Showing papers in "Canadian Journal of Chemical Engineering in 2012"

Mathematical modelling of chemical processes—obtaining the best model predictions and parameter estimates using identifiability and estimability procedures

Abstract: Chemical engineers who develop fundamental models often have difficulties estimating all model parameters due to problems with parameter identifiability and estimability. These two concepts are reviewed, as are techniques for assessing identifiability and estimability. When some parameters are not estimable from the data, modellers must decide whether to conduct new experiments, change the model structure, or to estimate only a subset of the parameters and leave the others at fixed values. Estimating a reduced number of parameters can lead to better model predictions with lower mean squared error (MSE). MSE-based techniques for parameter subset selection are discussed and compared. © 2011 Canadian Society for Chemical Engineering

Fixed bed catalytic reactor modelling—the radial heat transfer problem

Abstract: An interpretation of the state-of-the-art in modelling radial heat transfer in fixed bed catalytic reactors is presented. The persistence of the classical kr–hw model is discussed, problems with typical approaches to obtaining and analysing experimental heat transfer data to get kr and hw are explained, current correlations for kr are evaluated and the contentious history of hw is elaborated. A brief discussion of alternatives to the kr–hw approach and their pros and cons is attempted, and the review is concluded by a look at computational fluid dynamics (CFD) in fixed bed radial heat transfer modelling. © 2011 Canadian Society for Chemical Engineering

In situ upgrading of bitumen and heavy oils via nanocatalysis

Abstract: Thermal in situ bitumen production has introduced a different engineering approach compared to conventional oil exploitation. Steam injection for example, allows the development of a relatively confined liquid and gas chamber surrounding and along the length of the production wells. This heated place can be converted into a reactor for upgrading processes founding expectations of extensive reservoir upgrading of unconventional oils reducing the total energy currently required to both exploit the reservoir and surface upgrade the produced bitumen. These could also selectively transform contaminants into harmless products remaining in the reservoir. This article highlights the nanocatalytic in situ upgrading paths that may result in economical and environmentally efficient oil sands exploitation. © 2012 Canadian Society for Chemical Engineering

Kinetics, Equilibrium and Thermodynamic Studies on the Adsorptive Removal of Nickel, Cadmium and Cobalt from Wastewater by Superparamagnetic Iron Oxide Nanoadsorbents

Abstract: Because of its unique properties, such as specific functionality and large specific surface area, iron oxide nanoadsorbents had showed potential for energy and environmental applications. This work investigated the adsorptive removal of different metal ions from wastewater by superparamagnetic iron oxide nanoadsorbents (Fe3O4). Batch-adsorption technique was employed to assess the kinetic behaviour and adsorption equilibrium of cadmium, cobalt and nickel. Accordingly, the effect of the following variables on the adsorption reaction was tested, namely: solution pH, contact time and temperature. Metal ion adsorption was found to be highly pH dependent with a maximum uptake achieved around pH 5.5. Kinetic studies showed that adsorption was fast and equilibrium was achieved in less than 60 min. The external mass transfer kinetic model was applied to the experimental results and provided reasonable overall volumetric mass transfer coefficients. Adsorption isotherms were determined and appropriately described by the Freundlich and Langmuir models, with a better fit to the Freundlich model. The amount of metal ion adsorbed increased as the temperature increased, suggesting an endothermic adsorption process. The thermodynamics studies indicated that the adsorption process was spontaneous and endothermic in nature. © 2011 Canadian Society for Chemical Engineering

Removal of reactive blue 19 and reactive blue 49 textile dyes by citrus waste biomass from aqueous solution: Equilibrium and kinetic study

