Biodiesel Production by Esterification of Oleic Acid over Brønsted

Article pubs.acs.org/IECR

Biodiesel Production by Esterification of Oleic Acid over Brønsted Acidic Ionic Liquid Supported onto Fe-Incorporated SBA-15 Lin Zhang, Yadong Cui, Chunping Zhang, Lei Wang, Hui Wan, and Guofeng Guan* College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, People's Republic of China S Supporting Information *

ABSTRACT: The esterification of oleic acid with short-chain alcohols using Brønsted acidic ionic liquid supported onto Feincorporated SBA-15 (Fe-SBA-15) was studied to develop a green method for biodiesel production. This catalyst was prepared by immobilization of Brønsted acidic ionic liquid 1-(propyl-3-sulfonate)-3-(3-trimethoxysilylpropyl) imidazolium hydrogen sulfate ([SO3H-PIm-CPMS][HSO4]) onto Fe-SBA-15 (IL/Fe-SBA-15). The structure of the catalyst was characterized by XRD, N2 adsorption−desorption measurement, FT-IR and TEM. The results demonstrated that Fe was incorporated into the framework of SBA-15, bringing Lewis acidic site. After the ionic liquid was successfully immobilized onto the surface of Fe-SBA15, the structure of the catalyst remained intact. This catalyst displayed relatively high catalytic activity in esterification of oleic acid with short-chain alcohols because of the synergistic effect of Lewis and Brønsted acidic sites. Under the optimum reaction conditions (reaction temperature 363 K, molar ratio of methanol to oleic acid 6: 1, catalyst amount 5 wt %, and reaction time 3 h), the conversion of oleic acid reached to 87.7% when methanol was used as reactant.

1. INTRODUCTION Biodiesel, which is defined as long-chain fatty acid alkyl ester (FAAE) derived from renewable lipid feedstock, such as animal grease and vegetable oil, can be used as an alternative fuel or an additive for petroleum diesel. Compared with traditional petroleum diesel, biodiesel has many advantages such as nontoxic, biodegradable, lower carbon and sulfur monoxide emissions, less particles and smoke, among other benefits.1−4 Normally, FAAE is obtained through a process known as transesterification, which is usually carried out by reacting triglycerides with short-chain alcohols using strong base as catalysts.5 However, the oil that is used to provide triglycerides should contain no more than 1% free fatty acids (FFA).6−8 When the FFA amount in the feedstock exceeds this critical value, the unwanted soap byproduct deactivates the catalyst and increases the downstream separation and purification costs.9,10 Therefore, the materials should be pretreated before application. Esterification of FFA with alcohol is another feasible route for biodiesel production. It is usually carried out in the presence of mineral strong acid catalysts like H2SO4. Unfortunately, these liquid acid catalysts inevitably bring about many problems such as corrosion of equipment, troublesome product separation, and environmental pollution. To overcome the weaknesses of liquid acids, various heterogeneous catalysts such as zeolites,11 resins,12,13 solid acids,14−16 solid super acids,17 and immobilized catalysts18,19 have been investigated for esterification reactions. However, the catalytic activities of most zeolites, resins and solid acids were not satisfactory because of their relatively weak acidities. Solid super acids displayed excellent catalytic activities, but they deactivated quickly because the acid radical was easily washed down. Recently, immobilized ionic liquid catalysts gained increasing attentions for their particular properties, such as excellent catalytic activities, tunable acidities and easy separation. © 2012 American Chemical Society

