Environmental Engineering Reference
In-Depth Information
9.2.11 p
hoSphoruS
c
ontEnt
Phosphorus in FAME stems from phospholipids (animal and vegetable material) and inorganic salts
(used frying oil) contained in the feedstock (Prankl et al. 2004; White Paper 2007). The phosphorus
content of the vegetable oil mainly varies according to the process (Mittelbach 1996; Prankl et al.
2004). Cold-pressed plant oils usually contain less phosphorus than hot-pressed plant oils (Prankl
et al. 2004). Moreover, this parameter increases with the decrease of the grade of refined oil; that is,
the phosphorus content of fully refined oils is only several parts per million, whereas that of unre-
fined or water-degummed oil is more than 100 ppm (Mittelbach 1996). The phosphorus content is
highly correlated with the sulfate ash content (see Section 9.2.3) (Mittelbach 1996).
A high level of phosphorus in the fuel can increase particulate emissions and clog the filter (Nylund
et al. 2008) of the emissions control system and as a result damage the operation of the catalytic con-
verter (Mittelbach 1996; Gray 2005; Bacha et al. 2007; White Paper 2007; Rilett and Gagnon 2008).
However, its value can be reduced by various forms of degumming before transesterification (Prankl
et al. 2004) as well as by using alkaline catalysts during transesterification. Distillation of the final
product can eliminate the residual phosphorus of the fuel (Prankl et al. 2004).
A phosphorus content of 10 ppm is suspected of being the critical point from where the efficiency
of oxidation catalytic converters starts to decrease (Prankl et al. 2004). The wide use of catalytic
converters on diesel-powered equipment as well as the tight emission limits justifies the importance
of setting limits for the phosphorus content of biodiesel (Rilett and Gagnon 2008). Currently, the
CEN specification (EN 14107) is aligned with the ASTM specification (ASTM D4951) to this criti-
cal limit of 10 ppm phosphorus content. However, the CEN specification will shortly be changed to
limit phosphorus to 4 mg/kg to ensure that all biodiesel, regardless of the source, has a low enough
phosphorus content (Rilett and Gagnon 2008) to avoid long-term effects on the emission treatment
systems (White Paper 2007).
9.2.12 d
iStillation
t
EmpEraturE
, t90
Distillation temperature, T90, is an indication of the purity of the diesel. In the case of biodiesel, this
parameter is used to make sure unscrupulous blenders did not adulterate B100 with heavy petroleum
components (White Paper 2007). The distillation temperature is mainly part of the ASTM specifi-
cation (ASTM D1160) and is similar to the ester content limit used by the EU (White Paper 2007).
T90 is the temperature at which 90% of a particular biodiesel fuel distills in a standardized distilla-
tion test (Bacha et al. 2007). A high T90 may dilute the engine oil and cause difficulties during cold
start (Nylund et al. 2008). Reducing T90 slightly decreases NO
x
emissions but increases HC and CO
emissions. PM emissions are unaffected (Bacha et al. 2007).
Contrary to diesel, biodiesel exhibits a narrow boiling range rather than a distillation curve
(Bacha et al. 2007; Rilett and Gagnon 2008). This fact can be explained by the difference
between the composition of diesel (many compounds boiling at differing temperatures) and
biodiesel (contains only a few compounds) (Prankl et al. 2004). The fatty acid chains in the raw
oils and fats from which biodiesel is produced are mainly composed of straight-chain HCs with
16-18 carbons (Table 9.A1) that boil at approximately the same temperature (Prankl et al. 2004;
Bacha et al. 2007).
The atmospheric boiling point of biodiesel generally ranges from 330 to 357°C, thus the speci-
fication value of 360°C maximum for the T90 (ASTM D1160) is reasonable. This specification
was incorporated as an added precaution to ensure that the fuel has not been adulterated with high
boiling contaminants (Bacha et al. 2007; Rilett and Gagnon 2008). However, the method used is
difficult, costly, and has dubious precision. The T90 limit plays the same role as with ester content
limit (see Section 9.2.16), and currently the choice of only one method, the upgrade of the existing
methods or the replacement of both by another method, such as content of unsaponifiable material,
is discussed (White Paper 2007).
