On the size of drops in pulsed and vibrating plate extraction columns

An equation, based on the Kolmogorov-Obukhov theory of the local structure of turbulent pulsations is proposed for calculation of the mean drop diameter in pulsed and vibrating plate extraction columns. By means of this equation the mean drop diameter could be evaluated for intensive flow pulsation (or plate vibration) within 20% accuracy.     

Experimental determination of axial dispersion coefficient in a bubble column

A new graphical method of finding axial dispersion coefficients in a bubble column is developed. This method requires only the area above an experimental curve, thus is simpler than the conventional method of curve fitting. The new method is used to find the dimensionless dispersion number in the bubble column and shows that the dispersion number decreases with column Reynolds number due to increasing coalescence of bubbles at higher gas flow-rates.     

Simulation of an extraction column

An efficient program for the simulation of an extraction column is described. Many alternate numerical methods were tested. The final version of the program uses Newton's method combined with a search along the damping factor, and Gauss Elimination with limited normalization for the inversion of the Jacobian. The Jacobian is stored as a vector. The program is compared with published programs and is efficient and reliable.     

Comparison of plate numbers and column lengths in chromatography and distillation

It is sometimes suggested that the number of plates required in chromatography is approximately equal to the square of the number required for distillation. It is shown that this proposition overestimates the number of chromatographic plates by a factor of at least 5 and typically about 30. For a given separation specification, a gas chromatographic column is 3–30 times shorter than the equivalent distillation column. The variation of the two column lengths with relative volatility and desired purity level is shown graphically.     

Electrochemical behaviour of nickel in nitric acid

The electrochemical investigations of nickel in a wide range of concentrations (1–14.6 M) of nitric acid were studied by potentiostatic, potentiodynamic and coulostatic method and by weight-loss measurements. The potentiostatic current-potential curves of nickel in nitric acid solutions can be classified into three categories, according to the proportion of the concentration of the acid. An increase of nitric acid concentration increases the influence of the cathodic reactions in the systems. The importance of cathodic reactions has been investigated by eliminating HNO₂ by additions of p-nitro aniline in the electrolyte. The coulostatic polarization has given distinct repassivation curves, indicating an intermediate state of nickel electrode between active and passive state. In the first part of repassivating process the potential value is more positive than the stationary potential of spontaneous passivation of nickel electrode in concentrated nitric acid. The return of the stationary potential of the passivity is a slow, time-dependent process. According to the experimental results and data given in the literature, it may be possible that in the beginning of the passivation process on nickel Ni(NO₃)₂ × 4 H₂O forms which changes to NiO₂ and than transforms slowly to NiO.     

Acidization—V: The prediction of the movement of acid and permeability fronts in sandstone

A new model has been developed which describes the acidization of sandstone cores. The results show that the reaction of hydrofloric acid with the dissolvable minerals occurs in a narrow zone which moves as a reaction front through the sandstone core. The width of the reaction front is related to the Damkohler Number and the velocity of the reaction front is related to the acid capacity number. The model has virtually no adjustable parameters and agrees extremely well with the experimental results.     

Acidization—II. The dissolution of calcite in hydrochloric acid

The dissolution of calcite in hydrochloric acid was studied with the aid of a rotating disk system at 800 psig in the temperature range ?15·6–25°C. At 25°C the dissolution process is mass transfer limited even at high disk rotation speeds whereas at ?15·6°C both mass transfer and surface reaction rates limit the dissolution rate. The multicomponent coupled ionic diffusive fluxes of reactants and products were defined by using the gradient of the electrochemical potentials as driving forces for the diffusion. The activity coefficients used in calculating the multicomponent diffusivities of the diffusing species were estimated by Harned's rule. The concentration profiles of the ions in the boundary layer were then determined by numerically integrating the system of coupled convective diffusion equations. The effects of variable density, viscosity, and high mass fluxes on the fluid velocity in the boundary layer were taken into account. The rate of the surface reaction was found to be proportional to the 0·63 power of the surface hydrochloric acid concentration. Analysis of the experiments suggests that the absorption of hydrogen ion (described by a Freundlich adsorption isotherm) on the solid calcite surface and subsequent reaction of the adsorbed hydrogen ion with the solid calcite matrix is the reaction mechanism.     

