Long term activity of modified ZnO nanoparticles for transesterification

Fuel 89 (2010) 2844–2852

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Long term activity of modified ZnO nanoparticles for transesterification Shuli Yan, Siddharth Mohan, Craig DiMaggio, Manhoe Kim, K.Y. Simon Ng, Steven O. Salley * Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, MI 48202, USA

a r t i c l e

i n f o

Article history: Received 3 November 2009 Received in revised form 18 May 2010 Accepted 18 May 2010 Available online 31 May 2010 Keywords: Biodiesel Unrefined and waste oils Transesterification Esterification Catalyst life

a b s t r a c t Biodiesel can be produced by the transesterification of natural oils with methanol using modified ZnO nanoparticles as catalyst. Crude algae oil, corn oil from DDGs, crude palm oil, crude soybean oil, crude coconut oil, waste cooking oil, food-grade soybean oil and food-grade soybean oil with 3% water and 5% FFA addition were converted into FAME within 3 h using this new catalyst. The ZnO nanoparticles were reused 17 times without any activity loss in a batch stirred reactor and the average yield of FAME was around 93.7%. ZnO nanoparticles were used continuously for 70 days in a fix bed continuous reactor and the average yield of FAME was around 92.3%. XRD, ICP, TEM and HRTEM were used to characterize the long term used catalyst structure. Results show that this catalyst is a mixture of wurtzite ZnO nanoparticles and some amorphous materials and that the used catalysts have similar crystal structure to fresh catalyst. ICP results show that this catalyst does not dissolve in biodiesel, methanol, oil and glycerine–methanol solutions. It has a stable crystal structure under the reaction conditions. The high catalytic activity, long catalyst life and low leaching properties demonstrate these modified ZnO nanoparticles have potential in a commercial biodiesel production process. Published by Elsevier Ltd.

1. Introduction Biodiesel, a renewable fuel with similar combustion properties to petroleum diesel, is normally produced by the transesterification of highly refined oils with short-chain alcohols. Biodiesel can significantly decrease the exhaust emission of CO2, SOx and unburned hydrocarbons from motor vehicles [1,2]. It is environmentally beneficial, and therefore is a promising alternative to fossil diesel [3]. The transesterification reaction of triglycerides for the production of biodiesel is as follows:

Conventionally, transesterification is performed using strong base or acid catalysts such as NaOH, NaOCH3 and H2SO4 [4,5]. These traditional homogeneous catalysts have certain advantages includ* Corresponding author. Tel.: +1 313 577 5216; fax: +1 313 578 5636. E-mail address: [email protected] (S.O. Salley). 0016-2361/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.fuel.2010.05.023

ing cost-effectiveness, high activity, and mild reaction conditions (65–150 °C and 15–30 Psi). However, these homogeneous catalysts also have associated problems. Firstly, usage of homogeneous catalysts is normally limited to batch-mode processing followed by a catalyst separation step [5]. The catalysts are soluble in products and after reaction both fatty acid methyl esters and glycerine phases are required to be neutralized by mineral acids or bases, washed with water, and dried by vacuum. The post-reaction treatment process is long and complicated. Furthermore, a lot of waste washing water is generated which is not environmentally beneficial.

Homogeneous catalysts are also sensitive to free fatty acids (FFAs) and water. FFAs react with basic catalysts (NaOH and KOH) and form soaps, which complicates the glycerol separation, and drastically reduces the methyl ester yield. Water in the feedstock leads to hydrolysis of oils and fatty acid methyl esters (FAME) in the presence of strong basic or acidic catalysts. Thus, some

