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246                              Advances in Eco-Fuels for a Sustainable Environment

         catalysts can be applied in homogeneous or heterogeneous reactions. Noncatalytic
         conversion uses high temperature and pressure to make sure that the reaction occurs.
            RBO is not a common source of edible oil compared to other traditional cereals or
         seed sources such as corn, sunflower, and soybean. Ju and Vali [4] and Zullaikah et al.
         [5–8] suggested the utilization of RBO for biodiesel production. Prices of the raw oil
         and byproduct meal cake are the two most important factors determining the cost of
         biodiesel. For example, soybean is a more expensive feedstock for biodiesel than
         canola, sunflower, rapeseed oils, and animal fat because of its low oil content. How-
         ever, the byproduct meal cake of soybean has the highest monetary credit, such that its
         total cost of biodiesel production is lower than the others. Crude RBO is a low cost
         feedstock for biodiesel production as compared to traditional oils derived from cereal
         or seed sources.
            Because RBO has high FFA content, the conventional biodiesel production method
         using the base catalyst is unsuitable because the base reacts with FFA, forming soap,
         lowering the FAME yield, and complicating the purification process [5]. Various cat-
         alytic methods involving multiple steps to produce biodiesel from crude and refined
         RBO have been reported. Lai et al. [62] employed two enzymes, Novozyme 435 and
         IM 60, as catalysts for the reaction of RBO and methanol. A stepwise addition of
         methanol was used. Their results show that at a reaction time of 2h, 60% FAME con-
         tent was obtained with both lipases. FAME content increased steadily with time,
         reaching 98% at 7h with Novozyme 435. With IM 60, FAME content increased with
         time, reaching a maximum of 81% at 4h and then decreasing slowly to 74% at 7h.
         Zullaikah et al. [6] developed a two-step acid-catalyzed methanolysis method to pro-
         duce FAME from dewaxed/degummed RBO with FFA content up to 76%. The first
         step was carried out at 60°C mainly to convert FFA to FAME while the second step
         was carried out at 100°C to convert the remaining triglycerides (TG) to FAME with a
         total reaction time up to 8h. Whereas Lin et al. [12] developed a three-step method to
         produce FAME from crude RBO, the first two pretreatment steps were carried out at
         50°C using an acid catalyst to reduce FFA content to below 1mg/g while the third step
         was carried out at 60°C using a base catalyst to convert TG into FAME. The total
         reaction time can be reduced to less than 3h. However, a separation step was required
         between the acid-catalyzed steps and the base-catalyzed step. Although the FFA con-
         tent in the feedstock and the methods were different, they reported that more than 98%
         of FFA and TG were converted into FAME under optimum conditions. A drawback of
         acid-methanolysis is the requirement for the reactor to be acid resistant. Another draw-
         back of the acid catalyst is the lower rate of reaction if the sample contains TG. There-
         fore, the acid catalyst followed by the base catalyst can reduce reaction time.
            Einloft et al. [63] reported employing tin compounds as a heterogeneous catalyst
         for biodiesel production from RBO. Tin compounds were chosen because tin shows
         higher acidity than other transition metals. Four kinds of tin compounds were tested.
         The highest yield was achieved when (C 4 H 9 ) 2 Sn(C 12 H 23 O 2 ) 2 was used as the catalyst.
         At 4h of reaction, the FAME yield was 68.9% as compared with 37.4% when sulfuric
         acid was used as the catalyst.
            In situ trans(esterification), that is, simultaneous oil extraction and methyl esteri-
         fication, is a possible way to decrease the cost of biodiesel production. Harrington and
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