Room-Temperature Transesterification of Edible and Nonedible Oils

Energy & Fuels 2008, 22, 1965–1971

1965

Room-Temperature Transesterification of Edible and Nonedible Oils Using a Heterogeneous Strong Basic Mg/La Catalyst N. Seshu Babu, Rekha Sree, P. S. Sai Prasad, and N. Lingaiah* Catalysis Laboratory, Inorganic and Physical Chemistry DiVision, Indian Institute of Chemical Technology, Hyderabad 500 007, India ReceiVed NoVember 15, 2007. ReVised Manuscript ReceiVed January 19, 2008

Magnesium-lanthanum-mixed oxide catalysts with different Mg/La ratios are prepared by coprecipitation at a constant pH method. The prepared catalysts were characterized by various techniques, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of CO2 (CO2TPD), and Brunauer-Emmett-Teller (BET) surface area. These catalysts are evaluated for transesterification of both edible and nonedible oils to their corresponding fatty acid methyl esters. The catalyst with a Mg/La weight ratio of 3:1 is showing optimum performance toward transesterification of oils, and it exhibited excellent activity even at room temperature. The disclosed catalyst is also tolerable for the transesterification of oils containing both water and free fatty acids. The catalyst can be easily recovered and reused with consistent activity. The exceptional activity of the Mg/La (3:1) catalyst during transesterification is endorsed because of the presence of the highest number of strong basic sites as evidenced by CO2-TPD compared to other Mg/La analogues. The higher basic strength of Mg/La (3:1) is also evidenced by XPS measurements, because the catalyst showed a negative shift in O1s binding energy, which indicates the presence of strong basic sites.

1. Introduction The majority of the energy needs of the world are supplied through petrochemical sources, such as coal and natural gases. All of these sources are finite and will be consumed shortly. Over the last few decades, there is an increasing worldwide concern for the conservation of nonrenewable natural resources and environmental protection. This has stimulated recent interest in alternative sources for petroleum-based fuels. An alternative fuel must be technically feasible, economically competitive, environmentally acceptable, and readily available. One possible alternative to fossil fuel is the use of oils of plant origin, such as vegetable oils and tree-borne oil seeds. This alternative diesel fuel can be termed as biodiesel. This fuel is biodegradable and nontoxic and has low-emission profiles as compared to petroleum diesel. Owing to the advantages of the environmental concerns with the biodiesel, there has been a renewed focus on biodiesel to make it from vegetable oils. Commercially, biodiesel is produced from edible vegetable oils, including rapeseed, sunflower, and soybean oils, as well as animal fats. These oils and fats are typically composed of C14-C20 fatty acid triglycerides (constituting 90–95% of the oil by weight). To produce a fuel that is suitable for use in diesel engines, the triglycerides (TG) are converted to the respective alkyl esters and glycerol by transesterification with short-chain alcohols, typically methanol.1 These lead to the formation of their respective fatty acid esters and glycerol by transesterification with short-chain alcohols. Transesterification is catalyzed both by acids and bases. Particularly, homogeneous catalysts, such as sodium, potassium hydroxides, or mineral acids, such as H2SO4, have been * To whom correspondence should be addressed. Telephone: +91-4027193163. Fax: +91-40-27160923. E-mail: [email protected]. (1) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 7, 1.

