Abstract
We present a new concept of implementing natural, hydrophilic antioxidants in lipophilic biofuels without the necessity of classical surfactants. Hydrotropic glycerol derivatives are used to solubilise hydrophilic anti-oxidative agents in biofuels, such as fatty acid methyl esters (FAME). This concept has several advantages, as the antioxidants are obtainable from plants and usually significantly ...
Abstract
We present a new concept of implementing natural, hydrophilic antioxidants in lipophilic biofuels without the necessity of classical surfactants. Hydrotropic glycerol derivatives are used to solubilise hydrophilic anti-oxidative agents in biofuels, such as fatty acid methyl esters (FAME). This concept has several advantages, as the antioxidants are obtainable from plants and usually significantly less hazardous than the synthetic antioxidants, such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) or hydroquinone (HQ), currently used in industry. Additionally, the hydrotropes - or better termed "oleotropes" here - used to solubilise the natural antioxidants exhibit favourable fuel properties, while being obtained by simple addition reactions with glycerol - a largely generated by-product during the biodiesel production in industry. Even more, certain natural antioxidants, such as gallic acid, are shown to exhibit significantly better anti-oxidative properties than their synthetic counterparts. In this context, the polar paradox theory is discussed, proposing that potent antioxidants for biofuels should be hydrophilic and exhibit a low solubility in the fuel. Additionally, the efficacy of phenolic antioxidants is correlated with the bond-dissociation enthalpy (BDE) of their phenolic ArO-H bonds and catechol as well as pyrogallol moieties are concluded to represent key structures for effective antioxidants in biofuels. This is shown by investigating the effects of antioxidants on the oxidative stabilities of FAME/rapeseed oil mixtures and a commercial biofuel. Lastly, the presented concept is further extended to use certain glycerol derivatives first to extract natural, hydrophilic antioxidants from a polyphenol-rich plant, and then to effectively stabilise biofuels with the extraction mixture.
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