High zeolites

Hydroisomerization of n-octane over Pt-containing micro/mesoporous catalysts obtained by recrystallization of zeolites BEA and MOR was investigated in the temperature range of 200-250 °C under 1-20 bar. Composite materials showed remarkably high activity and selectivity with respect to both pure microporous and pure mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores. 

Figure 16.7 Influence of support type on product distribution in hydrocracking hydrotreated light Arabian gasoil feed hydrocracked over amorphous and high zeolite catalysts differential yields measured in 50°F (10°C) increments.

The reference catalyst A and Catalyst B had both a low activity compared with catalyst C as shown in Fignre 3.14. One explanation for this might be the low zeolite surface area for both the reference catalyst and for Catalyst B. Catalyst C had the highest activity of the three catalysts because of its high zeolite surface area and despite its high matrix snrface area. 

For the first type of poisons, we can either try to apply the same approach as with vanadium meaning specific catchers or offer a sufficient excess of acid sites sacrificial sites in order to reduce the relative impact of the poisoning. For instance, in the case of a nitrogen resistant catalyst, usually the catalyst design will involve a relatively high rare-earth and high zeolite content catalyst with the option of additional sacrificial sites in the form of active alumina (12). 

The adsorption/separation process alone has long been used industrially for solvent recovery for cost saving by recycling. Retrofit of investment was gained in the very short term. However, as the cost of HMS is very high, zeolites are only used in applications for which carbons are not well suited. 

The survey teams subsequently identified many large-scale sedimentary zeolite deposits and today these are known to occur worldwide in vast quantities. The occurrences vary from those of high zeolite purity (>90%), such as those located in California, to tuffaceous materials of around 50-60% zeolite content (as in Italy). Commercial mining operations are known in USA, Japan, Cuba, Italy, Hungary, Bulgaria, Czechoslovakia, Indonesia, Korea, Russia, and South Africa. Workable deposits also exist in Mexico, Greece, and other Balkan states. 

This extra framework Al can be identified by MAS-NMR but is in at least two forms. It is these Al species that are thought to be the super acid sites inducing the high zeolite surface reactivity. 

Our investigations show that catalyst composition and architecture can have a significant effect on the initial quantity of adsorbed hydrocarbons, i.e. soft delta coke, as well as on stripping rate (table 4). A high zeolite content usually results in a high soft coke make, but not necessarily in a low stripping rate (cat. A vs B). At a constant activity, hard and soft coke make, the stripping rate increases with accessibility ( cat. B vs C). 

To further illustrate the differences between the methods, Fig. 2 and 3 show the yield and the Si/Al ratio, respectively, of the zeolite as a function of time of crystallization for synthesis runned by the four methods. Obviously, it is not possible to compare synthesis with the same chemical compositions because of the differences of the methods. Accordingly, in Fig. 2 and 3 we compare synthesis runs that gave, for every method, high Si/Al ratios and high zeolite yields. In this figures it is seen how our "classical" syntheses of Ti-Beta zeolite (amorphous silica and TEOS methods) have been surpassed by the new, previously unpublished methods (TEOS/seed and cogel methods), if the Si/Al ratio of the zeolite and its yield are compared. Furthermore, the TEOS/seed method is the most versatile one in terms of varying the chemical composition of the zeolite, and thus we have prepared materials wich are essentially pure silica (A1 plus Ti contents below 0.2 atoms per unit cell of 64 tetrahedra). 

To be noticed is that the overall efficiency may be improved by using materials richer in chabazite, either natural or artificial, e.g., self-bonded chabazite pellets obtained from highly zeolitized tuff powders (20). 

In principle there is a possibility to stabilize bivalent metal cation with a ligand, which transforms bivalent cations to monovalent species, for example, (ZnOH)+. It is reasonable to expect appearance of such species as a result of dissociative adsorption of water and it will be discussed below. However, the most interesting catalytic processes proceed at high temperatures when the above-mentioned species became unstable. It should be noted that all the above considerations are applicable to zeolites with rather high zeolite module Si/Al >5. The theoretical treatment of traps of exchange metal cations in zeolites with lower module requires different approach. The stabilization of bivalent metal cations in zeolites is considered in the Sect. 20.2 of this review which discusses the example of Zn/ZSM-5 zeolites. These zeolites are active in the catalytic process of small alkane dehydrogenation. Thus, we will explore the influence of the stabilization forms of zinc cation on different stages of this catalytic reaction. 

Acid soluble components of the zeolitic material were identified by monitoring the interaction of highly zeolitized product of the TSA with a strong acid. In this context, 1.2 N HCl (35 %, pH = 0.7), a strong acid, was used in this study. In order to quantify solubility of the residue, AAF, in such an acidic solution (i.e., similar to... 

Researchers [36, 38] have characterized NaOH activated fly ash residues (zeolites) and have ascertained their highly zeolitic nature [7]. It has also been opined [37,39] that the purity of these residues is mainly decided by their cation exchange capacity, mineralogy and morphology. However, study of pore characteristics (viz., size and volume) of such residues has not been explored in detail. 

Silica sol binders used in high-zeolite catalysts by Davison. 

Catalyst Early units sulfided nickel molybdate/silica alumina catalysts. Later units Catalysts with high zeolite content. 

Poly (vinyl alcohol) (PVA) has also been applied to alcohol-water pervaporation. ZSM-5 was again utilized, and mixed-matrix enhancements resulted. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water-isopropyl alcohol separation. Membrane swelling and fluxes increase as the water concentration in the feed increases. " Sorption studies of ZSM-5/PVA systems indicate that this hybrid material is a good candidate for the extraction of water from alcohol. Modified poly (vinyl chloride) embedded with NaA zeolite has demonstrated both flux and selectivity enhancements for the ethanol-water separation at high zeolite loadings. Voids at the solid-polymer interface prevented seleetivity enhaneement at low zeolite loadings. ... 

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