Electro-membrane reactor for the conversion of lysine monohydrochloride to lysine by in situ ion...

Research ArticleReceived: 2 January 2012 Revised: 28 July 2012 Accepted: 31 July 2012 Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/jctb.3920

Electro-membrane reactor for the conversionof lysine monohydrochloride to lysine by in situion substitution and separationMahendra Kumar,a Moonis Ali Khanb∗ and Zeid Al Othmanb

Abstract

BACKGROUND: Commercially lysine (Lys) is produced as lysine monohydrochloride (LysCl). The presence of chloride ion (Cl−) inLys makes it unfit for use in pharmaceutical and livestock feed industries. Various separation methods are required to achieveLys from fermentation broths. This paper describes an electro-membrane reactor with three compartments (EMR-3) for theconversion of LysCl into Lys by in situ ion substitution and separation.

RESULTS: The conversion of LysCl into Lys in EMR-3 is achieved by in situ ion substitution and separation using organic-inorganichybrid anion-exchange membrane (AEM). It is found that the rate of Lys formation is dependent on applied current densitiesand LysCl concentration. The 96.2% Lys is recovered and low energy (2.07 kWh kg−1) is consumed during the conversionof 0.10 mol L−1 LysCl in EMR-3 at 10 mA cm−2. Moreover, high current efficiency (93.02%) is achieved under the similarexperimental conditions.

CONCLUSIONS: On the basis of process parameters (high Lys recovery and CE and low W), it is concluded that the developedelectro-membrane reactor can be efficiently applied for the conversion of LysCl into Lys in an economically viable manner.c© 2012 Society of Chemical Industry

Keywords: anion-exchange membrane; electro-membrane reactor; lysine monohydrochloride; lysine; basic amino acid separation

INTRODUCTIONLysine (Lys) [C6H14N2O2], is an essential amino acid (α-amino acid),which is found in various living organisms. It is widely used inpharmaceutical, food and feed industries and is being used asan additive in livestock feed to enhance the nutritive values. Theannual consumption of Lys as an additive in livestock feed is morethan 6.0×105 tons.1,2 Lysine is an essential amino acid for physicaland skeletal growth in children. It also helps to absorb calcium,maintains nitrogen balance, and ensure lean body mass.3,4 It isobtained as lysine monohydrochloride (LysCl) from fermentationbroth using strains of corynebacteria (Corynebacterium glutam-icum).1 Various steps such as centrifugation, evaporation anddrying are applied to separate and recover LysCl from fermenta-tion broths.5 However, due to the presence of toxic Cl− in LysCl itcannot be used directly in pharmaceutical, food and feed indus-tries. Thus, the removal of Cl− from LysCl is essential for its furtheruse.6

The ion-exchange process,7 nano-filtration,8 ultrafiltration9 andelectrodialysis (ED)10,11 have been applied for the separation andrecovery of Lys from fermentation broth solutions. The largeamounts of acid and base, membrane fouling and salt leakageare the major shortcomings of these processes. In the ion-exchange process, large amounts of acid and base are consumedto regenerate the ion-exchange resins, and thus large amounts ofwastewater are produced, which cause a serious environmentalproblem. Due to the consumption of large amounts of acidand base, the process is costly and economically unfavorable.Ultrafiltration has been explored to separate and recover the amino

acids from the fermentation broth but in this process, a greatervolume of fermentation broth solution is required. In addition, theflux and recovery of amino acids decrease with increased processtime because there is a chance of biomolecules (amino acids)deposition onto the membrane surface due to the hydrophobicnature of the membrane.9 Electrodialysis has been applied forthe separation of different amino acids such as l-tryptophan fromcrystallization wastewater, proline and tyrosine from amino acidmixtures, and the separation of lysine, methionine and glutamicacid from their mixture.12 – 15

Electrodialysis is an electro-membrane process in which anelectrical potential difference is applied as driving force for theselective separation and recovery of ions from solutions.11 Duringthe process, ions migrate from the feed compartment to thereceiving compartment through ion-exchange membranes (IEMs)under the influence of an applied electrical gradient across theelectrodes. The ion exchange membranes commonly used in EDcontain either fixed positive groups (anion exchange membrane,AEM) or fixed negative groups (cation exchange membrane, CEM).

∗ Correspondence to: Moonis Ali Khan, Chemistry Department, College of Science,King Saud University, Riyadh 11451,Saudi Arabia.E-mail: [email protected]

a Technical Chemistry II, University of Duisburg-Essen, 45117 Essen, Germany

b Chemistry Department, College of Science, King Saud University, Riyadh 11451,Saudi Arabia

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www.soci.org M Kumar, M Ali Khan, Z Al Othman

The IEMs are selective for either negatively or positively chargedions, respectively. If an ionic solution comes in contact with anIEM, ions with the opposite charge to the fixed ions in the IEM(counter ions) can go through the membrane while ions with thesame charge (co-ions) are retained. This principle is also known asDonnan exclusion.16

Recently, Zhang et al. developed an electro-membrane processfor the conversion of LysCl to Lys using ion substitution.17

Electrodialysis with bipolar membrane (EDBPM) has also beenapplied to separate and recover amphoteric amino acids fromtheir mixture at pH 7.0. The product purity and performance of theEDBPM process are reduced due to salt leakage during the processand salt leakage is the main obstacle to the EDBPM process.18

