Hydrate Pellets Research Articles

Hydrate–based SF6 capture and sequestration: Insights from thermodynamics, kinetics, in–situ Raman spectroscopy, and molecular dynamic simulation

Sulfur hexafluoride (SF6) is currently the most potent greenhouse gas to date due to its remarkably long atmospheric lifespan and chemical inertness. Hydrate–based technology provides an innovative solution to capture SF6 under lower pressure conditions and enables the long–term storage of SF6 gas. Herein, we conduct a fundamental study to explore the potential of capturing and sequestering SF6 gas within clathrate hydrates. The three–phase coexistence conditions were measured at the pressure ranging from 0.33 to 1.06 MPa and at ambient temperatures. A thermodynamic model was employed to predict the equilibrium conditions, using an iterative method to calculate the phase equilibrium pressure. Molecular dynamic simulation (MD) was used to observe the growth of SF6 hydrate at the nanosecond scale. In-situ Raman spectroscopy was utilized for analyzing real-time vibrational bands of S–F and O–H in SF6 hydrate, offering crucial insights into hydrate stability and growth. Additionally, microscopic kinetic experiments were also carried out to clarify the impacts of different pressures (0.8, 1.0, and 1.2 MPa) on the nucleation time, gas consumption, and growth rate during hydrate formation in both pure water and seawater. An efficient approach is proposed for the separation of solid–liquid mixtures, fabricating hydrate pellets. The findings of this study establish a foundation for the development of hydrate–based SF6 capture and storage technology.

Comparative kinetics and enhanced desalination efficiency of hydrate-based desalination using HFC-125a, HFC-134a, and HFC-152a through hydrate pelletization and induced melting

The present study demonstrates the feasibility of gas hydrate technology for effective desalination of salt water without requiring pre- or post-treatment. The research highlights two main aspects: the thermodynamic and comparative kinetic properties of hydrofluorocarbon (HFC) gases, and the novel concept of hydrate pelletization enhanced by an induced pellet melting procedure. The thermodynamic viability of HFC gases such as HFC-125a, HFC-134a, and HFC-152a for hydrate formation in both saline and non-saline conditions is underscored. For the first time, a comparative analysis of the gas uptake kinetics for these three gases is presented under 0, 3.5, and 8.0 wt% NaCl conditions. Results indicate that HFC-134a and HFC-152a exhibit rapid gas uptake kinetics, while HFC-125a shows sluggish kinetics, attributed to the effective pressure driving force and subcooling temperature. Regardless of the guest gas, the chosen experimental conditions achieved salt removal efficiency of ~70 % in 3.5 wt% NaCl and ~ 75 % in 8.0 wt% NaCl. The novel induced hydrate pellet melting approach significantly improved salt removal efficiency, exhibiting a nonlinear behavior where the rate of salt removal efficiency increases asymptotically as more hydrate melts. New insights into salt distribution within the hydrate pellet reveal that the core contains higher salinity, than the outer layer.

Thermodynamic phase equilibria study of Hythane (methane + hydrogen) gas hydrates for enhanced energy storage applications

Hydrogen blending with natural gas has become an effective technique for incorporating the characteristics of natural gas and facilitating the storage and transportation of hydrogen gas. The transportation of hydrogen and natural gas (methane) blend, also referred to as Hythane, presents numerous challenges, advantages, and disadvantages that differ based on the technology employed. The current research showcased a thorough examination of the thermodynamics involved in studying the three phase equilibrium analysis of gas hydrate technology for storing Hythane gas mixtures. Three different Hythane compositions varying in hydrogen percentage were selected, and the isochoric gas hydrate phase equilibria study was performed. The experimental results of phase equilibria and thermodynamic modelling using CPA EOS in software were compared. A similar study was also conducted in the presence of a 5.56 mol % THF solution to understand the reduction in the pressure requirement for the phase equilibria. Results from the mixed Hythane+THF gas hydrate findings suggested stable gas hydrate formation at much lower pressure requirements, increasing the credibility of storing Hythane mixtures in gas hydrates at moderate conditions. The gas compositions for each experiment were analyzed using gas chromatography to evaluate the presence of the desired gas in the hydrate phase. Heat exchange during the gas hydrate dissociation was analyzed using a high pressure differential scanning calorimeter (DSC). The change in the heat release temperature also indicates the stability of the gas hydrate, and with increasing hydrogen gas in the blend, the gas hydrate stability decreased. The Clausius-Clapeyron equation was employed to compute the heat of gas hydrate dissociation, and a comparison was made with the heat of dissociation obtained from the DSC study. The experimental investigations on Hythane gas hydrates were performed to find the hydrogen storage inside the gas hydrate phase and compare it with the previous studies of pure hydrogen hydrates. To demonstrate the Hythane gas transportation, Hythane gas hydrate pellets were formed, followed by their storage in a controlled environment to observeany changes in pressure and temperature. The Hythane gas hydrate pellets demonstrated exceptional stability of Hythane gas presenting an intriguing prospect for utilizing gas hydrate technology in Hythane gas transportation.

