Technologies are generally described for a gas filtration device including an array of parallel carbon nanotubes. The carbon nanotubes may extend between first and second substrates, and the ends of the carbon nanotubes may be embedded in the substrates and cut to expose openings at each end of the carbon nanotubes. The carbon nanotubes may be composed from a graphene membrane which may be perforated with a plurality of discrete pores of a selected size for enabling one or more molecules to pass through the pores. A fluid mixture including two or more molecules for filtering may be directed through the first openings of the array of nanotubes, and the fluid mixture may be filtered by enabling smaller molecules to pass through the discrete pores of the graphene membrane walls of the carbon nanotubes to produce in a filtrate fraction including the smaller molecules and a retentate fraction including larger molecules.