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The purpose of this study was to compare toluene absorption performances using two PDMS of different viscosities (= 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 (F G = 0.99 Pa 1/2 ; 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®.

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International audienceBACKGROUND : Four silicone oils (PolyDiMethylSiloxane, PDMS) of different viscosities, namely 5, 20, 50, and 100 mPa s were characterized to select the most suitable polymer for the biol. treatment of toluene. The PDMS volatilities and the partition coeffs. of toluene between air and PDMS were investigated. Toluene biodegrdn. tests were also carried out to assess the absence of toxicity of the considered PDMS vis-a-vis the microorganisms. RESULTS : PDMS 20, 50 and 100 had negligible volatilities at 25 °C and 35 °C, whereas PDMS 5 was volatile even at 25 °C. The results indicate that the amt. of VOCs emitted by PDMS increased with the temp. according to a logarithmic law. The partition coeff. of toluene between air and the four PDMS were similar (H = 2.9 Pa m3 mol-1) indicating that the affinity between toluene and PDMS was identical whatever their viscosity. Moreover, biodegrdn. tests allowed the conclusion that the four PDMS tested are not toxic for microorganisms. CONCLUSION : PDMS 20, 50 and 100 were suitable at 25 °C for the biol. treatment of toluene. Since all these PDMS were satisfactory at 25 °C, it could make sense to select the least viscous oil for use in the process, i.e. PDMS 20. © 2015 Society of Chem. Industry