The homogeneous and heterogeneous catalysts that are used for the transesterifica­tion of Jatropha oil to biodiesel were shown in Table 10.6.

10.4.1 Two-Step-Catalyzed Reaction

Berchmans and Hirata (2008) reported that Jatropha oil with FFA content up to 15% was beyond the acceptable limit for alkaline-catalyzed reaction. Thus, two-step transesterification was performed including H2SO4-catalyzed esterification reaction to reduce the FFA level to <1% for 1 h at 50°C, followed by NaOH-catalyzed trans­esterification reaction for 2 h at 65°C. The authors showed that the pretreated Jatropha oil (two-step reaction) rendered high methyl ester yield of 90% than the non-pretreated oil (single-step alkaline-catalyzed reaction) with 55% of yield.

Patil and Deng (2009) produced Jatropha-based biodiesel via two-step trans­esterification reactions. The oil with initial acid value of 28 mg KOH/g was reduced to 2 mg KOH/g by using H)SO4 (0.5%) catalyst before KOH (2 wt%)-catalyzed reaction. The results showed that with insufficient amount of alkali catalyst loading, the reaction could not complete. However, excess amount of catalyst will lead to the formation of emulsion, which increases the viscosity of the biodiesel and resulted in

Catalysts Acid value/FFA Time (h) Temperature (°С) Methanol/oil ratio Catalyst amount (wt%) Yield (%) References (a) Two-step catalyzed reaction (esterification and transesterification) H, so4 ■ 28 mg KOH/g N/D 40—45 6 0.50 90-95 Patil and Deng KOHb 0.25% 2 60 9 2 (2009) H, so4 ■ FFA = 21.5% 3 65 3:07 1 21 Jain and Sharma NaOHb <1% 3 50 3:07 1 90 (2010a) H, so4 ■ 6.2 mg KOH/g. 3.1% 1.5 60 6.5 0.30 N/D El Sherbiny FFA et al. (2010) KOHb 1 60 7.5 1.50 100 KOHbc 0.03 60 yield 1. NaOH (one step 10.45 mg KOH/g 1 h 60 N/D N/D 47 Deng et al. reaction) (2010) 2. H, S04 (one step 0.95 mg KOH/g 4 h N/D 1 0.4 93 reaction) 3. Two-step reaction H, scv 10.45 mg KOH/g 1 N/D 40 4 N/D NaOHb 1.2 mg KOH/g 0.5 N/D 24 1.4 96 1. H2SO/ 5-12 mg KOH/g 1.5 45 4 1 95 Deng et al. 2. Mg/Al hydrotalciteb 0.7 mg KOH/g 1.5 45 (2011) h, scv FFA =15% 1 50 0.6 w/w 1 N/D Berchmans and NaOHb <1% 2 65 0.24 w/w 1.4 90 Hirata (2008) so42-/Tio, a 12% 2 90 20 4 C=9T Lu et al. (2009) KOHb 0.50% 0.33 64 6 1.3 98 SiO,-HFa 15.8 mg KOH/g 2 60 12 0.1 C=96e Corro et al. NaOHb 0.63 mg KOH/g N/D N/D N/D N/D N/D (2010)

“Esterification reaction b Transesterification reaction “Microwave heating d Ultrasonic heating eC conversion of oil

gel formation. This two-step esterification-transesterification process yielded 90-95% Jatropha-based biodiesel.

Jain and Sharma (2010a) studied the kinetic of two-step transesterification of high FFA containing oil (21.5% FFA to <1%). The results indicated that both esteri­fication and transesterification reaction are of first order. Within 3 h of reaction time, biodiesel yield of 21.2% and 90.1% was obtained under the optimum condition of 65°C and 50°C, respectively, with 1% catalyst loading for H2SO4 and NaOH from esterification and transesterification.

The present analysis and the optimization study by several researchers revealed that two-step reaction is the most suitable method for converting non-edible oils to biodiesel. However, further development of new method in two-step reaction had been performed in order to improve the quality of biodiesel.

El Sherbiny et al. (2010) reported that microwave irradiation heating in trans­esterification reaction is suitable for the use of high FFA content feedstock like Jatropha oil. In this study, the optimum condition from conventional technique (7.5:1 methanol/oil molar ratio, 1.5% KOH, and 65°C) was applied using micro­wave irradiation transesterification of Jatropha oil. The results showed that applica­tion of radio frequency microwave energy increased the reaction rate with easy route and simplify the separation process. The reaction time was reduced to 2 min instead of 150 min (90 min for the pretreatment process and 60 min for transesteri­fication), indicating no pretreatment technique is required if microwave technique is applied. Microwave energy provided selective heating to the mixture of vegetable oil, methanol, and potassium hydroxide which contain both polar and ionic compo­nents resulted in increment of energy interaction with the sample on a molecular level, thus enhanced the heating rate (Varma 2001).

