Preparation Features and Some Properties of Nickel Chloride Crystal Hydrates

Hydrates and asphaltene-resin-wax deposits are increasingly concerned as a terrible problem in the field of offshore oil and gas production and transportation. The rheological property of propane gas hydrate in the water-in-asphaltene-resin-wax deposit (W/ARWD) emulsion was in situ characterized by experiments in a stress-controlled rheometer with particular focus on the effects of pressure, emulsion component ratio, and deposit composition. Results demonstrated that the higher pressure could accelerate hydrate formation and aggregation in a shorter time, and exhibit more obvious shear-thinning behavior of hydrate slurry. The emulsion component ratio was positive correlation with the hydrate slurry viscosity and the yield stress, was negative correlation with the hydrate crystallization time. Asphaltene and wax occupied more nucleation sites on water droplets and formed physical barriers to hinder the hydrate crystallization. The promoting effect of resin on hydrate crystallization was stronger than inhibiting effect. With the increase of asphaltene, resin, and wax contents, the yield stress of hydrate slurry gradually increased, and the effect of wax on the yield stress was stronger than asphaltene and resin, which was associated with the multiple effects of capillary bridge between hydrate particles and spatial network of wax crystals. Furthermore, the coupling effect of pressure, emulsion component ratio, and deposit composition on the rheological properties of hydrate slurry had been studied. This study is significant in that it can helpfully support the development of subsea multiphase flow assurance in petroleum production.

Mechanical properties of polycrystalline tetrahydrofuran hydrates as analogs for massive natural gas hydrates

Replacement of the traditional thermodynamic hydrate inhibitors (methanol and glycols) in wet gas applications is more and more highly desirable for cost savings and for Health, Safety & Environment (HSE) considerations. This seems achievable by using alternative Kinetic Hydrate Inhibitors (KHI). KHIs are able to delay hydrate formation for the time needed to transport the effluents in hydrate region conditions. The KHI efficiency is generally based both on the subcooling that can be matched by the inhibitor and on the hydrate formation time delay that the inhibitor can provide. Within the frame of various Field Development studies carried out since 1990, we have had the opportunity to evaluate the performance of several KHIs. These evaluations have been conducted on two hydrate loop facilities with a service pressure of respectively 80 bara and 165 bara. Thanks to these two pilots, we have been able to observe and to quantify the influence of various parameters on the KHI efficiency. Among these parameters, two of them have proved to be of importance: the presence of other inhibitors, such as corrosion inhibitors (CI), and the operating pressure. Their strong influence is illustrated in this paper through the results obtained in three different case studies. The practical conclusion is that KHIs selected in "routine" lab tests may be not efficient in the field and that appropriate selection tests are required. Introduction From a flow assurance point of view, gas hydrate formation is undoubtedly dreaded as the major risk of plugging the oil and gas subsea production systems. Natural gas hydrates. Natural Gas hydrates are ice-like crystalline compounds that form whenever water molecules contact hydrocarbon gas molecules of low molecular weight (from methane to butane) or other gas molecules such as N2, CO2 or H2S. The hydrate crystals can be represented as a network of hydrogen-bonded water molecules forming cages with gas constituents trapped within. Three different structures have been identified: I, II and H. However, it is unlikely that the structure H exists in the oil and gas production systems. Consequently, only structure I and II are expected to form with natural gases under production conditions. These structures are illustrated in figure 1. Structure I and II are constituted by two kinds of cavity: a small one 512 found in both structures and a large one 512 62 and 512 64 for the structure I and II, respectively. These two structures can be stabilized by gas molecules having the molecular size in the range 3.5 - 7.5 Å. The structure I is stabilized by small gas molecules such as methane or ethane, and mixtures of both; but the presence of a small amount of a larger molecule like propane or iso-butane with methane/ethane results in the formation of structure II. As a consequence, structure II is, by far, the most common hydrate structure that can potentially form in the oil and gas production systems. Contrary to ice crystals, natural gas hydrate crystals are able to form at temperatures higher than 0°C as soon as the pressure is higher than a few tens of bar. Conditions promoting gas hydrate formation are high pressure (typically > 30 bara) and low temperature (typically < 20°C). Precise conditions in terms of pressure and temperature depend on the composition of the fluids. Hydrate formation can occur for all the produced fluids if required P-T conditions are reached: natural gas, gas with condensate and crude oil with associated gas, with condensed or formation water. Figure 2 shows typical curves delimiting, in a P-T diagram, the thermodynamic hydrate stability zones for a natural gas with condensate from North Sea, and for crude oil with associated gas from Gulf of Guinea. The region where hydrate crystals are thermodynamically stable is on the left side of the curve, no hydrate can form on the right side of the curve. General discussions on hydrate properties can be found in the literature1–4.

