(95a) Catalytic Membrane Reactors for Environmental Applications

Catalytic membrane reactors for environmental applications

Anne Giroir-Fendler

Université de Lyon, Lyon, F-69003, France, Université Lyon 1, Villeurbanne, F-69622, CNRS, UMR 5256, IRCELYON, 2 avenue Albert Einstein, Villeurbanne, F-69622, France.

Application of membrane reactor can improve the conversion of the catalytic processes considerably. In a wide range of applications and more particularly for environmental application, significant progresses have being made on membrane development. The feasibility on laboratory scale has been demonstrated for membrane reactor technology since 20 years. In this paper we will present some catalytic membrane reactors development devoted to environmental application like VOCs abatement, waste water treatment, gas separation and xylene isomerisation.

VOC abatement - The destruction of VOCs is a great challenge and also of great industrial importance. Our aim is to investigate the catalytic oxidation of propene and toluene in a membrane reactor used in a flow-through contactor configuration. In this case, the gas mixture of reactants is forced to go through the membrane, i.e. through the catalytic pores. This study on propene and toluene combustion showed that the catalytic membrane reactor performed better than the conventional monolithic reactor in term of efficiency. This confirms that membrane reactor is a promising alternative for the combustion of VOCs and that the flow-through membrane reactor may lead to decreased light-off and total VOC combustion temperature with a low overall Pt loading.

Waste water treatment - Wet air oxidation (WAO), earlier developed by Zimmerman during the 1950s, constitutes an attractive technology for the treatment of industrial effluents containing low to intermediate concentrations of refractory and toxic compounds for which incineration or biological remediation are inefficient. The efficiency of WAO can be improved by the use of heterogeneous catalysts. In order to improve the gas/liquid/solid contact in CWAO, the development of innovative catalytic reactors is desired. The use of catalytic membrane reactors (contactor-type), coupling a catalyst and a membrane in the same unit, could be an option. In this study, we have prepared catalytic membrane using several techniques of deposition in order to well control the position of the active phase in the porous structure. After optimization of the experimental parameters, the study of pollutants degradation has showed that catalytic membrane reactor, in contactor configuration present highest efficiency than conventional reactor due to optimized contacts between reactants and active sites.

Gas separation - Zeolite membranes are the good candidate to separate chemical products and in this study we focused on the preparation of highly reproducible nanocomposite MFI hollow fibers membranes via pore-plugging, and on the applications of CO2/N2 and p-xylene/m-xylene separations. In order to increase the separation factors of these materials, nanocomposite B-MFI hollow fibers were also successfully synthesized in one pot by substitution of Si with B during synthesis. B-MFI hollow fibers improved the separation performance compared to MFI membrane on the vapor separation of xylene and n-hexane isomers. A modeling study on n-hexane/2,2-dimethylbutane separation reflects that hexane separation within both MFI and B-MFI hollow fiber membranes is mainly driven by diffusion differences and configurationally entropy effects.

Xylene isomerisation - This part presents isomerisation of meta-xylene over Pt-HZSM-5 in an extractor-type catalytic membrane reactor (e-CMR) using tubular nanocomposite-alumina MFI membrane. The membrane used for the study was prepared via a pore-plugging synthesis technique and it showed p-xylene permeance of 11.4nmol/(m².s.Pa). Meta-xylene saturated in N₂ was fed into the membrane and N₂ gas swept over the outer surface of the membrane (for e-CMR). The performance of the e-CMR was compared with that of a fixed bed reactor (FBR) with similar reactor dimensions and operation conditions. Thus e-CMR showed 34.5% increase in para-xylene selectivity when compared to FBR at 400^oC and these results are in good agreement with the literature.