## 3 Result and Discussion
### Effects of Reaction Parameters on the Transesterification Process (Biodiesel Yield)  
#### 3.3.1. _Molar_ Ratio (Methanol to Oil)--Reaction Time  
One of the important factors in biodiesel production is investigating the molar ratio of methanol to oil. Methanol plays a fundamental role in biodiesel conversion. The amount of methanol added to a crude oil causes the large branched molecules of vegetable oils break down into smaller linear methyl ester oils. In the other words, the methanol requires transesterification of triglycerides into fatty acid methyl esters [57; 58]. In this study, the effect of molar ratios of methanol to CSO, ranging from 2:1 to 12:1, on the rate of biodiesel conversion was studied. As observed in Figure 3, three different mass ratios of methanol to oil molar ratio were tested; 2:1, 7:1, and 12:1. The methyl ester content was increased as the molar ratio of methanol to oil was raised from 2:1 to \(\sim\)10:1. However, further increase to 12:1 had negative effects on methyl ester conversion. Too much methanol could dilute the oil and as a result slow the reaction rate [59]. Another parameter that has an important effect on biodiesel production process is reaction time. The dependency of reaction time was studied at three different time intervals ranging from 2-10 min. The optimum conversion of 98.21% was observed at 10 min when the concentration of catalyst is 1.5 (wt %). The reaction time has a significant effect (\(p\)-value \(<\) 0.05) on biodiesel conversion. The interaction of the molar ratio (methanol to oil)--reaction time has a significant (\(p\)-value \(<\) 0.05) effect on biodiesel conversion.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Statistical Model** & **Std. Dev.** & **CV\%** & **R\({}^{2}\)** & **Adjusted R\({}^{2}\)** & **Predicted R\({}^{2}\)** & **PRESS** \\ \hline Linear & 6.52 & 7.78 & 0.6662 & 0.5828 & 0.3431 & 1002.89 & \\
2 FI & 5.36 & 6.4 & 0.8308 & 0.7180 & 0.1991 & 1222.48 & \\ Quadratic & 2.26 & 2.69 & 0.98 & 0.95 & N/A & N/A & Suggested \\ Cubic & 2.24 & 2.67 & 0.9869 & 0.9508 & N/A & N/A & Aliased \\ \hline \hline \end{tabular}
\end{table}
Table 6: Quadratic model statistics.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **df** & **Mean-Square** & **F-Value** & \(p\)**-Value** \\ \hline Model & 1496.219 & 9 & 166.2466 & 32.66114 & 0.0002 \\ A—Catalyst concentration (wt %) & 133.6698 & 1 & 133.6698 & 26.26103 & 0.0022 \\ B—molar ratio (methanol to oil) & 608.7634 & 1 & 608.7634 & 119.5989 & \(<\)0.0001 \\ C—reaction time (min) & 123.7505 & 1 & 123.7505 & 24.31228 & 0.0026 \\ AB & 27.80006 & 1 & 27.80006 & 5.461656 & 0.0581 \\ AC & 81.01741 & 1 & 81.01741 & 15.91684 & 0.0072 \\ BC & 61.22434 & 1 & 61.22434 & 12.02826 & 0.0133 \\ A\({}^{2}\) & 6.267942 & 1 & 6.267942 & 1.231413 & 0.3096 \\ B\({}^{2}\) & 212.6612 & 1 & 212.6612 & 41.77985 & 0.0007 \\ C\({}^{2}\) & 0.000162 & 1 & 0.000162 & \(3.19\times 10^{-5}\) & 0.9957 \\ Residual & 30.54025 & 6 & 5.090042 & \\ Lack of Fit & 10.51385 & 2 & 5.256923 & 1.049998 & 0.4300 \\ Pure Error & 20.02641 & 4 & 5.006602 & \\ Std. Dev. & 2.26 & & & & \\ C.V\% & 2.69 & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Analysis of variance (ANOVA) for response surface methodology (RSM) model.