Dehydrogenation of isoamylenes

Thus, it may be concluded that conjugated dehydrogenation of isoamylenes similar in isomeric composition to industrial fractions gives a high isoprene yield. Despite relatively... 

Hydrogenation of furan, 2,3-dihy-drofuran, silvan, and furfural Methanol steam reforming Coupling of dehydrogenation of isoamylenes and hydrodemethyN ation of toluene or oxidation of hydrogen ... 

V.S. Smirnov, VM. Gryaznov, M.M. Ermilova, and N.V. Orekhova, The study of coupling of dehydrogenation of isoamylenes with reactions of hydrogen consumption on palladium-nickel membrane catalyst, Dokl Akad. Nauk SSSR 224 39 (1975). 

Isoprene (2-methylbuta-1,3-diene) is produced mainly by the dehydrogenation of isoamylenes (2-methylbutenes) or isopentane (2-methylbutane), in processes similar to those used in the U.S.A. for butadiene manufacture. 

Some isopentane is dehydrogenated to isoamylene and converted, by processes analogous to those which produce methyl /-butyl ether [1634-04-4] (MTBE) to /-amyl methyl ether [994-05-8] (TAME), which is used as a fuel octane enhancer like MTBE. The amount of TAME which the market can absorb depends mostly on its price relative to MTBE, ethyl /-butyl ether [637-92-3] (ETBE), and ethanol, the other important oxygenated fuel additives. 

Although current United States synthetic capacity for isoprene is based entirely on dehydrogenation of refinery isoamylenes and demethanation of... 

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. 

A number of new processes exploiting metathesis have been developed by Phillips. A novel way to manufacture lubricating oils has been demonstrated.145 The basic reaction is self-metathesis of 1-octene or 1-decene to produce Ci4-C28 internal alkenes. The branched hydrocarbons formed after dimerization and hydrogenation may be utilized as lubricating oils. Metathetical cleavage of isobutylene with propylene or 2-butenes to isoamylenes has a potential in isoprene manufacture.136,146 High isoamylene yields can be achieved by further metathesis of C6+ byproducts with ethylene and propylene. Dehydrogenation to isoprene is already practiced in the transformation of isoamylenes of FCC C5 olefin cuts. 

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. 

Various industrial companies have developed a process for the production of isoamylene (2-methyl but-2-ene), which is a precursor of isoprene (obtained by oxidative dehydrogenation). It can be produced by cross-metathesis of isobutene with but-2-ene or propene ... 

A second route based on olefin disproportionation was developed by Phillips Petroleum (131). Here isobutylene reacts with propylene to form isoamylenes, which are dehydrogenated to isoprene. 2-Butene can be used in place of propylene since it also yields isoamylene and the coproduct propylene can be recycled. Use of mixed butylenes causes the formation of pentenes, giving piperjlene, which contaminates isoprene. 

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. 

Figure 4.2 Dependence of conjugated dehydrogenation selectivity (1), isoprene yield (2) and total side products yield (3) on isoamylenes and nitrogen mixture rate. T = 553 °C volume ratio C5H1() N2 = 1 10 20% aqueous H202 rate is 0.185 ml/h.

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. 

In these conditions, isoamylenes can yield isoprene by dehydrogenation. The production of 1 t of isoprene requires 1.16 t of isobutene and l.l t of n-butene. In addition. 

Figure 3.34 shows a schematic of the Ethermax process by Hiils AG and UOP [61]. Feed for the process includes methanol or ethanol and hydrocarbon streams containing reactive tertiary olefins such as isoamylene and isobutylene. Typical hydrocarbon streams are FCC light gasoline, steam cracker C4 hydrocarbons, or product from a butane dehydrogenation unit. In the production of MTBE, the feed first passes through an optional water wash system (1) to remove resin contaminants. The majority of the reaction is carried out in a... 

Cj olefmic components find fewer applications than the C4 compounds. The main applications concern isoamylenes with a tertiary carbon atom, ix. essentially 2-methyl butenes, which produce isoprene by dehydrogenation and Ter Amyl Methyl Ether (TAME) by etherification. The fust conversion is discussed in detail in Section 6. As for the second its value, like that of MTBE, is associated with the antiknock properties of TAME which make it an excellent octane promoter for gasolines. By cracking, the ether can even reproduce isoamylenes. This operation offers one means of separating 2-metbyl butenes and a method that is likely to be more economic than direct extraction to obtain isoprene. 

Various industrial companies have developed a metathesis process for the production of 2-methylbut-2-ene (isoamylene), which can be used to make isoprene via oxidative dehydrogenation. It is produced via cross-metathesis of isobutene and but-2-ene reaction (8). Cross-metathesis can also be carried out with propene instead of but-2-ene, or a mixture of the two. 

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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