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离子替代电渗析

离子替代电渗析
离子替代电渗析

Recovery of L-lysine from L-lysine monohydrochloride by ion substitution using ion-exchange membrane

Yaping Zhang ?,Yan Chen,Mingzhu Yue,Wenlong Ji

Engineering Research Center of Biomass Materials,Ministry of Education,Southwest University of Science and Technology,59Qinglong Road,Mianyang 621010,China

a b s t r a c t

a r t i c l e i n f o Article history:

Received 11August 2010

Received in revised form 9December 2010Accepted 9December 2010

Available online 14January 2011Keywords:

Ion substitution electrodialysis L-lysine

L-lysine monohydrochloride Ion-exchange membrane

Ion substitution electrodialysis (ISED)consisting of two anion-exchange membranes and one cation-exchange membrane was performed to achieve ef ?cient production of L-lysine from L-lysine monohy-drochloride.Several experimental parameters including the operation voltage,the L-Lys·HCl concentration,and the initial pH of L-Lys·HCl solution were compared and discussed in terms of ionic transport.The Cl ?removal ratio,the current density,the current ef ?ciency,and the energy consumption were presented and analyzed.When the initial concentration of L-Lys·HCl is 0.6mol L ?1and the constant voltage is 40V,the removal ratio of Cl ?reached 95.6%,the current ef ?ciency 20.5%and the energy consumption 9.0kW h kg ?1.Initial pH of L-Lys·HCl solution can affect the recovery ratio of L-Lys signi ?cantly.When the initial pH is kept at its isoelectric point,i.e.9.74,the recovery ratio of L-Lys is to be maximized (93.2%).Elevating temperature can improve the electrodialysis process.

?2010Elsevier B.V.All rights reserved.

1.Introduction

L-lysine (L-Lys)has a wide range of application in pharmaceuticals,food and feed industry,which is mostly used as a feed additive at a rate of above 6×105ton per year [1].More importantly,L-Lys is an essential amino acid necessary to physical growth and skeletal development especially for children [2].Concretely,it is bene ?cial to absorb calcium,keep nitrogen balance,and ensure lean body mass [3].Commercial L-Lys is usually produced as L-lysine monohydrochloride (L-Lys·HCl),because L-Lys is dif ?cult to preserve and easy to absorb moisture as a natural protein.However,L-Lys·HCl is not commonly suitable for eating directly,and Cl ?needs to be removed in order to gain the L-Lys of high medical and edible value [4].

Electrodialysis (ED)is an electro-membrane process for separation of ions across charged membranes from one solution to another under the in ?uence of an electrical potential difference used as a driving force between two electrodes [5].Namely,ED can selectively separate ions having a positive or negative charge and reject ions of the opposite charge [6].ED has the following advantages over traditional separation methods:the negative impact on the environment is reduced,products are puri ?ed and concentrated at the same time,and the technology itself is relatively simple [7].To date,ED has been used in recovery or separation of several kinds of amino acids,and many

literature papers have been devoted to it,such as separation of glutamic acid [8],recovery of L-tryptophan from crystallization wastewater [9],separation of L-proline [10]and separation of tyrosine from amino acids mixtures [11],etc.Specially,T.V.Elisseeva et al.[12]reported the separation of L-Lys,methionine,and glutamic acid by electrodialysis.It was showed that L-Lys streams through cation-exchange membrane and glutamic acid through anion-exchange membrane reached a maximum at a neutral range of pH.With an increase in current density,the stream of L-Lys and glutamic acid through membranes also increased.The electrodialysis experiments of the lysine fermentation waste were also performed to generate demineralized feed and ammonium sulfate by H.J.Lee et al.[13].The electrodialysis performances were compared for different ion ex-change membranes in terms of ammonium sulfate removal rate,resistance and conductivity change.With conventional electrodialysis method by adding sodium hydroxide to the initial solution,L-Lys has been also successfully produced from L-Lys·HCl in our earlier work [14].However,the highest Cl -removal ratio is 73.1%,which is slightly low for practical application.

Consequently,in order to further improve the Cl -removal ratio,the feasibility of recovery of L-Lys from L-Lys·HCl by ion substitution electrodialysis was evaluated in the present work.Effects of several parameters including the operation voltage,initial concentration and pH of L-Lys·HCl solution,and the operation temperature are presented one by one.The process performance parameters of the whole operation system,such as the current density,removal ratio of Cl ?,the current ef ?ciency,and the energy consumption are also studied.