To avoid these problems, electro-electrodialysis (EED) principlebased electro-membrane reactor (EMR) is a suitable process forthe conversion of LysCl into Lys because the chance of salt leakageand decline in process performance are negligible. EMR is acombination of membrane electrolysis and ED in which H+ andOH− are responsible for in situ ion substitution and separation.The H+ and OH− are produced by water splitting at the electrodes(cathode and anode). The following reactions occur due to watersplitting at the electrodes in EMR:19,20

At anode : 1/2H2O → 1/4O2 + H+ + e−

At cathode: H2O + e− → 1/2H2 + OH−

In addition, organic–inorganic hybrid membranes have receivedmuch research attention during the last decade.21 These mem-branes are developed from mixtures of nanosilica and polymerusing a sol-gel and solution casting method. Organic–inorganichybrid membranes are thermally stable and durable becauseorganic–inorganic phase can combine in a single solid phaseand contains an inorganic backbone in the membrane matrix.22

Organic–inorganic hybrid ion-exchange membranes have excel-lent physicochemical and electro-chemical properties and can beused efficiently in membrane based electro-membrane separationprocesses.

Considering the advantage of EMR and organic–inorganichybrid ion-exchange membranes, an electro-membrane reactorwith three compartments (EMR-3) is proposed in this study forthe conversion of LysCl into Lys by in situ ion substitution andseparation using the organic–inorganic hybrid anion-exchangemembrane (AEM). A schematic structure of the organic–inorganichybrid anion-exchange membrane is shown in Fig. 1. The effectof applied current density and initial feed concentration of Lyssolution have been studied to evaluate process performanceon the basis of Lys recovery, current efficiency (CE), energyconsumption (W) and percentage removal of Cl−.

MATERIALS AND METHODSMaterials and membrane preparationsGlycidyltrimethylammonium chloride (GDTMAC), 3-aminopropyltriethoxy silane (APTEOS), and tetraethoxysilane (TEOS) precursorswere purchased from Sigma Aldrich chemicals. Poly(vinyl alcohol)(PVA, MW: 125 000; degree of polymerization: 1700, degree ofhydrolysis:88%), LysCl, methanol, formaldehyde, Na2SO4, NaCland sulfuric acid were obtained from S.D. fine chemicals, India andused without further purification. Double distilled water (DDW)was used throughout the study. The electrodes were purchasedfrom Titanium Tantalum Products (TITAN, Chennai, India). AEM

O

O

O

O

O

O

O

SiNH

NH

HN

H

OH

OH

OH

OH Cl-N

N+

Cl-

Cl-

Cl-

N+

N+

N+

O

Si

O

O

Si

O

Si

O

O O

Figure 1. Schematic structure of organic–inorganic hybrid anion-exchange membrane.

was prepared from anion-exchange silica precursor (AESP) andPVA by a sol-gel method in acidic medium.22

In brief, AESP was synthesized from equi-molar ratios of APTEOSand GDTMAC monomers by epoxide ring opening reaction at80 ◦C. 10 g of PVA was dissolved in 100 mL of DDW under stirringat elevated temperature and then 70 wt% of AESP with respectto PVA was added to the PVA solution. The resulting mixture wasstirred for 1 h at room temperature and a predetermined amountof TEOS was added to the mixture. The pH of the resulting mixturesolution was adjusted to 2.0 by adding few drops of 4.0 mol L−1

HCl solution. The reaction mixture was stirred for 12 h at roomtemperature to hydrolyze the alkoxy groups of AESP and a highlyviscous white colored gel was obtained. The gel was then castonto a clean glass plate using a solution casting method and themembrane was formed. The membrane was initially dried underan IR lamp and thereafter, in a vacuum oven at 60 ◦C for 24 h. Thedried membrane was immersed in a crossing solution containedHCHO+H2SO4 for 2 h at 60 ◦C to crosslink the hydroxyl groups andmake the membrane water insoluble.23

Determination of anion-exchange membrane propertiesThe thickness of wet and dry membrane was measured usinga digital micrometer with 0.10 µm accuracy. The ion-exchangecapacity (IEC) of the AEM was measured by a back titrationmethod. A piece of AEM was soaked in 1.0 mol L−1 NaOH solutionfor 8 h and then washed with DDW to remove any traces of NaOH.The cleaned membrane was again immersed in a 50 mL solutionof 0.50 mol L−1 NaCl for 24 h. The concentration of liberatedOH− was estimated by titration with 0.01 mol L−1 standard HClsolution using phenolphthalein as an indicator. The IEC of AEMwas estimated using Equation (1):22,23

IEC =(

a × b

Wdry

)(1)

where a is the concentration of HCl solution (mol L−1) and b is thevolume of consumed HCl solution (mL), respectively. The watercontent of AEM was estimated from the weight of the membranein wet and dry state. AEM was immersed in DDW for 24 h at roomtemperature. Excess water on the membrane surface was removedwith tissue paper. The weight of the wet membrane was recordedand the wet membrane again dried in a vacuum oven at 60 ◦C

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to constant weight. Finally, the weight of the dried membranewas recorded. The water uptake of the membrane was calculatedusing Equation (2):22,23

