Low Temperature Solubility Limitations of Native Oxygenated Impurities in FAME Fuels I ‐Glycerol

ABSTRACT

Solubility limitations of glycerol residuals in dry FAME blended with conventional hydrocarbon diesel fuels are determined, revealing underlying physical and compositional factors associated with cold‐induced fuel filter obstructions. Glycerol heterophases (HPs) formed in situ are captured and retained by low micron filters, aided by dramatic increases in viscosity at low temperatures. When captured, HPs can choke fuel flow through commercial fuel filters, at minimum compromising optimum fuel mileage and exhaust emissions of diesel engines. Here, the equilibrium solubilities of glycerol residues are quantified at temperatures between 2°C and 30°C, using experimental approaches designed to evaluate compositional variations expected for regulated diesel fuels in the US and EU. Comprised strictly of hydrocarbons, the complexity of commercial diesel fuel compositions was investigated with the aid of simplified mixtures that closely simulate the solubility environment. The FAME was high purity and distilled, averting stability or uncontrolled variations of commercial varieties. In addition to declines induced by lower temperature, blending with hydrocarbons brings solubilities to levels below those expected by linear dilution alone, posing a significant challenge to existing ASTM or EN restrictions on glycerol residuals in FAME. Native fuel hydrocarbons, including aromatics up to 35%v/v, intended to mitigate influences of n‐paraffins on cloud points, exhibit minimal tendencies to dissolve glycerol. Interactions with other higher molecular weight polar hydroxylated or oxo containing impurities from FAME also induced lower solubilities. The measured solubilities at low temperatures agree with the sub‐0.020%m/m estimates reported earlier for FAME involved in filter obstruction incidents.