Desalination 271(2011)163–168

?Corresponding author.Tel./fax:+868166089372.E-mail address:zhangyaping@https://www.wendangku.net/doc/1c6133562.html, (Y.

Zhang).

0011-9164/$–see front matter ?2010Elsevier B.V.All rights reserved.doi:

10.1016/j.desal.2010.12.016

Contents lists available at ScienceDirect

Desalination

j o u r n a l h o me p a g e :w w w.e l sev i e r.c om /l oc a te /de sa l

2.Experimental

2.1.Materials

The heterogeneous cation-exchange membrane(CEM)and anion-exchange membrane(AEM)were purchased from Shanghai Shang-hua Water Treatment Material Co.,Ltd.(China),and their main characteristics are listed in Table1.In order to avoid the perturbation of the impurities in the membranes,the purchased membranes(CEM and AEM)were pretreated with1mol L?1HCl and NaOH for4h alternately and then washed with deionized water before electrodi-alysis.The CEM and AEM were then inverted to a hydrogen and chlorine type respectively.

L-lysine monohydrochloride,sodium hydroxide,sodium nitrate and sodium sulfate,etc.of AR grade were commercially obtained and

used without further puri?cation.Deionized water was used thoroughly.

2.2.Methods

In ion exchange electrodialysis,the laboratory-scale electrodialyzer consisted of one anode,one cathode,two pieces of anion-exchange membranes(AEMs),as well as one piece of cation-exchange membrane (CEM)inserted between them with the inter-membrane distance of 8mm(Fig.1).There were four compartments with a volume of25mL from left to right:compartment1containing0.5mol L?1of Na2SO4 solution,compartment2containing0.3mol L?1of NaNO3solution, compartment3composed of L-Lys·HCl solution of a certain concentra-tion,and compartment4composed of0.5mol L?1NaOH solution.All above compartments were connected to a separate external500mL beaker,allowing for continuous recirculation by four submerged pumps (AT-301,ATMAN)with the?ow rate of15L h?1.The size of the ion-exchange membrane was7cm×7cm with an effective area of25cm2.

A DC power(DF1731SLL3A,Zhongce Electronics Co.,Ltd.,China)was used to apply constant potential across the electrodes.The pH value of the solution in compartment3was regularly monitored by an acidity meter(PHS-2C,Shanghai Hongyi Instrumentation Co.,Ltd.,China).

The electrodialysis process of ion substitution involves four stages:(i)generation of OH?by dissociation of NaOH at cathode and its migration through AEM from catholyte to compartment3; (ii)substitution of Cl?by OH?in compartment3;(iii)migration of Cl?from compartment3to2through AEM;(iv)generation of H+ by water splitting at anode and its migration through CEM and subsequent formation of HCl in compartment2.

All experiments were repeated three times at room temperature and their mean value was taken as the?nal result.The estimated error is about±5%.

3.Results and discussion

3.1.Effect of operation voltage

Experiments for in situ ion substitution of L-Lys were carried out at different applied potentials ranging between20and50V with initial L-Lys·HCl concentration of0.2mol·L?1.The results of operation process including current density,removal ratio of Cl?,pH in various compartment,current ef?ciency and energy consumption were shown in Figs.2–6.By the way,in order to make the?gures in this work to be seen more clearly,error bars were given to show the level of uncertainty and the signi?cance of these behaviors.

3.1.1.Current density and removal ratio of Cl?

When an electric?eld is applied,OH?ion migrates from compartment4to3and also Cl?ion from compartment3to2 through AEMs,thus the L-Lys forms in compartment3.Variations of current density with time during such an ion exchange process at various operation voltages were depicted in Fig.2.

When the operation voltage is?xed,initial current density is low and then increases to some extent.After attaining the maximum value,it decreases with time gradually.During the electrochemical process,applied voltage is responsible for the formation or transpor-tation of OH?,H+and Cl?.At the beginning of electrodialysis,ion transfer under the drive of electric?eld force takes place,including electro-migration of OH?from compartment4to compartment3and that of Cl?from compartment3to compartment2,thus,the increase in ionic concentration in compartment2leads to the rising current density.However,after reaching the maximum current density, electrolyte(L-Lys·HCl)concentration in compartment3is sharply lowered,which causes an increase in the overall electrical resistance, and thus the current density decreased.In fact,such an experimental trend can be observed during the whole electrodialysis procedure, which is also in accordance with the results reported by M.Kumar et al.[15].

