Oxidation of sodium sulphide in a foam bed contactor

Oxidation of sodium sulphide to sodium thiosulphate has been experimentally investigated in a foam bed contactor using air as oxidizing medium. The var     

An experimental study of oxidation of zinc sulphide pellets

Oxidation of zinc sulphide pellets is carried out in the ranges of 600-826°C temperature, 0.3-0.5 porosity and 15-50 minutes of reaction time. An experimental technique is employed to simultaneously determine the rate of weight loss of the solid and conversions of the solid reactant at various levels in the pellet for different reaction times. A structural model is used to explain the experimental results. It is found that the model predicts both the experimental results obtained under various conditions reasonably well.     

A simple approximation of the error function

A very simple approximation formula of the error function, with sufficient accuracy for engineering calculations, is proposed in this investigation. The presented form is compared with some of the less sophisticated approximations available in the literature. Aspects such as mnemonic form, computation time, accuracy and ease of inversion are considered.     

Turbulent heat and mass transfer in dilute polymer solutions

A new model based on Levich's three-zone model is developed to discuss the turbulent heat and mass transfer in drag-reducing solutions. The proposed model, which has no adjustable parameters and is represented in an explicit form, provides satisfactory predictions of the maximum heat and mass transfer reduction in smooth and rough pipes. The mass transfer to a disk rotating in drag-reducing solutions is also discussed using the proposed model.     

Absorption of chlorine in aqueous solutions of phenols and aromatic sulfonic acids

The kinetics of absorption of Cl₂ in aqueous solutions of phenol, o-chlorpophenol, p-chlorpophenol, p-nitrophenol, m-aminophenol-hydrochloride, ptoluenesulfonic acid and m-nitrobenzenesulfonic acid, at 30°C, was studied in a model stirred contactor, with a plane liquid interface and independent stirrers for gas and liquid phases. A laminar jet apparatus was also used to study the kinetics of chlorination of aqueous p-toluenesulfonic acid and m-aminophenol-hydrochloride. All the reactions were found to be first order in Cl₂ and first order in the dissolved organic substance. The values of second order rate constants at 30°C varied from about 1.1 x 10⁶ to 5.7 x 10⁹ cm³/g mole sec for phenolic substances and from 1.1 x 10⁶ to 3.5 x 10⁶, cm³/g mole sec for the sulfonic acids.Chlorination of o- and p-chlorophenol in aqueous buffered solutions was analysed on the basis of absorption of Cl₂ followed by two parallel fast pseudo-first order reactions, where the hydrolysis of Cl₂, catalysed by buffer anion, and the chlorination of chlorophenol were found to occur in the liquid film.Measurements of the effective interfacial area and the liquid-side mass transfer coefficient were made in a mechanically agitated contactor and a bubble column by using some of these chlorination reactions.     

The absorption of CO2 by amine-potash solutions

CO₂ has been absorbed in a stirred vessel into aqueous solutions of MEA and DEA containing K₂CO₃, K₂SO₄ and Na₂SO₄ at 25° and 11°C. While electrolytes in general appear to increase the rate of reaction between CO₂ and both MEA and DEA, K₂CO₃ increases the rate of reaction of DEA much more than that of MEA. The addition of K₂CO₃ to solutions of DEA increases the absorption rate, in spite of the decrease in the solubility and diffusivity of CO₂. The observations help to explain why DEA is an effective promoter for the absorption and desorption of CO₂ by hot, concentrated potash solutions.     

The turbulent diffusion of drag-reducing polymer solutions from a point source in flow through a pipe

Solutions containing salt(NaCI) were injected into water flow through a fine tube at the centre of a pipe. Tests were made to ensure that the flow was turbulent and well developed at the injection point; and that neither the injection process nor the injector caused any appreciable flow disturbance. Radial concentration profiles were measured at various downstream distances by withdrawing samples from the flow and measuring their electrical conductivity. A comparison was made between water, and aqueous solutions of polyethyleneoxide and polyacrylamide. Results for the eddy diffusivity in water agreed with those from previous investigations. Turbulent diffusivities were found to be greatly reduced in the polymer solutions (even after allowance had been made for the reduced wall shear stress) compared to the values for water alone. There were detailed differences in the effects of the two different kinds of polymer and these were attributed to their different viscoelasdc properties in the concentration ranges studied.     

