Catalytic cracking of hydrocarbons

The catalysts used for cracking before the 1960s were amorphous [Si-Al] catalysts. The replacement of these catalysts by faujasite zeolites was a big step forward in the oil refining industry, which led to an increase in the production of gasoline [20], The acid catalyst, currently used in FCC units, is generally composed of 5-40 wt % of 1-5 pm crystals of the H-Y zeolite included in a porous particle composed of an active matrix, which in turn is composed of amorphous alumina, silica, or [Si-Al] and a binder. The porous particle allows the diffusion of the reactants and products of the cracking reaction to and from the micropores of the zeolite [10]. 

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To complete this picture, it is necessary to show how the carbonium ion intermediate is formed in the catalytic cracking of hydrocarbons. For olefins, it is the reaction of proton addition ... 

A central feature of the mechanism that accounts for the catalytic cracking of hydrocarbons by appropriately cation exchanged zeolites is the formation of carbonium ions (also designated carbocations and alkylcarbenium ions) as intermediates. Many other reactions for which aluminosilicates, be they clay-or zeolite-based, also predicate (320) the existence of carbonium ion intermediates, formed usually by proton donation from Bronsted acid sites, have been discussed earlier (Section III,K). 

A patent application [25] was filed on March 13, 1956 on the catalytic cracking of hydrocarbons with hydrogen X in the names of Milton and Breck. This application, too, was rejected by the examiner because he could not understand wherein our crystalline zeolite X was different from the amorphous, water softening zeolites of the prior art. This objection should have been easily overcome as it was in the basic A and X cases. For some unknown and still unexplained reason, however, this application was abandoned by our patent department on June 30, 1959. 

About 80% of the hydrogen used is produced petro-chemically, which includes the thermal or catalytic cracking of hydrocarbons e.g. in refineries. 

The catalytic cracking of hydrocarbons is a chain reaction that is believed to follow the carbonium ion theory, involving three steps initiation, propagation, and termination. The initiation step is represented by the attack of an active site on a reactant molecule to produce the active complex that corresponds to the formation of a carbo-cation. Chain propagation is represented by the transfer of a hydride ion from a reactant molecule to an adsorbed carbonium ion. Finally, the termination step corresponds to the desorption of the adsorbed carbenium ion to give an olefin while restoring the initial active site. ... 

USE In chromizing in catalytic cracking of hydrocarbons alkylation catalyst in nuclear reactor fuels. Caution A strong irritant. 

It is widely known that catalytic cracking of hydrocarbons takes place on the sites of the catalyst that possess the properties of Bronsted or Lewis acids catalytic activities for cracking and acidity run in parallel. 

Control of the selectivity in catalytic reactions is one of the challenging topics. For example, the shape selectivity in catalytic reactions was described for the first time by Mobil research workers [3]. At the present, some categories of shape selectivity have been described in the literatures, i.e. reactant shape selectivity, product shape selectivity and transition state shape selectivity [4,5]. Zeolites such as ZSM-5 show the promising catalytic performance for the shape selectivity of reactants or products in the alkylation of aromatics and in the catalytic cracking of hydrocarbons [6]. The shape selectivity by zeolite catalysts... 

Propylene is obtained from refining of gasoline and thermal or catalytic cracking of hydrocarbons. It is used to produce polypropylene (plastic) and in the manufactnre of acetone, isopropanol, cumene, and propylene oxide. 

The catalysts of this invention are also useful for catalyzing hydrogenation-dehydrogenation reactions and catalytic cracking of hydrocarbons in the same manner as prior art catalysts containing the same active catalytic materials are so used. 

Various kinds of Zeolites are engaged in the catalytic cracking of hydrocarbon feedstocks, such as ZSM-5, Beta, Y, in addition to other known acid solids such as silica-alumina, alumina and clays. Various combinations of these catalysts such as SAHAyZSM-5 and MCM-41/ZSM-5 have been also employed for the recycling of polyolefins [30]. 

In a fluidized-bed combustor, heat and mass transfer between the fluidizing gas and the solid particles are extremely efficient and fluidized-bed reactors are used for carrying out many chemical reactions on an industrial scale (e.g., catalytic cracking of hydrocarbons) (Speight, 2007). An additional advantage of fluidized-bed combustors is that they can use fairly coarse coal particles (ca. 0.04 in., ca. 1 mm diameter) and there is no need for much of the costly crushing equipment associated with the preparation of pulverized fuel. 

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