Helium Separation Using Porous Graphene Membranes

Graphene has been demonstrated to be impermeable to gases but can be made selectively permeable by introduction of pores. The permeability of a recently synthesized porous graphene structure to He, Ne, and CH₄ is studied using MP2/cc-pVTZ potential energy surfaces. The role of quantum and classical transmission effects as a function of temperature are investigated. At room temperature, there is a 20 and 16% increase in transmission due to quantum tunneling for ³He and ⁴He, respectively, over the purely classical result. The large differences in classical barrier heights for transmission through this membrane (0.523, 1.245, and 4.832 eV for He, Ne, and CH₄, respectively) allow for highly selective separation. This is proposed as an economical means of separating He from the other noble gases and alkanes present in natural gas