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,
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