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Hydrate Formation (hydrate + formation)
Selected AbstractsStudy of the Kinetics and Morphology of Gas Hydrate FormationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2006Abstract The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270,280,K, over a pressure range of 8.83,16.67,bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas-water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110,190,rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis-like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton-like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate. [source] Specific critical concentrations of low dosage hydrate inhibitors in a THF,NaCl hydrate formation solutionASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Ailin Ding Abstract Hydrate formation and its attendant problems are well known in the oil and gas industry. The desire to reduce the costs and environmental impact of traditional hydrate inhibitors has led to a focus on the design, development and evaluation of novel and environmentally friendly low dosage hydrate inhibitors (LDHIs). In this study, two LDHIs, namely Luvicap® EG and Gaffix® VC-713, were tested using tetrahydrofuran (THF) as a hydrate promoter and a ball-stop rig. The ball stop-time was used to determine the inhibition efficiency. The concentration effect of inhibitors, salts and solvents on the ball-stop time was investigated. Results indicated that the inhibition efficiency of an inhibitor is sensitive to the micro-environment of the THF-hydrates activities which includes the concentration and types of these additives. The reproducibility and consistency of the test results were also largely dependent on the concentration of inhibitors. Reliable information was provided only if the concentration of the inhibitor was above a critical concentration, below which the testing results scattered drastically and were inconsistent. As the critical concentration was inhibitor-dependent, a specific critical concentration (SCC) was proposed which is the first reported in such investigations. We concluded that the inhibition efficiency of an LDHI should be determined by both the ball-stop time and its SCC. Comparison of ball-stop times between two inhibitors should be made above their SCCs. Salt and solvent concentrations and other additives present in the operating systems should also be considered when a suitable LDHI concentration is determined for a particular field application. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of surfactants and liquid hydrocarbons on gas hydrate formation rate and storage capacityINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2003Zhigao Sun Abstract Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non-ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69,6.82 MPa and the temperature range 274.05,277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non-ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd. [source] An analysis of liquid CO2 drop formation with and without hydrate formation in static mixersAICHE JOURNAL, Issue 10 2010Hideo Tajima Abstract The formation process of CO2 drops in various types of Kenics Static Mixers was analyzed from the perspective of energy dissipation in the mixer, focusing on the formation of drop surfaces. Experimental studies on CO2 drop formation were conducted under varying temperatures, pressure, and flow rates, with and without hydrate formation. Analysis of the CO2 drop size and distribution at several locations within the static mixer was conducted, as of pressure drop in the mixer, to determine dissipation energies. In all the experimental conditions, by considering the surface energy for hydrate formation, the energy required for the formation of CO2 drops correlated well with total energy dissipation by mixer flow, which is represented by a pressure drop along the mixer. This process has important applications to the formation of liquid CO2 for ocean disposal as a countermeasure to global warming. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Clathrate-hydrate formation by water spraying onto a porous metal plate exuding a hydrophobic liquid coolantAICHE JOURNAL, Issue 4 2009Shinya Fujita Abstract A novel technique for producing a clathrate hydrate from a gaseous guest substance was devised and experimentally tested. This technique employs a horizontally oriented spray nozzle and a vertically oriented porous metal plate placed in opposition to each other in a guest-gas phase. Water is sprayed onto the plate while a precooled hydrophobic liquid coolant is seeping out of the plate to form a continuous film flowing down the plate surface. The coolant film is expected to sweep the heat released by hydrate formation away from the plate surface and, at the same time, to prevent the hydrate crystals from agglomerating on the surface thereby hindering the successive contact of the water spray with the coolant. A series of experiments has been performed to reveal the behavior of hydrate formation in the above scheme of guest-gas/water/coolant contact operations. