Advanced membrane development material requirements

Reverse Osmosis. In reverse osmosis (qv), a solution or suspension flows under pressure through a membrane the product is withdrawn on the other side. This process can treat dissolved soHds concentrations ranging from 1 mg/L to 35 g/L (14). The principal constraint is the requirement that the waste material be relatively nonfouling. Recent advances have been mosdy in membrane development, and pilot studies are required (15). Energy costs can be significant, and it is frequently necessary to pretreat influent in order to minimize fouhng. Reverse osmosis can deal with particles < 1 to 600 nm in size. 

This review will outline the materials requirements for advanced alternative proton exchange membranes for fuel cells, assess recent progress in this area, and provide directions for the development of next-generation materials. The focus will be on the synthesis of polymeric materials that have attached ion conducting groups. State-of-the-art Nation and its commercially available perfluorosulfonic acid relatives will initially be discussed. Other chain-growth co-... 

Nevertheless, the development of zeolite-membrane reactors still requires improvements in the fluxes and separation factors attained to date, an objective to which many efforts have been devoted in recent years with the aim of materializing an industrial application of zeolite-membrane reactors. Several reviews have been published in the last 5 years dealing completely or partially with zeolite membranes [2,3,5,161,162,165-167]. Particularly, noteworthy have been the advances regarding the use of supports of different natures and characteristics (see Section 10.6.4), the control of the orientation and thickness of zeolite layers (see Section 10.2.1.2), and the preparation of new zeolite materials such as membranes (see Section 10.3). In spite of these advances, before zeolite-membrane reactors are used in industry (see Section 10.6.5), signihcant progress must be achieved in more prosaic issues such as scale-up and control of the synthesis process to increase membrane reproducibility. 

The techniques given in Table 4.2 are well established and have been sub-divided into those which are described as either static or dynamic. We feel this distinction is of particular importance in the characterisation of the porous structure of membranes. Here the performance is determined by the complex link between the structural texture and transport behaviour. An insight into this complexity is frequently provided by dynamic techniques, which are not restricted by the limited quantity of membrane material and are sensitive to the active pathways through the porous structure. Further developments are required in this area both in the improvement of existing techniques and introduction of new techniques. Progress will also come from advances in the theory and modelling of flow behaviour in such porous media, which involve percolation theory and fractal geometry for example. With the refinement of such... 

Various reviews on PFSA technology development have been published and detailed explanations of the individual items are available from those materials. In this chapter, the fundamentals of PFSA membranes, the requirements for advanced PEFCs, development trends for high temperature membranes, reinforcement technology, membranes for DMFC, and topics on analysis technology are reviewed. 

Partly in order to address the morphologically related heterogeneity, but also in order to develop MIPs for advanced applications, different materials formats are being developed. These can be in the form of beads, fibers, tubes, films, membranes, or nanoparticles. An effective development of MIPs hence requires the mastering of multiple disciplines in chemistry and materials science. 

We have tried to relate the performance of a deteriorated membrane to its structure by classical methods. Recent advancement in the techniques of morphological and physicochemical analyses is remarkable, and is much contributing to better understanding of the membrane behaviour. We have now various types of RO membranes made of synthetic polymers available, and most these analytical procedures are applicable for the analysis of these membranes. Investigations on the membrane structures are much more required, and they will reveal the relations between materials and structure, and structure and performance. We believe these Investigations will contribute to development not only in the membrane Itself, but in the application of the membrane. We hope the progress of membrane science will expand RO marke t. 

Commercial applications have been identified primarily in the electronics industry where requirements for dimensional stability, mechanical properties, and high temperature resistance make these systems attractive in advanced circuit board technology. Other commercial applications include high temperature membranes and filters where these materials offer performance improvements over glass, Kevlar, and graphite composites. Industrial development of these types of materials will most likely be dependent on monomer cost and advances in various product properties requirements. 

Finally it should be noted that the characterisation of membranes is more demanding than most other porous materials. Firstly, the membranes separation layer is generally thin and supported, which requires a sensitive technique capable of analysing a sample in such a form. The characterisation of a powder "equivalent" to the membrane carmot in all cases be considered as representative of the membrane texture. Secondly, the structure is frequently anisotropic and moreover often microporous. Assessment of the microporosity is much less advanced compared to meso- and macro-porosity, despite emphasis given to this in the recent lUPAC symposia [6-8]. The current and widespread interest in the characterisation of microporous matericds is well illustrated by the numerous and varied publications found in these symposia proceedings. These highlight recent developments in characterisation techniques, their applications and limitations. The particular features of importance in membrane studies will be considered in the light of the characterisation techniques to be described. 

The features of the more important characterisation techniques described here are summarised in Table 4.2. As is evident from this review, there is no technique which is universally applicable for the characterisation of the porous properties of all materials. The choice is made on the basis of many criteria, such as the range of pore size, the nature of the material and its form, together with the application envisaged. Frequently, more than one technique is required in a detailed examination. In the case of membranes, particular problems are encountered because of their form and the small quantity of active material involved. Furthermore, other complexities arise in the case of microporous thin films, although, as we have noted here, currently this is an area of active progress. This involves the development of new techniques and advances in phenomenological theories to describe the properties of such nanostructured supported materials. 

In Section 13.63, it was stated that oxygen-conductive membranes are under development. These membranes are suitable for advanced power generation requiring oxygen for combustion or gasification and are based on zirconia and perovskite where oxygen is transported throngh the material as 0 . 

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