Liquid Membrane Module Research Articles

Conjugated Mass Transfer of CO2 Absorption through Concentric Circular Gas–Liquid Membrane Contactors

A new design of gas absorption that winds the permeable membrane onto an inner concentric tube to conduct a concentric circular gas–liquid membrane module has been studied theoretically in the fully developed region. An analytical formulation, referred to as conjugated Graetz problems, is developed to predict the concentration distribution and Sherwood numbers for the absorbent fluid flowing in the shell side and CO2/N2 gas mixture flowing in the tube side under various designs and operating parameters. The analytical solutions to the CO2 absorption efficiency were developed by using a two-dimensional mathematical modeling, and the resultant conjugated partial differential equations were solved analytically using the method of separation variables and eigen-function expansion in terms of power series. The predictions of CO2 absorption rate by using Monoethanolamide (MEA) solution in concentric circular membrane contactors under both concurrent- and countercurrent-flow operations are developed theoretically and confirmed with the experimental results. Consistency in both a good qualitative and quantitative sense is achieved between the theoretical predictions and experimental results. The advantage of the present mathematical treatment provides a concise expression for the chemical absorption of CO2 by MEA solution to calculate the absorption rate, absorption efficiency, and average Sherwood number. The concentration profiles with the mass-transfer Graetz number, inlet CO2 concentration, and both gas feed and absorbent flow rates are also emphasized. Both theoretical predictions and experimental results show that the device performance of the countercurrent-flow operation is better than that of the concurrent-flow device operation. The availability of such simplified expressions of the absorption rate and averaged Sherwood as developed directly from the analytical solutions is the value of the present study.

3D Printed Microfluidic Supported Liquid Membrane Module for Radionuclide Separations

Microfluidic supported liquid membrane extraction is a promising technique for microliter-scale radionuclide separations because it requires very small reagent volumes and combines extraction and s...

Augmenting CO2 Absorption Flux through a Gas-Liquid Membrane Module by Inserting Carbon-Fiber Spacers.

We investigated the insertion of eddy promoters into a parallel-plate gas–liquid polytetrafluoroethylene (PTFE) membrane contactor to effectively enhance carbon dioxide absorption through aqueous amine solutions (monoethanolamide—MEA). In this study, a theoretical model was established and experimental work was performed to predict and to compare carbon dioxide absorption efficiency under concurrent- and countercurrent-flow operations for various MEA feed flow rates, inlet CO2 concentrations, and channel design conditions. A Sherwood number’s correlated expression was formulated, incorporating experimental data to estimate the mass transfer coefficient of the CO2 absorption in MEA flowing through a PTFE membrane. Theoretical predictions were calculated and validated through experimental data for the augmented CO2 absorption efficiency by inserting carbon-fiber spacers as an eddy promoter to reduce the concentration polarization effect. The study determined that a higher MEA feed rate, a lower feed CO2 concentration, and wider carbon-fiber spacers resulted in a higher CO2 absorption rate for concurrent- and countercurrent-flow operations. A maximum of 80% CO2 absorption efficiency enhancement was found in the device by inserting carbon-fiber spacers, as compared to that in the empty channel device. The overall CO2 absorption rate was higher for countercurrent operation than that for concurrent operation. We evaluated the effectiveness of power utilization in augmenting the CO2 absorption rate by inserting carbon-fiber spacers in the MEA feed channel and concluded that the higher the flow rate, the lower the power utilization’s effectiveness. Therefore, to increase the CO2 absorption flux, widening carbon-fiber spacers was determined to be more effective than increasing the MEA feed flow rate.

