# Green Production of Glycerol Ketals with a Clay-Based Heterogeneous Acid Catalyst
## 3 Results and Discussion
### Glycerol Ketalization Kinetic Studies
#### 3.3.2 Systems 2 and 3: Ketalization with Butanone -MEK- and Cyclohexanone. Preliminary Analysis  
The effect of the catalyst AC concentration on the initial reaction rate (that is, the rate of the ketalization reaction) is linear in both systems, as can be seen in Figure 12. The direct comparison to system 1 is not totally feasible, as these runs were performed at 40 \({}^{\circ}\)C, because the ketones are not as volatile as acetone, but it can be said that cyclohexanone has a reactivity similar to that of acetone: r\({}_{0}\) at 35 \({}^{\circ}\)C and 50 g/L catalyst is about \(1.02\times 10^{-3}\) mol/(L\(\cdot\)s) for acetone and this same parameter at 40 \({}^{\circ}\)C approaches \(1.2\times 10^{-3}\) mol/(L\(\cdot\)s). On the other hand, it is evident that the reaction rate is much lower for MEK than for the other two ketones, resulting in the need of more catalyst (from 100 to 300 g/L) to reach similar reaction rates. As the acidity and mass transfer is identical in all cases, this fact may be due to a worse distribution of MEK on the catalyst surface, probably displacing glycerol from it, by its adsorption onto the surface via the hydrophobic backbone of its C4 chain.  
The yields at equilibrium positions for butanone are similar than those for acetone (\(\sim\)70%), while the values are higher for cyclohexanone (near 85%), suggesting a higher displacement of water in system 3 in comparison to the other systems (Figure 12).  
As in the previous sections, yields of ketals 2 and 3 at 24 h and initial rates for the ketalization reaction are shown in Figure 13. It can be appreciated that the temperature affects the ketalization initial rate in an exponential manner (Arrhenius). The effect on r\({}_{0}\) is more pronounced for cyclohexanone, seemingly with a higher activation energy than the MEK-glycerol ketalization.  
If the yields at different temperature values in both systems are considered, it seems that temperature scarcely affects the equilibrium position for MEK, but the yield to ketal 3, the case of cyclohexanone, is reduced with temperature. Therefore, as in the solketal case, the ketalization reaction of MEK and glycerol seems to be thermoneutral, whereas the same reaction for cyclohexanone appears to be slightly exothermic. Therefore, depending on the ketone, these processes can be either slightly endothermic or exothermic [40; 41].  
Figure 12: Effect of catalyst amount on the yield of ketals 2 and 3 at 24 h and the initial reaction rate (Reaction conditions: butanone/glycerol or cyclohexanone:glycerol molar ratio, 6:1; temperature, 40 \({}^{\circ}\)C).  
Effect of Initial Molar Ratio of Reactants  
The influence of molar ratio of the ketones to glycerol resulted in yields to the corresponding ketals 2 and 3 at 24 h and initial reaction rates that are displayed in Figure 14. The overall trend in the initial reaction rate as the excess of the ketone increases is not clear, but it is decreasing somewhat, as can be expected when the product of the reagents concentrations is reduced by 14%. The effect on the ketal yield with increasing ketone excess, as expected, is the increment of this parameter. Fitting yields at equilibrium to rectangular hyperbolas resulted, as in the case of solketal, in a value lower than 100% (about 92-95%), showing that the complete shift of the equilibrium towards the products is not possible, supporting in this way the hypothesis of deactivation, a phenomenon that happens, at least, when using strong acid exchange resins [39].