Fine-scale structural stability of carbon dioxide hydrate pellets under coarse-scale deformation using multi-scale coupled FEM-MD simulations

In this study, we use a coupled finite element method (FEM)–molecular dynamics (MD) methodology to examine the complex deformation response at fine and coarse scales of carbon dioxide hydrate pellets. While previous studies in this area have focused on simple deformations of fine-scale structures using MD simulations, none have attempted to model the stability of hydrate pellets under complex deformations. To accurately represent the geometry of hydrate pellets, we employ FEM to model these cylindrical shapes and extract deformation gradients at each integration point. Subsequently, MD simulations are carried out to capture the detailed fine-scale response to the imposed deformation at each integration point. Further study of constrained expansion within a hydrate pellet uncovers differing responses depending on the location of the integration points. We observe higher peaks of von-Mises equivalent stress where a shear deformation mode is dominant. In all cases, the hydrate cage structure remains intact at an total equivalent strain of around 0.14, which is already beyond the critical point, where the stress of hydrate reaches its maximum value. This indicates that gas hydrate pellets are safe for carbon storage applications when not subjected to deformations above the critical point.

Greenhouse gas (GHG) transport as solid natural gas (SNG) hydrate Pellets: Assessment of Self-Preservation & dissociation controls

Safe greenhouse gas (GHG) transport is an integral part of any carbon capture, utilization, and storage (CCUS) operations. This manuscript discusses the assessment of solid natural gas (SNG) hydrate technology to safely transport GHG utilizing the self-preservation capability of hydrates around 248 K. Ice shielding around hydrate grains has been previously implicated as a key mechanism for self-preservation of hydrates. However, there is a lack of thorough understanding of the hydrate grains sintering and compaction effects on self-preservation prior to the ice crust formation around the grains. In a first of its kind study, the promotional effects of hydrate grains compaction and sintering via pellet porosities, aging times, and formation times on self-preservation are presented. Furthermore, real time operational variables such as depressurization rates and system pressure build-up are studied. A unique integrated apparatus was designed to assess in-situ hydrate pellets formation, compaction, and dissociation. This method eliminated the uncertainties of possible hydrate dissociation during material transfer between the operational stages. Around 248 K, hydrate pellet stability occurs in two states: pre-self-preservation (initial fast hydrate dissociation) and extended self-preservation (slow hydrate dissociation over 200 + hours). Decreasing porosity via compaction and increasing formation and pellet-aging times via prolonged sintering increases hydrate pellet stability. The pellet stability can be further promoted by slowly depressurizing the pellet to ambient pressure and allowing pressure build-up from the dissociating hydrates. Additional transport risks are assessed through a sudden loss of temperature from 248 K, which are missing in the literature. Refrigeration failure of the pellet progresses in two stages: (1) a safe insulation stage characterized by slow dissociation and minimal gas evolution, followed by (2) a rapid dissociation stage during which complete dissociation of the pellet took place. Overall, this work elucidates the transportation factors governing self-preservation and dissociation, thus indicating the feasibility for safe GHG transport via SNG technology.