Membrane-assisted enrichment of zinc(II) from and into ammoniacal media through non-dispersive synergistic extraction

Abstract The enrichment of zinc(II) in ammoniacal media with non-dispersive synergistic extraction (NDSX) was achieved in a sandwich-supported liquid membrane module, in which a mixed extractant containing 4-ethyl-1-phenyl-1,3-octadione (HA) and trioctylphosphine oxide (TOPO) was used as the carrier. Several parameters of Zn(II) transport, including carrier concentration, diluent type, feed pH, total ammonia concentration, and temperature, were systematically investigated. The results showed that the mixing of TOPO with HA can effectively improve the Zn(II) enrichment from and into ammoniacal solutions. The transport efficiency of zinc increases with increasing carrier concentration and temperature. Moreover, Zn(II) transport is dependent on the total ammonia concentration and solution pH of the feed phase. The nonpolar n-octane is more beneficial to zinc transport than the polar octanol. Five successive transports exhibit excellent membrane stability and the effective uphill transport of zinc from and into ammoniacal media with NDSX.

Studies on yttrium permeation through hollow fibre supported liquid membrane from nitrate medium using di-nonyl phenyl phosphoric acid as the carrier phase

The transport behaviour of yttrium from nitrate medium was investigated using dinonyl phenyl phosphoric acid (DNPPA) as a carrier in liquid membrane phase, employing microporous hydrophobic hollow fibre supported liquid membrane (HFSLM) module. The influence of feed composition, carrier concentration, feed acidity, strip acid concentration and flow rate of feed on permeability and flux of Y(III) is discussed. The stripping solution was sulphuric acid solution. Increasing the carrier concentration increased the % transport of yttrium, while an increase in the feed metal concentration decreased the percentage transport. A lower acidity in the feed solution and 3M H2SO4 concentration in the stripping phase are favourable for the transport process due to the increase of mass transfer driving forces. The % transport of yttrium increased with an increase in flow rates up to 100mL/min. Under optimized conditions of 0.2M DNPPA, 1g/L Y(III), 0.05M feed acidity, 3M strip acid (H2SO4) and 100mL/min flow rate, the % transport of yttrium was more than 95% in 5h of operation.

Separation of medicinal catechins from tea leaves (Camellia sinensis) extract using hollow fiber supported liquid membrane (HF-SLM) module

Catechins have been recovered in medicinal grade ethanol from tea leaves through hollow fiber supported liquid membrane (HF-SLM) module. In the first phase, synthetic solution of single catechin compound has been used for experimentation to optimize operating conditions. The tests with real extract of green tea leaves followed in the second phase with the similar operating conditions as optimized in the first phase. Tributyl phosphate (or TBP) as a carrier component dissolved in solvent n-decane was used as liquid membrane (LM). Ethanol was found to be ideal strippant of catechins. The flow rates of feed/strip streams and differential pressures across the membrane surfaces were optimized for achieving a stable liquid membrane. The established models for the solute transportation in LM, as found in various literatures, were revisited to explain the experimental results. Preliminary suggestions for the once-through transportation of catechins have also been provided for possible application in a pilot-plant.

Dehumidification and humidification of air by surface-soaked liquid membrane module with triethylene glycol

A novel liquid membrane system, a surface-soaked liquid membrane, with triethylene glycol (TEG) on the hydrophilic-treated surface of the hydrophobic microporous membrane was developed and used for the dehumidification and humidification of air. The selectivity of the TEG liquid membrane for water vapor with respect to air was over 2000, which was derived from the selective absorption of the TEG liquid. A flat-type liquid membrane module with a dual membrane surface was designed, of which the TEG liquid membrane thickness was 18 μm and the permeation area was 0.13 m 2. The liquid membrane humidifier and dehumidifier consisted of the membrane module and a vacuum pump. As a dehumidifier, the membrane system recovered water vapor at 4.1 g/h from 70%RH room air at 298 K. For use as a humidifier, the air flow was effectively humidified by the permeated water vapor through the membrane module. The effects of the air humidity and sweep air flow rate were studied and discussed. Simple model calculations based on the permeability of the water vapor well predicted the experimental results.

