Modeling and analysis of vacuum membrane distillation for the recovery of volatile aroma compounds from black currant juice

A vacuum membrane distillation (VMD) model has been developed and validated with experimental data. The model consists of an extended transport model for the VMD process and is able to predict the effects of concentration and temperature polarization on the overall process performance. To validate the model, first it was tested with few experimental case studies from literature [S. Bandini, G.G. Sarti, Heat and mass transport resistances in vacuum membrane distillation per drop, AIChE J. 45 (7) (1999) 1422–1433; K.W. Lawson, D.R. Lloyd, Membrane distillation. I. Module design and performance evaluation using vacuum membrane distillation, J. Membr. Sci. 120 (1996) 111–121; A.M. Urtiaga, G. Ruiz, I. Ortiz, Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions, J. Membr. Sci. 165 (2000) 99–110]. Then the VMD model has been validated with experimental data collected from the recovery of aroma compounds from black currant [R.B. Jørgensen, A.S. Meyer, C. Varming, G. Jonsson, Recovery of volatile aroma compounds from black currant juice by vacuum membrane distillation, J. Food Eng. 64 (2004) 23–31]. In this work, recovery of 12 characteristic volatile aroma compounds from black currant juice has been studied. The simulated results from the VMD model, in terms of aroma concentration in the permeate have been compared with those obtained from laboratory experiments. The validated model has been used to study the effects of various process and membrane parameters on the concentration factor. The physical properties of various aroma compounds have been predicted using group contribution method as a function of temperature.     

Factors affecting flux and ethanol separation performance in vacuum membrane distillation (VMD)

Membrane distillation (MD) has a great potential as a concentration process for temperature labile liquids such as fruit juices, etc. Besides water, also aroma compounds will permeate through the membrane depending on their volatility and how the MD process is operated on the permeate side.In this paper, an experimental and theoretical investigation of the influence of concentration polarisation and temperature polarisation on the flux and selectivity of binary aqueous mixtures of ethanol is presented for vacuum membrane distillation (VMD) processes. Experimental results include changes of the following parameters: nature of solutions, membrane material and pore size, feed temperature, recirculation flow rate. One method was proposed in order to evaluate the concentration polarisation effects from the fit of the experimental data. General models taking into account Knudsen and viscous flows were proposed, but viscous contribution resulted to be negligible under our operating conditions. Therefore, theoretical fluxes were estimated using Knudsen model and a good agreement between them and the experimental ones was found.     

Mathematical modeling of silver extraction by an emulsion liquid membrane process

A general physical model of a typical batch extraction system employing an emulsion liquid membrane process for the extraction of silver has been developed. The model takes into account the extraction reaction between the silver ion and the carrier molecules at the external interface, the diffusion of the complex in the membrane phase, the stripping reaction at the internal interface and the reaction of silver ion with the reagent, HCL, in the internal phase to yield silver chloride incapable of permeating through the membrane phase. In addition, the leakage of the internal aqueous phase to the external aqueous phase due to membrane breakage has been incorporated in this model. The batch extraction of silver using D2EHPA as a carrier has been carried out under various experimental conditions. The experimental data can be well explained by the present model.     

新型复合膜优先透醇性能的研究

有机物优先透过膜不仅可以用于有机物的浓缩和回收,还可以用于污水的净化等,因而有机物优先透过型渗透蒸发膜的研究倍受重视^[1].但由于透醇型膜的研究起步较晚,以及膜材料选择和膜制备等诸多原因,致使透醇膜的研究进展缓慢.     

Carrier-facilitated liquid membrane extraction of penicillin G from aqueous streams

Kinetics and mechanism for the carrier-facilitated transport of penicillin G from aqueous solutions through a supported liquid membrane containing Amberlite LA-2 were investigated. The strip phase was either phosphate buffer or sodium carbonate solution. Experiments were performed as a function of the pH, the concentrations of penicillin G in the feed phase and of amine in the membrane phase. A transport model was proposed considering aqueous film diffusion, interfacial chemical reaction, and membrane diffusion. The calculated rates were found to agree with the measured ones (average standard error, 12%). Under the conditions investigated (feed pH 5.02–7.83, penicillin G concentration 10–500 mol/m³, amine concentration 50–1000 mol/m³), the present transport process was shown to be governed by combined interfacial chemical reaction and membrane diffusion.     

