Equilibrium Partitioning of Di-ethylene Glycol Monomethyl Ether (DiEGME) between Fuel and Aqueous Phases at Sub-Ambient Temperatures

Abstract

Improved understanding of the effect of temperature and concentration on the equilibrium partitioning of Fuel System Icing Inhibitor (FSII) additive between fuel and aqueous phases can assist in identifying required dose concentrations for safe aircraft operability. A novel experimental system was designed and used to quantify the equilibrium partitioning of the currently approved FSII, di-ethylene glycol monomethyl ether (DiEGME), under conditions relevant to actual aircraft fuel system operation. This included temperatures from ambient to −47 °C, total water contents from 130 to 560 ppmV, and initial FSII concentrations from 100 to 1500 ppmV. The partitioning of DiEGME was a strong function of temperature, exhibiting nonideal solution behavior. For a constant temperature, the resulting phase partitioning was independent of initial FSII and total water concentrations, with a single equilibrium correlation established. FSII partitioning into the aqueous phase increased with both decreasing temperature and initial FSII dose concentration in the fuel. The overall behavior was attributed to hydrophilic interactions between the glycol ether and water, which become more favored at lower temperatures and concentrations. The behavior is consistent with that expected based on the effect of temperature and concentration on the corresponding FSII activity coefficients in each phase, and has previously been observed for analogous glycol ethers. Based on the partitioning behavior, very low concentrations of FSII are expected to be sufficient to prevent water solidification to temperatures below the specification freeze point of the fuel.

Dual Action Additives for Jet A-1: Fuel Dehydrating Icing Inhibitors

“…The relationship between freezing point depression as a function of concentration is nonlinear, indicating that the freezing point of the solution does not depend solely on the concentration of the solute, indicating some nonbonded intermolecular interactions between water and the additive (i.e., hydrogen bonding). The measured freezing point values as a function of FSII concentration obtained during these studies were in agreement with those previously reported …”

“…DiEGME significantly reduced the measured freeze point and broadened the temperature range over which the phase transition occurred. The broadening of the temperature range agreement with those previously reported [37].…”

“…Differential scanning calorimetry (DSC) was used to determine the ice inhibition properties of the hydrolysis products in water, since it is a thermal analysis technique that can provide information on phase transition temperatures . It has been previously used to study the phase change characteristics of Fuel System Icing Inhibitors and jet fuels with and without additives . The freezing point of neat DiEGME is −70 °C …”

“…It has been previously used to study the phase change characteristics of Fuel System Icing Inhibitors [37], and jet fuels with and without additives [30]. The freezing point of neat DiEGME is -70 °C [37].…”

Complexities associated with nucleation of water and ice from jet fuel in aircraft fuel systems: A critical review

“…that more closely replicate actual aircraft system operation (temperature of -47 °C) were simulated. However, the study concentrated on the quantification of equilibrium partitioning of fuel system icing inhibitor (FSII) [116]. Furthermore, from work carried out by the AAIB, a fuel temperature of -35 ºC was estimated with water content between 35 and 40 ppm [1].…”