Sapphire Cell Research Articles

Equilibrium Conditions Hydrate Dissociation for a Ternary Mixture of Methane, Ethane, and Propane in Aqueous Solutions of Ethylene Glycol and Electrolytes

Hydrate dissociation conditions for a mixture of methane, ethane, and propane in aqueous solutions of ethylene glycol and electrolytes (NaCl/CaCl2) were experimentally studied in the pressure range of (0.78 to 8.1) MPa and the temperature range of (263.52 to 288.96) K. A new variable-volume sapphire cell was used for the measurements.

Hydrate Equilibrium Conditions for Cyclopentane and a Quaternary Cyclopentane-Rich Mixture

Experimental data on hydrate formation of cyclopentane and a 98.40 mass % purity cyclopentane mixture containing three impurities (0.48 mass % pentane, 0.48 mass % 2-methyl butane, and 0.72 mass % 2-methyl propane) in water were measured. The measurements were carried out in a transparent sapphire cell (100-cm3 effective volume) by applying a pressure-search method in the temperature range (273.3−280.8) K and the pressure range (6.9−19.8) kPa.

EXAFS measurements for liquid Ge-Si alloys.

EXAFS measurements around the Ge-K edge have been carried out for liquid Ge-Si alloys for the first time to investigate the local structure around a Ge atom. To perform the EXAFS measurements for the liquid alloys with high melting temperatures, a new sapphire cell have been developed. The measurements were carried out for the liquid alloys from 10% to 60% of Si and the crystalline ones from 10% to 70% of Si as a reference. EXAFS oscillations, x(k), are observed even at 1480 degrees C for liquid Ge(0.4)Si(0.6). The position of the first peak in the radial distribution function obtained from Fourier transform of x(k) is shifted towards smaller distance for liquid and crystalline alloys with increasing Si concentration. The results of a curve-fit analysis in a harmonic approximation show that Ge-Ge and Ge-Si bonds in the liquid alloys become long with increasing Si concentration while those become slightly short in the crystaline ones.

High-pressure vessel for elastic and inelastic x-ray diffraction experiments for liquids over a wide temperature range

A new x-ray scattering environment is presented which can be employed at high temperatures up to 2000 K and high pressures up to 150 bar. This device is especially designed for angle-dispersive scattering experiments. It consists of a thick closed-end aluminum cylinder equipped with a steel flange. Incident and scattered radiation passes through continuous Be windows which cover an angle range up to 55°. The high potential of this scattering setup is demonstrated by representative example experiments at high temperatures and high pressures, which could be carried out in combination with a single-crystal sapphire cell. Inelastic-, elastic-, and anomalous scattering experiments using synchrotron radiation and energy dispersive static measurements employing a conventional tube device are reported.

Implementation of a sapphire cell with external electrodes for laser excitation of a forbidden atomic transition in a pulsed E-field

We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment. We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×1014 at/cm3 without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further improvements obtained with sapphire cells are also presented.

Hydrate Formation of Hydrogen + Hydrocarbon Gas Mixtures

Hydrate formation conditions of hydrogen + hydrocarbon gas mixtures (H2 + CH4, H2 + C3H8, H2 + CH4 + C3H8, and H2 + CH4 + C2H6 + C3H8) in pure water have been measured in a sapphire cell using the “pressure search” method. The experimental temperature range was (274−280) K, and the pressure-range was (0.65−7.0) MPa. The hydrogen content in the gas mixtures varies from 22 mol % to 92 mol %.

Splitting of libration mode frequencies in the vicinity of orientation phase transition in NH4Br

Vibrational spectra of NH4Br at high pressures up to 4·5GPa have been studied by means of incoherent inelastic neutron scattering using sapphire anvil high pressure cell technique. Libration mode splitting was investigated in the vicinity of the orientation phase transition (Ptr = 2·7 GPa) and this effect disappears if pressure is less or higher than Ptr. This effect is explained in terms of two-well asymmetric potential.

Experimental and modeling studies on the hydrate formation of CO 2 and CO 2-rich gas mixtures

The hydrate formation conditions of CO 2 and CO 2-rich gas mixtures (CO 2>90 mol%) containing N 2/CH 4/C 2H 6 and (N 2+CH 4+C 2H 6) in the presence of aqueous solutions of ethylene glycol were measured in a sapphire cell equipped with magnetic stirrer and data acquisition system. Isothermal pressure-search method was adapted in the pressure range of 0.8–3.5 MPa and a temperature range of 267.2–279.7 K. Eight systems have been studied and a total of 36 data points were measured. In the modeling part, the hydrate models recently developed by this group (Chen–Guo and Zuo–Guo model) and a typical literature reported van der Waals–Platteeuw type model were tested against the hydrate formation data of CO 2-rich gas mixtures in water and aqueous solutions of ethylene/sodium chloride. The performance of various models is evaluated.