Multivariate Analysis of Selected Metal Ion Transport through a Hollow‐Fiber Supported Liquid Membrane Device used for Passive Sampling Monitoring

A hollow fiber supported liquid membrane module using one single fiber impregnated with a mixture of 1,10‐dibenzyl‐1,10‐diaza‐18‐crown‐6 and bis(2‐ethylhexyl)phosphate dissolved in hexylbenzene was used for passive sampling of ppb levels of Pb(II), Cu(II), Zn(II), Mn(II), Ni(II), and Cd(II) in water. The target ions were simultaneously transported and preconcentrated into a citric acid acceptor solution within the lumen of the hollow fiber with enrichment factors between 5 and 4000 times. A multivariate analysis of several physical and chemical parameters that affect transport was performed. Under conditions of constant concentration profiles a more robust performance of the device was observed.

CO 2 transfer in an aqueous potassium carbonate liquid membrane module with dense polymeric supporting layers: Influence of concentration, circulation flow rate and temperature

Gas–liquid separation systems have already received considerable attention in a great number of situations of industrial interest. The attention paid to membrane contactors and immobilized liquid membranes have recently increased due to their separation performances. For the sake of simplicity, most experiments are usually performed at room temperature. It is, however, obvious that increasing the temperature would increase the reaction rate and thereby also possibly enhance the system's productivity. This work presents a systematic study of CO 2 and H 2 transport in a novel flowing liquid membrane (FLM) module with dense membranes separating layers and aqueous potassium carbonate (concentration 0.1–3 kmol/m 3) solutions in the temperature range 295–353 K. A model of CO 2 transport with reversible chemical reactions through the FLM was developed and compared to a series of experimental data. It was found that increasing the concentration of potassium carbonate as well as the temperature led to large increases in both the CO 2 productivity and the CO 2/H 2 selectivity. The industrial implications of these observations were discussed. Unsteady state transport of CO 2 was also investigated and a simple model of gas transfer in the FLM with physical absorption in the liquid phase was developed.

Facilitated transport of organic acid through a supported liquid membrane with a carrier

The transport rates of citric acid (HA) in supported liquid membrane module containing a carrier of tri-n-octylamine (TOA) were measured using a batch type, and a simple model (HA + TOA ↔ complex) was applied to investigate the mass transfer mechanism of HA with TOA. The measured values of the forward- and backward-reaction rate constant in the reversible reaction between HA and TOA were used to simulate the model with the mass conservation equation and associated boundary conditions. Comparison between the experimental and simulated facilitated factor of HA transport led to classification of reaction regions.

Chromium(VI) removal in a semi-continuous process of hollow fiber membrane with organic extractants

Chromium(VI) extraction from aqueous metal solution was experimentally studied by using a hollow fiber supported liquid membrane module. Organic extractants of D2EHPA, TBP, Lix79 and TOA were used to investigate the extraction performance. The extraction efficiencies of single and multiple component systems were examined with single or multiple extractants, and the role of multiple extraction operations and the difference between batch and continuous processes were inspected to find the optimum extraction condition. The experimental outcome indicates that the extraction process is controlled by aqueous phase mass transfer and multiple extraction operations do not reduce the extraction efficiency. The coexisting elements give no significant effect on chromium removal, while the mixed extractants of D2EHPA and TBP enhance the extraction efficiency by 84%. The efficiencies of batch and continuous extraction processes are nearly identical.

Braided silicone rubber membranes for organic extraction from aqueous solutions: II. Application to contained liquid membranes

