Microwave-Driven Intensification of Diglycerol Transesterification through Dynamic Temperature Operation

The transition to nonisocyanate polyurethanes (NIPUs) relies on sustainable routes to precursors like diglycerol dicarbonate (DGC). However, its synthesis via transesterification is hampered by equilibrium limitations, inefficient heat transfer, and high energy demands under conventional heating (CH). This work investigates the transesterification of diglycerol (DIG) with dimethyl carbonate (DMC) under CH and microwave heating (MWH) in batch autoclave reactors. The effects of catalyst loading, DMC:DIG ratio, and temperature were assessed under isothermal and dynamic (temperature-cycling, TC) operation. At 130 °C, MWH achieved 97% DIG conversion and 66% DGC yield, matching the performance of CH at 150 °C. This enhancement is attributed to efficient volumetric heating and methanol removal, which continuously shifts the equilibrium toward product formation. Dynamic MWH via optimized TC further intensified the process, achieving 73% DGC yield with an 85% reduction in reaction time and lower byproduct formation. These findings establish MWH, particularly under optimized dynamic operation, as a versatile intensification platform for equilibrium-limited reactions, enabling faster and more sustainable synthesis of polyurethane precursors.