Propylene Metathesis

Cyclic Polyolefins (GPO) and Gycloolefin Copolymers (GOG). Japanese and European companies are developing amorphous cycHc polyolefins as substrate materials for optical data storage (213—217). The materials are based on dicyclopentadiene and/or tetracyclododecene (10), where R = H, alkyl, or COOCH. Products are formed by Ziegler-Natta polymerization with addition of ethylene or propylene (11) or so-called metathesis polymerization and hydrogenation (12), (101,216). These products may stiU contain about 10% of the dicycHc stmcture (216). 

Disproportionation of Olefins. Disproportionation or the metathesis reaction offers an opportunity to convert surplus olefins to other desirable olefins. Phillips Petroleum and Institut Fransais du Petrc le have pioneered this technology for the dimerization of light olefins. The original metathesis reaction of Phillips Petroleum was intended to convert propylene to 2-butene and ethylene (58). The reverse reaction that converts 2-butene in the presence of excess ethylene to propylene has also been demonstrated (59). A commercial unit with a capacity of about 136,000 t/yr of propylene from ethylene via 2-butene has been in operation in the Gulf Coast since 1985 (60,61). In this process, ethylene is first dimerized to 2-butene foUowed by metathesis to yield propylene. Since this is a two-stage process, 2-butene can be produced from the first stage, if needed. In the dimerization step, about 95% purity of 2-butene is achieved at 90% ethylene conversion. 

Olefin Metathesis. The olefin metathesis (dismutation) reaction (30), discovered by Eleuterio (31), converts olefins to lower and higher molecular weight olefins. For example, propylene is converted into ethylene and butene... 

Metathesis is the rupture and reformation of carbon-carbon bonds—for example, of propylene into ethylene plus butene. Catalysts are oxides, carbonyls, or sulfides of Mo, W, or Re. 

Table 8-5 indicates the wide variety of catalysts that can effect this type of disproportionation reaction, and Figure 8-7 is a flow diagram for the Phillips Co. triolefm process for the metathesis of propylene to produce 2-butene and ethylene. Anderson and Brown have discussed in depth this type of reaction and its general utilization. The utility with respect to propylene is to convert excess propylene to olefins of greater economic value. More discussion regarding olefin metathesis is noted in Chapter 9. 

Figure 8-7. The Phillips Petroleum Co. process for producing 2-butene and ethylene from propylene (1) metathesis reactor, (2) fractionator (to separate propylene recycle from propane), (3, 4) fractionator for separating ethylene, butylenes, and Cg. ...

Olefin metatheses are equilibrium reactions among the two-reactant and two-product olefin molecules. If chemists design the reaction so that one product is ethylene, for example, they can shift the equilibrium by removing it from the reaction medium. Because of the statistical nature of the metathesis reaction, the equilibrium is essentially a function of the ratio of the reactants and the temperature. For an equimolar mixture of ethylene and 2-butene at 350°C, the maximum conversion to propylene is 63%. Higher conversions require recycling unreacted butenes after fractionation. This reaction was first used to produce 2-butene and ethylene from propylene (Chapter 8). The reverse reaction is used to prepare polymer-grade propylene form 2-butene and ethylene ... 

In this process, which has been jointly developed by Institute Francais du Petrole and Chinese Petroleum Corp., the C4 feed is mainly composed of 2-butene (1-butene does not favor this reaction but reacts differently with olefins, producing metathetic by-products). The reaction between 1-butene and 2-butene, for example, produces 2-pentene and propylene. The amount of 2-pentene depends on the ratio of 1-butene in the feedstock. 3-Hexene is also a by-product from the reaction of two butene molecules (ethylene is also formed during this reaction). The properties of the feed to metathesis are shown in Table 9-1. Table 9-2 illustrates the results from the metatheses reaction at two different conversions. The main by-product was 2-pentene. Olefins in the range of Ce-Cg and higher were present, but to a much lower extent than C5. 

Figure 9-3. A flow diagram showing the metathesis process for producing polymer grade propylene from ethylene and 2-butene.

They correspond to the cross-metathesis of propylene with the neopentyli-dene fragment (Scheme 18), and their relative ratio corresponds to a photograph of the active site as they are formed. Depending on how propylene will approach the carbene, it will generate different metallacyclobutanes, whose stabilities can direct the relative amounts of cross-metathesis (and selfmetathesis) products. This model is based on the following the favoured cross-metathesis product arises from the reaction pathway, in which [1,2]-interactions are avoided and [1,3]-interactions are minimized (here shown with both substituents in equatorial positions) [83]. 

On the other hand, the reaction of CpfLnR with propylene did not afford any polymers but rather an allyl complex, Cp Ln(f/3-allyl), via a cr-bond metathesis reaction [56,117]. One molecule of propylene can insert itself into the Lu-Me bond of CpfLuMe to give the corresponding isobutylene complex. The successive insertion of propylene is 1000-fold slower than the first insertion [57]. The gas-phase reaction of Sc(CH3)2 with propylene also produces a... 

