A molecular model for H2 interactions in aliphatic and aromatic hydrocarbons

Abstract

A model for molecular hydrogen interacting with aliphatic and aromatic hydrocarbons is presented. The model has been derived using ab initio techniques and molecular dynamics simulations. In particular, quadrupole moments of hydrogen, and variation on energy with intermolecular distance of different conformations for the hydrogen-benzene couple were calculated using the Møller-Plesset method. Hydrogen was modelled using a two-centre Lennard-Jones potential plus electrostatic interactions. Lennard-Jones parameters were optimized on the basis of a correct reproduction of experimental data of hydrogen solubility in benzene and cyclohexane, calculated using the test particle insertion method. Different sets of parameters for specific interactions (hydrogen-aliphatic and hydrogen-aromatic systems) were considered avoiding the simple use of Lorentz-Berthelot combining rules. Additionally, structural and thermodynamic properties of hydrogen-benzene, hydrogen-cyclohexane and hydrogen in an equimolar mixture of benzene-cyclohexane at different low concentrations of hydrogen were investigated by means of molecular dynamics simulations. Electrostatic charges were taken from ab initio quantum mechanical calculations but after careful analysis of the calculated properties, their irrelevance was evidenced. Moreover, Coulombic interactions make simulations more expensive and, therefore, we do not recommend their inclusion in the modelling of hydrogen-aliphatic and aromatic interactions.

Measurement of the vapour–liquid equilibrium of binary and ternary mixtures of CO2, N2 and H2, systems which are of relevance to CCS technology

“…We then modify the force-field using an optimisation routine to search for improved parameter values in the vicinity of this initial estimate. For H 2 , we adopt Lennard-Jones parameters of H = 2.59 Å and H /k B = 12.5 K for a bond length of l H2 = 0.74 Å, from Cracknell (2001); and a quadrupole of Q H2 = 0.4233 DÅ from Figueroa-Gerstenmaier et al (2009). We determine the Lennard-Jones interactions for CO 2 with H 2 by the Lorentz-Bertholet mixing rules,…”

Formation of bilayer clathrate hydrates

“…The water molecule is described by the TIP5P model, 34 while TIP4P model is also examined for test simulations which give the same qualitative results of the bilayer hydrates formation as with the TIP5P model (see † Electronic Supplementary Information (ESI) for details). 37 The CO 2 molecule is treated by EPM2 model. 35,36 For proper electrostatic interaction representation, hydrogen molecule (H 2 ) is specifically modeled as a quadrupole with -0.64e charge at the center and +0.325e charge positioned at the two ends.…”

“…35,36 For representing proper electrostatic interaction, hydrogen molecule (H 2 ) was specically modeled as a quadrupole with À0.64e charge at the center and +0.325e charge positioned at the two ends. 37 CO 2 molecule was treated using the EPM2 model. 38 A cut-off of 1.0 nm was used for interatomic interactions.…”

Study of highly porous polymers for H2 fuel storage using positron annihilation lifetime spectroscopy

“…In future work, we plan to study additional samples under controlled conditions. With additional published data on the chemical potential of H 2 adsorption on aliphatic/aromatic molecules [37], technically, we may be able to find the adsorption enthalpy (DH ads ) in ultra-micropores using the above Eq. (2).…”