Article pubs.acs.org/IECR
Preparation and Properties of Lubricant Base Stocks from Epoxidized Karanja Oil and Its Alkyl Esters Geethanjali Gorla, Sony M. Kour, Korlipara V. Padmaja, Mallampalli S. L. Karuna, and Rachapudi B. N. Prasad* Centre for Lipid Research, Indian Institute of Chemical Technology, Hyderabad 500- 007, India S Supporting Information *
ABSTRACT: Lubricant base stocks of epoxidized oil and its alkyl esters namely epoxidized karanja fatty acid methyl, butyl, 2methyl-1-propyl, and 2-ethylhexyl esters were synthesized from renewable nonedible source karanja oil (Pongamia glabra). The reaction was carried out using peroxy formic acid (HCOOH) generated in situ, 30 wt % aqueous hydrogen peroxide (H2O2) by monitoring oxirane oxygen value. The optimized conditions to obtain epoxidized products were oil/ester: HCOOH: H2O2 (1:2:8/1:1.5:3 mol/mol/mol). The epoxidized products were obtained in 90−97% conversion by GC analysis. All the products were characterized by GC, GC-MS, IR, 1H NMR spectral studies. The synthesized products were evaluated for physicochemical and lubricant properties. Based on viscosity index all the products belong to group III, category of base fluids as per API classification. Expecting pour point values that are on higher side, other lubrication properties such as viscosity, VI, flash point, Cu corrosion value, and air release value were found to be good.
1. INTRODUCTION Vegetable oils are the part and parcel of chemical compounds known as fats or lipids. All types of fats are being used down the ages as food, fuels, and lubricants and for other chemical applications.1 Due to the depletion of mineral oil resources and their inherent toxicity and non-biodegradable nature pose a continuous threat to the ecology. These environmental concerns have led to the use of vegetable oils as an alternative, renewable source for replacement of the existing resources of fossil fuels. The rich forest resources comprising of plants and oil seeds present in India, especially the nonedible oils such as babassu (Attalea speciosa), mahua (Madhuca indica), neem (Azadirachta indica), karanja (Pongamia glabra), jatropha (Jatropha curcas), etc. are very cheap compared to edible oils being investigated as potential sources of environmentally favorable lubricants. Utilization of nonedible oils mainly depends on the properties of various fatty acids and fats. Different applications of derivatized fatty acids such as surface coatings, plastics, detergents, lubricants etc., are mainly due to a combination of biodegradability, low volatility due to their higher viscosity index, lower toxicity, renewability, and excellent lubrication performance.2 However, the vegetable oil based lubricant base stocks suffer from main disadvantage such as low oxidation and hydrolytic stabilities. Chemical derivatization of the unsaturation in vegetable oils or their alkyl esters by epoxidation, hydrogenation, and alkylation can be performed to synthesize improved products.3−5 Among the methods to improve thermo-oxidative stability, epoxidation received special attention due to its high reactivity of the oxirane ring and also acts as a raw material for a variety of chemicals, such as alcohols, glycols, alkanolamines, hydroxyl nitriles, mercapto alcohols, carbonyl compounds.6,7 Epoxidized vegetable oils have also been used as oleo chemicals in the field of polymer science, polyesters, polyurethanes, rubbers, monomers in photo © 2013 American Chemical Society
initiated cationic polymerization, and epoxy resins and coatings.8−13 Epoxidation of oleochemicals has been known for many years14,15 due to its wide range of applicability commercially. Epoxidation of unsaturated fatty acid derivatives using soybean oil and other plant oils was carried out on industrial scale.16 Epoxidized soybean oil was found to be a potential source for high temperature lubricant application, as reported by Adhvaryu and Erhan et al.17 In the case of unsaturated fatty acid esters, it is often performed in situ using the performic acid method, which is an industrially performed process on a large scale. Epoxidation of the unsaturated methyl esters of soybean such as methyl oleate, methyl linoleate, and methyl linolenate, and their evaluation as lubricant additives was reported by Erhan et al.18 Epoxidation of methyl oleate using heterogeneous catalyst was studied by Erhan et al.19 The use of organic per acids in the epoxidation process also has the advantage of low costs of synthesis of peracids themselves. Vaibhav V. Goud et al. have studied the epoxidation of karanja oil catalyzed by acidic ion-exchange resin, sulphuric acid using acetic acid and 30% hydrogen peroxide and they proposed a kinetic model for epoxidation.7,20 Further, no systematic study on the synthesis, optimization, and evaluation of physicochemical properties of different epoxy karanja fatty acid esters was carried out. Very few researches have explored karanja oil, such as development of sulfurized karanja oil, cosulfurization of karanja oil, karanja oil as EP additive, lubricity booster in metal working fluids, and karanja oil and 2-ethylhexyl esters of karanja oil fatty acids in 2-stroke gasoline engines. Received: Revised: Accepted: Published: 16598
