The behavior and critical properties of fluids confined in nanoscale porous media differ from those of bulk fluids. This is well known as critical shift phenomenon or pore proximity effect among researchers. Fundamentals of critical shift modeling commenced with developing equations of state (EOS) based on the Lennard–Jones (L–J) potential function. Although these methods have provided somewhat passable predictions of pore critical properties, none represented a breakthrough in basic modeling. In this study, a cubic EOS is derived in the presence of adsorption for Kihara fluids, whose attractive term is a function of temperature. Accordingly, the critical temperature shift is modeled, and a new adjustment method is established in which, despite previous works, the bulk critical conditions of fluids are reliably met with a thermodynamic basis and not based on simplistic manipulations. Then, based on the fact that the macroscopic and microscopic theories of corresponding states are related, an innovative idea is developed in which the energy parameter of the potential function varies with regard to changes in pore size, and is not taken as a constant. Based on 94 available data points of critical shift reports, it is observed that despite L–J, the Kihara potential has sufficient flexibility to properly fit the variable energy parameters, and provide valid predictions of phase behavior and critical properties of fluids. Finally, the application of the proposed model is examined by predicting the vapor–liquid equilibrium properties of a ternary system that reduced the error of the L–J model by more than 6%.
Two different paths were followed to calculate the solubility parameters (SP) of 133 alkanes. The first approach calculates SP from the points of view of internal pressure and residual energy, whereby Soave‐Redlich‐Kwong and Peng‐Robinson equations of state (EOSs) are employed with and without the volume‐shift correction. In the second approach, the cohesive energy concept is used and the saturation pressure and saturated liquid molar volume are separately computed by different models and coupled to one another. The results indicated that Approach 1 predicts SP with an error of 2.24 %, which is in the same order as that of Approach 2 but slightly better. The performance of Approach 1 was assessed by estimating the SP values of 33 substances from various families and comparing the results to an EOS‐based study.
A multitude of research works have been conducted in the past decade to better predict the change of critical properties of fluids confined in nanopores, known as critical shift, due to its great impact upon calculations of fluid properties in tight reservoirs. Modeling of this phenomenon commenced with developing equations of state (EOS) and has been continuing with correlations, all based on the two-parameter Lennard–Jones (L–J) potential function. Although these approaches have tried to present passable estimations of critical shift, sufficiently accurate predictions of critical shift are still missing in the literature. In this study, the three-parameter Kihara potential, as a more physically realistic alternative, is used to develop the van der Waal (vdW) EOS, and accordingly, a fluid-dependent expression is derived to calculate the critical temperature of confined fluids, i.e., pore critical temperature ($${T}_{\mathrm{cp}}$$
T
cp
). Using 50 data points of $${T}_{cp}$$
T
cp
reports for normal alkanes in the literature, the average error of our model is only 2.23%, 6.4% less than that of the L–J model. Furthermore, despite simple correlations of previous works, herein the Kihara parameters are exclusively tuned for each component based on their $${T}_{cp}$$
T
cp
reports, which resulted in an average error of 0.4% for normal alkanes. Finally, the pressure–volume diagrams of vdW and Peng–Robinson EOSs associated with the Kihara potential function are comprehensively discussed. The findings of this study can help researchers with more accurate predictions of the critical temperature of fluids confined in tight porous media, thereby providing more precise calculations of fluid properties and behavior at equilibrium conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.