Removal ratio of Cl?is one of the most important parameters to examine the practical feasibility in this work.In the electrodialysis process,almost all Cl?ions transfer across the AEM and concentrate in

Table1

Main characteristics of the ion-exchange membrane.

Membrane Cation-exchange

membrane Anion-exchange membrane

Water content(%)35~5530~45 Exchange capacity

(mol kg?1)

≥2.0≥1.8

Resistance(Ω?cm2)1112 Thickness(mm)0.420.42 Transport number(%)90

89

Fig.1.Schematic of the electrodialyzer for L-Lys production

(ISED).

Fig.2.Variation of current density with time at different voltages(-■-20V;-●-30V; -▲-40V;-▼-50V).

164Y.Zhang et al./Desalination271(2011)163–168

compartment 2,no Cl 2can be measured in compartment 1.Thus the removal ratio of Cl ?can be calculated as R m in Eq.(1):R m %eT=

n t eT

S ×100e1T

Where n (t )is the mole amount of Cl ?titrated by AgNO 3with K 2CrO 3as an indicator in compartment 2(mol);n s (0)the mole amount of initial L-Lys·HCl (mol)in compartment 3.

Removal ratios of Cl ?at different applied voltages were presented in Fig.3.Obviously,the removal ratio of Cl ?increases with time and then keeps almost unchanged at each voltage.When the voltage increases from 20V to 40V,the ?nal removal ratio of Cl ?also increases from 77.5%to 91.1%.That means,the higher the applied voltage,the higher the removal ratio of Cl ?is.Such a result is caused by a stronger electrical force at 40V than 20V.However,this tendency doesn't exist anymore when a higher voltage of 50V was applied.It can be seen from Fig.3that the removal ratio of Cl ?at 50V was 83%,which is lower than that at 40V (91.1%).This is because that the higher applied voltage induces quite large amount of OH ?by water splitting in the catholyte [16],and fast migration of OH ?from compartment 4to compartment 3will lower the exchange process of Cl ?by OH ?[17].

In addition,the pH of the solution in each compartment also changes with the electrodialysis time as shown in Fig.4,with an applied voltage of 40V and an initial L-Lys·HCl concentration of 0.2mol L ?1respectively.When the electrodialysis process begins,the electrode reaction occurs as below:

Anode reaction:2OH ?

?2e →H 2O +

12O 2

↑e2T

Cathode reaction:2H t

t2e →H 2↑e3T

Initially,the anolyte in compartment 1offers nearly pH 7.2because the Na 2SO 4solution is neutral,and afterwards it decreases to some extent due to the formation of H +by water splitting.Likely,the pH of catholyte in compartment 4is initially 13.3and then increases slightly,which is due to the dissociated OH ?from NaOH and H 2O,according to Eq.(3).The pH in compartment 3was ?rstly 6.7and ?nally 10.2,close to be 9.74.The reason is that the initial L-Lys·HCl solution is nearly neutral,and amount of L-Lys are produced companied with the electrodialysis process,thereby,the pH increases gradually until the end of the electrodialysis process,when the pH in compartment 3is about the isoelectric point of L-Lys.Besides,the pH of compartment 2decreases with time on account of immigration of H +from compartment 1.As a matter of fact,a similar relationship between the pH value in each compartment and electrodialysis time can be always observed during all of our experiments,and explana-tions are also

analogous.

Fig.3.Variation of removal ratio of Cl ?with time at different voltages (-■-20V;-●-30V;-▲-40V;-▼-50

V).

Fig.4.Variations of solution pH with time (-■-:compartment 1;-●-:compartment 2;-▲-:compartment 3;-▼-:compartment

4).

Fig.5.Variation of current ef ?ciency with removal ratio of Cl ?at different voltages (-■-20V;-●-30V;-▲-40V;-▼-50

V).

Fig.6.Variation of energy consumption with removal ratio of Cl ?at different voltages (-■-20V;-●-30V;-▲-40V;-▼-50V).

165

Y.Zhang et al./Desalination 271(2011)163–168

3.1.2.Energy consumption and current ef ?ciency

Energy consumption (W)and current ef ?ciency (CE)are also important parameters for assessing the suitability of any electro-chemical process for their practical application,which were shown in Figs.5and 6.The energy consumption (kW h kg ?1of L-Lys recovered)was de ?ned as Eq.(4):W kW h kg

?1

=∫t

0IUdt m

e4T

where m was the weight of recovered L-Lys (kg);I the current (A);t the time (h)and U the voltage (V).

