CO2 Clathrate Research Articles

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.

Stability and structure of multiply occupied sII CO2 clathrate hydrates: A possibility for carbon capturing

The hydrate method is an important technology that has been widely studied for carbon dioxide (CO2) capture, utilization and storage (CCUS). Improving the gas reserves per unit volume is the key goal for this technology. Therefore, the occurrence behaviors of large CO2 hydrate cages, the structure II, occupied with 1–5 gas molecules were investigated via molecular dynamics (MD) in this study. The occupancy rate, stability and decomposition laws of CO2 hydrate were systematically analyzed. The results indicate that the large hydrate cages occupied with 4–5 molecules were directly broken due to excessively large intermolecular repulsion. In contrast, the large hydrate cages occupied with 3 molecules showed an obvious four-rupture-stage: (1) a small part of cages rupturing; (2) metastable cages formation along with the escape of CO2 molecules, and the cages do not continue to break until all the CO2 molecules escape; (3) pure residual cages rupturing, with no CO2 gas existing in cages in this stage; and (4) complete decomposition of the CO2 hydrate. It is interesting that the large hydrate cages occupied with 2 gas molecules are stable, and 2 is the maximum occupancy number. The pressure is more important for improving the stability of the double-occupancy hydrate, and a higher pressure (20 MPa) strengthens the stability of the CO2 hydrate structure. The findings in this study indicate that the sII CO2 hydrate under sufficiently high pressure can maximally increase the storage efficiency by 36.5 wt%.

Cluster approximation applied to multisite-occupancy adsorption: configurational entropy of the adsorbed phase for dimers and trimers on triangular lattices.

The adsorption of dimers and trimers on triangular lattices is studied by combining theoretical modeling and Monte Carlo (MC) simulations. The thermodynamic process is analyzed through the behavior of the configurational entropy per site of the adsorbed phase as a function of the coverage. MC calculations, supplemented by the thermodynamic integration method, are performed in the grand canonical ensemble. The theoretical model used in the present study is called Cluster Approximation (CA), and it is based on exact calculation of states on finite cells. An efficient algorithm allows us to determine the detailed structure of the configuration space for m = l1 × l2 cells. From there, the thermodynamic properties can be obtained. Five systems are investigated, according to the size and shape of the molecule in the adsorbed state: (i) dimers, (ii) linear trimers, (iii) triangular trimers, (iv) 60°-angular trimers and (v) 120°-angular trimers on triangular lattices. Dimer and trimer are the simplest cases of a polyatomic adsorbate, containing all the properties of the multisite-occupancy adsorption and can be used to model several experimental systems. CA solutions are tested by comparison with MC simulations and previous data in the literature. Special interest is devoted to the calculation of the configurational entropy per site in the limit case of θ → 1 (full coverage), where some exact results are available. The theoretical formalism is also applied to model CH4 and CO2 clathrate hydrates. In these systems, a triangular lattice is used to simulate the substrate, and methane(carbon dioxide) molecules can be well represented by triangular(linear) trimers. The good qualitative agreement between simulation and analytical data supports the validity of the CA scheme to predict the behavior of a wide variety of multisite-adsorption models, for which theoretical solutions are very difficult to obtain.

Molecular dynamics simulations of CO2 clathrate hydrate in the presence of organic components

As the major greenhouse gas emission, releasing CO2 through human activities has already devastating consequences on the planet. In this context, hydrate-based (HB) techniques in favour of CO2 capture, sequestration, or utilization (CCSU) are perceived to be a novel option to arrest increasing concentrations of CO2 in the atmosphere. The end uses of captured CO2 encompass its utilization for different realms of industry such as food and beverage manufacturing plants; water desalination; metal fabrication plants; and secondary refrigeration. To offset the cost of CO2 capture as well as generating revenue, the increasing effectiveness of aforesaid techniques is crucial. Although HB approaches are faced with several limitations, the solution would be the inclusion of organic promoters which are classified as environmentally-friendly substances. However, the microscopic influences of such components on CO2 hydrates are mostly unexplored. This work highlights the CO2 clathrate hydrate stability and decomposition in the existence of organic additives through classical molecular dynamics (MD) simulations. The results can help to understand the molecular mechanisms involved in such CO2 hydrate systems which may also aid to find the more efficient organic promoters for HB applications.

