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Thermodynamic measurements and Raman spectroscopy are performed to investigate the structure, selectivity and capture efficiency in mixed gas hydrates containing CO 2 and N 2 . Clathrates forming conditions and dissociation pressures are provided between 270.5 K and 278.3 K (−2.5 °C and 5.3 °C). Specific CO 2 Raman signatures show structure sII to be thermodynamically stable at feed gas composition of 1% and kinetically favored at ∼2%. Structure sI is stable at feed gas CO 2 ranging from ∼2% up to 70%. Our Raman quantitative analysis demonstrates the removal of CO 2 from a typical flue gas mixture (1–20% CO 2 ) and from samples of 47% and 70% CO 2 during hydrate crystallization. For the first time, quantitative bulk guest compositions in hydrates are directly obtained by Raman using relative cross sections of the guests’ (CO 2 and N 2 ) vibrational modes. The equilibrium data thereby generated satisfactorily compare with predictions based on thermodynamic models (CSMGem) and thus remove any ambiguity from previous literature data. It appears that CO 2 molecules preferentially occupy sI large cages (5 12 6 2 ) for a CO 2 feed gas concentration in the range of 2–20% (i.e. ∼1–16% equilibrium gas compositions), whereas CO 2 molecules severely compete with N 2 to fill sI small cages (5 12 ) at equilibrium CO 2 concentrations greater than 30%. As a consequence, the derived selectivity shows a significant decrease from ∼7.2 (at 20% CO 2 ) to ∼3.8 for CO 2 -rich feed gas compositions (i.e. above 20%). In addition, the selectivity is reduced in structure sII formed at 1% CO 2 feed gas composition. Then, the influence of thermodynamic parameters on hydrate selectivity and recovery fraction is described qualitatively at typical CO 2 flue gas concentrations found in conventional power plants. [ABSTRACT FROM AUTHOR] more...

• Soot inception causes a discontinuity in the properties of flame-generated matter. • The physical-chemical properties of incipient soot are unique. • Incipient soot acts as sink for large aromatics. • The structure of incipient soot is closely related to amorphous carbon. The transformation of molecular precursors in the gas phase into nanoparticles in the condensed phase (soot inception) during combustion has not yet been fully understood. While several hypotheses on soot inception are currently being examined, their validation requires detailed knowledge of the physical–chemical properties of the matter first formed in the condensed phase (incipient soot). However, characterizing short–lived species in a reactive environment at high temperature is inherently difficult. In this work, we propose a multi–analytical approach to indirectly characterize chemical composition and structure of incipient soot obtained in controlled laboratory conditions. The results are explained in light of recent developments on the characterization of the optical and magnetic properties of incipient soot, and used to build a phenomenological model of soot inception. The acquired information is key to support the hypothesis selection and to understand the reactivity of combustion byproducts and thus their impact on health and the environment. [ABSTRACT FROM AUTHOR] more...

• Exchange kinetic in CH 4 -hydrates using CO 2 or CO 2 -N 2 gas. • Impact of the initial CH 4 -hydrate system properties on the kinetic. • Structure, cage occupancy and phase composition monitored by Raman spectroscopy. • Quantitative and qualitative estimates of factors influencing the kinetic. Recovering methane from natural gas hydrate deposits using carbon dioxide injection is currently of great environmental and energetic interest as it shows potential for producing an energy resource while mitigating CO 2 emissions through CO 2 sequestration. This work investigates the exchange kinetic between CH 4 and CO 2 (or CO 2 -N 2 (v)) in synthetic hydrates, with an emphasis on the impact of CH 4 hydrate formation conditions (e.g. driving force Δ p) on the subsequent exchange reactions. Different driving forces Δ p are utilized and show that the exchange kinetic is improved by a factor of ~3 when the exchange is performed with low Δ p CH 4 hydrates, for which there is a higher relative amount of free H 2 O(liq) (277 K); the kinetic is further improved when stirring is applied. Isobaric CH 4 hydrates exhibit a fast primary hydrate dissociation and CH 4 release, followed by a slower exchange kinetic, possibly limited by solid-state exchange diffusion or secondary CO 2 -rich hydrate formation within the stability field of CH 4 hydrates. Upon exposure to a mixed CO 2 -N 2 (v) gas stream, secondary hydrate production is governed by the effective Δ p remaining after dissolution of the gas mixture, and results in an even slower exchange reaction rate. These results may help optimizing recovery processes in field trial experiments, where both hydrates and liquid water coexist, and aid in predicting the risk of geo-hazards induced by unstable secondary hydrate formation. Furthermore, the exchange kinetic dependencies highlighted here are important as they affect the overall energy efficiency and energy cost of CH 4 recovery processes in gas hydrate field trials. [ABSTRACT FROM AUTHOR] more...

• Semi-clathrate hydrates separation efficiency is studied from a CO 2 -N 2 gas mixture. • Influence of formation parameters evaluated by in-situ Raman spectroscopy. • Structure, equilibrium gas and hydrate compositions inferred from Raman analyses. • Higher selectivity in semi-clathrates type A compare to type B/polymorphs. • CO 2 capture efficiency depends on crystallization parameters. Carbon dioxide (CO 2) capture from flue gas mixture analogs based on ionic clathrate hydrates crystallization (using tetra-n-butyl ammonium bromide, TBAB) is investigated by optical microscopy and Raman spectroscopy. The purpose of this research is to investigate the influence of the crystallization protocol (slow versus fast cooling/heating) on the subsequent semi-clathrate structures formed from a 35 wt% TBAB-H 2 O solution and CO 2 separation efficiency from an initial gas mixture of 10%CO 2 + 90%N 2. In-situ Raman analyses reveal that structure type B (sometimes associated with several polymorph phases) is readily observed at the onset of the formation process regardless of the crystallization protocol. Structure type B remains stable up to a temperature close to that of dissociation, whereas polymorphs form and evolve continuously until then. Just before dissociation, structure type A is additionally observed. The protocol involving slow cooling and heating steps (similar to the isochoric pressure search method) performs slightly better in terms of selectivity than the one using the multi-cycling temperature approach (fast cooling and heating). However, within the same protocol, the selectivity greatly depends on the specific semi-clathrate structures formed. We find that the best CO 2 selectivity is achieved when structure type A is formed compared to all other semi-clathrate phases. The CO 2 recovery fraction is found at lower value than that measured in canonical clathrate hydrates. [ABSTRACT FROM AUTHOR] more...