Hydrate Formation Experiments Research Articles

Effects of leucine on hydrate formation: A combined experimental and molecular dynamics study

Compared to conventional natural gas storage and transportation methods, hydrates offer a safer, more compact alternative with broad future potential. To enhance hydrate formation, there has been considerable interest in environmentally friendly and cost-effective amino acid promoters, such as leucine. This study utilized a transparent vessel for CH4 hydrate formation experiments, identifying the optimal 0.5–0.6 wt% leucine concentration, which led to enhanced gas consumption, shorter induction time, and maximum gas storage density. In the leucine system, hydrates exhibited distinctive branching growth on container walls, both upward and downward. The formation of numerous microchannels amplified capillary effects, enhancing gas–liquid contact and fostering hydrate formation. Simultaneously, isobaric-isothermal molecular dynamics (MD) simulations integrated system growth configurations, structural parameters, radial distribution functions, energy barriers and mean square displacements, unveiling leucine’s microscopic impact on hydrate formation. Simulation results unequivocally show that leucine significantly accelerates CH4 hydrate growth by momentarily adsorbing at the solid–liquid interface, expediting water molecule ordering into cage-like structures. Leucine also enhances water molecule structural order around the mobile leucine molecule. Moreover, leucine lowers the energy barrier for methane transitioning from gas to liquid, facilitating gas molecule diffusion into the liquid phase and affording plenty interaction time for water and methane molecules, thereby providing favorable conditions for hydrate formation. These findings provide crucial perspectives for future research in the field of eco-friendly hydrate promoters, paving the way for innovative solutions in natural gas storage and transportation.

Pore Water Conversion Characteristics during Methane Hydrate Formation: Insights from Low-Field Nuclear Magnetic Resonance (NMR) Measurements

Understanding the conversion characteristics of pore water is crucial for investigating the mechanism of hydrate accumulation; however, research in this area remains limited. This study conducted methane hydrate formation experiments in unconsolidated sands using an in-house low-field nuclear magnetic resonance (NMR) system. It focused on pore water conversion characteristics and influencing factors such as initial water saturation and sand particle sizes. Results show that methane hydrate formation enhances the homogeneity of the effective pore structure within sand samples. The conversion rate of pore water is significantly influenced by differences in heat and mass transfer capacity, decreasing as initial water saturation and sand size increase. Pore water cannot be fully converted into hydrates in unconsolidated sands. The final conversion ratio of pore water in water-poor sand samples nears 97%, while in water-rich sand samples, it is only 65.80%. Sand particle size variation has a negligible impact on the final conversion ratio of pore water, with ratios exceeding 94% across different particle sizes, differing by less than 3%.

Pore-scale investigation on the morphology evolution and micro-mechanism of methane hydrate formed from free gas and dissolved gas

The distribution characteristics of gas hydrates in the pores of sediments are critical to predict the macroscopic properties of hydrate reservoirs and the efficient production of gas hydrates. In this study, the experiments of methane hydrate formation were conducted in a glass micromodel, and the morphology evolution of hydrate formed from the free gas and dissolved gas in the pores were observed through a video microscope. Observation results showed that the hydrate formed from free gas grew preferentially along the gas–water interface and subsequently toward the center of the gas phase. For the hydrate formed from dissolved gas, it was preferentially occurred on the surface of the hydrate crust formed from free gas and gradually grew toward the water phase. The hydrate formation rate was determined by the concentration of methane molecules in surroundings water. The hydrate formed from free gas was porous structure and composed of many tiny hydrate crystals, and the hydrate formed from dissolved gas was smooth and transparent polyhedral hydrate crystal. For the hydrate formed by free gas, the occurrence pattern of hydrate in the pores might change from the grain-cementing to the contact-cementing or the patchy. The occurrence pattern of the hydrate formed from dissolved gas could be the pore-filling or the load-bearing. This study could be helpful for explaining the phenomenon of macro-experiments, the model construction for the macro-properties of hydrate-bearing sediments, and the exploring of gas hydrates reservoirs.

