Performance of an RTL contactor for gas-liquid systems: Effective interfacial area and volumetric mass transfer coefficient by oxidation of sodium sulphite solution

Effective interfacial area a and volumetric liquid-side mass transfer coefficient k_La of an RTL contactor were obtained at different stirring speeds by absorption of oxygen from air into 0.8 kmol/m³ sodium sulphite solution, in the presence of Co⁺⁺ ions. The values of a and k_La ranged from 80 to 150 m²/m³ and 0.0003 to 0.00053 s^?1, respectively, when stirrer speed was increased from 8 to 40 rpm. When k_L alone was evaluated, it was found to be practically constant, irrespective of stirring speed.     

Absorption of carbon dioxide in aqueous colloidal silica solution with NaOH

The absorption rate (R _A ) of carbon dioxide was measured into an aqueous nanometer-sized colloidal silica solution of 0–31 wt% and NaOH of 0–2 kmol/m³ in a flat-stirred vessel for various sizes and speeds of 25 °C and 101.3 N/m² to obtain the volumetric liquid-side mass transfer coefficient (k _L a _L ) of CO₂. The film theory accompanied by chemical reaction between CO₂ and NaOH was used to estimate the theoretical value of absorption rate of CO₂. The empirical correlation formula containing the relationship between k _L a _L and rheological property of the aqueous colloidal silica solution was presented. The value of R _A in the aqueous colloidal silica solution was decreased by the reduction of k _L a _L due to elasticity of the solution.     

Separation of phenylacetic acid using tri-n-butyl phosphate in hexanol: Equilibrium and kinetics

Equilibrium and kinetics studies are required to design the continuous extraction process for the acid-extraction system. In the present study, an attempt has been made to investigate the equilibrium and kinetics parameters for the reactive extraction of phenylacetic acid (PAA) with tri-n-butyl phosphate (TBP) in hexanol. The equilibrium results show that the formation of the (1:1) PAA–TBP complex in the organic phase with an overall equilibrium complexation constant (K_e) was 78.74 and 29.15 m³.kmol^?1 for TBP concentrations of 0.734 and 1.464 kmol.m^?3, respectively. The mass transfer coefficients (k_L) for PAA were found to be in the range of 3.7 × 10^–5–6.2 × 10^–5 m.s^?1. Based on the Hatta number (H_a = 8.48), the reaction was found to be fast chemical reaction (regime 3) with the order of reaction as 0.77 and 0.36 with respect to PAA and TBP, respectively. The rate constant of the reaction was obtained as 0.017 kmol.m^?3.s^?1.     

Mass transfer characteristics of low H/D bubble columns

The mass transfer characteristics of 0.2, 0.6 and 1.0 m diameter bubble columns having a low height to diameter ratio (0.6 < H/D < 4) and operated at low superficial gas velocities (0.01 < V_G < 0.08 m/s) were investigated. Different types of spargers were used to study their effect on the column performance. The values of effective interfacial area, a , and volumetric mass transfer coefficient, k_L a , were measured by using chemical methods. The values of a and k_L a were found to vary from 40 to 420 m²/m³ of clear liquid volume and from 0.01 to 0.16 s^?1, respectively, in the range of V_G, and V_L covered in this investigation. The value of the liquid-side mass transfer coefficient, k_L, was found to vary from 3 × 10^?4 to 7 × 10⁴ m/s. The effect of the physical properties of the system on the values of a was also investigated. The height to diameter ratio and the column diameter did not have significant effect on the values of gas holdup, a and k_L a . It was found that the sparger design is not of critical importance, provided multipoint/multiorifice gas spargers are used. The comparative performance of bubble columns having low H/D with horizontal sparged contactors and tall bubble columns has been considered.     

Comparison of Different HFSLM Configurations for Separation of Neodymium and Uranium

Different feed and strip operating modes have been compared for the transport of neodymium (Nd³⁺) and uranyl (UO₂²⁺) ions in nitric acid media. The flux values of UO₂²⁺ for feed in recycling and once through mode with fresh strip were 2.26 × 10^?9 kmol/m²-s and 2.33 × 10^?9 kmol/m²-s, respectively. So, this resulted in low separation factors. The flux values of Nd³⁺ for feed and strip—both in recycling and in once through mode—were 2.21 × 10^?9 kmol/m²-s and 2.14 × 10^?9 kmol/m²-s, respectively. The operating modes—feed and strip both recycling and feed and strip both in once through—were found to be the best configurations.     

