Oxidation of paraffins

OXIDATION OF PARAFFINS (Fatty Acids and Fatty Alcohols) 

The catalytic oxidation of long-chain paraffins (C18-C30) over manganese salts produces a mixture of fatty acids with different chain lengths. Temperature and pressure ranges of 105-120°C and 15-60 atmospheres are used. About 60 wt% yield of fatty acids in the range of C12-C14 is obtained. These acids are used for making soaps. The main source for fatty acids for soap manufacture, however, is the hydrolysis of fats and oils (a nonpetroleum source). Oxidation of paraffins to fatty acids may be illustrated as  

Oxidation of C12-C14 n-paraffms using boron trioxide catalysts was extensively studied for the production of fatty alcohols.Typical reaction conditions are 120-130°C at atmospheric pressure. ter-Butyl hydroperoxide (0.5 %) was used to initiate the reaction. The yield of the alcohols was 76.2 wt% at 30.5% conversion. Fatty acids (8.9 wt%) were also obtained. Product alcohols were essentially secondary with the same number of carbons and the same structure per molecule as the parent paraffin hydrocarbon. This shows that no cracking has occurred under the conditions used. The oxidation reaction could be represented as  

Nonionic detergents are discussed in Chapter 7. Other uses of these alcohols are in the plasticizer field and in monoolefin production. 

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Unlike spark-induced combustion engines requiring fuel that resists autoignition, diesel engines require motor fuels, for vhich the reference compound is cetane, that are capable of auto-igniting easily. Additives improving the cetane number will promote the oxidation of paraffins. The only compound used is ethyl-2-hexyl nitrate. 

Technically, acetaldehyde is mainly made by the oxidation of ethylene using a CuCl2/PdCl2 catalyst system.. Although some acetic acid is still prepared by the catalytic oxidation of acetaldehyde, the main process is the catalytic oxidation of paraffins, usually -butane. 

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). 

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. 

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). 

Oxidation of -paraffins to C13 brassylic acid (dicarboxylic acid)... 

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],... 

The variety of functions of the catalyst is pronounced, in particular, in the technological catalytic oxidation of -paraffins to aliphatic acids [5]. This technology consists of several stages among which the central place is occupied by oxidation. It is conducted at 380 420 K in a series of reactors, with a mixture of salts of aliphatic acids of K+ and Mn2+ or Na+ and Mn2+ as the catalyst. The alkaline metal salt stabilizes (makes it more soluble and stable) the manganese salt [152]. Studies have revealed the multifunctional role of the catalyst (manganese ions) (Mn) [152-154]. 

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... 

Thus, oxidation of paraffins yields alcohols, aldehydes, ketones and acids. The acids formed are vigorously corrosive to copper, lead and cadmium engine bearings. 

Cobalt- or manganese-substituted PW12O40 and SiWiiOj9Ru(OH2)5 catalyze the oxidation of paraffins such as cyclohexane and adamantane (320, 321) as well as the epoxidation of cyclohexene with ter/-butyl hydroperoxide, iodosylbenzene potassium persulfate, and sodium periodate (321, 322). The reactivity depends on the transition metals. In the case of epoxidation of cyclohexene with iodosylbenzene, the order of catalytic activity of PW] i(M)03 is M = Co > Mn > Cu > Fe, Cr. 

Crandall JW, Grimm RC. Separation of organic acids from the products of partial oxidation of paraffins by reactive extraction with amines. U.S. Patent 3,541,121, Union Carbide Corp., 1970. 

Example 5.5. Oxidation of paraffins to secondary alcohols. Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of boric-acid esters or boroxines [16-18], These intercept the alkyl peroxide, the first oxidation product, preventing it from generating free radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids (see also Section 9.6.2). The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. The reaction does not stop at... 

Examples include reversible lactone formation, hydroformylation of propene and 1-pentene, ethoxylation of aliphatic alcohols, and oxidation of paraffins to secondary alcohols. 

The high-temperature oxidation of paraffins larger than methane is a fairly complicated subject owing to the greater instability of the higher-order alkyl... 

Oxidations of paraffins with high concentrations of cobalt catalyst have very special characteristics. Such oxidations will proceed at lower temperatures than in the case of lower concentrations of cobalt or with other catalysts, or in the absence of catalysts [10, 18, 60-66]. For example, the high-concentration cobalt-ion oxidation of -butane can be conducted at 100-110 °C compared with 150-180 °C for the other cases. Significantly higher efficiencies to acetic acid are reported (75-84 % vs. about 50-60 %). Co-reductants such as acetaldehyde, MEK, or p-xylene (especially p-xylene [65]) are reported to be useful, but not essential [66]. In high-concentration cobalt-ion catalyzed oxidations, rates are generally lower than in the conventional oxidations. 

Many other metal ions have been reported as catalysts for oxidations of paraffins or intermediates. Some of the more frequently mentioned ones include cerium, vanadium, molybdenum, nickel, titanium, and ruthenium [21, 77, 105, 106]. These are employed singly or in various combinations, including combinations with cobalt and/or manganese. Activators such as aldehydes or ketones are frequently used. The oxo forms of vanadium and molybdenum may very well have the heterolytic oxidation capability to catalyze the conversion of alcohols or hydroperoxides to carbonyl compounds (see the discussion of chromium, above). There is reported evidence that Ce can oxidize carbonyl compounds via an enol mechanism [107] (see discussion of manganese, above). Although little is reported about the effectiveness of these other catalysts for oxidation of paraffins to acetic acid, tests conducted by Hoechst Celanese have indicated that cerium salts are usable catalysts in liquid-phase oxidation of butane [108]. 

Lanning, H. J., Manufacture of Fatty Acids by Oxidation of Paraffins, Hydrogenation of the... 

It possesses centres able to perform the allylic oxidation with high specificity. This is the reason why vanadyl pyrophosphate does not yield olefins with high selectivity in the oxidation of paraffins. In fact the desorption of intermediate olefins is not rapid, since they are quickly transformed to the oxygenated products. Only when molecular oxygen is absent (and the catalyst possesses a low number of 0-insertion sites), can the olefin be saved from consecutive transformations, and a good selectivity to the olefin can be achieved. 

The rational design of catalysts has been a desired aim of catalyst researchers for a long time. Our current attempt at this goal centers on the partial oxidation of paraffins, and entails the incorporation of key catalytic elements into a structural freimework which by its very nature would favor structural isolation of such catalytic functionalities. It is well known by now, that vanadium is one of the key elements for the oxidative activation of paraffins [1-5]. It is also well known, that structural isolation of catalytic moieties is desirable to achieve selectivity to useful oxidized products, thereby preventing overoxidation to waste products, CO and CO2 [6-8]. 

We conclude therefore, that the Nb-Ti-V-P-oxide catalyst investigated is relatively active for the oxidation of paraffins, since it has a V/P ratio of only 1/12 as compared to a 1/1 ratio for (VO)2P207. Of course, we had hoped that the V in the NASICON structure would be sufficiently site isolated to yield products less oxidized than maleic anhydride from n-butane. However, unfortunately that does not appear to be the case. One explanation for this might be that there are still too many adjacent V atoms, i.e., (V-0-V) moieties, where n > 0. Nonetheless, the NASICON structure provides for some desired V site isolation, however, apparently not complete and hence not sufficient to achieve our desired catalytic goal. Another observed fact is, that the Nb-Ti-V-P-oxide under investigation shows an amorphous overlayer via TEM which is enriched in vanadium. The (V/P)s ,face > (V/P)pa icie- One can reason that at the temperature of 900 °C required to obtain the NASICON structure, the more... 

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