Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor (PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.     

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

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 Gröber 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 Eötvös 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     

A HOMOGENEOUS MODEL FOR MASS TRANSFER ENHANCEMENT IN GAS-LIQUID-LIQUID SYSTEMS

A modified homogeneous mass transfer model based on penetration theory is proposed for the mass transfer enhancement in gas-liquid-liquid systems. The present model assumes the existence of a shuttle mechanism between the organic dispersed phase and the continuous aqueous phase and considers the effect of diffusivity along with the solubility ratio and the dispersed phase holdup. The concept of effective diffusivity for gas in liquid-liquid emulsions has been used to consider the effect of diffusivity on mass transfer enhancement. The proposed model predicts the experimentally obtained enhancement factor with reasonable accuracy and numerical simplicity. Fresh experiments were also conducted to further validate the proposed model.     

A HOMOGENEOUS MODEL FOR MASS TRANSFER ENHANCEMENT IN GAS-LIQUID-LIQUID SYSTEMS

A modified homogeneous mass transfer model based on penetration theory is proposed for the mass transfer enhancement in gas-liquid-liquid systems. The present model assumes the existence of a shuttle mechanism between the organic dispersed phase and the continuous aqueous phase and considers the effect of diffusivity along with the solubility ratio and the dispersed phase holdup. The concept of effective diffusivity for gas in liquid-liquid emulsions has been used to consider the effect of diffusivity on mass transfer enhancement. The proposed model predicts the experimentally obtained enhancement factor with reasonable accuracy and numerical simplicity. Fresh experiments were also conducted to further validate the proposed model.     

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.     

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.     

Modeling the axial distribution of mass transfer coefficient in an agitated-pulsed extraction column

The dispersed phase holdup and drop size in solvent extraction columns vary along the column height and this affects the mass transfer coefficient and interfacial area. In this article, mass transfer study was performed experimentally using a 25 mm diameter agitated pulsed column. The axial distribution of mass transfer coefficient was determined by coupling population balance equation and axial dispersion model by taking the longitudinal variation in hydrodynamic performance into consideration. Feasibility of different mass transfer models in predicting concentration profiles was evaluated and a novel correlation based on effective diffusivity was developed. The results showed that both overall and volumetric mass transfer coefficients have significant change along the column height and greatly depends on the agitation speed and pulsation intensity. Increasing dispersed phase velocity also augments the overall mass transfer coefficient. The maximum number of transfer unit was measured to be 10 m⁻¹ at agitation speed of 1000 rpm.     

PARTLCLE SURFACE ROUGHNESS EFFECTS ON THE INTERFACIAL MASS TRANSFER DYNAMICS OF MICROPOROUS ADSORBENTS

The surface roughness characteristics of several microporous adsorbents are qualitatively explored by scanning electron microscopy. Interfacial (film) mass transfer coefficients for adsorption of a number of different solutes by these adsorbents are investigated. Significant differences between coefficients for different adsorbents are reported. Rough spheres are shown to exhibit a seven-fold mass transfer enhancement over smooth spheres. The results indicate that mass transfer enhancement is more dependent on surface roughness than on overall particle shape. The surface roughness is investigated quantitatively by fractal analysis in a companion paper (Van Vliet and Young, 1988).     

Hydrodynamics and mass transfer performance of rotating sieved disc contactors used for reversed micellar extraction of protein

The extraction of protein by continuous liquid-liquid extraction was investigated in a rotating disc contactor (RDC) and a rotating sieved disc contactor (RSDC) with and without stators. Hydrodynamics and mass transfer performance for reversed micellar extraction of lysozyme in RDC/RSDC I and RSDC II have been investigated. The dispersed phase holdup has increased with the increase of rotor speed. Pratt's equation was used for calculating the characteristic velocity. An inverse relation was observed between the characteristic velocity and rotor speed. The estimated overall mass transfer coefficient was increased by increasing the rotor speed. For an extraction column, the overall hydrodynamics and mass transfer performance can be judged by a volumetric utilization factor. At high rotor speeds, volumetric utilization factor for RSDCs is higher than that of RDC. The RSDC II has been successfully applied in reversed micellar extraction of protein.     