Water uptake (%) =(

Wwet − Wdry

Wdry

)× 100 (2)

where Wdry is the weight of dry membrane (g) and Wwet is theweight of wet membrane (g). The thermal stability of the AEM wasevaluated by recording thermograms in the temperature range50–600 ◦C using a thermo-gravimetric analyzer (TGA, MettlerToledo TGA/SDTA851 with Starc software) under N2 atmosphere ata heating rate of 10 ◦C min−1. The counter ions transport numberin the membrane phase was determined by Hittorf method; thedetailed procedure is reported elsewhere.22,24 The Cl− transportnumber of AEM was calculated using:

tmCl− = nF

It(C−V− − C0V0) (3)

where n is the charge on Cl−, F is the Faraday constant (96 500coulombs), I is the applied current (A), t is the time (s), C0 andC− are the initial and final concentration of Cl− in the anodecompartment (mol L−1) and V0 and V− are the initial and finalvolume of the anode compartment (L). The conductivity of the AEMwas measured by impedance spectroscopy using a potentiostat-galvanostat frequency analyser (Auto Lab, Model PGSTAT 30, EcoChemie, B.V. Utrecht, The Netherlands). The AEM was equilibratedin NaCl, LysCl and Lys solutions of different concentrations for24 h. Then, the equilibrated membrane was placed betweenfabricated stainless steel circular electrodes of 4.0 cm2 effectivearea. Direct and sinusoidal alternating currents were applied acrossthe electrodes to record the frequency change at the scanning rateof 1.0 µA s−1. The experiments were performed over a frequencyrange of 1.0–106 Hz and the membrane resistance in differentsolutions of NaCl, LysCl and Lys was recorded. The membraneresistance (Rmem) was calculated from the electrolyte resistance(Rsol) and the membrane resistance in the electrolyte solution (Rcell)using Equation (4):

Rmem = Rcell − Rsol (4)

The AEM conductivity (κm, mS cm−1) was then calculated fromthe resistance of AEM in different solutions of NaCl, LysCl and Lysusing Equation (5):22,23

κm = L

RmemA(5)

where Rmem is the membrane resistance (ohm), L is the thickness ofthe membrane (cm), and A is the effective area of the membrane(cm2).

Experimental procedure for the conversion of LysCl to Lys byelectro-membrane reactor with three compartmentsA schematic diagram of the EMR-3 cell is depicted in Fig. 2. Thecell was divided into three compartments, central, cathode, andanode compartments by placing two pieces of AEM betweenthe electrodes. The electrodes were made of expanded titaniumoxide (TiO2) sheets coated with a triple precious metal oxide(titanium–ruthenium–platinum) (6.0 µm thickness). The thicknessand effective area of the electrodes were 1.5 mm and 8.0×10−3 m2.The inter-membrane distance was 8.0 mm and the effective

Figure 2. Schematic presentation of electro-membrane reactor with threecompartments for the conversion of lysine monohydrochloride into lysineby in situ ion substitution and separation.

membrane area was 8.0 × 10−3 m2. All the compartments wereconnected to separate storage tanks in batch mode. Peristalticpumps at 12 L h−1 flow rate were used for the continuousrecirculation of DDW and LysCl solution into the respectivecompartments. A DC power supply (Aplab India, model L1285)was used to apply constant current across the electrodes and thevariation in potential (V) was recorded using a digital multimeter(model 435, Systronics, India) by connecting it in a parallel mode. Inthis study, all experiments were performed at room temperature(30 ◦C). Initially 500 cm3 of DDW was fed into the cathode andanode compartments while LysCl solution of known concentrationwithout pH control was fed into the central compartment (CC). Theeffect of applied current density and feed concentration of LysClsolution on process performance parameters such as recovery,current efficiency and energy consumption was measured. Thechange in pH of all the compartments during the conversion ofLysCl into Lys was regularly monitored using a pH meter. Thevariation in conductivity of anode and central compartments wasmonitored using a digital conductivity meter. Changes in HCland Cl− concentration in the anode and central compartmentswere estimated by acid-base titration and the Mohr method,while the concentration of Lys was determined using a UV-visiblespectrophotometer at λ = 504 nm wavelength.25,26

Process evaluationTo assess Lys flux, recovery, current efficiency and energyconsumption were determined and their values calculated usingEquations (6) to (9). The Lys flux (J) is estimated from the changein Cl− concentration in the central compartment (CC) using theequation:19,20

J = V

A

Ct − C0

� t(6)

where C0 and Ct are the initial and final concentration of Lys in CC(mol m−3), �t is the time allowed for electro-membrane reactor(s), V is the total volume of the CC (0.50 × 10−3 m3), and A is theeffective membrane area (8.0 × 10−3 m2). The recovery of Lys (%)is estimated from the change in Cl− concentration in the CC by

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Table 1. Physicochemical and electrochemical properties of anion-exchange membranes used in EMR-3

Properties AEM

Thickness1 (µm) 150

Water content2 (%) 35.2

Ion-exchange capacity3 (mequiv.g −1of dry membrane) 1.36

Counter -ion transport numbera,4 (tm− ) 0.96

Specific membrane conductivityb,5 (S cm−1) 7.6 × 10−3

a Measured by membrane potential in equilibration in with 0.01 mol L−1

and 0.10 mol L−1 NaCl solutions.b Measured in equilibration with 0.10 mol L−1 NaCl solution.Uncertainty of measurements: 1 1.0 µm; 20.1%; 30.01 mequiv. g−1 ofdry membrane; 40.01; and 5 0.01 × 10−3 S cm−1.

using Eq. (7):11,19

Lys recovery(%) = CtpVtp

C0F V0F× 100 (7)

where V0F and Vtp are the initial and final volumes of the CC,C0F and Ctp are the initial and final concentration of Cl− in theCC. The CE is defined as the fraction of coulombs utilized for theconversion/separation of Lys from LysCl and CE(%) is estimatedusing Eq. (8):19,20

CE(%) = mnF

MQ× 100 (8)

where M is molecular weight of Lys, n is stoichiometric number(n = 1 in this case), and Q is electricity passed (coulombs). Theenergy consumption (W) is defined as the energy consumed in theconversion of 1 kg LysCl to Lys. W is estimated using Eq. (9):19,20

W(kWhkg−1) =∫ t

0

VIdt

m(9)

where V is the cell voltage (V), I is the current (A), t is the timeallowed (s) for the process and m is the weight of Lys produced(kg).

