Solvent-Free Glycerol Transesterification with Propylene Carbonate to Glycerol Carbonate over a Solid Base Catalyst

Abstract

Glycerol transesterification using propylene carbonate (PC) to glycerol carbonate (GC) could be efficiently performed under solvent-free conditions using solid base as catalysts involving non-noble metal oxide in combination with hydrotalcites (HTs). Among all of the catalysts studied for transesterification, the best result was obtained over a calcium-doped hydrotalcite (Ca-HT) catalyst, giving 84% conversion of glycerol and almost complete GC selectivity. The crystal structure of HT was modified by incorporation of Ca and La into HT, as revealed by X-ray diffraction studies. The temperature-programmed desorption of carbon dioxide study confirmed the presence of the highest basic site density in terms of 1.94 mmol of CO 2 desorbed/g of catalyst, responsible for its higher transesterification efficiency of the Ca-HT catalyst. The Fourier transform infrared spectroscopy study showed peaks at 3036 and 3042 cm −1 for Ca-HT and lanthanum-doped hydrotalcite (La-HT), respectively, confirming the presence of hydrogen bonding between water and interlayer carbonate anions responsible for abstracting proton from the primary hydroxyl group of glycerol to attack over carbonyl carbon of PC. The presence of intercalated carbonate ions is also confirmed by the Raman study, in both HT and Ca-HT catalysts and even after use of the Ca-HT catalyst. The thermogravimetry−differential thermal analysis study evidenced the higher thermal stability of the Ca-HT (T 4 = 765 °C) catalyst than that of parent HT with a Mg/Al ratio of 3:1 (T 4 = 630 °C). Various process conditions, such as the temperature, molar ratio of glycerol/PC, and catalyst loading, significantly influenced conversion and selectivity of glycerol and GC, respectively.

One‐pot Fixation of CO2 into Glycerol Carbonate using Ion‐Exchanged Amberlite Resin Beads as Efficient Metal‐free Heterogeneous Catalysts

“…This trend in activity is ascribed to the stronger basicity of OH − compared to Cl − and I − [30] . The hydroxide ion can promote this reaction by abstracting a proton from glycerol, leading to the formation of a nucleophilic alkoxy ion, which facilitates the nucleophilic attack on the carbonyl group of propylene carbonate [33] . As a consequence, a carbonate intermediate ion is formed, which undergoes ring closure, yielding glycerol carbonate [33] .…”

“…MgO, CaO and MgO@ZIF‐8) [17,40–42] and hydrotalcites [43–45] . Based on these previous studies, the presence of a basic catalytic site is crucial to initiate this reaction by abstracting a proton from glycerol, which results in the formation of the glyceroxide ion, thus enhancing the nucleophilicity in the attack on the carbonyl group of propylene carbonate [12,33] . Moreover, this reaction is a reversible process, meaning that the molar ratio between the organic carbonate and glycerol plays a critical role in determining the equilibrium concentrations of reactants and products [13,34] …”

“…Conversely, the transcarbonation reaction of glycerol with organic carbonates is considered the most viable route for the synthesis of glycerol carbonate due to its environmental friendliness, mild operation conditions, high yield and selectivity [12,14] . This reaction has been broadly studied with dimethyl carbonate [17,30] or diethyl carbonate [31,32] as reactants, while only few works reported the reaction with propylene carbonate (PC) [33,34] . The synthesis of dimethyl or diethyl carbonate from CO 2 requires stoichiometric amounts of a drying agent to achieve acceptable products yields, [35] or can be achieved with high yields through a greener path involving a transcarbonation reaction from propylene carbonate [36] .…”

“…[12,14] This reaction has been broadly studied with dimethyl carbonate [17,30] or diethyl carbonate [31,32] as reactants, while only few works reported the reaction with propylene carbonate (PC). [33,34] The synthesis of dimethyl or diethyl carbonate from CO 2 requires stoichiometric amounts of a drying agent to achieve acceptable products yields, [35] or can be achieved with high yields through a greener path involving a transcarbonation reaction from propylene carbonate. [36] Based on these considerations, the direct reaction of glycerol with propylene carbonate (Scheme 2) is preferable in the context of sustainability compared to the routes involving dimethyl or diethyl carbonate.…”

Layered Double Hydroxides: A Toolbox for Chemistry and Biology

“…Kondawar et al worked on glycerol transesterification preparing MgAl LDHs, pure or doped with Ca and La [112] (see Figure 6). While the study also interested the simple metal oxides, and CaO showed the highest activity, the formation of soluble calcium glycerate prevented its recovery and recyclability.…”