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inexpensive oils, such as crude vegetable oils, waste cooking oil, and rendered animal fats, which generally contain a high content of FFA and water, cannot be directly utilized with homogeneous catalysts. For conventional processes using homogenous catalysts, FFA content in the feedstock must be lower than 0.50 (wt.%) [6] and water content lower than 0.06 (wt.%) [7]. Thus the feedstock cost for traditional biodiesel production processes is very high. It has been reported that the cost of oil feedstock in 2006 accounts up to a total of 80% of the biodiesel production cost [8,9], which greatly influenced the biodiesel price. Since heterogeneous catalysts can be easily removed from the reaction mixture and reused many times, the development of a continuous reaction system based on a heterogeneous catalyst can greatly decrease the process and catalyst consumption costs. There have been many reports about highly active heterogeneous catalysts for biodiesel production. Kim et al. [10] prepared a Na/NaOH/c-Al2O3 heterogeneous base catalyst and found it showed almost the same activity under the optimized reaction conditions compared to conventional homogeneous NaOH catalyst. Suppes et al. [11] carried out the transesterification of soybean oil with methanol in the presence of sodium species loaded on NaX zeolite and ETS-10 zeolite. At 60 °C, ETS-10 yielded a conversion of 80.7%. Yan et al. [12] prepared supported CaO catalysts, achieving rapeseed oil conversion at 65 °C as high as 92% within 1 h. However, the catalyst durability is seldom reported, which has a practical impact on the potential for catalyst commercialization. Of late, several researchers reported that some solid transesterification catalysts partially dissolved in the reaction mixtures threatening the reusability of the catalyst. Granados et al. [13,14] found that the transesterification mechanism of activated calcium oxide catalysts is a combination of heterogeneous and homogeneous reaction. He observed that part of the transesterification reaction takes place on basic sites at the surface of the catalyst, while the rest is due to the dissolution of the activated CaO in methanol that creates a homogeneous leached active phase. Later, Martyanov and Sayari [15] investigated the catalytic activities of sodium, magnesium and calcium methoxides and found that the transesterification starts as a heterogeneous process, but then the methoxide salts interact with products such as glycerol and form an active homogeneous species. Kim et al. [16] prepared ZnO–Al2O3/ZSM-5 and SnO–Al2O3/ZSM-5 catalysts and they observed that the residue sodium on supported zeolite catalysts provided the active site for the catalyst activity. Many attempts have been made to develop a heterogeneous catalyst with high tolerance to FFA and water in the raw materials. Bournay and Hillion [17] claimed in a patent that a Lewis acid catalyst (zinc aluminate) for biodiesel production has a high tolerance to FFA in oil. Insitut Francais Petrole (IFP) has promoted the Esterfip-HTM process based on this kind of catalyst. Axens has commer-

cialized this process and Sofiproteol in Sète had it first industrially used in 2006 [18,19]. However, this catalyst is quite sensitive to water, limiting water content in oils to 0.15 (wt.%). Thus, some unrefined oils cannot be used in this system. Furthermore, until now there is no report about the long term catalyst activity and catalyst structural stability. In our previous work [20,21], we reported a series of ZnO–La2O3 catalysts which were highly active in biodiesel formation reactions and highly tolerant to water and FFA. Yan et al. [20] reported that ZnO–La2O3 catalysts can process soybean oil which has 3% water and 5% oleic acid. The catalyst with 3:1 ratio of zinc to lanthanum (Zn3La1) was found to simultaneously catalyze the oil transesterification and fatty acid esterification reactions, while minimizing oil and biodiesel hydrolysis. Our research goal is to develop a heterogeneous catalyst which has the advantages of high catalytic activity, stable crystal structure under reaction conditions, long catalytic life, and high tolerance to water and FFA. In this study, we tested the catalytic activity of Zn3La1 with multiple inexpensive oils in both batch and continuous reactors as well as the catalyst durability and the solubility of catalyst in reaction mixtures. We also investigated the interaction between zinc and lanthanum and found how it influenced the catalyst life and crystal structures.

2. Materials and methods 2.1. Materials Food-grade soybean oil was purchased from Costco warehouse (Detroit, MI), crude coconut oil was from TWA Inc. (Selangor, Malaysia), crude algae oil and corn oil from DDGs was obtained from SRS (Dexter, MI), crude soybean oil was from BDI (Denton, TX), crude palm oil was from Malaysia Palm Oil Board (Selangor, Malaysia) and waste cooking oil was obtained from a local restaurant. The fatty acid compositions of these seven kinds of oil were determined by GC–MS (Table 1). Zinc nitrate hexahydrate (98%), lanthanum nitrate hydrate (98%), and urea (99%), analysis grade, were purchased from Sigma–Aldrich Company (St. Louis, MO).

2.2. Catalyst preparation and characterization The modified ZnO nanoparticles were prepared by the urea hydrolysis method as described in our previously published report [20]. Solutions of 2 M Zn(NO3)2 and 1 M La(NO3)3 were prepared with distilled water. Then, solutions with 3:1 ratios of Zn:La were mixed with a 2 M urea solution. The mixture was boiled for 4 h, and then dried at 150 °C for 8 h, followed by step-rising calcination at 250, 300, 350, 400 °C, finally at 450 °C for 8 h. The catalysts are noted as Zn3La1.

