Electrical Conductivity and pHeResponse of Fuel Ethanol Contaminants

Electrical conductivity and pH e are used in some parts of the world as fuel specification parameters for denatured fuel ethanol (DFE). Conductivity has been correlated with the presence of corrosive ions such as chloride, and high-conductivity fluids are more likely to cause electrochemical or galvanic corrosion. This study examined how electrical conductivity and pH e of DFE are affected by impurities, including sodium chloride (NaCl), magnesium chloride (MgCl 2 ), hydrochloric acid, magnesium sulfate (MgSO 4 ), sulfuric acid, acetic acid, water, and hydrocarbon denaturant. Conductivity and pH e response data were measured at impurity concentrations permissible by ASTM D4806, the most commonly used specification for DFE. Conductivity was determined to be very responsive to strong acids, NaCl, and MgCl 2, which have high solubility and dissociation constants in DFE. Molar conductivity of solutions containing these ions measured 40–60 S cm 2 /mol. Conductivity was relatively unresponsive to MgSO 4 (a salt with low solubility), water (up to 1 wt %), hydrocarbon denaturant, and acetic acid, with molar conductivities measuring <2 S cm 2 /mol. Although water produced no conductivity response, it did reduce the molar conductivity of the strong acids by 38% and increased it for MgCl 2 by 25%. Water at 1% by volume also increased the pH e value for all samples to varying degrees. Three common pH e buffering/corrosion-inhibiting additives were tested for pH e and conductivity response. The two products containing pH e buffer raised pH e by about 2 units; the stand-alone corrosion inhibitor decreased pH e by 0.5 units. Sample handling proved to be extremely important because the use of some glass containers versus high-density polyethylene (HDPE) containers resulted in background conductivity as high as 2 μS/cm and could increase pH e by more than 100%. The best results for DFE conductivity and pH e measurement are realized using ethanol-rinsed HDPE containers.