Aqueous–aqueous extraction experiments were performed in a double tube mass exchanger (DTMEx) in order to investigate mass transfer characteristics of steel-braided non-porous membranes in a contained liquid membrane (CLM) module. Toluene was the permeating molecule, polydimethylsiloxane (PDMS) and ethylene propylene diene monomer (EPDM), were used as non-porous membrane materials, and silicone oil and polypropylene glycol (PPG) as liquid membranes. The liquid membrane contribution to the overall mass transfer resistance was assessed for different module configurations (e.g. varying membrane separation distance) and operating modes (e.g. stationary and mobile liquid membrane). The liquid membrane was found to be the dominant resistance when the module was operated with a stationary liquid membrane, a large separation distance between the braided membranes, and non-porous membranes with high affinity for the permeating molecules. When the liquid membrane was circulated through the module this resistance became negligible compared to the cumulative resistances in the aqueous hydrodynamic boundary layers (HBLs) and membrane at the feed and extractive side, resulting in overall mass transfer coefficients (OMTCs) up to 2.7×10 −5 m s −1. CLMs with braided membranes and mobile liquid membrane may therefore be advantageously used for aqueous–aqueous separation of hydrophobic molecules in modules operating with high liquid velocity in the membrane tubes.

FACILITATED TRANSPORT OF CR(VI) THROUGH A SUPPORTED LIQUID MEMBRANE WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE AS A CARRIER

This paper has applied a simple model (H2CrO4 + Aliquat 336 ↔ complex) to the mass transfer mechanism of Cr(VI) with Aliquat 336 in a batch-type, supported liquid membrane module. Concentrations at pH 3 are as follows: 0.019 kmol/m3 ≤ Aliquat 336 ≤ 0.035 kmol/m3 and 20 g/m3 ≤ Cr (VI) ≤ 500 g/m3. The measured values of forward- and backward-reaction rate constants between Cr(VI) and Aliquat 336 were used to simulate the model with the mass conservation equation and associated boundary conditions. Comparison between the experimental and simulated facilitated factors of Cr(VI) transport led to classification of reaction regions.

Mass transfer in supported liquid membranes: A rigorous model

A rigorous steady-state model for the facilitated solute transport across ceramic-tube-supported liquid membranes is presented. The proposed permeation model accounts for the effect of the variation of the distribution coefficient, as well as nonconstant solute concentration in the strip phase and nonequilibrium interfacial reactions. The resulting convection-diffusion transport equations form a set of boundary-coupled partial differential equations. As a case system taken from hydrometallurgy, the extraction of copper using ceramic tubes impregnated with LIX-84 as a carrier is considered. It is shown that the variation of the distribution coefficient is a factor that must be considered when designing or analyzing the performance of supported liquid membrane modules. The model is also used to examine the effect of key operating conditions on the module's performance.

Lipase-facilitated separation of organic acids in a hollow fiber contained liquid membrane module

A lipase-facilitated selective and continuous separation of difficult-to-separate mixtures of organic acids has been developed in a hollow fiber contained liquid membrane (HFCLM) device. The device consists of a well-mixed two-fiber-set hydrophobic microporous polypropylene hollow fiber membrane module where lipase from Candida rugosa (CRL) and lipase from porcine pancreas (PPL) were immobilized on the internal diameter of two identical sets of hollow fibers, respectively. The module shell side contained 20 v/v% octanol in n-heptane acting as the organic liquid membrane between the two commingled fiber sets. Two systems of model acid mixtures were selected to demonstrate this technique: (1) phenylacetic acid (PAA) and mandelic acids (MAs); (2) PAA and 6-aminopenicillanic acid (6-APA). Aqueous feed solution containing the acid mixtures and ethanol flowed through one fiber set; a stripping aqueous solution flowed through the second fiber set and was highly enriched in PAA. The separation factors of PAA over MAs and PAA over 6-APA were as high as 20 and 10, respectively. The esterification kinetics of PAA and ethanol catalyzed by CRL in batch experiment yielded V max and K m′ values to be 0.139 mmol/(h(mmol) CRL) and 62.2 mM, respectively. Much higher enzyme activities and enzyme stability were achieved in the HFCLM device due to immobilization of the lipases on the hydrophobic membrane surface where the organic–aqueous interface was immobilized and the ester produced was simultaneously transferred into the organic liquid membrane. The transport rate of PAA in the HFCLM device was 224 times higher than the V max measured in batch experiments.

