Gas-water Interface Research Articles

Genetic Relationship between Mississippi Valley-Type Pb–Zn Mineralization and Hydrocarbon Accumulation in the Wusihe Deposits, Southwestern Margin of the Sichuan Basin, China

The coexistence of numerous Mississippi Valley-type (MVT) Pb–Zn deposits and oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. The Wusihe MVT Pb–Zn deposits are located along the southwestern margin of the Sichuan Basin. Based on the spatiotemporal relation between Pb–Zn deposits and paleo-oil/gas reservoirs, ore material sources, and processes of mineralization and hydrocarbon accumulation, a new genetic relationship between mineralization and hydrocarbon accumulation is suggested for these deposits. The Wusihe Pb–Zn deposits are hosted in the Ediacaran Dengying Formation dolostone, accompanied by a large amount of thermally cracked bitumen in the ore bodies. The Pb–Zn deposits and paleo-oil/gas reservoirs are distributed along the paleokarst interface; they overlap spatially, and the ore body occupies the upper part of the paleo-oil/gas reservoirs. Both the Pb–Zn ore and sphalerite are rich in thermally cracked bitumen, in which µm sized galena and sphalerite may be observed, and the contents of lead and zinc in the bitumen are higher than those required for Pb–Zn mineralization. The paleo-oil/gas reservoirs experienced paleo-oil reservoir formation, paleo-gas reservoir generation, and paleo-gas reservoir destruction. The generation time of the paleo-gas reservoirs is similar to the metallogenic time. The source rocks from the Cambrian Qiongzhusi Formation not only provided oil sources for paleo-oil reservoirs but also provided ore-forming metal elements for mineralization. Liquid oil with abundant ore-forming metals accumulated to form paleo-oil reservoirs with mature organic matter in source rocks. As paleo-oil reservoirs were buried, the oil underwent in situ thermal cracking to form overpressure paleo-gas reservoirs and a large amount of bitumen. Along with the thermal cracking of the oil, the metal elements decoupled from organic matter and H2S formed by thermochemical sulfate reduction (TSR) and minor decomposition of the organic matter dissolved in oilfield brine to form the ore fluid. The large-scale Pb–Zn mineralization is mainly related to the destruction of the overpressured paleo-gas reservoir; the sudden pressure relief caused the ore fluid around the gas–water interface to migrate upward into the paleo-gas reservoirs and induced extensive metal sulfide precipitation in the ore fluid, resulting in special spatiotemporal associated or paragenetic relations of galena, sphalerite, and bitumen.

Pore-scale investigation on methane hydrate formation and plugging under gas–water flow conditions in a micromodel

Hydrate formation in the pores of porous media is known to decrease reservoir permeability. Current research on hydrate formation in porous media primarily focuses on the static state. In this study, the formation and plugging of methane hydrate under gas–water flow conditions in a visible heterogeneous micromodel were investigated. The experimental results show that the hydrates formed in the pores tended to deposit in situ, and the intersection of different pore channels is critical for hydrate plugging in the micromodel. The higher the pressure in the pore channels, the higher the risk of hydrate formation and plugging. Meanwhile, the hydrate fraction in the pore channels was quantitatively analyzed to describe the hydrate formation and plugging behaviors, which are affected by the hydrate formation and dissolution processes. Based on the experimental results, the formation mechanism of hydrate plugging in microporous channels was proposed, which primarily includes four stages: formation of a water film by the gas–water flow, formation of a hydrate thin shell at the gas–water interface, hydrate deposition in situ and growth, and formation of hydrate plugging. This study establishes the experimental foundation for hydrate plugging prediction models and prevention methods for porous media.

Direct C(sp3)-N Bond Formation between Toluene and Amine in Water Microdroplets.

