Ab initio intermolecular potential energy surface and thermophysical properties of hydrogen sulfide

Abstract

A six-dimensional potential energy hypersurface (PES) for two interacting rigid hydrogen sulfide molecules was determined from high-level quantum-mechanical ab initio computations. A total of 4016 points for 405 different angular orientations of two molecules were calculated utilizing the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory and extrapolating the calculated interaction energies to the complete basis set limit. An analytical site-site potential function with eleven sites per hydrogen sulfide molecule was fitted to the interaction energies. The PES has been validated by computing the second pressure virial coefficient, shear viscosity, thermal conductivity and comparing with the available experimental data. The calculated values of volume viscosity were not used to validate the potential as the low accuracy of the available data precluded such an approach. The second pressure virial coefficient was evaluated by means of the Takahashi and Imada approach, while the transport properties, in the dilute limit, were evaluated by utilizing the classical trajectory method. In general, the agreement with the primary experimental data is within the experimental error for temperatures higher than 300 K. For lower temperatures the lack of reliable data indicates that the values of the second pressure virial coefficient and of the transport properties calculated in this work are currently the most accurate estimates for the thermophysical properties of hydrogen sulfide.

Cross second virial coefficients and dilute gas transport properties of the (CH 4 + CO 2 ), (CH 4 + H 2 S), and (H 2 S + CO 2 ) systems from accurate intermolecular potential energy surfaces

“…Two ab initio potentials are available in the literature for the CH 4 -CO 2 molecule pair [18,19]. Oakley et al [18] calculated the interaction energies only at the MP2 level of theory, which is not accurate enough for the present purpose.…”

“…Such calculations have been performed for a number of simple gases, such as methane [9,10], carbon dioxide [5], hydrogen sulfide [4,11], water vapor [12,13], or ethylene oxide [6], yielding transport property values with an uncertainty commensurate with the best experimental measurements over wide temperature ranges. We have recently extended the calculations to binary mixtures and have reported values for three traditional transport properties (viscosity, thermal conductivity, binary diffusion coefficient) and for the cross second virial coefficient of (CH 4 + N 2 ) mixtures [8,14].…”

“…The increasing preponderance of sour natural gas and natural gas with a high CO 2 content from pre-salt fields in the supply market will require the development of further treatments for the removal of H 2 S and CO 2 [16]. The provision of accurate and reliable thermophysical property data forms an important element not only in optimizing natural gas utilization, but also in Carbon Capture and Storage (CCS), which relies on treating and injecting CO 2 streams that are never pure but contain CH 4 , H 2 S, and N 2 among the impurities. Gas processing using membranes [17], where diffusion coefficients and viscosity play an important part, also involves mixtures that contain the four components for which we have calculated the thermophysical properties.…”

“…We could have improved their PES by fitting a more accurate analytical function, but when the paper of Pai and Bae was published, we had already completed the development of our own PES, which is presented in this paper. For the CH 4 -H 2 S interaction, the only available PES based on ab initio calculated interaction energies is that of Woon et al [21], which was published in 1990. It is based on a fit to only 38 interaction energies, which were computed at the MP2 level with very small basis sets by today's standards.…”

“…The macroscopic properties of a dilute gas are governed by binary molecular interactions, and the recent computational advances in the field have allowed us not only to accurately determine the intermolecular potential energy surfaces (PESs) using quantum-chemical ab initio methods [3][4][5][6], but also to calculate the transport properties by making use of a rigorous molecular description [7,8]. Such calculations have been performed for a number of simple gases, such as methane [9,10], carbon dioxide [5], hydrogen sulfide [4,11], water vapor [12,13], or ethylene oxide [6], yielding transport property values with an uncertainty commensurate with the best experimental measurements over wide temperature ranges.…”