Counter-current absorption using wire gauze packings

The dynamic liquid hold-up, ?_LD, effective interfacial area, a, and the liquid side mass transfer coefficient k_La were determined for 0.1 m and 0.2 m multifilament wire gauze packings, 0.0125 m double walled wire gauze partition rings and 0.025 m wire gauze saddle packings in columns operated countercurrently. The theory of gas absorption accompanied by fast pseudo mth order reaction was used to determine the effective interfacial area. The values of liquid side mass transfer coefficient for the multifilament wire gauze packings were obtained by absorbing lean carbon dioxide in a buffer solution of sodium carbonate and sodium bicarbonate. K_La values for the other packings were obtained by absorbing pure carbon dioxide in tap water. The values of a and k_La for multifilament wire gauze packings were found to be two to four times higher as compared to the conventional ring or saddle packings. Further, the superficial liquid velocity was found to have marginal effect on a. The double walled wire gauze partition rings offered a values which were 1.5–2.0 times higher than that offered by 0.016 m s.s. Pall rings at low values of superficial liquid velocity (<3 × 10^{?3 m/s}.     

The scale-up of aerated mixing vessels for specified oxygen dissolution rates

Values of the mass transfer product, k_La, have been determined using unsteady state measurements of oxygen dissolution rates in water, in 0.60 m³ and 0.043 m³ baffled mixing vessels fitted with geometrically similar flat-bladed turbines and spargers. It was seen that the assumption of quasi steady-state in the gas phase, as often practised hitherto, can lead to large errors in k_La. A correlation for the scale-up of aerated mixing vessels is proposed.     

Absorption of Carbon Dioxide into Aqueous Xanthan Gum Solution Containing Monoethanolamine

Abstract

Carbon dioxide was absorbed into the aqueous xanthan gum (XG) solution in the range of 0–0.151 wt% containing monoethanolamine (MEA) of 0–2 kmol/m³ in a flat‐stirred vessel with the impeller of 0.05 m and agitation speed of 50 rpm at 25°C and 0.101 MPa to measure the absorption rate of CO₂. The volumetric liquid‐side mass transfer coefficient (k_La_L) of CO₂ decreased with increasing XG concentration, and was correlated with the empirical formula having the rheological behavior of XG solution. The chemical absorption rate of CO₂ was estimated by the film theory using the values of k_La_L and physicochemical properties of CO₂ and MEA. The aqueous XG solutions made the rate of absorption of CO₂ accelerated compared with the Newtonian liquid based on the same viscosity of the solution.     

Mass transfer coefficients in mechanically agitated gas—aqueous electrolyte dispersions

The oxygen transfer characteristics of gas-aqueous electrolyte solution dispersions have been studied in a laboratory-size, mechanically-agitated tank equipped with a 6-flat blade turbine of standard dimensions (D_I/T = 1/3). The effects of mechanical agitation power input per unit volume (P_g/V), gas superficial velocity (v_S) and aqueous-phase ionic strength (Γ) upon the overall volumetric mass transfer coefficient (k_L a) and the liquid-phase mass transfer coefficient (k_L) are presented. In the range of 0.2 ≤ Γ ≤ 1.2 kmol(ions)/m³, the results of this study indicate that k_L increases with increasing Γ is independent of P/V for P_g/V < 2000 W/m³ but decreases with increasing P_g/V above that level and is independent of v_s over the range of gas velocities studied. On the other hand, K_L a was found to be dependent on all three variables (P_g/V, v_g, and Γ).     

