Esterification of Glycerol with Acetic Acid over Highly Active and Stable Alumina-based Catalysts: A Reaction Kinetics Study

Abstract

The catalytic activity of Cu-or Ni monometallic and Cu-Ni bimetallic (Cu/Ni ratio = 3, 1, 0.33) catalysts supported on γ-Al 2 O 3 and SO 4 2-/γ-Al 2 O 3 catalysts were evaluated for esterification of glycerol. The reactions were performed in a batch reactor under reflux at standard reaction conditions: temperature 110 °C, atmospheric pressure, glycerol to acetic acid molar ratio 1:9, and catalyst loading 0.25 g. The best catalytic activity was observed over 2 M SO 4 2-/γ-Al 2 O 3 catalyst, which showed the glycerol conversion of 97 % within 2 hours of reaction. At this condition, the selectivity to glyceryl monoacetate (MAG), glyceryl diacetate (DAG), and glyceryl triacetate (TAG) were 27.0 %, 49.9 % and 23.1 %, respectively, after 5 h of reaction. After three consecutive runs, the 2 M SO 4 2-/γ-Al 2 O 3 catalysts showed superior performance and no loss in activity was observed. The reaction kinetics results over 2 M SO 4 2-/γ-Al 2 O 3 catalyst showed that the dependence on the reaction rate to glycerol concentration was of pseudo-second order, while the activation energy was found to be 106 kJ mol -1 .

The Kinetics of Calcium Oxide Catalyzed Esterification of Glycerol with Free Fatty Acids Using Pseudo-homogeneous Model Approach

“…It can be seen that at 5 minutes the conversion reaches 50%, whereas at 10 minutes the conversion can reach about 72%, and it is almost constant at the 20 th minutes. Similar trend was reported by Rane et al (2016). They found that at higher temperature (70, 90, and 110 o C), the ratio of glycerol concentration and the initial concentration also rises from 0.98; 0.6; and 0.1 at 30 minutes, which Signal Initial Retention time corresponded to reaction conversions of 2, 40 and 90%, at 70, 90, and 110 o C, respectively.…”

“…The conversion starts to be constant at 60 minutes at 110 o C, When the glycerol is used in excess, the esterification reaction of glycerol with FFA can be assumed to be an irreversible reaction (Freedman et al, 1984). This idea is supported by Narvaez (2007) and Rane et al (2016) who assumed that the value of k for the reverse reaction is assumed as zero when the glycerol is in excess. This esterification reaction used solid catalyst sized less than 840 µm, so that the reaction kinetics can be approached using the pseudohomogeneous model (Joksimovic and Markovic, 2007).…”

“…Its reaction order was tested until it was obtained the order of reaction which produced the smallest average error. Arrhenius' reaction rate constants (k) of the resulted calculation for each temperature variables were used to find the values of collision factors (A) and activation energy (Ea) (Rane et al, 2016).…”

“…Theoretically, esterification reaction of glycerol with FFA is a reversible reaction. This reaction can be shifted into an irreversible reaction if the products are immediately separated from the reaction system or when one of the reactant is in excess (Freedman, 1984;Narvaez, 2007;Rane et al, 2016). In this research, molar ratio of glycerol with FFA was set to be very high so that the reaction can be assumed as an irreversible reaction.…”

“…Based on the explanation above, this research has an aim to study the effects of reaction time and temperature on the esterification reaction conversion of glycerol with FFA into MDAG using calcium oxide catalyst and the reaction kinetics using a pseudo-homogeneous model approach. The reaction rate was assumed to follow either the first or second order kinetics as described in equation (1) and (2), where C = concentration, A = FFA (taken from the highest component, it is palmitic acid), r = reaction rate, k = Arrhenius' reaction rate constant, and t = time (Rane et al, 2016).…”