Evidence for a methylene-metal-initiating species was provided by detection of propylene early in the course of metathesis of 2,8-decadiene with Me4Sn/WCl6, in addition to normal metathesis products ... 

Several studies now exist which add credence to Casey s attractive proposal that metallocyclobutanes intervene in metathesis and cyclopro-panation reactions. Additionally, metallocyclobutanes have been observed to interconvert to propylene derivatives by way of /3-hydrogen transfer reactions. It is not well established, however, whether precoordination of the reacting olefin is required in all these processes. The proposed interrelation of these reactions may be formally presented as follows ... 

Thus, reactions affording either cyclopropanes or propylenes would most likely represent forms of termination of metathesis activity. As a corollary, any catalytic conversion of cyclopropanes to metathesis olefins via Eq. (26) would seem to require decomposition of the metal-carbene species in order to regenerate a naked metal species (M ) capable of further reactions with cyclopropanes. Of course, bimolecular carbene decomposition to yield an olefin as in Eq. (11) (e.g., ethylene from 2M=CH,) is one accepted process which could account for regeneration of M ... 

Reaction pathways apparently analogous to d and f of Eq. (26) yield a mixture of propylene and cyclopropane. Only when photochemical activation was employed were the major products olefins derived from metathesis-decomposition of the metallocycle. The failure to form metathesis olefins under moderate conditions is significant. It may be that either unimolecular dissociation of the olefin from the complex (in the absence of excess olefin to restabilize the carbene) is energetically unfavored, or the metallocyclobutane structure in the equilibrium given by steps a and b in Eq. (26) is highly stabilized and favored. These results... 

META-4 [Metathesis-C4] A process for converting a mixture of C4 hydrocarbons to propylene by metathesis in the presence of ethylene. Developed by Institut Frangais du Petrole. 

Olefin metathesis technology, in polymer synthesis, 26 944-948 Olefin oligomerization, 16 111 Olefin oxides, alkanolamines from (with ammonia), 2 122-140 Olefin polymerization, organic titanium compounds in, 25 122 Olefin(ic) polymers, 17 699-709 ethylene-propylene elastomers, 17 705-707... 

We studied the metathesis of propylene over W03-S102, an example of a single-reactant, bimolecular surface reaction. We calculated L for various conceivable rate-determining steps, including the step for which Eq. (34) applies (12). 

Metathesis of ethylene and butylenes to propylene. Another on-purpose route to propylene is metathesis, a chemical reaction that starts with two compounds, involves the displacement of groups from each and produces two new compounds. The application in this case converts ethylene and mixed butylenes to propylene and butene-1. This route could appeal to a company with refinery or olefins plant ethylene and butylenes that both have market values less than propylene, which could be the case in some local markets. 

In the chapter on olefms plants, in the section on propylene, a route to making propylene involved butene-2. In this process, called metathesis, ethylene and butene-1 are passed over a catalyst, and the atoms do a musical chair routine. When the music stops, the result is propylene. The conversion of ethylene to propylene is an attraction when the growth rate of ethylene demand is not keeping up with propylene. Then the olefins plants produce an unbalanced product slate, and producers wish they had an on-purpose propylene scheme instead of just a coproduct process. The ethylene/butene-2 metathesis process is attractive as long as the supply of butylenes holds out. Refineries are big consumers of these olefins in their alkylation plants, and so metathesis process has, in effect, to buy butylene stream away from the gasoline blending pool. 

The diagram doesn t show the ethylene and propylene made by metathesis of methanol or the propylene made by catalytic reaction of ethylene and butylene or by dehydrogenation of propane. The volumes are small, and besides, it would make the diagram too messy. 

This is a major achievement, mainly due to Basset and his group, in surface organometallic chemistry because it has been thus possible to prepare single site catalysts for various known or new catalytic reactions [53] such as metathesis of olefins [54], polymerization of olefins [55], alkane metathesis [56], coupHng of methane to ethane and hydrogen [57], cleavage of alkanes by methane [58], hydrogenolysis of polyolefins [59] and alkanes [60], direct transformation of ethylene into propylene [61], etc. These topics are considered in detail in subsequent chapters. 

Metathesis activity. A quantitative comparison of metathesis activities was made in the gas phase homometathesis of propylene. The reaction kinetics are readily monitored since all olefins (propylene, ethylene, cis- and fra/3s-2-butylenes) are present in a single phase. Metathesis of 30 Torr propylene was monitored in a batch reactor thermostatted at 0 °C, in the presence of 10 mg catalyst. The disappearance of propylene over perrhenate/silica-alumina (0.83 wt% Re) activated with SnMe4 is shown in Figure 2a. The propylene-time profile is pseudo-first-order, with kob (1.11 + 0.04) X 10" slightly lower rate constant, (0.67 constants are linearly dependent on Re loading. Figure 3. The slope yields the second-order rate constant k = (13.2 + 0.2) s (g Re) at 0°C. 

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... 

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. 

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... 

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