RESULTS AND DISCUSSIONProperties of anion-exchange membraneThe physicochemical and electrochemical properties of or-ganic–inorganic hybrid AEM used in EMR-3 are given in Table 1.The desired properties of AEM are comparable with the bestknown ion-exchange membranes for an electro-driven separationprocess.27,28 The prepared AEM has better water content, IEC,counter ion transport number and high membrane conductivity.The mechanical stability of AEM was investigated using a dynamicmechanical analysis at 1.0 N applied force. No elongation/breakwas observed in the membrane at 1.0 N applied force.22 Thethermo-gravimetric analysis curve of AEM is depicted in Fig. 3 andtwo steps in weight loss occurred during the analysis. The initialweight loss occurs at 100 ◦C, and is due to the evaporation ofabsorbed water in the membrane matrix. The second weight lossoccurs in the temperature range 270–350 ◦C. This is attributed tothe degradation of quaternary ammonium group and the mem-brane matrix.22 The results confirm that AEM is suitable to fabricateEMR-3 for the conversion of LysCl into Lys.

Figure 3. TGA curve of organic–inorganic hybrid anion-exchange mem-brane with 70 wt% AESP.

Figure 4. Variation in conductivity of AEM in equilibration with NaCl, LysCland Lys solutions of different concentration.

The knowledge of membrane conductivity under operatingconditions is also an essential parameter to develop an electro-membrane reactor for in situ ion substitution and separation ofLys.19,27 The variation in κm of AEM in equilibration with NaCl,LysCl and Lys solutions of various concentrations is presented inFig. 4. The κm of AEM is highly dependent on the concentrationof NaCl, LysCl and Lys. The conductivity of AEM in equilibrationwith NaCl solution of different concentrations increases as thesolution becomes more concentrated. The reason for this isthe electroneutral solution, which is identical to the externalsolution contained in the central part of the macropores and widechannels. It is reported that the electroneutral solution fills theintergel spaces in the membrane and the gel phase combines theregions of charged matrix containing micropores in which mobilecounter ions and coions balance the matrix charge.29 At higherconcentrations of NaCl solution, the high electrical conductivity ofNaCl solution in the intergel spaces also causes high membraneconductivity. Thus, the conductivity of AEM in equilibration withNaCl solution of various concentrations is enhanced because theelectrical conductivity of NaCl solution in the intergel spaces isenhanced with increase in NaCl concentration. The conductivity ofAEM in equilibration with LysCl solution of different concentrations



is lower than with NaCl solution. The conductivity of AEM inequilibration with LysCl solution of different concentrations isdependent on several factors such as the chemical structureand electrochemical behaviour of the ampholyte (LysCl) underinvestigation. Cl− ions enter into the intergel space while large Lyscations do not enter into the intergel space of the membrane due tosteric hindrance and the very low diffusion coefficient (0.73) of Lys+at infinite dilution.29 Thus, electro-neutrality of counter ion (Cl−)and coion (Lys+) is not maintained in the membrane matrix duringthe determination of AEM conductivity in equilibration with LysClsolution. Therefore, the conductivity of AEM in equilibration withLysCl is lower than with NaCl solution under similar experimentalconditions. Furthermore, the conductivity of AEM in equilibrationwith Lys solution is very low compared with that for LysCl and NaClsolution. This is attributed to the low degree of Lys dissociation.Hence, the comparable conductivity of AEM in equilibration withNaCl and LysCl solutions reveals its suitability to develop EMR-3for the conversion of LysCl into Lys by in situ into substitution andseparation.

In situ ion substitution of LysCl in electro-membrane reactorwith three compartmentsIn situ ion substitution of LysCl occurs in EMR-3 and allows themigration of Cl− from CC to the anode compartment. There isa chance of Lys migration from CC to the other compartmentsbut this is hindered by organic–inorganic hybrid AEM due to theopposite charge nature. The electrochemical principal of EMR-3used in the conversion of LysCl into Lys is described in Fig. 2.The conversion of LysCl into Lys occurs in four steps: (i) OH− aregenerated by water splitting and subsequently OH− migrates intothe CC through AEM; (ii) in situ substitution of Cl− by OH− in theCC and thus Lys is formed; (iii) the migration of Cl− from CC to theanode compartment through AEM; and (iv) H+ are produced inthe anode compartment by water splitting, which reacts with Cl−present in the anode compartment and thus HCl is formed. In thisprocess, in situ ion substitution is achieved due to the electrodepolarization and simultaneous migration of OH− from the cathodecompartment to the CC. The presence of Lys in the anode andcathode compartments due to electro-migration of Lys from theCC at higher pH was checked at regular time intervals by takingthe electrode rinse solutions. It is found that Lys was absent in theelectrode compartments during the conversion of LysCl into Lys.

