Open-Source CFD Simulations of Liquid–Liquid Flow in the Annular Centrifugal Contactor

Simulation of the fluid dynamics of solvent extraction in centrifugal contactors requires advanced models to account for complex physical phenomena including turbulent free-surface flow and liquid-liquid dispersion physics. The use of an open-source computational fluid dynamics (CFD) framework allows for implementation of advanced models not feasible in commercial CFD applications. The open-source CFD package OpenFOAM has been used to simulate turbulent, multiphase flow in the annular centrifugal contactor, including simulations of the mixing zone (annular region), and of the coupled operation of the mixing and separation (rotor interior) zones. These simulations are based on the Volume of Fluid (VOF) methodology along with Large Eddy Simulation (LES) for turbulence. The results from these simulations compare favorably with previous simulations using a commercial CFD tool and with available experimental data. They also give insight into the requirements for more advanced multiphase models needed to accurately capture flows in these devices.     

On the Operation of Centrifugal Extractors in Liquid–Liquid Chromatography Mode

Theoretical Foundations of Chemical Engineering - We studied the possibility of using a modified cascade of mixing and settling centrifugal extractors as a device for carrying out...     

Liquid–Liquid Equilibria in Biodiesel Production

During biodiesel production, the product is contaminated with impurities such as some non-reacted alcohol, glycerol, and catalyst. In order to comply with product requirements, these impurities must be removed, for example, by washing with water. Knowledge of the extent of water solubility in biodiesel is required to design the drying system and determine fuel quality. In the present work, the solubilities of water in biodiesels produced from sunflower and canola oils were measured within the temperature range of 24–60 °C. The solubility of water increased with increasing temperature and biodiesel unsaturation. The liquid–liquid equilibria of ternary systems of glycerol, methanol, and the above-mentioned biodiesels were investigated experimentally at 20, 30, and 40 °C. The binodal curves were determined by using the cloud point titration method and the tie lines were measured by evaporating the methanol. Both binary and ternary data were modeled using the UNIQUAC model. The model showed good agreement with the data. Othmer-Tobias correlations were applied and the corresponding constants were obtained. The results validated the consistency of the tie-line data obtained experimentally.     

Semi-Empirical Modeling of Gas–Liquid Mass Transfer in Gas–Liquid–Liquid Systems in Stirred Tanks

Two semi-empirical models of gas–liquid mass transfer in gas–liquid–liquid systems are presented, one for the case where the dispersed liquid phase has a positive spreading coefficient S > 0, the other for S < 0. The models are based on mathematical expressions inspired by assumed mass transfer mechanisms, which are different depending on the oil spreading characteristics. Model simulations compare well with experimental data (up to oil phase holdup ? ～ 0.1), managing to simulate the shape of the experimental curves of oxygen mass transfer enhancement factor E vs. ? for the air–water–heptane (S > 0) and air–water–dodecane (S < 0) systems, better than other models available in the literature.     

Mathematical Modeling of Gas–Liquid Flow Patterns in an Annular Space with a Rotating Inner Cylinder

Theoretical Foundations of Chemical Engineering - Gas–liquid flow patterns were mathematically modeled in the annular space between two coaxial cylinders, the inner cylinder of which rotates...     

Calculation Studies of the Separation of Rare-Earth Metals by Countercurrent Liquid–Liquid Chromatography

Theoretical Foundations of Chemical Engineering - Calculation studies have been made of the separation and concentration of rare-earth metals by countercurrent liquid–liquid chromatography...     

Demonstration of a SANEX Process in Centrifugal Contactors using the CyMe4‐BTBP Molecule on a Genuine Fuel Solution

Efficient recovery of minor actinides from a genuine spent fuel solution has been successfully demonstrated by the CyMe₄‐BTBP/DMDOHEMA extractant mixture dissolved in octanol. The continuous countercurrent process, in which actinides(III) were separated from lanthanides(III), was carried out in laboratory centrifugal contactors using an optimized flow‐sheet involving a total of 16 stages. The process was divided into 9 stages for extraction from a 2 M nitric acid feed solution, 3 stages for lanthanide scrubbing, and 4 stages for actinide back‐extraction. Excellent feed decontamination factors for Am (7000) and Cm (1000) were obtained and the recoveries of these elements were higher than 99.9%. More than 99.9% of the lanthanides were directed to the raffinate except Gd for which 0.32% was recovered in the product.     

Numerical Investigation of Bubble Motion Behavior in a Centrifugal Vacuum Gas–Liquid–Solid Separator for the Treatment of Contaminated Hydraulic Fluid

Contaminants in hydraulic fluid are the primary causes of premature oil degradation. In this study, we propose a method for removing contaminants from contaminated oil. This method combines centrifugal separation and vacuum negative pressure. Centrifugal separation is utilized to separate solid particulates and free water. Vacuum negative pressure can be used to remove dissolved air. A mathematical model is developed for predicting bubble motion behavior under the complex actions of centrifugal force and vacuum negative pressure. Three performance indices that describe the purification capacity of the separator are proposed to optimise the gas–liquid–solid separator.     

