Electrical Conductivity and pH_eResponse of Fuel Ethanol Contaminants

Abstract

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.

Unified pH Measurements of Ethanol, Methanol, and Acetonitrile, and Their Mixtures with Water

“…In the case of ethanol–water mixtures, anhydrous and hydrous bioethanol fuel is required to have a solvent-specific pH (pHe) between 6.5 and 9.5 at 25.0 °C [ 17 , 33 ]. This range exists to encompass variations arising from the bioethanol production process, water content (hydrous bioethanol), and presence of additives [ 33 ].…”

“…In the case of ethanol–water mixtures, anhydrous and hydrous bioethanol fuel is required to have a solvent-specific pH (pHe) between 6.5 and 9.5 at 25.0 °C [ 17 , 33 ]. This range exists to encompass variations arising from the bioethanol production process, water content (hydrous bioethanol), and presence of additives [ 33 ]. Further, a report of ethanol–water mixtures used in the preservation of museum collections has shown a wide dispersion in the of solutions of identical measured ethanol content [ 41 ].…”

“…Although individual s pH results have been published for methanol and acetonitrile [ 4 , 31 , 32 ], the evaluation of the reliability of these results over a wider composition range are missing from the literature. Although applications of methanol and acetonitrile to liquid chromatography are combined with buffering agents [ 29 ], the use of ethanol in biofuels is un-buffered [ 33 ]. Here, measurements with un-buffered solutions, without the addition of other spectator ions, are examined.…”

Application of classical thermodynamics to the conductivity in non-polar media

“…27 Moreover, it has been recently shown that the conductivity of ethanol depends on the material of the beaker in which it is measured, with a conductivity varying from 2 to 250 µS/m for the same sigma-aldrich ethanol. 28 Therefore, it is logical to assume that the conductivity of ethanol mixed with toluene depends on the material of the glassware in which they have been mixed. In water, the pyrex glassware releases sodium and dihydrogenosilicate ions, 29 maybe it releases sodium and trihydrogenosilicate ions in ethanol.…”

Sulfate Salts in Gasoline and Ethanol Fuels -- Historical Perspective and Analysis of Available Data

“…Very little data on salt solubility in reagent grade ethanol or denatured ethanol meeting ASTM D4806 are available. Luecke and McCormick (2014) found sodium sulfate to be insoluble in reagent grade ethanol denatured with natural gasoline in a study of how salts affect denatured ethanol's electrical conductivity. A review of laboratory notes from that project shows that sodium sulfate solubility was no more than 0.3 ppm, and likely much lower.…”