CO2 Hydrate Formation Research Articles

Thermal analysis and kinetic investigation of using a hybrid adsorption-hydration method to promote CO2 capture

In this work, a hybrid adsorption-hydration method was utilized to promote CO2 capture. The CO2 capture performance in the fixed bed of coal particles was assessed at various water saturations (0 %, 20 %, 40 %, 70 %, and 100 %), 277.15 K, and 3.2 MPa. It was found that gas consumption at 100 % water saturation increased by 45 % compared to that at 0 % water saturation (dry coal particles). Moreover, as the water saturation increased, CO2 capture became dominated by hydrate formation rather than gas adsorption. The thermal analysis for CO2 capture at 0 % and 100 % water saturation detected the exothermic peaks associated with CO2 adsorption and CO2 hydrate formation, as well as the endothermic peaks corresponding to CO2 desorption and CO2 hydrate dissociation. This confirms that CO2 capture in the fixed bed of water-saturated coal particles consists of CO2 adsorption followed by hydrate formation. The morphologies of CO2 hydrate formation in the fixed bed of 100 % water-saturated coal particles were observed, and the mechanism of CO2 capture using the hybrid adsorption-hydration method was illustrated based on the thermal analysis and kinetic investigations. It was also found that after the adsorption-hydration process, the average cumulative pore volume of the coal particles decreased by 14.47 % compared to the original coal particles, and the micropores and mesopores were predominantly affected. Therefore, utilizing the hybrid adsorption-hydration process in a fixed bed of coal particles provides a promising method to enhance CO2 capture.

Carbon dioxide hydrate formation in porous media under dynamic conditions

AbstractInjecting carbon dioxide (CO2) into subsea water zones where the in situ temperatures are below the hydrate‐forming temperature of CO2 has been recently proposed to lock CO2 inside the water zones in solid hydrate form. It is a common concern that CO2 may form hydrates during the injection period that will reduce well injectivity. CO2 injection into sandstone cores under simulated subsea temperatures of 2°C and 3°C was investigated in this study. Experimental result shows that, at 2°C temperature, flowing CO2 at Darcy velocity 0.033 cm/s begins to form hydrate in the sandstone core at about 3.06 MPa (450 psi), which is much higher than the minimum required pressure of 1.5 MPa (220 psi) for CO2 to form hydrate in static condition. The pressure ratio is 450/220 = 2.05. At 3°C temperature, flowing CO2 at Darcy velocity 0.045 cm/s begins to form hydrate in sandstone core at about 3.67 MPa (540 psi), which is much higher than the minimum required pressure of 1.87 MPa (275 psi) for CO2 to form hydrate in static conditions. The pressure ratio is 540/275 = 1.96. The reason why the required minimum pressure for CO2 to form hydrates in dynamic conditions is about double the required hydrate‐forming pressure in static conditions is not fully understood. It is speculated that the shear rate effect of flowing fluids should slow down the growth of hydrate crystals or break down hydrate films, resulting in delayed formation of bulk CO2 hydrates. More investigations in this area are needed in the future.

CO2 hydrate formation in superabsorbent hydrogels for carbon capture—A comparison of water-confined framework vs non-water framework

This study investigates the kinetics of CO2 hydrate formation in saturated hydrogel particles—water-confined frameworks—through both experimental and numerical methods, and compares the results with those obtained in silica gels, silicon-based frameworks. Three hydrogel materials with varying swelling ratios were synthesized via radical polymerization. An advanced shrinking core model was developed, incorporating factors of CO2 solubility, gas diffusion, gas–water reaction, capillary effects, and hydrogel functional groups. Results showed rapid CO2 hydrate growth within the first 100 min, with CO2 uptake reaching 78%–82% of the final amount by 600 min. The highest percent water conversion achieved was 96.6%. Simulations indicated a significant decrease in CO2 diffusion coefficient through the hydrate shell over time, especially in hydrogels with higher methacrylic acid content. Capillary effects diminished as the reaction proceeded, with final water consumption via capillaries accounting for 14.4%–26.7% of the total. Hydrogels with higher swelling ratios and higher agglomeration degree formed more porous hydrate shells, enhancing CO2 diffusion but resulting in lower overall CO2 uptake due to their lower water content. Comparisons with hydrophilic porous silica gel revealed that, although hydrogels initially posed greater mass transfer resistance, they ultimately exhibited superior CO2 absorption capacity and rate.