July 28, 2013 October 16, 2013 October 31, 2013 October 31, 2013 dx.doi.org/10.1021/ie4024325 | Ind. Eng. Chem. Res. 2013, 52, 16598−16605
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2.4.2. Pour Point. Pour points were determined by ASTM D 9723 method with an accuracy of ±3 °C using pour point test apparatus manufactured by Dott. Gianni Scavini & Co., Italy. All runs were carried out in duplicate. Sample temperature was measured in 3 °C increments at the top of the sample until it stopped pouring. 2.4.3. Flash Point. Flash point of the products was determined using Koehler Inc. apparatus as per ASTM D 93 method.24 The lowest temperature at which application of the test flame causes the vapor above the surface of the liquid to ignite is taken as the flash point of the product at ambient barometric pressure. 2.4.4. Copper Strip Corrosion Test. Copper strip corrosion test of corrosiveness of the products was elucidated by using Koehler Inc. apparatus as per ASTM D 13025 method. A polished Cu strip was dipped in 30 mL of the sample, which is being tested at 100 °C for 3 h. After completion of the test the Cu strip was removed, washed with n-hexane then the color and tarnish level were correlated using the ASTM Copper strip Corrrosion standards. 2.4.5. Rotating Bomb Oxidation Tests (RBOT). Rotating Bomb Oxidation Tests (RBOTs) of the sample size 50 g were done in the presence of copper catalyst in dry conditions at 150 °C using the ASTM method D-2272.26 The vessel used in the RBOT is sealed, charged with 90 psi pressure with oxygen, and rotated axially in a constant temperature oil bath set at 150 °C. The pressure in the bomb is continuously recorded. The RBOT time is the time at which the pressure of the bomb has dropped by 25 psi. 2.4.6. Air Release Value. Air release value of the products was evaluated using the ASTM method D 342727 Standard Test Method using Koehler Inc., U.S.A. apparatus. 180 mL of the test sample is required for measuring the Air Release value. Density of the test sample was measured before and after passing air through the sample at 20 kPa for 7 min at 50 °C. The test requires the measurement of the time until the air content of the fluid is reduced back to a value of 0.2% and the value is reported in minutes. 2.4.7. Noack Volatility. Evaporative loss determinations were conducted on a nonwoods metal Noack evaporative tester apparatus manufactured by Koehler (Bohemia) using the ASTM Method D 5800.28 Samples were measured to 65.0 ± 0.1 g to a precision of 0.01 g. The test was about the determination of weight loss of a sample experiences through volatization. The test results were reported in percentage by weight lost. 2.5. Synthesis of Epoxidized Karanja Oil and Its Alkyl Esters. 2.5.1. Synthesis of Epoxidized Karanja Oil. Karanja oil (100 g, 0.11 mol), formic acid (8.7 mL, 0.23 mol), and sulphuric acid (1.2 mL, 2 wt % of formic acid and hydrogen peroxide) were taken into a three necked round bottomed flask and the temperature of the medium was maintained at 15−20 °C. Aqueous hydrogen peroxide (30%) (89.8 mL, 0.88 mol) was added slowly to the contents under mechanical stirring at 15−20 °C for about 1 h. After the addition, contents were stirred at 55−60 °C for a period of 5 h. The course of the reaction was followed by taking the aliquots of the reaction mixture hourly. The samples were extracted with ethyl acetate and washed with water until they were acid free and dried over anhydrous sodium sulfate. The epoxidized oil was concentrated by removing the solvent and dried under reduced pressure then analyzed for oxirane oxygen content. The epoxide with maximum oxirane oxygen obtained at 2 h, which was confirmed
In the present study, karanja oil and its alkyl esters were epoxidized by conventional Prilezhaev peracid process,21 where peroxyformic acid was generated in situ at 55−60 °C. Advantages of per acids include we can accurately assess reaction parameters, quenching of reaction, out scaling to preparative synthesis and industrially widespread method. The reaction conditions were optimized to obtain maximum conversion of unsaturation to epoxy group varying the mole concentration of reactants and reaction time. A systematic study was carried out on the physicochemical properties such as oxirane content, iodine number, and lubricant properties, namely, density, viscosity, viscosity index, flash point, pour point, copper strip corrosion, oxidation stability, air release value, and Noack evaporation loss for the synthesized lubricant base stocks.
