Bio‐based Ester Oils for Use as Lubricants in Metal Working

Abstract

The potential application of bio-based ester oils for use as lubricants in metal working has been investigated for sustainable production processes in the future. When waste edible and animal fats came into focus as starting materials, it was already proven, that ester oils produced from plant fats performed very well as cooling lubricants. Waste fats were first characterized by analyzing and monitoring samples for one complete year. Inorganic and organic contaminations were found to be low and without seasonal variations. Fatty acid methyl esters (FAME) were produced by transesterification of the waste fats and they were separated into fractions with saturated FAME or unsaturated FAME by fractional crystallisation (winterisation). Further transesterification with 2-ethylhexanol led to products that could be successfully tested as lubricants. The development of an extraction process aimed at the recycling of oil containing grinding mud by enabling the recirculation of lubricating oil and reutilization of oil-free metal chips. Aims and ScopeIn order to save limited resources of mineral oils and to use renewable feedstock it is an urgent issue to develop alternative working substances for different application areas and for a sustainable production management of goods in the near future. An example for this is the substitution of non-watermiscible lubricating oils for metal processing. The consumption of these lubricants in Germany is assessed as 40,000 t per year. It already has been reported in the literature that mineral oil fractions applied as lubricant base oils can be replaced by fatty acid ester oils, bearing technical and ecological advantages. Nevertheless, so far ester oils are barely applied in industrial practice, mainly due to their price which is still slightly higher compared to the mineral oil products and due to a lack of acceptance by users, as well. The aim of this paper is to give an insight into steps that have already been undertaken at Braunschweig University of Technology together with cooperating partners in order to prepare a marketability of bio-based ester oils for lubricants applied in metal working processes. Actions and Results Fats and Ester Oils as Starting Materials of LubricantsThe renewable basis of ester oil lubricants can be plant oils and fats, technical animal fats, or waste edible fats. First, successful investigations have been performed with plant oils, transesterified stepwise with methanol and 2-ethylhexanol. The resulting esters showed very good performance when applied as lubricating oils [1]. At present, these plant oils are too expensive as starting materials because of high market demand due to the fastly growing biodiesel production. Recently, waste fats came into focus. German rendering plants produce 300,000 t animal fat per year. Additionally, 120,000 t/a of waste edible fats are collected from catering services and food industry. In the past, these raw materials have been widely used as nutritional additives for animal fodder. But some years ago, they have be...

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