Experiments Related to the Performance of Gas Hydrate Kinetic Inhibitors

Abstract: (1) The hydrate formation process and growth is described through three different stages: (a) an induction period (nucleation), (b) a slow growth period prior to (c) a final stage described by a catastrophic, fast growth rate. In this paper the effect of kinetic hydrate inhibitors (KI) is characterized by the total delay of the catastrophic growth process at given subcooling ratios at given pressures. (2) The effects of a 20,000 Mw PVCap on a structure I (sI) ethane hydrate and a sII synthetic natural gas (SNG) hydrate have been examined in sapphire cells. A baseline was first established for each of two hydrate forming systems to describe the respective induction periods, slow growth periods, and initial growth rates. Without inhibitor, at similar subcoolings, and at similar pressures a longer induction period and a slower growth rate were observed prior to the catastrophic stage for the sII hydrate system as compared to the sI hydrate system. By the addition of 5,000 ppm PVCap to the aqueous phase the total delay of the catastrophic growth stage increased by a factor 12 for the sII SNG‐hydrate system and by a factor 5 for the sI ethane‐hydrate system. (3) The effect of different kinetic hydrate inhibitors (KI) at various pressures ranging from about 65 bar and up to about 200 bar has been examined in high pressure sapphire cells using a sII hydrate forming condensate‐SNG‐synthetic sea water system (SSW, 3.6% salt). For all the experiments reported the degree of subcooling (ΔT) with respect to the hydrate equilibrium properties of the fluid system used was kept at a similar magnitude. This was done to examine KI effects at similar degrees of subcooling within the different pressure regions. The experiments at constant ΔT showed that the KI effect (i.e., total delay of the catastrophic growth stage) decreased with increasing pressure and that a dramatic decrease was observed for increasing pressures above 90 bar. The true driving force of a hydrate forming system is described through a chemical potential, Δμ, which is a function of pressure (i.e., fugacity) and absolute temperature (K). At a given ΔT the chemical potential is greater in the high‐pressure region than in the low‐pressure region.

Thirty-Minute Coherence in Free Induction Decay Signals in Superfluid 3He-B

The persistent induction signal (PIS) is an extremely long lived NMR mode in the B-phase of superfluid 3 He. The first signals observed lived for up to 25s following a moderate NMR tipping pulse, but were found to be highly irreproducible. Here we present new measurements obtained in a smooth sapphire cell designed to achieve the lowest possible temperatures. The signals observed in this cell are quite reproducible but are only excited over a restricted range of magnetic field gradients. The free induction signals exceed 30 minutes at the lowest temperatures.

Equilibrium Hydrate Formation Conditions for Hydrogen Sulfide, Carbon Dioxide, and Ethane in Aqueous Solutions of Ethylene Glycol and Sodium Chloride

Incipient equilibrium hydrate formation conditions for hydrogen sulfide, carbon dioxide, and ethane in aqueous solutions of ethylene glycol and sodium chloride were experimentally obtained in the temperature range 264−290 K and the pressure range 0.23−3.18 MPa. A variable-volume sapphire cell was used for the measurements.

Small angle X-ray scattering measurements for expanded fluid Se near the critical point

Small angle X-ray scattering (SAXS) measurements have been carried out to investigate density fluctuations near the critical point of expanded fluid Se. The experiments were performed using a polycrystalline sapphire cell of our design and a high pressure vessel. The vessel has a diamond window for an incident X-ray beam and a Be window for the scattered beams. The absolute scattering intensity was deduced from the measurements on the He gas used as the pressure transmitting medium. The pressure variation of the SAXS intensity for fluid Se at 1630°C shows a maximum intensity at 401 bar just below the isochor of the critical density. This is the first observation of critical scattering for fluid Se and a correlation length of 19 ± 3 Å was obtained from an Ornstein–Zernike plot.

