Separation of methyl linolenate and its analogues by functional mixture of imidazolium based ionic liquid-organic solvent-cuprous salt

Xianghong Lu*,Jiajian Zhu,Xing Qian,Jianbing Ji

Zhejiang Provincial Key Laboratory of Biofuel,College of Chemical Engineering,Zhejiang University of Technology,Hangzhou 310014,China

Keywords:Methyl linolenate Cuprous salt Ionic liquid Cosolvent Extraction

ABSTRACT Methyl linolenate w as separated from its analogues by a new extraction system constructed by solvent,imidazolium based ionic liquidsand cuproussalt.Firstly,the effect of ionic liquid on the dissolution of Cu Cl in acetonitrile,N,N-dimethylformamide(DMF),methanol and water wasevaluated by visual observation.[C4Mim][Cl]can improve the dissolution of CuCl in acetonitrile.Then,for the new system as acetonitrile-ILs-Cu Cl,extraction equilibrium,distribution ratio and selectivity of methyl linolenate and its analogues were determined by gas chromatography analysis and the mass balance.The extraction time,IL structures and Cu Cl concentrations w ere investigated.Distribution ratio decreased slightly,but selectivity increased signi fi cantly with the addition of CuCl,[C4Mim][Cl]or[C4Vim][NTF2]into acetonitrile.[C4Vim][NTF2]had higher selectivity than[C4Mim][Cl].But the selectivity of the system combining Cu Cl w ith[C4Vim][NTF2]w as much lower than w ith[C4Mim][Cl].For the CuCl-[C4Mim][Cl]-acetonitrile,the extraction ef fi ciency w as better than Cu Cl-acetonitrile,increasing Cu+concentration effectively improved the separation selectivity w hen ratio of Cu Cl/[C4Mim][Cl]w as less than 1.Compared w ith previous aqueous AgNO3 extractions,the method of using Cu Cl is a much cheaper and practical way to enrich unsaturated fatty acid.

1.Introduction

Omega-3 polyunsaturated fatty acids,such as DHA,EPA andαlinolenic acid,are used to lower the level of lipids in blood,treat cardiovascular and cerebrovascular diseases[1].Unfortunately,humans cannot biosynthesize omega-3 fatty acid.Omega-3 polyunsaturated fatty acids have to be obtained from oils or fats in fi sh,microalgae,linseeds and tallow seeds.In order to obtain unsaturated fatty acid w ith a high purity,there are some separation methods applied,including urea inclusion[2,3],low-temperature crystallization[4],molecular distillation[5],lipase-enrich method[6],supercritical fl uid extraction[7].Silver ion is also applied to separate polyunsaturated fatty acid[8].Theπ orbit of C═Cdouble bond of unsaturated fatty acids is fi lled w ith two electrons,and the 5 sorbit of Ag+isempty.Theπelectronsof C═Cdouble bond formσcoordination bond w ith the 5 s orbital of Ag+.In the meantime,Ag+provides a pair of 4 d electrons to the anti-bonding orbit of the C═Cdouble bond,and forms theπback bonding coordination.Theπcomplexation betw een C═Cdouble bond and silver ion has been studied in several w orks including ole fi n/alkane gas separation[9-11],separation of highly unsaturated fatty acid of EPA/DHA from fi sh liver oil[8,12,13].Similarly,as another IBelement,empty 4 s orbit and 3 d electronsof Cu+can also formπcomplexation w ith C═Cdouble bond.Cu+hasthepotential to beapplied in theseparation fi elds.Moreover,copper salt is much cheaper,w hich makes it more promising in these applications.But there is a little inconvenience for Cu Cl use because of its unstability and poor dissolution in water and many organic solvent.Gabriel Zarca[14]used theionic liquidswith chlorineanion and Cu Cl to form the corresponding chlorocuprate(I)-based ionic liquids(e.g.[C4Mim][Cu(Cl)x].Chen[15]and Yu[16]thought that the formation of chlorocuprate(I)-based ionic liquidscould increasethesolubility and stability of Cu Cl.

