Oxidation of paraffinic hydrocarbons

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). 

JS/oble Metals. Noble or precious metals, ie, Pt, Pd, Ag, and Au, are ftequendy alloyed with the closely related metals, Ru, Rh, Os, and Ir (see Platinum-GROUP metals). These are usually supported on a metal oxide such as a-alumina, a-Al202, or siUca, Si02. The most frequently used precious metal components are platinum [7440-06-4J, Pt, palladium [7440-05-3] Pd, and rhodium [7440-16-6] Rh. The precious metals are more commonly used because of the abiUty to operate at lower temperatures. As a general rule, platinum is more active for the oxidation of paraffinic hydrocarbons palladium is more active for the oxidation of unsaturated hydrocarbons and CO (19). 

The literature is limited. It is generally agreed that platinum is superior to palladium for the oxidation of paraffinic hydrocarbons, whereas palladium is preferred for the oxidation of carbon monoxide and probably unsaturated hydrocarbons also. However, at very low concentrations of active components, palladium is probably more effective than platinum for total hydrocarbon and carbon monoxide emission control, at the same weight-percent of noble metal, and this difference was more definite for CO alone only fresh catalysts were used in this study by Barnes and Klimisch (I). 

The scope of oxidation chemistry is enormous and embraces a wide range of reactions and processes. This article provides a brief introduction to the homogeneous free-radical oxidations of paraffinic and alkylaromatic hydrocarbons. Heterogeneous catalysis, biochemical and hiomimetic oxidations, oxidations of unsaturates, anodic oxidations, etc, even if used to illustrate specific points, are arbitrarily outside the purview of this article. There are, even so, many unifying features among these areas. 

The initiating action of ozone on hydrocarbon oxidation was demonstrated in the case of oxidation of paraffin wax [110] and isodecane [111]. The results of these experiments were described in a monograph [109]. The detailed kinetic study of cyclohexane and cumene oxidation by a mixture of dioxygen and ozone was performed by Komissarov [112]. Ozone is known to be a very active oxidizing agent [113 116]. Ozone reacts with C—H bonds of hydrocarbons and other organic compounds with free radical formation, which was proved by different experimental methods. 

YM Potekhin. To the problem of mechanism of oxidation of paraffin and alkylcycloparaffin hydrocarbons. Doctor diss. Thesis, LTI, Leningrad, 1972 [in Russian],... 

When variable-valence metals are used as catalysts in the oxidation of hydrocarbons, the chain termination via such reactions manifests itself later in the process. This case has specially been studied in relation to the oxidation of paraffins to fatty acids in the presence of the K Mn catalyst [57], which ensures a high oxidation rate and a high selectivity of formation of the target product (carboxylic acids). As the reaction occurs, alcohols are accumulated in the reaction mixture, and their oxidation is accompanied by the formation of hydroxyperoxyl radicals. The more extensively the oxidation occurs, the higher the concentration of alcohols in the oxidized paraffin, and, hence, the higher is the kinetic... 

All hydrocarbon oils react with oxygen upon exposure to air at sufficiently elevated temperatures for long periods of time. Over the range of temperatures developed in engine crankcase, the rate of oil oxidation has been found to double for every 20°F rise in temperature. Although all lubricating oil hydrocarbons are susceptible to oxidation, of more importance to engine performance are the oxidation products. Paraffinic hydrocarbons... 

The initial step in the oxidation of a hydrocarbon is substitution. For saturated hydrocarbons such as open- and closed-chain paraffins and the alkyl groups of other hydrocarbons, the substitution reaction moves by a free radical mechanism, and sets up a chain reaction. Such a reaction Ls best illustrated by halogenation. 

This question is discussed in detail in the book by Skarchenko [52], It is noted that dehydrogenation of paraffin hydrocarbons dominates by selectivity over thermal cracking in the presence of iodine or other halogens, sulfur-containing compounds, oxygen and nitrous oxide. For example, in the presence of iodine dehydration dominates in the system, whereas in the case of other additives, independently of their amounts—oxygen, ethylene oxide and nitric acid—the main shift of the process toward cracking is preserved. 

Vapor-phase nitration of paraffin hydrocarbons, particularly propane, can be brought about by uncatalyzed contact between a large excess of hydrocarbon and nitric acid vapor at around 400°C, followed by quenching. A multiplicity of nitrated and oxidized products results from nitrating propane nitromethane, nitroethane, nitropropanes, and carbon dioxide all appear, but yields of useful products are fair. Materials of construction must be very oxidation-resistant and are usually of ceramic-lined steel. The nitroparaffins have found limited use as fuels for race cars, submarines, and model airplanes. Their reduction products, the amines, and other hydroxyl compounds resulting from aldol condensations have made a great many new aliphatic syntheses possible because of their ready reactivity. 

Hydrogenation of carbon oxides with iron, cobalt, or nickel catalysts (Fischer-Tropsch process). Hydrocarbons are the main products Recovery and separation of oxygenated products obtained from CO and H2 Partial oxidation of nonaromatic hydrocarbon mixtures, e.g., petroleum, paraffins, and natural gas, to produce a mixture of products, such as esters, acids, aldehydes, ketones, and alcohols. This also includes higher fatty acids from petroleum and patents on formaldehyde production... 

Reid98 recently employed high pressures while attempting the oxidation of heavy hydrocarbons but does not give detailed data. Extensive investigations on the oxidation of paraffin wax under high pressures have been made by Fischer.90 This work showed iron and copper salts to be the best catalysts and yields as high as 74 per cent of fatty acids were obtained. 

Further evidence in support of the peroxide theory has resulted from a study of the slow oxidation of pentene/5 This work is of more particular interest from the point of view of paraffin hydrocarbon oxidation as applied to knocking phenomena, however, and will not be discussed here. 

For the oxidation of CO, methane and olefins, Pd is a better catalyst than Pt. For the oxidation of paraffins higher than propane, Pt is better than Pd. Under conditions of hydrocarbon oxidation, the metal surface is fully covered with oxygen. Hence there is no influence of oxygen pressure on the reaction rate (sometimes there is even a slight negative influence on the rate). 

Gum formation. Heating of paraffinic hydrocarbon mixtures found in jet fuels, gas oils and similar products may result in the precipitation of gum-like material. A sequence of events has been proposed by Taylor [1967, 1968]. Autoxidation forms a soluble oxidation product, with further oxidation to an insoluble polymer. The polymer may be formed on the wall or transported as particles to the wall. 

Bulfonation are, in turn, suited for use as detergents. Sodium and lithium soaps of these acids have been described as promising for the manufacture of lubricating g ases. Much of this work has centered on the oxidation of paraffin wax and hydrocarbons of comparable molecular weight. It is reported that some 100,000 tons per year of fatty acids was produced by oxidation of various hydrocarbons in Germany during World War II. ... 

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