Unlike the inertness of bulk water, water microdroplets exhibit some remarkable reactivities. We report that water microdroplets can directly produce stable C7H7+ cations (a combination of benzylic and tropylium cations) from toluene and other substrates at room temperature with a positive voltage (+4 kV) applied to the droplet spray source. The C7H7+ cation and the benzyl radical (C6H5CH2·) are both generated via hydroxyl radicals at the water-gas interface of the microdroplets. The C7H7+ signal is observed directly by mass spectrometry. Dissolved amines (primary, secondary, and tertiary) in the microdroplets can react with both C7H7+ and C6H5CH2· to form the corresponding alkyl C(sp3)-N coupling products in one step, which cannot be achieved in bulk water or other solvents. The products were identified using tandem mass spectrometry (MS2) and 1H NMR spectroscopy. Notably, the direct C(sp3)-N bond formation products were obtained in the absence of a catalyst. In the presence of a radical scavenger, the mass spectra of the C(sp3)-N coupling products are strongly suppressed, which supports the hypothesis that this reaction is driven by hydroxyl radicals generated in the water microdroplets. Taken together, these results show that water microdroplets provide a new method for direct one-step C(sp3)-N bond formation without the need for a metal catalyst.

Mechanism and characteristics of thrust generated by a submerged detonation tube for underwater propulsion

The detonation engine, which can produce high specific impulse during the underwater detonation process (UDP), has become the forefront of underwater propulsion. In this paper, the thrust mechanism conducted in UDP and the propagation characteristics of the complex pressure waves are numerically studied, and the correlation between those two features is analyzed. The thrust from UDP is generated in a submerged detonation tube (SDT) and driven by the stoichiometric methane-oxygen mixture. The results show that detonation of the pre-filled combustible gas mixture gives rise to complex pressure waves and delivers several force impulses to the SDT. The impulses present different effects on the thrust performance, which is divided into two stages. In the first stage, before the detonation wave collides with the exterior water, the thrust is provided by the persistent back pressure effect of the detonation product. When the detonation wave propagates through the SDT exit and strikes the gas–water interface, a transmitted shock wave and a reflected shock wave are formed, which produce the impulses dominating the second stage. The reflected shock wave eventually impinges on the inner wall, imposing a force impulse on it. The pressure disturbance on the annular wall caused by the transmitted shock wave and subsequent detonation gas jet leads to another two thrust impulses. Finally, a comparison between the thrust of the SDT and its counterpart in the air is conducted to characterize the influence of UDP, and the effects of dimensional parameters of the SDT are also investigated.

Effects of chemical potential differences on methane hydrate formation kinetics

To underpin the increasing interest in practical applications of gas hydrates, for gas storage and separation for instance, the formation and growth of hydrates at liquid-gas interfaces are of fundamental importance. Although the thermodynamics of hydrate formation has been widely studied and is well understood, the kinetics of these processes is not well characterised. In this work, a high-pressure, low-temperature stirred reactor was used to conduct hydrate formation kinetic studies in a temperature range from 276.5 to 283.5 K and a pressure range from 5 to 10.5 MPa, with a special focus on 1) the impact of agitation conditions on the available water-gas interfacial surface area for mass transfer and growth rate during hydrate formation, and 2) the effect of the chemical potential driving force on the formation rate. Five hydrate growth regimes were identified, with varying degrees of gas mass transfer control across the gas-water interface depending on the extent to which hydrate layers built up at this interface, gas needed to move through solid hydrate layers, and the extent to which the gas was entrained within the water phase. The formation rate in the initial linear growth regime, before the onset of solid hydrate gas mass transfer effects, was found to depend in an essentially exponential manner on the chemical potential difference from the equilibrium state. Semi-empirical models related to Arrhenius-type kinetic models were used to correlate the data, the best of which reproduced the formation rates from the chemical potential differences to within ± 5 %. The approach has general applicability to help determine the balance between kinetic and thermodynamic factors in identifying the optimum pressure-temperature conditions for processes for gas storage, gas separation and other hydrate applications.

