NOVELTY - Membrane comprises a graphene monolayer (100) including many discrete pores that are chemically perforated in it, where each of the discrete pore has a substantially uniform pore size characterized by at least one carbon vacancy defects in the graphene monolayer such that the graphene monolayer has substantially uniform pore sizes throughout.    USE - The membrane is useful for separating compound from fluid mixture (claimed).    ADVANTAGE - The membrane: exhibits improved properties (greater selectivity and greater gas permeation rates) compared to conventional polymeric membranes for gas separations. The graphene monolayer has substantially uniform pore sizes throughout.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) forming (M1) many discrete pores in graphene monolayer, comprising: contacting alkyl substituted heteroatom compound of formula (R-Het1) (I) to many locations at the graphene monolayer; providing separation distance of at least Rr (where R is a minimum steric radius of r) between adjacent locations in the locations; reacting (I) with at least one graphene carbon atom (Cg) at each of the locations to form many p heteroatom-carbon moieties of formula ((R-Het1-Cg)p-graphene) (II) at the graphene monolayer; and forming many discrete pores in the graphene monolayer by removing (II), where the discrete pores comprise many carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms Cg from the locations such that the graphene monolayer has substantially uniform pore sizes throughout;    (2) separating (S1) a compound from a fluid mixture, comprising: providing a fluid mixture that contains a first compound and a second compound; providing a membrane that includes a graphene monolayer that is chemically perforated by many discrete pores, and each of the discrete pores has diameter that is selective for passage of the first compound compared to the second compound; contacting the fluid mixture to a first surface of the graphene monolayer; and directing the first compound through the discrete pores to separate the first compound from the second compound; and    (3) a system for preparing graphene membrane with substantially uniform pores, comprising: a reagent activator for preparing an activated reagent from a precursor reagent; a reagent applicator configured to contact the activated reagent to many locations at a graphene monolayer; a reaction chamber configured to hold the graphene monolayer; a heater configured to thermally cleave many heteroatom-carbon moieties at the graphene monolayer to form a perforated graphene monolayer; and a support substrate applicator configured to contact the perforated graphene monolayer to a support substrate.    Het1 = nitrene (preferred) or activated oxy;    R = R1a, SO2R1a, (CO)OR1a or -SiR1aR1bR1c; and    R1a-R1c = aryl or heteroaryl.    DESCRIPTION OF DRAWING(S) - The figure illustrates schematic view of the graphene monolayer with hexagonal lattice of carbon atoms and aromatic bonds of graphene.    Graphene monolayer (100)