Ionic liquids are gradually becoming the new promising green solvent because of its unique chemical and physical properties[17-19].Over the past decade,ILs have been w idely studied as solvents for aromatic/aliphatic liquid-liquid separations[20-24].And some studies[12,25-28]using ILs to separating highly unsaturated fatty acid and esters also have been reported,and ILs w ere screened by experiments or theoretical calculation.When the anionsare identical,ILhydrophobicity increases w ith the increase of the imidazolium cation's alkyl chain length,and the more hydrophobic ILs exhibited signi fi cantly higher extraction capabilities[25].Zhu[28]observed that the selectivity of methyl linolenate to its analogues increased w ith the decrease of the hydrogenbond basicity of ILs'anions,and ILs with the anion of[NTF2]exhibited good performance.Recently,the w orks on ole fi ns/alkanes separation using Ag+or Cu+w ith ILs have been reported[29-31].The separation ef fi ciency is better than the pure IL or Ag+no matter in aqueous or solid phase[32].As a novel solvent,imidazolintum chloride ionic liquids wereused to dissolve copper(I)chloride,w hich w ere applied in the separation of propane and propylene,and the interaction between transition metal and double bonds ensured an ideal separation ef fi ciency[33,34].The ILs&Cu system could also be applied in liquid-liquid extraction to separate long chain unsaturated compounds,which was worth exploring.In this work,we prepared tw o groups of cuprous salts with ILs:(1)CuCl-[C4Mim][Cl]and(2)CuCl-[C4Mim][Cl]-[C4Vim][NTF2].Dissolved in acetonitrile,Cu+&ILs w ere used to extract unsaturated fatty acid methyl esters by liquid-liquid extraction.A good separation ef ficiency w as obtained.During the procedure,the solubility of CuCl,the suitable solvent,the effects of concentration of CuCl and the results of the different combination w ere evaluated.The w ork show ed that the imidazolium-based ionic liquid and Cu Cl could be a class of promising separation agent for omega-3 unsaturated fatty acid methyl ester.

2.Experimental

2.1.Materials

The ionic liquidsw ere commercially purchased from Lanzhou Green Chemistry and Catalysis,LICP,including[C4Vim][NTF2](1-butyl-3-vinylimidazolium bis((tri fl uoromethyl)sulfonyl)imide)and[C4Mim][Cl](1-butyl-3-methyl chloride).The Cu Cl(AR,＞97%)used in the experiments w as obtained from Aladdin(Shanghai,China).The Cu Cl was light gray-green because tiny amount of CuCl w as oxidized.Methanol,DMF,n-hexane and acetonitrile(all ARgrade)w ere commercially obtained from Shanghai Ling Feng Chemical Co.LTD.All the agentsand chemicals w ere used w ithout further puri fi cation.

The fatty acid methyl esters(FAMEs)w ere obtained by transesteri fi cation of natural sapium seeds oil,and used in the extraction procedure.The constituents of FAMEmixture w ere analyzed by the GC-Mass and GC-FID.The composition and the content w ere listed in Table 1.

2.2.Extraction procedure

The method of extraction procedure w as similar to the one mentioned in thepreviousliterature[25].Brie fl y,the fatty acid methyl esters were dissolved in n-hexaneand extracted by afunctional mixture of organic solvent-imidazolium ionic liquid(IL)-cuprous salt(Cu+).Careful attention should be paid to that the cuprous ion is very sensitive to light,heat and oxygen.So the extraction procedure w as operated in the darkness.Before dissolving thecuproussalt,an ultrasonic treatment should be applied to the IL-solvent solution.An equal volume(5 ml)of FAMEs(dissolved in hexane)and the mixture of solvent-IL-CuCl were added to a 50 ml brow n Erlenmeyer fl ask.The sealed fl ask w hich w as fi lled w ith nitrogen w as placed in a rotary shaker w ith a w ater bath at 298.15 K.The mixture w as mechanically shaken at 200 r·min-1for a period and then settled for 1 h to ensure fully layered.The volumes of theextract and raf fi natephasesw ere measured(VEand VR)by volumetric cylinder,respectively.0.5 ml of theupper hexanephasew ascarefully pipetted out and transferred to a vial(10 ml)containing 5 ml the internal standard solution.Then the amount of FAMEs in hexane was determined by GC-FID.The amount of FAMEs left in ILphase after extraction was calculated by the mass balance[see Eq.(1)].The distribution ratiosof FAMEs betw een IL phase and hexane phase w ere calculated by Eq.(2).The selectivity of methyl linolenate to itsanalogueswere calculated by Eq.(3).

w here Ci0,CiEand CiRrepresented the concentration of FAMEin feedstock solution,the extract phase and the raf fi nate phase respectively.V0,VEand VRrepresented the volume of feedstock solution,the extract phase and the raf fi nate phase respectively.

