(657f) Diffusion of Hydrogen through Layered Polymer Composite Pipes | AIChE

(657f) Diffusion of Hydrogen through Layered Polymer Composite Pipes

Authors 

Blencoe, J. G. - Presenter, Hydrogen Discoveries, Inc.


The diffusion of hydrogen through polymeric pipeline materials is associated, on the one hand, with potentially significant losses, and on the other, with safety hazards arising from accumulation of hydrogen in confined spaces. The purpose of this paper is to consider the possibility of mitigating the diffusion of hydrogen through pipelines by use of layered polymeric composite materials. For cylindrical pipes constructed from layers of polymeric material, analytical solutions of the steady-state concentration profile are derived, together with the limiting forms that are appropriate for large numbers of extremely thin layers. These analytical results can be used to construct a figure of merit expressing the ratio of the multi-wall diffusion flux to that through a single-walled pipe of the same overall thickness, in terms of the (usually unknown) layer-to-layer diffusional contact resistance or the corresponding dimensionless mass-transfer coefficient. Conservative estimates of this parameter lead to the conclusion that the reduction achievable in this way is rather limited. An analysis of an alternative design concept in which a thin metallic foil is sandwiched between two coaxial layers of polymer is also given. Application of equilibrium and flux-matching conditions at the interfaces results in a nonlinear boundary value problem for the Laplace equation defining the steady concentration profile. Making use of published solubilities and diffusivities of hydrogen in polymers and metals, calculations indicate that reductions of several orders of magnitude could be achieved with foils as thin as 0.01 mm.