Hydrate

Through cocrystallization of the broad-spectrum antifungal agent fluconazole (FLZ) with a number of nutraceuticals, we have isolated three distinct solid forms of the drug, namely, anhydrous cocrystal with vanillic acid (VA) and anhydrous and hydrated cocrystals of 4-hydroxybenzoic acid (4OHBA). The new cocrystals have been thoroughly investigated by different analytical techniques, including powder and single crystal X-ray diffractometry (XRD), differential scanning calorimetry (DSC), thermogravi-metric analysis (TG), scanning electron microscopy (SEM), and dissolution and solubility methods. Analysis of hydrogen bond patterns in the crystals has shown structural similarity in the packing of FLZ molecules between the new crystal forms and the structures taken from the CSD. Comparing the theoretical lattice energies of multicomponent crystals and their constituents, we have found that hydrated crystal forms are more energetically preferable than the anhydrous cocrystals. Analysis of noncovalent interaction energies performed within the framework of quantum theory of atoms in molecules and crystals (QTAIMC) has confirmed the structure-forming role of water molecules in the hydrated cocrystal of FLZ with 4OHBA. Thermal analysis and SEM investigations have shown that the dehydration behavior of FLZ monohydrate (FLZ·H 2 O) is highly sensitive to particle size and morphology of crystals. The pH-solubility behavior of the cocrystals has been investigated at different pH values using eutectic concentrations of the components, and the driving force of the cocrystal formation process for each solid phase has been estimated. Possible cocrystallization pathways between FLZ and 4OHBA have been examined under mechanochemical conditions. A two-step formation mechanism of cocrystallization reaction, which includes generation of an anhydrous [FLZ+4OHBA] (1:1) cocrystal as an intermediate, has been proposed.

NoThe surface energy of a-lactose monohydrate measured by inverse gas chromatography (IGC) is reported along with a dynamic molecular modelling study of the interaction of the various molecular probes with different surfaces of a-lactose monohydrate. The IGC results show that a-lactose monohydrate is acidic in nature. Using quantitative calculations of the energy of adsorption, the acidic nature of the surface is confirmed and the calculated values agree closely with the experimentally measured values. Along with the acidic nature, dynamic molecular modelling also reveals that the presence of a channel and water molecules on a surface affects the surface energetics of that face. The presence of water on the surface can decrease or increase the surface energy by either blocking or attracting a probe molecule, respectively. This property of water depends on its position and association with other functional groups present on the surface. The effect of a channel or cavity on the surface energy is shown to depend on its size, which determines whether the functional groups in the channel are assessable by probe molecules or not. Overall molecular modelling explains, at the molecular level, the effect of different factors affecting the surface energy of individual faces of the crystal

The technology of transportation and storage of gas in a gas-hydrated form under atmospheric pressure and slight cooling – the maximum cooled gas-hydrated blocks of a large size covered with a layer of ice are offered. Large blocks form from pre-cooled mixture of crushed and the granulated mass of gas hydrate. The technology of forced preservation gas hydrates with ice layer under atmospheric pressure has developed to increase it stability. The dependence in dimensionless magnitudes, which describes the correlation-regressive relationship between the temperature of the surface and the center gas hydrate block under its forced preservation, had proposed to facilitate the use of research results. Technology preservation of gas hydrate blocks with the ice layer under atmospheric pressure (at the expense of the gas hydrates energy) has designed to improve their stability. Gas hydrated blocks, thus formed, can are stored and transported during a long time in converted vehicles without further cooling. The high stability of gas hydrate blocks allows to distributed in time (and geographically) the most energy expenditure operations – production and dissociation of gas hydrate. The proposed technical and technological solutions significantly reduce the level of energy and capital costs and, as a result, increase the competitiveness of the stages NGH technology (production, transportation, storage, regasification).

The adhesion forces and free energies of separation of structure II clathrate hydrates in vacuum and submerged in water and a model oil are investigated by molecular dynamics simulation. The water molecules are modeled by the TIP4P/ice model and the alkanes by the OPLS_AA force field. The results are compared with theory and earlier work. It is observed that the adhesive forces between the simulated surfaces have an effective range of no more than 1.5-2 nm. The hydrate-hydrate interaction force is attractive in vacuum and oil, larger in vacuum. In water the interaction force is very slightly repulsive on average and much weaker than in the two other systems with a larger uncertainty. In all cases the interaction is largely entropically driven. The separation energies in vacuum and oil (octane) are stronger than predicted by theory, with free energies of approximately 4 and 0.7 aJ, respectively, likely due to lack of polarization effects. The hydrate-hydrate interaction in water is too weak for quantitative comparisons to be made.

