4.3.2. Alcohol/oil molar ratio
RSO transesterification reaction involves excess alcohol to drive the process to completion. For alkaline homogeneous catalyst such as KOH, a 6:1 M alcohol/oil ratio is reported by researchers for maximum biodiesel yield of 75–96.8 wt.% [30], [40] and [55]. Ahmad et al. [40] observed that alcohol/oil molar ratio is the most influencing factor in RSO biodiesel production up to a certain limit beyond which the amount of methanol has no effect on the biodiesel yield and higher methanol concentration may result to high downstream processing.
4.3.3. Catalyst concentration
RSO biodiesel yield increases with increase in catalyst concentration up to an optimum level of 6 wt.% with conversion of 92.3 wt.% [13]. Catalyst weight (%), calcination temperature and time are usually determined through optimization process [16] and [17]. In transesterification of RSO, catalyst concentration is the second most influencing factor that determines higher yield of biodiesel [40] and [48]. The addition of a suitable concentration of catalyst determines the physical appearance of RSO biodiesel while higher concentration may give rise to darker color [30] and [56].