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...

A fixed volume packed column was simulated for the absorption at counter-current of four more or less hydrophobic volatile organic compounds (VOCs) in water and in two heavy organic solvents (PDMS 50, a silicone oil) and DEHA (Bis(2-ethylhexyl) adipate)). Reliable values of the mass-transfer coefficients were deduced allowing to calculate the VOCs removal efficiency. Disappointing performances in heavy solvents, lower than 60% for isopropanol and acetone, were computed in a 3 m height column and using mild conditions (atmospheric pressure and a liquid-togas mass flow rate ratio around 2). However, toluene removal efficiencies higher than 90% were simulated.

Heterogeneous catalysts were synthesized with a glass foam support mainly composed of recycled glass and impregnated with zerovalent ruthenium nanoparticles (aiming to 0.1 wt.% ruthenium). Different glass foams were developed, playing on the nature and quantity of foaming/doping agents as well as the operating conditions (heat temperature and time of heating). They were characterized in terms of open porosity, pore diameter, wettability and pressure drops. High open porosity can be achieved (between 73% and 92%) with mean pore diameter up to 0.55 mm, resulting in the lowest pressure drops measured among all glass foams. The deposit of zerovalent ruthenium nanoparticles was confirmed by TEM images and changes in surface charge showed by zeta potential determination. Finally, the removal of ozone from air at room temperature and inlet concentration of 9 g.Nm-3 was performed to prove the catalyst activity. Up to 52% of ozone decomposition was achieved in less than 13 seconds of residence time. The activity did not seem to be linked with the characteristics (open porosity and mean pore size) of the glass foams but it was shown that the external mass transfer was still limiting the process performances in the range of superficial gas velocity tested (4 mm.s-1 to 11 mm.s-1).

International audienceA simple dynamic absorption procedure to assess the mass-transfer performances of a solvent toward a selected gaseous solute is presented. Absorption was operated semi-continuously at transient state until the equilibrium was reached without solvent recirculation. Four volatile organic compounds (VOC) more or less hydrophobic (toluene, acetone, dichloromethane, isopropanol) were absorbed in water and two heavy organic solvents (Bis(2-ethylhexyl) adipate DEHA and polydimethylsiloxane PDMS). A numerical resolution procedure was developed to simulate the gas-liquid mass-transfer and to deduce the VOC partition coefficients, expressed as the Henry's law constants, as well as the overall liquid-phase mass-transfer coefficients. The overall liquid-phase mass-transfer coefficients were correlated to the diffusion coefficients using the Higbie penetration theory. The results confirm the high selectivity of water whereas the two organic solvents, especially DEHA, exhibit rather good affinity with all VOC even if the Henry's law constants of the most soluble and the less soluble compounds for those solvents differ by 1 or 2 orders of magnitude. The liquid-film mass-transfer coefficients in the two organic solvents, even being more viscous, are larger than in water which confirms their good potential for hydrophobic VOC treatment

A jacketed stirred-cell reactor, operated semi-continuously, was used to assess the kinetics of fast ozonation reactions by reactive absorption. The method was applied to the direct ozone reaction with resorcinol. A high resorcinol concentration was used to reach a steady state and to neglect the byproducts accumulation. Thus, the mass-transfer rate, and consecutively the reaction rate, were deduced from the ozone mass balance in the gas phase. The gas-phase and liquid-phase mass-transfer coefficients were previously measured directly through the ozone absorption in appropriated conditions. The results emphasized the high sensitivity of the reaction rate constant to the ozone physicochemical properties, especially its solubility, which is controversial in the literature. Therefore, several correlations used to calculate the ozone solubility in water were considered to calculate the second-order reaction rate constant, which varied from 3.57-4.68 10 5 L mol -1 s -1 at 20°C to 9.50-12.2 10 5 L mol -1 s -1 at 35°C. The activation energy was in the range 35-59 kJ mol -1 depending on the considered ozone solubility correlation. A sensitivity analysis is provided to assess the influence of the experimental conditions and ozone physicochemical properties on the model. Finally, the applicability of this method is thoroughly discussed.2

International audienceHydrogen sulfide (H2S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H2S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H2S oxidation rate by reactive absorption in a mechanically agitated gas-liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas-liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H2S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H2S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H2S is oxidized irreversibly by both hypochlorite anion ClO- (k = 6.75 106 L mol-1 s-1) and hypochlorous acid ClOH (k = 1.62 105 L mol-1 s-1)

This study investigates the influence of inlet concentration and of flow rate on the degradation rate of two Volatile Fatty Acids (butyric and propionic acids). TiO2-coated nonwoven fiber textile was used as the photocatalyst in an annular plug-flow reactor at laminar flow regime. The kinetic follows a Langmuir-Hinshelwood form. The oxidation rate increased with the flow rate, which emphasizes the influence of the mass transfer. A first design equation is proposed considering that the mass transfer could be neglected. Despite a good accuracy of the model, the determined kinetic constants are dependent on the flow rate which highlights the contribution of the mass transfer rate on the global degradation rate. Thus, a new design equation which includes the mass transfer rate was developed. Using this model, the degradation rate can be determined for any given flow rate. Moreover, it allows the estimation of the contribution of mass transfer and chemical reaction steps at given experimental conditions; and thus providing an interesting tool for reactor optimization or design.

An innovative implementation of the O 3 /H 2 O 2 advanced oxidation process was proposed to intensify the hydroxyl radical generation. Natural or drinking waters, containing atrazine as a probe compound, were spiked with H 2 O 2 and further continuously mixed to a pre-ozonated solution in a homogeneous tubular reactor filled with static mixers. Hydraulic residence times in the range 10 s-140 s were set at different sampling ports. The experimental results confirmed a very high ozone decomposition rate, concomitant with a high hydroxyl radical exposure (R ct in the range from 10-7 to 10-6), especially during the initial ozone decomposition phase (between 10 and 20 s). Equimolar initial concentrations of hydrogen peroxide and ozone were optimal to maximize the hydroxyl radical generation and to minimize their relative consumptions. The influence of the water matrix on the ozone decomposition and the hydroxyl radical generation was limited. This study is a proof of concept that using a homogeneous tubular reactor would be more effective than a gas-liquid reactor to apply the peroxone process.