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Thermodynamic hydrate promoters and kinetic hydrate promoters can be used to reduce the P–T conditions for clathrate hydrate synthesis to decrease the nucleation induction time while increasing growth rates. Two commonly used promoters for hydrate research are tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS), which can increase the overall hydrate promotion when used in tandem as compared to individually. There are several molecular theories regarding how SDS promotes hydrate growth. This study explores the micellular theory, for which hydrate formation depends on surfactant aggregates (micelles) at a critical micelle concentration (CMC) to increase the interfacial surface area. The micellular theory is the most investigated and criticized surfactant hydrate promotion theory. To address questions related to micellar behavior, this study investigates the intermolecular behavior between SDS and THF for the identification of micelles at hydrate-forming conditions. The systems explored contained THF at 3 and 5 wt. % with varying concentrations of SDS below and above the CMC. Several methods including a qualitative visual method, conductivity, interfacial tensiometry, 13C Liquid-state Nuclear Magnetic Resonance (NMR) spectroscopy, and 1H diffusion NMR spectroscopy were evaluated at temperatures below the Krafft point of SDS and above 0 °C. The presence of THF at low concentrations decreased the critical temperature for the formation of SDS micelles, where SDS is solubilized in THF/water solution at hydrate-forming temperatures without precipitation. The CMC of SDS was decreased significantly even at hydrate-forming conditions. Mixed surfactant–cosolvent micellular behavior of SDS in the presence of low concentrations of THF was confirmed at hydrate-forming conditions above 0 °C. [ABSTRACT FROM AUTHOR]

The conversion of CO2 into solid hydrates for seabed storage is a promising greenhouse gas mitigation method, but the influence of reservoir types on hydrate formation remains unclear due to the complexity of marine sediments. This study examines three endmember sediments-montmorillonite, diatoms, and glass beads-representing clay-, silt-, and sand-dominated reservoirs, respectively. A series of kinetic experiments, morphological observations, and electrical sensitivity tests were conducted to assess the impact of these sediments on hydrate formation. The results show that the surface electric field and water migration properties of montmorillonite provide additional nucleation sites, promoting hydrate formation during the induction period. Gas consumption and hydrate conversion rate in the montmorillonite system were five times higher than those in the deionized water control group and ten times higher than those in the diatom and glass bead systems. While diatoms facilitated milder reactions in later stages, rapid hydrate formation in montmorillonite impeded further CO2 mass transfer. Glass beads exhibited stringent formation conditions with Ostwald ripening effects. Hydrate films initially formed at the gas-liquid interface and spread into gas and water phases via surface tension-driven water migration. Electrical sensitivity tests revealed an inverse correlation between sensitivity and induction/reaction times across sediment types. [ABSTRACT FROM AUTHOR]

A comprehensive crystallographic study is presented of the complete series of rare-earth(III) chloride hydrates. Early lanthanides form dimeric [(H2O)7RE(μ-Cl)2RE(H2O)7]4+ binuclear complexes in which each RE atom (RE = La3+, Ce3+) is coordinated by seven H2O mol­ecules and two bridging inner-sphere chloride ions. Di-μ-chlorido-bis­[hepta­aqua­lanthanide(III)] tetra­chloride, [(H2O)7RE(μ-Cl)2RE(H2O)7]Cl4, crystallizes in the triclinic space group P⥘. Heavier lanthanides exhibit monomeric [RECl2(H2O)6]+ units where each RE atom (RE = Pr3+, Nd3+, Sm3+–Lu3+) is coordinated by six H2O mol­ecules and two inner-sphere chloride ions. Hexa­aqua­dichlorido­lanthanide(III) chlorides, [RECl2(H2O)6]Cl, adopt the monoclinic space group P2/c. In both structures, the cationic inner-sphere complex is counter-charged by the corresponding number of outer-sphere Cl− anions, in which the metal ion and outer-sphere chloride ion lie on crystallographic twofold axes. Crystal structures for all compounds were determined in high quality with refined H-atom positions and were collected at the same temperature (100 K), providing a uniform structural dataset and addressing discrepancies in previous reports. The crystal structure of [HoCl2(H2O)6]Cl is reported for the first time. [ABSTRACT FROM AUTHOR]

