Biodiesel Synthesis from Palmitic Acid and Oleic Acid via Esterification Method using MgO base catalyst

 

M. Shanmugam¹, T. Somanathan^1*, P. Rebecca¹, A.R. Sasieekhuma²

¹Department of Chemistry, School of Basic Sciences, Vels University, Pallavaram,  Chennai - 600 117

²Department of Chemistry, AVS College of Technology, Chinnagoundapuram, Salem – 636 106, Tamilnadu, India.

 

ABSTRACT:

In this study, a base catalyst was used for the biodiesel synthesis via esterification method using palmitic and oleic acid. By varying the parameters such as catalyst weight, reaction time and temperature, the maximum conversion (98%) of fatty acid methyl ester (FAME) was obtained. The product was analysed by FT-IR spectroscopy, ¹H and ¹³C NMR. The result shows that the characteristic peak of methoxy protons was observed as a singlet at 3.65 ppm and a triplet of α-CH₂ protons at 2.27 ppm. ¹³C NMR analysis indicates the conversion of palmitic acid and oleic acid into methyl palmitate and methyl oleate by the emergence of the resonance signal at 51.24 ppm in methyl ester due to methoxy carbon. These two peaks are the distinct peaks for the confirmation of methyl esters present in biodiesel. The shifting of absorption peaks of the acid to methyl ester were at 1748, 1377, 1157, 1026 and 856 cm⁻¹ to 1742, 1361, 1168, 1015 and 878 cm⁻¹, respectively. From this investigation, MgO is a promising base catalyst for the esterification of palmitic acid and oleic acid to biodiesel and it would be alternate catalyst for the production of petro products.

 

 

 

1. INTRODUCTION:

Biodiesel, a renewable fuel is normally produced by transesterification of highly refined oils with short-chain alcohols. Biodiesel production cost depends greatly on the price of used oil sources. It is also called fatty acid methyl ester (FAME) which usually produced through the transesterification reaction of various oils such as edible, non-edible, microalgae oil, waste oils and animal fats^1-3 with alcohol in the presence of various catalysts such as alkaline, acid or enzyme catalyst⁴. The selection of an appropriate catalyst is of fundamental importance for the design of a sustainable transesterification process.

Catalysts mainly belong to the two categories: homogeneous catalysts act in the same phase as the reaction mixture, whereas heterogeneous catalysts act in a different phase from the reaction mixture. Being in a different phase, heterogeneous catalysts is a more effective than homogeneous catalyst, because it has a higher activity, easier to separate from the reaction mixture, reuse and release less pollution to the environment. In this study, we have chosen commercially available free fatty acids (FFA) such as palmitic and oleic acid for the production of biodiesel through base catalysed via esterfication method. The obtained biodiesel were confirmed by ¹H and ¹³C NMR analysis, FT-IR spectroscopy.

 

2. EXPERIMENTAL:

2.1       MATERIALS AND METHODS:

Chemicals such as magnesium nitrate and sodium hydroxide were purchased from E-Merck for the synthesis of metal oxide nanoparticles. Palmitic acid, oleic acid and methanol were also purchased from E-Merck for the esterification reaction. The magnetic stirrer was purchased from Technico Instruments India Ltd. The glasswares used in all the experiments were made up of Schott Duran.

 

2.2 Synthesis of MgO Nanoparticles:

MgO nanoparticles were synthesized using a typical procedure with our previous work^5,6 by utilizing 0.5 M solution of magnesium nitrate as a precursor and 1 M of sodium hydroxide as a precipitating agent. 50 ml of NaOH solution was added drop by drop slowly under vigorous stirring to the 250 ml round bottom flask that contained 50 ml of precursor solution at the temperature of 50 - 55°C. Subsequently stirring was continued for 1 h at the same temperature and formed precipitate was filtered and dried in an oven at 100ºC overnight. Dried precipitate (magnesium hydroxide) was then crushed into fine powder followed by sintering process at 400 ºC for 3 h in muffle furnace.

 

2.3 Characterization:

UV-Visible analysis was done by using Jasco V160 UV-Vis-NIR spectrophotometer.

 

X-ray diffraction (XRD) patterns collected from Bruker, Germany, D8 Advance model, equipped with Ni filtered, a graphite mono-chromatized Cu-Kα radiation (λ = 0.15406 nm) operated at

 

40 kV accelerating voltage and 30 mA. The sample was scanned at a scanning rate of 4 °/min and step interval is 0.02^o, in the 2θ range of 10 - 90°. Scanning electron microscope (SEM) equipped with energy dispersive x-ray spectroscopy (EDX) (JSM-6610) was performed to study the morphology and elemental composition of the sample at 20 kV accelerating voltage. The powder sample was coated with gold on a double sided carbon tape for SEM and EDX. Transmission Electron Microscope (TEM) images were recorded on a TecnaiT20 G2 200kV, FEI Brand (Netherlands) microscope and operating at an accelerating voltage of 200 kV. Functional groups were interpreted with Perkin Erlenmeyer Spectrum One fourier transform - infra red (FT-IR) photospectrometer.