Modeling of a continuous rotating disk polycondensation reactor for the synthesis of thermoplastic polyesters

A dynamic multicompartment model is proposed for a continuous flow rotating disk reactor for the finishing stage melt polycondensation of poly(ethylene terephthalate). In the multicompartment reactor model, ethylene glycol is removed from both the bulk melt phase and the film phase formed on the rotating disks. The specific interfacial area for the film phase is estimated using the empirical correlation for polymer film thickness, and the mass transfer coefficient is calculated using the penetration theory. The mass transfer enhancement factor is introduced to account for the increased interfacial area due to ethylene glycol bubbles. The effects of reactor design and operating parameters on molecular weight and ethylene glycol removal have been investigated through model simulations. In particular, a detailed analysis is presented on the ethylene glycol removal rate from the two phases. © 1996 John Wiley & Sons, Inc.     

开式涡轮转盘塔用于液液固体系的性能研究

由转盘塔改型的开式涡轮转盘塔是一种新型的搅拌萃取塔,它适用于固含量较高的体系.其特点是每个转盘下方有3条叶片.选用水-煤油-石英砂体系,以丁酸为溶质,在内径52mm的塔中作流体力学和传质实验.结果表明,传质方向对液体分散相滞留率、固相滞留率和体积传质系数都有一定影响.固体颗粒的存在可降低扩散单元高度,但对传质并不总是有利.     

Investigation of reactive extraction on single droplets

Extraction of dichlorphenol from freely suspended single drops into a continuous phase enhanced by an instantaneous chemical reaction was investigated using NaOH solutions of different concentrations. Also, the reverse mass transfer direction from the continuous phase into the dispersed phase was studied by extracting salicylic acid with the liquid ion exchanger LA-2. Concentrations were measured continuously without taking samples by means of a modified liquid scintillation technique. For appropriate concentrations of NaOH the continuous phase side mass transfer resistance vanishes with increasing extraction time and hence, for the first time, the individual mass transfer coefficients in the dispersed and continuous phase were determined from the overall value for exactly the same fluiddynamical conditions. Experimentally determined enhancement factors are larger than those predicted by the film theory.     

加入分散有机相强化气体吸收的传质过程(英文)

Mass transfer enhancement of gas absorption by adding a dispersed organic phase has been studied in this work. Various dispersed organic phases (heptanol, octanol, isoamyl alcohol, heptane, octane, and isooctane) were tested respectively in the experiment. According to the theoretical model and experimental data, the overall volumetric mass transfer coefficient and enhancement factor were obtained under different dispersed organic phase volume fraction and stirring speed. The experimental results indicate that gas-liquid mass transfer is enhanced at different level by adding a dispersed organic phase. The best performance of enhancement were achieved with the dispersed organic phase volumetric fraction of 5% and under an intermediate stirring speed of 670 r·min-1. Among the organic phases tested in the experiment, alcohols show better performance, which gave 20% higher enhance-ment of overall volumetric mass transfer coefficient than adding alkanes.     

水溶液中甲苯分散相增强难溶气体吸收

利用难溶气体的物理吸收过程,在具有恒定气液界面面积的吸收装置中研究了常压和室温条件下分散液相(甲苯)对气液传质的增强作用。通过测定气相(丙烷和氢气)压力随时间的变化,计算出液侧传质系数和传质增强因子。试验发现,当传质组分在分散液相与连续液相内的分配系数较大,或在两相间的相对扩散系数较大,且分散相形成的液滴较小时,加入分散液相可显著增强气液传质;增强因子随分散液相含率的增大而增大,但增大幅度逐渐减小;当气体在纯水中的传质系数增大时,同等条件下分散相对气液传质的增强作用减小。     

Performance improving with temperature in liquid–liquid extraction using cumene–isobutyric acid–water chemical system

The performance of single drops was investigated in liquid–liquid extraction while temperature was changed within the range of 15–40 °C. The recommended system of cumene–isobutyric acid–water with mass transfer resistance mainly in aqueous phase was used. An average enhancement of 75.6% in the rate of transfer was revealed. The extraction efficiency is the most influencing term due to molecular diffusivity enhancement. For modeling, a simple correlation was proposed for the effective diffusivity in Newman's equation, while continuous phase mass transfer coefficient was directly included. Using this model, relative deviation of the overall mass transfer coefficient was within only ±5.6%.     