The management and prevention of hydrates are crucial for the gas industry. This study delves into the intricate challenges associated with gas hydrate formation, with a specific focus on investigating the impact of corrosion by‐products on prevention strategies. Employing a distinctive methodology, the sapphire pressure–volume temperature (PVT) cell was utilized. Experimental tests were conducted using sodium chloride (NaCl) concentrations of 1% and 3% to simulate brine solution levels at the wellhead, incorporating 3% filtrate and unfiltered iron carbonate (FeCO3) as corrosion products associated with the production process. The 1% and 3% salt concentrations were chosen to encompass a broad range of temperature depressions, reflecting common industry standards for simulating realistic environmental conditions. PVT cell test conditions ranged from 80 to 200 bar, with increments of 40 bar. The experiments investigate the effects of common pipeline salts on a monoethylene glycol (MEG)/water mixture in the presence of methane gas at typical industry high‐pressure conditions. The investigation uncovers that the introduction of salts to water, methane, and MEG solutions serves as a hydrate inhibitor, with inhibitory effects directly correlated to salt concentration. While generally hydrate growth inhibition is beneficial in natural gas pipelines, the findings indicate that elevated salt concentrations and lower pressure conditions contribute to the formation of larger hydrates, heightening the risk of surface adhesion and potentially introducing complications in piping equipment, despite the decreased temperature at which these hydrates form due to the inhibitory effects of the salts. In particular, the mixed condition of 3% NaCl and 3% FeCO3 (filtered) has the strongest effect. Examination of hydrate formation temperature and macroscopic observations suggests that the existence of substantial precipitates, as evidenced in the unfiltered FeCO3 sapphire cell experiment, may have the potential to enhance hydrate growth. [ABSTRACT FROM AUTHOR]

Rb2[TeS3] and Rb2[TeS3] ⋅ 1/3 H2O were obtained from rubidium azide (RbN3), tellurium and sulfur in 2 : 1 : 3 molar ratios from evacuated fused silica ampoules at 500 °C under more or less anhydrous conditions. Both compounds crystallize orthorhombically in the space group P212121 (Rb2[TeS3]: a=873.42(6) pm, b=1316.73(9) pm, c=2064.59(14) pm; Rb2[TeS3] ⋅ 1/3 H2O: a=872.97(6) pm, b=1299.82(9) pm, c=2148.26(15) pm, both at –173 °C for Z =12) and contain discrete ψ1‐tetrahedral [TeS3]2− anions (d(Te−S)=232–236 pm) in layerwise arrangements. The difference results from the water of hydration in Rb2[TeS3] ⋅ 1/3 H2O, which increases the coordination numbers of half of the six crystallographically distinct Rb+ cations from six and seven (only sulfur) to seven and almost eight by providing with oxygen from H2O an extra ligand (d(Rb−O)=290–318 pm). Red Rb2[TeS3] transforms pseudo‐topotactically into yellow Rb2[TeS3] ⋅ 1/3 H2O immediately upon contact with moist atmosphere. The compounds were screened with X‐ray diffraction, Raman and diffuse reflectance spectroscopy as well as thermal analysis. [ABSTRACT FROM AUTHOR]

Measurements of terahertz absorption spectra of pharmaceutical hydrate samples are achieved under a normal humidity condition by combining terahertz frequency-domain spectroscopy with a newly proposed method for suppressing absorption peaks caused by water vapor. In this method, only simple mathematical operations such as subtraction, thresholding, interpolation, and smoothing are applied to extinction (or absorbance) data obtained by locating samples under a normal humidity condition. By considering the difference in spectral line width between narrow absorption peaks caused by water vapor and the relatively wide absorption peaks caused by active pharmaceutical ingredients (APIs) in solid forms, the absorption peaks caused by water vapor can be effectively suppressed without affecting the absorption peaks of the APIs in the samples. In the present study, levofloxacin hydrates were used as samples to investigate the performance of the proposed method. Spectra were obtained under both dry and normal humidity conditions. The temperature of the samples was raised from 300 to 363 K to dehydrate them and brought back to 313 K to observe hydration under the normal humidity condition. Spectra obtained under the normal humidity condition were processed with the proposed method. The spectra of the hydrates obtained under the dry condition were slightly different from those obtained under the normal humidity condition and processed by our method. Dehydration during the measurements under the dry condition was suggested. Stable and reliable results are expected by measuring spectra under normal humidity conditions and applying the proposed method to suppress absorption peaks by water vapor. [ABSTRACT FROM AUTHOR]

Polymer crystal hydrates (PCHs) are crystalline solids that form between a polymer and water. To date, only four distinct PCHs have been discovered—one of polyoxacyclobutane (POCB) and water, and three different polymorphs of polyethyleneimine (PEI) and water. These PCHs were first reported decades ago and have fascinating structures and peculiar properties that make them potentially useful for a wide range of applications including refrigeration, proton conduction membranes, and desalination. This perspective revisits what is known about these compounds, categorizes their similarities and differences with other known compounds, and offers a perspective into future efforts to discover new PCHs to address technological needs for society. [ABSTRACT FROM AUTHOR]

