Long-term storage oxidation stability of Karanja biodiesel with the use of antioxidants

Vegetable oils and their esters (biodiesel) undergo oxidation and degenerate more quickly than mineral diesel. The unsaturated fatty acids present in vegetable oils are susceptible to oxidation. One of the main criteria used for the quality assessment of biodiesel is ‘storage oxidation stability’. Oxidation of the esters during the long-term storage can lead to problems in the utilization of biodiesel in the engine and can lead to rough engine operation. Contact with ambient air, exposure to sunlight, metals, and exposure to high temperature conditions accelerate the oxidation reactions leading to lower oxidation stability of biodiesel. The EU biodiesel standard (EN14214) specifies a minimum value of 6 h for biodiesel induction period at 110 °C, measured using Rancimat instrument. In order to ensure the oxidation stability specification limit 6 h for biodiesel at the filling station, the initial oxidation stability at the time of production should be definitely higher than 6 h. Addition of synthetic antioxidants is an efficient way to increase the initial oxidation stability of biodiesel. Reduction in oxidation stability can be minimized during long-term storage, if biodiesel is stored in suitable conditions because some conditions lead to quick reduction in oxidation stability.Present experimental study investigates the effectiveness of five antioxidants viz. 2,6-di-tert butyl-4-methyl phenol (BHT), 2-tert butyl‐4-methoxy phenol (BHA), 2-tert butyl hydroquinone (TBHQ), 1,2,3 tri-hydroxy benzene (PY) and 3,4,5-tri hydroxy benzoic acid (PG) on the long-term storage oxidation stability of Karanja oil methyl esters (KOME), which is produced from a very popular highly unsaturated, non-edible oil feedstock for biodiesel production in Indian sub-continent. All the samples were stored in dark room and in air-tight bottles. The aim of this study is to find the most effective antioxidant and the minimum concentration of antioxidant required to meet the storage oxidation stability specifications. KOME samples were stored in different storage conditions (viz. in dark/sunlight exposure, with air/without air exposure, with metal/without metal exposure) at ambient temperature with an aim to assess the effect of storage conditions on the oxidation stability and the most appropriate conditions for biodiesel storage.

► Storage stability of KOME was evaluated for different antioxidants and concentrations.
► PY met the stability specifications of 6 h for longer time followed by PG.
► Biodiesel samples with TBHQ, BHT and BHA did not meet the storage oxidation stability criterion.
► Exposure to sunlight and air were the worst conditions for storing biodiesel.
► Indoor samples retained the oxidation stability specification limit of 6 h after longer time.
► Samples with contact to metal degraded faster than the ones without exposure to the metal.