Cyclopentane Hydrate Research Articles

Kinetic study on cyclopentane hydrates in the presence of sodium chloride

Water is an important resource for human life. The lack of clean water in the world now becomes more serious. As a result, seawater desalination to produce fresh water is becoming indispensable. In recent years, hydrate-based desalination is a potential solution for the drinking water shortage issue. Recently, Cyclopentane (CP) is used as a hydrate former for desalination process via crystallization at low temperature and atmospheric pressure. The objective of this study is to provide the new kinetic data of CP hydrates in the presence of sodium chloride with a concentration of 3.5 wt.%. The experimental data for CP hydrates in the presence of sodium chloride are obtained in a batch reactor system with a setup temperature range of -2.5 to -0.5 oC and at atmospheric pressure. The effects of temperature, agitation speed and amount of CP on kinetics of CP hydrate formation are also performed.

Interfacial rheology of cyclopentane hydrate formation: Insights into mechanical behavior and inhibitor efficiency

Hydrates are crystalline solids with an ice-like texture, which are formed when light hydrocarbon molecules and water combine to form a specific ordered structure. Hydrate formation begins at the water–hydrocarbon interface, which highlights the critical role that interfacial rheology plays in this process. Despite the significance of this interface in hydrate formation, a gap in research persists, particularly in employing shear rheology approaches. This study helps to fill this void by investigating the mechanical and flow properties of the interface, using a feature in a rotational rheometer, a “double wall ring cell,” for precise temperature control. Cyclopentane serves as the hydrate former, allowing experimentation under atmospheric pressure and varied temperatures. Protocols explore temperature and hydrocarbon concentrations, with emphasis on ice crystal involvement in hydrate formation initiation. Following complete saturation of the hydrocarbon/water interface by hydrates, interfacial elastic and viscous moduli are obtained through strain sweeps to assess hydrate film fragility and mechanical response. Additionally, the impact of aging time and shear type (static or dynamic) on hydrate stiffness is examined. Tests with thermodynamic inhibitors, such as sodium chloride and monoethylene glycol, demonstrate significant induction time extension. Furthermore, systematic changes in the shear rate are investigated to comprehensively understand their influence on hydrate film characteristics and properties under varying shear history conditions. This study reveals that increasing shear rate correlates with decreased viscosity of the hydrate film, indicative of non-Newtonian behavior. Overall, this research sheds light on the nuanced dynamics of the water–hydrocarbon interface in hydrate formation and mitigation.

Experimental study on the evolution process of hydrate deposition, blockage and decomposition in reducing pipeline

BackgroundIn the process of deep-water oil and gas extraction, due to the special structure of the reducing pipeline, the flow field of the pipeline changes here, making it easier for hydrates to form and accumulate at reduced-diameter zone and increasing the risk of pipeline blockage. MethodsAiming at the problem of hydrate deposition and blockage in reducing pipeline, an experimental study was carried out through the self-designed and reduced-diameter transparent flow loop to investigate the hydrate deposition and blockage and decomposition evolution of hydrate at reduced-diameter zone under different conditions of flow velocities and initial cyclopentane volume contents. Significant FindingsThe study found that the flow field formed at reduced-diameter zone was the main reason affecting the distribution of hydrate particles, and the flow velocity and the initial hydrate volume fraction were the main controlling factors affecting the blockage in reducing pipeline. The flow velocity of 1.6 m/s was determined as the safe boundary for cyclopentane hydrate in reducing pipeline. Based on the experimental results, the mechanism of cyclopentane hydrate deposition and blockage in reducing pipeline was revealed, and targeted prevention and control methods for hydrate blockage at reduced-diameter zone were proposed. It is of great significance to ensure the safe flow of hydrate in reducing pipeline.

