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54 articles found

B3283 – Hydrogen Storage in Semiclathrate Hydrates of Tetrabutyl Ammonium Chloride and Tetrabutyl Phosphonium Bromide

Original calorimetric and phase equilibrium properties for hydrogen + tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBACl), or tetrabutylphosphonium bromide (TBPB) semiclathrate hydrates were measured using differential scanning calorimetry under pressure. The dissociation temperatures of H2 + TBACI and H2 + TBPB semiclathrate hydrates are very close to the ambient temperature at low pressures around 15.0 MPa. H2 + TBACI and H2 + TBPB systems therefore exhibit better and comparable stability than the H2 + TBAB system at equivalent pressure, respectively. The amount of hydrogen stored in H2 + TBACI and H2 + TBPB semiclathrate hydrates was estimated in terms of the H2-to-water mole ratio (nH2/ nH2O) calculated from disssociation enthalpies and (p, T) equilibrium data. In terms of mass fraction deduced from the ratio (nH2/nH2O), H2 + TBACl and H2 + TBPB semiclathrate hydrates can store 0.12 % and 0.14 % of hydrogen, respectively. Moreover, the quantity of hydrogen stored in these two semiclathrate hydrates is significantly higher than that stored in the H2 + TBAB system
Johnny Deschamps, Didier Dalmazzone, J. Chem. Eng. Data 2010, 55, 3395–3399

B3276 – Dialkylimidazolium halide ionic liquids as dual function inhibitors for methane hydrate

Six dialkylimidazolium halide ionic liquids have been investigated for their potential application as novel gas hydrate inhibitors. Their effects on the equilibrium methane hydrate dissociation curve in a pressure range 105–205 bar and the induction time of methane hydrate formation at 114 bar and a high degree of supercooling, i.e., about 25 °C, are measured in a high-pressure micro-differential scanning calorimeter. Similar to dialkylimidazolium tetrafluoroborate investigated in our previous work, these ionic liquids are found to shift the equilibrium hydrate dissociation/stability curve to a lower temperature and, at the same time, retard the hydrate formation by slowing down the hydrate nucleation rate. To understand the performance of these ionic liquids in inhibiting the hydrate formation, the electrical conductivity and infrared spectra of ionic liquids are also obtained and analyzed.
Chongwei Xiao, Nico Wibisono, Hertanto Adidharma, Chemical Engineering Science 65 (2010) 3080–3087

B3274 – Isotope Effect on Eutectic and Hydrate Melting Temperatures in the Water-THF System

Differential scanning calorimetry was used to study the effect of isotopic substitution on the eutectic and melting temperatures in the water-tetrahydrofuran (THF) system with THF molar fractions near the stoichiometry of the hydrate phase. Deuteration of the host causes an opposite effect from that of the guest with respect to the hydrate liquidus curve and eutectic melting temperature. The eutectic temperature in -containing systems is approximately 3.7?K higher than that in -containing systems. The melting temperatures of THF and deuterated THF hydrates increase by roughly 3.5?K with heavy water. The inclusion of deuterated THF causes a depression of the hydrate liquidus temperatures and a small but measurable effect on the eutectic temperature.
C. Y. Jones, J. S. Zhang, J.W. Lee, Journal of Thermodynamics, Volume 2010, Article ID 583041

B3119 – Mesure et modélisation des conditions de dissociation d’hydrates de gaz stabilisés en vue de l’application au captage du CO2

La capture et la séquestration du CO2 en sortie des usines d'incinération, des centrales thermiques ou des cimenteries est devenu un enjeu mondial. La capture de ce gaz par voie hydrate est une alternative prometteuse. L’objet de cette thèse est l’étude de la stabilité des systèmes d’hydrates mixtes contenant du CO2 et un autre gaz (N2, CH4 et H2) avec l’eau pure, ou encore avec un additif permettant l’abaissement des pressions de formation : le tetrabutylamonium bromure (TBAB), dans une perspective de séparation de gaz. La technique expérimentale que nous avons utilisée est la calorimétrie différentielle programmée (DSC). Elle nous a permis de mesurer les températures et les enthalpies de dissociation des différents systèmes d’hydrates avec l’eau pure : N2, CH4, N2+ CO2, CH4+CO2, H2+CO2 ; mais aussi des systèmes semi-clathrates: CO2+CH4 et CO2+N2 à différents pourcentages massiques de TBAB (10, 20, 30 et 40). La dernière partie de cette thèse concerne la modélisation thermodynamique des semiclathrates, où nous avons développé le cas particulier du système d’hydrate: CH4+TBAB.
Wassila Bouchafaa, Thèse Ecole Polytechnique (Paris) 2011

B3083 – Conception, construction, expérimentation et modélisation d’un banc d’essias grandeur nature de climatisation utilisant un fluide frigoporteur diphasique à base d’hydrates de TBAB

Ces travaux de thèse ont donc consisté à adapter une technologie de réfrigération disponible sur le marché européen au domaine de la climatisation. Le fluide utilisé est une solution de TBAB (Bromure de Tetra-ButylAmmonium) qui est une solution aqueuse dont la température de cristallisation à pression atmosphérique peut être ajustée entre environ 6 et 12°C. Le dispositif expérimental conçu et construit est donc un prototype industriel de taille réelle capable de climatiser 4 pièces. A la fois démonstrateur industriel et banc d’essais instrumenté, il est destiné à mener à bien des séances d’essais afin de démontrer la faisabilité du procédé, de diagnostiquer des améliorations et de prévoir de nouvelles évolutions. Parallèlement aux travaux de construction et aux séances d’essais, des mesures complémentaires concernant certaines caractéristiques thermo-physiques des sorbets d’hydrates de TBAB ont été menées en laboratoire. Enfin, un outil de modélisation a également été développé afin de rattacher les expériences à des phénomènes thermo-physiques théoriques. Cette modélisation a pour but d’être un outil prédicatif à la conception de nouvelles installations et au développement du prototype.
Jérôme Douzet, Thèse École Nationale Supérieure des Mines de Saint-Étienne, Juillet 2011

B3077 – Natural Gas Hydrate Formation and Decomposition in the Presence of Kinetic Inhibitors. 1. High Pressure Calorimetry

The effect of kinetic inhibitors, both chemical (PVP and H1W85281) and biological (type III antifreeze protein), on natural gas hydrate formation was investigated using high pressure differential scanning calorimetry (HP-DSC). The presence of inhibitors decreased the overall formation of methane/ethane/propane hydrate compared to systems without added inhibitors. As well, all of the inhibitors significantly delayed hydrate nucleation as compared to water controls. However, the two classes of inhibitors were distinguished by the formation of hydrates with different stabilities. A single hydrate melting peak was seen with the antifreeze protein (AFP), and this was consistent after recrystallization. In contrast, multiple hydrate melting events, some indicating the formation of hydrate structures with high stability, were observed in the presence of the chemical inhibitors, and these varied depending on the crystallization cycle. This heterogeneity suggests that the use of these chemical inhibitors (PVP and H1W85281) may present a special challenge to operators depending upon the gas mixture and environmental conditions and that AFPs may offer a more predictable, efficacious solution in these cases
Nagu Daraboina, John Ripmeester, Virginia K. Walker, Peter Englezos, Energy Fuels 2011, 25, 4392–4397

