Lubricants based on renewable resources - an environmentally compatible alternative to mineral oil products

The development of lubricants like, e.g, engine and hydraulic oils was trad itionally based on mineral oil as a base fluid. This fact is related to the good technical properties and the reasonable price of mineral oils. The Re port to the Club of Rome (W.W. Behrens III, D.H. Meadows, D.I. Meadows, J. Randers, The limits of growth, A Report to the Club of Rome, 1972) and the two oil crises of 1979 and 1983, however, elucidated that mineral oil is on principle a limited resource. In addition, environmental problems associat ed with the production and use of chemicals and the limited capacity of nat ure to tolerate pollution became obvious (G.H. Brundtland, et al., in: Hauf f, Volker (Ed.), World Commission on Environment and Development (WCED), Re port of the Brundtland-Commission, Oxford, UK, 1987), and the critical disc ussion included besides acid rain, smog, heavy metals, and pesticides also mineral oil (especially oil spills like the case Exxon Valdes). A disadvant age of mineral oil is its poor biodegradability and thus its potential for long-term pollution of the environment. From the early development of lubri cants for special applications (e.g. turbojet engine oils) it was known, th at fatty acid polyol esters have comparable or even better technical proper ties than mineral oil. Subsequently, innumerable synthetic esters have been synthesized by systematic variation of the fatty acid and the alcohol comp onents. Whereas the alcohol moiety of the synthetic esters are usually of p etrochemical origin, the fatty acids are almost exclusively based on renewa ble resources. The physico-chemical properties of oleochemical esters can c over the complete spectrum of technical requirements for the development of high-performance industrial oils and lubricants (e.g. excellent lubricatin g properties, good heat stability, high viscosity index, low volatility and superior shear stability). For a comprehensive review of their technical p roperties see F. Bongardt, in: Jahrbuchfur Praktiker, H. Ziolkowsky (Ed.), Verlag fur chemische Industrie GmbH, 1996, pp. 348-361. This article will f ocus on the ecological properties of oleochemical (synthetic) esters. The e nvironmental relevance of oleochemicals in comparison to petrochemicals is discussed, and then the principles of an ecological assessment are describe d. The ecotoxicological properties and the biodegradability of oleochemical esters are presented. Finally, the ecological properties of the oleochemic al esters are discussed with regard to existing environmental classificatio n and labeling systems. (C) 2001 Elsevier Science Ltd. All rights reserved.