Process analytical technology (PAT) as a versatile tool for real-time monitoring and kinetic evaluation of photocatalytic reactions

In this work, we present a methodology for the real-time monitoring of light induced reactions. Employing process analytical technology (PAT) permits an in situ approach to disclose kinetic insights into photocatalytic reactions. The applicability of this methodology was tested on the eosin Y (EY) catalysed photooxidation of 4-methoxythiophenol (4-MTP) to bis(4-methoxyphenyl)disulfide (4-MPD). The reaction was monitored by in situ Raman and UV/Vis spectroscopy under various process conditions including the stirrer speed, oxygen pressure, EY concentration and light intensity. Evaluation by an indirect hard modelling approach (IHM) disclosed the contributions of rate limiting effects like the oxygen mass transport and the degradation of EY. Detailed investigations on the influence of EY concentration and light intensity led to an empirical model for the correlation of the initial photooxidation rate with the averaged rate of photon absorption. These results confirmed the applicability of the methodology to support the development of photocatalytic reactions.