SOLVENT EXTRACTION OF PHENOL FROM AQUEOUS SOLUTION IN A HOLLOW FIBER DEVICE

The extraction of phenol from aqueous solution was studied in a novel type of device—a hollow fiber “shell and tube bundle” unit. The need for coalescence and settling of the two phases involved is avoided with this type of contacting scheme. Various solvents (n-hexanol, n-octanol, ii-decanol, methyl isobutyl ketone, and n-butyl acetate) were used on the shell-side; the phenol solution was pumped through the tube-side. In other runs, powdered activated carbon was packed into the shell-side. The effects of solvent type, powdered carbon use, feed stream flow rate, and the addition of acid or base to the feed were studied. A successful mathematical model for the system was developed.     

中空纤维管随机分布时透析器内的管外传质

利用Matlab软件计算了中空纤维透析器外壳内壁面(简称壁面)影响下,中空纤维随机分布、管外流场充分发展、纤维表面定质量流量时的管外流场分布,进而求得了不同填充密度下透析器的管外传质系数. 结果表明,中空纤维的排布方式对传质系数有很大的影响;在所研究的中空纤维填充密度范围内(10%～50%),随着填充密度的增大,透析器的管外传质系数先变大,后变小;其随机性整体上逐渐减小.     

Phenol Removal from Aqueous Solution through Hollow Fiber Membrane Extraction

In this work,mass transfer mechanism was studied for 50%TBP( in kerosene) -phenol-water as the working system in different bydrophobic microporous hollow fiber modules. The effect of different operating conditions on the removal of phenol was aanlyzed. Solvent entraimment in this process was detected with MALVERN-2600 laser pellet diameter analytical equipment. Experimental reaults indicate the mass transfer coefficient is incressed while the two phase flow raten are inerassed. With incesses in the flow rate of the water phase,the removal ratio of phenol will be decreased. Highly effective removal of phenol could be reached by changing the experimental conditioms and the module configurstion. The solvent entraimment in the water phase in the mernbrane extraction process was found to be 5%-8% of that in conventional liquid-liquid extraction process. Thus,solvent pollution could be better controlled.     

Non-Dispersive Solvent Extraction and Stripping of Neodymium (III) using a Hollow Fiber Contactor with TODGA as the Extractant

Membrane based non-dispersive solvent extraction (NDSX) of Nd(III) from aqueous nitric acid medium was carried out using a commercial liquid-liquid extraction system consisting of an extra-flow hollow fiber module with about 10,000 microporous hydrophobic polypropylene capillaries with an effective surface area of 1.4 m². The NDSX operation was carried out by pumping about 1 g/L Nd(III) solutions at a fixed nitric acid concentration of 3.57 M through the tube side and organic solvent (tetra-n-octyl-3-oxapentane-diamide (TODGA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fiber capillaries. NDSX studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Conditions for quantitative extraction and stripping were also identified. Reproducibility of the results from multiple runs was found to be excellent after five different identical runs.     

Phenol recovery with tributyl phosphate in a hollow fiber membrane contactor: Experimental and model analysis

The extraction and stripping of phenol using a solution of tributyl phosphate in kerosene in a hydrophobic polypropylene hollow fiber membrane contactor has been studied. The effect of the aqueous and the organic phase flow rates on the overall mass transfer coefficient for both extraction and stripping steps was investigated. Experimental values of the overall mass transfer coefficient were determined and compared with predicted values from the resistance in series model. Results showed that the overall mass transfer coefficients for extraction were about one order of magnitude greater than those measured during the stripping process. The experimental values were in good agreement with the predicted values for the extraction module. However, the predicted values were slightly overestimated for the stripping module. The individual mass transfer resistances were analyzed and the rate-controlling steps of mass transfer were also identified in both extraction and stripping modules. The major resistance in extraction and stripping was in the aqueous phase and in the membrane phase, respectively.     

填充密度对中空纤维膜接触器精馏过程壳程传质的影响

探讨了填充密度对新型聚丙烯中空纤维膜接触器精馏过程中壳程传质的影响。中空纤维膜接触器在填充密度为4.7%、9.5%、19%时均可在远离常规填料液泛线以上的气速范围操作。低填充密度下,壳程的Sherwood数理论值大于实验值,但填充密度较高时,实验值大于理论值。高Reynolds数有利于壳程传质,低填充密度时的Sherwood数高于高填充密度时。随着F因子逐步增大,壳程气相传质阻力随之变小,且膜接触器的填充密度越高,气相传质阻力越大。3种不同填充密度膜接触器的气相总传质系数随着接触器填充密度的增大而迅速减小,由391.84×10^-5 m·s^-1降低为83.28×10^-5 m·s^-1。     