Dependence of the hydrate-based CO2 storage characteristics on sand particle size and clay content in unconsolidated sediments

Storing carbon dioxide (CO2) in the form of hydrate in marine sediments is considered an effective way of carbon reduction. Understanding the influence of sediment properties on CO2 hydrate formation is important for the site selection of CO2 hydrate storage in marine sediments. In this study, the effects of sand particle size and bentonite content on the kinetics of CO2 hydrate formation are analyzed using low-field nuclear magnetic resonance technology, and the hydrate-based liquid CO2 storage capacity is evaluated. Results show that CO2 hydrate forms preferentially in large pores of sand samples, the water content in small pores begins to decrease before the hydrate saturation reaches 20%, and the unhydrated water mainly concentrates in small pores. With the increase of sand particle size, the CO2 storage rate of the early rapid growth stage increases first and then decreases, the CO2 storage rate of the whole hydrate formation process decreases continuously, but the final CO2 storage density is weakly affected by sand particle size. With the increase of hydrate saturation, the CO2 storage rate undergoes a trend of rapid decrease, stability, rapid decrease, and low-speed decrease in sequence. The larger the sand particle size or the higher the bentonite content, the shorter the stability stage of CO2 storage rate. The effect of bentonite on CO2 storage rate is the promotion at low content, the inhibition at medium content, and the weakening of inhibition at high content. The sediments with more than 25% bentonite are beneficial to the storage of more CO2.

Hydrate management strategies for CO2 injection into depleted gas reservoirs

Sequestering CO2 in depleted gas reservoirs using carbon capture, utilization, and storage technologies has emerged as a viable strategy for mitigating global carbon emissions. However, CO2 hydrate formation during injection processes is challenging and poses a risk to the operational integrity and efficiency of sequestration projects. This study investigated CO2 hydrate formation dynamics within silica gel environments that closely mimicked the median pore size of natural sandstone reservoirs, particularly targeting depleted gas fields in the East Sea of Korea. Integrating kinetic insights into experimental hydrate formation assessments and molecular dynamics simulations provided a comprehensive understanding of the CO2 hydrate formation mechanisms, as well as the formation dynamics and stability of the CO2 hydrates. For example, the hydrate formation kinetics were significantly reduced in the small pores, suggesting the feasibility of implementing more economical hydrate inhibitor injection strategies during CO2 injection. Moreover, this study evaluated the inhibitory effects of NaCl and methanol on CO2 hydrate stability by accurately measuring the three-phase (H-Lw-V) equilibria and employing silica gels (6 nm pore size). The presence of methanol and amorphous silica significantly impacted hydrate formation, with methanol potentially influencing the local structure around the hydrate phase and silica hindering hydrate growth through dynamic interactions with CO2 molecules. In addition, we elucidated the complex interplay between CO2, water, and methanol (hydrate inhibitor) within the constrained environments of porous media, offering strategic insights for the development of effective CO2 injection and sequestration strategies. Integrating molecular-level observations with real-world geological modeling presents a novel methodology for enhancing the safety, efficiency, and environmental sustainability of carbon capture and storage operations. The findings of this study provide critical insights into hydrate phase behavior, highlighting the importance of precise equilibrium determination under simulated reservoir conditions to effectively anticipate and mitigate hydrate formation challenges.

