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Application of nonlinear frequency response to investigation of membrane transport

SEPARATION SCIENCE AND TECHNOLOGY 2006年第1期41卷 43-72页

作者： Petkovska, M Petkovska, LT Univ Belgrade Fac Technol & Met Dept Chem Engn Belgrade 11000 Serbia Vinca Inst Nucl Sci Dept Phys Chem Belgrade Serbia Monteneg

The concept of higher order frequency response functions, used for investigation of weekly nonlinear systems by frequency response techniques, is applied to investigation of membrane systems. Isothermal permeation of single gases through non-porous and porous membranes is analysed for three transport mechanisms: solution-diffusion, pore-surface diffusion, and viscous-flow. In the course of definition of the transmembrane transport in dynamic conditions, a new concept of generalized membrane permeability, defined as an indefinite sequence of the permeabilities of the first, second, third,...order, dependent on the equilibrium and transport parameters of the membrane in steady-state, is introduced. A simple two-reservoir system, with variation of the volume of one reservoir, is defined and its first and second order frequency response functions are derived. It is shown that these functions can be used for identification of the transport mechanism, i.e., of the corresponding model and for estimation of the model parameters: permeabilities of different orders, as well as the separate values of the relevant equilibrium and transport parameters.

关键词： membrane transport nonlinear frequency response higher order frequency response functions generalized membrane permeability solution-diffusion model pore-surface diffusion model viscous-flow model parameter estimation

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The role of adsorption on nanofiltration of azo dyes

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JOURNAL OF MEMBRANE SCIENCE 2005年第1-2期255卷 157-165页

作者： Gomes, AC Gonçalves, IC de Pinho, MN Univ Beira Interior Dept Chem Text & Paper Mat Unit P-6201001 Covilha Portugal Inst Super Tecn Dept Chem Engn P-1049001 Lisbon Portugal

The influence of osmotic pressure and solute adsorption on permeate flux during nanofiltration (NF) of a wool textile dye solution was investigated. solutions of C.I. Acid Orange 7 with concentrations ranging from 2 to 2000mg/l were subjected to nanofiltration with a NF 45 membrane. An increase of flux decline with dye concentration was observed. The resistance-in-series model gives evidence that the main factor causing this flux decline is the solute adsorption. This is reinforced by the increase in the apparent rejection with dye concentration. Although osmotic pressure was taken into account, its contribution to a decrease of the driving force seems not to be significant. Adsorption resistance was calculated from a correlation between the pure water fluxes, measured before and after the essays, and feed dye concentration. A Langmuir isotherm type curve agreed well with experimental data. From the solution-diffusion model, the intrinsic rejection coefficient can be predicted as function of feed dye concentration. (c) 2005 Elsevier B.V. All rights reserved.

关键词： textile industry nanofiltration solution-diffusion model azo dyes adsorption

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Pervaporation properties of PDMS membranes for removal of benzene from aqueous solution: Experimental and modeling

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CHEMICAL ENGINEERING JOURNAL 2005年第1-3期114卷 123-129页

作者： Peng, FB Pan, FS Li, D Jiang, ZY Tianjin Univ Sch Chem Engn & Technol Tianjin 300072 Peoples R China

Polydimethylsiloxane (PDMS) pervaporation membranes were employed to remove benzene from aqueous solution. A predictive model was proposed based on solution-diffusion mechanism to predict mass transfer during pervaporation process. The solubility of components in the membrane was described by UNIFAC-FV model, and the diffusion coefficients in polymeric membrane were calculated by free volume theory. The effects of feed concentration and operating temperature on pervaporation properties were investigated to validate the model. It has shown that the proposed model can be applied to select membrane materials and predict the permeation flux and selectivity of components through the polymeric membrane. (c) 2005 Elsevier B.V. All rights reserved.

关键词： pervaporation PDMS solution-diffusion model UNIFAC-FV free volume theory

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Observation of the solute transport in the permeation through hydrogel membranes by using FTIR-microscopy

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JOURNAL OF MEMBRANE SCIENCE 2005年第1-2期253卷 191-198页

作者： Cheng, ML Sun, YM Yuan Ze Univ Dept Chem Engn & Mat Sci Chungli 320 Taoyuan Taiwan Chung Yuan Christian Univ R&D Ctr Membrane Technol Chungli 320 Taoyuan Taiwan