Consequently, many researchers grafted ionic liquids onto various supports such as metallic oxide,20 polystyrene,21 and silica gel.22−24 Since MCM family and SBA family materials were successively synthesized,25,26 ordered mesoporous silica materials were used as supports for various kinds of active component27−29 because of their excellent characteristics, such as a plenty of mesoporous pores for mass and heat transfer, abundant pendent silanol groups on the high surface area for immobilization and good thermal stability. Recently, many researchers have successfully incorporated various metals into mesoporous silica materials to adjust their performance.30−33 However, ionic liquid immobilized onto metalincorporated mesoporous materials used as catalysts has not been reported. Considering the esterification reaction could be catalyzed by both Lewis acid and Brønsted acid,34,35 Brønsted acidic ionic liquid [SO3H-PIm-CPMS][HSO4] was first prepared and then immobilized onto Fe-incorporated SBA-15 for biodiesel production in this paper. The catalysts were characterized by small-angle X-ray diffraction (XRD), N2 adsorption−desorption measurement, Fourier Transform Infrared (FT-IR) and Transmission electron microscopy (TEM). Catalytic activity of IL/Fe-SBA-15 for biodiesel production was also examined.

2. EXPERIMENTAL SECTION 2.1. Chemical Reagents. EO20PO70EO20 (P123, Mw5800) and oleic acid (95%, The impurities were other fatty acids such as stearic, linoleic, and linolenic acids) were purchased from Sigma-Aldrich (Shanghai) Trading Co, Ltd. (Shanghai, P.R. Received: Revised: Accepted: Published: 16590

September 8, 2012 November 21, 2012 December 2, 2012 December 3, 2012 dx.doi.org/10.1021/ie302419y | Ind. Eng. Chem. Res. 2012, 51, 16590−16596

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Scheme 1. Synthesis of the [SO3H-pIM-CPMS][HSO4] Ionic Liquid

obtained by washing with diethyl ether and drying under vacuum. 2.4. Synthesis of IL/Fe-SBA-15. In a typical process, 3.0 g of template-free Fe-SBA-15 was first activated at 423 K for 10 h, and then both Fe-SBA-15 and 1.5 g of [SO3H-pIM-CPMS][HSO4] were placed in a flask containing 100 mL dry toluene and heated to reflux for 24 h in the nitrogen atmosphere. The resultant was washed with diethyl ether and dried in vacuum. 2.5. Characterization. The XRD was performed on a Philips X’pert MPD Pro diffractometer equipped with Nifiltered Cu Kα radiation (λ = 0.15418 nm). The X-ray tube was operated at 40 kV and 40 mA. The scanning angle was from 0.5° to 5.0° with scan-steps of 0.01° per second. N2 adsorption−desorption measurements were carried out on a Micromeritics ASAP 2020 system model instrument at 77 K. The specific surface area was calculated by Brunauer− Emmett−Teller (BET) algorithm. The mesoporous pore size distribution was obtained through the Barrett−Joyner− Halenda (BJH) theory. FT-IR spectra were collected on a Thermo Nicolet 870 spectrophotometer with a resolution of 5 cm−1 using anhydrous KBr (Nicolet, United States) as dispersing agent. TEM images were obtained with a JEOL (model 794) instrument employing an acceleration voltage of 120 kV. The samples were daubed onto carbon film supported on copper grids after sonicate in ethanol for 15 min. 2.6. Esterification and Analysis. The reaction was carried out in liquid phase under atmospheric pressure. Taking the esterification of oleic acid with methanol as an example, 10 mmol of oleic acid was added into a 50 mL round-bottom flask equipped with a magnetic stirring and a water-cooled condenser. Then defined amounts of methanol and catalyst were added according to the experimental design. The reaction temperature was controlled by a constant temperature heater. First, an orthogonal experiment was carried out to investigate the effect of the factors including reaction temperature, molar ratio of methanol to oleic acid, amount of catalyst, and reaction time. Data analyses were carried out at a 95% level of confidence. Next, the influence of each factor was studied. The temperatures changing from 333 K to 383 K were researched. The reaction molar ratios of methanol to oleic acid ranging from 1:1 to 10:1 were studied. The amount of catalyst ranging from 0.5 wt % to 10 wt % was studied. The reaction times