Comparison of carrier-facilitated copper(II) ion transport mechanisms in a supported liquid membrane and in a plasticized cellulose triacetate membrane

Transport of copper ions through a plasticized cellulose triacetate membrane containing lauric acid as carrier and tris(2-ethylhexyl)phosphate (TEHP) as plasticizer has been investigated. A comparative study of transport mechanism across such a membrane and a supported liquid membrane (SLM) containing the same carrier in THEP has been made. In both cases, transport mechanisms were controlled by the diffusion of 1:2 metal/carrier complex in the membrane and of copper ions through the aqueous diffusion layer at the source/membrane interface. Diffusion coefficient in the cellulose triacetate membrane, after normalization, was found to be 22 times lower than in the corresponding SLM.     

Ultrafiltration of BSA in pulsating conditions: an artificial neural networks approach

The aim of the present paper is to analyze membrane systems behavior, operating in pulsating conditions, by means of artificial neural networks (ANNs). Different ANNs have been developed, by means of Matlab^® Neural Network Toolbox, to model the ultrafiltration process of aqueous BSA solutions through poly-ethersulfone membranes. A specific neural network architecture, constituted by one input layer, two hidden layers and one output layer, has been finally identified by a trial-and-error procedure. The network has been trained through a selected set of experimental data obtained for a lab-scale flat sheet membrane module, equipped with a device capable of producing periodic pulses of the applied trans-membrane pressure (TMP) and feed flow rate. It has been found that the developed neural network is capable of offering very accurate predictions of actual system behavior either when it is tested within the range used for training or when the inputs combination has been never exploited during learning phase. The observed reliability of neural networks predictions of membrane performances has suggested to use them for searching an optimal pulsation frequency profile able to maximize permeate flux. The utilization of such a pulse frequency profile allows obtaining, on the basis of theoretical evaluations only, significant improvements of membrane performances with respect to UF experiments performed at fixed and constant pulsation frequencies.     

Erythrocyte membrane permeability for a series of diols

Erythrocyte membrane permeability coefficients for a series of diols have been defined by the method developed. The method is based on the physical and mathematical modeling of hypotonic hemolysis process. There have been also determined membrane permeability coefficients for erythrocytes treated with p-chloromercuribenzenesulfonic acid monosodium salt (pCMBS), which is known to block aqueous protein channels. Permeating process is shown to be conditioned both by hydrophilic/hydrophobic properties of the molecules and their geometrical parameters. The obtained results propose that, when exceeding the molecules diameter over a value of 4 A, the permeability coefficient reduces due to decreasing of flow through the aqueous protein pores of a constant size. Permeability coefficients for comparatively hydrophobic molecules are almost directly proportional to the coefficients of partition between hydrophobic and hydrophilic phases, by pointing to a lipid way of permeation of these molecules through erythrocyte membranes.     

Mechanism of nitromethane liquid membrane oscillator containing sodium oleate

The oscillatory behavior of a liquid membrane oscillator with anionic surfactant was investigated in order to understand the oscillation mechanism at the molecular level. As a theoretical framework, an approach based on chemical kinetics laws has been used. The chosen system involved nitromethane with 2,2(')-bipyridine as liquid membrane. The aqueous donor phase contained sodium oleate and butanol, while sodium chloride was added to the aqueous acceptor phase. It was established that the oscillations take place exclusively at the aqueous acceptor phase/membrane interface. Therefore, liquid membrane oscillators with anionic surfactants behave the same way as oscillators with cationic surfactants as to the location of oscillations. An oscillation mechanism involving three stages is proposed and confirmed by numerical simulations. The oscillations of electrical potential differences between the two aqueous phases are produced by sudden adsorption and desorption of anionic surfactant in solvated form and butanol at the acceptor/membrane interface. The whole process is controlled by the slow diffusion of these species across the liquid membrane. The chaotic character of the oscillations was demonstrated by Lyapunov exponents obtained from the strange attractor of the system.     

