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Short Communication

Hydrogenation of biodiesel using thermoregulated phase-transfer catalyst

for production of fatty alcohols

Shi-wei Liu a, Cong-xia Xie b,*, Rui Jiang b, Shi-tao Yu a, Fu-sheng Liu a

a College of Chemical Engineering, Qingdao University of Science and Technology, No. 53 Zhengzhou Road, Qingdao 266042, Chinab College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, No. 53 Zhengzhou Road, Qingdao 266042, China

a r t i c l e i n f o

Article history:

Received 6 January 2010

Received in revised form 25 February 2010

Accepted 3 March 2010

Available online 24 March 2010

Keywords:

Thermoregulated phase-transfer catalyst

Biodiesel

Fatty alcohol

Hydrogenation

a b s t r a c t

The hydrogenation of biodiesel was investigated in presence of thermoregulated phase-transfer catalysts

to produce fatty alcohols. The thermoregulated catalytic system Pd/IV (IV: P-ligand, tri-(methoxyl poly-

ethylene glycol)-phosphite) exhibited an efficient catalytic performance for the hydrogenation. It was

also found that the steric resistance of theP-ligand, to a large extent, affected theperformanceof catalytic

system. Using Pd/IV as catalyst, the product could be easily separated from the catalytic system and the

catalyst was of good reusability. Thus, a clean and environmentally friendly strategy for the production of

fatty alcohol is provided.

2010 Published by Elsevier Ltd.

1. Introduction

Natural fats are converted into biodiesel in typical process of

methanolysis. This process seems now more attractive because of

a growing interest in an ecological diesel fuel. However, due to

the higher raw material cost, biodiesel is difficult to compete with

petroleum diesel. Therefore, new method must be found to enlarge

the value of biodiesel. Fatty alcohol, produced by the hydrogenation

of fatty acid methyl ester, is an important chemical raw material

andwidely used in the fields of detergents, plasticizers, synthetic fi-

bers, surfactants and cosmetics(Bryan, 2009;Krzysztof et al., 2003).

At present, the hydrogenation popularly uses supported ruthenium

and rhodium (Miyake et al., 2009), copper chromite (Deepak et al.,

1999), palladium (Agustn et al., 2006), zinc, ferrum and thulium

oxide catalysts (Buchold, 1983). The drawbacks of these processes

are much more catalyst requirements, higher reaction temperature

and higher hydrogen pressure, especially, inactivation of catalyst.Therefore, to design and synthesize a catalytic system which is sta-

ble, easily separable and reusable has been pursued.

Based on the property of cloud point of nonionic P-ligands, a no-

vel aqueous biphasic homogeneous catalysis system termed as

thermoregulated phase-transfer catalysis (TRPTC) was proposed

in recent years (Jiang et al., 2002; Jin et al., 1997; Kevin, 2009;

Jin and Wang, 2005). The introduction of TRPTC is free from the

shortcomings of classical biphasic catalysis, in which the scope of

application is restrained by the water-solubility of the substrate.

The character of this catalytic process can be described as follows:

At a temperature lower than cloud point (CPT), the catalyst would

remain in the aqueous phase. On heating to a temperature higher

than CPT, the catalyst would transfer into the organic phase. Thus,

the catalyst and the reagents are in the same phase and the reac-

tion is carried out in the organic phase. As soon as the reaction is

completed and the system is cooled to a temperature lower than

CPT, the catalyst would return to the aqueous phase. Therefore,

TRPTC is a monophasic reaction combined with a biphasic separa-

tion, which contributes to the separation and reusability of the cat-

alyst, and it has been successfully used in the hydrogenation of

high-carbon olefins with excellent conversion and selectivity (Jiang

et al., 1999; Wei et al., 2004). However, the reported hydrogena-

tions mainly use linear olefins with little steric hindrance as re-

agents, no literature about the hydrogenation of carboxylic ester

in presence of TRPTC was found. Here we first report the hydroge-

nation of fatty acid methyl ester in presence of TRPTC. It is foundthat TRPTC was an efficient catalyst for the hydrogenation. The

mixture of product higher alcohol and unreacted ester was easily

separated from the ionic liquid by decantation, and the desired

product higher alcohol was easily separated from the unreacted es-

ter which could be used as biodiesel by distillation.

2. Methods

2.1. Materials

Tetrahydrofuran, triethylamine and catechol were distilled over

calcium hydride or 3A molecular sieve under reduced pressure,

0960-8524/$ - see front matter 2010 Published by Elsevier Ltd.doi:10.1016/j.biortech.2010.03.016

* Corresponding author. Tel.: +86 532 84022864; fax: +86 532 84022719.