Control of membrane-attached biofilms in extractive membrane bioreactors

Control of Membrane Attached Biofilm (MAB) formation and accumulation is a key aspect in the operation of Extractive Membrane Bioreactors (EMBs). In this work, MAB control was attempted in a novel EMB configuration which presents two innovative aspects: the presence of a biphasic biomedium and a contained liquid membrane module. This reactor, where the benefits of high shear forces and the use of a biphasic biomedium are effectively combined, was operated without any biofilm formation or reduction in organic substrate flux over time.

Effect of Recycling of Feed Solution on the Efficiency of Supported Liquid Membrane Module

Abstract The effect of recycling of a feed solution from the outlet to the inlet of the feed channel of a plate-and-frame type supported liquid membrane module on the recovery of zinc was investigated under the condition that the feed side mass transfer resistance is predominant. Di(2-ethylhexyl)phosphoric acid was used as the carrier. It was found that at a given feed flow rate, recycling of the feed solution is effective for improving the recovery of zinc since recycling brings about an increase of the flow rate in the feed channel and also the mass transfer coefficient in the feed side. The experimental data could be satisfactorily simulated by a proposed theoretical model.

Separation of gallium and indium by supported liquid membranes containing 2-bromodecanoic acid as carrier: design of supported liquid membrane module based on batch permeation experiments

The recovery of gallium and indium from sulfate media by supported liquid membranes containing 2-bromodecanoic acid (2-BDA) as a carrier was performed by using both a batch type stirred permeation cell and a continuous-type supported liquid membrane module with flat geometry. The effect of various experimental conditions on the permeation rates of gallium and indium were studied. A simple method is proposed for designing continuous supported liquid membrane modules from the data obtained with the batch type permeation cell on the basis of the correspondence of the parameters in batch operation to those of continuous operation. By this method, the membrane area required for given feed flow rate and the percentage recovery can be easily determined even for the case of multi-component separation.

Internal mass transfer in hollow fiber supported liquid membranes

The study of mass transfer in hollow fiber supported liquid membranes is justified by a large number of separation processes. The analysis starts from the definition of an overall permeability coefficient which is a lumped parameter of a particular system and process conditions which gathers both mass transfer and operation parameters. By applying the film theory the contribution of the interfacial mass-transfer coefficient due to the inner boundary layer and the contribution of the supported liquid membrane permeability coefficient can be separated and analyzed. The study yields overall permeability coefficients that can be compared with those expected from hollow fiber design equations suggested earlier. The second approach considers the continuity mass conservation equation and the associated boundary conditions for the solute in the inner fluid. The analysis by means of the fundamental equations separates the effects of the operation variables such as the hydrodynamic conditions and length and diameter of the fibers from the mass-transfer properties of the system, described by the wall Sherwood number. The scope of the present work is to compare both methods of describing a hollow fiber supported liquid membrane module, analyzing the influence of the internal mass transfer on the design of such systems. Inmore » the experimental system under consideration, the simultaneous separation-concentration of phenol from aqueous solutions with hollow fiber supported liquid membrane modules is performed. The influence of the flow rate of the inner aqueous phase on the phenol separation rate has been studied.« less

Development of a Spiral-Type Flowing Liquid Membrane Module with High Stability and Its Application to the Recovery of Chromium and Zinc

Abstract A new type of liquid membrane named a “flowing liquid membrane” is proposed. In this type of liquid membrane, a liquid membrane solution containing a carrier flows in thin channels between two hydrophobic micro-porous membranes which separate the membrane solution from a feed and a strip solution, and forms a stable liquid membrane. The flowing liquid membrane was made into a spiral-type module, and experiments on the separation and enrichment of Cr(VI) in aqueous solutions were performed with the flowing membrane module using tri-n-octylamine as the carrier. It was found that this type of module has high stability as well as high performance, and Cr(VI) was successfully removed and concentrated from its dilute solutions. The result on the recovery of zinc using di(2-ethylhexyl)phosphoric acid as the carrier is also presented.