Investigation of theoretical maximum water yield and efficiency-optimized temperature for cyclopentane hydrate-based desalination

Hydrate-based desalination (HBD) shows promise as a freshwater production technology for saline water. Liquid-phase hydrate formers, with their ability to facilitate hydrate formation at atmospheric pressure, have gained attention for their high energy efficiency in HBD. This study explored cyclopentane (CP) HBD by experimentally measuring the thermodynamic properties of CP hydrate in saline solutions and developing a theoretical framework to estimate the water yield of CP HBD under various operating conditions. The measured dissociation enthalpy of CP hydrate was found to be 12 % and 22 % lower compared to those of propane and R134a hydrates, respectively. The equilibrium dissociation temperatures of CP hydrate at different NaCl concentrations under atmospheric pressure were experimentally measured and then predicted using the Hu–Lee–Sum correlation. The theoretically achievable maximum salinity and water yield for CP HBD were calculated in the temperature range of 268–280 K and the initial salinity range of 0–8 wt.%. Additionally, the concept of HBD heat efficiency, representing the maximum amount of pure water producible per unit of heat, was introduced to identify an optimal operating condition for the HBD process. Efficiency-maximized temperatures, where the HBD heat efficiency reached its peaks, were determined for various initial salinities in the process, for example, 273.4 K for NaCl 3.5 wt.% solution. This novel approach provides invaluable guidance for determining the most energy-efficient operating conditions in the HBD process and establishes a solid foundation for further advancements in this field.

Kinetics studies of methane hydrate formation and dissociation in the presence of cyclopentane

The work systematically investigates the kinetic of methane(CH4) hydrate formation in the presence of cyclopentane（CP）by measuring induction time, hydrate formation rate, and gas uptake. The results showed that there are two steps for CH4 hydrate formation in the presence of CP: Step 1, pure CP hydrate formation. Step 2, gas enters the empty cages of pure CP hydrates to form CP/CH4 mixed hydrates. Besides, the rapid hydrate formation rate and high CH4 uptake are observed from hydrate formation in this work. At the optimum conditions of 288.15 K and CP mole fractions of 5.6 mol%, the gas uptake and the time required for completion of hydrate formation are 131.80 mmol/mol H2O and 138 min, respectively. Relative to the highest reported gas uptake obtained in the presence of thermodynamic promoter (72.0 mmol/mol H2O), the value increased by 83%. More strikingly, the work shows that high gas uptake hydrates formed at relatively low temperatures can be stored and transported at relatively high temperatures, as high as 298.15 K, without significantly reducing the gas uptake, thereby providing one of the cost-effective methods for hydrate storage and transportation, that is forming hydrates at relatively low temperatures and storing and transporting hydrates at relatively high temperatures. Further, we proposed a schematic of the process chain of SNG(storing natural gas via solid hydrate) technology in vehicular and detailed discuss the current status of SNG technology development. It can be concluded that using the strategy that storage and transportation hydrates at a low-pressure condition instead of at ambient pressure (1.0 atm) may be a more realistic choice to industrialize SNG technology.

Cyclopentane hydrate wettability measurements used to evaluate the efficacy of oil natural surfactants using ultra-low volume samples

Hydrate surface wettability is a fundamental aspect to better understand agglomeration present in oil bearing petroleum pipelines. Coupling these measurements with hydrate film growth gives further information on kinetic effects that may also be present from natural surfactants in different oils. In situ measurements of wettability (quantified by the contact angle) and film growth rates were performed on cyclopentane hydrate surfaces at atmospheric pressure and subcooling of 4 °C. Contact angle and film growth results were obtained for the baseline system (pure cyclopentane), one model oil, and seventeen natural oils (diluted to 0.02 vol% in cyclopentane). Results showed a wide variety of contact angles and film growth values where higher asphaltene contents in the oils corresponded to higher contact angles and lower film growth rates, thought to be from better alignment of natural surfactant molecules at the hydrate/hydrocarbon interface. It was also shown for select oils that increasing the oil concentration in the cyclopentane increases the contact angle and decreases the film growth rate compared to the baseline system. For select oils that had higher contact angles, increasing the water content of the system decreases their contact angle and film growth compared to the baseline system. Isolating different oil fractions for select oils also shows which fractions tend to play a larger role in wettability behavior. Typically, the fractions with more surface active components (asphaltene and resins) are shown to contribute to the higher contact angle and slower film growth rates for select oils. Evidence of the competition between film growth and capillary suction of water into the hydrate has been shown, and a mechanistic breakdown of three different transient scenarios has been proposed. Each of these observed interfacial behaviors gives information on what can be expected from larger scale phenomena, including hydrate agglomeration, with very small oil samples.