Atmospheric preservation of CH4 hydrate above ice point: A potential application for high-density natural gas storage under moderate conditions

Clathrate hydrates is an ideal host for natural gas, by entrapping CH4 molecules in cage-like structures composed of hydrogen-bonded water molecules, natural gas can be stored in solid form with high density. However, the suppression of hydrate dissociation under moderate thermodynamic conditions is still challenging. In this study, to increase the preservation stability of CH4 hydrate at atmospheric pressure, a new surface-treatment method was proposed by coating CH4 hydrate with CP-CH4 hydrate. CH4 hydrate pellets formed from ice powder or 0.03 wt% Sodium dodecyl sulfate (SDS) solution were mechanically pressurized with CP to form hydrate pellets. The presence of CP-CH4 hydrate layer on the sample surface was confirmed by Raman spectroscopy, and the hydrate pellet was successfully preserved under superheated conditions, i.e., 0.1 MPa − 0.3 MPa, 279 K − 284 K with a storage volume density up to ~146 VCH4 (STP)/Vwater, and the accumulated CH4 loss was less than 0.3 mol% for hydrate pellet formed from ice powder, and 3 mol% for hydrate pellets formed from SDS solution for at least 8 h.

Stability analysis of methane hydrates for gas storage application

Solidified Natural Gas (SNG) technology offers an attractive option for compact and safe, large-scale natural gas storage. Gas storage technologies are gaining traction due to the increasing demand for natural gas and the expected transition to hydrogen gas-based economies in the near future. Introduction of thermodynamic promoters like THF into the classical methane-water system enables rapid gas uptake at moderate pressure and temperature due to sII hydrate formation, with highly stable storage characteristics. Herein, we compare the stability of cylindrical mixed methane-THF (sII) and pure methane (sI) hydrate pellets, produced using freshwater. Storage pressure for both types of pellets was 1 atmosphere (atm) whereas the storage temperature was 268 K for sII hydrate and 268 K and 253 K for sI hydrate. While only 7.06% gas evolution occured from a methane-THF (sII) hydrate pellet stored at 1 atm and 268 K over a 10 day period, % gas evolution from two pure methane (sI) hydrate pellets stored at 268 K for similar duration was 41.45% and 37.05% individually. Correspondingly, % gas evolution from an sI pellet stored at 253 K was 51.09%. We also report 2 year uninterrupted stability testing of methane-THF (sII) hydrate pellets produced using both fresh and seawater, stored at atmospheric pressure and temperatures of 271 K and 268 K, respectively. To the best of our knowledge, this is the longest successful storage demonstration of any type of methane hydrates ever reported, showcasing the extraordinary stability of sII hydrates produced using both fresh and seawater. The results obtained in the present study resolve the challenge of hydrate stability in SNG technology and strengthen its commercial viability by reducing downstream complications related to gas hydrate storage.

Gas Hydrate Pellets Measured by Means of Phase Contrast X-ray Imaging

Gas Hydrate Pellets Measured by Means of Phase Contrast X-ray Imaging

Seawater Desalination by Hydrate Formation and Pellet Production Process

In order to improve the efficiency of CO2 hydrate-based desalination, cyclopentane (CP) was used as secondary hydrate guest to alleviated temperature requirements for hydrate formation. The cations (Na+, K+, Mg2+, Ca2+) and the anions (Cl− and SO42−) were analyzed by inductively coupled plasma optical emission spectrograph (ICP-OES) and ion chromatography (IC), respectively. Dissociated water from the extracted hydrate pellets showed that the removal efficiency of each ion was 55.72-85.52%.This study illustrated that the apparatus may solve the separation difficulty between hydrate slurry and concentrated seawater, and improve ion removal efficiency, thus it can be applied for more effective desalination and solution concentration.

Investigation of Pore-Formers to Modify Extrusion-Spheronized CaO-Based Pellets for CO2 Capture

The application of circulating fluidized bed technology in calcium looping (CaL) requires that CaO-based sorbents should be manufactured in the form of spherical pellets. However, the pelletization of powdered sorbents is always hampered by the problem that the mechanical strength of sorbents is improved at the cost of loss in CO2 sorption performance. To promote both the CO2 sorption and anti-attrition performance, in this work, four kinds of pore-forming materials were screened and utilized to prepare sorbent pellets via the extrusion-spheronization process. In addition, impacts of the additional content of pore-forming material and their particle sizes were also investigated comprehensively. It was found that the addition of 5 wt.% polyethylene possesses the highest CO2 capture capacity (0.155 g-CO2/g-sorbent in the 25th cycle) and mechanical performance of 4.0 N after high-temperature calcination, which were about 14% higher and 25% improved, compared to pure calcium hydrate pellets. The smaller particle size of pore-forming material was observed to lead to a better performance in CO2 sorption, while for mechanical performance, there was an optimal size for the pore-former used.