2.3.Analysisof FAMEsby GC-FID

GCanalysis of FAMEs w as performed using Agilient 7890N gas chromatograph equipped w ith an auto-injector(Model 7683B)and a fl ame ionization detector(FID).A J&W DB-WAX capillary column(30 m ×32μm × 0.25μm)w as used.The split ratio w as 15.The oven temperature w as programmed as follow:held constant at 150 °Cfor 2 min;and then increased at 10 °C·min-1to 200 °C;and kept 200 °C for 4 min;increased at 40 °C·min-1to 230 °C;and kept 230°Cfor 9 min.The internal standard method w as used for quantifying FAMEcomposition via the Eq.(4).

w here f is the response factor of the individual fatty acid methyl ester,miand misare the amount of any FAME i and the internal standard Aiand Aisare the corresponding peak area of FAME i and internal standard respectively.Methyl undecenoate(C11-1,GCgrade)w as used as the internal standard.The response factor f of methyl linolenate,methyl linoleate,methyl oleate and methyl stearate is regarded asthe same because of their highly similar molecular structure and physicochemical property.The response factor f w as determined as 0.9997 by methyl heptadecanoate.

3.Results and Discussion

3.1.Dissolution of CuCl

Thedissolution of CuCl w asdirectly evaluated by visual observation.A know n amount of CuCl and[C4Mim][Cl]were dissolved in different solvents.The dissolution situation was show n in Table 2 clearly.Although it w asreported that CuCl could form coordination compoundsand be dissolved in acetonitrile,the situation where CuCl wasdissolved in the acetonitrile w ithout[C4Mim][Cl]w as not similar to that reported in the literature[35].As we can observe from Table 2,when dissolved in acetonitrile,the color of theone without[C4Mim][Cl]turned brown and thesolution w as a little turbid due to unstability and low solubility of cuprous ions.Cu+could bring about disproportionation reaction,and reddish brown copper metal was produced along with Cu2+[36].With the addition of[C4Mim][Cl],a stable and clear solution w as obtained.The phenomenon demonstrates that[C4Mim][Cl]can promote dissolution and stability of Cu Cl.The ionic liquids w ith chloride anions and CuCl could form the corresponding chlorocuprate(I)-based ionic liquids(e.g.[C4Mim][Cu(Cl)x][14],w hich leaded to the increase of solubility and stability of CuCl[15,16].

The ratio of CuCl/[C4Mim][Cl]also had an effect on the stability and clarity of the solution.When the ratio of Cu Cl/[C4Mim][Cl]increases from 0.2 to 1.5,the color of the solution gradually turns to brow n,andthe gray-green deposition w as found.Moreover,the dissolution of Cu Cl in different polar solventsw ith the presence of[C4Mim][Cl]w asfurther investigated.The results w ere also show n in Table 2.No matter dissolved in acetonitrile,DMF,methanol or w ater,the color of the solution did not turn to brow n w hen[C4Mim][Cl]w as added.The presence of[C4Mim][Cl]could prevent Cu Cl from being oxidized and kept the solution stablein thefour cases.Although thesolution of CuCl could stay stable,the dissolution situations w ere different.Except in the acetonitrile,Cu Cl could not be dissolved w ell in the other three solutions.The w orst dissolution w as found in w ater,w here green-gray deposition w as found in the bottom of the fl ask.Based on the results,an acetonitrile-[C4Mim][Cl]-Cu Cl solution w as selected as an extracting agent for further study,and the mole ratio of CuCl to[C4Mim][Cl]was 0.2.

Table 2 The dissolution situation of CuCl with the presence of[C4Mim][Cl]