Experimental investigation to elucidate the hydrate Anti-Agglomerating characteristics of 2-Butoxyethanol

To alleviate the severity of hydrate formation in subsea oil and gas pipelines, the injection of anti-agglomerants (AAs) is one of the promising approaches. In this work, we investigate the hydrate anti-agglomerating characteristics of 2-butoxyethanol, also called butyl glycol ether (BGE), which has been reported in the literature as an effective synergist for kinetic hydrate inhibitors (KHIs), and a solvent for low dosage hydrate inhibitors (LDHIs). In view of its hydrophobic and hydrophilic moieties, we evaluate the adsorption affinity of BGE for the oil–water interface employing the interfacial tensiometer (IFT) apparatus. Moreover, a micromechanical force (MMF) apparatus was used to probe the interfacial behavior of hydrate particles, wherein we measured the cohesive forces between cyclopentane hydrate particles in the presence of BGE at atmospheric pressure and 274.2 K. The kinetics of methane hydrate formation and resistance-to-flow were assessed while measuring the dynamic pressure–temperature data and motor torque signals alongside with visual observations, respectively, employing a high-pressure visual autoclave (HPVA). IFT results reveal the strong surface active properties of BGE with a substantial reduction in oil–water interfacial tension at ambient conditions. However, no considerable change in the cohesive forces between cyclopentane hydrate particles was observed through MMF measurements. In contrast, HPVA results reveal that the addition of BGE enhanced the kinetics of methane hydrate formation; however, the corresponding torque pattern/visual interpretations indicated an anti-agglomerating action of BGE. While synergistically combining the BGE with under-inhibited dosages of mono-ethylene glycol, we further demonstrated a significant improvement in the hydrate transportability, wherein this synergism led to a non-plugging scenario (flowable hydrate slurry). Our findings will offer new insights into the development of new anti-agglomerant chemistries.

Rheology Properties of Cyclopentane Hydrate Slurry in the Presence of Wax Crystals

ABSTRACT There are several flow assurance problems for the energy development in deep-water, the coexistence of wax and hydrate resulting to multi-solid phase deposition is among the most difficult to overcome. The results of an experimental study on the effect of wax content, water cut, subcooling and static time on the CP hydrate-forming mixtures are reported. The droplet distribution at different wax contents is determined by using microscopic observation method. Using dynamic stress measurements method, a correlation between rheological properties and water cut is obtained. Hydrate nucleation, growth, dissociation, and slurry rheological properties, including critical time, growth time, final viscosity, and yield properties are determined. Results indicated that wax inhibit hydrate nucleation and growth, but the viscosity of hydrate slurry in waxy system is still higher than wax-free system due to the wax-hydrate aggregates contribute more to the viscosity of the system. The structure of hydrate slurry containing wax system is more stable and more difficult to be damaged by shear. Wax increases the hydrate slurry yield stress, and this effect is more significant at higher water cut and longer static times. The yield stress of the hydrate slurry was linearly related to the water cut. 35% was the critical water cut. Below the critical water cut, the slurry had better flow ability and less yield stress. Above the critical water cut, the yield stress increased significantly with water cut. The yield stress increased with increasing static time and decreases with increasing temperature. Nevertheless, the coupling effect of temperature with water cut and wax content was complex. Below 3 wt% wax content, temperature only has a significant effect on the yield stress of slurries with 40% and 50% water cut. Above 3 wt% wax content, temperature has a significant effect on the yield stress of all slurries with a 20–50% water cut. No ice formation in the CP hydrate-forming mixtures at −4°C, and the dissociation temperature of the hydrate decreases as the concentration of CP in the oil phase decreases.

