B. Peter McGrail

Flexible metal–organic supramolecular isomers for gas separation

Three interpenetrated metal-organic supramolecular isomers were synthesised using a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2), H(2) and methane at room temperature.

Gas-induced transformation and expansion of a non-porous organic solid

Organic solids composed by weak van der Waals forces are attracting considerable attention owing to their potential applications in gas storage, separation and sensor applications. Herein we report a gas-induced transformation that remarkably converts the high-density guest-free form of a well-known organic host (p-tert-butylcalix[4]arene) to a low-density form and vice versa, a process that would be expected to involve surmounting a considerable energy barrier. This transformation occurs despite the fact that the high-density form is devoid of channels or pores. Gas molecules seem to diffuse through the non-porous solid into small lattice voids, and initiate the transition to the low-density kinetic form with approximately 10% expansion of the crystalline organic lattice, which corresponds to absorption of CO2 and N2O (refs 4,5). This suggests the possibility of a more general phenomenon that can be exploited to find more porous materials from non-porous organic and metal-organic frameworks that possess void space large enough to accommodate the gas molecules.

Porous organic molecular materials

Most nanoporous materials with molecular-scale pores are composed of directional covalent or coordination bonds, such as porous metal–organic frameworks and organic network polymers. By contrast, nanoporous materials comprised of discrete organic molecules, between which there are only weak non-covalent interactions, are seldom encountered. Indeed, the majority of organic molecules pack efficiently in the solid state to minimize the void volume, leading to nonporous materials. In recent years, a large number of nanoporous organic molecular materials (crystalline or amorphous) were discovered and their porosity was confirmed by gas adsorption. All of these materials were compiled in this highlight. In addition, advantages of porous organic molecular materials over porous networks are discussed.

Semi-analytical approaches to modeling deep well injection of CO2 for geological sequestration

Abstract Geological sequestration of CO2 has been recognized as an important strategy for reducing the CO2 concentration in the atmosphere. Simple and easy to use modeling tools would be valuable in assessing the performance of a deep well operation during and after injection. Presented here is a semi-analytical model to simulate the deep well injection of CO2 for geological sequestration. Equations governing the radial injection of an immiscible CO2 phase into saturated confined formations (representing deep saline aquifers and reservoirs), its axisymmetric flow around the injector and eventual buoyancy driven floating with simultaneous dissolution were formulated. The effect of pertinent fluid, reservoir and operational characteristics on the deep well injection of CO2 was investigated. The results indicate that the injected CO2 initially grows as a bubble radially outward, a part of which eventually dissolves in the formation waters, floats toward the top due to buoyancy and settles near the top confining layer. It was shown that the formation permeability and porosity, as well as the rate and pressure of injection, all have a significant influence on the growth and ultimate distribution of the immiscible CO2 phase. Further, dissolution of CO2 also was shown to have a significant effect on the growth and distribution of the CO2 bubble.

Prussian Blue Analogues for CO2 and SO2 Capture and Separation Applications

Adsorption isotherms of pure gases present in flue gas including CO(2), N(2), SO(2), NO, H(2)S, and water were studied using prussian blues of chemical formula M(3)[Co(CN)(6)](2).nH(2)O (M = Co, Zn) using an HPVA-100 volumetric gas analyzer and other spectroscopic methods. All the samples were characterized, and the microporous nature of the samples was studied using the BET isotherm. These materials adsorbed 8-10 wt % of CO(2) at room temperature and 1 bar of pressure with heats of adsorption ranging from 200 to 300 Btu/lb of CO(2), which is lower than monoethanolamine (750 Btu/lb of CO(2)) at the same mass loading. At high pressures (30 bar and 298 K), these materials adsorbed approximately 20-30 wt % of CO(2), which corresponds to 3 to 5 molecules of CO(2) per formula unit. Similar gas adsorption isotherms for SO(2), H(2)S, and NO were collected using a specially constructed volumetric gas analyzer. At close to 1 bar of equilibrium pressure, these materials sorb around 2.5, 2.7, and 1.2 mmol/g of SO(2), H(2)S, and NO. In particular, the uptake of SO(2) and H(2)S in Co(3)[Co(CN)(6)](2) is quite significant since it sorbs around 10 and 4.5 wt % at 0.1 bar of pressure. The stability of prussian blues before and after trace gases was studied using a powder X-ray diffraction instrument, which confirms these materials do not decompose after exposure to trace gases.

Metal organic gels (MOGs): a new class of sorbents for CO2 separation applications

MOGs with excellent thermal stability and porosity have been synthesized at room temperature. The strength of the MOGs obtained depend on the raw materials used, reaction time, temperature, concentration of reactants and the processing conditions. MOGs with higher internal surface areas were obtained using near supercritical processing conditions. Measurement of CO2 sorption isotherm of MOG-1a at high pressure (30 bar) suggests 33 wt% (7.5 mmol g−1) of CO2 with a reversible uptake and release. To our knowledge this is the first study on the utilization of the MOGs for CO2 capture applications. Significant uptake of CO2 at high pressure (∼30 bar) clearly reveals the significant potential of these materials for their applications as solid sorbents.

Dissolution Kinetics of Pyrochlore Ceramics for the Disposition of Plutonium.

