Microwave-Absorbing CaO-CNT Catalyst for Enhanced Transesterification: Bridging Dielectric Loss to Energy-Efficient Fatty Acid Methyl Ester Production

Microwave-assisted technology effectively enhances heterogeneously catalyzed transesterification reactions for production of fatty acid methyl esters (FAME), which are the components of biodiesel. FAME are key intermediates for sustainable aviation fuels. Nevertheless, the impact of the microwave-absorbing capacity of a catalyst on catalytic performance is still ambiguous. Herein, we successfully synthesized a microwave-absorbing catalyst (CaO-CNT) and a microwave-transparent catalyst (CaO-SiO2) and evaluated the catalytic performance in the transesterification reaction of palm oil and methanol. The microwave-absorbing capacity of the catalyst enhanced the catalytic performance in the microwave field, and the dielectric loss (tan δε = 0.172) of CaO-CNT was much stronger than that of CaO-SiO2 (tan δε = 0.002), demonstrating a superior microwave-absorbing capacity. The CaO-CNT in situ provided essential energy to reactants heated by microwave heating and the transesterification conversion by 11.44%, while that of CaO-SiO2 only increased by 0.83%. Notably, CaO-CNT saves 15% of energy consumption and reduces 303.72 kg of CO2 per ton of FAME produced compared to that of the microwave-transparent catalyst, CaO-SiO2.