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Alkylation isoalkane-alkene

The technology and chemistry of isoalkane-alkene alkylation have been thoroughly reviewed for both liquid and solid acid catalysts (15) and for solid acid catalysts alone (16). The intention of this review is to provide an up-to-date overview of the alkylation reaction with both liquid and solid acids as catalysts. The focus is on the similarities and differences between the liquid acid catalysts on one hand and solid acid catalysts, especially zeolites, on the other. Thus, the reaction mechanism, the physical properties of the individual catalysts, and their consequences for successful operation are reviewed. The final section is an overview of existing processes and new process developments utilizing solid acids. [Pg.255]

Although not a separate process, isomerization plays an important role in pretreatment of the alkene feed in isoalkane-alkene alkylation to improve performance and alkylate quality.269-273 The FCC C4 alkene cut (used in alkylation with isobutane) is usually hydrogenated to transform 1,3-butadiene to butylenes since it causes increased acid consumption. An additional benefit is brought about by concurrent 1-butene to 2-butene hydroisomerization. Since 2-butenes are the ideal feedstock in HF alkylation, an optimum isomerization conversion of 70-80% is recommended.273... [Pg.193]

Concentrated sulfuric acid and hydrogen fluoride are still mainly used in commercial isoalkane-alkene alkylation processes.353 Because of the difficulties associated with these liquid acid catalysts (see Section 5.1.1), considerable research efforts are still devoted to find suitable solid acid catalysts for replacement.354-356 Various large-pore zeolites, mainly X and Y, and more recently zeolite Beta were studied in this reaction. Considering the reaction scheme [(Eqs (5.3)—(5.5) and Scheme 5.1)] it is obvious that the large-pore zeolitic structure is a prerequisite, since many of the reaction steps involve bimolecular bulky intermediates. In addition, the fast and easy desorption of highly branched bulky products, such as trimethylpentanes, also requires sufficient and adequate pore size. Experiments showed that even with large-pore zeolite Y, alkylation is severely diffusion limited under liquid-phase conditions.357... [Pg.261]

Ipatieff and coworkers carried out the first alkylation with alkenes and branched and normal chain alkanes (except methane and ethane) in the presence of AlCb as the catalyst. The sulfuric acid catalyzed alkylation reaction of arenes and isoalkanes, developed in 1938, is a still widely used industrial process to produce alkylates with high octane numbers. For synthetic applications, however, Friedel-Crafts-type alkylations of alkenes and alkanes have limited value since they tend to give mixtures of products, including oligomers of alkenes. ... [Pg.331]

Weitkamp, J., 1980b, Isoalkane/alkene alkylation and alkene oligomerization on zeolites. 1. Time on stream effects with isobutane/cis-2-butene on CeY, in Catalysis by Zeolites, eds B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud, Vol. 5 of... [Pg.312]

Bronsted Acids. Sulfuric acid (H2SO4) is an inexpensive, easy to handle protic acid used widely as catalyst in hydrolysis, hydration and dehydration, elimination, substitution, and rearrangements. It also catalyzes aromatic electrophilic substitutions mostly Friedel-Crafts acylations and alkylations (22). A very important application of sulfuric acid is its use in commercial isoalkane-alkene alkylation technologies. These commercial processes are still based on the use of sulfuric acid (and hydrogen fluoride) catalysts (23). [Pg.15]

Alkylation of isoalkanes with alkenes is of particular significance. The industrially used alkylation of isobutane with isobutylene to iso-... [Pg.164]

Products do not contain 2,2,3-trimethylbutane or 2,2,3,3-tetramethylbutane, which would be expected as the primary alkylation products of direct alkylation of isobutane with propylene and isobutylene, respectively. In fact, the process iavolves alkylation of the alkenes by the carbocations produced from the isoalkanes via intermolecular hydride abstraction. [Pg.556]

Theoretically, even the direct alkylation of carbenium ions with isobutane is feasible. The reaction of isobutane with a r-butyl cation would lead to 2,2,3,3-tetramethylbutane as the primary product. With liquid superacids under controlled conditions, this has been observed (52), but under typical alkylation conditions 2,2,3,3-TMB is not produced. Kazansky et al. (26,27) proposed the direct alkylation of isopentane with propene in a two-step alkylation process. In this process, the alkene first forms the ester, which in the second step reacts with the isoalkane. Isopentane was found to add directly to the isopropyl ester via intermediate formation of (non-classical) carbonium ions. In this way, the carbenium ions are freed as the corresponding alkanes without hydride transfer (see Section II.D). This conclusion was inferred from the virtual absence of propane in the product mixture. Whether this reaction path is of significance in conventional alkylation processes is unclear at present. HF produces substantial amounts of propane in isobutane/propene alkylation. The lack of 2,2,4-TMP in the product, which is formed in almost all alkylates regardless of the feed (55), implies that the mechanism in the two-step alkylation process is different from that of conventional alkylation. [Pg.263]

In this and other conventional acid-catalyzed reactions the key is the reactivity of alkenes, giving on protonation alkyl cations that then readily react with excess alkene, giving the alkylate cations. These carbocations then abstract hydrogen from the isoalkane, yielding the product alkylate and forming a new alkyl cation to reenter the reaction cycle. Chapter 5 discusses acid-catalyzed alkylations and their mechanism. [Pg.22]