Gas hydrates form at high pressure and low temperatures in marine sediments and permafrost regions of the earth. Despite forming in nanoporous structures, gas hydrates have been extensively studied only in bulk. Understanding nucleation and growth of gas hydrates in nonporous confinement can help create ways for storage and utilization as a future energy source. Herein, we introduce a new method for studying crystal orientation/tilt during tetrahydrofuran (THF) hydrate crystallization under the influence of nano-confinement using polarized Raman spectroscopy. Uniform cylindrical nanometer size pores of anodic aluminum oxide (AAO) are used as a model nano-confinement, and hydrate experiments are performed in a glass microsystem for control of the flash hydrate nucleation kinetics and analysis via in situ polarized Raman spectroscopy. The average THF hydrate crystal tilt of 56 ± 1° and 30.5 ± 0.5° were observed for the 20 nm and 40 nm diameter pores, respectively. Crystal tilt observed in 20 and 40-nanometer-size pores was proportional to the pore diameter, resulting in lower tilt relative to the axis of the confinement at larger diameter pores. The results indicate that the hydrates nucleation and growth mechanism can depend on the nanoconfinement size. A 1.6 ± 0.01 °C to 1.8 ± 0.01 °C depression in melting point compared to the bulk is predicted using the Gibbs-Thomson equation as a direct effect of nucleation in confinement on the hydrate properties.

Thermodynamic and crystallographic properties depending on hydration numbers in tetra-n-butylammonium chloride semiclathrate hydrates

In recent years, carbon nitride (CN) compounds, such as g-C3N4 and melem, have attracted attention as new visible light-driven photocatalysts with a variety of functions, including water splitting, organic decomposition, and dark photocatalysis. The building unit of these materials is the heptazine ring, and molecules with this structure have attracted considerable attention as luminescent materials. Melem is an organic molecule with amino groups at the three termini of its heptazine ring. Melem exhibits near-UV (NUV) emission with high quantum yield via thermally activated delayed fluorescence (TADF). Materials exhibiting TADF can achieve highly efficient luminescence without the use of heavy metals, generating interest in their potential as luminescent materials for organic electroluminescent devices. Compared to materials that emit in the visible-light region, there are few reports on TADF materials such as melem that exhibit NUV emissions. Melem hydrate is easily obtained by hydrothermal treatment of melem. Unlike melem crystals, melem hydrate (Mh) has a porous structure because of a hydrogen-bond network formed between melem and water molecules. To date, only one type of Mh has been well-investigated. Mhs are expected to exhibit novel properties, such as photocatalysis, molecular adsorption, and highly efficient NUV emission. Mh also provides an opportunity to investigate how hydrogen bonds between the melem molecule and crystal water affect the TADF NUV emissions. This provides clues to the mechanism of the TADF action exhibited by other melem compounds. In this study, we focus on a new melem hydrate with a parallelogram shape, Mhp, first reported by Dai et al. in 2022. The crystal structure of Mhp reportedly differs from that of Mh; however, the Mhp crystal structure has not been determined to date, and its physical properties have not been investigated. Therefore, in this study, we reexamined the conditions for growing single crystals of Mhp and succeeded in growing samples that could be used to measure physical properties. We also determined its crystal structure and investigated the role in crystal formation of the hydrogen bonds between melem and water molecules. We evaluated the thermal behavior and optical properties and discussed their correlation with the crystal structure. Similar to melem, Mhp displayed NUV luminescence in its photoluminescence (PL) spectrum. This luminescence was found to have high quantum yield and delayed fluorescence. At low temperatures, the PL of Mhp dramatically increased at a wavelength of approximately 350 nm. This behavior was attributed to a significant change in the hydrogen-bond network between melem and water molecules in the Mhp crystal at low temperatures. We found that distortion of the melem molecule in the excited state at low temperatures was suppressed by its strong hydrogen bonds with water molecules. As a result, the displacement of the atomic nuclei of the atoms that make up the melem molecules in the excited state produced by light absorption is small, and in the de-excitation process, radiative transitions to low-energy vibrational levels are promoted. At the same time, nonradiative deactivation was suppressed, resulting in high fluorescence quantum efficiency. The results of this research provide deep insight into the role of hydrogen bonds in the optical properties of hydrate crystals that exhibit highly efficient luminescence, including TADF.

