Pentane isomerization disproportionation reactions

Pentane Isomerization. Pentane isomerization, although carried out on a much smaller scale, increased the critical supply of aviation gasolines toward the end of the war. Two pentane processes—one developed by Shell and one by Standard (Indiana) —were commercialized before the end of the war. The principal differences between the butane and pentane processes are the use in pentane isomerization of somewhat milder conditions and the use of an inhibitor to suppress side reactions, principally disproportionation. In general, the problems of the butane processes are inherent also in pentane isomerization, but the quality of the feed stocks is less important. Catalyst life is much... 

The cyclodimerization of cyclopropenes, a novel reaction, was foundto be catalysed by KA and NaX zeolites. Carbanion intermediates were proposed and the selectivity of the reaction was attributed to spatial constraints. Paraffin disproportionation, with isomerization, at about 500 K has been shownto occur over H-mordenite and HZSM-4 catalysts. Synthetic H-ferrierite is an active and very selective catalyst for n-paraffin cracking and hydrocracking. Palladium on zeolite L comparesfavourably with Pd/HY as a catalyst for pentane isomerization. 

The results of these studies are given in Figs. 4 and 5. The benzene inhibited the disproportionation reaction only 4% butanes were produced whereas the isomerization reaction proceeded readily. At a catalyst age of 212 moles pentane per mole aluminum chloride, the reaction product contained 66 volume % isopentane. In the absence of benzene the isomerization ceased after 55 moles pentane per mole aluminum chloride had been reacted. 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

The butanes show little tendency to crack or disproportionate (7) thus butane isomerization is fairly straightforward. However, the suppression of side reactions becomes more difficult as the molecular weight increases. With pentanes, disproportionation to isobutane and hexane is pronounced, amounting to as much as 63%. A typical composition of pentane disproportionation products is shown in Table III. Besides lowering the yield of isopentane, such side reactions shorten the life of the catalyst. Adding small amounts of cyclic hydrocarbons (7,15,18)... 

The effect of 0.5 vol.% benzene added to the pentane feed on disproportionation and on the life of aluminum chloride catalyst is shown in Figure 4A and B (7). When no benzene was added to the feed, the major reaction was disproportionation and the catalyst activity declined rapidly until no further isomerization occurred after a catalyst life of... 

In the first step (equation 50) pentane is oxidized to a cation radical which on losing a proton becomes a radical. Pentyl radicals can react to form a C p-dimer (equation 51) or disproportionate with pentane and pentene formation (equation 52). Pentene may be alkylated also forming a C.jQ-dimer intermediate (equation 53). The final products of the reaction are formed as a result of C Q-isomerization and decomposition. 

The anodic oxidation of alkanes in anhydrous hydrogen fluoride has been studied at various acidity levels from basic medium (KF) to acidic medium (SbFs) to establish optimum conditions for the formation of carbenium ions . The oxidation potential depends on the structure of the hydrocarbon methane is oxidized at 2.0 V, isopentane at 1.25 V vs Ag/Ag. Three cases of oxidation can be distinguished. In basic medium, direct oxidation of the alkane to its radical cation occurs. In a slightly acidic medium, the first-formed radical cation disproportionates to cation, proton and alkane. The oxidation is, however, complicated by simultaneous isomerization and condensation reactions of the alkane. In strongly acidic medium, protonation of the alkane and its dissociation into a carbenium ion and molecular hydrogen occurs. In acidic medium n-pentane behaves like a tertiary alkane, which is attributed to its isomerization to isopentane. The controlled potential electrolysis in basic medium yields polymeric species. 

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