Energy and environmental issues have increasingly garnered significant attention for sustainable development. Flexible and shape‐stable phase change materials display great potential in regulation of environmental temperature for energy saving and human comfort. Here, inspired by the water absorption behavior of salt‐tolerant animals and plants in salinity environment and the Hofmeister theory, highly stable phase change salogels (PCSGs) are fabricated through in situ polymerization of hydrophilic monomers in molten salt hydrates, which can serve multiple functions including thermal management patches, smart windows, and ice blocking coatings. The gelation principles of the polymer in high ion concentration solution are explored through the density functional theory simulation and verified the feasibility of four types of salt hydrates. The high concentration chaotropic ions strongly interacted with polymer chains and promoted the gelation at low polymer concentrations which derive highly‐stable and ultra‐moisturizing PCSGs with high latent heat (> 200 J g−1). The synergistic adhesion and transparency switching abilities accompanied with phase transition enable their smart thermal management. The study resolves the melting leakage and thermal cycling stability of salt hydrates, and open an avenue to fabricate flexible PCM of low cost, high latent heat, and long‐term durability for energy‐saving, ice‐blocking, and thermal management. [ABSTRACT FROM AUTHOR]

The double oxalates MI3[MIII(C2O4)3] possess rich crystallochemistry and can be used as precursors for various ceramic materials. The article discusses a case of Li3[Al(C2O4)3]. A series of previously unknown hydrates (Li3[Al(C2O4)3] ⋅ 5.5H2O, Li3[Al(C2O4)3] ⋅ 4H2O, Li3[Al(C2O4)3] ⋅ H2O) was found for this composition, their crystal structure and temperatures of mutual transformations determined. Transformation from Li3[Al(C2O4)3] ⋅ 4H2O to Li3[Al(C2O4)3] ⋅ H2O was found to be accompanied by a change in the topology of the bonding network. Uniaxial negative thermal expansion was found for anhydrous Li3[Al(C2O4)3]. Thermal decomposition of Li3[Al(C2O4)3] was demonstrated to be a promising way to obtain precursors for aluminate ceramics. [ABSTRACT FROM AUTHOR]

The structure of the title compound (4d), unexpectedly obtained in the reaction between o-phenylenediamine and 2-benzoylcyclohexanone instead of the target 3H-benzo[b][1,4]diazepine derivative 3d, was determined spectroscopically in solution and by a single-crystal X-ray diffraction (XRD) study. It involves two enantiomeric rotamers, called forms D and U, of which the structure was elucidated based on NMR spectra measured and predicted in DFT-GIAO calculations. An averaging of δCs for all tautomeric positions in the benzimidazole part of the 4d hydrate studied in wet (probably slightly acidic) CDCl3 unambiguously indicates tautomeric exchange in its imidazole unit. An XRD analysis of this material confirms the existence of only one tautomer in the solid phase. The non-covalent interactions forming between molecules of water and benzimidazole derivative are shorter than the sum of van der Waals radii and create an infinite-chain hydrogen bond motif along the b-axis. A possible mechanism for the observed cyclocondensation is also proposed. [ABSTRACT FROM AUTHOR]

Atom Sums are optimized additive values for the chemical elements which may be used to predict thermochemical values of inorganic solids. Since they are based on the elements of the Periodic Table they are a complete set of parameters, subject only to the availability of reference thermochemical data. In the present publication, optimized data is presented for ambient formula unit volumes, enthalpies, entropies and heat capacities for both inorganic hydrates and anhydrates. These data complement previously published Atom Sum parameters for formation reaction entropies and for formation reaction Gibbs energies as well as complementing earlier data for undifferentiated inorganic solids.

Levofloxacin (LF), a pure levo-isomer of ofloxacin, is a quinolone-class antibiotic marketed in its hemihydrate (LF-½H) crystal form. Another LF hydrate is known as monohydrate (LF-1H), and LF-½H and LF-1H dehydration results in a pair of anhydrous polymorphs: LF-γ (from LF-½H) and LF-α (from LF-1H). Herein, a pure crystalline material of each of these four LF crystal forms has been successfully produced and systematically characterized by X-ray powder diffraction (PXRD), infrared attenuated total reflectance spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analyses. Coupling cyclic DSC and ex-situ PXRD analyses allowed probing dehydration, melting, crystallization and polymorphic phase transitions involving LF-½H, LF-1H, LF-α, LF-γ, and LF-δ (an enantiotropic polymorph of LF-γ). Furthermore, for the first time, the LF-½H, LF-1H, LF-γ and LF-α equilibrium solubilities were individually measured in five different aqueous media (pH from 1.0 to 7.2). The general solubility order is: LF-γ > LF-½H = LF-α > LF-1H. The crystal phases identified in the residual solid materials separated from equilibrium solutions show that LF-½H and LF-α forms in converted to LF-1H. The information provided herein about stability and solubility of known LF crystal forms proved to be essential to control the hydration/dehydration/rehydration process between the LF crystalline phases and ensure safe drugs with low toxicity or design LF solids with properties improved physical chemistry. [ABSTRACT FROM AUTHOR]