preferred.2,3 These catalysts showed greater performance toward transesterification to obtain biodiesel. However, these catalysts are associated with several disadvantages, such as corrosive medium and form unwanted soap byproduct by reacting with free fatty acids (FFAs). These are more toxic and corrosive and produce many byproducts.4 However, base catalysts are more active than acid catalysts for transesterification of oils. The problems associated with the homogeneous catalysts are the high consumption of energy and expensive separation of the homogeneous catalyst from the reaction mixture.5 In view of it, the heterogeneous catalysts have been explored to circumvent the difficulties with homogeneous catalysts. The use of heterogeneous catalysts is a new area in the development of suitable catalysts for transesterification of high FFA-containing oils. This approach eliminates the need for an aqueous quench and largely eliminates the formation of metal salts, thereby simplifying downstream separation steps; consequently, biodiesel production can be more economical. In the literature, a series of basic catalysts have been screened that include simple metal oxides, such as MgO and CaO in supported or unsupported form,6–8 Zn-Al-mixed oxides,9,10 cesium-exchanged zeolite X,8 anion(2) Watkins, R. S.; Lee, A. F.; Wilson, K. Green Chem. 2004, 6, 335. (3) Cantrell, D. G.; Gillie, L. J.; Lee, A. F.; Wilson, K. Appl. Catal., A 2005, 287, 183. (4) Mohamed, S. Z.; Shamshuddin; Nagaraju, N. Catal. Commun. 2006, 7, 593. (5) Vargas, R. M. J. Braz. Chem. Soc. 1998, 9, 199. (6) Peterson, G. R.; Scarrah, W. P. J. Am. Oil Chem. Soc. 1984, 61, 1593. (7) Gryglewicz, S. Bioresour. Technol. 1999, 70, 249. (8) Leclercq, E.; Finiels, A.; Moreau, C. J. Am. Oil Chem. Soc. 2001, 78, 1161. (9) Hillion, G.; Delfort, B.; Le Pennec, D.; Bournay, L.; Chodorge, J.A. Prepr. Symp.sAm. Chem. Soc., DiV. Fuel Chem. 2003, 48, 636. (10) Hillion, G.; Leporq, S.; Le Pennec, D.; Delfort, B. European Patent EP1468734, 2004.

10.1021/ef700687w CCC: $40.75  2008 American Chemical Society Published on Web 04/05/2008

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exchange resins,6 polymer-supported guanidines,11 Na/NaOH/ Al2O3,12 and K- and Li-promoted oxides, prepared by impregnating the corresponding nitrate or halide salt onto an oxidic carrier, such as Al2O3,13,14 ZnO,15 or CaO.16 Recently, layered double hydroxides (LDHs) have attracted much interest for vegetable oil transesterification because of its tunable basicity by modification of the chemical composition and high surface area.17 LDHs decompose to mixed oxides with the loss of water and CO2 (for the carbonate form of the LDH) during calcination. The mixed oxides are of particular interest because of their increased basicity, increased surface area, and homogeneous mixing of the different elements relative to the precursor LDHs. Indeed, several recent studies18–21 have shown that calcined Mg-Al LDHs possess moderate activity in transesterification reactions. Further, Corma et al.20 have reported that calcined Li-Al and Mg-Al LDHs are also able to catalyze the glycerolysis of fatty acid methyl esters to monoglycerides (the reverse of biodiesel synthesis). Among these, the Li-Al catalyst was reported to be more active than the Mg-Al or MgO because of its higher Lewis basicity. Leclerq et al.22 tested the use of commercially calcined hydrotalcites in the transesterification of rapeseed oil at 60 °C with poor results for this catalyst, probably because of the very low temperature adopted in the performed runs. Cantrell et al.23 on the contrary successfully used calcined hydrotalcites in promoting the transesterification of glyceroltributirrate with methanol. Many other heterogeneous basic catalysts, such as alkali-metal-exchanged Al2O3, such as KNO3/ Al2O3,24 Na/NaOH/γ-Al2O3,25 and Li/CaO26,27 have also been explored for the transesterification of vegetable oils. All of the basic catalysts reported above are overwhelmed by several disadvantages despite of their merits toward the transestrification of oils. In most of the experiments using heterogeneous catalysts, the transesterification reaction proceeds at a relatively slow rate compared to those conducted with homogeneous catalysts. The slow reaction rates are due to diffusion problems because these heterogeneous media behave as a three-phase system (oil/ methanol/catalyst) and are not possessing strong basic sites required for transesterification. Therefore, new catalytic materials with a high reaction rate are extremely desirable for transesterification. In the developments of a suitable heterogeneous solid basic catalyst for the transestrification of oils, we have found Mg/La-mixed oxide as a suitable catalyst for the (11) Sercheli, R.; Vargas, R. M.; Schuchardt, U. J. Am Oil Chem. Soc. 1999, 76, 207. (12) Kim, H.-J.; Kang, B.-S.; Kim, M.-J.; Park, Y. M.; Kim, D.-K.; Lee, J.-S.; Lee, K.-Y. Catal. Today 2004, 93, 315. (13) Xie, W.; Peng, H.; Chen, L. Appl. Catal., A 2006, 300, 67. (14) Xie, W.; Li, H. J. Mol. Catal. A: Chem. 2006, 255, 1. (15) Xie, W.; Huang, X. Catal. Lett. 2006, 107, 53. (16) Watkins, R. S.; Lee, A. F.; Wilson, K. Green Chem. 2004, 6, 335. (17) Cavani, F.; Trifiro, F.; Vaccari, A. Catal. Today 1991, 11, 173. (18) Xie, W.; Peng, H.; Chen, L. J. Mol. Catal. A: Chem. 2006, 246, 24. (19) Cantrell, D. G.; Gillie, L. J.; Lee, A. F.; Wilson, K. Appl. Catal., A 2005, 287, 183. (20) Corma, A.; Hamid, S. B. A.; Iborra, S.; Velty, A. J. Catal. 2005, 234, 340. (21) Corma, A.; Iborra, S.; Miquel, S.; Primo, J. J. Catal. 1998, 173, 315. (22) Leclercq, E.; Finiels, A.; Moreau, C. J. Am. Oil Chem. Soc. 2001, 78, 1161. (23) Cantrell, D. G.; Gillie, L. J.; Lee, A. F.; Wilson, K. Appl. Catal., A 2005, 287, 183. (24) Xie, W.; Peng, H.; Cheng, L. Appl. Catal., A 2006, 300, 67. (25) Kim, H. J.; Kang, B. S.; Kim, M. J.; Park, Y. M.; Kim, D. K.; Lee, J. S.; Lee, K. Y. Catal. Today 2004, 93–95, 315. (26) Serio, M. D.; Ledda, M.; Cozzolino, M.; Minutillo, G.; Tesser, R.; Santacesaria, E. Ind. Eng. Chem. Res. 2006, 45, 3009. (27) Watkins, R. S.; Lee, A. F.; Wilson, K. Green Chem. 2004, 6, 335.

