Intensification of G/L absorption in microstructured falling film. Application to the treatment of chlorinated VOC’s – part I: Comparison between structured and microstructured packings in absorption devices

The absorption of tetrachloroethylene – the VOC – in di-ethyl-hexyl-adipate – the solvent – was carried out as an example of gaseous waste treatment. Two gas–liquid contactors were used: a column provided with as structured Sulzer EX® packing and a microstructured falling-film absorber provided with thin vertical channels, manufactured by the Institut für Mikrotechnik Mainz (IMM). The overall transfer coefficient of VOC, KGa, was calculated from the absorption efficiency of the various runs carried out, allowing comparison of the two gas–liquid contactors. Due to the high solubility of the considered VOC, mass transfer was shown to be mainly controlled by gas-side transfer rates. Transfer coefficient KGa of the two absorbers were found to be comparable, but with gas and liquid velocity in the microstructured absorber from one to two orders of magnitude below those in the column, expressing the high transfer performance offered by the microsystem. Moreover, the thickness of the liquid film in the channels was below 100 μm, much lower than that in a structured packing near 500 μm. This shows that lower liquid flow rates can be used for efficient absorption in the microsystem. It is shown that contrary to conventional structured packing, the designed contact specific area in the microabsorber strictly corresponds to the interfacial G/L surface. This enables more compact and to miniaturize G/L contactors to be designed.