Hydrophobic VOC absorption in two-phase partitioning bioreactors; influence of silicone oil volume fraction on absorber diameter

A methodology to determine the diameter of an absorber contacting a gas phase and two immiscible liquid phases (water/silicone oil mixture) is presented. The methodology is applied to a countercurrent gas/liquid randomly packed column for the absorption of three VOCs (toluene, dimethyl sulfide, or dimethyl disulfide). Whatever the silicone oil volume fraction, Eckert's generalized pressure drop correlation was used. The results present the change in the column diameter through the change in the dimensionless ratio D(ϕ)/D(ϕ=1) versus the silicone oil volume fraction for the same operating conditions. For toluene and dimethyl disulfide, characterized by Hvoc,silicone oil values equal to 2.3 and 3.4 Pa m3 mol−1, respectively, it is highlighted that it is unwise to use water/silicone oil mixtures for mass transfer. In these cases, the contact between the polluted air and pure silicone oil requires roughly the same amount of silicone oil as for a (90/10 v/v) water/silicone oil mixture, but enables a 2-fold decrease in the column diameter. For dimethyl sulfide, which is characterized by a larger partition coefficient value (Hvoc,silicone oil=17.7 Pa m3 mol−1), the mass transfer operation should not be considered because large amounts of silicone oil are required (whatever the silicone oil volume fraction), which is not acceptable from an economic point of view.The feasibility of using a bioscrubber for the treatment of hydrophobic pollutants depends mainly on the partition coefficient Hvoc,silicone oil. VOC absorption in TPPB should therefore be restricted to pollutants characterized by a Hvoc,silicone oil value of around 3 to 4 Pa m3 mol−1 or less. In this case, absorption can be efficiently carried out in a biphasic air/silicone oil system.

► A design of absorbers contacting a gas phase and water/silicone oil mixture is presented.
► The methodology is based on the “equivalent absorption capacity” concept.
► Toluene and DMDS mass transfer must be carried out between gas and pure silicone oil.
► In this case, the column diameter is the lowest possible.
► For DMS, absorption must not be considered in relation with its weak solubility in silicone oil