No abstract

Five soldiers were injured by inhalation of hexite smoke (ZnCl2) during military training. Two soldiers, not wearing gas masks breathed hexite for 1 or 2 min, they slowly developed severe adult respiratory distress syndrome (ARDS) over the ensuing 2 weeks. This slow, progressive clinical course has not been previously described. In both patients, an increased plasma zinc concentration was measured 3 weeks after the incident. Intravenous and nebulized acetylcysteine increased the urinary excretion of zinc, and briefly decreased the plasma levels. In an attempt to arrest collagen deposition in the lungs, L-3,4 dehydroproline was administered. Both patients died of severe respiratory failure (25 and 32 days after inhalation). At autopsy diffuse microvascular obliteration, widespread occlusion of the pulmonary arteries and extensive interstitial and intra-alveolar fibrosis was observed. Three soldiers wearing ill fitting gas masks, immediately developed severe coughing and dyspnea. They improved, and 12 months after exposure their lung function tests were nearly normal, but they still had slight dyspnea on exercise.

An experimental evaluation of the kinetics and equilibrium capacities of pure fluids as a fast and effective means to screen an adsorbent's gas separation potential is described. Equilibrium adsorption capacities for pure N2, CH4, and CO2 have been determined using a Micromeritics ASAP2020 sorption analyzer, for three commercially available zeolites: natural chabazite, H+ mordenite, and Linde 4A molecular sieve over the temperature range from (248 to 302) K and pressure range from (0.001 to 120) kPa. Toth models were regressed to the equilibrium data for each gas and used to generate inferred equilibrium selectivity maps over a wider range of temperature and pressure for the purpose of targeting any future mixture measurements. For each gas, the rate of adsorption at 100 kPa was measured as a function of temperature and used with a linear driving force model to calculate mass transfer coefficients. In most cases the ratio of the mass transfer coefficients for each pair of gases was close to unity and did not give rise to a significant kinetic selectivity. However the Linde 4A molecular sieve at 273 K and 100 kPa had a kinetic selectivity for CO2 over CH4 of 6.2. This approach to screening adsorbents with pure fluids can assist in optimizing the design of subsequent mixture measurements by identifying the most promising temperature and pressure ranges to target.

While it has long been known that some highly adsorbing microporous materials suddenly become inaccessible to guest molecules below certain temperatures, previous attempts to explain this phenomenon have failed. Here we show that this anomalous sorption behaviour is a temperature-regulated guest admission process, where the pore-keeping group's thermal fluctuations are influenced by interactions with guest molecules. A physical model is presented to explain the atomic-level chemistry and structure of these thermally regulated micropores, which is crucial to systematic engineering of new functional materials such as tunable molecular sieves, gated membranes and controlled-release nanocontainers. The model was validated experimentally with H2, N2, Ar and CH4 on three classes of microporous materials: trapdoor zeolites, supramolecular host calixarenes and metal-organic frameworks. We demonstrate how temperature can be exploited to achieve appreciable hydrogen and methane storage in such materials without sustained pressure. These findings also open new avenues for gas sensing and isotope separation.

The separation of methane and nitrogen from binary mixtures using a commercial activated carbon, Norit RB3, was investigated. The adsorption of pure fluids and CH4 + N2 mixtures were measured at temperatures of 242, 273, and 303 K, at pressures ranging from 53 to 5000 kPa using a high pressure volumetric apparatus and at pressures from 104 to 902 kPa using a dynamic column breakthrough apparatus (DCB). The pure gas equilibrium adsorption capacities were regressed to Toth, Langmuir, Langmuir–Freundlich, and Sips isotherm models; the Toth model gave the best prediction of measured capacities at pressures from 800 to 5000 kPa. The uptake of components from gas mixtures calculated using the Ideal Adsorbed Solution Theory (IAST), Extended Langmuir and Multi-Sips models were all within the uncertainties of the measured adsorption capacities, suggesting that for this adsorbent there is no significant advantage in using the more computationally intensive IAST method. A linear driving force (LDF)-based model of adsorption in a fixed bed was developed to extract the lumped mass transfer coefficients for CH4 and N2 from the pure gas DCB experimental data. This model was used with results from the pure gas experiments to predict the component breakthroughs from equimolar CH4 + N2 mixtures in the DCB apparatus. The Norit RB3 exhibited equilibrium selectivities for CH4 over N2 in the range 3 to 7 (measured selectivites have an average uncertainty of 37%), while the lumped mass transfer coefficients of CH4 and N2 were similar for this activated carbon, ranging from 0.004 to 0.052 s–1. The results presented can serve as a reference data set upon which industrial PSA processes for separating CH4 + N2 mixtures using generic activated carbons can be developed and optimized over a wide range of pressures and temperatures.