Effect of applied current densityExperiments for the conversion of LysCl into Lys in EMR-3by in situ ion substitution and separation were performed atdifferent applied current densities in the range 5–10 mA cm−2

and 0.10 mol L−1 LysCl solution as an initial feed of the CC. Thevariation in cell voltages (V) during the conversion of LysCl intoLys at various applied current densities are presented in Fig. 5 asa function of electricity passed (coulombs). At the beginning ofthe experiment, the initial cell voltage is high because DDW wasfed into the electrode compartments. For this reason, resistanceof the anode and cathode compartments is high and resistanceof the CC is low because of the 0.10 mol L−1 solution of LysClfed into the CC. Thus, the overall initial cell voltage of EMR-3 ishigh. The cell voltages decrease with increase in process time andlater become constant at the different applied current densities.In electro-membrane reactors, the applied electrical gradient ismainly responsible for the formation and migration of H+, OH−and Cl− from one compartment to the other compartments.11,19,20

OH− migrates from the cathode compartment to the CC and

Figure 5. Variation in cell voltage during the conversion of LysCl into Lysin EMR-3 at various applied current densities.

simultaneously, Cl− drifts into the anode compartment throughAEM under the influence of the applied electrical gradient. Thus,the resistance of the anode and cathode compartments is reduced,while the resistance of the CC is enhanced because the Cl−

concentration reduces sharply and less soluble Lys is formed inthe CC.30 – 32

Lysine has basic amino group, an acidic carboxyl group, andcharacteristic side chain. The net charge on Lys depends onsolution pH and the degree of protonation of functional groups(NH2 ↔ NH+

3 , COOH ↔ COO−) present in the molecule. Lys carriespositive and negative charges below and above the isoelectricpoint (pI)–9.8. The change in the dissociation states of Lys as afunction of solution pH is depicted in Fig.6.33 The change in pHof CC, anode, and cathode compartments during the conversionof 0.10 mol L−1 LysCl into Lys at 10 mA cm−2 is shown in Fig. 7.Initially, the pH of the anode compartment is ∼ 7.0 and afterwardsdecreases to some extent because H+ is generated by watersplitting at the anode. The initial pH of the cathode compartmentis ∼ 7.0, which is increased instantly after applying current acrossthe electrodes. The reason for the increase in pH of the cathodecompartment is the production of OH− by water splitting at thecathode. The pH of the CC is also∼7.0 because aqueous solution ofLysCl was fed into the CC; the pH of CC and anode compartmentsreached 9.85 and ∼ 2.05, respectively, after the completion ofthe process. The data obtained confirms simultaneous formationof Lys in CC and HCl in the anode compartment. The electrodereactions and electro-transport of ions (Cl− and OH−) from theCC to the anode compartment are also confirmed from the dataobtained (Fig. 2). There is a possibility of negatively charged Lys(LYS−) migration at pH 9.85 from the CC to the anode compartmentduring the conversion of LysCl into Lys. But the electro-migrationof LYS− from the CC to anode compartment is not feasible becausethe extent of net negative charges on Lys at pH 9.85 (very closeto pI of Lys) is very low. Furthermore, the presence of LYS− inthe anode compartment was checked and found to be absent.This observation is also validated from the mass balance of Lysin the CC before and after the experiments, which is found to beabout 97%. The variations in solution conductivity of CC and theanode compartment at 10 mA cm−2 are presented in Fig. 8. Theconductivity of CC decreases with increase in process time for theconversion of LysCl into Lys. This occurs because the concentrationof Cl− in the CC is depleted through in situ substitution of Cl− with



Figure 6. Changes in the dissociation states of lysine as a function ofsolution pH.33.

Figure 7. Variations of pH in anode, cathode, and central compartmentsduring the conversion of LysCl into Lys in EMR-3 at 10 mA cm−2.

OH−. As a result, the conductivity of the anode compartmentincreases with time because the concentration of Cl− in the anodecompartment is enhanced due to the migration of Cl− from theCC to the anode compartment through AEM, and HCl is formed.

The rate of Lys formation (J) in EMR-3 can be defined as therate of Cl− migration from the CC to anode compartment or therate of HCl formation in the anode compartment. The rate of Lysformation in CC is estimated from the change in Cl− concentrationbecause the determination of Cl− concentration in the anodecompartment was difficult due to the partial oxidation of Cl−

into Cl2 at anode. The rate of Lys formation in CC at differentapplied current densities (5.0–10 mA cm−2) and 0.10 mol L−1

LysCl solution is presented in Fig. 9. The rate of Lys formationin EMR-3 is highly dependent on the applied current density.The rates of Lys formation at 5.0, 7.5 and 10 mA cm−2 increaseand attain maximum value after a certain time interval. The rateof Lys formation decreased with increase in conversion time inthe EMR-3. The rate of Lys formation increases linearly duringthe initial stage of LysCl conversion into Lys. The reason for theincrease in rate of Lys formation during the initial stage is thatmore Cl− in the CC available for in situ ion substitution with OH−

0 10 20 30 40 50 600

4

8

12

16

20

24

28Central compartmentAnolyte

Time (min)

κs (

mS

cm

-1) κ s (m

S cm

-1)

0

2

4

6

8

10

Figure 8. Variation in anode and central compartment conductivity duringthe conversion of LysCl into Lys in EMR-3.

due to the high concentration of LysCl solution. In addition, therate of Lys formation is further reduced with increase in processtime in the EMR-3 because appropriate Cl− is not available forsubstitution.20,32 Thus, the transport of Cl− is decreased due tothe barrier effect and increase in transport of free water acrossthe membrane.34,35 Moreover, the rate of Lys formation dependson applied current density during the conversion of 0.10 mol L−1

