Chemical Engineering Journal 174 (2011) 396 399

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Chemical Engineering Journal

jo u r n al hom epage: www.elsev ier .c

Dimeri ras cata

Shiwei L shea College of Che oad, Qb College of Che 53 Zhe

a r t i c l

Article history:Received 14 FeReceived in reAccepted 4 Sep

Keywords:BrnstedLewFatty acid metDimerizationCatalysis

thyl that

= 0.6s of

g, reaas 96

yielded th

1. Introdu

Natural fats are converted into biodiesel (fatty acid methyl ester,FAME) in typical process of methanolysis. This process seems nowmore attractive because of a growing interest in biodiesel. However,even applying the latest and the most modern technology, the costof biodiesel fuel is rather high. Thus there is a need to look for newways to maattractive. Ovegetable fafrom thesewhich makacid methylurated FAMelds of poetc. [13]. Tof fatty acidand dimeriing the procarboncardrogenationacid ester isof a normalgive the proand a Lewis

CorresponE-mail add

ls, inas catalysts in the dimerization. This is a commonly practiced com-mercial procedure and these catalysts are extremely effective forpromoting the formation of DAME. However, these catalysts can-not be reused, and substantial quantities of DAME are retained bythe clay and lost when the clay is disposed of. This results in con-siderable economic loss in addition to creating an environmental

1385-8947/$ doi:10.1016/j.ke the production of biodiesel fuel more economicallyne such alternative could be utilization of animal andtty wastes for biofuel production. However, biodiesel

wastes contains lots of carboncarbon double bondse the product unstable for use in an engine. Dimeric

esters (DAME), produced by the dimerization of unsat-E, is an high value ne chemical, and widely used in thelyamides, polymer applications and as anticorrosives,he dimerization mechanism of FAME is similar to that

[4,5]. It is that the catalyst promotes dehydrogenationzation of FAMEs through a DielsAlder process. Dur-cess of reaction, the unsaturated FAME containing onebon double bond forms the diene acid ester by dehy-

in the acidic catalyst. Then, the non-conjugated diene conjugated to act as a diene and adds to a double bond

(or conjugated) FAME, which acts as a dieneophile, toduct. Usually a Brnsted acid is active for conjugation

acid for the DielsAlder reaction. The crystalline clay

ding author. Tel.: +86 532 84022719; fax: +86 532 84022719.ress: yushitaoqust@126.com (S. Yu).

problem. Attempts to recover the DAME from the clay catalyst andlter cake by extraction with solvents such as hexane, heptane andother low boiling solvents have not been satisfactory because thatDAME recovered in this way are discolored and unsuitable for mostapplications without further purication. Mesoporous molecularsieves were reported as catalysts in the dimerization [6,7]. They alsohave shortcomings, such as restricted accessibility to the matrix-bound acidic sites, high molecular weight/active site ratios, andrapid deactivation from coking. Therefore, it is necessary to explorea new approach for the synthesis of DAME. In addition, comparedwith the expensive reagents, such as methyl oleate and methyllinoleate, biodiesel is more promising and economical as a feed forthe preparation of DAME.

As a kind of environmental-friendly catalyst, Brnsted or Lewisacidic ionic liquids (ILs) gets attention of researchers, and manyorganic reactions, such as esterication [8], dehydration [9], alkyla-tion [10], acylation [11], and carbonylation [12], were reported withexcellent selectivity, and the used ILs were of outstanding recy-clability. In our laboratory, some BrnstedLewis acidic ILs weresynthesized, characterized and used in the polymerization [13,14].The results indicated that the BrnstedLewis acidic ILs was bothBrnsted and Lewis acidic and had better catalytic performance

see front matter 2011 Elsevier B.V. All rights reserved.cej.2011.09.017zation of fatty acid methyl ester using Blyst

iua, Hongxia Zhoua, Shitao Yua,, Congxia Xieb, Fumical Engineering, Qingdao University of Science and Technology, No. 53 Zhengzhou Rmistry and Molecular Engineering, Qingdao University of Science and Technology, No.