China). Toluene, diethyl ether, and tetraethyl orthosilicate (TEOS) were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. (Beijing, P.R. China). 3-Chloropropyltrimethoxysilane (CPMS) was purchased from Acros Organics (Geel, Belgium). Fe(III) nitrate nonahydrate (Fe(NO3)3·9H2O, 98.5%) was purchased from Xilong Chemical Co., Ltd. (Guangzhou, P.R. China). Imidazole (99%) was purchased from Shanghai Qingxi Chemical Co., Ltd. (Shanghai, P.R. China). 1,3-Propane sultone (99%) was purchased from Wuhan Fengfan Surface Engineering Co., Ltd. (Wuhan, P.R. China). Hydrochloric acid and sulfuric acid were purchased from Wuxi City Yasheng Chemical Co., Ltd. (Wuxi, P.R. China). All of the reagents were used without further purification. 2.2. Synthesis of Fe-Incorporated SBA-15. The mesoporous Fe-SBA-15 was synthesized referring to the previous protocol.31,33 Pluronic P123 was used as structure directing agent. Briefly, 4.0 g of P123 was dispersed in 90 g of deionized water and 2 mL of 2 mol/L HCl solution. The solution was stirred at 313 K for 4 h in order for the alkylene oxide units to be associated with the hydronium ions. Then, 0.7 g Iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O; Si/Fe = 25) was directly placed into the mixture with stirring for 1 h. After adjusting the pH value to 2.3, 9.0 g of TEOS was slowly added into the solution with continuously stirring at 313 K for 24 h. Next, the mixture was aged in a Teflon-lined autoclave at 373 K for another 24 h. Finally, the raw Fe-SBA-15 was obtained by filtering the mixture, washing the precipitate with water and drying the powder at room temperature. The template in the raw Fe-SBA-15 was removed by calcination at 773 K for 6 h. The pure SBA-15 was prepared at the same conditions. 2.3. Synthesis of the Acidic Ionic Liquid [SO3H-pIMCPMS][HSO4]. The acidic ionic liquid [SO3H-pIM-CPMS][HSO4] was synthesized as shown in Scheme 1. First, equivalent mole of imidazole (6.8 g) and sodium ethylate (6.8 g) were added into 100 mL ethanol with stirring at 343 K for 8 h. Second, CPMS (19.8 g) was added dropwise. The mixture was stirred for another 12 h in nitrogen atmosphere. Then the byproduct sodium chloride was removed by filtration. Third, 0.1 molar of 1,3-propane sultone was added. After stirring at 323 K for 12 h, an equal mole of sulfuric acid was added dropwise. Six hours later, the target product was 16591

dx.doi.org/10.1021/ie302419y | Ind. Eng. Chem. Res. 2012, 51, 16590−16596

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changing from 0.5 h to 5 h were discussed too. Finally, the reusability of catalyst was tested. Unless otherwise specified, other esterification reactions were carried out according to this procedure. Products were analyzed by an SP6890 gas chromatograph equipped with an FID detector and an SE-54 capillary column (30 m × 0.25 mm ×0.3 μm). Benzyl acetate was used as internal standard. Nitrogen was used as carrier gas and the temperature of the injector was set at 563 K. The oven temperature increased from 323 K to 453 K and retained for 5 min, then it increased to 563 K. Temperature increase for both ramps was set at 20 K/min.

3. RESULTS AND DISCUSSION 3.1. XRD. The small-angle XRD patterns of SBA-15, FeSBA-15, and IL/Fe-SBA-15 were shown in Figure 1. All of

Figure 2. N2 adsorption−desorption isotherms (A) and pore size distributions (B) of the samples: SBA-15(a), Fe-SBA-15(b), and IL/ Fe-SBA-15(c).

liquid significantly affected the surface area and pore prize distribution of the Fe-SBA-15 support. As expected, the BET surface area, pore volume and average pore diameter of IL/FeSBA-15 (647 m2/g, 0.87 cm3/g, 6.2 nm) were correspondingly decreased in comparison with those of Fe-SBA-15 (305 m2/g, 0.50 cm3/g, 5.8 nm). The reason was that the ionic liquid had been successfully grafted onto both the inner and outer surface of the support. 3.3. FT-IR. FT-IR characterization was applied to the confirmation of the [SO3H-PIm-CPMS][HSO4] immobilized onto Fe-SBA-15 and pyridine adsorption was used for the identification of the nature of the acid sites on the samples (Figure 3). Figure 1. The small-angle XRD patterns of SBA-15(a), Fe-SBA-15(b) and IL/Fe-SBA-15(c).