 

2.4 Esterification Reaction of Palmitic acid and Oleic acid with Methanol:

Catalytic reaction was carried out in a 250 mL single neck round bottom flask equipped with a condenser. Typical reaction was performed with molar ratio 1׃2 of palmitic acid and methanol using 0.2 g of MgO nanoparticles as a catalyst at temperature 140°C for reaction period of 6 hr. After reaction, the samples were analyzed with ¹H NMR, ¹³C NMR and FT-IR to confirm the products. Similarly, Catalytic reaction was performed separately with molar ratio 1׃2 of oleic acid and methanol at same reaction condition and the products were also analyzed.

 

3.  RESULTS AND DISCUSSION:

3.1  Catalytic activity of MgO catalyst on Palmitic and Oleic acid:

3.1.1.Effect of Temperature:

The influence of temperature ranging between 70 and 140°C is depicted in Fig.1. The esterification of palmitic acid and oleic acid with methanol using 0.2 g MgO as a catalyst over a reaction period of 6 h. Conversion increases with increase in temperature ascribed to increase in the removal of by-product water formed in the reaction and reaches 95 % at 140°C in the case of methyl palmitate where as 98 % conversion of methyl oleate at same temperature. A common trend in conversion over catalyst is increase of acid conversion while increase in temperature^7,8.

 

Since esterification involves establishment of equilibrium, it is evident from these results that the shift in equilibrium towards ester side occurs with increase in temperature due to increase in activation energy^9,10. From the results, 140°C was chosen for further reaction conditional optimizations.

 

 

Figure 1: Effect of reaction temperature on 0.2 g MgO catalyst

 

3.1.2 Effect of Catalyst:

To study the influence of catalyst using 0.2 - 0.5 g of MgO were carried out in the esterification of palmitic acid and oleic acid with methanol, as presented in Fig. 2. Before starting up the reaction, all the catalysts were activated at 200 °C to eliminate the adsorbed moisture. The order of activity is 0.2 g MgO > 0.3 g MgO  > 0.4 g MgO > 0.5 g MgO. The high conversion occur at 0.2 g MgO catalyst, it is due to the low amount of catalytic basic sites of nano size MgO present in it² and further reaction was carried out using the optimized catalyst.

 

 

Figure 2: Effect of catalyst weight

 

3.1.3 Effect of Reaction Time:      

The influence of the run duration on the esterification reaction of palmitic and oleic acid with methanol using 0.2 g MgO catalyst at 140°C reaction temperature is shown in Fig. 3. Considerably, the conversions of the reaction were increases linearly from 2 h to 6 h which clearly shows the maximum conversion of methyl palmitate in the range of 79–95 %. Similarly, the isolated products of methyl oleate are in the range of 91–98 %. Here, the complete conversions of fatty acids are difficult, even for the longer run durations. This might be due to the formed byproduct water, which during the reaction, might hamper the complete conversion of fatty acids^11-13.

 

3.2 NMR Analysis:

3.2.1 ¹H and ¹³C NMR Analysis of Methyl Palmitate:

Esterification of palmitic acid with methanol using 0.2g MgO catalyst at 140°C with a reaction period of 6 hr. After completion of the reaction, the catalyst was separated by filtration and methanol was removed from the reaction mixture using a rotary vapor. The sample was then analyzed using ¹H NMR and ¹³C NMR and its spectrum were shown in Fig 4 (a) and 4. (b), respectively

 

The characteristic peak of methoxy protons was observed as a singlet at 3.65 ppm and a triplet of α-CH₂ protons at 2.27 ppm. These two peaks are the distinct peaks for the confirmation of methyl esters present in biodiesel¹⁴. Other observed peaks were at 0.86 ppm of terminal methyl protons, a strong signal at 1.26 ppm related to methylene protons of carbon chain, a signal at 1.60 ppm from β-carbonyl methylene protons and at 5.34 ppm due to olefinic hydrogen. The relevant signals chosen for integration were those of methoxy group in the methyl esters at 3.65 ppm and of the α-carbonyl methylene protons at 2.27 ppm. The characteristic peaks of ester carbonyl (−COO−) and C−O at 174.07 and 51.24 ppm, respectively. ¹³C NMR analysis indicates the conversion of palmitic acid into methyl esters by the emergence of the resonance signal at 51.24 ppm in biodiesel due to methoxy carbon.

 

  

Figure 3: Effect of reaction time at 140 °C using 0.2g MgO catalyst

 

3.2.2 ¹H NMR Analysis of Oleic Acid and Methyl Oleate:

Esterification of oleic acid with methanol using 0.2g MgO catalyst at 140°C with a reaction period of 6 hr. At the end of the reaction, the catalyst was separated by filtration and methanol was removed from the reaction mixture using a rotavapor. The sample was then analyzed using ¹H NMR spectroscopy and its spectrum of oleic acid and methyl oleate was shown in Fig 5 (a) and (b), respectively.

