Papers

48 written papers (including 36 articles, 4 patents and 8 conference proceedings).
38 oral communications, 26 posters.

ARTICLES: (recent ones first)

Nanocomposite MFI-alumina membranes via pore-plugging synthesis: Genesis of the zeolite material
Li Y., Pera-Titus M., Xiong G., Yang W., Landrivon E., Miachon S. and Dalmon J. A.
Journal of Membrane Science 325:973-81 (2008)
This paper presents a study of MFI-type zeolite crystal growth during hydrothermal synthesis of nanocomposite MFI-alumina membranes by the pore-plugging method, using the standard protocol described in a previous study [S. Miachon, E. Landrivon, M. Aouine, Y. Sun, I. Kumakiri, Y. Li, O. Pachtová Prokopová, N. Guilhaume, A. Giroir-Fendler, H. Mozzanega, J.-A. Dalmon, Nanocomposite MFI-alumina membranes via pore-plugging synthesis: specific transport and separation properties, J. Membr. Sci. 281 (2006) 228]. To this aim, the materials have been characterized by SEM, EDX, pure H2 gas permeance and n-butane/H2 mixture separation at different stages of the synthesis. The effect of synthesis time in the range of 4–89 h and the effect of a 9-h interruption after a 8-h hydrothermal synthesis have been surveyed, as well as the mean pore size and the alumina phase of the support inner layer. Our results suggest that an interruption during the synthesis is necessary to allow the zeolite precursor to diffuse into the support pores. This diffusion leads to a further growth of zeolite crystals into the support matrix without formation of a continuous zeolite film on top of the support, as is usually reported in the literature. The zeolite crystals are fully embedded into the support top layer after at least 53-h synthesis time, leading to high quality membranes in only one synthesis run. The nanocomposite MFI-alumina architecture at the nanoscale has important consequences in improving the gas separation performance of this kind of materials when compared to more conventional film-like structures. A method based on gas transport measurements has been used to determine the effective thickness of the separating material.
Full text: doi (publisher's site), direct (preprint) PDF.

Influence of desorption conditions before gas separation studies in nanocomposite MFI – alumina membranes
Alshebani A., Pera-Titus M., Yeung K. L., Miachon S. and Dalmon J. A.
Journal of Membrane Science accepted (18.01.2008)
The gas permeation and separation performance of polycrystalline MFI-type zeolite membranes is strongly dependent on the number and type of intercrystalline pores in its structure. Herein we show that the role of such domains is affected by how a membrane is pre-treated before use to remove adsorbed species (e.g. moisture and organics). This ‘pre-treatment’ step appears to be crucial not only to obtain reliable permeation data, but also to improve the membrane separation performance in practical applications. We illustrate this idea by using a collection of tubular nanocomposite MFI-alumina membranes showing different quality for the separation of n-butane/H2 mixtures and submitted to different pre-treatment protocols. The influence of each protocol on the final separation performance of the membranes depends on their quality, namely on the density of intercrystalline defects or non-zeolite pores in their structure. Moreover the quality of the support affects the final membrane performance.
direct (preprint) PDF.

Nanocomposite MFI – ceramic hollow fibres: prospects for CO2 separation
Alshebani A., Pera-Titus M., Landrivon E., Schiestel T., Miachon S. and Dalmon J. A.
Microporous and Mesoporous Materials accepted (2007)
The membrane surface / module volume ratio is one of the main criterion in designing separation units. This parameter can be increased by one order of magnitude when dropping the membrane tube diameter from the cm to the mm scale. Alumina hollow fibres have been used as supports and submitted to pore-plugging MFI zeolite synthesis. An alumina-MFI nanocomposite structure, showing no surface film, has been obtained, as observed by SEM and EDX analysis and confirmed by high temperature variation of H2 and N2 permeances. Maxwell-Stefan modeling provides an equivalent thickness lower than 1 µm. The membrane quality has been assessed by gas separation of n-butane/H2. A first application to CO2/H2 separation has been achieved, reaching separation factors close to 10. Such a system, based on cheap symmetric supports, could lead to an important decrease in module costs for gas separation applications.
direct (preprint) PDF.