Abstract Single-pass β ow-through (SPFT) experiments were conducted on a set of non-radioactive Ti-based ceramics at 90 °C and pH = 2 to 12. The specimens contained 27.9 to 35.8 wt%CeO2 as a surrogate for UO2 and PuO2. Compositions were formulated as TiO2-saturated pyrochlore (CeP1) and pyrochlorerich baseline (CePB1) ceramic waste forms. Pyrochlore + Hf-rutile and pyrochlore + perovskite + Hf-rutile constituted the major phases in the CeP1 and CePB1 ceramics, respectively. Results from dissolution experiments between pH = 2 to 12 indicate a shallow pH-dependence with an ill-defined minimum. Element release rates determined from experiments over a range of sample surface areas (S) and β ow rates (q) indicate that dissolution rates become independent of q/S values at 10.8 to 10.7 m/s. Dissolution rates dropped sharply at lower values of q/S, indicating rates that are subject to solution saturation effects as dissolved constituents become concentrated. Forward dissolution rates were 1.3(0.30) x 10-3 and 5.5(1.3) x 10-3 g/m2·d for CeP1 and CePB1 ceramics, respectively. Dissolution rates obtained in other laboratories compare well to the findings of this study, once the rate data are placed in the context of solution saturation state. These results make progress toward an evaluation of CeO2 as a surrogate for UO2 and PuO2 as well as establishing a baseline for comparison with radiation- damaged specimens.

Waste Form Release Data Package for the 2001 Immobilized Low-Activity Waste Performance Assessment

This data package documents the experimentally derived input data on the representative waste glasses LAWABP1 and HLP-31 that will be used for simulations of the immobilized lowactivity waste disposal system with the Subsurface Transport Over Reactive Multiphases (STORM) code. The STORM code will be used to provide the near-field radionuclide release source term for a performance assessment to be issued in March of 2001. Documented in this data package are data related to 1) kinetic rate law parameters for glass dissolution, 2) alkali-H ion exchange rate, 3) chemical reaction network of secondary phases that form in accelerated weathering tests, and 4) thermodynamic equilibrium constants assigned to these secondary phases. The kinetic rate law and Na+-H+ ion exchange rate were determined from single-pass flow-through experiments. Pressurized unsaturated flow and vapor hydration experiments were used for accelerated weathering or aging of the glasses. The majority of the thermodynamic data were extracted from the thermodynamic database package shipped with the geochemical code EQ3/6. However, several secondary reaction products identified from laboratory tests with prototypical LAW glasses were not included in this database, nor are the thermodynamic data available in the open literature. One of these phases, herschelite, was determined to have a potentially significant impact on the release calculations and so a solubility product was estimated using a polymer structure model developed for zeolites. Although this data package is relatively complete, final selection of ILAW glass compositions has not been done by the waste treatment plant contractor. Consequently, revisions to this data package to address new ILAW glass formulations are to be regularly expected.

Microstructural Response of Variably Hydrated Ca-Rich Montmorillonite to Supercritical CO2

First-principles molecular dynamics simulations were carried out to explore the mechanistic and thermodynamic ramifications of the exposure of variably hydrated Ca-rich montmorillonites to supercritical CO2 and CO2-SO2 mixtures under geologic storage conditions. In sub- to single-hydrated systems (≤ 1W), CO2 intercalation causes interlamellar expansion of 8-12%, while systems transitioning to 2W may undergo contraction (∼ 7%) or remain almost unchanged. When compared to ∼2W hydration state, structural analysis of the ≤ 1W systems, reveals more Ca-CO2 contacts and partial transition to vertically confined CO2 molecules. Infrared spectra and projected vibrational frequency analysis imply that intercalated Ca-bound CO2 are vibrationally constrained and contribute to the higher frequencies of the asymmetric stretch band. Reduced diffusion coefficients of intercalated H2O and CO2 (10(-6)-10(-7) cm(2)/s) indicate that Ca-montmorillonites in ∼ 1W hydration states can be more efficient in capturing CO2. Simulations including SO2 imply that ∼ 0.66 mmol SO2/g clay can be intercalated without other significant structural changes. SO2 is likely to divert H2O away from the cations, promoting Ca-CO2 interactions and CO2 capture by further reducing CO2 diffusion (10(-8) cm(2)/s). Vibrational bands at ∼ 1267 or 1155 cm(-1) may be used to identify the chemical state (oxidation states +4 or +6, respectively) and the fate of sulfur contaminants.

Technetium incorporation into hematite (α-Fe2O3)

Quantum-mechanical methods were used to evaluate mechanisms for possible structural incorporation of Tc species into the model iron oxide, hematite (alpha-Fe2O3). Using periodic supercell models, energies for charge-neutral incorporation of Tc4+ or TcO4- ions were calculated using either a Tc4+/Fe2+ substitution scheme on the metal sublattice, or by insertion of TcO4- as an interstitial species within a hypothetical vacancy cluster. Although pertechnetate incorporation is found to be invariably unfavorable, incorporation of small amounts of Tc4+ (at least 2.6 wt %) is energetically feasible. Energy minimized bond distances around this impurity are provided to aid in future spectroscopic identification of these impurity species. The calculations also show that Fe2+ and Tc4+ prefer to cluster in the hematite lattice, attributed to less net Coulombic repulsion relative to that of Fe3+-Fe3+. These modeling predictions are generally consistent with observed selective association of Tc with iron oxide under reducing conditions, and in residual waste solids from underground storage tanks at the U.S. Department of Energy Hanford Site (Washington, U.S.). Here, even though relatively high pH and oxidizing conditions are dominant, Tc incorporation into iron oxides and (oxy)hydroxides is prospectively enabled by prior reduction of TcO4- to Tc4+ via interaction with radiolytic species.