Ultrastable zeolite

Adnadjevid et al. (1997) studied the effect of three different types of hydrophobic zeolites (ultrastable zeolite type Y, pentasyl-type zeolite (ZSM-5), and ALPO-5 type zeolite) on the PV properties of zeolite-tilled PDMS membranes. The physiochemi-cal properties of the zeolite used, primarily the degree of hydrophobicity, as well as the sorption capacity for EtOH, the specific pore volume, specific area, and mean crystallite size of the zeolite, significantly influence the membrane s PV properties. An increase in the zeolite content results in an increase in both membrane permeability and membrane selectivity, while an increase in the PV temperature results in an increase in the permeability and a decrease in the selectivity, as opposed to the effect of membrane thickness. 

Zeolites with lower UCS are initially less active than the conventional rare earth exchanged zeolites (Figure 3-5). However, the lower UCS zeolites tend to retain a greater fraction of their activity under severe thermal and hydrothermal treatments, hence the name ultrastable Y. 

Abramova, A. V., Slivinsky, Ye. V., Goldfarb, Y.Y., Kitaev, L. Ye., Kubasov A. A., Modeling of Nature and Strength of Acid Centres in Ultrastable Zeolites as a Component of Hydrocracker Catalysts, in Hydrotreatment and Hydrocracking of Oil Fractions. 1999, Elsevier Science B. V New York. pp. 377-380. 

Samples of Y faujasites were prepared by sodium exchange of a starting ultrastable Y zeolite (H form, denoted in the following as USY). Global Si/Al ratio is 16 according to X fluorescence measurements framework Si/Al is 21 as measured by 29Si MAS NMR. 

R2R A catalytic cracking process using an ultrastable zeolite catalyst with two-stage regeneration. Developed by Institut Frangais du Petrole and used at Idemitsu Kosan s refineries at Aichi and Hokaido. In 1994, 13 existing plants had been converted to this process. 

Kerr, G.T. (1973). Hydrogen zeolite Y, ultrastable zeolite Y, and aluminum-deficient zeolites. Adv. Chem. Ser. 121, 219-229... 

As in FCC, the hydrocarbons can be burned off the catalyst surface. This requires a catalyst with extreme temperature stability, which only ultrastable zeolites achieve. Moreover, as the alkylation process is exothermic and conducted at low to moderate temperatures, large amounts of process heat have to be removed. 

An example of such thermal dealumination is the formation of ultra-stable Y zeolites (USY zeolites). McDaniel and Maher (6) reported the preparation of two types of ultrastable Y zeolites (a) one type prepared by the hydrothermal... 

C. Hydrothermal and chemical treatment Reaction of ultrastable Y zeolites with ... 

Reactions with acids. Hydrochloric acid was used in the dealumination of clinoptilolite (1), erionite (14) and mor-denite (2,3,15,92). In the case of Y zeolite, dealumination with mineral acids was successful only after conversion of the zeolite into the ultrastable form (vide infra). Barrer and Makki (1) were the first to propose a mechanism for the removal of aluminum from mordenite by mineral acids. It involves the extraction of aluminum in a soluble form and its replacement by a nest of four hydroxyl groups as follows ... 

A modification of the above cyclic method has proved more effective in the dealumination of Y zeolites. An almost aluminum-free, Y-type structure was obtained by using a process involving the following steps a) calcination, under steam, of a low-soda (about 3 wt.% Na O), ammonium exchanged Y zeolite b) further ammonium exchange of the calcined zeolite c) high-temperature calcination of the zeolite, under steam d) acid treatment of the zeolite. Steps a) and c) lead to the formation of ultrastable zeolites USY-A and USY-B, respectively. Acid treatment of the USY-B zeolite can yield a series of aluminum-deficient Y zeolites with different degrees of dealumination, whose composition depends upon the conditions of the acid treatment. Under severe reaction conditions (5N HC1, 90°C) an almost aluminum-free Y-type structure can be obtained ("silica-faujasite") (28,29). 

Aluminum-deficient Y zeolites. The properties of aluminum-deficient Y zeolites, including ultrastable zeolites, have been reviewed in several papers (9,33-35). During the last several years, new techniques have been applied to study these materials. This led to a better understanding of their structural characteristics and of the correlations between structure and properties. We shall discuss the structure and properties of aluminum-deficient Y zeolites, with the emphasis on more recently published results. 

It has already been mentioned that the formation of ultrastable Y zeolites has been related to the expulsion of A1 from the framework into the zeolite cages in the presence of steam (8,9), and the filling of framework vacancies by silicon atoms (11,12). This results in a smaller unit cell size and lower ion- exchange capacity (6). It also results in a shift of X-ray diffraction peaks to higher 20 values. Ultrastable Y zeolites prepared with two calcination steps (USY-B) have a more silicious framework than those prepared with a single calcination step (USY-A). Furthermore, since fewer aluminum atoms are left in the USY-B framework, its unit cell size and ion-exchange capacity are also lower and most of the nonframework aluminum is in neutral form (18). 

Stability. Ultrastable Y zeolites, prepared by the hydrothermal treatment of ammonium Y zeolites, have considerable thermal and hydrothermal stability (6) The high... 

Infrared spectra. The infrared spectra of ultrastable Y zeolites have been investigated by Ward (10), Jacobs and Uytterhoeven (50,53), Scherzer and Bass (51) and Peri (52). 

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). 

In 1962 Mobil Oil introduced the use of synthetic zeolite X as a hydrocarbon cracking catalyst In 1969 Grace described the first modification chemistry based on steaming zeolite Y to form an ultrastable Y. In 1967-1969 Mobil Oil reported the synthesis of the high silica zeolites beta and ZSM-5. In 1974 Henkel introduced zeolite A in detergents as a replacement for the environmentally suspect phosphates. By 2008 industry-wide approximately 367 0001 of zeolite Y were in use in catalytic cracking [22]. In 1977 Union Carbide introduced zeolites for ion-exchange separations. 

Rocha,). and Klinowski, J. (1991) Al solid-state NMR spectra of ultrastable zeolite Y with fast magic-angle spinning and H- A1 cross-polarizabon. . Chem. Soc. Chem. Commun., 1121-1122. 

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. 

Catrinescu, C Neamtu, M Yediler, A Macoveanu, M Kettrup, A. Catalytic wet peroxide oxidation of an azo dye. Reactive Yellow 84, over Fe-exchanged ultrastable Y zeolite. Environmental Engineering and Management Journal, 2002 1, 177-186. 

Tetrahedral and Octahedral Extraframework Aluminum in Ultrastable Y Zeolites... 

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... 

The starting NaY zeolite was an SK-40 from Union Carbide with a framework Si/Al ratio of 2.4. Ultrastable HY zeolites (HYUS) were prepared by steam-calcination of partially ammonium exchanged zeolites at atmospheric pressure and 550-750 °C during 3-20 hours. After dealumination they were exchanged twice with an NH solution at 80 C for one hour and then calcined at 550 °C for 3 hours. In this way dealuminated samples containing less than 2% of the original Na were obtained. One of these (HYUS-8) was subjected to different treatments (1) washed with a solution of citric acid or HCl (pH=3) at 25 °C for one hour (samples HYUSAC and HYUSl, respectively) (2) washed with a solution 0.1 M of NaOH at 40 °C for one hour (HYUSN), and (3) washed with a 38% v/v solution of acetylacetone in ethanol at 20 °C for 2 hours (HYUSA). 

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