Hydrate Growth over a Sessile Drop of Water in Cyclopentane

Liquid cyclopentane is frequently used in hydrate formation studies as an analogue of natural gas because cyclopentane hydrates are stable above the ice melting point at ambient pressure. In this study, hydrate growth was established on a sessile water drop of 11 mm in diameter and 4.5 mm in height (volume of 0.25 mL) immersed in liquid cyclopentane. The hydrate formation mechanism and growth processes were observed optically over an extended range of subcooling temperatures from 5.1 to 15.2 °C, with the cyclopentane bulk temperature maintained in different experimental runs between 2.6 and −7.5 °C. Qualitative and quantitative comparisons were performed to confirm the absence of ice freezing during hydrate formation, and thus, the lack of contamination of the latter from the former in the experiments. Different transformations in the hydrate film morphology were registered from macroscopic observation over the considered range of subcooling temperatures, with the hydrate crystals composing the film taking the form of polyhedral, dendritic, or spherulitic structures. It was also found that the hydrate growth rate varied depending on the subcooling temperature, with the variation of the growth rate as a function of this temperature changing from a power to an (approximately) linear law with an increase in the degree of subcooling. We postulate that hydrate film growth can be governed by different mechanisms, whose roles change over the range of explored subcooling temperatures.

Crystal Dewetting at the Water–Guest Interface in Macropores Sidesteps the Hydrate Mass-Transfer Bottleneck

Unprecedented massive growth of fibrous cyclopentane hydrate on an activated carbon was shown recently to circumvent the mass-transfer bottleneck caused by hydrate crust at guest–host interfaces. Here, we generalize to other carbons and to porous silicas, confirming hydrate formation in surface macropores. Experiments with hydrophilic or -phobic porous substrates and with single glass capillary model pores elucidate the growth process. Surprisingly, wettability is of indirect importance. Detailed observation of unlimited single fibers with the better optical access and well-defined geometry of the glass model pores reveals the growth mechanism: crystal dewetting at pinned guest–host interfaces, in surface macropores in the case of porous substrates, where hydrophobicity serves only indirectly, to conduct the guest to the active interface. Fiber growth is closely analogous to the dewetted Bridgman process observed decades ago in microgravity. “Micro” or negligible gravity is provided here by the small size of the pores compared to the capillary length. Transposing the theory to the present system, we correlate fiber diameter and dynamic contact angles on the fiber and the pore wall, which in turn depend on the growth rate, hence on the supercooling. The model prescribes for generalization to further combinations of guest and porous substrates.

Blended hydrate seed and liquid promoter for the acceleration of hydrogen hydrate formation

The slow formation rate of hydrogen clathrate hydrate is one of the most challenging factors impeding the utilization of clathrate hydrate as a hydrogen storage media. Blending of a hydrate seed solution and a liquid phase thermodynamic promoter is introduced in this study to promote the formation of hydrogen hydrates for safe hydrogen storage. Cyclopentane hydrate seeds induced instantaneous growth of cyclopentane + hydrogen mixed hydrates by providing nucleation sites for hydrate formation. Increasing the amount of hydrate seeds accelerated the formation rate of hydrates at the early stage of the reaction because the surface area of hydrate crystals increased. However, the total storage capacity was not so high because the diffusion of hydrogen molecules into empty cages of pre-constructed hydrate crystals was difficult. This diffusion limitation was overcome by the addition of the cyclopentane liquid phase promoter for the simultaneous formation of cyclopentane and hydrogen hydrates with their porous vertical growth. Tetrahydrofuran, one of the most commonly used organic promoters for hydrogen hydrates, was not suitable for the blended hydrate seed and liquid promoter system because its miscibility with water hindered the formation of hydrogen-bond cages and did not induce vertical growth of porous hydrates. This study provides insights into the role of liquid promoter blended with hydrate seeds in enhancing formation of hydrogen hydrates as sustainable hydrogen storage.