Synthesis and characterization of nanocomposite MCM-41 (‘LUS’) ceramic membranes
Hamad B., Alshebani A., Pera-Titus M., Wang S., Torres M., Albela B., Bonneviot L., Miachon S. and Dalmon J. A.
Microporous and Mesoporous Materials accepted (2007)
A new type of nanocomposite membranes, MCM-41 (‘LUS’)-based material networks grown into porous ceramic membrane support walls (alu-mina and zirconia), were prepared. Physical characterization (low-angle XRD, TPD, SEM-EDX) confirm the sole presence of the LUS mesostructure (BJH pore size ≈ 3.2 nm), and in a high enough amount to plug the pores of the tubular supports. Single gas hydrodynamic characterization shows that the contribution of defects (i.e. viscous flux) is negligible or comparable to reference mesoporous commercial membranes (5-nm pore size γ-alumina), but with a considerably enhanced permeance for gases and water, as well as a single pore size. When compared to literature results on similar orga-nized mesoporous membranes, this work shows even greater improvements.
direct (preprint) PDF.

Higher gas solubility in nano-confined solvents?
Miachon S., Syakaev V., Rakhmatoulline A., Titus M. P., Caldarelli S. and Dalmon J. A.
ChemPhysChem 9(1):78-82 (2008)
The nature and physical properties of condensed matter in nanometre-confining porous media can differ from what is observed at the macroscopic level. Here we provide 1H-NMR spectroscopic evidence of a dramatic increase of hydrogen and light hydrocarbon solubility in solvents when confined in mesoporous materials. Gas solubility appears to be promoted when the gas/liquid interface is located within the confining mesopores. An explanation based on this observation is proposed. This oversolubility effect could bear a key role in many different applications involving gas-liquid processes or hydrogen storage.
Full text: doi (publisher's site), direct (preprint) PDF.

Nanocomposite MFI-alumina membranes via pore-plugging synthesis. Gas transport and separation properties
Miachon S., Ciavarella P., van Dyk L., Kumakiri I., Fiaty K., Schuurman Y. and Dalmon J. A.
Journal of Membrane Science 298:71-9 (2007)
Nanocomposite MFI-alumina membranes, obtained by growing zeolite crystals within the porosity of a host macroporous support (pore-plugging method), as described in a previous paper, were studied for their behaviour for pure gas permeation and gas mixture separation. Hydrogen, nitrogen and light hydrocarbons were permeated on a wide range of temperatures, up to 873 K for hydrogen. All pure gases results are well described by the generalised Maxwell-Stefan equation, with no need for an additional “activated gas transport” term, as no flux increase was observed at higher temperatures. Two examples of gas separations were carried out up to 723 K (n-butane / hydrogen) and 673 K (xylene isomers) that similarly show regular flux decreases at higher temperatures.
These results were compared to literature data on film-like MFI zeolite membranes that generally show a flux increase at high temperature. This discrepancy was attributed to the reversible opening of intercrystalline pathways in film-like membranes upon heating. These openings were computed, taking benefit of recently published zeolite thermal expansion data, and their contribution to the permeation was evaluated.
Full text: doi (publisher's site), direct PDF.

Oxidation in catalytic membrane reactors
Dalmon J. A., Cruz-López A., Farrusseng D., Guilhaume N., Iojoiu E., Jalibert J., Miachon S., Mirodatos C., Pantazidis A., Rebeilleau-Dassonneville M., Schuurman Y. and Veen A. C. V.
Applied Catalysis A: General 325:198-204 (2007)
This paper presents a series of applications of Catalytic Membrane Reactors to oxidation reactions. Four reactions were tested in our group. Alkane activation (C2, C3 and C4) or total oxidation (WAO) are implemented in various membrane reactor modes, using dense, microporous or mesoporous membranes. In some cases, a catalyst bed is associated with a membrane, whereas other applications use a intrinsically active membrane. Progresses in catalyst and membrane design, along with careful operational conditions led to overall higher performances when compared to conventional processes.
Full text: doi (publisher's site), direct PDF.

