Ultrastable Y zeolite catalysts

Pater, J.P.G., Jacobs, P.A., and Martens, J.A. (1998) 1-Hexene oligomerization in liquid, vapor and supercritical phases over beidellite and ultrastable Y zeolite catalysts. J. Catal., 179, 477. 

The development of ultrastable Y-zeolite catalyst led to the production of gasoline with higher olefin content and increased octane niunber. However, the need for improved catalysts continued because the zeohte was not sufficiently stable and the motor octane number did not rise as much as the research octane number. As discovered previously with other zeolites in the 1960 s, partial exchange of USY-zeolite with rare earth (REUSY) gave better stability as well as activity and provided more branched hydrocarbons and aromatics. Both motor octane number and gasoline production could thus be increased. 

A fairly large number of patents has been issued describing the application of aluminum-deficient Y zeolites in different areas of catalysis. Ultrastable Y zeolites have been used in the preparation of catalysts applied in hydrocarbon cracking, e.g. (94,95) hydrocracking, e.g. (96,97) hydrotreating, e.g. (98) and disproportionation, e.g. (99). 

Different procedures can be used in practice to activate the zeolite, and the choice of a particular method will depend on the catalytic characteristics desired. If the main objective is to prepare a very active cracking catalyst, then a considerable percentage of the sodium is exchanged by rare earth cations. On the other hand, if the main purpose is to obtain gasoline with a high RON, ultrastable Y zeolites (USY) with very low Na content are prepared. Then a small amount of rare earth cations is exchanged, but a controlled steam deactivation step has to be introduced in the activation procedure to obtain a controlled dealumination of the zeolite. This procedure achieves a high thermal and hydrothermal stability of the zeolite, provided that silicon is inserted in the vacancies left by extraction of A1 from the framework (1). The commercial catalysts so obtained have framework Si/Al ratios in the... 

Faced with the need of obtaining more transportation fuels from a barrel of crude, Ashland developed the Reduced Crude Conversion Process (RCC ). To support this development, a residuum or reduced crude cracking catalyst was developed and over 1,000 tons were produced and employed in commercial operation. The catalyst possessed a large pore volume, dual pore structure, an Ultrastable Y zeolite with an acidic matrix equal in acidity to the acidity of the zeolite, and was partially treated with rare earth to enhance cracking activity and to resist vanadium poisoning. 

This work has shown that such a catalyst must possess very high cracking activity that is stable in the presence of steam and high temperature, but must have good selectivity as well. This has been achieved by employing Ultrastable Y zeolite, partially enhanced in activity by addition of a small amount of rare earth, both in the zeolite and in the matrix. 

The most widely used zeolite in petroleum refining so far is Y zeolite. Currently, REUSY zeolite is the main active component of RFCC catalysts. However, in the course of hydrothermal preparation of ultrastable Y zeolite, nonframework aluminum debris formed by dealumination could block the channels thus influencing the ion-exchange ratio of rare earth as well as the accessibility of active sites [2],... 

Epoxidation of olefins over Mo containing Y zeolites was studied by Lunsford et al. [86-90]. Molybdenum introduced in ultrastable Y zeolite through reaction with Mo(C0)g or M0CI5, shows a high initial activity for epoxidation of propylene with t-butyl hydroperoxide as oxidant and 1,2-dichloroethane as solvent [88]. The reaction is proposed to proceed via the formation of a Mo +-t-butyl hydroperoxide complex and subsequent oxygen transfer from the complex to propylene. The catalyst suffers however from fast deactivation caused by intrazeolitic polymerization of propylene oxide and resulting blocking of the active sites. 

CATALYST PREPARATION ZSM-5 was prepared according to procedures discussed in the literature (8.9) and identified as such by X-ray diffraction analysis. Ultrastable Y zeolite was obtained from the... 

In general, we have outlined how the conversion of isobutane on sohd acid catalysts takes place according to well-established carbenium ion transition state chemistry. The difficulty with using isobutane conversion as a probe of catalyst performance is that many combinations of oligomcrization// -scission processes with isomerization steps are possible, resulting in a wide variety of adsorbed species and observable reaction products. For example, the following products are observed from isobutane conversion in the presence of ultrastable Y zeolite at temperatures near 520 K (where the reaction is initiated by the addition of isobutylene to the feed) ... 

In conclusion, the operation with Ti-BEA at industrially practicable temperatures (90° - 100°C) is of high interest, while for other catalysts based on ultrastable Y-zeolite, low temperatures are required for high selectivity (7). 

High amounts of 24 were also obtained by the use of H-US-Y (96) followed by H-US-Y (96)-HCl. The H-US-Y (96)-HCl used, a modified highly dealuminated ultrastable Y zeolite, was pretreated with diluted acid according to the method described before (28, 31). This zeolitic catalyst, unlike many others, remains active at lower temperatures and also at high loading, as was previously demonstrated in the isomerization of alpha-pinene oxide using this heterogeneous catalyst (28, 31). 

Now zeolite catalysts have been employed by most FCCUs. Although zeolite catalysts have a much higher initial activity as compared to amorphous catalysts, coke deposit on the catalyst particles rapidly lowers their activity. As the carbon content of zeolite catalysts increases by 0.1 wt%, the activity decreases by 2-3 units. Generally the carbon content of regenerated zeolite catalysts should not be allowed to exceed 0.2 wt. %, or preferably less than 0.1 wt. % in the case of ultrastable Y zeolite (USY). Therefore, how to decrease CRC efficiently for zeolite catalysts in FCCUs has become a significant problem. 

G. Manos, I. Y. Yusof, N. Papayannakos, and N. H. Gangas, Catalytic cracking of polyethylene over clay catalysts. Comparison with an ultrastable Y zeolite, Ind. Eng. Chem. Res. 40, 2220 (2001). 

The introduction of ultrastable Y zeolites as the acid component (74) even if producing lower middle-distillates than amorphous catalysts, they show a better temperature performance, i.e. zeolite catalysts exhibits higher start-ofr run activity and lower deactivation rates (Fig. 16). 

Obviously another way of eliminating the excess amount of heat is to use catalysts with low coke selectivity. Moreover these catalysts based on ultrastable Y zeolites present the advantage of having a higher hydrothermal stability. Passivators or metal traps can be used... 

Hydroconversion of heptane (H2/ -C7 = 16) was carried out under temperature-programmed conditions over pillared beidellite, pillared montmorillonite, a ultrastable Y-zeolite, H-ZSM-5 and silica-alumina, all containing 1 wt% of Pt. The conversions of heptane over five catalysts are shown as a function of the reaction temperature. As shown in Fig. 3.59, pillared beidellite is more active than pillared montmorillonite, and the former is almost as active as the zeolites. Silica — alumina is the least active. 

Currently, only Y-type zeolites are of any commercial importance as cracking catalysts. In many cases, rare earth ions are incorporated into Y-type zeolites. So-called ultrastable forms of Y-zeolites are also used. These may be prepared by extracting some of the aluminum from the zeolite framework. The ultrastable Y-zeolites can retain their crystal form at temperatures as high as 1200 K. 

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