Hydrate growth and agglomeration in the presence of wax and anti-agglomerant: A morphology study and cohesive force measurement

During deep-sea and ultra-deep-sea oil and gas exploitation, multiphase transmission lines are prone to be clogged by sediments produced by the various components in crude oils under extreme subsea conditions, such as hydrates, wax, resins, and asphaltenes. The pipelines face higher plugging risks when these deposits exist simultaneously. In order to elucidate the effects of wax and anti-agglomerants (AA) on hydrate growth and aggregation, microscopic morphology observation and cohesive force measurement of cyclopentane hydrate particles were conducted through a piece of equipment similar to the micromechanical force (MMF) apparatus. Results showed that in the low concentration of AA (0.05 wt%), hydrate particles experienced an approximately 10 % reduction in the profile area after converting water droplets to hydrate particles. Furthermore, the cohesive force between hydrate particles decreased from 8.57 ± 0.90 mN/m to 3.51 ± 0.43 mN/m as the AA concentration increased from 0.05 to 0.2 wt%. On the other hand, the presence of wax significantly altered the morphologies of hydrate particles. When wax coexisted with AA, the hydrate cohesive force was reduced by wax under low AA concentration (0.05 wt%) but increased under higher AA concentration. For a given concentration of AA, the hydrate cohesive force increased with the increasing wax content (from 0.1 to 0.3 wt%), indicating that wax crystals weakened the efficiency of AA, such as Span 80. Additionally, the effect of surface wetness of waxy hydrate particles on their cohesion was also investigated. The liquid bridge appeared between wet waxy hydrate particles, while the solid–solid contact existed between dry waxy hydrate particles. The cohesive force between dry waxy hydrate particles was smaller. Either liquid bridge or solid–solid contact that dominated hydrate cohesive force was affected by wax.

Continuous hydrate-based CO2 separation from H2 + CO2 gas mixture using cyclopentane as co-guest

CO2 separation from H2 + CO2 gas mixture is a necessary technology for a stable supply of blue hydrogen. Among CO2 separation technology, hydrate-based CO2 separation is an environmentally and economically superior technology. Cyclopentane (CP) was selected as guest compound to enable hydrate-based CO2 separation under thermodynamic conditions closer to normal pressure and temperature. Hydrate-based continuous CO2 separation experiments are conducted in the H2 + CO2 + CP + H2O system at 284 K. The results of these experiments showed that mole fraction of H2 in the gas phase reached 0.9 at the steady state in the H2 + CO2 + CP + H2O system after the CO2 was extracted via hydrate formation. At the same time, more H2 was incorporated into the mixed hydrate during this process as the concentration of H2 in the gas phase increases post hydrate formation. Therefore, it was demonstrated that hydrate-based CO2 separation was successful in H2 + CO2 + CP + H2O system at 284 K but there is also increase of energy costs caused by H2 loss. The PXRD results identified H2 + CO2 + CP hydrate as structure II hydrate. Although H2 + CO2 + Tetrahydropyran (THP) hydrate also forms structure II hydrate, more H2 is encapsulated in the H2 + CO2 + CP mixed hydrate than in the H2 + CO2 + THP mixed hydrate. This difference may be caused by the difference in the lattice constants of CP and THP hydrates, which arises from the difference in molecular size of CP and THP, from the differences between the large guest–host interactions, and from differences arising from hydrogen bonding of THP with the host water framework which can decrease the H2 holding capacity. In this study, it was revealed that the molecular diameter of the guest molecules need also to be considered in addition to the phase equilibrium conditions of the hydrates when selecting guest compound of hydrates.

