Zeolite cracking activity

Gas Oil Cracking by the Dual Zeolite Catalyst. After the steam pre-treatment, the gas oil cracking activity of REY was about 100 times greater than the activity of the pure matrix catalyst. 

Figures 13 and 14 also show that hydrotreating the catalytic cracker feedstock increases the zeolite cracking. C3, and C5+ compounds are possible products of primary zeolite cracking. These figures show that hydrotreating of the feedstock results in larger yields of these primary cracking products and hence more valuable products. This improvement is most likely due to the heteroatom removal and the saturation of aromatic compounds during hydrotreating which tend to block active sites and reduce the activity of the catalyst.

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. 

Generally speaking, resid FCC (RFCC) catalysts should be very effective in bottoms cracking, be metals tolerant, and coke and dry gas selective. Based on many years of fundamental research and industrial experiences, a series of RFCC catalysts, such as Orbit, DVR, and MLC, have been developed by the SINOPEC Research Institute of Petroleum Processing (RIPP) and successfully commercialized [1]. These catalysts are very effective in paraffinic residue cracking. However, in recent years more and more intermediate-based residue has been introduced into FCC units, and the performances of conventional RFCC catalysts are now unsatisfactory. Therefore, novel zeolites and matrices have been developed to formulate a new generation of RFCC catalysts with improved bottoms cracking activity and coke selectivity. 

To improve bottoms cracking activity and coke selectivity of RFCC catalysts, novel zeolites and matrices have been developed recently. Commercial results showed that both VRCC-1 catalyst containing SOY zeolite and RSC-2006 based on silica modified alumina matrix have demonstrated excellent bottoms cracking capability and... 

Zeolites are crystalline aluminosilicates with a regular pore structure. These materials have been used in major catalytic processes for a number of years. The application using the largest quantities of zeolites is FCC [102]. The zeolites with significant cracking activity are dealuminated Y zeolites that exhibit greatly increased hydrothermal stability, and are accordingly called ultrastable Y zeolites (USY), ZSM-5 (alternatively known as MFI), mordenite, offretite, and erionite [103]. 

The activity advantage of zeolite catalysts over amorphous silica-alumina has well been documented, Weisz and his associates [1] reported that faujasite Y zeolite showed 10 to 10 times greater activity for the cracking of n-hexane than silica-alumina. Wang and Lunsford et al. [2] also noted that acidic Y zeolites were active for the disproportionation of toluene while silica-alumina was inactive. The activity difference between zeolite and silica-alumina has been attributed to their acidic properties. It is, however, difficult to explain the superactivity of zeolite relative to silica-alumina on the basis of acidity, since the number of acid sites of Y-type zeolite is only about 10 times larger than that of silica-alumina. To account for it, Wang et al. [2] proposed that the microporous structure of zeolite enhanced the concentration of reactant molecules at the acid sites. The purpose of the present work is to show that such a microporous effect is valid for pillared clay catalysts. 

As in previous conferences, the section on catalysis contains the most papers. A general review of the different reactions which can be catalyzed by zeolites is presented by Kh. M. Minachev. H. W. Kouwenhoven discusses the isomerization of paraffins on zeolites. Cracking, isomerization, and electron transfer reactions are discussed in several papers. Correlations between particular activities and physicochemical properties are covered. Selectivities related to crystal size and molecular shapes are also studied. Most of the work is still done on modified Y zeolites, but mor-denite and erionite also receive attention. 

Kerr, Plank, and Rosinski reported the preparation and catalytic properties of aluminum-deficient zeolite Y materials 35). Topchieva and co-workers studied the catalytic properties of cationic forms of aluminum-deficient Y zeolites, the aluminum deficiency being effected by the H4EDTA method 36-40). They found that up to 50% aluminum removal increased both stability and cumene cracking activity maximum activity was observed at the 50% removal level. Increased catalytic cracking activity was observed by Eberly and Kimberlin for mordenites from which about 80% aluminum had been removed (. 1). Weiss et al. removed over 99% of the aluminum from a hydrogen mordenite and found the zeolite retained catalytic activity of the type induced by Bronsted acids 42). Although the initial activity of this material was lower than that of more aluminum-rich mordenites, the aging rate was markedly reduced, and in a relatively short time the aluminum-deficient catalyst was the most active. 

The relationship between acid site density and effective acidity may account for the interesting observation of Hopkins that maximum cracking activity of n-hexane was obtained over a partially dehydroxylated hydrogen zeolite Y (45). While the normal hydrogen form would contain a greater overall concentration of acid sites, the partially dehydroxylated form may have a greater overall acid activity because of the increased effective acidity of the remaining sites. 

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