Oligomerization processes

In refining, the oligomerization process produces gasoline from C3 fractions containing approximately 75% propylene or fuel-gas containing ethylene and propylene. 

The direct methane conversion technology, which has received the most research attention, involves the oxidative coupling of methane to produce higher hydrocarbons (qv) such as ethylene (qv). These olefinic products may be upgraded to Hquid fuels via catalytic oligomerization processes. 

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

Figure 9-4. The Octol Oligomerization process for producing Os s and Ci2 s and Cis s olefins from n-butenes (1) multitubular reactor, (2) debutanizer column, (3) fractionation tower.

Homologous even-numbered n-a-olefins by oligomerization processes of ethylene... 

Figure 7 shows a simplified scheme of the oligomerization process. The ethylene is compressed in compressor C and fed into reactors R1-R3. It finds its way into the vessel VI in which the catalyst solution is stored. The ethylene enriched catalyst solution, as shown in Fig. 7, proceeds to the reactors. Heat from the reactors is led off through heat exchangers situated between the... 

FIGURE 6.32 Configurationally different spiro tetramers 44a and 44b formed by spiro tetramerization of l,3-bis(5-tocopheryl)propane (43) in a 15 1 ratio in agreement with theory. Reduction of each of the tetramers provides c s-l,2-c s-4,5-tetrakis(5-tocopheryl)cyclohexane (45). The dashed lines separate the two former units of 43, indicating where bond formation during the spiro oligomerization process occurred. 

Scheme 1. Reaction network in the ethylene oligomerization process...

Benzyl Alcohols. Benzyl alcohols of nearly all kinds undergo reduction when treated with acid in the presence of organosilicon hydrides. The most obvious exception to this is the behavior of benzyl alcohol itself. It resists reduction by the action of trifluoroacetic acid and triethylsilane, even after extended reaction times.26 Reducing systems consisting of triethylsilane and sulfuric acid/acetic acid or p-toluenesullonic acid/acetic acid mixtures also fail to reduce benzyl alcohol to toluene.134 As previously mentioned, substitution of boron trifluoride for trifluoroacetic acid results in the formation of modest yields of toluene, but only when a very large excess of the silane is used in order to capture the benzyl cation intermediate and suppress Friedel-Crafts oligomerization processes.129,143... 

Hitherto no monometalated molecular pnictide exists without solvation of the main group metal atom. Therefore, the monomeric species L (Fig. 2) can only be stabilized if the Li ion has its coordination sphere enlarged through donor solvation. More importantly, the lithium phosphanides of the type K undergo oligomerization processes to form dimer, tetramer, hexamer, or polymeric assemblies M—Q (Fig. 2), which dissociate in solution more easily than related amides (2, 11, 12). 

Extracellular, transmembrane (TM), and/or C-terminal regions have been suggested to be involved in the oligomerization process of GPCRs. 

For a brief introduction to the oligomerization process, see a) J. P. Collman, L. S. He-gedus, J.R. Norton, R.G. Finke, in Principles and Applications of Organotransition Metal Chemistry, University Science Books Mill Valley, CA, 1987, 593-600 b) For a recent review, see ... 

Since vanadium is tetrahedral in all these ions the number of bonds in the oligomerization process remain the same. The favorable enthalpy therefore emanates mainly from the stronger bonds in the stable water molecules that are condensed out. The net gain in enthalpy, for each linkage of two vanadates accompanied by the formation of a molecule of water is about 20 kJ/mol. 

Interestingly, the catalysts used here are similar to the nickel-ligand complexes used by Shell for their commercial ethene oligomerization process. Similar catalysts for making polyketone have also been patented by Keim et al. 

In contrast, in the related ylide complexes of stoichiometry [Au2(L-L) (CH2)2S(0) NMe2 ] (L-L = dpmp, dppm, dppe) [32], the same group describes oligomerization processes in solution, even when these molecules are not polymers in the solid state. 

In this case, the oligomerization process is detected by absorption measurements because the spectra of the dppm and dpmp complexes are concentration dependent. 

---