Shape-selective reforming

Figure 7.8 Shape-selective reforming. The straight-chain alkane (left) can enter the zeolite pore and penetrate to the catalytic site, whereas the branched-chain isomer cannot.

Shape-Selective Reforming Possibie Reaction Pathways on Platinum-Containing Erionite/Alumina Catalysts... 

Fig.9 Reaction network shape-selective reforming of C7-hydrocarbons over platinum-erionite/alumina catalysts...

Another property of zeolites is the high conversion rates in the channel system. It was also observed that with different spatial configurations of channels, cavities, windows, etc, the catalytic properties are changed and the selectivity orientates toward less bulky molecules due to limitation in void volume near the active sites or to resistance to diffusivity. This feature termed shape-selectivity, was first proposed by McBain (20) demonstrated experimentaly by Weisz et al (21) and reviewed recently (22). For instance CaA zeolite was observed to give selective dehydration of n-butanol in the presence of more bulky i-butanol (23) while CaX non selective zeolite converted both alcohols. In a mixture of linear and branched paraffins, the combustion of the linear ones was selectively observed on Pt/CaA zeolite (24). Moreover, selective cracking of linear paraffins was obtained from petroleum reformate streams resulting in an improvement of the octane number known to be higher for branched paraffins and for aromatics than for linear paraffins. Shape selectivity usually combines acidic sites within... 

The role of catalysis in the petroleum industry has been equally revolutionary. Meta I-supported systems (e.g. of Topsoe and Shell) for catalytic reforming, hydrodesulfurization and hydrodenitrification, alkylation catalysts and shape selective systems (e.g. zeolites and pillared clays) for catalytic cracking (FCC) and production of gasoline from methanol (Mobil MTG) all represent significant technical and commercial achievements. 

Naphtha reforming catalysts are mostly based on metals (Pt, Pt-Re, Pt-lr, Pt-Sn, Pt-Re-Sn) supported on chlorinated-ALOs or on a KL zeolite. Non-acidic KL zeolite in combination with Pt has been applied in a new reforming process. The non-acidic zeolite support inhibits undcsircd isomerization and hydrocracking reactions leading to enhanced aromalization selectivities [69]. Besides the absence of acidity, the presence of highly dispersed Pt clusters inside the zeolite channels and the shape-selective effects imposed by the monodirectional channel structure (0.71 nm diameter) of the zeolite may also contribute to the excellent aromatization performance of Pt/KL catalysts. 

The efficiency of the catalytic reforming process is determined by the relationship between the octane number (ON) and the liquid yield. For improvement of the ON of reformates the n-alkanes can be hydrocracked shape-selectively on narrow-pores zeolites, i.e. in case of the Selectoforming process (ref. 1) on metal containing H-erionite. During the past 15 years efforts were directed towards the integration of the shape-selective catalyst into the reforming unit (ref. 2). 

Thus erionite, with the smallest pore opening of 0.38-0.52 nm, has the highest shape selectivity. It was found that with certain zeolites, the linear alkane n-hexane is cracked 40-100 times faster than the branched isomer 3-methylpentane. This is exploited industrially in the Selectoforming process, in which erionite is added to the reforming catalyst. 

One of the first success of zeolites as catalysts, and the first commercial molecular shape selective catalytic process, was the use of erionite in a post-reforming process named selectoforming (39). Ihis 8 MR zeolite was able, based on the principle of size exclusion, to selectively crack the short chain n-parafiins to produce LPG. To avoid the deactivation by coke NiS was deposited on the zeolite. The erionite based catalyst is generally located at the bottom of the last reactor of the reformer unit and operates then at the reformer pressure, and at the temperature of the last reformer reactor. When more flexibility was to be achieved from the selectoforming, the catalyst is introduced... 

Textured Soy Proteins. Textured vegetable proteins, primarily textured flours and concentrates (50% protein and 70% protein, dry basis, respectfully) are widely used in the processed meat industry to provide meat-like structure and reduce ingredient costs (3-6, 9-10). Available in a variety of sizes, shapes, colored or uncolored, flavored or unflavored, fortified or unfortified, textured soy proteins can resemble any basic meat ingredient. Beef, pork, seafood and poultry applications are possible 03, 4-7, 15, 19) Proper protein selection and hydration is critical to achieving superior finished product quality. Textured proteins have virtually no solubility and, thus, no ability to penetrate into whole muscle tissue Therefore, textured soy proteins are inherently restricted to coarse ground (e.g. sausage) or fine emulsion (e.g. weiners and bologna) products, and comminuted and reformed (i.e. restructured) meat products. None are used in whole muscle absorption or injection applications (2-4, 6, 11). 

Tourist destinations, even more than basic consumer products such as food or household items, are viewed and presented in selective and diverse ways. Tourist places are not just used or promoted by the tourism industry, but are frequently shaped by marketing efforts. In this sense tourism forms and reforms its own product. At the same time, other community and economic forces also shape the destination. As Hughes suggests ... 

Reforming catalysts usually involve both transition metals, often platinum, and minerals, particularly zeolites modified with various metals the zeolites are aluminum silicates. Depending on the exact structure, there are a number of anionic sites, which must be neutralized by metal cations or protons. The protonic forms are strongly acidic. The zeolites have distinctive pore sizes and are selective for certain molecular sizes or shapes. For example, pore size can be a factor in determining the ratio of the 0-, m-, and /i-isomers of xylenes, with narrower pores favoring the last. Under normal... 

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