Biomedical Engineering Reference
In-Depth Information
Table 17. Properties of supercritical and conventional transesterification
Properties
Supercritical
Conventional
Catalyst required
NO
YES
Reaction time
Second to minutes
Minutes to hours
200-300
50-80
Reaction Temp. (
℃
)
Pressure (bar)
100-200
1
Free fatty acid sensitive
NO
YES
Water sensitive
NO
YES
Pretreatment
NO
YES
Catalyst removal
NO
YES
Soap removal
NO
YES
Table 18. Critical state of various solvents studied and their pressure in batch-type
reaction system for designated temperatures
Critical
temperature(
℃
)
Pressure
Critical
pressure (MPa)
Solvent
270
℃
300
℃
350
℃
Methanol
239
8.09
43
20
17
Ethanol
243
6.38
25
15
-
1-Butanol
290
4.41
23
10
-
Methyl formate
214
6.00
31
-
5
Diiosprophy ether
227
2.88
12
-
5
Post-Reaction Processing
A common issue with biodiesel is its stability in oxygen environments. In the presence of
oxygen, it can hydrolyze to alcohol and acid [37]. When alcohol and acid are formed, this
reduces the flash point and increases acid number of the fuel [37]. A solution is to include
antioxidants in the biodiesel. The two most common types are phenolic-types and aminic-
types, whose mechanisms are shown in Figure 19. They basically work by interrupting the
chain oxidation process [37]. The stability problem is especially pertinent to Jatropha oil
based biodiesel [36, 37].
Biodiesel Quality Control
Biodiesel processing and quality are closely related. The processes used to refine the
feedstock and convert it to biodiesel determine whether the fuel will meet the applicable
specifications. The primary criterion for biodiesel quality is adherence to the appropriate
standard. In the United States, this standard is ASTM D 6751-02 “Standard Specification for
Biodiesel Fuel (B100) Blend Stock for Distillate Fuels” and EN14214 standard for European
union. Generally, the fuel quality of biodiesel can be influenced by several factors:
•
The quality of the feedstock.
•
The fatty acid composition of the parent vegetable oil or animal fat.
