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increasing the MgO calcination temperature because the reaction inter-
mediate is formed on medium-strength Mg
2
รพ
-O
2
pair basic sites.
3.3 DFT molecular modeling studies of MgO active sites
We performed DFT calculations to obtain additional information on the
role played by the MgO active sites on the kinetics of base-catalyzed
reactions. Specifically, we present molecular modeling studies on our
MgO-x catalysts for the synthesis of monoglycerides (MG) from glycerol
(Gly) by transesterification (glycerolysis) of methyl oleate (C18 : 1), an
unsaturated fatty acid methyl ester (FAME) (Fig. 13).
Monoglycerides present surfactant and emulsifying properties that
help hydrophilic and lipophilic substances mix together. Therefore, they
can be used in food, detergent, plasticizer, cosmetic and pharmaceutical
formulations [78]. The commercial liquid-catalyzed synthesis route to
produce MG involves strong mineral bases such as Ca(OH)
2
and KOH;
this process yields only 40-60% MG, the rest being diglycerides and tri-
glycerides, and entails concerns related to corrosion and disposal of
spent base materials. The use of solid catalysts for MG synthesis presents
not only the known environmental and practical advantages but also
provides the opportunity to increase the MG yield. However, industrial
implementation of heterogeneously catalyzed processes for FAME
glycerolysis able to eciently replace the use of liquid bases is still a
challenge. Previous works have discussed the different routes for MG
synthesis by esterification of fatty acids or by transesterification of
triglycerides or fatty acid methyl esters [7, 79]. The base-catalyzed MG
synthesis from Gly using FAME instead of fatty acids or triglycerides has
several advantages, e.g., FAME is less corrosive than FA, has lower
hydrophobic character than triglycerides, and exhibits higher miscibility
with glycerol; therefore, the process can be carried out at lower tem-
peratures than TG transesterification. Furthermore, the reaction route
from FAME yields MG with a definite acyl group composition (FAME are
easier to separate by fractional distillation than fatty acids) whereas in TG
glycerolysis the products contain the acyl group distribution of the oil or
fat [80]. MgO-based catalysts such as Mg/MCM-41 and Mg-Al mixed oxi-
des have been investigated for the MG synthesis from glycerolysis of
FAME [79, 81]. In particular, we have studied the glycerolysis of methyl
oleate on MgO-based catalysts [7, 49, 82] and reported the reaction con-
ditions needed to implement this reaction in a four-phase reactor under
kinetic control and to reach maximum MG yields. Here, we present the
results obtained on our MgO-x samples to get insight into the base site
strength requirements for glycerolysis reactions.
Fig. 13 Synthesis of monoglycerides by transesterification of FAME with glycerol.