The overall current ef ?ciency (CE)was de ?ned as Eq.(5):CE %eT=

zF Δn ∫t

0Idt

×100e5T

where Δn was the mole amount of recovered L-Lys (mol);z the ionic valency and F the Faraday constant (96,500C mol ?1).

As shown in Figs.5and 6,as a whole,the current ef ?ciency decreases with removal ratio of Cl ?and the energy consumption increases with time at the ?xed voltage,which conforms to the typical trends reported by T.W.Xu et al.[18].However,for the current ef ?ciency at the same removal ratio of Cl ?,its order follows:40V N 30V N 20V N 50V;while the order of energy consumption at different voltages is 50V N 40V N 30V N 20V.It can be explained from such aspects:While the applied voltage is as high as 50V,much water dissociation in the catholyte results in competitive transfer of OH ?with Cl ?.Furthermore,the water dissociation at the surface of the membrane leads to the quick increase of membrane stack resistance [19].In addition,heat emission transformed from part of the electric energy may occur at a higher voltage [20].The above three aspects can give rise to the decrease of current ef ?ciency and increase of energy consumption at 50V undoubtedly.Of course,decreasing the voltage to 20V can bene ?t the energy consumption as seen from Fig.5.Nevertheless,when the applied voltage is lowered (20V),the electronic ?eld force is weakened and the transference of Cl ?ions is limited,leading to the lower current ef ?ciency.In conclusion,a lower or higher applied voltage is both disadvantageous to the electrodial-ysis process considering such three parameters as removal ratio of Cl ?,current ef ?ciency and energy consumption.3.2.Effect of initial L-Lys·HCl concentration

In this part,the effect of initial L-Lys·HCl concentration was investigated with an applied voltage of 40V.Various electrodialysis experiments were carried out at the L-Lys·HCl concentrations of 0.2mol L ?1,0.6mol L ?1and 1.0mol L ?1.The obtained removal ratio of Cl ?,current density,energy consumption and current ef ?ciency were shown in Figs.7–10.

The initial concentration of L-Lys ·HCl also affected the current density and removal ratio of Cl ?during ionic exchange.Figs.7and 8present the variation of current density and removal ratio of Cl ?with time respectively.At a ?rst glance,the experimental trends of current density and Cl ?removal ratio with time are similar to that at different voltages.That is to say,at different initial L-Lys ·HCl concentrations current density ?rst increases with electrodialysis time,then reaches a maximum and ?nally falls to some extent.As for the removal ratio of Cl ?,it increases with time,reaches a maximum and then keeps almost unchanged.If electrodialysis time is ?xed,the order of current density is as the following: 1.0mol L ?1N 0.6mol L ?1N 0.2mol L ?1,this is quite apparent,since the higher the initial concentration of L-Lys ·HCl,the more the ions there are,and so is the current density.However,there is a little difference in the removal ratio of Cl ?.When the initial L-Lys ·HCl concentration is as low as 0.2mol L ?1,the ionic amount in compartment 3is less,and the ionic transfer to compartment 2is

faster under the same operation voltage,which means the time that must be taken to reach the highest current density is shorter than that at higher concentrations.Such a result can be also veri ?ed by Fig.7,namely,the lower the initial concentration of L-Lys·HCl,the shorter the time that must be taken to reach the largest current density.So

the

Fig.7.Variation of current density with time at different initial L-Lys·HCl concentra-tions (-■-0.2mol L ?1;-●-0.6mol L ?1;-▲-1.0mol L ?1

).

Fig.8.Variation of removal ratio of Cl ?with time at different initial L-Lys·HCl concentrations (-■-0.2mol L ?1;-●-0.6mol L ?1;-▲-1.0mol L ?1

).

Fig.9.Variation of current ef ?ciency with removal ratio of Cl ?at different initial L-Lys·HCl concentrations(-■-0.2mol L ?1;-●-0.6mol L ?1;-▲-1.0mol L ?1).