Insights into the synergistic effects of metal particles (Ag, Cu, and Fe) and urea on CO2 clathrate hydrate growth using molecular dynamics simulations

A variety of industrial applications of hydrate-based CO2 capture and utilization technologies are hindered by the complex and slow hydrate formation; however, improving CO2 hydrate formation kinetics can be facilitated by adding the accelerators (promoters). In this regard, understanding the promotion mechanisms of these compounds on the hydrate formation at the molecular level would assist in either establishing feasible processes or finding more efficient promoters. In this work, CO2 hydrate growth and formation in the presence of hybrid metal particles (Ag, Cu, and Fe) and urea molecule has been explored through molecular dynamics (MD) simulation at below and above water freezing point. Different criteria were used to characterize and analyse the CO2 hydrate formation kinetics. The outcomes reveal that, although the mixture of Cu, Ag, and Fe metal particles has positive effects on the rate of hydrate formation above the ice point, the mixture of Cu, Fe, and urea (without the inclusion of Ag) in comparison with the other investigated systems, possesses the highest promotion effect on the clathrate hydrate growth rate. This combination of metal particles creates various functions in the solution phase adjacent to the hydrate surface. The metal particles and urea could promote the formation of new cages at the hydrate-solution boundary by decreasing the heat and mass transport resistances of CO2 in water. In addition, the improvement of combined metal particles and urea under water freezing was found to be less substantial. However, the behaviours of combined metal particles without urea at different thermodynamic conditions are quite dissimilar.

Mechanical Destabilization and Cage Transformations in Water Vacancy-Contained CO2 Hydrates

Clathrate hydrates show wide applications in energy recovery and storage, CO2 capture and storage, and other sustainable technologies. Water vacancy in clathrate hydrates is a common defect; however, its effects on the mechanical properties of clathrate hydrates, especially CO2 hydrates, have not been well studied. Herein, the mechanical characteristics of CO2 hydrates with three different types of water vacancy defects are investigated for the first time through molecular dynamics simulations with several popular water force fields. It turns out that the mechanical properties of CO2 clathrate hydrate vary with the type of water vacancy and water force field. Upon critical strains, a variety of unconventional cages of 425862, 425863, 425864, 4151062, 4151063, and 4151064 form, of which 4151062 predominates and is identified to be transient and a clathrate intermediate in forming 425862, 425863, and 425864. Moreover, diverse cage transformations of 51262 ↔ 4151063, ↔ 4151062, ↔ 425863, ↔ 425864 and 512 ↔ 4151062, ↔ 425862 occur via two distinct transformation mechanisms including insertion/removal and rotation of a pair of water molecules. This study provides new perspectives on the mechanics and microstructural transformations of CO2 hydrate, which are crucial for evaluating the formation and mechanical stability of CO2 hydrate-bearing sediments as well as the CO2 geological storage by hydrate-based technologies.

Molecular Dynamics Simulation Studies on the Stability and Dissociation of Clathrate Hydrates of Single and Double Greenhouse Gases

