Catalytic cracking, general catalysts

One point not mentioned above is the thermal stability of zeolites. Most zeolites are thermally stable at elevated temperatures (>200°C to 300°C), with the result that the crystalline stmcture is not lost. Typically the thermal stability of a zeohte depends strongly on the zeolite Si/Al ratio, with the general trend that increasing Si/Al leads to enhanced stability. There are also exceptions to this one in particular that will be discussed below is significant for fiuid catalytic cracking (FCQ catalysts. The thermal stability of zeolites facilitates catalytic applications as many of the reactions discussed above and below are at elevated temperatures (>200°C). 

Catalysts were expensive, however, so the petroleum industry did not solve the problem of cheap, lead-free, knock-free gasoline until the 1970s, after General Motors adopted the catalytic converter. Lead compounds inactivate the catalysts, and sophisticated catalytic cracking techniques had to be developed to replace the fuel additive. Ironically, an even more difficult job was finding a substitute for the protective coating that tetraethyl lead formed on exhaust valve seats not even newly developed, extremely hard materials prevent wear and tear on them as well as tetraethyl lead did. 

Petroleum coke is the residue left by the destructive distillation (thermal cracking or coking) of petroleum residua. The coke formed in catalytic cracking operations is usually nonrecoverable because of adherence to the catalyst, as it is often employed as fuel for the process. The composition of coke varies with the source of the crude oil, but in general, is insoluble on organic solvents and has a honeycomb-type appearance. 

Figure A, however, does depict the general relationship between API gravity, sulfur, asphaltene and total metal content of crudes in general. Certainly none of these ingredients, especially in such large amounts, could be considered "friendly" for catalysts used in normal catalytic cracking.

Anyone who is seriously involved in catalytic cracking, whether as an operator, a catalyst manufacturer, or a researcher, soon learns how severely sodium, vanadium, nickel, iron, and copper act as poisons. In the past, FCC feedstock preparation via vacuum distillation was to a considerable extent, determined by metal carryover. Generally, metal carryover to the fluid unit was limited to 0.1 ppm or less of each of these metals. 

Some years later Statoil decided to start a project within catalytic cracking in order to learn more abont residue fluid catalytic cracking in general, and particnlarly abont catalysts suitable for this process. The project started as a prestudy for the residue fluid catalytic cracker unit (FCCU) that Statoil was planning to bnild at the Mongstad refinery in Norway. The intention was to crack North Sea atmospheric residue directly, without first using a vacuum gas distillation tower followed by cracking... 

Bayraktar, O., and Kugler, E. Characterization of Coke on Equilibrium Fluid Catalytic Cracking Catalysts by Temperature-Programmed Oxidation. Applied Catalysis A General 233 (2002) 197-213. 

The acidic nature of the SiO2 (AI2O3) catalysts over the whole range was explored by Thomas (78) using a titration procedure with potassium hydroxide as neutralizer. A general relationship was observed between the amount of catalytic cracking and acidity. His method of determining the acid nature of the catalyst has been criticized by Miesserov (79) whose work indicated that NaOH solutions reacted with other protons... 

The processes described below are the evolutionary offspring of the fluid catalytic cracking and the residuum catalytic cracking processes. Some of these newer processes use catalysts with different silica/alumina ratios as acid support of metals such as Mo, Co, Ni, and W. In general the first catalyst used to remove... 

Isobutene is present in refinery streams. Especially C4 fractions from catalytic cracking are used. Such streams consist mainly of n-butenes, isobutene and butadiene, and generally the butadiene is first removed by extraction. For the purpose of MTBE manufacture the amount of C4 (and C3) olefins in catalytic cracking can be enhanced by adding a few percent of the shape-selective, medium-pore zeolite ZSM-5 to the FCC catalyst (see Fig. 2.23), which is based on zeolite Y (large pore). Two routes lead from n-butane to isobutene (see Fig. 2.24) the isomerization/dehydrogenation pathway (upper route) is industrially practised. Finally, isobutene is also industrially obtained by dehydration of f-butyl alcohol, formed in the Halcon process (isobutane/propene to f-butyl alcohol/ propene oxide). The latter process has been mentioned as an alternative for the SMPO process (see Section 2.7). 

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