B3073 – CO2 Hydrate Slurry

CO2 hydrate slurry is one of the newly developed secondary cooling fluids based on CO2, an inoffensive gas in combination with water under suitable pressure and temperature conditions. A new CO2 hydrate slurry production system was built and tested. Based on previous studies, a comprehensive kinetic study of CO2 hydrates formation and growth was conducted. Solid mass fraction of CO2 hydrate slurry was determinated. The experimental results show that besides pressure and temperature, density and apparent viscosity change can also be good indicators of the hydrate formation. The results have shown that hydrate creation through the heat exchanger by super cooling of the saturated CO2 solution is feasible. Continuous CO2 hydrate slurry formation and dissociation by heat exchanger was proved to be feasible. The pressure drop of CO2 hydrate slurry with different solid mass fraction on heat exchanger as function of steady flow mean velocities were presented and verified. The stability of CO2 hydrate slurry was examined. CO2 hydrate slurry displayed very good stability at steady state during 11.5 hours running test. Longer stability period should be expected if the running conditions are maintained.
Jin Hu, Osmann Sari, Cyril Mahmed, Raffaele Cereghetti, Paul Homsy, Final report, Yverdon les Bains (Switzerland), July 2010

B3052 – Calorimetric investigation of cyclopentane hydrate formation in an emulsion

Differential scanning calorimetry (DSC) is applied to investigate the formation of cyclopentane hydrates in a water-in-oil emulsion. Protocols of cooling below the ice formation temperature and warming to a temperature above the ice and hydrate melting temperatures are applied. Cyclopentane, which forms hydrates at atmospheric pressure, is a component of the continuous oil phase in the hydrate-forming emulsion and is replaced by iso-octane to obtain a comparable ice-forming emulsion. A method based on comparing the heat flow measured by DSC for samples of identically prepared hydrate-forming and non-hydrate (ice-forming) emulsions is developed to obtain the rate of cyclopentane hydrate growth. Results are reported for a 40% water volume fraction emulsion. Experimental results lead to the conclusion that the hydrate formation takes place primarily at the interface between water drops and the continuous oil phase. In the absence of surfactants, a robust hydrate “shell” develops around the water drop limiting transport of hydrate former to the free water which remains trapped inside the hydrate layer. Direct visualization of hydrate formation in larger water drops under the influence of oil-soluble surfactants shows that the hydrate crystals have much smaller features and the appearance is hairy or mushy. A three-step mechanism – nucleation, surface growth and radial growth – is described to capture the main features of the hydrate formation process. Mechanical stresses developed in the hydrate shell due to volume expansion upon hydrate formation (a liquid–solid transition) are analyzed.
Prasad U.Karanjkar, Jae W.Lee, Jeffrey F.Morris, Chemical Engineering Science 68 (2012) 481–491

B3026 – Low temperature chemical reaction systems for thermal storage

This paper presents recent research works regarding the development of materials for thermal storage at temperatures below 200°C. The main idea is to utilize reversible chemical reaction systems to enable high storage densities. Current work focuses on the retrofitting of CO2 hydrates through selected additives for climate and cooling purposes and the activation of thermoreversible organic reaction systems for the waste heat utilization at low temperatures.
Baerbel Egenolf-Jonkmanns, Stefano Bruzzano, Goerge Deerberg, Matthias Fischer, Thomas Marzi, Maria Tyukavina, Jorge Salazar Gomez, Holger Wack, Barbara Zeidler-Fandrich, Energy Procedia 30 ( 2012 ) 235 – 243

B2982 – Phase behaviour of tri-n-butylmethylammonium chloride hydrates in the presence of carbon dioxide

The phase behaviour of the system water–tri-n-butylmethylammonium chloride (TBMAC)–CO2 was investigated by pressure-controlled differential scanning calorimetry in the range 0–10 mol% TBMAC in water and at CO2 pressures ranging from 0 to 1.5 MPa. In the absence of CO2, an incongruent melting hydrate, which estimated composition corresponds to TBMAC 30H2O, crystallizes at temperatures below -13.6 °C and forms with ice a peritectic phase at approximately 3.9 mol% TBMAC. In the presence of CO2 at pressures as low as 0.5 MPa, curves evidenced the presence of an additional phase exhibiting congruent melting at temperatures that are strongly pressure dependent and significantly higher than those of hydrates obtained without CO2. This new phase, whose enthalpy of dissociation and CO2 content increase slightly with CO2 pressure, was identified as a mixed semi-clathrate hydrate of TBMAC and CO2 of general formula: (TBMAC + xCO2) 30H2O.
Nadia Mayoufi, Didier Dalmazzone, Walter Fürst, Leila Elghoul, Adel Seguatni, Anthony Delahaye, Laurence Fournaison, J Therm Anal Calorim (2012) 109:481–486

B2846 – The heats of fusion of tetrabutylammonium fluoride ionic clathrate hydrates

Two ionic clathrate hydrates with different structures are formed in the binary system tetrabutylammonium fluoride–water, namely tetragonal structure-I hydrate (TS-I) (n-C4H9)4NF 32.8H2O, and cubic superstructure-I hydrate (CSS-I) (n-C4H9)4NF 29.7H2O. The heats of fusion (DHf) of these polyhydrates were measured calorimetrically with differential scanning calorimeter. For TS-I polyhydrate ?Hf = (204.8 ± 2.3) kJ/mol hydrate, for CSS-I hydrate ?Hf = (177.5 ± 3.1) kJ/mol polyhydrate. The change of water molecules energy state in the water lattices of TS-I and CSS-I polyhydrates are discussed.
T. V. Rodionova, A. Yu. Manakov, Yu. G. Stenin, G. V. Villevald, T. D. Karpova, J Incl Phenom Macrocycl Chem (2008) 61,107–111

B2772 – Calorimetric investigation of cyclopentane hydrate formation in an emulsion

Differential scanning calorimetry (DSC) is applied to investigate the formation of cyclopentane hydrates in a water-in-oil-emulsion.Protocols of cooling below the ice formation temperature and warming to a temperature above the ice and hydrate melting temperatures are applied. Cyclopentane, which forms hydrates at atmospheric pressure, is a component of the continuous oil phase in the hydrate-forming emulsion and is replaced by iso-octane to obtain acomparable ice-forming emulsion. Amethod based on comparing the heatflow measured by DSC for sample sofidentically prepared hydrate-forming and non-hydrate (ice-forming) emulsions is developed to obtain the rate of cyclopentane hydrate growth.
Prasad U.Karanjkar, Jae W.Lee, Jeffrey F.Morris, Chemical EngineeringScience 68 (2012) 481–491

B2599 – Measurements of methane hydrate equilibrium in systems inhibited with NaCl and methanol

Natural gas hydrates are ice-like inclusion compounds that form at high pressures and low temperatures in the presence of water and light hydrocarbons. Hydrate formation conditions are favorable in gas and oil pipelines, and their formation threatens gas and oil production. Thermodynamic hydrate inhibitors (THIs) are chemicals (e.g., methanol, monoethylene glycol) deployed in gas pipelines to depress the equilibrium temperature required for hydrate formation. This work presents a novel application of a stepwise differential scanning calorimeter (DSC) measurement to accurately determine the methane hydrate phase boundary in the presence of THIs. The scheme is first validated on a model (ice + salt water) system, and then generalized to measure hydrate equilibrium temperatures for pure systems and 0.035 mass fraction NaCl solutions diluted to 0, 0.05, 0.10, and 0.20 mass fraction methanol. The hydrate equilibrium temperatures are measured at methane pressures from (7.0 to 20.0) MPa. The measured equilibrium temperatures are compared to values computed by the predictive hydrate equilibrium tool CSMGem.
Patrick G. Lafond, Kyle A. Olcott, E. Dendy Sloan, Carolyn A. Koh, Amadeu K. Sum, J. Chem. Thermodynamics 48 (2012) 1–6