Numerical modelling of CO2-in-water emulsion injection into a water-saturated core

Depressurization method shows promise for methane hydrate (MH) reservoir production, but the reformation of hydrates due to a lack of geothermal heat presents a significant challenge for commercial production. This study proposes a novel approach for MH gas recovery by injecting a CO2-in-water (C/W) emulsion into an MH reservoir aquifer. The exothermic nature of CO2 hydrate formation and liquid CO2 dissolution in water in this method provides heat to the MH layer, effectively preventing hydrate reformation. Subsequently, 1-D numerical models were developed and implemented using the MATLAB Reservoir Simulation Toolbox (MRST). These models were rigorously validated against experimental data under homogeneous conditions and varying injection schemes. The investigation indicated that the average volume fraction of CO2 hydrate within the hydrate particles was found to be 55% of the volume of liquid CO2 droplets. The alternating C/W emulsion injection increased the driving force for CO2 dissolution in water, thereby promoting subsequent hydrate particle decomposition and CO2 hydrate dissolution in water, which effectively mitigated blockage within the porous medium. In conclusion, water alternating C/W emulsion injection, along with the continuous injection of a low volume fraction of liquid CO2 within the C/W emulsion, exhibits promising potential for sustained injection and provides adequate heat to the MH layer, preventing hydrate reformation. Furthermore, the developed numerical model reasonably predicts the behavior of various injection schemes. This developed model can be used for devising long term sub-seabed carbon capture and storage development plan.

Kinetics of CO2 hydrate formation in clayey sand sediments: Implications for CO2 sequestration

Hydrate-based CO2 sequestration beneath oceanic sediments is an emerging technique that involves the injection of CO2 into the hydrate stability zone (HSZ) beneath the seabed, forming hydrate cap that structurally traps the injected CO2 and reduces the risk of leaking CO2 from the storage sediment. Gas hydrates are adequately stable in sand sediments saturated with fresh water; however, the salinity of oceanic water impairs hydrate formation kinetics, stability, and CO2 storage capacity. In addition to sandstones, marine sediments are composed of many clay minerals that could affect hydrate formation. Therefore, this study experimentally simulates CO2 injection into sand and clayey sand sediments to assess the potential of CO2 hydrate formation. CO2 hydrates are formed inside a high-pressure reactor, which contains unconsolidated sediment bed/pack (silica sand; mixed sand with bentonite clay: 5 wt% and 10 wt%), saturated with de-ionized water or brine (3.3 wt% NaCl). Hydrate formation experiments were performed at 4 MPa pressure and 274.15 K temperature. Results show that CO2 hydrate formed within the sand sediment, with induction times of 6 and 8.5 h, for the de-ionized and brine systems, respectively. CO2 gas mole uptake in the de-ionized system was 71.54 mmol/mol however, in the brine system the gas uptake was 56.95 mmol/mol. Hence this 20.4% reduction in the gas uptake indicated the inhibition effect of salinity. In contrast, in the brine-saturated 5 wt% clay-sand sediment, the induction time was 6.5 h, indicating the promoting effect of the nano-sized clay particles. However, the gas uptake in this brine-saturated clay-sand sediment was reduced by 45.51% compared to the brine-saturated sand sediment. Increasing the clay content to 10 wt% prevented CO2 hydrate formation due to porosity reduction. Moreover, de-ionized water in clayey sand sediments prevented hydrate formation due to clay swelling. Finally, CO2 hydrate formation at the end of each experiment was visually confirmed.

