3.2. Influence of reaction factors on the conversion yield of biodiesel
The results of the influence of the n-hexane to 75% ethanol ratio (v/v), mixed solvent dosage, reaction temperature, time and catalyst volume on the conversion yield of direct transesterification were shown in Table 1. It was indicated that a lower ratio of the n-hexane to 75% ethanol played a positive role on the conversion yield, assigned to the high content of 75% ethanol in the mixed solvent, which could help microalgae lipid to be extracted and react with ethanol. The effect of solvent dosage on the conversion yield was illustrated in Table 1. The FAEE yield was increased significantly from 71.27% to 89.96% when the solvent dosage was increased from 3.0 mL to 6.0 mL. Although mixed solvent enhances direct transesterification, excess solvent is estimated to reduce lipids contact with ethanol so that the conversion yield is reduced. Additionally, n-hexane excess reduces the mass transfer between lipid and ethanol also reduces heat transfers so that the transesterification reaction is not running optimally (Dianursanti et al., 2015). As shown in Table 1, the FAEE yield increased with the increasing of reaction temperature from 60 C to 90 C, and the maximum yield of 88.78% was obtained at 90 C. It could be 7