Objective
Since the early 1990s, an intensive research effort has been aimed to the synthesis of zeolite membranes and related separation applications. Ideally, a zeolite membrane should consist in a continuous, defect-free layer of connected zeolite crystals, so that only transport through the zeolite pores (calibrated and of molecular dimension) takes place. This statement represents a significant challenge to the present state-of-the-art in preparation techniques. Therefore, a precise knowledge of the membrane porous structure (including micro or mesoporous intercrystalline defects) is essential for controlling membrane quality, improving preparation procedure and predicting the transport mechanisms and performances.
Gas adsorption/desorption isotherms are extensively used for the textural characterization of porous inorganic materials. Nevertheless, the classical equations (e.g. Kelvin one) used for interpreting adsorption data are of uncertain validity for micropores and small mesopores mainly because of increased adsorbate-adsorbate and adsorbate-adsorbent interactions. Many papers in the literature deal with this ambiguous problem of micropore sizes determination: new theories, models, mechanisms and simulations are still under study. At present the most promising (but time consuming) approach appears to be the pre-adsorption of various probe molecules of known size and shape.
On the other hand, permeation measurements provide extremely useful information on the "active pores" structure of membranes and on the existence of defects affecting the transport. A selective blocking of membrane pores combined with permeation measurements (e.g. permporometry) has been revealed useful for determining active pore size distributions in mesoporous membranes. Such an attractive method (based on the Kelvin equation) is not applicable to microporous membranes whose characterization is still subject to discussions.
This interdisciplinary research project, involving specialists in microporous membrane synthesis (P1, P2), porous structure characterization (P3) and modeling (P4), is aimed to fill the current gap existing for the characterization of microporous membranes and materials. The strategy is based on the adaptation of a novel technique called "dynamic desorption porometry" (DDP) recently patented by one of the project partners (P3) and on the development of a new "non-Kelvin" nanopore filling model.
A number of microporous materials and membranes with defined characteristics (composition, zeolite pore sizes, and hydrophilic/hydrophobic properties) will be provided by partners P1 and P2, tested in DDP by P3 and results will be modeled by P4. Correlation with other characterization techniques and with membrane performance will be used for the interpretating DDP data. The final goal of the project is the development of an efficient dynamic method, based simultaneously on desorption isotherms and permeation data, for the determination of active pore sizes distribution in microporous membranes (including defects) and consequently a rapid evaluation of their quality.
Topic(s)
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34296 Montpellier Cedex 5
France