Suitable cracking catalysts

Steam pre-treatment of fluid cracking catalysts has been conventionally employed to represent the deactivation occurring in a commercial FCC unit. Appropriate steam pre-treatment methods have been developed so that the activity and selectivity of the steam pre-treated catalyst is equivalent to a commercially deactivated catalyst (12). However, a unique steaming method may not be suitable for catalysts of varying compositions (12). Two steaming methods designed to simulate deactivation in a commercial unit of the two types of catalysts used in this work were employed. Super-D was treated for 8 hours at 732 C with a steam pressure of 2 atmospheres. The catalysts containing ZSM-5 were treated for 12 hours at 827°C with a steam partial pressure of 0.2 atmosphere. 

Fluidised bed reactors are rarely suitable for catalytic studies because of their relatively large volume, the large quantity of catalyst to use and the difficulty to control bubble agglomeration and instabilities. However, it is still almost irreplaceable for the testing of fluid-bed cracking catalysts. On a laboratory scale a modification is applied in which an intensive mixing of particles is achieved by means of mechanical vibration. In this case, the gas flow rate can vary over a... 

The ASTM-MAT test is in fact only intended to determine and compare the activity of cracking catalysts (2), and is not suitable for simulating the real FCC operation, using the conditions (Table l) as defined by the ASTM (3). 

Zeolites are widely used in acidic processes and they are an obvious catalyst choice. The suitability of commercial cracking catalysts to degrade polymer waste is vital as one of the options of commercializing this polymer recychng method is to co-feed polymer waste to existing refinery crackers [13]. Furthermore, in the search for cheaper catalysts, clays and their pillared analogues are also introduced in the polymer catalytic degradation [16, 17]. 

The modification of zeolites mainly relies on secondary synthesis methods. The aim of modification is to reprocess the zeolites using suitable techniques to improve the properties and functions such as (1) acidity, (2) thermal and hydrothermal stability, (3) catalytic performance such as redox catalytic and coordination catalytic properties, etc., (4) channel structures, (5) surface properties and microporous frameworks and charge-balancing ions. Modification is also called secondary synthesis and can lead to new properties that cannot be achieved through direct synthesis. Let us consider the case of faujasite (FAU), the main component of the cracking catalyst, and its catalytic performance (represented by the catalytic activity K/K Std for n-hexane cracking). From Table 6.1 it is seen that the secondary synthesis affects the catalytic performance to a considerable degree. 

Amorphous silica, alumina and alumina-silica are commonly used in supported catalysis as they can be obtained with large specific surface values [1]. Aluminophosphates are also suitable catalyst support, mainly used as cracking catalyst [2-5], for polymerization of ethylene [6,7], for oxidation or isomerization reactions [2]. 

These new constraints on gasoline formulation focused attention on the decreased octane levels of gasoline produced with REY-zeolite cracking catalysts and the octane dip, or low octane number, of C6-C10 paraffins. To compensate, the aromatic content of the gasoline pool was increased from about 20% in 1973 to almost 40%, but the need for new octane catalysts was soon an important objective for refiners and catalyst producers. Octane catalysts require a suitable zeolite that can limit the hydrogen transfer reactions that convert olefins to paraffins. 

Early attempts to control vanadium deactivation involved the addition of amorphous alumina to the cracking catalyst matrix. This was not particularly suitable because alumina increased coke formation and led to wider dispersion of nickel impurities. Hydrodesulfurization of FCC feeds is nseful it not only removes sulfhr, but the desulfurisation catalyst also adsotbs a significant proportion of the metal porphyrins. 

The cyanoacryhc esters are prepared via the Knoevenagel condensation reaction (5), in which the corresponding alkyl cyanoacetate reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequendy, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids are normally used in combination with small amounts of a free-radical stabilizer. 

Final Purification. Oxygen containing compounds (CO, CO2, H2O) poison the ammonia synthesis catalyst and must be effectively removed or converted to inert species before entering the synthesis loop. Additionally, the presence of carbon dioxide in the synthesis gas can lead to the formation of ammonium carbamate, which can cause fouHng and stress-corrosion cracking in the compressor. Most plants use methanation to convert carbon oxides to methane. Cryogenic processes that are suitable for purification of synthesis gas have also been developed. 

Active matrix contributes significantly to the overall performance of the FCC catalyst. The zeolite pores are not suitable for cracking of large hydrocarbon molecules generally having an end point > d00 [-(482°C) they are too small to allow diffusion of the large molecules to the cracking sites. An effective matrix must have a porous structure to allow diffusion of hydrocarbons into and out of the catalyst. 

The high-surface-area TUD-1 can serve as an anchor for many catalysts. Si- or Al-Si-TUD-1 (24,25) can be used as a support for various noble metals (Pt, PtPd, Ir, etc.). This will provide catalysts suitable for the hydrogenation of olefins and aromatics. In the refining industry, one use is the hydrogenation of polynuclear aromatics ( PNAs ) in diesel fuel, which can lower the fuel s toxic properties. Also, jet fuel has an aromatics constraint, designed to lessen smoke formation. Cracked stocks (e.g., coker or visbreaker liquids) generally have undesirable olefins (especially a-olefins) that also need to be saturated prior to final processing. 

In the catalytic cracking method, a suitable catalyst such as aluminum silicate or alumina is used. This provision produces an improved quality and yield of gasoline. This method has several advantages over the thermal cracking method. Among these, special mention... 

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