Isoprene, hydrogenation, selective

The catalysts were tested in isoprene, benzene and naphthalene hydrogenation reactions. The catalysts prepared by oxidation of the intermetallic at 703 K were found to be more active than those oxidized at room temperature. In isoprene hydrogenation the catalyst based on mischmetal has a larger activity than the other alloys and is comparable to the catalysts prepared by other routes. In benzene hydrogenation the Ni and Ce based catalysts prepared by coprecipitation were found the most active. In naphthalene hydrogenation the fully oxidized intermetallics are four times more active than the partially oxidized ones. In addition they are independent of hydrogen pressure and selective into decaline formation. 

The initial selectivity will be independent on the pressure of B. Moreover, if the ratio k K4 CB/ ki is small enough, the selectivity remains essentially equal to unity up to high conversions, decreasing thereafter. The character of selectivity beyond the point of high conversions will be pressure dependent, so that at higher pressures (concentrations) of B, the selectivity towards C will be lower. Such dependencies have been observed for isoprene hydrogenation over a palladium catalyst (Figure 4.26). 

Figure 4.26. Selectivity as a function of conversion in isoprene hydrogenation at different ratios Pje/Pf 1- 0.7 2 -6.5 3- 10. (S.L. Kiperman, Foundations of chemical kinetics in heterogeneous catalysis, Moscow, Chimia, 1979)...

The reaction of [Bu3Sb] in heptane solution with a reduced Pd/Al203 catalyst yields a supported alloy. " When these final solids are reduced at 573 or 773 K, the second metal locates preferentially at the outer layer of the bimetallic aggregates. After reduction at 773 K, large metallic aggregates are obtained (particle size around 15 nm). The specific activity of the Pd surface atoms for isoprene hydrogenation is then lowered and the selectivity increased. 

The ethynylation reaction takes place at 10—40°C and 2 MPa (20 atm) and hquid ammonia is the solvent. The methylbutynol is converted into methylbutenol by selective hydrogenation and then is dehydrated over alumina at 250—300°C. Polymerization-grade isoprene is obtained. 

The idea of this work was the realization of a not easily selective hydrogenation under conditions relevant to the surface science, in order to get a better understanding of the mechanism. Such an approach already led to interesting conclusions concerning the hydrogenations of butadiene and isoprene (ref. 2). 

The way sulfur treatment is applied gives rise to pronounced differences in selectivities21. A decrease in the overall alkene yield was observed when 1,3-butadiene was hydrogenated on presulfided Pd. In contrast, much improvement in selective alkene formation from isoprene was achieved when sulfur was present in the feed. In the latter case adsorption competition was suggested to account for the favorable effect of sulfur. 

Application Increase the value of steam cracker pyrolysis gasoline (py-gas) using conversion, distillation and selective hydrogenation processes. Pygas, the C5-C9 fraction issuing from steam crackers, is a potential source of products such as dicyclopentadiene (DCPD), isoprene, cyclopentane, benzene, toluene and xylenes. 

To increase the amounts of TAME, ie. an olefinic precursor, the presence of certain diolefms, such as isoprene, can be exploited. Prior selective hydrogenation, whidi is... 

Several complexes having arenes, [Cr(CO)3(arene)] (arene = benzene, mesitylene, methyl benzoate, etc.) and [Cr(CO)3(cycloheptatriene)], are excellent catalysts for selective 1,4-hydrogen addition to 1,3-dienes. " 1,4-Hydrogenation of methyl sorbate (34), isoprene (36) and 1,3-pentadiene (38) in cyclohexane affords methyl cw-3-hexenoate (35), 2-methyl-2-butene (37) and cw-2-pentene (39), respectively. [Cr(CO)3(MeCN)3] is also an active catalyst under mild conditions (40 C, H2 1.4 atm), as are [Cr(CO)e] or [Cr(NBD)(CO)4] under UV irradiation. ... 

Selective catalytic hydrogenation of dienes and polyenes to monoenes over nickel sulphide supported on alumina or silica finds application in the partial hydrogenation of soybean oil and isoprene in the presence of methylbutenes. A sulphided C0-W/AI2O3 catalyst has been proposed for the selective hydrogenation of dienes in pyrolysis gasoline. 

Since the dimensions to be probed are of the order of few nanometers, the most useful microscopic method would be that of the transmission electron microscopy (TEM). Using this technique Fayt et al. [1986] observed location of P(S-b-HB) compatibilizer in a PE/PS blends. The authors inserted a short sequence of isoprene between the styrenic and hydrogenated butadiene blocks. After staining the isoprene double bonds with OsO, the authors were able to observe presence of the copolymer at the interface between the matrix and dispersed phase. Thickness of the interphase could then be measured. The experiments also demonstrated presence of the added compatibilizer as dispersed micelles inside the PE phase. This technique is applicable, however, only when selective staining affects only the compatibilizer. 

A synthetic industrial process for making isoprene has been developed the process involves the selective hydrogenation of 3-methylbutyn-3-ol to... 

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