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

Abstract

deltif Amrane, et al.. Assessment of VOC absorption in hydrophobic ionic liquids: Measurement of partition and diffusion coefficients and simulation of a packed column. Chemical Engineering Journal, Elsevier, 2019, 360, pp. AbstractPartition 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 to 1300 times for toluene and 10 to 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][NTf 2 ] using a thermogravimetric microbalance. Diffusivity measurements were performed at 298K for toluene and between 278 and 308K for DCM. Diffusion coefficients in ILs, ranging between 1 and 4×10 -11 m 2 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 [AllylEt 2 S][NTf 2 ] and [bmim][NTf 2 ], which both present moderate viscosities of nearly 50 mPa s at 293K. 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 * Corresponding author : pierre-francois.biard@ensc-rennes.fr, Tel: + 33 2 23 23 81 49 2 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. Highlights Toluene partition coefficients in 23 ILs were in the range 0.5-3.5 Pa m 3 mol -1  Dichloromethane partition coefficients in 23 ILs were in the range 5-17 Pa m 3 mol -1  VOC diffusion coefficients in the range 1-4×10 -11 m 2 s -1 were measured in 4 ILs  The computed toluene removal efficiency in a packed column was from 52 to 99.6%  The computed dichloromethane removal efficiency in a packed column was lower than 44% Graphical abstractVicious air containing VOC: Treated air Ionic liquid Loaded ionic liquid Metal Pall rings 3.0 m 1.0 m •Toluene •Dichloromethane Operating conditions Hydrodynamics Mass-transfer rate (K l a°) Pressure drop Removal efficiency Solvent assessment for VOC removal in a packed column Partition coefficient Diffusion coefficient Ionic liquid properties (m, r, s) Static headspace method Static thermogravimetric method Measurements Simulation •[bmim][NTf 2 ] •[AllylEt 2 S][NTf 2 ] Finally, the hydrodynamics and mass-transfer in a packed column fed with [Bmim][NTf 2 ] and [AllylEt 2 S][NTf 2 ] were simulated for DCM and toluene absorption. * AR is the affinity r...

Experimental evaluation and modeling of the hydrodynamics in structured packing operated with viscous waste oils

“…Moreover, a low superficial gas velocity would affect the turbulences in the gas phase, decreasing the gas-phase mass transfer rate. Since a significant part of the mass transfer resistance can be located in the gas phase during hydrophobic VOC absorption, even using viscous solvents (Biard et al, 2018;Rodriguez Castillo et al, 2019), would decrease the overall mass transfer rate. Finally, for a high L/G ratio, the loading zone is narrower.…”

“…The transformer oil was selected among the three solvents considering the observations of the parts 3.3 and 3.4. Biard et al (Biard et al, 2018;Rodriguez Castillo et al, 2019) already studied the hydrodynamics of DEHA (12.5 mPa s), PDMS (50 mPa s) and two ionic liquids (50-60 mPa s) in a packed column (Dcol = 1 m) filled with bulk Pall® rings for with the same gas flowrate using the Billet-Schultes correlations. Apart from a different packing nature (corrugated sheets vs. random rings), Pall® rings offer a geometric surface area of only 139.4 m 2 m -3 , around 3 times lower than Flexipac®500 Z HC.…”

“…Thus, both the computed loading and flooding superficial velocities for similar L/G ratio (in the range 1-5) are significantly lower with the Flexipac® packing. Thus, it was impossible to select the same working velocity of 1.52 m s -1 as Biard et al (Biard et al, 2018;Rodriguez Castillo et al, 2019) since this one is higher than the computed flooding velocity for the Flexipac® packing whatever the L/G ratio considered.…”

“…These results emphasize the good hydrodynamic performance offered by this packing. Nonetheless, the use of a low gas velocity would be detrimental for the mass transfer rate in the gas phase, in which the main part of the resistance can be located, especially during the absorption of hydrophobic VOCs for which the selection of viscous absorbents is justified (Rodriguez Castillo et al, 2019).…”

“…Several mature technologies can be implemented to remove VOCs from air such as adsorption on activated carbon filters, thermal and catalytic oxidations, absorption (gas-liquid scrubbing) or biofiltration (Ruddy and Carroll, 1993). To target hydrophobic VOCs, absorption in a non-aqueous phase (NAP) using silicone oils, phtalates, adipates or even ionic liquids, would be a promising treatment (Hadjoudj et al, 2004;Heymes et al, 2006;Bourgois et al, 2006Bourgois et al, , 2009Darracq et al, 2010a;Darracq et al, 2010b;Guihéneuf et al, 2014;Biard et al, 2016Biard et al, , 2018Rodriguez Castillo et al, 2018, 2019. Nonetheless, all these commercial or laboratory made solvents are very expensive, which would increase the CAPEX of an industrial process.…”