2.2.2 What Is “Biodiesel?”
In its most general sense, “biodiesel” has been used to refer to any diesel fuel substitute that is derived
from renewable biomass. In the past few years, biodiesel has taken on a more specific definition and
currently refers to a family of products made from vegetable oils or animal fats and alcohol, such as
methanol or ethanol. These are called alkyl esters of fatty acids. In order for these alkyl esters of fatty
acids to be considered as viable transportation fuels, they must meet stringent quality standards, otherwise
they become standard industrial chemicals that are not suitable for diesel applications. Thus, alkyl estersLife Cycle Inventory of Biodiesel and Petroleum Diesel 5 NREL/SR-580-24089
of fatty acids that meet transportation fuel standards are called “biodiesel.” One popular process for
producing biodiesel is known as “transesterification.” This is the technology modeled in this report.
Today, biodiesel is made from a variety of natural oils. Chief among these are soybean oil and rapeseed
oil. Rapeseed oil, a close cousin of canola oil, dominates the growing biodiesel industry in Europe. In
the United States, biodiesel is being made from soybean oil because more soybean oil is produced than all
other sources of fats and oil combined. There are many candidates for feedstocks, including recycled
cooking oils, animal fats, and a variety of other oilseed crops. We selected soybean oil as the feedstock
used for biodiesel production because of the vast number of data that have been generated about biodiesel
from soybean oil.