# Biodiesel and Biolubricant Production from Waste Cooking Oil: Transesterification Reactor Modeling
## 3 Results and Discussion
### Effects of Pressure, Temperature, and Catalyst Concentration on WCO-TMP Production  
Figure 3 shows the evolution of the conversion of FAMEs during different runs of the experiment. Once WCO-FAMEs were produced and characterized, different experiments about the effects of the pressure, temperature, and catalyst concentration on the FAME conversion were carried out during WCO-TMP production at different pressures (a), temperatures (b), and concentrations of sodium methoxide (i.e., the catalyst) (c). Figure 2: Scheme of the main stages accomplished in this work. Regarding the effect of the pressure on the FAME conversion (Figure 3a, where the rest of the variables were kept constant; that is, the temperature was 80 \({}^{\circ}\)C, the FAME/TMP ratio was 3, the catalyst concentration was 0.3% \(w/w\), and the stirring rate was 350 rpm), the lower the pressure, the higher the conversion of FAMEs at a given time. This could be due to the fact that methanol, a product of the transesterification reaction, which is generated in this step, is removed from the reaction medium under vacuum, thus increasing the overall conversion rate of FAMEs and facilitating the reaction of the reagents to produce WCO-FAMEs. The same trend was observed in previous works, where different alcohols, such as pentaerythntyl [49] or TMP [33], were used. Nevertheless, in this case, it should be noted that a working pressure of 510 mmHg offered similar conversion values close to those observed at lower pressure values (360 and 210 mmHg), so one can assume that a vacuum of 250 mmHg was enough to remove almost all the methanol that was generated. And the  
Figure 3: Effects of different factors on FAME conversion for biolubricant production: (**a**) pressure; (**b**) temperature; (**c**) catalyst concentration. Experimental conditions, unless otherwise indicated: FAME/TMP molar ratio = 3; P = 510 mmHg; T = 80 \({}^{\circ}\)C; catalyst concentration = 0.3% \(w/w\); stirring rate = 350 rpm. FAME conversion rates were comparable to those obtained at lower working pressures used in this experiment, suggesting the selection of 250 mmHg for further analysis. As expected, higher temperatures increased the conversion rate of the FAMEs (see Figure 3b). In the case of the temperature (Figure 3b, where the rest of the variables were kept constant; that is, the pressure was 510 mmHg, the FAME/TMP ratio was 3, the catalyst concentration was 0.3% \(w/w\), and the stirring rate was 350 rpm), there was a growth in the WCO-TMP yield as the temperature increased, with gradual increases in conversion rates at the beginning of the reaction, especially for the first 30 min. Thus, high temperatures would be advisable from the kinetic point of view. However, a negative effect on the oxidation stability could take place, as was observed in previous work [55]. Therefore, an intermediate temperature should be recommended to balance these opposite effects. Finally, the catalyst concentration (Figure 3c, where the rest of the variables were kept constant; that is, the temperature was 80 \({}^{\circ}\)C, the pressure was 510 mmHg, the FAME/TMP ratio was 3, and the stirring rate was 350 rpm) also accelerated the rate of the transesterification reaction. In this case, the catalyst addition contributed to an increase in the reaction rate, reaching similar conversions at the end of the reaction. The presence of catalyst traces in the final product could catalyze oxidation processes, which are not desirable [55].