Petroleum cracking catalysts zeolites

The catalyst chosen for this study was a low metal, equilibrium, commercial zeolite-containing cracking catalyst obtained from Phillips Petroleum Company. No specific characterization of the catalyst is available. 

Chemical prqperties are also used in the largest field of application for the rare earth elements as catalysts. Most important are the cracking catalysts for the petroleum industry. The rare earth elements are combined into molecular sieves (Y-Zeolite) and serve in fluid bed or fixed bed reactors to increase the yield of gasoline. In addition thereto, there are the combustion catalysts for automobiles and for air pollution control. 

Since 1962 rare earths have been used to stabilize zeolite cracking catalysts for the petroleum industry (1, 2. Until recently this application to catalysis has been the only commercially significant one. Currently, however, a number of new applications of potential commercial significance are appearing. One of the most important of these is the use of cerium in catalysts for automobile exhaust emission control. We will emphasize this application in our review without neglecting other applications. 

In practice, short-chain alkanes and alkenes are normally used as feedstock for shape-selective catalytic formation of isooctanes at relatively low temperatures. Until the 1980s, lead alkyls (Section 18.1) were added to most automotive fuels to help suppress engine knock, but they have been phased out in North America because of the chronic toxicity of lead and lead compounds. The most commonly used nonlead antiknock additive is now methyl tert-butyl ether [MTBE CH30C(CH3)3], which is made by the reaction of methanol with 2-methylpropene, (CHs C—CH2 (see Section 7.4). The latter is obtained by catalytic cracking of petroleum fractions to give 1-butene, which is then shape-selectively isomerized on zeolitic catalysts. 

Acid-treated clay minerals were employed as cracking catalysts in the first commercial process, the Houdry process, widely used in the early petroleum industries to produce high-octane gasoline. The Houdry process catalysts had been discussed extensively by many investigators (2) but were eventually completely replaced by synthetic silica-alumina or zeolite catalysts. Recently, the need for new catalytic materials has revived special interest in the layer lattice silicates because of their ion-exchange properties and their expandable layer structures. 

Y zeolites exchanged with rare earth cations are widely used as the active component for cracking catalysts in petroleum industry. Such cations improve the catalytic activity and the gasoline yield, lowering the gas production and the coke formation. They also promote the thermal and hydrothermal stability of the catalyst. 

Ac id i c Cat al y s is. The interest of zeolites in catalytic reactions has appeared in the early sixties with the observation that small quantities of zeolites incorporated in silica-alumina and silica-clay materials significantly improve the properties of petroleum cracking catalysts (19). The resulting savings to the industry amounts to over several billions dollars a year. 

Over the years, the savings in petroleum resources have been enormous. In the U.S. alone, the zeolite cracking catalyst has saved the U.S. petroleum industry the equivalent of some 3.5 billion barrels (500 million tonnes) of crude oil since 1962. It lowered crude imports even more and enabled industry to produce higher gasoline volumes without additional investments in refinery expansion. 

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