RECOVERY OF PHENOL WITH CYANEX® 923 IN MEMBRANE EXTRACTION-STRIPPING SYSTEMS

The recovery of phenol from aqueous solutions with CYANEX® 923 was studied. Classical dispersive extraction and three membrane extraction-stripping systems (bulk liquid membranes, three-phase hollow fiber contactor and two hollow fiber modules set-up) were used. It was found that CYANEX® 923 was a convenient carrier for recovery of phenol from aqueous streams in extraction-stripping membrane processes. The problem of emulsion formation, so important in dispersive extraction, was avoided. Both mass transfer experiments in different membrane systems and measurement of the dynamic interfacial tension demonstrated importance of the interfacial phenomena occurring in the stripping stage. A blocking of this interface was observed that resulted in a decrease of phenol mass transfer.     

Mass transfer enhancement in non‐dispersive solvent extraction with helical hollow fiber enabling Dean vortices

In this work mass transfer enhancement of non‐dispersive solvent extraction by use of helical hollow fiber membranes (HHFM) was investigated by means of experiment and model simulation. Purified terephthalic acid wastewater treatment by extraction with p‐xylene as solvent was chosen as the application case. Experiments showed that extraction efficiency of the HHFM was doubly enhanced compared with that of the straight hollow fiber. A comprehensive mathematical model of the HHFM extraction was developed in an orthogonal helical coordinate system with an analytical solution of the 3D velocities. Model simulation revealed that Dean vortices circulate the peripheral fluid to the center, which enhances the mass transfer in the lumen side where radial diffusion is the rate determining step of the extraction. Relations of effluent impurity concentration and enhancement factor with the Graetz number and dimensionless curvature, were obtained by model simulation. Optimal parameters were selected for HHFM extraction design. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3479–3490, 2017     

随机填充中空纤维膜组件中非稳态渗透传质数学模型

Based on the membrane-based absorption experiment of CO2 into water, shell-side flow distribution and mass transfer in a randomly packed hollow fiber module have been analyzed using subchannel model and unsteady penetration mass transfer theory. The cross section of module is subdivided into many small cells which contains only one hollow-fiber. The cross sectional area distribution of these cells is presented by the normal probability density distribution function. It has been obtained that there was a most serious non-ideal flow in shell side at moderate mean packing density, and the large amount of fluid flowed and transferred mass through a small number of large voids. Thus mass transfer process is dominated by the fluid through the larger void area. The mass transfer process in each cell is described by the unsteady penetration theory. The overall mass transfer coefficient equals to the probability addition of the mean mass transfer coefficient in each cell. The comparisons of the values calculated by the model established with the empirical correlations and the experimental data of this work have been done.The predicted overall mass transfer coefficients are in good agreement with experimental data.     

Scale-up of Hollow Fiber Extractors

Abstract

The performance of a commercial-scale hollow fiber extraction system was investigated by the Separations Research Program (SRP) at the University of Texas at Austin. In this work, hexanol was extracted from water into octanol using a large-scale extraction/distillation system. In the membrane extractor studies, the octanol-rich phase was fed on the tube-side while in the packed column studies, the octanol-rich phase was chosen as the dispersed phase. This chemical system was selected because of its high solute distribution coefficient. As a result, the required solvent to feed ratio was low which creates hydraulic problems for conventional dispersive extractors such as the packed column. Under identical operating conditions, the mass transfer performance of the hollow fiber extractor compared favorably with that of a commercial-scale type 2 structured packing. A height equivalent to a theoretical stage (HETS) of 1.5 meters was obtained with the membrane extractor as compared to 15 meters for the type 2 structured packing. A staged hollow fiber extraction mass transfer model for scale-up was developed and found to agree with data obtained in this work and with data obtained earlier using the n-butanol/succinic acid/water system.     

Treatment of phenol-containing aqueous solutions by membrane-based solvent extraction in coupled ultrafiltration modules

Extractive treatment of phenol-containing aqueous streams by two coupled hollow fiber modules (for simultaneous extraction and stripping) is experimentally and theoretically studied. The effects of hydrodynamic conditions (linear velocities of all three liquids) and concentrations (initial phenol concentrations) are explored and an optimal combination of these process parameters is found for maximisation of the phenol fluxes in both modules. The extraction/stripping performance of the coupled HF modules was compared when using different organic solvent (alcohols and alkanes). Analysis of the mass-transfer resistances of the different liquid layers in both modules is presented based on mathematical model and experimental data from equilibrium measurements and kinetic experiments. It is found that an important part of the overall resistance is located in the aqueous phase’s boundary layers. A substantial improvement of the stripping yield is reached by using a series of stripping modules.     

