Effect of Energetical and Geometrical Heterogeneity of Kerogen on BET Surface Area Characterization and Methane Adsorption

Abstract

Surface area is an important parameter for the estimation of methane (CH4) adsorption in shale nanoporous media. Kerogen, as the main constituent of shale organic matters, has exceptionally high surface area due to extensive nanoscale pores. The Brunauer–Emmett–Teller (BET) method has been extensively used to characterize the surface area of various porous materials. However, its applicability for the surface area characterization of kerogen mesopores has not been investigated yet. In this work, the effect of geometrical and energetical heterogeneity on N2 adsorption isotherms and the subsequent BET surface area (S BET) characterization is studied by using grand canonical Monte Carlo simulations. We find that N2 adsorption sites are mainly within the “basin” and “valley” regions on kerogen surfaces, while in the “ridge” regions, its adsorption rarely takes place at 77 K from 0.005 to 0.05 bar. On the other hand, surface chemistry shows a significant effect on external potential and N2 adsorption amount. In addition, while S BET agrees well with geometric surface area (S geo) in graphite mesopores, in kerogen and pseudokerogen mesopores, S BET is generally lower than S geo. Interestingly, for our samples, S BET correlates well with CH4 excess adsorption in kerogen mesopores at 333.15 K and 300 bar, outperforming S geo. This work provides some crucially important fundamental understanding about the S BET characterization of kerogen mesopores which can guide the prediction of CH4 adsorption capacity in kerogen nanoporous media and the estimation of shale gas-in-place.

Applicability of Consistency Criteria To Calculate the Brunauer–Emmett–Teller Surface Area of Graphite and Kerogen Mesopores

“…Heterogeneous density distributions of N 2 adsorption are observed at both pressure conditions in the x – y plane as a result of the rough kerogen surfaces in panels a and b of Figure . The surface amplitude is used to study N 2 adsorption behaviors in panels c and d of Figure , and the kerogen surface is classified into “basin”, “valley”, and “ridge” regions according to topology . At 0.05 bar, high-density adsorption sites are predominantly found in the “basin” and “valley” regions, with few in the “ridge” regions as a result of topology-induced external potential.…”

“…Then, we introduce basic assumptions in the BET theory and illustrate BET_STD and BET_CC for surface area characterization. More details are provided in the Supporting Information and ref . As a follow-up study to our prior work, the kerogen construction processes are identical.…”

“…However, we note that the primary focus and novelty of these two studies are drastically different. While ref chiefly investigated the impact of geometrical and energetic heterogeneity on N 2 adsorption within kerogen mesopores, this study seeks to examine the applicability of consistency criteria under such circumstances.…”

“…The process of kerogen matrix density calculation is shown in section S3 of the Supporting Information. For characterizations of the kerogen surface and its slit pores, the surface roughness, pore size, and effective pore volume have been measured in our previous work . The infiltration of CH 4 into the kerogen matrices is prevented through the introduction of dummy particles that effectively block all internal cavities present within the kerogen matrices. , …”

Effect of Surface Characteristics of Graphene Aerogels and Hydrophilicity of Ionic Liquids on the CO2/CH4 Separation Performance of Ionic Liquid/Reduced Graphene Aerogel Composites

“…Also, the densely populated pore widths for IL-loaded composites shifted to values that were exceeding the mesopores of the pristine materials, which show the overestimation of pore sizes by the BJH method. 46 In addition to the consistent decrease in the surface area and total pore volume upon IL impregnation, it is important to note that the N 2 solubility of ILs might be very poor at the liquid nitrogen temperature, which directly affects the uptakes, and hence the accuracy of the BET measurements. 47 Figure 5 presents the results of the TG and DTG analyses.…”