Formulation and Evaluation of Teneligliptine Pellet

The present study is an attempt to formulate and evaluate Teneligliptin hydrobromide hydrate pellets. Teneligliptin is a potent, selective DPP-4 inhibitor, which is believed to exert its actions in diabetes mellitus patients. Teneligliptin increases insulin release and decreases glucagon levels in the circulation in a glucose dependent manner. The Teneligliptin pellets were prepared by using blend of MCC, Lactose, Crospovidone and PVP K-30. Pellet formulation was optimized for formulation parameters (concentration of Crosspovidone and PVP K-30) using 32 factorial design. FTIR studies showed absence of chemical interaction between the drug and polymer. The pellets were prepared and evaluated in terms of bulk density, tapped density, angle of repose and in-vitro release study. In-vitro release of drug was compared with in-vitro release of drug from marketed formulation (Dynaglipt Tablet).

Direct use of seawater for rapid methane storage via clathrate (sII) hydrates

Storing natural gas in the form of clathrate hydrates (termed as Solidified Natural Gas, SNG) is highly advantageous as it is non-explosive, environmentally benign and offers compact mode of natural gas storage with high volumetric storage capacity. In this work, we demonstrate rapid methane storage in saline water (1.1 mol% NaCl solution) and seawater via clathrate hydrates aided by 5.56 mol% THF in a simple unstirred tank reactor. We report extremely fast hydrate formation kinetics with methane uptake of 89.2 (±2.4) v/v in 13.8 (±2.4) minutes with saline water and 86.3 (±4.3) v/v in 15.1 (±0.8) minutes with natural seawater (t90). This uptake corresponds to an yield of 77.6 (±2.2)% for saline water and 75.0 (±3.4)% for natural seawater system respectively for the stated hydrate growth time. Further, molecular insights of the mixed hydrate formation in presence of NaCl is derived through high-pressure calorimetry, in-situ Raman, and powder X-ray diffraction analysis. Finally, we demonstrate the stability of the hydrate pellet formed employing direct seawater in presence of THF for two weeks. The direct use of natural seawater makes the SNG technology highly attractive to store/transport methane for large-scale storage needs and for low capacity natural gas production facilities like biogas manufacturing plants.

Methane storage in water frameworks: Self-preservation of methane hydrate pellets formed from NaCl solutions

The use of methane (CH4) hydrate as a CH4 or natural gas storage medium offers an efficient and green source of energy. In this study, we produced CH4 hydrate pellets containing NaCl at up to 2.7 wt%, and storage tests were performed to investigate the stability of CH4 hydrates with NaCl at 253 or 248 K under ambient pressure. Based on assessing mass variations and powder X-ray diffraction analyses, it was determined that the dissociation rate of the hydrate greatly depends on the storage temperature. Below the eutectic point of the water-NaCl system, the hydrate exhibited self-preservation, while specimens readily dissociated at 253 K. The experimental results obtained in this study elucidate the effects of the NaCl solution on the self-preservation of CH4 hydrates, and allow a kinetic model for this self-preservation phenomenon to be proposed. The results indicate that CH4 hydrate pellets formed from sea water are a viable CH4 storage and transportation media below the eutectic temperature.

Swapping methane with carbon dioxide in spherical hydrate pellets

Recovering CH4 with CO2 in hydrocarbon hydrates is renowned as an eco-friendly method for potential energy production and climate change mitigation. Due to the foamy nature of hydrates, determining the effect of hydrate surface area on the CH4 recovering rate has always been a challenge. CH4 hydrates in this work were shaped into spherical pellets 16 mm in diameter, and the CH4-CO2 replacements were carried out at about 274 K, 3.0 MPa by adding different amount of pellets in the reactor. To reveal the kinetic properties, cryo-SEM and a model based on gas diffusion theory was also employed. Results indicated that the CH4 recovery rate in the replacement was proportional to the surface area of hydrate pellets. In each 1400-h replacement, the CH4 production level was found to be about 4.5%, suggesting the gas swapping process took place in each pellet was the same. The kinetic model provided well descriptions of the replacements with the average deviation no more than 10%. The SEM images and the gas diffusion constants obtained from the kinetic model suggested that water mobility determined the gas diffusion rate in hydrates and help to smooth the hydrate surface during replacements.

