Molecular Simulation of Carbon Dioxide Adsorption for Carbon Capture and Storage.

Capture of CO2 from fossil fuel power plants and sequestration in unmineable coal seams are achievable methods for reducing atmospheric emissions of this greenhouse gas. To aid the development of effective CO2capture and sequestration technologies, a series of molecular simulation studies were conducted to study the adsorption of CO2 and related species onto heterogeneous, solid adsorbents. To investigate the influence of surface heterogeneity upon adsorption behavior in activated carbons and coal, isotherms were generated via grand canonical Monte Carlo (GCMC) simulation for CO2 adsorption in slit-shaped pores with several variations of chemical and structural heterogeneity. Adsorption generally increased with increasing oxygen content and the presence of holes or furrows, which acted as preferred binding sites. To investigate the potential use of the flexible metal organic framework (MOF) Cu(BF4)2(bpy)2 (bpy=bipyridine) for CO2capture, pure- and mixed-gas adsorption was simulated at conditions representative of power plant process streams. This MOF was chosen because it displays a novel behavior in which the crystal structure reversibly transitions from an empty, zero porosity state to a saturated, expanded state at the “gate pressure”. Estimates of CO2 capacity above the gate pressure from GCMC simulations using a rigid MOF model showed good agreement with experiment. The CO2 adsorption capacity and estimated heats of adsorption are comparable to common physi-adsorbents under similar conditions. Mixed-gas simulations predicted CO2/N2and CO2/H2selectivities higher than typical microporous materials. To more closely investigate this gating effect, hybrid Monte-Carlo/molecular-dynamics (MCMD) was used to simulate adsorption using a flexible MOF model. Simulation cell volumes remained relatively constant at low gas pressures before increasing at higher pressure. Mixed-gas simulations predicted CO2/N2 selectivities comparable to other microporous adsorbents. To study the molecular processes relevant to storage of CO2 in unmineable coal seams with enhanced methane recovery, a representative bituminous coal was simulated using MD and a hybrid Gibbs-ensemble-Monte-Carlo/MD method. Simulation predicted a bulk density of 1.24 g/ml for the dry coal, which compares favorably with the experimental value of 1.3 g/ml. Consistent with known coal properties, simulation models showed stacking of macromolecular graphitic regions and preferential adsorption of CO2 relative to methane.Ph.D.Applied Physics and Environmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/62442/1/ctenney_1.pd

Toward First Principles Prediction of Voltage Dependences of Electrolyte/Electrolyte Interfacial Processes in Lithium Ion Batteries

In lithium ion batteries, Li⁺ intercalation into electrodes is induced by applied voltages, which are in turn associated with free energy changes of Li⁺ transfer (Δ<i>G</i>_<i>t</i>) between the solid and liquid phases. Using <i>ab initio</i> molecular dynamics (AIMD) and thermodynamic integration techniques, we compute Δ<i>G</i>_<i>t</i> for the virtual transfer of a Li⁺ from a LiC₆ anode slab, with pristine basal planes exposed, to liquid ethylene carbonate confined in a nanogap. The onset of delithiation, at Δ<i>G</i>_<i>t</i> = 0, is found to occur on LiC₆ anodes with negatively charged basal surfaces. These negative surface charges are evidently needed to retain Li⁺ inside the electrode and should affect passivation (“SEI”) film formation processes. Fast electrolyte decomposition is observed at even larger electron surface densities. By assigning the experimentally known voltage (0.1 V vs Li⁺/Li metal) to the predicted delithiation onset, an absolute potential scale is obtained. This enables voltage calibrations in simulation cells used in AIMD studies and paves the way for future prediction of voltage dependences in interfacial processes in batteries

Molecular Simulation of Carbon Dioxide, Brine, and Clay Mineral Interactions and Determination of Contact Angles

