Hydrate Growth Research Articles

The crystal orientation of THF clathrates in nano-confinement by in situ polarized Raman spectroscopy.

Gas hydrates form at high pressure and low temperatures in marine sediments and permafrost regions of the earth. Despite forming in nanoporous structures, gas hydrates have been extensively studied only in bulk. Understanding nucleation and growth of gas hydrates in nonporous confinement can help create ways for storage and utilization as a future energy source. Herein, we introduce a new method for studying crystal orientation/tilt during tetrahydrofuran (THF) hydrate crystallization under the influence of nano-confinement using polarized Raman spectroscopy. Uniform cylindrical nanometer size pores of anodic aluminum oxide (AAO) are used as a model nano-confinement, and hydrate experiments are performed in a glass microsystem for control of the flash hydrate nucleation kinetics and analysis via in situ polarized Raman spectroscopy. The average THF hydrate crystal tilt of 56 ± 1° and 30.5 ± 0.5° were observed for the 20 nm and 40 nm diameter pores, respectively. Crystal tilt observed in 20 and 40-nanometer-size pores was proportional to the pore diameter, resulting in lower tilt relative to the axis of the confinement at larger diameter pores. The results indicate that the hydrates nucleation and growth mechanism can depend on the nanoconfinement size. A 1.6 ± 0.01 °C to 1.8 ± 0.01 °C depression in melting point compared to the bulk is predicted using the Gibbs-Thomson equation as a direct effect of nucleation in confinement on the hydrate properties.

Study of hydrate nucleation and growth aided by micro-nanobubbles: Probing the hydrate memory effect

Gas hydrates have been considered promising in gas storage, gas separation, and water desalination. The hydrates' technical application is affected by the long kinetics time. Of interest is gas hydrates show strong facilitation in dissociated water containing a high concentration of micro-nanobubbles. Here, it was discovered that the nano-particles present in the dissociated water were identified as nano-bubbles, characterized by nanoparticle track analyzer and infrared spectrum. The presence of bubbles increased the nucleation probability, likely attributed to the provision of nucleation sites. Results indicated that the ability of facilitation was related to the nanobubble types: the bubble solution with the same guest molecules exhibited similar facilitation to dissociated water; specifically, the average induction time was shortened by 27.48 %, the nucleation probability was increased by 50 % compared to deionized water. Moreover, the time hydrate filled the field of view with high bubble concentration was reduced by 60 % compared with low bubble concentration. The facilitation effect mechanism could be related to the presence of gas-dense regions inside the bubbles, based on the Raman results. This finding may offer valuable insights for the application of hydrate-based energy storage technology and shed light on the potential role of bubbles in causing memory effects.

The effect of winter flounder antifreeze protein and its mutants on methane hydrate growth: A molecular dynamic simulation study

The effect of winter flounder antifreeze protein and its mutants on methane hydrate growth: A molecular dynamic simulation study

Influence mechanism of interfacial organic matter and salt system on carbon dioxide hydrate nucleation in porous media

CO2 carbon sequestration in marine gas hydrate occurrence areas is a potential way to mitigate the continued growth of CO2 in the atmosphere. The organic matters of marine sediment can affect the phase equilibrium conditions of CO2 hydrate in salt system, and the organic salt system in pore medium has effect on the nucleation growth of CO2 hydrate. The organic matters on the surface of the sediment is mainly composed of lipids, proteins, carbohydrates, and unsaturated hydrocarbon organic compounds, and these polar functional groups weaken the inhibitory effect of salt ions on hydrates through coordination bonds and Ca ion complexation. The nucleation kinetics of CO2 hydrate under organic salt system in pore medium in marine environment is an important parameter determining the carbon sequestration of hydrate. In addition, experimental results show that clay surface organic matters (CSOM) can reduce the surface tension of pore water, and thus pore water migration occurs during hydrate growth and expansion. The basic background in our findings will bring a much better recognition of phase equilibrium conditions among the offshore marine sediment CO2 sequestration process and further assess the location of potential marine CO2 storage sites.