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transesterification of edible and nonedible oils under ambient reaction conditions. In the present study, Mg/La-mixed oxide catalysts with a varying Mg/La ratio are prepared and studied for transesterification of both edible and nonedible oils to biodiesel. The tolerance of the catalysts toward transesterification of oils in the presence of a considerable amount of FFA and water is also studied. The reasons for the activity of the catalysts are correlated with the physicochemical properties of the catalysts. 2. Experimental Section 2.1. General Procedure for Mg/La Catalyst Preparation. The catalysts with different Mg/La ratios (1:1, 2:1, and 3:1 wt/wt %) were prepared by coprecipitation at a constant pH method. In a typical method of catalyst preparation, required amounts of Mg(NO3)2 and La(NO3)3 were dissolved in a calculated quantity of deionized water. The two precursor solutions were mixed homogeneously and allowed to precipitate using a basic solution of 1 M KOH and 0.25 M K2CO3 at a constant pH of 10. After ensuring complete precipitation, the precipitate was filtered and washed thoroughly with deionized water. The resultant catalyst mass was oven-dried at 120 °C for 12 h and finally calcined at 650 °C for 4 h. The three catalysts are herewith referred as ML-1, ML-2, and ML-3 for Mg/La weight ratios of 1:1, 2:1, and 3:1, respectively. 2.2. Procedure for Catalytic Experiments. All of the oils were commercially available and were purchased from local suppliers. The dried methanol and palmtic acid were purchased from Sd-fine (India). All of the transesterification reactions were performed in a 10 mL round-bottom flask equipped with a reflux condenser. The temperature of the reaction was monitored by a thermometer. In a typical reaction, 0.05 g of the catalyst was added to the reaction mixture of 1 g of oil and 2.5 mL of methanol. The reaction mixture was stirred at methanol reflux temperature (65 °C), and progress of the reaction was monitored by thin-layer chromatography (TLC). After completion of the reaction or stipulated reaction time, the catalyst was separated from the reaction mixture by filtration. The crude product after removing the catalysts was washed with water to remove glycerol. The obtained organic phase was analyzed by a 1H nuclear magnetic resonance (NMR) spectrum to estimate the yield of fatty acid methyl ester (FAME) using the following formula:28 yield ) A1X2/A2X3 where A1 and A2 are the areas of 1H NMR peaks corresponding to methoxy and methylenic protons, respectively. 2.3. Procedure for Recycling Experiments. The catalyst was separated from the reaction mixture by filtration, washed several times with methanol to remove any organic residues over the catalyst surface, and dried in oven at 120 °C for 4 h. It was further reused for the subsequent transesterification experiments. The same procedure is followed for all recycled experiments. 2.4. Catalyst Characterization. The physicochemical properties of the Mg/La catalyst were studied by various techniques, such as Braunner-Emmet-Teller (BET) surface area, X-ray diffraction (XRD), and temperature-programmed desorption (TPD) of CO2. 2.4.1. XRD. XRD patterns of the catalyst were recorded on a Rigaku diffractometer using Ni-filtered Cu KR radiation (1.5405 Å). The measurements were recorded in steps of 0.045°, with a count time of 0.5 s and a 2θ range of 2–80°. Identification of the crystalline phases was made with the help of Joint Committee on Powder Diffraction Standards (JCPDS) files. 2.4.2. TPD of CO2. In a typical experiment of TPD, 0.1 g of catalyst was loaded in a quartz reactor between two quartz plugs. Prior to CO2 adsorption, the catalyst was pretreated in He gas at 300 °C for 2 h and then cooled to room temperature. The adsorption of CO2 was carried out by passing a mixture of 10% CO2-balanced (28) Meher, L. C.; Kulkarni, M. G.; Dalai, A. K.; Nain, S. N. Eur. J. Lipid Sci. Technol. 2006, 108, 389.

