5.5. Rubber

Several researchers produced biodiesel from rubber seed oil [25, 29, 48]. Ikwuagwu et al. [48] produced biodiesel from fresh rubber seed oil, where the FFA in crude oil was 2% and in refined oil 0.5%. The reaction carried out under condition of molar ratio of methanol to oil was 6:1 and 1% NaOH as catalyst, ester yield from crude seed oil was just 76.64% compared to refined oil (84.46%). Ramadhas et al. [29] produced biodiesel from rubber seed oil with high free fatty acid by two stages reaction. Acid esterification reduced FFA of oil from 17% to less than 2% when reaction with 0.5% v H2SO4, methanol to oil molar ratio of 6:1, temperature at 50C for 20–30 min. Final stage was alkaline transesterification, where the oil mixture with methanol to oil molar ratio of 9:1 and 0.5%w of NaOH at temperature 40–50C during 30 min for achieving conversion efficiency almost 100%. Result from Ramadhas et al. [29] showed rubber seed oil is appropriate as biodiesel feedstock. The viscosity of biodiesel obtained is close to diesel, although yield that Ikwuagwu et al. [48] achieved was considered uneconomical. However, further research is needed for fostering the biodiesel quality as well as more acceptability.

#### 5.6. Mahua

Ghadge and Raherman [35, 49] studied the process optimization for biodiesel production from M. indica oil using response surface methodology. FFA content can be reduced from 27% to less than 1% by 0.32 v/v methanol using 1.24% w/v H2SO4 as catalyst under reaction condition at 60C for 1.26 h. Next step was conducted by adding 0.7% w/v KOH, 0.25 v/v methanol to oil molar ratio of methanol 6:1. The biodiesel yield was achieved 98%.
