Cracking ring-opening

A great deal of kinetic information has been obtained for different types of catalyzed hydrocarbon reactions carried out over metal catalyst surfaces. These reactions include dehydrogenation, hydrogenation, hydrogenolysis and cracking, ring opening. 

Furthermore, while no significant difference in the product distribution, with the exception of the trans-decalin/cis-decalin ratio, is observed for the tested proton-form zeolites, dissimilarity between Pt/H-Y on one hand and both Pt/H-Beta zeolites on the other hand is found (Figure 6). More ROP and CP, accompanied by less Iso, are formed on Pt/H-Y than on Pt/H-Beta zeolites. This implies that the consecutive ring opening and cracking are faster over Y-zeolite than over Beta-zeolites resulting in lower concentration of isomers and higher concentrations of ROP and CP. 

The benefits related to the particular topology of ITQ-21 when used as heterogeneous catalyst have been reported for different processes, such as catalytic cracking [1], hydrocracking [2] or hidrogenation and ring opening of (poly)aromatics [3]... 

Fig. 15 A proposed reaction network of direct ring opening of decalin reaction over acidic zeolites. PC Protolytic cracking HeT Hydride transfer HT Hydrogen transfer I Isomerization P /i-scission DS Desorption TA Transalkylation. Adapted from ref. 47.

Fig. 16 Concentration of decalin and product groups as a function of conversion over H-Beta (filled), HY (open), and H-Mordenite (half-filled). CP = cracking products ROP = ring opening products HP = heavy products. Adapted from refs. 44 and 45. 

Ring opening. This occurs selectively (far from the substituent) with C5 (and smaller) cycles, under hydrogen-rich conditions. Over four metals (Pt, Pd, Ir, and Rh) it may be much more rapid than cracking. The cycle is not liable to open over metals. 

Protonated cyclopropane ring closure and ring opening steps are discussed in Section 13.8.1 within the context of alkene skeletal siomerization. Carbonium ion decomposition is further discussed in Section 13.8.4.2 within the context of mono-molecular cracking of alkanes. 

The presence of metal may catalyze demethylation and can occur to some extent in catalysts where the metal function is under-passivated, as by incomplete sulfiding. This would convert valuable xylenes to toluene. The demethylation reaction is usually a small contributor to xylene loss. Metal also catalyzes aromatics saturation reactions. While this is a major and necessary function to facilitate EB isomerization, any aromatics saturation is undesirable for the process in which xylene isomerization and EB dealkylation are combined. Naphthenes can also be ring-opened and cracked, leading to light gas by-products. The zeolitic portion of the catalyst participates in the naphthene cracking reactions. Cracked by-products can be more prevalent over smaller pore zeolite catalysts. 

The isomerization of cycloalkanes over SbF5-intercalated graphite can be achieved at room temperature without the usual ring opening and cracking reactions, which occur at higher temperatures and lower acidities.110 In the presence of excess hydrocarbon after several hours, the thermodynamic equilibrium is reached for the isomers. Interconversion between cyclohexane (20) and methylcyclopentane (21) yields the thermodynamic equilibrium mixture [Eq. (5.46)]. 

The product yields by carbon number are plotted in Figure 6. At all except the most severe conditions studied,the major component in the gas phase was n-butane. This observation is consistent with the a-ring opening and dealkylation mechanism proposed for tetra-and octa-hydrophenanthrene cracking. At the most severe conditions ethane was present in the greatest quantities. This can be explained by side chain cracking of n-butylbenzene according to the Rice-Kossiakoff mechanism or by secondary reactions of the n-butane. 

The isomerization of a series of cyclic and bicyclic saturated hydrocarbons over SbF,-intercalated graphite was achieved at or below room temperature without the ring opening and cracking reactions, and the thermodynamic equilibrium was reached for the isomers in all cases (39). Interconversion between cyclohexane and methylcyclopentane also yielded the thermodynamic equilibrium mixture. 

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