Abstract
Some vegetable oils were hydrogenated with scrap automobile catalyst (SAC) as a catalyst. The optimum reaction conditions (solvent, reaction time, and catalyst amount) were determined. Our results showed that the linoleic acid was reduced to elaidic acid in the sunflower oil. This procedure not only gives high yields but also allows recycling of automobile wastes as a catalyst in organic reactions and is representative of green chemistry.
1. Introduction
Hydrogenation of fats and oils is a very important operation in the industrial process of producing vegetable tallow, vegetable fats, margarines, and starting components for the cosmetic and chemical industry such as emulsifiers, soaps, creams, pastes, and similar substances [1]. There are two main reasons why hydrogenation is important to the industry. The first is increasing the stability of the oil. Highly unsaturated oil is susceptible to autoxidation, thermal decomposition, and other reactions that affect the flavor. Consequently, it is desired to partially hydrogenate the oil to improve shelf life. The second reason to partially hydrogenate vegetable oil is to improve its utility. For most products, such as shortenings, margarines, or confectionery fats, the desired softening and melting characteristics correspond to oils that are partially hydrogenated. The choice of catalyst to use for hydrogenation greatly affects the properties of the final product [2].
Several catalysts for hydrogenation of oils are known in the literature, such as Rh/TPPTS complexes [3], Cu/SiO2 [4], Ni/SiO2 [5] and Pd/SiO2 [6–8] catalysts, Ni/Ru mixture [9], and Ni/Al2O3 catalyst [10].
In continuation of our studies on the development of novel heterogeneous synthetic methodologies [11–14], we have achieved a novel procedure for the hydrogenation of sunflower oils catalyzed by scrap automobile catalyst (SAC) which was used for the hydrogenation of carbon-carbon double bonds in our previous study [15].
The lifetime of catalytic converters is limited and thus their recycling is crucial. Catalytic converters consist of a ceramic substrate coated with aluminum oxide (Al2O3) and other rare earth oxides, such as CeO2, ZrO2, Pt, Pd, and Rh which are responsible for the catalytic function [16]. A used automobile catalytic converter was taken from a Fiat Siena after running for 140,000 km. After purification of the SAC, it was activated in an oven maintained at 120°C for 12 h and found to contain 0.465% Pd and 0.040% Rh by XRF analysis.
2. Experimental Procedures
2.1. General
1H and 13C NMR spectra were measured on spectrometer at VARIAN Infinity Plus 300 and at 75 Hz, respectively. 1H and 13C chemical shifts are referenced to the internal deuterated solvent. Solvents were dried following standard methods. All chemicals were purchased from Merck, Alfa Easer, Sigma-Aldrich, and Fluka and the oils were purchased from local supermarket.
2.2. Purification of the Catalyst
A piece of scrap catalyst (50 g) cut by hacksaw was taken from the automobile catalytic converter and washed with chromic acid and distilled water to remove dust and carbonaceous particles. The scrap catalyst was dried in an oven maintained at 120°C for 12 h, crushed in agate mortar and sieved (<100 μm in diameter), and analyzed by XRF.
2.3. Optimization of Reaction Conditions
To optimize the hydrogenation reaction, we examined the reaction conditions in different solvents, such as THF, diethyl ether, hexane, isopropanol, and acetone, for the different reaction times (6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, 48 h, and 72 h) and different amount of catalyst (1 g, 2 g, 3 g, and 4 g). We determined optimization by low iodine value. Thus, the best results were obtained in THF for 48 h with 4 g catalyst (Table 1).
2.4. Hydrogenation Procedures
A solution of the sunflower oil (4.0 g) in anhydrous THF (25 mL) was transferred into a two-neck round bottom flask containing the purified catalyst (4 g). Reactions were carried out by stirring under atmospheric pressure of H2 at room temperature for 48 h. The reaction mixture was filtered and the filtrate was evaporated under vacuum.
2.5. Iodine Value
Iodine values of the partially hydrogenated oils were determined by the known procedures [17].
3. Results and Discussion
To optimize study of this hydrogenation reaction, the solvent effect of these liquid phase hydrogenation reactions depended on the solubility and chemisorption of H2 and on the catalyst suspended in the solvent. The solubility and chemisorption of H2 in a nonpolar solvent are greater than in polar solvents [18]. Also, rising reaction times and amount of catalyst increased the amount of hydrogenated oils. After 48 hours, rising the hydrogenation was quite sluggish (Table 1). So, the optimum reaction time was considered 48 hours.
The 1H and 13C NMR spectra of oils have been reported in the literature [19–21]. The 1H NMR spectra of sunflower oil, which contains linoleic acid (58%), oleic acid (31%), stearic acid, and palmitic acid (11%), show signals between 5.30 and 5.40 ppm relating to olefinic protons of all acyl chains, at 2.75 ppm for bisallylic protons and at 2.04 ppm for allylic protons of linoleyl chains (Figure 1(a)). On the other hand, the signals of bisallylic protons and allylic protons of linoleyl chains cannot be seen at the 1H NMR spectra of hydrogenated sunflower oil (Figure 1(b)) and it shows that the intensity of signals of the olefinic protons decreased. Although the signals of C9-10 and C12-13 carbons of linoleic acid can be seen between 128.1 and 130.3 ppm at the 13C NMR spectra of sunflower oil (Figure 2(a)), they cannot be seen at 13C NMR spectra of hydrogenated sunflower oil (Figure 2(b)). Additionally, the 13C NMR spectra of hydrogenated sunflower oil showed a chemical shift for the trans-allylic carbons at 32.8 ppm but no chemical shift at 27.3 ppm [22], confirming that no cis-isomers were present in this product. Based on these results, the linoleic acid was hydrogenated to elaidic acid in the sunflower oil. These results are consistent with declining iodine value and confirm the hydrogenation of sunflower oil.
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After the sunflower oil was hydrogenated with SAC successfully, the hazelnut oil and tea seed oil were hydrogenated with the same procedures and similar results were observed. The iodine values were given in Table 1.
4. Conclusions
In conclusion, we have developed a process-friendly, efficient, cheap, and green procedure for the hydrogenation of sunflower oil catalyzed by scrap automobile catalyst (SAC) and this hydrogenation procedure was performed on the hazelnut oil and tea seed oil successfully. This method can be used in the fats, oils, and chemical industry.
Acknowledgments
The authors thank Mr. Malik Kurtuldu from Ozen Ekzost, Sakarya for supplying spent automotive catalyst and Senol Ozturk (Gizem Frit Sakarya) for XRF analysis.