The article proposes to using Ocean Thermal Energy Conversion (OTEC) to increase the energy efficiency mining of methane from deposits subaquatic gas hydrates on the gas hydrate cycle (GHET), that will allow not to spend 10-15% of the extracted methane for power supply of a gas-producing complex (GPC). The circuit-technological solution GPC is described, according to which carbon dioxide is introduced into the gas hydrate layer to extract methane from gas hydrates. To improve the kinetics of the process of replacement of methane with carbon dioxide in gas hydrates, it is proposed do recirculation part of CO2. The scheme and cycle of gas-hydrate energy-technological installation GHET are given, which operates using OTEC and generates together with electricity for GPC, fresh water and cold. Based on the method proposed in this paper, a comparative thermodynamic analysis of installations using OTEC for Black Sea conditions was performed. by GHET and Anderson cycles and it is shown that...

Hydrate formation along the natural gas pipeline has been identified as a serious threat to the survival of oil and gas industry. The formation if not quickly removed may plug the flowline to collapse the system. This problem costs the industry billions of dollars in revenue loss annually. While all the available literatures on hydrate formation process have focused on its ability to plug the flow line, there has been little or no recognition of its ability to initiate internal corrosion of the pipeline which is a bigger problem to the industry, hence, the importance of this study. This work focuses on this new area for research interest aimed at revolutionalizing the field of corrosion science and technology.In this study, the composition of the lattice which includes methane (CH4), carbondioxide (CO2) or hydrogen sulphide (H2S) and water molecules (H2O) amongst others is considered. These gases have the ability to easily undergo chemical and/or electrochemical reactions with the p...

We present a detailed theoretical characterization of the structure and interactions in dichlorine clathrate hydrate cages. In the case of the dodecahedral cage, there is clear evidence of the presence of halogen bonding, whereas in the tetrakaidecahedral cage, the expected signatures are there but in a weaker form. Comparison is made with the available structural data from x-ray experiments, where the rotational motion of dichlorine has been taken into account through Monte Carlo simulations illustrating delocalization effects associated with sampling multiple minima, specifically for the larger cage. Finally, the intermolecular potentials have been calculated with local correlation methods, and energy decomposition analysis has been applied to shed light on the nature of the interactions.

Abstract The present work deals with evaluating the dual-functional gas hydrate impact of tetramethylammonium chloride (TMACl) in the presence of different CO2-CH4 content mixed gas hydrate systems (30%CO2 + 70%CH4, 50%CO2 + 50%CH4, and 70%CO2 + 30%CH4). A custom-made high-pressure gas hydrate reactor was used to acquire the temperature–pressure loops for the studied systems in the absence/presence of different concentrations of aqueous TMACl solutions via T-Cycle and isochoric constant cooling method for both THI and KHI investigations, respectively. The electrolyte-based thermodynamic model was also applied to validate the obtained HLwVE results for all the studied systems. The obtained results revealed that TMACl acts dual-functional (thermodynamic and kinetic) hydrate inhibitor for high CO2 content gas systems. The increased concentration of TMACl induces more shifts in HLwVE data with maximum variation attained at10 wt% concentration up to 1.46 K for a high CO2 content methane system owing to the increased hydrogen bonding ability of TMACl. Moreover, TMACl delayed the hydrate formation up to 1.4 and1.5 folds for 274.0 and 277.0 K conditions for high CO2 content mixed gas systems. Moreover, the applied electrolyte-based model could predict the HLwVE data of TMACl in the presence of a mixed gas system within the AAE value of 0.1 % for all the studied mixed gas systems. Furthermore, the KHI performance of TMACl was also compared with commercial inhibitor, i.e., polyvinyl pyrrolidone (PVP), and obtained comparable results. Therefore, the acquired dual-functional results (THI = 1.46 K, KHI = 1.5-fold delay) signpost that TMACl can efficiently work as a potential dual-functional hydrate inhibitor for CO2 enriched mixed gas systems.

The paper deals with methane hydrates generated from natural gas. Methane hydrates in nature. Thermobaric conditions necessary for their generation from the natural gas, composition of december 2015 from the company SPP - distribucia, a.s. It deals with the estimated time of their formation, at a constant pressures of 5, 10 and 15 MPa and at different subcooling temperature. Determination the temperature required for the generation of methane hydrates at these pressures and temperature range based on the equation from research by Kim et. al..