Acidization—VI: On the equilibrium relationships and stoichiometry of reactions in mud acid

A method is presented for determining the distribution of reaction products and the stoichiometric coefficient for the reaction of mud acid (HF/HCl) with various minerals. To illustrate the techniques, the dissolution of two common alumino-silicates, potassium feldspar and kaolinite, in mud acid is investigated for various temperatures and acid concentrations. After determining the product distribution from the ionic equilibrium relationships involving the various fluoride ion complexes, the stoichiometric coefficient [moles HF consumed per mole mineral dissolved] is arrived at through a numerical solution of the coupled equilibrium and mole balance equations. The HF acid stoichiometric coefficient was found to decrease significantly with increasing temperature and HCl acid concentration. This information is of great importance in determining design conditions for the matrix acid stimulation of oil reservoirs.In the above analysis we have found how the HF stoichiometric coefficient in the reaction between mud acid and two alumino-silicates varies with acid concentration and temperature. The HF stoichiometric coefficient is defined as the moles of HF acid consumed per mole of mineral dissolved. The information obtained in this study is of great importance in the design of the acid stimulation of well reservoirs. It was found that the same stoichiometric coefficient can result for two different sets of mud acid concentrations. Consequendy, one could evaluate which set of mud acid concentrations would be most economically feasible. In addition to the economical considerations, the prediction of the overall stoichiometric coefficient for the dissolution of a sandstone is of vital importance in determining the acid capacity number. From this number, one can calculate the penetration radius of the permeability front resulting from matrix acid stimulation of the reservoir.In calculating the stoichiometric coefficient we first determined the distribution of the aluminum-fluoride and silicon-fluoride complexes resulting from the dissolution of the mineral using the ionic equilibrium relationships. A numerical solution of the coupled mole balance and equilibrium equations was then carried out to determine the stoichiometric coefficient with respect to HF and HCl for the specified mineral dissolution. These results were found to agree satisfactorily with previously reported experimental values.The results of this analysis showed that the HF stoichiometric coefficient decreases with increasing temperature. In addition it was found to decrease during the course of the mud acid-mineral reaction. The most important results of this study are related to the variation of the HF stoichiometric coefficient with HCl concentration. This coefficient was found to be virtually independent of HCl concentration below concentrations of ca. 5 × 10^?2 M HCl. Above this concentration it was found to decrease significantly with increasing HCl concentration.A technique for estimating the overall stoichiometric coefficient for a sandstone from the coefficients of the individual minerals has been found to be in satisfactory agreement with the numerical technique involving the ionic equilibria for the sum of all minerals present which had to be carried out on the computer, for each sandstone composition.     

Calculation of the drop size in pulsed sieve-plate extraction columns

A new method for the calculation of drop sizes in pulsed sieve-plate extraction columns is reported. Under certain assumptions for the motion of the drops in the vicinity of the plates, it is possible to develop an equation that is confirmed by measurements in a much greater range, especially of the pulsation intensity, than other equations being known up to now. Additionally, a dependence of the drop diameter on the hole diameter at constant fractional free area results from that new equation, which has been proven so far only experimentally. Finally, with the developed equation under consideration of the time-dependent variations of the effective forces it is possible to make qualitative predictions on the type of the drop size distribution to be expected.     

Kinetics,poisoning and mass transfer effects in liquid-phase hydrogenations of phenolic compounds over a palladium catalyst

The influence of poisoning and mass transport on the performance of a suspended palladium catalyst for the liquid-phase hydrogenation of o-cresol h for the various transport and reaction steps occuring in the three-phase slurry system and these were combined into an overall rate expression. From th analysed either by an experimental approach or by calculation.The hydrogenation in the absence of poison is described by a Langmuir—Hinshelwood adsorption model with adsorption of hydrogen and substrate on diffe present in the feed, the activity loss can be described by an extended model of the same type; experimental results show that the poison is very strong between poison and substrate on the remaining catalyst surface. The selectivity is not affected by increasing poison concentration.     