Multi‐walled carbon nanotubes (MWCNTs) are an excellent hydrate promoter, with their own Brownian motion of nanoparticles effectively shortening hydrate nucleation and accelerating hydrate formation. In this work, the properties of methane hydrate formation in a complex system of MWCNTs, sodium dodecyl sulphate (SDS) and NaCl were investigated. It was shown that the compounding system effectively enhanced the kinetics of methane hydrate formation, and the gas consumption of the reaction reached 0.38 MPa at 100 ppm MWCNTs, an increase of 865.8% compared to the pure water system, effectively promoting methane hydrate. In the complexed system, NaCl significantly enhanced the dispersion of MWCNTs, with 1000 ppm NaCl showing the best kinetic promotion effect. SDS not only increases the gas–liquid contact area through the wall attachment effect, but also enhances the dispersion of MWCNTs by adsorbing on the surface of carbon nanotubes and forming an electronic layer with NaCl. MWCNTs not only improve the mass transfer of the system through Brownian motion, but their large heat transfer coefficients can also effectively conduct the heat generated by the system. However, MWCNTs become agglomerated with increasing concentration, making the kinetic promotion effect weaker and the solution less stable, resulting in shorter shelf life. This study confirmed the effective promotion of hydrate formation by MWCNTs under the ultrasonic compounding system, and also provided a reference for related studies on the compounding of MWCNTs with NaCl. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) are greatly limited in their practical application because of their poor cycle performance, low conductivity and volume expansion. Herein, molten salts (MSs) FeCl3·6H2O-NMP with low temperature via simple preparation are used as the anode material of LIBs for the first time to break through the bottleneck of LIBs. The good fluidity and high self-healing of FeCl3·6H2O-NMP effectively avoid the collapse and breakage of the structure. Based on this feature, the initial discharge specific capacity reached 770.28 mA h g-1, which was more than twice that of the commercial graphite anode. After 200 cycles at a current density of 100 mA g-1, the specific capacity did not decrease rather it was found to be higher than the initial discharge specific capacity, reaching 867.24 mA h g-1. Besides, the good conductivity of MSs provides convenience for the removal and intercalation of Li+. The active H sites that can combine with lithium ions form LiH and provide capacity for LIBs. Density functional theory (DFT) calculation also provided theoretical proof for the mechanism of LIBs. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of tests carried out on a titanium plate of a heat exchanger in which the flowing medium was hot gases with a temperature of 110 °C and a pH of less than 1. Strong hydrogenation of the titanium plate caused by the corrosion of the adjacent steel frame plate was detected. As a result of the synergy of the hydrogenation and erosion, a relative reduction in the thickness of the plate was observed locally by up to 94% in relation to the thickness of the titanium plate in the area not affected by degradation. The results of this study are not only of key engineering importance with regard to equipment design and the prevention of mechanical failures in titanium heat exchangers, but also with regard to equipment in other industries. [ABSTRACT FROM AUTHOR]

Hydrates are crystalline solids with an ice-like texture, which are formed when light hydrocarbon molecules and water combine to form a specific ordered structure. Hydrate formation begins at the water–hydrocarbon interface, which highlights the critical role that interfacial rheology plays in this process. Despite the significance of this interface in hydrate formation, a gap in research persists, particularly in employing shear rheology approaches. This study helps to fill this void by investigating the mechanical and flow properties of the interface, using a feature in a rotational rheometer, a "double wall ring cell," for precise temperature control. Cyclopentane serves as the hydrate former, allowing experimentation under atmospheric pressure and varied temperatures. Protocols explore temperature and hydrocarbon concentrations, with emphasis on ice crystal involvement in hydrate formation initiation. Following complete saturation of the hydrocarbon/water interface by hydrates, interfacial elastic and viscous moduli are obtained through strain sweeps to assess hydrate film fragility and mechanical response. Additionally, the impact of aging time and shear type (static or dynamic) on hydrate stiffness is examined. Tests with thermodynamic inhibitors, such as sodium chloride and monoethylene glycol, demonstrate significant induction time extension. Furthermore, systematic changes in the shear rate are investigated to comprehensively understand their influence on hydrate film characteristics and properties under varying shear history conditions. This study reveals that increasing shear rate correlates with decreased viscosity of the hydrate film, indicative of non-Newtonian behavior. Overall, this research sheds light on the nuanced dynamics of the water–hydrocarbon interface in hydrate formation and mitigation. [ABSTRACT FROM AUTHOR]

Accurate estimation of formation conditions plays a pivotal role in effectively managing various processes related to hydrates, including flow assurance, deep-water drilling, and hydrate-based technology development. The formation temperature of methane hydrates in the presence of brine greatly affects the efficacy and accuracy of these processes. This work presents a comprehensive and novel comparative analysis of nine distinct machine learning models for accurate prediction of formation temperatures of methane hydrate. This study investigated the application of major machine learning (ML) algorithms including multiple linear regression (MLR), long short-term memory (LSTM), radial basis function (RBF), support vector machine (SVM), artificial neural network (ANN), gradient boosting regression (GBR), gradient process regression (GPR), random forest (RF), and K-nearest neighbor (KNN). The model accuracy was validated against a large dataset comprising of over 1000 data points with diverse range of salt concentrations. In this regard, model accuracies were compared using several metrics including R2, ARD, and AARD. The experimental results exhibited KNN algorithm to be fast-converging, accurate, and consistent over the entire range of data points with an R2 score of 0.975 and AARD of 0.385%. The results enable efficient and accurate temperature estimation with ML algorithms for multiple hydrate-related processes. [ABSTRACT FROM AUTHOR]

