Shell higher olefin process metathesis

Alkenes. At present alkene isomerization is an important step in the production of detergent alkylates (Shell higher olefin process see Sections 12.3 and 13.1.3).264 265 Ethylene oligomerization in the presence of a nickel(O) catalyst yields terminal olefins with a broad distribution range. C4-C6 and C2o+ alkenes, which are not suitable for direct alkylate production, are isomerized and subsequently undergo metathesis. Isomerization is presumably carried out over a MgO catalyst. 

By far the largest application of metathesis is a principal step in the Shell higher olefin process (SHOP),24 140 141 with the aim of producing detergent-range olefins... 

Applications of the olefin metathesis reversible chemical reaction, discovered by Phillips Petroleum in the 1960s, were also developed in the subsequent years. By this reaction, Arco produces propylene from ethylene and butene-2 Hercules prepares its plastic, Metton, from dicyclopentadiene and Shell synthesizes its C12-C14 SHOP (Shell Higher Olefin Process) alcohols used for detergents. 

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. 

The alkene metathesis reaction see Alkene Metathesis) exchanges alkylidene groups between different alkenes, and is catalyzed by a variety of high oxidation state, early transition metal species (equation 40). The reaction is of interest because it is the strongest bond in the alkene, the C=C bond, that is broken during the reaction. It is also commercially important in the Shell higher olefins process and in the polymerization of cycloalkenes. It is relevant to this article because carbenes are the key intermediates, and the best-known catalyst, (1), is a carbene complex. 

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]. 

The i-oleftns obtained have a purity of more than 95 molar per cent of terminal olefins and are devoid of branched structures or diolefinic or cyclic impurities. These z-olefms, which all have an even number of carbon atoms, are produced with yields that vary according to a statistical distribution, with a maximum of C, 0-C, 2-Cj, for example, if the final product is intended for the manufacture of linear alkylbenzene. Due to the low yield of a given cut, it is understandable that the upgrading of all the other fractions is economically necessary. Since the upgrading of the light and heavy fractions is often a problem. Shell in the United States has developed the SHOP (Shell Higher Olefin Process), in which these effluents are converted to a cut for detergents by isomerization and metathesis. 

It is still unclear how the initiation step in alkene metathesis occurs and how the initial carbene forms. Commercial applications of metathesis include the triolefin process, in which propylene is converted to ethylene and butene, the neohexene process, in which the dimer of isobutylene, Me3CCH=CMe2, is metathesized with ethylene to give Me3CCH=CH2, an intermediate in the manufacture of synthetic musk, and a 1,5-hexadiene synthesis from 1,5-cy-clooctadiene and ethylene. Two other applications, SHOP and ROMP (Shell higher olefins process and ring-opening metathesis polymerization), are discussed in the next section. 

In the Shell Higher Olefins Process (SHOP) a much more efficient catalyst based on transition metal compounds (probably nickel) is used to effect the oligomerization. Initially about 30% of the ethene is converted into the desired olefins. The remainder (C -Cj and above are isomerized to internal alkenes and then converted into more useful fractions by metathesis. 

The required terminal olefins used as substrates for the hydroformylation, such as 1-pentene or 1-octene, are available in large scales and can be derived either from Sasol s Fischer-Tropsch process or from the shell higher olefins process (SHOP), respectively [43, 44]. Alternatively, trimerization or tetramerization of ethylene affords 1-hexene [45] or 1-octene [46]. Dimerization of butadiene in methanol in the presence of a Pd catalyst (telomerization) is another industrially used access for the manufacture of 1-octene [46]. 1-Octene can also be produced on a large scale from 1-heptene via hydroformylation, subsequent hydrogenation, and dehydration (Scheme 6.2) [44]. This three-step homologation route is also valuable for the production of those higher olefins that bear an odd number of C atoms. (X-Olefins can also be derived from internal olefins by cross-metathesis reaction with ethylene [47]. 

Figure 6.16.5 Flow scheme of the Shell higher olefins process (SHOP) - P= purification I = isomerization M = metathesis. Adapted from Vogt (2005).

A large-scale industrial process incorporating olefin metathesis is the Shell higher olefins process (SHOP) for producing linear higher olefin from ethene in the metathesis step, an alumina-supported molybdate catalyst is used. 

---