2. EXPERIMENTAL SECTION 2.1. Materials. Hydrogen peroxide (30% aqueous solution), 2-ethylhexanol, n-butanol, 2-methyl-1-propanol, methanol, sodium hydroxide, sodium sulfate, xylene, and p-toluene sulfonic acid (pTSA) were purchased from M/s SD Fine Chem Ltd., Mumbai, India. 85% Formic acid solution and sulfuric acid (AR grade) were purchased from M/s Rankhem, New Delhi, India. Hexane and ethyl acetate were purchased from M/s Spectrochem Pvt. Ltd., Mumbai, India. All the chemicals were of analytical reagent grade and were used directly without further purification. 2.2. Analytical Methods. The analytical determinations of the karanja oil and its derivatives were accomplished according to the official methods of the American Oil Chemists’ Society (AOCS) as follows: acid value (AOCS Cd 63), iodine value (IV, AOCS Da 15−48), and oxirane oxygen content (OO, AOCS Cd 9-57). 2.3. Analytical Techniques. 2.3.1. Gas Chromatography Analysis (GC). The fatty acid composition of the products was determined as methyl esters by using GC and GC-MS analysis. GC analysis was carried out using Agilent GC on HP 6890 Series gas chromatograph equipped with a FID detector using HP-1 column. Column temperature was programmed from 150 to 300 °C at a rate of 8 °C/min and a hold time of 15 min. The injector and detector port were maintained at 250 and 350 °C, respectively. Flow rate of the carrier gas (N2) was 30 mL/min. GC-MS was carried out with Agilent 6890 N gas chromatograph connected to Agilent 5973 mass spectrometer (Palo Alto, CA, U.S.A.) using HP-1 column and oven temperature programming is similar to that of GC. 2.3.2. Nuclear Magnetic Resonance (NMR). 1H Nuclear Magnetic Resonance (1H NMR) spectra were recorded on a Bruker (Wissenbourg, France) AR X 400 Spectrometer (400, 200 MHz) with CDCl3 solvent. 2.3.3. Fourier Transform-Infrared (FTIR) Spectrum. A Fourier transform-infrared (FTIR) spectrum was performed on a 1600 FT-IR Perkin-Elmer spectra photometer (Norwalk, CT, U.S.A.) with a liquid film between NaCl discs. 2.4. Lubricant Analysis. 2.4.1. Viscosities Measurements. Kinematic viscosity measurements were made at 40 and 100 °C using calibrated Cannon Fenske viscometer tubes in a Cannon Constant Temperature Viscosity Bath (Cannon Instrument Co., State College, PA, U.S.A.). Viscosity and viscosity index (VI) were calculated using ASTM D 44522 and ASTM D 2270 methods, respectively. All viscosity measurements were run in duplicate and the average value was reported. 16599
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Scheme 1. Generalized Reaction Scheme of Epoxidation of the Major Fatty Acid Present in the Karanja Oil As Mixture of Fatty Acids
the reagents and hydrogen peroxide at constant reaction temperature. KFAME (100 g, 0.34 mol) and a mixture of formic acid (19.7 mL, 0.51 mol) and sulfuric acid (1.5 mL, 2 wt % of HCOOH and hydrogen peroxide) were taken in a 500 mL three necked RB flask equipped with an overhead stirrer. 30% Aqueous hydrogen peroxide (104.1 mL, 1.02 mol) was slowly added to the contents at 15−20 °C for a period of 1 h. The rest of the experimental procedure was similar to that of epoxidation of karanja oil. The epoxide was analyzed for oxirane oxygen content and the epoxide with maximum oxirane value obtained after 1 h which was further confirmed by iodine number and GC analysis (given in Supporting Information (SI)). The epoxidized karanja fatty acid esters were characterized by FT-IR and 1HNMR. Detailed spectral data is given in Supporting Information.