Wet air oxidation in a catalytic membrane reactor: model and industrial wastewaters in single tubes and multichannel contactors
Iojoiu E. E., Miachon S., Landrivon E., Walmsley J., Raeder H. and Dalmon J. A.
Applied Catalysis B: Environmental 69(3-4):196-206 (2007)
Recent results on catalytic Wet Air Oxidation applied to a membrane contactor are presented, giving new insight after a series of previous publications. Model and industrial effluents are treated in both single-tube and multichannel catalytic systems. Characterisations of the catalytic material (solid analyses, electron microscopy, EDS and EPMA) are carried out, in order to determine the catalyst distribution. Catalytic results show performances heavily dependent on the nature of the effluent and the operating conditions, and to a lesser extent on the catalytic membrane characteristics. At 80°C, an industrial effluent is oxidised at a membrane surface related rate of 3.8 mmol/s/m2. This result is achieved using a membrane containing about 0.1 wt%Pt. This allows a revised and improved technico-economical evaluation of the Watercatox process.
Full text: doi (publisher's site), direct PDF.

Ceramic membranes for ammonia recovery
Camus O., Perera S., Crittenden B., van Delft Y. C. V., Meyer D. F., Pex P. P. A. C., Kumakiri I., Miachon S., Dalmon J. A., Tennison S. and Chanaud P.
AIChE Journal 52(6):2055-65 (2006)
An extensive screening programme has been performed to find a suitable membrane configuration and operating conditions for the effective recovery of ammonia from the syngas loop. Tubular MFI zeolite and ceramic monolithic fibre configurations have been tested along with tubular silica membranes. At 80°C, a high ammonia permeance (2.1 x 10-7 mol.m-2.s-1.Pa-1) and a selectivity of about 10 were found with the tubular zeolite membrane. For both silica and zeolite membranes, the selectivity was found to increase with increasing temperature up to 80°C. This is a combined effect of stronger adsorption of ammonia at lower temperature and increased diffusion at higher temperature. Whilst the homogeneous ceramic fibre membranes tested also showed very high selectivity (ca. 15), their permeances were lower than those obtained with the tubular membranes. The results have been modelled using both the well-mixed reactor and the log mean pressure difference approaches. To overcome their limitations, an improved model has been developed to obtain suitable operating conditions and membrane areas required for an industrial application.
Full text: doi (publisher's site), direct PDF.

The “Watercatox” process: wet air oxidation of industrial effluents in a CMR. From lab-scale to pilot unit
Iojoiu E. E., Landrivon E., Raeder H., Torp E. G., Miachon S. and Dalmon J. A.
Catalysis Today 118:246-52 (2006)
A new and innovative method for oxidation of dissolved compounds in water – the “Watercatox” process – has been developed in order to reduce the chemical oxygen demand and the total organic carbon in industrial wastewaters. This process is the result of a European Fifth Framework Program project. It can operate at much lower temperatures and pressures than conventional wet air oxidation or incineration, and it offers much smaller volume requirements than biological treatment plants. The operating principle of the Watercatox process is the oxidation of the dissolved molecules using oxygen from air within a catalytic membrane reactor in an interfacial contactor configuration. The catalytic contactor membranes, as well as the operating conditions, have been up-scaled from lab-scale to pilot unit. The technological efficiency was demonstrated by the results obtained using the pilot test unit on different industrial effluents from several origins.
Full text: doi (publisher's site), direct PDF.

Nanocomposite MFI-alumina membranes via pore-plugging synthesis. Preparation and morphological characterisation
Miachon S., Landrivon E., Aouine M., Sun Y., Kumakiri I., Li Y., Pachtová Prokopová O., Guilhaume N., Giroir-Fendler A., Mozzanega H. and Dalmon J. A.
Journal of Membrane Science 281:228-38 (2006)
A specific synthesis protocol, based on zeolite crystallisation within the pores of a host support, the pore-plugging method, has been designed and optimised. A composite membrane has been obtained and its quality evaluated using the separation of adsorbing and non-adsorbing gas mixture. A series of parameters were studied, including the pore size of the support, the composition of the precursor solution and the hydrothermal synthesis temperature program. Accordingly, the membrane quality showed large variations. The material structure was characterised using scanning and transmission electron microscopies. These observations showed a composite organization at the support pore scale, with an architecture very different from conventional supported zeolite films. The final optimisation of the synthesis conditions concluded to a precursor solution containing 2 mol/l of silica, 0.9 mol/l of TPAOH, and the use of an interrupted hydrothermal temperature program, among other parameters. Thanks to this optimisation process, an average increase of one order of magnitude in the separative performance was obtained.
Full text: doi (publisher's site), direct PDF.

