Absorption of toluene in silicone oil: Effect of the solvent viscosity on hydrodynamics and mass transfer

The purpose of this study was to compare toluene absorption performances using two PDMS of different viscosities (η = 5 and 50 mPa s, respectively) in terms of hydrodynamics and mass transfer. Three types of packing were tested in a counter-current packed gas-liquid contactor, Raschig rings, IMTP®, and Flexipac®. Hydrodynamic results showed that the viscosity of PDMS 50 is not a hurdle to be used with IMTP® or Flexipac®; the pressure drop being around 288 Pa m−1 for Flexipac® at the flooding point (FG = 0.99 Pa1/2; L′ = 4.95 kg m−2 s−1), which corresponds to an acceptable value for an industrial application. The determination of the loading zones showed that Raschig rings were not suitable for solvents having a high viscosity, such as PDMS 50; they resulted in high pressure drops if compared to IMTP® and Flexipac®. The mass transfer study showed that 100% removal efficiency can be reached for both PDMS using Flexipac®. For IMTP®, the removal efficiency is limited to 88% in the presence of PDMS 50. As a result, PDMS 50 should be a relevant absorbing liquid for the removal of toluene in the absorption-biodegradation process, and Flexipac® packing should be preferred to IMTP®.