B2598 – Calorimetric investigation of cyclopentane hydrate formation in an emulsion

Differential scanning calorimetry (DSC) is applied to investigate the formation of cyclopentane hydrates in a water-in-oil emulsion. Protocols of cooling below the ice formation temperature and warming to a temperature above the ice and hydrate melting temperatures are applied. Cyclopentane, which forms hydrates at atmospheric pressure, is a component of the continuous oil phase in the hydrate-forming emulsion and is replaced by iso-octane to obtain a comparable ice-forming emulsion. A method based on comparing the heat flow measured by DSC for samples of identically prepared hydrate-forming and non-hydrate (ice-forming) emulsions is developed to obtain the rate of cyclopentane hydrate growth. Results are reported for a 40% water volume fraction emulsion. Experimental results lead to the conclusion that the hydrate formation takes place primarily at the interface between water drops and the continuous oil phase. In the absence of surfactants, a robust hydrate ‘‘shell’’ develops around the water drop limiting transport of hydrate former to the free water which remains trapped inside the hydrate layer. Direct visualization of hydrate formation in larger water drops under the influence of oil-soluble surfactants shows that the hydrate crystals have much smaller features and the appearance is hairy or mushy. A three-step mechanism – nucleation, surface growth and radial growth – is described to capture the main features of the hydrate formation process. Mechanical stresses developed in the hydrate shell due to volume expansion upon hydrate formation (a liquid–solid transition) are analyzed.
Prasad U. Karanjkar, Jae W. Lee, Jeffrey F. Morris, Chemical Engineering Science 64 (2009) 4732 -- 4736

B2597 – Thermodynamic analysis of hydrate-based pre-combustion capture of CO2

This paper presents the phase equilibria of quaternary CO2 + H2 + cyclopentane (CP) + water systems containing gas hydrates and proposes a staged-separation scheme based on the thermodynamic data. The phase equilibria of HLLV of quaternary CO2 + H2 + CP + water systems are determined by using a high-pressure differential scanning calorimeter (DSC). The equilibrium dissociation pressures are dependent on the vapor composition and they shift to lower values with the increase in the CO2 mole fraction. The difference in the dissociation pressures between various CO2 fractions vanishes as the temperature approaches the melting point of CP hydrates at 0.1 MPa. The hydrate dissociation enthalpy is independent of vapor compositions and it is 144 kJmol (gas)?1 over the temperature range. Experimental data are compared to the calculated ones from John–Holder's three-shell model. The prediction matches well with experimental data. The presence of CP reduces the operation pressure of a hydrate-based CO2 capturing process from the pre-combustion stream. Two equilibrium stages of hydrate crystallization and dissociation can enrich CO2 in the vapor-phase significantly from 0.4 of CO2 mole fraction to 0.98 at 282K. This thermodynamic analysis provides a conceptual design for developing a new process of pre-combustion CO2 capture in IGCC plants.
Junshe Zhang, Prasad Yedlapalli, Jae W. Lee, Chemical Engineering Science 64 (2009) 4732 -- 4736

B2507 – Evaluation of hydrate nucleation trends and kinetic hydrate inhibitor performance by high-pressure differential scanning calorimetry

Due to the large number of tests, fluid volumes, and test times for traditional KHI evaluation; it was desirable to develop a quicker KHI performance-screening tool. This paper discusses a potential new method for evaluating KHI performance, which utilizes a high-pressure differential scanning calorimeter to study the nucleation of hydrates. Although the limits of the DSC method do not allow testing under exact field conditions, nor under shear conditions, it could be used to facilitate quicker initial screening of KHIs and evaluate KHI compatibility trends with other chemicals/fluids. Since hydrate formation is a stochastic event a large number of long traditional experiments are required to account for the dispersion of nucleation times. HP-DSC tests are significantly shorter, resulting in a higher out-put of data in a shorter time frame. Two DSC methods were explored to develop a quicker KHI screening tool. The first method utilized a stable water-in-oil emulsion to provide a large number of primarily independent nucleation events with uniform nucleation probability, in a single test. This method provides a very high statistical out-put in a single test, as each droplet can be treated as an individual nucleation event, analogous to a single rocking-cell or autoclave test. The second method was conducted in 100 % water-cut systems. Both methods reduce the overall test time required for KHI performance evaluation. In parallel studies at Nalco and CSM the hydrate nucleation trends were examined on a HP-DSC, for uninhibited and KHI inhibited fluids. The data from a select number of tests will be presented to illustrate the effectiveness of using the DSC for evaluating hydrate nucleation and KHI performance trends. This paper will also provide comparative data between traditional autoclave testing performed at Nalco, and the HP-DSC experiments, in an effort to develop a faster means to evaluate KHI performance.
Kevin McNamee, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2506 – Thermodynamic equilibrium data for mixed hydrates of CO2-N2 , CO2-CH4 and CO2-H2 in pure water and TBAB solutions

Mixed hydrates containing CO2 and N2, H2 or CH4 have been studied in this paper. Dissociation temperatures as function of the pressure of these hydrates, as well as the dissociation enthalpies, were determined at different gas proportions in pure water and TBAB solutions at 10, 20 30 and 40% using differential scanning calorimetry under pressure. The addition of TBAB in the solution increases the dissociation temperature of the hydrate and stabilizes it until a certain concentration comprised between 30 and 40 mass percent; after what the temperature decreases. The mixed hydrates of CO2+N2 have a thermodynamic behaviour which is closer to the pure CO2 hydrate at low prerssures; whereas the CO2+CH4 mixed hydrate dissociation temperatures as function of the pressure are quite close when the gas proportion varies. This indicates the selectivity of these mixed hydrates for one gas rather than another which is very useful for separation purposes.
Wassila Bouchafaa, Didier Dalmazzone, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2505 – The phase behaviours in mixed G + Tetra–N-Butylphosphonium borohydride and G + Tetra-N-Butylammonium hydroxie hydrates (where G = H2, N2)

The use of hydrogen hydrates stabilized by tetra-n-butylphosphonium borohydride (TBPBH4) and tetra-n-butylammonium hydroxide (TBAOH) as media for hydrogen storage was investigated using High Pressure Differential Scanning Calorimetry (HP-DSC) and gas volumetric analysis. In this study the TBPBH4 was obtained by reacting sodium borohydride with tetra-n-butylphosphonium bromide (TBPB). The TBPBH4 solutions were found to form hydrates at low temperature, and HP-DSC was used for determining the dissociation (p, T) points of mixed N2 + TBPBH4 and H2 + TBPBH4 hydrates at various salt concentrations. The results show that the new additive has very efficient stabilizing effect on the hydrate structure, the dissociation temperatures ranging from 280 to 295K, depending on the gas, in a pressure range of 0 to 40 MPa. The amount of chemically stored hydrogen was found to be 1.26 % in mass, using volumetric analysis of the H2 released by hydrolysis of the TBPBH4 compound in presence of acetic acid. The influence of the gas nature on the hydrate stability was investigated. The higher stabilization effect of nitrogen comparing to hydrogen was discovered. The possibility of gas enclathration and stabilizing effect of hydrogen into TBAOH - H2O hydrates was investigated as well. The formation of two hydrates with high dissociation temperatures were found in this system. Analysis of the p-T data of the TBAOH + water + H2 system revealed the quite promising hydrogen absorption properties of one of these hydrates.
Oleksandr Dolotko, Amir Abbas Karimi, Didier Dalmazzone, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2504 – Multi-scale assessment of the performance of kinetic hydrate inhibitors