by OO, IV, GC, GC-MS. The conversion of the product obtained was found to be 91.6% by GC analysis. 1 H NMR (200 MHz, CDCl3). 0.88 (m, CH̲ 3); 1.2−1.6 (m, (CH̲ 2 ) n CH 3 ); 1.4−1.5 (m, ); 2.8−3.2(m, ); 2.2−2.4 (t, CH̲ 2CO); 4.0−4.2 (m, sn −1, sn −3); 5.2 (m, sn −2). IR (neat, cm−1). 2926 (CH), 1740 (CO), 822−928 (epoxy ring), 1218−1165 (CC(O)O). 2.5.2. Synthesis of Karanja Fatty Acid Methyl Esters (KFAME). Karanja oil (200 g, 0.2 mol) and sodium hydroxide (2 g, 1 wt % of substrate) dissolved in methanol (48 mL, 1.2 mol) were taken into a three neck RB flask and refluxed at 75−78 °C under constant stirring for 4 h. The progress of the reaction was monitored by TLC (hexane/ethyl acetate) 90/10 (v/v). The yield of the obtained methyl esters was found to be 98%. The structure of the product was established by GC-MS. 2.5.3. Typical Procedure for the Preparation of n-Butyl Esters of Karanja Fatty Acids. KFA-n-BuE was prepared by esterification of karanja fatty acids (200 g, 0.7 mol) and nbutanol (77.7 g, 1.1 mol) in 1:1.5 molar ratio using 1% p-TSA (2 g) as catalyst and xylene (150 mL) taken in a three necked reaction flask equipped with stirrer, thermometer, water condenser, and a nitrogen purger. The reaction mixture was stirred at 145−150 °C under nitrogen atmosphere until theoretical amount of water was collected. The crude product was distilled at 79−145 °C temperature and 2−3 mmHg to remove xylene and excess alcohol. The crude reaction product was extracted using ethyl acetate and washed with sodiumbicarbonate and dried over anhydrous sodium sulfate. The product was concentrated by removing the solvent and dried under reduced pressure. The yield of the n-butyl esters of karanja fatty acids was found to be 98.1%. The structure of the product was established by GC-MS. Similar experimental protocol was carried out for the preparation of 2-methl-1-propyl (KFA-2-Me-1-Pr) and 2ethylhexyl esters of karanja fatty acids (KFA-2-EtHE). The yield of KFA-2-Me-1-Pr and KFA-2-EtHE obtained was 96 and 95%. 2.5.4. Typical Procedure for the Epoxidation of Karanja Fatty Acid Alkyl Esters. Epoxidation of KFAME (Scheme 1) was carried out using in situ peroxyacetic/formic acid. The reaction conditions for the epoxidation of KFAME were optimized by varying the reaction parameters like molar ratio of
3. RESULTS AND DISCUSSION 3.1. Epoxidation of Karanja Fatty Acid Methyl Esters (KFAME). Epoxidation of KFAME was carried out using two different epoxidising reagents (RA), acetic (AcOH), and formic (HCOOH) acid. The reaction conditions were optimized varying the mole ratio of RA to KFAME and the concentration of 30% H2O2 at constant temperature, 60 °C (Scheme 1). 3.1.1. Effect of Concentration of RA. Initially, the reaction was carried out using KFAME:RA:H2O2, 1:0.5:3 (mol/mol/ mol) at 55−60 °C using H2SO4 (2 wt % of RA and H2O2) as catalyst. As epoxidation is an exothermic reaction, addition of H2O2 to a mixture of KFAME and RA was carried out at 15−20 °C for 1 h. After the addition, temperature was gradually increased to 55−60 °C. The course of the reaction was monitored taking aliquots of the reaction mixture hourly to determine oxirane content. The collected aliquots of samples were extracted with ethyl acetate and washed with water until they were acid free and analyzed for oxirane content. Maximum oxirane oxygen of 2.1% for 5h and 3.3% after 4 h was observed in case of AcOH and HCOOH respectively (Figure 1). Further series of reactions were carried out varying the mole ratio of KFAME/RA ranging from 1:0.5 to 1:2 (mol/mol). As the mole ratio of RA increased from 0.5 to 1 mol, different oxirane values were observed in both the cases, that is, 2.2% for 5 h using AcOH and 3.2% for 3 h in case of HCOOH and on further increase in the mole ratio of RA from 1 to 1.5 mol, 16600
