Article pubs.acs.org/IECR
Novel Acyl Derivatives from Karanja Oil: Alternative Renewable Lubricant Base Stocks 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 500007, India S Supporting Information *
ABSTRACT: Lubricant base stocks of acylated oil and its derivatives, namely, propionylated, butanoylated, and hexanoylated karanja oil and fatty acid methyl esters, were synthesized from renewable nonedible source karanja oil (Pongamia glabra). The reaction was carried out by Prilezhaev dihydroxylation, an in situ peroxyformic acid generated using hydrogen peroxide and formic acid. The hydroxylated derivatives were acylated with three acid anhydrides (C3, C4, and C6). All of the synthesized products were examined for their purity by GC and GC-MS and characterized by IR and 1H NMR spectral studies. The acylated derivatives were evaluated for physicochemical and lubricant properties. Propionylated and butanoylated esters of KFAME were found suitable as IS: 3098 hydraulic fluids in ISO VG 46 and ISO VG 68 categories, respectively. In addition, propionylated esters of KFAME are also suitable as IS: 8406 gear oils (R&O type). Other lubrication properties such as viscosity, viscosity index of all products belonging to group III, category of base fluids as per API classification, Cu corrosion value, weld point, and air release value were found to be good. These base stocks may find applications in hydraulic fluids and metal-working fluids.
1. INTRODUCTION Global demand, depletion of world fossil fuel resources, and environmental concerns have prompted the use of renewable biobased resources toward sustainability. The mounting demand for environmentally friendly lubricants has led to the utilization of vegetable oils. Inherent characteristic features such as excellent lubricity, biodegradability, low voltality, and high viscosity index have made these vegetable oils potential candidates as base fluids for ecofriendly lubricants. Some of their drawbacks, such as poor oxidation and low temperature stability, must be improved1−6 to meet most of the technical requirements of lubricants. However, these can be resolved by chemical modification of vegetable oils at the sites of unsaturation, which includes epoxidation, alcoholysis, acylation, partial hydrogenation, and transesterification7,8 to achieve the required performance of lubricant base stocks and to compete with mineral oil based lubricants. The literature-reported methodologies for the synthesis of acylated derivatives include epoxidation, hydroxylation, and acylation by utilizing vegetable oils such as linseed, corn, and soybean, which are edible oils, and milkweed, a nonedible oil.9−19 Hwang and Erhan have studied the modification of epoxidized soybean oil for lubricant formulations with improved oxidative stability and low pour point.9 Adhvaryu et al. reported the preparation of biofluids, namely, soybean oil (SBO), thermally modified soybean oil (TMSO), and chemically modified soybean oil (CMSO), and their potential application as industrial fluids.10 Erhan et al. have studied the chemical modification of soybean oil, using ESBO and acid anhydrides using BF3 etherate as catalyst. These derivatives were evaluated for lubricant properties. Improved thermo-oxidative stability and cold flow property were achieved with suitable additives when used with CMSO.13,14 HarryO’kuru et al. studied the modification of HMWO by esterifying its hydroxyl groups using anhydrides of C2−C5 chain lengths © 2014 American Chemical Society
and investigated the effect of acyl derivatives on lubricating properties of oxidative stability, low temperature, and tribological properties.15 However, very few chemically modified vegetable oils14,19 have been evaluated for physicochemical and lubricant properties. The vegetable oils with high oleic acid content are assessed to be possible replacements for conventional mineral oil based products.20,21 The underutilized, promising nonedible karanja oil is widely available in India22 and is not well explored for lubricant base stock preparation. Although there are a few studies on the utilization of karanja oil,23−25 a detailed study on its chemical modification to improve its properties as a lubricant base stock has not been carried out. Epoxidation of karanja oil using different catalysts such as sulfuric acid, acidic ion-exchange resin using acetic acid, and 30% hydrogen peroxide was studied by Goud et al., and they proposed a kinetic model for epoxidation.23,24 Chauhan et al. have studied the extraction of karanja oil, its composition, and the physicochemical properties of the oil. Furthermore, they synthesized the triesters of oleic acid and evaluated low-temperature behavior.25 Although a few applications using karanja oil have been developed, such as 2ethylhexyl esters of karanja oil in two-stroke gasoline engines and lubricity booster in metal-working fluids, and EP additive, preparation of lubricant base stocks using chemically modified karanja oil via epoxy karanja oil (EKO) is a promising intermediate and is readily functionalized. In continuation of our work on karanja oil, previously we reported the synthesis of epoxidation of karanja oil and its alkyl esters and their evaluation for physicochemical and lubricant properties.26 In Received: Revised: Accepted: Published: 8685
