Olefin chain growth

Homogeneous polyaUcene catalysis has progressed to the point where metals not generally associated with coordination polymerization can now be made to promote olefin chain growth and metals long ago associated with polyalkene catalysis have been given new life. 

The proton adds to the more negative carbon atom in the olefin to initiate chain growth ... 

This second reaction leads to the small amount of branching (usually less than 5%) observed in the alcohol product. The alpha olefins produced by the first reaction represent a loss unless recovered (8). Additionally, ethylene polymerisation during chain growth creates significant fouling problems which must be addressed in the design and operation of commercial production faciUties (9). 

A.luminum Jilkyl Chain Growth. Ethyl, Chevron, and Mitsubishi Chemical manufacture higher, linear alpha olefins from ethylene via chain growth on triethyl aluminum (15). The linear products are then used as oxo feedstock for both plasticizer and detergent range alcohols and because the feedstocks are linear, the linearity of the alcohol product, which has an entirely odd number of carbons, is a function of the oxo process employed. Alcohols are manufactured from this type of olefin by Sterling, Exxon, ICI, BASE, Oxochemie, and Mitsubishi Chemical. 

In the foUowiag cases, only those reactions ia which there is no chain growth, or at most dimerisation, are considered (see Olefin polymers). Alkyl titanium haUdes can be prepared from alkyl aluminum derivatives. The ring stmcture imparts regiospecificity to the ensuing carbometalation (216) ... 

In this reaction one ligand is inserted between the metal and another ligand, creating a site of coordinative unsaturation so that another reactant ligand can be associated with the metal. The insertion reaction accounts for the chain-growth steps of olefin polymeri2ation reactions. 

The transition metal-catalyzed polymerization of olefins yields high molecular weight polymers as the result of the successive insertion of monomer into the metal-carbon bond of the growing polymer chain. This chain growth is... 

When determining the product selectivities, all compounds of equal carbon numbers (paraffines, olefins, isomers, and oxygen compounds) were summarized to one product fraction. The chain growth probability was determined by the Anderson-Schulz-Flory (ASF) distribution ... 

Along with catalyst activity, product selectivity is a key issue in cobalt-based FTS.1 For GTL processes the preferred product is long-chain waxy hydrocarbons. It is well known that FT reaction conditions have an important effect on product selectivities. High temperatures and H2/CO ratios are associated with higher methane selectivity, lower probability of hydrocarbon chain growth, and lower olefinicity in the products.105... 

Olefins react secondarily for isomerization and hydrogenation (on cobalt sites that are not active for chain growth lower scheme in Figure 9.15). There is a first reversible H-addition (at the alpha- or beta-C-atom of the double bond) to form an alkyl species, and a slow irreversible second H-addition to form the paraffin (lower scheme in Figure 9.15). Thus, double-bond shift and double-bond hydrogenation are interrelated by a common intermediate to produce olefins with internal double bonds or paraffins from the primary FT alpha-olefins. Experimental results1018 are presented in Figures 9.16 and 9.17. 

Another explanation for the changing slope has been proposed by Schulz and Claeys,7 who suggest that the product olefins undergo secondary reactions and, because of changing product olefin solubility, result in chain length dependence on the chain growth probability (a). 

Scheme 4 Mechanism of chain growth for a all Pd(II) polymerizations and ethylene polymerizations with Ni(II), and b a-olefin polymerizations with Ni(II). Specific kinetic data shown for Ni catalyst 1.15b [63]...

N. O. Elbashir and C. B. Roberts, Enhanced Incorporation of a-Olefins in the Fischer-Tropsch synthesis Chain-Growth Process over an Alumina-Supported Cobalt Catalyst in Near-Critical and Supercritical Hexane Media, Ind. Eng. Chem. Res., 2005, 44, 505-521. 

---