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alkyl esters. The optimized reaction conditions were KFAME:HCOOH:H2O2, 1:1.5:3 (mol/mol/mol) to attain maximum oxirane oxygen of 3.6% and reduction in IV from 86 to 5.4, and the yield was 90.4% by GC. The rate of epoxidation (Figure 2) was also more in the case of HCOOH compared to AcOH. Using the optimized conditions KFAES:HCOOH:H2O2, 1:1.5:3 (mol/mol/mol), epoxidation of karanja fatty acid alkyl esters KFA-n-BuE, KFA2ME-1PrE, and KFA-2-EtHE was also carried out. 3.2. Epoxidation of KFA-n-BuE. Epoxidized KFA-n-BuE was prepared by taking KFA-n-BuE: HCOOH: H2O2 (1:1.5:3, mol/mol/mol), in the presence of H2SO4 (2 wt % of KFA-nBuE and 30% H2O2) as catalyst. The progress of the reaction was monitored hourly by oxirane oxygen content and a maximum oxirane value of 3.9% was obtained after 4 h. The epoxidized product was characterized using GC, GC-MS, IR, and 1H NMR. The epoxidized KFA-n-BuE was found to be 94% by GC analysis and a reduction in IV from 65.3 to 2.8 was observed. The epoxidized KFA-n-BuE was further evaluated for lubricant properties. 3.3. Epoxidation of KFA-2-Me-1PrE. Epoxidized KFA2Me-1PrE was prepared taking KFA-2ME-1PrE:HCOOH:H2O2 (1:1.5:3, mol/mol/mol), in the presence of H2SO4 (2 wt % of KFA-i-BuE and 30% H2O2) as catalyst. The reaction was monitored hourly by oxirane oxygen content, and maximum oxirane value of 3.7% was obtained for 4 h. The epoxidized product was characterized using IR, GC, GC-MS, IR, and 1H NMR. The epoxidized KFA-2Me-1PrE was found to be 95% by GC analysis and a reduction in IV from 58.3 to 3.3 was observed. The epoxidized KFA2-Me-1PrE was further evaluated for lubricant properties. 3.4. Epoxidation of KFA-2-EtHE. KFA-2-EtHE was prepared taking KFA-2-EtHE:HCOOH:H2O2 (1:1.5:3, mol/ mol/mol), in the presence of H2SO4 (2 wt % of KFA-2-EtHE and 30 wt % H2O2) as catalyst. The reaction was monitored hourly by oxirane oxygen content and maximum value of 3.2 was obtained for 2 h. The epoxidized product was characterized using 1H NMR, IR, GC, and GC-MS. The epoxidized KFA-2EtHE was found to be 97% by GC analysis and was reduced IV from 57.6 to 2.5. It has been further evaluated for lubricant properties. 3.5. Epoxidation of Karanja Oil (KO). Karanja oil was epoxidized under the optimized conditions as those used for maximum epoxidation of karanja fatty acid esters. However, the extent of epoxidation was found to be low under such condition. An excess amount of hydrogen peroxide was needed in the reaction in order to achieve maximum epoxidation.29 Therefore, the mole ratio of HCOOH: H2O2 was increased to 2:8 and maximum epoxidation was achieved. Epoxidation of karanja oil was carried out taking karanja oil:HCOOH: 30% H2O2 at a mole ratio of 1:2:8. The progress of the reaction was monitored by oxirane oxygen content and a maximum oxirane oxygen of 4.2% was obtained after 2 h which resulted in epoxidized oil with 91.6% conversion by GC analysis (Scheme 2) and also by IV, which decreased from 85 to 5.1. The epoxidized oil was evaluated for physicochemical and lubricant properties. A systematic study of the lubricant properties for epoxy alkyl esters was carried out for the first time, for evaluation of physicochemical and lubricant properties. Though few reports exist on physicochemical properties of epoxidized tropical oils such as palm or karanja oil.7,20
Figure 1. Effect of concentration of reagents on epoxidation of KFAME on relative conversion to oxirane. Conditions: KFAME, 1 mol; HCOOH/AcOH, 0.5−2 mol; H2O2, 3 mol; temperature, 60 °C.
oxirane content increased from 2.2 to 2.7% after 4 h in case of AcOH and 3.2 to 3.6% after 1 h in case of HCOOH (Figure 1). Further, upon increase in the mole ratio of RA from 1.5 to 2 mol, no increase in the oxirane content was observed in both the cases. The product with maximum oxirane oxygen of 3.6% using HCOOH was analyzed by IV, GC, and GC-MS. The study revealed that an optimum concentration 1.5 mol was sufficient to obtain maximum conversion in both the cases AcOH and HCOOH (Figure 1). 3.1.2. Effect of Concentration of H2O2. Reactions were further optimized taking KFAME/RA, 1:1.5 (mol/mol) and varying the concentration of 30% H2O2 from 3 to 7.5 (mol/ mol). The reactions were monitored by oxirane oxygen (Figure 2) and maximum of 3.5% in case of HCOOH after 3 h and
Figure 2. Effect of concentration of 30% hydrogen peroxide on epoxidation of KFAME on relative conversion to oxirane. Conditions: KFAME, 1 mol; HCOOH/AcOH, 1.5 mol; H2O2, 3−7.5 mol; temperature, 60 °C.