Inhibition of N-vinylpyrrolidone on hydrate in high-pressure flow system under the synergistic effect of ether compounds

Through the experimental tests as performed on a high-pressure flow loop test bench, the synergistic effect of diethylene glycol monoethyl ether (DEGEE), propylene glycol methyl ether (PM), and ethylene glycol phenyl ether (EPH) on the inhibition of inhibitors on hydrate growth was explored under the same initial temperature (285.15 K), pressure (5.0 MPa) and flow rate (230 L/h). The average particle size, relative inhibition performance factor (RIP), and initial formation rate of methane hydrate in the system with a single kinetic inhibitor (or monoalcohol ether synergistic agent) were obtained by experiments, and compared with the relevant parameters in the system with a kinetic inhibitor and a synergistic agent. The experimental results show that the presence of PVP in the system increases the average particle size, which may be due to the adsorption of kinetic inhibitors on hydrate crystals. When the relative inhibition performance factor was used as the index, all the three kinds of synergistic agents promoted the inhibition performance of PVP. DEGEE had the best promotion effect, EPH was the weaker, and PM was the weakest. The synergistic agents in the composite system had little effect on the initial formation rate of hydrate. The addition of kinetic inhibitors and synergistic agents would transform the hydrate formation medium from the wall to the gas–water interface, while the presence of the oil phase in the system significantly weakened the inhibition performance in the kinetic inhibitor-synergist system. The results and theories obtained in this experiment can provide a theoretical basis for the flow guarantee in actual pipelines.

Effect of Surfactants with Different Hydrophilic–Lipophilic Balance on the Cohesive Force between Cyclopentane Hydrate Particles

Effective control of the cohesive force between hydrate particles is the key to prevent their aggregation, which then causes pipeline blockage. The hydrophilic–lipophilic balance (HLB) value of surfactants was proposed as an important parameter for the evaluation and design of hydrate anti-agglomerants. A microscopic manipulation method was used to measure the cohesive forces between cyclopentane hydrate particles in the presence of Tween and Span series surfactants with different HLB values; moreover, the measured cohesive force was compared with the results of calculations based on the liquid bridge force model. Combined with the surface morphology and wettability of the hydrate particles, we analyzed the mechanism by which surfactants with different HLB values influence the cohesion between hydrate particles. The results show that for both Tween (hydrophilic, HLB > 10) and Span (hydrophobic, HLB < 10) surfactants, the cohesive force between cyclopentane hydrate particles decreased with decreasing HLB. The experimental results were in good agreement with the results of calculations based on the liquid bridge force model. The cohesive force between hydrate particles increased with increasing concentration of Tween surfactants, while in the case of the Span series, the cohesive force decreased with increasing surfactant concentration. In the formation process of cyclopentane hydrate particles, the aggregation of low-HLB surfactant molecules at the oil–water or gas–water interface increases the surface roughness and hydrophobicity of the hydrate particles and inhibits the formation of liquid bridges between particles, thus reducing the cohesion between particles. Therefore, the hydrate aggregation and the associated blockage risks can be reduced.

Bubble-growth regime for confined foams: Comparison between N2–CO2/foam and CO2/foam stabilized by silica nanoparticles