166Y.Zhang et al./Desalination 271(2011)163–168

Cl ?removal ratio at the initial concentration of 0.2mol L ?1

is slightly higher than concentrations 0.6mol L ?1and 1.0mol L ?1in the ?rst hours of the electrodialysis process.But after some time,the removal ratio of Cl ?changes much slowly,and even stays almost constant,the ?nal removal ratio at 0.2mol L ?1is lower than that at 0.6mol L ?1.The reason considered is that a lower concentration implies fewer amounts of ions which can migrate across the ion-exchange membrane,leading to the lower ?nal Cl ?removal https://www.wendangku.net/doc/1c6133562.html,ck of ion causes an increase in electrical resistance undoubtedly,which leads to the increase in energy consumption and reduction in current ef ?ciency as shown in Figs.9and 10.However,when the initial concentration of L-Lys is too high (e.g.,1.0mol L ?1),the Cl ?removal ratio decreases contrarily.It can be also found from Figs.9and 10that when the initial concentration increases from 0.6mol L ?1to 1.0mol L ?1,the energy consumption and current ef ?ciency increases and falls,respectively.The reasons are considered as below:On one hand,while initial concentration of L-Lys·HCl is higher,the current increases too.The current density is possibly higher than the limit one at the anion-exchange membranes,water dissociation appears and then amount of OH ?competes with Cl ?,which is responsible for the decreasing removal ratio of Cl ?and current ef ?ciency,together with the increasing energy consumption;On the other hand,the time which is taken to reach the same Cl ?removal ratio for higher concentration is longer than that for lower one,leading to higher energy consumption and lower current ef ?ciency.Thus,too high initial concentration is also disadvantageous to electrodialysis.3.3.Effect of initial pH of L-Lys·HCl solution

Here,initial pH in compartment 3was controlled to be 3,9.74and 13by buffer solution to measure the effect of initial pH of L-Lys·HCl solution.In the meantime,another testing with initial pH uncon-trolled was also carried out for comparison.Four experiments with initial pH=3,not control,9.74and 13were carried out with the L-Lys·HCl concentration 0.6mol L ?1at constant voltage of 40V,the results including the variation of pH in compartment 3and recovery ratio of L-Lys were shown in Figs.11and 12.

It can be seen from Fig.11that all pH values in compartment 3at different initial pHs tend to be close to the isoelectric point of L-Lys,i.e.9.74,with the electrodialysis process going on.Such a result seems plausible,because more and more L-Lys are produced in compartment 3with time elapsed,further the pH should approaches its isoelectric point ?nally.

In addition,initial pH of L-Lys·HCl mainly affects the recovery ratio of L-Lys.Recovery ratio of L-Lys (%),R is calculated by Eq.(6),among

which the content of L-Lys was determined according to Formol titration method [21]:R =

n R t eT

n S 0eT

×100%e6T

where n R (t)is the mole amount of L-Lys in compartment 3(mol).

It can be seen from Fig.12that the highest recovery ratio of L-Lys (93.2%)can be achieved at the isoelectric point 9.74.This may be explained from the following facts:L-Lys is electrically neutral in aqueous solution at the isoelectric point,and its transfer through the ion-exchange membrane reaches the minimum level.Of course,a fraction of L-Lys is still ionized which contributes to its little loss.When initial pH equals 13,L-Lys exists preferably in form of anion,which is transferred through anion-exchange membrane by electric ?eld force,causing the lowest recovery ratio of L-Lys (78.7%).When initial pH is controlled or kept at 3,there are a mass of L-Lys +in the solution because of the dissociation of L-Lys.Further they can also transfer through the cation-exchange membrane,leading to the loss of L-Lys.Thus,the closer the initial pH to the isoelectric point,the higher the recovery ratio of L-Lys is.3.4.Effect of operation temperature

As is known,ionic transfer is largely affected by operation temperature during electrodialysis.However,there is little attention paid to such an aspect up to now.In order to study the effect

of

Fig.10.Variation of energy consumption with removal ratio of Cl ?at different initial L-Lys·HCl concentrations (-■-0.2mol L ?1;-●-0.6mol L ?1;-▲-1.0mol L ?1

).

Fig.11.Variation of pH in compartment 3at various initial pHs (-▲-pH =3;-■-not control;-●-pH=9.74;-▼-pH=

13).

Fig.12.Variation of L-Lys recovery ratio with pH.

167

Y.Zhang et al./Desalination 271(2011)163–168

operation temperature,several experiments were carried out at20,40 and60°C,respectively.Here,the initial concentration of L-Lys·HCl was0.6mol L?1,the applied voltage was40V and the initial pH in compartment3was controlled to be9.74.The comparisons of operation process performance parameters were also listed in Table2. Here,the operating time was de?ned as the time when the removal ratio of Cl?keeps almost unchanged and doesn't increase sharply any more.

