Hydrate Nucleation Research Articles

Ground granulated iron silicate slag as supplementary cementitious material: Effect of prolonged grinding and granulation temperature

The metallurgical and cement industries contribute significantly to anthropogenic carbon dioxide emissions. Utilizing oxidic by-products from the metallurgical industry as supplementary cementitious materials (SCMs) can improve resource efficiency and reduce emissions from cement production. Iron silicate copper slags have been studied as SCMs, but mainly in systems where Portland cement is used as an activator. There is limited research on the inherent reactivity of the slag under changing processing conditions. The present study offers insight into the effect of granulation temperature and grinding on the inherent reactivity of an industrially produced iron silicate copper slag. The results showed that granulation temperature had an insignificant effect on reactivity, while grinding generated substantial improvements. The latter effect was concluded to stem from the increased specific surface area, increased number of sites for nucleation and growth of hydrates, and changes in the inherent reactivity owing to structural changes induced by the grinding.

Inhibition on methane hydrate formation by polyacrylate superabsorbent hydrogel

Hydrate blockage in submarine oil and gas transport pipelines has always been the focus of attention in the oil and gas industry. Using superabsorbent hydrogels (SAHs), three-dimensional network structures with numerous hydrophilic groups, to prevent hydrate formation in gas/oil pipeline has been endowed with theoretical potential. In this work, the inhibition of traditional polyacrylate SAHs on methane hydrate formation was systematically studied via both numerical and morphological analysis. In methane hydrate formation from SDS solution (1 mmol/L), SAHs at relatively low swelling ratio of 10 and 5 produced obvious inhibition on hydrate nucleation, prolonging the induction time from 27.6 ± 14.5 min to 155.5 ± 157.1 and 334.2 ± 126.6 min, respectively. And the water fixation effects of SAHs could prevent methane hydrate growth from efficiently, with the inhibition efficiency reaching 65.83 ± 1.82 %, 81.82 ± 1.83 %, and 87.96 ± 1.66 % at swelling ratio of 20, 10, and 5, respectively. When used in simulated DI water/decane (W/O) mixture, at water content of 30 %, SAHs performed well at swelling ratio of 50 (mass ratio of 0.6 %), preventing methane hydrate formation by 94 % and keeping the mixture with low viscosity and good fluidity; at water content of 70 %, SAHs produced excellent performance at swelling ratio of 50–100 (mass ratio of 1.4%–0.7 %), preventing methane hydrate formation by 80 % and avoiding increasing the viscosity of the mixture. The results in this work confirmed the promising application potential of SAHs in gas/oil pipeline flow assurance.

CO2 hydrates phase behaviour and onset nucleation temperatures in mixtures of H2O and D2O: Isotopic effects

In this work, we report the CO2 hydrate phase equilibria in water (H2O), heavy water (D2O), and their binary mixtures following the isochoric pressure search method using a rocking cell apparatus. The phase behaviour was mapped within the temperature and pressure range of 276.32 – 284.80 K and 1.59 – 3.78 MPa, respectively. It was found that there is a difference of ∼ 2 K in the equilibrium line of CO2 hydrates formed in H2O and in D2O, respectively. The hydrate dissociation enthalpies obtained using the Clausius-Clapeyron equation indicate almost similar values formed either in D2O, H2O or their mixtures. These shifts in this equilibrium temperature were compared with the triphasic equilibrium temperature variation estimation obtained using Molecular Dynamics Simulations and a very good agreement with the experimentally obtained values was observed. Further, a constant cooling method was used to obtain the onset temperature of hydrate nucleation for these systems at 3.6 MPa. It has been found that during the cooling ramps, the nucleation always occurred in the vicinity of the temperature of maximum density (TMD) of the systems where water still retains some structuredness. The nucleation experiments also give information about the metastable zone width (MSZW) of the studied systems. The results reported in this work indicate the magnitude of the isotopic effect on CO2 hydrate formation and dissociation that may have implications towards the application of hydrate technology for separation and purification processes.