Catalytic membrane structure influence on the pressure effects in an interfacial contactor CMR applied to WAO
Iojoiu E. E., Walmsley J. C., Raeder H., Miachon S. and Dalmon J. A.
Catalysis Today 104:329-35 (2005)
This paper deals with the influence of catalytic membrane structure on the way the gas pressure affects a Catalytic Membrane Reactor efficiency. The CMR is an interfacial contactor, used for wet air oxidation, formic acid solution and air being fed separately from both side of the catalytic membrane. The gas overpressure can shift the gas-liquid interface into the membrane wall, closer to the catalytic zone, and therefore greatly increase the reaction rate. It has been confirmed that this was not an oxygen partial pressure effect. When compared to a conventional slurry reactor, the contactor CMR showed a reaction rate more than three times higher.
Full text: doi (publisher's site), direct PDF.

Xylene isomerization in an extractor type Catalytic Membrane Reactor
van Dyk L., Lorenzen L., Miachon S. and Dalmon J. A.
Catalysis Today 104(2-4):274-80 (2005)
A zeolite / alumina pore plugging membrane was used to successfully separate xyleneisomers. It was then applied as a selective membrane in an extractor type CatalyticMembrane Reactor (CMR), used to enhance the xylene isomerization reaction selectivity towards para-xylene. The results of the CMR in different configurations (permeate-onlyand combined permeate-&-retentate mode) were compared to conventional reactorresults. In both cases, the selectivity was significantly enhanced (up to 100% in permeateonly mode). In combined mode, the CMR also provided a net increase in productivityover the conventional reactor.
Full text: doi (publisher's site), direct PDF.

Selective oxidation of butane to maleic anhydride in a Catalytic Membrane Reactor adapted to rich butane feed
Cruz-López A., Guilhaume N., Miachon S. and Dalmon J. A.
Catalysis Today 107-108:949-56 (2005)
The n-butane selective oxidation has been studied in a membrane reactor, using high butane concentrations. Thanks to the oxygen distribution by the membrane, it is possible to keep the local composition outside the flammability zone. A MFI ceramic membrane was used to distribute oxygen (or part of it) in the catalyst bed, made of a VPO mixed oxide, either conventional or Co-doped. In a first step, the effect of the oxygen distribution has been studied, showing that, under standard reactant mixtures (O2/butane=12, low butane concentration), the membrane reactor performed very close to the conventional one. Under high butane concentrations, the VPO system suffered from a drastic decrease of the selectivity towards maleic anhydride (MA). The addition of cobalt to the VPO catalyst allowed keeping the MA selectivity at a high level (75%). The combination of the CoVPO catalyst and the MFI membrane was used to explore the membrane reactor performance with high butane concentrations in the feed, corresponding to the flammability zone in a conventional reactor. For these conditions, the MA productivity was 3 times higher than that observed with the conventional reactor.
Full text: doi (publisher's site), direct PDF.

Progress in performance and stability of a contactor-type Catalytic Membrane Reactor for wet air oxidation
Iojoiu E. E., Miachon S. and Dalmon J. A.
Topics in Catalysis 33(1-4):135-9 (2005)
Catalytic Membrane Reactors combine a membrane that controls transfers and a catalyst that provides conversion. This paper focuses on the performance and catalytic stability of interfacial contactor membranes in the wet air oxidation of formic acid. Stable catalytic membranes with high activity have been developed.
Full text: doi (publisher's site), direct PDF.

Performance of Catalytic Membrane Reactor in Multiphase Reactions
Vospernik M., Pintar A., Bercic G., Levec J., Walmsley J., Ræder H., Iojoiu E. E., Miachon S. and Dalmon J. A.
Chemical Engineering Science 59(22-23):5363-72 (2004)
Single-channel catalytic membranes were prepared using evaporationcrystallization Pt deposition method and characterised by employing SEM, EDX and EPMA technique. Their activity was tested by conducting liquid-phase formic acid oxidation, and effects of trans-membrane pressure difference, catalyst loading and re-circulation rate on their performance is reported. Obtained results have revealed that measured conversions are preferentially determined by diffusion of formic acid through the top and intermediate layers to the reaction zone on one hand, and by concentration gradient of gaseous reactant on the other hand. Which effect prevails, depends on the position of gas-liquid interface and the instantaneous molar ratio of reactants. Finally, thickness and reactants’ concentrations in the reaction zone established within the membrane wall were calculated.
Full text: doi (publisher's site), direct PDF.

