A Sustainable-by-Design Process for the Selective Photooxidation of Ethylbenzene in a Scalable Agitated Baffle Reactor

This study presents a sustainable-by-design approach for the selective photooxidation of ethylbenzene under continuous flow conditions using sodium anthraquinone-2-sulfonate (SAS) as a water-soluble photocatalyst. The reaction was conducted in a scalable agitated baffle reactor (SABRe) under ultraviolet (UV)-A irradiation (365 nm), enabling enhanced mixing, illumination, and gas−liquid contact. To systematically optimize the process, a four-factor central composite design based on response surface methodology (RSM) was employed, evaluating the influence of catalyst loading, liquid and gas flow rates, and light intensity. The study revealed that oxygen mass transfer from air is a key limiting factor, which was successfully addressed by implementing counter-current gas−liquid flow and increased agitation speeds. These modifications led to a significant improvement in ethylbenzene conversion and selectivity toward acetophenone. The SABRe reactor achieved a space−time yield (STY) of 14.8 g L−1 h−1, representing a three fold improvement over the conventional microchannel reactor configuration. Under optimized conditions, an extended 8 h continuous operation processed 1.44 L of feed solution, delivering an 87% isolated yield with ≥98% product purity. The modular and scalable nature of the SABRe platform, combined with efficient process intensification strategies, underscores its potential for sustainable chemical manufacturing and future scale-up via a numbering-up approach for photocatalytic C−H functionalization using our intensified continuous flow technology.