Transesterification of Edible and Nonedible Oils

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Table 1. Physicochemical Properties of Mg/La Catalysts amount of basic sites (µmol of CO2/g)

total surface basicity area Tmax Tmax Tmax (µmol of catalyst (m2/g) ( ML-2 > ML-1. The total number of basic sites for the ML-3 catalyst is calculated by integrating the individual CO2 desorption peak areas and is found to be 596 µmol of CO2/g. This amount of basic strength recorded for the ML-3 catalyst is high compared to calcined Mg-Al HT. In the literature, the total basicity for calcined HT is reported as 369 µmol of CO2/g.31 (29) Mariscal, R.; Pena, M. A.; Fierro, J. L. G. Appl. Catal., A 1995, 131, 243. (30) Ivanova, A. S.; Moroz, B. L.; Moroz, E. M.; Larichev, Yu. V.; Paulshitis, E. A.; Bukhtiyarov, V. I. J. Solid State Chem. 2005, 178, 3265. (31) Di Serio, M.; Ledda, M.; Cozzolino, M.; Minutillo, G.; Tesser, R.; Santacesaria, E. Ind. Eng. Chem. Res. 2006, 45, 3009.

In the present case, the high basicity of the ML-3 catalyst is mainly due to the presence of La2O3 species in the close proximity of MgO. Thus, the total basicity can be tuned by varying the Mg/La ratios and is found maximum for the ML-3 catalyst. The literature also shows that the textural properties of the MgO solid surfaces are affected by the presence of a second precursor and the preparation procedure, and this is in good agreement with the findings of other authors.32–34 The formation of MgO and La2O3 solid solution suggests a close interaction of these oxides, thus leading to create strong basic sites. Apart from this, in the ML-3 catalyst, lanthanum hydroxide/carbonate species are present (as evident from XRD), and these species might be responsible for strong basic sites. The results obtained from XPS measurements are also in good agreement with the TPD profiles. The presence of lower binding energy of O 1s of ML-3 indicates the presence of strong basic sites, which corroborates with the presence of a high-temperature desorption peak with its peak maxima. 3.5. Catalytic Activity Measurements. Generally, the process of transesterification is affected by the mode of the reaction condition, molar ratio of alcohol/oil, type of oil, amount of catalyst, reaction time and temperature, and purity of reactants. 3.5.1. Optimization of the Catalyst Composition. The present catalysts were screened for the transesterification reaction of sunflower oil, and the results are shown in the Figure 4. All of the catalysts exhibit good activity toward transesterification of sunflower oil under methanol reflux temperature, with trivial variation in the reaction time. A close comparison of results suggests that complete conversion of sunflower oil is taking place within 20 min of the reaction time in the case of the ML-3 catalyst, whereas ML-1 and ML-2 catalysts catalyze the same reaction with 100% conversion in 120 and 60 min, respectively. Among the three catalysts, ML-3 exhibits high transesterification activity compared to the other two catalysts. These catalysts are selectively forming fatty acid methyl esters by transesterification of triglycerides. The reaction mixture is taken after removing the catalyst and washing with water and analyzed by 1H NMR spectroscopy to know the formation of mono- or diglycerates. The relevant spectra are shown in the Supporting Information. The spectral data suggest that there is no formation of mono- or diglycerides. The high activity within the short reaction time is due to the presence of a large number of strong basic sites in the ML-3 catalyst. There exist a linear relationship (32) Bancquart, S.; Vanhove, C.; Pouilloux, Y.; Barrault, J. Appl. Catal., A 2001, 218, 1. (33) Martra, G.; Cacciatori, T.; Marchese, L.; Hargreaves, J. S. L.; Mellor, I. M.; Joyner, R. W.; Coluccia, S. Catal. Today 2001, 70, 121. (34) Choudary, V. R.; Pandit, M. Y. Appl. Catal. 1991, 71, 265.