CO2 capture through gas hydrate formation in the presence of polyethyleneimine-surface-grafted clay

CO2 capture through gas hydrate formation was performed using a stirring-type vessel in the presence of nanoclay and polyethyleneimine-grafted nanoclay. First, the grafting process was implemented via the wet impregnation method. The nanoparticles were characterized using FT-IR, FESEM, EDS, BET, XRD, TGA, Zeta potential, and DLS analyses. The characterization analyses confirmed surface-grafting of the nanoclay. Then, the hydrate formation experiments were implemented at three various nanoparticle loadings (200, 400, and 500 ppm). Water-to-hydrate conversion, CO2 gas consumption, apparent rate constant, and hydrate storage capacity were obtained and compared. Prior to conducting the CO2 hydrate formation experiments in the presence of nanoparticles, the rocking-type and stirring-type vessels were compared to evaluate the hydrate formation rate (using pure water). Stirring-type vessel exhibited higher hydrate formation rates than rocking-type vessel along with improved gas storage performance which resulted in a 22.4% increase in CO2 consumption. Thus, the effect of additives was examined using the stirring-type vessel. Surface-grafted nanoclay led to higher CO2 consumption compared to nanoclay at all concentrations. Using 500 ppm of modified nanoclay, grafted by 50 mass% polyethyleneimine (PEI) solution as additive, the maximum enhancement of CO2 consumption in the hydrate phase in comparison with pure water was obtained, along with the greatest water to hydrate conversion value (39.67). This study introduces a new technique by modifying nanoclay with PEI to improve CO2 storage in gas hydrate phase, presenting potential advancements in gas storage technology.

Novel core–shell and recyclable gas hydrate promoter for efficient solidified natural gas storage

The storage and transportation of gases, including hydrogen, methane, and carbon dioxide in the form of gas hydrates, have recently garnered considerable attention. The practical implementation of gas hydrates crucially depends on the development of efficient and reusable promoters. In this study, novel core–shell magnetic nanoparticles (CSNs) developed as recyclable promoter to enhance gas uptake. Hydrate formation experiments indicated that the storage capacity can reach up to 132.7 ± 1.4 v/v and 160.6 ± 2.5 v/v in CSNs and CSNs + SDS solutions, respectively. Compared to pure water and SDS solution, the initial methane consumption rate (0.5972 mol/h) of CSNs increased by 12.2 times and 1.08 times at 3000 ppm, respectively. CSNs exhibited favorable characteristics in terms of cycling ability and preventing foam formation during repeated methane hydrate formation and dissociation experiments. Furthermore, the combination of CSNs and SDS resulted in a 72 % reduction in hydrate nucleation induction time and a 58.3 % decrease in foam formation ability compared to the sole use of SDS. In comparison to pure water, the addition of CSNs increased the onset temperature of hydrate formation by 4 °C and reduced the driving force required for methane hydrate formation. Additionally, molecular dynamics simulation studies revealed that CSNs effectively improved the amount of the ordered water structure, hydrate cage formation, and the growth state of methane hydrates. These properties make CSNs promising for potential use in the storage and transportation of gas, considering the economic and environmental advantages associated with the use of promoters.

Amino acid-assisted effect on hydrate-based CO2 storage in porous media with brine.

