Effect of gas sparging on mass transfer in zinc electrolytes

The effect of sparging on mass transfer is reported for zinc electrolytes containing antimony and antimony-free electrolytes. Comparative results with non-sparged electrolytes show, an enhancement in mass transfer. In the sparged electrolyte, the mass transfer coefficients,K _Zn, increase with increasing current density, antimony additions, and sulphuric acid concentration. The deposition morphology is consistent with the mass transfer results. A relationship between the mass transfer coefficients for sparged and non-sparged systems is obtained. The relationship correlates satisfactorily with the data and provides a quantitative method for determining the degree of enhancement in mass transfer coefficients due to sparging. The correlation which best represents the mass transfer data for sparged zinc electrolytes is $$Sh = 105(ReSc)^{0.23} $$ whereSh, Re, andSc are the Sherwood, Reynolds, and Schmidt numbers, respectively. The correlation represents the case where sparging is applied to a gas evolving electrode, hydrogen in this case.     

Mass transfer downstream of nozzles in turbulent pipe flow with varying Schmidt number

Local mass transfer rates at the wall of a pipe downstream of constricting nozzles have been measured using the electrochemical limiting diffusion current technique for different electrolyte Schmidt numbers. The familiar peaked axial distribution of mass transfer downstream of the nozzle was verified and the peak mass transfer values were found to agree well with the data of Tagget al. [1]. An overall correlation of the data in terms of both Reynolds number and nozzle expansion ratio produced the equation $$({{Sh_{2P} } \mathord{\left/ {\vphantom {{Sh_{2P} } {Sh_{2FD} }}} \right. \kern-\nulldelimiterspace} {Sh_{2FD} }})({{D_1 } \mathord{\left/ {\vphantom {{D_1 } {D_2 }}} \right. \kern-\nulldelimiterspace} {D_2 }})^{ - 0.7} = 14.39Re_2^{ - 0.182} $$ Limiting current-time traces produced evidence of the highly turbulent flow in the recirculation zone near the position of peak mass transfer.     

Enhancement of mass transfer at a spherical electrode in pulsating flow

The effect of pulsation on the overall mass transfer coefficient between a sphere and a liquid at low Reynolds number (Re < 6.36) has been studied. When there is no flow reversal, pulsations have a negative effect on the mass transfer coefficient, it being minimum when the dimensionless group α = a/u ₀ = 1. When flow reversal occurs the mass transfer coefficient increases with both frequency, f, and amplitude, a, of the pulse and decreases with the mean fluid velocity, u ₀. The variation of the mass transfer coefficient has been studied with a model based on the quasisteady-state assumption. In this way two correlations have been obtained for the mass transfer coefficient: $$\operatorname{Re} < 20\user1{ }Sh = 1.23Sc^{1/3} \operatorname{Re} ^{0.23} $$ $$\operatorname{Re} < 20\user1{ }Sh = 0.39Sc^{1/3} \operatorname{Re} ^{0.58} $$      

Mass transfer characteristics of gas-sparged fixed-bed electrodes composed of stacks of vertical screens

Mass transfer rates at a gas-sparged fixed-bed electrode made of stacks of vertical screens were studied by measuring the limiting current for the cathodic reduction of potassium ferricyanide. Variables studied were air flow rate, physical properties of the solution and bed thickness. The mass transfer coefficient was found to increase with increasing air flow rate up to a certain point and then remain almost constant with further increase in air flow rate. Increasing bed thickness was found to decrease the mass transfer coefficient. Mass transfer data were correlated by the equation $$J = 0.2(ReFr)^{ - 0.28} ({L \mathord{\left/ {\vphantom {L d}} \right. \kern-\nulldelimiterspace} d})^{ - 0.28} $$ For a single vertical screen electrode the data were correlated by the equation $$J = 0.187(ReFr)^{ - 0.26} $$      

Experimental determination of the factors affecting zinc electrowinning efficiency

A series of experiments were conducted to investigate the factors affecting the efficiency of zinc electrowinning. The experiments were conducted in 10-1 cells using a high purity industrial zinc sulphate solution. The lowest specific energy consumption achieved in the cells was 2637 kWh t^?1 Zn under the following conditions: $$\begin{gathered} 70 g1^{ - 1} Zn in cell solution \hfill \\ 180 g1^{ - 1} H_2 SO_4 in cell solution \hfill \\ 45^\circ C cell temperature \hfill \\ 400A m^{ - 2} current density \hfill \\ \end{gathered} $$ Further energy savings can be achieved by reducing the current density but this would also reduce the cellroom production capacity. Increasing the electrolyte temperature to 50° C also reduced the energy consumption, however additives capable of controlling deposit morphology at these high temperatures were required. The effects of zinc concentration, acid concentration, deposition time and additive levels are also reported.     

