Overcoming the Achilles Heel of flow chemistry: strategies for solid handling in heterogeneous continuous-flow reactors

Handling of solids remains one of the most persistent challenges in continuous-flow chemistry. While the field has achieved remarkable progress in process intensification and scalability, the presence or formation of solids often disrupts smooth operation through clogging, fouling, and hydrodynamic instability. Over the past two decades, an array of reactor concepts and engineering strategies, ranging from improved passive geometries to advanced active systems, have been developed to overcome these issues. This review provides a comprehensive overview of the latest innovations for managing solid–liquid and multiphase mixtures in flow. Technologies discussed include rotating and oscillatory flow reactors, ultrasound-assisted systems, and emerging designs such as liquid-walled reactors. Each strategy is examined in the context of mixing behavior, mass transfer, scalability, and process robustness. By bridging insights from chemical engineering and synthetic methodology, this article aims to guide the rational design of heterogeneous continuous-flow systems that fully exploit the advantages of flow chemistry while embracing its most challenging domain: solid handling.