Influence of polymers on the nucleation of calcium silicate hydrates

This work focuses on the investigation of ongoing processes in the pre- and postnucleation stage of C-S-H precipitation at pH 12 and pH 13. Calcium induces the condensation of smaller silicate species to bigger oligomers in the prenucleation stage. By titration in combination with ion-selective electrodes, the effects of additives on the formation of C-S-H can be monitored and quantified in terms of calcium binding, nucleation times, supersaturation, and the post-nucleation behavior showing detailed differences between polymers. Negatively charged polymers inhibit nucleation, neutral or almost neutral polymers do not have an influence on nucleation time and supersaturation and the rare promotion of nucleation has been identified with cationic polymers. The post-nucleation data show the polymer influence on solubility and C/S ratio of the precipitated phase and stabilization of primary nucleated particles against further aggregation or growth. This work can be regarded as a step towards better control of C-S-H precipitation.

The effects of rhamnolipid on the formation of CH4 hydrate and separation of CH4/N2 via hydrate formation

Rhamnolipid (Rha) is an efficient green surfactant that is able to promote hydrate generation, it can be applied to the hydrate method of separating. However, the effect of rhamnolipid on the separation of methane and nitrogen by the hydrate method is not clear. Therefore, in this paper, we investigated the effect of rhamnolipid on methane hydrate formation and the separation between methane and nitrogen via hydrate method. Firstly, the effects of five concentrations (0 ppm, 200 ppm, 400 ppm, 600 ppm and 800 ppm), temperatures and pressures on methane hydrate formation were studied separately. The rate of methane hydrate formation was positively correlated with experimental pressure. The gas consumption increased rapidly with the rhamnolipid concentration, and then increased slowly to a steady state. The final gas consumption above 200 ppm rhamnolipid concentrations could be increased more than five times compared with pure water conditions. The promotion of methane hydrate production is most pronounced at 274.15 K, mainly depending on the diffusion of gas molecules in solution and the ease of hydrate nucleation. Then, the interfacial tension at different concentrations was measured by the suspension drop method, and the relationship between the interfacial tension and the rate of hydrate formation was studied. Hydrate formation rate shows a multiplicative power function with the interfacial tension. What’s more, the kinetics of hydrate formation and gas separation effect of 3:1 CH4/N2 at 274.15 K and 7 MPa were studied with five concentrations. And 200 ppm was found to be the optimum concentration for separation, the separation factor is 8.25. Finally, the kinetics and thermodynamics of hydrate formation and gas separation effect of 1:1 CH4/N2 at 274.15 K and 9 MPa were also investigated, and the separation factor reached a maximum of 12.7 at 800 ppm, and the methane gas recovery rate also reached the maximum at 40.46%. The results of this study can provide some theoretical guidance for the optimal selection of green surfactants in separation by hydrate method.

Interfacial effects on the nucleation probability of gas hydrates in porous media

Understanding how interfacial properties affect the nucleation process of gas hydrates allows for the prediction of formation patterns of gas hydrates in natural sediments, facilitation of gas-hydrate production for energy storage, or inhibition of gas-hydrate formation for flow assurance. A predictive macroscopic mathematical model describing the kinetic nucleation of gas hydrates was developed based on Classical Nucleation Theory (CNT) in order to incorporate the interfacial properties of sediments and other interfaces. The model provides insights into the dependence of the formation mechanism of gas hydrates on a wide range of interfacial properties. The models for nucleation of gas hydrates presented in this work predict two different scenarios for gas hydrates formation in sediments. In hydrophilic sediments, gas hydrates start nucleating at the sediment wall towards a slowly nucleating hydrate phase at the center of the pore. In hydrophobic sediments, gas hydrates start nucleating at the center of the pores, growing towards the pore walls and a slowly nucleating hydrate phase anchored at the point where the gas, liquid and solid phases meet. The model predictions capture the qualitative information obtained from examination of gas-hydrate core samples and experimental observations of gas hydrate formation.

Effects of wax on the formation of methane hydrate in oil-dominate systems: Experiments and molecular dynamics simulations

Hydrate formation and wax deposition in underwater multiphase pipelines have become two vital problems affecting the flow assurance safety. Experiments and molecular dynamics (MD) simulations were performed to investigate the effect of wax crystals on hydrate nucleation and growth. Our experimental results showed that wax crystals had an inhibitory effect on hydrate growth, but played a dual role in methane hydrate nucleation (promotion and inhibition). The addition of wax could decrease mass transfer coefficient of methane by increasing viscosity of oil phase, which lower methane supply from the oil bulk phase to the oil–water interface. The simulation results revealed that the wax crystals at the interface influenced the mass transfer of methane molecules instead of providing heterogeneous nucleation sites. Small wax crystal adjacent to the oil–water interface accelerated methane supersaturation dissolution and restricted gas diffusion in the aqueous phase because of adsorption to methane, which promoted hydrate nucleation and shifted the nucleation position toward the oil–water interface. While the large wax crystal could effectively block the methane mass transfer from oil phase to aqueous phase by covering the oil–water surface, which reduced the concentration of methane in the aqueous phase and prolonged the induction time of hydrate formation. These results of this work would provide a better understanding of the interaction mechanism between hydrate and wax.