Mass transfer at vertical cylinders under forced convection induced by the counter electrode gases

Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a vertical cylinder cathode stirred by oxygen evolved at a horizontal lead anode placed below the cylinder. Variables studied were: oxygen discharge rate, electrolyte concentration and cylinder height. The mass transfer coefficient was found to increase by a factor of 1.8–2.6 depending on oxygen discharge rate and cylinder height. The mass transfer coefficient was related to oxygen discharge rate and cylinder height by the equation: $$K = 65.8 \times 10^{ - 4} \frac{{V^{0.358} }}{{h^{0.29} }}$$      

Mass transfer in a stirred transfer cell with a flat interface

A agitated vessel of Lewis cell type was used to investigate the effect of physical properties on the mass transfer coefficient for partially miscible binary systems. Some measurements were performed with ternary systems transferring only one solute across two immiscible solvents. The mass transfer coefficients were measured under the conventional contra-rotating conditions which were behaved as if the interface was not rotating for some combinations of agitation speeds in each of the two phases. The mass transfer coefficient was deduced from solving a steady-state two dimensional convective-diffusion equation with the assumption of sinusoidal motion of eddies. Owing to the complexity of the hydrodynamic conditions near the liquid-liquid interface, theoretical approach was impossible. Thus, the effects of forced turbulence and physical properlies on the effective surface renewal time were experimentally investigated. The relation between the mass transfer coefficients and the relevant variables was obtained by conventional dimensional analysis as follow: 1 $$Sh_w = 1.93 \times 10^{ - 3} Ca^{1/2} Sc_w^{0.5} Re_w^{0.70} exp(1.60 \times 10^{ - 4} \frac{{v_w }}{{v_o }}Re_o )$$      

Mass transfer in electrolytic cells with gas stirring

Mass transfer to wall electrodes was investigated in a circular cell agitated by gas bubbles. Perforated and porous plates were used as gas spargers. Electrodes with varying height and electrolytic solutions having different physical properties were tested. It was found that the enhancing effect of gas bubbles on the mass transfer coefficient is a function of the gas hold-up, irrespective of the velocity of the gas flow and the gas distributor employed. The results were correlated for short mass transfer lengths by the relationship $$Sh = 0.231(ScGa)^{\frac{1}{3}} (L/D_c )^{--0.194 _\varepsilon 0.246}$$ and for fully developed mass transfer by $$Sh_\infty = 0.256(ScGa)^{\frac{1}{3}} \varepsilon ^{0.254}$$      

The effect of electro-osmosis on the synthesis of lead and tin fluoroborates

Pronounced electro-osmosis phenomena were observed during the anodic dissolution of lead and tin in fluoroboric acid with an anionic exchange membrane separating the anode compartment from the cathode compartment. The consequent volumetric increment of anolyte was influenced by the current density and the initial volume and concentration of catholyte. The selectivities (S _i) of the given membrane were found to be $$\begin{gathered} 50\% Sn(BF_4 )_2 solution: S_{BF^{4 - } } = 0.952; S_{Sn^{2 + } } = 0.048 \hfill \\ 50\% Pb(BF_4 )_2 solution: S_{BF^{4 - } } = 0.887; S_{Pb^{2 + } } = 0.113 \hfill \\\end{gathered}$$      

Mass transfer in annular electrolytic cells with gas stirring

Mass transfer towards the inner electrode and the wall electrode was studied in an annular cell stirred with an inert gas bubble flow. Experimental data obtained for the wall electrode follow the relationship found previously for circular cells; namely $$Sh = 0.231(ScGa)^{1/3} (L/D_e )^{ - 0.194_\varepsilon0.246}$$ Study of the influence of gas hold-up on the mass transfer rate towards the inner wall electrode has yielded the following relationship: $$Sh_\infty= 0.315(ScGa)^{1/3_\varepsilon0.231}$$      

