Experimental mass transfer coefficients in a pilot plant multistage column extractor

The volumetric overall mass transfer coefficients in a multistage column have been measured using axial dispersion model for toluene–acetone–water system. The effect of operating parameters on the volumetric overall mass transfer coefficients has been investigated for both mass transfer directions. The results show that the mass transfer performance is strongly dependent on rotor speed and mass transfer direction, although only slightly dependent on phase flow rates. In addition, empirical correlations to predict the overall mass transfer coefficients have been developed. The proposed correlations based on dimensionless numbers can be considered as a useful tool for the possible scale up of the multistage column extractor.     

Reactive extraction of acids or metals—the state of the art of column design

Liquid ion exchangers are used in reactive extractions and the modelling of reactive-phase equilibria with Gibbs excess models takes into account complex formation in aqueous electrolytes or organic media. The chemical kinetics and effective diffusivity are evaluated in small-scale laboratory devices and applied in models using the chemical potential as the driving force. The simulation of lab-scale columns is performed on simple hydrodynamic models, whereas for industrially sized equipment droplet populance-based modelling is the challenge of the future. Parameter estimation regarding this is discussed and stirred column simulations are presented.     

A dynamic forward mixing model for evaluating the mass transfer performances of an extraction column

It is well known that the droplet behavior of the dispersed phase in extraction equipments has a strong influence on the mass transfer performances. It is, and will continuously be a key project for design and scaling up of extraction columns. In this work, a dynamic mass transfer model, considering the effect of forward mixing led by the drop size distribution and the axial mixing of the continuous phase, has been developed, by which the axial mixing characteristic can be easily evaluated when a stimulus-response dynamic curve is obtained. In order to test the mass transfer model and to study in the effect of droplet coalescence on mass transfer performance, a typical experimental system of 30% tributyl phosphate (in kerosene)-nitric acid-water with interface intension of 0.00995 N/m was chosen to investigate the mass transfer in a coalescence-dispersion pulsed-sieve-plate extraction column (CDPSEC) with 150 mm in diameter. The two-point dynamic method was applied to get the stimulus-response curves. With these results the axial mixing of the CDPSEC were evaluated. The calculated results showed that the response curves could be predicted with the new mass transfer model very well. The model has marked advantages over the traditional diffusion model. It is closer to the practice, easier to solve for the mathematical equations and boundary conditions, and has only one parameter to be optimized. The calculated results also showed that the influence of local coalescence of droplets on mass transfer performances is obvious.     

The use of an ionic liquid in a Karr reciprocating plate extraction column

Ionic liquids offer an alternative to volatile organic solvents for extraction of a range of materials. This work examines the mass transfer performance of a Karr reciprocating plate column with an ionic liquid as an alternative solvent for the extraction of phenol from water. The results indicate that ionic liquids can be used in existing solvent extraction equipment and that existing correlations and models can be used to predict mass transfer performance.     

塔板最新研究和展望

综述了板式塔板研究的最新进展及其相关的工业化情况,同时根据塔板结构简图介绍了各个塔板的原理和特点,对其传质和流体力学性能进行了简要的分析,讨论了塔板的发展前景。     

Estimation of axial dispersion in pulsed-plate extraction columns

In this study, a two-region physical model was used to quantitatively estimate axial dispersion in pulsed-plate extraction columns, considering the operating conditions, geometry parameters and the physical properties of the experimental system. The calculated results fit the experimental axial dispersion coefficients well in nine geometries of pulsed-plate columns. This model is of importance to the design and scale-up of pulsed-plate extraction columns.     

Mass transfer coefficient in the eductor liquid-liquid extraction column

In this research gasoil desalting was investigated from mass transfer point of view in an eductor liquid–liquid extraction column (eductor-LLE device). Mass transfer characteristics of the eductor-LLE device were evaluated and an empirical correlation was obtained by dimensional analysis of the dispersed phase Sherwood number. The Results showed that the overall mass transfer coefficient of the dispersed phase and extraction efficiency have been increased by increasing Sauter mean diameter (SMD) and decreasing the nozzle diameter from 2 to 1 mm, respectively. The effects of Reynolds number (Re), projection ratio (ratio of the distance between venturi throat and nozzle tip to venturi throat diameter, R_pr), venturi throat area to nozzle area ratio (R_th-n) and two phases flow rates ratio (R_Q) on the mass transfer coefficient (K) were determined. According to the results, K increase with increasing Re and R_Q and also with decreasing R_pr and R_th-n. Semi-empirical models of drop formation, rising and coalescence were compared with our proposed empirical model. It was revealed that the present model provided a relatively good fitting for the mass transfer model of drop coalescence. Moreover, experimental data were in better agreement with calculated data with AARE value of 0.085.     

