An upper bound to gas storage and delivery via pressure-swing adsorption in porous materials

We present a theoretical upper bound on the deliverable capacity of a gas in a rigid material via an isothermal pressure-swing. To provide an extremum, we consider a substrate that provides a spatially uniform potential energy field for the gas. Our bound is unique in that it directly relies on experimentally measured properties of the (real) bulk gas, without making approximations. We conclude that the goals set by the United States Department of Energy for room temperature natural gas and hydrogen storage are theoretically possible, but sufficiently close to the upper bound as to be impractical for any real, rigid porous material. However, limitations to the scope of applicability of our upper bound guide fuel tank design and future material development. Firstly, one could heat the adsorbent to drive off trapped, residual gas in the adsorbent. Secondly, the physics of our upper bound do not pertain to any material that changes its structure in response to adsorbed gas, suggesting that flexible materials could still satisfy the DOE targets.