The hydrate-inhibiting action of a fish Type III antifreeze protein (AFP), polyvinylpyrrolidone (PVP), and a proprietary, commercial chemical (HIW85281) was investigated at the macro scale using a stirred tank reactor and a high pressure differential scanning calorimeter, as well as at the molecular level using Raman an d NMR spectroscopy. The effect of the inhibitors on the induction time, growth and dissociation of a mixed gas hydrate (methane/ethane/propane) was assessed. Induction times were longer in the presence of all the inhibitors than in controls. Hydrate growth profiles demonstrated that the fastest to slowest growth rates were in order: water controls, PVP, AFP-III and HIW85281. Raman spectroscopic analysis showed that there was an in-homogeneity in guest composition within hydrates formed in the presence of kinetic inhibitors. In such cases, heavier hydrocarbon components tend to participate more in hydrate formation. The hydrate phase composition, cage occupancies of individual gases and hydration number were calculated in the presence of inhibitors using NMR spectroscopy
Nagu Daraboina, John Ripmeester, Virginia K. Walker, Peter Englezos, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2503 – Characterization of mixed CO2-TBPB hydrate for refrigeration applications

The present work investigates the use of semiclathrate hydrates, formed from CO2 + tetra-nbutylphosphonium bromide (TBPB) + water mixtures, as appropriate media for cold storage and distribution in refrigeration applications. Previous studies show that these hydrates are able to trap molecules of carbon dioxide resulting in mixed hydrates. Calorimetry devices were used for determining the dissociation enthalpies of mixed CO2 + TBPB hydrates under various stability conditions (P, T) and salt concentrations. The results reveal that mixed CO2 + TBPB hydrates can be considered as good candidates for air-conditioning, due to positive melting temperatures (between 282 to 289 K) at moderate CO2 pressures (between 0.5 to 2 MPa). A hydrate solid fraction model was developed based on a CO2 mass balance taking into account CO2 solubility in aqueous tetrabutylphosphonium salt solution. The salt effect parameter was evaluated in order to estimate the influence of TBPB on the CO2 solubility. Finally, in order to characterize the flow behavior of mixed CO2 + TBPB hydrate slurries, a rheological study was carried out in a dynamic loop and an Ostwald-de Waele model was obtained.
Pascal Clain, Anthony Delahaye, Laurence Fournaison, Salem Jerbi, Nadia Mayoufi, Didier Dalmazzone, Walter Fürst, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2502 – Morphological and calorimetric investigation of hydrate-forming water in oil emulsions

Clathrate hydrates generate great interest and concern in the petroleum industry because of the potentially severe consequences of pipeline blockage by hydrate plug formation. A proper analysis of hydrates requires knowledge of their morphological, rheological and solid mechanical properties. This will require an understanding of the dynamic processes of formation and dissociation. This work addresses the issues of hydrate formation in water-in-oil emulsions through direct visualization and thermal analysis. Morphological analysis of hydrate growth at a single water drop immersed in a hydrocarbon phase is presented. Cyclopentane, which can form hydrates under atmospheric conditions, is used as a hydrate former and constitutes part or all of the oil phase in the emulsions studied. A hypothesis for hydrate formation in an emulsion is proposed based on the experimental findings from calorimetric studies. An analysis method is presented based on comparison of the heat flow for samples of hydrate-forming and non-hydrateforming emulsions. The proposed mechanism, supplemented by direct visualization of hydrate growth at single water drops, is that the hydrate formation is an interfacial process taking place at the interface between water drop and the continuous oil phase, leading to formation of a hydrate shell limiting the transport of hydrate former to free (liquid) water which remains trapped inside the hydrate layer. Generally crude oils carry a significant amount of natural surface-active agents (e.g. asphaltenes) and such surface-active agents will affect the hydrate morphology in a manner which increases the potential for hydrate plug formation in pipeline flow of emulsions. Evidence will be presented to show that surface active agents in the oil phase have a great impact on the cyclopentane hydrate morphology. Results are reported for Span 80 surfactant in the oil phase at different concentrations; sufficient levels of this surfactant lead to a hairy, mushy hydrate morphology as compared to an otherwise faceted shell formation. A detailed analysis is presented to explain the role of Span 80 on transport and driving force for the morphological development.
Prasad U. Karanjkar, Jae W. Lee, Jeffrey F. Morris, Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011.

B2444 – Dissociation Enthalpies of Synthesized Multicomponent Gas Hydrates with Respect to the Guest Composition and Cage Occupancy

This study presents the influences of additional guest molecules such as C2H6, C3H8, and CO2 on methane hydrates regarding their thermal behavior. For this purpose, the onset temperatures of decomposition as well as the enthalpies of dissociation were determined for synthesized multicomponent gas hydrates in the range of 173-290 K at atmospheric pressure using a Calvet heat-flow calorimeter. Furthermore, the structures and the compositions of the hydrates were obtained using X-ray diffraction and Raman spectroscopy as well as hydrate prediction program calculations. It is shown that the onset temperature of decomposition of both sI and sII hydrates tends to increase with an increasing number of larger guest molecules than methane occupying the large cavities. The results of the calorimetric measurements also indicate that the molar dissociation enthalpy depends on the guest-to-cavity size ratio and the actual concentration of the guest occupying the large cavities of the hydrate. To our knowledge, this is the first study that observes this behavior using calorimetrical measurements on mixed gas hydrates at these temperature and pressure conditions
Marisa B. Rydzy, Judith M. Schicks, Rudolf Naumann, Jörg Erzinger, J. Phys. Chem. B 2007, 111, 9539-9545

B2411 – DSC measurements and modelling of the kinetics of methane hydrate formation in water-in-oil emulsion

The kinetics of formation of clathrate hydrates of methane was investigated in a water-in-oil emulsion using high-pressure differential scanning calorimetry in the range 10–40 MPa, at various temperatures. At high driving force, the heat peak related to the formation of hydrates has a regular and symmetric shape, and its height and width depend on the gas pressure and sub cooling degree. At near equilibrium conditions, hydrate formation is delayed by more than 1 h, but is still clearly observable. A model based on crystal growth theory, coupled with a normal distribution of induction times to take into account the germination in a population of micro-sized droplets, is proposed to represent the hydrate formation rate versus time in the particular case of water-in-oil emulsions. It uses four parameters which appear strongly correlated to the experimental conditions: the growth rate constant, the over saturation of gas in the water phase, the average and standard deviation of the induction time distribution.
Didier Dalmazzone, Néjib Hamed, Christine Dalmazzone, Chemical Engineering Science 64 (2009) 2020 -- 2026

B2403 – Thermophysical and Compositional Properties of Natural Gas Hydrate

Thermophysical properties .dissociation enthalpy, heat capacity, metastability4 and compositional properties .hydrate number free water and fractionation of natural gas hydrate were studied experimentally on samples that contained large amounts of ice: Methods for continuous hydrate production and sampling and for quantifcation of the properties were developed: Hydrate was produced from a natural gas of ethane (5%mol) and propane (3% mol) in methane. A low temperature scanning calorimetry method was developed to measure dissociation enthalpy, heat capacity, hydrate number and free water .ice. During the analysis the hydrate samples were pressurized to 1.7 MPa with methane and the system operated between the hydrate equilibrium curves of methane and the hydrate forming natural gas. A sample conditioning procedure eliminated thermal eIects of desorption as the ice melted. Desorption occurred since the samples were produced and refrigerated to 255 K under a natural gas pressure of 6-10 MPa but were analyzed and melted under a methane pressure of 1.7 MPa.
Odd Ivar Levik, Thesis Norwegian University of Science and Technology, September 2000

