Environmental Engineering Reference
In-Depth Information
The parameters are interrelated with several other fuel quality criteria, such as sulfated ash
content and carbon residue (Mittelbach 1996), therefore they are partially limited by these param-
eters. However, some engine and fuel injection equipment manufacturers have requested a specific
limit on these metal ions, especially for vehicles with particulate traps (Prankl et al. 2004; Bacha
et al. 2007; White Paper 2007). Hence, for alkali and alkaline metals, their concentration should
be below 5 ppm as measured by the EN 14108 and EN 14109 methods and the EN 14538 method,
resp e ct ively.
9.2.15 w
atEr
and
S
EdimEnt
(w
atEr
c
ontEnt
and
t
otal
c
ontamination
)
The water content and sediment parameters are treated together or as separate parameters, with the
sediment being treated by the total contamination property.
Water is introduced into biodiesel at the final washing step of the production process. Then the
water content value has to be reduced by drying (Wörgetter et al. 1998), otherwise even a very small
quantity of water on the production point could inhibit the biodiesel and cause it to fail to meet the
water content specification at the combustion stage (White Paper 2007; ARDD 2009). Biodiesel can
fix relatively higher quantities of water than mineral diesel (Mittelbach 1996; Prankl et al. 2004;
Rilett and Gagnon 2008) and can absorb water up to a concentration of approximately 1000 ppm
during storage (Mittelbach 1996).
Free water in the biodiesel is the ideal environment for the growth of microorganisms because
they can take the nutrients required for their growth from the fuel. The higher ambient temperatures
also favor their growth. As a result, during fuel storage microorganisms can produce enough acidic
by-products to accelerate tank corrosion and enough biomass (microbial slime) to plug filters and
fuel lines (Prankl et al. 2004; Bacha et al. 2007; Rilett and Gagnon 2008). Additionally, high water
content can cause filter blockages by hydrolyzing FAME to free fatty acids. Moreover, the water
may damage the engine and injection system by causing corrosion to their chromium and zinc parts
(Kobmehl and Heinrich 1997). To avoid these effects, seals and valves of storage tanks should be
checked to prevent humidity from entering the fuel. If the water content is already high, water can
be drained (Prankl et al. 2004).
Total contamination is defined as the concentration of insoluble material retained after filtration
of a fuel sample under standardized conditions (Prankl et al. 2004; White Paper 2007). The total
contamination has turned out to be an important quality criterion because biodiesel with a high
concentration of insoluble impurities tends to cause filter blocking at filling pumps and on vehicles,
resulting in premature wear of the injection system components (Prankl et al. 2004). These effects
result from high soap and sediment concentrations (Mittelbach 2000).
To prevent biodiesel fuel from acquiring a high water content and the resulting risk of corrosion
and microbial growth, special limits were set at 0.050% v/v maximum (ASTM D2709) for water
content and sediment when they are treated together, and 500 mg/kg maximum (EN ISO 12937)
for water content and 24 mg/kg maximum (EN ISO 12662) for total contamination when they are
treated separately. Currently, ASTM is working toward the separation of water standards from sedi-
ment standards (White Paper 2007). Although only the upper limit of water content is defined, a
very low water content in biodiesel also has to be avoided because it may result in a separation phase
in blends with fossil diesel (Prankl et al. 2004; White Paper 2007).
9.2.16 E
StEr
c
ontEnt
Ester content is an indication of biodiesel's purity and sometimes a confirmation that the fuel meets
the legal definition of biodiesel (i.e., monoalkyl esters) (White Paper 2007). Biodiesel that contains
various minor components within the original fat or oil source or originates from inappropriate
reaction conditions scores a low ester content value (Prankl et al. 2004; White Paper 2007). The
