Using molecular dynamics simulations, we have investigated hydrogenated graphyne layers as molecular-sieving membranes. Hydrogenated alpha-graphyne layer with no defect indicated a complete separation capability for a mixture of H-2/CH4. The separation selectivity for H-2/N-2 mixture was about 700 at room temperature using the same membrane. This value reduced by increasing the temperature. However, presence of defects in the membrane dramatically decreased the separation selectivity for both studied mixtures. Surprisingly, increasing the temperature enhanced the separation selectivity using the defected hydrogenated alpha-graphyne membrane. Hydrogenated gamma-graphyne layer with no defect did not show any permeability effect for the studied gases. (C) 2015 Elsevier B.V. All rights reserved.