them had one intense peak and two relative low-intensity peaks successively assigned to reflections at (100), (110), and (200), which was indicative of a long-range ordered structure and wellformed hexagonal lattice of the mesoporous materials. Compared with the pure silica SBA-15, all three peaks of FeSBA-15 moved obviously to a lower angle. The reason was that Fe atom replaced part of Si atom into the framework of SBA-15 and the Fe−O bond length (0.197 nm) was larger than Si−O bond length (0.161 nm), leading to the expansion of the crystal structure. The similar results have also been reported in previous literatures.31,36 Compared with Fe-SBA-15, the three diffraction peaks of IL/Fe-SBA-15 decreased and shifted toward higher angle. 3.2. N2 Adsorption−Desorption. N2 adsorption−desorption isotherms and pore size distributions of SBA-15, Fe-SBA15, and IL/Fe-SBA-15 were presented in Figure 2 As shown in Figure 2A, all of the three nitrogen adsorption− desorption isotherms were typical IV isotherms with an H1type hysteresis loop according to the IUPAC classification, which was characteristic of mesoporous materials with 2Dhexagonal structure. For SBA-15 and Fe-SBA-15, the adsorbed volume exhibited a sharp increase in the relative pressure (P/ P0) range of 0.6−0.8, implying narrow pore size distributions. Compared with Fe-SBA-15, the sharpness and height of the capillary condensation step for IL/Fe-SBA-15 decreased obviously, illustrating pore size uniformity turned lower. The BJH pore size distributions in Figure 2B directly displayed this phenomenon. It demonstrated that the immobilization of ionic

Figure 3. FT-IR spectra of [SO3H-PIm-CPMS][HSO4] (a), IL/FeSBA-15+Pyridine (b), IL/Fe-SBA-15(c), Fe-SBA-15+Pyridine (d), and Fe-SBA-15 (e).

For [SO3H-PIm-CPMS][HSO4] ionic liquid (Figure 3a), the peaks at 3152 and 1589 cm−1 were attributed to the C−H and CN stretching vibration of imidazole ring,37 and the bands at 1208 cm−1 and 1041 cm−1 were due to the SO asymmetric and symmetric stretching vibrations of −SO3H group. Additionally, the bands around 2961 cm−1 and 1457 cm−1 were assigned to stretching vibrations and deformation vibrations of the alkyl chain. In Figure 3e, the bands at 1643 and 459 cm−1 were attributed to the Si−OH group and the rocking vibration of silicon− oxygen tetrahedral ([SiO4]),34 and the band at 806 cm−1 was assigned to symmetric stretching vibration of [SiO4]. Comparatively, almost all of the characteristic peaks of [SO3H-PIm-CPMS][HSO4] and Fe-SBA-15 appeared in the infrared spectrum of IL/Fe-SBA-15, which was indicative of the 16592

dx.doi.org/10.1021/ie302419y | Ind. Eng. Chem. Res. 2012, 51, 16590−16596

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successful immobilization of acidic ionic liquid onto Fe-SBA-15 support. Pyridine adsorption was used for the identification of the nature of the acid sites on Fe-SBA-15 and IL/Fe-SBA-15. Compared with Figure 3e, a new peak at 1449 cm−1 appeared in Figure 3d, suggesting Lewis acid site created in Fe-SBA-15. As could be seen from Figure 3b, two additional absorption bands at 1544 (B) cm−1 and 1488 (L+B) cm−1 appeared. Hence, the IL/Fe-SBA-15 catalyst owned both Lewis and Brønsted acid sites.16 The results of XRD, BET, and FT-IR illustrated that the mesoporous structure still kept intact and part of ionic liquid was immobilized onto the inner surface of the pore channels.38 3.4. TEM. The TEM images shown in Figure 4 directly confirmed the results of XRD and N2 adsorption−desorption.