Determining how gas hydrate distribution evolved along continental margins in the past is essential to understanding its evolution in the future. Moreover, hydrate decomposition has been linked to several catastrophic events, including some of the largest submarine landslides on Earth and the massive release of greenhouse gases into the ocean. Offshore Romania, the presence of a second bottom‐simulating reflector (BSR) provides an opportunity to gain valuable insights into hydrate dynamics since the Last Glacial Period (LGP). We conducted transient modeling of hydrate thermodynamic stability by merging in‐situ observations with indirect assessments of sea‐bottom temperature, thermal conductivity, salinity, sedimentation rate, and sea‐level variations. We reveal a strong correlation between the BSRs and the base of the Gas Hydrate Stability Zone (GHSZ) during both the present and LGP periods. The gradual evolution of the GHSZ over the past 34 ka presented here supports a conceptual model that excludes catastrophic environmental scenarios. Plain Language Summary: Methane hydrate is an ice‐like compound composed of a cage of water molecules enclosing a methane molecule. Hydrates can form in marine sediments along continental margins where water and methane are present under high pressure and low temperatures. As a result of climate change, hydrate melting has been linked to catastrophic events, including submarine landslides and the release of greenhouse gases into the ocean. Offshore Romania, the presence of a relic of the base of the hydrate layers formed in sediments during past glacial conditions, reveals the evolution of the hydrate stability zone since the last glacial period. The 2D modeling results have enabled us to define the area where hydrates alternately melt and reform in response to environmental changes such as rising temperatures and sea levels. Our results show that the evolution of gas‐hydrate accumulations generates multiple, slow chain reactions, preventing the system from disastrous destabilization, sequentially provoking catastrophic events. Key Points: A 2D modeling reveals the observed deeper secondary BSR is mostly consistent with a paleo‐BSR developed during the last glacial periodA paleo‐BSR can only be preserved in sediments if the period of stagnation of the base of hydrate layers is sufficient to trap enough gasAlthough rapid environmental changes, the hydrate‐free gas system reacts much more slowly preventing catastrophic submarine destabilization [ABSTRACT FROM AUTHOR]

The number of crystal structures of pertechnetates derived from aqueous solutions has been expanded from seven to over 30. We report the conversion of NH4TcO4 to aqueous HtcO4 via acidic cation exchange. This is followed by the synthesis and structural elucidation of pertechnetate salts of alkaline earth (AE), transition metal I and lanthanoids (Ln) elements. Various degrees of hydration and coordination are discussed. Where possible, a comparison with the perrhenate homologues is made. The described syntheses and materials may be used as novel starting materials for extended technetium research. [ABSTRACT FROM AUTHOR]

The exploitation of natural gas hydrates is in essence the process of hydrate dissociation from the solid phase into the gas and liquid phases, which is a complex problem involving phase transition and gas-water multi-phase flow. Permeability is a useful parameter for characterizing the flow capacity of sediments, and the pore-structure changes caused by hydrate dissociation make this parameter characterized by spatial and temporal evolution. Clayey silt sediments form the hydrate accumulation reservoir in the South China Sea, whose lithological characteristics (shallow buried deep, poor permeability, and low cementation) are unfavorable to fluid flow, leading to difficulties in the production prediction of clayey silt hydrate-bearing sediments. In this paper, the mutual feed-back mechanism between pore-structure and permeability during hydrate dissociation was clarified using the lattice Boltzmann model method. Core-scale seepage experiments were carried out to validate the dynamic evolution of permeability relationship. The permeability calculation module of Tough+Hydrate code was developed to quantitatively describe the evolution of this relationship, and the first hydrate production test in the Shenhu area was evaluated to validate the applicability of pore- and core-scale study at the site scale. This study clarifies the dynamic evolution mechanism of permeability during hydrate dissociation, and establishes a permeability evolution model in a S-shape suitable for clayey silt hydratebearing sediments. [ABSTRACT FROM AUTHOR]

In the initial two publications in this series we established predictive additive Atom Sum thermochemical quantities for inorganic solids for each of the chemical elements. With the chemical elements being a finite set, these data cover the whole of the domain of inorganic solids so far as reference data is currently available.We here introduce a dataset augmented in hydrates, and divide our analysis between the hydrates and anhydrates. The Atom Sum terms are better directed independently to these disparate inorganic groups thus providing improved estimates of the corresponding predicted thermochemical quantities. In this paper we provide both updated formation reaction entropies and previously unpublished Gibbs energies.

