ARS | Publication request: Efficacy of Gossypol as an antioxidant additive in biodiesel

Submitted to: Renewable Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2011
Publication Date: October 5, 2011
Citation: Moser, B.R. 2012. Efficacy of Gossypol as an antioxidant additive in biodiesel. Renewable Energy. 40:65-70.

Interpretive Summary: Biodiesel derived from soybean oil suffers from poor oxidative stability in comparison to conventional petroleum diesel fuel. Oxidative degradation of biodiesel, which commonly occurs during storage, negatively impacts important fuel properties. As a result, biodiesel which has undergone unwanted oxidative degradation no longer satisfies fuel quality standards. Therefore, antioxidant additives are commonly added to biodiesel to prevent or delay oxidative deterioration of the fuel during storage. These additives are normally synthetic and non-biodegradable, and are often derived from petrochemical feedstocks. The objective of this study was to evaluate the effectiveness of a biodegradable antioxidant obtained from a natural source at preventing or delaying oxidative degradation of biodiesel. This antioxidant is called gossypol and is found in cottonseed. When added to biodiesel, it significantly improved the storage stability by preventing unwanted oxidative degradation of the fuel. This result is important because it demonstrates the effectiveness of certain natural antioxidants as additives in biodiesel, thus displacing materials potentially derived from petrochemical feedstocks. These results will be important to biodiesel producers, distributors and end-users (customers) because a new antioxidant additive was described that improves oxidative stability of biodiesel. This research may ultimately improve market penetration, availability and public perception of domestically produced agricultural fuels, such as biodiesel, thus affording greater national independence from imported petroleum-based fuels.

Technical Abstract: The efficacy of gossypol as an antioxidant additive in fatty acid methyl esters (FAMEs) prepared from soybean oil (SME), waste cooking oil (WCME) and technical grade methyl oleate (MO) was investigated. Gossypol is a naturally-occurring polyphenolic aldehyde with antioxidant properties isolated from cottonseed that is toxic to humans and animals. At treatment levels of 250 and 500 ppm, gossypol exhibited statistically significant improvements in the induction periods (IPs; EN 14112) of SME, WCME and MO. Efficacy was most pronounced in SME, which was due to its higher concentration of endogenous tocopherols (757 ppm) vs. WCME (60 ppm) and MO (0 ppm). A comparison of antioxidant efficacy was made with butylated hydroxytoluene (BHT) and gamma-tocopherol. For FAMEs with low concentrations of endogenous tocopherols (WCME and MO), gamma-tocopherol exhibited the greatest efficacy, although treatments employing BHT and gossypol also yielded statistically significant improvements to oxidative stability. In summary, gossypol was effective as an exogenous antioxidant for FAMEs investigated herein. In particular, FAMEs containing a comparatively high percentage of endogenous tocopherols were especially suited to gossypol as an antioxidant additive.