B2384 – Investigation of gas hydrates using differential scanning calormetry with water-in-oil emulsions

As oil/gas production moves to deeper water, evaluating hydrate risk management techniques is a growing concern. This work uses Differential Scanning Calorimetry (DSC) to investigate hydrate risk management techniques. Emulsified systems will be shown to be useful in applications ranging from evaluating plugging tendencies of crude oils to determining the effectiveness of kinetic inhibitors.
Jason W. Lachance, Thesis 2008

B2375 – Le coulis de glace et d’hydrates de CO2

L’Institut de génie thermique d’Yverdon-les-Bains, en partenariat avec Axima Réfrigération et Nestlé, a mis au point un nouveau fluide frigoporteur très prometteur, notamment pour la climatisation : le coulis de glace et d’hydrates de CO2. Le MicroDSC7 de Setaram est utilisé pour étudier la formation et la dissociation des hydrates de CO2.
Osmann Sari, Jin Hu, Frédéric Brun, Sara Eicher, Paul Homsy, Jean-Claude Logel, RPF 961 · décembre 2007

B2342 – The stability of methane hydrates in highly concentrated electrolyte solutions by differential scanning calorimetry and theoretical computation

The stability limits of methane hydrates have been investigated at pressures from 5 to 12 Mpa by high pressure DSC, in sodium cholride and calcium chloride solutions at concentrations ranging from pure water to saturated salt, in continuous solutions, in water in oil emulsions as well as in dispersed complex media used as drilling fluids..
D. Dalmazzone, D. Clausse, C. Dalmazzone, B. Herzhaft, American Mineralogist, Vol. 89 (2004) 1183–1191

B2341 – Phase behaviour of tri-n-butylmethylammonium chloride hydrates in the presence of carbon dioxide

The phase behaviour of the system water–tri-n-butylmethylammonium chloride (TBMAC)–CO2 was investigated by pressure-controlled differential scanning calorimetry in the range 0–10 mol% TBMAC in water and at CO2 pressures ranging from 0 to 1.5 MPa. In the absence of CO2, an incongruent melting hydrate, which estimated composition corresponds to TBMAC 30H2O, crystallizes at temperatures below -13.6 °C and forms with ice a peritectic phase at approximately 3.9 mol% TBMAC. In the presence of CO2 at pressures as low as 0.5 MPa, curves evidenced the presence of an additional phase exhibiting congruent melting at temperatures that are strongly pressure dependent and significantly higher than those of hydrates obtained without CO2. This new phase, whose enthalpy of dissociation and CO2 content increase slightly with CO2 pressure, was identified as a mixed semi-clathrate hydrate of TBMAC and CO2 of general formula: (TBMAC + xCO2) 30H2O.
Nadia Mayoufi, Didier Dalmazzone, Walter Fürst, Leila Elghoul, Adel Seguatni, Anthony Delahaye, Laurence Fournaison, J Therm Anal Calorim, 2011

B2340 – Stockage d’hydrogène sous forme d’hydrate de gaz

Ce travail a pour objectif de déterminer les conditions de formation et de dissociation d’hydrates d’hydrogène à haute stabilité en vue de leur utilisation comme matériaux pour le stockage. Les propriétés visées sont les domaines de pression et de température d’existence de tels hydrates, les quantités d’énergies mises en jeu par leur formation et leur dissociation, les capacités de stockage offertes par ces structures, ainsi que les aspects cinétiques de leur formation (stockage) et de leur décomposition (déstockage).
Didier Dalmazzone, Poster

B2339 – Experimental determination of stability conditions of methane hydrate in aqueous calcium chloride solutions using high pressure differential scanning calorimetry

The validity of differential scanning calorimetry (d.s.c.) as an alternate method of determination of thermodynamic conditions of stability of gas hydrates in aqueous media was asserted by comparison to literature data, in the case of methane hydrate in pure water and in sodium chloride solutions. Requirements for thermodynamic validity of the equilibrium temperatures measured by this technique were investigated and are discussed in details. New equilibrium data of (methane hydrate + water +methane) in aqueous calcium chloride so- lutions, in the concentration range from x = 8.47 10-3 to x = 53.27 10-3, were determined using the same method, in the pressure range 5 MPa to 11 MPa. Experimental results were compared to data computed using a model that is presented, showing very good agreement over a wide range of salt concentration. These results confirm the interesting perspectives of application of this technique in the field of gas hydrate thermodynamics.
M. Kharrat, D. Dalmazzone, J. Chem. Thermodynamics 35 (2003) 1489–1505

B2338 – Dissociation enthalpies and phase equilibrium for TBAB semi-clathrate hydrates of N2, CO2, N2 + CO2 and CH4 + CO2

Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper, dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning calorimetry (DSC) under pressure. Pure gases such as N2 and CO2 and gases mixtures such as N2 ? CO2 and CH4 ? CO2 were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N2 for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent melting point whose hydration number corresponds to 26.
Johnny Deschamps, Didier Dalmazzone, J Therm Anal Calorim (2009) 98:113–118

B2337 – Characterization of CO2 clathrate hydrate slurries for secondary refrigeration applications

The aim of this work is to study how additives can improve formation conditions, thermal efficiency and flowing of clathrate hydrate slurries. In the case of PCM storage applications for refrigeration, hydrates must have a high dissociation enthalpy. In addition, the stability conditions must be adapted, the temperature being consistent with the application (between 273.15 and 298.15 K) and the pressure being suitable for an industrial facility. In the present study, different quaternary salts are used to reduce the formation pressure of CO2 hydrate: TBACl (tetra-n-butylammonium chloride), TBANO3 (tetra-n-butylammonium nitrate), and TBPB (tetra-n-butylphosphonium bromide). Firstly the influence of additives on the thermodynamic properties of the CO2-H2O system is studied. Results acquired by Differential Scanning Calorimetry, DSC, on formation temperatures and dissociation enthalpies show that each of the studied quaternary salts may form a mixed hydrate with CO2. These mixed hydrates are more stable than without additives, resulting in a significant decrease of the CO2 pressure needed for the hydrate formation. They also reveal that mixed TBPB + CO2 hydrate has suitable (P, T) conditions and latent heat content and therefore seems very appropriate as PCM for cold storage applications. After the previous thermodynamic study, a preliminary rheological characterisation of the TBPB hydrate slurry was also performed using a dynamic loop allowing pressure drop and flow rate measurements
N. Mayoufi, A. Delahaye, L. Fournaison, D. Dalmazzone, W. Fürst, IIR Proceedings Series 'Refrigeration Science and Technology', 2010/5: 57-65

B2336 – Studies of hydrate nucleationwith high pressure differential scanning calorimetry

Current models for hydrate formation in subsea pipelines require an arbitrary assignment of a subcooling criterion for nucleation. In reality hydrate nucleation times depend on both the degree of subcooling and the amount of time the fluid has been subcooled. In this work, differential scanning calorimetry was applied to study hydrate nucleation for gas phase hydrate formers. Temperature ramping and isothermal approaches were combined to explore the probability of hydrate nucleation for both methane and xenon. A system-dependent subcooling of around 30K was necessary for hydrate nucleation from both guest molecules. In both systems, hydrate nucleation occurred over a narrow temperature range (2–3 K). The system pressure had a large effect on the hydrate nucleation temperature but the ice nucleation temperature was not affected over the range of pressures investigated (3–20MPa). Cooling rates in the range of (0.5–3K/min) did not have any statistically significant effect on the nucleation temperature for each pressure investigated. In the isothermal experiments, the time required for nucleation decreased with increased subcooling.
Simon R. Davies, Keith C. Hester, JasonW. Lachance, Carolyn A. Koh, E. Dendy Sloan, Chemical Engineering Science 64 (2009) 370 -- 375