Investigating cyclopentane hydrate nucleation and growth using microfluidics

The success of geological storage of carbon dioxide (CO2) in depleted oil and gas reservoirs relies among other aspects on the efficiency of CO2 injection, especially in the near-wellbore area where flow rates are high. CO2 hydrates pressure/temperature equilibrium conditions may be reached in this zone due to cooling associated with the Joule–Thomson effect; such CO2 hydrate formation may lead to strong injectivity loss and impair drastically the onsite well operations. In this study, cyclopentane hydrates (CPH) were employed as CO2 hydrate proxy (i.e. formation at atmospheric pressure) to mimic CO2 hydrate formation at higher pressure. In this study, the nucleation and growth processes were determined using a droplet-based in-house-microfluidic device. The generation of water droplets in cyclopentane liquid using the co-flow method was achieved. Trains of identical water droplets were stored in a serpentine channel. Each isolated droplet in this channel serves as a separate reactor. The temperature was controlled using a Peltier module to initiate hydrate nucleation at low temperatures. The isolated droplets provided the opportunity to statistically analyze the kinetic behaviors by varying key parameters, such as thermal history and water salinity. Detection of the onset of crystallization in water droplets over time and temperature allowed us to plot conversion curves based on imposed parameters. The effect of thermal history and dissociation temperature was first compared using pure water. This study marks the initial investigation into how NaCl influences CPH formation in microfluidic devices, focusing on isolated water droplets within serpentine tubes. The progression of ice nucleation, ice melting, the onset of CPH crystallization, CPH growth, and CPH dissociation are illustrated in water droplets exposed to changing temperatures. The addition of NaCl in the water during the procedure exhibited a noteworthy impact on CPH formations. With the same temperature profile, salt concentration delays nucleation (thermodynamic effect) and slows down growth. Our findings suggest that higher subcooling accelerates nucleation and growth rates. Initial lateral growth rates ranged from 4.22 μm/s to 2.14 μm/s, with a subcooling of 4.2 °C observed between 2 and 7 min for a pure water droplet.

Application of a biomimetic wellbore stabilizer with strong adhesion performance for hydrate reservoir exploitation

Natural gas hydrate (NGH) in marine is usually reserved in the pores or cracks of weakly cemented argillaceous siltstones. Moreover, the hydrates are susceptible to variations in temperature and pressure conditions when water-based drilling fluids (WBDFs) are drilled into hydrate reservoirs, leading to the hydrate in-situ decomposition and severe sand production. In this work, an inexpensive and facilely prepared biomimetic wellbore stabilizer with strong adsorption of multiple hydrogen bonds was prepared by fusing catechol-rich tannic acid (TA) and polyvinyl alcohol (PVA) with polyol hydroxyl adsorption function, referred to as TA-PVA complex (TA-PVA). TA-PVA was added to WBDFs to strengthen the NGH reservoir wellbore for ensuring the safety of drilling process in a wide temperature range (2-60℃). The microscopic characterization of TA-PVA and its cohesion mechanism with argillaceous siltstone was investigated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties of skeleton of the artificial hydrate cores were evaluated by compressive strength test, with maximum compressive strength reaching 0.45 MPa. And the adhesion force of TA-PVA to the probe modified by silica microsphere (PSM) was further studied by AFM. Meanwhile, the adhesion forces between TA-PVA and cyclopentane hydrate particles were measured at 1.5℃. Adhesion test results demonstrate that TA-PVA can bond clay particles, quartz sand and hydrate particles together. In detail, the adhesion force between TA-PVA and PSM reaches more than 164.46 mN/m, the adhesion force between TA-PVA droplet and cyclopentane hydrate particle reaches 43.19 mN/m. The differential scanning calorimetry (DSC)curves demonstrate that TA-PVA releases no heat between 0 and 60 °C, indicating that TA-PVA has no impact on the decomposition of NGH, showing the potential to maintain the integrity of NGH reservoir.

Rheological study of mixed cyclopentane + CO2 hydrate slurry in a dynamic loop for refrigeration systems

The use of CO2 hydrates as phase change materials is promising for secondary loop refrigeration, as these compounds present adjustable dissociation temperature that can be higher than 273.15 K and have high enthalpy of dissociation. In the present work, by using various promoters, cyclopentane (CP) in this study, the formation pressure of hydrates may be significantly lowered than CO2 hydrates. For their application as a secondary refrigerant, the rheological properties of mixed CP + CO2 hydrate slurry need to be controlled. The flow properties of CP and mixed CP + CO2 hydrate slurries were studied in a dynamic flow loop at different cyclopentane contents ranging from 3 wt% to 15 wt%, using a capillary viscometer based on Rabinowitch and Mooney equation. Rheological parameters (viscosity, flow behavior…) related to these two slurries were compared. The experimental results demonstrate that CP and mixed CP + CO2 hydrates slurries exhibit a shear thinning behavior and the viscosity values vary between 3 and 12 mPa.s-1 at [100–1000 s−1] for CP hydrates slurries and between 2 and 10 mPa s−1 at [100–1200 s−1] for CP + CO2 hydrates slurries. CP hydrate and CP + CO2 hydrate slurry viscosity is close to that of TBPB hydrate and lower than that of CO2 hydrate. Moreover, mixed CP + CO2 have shown a time-evolution of the rheological behavior.