The use of foam technology in Pre-Salt reservoirs is a potential solution to control gas mobility in highly heterogeneous reservoirs. However, achieving stable CO2-foams under reservoir conditions can be challenging since high solubility in water of supercritical CO2 enhances coarsening and coalescence of bubbles. Coarsening is the evolution of foam structure with time due to gas diffusion between bubbles. In this phenomenon, gas normally diffuses from smaller to larger bubbles, which for confined foam is relevant because this ends up decreasing the number of bubbles in a determined area/volume of the pore space (foam texture). When foam texture coarsens, gas mobility control is impaired, and it can also affect foam rheology. Therefore, it is important to characterize bubble growth kinetics to compare strategies to reduce coarsening and investigate their impact on gas mobility reduction due to foam injection. In a previous work, we reported the use of nanoparticles and a CO2/N2 gas mixture as strategies for improving gas mobility of CO2-foams formed with a zwitterionic surfactant in a micromodel experiment. The present study focuses on quantitatively assessing the bubble growth regime related to coarsening for these two strategies. Indeed, bubble growth is a key parameter for population balance mathematical models that simulate CO2-foams in porous media. Image analysis was used to characterize the foam texture by calculating the bubble density and bubble size distribution of the foam confined in dead-end pores areas of the micromodel. Our results showed that, the number of trapped bubbles was twice as high for the foam formed with the gas mixture compared to those containing nanoparticles, and this higher bubble density was correlated with the higher pressure drop observed for this system, indicating lower gas mobility. The coarsening rates obtained by analyzing the change in trapped bubble area with time of CO2-foam containing nanoparticles (0.25 μm2 s−1) was in the same order of magnitude compared to that obtained by a CO2/N2 gas mixture-foam (0.44 μm2 s−1), under the same high-pressure high-temperature (HPHT) conditions. These results meant that both strategies were able to stabilize the weak foam formed between zwitterionic surfactant and CO2, and that the initial foam texture determined resistance to flow. The semi-automatic algorithm successfully identified the bubbles trapped within the system during the period of analysis, which allowed us not to add dyes that could change interfacial behavior at the water-gas interface. The novel results that evaluate the coarsening rate for CO2-foam under HPHT conditions can positively impact the estimation of foam destruction parameters for population balance models for more representative reservoir conditions of trapped gas. Our findings fill part of the gap in terms of evaluation of coarsening rate under more representative reservoir conditions, improving the understanding of kinetics of foam destruction. This information is relevant for establishing a correct range of the destruction term for populational balance models. Moreover, our results reveal that the type of strategy chosen to delay coarsening can significantly impact gas mobility reduction and that using nanoparticles impacted significantly interfacial properties of the formed foam.

Effects of water on gas flow in quartz and kerogen nano-slits in shale gas formations

Understanding the gas-water two-phase flow behavior in a shale gas formation is important for reservoir simulation and production optimization. A molecular simulation study of gas-water flow in quartz and kerogen nano-slits (2–6 nm) at shale reservoir conditions (temperature: 313.15–393.15 K, pressure: 20–60 MPa) is reported in this work. The simulation results show that the existence of water in the hydrophilic quartz slits will form water films on the slit walls; while the presence of water in the hydrophobic kerogen slits will form water clusters in the central of the gas phase at low water saturation and a water layer at high water saturation. In both wetting conditions, water will take flow space and reduce gas flow path. However, water affects gas flow velocities in the two wetting types nano-slits in different ways due to the two opposite occupancies in the slits. The momentum transfer between water and methane molecules in the gas-water interface region plays an important role in the gas-water two-phase flow. The gas flow is more readily affected by water content in the quartz slit with an aperture greater than 2 nm. When the slit aperture is reduced to 2 nm, it is difficult to form a continuous gas or water phase, and the existence of water in both types of slits will reduce the velocity of methane. Increasing the temperature will accelerate the flow of methane and water because hydrogen bonds between water molecules as well as hydrogen bonds between water molecules and the walls are reduced. High pressure promotes the mixing of the methane and water molecules, resulting in the gas velocity decreasing in both quartz and kerogen slits. The flow mechanism of methane and water in nano-slits provide insights into theoretical models for shale gas production.

