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Catalysis Communications 8 (2007) 1969–1972

A novel solid superbase of Eu2O3/Al2O3 and its catalyticperformance for the transesterification of soybean oil to biodiesel

Xu Li, Guanzhong Lu *, Yanglong Guo, Yun Guo, Yanqin Wang, Zhigang Zhang,Xiaohui Liu, Yunsong Wang

Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, China

Received 19 October 2006; received in revised form 9 March 2007; accepted 12 March 2007Available online 20 March 2007

Abstract

A novel solid superbase catalyst of Eu2O3/Al2O3 was prepared and its basic strength reached 26.5 measured by indicators according toHammett scale. The catalytic activity of Eu2O3/Al2O3 was evaluated for the transesterification of soybean oil with methanol to biodieselin the fixed bed reactor and under atmospheric pressure. The results show that Eu2O3/Al2O3 is an excellent catalyst for the transesteri-fication of soybean oil, and the conversion of soybean oil can reach 63.2% at 70 �C for 8 h.� 2007 Elsevier B.V. All rights reserved.

Keywords: Eu2O3/Al2O3; Solid superbase catalyst; Biodiesel; Soybean oil; Catalytic transesterification

1. Introduction

The production of biodiesel has been drawn attentionmore and more in recent years, because of the less detri-mental effects of this fuel on the environment, comparedwith the conventional diesel obtained from petroleum [1].Biodiesel is usually produced by the transesterification ofvegetable oils or animal fats with methanol or ethanol,which is commonly catalyzed by the basic catalysts, includ-ing hydroxides of sodium or potassium, their carbonates oralkoxides, and so on [2,3]. The most commonly used tech-nology is based on the batch plants and homogeneous basiccatalyst (such as NaOH, KOH or NaOCH3, dissolved inmethanol). At the end of the reaction, the homogeneousbasic catalyst should be neutralized with acetic acid or amineral acid, and the biodiesel produced should be purifiedby washing gently with warm water to remove residual cat-alyst or soaps and dried, which leads to the production ofemulsion to increase the production cost in the followingprocesses [1]. Considering the drawbacks above, recently

1566-7367/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.catcom.2007.03.013

* Corresponding author. Tel.: +86 21 64252923; fax: +86 21 64253703.E-mail address: gzhlu@ecust.edu.cn (G.Z. Lu).

the more easily separated heterogeneous catalysts havebeen investigated [4–12].

Preparation and study of the solid superbase catalysts isa developing area attracting more and more attentions,because the solid superbase catalysts possess a high activityfor the various reactions under mild conditions and substi-tute for the homogeneous base catalyst to minimize theproduction of pollutants. Various kinds of inorganic solidsuperbases (Na–NaOH/Al2O3, Na/MgO, NaOH/MgO,KF/ZrO2, etc.) [13,14] and organic solid superbases (LIC-KOR, KCH3, RbNH2, etc.) [15,16] were prepared in recentyears. The solid superbases can be used as the catalysts formany organic chemical reactions, such as the isomerizationof safrole [17], Aldol condensation [18–22], Knoevenagelcondensation [23,24], Claisen–Schmidt condensation [25],nitroaldol reactions [26], Michael addition [27], transesteri-fication [28], mixed Tishchenko reaction [29], mercaptanoxidation [30], cyanogenation of methanol [31], formationof the Si–C bond [32], side-chain alkylation [33], etc.

In this paper, we have developed a novel solid superbaseof Eu2O3/Al2O3 that has superstrong basic sites on its sur-face and is prepared by an impregnation method, whichhas not been reported. The transesterification of soybean

1 2 3 4 5 6 7 8 9 1014

16

18

20

22

24

26

28

H_

Content of Eu/wt%

Fig. 1. Basicity of Eu2O3/Al2O3 as a function of the Eu content.

Table 2Influence of the Eu content in the catalysts on the conversion of SBO

Eu content/wt% 1.35 2.25 3.60 4.50 6.75 9.00

Conversion of SBO/% 17.7 29.4 38.3 51.4 63.2 63.3Reaction time/h 12 11 11 10 8 8

1970 X. Li et al. / Catalysis Communications 8 (2007) 1969–1972

oil to biodiesel in the fixed bed reactor under atmosphericpressure was used as the model reaction, and the catalyticperformance of Eu2O3/Al2O3 was studied, in order to pro-mote the application of the solid superbasic catalyst in theproduction of biodiesel.

