(308a) Application of Structured Porous Reactors for Heat Sensitive Liquid-Liquid Reactions

For biphasic transformations, packed beds represent a versatile reactor system to improve mixing and mass transfer. However, the main drawbacks limiting their use, especially for scale-up applications, is their large associated pressure drop, flow mal-distribution resulting in non-uniform contact time, and attrition of the small particles. An interesting alternative to overcome these drawbacks is the use of porous structures based on open cell metal foams, which combine the improved transport processes of the micro-scale with the throughput of milli-scale reactors [1].

In terms of multiphase flow, open cell metal foams were primarily investigated for gas-liquid systems to study hydrodynamics and mass transfer in both co-current and counter-current operation in solid foam packings [2]. In our previous work, we have investigated liquid-liquid flow hydrodynamics and mass transfer in various structured and well-defined porous media similar to open cell foams [3]. We have found that depending on the fluid properties, different design parameters of the porous structures play a crucial role in determining the overall mass transfer performance. In general, it is observed that the porous reactors enhance slug breakup, resulting in lower mean slug lengths for both phases and an associated enhancement in surface renewal velocities. The designed porous milli-scale reactors provide enhanced mass transfer performance, with a two orders of magnitude reduced energy dissipation compared to conventional milli-scale packed bed reactors.

We extend this study to investigate the heat transfer performance of these structured porous reactors. In single phase flow, we use planar laser-induced fluorescence (PLIF) and apply a two-color ratiometric technique which allows the in-situ determination of the fluid temperature field [4]. In addition, the effect of different design parameters on two-phase flow heat transfer is analyzed globally.

Based on the results of the heat and mass transfer study, we have applied these novel designed porous reactors for the amination reaction of aryl halides in the presence of a phase transfer catalyst (PTC). The palladium catalysed amination reaction of aryl halides is one of the important transformations for pharmaceutical industry, and the biphasic amination with use of a PTC provides a solution to the problem of solid formation in continuous flow reactors [5]. The effect of mixing on the yield of the C-N cross coupling reaction is studied in detail at optimum reaction conditions. Finally, the performance of the designed porous reactors is assessed by comparing with an equivalent void volume milli-scale packed bed reactor.

References:

1. Hutter, C., et al., Axial dispersion in metal foams and streamwise-periodic porous media. Chemical Engineering Science, 2011. 66(6): p. 1132-1141.

2. Stemmet, C.P., et al., Hydrodynamics of gas–liquid counter-current flow in solid foam packings. Chemical Engineering Science, 2005. 60(22): p. 6422-6429.

3. Potdar, A., et al., Designed porous milli-scale reactors with enhanced interfacial mass transfer in two-phase flows. React. Chem. Eng., 2017.

4. Kuhn, S. and Rudolf von Rohr, Ph., Experimental study of heat flux in mixed convective flow over solid waves. Experiments in Fluids, 2008. 44(6): p. 973-984.

5. Naber, J.R. and Buchwald, S.L., Packed-Bed Reactors for Continuous-Flow C-N Cross-Coupling. Angewandte Chemie International Edition, 2010. 49(49): p. 9469-9474.