CO2 storage as hydrates in porous media is a promising method for storing carbon dioxide (CO2). However, the sluggish formation kinetics of hydrates urge the need to focus on the use of additives (promoters) to accelerate hydrate kinetics. This study investigates the effect of amino acid solutions in brine on CO2 hydrate formation and dissociation kinetics in quartz sand particles QS-2 (0.6-0.8 mm) with 38% porosity. The amino acids l-methionine (l-meth), l-isoleucine (l-iso), and l-threonine (l-threo) were studied at 0.2 wt% using an autoclave hydrate reactor at 4 MPa and 274.15 K in the presence and absence of salt (3.3 wt% NaCl) in 100% water saturation. The hydrate dissociation kinetics was studied at a temperature of 277.15 K. These conditions represent the normal seabed temperature range in Malaysia and hence were used for testing CO2 hydrate formation and dissociation kinetics in quartz sand in this study. Further, CO2 hydrate formation and dissociation experiments were conducted with sodium dodecyl sulphate (SDS) and brine systems as standards for comparison. The findings reveal the best kinetics for l-meth exhibiting the highest CO2 hydrate storage capacity. l-meth recorded a gas-to-hydrate conversion ratio of about 93% at 0.2 wt% in quartz sand with brine. Moreover, l-meth exhibited the lowest hydrate dissociation rate compared to l-iso and l-threo systems, thereby enhancing CO2 hydrate stability in quartz sand. Comparatively, l-meth enhanced the storage capacity by 36% and reduced the induction time by more than 50% compared to conventional promoter SDS in quartz sand with brine, suggesting it to be favorable for CO2 storage applications. CO2 hydrate nucleation time was predicted in quartz sand with and without the best-studied amino acid l-meth system with high prediction accuracy and an absolute average deviation of 2.4 hours. The findings of this study substantiate the influence of amino acids in promoting the storage capacity of CO2 in sediments as hydrates.

Investigation of flow and viscosity characteristics of hydrate slurries within a visual-loop system

With the gradual advancement of oil and gas exploration into deep offshore, the hydrate blockage has emerged as a critical concern for the flow assurance. We conducted constant-velocity hydrate formation and variable-velocity rheology experiments with a novel visual-loop to analyze slurry flow and viscosity change in pipelines. Results showed staged pressure variations during hydrate formation-aggregation-deposition process, and it could be analyzed judiciously with a developed viscosity model. Initially, hydrates dispersed as small flocculent particles with minor aggregation, gradually raising differential pressure, and the critical viscosity model parameter, hydrate aggregation rate (m) was <1. Subsequently, particle aggregation and wall adhesion dominated, resulting in reduced hydrate flow volume and possible blockage of special pipelines (e.g., dead-leg), with m-values >1. Finally, as hydrate growth continued, substantial adhesion to the pipeline reduced flow diameter, significantly increasing blockage risk. However, the addition of sufficient surface-active ingredients improved hydrate dispersibility and enabled the slurry to maintain the first stage, exhibiting long-term stability with an m-value <1. Additionally, the apparent viscosity of the hydrate slurry within the pipeline was accurately determined utilizing a novel approach, accounting for its yield-pseudoplastic behavior. The calculated viscosities closely matched post-sampling rheometer measurements, and were effectively predicted by the developed viscosity model.

Micro kinetic analysis of the CO2 hydrate formation and dissociation with L-tryptophan in brine via high pressure in situ Raman spectroscopy for CO2 sequestration

Hydrate-based CO2 sequestration (HBCS) is widely recognized as a promising, long-term, and stable approach for CO2 sequestration, but its slow formation kinetics in saline systems pose a significant challenge. In order to address this challenge, this experimental study investigated the potential of L–Tryptophan (L–Trp) as a CO2 hydrate kinetic promoter in deionized water and brine systems. A high-pressure reactor coupled with in situ Raman spectroscopy was used to examine macro-level kinetics and micro-level Raman spectra. The CO2 hydrate formation experiments were conducted at 3.5 MPa and 275.15 K, with different L–Trp concentrations (0–3000 ppm) in deionized water (DI) and brine systems. Raman spectra were monitored throughout the hydrate formation process, identifying distinct peaks corresponding to dissolve CO2, CO2 hydrates, and water activity. The experimental results indicate that the addition of 1000 ppm L–Trp in deionized water significantly enhances CO2 uptake by 3.6–fold and promotes hydrate formation kinetics by 3.3–fold compared to the system without L–Trp. In the brine system (3.5 wt% NaCl), the optimal L–Trp concentration was found to be 2000 ppm, leading to a 1.5-fold increase in CO2 uptake. Remarkably, L–Trp not only enhances the formation kinetics but also facilitates dissociation and CO2 recovery in DI water. Nevertheless, the presence of NaCl hinders the promoting effect of L–Trp on the dissociation kinetics. These findings represent a significant advancement in feasible HBCS technology for CO2 sequestration.