B2335 – Determining gas hydrate kinetic inhibitor effectiveness using emulsions

In this study we measure the effect of hydrate kinetic inhibition in emulsions. Because hydrate nucleation is stochastic, many experiments normally are needed to obtain accurate analysis of the effectiveness of kinetic inhibitors. Using differential scanning calorimetry (DSC), we show how emulsions can reduce the number of kinetic samples needed to obtain a statistical analysis of the effectiveness of polyvinylcaprolactam, PVCap, a common kinetic inhibitor. PVCap is shown to delay the average hydrate nucleation time and also causes hydrate nucleation to become more stochastic. This novel method uses less material and experimental time compared to traditional methods used to test kinetic inhibitors.
Jason W. Lachance, E. Dendy Sloan, Carolyn A. Koh, Chemical Engineering Science 64 (2009) 180 -- 184

B2334 – Effect of hydrate formation/dissociation on emulsion stability using DSC and visual techniques

A key factor in hydrate risk management for an oil-dominated system is the stability of the emulsified water with gas hydrate formation. We show via differential scanning calorimetry (DSC) that gas hydrate formation and dissociation has a destabilizing effect on water-in-oil (W/O) emulsions, and can lead to a free water phase through agglomeration and coalescence of dissociated hydrate particles. High asphaltene content crude oils are shown to resist hydrate destabilization of the emulsion. Span80 was successfully used as an analog to asphaltene surface activity. Based on our experimental results, a new conceptual hydrate-induced destabilization model is proposed
Jason W. Lachance, E. Dendy Sloan, Carolyn A. Koh, Chemical Engineering Science 63 (2008) 3942 -- 3947

B2333 – Measurements of methane hydrate heat of dissociation using high pressure differential scanning calorimetry

The methane hydrate heat of decomposition was directly measured up to 20MPa and 292K using a high pressure differential scanning calorimeter (DSC). The methane hydrate sample was formed ex-situ using granular ice particles and subsequently transferred into the DSC cell under liquid nitrogen. The ice and water impurities in the hydrate sample were reduced by converting any dissociated hydrate into methane hydrate inside the DSC cell before performing the thermal properties measurements. The methane hydrate sample was dissociated by raising the temperature (0.5–1.0K/min) above the hydrate equilibrium temperature at a constant pressure. The measured methane hydrate heat of dissociation (H?W+G), ?Hd, remained constant at 54.44 ± 1.45 kJ/mol gas (504.07 ± 13.48 J/gm water or 438.54 ± 13.78 J/gm hydrate) for pressures up to 20MPa. The measured ?Hd is in agreement with the Clapeyron equation predictions at high pressures; however, the Clausius–Clapeyron equation predictions do not agree with the heat of dissociation data at high pressures. In conclusion, it is recommended that the Clapeyron equation should be used for hydrate heat of dissociation estimations at high pressures.
Arvind Gupta, Jason Lachance, E.D. Sloan Jr., Carolyn A. Koh, Chemical Engineering Science 63 (2008) 5848 -- 5853

B2332 – Hydrate nucleation measurements using high pressure differential scanning calorimeter

In this study, DSC has been appied to determine the hydrate nucleation point for gas hydrtae formers. Constant cooling ramps and isothermal approaches were combined to explore the probability of hydrtae nucleation. In the temperature ramping experiments, methane an xenon were used at various pressures and cooling rates. the isothermal method was used for a methane with pure water and a water-in-West African crude emulsion. Two isotherms (-5°C and -10°C) were used to meausre nucleation time.
Keith C. Hester, Simon R. Davies, Jason W. Lachance, E. Dendy Sloan, Carolyn A. Koh

B2188 – Gas solubility of H2S in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol at 313, 343, and 393K in the range 2.5-1036 kPa

The gas solubility of hydrogen sulfide in aqueous solutions of 32.5 wt.% N-methyldiethanolamine (MDEA) and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol, at 313.15, 343.15, and 393.15 K, has been measured, using a volumetric method for the analysis of the liquid phase, over a range of pressure from 2.5 to 1036 kPa. The experimental results of the gas solubility are given as the partial pressure of H2S against its mole ratio alpha (mol H2S/mol total alkanolamine) and mole fraction of H2S at each temperature studied. Enthalpies of solution of H2S have been derived from the pressure-temperature concentration data. Experimental solubility data obtained in our laboratory for H2S and CO2 are compared, and it is possible to establish that the aqueous solutions of MDEA, DEA, and AMP studied in this work are highly selective towards H2S under the same conditions of pressure and temperature.
M.E. Rebolledo-Libreros, A. Trejo, Fluid Phase Equilibria 224 (2004) 83-88

B1932 – Study of CCl3F hydrate formation and dissociation in W/O emulsion by differential scanning calorimetry and X-ray diffraction

Differential scanning calorimetry (DSC) and time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) were combined in a novel way in order to study conditions of formation and the amount of gas clathrate formed in dispersed systems. The formation and dissociation of trichlorofluoromethane hydrate CCl3F.(H2O)17 in a water-in-oil emulsion were followed by using these combined techniques. An emulsion containing 3 wt.% NaCl was submitted to a cooling and heating cycle between 20 and -50°C. During cooling, a single exothermic peak at -43°C, found in DCS thermograms was assigned to the freezing of under-cooled water droplets; however, no noticeable signal related to hydrate crystallisation was detected. Conversely, during subsequent heating, the progressive melting of ice was followed by an endothermic signal indicative of hydrate decomposition. From X-ray diffraction performed on an emulsion sample, it was possible to identify the exact condition of CCl3F.(H2O)17 formation. XRDT diffraction patterns clearly demonstrated that only ice crystallised in the aqueous droplets during cooling and that the hydrate only formed during heating simultaneously with melting of ice. From the solid-liquid phase diagrams of systems H2O NaCl and CCl3F H2O NaCl and from the DSC and XRDT experiments, the composition of the droplets was deduced. The upper limit of the amount of hydrate that could form in the system was calculated.
B. Fouconnier, L. Komunjer, M. Ollivon, P. Lesieur, G. Keller, D. Clausse, Fluid Phase Equilibria 250 (2006) 76-82

B1882 – Effect of THF on Equilibrium Pressure and Dissociation Enthalpy of CO2 Hydrates Applied to Secondary Refrigeration

The present work investigates the formation conditions and the latent heat of dissociation of hydrates formed from tetrahydrofuran (THF)-CO2-water mixtures. The conditions investigated are 3.8-15 wt % for THF concentration and 0.2-3.5 MPa for the CO2 partial pressure range, conditions that are adapted to the use of the corresponding hydrate slurries as secondary refrigerants. Both differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods were used for the experimental determinations. Experimental values were compared with modeling, combining the van der Waals and Platteeuw approach with the Redlich- Kwong equation of state associated to a modified Huron-Vidal (MHV2) mixing rule. At fixed temperature, adding THF to the systems results in a drastic reduction of CO2 equilibrium pressure. For instance, at 280 K, a 78.9% decrease of CO2 pressure is experimentally observed if the solution contains 3.8 wt % of THF. Furthermore, a dissociation enthalpy of (CO2 + THF) hydrates roughly two times higher that that of CO2 hydrates was calculated from measured and predicted data of hydrate formation.
A. Delahaye, L. Fournaison, S. Marinhas, I. Chatti, J-P. Petitet, D. and W. Furst, Ind. Eng. Chem. Res. 45 (2006) 391-397

