Metathesis Phillips 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... 

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. 

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. 

Metathesis is a versatile reaction that forms the basis for several important industrial processes, such as the Phillips triolefin process, which produces propene by cross-metathesis of 2-butene with ethene, and the Shell higher olefins process (SHOP), which involves a combination process that converts ethene to detergent-range olefins. Several interesting polymeric materials are commercially produced via the ROMP of different types of unsaturated cyclic monomers, including nor-bornene, cyclooctene, and dicyclopentadiene [1]. 

Commercialization of olefin metathesis was accomplished in 1966 (12), Shawinigan Chemical Ltd., at their Varennes complex near Montreal, Quebec, brought the Phillips Triolefin Process on stream. With an excess of propylene at that location,... 

Metathesis of mono- and diolefins can be performed with both homogeneous and heterogeneous catalysis. The most important processes involving metathesis steps, the SHOP process and the Phillips triolefin process, are based on heterogeneous catalysts. Homogeneous catalysts are used in the ring opening metathesis of norbor-nene (Norsorex, CDF-Chemie) and cyclooctene (Vestenamer, Hills) [7]. 

Having traversed some of the key events in the history of olefin metathesis, it is now appropriate to discuss some of the resultant fruits of that early labor in the form of practical applications in organic synthesis. Since the general reaction was bom in the industrial sector, we felt it appropriate to commence with some examples of commercial processes. Among several of the profitable industrial procedures that benefit from olefin metathesis, one of the oldest is the Phillips triolefin process (Scheme 7a) which utilizes a molybdenum-based catalyst system to convert propene (17) into a mixture of 2-butene (18) and ethene (19). These products are then used as monomers for polymer synthesis as well as for general use in petroleum-related applications. The reverse reaction can also be employed to prepare propene for alternative uses. 

Scheme 7. Industrial olefin metathesis applications the Phillips triolefin process for the production of butene and ethene (a) and the Norsorex process for the ring-opening metathesis polymerization (ROMP) of norbornene (b).

For organic chemists, the term metathesis is used most often to mean alkene or olefin metathesis. This process, which can be catalysed by a range of transition metals, was discovered accidentally in the petrochemical industry. Its first commercial application was in the Phillips triolefin process in which propene was converted to an equilibrium mixture of ethene, 2-butene and the starting propene at 400 °C in the presence of an unknown tungsten species (Scheme 8.51). The process was in use between 1966 and 1972. Interestingly, with changes in feedstock prices and demands, the process is now run in reverse, producing propene from ethene and 2-butene. 

This process, called OCT (olefin conversion technology), formerly the Phillips Triolefin Process, which utilizes a heterogeneous catalyst system, was originally developed by Phillips Petroleum Co. for the conversion of propene into ethene and butene. The reaction takes place in a fixed-bed reactor over a mixture of the metathesis catalyst W03/S102 and the isomerization catalyst MgO at temperatures above 540 K and an overall pressure of approximately 30 bar [3]. 1-Butene present in the feedstock is isomerized to 2-butene as the original 2-butene is consumed in the metathesis reaction. 

Metathesis can be catalyzed homogeneously and heterogeneously. The biggest applications of metathesis such as the SHOP process [4] and Phillips Triolefin process use heterogeneous catalysts. Norbornene (Norsorex by CdF Chimie), cyclooctene (Vestenamer by Hiils AG), and dicyclopenta-diene (Hercules) practice homogeneous catalysis. 

When highly pure propene is not available commercially, it can be prepared by the reverse metathesis reaction of ethene and 2-butene [Eq. (1)]. The process is performed either at high temperatures (150-350°C) in the gas phase, over molybdenum or tungsten catalysts (Phillips triolefin process) [4], or at low temperatures (50°C) in the liquid phase, in the presence of rhenium-based catalysts (IFP-CPC process) [13], The raw material may be either ethene and the C4 fraction available from the hydroisomerization unit (previously submitted to an isomerization step to maximize its 2-butene content) or ethene alone, which, before admission to the metathesis unit, is partly dimerized to 1-butene, then isomerized to 2-butene in separate units. The process is useful in the event of a high demand for propene, since the C4 fraction is readily available from a cracking unit. 

The first commercial olefin metathesis process, known as the Phillips Triolefin Process, was implemented by Phillips Petroleum Company just a few years after their initial report on the conversion of propylene to 2-butenes and ethylene. Hie process employed a heterogeneous W03/S102 catalyst at a temperature of approximately 400 ° C. The plant, operated by Shawinigan near Montreal, Quebec (Canada), opened in 1966 to convert excess propylene to butenes and polymer grade ethylene that were in short supply at the time. It operated at a capacity of 30 000 metric tons of butenes and 15000 metric tons of ethylene per year until the early 1970s, when an increased demand for propylene rendered the process tmeco-nomical. Produaion was halted in 1972. ... 

Because olefin metathesis is an equilibrium reaction, the Triolefin Process can be mn in the reverse direction to produce propylene from 2-butene and ethylene. Lyondell licensed the Phillips Triolefin process and opened the first propylene plant based on this technology in 1984, eventually expanding capacity to 450 000 metric tons per year. In 1997, Lummus Technology, who engineered the first two applications under license from Phillips, purchased the technology from Phillips. The metathesis of ethylene and butenes to propylene is now commercialized as Olefins Conversion Technology (OCT )... 

The Phillips triolefin process [56] developed at Phillips Petroleum, used a heterogeneous WOj/SiOj catalyst in metathesis reaction to convert propene 127 into mixture of ethene 125 and 2-butene 126. As it is a reversible reaetion (Scheme 9.32) and the price of propene rose high, the reverse reaction of Philips process offered is now by using Lummus teehnology to produce propene known as Olefin Conversion Technology (OCT). 

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... 

Early in 1962, following Phillips Management s decision to develop the Triolefin Process, laboratory studies were resumed and expanded. In addition to conducting a detailed investigation of cobalt molybdate catalyst systems, an extensive search for other catalyst compositions active for olefin metathesis was made. Concurrent with these investigations were studies designed to expand the scope and explore other applications of olefin metathesis reactions. Pilot plant development of Triolefin Process technology was initiated about six months after laboratory studies had been resumed. 

Historically, the triolefin process, developed by Phillips, was the first industrial application of olefin metathesis [9-11]. It involved the preparation of high purity ethylene and but-2-ene from propene ... 

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