The effect of tetrethylenepentamine (TEPA) on the oxidation stability and the lubrication performance of biodiesel

•Evaluated the superior performance of TEPA as a biodiesel antioxidant.•The oxidation reaction product of TEPA is a strong free radical inhibitor.•TEPA can significantly improve the lubricating performance of biodiesel.•High viscosity and chelating metal properties promote TEPA to improve lubricity. The oxidation stability and lubrication properties of biodiesel have been the focus of research, this study focuses on the oxidation and lubrication properties of TEPA on biodiesel and its anti-oxidation and lubrication mechanisms. The Rancimat method was used to study the oxidation resistance of TEPA. The results showed that when 3‰ of trace TEPA was added, the oxidation performance of Jatropha biodiesel was improved by 11.41 times, and the stability factor of TEPA's antioxidant activity is greater than 1 under micro conditions, and the oxidation resistance was significantly improved. The kinetic parameters and thermodynamics of the oxidation degradation process of TEPA were analyzed. The results showed that the kinetic activation energy was 86.756 kJ mol−1, the reaction order was 1, the frequency factor A is 1.235 × 1011, the thermodynamic activation entropy was −43.059 J mol−1 K−1, by the results shown, the existence of an endothermic and non-spontaneous process and the antioxidant product of TEPA was a good free radical inhibitor. The High Frequency Reciprocating Rig (HFRR) was used to study the lubricating performance of TEPA for Jatropha biodiesel at different temperatures (40 ℃–80 ℃) and different adding amount (0–2.5 wt.%). The average friction coefficient of Jatropha biodiesel with the addition of 2.5‰ TEPA decreased by 88.89 % (at 40 ℃), and the lubrication performance was greatly improved, However, the increase in temperature will have a greater impact on the lubrication improvement effect of TEPA. When the experimental temperature is, 50 ℃, 60 ℃, 70 ℃, 80 ℃, the average friction coefficient when adding 2.5‰ TEPA decreases respectively. 81.82 %, 76.92 %, 57.14 %, 52.94 %, the lubrication improving effect of Jatropha biodiesel gradually decreases. The high viscosity characteristics of TEPA and the ability to chelate metal ions in biodiesel are the main reasons for improving the lubricating performance of biodiesel.