Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1 cm(3)/g) and high packing density (0.7 g/cm(3)) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160 cm(3) (STP)/cm(3) at 25 degrees C and 3.5 MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700 degrees C), with a medium KOH: precursor ratio (3: 1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175 cm(3) (STP)/cm(3) at 25 degrees C and 5 MPa and 200 cm(3) (STP)/cm(3) at 25 degrees C and 10 MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5 nm at pressure up to 10 MPa was estimated to understand their contribution to the total adsorption capacity. (C) 2015 Elsevier Ltd. All rights reserved.