Comprehending and controlling the stability and dissociation of greenhouse gases hydrates are critical for a variety of hydrate-based industrial applications, such as greenhouse gas separation, sequestration, or utilization. Although the promotion effects of greenhouse F-gases (F-promoters) and new cyclic promoters on CO2 hydrates have been acknowledged, the involved molecular mechanisms are poorly understood. This work was therefore conducted to investigate the intermolecular mechanisms of the properties of CO2 and NF3 hydrates using molecular dynamics (MD) simulation to better understand their stability and dissociation and the effects of thermodynamic conditions as well as cage occupancy. In addition, the stability of CO2/CO2 + CH4 hydrates in the presence of seven thermodynamic hydrate promoters (THPs) from different molecular groups or substituents was evaluated. Results reveal that after the breakup of the hydrate, the propensity of NF3 to form nanobubbles is more than that of CO2 molecules. The relative concentration distribution of partially occupied hydrates was also found to be greater than that of completely filled by guest gases. MD simulation results of CO2 double and mixed hydrates also show that the type of large molecular guests in the large cages plays a major role in the stabilization of the clathrate hydrate network. The structural properties, however, indicate that the resistance against being dissociated for CO2 + promoter can be somewhat increased when half of the CO2 molecules in small cages is replaced by CH4. In addition, the existence of neopentyl alcohol in large cavities was found to facilitate the process of hydrate dissociation by making new hydrogen bonds between hydroxyl groups and water molecules. Among studied systems with THPs, cyclopentane, and cyclohexane in comparison with F-promoters seem to be more susceptible to maintaining the stability of CO2 clathrate hydrate.

Thermodynamic modeling and measurement of CO2 clathrate equilibrium conditions with a hydrophobic surface – An application in dry water hydrate

Dry water is a powdery liquid composed of tiny water droplets surrounded by super-hydrophobic nanosilica. We used a high-pressure cell to determine the equilibrium temperature and pressure of CO2 hydrate in the presence of dry water. The Bridging-Cluster model for the hydrophobic attraction force was used to evaluate the hydrophobic force effect on the excess properties of water in the liquid phase. We modified Ballard and Sloan's framework for the CO2 clathrate hydrates in the hydrate phase by introducing the Bridging-Cluster model. The distance of hydrate cells from the hydrophobic surface (δ) was calculated by optimizing the measured hydrate formation conditions. An absolute average relative deviation for pressure was 1.99% and 1.22% for silica 5 and 10 wt% dry water systems, respectively. The present model explains the promotion effect of the dry water hydrate system and the calculated equilibrium formation conditions with high accuracy.

Do Oceanic Convection and Clathrate Dissociation Drive Europa’s Geysers?

Abstract Water vapor geysers on Europa have been inferred from observations made by the Galileo spacecraft, the Hubble Space Telescope, and the Keck Observatory. Unlike the water-rich geysers observed on Enceladus, Europa’s geysers appear to be an intermittent phenomenon, and the dynamical mechanism permitting water to sporadically erupt through a kilometers-thick ice sheet is not well understood. Here we outline and explore the hypothesis that the Europan geysers are driven by CO2 gas released by dissociation and depressurization of CO2 clathrate hydrates initially sourced from the subsurface ocean. We show that CO2 hydrates can become buoyant to the upper ice–water interface under plausible oceanic conditions, namely, if the temperature or salinity conditions of a density-stratified two-layer water column evolve to permit the onset of convection that generates a single mixed layer. To quantitatively describe the eruptions once the CO2 has been released from the hydrate state, we extend a one-dimensional hydrodynamical model that draws from the literature on volcanic magma explosions on Earth. Our results indicate that for a sufficiently high concentration of exsolved CO2, these eruptions develop vertical velocities of ∼700 m s−1. These high velocities permit the ejecta to reach heights of ∼200 km above the Europan surface, thereby explaining the intermittent presence of water vapor at these high altitudes. Molecules ejected via this process will persist in the Europan atmosphere for a duration of about 10 minutes, limiting the timescale over which geyser activity above the Europan surface may be observable. Our proposed mechanism requires Europa’s ice shell thickness to be d ≲ 10 km.