Abstract: The purpose of this study was to establish the potential of inexpensive and locally available biomaterial, that is, lignocellulosic waste of Citrus sinensis as biosorbent to remove reactive anthraquinone dyes from aqueous solution. The effects of immobilisation and chemical treatment of biosorbent were also explored for the enhanced sorption of dyes. Biosorbent was chemically treated with organic and inorganic reagents of which acetic acid augmented the sorption capacities for Reactive blue 19 and Reactive blue 49 attaining equilibrium in 60 min. While immobilisation of biosorbent into calcium alginate beads reduced the sorption capacity and the time to achieve equilibrium was prolonged up to 120 min. Sorption of both reactive dyes was found to be dependent on pH of media and maximum removal was observed at pH 2. The sorption process was fast and the data followed pseudo-second-order kinetic rate equation (R2 = 0.99). The equilibrium data were also fitted to Freundlich, Langmuir and Temkin isotherms. The mechanism of sorption was found to be physiosorption. FTIR analysis and SEM imaging of biosorbent were also carried out to study functional groups involved and morphological changes at the surface of biomass. © 2011 Canadian Society for Chemical Engineering

Electrochemical removal of boron from water: Adsorption and thermodynamic studies

Abstract: The present work provides an electrochemical removal of boron from water and its kinetics, thermodynamics, isotherm using mild steel and stainless steel as anode and cathode respectively. The various operating parameters on the removal efficiency of boron were investigated, such as initial boron ion concentration, initial pH, current density and temperature. The results showed that the optimum removal efficiency of 93.2% was achieved at a current density of 0.2 A dm−2 at pH of 7.0. First-, second-order rate equations, Elovich and Intraparticle models were applied to study adsorption kinetics. Adsorption isotherms of boron on Fe(OH)3 were determined and correlated with isotherm equations such as Langmuir, Freundlich and D-R models. Thermodynamic parameters, such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°), were also evaluated by Van't Hoff equation. The adsorption process follows second-order kinetics. The adsorption of boron preferably fits with Langmuir adsorption isotherm suggesting monolayer coverage of adsorbed molecules. The adsorption of boron onto Fe(OH)3 was found to be spontaneous and endothermic. © 2011 Canadian Society for Chemical Engineering

Determining the state of a process control system: Current trends and future challenges

Abstract: In many industrial plants, multiple, interconnected control loops are common. Their maintenance and improvement requires detailed controller performance assessment to determine not only whether they are behaving well, but also to determine the potential cause of any observed problems. Techniques for performance assessment can be divided into two broad categories (1) performance assessment of regulatory control loops; and (2) performance assessment of supervisory control loops that evaluate the economic performance of advanced control strategies, such as model predictive control (MPC). A comprehensive review of the literature on the industrial applications of performance assessment, as well as some of the currently available software, is also presented. © 2011 Canadian Society for Chemical Engineering

Adsorption equilibrium, thermodynamics, kinetics, mechanism and process design of zinc(II) ions onto cashew nut shell

Abstract: Cashew nut shell (CNS) is an agricultural waste was investigated as a new adsorbent for the removal of zinc(II) from aqueous environment. Effects of solution pH, CNS dose, contact time, initial zinc(II) concentration and temperature on removal efficiency were tested and optimum conditions were evaluated. The equilibrium data were fitted well with Langmuir isotherm model and pseudo-second-order kinetic model. Langmuir monolayer adsorption capacity of CNS was examined as 24.98 mg/g. Changes in standard Gibbs free energy (▵G°), standard enthalpy (▵H°) and standard entropy (▵S°) showed that the sorption of zinc(II) ions onto CNS are spontaneous and exothermic at 303–333 K. Sorption process was found to be controlled by both surface and pore diffusion. A batch adsorber was designed for different CNS dose to effluent volume ratios using Langmuir equation. Effective diffusivity values were found to be 1.927 × 10−11 (10 mg/L), 2.135 × 10−11 (20 mg/L), 2.267 × 10−11 (30 mg/L), 2.305 × 10−11 (40 mg/L) and 2.362 × 10−11 (50 mg/L) m2/s. © 2011 Canadian Society for Chemical Engineering

Steam reforming of ethanol on a Ni/Al2O3 catalyst coupled with a hydrotalcite‐like sorbent in a multilayer pattern for co2 uptake