Obviously,the process of electrodialysis can be strongly affected by operation temperature as indicated in Table2.A higher operation temperature can improve the electrodialysis process,such as shortening the time which is taken to reach the highest Cl?removal ratio,consuming less energy and obtaining higher current ef?ciency, The reason for these results is that the migration of ions through the ion-exchange membranes is faster at a higher temperature,which gives rise to the decrease in the electrical resistance and then brings out a higher current ef?ciency and lower energy consumption.

4.Conclusions

An ion substitution electrodialysis(ISED)process with four compartments was proved to be successful in recovery of L-Lys from L-Lys·HCl.Effects of such parameters,such as the applied voltage,initial L-Lys·HCl concentration,the initial pH of L-Lys·HCl, and the temperature on operation process performance were studied. High removal ratio of Cl?(95.6%)was achieved at the initial concentration and pH of L-Lys·HCl of0.6mol L?1and9.74respec-tively,the applied voltage40V and the room temperature.The initial pH value of L-Lys·HCl can affect the recovery ratio of L-Lys.When the pH value of L-Lys·HCl is controlled to be its isoelectric point,the recovery of L-Lys is highest(93.2%).Increasing the operation temperature can promote the electrodialysis process.That is to say, the higher the operation temperature,the higher current ef?ciency and the lower energy consumption are.

Acknowledgements

Financial supports from Doctoral Research Foundation of South-west University of Science and Technology(No.06zx7119)and Opening Foundation of Key Laboratory of Solid Waste Treatment and Resource Recycle(Southwest University of Science and Technology) (No.09zxgk03)Opening Foundation of Engineering Research Center of Biomass Materials,Ministry of Education(Southwest University of Science and Technology)(No.10zxgk08)are greatly appreciated. References

[1]Y.Gunji,H.Yasueda,Enhancement of L-lysine production in methylotroph

Methylophilus methylotrophus by introducing a mutant LysE exporter,Journal of Biotechnology127(2006)1–13.

[2]P.Arruda,E.L.Kemper,F.Papes,A.Leite,Regulation of lysine catabolism in higher

plants,Trends in Plant Science5(2000)324–330.

[3]S.Harakeh,M.Diab-Assaf,K.Abu-El-Ardat,A.Niedzwiecki,M.Rath,Mechanistic

aspects of apoptosis induction by L-lysine in both HTLV-1-positive and-negative cell lines,Chemico-Biological Interactions164(2006)102–114.

[4]T.Mohammadi,O.Bakhteyari,Concentration of L-lysine monohydrochloride

(L-lysine·HCl)syrup using vacuum membrane distillation,Desalination200 (2006)591–594.

[5] C.H.Huang,T.W.Xu,Y.P.Zhang,Y.H.Xue,G.W.Chen,Application of electrodialysis

to the production of organic acids:state-of-the-art and recent developments, Journal of Membrane Science288(2007)1–12.

[6]V.H.Thang,W.Koschuh,K.D.Kulbe,S.Novalin,Detailed investigation of an

electrodialytic process during the separation of lactic acid from a complex mixture,Journal of Membrane Science249(2005)173–182.

[7]S.Novalic,T.Kongbangkerd,K.D.Kulbe,Recovery of organic acids with high

molecular weight using a combined electrodialytic process,Journal of Membrane Science166(2000)99–104.

[8]J.Y.Shen,J.R.Duan,Y.S.Liu,L.X.Yu,X.H.Xing,Demineralization of glutamine

fermentation broth by electrodialysis,Desalination172(2005)129–135.

[9]L.F.Liu,L.L.Yang,K.Y.Jin,D.Q.Xu,C.J.Gao,Recovery of L-tryptophan from

crystallization wastewater by combined membrane process,Separation and Puri?cation Technology66(2009)443–449.

[10] A.E.Aghajanyan,A.A.Hanbardzumyan,A.A.Vardanyan,A.S.Saghiyan,Desalting of

neutral amino acids fermentative solutions by electrodialysis with ion-exchange membranes,Desalination228(2008)237–244.

[11] A.E.Bukhovets, A.M.Savel'eva,T.V.Elisseevam,Separation of amino acids

mixtures containing tyrosine in electro-membrane system,Desalination241 (2009)68–74.