2. Experimental

2.1. Preparation and characterization of solid base

Eu(NO3)3/Al2O3 was prepared by impregnating pseud-oboehmite (Jiangyin Chemical Co. Ltd., China) in theEu(NO3)3 (AR, Ruike National rare earth metal materialsCo. Ltd., China) aqueous solution and dried at 110 �C for24 h, then broken to 20–40 mesh. After being calcined at300 �C for 2 h, 550 �C for 3 h, and 900 �C for 8 h in themuffle oven, this sample was transformed into Eu2O3/Al2O3. The content of Eu of catalyst was 0.45–9.00 wt%.Some sample was used to test its H� (Hammett function)by indicators[13] and the rest was quickly removed intothe fixed bed reactor under protection of nitrogen.

According to Hammett scale, when Hammett functionH� of a solidbase is over 26, this solid base can be definedas the super solidbase or solid superbase. In this paper, thebasicity of Eu2O3/Al2O3 was measured by the indicatorsshowed in Table 1.

2.2. Transesterification of soybean oil

The catalytic transesterification of soybean oil to biodie-sel was carried out in the fixed bed reactor under atmo-spheric pressure at 25–80 �C for 1–12 h. The stainlesssteel reactor (U12 mm · 360 mm) was heated in the electricheating furnace and thermocouple was used to control thetemperature of the reactor. The soybean oil and methanolwere dehydrated before being used, because the vegetableoils usually contain water [34] that will affect the perfor-mance of solid base catalyst. After dehydration, the mix-ture of methanol and oil was pumped into the bottom ofreactor from a round flask by a precise pump, the effluentfrom the top of reactor returned to the round flask, thenpumped to the reactor circularly. After the reaction wasfinished, the reacted solution was pumped back to theround flask. The molar ratio of methanol/oil was 1:1–1:10. The transesterification of soybean oil to biodieselcan be represented as the equation, TG + 3CH3OH = 3-ME + GL, TG-triglyceride, ME-methyl ester of fatty acid,GL-glycerol.

Table 1H� measurement indicators

Indicator 2,4-Dinitroaniline 4-Chloro-2-nitroaniline

Original color Yellow YellowBasicity color Purple OrangeH� 15.0 17.2

The products were analyzed by gas chromatograph(GC) with the capillary column of MPEG (30 m), N2 flowrate was 0.5 ml/min, H2 flow rate was 4 ml/min, and thecolumn temperature was 200 �C. The conversion (X) ofsoybean oil (SBO) could be calculated by X = 1 �Mx/92m1, here M is the average molecular weight of SBO, x isthe weight of glycerol (GL) corresponding to the unreactedtriglyceride, m1 is the total weight of methyl esters.

3. Results and discussion

3.1. Basicity testing

The effects of the Eu content on H� of Eu2O3/Al2O3 areshown in Fig. 1. The results showed that H� of Eu2O3/Al2O3 was about 15 when the Eu content was <2.25 wt%;in the Eu content of 2.25 � 6.75 wt%, H� of Eu2O3/Al2O3 increased with the increasing of Eu content; whenEu content was over 6.75 wt%, its H� was about 26.5and changed hardly with the Eu content. That is to say,when the Eu content is over 6.75 wt%, Eu2O3/Al2O3 hasthe superbase sites on its surface.

The effects of the content of Eu on the conversion ofSBO are shown in Table 2. The results showed that, withthe increasing of H� of catalyst, the conversion of SBOincreased. When the Eu content of catalyst was over6.75 wt%, the conversion of SBO had no obvious changewith the Eu content. So the catalyst with 6.75 wt%Eu

4-Nitroaniline Diphenylamine 4-Chloroaniline

Yellow Colorless ColorlessOrange Green–blue Peach18.4 22.3 26.5

0 2 4 6 8 10 12

0

10

20

30

40

50

60

70

Con

vers

ion

of S

BO

/%

Reaction time /h

Fig. 3. Influence of the reaction time on the conversion of SBO at 70 �C.(The reaction condition, methanol/oil = 6 (mol), 50 g oil, 5 g catalyst).

0 10

10

20

30

40

50

60

70

Con

vers

ion

of S

BO

/%

Ratio of methanol/oil /mol2 4 6 8

Fig. 4. Influence of the molar ratio of methanol/oil on the conversion ofSBO. (The reaction condition, 50 g oil, 5 g catalyst, at 70 �C for 8 h).

X. Li et al. / Catalysis Communications 8 (2007) 1969–1972 1971

was chosen as the model catalyst in the followingexperiments.

