Environmental Engineering Reference
In-Depth Information
The analysis presented here was based on the specifications, methods, and limits on biofuel qual-
ity set by ASTM International (United States) and the European Committee for Standardization
(CEN; European Union). The existing standards from ASTM International and CEN are mainly
used as examples because of their worldwide use. In the case of bioethanol, the Brazilian specifica-
tions will also be mentioned because of the lion's share that Brazil owns in the bioethanol market.
At the same time, the current and future quality of biofuels is based on the requirements of these
specifications, and at the same time these specifications are adjusted to the fuel quality that produc-
ers manage to achieve as a result of several influences, such as the demand of the market, the climate
conditions of each region, the existing technology and infrastructure, and so on.
A general observation is that for the control of biodiesel quality, more sophisticated and chal-
lenging standards are required than for that of bioethanol. This could be explained from the follow-
ing factors:
• Bioethanol consists of a single chemical compound (i.e., ethanol), whereas biodiesel can be
derived from several feedstocks, such as animal fat, vegetable oil, and used fried oil, with
various chemical compositions (e.g., from saturated to polyunsaturated fatty acids with
different length chains). These variations are reflected in the final product.
• Bioethanol feedstock is derived almost exclusively from one country, Brazil. The feed-
stocks of biodiesel are more widely distributed, so biodiesel has many different regulations
that have to be respected and met, as well as climate conditions that influence some of its
characteristics.
• Fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) can be called biodies-
els. However, these two chemicals do not have the same properties (see Section 9.2.19) and,
as a result, nor do the final products.
Given that some fuel specifications (e.g., sulfur content and cloud or cold filter plugging point)
depend on given national regulations, the examination of the fuel quality in several countries also
has to be presented. This overview provides a better view of the current fuel quality situation and
future trends as well as demonstrates the differences of specifications related to the climate and the
feedstock preferred as well as the biofuel trade pathways in-between.
9.2 BIodIesel
9.2.1 f
laSh
p
oint
Flash point is a measure of the flammability of fuels; that is, the tendency of fuel to form a
flammable mixture with air (Prankl et al. 2004; White Paper 2007). At the same time, the flash
point for biodiesel is an indirect control of the level of the nonreacted alcohol remaining in the
finished fuel (i.e., the free monoalcohol; Mittelbach 1996; Costenoble 2006; Bacha et al. 2007;
White Paper 2007; De Klerk 2008; Rilett and Gagnon 2008) given that a very small amount of
residual alcohol will reduce the flash point greatly (Prankl et al. 2004; Foon et al. 2005; White
Paper 2007). Thus, the flash point for biodiesel is an important safety criterion of its handling and
storage (Prankl et al. 2004; Costenoble 2006; White Paper 2007) that is not directly related to
engine performance (Bacha et al. 2007). Moreover, alcohol residues of biodiesel can also affect
fuel pumps, seals, and elastomers (Foon et al. 2005). It should be noted that the flash point of
biodiesel is approximately double the value of that for diesel (Prankl et al. 2004; White Paper
2007; see Table 9.2).
The main reason for this difference is that the composition of the naturally occurring oils and
fats of biodiesel (i.e., long fatty acid chains) means that it has a high flash point. The composition of
biodiesel varies within a small range regardless of the feedstock (Table 9.2; Prankl et al. 2004), so
the flash point is process dependent rather than feedstock dependent. Hence, the flash point serves
