Bioresource Technology 109 (2012) 312–315

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Bioresource Technology

journal homepage: www.elsevier .com/locate /bior tech

Ionic liquid-mediated extraction of lipids from algal biomass

Young-Hoo Kim a, Yong-Keun Choi a, Jungsu Park a, Seongmin Lee a, Yung-Hun Yang a, Hyung Joo Kim a,Tae-Joon Park b, Yong Hwan Kim c, Sang Hyun Lee a,⇑a Department of Microbial Engineering, Konkuk University, Seoul 143-701, South Koreab Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749, South Koreac Department of Chemical Engineering, Kwangwoon University, Seoul 139-701, South Korea

a r t i c l e i n f o a b s t r a c t

Article history:Available online 1 May 2011

Keywords:Ionic liquidLipid extractionMicroalgaeBiodieselChlorella vulgaris

0960-8524/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.04.064

⇑ Corresponding author. Tel.: +82 2 2049 6269; faxE-mail address: sanghlee@konkuk.ac.kr (S.H. Lee).

Lipids from algal biomass were extracted using mixtures of ionic liquids (ILs) and methanol, and fattyacid profiles of the extracted lipids were characterized in this work. Mixtures of ILs and methanol suc-cessfully dissolved biomass leaving lipids insoluble. The total contents of lipids extracted from commer-cial and cultivated Chlorella vulgaris were 10.6% and 11.1%, respectively, by the conventional Bligh andDyer’s method, while a mixture of [Bmim][CF3SO3] and methanol extracted 12.5% and 19.0% of the lipids,respectively. Multi-parameter regression by the linear solvation energy relationship showed that dipolar-ity/polarizability and hydrogen bond acidity of ILs are more important than their hydrogen bond basicityfor effectively extracting lipids from algal biomass. Fatty acid profiles of the lipids extracted usingIL–methanol mixtures showed that C16:0, C16:1, C18:2, and C18:3 fatty acids were dominant. This sug-gests that the lipids extracted from C. vulgaris can be used as a source of biodiesel production.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The rapidly growing demand for energy, a dwindling and unsta-ble supply of petroleum, and the exacerbation of global warmingdue to the use of fossil fuels have rekindled a strong interest in pur-suing alternative and renewable energy sources (Lee et al., 2009).Thus, the production of biodiesel from various materials, such asplants, microalgae, and animal fat, has been pursued as an alterna-tive energy source (Lee et al., 2010). Of the biodiesel feedstocks,microalgae is the only source that can be sustainably developedin the future, because food crops are inefficient and unsustainablebiodiesel sources (Ahmad et al., 2011).

Conversion of microalgae into biodiesel typically includes thefollowing steps: cultivation of algae, cell harvest, lipid extraction,and esterification of lipids. In order to extract lipids from algal bio-mass, Soxhlet extraction using hexane as the solvent and Bligh andDyer’s method using a mixture of chloroform and methanol aretypically used (Bligh and Dyer, 1959). However, the health, secu-rity, and regulatory problems associated with the use of organicsolvents should be addressed. In addition, efficient solvent recov-ery processes are needed to commercialize these processes. There-fore, several groups have reported the use of supercritical CO2, lesstoxic solvent mixtures, and ionic liquids to replace toxic organicsolvents (Demirbas and Demirbas, 2011; Young et al., 2010).

ll rights reserved.

: +82 2 3437 8360.

ILs are organic salts that melt below 100 �C. Interest in ILs stemsfrom their potential application as ‘‘green solvents’’. Specifically,their non-volatile character and thermal stability make themattractive alternatives for volatile organic solvents. Moreover, ILsare referred to as ‘‘designer solvents’’ because of their syntheticflexibility (Freemantle, 1998).

Recently, Lateef et al. (2009) used halide-containing ILs such as[Cyano-mim][Br] and [Propyl-mim][Br] to recover fat from food-stuffs. Young et al. (2010) demonstrated the feasibility of lipidextraction processes using mixtures of [Emim][MeSO4] and polarorganic solvents. However, investigations on the influence of ILson lipid extraction efficiency have not been reported. In this work,mixtures of ILs and methanol were used to extract lipids from algalbiomass. The influence of ILs on the extraction efficiency was ana-lyzed using multi-parameter linear regression, and fatty acid com-position of extracted lipids was determined by fatty acid methylesters (FAMEs) analysis.