Capture and subsequent geologic storage of CO₂ in deep brine reservoirs plays a significant role in plans to reduce atmospheric carbon emission and resulting global climate change. The interaction of CO₂ and brine species with mineral surfaces controls the ultimate fate of injected CO₂ at the nanoscale via geochemistry, at the pore-scale via capillary trapping, and at the field-scale via relative permeability. We used large-scale molecular dynamics simulations to study the behavior of supercritical CO₂ and aqueous fluids on both the hydrophilic and hydrophobic basal surfaces of kaolinite, a common clay mineral. In the presence of a bulk aqueous phase, supercritical CO₂ forms a nonwetting droplet above the hydrophilic surface of kaolinite. This CO₂ droplet is separated from the mineral surface by distinct layers of water, which prevent the CO₂ droplet from interacting directly with the mineral surface. Conversely, both CO₂ and H₂O molecules interact directly with the hydrophobic surface of kaolinite. In the presence of bulk supercritical CO₂, nonwetting aqueous droplets interact with the hydrophobic surface of kaolinite via a mixture of adsorbed CO₂ and H₂O molecules. Because nucleation and precipitation of minerals should depend strongly on the local distribution of CO₂, H₂O, and ion species, these nanoscale surface interactions are expected to influence long-term mineralization of injected carbon dioxide

Make the World a Better Place

Representing the Center for Frontiers of Subsurface Energy Security (CFSES), this document is one of the entries in the Ten Hundred and One Word Challenge. As part of the challenge, the 46 Energy Frontier Research Centers were invited to represent their science in images, cartoons, photos, words and original paintings, but any descriptions or words could only use the 1000 most commonly used words in the English language, with the addition of one word important to each of the EFRCs and the mission of DOE: energy. The mission of the CFSES is to pursue the scientific understanding of multiscale, multiphysics processes and to ensure safe and economically feasible storage of carbon dioxide and other byproducts of energy production without harming the environment

Pinpointing Pseurotins from a Marine-Derived Aspergillus as Tools for Chemical Genetics Using a Synthetic Lethality Yeast Screen

A new compound of mixed polyketide synthase-nonribosomal peptide synthetase (PKS/NRPS) origin, 11- O-methylpseurotin A ( 1), was identified from a marine-derived Aspergillus fumigatus. Bioassay-guided fractionation using a yeast halo assay with wild-type and cell cycle-related mutant strains of Saccharomyces cerevisiae resulted in the isolation of 1, which selectively inhibited a Hof1 deletion strain. Techniques including 1D and 2D NMR, HRESIMS, optical rotation, J-based analysis, and biosynthetic parallels were used in the elucidation of the planar structure and absolute configuration of 1. A related known compound, pseurotin A ( 2), was also isolated and found to be inactive in the yeast screen

A Computational and Experimental Study of the Heat Transfer Properties of Nine Different Ionic Liquids

New experimental thermal conductivity, density, viscosity, glass transition temperature, and heat capacity values were measured for nine ionic liquids (ILs): [emim]­[TFA], [emim]­[OTf], [emim]­[DEP], [emim]­[MeSO₃], [emim]­[SCN], [hmim]­[Tf₂N], [bDMApy]­[Tf₂N], [hDMApy]­[Tf₂N], and [hmDMApy]­[Tf₂N]. Classical molecular mechanics force fields were developed and used to calculate thermodynamic and transport properties for these ILs using molecular dynamics. Two versions of each force field were developed: one with integer charges of ± 1 and one with all charges scaled by 0.8. The force fields with total charges of ± 0.8 generally gave better agreement with experimental results. Very good agreement was obtained for density and heat capacity. Simulated values for thermal conductivity slightly overpredicted experimental results but captured trends between different ILs very well. Experimental Prandtl numbers were determined as a function of temperature and can exceed 10 000 at low temperature. Prandtl numbers on the order of 100–1000 were observed above 330 K. These values suggest that heat transfer with ionic liquids will be dominated by convective effects