Pseudo 3-D simulation of a falling film microreactor based on realistic channel and film profiles

A falling film microreactor has demonstrated in the past high potential for sustainable chemical processes, e.g. by better use of resources (selectivity), enabling direct routes (saving of waste), or smaller reactor footprint (space-time yield). Due to the extremely high liquid based specific area (up to 20, 000 m² / m³) it is especially equipped to carry out fast exothermic and mass transfer limited reactions. However, to maximize the process intensification in the falling film microreactor there is a need to characterize and investigate the design parameters of the reactor. In general, the major rate limiting steps occur on the liquid side. Therefore a realistic description of the liquid film is needed which requires the use of a 3-D reactor model. In the current study we present a so-called pseudo 3-D computational fluid dynamic (CFD) model. Based on the realistic channel geometry profiles we compute liquid menisci, flow velocities, species transport, and reactions. The reactor model was developed and validated experimentally by the absorption of CO₂ in NaOH aqueous solution. This 3-D model allows investigating the effects of channel fabrication precision, liquid flow distribution, gas chamber height, and hydrophilic-hydrophobic plate material. Result shows that fabrication imprecisions of the investigated microchannels by 11% in channel width and 6% in channel depth has only a 2% impact on the reaction conversion. Moreover we show that a liquid flow mal distribution, in the parallel microchannels assembled on plate, with a relative standard deviation of 0.37 lowers the reaction conversion by about 2%. A reduction of gas chamber height slightly improves the conversion and gas phase mass transfer limitation can be overcome. Moreover the material of the reactor plate has to provide sufficient wetability for the liquid falling film.