Sustainable valorization of agro-waste by microwave pyrolysis: mechanisms, optimization, catalyst pathways, integration strategies, and perspectives.

In this review, the difference between microwave (MAP) and conventional pyrolysis (CP), reactor types, parameters affecting, and optimization were reported and compared in detail. Also, the catalysts used and their systematic role in enhancing the pyrolytic products with their effect were reviewed. In addition, the potential integration of microwave pyrolysis with other pretreatments, torrefaction, and anaerobic digestion for high-quality production, along with technology challenges and future direction, have been illustrated. The review revealed that MAP produced higher combustible gases (H, CH, and CO), higher phenolic and calorific value bio-oil, and high-quality biochar compared to CP. ML is a superior option for optimizing MAP parameters due to utilizing and predicting effectively several input parameters with their interaction. Zeolite catalyst is favorable for biochar and gas production, while metal and carbon catalysts are favorable for bio-oil production. Also, zeolites improved the hydrocarbon content in the bio-oil, while metal oxides enhanced the phenolic. Introducing the digestate from anaerobic digestion as a MAP feedstock is highlighted for high-quality production. This review provides intensive information for MAP mechanism, focusing on the complete technology set for a better understanding of the reaction and transferring the technology to scalability in the industry.