2. Methods

2.1. Materials

All ILs, chloroform, sulfuric acid, methanol, and n-hexane werepurchased from Sigma–Aldrich (USA). Commercial Chlorella vulgariswas obtained from Daesang Wellife (Korea). The C. vulgaris strain(KCTC AG10002) was provided by the Korean Culture Type Collec-tion (Korea). All other chemicals used in this work were of analyti-cal grade and used without further purification.

[Em

im][

Br]

[Em

im][

Ac]

ND

ND

0.17

(0.9

%)

ND

5.68

(28.

6%)

5.47

(20.

7%)

4.49

(22.

6%)

7.17

(27.

1%)

0.18

(0.9

%)

0.26

(1.0

%)

0.36

(1.8

%)

0.43

(1.6

%)

ND

2.59

(9.8

%)

8.12

(40.

8%)

10.3

0(3

9.0%

)N

DN

DN

D0.

13(0

.5%

)N

D0.

08(0

.3%

)N

DN

D19

.88

(100

%)

26.4

3(1

00%

)

49.2

28.2

Y.-H. Kim et al. / Bioresource Technology 109 (2012) 312–315 313

2.2. Microalgae cultivation and harvest

The inoculum of C. vulgaris was grown in a 500 ml flask contain-ing 150 ml of bold basal medium with continuous aeration andillumination. C. vulgaris was cultured in the sediment microbialfuel cell (SMFC) system previously developed by our group (Jeonet al., 2010). The biomass of cultured cells was harvested by centri-fugation, and the wet cell mass was frozen overnight at �70� andfreeze-dried.

l][E

mim

][M

eSO

4]

[Em

im][

Cl]

ND

0.39

(0.5

%)

)1.

18(1

.2%

)0.

28(0

.4%

))

21.3

6(2

2.4%

)16

.81

(23.

0%)

21.1

5(2

2.2%

)18

.35

(25.

1%)

ND

ND

1.00

(1.0

%)

1.17

(1.6

%)

ND

7.4

(10.

1%)

50.1

5(5

2.6%

)27

.81

(38.

0%)

ND

ND

ND

0.28

(0.4

%)

ND

0.28

(0.4

%)

ND

ND

%)

95.2

7(1

00%

)73

.09

(100

%)

118.

894

.6

2.3. Lipid extraction via Bligh and Dyer’s method

The total lipids were extracted by mixing chloroform–methanol(1:1 v/v) with the freeze-dried samples using Bligh and Dyer’smethod (Bligh and Dyer, 1959). The mixtures were transferred intoa separatory funnel and shaken for 5 min. The chloroform fractioncontaining lipids was removed from the separatory funnel, and thesolvent was evaporated using a rotary evaporator. The weight ofthe total lipids was measured using an electronic scale.

][B

mim

][C

H3SO

3]

[Bm

im][

BF 4

][B

mim

][PF

6]

[Bm

im][

Tf2N

][B

mim

][C

0.21

(0.4

%)

ND

ND

ND

ND

0.86

(1.7

%)

0.23

(0.6

%)

ND

0.24

(0.9

%)

0.07

(2.3

%10

.93

(21.

0%)

11.6

7(2

8.1%

)8.

76(2

7.9%

)6.

00(2

2.2%

)0.

25(8

.1%

12.0

7(2

3.2%

)9.

51(2

2.9%

)7.

06(2

2.4%

)6.

83(2

5.2%

)0.

47(1

5.3%

)0.

33(0

.6%

)0.

36(0

.9%

)0.

20(0

.6%

)0.

17(0

.6%

)N

D0.

60(1

.2%

)0.

45(1

.1%

)N

D0.

41(1

.5%

)N

DN

D0.

58(1

.4%

)N

DN

DN

D26

.32

(50.

6%)

18.5

3(4

4.6%

)15

.33

(48.

7%)

13.1

4(4

8.6%

)2.

20(7

1.4%

)N

DN

DN

DN

DN

D0.

42(0

.8%

)N

DN

D0.

07(0

.3%

)N

D0.

16(0

.3%

)N

DN

D0.

07(0

.3%

)N

D0.

12(0

.2%

)0.

23(0

.6%

)N

D0.

12(0

.4%

)N

D52

.02

(100

%)

41.5

6(1

00%

)31

.45

(100

%)

27.0

5(1

00%

)3.