E-mail address:xiecongxia@126.com(C.-x. Xie).

Bioresource Technology 101 (2010) 62786280

Contents lists available at ScienceDirect

Bioresource Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o r t e c h

http://dx.doi.org/10.1016/j.biortech.2010.03.016mailto:xiecongxia@126.comhttp://www.sciencedirect.com/science/journal/09608524http://www.elsevier.com/locate/biortechhttp://www.elsevier.com/locate/biortechhttp://www.sciencedirect.com/science/journal/09608524mailto:xiecongxia@126.comhttp://dx.doi.org/10.1016/j.biortech.2010.03.016

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and poly(ethylene glycol) alkyl ethers were dehydrated by 3A

molecular sieve before use. Fatty acid methyl ester was prepared

from soybean oil by transesterification with methanol at 65 C

for 4 h using 0.2 wt% sodium hydroxide as catalyst. (Saponification

value 188 mg KOH/g, acid number 5 mg KOH/g, value of iodine

(IV) 135 mg I2/g, hydroxyl value (OHV) 1 mg KOH/g). Other chem-

icals used were reagent grade procured commercially and used

without pretreatment.

2.2. Preparation of P-ligands

The P-ligands IIV (Fig. 1) were synthesized according to the lit-

eratures (Jiang et al., 1999; Wei et al., 2004). For example, the gen-

eral process for the preparation of P-ligand I is following: Under

nitrogen, 0.15 mol phosphorus trichloride was mixed with

0.1 mol catechol under 20 C with an ice bath and reacted for

30 min at room temperature, then another 0.1 mol phosphorus tri-

chloride was added and further reacted for 2 h at 80 C. After that,

the mixture was distilled to remove the unreacted phosphorus tri-

chloride at 80 C under reduced pressure (7090 mm Hg), giving

1,2-phenylene phosphorochloridite with 82.5% yield. Next,

0.01 mol 1,2-phenylene phosphorochloridite was dissolved in the

mixture of tetrahydrofuran and triethylamine (V/V = 3), and

0.075 mol fatty alcohol polyoxyethylene (RO-(CH2CH2O)n-H) dis-

solved in tetrahydrofuran. Both was mixed and reacted at 5 C

for 6 h, then further reacted at room temperature for 12 h. The

mixture was filtrated to remove ammonium salt, and distilled to

remove the solvents. 100 ml anhydrous ethyl ether was added to

the residue and filtrated to get the white precipitate, giving P-li-

gand I with 92% yield (Fig. 2). The cloud points were measured

according to the literature (Jiang et al., 1999). I: IR (KBr disc,

cm1): m 2923, 2860, 1600, 1498, 1467, 1108, 1032, 953, 749. 1H

NMR (500 MHz, D2O, ppm): 01.50(m, C15H21C20H41), 3.04.0(s,

OCH2), 6.77.2(m, ArH). 31P NMR (200 MHz, D2O, ppm, external

standardization: 85% H3PO4): 7.40(s). Cloud points: 103 C. II: IR

(KBr disc, cm1):m 3056, 1721, 1645, 1455, 997, 950, 699. 1H

NMR (500 MHz, D2O): 1.11.2(m, CH3), 3.53.7(s, OCH2), 7.37.8

(m, ArH). 31P NMR (200 MHz, D2O, ppm, external standardization:

85% H3PO4): 10.26(s). Cloud points: 112 C. III: IR (KBr disc,

cm1): m 2924, 2869, 1604, 1489, 953, 694, 757. 1H NMR

(500 MHz, D2O) 1.11.3(m, C15H21C20H41), 3.403.80(s, OCH2),

6.707.4(m, ArH). 31P NMR (200 MHz, D2O, ppm, external stan-

dardization: 85% H3PO4): 10.10(s). Cloud points: 106 C. IV: IR

(KBr disc, cm1): m 2920, 2868, 1110, 951. 1H NMR (500 MHz,

D2O) 1.01.2(m, CH3), 3.23.6(s, OCH2). 31P NMR (200 MHz, D2O,

ppm, external standardization: 85% H3

PO4

): 7.18 (s). Cloud points:

107 C.

2.3. Hydrogenation of fatty acid methyl ester

The mixture of 2.5 g fatty acid methyl ester, 3 mg metal chlo-

ride, 1 g ligand, 2.5 g water and 2.5 g toluene was reacted in a

100 ml stainless-steel autoclave with 7 MPa H2 at 200 C for 4 h.

After that, the reactor was cooled to room temperature and depres-

surized. The upper organic phase was separated from the aqueous

phase by decantation and distilled under reduced pressure to ob-

tain the product higher alcohol. The OHV and IV of the product

were measured according to the literature (Wang, 1993). All re-

sults were repeated at least five times (10 times for Pd/IV).