Ellipsometric response of titanium electrodes in sulphate acid solutions under different potential perturbations

Optical characteristics and thickness of thin oxide films potentiodynamically formed on a titanium electrode in acidic sulphate solutions at pH 4.0 were investigated by dynamic and steady ellipsometric measurements. The dynamic ellipsometric response of an electrode polarized up to 1.0 V vs rhe depends on the charge involved in the massive oxide electroformation. Cycling the electrode at a constant potential sweep rate between −0.65 and 0 V produces a decrease on film thickness and the electrode reactivation. This electrode treatment becomes less effective as oxide electroformation is repeated several times. Experiments performed by holding the potential at the negative limit were not so effective in reducing film thickness and an appreciable change on optical constants was found. Results were interpreted as hydrogenated species formation within the oxide film.     

Acidization III—The kinetics of the dissolution of sodium and potassium feldspar in HF/HCl acid mixtures

The dissolution of a potassium and a sodium feldspar in hydrochloric-hydrofluoric acid mixtures was studied in a rotating disk system at 25 and 100°C under a pressure of 40 psig. Under these conditions, the dissolution rate is limited by the rate of reaction of the acids with the solid surface.The rate of dissolution may be described by the following type of rate law:

The parameters a and b for potassium feldspar have the values 0·4 and 1·2, respectively, whereas for sodium feldspar both have a value of 1·0. A mechanism for the dissolution reaction is proposed which is consistent with experimental observation. The analysis suggests that the dissolution is limited by the rate at which the hydrofluoric acid reacts with the solid surface and that the strong influence of the hydrochloric acid on the dissolution rate is due to the adsorption of hydrogen ions on the mineral surface.     

Electrochemical reduction of 4-(2′-thienyl)quinazoline in acid solutions

The electrochemical behaviour of 4(2′-thienyl)quinazoline (4-TQ) was studied in acid solutions of varying ionic strengths using polarography, cyclic voltammetry and controlled-potential electrolysis. 4-TQ is reduced in two single electron steps to give the dihydro-4-TQ product. The two polarographic waves were found to be diffusion-controlled, the first wave being reversible and the second wave irreversible. On the basis of the results obtained, a mechanism is suggested for 4-TQ reduction in which a dimerization reaction goes in parallel with the electron-transfer step.     

Adsorption of acid dye onto woodmeal by solid diffusional mass transfer

The adsorption of Telon Blue (Acid Blue 25) dye onto wood has been studied using an agitated batch adsorber. The variables studied include agitation, initial dye concentration, wood mass, wood particle size and dye solution temperature. Isotherms were measured and the isotherm parameters were determined.

A mathematical model has been developed using the basis of the model proposed by Mathews and Weber Jr. This model is based on external mass transfer and solid-phase diffusion, and has been used to generate theoretical concentration—time decay curves. The results of the model were adjusted to the experimental data using a ‘best fit’ approach. The external mass transfer coefficient was found to vary with the degree of agitation, and consequently all other variables were considered at a constant agitation speed of 400 rev min⁻¹. A good agreement between the theoretical generated and the experimental concentration—time decay curves was achieved using a constant external mass transfer coefficient, 0.30 × 10⁻³ cm ⁻¹, and a constant solid-phase diffusivity, 0.200 × 10⁻⁸ cm² s⁻¹, for varying initial dye concentrations as well as wood mass. In experiments where the particle diameter was varied, a constant external mass transfer coefficient was sufficient to describe the system, but a decreasing diffusivity was required with increasing particle size. To simulate the effect of varying temperature, both external mass transfer coefficient and diffusivity were varied.     

Walden product, ion-solvent interactions and solvent structure in water-rich mixtures ionic conductances in water-sulfolane, water-acetonitrile and water-dimethylsulfoxide

Conductance measurements are reported for several salts in binary aqueous mixtures containing up to 60 mole % sulfolane, 20 mole % acetonitrile and 20 mole % dimethylsulfoxide. The variations of R = (λ^±₀η₀)_s/(λ^±₀η₀)_w with solvent composition have been compared with those observed in other water-rich mixtures. Alkali cations show R values greater than one with maxima in all the solvent mixtures. This behaviour has been discussed in terms of “sorting”, “averaging” and “steric” effects. Contrary to what happens to alkali cations, halide ions show R values greater or lesser than one according to whether the organic solvent respectively increases or decreases water structure. On these bases we suggest that conductometric behaviour of the halide ions may be indicative of the effect of the cosolvent on the water structure in water-rich mixtures and that DMSO is a water structure breaker.     

