Falenty, Andrzej

[["dc.bibliographiccitation.firstpage","27159"],["dc.bibliographiccitation.issue","48"],["dc.bibliographiccitation.journal","The Journal of Physical Chemistry C"],["dc.bibliographiccitation.lastpage","27172"],["dc.bibliographiccitation.volume","120"],["dc.contributor.author","Falenty, A."],["dc.contributor.author","Qin, Jian-Chun"],["dc.contributor.author","Salamatin, Andrey N."],["dc.contributor.author","Yang, L."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T10:04:36Z"],["dc.date.available","2018-11-07T10:04:36Z"],["dc.date.issued","2016"],["dc.description.abstract","The exchange process between CO2 and methane hydrate has been observed in numerous laboratory experiments, computer simulations, and recently confirmed in a field test. Yet, to date there is no kinetic model capable of accurately predicting the swapping process at given fluid composition and p-T conditions. Major obstacles on the way to an adequate mathematical description are caused by the insufficient characterization of experimental environments and a nearly complete lack of information on the time-resolved composition of the two-phase fluid at the gas hydrate interface. Here we show that all necessary data can be provided by a combination of cryo-SEM, Raman, and neutron diffraction measurements that deliver accurate space-averaged, time-resolved in situ data on the CH4-CO2 exchange reactions at conditions relevant to sedimentary matrixes of continental margins. Results from diffraction are cross-correlated with ex situ Raman spectroscopy to provide reliable information on the preferential sites for CO2 and CH4 in the (partially) exchanged hydrate. We also show a novel approach based on scattering of neutrons to probe the fluid composition during the in situ replacement in a time-resolved, noninvasive manner. The replacement is seen as a two-step process including (1) a fast surface reaction parallel to a fast enrichment of the surrounding fluid phase with CH4 followed by (2) a much slower permeation-limited gas swapping between the gas hydrate and mixed ambient CH4-CO2 fluid. The main part of the replacement reaction takes place in the second stage. Based on our earlier experimental studies and existing literature we work toward a quantitative gas exchange model which elaborates the hole-in-cage-wall diffusion mechanism to describe the two-component gas replacement."],["dc.identifier.doi","10.1021/acs.jpcc.6b09460"],["dc.identifier.isi","000389624400009"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/38730"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1932-7447"],["dc.title","Fluid Composition and Kinetics of the in Situ Replacement in CH4-CO2 Hydrate System"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","4022"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","The Journal of Physical Chemistry C"],["dc.bibliographiccitation.lastpage","4032"],["dc.bibliographiccitation.volume","115"],["dc.contributor.author","Falenty, Andrzej"],["dc.contributor.author","Genov, Georgi"],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Kuhs, Werner F."],["dc.contributor.author","Salamatin, Andrey N."],["dc.date.accessioned","2018-11-07T08:58:05Z"],["dc.date.available","2018-11-07T08:58:05Z"],["dc.date.issued","2011"],["dc.description.abstract","The gas hydrate growth from frostlike powders composed of micrometer-sized ice particles does not start with hydrate shell formation, because the initial hydrate film thickness established in earlier work exceeds the ice particle dimensions. In this limiting case, the ice, grains are directly consumed by a growing nucleus created on the particle surface. The conventional Johnson-Mehl-Avrami-Kolmogorov (JM-AK) model,(1) which considers (re-) crystallization reactions phenomenologically in terms of the constituent nucleation and subsequent growth processes, cannot be directly applied to the hydrate formation from frost due to the assumption of an infinitely large domain of crystallization. We present here a modified approach to account for the small particle sizes of the starting material and extend the existing theory of gas hydrate formation from monodisperse ice powders(3-5) to the low-temperature and low-ice-particle-size limit. This approach may also prove to be very useful for applying chemical reactions starting on the surface of nanomaterials. In situ neutron scattering was used to obtain the experimental degree of transformation as a function of temperature between 185 and 195 K. The data were analyzed with the modified JMAK model constrained by information from cryo-SEM and BET measurements. Based on the obtained activation energies for hydrate nucleation and growth, an estimate is given for the probability of formation of CO2 hydrates at conditions relevant for Mars; a direct reaction of CO2 gas with water frost is considered to be very unlikely on the Martian surface under current conditions."],["dc.identifier.doi","10.1021/jp1084229"],["dc.identifier.isi","000288113400026"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23558"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1932-7447"],["dc.title","Kinetics of CO2 Hydrate Formation from Water Frost at Low Temperatures: Experimental Results and Theoretical Model"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","8443"],["dc.bibliographiccitation.issue","16"],["dc.bibliographiccitation.journal","The Journal of Physical Chemistry C"],["dc.bibliographiccitation.lastpage","8457"],["dc.bibliographiccitation.volume","117"],["dc.contributor.author","Falenty, A."],["dc.contributor.author","Salamatin, Andrey N."