An Equation of State for Associating Fluids

An accurate density functional theory for the vapor–liquid interface of chain molecules based on the statistical associating fluid theory for potentials of variable range for Mie chainlike fluids

A new Helmholtz free energy density functional is presented to predict the vapor–liquid interface of chainlike molecules.

Experiment and prediction of water content of sour natural gas with an modified cubic plus association equation of state

In this work, new experimental value for water content in sour natural gas were reported. In addition, to predict the water content in sour natural gas, a modified cubic plus association equation of state (CPA-EoS) was also proposed. In this model, a new energy parameter a was proposed to make an accurate description of saturated liquid density. Additionally, a temperature dependent binary interaction parameter kij for six binary systems was also obtained. Lastly, a comparison between the prediction results of the modified CPA-EoS and the experimental data was presented, and the results showed that the modified CPA-EoS could predict the water content in sour natural gas with high accuracy, which has an AAD of 3.6722% with experimental data in literatures and an AAD of 1.946% for experimental data reported in this work.

A density functional theory for association of fluid molecules with a functionalized surface: fluid-wall single and double bonding

In this manuscript we extend Wertheim's two-density formalism beyond its first order to model a system of fluid molecules with a single association site close to a planar hard wall with association sites on its surface in a density functional theory framework. The association sites of the fluid molecules are small enough that they can form only one bond, while the wall association sites are large enough to bond with more than one fluid molecule. The effects of temperature and of bulk fluid and wall site densities on the fluid density profile, extent of association, and competition between single and double bonding of fluid segments at the wall sites versus distance from the wall are presented. The theory predictions are compared with new Monte Carlo simulation results and they are in good agreement. The theory captures the surface coverage over wide ranges of temperature and bulk density by introducing the effect of steric hindrance in fluid association at a wall site.

Association Equilibrium for Cross-Associating Chains in a Good Solvent: Crowding and Other Nonideality Effects

Association equilibrium has been studied by molecular dynamics (MD) for mixtures of cross-associating molecules (n-decamer+p-dimer and n-decamer+p-decamer) in a good solvent. Each monomer of n-decamers carries an associative site (n-sticker); each molecule of the second component contains two terminal associative sites (p-stickers). To model the univalent association between the n-sticker and the p-sticker, a technique based on introduction of dummy atoms has been used. We report MD data on the effects of temperature, chain flexibility, and location of the sticker within the chain on the association equilibrium. We find that the presence of nonassociating monomer units of p-chain has a substantial effect on the association equilibrium. This effect is similar to "crowding" in reactive mixtures known to be caused by the presence of inert molecules. Widely used mean field theories of associating chains (e.g., SAFT or Semenov-Rubinstein theory) do not account for the effect of crowding caused by the inert fragments of reactive chains. We introduce simple empirical corrections for crowding that describe association equilibrium in the presence of nonassociating fragment in a chain-like molecule.