Investigation of new modification strategies for PVA membranes to improve their dehydration properties by pervaporation

International audienceNovel supported membranes based on polyvinyl alcohol (PVA) were developed using two strategies: first, by the modification of the PVA network, via so-called bulk modification, with the formation of the selective layer accomplished through the introduction of fullerenol and/or poly(allylamine hydrochloride), and second, by the functionalization of the surface with successive depositions of multilayered films of polyelectrolytes, such as poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on the PVA surface. The membrane surface modifications were characterized by scanning electron microscopy and contact angle measurements. The modified PVA membranes were examined for their dehydration transport properties by the perva-poration of isopropyl alcohol-water (80/20% w/w), which was chosen as a model mixture. Compared with the pristine PVA membrane, the main improvement was a marked increase in permeance. It was found that the surface modifications mainly gave rise to a higher global flux but with a strong reduction in selectivity. Only the combination of both bulk and surface modifications with PEL could significantly increase the flux with a high water content in the permeate (over 98%). Lastly, it should be noted that this study developed a green procedure to prepare innovative membrane layers for dehydration, making use of only water as a working medium

Potentials of pervaporation to assist VOCs' recovery by liquid absorption

International audienceGas treatment by liquid absorption is a well-known process to remove volatile organic compounds (VOCs) from industrial waste gases. Usually the liquid is an organic solvent of high boiling point; however, after VOCs' absorption it must be regenerated for the possible reuse and this step is classically achieved by heating the liquid. The paper presents the work directed to investigate an alternative regeneration step based on a liquid–vapour membrane separation, i.e. pervaporation. Because most of the energy required in pervaporation processes is consumed to remove the minor component from the initial mixture by selective permeation through the membrane, one can expect a significant energy cut in the operational costs linked to the regeneration of the liquid if the pervaporation step can substitute the heating one. The results reported here show that the technological possibility to use pervaporation is first governed by the stability of the membrane in the absorption liquid. The viability of the overall process is actually controlled by the mutual affinity between the VOCs, the solvent phase and the polymeric material. As a matter of fact, whereas VOCs have to exhibit strong affinities to both the solvent and the membrane material, the polymer has to be well resistant and even repellent to the solvent to avoid the possible sorption in the membrane that would drastically depress the pervaporation efficiency. In other words the membrane transport properties must be specific for the VOCs. This goal was reached following several experimental approaches, going from membrane modifications to the selection of suitable heavy protic solvents. Hence it has been shown for the case of dichloromethane (DCM) that low molecular weights polyalcohols (e.g. glycols) appeared to be suitable media to allow in particular the specific transport of DCM. On the other hand, polydimethylsiloxane (PDMS) based membranes were selected for their stability in these polyglycols and for their marked affinity for DCM. The simulation of the hybrid gas treatment process at pilot-scale was also achieved by a simple model relying on experimental data for both vapour liquid equilibria and permeation flux. A simple comparison of the energy needed to regenerate the heavy solvent by each possible step has also been made

PVC–activated carbon based matrices: A promising combination for pervaporation membranes useful for aromatic–alkane separations

International audienceThe separation of aromatic-aliphatic liquid mixtures is difficult perform in a satisfactory technico-economic manner by conventional methods, such as extractive distillation, azeotropic distillation, or liquid-liquid extraction. The separation by pervaporation (PV) of liquid toluene-heptane mixtures, selected as a model mixture, was performed with several dense membranes based on poly(vinylchloride) (PVC) as the starting material. Aiming to improve the performances of pure PVC films, i.e. high selectivity and very low flux, composite membranes were prepared by incorporating different percentages of activated carbon introduced as selective sorbent fillers for toluene. In this study, we report the results obtained with composite PVC membranes containing up to 40 wt% Maxsorb SPD30. The transport properties of these membranes were characterized by measurements of isothermal sorption and by pervaporation of binary mixtures. It was found that the performances of certain composite membranes were significantly increased compared with pure PVC membranes. Under the same experimental conditions, the pervaporation toluene flux was seven times higher, whereas the toluene selectivity was only slightly decreased (the permeate enrichment decreased from 89 to 83 wt% at 74 degrees C). Thus, the combination PVC with activated carbon appears to be a promising method to obtain effective PV membranes for aromatic-alkane separations

CO2 capture in HFMM contactor with typical amine solutions: A numerical analysis

International audienceThe absorption behavior of carbon dioxide using a hollow fiber membrane contactor was numerically analyzed. In this analysis, the absorbent solution is flowing in the inner side of the fiber bore and the pure gas in the shell and the module operated in a non-wetted mode. The derived coupled non-linear govern- ing partial differential equations were numerically solved by the orthogonal collocation technique. Three typical alkanolamines of industrial use, the diethanolamine (DEA), the 2-amino-2-methyl-1-propanol(AMP), and the diisopropanolamine( DIPA)were used as absorbents in this work. One important feature of this study was building the mathematical model based on the two-step carbamate formation model instead of the one-step model used by previous investigators. The outlet absorbed dioxide concentration was simulated and studied with respect to the liquid velocity, initial amine concentration and external mass transfer coefficient. The analysis includes the effects of the diameter and length of the fibers on the liquid outlet gas concentration as a function of the liquid velocity in the fiber. Simulation results show that AMP solutions present a much higher absorption capacity compared to the other two amines olutions