 

During the esterification of oleic acid with methanol, the decrease of the oleic acid content in the reaction mixture was clearly seen in both the ¹H NMR of oleic acid and methyl oleate in Fig 5 (a) and (b), respectively. At the start of the reaction, ¹H NMR spectrum in the α-CH₂ region (2.3-2.4 ppm) showed a triplet pattern corresponding to oleic acid. As the reaction progressed, a quartet like pattern developed. The intensity of the triplet signals of oleic acid decreased that of the methyl ester increased with the reaction time, which is confirmed and clearly shown in Fig 5 (b). Finally, at the end of reaction time of 6 h, the peaks corresponding to oleic acid had almost disappeared, and only a triplet corresponding to that of the methyl ester was detected.

 

Figure 4 (a): ¹H-NMR Spectra of Methyl Palmitate

 

 

Figure 4 (b): ¹³C-NMR Spectra of Methyl Palmitate

 

3.2.3 ¹³C NMR Analysis of Oleic Acid and Methyl Oleate:

The ¹³C NMR of the oleic acid and methyl oleate was shown in Fig 6 (a) and (b), respectively. The characteristic peaks of ester carbonyl (−COO−) and C−O at 174.07 and 51.24 ppm, respectively. ¹³C NMR analysis indicates the conversion of oleic acid into methyl oleate by the emergence of the resonance signal at 51.24 ppm in methyl ester due to methoxy carbon. The peaks around 130.05 and 127.85 ppm indicated the unsaturation in methyl esters. Other peaks at 14.01 ppm are due to terminal carbon of methyl groups and signals at 22.64–33.99 ppm are related to methylene carbons of long carbon chain in fatty acid methyl esters (FAMEs).

 

 

Figure 5 (a): ¹H-NMR Spectra of Oleic Acid

 

Figure 5 (b): ¹H-NMR Spectra of Methyl Oleate

 

3.2.4 FT-IR spectrum of methyl palmitate and methyl oleate:

The FT-IR spectra in the mid-infrared region have been used to identify the functional groups and the bands corresponding to various stretching and bending vibrations in the samples of esterification reaction. The spectrum of both methyl palmitate and methyl oleate was shown in Fig. 7 (a) and (b), respectively are almost similar but various differences could be observed for identification purposes. The shifting of absorption peaks of the acid at 1748, 1377, 1157, 1026 and 856 cm⁻¹ to 1742, 1361, 1168, 1015 and 878 cm⁻¹ in the methyl ester^15,16, respectively. The disappearance of peaks at 1465, 1095 and 964.4 cm⁻¹ from the spectrum of methyl palmitate and appearance of new bands in the biodiesel at 1435 and 1195 cm⁻¹ indicate the conversion of acid into methyl ester.

 

 

Figure 6 (a): ¹³C-NMR Spectra of Oleic Acid

 

Figure 6 (b): ¹³C-NMR Spectra of Methyl Oleate

 

 

Figure 7 (a): FT-IR Spectrum of Methyl Palmitate

 

Figure 7(b): FT-IR Spectrum of Methyl Oleate

 

 

 

4. CONCLUSIONS:

Magnesium oxide (MgO) were successfully synthesised at low temperature by precipitation method and it was utilized for the esterification of palmitic acid and oleic acid with methanol at 140°C with a reaction period of 6 hr. Optimizing the reaction conditions such as temperature, catalyst and reaction time to achieve higher conversion of methyl esters (methyl palmitate (95 %) and methyl oleate (98 %)). The result of ¹³C NMR analysis indicates the conversion of palmitic acid and oleic acid into methyl esters by the emergence of the resonance signal at 51.24 ppm in ester due to methoxy carbon. The characteristic peak of ¹H NMR of methoxy protons was observed as a singlet at 3.65 ppm and a triplet of α-CH₂ protons at 2.27 ppm. These two peaks are the distinct peaks for the confirmation of methyl esters. The shifting of absorption peaks of the acid at 1748, 1377, 1157, 1026 and 856 cm⁻¹ to 1742, 1361, 1168, 1015 and 878 cm⁻¹ in the methyl ester, respectively. From this study, we have concluded MgO is a promising base catalyst for the esterification of palmitic acid and oleic acid to methyl esters and it would be alternate catalyst for the production of petro diesel products.

 

5. ACKNOWLEDGEMENTS:

One of the authors, T. Somanathan would like to thank the Department of Science and Technology (DST) for the award of Fast Track Young Scientist Award and also for providing financial support (SR/FT/CS-111/2011).

 

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Accepted on 16.08.2017           © RJPT All right reserved

Research J. Pharm. and Tech 2017; 10(11): 3945-3950.