Given the scale and urgency of the climate crisis, the exploration of innovative approaches for greenhouse-gas CO2 capture and sequestration is imperative. This hinges on capturing of CO2 emissions from sources, and storing it into other long-lived, stable carbon “pools” or “sinks”, such as in the form of gas hydrates. Being crystalline solids, gas hydrates have the ability to store gas effectively therein –with gas molecules “imprisoned” in cavities within an otherwise ice-like lattice. To address the limitations of hydrate-based methods for carbon capture, such as stability, scalability, and environmental impacts, gas-nanobubble technology may be integrated into hydrate formation to enhance the efficiency and viability of gas-hydrate formation. Nanobubbles (NBs) have been confirmed to accelerate gas-hydrate crystallisation through the so-called memory effect. However, the mechanism of interactions between NBs and hydrate crystals has not been fully addressed. It is also vital to investigate the optimal conditions for hydrate formation in the presence of NBs for higher stability and scalability. In this study, a novel method, combining NBs and gas hydrates to enhance the capturing of CO2, is reported. It aims to demonstrate the effects of NBs on hydrate-formation kinetics, and reveals the mechanism of their interactions during the hydrate-crystallisation process by an integration of laboratory experiments and molecular dynamics simulations. NBs were generated by external electric fields with CO2 gas in deionized water. By controlling the processing time and applied voltage, different size and concentration of NBs were expected. DLS measurements were applied to characterise the generated NBs. The kinetic properties of CO2 hydrate formed by NBs solution were analysed experimentally. Numerical dynamics simulations were also applied to simulate the hydrate-formation process in the presence of CO2 NBs with different concentrations. These modelling efforts help in predicting the behavior of the system under different conditions. The simulation results revealed that throughout the growth process, the size and shape of NBs changed, progressively reducing in size. It appears that the hydrate clusters absorbed gas molecules from the surrounding gas clusters, leading to the disappearance of the NB in some systems. These bubble remains in the vicinity of the hydrate interface and supplies CO2 for the hydrate growth. When these bubbles reached a critical size where stability was compromised, they collapsed, resulting in a localized increase in CO2 concentration in the aqueous phase, further promoting hydrate growth. The interaction between water and CO2 molecules increased as the hydrate surface absorbed the gas molecules from the solution and consumed them to form new hydrate cavities. Therefore, CO2 molecules have less preference to interact with each other and thus the gas clusters were shrinking during the simulation. The outcome of this study deepens the understanding of nanobubble dynamics and addresses the critical role of nanobubbles in CO2 hydrate-crystallization processes - directly contributing to the mitigation of climate-change impacts. 

Experimental investigation on the synergistic influence of tetra-n-butyl ammonium bromide(TBAB) and cyclopentane(CP) in hydrate-based gas separation

1. On the basis of a crystal chemical study of crystals of 3,5-dinitro-[(N′-(5-nitrofurfuliden)] benzhydrazide, we have established that the increase in their photosensitivity is due to the new way in which the crystal hydrates are formed (with participation of dimer associates of water). 2. The molecules of the studied ketohydrazone are close-packed into energetically favorable shifted stacks; as a result, the stacks themselves are also close packed. The dimer water associates are located in the channels between the stacks. 3. We have assigned the stretching vibration bands for the four nonequivalent hydrogen atoms of the water molecules in the IR spectra. We have shown that in the water dimer, the oxygen atom forming the N-H...OH2O hydrogen bond is a stronger proton acceptor than the oxygen atom of the monomeric water molecule.