CFD simulation of acetone separation from an aqueous solution using supercritical fluid in a hollow-fiber membrane contactor

In the present study, separation and mass transfer of acetone using a polymeric hollow fiber membrane by a supercritical fluid as a dense solvent was simulated. The propane is used as supercritical fluid for extraction of acetone. The simulated hollow-fiber membrane contactor has three compartments: tube, porous membrane and shell. The aqueous solution and solvent pass in the lumen and shell sides, respectively. The model equations have been solved by CFD technique using a finite element as numerical method. The simulation results were compared with experimental data obtained from literature and showed great agreement with the measured values. The simulation results of acetone extraction also showed that reducing the feed rate and increasing the solvent velocity will enhance the separation of acetone.     

Hydraulics and Mass Transfer Efficiency of a Commercial-Scale Membrane Extractor

Abstract

In recent years there has been significant interest in utilizing microporous hollow fiber membranes for liquid-liquid extraction. The membrane extractor resembles the shell and tube heat exchanger with the tube section composed of 1000–2500 fibers/in². The diameter of each fiber is approximately 300 microns. In this process, the feed may be passed through the shell side, while the solvent is passed through the fiber side, or vice versa. Mass transfer occurs across the liquid-liquid interface formed in the pores of the fiber wall. The advantages of this technology are high throughput capacities, independence of density difference between the feed and solvent, and potentially high mass transfer areas. The mass transfer performance of an available commercial scale nonbaffled membrane extraction module was determined to be lower than expected from results obtained in smaller scale modules. Mass transfer studies of a commercial-scale membrane extraction module at the Separations Research Program have shown that a significant portion of the fibers are bypassed by the shell side fluid and consequently only a fraction of the total fiber surface area is utilized. A hydraulic study using a dye tracer technique verified this finding with an aqueous flow on the shell side. A model which incorporates mass transfer correlations reported by others has been developed and shown to have excellent agreement with the experimental data obtained. In this paper, the efficiency of the membrane extractor is compared with conventional spray, sieve tray, and packed columns; the effect of shell side bypassing is also presented.     

Modeling and simulation of mass transfer in near-critical extraction using a hollow fiber membrane contactor

In this study is presented a general methodology to predict the performance of a continuous near-critical fluid extraction process to remove compounds from aqueous solutions using a hollow fiber membrane contactor. The stabilization of the gas-liquid interface in the membrane porosity and a high surface area to contact both phases represent some of the advantages that hollow fiber contactors offer over conventional contactor devices for the extraction of compounds from liquid feeds.A mathematical model has been developed integrating a resistances-in-series mass transfer system that takes into account boundary layers, membrane porosity and thermodynamic considerations with mass balances of the membrane contactor. Simulation algorithms were easily implemented with low calculation requirements.The system studied in this work is a membrane based extractor of ethanol and acetone from aqueous solutions using near-critical CO₂. Predictions of extraction percentages obtained by simulations have been compared to the experimental values reported by Bothun et al. [2003a. Compressed solvents for the extraction of fermentation products within a hollow fiber membrane contactor. Journal of Supercritical Fluids 25, 119-134]. Simulations of extraction percentage of ethanol and acetone show an average difference of 36.3% and 6.75% with the experimental data, respectively. More accurate predictions of the extraction of acetone could be explained by a better estimation of the transport properties in the aqueous phase that controls the extraction of this solute.When the model was validated, the effect of the configuration and the operating parameters was studied and local mass transfer resistances were evaluated. The proposed approach allows the evaluation of the relevance of membrane hydrophobicity for extraction in solutions under different thermodynamic conditions. This original methodology based on well-known phenomenological equations represents a general approach which could be applied in other processes using membrane contactors with different configurations.     

溶胀对中空纤维膜萃取器中的流动和传质性能的影响

溶胀是中空纤维膜萃取工业化必须要解决的关键问题之一。本文通过拍摄电镜照片，观察了溶胀前后中空纤维膜表面形态，孔隙率，膜孔径，膜孔道弯曲状况等微观结构的变化。结果表明，溶胀会使中空纤维膜孔隙率减小，膜孔径变小，弯曲因子增大，通过测量发现，溶胀后膜长度增加，而膜的内外径，膜厚基本不变。本文还研究了溶胀时间对中空纤维膜器中的流动及传质效果的影响，通过测量聚丙烯和聚砜中空纤维膜器管程和壳程的停留时间分布曲线表明，对于装填密度较高的膜器，溶胀时间对壳程和管程中的流动状况的影响可以忽略。此外，本文以正辛醇－苯胺－水为实验体系，在中空纤维膜器中进行了循环逆流传质实验。实验证明，由于溶胀使纤维膜阻增加，膜器的传质性能随时间的增加而下降。     