3.2.Extraction equilibrium

Some transition metal salt(e.g.,silver(Ag+)or cuprous(Cu+)salt)can selectively form complex compounds w ith UFAMEs via theπcomplexing interaction betw een transition metal ions and double bonds[37].Cuprous salt is much cheaper than silver salt,but cuprous salt(e.g.,Cu Cl)is reasonably insoluble in w ater and most solvents,and can be easily oxidized and decomposed.As mentioned in Section 3.1,the presence of ILs w ith Cl-as anion can improve the solubility of CuCl in acetonitrile and keep the solution stable.In our w ork,Cu Cl-ILs w as used to separate methyl linolate from the FAMEs mixture.It w as reported that some ILs have been directly used to extract highly unsaturated fatty acid[38].The structure of ionic liquids has a huge impact on its physical and properties[12,39,40].Chenong[26]strongly suggested the correlation of omga-3 PUFA extraction w ith aromatic/delocalized cation structure of ILs because ofπ-π complexation between aromatic/delocalized cation and--C═C--.Lireported that the alkyl substituents on the cation of ILs could increase the lipotropism of the ILs[27].Normally,theimidazolium-based ILsw ith long alkyl chain have low er polarity and higher dissolving capacity for low polar components.But the steric hindrance of the substituent increases w ith the increase of alkyl chain length[41].Based on the fi ndings,1-butyl-3-methyl(or vinyl)-imidazolium ionic liquids w ere selected to improve the solubility of FAMEs in the ILs phase.The results from our preliminary research[28]show ed the selectivity of methyl linolate to its analogues increases w ith the decrease of the hydrogen-bond basicity of IL's anions,NTF2-anion has highest selectivity among the investigated anions,including Ala-,Ac-,(EtO)2PO2-,N(CN)2-,SCN-,CF3SO3-,NTF2-,and BF4-.In the present w ork,[C4Mim][Cl]-[C4Vim][NTF2]-CuCl-acetonitrile was selected as the extracting agent.Hexane w as selected to dissolve FAMEs because it's immiscible w ith ILs and has good solubility for FAMEs.The effect of the extractant composition was studied by determining distribution ratio and selectivity.

3.2.1.Determination of equilibrium time

Althoughπ-π complexing interaction betw een cuprous ions and double bonds of UFAMEs enables the selective extraction of UFAMEs from hexane into the ILphase.The low solubility of UFAMEs in polar ILs brings large interphase mass transfer resistance.The process takes time to reach equilibrium.Therefore,the change of UFAMEconcentration in ILphase with time w as evaluated and show n in Fig.1.The concentration of the three methyl octadecanoate increased w ith time,and the increase gradually leveled off after 20 min extraction,indicating that extraction equilibrium w as reached.A 120 min shaking w as long enough and selected as the standard extracting time in order to ensure extraction stability.

Fig.1.Concentration of FAMEs in the ILphase change with extraction time.

3.2.2.Species of extractant

The addition of ionic liquids into acetonitrile could increase the extractant's polarity,then decrease its dissolving capacity for hydrophobic methyl linolenate.The effects of IL'sconcentration on extraction performance was show n in Fig.2.The results show ed that 0.1 mol·L-1and 0.2 mol·L-1[C4Mim][Cl]had similar extraction performance,but the increase of theconcentration of[C4Mim][Cl]to 0.4 mol·L-1could decrease of the distribution ratio of C18-3 and the selectivity of C18-3 to its analogues.Furthermore,the addition of[C4Mim][Cl]could promote the dissolution of CuCl.As a results,0.2 mol·L-1ILs in acetonitrile was chosen in the following extraction experiments.

The initial concentration of FAMEs in hexane is50 mg·L-1.The concentration of Cu Cl,[C4Mim][Cl]and[C4Vim][NTF2]in acetonitrile is 0.08 mol·L-1,0.2 mol·L-1and 0.2 mol·L-1respectively.The volume ratio of feedstock(hexane phase)and the acetonitrile phase is 1:1.The performance of CuCl,[C4Mim][Cl],[C4Vim][NTF2]was investigated.The results w ere show n in Fig.3.It w as clearly show n that the addition of Cu Cl and ILs had signi fi cant effects on distribution ratio and selectivity.Oppositely pureacetonitrilehad relatively poor selectivity.Theaddition of Cu Cl and ILs somew hat decreased the distribution ratio,but enhances the selectivity of methyl linolate to its analogues,especially to methyl stearate.The selectivity of C18-3 to C18-0 w as1.248 in acetonitrile,w hile the values in CuCl-acetonitrile,[C4Mim][Cl]-acetonitrile,and[C4Vim][NTF2]-acetonitrile raised to 8.898,5.336,and 7.296 respectively,w ith approximately seven-fold increase for the addition of CuCl.CuCl with the concentration of 0.08 mol·L-1had greater impact on the selectivity than 0.2 mol·L-1[C4Mim][Cl]or 0.2 mol·L-1[C4Vim][NTF2],which indicated that Cu+interacts much more strongly with double bonds than aromatic/delocalized cation core of ILs.Cu Cl could not be w ell dissolved in the acetonitrile.The solution w ith 0.04 mol·L-1CuCl in acetonitrile was brow n and a little turbid(show n in Table 2),w hich implied only a little CuCl w as dissolved and w orked w hen 0.08 mol·L-1Cu Cl-acetonitrile w as used as extractant.Therefore ILs w ere added into the CuCl-acetonitrile in order to promote the dissolution of CuCl.The performance of Cu Cl w ith the presence of[C4Mim][Cl]and[C4Vim][NTF2]w ere also show n in Fig.3.Compared w ith Cu Cl(Fig.3-B),the addition of[C4Vim][NTF2](Fig.3-F)low ered theselectivity,but the addition of[C4Mim][Cl](Fig.3-E,G)enhanced the selectivity.The highest selectivity was obtained using CuCl-[C4Mim][Cl]-acetonitrile system.The selectivity of methyl linolate to methyl stearate w as high up to 12.49 in Cu Cl-[C4Mim][Cl]-acetonitrile from 8.898 in CuCl-acetonitrile.The vinyl group on imidazolium ring of[C4Vim][NTF2]w as an electron-w ithdraw ing group.It could increase the aromaticity of imidazolium ring and form strongerπ-π complexing w ith double bond.Asa result,[C4Vim][NTF2]had higher selectivity than[C4Mim][Cl]in the extractant w ithout CuCl.But careful attention should be paid to the fact that Cu+would formσcoordination with the double bond of the vinyl group,w hich hindered the coordination betw een the Cu+and unsaturated fatty acid methyl esters.The interaction betw een vinyl group of[C4Vim][NTF2]and Cu+could counteract or neutralizeextraction performance.So the addition of[C4Vim][NTF2]into the extractant containing Cu Cl had negative effect on the selectivity,w hich accorded with the difference betw een Band F,Dand F,Gand Ein Fig.3.

