Oligomerization olefin

The mechanistic steps are as follows paraffins dehydrogenate to olefins the olefins oligomerize and cyclize and the cycHcs aromatize. Because the first step is rate controlling, very Httie olefin is actually present. The BTX product is relatively free of nonaromatics and therefore is very desirable as a chemical feed. As in reforming, some C —C2 fuel gas is produced along with a valuable hydrogen stream. Prom a C —feed the BTX product is roughly 35 45 20, respectively. 

Epoxides are often encountered in nature, both as intermediates in key biosynthetic pathways and as secondary metabolites. The selective epoxidation of squa-lene, resulting in 2,3-squalene oxide, for example, is the prelude to the remarkable olefin oligomerization cascade that creates the steroid nucleus [7]. Tetrahydrodiols, the ultimate products of metabolism of polycyclic aromatic hydrocarbons, bind to the nucleic acids of mammalian cells and are implicated in carcinogenesis [8], In organic synthesis, epoxides are invaluable building blocks for introduction of diverse functionality into the hydrocarbon backbone in a 1,2-fashion. It is therefore not surprising that chemistry of epoxides has received much attention [9]. 

C3H5)Ni(EPh3)2](PF6) (E = P, As, Sb) are active catalysts for olefin oligomerization. The stibine species is the most active in the 1,4-polymerization of butadiene.707,708... 

Olefins in the C3-320°C range had significant synthetic value, and additional olefins were produced by thermal cracking in some facilities. Acid-catalyzed and thermal olefin oligomerization were important technologies for the upgrading of Fischer-Tropsch products. 

The transportation fuels produced and marketed (Table 18.9)40 met the South African fuel specifications of that time and included some coal-derived liquids (not shown in Figure 18.5). Although the refinery originally produced no jet fuel, it was demonstrated that the hydrogenated kerosene range oligomers from olefin oligomerization over a solid phosphoric acid catalyst met the requirements for jet fuel.38 (Semisynthetic jet fuel was approved in 1999 and fully synthetic jet fuel was approved in 2008 DEFSTAN 91-91/Issue 6). 

A light diesel fuel was produced by distillate hydrotreating of the straight-run Fe-HTFT material, while the heavier fraction was hydrocracked over a dewaxing catalyst, which produced a heavy diesel (Table 18.10). Some diesel fuel was also produced by C3-C4 olefin oligomerization over solid phosphoric acid by recycling the naphtha thus produced. It has previously been pointed out that solid phosphoric acid is not well suited for distillate production,42 and the hydrogenated... 

Olefin oligomerization over solid phosphoric acid was a key technology in the refinery, and most of the C3-C4 gaseous olefins were converted to liquid products. 

Diesel production involved a straightforward design. The olefinic distillate from olefin oligomerization was combined with the straight-run HTFT distillate and hydrotreated. The hydrotreated Fischer-Tropsch-derived distillate was blended with the distillate fraction from the natural gas liquids to produce diesel fuel. In 2003 another hydrotreater (noble metal catalyst) was added to the refinery to convert part of the hydrotreated HTFT distillate into low aromatic distillate to serve a niche market.56... 

Olefin oligomerization is a key refining technology, and in the Mossgas refinery the COD process is used not only to convert normally gaseous olefins to liquid products, but also to refine oxygenates to fuel. 

Short-chain olefins are not refined and the gaseous LTFT products are employed as fuel gas. Production of this fraction is limited by Co-LTFT synthesis, and with the product being less olefinic than iron-based Fischer-Tropsch syncrude, less benefit would be derived from the inclusion of an olefin oligomerization unit. Furthermore, adding complexity would go against the design objectives of the SMDS process. 

Olefin oligomerization is a key Fischer-Tropsch refining technology. 

Fig. 1 Early examples of late transition metal olefin oligomerization and polymerization catalysts...

Selectivity Control in Nickel-Catalyzed Olefin Oligomerization... 

A. General Course of Olefin Oligomerization and Related Reactions 119... 

A particularly challenging situation in catalysis in general and in olefin oligomerization in particular is that of stereoselectivity control, including diastereoselectivity and enantioselectivity (6). 

It is apparent from this short introduction that optimal control of the overall selectivity of olefin oligomerization reactions depends on the simultaneous control of several different types of selectivity. 

Examples of w-allylnickel-X compounds (X = anionic ligand) other than 77-allylnickel halides which have been used in combination with (alkyl)aluminum halides as olefin oligomerization catalysts are 7r-allyl-nickel acetylacetonate (11) (Section III), 7r-allylnickel aziridide (4, 56), and bis(7r-allyl)nickel (6) (59). In addition to ir-allylnickel halides, organo-nickel halides such as tritylnickel chloride (60, 61) and pentafluoro-phenylbis(triphenylphosphine)nickel bromide (62), or hydridonickel halides, e.g., trans-hydridobis(triisopropylphosphine)nickel chloride (12) (Section III), give active catalysts after activation with aluminum halides... 

Method C2 Nickel catalysts for olefin oligomerization may also be... 

Reactions leading to the formation of the catalytically active nickel hydride species from organonickel precursors (Section III) can be regarded as model reactions for olefin oligomerization reactions. The reactions described by Eq. (8) and Scheme 3 (Section III) show that RNiX compounds (R = methyl orallyl, X = halide or acetylacetonate) activated by Lewis acids add to double bonds under mild reaction conditions (-40° or 0°C). It follows further from these reactions that under conditions leading to olefin dimerization a rapid nickel hydride /3-hydrogen elimination reaction occurs. The fact that products resulting from olefin insertion into the nickel-carbon bond are only observed when /3-hydride... 

The reversal of the insertion reaction [Eq. (10)] is not normally observed [in contrast to nickel hydride addition to olefins, Eq. (9)]. An exception is the skeletal isomerization of 1,4-dienes (88, 89). A side reaction—the allylhydrogen transfer reaction [Eq. (5)]—which results in the formation of allylnickel species such as 19 as well as alkanes should also be mentioned. This reaction accounts for the formation of small amounts of alkanes and dienes during the olefin oligomerization reactions (51). 

The nature and distribution of the products of an olefin oligomerization reaction will depend, inter alia, on the relative rate constants of the insertion step (ki)vs. the displacement step (fcd) [Eq. (11)] ... 

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