Short Chain Alkanes on

The oxidative activation of short chain alkanes on microporous metal aluminophosphates... 

Blasco, T. and Lopez Nieto, J. (1997). Oxidative Dehydrogenation of Short Chain Alkanes on Supported Vanadium Oxide Catalysts, Appl Catal A Gen., 157, pp. 117-142. 

Blasco T, Nieto JML (1997) Oxidative dehydrogenation of short chain alkanes on supported vanadium oxide catalysts. Appl Catal Gen 157 117-142... 

Guisnet M, Gnep NS, Alario F. Aromatization of short chain alkanes on zeolite catalysts, Appl Catal A GeneraL 1992 89 1. 

Several reaction pathways for the cracking reaction are discussed in the literature. The commonly accepted mechanisms involve carbocations as intermediates. Reactions probably occur in catalytic cracking are visualized in Figure 4.14 [17,18], In a first step, carbocations are formed by interaction with acid sites in the zeolite. Carbenium ions may form by interaction of a paraffin molecule with a Lewis acid site abstracting a hydride ion from the alkane molecule (1), while carbo-nium ions form by direct protonation of paraffin molecules on Bronsted acid sites (2). A carbonium ion then either may eliminate a H2 molecule (3) or it cracks, releases a short-chain alkane and remains as a carbenium ion (4). The carbenium ion then gets either deprotonated and released as an olefin (5,9) or it isomerizes via a hydride (6) or methyl shift (7) to form more stable isomers. A hydride transfer from a second alkane molecule may then result in a branched alkane chain (8). The... 

However, the value of yab needs to be considered as the equilibrium value, and therefore if one considers the system at nonequilibrium, then the spreading coefficients would be different. For example, the instantaneous spreading of benzene is observed to give a value of Sa/b as 8.9 dyn/cm, and therefore benzene spreads on water. On the other hand, as the water becomes saturated with time, the value of water decreases, and benzene drops tend to form lenses. The short-chain hydrocarbons such as hexane and hexene also have positive initial spreading coefficients, and spread to give thicker films. Longer-chain alkanes, on the other hand, do not spread on water (e.g., the Sa/b for C16(hexadecane)/water is -1.3 dyn/cm at 25°C. 

In practice, short-chain alkanes and alkenes are normally used as feedstock for shape-selective catalytic formation of isooctanes at relatively low temperatures. Until the 1980s, lead alkyls (Section 18.1) were added to most automotive fuels to help suppress engine knock, but they have been phased out in North America because of the chronic toxicity of lead and lead compounds. The most commonly used nonlead antiknock additive is now methyl tert-butyl ether [MTBE CH30C(CH3)3], which is made by the reaction of methanol with 2-methylpropene, (CHs C—CH2 (see Section 7.4). The latter is obtained by catalytic cracking of petroleum fractions to give 1-butene, which is then shape-selectively isomerized on zeolitic catalysts. 

The distribution of volatile products of low molar mass from the irradiation of poly (olefin) s is strongly dependent on the nature of substituents (short-chain branches) on the backbone chain. Hydrogen is the main volatile product with smaller quantities of alkanes and alkenes. 

Alkanes, which are the principal components of natural gas and crude oil, are still the preferred energy source of our society. In regard to the prime importance of alkanes as feedstock for the chemical industry, it appears a waste of resources simply to burn these precious raw materials. Unfortunately, attempts to transform alkanes into more valuable products are hampered by their low reactivity, as best illustrated by the use of alkanes as inert solvents. For example, the cracking process requires temperatures of about 1000 °C in order to convert long-chain alkanes into short-chain alkanes. Controlled conversion of hydrocarbons is difficult to achieve and limited to partial oxidations, such as the conversion of butane into acetic acid. It is obvious that processes that would enable efficient functionalization to occur at low temperature would have enormous potential application. Achievements towards this goal will almost certainly rely on the use of catalysts, which will have to activate the stable C-H bond (375-440 kf mol-1) in order to induce its scission. 

Several new pathways of zeolite catalysis are offered by ZSM-5 based catalysts [1]. One of their applications is production of aromatics from short-chain alkanes [2]. The presence of metals such as platinum (partly as Pt " ") has been foimd to promote conversion of propane to aromatics [3, 4], although Pt was not the best additive for this purpose. Alkanes with longer carbon chain have also been foimd to form aromatics [5] or skeletal isomers [6] on various Pt-ZSM catalysts. 

