Inorganic Chloride
Very low levels of chloride ions can be corrosive to many metals. Inorganic chloride content can be determined by ASTM test methods D7319 and D7320. Note: Ethanol producers need to be aware of why these properties are limited. Moreover, various process changes may affect some properties such as inorganic chloride or sulfate. Any time a process change is implemented the producer should run tests to ensure that the finished product still meets the requirements of ASTM D4806. Similar action should be taken in the event of a process upset or temporary malfunctions.
16.1.3 ASTM D 5501 — GC Analysis for Ethanol, Methanol and Denaturant
The US standard ASDM D 4806 requires the fuel ethanol to contain a minimum of 92.1% ethanol, maximum of 0.5% by volume methanol and 1.96-5.0% by volume of denaturant. The analysis and monitoring of these parameters are accomplished by following analytical method ASTM D5501 — Determination of Ethanol Content of Denatured Fuel Ethanol by Gas Chromatography (GC). The GC method ASTM D5501 specifies the use of temperature program and a flame ionization detector to analyze the sample on a long polydimethylsiloxane capillary column, such as the Supelco Petrocol™ DH 150. Suggested analysis conditions and typical gas chromatogram for gasoline denatured fuel ethanol is shown in Figure 16.1. Low boiling methanol elutes before ethanol and hydrocarbon compounds in gasoline added as the denaturant elutes after ethanol. The sum of hydrocarbon peaks is used as the quantitative measure for denaturant.
The method cites establishing peak identification, followed by the quantitation of ethanol. The identification of ethanol and methanol is performed by injecting into the GC column a mixture containing known amounts of each alcohol in proportion to what is expected in the final blend, using и-heptane as a solvent. Retention times of the fuel ethanol sample are then compared to the analytical standard to verify identity. Quantitation requires preparation of six multi-component calibration solutions, each containing ethanol, methanol and и-heptane in varying concentrations, to establish a linearity curve for the GC system.