3.2. Catalytic performance of Eu2O3/Al2O3 for the

transesterification of soybean oil

3.2.1. Effect of the reaction temperature

After the catalytic transesterification of soybean oil tobiodiesel over Eu2O3/Al2O3 (6.75 wt%Eu) was operatedfor 8 h to make the catalyst have a stable catalytic perfor-mance, the conversions of SBO were tested at different tem-peratures. The results in Fig. 2 showed that, with anincrease of the reaction temperature from 25 to 70 �C,the conversion of SBO increased gradually to the maximalvalue, at 70 �C the conversion of SBO reached 63%, andthen the conversion of SBO reduced with the reaction tem-perature. As the boiling point of methanol is only 64.7 �Cunder atmosphere pressure, methanol would gasify tempes-tuously in the reaction solution when the reaction temper-ature is higher than 70 �C. Once the critical reactant in thereaction decreases quickly, the reaction would be affecteddrastically and the conversion of SBO correspondinglydecreases immediately. Therefore, the appropriate reactiontemperature is 70 �C.

3.2.2. Effect of the reaction time

The results in Fig. 3 showed that no conversion of oilwas observed in the first 30 min, and the conversion ofoil was very low in the first 2 h. After 2 h, the conversionof SBO increased gradually with the reaction time, andreached the maximum (�63%) after 8 h. Further increasingthe reaction time, the conversion of oil increased hardly, sothat the appropriate reaction time is 8 h.

3.2.3. Effect of the molar ratio of methanol/oil

The effects of the molar ratio of methanol/oil on theconversion of SBO are shown in Fig. 4. When methanol/oil = <4, the conversion of SBO increased with the ratioof methanol/oil; when methanol/oil = >4, the conversionwas affected hardly by the ratio of methanol/oil. Theoret-

20 30 40 50 60 70 80 90 100 1100

10

20

30

40

50

60

70

Con

vers

ion

of S

BO

/%

Reaction temperature /°C

Fig. 2. Influence of the reaction temperature on the conversion of soybeanoil. (The reaction condition, methanol/oil = 6 (mol), 50 g oil, 5 g catalyst).

ically, the higher ratio of methanol/oil favors to acceleratethe reaction, because the viscosity coefficient of soybean oilis larger, the presence of methanol can dilute soybean oiland promote the transfer of mass. However, excessivemethanol is not favorable for the purification of as-synthe-sized biodiesel in the following separation processes,resulting in the consumption of much energy to recoverthe large amount of unreacted methanol. Therefore, theappropriate molar ratio of methanol/oil should be con-trolled to 5–6.

3.3. Deactivation and regeneration of catalyst

It was found that, after the Eu2O3/Al2O3 catalyst wasused for 40 h in the transesterification reaction, the conver-sion of SBO declined from 63.2% to 35.3%, which is prob-ably due to a little water and the acidic substances in thereactants making the deactivation of the basic sites onthe catalyst. The deactivated catalyst was regenerated bythe calcination at 900 �C for 8 h in air. Table 3 shows theeffect of repeated run times on the recovery amount andsurface area of catalyst, and the conversion of SBO. Theresults indicate that the conversion of SBO decreased grad-ually with the increase of the regeneration (or repeated run)

Table 3Effect of repeated run times on the conversion of SBO

Times of repeated run 1 2 3 4 5

Catalyst amount/g 5.00 4.78 4.34 4.14 3.92BET surface area/m2 g�1 103.6 83.2 71.4 64.8 53.4Conversion of SBO/% 61.3 58.6 55.4 53.6 52.3

1972 X. Li et al. / Catalysis Communications 8 (2007) 1969–1972

times. The main reasons are the loss (about 6%) of catalystin the process of filtrating and calcinating, and the reduc-tion of BET surface area of catalyst calcined at 900 �C(Table 3). Such as, the BET surface area of the fresh cata-lyst was 103.6 m2/g; after being regenerated for one timesits surface area reduced to 83.2 m2/g, and for 5 times,reduced to 53.4 m2/g. The losses of the catalyst amountand the surface area lead to the decreases of the perfor-mance of catalyst and the conversion of SBO. Besides,the active components on the catalyst would be graduallycarried away in the reaction, resulting in the decrease ofthe catalyst activity, also.

4. Conclusion

In conclusion, the solid superbase catalyst Eu2O3/Al2O3

was prepared successfully and its basic strength H� reached26 of Hammett scale. For the transesterification reaction ofsoybean oil with methanol in the fixed bed reactor underatmospheric pressure, Eu2O3/Al2O3 behaved higher activ-ity. In the reaction condition of methanol/oil = 6 (mol) at70 �C for 8 h, the conversion of soybean oil reached 63%.

Acknowledgements

We would like to acknowledge the support financially ofthe National Basic Research Program of China (No.2004CB719500) and the Commission of Science and Tech-nology of Shanghai Municipality (No. 06JC14095).

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