Development of a Dispersive Liquid–Liquid Microextraction Procedure for Biodegradation Studies on Nonylphenol Propoxylates Under Aerobic Conditions

Aerobic biodegradation behavior of nonylphenol propoxylates was investigated using dispersive liquid–liquid microextraction as a simple and fast technique for sample preparation. The developed method proved to be efficient for the isolation and concentration of nonylphenol propoxylates before their quantification with the use of high performance liquid chromatography. The primary biodegradation of nonylphenol propoxylates was approximately 80 % by 10 days after the beginning of the test. However, the biodegradation products which were identified with the use of mass spectrometric detection persisted for many days.     

Rapid Removal of Nitrobenzene in a Three-Phase Ozone Loaded System with Gas–Liquid–Liquid

This study explores the removal rate of nitrobenzene (NB) using a new gas–liquid–liquid (G–L–L) three-phase ozone-loaded system consisting of a gaseous ozone, an aqueous solvent phase, and a fluorinated solvent phase (perfluorodecalin, or FDC). The removal rate of NB was quantified in relation to six factors including (1) initial pH, (2) initial NB dosage, (3) gaseous ozone dosage, (4) free radical scavenger, (5) FDC pre-aerated gaseous ozone, and (6) reuse of FDC. NB removal rate is positively affected by the first three of these factors. Compared with the conventional gas–liquid (water) (G–L) two-phase ozonation system, the free radical scavenger (tertiary butyl alcohol) has much less influence on the removal rate of NB in the G–L–L system. The FDC-loaded ozone acts as an ozone reservoir and serves as the main reactive phase in the G–L–L three-phase system. The reuse of FDC has little influence on the removal rate of NB. These experimental results suggest that the oxidation efficiency of ozonation in the G–L–L three-phase system is better than that in the conventional G–L two-phase system.     

Centrifugal float–sink separation of fine Turkish coals in dense media

Zonguldak bituminous coal, Tunçbilek and Soma–Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float–sink separation technique in heavy media. An isopropyl alcohol (IPA)–carbon tetrachloride (CCl₄) mixture and a zinc chloride (ZnCl₂) solution, with a specific gravity of 1.40 g cm⁻³ at 25°C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles.     

The Effect of Nanoparticles on the Mass Transfer in Liquid–Liquid Extraction

This article investigates the effect of nanoparticles on mass transfer in the liquid–liquid extraction for the chemical system of n-butanol–succinic acid–water. For this purpose, nanofluids containing various concentrations of ZnO, carbon nanotubes (CNT), and TiO₂ nanoparticles in water, as base fluid, were prepared. To examine the flow mode effect on mass transfer rate, different fluid modes including dropping and jetting were employed in the process. Results show that mass transfer rate enhancement depends on the kinds and the concentration of nanoparticles and the modes of flow. It was observed that after adding nanoparticles, the mass transfer rate significantly increases up to two-fold for ZnO nanoparticles. Furthermore, the results indicate that under the circumstances in which the mass flow rate is high enough, the effect of nanoparticles on the mass transfer phenomenon is too slight.     

Sequential Reaction-Separation in a Microchannel Reactor for Liquid–Liquid Phase Transfer Catalysis

A microchannel reactor with guideline structure was investigated to carry out sequential reaction- separation. The catalytic reaction between benzyl chloride and sodium sulfide was demonstrated. Under parallel multiphase flow conditions, the catalytic reaction proceeded with phase separation could be ensured. The phase separation performance was enhanced by performing surface modification.     

Liquid–Liquid Equilibrium Constant for Acetic Acid in an Epoxidized Soybean Oil–Acetic Acid–Water System

Dependency of the liquid–liquid equilibrium constant for acetic acid (A) in a system of epoxidized soybean oil–acetic acid–water from temperature and composition was experimentally determined. To estimate the liquid–liquid equilibrium constant for acetic acid (K _A), the interaction parameters of the Wilson, NRTL (non-random two liquid) and UNIQUAC (universal quasi chemical) models for the activity coefficient were calculated by fitting the experimental values of the equilibrium constant for acetic acid. The Marquardt method was used to fit the data. In spite of all applied simplifications, small deviations of the calculated values from those experimentally determined indicate the adequacy of all three models for the prediction of the liquid–liquid equilibrium constant for acetic acid. Comparison of the experimentally determined values of the equilibrium constant for acetic acid in the investigated system with those reported in the literature for the system with soybean oil, shows that the value of the liquid–liquid equilibrium constant for acetic aid in the system of epoxidized soybean oil–acetic acid–water is about 1.5 times higher than in the system of soybean oil–acetic acid–water for the same temperature and similar composition. For the investigated conditions, the influence of the changing of the oil phase composition on the equilibrium constant for acetic acid is more prominent than the influence of the temperature or the total acetic acid content in the system.     

