*2.2. Reaction Studies*

Experimental tests on how catalyst amount, reaction time, methanol–vegetable oil, and reusability of the catalysts affect efficiency have been evaluated to detect the optimum conditions for the study of biodiesel production.

Figure 4 shows different calcination temperatures and times, for a bauxite-Li2CO3 molar ratio of 4, through the transesterification process. The reaction rate is shown in the results. With the calcination temperature between 600 ◦C and 1000 ◦C, the reaction rate of soybean oil increases to the maximum value, and the reaction rate then begins to decrease when the calcination temperature exceeds 800 ◦C, as shown in Figure 4. Conversion is consequently lower because catalysts begin to form agglomerated blocks at higher calcination temperature. Hence, the optimal condition occurs at 800 ◦C in this study. Furthermore, the conversion is found to increase with the increase in time from 1

to 5 h and then to decrease as time elapses past 3 h. In Figure 4, the reaction efficiency suggests that FAME production efficiency is lower at lower calcination times and increases when the calcination time reaches the maximum value of 3 h. The conversion rate then decreases, probably due to the formation saponification for longer calcination times. This result is attributed to the fact that Li4SiO4 and LiAlO2 start to form agglomerated blocks in the Li4SiO4 and LiAlO2 phases for long calcination times. Therefore, regardless of the calcination time, the LiAlO2 and Li4SiO4 phase is achieved. A correct calcination time was consequently required to guarantee completion.

**Figure 4.** Influence of calcination temperature (◦C) and time on the conversion reaction conditions: methanol/oil molar ratio 12:1, with 6 wt.% catalyst loading, reaction time 3 h.

Table 2 presents the efficiency for a bauxite and Li2CO3 molar ratio of 4. As shown, the catalyst exhibits a much higher conversion rate than the latter. In addition, increasing the molar ratio of oil to methanol increased the reaction rate (Table 2). Methanol is a reactant for transesterification reactions [8]. Increasing the reactant quantities shifts the equilibrium to the products side [20]. A molar ratio of 6 yielded a lower conversion rate. The highest reaction rate was obtained at a methanol–oil molar ratio of 12. This molar ratio of 12 was considered the optimal condition and was favorable for the transesterification procedure. Throughout the procedure, the catalyst amount represented a crucial parameter for high efficiency. The catalysts possessing strong main activity sites and a high surface area should exhibit higher conversion. Catalytic sites for transesterification are too few when the catalyst–oil ratio is too low. Catalyst amount was varied from 2 to 10 wt.% to oil to evaluate its effect on the conversion rate of the transesterification procedure at 65 ◦C and a methanol–oil molar ratio of 12. Catalysts loading of 2 wt.% of oil yielded a lower transfer rate. The maximum efficiency was obtained at a catalyst loading of 6 wt.% (Table 2). A catalyst loading of 6 wt.% for oil was considered the optimal condition and favorable for the transesterification process. This may have been due to the formation of resistance to mass transfer [21] for high catalyst quantities. In addition, to determine the catalytic activity of catalysts in the experimental tests, the efficiency of transesterification is presented in Table 2. This indicates that the reaction rate increased with increasing reaction time in the alkali silicate catalysts at a constant reaction temperature. The transesterification comprised three processes: The first process, whereby triglyceride reacted with one molecule of methanol, yielded diglyceride and one molecule of ester. The second process, the reaction of the diglyceride with a second molecule of methanol, yielded monoglyceride and an additional molecule of ester. In the third process, monoglyceride reacted with the third molecule of methanol, yielding glycerin and ester. Consequently, correct transesterification was required to guarantee completion of the reaction. Table 2 demonstrates that the efficiency increases with time and has an optimum value after 3 h.


**Table 2.** The catalytic performance of catalysts for transesterification of soybean oil with methanol.

\* Reaction conditions: 12.5 g oils; reaction temperature, 65 ◦C; methanol reflux temperature and conventional heating method.

The e fficiencies of oils other than FAME are indicated in Table 2. FAME was successfully synthesized from soybean oil through a transesterification procedure with catalysts using a simple method. The results demonstrate that the e fficiency with high free fatty acid concentration was significantly influenced [22].

The reusability for a bauxite–Li2CO3 molar ratio of 4 was evaluated for soybean oil. The catalyst was reusable up to the sixth repetition, with retention of catalyst e fficiency, providing a conversion efficiency of >90% and then declining to a conversion e fficiency of 80% after the 6th run repetition (Figure 5).

**Figure 5.** Reusability study after six reaction cycles for catalyst. Reaction conditions: methanol/oil molar ratio 12:1, with 6 wt.% catalyst loading, reaction time 3 h.

### **3. Experimental Methods and Chemical Materials**