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T09:25:52Z"],["dc.date.available","2018-11-07T09:25:52Z"],["dc.date.issued","2013"],["dc.description.abstract","The shrinking-core model of the formation of gas hydrates from ice spheres with a well-defined geometry gives experimental access to the gas permeation in bulk hydrates. Here we report on results obtained for CO2 clathration experiments in the temperature range from 185 to 272 K, extending earlier work to much lower temperature conditions. The activation energy deduced from the permeation coefficients changes its value from similar to 46 kJ/mol at higher temperatures to similar to 19 kJ/mol below 225 K. We compare our results with published molecular dynamics simulation as well as nuclear magnetic resonance studies and provide arguments that the rate limiting process at lower temperatures is the cage-to-cage jumping of CO2 molecules via a \"hole-in-the-cage\" mechanism involving extrinsic vacancies in cage walls. The rate-limiting process at higher temperatures can be explained by the temperature-dependent creation of intrinsic water-vacancy-interstitial pairs. The results obtained for CO2-hydrate are compared to earlier results for CH4-hydrate formation. The permeation of CO2 molecules through bulk hydrate is found to be about three times faster when compared to the CH4 case. This explains the faster clathration reaction of CO2-hydrate in comparison to CH4-hydrate."],["dc.description.sponsorship","Institut Laue-Langevin (ILL) at Grenoble"],["dc.identifier.doi","10.1021/jp310972b"],["dc.identifier.isi","000318211200059"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30165"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1932-7447"],["dc.title","Kinetics of CO2-Hydrate Formation from Ice Powders: Data Summary and Modeling Extended to Low Temperatures"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","5681"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Energy & Fuels"],["dc.bibliographiccitation.lastpage","5691"],["dc.bibliographiccitation.volume","29"],["dc.contributor.author","Salamatin, Andrey N."],["dc.contributor.author","Falenty, A."],["dc.contributor.author","Hansen, Thomas C."],["dc.contributor.author","Kuhs, Werner F."],["dc.date.accessioned","2018-11-07T09:52:11Z"],["dc.date.available","2018-11-07T09:52:11Z"],["dc.date.issued","2015"],["dc.description.abstract","The shrinking-core model of the formation of gas hydrates from ice spheres with well-defined geometry gives experimental access to the gas permeation in bulk hydrates which is relevant to their use as energy storage materials, their exploitation from natural resources, as well as to their role in flow assurance. Here we report on a new approach to model CO2 dathration experiments in the temperature range from 230 to 272 K. We develop a comprehensive description of the gas permeation based on the diffusion along the network of polyhedral cages, some of them being empty. Following earlier molecular dynamics simulation results, the jump from a cage to one of its empty neighbors is assumed to proceed via a \"hole-in-cage-wall\" mechanism involving water vacancies in cage walls. The rate-limiting process in the investigated temperature range can be explained by the creation of water-vacancy-interstitial pairs. The gas diffusion leads to a time-dependent cage filling which decreases across the hydrate layer with the distance from the particle surface. The model allows a prediction of the time needed for a complete conversion of ice spheres into clathrate as well as the time needed for a full equilibration of the cage fillings. The findings essentially support our earlier results obtained in the framework of a purely phenomenological permeation model in terms of the overall transformation kinetics, yet it provides for the first time insight into the cage equilibration processes. The diffusion of CO2 molecules through bulk hydrate is found to be about three to four times faster in comparison with the CH4 case."],["dc.identifier.doi","10.1021/acs.energyfuels.5b01217"],["dc.identifier.isi","000363068200023"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/36063"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","1520-5029"],["dc.relation.issn","0887-0624"],["dc.title","Guest Migration Revealed in CO2 Clathrate Hydrates"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]