Isoprene from propylene

Propylene Dimer. The synthesis of isoprene from propylene (109,110) is a three-step process. The propylene is dimerized to 2-methyl-1-pentene, which is then isomerized to 2-methyl-2-pentene in the vapor phase over silica alumina catalyst. The last step is the pyrolysis of 2-methyl-2-pentene in a cracking furnace in the presence of (NH4)2S (111,112). Isoprene is recovered from the resulting mixture by conventional distillation. 

Isoprene (melting point -146°C, boiling point 34°C, density 0.6810) may be produced by the dehydrogenation of iso-pentane in the same plant used for the production of butadiene. However, the presence of 1,3-pentadiene (for which there is very little market) requires a purification step. One method produces isoprene from propylene. Thus, dimerization of propylene to 2-methyl-1-pentene is followed by isomerization of the 2-methyl-1-pentene to 2-methyl-2-pentene, which upon pyrolysis gives isoprene and methane. 

The Ziegler oligomerization of propylene is used as the first stage in the production of isoprene from propylene [555]. The Goodyear Tire and Rubber Co., which produces 2-methyl-l-pentene on an industrial scale, has carried out extensive research on the use of a propylene dimer as a starting material in the industrial... 

Baas, C. J., De synthesis van isopren uit propen. Delft, 1963 (Netherlands). Feldblyum, V. Sh., and Farverov, M. 1., Synthesis of isoprene from propylene. Kinetics of propylene dimerization, Neftekhimia, 5, 493, 1965 (Russian). 

Natural mbber comes generally from southeast Asia. Synthetic mbbers are produced from monomers obtained from the cracking and refining of petroleum (qv). The most common monomers are styrene, butadiene, isobutylene, isoprene, ethylene, propylene, and acrylonitrile. There are numerous others for specialty elastomers which include acryUcs, chlorosulfonated polyethylene, chlorinated polyethylene, epichlorohydrin, ethylene—acryUc, ethylene octene mbber, ethylene—propylene mbber, fluoroelastomers, polynorbomene, polysulftdes, siUcone, thermoplastic elastomers, urethanes, and ethylene—vinyl acetate. 

Some Available Data. A brief list of extractive distillation processes of actual or potential commercial value is in Table 13.7 the column of remarks explains why this mode of separation is adopted. The leading applications are to the separation of close-boiling aromatic, naphthenic, and aliphatic hydrocarbons and of olefins from diolefins such as butadiene and isoprene. Miscellaneous separations include propane from propylene with acrylonitrile as solvent (DuPont, U.S. Pat. 2,980,727) and ethanol from propanol with water as solvent [Fig. 13.24(b)],... 

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. 

The primary source of isoprene today is as a by-product in the production of ethylene via naphtha cracking. A solvent extraction process is employed. Much less isoprene is produced in the crackers than butadiene, so the availability of isoprene is much more limited. Isoprene also may be produced by the catalytic dehydrogenation of amylenes, which are available in C-5 refinery streams. It also can be produced from propylene by a dimerization process, followed by isomerization and steam cracking. A third route involves the use of acetone and acetylene, produced from coal via calcium carbide. The resulting 3-methyl-butyne-3-ol is hydrogenated to methyl butanol and subsequently dehydrogenated to give isoprene. The plants that were built on these last two processes have been shut down, evidently because of the relatively low cost of the extraction route. 

Although presently lacking industrial importance, alternating copolymers can be made from propylene and butadiene, also from propylene and isoprene. Copolymers of propylene and butadiene form with vanadium- or titanium-based catalysts combined with aluminum. alkyls. The catalysts have to be prepared at very low temperature (-70 C). Also, it was found that a presence of halogen atoms in the catalyst is essential.Carbonyl compounds, such as ketones, esters, and others, are very effective additives. A reaction mechanism based on alternating coordination of propylene and butadiene with the transition metal was proposed by Furukawa. ... 

Isoprene l-s3-ipren [prob. fr. is- - - propyl -f -ene] (1860) (3-methyl-1,3-butadiene, 2-methyl-1,3-butadiene) n. CH2=C-(CH3) CH=CH2- a colorless, volatile liquid derived from propylene or from coal gases or tars, chemically similar to the mer unit of natural rubber. Its polymer of the cis-1, 4-type of polyisoprene is chemistry s nearest approach to synthesizing the natural product and it has sometimes been called synthetic natural rubber . It has a molecular weight of 68.06, a mp of—120°C, and a bp of 34°C. Ash M, Ash I (1982-1983) Encyclopedia of plastics polymers, and resins, vols 1-3. Chemical Publishing Co., New York. 

Isoprene is obtained from propylene by the following route ... 

Polymers produced by biological routes invariably are made by some kind of stepwise polymerization rather than a chain polymerization. An interesting example is afforded by di -l,4-polyisoprene. Isoprene can be made from propylene through a sequence of dimerization, isomerization, and steam demethanization [59] ... 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

Double-bond isomerization was once used in the multistep synthesis of isoprene developed by Goodyear.266-268 2-Methyl-1-pentene produced by the dimerization of propylene was isomerized to 2-methyl-2-pentene over a silica-alumina catalyst at 100°C. The product was cracked to isoprene and methane. Because of the lower cost of isoprene isolated from naphtha or gas oil-cracking streams, synthetic isoprene processes presently are not practiced commercially. 

The reaction between olefins and ozone produces light that can be measured and related to the concentration of the reactants. One of the preferred methods for measuring ambient ozone concentrations utilizes the chemiluminescence generated in the ozone-ethylene reaction for detection. Recently, Hills and Zimmerman (16) described the use of this detection principle for determining hydrocarbon concentrations. They utilized the chemiluminescence created when ozone reacts with isoprene for development of a continuous, fast-response isoprene analyzer. This real-time isoprene system is reported to be linear over three orders of magnitude and to have a detection limit of about 1 ppbv. Because the system doesn t include a preseparation of hydrocarbons, interferences from other olefins (ethylene, propylene, and so forth) could occur. Thus far the chemiluminescent detector has been used to monitor isoprene emissions under conditions in which the concentrations of olefins that could interfere are negligible compared to those of the biogenic hydrocarbon. 

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