2-15.船舶ばら積み貨物としてのメタンハイドレートペレットの自己保存効果と温度との関係((4)天然ガス・メタンハイドレート等IV,Session 2 天然ガス・メタンハイドレート等)

2-15.船舶ばら積み貨物としてのメタンハイドレートペレットの自己保存効果と温度との関係((4)天然ガス・メタンハイドレート等IV,Session 2 天然ガス・メタンハイドレート等)

2-3 天然ガスハイドレート海上輸送を目的としたメタンハイドレートペレットの分解限界温度及び分解速度に関する実験的検討((1)ガスハイドレート,Session 2 天然ガス・メタンハイドレート等)

2-3 天然ガスハイドレート海上輸送を目的としたメタンハイドレートペレットの分解限界温度及び分解速度に関する実験的検討((1)ガスハイドレート,Session 2 天然ガス・メタンハイドレート等)

2-11.メタンハイドレートペレットの分解ガス化特性((3)メタンハイドレートIII,Session 2 天然ガス・メタンハイドレート等)

2-11.メタンハイドレートペレットの分解ガス化特性((3)メタンハイドレートIII,Session 2 天然ガス・メタンハイドレート等)

Effect of Long-Term Storage and Thermal History on the Gas Content of Natural Gas Hydrate Pellets under Ambient Pressure

The use of natural gas hydrate (NGH) as a natural gas transportation and storage medium is expected to meet further energy demand in the near future. To exploit NGH for industrial porposes, it is necessary to establish NGH storage systems using their self-preservation properties. In this report, NGH pellets containing CH4, C2H6, and C3H8 were produced by continuous production using a bench-scale unit and successfully stored for 3 months at 253 K under atmospheric pressure. Qualitative and quantitative analyses [phase-contrast X-ray computed tomography (CT) by means of diffraction-enhanced imaging, cryogenic scanning electron microscopy, powder X-ray diffraction, and gas chromatography] were conducted to investigate the progression of dissociation. Some of the NGH pellets were also examined for their thermal history dependence between approximately 85 and 253 K after storage for 1 day or less to assess their stability under a rapid temperature change. The internal texture of the original NGH pellets was de...

Risk Assessment for Natural Gas Hydrate Carriers: A Hazard Identification (HAZID) Study

Sea transport of natural gas in the form of hydrate pellets is a new technological approach. Introducing new technologies bears raises the possibility of introducing unknown risks or—in case of alternatives for already existing technical solutions—higher risk, either human-, environmental-, or property-related. The option of gas transport by natural gas hydrate pellets has been introduced within the Korean joint research project. One key task was the safety evaluation of the novel natural gas hydrate carrier (NGH carrier) developed in the project. The aim of this work was to support and assess the risk aspects of the development to ensure that the risk level for the newly developed concept is as low as for existing competing concepts, especially LNG carriers. The NGH carrier is based on the concept of the self-preservation effect and thereby preserves NGH in the form of pellets at atmospheric pressure and temperatures lower than −20 °C. In order to identify all the possible hazards in the system and then enhance the system safety, a Hazard Identification (HAZID) study was conducted. As a result of the HAZID, 80 identified hazards in total were explored and ranked in terms of risk index for the semi-quantitative risk evaluation. Among the hazards identified, three hazards were found to have unacceptable risk level and twenty eight to have acceptable but ALARP risk level. Regarding the hazards with unacceptable risk or ALARP risk, additional safety actions and recommendations for risk control were discussed and proposed in a SAFETY ACTION REGISTER, which would be considered and utilized by designers when developing the detailed system design in the future. In conclusion, the overall safety level of the NGH carrier is considered acceptable. However, it was found that a few external hazards associated with extremely harsh weather could be critical threats to the system. Relevant safety actions against them, therefore, must be provided in the system design.

Influence of production parameters on gas hydrate and ice powder pelletizing

A lab scale twin roll press machine was developed for pelletizing natural gas hydrate powder. Ice and hydrate powder were used for the pellet extrusion system. The effects of feeding pressure, pressure ratio, and rotating speed of the twin roll were investigated for producing high strength and stiffness hydrate pellets. The compressive strength and stiffness of pellet increased with increasing feeding pressure and rotation speed. In particular, there was a relatively large increase in the stiffness with an increase in rotating speed, and a relatively large increase in strength with increasing feeding pressure. The production ratio of pellets largely depended on the rotating speed of the twin roll. The results indicate the promising future of solid transportation of natural gas.