Abstract: Steam reforming of ethanol (SRE) on a Ni/Al2O3 catalyst was studied. The effects of the operating conditions and catalyst nature on the course of reaction were evaluated. Hydrogen was generated in the temperature range between 100 and 600°C. A mechanism was used to explain the reaction pathways. A commercial hydrotalcite-like sorbent arranged in a multilayer pattern of catalyst and sorbent was used for CO2-uptake to enhance hydrogen production. The concept of sorption enhanced reaction process on SRE is illustrated by the operation of catalyst and CO2-sorbent at 400°C. A lower flow rate regime and multilayer pattern system enhances hydrogen production in the initial breakthrough periods. CO appears in traces in the product gas stream. © 2011 Canadian Society for Chemical Engineering

Synthesis of CaCO3 nanoparticles by controlled precipitation of saturated carbonate and calcium nitrate aqueous solutions

Abstract: Calcium carbonate nanoparticles (CCNP) were synthesised by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions. The effect of agitation rate, mixing time, calcium/carbonate ions concentration and temperature on particle size and morphology were investigated. Particles were characterised using X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Increasing the mixing time from 30 to 180 min resulted in a decrease in particles size. Mixing rate variation between 300 and 14 000 rpm decreased the particle size. Temperature increase favoured a significant growth in particle size and in the formation of aragonite beginning from 80°C. Calcium and carbonate ion concentrations are key parameters controlling the CCNP particle size. Calcite is the main polymorph obtained as revealed by XRD analysis. © 2011 Canadian Society for Chemical Engineering

Comparative kinetics of transesterification for biodiesel production from palm oil and mustard oil

Abstract: The kinetics of palm oil and mustard oil transesterification are compared. Transesterification of palm oil and mustard oil using KOH as a catalyst was performed at various reaction temperatures ranging from 40 to 60°C. The reaction steps are reversible and transesterification is favoured at elevated temperatures. The reaction step of triglyceride to diglyceride is the rate determining step (RDS) that controls kinetics of overall transesterification with activation energies of 30.2 and 26.8 kJ/mol for palm oil and mustard oil transesterification, respectively. It is found that percentage of saturated compounds play a vital role on transesterification kinetics. © 2011 Canadian Society for Chemical Engineering

Torrefaction of non ‐lignocellulose biomass waste

Abstract: Torrefaction of some non-lignocellulose waste biomass was attempted to examine if such materials could benefit from this process as conventional lignocellulose biomass does. Experiments were conducted on chicken litter, digested sludge, and undigested sludge from a municipality in Canada. Effects of two important torrefaction process parameters: temperature and residence time on the torrefaction yield were studied. For reference, torrefaction of three lignocellulose biomass (switch grass, coffee husk, and wood pellet) was also carried out in the same apparatus under identical conditions. A comparison of torrefaction yield and other properties of these biomass showed that in spite of the large difference in their constitution the torrefaction behaviour of non-lignocellulose and lignocellulose biomass were similar. The increase in energy density after torrefaction and the effect of temperature and residence time on torrefaction were also similar for these two types. The present research made an important addition to the existing database on torrefaction of biomass by adding missing information on torrefaction of sludge and poultry litter. Additionally, this work unearthed a potential option for production of composite pellets of waste (e.g., sludge) mixed with biomass (e.g., switch grass). © 2011 Canadian Society for Chemical Engineering

Supported single‐site catalysts for slurry and gas‐phase olefin polymerisation

Abstract: Early and late transition metal single-site catalysts revolutionised the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resided in the fact that they could be used without major modifications in the polymerisation reactors that previously used heterogeneous Ziegler–Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, the soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. In this article, we will review several methods used for supporting single-site early and late transition metal catalysts on a variety of supports. © 2011 Canadian Society for Chemical Engineering

Screening CO2/N2 selectivity in metal‐organic frameworks using Monte Carlo simulations and ideal adsorbed solution theory

Abstract: Selective adsorption of CO2 over N2 is important in the design and selection of adsorbents such as metal-organic frameworks (MOFs) for CO2 capture and sequestration. In this work, single-component and mixture adsorption isotherms were calculated in MOFs using grand canonical Monte Carlo (GCMC) simulations at conditions relevant for CO2 capture from flue gas. Mixture results predicted from single-component isotherms plus ideal adsorbed solution theory (IAST) agree well with those calculated from full GCMC mixture simulations. This suggests that IAST can be used for preliminary screening of MOFs for CO2 capture as an alternative to more time-consuming mixture simulations or experiments.

