Cyclopentane Hydrate Formation Research Articles

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.

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.

Desalination of high-salt brine via carbon materials promoted cyclopentane hydrate formation

Significant advances in seawater desalination have been made to meet the world's increasing demand for clean water. However, the accompanying hypersaline concentrate discharge has negative environmental impact and is challenging for treatment. Herein, we demonstrate the potential of hydrate-based desalination (HBD) in treating brine with concentrations up to 16 wt%. It is difficult for hydrate nucleation to occur in strong brine without nucleation agents, as this results in lengthy induction time, the challenge can be resolved using carbon materials. We found that crystallinity and surface compositions have critical impact on cyclopentane hydrate formation and desalination efficiency. Carbon material with high crystallinity is more effective in inducing hydrate nucleation in NaCl solution due to the properly tuned interface hydrogen-bonding network as confirmed by Raman spectra. The improved hydrophilic property would degrade the desalting efficiency due to the tightly trapped brine among carbon materials and hydrate crystals. Although high concentration of NaCl would hinder hydrate formation, leading to a lower water recovery, desalting efficiency unexpectedly increases due to interfacial pre-melting in the presence of salt, reaching up to 79% in 16 wt% NaCl. The findings would help to identify and fabricate the good hydrate promoters used for HBD for treating hypersaline brine.

Numerical Simulation of Multiphase Flow in a Biaxial Agitator for Cyclopentane Hydrate Formation

Numerical Simulation of Multiphase Flow in a Biaxial Agitator for Cyclopentane Hydrate Formation

Kinetic and rheological investigation of cyclopentane hydrate formation in waxy water-in-oil emulsions

Hydrates and waxes are supposed to coexist in the deep-water pipelines under suitable conditions of low temperature and high pressure. Understanding the effect of precipitated wax crystals on hydrate formation and rheological properties of hydrate slurry is crucial to the flow assurance in offshore petroleum production. In this work, a stress-controlled rheometer was used to carry out the rheological experiments for investigating the impact of wax crystals on hydrate formation and yield property of hydrate slurry. The effects of wax content and water cut on cyclopentane (CP) hydrate nucleation and growth were investigated in terms of the measured viscosity data. Log-normal distribution could well fit the probability density histogram of CP hydrate critical time. The logarithmic mean values of CP hydrate critical time decreased with increasing water cut but increased with increasing wax content in water-in-oil (w/o) emulsions. Semi-empirical models were proposed to describe the inhibitory effect of wax crystals on CP hydrate nucleation kinetics by considering the inhibition of mass transfer based on the Freundlich and Langmuir adsorption functions, respectively. Hydrate slurry viscosity rate showed the two-stage characteristics in wax-free w/o emulsions, while four stages could be clearly observed in waxy w/o emulsions. The maximum values of hydrate slurry viscosity rate and calculated hydrate effective volume fraction decreased with increasing wax content. Hydrate growth time was gradually extended as wax content increased. Furthermore, the measured yield stress and yield strain increased with increasing wax content at different water cuts, which was associated with the multiple effect of capillary bridge between hydrate particles, spatial network of wax crystals and coalescence of water droplets. At last, compared to the stress ramp rate, the influence of annealing time on yield stress was more significant.

Rheology Impact of Various Hydrophilic-Hydrophobic Balance (HLB) Index Non-Ionic Surfactants on Cyclopentane Hydrates.

In this study, series of non-ionic surfactants from Span and Tween are evaluated for their ability to affect the viscosity profile of cyclopentane hydrate slurry. The surfactants; Span 20, Span 40, Span 80, Tween 20, Tween 40 and Tween 80 were selected and tested to provide different hydrophilic–hydrophobic balance values and allow evaluation their solubility impact on hydrate formation and growth time. The study was performed by using a HAAKE ViscotesterTM 500 at 2 °C and a surfactant concentration ranging from 0.1 wt%–1 wt%. The solubility characteristic of the non-ionic surfactants changed the hydrate slurry in different ways with surfactants type and varying concentration. The rheological measurement suggested that oil-soluble Span surfactants was generally inhibitive to hydrate formation by extending the hydrate induction time. However, an opposite effect was observed for the Tween surfactants. On the other hand, both Span and Tween demonstrated promoting effect to accelerate hydrate growth time of cyclopentane hydrate formation. The average hydrate crystallization growth time of the blank sample was reduced by 86% and 68% by Tween and Span surfactants at 1 wt%, respectively. The findings in this study are useful to understand the rheological behavior of surfactants in hydrate slurry.