Experimental study on effects of non-ionic anti-agglomerants in preventing deposition of hydrate particles microscopically and macroscopically

Non-ionic anti-agglomerants (AAs) are important agents to prevent hydrate deposition. In this study, the microscopical experimental results show that the adhesion force between hydrate particle and droplet on wall surface mainly depends on the force of the liquid bridge under low subcoolings; while it is dependent on the resultant force of the liquid bridge and hydrate shell under high subcoolings. Below the concentration of 2 wt%, the optimal concentrations of CDEA and AEO-9 to reduce the adhesion are 0. 5 wt% and 0. 1 wt%, respectively. The adhesion force decreases gradually with the increase of their concentrations when their concentrations are lower than the optimal values, but gradually rises with the increase of their concentrations when higher than the optimal values. Moreover, the hydrate formation experiments in a stirred reactor show that the feedback torques are the smallest at the optimal concentrations of them, which is consistent with the results of the microscopical experiments.

Kinetic studies of the secondary hydrate formation in porous media based on experiments in a cubic hydrate simulator and a new kinetic model

The challenge of secondary hydrate formation (SHF) is frequently encountered in hydrate formation and dissociation experiments. However, there is currently a lack of modeling theory of SHF kinetics in the field and laboratory tests. In this work, the hydrate formation experiments concerning the SHF are carried out in a cubic hydrate simulator (CHS), where the pressure profiles and temperature spatial distributions are measured. A new kinetic model of hydrate formation integrating hydrate pore-scale morphology and SHF characteristics is developed. The newly developed model with unified kinetic parameters is employed in the Tough + hydrate (T + H) simulator to duplicate the experiment processes numerically, which achieves excellent agreement with the experimental data. The results show that the evolutions of the spatial distributions of the temperature and hydrate saturation behave in heterogeneous manners in the hydrate formation processes. This also reveals that the SHF can significantly exacerbate the hydrate heterogeneity in the CHS. Two additional experiments and comparisons with currently available models have validated the feasibility and accuracy of the new model. This work provides a reliable and adaptable model for describing the entire lifecycle of the hydrate formation kinetics in the porous media.

Purification of Industrial Effluent by Gas Hydrate-based (HyPurif) Process

This study presents a sustainable HyPurif process for managing and recycling industrial water effluent, utilizing gas hydrate-based technology to purify complex effluent. This work purifies two effluents: one from a wastewater treatment plant (WWTP) and the other from a spent caustic treatment plant (SCTP). Various hydrate formers, including propane, HFC134a, and cyclopentane (6 mol %), were selected, as they typically form hydrates closer to ambient conditions. Hydrate formation experiments with effluent water were performed at 278.30 K using pure propane and HFC134a gas. Based on the kinetics of hydrate growth, the study was extended to a mixture (50:50%) of propane and HFC134a, operating at a pressure of 0.6 MPa. The mixture of propane and HFC134a has shown the desired result of forming the hydrate in the gas phase and having high separation efficiency. The results showed that the formation and dissociation of hydrates resulted in a separation efficiency of 80–95%. For instance, in the purified water, the biological oxygen demand (BOD) decreased from 2097 mg/L in the effluent sample to 220 mg/L in purified water (purification efficiency of 90.5%). The chemical oxygen demand (COD) decreased from 3100 mg/L in the effluent sample to 503 mg/L in purified water (purification efficiency of 84%). Total dissolved solids (TDS) were reduced from 89,632 mg/L in the effluent water to 14,698 mg/L in purified water (purification efficiency of 84%). Total suspended solids (TSS) were reduced from 35 mg/L in the effluent water to 3.5 mg/L in purified water (purification efficiency of 90%). However, the purification efficiency for free ammonia and residual chlorine was lower. The concentration of free ammonia decreased from 7 mg/L in the effluent sample to 1.89 mg/L in the purified water (purification efficiency of 73%), and residual chlorine reduced from 0.8 mg/L in the effluent sample to 0.2 mg/L in the purified water (purification efficiency of 75%). Water recovery of ≥40% was achievable per pass, which could be increased, but at the expense of purification efficiency. To the best of our knowledge, this is the first study on the purification of such complex wastewater containing organic and inorganic compounds, heavy metals, and various minerals using the HyPurif process.