Numerical analysis of ventilated cavitating flow around an axisymmetric object with different discharged temperature conditions

Nowadays, with the widespread use of modern technology in underwater vehicles, particularly in naval applications, the artificial gas ejected from ventilated holes is normally heated because of engine operations. However, the dynamics of ventilated hot gas have not yet been fully studied. In this study, the cavitating flow around an axisymmetric body with different ventilated temperatures was numerically investigated. A fully compressible mixture model based on a homogeneous multiphase approach was employed. A high-order accuracy flow solver based on the numerical models of a dual-time preconditioning technique, a sharp interface-capturing scheme, and an enhanced cavitation model was used to examine the effects of temperature on the cavitating flow. First, the numerical results were validated by comparison with available experimental data of cavitating flow around a conical cavitator. Reasonable agreements on the cavity shape, cavity length, and cavity thickness were achieved. The solver was then applied in simulations to analyze the development of the ventilated cavity, including the cavity formation at the early stage, the re-entrant jet phenomenon, and the cavity shedding mechanism. In addition, the effects of ventilated temperatures on the cavity length and cavity thickness were studied. Further insight into the distributions of the flow field inside the cavity, and the instability of the gas-water interface when temperature increases were also provided.

Enhancing Gas Solubility in Water via Femtosecond Laser-Induced Plasma.

The generation of laser-induced plasma at the gas–liquid interface provides many fundamental and interesting scientific phenomena such as ionization, sharp explosion, shock wave radiation, bubble creation, and water splitting. However, despite the extensive research in this area, there is no reference on the effect of the surrounding environment on the chemical processes that occur during the laser-induced plasma–water interaction. In this work, we investigate the effect of the surrounding gas environment on femtosecond laser-induced plasma when generated at the pure water–gas interface. Ultrashort laser pulses were applied to water in the presence of air and N2 and Ar gas environments. Formation of a significant number of nitrate-based species in water was observed after exposure to femtosecond laser-induced plasma in air and N2 environments. The detected NO3 ions formed in the laser-treated water led to the appearance of an absorption peak in the UV range, a significant decrease in the water pH value, and a significant increase in water’s electrical conductivity. All induced properties of water were stable for 3 months of monitoring after laser treatment. Our work shows that the generation of laser-induced plasma in water propagating into a gaseous medium facilitates the interaction between the two media, as a result of which the compositions of substances present in the gaseous medium can be dissolved in water without increasing the gas pressure. The presented approach may find applications in areas such as water purification, material synthesis, and environmental stewardship.

Integration of Pore-Scale Visualization and an Ultrasonic Test System of Methane Hydrate-Bearing Sediments

The acoustic characteristics of hydrates are important parameters in geophysical hydrate exploration and hydrate resource estimation. The microscale distribution of hydrate has an important influence on the acoustic response of a hydrate-bearing reservoir. Although microscale hydrate distributions can be determined using means such as X-ray computed tomography (X-CT), it is difficult to obtain acoustic parameters for the same sample. In this study, we developed an experimental system that integrated pore-scale visualization and an ultrasonic testing system for methane-hydrate-bearing sediments. Simultaneous X-CT observation and acoustic detection could be achieved in the same hydrate sample, which provided a new method for synchronously monitoring microscale distributions during acoustic testing of natural gas hydrate samples. Hydrate formation experiments were carried out in sandy sediments, during which the acoustic characteristics of hydrate-bearing sediments were detected, while X-ray computed tomography was performed simultaneously. This study found that hydrates formed mainly at the gas–water interface in the early stage, mainly in the pore fluid in the middle stage, and came into contact with sediments in the later stage. The development of this experimental device solved the difficult problem of determining the quantitative relationship between the microscale hydrate distribution and the acoustic properties of the reservoir.

Shock wave and bubble pulsation characteristics in a field generated by single underwater detonation

To promote the development and application of underwater detonation propulsion technology, we built a single underwater detonation experimental system and established the corresponding axisymmetric five-equation model to study the characteristics of the flow field generated by a single underwater detonation. The shock wave formed by the degeneration of the detonation wave in the detonation tube interacted with the water–gas interface. Moreover, the jetting of detonated gas was blocked by water, which sharply increased the gas pressure and yielded a transmitted wave entering the water and a reflected wave returning to the tube. The transmitted wave reached a peak pressure of 16.77 MPa at 1280 Hz. The extremely transient gas generated by detonation jetted into the water, forming bubbles with unique pulsation characteristics and completing the first pulsation cycle (28.4 ms) under the effects of the internal gas pressure and the inertia of water. In the contraction stage, the bubble changed into a complex linked annular bubble under the effects of gravity and a free surface. However, in the expansion stage, the bubble was less affected.

