Optimization of Photooxygenation of Dihydroartemisinic Acid in a Continuous Micro-reactor utilizing Physically Immobilized Methylene Blue on Polystyrene Micro-particles

Extensive studies reported upon the application of microfluidic devices for photooxygenation reactions. Only a few researches, however, have studied the optimization of experimentally controllable parameters towards achieving the best reaction conversion. Accordingly, in the current study, the optimum values of operating parameters towards achieving the highest dihydroartemisinic acid (DHAA) conversion were determined through the response surface methodology (RSM) technique. In order to do that, first, heterogenized microphotosensitizers were synthesized during a super facile procedure not requiring any chemical reaction or modifications. Then, these micro-photosensitizers were utilized to perform continuous photooxygenation of the DHAA by means of a glass micro-reactor at room temperature and atmospheric pressure. Finally, the impacts of experimental parameters such as the flow ratios of solution to oxygen as well as DHAA and microphotosensitizers' concentrations upon the DHAA conversions were examined by using Design of Experiments (DOE) software in order to optimize and statistically model the DHAA conversion. The optimum value for this conversion was predicted by the RSM technique to be 70 % which was in a very good agreement with that of the experimental value of 69 % obtained in this study. The optimal values for the flow rates ratio, DHAA initial concentration, and micro-photosensitizer's concentration were obtained to be 0.5, 0.5 mg/ml, as well as 1.5 mg/ml, respectively.