Leaf Coppin Eco-friendly Formulations Base Fluids for Lubricant Oil R.P.S. Bisht, Savita Kaul, P. Nagendramma, V.K. Bhatia, and A.K. Gupta Indian Institute of Petroleum, Dehradun, India Abstract There is an increasing move towards the use of environmentally safe lubricants. However, the development ofa common hiodegradahle base stock that could replace conventional ones is a hig challenge. Synthetic lubricants, whether synthetic hydrocarbons, organic esters, or others, all have problems associated with their use. However, in general terms synthetic lubricants protect better, last longer, and outperform their conventional mineral-based counterparts in certain applications. Future lubricant specifications in I'iew of the demand for improved performance to meet stringent environmental regulations are the main drivers for new technological developments. As part of a study to produce polyol ester lubricant hase stocks from C 5 polyols and C o -C I4 carboxylic acids in the presence of eco-friendly catalysts, a series of products has been synthesised. A biodegradable luhricant formulation for automotive transmission fluids has been developed based on a svnthesised product as a base fluid. This paper reports on the physico-chemical characteristics and performance evaluation results of this formulation, which is a promising base stock for automotive transmission fluids. Keywords synthetic lubricant, eco-friendly base stock, biodegradability, polyol ester, automotive transmissionfluid, ATF INTRODUCTION Over the past decade there has been a steady increase in the demand f r biodegradable, environmentally friendly lubricants, especially for use in ecologically sensitive areas. In recent years, the environmental impact of large amounts of lubricants and industrial fluids has become an increasingly important issue, and the need for ceo-friendly products has been discussed at length. New applications are continually being found for these ecologically harmless 1. Synthetic Lubrication 19-3, Oct. 2002. (19) 2431SSN 0265-6582 $10.00 + $10.00 (2166/1002)
244 Bisht, Kalil, Nagendramma, Bhatia, and Gupta lubricants, and for every successful application, the results obtained serve as pointers for further use of these products, underl ining the need to develop novel biodegradable and ecologically harmless base stocks for future generations of lubricants. Currently the synthetic fluids that are manufactured commercially are mainly ester-based polyalkylene glycols or vegetable-oil based fluids. Before ecological aspects became a consideration in lubricant development, ester oils were used in speciality lubricants for technical reasons, e.g., as base fluids for aviation turbine oils and components for fuel economy oils, compressor oils, and other applications of industrial oils and greases. The present work was initiated as part of a development programme for formulating environmentally acceptable lubricants. A set of synthetic polyol esters has been developed, using a specific type of unconventional eco-friendly catalyst, for use as base stocks for biodegradable oil formulations. The paper reports on some studies carried out on the synthesis of the polyol esters, and their evaluation as potential base fluids for industrial applications. EXPERIMENT AL A variety of polyol esters of molecular weight in the range 300-864 were synthesised from polyols (C 5 ) and acids (C(\-Cj~)' The acids and alcohols in equimolar ratios and about 3-30% of the catalyst were mixed and the contents were refluxed for 30 min to 4 h depending on the nature of the reactants. The catalysts used in the reaction were eco-friendly unconventional IIP Cj-IIP C~. The experimental conditions were much milder compared to those required for a conventional catalyst. RESULTS AND DISCUSSION Esters are normally synthesised using catalysts based on PTS, Ni, Cu, Fe, V, CO, and Sn, Cu and Cr oxides, alkoxy zirconate, and heteropolyacids. In these processes the catalysts are used for once-through application, have disposal problems, yield base oi Is with significant acidity, and are not eco-friendly.l-' The use of the unconventional eco-friendly catalysts gives the products (esters) negligible free acidity. The process has the advantages of easy handling, shorter reaction time, lower molar ratio of acid to alcohol, energy savings and yields of the order of 94.2-99.8%. Another advantage of these catalysts is that they can be recycled without loss of reactivity and decrease in yield. Table 1 J. Svnthetic Lubrication 19-3, October 2002. (19) 244 ISSN 0265-6582 $10.00 + $10.00
Eco-friendly basefluidsfor lubricant oil formulations 245 Table 1 Physico-chemical characteristics of synthesised polyol esters Sample Viscosity (cst) Viscosity in- Pour point Density, [J! 4 code dex (0C) too C 40 C PP-12* 5.30 26.37 138 <-27 0.9403 PP-ll 3.78 15.75 133 <-27 0.9542 PP-l0 3.07 12.33 104 <-24 0.4705 PP-3* 4.22 18.22 139-6 0.9031 PP-2 3.30 12.94 128 <-27 0.9095 PP-l 2.46 8.74 104 <-24 0.9060 Sample ph Evaporation Acid value Sap. value Flash point code loss at 40 C (OC) PP-12* 3.8 0.06 0.09 275 190 PP-ll 5.1 0.12 0.09 320 198 PP-l0 5.3 0.29 0.07 381 194 PP-3* 5.4 0.04 0.06 218 204 PP-2 5.3 0.12 0.05 242 204 PP-l 5.3 0.11 0.06 280 130 Sample Copper strip Noack Foaming code corrosion volatility Seq I (24 C) Seq 1/ (93.5) Seq 1/1 (24 C) PP-12* <1 4.7 Nil/Nil Nil/Nil Nil/Nil PP-ll <1 14.0 40/Nil 10/Nil 40/Nil PP-l0 <1 15.4 10/Nil 40/Nil 190 ' Nil PP-3* <1 5.0 Nil/Nil Nil/Nil Nil/Nil PP-2 <1 NO NO NO NO PP-l <1 NO NO NO NO * Selected for biodegradable ATF base oils. J. Synthetic Lubrication 19-3, October 2002. (19) 245 1SSN 0265-6582 $10.00 + $10.00