2.7% after 4 h in case of AcOH was observed when at 5 mol of H2O2 concentration. Further increase in molar concentration from 5 to 7.5 resulted in decrease in oxirane oxygen value in the case of AcOH and 3.6% after 2 h using HCOOH. Therefore, in both the cases, the optimum concentration of H2O2 required to get maximum conversion was 3 mol. The utilization of excess of H2O2 for the epoxidation of karanja oil and its derivatives was in accordance with the studies of Meyer et al.29 on conventional epoxidation of soybean oil and jatropha oil. The degree of conversion of these oils into their epoxidized oils highly depended on the excess utilization of H2O2 in order to obtain high epoxy content in the respective oils. Overall results have shown that HCOOH was a better epoxidising agent compared to AcOH for karanja fatty acid 16601
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Scheme 2. Generalized Structure of Epoxidation of Karanja Oil
It was achieved by optimizing the reaction parameters such as concentration of RA, 30 wt % H2O2, maintaining the controlled low reaction temperature as well as reaction time. The course of the reaction was closely monitored by GC to avoid the undesired side product 9, 10-dihydroxystearate, and other by products. The percentage conversion of epoxidation of karanja oil and its derivatives obtained was greater than 90%. The structures of the epoxidized karanja oil and its fatty acid alkyl esters were confirmed by FTIR, GC, GC-MS, and 1H NMR spectra. Based on the iodine value, the percentage conversion to epoxide was found to be 90−98.9% as in the case of derivatives KO. From the FTIR spectra, the disappearance of CC absorption at 3018 cm−1, absence of OH bands and appearance of epoxide absorption at 830−926 cm−1 indicated the complete conversion under the reaction conditions in all the epoxidized karanja fatty acid alkyl esters. From GC-MS analysis, less than 5% of high molecular weight products were observed indicating that side reactions were minimized. GC analysis showed the conversion of 90−97% in all the epoxidized alkyl esters and no unsaturation peaks, except in epoxy KFA-nBuE (2.9% of unreacted 18:1). The reaction completion was further confirmed by 1H NMR spectra of the epoxy karanja fatty acid alkyl esters where, the absence of peaks at 1.9−2.0 ppm (CH2 protons adjacent to the unsaturation)
The epoxidized oil was characterized using FTIR, GC, GCMS, and 1H NMR spectral studies. From the FTIR spectra, the disappearance of CC absorption at 3018 cm−1 and appearance of absorption at 830−926 cm−1 confirmed epoxidation. GC chromatogram of the transesterified product showed 98.1% conversion and no peaks related to unsaturation, indicating that almost complete conversion were observed. Formation of epoxy ring was further confirmed by 1H NMR spectra of the epoxy karanja oil, where the absence of peaks at 1.9−2.0 ppm (CH2 protons adjacent to the unsaturation) indicated complete disappearance of unsaturation and appearance of new peaks at 2.8 to 3.2 ppm corresponding to CH protons of the epoxy carbon and at 1.4 to 1.5 ppm corresponding to CH2 proton adjacent to two epoxy carbon confirmed the presence of epoxy group. Hilker et al.30 and Cai et al.31 reported that conventional epoxidation process would lead to side reactions and reduce its selectivity toward epoxidized products and ultimately give rise to side reactions. Klass and Warwel32 also mentioned that the selectivity of epoxidation of vegetable oils using conventional method rarely exceeded 80%. In the present study, epoxidation was carried out using the conventional process, using peracetic or performic acid by the transfer of oxygen to the unsaturated double bonds to obtain fully epoxidized oil and its derivatives. 16602
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when compared to its epoxy derivatives, which is in accordance with the studies Xuedong Wu et al40 reported that epoxidized rapeseed oil exhibited superior oxidative stability when compared to the native oil. As the chain length of alcohol moiety increased, an increase in RBOT time was observed in the case of straight chain alcohols. Whereas the decrease in the RBOT time was observed as the chain length increased in isoalcohols particularly epoxy 2-ethylhexyl karanja fatty acid esters. 3.6.8. Air Release Value. Entrained air in the oil contains finely divided air bubbles, which reduces the lubricating quality. This will enable the engine to maintain oil pressure, reduce oil films on bearing, and increase wear. The air release value of the epoxidized products was found to be good in the range of 0.9 to 1.76 min. 3.6.9. Noack Volatility. Noack volatility determines the evaporation loss of lubricant at high temperatures, which is of particularly importance in engine lubrication. Low voltality is important in high temperature operations in order to prevent loss of lighter components, otherwise the lubricant becomes too viscous, thicker, and heavier which leads to wear and emission. EKO exhibited low evaporation loss of 2.7% and epoxidized esters were in the range of 17.2 to 39.2% with moderate voltality.