Functionalized Nanoparticles for the Dispersion of Gas Hydrates in Slurry Flow.

Gas hydrates are crystals that can form in oil and gas production. Their agglomeration in flowlines may disrupt the normal production. One current strategy of hydrate management is to inject an anti-agglomerant, a type of low-dosage hydrate inhibitor that prevents hydrate agglomeration. Concerns in the use of these chemicals include their toxicity, cost, and environmental impacts. In this study, we exploited functionalized nanoparticles in place of anti-agglomerants to produce hydrate slurry, with the potential benefit of nanoparticles to be more environmentally friendly and conveniently recyclable. We coated 256 nm spherical silica nanoparticles with different hydrophobicity and evaluated their performance for the hydrate dispersion at atmospheric and high pressure. Nanoparticles with moderate hydrophobicity stabilized oil-in-water (O/W) or water-in-oil (W/O) emulsions. Direct visualization of the cyclopentane hydrate formation from the nanoparticle-stabilized emulsions revealed different morphologies of hydrate particles depending on whether the nanoparticles prevented agglomeration. We also measured the apparent viscosity of a hydrate–nanoparticle mixture using a high-pressure rheometer. Nanoparticles with moderate hydrophobicity during hydrate formation slowed the viscosification, reduced the maximum viscosity, increased the water conversion, and ultimately helped to maintain a low steady-state viscosity. Increasing nanoparticle or salt concentrations also improved the gas hydrate dispersion. Our study demonstrated the great potential of using nanoparticles in preventing agglomeration of gas hydrates under realistic pipeline flow conditions.

An in situ method on kinetics of gas hydrates

Gas hydrate formation is a high-risk and common flow assurance problem in subsea oil production plants. The modern strategies to mitigate hydrate formation have switched from thermodynamic inhibition to risk management. In this new mitigation strategy, hydrate formation is allowed as long as it does not lead to plugging of pipelines. Thus, understanding the growth kinetics of gas hydrates plays a critical role in risk management strategies. Here, we report a new accurate and in situ approach to probe the kinetics of gas hydrate formation. This approach is based on the hot-wire method, which probes the thermal properties of the medium surrounding the hot-wire. As the thermal properties of gas hydrate and its initial constituents are different, variation in these properties is used to probe kinetics of hydrate growth front. Through this in situ method, we determine kinetics of cyclopentane hydrate formation in both mixing and flow conditions. The findings show that at ambient pressure and a temperature of 1-2 °C, the hydrate formation rate under mixing condition varies between 1.9 × 10-5 and 3.9 × 10-5 kg m-2 s-1, while in flow condition, this growth rate drops to 4.5 × 10-6 kg m-2 s-1. To our knowledge, this is the first reported growth rate of cyclopentane hydrate. This in situ approach allows us to probe kinetics of hydrate formation where there is no optical access and provides a tool to rationally design risk management strategies for subsea infrastructures.

A droplet-based millifluidic method for studying ice and gas hydrate nucleation

We design and implement a simple and versatile droplet-based millifluidic method for investigating nucleation and growth processes in crystal-forming aqueous systems. It consists in generating and storing in a transparent capillary a train of identical and regularly-spaced droplets of an aqueous phase in a carrier oil phase, and then in video-monitoring crystal nucleation and subsequent growth and melting events as temperature and/or pressure are varied. Compared to previous investigations, the novelty is the possibility of working with aqueous solutions containing dissolved gas under controlled pressure, thus opening the way to gas hydrate studies. In the absence of dissolved gas, i.e., at ambient pressure, we observe ice nucleation to be weakly promoted by titanium oxide and montmorillonite particles, and strongly promoted by silver iodide, in agreement with literature results. Ice nucleation is also promoted when the carrier oil is more wetting towards the capillary, which is the case for fluorinated oil as compared to n-hexane. With cyclopentane, a hydrate-former, as the carrier oil, and dissolved CO2, also a hydrate-former and a “help gas” for cyclopentane hydrate formation, we find evidence for hydrate nucleation along with that of ice, and monitor the different solid phases as temperature varies.

