Zeolite membranes applications

The unique properhes of zeolite materials combined with the conhnuous separahon properhes of membranes make zeolite membranes very attrachve for a wide range of separahon and catalysis applications. Zeolite membranes, however, have poor processability, poor mechanical stability and are much more expensive than the commercial polymer membranes with current state-of-the-art membrane manufacturing process. So far, the only large-scale commercial zeolite membrane is the A-type zeolite membrane and it has been used for dehydrahon of alcohols [22]. Further advancement in making thinner zeolite membranes and continuous improvement in membrane produchon techniques and reproducibility will make zeolite membranes more successful in commercial applicahons. 

Crystallite morphology prediction and morphology control are important for several kinds of applications. Zeolite membranes can require alignment of many distinct crystallites, this being facilitated by having uniformly shaped... 

Mizumaki F 1999 Application of zeolite membranes, films and coatings Stud. Surf. Sol. Catal. 125 1-12... 

In this chapter, we Hmit ourselves to the topic of zeolite membranes in catalysis. Many types of membranes exist and each membrane has its specific field where it can be appHed best. Comparing polymeric and inorganic membranes reveals that for harsher conditions and high-temperature applications, inorganic membranes outperform polymeric membranes. In the field of heterogeneous catalYsis, elevated temperatures are quite common and therefore this is a field in which inorganic membranes could find excellent applications. 

The principles of application of zeolite membranes at the microlevel can be very similar to those on the particle level, but now at the crystal (micrometer) scale, enclosing the active catalytic material. 

In this section, an attempt is made to sketch the current status of zeohte MRs with respect to specific applications. The application of zeohte MRs is strongly related to the development status of zeolite membranes. Topics that are discussed are the most often studied reactions for zeolite membrane apphcations dewatering. 

Separation of isomers is an application where zeolite membranes could be specifically interesting because of their well-defined pores that lead to molecular sieving effects. An application that is often considered is the xylene isomerization and related reactions. 

The application of zeolite membranes in microreactors is still in an early stage of development, and suffers sometimes from unexpected problems arising from template removal [70]. However, several application examples of zeolite membranes in microstructured devices have been demonstrated yielding similar advantages as were to be expected from experiences on the macroscale. Because of the high surface to volume ratio of microreactors, the application of zeolite membranes in these systems has great potential. 

The considerations above apply to zeolite membranes as applied on the macrolevel (e.g., PBMR). Zeohte membranes apphed on the particle level or smaller might lead to a more optimistic outlook since this type of application neither involves expensive modules and supports nor expensive sealing material. 

The reproducibility of zeolite membranes is sometimes questioned. But, taking into account the large surface areas that are produced for the mentioned application examples, for well-studied zeolite membrane syntheses this does not appear to be a limiting factor. 

As is obvious, many potential hurdles discussed in the previous sections do not apply to appHcation of zeolite membranes at the micro- and particle levels. Issues Hke scale-up and high-temperature sealing do not play a role here. Additionally, coated catalyst particles do not require a change of reactor, but only replacement of the catalyst. Application of zeoHte membranes at these levels is therefore considered to be easier and their implementation will probably occur earlier. 

A zeolite membrane, where the pores originate from the structure, presents only one type of (ultramicro)pore and therefore seems to be a good candidate for CMRs application. Moreover the structural origin of the pores should induce a much better thermal stability of the... 

Hong, M., R.D. Noble, and J.L. Falconer, Highly selective H2 Separation Zeolite Membranes for Coal Gasification Membrane Reactor Applications, Annual Technical Progress Report, U.S. DOE Contract DE-FG26-02NT41536, December 2005. 

The present review of zeolite membrane technology covers synthesis and characterization methods as well as the theoretical aspects of transport and separation mechanisms. Special attention is focused on the performance of zeolite membranes in a variety of applications including liquid-liquid, gas/vapor and reactive... 

Current state-of-the-art research in zeoUte membranes has shown the significant potential of these materials in numerous applications. However, there are a number of challenges that need to be addressed before zeolite membranes will be utilized commercially. These include the following [8, 39, 44] ... 

Caro,)., Noack, M Kolsch, P and Membranes, Z. (2005) Zeolite membranes from the laboratory scale to technical applications. Adsorption, 11, 215-227. 

J. L. (2004) Fundamentals and applications of pervaporation through zeolite membranes./. Memhr. Sci, 245, 1-33. 

This chapter provides a brief introduction to polymer and inorganic zeolite membranes and a comprehensive introduction to zeolite/polymer mixed-matrix membranes. It covers the materials, separation mechanism, methods, structures, properties and anticipated potential applications of the zeolite/polymer mixed-matrix membranes. 

In recent years, extensive work has been reported on the synthesis, characterization and applications of zeoUte membranes [5]. ZeoUte membranes are capable of overcoming some of the challenges facing polymer membranes. Under conditions where polymer membranes cannot be used zeolite membranes have the potential... 

The second part of the book covers zeolite adsorptive separation, adsorption mechanisms, zeolite membranes and mixed matrix membranes in Chapters 5-11. Chapter 5 summarizes the literature and reports adsorptive separation work on specific separation applications organized around the types of molecular species being separated. A series of tables provide groupings for (i) aromatics and derivatives, (ii) non-aromatic hydrocarbons, (iii) carbohydrates and organic acids, (iv) fine chemical and pharmaceuticals, (v) trace impurities removed from bulk materials. Zeolite adsorptive separation mechanisms are theorized in Chapter 6. 

As an example of hybridization of zeolites with cellulose derivatives, self-supporting zeolite membranes with a sponge-like architecture and zeolite microtubes were prepared by using CA filter membranes as a template [154]. The hierarchical structure with sub-nanometer- to micrometer-sized pores is a characteristic of great promise for a wide range of applications such as catalysis, adsorption, and separation. There was also an attempt to prepare alginate membranes incorporated with zeolites, e.g., for pervaporation separation of water/acetic acid mixtures [155]. 

Current polymeric materials are inadequate to fully meet all requirements for the various different types of membranes (cf. Section 2.2) or to exploit the new opportunities for application of membranes. Mixed-matrix membranes, comprising inorganic materials (e.g., metal oxide, zeolite, metal or carbon particles) embedded in an organic polymer matrix, have been developed to improve the performance by synergistic combinations of the properties of both components. Such improvement is either with respect to separation performance (higher selectivity or permeability) or with respect to membrane stability (mechanical, thermal or chemical). 

A zeolite membrane is a membrane in which the transfer is controlled by the porous structure of the zeolite. Compared to sol-gel membranes, zeolite membranes can present some advantages for CMR applications. The most useful feature is that the pores of zeolites arc in the ultramicroporous range and have a very narrow size distribution (in this case pores are linked to the structure and not to the texture as in sol gel membranes). These characteristics of zeolite... 

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