08(1

00

62.4

52.0

38.2

31.6

5.8

2.4. Lipid extraction using mixtures of ILs and methanol

In all experiments, mixtures of various ILs and methanol at a 1:1volume ratio were used to investigate the effect of IL structure onthe extraction efficiency of lipids from algal biomass. Methanolwas used to decrease the high viscosity of some ILs, and it alsocan be used as a reactant for transesterification after extractionof lipids from the biomass. C. vulgaris (500 mg) was mixed with amixture of 2.5 ml IL and 2.5 ml methanol under magnetic stirringat 65 �C for 18 h. The mixture was cooled at room temperatureand centrifuged to separate the IL–methanol and lipid phases.Phase separation was more easily conducted by adding water tothe mixture. For commercial applications, the upper lipid phasecan be used directly. However, in this work, n-hexane was addedto the mixture to dissolve the lipid in order to calculate exactyields. The n-hexane phase containing lipids was separated fromthe IL–methanol phase by centrifugation. The recovered n-hexanephase was washed five times with water to remove polar com-pounds. Crude lipids were then obtained by evaporation of the n-hexane phase using a rotary evaporator, and the residue wasweighed to measure the gravimetric yield.

Tabl

e1

Fatt

yac

idco

mpo

siti

onof

lipid

sex

trac

ted

from

C.vu

lgar

isus

ing

ILs.

Fatt

yac

ids

Extr

acte

dam

oun

tsof

fatt

yac

ids

(mg/

gD

.W.)

Bli

gh&

Dye

r[B

mim

][C

F 3SO

3]

[Bm

im][

MeS

O4

C14

0.23

(0.2

%)

0.12

(0.1

%)

ND

C15

0.39

(0.4

%)

1.09

(1.0

%)

1.23

(1.4

%)

C16

:018

.96

(20.

2%)

23.7

4(2

1.3%

)19

.76

(22.

5%)

C16

:122

.39

(23.

9%)

26.6

4(2

3.9%

)21

.03

(24.

0%)

C17

2.69

(2.9

%)

1.45

(1.3

%)

ND

C18

:00.

69(0

.7%

)0.

58(0

.5%

)N

DC

18:1

0.63

(0.7

%)

ND

ND

C18

:246

.93

(50.

0%)

56.8

2(5

1.0%

)45

.75

(52.

1%)

C18

:30.

27(0

.3%

)N

DN

DC

200.

32(0

.3%

)0.

65(0

.6%

)N

DC

220.

17(0

.2%

)0.

08(0

.1%

)N

DC

240.

14(0

.1%

)N

DN

DTo

tal

fatt

yac

ids

93.8

1(1

00%

)11

1.36

(100

%)

87.7

7(1

00%

)

Extr

acte

dto

tal

lipi

ds10

6.2

125.

411

8.4

ND

:n

otde

tect

ed.(

):Fa

tty

acid

com

posi

tion

(wt.

%).

2.5. Fatty acid composition analysis

To determine the fatty acid composition of lipids, fatty acidswere converted to methyl esters by methanolysis and analyzedwith gas chromatography. Each 10 mg of extracted lipid was dis-solved in 1 ml chloroform and mixed with 1 ml methanol contain-ing 15% (v/v) H2SO4. Methanolysis was conducted at 100 �C for2.5 h. After cooling to room temperature and on ice, 0.5 ml ofdeionized water was added to the solution, which was vortexedfor 1 min (Kurosawa et al., 2010). The organic phase containingFAMEs was analyzed using a YL6100 GC System (Korea) equippedwith a Supelco DB-1 column (30 m by 0.32 mm, 10 lm thick film)using hydrogen as the carrier gas. A 2 ll portion of the organicphase was injected, and the inlet was maintained at 250 �C. Theoven was maintained at 80 �C for 2 min, heated to 300 �C at10 �C/min, and then maintained at 300 �C for 5 min (Stránskyand Jursik, 1996). Peak detection was performed with a flame ion-ization detector, which was maintained at 300 �C. The fatty acidswere identified and quantified by comparing their retention timesand fragmentation patterns with those of standards.

Table 2Yield and fatty acid composition of lipids extracted from cultivated C. vulgaris.

Fatty acids Extracted amounts of fatty acids (mg/g D.W.)

