Carbon based membranes as filtering materials for gaseous mixtures.

Abstract

Carbon-based membranes are a novel approach to gas separation. More precisely, new graphene-like structures are of utmost importance in this field of research. The scope of this work is to prove the effectiveness of grazyne membranes in the separation of different gaseous mixtures: carbon dioxide (CO2) with methane (CH4) and CO2 with oxygen (O2). To determine the efficiency of the membrane, a molecular dynamics simulation is carried via Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) undergoing an adaptive intermolecular reactive bond order (AIREBO) force field. Grazynes are a recently proposed family of 2D carbon allotropes consisting in graphene-like stripes bonded via acetylenic links, which allow for the design of pores of variable size, an important property for gas separation. For these simulations, the studied membrane was [1],[2]{2}-grazyne. The focus of the research was to determine their permeability and selectivity for both mixtures at different sets of pressures and constant temperature. To achieve this, a box was simulated in which a piston-like wall was set at different heights. Due to computational restraints, simulations at low pressure values (i.e. lower than 10 atm) were performed with c(2x2) supercells. The results were conclusive in determining the [1],[2]{2}-grazyne membrane as infinitely selective for CO2 over CH4 between 1 and 20 atm, meaning the membrane was impermeable for methane. For the CO2/O2 mixture, further simulations were performed with [1],[3]- and [1],[m]{1}-grazynes (m=1,2,3) as no selective separation could be carried out. No conclusive data could be obtained from such simulations, as the only selective separations occurred when only a single molecule was filtered.