Industrial applications of zeolites

Industrial applications of zeolites cover a broad range of technological processes from oil upgrading, via petrochemical transformations up to synthesis of fine chemicals [1,2]. These processes clearly benefit from zeolite well-defined microporous structures providing a possibility of reaction control via shape selectivity [3,4] and acidity [5]. Catalytic reactions, namely transformations of aromatic hydrocarbons via alkylation, isomerization, disproportionation and transalkylation [2], are not only of industrial importance but can also be used to assess the structural features of zeolites [6] especially when combined with the investigation of their acidic properties [7]. A high diversity of zeolitic structures provides us with the opportunity to correlate the acidity, activity and selectivity of different structural types of zeolites. 

Industrial applications of zeolitic separation processes fall into the following general appHcation categories ... 

Sorption capacity is one of the major properties used for industrial applications of zeolites. H. Lee reviews the aspects of zeolites used as adsorbents. The other papers in the section deal with the theory of sorption and diffusion in porous systems, the variation of sorption behavior upon modification, and the variation of crystal parameters upon adsorption. NMR and ESR studies of sorption complexes are reported. H. Resing reviews the mobility of adsorbed species in zeolites studied by NMR. 

Vne of the major industrial applications of zeolites is in the area of ad-sorption processes. Zeolite adsorbents are not only the most important adsorbents today, but their importance is increasing, mainly because of the following unique adsorptive properties (a) selective adsorption of molecules based on molecular dimensions, (b) highly preferential adsorption of polar molecules, (c) highly hydrophilic surface, and (d) variation of properties by ion exchange. 

The study of zeolites as adsorbent materials began in 1938 when Professor Barrer published a series of papers on the adsorptive properties of zeolites [28], In the last 50 years, zeolites, natural and synthetic, have turned out to be one of the most significant materials in modem technology [27-37], Zeolites have been shown to be good adsorbents for H20, NH3, H2S, NO, N02, S02, C02, linear and branched hydrocarbons, aromatic hydrocarbons, alcohols, ketones, and other molecules [2,31,34], Adsorption is not only an industrial application of zeolites but also a powerful means of characterizing these materials [1-11], since the adsorption of a specific molecule gives information about the microporous volume, the mesoporous area and volume, the size of the pores, the energetics of adsorption, and molecular transport. 

There are no experimental data regarding the resistance of zeolitic membranes to fouling. Regeneration of zeolites after, for example, coke deposition is known to be feasible from industrial applications of zeolites. However, the influence of regeneration conditions on zeolitic, composite membranes is not known. 

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. 

Rhodia [2] has operated the first industrial application of zeolite for the acylation of anisole to para-methoxyacetophenone, which is a precursor of avobenzone (trade names PARSOL 1789, EUSOLEX 9020, ESCALOL 517, etc.) used in sun creams (Equation 14.1) ... 

Significant advances resulting from the use of aluminosilicate solids were made during the last few years [3-6] and the first industrial application of zeolites in large scale Friedel-Crafts acylations was reported very recently [7]. However, most of the efforts devoted so far focused on the acylation of aromatic compounds. To the best of our knowledge, recourse to heterogeneous aluminosilicate catalysts for the acylation of alkenes has not yet been reported. Conventional methods for alkene acylation [8] involve the use of Br0nsted or Lewis acids such as sulfuric acid [9], boron trifluoride [10], zinc chloride [11], or... 

Industrial applications of zeolite membranes can be considered only for separations where they offer some unique advantage in terms of flux, selectivity, or thermal and chemical stability. The very high fluxes obtained with LTA membranes (typically 100 times higher than those obtained with a polyacrylonitrile membrane at the same FLO/alcohol selectivity) explain the rapid expansion of this type of application at the end of the 90s [8J. 

A. Pfenninger, Proceed. Symp. on Industrial Applications of Zeolites , Oct. 22-25, 2000, Brugge, Belgium, Technol. Instituut vzw, 73-82, 2000. 

The 13 International Zeolite Conference has been held in Montpellier, France, from July 8 to 13,2001, organized by the French Zeolite Group on behalf of the IZA. It has been preceded by a School on the Industrial Applications of Zeolites, held in Poitiers, and followed by a Field Trip in the natural zeolite localities of Massif Central. 

Until now, the most powerful contribution of neutron diffraction, even on powders, has been the guest location, especially for deuterated hydrocarbon molecules. As a matter of fact, one of the most important industrial applications of zeolites is hydrocarbon conversion catalysis and separation. The advantage of neutrons over X-rays comes from the fact that deuterium and carbon have similar scattering lengths (be = 6.65 fm, b = 6.67 fm) which involves participation of all the nuclei of the guest molecule in the structure factor. 

The zeolite structure remains the fundamental factor responsible for their technological importance. The industrial application of zeolites can be outlined in terms of structurally related properties. Some of the most important zeolitic properties are adsorption, catalysis, ion-exchange and shape selectivity. 

Figure 2. Some useful industrial application of zeolites...

Supported LTA membranes have been successfully installed during the last 10 years worldwide in about 25 plants for the dewatering of (bio)ethanol and i-propanol. Whereas there are outstanding separation performances of a new generation of zeolite membranes type SAPO-34 and DD3R on the lab scale, no short-term large-scale industrial application of zeolite membranes for gas separation can be predicted. 

It is worth noting that a number of excellent reviews have been published in the recent literature describing the state of the zeolite science and summarizing the achievements and progress made since the discovery of zeolites and especially focusing on the new applications of zeolite-like materials. The reader may wish to learn more about the industrial applications of zeolites in [3-5]. 

In chapter 1, a short introduction to molecular simulations is presented, as well as an introduction to the structure and industrial applications of zeolites. 

It has been emphasised already that accurate and reliable data are essential in the construction of adequate ion exchange models for the industrial applications of zeolite and other ion exchangers. In this section we will discuss ion exchange experimentation and its utility for industrial appHcations. We also discuss major pitfalls that may lead to unreliable results. Although industrial appHcations always involve more than two exchanging ions, seeing trends in the overaU equilibria under these circumstances may be difficult. Therefore, in this section, only binary ion exchange equilibria are considered in order to keep the major issues in focus. 

Efforts are ongoing to find a way to avoid, reduce or eliminate the presence of inter-crystalline defects, which, aside from poor synthesis reproducibility, are the main obstacle to the industrial application of zeolite membranes for gas separation. 

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