LysCl into Lys and the highest conversion of LysCl to Lys is achievedat 10 mA cm−2. This is attributed to the generation of more OH−

by water splitting in the cathode compartment at 10 mA cm−2,which is responsible for fast substitution and migration of Cl−

from CC to the anode compartment.28,29 Thus, the maximum Lysis formed in CC and 96.2% Lys is obtained at 10 mA cm−2 and0.10 mol L−1 LysCl feed solution. However, this trend does notcontinue with further increase in applied current density from 10to 12.5 mA cm−2 (Fig. 10 (A)). It can be seen clearly from Fig. 10(A)that Lys recovery at 12.5 mA cm−2 is 81%, which is lower thanthat (96.2%) at 10 mA cm−2. The rate of Lys formation in EMRat high applied current density is dependent on the extent ofOH− and exchange rate of Cl− with OH− in the CC. At higherapplied current density, the polarization starts when the rate ofCl− transfer becomes constant. Thus, more OH− is produced atthe membrane surface. The high OH− content in the CC slowsdown the exchange rate of Cl− with OH− during the conversionof LysCl into Lys.17,20 For this reason, the rate of Lys formationreduces and thus, less Lys is formed at higher applied currentdensity. The decline in Lys recovery at 12.5 mA cm−2 might bedue to water splitting, which takes place in CC on the anodic AEMand generated H+ act with OH− in the cathode compartment.The pH of the CC locally decreases and recovery of Lys is reducedat 12.5 mA cm−2. Therefore, all the experiments during this studywere performed at 10 mA cm−2 to obtain optimum Lys recovery.The percentage Cl− removal (%Cl−) during the conversion of LysClinto Lys at various applied current densities and 0.10 mol L−1 LysClsolution is depicted in Fig. 10(B), which shows that the maximum%Cl− removal is achieved at 10 mA cm−2. The %Cl− removal isalso dependent on applied current density, and decreases withincrease in applied current density (Fig. 10 (B)). This occurs becauseconcentration polarization and water splitting take place at theboundary layer of the membrane surface so that the rate of Cl−

exchange with OH− is reduced.36



Figure 9. Variation synthesis rate of lysine (J) in EMR-3 at different appliedcurrent densities with 0.10 mol L−1 LysCl solution as initial feed of thecentral compartment.

Effect of LysCl feed concentrationExperiments were performed at various feed concentrations ofLysCl (0.10–0.14 mol L−1) and current density 10 mA cm−2. Thevalues of Lys recovery obtained at various feed concentrations ofLysCl as a function of electricity passed are presented in Fig. 11.The highest recovery of Lys (96%) is obtained at 10 mA cm−2 and0.10 mol L−1 LysCl solution as initial feed to the CC. Furthermore,the recovery of Lys is reduced to 83.8% and 70%, when theconcentration of LysCl feed solution is increased to 0.12 and0.14 mol L−1, respectively. The recovery of Lys during the processdepends on the initial feed concentrations of LysCl because itaffects the current density and percentage removal of Cl− duringin situ ion substitution.17 Current density is enhanced during theconversion of LysCl into Lys because current increases at high initialconcentration of LysCl.17,37 For this reason the current densitybecomes higher than the limiting value at the anion-exchangemembranes. Thus, water splitting starts at the membrane interfaceand then OH− competes with Cl−, which slows down the exchangeof Cl− with OH−. The recovery of Lys is reduced at high LysClconcentration because the recovery of Lys is directly related tothe rate of Lys formation in the EMR-3. In addition, the rate

Figure 11. Variation in recovery of Lys (%) with various feed concentrationsof LysCl solution at 10 mA cm−2.

of Cl− migration from CC to anode compartment becomesindependent above a certain feed concentration because thetransport rate of counter ion is dependent on IEC and membranepermselectivity.19,38 The recovery of Lys is decreased becausethe number exchangeable anion at high feed concentration ofLysCl is higher than the permselectivity of AEM. Therefore, a highinitial feed concentration of LysCl is not appropriate for efficientconversion of LysCl into Lys in the EMR-3 by in situ ion substitutionand separation at 10 mA cm−2.

Current efficiency and energy consumptionCE and W are important parameters to assess the suitabilityof membrane based electrochemical processes for practicalapplications. The membrane based electrochemical process mustnot only be technically feasible but should also be less expensiveand eco-friendly. W and CE values are estimated from the change inrecovery of Lys at various feed concentration of LysCl solution usingEquations (8) and (9). The current efficiency values at 10 mA cm−2

are depicted in Fig. 12 as a function of feed concentration ofLysCl solutions. CE decreases with increase in feed concentrationof LysCl solutions from 0.10–0.14 mol L−1 and the highest CEis achieved at 0.10 mol L−1 LysCl feed solution at 10 mA cm−2

Figure 10. Variation in (A) recovery of Lys and (B) percentage removal of Cl− at different applied current densities with 0.10 mol L−1 LysCl solution asfeed to central compartment during the conversion of LysCl into Lys in EMR-3 by in situ ion substitution and separation.