The polycrystalline samples and single crystals of crystal hydrates of inorganic triphosphates with ring-like and chain-like anion structured were synthesized: lithium and sodium cyclotriphosphates, sodium and ammonium chain triphosphates, and double salts of chain triphosphoric acid (ammonium-potassium, ammonium-magnesium, ammonium-manganese). The crystallization field of the double salt of variable composition (NH4,K)3H2P3O10 ·xH2O (NH4 :K=0.23–3.60; x=0.8–1.5) from aqueous solutions was established. Synthesis of Na5P3O10 · 6D2O crystals has been performed by the interaction of the high temperature form Na5P3O10 (I) with D20. At 20°C and relative humidity RH < 70–80% the (NH4) 5P3O10·2H2O crystals lose their transparency and generate different crystalline products depending on RH value: (NH4)5P3O10 at RH=0% or (NH4)5P3 10 · H2O at RH=32%. The (NH4) 5P3 O10 · H2O crystals are stable at RH < 60–70%, at RH=80% they absorb water and transform into (NH4) 5P3O10 · 2H20. In the latter case a characteristic picture is registered: on active sites situated on the (NH4) 5P3O10 · H2O crystal face the appearance and epitaxial growth of (NH4) 5P3O10 · H2O crystals is observed. For some single crystals the character of dehydration localization has been shown to correlate with space arrangement of phosphate groups in crystal structure. On the basis of the obtained results a model of dehydration front propagation in crystals has been suggested.

The crystal structure determines the properties of compounds and materials, although one can find simple yet industrially relevant compounds such as potassium acetate (KOAc) and its hydrates for which the properties and even the composition still remain misunderstood, owing to the lack of structural data. In this study, the crystal structures of KOAc polymorphs and hydrates were determined for the first time. The water content in the crystal hydrates was reliably determined revealing two new phases 3KOAc·2H2O and KOAc·xH2O (x = 0.38-0.44), instead of the "sesquihydrate" and "hemihydrate" that for a century were believed to be the main hydrated forms of KOAc at ambient temperature. The number and nature of phase transitions were clearly established, and the hydration-dehydration processes were studied in detail by variable-temperature X-ray diffraction and thermal analyses.

The aim of work is to determine the lowest and effective amount of nano SiO2 (NS) for cementitious paste and identify the complex impact of NS and chemical admixtures on cement hydration and physical-mechanical properties. In order to achieve the aim, cementitious specimens with different types and amounts of NS were formed. Further, after the selection of NS and its amount, specimens were formed with various superplasticizers. The work analysis the following properties of cementitious mixtures and hardened cement stone: flow diameter, exothermal temperature, density, ultrasound pulse velocity, compressive strength, microstructure and mineralogical composition. It was determined that the greatest strength of cementitious specimens was obtained when 0.02 wt.% of NS was used, and, compared to control specimens, it increased by ∼15%. Additionally, the greatest increment in strength was observed for specimens with melamine-based superplasticizer. Compared to control specimens, the strength increased up to 23% and the obtained density and ultrasound pulse velocity were the greatest. XRD analysis showed that all specimens had analogue crystal hydrates formed but their amounts are different. SEM analysis showed that structure of the specimens with NS is denser.

Novel report on SHG efficiency, Z-scan, laser damage threshold, photoluminescence, dielectric and surface microscopic studies of hybrid inorganic ammonium zinc sulphate hydrate single crystal

Effect of strontium slag on early hydration and mechanical properties of belite-C4A3$ cement

Understanding the crystal properties of semiclathrate hydrates is important for their potential application in gas storage and separation. In this work, the phase equilibria of TBAB–CO2 hydrates were measured and hydrates formed from the solutions where TBAB concentrations ranged from 0.01 to 0.32 mass fraction were analyzed using Raman and powder X-ray diffraction. Results showed that the equilibrium pressure of TBAB–CO2 hydrate was more sensitive to temperature than that of simple CO2 hydrate, and the equilibrium temperature also got increased with a rise in TBAB concentration. By measuring the hydrate samples formed at 274 K and 3 MPa, the simple CO2 hydrates could be found distributed randomly and discontinuously in the samples, while the TBAB–CO2 hydrate crystals were relatively large. The simple CO2 hydrate was found to coexist with TBAB–CO2 hydrate, and the TBAB·38H2O was the only semiclathrate hydrate structure regardless of the initial concentrations of TBAB. When the TBAB concentration was high,...