Process Intensification for Sustainable Microwave-Assisted Bio p-Cymene Production from Limonene

Limonene is the most abundant terpene in citrus byproducts, such as lemon and orange peels. Due to its six-membered ring structure, it is considered a valuable feedstock for the synthesis of important bioaromatics, such as p-cymene. This study aims to develop a rapid and sustainable method to produce bio p-cymene from biomass-derived limonene. The use of enabling technologies, such as microwaves (MWs), can significantly intensify the process, leading to further improvements in sustainability. Several mono- and multimode MW reactors have been tested in this context. Monomodal systems have yielded the highest p-cymene output (up to 22.61% selectivity), while multimode reactors allow for a scaling-up approach that overcomes the limitations of the monomodal ovens while still providing noticeable p-cymene yields (up to 17.79%). An environmentally friendly protocol that utilizes mild temperatures (80–165 °C), has reduced time requirements (0–5 min), and can be performed in solvent-free conditions was employed throughout the process. This approach makes use of a wide range of biorefinery-based practices and is aligned with green processing, the circular economy, and process intensification principles.