Investigation of salt removal using cyclopentane hydrate formation and washing treatment for seawater desalination

Salt removal via formation of gas hydrate was investigated by experimental measurement of the salt concentration in filtered water and water retrieved from hydrate crystals. Gas hydrate formation was carried out at 277.15K, using seawater of 3.4wt% salinity and 3mol% cyclopentane to water-cyclopentane mixture. Single-stage hydrate formation followed by filtration removed 63% of the salt ions. Successive washing treatment with 274.15 and 277.15K freshwater was applied with different amounts of washing water, and several major cations and anions in seawater were analyzed in each treatment step. Ions having larger radii showed less salt removal by hydrate formation, and salt removal decreased as the conversion of water to hydrate progressed. However, salt removal was improved by washing treatment to nearly the same degree regardless of the kind of salt ions and the salt removal efficiency improved up to 42% more than that of filtration only. The results presented in this study can be used as basic design values for the development of a hydrate-based desalination process.

Can cyclopentane hydrate formation be used to screen the performance of surfactants as LDHI anti-agglomerants at atmospheric pressure?

Anti-agglomerants (AAs) are a class of low dosage hydrate inhibitors (LDHIs) that have been used commercially in oilfield operations for almost two decades to prevent the plugging of flow lines with gas hydrates. AAs are surfactants and the ranking of their AA performance usually requires high pressure equipment with the ability to collect visual data to determine the plugging tendency. A simple but crude screening method for determining the AA performance of a chemical has been developed using cyclopentane hydrate at atmospheric pressure. The method requires is limited by the maximum subcooling allowable, which for our system was found to be 5.3°C from hydrate dissociation experiments if ice formation is to be avoided. The reproducibility of the screening method was found to be good although no hydrate formation occurred for some chemicals with significant kinetic inhibition activity due to the low subcooling. These chemicals were usually the commercial AAs which have good crystal growth inhibition properties. Therefore, the method was not able to distinguish good AA performance between the best AAs. In general, the AA performance results with cyclopentane hydrate correlated well with those obtained in high pressure natural gas hydrate equipment. Those surfactants with poor results with the cyclopentane hydrate method gave also poor performance using the gas hydrate method. However, some discrepancies between the results for the two test methods were found, which is sufficient to conclude that the cyclopentane hydrate test method is only a simple, crude method for first time screening of a surfactant to determine if it has any potential for further testing in high pressure gas hydrate systems.

Kinetic promotion of non-ionic surfactants on cyclopentane hydrate formation

Clathrate hydrates are among the most important cold storage materials studied which are known to enhance the coefficient of performance in air conditioning systems. In the present work, the kinetics of cyclopentane (CP) hydrate formation is investigated in an atmospheric stirred reactor, with and without additives. The effects of 14 surfactants and polymers on hydrate promotion are experimentally investigated. These surfactants and polymers belong to the family of Nonyl Phenol ethoxylates (NPE), Lauryl Alcohol Ethoxylates (LAE), Poly Ethylene Glycols (PEG), Ethylene Oxide/Propylene Oxide copolymer (EO/PO), polyoxyethylene sorbitan monopalmitate (Tween), butyl phenol ethoxylates (TritonX-100), and sodium alkyl sulfate. The results indicate that while the CP/water system exhibits high induction time and low formation rate, addition of surfactants can highly decrease the induction time and increase the formation rate. Among the studied surfactants, LAE8EO, TritonX-100 and NPE6EO were the best. The rate of hydrate formation is increased 1533% and the induction time is lowered to 0.04 its original value. Also our studies show that surfactants that form oil in water emulsions in general can promote hydrate formation better than surfactant that forms water in oil emulsions. For better understanding of the promotion mechanism, the interfacial tension (IFT) of CP/water, in the presence of some surfactants, is measured. Results show that addition of TritonX-100 can lower the CP/water IFT from 31.6 to 2.1mN/m. The IFT data along with a simple mass transfer analysis are utilized to uncover the CP hydrate promotion mechanism.

Investigation into the strength and source of the memory effect for cyclopentane hydrate

The memory effect for cyclopentane hydrate formation has been investigated for various degrees of superheating and time periods. It was found that provided the superheating above the equilibrium temperature for cyclopentane hydrates (7.7°C) was no more than 2–3°C, we could consistently obtain hydrates much faster during cooling to 0.0°C than if hydrates were formed from the liquids for the first time. The memory effect did not always disappear with as much as 8.4°C superheating for 20min, or with 1.5°C superheating for 20h. It was also found that transference of a small amount of water from melted cyclopentane hydrates (made with no more than 2–3°C superheating) to a much larger amount of fresh water and cyclopentane, with no previous cyclopentane history, initiated cyclopentane hydrate formation significantly faster than using the unspiked fresh water alone. This suggests that the memory effect is in the bulk water phase and is probably due to residual clathrate hydrate structure.