Modeling extraction separation of Cu(II) in hollow-fiber modules

The mass transfer problems in the hollow-fiber membrane extractor module with concurrent- and countercurrent-flow were investigated theoretically and experimentally in this study. A two-dimensional mathematical model of the hollow-fiber membrane extractor module was developed theoretically and the shell side flow described by Happel's free surface model was taken into account. The analytical solution is obtained using an eigenfunction expansion in terms of the power series and an orthogonal expansion technique. The theoretical predictions were represented graphically with the mass-transfer Graetz number (Gz), flow pattern and packing density (φ) as parameters and the theoretical results were also compared with those obtained by experimental runs. The highest extraction rate, extraction efficiency and mass transfer efficiency can be achieved by arranging the packing density φ=0.3. The results show that the device performance of the countercurrent-flow device is better than that of the concurrent-flow device. The experiments of the extraction of Cu²⁺ by using D2EHPA with PVDF hollow fibers is also set up to confirm the accuracy of the theoretical predictions. The accuracy of the theoretical predictions for concurrent- and countercurrent-flow are 5.87×10^-2≤E₁≤6.69×10^-2 and 2.46×10^-2≤E₁≤3.48×10^-2, respectively, for Gz_a=40.8.     

Mathematical modeling of penicillin G Extraction by a bifunctional surfactant in a continuous extraction column

A bifunctional surfactant was used as a carrier of penicillin G for its continuous extraction by an emulsion liquid membrane without an extradant in a countercurrent extraction column of Oldshue-Rushton type. A permeation model was presented to describe transport mechanism of penicillin G in the continuous extraction system, including an axial dispersion model for the continuous phase and a mass transfer model for the dispersed emulsion phase. The mass transfer model describes the external mass transfer around the emulsion drop, the reaction at the external interface, the diffusion as well as the reaction equilibrium within the w/o emulsion drop, and the pH change of internal aqueous phase. Here, we considered three experimental variables: penicillin G concentration, pH of continuous phase and surfactant concentration. The calculated results from the permeation model fitted the experimental data well. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Mass transfer coefficients in a pulsed packed extraction column

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for the toluene/acetone/water system. The experiments were carried out for both mass transfer directions. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The experimental findings indicate that pulsation intensity and mass transfer direction have great influence on volumetric overall mass transfer coefficient. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. The experimental results obtained in the present work are compared with some other types of extraction columns. Finally, two empirical correlations for prediction of the continuous phase overall mass transfer coefficient is derived in terms of Sherwood and Reynolds numbers. Good agreement between prediction and experiments was found for all operating conditions that were investigated.     

Gas-liquid mass transfer in a slurry bubble column operated at gas hydrate forming conditions

Gas-liquid interphase mass transfer was investigated in a slurry bubble column under CO₂ hydrate forming operating conditions. Modeling gas hydrate formation requires knowledge of mass transfer and the hydrodynamics of the system. The pressure was varied from 0.1 to 4 MPa and the temperature from ambient to 277 K while the superficial gas velocity reached 0.20 m/s. Wettable ion-exchange resin particles were used to simulate the CO₂ hydrate physical properties affecting the system hydrodynamics. The slurry concentration was varied up to 10%vol. The volumetric mass transfer coefficient (k_la_l) followed the trend in gas holdup which rises with increasing superficial gas velocity and pressure. However, k_la_l and gas holdup both decreased with decreasing temperature, with the former being more sensitive. The effect of solid concentration on k_la_l and gas holdup was insignificant in the experimental range studied. Both hydrodynamic and transport data were compared to best available correlations.     

往复振动筛板萃取塔萃取机理研究进展

介绍了往复振动筛板萃取塔（RPEC）流体力学性能和传质性能研究现状。     

Droplet coalescence model optimization using a detailed population balance model for RDC extraction column

Single droplet experiments in a small lab scale Rotating Disk Contactor (RDC) for two different liquid–liquid systems were used to evaluate the coalescence parameters necessary for column simulations. Five different coalescence models are studied; the models parameters were obtained by an inverse solution of the population balance model using the extended fixed-pivot technique for the discretization of the droplet internal coordinate. The estimated coalescence parameters by solving the inverse problem were found dependent on the chemical test system. The Coulaloglou and Tavlarides model was found to be the best model to predict the experimental data for both test systems. These parameters were used to study the hydrodynamics and mass transfer behavior of pilot plant RDC extraction column using the simulation tool LLECMOD. This is performed for two different liquid–liquid systems as recommended by the European Federation of Chemical Engineering (EFCE) (butylacetate–acetone–water (b–a–w) and toluene–acetone–water (t–a–w)). The simulated Sauter mean droplet diameter, hold-up values and concentration profiles for organic and aqueous phase were found to be well predicted compared to the experimental data.     

