Carbon capture and storage (CCS) is vital to climate change mitigation, and has application across the economy, in addition to facilitating atmospheric carbon dioxide removal resulting in emissions offsets and net negative emissions. This contribution reviews the state-of-the-art and identifies key challenges which must be overcome in order to pave the way for its large-scale deployment.

As a continuation of our work on spherical associating molecules, we have derived expressions for changes in the thermodynamic properties due to association in mixtures of molecules with multiple bonding sites. The equations are written in terms of a hard-core reference whose pair distribution function is known. In practise, the hard-sphere reference mixture is the easiest to use. A reference system of homonuclear chains is examined in order to account for asymmetries in molecular shape; chains are constructed by bonding equal-sized spheres together. An equation of state for hard-sphere chains is obtained which is in good agreement with recent simulation data. Expressions for mixtures of homonuclear chains of different sizes are also presented. The approach is extended to examine associating chain molecules with multiple bonding sites. The phase equilibria of non-associating chains, and of associating chains with one or two bonding sites are determined. In this study, the separate effects of molecular association and chain size on the coexistence properties are investigated.

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We report classical atomistic molecular dynamics simulations of four structurally diverse model asphaltenes, a model resin, and their respective mixtures in toluene or heptane under ambient conditions. Relatively large systems (∼50 000 atoms) and long time scales (>80 ns) are explored. Wherever possible, comparisons are made to available experimental observations asserting the validity of the models. When the asphaltenes are dissolved in toluene, a continuous distribution of cluster sizes is observed with average aggregation number ranging between 3.6 and 5.6, monomers and dimers being the predominant species. As expected for mixtures in heptane, the asphaltene molecules tend to aggregate to form a segregated phase. There is no evidence of the distinct formation of nanoaggregates, and the distribution of clusters is found to be continuous in character. Analysis of the shape of the clusters of asphaltenes suggests that they are generally spherical in character, with the archipelago models favoring longer prolate structures and the continental model tending toward oblate structures. The aggregates are seen to be diffuse in nature, containing at least 50% solvent on average, being denser in heptane than in toluene. Mixtures of asphaltenes with different architecture are found to have cluster properties that are intermediate between those of the individual components. The presence of resins in the mixture does not appear to alter the shape of the asphaltene aggregates or their size or density when toluene is the solvent; on the other hand, the resins lead to an increase in the density of the resulting aggregates in heptane. Quantification of these observations is made from histograms of the cluster distributions, potential of mean force calculations, and an analysis of the shape factors. We illustrate how the time scales for complete aggregation of molecules in heptane are longer than the longest of the simulations reported in the open literature and as an example report a long simulation (0.5 μs) that fails to reach an equilibrium state, suggesting that acceleration techniques (e.g., using coarse-grained models) are needed to appropriately explore these phenomena.

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