Evaluation of the Effectiveness and Adaptability of a Composite Water Control Process for Horizontal Wells in Deepwater Gas Reservoirs

Deepwater gas fields have high bottom water energy and a high risk of seeing water. Higher requirements are put forward for the water control process to control the water effect. This article is based on the actual background and well design of the X gas field in the South China Sea and on three sets of physical simulation experiments and three sets of numerical simulation experiments. An analysis and comparison of the water control effect of a combination of continuous packer, continuous packer and variable density screen tube, and their adaptability evaluation in deepwater gas reservoirs were performed. The results obtained from the numerical and physical simulations are consistent. The experimental results show that the water control process of a continuous packer is mainly based on the water-seeing and water-blocking ability. It is less capable of extending the time to produce water in the horizontal section. However, its water-blocking ability is strong and is able to seal the water spot quickly. It extends the total production time by 12.29% and increases the total gas production by 5.96%; the combined water control process of the continuous packer and variable density screen tube can effectively play their respective advantages of water control. The combination of the continuous packer and variable density screen tube can effectively be advantageous of their respective water control processes, enabling the gas–water interface to advance in a balanced manner, extending the water-free gas recovery period by 11.61%, extending the total gas production time by 15.76%, and increasing the total gas production volume by 13.75%. Both water control processes have good applicability in deepwater gas fields and have certain sand control capability. It is conducive to the one-time completion operation for the commissioning of deepwater gas fields.

Encapsulated Microbubble Fiber-Tip Fabry-Perot Cavity With Tunable Bandwidth for Sensitive Acoustic Detection

A photothermally generated microbubble on a single-mode fiber tip with tunable frequency bandwidth was demonstrated for sensitive detection of acoustic waves. The microbubble with spherical gas-water interface formed a flexible Fabry-Pérot cavity at the fiber tip and detected the acoustic waves by interferometric readout of the bubble deformation. To work in different liquids besides water, the sensor was encapsulated into a water-filled tube and the effects of the encapsulation process on the optical and acoustic characteristics of the sensor were investigated. A 40 μm-diameter microbubble based sensor exhibited a noise-equivalent pressure level of ∼1.0 mPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> at the frequency of ∼100 kHz. The bubble diameter was photothermally changed from 20 μm to 60 μm, which enabled online tuning of the sensor resonant frequency from 100 kHz to 300 kHz. This tunable feature is attractive to applications that requires the detection of acoustic waves covering different frequency bands. The encapsulated microbubble sensor with advantages of high sensitivity, tunable bandwidth and low-cost would be interesting for applications in biomedical and industrial areas involving various liquid environments.

Research on Well Area Connectivity of Carbonate Gas Reservoir in Eastern Sichuan Basin—A Case Study of Wubaiti Block

Carbonate gas reservoirs in the eastern Sichuan Basin are featured by low matrix permeability and well-developed fractures, caves, and faults, which result in complicated fluid flow and connectivity. The Wubaiti Carboniferous gas reservoir is an earlier developed block in Eastern Sichuan with a development history of 27 years. The geological features, e.g., block structure and fault development, have been extensively studied, but a few studies address the connection relationship and gas–water interface of the DT 2 well area in the north. To solve this problem, this paper proposes a reserve simulation method based on the conventional connectivity analysis, which calculates the reserves of different gas–water interfaces in the well area. Combined with production performance analysis, the well-controlled reserves and drainage area were also determined. The analysis verifies the connectivity between wells. Integrating with interference testing, fluid properties, and seismic and geological data, the connection relationship between well areas is further clarified. The results show that the northern water bodies of the DT 2 well area consist of two independent and disconnected water bodies. There is a blocking zone between the DT 2 and DT 3 and DT 4 wells, which causes the disconnection of water bodies but the connection of gas. The results also indicate that the eastern water body of the main area and the eastern water body of the DT 2 well area are part of a uniform water body with a uniform gas–water interface. The research method is significant for the connectivity research of similar gas reservoirs.