The influence of cold seep methane on the surrounding benthos is well-documented but the fate of dissolved methane and its impact on water column biogeochemistry remains less understood. To address this, the distribution of dissolved methane was determined around three seeps on the south-east Hikurangi Margin, south-east of New Zealand, by combining data from discrete water column sampling and a towed methane sensor. Integrating this with bottom water current flow data in a dynamic Gerris model determined an annual methane flux of 3 x 105 kg at the main seep. This source was then applied in a Regional Ocean Modelling System (ROMS) simulation to visualize lateral transport of the dissolved methane plume, which dispersed over ~100 km in bottom water within 1 year. Extrapolation of this approach to four other regional seeps identified a combined plume volume of 3,500 km³ and annual methane emission of 0.4-3.2 x 106 kg CH4 y-1. This suggests a regional methane flux of 1.1-10.9 x 107 kg CH4 y-1 for the entire Hikurangi Margin, which is lower than previous hydroacoustic estimates. Carbon stable isotope values in dissolved methane indicated that lateral mixing was the primary determinant of methane in bottom water, with potential methane oxidation rates orders of magnitude lower than the dilution rate. Calculations indicate that oxidation of the annual total methane emitted from the five seeps would not significantly alter bottom water dissolved carbon dioxide, oxygen or pH; however, superimposition of methane plumes from different seeps, which was evident in the ROMS simulation, may have localized impacts. These findings highlight the value of characterizing methane release from multiple seeps within a hydrodynamic model framework to determine the biogeochemical impact, climate feedbacks and connectivity of cold seeps on continental shelf margins. [ABSTRACT FROM AUTHOR]

We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6‐amino‐6‐methylperhydro‐1,4‐diazepinetetraacetic acid) that contain a dimethyl‐amide group (AAZTA‐MA)3−, two dimethyl‐amide groups (AAZTA‐BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: kex298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA‐MA)(H2O)2], [Gd(AAZTA‐BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine‐coordinated complexes. [ABSTRACT FROM AUTHOR]

CO2 hydrate technology can be applied to seawater desalination. However, the kinetics of CO2 hydrate formation were inhibited in the aqueous solution with inorganic salts, and the kinetic mechanism of CO2 hydrate formation for inorganic salts with different metal cations and anions was still unclear. In this work, CO2 hydrate nucleation and growth were studied in aqueous solutions of metal chlorides. Instead of Na+ and K+ ions, CO2 hydrate nucleation was promoted in the presence of Ni2+, Mn2+, Zn2+ and Fe3+ ions due to the co‐ordination bonds between transition metal ions and water molecules to enhance the formation of the critical crystal nuclei. The induction time was increased by 61.1% in aqueous solution with 0.32 mol/L NaCl, while it was shortened by 55.6% in FeCl3 aqueous solution at the same concentration of Cl− anions. In the process of CO2 hydrate growth, Cl− ions played a more important role than the metal ions in affecting the stability of CO2 hydrate cages. The gas storage capacity was reduced by 10.3% in the presence of NaCl, and was lower than that of other metal chlorides. Cl− anions were absorbed on the hydrate surface and involved in hydrate cages to inhibit the hydrate growth due to the hydrogen bonds between the Cl− ions and water molecules of the hydrate cages. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hypothesis Additives like Tetrahydrofuran (THF) and Sodium Dodecylsulfate (SDS) improve Carbon Dioxide (CO 2) hydrates thermal stability and growth rate when used separately. It has been hypothesised that combining them could improve the kinetics of growth and the thermodynamic stability of CO 2 hydrates. Simulations and Experiments We exploit atomistic molecular dynamics simulations to investigate the combined impact of THF and SDS under different temperatures and concentrations. The simulation insights are verified experimentally using pendant drop tensiometry conducted at ambient pressures and high-pressure differential scanning calorimetry. Findings Our simulations revealed that the combination of both additives is synergistic at low temperatures but antagonistic at temperatures above 274.1 K due to the aggregation of SDS molecules induced by THF molecules. These aggregates effectively remove THF and CO 2 from the hydrate-liquid interface, thereby reducing the driving force for hydrates growth. Experiments revealed that the critical micelle concentration of SDS in water decreases by 20% upon the addition of THF. Further experiments in the presence of THF showed that only small amounts of SDS are sufficient to increase the CO 2 storage efficiency by over 40% compared to results obtained without promoters. Overall, our results provide microscopic insights into the mechanisms of THF and SDS promoters on CO 2 hydrates, useful for determining the optimal conditions for hydrate growth. • SDS and THF promoters are antagonistic when above a temperature threshold. • In the presence of THF and CO 2 , SDS forms micellar aggregates. • Experiments support the simulation insights. [ABSTRACT FROM AUTHOR]