Table 1 Fatty acid composition and TON of food-grade soybean oil, crude soybean oil, crude palm oil, waste cooking oil, crude corn oil from DDGs, crude algae oil and crude coconut oil. Fatty acid components

Food-grade soybean oil (%)

Crude soybean oil (%)

Crude palm oil (%)

Waste cooking oil (%)

Crude corn oil from DDGs (%)

Crude algae oil (%)

Crude coconut oil (%)

C 12:0 C 14:0 C 16:0 C 16:1 C 18:0 C 18:1 C 18:2 C 18:3 Others TAN

0 0 11.07 0.09 3.62 20.26 57.60 7.36 0 0.03

0 0.27 13.05 0.39 4.17 22.75 52.78 6.59 0 6.62

0 0.21 41.92 0.23 3.85 42.44 11.30 0.04 0 0.48

0 0 11.58 0.18 4.26 24.84 53.55 5.60 0 7.56

0 0 10.76 0 4.46 24.55 52.55 1.19 6.50 25.19

0 2.72 20.91 10.62 6.95 33.33 18.45 1.16 6.86 26.38

49.13 19.63 10.12 1.79 2.83 7.59 2.75 0.15 6.01 8.48

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Powder X-ray diffraction (XRD) patterns were taken with a Rigaku RU2000 rotating anode powder diffractometer (The Woodlands, TX) equipped with Cu Ka radiation (40 kV, 200 mA). Transmission Electron Microscopy (TEM) and high resolution TEM (HRTEM) analyses were carried out using a JEOL 2010 (FasTEM, Japan) operating at 200 kV for microstructural, morphological and chemical quantification studies. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was carried out with a Perkin–Elmer Optima 2100 DV (Wellesley, MA). The dilutions of biodiesel, oil and FAME with kerosene were 0.1 g/g, and the dilutions of glycerine, methanol, and glycerine–methanol solution with distilled water were 0.01 g/g.

2.3. Biodiesel reactions and product analysis Batch catalytic reactions were carried out in a 500 mL stainless steel stirred reactor (Parr 4575 HT/HP Reactor). The reaction mixture consisted of 126 g of oil, 180 g of methanol, and 3 g of catalyst. Continuous catalytic reactions were carried out in a BTRS-JR Laboratory Reactor Systems (Parr) or a tubular continuous reactor which has a similar structure to the BTRS-JR. The tube reactor had dimensions of 20 mm i.d.  533 mm length in which 20 g of Zn3La1 catalyst was packed. Reactants were premixed in a beaker and then pumped into the top of the vertically oriented reactor using an HPLc liquid pump (Chrom Tech Inc., Apple Valley, MN). The flow rate was fixed at 0.3 mL/min; with a residence time of 2 h; and a biodiesel production rate of 0.15 mL/min; the reaction temperature was held at either 200 °C or 140 °C; reaction pressure was 300 Psi; the molar ratio of methanol to oil was varied from 14:1 to 26:1. The methanol was vaporized from the liquid product, and then the remaining product was settled in a separating funnel. The fatty acid methyl esters in the upper layer from the separating funnel was characterized with a GC–MS spectrometer (Clarus 500 MS System, Perkin–Elmer, Shelton, CT) equipped with a capillary column (Rtx-WAX Cat. No. 12426) (Bellefonte, PA). Methyl arachidate (Nu-Chek Prep Inc., Elysian, MN) was used as an internal standard. The total acid number (TAN) in the FAME phase was determined using a Brinkman/Metrohm 809 titrando (Westbury, NY) according to ASTM D 664 (TAN is the amount of potassium

hydroxide in milligrams that is needed to neutralize the acids in one gram of oil). 3. Results and discussion 3.1. Catalyst performance in a batch reactor 3.1.1. Oil flexibility of Zn3La1 catalyst Table 1 summarizes the composition of several oils for which this catalyst was evaluated. Crude corn oil from DDGs contains 93% triglycerides and a total acid number (TAN) of 25.19 mg KOH/g. Crude algae oil contains only 80% triglyceride, with a TAN of 26.38 mg KOH/g. The TAN of crude coconut oil was 8.48 mg KOH/g. It should be noted that many of these oils cannot be directly used in the traditional biodiesel production processes because of high TAN. Fig. 1 shows the FAME yield versus time for the above oils when using the Zn3La1 catalyst in a batch reactor. Nearly complete conversion is obtained within 3 h at 200 °C and 500 Psi. The TAN of the product of the algae oil reaction was 0.94 mg KOH/g while that of the corn oil from DDGs product was 1.32 mg KOH/g. These results imply that during the reaction process esterification of FFA is simultaneously accomplished with the transesterification of triglyceride. 3.1.2. Catalyst durability in the batch stirred reactor The Zn3La1 catalyst was reused 17 times in the batch reactor for the transesterification of refined soybean oil with methanol without any catalyst regeneration (Fig. 2a) and reused six times with crude coconut oil and methanol (Fig. 2b). Fig. 1 shows that the average yield of soybean methyl esters was maintained around 93.7% and coconut methyl esters around 91.3%. There was no drop in the FAME yield during these catalyst durability tests. 3.2. Catalyst performance in a continuous reactor 3.2.1. Oil flexibility of Zn3La1 in the continuous reactor In our previous work [20], Zn3La1 was shown to be active for esterification even when the reaction temperature was as low as 140 °C. As crude corn oil contains a high content of FFA, the