Enhanced Study of CO2 Hydrate Formation in Marine Oil–Gas Based on Additive Effect

During marine oil–gas extraction, significant amounts of carbon dioxide (CO2) gas are often produced. Effectively separating these associated CO2 gases during extraction has become a critical technical challenge. Therefore, this paper aims to enhance the efficiency of CO2 hydrate-based capture technology and conduct relevant research. The goal is to increase the driving force for hydrate formation by combining the traditional thermodynamic additive TBAB with pressure modulation and to improve the hydrate formation rate through the use of multiple kinetic promoters. This paper presents the initial investigation into the effect of the thermodynamic accelerator tetrabutylammonium bromide (TBAB) on the characteristics of CO2 hydrate formation. The promotion effects of TBAB solutions with varying mass concentrations (3%, 5%, 7.5%, 10%) and reaction pressures (3 MPa, 4 MPa) were subjected to a systematic analysis, and the optimal conditions were identified as 4 MPa and a 5 wt% TBAB concentration. Subsequently, the impact of combining TBAB with kinetic promoters (SDS, nano Al2O3, L-methionine, L-leucine) on CO2 hydrate generation characteristics was further investigated. In this paper, the effect of a single promoter on the generation characteristics of CO2 hydrate was investigated, and the efficient carbon trapping ability of the complex promoter was verified, which provides theoretical support for the application of CO2 trapping technology using the hydrate method.

Evaluation of the synergic effect of amino acids for CO2 hydrate formation and dissociation

Gas hydrate formation is a very challenging problem in the oil and gas industry. The chemical inhibition method is the best practicable hydrate mitigation method by injecting hydrate inhibitors such as Thermodynamic Hydrate Inhibitors (THIs) and Kinetic Hydrate Inhibitors (KHIs) into the pipeline. However, the hydrate inhibitors' biodegradability and limited data on dual functional inhibitor mixtures raise concerns in this study. This study aims to investigate and compare thermodynamic and kinetic inhibition on CO2 hydrate by using biodegradable amino acid inhibitor mixtures of Glycine and Alanine. In this study, the inhibitor mixtures were prepared by mixing Glycine and Alanine in 3 different mixture ratios, followed by the Thermodynamic and Kinetic inhibition tests. Thermodynamic Inhibition Test was conducted by using 10 wt% of inhibitor mixtures in a CO2-water system under pressure of 4.0, 3.5, 3.0 and 2.5 MPa, while Kinetic Inhibition Test was carried out by using 1 wt% of the sample in the CO2-water system at a constant pressure of 4.0 MPa and temperatures at 274.15K. The analysis methods for the Thermodynamic Inhibition Test were Hydrate Liquid-Vapor Equilibrium (HLVE) Curve, Average Depression Temperature and Molar Dissociation Enthalpy, while the Induction Time method, the number of CO2 moles consumed, the formation rate of CO2 gas hydrate and RIP were used in the Kinetic Inhibition Test. In this study, all inhibitor mixtures exhibit dual functional inhibition on the CO2 hydrate. For THI, 50% Gly: 50% Ala shows the best thermodynamic inhibition strength with an average depression temperature of 2.42 K. All the inhibitor mixtures for THI have the dissociation enthalpies within the CO2 hydrate enthalpy range, which show that the inhibition is due to the influence on the water molecules’ interaction only. For KHI, 75% Gly: 25% Ala shows the highest kinetic inhibition strength on CO2 formation with the longest induction time of 115.2 min and the highest RIP of 0.40. In the KHI experiment, there is a drop in the CO2 uptake capacity with the presence of inhibitors used, where the highest difference of CO2 moles consumed is 0.0057 mol. A synergistic effect of inhibitor mixtures was observed in this study on 50% Gly: 50% Ala for THI and 75% Gly: 25% Ala for KHI. However, the “degradation” effect was also exhibited on 75% Gly: 25% Ala and 25% Gly: 75% Ala for THI and 50% Gly: 50% Ala and 25% Gly: 75% Ala for KHI, where the performance of the inhibitor mixtures is poorer than the concentrated amino acids. The “degradation” effect of the inhibitor mixtures at certain ratios was not covered in this study and it requires a further understanding of the chemistry behind the inhibition mechanism.

