Sylvain Miachon

Isobutane dehydrogenation in a membrane reactor influence of the operating conditions on the performance

Abstract Isobutane dehydrogenation has been investigated in a membrane reactor combining a bimetallic PtIn/zeolite fixed-bed catalyst and a microporous MFI-alumina tubular membrane. The membrane reactor performance has been studied as a function of the feed and sweep flow rates and of the sweep (co- or counter-current sweep modes). Isobutene yields up to four times higher than that observed in a conventional reactor have been obtained. Depending on the conditions, it is shown that the performance of the membrane reactor is controlled either by the membrane or by the catalyst.

Membrane reactor for selective oxidation of butane to maleic anhydride

A simulation of a packed-bed membrane reactor acting as an oxygen distributor for the selective oxidation of n-butane to maleic anhydride (MA) has been performed by recreating specific reactive atmospheres in a microreactor. In the membrane reactor, the oxidation state of the catalyst depends on its position in the bed, leading to an important change in the MA yield. However, this heterogeneity can be turned to an advantage using a reverse of n-butane flow. Co-promoted catalysts have also been developed to enhance the global performance of the membrane reactor.

Comparison of a contactor catalytic membrane reactor with a conventional reactor: example of wet air oxidation

Abstract A wet air oxidation reaction was carried out in a gas/liquid catalytic membrane reactor of the contactor type. The oxidation of formic acid was used as a model reaction. The mesoporous top-layer of a ceramic tubular membrane was used as catalyst (Pt) support, and was placed at the interface of the gas (air) and liquid (HCOOH solution) phases. A similar reaction was carried out in a conventional batch reactor, using a steering rate high enough to avoid gas-diffusion limitations, and exactly identical conditions than for the CMR (amount of catalyst, pressure, etc.). At room temperature, the CMR showed an initial activity three to six times higher than the conventional reactor. This activity increase was attributed to an easier oxygen access to the catalytic sites. Nevertheless, the catalytic membrane gradually deactivated after a few hours of operation. Different deactivation mechanisms are presented.

A comparative study of template removal from silicalite-1 crystals in pyrolytic and oxidizing regimes

Abstract The removal of tetrapropylammonium cations (TPA + ) from silicalite-1 crystals with a morphology of 90°-intergrowth and different crystal sizes was investigated. The effects of the nature of the gas (air or nitrogen) and of the hydrodynamics were examined using a stream flowing in parallel or across the crystal layer. The only process variable was the plateau temperature ( T max ). Crystal domain boundaries became permeable to template degradation products when T max exceeded 300 °C. The template removal was monitored by (i) light microscopy, (ii) degree of removal of the total organics α , of nitrogen species α N and of carbon species α C and (iii) accessibility of the channel system for N 2 molecules. The sorption isotherms for N 2 exhibited two steps. The upper step started to be perceptible for a degree of organic removal higher than 55%. Its height increased with α , and its position moved to lower pressure values. The plots of the gas accessibility versus the degree of removal were modelled. For template removal in air, all plots were linear. In a non-oxidizing atmosphere, the accessibility lagged behind α N . Light microscopy showed that template degradation started along domain boundaries. Sorption kinetics of iodine into silicalite-1 crystals treated in a non-oxidizing atmosphere was considerably slower than that observed into crystals calcined in air. The tendency to crack formation increased with crystal size. The template removal efficiency was higher when using cross-flow than parallel flow calcination.

Comparison of microporous MFI and dense Pd membrane performances in an extractor-type CMR.

An extractor-type CMR, including a Pt-based fixed-bed catalyst, was combined with two different membranes, either a Pd membrane, obtained by electroless plating, or an MFI zeolite membrane, obtained by hydrothermal synthesis. These two configurations were compared in isobutane dehydrogenation. Both CMRs give better results than conventional reactors. However, though the two membranes presented different separative properties, the two CMRs showed very similar yields. This has been attributed to the limitation of both CMRs by the catalyst lack of efficiency, when compared to the membrane performance. A modeling approach that combines catalyst kinetic law and membrane gas transfer equations also contributes to the description of the CMRs performance.

Controlled Pt deposition in membrane mesoporous top layers

Different methods of platinum deposition in the porous framework of a tubular ceramic membrane have been investigated. Metal loading, localization, and dispersion were studied using electron microscopy techniques. Results shows the characteristics of the platinum deposit deeply depended on the membrane structure, Pt precursor nature, and application procedure.

A wet air oxidation process using a catalytic membrane contactor

A new process for oxidation of toxic compounds in liquids has been demonstrated. The concept is based on the same principles as catalytic wet air oxidation (CWAO), but the metal catalyst is fixed to a ceramic porous membrane in a catalytic membrane reactor of the contactor type (CMR-C). Air is flowing along the surface of the contactor, and the waste liquid is supplied from the other side of the contactor through the porous contactor wall. In this way, the gas and liquid phases are driven to contact in the porous network of the catalytic contactor separating them. Fifty percent of conversion of formic acid model solution (5 g/l) was obtained in initial reactor experiments at 150 8C and 10 bar pressure, but the observed oxidation rate was low: about 0.13 mmol/s per gPt. TEM and EDS investigations of the contactor showed that 5 � /10 nm Pt particles were evenly distributed close to the surface of the mesoporous TiO2 top layer. After the experiments, a 10 � /50 nm thick aluminium-rich amorphous deposit was observed in the porous structure. The low conversion rate has been attributed to this deposit causing deactivation by encapsulation of the catalyst and plugging of the mesoporous layer of the contactor. The deposits are believed to be caused by chemical instability of a-Al2O3 in acidic aqueous environment at elevated temperature. a-Al2O3 is present in the coarse-grained membrane support. # 2003 Elsevier Science B.V. All rights reserved.

Diffusion of n-butane, isobutane and ethane in a MFI-zeolite membrane investigated by gas permeation and ZLC measurements

The diffusion of n-butane, isobutane and ethane in a composite-membrane alumina-MFI zeolite has been investigated using gas permeation and ZLC (zero-length column) techniques. The diffusion of isobutane in the sample is faster than that of n-butane although isobutane molecule has a larger kinetic diameter, and its activation energy is comparable to the results obtained from the gas permeation and QENS measurements reported in the literature. For ethane, the diffusivity is much higher in comparison to n-butane and isobutane. When isobutane is present at a high concentration, the diffusion of ethane is remarkably hindered due to a relatively strong adsorption of isobutane in the membrane micropores. By comparing the diffusivity data obtained from the permeation and ZLC measurements, it was possible to evaluate the thickness of the zeolite membrane effective for gas permeation.

Catalysis of palladium salt reduction in a gas-liquid membrane reactor

This paper deals with a new way to prepare a palladium-alumina nanoscale composite membrane, using a catalytic membrane reactor of the gas-liquid contactor type.

14-P-38-Topochemical changes in large MFI-type crystals upon thermal treatment in oxidizing and non-oxidizing atmosphere

Publisher Summary This chapter discusses topochemical changes in large MFl-type crystals upon thermal treatment in oxidizing and nonoxidizing atmosphere. Tetrapropylammonium hydroxide (TPAOH) removal from large as syntesized silicalite-1 crystals with internal morphology of 90°-intergrowths has been investigated in regimes with gas flow in parallel to and through the crystal layer both in the absence and presence of oxygen. The void space accessibility of crystals is estimated from the sorption isotherms of nitrogen (N2), which is exhibited as a rule two step. The topochemical changes in crystals after a partial template removal are evaluated using light microscopy, electron spectroscopy for chemical analysis (ESCA) measurements, and elemental analysis of organic residues.