March 11, 2014 April 27, 2014 May 4, 2014 May 5, 2014 dx.doi.org/10.1021/ie5009986 | Ind. Eng. Chem. Res. 2014, 53, 8685−8693
Industrial & Engineering Chemistry Research
Article
in 3 °C increments at the top of the product until it stopped pouring, and all of the runs were carried out in duplicate. 2.4.3. Flash Point. Flash points of the synthesized products were evaluated using a Koehler Inc. apparatus as per ASTM D 93 method as described elsewhere in detail.26 The flash point is defined as the lowest temperature at which application of the test flame causes the vapor above the surface of the liquid to ignite at ambient barometric pressure. Duplicate measurements were made, and the average values were reported. 2.4.4. Copper Strip Corrosion Test. The copper strip corrosion test of the synthesized products was evaluated using ASTM D 130 method by using a Koehler Inc. apparatus. The color and tarnish level of the test specimen of the Cu strip were correlated using the ASTM copper strip corrosion standards and the experimental procedure followed as described elsewhere in detail.26 2.4.5. Rotating Pressurized Vessel Oxidation Test (RPVOT). RPVOTs for the synthesized acylated products were determined as per ASTM method D 2272. The experiments were carried out using a sample size of 50 g, copper catalyst at 150 °C, and 5.0 mL of reagent grade water; the vessel was sealed and charged with oxygen to 90 psi pressure. The RPVOT time is the time at which the pressure of the bomb has dropped by 25 psi. 2.4.6. Air Release Value. The air release value of the synthesized products was determined using ASTM method D 3427 using a Koehler Inc. apparatus. The test requires the measurement of the time required for the air entrained in the oil to be reduced back to a value of 0.2%, and the value is reported in minutes as the air release time; the test method was described in detail elsewhere.26 2.4.7. NOACK Volatility. The NOACK volatility of a sample in percentage by weight lost was determined as evaporative loss using ASTM method D 5800 using a Koehler (Bohemia) apparatus. NOACK volatility can be determined as the weight loss a sample experiences through volatization, and the test results were reported in percentage by weight lost. 2.4.8. Emulsion Characteristics. Emulsion stability was determined by using ASTMD 140127 using a Dott. Gianni Scavini apparatus equipped with a tachometer, a thermostated heater, and a speed variator. Distilled water and 40 mL of sample are stirred at 54 °C for 5 mn. The time required for the separation of the emulsion thus formed is determined. 2.4.9. Hydrolytic Stability. Hydrolytic stability of the synthesized products was determined using ASTMD 2619 using a Dott. Gianni Scavini apparatus. A sample size of 75 g, water (25 g), and copper test specimen are sealed in a pressuretype beverage bottle, which is subjected to rotation for 48 h in an oven at 93 °C. The test result was found as the weight of insolubles, and changes in the weight of copper strip, viscosity, and acid number of the fluid were measured. 2.4.10. Extreme Pressure Test. The extreme pressure tests were made with a precision scientific four-ball extreme pressure tester, using IP 239.28 Tests were run at 1475 rpm, without application of external heat, for 1 mn or until the balls welded, whichever occurred first. The weld point loads reported are reproducible to within one loading increment (±10 kg for 10 kg loading increments). 2.4.11. Foam Stability. The standard test method for foaming characteristics of lubricating oils was carried out using the ASTM D 892-02, using Koehler instruments. This method is used to measure the tendency of growth and stability of foam at three different temperatures. Air is blown into the sample in
the present study, the structural modification of the karanja oil and karanja fatty acid methyl esters was carried out by the acylation of dihydroxy karanja oil and fatty acid methyl esters, and their physicochemical and lubricant properties were investigated.