Clay mineral mediated dynamics of CO2 hydrate formation and dissociation: Experimental insights for carbon sequestration

Marine sediment-based CO2 sequestration through hydrate formation is a promising approach for long-term CO2 storage. Despite the prevalence of clay minerals in marine sediments, their impact on CO2 hydrate dynamics remains disputed and necessitates validation. This study systematically investigated the effect of clay minerals, specifically Ca-montmorillonite (Ca-mmt) and illite, on CO2 hydrates nucleation, growth, and dissociation in clay suspensions (0–10 wt% concentrations). Clay minerals significantly promoted CO2 hydrate nucleation by providng additional nucleation sites and influencing water distribution through the surface electric field. Ca-mmt exhibited a more pronounced nucleation effect due to stronger hydration ability of Ca2+ increasing nucleation sites and local CO2 concentration. Both clay minerals enhanced CO2 hydrate growth, with concentration-dependent effects that differ between clay types. Ca-mmt exhibited a higher growth rate at lower concentrations (≤1 wt%), but a lower rate at higher concentrations (>1 wt%) due to the stronger swelling and aggregation ability upon water contact. Morphological analysis revealed the clay minerals’ impact on fluid behavior and mass transfer during hydrate growth. During dissociation, clay minerals impeded the process, prolonging overall dynamics. This study highlights the impact of physicochemical disparities between Ca-mmt and illite on CO2 hydrate dynamics, underscoring the importance of these interactions for CO2 sequestration.

Optimizing CO2 Hydrate Sequestration in Subsea Sediments through Cold Seawater Pre-Injection

Carbon sequestration technology offers a solution to mitigate excessive carbon dioxide emissions and sustainable development in the future. This study proposes a method for subsea carbon sequestration through the injection of cold seawater to promote CO2 hydrate formation. Using a self-developed simulator, we modeled and calculated the long-term sequestration process. The study focuses on analyzing the thermal regulation of the seabed following cold seawater injection, the multiphysical field evolution during CO2 injection and long-term sequestration, and the impact of seawater injection volumes on sequestration outcomes. The feasibility and leakage risks of this method were evaluated on a 100,000-year timescale. Results indicate that the injection of cold seawater significantly improves the pressure–temperature conditions of subsea sediments, facilitating early hydrate formation and markedly increasing the initial CO2 hydrate formation rate. Consequently, the distribution pattern of hydrate saturation changes, forming a double-layer hydrate shell. Over the long term, while cold seawater injection does not significantly reduce CO2 leakage, it does increase the safety margin between the hydrate layer and the seabed, enhancing the safety coefficient for long-term CO2 hydrate sequestration. Through detailed analysis of the behavior of CO2 components during sequestration, this study provides new theoretical insights into subsea CO2 hydrate storage.

On the Significance of Hydrate Formation/Dissociation during CO2 Injection in Depleted Gas Reservoirs

Summary The study aims to quantitatively assess the risk of hydrate formation within the porous formation and its consequences on injectivity during storage of CO2 in depleted gas reservoirs considering low temperatures caused by the Joule-Thomson (JT) effect and hydrate kinetics. Hydrates formed during CO2 storage operation can occupy porous spaces in the reservoir rock, reducing the rock’s permeability and thus becoming a hindrance to the storage project. The aim was to understand which mechanisms can mitigate or prevent the formation of hydrates. The key mechanisms we studied included water dry-out, heat exchange with surrounding rock formation, and capillary pressure. A semicompositional thermal reservoir simulator is used to model the fluid and heat flow of CO2 through a reservoir initially composed of brine and methane. The simulator can model the formation and dissociation of both methane and CO2 hydrates using kinetic reactions. This approach has the advantage of computing the amount of hydrate deposited and estimating its effects on the porosity and permeability alteration. Sensitivity analyses are also carried out to investigate the impact of different parameters and mechanisms on the deposition of hydrates and the injectivity of CO2. Simulation results for a simplified model were verified with results from the literature. The key results of this work are as follows: (1) The JT effect strongly depends on the reservoir permeability and initial pressure and could lead to the formation of hydrates within the porous media even when the injected CO2 temperature was higher than the hydrate equilibrium temperature; (2) the heat gain from underburden and overburden rock formations could prevent hydrates formed at late time; (3) permeability reduction increased the formation of hydrates due to an increased JT cooling; and (4) water dry-out near the wellbore did not prevent hydrate formation. Finally, the role of capillary pressure was quite complex, as it reduced the formation of hydrates in certain cases and increased in other cases. Simulating this process with heat flow and hydrate reactions was also shown to present severe numerical issues. It was critical to select convergence criteria and linear system tolerances to avoid large material balance and numerical errors.