Catalysis in membrane reactors: what about the catalyst?
Miachon S. and Dalmon J. A.
Topics in Catalysis 29(1-2):59-65 (2004)
Catalytic Membrane reactors (CMRs) combine a membrane that controls transfers and a catalyst that provides conversion. This paper focuses on the catalyst itself. Depending on the application, the environment of the catalyst in the CMR may be quite different from that existing in conventional reactors. This could originate changes of the catalyst properties. In some cases, catalysts for CMRs might require a specific design.
Full text: doi (publisher's site), direct PDF.

Comparison of microporous MFI and dense Pd membrane performances in an extractor-type CMR
van Dyk L., Miachon S., Lorenzen L., Torres M., Fiaty K. and Dalmon J. A.
Catalysis Today 82:167-77 (2003)
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.
Full text: doi (publisher's site), direct PDF.

Controlled Pt deposition in membrane mesoporous toplayers
Uzio D., Miachon S. and Dalmon J. A.
Catalysis Today 82:67-74 (2003)
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.
Full text: doi (publisher's site), direct PDF

Comparison of a contactor Catalytic Membrane Reactor with a conventional reactor: example of wet air oxidation
Miachon S., Perez V., Crehan G., Torp E., Ræder H., Bredesen R. and Dalmon J. A.
Catalysis Today (82):75-81 (2003)
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.
Full text: doi (publisher's site), direct PDF.

Dynamic desorption of adsorbing species under cross membrane pressure difference: a new defect characterisation approach in zeolite membranes
Pachtová O., Kumakiri I., Kocirik M., Miachon S. and Dalmon J. A.
Journal of Membrane Science 226(1-2): 101-10 (2003)
Alumina–zeolite composite membranes were prepared on alumina porous tubular supports by single-step in situ hydrothermal synthesis. Hydrogen/n-butane separation factor was used as a criterion to evaluate the presence of defects. Five membranes of different qualities were selected. The hydrogen permeance through the membranes, plugged beforehand with two strongly adsorbing gases (water and n-butane), was followed with time at room temperature. The dynamic desorption thus observed was correlated to the quality of the membrane.
Full text: doi (publisher's site), direct PDF.

Comparison of different support types for the preparation of nanostructured catalytic membranes
Iojoiu E. E., Walmsley J., Ræder H., Bredesen R., Miachon S. and Dalmon J. A.
Reviews on Advanced Materials Science 5:160-5 (2003)
Different nanostructured catalytic membranes have been prepared by platinum deposition (evaporation and ionic impregnation) within the porous framework of different tubular porous supports of a few nanometer pore size. The aim of the work is to investigate the influence of preparation methods and the influence of the type of support on the properties of the obtained catalytic membranes. Some parameters of the preparation procedure, controlling the deposition performance, have been explored. The platinum deposition was carried out using different techniques. Various types of supports made of different types of oxides and carbon with different layer distribution and pore diameters have been investigated. The catalytic membranes have then been characterized by hydrodynamic measurements as well as scanning and transmission electron microscopy. The distribution of platinum within the thickness of the membrane wall has been correlated to the preparation parameters and material of the support.
Full text: direct PDF.

A wet air oxidation process using a catalytic membrane contactor
Ræder H., Bredesen R., Crehan G., Miachon S., Dalmon J. A., Pintar A., Levec J. and Torp E. G.
Separation Science & Technology 32(1-3):349-55 (2003)
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, 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. 50% conversion of formic acid model solution (5 g/l) was obtained in initial reactor experiments at 150 ºC and 10 bar pressure, but the observed oxidation rate was low: about 0,13 mmol/(s◊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.
Full text: doi (publisher's site), direct PDF.