Using the techniques of FTIR-microscopy and cryomicrotomy, the diffusion behavior of a model solute, 4-cyanophenol, through PHEMA hydrogel membranes was observed. In a side-by-side membrane permeation study, the experiment was stopped before or when the steady state was achieved. The membrane was removed from the experimental device, freeze-dried, and sectioned using a cryomicrotome. The solute concentration profile across the membrane could be determined by an FTIR-microscope. Based on Fick's law and the solution-diffusion model, the diffusion coefficient of the solute in a membrane permeation study can be determined from the pseudo-steady state permeation rate, time-lag method, and the concentration profiles within the membrane in the transient and pseudo-steady states. The results showed that the diffusion coefficients determined by different methods were not the same and distributed from 8.9 x 10(-9) to 1.7 x 10(-7) cm(2)/s. The variation in diffusion coefficients was most likely due to the strong interaction between 4-cyanophenol and PHEMA. Some portion of absorbed 4-cyanophenol was immobilized on the polymer chains or trapped by the networks so that it was not able to diffuse. As a result, the diffusion coefficients obtained from different methods may represent different physical meanings and need a careful justification. (c) 2005 Elsevier B.V. All rights reserved.

关键词： FTIR-microscope permeation diffusion coefficient hydrogel solution-diffusion model

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Solvent transport in organic solvent nanofiltration membranes

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JOURNAL OF MEMBRANE SCIENCE 2005年第1-2期262卷 49-59页

作者： Silva, P Han, SJ Livingston, AG Univ London Imperial Coll Sci Technol & Med Dept Chem Engn & Chem Technol London SW7 2AZ England

Solvent transport in organic solvent nanofiltration membranes has been studied in a lab-scale cross-flow nanotiltration rig over extended periods using the common solvents methanol, toluene, ethyl acetate and their mixtures. The organic solvent nanofiltration membranes STARMEM (TM) 122(1) (W.R. Grace and Co.) and MPF50 (Koch Membrane Systems) were investigated. It was found that it took a few days to obtain stable solvent flux using STARMEM (TM) 122, and that the solvent flux in this membrane showed good repeatability between different sample discs. MPF50 did not provide reproducible results, therefore, no modelling/data analysis was performed for this membrane. Our experimental data shows that both solution-diffusion and pore-flow models can be used to predict permeation of solvent mixtures, using only the permeabilities of the pure solvents to obtain input parameters to each model. The solution-diffusion model gave more accurate predictions. Our conclusion is that for the solvents studied, it is possible for reasonable predictions of solvent mixture flux to be made over the whole concentration range, based on the data for pure solvents. (c) 2005 Elsevier B.V. All rights reserved.

关键词： organic solvent nanofiltration solvent mixtures solution-diffusion model pore-flow model cross-flow

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A simplified solution-diffusion theory in pervaporation: the total solvent volume fraction model

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JOURNAL OF MEMBRANE SCIENCE 2004年第1-2期244卷 117-127页

作者： Schaetzel, P Vauclair, C Nguyen, QT Bouzerar, R Univ Caen Dept Genie Chim Lab Proc Mat Inst Univ Technol F-14032 Caen France

A simplified solution-diffusion model called total solvent volume fraction model is developed for the description of the permeant transport through highly selective membranes in pervaporation. It is based on the assumption that the diffusion coefficient is the product of a limit diffusivity and an analytic function depending only on the total volume fraction of all the solvent species in the membrane. The equations developed for binary liquid mixtures in the particular case where the analytical functions are the same for both permeant species were checked with the experimental data obtained from the pervaporation of water-ethanol mixtures through a PVA-based membrane. The three computed parameters obtained by fitting were successfully used to predict the variations of the partial fluxes with the downstream pressure, particularly the maximum in the ethanol flux, and the inversion of the membrane selectivity. The model appears to be also valid for a moderately selective membrane, the cellulose acetate membrane, in the pervaporation of water-ethanol mixtures. (C) 2004 Elsevier B.V. All rights reserved.

关键词： pervaporation dehydration solution-diffusion model PVA membrane downstream pressure

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Nonlinear parameter estimation for solution-diffusion models of membrane pervaporation

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ADVANCED MEMBRANE TECHNOLOGY 2003年第1期984卷 370-385页

作者： Cao, B Henson, MA Univ Massachusetts Dept Chem Engn Amherst MA 01003 USA Louisiana State Univ Dept Chem Engn Baton Rouge LA 70803 USA

An optimization-based procedure for estimating unknown parameters in solution-diffusion models of membrane pervaporation is presented. Permeation of two components through a polymer membrane is described by distinct solution and diffusion models. The solution model is based on a modified form of Flory-Huggins theory that accounts for interactions between the two penetrants. The diffusion model is derived from Fick's law, where the diffusion coefficients are allowed to depend on the local concentration of each component in the membrane. A phenomenologic relation is used to account for the effect of temperature on the component fluxes. The solution and diffusion models, as well as the temperature-flux relation, contain parameters that are not directly measurable. It is shown that these parameters can be estimated effectively from sorption and flux data by the solution of suitably formulated nonlinear optimization problems. The separation of styrene and ethylbenzene with a polyurethane membrane is used to illustrate the parameter estimation procedure.

