CO2 is the primary greenhouse gas with an annual emission of 30 Gt. Therefore CO2 separation from flue gas has gained the interest of many researchers. Graphyne is a newly discovered synthetic carbon allotrope of hexagonal carbon rings cross linked by acetylene linkages. The flat and one atom thick carbon framework offers uniformly distributed pores of constant size. The pore size of the membrane can be tailored by changing the number of acetylene bonds between adjacent phenyl rings. Here we report the study of a single layer graphyne membrane as a potential candidate for CO2 separation. Molecular Dynamics (MD) simulations are used to study the gas permeation characteristics and the CO2/flue gas selectivity of graphyne membranes. The MD simulations enable the study of a large number of molecular trajectories and thereby reduce the statistical uncertainty of the obtained estimates.