Investigation of hydrogen-propane hydrate formation mechanism and optimal pressure range via hydrate-based hydrogen storage

Hydrogen-propane hydrate is a promising practical hydrogen storage medium. However, the optimal conditions for the hydrogen-propane hydrate remain unclear. In this study, the thermodynamic and kinetic characteristics of hydrogen-propane gas (molar ratio 0.67/0.33) hydrate formation were investigated using experiments and molecular dynamics simulation. Moreover, the effect of liquid propane on hydrogen-propane hydrate formation in the pressure range of 0.5–2.8 MPa was investigated. The characteristic peaks of the heat flow curve during the experiment showed that under the pressure range of 2.0–2.8 MPa, propane hydrate and the ice-liquid propane mixture formed but not hydrogen-propane hydrate. Raman spectroscopy verified that when the initial pressure was higher than 2.0 MPa, only propane hydrate formed. Molecular dynamics simulation results showed that if liquefied propane exists, propane molecules will aggregate, preventing water molecules from contacting crystal nuclei and inhibiting hydrogen bonding, further hindering the growth of hydrogen-propane hydrate. Based on the experimental and theoretical analysis, the pressure range of 0.8–1.8 MPa is optimal for hydrogen-propane hydrate formation, specifically corresponding to the initial molar ratio of hydrogen to propane at 0.67/0.33. This study aids in determining the optimal operating conditions for hydrate-based hydrogen storage.

Post-combustion CO2 capture via the hydrate formation at the gas-liquid-solid interface induced by the non-surfactant graphene oxide

CO2 capture is currently the most effective way to reduce global carbon emissions, which leads to the emergence of novel gas hydrate method. In this work, the significant role of graphene oxide (GO) in enhancing the dynamic behaviors of post-combustion CO2 capture via the hydrate formation was investigated. Firstly, at the gas-liquid interface, the induction of GO increased the amount of gas transfer, and shortened the induction time for the hydrate nucleation at the heterogeneous nucleation sites provided by GO, which attracted CO2 molecules assembling on the GO layer to participate in the hydrate nucleation based on the molecular dynamics (MD) simulations. More importantly, the hydrate growth rate was nearly doubled in 0.05 wt% GO and 4 mol% tetrahydrofuran (THF) mixed accelerators than that in pure THF and sodium dodecyl sulfate (SDS) mixed systems, which greatly boosted the gas storage capacity of CO2 in the form of compact solid hydrates. Consequently, CO2 separation efficiency achieved up to 76 % in the GO based accelerators, enhanced by 23.2 % compared to that in pure THF and the SDS mixed systems. The present study could provide insights into the development of new type of nanomaterial accelerators for CO2 capture via the gas hydrate method.

Molecular insights into the wettability of antifreeze protein-adsorbed hydrate surface: Application to hydrate anti-agglomeration

Adding kinetic inhibitors (KIs) to prevent hydrate formation or anti-agglomerate agents (AAs) adsorbed on hydrate crystals to suppress particle aggregation are both effective means to eliminate hydrate blockage in pressurized pipelines. Antifreeze proteins (AFPs) are representative KIs that hinder hydrate growth via the interfacial adsorption mechanism. This implies the possibility of interfacial modification and simultaneous anti-aggregation effects, which yet have not been explored. Here molecular dynamics (MD) simulations were employed to determine the possible anti-aggregation performance of AFP. Specifically, we identified larger contact angles, that is, the enhanced hydrophobicity, of AFP-adsorbed CH4 hydrate under the dodecane oil phase. This indicates the possible dual inhibition effects of AFP to ensure oil transportation. However, no significant effects of AFP on wettability were observed in the systems with the CO2 hydrate substrate or gas environment. This contrasting behavior was explained by the differences in the hydrogen-bonding formation and interaction strength between substrates and water droplets, which are strongly influenced by the charged residues of AFP. Additionally, we compared AFP with traditional surfactants and emphasized that the anti-aggregation abilities of additives are intricately linked to their functional group arrangements and inherent structures. Our work provides molecular-level guidance for designing effective hydrate inhibitors with dual performance to ensure flow assurance.

