Shunsuke Hashimoto

Correlation of Power Consumption for Several Kinds of Mixing Impellers

The authors reviewed the correlations of power consumption in unbaffled and baffled agitated vessels with several kinds of impellers, which were developed in a wide range of Reynolds numbers from laminar to turbulent flow regions. The power correlations were based on Kamei and Hiraokas expressions for paddle and pitched paddle impellers. The calculated correlation values agreed well with experimental ones, and the correlations will be developed the other types of impellers.

Cage Occupancy of Hydrogen in Carbon Dioxide, Ethane, Cyclopropane, and Propane Hydrates

We have already reported the cage unoccupancy of hydrogen in the CO2 hydrate from the Raman spectroscopic analysis and the thermodynamic analysis using Soave Redlich Kwong equation of state. On the other hand, at the low temperatures, Kim and Lee (Journal of American Chemical Society, vol. 127, pp. 9996-9997, Jul. 2005) claimed that hydrogen is enclathrated in the CO2 hydrate. In the present study, the cage unoccupancy of hydrogen in the CO2 hydrate was reconfirmed clearly by in situ Raman spectroscopy for single crystal of gas hydrates. Isothermal phase equilibria (pressure composition) and Raman spectra for three ternary systems of hydrogen + hydrocarbon (ethane, cyclopropane, propane) + water with same experimental procedures as hydrogen + CO2 + water system were measured at 276.1 K in the pressure range up to 5 MPa. In addition, the released gas from hydrates was analyzed to confirm the occupancy or unoccupancy of hydrogen at the temperature. All analyses arrive at the single conclusion that hydrogen is enclathrated in only propane hydrate under the present experimental conditions.

Thermodynamic Properties of Hydrogen

Thermodynamic stability and hydrogen occupancy on the hydrogen + tetra- -butyl ammonium bromide semi-clathrate hydrate were investigated by means of Raman spectroscopic and phase equilibrium measurements under the three-phase equilibrium condition. The structure of mixed gas hydrates changes from tetragonal to another structure around 95 MPa and 292 K depending on surrounding hydrogen fugacity. The occupied amount of hydrogen in the semi-clathrate hydrate increases significantly associated with the structural transition. Tetra- -butyl ammonium bromide semi-clathrate hydrates can absorb hydrogen molecules by a pressure-swing without destroying the hydrogen bonds of hydrate cages at 15 MPa or over.

Isothermal Phase Equilibria for Methane + Ethane + Water Ternary System Containing Gas Hydrates

It is well known that methane + ethane mixed-gas hydrate exhibits the structural phase transition between struc- ture-I and -II although both of pure guest species form the structure-I hydrate at certain pressures and temperatures (Subramanian, Kini, Dec and Sloan, Chem. Eng. Sci., vol. 55, pp. 1981-1999, June 2000). In the present study, isothermal phase equilibrium (pressure - composition) relations for the methane + ethane mixed-gas hydrate system were measured accurately at 279.1 K - 288.1 K. In addition, the equilibrium composition in the mixed-gas hydrate phase was investigated by mass and volume balances analysis. At all temperature conditions, the equilibrium curves exhibit discontinuity around given equilibrium compositions (water free), which supports that the structural phase transition occurs. The pressure of structural transition point increases as temperature rises, and the mole fractions of both hydrate phases at the structural transition point are almost independent of temperature.

Viscosity Reduction with Self-Assembly of Cationic Surfactant on Tetra-n-butyl Ammonium Bromide Semi-Clathrate Hydrate Aqueous Slurry

Aims: To utilize hydrate slurry for phase change refrigerants, the rheological properties are essential. In the present study, the viscosity characteristics of hydrate slurry are investigated. Additionally, the effect of cationic surfactant on viscosity is also evaluated. Study Design: Experimental and analytical study.