Can cyclopentane hydrate formation be used to rank the performance of kinetic hydrate inhibitors?

The equilibrium temperature for cyclopentane hydrate formation is approximately 7.7°C. Since these hydrates are Structure II and are formed at atmospheric pressure it was of interest to determine if cyclopentane hydrate-forming fluids could be used in the performance ranking of kinetic hydrate inhibitors (KHIs), avoiding the use of high pressure equipment and flammable gases. We have carried out a series of tests with well-known classes of KHIs in four parallel cells using cyclopentane hydrate-forming fluids. The superheated hydrate method was used since it was found that cyclopentane hydrate formation was inconveniently slow using fluids with no hydrate history. The amount of KHI needed to obtain significant kinetic inhibition was found to be in the region of 100–200ppm, a fraction of that needed for high pressure Structure II gas hydrate inhibition with the same KHI. This may be due to the fairly low subcooling used (7.8°C) as well as the lower solubility of cyclopentane in water compared to small hydrocarbon hydrate-formers at elevated pressures. The results of testing a range of KHIs using this superheated CP hydrate test method correlated fairly well with tests carried out on Structure II-forming gas hydrates in high pressure stirred autoclaves, but there were some notable exceptions, which meant that this method is unlikely to be reliable for ranking all KHIs under atmospheric conditions. Furthermore, raising the KHI concentration from 100ppm to 400ppm did not lead to the expected increase in KHI performance for all the KHIs tested.

Surfactant Effects on Hydrate Crystallization at the Water–Oil Interface: Hollow-Conical Crystals

Clathrate hydrates are icelike crystalline compounds with small guest molecules trapped inside the cages of hydrogen bonded water molecules. Clathrate hydrate crystal growth is studied for the specific case of the guest molecule cyclopentane. Cyclopentane hydrate formation is visualized at a millimeter-scale water drop. Crystal formation takes place at the water–organic interface and has been shown in prior work to occur in a three-step sequence of nucleation, lateral surface growth, and radial growth. This study describes cyclopentane hydrate crystal characteristics during the lateral surface growth and demonstrates the effect of the oil-soluble surfactant sorbitan monooleate (Span 80) on the hydrate crystal growth. A faceted polycrystalline hydrate shell is formed around the water drop in the absence of surfactant. A unique hollow-conical crystal is observed at Span 80 concentrations greater than 0.01% by volume in cyclopentane; the critical micelle concentration is 0.03% Span 80. The conical crystals h...

Calorimetric investigation of cyclopentane hydrate formation in an emulsion

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

Effect of subcooling and amount of hydrate former on formation of cyclopentane hydrates in brine

As a concept for a new water desalination technology, the use of gas hydrates is under development. In support of this work, experiments have been conducted to observe the behavior of cyclopentane hydrates and to provide data on thermodynamics, kinetics, the effective hydrate number and the purity of the water recovered from the hydrates. The cyclopentane hydrate formation experiments are performed at subcooling temperatures of 5.6 K and 3.6 K at atmospheric pressure. The brine used is 3 wt.% NaCl. The results show that the kinetics of hydrate formation at a subcooling of 3.6 K is significantly slower than the kinetics for a subcooling of 5.6 K. The effective hydrate number seems to be a function of the subcooling temperature, with 3.6 K subcooling giving a number close to the theoretical value. The quality of the desalinated water is strongly dependent on the experimental procedure and the general observation is that subcooling at 5.6 K provides better purification of the water.

Evaluation of rate of cyclopentane hydrate formation in an oscillatory baffled column using laser induced fluorescence and energy balance

We report a novel method using laser induced fluorescence (LIF) for observing cyclopentane hydrate formation in an oscillatory baffled column (OBC). In LIF, a dye fluoresces in a hydrate system when induced by a laser; this highlights the areas in which hydrates are present, allowing the hydrate formation regimes to be identified and rates evaluated. Using temperature measurements of the system, the rates of hydrate formation are also determined by a thermal method. The work shows that there is a high correlation between the LIF and the thermal techniques in obtaining kinetic information on cyclopentane hydrate. The results indicate that there are possibly three mechanisms governing hydrate growth. With the absence of mixing, a film formation is observed. At high mixing intensities uniform droplet dispersion is resulted, where fluid mechanics is the controlling parameter. At low mixing conditions a combination of the two mechanisms co-exists, interfacial mechanics is thought to be the dominant factor. The trends in the rates of hydrate formation are different in each of these regimes.