Continuous Photo-Oxidation in a Vortex Reactor: Efficient Operations Using Air Drawn from the Laboratory

Abstract

We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor.

One‐Pot Synthesis of Diverse γ‐Lactam Scaffolds Facilitated by a Nebulizer‐Based Continuous Flow Photoreactor

“…To solve these problems both the surface area of the reaction solution that is exposed to light and the gas‐liquid interface surface area should be maximized. Examples of how one, or sometimes both, these surface areas have been maximized include; using lengths of flexible tubing wrapped around the light source (fluorinated ethylene propylene‐FEP tubing,– perfluoroalkoxy‐PFA tubing,,, microcapilliary,,,, parallel systems,), thin‐walled annular vessels, falling films, thin film, gas‐liquid membranes, vortexes or mesofluidic devices . In our system (Figure ), very high specific surface areas (conservatively estimated to be in the range of 100,000 to 1,000,000 m 2 m −3[7a,14] ) have been attained by nebulizing the reaction solution.…”

Light on the Horizon: Current Research and Future Perspectives in Flow Photochemistry

“…In this case a rapid rotation generates a Taylor vortices flow presenting certain advantages for gas/liquid heterogeneous reactions. 41 The high mass transfer between both layers allows a more efficient dissolution of gases, owing to which air from the lab can be used instead of pressurized oxygen. The versatile application of a vortex reactor could be demonstrated in different photochemical reactions using 1…”

Process Intensification – An Unbroken Trend in Chemical Engineering

“…Further process intensification can be achieved through continuous flow reactors . Furthermore, several recent publications illustrate the benefits of advanced reactor concepts, e.g., packed‐bed‐, pneumatic nebulizer‐, slug flow, annular flow, vortex or luminescent solar concentrator reactors .…”