The distillation of biodiesel fuel is a method that can provide a demonstration of the FAME content. While petroleum-based fuels such as diesel contain hundreds of different compounds (resulting in highly variable distillation curves), biodiesel generally contains 4 or 5 major compounds that boil at roughly the same temperature (approximately 330-357°C at atmospheric pressure). Compounds remaining that have higher boiling points indicate the presence of contaminants and/or leftover di- and triglycerides. ASTM D6751 specifies that at least 90% of the biodiesel sample needs to be distilled at 360°C (at a reduced pressure).
Typical boiling points for biodiesel samples at atmospheric pressure are high enough that they generally decompose/crack during distillation tests at atmospheric conditions (Test method D86). As a result, ASTM D6751 specifies the use of ASTM D1160, which conducts the distillation under a vacuum and prevents the biodiesel from decomposing. D1160 also specifies a table of 10% volume distillation levels between the initial boiling point and final boiling point of the sample to be provided. This boiling range is directly related to viscosity, vapour pressure, heating value, average molecular weight, and many other properties that could potentially be the determining factor in the suitability of the product for its intended application.