X-ray diffraction measurements for expanded fluid-Se using synchrotron radiation

X-ray diffraction measurements at temperatures up to 1500∘C and pressures up to 843 bar have been carried out using synchrotron radiation at SPring-8 to investigate structural change in the semiconductor-to-metal transition in expanded fluid-Se. The signal-to-noise ratio in the intensity spectra was better than the previous one using in-house X-ray source. It is found important to estimate the background from a sapphire cell to deduce a structure factor of fluid Se with greater accuracy from the spectra. The preservation of the twofold coordinated chain structure and the contraction of the covalent bond are reconfirmed in the transition. When metallic properties were increased, the first peak in the pair distribution function became asymmetric towards larger distance and the first minimum became larger. These results may imply the modification on the chain structure in the transition.

Hydrate Formation of CO2-Rich Binary and Quaternary Gas Mixtures in Aqueous Sodium Chloride Solutions

Hydrate formation data of CO2-rich mixtures, three binaries (CO2 + CH4, CO2 + C2H6 and CO2 + N2) and one quaternary (CO2 + CH4 + C2H6 + N2), in water and aqueous sodium chloride solutions were measured. The measurements were carried out in a transparent sapphire cell by applying an isothermal pressure search method in the temperature range 264 K to 284 K and the pressure range 0.5 MPa to 5.0 MPa.

Electrical conductivity of glass and sapphire cells exposed to dry cesium vapor

We demonstrate that the walls of glass cells become electrically conductive when exposed to a dry cesium vapor, glasses of different compositions leading to similar effects. We find dramatically different results for monocrystalline sapphire cells, which exhibit typical resistances of a few GΩ, nearly five orders of magnitude larger than glass cells in similar conditions. In spectroscopy experiments requiring the application of an electric field, low cell resistances imply leakage currents generating stray magnetic fields. The latter, at the origin of harmful effects in precise tests of the fundamental laws of physics performed in cesium cells, will thus be suppressed in sapphire cells. Moreover, with such cells it becomes possible to place the electrodes outside. A tentative interpretation of the surface electrical conductivity of glass cells is propounded by establishing a connection with the surface coverage by cesium atoms physically adsorbed on the glass surface. This results from the observed dependences of the cell conductance versus Cs vapor density in the mtorr range and versus the wall temperature up to 200 °C, which indicates an activation energy of 0.66±0.05 eV. In the sapphire cell, where there is no hint of surface effects, the conductivity looks instead attributable to collisional processes occuring inside the vapor for Cs number densities ≳1014 at/ cm3.

Equilibrium conditions for hydrate formation for a ternary mixture of methane, propane and carbon dioxide, and a natural gas mixture in the presence of electrolytes and methanol

Methanol and electrolytes are often used to inhibit gas hydrate formation in industrial operations. In order to design such equipment it is required to compute the inhibition effects of these additives. Development of methods for calculating the inhibition effects require accurate experimental hydrate equilibria data. In the present work, experimental three phase (aqueous liquid solution, vapor and incipient solid hydrate) equilibrium data for a ternary mixture of methane, propane and CO 2 and a natural gas mixture in the presence of methanol and electrolytes were obtained. The experiments were carried out in the temperature range of 274–291 K and pressure range of 1.5–10.1 MPa. A `full view' variable volume sapphire cell with a movable piston, described earlier by Dholabhai et al. [P.D. Dholabhai, J.S. Parent, P.R. Bishnoi, Equilibrium conditions for hydrate formation from binary mixtures of methane and carbon dioxide in the presence of electrolytes, methanol and ethylene glycol, Fluid Phase Equilibria 141 (1997) 235-246.], was used to gather the data.

Technique for Measuring Thermophysical Properties of Refractory Metals at Supercritical Temperatures

A foil confined in a sapphire cell is heated by an electrical current pulse at rates from 1010 to 1011 K·s−1. Temporal evolutions of the temperature and pressure distributions in the foil is investigated by means of numerical modeling. It is demonstrated that such a technique allows reaching temperatures far above 10,000 K and pressures up to 50 kbar and provides a uniform temperature and pressure in the foil. The technique has been applied for investigation of liquid tantalum. Experimental results on temperature measurement are discussed. Data on specific heat of liquid tantalum at temperatures up to 11,000 K are reported.