Growth behavior and resource potential evaluation of gas hydrate in core fractures in Qilian Mountain permafrost area, Qinghai-Tibet Plateau

The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment, due to its well-developed fractures and abundant gas sources. Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area. The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area. The formation and distribution characteristics of multi-component gas hydrates in core samples were observed <em>in situ</em> by X-ray Computed Tomography (X-CT) under high pressure and low temperature conditions. Results show that hydrates are mainly formed and distributed in the fractures with good connectivity. The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8% and 60.67% in two different core samples. This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples. Based on the field geological data and the experimental results, it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×10¹³ m³, with a resource abundance of 8.67×10⁸ m³/km². This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.

Experimental investigation and modelling of the hydrate formation kinetics based on hydrate pore-scale distribution in porous media

Hydrate technology has a bright future for innovations in water, energy, and environmental applications. A reliable and applicable kinetic model of gas hydrate formation is essential for developing hydrate technology. In this work, the experiments of methane hydrate formation with different water saturation SA are conducted in the Cubic Hydrate Simulator (CHS), where the pressure profile and temperature distribution are measured. A new kinetic model integrating hydrate pore-scale distribution is established, assuming that the reaction area AS is controlled by the aqueous phase surface area along the gas-soluble direction. This new model is employed to replicate the experimental process numerically by the history-matching method, and the intrinsic reaction rate constant K0 is determined to be 850.0 mol/m2/Pa/s. In addition, we quantitatively distinguish the characteristics of the water pore-scale distribution in the excess-water, cementing-water, and excess-gas environments. The new model has been validated to be more excellent than those with four currently available models for the hydrate formation, and the sensitivities of the kinetic parameters are discussed in detail. The results show that the spatial distributions of the temperature T and hydrate saturation SH spatial distribution are heterogeneous in CHS due to the phase change and heat transfer effect. The excellent performance of the hydrate formation kinetics gives us strong confidence in the reliability and accuracy of the new model. This provides reliable predictions and mechanistic understandings of hydrate formation kinetics in the porous media.

Investigation on Hydrate Formation and Viscosity of the Gas–Water System in Lingshui Gas Field of South China Sea

With gas production moving into the deep sea, the prediction of hydrate formation and blockage prevention are of great significance in flow assurance. In this work, hydrate formation experiments at a wide range of pressures and temperatures based on the production conditions of the Lingshui gas field were conducted by a high-pressure rheometer, and the evolution of viscosity was investigated. The experimental results showed that the slurry viscosity changed in stages during the formation of the hydrate, and the aggregation of hydrate particles was the essential cause of the significant increase in viscosity. The more severe the temperature and pressure conditions, the faster the hydrate formation and the greater the tendency of increasing viscosity. In experiments, the formation of hydrates would lead to severe blockages when the pressure exceeded 10 MPa. Compared with 100 and 300 rpm, the average hydrate formation rate was the fastest at 200 rpm. In addition, the relationship between hydrate volume fraction and viscosity was analyzed, and a critical hydrate volume fraction was proposed for a sharp increase in viscosity, which had a low value at high pressures and low temperatures and tended to cause blockages. This study can provide helpful theoretical support for hydrate formation prediction and blockage prevention in natural gas production.