e i n f o

bruary 2011vised form 30 August 2011tember 2011

is acidic ionic liquidhyl esters

a b s t r a c t

The dimerization of fatty acid meliquids (ILs) as catalysts. It is foundnate [HO3S(CH2)3NEt3]ClZnCl2 (xZnCl2 + moles of ammonium salt) wam(biodiesel):m(IL) 15:1, biodiesel 15product dimeric acid methyl ester wtimes, the dimeric acid methyl esterBrnsted and Lewis acid sites enhanc

ction mineraom/ locate /ce j

nstedLewis acidic ionic liquid

ng Liua, Zhanqian Songa

ingdao 266042, Chinangzhou Road, Qingdao 266042, China

ester was investigated using BrnstedLewis acidic ionic IL (3-sulfonic acid)-propyl-triethylammonium chlorozinci-4, x: molar fraction of ZnCl2, x = moles of ZnCl2/(moles ofgood catalytic performance. Under the optimum conditionsction temperature 240 C, and reaction time 5 h, the yield of.8%. The reusability of IL was good and after it was used ve

was still more than 94%. Otherwise, a synergetic effect ofe catalytic performance of the IL.

2011 Elsevier B.V. All rights reserved.

cluding bentonite, kaolinite, hectorite, etc., were used

S. Liu et al. / Chemical Engineering Journal 174 (2011) 396 399 397

SO3HN(CH2)3

C2H5

C2H5

C2H5

ClZnCl2 SO3HN

(CH2)3

C2H5

C2H5

C2H5ZnCl3

ZnCl2SO3HN

(CH2)3

C2H5

C2H5

C2H5Zn2Cl5

ZnCl2SO3HN

(CH2)3

C2H5

C2H5

C2H5Zn3Cl 7+

_ +_

+_

+_

Scheme 1. Synthesis of IL [HO3S(CH2)3NEt3]ClZnCl2.

for the polymerization than the traditional catalysts. Due to thepresence of Brnsted and Lewis acid sites, these ILs can selectivelycatalyze different reaction mechanisms to enhance the conversionand selectivity of the reaction. Therefore, we studied the dimer-ization of FAME using biodiesel as the feed in the presence ofBrnstedLewis acidic ILs.

2. Materials and methods

2.1. Materials

FAME (methyl oleanate 3.2 wt%at 79.8 wt%used withowith an Allt(column: IPColumn temmethanol sFT-IR spectwere takenwith referethe sample.

2.2. Prepara

Using thwas reactepropane-1-reacted witacid)-propyas a white vacidic ILs wwith metalLewis aciditmolar fractisted acidityIL was Brnsynthesis oin Scheme 1cm1): 33

1039, 948, 813, 791, 735, 694, 598, 521. 1H NMR (500 MHz, D2O,ppm): 2.11 (m, 2H), 2.71(t, 2H), 3.71(s, 3H), 4.16(t, 2H), 7.25(s,1H), 7.32(s, 1H), 8.53(s, 1H). 13C NMR (500 MHz, D2O, ppm): 24.75,35.28, 46.94, 47.73, 122.12, 123.34, 134.75.

2.3. Dimerization of FAME

In a typical experiment, 15 g biodiesel and 1 g IL were addedand reacted at 240 C for 5 h in a ask under dry nitrogen. Afterthe reaction, the reaction mixture was cooled to 120 C, and thenthe upper layer, containing the polymerized products and unre-

eactamplyxperreactHg) o%) = Ws thenalyLC.

ults

fects

can bts, thally, ic pr

com FAMl steanoatratedost uanc

ynervely d thhichtyl-37) w

Table 1Effects of kind

Entry

1 2 3 4 56 7 89 1011methyl palmitate 8.5 wt%, methyl stearate 5.1 wt%,te 30.8 wt%, methyl linoleate 45.3 wt%, methyl linole-, others 7.1 wt%, with the content of unsaturated FAME

), and other chemicals were obtained commercially andut further purication. HP-LC spectra were measuredech ELSD-2000ES evaporative light-scattering detector-18. Mobile phase: methanol. Flow rate: 1.0 mL/min.perature: 25 C. Sample injection volume: 10 L 1%

olution). IR spectra were recorded by a Nicolet 510Prometer in the range of 4500400 cm1. NMR spectra

by a Bruker AV500 Fourier-Transform spectrometernce to SiMe4, using solvent DMSO containing 5 wt% of

tion of ILs

e procedure in the literature, 1,3-propane sultoned with triethylamine to give 3-(triethylamine-N-yl)-sultonate (TEA-PS) as a white powder. Then TEA-PS wash an equal mole of hydrochloric acid to give (3-sulfonicl-triethylammonium chloride [HO3S(CH2)3NEt3]Cliscous liquid at room temperature. The BrnstedLewisere prepared by the reaction of [HO3S(CH2)3NEt3]Cl

chlorides, including FeCl3, ZnCl2, CuCl and CuCl2. They of IL depended on the metal chloride mass. When theon of metal chloride was less than 0.5, IL only had Brn-

and no Lewis acidity, and above this value, the obtainedstedLewis acidic [13]. The reaction formula for the

f IL [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.67) was shown. [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.64): IR (KBr disc,51, 2989, 1621, 1484, 1455, 1396, 1255, 1228, 1151,

acted rask sicycle eacted (5 mmby: Y (WALL iwere aby HP-

3. Res

3.1. Ef

As catalysEspecicatalyt6). Theuratedmethydocosaunsatuthat mperformand a sselectition, anof IL, wIL 1-bu(x = 0.6

s of catalysts on results of the reaction.

