Environmental Engineering Reference
In-Depth Information
Table 1
Comparison between petrodiesel and biodiesel
Properties
have the same physical properties (temperature
stability, energy content, etc.) as petroleum die-
sel and other biomass-based diesels (National
Renewable Energy Laboratory
2009
). Therefore,
biodiesel can only be used interchangeably to a
limited extent in the form of blends and in the
few engines that are specifi cally designed to
handle pure biodiesel (B100).
The reason for the differences in physical
characteristics is the different types of mole-
cules that constitute biodiesel and petroleum
diesel. Biodiesel is composed of straight chain
hydrocarbon esters that have one oxygen atom
per molecule; petroleum diesel is composed of
non-oxygenated straight and cyclic hydrocarbon
chains. Biodiesel does not meet all of the stabil-
ity, distribution, and engine requirements of
standard diesel fuels because the compound
includes oxygen, called esters. The use of pure
biodiesel in the existing infrastructure can cause
problems during transportation through pipe-
lines and when used in engines; however, these
diffi culties can be managed without a substan-
tial amount of monetary costs (McElroy
2007
).
A comparison between petro-diesel and bio-
diesel is shown in Table
1
.
Microalgae are one of the most promising
alternative and renewable feedstock sources for
production of third-generation biodiesel.
Microalgae have been found to have incredible
oil production levels when compared with other
oil seed crops such as soybeans, palm oil, etc.
Biodiesel from microalgae is a sustainable devel-
opment as they are carbon neutral, or reduce
atmospheric CO
2
as they are carbon negative
(Naik et al.
2010
). It is estimated that 1.8 tonnes
of CO
2
would be consumed (180 % reduction) by
each tonne of microalgal biomass produced. This
chapter mainly focused on microalgae as a poten-
tial source of biodiesel production.
Petrodiesel
Biodiesel
Lower heating value
(Btu/gal)
~129,050
~118,170
Kinematic viscosity
@ 40 °C (mm
2
/s)
1.3-4.1
1.9-6.0
Specifi c gravity
@ 40 °C (Kg/l)
0.85
0.88
Density (lb/gal)
7.079
7.328
Water and sediment
(% volume)
0.05 max
0.05 max
Carbon (wt.%)
87
77
Hydrogen (wt.%)
13
12
Oxygen
0
11
Sulfur (wt.%)
0.0015
0.0-0.0024
Boiling point (°C)
180-340
315-350
Flash point (°C)
60-80
130-170
Cloud point (°C)
−15 to 5
−3 to 12
Pour point (°C)
−35 to −15
−15 to 10
Cetane number
40-55
47-65
Oxidative stability
-
3-6 min
Lubricity SLBOCLE
(grams)
2,000-5,000
>7,000
Lubricity HFRR
(microns)
300-600
<300
Adapted from Crimson Renewable Energy, LP;
http://
pdf
; Knothe (
2010
) and Hemaiswarya et al. (
2012
)
HFRR = High Frequency Reciprocating Rig,
SLBOCLE = Scuffi ng Load Ball-on-Cylinder Lubricity
Evaluator
right oils to be converted to biodiesel. However, a
microscope becomes superfl uous when it comes
to visualizing the potential of these organisms for
biofuel production (Fig.
1a-e
). With improved oil
and biomass yield, algae can produce a consider-
ably higher level of biomass and lipids per hect-
are than terrestrial biomass. Most microalgae are
found in freshwater and marine environments; a
few grow in terrestrial habitats. But the choice of
microalgae species for cultivation is based on
their lipid and biomass productivity as well as
cultivation location. Marine and freshwater
species have shown similar biomass and lipid
productivities, thus making strain selection
dependent on other factors (Ahmad et al.
2011
).
Some of the fresh and marine water microalgae
and their lipid productivity (% dry weight) are
shown in Table
2
.
3
Microalgae
Microalgae are microscopic aquatic (freshwater
or marine forms) photosynthetic plants that
require the aid of a microscope to be seen and can
be measured in microns. Microalgae have the
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