Isomerization of straight-chain to branched alkanes also increases the octane number, as do alkylates produced by alkene-isoalkane alkylation (such as that of isobutane and propylene, isobutylene, etc.). These large-scale processes are by now an integral part of the petroleum industry. Refining and processing of transportation fuels became probably the largest-scale industrial operation. [Pg.24]

As is apparent, the reaction is properly designated as one in which the alkene is alkylated by a carbocation, the isoalkane serving only as the reservoir for the... [Pg.218]

Besides the rearrangement of carbocations resulting in the formation of isomeric alkylated products, alkylation is accompanied by numerous other side reactions. Often the alkene itself undergoes isomerization prior to participating in alkylation and hence, yields unexpected isomeric alkanes. The similarity of product distributions in the alkylation of isobutane with n-butenes in the presence of either sulfuric acid or hydrogen fluoride is explained by a fast preequilibration of n-butenes. Alkyl esters (or fluorides) may be formed under conditions unfavorable for the hydride transfer between the protonated alkene and the isoalkane. [Pg.220]

A problem that is characteristic of sulfuric acid-catalyzed alkylation is its capabihty to oxidize hydrocarbons. H2SO4 decomposes in the presence of isoalkanes to form water, SO2, and alkenes. This is a slow process, and so it occurs predominantly when the acid is in contact with hydrocarbons for a longer period. Higher temperatures favor the formation of SO2 (10). Some irreversible reactions between acid and hydrocarbons also take place during alkylation. Sulfone, sulfonic acid, and hydroxy groups have been detected in conjunct polymers produced with H2SO4 as the catalyst (8,96). Kramer (97) reported that... [Pg.273]

In the petrochemical industry sulfuric acid is utilized, for example, in the alkylation of isoalkanes with alkenes, in the chemical industry in the manufacture inorganic chemicals (e.g. hydrofluoric acid, chromic acid, aluminum sulfate) and organic products (e.g. dyes, explosives, isocyanates, soaps, detergents, fibers and pharmaceuticals). Sulfuric acid is also utilized in the manufacture of titanium oxide pigments, uranium and copper extraction, in steel pickling and in batteries. [Pg.115]

The regenerated carbonium ion can of course continue the process, a key feature being that under alkylation conditions this active species is formed from saturated alkane, not an olefin as required by polymerization. Different alkenes, such as propylene, 1-butene, or the 2-butenes may also form carbonium ions in a similar manner to the process of Eq. 18.25. However, neither /7-butane nor /7-pentane can replace an isoalkane for the hydride transfer since an /7-alkane is not capable of forming a stabilized carbonium ion. Nevertheless, this is one advantage that the alkylation process has over polymerization as a route to gasoline it is able to use both light hydrocarbon alkanes (as long as they are branched) and alkenes. Alkylation and polymerization both produce branched products, but the alkylation products are saturated (Table 18.5) whereas the polymerization products are alkenes. [Pg.612]

Although zeolitic solid acids have replaced supported mineral acids in many reactions, they cannot be used universally. For some reactions their acidity is too strong and their pore structure is readily blocked (etherification, alkene hydration) for others they are not strong enough acids. An example where zeolites have not been applied successfully is in the alkylation of alkanes with alkenes. Hydrocarbon fuels with high octane numbers are in constant demand for the majority of automobile engines, and branched alkanes of the gasoline fraction possess the required properties. Isoalkanes such as these are currently... [Pg.365]

Aliphatic alkylation is widely used to produce high-octane gasolines and other hydrocarbon products. Conventional paraffin (alkane)-olefin (alkene) alkylation is an acid-catalyzed reaction it involves the addition of a tertiary alkyl cation, generated from an isoalkane (via hydride abstraction) to an olefin. An example of such a reaction is the isobutane-ethylene alkylation, yielding 2,3-dimethylbutane. [Pg.303]

The main observations can be accounted for by a carbocationic mechanism incorporating intermolecular hydride transfer (77). The multistep transformation illustrated by the reaction between isobutane and 1-alkenes is initiated by the carbocation formed by protonation of the alkene (by the protic acid or the promoted metal halide catalysts) (eq. 48). Intermolecular hydride transfer between isobutane and the cation then generates a new carbocation (tert-butyl cation 13 eq. 49). The cation 13 adds to the alkene to form cation 14 (eq. 50), which then, through intermolecular hydride transfer, forms the product (eq. 51). In this final product-forming step, 13 is regenerated from the isoalkane and then starts a new cycle. Alkane-alkene alkylation, therefore, can be considered a chain reaction with 13 as the chain carrier. [Pg.24]

Fragmentation Dominant loss of alkyl residues and neutral alkenes. The position of highly substituted double bonds can be localized because in this case alkene ehminations are specific McLafferty-type reactions. Otherwise, double bonds can be localized in derivatives, such as epoxides and glycols, or by means of low energy ionization techniques. Branching effects are less characteristic than in isoalkanes. Alicyclic compounds exhibit very similar spectra. [Pg.339]


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See also in sourсe #XX -- [ Pg.254 ]




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