Réacteurs catalytiques : nouvelles technologies pour une chimie moderne
Bordes E., Vanhove D., Schuurman Y., Mirodatos C., Miachon S., Dalmon J. A. and Schweich D.
L'actualité chimique 5-6:68-70 (2002)
New reactors recently proposed in open and patent literature are described. Their advantages in some fields like alkane functionalization or pollutant abatement are described.

A comparative study of template removal from silicalite-1 crystals in pyrolytic and oxidizing regimes
Pachtová O., Kocirík M., Zikánová A., Bernauer B., Miachon S. and Dalmon J. A.
Microporous and Mesoporous Materials 55(3):285-96 (2002)
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 (Tmax). Crystal domain boundaries became permeable to template degradation products when Tmax exceeded 300 °C. The template removal was monitored by (i) light microscopy, (ii) degree of removal of the total organics α, of nitrogen species αN and of carbon species αC and (iii) accessibility of the channel system for N2 molecules. The sorption isotherms for N2 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 αN. 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.
Full text: doi (publisher's site), direct PDF.

Preparing and testing Pd films of thickness 1 to 2 micrometers with high selectivity and high hydrogen permeance
Keuler J., Lorenzen L. and Miachon S.
Separation Science & Technology 37(2):379-401 (2002)
Thin Pd films with high selectivity are advantageous both from a cost point of view as well as for achieving higher hydrogen fluxes through the film. Pd films of thickness down to 1 mm were deposited on the inside of asymmetric a-alumina membranes from the Societé des Céramiques Techniques (SCT) (200 nm pore size) by a modified electroless plating process. Pre-treatment, the plating rate during electroless plating and membrane post-plating treatment must be optimized individually to obtain very high quality films. Membrane defects develop when the substrate is not catalyzed properly before plating, when the plating rate is too fast and/or when the membrane is not cleaned thoroughly after plating. Hydrogen permeances varied between 6 and 15 mmol/m 2 Pa sec for temperatures from 330 to 450°C and Pd films from 1.0 to 1.5 mm thickness. Hydrogen to nitrogen selectivity was above 100 for all membranes tested and above 400 for all but two membranes (thickness 1.0–1.5 mm).
Full text: doi (publisher's site), direct PDF.

The dehydrogenation of 2-butanol over copper-based catalysts: optimising catalyst composition and determining reaction kinetics
Keuler J., Lorenzen L. and Miachon S.
Applied Catalysis A: General 218(1-2):171-80 (2001)
This work examines the dehydrogenation of 2-butanol over copper-based catalyst. The effects of support type (MgO and SiO2 ) and copper loading on methyl ethyl ketone (MEK) yield were studied. The effects of reaction temperature, 2-butanol feed flow rate and catalyst particle size were also investigated. The highest MEK yields were obtained with a 15 wt.% copper on silica catalyst. The optimum catalyst was used to measure the kinetic parameters of the 2-butanol dehydrogenation reaction at temperatures from 190 to 280◦ C. At higher temperatures catalyst deactivation took place.
Full text: doi (publisher's site), direct PDF.

Membrane Reactor for selective oxydation of butane to maleic anhydride
Mota S., Miachon S., Volta J. -. C. and Dalmon J. A.
Catalysis Today 67:169-76 (2001)
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.
Full text: doi (publisher's site), direct PDF.

Isobutane dehydrogenation in a membrane reactor. Influence of the operating conditions on the performance
Ciavarella P., Casanave D., Moueddeb H., Miachon S., Fiaty K. and Dalmon J. A.
Catalysis Today 67:177-84 (2001)
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.
Full text: doi (publisher's site), direct PDF.

Preparation and Characterisation of a Pt/Ceramic Catalytic Membrane
Perez V., Miachon S., Dalmon J. A., Bredesen R., Pettersen G., Ræder H. and Simon C.
Separation & Purification Technology 25:33-8 (2001)
Anionic impregnation was used to depose platinum onto a porous membrane to be used in gas-liquid contactor Catalytic Membrane Reactor. This membrane was a tube made of several layers, with a decreasing pore size in the radial direction to the axis. The toplayer was mesoporous (pore diameter ≈ 5 nm), and made of titania. 5 nm Pt crystallites were selectively deposited to this porous zone and formed branched-shape particles. Their distribution in the membrane was precisely monitored using electron microscopies (SEM, TEM and attached analysis methods). The membrane integrity was checked by nitrogen permeation experiments. Other characterisation techniques included XRD (crystallite size) & N2 adsorption (pore size distribution).
Full text: doi (publisher's site), direct PDF.