Deng et al. (2010) utilized the ultrasonic reactor for the transesterification of high acid value Jatropha oil (10.45 mg KOH/g) with methanol by using NaOH, H2SO4, or by two-step reaction. The NaOH-catalyzed reaction rendered 47.2% of biodiesel yield with the formation of soap-like material. With H2SO4 as a catalyst, high yield of biodiesel (92.8%) was obtained with longer reaction time (4 h) and unstable bio­diesel yield (formation of flocs precipitate after 15 days). The results revealed that 96.4% of stable and clear yellowish biodiesel was obtained from two-step reaction within 1.5 h (1 h for esterification and 0.5 h for transesterification) which was faster than conventional heating. It could be concluded that the two-step process coupled with ultrasonic radiation is an efficient and practical method for biodiesel produc­tion from crude oil with high FFA value. The study was continued by transforming homogeneous catalyzed system to heterogeneous system. Deng et al. (2011) applied the methanolysis of Jatropha oil (acid value of 5-12 mg KOH/g) using hydrotalcite — derived catalyst. The catalyst was prepared via coprecipitation method and heated using microwave-hydrothermal treatment in order to obtain nanosized particle. Before reaction, the high acid oil underwent pretreatment in order to remove FFA. Under transesterification condition (45°C), the biodiesel yield was 95.2% using 1 wt% catalyst amount, 4:1 methanol/oil molar ratio, and 1.5 h in ultrasonic reactor (210 W ultrasonic power). The catalyst was reused for eight times with biodiesel yield maintained at >80%. But at the ninth run, the biodiesel yield was decreased sharply to 43.7% indicating deactivation of catalyst due to surface absorption of glycerol by-product and the collapsed the hydrotalcite layered structure.

Most of the previous studies reduce the FFA content in Jatropha oil via pre­esterification reaction using homogeneous acids, such as sulfuric acid, phosphorous acid, or sulfonic acid (Kumar Tiwari et al. 2007). Some of the researchers had stated that using solid acid catalyst in esterification reaction is more environmental friendly than the homogeneous acid catalyst.

Lu et al. (2009) compared the effectiveness of H2 SO4 liquid acid catalyst and SO4- / TiO2 solid acid catalyst in the pre-esterification reaction before performing KOH alkaline-catalyzed transesterification reaction. The results showed that the esterification activity of solid acid catalyst, SO4- /TiO2, is comparable to H2SO4. More than 97% of FFA conversion was achieved under 90°C for 2 h, 20:1 methanol/ FFA ratio using 4 wt% SO4- / TiO2 catalyst. In both reaction conditions, the FFA content of the Jatropha oil was reduced from initial 12% to <0.5% before converted into biodiesel via transesterification. The yield of biodiesel by transesterification was higher than 98% in 20 min of reaction time using 1.3% KOH as catalyst, and 6:1 methanol/oil molar ratio at 64°C.

Besides, Corro et al. (2010) performed two-step transesterification reaction using solid acid catalyst (SiO2HF) for Jatropha oil (15.8 mg KOH/g) pretreatment before performing NaOH catalyzed reaction. The authors found that SiO2 HF consist of high number of Lewis acid surface without deactivation activity by CO2 and H2O adsorption. The SiO2 HF was prepared by impregnation of HF solution on SiO2 sup­port, this catalyst showed high esterification activity (96% of FFA conversion) under optimum esterification condition of 60°C, 0.1 wt% catalyst loading, methanol/oil molar ratio of 12:1 for 2 h. Besides, the high stability of SiO2HF is capable of per­forming 30 cycles without any activity degradation. In second step, the treated Jatropha oil (0.63 mg KOH/g) was transesterified with methanol catalyzed by NaOH.

Although two-step transesterification process is suitable to transesterify crude Jatropha oil with high FFA, this approach required two-step oil conversion process which resulted in higher production cost as compared to conventional process. Furthermore, the use of strong acid catalyst such as H2SO4 will lead to wastewater problem and extra production cost is needed to separate and purify the homoge­neous catalyst from the biodiesel product. Thus, research on utilization of heteroge­neous catalyst for biodiesel production has arisen in order to overcome the drawbacks in two-step transesterification reaction.