Microwave Hybrid Heating for Sustainable Biodiesel Production: Innovations in Transesterification and Feedstock Processing

This chapter examines microwave hybrid heating (MHH) as an advanced technology for eco-friendly biodiesel production that integrates microwave irradiation with complementary technologies such as ultrasound, enzymatic catalysis, and conventional heating for biodiesel production. MHH achieves high biodiesel yields (93.5–99.8% for waste oils and microalgae) in 10 s to 2 min, with up to 80% energy savings for transesterification, and up to 97% savings for wet microalgae by eliminating drying compared to conventional transesterification (90–96.6% yields, 1–2 h). It leverages electromagnetic mechanisms, such as dipolar polarization, ionic conduction, and molecular-surface interactions, for rapid heating and efficient mass transfer. Hybrid configurations optimize the processing of third-generation feedstocks, including microalgae, waste cooking oil (WCO), and high fatty acid materials, thereby supporting waste-to-energy conversion. MHH’s versatility spans catalytic (homogeneous, heterogeneous, and enzymatic) and non-catalytic processes (e.g., supercritical alcohol and direct transesterification), promoting resource efficiency. Despite these advantages, challenges in reactor scalability, catalyst durability, feedstock consistency, and safety compliance persist, necessitating the use of continuous-flow reactors, waste-based catalysts, and standardized protocols. Future research should prioritize pilot-scale trials, biorefinery integration, advanced catalysts, and policy-driven incentives (e.g., blending mandates). Bridging chemical engineering, environmental science, and energy transition policies, MHH offers a key pathway for scalable and cost-effective biofuel systems that align with the sustainability goals.