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soybean oil with 3ater and 5 % FFA soybean oil waste cooking oil crude soybean oil algae oil crude palm oil coconut oil corn oil from DDGs brown grease H 2 SO 4 NaOH Fig. 1. FAME yield of crude corn oil from DDGs, crude algae oil, crude coconut oil, crude palm oil, crude soybean oil, waste cooking oil, food-grade soybean oil and food-grade soybean oil with 3% water and 5% oleic acid addition. Reaction conditions: 126 g of oil, 180 g of methanol, 3 g of catalyst, 200 °C, 500 Psi, in the batch stir reactor. Note that all of these oils were converted into FAME within 3 h.

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Fig. 3. FAME yield in the continuous reactor using crude corn oil from DDGs and crude coconut oil. (a) Yield of corn methyl esters. Note crude corn oil was run for 4 days. Reaction conditions: 140 °C, 300 Psi, 12:1 of mole ratio of methanol to oil, 20 g of catalyst, 0.3 mL/min of flow rate, 2.5 h of resident time. (b) Yield of coconut methyl eaters. Note crude coconut oil was run for 1.5 days based on a 32 days used catalyst. Reaction conditions: 200 °C, 300 Psi, 42:1 of mole ratio of methanol to oil, 8 g of 32-day-used catalyst, 0.3 mL/min of flow rate, 2 h of resident time.

catalyst was utilized at 140 °C, 300 Psi and 12:1 mol ratio of methanol to oil for 4 days (Fig. 3a). The TAN of the methyl ester product was 1.716 mg KOH/g and the average yield of corn methyl esters was 72.5%, which is a little lower than the results in the batch reactor. This can be explained by the low reaction temperature and low mole ratio of methanol to oil. Crude coconut oil was reacted at 200 °C, 450 Psi and 42:1 mol ratio of methanol to oil in the continuous reactor for 1.5 days using the same catalyst which had already been used for 32 days (Fig. 3b). The average yield of coconut methyl esters was 85.4% with a TAN of the methyl ester product of 1.23 mg KOH/g. 3.2.2. Catalyst durability in the continuous reactor Fig. 4 shows the yield of FAME over 70 days in the Zn3La1 catalyst continuous reactor for refined soybean oil. As observed for other long term heterogeneous catalysts [22], steady state opera-

tions were not obtained immediately. Fig. 4 shows that during the initial 6 days there is an increasing trend in FAME yield, and past the 7th day the yield of FAME is stable around 92.3%, continuing for 63 days. The delay in attaining steady, high yields may be related to the time required to achieve good liquid–solid contact at such low flow rates. To our knowledge, there is no transesterification catalyst with a reported longer catalyst life than Zn3La1. The long term stability of FAME yield shows a potential for commercialization of this kind of ZnO-containing particles for biodiesel production. Mole ratio of methanol to oil has a significant effect on the process cost of continuous biodiesel production. Therefore, raw materials with mole ratio of 13:1, 18:1, 26:1 were tested. Fig. 5a–c illustrate that the average yield of FAME for 13:1 is 40.5%, for 18:1 is 53.5%, and for 26:1 is 95.0%. Molar ratio of 26:1 is suggested here. Effect of residence time was also tested (Fig. 6). In the same

