Page 284 - Advances in Eco-Fuels for a Sustainable Environment
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Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 247
Catherine [64] described the in situ trans(esterification) of sunflower seed oil with
acidified methanol and showed a significant increase in methyl ester yields. Ozgul-
Yucel and Turkay [65] reported the in situ trans(esterification) of high acidity
RBO with methanol and ethanol with sulfuric acid as the catalyst. Their results
showed that the yield of FAME strongly depends on the FFA content of RBO; about
24% and 86% of oil was converted to FAME in rice bran containing 19% and 68%
FFA, respectively. Similar results were shown by Yustianingsih et al. [7] and
Gunawan et al. [66]. In another study, Ozgul-Yucel and Turkay [67] reported the
effects of the FFA content of RBO, reaction time, temperature, amount of catalyst,
rice bran moisture, and amount of methanol on the yield and purity of FAME in
in situ trans(esterification). They reported that high FFA bran is most suitable for
in situ trans(esterification). FAME synthesis increased with increasing initial FFA
content. Ozgul-Yucel and Turkay [68] also investigated the effects of FFA content
of RBO and the chain length of alcohol on the in situ esterification of RBO. The
highest monoester content was obtained with methanol. This method showed efficient
esterification of FFA but transesterification of glycerides was poor and therefore the
FAME yield increased with the FFA content. Another limitation of in situ
trans(esterification) is the use of high amounts of methanol and acid-catalyst, and sat-
isfactory results can only be obtained from rice bran with high FFA content.
Shiu et al. [69] investigated a two-step in situ method where the acid catalyst was
used in the first step followed by the basic catalyst in the second step. They found that
lipid extraction from rice bran was a slow process that could take 4–5h to extract most
lipids in the bran using Soxhlet with n-hexane as the solvent.
In situ method under supercritical methanol at 300°C and 30MPa with CO 2 as the
pressurizing gas was reported by Kasim et al. [70]. However, the result of noncatalytic
in situ biodiesel production from rice bran was rather disappointing, with an overall
conversion of 51.3%. It was because at high temperature, the rice bran was charred,
hindering oil extraction. Therefore, although the noncatalytic in situ method could
potentially reduce the biodiesel production cost, many obstacles need to be overcome.
Another noncatalytic in situ method to produce biodiesel is by using subcritical
water. One advantage of this method is that it can be carried out without an acid or
base catalyst. Besides that, subcritical water can reduce the amount of alcohol and
it is able to hydrolyze complex carbohydrates into soluble sugars that can be utilized
as a medium to grow yeast [71], feedstock for bioethanol production, and other indus-
trial applications [72].
The effectiveness of a subcritical water-methanol mixture to produce FAME from
rice bran without a preliminary oil extraction step has been investigated by Zullaikah
et al. [4]. This process was found to be insensitive to initial moisture and FFA content
in bran and therefore no pretreatment was required. Oil recovery, FAME yield, and
FAME content were higher under a CO 2 atmosphere than those under an N 2 atmo-
sphere due to the ability of CO 2 to acidify the water-methanol mixture. The data
suggested that oil extraction from bran was the limiting factor and that the hydrolysis
of glycerides into FFA followed by methyl esterification of FFA into FAME may be
the preferred reaction path rather than the direct transesterification of glycerides into
FAME. Under optimum conditions (T ¼200°C, P ¼4MPa under CO 2 atmosphere,