B1881 – Effect of THF on Equilibrium Pressure and Dissociation Enthalpy of CO2 Hydrates Applied to Secondary Refrigeration

The present work investigates the formation conditions and the latent heat of dissociation of hydrates formed from tetrahydrofuran (THF)-CO2-water mixtures. The conditions investigated are 3.8-15 wt % for THF concentration and 0.2-3.5 MPa for the CO2 partial pressure range, conditions that are adapted to the use of the corresponding hydrate slurries as secondary refrigerants. Both differential thermal analysis (DTA) and differential scanning calorimetry (DSC) methods were used for the experimental determinations. Experimental values were compared with modeling, combining the van der Waals and Platteeuw approach with the Redlich- Kwong equation of state associated to a modified Huron-Vidal (MHV2) mixing rule. At fixed temperature, adding THF to the systems results in a drastic reduction of CO2 equilibrium pressure. For instance, at 280 K, a 78.9% decrease of CO2 pressure is experimentally observed if the solution contains 3.8 wt % of THF. Furthermore, a dissociation enthalpy of (CO2 + THF) hydrates roughly two times higher that that of CO2 hydrates was calculated from measured and predicted data of hydrate formation.
A. Delahaye, L. Fournaison, S. Marinhas, I. Chatti, J-P. Petitet, D. and W. Furst, Ind. Eng. Chem. Res. 45 (2006) 391-397

B1880 – Modelling of the available latent heat of a CO2 hydrate slurry in an experimental loop applied to secondary refrigeration

The present study investigates the suitability of CO2 hydrate for a use as phase change material in two-phase secondary refrigeration. Unlike the generation of the classical two-phase refrigerants, power limited by mechanical parts, hydrate slurry production has the advantage of being performed using a nonmechanical process. Nevertheless, in order to be efficient, the hydrate slurry needs to fulfil two major conditions: a high latent heat of melting of the solid phase and appropriate flowing conditions of the slurry carrying a sufficient amount of solid. Consequently, in the present work, multi-cycle differential scanning calorimetry (DSC) measurements were performed and confirmed a value of CO2 hydrate dissociation enthalpy of approximately 500 kJ kg-1w , one and a half higher than that of ice (333 kJ kg-1w ). Moreover, an experimental loop made it possible to study the CO2 hydrates in suspension in a carrying liquid and to model the available enthalpy of the system related to the solid fraction of the slurry.
S. Marinhas, A. Delahaye, L. Fournaison, D. Dalmazzone, W. Furst, J-P. Petitet, Chemical Engineering and Processing 45 (2006) 184-192

B1730 – Prediction of gas hydrates formation with DSC technique

With the increasing number of deep offshore drilling operations, operators and service companies are now faced with new problems related to the possible formation of gas hydrates in drilling muds. Actually, the appearance of gas hydrate crystals in drilling fluids can lead to dreadful effects and safety problems, like modification of mud rheological properties, interruption of the drilling operations due to plugging and even destruction of rig equipment when gas hydrates dissociate. Propulsion of gas hydrate plugs at very high velocity is also a great risk. To prevent these problems, formulations of drilling muds (WBM or OBM) have to be optimized with thermodynamic inhibitors of hydrate formation (salts and glycols), which cause important problems of density adjustment, corrosion and toxicity. In previous papers (SPE 62962, 71379), an innovative calorimetric technique (DSC) was presented to characterize hydrate formation in drilling mud up to 100 bar. This rapid, easy and reliable technique was applied to fluids of increasing complexity, from solutions and emulsions to complete oil-base and water-base muds. Results were validated from classical PVT measurements. In this study, this work was continued on thermodynamic properties of hydrate formation in complex solutions. The main objective was to establish phase diagrams of ternary and quaternary mixtures (water-CH4-salt and water-CH4-saltglycol) and also to understand the mechanisms that govern hydrate formation in such mixtures. In parallel, a new microcalorimeter was developed, that allows measurements on gas hydrates up to 400 bar, whatever the mud composition (WBM or OBM). This apparatus can analyze complete muds, in presence of solids, and is designed to be implemented on drilling platforms. Hence, it will be possible to follow the risk for hydrates formation as a function of drilling conditions on site. Furthermore, this apparatus will allow the establishment of a database on different muds. A coupling of this database with a software that calculates the thermal profile along the riser should give birth to a predictive method for gas hydrate formation risks.
C.Dalmazzone, B.Herzhaft, L.Rousseau, P.Le Parlouer, Society of Petroleum Engineer PE84315

B1692 – Application of high pressure DSC to the kinetics of formation of methane hydrate in water-in-oil emulsion

A micro DSC analyzer fitted with special high-pressure vessels was used to investigate the kinetics of methane hydrate formation in the water phase dispersed as a stable emulsion in deep offshore drilling fluids. At high sub-cooling conditions, the peak of hydrate formation is perfectly visible and regular-shaped, and could be fitted by a Gaussian law. The average time for hydrate crystallization of the water droplets' population was represented as a logarithmic function of the inverse of absolute temperature. At low sub-cooling conditions, the formation appears confused with the baseline; the amount of hydrate formed was thus measured from its enthalpy of dissociation, after periods of formation of variable duration.
D. Dalmazzone, N. Hamed, C. Dalmazzone and L. Rousseau, Journal of Thermal Analysis and Calorimetry 85 (2006) 361-368

B1582 – Characterisation and emulsion behaviour of Athabasca extra heavy oil produced by SAGD

The production of extra heavy oil (or bitumen) through the SAGD method (Steam Assisted Gravity Drainage) requires the generation and injection into the reservoir of a great quantity of steam. A typical value of the steam/oil ratio is around 3, which means that a 100,000 bopd development requires the injection of 300,000 bcwepd (barrels of cold water equivalent per day) of steam, and that a corresponding quantity of hot water will be co- produced with the oil. The production of extra heavy oil containing many active components with the tendency to form an emulsion combined with the high water-cut ratio (above 80%) leads to a phase separation process with specific issues. This study considers an extra heavy oil field produced in SAGD in Athabasca. The objective of the study was firstly to characterise the produced fluids and then to analyse their tendency to form an emulsion under controlled hydrodynamic conditions. An innovative technique - Differential Scanning Calorimeter (DSC) - was used to characterise the emulsion. This method is able to define the water-in-oil or reverse emulsion nature and to quantify the water amount without sample dilution. DSC analysis combined with microscopy and image analysis treatments was used to determine the droplet size distribution. Reconstituted emulsions were then formed using a "Dispersion Rig" set-up that allows the simultaneous pumping of crude oil and water through a calibrated restriction in the pipe. The amount of energy dissipated to the fluids systems can be quantified due to the strict control of the hydrodynamic conditions. Consequently a relationship between granulometry distribution of the emulsion and the fixed energy or pressure drop can be established. The main experimental parameters investigated were the oil dilution and water-cut ratios. It is concluded that there is a residual emulsion in extra heavy oil which has a very small average droplet size whatever the temperature and solvent dilution ratio. This small droplet size results in a difficult oil/water separation which is only possible either by addition of large quantities of additives at high temperature and with long residence time and probably by applying an electrostatic field.
Noik, Dalmazzone, Goulay, Glenat

B1515 – Characterisation of gas hydrates formation using a new high pressure micro-DSC

