Naturally occurring clay minerals provide a distinctive material for carbon capture and carbon dioxide sequestration. Swelling clay minerals, such as the smectite variety, possess an aluminosilicate structure that is controlled by low-charge layers that readily expand to accommodate water molecules and, potentially, CO2. Recent experimental studies have demonstrated the efficacy of intercalating CO2 in the interlayer of layered clays, but little is known about the molecular mechanisms of the process and the extent of carbon capture as a function of clay charge and structure. A series of molecular dynamics simulations and vibrational analyses have been completed to assess the molecular interactions associated with incorporation of CO2 and H2O in the interlayer of montmorillonite clay and to help validate the models with experimental observation. An accurate and fully flexible set of interatomic potentials for CO2 is developed and combined with Clayff potentials to help evaluate the intercalation mechanism and examine the effect of molecular flexibility on the diffusion rate of CO2 in water.

Molecular dynamics simulations using classical force fields were carried out to study the structural and transport properties of clay mineral−water−CO 2 systems at pressure and temperature relevant to geological carbon storage. The simulations show that the degree of swelling caused by intercalation of CO 2 strongly depends on the initial water content in the interlayer space and that CO 2 intercalation stimulates inner-sphere adsorption of the positively charged interlayer ions on the internal clay surfaces, which modifies the wetting properties of the surfaces. DFT-based molecular dynamics simulations were used to interpret the origin of the observed shift in the asymmetric stretch vibration of CO 2 trapped in montmorillonite. The origin of the shift is attributed to the electric field effects on the CO 2 molecules induced by the water molecules.

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Research on carbon capture and storage has been focused on CO 2 storage in geologic formations, with many potential risks. An alternative to conventional geologic storage is carbon mineralization, where CO 2 is reacted with metal cations to form carbonate minerals. Mineralization methods can be broadly divided into two categories: in situ and ex situ. In situ mineralization, or mineral trapping, is a component of underground geologic sequestration, in which a portion of the injected CO 2 reacts with alkaline rock present in the target formation to form solid carbonate species. In ex situ mineralization, the carbonation reaction occurs above ground, within a separate reactor or industrial process. This literature review is meant to provide an update on the current status of research on CO 2 mineralization.

Several commercially available and a few experimental, nonionic surfactants were identified that are capable of dissolving in carbon dioxide (CO 2 ) in dilute concentration at typical minimum-miscibility-pressure (MMP) conditions and, upon mixing with brine in a high-pressure windowed cell, stabilizing CO 2 -in-brine foams. These slightly CO 2 -soluble, water-soluble surfactants include branched alkylphenol ethoxylates, branched alkyl ethoxylates, a fatty-acid-based surfactant, and a predominantly linear ethoxylated alcohol. Many of the surfactants were between 0.02 to 0.06 wt% soluble in CO 2 at 1,500 psia and 25 C, and most demonstrated some capacity to stabilize foam. The most-stable foams observed in a high-pressure windowed cell were attained with branched alkylphenol ethoxylates, several of which were studied in highpressure small-angle-neutron-scattering (HP SANS) tests, transient mobility tests using Berea sandstone cores, and high-pressure computed-tomography (CT)-imaging tests using polystyrene cores. HP SANS analysis of foams residing in a small windowed cell demonstrated that the nonylphenol ethoxylate SURFONIC V R N-150 [15 ethylene oxide (EO) groups] generated emulsions with a greater concentration of droplets and a broader distribution of droplet sizes than the shorter-chain analogs with 9-12 ethoxylates. The in-situ formation of weak foams was verified during transient mobility tests by measuring the pressure drop across a Berea sandstone core as a CO 2 /surfactant solution was injected into a Berea sandstone core initially saturated with brine; the pressure-drop values when surfactant was dissolved in the CO 2 were at least twice those attained when pure CO 2 was injected into the same brine-saturated core. The greatest mobility reduction was achieved when surfactant was added both to the brine initially in the core and to the injected CO 2 . CT imaging of CO 2 invading a polystyrene core initially saturated with 5 wt% KI brine indicated that despite the oilwet nature of this medium, a sharp foam front propagated through the core, and CO 2 fingers that formed in the absence of a surfactant were completely suppressed by foams formed because of the addition of nonylphenol ethoxylate surfactant to the CO 2 or the brine.

Abstract. We advance the achievements of Interball-1 and other contemporary missions in exploration of the magnetosheath-cusp interface. Extensive discussion of published results is accompanied by presentation of new data from a case study and a comparison of those data within the broader context of three-year magnetopause (MP) crossings by Interball-1. Multi-spacecraft boundary layer studies reveal that in ∼80% of the cases the interaction of the magnetosheath (MSH) flow with the high latitude MP produces a layer containing strong nonlinear turbulence, called the turbulent boundary layer (TBL). The TBL contains wave trains with flows at approximately the Alfvén speed along field lines and "diamagnetic bubbles" with small magnetic fields inside. A comparison of the multi-point measurements obtained on 29 May 1996 with a global MHD model indicates that three types of populating processes should be operative:-large-scale (∼few R E ) anti-parallel merging at sites remote from the cusp; -medium-scale (few thousand km) local TBL-merging of fields that are anti-parallel on average;Correspondence to: S. Savin (ssavin@iki.rssi.ru) -small-scale (few hundred km) bursty reconnection of fluctuating magnetic fields, representing a continuous mechanism for MSH plasma inflow into the magnetosphere, which could dominate in quasi-steady cases.The lowest frequency (∼1-2 mHz) TBL fluctuations are traced throughout the magnetosheath from the post-bow shock region up to the inner magnetopause border. The resonance of these fluctuations with dayside flux tubes might provide an effective correlative link for the entire dayside region of the solar wind interaction with the magnetopause and cusp ionosphere. The TBL disturbances are characterized by kinked, double-sloped wave power spectra and, most probably, three-wave cascading. Both elliptical polarization and nearly Alfvénic phase velocities with characteristic dispersion indicate the kinetic Alfvénic nature of the TBL waves. The three-wave phase coupling could effectively support the self-organization of the TBL plasma by means of coherent resonant-like structures. The estimated characteristic scale of the "resonator" is of the order of the TBL dimension over the cusps. Inverse cascades of kinetic Alfvén waves are proposed for forming the larger scale "organizing" structures, which in turn synchronize all nonlinear cascades within the TBL in a self-consistent manner. This infers a qualitative differ-184 S. Savin et al.: Magnetosheath-cusp interface ence from the traditional approach, wherein the MSH/cusp interaction is regarded as a linear superposition of magnetospheric responses on the solar wind or MSH disturbances.