Methane-Induced Deformation of Porous Carbons: From Normal to High-Pressure Operating Conditions

Applying developed recently thermodynamic model of adsorption-induced deformation of microporous carbons (Kowalczyk, P.; Ciach, A.; Neimark, A. Langmuir 2008, 24, 6603), we study the deformation of carbonaceous porous materials due to adsorption of methane at 313 K and pressures up to 19 MPa. The internal adsorption stress induced by adsorbed/compressed methane is very high in the smallest micropores (for instance, adsorption stress in 0.315 nm ultramicropore reaches 1.8 GPa at 19 MPa). Model calculations show that depending on pore structure both monotonic (i.e., expansion) and nonmonotonic (i.e., initial contraction and further expansion) methane stress–strain isotherm are theoretically predicted. Our calculations reproduce quantitatively the methane stress–strain isotherm on carbide-derived activated carbon at 313 K and experimental pressures up to 5.9 MPa. Moreover, we extrapolate methane stress–strain isotherm measured by the dilatometric method up to 19 MPa to mimic high pressure operating conditions. We predict that expansion of the studied carbon sample reaches 0.3% of volume at 19 MPa and 313 K. From our extrapolation of experimental dilatometric deformation data to high pressure conditions, we predict that the reduction of pressure from 19 to 1 MPa is accompanied by shrinkage of carbon sample by about 0.28% of volume. Comparison with recent study due to Yang et al. (Yang, K.; Lu, X.; Lin, Y.; Neimark, A. V. Energy Fuels 2010, 24, 5955–5964) shows that studied activated carbon is more resistant to adsorption stress than various coal samples. Presented study can be useful for optimization of operating conditions used in methane gas-extraction technologies.