Leszek Gora

Evaluation of reproducible high flux silicalite-1 membranes: gas permeation and separation characterization

The permeation of helium, ethane, propane, n-butane, i-butane through a newly developed silicalite-1 membrane was performed using by a batch method and a Wicke–Kallenbach (WK) method. This membrane exhibits high flux properties and maintains a good separation selectivity. A procedure is outlined to interpret measured fluxes and estimate the various contributions of transport modes. The experimental fluxes of helium, ethane, propane and n-butane in the batch method could be divided into different parallel contributions, such as surface diffusion, activated gaseous diffusion and viscous flow. The permeation of helium was mostly governed by activated gaseous diffusion at 303–573 K. For adsorbing gases such as ethane, propane and n-butane, surface diffusion was dominant at temperatures up to 393 K. Their permeation mechanism shifted to activated gaseous diffusion with increasing temperature. In the WK method, both single component measurements and binary mixture separations using n-butane and i-butane were performed in the temperature range of 303–573 K. The selectivity for n-butane in a 1:1 mixture n-butane/i-butane was about 28 up to 400 K, which was higher than the ideal selectivity calculated from the single component measurements because of the competitive adsorption of the butanes. The selectivity of the membrane for n-butane/i-butane mixtures was highly dependent on feed composition and feed pressure.

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO2 ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO2/Y2O3 coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu0.03Ti0.97O2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P0.03Ti0.97O2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ∼ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.

Highly reproducible high-flux silicalite-1 membranes: optimization of silicalite-1 membrane preparation

Abstract Silicalite-1 membranes were prepared on a TiO 2 coated porous stainless steel support. Different thicknesses of the membranes were achieved by changing the synthesis temperature. Increasing the crystallization temperature resulted in the formation of a monolith-type layer, which is close to a perfect microporous phase (without pores between crystals forming the layer). The silicalite-1 membranes were characterized by permeation measurements using single gases and a mixture of n -butane and i -butane in a Wicke–Kallenbach set-up. A direct relationship between the membrane thickness and the selectivity of n -butane to iso-butane was observed; the selectivity improved with an increase in the membrane thickness. The improvement in the selectivity was correlated with decreasing the intercrystalline spaces between the crystals forming the membrane. The best performing membranes were synthesized in the temperature range of 453–463 K. The competitive adsorption of the butanes at 303 K was governing the separation properties of the membranes. The selectivity for n -butane in a 50:50 n -butane/iso-butane mixture was as high as 55, and the flux equal to 2.75 mmol/m 2 per s (WK method at 101 kPa, 303 K). The ideal selectivities, calculated from the single component measurements towards n -butane, were between 33–48 and n -butane fluxes between 7–12 mmol/m 2 per s (WK method at 101 kPa, 303 K). Small variations in the selectivity performance of the membranes synthesized under the same conditions show that the optimized preparation method was highly reproducible.

Selective sensor utilizing a thin monolayer of b-oriented silicalite-1 crystals–magneto-elastic ribbon assembly

This report presents the development of new selective gas sensors utilizing a b-oriented silicalite-1 layer-magneto-elastic ribbon assembly. The key principle for the operation of these sensors is monitoring the changes in the resonance frequency of the Metglas strip in relation to the concentration of a component in the gas phase. This technique provides a simple way for monitoring the effects of the amount of adsorbed gases in the silicalite-1 coating. The thickness of the zeolite layer is that of a single crystal. The silicalite-1 crystals are oriented in the b-direction, meaning that the straight channels are perpendicular to the sensor surface, which is confirmed by X-ray diffraction (XRD) analysis. The sensor was able to repeatedly sense carbon dioxide in air and could discriminate between linear and branched hydrocarbons. The sensor was able to detect n-butane, while it did not respond to the presence of iso-butane, indicating sensing selectivity.

Controlling the Performance of Silicalite‐1 Membranes

The structural and performance characteristics (for n- and i-butane separation) of self-supported silicalite-membranes, were optimised by fine-tuning their syntheses by screening a total of nine silica sources and many reaction conditions. The mass balances indicate that membrane thickness is a function of both the synthesis volume and the silica source used. The excellent properties of the final membrane are demonstrated by its high permselectivity of 31 for n-butane combined with a n-butane flux of 10 mmol m(-2)s(-1), indicating perfect performance. For 50/50 mixtures (of n and i) the selectivity for nbutane was 48 and its flux was 3.8 mmol m(-2)s(-1). For the given selectivities, in relation to the membrane thickness, the theoretical fluxes are the highest values ever reported, underlining the point that high structural integrity is essential to achieve superior functionality.

Membrane reactor technology for C5/C6 hydroisomerization

In this paper, we propose an improved hydroisomerization process, making use of membrane reactor technology. Linear alkanes are selectively supplied from a hydrocarbon feed (consisting of branched and linear alkanes) through an inert tubular membrane to a packed bed of catalyst. The results indicate that n-, mono- and di-branched components in a gas mixture can be separated with a selectivity factor of greater than 20 with a zeolite membrane under dedicated parameter settings. The RON-value of the product was calculated to be as high as 90 in a single pass reactor, which is 50 points higher than the feed value. The flux through the membrane could be optimized to give a STY/ATY ratio for the reactor of 877 m−1, which falls within the limits of technical feasibility.

An alternative synthesis method for zeolite Y membranes

A new approach for the synthesis of supported zeolite Y membranes is presented, using a synthesis gel containing seeds to avoid any unnecessary ex situ pre-treatment of the support.

Quality enhancement of NaA zeolite membranes

Abstract UV-irradiation of a TiO2 support prior to synthesis enhances the zeolite 4A crystallization rate hereon by decreasing the induction time and increasing the number of nuclei. As a result, well-attached NaA membranes with a zeolite-layer, thickness of 3.5 μm are formed. These membranes separate H2O from a binary EtOH mixture with high selectivities up to 54000. The H2O/H2, H2O/CH4, and H2O/CO separation factors are as high as 309, 615, and 244 at 303, K and 72, 323, and 30 at 373 K, respectively. The permselectivities of He/N2 and, H2/N2 are 3.6 and 4.6, respectively, higher than those of the Knudsen diffusion. Furthermore, the fluxes of the permeating gases and vapours are considerably higher than reported in the literature [1,2]. These high selectivities with high fluxes indicate the high quality of the zeolite 4A membranes synthesized on UV-irradiated TiO2 supports.

Modelling of n-hexane and 3-methylpentane permeation through a silicalite-1 membrane

Abstract The permeation of the single components n -hexane (NC6) and 3-methylpentane (3MP) and their mixtures through a silicalite-1 membrane has been investigated. The separation factor in a binary mixture decreases from 57 to 23 with increasing the feed pressure, which is not predicted by the Generalized Maxwell-Stefan (GMS) equations in combination with the Ideal Adsorbed Solution (IAS) theory. The mixture adsorption in the zeolite layer plays a key role in the prediction of the component fluxes of binary mixtures across a silicalite-1 membrane. Plausible reasons for the discrepancy between model predictions and experimental results are discussed.

New routes to synthesis of reproducible, high-performance supported silicalite-1 membranes

Unsupported and supported silicalite-1 zeolite membranes were synthesised in a highly reproducible manner. The type of silica sources used in the syntheses determines the thickness and porosity of the layers. Tetraethylorthosilicate was found to be the best silica source for making dense, well-intergrown membranes without any visible macropores between the crystals that form the membranes. These synthetically optimised zeolite membranes are characterised by significantly higher n-butane fluxes compared to the highest values reported in the literature (at a given n-butane to iso-butane flux ratio).