Matching of models of Titan with tidal Love numbers

The restrictions on the heat flux, the structure of the water-ice shell, and the composition of the Titan ocean, which are necessary to match the calculated (model) and experimental Love numbers, are considered. Estimates are obtained for model Love numbers and maximum surface heat fluxes for the L/LL chondrite composition of the rock-iron component of Titan, taking into account the radiogenic and tidal energy, as well as the energy of ice crystallization in the ocean due to satellite cooling. The values of the tidal Love numbers k2 of Titan were calculated for various models of the water-ice shell of the satellite, including the outer ice crust (ice Ih ± CO2 clathrates) and the internal ocean of various compositions (pure or sea water, ammonia + dissolved salts solution, aqueous solutions of ammonia and methanol). Titan models with an outer ice crust (ice Ih + 5% CO2 clathrates) and with an internal ocean of low salinity based on ammonia (5% NH3) aqueous solution better than other tested models satisfy the k2 experimental values.

A compare review about equilibrium conditions of semi-clathrate hydrate: experimental measurements visions and thermodynamic modeling aspects

The formation of gaseous (gas) hydrates for storage, separation and transportation application is essential. In this regard, a comprehensive study of this case is essential. Semi-clathrate hydrates have higher temperature stability and are formed in a stable range. The purpose of this study is review the experimental and modeling of the semi-clathrate hydrates, to investigate the equilibrium conditions for the formation/dissociation of them based on the type of thermodynamic promoters like TBAB, TBAC, TBAF, TBANO3 and TBP groups. This review is consist of 4 overall section, at first an introduction to semi-clathrate hydrates has defined. After that, the experimental research has discussed through different gas systems such as CO2, CH4, N2, H2 etc. Also, the target of each study, like the CO2 capture, separation of CH4, formation/dissociation equilibrium conditions, are expressed. Then, in the modeling section, the different types of thermodynamic modeling like, equaling fugacity, intelligence computing, Gibbs free energy minimization and Chen-Guo method are collected. At final section, a comparison between types of promoter showed that the addition of TBAF to aqueous solution has the best promotion effect on the CO2 clathrate hydrate formation. Also, the results of comparing the concentration of promoters have shown that up to a certain amount of TBAB, the salt's role as a promoter and by addition concentration of promoter, has an inhibition effect. Also, besides the results of the comparison different promoters on equilibrium conditions of different gaseous hydrates, have indicated that, TBAB has the most significant impact on carbon dioxide hydrate.

Carbon dioxide occupancies inside ice XVII structure from grand-canonical Monte Carlo simulation

Clathrate hydrate is a promising material that can be used to trap the carbon dioxide (CO2) as a mean for the greenhouse-gas emission control. A compromise between experimental findings and density functional theory calculations was recently made to determine the occupancy of the newly reported CO2 clathrate hydrate of ice XVII structure. In this work, a hybrid isobaric Grand-Canonical Monte Carlo simulation is performed as a direct approach to determine CO2 occupancy inside ice XVII structure. The simulation results show that the CO2-to-water ratio starts at about 1:3.55 under lower pressure and ends at about 1:4 under high pressure. The potential energy of CO2-water interaction as a function of CO2 molecule displacement inside the voids shows a cage-like character, and the orientation of CO2 molecules inside the spiral void is shown to be well-ordered. The simulation results support the experimental observation and provide molecular insight into the structure of CO2 molecules inside the ice XVII structure.

Accurate Calculation Procedure for V-x Parameters of Hydrothermal Gold Ore Fluid Inclusions

Determining the V-x parameters of H2O–NaCl–CO2 fluid inclusions (total density of inclusions, gas content, homogenization pressure, etc.) is of great value for the exploration of hydrothermal deposits. However, previous accurate calculation methods are only applicable to H2O–NaCl–CO2 fluid inclusions with homogenization temperature above 300 °C and CO2 phase homogenization temperature above the CO2 clathrate melting temperature. In this paper, a new calculation method is proposed to accurately solve the V-x parameters of H2O–NaCl–CO2 fluid inclusions with complete homogenization temperature lower than 300 °C. The algorithm first determines the salinity of inclusions with respect to the melting temperature of CO2 clathrate and the partial homogenization temperature of the CO2 phase and then determines the internal pressure of inclusions when CO2 clathrate is completely melted. The V-x parameters of the inclusions are then iteratively solved. The new algorithm does not require a visual estimation of the volume fraction of the CO2 phase as an input parameter. It is possible to avoid the significant error brought about by traditional method of calculating the inclusion V-x parameters involving visual estimation of the CO2 phase volume fraction. A computer program is developed on the basis of the new method and is applied to the analysis of fluid inclusions in medium and low temperature hydrothermal gold ore.