Research on the Inflow Performance of the Plunger Lift in the Shale Gas Horizontal Well

Shale gas wells in the Changning block of Weiyuan, Sichuan, China, experience water production problems throughout their life cycles. In actual field production, plunger lift is typically used to discharge liquid from a shale gas well. However, it is difficult to test the formation inflow performance relationship curve (IPR) of a plunger lift well. Hence, data on the formulation and optimization of plunger lift well systems are lacking. Based on actual measured data related to casing pressure changes at the wellhead and the gas-liquid distribution characteristics in a wellbore during the shut-in phase, this paper establishes a method for calculating the formation IPR curve of a shale gas plunger lift well by calculating changes in wellbore gas volume continuously. This method has a fast calculation speed. The gas-water interface distribution can be obtained in 3–5 iterations, and the inflow dynamic curve can be calculated in less than 5 seconds. This method tested the IPR curves of gas wells in the Changning block. The IPR curves of plunger lift wells showed concave characteristics contrary to the conventional upward convex curves. This is because the bottom hole flowing pressure changes caused variations in the water saturation of the near-wellbore zone. Consequently, the productivity equation of the plunger lift well is established by introducing the variation coefficient of water saturation expressed by bottom hole flow pressure. This equation fits with the measured IPR curve with an average R2 of approximately 0.9989.

Location optimization of silicon carbide foam packings in the unstirred packing trays reactor for the enhancement of solidified natural gas storage

Solidified natural gas technology shows significant potential for storing safely multi-fold volumes of natural gas in clathrate hydrates, but the main concern is the stochastic and slow process of hydrate nucleation making it unstable and unpredictable in practice. To overcome this limitation, methane hydrate was synthesized in a silicon carbide (SiC) ceramic foam packing trays reactor without stirring. Results suggested that the packing trays should be located near the gas-water interface instead of immersed in the aqueous phase, which decreased the induction time by about 98%. Results also highlighted the synergistic effects between the capillary wicking from the porous packings and the water suction from the initially formed hydrate clusters, which pumped water from the aqueous phase into the packings’ pores to provide an unsaturated porous environment for hydrate nucleation. It demonstrated that these two driving forces might also compete for water which became adverse to hydrate formation.

Photoelectron angular distributions as sensitive probes of surfactant layer structure at the liquid-vapor interface.

The characterization of liquid–vapor interfaces at the molecular level is an important underpinning for a basic understanding of fundamental heterogeneous processes in many areas, such as atmospheric science. Here we use X-ray photoelectron spectroscopy to study the adsorption of a model surfactant, octanoic acid, at the water–gas interface. In particular, we examine the information contained in photoelectron angular distributions and show that information about the relative depth of molecules and functional groups within molecules can be obtained from these measurements. Focusing on the relative location of carboxylate (COO−) and carboxylic acid (COOH) groups at different solution pH, the former is found to be immersed deeper into the liquid–vapor interface, which is confirmed by classical molecular dynamics simulations. These results help establish photoelectron angular distributions as a sensitive tool for the characterization of molecules at the liquid–vapor interface.

Direct Ozonation of Antibiotics in Water: Effect of Ozone Reactions in the Proximity of Gas-Water Interface

Direct Ozonation of Antibiotics in Water: Effect of Ozone Reactions in the Proximity of Gas-Water Interface