Isooctane cracking

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. 

The thermal stability of NH4Y zeolite in which ammonium ions have been exchanged at various levels with La3+ ions was studied. The catalytic activity of these La zeolites in isooctane cracking was measured as a function of pretreatment temperature, and an IR study of the chemisorption of pyridine was used to determine the numbers of Bronsted and Lewis sites. The structural damage resulting from high temperature calcination was examined qualitatively. 

Figure 1. Percent conversion in isooctane cracking vs. cations content after (a) 550°C pretreatment, (6) 900°C pretreatment O isobutane, A isobutene. , A Nar8.7., A D.La-4 sample.

Cracking of isooctane is used to check catalytic activity of progressively exchanged Na-zeolites and to try to correlate acid and catalytic properties. 

Catalytic Activity. The cracking of isooctane was studied. For catalytic activity measurements, the samples were heated in flowing helium or hydrogen from room temperature to 465°C for 15 hours. Then the gas saturated with isooctane passed through the catalyst in the microreactor and was analyzed by gas chromatography. 

Catalytic activity is influenced also by ions in (or near) the supercage. As long as these ions are not exchanged, the cracking of isooctane is not important. In Na-H-Y zeolites, only the exchange of the last ions noticeably increases it. 

The strong acidity of the zeolite without and with silica binder were measured in terms of the pyridine chemisorbed at 400°C, GC adsorption/ desorption method [16. The zeolite without and with silica binder were also characterized for their acid function by carrying out over them two catalyzed model reactions - cracking of isooctane (at 400°C) for measuring external acidity and toluene disproportionation (at 500 C) for measuring the intracrystalline or overall acidity, using pulse micro-reactor (id 4.5 mm) made of quartz, connected to a gas chromatograph [11, 14, 17]. 

Catalyst deactivation during catalytic cracking of n-octane, isooctane and 1-octene over USHY zeolite at mild conditions and short times on stream... 

Aim of this work is to study the influence of the reactant on the coking process and the catalyst deactivation, as well as the product distributions. Therefore, the cracking of n-octane, isooctane and 1-octene was investigated in a fixed bed reactor, over USHY zeolite (0.5gr), at a range of temperatures, with two different reactant mole fi actions in the feed stream, and 20 min. time on stream. 

The first and most Important observation made, comparing isooctane graphs (Fig.4) with the other two reactants, is the amount of isobutane produced (Fig.3) as a result of isooctane cracking. 

The cracking of 1-octene yields as the primary product isobutane. What is different comparing the cracking of 1-octene with that of n-octane and isooctane is the very high conversion rates, wdiich are followed throughout the 20 minutes of TOS allowed, with peak... 

When butenes are used instead of ethylene, a lower temperature and a fine tuning of the acidity of the IL are required to avoid cracking reactions and heavy byproduct formation. The continuous butene alkylation has been performed for more than 500 h with no loss of activity and stable selectivity (80-90% isooctanes are obtained containing more than 90% trimethylpentanes MON = 90-95 RON = 95-98). A high level of mixing is essential for a high selectivity and then for a good quality alkylate. It has been shown that the addition of copper(I) chloride to the acidic chloro-aluminate improves the reaction performances [29]. 

The process of catalytic reforming introduces chains, and catalytic cracking introduces double bonds. Not only do these two processes increase the amount of gasoline that s produced, but they also improve the quality of the gasoline s burning characteristics. Also notice that benzene, an aromatic compound, has an octane value of 106. Its burning characteristics are better than isooctane. Other substituted aromatic compounds have octane ratings of almost 120. However, benzene and some related compounds are health hazards, so they re not used. 

The CR specimens containing intercalated compound which were immersed in organic solvent showed more improved ozone-cracking resistance than that of standard composition and that of with talc composition. These results and the result of the analysis of residual DPD indicated that the intercalated compound had an excellent effect on retarding or preventing the dissolution of DPD into the mixture of isooctane and toluene. 

The interaction between the montmorillonite and non-polar molecules such as isooctane or toluene is limited, while the interaction between the montmorillonite and polar molecules such as water is very strong. The roles of montmorillonite to prevent access of non-polar solvents, as shown above, and to keep DPD on the surface or in the interlayer region, are considered to prolong the effective life of DPD, thus providing rubbers with good ozone-cracking resistance. 

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