Improvement of oxygen mass transfer estimation from oxygen concentration measurements in bubble column reactors

An original procedure has been established for estimating the overall volumetric mass transfer coefficient using the oxygen concentration curves resulting from the usual gassing-in and gassing-out method. This procedure was applied to experimental data obtained in a small scale bubble column using both tap water and a coalescence-inhibiting liquid mixture that represents the coalescence behavior of biological media. It is based on the analysis of the characteristics times of the system, including those of the hydrodynamics of the two phases, the sensor dynamics and the system inertia when the gas composition is modified. A numerical procedure was developed to estimate the characteristic time of the system inertia t_i, using the assumption that this inertia is nearly independent of superficial gas velocity U_G. The calculations confirmed that the optimized t_i value was nearly independent of U_G and of the coalescence behavior of the liquid phase. Additionally, the resulting K_La_L values for tap water were closer to the correlation of Shah et al. [1982. Design parameters estimations for bubble column reactors. A.I.Ch.E. Journal 28, 353-379] than those of other conventional models. Finally, the original procedure was also reported to reduce significantly the square sum deviation between the predicted and the measured oxygen response curves.     

梯形波脉冲筛板萃取柱传质性能

本文以UO_2(NO_3)_2—30％TBP(KO)为实验体系,进行了梯形波脉冲筛板柱传质性能的研究。实验中测量了两组分的两相稳态浓度剖面共13组,以扩散模型为基础,求得了梯形波脉冲柱的“真实”传质单元高度HTU_(ox),分散单元高度HDU及表观传质单元高度HTU_(oxp)。通过对实验结果进行分析,选择出了适于本实验体系的较好的操作条件。     

Hydrodynamics and mass transfer in a packed column: Case of toluene absorption with a viscous absorbent

Volatile organic compounds (VOCs) cause nuisance to humans and the environment. Recent legislation encourages industrialists to set up equipment for treating their VOC-loaded gaseous effluents. This piece of research studies the absorption process, using a viscous organic absorbent (di(2-ethylhexyl) adipate=DEHA) to treat a toluene-loaded vent gas, in terms of hydrodynamics and mass transfer. It is shown that DEHA does not lead to an excessive pressure drop. Correlations predicting hydrodynamic parameters from previous literature are summarised and tested against experimental results. It is shown that acceptable prediction accuracy can be achieved for counter-current pressure drop and liquid hold-up. Treatment efficiency for the toluene-loaded vent gas is shown to be very good. Calculation of mass transfer constants (k_La) enables to test literature correlations against the experimental results. The mass transfer is supposed to be limited by the liquid-side resistance. Our experimental results showed that the k_La of the system depends on the liquid velocity but also on the gas velocity. This behaviour has also been observed by the few authors who have used viscous fluids in their experiments, but is contrary to all the authors who have work on low-viscosity fluids. It is therefore clear that the influence of viscosity on the phenomenon is considerable. Not one current correlation is currently accurate in the case of a viscous absorbent.     

A simplified method of obtaining the backmixing coefficient of a solvent extraction column from tracer pulse data

A method based on transfer function matching is used to obtain the backmixing coefficient of a solvent extraction column. The method demonstrates the exploitation of the symbolic manipulation capability of the current generation of scientific computing software. It starts with the dynamic model of Dongaonkar et al. and makes use of a set of tracer pulse data of Dongaonkar for a Kühni column. Compared to the existing methods of evaluating backmixing coefficient, this new method is more direct and simple to implement on computers. It has the potential of being applicable to more elaborate dynamic models of plate columns.     

Mass transfer in bubble column for industrial conditions—effects of organic medium, gas and liquid flow rates and column design

Most of available gas-liquid mass transfer data in bubble column have been obtained in aqueous media and in liquid batch conditions, contrary to industrial chemical reactor conditions. This work provides new data more relevant for industrial conditions, including comparison of water and organic media, effects of large liquid and gas velocities, perforated plates and sparger hole diameter.The usual dynamic O₂ methods for mass transfer investigation were not convenient in this work (cyclohexane, liquid circulation). Steady-state mass transfer of CO₂ in an absorption-desorption loop has been quantified by IR spectrometry. Using a simple RTD characterization, mass transfer efficiency and k_La have been calculated in a wide range of experimental conditions.Due to large column height and gas velocity, mass transfer efficiency is high, ranging between 40% and 90%. k_La values stand between 0.015 and and depend mainly on superficial gas velocity. No significant effects of column design and media have been shown. At last, using both global and local hydrodynamics data, mass transfer connection with hydrodynamics has been investigated through k_La/ε_G and k_La/a.     

Extraction behavior of selected rare earth metals from acidic chloride media using tetrabutyl diglycolamide

Rare earth elements (REEs) are vital to modern, high-tech devices. Recycling REEs from post-consumer electronics can potentially diminish supply chain risks. Toward that end, liquid–liquid solvent extraction of various REEs was investigated with tetrabutyl diglycolamide (TBDGA) in 1-octanol from hydrochloric acid media. Metal partitioning to the organic phase was shown to increase as [Cl^?] increased. In contrast, increasing [H⁺] did not improve extraction. The use of the polar diluent 1-octanol provided high extraction efficiency, especially for the partition of heavy lanthanides from solutions of high chloride concentration. Although the polar diluent also extracted molar amounts of water and acid, it was concluded that a neutral metal/TBDGA complex as mainly the di-solvate was extracted, and that complexation was observed to be exothermic. These results indicate that REE extraction from aqueous chloride solutions can be efficient without the use of high acid concentrations.