High pressure physical solubility of carbon dioxide (CO2) in mixed polyethylene glycol dimethyl ethers (Genosorb 1753)

Abstract: Solubility of carbon dioxide in a mixture of polyethylene glycol dimethyl ethers (Genosorb 1753) was determined at 298.15, 313.15, 323.15 and 333.15 K at pressures up to 7940 kPa. The obtained solubility data are compared with those of CO2 in other physical solvents. The results were correlated with the Peng–Robinson (Peng and Robinson, Ind. Eng. Chem. Fundam. 15, 59–64 1976) equation of state, and the interaction parameters are reported. Data at 323.15 K were predicted. Henry's Law constants were obtained from the data and the excess properties (excess Gibbs free energy, excess entropy and excess enthalpy) of the liquid mixture over the full range of composition were predicted at each temperature using the NRTL activity coefficient model. Enthalpy of solution and the enthalpy of mixing were determined at infinite dilution. In addition, the heats of absorption were determined using Clausius–Clapeyron equation. La solubilite du dioxyde de carbone (CO2) dans un melange de polyethylene glycol dimethyl ethers (Genosorb 1753) a ete determinee a 298.15, 313.15, 323.15 et 333.15 K a des pressions allant jusqu'a 7940 kPa. Les donnees de solubilite obtenues sont comparees avec celles de CO2 dans d'autres solvants physiques. Les resultats ont ete correles avec l'equation d'etat de Peng–Robinson (Peng and Robinson, Ind. Eng. Chem. Fundam. 15, 59–64 1976) et les parametres d'interaction sont presentes. La solubilite a 323.15 K a ete predite. Les constantes de la loi d'Henry ont ete obtenues a partir des donnees. Les proprietes en exces (l'energie libre de Gibbs d'exces, l'entropie et l'enthalpie d'exces) du melange liquide sur toute la gamme de composition a ont ete predites a chaque temperature en utilisant le modele NRTL. L'enthalpie de solution et l'enthalpie de melange ont ete determinees dilution infinie. Finalement, les chaleurs d'absorption ont ete determinees en utilisant l'equation de Clausius–Clapeyron. © 2011 Canadian Society for Chemical Engineering

Competitive no, co and hydrocarbon oxidation reactions over a diesel oxidation catalyst

Abstract: The oxidation of NO, CO and hydrocarbons (HC) individually, in mixtures, and with NO2 were investigated over a monolith-supported Pt/Al2O3 catalyst under oxidising conditions. Although competitive adsorption and inhibition by other species on oxidation reactions is a relatively well-known phenomenon, this study represents a more comprehensive examination of such effects between key components in vehicle exhaust gases. NO2 was completely reduced by CO and C3H6, under NO2 limited conditions, at temperatures as low as 110°C and at temperatures above 140°C with dodecane and m-xylene. NO2 was then again observed once the extent of oxidation of the other species by oxygen was significant. Under the conditions tested, NO, CO and HC oxidation was inhibited by NO2 in the feed gas mixture. HC were also found to inhibit the oxidation of NO and other HC species due to site adsorption competition. For CO, HC did not change the onset of oxidation, but did inhibit the extent after their light off began. At low temperatures, CO was initially found to inhibit NO oxidation, but at higher temperatures, once CO oxidation was significant, CO promoted NO conversion to NO2. The observed inhibition effects of the different gases on HC oxidation were not additive, indicating one species would cause inhibition, but once its inhibition ended, another species could still then cause inhibition. The combined effect of C3H6, NO and NO2 on CO conversion was found to be additive. This is because CO oxidation started prior C3H6. © 2011 Canadian Society for Chemical Engineering

Utilisation of immobilised activated sludge for the biosorption of chromium (VI)