The removal of metals from edible oil by a membrane extraction procedure

Edible oils may contain traces of metals. In oil refining procedures these metals have to be removed to guarantee oxidatively stable products. In this study we present a hollow fiber membrane extraction system for the removal of metals from an oil. Several extraction liquids were tested, of which an ammonia solution gives the best distribution coefficient (m=11.7). From mass transfer calculation it follows that the resistance to mass transfer in the extraction phase in the fiber wall can be neglected compared to the resistances in the oil phase inside the fibers and the extraction phase outside the fibers. A cost evaluation shows that such a membrane extraction can be profitable in conventional refining if more than 1.5% bleaching earth has to be added in surplus to remove metals.     

中空纤维膜萃取镉离子的研究

处理重金属离子水溶液是环境治理中的一个重要方面 ,应用新型膜萃取技术对去除水溶液中镉离子进行了研究。首先测定镉离子在不同萃取体系中的分配系数 ,选择合适的萃取剂 ,在中空纤维膜器中研究膜萃取去除镉离子的分离效果和传质特性 ,探讨不同装填因子、两相流速、水相初始浓度等实验条件对分离和传质的影响。实验结果表明 ,体积分数为 5 0 %的P2 0 4 正庚烷溶剂对于镉离子有较好的萃取效果。当装填因子为 0 .732 8时 ,经 33cm长的中空纤维膜器一级萃取可将溶液质量浓度由 40 0mg/L降至 0 .2mg/L以下 ,证明了膜萃取的高效性     

Modeling investigation of geometric size effect on pervaporation dehydration through scaled-up hollow fiber NaA zeolite membranes

A mass transfer model in consideration of multi-layer resistances through NaA zeolite membrane and lumen pressure drop in the permeate sidewas developed to describe pervaporation dehydration through scaled-up hollowfiber supported NaA zeolitemembrane. Itwas found that the transfer resistance in the lumen of the permeate side is strongly related with geometric size of hollow fiber zeolite membrane,which could not be neglected. The effect of geometric size on pervaporation dehydration could bemore significant under higher vacuumpressure in the permeate side. The transfer resistance in the lumen increaseswith the hollowfiber length but decreaseswith lumen diameter. The geometric structure could be optimized in terms of the ratio of lumen diameter to membrane length. A critical value of dI/L (Rc) to achieve high permeation flux was empirically correlated with extraction pressure in the permeate side. Typically, for a hollow fiber supported NaA zeolite membrane with length of 0.40 m, the lumen diameter should be larger than 2.0 mm under the extraction pressure of 1500 Pa.     

Removal of Benzene/Toluene from Water by Vacuum Membrane Distillation in a PVDF Hollow Fiber Membrane Module

Abstract

Asymmetric polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by a phase inversion method using dimethylacetamide (DMAc) and a mixture of water/LiCl as solvent and a nonsolvent additive, respectively. The prepared membranes were characterized by scanning electron microscopy (SEM) for observing its microstructures and by a gas permeation method for measuring its surface porosity, pore size, and pore size distribution. Wetting pressures of the dry hollow fiber membranes were also measured. Using the prepared PVDF hollow fiber membranes, a membrane module was fabricated for removal of benzene/toluene from water. Effects of various operating parameters such as downstream vacuum levels, feed temperatures, and feed flow rates on performances of the module were investigated experimentally. The benzene/toluene removal was achieved over 99% under an optimal operating condition. Mass transfer of benzene or toluene removal is controlled not only by the liquid phase resistance but also by the membrane and gas phase resistances. Benzene and toluene can be removed from water simultaneously with no adverse coupling effects.     

中空纤维膜萃取苯酚的传质及流动特性

以体积分数为30％的磷酸三丁酯＋煤油－水为实验体系，研究了中、高装填密度的中空纤维膜萃取处理苯酚衡溶液的传质效果和传质特性以及膜器壳程流动状况。实验结果表明，中空纤维膜萃取可以高效去除水中的苯酚，萃取率最高可达到99．9％。比较了总传质系数的实验值与多个传质系数关联式的预测值之间的偏差，发现从中、高装填密度膜器得到的传质关联式偏差较小，而从低装填密度膜器得到的传质关联式偏差较大。通过测量膜器壳程流动的停留时间分布曲线，证实了偏差是由于中、高装填密度的膜器壳程流动的复杂性造成的。