topics so you will find data if you look hard enough. Hydrogen diffuses even through solid metal so I would not rely on using PMMA to hold it, furthermore the extremely low temperatures will make the polymer very brittle and fragile. Thermal cylcling between warm and cold (empty & full) will put strain on the polymer and may break it.

To dramatically improve the barrier properties the most effective thing is either aligned platy fillers like nano-clays or mica. The other way is more effective and that is to use a thin layer of glass deopisites for example using plasma or by sol-gel methods. Such SiOx layers are commonly uses and effective for dramatically improving the barrier properties of polymers.

For some expert advise on barrier properties of polymers contact the research group of Professor Ulf Gedde at the KTH in Stockholm.

 

[kenvlach]

thermcool,
You need to do a permeation (not really diffusion) calculation. Permeation constants are available in Lange's Handbook of Chemistry (can't locate my copy at the moment).

The US Dept. of Energy studied the permeation of hydrogen through acrylic (PMMA) and other plastics in 2004:

http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/review04/hpd_p9_blake.pdf

so search for a follow-up report.

Or maybe find this book: Permeability and Other Film Properties of Plastics and Elastomers

http://www.knovel.com/knovel2/Toc.jsp?BookID=376