Shelf-life of biodiesel by isothermal oxidation induction period at variable temperatures

Authors: Dunn, Robert

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2024
Publication Date: 5/15/2024
Citation: Dunn, R.O. 2024. Shelf-life of biodiesel by isothermal oxidation induction period at variable temperatures. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.12848.
DOI: https://doi.org/10.1002/aocs.12848

Interpretive Summary: New mathematical model provides more accurate calculations of the shelf-life of biodiesel during storage. Biodiesel (fatty acid methyl esters [FAME]) is a renewable biomass-based diesel fuel made from plant oils, animal fats and waste greases. Its production is increasing worldwide as more countries are moving to boost the use fuels from renewable energy sources. However, biodiesel has poor oxidative stability, an important property since the degradation of fuel during long storage periods can adversely affect its fuel quality. This research was conducted to develop mathematical models that more accurately determine the shelf-life of biodiesel made from canola, palm and soybean oil. Experimental oxidation induction period (IP) data were collected for a series of high temperatures. The IP is defined as the period of time that expires before the fuel starts to experience significant degradation caused by exposure to ambient air (oxygen). Once the mathematical models were determined, the equations were extrapolated to obtain shelf-life data at a low storage temperature. The best results were obtained from model equations correlating IP with the inverse of temperature (1/T). This was remarkable because the standard method for estimating the shelf-life used by the fats and oils industry requires a different correlation between IP and T. This research will benefit fuel producers, terminal operators and consumers that need to store biodiesel in warm weather.

Technical Abstract: Biodiesel (fatty acid methyl esters [FAME]) is a renewable biomass-based diesel (BBD) fuel made from plant oils, animal fats and waste greases. One of the main disadvantages of biodiesel is its relatively poor oxidative stability, which is caused by the presence of high concentrations of unsaturated FAME. When stored in fuel terminals, vehicle tanks and fuel systems, biodiesel can react with oxygen in ambient air, causing it to degrade, which can adversely affect its viscosity and ignition quality. The shelf-life (SL) of biodiesel is an important property that defines how long it can be stored at low temperatures. The objective of this work is to develop reliable mathematical models to estimate the SL of biodiesel at T = 25°C (298.15 K). This was done by measuring oxidation induction period with a Rancimat instrument (IP[R]) at variable temperatures. The data were analyzed by linear regression to determine In(IP[R]) as a function of T (Model A) and and T-1 (Model B) for canola, palm and soybean oil FAME (CaME, PME and SME), methyl oleate (MeC18:1) and methyl linoleate (MeC18:2). Statistical analysis of the Model A and Model B type equations showed that all inferred equations were good fits of the experimental data (adjusted coefficients of determination, R2'='0.985). The most dependable results were obtained from extrapolation of Model B type equations to predict the SLB values. For CaME, PME, SME and MeC18:1, SLB'='559.0, 1135, 378.3 and 4515 d were inferred. However, the reliability of SLA (extrapolated from its Model A type equation) and SLB values calculated for MeC18:2 (3.1 and 4.8 d) were questionable as estimates of its SL at 298.15'K.