Investigations on Gradual and Accelerated Oxidative Stability of Karanja Biodiesel and Biodiesel–Diesel Blends

Abstract

One of the major limitations that hinder widespread application of biodiesel in automotive engines is its poor oxidative stability, which in turn depends upon methyl ester constituents of biodiesel as well the storage conditions. Hence, a relative assessment of the oxidative stability of biodiesels across the different parts of the world is rather difficult. In the present work, oxidative stability of biodiesel based on the ASTM D4625 accelerated oxidative stability test is compared with that of gradual oxidation under two different long-term storage conditions, namely, open to air and sunlight and closed to air and sunlight. Neat Karanja biodiesel and its blends with diesel at 25, 50, and 75% by volume are used for the present study. The important physicochemical properties of fuel samples are measured at regular time intervals to evaluate the rate of oxidation and the extent of fuel quality degradation. The results obtained show that neat Karanja biodiesel stored under open to air and sunlight conditions has the highest rate of oxidation and fuel quality degradation with a 32% increase in kinematic viscosity, 1.5% increase in density, and 3% decrease in calorific value. The acid value of all the tested fuel samples increased beyond ASTM and EN standard specification limits within the first 3 months of storage period. The peroxide value showed a steep increase during the first 6 months of storage period and decreased afterward. The effects of adding the TBHQ antioxidant in Karanja biodiesel at varying concentrations are also evaluated based on the measured Rancimat induction period, and it is observed that 250 ppm TBHQ is required to meet EN 41214 standard specifications for biodiesel. No correlations are found to exist between the properties of fuel samples stored under gradual and accelerated oxidation conditions. However, adopting the ASTM D4625 standard test method to evaluate the storage stability of biodiesel avoids any ambiguity owing to the variations in the storage and the ambient conditions across the different parts of the world.

Abiding effects of phenolic antioxidants on oxidative behaviour of fatty acid methyl esters derived from waste cooking oil

“…All the WCO biodiesel samples with antioxidants easily met the biodiesel standard limits for viscosity even after 6 months of storage, while fresh WCO biodiesel fuel sample exceeded the highest limit set by the EN or ASTM standard in 6 months of storage period. In the case of fuel samples stored at 43 ℃, neat Karanja biodiesel crossed the maximum limit set by the ASTM standard specifications (ASTM D4625-16e1 ( 2016)) within 4 months of storage (Suraj et al 2019). Karavalakis et al (2011) reported that viscosity increases over 10 weeks of storage time for B10 with synthetic antioxidants (BHT, BHA, PG, PY, and TBHQ); all values are within the limit of standard.…”

“…The higher rate of increasing acid value of test samples in lower concentrations (100 and 250 ppm) and fresh biodiesel samples at stored conditions was due to a higher rate of secondary oxidation. After two months of storage periods at 43 °C, Karanja biodiesel without antioxidant failed to meet the biodiesel standard (ASTM D4625-16e1 ( 2016)) (Suraj et al 2019). The acid value increased over 10 weeks of storage time for B7, B10, and B20 with synthetic antioxidants (BHT, BHA, PG, PY, and TBHQ), but all values were within the limit of the standard according to Karavalakis et al (2011).…”

“…Yang et al (2013) studied the influences of TBHQ, PG, PY, BHA, BHT at 3000 ppm concentration on the oxidation stability of soybean biodiesel and found that the synthetic antioxidants are more effective in the rank order as PY˃TBHQ˃PG˃BHA˃BHT. Suraj et al (2019) observed that 250 ppm TBHQ meet biodiesel fuel blend stock for middle distillate fuels standard (ASTM D4625-16e1 ( 2016)) after 100 days of storage.…”

“…Fatty acid methyl esters containing more poly unsaturation double bonds in the structure are more prone to oxidation to produce primary products hydroperoxides. These primary products mostly decompose and form secondary oxidation products at suitable conditions (Suraj et al 2019). The secondary oxidation products are usually alcohols and aldehydes such as propanal, hexanal, etc.…”

“…It is essential to observe kinematic viscosity during the storage period. In the storage time, kinematic viscosity increases periodically during storage time because hydroperoxides decompose, and finally, it will create polymeric products by oxidation (Suraj et al 2019). Sometimes fatty acid methyl esters lead to the isomerization reaction of double bonds in a long-chain structure such as cis to trans,enlarging kinematic viscosity.…”