Assessment of VOC absorption in hydrophobic ionic liquids: Measurement of partition and diffusion coefficients and simulation of a packed column

Abstract Partition coefficients of toluene and dichloromethane (DCM) in 23 hydrophobic ionic liquids (ILs), which can be used potentially for the physical absorption of volatile organic compounds (VOCs), were measured at 298 K. The partition coefficients, expressed as Henry’s law constants, were 400–1300 times for toluene and 10–47 times for DCM lower in the selected ILs than in water. Thus, the toluene and DCM diffusion coefficients were measured in three high potential hydrophobic ILs and in [Bmim][NTf2] using a thermogravimetric microbalance. Diffusivity measurements were performed at 298 K for toluene and between 278 and 308 K for DCM. Diffusion coefficients in ILs, ranging between 1 and 4 × 10−11 m2 s−1, were from 18 to 90 times lower than in water at 298 K. The diffusion coefficients were correlated to the temperature, the solute molar volume, the IL viscosity and molar volume with an average error of 4.2%. Finally, a 3 m industrial packed column was simulated for the removal of DCM and toluene in [AllylEt2S][NTf2] and [bmim][NTf2], which both present moderate viscosities of nearly 50 mPa s at 293 K. The overall mass-transfer coefficient, the removal efficiency and the pressure drop were calculated and compared to those obtained using other heavy solvents (a silicon oil and di-(2-ethylhexyl) adipate). This prospective simulation has demonstrated a good potential of ionic liquids for the toluene removal. Nonetheless, the DCM removal efficiencies simulated were lower than 44%. It suggests that even more efficient ionic liquids can be tuned and synthesized in the future for this specific application.