Environmental Engineering Reference
In-Depth Information
taBle 9.5
the density (15
°
c) of Biodiesel in europe
value
unit
EN 14214
860-900
kg/m
3
Minimum
879.3
mm
2
/s
Maximum
885.7
mm
2
/s
Average
883.4
mm
2
/s
Standard deviation
1.2
mm
2
/s
Range 95% maximum
885.8
mm
2
/s
Range 95% minimum
881.0
mm
2
/s
Out of specification
0
-
Source:
European Biodiesel Board (EBB),
EBB European Biodiesel Quality Report (EBBQR)—
Results of the Third Round of Tests (Winter 2007/2008),
European Biodiesel Board,
Brussels, Belgium, 2008.
Samples from 39 biodiesel plants in Europe. Sampling period January to February 2008.
Variations in fuel density therefore result in nonoptimal exhaust gas recirculation rates for a
given load and speed point in the engine map and, as a consequence, influence the exhaust emission
characteristics (WWFC 2006). Low fuel density reduces PM and slightly reduces carbon dioxide
(CO
2
) emissions from all diesel vehicles and NO
x
emission from heavy-duty vehicles but increases
fuel consumption and reduces power output (WWFC 2006). However, the emission influence of fuel
density concerns mainly older technology engines and not modern engines with electronic injection
and computer control (Lee et al. 1998).
The density of biodiesel depends on the feedstock (Mittelbach 1996), and in general the density
of a biodiesel blend is higher than that of the base diesel (White Paper 2007; Nylund et al. 2008).
Density increases with decreasing chain length and increasing number of double bonds of biodiesel
fatty acid composition (Prankl et al. 2004; White Paper 2007); that is, high-density values for fuels
are derived from feedstocks with many unsaturated compounds, such as sunflower oil and linseed
oil (Prankl et al. 2004). Also, the density of biodiesel depends on the fuel purity and is decreased by
the presence of low-density contaminants, such as methanol (White Paper 2007).
In general, density limits are in the range of 860-900 kg/m
3
at 15°C (ISO 3675/12185). However,
fuels that meet the other specifications fall between these limits (Table 9.5), and some countries
(e.g., the United States and Brazil) doubt the need of this specification (White Paper 2007).
9.2.19 E
thanol
and
m
Ethanol
c
ontEnt
During the transesterification process for the production of biodiesel, vegetable oil or animal fat
reacts with a catalyst (usually sodium hydroxide) and methanol or ethanol to form one of two fatty
acid esters, FAME or FAEE, respectively, and glycerin (also called glycerol) (Combs 2008). The
remaining alcohol (methanol or ethanol) is removed by distillation or by repeated aqueous wash-
ing steps (Prankl et al. 2004). Methanol is most commonly used and the least expensive (McGill
et al. 2008), has a short chain, and is polar (Khan 2002). However, ethanol is less toxic (Singh
2005; Nylund et al. 2008), less corrosive, and more soluble than methanol (Nylund et al. 2008); and
biodiesel produced has improved cold-flow properties (McGill et al. 2008).
Even a low methanol or ethanol content can greatly reduce the flash point (Foon et al. 2005),
posing safety risks in biodiesel handling and storing (Prankl et al. 2004) (see impacts from the flash
point reduction in Section 9.2.1). Methanol or ethanol has high volatility that can cause fuel system
corrosion, low lubricity, and adverse effects on injectors as well as harm some materials in fuel