Characteristic velocity and mass transfer in rotating impeller column

The effects of system variables on flow characteristics and mass transfer rate were studied in a rotating impeller column using a ternary system of water (continuous phase)-acetone (solute)-cyclohexane (dispersed phase). The characteristic velocity, Peclet numbers in both phases and mass transfer coefficient between phases were correlated as; $$\begin{gathered} \bar U_o = 6.3(10^2 )(Nd_I )^{ - 2.1} Z_C^{0.83} \hfill \\ \frac{{\bar U_C L}}{{D_C }} = 1.26N^{ - 1.11} d_I ^{ - 2.17} Z_C^{0.59} \bar F_C^{1.9} \hfill \\ \frac{{\bar U_d L}}{{D_d }} = 20.5N^{ - 0.78} d_I ^{ - 1.36} Z_C^{0.25} \bar F_C^{0.09} \hfill \\ \frac{{k_{OC} aL}}{{\bar U_d }} = 13.2N^{ - 1.33} d_I ^{0.74} Z_C^{0.93} \bar F_C^{0.78} \hfill \\ \end{gathered} $$      

Micellization of Some Bile Salts in Binary Aqueous Solvent Mixtures

The micellization behavior of bile salts—sodium cholate and sodium deoxycholate was studied in aqueous methanol, ethanol and ethylene glycol mixtures (10–20 % v/v) over a temperature range (300–320 K) by surface tension and conductivity methods. Critical micelle concentration, extent of counter ion binding (α), interfacial property (A _min, ζ_max, π-CMC, $ \Updelta G_{\text{ad}}^{ \circ } $ ) and thermodynamic parameters ( $ \Updelta G_{\text{m}}^{ \circ } $ , $ \Updelta H_{\text{m}}^{ \circ } $ , $ \Updelta S_{\text{m}}^{ \circ } $ ) for the micellization process are reported and discussed.     

Structure and Biological Behaviors of Some Metallo Cationic Surfactants

In this study, different cationic surfactants were prepared by esterification with bromoacetic acid of different fatty alcohols, i.e., dodecyl, tetradecyl and hexadecyl species. The products were then reacted with diphenyl amine, and the resulting tertiary amines were quaternized with benzyl chloride to produce a series of quaternary ammonium salts. The metallocationic surfactants were prepared by complexing the cationic surfactants with nickel and copper chlorides. Surface tension of these surfactants were investigated at different temperatures. The surface parameters including critical micelle concentration (CMC), maximum surface excess (Γ _max), minimum surface area (A _min), efficiency (PC₂₀) and effectiveness (π _CMC) were studied. The thermodynamic parameters such as the free energy of micellization ( $\Updelta G_{\text{mic}}^{^\circ }$ ) and adsorption ( $\Updelta G_{\text{ads}}^{^\circ }$ ), enthalpy ( $\Updelta H_{\text{m}}^{^\circ }$ ), ( $\Updelta H_{\text{ads}}^{^\circ }$ ) and entropy ( $\Updelta S_{\text{m}}^{^\circ }$ ), ( $\Updelta S_{\text{ads}}^{^\circ }$ ) were calculated. FTIR spectra and ¹H-NMR spectra were obtained to confirm the compound structures and purity. In addition, the antimicrobial activities were determined via the inhibition zone diameter of the prepared compounds, which were measured against six strains of a representative group of microorganisms. The results indicate that these metallocationic surfactants exhibit good surface properties and good biological activity on a broad spectrum of microorganisms.     

Conduction in Bi2O3-based oxide ion conductor under low oxygen pressure. II. Determination of the partial electronic conductivity

In order to investigate the partial electronic conduction in the high oxide ion conductor of the system Bi₂O₃-Y₂O₃ under low oxygen pressure, e.m.f. and polarization methods were employed. Although the electrolyte was decomposed when the \(P_{{\text{O}}_{\text{2}} }\) was lower than the equilibrium \(P_{{\text{O}}_{\text{2}} }\) of Bi, Bi₂O₃ mixture at each temperature, the ionic transport number was found to be close to unity above that \(P_{{\text{O}}_{\text{2}} }\) . The hole conductivity (σ _p) and the electron conductivity (σ _p) could be expressed as follows, $$\begin{gathered} \sigma _p \Omega cm = 5 \cdot 0 \times 10^2 \left( {P_{O_2 } atm^{ - 1} } \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 106 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \sigma _p \Omega cm = 3 \cdot 4 \times 10^5 \left( {P_{O_2 } atm^{ - 1} } \right)^{ - {1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 213 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \end{gathered} $$ These values were much lower than the oxide ion conductivity under ordinary oxygen pressure.     

