Isomerization activity, hexane

The values of these Arrhenius parameters contrast dramatically with those obtained for the bicyclo[2,2,0]hexane isomerization. In this compound there is no weak bridgehead bond, and hence the reaction path is more closely akin to that for cyclobutane itself. The similarity of the A factors for this reaction and that for other simple cyclobutanes supports this contention. If this is so, then the lowering of the energy of activation in this bicyclic compound by some 7 kcal mole from that observed in the alkylcyclobutanes is to be attributed to extra strain energy in this molecule. 

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. 

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 20.5 Activation period for n-hexane isomerization over Mo2C-oxygen-modified at atmospheric pressure (623 K, p(C6) = 5 Torr).

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... 

Fig. 67. Effect of Pd content on activities for isomerization of hexane catalyzed by PdrH3-2,PW 12O40. (From Ref. 378.)...

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. 

A relation exists between the T-O-T bond angles and the acid strength of zeolites20. Thus, the protonic sites of HMOR (bond angle range of 143-180°) and HMFI (133-177°) zeolites are stronger than those of HFAU (133-147°). This explains why HMOR is active for butane and n-hexane isomerizations at 200-250°C which require very strong acid sites whereas it is not the case for HFAU. 

The data given for a reaction temperature of 300°C clearly showed the mordenite catalyst to be the more active for isomerization of both the C5 and Ce fractions. Conversions quoted were precious-metal-H-mordenite C5 —65 wt %, Cq >— 15 wt % precious metal-H-Y C5 — 40 wt %, Ce 4 wt %. These data suggest that the pentane fraction may be slightly easier to isomerize over mordenite than the hexane. The equilibrium conversions to isopentane and 2,2-DMB at 300°C are in the vicinity of 65 and 18 wt %, respectively. A possible explanation is that impurities present—e.g., cyclohexane and/or benzene—aifect the rate of 2,2-DMB formation more than that of the isopentane. 

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.

Ri and R2 could be alkyl groups. The electron-deficient carbon atom of a C—H bond so polarized could then serve as the active center for reactions of the carbonium ion type complete cleavage of the C—H bond is not required. The Linde workers were unable to correlate zeolite hydrogen content with hexane isomerization activity (40) nor did they attribute the great rise in cumene cracking activity (48) obtained by replacing univalent cations with bivalent cations in zeolite Y as arising... 

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. ... 

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. 

In this article the methods of synthesis of W03/Zr02 systems with surface area from 40 to 250 m /g are described. These samples exhibit high activity in n-hexane isomerization and gas-phase benzene nitration reactions. 

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

Investigations carried out have shown that controlled hydrolysis co-precipitation method and sol-gel method with use of polyvinylalcohol as template allow to prepare superacid WO3/Z1O2 materials which are highly active in n-hexane isomerization and vapour-phase benzene nitration with nitric acid. Doping of WO3/Z1O2 with Fe and Mn ions, as well as with silica and alumina [6] does not improve the catalytic properties in n-hexane isomerization. 

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