Biomedical Engineering Reference
In-Depth Information
the second stage is also dehydration, this time over a zeolite catalyst, ZSM-5,
to give gasoline.
2CH
3
OH
-ð
H
2
O
Þ-
CH
3
OCH
3
-ð
H
2
O
Þ-
C
2
C
5
-
paraffins
1
aromatics
1
cycloparaffins
420
C
alumina catalyst ZSM catalyst
320
C
300
400
(11.21)
where (
H
2
O) represents the dehydration step.
The typical composition of the gasoline in weight percentage (see
nzic.
org.nz/ChemProcesses/energy/7D.pdf
) is as follows:
2
Highly branched alkanes: 53%
Highly branched alkenes: 12%
Napthenes: 7%
Aromatics: 28%.
The dehydration process produces a large amount of water. For example,
from 1000 kg of methanol, 387 kg of gasoline, 46 kg of liquefied petroleum
gas, 7 kg of fuel gas, and 560 kg of water are produced (Adrian et al., 2007).
Figure 11.7
shows a simplified scheme for the production of gasoline from
methanol. This gasoline, sometimes referred to as MTG, is completely com-
patible with petrogasoline.
11.5.3 Diesel
Generally, the oil burnt in a diesel (compression-ignition) engine is called
diesel. If produced from petroleum, it is called petrodiesel, and if produced
from biomass, it is called biodiesel. Mineral diesel (or petrodiesel) is made
up of a large number of saturated and aromatic hydrocarbons. The average
chemical formula can be C
12
H
23
. Petrodiesel (also called fossil diesel) is pro-
duced from the fractional distillation of crude oil between 200
C and 350
C
at atmospheric pressure, resulting in a mixture of carbon chains that typically
contain between 8 and 21 carbon atoms per molecule (Collins, 2007).
According to the American Society for Testing and Materials (ASTM),
biodiesel (B100) is defined as a fuel comprised of mono-alkyl (methyl) esters
of long chain fatty acids derived from vegetable oils or animal fats, and
meeting the requirements of ASTM D 6751. Biodiesel's characteristics are
similar to those of petrodiesel but not identical. Biodiesel, which can be
mixed with petrodiesel for burning in diesel engines, has several positive fea-
tures for use in engines, and are as follows:
Petrodiesel contains up to 20% polyaromatic hydrocarbon, while biodiesel
contains none, making it safer for storage.
Biodiesel has a higher flash point, making it safer to handle.
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