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3.2.3. Leaching from modified ZnO nanoparticles Determination of the amount of metal (Zn or La) leached by dissolution of the catalyst in the reaction medium is relevant for the following two reasons. First, the presence of Zn2+ and La3+ in the biodiesel and glycerine products necessitates purification of the products, especially the biodiesel. Second, leaching directly affects the lifetime of the catalyst. In this study, we prepared four different solutions: pure methanol, refined soybean oil, soybean biodiesel and 20% (wt.) glycerine in methanol (glycerine–methanol), and measured leaching of Zn3La1 in these solutions. One gram of catalyst was soaked in 500 mL of solution for 12 h with vigorous stirring at 500 rpm. The mixture was then filtered, and the solid was washed with fresh solution. Fig. 7 shows that Zn and La levels in the washing solution were high in the initial period, which implies a partial leaching of catalyst components. But Zn and La levels decreased quickly during the washing process. After 200 mL of washing solution was used, the Zn and La concentration were lower than 2 ppm. This low level of Zn and La suggests that very little leaching of catalyst components occurs after the initial period. The metal ion contents in the FAME and glycerine phases obtained during continuous reactor operation over 70 days are reported in Fig. 8. Fig. 8a shows that Zn and La levels in FAME were relatively high in the first 3 days, but decreased as operation proceeded and stabilized around 6 and 2 ppm over the remainder of the 67 days of operation. Fig. 8b shows the Zn and La levels in the glycerine product. They decreased in the initial 7 days and

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reaction system, raw materials flow rate was increased to 0.6 mL/ min and residence time was decreased to 1 h. The results show that FAME yields still maintain around 90.4%.

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60

associated with the yield of FAME reaching the highest and steady value of 92.3%. This phenomenon can be closely related with the polarity of products. The polarization index of glycerine is much higher than that of FAME, therefore, the solubility of metal ions in glycerine is higher than in FAME and requiring more time to stabilize the catalyst in glycerine.

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became stable around 8 and 4 ppm over the next 63 days. The low level of Zn and La in FAME and glycerine products suggests that leaching of catalyst components is negligible once the catalyst bed attains a stable status. The amount of metal leached stabilized more rapidly in the FAME product than in the glycerol product, which took 7 days to reach a stable value. The 7th day of the reaction period is also

a

Fig. 9 displays the XRD spectra of the fresh catalyst, catalyst used 18 and 32 days in the continuous reactor and the catalyst used 17 times in the batch stirred reactor. The used catalysts show a similar crystal structure to the fresh Zn3La1 catalyst. This indicates that all of these catalysts are a mixture of hexagonal wurtzite structure of zinc oxide and La2CO5. The mean grain size of ZnO in the fresh catalyst is around 15.5 nm calculated by the Deby–Scherrer equation based on the reflection peak of ZnO (1 0 1) while used catalysts had a slightly reduced grain size. XRD results show that the used catalysts have a similar distribution of average critical size distribution. Fig. 9 also shows a slight shift of peaks of ZnO (1 0 0) and ZnO (1 0 1). We calculated the crystal parameters of ZnO, such as a, c, volume and density. Table 2 shows that the a and c values slightly increased for the used catalyst. Fig. 9 also indicates that the peak intensity of the used catalyst slightly decreases in comparison with fresh catalyst. This is possibly due to the

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Fig. 9. XRD spectra of fresh Zn3La1, 18 days used Zn3La1 in the continuous reactor, 32 days used Zn3La1 in the continuous reactor, and the 17th times used Zn3La1in the batch reactor. (1) ZnO and (2) La2CO5. Note that they have similar X-ray structure.

Table 2 Crystal size and crystal parameters of ZnO in fresh Zn3La1, 18 days used Zn3La1 in the continuous reactor, 32 days used Zn3La1 in the continuous reactor and the 17th times used Zn3La1 in the batch reactor. Catalyst samples

Crystal size (nm)

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c (Å)

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D (c)

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15.5 14.3 14.2 13.2

3.22 3.26 3.26 3.26

5.18 5.21 5.26 5.27

46.40 47.88 48.35 48.48

5.83 5.64 5.58 5.57

attached amorphous fat on the used catalyst surface, which will increase noise and bother the peak detection. TEM images of fresh catalyst (Fig. 10a) show that Zn3La1 is a mixture of amorphous material and hexagonal nanoparticles around 20–80 nm. Some of the nanoparticles indicate a ‘‘single crystalline” textured orientation (Fig. 10b). This polyhedron is enclosed by (0 0 0 1) (top and bottom surface), {1 0 1 0} (side surfaces), stepped {1 0 1 1} (inclined surface), and high index planes with defect surface. The high resolution TEM image (Fig. 10c) is recorded along [0 0 0 1] of the crystal. Fig. 10d indicates ZnO nanocrystals partially covered by small amorphous