Table 1. Catalytic Activity of the Catalysts entry

catalyst

1

without catalyst SBA-15 Fe-SBA-15 IL/SBA-15 IL/Fe-SBA-15

2 3 4 5

acidity (mmol H+/g)

T (K)

time (h)

conversion (%)

0

363

3

5.3 ± 0.3

0.04 0.04 1.35 1.22

363 363 363 363

3 3 3 3

7.4 16.6 81.4 87.7

± ± ± ±

0.5 0.6 0.4 0.6

a

Methanol (60 mmol); Oleic acid (10 mmol); IL/Fe-SBA-15 (5 wt %).

more Brønsted acid site. It was due to the cooperation of Lewis acid and Brønsted acid. In comparation with the previous heterogeneous catalysts, resins, zeolites, and solid acids as the representatives, IL/FeSBA-15 had certain advantages such as relatively high catalytic activity, mild reaction conditions, and suitable feeding amount.8,11,12,14,19,41 3.6. Effect of Reaction Conditions. The effect of reaction conditions including the reaction temperature, the molar ratio of methanol to oleic acid, the catalyst amount, and the reaction time were investigated. The orthogonal experiment design and results were shown in Table 2. An analysis of perturbation of factors on conversion of Table 2. Conversion of Oleic Acid at Different Operating Conditions

Figure 4. TEM image of SBA-15 (a,b) and IL/Fe-SBA-15 (c,d).

In the case of Fe-SBA-15 (Figure 4a,b), rows of ordered hexagonal pore arrays were clearly observed. In comparison, the highly ordered mesoporous structure was conserved after immobilization of the ionic liquid. 3.5. Catalytic Activity IL/Fe-SBA-15 for Esterification of Oleic Acid. The esterification of oleic acid with methanol was used to evaluate the catalytic activity of IL/Fe-SBA-15, the reaction was taken at 363 K for 3 h. The Brønsted acid site was determined through acid−base back-titration referring to previous literature.39,40 Briefly, 0.4 g dry catalyst sample was added into 40 mL of NaCl aqueous solution (2 g/L) and stirred at room temperature for 24 h. Then the solids were filtered off and washed with 20 mL water for four times. Ten mL filtrate was taken out and titrated with 0.125 mmol/L NaOH aqueous solution using phenol red as indicator. The acidity was calculated according to the consumed NaOH volume. As shown in Table 1, SBA-15 and Fe-SBA-15 had almost no Brønsted acid site. However, Fe-SBA-15 revealed much higher catalytic activity than SBA-15 because of the Lewis acid site brought by Fe. After IL was immobilized onto Fe-SBA-15, the conversion of oleic acid reached to 87.7%. This result was also better than that of IL/SBA-15, although IL/SBA-15 had a little

entry

catalyst/acid (wt %)

n(alcohol)/ n(acid)

time (h)

T (K)

conversion (%)

1 2 3 4 5 6 7 8 9

2.5 2.5 2.5 5.0 5.0 5.0 7.5 7.5 7.5

4 6 8 4 6 8 4 6 8

2 3 4 3 4 2 4 2 3

343 353 363 363 343 353 353 363 343

63.2 80.8 90.5 83.8 77.5 81.6 80.4 90.1 82.2

± ± ± ± ± ± ± ± ±

0.5 0.4 0.4 0.6 0.7 0.2 0.5 0.3 0.4

Table 3. Analysis of Perturbation of Factors on Conversion of Oleic Acid mean catalyst/acid (wt %) n(alcohol)/n(acid) time (h) T (K)

effect

p

81.122 6.067 8.967 4.500 13.833

0.000 0.027 0.007 0.064 0.001

oleic acid was summarized in Table 3. The “effect” column shown in Table 3 was a statistical parameter that measured the influence degree of each factor. A high “effect” value meant that a small change of this factor would produce a significant change of the conversion. From a process point of view, factor with high “effect” value could be considered the important variable for a given process. The “p” column explained the probability of the factor effect on the conversion. The low “p” value meant high probability that a change in the factor would produce a significant change in the conversion.8 16593