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions: A kinetic study

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions was studied in a standard stirred reactor. Each test was carried out at constant pH and under stable hydrodynamic conditions. The effect of stirring speed, solution volume, temperature, pH, oxygen partial pressure, chloride and copper ion concentration of the solution were evaluated.The oxidation of Cu(I) followed linear kinetics up to 85% of the copper ions in the cupric state. The experimental results were interpreted by using the film theory of mass transfer with chemical reaction. In the linear range, the chemical reaction was found to be first order with respect to oxygen concentration. The kinetic constant is given. The flux equation was specific of a fast reaction regime and the overall reaction rate was independent of the mass transfer coefficient k_L up to a k_L-value of about 10^?2 cm/sec. A parallel study of the oxidation of SO₃^2? by oxygen gas was carried out in the same reactor. The effects of stirring speed and solution volume were similar for both systems.     

The transient response of a CSTR containing porous catalyst pellets: Asymptotic solutions

Transient response of a CSTR containing porous catalyst pellets is analyzed theoretically using a matched asymptotic expansion technique. This singular perturbation technique leads directly to the conditions under which the minima of reservoir concentration occur. The existence of the minima may be used to estimate some inherent parameters of the catalyst pellet.     

Interferometric study of concentration profiles in solutions near membrane surfaces

A new technique for the observation and interpretation of concentration profiles in diffusion layers at membrane-solution interfaces was developed. The concentration profiles in dilute (0·01N) KCl solutions near an ion-exchange membrane were observed in a modified O'Brien-type wedge laser interferometer while electric current (1·15 and 2·3 mA cm^?2) passed through the solution (25°C). After current reversal, following prepolarization periods of 5–60 s, a concentration minimum develops. The image of this minimum in relation to the membrane surface is not subject to optical deflection and can therefore be accurately determined. From its trajectory, the salt concentration at the membrane surface at the time of current reversal was determined. It was found that as this concentration dropped to the order of 10^?3–10^?4M (“critical concentration”) significant deviations occurred between observed trajectories and those computed from a theory based on the Nernst-Planck equations. These deviations are believed to be caused by substantial migration of H⁺ and OH^?. While these measurements indicate the order of magnitude of the critical concentration, additional measurements are necessary for quantitative determination of this concentration under different physicochemical and hydrodynamic conditions.     

Coalescence behaviour of gas bubbles in aqueous solutions of n-alcohols and fatty acids

Coalescence frequency and coalescence times of bubble pairs formed on two adjacent capillary tubes were determined in aqueous solutions of n-alcoho and fatty acids. The results show, that coalescence times of bubbles are proportional to the surface excess concentration of the solute. Coalescence ti increase with the polarity of the hydrophilic group of the solute, its chain length and the bubble size. Coalescence frequency decrease drastically fro 100% to 0% at a distinct solute concentration. The transition in coalescence behaviour occurs, if the coalescence times becomes greater than the availa contact times of the bubbles. The transition concentration therefore decreases with increasing rate of bubble formation.     

Promotion of CO2 mass transfer in carbonate solutions

A general, physico-chemical analysis of mass transfer rate promotion in the system CO₂-potassium carbonate-water-promoter is presented. Different possible mechanisms of promoter action including homogeneous catalysis, “shuttle” mechanism and surface reactions are discussed and classified. A unified picture of promoter chemistry is presented, showing that differences between inorganic and organic promoters are predominently quantitative, not qualitative.The “shuttle” mechanism is analyzed for absorption. The analysis leads to the prediction that the CO₂ mass transfer rate may be influenced by the liquid hold up. This is related to the fact that, although the reaction in the interface region may be fast enough to enhance the mass transfer rate, the different reaction in the bulk may not be fast enough to maintain chemical equlibrium. This complex type of chemical absorption process has not been considered previously in the literature.     