indicated complete disappearance of unsaturation and appearance of new peaks at 2.8 to 3.0 ppm corresponding to CH protons of the epoxy carbon and 1.4 to 1.6 ppm corresponding to CH2 protons adjacent to the epoxy carbon further confirms the structure of the product. 3.6. Evaluation for Physicochemical and Lubricant Properties. Vegetable oil lubricants find several applications due to their biodegradability and renewability. They inherently possess the properties required for lubricants such as high viscosity index, low volatility, and good lubricity. As of now, based on literature study very few epoxidized oils have been evaluated for physicochemical properties. Therefore, in the present study epoxidized karanja oil and their fatty acid esters were synthesized and evaluated for the physicochemical and lubricant properties (given in SI). 3.6.1. Kinemtic Viscosity. Viscosity of Karanja oil was found to be 40.2, 8.36 cSt at 40 and 100 °C, respectively. On epoxidation, the viscosity increased to 256.2 and 28.0 cSt, respectively. Whereas in case of epoxy karanja fatty acid esters, the viscosity range decreased, but the effect of chain length of alcohol moiety in the fatty acid esters was in accordance with the studies reported earlier.33 As the chain length increased from methyl to butyl the viscosity increased, whereas the branching effect of decrease in viscosity was noticed in the case of isobutyl ester compared to n-butyl ester. As the chain length increased in branching, viscosity got increased in the case of 2ethyl hexyl ester. 3.6.2. Viscosity Index. Viscosity index describes the variation of viscosity over a wide range of temperatures. Viscosity index of EKO was less compared to KO, also the viscosity index of epoxy esters was found higher compare to EKO. Among them butyl and 2-ethylhexyl esters showed highest viscosity index. Methyl ester exhibited viscosity index comparable to EKO, however the decrease in viscosity index was found in the case of isobutyl ester (given in SI). 3.6.4. Pour Point. The low temperature fluidity characterization of a lubricant is determined using pour point measurement.34 The pour point of EKO was higher than KO and the observation was similar to that reported higher pour point of ESO, when compared to the native soybean oil.35 Pour point values of different epoxy fatty acid ester derivatives of KO were given in SI. The ester derivatives of EKO products were characterized by higher pour points, except the epoxy 2ethylhexyl esters of KFAES with a pour point 3 °C, which is in accordance with the studies reported by P. S. Lathi et al.36 The researchers observed that as the chain length of the branched alcohol increased, lower pour point were obtained. The tendency of formation of macro crystalline structures at low temperature of unmodified vegetable oils37−39 exhibited lower pour points compared to the chemically modified products. 3.6.5. Flash Point. In practice, the lubricant of high flash point are desirable.35 The flash point of vegetable oil (KO) as well as the EKFAES was also high when compared to chemically modified EKO. These derivatives followed a trend of increase in flash points as the chain length of the branching increased in the alcohol moiety when compared to straight chain alcohol. 3.6.6. Copper Corrosion. Corrosiveness of the products is found to be very good (1 a) for all the synthesized epoxidized karanaja oil and fatty acid esters. 3.6.7. Rotating Bomb Oxidation Tests (RBOT). Epoxy KO and its derivatives were evaluated for RBOT time and found that EKO exhibited the highest RBOT time of 45 min
4. CONCLUSIONS The epoxidation of karanja oil and fatty acid esters was carried out using Prilezhaev peracid process, which is an industrially acceptable, more viable and associated with economical benefits. Epoxidation was perfomed using peroxy formic acid generated in situ and summarized that epoxidation was strongly affected by the reaction parameters studied in this work. The optimized studies reveal that 8 mol of aqueous hydrogen peroxide (30 wt %) and 2 mol of HCOOH were required to obtain maximum oxirane content of 4.2% for epoxidized oil, 3 mol of aqueous hydrogen peroxide (30 wt %), and 1.5 mol of HCOOH was required to obtain maximum oxirane content of 3.2−3.9% for epoxidized esters and reaction yield was observed to be 90−98%. The epoxidized products were characterized by GC, GC-MS, IR, and 1HNMR spectral studies. In this direction, a systematic study was carried out for the evaluation of physicochemical and lubricant properties. Viscosities of the products ranged from 8.9 to 256.2 cSt at 40 °C, and from 2.52 to 27.98 cSt 100 °C. Based on viscosity index all the products belong to group III, category of base fluids as per API classification. Despite their higher pour points other lubrication properties such as viscosity, VI, flash point, and Cu corrosion value were good. Based on the lubricant characterization one of the product namely epoxy 2-ethyl hexyl esters is suitable as neat cutting oil and meets to its specifications. All the products have low oxidation stability as indicated by their RBOT values, although their oxidation stabilities increased after epoxidation. Therefore, these products can be used for metal working and hydraulic fluid applications with suitable antioxidants and pour point depressants. These base stocks can also be used for developing biobased industrial materials such as surfactants and additives.