A contribution to the measurement of oxygen mass transfer in a laboratory pressure reactor

A method was used to measure the liquid‐side volumetric coefficient of oxygen mass transfer (k_La) in closed, semi‐batch pressure reactors used in hydrometallurgical laboratories. In this method, the oxygen pressure was monitored as oxygen was continuously sparged into a pressure vessel containing a sodium sulfite solution. A material balance equation was derived for oxygen in the vessel and the experimental data were fitted to this equation. From the constant parameters of the equation, k_La was calculated. The solution in the vessel also contained an appropriate amount of cobalt catalyst so that oxygen was consumed rapidly by oxidation of sulfite to sulfate. Under these conditions, the oxygen concentration in the bulk liquid phase could be assumed to be equal to zero. Values of k_La determined by the method under various conditions were reproduced within 12% deviation from the average values. k_La was found to increase moderately with temperature in the range of 25 to 75 °C, with an activation energy of 33.09 ± 1.33 kJ mol⁻¹. The presence of hydrophobic or hydrophilic solids was found to have a deleterious effect on k_La. © 2000 Society of Chemical Industry     

Oxidation of cyclohexanone to adipic acid with a cobalt acetate/oxygen/acetic acid system

The liquid phase oxidation of cyclohexanone to adipic acid at 378 K using oxygen as the oxidising agent and cobalt acetate as the catalyst in an acetic acid medium was investigated both at atmospheric pressure and at a pressure of 0.5MN m⁻². The effects of catalyst concentration, solvent concentration and partial pressure of oxygen, were studied at a constant stirrer speed of 535 rev min⁻¹. Increasing the solvent concentration and decreasing the catalyst concentration (up to 0.113×10⁻³ kmol m⁻³) had positive effects on the overall first order reaction rate constant. It was also found to vary linearly with gas flow rate.     

Kinetic model of asymmetric reduction of 3-oxo-3-phenylpropionic acid ethyl ester using <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> CGMCC No.2266

The kinetic model of asymmetric reduction of 3-oxo-3-phenylpropionic acid ethyl ester using Saccharomyces cerevisiae CGMCC No.2266 with 10% glucose as co-substrate to realize the regeneration of NADPH was established. The effect factors on reduction, the type and the content of co-substrate and coenzyme, and the changes of the substrate and product content vs. time during the reaction process were investigated. The results indicate that 10% glucose can increase the reaction conversion from 23.0% to 98.4% and NADPH is reducer. The reduction process conforms with sequence mechanisms. The model parameters are as follows: v _m =5.0×10⁻⁴ mol·L⁻¹·h⁻¹, k₁=1.5×10⁻⁶ mol·L⁻¹·h⁻¹, k₂=3.0×10⁻³ mol·L⁻¹·h⁻¹. The kinetic model is in good agreement with the experimental data.     

Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P₂O₅). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, k_L°, vary from 3 × 10^?3 to 8 × 10^?3 m ·s^?1. The corresponding diffusion coefficients, D, lies between 6 × 10^?7 and 27 × 10^?7 m²·s^?1. Activation energy is equal to 14 kJ·mol^?1 and values of k_L°, at 25°C, are in the range of 0.28 × 10^?3 and 4 × 10^?3 m·s^?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.     

Faradaic rectification studies of two electron charge transfer redox couples at the metal (solid) interface

The Faradaic rectification studies of the two electron charge transfer processes, cationic and anionic redox couples, have been carried out. The mechanism of the iodide—iodine reaction through single charge transfer comprises the following steps, of which reaction (b) is the slowest and controls the rate of overall reactions.

The values of the transfer coefficient and rate constant are obtained for the second step, which is rate determining in both the directions. The values of the parameters obtained when the concentration of the electrochemical species (I₂) is much less in comparison to that of iodide, are α_c = α_a = 0·5 and k^O_a of the order of 5 × 10^?5 cm/s. The parameters for the iodide—iodine reaction, using 1·0 M KNO₃ as supporting electrolyte, are α_c = 0·49, α_a = 0·51 and k^O_a of the order of 5 × 10^?3 cm/s. For the stannous-stannic reaction either of the two steps appears to be rate determining in both directions and the values of the parameters obtained are α_c = 0·48, α_a = 0·52 and k⁰_a = 2·1 × 10^?3 cm/s.     

