Biodiesel Standards & Properties

Hannu Jääskeläinen

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• Standard Specifications
• Engine Operation Properties
  • Low Temperature Operability
  • Lubricity
  • Cetane Number
  • Bulk Modulus of Compressibility
• Fuel Quality Properties
  • Fuel Stability
  • Acid Number
  • Ester Content
• Contaminates
  • Glycerin
  • Water and Sediment
  • Phosphorus
  • Metals
  • Sulfur
  • Ash/Sulfated Ash
  • Carbon Residue
• Distillation Temperature
• Flash Point
• Kinematic Viscosity
• Copper Strip Corrosion

Standard Specifications

Development of biodiesel standards started in the 1990s, to support the increasing use of alkyl esters-based biodiesel and its blends as automotive fuels. ASTM International (formerly American Society for Testing and Materials) adopted a provisional specification PS121 for biodiesel in 1999. The first ASTM standard (ASTM D6751) was adopted in 2002 [767]. In Europe, EN 14214 biodiesel standard (based on former DIN 51606) was finalized in October 2003. The US and EU standards have international significance; they are usually the starting point for biodiesel specifications developed in other countries (see also Fuel Regulations).

Approaches to US and EU standards for biodiesel differ. In the USA, ASTM D6751 establishes specifications for a biodiesel blend stock for middle distillate fuels. While the specification was written for B100, it is not intended for neat biodiesel used as automotive fuel. Rather, it is for the biodiesel component that is to be blended to produce biodiesel/diesel fuel blends. ASTM D6751 defines several grades of biodiesel based on sulfur content, low temperature properties and the concentration of metals. Early versions of the standard defined two grades based on sulfur—one grade with a maximum sulfur limit of 15 mg/kg and the other with a maximum sulfur limit of 500 mg/kg. In 2012, two additional grades were added based on low temperature properties: grade 2-B (identical to biodiesel defined by earlier versions of the standard) and grade 1-B with tighter controls on monoglycerides and cold soak filterability. In 2023, two low metal, ultra-low sulfur grades were added with a limit on Na+K+Ca+Mg of 4 mg/kg [6181]. Two automotive standards for biodiesel/diesel fuel blends have been published by ASTM:

• The ASTM Standard Specification for Diesel Oil, ASTM D975, was modified in 2008 to allow up to 5% biodiesel to be blended into the fuel.
• ASTM D7467 is a specification for biodiesel blends from B6 to B20.

In Europe, standard specifications have been developed for unblended FAME diesel fuel as well as for certain higher level biodiesel blends, while low level blends are covered by EN 590, the European diesel fuel specification:

• EN 14214 establishes specifications for fatty acid methyl esters for diesel engines. In contrast to ASTM D6751, B100 that meets this standard could be used unblended in a diesel engine (if the engine has been adapted to operate on B100) or blended with diesel fuel to produce a blend in accordance with EN 590 or other applicable standards. EN14214:2012 introduced a number of changes including an expansion of the scope to cover heating oil applications and updates to cover blends up to B10. An additional set of climatic classes based on monoglycerides content was also established.
• Biodiesel/diesel fuel blends up to B7 are covered by EN 590. EN 590:2004 allowed blends up to 5% of fatty acid methyl ester (FAME) in diesel fuel while EN 590:2009 increased the allowable FAME content to 7%.
• EN 16709, introduced in 2015, covers B20 and B30 blends for use by captive fleets. The FAME component in EN 16709 is required to comply with EN 14214 and the diesel component with EN 590.
• A standard similar to EN 590, EN 16734, covering blends up to B10 was published in 2016.

Biodiesel specifications and test methods according to ASTM D6751 and EN 14214 are compared with those of petroleum diesel in Table 1. Both ASTM D6751 and EN 14214 establish specifications for key fuel properties for biodiesel—the former for the biodiesel blend component, the latter for both blend stock and neat biodiesel automotive fuel. Table 1 is intended only as a general comparison between the different fuels and the standards shown do not represent the latest versions. More up-to-date summaries of the standards can be found under Fuel Regulations.

The US specification, ASTM D6751, defines biodiesel as mono-alkyl esters of long chain fatty acids derived from vegetable oils and animal fats. The type of alcohol used is not specified. Thus mono-alkyl esters could be produced with any alcohol (methanol, ethanol, etc.) so long as it meets the detailed requirements outlined in the fuel specification. By requiring that the fuel be mono-alkyl esters of long chain fatty acids, other components, with the exception of additives, would inherently be excluded.

The European biodiesel specification, EN 14214, is more restrictive and applies only to mono-alkyl esters made with methanol, fatty acid methyl esters (FAME). The minimum ester content is specified at 96.5%. The addition of components that are not fatty acid methyl esters—other than additives—is not allowed.

Guidelines for B100 used to make biodiesel/diesel fuel blends have also been adopted by automobile and engine manufacturers from North and South America, Europe and Asia [1849]. These guidelines bear some resemblance to EN 14214 but there are some notable differences including:

• limiting blends to B5 maximum,
• increasing oxidation stability of B100 to 10 h,
• introduction of an oxidation stability requirement for blends that limits the increase in TAN to less than 0.12 mg KOH/g,
• reducing the sulfated ash limit to 0.005% from 0.02% and introducing an ash limit of 0.001%,
• introduction of a ferrous corrosion limit,
• addition of free water and sediment limit,
• loosening of limits for kinematic viscosity, iodine number and flash point,
• labeling pumps dispensing any blend—including B5 or less.

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