Anita Buekenhoudt

Alumina and titania multilayer membranes for nanofiltration: preparation, characterization and chemical stability

Abstract The preparation and characterization of porous ceramic multilayer nanofiltration (NF) membranes is described. During preparation, special care was given to each sub-layer that forms a part of the multilayer configuration: the macroporous substrate, the membrane interlayers and the NF toplayers. High-quality macroporous supports are prepared from α-Al 2 O 3 . Three types of colloidal sol–gel derived mesoporous interlayers are considered: Al 2 O 3 , TiO 2 and mixed Al 2 O 3 –TiO 2 . The active NF toplayer is a very thin and fine textured polymeric TiO 2 toplayer. Optimized α-Al 2 O 3 /γ-Al 2 O 3 /anatase and α-Al 2 O 3 /anatase/anatase multilayer configurations show high retentions for relatively small organic molecules (molecular weight cut-off 2 O 3 layers is restricted to mild aqueous media (pH 3–11) or non-aqueous media (organic solvents). For NF applications in aqueous media with a lower or higher pH, the multilayer membrane composed of anatase on a α-Al 2 O 3 support is to be preferred.

Preparation of LaSrCoFeO3−x membranes

The last 10 years an alternative production route for oxygen production by using mixed conductors has been investigated. Perovskite mixed electron-oxygen conducting membranes are bulk membranes with a thickness of the order of 1 mm, showing sufficient oxygen fluxes only at temperatures above 800°C. To reach commercially interesting fluxes at lower temperatures, membrane modules with a much higher surface/volume ratio or multilayer membranes with a thin dense skin need to be developed. In our laboratory, dense hollow fibres and porous multilayer substrates were synthesised. The hollow fibres were produced using a polymeric spinning technique based on phase inversion. The multilayer porous substrates were manufactured following conventional ceramic processing routes.

Evaluation of the phase composition of BPSCCO bulk samples by XRD- and susceptibility analysis

Abstract This paper describes the comparison of the phase purity analysis, using XRD and AC-susceptibility measurements, on a number of BPSCCO samples, containing different ratios of the Bi-2212 and Bi-2223 phase. The differences observed in the results of both techniques were correlated with the growth mechanism of the Bi-2223 phase. The higher values for the percentage of the Bi-2223 phase observed in AC-susceptibility analysis, could be explained by the assumption that there is a specific distribution of the Bi-2212 and Bi-2223 phase during particle growth, resulting in shielding effects.

Stability of Porous Ceramic Membranes

Publisher Summary This chapter discusses the stability of porous ceramic membranes. These membranes with pores of ∼1 nm, and below, are suitable for nanofiltration, pervaporation, and gas separation. Besides the porous ceramic membranes, dense ion-conducting membranes have also been developed during the last decades. These materials are used as electrolytes in fuel cells, or as hydrogen- and oxygen-selective membranes. The majority of the porous membranes, including almost all commercially available membranes, are made up of metal oxides. The oxides preferably used are aluminum oxide or alumina (Al2O3), zirconium oxide or zirconia (ZrO2), titanium oxide or titania (TiO2), and silicium oxide or silica (SiO2). Mixtures of these metal oxides are also frequently used. Membrane supports are mainly produced by slip casting or extrusion. The main method for the preparation of metal oxide intermediate and top layers is the sol–gel technique. In this technique, mesoporous intermediate layers are made by colloidal sols and microporous top layers by polymeric sols. The sols are prepared from metal salts or metal organic precursors. The layers are deposited on the supports or on the previous multilayer structure by dip coating. The porosity of the supports or of the previous multilayer structure leads to the gelling of the sols. These gel layers are further dried and thermally treated to form the final membrane layers. This final thermal treatment—called “calcination” or “sintering”—stabilizes the crystallographic and morphological structure of the dried layer.

Recycling of the homogeneous Co-Jacobsen catalyst through solvent-resistent nanofiltration (SRNF)

The Co-Jacobsen complex, catalysing a hydrolytic kinetic resolution, was recycled in a semi-continuous operation using a laboratory prepared polymeric SRNF-membrane.

New insights into the fouling mechanism of dissolved organic matter applying nanofiltration membranes with a variety of surface chemistries.