Transformation of hydrogen bond network during CO2 clathrate hydrate dissociation

The kinetic process of the solid-liquid first-order phase transition of carbon dioxide CS-I hydrates with various cavity occupation ratios has been investigated in order to understand the framework of the H-bond network and the local structure of each water molecule. This includes the time dependent change in short-range order at temperatures close to the melting point and comparison with the hexagonal ice structure. Using the molecular dynamics method, dependencies of the internal energy of the studied systems on the time of heating were found. Jumps in the internal energy of solids in the range at 275–300K indicate a phase transition. The study of the oxygen‑oxygen radial distribution and hydrogen‑oxygen‑oxygen mutual orientation angles between molecules detached at no >3.2Å led to the determination of the H-bond coordination number for all molecules and the total number of H-bonds and showed instantaneous (<1ns) reorganization of the short-range order of all molecules. Structural analysis of neighbor water molecule pairs showed ~10–15% decrease in the H-bond number after melting whereas all molecules form a single long-range H-bond network. Analysis of the H-bond network showed minor changes in the H-bond interaction energy at the solid-liquid phase transition.

The CO2 inventory on Mars

We use spacecraft measurements to determine the inventory of CO2 gas on Mars. We estimate the amounts of gas from an early, thicker Martian atmosphere that have been lost to space by impact ejection and by solar and solar-wind stripping, and that have been removed to non-atmospheric reservoirs of CO2 ice, clathrate hydrate, adsorbed gas, or carbonate minerals. Loss to space has removed 1–2 bars of CO2. Deeply buried carbonates may contain up to the equivalent of a bar of CO2, with the other sinks likely containing no more than ∼90 mbar of CO2. These sinks can readily account for loss of the bulk of an early CO2 atmosphere thought to be necessary to provide early greenhouse warming. Loss of CO2 from the atmosphere to these sinks is the likely explanation for the transition in climate from an early, warmer atmosphere to the cold, dry atmosphere that has been present since early in the Hesperian epoch.

Experimental and modelling studies on the effects of nanofluids (SiO2, Al2O3, and CuO) and surfactants (SDS and CTAB) on CH4 and CO2 clathrate hydrates formation

Sodium dodecyl sulfate (SDS) with concentrations of 300 ppm and 500 ppm; cetyl trimethylammonium bromide (CTAB) with concentrations of 220 ppm and 700 ppm; and water-based nanofluids of SiO2, Al2O3, and CuO with concentrations of 0.1, 0.3, and 0.5 wt% were used as kinetic promoters in methane hydrate formation process at initial conditions of 274.15 K and 5.5 MPa and carbon dioxide hydrate formation process at initial conditions of 274.15 K and 3 MPa. Englezos and Bishnoi model was utilized for calculating the apparent rate constant of hydrate growth and van der Waals-platteeuw model coupled with CPA equation of state was used to model hydrate phase equilibrium conditions. SDS with a concentration of 500 ppm and CTAB with a concentration of 700 ppm are the most effective promoters in increasing the average apparent rate constant and water to hydrate conversion. SiO2 nanofluid with a concentration of 0.3 wt% shows the most promising promotion effects by reducing the induction times of CO2 and CH4 hydrates formation by 70 and 74%, respectively. Aqueous solution of SDS with a concentration of 500 ppm is the most effective promoter that can enhance the average apparent rate constant of CO2 and CH4 by 350 and 200%, respectively.