materials. Fig. 10e is a TEM image of the 32 days used catalyst. The size distribution of the used nanoparticles in Fig. 10d is closed to the fresh catalyst in Fig. 10a. ICP analysis shows that the molar ratio of Zn to La for the fresh catalyst is 3.18 while the ratio is 3.29 for the catalyst used for 32 days. This suggests that some of the components in the catalyst may have leached out during reaction, as indicated by the leaching results above. Generally speaking, amorphous materials are not stable and can easily be flushed out with reactants. Therefore it is likely that the slight leaching in the initial period is caused by the dissolution of amorphous materials, which are not considered active centers for transesterification. Therefore we can assume that only after amorphous materials are flushed out the catalyst shows a high activity in transesterification. Two kinds of surface could be supposed on the ZnO crystal, like the polar faces of (0 0 0 1)-Zn, (0 0 0 1)-O, and the non-polar faces of side (1 0 1 0) and stepped (5 0 5 1). The polar faces of (0 0 0 1) consist of only Zn atoms and (0 0 0 1) consist of only O atoms, while (1 0 1 0) and (5 0 5 1) are a mixture of Zn and O atoms. The transesterification reaction rate on non-polar faces is low [23,24]. Our previous study [20] has shown that O rich faces have a high catalytic activity in the triglyceride transesterification reaction and the Zn rich faces are active in fatty acid esterification reaction. Thus having the {0 0 0 1} surface exposed to reactants becomes important. In our previous work [20], we have found a strong interaction between zinc and lanthanum species. Lanthanum partially replaces zinc atoms in ZnO crystal. Thus, it weakens the bond of some of the oxygen atoms in its neighborhood, and makes them more reactive [25]. Therefore, the Zn3La1 catalyst shows a higher activity for transesterification than ZnO. Since the crystal of wurtzite ZnO doped with La is stable under reaction conditions, it has a long catalytic life in transesterification. Fig. 11 illustrates a possible transesterification reaction mechanism for the catalytic process. For fresh catalysts some amorphous fractions cover the (0 0 0 1) plane of ZnO. Therefore the catalyst shows a lower activity in the initial period. After a washing process, amorphous material partially dissolves in reaction mixture and active centers (atomic oxygen) are exposed. The bulk terminated ZnO (0 0 0 1)-O is composed of a topmost layer of nearlyclose packed oxygen anions, located at a short distance of 0.6 Å above a second layer of Zn cations and 2.6 Å above a second layer of O anions [26,27]. Methanol is adsorbed on the oxygen and then the oxygen anion forms. The nucleophilic attack of alcohol to the

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Fig. 10. TEM images of fresh and long term used Zn3La1 catalysts. Fresh Zn3La1 (a), a ZnO nanoparticle in fresh Zn3La1 (b), HRTEM image of a ZnO nanoparticle in fresh Zn3La1 (c), ZnO nanoparticles sticked by small fractions (d) and the 32 days used Zn3La1 (e). Note that both fresh Zn3La1 and the used Zn3La1 are a mixture of nanoparticles and amorphous material.

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Fig. 11. Schematic representation of possible mechanism for transesterification of triglyceride with methanol.

esters produces a tetrahedral intermediate. Then the hydroxyl group breaks and forms two kinds of esters. This transesterification mechanism can be extended to di- and mono-glycerides. 4. Conclusion The synthesis of FAME from unrefined and waste oils was investigated using modified ZnO nanoparticles as catalysts. We have found that at 200 °C the catalyst is active in both transesterification and esterification reactions, and can be directly used in inexpensive oil systems for biodiesel production, such as crude algae oil, crude corn oil from DDGs, crude coconut oil, crude palm oil, crude soybean oil, and waste cooking oil. There is a strong interaction between zinc and lanthanum species which is closely related with long catalyst life and stable crystal structure under reaction conditions. At 200 °C, this catalyst has continuously run for 70 days in a fix bed reactor and has been reused for 17 cycles in a batch stirred reactor. Furthermore, leaching of catalyst components in reaction mixtures and product streams is negligible. Hence this class of catalysts, which is relatively inexpensive because of low raw materials and manufacturing cost, significantly simplifies the oil pretreatment process and product purification process, and greatly decreases the feedstock cost and production cost of biodiesel. Acknowledgements Financial support from the Department of Energy (Grant DEFG36-05GO85005) and Michigan’s 21st Century Job Fund is gratefully acknowledged.

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