L. Lorenzen

Developing a heating procedure to optimise hydrogen permeance through Pd-Ag membranes of thickness less than 2.2 μm

The Pd–Ag films, with a total thickness of <2.2 μm, were deposited by electroless plating on the inside of α-alumina membranes from SCT. The H2 permeances through separated Pd–Ag layers were poor and heating conditions were investigated to improve the H2 permeances through the metal films. The heating temperature, heating time and heating environment all had a significant effect on the H2 permeance and the H2 to N2 selectivity of the Pd–Ag films. The films were oxidised at 310°C for 1 h after heat treatment in Ar at 550°C, and then reduced in H2. This additional surface modification step more than doubled the H2 permeance through the film and only created a moderate amount of membrane defects as indicated by the increase in the N2 permeance. After the heating process, the membranes were characterised from 250 to 410°C using both a sweep gas and a positive pressure difference.

Characterization of electroless plated palladium–silver alloy membranes

Abstract Palladium and silver coated membranes were prepared using electroless plating. Palladium–silver alloy membranes were synthesized by successive palladium and silver depositions on the same membrane support. Full characterizations of the pure palladium and pure silver membranes were performed using scanning electron microscopy (SEM), X-ray diffractometry (XRD) and proton induced X-ray emission (PIXE). Metal coated membranes were heat treated for 5 h in a hydrogen atmosphere at 650°C. The effect of the palladium and silver deposition sequence on coating adhesion and metal distribution in the alloy matrix after heating were investigated. By depositing first silver and then palladium, the palladium to silver ratio across the thickness of the film remained constant after heat treatment and it resulted in only a small amount of the alloy penetrating into the support membrane pores. However, when palladium was deposited first, the alloy penetrated at least 3 μm into the support and the palladium and silver concentration profiles across the thickness of the film were asymmetric.

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.

Preparing and testing Pd films of thickness 1–2 micrometer with high selectivity and high hydrogen permeance

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 μm were deposited on the inside of asymmetric α-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 μmol/m2 Pa sec for temperatures from 330 to 450°C and Pd films from 1.0 to 1.5 μm 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 μm).

New methodology for hazardous waste classification using fuzzy set theory Part II. Intelligent decision support system.

In part 1 of this paper, factors that influence hazards and eco/toxicity in composite hazardous wastes were described. In part 2, a computer-aided decision support tool based on fuzzy set theory is proposed to support the classification of composite wastes. Given the chemical properties, the nature of microorganisms that may be present, the behaviour of chemicals in humans and ecosystems, and the quantities of wastes, the computer-aided tool automatically classifies the waste as benign, partially hazardous, hazardous or highly hazardous. The functionality of the computer-aided decision tool is demonstrated through nine worked examples and the results are discussed in detail.

Xylene Vapor Mixture Separation in Nanocomposite MFI-Alumina Tubular Membranes: Influence of Operating Variables

In this study, we present the results of a preliminary investigation on the influence of operating variables (temperature, sweep gas flow rate, and total feed vapor pressure) on xylene vapor mixture separation using tubular nanocomposite MFI-alumina zeolite membrane prepared by the pore-plugging synthesis technique. Within the detection limit of our analytical system, neither m- nor o-xylene was detected in the permeate stream, the membranes displaying therefore “infinite” p-xylene selectivity. The mixtures p-xylene flux displayed a maximum value of ca. 3.5 µmol·m−2·s−1, corresponding to a mixture permeance of 11 nmol·m−2·s−1·Pa−1, at 473 K and for a feed composition 0.63 kPa p-xylene/0.27 kPa m-xylene/0.32 kPa o-xylene, being almost unchanged for sweep gas flow rates (N2) higher than 20 mL(STP)/min and increasing with the total xylene vapor pressure at 1 : 1 : 1–3 p/m/o-xylene composition. The experimental p-xylene fluxes can be well predicted by a Maxwell-Stefan model, as expected for a mass transfer process driven by competitive adsorption / surface diffusion. Unlike film-like MFI membranes, the membranes presented here preserved their selectivity to p-xylene for total xylene pressures as high as 150 kPa. This behavior is attributed to the intimate contact between the alumina confining pores and MFI nanoparticles, reducing long-term stresses and thus preventing distortion of the MFI framework during p-xylene adsorption. These results open up potential applications of nanocomposite MFI-alumina for selective p-xylene separations at high loadings, for instance in pervaporation, where the use of film-like MFI membranes is discouraged.

Characterising palladium–silver and palladium–nickel alloy membranes using SEM, XRD and PIXE

Abstract Palladium alloy membranes were prepared by successive electroless plating steps on an alumina–zirconia support membrane. Palladium, silver and nickel were deposited in layers and then the metal films were heat treated for 5 h in a hydrogen atmosphere at 650°C. The topography of the metal coatings and cross-sections of the films (before and after heating) were characterised using scanning electron microscopy (SEM). XRD was used to determine the crystal phase of the alloy coatings. Both SEM and XRD provide only surface information and therfore micro-PIXE was used to extract depth information of the alloy coating. Concentration profiles across the thickness of the films were constructed to determine penetration of the coating into the support membrane pores during electroless plating and to investigate diffusion of coated layers during the heating step.

A Fuzzy - Based Methodology for Aggregative Waste Minimization in the Wine Industry

The wine industry generates large quantities of waste annually, including organic solid wastes (solids, skins, pips, marc, etc.), inorganic solid wastes (diatomaceous earth, bentonite clay, perlite), liquid waste (cleaning wastewater, spent cleaning solvents, cooling water), and gaseous pollutants (carbon dioxide, volatile organic compounds, ammonia, sulphur dioxide, etc.) (Chapman et al., 2001; Musee, 2004a; Musee et al., 2007). Several factors give rise to these diverse waste streams (Musee, 2004a; Musee et al., 2007), however, only the most salient ones are highlighted here. Firstly, wine production evolved from a cottage industry to a global industry. Because of their antiquated origin, the design and development of many wineries made no provision for in-plant modern waste minimization (WM) approaches. Secondly, because the wine industry is dependent on an agricultural feedstock (grapes), the resultant waste streams tend to have a high concentration of organic material. This is because the grape feedstock cannot be altered, replaced, or eliminated before the vinification process begins – if the finished wine quality is to remain consistent. And finally, although auxiliary process feedstock, such as filter aids and diatomaceous earth are essential for clarifying the wine, they cannot be incorporated into the final product. Consequently, the clarification agents constitute part of the waste streams generated from the wine industry. In view of these unique constraints facing the wine industry, among others, necessitates the development of appropriate WM strategies to address the waste management challenges facing the wine industry (Musee et al., 2007). In recent years, there has been continuous pressure on the operating profits of wine makers, mainly owing to increasing competitiveness in the global wine market. This can be attributed to increased variety of wine brands, rise in operational and input material costs, as well as the emergence of an onerous environmental regulatory framework in many wine producing countries (Bisson et al., 2002). Notably, the impact of stringent environmental legislation on the cost of production is expected to continue to be a key determinant in the international competitiveness of wine products (Katsiri & Dalou 1994; Massette, 1994; Muller, 1999). This, and a combination of other powerful intrinsic and external drivers should motivate the wine industry to consider the possibility of incorporating WM strategies as an integral part of wine making processes. As such, the identification and implementation of appropriate WM strategies should be part of the drive to reduce the cost of wine production – particularly in the context of ensuring its future sustainability.