Abstract: The objective of this investigation was to study the biosorption of Cr (VI) on immobilised activated sludge (IAS) and calcium alginate (CA) using batch system. The optimal pH for Cr (VI) biosorption by IAS and CA was 2.0 and 4.0, respectively. Equilibrium was attained at approximately 120 min for both biosorbents. For both biosorbents, the equilibrium biosorption capacity (mg/g) increased as the initial metal ion concentration increased and the concentration of biosorbent decreased. The rate of biosorption onto IAS and pure CA (as mg/g) increased from 5.02 to 87.66 and 4.97 to 79.09 as the concentration of Cr (VI) ions increased from 10 to 1000 mg/L, respectively. In the case of biosorbent concentration, as the concentration of IAS and pure CA increased from 1 to 20 g/L, the equilibrium uptake (qe) decreased from 21.33 to 1.57 and 19.41 to 1.38 mg/g, respectively. The biosorption data showed that the Langmuir model was more suitable than the Freundlich model. Also, the results indicated that the pseudo-second order model was the most suitable for Cr (VI) biosorption onto IAS and CA. © 2011 Canadian Society for Chemical Engineering

Steam assisted biomass gasification—an overview

Abstract: Biomass gasification technologies have matured over the years. In the past decade, numerous types of gasifiers have been developed and tested. This article reviews the status of steam assisted biomass gasifiers. It first discusses the challenges and the key operating parameters for steam-biomass gasification and their effects on the gasifier performance. The article then summarises the progress and status of commercial or demonstration scale steam assisted biomass gasifiers available in the world.

MHD flow and heat transfer over stretching/shrinking sheets with external magnetic field, viscous dissipation and Joule effects

Abstract: The present article considers the steady magnetohydrodynamic (MHD) laminar boundary layer flow of a viscous and incompressible electrically conducting fluid near the stagnation point on a horizontal stretching or shrinking surface, with variable surface temperature and a constant magnetic field applied normal to the surface of the sheet. The governing system of partial differential equations is first transformed into a system of ordinary differential equations by introducing an appropriate similarity transformation, which is then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the skin friction coefficient, the local Nusselt number as well as the velocity and temperature profiles are determined and discussed. Results indicate that for the stretching sheet, solution exists and is unique for all values of the stretching/shrinking parameter , while for the shrinking sheet, solutions only exist up to some critical values , and these solutions may be unique, dual and sometimes triple. © 2011 Canadian Society for Chemical Engineering

Design and CFD studies of multiphase separators—a review

Abstract: The multiphase separators are generally the first and largest process equipment in an oil production platform. This primary separation step is a key element in the oil and gas production facilities in that downstream equipment, such as compressors, are completely dependent on the efficient performance of these multiphase separators. The literature on this critical unit operation, multiphase separators, abounds with macro studies and design methodologies for two- and three-phase vertical and horizontal separators. There are very few studies that provide the micro details of the actual separation process. In fact, the popular classic methods for separator design, mostly due to a lack of a usable mathematical model for estimation of droplet ‘separation velocities’, do result in a conservative design and would specify extremely oversized separators. In order to reflect the current situation and address recent findings, this study will review the important literature on design and CFD simulation of multiphase separators. This review will show the benefits that CFD analyses can provide in optimising the design of new separators and solving problems with existing designs. © 2011 Canadian Society for Chemical Engineering

Flow of nanodispersed catalyst particles through porous media: Effect of permeability and temperature

Abstract: The proposed in situ catalytic upgrading of heavy oil to achieve an environmentally sustainable method for heavy oil recovery requires the placement of nanodispersed catalyst particles deep into the formation where it can accelerate the high-temperature upgrading reactions. In continuation of the previous work [Zamani et al., Energy Fuels 24, 4980-4988 (2010)], this paper presents results of several new experiments carried out to examine the effects of other parameters, including the connate brine salinity, absolute permeability, sand-bed temperature and particle concentration on the propagation of nanoparticles in porous media. The results show that lower permeability, increased operating temperature and higher particle concentration did not significantly affect the propagation of nanodispersed catalyst suspension through the sand-bed. Virtually the same filtration behaviour, displaying a rapid increase of effluent concentration at 1 pore volume injected to a steady concentration close to the inlet concentration was seen in all experiments. A classical phenomenological approach was used to model the macroscopic propagation behaviour of suspended particles in the porous medium. The model was successful in history matching the effluent composition profile observed in the experiments and the deposition profile obtained from post-test analysis of the sand-bed. © 2011 Canadian Society for Chemical Engineering

