What’s the Difference between Biodiesel and Renewable (Green) Diesel?
editor’s note: We have observed confusion in conversations about biodiesel and renewable diesel. Just as many people ask for a “Kleenex” when they have a cold, many people say “biodiesel” for any kind of diesel derived in part of recently living biomass, including animal processing and cooking residues. This paper focuses on legal and technical definitions of the terms “biodiesel” and “renewable diesel.”
by Jesse Jin Yoon (Advanced Biofuels USA) With the intensifying search for a sufficient alternative to oil-based energy, the development of alternative energy sources becomes increasingly relevant. Fuels derived from biomass or biological sources have received much attention. Among the various alternative fuel options, biodiesel and renewable diesel have been gaining traction in popularity.
Although both fuels can be derived from biomass, they are two distinctly different fuels. The purpose of this paper is to define both fuels and provide a general comparison between the two fuels.
…Biodiesel is produced using a transesterification process, “reacting vegetable oils or animal fats catalytically with a short-chained aliphatic alcohol (typically methanol or ethanol).” Glycerol is a by-product of this transesterification process. 
Biodiesel is defined under the standard of ASTM D6751 as “a fuel comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats.” Biodiesel is also referred to as FAME (fatty acid methyl ester) or RME (rape seed methyl ester) in Europe.
…Biodiesel is chemically different from petrodiesel and renewable diesel because it contains oxygen atoms (note the “O” in the biodiesel (3) structure above). This leads to different physical properties for biodiesel. 
…Renewable Diesel, often called “green diesel” or “second generation diesel,” refers to petrodiesel-like fuels derived from biological sources that are chemically not esters and thus distinct from biodiesel. Renewable diesel is chemically the same as petrodiesel, but it is made of recently living biomass. 
In addition, the terms renewable diesel and green diesel have been further distinguished based on the processing method to create the fuel with petrodiesel-like chemical composition. A brief description of this can be found in the appendix. 
For the purpose of this discussion, the term “renewable diesel” will refer to all diesel fuels derived from biomass that meet the standards of ASTM D975 and are not mono-alkyl esters.
The definition of renewable diesel is not as straight forward as that of biodiesel. The term “renewable diesel” has been defined separately by the Department of Energy (DOE) with the Internal Revenue Service (IRS) and the Environmental Protection Agency (EPA). READ MORE and MORE and MORE (Pennsylvania State University paper on the difference between biodiesel and petroleum diesel) and MORE (Diesel Technology Forum) Download paper