An Overview of the Latest Advances in the Catalytic Synthesis of Glycerol Carbonate

In recent years, the development of renewable energy alternatives to traditional fossil fuels has become one of the major challenges all over the world, due to the decline of fossil fuel reserves and their effect on global warming. Biodiesel has become a popular alternative energy source to reduce gas emissions compared to traditional fossil fuels. According to statistics, a nine-fold increase in global biofuel production between 2000 and 2020 was observed. However, its production generates a large amount of glycerol as a by-product, posing an environmental problem when disposed directly in landfills or by incineration. Therefore, low-value glycerol should be converted into high value-added derivatives. As glycerol carbonate is one of the most important derivatives of glycerol, this review aims to discuss the studies over the last ten years about glycerol carbonate synthetic methods, including the typical routes such as phosgene, esterification reaction, urea, oxidative and direct carbonylation as well as several rare synthetic procedures. At the same time, it summarizes the different catalytic reaction systems of each route comparing the advantages and disadvantages of various catalysts and evaluating their catalytic activity. Finally, the future development of glycerol carbonate synthesis is prospected from the point of view of development, technology research and industrialization.

Synthesis of Glycerol Carbonate from Glycerol and Dimethyl Carbonate Catalyzed by Solid Base Catalyst Derived from Waste Carbide Slag

Na2CO3 was loaded onto waste carbide slag (CS) by impregnation-calcination method to prepare the solid base catalyst, which was used to synthesize glycerol carbonate (GC) by the transesterification of glycerol with dimethyl carbonate (DMC). The prepared catalysts were characterized by a scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Brunner−Emmet−Teller (BET) techniques. The catalyst 15 wt.% Na2CO3-CS-800, which was prepared by impregnating CS to the Na2CO3 solution with the concentration of 15 wt.% weight of CS and calcined at 800°C for 3 hours, showed an excellent catalytic ability. When it was applied in the catalytic synthesis of GC, 98.1% glycerol conversion and 96.0% GC yield were achieved in 90 mins at 75°C with the catalyst dosage of 3 wt.% to total reactants and the DMC to glycerol molar ratio of 5. More importantly, the loading of Na2CO3 can effectively improve the reusability of catalyst. The 15 wt.% Na2CO3-CS-800 can still achieve 83.6% glycerol conversion and 80.5% GC yield after five-time reuse. Meanwhile, under the same reaction conditions, the CS-800, which was obtained by calcining CS at 800°C for 3 hours, experienced significant activity reduction with only 15.2% glycerol conversion and 14.1% GC yield after five-time reuse. FTIR and XRD characterization revealed that CO32- might play a key role in preserving active catalytic CaO component by forming protective CaCO3 shell on the catalyst surface.

Effect of Calcination on Shell Powder Catalyst Towards Effectiveness on Catalysing Transesterification of Crude Glycerol to Glycerol Carbonate

Valorisation of crude glycerol has gained much interest in the industry associated with the surplus of crude glycerol caused by the increase usage of biodiesel. Transesterification of crude glycerol using a heterogenous base catalyst is one of the effective ways to utilize the additional glycerol. Seawater clams commonly serve as a food source to us and the waste shells are a source of calcium carbonate that is abundantly available and can be converted into a heterogenous base catalyst for the transesterification process. Therefore, this study focuses on the utilization of catalyst synthesized from a species of seawater clam, Paratapes Undulatus in a transesterification reaction using crude glycerol (C.GLY) as a reactant together with dimethyl carbonate (DMC) to synthesize glycerol carbonate (GLYC). The catalysts are characterized using Field Emission Scanning Electron Microscope (FESEM), Attenuated Total Reflectance (ATR), Thermogravimetric Analysis (TGA), X-ray diffraction (XRD) and Particle Size Analyser (PSA). The product is characterized using Gas Chromatography (GC-FID). The performance of the synthesized shell catalyst with different calcination condition was studied. The reaction using the calcined shell catalyst is carried out at 75°C, molar ratio of 2 and 2wt% of catalyst for 1 hour. The catalyst that has the best performance is the shell catalyst that is calcined for 3h, which give the yield of 54.16%.

Alternative Route for Biodiesel Synthesis with Co-Production of Glycerol Carbonate

As an alternative route from the conventional alkali-catalyzed biodiesel production, the supercritical dimethyl carbonate method had been proven to successfully produce biodiesel with the co-production of glycerol carbonate in a one-step and two-step non-catalytic methods. Biodiesel or fatty acid methyl esters (FAME) obtained were high in yield, comparable with supercritical methanol method and satisfy the international standards for use as biodiesel in engines. In this paper, key parameters for the processes such as reaction temperature, pressure, time, molar ratio of dimethyl carbonate to oil, the FAME yield, thermal decomposition, degree of denaturation, tocopherol content, oxidation stability and fuel properties were discussed. The optimized condition for supercritical dimethyl carbonate method is at 300°C/20MPa/20min/42:1 molar ratio of dimethyl carbonate to oil with a satisfactory yield of FAME at 97.4wt%. The extensive approach in this study is very important to complement mathematical model for optimization in the literatures, and to ensure that only high-quality biodiesel could be produced by supercritical dimethyl carbonate method under an optimized condition.

The Synthesis of Glycerol Carbonate from Glycerol and Dimethyl Carbonate in the Presence of Strongly Basic Anion-Exchange Styrene-Divinylbenzene Anionites Dowex

The synthesis of glycerol carbonate from glycerol and dimethyl carbonate in the presence of strongly basic styrene-divinylbenzene anionites Dowex 1×2, Dowex 1×4 and Dowex 1×8 in the –OH form with different cross-linking degree of polystyrene matrix (the divinylbenzene content of 2, 4 and 8 wt.%) at 90–105 °C and a dimethyl carbonate/glycerol molar ratio equal to 2 was studied. The yield of glycerol carbonate was shown to decrease with an increase in the cross-linking degree of the anion-exchange resin. The maximum conversion of glycerol (95 %) and selectivity to glycerol carbonate (45.5 %) were observed in the presence of Dowex 1×2 at 105 °C after 5 h of the reaction. Advantages of the studied systems were demonstrated in comparison with the anion-exchange and cationexchange resins proposed in the literature.

β-Cyclodextrin-Calcium Complex Intercalated Hydrotalcites as Efficient Catalyst for Transesterification of Glycerol

β-cyclodextrin derivative intercalated MgAl-hydrotalcites (β-CD-Ca/LDH) was synthesized to convert glycerol into high value-added glycerol carbonate(GC) by transesterification of dimethyl carbonate (DMC) and glycerol in this paper. β-cyclodextrin-metal complexes and β-CD-Ca/LDH was characterized by XRD, FT-IR, SEM, XPS and nitrogen adsorption-desorption. The enrichment of organic reactants in the hydrophobic cavity of β-cyclodextrin improved the collision probability of reactants. The intercalation of β-cyclodextrin-calcium complex (β-CD-Ca) increased the pore size and basic strength of catalyst. The experiment results showed that the glycerol conversion was 93.7% and the GC yield was 91.8% catalyzed by β-CD-Ca/LDH when the molar ratio of DMC and glycerol was 3:1, the catalyst dosage was 4 wt.%, the reaction temperature was 75 °C and the reaction time was 100 min while the glycerol conversion was 49.4% and the GC yield was 48.6% catalyzed by MgAl-LDH under the same conditions.