Experiments on the Capillary Condensation/Evaporation Hysteresis of Pure Fluids and Binary Mixtures in Cylindrical Nanopores

Abstract

A new experimental method, i.e., isochoric cooling/heating cycle measurement using differential scanning calorimetry (DSC), is applied to investigate the hysteretic phenomenon of pure components and mixtures confined in two different types of cylindrical nanopores (SBA-15 and KIT-6). The capillary condensation/evaporation hysteresis end point T he for a specific system is determined by performing a series of measurements with different densities by increasing initial temperature and pressure. We confirm that for a pure component, T he is lower when confined in smaller nanopores, whereas the T he values for CH4/CO2 and CH4/C2H6 mixtures at the specific composition investigated are higher than those of pure CO2 and C2H6, respectively, when confined in the same nanopores. To the best of our knowledge, this is the first time that T he of fluid mixture is experimentally studied, which further demonstrates that binary mixtures behave similarly to pure fluids when confined in nanoporous media. At low temperatures, where hysteresis is observed, the shape as well as the duration of the exothermic peak (due to capillary condensation) and endothermic peak (due to capillary evaporation) indicate that capillary condensation, rather than capillary evaporation, takes place at/near thermodynamic equilibrium. Within the accuracy of the measurements, we find that the total heat of capillary condensation is identical to that of capillary evaporation for all systems examined, regardless of the presence of hysteresis. By comparing the heat per unit volume among different systems, we also find that the heat per unit volume of the phase transition of confined pure fluid is lower than that of bulk, which further demonstrates that at the same temperature the molar density of confined pure liquid is less than that of bulk pure liquid at saturation.

First-order and gradual phase transitions of ethane confined in MCM-41

“…, 15 ± 0.3% methane/85 ∓ 0.3% ethane and 12 ± 0.24% methane/88 ∓ 0.24% carbon dioxide) confined in SBA-15/MCM-41 with different pore sizes using an isochoric cooling/heating procedure. 9–15 With the measured capillary condensation data, the PCP of pure fluids ( i.e. , carbon dioxide, ethane, and methane) confined in SBA-15/MCM-41 has also been determined using the three-line method, 9,14 whereas that of methane/ethane gas mixture confined in SBA-15 has been bracketed.…”

“…5 However, the understanding of this phase behavior is still far from complete, such as the condensation/evaporation and the shift of the pore critical point (PCP) due to nanoconfinement effects. For fluids confined in nanopores, first-order phase transitions, e.g., capillary condensation and evaporation, have been investigated extensively in the literature using various experimental methods, such as adsorption-desorption, 6,7 microfluidic-based analyses, 8 calorimetric-based analyses, [9][10][11][12][13][14][15][16][17] nuclear magnetic resonance (NMR), 18 and small-angle neutron scattering (SANS). 19 The adsorption-desorption experiment is the most widely used and thus data from such experiments are more widely available.…”

Quantitative characterization of pore network and influencing factors of methane adsorption capacity of transitional shale from the southern North China Basin

“…Therefore, the pore in shale is complex and heterogeneous with different pore sizes, pore origins and pore types. Some studies indicate that the pore size can influence the adsorption force between the pore walls and adsorbed gas molecules (Burggraaf 1999;Cao et al 2020;Chen et al 2019;Cui et al 2004;Qiu et al 2021;Wang and Jin 2019). Generally, the adsorption force decreased with increasing pore width (Burggraaf 1999;Cui et al 2004).…”

Effect of Wetting Hysteresis on Fluid Flow in Shale Oil Reservoirs

“…It has been demonstrated that, during the fluid flow process in shale reservoirs, the threshold pressure for the oil–water two-phase system is much larger than that for the single-phase system, which is mainly attributed to the capillary pressure and Jamin effects. , For a two-phase fluid system, there exists two capillary pressures at the two interfaces of oil and water phases . As a result of the wetting hysteresis, the difference of the two capillary pressures acts as an obstruction of the fluid movement, , which is presented in the form of the threshold pressure and flow resistance for the systems with the static wetting hysteresis and dynamic hysteresis, respectively. , Unfortunately, quantitatively characterizing the effect of the wetting hysteresis on the fluid flow behavior for the oil–water two-phase system at the nanoscale has not been reported because it is a very complex problem. On the one hand, as a result of the static wetting hysteresis, there is a difference between the capillary pressures at both ends of the oil or water droplet, thus forming the threshold pressure.…”

“…9,10 For a two-phase fluid system, there exists two capillary pressures at the two interfaces of oil and water phases. 11 As a result of the wetting hysteresis, the difference of the two capillary pressures acts as an obstruction of the fluid movement, 12,13 which is presented in the form of the threshold pressure and flow resistance for the systems with the static wetting hysteresis and dynamic hysteresis, respectively. 14,15 Unfortunately, quantitatively characterizing the effect of the wetting hysteresis on the fluid flow behavior for the oil−water two-phase system at the nanoscale has not been reported because it is a very complex problem.…”