Ethylene and ethane were effectively separated from a mixture comprising these two gases by means of a large-scale liquid-membrane contactor (membrane permabsorber). The contactor comprised composite flat-sheet membranes with a nonporous diffusional layer made from polyblock copolymer poly(dimethylsiloxane)/poly(phenylsilsesquioxane) and an aqueous solution of silver nitrate flowing along turbulence-promoter spacers between the membranes. The membrane permabsorber permitted ethylene and ethane to be separated effectively from a binary mixture. The problem with the selection of suitable membranes is discussed. It was shown that the efficiency of the separation process could be varied by changing the liquid-flow rate, the membrane area, the concentration of the selective carrier in the liquid, the temperature of the liquid absorbent, and the gas-separation properties of the membranes.