Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2006
Publication Date: 2/19/2007
Citation: Sharma, B.K., Perez, J.M., Erhan, S.Z. 2007. Soybean oil-based lubricants: a search for synergistic antioxidants. Energy and Fuels. 21:2408-2414. Interpretive Summary: Vegetable oils are promising candidates for eco-friendly lubricants, because they are derived from naturally renewable resources, are environmentally safe, possess good lubricity and viscosity-temperature characteristics. Vegetable oils have some shortcomings like poor low temperature flow properties and oxidation stability. This paper presents a systematic approach to improve their oxidation behavior by searching for a suitable additive combination. The study of antioxidant/antiwear additive synergism was investigated on a set of four antioxidants and three antiwear additives in vegetable oils using various oxidation tests. The results indicated that one additive combination showed excellent synergism and provided improved superior oxidative stability to vegetable oils. This additive combination can be used to formulate biobased lubricants for applications such as hydraulic fluids, metal working fluids, crankcase oils, drilling fluids, two-cycle engine oils, wear resistant fluids, and greases. This approach will improve the agro-economy of the locally grown renewable resource with the new markets for soybean oil.
Technical Abstract: Vegetable oils can contribute towards the goal of energy independence and security due to their naturally renewable resource. They are promising candidates as base fluid for eco-friendly lubricants because of their excellent lubricity, biodegradability, superior viscosity-temperature characteristics, and low evaporation loss. Their use, however, is restricted due to low thermo-oxidative stability and poor cold-flow behavior. This paper presents a systematic approach to improve their oxidation behavior by searching for a suitable additive combination. The study of antioxidant/antiwear additive synergism was investigated on a set of four antioxidants and three antiwear additives in vegetable oils using pressure differential scanning calorimetry (PDSC) and Rotary Bomb Oxidation Test (RBOT). The results indicate that antioxidant like zinc dialkyldithiocarbamate performed better than diphenylamine and hindered phenol. The antioxidant zinc dialkyldithiocarbamate showed excellent synergism with antiwear additive antimony dithiocarbamates.