Mass transfer simulation on pervaporation dehydration of ethanol through hollow fiber NaA zeolite membranes

A multi‐layer series‐resistance mass transfer model was developed to simulate mass transfer behaviors of water/ethanol mixture through hollow fiber NaA zeolite membranes. The mass transfer through zeolite layer was described by Maxwell‐Stefan mechanism based on adsorption and diffusion parameters obtained from molecular simulation. The mass transfer through asymmetric hollow fiber support was described by dusty gas model involving Knudsen diffusion and viscous flow. It was found that the sponge‐like layer of support besides of zeolite layer made an important contribution to overall membrane transfer resistance while the finger‐like layer had less effect. When permeate pressure shifted from 0.2 to 7.5 kPa, the mass transfer resistance contribution of sponge‐like layer varied from 27.1 to 17.8%. Effects of microstructure parameters of support on mass transfer through membrane were investigated extensively. Large pore size and thin thickness for sponge‐like layer of support were beneficial to improve water permeation flux. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2468–2478, 2016     

LIQUID-LIQUID EXTRACTION IN A HOLLOW-FIBER DEVICE

Liquid-liquid extraction operations were conducted in a hollow fiber mass transfer device using two systems: phenol/water vs. n-octanol and phenol/hexane vs. water. Individual mass transfer resistances due to the tube-side fluid, the hollow fiber wall (membrane), and the shell-side fluid were determined for runs in which the solvent was held stagnant on the shell-side. Countercurrent flow runs with moving solvent were conducted to show that the degree of extraction rises steadily as the solvent-to-raffinate ratio increases. Factors affecting the mass transfer resistances in this type of device are discussed, and the advantages of hollow fiber units over conventional mixer-settler units are pointed out.     

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.     

Heat‐transfer characteristics of polymer hollow fiber heat exchanger for vaporization application

The heat‐transfer characteristics of polymer hollow fiber heat exchanger were investigated by analyzing the heat‐transfer coefficient (HTC) and the heat‐transfer resistance (HTR) distributions of both the lumen side and the shell side. The influences of the fiber wall thickness and the polymer thermal conductivity on the heat‐transfer performance were studied numerically based on the experimental validated simulation model. It is found that the original overall HTC value is below 1032 W/m²·K and the HTR is focus on the fiber wall. However, if enhancing the polymer thermal conductivity to be higher than 1.0 W/m·K and/or lowering the fiber wall thickness to be less than 0.1 mm, the overall HTC could be improved to over 2000 W/m²·K, which indicates that the fiber wall HTR is no longer the limiting factor of the polymer hollow fiber heat exchanger applications. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1783–1792, 2018     

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.     

Preparation of a heterogeneous hollow‐fiber affinity membrane modified with a mercapto chelating resin

A high‐quality, heterogeneous hollow‐fiber affinity membranes modified with mercapto was prepared through phase separation with blends of a chelating resin and polysulfone as membrane materials, poly(ethylene glycol) as an additive, N,N‐dimethylacetamide as a solvent, and water as an extraction solvent. The effects of the blending ratio and chelating resin grain size on the structure of the hollow‐fiber affinity membrane were studied. The effects of the composition of the spin‐cast solution and process parameters of dry–wet spinning on the structure of the heterogeneous hollow‐fiber affinity membrane were investigated. The pore size, porosity, and water flux of the hollow‐fiber affinity membrane all decreased with an increase in the additive content, bore liquid, and dry‐spinning distance. With an increase in the extrusion volume outflow, the external diameter, wall thickness, and porosity of the hollow‐fiber affinity membrane all increased, but the pore size and water flux of the hollow‐fiber affinity membrane decreased. It was also found that the effects of the internal coagulant composition and external coagulant composition on the structure of the heterogeneous hollow‐fiber affinity membrane were different. The experimental results showed that thermal drawing could increase the mechanical properties of the heterogeneous hollow‐fiber affinity membrane and decrease the pore size, porosity, and water flux of the heterogeneous hollow‐fiber affinity membrane, and the thermal treatment could increase the homogeneity and stability of the structure of the heterogeneous hollow‐fiber affinity membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A Study of the Mass Transfer of CO2 through Different Membrane Materials in the Membrane Gas Absorption Process

Abstract

The mass transfer of carbon dioxide through hydrophobic membrane materials into aqueous solutions of monoethanolamine has been studied. Microporous polypropylene, polytetrafluoroethylene and polyvinylidene fluoride hollow fiber membranes were compared. Membranes were characterized before and after use and wetting studies showed that the mass transfer resistance increased by 15% for polypropylene after 45 hours. Wetting may be due to membrane degradation as a result of contact with the solvent. This study highlights the need to choose membrane‐solvent systems that utilize a low cost membrane that remains unwetted by the solvent over long periods and when subjected to reasonable solvent‐side pressures.     

