Zeolite selectivity

Haag W O, Lago R M and Weisz P B 1982 Transport and reactivity of hydrocarbon molecules in a shape-selective zeolite Faraday Disouss. Chem. Soo. 72 317-30... 

ZSM-5 is Mobil Oil s proprietary shape-selective zeolite that has a different pore structure from that of Y-zeolite. The pore size of ZSM-5 is smaller than that of Y-zeolite (5.1°A to 5.6°A versus 8°A to 9 A). In addition, the pore arrangement of ZSM-5 is different from Y-zeolite, as shown in Figure 3-16. The shape selectivity of ZSM-5 allows... 

The cations that replace the sodium ions determine the catalyst s activity and selectivity. Zeolites are synthesized in an alkaline environment such as sodium hydroxide, producing a soda-Y zeolite. These soda-Y zeolites have little stability but the sodium can be easily... 

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.)... 

Shape-selective zeolites can also be used to discriminate among potential products of a chemical reaction, a property called product shape selectivity. In this case, the product produced is the one capable of escaping from the zeolite pore structure. This is the basis of the selective conversion of methanol to gasoline over... 

Zeolite chemistry is an excellent example of how a three-dimensional surface can alter the course of chemical reactions, selecting for one product out of a host of potential candidates. In addition to the many commercial applications that they have found, shape-selective zeolites have provided the basis for a rich new area of catalytic science and technology, one expected to spawn yet more materials, knowledge, and applications. 

The density of Bronstcd and Lewis acid sites was determined by IR spectroscopy (Nicolet 710) of adsorbed pyridine, after desorption at 250°C, using the molar extinction coefficients previously obtained by Emeis [11]. The acid strength distribution of selected zeolites was studied by NH3-TPD in an Autochem 2910 Equipment (Micromeritics) coupled to a quadrupole mass spectrometer. First, NH3 was adsorbed at 175°C until saturation and then desorbed by increasing the temperature up to 800°C at a heating rate of 10°C/min. 

The catalyst used for the conversion of methanol to gasoline is based on a new class of shape-selective zeolites (105-108), known as ZSM-5 zeolites, with structures distinctly different from other well-known zeolites. Apparently, the pore dimensions of the ZSM-5 zeolites are intermediate between those of wide-pore faujasites (ca. 10 A) and very narrow-pore zeolites such as Zeolite A and erionite (ca. 5 A) (109). The available structural data indicate a lattice of interconnecting pores all having approximately the same diameter (101). Hydrocarbon formation... 

Csicsery, S.M. (1986). Catalysis by shape selective zeolites - science and technology. Pure Appl. Chem. 58, 841-856... 

The first mode of the high resolution C-NMR of adsorbed molecules was recently reviewed Q-3) and the NMR parameters were thoroughly discussed. In this work we emphasize the study of the state of adsorbed molecules, their mobility on the surface, the identification of the surface active sites in presence of adsorbed molecules and finally the study of catalytic transformations. As an illustration we report the study of 1- and 2-butene molecules adsorbed on zeolites and on mixed tin-antimony oxides (4>3). Another application of this technique consists in the in-situ identification of products when a complex reaction such as the conversion of methanol, of ethanol (6 7) or of ethylene (8) is run on a highly acidic and shape-selective zeolite. When the conversion of methanol-ethylene mixtures (9) is considered, isotopic labeling proves to be a powerful technique to discriminate between the possible reaction pathways of ethylene. 

There are several means to maximize the yield in the desired monoalkylation product high aromatic/alkylation agent ratio, association of a transalkylation unit to the alkylation unit, and use of a shape selective zeolite as catalyst. 

Thomas, J.M., Millward, G.R., and Ramdas, S. (1981) New methods for the strucmral characterization of shape-selective zeolites. Faraday Discuss. 

Chou, Y.C.T. (1986) Process for separation of ethylene glycol and propylene glycol on selected zeolites. U.S. Patent 4,588,847. 

The Maxwell model can also guide the selection of a proper polymer material for a selected zeolite at a given volume fraction for a target separation. For most cases, however, the Maxwell model cannot be applied to guide the selection of polymer or zeolite materials for making new mixed-matrix membranes due to the lack of permeabihty and selectivity information for most of the pure zeolite materials. In addition, although this Maxwell model is well-understood and accepted as a simple and effective tool for estimating mixed-matrix membrane properties, sometimes it needs to be modified to estimate the properties of some non-ideal mixed-matrix membranes. 

P., and Romano, U. (2003) A priori selection of shape-selective zeolite catalysts for the synthesis of 2,6-dimethylnaphthalene. J. Catal., 217, 298-309. 

P.B. (1982) Transport and reactivity of hydrocarbon molecules in shape selective zeolites. J. Chem. Soc., Farad. Disc., 72, 317. 

The use of a shape-selective zeolite, such as Mobil s ZSM-5, has attracted the refiner s interest because this zeolite... 

ZSM-5 is a Mobil-proprietary, shape-selective zeolite which is used commercially in synthetic fuels (methanol-to-gasoline), petrochemicals (xylene isomerization, toluene disproportionation, benzene alkylation) and in petroleum refining (lube and... 

A different product distribution is obtained by shape-selective zeolites.85,86 Since the diffusion coefficient of p-xylene with its preferred shape into the zeolite... 

---