Effects of carbon nanotube on the nucleation and growth of CO2 hydrate: Insights from the molecular dynamics simulations

As an essential technology for achieving carbon neutralization, hydrate technology shows broad prospects in CO2 capture and storage. Carbon nanotubes have been used to promote gas hydrate formation as a material with good physical and chemical properties. In this work, molecular dynamics simulations were performed at a pressure of 40 MPa and a temperature of 250 K by adding carbon nanotubes with different quantities and lengths. The simulation results showed that adding one carbon nanotube had little effect on the formation of CO2 hydrate. As the cage structure formed, the hydrate moved away from the carbon nanotubes and repelled them into the critical aqueous phase. When three carbon nanotubes were added, they appeared to agglomerate due to hydrophobicity, which inhibited the formation of CO2 hydrate. Only when two carbon nanotubes were added can they effectively promote the nucleation and growth of CO2 hydrate. At the same time, shorter carbon nanotubes can maximize their excellent thermal conductivity, thus promoting nucleation and stable growth of hydrates. Therefore, the promotion or inhibition effect of CO2 hydrate by carbon nanotubes depends on their size and amount.

Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules. Nucleation is the critical controlling step in gas hydrate formation. Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation. However, how the solid surface compositions control the gas hydrate nucleation remains unclear. Benefiting from the fact that the surface compositions of graphene oxide (GO) can be finely tuned, we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation. The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes. Surface energy, zeta potential, Raman spectra, and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation. The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl. The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions. Therefore, the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes. The ordered water arrangement, similar to methane hydrate cages, significantly accelerated methane hydrate nucleation. Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.

Nucleation of carbon dioxide hydrate in water with variable salt composition

It has been shown that in the carbon dioxide–water system, the rate of gas hydrate nucleation increases with decreasing pH of the aqueous phase. Thus, a new approach has been demonstrated to control the rate of nucleation of carbon dioxide hydrate. Of interest is the question of the prospects for extending this approach to control the nucleation of other hydrates.

Effect of Methanol on the Kinetics of Nucleation and Growth of Methane Hydrate

Effect of Methanol on the Kinetics of Nucleation and Growth of Methane Hydrate

Comparison of the Promoting Activity of Amides of Ethylenediaminetetraacetic Acid and Some Amino Acids in the Nucleation and Growth of Hydrates of Methane and Carbon Dioxide

Comparison of the Promoting Activity of Amides of Ethylenediaminetetraacetic Acid and Some Amino Acids in the Nucleation and Growth of Hydrates of Methane and Carbon Dioxide

Characterization of carbon dioxide hydrate growth kinetics in carbon micron tube oil-water system

Abstract Carbon nanotubes have a significant impact on hydrate formation. However, as the effect and mechanism of carbon micrometer tubes, which have a similar structure to carbon nanotubes, on the promotion of hydrate growth is not yet clear. Therefore, in this paper, experiments on the growth kinetics of CO2 hydrate in oil-water systems under the effect of multi-walled carbon microtubes(MWCMTs) were carried out. The effects of pressure, temperature, and oil- water ratio on the induction period and gas consumption of CO2 hydrate were investigated. It also revealed the hydrate growth promotion mechanism of MWCMTs. The conclusions were as follows: (1) MWCMTs could significantly improve the hydrate gas storage capacity in an oil-water system by up to 80.3% over the pure water system. (2) Pressure and temperature had a large effect on the storage capacity and induction time of CO2 hydrate, and the results showed that the induction time decreased significantly with increasing pressure and decreasing temperature. At the same time, the hydrate growth time was significantly shortened, but the gas storage capacity first increased and then decreased. One reason for this was that the hydrate film hindered gas-water mass transfer, and the other was that the gas dissolved by the oil droplets rapidly generated hydrates and could not continue to transfer gas molecules. (3) In the oil-water system, lipophilic MWCMTs carried adsorbed CO2 to contact water, at the same time provided a large number of hydrate nucleation sites to promote hydrate formation.