Bligh&Dyer [Bmim][CF3SO3] [Bmim][MeSO4]

C14 7.16 (7.1%) 8.53 (4.8%) 10.68 (7.0%)C15 0.23 (0.2%) 0.30 (0.2%) 0.99 (0.7%)C16:0 29.54 (29.2%) 51.94 (29.5%) 44.06 (29.0%)C16:1 3.39 (3.4%) 5.39 (3.1%) 4.89 (3.2%)C17 0.33 (0.3%) 0.72 (0.4%) 0.49 (0.3%)C18:0 7.63 (7.5%) 13.94 (7.9%) 11.38 (7.5%)C18:1 ND ND NDC18:2 36.07 (35.7%) 66.77 (37.9%) 53.81 (35.4%)C18:3 11.22 (11.1%) 20.86 (11.8%) 16.74 (11.0%)C20 0.94 (0.9%) 1.70 (1.0%) 1.40 (0.9%)C22 1.60 (1.6%) 2.71 (1.5%) 2.39 (1.6%)C24 3.02 (3.0%) 3.49 (2.0%) 4.51 (3.0%)Total fatty acids 101.13 (100%) 176.35 (100%) 152.19 (100%)Extracted total lipids 110.6 189.8 174.2

ND: not detected. ( ): Fatty acid composition (wt.%).

314 Y.-H. Kim et al. / Bioresource Technology 109 (2012) 312–315

3. Results and discussion

3.1. Extraction of lipids from C. vulgaris using mixtures of ILs andmethanol

Mixtures of ILs and methanol dissolved algal biomass leavinglipids insoluble. Undissolved lipids floated during the dissolutionprocess because they had a lower density than the IL–methanolmixture, and the lipid phase was simply separated by centrifuga-tion. The separation of lipids was more efficiently achieved by add-ing water to the mixture. The total contents of separated lipidsdepended on the structure of the ILs (Table 1). Total content of lip-ids extracted from C. vulgaris by the conventional Bligh and Dyer’smethod was 10.6%, while [Bmim][CF3SO3] and [Emim][MeSO4] ex-tracted 12.5 and 11.9% of the lipids, respectively. Among [Bmim]+

containing ILs, the lipid extraction efficiency of ILs followed the or-der ½CF3SO3�� > ½MeSO4�� > ½CH3SO3�� > ½BF4�� > ½PF6�� > ½Tf2N��

> ½Cl��. This suggests that the extraction efficiency of lipids ishighly dependent on the anion structure of ILs. Generally, hydro-phobic and water immiscible ILs such as [Bmim][PF6] and[Bmim][Tf2N] showed a low extraction efficiency, while hydro-philic and water miscible ILs such as [Bmim][CF3SO3], [Bmim][MeSO4], and [Emim][MeSO4] showed a high extraction efficiency,with the exception of [Bmim][Cl] and [Emim][Ac]. These resultscan be partially attributed to the solubility of lipids in the ILs.Although the solubilities of lipids in most ILs are very low,hydrophobic ILs have higher solubilities for lipids than hydrophilicILs. Higher solubility of hydrophobic ILs for lipids can induce thepartitioning of lipids to the methanol and IL mixture phase.[Emim][Ac] is an unusual example, because it is highly hydrophilicand completely water miscible. However, [Emim][Ac] has a veryhigh solubility for lipids.

3.2. LSER analysis to determine the influence of ILs on the extractionefficiency

It is generally difficult to understand the effect of a solvent onvarious physicochemical systems using only one solvent parame-ter. Therefore, Kamlet et al. (1986) evaluated solvent propertiesby their solvatochromic parameters such as dipolarity/polarizabil-ity (p⁄), acidity (a), and basicity (b). Using their solvatochromicparameters, Kamlet et al. (1988) also developed a linear solvationenergy relationship (LSER), which has been successfully appliedto many equilibrium and kinetic phenomena, including solubilities,partition coefficients, toxicities, and catalytic reactions. The gen-eral form of the LSER for the solvent effect follows.