0.10 0.11 0.12 0.13 0.14

64

72

80

88

96

LysCl Conc. (M)

CE

(%

)

1.6

2.4

3.2

4.0

4.8

W (kW

h kg-1)

Figure 12. Variation in current efficiency (%) and energy consumptionwith various feed concentration of LysCl solution at 10 mA cm−2 appliedcurrent density.

current density. CE depends on the IEC, permselectivity of AEMand the competitive transfer of OH− with Cl−.11,19,32 Bargemanet al. developed an electro-membrane filtration process for theseparation of bioactive peptides. They reported that processperformance parameters are dependent on membrane selectivitytowards the counter ions. The process performance is better ifthe membrane has better selectivity towards the counter ions andhigh IEC.39 As explained above, the exchange rate of Cl− slowswith increase in concentration of LysCl solution because moreOH− are produced at high feed concentration of LysCl solutiondue to the increase in current during the conversion of LysCl intoLys. Also, the rate of Cl− substitution with OH− is reduced whenIEC and permselectivity of the AEM are lower than that duringthe electrochemical conversion. This might be another reason forreduction in CE as the increase in feed concentration of LysClsolution. Similar results were reported by Xu et al.40 The values ofW as a function of LysCl feed concentration at 10 mA cm−2 arealso depicted in Fig. 12. It reveals that W increased with increasein LysCl solution concentration. W depends on parameters suchas process time, current density and electric resistance. A muchlonger time is required in the membrane based electrochemicalprocesses to achieve a desired product if the concentration offeed solution is too high.11,17,32 The energy consumed duringthe conversion of 0.12 mol L−1 LysCl solution into Lys is higherthan the 0.10 mol L−1 LysCl solution. W increases with increasein LysCl concentration from 0.10 to 0.12 mol L−1 because moretime is required to reach an equal percentage removal ratio ofCl− for 0.12 mol L−1 LysCl under similar experimental conditions.Moreover, the current density also decreases with increase inprocess time and thus, the electrical resistance is increased,which is responsible for high energy consumption.17,19 Themaximum current efficiency (93.07%) is achieved at 10 mA cm−2

and 0.10 mol L−1 LysCl feed solution. Under similar experimentalconditions, recovery of Lys and energy consumption is 96.2%and 2.07 kWh kg−1, respectively. The obtained results confirmthat the process performance parameters (Lys recovery, CE and W)obtained during the study are superior to those reported by Zhanget al.17 The EMR-3 can be efficiently applied for the conversion ofLysCl into Lys by in situ ion substitution and separation in aneconomically viable manner.

CONCLUSIONSThermally and mechanically stable organic–inorganic hybrid AEMwas prepared by a sol-gel method. The AEM has good watercontent, IEC, high selectivity for OH−/Cl− ion and membraneconductivity. The AEM was used to develop EMR-3 based on EEDfor the conversion of LysCl into Lys by in situ ion substitution andseparation without use of any hazardous chemicals and furtherseparation. Effects of the applied current density and initial feedconcentrations of LysCl solutions on the process performancewere studied. The process parameters are dependent on appliedcurrent density and concentration of LysCl solution. CE and Wvalues are 93.07% and 2.07 kWh kg−1, which correspond to96.2% recovery of Lys at 10 mA cm−2. The process performanceparameters are also dependent on nature, stability, performanceof AEM and reactor design. Thus, the complete optimization ofEMR-3 is necessary for efficient conversion of LysCl into Lys. Inaddition, no hazardous chemicals and reagents are used in thisinvestigation. In the developed EMR-3, in situ ion substitution andseparation occurs through water splitting and provides an eco-friendly and economically viable route for the conversion of LysClinto Lys.

REFERENCES1 Anastassiadis S, L-lysine fermentation. Recent Patents Biotechnol

1:11–24 (2007).2 Gunji Y and Yasueda H, Enhancement of L-lysine production

in methylotroph methylotrophus by introducing a mutantLysexporter. J Biotechnol 127:1–13 (2006).

3 Arruda P, Kemper EL, Papes F and Leite A, Regulation of lysinecatabolism in higher plants. Trends Plant Sci 5:324–330 (2000).

4 Harakeh S, Diab-Assaf M, Abu-El-Ardat K, Niedzwiecki A and Rath M,Mechanistic aspects of apoptosis induction by L-lysine in bothHTLV-1-positive and -negative cell lines. Chem Biol Interactions164:102–114 (2006).

5 Mohammadi T and Bakhteyari O, Concentration of L-lysinemonohydrochloride (L-lysine· HCl) syrup using vacuum membranedistillation. Desalination 200:591–594 (2006).

6 Fischer A, Martin C and Muller J, Method for purification of aminoacid containing solutions by electrodialysis. US Patent 6551803 B1(2003).

7 Kawakita T and Matsuishi T, Elution kinetics of Lysine from a strongcation-exchange resin with ammonia water. Sep Sci Technol26:991–1003 (1991).

8 Hong SU and Bruening ML, Separation of amino acid mixtures usingmultilayer polyelectrolyte nanofiltration membranes. J Membr Sci280:1–5 (2006).

9 Zhang G, Liu Z, Zhao L, Li H, Zhou Q, He F, Xu Z and Wan H, Recoveryof glutamic acid from ultrafiltration concentrate using diafiltrationwith isoelectric supernatants. Desalination 154:17–26 (2003).

10 Teng Y, Scott EL, Van Zeeland ANT and Sanders JPM, The use of L-lysinedecarboxylase as a means to separate amino acids by electrodialysis.Green Chem 13:624–630 (2011).

11 Readi OMK, Mengers HJ, Wiratha W, Wessling M and Nijmeijer K, Onthe isolation of single acidic amino acids for biorefinery applicationsusing electrodialysis. J Membr Sci 384:166–175 (2011).

12 Liu LF, Yang LL, Jin KY, Xu DQ and Gao CJ, Recovery of l-tryptophanfrom crystallization wastewater by combined membrane process.Sep Purif Technol 66:443–449 (2009).

13 Aghajanyan AE, Hanbardzumyan AA, Vardanyan AA and Saghiyan AS,Desalting of neutral amino acids fermentative solutions byelectrodialysis with ion-exchange membranes. Desalination228:237–244 (2008).

