Catalysts hexane isomerization

Penex [Pentane and hexane isomerization] A process for converting n-pentane and n-hexane and their mixtures into branched-chain pentanes and hexanes of higher octane number by catalytic isomerization. The catalyst is similar to the Butamer catalyst. The product is used in high-octane gasoline. First commercialized by UOP in 1958. More than 75 units were operating as of 1996. 

Noble metals (e.g., Pt) can be introduced within the micropores of zeolites by exchange with a complex cation (e.g., Pt(NH3)4 ) followed by calcination and reduction. This mode of introduction generally leads to very small clusters of Pt (high Pt dispersion) located within the micropores. Pt supported on acid zeolites are used as bifunctional catalysts in many commercial processes. The desired transformations involve a series of catalytic and diffusion (D) steps, as shown in n-hexane isomerization over Pt acidic zeolite (Equation 12.1). 

Under the operating conditions, the reaction intermediates (w-hexenes and i-hexenes in n-hexane isomerization) are thermodynamically very adverse, hence appear only as traces in the products. These intermediates (which are generally olefinic) are highly reactive in acid catalysis, which explains that the rates of bifunctional catalysis transformations are relatively high. The activity, stability, and selectivity of bifunctional zeolite catalysts depend mainly on three parameters the zeolite pore structure, the balance between hydrogenating and acid functions, and their intimacy. In most of the commercial processes, the balance is in favor of the hydrogenation function, that is, the transformations are limited by the acid function. 

Table 12.3 Zeolitic pentane and hexane isomerization catalysts. 

Catalyst Testing. The hexane isomerization activity was measured for several catalysts containing about 0.2 wt % Pt. Appreciable differences in activity were evident which depended upon the method of preparation (Table VI). None of the catalysts is particularly active (c/. equilibrium values in Table VI). The surface areas of the catalysts (Table VI) are somewhat less than expected, and thus one can speculate that better activation procedures will lead to some improvement in performance. 

Figure 20.8 (a and b) show a comparison of the Pt// -zeolite catalyst which activated molybdenum oxycarbide catalysts, prepared from both Mo2C and Mo03, for the isomerization of n-heptane and n-octane at elevated pressure. For the platinum catalyst the chain length is important, as explained above, with the isomerization selectivity obtained for n-octane dropping more quickly with increasing conversion than that for n-heptane over this plantinum catalyst the isomerization of n-hexane can be... 

However, Pdi,5PWi204o is active for esterification and MTBE synthesis even in the absence of H2 (378). Therefore, it is concluded that this catalyst is not as simple as Ag3PWi2O40. The catalytic activity of PdrH3 tPW,2O40/SiO2 for hexane isomerization is plotted as a function of x in Fig. 67. The addition of a... 

The SZNbPt catalyst shows a higher isomerization selectivity and activity for all hydrocarbons. While n-pentane and n-hexane isomerization selectivity is very similar on both catalysts, important differences occur with n-heptane. When comparing both catalysts at the same conversion level (60%), SZNbPt shows a higher selectivity (— 5096) than the conventional sulfated zirconia ( 30%). However, the isomerization selectivity of n-heptane SZNbPt is still too low when the temperature is increased to achieve high C5-C6 isomerization yields. 

Poly step Hexane Isomerization on Coarse Catalyst Mixtures... 

Fig. 15. Observed variation of n-hexane isomerization selectivity with degree of activity of the X-oomponent in a platinum (X) acidic oxide (F) catalyst.

The results described above indicate that the protons in Pd°/HTP under hydrogen are more mobile than those in HTP. The difference of the mobility between the protons in Pd /HTP and those of HTP may explain the difference in the catal5rtic activities of the two catalysts for methanol conversion and hexane isomerization. ... 

Superacid W0x/Zr02 catalysts for isomerization of n-hexane and for nitration of benzene... 

Methods of synthesis of superacid catalysts based on WOs/ZrOa system (surface area 40 - 250 m /g) are developed. This catalysts exhibit high activity in n-hexane isomerization reaction yield of branched isomers at 230 - 250°C amounts to 65 - 70% with selectivity for i-Ce of 70 - 94% and 80% conversion of n-hexane. Promoting of the catalysts with Fe and Mn compounds does not effect their activity in n-hexane isomerization. 

For testing in n-hexane isomerization reaction the catalysts were promoted with 0.5wt % of Pt by impregnation with H2PtCb solution. Prior to testing the platinated catalysts were reduced for 4 h at 400°C in dihydrogen. 

Activity and selectivity of catalysts on hexane isomerization reaction (LHVS = wt.%)... 

The bifunctional catalytic n-hexane isomerization was performed in a microflow reactor under atmospheric pressure, using a mechanical mixture (Iw/w) of catalyst and a standard Pt/A Os reforming catalyst (0.35 wt% Pt). The latter was previously reduced at 723 K for 4 h. The catalytic test was performed as follows The mixture Pt/A Os + catalyst was pretreated first under He flow at 723K for 2 hours and then under H2 for 30 min at 493K. 

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