MG ¼ MG0 þ d2d1 þ s2p�1 þ a2a1 þ b2b1 þ h2ðdHÞ21 ð1Þ

where subscripts 1 and 2 refer to the solvent and solute, respec-tively, and where d, p⁄, a, b, and dH represent the polarizability cor-rection, dipolarity/polarizability, acidity, basicity, and Hildebrandsolubility parameter, respectively. Recently, LSER equations havebeen successfully used to analyze the effect of ILs on various chem-ical reactions, enzyme reactions, and equilibrium phenomena(Chiappe et al., 2010). Typically, three solvatochromic parametersare used for LSER analysis, because p⁄, a, and b values for variousILs have been reported, while dH values have rarely been measured.LSER analysis was conducted for our extraction system using ILsand methanol to elucidate the effect of ILs. Detailed LSER analysisresults are described in the electronic Supplementary Material.The multiple-parameter, linear regression analysis of total lipidcontent data yielded:

logðlipid contentÞ ¼ 1:39ð�1:85Þ � 7:84ð�1:80Þp�

þ 11:35ð�3:02Þaþ 4:17ð�1:13Þb ð2Þ

for which n = 8, r = 0.921, and SD = 0.23. The experimental total li-pid content data were well predicted by the LSER correlation equa-tion. Equation 2 implies that the contribution of the p⁄ and a termsare statistically more significant than the b term. Extraction effi-ciency of lipids generally increased with decreasing p⁄ values andincreasing a values of ILs.

3.3. Fatty acid composition of extracted lipids

The fatty acid composition of lipids extracted from C. vulgarisusing mixtures of ILs and methanol were determined using GC anal-ysis (Table 1). In the lipids extracted from C. vulgaris, palmitic(C16:0), palmitoleic (C16:1), and linoleic (C18:2) acid were com-monly dominant. When the fatty acid profiles of extracted lipidswere compared, the greatest number of varieties of fatty acids wasobtained by the Bligh and Dyer’s method. Fatty acids extracted bymost ILs showed very similar profiles, with the exception of[Emim][Cl] and [Emim][Ac]. [Emim][Cl] and [Emim][Ac] extractedhigh levels of oleic acid (C18:1), but oleic acid was not detected inthe fatty acids extracted by other ILs. These results may be causedby particularly high b values for these ILs, because it was reportedthat ILs that show high hydrogen bond basicity can efficiently dis-solve lignocellulosic biomass (Brandt et al., 2009). Levels of primaryfatty acids (palmitic, palmitoleic, and linoleic acid) extracted by[Bmim][MeSO4] and [Emim][MeSO4] were very close to thoseextracted by the Bligh and Dyer’s method. When considering the

Y.-H. Kim et al. / Bioresource Technology 109 (2012) 312–315 315

extraction yield and profile of fatty acids, [Bmim][CF3SO3] was themost efficient IL for extracting lipids from C. vulgaris.

3.4. Extraction of lipids from cultivated C. vulgaris

Lipids from C. vulgaris cultivated using a microbial fuel cellsystem were also extracted (Table 2). Total lipid contents extractedfrom cultivated C. vulgaris were 11.1%, 19.0%, and 17.4% using theBligh and Dyer’s method, [Bmim][CF3SO3] system, and [Bmim][MeSO4] system, respectively. IL–methanol systems more effi-ciently extracted lipids from cultivated C. vulgaris than the Blighand Dyer’s method. Fatty acid compositions of lipids extractedfrom cultivated C. vulgaris by three methods were very similar toeach other, while the compositions were slightly different fromthose of commercial C. vulgaris. Of the lipids extracted from culti-vated C. vulgaris, palmitic, linoleic, and a-linolenic (C18:3) acidwere the primary fatty acids. Lower palmitoleic acid and highera-linolenic acid levels were detected in the cultivated C. vulgaristhan in the commercial variety.

4. Conclusions

In this work, IL–methanol systems showed higher extractionefficiencies than the conventional method. Fatty acid profiles oflipids extracted by the IL–methanol system also showed that abroad range of fatty acids was extracted. LSER equation success-fully predicted the experimental lipid content and it will be usefulfor selecting and synthesizing optimal ILs. Although imidazolium-based ILs have some problems such as price and aquatic toxicity,IL–methanol mixture will be used to develop a very efficient andenvironmentally-friendly system in order to extract lipids from al-gal biomass due to the various properties of ILs as green solvent.

Acknowledgement

This subject is supported by the Korea Ministry of Environmentas a ‘‘Converging Technology Project (201-101-007)’’. This work isalso supported by the Converging Research Center Program (2009-0082832) and the Basic Science Research Program (2010-0004228)through the National Research Foundation of Korea (NRF) fundedby the Ministry of Education, Science and Technology.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.biortech.2011.04.064.

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