Equivalent Absorption Capacity (EAC) concept applied to the absorption of hydrophobic VOCs in a water/PDMS mixture

• Absorption of hydrophobic VOCs in multiphase system gas/water/PDMS was considered.
• Experiments were carried out in a gas–liquid absorber filled with Raschig rings.
• Water, PDMS and a mixture of water/PDMS (90/10 v/v) were used as absorbing liquids.
• The EAC concept characterizes well the absorption behavior of water/PDMS mixture.
• Pure PDMS has to be used rather than the mixture for hydrophobic VOC absorption.

Absorption of hydrophobic Volatile Organic Compounds (VOCs) in multiphase system gas water PolyDiMethylSiloxane (PDMS, i.e. silicone oils) was considered. Absorption experiments were carried out in a countercurrent gas–liquid absorber filled with Raschig rings as packing. Three absorbing liquids, water, PDMS and a mixture of water/PDMS (90/10 v/v) were used to transfer toluene and dimethyl disulfide (DMDS) selected as VOC targets. Moreover, the Equivalent Absorption Capacity (EAC) concept previously developed to characterize the mixtures of water/PDMS was applied to the experimental data obtained at three different gas flow rates (18, 25 and 32 m3 h−1). Experimental measurements showed that absorption efficiencies (E) were low for water (around 2–8% for toluene and around 12–25% for DMDS) and higher for PDMS (from 88% to 98% according to the operating conditions). For the water/PDMS mixture, it was shown that the PDMS addition increased significantly the absorption of pollutants (E values in the range 25–65% according to the operating conditions). Besides, it was emphasized that the EAC concept describes satisfactorily the absorption behavior of the water/PDMS mixture. Finally, results confirmed that pure PDMS has to be used rather than a (90/10 v/v) water/PDMS mixture for hydrophobic VOC absorption. Using pure PDMS as absorbing liquid (dynamic viscosity of 5 mPa s), high absorption efficiencies (up to 98%) were obtained for L′/G′ value around 5 (L′/G′ corresponding to the ratio between the specific flow of the liquid and the specific flow of the gas). Under such conditions, pressure drops (ΔP) in the packed column and overall mass transfer coefficients (KLa) were around 1000 Pa m−1 (G′ = 1.06 kg m−2 h−1) and 5 × 10−3 s−1, respectively.