Catalysts Y/%

H2SO4 (1 g) 40.7 H2SO4 + ZnCl2 (0.5 g + 0.5 g) 32.5 ZnCl2 (2 g) 37.3 [HO3S(CH2)3NEt3]Cl 39.5 [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.64) 78.0 [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.67) 96.8

[HO3S(CH2)3NEt3]ClZnCl2 (x = 0.75) 95.3 [HO3S(CH2)3NEt3]ClFeCl3 (x = 0.67) 88.9 [HO3S(CH2)3NEt3]ClCuCl2 (x = 0.67) 32.4 [HO3S(CH2)3NEt3]ClCuCl3 (x = 0.67) 35.9 [C4mim]ClZnCl2 (x = 0.67) 24.3 nts, was separated from the IL layer at the bottom of the by decantation. The IL layer was reused directly in theiments. The product was obtained after removing unre-ants by distillation at 220 C under reduced pressurever 20 min. The yield of products (Y, %) was calculatedp/WALL 100, where Wp is the mass of product, and

mass of the unsaturated FAME. All product sampleszed to determine the FAME, dimer, and trimer contents

and discussion

of different catalysts on the dimerization

e seen from Table 1, comparing with the traditionale examined ILs exhibited better catalytic performance.[HO3S(CH2)3NEt3]ClZnCl2 (x = 0.67) exhibited goodoperty with the yield of product more than 96.8% (entryponents of the uncreated reactants were main sat-Es (83.9 wt%), such as methyl palmitate (35.2 wt%),rate (15.1 wt%), methyl eicosanoate (7.6 wt%), methyle (12.6 wt%), methyl tetracosanoate (8.0 wt%). The

FAMEs were only 14.1% (entry 6). It was indicatednsaturated FAMEs were dimerized. The good catalytice was due to the Brnsted and Lewis acidities of the ILgetic effect. The Brnsted and Lewis acid sites of IL cancatalyze dehydrogenation, conjugation and dimeriza-e synergetic effect enhanced the catalytic performance

was similar to that of a zeolite [15]. The result from-methylimidazolium chlorozincinate [C4mim]ClZnCl2as also determined to show these effects on the

Distribution/%

FAME Dimer Trimer

2.9 88.6 8.53.5 93.6 2.92.4 96.0 1.62.0 97.4 0.62.6 94.3 3.11.8 95.7 2.5

1.7 91.1 7.22.2 96.3 1.43.1 94.8 2.12.0 95.59 2.55.2 93.0 1.8

398 S. Liu et al. / Chemical Engineering Journal 174 (2011) 396 399

Table 2Effects of reaction conditions on the dimerization.

T/C t/h IL/g Y/% Distribution/%

220 5 1.0 88.3 240 5 1.0 96.8 270 5 1.0 97.2 240 4 1.0 90.2 240 6 1.0 97.5 240 5 1.5 96.2 240 5 0.5 81.3

Reaction conditions: Biodiesel 15 g.

catalytic performance of IL (entry 11). Among the chlorozincinateILs (entriestion of ZnClwas effectivof DAME dproduct incthe molar was Lewis ity was incrThe metal cformance o(x = 0.67) shIL [HO3S(Cactivity (enin the Lewiof the metahad a higheof [HO3S(C

3.2. Effects

The effection tempethe tempertemperaturthe trimer cwas increation tempertrimer. Witproduct incincreased fr1.5 g to 0.5 the trimer ca reaction tquality of D