14 Bukhovets AE, Saveleva AM and Eliseeva TV, Separation of aminoacids mixtures containing tyrosine in electromembrane system.Desalination 241:68–74 (2009).

15 Kumar M, Tripathi BP and Shahi VK, Electro-membrane process for theseparation of amino acids by iso-electro focusing. J Chem TechnolBiotechnol 85:648–657 (2010).

16 Mulder M, Basic Principles of Membrane Technology. Kluwer AcademicPublishers (1996).



17 Zhang Y, Chen Y, Yue M and Ji W, Recovery of L-lysine from L-lysine monohydrochloride by ion substitution using ion-exchangemembrane. Desalination 271:163–168 (2011).

18 Grib H, Bonnal L, Sandeaux J, Sandeaux R, Govach C and Mameri N,Extraction of amphoteric amino acids by an electromembraneprocess: pH and electrical state control by electrodialysis withbipolar membranes. J Chem Technol Biotechnol 73:64–70 (1998).

19 Kumar M, Tripathi BP and Shahi VK, Electro-membrane reactor forseparation and in situ ion substitution of glutamic acid from itssodium salt. Electrochim Acta 54:4880–4887 (2009).

20 Kumar M, Tripathi BP and Shahi VK, Electro-membrane process forin situ ion substitution and separation of salicylic acid from itssodium salt. Ind Eng Chem Res 48:923–930 (2009).

21 Kumar M, Tripathi BP and Shahi VK, Ionic transport phenomenonacross sol-gel derived organic-inorganic composite mono-valentcation selective membranes. J Membr Sci 340:52–61 (2009).

22 Singh S, Jasti A, Kumar M and Shahi VK, A green method for thepreparation of highly stable organic-inorganic hybrid anion-exchange membranes in aqueous media for electrochemicalprocesses. Polym Chem 1:1302–1312 (2010).

23 Kumar M, Singh S and Shahi VK, Cross-linked poly(vinyl alcohol)-poly(acrylonitrile-co-2-dimethylamino ethylmethacrylate) basedanion-exchange membranes in aqueous media. J Phys Chem B114:198–206 (2010).

24 Rajesh AM, Kumar M and Shahi VK, Functionalized biopolymer basedbipolar membrane with poly ethylene glycol interfacial layer forimproved water splitting. J Membr Sci 372:249–257 (2011).

25 Jeffery GH, Basset J, Mendham J and Denney RC, Textbook ofQuantitative Chemical Analysis, 5th edn. John Wiley and Sons (1989).

26 Gao Q, Xu W, Xu Y, Wu D, Sun Y, Deng F, and Shen W, Aminoacid adsorption on mesoporous materials: influence of types ofamino acids, modification of mesoporous materials, and solutionconditions. J Phys Chem B 112:2261–2267 (2008).

27 Nagarale RK, Gohil GS and Shahi VK, Recent developments on ion-exchange membranes and electro-membrane processes. AdvColloid Interface Sci 119:97–130 (2006).

28 Dlugolecki P, Nijmeijer K, Metz S and Wessling M, Current status of ionexchange membranes for power generation from salinity gradients.J Membr Sci 319:214–222 (2008).

29 Pismenskaya ND, Belova EI, Nikonenko VV and Larchet C, Electricalconductivity of cation- and anion-exchange membranes inampholyte solutions. Russian J Electrochem 44:1285–1291 (2008).

30 Wang QS, Ying TJ, Jiang TJ, Yang DM and Jahangir MM,Demineralization of soybean oligosaccharides extract from sweetslurry by conventional electrodialysis. JFoodEng 95:410–415 (2009).

31 Vallejo ME, Persin F, Innocent C, Sistat P and Pourcelly G,Electrotransport of Cr(VI) through an anion exchange membrane.Sep Purif Technol 21:61–69 (2000).

32 Lee EG, Moon SH, Chang YK, Yoo IK and Chang HN, Lactic acid recoveryusing two-stage electrodialysis and its modeling. J Membr Sci145:53–66 (1998).

33 Kitadai N, Yokoyama T and Nakashima S, ATR-IR spectroscopic studyof L-lysine adsorption on amorphous silica. J Colloid Interf Sci329:31–37 (2009).

34 Eliseeva TV, Krisilova EV and Chernikov MA, Concentration of basicamino acids by electrodialysis. Petroleum Chem 51:626–633 (2011).

35 Eliseeva TV, Shaposhnik VA, Krisilova EV and Bukhovets AE, Transportof basic amino acids through the ion-exchange membranes andtheir recovery by electrodialysis. Desalination 241:86–90 (2009).

36 Rubinstein I and Zaltzman B, Electro-osmotically induced convectionat a permselective membrane. Phys Rev E 62:2238–2251 (2000).

37 Choi JH, Oh SJ and Moon SH, Structural effects of ion-exchangemembrane on the separation of L-phenylalanine (L-Phe) fromfermentation broth using electrodialysis. J Chem Technol Biotechnol77:785–792 (2002).

38 Madzingaidzo L, Danner H and Braun R, Process development andoptimization of lactic acid purification using electrodialysis. JBiotechnol 96:223–239 (2002).

39 Bargeman G, Koops GH, Houwing J, Breebaart I, Horst van der HC andWessling M, The development of electro-membrane filtration forthe isolation of bioactive peptides: the effect of membrane selectionand operating parameters on the transport rate. Desalination149:369–374 (2002).

40 Xu TW and Yang WH, Citric acid production by electrodialysis withbipolar membranes. Chem Eng Process 41:519–524 (2002).


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