Isoamylenes isoprene from

The isoprene monomer is not readily available from direct cracking processes. Several routes are employed for its synthesis. One route begins with the extraction of isoamylene fractions from catalytically cracked gasoline streams. Isoprene is produced by subsequent catalytic dehydrogenation. 

Laboratory development of Triolefin Process technology for synthesizing isoamylene, an intermediate in polyisoprene production, was reported by Banks and Regier 571. Isoamylene purity of 92 per cent and isoamylene yield of 1.0 pounds per pound of isobutene converted were obtained with feeds containing isobutene, propylene, and n-butenes. Isobutene converted to C6+ byproduct was recovered by cleaving the C6+ material with ethylene or propylene to yield butenes and pentenes. Process for producing isoprene from butene streams is the subject of a patent issued to McGrath and Williams 1011. 

Application To produce butadiene from butane or mixed butane/ butylenes isoprene from isopentane or mixed isopentane/isoamylenes using the Catadiene process. 

A somewhat different application of perovskites is the oxidative dehydrogenation of olefins. Kehl et al. (202) reported that Lao.8Cro.65Feo.55Ch can be used for butene dehydrogenation to butadiene and also for the conversion of other monoolefins containing at least four C atoms, such as the production of isoprene from isoamylenes. 

Similar to the processes used in the manufacture of 1,3-butadiene, isoprene can be prepared from isopentane, isoamylenes, or a mixed isoC5 feed.172 176 177 The Shell process177 dehydrogenates isoamylenes to isoprene in the presence of steam with 85% selectivity at 35% conversion, over a Fe203—K2CO3—Cr2Oj catalyst at 600°C. 

This conversion, similar to that of butenes to butadiene (see Section 6.1.1.1), is carried out by Shell in the presence of steam, on an Fe203/Cr203/K2C03 catalyst, at about 600"C The effluent is cooled by oil which absorbs the polymers formed The gas is then compressed before separation, which comprises extractive distillation with aqueous aceto> nitrile, followed by rectification of the isoprene. Shell daims the ability to treat butenes and isoamylenes simultaneously to produce butadiene and isoprene. Some idea of the composition of the effluents from sulfuric add extraction and dehydrogenation is given by Table 6.6. 

Methyl-1-butene and 3-methyl-1-butene (isoamyl-ene), a valuable raw material for production of iso-prene, have been efficiently obtained from propene via disproportionation. In fact, the process occurs by a two-step pathway involving dimerization and disproportionation [18] (Fig. 4). In a first reactor propene is dimerized to a branched product, which is further codisproportionated with propene to a fraction rich in 2-methyl-2-butene. After separation, 2-methyl-2-butene may be used as a monomer, whereas the remainder, consisting of 2-methyl-l-butene and 3-methyl-1-butene (isoamylene), is further dehydrogenated to isoprene. 

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