Study on Prompt Methane Hydrate Formation Derived by Addition of Ionic Liquid

Aims: The objective of this study is to establish the fundamental model on methane hydrate formation and to accelerate the rate of methane hydrate formation with a small amount of ionic liquid and to investigate the effect of ionic liquid on hydrate formation. Study Design: Experimental study containing modeling. Place and Duration of Study: The present study was held between April 2010 and February 2012 at Division of Chemical Engineering, Department of Materials Engineering Science, Osaka University. Methodology: Methane hydrate formation was modelized based on the driving force, fugacity difference before and after hydrate formation. BMIM-hexafuorophosphate (BMIMPF6) was adopted as a representative of 1-butyl-3-methylimidazolium (BMIM) salts. The temperature dependence of methane hydrate formation rate was investigated and activation energy of hydrate formation was evaluated for the pure water and BMIM-PF6 aqueous solution systems. Research Article American Chemical Science Journal, 2(3): 100-110, 2012 101 Results: An addition of small amount of BMIM-PF6 is able to accelerate the methane hydrate formation. The pseudo-first order reaction model is applicable to the methane hydrate formation in both the pure water and BMIM-PF6 aqueous solution systems. The activation energies of methane hydrate formation are large negative values in the both systems, that is, the methane hydrate formation process is considered to be composed of the precursory hydration and succeeding hydrate formation. A very small amount of BMIMPF6 seems to change the interfacial energy between guest molecules and precursor or initial hydrate particles without the change of the activation energy for overall methane hydrate formation.

Storage capacity of hydrogen in gas hydrates

The storage capacity of H2 in the THF, THT, and furan hydrates was studied by p-V-T measurements. We confirmed that the storage and release processes of H2 in all hydrates could be performed reversibly by pressure swing without destroying of hydrate cages. H2 absorption in both THT and furan hydrates is much faster than THF hydrate in spite of same unit-cell structure. On the other hand, the storage amounts of H2 are coincident in the all additive hydrates and would reach at about 1.0 mass% asymptotically.

Structure-H Methane + 1,1,2,2,3,3,4-Heptafluorocyclopentane Mixed Hydrate at Pressures up to 373 MPa

Thermodynamic stability boundary of structure-H hydrates with large guest species and methane (CH4) at extremely high pressures has been almost unclear. In the present study, the four-phase equilibrium relations in the structure-H CH4 + 1,1,2,2,3,3,4-heptafluorocyclopentane (1,1,2,2,3,3,4-HFCP) mixed hydrate system were investigated in a temperature range of (281.05 to 330.12) K and a pressure range up to 373 MPa. The difference between equilibrium pressures in the structure-H CH4 + 1,1,2,2,3,3,4-HFCP mixed hydrate system and the structure-I simple CH4 hydrate system gets larger with increase in temperature. The structure-H CH4 + 1,1,2,2,3,3,4-HFCP mixed hydrate survives even at 330 K and 373 MPa without any structural phase transition. The maximum temperature where the structure-H CH4 + 1,1,2,2,3,3,4-HFCP mixed hydrate is thermodynamically stable is likely to be beyond that of the structure-H simple CH4 hydrate.

Advances in Mixing Technology: Recent Advances in Mixing Research and Development

Mixing has been one of essential unit operations for chemical engineering processes. Among a number of mixers, stirred tanks that are available in a wide variety of tank sizes and impeller shapes are the most frequently adopted to homogenize different substances and to conduct chemical reactions in industrial chemical processes. In addition, there are various technologies for fluid mixing: static mixer, micromixer, unsteady agitation, eccentric agitation, and so on. Recently in various industrial processes, a wide range of operation for stirred tank is required depending on purposes and conditions, and high efficiency on mixing has been strongly required. In addition, the techniques of computer simulation analyses by the use of CFD software have been dramatically developed, which is essential to analyze the mixing mechanism. The main goal of this special issue was to gather contributions dealing with the latest breakthrough of mixing techniques. There is a collection of twelve papers in this special issue focused on mixing fundamental (2 papers), multiphase mixing (3 papers), chemical reactive mixing for metallurgical industry, and biotechnology (4 papers), and new technology of mixing (3 papers) ranging in topic from laminar-to-turbulent mixing by means of both experimental analyses and numerical simulations. The highlights of each paper are introduced as follows.

Thermodynamic Stability of Mixed Gas Hydrates Containing Hydrogen

Phase equilibrium curves of H2 + tetrahydrofuran and H2 + tetra-n-butyl ammonium bromide mixed gas hydrates were measured. Each three-phase equilibrium curve converges at three-phase equilibrium point of pure tetrahydrofuran and tetra-n-butyl ammonium bromide hydrates, respectively. It is directly confirmed by use of Raman spectroscopy that H2 is enclathrated in the hydrate cages by adding a small amount of tetrahydrofuran or tetra-n-butyl ammonium bromide. In both mixed gas hydrates, H2 is selectively enclathrated in the small cage despite the concentrations of aqueous solution.