Preparation of a heterogeneous hollow‐fiber affinity membrane having a mercapto chelating resin and its recovery of Hg2+ cations

A kind of heterogeneous hollow‐fiber affinity filter membrane with a high chelating capacity for Hg²⁺ was prepared by phase separation with blends of a mercapto chelating resin and polysulfone as the membrane materials, N,N‐dimethylacetamide as the solvent, and water as the extraction solvent. The adsorption isotherms of the hollow‐fiber affinity filter membrane for Hg²⁺ were determined. The heterogeneous hollow‐fiber affinity filter membrane was used for the adsorption of Hg²⁺ cations through the coordination of the mercapto group and Hg²⁺ cations, and the effects of the morphology and structure of the affinity membrane on the chelating properties were investigated. The chelating conditions, including the chelating resin grain size, pH value, concentration of the metallic ion solution, mobile phase conditions, and operating parameters, had significant effects on the chelating capacity of the hollow‐fiber affinity filter membrane. The results revealed that the greatest chelating capacity of the hollow‐fiber affinity filter membrane for Hg²⁺ was 1090 μg/cm² of membrane under appropriate conditions, and the adsorption isotherms of Hg²⁺ could be described by the Langmuir isotherm. The dynamic chelating experiments indicated that the hollow‐fiber affinity membrane could be operated at a high feed flow rate and that large‐scale removal of Hg²⁺ could be realized. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mass Transfer in Molybdenum Extraction from Aqueous Solutions Using Nanoporous Membranes

Modeling of non‐disperse solvent extraction of molybdenum(VI) with PC‐88A as extractant and a nanoporous hollow‐fiber membrane contactor as extractor was performed. Computational fluid dynamics was applied for modeling and simulation of molybdenum extraction. Concentration, pressure, and velocity distributions for molybdenum were determined. The extraction of Mo⁶⁺ was greatly influenced by the flow rate of feed solution. The extraction efficiency was reduced with higher feed flow rate and increased with the molybdenum content in the feed. The pressure drop along the shell side of the membrane extractor was found to be not significant, being one of the advantages of membrane extractors which assist in reducing the operational costs. The proposed simulation method is capable to prognosticate the performance of solvent extraction of molybdenum in membrane extractors.     

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     

萃取塔数学模型及过程强化的若干研究进展

萃取塔因生产能力大、占地面积小、密闭性好等优点,在石油、化工、生物、医药和环境工程等多领域被广泛应用。本文从以下几个方面介绍了萃取塔近些年的研究进展：综述了传统萃取塔（脉冲萃取塔、转盘塔与Kühni塔等）的水力学、轴向扩散与传质模型的发展,分析比较了表面张力、传质方向、放大效应等因素对模型的影响;介绍了计算流体动力学（CFD）在萃取塔中单液滴、单相流模拟、液-液两相流模拟、外加能量模拟、与群体平衡模型（PBM）耦合模拟中的应用进展;介绍了国内外设计开发的新型萃取塔,包括改变传统塔的内构件和引入多种外场能量等方式来强化相间传质。研究表明,将先进实验研究方法、准确经验模型和可靠理论计算相结合,将会是萃取塔研究的重要手段和方向。     

Computational Simulation of Mass Transfer in Molecular Separation Using Microporous Polymeric Membranes

Computational simulation was conducted to predict mass‐transfer phenomenon in the molecular separation of solute using microporous membrane contactors. Both diffusional and convectional mass‐transfer mechanisms were considered. The membrane system was a hollow‐fiber contactor in which an aqueous phase containing an organic compound was contacted with an organic phase for extractive separation of the solute. Benzoic acid was used as the solute. The main focus was on understanding the mass transfer of solute in the process. The concentration equation for the solute was solved numerically using a computational fluid dynamics approach. It was found that the model can predict the solute transport from the aqueous phase to the organic phase and can be used as a predictive model for process understanding.     

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.     

