Environmental Engineering Reference
In-Depth Information
can serve to illustrate the potential effect on cloud point and thus cold flow. The melting point of
methyl palmitate is approximately 30°C, and that of methyl stearate is 38°C, but that of methyl
oleate is -20°C. Again, chain length and degree of unsaturation have a significant influence on this
property. Because of the different requirements on cold flow caused by time of year and geographic
location, cold flow is a “soft” specification in biodiesel standards, with a report for cloud point being
required by ASTM D6751 and limits varying by time of year and location using a method termed
the “cold filter plugging point” are prescribed in EN 14214. It is important to note that improvement
of biodiesel properties is rendered difficult because improvement of cold flow (e.g., less saturates,
more unsaturates) negatively affects oxidative stability and cetane number and vice versa.
33.1.2 h
iStorical
p
ErSpEctivES
The first vegetable oil to be tested in a diesel engine was peanut oil (Diesel 1912, 1913). This
event occurred at the 1900 World Exhibition in Paris at the request of the French government as
the inventor of the diesel engine, Rudolf Diesel (1858-1913), himself states (Diesel 1912). Diesel
experimented later with vegetable oils and expressed support for the concept (Diesel 1912). There
is abundant literature dating from the 1920s to the late 1940s describing the use of vegetable oils as
diesel fuel (Knothe 2005). Interestingly, a theme in many of these reports was to provide the tropical
colonies of European countries with a domestic source of fuel to ensure some degree of energy
independence. Accordingly, the first description of what is today known as biodiesel, the mono-
alkyl esters of vegetable oils or animal fats (or other lipid feedstocks), can be found in the Belgian
patent 422,877 issued in 1937 (Chavanne 1937). A later report provides considerably more details on
this project, mainly concerned with the ethyl esters of palm oil, including the first commercial bus
running on this fuel (van den Abeele 1942). Several reports from this time describe or summarize
the use of various vegetable oils as fuel (Walton 1938; Chowhury 1942; Pacheco Borges 1944).
Vegetable oils in addition to the aforementioned peanut and palm oils that were investigated in
“historic times” include castor, cottonseed, olive, rapeseed, soybean, sunflower, and others (Knothe
2005 and references therein); however, no fuel meeting the current definition of biodiesel was
prepared from them.
Table 33.1 lists vegetable oils that are emerging energy feedstocks by their common names and/
or their scientific names and provides relevant literature references. Table 33.2 provides the fatty
acid profiles of the oils listed in Table 33.1 as far as they have been reported. Tables for analytical
data and fuel property data for these oils are not provided here, although the original literature
often reports such data. However, many literature data do not appear to stand up to close scrutiny
of their correctness. A major issue is kinematic viscosity which in many cases in the literature
appears to be too high (often by ~0.5-1 mm
2
/s) to be correct and may be an indication of incomplete
conversion of the investigated oil to biodiesel. Other data, such as cetane number and properties
related to cold flow, also do not always appear correct. For example, some papers may mention
the “melting point” of an oil or fat or the corresponding biodiesel fuels, but, because of their
multicomponent nature, this is not correct; instead, these materials have cloud and pour points
(i.e., melting ranges). Therefore, analytical or fuel property data will only be mentioned in the
text for some oils, which are discussed in more detail. However, considering that most biodiesel
fuels obtained from feedstocks discussed in this chapter largely contain the five major fatty acids
previously mentioned in their fatty acid profiles, most of these fuels will, if properly prepared,
meet the specifications in biodiesel standards. Note also that various methods have been used for
preparing the biodiesel fuels referenced here, also taking into consideration the various degrees
of refining of the available feedstocks. Many of these oils exhibit high contents of free fatty acids
which make acid pretreatment necessary before the usual alkaline transesterification to biodiesel.
Furthermore, exhaust emissions tests have been performed on the biodiesel fuels obtained from
some of these oils, with the results generally agreeing with the exhaust emissions tests conducted
with biodiesel fuels derived from commodity oils.