Supported vanadium oxides have been proposed as selective catalysts in partial oxidation reactions [1] and more specifically in the oxidative dehydrogenation (ODH) of short chain alkanes [2, 3]. However, it has been observed that the catalytic behavior of these catalysts during the oxidation of alkanes depends on the vanadium loading and the acid-base character of metal oxide support. In this way, alumina-supported vanadia catalysts with low V-loading are highly active and selective during the ODH of ethane [4-7] and propane [8] but they show a low selectivity in the ODH of n-butane [4, 5, 9, 10]. 

Many investigations were also conducted with mould fungi (Nyns et al, 1968). Some strains of Aspergillus, Penicillium, Fusarium and Cladosporium grow on hydrocarbon mixtures (Ci2-Ci4). Mould fungi can, however, assimilate short-chain alkanes in extremely few cases... 

Inhaled ozone is known to initiate free-radical autooxidation of unsaturated fatty acids in animal pulmonary lipids (Pryor et al., 1981). These reactions lead to the formation of such typical autooxidation products as conjugated dienes and short-chain alkanes like ethane and pentane. Whether these reactions also occur in water treatment is uncertain. Glaze et al. (1988) showed that 9-hexadecenoic acid (83) reacted readily in aqueous solution to form the expected C, and C, aldehydes and acids. Linoleic acid (84) was converted to a mixture of aldehydes and acids (Carlson and Caple, 1977) notably, 3-nonenal (85) was among the products. Isolation of an unsaturated aldehyde is significant because of the high reported toxicity of these compounds. Carlson and Caple (1977) also implied that the epoxide of stearic acid was formed when an aqueous solution of oleic acid was ozonized the product probably derives from an indirect attack on the double bond by peracids or peroxy radicals (Equation 5.39). Nevertheless, it is conceivable that similar reactions could occur in natural waters. 

Studies conducted in rabbit liver microsomes on the metabolism of methyl, ethyl, isopropyl and propyl thiols show that rabbit liver catalyses the S-methylation of short-chain alkane thiols to yield the corresponding methyl sulfides. The coenzyme in this process is S-adenosyl-L-methionine. The resulting methyl sulfides are further metabolized by formation of the corresponding sulfoxide and sulfone (Holloway et al., 1979). The methylation of short-chain alkyl thiols to methylthioethers acts as a detoxication mechanism for the reactive sulfhydryl group (Holloway et al., 1979),... 

It can be seen that major differences occur in the products of thermal degradation that are obtained for these three similar polymers. PE produces major amounts of normal to Cg alkanes and minor amounts of 2-methyl and 3-methyl compounds such as isopentane and 3-methylpentane, indicative of short-chain branching on the polymer backbone. For PP, branched alkanes predominate, these peaks occurring in regular patterns, e.g., 2-methyl, 3-ethyl, and 2,4-dimethylpentane and 2,4-dimethylheptane, which are almost absent in the PE pyrolysate. Minor components obtained from PP are normal paraffins present in decreasing amounts up to -hexane. This is to be contrasted with the pyrogram of PE, where n-alkanes predominate. The ethylene-propylene copolymer, as might be expected, produces both normal and branched alkanes. The concentrations of 2,4-dimethylpentane and 2,4-dimethylheptane are lower than those that occur in PP. 

It can be seen that major differences occur between the pyrograms of these three similar polymers. PE produces major amounts of normal C2 to Cg alkanes and minor amounts of 2-methyl and 3-methyl compounds such as isopentane and 3-methylpentane, indicative of short-chain branching on the polymer backbone. For PP, branched alkanes predominate,... 

Catal3Ttic oxidation has been established as one of the most appropriate technologies for VOC abatement. An assessment of the suitability of catalytic oxidation for hydrocarbon control, along with competing processes, is given in Table 3.2. In the literature there are many studies focusing on the catalytic oxidation of VOCs, however, it is beyond the scope of this work to comprehensively review these studies. Rather we will concentrate on the catalytie total oxidation of simple short-chain alkanes and aromatic compounds as illustrative examples of VOC abatement. 

Some specific reviews on the total oxidation of short-chain alkanes have been published previously and these focus particularly on catalysts based on palladium... 

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