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Liquid,liquid miscibility gaps and hydrate formation in drug,water binary systems: Pressure,temperature phase diagram of lidocaine and pressure,temperature,composition phase diagram of the lidocaine,water systemJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2010René Ceolin Abstract The pressure,temperature (P,T) melting curve of lidocaine was determined (dP/dT,=,3.56,MPa,K,1), and the lidocaine,water system was investigated as a function of temperature and pressure. The lidocaine,water system exhibits a monotectic equilibrium at 321,K (ordinary pressure) whose temperature increases as the pressure increases until the two liquids become miscible. A hydrate, unstable at ordinary pressure, was shown to form, on increasing the pressure, from about 70,MPa at low temperatures (200,300,K). The thermodynamic conditions of its stability were inferred from the location of the three-phase equilibria involving the hydrate in the lidocaine,water pressure,temperature,mole fraction (P,T,x) diagram. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2756,2765, 2010 [source] Process-induced phase transformation of berberine chloride hydratesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2010Henry H.Y. Tong Abstract Berberine is a natural quaternary ammonium alkaloid used clinically in the chloride salt form for the treatment of diarrhea in many Asian countries. Although the hydrate formation of berberine chloride (BCl) is well documented, the associated mechanism and implications in pharmaceutical formulation have not been studied in detail. In this study, pure BCl dihydrate and BCl tetrahydrate were recrystallized from water and their phase transformation behaviors under defined conditions were investigated. Additionally, pharmacopoeial grade BCl material consisting predominantly of the dihydrate form was examined for potential phase changes when being subjected to a conventional wet granulation procedure for tablet production. Results from solubility measurements, thermal analysis, variable temperature-powder X-ray diffraction (VT-PXRD), and variable temperature-Fourier transform infrared spectroscopy (VT-FTIR) confirmed the solid-state interconversions between the tetrahydrate and dihydrate at 30,49°C and between the dihydrate and anhydrate at 70,87°C. Consistent with the observed phase changes of the two pure hydrates, wet massing of the pharmacopoeial grade BCl sample led to a thermodynamics-driven transition to the tetrahydrate form at room temperature while subsequent tray drying at 50°C caused a reversion back to the dihydrate form. The rate and extent of such hydrate conversion depended largely on the water activity of the granulated powder matrix, which in turn was governed by the particular excipients employed. The present findings have important implications in the regulation of the hydrate forms of BCl in the finished products using specific excipients. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1942,1954, 2010 [source] Solvent-mediated solid phase transformations of carbamazepine: Effects of simulated intestinal fluid and fasted state simulated intestinal fluidJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2009Paula Lehto Abstract Solvent-mediated transformations of carbamazepine (CBZ) anhydrate form III were investigated in Simulated Intestinal Fluid, a simple USP buffer medium, and in FaSSIF, which contains sodium taurocholate (STC) and lecithin, important surfactants that solubilize lipophilic drugs and lipids in the gastrointestinal tract. Raman spectroscopy (in situ) was utilized to reveal the connection between the changes in solid phase composition and dissolution rate while simultaneously detecting the solid state and the dissolved amount of CBZ. Initial dissolution rate was clearly higher in FaSSIF, while the solid phase data revealed that the crystallization of CBZ dihydrate was inhibited in both the dissolution media, albeit by different mechanisms. In SIF this inhibition was related to extensive needle growth, which impeded medium contact with the solid surface by forming a sterical barrier leading to retarded crystallization rates. Morphological changes from the needle-like dihydrate crystals to plate-like counterparts in FaSSIF, combined with the information that the transformation process was leveled off, evidenced strong hydrogen bonding behavior between the CBZ and STC molecules. These results underline the importance of biologically representative dissolution media in linking the in vitro dissolution results of solids that are capable of hydrate formation to their in vivo dissolution behavior. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:985,996, 2009 [source] Study of the Kinetics and Morphology of Gas Hydrate FormationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2006Abstract The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270,280,K, over a pressure range of 8.83,16.67,bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas-water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110,190,rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis-like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton-like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate. [source] | ||||||||||