Methane hydrate formation enhanced by thermally expanded graphite with multi-sized pores

Methane hydrate has been endowed with great potential in energy storage and transportation, but the sluggish formation kinetics restrict its industrial application. Herein the thermally expanded graphite (EG), with multi-sized pore structure that can be effectively controlled by expanding and grinding processes, is used to promote the nucleation and growth of methane hydrates. The results demonstrate that the EG exhibits a remarkable promotion in the formation of methane hydrate from water, with high gas storage capacity of 143 V/V, short induction time of 10 min, and rapid gas storage rate of 1 V·V·min−1, which are attributed to its well-designed multi-sized pore structure. Thereinto, the nano-sized pores can effectively adsorb guest molecules, increasing the guest–host contact area; meanwhile, the micron-sized pores with moderate scale not only provide abundant channels for mass transfer of reactants but also enable good thermal conductivity for heat transfer to soundings. This work provides an insight into the promotion effect of multi-sized porous medium in hydrate formation, and offers an effective strategy for fabricating high-performance promotors through pore designing.

Molecular insights into the effects of mass transfer ability of anti-agglomerant monolayers with different densities on the growth and wetting behavior of methane hydrate

Anti-agglomerants (AAs) have been recognized as an effective method for gas hydrate risk management in oil and gas pipelines. However, a limitation of AAs is their poor inhibitory effect on hydrate growth and aggregation in gas–water systems. In addition, the density of the AAs monolayer is considered one of the main factors affecting the growth and aggregation of hydrate particles, but the mechanism of this effects remains unclear. Herein, molecular dynamics (MD) simulations were employed to investigate the effects of anti-agglomerant (cocamidopropyl dimethylamine) monolayers with different densities on hydrate growth and the wetting behavior of hydrate surface. The results revealed that AA monolayers primarily suppress hydrate growth and reduce the wetted area by modulating mass transfer processes of gas and water molecules. The high-density monolayer can effectively hinder the flattening and diffusion of droplet on the hydrate surface due to its ability to maintain the aggregation state of water molecules and reduce the contact area between droplet and hydrates. The high-density AA monolayers simultaneously enhance the bonding strength between the monolayer and the hydrate, as well as the intermolecular interactions between AA molecules. The Coulomb interaction and h-bonds make the main contributions to the binding strength. Therefore, enhancing the adsorption density of AAs on the hydrate surface and the binding strength between AA molecules in the gas–water system should serve as a strategic approach in designing efficient AAs. These molecular insights on the anti-agglomeration mechanism are beneficial to guide the screening and design of efficient AAs molecules.

Hydrate formation and deposition behaviors with kinetic inhibitors under pseudo multiphase flow

With the successful application of kinetic hydrate inhibitors (KHIs) on hydrate plug prevention, there is a growing trend towards the development of affordable and environmentally friendly KHIs for solving challenges of high cost and inadequate biodegradability from their commercial KHIs. Therefore, further evaluation on the inhibitory effect of the developing inhibitors is needed under multiphase flow conditions. In this study, a high-pressure, fully visible rocking cell were used to simulate the multiphase transportation and both commercial KHIs and environmentally friendly KHIs were considered. Under the flow conditions of 60 % liquid loading and 20 % water cut, the results demonstrated that PVCap showed excellent inhibition performance with no hydrate formation at concentrations of 0.5 wt%, 0.2 wt% and 0.1 wt%. Although pectin exhibited certain inhibitory effect on hydrate growth rate and formation quantity, but it demonstrated a strong promoting effect on hydrate nucleation opportunities and rates. However, sodium alginate, which shares similar hydrate inhibition characteristics with pectin, exerted significantly promotional effects in terms of induction time, growth rate, and water conversion. Furthermore, the addition of pectin and sodium alginate led to the formation of hydrate balls in several test runs, resulting in complete pipeline blockage. Another noteworthy discovery was the relationship between the growth rate and final water conversion of hydrates, which exhibited an initial increase followed by a decrease, while the induction time exhibits an inverse trend, as the flow velocity increased.

Kinetics behaviors of CH4 hydrate formation in porous sediments: Non-unidirectional influence of sediment particle size on hydrate formation

The kinetic characteristics governing methane conversion into solid hydrates within seabed sediments influence hydrate accumulation and resource distribution, which is significant for the evaluation of global natural gas hydrate reserves and the implication of hydrate development. However, the influence of sediment particle size on methane hydrate formation kinetics remains unclear. In this study, simulating in situ conditions of the seafloor, the kinetics behaviors of CH4 hydrate formation within saline porous sediments were investigated. The experimental results indicate that the methane hydrate formation rate does not exhibit a strictly unidirectional change with changed quartz sand particle size. The unidirectionality and magnitude of hydrate formation rate change are simultaneously influenced by both quartz sand particle size and water saturation levels. The different effective gas-liquid contact area is the primary factor underlying the occurrence of these phenomena. However, for more porous clay sediments with greater specific surface area, the theory of effective gas-liquid contact area becomes inapplicable. The addition of clay to quartz sand sediment inversely inhibits the methane hydrate formation, which is caused by water absorption. This work can advance the comprehension of the intricate interplay between hydrate growth kinetics and the attributes of sedimentary hosts.