2. EXPERIMENTAL SECTION 2.1. Materials. Hydrogen peroxide (30% aqueous solution), sodium hydroxide, hydrochloric acid (HCl), sulfuric acid (AR grade), xylene, and dimethylaminopyridine (DMAP) were purchased from M/s SD Fine Chem Ltd., Mumbai, India. Formic acid (85%), acetic acid, acetic anhydride, sodium bicarbonate, and sodium sulfate were purchased from M/s Rankhem, New Delhi, India. Propionic, butyric, and hexanoic anhydrides were procured from Sigma-Aldrich (St. Louis, MO, USA). Hexane and ethyl acetate were purchased from M/s Spectrochem Pvt. Ltd., Mumbai, India. All of the chemicals were of analytical reagent grade and were used directly without further purification. Karanja oil was purchased from a local company (Hyderabad, India). 2.2. Analytical Methods. The American Oil Chemists’ Society (AOCS) official methods were employed in the analytical determinations of the acylated derivatives of karanja oil and fatty acid methyl esters as follows: acid value, AOCS Cd 3d-63; iodine value (IV), AOCS Da 15-48; oxirane oxygen content (OO), AOCS Cd 9-57; and hydroxyl value (HV) AOCS Cd 13-60. 2.3. Analytical Techniques. 2.3.1. Gas Chromatography (GC) Analysis. GC and GC-MS analyses were carried out for the determination of the fatty acid composition as methyl esters. An Agilent GC on HP 6890 series gas chromatograph equipped with a FID detector using an HP-1 column (30 m × 0.25 mm × 0.5 μm) was employed in GC analysis. The injector and flame ionization detector were at 300 °C. The oven temperature was programmed at 150 °C for 2 min and then increased to 300 °C at 10 °C/min. The carrier gas used was nitrogen at a flow rate of 1.5 mL/min. The GC-MS analysis was performed using an Agilent 6890 gas chromatograph with an HP-1 MS capillary column (30 m × 0.25 mm × 0.5 μm) connected to an Agilent 5973 mass spectrophotometer (Palo Alto, CA, USA) at 70 eV (m/z 50−600; source at 230 °C and quadruple at 150 °C) in the EI mode. The oven temperature was programmed at 150 °C for 2 min, raised at 10 °C/min to 300 °C, and held for 20 min at 300 °C. The carrier gas used was helium at a flow rate of 1.0 mL/min. 2.3.2. Nuclear Magnetic Resonance (NMR). 1H nuclear magnetic resonance (1H NMR) spectra were obtained using a Bruker (Wissenbourg, France) AR X 400 spectrometer (400, 200 MHz) with CDCl3 solvent and TMS as an internal standard. 2.3.3. Fourier Transform Infrared (FTIR) Spectrum. A Fourier transform infrared (FTIR) spectrum was performed on a 1600 FTIR PerkinElmer spectrophotometer (Norwalk, CT, USA) with a liquid film between NaCl disks. 2.4. Lubricant Analysis. 2.4.1. Viscosity. Viscosity was determined as described by the ASTMD 445 and ASTM D 2270 methods. Kinematic viscosity measurements were made at 40 and 100 °C as described elsewhere in detail.26 2.4.2. Pour Point. Pour points were measured by following the ASTM D 97 method with an accuracy of 3 °C using a pour point test apparatus manufactured by Dott. Gianni Scavini & Co., Italy. Pour points of the acylated products were measured 8686
dx.doi.org/10.1021/ie5009986 | Ind. Eng. Chem. Res. 2014, 53, 8685−8693
Industrial & Engineering Chemistry Research
Article
in methanol (48 mL, 1.2 mol) was added to karanja oil (200 g, 0.2 mol) and refluxed at 75−78 °C under constant stirring for 4 h. The completion of the reaction was monitored by TLC using hexane/ethyl acetate 90:10 (v/v). The yield of the karanja fatty acid methyl esters was found to be 98%. The structure of the product was confirmed by GC-MS. 2.5.4. Synthesis of Dihydroxy Karanja Fatty Acid Methyl Esters. Karanja fatty acid methyl esters (100 g, 0.34 mol), formic acid (19.7 mL, 0.51 mol), and concentrated sulfuric acid (1.5 mL, 2 wt % of HCOOH and H2O2) were taken in a threenecked round-bottom flask, and the temperature of the medium was maintained at 15 °C. Aqueous H2O2 solution, 30% concentration (104.1 mL, 1.02 mol), was added slowly to the contents under mechanical stirring at 15 °C for 1 h. After addition, the contents were stirred at 60 °C for 1 h and obtained maximum epoxidation, and followed by hydroxylation by increasing the temperature to 85 °C for 7 h. The final product was extracted with ethyl acetate and washed with water until it was acid free. The completion of the reaction was monitored hourly by oxirane value, hydroxyl value, and IR. The formation of hydroxyl product was confirmed by GC and GCMS after silylation with N,O-bis(trimethylsilyl)trifluoroacetamide, IR, and 1H NMR spectral studies. 1 H NMR (400 MHz, CDCl3) δ 0.88 (t, −CH3), 1.2−1.6 (m, −(CH2)n−CH3), 1.5−1.6 (m, −CH2−CH2−CO), 2.1−2.2 (t, −CH2−CO), 3.2−3.4 (m, −CH−OH−), 3.7 (−O− CH3); IR (neat, cm−1) 3445 (−OH), 2925 (C−H), 1743 (C O), 1102 (C−C(O)−O). 2.5.5. Typical Procedure of Acylation of Dihydroxy Karanja Fatty Acid Methyl Esters. Dihydroxylated karanja fatty acid methyl esters (0.3 mol), alkanoic anhydride (0.6 mol), DMAP (0.1 wt % of hydroxylated karanja oil), and xylene (150 mL) were taken in a three-necked round-bottom flask and stirred at 140−150 °C for a period of 7−9 h, and the reaction was continued as described in section 2.5.2. The acylated products were analyzed for hydroxyl and acid value and obtained without any hydroxyl value and with an acid value of 1.6%. This was further purified by passage through a basic alumina column to obtain acylated esters with an acid value of