Fig.2.The effects of IL's concentration on extraction performance.

Fig.3.Distribution ratio of FAMEs(a)and selectivity of C18-3 to its analogues(b)in different extractants.A:acetonitrile;B:acetonitrile-CuCl;C:acetonitrile-[C4Mim][Cl];D:acetonitrile-[C4Vim][NTF2];E:acetonitrile-CuCl-[C4Mim][Cl];F:acetonitrile-CuCl-[C4Vim][NTF2];G:acetonitrile-CuCl-[C4Mim][Cl]-[C4Vim][NTF2].

3.2.3.Cu+concentration

Fig.4.Distribution ratio of FAMEs and selectivity of C18-3 to its analogues in acetonitrile(a),acetonitrile-CuCl-[C4Vim][Cl](b),and acetonitrile-CuCl-[C4Vim][Cl]-[C4Vim][NTF2](C)with different Cu+concentration.

Table 3 Comparison on extraction performance betw een Cu+and Ag+

The effects of CuCl concentration on the distribution ratio and selectivity w ere investigated and show n in Fig.4.In the work,the initial concentration of FAMEsin hexane was50 mg·L-1,and theconcentration of both[C4Mim][Cl]and[C4Vim][NTF2]in acetonitrile w as 0.2 mol·L-1.The investigated Cu Cl concentration in acetonitrile w as low er than in acetonitrilel-[C4Mim]Cl and acetonitrilel-[C4Mim][Cl]-[C4Vim][NTF2]based on low solubility of CuCl in acetonitrile and promoting effect of[C4Mim][Cl]for CuCl dissolution.As show n in Fig.4,the extraction performance w as related to Cu+concentration,and Cu+concentration had different in fl uence in the different systems.In the tw o systems of acetonitrile-Cu Cl and acetonitrile-[C4Mim][Cl]-CuCl,thedistribution ratios decreased,and the selectivity for methyl linolenate increased w ith the increase of Cu Cl concentration.Especially in the system of acetonitrilel-[C4Mim][Cl]-CuCl,the selectivity of methyl linolenate to methyl stearate signi fi cantly increased with the growing CuCl concentration,it raised to 29.44 from 8.82 w hen CuCl concentration w ent up to 0.2 mol·L-1from 0.04 mol·L-1.However,the selectivities of methyl linolenate to the other three FAMEs increased rather slowly,only reached 1.77,3.24 and 3.69 respectively w hen Cu Cl concentration w as 0.2 mol·L-1.Thedifference in theselectivity could beascribed to theinteraction betw een double bond and Cu+,and the difference in the polarity of FAMEs.The great difference in the number of double bonds between methyl linolenate and methyl stearate resulted in the good selectivity.Methyl palmitate has shorter chain and higher polarity than methyl stearate,can dissolve in the polar extracting phase more preferably than methyl stearate.Asaresult,theselectivity of C18-3/C16-0 w as much less than the one of C18-3/C18-0.It w as worth mentioning that the selectivity of methyl linolenate to methyl stearate w as 30.85 at Cu Cl concentration of 0.3 mol·L-1,only increased 4.8%compared with CuCl concentration of 0.2 mol·L-1.It is easily understood by the limited solubility of CuCl in acetonitrile.Although[C4Mim][Cl]could enhance dissolution of CuCl,the ratio of CuCl/[C4Mim][Cl]w as preferably less than 1 to keep the solution stable and clear as mentioned above.When more amount of Cu Cl w as added in the mixture,just a little part could be dissolved,w hich resulted in slight grow th in the selectivity w as obtained.

