## 3 Results and Discussion  
The FAEE yields in the continuous reaction system at different flow rates and molar ratios are listed in Table 2 and displayed in Figure 3. Figure 3 shows that the MX-mixer provides higher yields at lower flow rates and otherwise similar parameters compared to the T-mixer. An opposite effect can be observed at higher flow rates. This could be explained by diverging flow dynamics [8]. Because of the MX-mixer geometry, the efficient mixing of components at lower flow rates can be observed. In the T-mixer, the higher flow rate is required for good mixing. \begin{table}
\begin{tabular}{c c c} \hline \hline \(\mathbf{n_{EOH}/n_{oil}}\) & \(\dot{V}\) [mL/min] & \(\mathbf{wt.\text{-}\%\ koh}\) \\ \hline
8:1 & 2.6 & 0.860 \\
6:1 & 1.5 & 0.645 \\
10:1 & 1.5 & 0.645 \\
6:1 & 3.7 & 0.645 \\
10:1 & 3.7 & 0.645 \\
6:1 & 1.5 & 1.075 \\
10:1 & 1.5 & 1.075 \\
6:1 & 3.7 & 1.075 \\
10:1 & 3.7 & 1.075 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Full factorial design for the continuous reaction system with MX-mixer. In order to consider the significance of the parameters, the dimensionless coefficients (ethanol/oil ratio, flow rate and the mass percentage of catalyst) have to exceed the value for the Student's t-distribution (Table 3) [11]. The regression analysis of the reaction in the MX-mixer shows that only the ethanol/oil ratio (a\({}_{1}\)) has a significant impact on the yield of FAEE. The flow rate (a\({}_{2}\)) has a negative sign and is not significant. In the T-mixer only flow rate (a\({}_{2}\)) and ethanol/oil ratio (a\({}_{1}\)) are significant. The variation of the flow rate in this system provides a higher impact on the yield than the molar ethanol/oil ratio. This result confirms that the flow rate has a great influence on the blending of the components in the T-mixer. The amount of the catalyst (a\({}_{3}\)) shows no significant impact on the experiment in both reactor systems. The calculated dimension specific coefficients for the MX- and the T-mixer are presented in Table 4.  
In Equations (6) and (7) the significant coefficients for both investigated reactor systems (with MX-mixer and T-mixer) are presented. \[\rm{y}=f(x_{k})=44.9+3.1\rm{x}_{1} \tag{6}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mixer** & \(\dot{V}\) **[mL/min]** & **Ethanol/Oil** & **W\({}_{\rm FAEE}\) [\%]** \\ \hline mx & 1.5 & 6:1 & 67.2 \\  & 1.5 & 10:1 & 85.9 \\  & 3.7 & 6:1 & 60.7 \\  & 3.7 & 10:1 & 70.6 \\ \hline T & 1.79 & 6:1 & 50.3 \\  & 1.79 & 10:1 & 68.2 \\  & 3.99 & 6:1 & 65.4 \\  & 3.99 & 10:1 & 88.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fatty acid ethyl ester (FAEE) yields for MX- and T-mixer at KOH = 0.645 wt.-%. Figure 3: FAEE yields in MX- and T-mixer at KOH = 0.645 wt.-%. \[y=f(x_{k})=7.0+4.1\cdot x_{1}+9.8\cdot x_{2}) \tag{7}\]  
Regression equations depending on the ethanol/oil ratio at a constant flow rate \(x_{2}\) = 2.89 mL/min in the MX-V and T-V reactor system can be formulated (Figure 4). It shows that raising the ethanol/oil ratio in the reactor system with T-mixer would lead to higher yields of FAEE (w\({}_{\text{FAEE}}\) [%]) than in the reactor system with MX-mixer. At ethanol/oil ratios under 9.5:1 the MX-V reactor system is more efficient than the T-V reactor system, while higher ethanol/oil ratio provides a slightly higher efficiency in the case of T-mixer. The influence of the flow rate on the FAEE yield in the T-reactor system at a constant molar ethanol/oil ratio = 10:1 is shown in Figure 5. A high positive impact of the flow rate in the T-mixer, and a reverse phenomenon in the MX-mixer can be observed. Due to a better blending in the T-mixer, the T-reactor system is more suitable for flow rates higher than 2.2 mL/min compared to the MX-V reactor system. The optimization was conducted in both continuous systems according to the Box-Wilson method [12]. New values for the parameters were calculated based on the regression coefficient with the greatest impact on the respective reactor system.