Crystallization conditions effect on molecular weight of solid-state polymerized poly(ethylene terephthalate)

Number-average molecular weight ( $ \overline{M}_{n} $ ) variation of polyethylene terephthalate with respect to crystallization temperature and time, and solid-state polymerization (SSP) time were studied using response surface experimental design method. All experiments were conducted in a fluidized bed reactor. $ \overline{M}_{n} $ values were calculated by Mark?CHouwink equation upon determining intrinsic viscosity (IV) of samples. Two suitable models were proposed for $ \overline{M}_{n} $ and IV, based on the regression coefficient. It was observed that $ \overline{M}_{n} $ increases with decrease in crystallization temperature and increase in crystallization time and SSP time. It was shown that SSP time is the most important parameter based on statistical calculations. Crystallization time, crystallization temperature and SSP time were determined 60?min, 160?°C and 8?h, respectively, in order to achieve maximum $ \overline{M}_{n} $ . Density measurements were applied to study the overall crystallinity of samples. Based on density results it was revealed that percent of crystallinity is not the only factor that affects the $ \overline{M}_{n} $ of polymer. Differential scanning calorimeter was used to analyze thermal properties of the samples. All samples showed two melting peaks. It was observed that the lower melting temperature peak is related to the isothermal crystallization process temperature. Polarized light microscopy was used to study spherulitic structures of polymer films after crystallization process. It was shown that the sample with smallest spherulite size had the maximum $ \overline{M}_{n} $ equal to 26,000?g/mol.     

The mechanism of manganese electrodeposition

The mechanism of manganese electrodeposition from a sulphate bath on to a stainless-steel substrate has been studied by using current efficiency data to resolve the totali-E curves. A simple, two-step electron transfer mechanism: $${\text{Mn}}^{{\text{ + + }}} + {\text{e}}\xrightarrow{{{\text{r}}{\text{.d}}{\text{.s}}}}{\text{Mn}}^{\text{ + }} $$ $${\text{Mn}}^{\text{ + }} + {\text{e}} \to {\text{Mn}}$$ is proposed to explain the following experimentally obtained parameters: cathodic and anodic transfer coefficients, reaction order and stoichiometric number. The mechanism also explains the effect of pH oni _o,Mn and on the corrosion currents.     

Synthesis and Properties of X-Type Alkyl Sulfonate Gemini Surfactants Derived from Cyanuric Chloride

A series of X-type alkyl sulfonate Gemini surfactants (XC_n, n?=?6, 8, 10) was synthesized by a simple method. The chemical structures of the prepared compounds were confirmed by ¹H NMR, ¹³C NMR, ESI?CMS and Elementary analysis. The surface activity and thermodynamic properties of micellization of the X-type alkyl sulfonate Gemini surfactants were compared with sodium dodecylsulfate by means of surface tension. The properties of XC_n are superior to those of SDS such as the ??_CMC and CMC of XC₁₀ are 26.3?mN/m and 0.2?mmol/L respectively. The adsorption isotherms for XC_n were established by fitting the pre-CMC surface tension data with a quadratic function. The thermodynamic parameters of micellization ( $ \Updelta G_{m}^{ \circ } $ , $ \Updelta H_{m}^{ \circ } $ , $ \Updelta S_{m}^{ \circ } $ ) derived from electrical conductivity indicate that the micellization of XC_n is entropy-driven.     

Thermodynamics of Micellization of Sulfobetaine Surfactants in Aqueous Solution

The thermodynamics of micellization of the sulfobetaine (SB) amphoteric surfactants, that is N-alkyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and N-alkyl-N,N-dimethyl-3-ammonio-1-butanesulfonate (the carbon atom number of the alkyl chain is 12, 14 and 16 respectively) in aqueous solution, have been studied by surface tension measurements with the temperature range from 298.15 to 318.15?K. The critical micelle concentrations (CMC) of SB n-3 and SB n-4 surfactants were determined from the drop-volume methods at different temperatures. The obtained results indicated that the values of critical micelle concentration strongly depended on the surfactants species and temperatures. Thermodynamic parameters ( $ \Updelta G_{\text{mic}}^{ \circ } $ , $ \Updelta H_{\text{mic}}^{ \circ } $ and $ \Updelta S_{\text{mic}}^{ \circ } $ ) of the micelle formation were determined. The micellization was found to be enthalpy-driven at lower temperatures, while this process was entropy-driven at higher temperatures. The enthalpy?Centropy compensation were also investigated. The compensation temperature T _c and $ \Updelta H_{\text{mic}}^{*} $ decreased, while $ \Updelta S_{\text{mic}}^{*} $ increased with the increase in the hydrophobic chain length.     

