Aromatization selectivities

In some cases, a mixture of natural petroleum feedstock is preblended with synthetic alkylated aromatics, such as detergent aromatic alkylate bottoms or with first-intent synthetic mono- or dialkylated aromatics, selected to provide a suitable molecular weight for cosulfonation and subsequent processing. The use of blended feedstocks may eliminate the need for conducting an oil extraction—concentrating step, particularly for a typical 40% Ca or Mg petroleum sulfonated product. 

Methacrylate polymers are as physically strong as polystyrene gels. Their hydrophobicity is weaker than that of polystyrene gel, and the aromatic selectivity is similar to that of octadecyl-bonded silica gel. A chromatogram of hydantoins on a methacrylate polymer is shown in Figure 3.16. The elution order is related to the hydrophobicity of the chemicals. 

Open chain hydrocarbons, skeletal rearrangements, 29 298-302 aromatic selectivities, 29 302 atomization, 29 298-302 cyclization, 29 298-302 Open sequence in reaction mechanisms, 32 ... 

A monotonic decrease of benzene yield from methylpentanes is observed as a function of the hydrogen pressure over both metals (27a, 91a). The intermediates of bond shift type dehydroisomerization are likely to be unsaturated. This points to the McKervey-Rooney-Samman mechanism (55). This pathway obviously has a higher energy barrier over platinum than over palladium as compared with the aromatization of -hexane. This is reflected also by the similar aromatization selectivity (iS r) values of -hexane and methylpentanes over palladium (Table IV). 

Aromatic Selectivities in Dehydrocyclization of Various Hydrocarbons with Quaternary Carbon Atoms." After (94b)... 

Starting hydrocarbon Catalyst Ethyl- benzene Aromatic selectivity (%) Xylenes Toluene... 

Zeolite S1O2/ AI2O3 ratio Metal (wt%) Feed SV Temp Pressure Conversion Aromatics Selectivity Benzene Selectivity Notes Reference... 

Under dehydrogenation conditions (385 °C ratio H2/HC = 4), an increase in the selectivity for aromatics with PtSn,(/Si02 catalyst has been observed. The increase in aromatic selectivity with tin content seems to be due to a geometric effect, favoring aromatic desorption. When the catalyst contains only small amounts of tin, an important poisoning by coke has been observed. As a consequence, it is possible that coke comes from adsorbed aromatic degradation. If aromatic formation starting from olefins had already and previously been proposed in the literature, their formation mechanism was still unknown. The coexistence of two possible dehydrocycHzation mechanisms has been proposed (Scheme 3.24). 

Fig. 25. Effect of charge stock lype on aromatic selectivity.

Direct Fluorination of Heterocyclic Aromatics Selective fluorination of quinoline aromatics leads to various commercially important products such as 5-fluoroadl, 5-fluoroprimaquine and ciprofloxacin with the fluorine moiety being decisive of their chemical and biological properties. 

Some metals show such a pronounced tendency to adopt rj4-butadi-ene coordination that this may override the driving force to aromaticity. Selected complexes of d8 M(CO)3 (M = Fe, Ru) fragments illustrating this point are included in Figure 6.29. Phenol is far more stable than its keto tautomer (cyclohexadienone), which may be stabilized, however, by... 

The very light naphtha (FBP 116°C) consisting of 4 wt% C5, 24 wt% Cj, 54 wt% C7 and the rest Cg components (no Cg aromatics), produced lower reformate yields than expected just from the extrapolated (N+2A) parameter. This can be explained considering the lower aromatization selectivity of Cj and C, than of Cg paraffins and cyclopentanes (9). However, within certain limits, the parameter (N+2A) describes the changes in feedstock "richness" with changing boiling points well. As the selectivity to aromatics is much lower for paraffins than for cyclopentanes and in particular cyclohexanes and aromatics, also dependent on carbon... 

Fig. 29. Aromatization selectivity versus C5/C4 molar ratio for Pt/KL and Pt/Si02. I, Pt/SiOa , Pt/KL (24).

Ahhou platinum alone or on a variety of neutral supports selectively converts n-hexane to benzene most of these catalysts deactivate rapidly due to coke formation. With the neutral zeolite KL as a support, however, much longer on-stream times are feasible and within a few years of Bernard s origind publication [130] 4e Aromax process had been developed by Chevron [131], Table 6 corrqrares the aromatic selectivity obtained with Pt-Ba KL and Pt Re Sn / AI2O3 - Cl reforming catalysts [58]. Associated with the much hi er aromatic selectivity is a lower amount of light gas production. 

Zeolite supports oAer than KL have also been investigated. Pt/K Beta because of its higher acidity yielded more isomerized and cracked products than Pt/KL [145]. Ion exchanging w Cs reduced its acidity and mproved Ae aromatic selectivity and Ba irrproved... 

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