Activated carbon (AC) was produced by phosphoric acid activation and microwave pyrolysis of Douglas fir biomass. A low temperature activated carbon surface modification method was tested Using ammonium sulfate. This method successfully enhanced the carbon dioxide adsorption capacity of Douglas fir biomass based activated carbons. The activated carbon produced, was Comparable to commercial grade modified carbon in terms of breakthrough time and adsorption capacity. All modified carbons were selective to carbon dioxide over methane. Activated carbon produced by a phosphoric acid impregnation ratio of 3:1, and modified with an ammonium sulfate mass fraction of 9.1%, had the highest breakthrough time and exhaustion time of 3.5 min and 13.5 min respectively. This carbon adsorbed 97% carbon dioxide from the inlet stream containing methane and other gases with a carbon dioxide over methane selectivity of 5.27. A 1 h exposure of the used carbon to a 105 degrees C regeneration removed a majority of the carbon dioxide and methane on the carbon surface, facilitating regeneration. (C) 2017 Elsevier Ltd. All rights reserved.