Pore structure and properties of poly(ether ether ketone) hollow fiber membranes: influence of solvent‐induced crystallization during extraction

Poly(ether ether ketone) (PEEK) hollow fiber membranes were prepared by a thermally induced phase separation method with polyetherimide as diluent, and N‐methyl pyrrolidone (NMP), dichloromethane and a composite extractant composed of NMP, ethanolamine and water as extractant. The effects of the different solvents induced crystallization on the pore structure during extraction and the properties of the PEEK hollow fiber membranes were investigated in detail. The crystallization behaviors of the membranes were characterized by DSC and XRD. The effect of the extractants on the microscopic morphologies, pore structures, water fluxes and mechanical properties of the membranes were investigated. The results showed that the extraction ability of the composite extractant was the most significant, followed by NMP and dichloromethane. The crystallinity of the hollow fiber was 39.0% before extraction and was elevated to 39.2% after the extraction with NMP, 46.6% with dichloromethane and 46.7% with the composite extractant, which shows that dichloromethane and the composite extractant have strong ability to induce the crystallization of PEEK. The inner and outer surfaces of the membranes obtained after extraction by the composite extractant had the largest pore size and the highest surface porosity. The most probable pore diameter of the membranes obtained after extraction by NMP, dichloromethane and the composite extractant was 23.26 nm, 24.43 nm and 24.43 nm, respectively, which indicated that solvent‐induced crystallization was beneficial for the formation of larger pores. The pure water flux of the PEEK membrane prepared by the composite extractant was the largest, but the tensile strength was the lowest. © 2019 Society of Chemical Industry     

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。     

Liquid–liquid two‐phase flow in ultrasonic microreactors: Cavitation,emulsification, and mass transfer enhancement

The effects of ultrasound on the hydrodynamic and mass transfer behaviors of immiscible liquid–liquid two‐phase flow was investigated in a domestic ultrasonic microreactor. Under ultrasonic irradiation, cavitation bubble was generated and underwent violent oscillation. Emulsification of immiscible phases was initiated by virtue of oscillating bubbles shuttling through the water/oil interface. The pressure drop was found to decrease with increasing ultrasound power, with a maximum decrement ratio of 12% obtained at power 30 W. The mass transfer behavior was characterized by extraction of Rhodamine B from water to 1‐octanol. An enhancement factor of 1.3–2.2 on the overall mass‐transfer coefficient was achieved under sonication. The mass transfer performance was comparable to passive microreactor at similar energy dissipation rate (61–184 W/kg). The extraction equilibrium was reached under a total flow velocity 0.01 m/s and input power 20 and 30 W, exhibiting its potential use in liquid‐liquid extraction process. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1412–1423, 2018     

Effects of air‐cooling on skin cells of hollow‐fiber membranes prepared via thermally induced phase separation

A new coarsening model was established to describe the growth of skin droplets on a hollow‐fiber membrane prepared by liquid–liquid thermally induced phase separation. Forced air‐cooling was performed to trigger the phase separation. The heat and mass transfer processes of the skin layer are considered simultaneously. With the aid of a transfer model and data from the phase diagram, the skin cell sizes could be calculated. The effects of air velocity, air temperature, and dimensions of the hollow fiber on the skin cell sizes of the isotactic polypropylene–di‐n‐butyl phthalate–dioctyl phthalate system were investigated. The growth of the skin droplets follows an exponential relationship with time, and the exponent increases with the decrease in the polymer content. All exponents are close to 1/3. The air temperature plays less important roles on the skin cell sizes as compared with those of the air velocity and fiber dimension. Calculated values of cell sizes agree well with the experimental values. POLYM. ENG. SCI., 55:1661–1670, 2015. © 2014 Society of Plastics Engineers     

减压膜蒸馏过程纤维膜表面热质传递特征模拟分析

采用CFD数值模拟的方法,建立了错流式单根中空纤维减压膜蒸馏过程的三维计算模型,对纤维膜表面不同位置的局部热量和质量传递特征进行了研究。研究结果表明,纤维膜表面的速度分布、温度分布、对流传热系数分布以及蒸发速率均随着位置的改变而改变,且具有相似的规律,在相位角60°到90°之间有最大值,而在相位角0°和180°附近其值较小;料液流速显著影响纤维膜表面的热质传递参数的分布,蒸发速率和传热系数均随着流速的提高而增大;传热系数随着真空度的提高而迅速降低。本研究结果加深了对中空纤维减压膜蒸馏过程的认识,对膜过程强化具有指导意义。     

Hydrogen separation at elevated temperatures using metallic nickel hollow fiber membranes

Nickel is a cheaper metallic material compared to palladium membranes for H₂ separation. In this work, metallic Ni hollow fiber membranes were fabricated by a combined phase inversion and atmospheric sintering method. The morphology and membrane thickness of the hollow fibers was tuned by varying the spinning parameters like bore liquid flow rate and air gap distance. H₂ permeation through the Ni hollow fibers with N₂ as the sweep gas was measured under various operating conditions. A rigorous model considering temperature profiles was developed to fit the experimental data. The results show that the hydrogen permeation flux can be well described by using the Sieverts’ equation, implying that the membrane bulk diffusion is still the rate‐limiting step. The hydrogen separation rate in the Ni hollow fiber module can be improved by 4–8% when switching the co‐current flow to the countercurrent flow operation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3026–3034, 2017     

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.