Seawater desalination by coupling cyclopentane hydrate formation and capacitive deionization processes in the presence of Fe3O4 nanoparticles and magnetic field

This study investigates seawater desalination by coupling cyclopentane hydrate formation and capacitive deionization processes. High induction time, low conversion of water to hydrate, and low ion removal efficiency are the challenges of the hydrate desalination process. In order to reduce the cost of hydrate formation, cyclopentane was used as a hydrate former. Also, the promotion effects of Fe3O4 nanoparticles and magnetic field on the cyclopentane hydrate formation in pure water, seawater, and synthetic saline waters containing NaCl, KCl, CaCl2, and MgCl2 at different concentrations were investigated. The results showed that the Fe3O4 nanoparticles and magnetic field could improve the hydrate formation and the effect of Fe3O4 nanoparticles is greater than the magnetic field. However, the promoting effect on the induction time and removal efficiency was intensified when the Fe3O4 nanoparticles and the magnetic field were used simultaneously. The results of hydrate formation in seawater showed that the induction time in the presence of 0.07 wt.% Fe3O4 nanoparticles, magnetic field, and simultaneous use of both of them were reduced by 89, 22, and 92%, respectively. The ion removal efficiency reached 79% for Na+ and higher than 99% for K+, Ca2+, and Mg2+ when capacitive deionization was used as post-treatment.

Durable Hydrate-phobic Coating with In Situ Self-Replenishing Hydrocarbon Barrier Films for Low Clathrate Hydrate Adhesion.

Clathrate hydrate growth, deposition, and plug formation during oil and gas transportation causes blockage of pipelines. An effective strategy to solve this problem is to mitigate the hydrate formation and reduce its adhesion on pipe walls through a coating process. However, durability failure, corrosion, inability to self-heal, high cost, and strong hydrate adhesion remain unsolved issues. To address these challenges, in this work, we present an in situ self-replenishing nonfluorinated durable hydrate-phobic coating of candle soot particles. The candle soot coating reduces hydrate adhesion by promoting a thick barrier film of hydrocarbons between the hydrate and the soot coated substrate. The hydrocarbons permeating the soot coating display a high contact angle for water and inhibit the formation of water bridges between the hydrate and soot coated substrate. The spherical cyclopentane hydrate slides off easily on the candle soot coating inside the cyclopentane environment. The hydrate former, cyclopentane-water emulsion, and THF-water mixture have high contact angles as well as low hydrate adhesion on soot coating simultaneously. In addition, the coating is flow-induced long-term slippery, durable, low cost, anticorrosion, self-cleaning, and suitable for practical applications.

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.

Phase equilibrium conditions in cyclopentane hydrate forming systems coexisting with sodium chloride aqueous solution under atmospheric pressure and vacuum condition

The equilibrium condition measurements were performed in the cyclopentane clathrate hydrate forming systems coexisting with sodium chloride as a technological basis for the development of seawater desalination technology using clathrate hydrates. The experiments were performed in the system under vacuum condition in addition to the system under atmospheric pressure. The equilibrium conditions in the system under the vacuum condition are essential to accurately construct the phase diagram in the cyclopentane clathrate hydrate forming system without the effects of the surrounding air. The equilibrated phases were sodium chloride aqueous solution + cyclopentane clathrate hydrate + liquid cyclopentane + vapor cyclopentane in the system under the vacuum condition. The concentration of sodium chloride investigated in this study, wNaCl, was 0 ≤ wNaCl ≤ 0.210 in mass fraction. The equilibrium temperature in both systems decreased with increasing wNaCl. The equilibrium temperature at a fixed concentration of sodium chloride under the vacuum condition was lower than that under the atmospheric pressure. It was attributed to the compression by the atmospheric pressure in addition to the incorporation of molecules constituting the atmospheric air.