Transesterification of Edible and Nonedible Oils

Figure 5. Transesterification of edible and nonedible oils at room temperature using the ML-3 catalyst.

Figure 6. Transesterification of edible and nonedible oils at reflux temperature using the ML-3 catalyst.

between activity and basicity of the catalyst. The CO2-TPD of this catalyst suggests the presence of mainly super basic sites with a high amount of total basicity. Moreover, the XRD results suggest the formation of MgO and La2O3 mixed solid solution along with lanthanum hydoxyl/carbonate species. XPS results are also in support for the observed activity of the ML-3 catalyst that exhibits the presence of a greater number of surface hydroxyl/carbonate species. 3.5.2. Transesterification of Edible and Nonedible Oils. With the preliminary success of the transesterification of sunflower oil using the ML-3 catalyst, we tuned our attention to test the transesterification of other edible (soybean and rice bran) and nonedible (jatropha) oils using this catalyst at both room temperature and reflux, and the results are shown in Figures 5 and 6, respectively. These results suggest that, at reflux temperature, all of the oils are completely converted into their corresponding methyl esters within 20–30 min of reaction time, irrespective of the nature of the oil. During the transesterification of the oils at room temperature, complete conversion of oil takes place within 120–140 min. It is noteworthy to mention that the present catalyst is highly active even at room temperature. The conversion profile also shows that edible oils underwent transesterification relatively at a higher reaction rate compared to the nonedible oils. Therefore, the rate of the transesterification reaction not only depends upon the reaction temperature but also on the nature of the oil. 3.5.3. Effect of Catalyst Loading on the Transesterification of Sunflower Oil. The room-temperature transesterification of sunflower oil is conducted with different loadings of the ML-3 catalyst by taking an example of sunflower oil (1 g) and MeOH

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Figure 7. Effect of catalyst loading on the transesterification of sunflower oil.

Figure 8. Effect of the reaction time and reaction temperature on the transesterification activity of edible and nonedible oils using the ML-3 catalyst.

(2.5 mL) over a period of reaction time of 120 min. The results shown in Figure 7 suggest that the rate of the transesterification reaction increases with an increase in the weight of the catalyst and reaches a maximum at 0.05 g of the catalyst. These results suggest that about 85% conversion can be achived even with 0.025 g of the catalyst. These results manifest the high transesterification activity of the catalyst. 3.5.4. Effect of the Reaction Temperature and Reaction Time during the Transesterification of Sunflower Oil. To know the effect of the reaction temperature and reaction time, the transesterification of sunflower oil is conducted using the ML-3 catalyst at varied reaction temperatures and reaction times. These results are presented in Figure 8. The results suggest that the conversion of oil increased linearly with an increase in the reaction temperature. However, complete conversion of oil is achieved at both reflux and ambient temperatures at their stipulated reaction time. Further, the effect of the reaction time on the conversion of oil is studied at room temperature. The activity data reveal that, at a shorter reaction time (60 min), conversion of oil is comparatively low, while complete conversion of oil is recorded with a further increase in the reaction time up to 120 min. 3.5.5. Effect of the Molar Ratio of Methanol/Oil for the Room-Temperature Transestrification of Sunflower Oil. As suggested above, the transesterification activity depends upon the catalyst loading, reaction temperature, and reaction time. Besides, the transestrification activity also depends upon the molar concentrations of methanol/oil. Thus, the effect of the

1970 Energy & Fuels, Vol. 22, No. 3, 2008

Babu et al.

