Continuous Hydrate Research Articles

Solubility measurements of methane and ethane in water at and near hydrate conditions

The isobaric solubility of pure methane and ethane gases in liquid water was measured under different conditions, including hydrate formation points, using a ramping method in which measurements are made through the entire and continuous hydrate formation/decomposition cycle. The work was conducted for methane at 3.45 MPa (500 psia) and temperatures ranging from 17.0 to 0.0°C (290.2 to 273.2 K), and for ethane at 0.66 MPa (95 psia) and a temperature range of 17.0 to 0.0°C (290.2 to 273.2 K). The isobaric solubilities obtained show a significant divergence from (normal) Henry's law solubility as the temperature is lowered. The increase in the solubility is presumably the result of the onset of a sorption process that traps the gas molecules in the water structure. Several sub-processes were observed as the hydrate formation was taking place: (1) the dissolution of the gas in the liquid water, or interstitial solubility, (2) the onset of the sorption sub-process and build-up of the hydrate precursors, (3) the catastrophic formation and the existence of the solid phase with its slushy characteristics, and (4) the solidification of the hydrates, therefore causing the total plugging of the experimental cell.

The nature, distribution, and origin of gas hydrate in the Chile Triple Junction region

A bottom simulating reflector (BSR) is regionally distributed throughout much of the Chile Triple Junction (CTJ) region. Downhole temperature and logging data collected during Ocean Drilling Program (ODP) Leg 141 suggest that the seismic BSR is generated by low seismic velocities associated with the presence of a few percent free gas in a ∼ 10 m thick zone just beneath the hydrate-bearing zone. The data also indicate that the temperature and pressure at the BSR best corresponds to the seawater/methane hydrate stability field. The origin of the large amounts of methane required to generate the hydrates is, however, problematic. Low total organic carbon contents and low alkalinities argue against significant in situ biogenic methanogenesis, but additional input from thermogenic sources also appears to be precluded. Increasing thermal gradients, associated with the approach of the spreading ridge system, may have caused the base of the hydrate stability field to migrate 300 m upwards in the sediments. We propose that the upward migration of the base of the stability field has concentrated originally widely dispersed hydrate patches into the more continuous hydrate body we see today. The methane can be concentrated if the gas hydrates can form from dissolved methane, transported into the hydrate zone via diffusion or fluid advection. A strong gradient may exist in dissolved methane concentration across the BSR leading to the steady reabsorbtion of the free gas zone during the upward migration of the BSR even in the absence of fluid advection.

Study of the pseudo‐steady‐state kinetics of CO2 hydrate formation and stability

AbstractThis article describes a dynamic model for formation and stability of CO2‐hydrate on the interface of liquid CO2(LCO2) and ocean water at large depths. Experimental results indicate that a thin film of hydrate naturally forms on the interfaces between LCO2 and water, and inhibits diffusion between the two phases. Experiments further shows that the flux of CO2 through the hydrate film is dependent of the CO2‐concentration in the ambient sea water. The model proposed here explains these phenomena by introducing four major mechanisms; diffusion of water to the LCO2‐phase, formation of hydrate in the LCO2‐hydrate interface, decay of hydrate in the water‐hydrate interface, and diffusion of CO2 through the water phase. The model explains the CO2 flux not by diffusion through the hydrate film, but suggest a mechanism of continuous hydrate formation and decay. The overall effect is a “moving,” pseudo‐steady‐state hydrate film due to transport of CO2 through the film. The film velocity is dependent of liquid‐liquid diffusivity parameters and reaction constant, and lacking experimental values of these parameters, an order–of‐magnitude analysis is done by fitting the model to experimentally obtained data for the overall film velocity. The motivation for this work is to elucidate options for CO2 depositions in deep oceans, of which liquid CO2 sequestration is believed to be one of the most feasible. Spreading of CO2 from a liquid CO2‐lake and associated lowering of pH in the ecosystem surrounding the lake is of large concern. The work presented here concludes that diffusion of CO2 in the ocean is largely reduced by the hydrate film and suggests that hydrate formation may alleviate some of the environmental concerns regarding deep ocean sequestration of liquid CO2. © 1994 John Wiley & Sons, Inc.

On the continuum emissions observed upon oxidation of aluminum and its compounds

The reactions of aluminum with H 2O, H 2O 2, N 2O, and O 3 have been studied under “single-collision” conditions. We have also examined the reactions of aluminum with moist laboratory air, water, ozone, nitric oxide, and hydrogen peroxide under “multiple-collision” rotationally relaxed conditions. Under multiple-collision conditions, the aluminum-ozone and aluminum-nitric oxide reactions are found to yield resolvable vibronic levels in the spectrum of AlO, whereas reactions with water and moist laboratory air yield a broad emission continuum that must be assigned to a polyatomic emitter. No emission is observed for aluminum oxidation with hydrogen peroxide, this result indicating the unlikely assignment of the continuum emitter to a metal monohydroxide. The combination of single- and multiple-collision studies is used to demonstrate that the continuous emission results from the formation of a metal hydrate. Mechanisms are proposed for this hydration. The current studies are correlated with recent matrix-isolation spectroscopic studies of metal atom-water interactions and theoretical studies of the binding of aluminum-water adducts, both of which corroborate the current analysis. Quenching of the continuous aluminum hydrate emission by H 2O, CO 2, and O 2 has been examined and found to be efficient. It appears that the continuous aluminum hydrate emission may represent a portion of the optical signature of the nighttime and twilight glows observed when trimethyl aluminum is released or aluminum grenades are exploded into the upper atmosphere (90–200 km). This possibility is supported by comparison of upper-atmospheric chemiluminescent intensity distributions observed for the NO + O and aluminum oxidation systems.

Interaction between chloral hydrate and warfarin. A report from the Boston Collaborative Drug Surveillance Program, Boston Universtiy Medical Center.

Abstract Data from a comprehensive drug surveillance program were analyzed to determine the clinical importance of the interaction between chloral hydrate and the oral anticoagulant warfarin. Patients anticoagulated during hospitalization were divided into three groups receiving continuous, occasional or no chloral hydrate during the first four days of warfarin therapy. Those receiving continuous chloral hydrate therapy required significantly less warfarin (p <0.01) during the induction phase of anticoagulation than those receiving no chloral hydrate. Patients given occasional chloral hydrate required an intermediate dose. All patients received similar loading doses of warfarin and similar doses from the fifth day onward. The results indicate that the interaction between these drugs is of clinical importance and that care should be exercised when they are administered concurrently.