Nanofiltration (NF) membrane fouling by DOM remains a major and poorly understood issue. To acquire a better insight we studied the fouling of the DOM fractions humic acids (HAs) and fulvic acids (FAs), with and without Ca(2+), on native and grafted ceramic NF membranes. Grafting with two methods and three different grafting groups allowed to create a range of membranes with a variety of surface chemistries, and a wide range of surface polarity, much broader than ever used in previous studies. A typical polymer (polyamide) NF membrane was included for comparison. All obtained results reveal that membrane fouling is not determined by membrane hydrophilicity/hydrophobicity as a general and sole criterion, but rather on the whole of the surface chemistry determining the amount and strength of the possible foulant-membrane interactions. As a consequence the effect of inorganic ions on the fouling is also dependent on the surface chemistry. Important new insight in the DOM fouling mechanism was acquired, shedding new light on the state-of-the-art knowledge.

Separation of metathesis catalysts and reaction products in flow reactors using organic solvent nanofiltration

Organic solvent nanofiltration (OSN), a relatively new low energy separation technology, has been used to reduce metal contamination of ring closing metathesis reaction products. The catalysts used were readily available commercial Hoveyda–Grubbs and Umicore M series catalysts. These reactions were performed in a flow reactor with in-line membrane separation, and high catalyst retention can be achieved. In the flow reactor set up a beneficial effect on catalyst life-time on changing from solvents such as dichloromethane to environmentally more benign acetone, which reduces initiation rates, was demonstrated.

Ceramic Foams Coated with Zeolite Crystals

Ceramic foams can be used as filters, dust collectors, light weight components and catalyst carriers. They can be produced by a variety of techniques. The performance of ceramic foams will be strongly improved when their mechanical properties are improved. For this reason, we produced ceramic foams both by a modified reaction bonded (RB) replica technique and by gel casting. With both methods, reticulated foam structures with enhanced mechanical strength were obtained. Zeolites are a special type of materials that are characterized by high catalytic properties. They can be brought on a structured carrier by dip and slurry coating. Nevertheless, in situ coating has as main advantage that the support is used as the base for nucleation. This results in the formation of a chemical bond between the zeolite crystals and the support. The goal of this contribution is twofold: at first we demonstrate how Al2O3 foams with improved mechanical strength can be produced both by the modified RB-alumina replica technique and by gel casting. Secondly, it is shown that these ceramic foams can be coated with (silicalite) zeolite crystals by insitu crystallization from a precursor sol. The two-layer material combinations have been characterized with FESEM, XRD, CT (computer assisted tomography), IA (Image Analysis) and by mechanical tests.

Controlling pore size and uniformity of mesoporous titania by early stage low temperature stabilization.

The control of the formation process during and after self-assembly is of utmost importance to achieve well structured, controlled template-assisted mesoporous titania materials with the desired properties for various applications via the evaporation induced self-assembly method (EISA). The present paper reports on the large influence of the thermal stabilization and successive template removal on the pore structure of a mesostructured TiO(2) material using the diblock copolymer Brij 58 as surfactant. A controlled thermal stabilization (temperature and duration) allows one to tailor the final pore size and uniformity much more precise by influencing the self-assembly of the template. Moreover, also the successive thermal template removal needs to be controlled in order to avoid a structural collapse. N(2)-sorption, TGA, TEM, FT-Raman spectroscopy, and small angle & wide angle XRD have been used to follow the crystal growth and mesostructure organization after thermal stabilization and after thermal template removal, revealing its effect on the final pore structure.

Class II hybrid organic-inorganic membranes creating new versatility in separations

Membrane technology is becoming more important as a low energy separation process that can replace or enhance the efficiency of currently often costly and energy-consuming separation processes. After an introduction on the potential of hybrid materials for membranes, we highlight and categorize the wide diversity of hybrid organic-inorganic membranes. In this review, we focus on the preparation and application of class II hybrid organic-inorganic membranes with mechanically stable inorganic supports. Class II points to the presence of covalent bonds between organic and inorganic moieties. The variety of synthesis approaches applied to prepare such separation layers can be divided into 2 types, i.e. direct coating of a pre-formed hybrid solution, and post-synthesis grafting of organic groups. In the last part, we focus on strategies delivering hybrid organicinorganic membranes that show promise for enhanced molecular separations in gas separation, hydrophilic and organophilic pervaporation and organic solvent nanofiltration. In addition, we will discuss the use of organically modified inorganic RO (reverse osmosis), UF (ultrafiltration) and MF (microfiltration) membranes for ameliorated pressure driven water filtration, membrane contactors, and low-fouling oil/water separation.