In this work, we investigate pore accessibility of carbon dioxide and methane in the sacharose char over a wide temperature range. The results calculated using TST show that there is no pore accessibility problem for carbon dioxide at 273 K with its very short crossing time (~10-5 second) while methane indicates slow diffusion even at high temperature (above 300 K) with its crossing time within practical time scale (seconds). Such significantly slower diffusion of methane at high temperature practically leads to underprediction of carbon dioxide adsorption in the same carbon, when using the pore size distribution extracted from supercritical methane adsorption, due to the latter's lower accessibility. From our recent work, the crossing time of methane at 300 K and argon at 87 K are rather similar and within practical time scale (several seconds). However, it can be inferred that the crossing time of methane above 300 K significantly exceeds that of argon at 87 K if the pore mouth becomes slightly smaller due to the former's larger molecular size. Consequently, it can be seen that accessibility of methane, argon, and carbon dioxide increases in that order.
Finally, The findings above are validated by prediction of high pressure methane and carbon dioxide adsorption measurements in several carbons over a wide range of temperatures using structural characteristics of these carbons, obtained from interpretation of experimental measurements of argon adsorption at 87 K by our finite wall thickness (FWT) and infinite wall thickness (IWT) DFT-based models. Lowest pore accessibility of methane in the PCB carbon is clearly evident with significant overestimation of experimental methane adsorption data but correct prediction of carbon dioxide.