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 CH(4) 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 (3)He and (4)He, 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 CH(4), 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.