[12]T.V.Elisseeva,V.A.Shaposhnik,I.G.Luschik,Demineralization and separation of

amino acids by electrodialysis with ion-exchange membranes,Desalination149 (2002)405–409.

[13]H.J.Lee,S.J.Oh,S.H.Moon,Recovery of ammonium sulfate from fermentation

waste by electrodialysis,Water Research37(2003)1091–1099.

[14]Y.Chen,Y.P.Zhang,M.Z.Yue,Y.L.Zhou,Production of L-lysine from L-lysine

monohydrochloride by electrodialysis,Desalination and Water Treatment(in press).

[15]M.Kumar,B.P.Tripathi,V.K.Shahi,Electro-membrane reactor for separation and

in situ ion substitution of glutamic acid from its sodium salt,Electrochimica Acta 58(2009)4880–4887.

[16]J.Khan,B.P.Tripathi,A.Saxena,V.K.Shahi,Electrochemical membrane reactor:in

situ separation and recovery of chromic acid and metal ions,Electrochimica Acta 52(2007)6719–6727.

[17]Q.S.Wang,T.J.Ying,T.J.Jiang,D.M.Yang,M.M.Jahangir,Demineralization of

soybean oligosaccharides extract from sweet slurry by conventional electrodial-ysis,Journal of Food Engineering95(2009)410–415.

[18]T.W.Xu,W.H.Yang,Citric acid production by electrodialysis with bipolar

membranes,Chemical Engineering and Processing41(2002)519–524.

[19]X.Y.Zhang,W.H.Lu,H.Y.Ren,W.Cong,Recovery of glutamic acid from isoelectric

supernatant using electrodialysis,Separation and Puri?cation Technology55 (2007)274–280.

[20]Z.X.Wang,Y.B.Luo,P.Yu,Recovery of organic acids from waste salt solutions

derived from the manufacture of cyclohexanone by electrodialysis,Journal of Membrane Science280(2006)134–137.

[21]H.H.Tang,X.Y.Xie,Determination of total amino acids in21processed animal

medicines by the formalin method,Journal of Naval General Hospital20(2007) 14–158(In Chinese).

Table2

Comparison of operation process performance parameters at different temperatures.

Temperature (°C)Operating

time(h)

Removal ratio

of Cl?(%)

Current

ef?ciency(%)

Energy consumption

(kw h kg?1)

201195.620.59.0

40995.423.97.92

60796.427.4 6.33

168Y.Zhang et al./Desalination271(2011)163–168

电渗析设备的工作原理及其基本概况

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闭阀3直到冲洗排水干净为止。然后再打开阀3关闭阀4,再打开阀1后关闭阀2,待阀3的排放水干净后关闭它。以上是石英砂过滤器的冲洗方法,活性炭过滤器的冲洗方法同上。接下来再做精密过滤器的冲洗:打开阀11再关闭阀12,然后打开阀9关闭阀10 直到冲洗干净后打开阀10关闭阀9,再打开阀12及13后关闭阀11待水干净后准备将电渗析投入运行使用。每次的运行时间是2—4小时不能超过4小时。 调节阀门14—16使浓淡水流量达到要求的流量,开启整流控制柜,可以选择正向或反向开启运行,逐渐调节电压直到水质达到要求为止(工作电压在每级膜对总数的1.3—1.4倍之间最好)然后开启相应的17或19阀,在上述调节过程中必须保证电流工作在额定范围内,如果电流过大时可以稍等片刻待电流下降后再逐渐调升电压。否则就会烧坏电气设备。 在使用电渗析设备的时候,要严格遵守以下事项: 1、水的预处理是保证电渗析器正常运行的因素之一,因此水进入电渗析器前必要的预处理,保证进入电渗析器的原水水质符合以下指标。浊度:≯3mg/l;含铁总量:<0.3 mg/l;含锰总量:<0.1 mg/l;色度<15度;含氧量:<3mg /l(kMno4);水温:5-40℃;污染指数:<7。 2、注意起动时,必须先通水,后通电,停止时先断水,严禁停水不停电。 3、淡水流量与浓,极水流量的比例要调节适当,为防止浓水渗漏,浓水,极水的压力可适当减小,一般小0.2×9.38 ×104Pa。 4、视水质情况,电渗析器工作2-8小时后要调换一次电极。 5、膜堆上禁止放金物件,以防产生短路。 6、电渗析器运行使用,详见设备使用说明书。

电渗析水处理技术的优点和不足

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离子交换膜

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电渗析课件

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电渗析法综述

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