Application of Molecular Sieves

and NaY zeolites, and derivatives prepared by ion exchange (Li, Ca, Co, Sc, La, Zr), were studied first in the transformation of 2-methyl-2,3-butane-diol (flow system, 483-583 K) [26]. The small-pore zeolite NaA proved to be completely inactive but the activity of large-pore samples varied, with conversion usually in the range 20-50%. The best selectivity for 3-methyl-2-butanone (ca 88 %) was achieved over NaCaX. Selectivity, however, was found to decrease with increasing temperature, because of competing p elimination. 

High activity and selectivity in the pinacol rearrangement of simple diols were observed in subsequent studies. Y zeolites (HY [27], LaHY [26,28], CaHY [28], NaY, and NaHY [29,30]) had the highest activity, and they were also more selective than X zeolites [29,30]. Though HZSM-5 was less active, its activity remained constant whereas substantial deactivation was observed for Y zeolites [28]. This is explained by the higher resistance of HZSM-5 to coke formation. 

These observations for the stereoisomeric 2,3 -butanediols can be explained by assuming concerted elimination of water and migration of H or Me. Such an E2- 

Studies with silicoaluminophosphate molecular sieves showed that SAPO-37 (faujasite geometry) and SAPO-5 (API structure) were good catalysts for the transformation of pinacol, with selectivity increasing with reaction time (batch reactor, 423 K) [31]. In contrast, the activity of two other samples (SAPO-11 and SAPO-34) was inferior, possibly because inadequate pore dimensions hindered access of the reacting pinacol to the active sites. 

The pinacol rearrangement proceeds over metal-substituted aluminophosphate molecular sieves (APOs) under mild conditions (batch reactor, solvent, g diol/ g catalyst = 5, 383 K, 3 h) [32]. Catalytic performance is best for APO-5 (Table 2) and surpasses that that of VPI and APO-11. Of the metals used Fe, Ni, and Cu have the highest activity and selectivity. No direct correlation was found between activity and acidity determined by pyridine TPD. For example. 

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The main applications of molecular sieves to purification comprise ... 

Characterization and Novel Applications of Molecular Sieve Materials (eds R.L Bedard, T. Bein, M.E. Davis, J. Garcia, V.A. Maroni, and G.D. Stucky),... 

Dehydration is by far the largest industrial separation of interest here. Removal of water was the first commercial application of molecular sieves. Dehydration and related fixed-bed adsorptive separations in the process industries account for more than half of the commercial molecular sieve business volume. 

TABLE 7.2 Applications of molecular sieves in industrial adsorption processes... 

The technological applications of molecular sieves are as v aried as their chemical makeup. Heterogeneous catalysis and adsorption processes make extensive use of molecular sieves. The utility of Ihc latter materials lies in their mierostructures. which allow access to large internal surfaces, and cavities that enhance catalytic activity and adsorptive capacity. 

The first synthetic zeolites were known as Linde Molecular Sieves but are now marketed as Union Carbide Molecular Sieves they are available from Union Carbide International Company, USA. or Union Carbide (UK) Ltd directly, or through the usual chemical suppliers, t Booklets giving detailed information on the structure, action and applications of molecular sieves are available from most suppliers of laboratory chemicals. 

To evaluate the applicability of molecular sieves, we compare the kinetic diameter of components. Low-size sieves would filter all, except chloro-ethane and benzene. Then, the remaining H2S may be handled by wet scrubbing. 

R.A. Jones initiated application studies in 1950, was coinventor of the first major application of molecular sieves [36], led our entire application engineering group prior to going into field sales, and later became Sales Manager. 

A. Corma, Mater. Res. Soc. Symp. Proc., 233 (Synthesis-Characterization and Novel Applications of Molecular Sieve Material), 17(1991). 

T. Bein, Synthesis and Application of Molecular Sieve Layers and Membranes. Chem. Mater., 1996, 8, 1636-1653. 

This contribution briefly highlights current trends in the synthesis of new types of zeolite-based molecular sieves showing recent development in this very topical area. We have tried to cover the most important examples of the development of these molecular sieves, in which a high potential for future applications of molecular sieves is expected. At the end of... 

Although adsorption processes represent an extremely large application of molecular sieves (49), applications in the area of heterogeneous catalysis have received the most attention for borosilicate molecular sieves. Due to the inherently weaker acidity of borosilicates relative to aluminosilicates, a number of advantages in using borosilicates have been reported due to improved product distributions or reaction selectivities. 

Fajula F and Plee D 1994 Application of molecular sieves in view of cleaner technology. Gas and liquid phase separations Stud. Surf. Sci. Catal. 85 633-51... 

The handbook will appear over several years with a total of ten to fifteen volumes. Each volume of the series will be devoted to a specific sub-field of the fundamentals or application of molecular sieve materials and contain five to ten articles authored by renowned experts upon invitation by the editors. These articles are meant to present the state of the art from a scientific and, where applicable, from an industrial point of view, to discuss critical pivotal issues and to outline future directions of research and development in this sub-field. To fhis end, fhe series is infended as an up-to-date highly sophisticated collection of information for those who have already been dealing with zeolites in industry or at academic institutions. Moreover, by emphasizing the description and critical assessment of experimental techniques which have been used in molecular sieve science, the series is also meant as a guide for newcomers, enabling them to collect reliable and relevant experimental data. 

For the production of fuel-grade ethanol, the ethanol has to be dried . Anhydrous ethanol cannot be produced by simple distillation because ethanol forms an azeotropic mixture with water. The maximum ethanol content achievable by distillation is approximately 97.2vol.%, which is usually not sufficient for the application as fuel-ethanol. The residual water can be removed either by azeotropic distillation by the addition of, e.g., cyclohexane or by the application of molecular sieves. Today, state-of-the-art plants operate with molecular sieves which provide considerable advantages in terms of investment and operating costs. 

Armen, M.J., Davis, M.E., Higgins, J.B. and Schlenker, J.L. (1991) "The first Microporous Zincosilicate with three-Membered Rings" in Symposium on Synthesis, Characterization and Novel Applications of Molecular Sieve Materials, Spring Meeting of the Material Research Society, Aruiheim CA. (USA) (to be puNished). 

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