In the case of acetonitrilel-[C4Mim][Cl]-[C4Vim][NTF2]-Cu Cl,the trend was similar to the other tw o cases w hen Cu+concentration w as betw een 0.04 mol·L-1and 0.1 mol·L-1.In this range,the distribution ratiosdecreased,and the selectivity w asgetting higher w ith theincrease of Cu+concentration.How ever,a reverse trend in the distribution ratio and the selectivity could be observed w hen Cu+concentration was in therange of 0.1 mol·L-1-0.3 mol·L-1.It wasclear that thehighest selectivity was obtained at Cu+concentration of 0.1 mol·L-1,the selectivity of C18-3/C18-2,C18-3/C18-1,C18-3/C18-0 and C18-3/C16-0 w as 1.77,3.16,33.56 and 3.47 respectively.

Although the selectivity decreased with the addition of[C4Vim][NTF2]into acetonitrile-[C4Mim][Cl]-CuCl within the most concentration range of CuCl,w hich was show n in Fig.4.But astoundingly,at CuCl concentration of 0.1 mol·L-1,the addition of[C4Vim][NTF2]brought approximately one fold of increase in the selectivity of C18-3/C18-0.The experiments were performed three times,and the Standard Deviation(the S value)and the coef fi cient variance(CV)w ere calculated.All of the coef fi cient variance(CV)were not greater than 5%,which suggested theexperimental results w ere reliable.Furthermore,the extraction performance of the mixture of several ILs and CuCl deserved further study for practical application.

3.3.Comparison on extraction performances between Cu+and Ag+

An ef fi cient extraction method based onπ-complexing interactions betw een silver ions and double bonds of polyunsaturated fatty acid methyl estershasbeen established using ILscontaining AgBF4asextraction phases[25].Cu locates in the same IBfamily as Ag,and they have similar properties.The comparison on extraction performance betw een Cu+and Ag+w asalso show n in Table 3.The results in columns 2 and 3 w ere got by experiments,and the results in columns 4 and 5 w ere from Li’w orks[25].Theextraction performanceof Cu+/Ag+-ionic liquid isinfl uenced by the ionic liquid type and the concentration of Cu+/Ag+.Comparing w ith 0.2 mol·L-1AgBF4-[BMim][BF4],0.2 mol·L-1Cu Cl-0.2 mol·L-1[BMin][Cl]-acetonitrile has better selectivity of C18-3 to C18-0,but the w orse selectivity of C18-3 to C18-1 and to C18-2.It is notew orthy that a small quantity of AgBF4in[HMim][PF6]can get large distribution ratio of C18-3.In summary,cuprous salt is cheaper and has good extraction performance,thus has the potential to be applied in the separation of polyunsaturated fatty acid and its esters,but for practical application,further w orks have to be done.

4.Conclusions

In this w ork,a new extraction system constructed by acetonitrile,imidazolium based ionic liquidsand Cu Cl w ereapplied in theseparation of methyl linolenate from its analogues by liquid-liquid extraction.With the presence of[C4Mim][Cl],the solubility of CuCl in acetonitrile could be improved.Distribution ratiosdecreaseslightly,but selectivities increase signi fi cantly w ith the addition of CuCl or ILs such as[C4Mim][Cl]and[C4Vim][NTF2]into acetonitrile.[C4Vim][NTF2]had higher selectivity than[C4Mim][Cl].Compared to pure ILs or pure CuCl,the combination of Cu Cl w ith[C4Mim][Cl]ensured a better separation performance,but the addition of[C4Vim][NTF2]into the extractant containing CuCl had a negative effect on theselectivity.For theacetonitrile-[C4Mim][Cl]-Cu Cl,increasing Cu+concentration effectively improved the separation selectivity w hen ratio of Cu Cl/[C4Mim][Cl]w as less than 1.The w ork show ed an extractant containing alkylimidazoliumbased ILs and cuprous salts were promising reactive agents to separate UFAMEs.