Coupled zinc transport through a bis(2-ethylhexyl)phosphoric acid solid-supported liquid membrane from aqueous perchlorate media

The rate of Zn(II) transport from 1.0 M (Na,H)ClO₄ aqueous media through a liquid membrane consisting of bis(2-ethylhexyl)phosphoric acid (HDEHP, HR) dissolved in Isopar-H and a teflon-type solid support, has been investigated as a function of the chemical composition of the system and the hydrodynamic conditions at 25°C. The measured transfer rates have been explained in terms of aqueous diffusion, diffusion of ZnR₂(HR)₂ and ZnR₂(HR) species through the liquid membrane and the rate of chemical reactions of Zn(II) in this system. The results are in agreement with the kinetic and equilibrium models proposed for this sytem in previous studies.     

Separation of aqueous organic mixtures by pervaporation and analysis by mass spectrometry or a coupled gas chromatograph—mass spectrometer

A method of analysis has been developed based on the use of selective membranes which gives the possibility of enriching, identifying and quickly analysing organic volatile compounds in dilute aqueous solution. The process used to separate water from organic products is pervaporation. p]One side of the selective membrane is in contact with the liquid mixture. The other side of the membrane, under vacuum, is directly connected with the ionization source of a mass spectrometer which analyses quantitatively and qualitatively the organic compounds in proportion as they pass through the membrane. p]A number of different pervaporation membranes were studied and the selectivity of the membranes to different aqueous mixtures has been measured. Four types of analytical applications are described.     

Sorption and pervaporation of dilute aqueous solutions of organic compounds through polymer membranes

Pervaporation of dilute aqueous binary mixtures of four organic compounds (benzene, chloroform, acetone and ethanol) through nitrile—butadiene and styrene—butadiene copolymers was investigated. A pervaporation device has been built, which allows measurement of the pervaporation flux and selectivity of a membrane as a function of the upstream composition of the feed and the downstream total pressure of the pervaporate. In order to relate pervaporation results to equilibrium properties of the membranes, the sorption of water and dilute aqueous solutions was mainly investigated. The pervaporation of dilute aqueous solutions of benzene and chloroform has been extensively studied, including the separation of traces of chloroform, and is modelled through a “sixcoefficients exponential model” [1]. This model is derived from a solution—diffusion analysis of the selective transfer, assuming an exponential dependence of both diffusivities on concentrations of both permeants. Semi-quantitative information about the potential interactions existing in the system solute i—solvent j—membrane and about the concentration profiles at steady-state may be derived from these coefficients.     

Selective Separation of Uranium(VI), Thorium(IV), and Lanthanum(III) from Their Aqueous Solutions using a Chelating Resin Containing Amine Functionality

A glycidyl methacrylate/divinylbenzene resin containing triethylenetetramine functional group was synthesized. The adsorption behavior of the obtained resin toward U(VI), Th(IV), and La(III) in aqueous solutions was investigated by batch and column techniques at different experimental conditions. Kinetic and thermodynamic characteristics of the adsorption process have been investigated. The regeneration of the loaded resin was also studied.     

Kinetics of americium(VI) mass transfer through solid supported liquid membrane with HDEHP

The main regularities of membrane extraction of americium under conditions of different redox potentials in aqueous phases have been studied. The physico-chemical model of the process including steps of americium oxidation in feed solution, extraction by membrane, partial reduction on membrane surface, trans-membrane diffusion and reextraction to strip solution has been developed. The calculation of reduction rate constant on membrane surface has been carried out.     

Selective membrane test for crude oil based model emulsions by use of video-enhanced microscopy

 A method for testing water/oil emulsion droplet membranes selectively has been demonstrated. The method uses electric fields to induce attraction, membrane thinning and coalescence between aqueous droplets deposited in an oil continuum. The coalescence process is monitored visually by the use of videomicroscopy. A set of model oils containing indigenous surfactants (asphaltenes) from a crude oil has been studied, and the effects of asphaltene concentration, oil phase aromaticity, aging of oils and interfacial exposure time have been investigated. The strength of the field at the point of coalescence is defined as the critical parameter describing membrane strength. In the current experiments a.c. fields were used and droplet sizes were of the order of 500–600 μm. Received: 8 October 1998 Accepted in revised form: 11 January 1999     