Experimental studies of nitrobenzene hydrogenation in a microstructured falling film reactor

Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5-3 ml/min) and pressure (1-6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10-30%. The k_La of this system was estimated to be 3-8 s⁻¹ with interfacial surface area per reaction volume 9000-15000 m²/m³. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes.     

Microstructure and permeability of porous zirconia ceramic foams prepared via direct foaming with mixed surfactants

The permeability performance of porous ceramics from particle-stabilized foams is closely associated with the connectivity between bubble-evolved pores. In order to regulate the connectivity of pore structure, the zirconia ceramic foams were fabricated by direct foaming with mixed surfactants of cetyltrimethyl ammonium bromide (CTAB) and sodium N-lauroyl sarcosinate (SLS). Different solid loadings and CTAB:SLS mixing ratios were used in this study. The results indicate that the pore structures of zirconia ceramic foams were interconnected by open windows on the cell walls, and the porosity and average size of cell and cell windows could be tailored by adjusting the solid loading and CTAB:SLS mixing ratio. The decrease in solid loading and CTAB:SLS mixing ratio caused larger porosity and size of cells and cell windows, and thus resulted in the obvious augment of Darcian (k₁) and non-Darcian (k₂) permeability constants. The ranges of k₁ and k₂ of the as-fabricated zirconia ceramic foams are 6.92 × 10^?13-4.05 × 10^?10 m² and 2.09 × 10^?5-3.19 × 10^?9 m respectively.     

Free-convective ionic mass transport at inclined circular disk electrodes

Electrochemical mass transport rates at circular disk electrodes and at arbitrary inclination angles, α, formed between the cathode and the horizontal were measured. The results can be correlated by the general regression relationship

for O° ≤ α ≤ 170° and 2.5 × 10⁸ < Ra_L < 6.3 × 10⁹, using the distance between electrodes, L, as the characteristic length. The range of the exponents n, m is $\text{1}\text{4}$–$\text{1}\text{3}$ and C(α) varies from 0.33 to 0.39.     

Chemical Absorption of Carbon Dioxide into Aqueous Colloidal Silica Solution with Diethanolamine

Abstract

The chemical absorption rate (R_A) of CO₂ was measured into the aqueous nanometer sized colloidal silica solution of 0–31 wt% and diethanoleamine of 0–2 kmol/m³ in the flat‐stirred vessel with the impeller size of 0.034 m and its agitation speed of 50 rev/min at 25°C and 0.101 MPa, and compared with the values estimated from the model based on the film theory accompanied by chemical reaction. The value of the volumetric liquid‐side mass transfer coefficient (k_La) of CO₂, which was used to estimate the value of R_A, was obtained by the empirical correlation formula presenting the relationship between k_La and the rheological behavior of the aqueous colloidal silica solution. The value of R_A in the aqueous colloidal silica solution was decreased by the reduction of k_La due to the elasticity of the solution.     

Edible oil hydrogenation rates in the presence of a homogeneous Ziegler—Natta catalyst in a film reactor

The rates of edible oil hydrogenation in the presence of a homogeneous Ziegler—Natta catalyst has been measured in a falling-film reactor with a view to the ultimate determination of the hydrogen/edible oil interfacial area in an agitated tank under a fast reaction regime. The catalyst is a combination of nickel diisopropyl salicylate (Ni(dips)₂) and aluminium triisobutyl (Al(iBu)₃).The reaction rates have been determined by measuring hydrogen absorption rates into soyabean and safflower oils under a fast reaction regime (Ha > 3). The gas absorption has been measured as a function of pressure, temperature, catalyst concentration, molar ratio (α) of Al(iBu)₃ to Ni(dips)₂ and concentration of unsaturated triglycerides in the oils (iodine value, I.V.).The hydrogenation rates can be described by R₂ = K_nc^1.7 for 50 < I.V. < 130 and R₁ = Kc^1.7b^0.55 for 5 < I.V. < 50 (c = concentration of hydrogen in oil, b = concentration of unsaturated triglycerides in oil), under the conditions 5×10⁴<P/(Pa)<1.4×10⁵, 55 <T/(°C)<95, 1.5×10^?3<Ni(dips)₂/(kmol·m^?3)<2.75x10^?2 and 4<α<10.