Table 3. Effect of the Molar Ratio of Oil/Methanol on the Conversion of Sunflower Oila entry

MeOH/sunflower (molar ratio)

conversion of sunflower oil (%)

1 2 3 4

21:1 32:1 42:1 53:1

34 67 93 100

a

Sunflower oil (1 g, 1.17 mmol); MeOH (62.5 mmol, 2.5 mL in entry 4); catalyst, ML-3 (0.05 g).

molar ratio of methanol/sunflower oil is studied using the ML-3 catalyst, and results are shown in Table 3. The results suggest that, at lower molar ratios of methanol/oil, the conversion of sunflower oil is poor and, with a further increase in their molar ratio, conversion of oil is proportionally increased and reached a maximum conversion at 53:1. The yield of FAME is increased with an increase in the molar ratio of methanol/oil. From these results, it is understood that a large excess of methanol is required. The increase in the methanol concentration increases the rate of reactions, such as transesterification, which has a positive reaction order in methanol. Using catalyst ML-3, it is found that a methanol/sunflower oil ratio of 53:1 is suitable for obtaining high product yields in a reasonable time (Table 3). It appeared that, although the sunflower oil/methanol ratio appears to be somewhat high at room temperature, others have reported 40–275 M excess of methanol for the transesterification of plant oils, which are operating at 70 °C or higher with a reaction time up to 22 h.35,36 However, the excess of methanol can be recovered and reused. 3.5.6. Transesterification of Oils Containing FFAs and Water Using the ML-3 Catalyst. Generally, edible and nonedible oils containing FFAs or water in considerable quantity underwent the transesterification reaction at a slower reaction rate using basic catalyst because of the adsorption of FFA on the catalyst surface. Basic catalysts are sensitive to moisture. Thus, oils containing water also inhibit the transesterification activity of the catalyst. Therefore, FFA should be converted to its methyl ester by esterification using an acid catalyst prior to the transesterification of oil. The additional step of esterification in biodiesel production makes it expensive. Recently, Ni et al.37 reported that esterification of FFA in oil could be performed cost-effectively over heterogeneous catalysts using a fixed bed reactor prior to the transesterification step, hence eliminating the need to have a combined esterification and transesterification step. This is effective when one takes full advantage of a fixed bed reactor, which is the ultimate goal for transesterification. The development of an efficient basic catalyst, which can be tolerable to both FFA and water to some extent, should be needed, for biodiesel synthesis to make it economically viable. With the transesterification of oil containing FFA or water, both FFA and water are carried out using the ML-3 catalyst, and the results are tabulated in Table 4. All of the experiments were performed with sunflower oil and a mixture of FFA of sunflower oil and also with palmitic acid. Initially, the effect of water on the transesterification activity of sunflower oil is checked with the ML-3 catalyst, and the results suggest that the catalyst is tolerable up to 10 wt % of water because it showed consistent activity as that of pure sunflower oil. Further, an effect of FFA on the transesterification of sunflower oil is studied on the same catalyst. Mixtures of FFA (35) Leclercq, E.; Finiels, A.; Moreau, C. J. Am. Oil Chem. Soc. 2001, 78, 1161. (36) Furuta, S.; Matsuhashi, H.; Arata, K. Catal. Commun. 2004, 5, 721. (37) Ni, J.; Meunier, F. C. Appl. Catal., A 2007, 333, 122.

Table 4. Effect of FFA and Water Content on the Transesterification of Sunflower Oila conversion of sunflower oil (%) water (wt %)

FFA (wt %)

reaction time (h)

1

3

5

10

2 3 4 5 6

100

100

100

100

1

2

3

5

100

92

94b 98

100c 97d

a Reaction conditions: sunflower oil (1 g); MeOH (2.5 mL); catalyst, ML-3 wt (0.05 g). b Conversion of oil in the presence of palmitic acid. c Conversion of oil in the presence of FFA and 5 wt % water. d Conversion of oil in the presence of FFA.

