Page 200 - Biofuels Refining and Performance

Processing of Vegetable Oils as Biodiesel and Engine Performance 183

100

80
Methyl ester yield (%) 60

40

20

0
0 2 4 6 8 10 12 14
Time (h)
Figure 6.15 Effect of the substrate ratio of methyl acetate to oil as biodiesel
production. Reaction conditions: 40 C; 150 ppm; 30% Novozym-435, based on
oil–methyl acetate molar ratio 6:1 ( ), 8:1 (•), 10:1 ( ), 12:1 (♦), and 24:1 ( ).
(Used with permission from Du et al. [52].)

They found 92% yield with a methyl acetate–oil molar ratio of 12:1,
and methyl acetate showed no negative effect on enzyme activity.
The comparison of biodiesel production by acid, alkali, and enzyme is
given in Table 6.2.

6.2.4 Engine performance with esters
of vegetable oil
Hawkins et al. [53] have conducted combustion studies on methyl and
ethyl esters of degummed sunflower oil, maize oil, cottonseed oil, peanut
oil, soybean oil, and castor oil. Fuel properties of the esters were very sim-
ilar to each other, except the esters of castor oil which were much more vis-
cous. The heating values of ethyl esters were also considerably lower.
Engine results indicated that the power output for esters varied from 44.4
to 45.5 kW, with diesel delivering 45.1 kW. The brake thermal efficiencies
were also slightly higher than diesel. High esterification yields (around 90%)
must be obtained to avoid choking of injector tips. Further, sticking of injec-
tor needles after a shutdown time of 48 h has been reported.
Fort and Blumberg [54] have tested a diesel engine with a mixture of
cottonseed oil and ME of this oil. Results indicate that viscosity and den-
sity increased whereas the heating value and the cetane number
decreased, when the percentage of the cottonseed oil was increased in
the blend. The durability test with 50–50% cottonseed oil and ME was
terminated after 183 h of running the engine, because the engine was
noisy. After disassembly, the engine indicated severe wear scouring and