Effects of salt content on secondary formation of hydrates in complex systems

AbstractThe phenomenon of ‘memory effect’ exists in the secondary generation of natural gas hydrates, which is mainly manifested in the fact that the induction time required for the nucleation of hydrates in the secondary generation of hydrates is significantly shorter than that of the primary generation, thus accelerating the generation of hydrates. At present, the research on the memory effect phenomenon has been proven to exist, and its influencing factors have become a research hotspot. In order to study the influence of decomposition time and salt content on the memory effect, the hydrate was generated under the system of porous medium alumina complexed with surfactant SDS, and hydrate secondary generation experiments were carried out by adding different contents of NaCl according to four different decomposition times. The influence of four different decomposition times on the memory effect phenomenon in the secondary generation of hydrates and the influence of different salt contents on the memory effect phenomenon were analyzed by observing the pressure drop changes in the reactor during the hydrate generation process and calculating the methane gas consumption. The experimental results show that different decomposition times can affect the effect and time of the memory effect, and the effect of decomposition time on the memory effect does not show a linear relationship. The addition of salt may have an inhibitory effect on the memory effect.

The first trial of hydrate continuous production: Paving way on hydrate-based carbon capture and storage

Hydrate-based solidified natural gas (SNG) technology presents wide promising prospect in the fields of carbon capture, utilization and storage (CCUS), but high-pressure production environment makes it difficult to separate and store the formed hydrate, causing difficulty in achieving continuous hydrate production. In this work, a spiral-agitated hydrate formation setup was proposed, which integrates the functions of hydrate formation, separation and storage, giving rise to hydrate continuous production for the first time. Amino acids were used to enhance hydrate growth kinetics, fast hydrate nucleation, growth and large conversion were obtained under the synergistic effect of amino acids and spiral agitation. CH4 uptake in hydrate in the storage tank is up to 166.71 (±3.44) V/V with a hydrate conversion of 96.92%, this gives rise to considerable CH4 apparent storage density in the storage tank, which is 109.22 (±3.76) V/V at a mild condition (5 MPa) and increases by 88.55% compared with compressed CH4. It totally requires 94.1 (±13.85) kW·h to stir and convey 1 m3 hydrate for continuous hydrate formation, which is significantly saved (40.61%) by pre-filled liquid. The presented technology can fulfill the continuous production of CH4, CO2 and H2 hydrate etc., promoting the application of hydrate-based SNG technology in CCUS.

Dimeric and oligomeric interactions between calcium silicate aqua monomers before calcium silicate hydrate nucleation

Understanding the formation mechanism of calcium silicate hydrate (C-S-H) is pivotal to control the kinetics of calcium silicates hydration and the evolution of C-S-H microstructure. However, the reactions between calcium- and silicate-based aqueous species before or during the process of C-S-H nucleation at molecular level are still unclear. Here, based on ab initio metadynamics simulations, we find that the dimeric interaction between calcium silicate aqua monomers leads to the formation of a calcium silicate aqua Q0-dimer through an ionic bond between calcium and silicate ions and a reduction of hydration number of the Ca ion, which is prior to the formation of silicate dimers (Q1). Besides, the first coordination shell of the Ca ion in the most stable calcium silicate aqua cluster has the characteristics of both tobermorite and jennite structures. We further propose a potential formation pathway for C-S-H, where the replacement of water ligands of the Ca ion by silicates initiates the clustering and dimerization of silicate monomers and promotes the formation of C-S-H.

Methane hydrate nucleation path and structure evolution revealed by Markov modelling

A deep understanding of hydrate formation path is currently one of the most important thresholds for the energy, environmental and safety applications of hydrate. Methane hydrate, a kind of clean energy and the most widespread hydrate clathrates, is selected as the research focus in this study. The trajectories of the hydrate growth are generated by Molecular Dynamics (MD) simulations. Then, these trajectories are analyzed by applying the Markov State Model for the first time, from which the evolution path and structure conversion are extracted. The results show that nine independent meta-stable states can be identified. The findings reveal the existence of nine distinct metastable states during the hydrate formation process. Transitions between these states occur at nanosecond timescales, considerably slower than conventional MD simulations. Moreover, based on the state transitions, a single-track path traversing the metastable states leads to the final state, while two bidirectional paths arise due to the infiltration or escape of methane molecules. These results facilitate the sampling and observation of the hydrate formation process in laboratory conditions and inspire strategies for controlling hydrate evolution.

