Extending an equation of state to confined fluids with basis on molecular simulations

• The Peng–Robinson equation of state was extended to confined fluids.
• The proposed model was based on molecular simulation data.
• Good agreement was obtained with experimental data of mixture adsorption.

The thermodynamic modeling of confined fluids is important to several systems of practical interest. However, the most accurate approaches for describing these systems have a huge computation cost. The development of equations of state is an attractive approach for most chemical engineering common applications. In previous work, the Peng–Robinson equation of state was extended to fluids confined in cylindrical pores, using as starting point the generalized van der Waals theory and proposing purely empirical expressions to model structural properties of the confined fluid. In the present work, the extended Peng–Robinson model was reformulated with basis on molecular simulation data of the confined fluid structure, in substitution to the purely empirical approach. Fluid molecules were considered hard spheres interacting with each other and with the pore wall through square-well potentials. The molecular simulations were performed for several pore sizes, molecule–wall interaction energies, and fluid densities. The obtained equation of state relates the usual thermodynamics properties with the pore size and two molecule–wall interaction parameters for each fluid component. Experimental pure fluid adsorption data were used to estimate the molecule–wall interaction parameters and mixture adsorption predictions were performed without the fitting of binary interaction parameters. Good results were obtained for some systems comprising nanoporous adsorbents, with an improvement over the previous, more empirical approach.