Experimental study of methane hydrate formation and agglomeration in waxy oil-in-water emulsions

In deep-water multiphase flow pipelines, hydrate and wax agglomeration can cause blockages. To clarify the influence of wax and Tween 80 on hydrate formation and agglomeration in water-in-oil (W/O) emulsions, hydrate generation experiments were conducted in a high-pressure reactor, focusing on W/O emulsions both with and without wax and Tween 80. Additionally, the paper further explored the characteristics of hydrate formation and agglomeration in wax-containing W/O emulsions with Tween 80 under various initial pressure conditions. Results indicated that wax presence curtailed the Tween 80's dual role: inhibiting hydrate nucleation and promoting rapid hydrate growth. The interplay of waxes and Tween 80 had a synergistic impact on hydrate formation, elevating the cumulative gas consumption by 0.74 mol and augmenting the water conversion rate by 9 %. This intensifies the likelihood of hydrate blockages. Under higher initial pressures, a notable multi-step pressure decrease occurred during hydrate formation, attributed to a high water cut, wax/Tween 80 presence, and initial pressure. Torque evaluations indicate that wax-Tween 80 interactions diminish particle agglomeration, enhancing hydrate slurry liquidity.

Experimental investigation on the methane storage by forming sH hydrate

Methane storage via clathrate hydrates is a promising method, the structure H (sH) hydrate can be formed at more moderate conditions compared to structure I (sI) hydrate and has a larger storage capacity than structure II (sII) hydrate. In this work, CH4 storage by forming sH hydrate in the tert-butyl methyl ether (TBME) solution was explored at an initial pressure of 5.0 MPa and within the temperature range of 274.15– 278.15 K. The CH4/TBME hydrate phase equilibrium condition was first determined with the isochoric pressure searching method, and the results revealed that the measured equilibrium data of CH4/TBME hydrate at different TBME concentrations were almost consistent. The effect of TBME concentration (0– 4.29 mol%), promoter type and sub-cooling on the hydrate formation kinetics and gas uptake was systematically investigated. The results showed that the hydrate formation rate increased with the increase of TBME concentration. The CH4 uptake achieved 117.7 ± 3.6 v/vw (volume ratio of gas to water at standard condition) in the 4.29 mol% TBME system, which was significantly increased than that of pure water (44.1 ± 5.0 v/vw). The cocamidopropyl dimethylamine (CDA) further improved the CH4/TBME hydrate formation kinetics and gas uptake, the CH4 storage capacity attained 145.6 ± 1.7 v/vw, which was slightly higher than that of the sodium dodecyl sulfate (SDS) system (143.6 ± 3.0 v/vw). As the sub-cooling increased, the formation kinetic profiles of CH4/TBME hydrate changed from a two-step to a one-step drop, indicating that the shift of mixed sH and sI hydrates to single sH hydrate. Additionally, the time taken for hydrate growth in the presence of TBME was significantly decreased than the pure water system, and the adding of CDA and SDS further shorten it. The CH4 recovery in each test was above 95.0 % and no foam generated during hydrate dissociation for the CDA-contained system. The stability test of CH4/TBME hydrate indicated that around 86 % CH4 was still enclosed in the hydrate phase after one week. This study would contribute to the application of the hydrate-based methane storage technology in future.

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.