Crystal growth of tetra-n-butylammonium bromide hydrate nucleated from metallic particles

Nucleation of tetra-n-butylammonium bromide (TBAB) hydrate is unlikely to occur; thus, nucleation promotion is required to nucleate TBAB hydrate. In a previous study, it was found that addition of specific metallic particles effectively promotes nucleation of TBAB hydrate. TBAB hydrate is known to have two stable crystal structures (type A and type B). It is expected that the type of TBAB hydrate crystals that initially grow will differ depending on the molecular structure of the precursor liquid phase influenced by the added metallic particles. In this study, the correlation between the type of added metallic particles and the crystal structure of the formed TBAB hydrate was experimentally investigated. Addition of Ag, Ag–AgBr, Zn, and Zn–ZnO particles promoted nucleation of TBAB hydrate. When Ag or Ag–AgBr was added, type-A TBAB hydrate crystals formed from 10 wt% TBAB aqueous solution, where type-B TBAB hydrate should preferentially be formed. In contrast, when Zn or Zn–ZnO was added, only type-B TBAB hydrate crystals formed from 10 wt% TBAB aqueous solution. These results suggest that Ag and Ag–AgBr affect the molecular structure of the liquid phase, facilitating formation of type-A TBAB hydrate crystals.

Development of novel natural gas hydrate inhibitor and the synergistic inhibition mechanism with NaCl: Experiments and molecular dynamics simulation

Drilling fluid systems with exceptional performance serve as a foundation for commercial hydrate extraction. However, most hydrate reservoirs are located at relatively deep water depths and have shallow burial depths. As a result, there are high demands on the density of a hydrate drilling fluid system. Thus, the traditional hydrate drilling fluid system no longer meet the drilling needs in deep water shallow hydrate reservoirs. In this paper, a copolymer SYZ-2 was synthesized based on N-Vinyl-ε-caprolactam and N, N-dimethyl acrylamide. The effects of SYZ-2 and its NaCl system on methane hydrate were first tested by a constant rate cooling method, and the inhibition mechanisms of the system on hydrate nucleation and formation were investigated by molecular simulations. Meanwhile, the formulation and properties of a low-density hydrate drilling fluid system (1.06 g/cm3) based on SYZ-2 were also described in detail. The experimental results show that the hydrate formation temperature with the influence of SYZ-2 decreases from 10.6 °C to 2.7 °C, which can even be significantly reduced to −3.1 °C in the presence of 7 % NaCl. The molecular dynamic simulation results show that SYZ-2 inhibits the nucleation of hydrates by decreasing the solubility of methane molecules, primarily by promoting the agglomeration of methane molecules. Additionally, SYZ-2 can also adsorb to the surface of hydrates and prevent the hydrate cage structure from capturing methane molecules. In contrast, NaCl inhibits hydrates formation by restricting the movement of water molecules. These results provide valuable insights into a better understanding of the gas hydrate inhibition mechanisms, the rational development of high-performance hydrate inhibitors for drilling fluids, as well as the construction of drilling fluid systems.

Nucleation and Crystallization of Ferrous Phosphate Hydrate via an Amorphous Intermediate.

The fundamental processes of nucleation and crystallization are widely observed in systems relevant to material synthesis and biomineralization; yet most often, their mechanism remains unclear. In this study, we unravel the discrete stages of nucleation and crystallization of Fe3(PO4)2·8H2O (vivianite). We experimentally monitored the formation and transformation from ions to solid products by employing correlated, time-resolved in situ and ex situ approaches. We show that vivianite crystallization occurs in distinct stages via a transient amorphous precursor phase. The metastable amorphous ferrous phosphate (AFEP) intermediate could be isolated and stabilized. We resolved the differences in bonding environments, structure, and symmetric changes of the Fe site during the transformation of AFEP to crystalline vivianite through synchrotron X-ray absorption spectroscopy at the Fe K-edge. This intermediate AFEP phase has a lower water content and less distorted local symmetry, compared to the crystalline end product vivianite. Our combined results indicate that a nonclassical, hydration-induced nucleation and transformation driven by the incorporation and rearrangement of water molecules and ions (Fe2+ and PO43-) within the AFEP is the dominating mechanism of vivianite formation at moderately high to low vivianite supersaturations (saturation index ≤ 10.19). We offer fundamental insights into the aqueous, amorphous-to-crystalline transformations in the Fe2+-PO4 system and highlight the different attributes of the AFEP, compared to its crystalline counterpart.