Hollow Fiber Contained Liquid Membrane Research Articles

Facilitated transport of CO 2 across a liquid membrane: Comparing enzyme, amine, and alkaline

In this work we compare the efficiency of facilitated transport of CO 2 across a liquid membrane by different facilitators as tested in either a supported liquid membrane (SLM) or a hollow fiber contained liquid membrane (HFCLM) configuration. Permeance and selectivity were evaluated by both experimental test and numerical simulation. These comparisons were used to define the best liquid membrane composition to maximize separation performance. We also consider other factors that affect the choice of the facilitator, e.g. operation temperature and cost. Under ambient operating conditions, carbonic anhydrase (CA) combined with an alkaline carbonate gives better performance than does diethanolamine (DEA).

Modeling CO 2-facilitated transport across a diethanolamine liquid membrane

We compared experimental and model data for the facilitated transport of CO 2 from a CO 2–air mixture across an aqueous solution of diethanolamine (DEA) via a hollow fiber, contained liquid membrane (HFCLM) permeator. A two-step carbamate formation model was devised to analyze the data instead of the one-step mechanism used by previous investigators. The effects of DEA concentration, liquid membrane thickness and feed CO 2 concentration were also studied. With a 20% (wt) DEA liquid membrane and feed of 15% CO 2 in CO 2–air mixture at atmosphere pressure, the permeance reached 1.51E−8 mol/m 2 s Pa with a CO 2/N 2 selectivity of 115. Model predictions compared well with the experimental results at CO 2 concentrations of industrial importance. Short-term stability of the HFCLM permeator performance was examined. The system was stable during 5-days of testing.

NONDISPERSIVE LIQUID-LIQUID EXTRACTION OF Zn(II), Cu(II), Co(II), AND Cd(II) FROM DILUTE SOLUTION WITH DEHPA IN A HOLLOW-FIBER MEMBRANE MODULE

The ability to concentrate dilute aqueous solutions containing metals is desirable both from the standpoint of waste volume reduction and increased ease of concentration measurement. The first challenge in designing a liquid-liquid extraction (LLE) system to concentrate metals is to find an organic system that can be used to simultaneously remove a number of metals. The goal of this work was to find a LLE system that extracts zinc, copper, cadmium and cobalt simultaneously. In the LLE extraction experiments, nearly 100% extraction of all four metals (Zn(II), Cu(II), Cd(II) and Co(II) at about 25 ppm initially) was achieved when all of them were extracted simultaneously using 0.3 mol/L DEHPA in n-heptane. The extraction order observed as the pH of the aqueous solution increased was Zn(II) > Co(II) > Cu(II) > Cd(II). Based on these results, a polysulfone Hollow Fiber Contained Liquid Membrane (HFCLM) system was designed and operated to study the nonequilibrium extraction of all four metals via nondispersive LLE. The aqueous and organic streams were operated at 100% recycle. Interference effects between the four metal ions are discussed.

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.

Hollow fiber contained liquid membrane pervaporation system for the removal of toxic volatile organics from wastewater

A novel configuration of a hollow fiber contained liquid membrane (HFCLM) pervaporation system was used to separate organic solutes such as trichloroethylene and toluene from water. In this system the highly selective organic liquid membrane is contained in the shell side between two sets of hollow fibers packed in a shell-and-tube heat exchanger arrangement. Wastewater is fed into one set of hollow fibers and vacuum is applied in the other set of hollow fibers. The separation factors and solute recoveries for the HFCLM system were higher and water fluxes lower than in a conventional pervaporation system based on silicone rubber with vacuum applied outside the silicone rubber hollow fibers. The effluent concentration data for the HFCLM were satisfactorily correlated with a material balance where the mass flux was expressed in terms of an overall mass transfer coefficient based on resistances-in-series model.

A modified hollow fiber contained liquid membrane technique for gas separation at high pressures

The hollow fiber contained liquid membrane (HFCLM) permeation technique has been modified by using microporous fibers having a thin nonporous silicone coating to handle higher gas pressures. Separation of various CO 2-N 2 mixtures have been studied over a feed pressure range of 50–200 psig. Pure water and aqueous 20% diethanolamine (DEA) were used as a liquid membranes. Two modes of operation, conventional polymeric membrane and sweep gas mode, were investigated. Permeator conditions studied include liquid membrane pressure higher and lower than the feed pressure. The aqueos 20% DEA resulted in significantly higher overall CO 2 permeabilities and selectivity. A mathematical model was developed which included the pressure drop inside the fiber bores. Numerical simulations of the model describe the experimental results well.