Rapid formation of carbon dioxide hydrate governed by the natural nano-clay for effective carbon dioxide capture

Gas hydrate can separate and capture enormous carbon dioxide (CO2) only using water cages. Capturing CO2 in hydrate form is viewed as a green and effective technology to reduce the global CO2 emission. However, the sluggish kinetics and high cost of kinetics promotors of CO2 hydrate formation limited the application of hydrate-based CO2 capture technology. Here, we used the nano-clay prepared by cheap natural clay to promote the formation kinetics of CO2 hydrate. At the low concentration range, the formation period of CO2 hydrate in the two-dimensional nano-clay dispersion was significantly shorter than that of the one-dimensional nano-clay dispersion. The induction time (5 min) obtained in vermiculite nanoflakes dispersion was shorter than most solid promotors of CO2 hydrate formation kinetics in reported works. Besides, we found that the water molecules near the negatively charged two-dimensional nano-clay surface were more likely to form the cage-like structure than those around the one-dimensional nano-clay surface. The similar hydrogen-bonded structure of the cage-like water with CO2 hydrate made them favorable for the CO2 hydrate formation. These results shed light on the design of the effective kinetics promotors of CO2 hydrate and contribute to develop the hydrate-based CO2 capture technologies.

Simulation of CO2 hydrate formation in porous medium and comparison with laboratory trial data

The storage of CO2 in gas hydrate form in the pore space in depleted natural gas reservoirs has been considered a method for greenhouse gas control. The formation of CO2 hydrate in porous medium is a strongly coupled Thermal-Hydraulic-Chemical (THC) problem under certain thermodynamic conditions. In this study, laboratory data on CO2 hydrate formation in silica sand, including the profiles of pressure, temperature, the amount of CO2, H2O, and CO2 hydrate, etc., were compared with results from numerical simulations. The minimized deviations between the simulation and experimental results, including the pressure drop, the significant temperature increase caused by hydrate formation, and the amount of CO2, water, and hydrate, were all less than 10 % in the numerical simulations. The sensitivities of the deviations between numerical simulations and experimental data to the domain discretization, thermal conductivity of the silica sand, absolute permeability, and kinetics of CO2 hydrate formation were analyzed. One of the major findings is that CO2 hydrate formation in the porous medium in this study is dominated by the kinetics of chemical reaction, rather than the heat or mass transfer. Another key finding of this study is the acquisition of the modeling parameters of the CO2 storage process in the laboratory-scale sand reservoir, including the thermal conductivity of the silica sand λs = 2.2 W/m/K, the absolute permeability k0 = 3.0 × 10−11 m2, and the kinetic constant Kf0 = 8.4 × 1011 kg/m2/Pa/s and the reduction exponent β = 5.3 in the kinetic model of CO2 hydrate formation. It is noteworthy that the mathematical models and the parameters faithfully fit three independent experiments of Run 1–3. The results of the experiments and corresponding numerical simulations provide a reliable method to evaluate the capacity, technical and commercial feasibility of CO2 storage in marine and permafrost reservoirs.

