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We present an extension of the statistical associating fluid theory (SAFT) for branched chain molecules using Wertheim's first- and second-order thermodynamic perturbation theory with a hard-sphere reference fluid (SAFT-B). Molecules are formed by hard spherical sites which are tangentially bonded. Linear chains are described as freely jointed monomeric units, whereas branched molecules are modeled as chains with a different number of articulation points, each of them formed by three arms. In order to calculate the vapor–liquid equilibria of the system, we have considered attractive interactions between the segments forming the chain at the mean-field level of van der Waals. The Helmholtz free energy due to the formation of the chain is explicitly separated into two contributions, one accounting for the formation of the articulation tetramer, and a second one due to the formation of the chain arms. The first term is described by the second-order perturbation theory of Phan et al. [J. Chem. Phys. 99, 5326 (1993)], which has been proven to predict the thermodynamic properties of linear chain fluids in a similar manner to Wertheim's approach. The formation of the chain arms is calculated at Wertheim's first-order perturbation level. The theory is used to study the effect of the chain architecture on the thermodynamic properties and phase equilibria of chain molecules. The equation predicts the general trends of the compressibility factor and vapor–liquid coexistence curve of the system with the branching degree, in qualitative agreement with molecular simulation results for similar models. Finally, SAFT-B is applied to predict the critical properties of selected light alkanes in order to assess the accuracy of the theory. Experimental trends of the critical temperature of branched alkanes are qualitatively captured by this simple theory. ; This work was supported by the Spanish Government under Project No. PB96-1025 and VI Plan Propio de Investigación de la Universidad de Huelva. One of the authors (F.J.B.) ...

[Image: see text] The use of hydrofluorocarbons (HFCs) as an alternative for refrigeration units has grown over the past decades as a replacement to chlorofluorocarbons (CFCs), banned by the Montreal's Protocol because of their effect on the depletion of the ozone layer. However, HFCs are known to be greenhouse gases with considerable global warming potential (GWP), thousands of times higher than carbon dioxide. The Kigali Amendment to the Montreal Protocol has promoted an active area of research toward the development of low GWP refrigerants to replace the ones in current use, and it is expected to significantly contribute to the Paris Agreement by avoiding nearly half a degree Celsius of temperature increase by the end of this century. We present here a molecular-based evaluation tool aiming at finding optimal refrigerants with the requirements imposed by current environmental legislations in order to mitigate their impact on climate change. The proposed approach relies on the robust polar soft-SAFT equation of state to predict thermodynamic properties required for their technical evaluation at conditions relevant for cooling applications. Additionally, the thermodynamic model integrated with technical criteria enable the search for compatibility of currently used third generation compounds with more eco-friendly refrigerants as drop-in replacements. The criteria include volumetric cooling capacity, coefficient of performance, and other physicochemical properties with direct impact on the technical performance of the cooling cycle. As such, R1123, R1224yd(Z), R1234ze(E), and R1225ye(Z) demonstrate high aptitude toward replacing R134a, R32, R152a, and R245fa with minimal retrofitting to the existing system. The current modeling platform for the rapid screening of emerging refrigerants offers a guide for future efforts on the design of alternative working fluids.

In this work we have implemented the fundamental-measure density functional theory due to Kierlik and Rosinberg to describe the adsorption of Lennard-Jones molecules in cylindrical pores. The accuracy of the theory in predicting adsorption isotherms and particle density profiles is checked by comparison with grand canonical Monte Carlo simulations for a wide range of pore sizes, showing very good agreement in all cases. In addition, the theory has been applied to the adsorption in slitlike pores to study the influence of the pore geometry on this property. The results indicate that the confinement of the cylindrical geometry introduces significant differences in the shape of the adsorption isotherms and density profiles. These differences are relevant for the characterization of porous materials. ; The authors thank Lev D. Gelb and Keith E. Gubbins for useful discussions. Alexander V. Neimark, Peter I. Ravikovitch, and Aleksey Vishnyakov are gratefully acknowledged for providing data for Fig. 10. This work was supported by the Spanish Government Ministerio de Ciencia y Tecnología (Grant Nos. PPQ2000-2888-E, PPQ2001-0671) and by URV (Project No. 2000PIR-21). S.F-G. thanks URV (Spain) and CONACyT (Me ́xico) for financial support. F.J.B. thanks the Universidad de Huelva and the Junta de Andalucía for financial support