Open Access Original Research Article

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

Shunsuke Hashimoto, Kazushi Kawamura

Chemical Science International Journal, Page 69-85
DOI: 10.9734/ACSJ/2012/1616

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.
Place and Duration of Study: Division of Chemical Engineering, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, between December 2010 and October 2011.
Methodology: Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate aqueous slurry was adopted. The viscosity of solutions and slurries was measured at various concentrations of solution and various solid fractions by use of stress-control-type rheometer. The measurements were performed in the both case without and with cationic surfactant. Additionally, the size and shape and aggregation property of hydrate particles in slurry were evaluated by means of direct observation and zeta potential analysis.
Results: The apparent viscosity of both TBAB solution and hydrate slurry increases as the temperature decreases, which is caused by the increase of solid fraction in slurry. The TBAB hydrate slurry behaves like pseudo-plastic fluid. In addition, the effect of minimal surfactant on rheological characteristics of TBAB hydrate slurry was investigated. A very small amount of surfactant drastically reduces the apparent viscosity of TBAB hydrate slurry, and then the morphology of TBAB hydrate particle does not change regardless of the existence of surfactant. From the measurement on zeta potential of the surface of TBAB hydrate particle, the viscosity reduction effect may be caused by the electric repulsion of surfactant-adsorbed hydrate particles.
Conclusion: A very small amount of surfactant drastically reduces the apparent viscosity of TBAB hydrate slurry, which is due to the electric repulsion among surfactant-adsorbed hydrate particles.

Open Access Original Research Article

Synthesis, Characterization and Antibacterial Activities of New Pd(II) And Pt(IV) Complexes of Some Unsymmetrical Tetradentate Schiff Bases

W. H. Hegazy, A. E.-D M. Gaafar

Chemical Science International Journal, Page 86-99
DOI: 10.9734/ACSJ/2012/1584

New palladium (II) and platinum (IV) complexes with a series of unsymmetrical tetradentate Schiff bases derived from aromatic 2-hydroxy aldehydes in an ethanolic medium were synthesized and characterized by elemental analyses, melting points, magnetic susceptibility, thermogravimetry, differential scanning calorimetry (DSC), infrared (IR), and electronic spectral measurements. The purity of the ligands and the metal complexes are confirmed by microanalysis, while the unsymmetrical nature of the ligands was further corroborated by 1H-NMR spectroscopy. Comparison of the IR spectra of the Schiff bases and their metal complexes confirm that the Schiff bases act as tetradentate and coordinated via the two azomethine nitrogens and the two phenolic oxygens. Magnetic moments and electronic spectral data confirm square planar geometry for the Pd(II) and Pt(IV) complexes. Thermal studies reveal a general decomposition pattern, whereby the complexes decomposed partially in a single step due to loss of part of the organic moiety. The Schiff bases and their complexes were screened in vitro against 10 human pathogenic bacteria.

Open Access Original Research Article

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

Takashi Kitajima, Naoto Ohtsubo, Shunsuke Hashimoto, Takashi Makino, Daisuke Kodama, Kazunari Ohgaki

Chemical Science International Journal, Page 100-110
DOI: 10.9734/ACSJ/2012/1512

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 (BMIM-PF6) 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.
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 BMIM-PF6 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.