Molecular insights into the formation of carbon dioxide hydrates on the external surface of sodium montmorillonite in the presence of various types of organic matters

To address the urgent challenge of global climate change due to the greenhouse effect resulting from increasing carbon dioxide (CO2) emissions, viable technologies for geological CO2 storage must be developed. Of such technologies, CO2 hydrates holds significant promise for CO2 storage in seabed sediments, which typically contain clay minerals and organic matter (OM). Thus, investigating the structure of clay mineral interfaces and their interactions with OM is crucial for understanding the nucleation and growth of CO2 hydrate in seabed sediments. In this study, molecular dynamics simulations were used to investigate CO2 hydrate formation on the external surface of sodium montmorillonite (Na-Mnt) in the presence of various types of OM. The results show that the Na-Mnt surface adsorbed certain numbers of sodium ions (Na+) and OM molecules. The hydration of Na + disrupted of the hydrogen bond structure of CO2 hydrates, while hydrogen bonds that formed between OM and H2O molecules hindered CO2 hydrate formation. Consequently, CO2 hydrates predominantly formed in the bulk-like solution away from the Na-Mnt. However, the electrostatic interaction between the carboxyl groups of OM and Na+ mitigated the inhibitory effect of Na+ on CO2 hydrate formation. Over all, these findings can serve as a fundamental theoretical basis for understanding the formation and occurrence characteristics of CO2 hydrates in seabed sediments with a rich Mnt content. Such understanding will help to advance the development of CO2 storage technologies utilizing CO2 hydrates in seabed sediments.

Optimized strategies for efficient CO2 trapping using hydrate technology by pressure adjustment

The hydrate-based method enhances oceanic CO2 storage capacity and is deemed beneficial for controlling greenhouse gas emissions. However, the non-uniform CO2 hydrate crystal interface in the sub-seabed storage layer acts as a barrier, slowing down mass transfer kinetics. This work employed in-situ nuclear magnetic resonance (NMR) technology to compare three different pressure adjustment strategies and observe CO2 bubble dispersion after hydrate dissociation, secondary nucleation, and crystal growth mechanism, along with pore water changes. The presence of micro/nano CO2 bubbles with high internal pressure and high specific surface area in the dissociation liquid significantly accelerated secondary micro-structural phase transition rates. The optimal hydrate-based CO2 storage efficiency reached up to 81.7 %. Moreover, the secondary formation of CO2 hydrates distributed more uniformly within the large, medium, and small pores and led to a significantly increased residual water conversion rate (reaching up to 88 %) in medium pores. The post-secondary formation of high-density hydrates resulted in low fluid mobility (T1/T2 mostly distributed in the range of 0 ∼ 10) and exhibited a mixed wettability state between pore fluids. Utilizing the “memory effects” of CO2 hydrate effectively overcame late-stage mass transfer barriers of solid hydrates films. Our findings extend the understanding of CO2 hydrate formation kinetics under pressure adjustment strategies.

Molecular insights into the performance of promoters for carbon dioxide hydrate

Hydrate-based CO2 storage is a cost-effective and environmentally friendly approach to reduce carbon emission, and the addition of hydrate promoters has shown a promising avenue for enhancing CO2 hydrate formation. In this work, the promotion mechanism and promotion performance of five different hydrate promoters (denoted as DIOX, CP, THF, THP, and CH) were investigated and compared by first-principles calculations and molecular dynamics simulations. The results show that the hydrate promoters prefer to singly occupy 51264 cages of the sII hydrate, and CO2 molecules can singly occupy 512 cage or multiply occupy 51264 cages. The cohesive energy density indicates that the optimum CO2 storage capacity can reach up to ∼28 wt%. The stabilization effects of hydrate promoters on the hydrate stability should follow the order of CP > CH > DIOX > THF ≈ THP. The hydrate promoters can increase the water-water interactions, and the molecular diffusivity shows that the dynamic stability of the hydrates is THP ≈ CH > CP > DIOX > THF. Further, the hydrate promoters can accelerate the hydrate formation kinetics, which reduce the induction time and increase the nucleation and growth process.