Heavy metal removal and recovery by contained liquid membrane permeator

AbstractHeavy metals like Cu2+, Cr6+, and Hg2+ were removed successfully from wastewater and concentrated in a strip aqueous solution for recycle using the hollowfiber‐contained liquid membrane (HFCLM) technique. Using cotransport, Cr6+ and Hg2+ present as anions in the feed solution were transferred individually through a liquid membrane containing tri‐n‐octylamine in xylene and concentrated in an alkaline solution on the strip side. The removal efficiency of each heavy metal was studied as a function of the aqueous feed flow rate in an HFCLM permeator. Copper present as cation Cu2+ was removed and concentrated by countertransport using LIX84 in n‐heptane as the liquid membrane. The efficiency of copper removal was studied as a function of feed copper concentration, feed flow rate, strip flow rate, and area ratio between the feed fiber set and strip fiber set. The strip side flow rate did not affect the Cu2+ transfer rate. A theoretical model presented predicts the copper transport rate from the feed solution to the strip solution in an HFCLM permeator with a variable feed to strip‐side membrane area. Both feed aqueous boundary layer and interfacial complexation reaction on the feed side dominate the observed Cu2+ removal process through LIX 84 in n‐heptane for feed concentration levels used 90–500 mg/L. It was verified by providing two times larger liquid‐liquid interfacial area in the feed aqueous side or in the strip aqueous side. The model can be used to design the membrane area required on the feed and strip fiber sides to remove essentially all of the copper from a given wastewater stream.

Simultaneous SO2/NO Separation from Flue Gas in a Contained Liquid Membrane Permeator

Separation Of SO[sub 2] and NO from a simulated gas mixture using the hollow fiber contained liquid membrane (HFCLM) technique has been explored. Separation Of SO[sub 2] from a gas mixture containing SO[sub 2], CO[sub 2], O[sub 2], and N[sub 2] has been studied with pure water and aqueous 1 N NaHSO[sub 3] solution. Combined separation Of SO[sub 2] and NO from a simulated flue gas mixture of SO[sub 2], NO, CO[sub 2], O[sub 2], and N[sub 2] has been achieved utilizing aqueous Fe[sup 2+]EDTA or Fe[sup 3+]EDTA solutions. In both cases, sweep and vacuum modes of operation have been investigated. The HFCLM technique has been applied successfully for flue gas cleanup at 24 C; it was also found to be quite effective at 70 C. A simplified multicomponent gas permeation model based on solution diffusion through the liquid membrane appears to describe the SO[sub 2] separation as well as CO[sub 2] separation through the water membrane satisfactorily for the sweep mode of permeator operation.

Pharmaceutical product recovery using a hollow fiber contained liquid membrane: a case study

Recovery of diltiazem as diltiazem malate in a l-malic acid containing aqueous strip stream from an alkaline aqueous feed solution has been studied using a hollow fiber contained liquid membrane (HFCLM) separation-reaction device. The resistance to mass transfer is primarily controlled by the feed side mass transfer coefficient due to the high partition coefficient of diltiazem for a decyl alcohol liquid membrane and the instantaneous reaction in the strip side of the membrane. However, for larger thicknesses of the liquid membrane, the membrane resistance becomes quite important. In spite of the very low diltiazem concentration in the feed solution, high concentrations of diltiazem malate in the stripping solution were achieved by using a high l-malic acid concentration and recirculation of the strip solution from a batch reservoir. A first order model describes effectively the observed behavior of the HFCLM separation-reaction device. A preliminary cost analysis and comparison with packed bed solvent extraction shows the technique to be highly competitive.

Gas separation modes in a hollow fiber contained liquid membrane permeator

The feasibility of gas purification using the hollow fiber contained liquid membrane (HFCLM) technique under four different operational modes, such as sweep gas, sweep liquid, conventional permeation, and vacuum, has been investigated. Separations of binary gas mixtures containing CO 2 and N 2 or CO 2 and CH 4 have been studied with special emphasis on model biogas mixture. Separation and purification through a nonreactive liquid membrane, e.g., water, and a reactive liquid membrane, such as an aqueous solution of diethanolamine (DEA), were investigated. Permeation models were proposed for all modes

Hollow fiber contained liquid membrane separation of citric acid

AbstractCitric acid was successfully separated from an aqueous solution using the hollow fiber contained liquid membrane (HFCLM) technique. In this technique, the organic liquid membrane is contained in the shell side between two sets of hollow fibers; feed solution flows through one set of fibers and the strip solution flows through the other set. Tri‐n‐octylamine diluted in various organic solvents was used as a complexing agent for facilitated transport of citric acid from an aqueous solution. Pure water and aqueous sodium hydroxide were used as stripping agents. Membrane life and stability problems encountered in supported liquid membranes are eliminated. A mathematical model of facilitated solute transport through HFCLM that accounts for the interfacial reversible reaction kinetics and diffusion process inherent in carrier‐facilitated transport is presented. Experimental data agreed well with the theoretical predictions for permeators achieving almost complete solute recovery.

A new liquid membrane technique for gas separation

AbstractA new liquid membrane separation technique for gas mixtures has been developed: feed and sweep gases flow through the lumen of two different sets of hydrophobic microporous hollow fibers while a liquid on the shell side acts as the membrane. This membrane is identified as the contained liquid membrane (CLM). Major shortcomings of immobilized liquid membrane techniques are eliminated. The novel separation device is identified as the hollow fiber contained liquid membrane (HFCLM) permeator. Experimental studies are made with different CO2‐N2 feed mixtures and a pure helium sweep stream, with special emphasis on model landfill gas purification. Either pure water or an aqueous solution of K2CO3 is used as membrane. The effects of several variables on the performance of the HFCLM permeator have been studied. A three‐component permeation model, incorporating axial pressure drop, is developed for binary mixture separation in a HFCLM permeator having a sweep gas stream. The experimental data show good agreement with the theoretical predictions.