Treatment of gas containing hydrophobic VOCs by a hybrid absorption–pervaporation process: The case of toluene

The work focuses on a hybrid process for treating air charged with a hydrophobic volatile organic compound (VOC), coupling an absorption process with membrane pervaporation in order to reuse the absorbent. Toluene was chosen as the target VOC. Four topics were investigated: choice of the absorbent, hydrodynamics and mass transfer in a packed column, regeneration by pervaporation and finally analysis of the coupling of the two processes. In a previous study, 7 absorbents were compared with regard to experimental data (gas–liquid equilibrium constants, viscosity) and data from the literature. Di(2-ethylhexyl) adipate (DEHA) was shown to be the most suitable absorbent. In the first part of this work, experiments in a packed column showed that the viscosity of DEHA led to an increase in pressure drop, which nevertheless remained at a reasonable level. Mass transfer experiments were performed and kinetic constants (KLa)(KLa) calculated. It was proven than washing with DEHA is highly efficient for toluene absorption. The most innovative part of the work is the regeneration of used absorbent by pervaporation. PDMS was chosen as the active membrane layer. Pervaporation flow rates of toluene were measured for the DEHA–toluene solutions corresponding to column foot concentrations. Transfer resistance is mainly controlled by the liquid boundary layer close to the membrane. The system was modelled and several interesting conclusions deduced. Solving the equations by means of a numerical method enabled calculation of the column height and membrane surface area required to treat a 10000m3h-1 gas flow charged with 5gm-3 of toluene.