3.3. Reusab

The reusinvestigatedshowed thaunchanged

Table 3The reusability

Cycle

1 2 34 5

0

a

b

T-IR satedly

edly ve times. It is indicated that the BrnstedLewis acidicof excellent reusability. This good reusability result could beed by the following two points. First, in the structure of IL,yl sulfonic acid group was covalently tethered in IL cation,

anion [Zn2Cl5] of IL was inert and stable in water and Brn-id. Therefore the acidity of IL was not easily lost. Second, theZnCl2 increased the density of the IL, which gave an easiertion of IL from the reaction mixture, and the IL was not easilythe separation process. Therefore, its activity was stable. Ino investigate the intactness of the repeatedly utilized IL, IR

of the reusedve time and unused ILs were given in Fig. 1.wn in Fig. 1, both IR spectra were similar, which indicatede structure of the reused IL was unspoiled.

clusion

dimerization of FAME was investigated usingedLewis acidic ILs as catalysts. IL (3-sulfonic acid)-propyl-lammonium chlorozincinate [HO3S(CH2)3NEt3]ClZnCl27) was of good catalytic property and the yield of product.8%. The BrnstedLewis acidic sites of IL can selectively 57), the DAME yield increased with the molar frac-2 (x). When x value was 0.67, the dimerization of FAMEely catalyzed. However, when x reached 0.75, the yieldid not increase further, but the trimer content in thereased (entry 9). This can be explained by that, whenfraction of metal chloride (x) was more than 0.5, ILacidic, and by increasing the x value, the Lewis acid-eased [16], which increased the catalytic activity of IL.hlorides had a decisive inuence on the catalytic per-f ILs (entries 6, 810). IL [HO3S(CH2)3NEt3]ClZnCl2owed the best catalytic performance (entry 8), andH2)3NEt3]ClCuCl (x = 0.67) had almost no catalytic

try 9). These results can be explained by the differences acidic strength of IL. With the increase of the acidityl chloride, the Lewis acidity of IL became stronger, andr catalytic activity [10]. As a result, the catalytic activityH2)3NEt3]ClZnCl2 (x = 0.67) was higher.

of reaction conditions on the dimerization

ts of reaction conditions are shown in Table 2. The reac-rature was very important for the dimerization. Whenature was 220 C, the DAME yield was 88.3%. When thee reached 240 C, the DAME yield was 96.8%. However,ontent in the product was 14.4% when the temperaturesed to 270 C. This may be because the higher reac-ature facilitated the dimerization of FAME to produceh increasing reaction time from 4 h to 6 h, the yield ofreased from 90.2% to 97.5%, and the trimer content alsoom 1.1% to 11.7%. When decreasing the IL dosage fromg, the DAME yield decreased from 86.2% to 81.3%, andontent also decreased from 9.5% to 1.2%. Both too longime and too small IL dosage were unfavorable to theAME.

ility of catalyst

ability of [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.67) was, and the results were given in Table 3. The resultst the yield and composition of product were almostafter [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.67) was used

400

Tran

smitt

ance

/%

Fig. 1. F(b) repe

repeatIL was explainthe alkand thested acuse of separalost in order tspectraAs shothat th

4. Con

TheBrnsttriethy(x = 0.6was 96 of the catalytic system.

Y/% Distribution/%

FAME Dimer Trimer

96.8 1.8 95.7 2.596.2 2.2 94.9 2.996.5 1.5 97.3 1.294.2 3.0 93.4 3.694.9 2.8 95.0 2.2

catalyze ththe reactiosites enhan

Acknowled

This worence FoundResearch oFAME Dimer Trimer

1.6 96.3 2.11.8 95.7 2.52.0 83.6 14.41.2 97.7 1.11.0 87.3 11.72.5 88.0 9.52.1 96.7 1.2

500100015002000250030003500

Wavenumber /cm-1

pectra of [HO3S(CH2)3NEt3]ClZnCl2 (x = 0.64). (a) Unused IL and used ve times of IL.e dehydrogenation, conjugation and polymerization inn, and a synergetic effect of Brnsted and Lewis acidced the catalytic performance of the IL.

gments

k was nancially supported by the National Natural Sci-ation of China (30571463), the Program of Science &f Shandong Province (2011GGB01046) and the Doctor

S. Liu et al. / Chemical Engineering Journal 174 (2011) 396 399 399

Foundation of Shandong Province (BS2010NJ006). The authors aregrateful for the nancial support.

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Dimerization of fatty acid methyl ester using BrnstedLewis acidic ionic liquid as catalyst1 Introduction2 Materials and methods2.1 Materials2.2 Preparation of ILs2.3 Dimerization of FAME

3 Results and discussion3.1 Effects of different catalysts on the dimerization3.2 Effects of reaction conditions on the dimerization3.3 Reusability of catalyst

4 ConclusionAcknowledgmentsReferences