Photocatalysis has emerged as a crucial activation strategy in synthetic organic chemistry, which has already attracted interest from pharmaceutical and agrochemical industries. However, in much contemporary research the critical aspect of reactor design remains underexposed - even though it is an essential component for translating academic breakthroughs into practical industrial applications. As a key contributor to the Horizon 2020 FlowPhotoChem project, Stefan Zondag has significantly advanced the integration of light energy into chemical reactor design, paving the way for more sustainable industrial practices.

Open source 3D-printable reactor designs

In Zondag’s thesis, six chapters offer revolutionary approaches to photoreactor design, scale-up methodologies, and renewable energy applications. Among the highlights are his novel method to characterize photoreactor systems, published in Nature Chemical Engineering, and his open-source 3D-printable photoreactor designs. The latter have already gained widespread use in academic and industrial laboratories worldwide.

This remarkable achievement reflects Zondag’s intellectual independence, technical ingenuity, and commitment to collaborative progress. During the COVID-19 pandemic, he seamlessly transitioned from experimental work to computational simulations, showcasing his adaptability and self-driven mastery of complex engineering tools. His dedication extends beyond his own research, earning him praise as an educator and a trusted collaborator. Zondag’s work exceeds the standards of academic excellence, leaving a lasting impact on photochemical engineering and sustainable innovation.

Abstract of the thesis

The thesis explores the transition from batch to continuous-flow processing in photochemistry, focusing on reactor design, characterization, and application. This shift introduces unique challenges and operating conditions. The work presented emphasizes understanding factors affecting photoreactor operation, which is essential for reactor characterization, benchmarking, and scaling up. Photochemistry's expanding applications involve a wide range of reaction media, reactor geometries, light sources, and control requirements, making reproducibility a critical concern.

Chapter 1 provides a broad introduction to continuous-flow photochemistry and luminescent solar concentrators. Chapter 2 showcases a methodology to determine photon flux and the newly introduced one-dimensional parameter, effective optical path length, which enhances reactor characterization. The work uses radiometry and ray-tracing simulations, validated with batch photochemistry and applied to continuous-flow reactors, to improve photon-efficiency assessment photoreactors. Chapter 3 discusses novel 3D-printed reactors, addressing key challenges in photochemistry, while Chapter 4 introduces a method to convert microreactors into light-harvesting systems using luminescent solar concentrators. This method separates reactor design from solar applications, enabling easy dye replacement and rapid screening. In Chapter 5, a scaled-up solar-powered system is demonstrated, allowing automated off-grid operation with photovoltaic cells and feedforward control for product quality. Chapter 6 focuses on handling solids in continuous-flow systems, introducing a photoreactor that avoids clogging while operating in gas-liquid-solid environments.

This research highlights the importance of reactor characterization, light-source matching, and the handling of multiphase systems for the future development and scale-up of photoreactors.

S.D.A. Zondag: Design, characterization and application of continuous-flow photoreactors. Download the PDF from the UvA repository.

See also

• H2020 FlowPhotoChem projectwebsite: 
• Flow Chemistry research group