Key factors controlling the kinetics of secondary hydrate formation in the porous media

Secondary hydrate formation (SHF) usually occurs in hydrate formation and decomposition experiments, and its manifestations behave differently in promoting gas consumption and water-hydrate conversion. In this work, in order to investigate the kinetic processes and controlling factors of the SHF in the porous media, we conduct a series of formation and dissociation experiments in a three-dimensional cubic hydrate simulator (CHS). Hydrate dissociation is accomplished by the depressurization method after the formation experiments. The experimental results reveal that a rapid growth rate of equal magnitude in the SHF stage follows a relatively slow hydrate growth in the process of hydrate formation. The occurrence of the SHF is accompanied by a sudden pressure drop and temperature rise, and a heterogeneous temperature distribution shows significant effects on hydrate formation behaviors in the vessel. It has been verified that the SHF is controlled by hydrate thermodynamic stability at a subcooling degree of −0.8 °C during the hydrate formation. The SHF is initiated by the collapse and crack of the local thin hydrate film, which results in an accelerated triggering of gas diffusion for further hydrate formation. In the dissociation experiments, the slight temperature increase caused by the SHF can promote the hydrate dissociation rate. The subcooling degree in the hydrate formation can also be suitable for predicting SHF in the dissociation experiment. It is found that a rapid depressurization rate can effectively shorten the duration of SHF. These insights can be beneficial for the energy transition and natural gas hydrate extraction in the future.

Cross-hole electrical resistivity tomography as an aid in monitoring marine gas hydrate reservoirs for gas recovery: an experimental simulation study

SUMMARY The in situ reservoir status monitoring plays a critical role in natural gas hydrate resource production. Considering the complexity of the field environment, a simulation framework for monitoring gas hydrates with cross-hole electrical resistivity tomography (CHERT) was developed to monitor the hydrate distribution during hydrate formation and dissociation. The simulation study comprised both numerical and physical experiments. The optimal CHERT array was designed through a numerical experiment. The effect of applying CHERT was verified through a physical experiment (a high-resistivity medium and hydrate formation experiment). The results show that improper electrode layouts will lead to varying degrees of low amplitude and blur boundary. An optimal CHERT array of a 100-mm electrode rod spacing, 8-mm electrode ring spacing and 48 electrode rings was obtained. The inversion results obtained using this CHERT array scheme can easily distinguish the distribution of high-resistivity targets and yield satisfactory results in hydrate formation experiments. These findings guarantee data processing and interpretation for applying CHERT in gas hydrate experiments and fields.

Role of different types of water in bentonite clay on hydrate formation and decomposition

The equilibrium and kinetic of hydrate in sediments can be affected by the presence of external components like bentonite with a relatively large surface area. To investigate the hydrate formation and decomposition behaviors in bentonite clay, the experiments of methane hydrate formation and decomposition using the multi-step decomposition method in bentonite with different water contents of 20%, 40% and 60% (mass) were carried out. The contents of bound, capillary and gravity water in bentonite clay and their roles during hydrate formation and decomposition were analyzed. In bentonite with water content of 20% (mass), the hydrate formation rate keeps fast during the whole formation process, and the final gas consumption under different initial formation pressures is similar. In bentonite with the water contents of 40% and 60% (mass), the hydrate formation rate declines significantly at the later stage of the hydrate formation. The final gas consumption of bentonite with the water contents of 40% and 60% (mass) is significantly higher than that with the water content of 20% (mass). During the decomposition process, the stable pressure increases with the decrease of the water content. Hydrate mainly forms in free water in bentonite clay. In bentonite clay with the water contents of 20% and 40% (mass), the hydrate forms in capillary water. In bentonite clay with the water content of 60% (mass), the hydrate forms both in capillary water and gravity water. The bound water of dry bentonite clay is about 3.93% (mass) and the content of capillary water ranges from 42.37% to 48.21% (mass) of the dry bentonite clay.