Interfacial polycondensation—Modeling of kinetics and film properties

Interfacial polycondensation (IP) is an important technique used in the encapsulation of a variety of active ingredients and synthesis of thin film composite membranes. The present work seeks to advance our understanding of the mechanisms underlying the reaction, phase separation and film formation in this process, and hence, of how the film properties are influenced by preparation conditions. The model presented here incorporates all the essential physicochemical processes at a fundamental level through simple phenomenologies: ionic equilibria in the aqueous phase, resistances due to external mass transfer, diffusion through polymer film, interfacial reaction, thermodynamics of phase separation, and formation of a coherent film. The model has been tested against the data previously communicated [S.J. Wagh, Studies in interfacial polycondensation. Ph.D. Thesis. IIT Bombay, 2004; S.J. Wagh, S.S. Dhumal, A.K. Suresh, An experimental study of polyurea membrane formation by interfacial polycondensation, Journal of Membrane Science, submitted for publication] on polyurea microcapsules. The influence of the model parameters and preparation conditions, on the properties of the polymer and film and their development during reaction, have been studied. The study provides important insights into the process and should help in designing synthesis methodologies to suit the application.     

Carrier‐Mediated Transport of Hg(II) through Bulk and Supported Liquid Membranes

The transport of Hg (II) ions from an aqueous solution into an aqueous receiving solution through bulk and supported liquid membranes containing a calix[4]arene derivative 1 as a carrier was examined. The kinetic parameters of bulk liquid membrane studies were analyzed assuming two consecutive, irreversible first‐order reactions. The influence of temperature, stirring rate, carrier concentration and solvent on the kinetic parameters (k₁, k₂, R_m ^max, t_max, J_d ^max, J_a ^max) has also been investigated. The membrane entrance rate, k₁, and the membrane exit rate, k₂, increased with increasing temperature and stirring rate. The activation energy values are calculated as 4.87 and 48.63 kj mol^?1 for extraction and reextraction, respectively. The values of calculated activation energy indicate that the process is diffusionally controlled by species. Also, the transport behavior of Hg²⁺ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivative 1 as carrier and Celgard 2500 as the solid support. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene.     

Nitrate removal of drinking water by means of catalytically active membranes

The reduction of nitrate to nitrogen in aqueous solutions by means of catalytically active membranes has been investigated. A heterogeneous catalyst (Pd/Cu) has been incorporated in a microporous polyetherimide membrane. After saturation with hydrogen nitrate containing water was filtered through these membranes. The nitrate reduction was studied as a function of pH, volume flow and temperature. It could be demonstrated that the catalyst remained active in the polymer matrix. The calculated activation energy for nitrate reduction is indicating that the reaction is dominated by mass transfer and diffusion.     

Permselectivity, solubility and diffusivity of propyl propionate/water mixtures in poly(ether block amide) membranes

This work is concerned with the separation of propyl propionate/water mixtures by pervaporation using PEBA membranes, which is relevant to aroma compound recovery from dilute aqueous solutions. The solubility and diffusivity pertinent to the permselectivity were investigated. The effects of feed concentration and the operating temperature on the separation performance were studied. Under the experimental conditions tested, the permeate concentration was much higher than the solubility limit, and upon phase separation substantially pure propyl propionate could be achieved. The diffusivity of propyl propionate through the membrane from its dilute aqueous solutions was affected by the solution concentration exponentially. It was shown that the permselectivity of the membrane for propyl propionate/water separation was mainly derived from its sorption selectivity due to the organophilicity of the membrane. The diffusivity of pure propyl propionate in the membrane was about 28 times higher than pure water diffusivity.     

Induction time in metal permeation processes through supported liquid membranes

The origin of the induction time observed in the permeation process of cadmium species through trilaurylammonium chloride in triethylbenzene supported liquid membranes is discussed. A model for the non-steady state transference process, where aqueous film diffusion coupled to an interfacial chemical reaction are the main rate determining processes, was developed. By comparison with experimental transference data, the rate constant of the interfacial reaction between cadmium chloride aqueous complexes and the membrane carrier, trilaurylammonium chloride, was evaluated. The time evolution of the concentration profiles through the aqueous diffusion film is also described.