Short-chain Olefins

The aromatic hydrocarbons are used mainly as solvents and as feedstock chemicals for chemical processes that produce other valuable chemicals. With regard to cyclical hydrocarbons, the aromatic hydrocarbons are the only compounds discussed. These compounds all have the six-carbon benzene ring as a base, but there are also three-, four-, five-, and seven-carbon rings. These materials will be considered as we examine their occurrence as hazardous materials. After the alkanes, the aromatics are the next most common chemicals shipped and used in commerce. The short-chain olefins (alkenes) such as ethylene and propylene may be shipped in larger quantities because of their use as monomers, but for sheer numbers of different compounds, the aromatics will surpass even the alkanes in number, although not in volume. 

The mechanism of the polymerization contains ionic intermediate steps. The free H+ goes to a carbenium ion and, as shown in route B, rearranges to form tetrapropylene. It is highly likely that this actual tetrapropylene exists only in very small concentrations. The product variety is explained by the rearrangement of the carbenium ion to dodecene isomers according to route C. In addition, short-chain olefins formed by fragmentation (route D). Polymerization proceeds at almost 100% to mono olefins. Aromatics, paraffins, and diolefins exist only in trace amounts. The propylene tetramer is best characterized by its distillation range. 

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. 

The selection of Co-LTFT synthesis, the associated refinery design, and the product slate for Oryx GTL all mimicked the SMDS process. Likewise, no provision has been made for the upgrading of short-chain olefins or oxygenates. 

The main components of FCC catalysts are Zeolite Y, e.g., REY orUSY as the major active component (10 to 50%), and a binder that is typically an amorphous alumina, silica-alumina, or clay material. In addition to these main components, other zeolite components, e.g., ZSM-5, and other oxide or salt components are quite frequently used additives in the various FCC catalysts available on the market. The addition of 1 to 5% ZSM-5 increases the octane number of the gasoline. ZSM-5 eliminates feed compounds with low octane numbers because it preferentially center-cracks n-paraffins producing butene and propene [14], These short-chain olefins are then used as alkylation feedstocks... 

Corma, A., Martinez-Soria, V., and Schnoeveld, E. (2000) Alkylation of benzene with short-chain olefins over MCM-22 zeolite catalytic behaviour and kinetic mechanism, f Catal, 192, 163-173. 

A number of heterogeneous systems have been developed for oxidation reactions using H2O2 as oxygen source . In 1981, Taramasso, Notari and collaborators at Enichem opened new perspectives in this field with the discovery of the Ti-silicalite (TS-1) ° , a new synthetic zeolite of the ZSM family. In the TS-1 zeolite, titanium atoms are located in vicariant positions in the place of Si atoms in the crystalline framework . The remarkable reactivity of TS-1 is likely ascribable to the site-isolation of tetrahedral Ti(IV) in a hydrophobic environment. TS-1 has proved to be an efficient catalyst for the epoxidation of unfunctionalized short-chain olefins, especially terminal ones (equation 28). In addition, polyunsaturated compounds are mainly converted into the mono epoxides (equation 29). 

Currently, two-phase industrial processes deal only with short-chain olefins (less than six carbon), because higher... 

Mention has already been made of the relatively small reactivity of allyl peroxy radicals compared with other alkyl peroxy radicals. Jost (88, 96) has reasoned that paraffins react by a small number of long chains, whereas olefins oxidize by a large number of short chains. Olefins are thus attacked more readily than paraffins but form less reactive allyl radicals. In addition, during oxidation chain transfer occurs in which alkyl radicals are replaced by allyl radicals. Shorter chains would then be expected. Comparison of the precombustion products of iso-octane and diisobutylene (154) indicates that marked self-inhibition of reaction chains was occurring in the latter case. 

Overall, it can be concluded that zeolites, and more specifically MFI, are adequate catalysts for oligomerization of short chain olefins to produce gasoline and even diesel range fuels. Selectivity and catalyst life is strongly dependent on parameters such as crystallite size, Si/Al ratio, and poisoning of external surface sites. The introduction of some metals (Ni) can be helpful. 

It has to be remarked that amorphous Ni-silica aluminas with a narrower distribution of pore diameter, and lower density of acid sites, can offer new opportunities for the production of diesel and lubes form short chain olefins. In this sense, MCM-41 materials could be of interest. 

