A Comparative Experimental Evaluation of an Automated Batchwise and Continuous Operation Mode for Scaling up a Falling Film Looping Photoreactor

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Abstract A falling film looping photoreactor consisting of three reactor modules (1 × A, 2 × A and 4 × A), with increasing irradiated areas (A) of 78.5 cm2, 179 cm2, and 314 cm2, was transferred from batch to continuous operation. The practical operability was demonstrated for the light-driven bromination of toluene with the 2 × A reactor module (space velocity s = 15 min–1, reactor volume Vr = 20 mL, toluene concentration = 500 mM) over 24 h operation under automized batch conditions with a productivity of up to 341.1 g • d–1 of benzyl bromide. The influence of the external flow rate V˙ext on the residence time distribution (RTD) within the falling film looping photoreactor was evaluated using pulsed tracer experiments. The resulting residence time distribution curves were evaluated by using an axial dispersion model to get deeper insight into the characteristic hydrodynamics within the falling film looping photoreactor during continuous stirred tank reactor (CSTR) operation. Based on this knowledge, a direct transfer from a batch stirred tank reactor (BSTR) to a CSTR was realized with a comparable productivity of up to 363.7 g • d–1 of benzyl bromide by adjusting the hydrodynamic residence time in the continuous setup to match the conditions in the batch system. With increasing V˙ext (3.3–40 mL min–1) in CSTR operation of the 2 × A reactor module, extrapolated productivities of up to 3045.8 g • day–1 were determined, with steady-state yields between 89.5 and 61.8%. CSTR operation was also applied to the 4 × A reactor module (Vr = 50 mL), realizing a scaling factor of ≈2.4 (ideal scaling factor = 2.5) for the observed productivities for the transfer between the different sized reactor modules.