Triolefin, process

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

As stated above, olefin metathesis is in principle reversible, because all steps of the catalytic cycle are reversible. In preparatively useful transformations, the equilibrium is shifted to one side. This is most commonly achieved by removal of a volatile alkene, mostly ethene, from the reaction mixture. An obvious and well-established way to classify olefin metathesis reactions is depicted in Scheme 2. Depending on the structure of the olefin, metathesis may occur either inter- or intramolecularly. Intermolecular metathesis of two alkenes is called cross metathesis (CM) (if the two alkenes are identical, as in the case of the Phillips triolefin process, the term self metathesis is sometimes used). The intermolecular metathesis of an a,co-diene leads to polymeric structures and ethene this mode of metathesis is called acyclic diene metathesis (ADMET). Intramolecular metathesis of these substrates gives cycloalkenes and ethene (ring-closing metathesis, RCM) the reverse reaction is the cleavage of a cyclo-... 

Classical metathesis such as that for the Phillips triolefin process (Eq. 3) or... 

Alkylation processes usually combine isobutane with an alkene or with mixed alkene streams (C3-C5 olefins from FCC units). The best octane ratings are attained when isobutane is alkylated with butylenes. Alkylation of higher-molecular-weight hydrocarbons (>C5) is less economic because of increased probability of side reactions. Phillips developed a technology that combines its triolefin process (metathesis of propylene to produce ethylene and 2-butenes) with alkylation since 2-butenes yield better alkylate than propylene.290 Since ethylene cannot be readily used in protic acid-catalyzed alkylations, a process employing AICI3 promoted by water was also developed.291... 

As discussed in Section 12.3, the triolefin process to transform propylene to ethylene and 2-butene developed by Phillips135,136 is not practiced at present because of the increased demand for propylene. The reverse process, that is, cross-metathesis of ethylene and 2-butene, however, can contribute to satisfy the global demand for propylene. Lyondell Petrochemical operates a 136,000-t/y (ton/year) plant for the production of propylene.236 In a joint project by BASF and FINA, Phillips metathesis technology will be used to enhance propylene production.237 A similar project was also announced by DEA.238 In a continuous process jointly developed by IFP and Chines Petroleum Corporation, cross-metathesis of ethylene and 2-butene is carried out in the liquid phase over Re207-on-Al203 catalyst (35°C, 60 bar).239,240... 

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. 

Olefin metathesis was first observed in the 1950s, and was used in industry to convert propylene to a mixture of but-2-ene and ethylene. This Phillips Triolefin Process used an aluminum/molybdenum catalyst whose exact structure was unknown. 

Propose a mechanism for the triolefin process using a metal alkylidene as the catalyst. 

The first large-scale application was the Phillips Triolefin Process (1966) in which propene was converted into ethene and 2-butene. Due to market changes the reverse process, in which propene is produced, became more attractive later. This process has been in operation since 1985. Another process is the Shell Higher Olefin Process (SHOP) in which ethene is oligomerized and the products are metathesized into detergent range olefins. The same company developed a process in speciality chemicals in which alpha-, omega-dienes are formed from cyclic alkenes. 

More than half a century ago it was observed that Re207 and Mo or W carbonyls immobilized on alumina or silica could catalyze the metathesis of propylene into ethylene and 2-butene, an equilibrium reaction. The reaction can be driven either way and it is 100% atom efficient. The introduction of metathesis-based industrial processes was considerably faster than the elucidation of the mechanistic fundamentals [103, 104]. Indeed the first process, the Phillips triolefin process (Scheme 5.55) that was used to convert excess propylene into ethylene and 2-butene, was shut down in 1972, one year after Chauvin proposed the mechanism (Scheme 5.54) that earned him the Nobel prize [105]. Starting with a metal carbene species as active catalyst a metallocyclobutane has to be formed. The Fischer-type metal carbenes known at the time did not catalyze the metathesis reaction but further evidence supporting the Chauvin mechanism was published. Once the Schrock-type metal carbenes became known this changed. In 1980 Schrock and coworkers reported tungsten carbene complexes... 

The reaction is applied in industrial processes (Phillips triolefin process. Shell higher olefin process) and has importance in ring opening-metathesis polymerization (ROMP) in polymer chemistry [1]. In the past, olefin metathesis was not commonly applied in organic synthesis [2] because of the reversibility of the reaction, leading to olefin mixtures. In contrast, industrial processes often handle product mixtures easily. In ROMP, highly strained cyclic olefins allow the equilibrium of the reaction to be shifted towards the product side. 

Phillips Triolefin Process Phillips ran from 1966-1972 propylene 15 kt/a ethylene-l-30 kt/a 2-butene WOg/SiOz 400°C... 

Reverse Triolefin Process Lyondell Petrochemical Co. operated since 1985 ethylene-h 2-butene 136 kt/a propylene WOs/SiOz 400°C... 

Tsao. U, Railly, J. W, Dehydrate ethanol to ethylene , Hydrocvbon Processing, 57 (2) 1 136 (1978). Farha, F. E, Banks, R. L, Triolefin process Chemistry and applications Petrochemical fotm-Americai Cor ressy Canqun, Mexico (12/18 Nov. 1978). 

N. Calderon, H. Y. Chen, and K. W. Scott, Tetrahedron Lett., 1967, 3327. Calderon was the first to coin the term olefin metathesis for the olefin exchange reaction that is typified by the Triolefin Process. 

Metathesis catalysts may be either homo- or heterogeneous. Although complexes of Ru, Mo, and W seem to show the most activity, metathesis may be catalyzed in some instances by Ti and Ta species. Heterogeneous substances, such as WOj/silica or Mo03 and Mo(CO)6 supported on alumina, catalyze the Triolefin Process and others performed on an industrial scale. Mechanistic studies of the type described in the previous section were essentially impossible to do with heterogeneous catalysts because the nature of these catalysts was so ill defined. Further discussion of the mechanism of metathesis under heterogeneous catalysis is beyond the scope of this textbook. 

Besides the Triolefin Process or OCT, metathesis is a key step in a number of other industrial transformations used to produce small molecules. By far the most important application of metathesis for this task is connected with the Shell... 

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