Development and Hydrodynamic Characterization of a Modular Mini-Plant Photoreactor

Abstract

The exponential decay of light intensity in absorbing media poses a particular challenge to the development of light-driven chemical reactions on an industrial scale. To counteract the challenges of the irradiation field, photoreactors are required to enable accelerated mass transport on both the laboratory and production scale. This contribution presents the development of a modular mini-plant photoreactor (MISCOP) designed to bridge the gap between small laboratory and industrial scale photoreactors. To improve the overall efficiency of the photoreactor, the acceleration of mass transport along the direction of light propagation through static mixers is experimentally and numerically investigated by exploiting the modularity of the photoreactor. The results reveal a significant narrowing of the residence time distribution as well as enhanced mass transport along the ray trajectory.

Enhancing mass transport to accelerate photoreactions and enable scale-up

“…Frequently, long residence times are required, associated with laminar flow conditions and slow mass transport, especially perpendicular to the main flow direction. 15,16 Since most photoreactors are irradiated in a cross-current fashion, a strong gradient of the reaction rate potentially leads to lower overall performance and/or product yield. 17–19 The use of static mixers is a meaningful approach to ensure fast mass transport even for laminar flow conditions.…”

“…17–19 The use of static mixers is a meaningful approach to ensure fast mass transport even for laminar flow conditions. 16,20–25 Mixing can also be enhanced by inducing defined vortices, e.g. in a Taylor–Couette reactor, which was recently applied to photochemical processes.…”

“…41–43 Industrial applications require a systematic scale-up strategy, that starts in the laboratory together with a comprehensive documentation and reporting strategy. 16,44–46 The scale-up of industrial applicable photoreactors must consider two geometric challenges: i) the scaling of light sources, e.g. internal/external multi-lamp systems, or the increase of lamp length, and ii) the scaling of the reaction volume.…”

“…For this reactor, experimental and numerical hydrodynamic studies have shown that the installation of static mixers significantly improves macro-mixing within the mini-plant photoreactor. 16…”

Development of a Horizontal Dynamically Mixed Flow Reactor for Laboratory Scale-Up of Photochemical Wohl–Ziegler Bromination

“…Coupled with the advent of cheaper monochromatic light sources, i.e., light emitting diodes (LEDs), there has been an explosion in new chemical transformations reported in the literature, from both academia and the pharmaceutical industry. − As these new transformations are implemented into the construction of active pharmaceutical ingredients (APIs), a perennial question arises: how do you scale photochemical transformations? Continuous flow chemistry has received much attention for scaling photochemistry due to the increased surface area to volume ratio which satisfies issues around the penetration of light (Beer–Lambert law) and the intensity of light (Bunsen–Roscoe law). , As intimated above, there are added complexities to reactor design for photochemistry, and both light penetration and the use of heterogeneous catalysis remain unresolved issues when designing reactors. In recent years, different types of reactors have been described in the literature as a solution to performing photochemistry on scale. − These reactors tend to follow a PFR design (Figure a), although the design of immersive modular photoreactors with static mixing has recently been reported to increase mass transfer in the system . There are some exceptions to these examples including the rotor–stator spinning disk reactor, the oscillatory plug flow reactor, the continuous stirred tank reactor (CSTR), , the falling film reactor, and a vertical Taylor vortex reactor. , …”