Gas hydrates are solid structures formed from water and gas under low temperature and high pressure conditions. Differential scanning calorimeter, operating under high pressure, is a very useful technique for the determination of the thermodynamic properties and the kinetics of gas hydrate formation. Specific gas tight controlled pressure vessels have to be used to obtain the hydrate formation in complex fluids. Based on the MicroDSC technology, a new High Pressure MicroDSC with a vessel (0.7 cm3) operating up to 400 bars between -45 and 120°C is introduced for this type of research. An example of the use of the HP MicroDSC is given with the formation of gas hydrates in drilling muds. With the increasing number of deep offshore drilling operations, operators and service companies have to solve more and more complex technical challenges. Extreme conditions encountered at these depths require an adaptation of the drilling muds. The range of temperature (down to -1°C) and pressure (up to 400 bars) are favorable conditions to the formation of hydrates. HP MicroDSC is used to determine the thermodynamic properties and kinetics of hydrate formation in mud formulations, particularly in the presence of large amounts of minerals. The technique allows the detection of phase transitions vs. time, temperature and pressure. Using such a technique, dangerous areas of hydrate formation in drilling muds formulations (water-base and oil-base) can be predicted.
P. Le Parlouër, C. Dalmazzone, B. Herzhaft, L. Rousseau and C. Mathonat, Journal of Thermal Analysis and Calorimetry 78 (2004) 165-172

B1417 – DSC and PVT measurements : Methane and trichlorofluoromethane hydrate dissociation equilibria

The dissociation of gas and model hydrates was studied using a classical thermodynamic method and a calorimetric method, in various aqueous media including pure water, high concentration calcium chloride solutions and water-in-oil emulsions. Methane hydrate dissociation temperatures vs. pressure curves were determined using pressure vs. temperature measurements in a constant volume cell (PVT), and high pressure differential scanning calorimetry (DSC), at 5 to 10 MPa gas pressure and at temperatures ranging from -10 to +12°C. PVT and DSC results are in good agreement, and concordant with data available in literature. From a thermodynamic point of view, there are no measurable differences between bulk solutions and emulsions. From a kinetic point of view, due to the considerable surface of interface between the two phases, emulsions allow the formation of much greater amounts of hydrate than solutions, without any agitation. Model hydrate of trichlorofluoromethane was studied in 9 to 27 mass% calcium chloride solutions in emulsion in oil, using DSC under atmospheric pressure, at temperatures ranging from -20 to +5°C. A diagram of dissociation temperature vs. salt concentration is proposed.
D. Dalmazzone, M. Kharrat, V. Lachet, B. Fouconnier, D. Clausse, Journal of Thermal Analysis 70 (2002) 493-505

B1051 – Thermochemical study of clathrate-forming host-guest reactions for the detection of organic solvent vapours.

The clathrate formation of a crystalline host with acetone and methanol vapours has been studied by means of simultaneous TG-DSC measurements in isothermal and scanning mode of operation. The directly measured enthalpies of inclusion at 25°C for acetone (-47.8 kJ mol-1) and methanol (-48.6 kJ mol-1) are significantly higher than known thermal desorption enthalpy data from DSC measurements. Concentration dependent measurements indicate a nearly linear concentration dependence for both the amount of guest included and the heat effect over a wide range supporting the recently suggested importance of this class of supramolecular hosts as chemical sensitive coating materials for sensor applications. Inclusion experiments at different temperatures indicate a strongly decreasing inclusion ability with increasing temperature.
J. Seidel, G. Wolf, E. Weber, Thermochimica Acta 271 (1996) 141-148

B0607 – Compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K for clathrate hydrates of methane, ethane, and propane, and enthalpy of dissociation of isobutane hydrate, as determined by a heat-flow calorimeter

Compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K were determined for the first time for clathrate hydrates of methane, ethane, and propane using a Tian-Calvet heat-flow calorimeter. The enthalpy of dissociation was also measured for isobutane hydrate. The enthalpy of dissociation for the process (hydrate = ice + gas) at 273.15 K and 101.325 kPa is (18.13±0.27) kJ.mol-1 for CH4.6.00H2O, (25.70±0.37) kJ.mol-1 for C2H6.7.67H2O, and (27.00±0.33) kJ.mol-1 for C3H8.17.0H2O. The enthalpy of dissociation of isobutane hydrate at 245 K is (31.07±0.20) kJ.mol-1. Molar heat-capacity contributions from the guests to their hydrates were found to be comparable with the ideal-gas heat capacity for methane and somewhat higher for ethane and propane.
Y.P. Handa, J. Chem. Thermodynamics 18 (1986) 915-921

B0528 – Topochemistry of thermal solid state transformations in Ni(II)-complexes

Solid state transformations in complex compounds of nickel: Nien2(NO2)2,Nien2(NCS)2 (en-ethylenediamine) were investigated by DTA and DSC methods, thermomicroscopy and X-ray. Structural transformations were shown to proceed via the growth of new phase nuclei. An interface advance is of anisotropic character and accompanied by crystal cracking. Rate of the transformation depends upon crystal thickness. This fact is of particular importance for thermoanalytical experiments.
T.P. Shahtshneider, E.Yu. Ivanov and V.V. Boldyrev, Thermochimica Acta 92 (1985) 469-472

B0511 – Calorimetric determinations of the compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K for clathrate hydrates of xenon and krypton

Molar heat capacities between 95 and 260 K, molar enthalpies of fusion, and melting temperatures are reported for the structure-II clathrate hydrates of propylene oxide, 1,3-dioxolane, 2,5-dihydrofuran, and 1,3-dioxane. All properties show dependence on the nature of the hydrate former. The molar enthalpies of fusion of the hydrates are lower by 4 to 12 per cent and the molar heat capacities are higher by 16 to 28 per cent than the corresponding values for ice. The molar heat capacities of the hydrates show a linear correlation with the corresponding unit-cell constants. An analysis of the heat-capacity results indicates that in the temperature range 95 to 260 K, the heat capacity of the empty hydrate lattice is greater than that of ice and its temperature dependence is different from that of ice.
Y.P. Handa, J. Chem. Thermodynamics 18 (1986) 891-902

B0510 – Calorimetric studies of laboratory synthesized and naturally occuring gas hydrates

Y. P. Handa, Proc. AIChE Annual Meeting, Miami Beach, (USA) (1986)

B0475 – Heat capacities in the range 95 to 260 K and enthalpies of fusion for structure-II clathrate hydrates of some cyclic ethers

A calorimetric technique is described which gives for a single sample-loading the composition, enthalpy of dissociation, and heat capacities of gas hydrates. Heat capacities in the range 85 to 270 K and enthalpies of dissociation were obtained for structure I: Xe . 5.90H2O, and structure II: Kr . 6.10H2O, clathrate hydrates. Molar heat-capacity contributions from xenon and krypton to their hydrates are less than 3R each. The standard enthalpy of dissociation for the process (hydrate = ice + gas) at 273.15 K and 101.325 kPa is (26.50 ± 0.17) kJ . mol-1 for Xe . 5.90H2O and (19.54 ± 0.24) kJ . mol-1 for Kr . 6.10H2O.
Y.P. Handa, J. Chem. Thermodynamics 17 (1985) 201-208

A1392 – Thermochemical study of clathrate-forming host-guest reaction for the detection of organic solvent vapours

The clathrate formation of a cristalline host with acetone and methanol vapours has been studied by means of simultaneous TG-DSC measurements in isothermal and sacnning mode of operation.
J. Seidel, G. Wolf, E. Weber, Thermochimica Acta 271 (1996) 141-148