Analysis of Glycerol Carbonate Production from Dimethyl Carbonate and Glycerol Using Different Alkaline Zirconates (Li _{2– <i>x</i>} Na _<i>x</i> ZrO ₃ , Where 0 ≤ <i>x</i> ≤ 2) as Efficient Catalysts

The growing demand for biodiesel has generated an excess of glycerol as a byproduct. Thus, catalytic conversion of glycerol into value-added products, such as glycerol carbonate (GC), is important. In the present study, Li2ZrO3 and different compositions of the lithium–sodium zirconate solid solution (Li2–xNaxZrO3) were tested for GC production from glycerol and dimethyl carbonate transesterification reaction. All the ceramic chemical compositions were synthesized by solid-state reaction and fully characterized. Then, gas chromatography-mass spectroscopy was used to analyze the catalytic reaction products, using as initial and main material Li2ZrO3. For lithium zirconate, the best reaction conditions (80 °C and 180 min, using 10 mol % of catalyst and a reagents molar ratio of 1:1.5) evidenced a maximum glycerol conversion of 94.5%, with a yield and selectivity of 92.6 and 98%, respectively, toward glycerol carbonate formation. In addition, the kinetic parameters of this reaction, using Li2ZrO3 as the catalyst, were also investigated, revealing that the process followed a pseudo-first-order kinetic model, with an activation energy of 57.07 kJ mol–1. Additionally, the associated thermodynamic parameters, including enthalpy, entropy, and Gibbs free energy, were also calculated. Based on lithium zirconate results, different Li2–xNaxZrO3 solid solution compositions were catalytically analyzed under the same physicochemical conditions. Results evidenced that GC formation strongly depends on the Li/Na ratio, where optimal yield and selectivity values were achieved for mixed Li-rich compositions, while Na-rich samples promoted side reactions, mainly glycidol formation. Moreover, it was determined that Na addition mainly modified the kinetic behavior, rather than thermodynamic data. Overall, Li2–xNaxZrO3, where (x ≥ 0.8), demonstrated good performance under moderate conditions, making them an attractive option for minimizing the costs associated with reagents and energy requirements.