Sodium Silicates Modified Calcium Oxide as a High-Performance Solid Base Catalyst for Biodiesel Production

Under the energy crisis and with greenhouse gases causing an ecological imbalance, biofuel has attracted worldwide attention due to its sustainability and low net-carbon emission. For years, the traditional biodiesel industry has been demanding a high-performance solid base catalyst. Its poor reusability is the bottleneck for a promising calcium-based solid-base catalyst. In this work, we successfully adopted a new silicate-strength strategy to improve the stability while preserving the activity of the catalyst. The newly synthesized catalyst, NCSO, had two main catalytic phases, Na2CaSiO4 and CaO, and showed a 98.2% FAMEs yield in 60 min at 80 °C with a methanol/oil molar ratio of 9:1 and 5 wt.% catalyst loading. After 12 consecutive reuses, a 57.3% FAMEs yield could still be achieved. The effect of the reaction temperature, methanol ratio, catalyst loading, and reaction time on the FAMEs yield was also investigated. With a combined characterization of XRD, XPS, and SEM, etc., we confirmed that Na2CaSiO4 and CaO showed a synergistic effect in catalyzing the transesterification reaction: the addition of the Na2CaSiO4 phase in NCSO could significantly improve the activity of CaO, while the CaO phase, in turn, helps to stabilize the Na2CaSiO4 phase. This silicate-strength strategy provides a new route to synthesize stable and highly active solid base catalysts.