Carbon dioxide capture, utilization and storage technology is considered to be one of the most effective strategies to mitigate CO2 emissions. In this process, CO2 that is injected into seabed sediments under specific temperature and pressure conditions is sealed in the form of CO2 hydrate, known for its high gas storage density and exceptional security features. This method has significant advantages compared with onshore geological storage schemes. Thus far, however, there has been no industrial demonstration of CO2 hydrate storage, and the CO2 hydrate storage potential in the South China Sea remains underexplored without targeted evaluations. In this study, the phase equilibrium mechanism is combined with the volumetric method to describe and evaluate the CO2 hydrate storage distribution range, effective thickness, and potential volume available for CO2 hydrate storage. Based on the latest exploration and development data from the Qiongdongnan Basin, along with geological structure data, multibeam bathymetry, local high-resolution three-dimension multichannel seismic reflection data, logging data, and submarine heat flow data, the distribution of the CO2 hydrate storage stability zone is determined. The results show that the effective thickness and regional scope of CO2 hydrate storage in the concerned area can be determined by virtue of the local water depths and the submarine temperature and pressure of 18 virtual wells. The minimum water depth in the Qiongdongnan Basin that satisfies the temperature and pressure conditions needed for CO2 sediment storage is established as 415 m. The theoretical geological storage capacity of CO2 hydrate in the Qiongdongnan Basin is determined as 5.75x1011 to 8.73x1011 t, where the value range of E is between 0.56 and 0.85. These findings offer a solid foundation for China to create, advance and execute a viable strategy for CO2 hydrate storage. [ABSTRACT FROM AUTHOR]

Hydrates are crystalline structures composed of water molecules and low molecular weight compounds, formed under appropriate conditions of pressure and temperature. Depending on the circumstances, these crystalline solids can be seen as a problem or a solution. In a negative context, gas hydrates tend to cause serious flow assurance problems in the petroleum industry. On the other hand, these hydrates can be used in the separation, transport and storage of gas, playing an important role in reducing the impacts caused by greenhouse gases (GHG). In this context, there is a need for a consistent assessment of the thermodynamic equilibrium of systems with a tendency to form hydrates in order to solve the problems and enable their largescale use. Therefore, this study presents a rigorous analysis of hydrate phase equilibrium in systems composed of carbon dioxide (CO2), methane (CH4), propane (C3H8) and glycerol (C3H8O3). For this, the is o fugacity and Gibbs energy minimization methodologies were used. With this work, it was possible to develop a rigorous evaluation of the phase equilibrium of hydrate-forming systems, investigate the use of C3H8 as a promoter and C3H8O3 as a hydrate inhibitor, and the influence of thermodynamic conditions on the occupation of hydrate cavities by molecules CO2 and CH4. The results obtained in this study were compared with experimental data available in the literature, enabling the conclusion about the satisfactory prediction of the phase equilibrium behavior of the investigated systems. [ABSTRACT FROM AUTHOR]

During deepwater drilling, testing, production, or hydrate mining, the circulating medium in the wellbore may contain solid particles, such as rock chips and sand, in addition to drilling fluids, gas, and water. In the high-pressure, low-temperature conditions of deep water, gas intrusion can easily combine with free water in the drilling fluid to form hydrates, increasing the drilling risk. Therefore, understanding the formation patterns of hydrates in drilling fluids is of significant importance for the prevention and control of hydrates. This study utilized a small-scale high-pressure reactor to investigate the impact of the stirring rate, NaCl, and methanol additives, as well as the sand content on the hydrate formation process and gas consumption. The results indicate that the hydrate formation process can be divided into an induction stage, a rapid formation stage, and a slow formation stage. The induction stage and rapid formation stage durations are significantly reduced under stirring conditions. In NaCl and methanol solutions, hydrate formation is inhibited, with the induction stage duration increasing with higher concentrations of NaCl and methanol. There was no apparent rapid formation stage observed. The final gas consumption decreases substantially with increasing concentrations of NaCl and methanol, reaching no significant hydrate formation at a 20% concentration. The sand content has a significant impact on the slow formation stage, with the final gas consumption increasing within a certain range (in this work, at a sand content of 20%), and being notably higher than in the pure water system under the same conditions. [ABSTRACT FROM AUTHOR]