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ASSOCIATED CONTENT
* Supporting Information S
Detailed spectral data, GC analysis (Table 1), and physicochemical properties (Table 2) of the synthesized products is given. Figures S1, S2, S3, S4: 1HNMR, IR spectra, GC, and GCMS chromatography of EKFAME. Figures S5, S6, S7: 1HNMR, 16603
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(17) Adhvaryu, A.; Erhan, S. Z. Epoxidized soybean oil as a potential source of high-temperature lubricants. Ind. Corp. Prod. 2002, 15, 247. (18) Sharma, B. K.; Doll, K. M.; Erhan, S. Z. Oxidation, friction reducing, and low temperature properties of epoxy fatty acid methyl esters. Green Chem. 2007, 9, 469. (19) Suarez, P. A. Z.; Pereira, M. S. C.; Doll, K. M.; Sharma, B. K.; Erhan, S. Z. Epoxidation of methyl oleate using heterogeneous catalyst. Ind. Eng. Chem. Res. 2009, 48, 3268. (20) Goud, V. V.; Patwardhan, A, V.; dinda, S.; Pradhan, N. C. Epoxidation of karanja (Pongamia glabra) oil catalysed by acidic ion exchange resin. Eur. J. Lipid Sci. Technol. 2007, 109, 575. (21) Gurbanov, M. S.; Mamedov, B. A. Epoxidation of flax oil with hydrogen peroxide in a conjugate system in the presence of acetic acid and chlorinated cation exchanger KU-2 × 8 as catalyst. Russ. J. Appl. Chem. 2009, 82, 1483. (22) American Society for Testing and Material (ASTM D 445-10). Standard test method for kinematic viscosity of transparent and opaque liquids. ASTM Book of Standards; ASTM: West Conshohocken, PA, 1998. (23) American Society for Testing and Material (ASTMD 5949). Standard test method for pour point of petroleum products (automatic pressure pulsing method). ASTM Book of Standards; ASTM: West Conshohocken, PA, 2010. (24) AOCS. American Oil Chemists Society official method for flash point closed cup method (modified closed cup method, ASTM designation D 93-80). Cc 9b-55. American Oil Chemists Society: Urbana, IL, 1997. (25) American Society for Testing and Material (ASTM). Copper strip Corrosion test D 4048-10 specification for lubricating grease. ASTM Book of Standards; ASTM: West Conshohocken, PA, 2010. (26) American Society for Testing and Material (ASTM D 2272-11). Standard test method for oxidtion stability of steam turbine oils by rotating pressure vessel. ASTM Book of Standards; ASTM: West Conshohocken, PA, 2002. (27) American Society for Testing and material (ASTM D 3427-12). Standard test method for Air Release properties of Petroleum Oils. ASTM Book of Standards; ASTM: West Conshohocken, PA, 2012. (28) American Society for Testing and Material (ASTM D 5800-10). Standard test method for evaporation loss of lubricating oils by the Noack method. ASTM Book of Standards; ASTM: West Conshohocken, PA, 2010. (29) Meyer, P. P.; Techaphattana, N.; Manundawee, S.; Sangkeaw, S.; Junlakan, W.; Tongurai, C. Epoxidation of soybean oil and jatropha oil. Thammasat Int. J. Sci. Technol. 2008, 13, 1. (30) Hilker, I.; Bothe, D.; Pruss, J.; Warnecke, J. Chemo-enzymatic epoxidation of unsaturated plant oils. Chem. Eng. Sci. 2001, 56, 427. (31) Cai, S. F.; Wang, L. S.; Fan, C. L. Catalytic epoxidation of a technical mixture of methyl oleate and methyl linoleate in ionic liquids using MoO (O2)2.2QOH (QOH=8-quinilinol) as catalyst and NaHCO3 as co-Catalyst. Molecules 2009, 14, 2935. (32) Klass, M.; Warwel, S. Complete and partial epoxidation of plant oils by lipase-catalyzed perhydrolysis. Ind. Crops Prod. 1999, 9, 125. (33) Schneider, M. P. Plant-oil-based lubricants and hydraulic fluids. J. Sci. Food. Agric. 2006, 86 (12), 1769. (34) Benchaita, M. T.; Lockwood, F. E. Reliable model of lubricant related friction in internal combustion engines. Lubr. Sci. 1993, 5, 259. (35) Erhan, S. Z.; Sharma, B. K.; liu, Z.; Adhvaryu, A. Lubricant base stock potential of chemically modified vegetable oils. J. Agric. Food Chem. 2008, 56, 8919. (36) Lathi, P. S; Mattiasson, B. O. Green approach for the preparation of biodegradable lubricant base stock from epoxidized vegetable oil. Appl Catal B: Envi. 2007, 69, 207. (37) Asadauskas, S.; Erhan, S. Z. Depression of pour points of vegetable oils by blending with diluents used for biodegradable lubricants. J. Am. Oil Chem. Soc. 1999, 76, 313. (38) Hernqvist, L. Crystal Structures of Fats and Fatty Acids: Hand Book of Food Science, Technology and Engineering; Marcel Dekker: New York, 1988, p 97.
IR spectra, and GC chromatography of EKFAnBUE. Figures S8, S9, S10, and S11: 1HNMR, IR spectra, GC and GC-MS chromatography of EKFA2ET-HE. Figures S12, S13, S14, and S15: 1HNMR, IR spectra, GC and GC-MS chromatography of EKFAiBE. Figures S16, S17, S18, and S19: 1HNMR, IR spectra, GC and GC-MS chromatography of EKO. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel: +91 040 27193370. Fax: +9140 27193370. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Authors gratefully acknowledge the financial grant received from the Department of Science and Technology, Government of India under Technology System Development (TSD) Program.
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REFERENCES
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