Magnetic nanopromoter enables excellent kinetic promotion and cycling performance in methane hydrate formation

Among several promising applications of gas hydrate-based technologies, storage and transportation of gases (H2, CH4, CO2, etc.) in the form of hydrate has aroused extensive concern. Currently, developing an effective and recyclable promoter holds the key to achieving the industrial application of hydrates. Herein, we proposed sulfonated magnetic polymer nanoparticles as the promoter for methane hydrate formation, which are synthesized by sulfonating the magnetic Fe3O4 particle in the soap-free emulsion system. Then the performance of the promoter was evaluated with regard to induction time, reaction time, and storage capacity at different concentrations. Hydrate formation results showed that when the mass concentration was 20 g/L, the storage capacity can reach up to 137.0 ± 2.8 v/v with the reaction time of 28 min while the induction time was only with the range of 44.1 ± 13.52 min. Further, the hydrate structure (sI) and dynamic occupancy change of 51262 and 512 cage were studied by the in-situ Raman at micro level and meanwhile the macroscopic morphology observation was also conducted. In addition to the high performance described above, the promoter also exhibited high-performance reliability in 15 cycles of hydrate formation experiments. This indicates that the promoter has great promise on economic benefit, environmental friendliness and recyclability for application in the methane hydrate-based technology.

Insights on CO2 Hydrate Formation and Dissociation Kinetics of Amino Acids in a Brine Solution

CO2 sequestration as hydrates has captured enormous research interest in recent years due to its high storage capacity. However, the slow hydrate formation kinetics poses a strong challenge in its applicability and urges the need for additives (kinetic promoters) to accelerate the hydrate formation kinetics. This study investigates the performance of amino acid solutions in brine (3.3 wt % NaCl) on CO2 hydrate formation and dissociation kinetics. The kinetics of hydrate formation and dissociation was evaluated at varying concentrations (0.2, 0.5, 0.8, and 1 wt %) of l-methionine, l-isoleucine, and l-threonine solutions in brine using a high-pressure hydrate reactor at 4 MPa, and formation temperature of 274.15 K, and a dissociation temperature of 277.15 K. CO2 hydrate formation and dissociation experiments were also conducted using sodium dodecyl sulfate (SDS), pure water, and brine systems as standards for comparison. The findings show that all the studied amino acid systems show hydrate inhibition as compared to the pure water system with 35–41% reduction in CO2 storage capacity. Further, l-methionine exhibited an optimum performance with a slight promotional effect at 0.2 wt % with the lowest induction time (35.6 min) and the highest CO2 uptake (42.08 mol/mmol) among the studied amino acid systems. However, comparing l-methionine with SDS shows less induction time for SDS (28.48 min), indicating kinetic promotion of SDS over l-methionine in the presence of brine. The dissociation kinetics findings reveal the lowest dissociation rate for l-methionine and a prolonged time of CO2 release compared to l-threonine and l-isoleucine, respectively. Nevertheless, all the considered amino acid systems exhibit more inhibition or stability for hydrate dissociation as compared to the pure water system. However, compared to SDS and brine systems, the amino acids l-methionine and l-isoleucine show a slight promotion effect, unlike l-threonine which exhibits strong kinetic inhibition. The results thus suggest that amino acid solutions in brine stabilize hydrate dissociation; however, the CO2 hydrate formation inhibition in brine is quite discouraging for CO2 storage purposes. Instead, applying amino acids in flow assurance could be an additional advantage due to the presence of brine in practical reservoir fluids during production.

A novel core–shell structure of CuNW@PSS accelerates the process of methane hydrate formation

Considering the high thermal conductivity of copper material and the promoting effect of sulfonate ions on methane hydrate formation, in this study, copper nanowires coated with sulfonate polymer (CuNW@PSS) were used in methane hydrate experiments. The morphology of synthesized CuNW@PSS was confirmed by SEM and TEM, and the composition was analyzed by elemental analysis, it has clearly core–shell structure. The surface wettability of the material changed from hydrophilic to hydrophobic after sulfonate modification. In methane hydrate formation experiments, compared with PSS, CuNW@PSS can shorten the induction time by 78.5 %, from 61.87 ± 21.71 min to 13.28 ± 5.47 min, the growth rate increased by 130 %, from 0.6 ± 0.13 mmol/min to 1.38 ± 0.34 mmol/min. In addition, CuNW@PSS has good cycling and defoaming performance in the multi-cycle methane hydrate formation and dissociation experiments, which would have potential application for natural gas storage and transportation.