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Therefore, reaction temperature, molar ratio of methanol to oleic acid, and catalyst amount were the most important factors affecting the conversion of oleic acid. These three variables were statistically significant at a 95% level of confidence (p < 0.05). Figure 5 showed the relationship between the oleic acid conversion and reaction temperature. The oleic acid conversion

Figure 7. Effect of catalyst amount on esterification of oleic acid with methanol. T = 363 K, t = 3 h, molar ratio = 6.

catalyst, the more active site which promoted the transformation of the reactant. The conversion of oleic acid increased from 61.3% to 87.7% as the amount of catalyst increased from 0.5 wt % to 5 wt % (based on oleic acid). This trend slowed down quickly when the amount of catalyst exceeded 5 wt %, since the reaction was restricted by other factors. So the appropriate catalyst amount was selected as 5w %. Figure 8 showed the effect of reaction time on oleic acid conversion. This reaction could be divided into three stages. In

Figure 5. Effect of reaction temperature on esterification of oleic acid with methanol. Molar ratio = 6, t = 3 h, catalyst amount = 5 wt %.

increased from 70.5% to 87.7% as the reaction temperature increased from 333 K to 363 K. As we all know, increasing the reaction temperature facilitated molecular collision and the miscibility of the reactants, enhancing the reaction rate and conversion of oleic acid. However, too high reaction temperature, for instance, 373 K and 383 K in this experiment, had little effect since a mass of methanol turned into vapor. As the esterification reaction was reversible, an excess amount of methanol used favored the conversion of oleic acid. The mole ratio of methanol to oleic acid varied from 1:1 to 10:1, and the conversions obtained were shown in Figure 6.

Figure 8. Effect of the reaction time on esterification of oleic acid with methanol. T = 363 K, t = 3 h, molar ratio = 6, catalyst amount = 5 wt %.

the first phase, the reaction happened quickly and 83.8% of oleic acid conversion was reached within 2 h. In the second stage, the reaction turned slow, extending from 2 to 3 h, and the conversion of oleic acid reached to 87.7% in 3 h. In the last stage, the reaction approached equilibrium after 3 h, and the conversion of oleic acid did not increase when the reaction time continued to extend, so the optimal reaction time was chosen as 3 h. To study the influence of different alcohols as raw materials, four most common alcohols (methanol, ethanol, n-propanol, and n-butanol) were selected and their activities were compared under the same reaction conditions. As shown in Figure 9, all of the conversion exceeded 90% except methanol. Methanol revealed relatively poor results because of its too low boiling point. When the reaction temperature reached to a certain degree, a mass of methanol liquid was transformed into methanol vapor. The conversion was highest when ethanol was

Figure 6. Effect of molar ratio on esterification of oleic acid with methanol. T = 363 K, t = 3 h, catalyst amount = 5 wt %.

The oleic acid conversion increased rapidly from 53.2% to 87.7% as the molar ratio of methanol to oleic acid increased from 1:1 to 6:1. Further increased molar ratio led to slight increase of the conversion probably because oleic acid and catalyst were too diluted with excess methanol. So 6:1 was selected as the appropriate molar ratio of methanol to oleic acid. The effect of catalyst amount on oleic acid conversion was shown in Figure 7. As we all know, the greater the amount of 16594

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and reaction time 3 h. Under these reaction conditions, the conversion of oleic acid reached to 87.7%. The catalytic activity of IL/Fe-SBA-15 only decreased slightly after 6 times of recycling. Furthermore, ethanol seemed to be the best choice for esterification with oleic acid, as it also could come from biological resource, instead of petrochemical resource.

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ASSOCIATED CONTENT

* Supporting Information S

The textural properties of the samples. Catalytic activities of various different catalysts for biodiesel production. This material is available free of charge via the Internet at http:// pubs.acs.org.

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Figure 9. Effect of the different alcohols. T = 363 K, t = 3 h, molar ratio = 6, catalyst amount = 5 wt %.