Probing the effect of amino acid-based ionic liquids on the CO2 (sI) and THF (sII) hydrate formation

In the present work, four acetyl glycinate-based ionic liquids (ILs) with distinct cations, namely 1-alkyl-3-methylimidazolium acetyl glycinate [C2mim][AcGly], ammonium acetyl glycinate [NH4][AcGly], N-(2-hydroxyethyl)-N,N,N-trimethyl ammonium N-acetylglycinate [N111(2OH)][AcGly] ≈ [Ch][AcGly], and N-Butyl-N,N-dimethyl-N-(2-hydroxyethyl) ammonium N-acetylglycinate [N411(2OH)][AcGly] ≈ [C4Ch][AcGly], were synthesized and tested for their effect on the formation of CO2 hydrates at elevated pressures and tetrahydrofuran (THF) hydrate formation at atmospheric pressure. The phase behaviour of the CO2 hydrates, sI type, was studied in the presence of the selected ILs using the isochoric pressure search method. The ILs shifted the phase boundary towards lower temperatures indicating a thermodynamic inhibition characteristic. The constant cooling method was used to determine the onset nucleation temperature of CO2 hydrates in the presence and absence of additives. The isothermal method was used to determine the induction time of CO2 hydrates in the presence of additives. The pressure drops in both experiments indicate the hydrate growth in the absence/presence of additives. Later, the THF hydrate crystal growth experiments at atmospheric pressure were carried out to understand the effect of additives on the sII-type hydrate growth. The crystal morphology also points out the mode of action of the tested additives on hydrate formation and growth. The extensive testing using the same additives at identical concentrations revealed the importance of the method and conditions, which become crucial in the absence of a standard screening procedure for kinetic hydrate additives.

Molecular dynamic simulation of H2-CH4 binary hydrate growth induced by methane hydrate

Hydrogen storage based on hydration is a promising technology, in which hydrogen molecules are captured in a three-dimensional cage structure formed by hydrogen bonds between water molecules. In this study, methane was selected as the accelerator guest molecule for hydrogen storage in hydrates, hydrogen-methane hydrate formation properties was investigated at 240 K and 110 MPa by molecular dynamic simulation. The combined TraPPE(CH4)-TIP4P/ice(H2O)-Diatomic(H2) force field was adopted. The molecular mechanism of the growth of CH4/H2 binary hydrates with different liquid methane concentrations (1.51–5.79 mol%) was explored, the effect of concentration on kinetic properties such as hydrate growth rate, hydrate hydrogen storage density, and properties related to cage occupancy and structural transformation were analysed. Any concentration of liquid-phase methane in this study increased hydrogen storage compared to a system without liquid methane. The growth rate of binary hydrates is related to the concentration and diffusion of liquid-phase methane: the higher the concentration of methane in liquid phase, the smaller the diffusion coefficient of hydrogen and water molecules in the solution, and the slower the growth rate of binary hydrates. The cage at the solid–liquid interface is preferentially occupied by hydrogen molecules, and the occupation process is gradually from the interface to the interior of the hydrate. At lower methane concentrations, the hydrate grows more uniformly along the interface. When the methane concentration is large, the hydrate not only grows along the interface, but also develops new nucleation sites in the liquid phase for growth, resulting in uneven growth of hydrate in the whole system. Methane acts as an accelerator to stabilize the cage while reducing diffusion. According to the hydrogen storage density of each system, it was found that hydrates have the best hydrogen storage efficiency when the concentration of methane in the liquid phase is 4.41 mol%. The transition from double-occupied cages to single-occupied cages indicated that the breakdown of the six-membered ring in the hydrate cage was the key to the passage of hydrogen molecules into and out of cages. This study will provide theoretical basis for the stable storage of H2 hydrate, and promote the industrial application of HHST technology.

Synergistic effect of ultrasound combined with bubble enhanced rapid nucleation and growth of methane hydrate

The synergistic effect between ultrasound and bubbles serves to amplify the nucleation-enhancing effect of bubbles, effectively addressing the crucial challenges of limited gas–liquid interface and intricate nucleation. Based on this, this study proposed a new method of ultrasound combined with microbubbles and bubbling to enhance hydrate nucleation and growth. A visualization experimental system for the growth of methane hydrates enhanced by ultrasound combined with bubbles was developed. The optimal conditions for ultrasound-enhanced methane hydrate nucleation were quantitatively determined. Subsequently, the enhancement effects of ultrasound combined with microbubbles and bubbling systems were systematically analyzed. Under the influence of ultrasound, the nucleation induction period was reduced from 860 min to 7.5 min, and the complete reaction time was shortened to less than 100 min, resulting in a 3.2-fold increase in methane gas conversion. The combination of ultrasound and microbubble method reduced the nucleation induction time to 6.7 min and increased the growth rate by 10.6%. Furthermore, the combination of ultrasound and bubbling method, by fragmenting large nuclei into smaller ones and inducing secondary nucleation, enhanced mass transfer and increased the growth rate of hydrates by 4.4–5.2 times, with a gas conversion increase of 77.5 %–80 %. A novel finding was made in this study, where under the combined effect of ultrasound and bubbling, the stable formation of slurry hydrates was discovered, providing a new idea for the promotion of high-efficiency energy storage technology for hydrates.

