Supercritical Fluids in Confined Geometries

Abstract

Understanding the influence of confinement on the structure and thermodynamic properties of supercritical fluids in pores of different surface chemistry and topology is fundamental to the successful development and optimization of the variety of technologies involving fluid-solid interactions. Adsorption behavior of supercritical fluids (SCFs) is fundamentally different from that of subcritical vapors and this chapter begins with a general description of the specifics of the supercritical adsorption. Presented examples illustrate the capability of SAS methods to deliver unique, pore-size-dependent information on the properties of supercritical CO 2 , hydrogen, methane, and other fluids confined in pores of different engineered and natural porous solids. Applications of SAS for studying pore interconnectivity and structural stability of porous materials under pressure are also discussed.

Using small angle neutron scattering to explore porosity, connectivity and accessibility, towards optimised hierarchical solid acid catalysts

“…The fractal dimension of the aggregates, 2.54, is typical of porous materials (between 2 and 3), and close to the value expected from weakly-segregated or percolating networks (2.5). 40 The two Gaussian peaks were centred at 0.523 and 0.911 Å −1 , corresponding to d values of 12.01 and 6.90 Å. These two values are in excellent agreement with both our experimental, and theoretical d spacings for the 100 and 110 Bragg peaks in the AFI framework at 2 θ = 7.4° (11.9 Å) and 12.9° (6.9 Å) with Cukα X-radiation.…”

“…S2–S5†). 40 The MP-SAPO-5 data is then largely featureless below 0.5 Å −1 , whereas two oscillations can be seen in the HP-SAPO-5 systems at Q values of roughly 0.02 and 0.04 Å −1 . It is only beyond these oscillations, in the 0.1 to 0.4 Å −1 Q range, that the three HP-SAPO-5 systems differ from one another.…”

“…38 These two phases could, for example, be the empty pore and the framework walls, therefore providing useful and complementary insights into porosity. 39 Loosely, the intensity of both SANS and SAXS comes from the square of the difference in scattering length density (SLD; ρ ) between the two phases, what is termed ‘contrast’, as well as the number ( N ) and sizes (volume, V ) of the pores: 38,40 I ( Q ) α ( ρ A − ρ B ) 2 NV 2 where ρ i is the SLD of phase i and Q is the magnitude of the scattering vector. The SLDs themselves are a function of each phases' mass density, stoichiometry and the scattering length of the elements present.…”

Pore Structure and Wettability of Bossier Shale, East Texas, United States: Insights from Integrated Porosimetry, Scattering, and Imbibition Approaches

“…The 1D scattering profiles, presented as the scattering intensity [ I ( Q ), cm –1 ] at a given scattering vector ( Q , Å –1 ) (Figure b), covering Q values of [0.0001, 0.3] Å –1 and [0.05, 1.7] Å –1 , were obtained in the USAXS and SAXS tests, respectively. I ( Q ) is proportional to the square of the difference between the scattering length density (SLD; ρ) of the matrix and pore spaces . The SLD of the pore space is 0 cm –2 , and the SLD of a multicomponent matrix (including inorganic minerals and organic matter) is commonly obtained from the sum of the product of the volume fraction and SLD of each component .…”

The Effect of Topology on Phase Behavior under Confinement

“…This phenomenon is known as capillary condensation and has applications in many fields of science and engineering, including the storage of hydrogen carriers [1][2][3], battery technology [4], hydrocarbon extraction from unconventional reservoirs [5], and carbon dioxide sequestration [6]. Capillary condensation can have a large effect on transport properties, including effective diffusion coefficients [7], imbibition [8], and mass flow rates [9], and it is reported in the literature that both morphology (i.e., the shape of a structure) and topology (i.e., how different structures are connected) have a strong effect on the sorption of both sub-and supercritical fluids [2,10,11]. For ordered porous media, the relation between capillary condensation and geometry is well understood [12]; however, in practice, many porous media are disordered rather than ordered.…”