CO2 hydrate formation characteristics inside seawater residual/saturated sediments under marine CO2 storage scenes

Marine CO2 storage by hydrate method is a promising technology expected to achieve permanent CO2 storage. Here, this study focuses on the formation kinetics and morphological characteristics of CO2 hydrate under two typical scenes with seawater residual zone (50 % porewater saturation) and seawater saturated zone (100 % porewater saturation). Four kinds of porous media were selected to simulate sediments with different permeability. The results indicate that in the seawater residual zone, hydrates are mostly flaky and form granular cementation, while in the seawater saturated zone, hydrates form from the pore center and are distributed as granular filling. Poor pore connectivity and gas-liquid contact in the seawater saturated zone hinder further hydrate formation, resulting in final hydrate saturation being at least 25 % lower than that in the seawater residual zone. Additionally, the final gas consumption and water-to-hydrate conversion decreased with increasing particle size. The maximum gas consumption was 118 mmol CO2/mol H2O, with only 28 % of the water converting into hydrate. These findings are significant for marine CO2 storage under different porewater saturation and particle size conditions.

Molecular insight into the dual effect of salts: Promoting or inhibiting the nucleation and growth of carbon dioxide clathrate hydrates

Facing the huge gap between the growing CO2 emissions and net-zero emissions target to mitigate global warming, the long-term storage of excess CO2 becomes an intractable issue. Sequestering CO2 in the oceans as clathrate hydrates is a promising solution. Many unanswered questions still exist at the molecular level regarding how ions in seawater kinetically affect the formation of CO2 hydrates, particularly the dual effect: as the concentration rises, salt ions shift from being a promoter of hydrate formation to becoming an inhibitor. Herein, we report the homogeneous nucleation process of CO2 hydrates in saline solutions via molecular dynamics simulations. Consistent with experimental findings, our results show that nucleation is promoted within certain salt concentration ranges; however, the evidence suggests that ions do not act as nucleation sites. Multiple ion-induced variations in the aqueous phase are analyzed, including changes in the mobility, structure, and CO2 solubility. We find that the presence of ions strengthens the hydrophobic interactions among the dissolved CO2 molecules, which are associated with the salting-out phenomenon, accounting for the promoting effect of salts at low concentrations. However, as the salt concentration increases, this advantage is offset, leading to the inhibiting effect at high salt concentrations. We demonstrate that anions are inevitably involved in the construction of the solid hydrate phase. Their presence disrupts the native tetrahedral connectivity of water molecules and imparts negative charges to the solid phase, thereby attracting cations. In addition to advancing our understanding of the intricate interactions among water, guest, and additive molecules to germinate ordered solid structures, these findings can accelerate the development and utilization of sustainable hydrate-based applications.

Hydrate Technologies for CO2 Capture and Sequestration: Status and Perspectives.

CO2 capture and sequestration based on hydrate technology are considered supplementary approaches for reducing carbon emissions and mitigating the greenhouse effect. Direct CO2 hydrate formation and CH4 gas substitution in natural gas hydrates are two of the main methods used for the sequestration of CO2 in hydrates. In this Review, we introduce the crystal structures of CO2 hydrates and CO2-mixed gas hydrates and summarize the interactions between the CO2 molecules and clathrate hydrate/H2O frames. In particular, we focus on the role of diffraction techniques in analyzing hydrate structures. The kinetic and thermodynamic properties then are introduced from micro/macro perspectives. Furthermore, the replacement of natural gas with CO2/CO2-mixed gas is discussed comprehensively in terms of intermolecular interactions, influencing factors, and displacement efficiency. Based on the analysis of related costs, risks, and policies, the economics of CO2 capture and sequestration based on hydrate technology are explained. Moreover, the difficulties and challenges at this stage and the directions for future research are described. Finally, we investigate the status of recent research related to CO2 capture and sequestration based on hydrate technology, revealing its importance in carbon emission reduction.