X-ray diffraction studies of expanded fluid mercury using synchrotron radiation

Energy-dispersive x-ray diffraction measurements using synchrotron radiation at SPring-8 for expanded fluid Hg were carried out over the wide density range from the liquid to the dense-vapour region including the metal-non-metal (M-NM) transition region. The density ranges from 13.6 to . We developed a high-pressure vessel and a sapphire cell for the x-ray diffraction measurements under high temperature and pressure up to and 1765 bar. We obtained the structure factor S(k) and the pair distribution functions g(r). The density variations of the interatomic distance and coordination number obtained were discussed in relation to the M-NM transition in fluid Hg. It was found that the volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of , but is mainly caused by a decrease of . When the transition region is crossed, the rate of decrease of becomes small and starts to elongate. We discussed some previous band calculations for expanded fluid Hg and concluded that it is essential for explaining the M-NM transition in liquid Hg to take the fluctuation of into account. When the density decreases down to the dense-vapour region, the first maxima of g(r) are located at around 3.3-3.4 Å, which is close to the interatomic distance of Hg dimers.

Fractionation of Hydrocarbons Between Oil and Gas Phases

The investigation of hydrocarbon fractionation between oil and gas phases is of interest for several purposes in reservoir exploitation. In reservoir geochemistry, the evolution of light hydrocarbon fractions of oils may explain some migration phenomena. In gas injection projects, the preferred dissolution of some components in gas may alter the composition as well as the properties of the oil. Underground gas storage in depleted oil reservoirs may also be concerned by these problems. Results of several IFP studies are described here to illustrate and to quantify the phenomenon. Two of them, using real reservoir fluids, concern reservoir geochemistry, while the third, which is a swelling test, aimed to study gas injection, investigated a synthetic reservoir fluid with hydrocarbon components up to C30. Two pieces of equipment were used: a sapphire cell with a maximum pressure rating of 400 bar and a high pressure apparatus called Hercule with a maximum pressure of 1500 bar. For each fluid, the saturation pressure was measured. For various pressure levels below saturation, the coexisting liquid and gas phases were sampled at constant pressure, and subsequently analyzed by gas chromatography. In the gas injection study, sampling was repeated with different quantities of injection gas. Compared to a n-paraffin with the same number of carbon atoms, aromatic hydrocarbons appear to stay preferentially in the liquid phase, as do cycloalkanes to a lesser extent. The gaseous phase is slightly enriched in isoalkanes. These fractionation effects are less pronounced near the critical region. These phenomena have been modeled with a cubic equation of state combined with a group contribution mixing rule.

Measurement and Prediction of Volumetric and Transport Properties of Reservoir Fluids At High Pressure

Discoveries of oil and gas fields under severe conditions of temperature (above 150°C) or pressure (in excess of 50 MPa) have been made in various regions of the world. In the North Sea, production is scheduled from deep reservoirs at 190°C and 110 MPa. This brings with it important challenges for predicting the properties of reservoir fluids, both from an experimental and a theoretical standpoint. In order to perform fluid studies for these reservoir conditions, IFP has developed a specific mercury-free high pressure apparatus with sapphire windows, a phase sampling device and viscosity determination by the capillary tube method. Its application is illustrated here using examples of real fluids and model mixtures. This equipment was first used to measure volumetric properties for gases. It has been shown that very high compressibility factors can be found with HP-HT gas condensates. This has a strong influence on recovery factors during primary depletion. In order to predict more accurately the volumetric properties of mixtures under these conditions, we propose to use a conventional equation of state, such as Peng-Robinson, with two improvements :- a modified temperature-dependent volume translation method, calibrated for high pressure density data; the method is simple, more accurate than other volume translation methods and fully consistent with lumping procedures;- a quadratic mixing rule on the covolume. Specific phase behavior can also be found. At low temperatures, wax crystallization can occur from a fluid which is a gas condensate at reservoir temperature. This feature is due to the simultaneous presence of abundant methane and heavy paraffins. A study of model fluids in a sapphire cell has allowed us to identify the possible types of phase diagrams. Although generally not considered to be an important parameter, gas viscosity may have some importance in the production of HP-HT accumulations, because of high flow rates. Viscosity models exhibit significant uncertainties because of large viscosity contrasts between the individual components of the reservoir fluid. In order to test and improve prediction methods, we started the acquisition of viscosity data under representative conditions. Special care was taken in the implementation of the capillary tube method, so that low viscosities (down to 0. 02 mPa. s) could be measured with high accuracy at pressures up to 120 MPa on simple systems, such as methane, n-pentane, nitrogen, and nitrogen-pentane mixtures. As a result, it was possible to evaluate mixing rules for viscosity predictions.