Synergistic Effect of Hyperactive Antifreeze Protein on Inhibition of Gas-Hydrate Growth by Hydrophobic and Hydrophilic Groups.

Antifreeze proteins (AFPs) are biodegradable inhibitors that effectively prevent the formation of natural gas hydrates that block pipelines. In this study, molecular dynamics simulations were employed to establish a kinetic model of the hyperactive insect antifreeze protein (Tenebrio molitor, TmAFP) and its mutants to inhibit the growth of sI natural methane hydrate. Simulations revealed that the hydrophobic and hydrophilic groups of threonine (Thr) residues at hydrate-binding sites played a synergistic role in binding hydrates. The hydrophobic groups anchored TmAFP to the hydrate surface through residues Thr39-Thr65 by migrating pendant hydrophobic methyl groups to the hydrate semicages. The hydrophilic groups stabilized TmAFP by hydrogen bonding with water molecules and integrating them into a quasi-hydrate structure, which more effectively inhibited hydrate growth. The results suggest that the hydrate growth inhibition is attributed to both the shape complementarity and the flexibility of binding residues. The synergy between hydrophobic and hydrophilic groups provides guidance for the design of more effective hydrate inhibitors.

Molecular simulation of imperfect structure I CO2 hydrate growth in brine.

In order to investigate the viability of carbon dioxide (CO2) storage in seawater, molecular dynamics techniques were employed to study the dynamic evolution of CO2 hydrate in saline water. The simulation was conducted under specific conditions: a temperature of 275 K, a pressure of 10 MPa and a simulated marine environment achieved using a 3.4 wt% sodium chloride (NaCl) solution. The total simulation time was 1000 ns. The results of the simulation indicate that the pre-existence of CO2 hydrate crystals as seeds leads to rapid growth of CO2 hydrate. However, analysis of the F3 and F4 order parameters reveals that the hydrate does not meet the standard values of the perfect structure I (sI) type, confirming the existence of an imperfect structure during the simulation. Additionally, the changes in the number of different phase states of water molecules during the hydrate growth process shows that there are always some liquid water molecules, which means some water molecules fail to form solid water cages. Further investigation suggests that the presence of Na+ and Cl- hampers the hydrogen bonds between water molecules, resulting in incomplete cage structures. By analyzing the density variations in the system, it is observed that CO2 hydrate, with a density of around 1.133 g cm-3, forms rapidly, surpassing the average density of seawater. This density increase facilitates the efficient and swift containment of CO2 on the seabed, thereby supporting the feasibility of the CO2 storage theory.

Understanding the effect of moderate concentration SDS on CO2 hydrates growth in the presence of THF

HypothesisAdditives like Tetrahydrofuran (THF) and Sodium Dodecylsulfate (SDS) improve Carbon Dioxide (CO2) hydrates thermal stability and growth rate when used separately. It has been hypothesised that combining them could improve the kinetics of growth and the thermodynamic stability of CO2 hydrates.Simulations and ExperimentsWe exploit atomistic molecular dynamics simulations to investigate the combined impact of THF and SDS under different temperatures and concentrations. The simulation insights are verified experimentally using pendant drop tensiometry conducted at ambient pressures and high-pressure differential scanning calorimetry.FindingsOur simulations revealed that the combination of both additives is synergistic at low temperatures but antagonistic at temperatures above 274.1 K due to the aggregation of SDS molecules induced by THF molecules. These aggregates effectively remove THF and CO2 from the hydrate-liquid interface, thereby reducing the driving force for hydrates growth. Experiments revealed that the critical micelle concentration of SDS in water decreases by 20% upon the addition of THF. Further experiments in the presence of THF showed that only small amounts of SDS are sufficient to increase the CO2 storage efficiency by over 40% compared to results obtained without promoters. Overall, our results provide microscopic insights into the mechanisms of THF and SDS promoters on CO2 hydrates, useful for determining the optimal conditions for hydrate growth.