Zeolites commercially significant

Commercially significant zeolites include the synthetic zeolites type A (LTA), X (FAU), Y (FAU), L (LTL), mordenite (MOR), ZSM-5 (MFI), beta ( BEA/BEC), MCM-22 (MTW), zeolites E (EDI) andW (MER) and the natural zeolites mordenite (MOR), chabazite (CHA), erionite (ERl) and clinoptiloUte (HEU). Details of the structures of some of these are given in this section. Tables in each section lists the type material (the common name for the material for which the three letter code was established), the chemical formula representative of the unit cell contents for the type material, the space group and lattice parameters, the pore structure and known mineral and synthetic forms. 

Structures of Commercially Significant Zeolites 45 Table 2.8 Known members of the ABC-6 family of frameworks. 

The history of commercially significant molecular sieve materials from 1954 to 2001 was reviewed in detail by one of us (E.M.F., ref [1]) Highhghts from that review and the subsequent history are presented here. The reader is referred to Chapter 2 for the structures of the materials and to Chapter 3 and ref [25] for a detailed discussion on zeolite synthesis. 

Since 1962 rare earths have been used to stabilize zeolite cracking catalysts for the petroleum industry (1, 2. Until recently this application to catalysis has been the only commercially significant one. Currently, however, a number of new applications of potential commercial significance are appearing. One of the most important of these is the use of cerium in catalysts for automobile exhaust emission control. We will emphasize this application in our review without neglecting other applications. 

Coke is formed through aromatic condensation reactions (21) which on the molecular scale are spatially quite demanding. Zeolites, with molecular-sized pore systems, tend to be significantly less prone to coke formation than ASA-based catalysts, which do not have such spatially restricted pore structures. Correspondingly, in commercial operation zeolitic catalysts tend to be significantly more stable than ASAs (see Fig. 6.5). 

Selective conversion of methanol or dimethyl ether to lower olefins is a process of commercial significance. It is generally accepted that lower olefins are intermediates in the conversion of methanol or dimethyl ether to higher hydrocarbons over ZSM-5-type zeolite catalysts. The reaction pathway can be simplified as follows ... 

The bulk of these investigations were directed to synthetic species, in accord with their commercial significance. Interest on natural zeolites has, in the main, focussed on their availability as economic, and abundant, materials for water treatment and environmental clean-up. Overall, study has shown that zeolites exhibit unique abilities to selectively take up specific cations from mixtures with other cations- even when the competing cations are present at much higher solution concentrations. Zeolites also have high cation exchange capacities (CEC). 

Studies of the fundamental adsorption phenomena on zeolites have continued in several different areas. These are reviewed by Kiselev and Barrer (Vol. II, p. 37). Adsorption studies have been confined largely to a few materials, chiefly those of commercial significance such as zeolites A, X, and Y. In recent years, interest in adsorption kinetics and diffusion... 

At the low-molecular-weight end of the spectrum, a process newly commercialized by Mobil for converting methanol into gasoline has significantly expanded opportunities in C-1 chemistry— the upgrading of one-carbon molectrles to mrrlticarbon products. The process involves the use of ZSM-5, a shape-selective zeolite catalyst. (See "Zeolite and Shape-Selective Catalysts" in Chapter 9.)... 

After a short description of the main features of zeolites, the significant contribution of zeolite catalysts in green chemistry will be shown in examples of commercial or the potential processes of refining, petrochemicals, and fine chemicals involving acid or metal acid bifunctional catalysts. 

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] ... 

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