Production of zinc ferrite in a mechano-chemical reaction by grinding in a ball mill

Zinc ferrite was obtained by prolonged dry grinding of stoichiometric powder mixtures of ZnO + -Fe₂O₃ or ZnCO₃ + -Fe₂O₃. The kinetics of transformation was studied by X-ray diffraction, Mössbauer spectroscopy and DTA. Crystallite size reduction followed the process, and defect structures resulted. The carbonate decomposed as a necessary step in the process. In the mixture of NiO + -Fe₂O₃, nickel ferrite was not obtainable, although considerable grain size reduction was observed. This was attributed to the inverse spinel configuration of the nickel ferrite, differing from the normal spinel configuration of the zinc ferrite. In the -Fe₂O₃ and the zinc ferrite, iron ions occupy octahedral sites, while in ZnO and the ferrite, zinc ions occupy tetrahedral sites, and metal ion—oxygen distance is almost identical. These facilitate the transformation. In the nickel ferrite, iron ions occupy both sites, which calls for high strains of -Fe₂O₃ before it can undergo transformation. Further implications of the processes are discussed.     

Cathodic polarization of variously corroded iron electrodes in acid perchlorate solutions

The steady-state cathodic reaction taking place on iron electrodes in deaerated, acid perchlorate solutions free of iron salts in the hydrogen evolution reaction. However, reduction of corrosion products formed during preceding anodic polarization will also occur in various potential regions. Cathodic polarization diagrams recorded with rotating disc electrodes (rde) show three reaction regions. In region I, starting below the corrosion potential, the reaction is influenced by pH of the solution and by potential. This is followed, at lower potentials, by region II, where the reaction is limited by diffusion of hydrogen ions to the electrode. The limiting cd is determined by pH of the solution and by the speed of rotation of the rde. At still lower potentials, in region III, there is a further increase of cd due to discharge of water molecules. This reaction is influenced by potential, but not by pH or rde rotation rate.Experiments lasting a few minutes demonstrate that the behaviours in the regions I and II depend on the type of preceding anodic polarization; the alternative effects will be cathodic peak in region I, attributed to the reduction of a previously formed oxidic iron compound approaching the composition of magnetite, or an additional contributon to the cd due to reduction of a different iron compound and in excess of the quantity accounted for the hydrogen evolution.A detailed, rather novel and powerful type of analysis of the reaction recorded in region I indicates a low and constant coverage by adsorbed hydrogen atoms giving rise to a parallel combination of a Volmer—Tafel mechanism (the minor part) and a Volmer—Heyrovsky mechanism (the major part) for the hydrogen evolution reaction.     

Photocatalysis in a slurry reactor

A series of experiments have been conducted on the photocatalytic reduction of methylene blue with zinc oxide catalyst in a slurry reactor. It is shown that by using a procedure involving separate experiments to determine the shielding effects of the suspended solid (inert solid of similar particle size with a standard actinometric solution) it is possible to identify experimentally the region in the reaction system where imperfect solids mixing influences the rate of reaction. The reactor employed here is also shown to provide a relatively simple means for kinetic measurements in photocatalytic reactions. The rate constants obtained in this study for methylene blue reduction were weakly dependent on zinc oxide concentration in the suspension. A value of 3·67 M^?1 sec^?1 at 0·1 wt.% ZnO at 31·9°C was obtained, where M is the molarity of the solution in methylene blue. This may be compared with 1·25 × 10⁴M^?1 sec^?1 reported by Yoneyama [14] for methylene blue reduction on a rutile crystal of titanium dioxide at room temperature, and 3·33 M^?1 sec^?1 for p-nitrosodimethylaniline reduction in a 0·1 wt. % ZnO suspension, also at room temperature[13].     

Verification of a model for estimating the void fraction in a three-component randomly packed bed

The void fraction in a three-component randomly packed bed was calculated from the authors' model, and the calculated values were compared with published experimental data for spherical and irregularly shaped particles and with results from computer simulations. Results from the model were in good agreement with simulated and published experimental data.