Carbon dioxide capture-related gas adsorption and separation in metal-organic frameworks

New force fields for carbon dioxide and nitrogen are introduced that quantitatively reproduce the vapor–liquid equilibria (VLE) of the neat systems and their mixtures with alkanes. In addition to the usual VLE calculations for pure CO2 and N2, calculations of the binary mixtures with propane were used in the force-field development to achieve a good balance between dispersive and electrostatic (quadrupole–quadrupole) interactions. The transferability of the force fields was then assessed from calculations of the VLE for the binary mixtures with n-hexane, the binary mixture of CO2/N2, and the ternary mixture of CO2 /N2/propane. The VLE calculations were carried out using configurational-bias Monte Carlo simulations in either the grand canonical ensemble with histogram–reweighting or in the Gibbs ensemble.

Vapor–liquid equilibria of mixtures containing alkanes, carbon dioxide, and nitrogen

Friction, wear and lubrication between materials in contact are of fundamental importance in many pure and applied sciences. Owing to the development of experimental and computer-simulation techniques for studying these phenomena at the atomic scale, an understanding is beginning to emerge of the molecular mechanisms of tribology in thin films and at surfaces.

Nanotribology: friction, wear and lubrication at the atomic scale

Commensurate adsorption of hydrocarbons and alcohols in microporous metal organic frameworks.

This Review focuses on research oriented toward elucidation of the various aspects that determine adsorption of CO2 in metal–organic frameworks and its separation from gas mixtures found in industrial processes. It includes theoretical, experimental, and combined approaches able to characterize the materials, investigate the adsorption/desorption/reaction properties of the adsorbates inside such environments, screen and design new materials, and analyze additional factors such as material regenerability, stability, effects of impurities, and cost among several factors that influence the effectiveness of the separations. CO2 adsorption, separations, and membranes are reviewed followed by an analysis of the effects of stability, impurities, and process operation conditions on practical applications.

CO2 Capture and Separations Using MOFs: Computational and Experimental Studies

Carbon Dioxide's Liquid-Vapor Coexistence Curve And Critical Properties as Predicted by a Simple Molecular Model

Molecular dynamics simulations are used to predict the equilibrium liquid-vapor interface structure and surface tension of n-alkanes decane and eicosanes, C 10 H 22 and C 20 H 42 , respectively. The model treats each methyl and methylene group as one united Lennard-Jones atom. Realistic bond lengths, bond angle potentials, and torsional potentials are included in the simulation. The simulations predict that although the total mass density profile is monotonic, the density profile of the chain centers of mass and central segments is strongly peaked. The outer edge of the surface is dominated by chain ends

Liquid-vapor interfaces of alkane oligomers: structure and thermodynamics from molecular dynamics simulations of chemically realistic models

We describe a lattice model of a supported monolayer of flexible amphiphile molecules which treats their full three‐dimensional structure and includes nearest neighbor interactions between segments of the amphiphile chains, an attraction between the chain segments and the underlying substrate, and the inter‐ and intrachain excluded volume. The thermodynamic and conformational properties of this system are determined by a Monte Carlo simulation technique using a Metropolis sampling. At low surface coverage, the thermodynamic behavior predicted by the simulations is significantly different from that predicted by the mean‐field theory of Wang and Rice; notably, the liquid–vapor critical point predicted by the mean‐field theory is too high. In contrast, the mean‐field theory prediction of the density profile along the normal to the surface is rather good. When the surface coverage is small, the conformations of the chains are sensibly independent of density. However, as the surface coverage increases the inte...

A lattice model of a supported monolayer of amphiphile molecules: Monte Carlo simulations

We study the thermodynamics and structure of a model monomolecular film of pentadecanoic acid on water. In this model the water is treated as a uniform polarizable continuum and the pentadecanoic acid molecules as chains of 15 pseudoatom with internal bond constraints, angle bending and torsional intramolecular interactions, and Lennard‐Jones atom–atom intermolecular interactions. The only low pressure phases exhibited by this model at temperatures between 300 and 400 K are the very low density vapor phase and a well ordered condensed phase with a reciprocal density ≤23 A2 per molecule. This is in sharp contrast with experimental studies which show the existence of a stable liquid‐expanded phase with a density of about 35 A2 per molecule at pressures <15 dyn cm−1.

A molecular dynamics study of the structure of a model Langmuir monolayer of amphiphile molecules

Experiments using the surface force apparatus indicate that the nature of the forces acting on two surfaces separated by liquid film less than 5.0 nm thick are extremely sensitive to the chemical structure of the molecules in the liquid. Using molecular dynamics simulations we probe the structure and solvation forces upon two model surfaces separated by liquid hydrocarbons. We examine two cases—films composed of n‐octane and films composed of iso‐octane (2‐methyl heptane). At certain surface separations the liquid films are strongly layered with chains lying parallel to the surface. These films produce a repulsive force equivalent to as much as 100 MPa on the surfaces, while exhibiting liquidlike self‐diffusion constants with no evidence of solidification or glassification. A plot of this force, known as the solvation force, as a function of surface separation reveals strong oscillations with a period of about 0.4–0.5 nm for both the linear and branched molecules. Although the branching in the iso‐octane significantly reduces the intensity of the layering, its solvation force curve shows oscillations which are just as strong as those seen in the films of the linear octane. This contradicts experimental results showing that the addition of a single methyl side chain significantly reduces the oscillatory nature of the solvation forces.

Jonathan G. Harris

Papers

Carbon Dioxide's Liquid-Vapor Coexistence Curve And Critical Properties as Predicted by a Simple Molecular Model

Liquid-vapor interfaces of alkane oligomers: structure and thermodynamics from molecular dynamics simulations of chemically realistic models

A lattice model of a supported monolayer of amphiphile molecules: Monte Carlo simulations

A molecular dynamics study of the structure of a model Langmuir monolayer of amphiphile molecules

Confined thin films of a linear and branched octane. A comparison of the structure and solvation forces using molecular dynamics simulations