Cis-Trans and Double Bond Isomerization

Other than a few fine chemicals reactions, cis-trans isomerization is seldom practiced using molecular sieve catalysts. 

Double bond isomerization using molecular sieves (5A) was reported in the patent literature by Fleck and Wight of Union Oil Company [34] only a few years after synthetic zeolites became commercially available. More recently [35] ferrierite has also been claimed. The major initial uses were to convert a-olefins (1-olefins) into mixtures of internal olefins for further conversion, usually by oligomerization into various products-lube oil base stocks predominating. Inevitably, patents were issued noting the ability to convert internal olefins into mixtures containing greater concentrations of 1-olefins (e.g., [36]), but few practical processes have resulted. 

Source Knocking Characteristics of Pure Hydrocarbons , ASTM Special Technical Publication number 225. 

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In view of the difference of a factor of 10 or more in peak delay between butene and thiophene at similar temperatures, butene adsorption was checked to see that chemisorption was in fact occurring below 200° C. Using the 50-foot propylene carbonate column, it was found that some butane was formed in spite of the H2S present down to 150° C. (without H2S butene was almost completely hydrogenated at this temperature) and both cis-trans and double bond isomerization of the butenes went to completion at temperatures below 100° C., indicating that chemisorption of butene must have occurred. It is therefore felt that extrapolation of the butene sorption results obtained to the temperature range of the desulfurization reaction (above 200° C.) should be valid. 

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