Assessment of threat arising by closed - volume explosions of fuel - air mixtures

The method of estimation of maximal parameters of combustion of gaseous mixtures in closed space is presented. Estimation of chemical composition of combustion products is based on simplified rules of decomposition of reactive medium. Exemplary calculations of temperature, pressure, heat of combustion of hydrocarbon/air mixtures are presented. The accuracy of presented method was validated by comparison with calculations performed by thermodynamic numerical code that include wide list of chemical substances present in combustion products. The obtained results confirm applicability of the proposed method to predict closed space combustion parameters of gaseous mixtures. Semi-empirical methods of estimation of flammability limits are briefly referred

Absolute optical chiral analysis using cavity-enhanced polarimetry

Chiral analysis is central for scientific advancement in the fields of chemistry, biology, and medicine. It is also indispensable in the development and quality control of chiral compounds in the chemical and pharmaceutical industries. Current methods for chiral analysis, namely optical polarimetry, mass spectrometry and nuclear magnetic resonance, are either insensitive, have low time resolution, or require preparation steps, and so are unsuited for monitoring chiral dynamics within complex environments: the current need of both research and industry. Here we present the concept of absolute optical chiral analysis, as enabled by cavity-enhanced polarimetry, which allows for accurate unambiguous enantiomeric characterization and enantiomeric-excess determination of chiral compounds within complex mixtures at trace levels, without the need for calibration, even in the gas phase. The utility of this approach is demonstrated by post chromatographic analysis of complex gaseous mixtures, the rapid quality control of perfume mixtures containing chiral volatile compounds, and the online in-situ observation of chiral volatile emissions from a plant under stress. Our approach and technology offer a step change in chiral compound determination, enabling online quality control of complex chemical mixtures, identification of counterfeit goods, detection of pests on plants, and assessment of chiral emission processes from climate relevant ecosystems.

Spectral lineshapes of collision-induced absorption (CIA) using isotropic intermolecular potential for N2-CH4

Quantum mechanical lineshapes of collision-induced absorption (CIA) at different temperatures are computed for gaseous mixtures of molecular nitrogen and methane using theoretical values for the induced dipole moments and intermolecular potential as input. Comparison with theoretical absorption spectra shows satisfactory agreement. An empirical model of the dipole moment which reproduces the experimental spectra and the first three spectral moments more closely than the fundamental theory, is also presented. Good agreement between computed and experimental absorption lineshapes is obtained when a potential model which is constructed from the thermophysical and transport properties is used.

Considerations on Temperature Dependent Effective Diffusion and Permeability of Natural Clays

A series of porous clay samples prepared at different pretreatment temperatures have been tested in a diffusion chamber. Diffusivity and permeability were examined in a temperature range from ambient to 900 °C. Gaseous mixtures of O2, CO2, and N2 have been applied, as these species are the relevant gases in the context of clay brick firing and similar thermochemical processes. Diffusive transport characteristics have been determined by means of the mean transport-pore model, and permeability has been evaluated by Darcy’s law. CO2 diffusivity increased strongly with temperature, whereas O2 diffusion was limited to a certain level. It is proposed that one should consider CO2 surface diffusion in order to explain this phenomenon. The diffusion model was expanded and surface diffusion was included in the model equation. The results of the model fit reflected the important role of incorporated carbonates of the clay foundation in gas-phase (molecular or Knudsen) diffusivity. CO2 surface diffusion was observed to exhibit similar coefficients for two different investigated clays, and is therefore indicated as a property of natural clays. Permeability showed a progressive rise with temperature, in line with related literature.

Graphyne-3: a highly efficient candidate for separation of small gas molecules from gaseous mixtures

Two-dimensional nanosheets, such as the general family of graphenes have attracted considerable attention over the past decade, due to their excellent thermal, mechanical, and electrical properties. We report on the result of a study of separation of gaseous mixtures by a model graphyne-3 membrane, using extensive molecular dynamics simulations and density functional theory. Four binary and one ternary mixtures of H$$_2$$ 2 , CO$$_2$$ 2 , CH$$_4$$ 4 and C$$_2$$ 2 H$$_6$$ 6 were studied. The results indicate the excellence of graphyne-3 for separation of small gas molecules from the mixtures. In particular, the H$$_2$$ 2 permeance through the membrane is on the order of $$10^7$$ 10 7 gas permeation unit, by far much larger than those in other membranes, and in particular in graphene. To gain deeper insights into the phenomenon, we also computed the density profiles and the residence times of the gases near the graphyne-3 surface, as well as their interaction energies with the membrane. The results indicate clearly the tendency of H$$_2$$ 2 to pass through the membrane at high rates, leaving behind C$$_2$$ 2 H$$_6$$ 6 and larger molecules on the surface. In addition, the possibility of chemisorption is clearly ruled out. These results, together with the very good mechanical properties of graphyne-3, confirm that it is an excellent candidate for separating small gas molecules from gaseous mixtures, hence opening the way for its industrial use.