关键词： pervaporation solution-diffusion model parameter estimation

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Polyurethane (PU) membrane preparation with and without hydroxypropyl-β-cyclodextrin and their pervaporation characteristics

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JOURNAL OF MEMBRANE SCIENCE 2003年第1-2期222卷 203-217页

作者： Lue, SJ Peng, SH Chang Gung Univ Dept Chem & Mat Engn Taoyuan 333 Taiwan

The objective of this research was to synthesize polyurethane (PU) membranes containing hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and investigate their pervaporation properties on benzene/cyclohexane (Bz/Cx) separation. PU membranes were synthesized from polypropylene oxide (PPO), 4,4-diphenylmethane diisocyanate (MDI), and 1,4-butanediol (BD) via a two-step polymerization process. The PU and CD/PU hybrid membranes were benzene-selective in nature. The membranes synthesized from lower molecular weight polyol (PPO1000) produced better results than the higher molecular weight polyol (PPO2000) analogue. The sorption selectivity of the membranes in binary mixtures was much higher than the sorption ratio of pure liquids. A competitive sorption mechanism was observed. Membranes containing HP-beta-CD yielded higher sorption selectivity due to greater Cx sorption suppression. Incorporating HP-beta-CD in the membrane also increased the Bz diffusivity inside the membrane. Thus, HP-beta-CD addition plays a two-fold benefit: enhancing the sorption selectivity and increasing the permeation flux on Bz/Cx mixtures. The CD/PU membrane demonstrated excellent Bz permeation flux (much higher flux compared with literature results) while maintaining good separation selectivity. (C) 2003 Elsevier B.V. All rights reserved.

关键词： benzene/cyclohexane pervaporation polyurethane (PU) membranes cyclodextrin solution-diffusion model

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Membrane permeation of a binary compound for co-current and cross flow modes

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DESALINATION 2000年第2期130卷 113-129页

作者： Basu, B Visvanathan, C Asian Inst Technol Environm Engn Program Klong Luang 12120 Pathumthani Thailand

This study reveals the behavior of air-sweep pervaporation in a mixture of two volatile organic compounds (VOCs) combination from a solution for two flow modes of operation, namely co-current and cross flow mode. Two models, single compound and binary compound permeation, were studied. Results indicated that the membrane shows a higher affinity for one of the compounds compared to the other. Higher affinity may have led to higher sorption and a higher permeability rate. The flux production in the cross flow mode is found to be higher than the co-current flow mode. However, selectivity is unaffected by the flow mode of operation. A study on the mutual coupling effect shows that, due to the presence of one compound, the flux of the other compound is reduced. The reduction in the flux production is found to be higher in the co-current flow mode than the cross flow mode, especially for a higher concentration of the interfering compound. The model study indicates that the transfer of the VOC through the bulk liquid phase to and sorption on the membrane surface is the rate-limiting step. A difference in the flux values from the experiments and that predicted by the binary compound permeation model is noted. The difference was found to be constant irrespective of the compound used. This may be mainly due to the flow mode of operation. To incorporate this effect and various other influencing effects, preliminary modification of the model is proposed in the form of an empirical constant.

关键词： pervaporation trichloroethylene 1,1,1-trichloroethane co-current flow mode cross flow mode air perstripping binary compound permeation solution-diffusion model resistance-in-series model

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Sodium cyanide separation and parameter estimation for reverse osmosis thin film composite polyamide membrane

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JOURNAL OF MEMBRANE SCIENCE 1999年第1期154卷 89-103页

作者： Murthy, ZVP Gupta, SK Indian Inst Technol Dept Chem Engn New Delhi 110016 India

Sodium cyanide separation data are obtained from synthetic binary aqueous solutions using a commercial thin film composite polyamide reverse osmosis membrane. The separation data are analyzed with the help of two membrane transport models, i.e., combined film theory-solution-diffusion (CFSD) model and combined film theory-Spiegler-Kedem (CFSK) model. The membrane transport parameters and mass transfer coefficients are estimated, simultaneously, from both the models, using a graphical method in case of CFSD model, and a nonlinear parameter estimation method for CFSK model. The new phenomena that there exists a maximum in rejection when it is plotted against product flux, which was observed previously using the same membrane for the phenol-water system, is observed in the present case too. This behavior is explained using the above said models. Though both the models predict the membrane performance reasonably, the values of CFSK model are more accurate and the mass transfer coefficients estimated from the CFSK model are comparable with the literature values. (C) 1999 Elsevier Science B.V. All rights reserved.

关键词： reverse osmosis maximum rejection solution-diffusion model Spiegler-Kedem model sodium cyanide separation

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