A mathematical model for equilibrium solubility of hydrogen sulfide and carbon dioxide in aqueous alkanolamine solutions

A thermodynamic model is proposed for the solubility of the acid gases (H₂S and CO₂) in alkanolamine solutions. The model is based on the exten Debye-Hückel theory of electrolyte solutions. Predicted partial pressures of the acid gases over monoethanolamine solutions are in good agreement wit experimental data over the temperature range 25—120°C.     

Structure of the steady-state solutions of lumped-parameter chemically reacting systems

A new, powerful mathematical technique enables a systematic determination of the maximal number of steady-state solutions of lumped parameter systems in which several chemical reactions occur simultaneously. The method can predict also the different types of diagrams describing the dependence of a state variable of the reactor on a design or operating variable.The technique is applied to several reaction networks giving new results and insight. For example, it is proven that when N independent, parallel exothermic reactions with equal and high activation energies occur in a CSTR there exist N! distinct regions of parameters in each of which 2N + 1 steady-state solutions exist.     

The electrochemistry of silver in koh at elevated temperatures—III. Potentiostatic study

The electrochemistry of polycrystalline silver in 1 mol kg^?1 KOH at temperatures between 295 K and 478 K has been studied using potentiostatic polarization. At potentials corresponding to silver dissolution and to the early stages of Ag₂O formation, the transient current data at all the temperatures studied exhibit regions that are linearly dependent on the inverse square root of time. This dependence indicates mass transport to be a rate limiting step in these processes. Log (steady-state current) vs potential data show that at all temperatures silver undergoes an active-to-passive transition. However, the potential of the transition shifts to less positive values and the passive current increases with increasing temperature. In the region of formation of surface oxide phases, the transients exhibit maxima due to nucleation and growth phenomena. The effect of temperature on the transients is similar to the effect of overpotential; in both cases, the time taken to reach the maximum current decreases.     

Simple relationships for predicting multi-solute adsorption from dilute aqueous solutions

This work presents simple relationships for predicting multi-solute adsorption from dilute aqueous solutions by means of the data for single-solute adsorption. These relationships are derived by assuming ideality of the surface and the bulk phase and energetic heterogeneity of the adsorbent surface. In the case of homogeneous adsorbent these relationships lead to simple expressions. The relationships are examined by using the experimental data for adsorption of acetone-propionitrile and p-cresol-p-chlorophenol mixtures from dilute aqueous solutions on activated carbon at 25°C.     

Simultaneous absorption of two gases reacting between themselves in a liquid—II: Approximate solutions

An attempt has been made to analyse the hitherto existing approximate solutions of nonlinear differential equations representing a mass balance of two gases which react between themselves in an inert liquid. New approximate analytical solutions of the problem have been obtained and compared with the numerical and the existing approximate solutions in order to show the best approximations and the most convenient mathematical formulas for calculating the concentration profiles and the enhancement factors.     

A unified approach to transport phenomena in polymeric media—I Diffusion in polymeric solutions,gels and melts

An altered free volume state model has been proposed to interpret transport phenomena in diverse media within a unified framework. Its specific application to the interpretation and correlation of data on diffusion in polymer solutions, protein solutions, polymeric gels and blends of polymeric melts has been elaborated. Extensive experimental data from the literature have been analysed within the framework of the model, which confirm its utility. Apart from providing quantitative predictions of the effect of polymer concentration or phase fraction and temperature, the model provides a semiquantitative assessment of the influence of diffusant size and shape, molecular weight of the polymer etc. on diffusional characteristics in the above media.