Alkylcyclopentanes aromatization

With platinum and palladium supported on acidic alumina, cyclopentanes are important intermediates of aromatization (44, 123-124). For example, n-heptane gave about 2-3 times more aromatic product than 2,4-dimethyl-pentane, whereas the formation of C5 cyclic products was about the same from both alkanes. Alkylcyclopentanes aromatized at a reasonable rate (123a). 

The alkylcyclopentane (AGP) to aromatics process (ACP ACH Ar) is less efficient than ACH dehydrogenation, owing to the slowness of the first step and to ACP ring opening. Under conditions where cyclohexane is converted to benzene with close to 100% efficiency, only 50—75% of methylcyclopentane may be converted to benzene. 

The isomerization reaction, which is acid-site controlled, includes the conversion of alkylcyclopentanes into alkylcyclohexanes, which, in turn, are quickly converted to aromatics by dehydrogenation. In addition, isomerization also includes the conversion of feed n-paraffms into higher octane I-paraffins. 

Dehydrocyclization refers to the conversion of feed paraffins into alkylcyclohexane and alkylcyclopentane naphthenes. These, in turn, are subsequently converted by isomerization and dehydrogenation into aromatics. Dehydrocyclization is controlled by both acid and platinum functions and is the most sensitive indicator of catalyst selectivity. 

Catalytic reforming. Catalytic reforming is a process for increasing the octane number of naphthas. It involves isomerisation of alkanes, dehydrogenation of cyclohexanes to aromatic hydrocarbons, isomerisation and dehydrogenation of alkylcyclopentanes, and dehydrocyclisation of alkanes. 

Weisz and Prater 28) have pointed out that, while on platinum reforming catalysts alkylcyclohexanes will proceed rapidly to aromatics, the conversion of alkylcyclopentanes to aromatics becomes the key dualfunctional reforming reaction in the neighborhood of 98 (R.O.N. with 3 ml. 

Naphtha. The compositions of the naturally occurring naphthas from seven different crudes have been determined by Forziati, Wellingham, Mair, and Rossini (55). All were found to contain normal paraffins, isoparaffins, alkylcyclopentanes, alkylcyclo-hexanes, and aromatics in varying proportions. 

Figure 5.1 Major reactions in catalytic reforming illustrated with specific examples (a) dehydrogenation of cyclohexanes to aromatic hydrocarbons (b) dehydroisomerization of alkylcyclopentanes to aromatic hydrocarbons (c) dehydrocyclization of alkanes to aromatic hydrocarbons (d) isomerization of n -alkanes to branched alkanes (e) fragmentation reactions (hydrocracking and hydrogenolysis) yielding low carbon number alkanes.

On the other hand, the application of Pt black or Pt/Si02 as catalyst for the hydro-genolysis of the alkylcyclopentanes 1-5 leads mainly to ring-opened products and alkylcyclopentene formation, whereas aromatization is not significant. The product distribution is strongly dependent on the hydrogen gas pressure. ... 

Effect on Gasoline Properties. The naphtha fed to the reforming reactor contains alkylcyclopentanes. These compounds can be isomerized, and then almost immediately they undergo dehydrogenation to an aromatic. One example is the conversion of methylcyclopentane (MCP) to benzene (B). The overall reaction is shown in (Scheme 3). 

Kinetics and Mechanism. The transformation of alkylcyclopentanes into aromatics occurs through dehydrogenation steps on the metal (M), and an... 

In the aromatization of alkylcyclopentanes, the Pt-BaK-L catalyst is nearly as active and selective as the acidic commercial catalysts. It is proposed that the efficiency of this catalyst in this reaction is related to the nonselective cyclic mechanism proposed by Gault and associates [36] which is also consistent with the nonequilibrium distribution of methylheptane isomers from the conversion of n-octane in the presence of the Pt-BaK-L catalyst (Table VI). 

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