Hansen solubility parameters of cellulose acetate butyrate–poly(caprolactone) diol blend by inverse gas chromatography

The specific retention volumes, $ V_{\text{g}}^{0} $ , for adsorption of 21 solute probes on the solid surface of cellulose acetate butyrate (CAB)–poly(caprolactone) diol (PCLD) blend determined in the temperature range by inverse gas chromatography were used to evaluate Hansen solubility parameters (HSP). The effect of plasticizer, PCLD, on the HSP of CAB was investigated. The three components of HSP namely dispersive $ \delta_{2}^{\text{d}} $ , polar $ \delta_{2}^{\text{p}} $ , and hydrogen bonding $ \delta_{2}^{\text{h}} $ of the blend surface were compared with the CAB surface. The $ \delta_{2}^{\text{h}} $ of CAB was increased due to the addition of PCLD, while the change in the dispersive and polar components was found to be insignificant. The three HSP were decreasing linearly with increase of temperature for the blend as well as for pure CAB. The variation of HSP with weight fraction of CAB shown that the $ \delta_{2}^{\text{p}} $ was positively deviating from linearity whereas $ \delta_{2}^{\text{d}} $ and $ \delta_{2}^{\text{h}} $ were negatively deviating from linearity.     

Evaluation of the N2O emissions from N in plant residues as affected by environmental and management factors

A review of the N₂O-N emission from crop residues was conducted based on new data published during the last decade. The result indicated that factors as type of crop, biochemical quality of residues, agricultural management, climate and season of the year, soil properties and soil moisture play a significant role in the rate of N₂O-N emissions. An emission factor (EF) equal to 1.055% of N applied in plant residues – derived from a simple linear regression of emitted N₂O-N (kg ha^?1) on N applied in crop residues (kg ha^?1) – represent an estimate that explains about 60% of emission variations. However, the EF of N applied in plant residues is not a constant but a variable coefficient that depends on environmental and management variables. The following two linear models – that estimate emitted N₂O-N (kg ha^?1) as a function of the variables N (kg ha^?1) applied in plant residues (NPR), rain (mm), temperature (°C) and temperature²(°C²) – were fitted to the dataset with 45 observations obtained from the reviewed literature. $$\hskip1.5pc\hbox{N}_{2}\hbox{O}\hbox{-}\hbox{N}=-4.154+0.00955\hbox{ NPR}+1.7278\hbox{ ApM}+0.003996\hbox{ Rain }+0.6242\hbox{ Tem }-0.0230\hbox{ Tem}^{2}$$ and $$\hbox{N}_{2}\hbox{O}\hbox{-}\hbox{N}= 0.6535 + [-0.0404 + 0.0078\hbox{ ApM }+ 0.000044\hbox{ Rain }+ 0.00567\hbox{ Tem }-0.0001975\hbox{ Tem}^{2}]\hbox{ NPR }$$ Both models provided almost equally good statistical fit to the data, with R ²=0.832 and R ²=0.829, respectively, and most regression coefficients being significant at $P < 0.01$ . Because of its internal structure, the second model is more appealing as it represents N₂O-N emission as a transformation that is affected by management and environmental variables. The following expression – that correspond to the quantities in the square bracket at the right hand side of the second model – is the coefficient for the variable N applied in crop residues, and represent the emission factor as a function of application method of plant residues, rain, temperature and temperature². $$\hskip3.5pc\hbox{EF }=-0.0404+0.0078\hbox{ ApM }+0.000044\hbox{Rain }+0.00567\hbox{ Tem }- 0.0001975\hbox{ Tem}^{2}$$ Standardization of research methodologies and data gathering and reporting, including kind of crop, N content of applied residues, agricultural management, length of the measuring period, climate, soils properties, soil temperature and water content, would facilitate further advances in studies oriented to increase the precision of N₂O-N emission estimates.