螺旋状中空纤维膜萃取传质特性

在对中空纤维膜萃取以及螺旋管技术进行充分调研的基础上 ,选择水 -苯酚 - 30 %TBP煤油为实验体系 ,溶质由水相萃取到有机相 ,在不同结构的单束螺旋状中空纤维膜器中研究了螺旋管纤维膜管内外流速以及螺旋管结构等因素对传质系数的影响 .实验结果表明 ,螺旋管中空纤维膜可以有效地提高中空纤维膜的传质特性 .随着管内流速的增加 ,传质系数将有很大提高 ,而管外流速对于传质系数的影响则较小 .至于螺旋结构的影响为 :随着螺旋内径的减小或者是螺旋螺距的减小 ,总传质系数相应地有很大提高 .最后得到了在本实验条件下计算总传质系数K的关联式     

微通道中液-液萃取传质特性的研究

研究了在一个内径为400 μm管式直线型玻璃微通道中的液-液两相的传质特性,其中去离子水为水相, 煤油（溶质是苯甲酸）为油相, 氮气为气相。实验研究了表面张力、黏度和气体分散相对体积传质系数的影响,结果表明：在内径为400 μm的微通道内,当停留时间为15 s时微通道内的萃取已达到平衡;水相的表面张力和液体黏度显著影响微通道内的传质效率;在液-液系统中引入气相后,水油两相之间的传质效率显著增加。     

Mass‐transfer enhancement in single drop extraction in the presence of magnetic nanoparticles and magnetic field

Magnetite nanoparticles with an average particle size of 28.8 nm were synthesized, coated with oleic acid, and characterized using various techniques such as DLS, FT‐IR, SEM, XRD, VSM, and UV‐Vis analysis. A nanofluid consisting of synthesized nanoparticles and 5 wt % acetic acid in toluene as the dispersed phase was prepared and used in the chemical test system, Toluene‐Acetic Acid‐Water, for the single drop extraction in the presence and absence of an external oscillating magnetic field. Influences of various operating and design parameters such as nanoparticle concentration, drop diameter, and the applied current and frequency on the overall mass‐transfer coefficients for the mass‐transfer direction from d→c were investigated carefully. The obtained results were used to propose a general correlation for the mass‐transfer enhancement. It was found that the maximum mass‐transfer enhancement compared with that obtained in the absence of nanoparticles and the oscillating magnetic field is about 259%. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4466–4479, 2016     

Deacidification of corn oil by solvent extraction in a perforated rotating disc column

The deacidification of corn oil by continuous liquid-liquid extraction was investigated in a rotating disc column. The solvent was ethanol containing approximately 6% water. The influence of rotor speed, oil phase flow, and column geometry upon the dispersed phase holdup and the mass transfer efficiency was studied. The dispersed phase holdup increased with the increase of rotor speed and oil phase flow. Pratt's equation was used for calculating the characteristic velocity. An inverse relation was observed between the characteristic velocity and rotor speed, which is different from data previously reported in the literature. The estimated volumetric mass transfer coefficients increased as rotor speed and oil phase flow increased. The experimental results proved that it is feasible to obtain a refined oil with an oleic acid content less than 0.3 wt% by continuous solvent extraction. They also indicated that the corresponding loss of neutral oil was less than 5 wt%. Such value for the loss of neutral oil is significantly lower than the results reported in the literature for alkali or physical refining of corn oil.     

Mass transfer into/from nanofluid drops in a spray liquid‐liquid extraction column

The performance of a spray liquid‐liquid extraction column at two mass‐transfer directions was experimentally studied in the presence of silica nanoparticles. Toluene‐based nanofluid drops containing 0.0005–0.01 vol % silica nanoparticles were dispersed in aqueous phase and acetic acid (AA) transfer between phases was investigated. The experiments were performed at fixed volumetric flow rates of dispersed and continuous phases. Maximum enhancement of 47.4% and 107.5% in overall mass‐transfer coefficient, respectively, for mass‐transfer direction of dispersed to continuous phase and vice versa were achieved for drops with 0.001 vol % silica nanoparticles. These enhancements can be referred to Brownian motion of nanoparticles and induced microconvection. The results showed that nanoparticles are more effective in augmenting AA transfer from continuous to dispersed phase. Probable reason is that smaller diameter and lower internal turbulence of drops in this transfer direction increase dispersed phase resistance potential to be manipulated by Brownian motion of nanoparticles. © 2015 American Institute of Chemical Engineers AIChE J, 62: 852–860, 2016