Remarkable Improvement of Organic Photoreaction Efficiency in the Flow Microreactor by the Slug Flow Condition Using Water

Abstract

A typical (Paterno-Buchi type) organic photoreaction is examined in flow microreactors. Compared to the results achieved for simple one-layer flow modes, slug flow conditions (with the unreactive reagent composed of organic solution and water) achieve higher efficiency (conversion and yield) irrespective of the light source, concentration, and solvent. Furthermore, remarkably high productivity is also observed when only 5% water is added as an unreactive reagent. This method is broadly applicable for achieving highly efficient organic photoreactions not only in the laboratory, but also on the industrial scale.

Photon Transport and Hydrodynamics in Gas‐Liquid Flows Part 1: Characterization of Taylor Flow in a Photo Microreactor

“…As can be seen in Figure 4, the variation found in our actinometric measurements is similar to the values obtained in the Paternò-Büchi photoreactions by Terao et al [4b] and Nakano et al [7] However, even if an exponential increase of conversion with the gas content is present also in the work of Telmesani et al, [6] the acceleration of the reaction observed by them is significantly higher. This could be due to the different physical properties of their solvent (ethyl acetate vs. toluene and hexane), smaller tube diameter (0.8 mm vs. 1 mm) and different light absorption properties of the employed reaction mixture.…”

“…To calculate the photon flux per liquid volume and the optical pathlength from the chemical actinometric measurements we need to determine how long the liquid was Nakano et al [7] and Telmesani et al [6] illuminated when passing through the microreactor. This was realized using residence time distribution (RTD) experiments.…”

“…Moreover, a lower productivity is expected in two-phase flow as a fraction of the reactor is occupied by the inert phase. However, higher productivities in two-phase flow compared to single-phase were achieved by using a very low fraction of the inert phase (Nakano et al [7] ) or by using highly concentrated solutions (Telmesani et al [6] ). Starting from our model, we can propose an additional optimization strategy which involves a rational design of the Taylor flow characteristics (i. e. bubble and slug lengths, film thickness) by finding the optimal liquid volume in the highly irradiated region of the film and in the darker region of the bulk liquid.…”

“…An additional study was realized by Nakano et al who analyzed in detail the influence of the light source, concentration, and solvent. [7] Moreover, water was used as the inert phase by Telmesani et al who investigated the photocycloaddition of cinnamates in an ethyl acetate-water Taylor flow. [6] They achieved a conversion of 43 % in two-phase flow at a water fraction of 0.9 in comparison to 6 % when the water was absent.…”

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 .…”