Experimental measurement of carbon dioxide clathrate hydrate in the presence of adamantane and other water soluble and insoluble additives

In this communication, hydrate thermodynamic equilibrium data of adamantane + water + carbon dioxide, 10, 20 and 30 wt fractions of tert-butanol(2-methyl 2-propanol) + water + CO2, 4.5 and 14.5 wt fractions of 2,5-dihydrofuran + water + CO2, 15 and 20 wt fractions of 1,3,5-trioxane + water + CO2, methyl-tert-butyl-ether (MTBE) + water + CO2 and mix of 10 wt% 1,3,5-trioxane and 3.5 wt% 2,5-dihydrofuran + water + CO2 were measured in the pressure range of 1.5–3.5 MPa using isochoric pressure search method. This work took advantage of the Gibbs Phase rule for adamantane and MTBE without considering their weight fraction. The results showed that 1,3,5-trioxane and 2,5-dihydrofuran are good promoters, especially mix of them. 2-methyl 2-propanol acts as an inhibitor in the presence of CO2. Methyl-tert-butyl-ether and adamantane had no impact on CO2 clathrate hydrate.

Macroscopic defects upon decomposition of CO2 clathrate hydrate crystals.

Micrometer- and submicrometer-sized pores and macroscopic defects like cracks and tubular channels can be found in a variety of clathrate hydrates (hydrates for short) during formation and decomposition. Their origin, their evolution in time, and their effect on hydrate decomposition kinetics are unclear. We used time-lapse micro computed tomography (μCT) in combination with temperature control and pressure monitoring to study the formation and evolution of pores and macroscopic defects in decomposing CO2 hydrates at subzero (Celsius) temperature. Our results suggest that the decomposition of hydrates is always accompanied by the formation of pores and an increase of the apparent hydrate volume by more than 3%. Hydrate decomposition often starts with the formation of cracks inside the hydrate and not necessarily at the free surface of the hydrate, which frequently remains intact for a long period and seems to be self-preserved in some regions. Decomposition spreads out from these cracks in a uniform fashion yielding a variety of macroscopic features. In some cases, the propagating decomposition front seems to get blocked by planar barriers inside the hydrate yielding regions with high resistance against decomposition. This, together with a generally heterogeneous distribution of decomposition resistant regions, challenges the shrinking core model of hydrate decomposition as well as the popular ice-rind theory used to explain the effect of self-preservation.

Formation of carbon dioxide clathrate hydrate from amorphous ice with warming

To investigate the formation mechanisms of CO2 clathrate hydrate under vacuum conditions, infrared spectra of vapor-deposited H2OCO2 amorphous ice were measured. From analyses of variations in the spectral features with warming, remarkable changes were found at ∼100 K. The results indicate that the deposited amorphous ice is transformed into CO2 clathrate hydrate at around ∼100 K. From the results, a phase diagram of CO2 clathrate hydrate from vapor deposited amorphous ice was predicted. The results suggest the existence of pure CO2 clathrate hydrates in space.

X-ray powder diffraction study of the stability of clathrate hydrates in the presence of salts with relevance to the Martian cryosphere

Water on the present day Martian surface is thought to exist in two thermally distinct sub-surface reservoirs: as ice in the cryosphere and as groundwater located deeper in the crust. These sub-surface environments are thought to contain saline, rather than pure, water and laboratory studies on whether or not clathrate hydrates can form in such environments are lacking. We fill this gap by performing synchrotron radiation X-ray powder diffraction to investigate the formation and evolution of clathrate hydrates in weak chloride solutions at CO2 pressures, and over temperature ranges, that are similar to those found in the Martian regolith. We have found that clathrate hydrates can form under conditions relevant to the Martian cryosphere, despite the presence of chloride salts. We find that the dissociation temperatures for CO2 clathrate hydrates formed in saline solutions are depressed by 10–20 K relative to those formed in pure water, depending on the nature of the salt and the CO2 pressure. We suggest that the inhibiting effect that salts such as MgCl2, CaCl2 and NaCl have on clathrate hydrate formation could also be related to the salts’ effect on the formation of the low temperature phase of ice. However, despite the inhibiting effect of the salts, we conclude that the presence of clathrate hydrates should still be possible under conditions likely to exist within the Martian cryosphere.