Gas/liquid interfacial area per unit volume and volumetric mass transfer coefficient in stirred slurry reactors

In three-phase systems, where the liquid constitutes the continuous phase, solid is the catalyst and gas represents the dispersed phase, there are decisive criteria which have to be observed in reactor design. These are e.g. the interfacial area per unit volume between gas and liquid, the volumetric mass transfer coefficient and the mass transfer coefficient. The basic aim of the present work was therefore the investigation of these parameters in relation to the main influencing parameters. Process parameters stirrer speed and superficial gas velocity were varied as well as the physical properties such as liquid viscosity, solids concentration, particle diameter and a geometrical parameter, i.e. reactor diameter. The sulphite method was employed for the determination of these values. The test results confirmed the known relationships of power consumption and superficial gas velocity. An increase in the liquid viscosity leads to a decrease in all the tested values. In most cases, suspended solid particles lead to a lowering of the test values. The influence of the tank diameter on the plots of the test values against specific power consumption turned out to be invariant so that a scale-up of geometrically similar systems can be carried out at constant power consumption, superficial gas velocity and liquid viscosity.     

Solution of the two-dimensional wave equation by using wave polynomials

The paper demonstrates a specific power-series-expansion technique to solve approximately the two-dimensional wave equation. As solving functions (Trefftz functions) so-called wave polynomials are used. The presented method is useful for a finite body of certain shape geometry. Recurrent formulas for the wave polynomials and their derivatives are obtained in the Cartesian and polar coordinate system. The accuracy of the method is discussed and some examples are shown.     

Interaction between copper chloride and caffeine as seen by diffusion at 25 °C and 37 °C

A Taylor dispersion method is used to measure ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂ and D₂₁) for aqueous solutions of CuCl₂ (1) + caffeine (2) + H₂O-(3) at 25 °C and 37 °C at carrier concentrations from (0.000 to 0.020 mol dm⁻³), for each solute, respectively. The results are compared with these obtained for the binary systems, that is, CuCl₂ (1) + H₂O (2) and caffeine (1) + H₂O (2), also reported here. From these data it is possible to make conclusions about the influence of the caffeine solutes in diffusion of copper chloride.     

Spectral studies of zinc octacarboxyphthalocyanine aggregation

The association of zinc octacarboxyphthalocyanine, was studied using UV–vis absorption and fluorescence emission spectroscopy; the effects of dye concentration, pH and solvents on spectra were discussed. Calculations showed that the dye dimerized in aqueous solutions ranging from 5.0 × 10^?7 to 5.0 × 10^?5 mol/dm³, at 25 °C. The dimerization constant of 10⁶ dm³/mol and the spectral Q band shift of 1185 cm^?1 imparted by dimerization indicated strong π–π interactions between phthalocyanine molecules. Red S₁ fluorescence of the dye monomer was observed in various solutions which was quenched owing to molecular association and other factors. The strong influence of pH on both aggregation and fluorescence was discussed. At pH < 5.0, only dye aggregates were present in solution; monomers appeared at pH ≥ 5.0 and, in alkaline solution, only the monomeric anions of phthalocyanine existed. The spectral absorption and emission data for the dye in binary solvents revealed that at concentrations ranging from 0.5 × 10^?5 to 1.0 × 10^?5 mol/dm³, the dye can be used in photosensitised oxidation reactions.     

Interactions between fecal bacteria,bile acids and components of tomato pomace

Food Science and Biotechnology - The tomato pomace obtained during processing as a residue of tomato processing from large industry. The interactions between tomato pomace and fecal bacteria, bile...     

Kinetics of lactose hydrolysis and galactooligosaccharides formation in beverages based on goat’s milk and its permeate

Food Science and Biotechnology - The aim of this work was the analysis of galactooligosaccharides (GOS) formation in a model mixture of goat’s milk and its permeate from microfiltration and...