Optimisation of vertical axis wind turbine: CFD simulations and experimental measurements

Abstract: A system for the conversion of kinetic energy of wind into thermal energy has been developed which can replace relatively expensive electro-mechanical equipment. The system consists of a vertical axis wind turbine (VAWT) which is coupled with the shaft of a stirred vessel. In the present work, computational fluid dynamic (CFD) simulations have been performed for the flow generated in a stirred tank with disc turbine (DT). The predicted values of the mean axial, radial and tangential velocities along with the turbulent kinetic energy have been compared with those measured by laser Doppler anemometry (LDA). Good agreement was found between the CFD simulations and experimental results. Such a validated model was employed for the optimisation of drag-based VAWT. An attempt has been made to increase the efficiency of turbine by optimising the shape and the number of blades. For this purpose, the combination of CFD and experiments has been used. The flows generated in a stirred tank and that generated by a wind turbine were simulated using commercial CFD software Fluent 6.2. A comparison has been made between the different configurations of wind turbines. Results show that a provision in blade twist enhances the efficiency of wind turbine. Also, a wind turbine with two blades has higher efficiency than the turbine with three blades. Based on the detailed CFD simulations, it is proposed that two bladed turbine with 30° twist shows maximum efficiency. © 2011 Canadian Society for Chemical Engineering

Comparisons of existing pretreatment, saccharification, and fermentation processes for butanol production from agricultural residues

Abstract: Some of the most recent, relevant, industrial and academic contributions made in the field of butanol production are reviewed here. The focus on butanol is due to the growing demand for non-fossil biofuels. In addition, butanol can be mixed with fossil fuels or can be used alone, allowing an alternative to gasoline. Butanol can be synthesised biologically using sugars extracted from biomass such as agricultural waste. This agricultural waste must be pretreated before it is suitable for sugar extraction. Following this stage, enzymatic hydrolysis is employed, before performing fermentation using microorganisms. This article summarises some of the economical methods such as simultaneous saccharification and fermentation (SSF). Different pretreatment and saccharification processes were compared. Acid pretreatment and saccharification achieved the highest sugar concentrations from wheat straw. Monoethanolamine pretreatment achieved highest sugars from hardwood. Comparisons and analysis of different types of fermentation processes illustrated that immobilised reactor provided the best butanol rate of production. Integration of fermentation with product removal process improved butanol production in immobilised reactor. Gas stripping method was illustrated to be the product removal process. © 2011 Canadian Society for Chemical Engineering

Low‐lying energy isomers and global minima of aqueous nanoclusters: Structures and spectroscopic features of the pentagonal dodecahedron (H2O)20 and (H3O)+(H2O)20

Abstract: We rely on a hierarchical approach to identify the low-lying isomers and corresponding global minima of the pentagonal dodecahedron (H2O)20 and the H3O+(H2O)20 nanoclusters. Initial screening of the isomers is performed using classical interaction potentials, namely the Transferable Interaction 4-site Potential (TIP4P), the Thole-Type Flexible Model, versions 2.0 (TTM2-F) and 2.1 (TTM2.1-F) for (H2O)20 and the Anisotropic Site Potential (ASP) for H3O+(H2O)20. The nano-networks obtained with those potentials were subsequently refined at the density functional theory (DFT) with the Becke-3-parameter Lee–Yang–Parr (B3LYP) functional and at the second order Moller–Plesset perturbation (MP2) levels of theory. For the pentagonal dodecahedron (H2O)20 it was found that DFT (B3LYP) and MP2 produced the same global minimum. However, this was not the case for the H3O+(H2O)20 cluster, for which MP2 produced a different network for the global minimum when compared to DFT (B3LYP). The low-lying networks of H3O+(H2O)20 correspond to structures having 9 ‘free’ OH bonds and the hydronium ion on the surface of the nanocluster. The IR spectra of the various networks are further analysed in the OH stretching (‘fingerprint’) region and the various bands are assigned to structural arrangements of the underlying hydrogen bonding network. © 2012 Canadian Society for Chemical Engineering