246 Bisht, Kaul, Nagendramma, Bhatia, and Gupta Table 2 Performance evaluation of synthesised polyol esters Sample code Wear-scar diameter Weld load (kgf) Coefficient of (mm) friction, f.1 PP-12 0.683 130 0.065 PP-11 0.675 130 0.069 PP-10 0.700 160 0.060 PP-3 0.500 120 0.052 PP-2 0.625 140 0.058 PP-1 0.508 140 0.056 lists the physico-chemical characteristics of the synthesised polyol ester lubricant base stocks using lip CI-IIP C 4 catalysts. Of the four catalysts used, lip C 1 has the most potential because it can be used five times without loss of reactivity and yields. The presence of an ester group implies polarity, which is reflected in the vapour pressure, lubricity, and solvency. Thus, in comparison with mineral oils, many esters have technical advantages. These include a naturally high viscosity index, good low-temperature properties (good cold flow), pour points <-26 C, low evaporation losses, good thermal stability, i.e., high-temperature properties, hydrolytic stability, good antifriction and anti wear characteristics, high flash points (>260 C), seal compatibility, and biodegradability. Synthetic base fluids prepared in the laboratory normally belong to group V of the API classification of base stocks.' Taking viscosity index as the basis for comparison with mineral base oils, it is observed (Table 1) that four of the products from the present study are in group III and two products, PP-l and PP-IO, are in group II. Three of these base fluids have a pour point of (-6 to <-27 C; evaluated as per ASTM D-97), which reflects their very good lowtemperature flow characteristics. Another important feature of these base fluids is their biodegradability, which is normally in the range 80-90% (evaluated as per ASTM D 5864-95). The performance evaluation of the synthesised products was carried out using a four-ball extreme-pressure tester and a four-ball wear tester. The test results are given in Table 2, and indicate that the lubricity characteristics of these products are better than those of comparable mineral oil base stocks. 1. Svnthetic LubricarionI9-3, October 2002. (19) 246 /SSN 0265-6582 $10.00 + $10.00
Eco-friendly basefluidsfor lubricant oilformulations 2-17 Table 3 Typical technical properties of synthetic transmission fluids Characteristic Method Target PP-3 PP-12 Kinematic viscosity ASTM D 445 100 C (cst) 4.8 4.22 5.30 40 C (cst) 23.8 18.22 26.37 Viscosity index ASTM D 2770 128 139 138 Flash point (0G) ASTM D 92 252 258 260 Fire point (0G) ASTM D 92 26.2 264 264 Pour point (0G) ASTM D 97-59 -6 <-27 Four-ball wear test, 40 kg, ASTM D 4172B 0.36 0.38 0.37 75 C, 1200 rpm, 1 h Noack, 250 C DIN 51581 10.2 5.0 4.7 From analysis of the physico-chemical test data, it was found that these products have a potential application as base stocks for automotive transmission fluids (ATFs). Development of biodegradable lubricants for ATFs Synthetic ATFs are used, for example, in power steering units and hydraulic systems, providing good lubricating protection. They have better performance and a wider temperature range of operation than do commercial petroleum fluids. Transmissions usually operate under severe conditions. In the field of lubrication it is difficult to formulate a product that will meet all the requirements for a particular use. Formulated oils provide cooling, lubrication, and rust protection for moving parts. A finished biodegradable lubricant can be produced using an appropriate base stock and suitable additives. To assess the environmental sensitivity of ATFs, two formulations of potentially biodegradable base stocks with commercial anti wear additives were made. These two formulations were compared to a commercial ATF. The results are given in Table 3. The results indicate that the formulations match the commercial ATF. Certain features of these synthetic polyol esters are comparable to vegetable oils, but their better thermal and oxidative stability and lower pour points can usefully extend the scope of their successful appl ication in lubricating oil formulations. Since a finished lubricant normally consists of greater than 90% base oil, the polyol base stocks are potentially biodegradable. J. Synthetic Lubrication 19-3, October 2002. (19) 2471SSN 0265-6582 $10.00 + $/0.00
248 Bisht, Kaul, Nagendramnia, Bhatia, and Gupta CONCLUSIONS Synthetic polyol esters developed by the authors have a good potential for use in biodegradable lubricating oil formulations. The use of the unconventional eco-friendly catalysts in the synthesis of the products (esters) is beneficial as compared to conventional catalysts, offering advantages in terms of reuse (of the catalyst), free acidity, shorter reaction time, and other benefits, and the products, in the present study a formulation for automotive transmission fluids, also show promise. Acknowledgement The authors are grateful to Mr. S. Singhal, Director, Indian Institute of Petroleum, Dehradun, for permission to present this work. References 1. Booser, R.E., CRC Handbook of Lubricants and Tribology, CRC Press, Boca Raton, FL, 1994, Vol. 3. 2. Gunderson, R.S., and Hart, A.W., Synthetic Lubricants, Reinhold, New York, 1962. 3. Singh, H., Bhatia, V.K., Sahai, P., 'Biodegradable/ecofricndly lubricants/base fluids', llp Report 23:96, 1996. This paper was first presented at the 12th LA WPSP Symposium, Bombay, India. J. Svnthetic Lubrication 19-3. October 2002. (19) 2481SSN 0265-6582 $10.00 + $10.00