Assessment of activated carbon fibers from commercial Kevlar® as nanostructured material for gas storage: Effect of activation procedure and adsorption of CO2 and CH4

Carbon-based nanostructures are considered promising materials for gas storage thanks to robust structure, tunable porosity, lightweight, high thermal/chemical stability and easy production. This study reports the development of activated carbon fibers prepared from commercial Kevlar® through an innovative pyrolysis method, consisting of carbonization in inert ambient and subsequent physical activation in oxidizing atmosphere, using a unique apparatus. Varying three key parameters, time (range 60- 240 min), temperature (range 1023- 1123 K) and gas-flow (0.3/0.9/1.2 Nl/min of CO2), the correlation between the activation procedure and the resulting samples structure was evaluated. The best results in terms of microporosity and gas adsorption properties have been obtained by reducing the activation times of the material. Furthermore, the purpose has been to optimize the characteristics in terms of Specific Surface Area, Total Pore Volume and optimal Pore Size Distribution. The method made it possible to develop an adsorbent material with a high fraction of micropores up to 94 % of the total pore volume, straddling the supermicroporosity (0.7- 2 nm) and ultramicroporosity (<0.7 nm) region. Such textural properties have resulted in high gases storage capacities, tested at different temperatures (280, 298, 314 K), with maximum uptake of 46 wt% for CO2 and almost 10 wt% for CH4. All produced samples were characterized by helium picnometry to estimate skeletal density, Scanning Electron Microscopy to obtain morphological information, porosimetry to know structural properties. The adsorption behaviour was tested using a Sievert-type apparatus in the pressure range of 0- 15 bar for CO2 and 0- 40 bar for CH4.