3. Results and discussion

3.1. Effect of different catalysts on hydrogenation results

As can be seen fromTable 1, some examined thermoregulated

phase-transfer catalysts exhibited better catalytic performance

than traditional catalysts Pd/C and PdCl2. This may be due to that,

at the reaction temperature, the catalyst is soluble in organic

phase, and the reaction proceeds homogeneously, while Pd/C and

PdCl2 are used as catalysts, the reaction is carried out in the so-

lidliquid two-phase system (Wang et al., 2002; Zhang et al.,

1999). It was indicated that the hydrogenation of fatty acid methyl

ester could be smoothly carried out in presence of thermoregulat-

ed phase-transfer catalysts. Among the investigated thermoregu-lated phase-transfer catalysts, Pd/IV showed the best catalytic

performance with 160 OHV and 0 IV (theoretical hydroxyl value

203 mg KOH/g, which was calculated according to the reference

Wang, 1993), but the results of others were not satisfied. This

may be because of the steric resistance of P-ligand. With increasing

the volume/size of the substituent group of the P-ligand, the steric

resistance of the catalyst complex was higher, which handicaps the

progress of hydrogenation reaction.

3.2. Effect of metal complex on hydrogenation results

As shown inTable 2, the TRPTC Pd/IV exhibited efficient cata-

lytic performances for hydrogenation of fatty acid methyl ester,

but the others were poor. Especially using Ni/IV as catalyst, OHV

and IV were only 5 and 106, respectively, which indicated that

the hydrogenation was almost no occurred. This may be because

of the differently catalytic activity of the metal complexes, and this

result is in line with that reported in literature (Szollosi et al.,

1996).

CH2CH

2O

nRP

O

O

O CH2CH

2O

nOP

CH2CH

2O

nO CH3P

CH3

CH2CH

2O

nOP R

R = C15

- C20

, n =

3

I II

III IV

12 - 18

Fig. 1. The structure of the used P-ligands.

OH

OHPCl3

O

O

P Cl 2HCl

O

O

P Cl HO CH2CH2O Rn

O

O

P O CH2CH2O Rn HCl

Fig. 2. Synthesis of P-ligand I (n= 1218,R = C15C20).

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3.3. Reusability of Pd/IV

When the reaction was finished, the upper organic phase was

separated from aqueous phase by decantation. Then by adding

fresh solvent and reagent, the aqueous phase was directly usedas catalyst and the reusability of the catalytic system was investi-

gated under optimum reaction conditions, the results were given

in Table 3. The results showed that the catalytic system was reused

five times without an obvious decrease in its catalytic activity.

Therefore, it was indicated that this catalyst system was of good

reusability. The good reusability of this catalytic systemwas attrib-

uted to the good thermally stable and effective phase-transfer per-

formance, which could well avoid the loss of catalyst during the

reaction and separation.

4. Conclusion

The hydrogenation of fatty acid methyl ester was investigated

in presence of thermoregulated phase-transfer catalysts. The ther-moregulated catalytic system Pd/IV exhibited an efficient catalytic

performance. Using Pd/IV as catalyst, not only the hydrogenation

of fatty acid methyl ester was of high selectivity to saturated fatty

alcohol, but also the product could be easily separated from the

catalytic system and the catalyst complex was of good reusability.

It is also found that the steric resistance of the nonionic P-ligand, to

a large extent, affects the performance of metal complex. Thus,

more research should be done to synthesize novel nonionic phos-

phine ligands with little steric resistance in order to extend the

field of the thermoregulated catalytic system.

Acknowledgments

This work was supported by Shangdong Province Natural Sci-

ence Foundation (No. Y2007B53) and Qingdao University of Sci-

ence and Technology Fetching in talent Research fund start-up

projects.

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Table 1

Effect of catalysts on the reaction results.

Entry Catalysts OHV IV

1 PdCl2 (3 mg) 0 3

2 Co(CH3COO)2(3 mg) 0 115

3 Pd/C (5%, 60 mg) 71 50

4 Pd/I 93 60

5 Pd/II 19 89

6 Pd/III 10 907 Pd/IV 160 0

Table 2

Effect of metal complex on the reaction results.

Entry Catalysts OHV IV

1 Pd/IV 160 0

2 Rh/IV 84 39

3 Ni/IV 5 106

4 Co/IV 65 62

5 Ru/IV 72 51

Table 3

The reusability of catalytic system.

Times OHV IV

1 163 0

2 160 0

3 158 0

4 156 2

5 155 3

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