Thursday, December 24, 2009

Belgian Scientists Create Zeolite-Like Membranes from Nano-Zeolitic Particles for Separation Applications



Belgian scientists have created a silicate-based microporous ceramic molecular sieve  which exhibits membrane zeolite-like properties.  The sieve features an ordered stack of nanometer-sized slab-shaped building blocks with a zeolite framework  The method for producing a membrane does not involve a hydrothermal treatment step, hence avoiding the formation of zeolite crystals.

The new supported microporous ceramic molecular sieve membrane with zeolite properties and a method of making such a membrane is disclosed in U.S. Patent Application 20090318282 by  Vlaamse Instelling Voor Technologish Onderzoek N.V. (VITO) (Mol, BE) and K.U. Leuven Research & Development (Leuven, BE) researchers. 

According to researchers Anita Buekenhoudt, Pierre Jacobs, Ivo Vankelecom and Johan Martens this new silicate based molecular sieve membrane overcomes the drawbacks of prior art membranes and combines high flux and high selectivity, exceeding the performance of the state-of-the-art zeolite membranes. The new membranes have great application potential in molecular separations and/or in catalytic and adsorption processes.

The new membranes are synthesized on a support. The support may be porous or non-porous. In case of a non-porous support, the membrane is in fact a thin film with different material and surface properties compared to the properties of the support. The term "membrane", as used in here should also be understood as having the meaning of "film" or "layer".

The synthesis of these microporous membranes involves the ordered stacking of regular nano-sized silicate-based particles having zeolite framework. A particular advantage of this membrane synthesis process is that it does not involve any hydrothermal treatment nor other type of zeolite crystal growth process. The new membranes have great application potential in molecular separations and in catalytic and adsorption processes.

In the prior state of the art, fabrication of practical zeolite membranes has long been a goal of separation science. Zeolites have the principal advantages of having a crystalline structure and a defined pore size, and of having modifiable surface properties in terms of hydrophilic/ organophilic nature and acidity, both linked to the chemical composition of the framework. This particular topology of zeolites and their cation exchange properties make them useful for applications of separation by selective adsorption and/or size exclusion, or for catalytic reactions.

However, separation on a powdered zeolite is a batch process. In contrast, a zeolite membrane offers the possibility of separating molecules by a continuous process, which may be particularly advantageous from a technological and economical viewpoint.

The new methodology offers several advantages over the classical synthesis routes for zeolite membranes. At first, it is a very simple synthesis procedure, avoiding the technically demanding hydrothermal treatment of the classical synthesis routes. Secondly, due to the real nano-size of the building blocks (1.3.times.2.times.4 nm3 or small multiples thereof for the case of silicalite-1 membranes) very thin zeolite-like membranes can be formed, having very high mass transport i.e. high flux. Moreover the small thickness reduces strongly the risk to create cracks in case of thermal cycling of the formed membranes. This is another clear advantage of the newly developed membranes compared to the state-of-the-art zeolite membranes.

Thirdly, the building blocks in the innovative membranes are only systematically ordered during the membrane synthesis, without any further crystallization or particle growth. This new synthesis method has great potential to avoid the formation of less-selective or non-selective interparticle voids accessible by molecules entering the membrane, as is inevitably the case for the zeolite membranes known to the art. This gives the new membranes at least equal but most likely extra high selectivity. These three advantages show that the present invention, clearly has the potential to lead to membranes combining high flux and high selectivity.




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