AUTHOR INFORMATION

Corresponding Author

used for this reaction, which was similar to the conclusion from the previous study.11 It could be attributed to the excellent solubility between ethanol and oleic acid. As ethanol also could come from biological resource, it would be the best choice for further studies and industrial applications. The reusability of IL/Fe-SBA-15 catalyst was also evaluated using the esterification of oleic acid and methanol as an example. As shown in Figure 10, the conversion of oleic acid decreased from 87.7% to 80.8% after 6 times of recycling. The main reason may be that part of catalyst was lost during the recycling.

*Tel: 86-25-83587198. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundation of China (No. 21176121).

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ABBREVIATIONS [SO3H-PIm-CPMS][HSO4] = 1-(propyl-3-sulfonate)-3-(3trimethoxysilylpropyl) imidazolium hydrogen sulfate Fe-SBA-15 = Fe-incorporated SBA-15 TEOS = tetraethyl orthosilicate CPMS = 3-chloropropyltrimethoxysilane FAAE = fatty acid alkyl ester FFA = free fatty acids FT-IR = Fourier transform infrared XRD = X-ray diffraction TEM = transmission electron microscope FID = flame ionization detector REFERENCES

(1) Vicente, G.; Martínez, M.; Aracil, J. Integrated biodiesel production: A comparison of different homogeneous catalyst systems. Bioresour. Technol. 2004, 92, 297. (2) Marchetti, J. M.; Miguel, V. U.; Errazu, A. F. Possible methods for biodiesel production. Renew. Sust. Energy Rev. 2007, 11, 1300. (3) Meher, L. C.; Vidya Sagar, D.; Naik, S. N. Technical aspects of biodiesel production by transesterification-a review. Renew. Sust. Energy Rev. 2006, 10, 248. (4) Van Gerpen, J. Biodiesel processing and production. Fuel Process. Technol. 2005, 86, 1097. (5) Chand, P.; Chintareddy, V. R.; Verkade, J. G.; Grewell, D. Enhancing biodiesel production from soybean oil using ultrasonics. Energy Fuels 2010, 24, 2010. (6) Liu, S.; McDonald, T.; Wang, Y. Producing biodiesel from high free fatty acids waste cooking oil assisted by radio frequency heating. Fuel 2010, 89, 2735. (7) Tesser, R.; Di Serio, M.; Guida, M.; Nastasi, M.; Santacesaria, E. Kinetics of oleic acid esterification with methanol in the presence of triglycerides. Ind. Eng. Chem. Res. 2005, 44, 7978. (8) Lucena, I. L.; Silva, G. F.; Fernandes, F. A. N. Biodiesel production by esterification of oleic acid with methanol using a water adsorption apparatus. Ind. Eng. Chem. Res. 2008, 47, 6885. (9) Zhang, J.; Jiang, L. Acid-catalyzed esterification of Zanthoxylum bungeanum seed oil with high free fatty acids for biodiesel production. Bioresour. Technol. 2008, 99, 8995.

Figure 10. Effect of the different alcohols. T = 363 K, t = 3 h, molar ratio = 6, catalyst amount = 5 wt %.

4. CONCLUSIONS In this study, Brønsted acidic ionic liquid [SO3H-PImCPMS][HSO4] was prepared and successfully supported onto Fe-SBA-15. The immobilization of ionic liquid happened on the surface of Fe-SBA-15 by chemical covalent bond, which made the active component strongly combined to the support. Moreover, the IL/Fe-SBA-15 catalyst had both Lewis and Brønsted acidic sites. Although the ionic liquid had mainly grafted onto the inside surface, the ordered pore structure was still intact. The high surface area and ordered pore helped to improve the contact between the active component and reactants. As a result, the IL/Fe-SBA-15 catalyst showed good activity for esterification of oleic acid with short-chain alcohols. The effect of reaction conditions were investigated, and the optimum reaction conditions were as follows: reaction temperature 363 K, molar ratio 6:1, catalyst amount 5 wt % 16595

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dx.doi.org/10.1021/ie302419y | Ind. Eng. Chem. Res. 2012, 51, 16590−16596