Effects of surfactants on hydrodynamics and mass transfer in a split‐cylinder airlift reactor

Abstract: Effects of various concentrations (0–5 ppm) of anionic (sodium dodecyl sulfate, SDS) and non-ionic (Tween-80 and Triton X-405) surfactants on gas hold-up and gas–liquid mass transfer in a split-cylinder airlift reactor are reported for air–water. Surfactants were found to strongly enhance gas hold-up. Non-ionic surfactants were more effective in enhancing gas hold-up compared to the anionic surfactant SDS. An enhanced gas hold-up and a visually reduced bubble size in the presence of surfactants implied an enhanced gas–liquid interfacial area for mass transfer. Nevertheless, the overall gas–liquid volumetric mass transfer coefficient was reduced in the presence of surfactants, suggesting that surfactants greatly reduced the true liquid film mass transfer coefficient and this reduction outweighed the interfacial area enhancing effect. Presence of surfactants did not substantially affect the induced liquid circulation rate in the airlift vessel.

CFD analysis of two‐phase turbulent flow in internal airlift reactors

Abstract: The hydrodynamic performance of three internal airlift reactor configurations was studied by the Eulerian–Eulerian k–e model for a two-phase turbulent flow. Comparative evaluation of different drag and lift force coefficient models in terms of liquid velocity in the riser and downcomer and gas holdup in the riser was highlighted. Drag correlations as a function of Eotvos number performed better results in comparison to the drag expressions related to Reynolds number. However, the drag correlation as a function of both Reynolds and Eotvos numbers fitted well with experimental results for the riser gas holdup and downcomer liquid velocity in configurations I and II. Positive lift coefficients increase the liquid velocity and decrease the riser gas holdup, while opposite results were obtained for negative values. By studying the effects of bubble size and their shape, the smaller bubbles provide a lower liquid velocity and a gas holdup. The effects of bubble-induced turbulence and other non-drag closure models such as turbulent dispersion and added mass forces were analysed. The gas velocity and gas holdup distributions, liquid velocity in the riser and downcomer, vectors of velocity magnitude and streamlines for liquid phase, the dynamics of gas holdup distribution and turbulent viscosity at different superficial gas velocities for different reactor configurations were computed. The effects of various geometrical parameters such as the draft tube clearance and the ratio of the riser to the downcomer cross-sectional area on liquid velocities in the riser and the downcomer, the gas velocity and the gas holdup were explored. © 2011 Canadian Society for Chemical Engineering

Effects of alternating current (AC) and direct current (DC) in electrocoagulation process for the removal of iron from water

Abstract: In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of iron from water using zinc as anode and cathode. The results showed that the optimum removal efficiency of 99.6% and 99.1% with the energy consumption of 0.625 and 0.991 kWh kL−1 was achieved at a current density of 0.06 A dm−2, at pH of 7.0 using AC and DC, respectively. For both AC and DC, the adsorption of iron was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature

Prediction of mass transfer coefficients in a pulsed disc and doughnut extraction column

Abstract: A study of the mass transfer performance for a pulsed disc and doughnut extraction column has been presented for a range of operating conditions. The mass transfer performance has been investigated for both directions of mass transfer. This study has examined the mass transfer coefficients which has incorporated the effects of back-mixing in the continuous phase. The effect of operating variables including pulsation intensity and dispersed and continuous phase velocities on volumetric overall mass transfer coefficient has been investigated. The experiments showed that mixer-settler, transition and emulsion regimes exist in the column depending on the pulse characteristics. In the present work, effective diffusivity is substituted for molecular diffusivity in the Grober equation for estimation of overall mass transfer coefficients. The enhancement factor is determined experimentally and there from a single empirical correlation is derived for prediction of enhancement factor in terms of Reynolds number, holdup and Eotvos number for all operating regimes and each mass transfer direction. The experimental results are in very good agreement with the values calculated by the proposed equation. © 2011 Canadian Society for Chemical Engineering