Diffusion of n-Butane, Isobutane and Ethane in a MFI - Zeolite Membrane Investigated by Gas Permeation and ZLC Measurements
Jiang M., Eic M., Miachon S., Dalmon J. A. and Kocirik M.
Separation & Purification Technology 25(1-3):287-95 (2001)
Suite ICIM6 Montpellier The diffusion of n-butane, isobutane and ethane in a composite membrane alumina – MFI zeolite has been investigated using gas permeation and ZLC 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.
Full text: doi (publisher's site): direct PDF.

Experimental study and numerical simulation of hydrogen/isobutane permeation and separation using MFI-zeolite membrane reactor
Ciavarella P., Moueddeb H., Miachon S., Fiatty K. and Dalmon J. A.
Catalysis Today 56:253-64 (2000)
A composite alumina–MFI-zeolite membrane has been prepared by a pore-plugging method. Transport through this membrane is controlled by molecular size and adsorption properties, as expected for a defect-free zeolite composite layer.
Single gas transport was studied for hydrogen and isobutane. In the studied temperature range, (323–723 K) for isobutane and (277–723 K) for hydrogen, transports were activated. Isobutane exhibited a flux maximum at 450 K, whereas hydrogen flux declined with temperature.
These different permeation behaviors were modeled using Maxwell–Stefan equations taking into account only surface diffusion. Activation energies were obtained from the model by fitting the experimental data. They were calculated to be 31 kJ mol−1 for isobutane and 1.9 kJ mol−1 for hydrogen. The diffusion coefficients calculated at 323 K differed by four orders of magnitude.
Separation experiments with a mixture of hydrogen and isobutane in a 293–723 K temperature range were performed. Typical permeation behavior was observed for a mixture of weakly and strongly adsorbed molecules. At room temperature, hydrogen permeation was hindered by stronger adsorbed isobutane molecules in the micropores. H2/i-C4H10 separation experiments showed a separation factor of 25 at 723 K, a typical temperature of the isobutane dehydrogenation in membrane reactors.
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Catalysis of palladium salt reduction in a gas-liquid membrane reactor
Miachon S., Mazuy A. and Dalmon J. A.
Studies in Surface Sciences and Catalysis 130:2693-8 (2000)
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.
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Théorie visco-élastique non extensive - 2. premiers tests expérimentaux de la théorie simplifiée à modes rotationnels
Volino F., Gérard H. and Miachon S.
Annales de Physique 22(1-2):43-82 (1997)
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Internal Hydration H2/O2 100 cm2 Polymer Electrolyte Membrane Fuel Cell
Miachon S. and Aldebert P.
Journal of Power Sources 56(1):31-6 (1995)
This work deals with a new arrangement of a polymer electrolyte membrane fuel cell (PEMFC) support which allows the operation of a 100 cm2 surface area fuel cell with cold and unhumidified gases. Hydrogen is not recycled. Both gases (pure hydrogen and oxygen) are heated and humidified internally, each one crossing a porous carbon block. This allows a simplified water management. Classical low platinum loading E-Tek® electrodes, hot-pressed on Nafion® 117 and 112 membranes, are used. Performances are then a little higher than those of comparable PEMFCs in the literature: 0.7 V at 0.7 A/cm2 for Nafion® 117, and 0.724 V at 1 A/cm2 for Nafion® 112, under 4/6 bar (absolute) of H2/O2 at 100 °C. The values of PEMFC resistance obtained in fitting the data were found to be R = 0.254 (with Nafion® 117) and 0.108 Ω cm2 (with Nafion® 112). The membrane contribution to the cell resistance was then estimated to be Rm = 0.204 and 0.058 Ω cm2, respectively (with Nafion® conductivity estimated at 0.103 S/cm at 100 °C in working fuel cell conditions). This membrane is therefore the major contributor to the total cell resistance.
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Miscibility in Binary Blends of Poly(a-methylstyrene) and Poly(methylmethacrylate)
Cowie J. M. G. and Miachon S.
Macromolecules 25:3295 (1992)
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Sylvain Miachon

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