of sunflower oil or palmtic acid are taken as FFA during the transesterification of sunflower oil, and the results reveal that, at lower concentrations of FFA (1 and 2 wt %), the conversion of oil reaches above 90% within 2 h of reaction time. Whereas for 3 and 5 wt % of FFA, the rate of the transesterification activity of the catalyst is slightly decreased and reaches the maximum conversion of oil in 4 h for 3 wt % and 6 h for 5 wt % of FFA. It is intriguing here that if water is added in catalytic amounts to the reaction mixture of 5 wt % FFA containing oil and methanol, the transesterification activity of the catalyst is increased dramatically, where complete conversion of sunflower oil took place within 4 h of the reaction time. The reason for improved activity of the catalyst could be due to preferential adsorption of the water over the catalyst surface prior to the FFA adsorption. It implies that, water addition to the reaction mixture leads to improvement in the transesterification activity of oils containing FFA to some extent. The CO2-TPD results suggests that the presence of super basic sites in the ML-3 catalyst could be the cause for the greater tolerance of the catalyst toward the transesterification activity of oils containing FFA or water at ambient reaction conditions. 4. Recycled Experiments. The recycled runs were performed by taking an example of transesterification of sunflower oil using the ML-3 catalyst, and its efficacy of the catalyst is tested up to five cycles. The procedure for recycled runs is described in the Experimental Section. The results of the recycled runs reveals that the transesterification activity of the catalyst showed consistent activity up to five runs with a marginal variation of conversion up to 5%. 5. Comparison of the Transesterification Activity of the Mg/La Catalyst with Reported Solid Basic Catalysts. The transesterification activity of sunflower oil using ML-3 is compared to other basic catalysts.38–41 The results are summarized in Table 5. The data show that most of the cited catalysts are reported under reflux conditions and took a longer reaction time to achieve complete conversion of oil. Moreover, the reusability of the catalyst is overwhelmed by some limitations, such as poor recyclability and difficulty in separation of the catalyst. Also, the reports on the effect of FFA and water during the transesterification of oil are limited. However, recently, Verkade et al.39,40 have reported room-temperature transesterification of soybean oil using nanocrystalline CaO and polymer-bound azidoproazaphosphatrane. The authors have (38) Liu, X.; He, H.; Wang, Y.; Zhu, S. Catal. Commun. 2007, 8, 1107. (39) Venkat Reddy, Ch.; Oshel, R.; Verkade, J.G.;. Energy Fuels 2006, 20, 1310. (40) Venkat Reddy, Ch.; Fetterly, B. M.; Verkade, J. G. Energy Fuels 2007, 21, 2466. (41) Shumaker, J. L.; Crofcheck, C.; Tackett, S. A.; Santillan-Jimenez, E.; Crocker, M. Catal. Lett. 2007, 115, 56.

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Table 5. Comparison of the Transesterification Activity of the ML-3 Catalyst with Other Basic Catalysts catalyst

oil/catalyst mass ratio

reaction temperature (°C)

time (h)

conversion of oil (%)

33 88 20

65 RT RT

0.5 6 3

95 100 100

37 38 39

20 20 20 20

180 65 65 RT

1 1 0.3 2.2

92 53 100 100

40 40 present study present study

SrO nano CaO polymer-supported azidoproazaphosphatrane Mg-Al Li-Al ML-3 ML-3

reported the catalyst showed complete conversion of oil within 24 h and that the catalyst is also recyclable. Moreover, the authors have not yet studied the effect of FFA and water during transesterification. In comparison to the above-listed catalysts, the activity of the present catalyst looks very impressive in terms of a shorter reaction time, i.e., 20 min and 1–3 h at reflux and room temperatures, respectively. The catalyst also exhibits exceptional activity even in the presence of FFA and water. The catalyst can be easily recovered by filtration and reused with consistent activity. 6. Conclusions In summary, the Mg/La with a 3:1 (wt/wt %) ratio is an efficient catalyst for the room-temperature transesterification of triglycerides of both edible and nonedible oils. The catalyst

reference

exhibited exceptional activity toward the transesterification of oils within a short period of reaction time and also showed good transesterification activity of oils even in presence of water and FFA at room temperature. The high activity of the ML-3 catalyst is endorsed because of the presence of strong basic sites over the catalyst surface as evidenced by CO2-TPD, XRD, and XPS results. The preparation of the catalyst is simple, inexpensive, easy to handle, and noncorrosive. The catalyst is separated easily from the reaction mixture and reused several times with consistent activity. Supporting Information Available: 1H NMR spectra of FAME obtained during room-temperature transesterification of sunflower (Figure S1) and jatropha (Figure S2) oils. This material is available free of charge via the Internet at http: //pubs.acs.org. EF700687W