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The low-pressure gas adsorption (LPGA) method for estimation of pore capacities, pore size distributions, and total surface area using adsorption−desorption isotherms is selected as an effective technique in pore characterization. A recent application of this method is to understand the complex and heterogeneous nature of shales across the globe. The LPGA experiments were conducted on shale samples from Barnett and Eagle Ford formations in the United States using CO 2 for micropores of 0.3−1.5 nm in diameter and N 2 and Ar as the adsorbates to focus on micropores from 1.5 to 2.0 nm and the lower range of mesopores above 2.0−27 nm in diameter. It was hypothesized that a significant error in estimations could occur due to inconsistencies in the shale outgas temperatures. It was observed that lower pore capacities result from lower outgas temperatures, and higher pore capacities result from increasing outgas temperatures. It is hypothesized that lower outgas temperatures fail to completely eliminate adsorbed moisture and adsorbed low-molecular weight hydrocarbon species from shale pores, which leaves the pores partially filled and as such result in lower values of pore capacity. By increasing the outgassing temperature, the adsorbed species in the pores are completely removed, yielding higher pore capacities. The cutoff temperature of 250 °C during outgassing for regeneration of "clean" shale pores was arrived at by analyzing the LPGA results of samples without any outgassing and samples outgassed at 60, 110, and 250 °C. The 250 °C maximum outgas temperature is intended to maximize the results of LPGA while minimizing structural changes to shales. Mass stabilization as shown by thermogravimetric analysis and magnetic suspension balance measurements support the assertion that the shale is not fundamentally altered by processes such as kerogen cracking until a temperature higher than 250 °C is reached. The kerogen had approximately 3.0% weight loss at 110 °C, with an additional 1.3% loss between 110 and 250 °C. Likewise, the desorption experiments carried out on clay at 110 °C were approximately 1.3%, with an additional 0.5% loss between 110 and 250 °C. On the basis of the interpretation of pore size distributions using the LPGA method, it was concluded that accurate shale characterization is achieved when the analysis is limited to results from relative pressures (P/P o ) less than or equal to 0.90. At higher relative pressures, the sizes of the adsorbate-occupied pores cannot be distinguished.

Reducing CO2 in the atmosphere and preventing its release from point-source emitters, such as coal and natural gas-fired power plants, is a global challenge measured in gigatons. Capturing CO2 at this scale will require a portfolio of gas-separation technologies to be applied over a range of applications in which the gas mixtures and operating conditions will vary. Chemical scrubbing using absorption is the current state-of-the-art technology. Considerably less attention has been given to other gas-separation technologies, including adsorption and membranes. It will take a range of creative solutions to reduce CO2 at scale, thereby slowing global warming and minimizing its potential negative environmental impacts. This review focuses on the current challenges of adsorption and membrane-separation processes. Technological advancement of these processes will lead to reduced cost, which will enable subsequent adoption for practical scaled-up application.