Besides the produciion of syntJietic fuels from synthesis gas, the selective preparation of base materials for the chemical industry is an important goal. Especially, the selective formation of short-chain olefins and alcohols has been tlie subject of recent research. Some illustrative examples have been chosen to point out recent development. However, it should be kept in mind that these new catalysts have so far not been proved under industrial conditions where they could lose part of their exceptional properties. 

The formation of hydrogenation by-products such as alcohols and hydrocarbons is favored at low p(CO). Extensive hydrogenation was often the aim of special cobalt process variants, in order to produce alcohols in one step - for instance, butanols. Especially for short-chain olefins, this technique has been replaced by two-step processes rhodium 0x0 synthesis along with a separate hydrogenation step. 

The oligomerization of olefins is mostly catalyzed by cationic complexes which are very soluble in ionic liquids. The Pd-catalyzed dimerization of butadiene [36] and the Ni-catalyzed oligomerization of short-chain olefins [5, 37], which is also known as the Difasol process [1 d] if chloroaluminate melts are used, can be mn in imidazolium salts 1 [38, 39]. Here, the use of chloroaluminate melts and toluene as the co-solvent is of advantage in terms of catalyst activity, product selectivity, and product separation. Cp2TiCl2 [6] and TiCU [40] in conjunction with alkylaluminum compounds were used as catalyst precursors for the polymerization of ethylene in chloroaluminate melts. Neither Cp2ZrCl2 nor Cp2HfCl2 was catalytically active under these conditions. The reverse conversion of polyethylene into mixtures of alkanes is possible in acidic chloroaluminate melts without an additional catalyst [41]. 

The industrial hydroformylation of short-chained olefins such as propene and butenes is nowadays almost exclusively performed by so-called LPO (low-pressure oxo) processes, which are rhodium-based. In other words, the former high-pressure technology based on cobalt has been replaced by the low-pressure processes, which cover nearly 80% of total C4 capacity due to their obvious advantages (cf. [8]). Nevertheless, some cobalt processes are still in operation for propene hydroformylation, for example as second stages in combination with a low-pressure process serving as the first stage [8, 9]. 

The patentee finds that short chain olefins dissolved in near critical or supercritical water oligomerize without the need of a catalyst. The patentee proposes an explanation of the findings. 

As a result of the competitive adsorption between HC and oxidizing species, the HC oxidation activity versus adsorption strength is a typical volcano curve. It shows a maximum with long chain alkanes and short chain olefins, and... 

For the different hydroformylation processes described above, the catalyst separation and recycling remain a constant preoccupation. This point is particularly crucial when a very expensive metal is used as catalyst (rhodium). The recycling is either operated by chemical transformation or by direct distillation, depending on the catalyst and its stability. In that way, the development of the aqueous biphasic process can be considered as an important breakthrough (4-6). The separation is operated by decantation, which simplifies the process scheme and limits the risks of catalyst decomposition during distillation. Even if the 0x0 Ruhrchemie/Rhone-Poulenc process presents undeniable advantages, this process remains limited to short-chain olefins (C2-C5) because of the low solubility of higher olefins in water which renders the reaction rates too low for viable processes [7]. 

Short-chain olefin oligomerization can provide gasoline, middle distillate, or lubricant oils. Typical acids used to catalyze these reactions are now solid-type catalysts such as silica-supported phosphoric acids or zeolites. 

The major interest in FT synthesis is to manufacture automotive fuels, of course. However, as the straight chain OL-olefin content of the overall olefin fraction may be as high as 85 % FT products are also considered starting materials for further chemical processing as, for instance, alcohols via 0x0-synthesis, tensides by alkylation of aromates, and polymers from short chain olefins. 

It is therefore obvious to combine the ability of the FTS slurry reactor to use syngases of low H2 to CO ratio with the high selectivity of the Mobil route in order to produce a C5 to C- 1 hydrocarbon mixture of a high RON. In particular, advantageous results can be expected if the FTS is carried out on catalysts which possess improved selectivity either to short chain olefins or to lower oxygenates. Mn/Fe and nonpromoted Fe/... 

Cu catalysts can be used in case of short-chain olefins, while nitrided fused Fe catalysts have proven to yield high selectivities to oxygenates (39,98). 

Both short-chain olefins and oxygenates can be converted on zeolites of ZSM-5 type to C5 to C- 1 hydrocarbons with a high content of aromates at temperatures between 350 to 400 °C. Fig. 27 presents a scheme of the... 

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