Mixing–segregation phenomena of binary system in a fluidized bed

A study on mixing–segregation phenomena in a gas fluidized bed of binary density system was performed by analysis of the residence time distribution and mixing degree. The effect of particle mixing on the residence time distribution and solid mixing was studied in a binary particle system with different densities. Residence time distribution curve and mean residence time of each particle were measured according to the flotsam particle size, mixing ratio and gas velocity in a gas fluidized bed (0.109 m I.D., 1.8 m height). The characteristics of residence time distribution and the deviation of mean residence time of each particle are consistent with previous mixing index based on the axial concentration of jetsam. From this study, mixing index of binary particle system with different densities should be considered by not only axial concentration distribution of jetsam particle but also characteristics of residence time distribution. This result suggests that the solid movement by fluidization gas is more important than solid axial dispersion.     

Centrifugal Contactors: Separation of an Aqueous and an Organic Stream in the Rotor Zone (LA‐UR‐05‐7800)

Abstract

A multi‐phase flow code is used to simulate the separation of an aqueous and an organic stream in the rotor zone of an annular centrifugal contactor. Different values for the mixture viscosity and for the initial volume fractions of the components are considered. A simple model for mass transfer of a species between phases is used. Geometrical effects are found to have significant influence on the separation of the two‐phase mixture.     

Mixing and recirculation characteristics of gas–liquid Taylor flow in microreactors

The effects of operating parameters (capillary and Reynolds numbers) and microchannel aspect ratio (α=w/h=[1;2.5;4]$\alpha =w/h=[1;2.5;4]$) on the recirculation characteristics of the liquid slug in gas–liquid Taylor flow in microchannels have been investigated using 3-dimensional VOF simulations. The results show a decrease in the recirculation volume in the slug and an increase in recirculation time with increasing capillary number, which is in good agreement with previous results obtained in circular and square geometries (Thulasidas et al., 1997). In addition, increasing the aspect ratio of the channel leads to a slight decrease in recirculating volumes but also a significant increase in recirculation times.     

Liquid–Liquid Equilibrium in an Extraction System Based on Polyvinylpyrrolidone-3500 and Sodium Nitrate

Theoretical Foundations of Chemical Engineering - Liquid–liquid phase equilibrium for a new extraction system based on polyvinylpyrrolidone-3500 and sodium nitrate at 298.15, 313.15, and...     

Studies on Surfactant–Ionic Liquid Interaction on Clouding Behaviour and Evaluation of Thermodynamic Parameters

The present study investigates the effect of tetraethyl ammonium tetrafluoroborate [TEA(BF₄)] ionic liquid (IL) on the cloud point (CP) of the following nonionic surfactants in aqueous solution: ter‐octylphenol ethoxylates with 9.5 and 4.5 ethylene oxide groups (abbreviated TOPEO9.5 and TOPEO4.5, respectively), cetyl alcohol ethoxylate with 10 ethylene oxide groups (C16EO10), and sorbitan monolaurate and monooleate both with 20 ethylene oxide groups (SMLEO20 and SMOEO20, respectively) in aqueous solutions. The thermodynamic parameters of these mixtures were calculated at different IL concentrations. The CP of most of the tested nonionic surfactants increased with the increment of IL concentrations with the exception of C16EO10 for which it decreased. The solubility of a nonionic surfactant containing polyoxyethylene (POE) hydrophilic chain was considered as maximum at the CP, hence the thermodynamic parameters were calculated at the same temperature. The results showed that the standard Gibbs free energy (?G_CP⁰), the enthalpy (?H_CP⁰) and the entropy (?S_CP⁰) of the clouding phenomenon were found to be positive for ethoxylated octylphenol and sorbitan esters, whereas ?H_CP⁰ and ?S_CP⁰ were found to be negative for C16EO10. It was found that the overall clouding process is endothermic for ethoxylated octylphenol and sorbitan esters and exothermic for C16EO10. For all the studied systems, ?H_CP⁰ > T?S_CP⁰ indicated that the process of clouding is guided by both enthalpy and entropy. The positive value of standard Gibbs free energy (?G_CP⁰) for the all mixed systems indicated that the process proceeds non‐spontaneously. The ?G_CP⁰ decreased with increasing IL concentration for all the nonionic surfactants; however, it decreased with increasing surfactant concentration for TOPEO9.5, C16EO10, and SMOEO20, and increased with increasing surfactant concentration for TOPEO9.5 and SMLEO20.