A series of granular activated carbons (GACs) of similar surface properties but different pore structures were prepared, and used to enrich methane from methane and nitrogen mixture (CH4/N-2) by vacuum pressure swing adsorption (VPSA) method. The adsorption isotherms of CH4 and N-2 illustrated that the adsorption affinity of GAC for CH4 over N-2 is dependent on the pore structure. It was found that larger surface areas are favorable to CH4 enrichment. The effective pore size for the CH4 enrichment is from 5.0 angstrom to 13 angstrom, with the optimum effect occurring in the range from 5.0 angstrom to 8.0 angstrom. By a single-bed VPSA measurement, the CH4 has a purity up to 66.6 vol%, enriched from CH4 (30 vol%)/N-2 (70 vol%) mixture by using optimum pore-size GAC. (C) 2015 Elsevier B.V. All rights reserved.