Thermodynamic modeling of the solubilities of fatty acids in supercritical fluids

Modeling the solubilities of fatty acids is important because these compounds are used in various industries. In this work, a thermodynamic model based on Redlich–Kwong equation of state with Kwak–Mansoori mixing rules was used to model the solubilities of fatty acids in supercritical carbon dioxide. The model uses only one adjustable parameter and this parameter varies linearly with the chain length of the fatty acid. Therefore, this model can be potentially used to predict the solubilities of various fatty acids in supercritical carbon dioxide.     

Distribution kinetics of Ostwald ripening at large volume fraction and with coalescence

Condensation phase transitions from metastable fluids occur by nucleation with accompanying particle growth and eventual Ostwald ripening. During ripening the subcritical particles dissolve spontaneously while larger particles grow and possibly coalesce if their volume fraction is large enough. The classical diffusion-influenced rates are also affected by large particle concentrations and are here described by mass-dependent rates. We represent the kinetics of ripening through growth, dissolution, and biparticle coalescence by a new population dynamics equation for the particle size distribution (PSD). Numerical solutions of the scaled governing equations show that coalescence plays a major role in influencing the PSD when the scaled mass concentration (volume fraction) or number concentration is relatively large. The solution describes the time range from initial conditions to the final narrowing of polydispersity. We show that the time dependence of the average particle mass in the asymptotic period of ripening has a power-law increase dependent on rate expressions for particle growth and coalescence at large values of volume fraction.     

Aqueous polymerization of acrylonitrile initiated by the Mn3+/citric acid redox system

Kinetics of polymerization of acrylonitrile initiated by the redox system Mn³⁺/citric acid were investigated in aqueous sulphuric acid in the range of 20–25°; initial rates of polymerization and Mn³⁺ disappearance etc. were measured. The effects of certain water miscible organic solvents and certain cationic and anionic detergents on the rate of polymerization have been examined. A mechanism has been suggested involving formation of a complex between Mn³⁺ and citric acid, decomposition of which yields the initiating free radical and with polymerization being terminated by mutual interaction of growing radicals.     

A novel sheet 4f-3d mixed-metal pyridine dicarboxylate: synthesis, structure, photophysical properties and its transformation to a perovskite oxide

The synthesis, characterization and photophysical properties of a 4f-3d mixed metal compound, Gd(H2O)3Co[C5N1H3(COO)2]3, are described; the structure is unique, consisting of sheets with large pores (ca. 7 Angstroms diameter) in the sheets and transforms to a perovskite oxide at moderate temperatures.     

Solubilities of palmitic and stearic fatty acids in supercritical carbon dioxide

The solubilities of two fatty acids, namely hexadecanoic acid (palmitic acid) and octadecanoic acid (stearic acid) in supercritical carbon dioxide (SCCO₂), were determined at T = (328 and 338) K from 12.8 MPa to 22.6 MPa. Three models, namely a thermodynamic model based on the Peng–Robinson equation of state with Kwak and Mansoori mixing rules, a model based on dilute solution theory proposed by Mendez-Santiago and Teja and a new reformulated Chrastil equation model, were used to correlate the solubilities. In all the models, the correlation constants are temperature independent. All the models successfully correlated the experimental results for the solubilities of hexadecanoic acid within 3%.     

Electrodeposition of nanocrystalline aluminium from a chloroaluminate ionic liquid

In this letter we show that nanocrystalline aluminium can be electrodeposited in the Lewis acidic ionic liquid based on AlCl₃ (60 mol%) and 1-(2-methoxyethyl)-3-methylimidazolium chloride ([MoeMIm]Cl) (40 mol%). The study comprised cyclic voltammetry, potentiostatic polarization, and SEM and XRD measurements. The methoxy group in the side chain of the imidazolium cation significantly influences the electrodeposition pathway of Al in comparison to [EMIm]Cl/AlCl₃. Cyclic voltammetry shows a significant current loop attributed to nucleation. Shiny Al layers are obtained with an average crystallite size of about 40 nm.     

Cluster kinetics and dynamics during spinodal decomposition

Spinodal decomposition (barrierless phase transition) is a spontaneous phase separation caused by conditions that force the system to become thermodynamically unstable. We consider spinodal decomposition to occur under conditions of large supersaturation S and/or small ratio of interfacial to thermal energies omega, such that the computed number of monomers in a critical nucleus xi*=(omega/ln S)3 is less than unity. The small critical nucleus size is consistent with a negligible energy barrier for initiating condensation. Thus, in contrast to conventional opinion, it is suggested that the spinodal decomposition is related to the homogeneous nucleation of metastable fluids. Population balance equations show how clusters aggregate and rapidly lead to phase separation. Different mass dependences of aggregation rate coefficients are proposed to investigate the fundamental features of spinodal decomposition. When the mass dependency is an integer, the equations are solved by the moment technique to obtain analytical solutions. When the mass dependency is a noninteger, the general cases are solved numerically. All solutions predict the two time regimes observed experimentally: the average length scale of condensed-phase domains increases as a power law with an exponent of 1/3 at early times, followed by a linear increase at longer times.     

Photocatalytic Activity of Microwave Plasma-Synthesized TiO2 Nanopowder

Nanocrystalline TiO₂ was synthesized using the microwave plasma technique and characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, laser particle size analyzer, UV–vis spectroscopy and BET surface area analyzer. The synthesized TiO₂ powder crystallized in anatase phase and the crystallite sizes were in nanometers. The photocatalytic activity of the compound was determined and compared against the activity of the commercial Degussa P-25 TiO₂ catalyst. The degradation rates of the dyes were found to be higher over the synthesized TiO₂ as compared to that over commercial Degussa P-25 TiO₂.     

Novel photocatalysts for the decomposition of organic dyes based on metal-organic framework compounds

Three novel metal-organic frameworks (MOFs) [Co(2)(C(10)H(8)N(2))][C(12)H(8)O(COO)(2)](2), 1, [Ni(2)(C(10)H(8)N(2))(2)][C(12)H(8)O(COO)(2)](2).H(2)O, 2, and [Zn(2)(C(10)H(8)N(2))][C(12)H(8)O(COO)(2)](2), 3, with three-dimensional structures have been synthesized and characterized. The structures of the three compounds appear somewhat related, formed by the connectivity involving the metal polyhedra (Co(4)N trigonal bipyramids in 1, NiO(4)N(2) octahedra in 2, and ZnO(4) tetrahedra and ZnO(3)N(2) trigonal bipyramids in 3), 4,4'-oxybis(benzoate), and 4,4'-bipyridine. The photocatalytic studies on 1-3 indicate that they are active catalysts for the degradation of orange G, rhodamine B, Remazol Brilliant Blue R and methylene blue. The compounds have also been characterized by powder X-ray diffraction, IR, thermogravitmetric analysis, UV-vis, photoluminescence, and magnetic studies.     

Gas chromatographic-mass spectrometric separation and identification of combustion products of organo-phosphorus and chlorine pesticides and evaluation of their impact on the environment

A simple and rapid GC-MS method for separation, identification and quantitative determination of combustion products of organophosphorus and chlorine pesticides viz; monocrotophos, chloropyriphos, butachlor and benzenehexachloride has been developed. The method provides a positive means of identifying organic combustion products and enables to assess not only their toxicity to human beings but also their impact on the environment. The data is useful for emergency preparations in case of fire in chemical plants and warehouses that store pesticides in large quantities.