The influence of cold seep methane on the surrounding benthos is well-documented but the fate of dissolved methane and its impact on water column biogeochemistry remains less understood. To address this, the distribution of dissolved methane was determined around three seeps on the south-east Hikurangi Margin, south-east of New Zealand, by combining data from discrete water column sampling and a towed methane sensor. Integrating this with bottom water current flow data in a dynamic Gerris model determined an annual methane flux of 3 x 105 kg at the main seep. This source was then applied in a Regional Ocean Modelling System (ROMS) simulation to visualize lateral transport of the dissolved methane plume, which dispersed over ∼100 km in bottom water within 1 year. Extrapolation of this approach to four other regional seeps identified a combined plume volume of 3,500 km3 and annual methane emission of 0.4–3.2 x 106 kg CH4 y-1. This suggests a regional methane flux of 1.1–10.9 x 107 kg CH4 y-1 for the entire Hikurangi Margin, which is lower than previous hydroacoustic estimates. Carbon stable isotope values in dissolved methane indicated that lateral mixing was the primary determinant of methane in bottom water, with potential methane oxidation rates orders of magnitude lower than the dilution rate. Calculations indicate that oxidation of the annual total methane emitted from the five seeps would not significantly alter bottom water dissolved carbon dioxide, oxygen or pH; however, superimposition of methane plumes from different seeps, which was evident in the ROMS simulation, may have localized impacts. These findings highlight the value of characterizing methane release from multiple seeps within a hydrodynamic model framework to determine the biogeochemical impact, climate feedbacks and connectivity of cold seeps on continental shelf margins.

This review discusses the entire progress made on the anthelmintic drug praziquantel, focusing on the solid state and, therefore, on anhydrous crystalline polymorphs, amorphous forms, and multicomponent systems (i.e., hydrates, solvates, and cocrystals). Despite having been extensively studied over the last 50 years, new polymorphs and the greater part of their cocrystals have only been identified in the past decade. Progress in crystal engineering science (e.g., the use of mechanochemistry as a solid form screening tool and more strategic structure-based methods), along with the development of analytical techniques, including Synchrotron X-ray analyses, spectroscopy, and microscopy, have furthered the identification of unknown crystal structures of the drug. Also, computational modeling has significantly contributed to the prediction and design of new cocrystals by considering structural conformations and interactions energy. Whilst the insights on praziquantel polymorphs discussed in the present review will give a significant contribution to controlling their formation during manufacturing and drug formulation, the detailed multicomponent forms will help in designing and implementing future praziquantel-based functional materials. The latter will hopefully overcome praziquantel's numerous drawbacks and exploit its potential in the field of neglected tropical diseases. [ABSTRACT FROM AUTHOR]

The Qiongdongnan Basin (QDNB), located in the north of the South China Sea, is a Cenozoic rift basin with abundant oil and gas resources. Large flake hydrates have been found in the core fractures of Quaternary formations in the deep-water depression of the QDNB. In order to understand the spatial distribution patterns of these fractures, their geneses in sedimentary basins, and their influences on gas migration and accumulation, such fractures have been observed using high-resolution 3D seismic images and visualization techniques. Four types of fractures and their combinations have been identified, namely bed-bounded fractures/microfaults, unbounded fractures, fracture bunches, and fracture clusters. Bed-bounded fractures/microfaults are mainly short and possess high density; they have developed in mass transport depositions (MTDs) or Meishan and Sanya Formations. The unbounded fractures/microfaults that occur in Miocene–Pliocene formations are mainly long and discrete, and are dominantly caused by strong tectonic movements, the concentration of stress, and sustained intense overpressure. The fracture bunches and fracture clusters that occur in Oligocene–Early Miocene formations have commonly developed with the accumulation of large numbers of fractures and may be related to the release of pressure, diapirs, and basement fault blocks (228.9 ± 1 Ma). In this study, six fluid charging or leakage models are proposed based on distinct fracture types, assuming the uniform conductivity of each fracture. In a 3D space view, a vertical decrease in the fracture scale (number or density) will more likely result in gas supply than dispersion, thus promoting the accumulation of gas in the reservoirs. Nevertheless, the fractures above the Bottom Simulating Reflect (BSR)/seismic anomaly are excessively developed, and bed-bounded fractures within a particular layer, such as MTDs, can easily cause seabed leakage. These results are useful for explaining the vertical migration of gas/fluids in areas and formations with less developed gas chimneys, faults, diapirs, and other structures, particularly in post-rifting basins. [ABSTRACT FROM AUTHOR]

Among the many different types of molecules that form clathrate hydrates, H2 is unique as it can easily diffuse into and out of clathrate cages, a process that involves the physical–chemical interactions between guest (H2) and host (water) molecules, and is unlike any other molecular system. The dynamic and nano-scale process of H2 diffusion into binary structure II hydrates, where the large cages are occupied by larger molecules, was studied using molecular dynamics simulation. As the H2 molecules diffused from one cage to another, two types of diffusion processes were observed: (i) when moving between a pair of large cages, the H2 molecules pass through the central part of the hexagonal rings; (ii) however, when the H2 molecules move from a large cage to a small one, it requires one of the pentagonal rings to partially break, as this allows the H2 molecule to pass through the widened space. While the diffusion of H2 molecules between large cages was found to occur more frequently, the presence of SF6 molecules in the large cages was found to inhibit diffusion. Therefore, in order to attain higher H2 storage capacities in binary hydrates, it is suggested that there is an optimal number of large cages that should be occupied by SF6 molecules. [ABSTRACT FROM AUTHOR]