Light butane oxidation products

Photolytic. Major products reported from the photooxidation of butane with nitrogen oxides under atmospheric conditions were acetaldehyde, formaldehyde, and 2-butanone. Minor products included peroxyacyl nitrates and methyl, ethyl and propyl nitrates, carbon monoxide, and carbon dioxide. Biacetyl, tert-butyl nitrate, ethanol, and acetone were reported as trace products (Altshuller, 1983 Bufalini et al, 1971). The amount of sec-butyl nitrate formed was about twice that of n-butyl nitrate. 2-Butanone was the major photooxidation product with a yield of 37% (Evmorfopoulos and Glavas, 1998). Irradiation of butane in the presence of chlorine yielded carbon monoxide, carbon dioxide, hydroperoxides, peroxyacid, and other carbonyl compounds (Hanst and Gay, 1983). Nitrous acid vapor and butane in a smog chamber were irradiated with UV light. Major oxidation products identified included 2-butanone, acetaldehyde, and butanal. Minor products included peroxyacetyl nitrate, methyl nitrate, and unidentified compounds (Cox et al., 1981). 

Butane from natural gas is cheap and abundant in the United States, where it is used as an important feedstock for the synthesis of acetic acid. Since acetic acid is the most stable oxidation product from butane, the transformation is carried out at high butane conversions. In the industrial processes (Celanese, Hills), butane is oxidized by air in an acetic acid solution containing a cobalt catalyst (stearate, naphthenate) at 180-190 °C and 50-70 atm.361,557 The AcOH yield is about 40-45% for ca. 30% butane conversion. By-products include C02 and formic, propionic and succinic acids, which are vaporized. The other by-products are recycled for acetic acid synthesis. Light naphthas can be used instead of butane as acetic adic feedstock, and are oxidized under similar conditions in Europe where natural gas is less abundant (Distillers and BP processes). Acetic acid can also be obtained with much higher selectivity (95-97%) from the oxidation of acetaldehyde by air at 60 °C and atmospheric pressure in an acetic acid solution and in the presence of cobalt acetate.361,558... 

The TD-GC-MS chromatograms from the headspace organic vapours above PBO exposed to UV light and from a blank air sample are shown in Fig. 6.20-Two main components were seen in the sample chromatogram which were absent from the blank. They have been identified as n-butanal c. 14 minutes) and n-butanol (c. 18 minutes). The butanol presumably arises from cleavage of the side chain of PBO at the oxygen furthest from the ring. The hutanal is, presumably, an oxidation product of the butanol. The approximate concentrations and published odour thresholds (Devos et at., 1990) are shown in Table 6.2. Both compounds would therefore be expected to contribute to the odour. 

Typically, the feedstocks used for the industrial production of these products are olefins, aromatic compounds, or molecules that already contain oxygen. These starting materials have high value and constitute a large portion of the cost of production. The only process where a cheaper alternative is found is the production of maleic anhydride from w-butane. Light alkanes are highly abundant as they constitute the major fraction of the natural gas, cheap and currently, mainly used as a fuel. In addition, alkanes are more environmental friendly as they are less reactive and produce less partial oxidation products. The main obstacle for the wider application of alkanes in industry is the alkane difficult and selective activation and its extensive complete oxidation. Therefore, it is critical to find catalysts, which can activate the alkane in a selective manner at reasonable temperatures. 

Currently, almost all acetic acid produced commercially comes from acetaldehyde oxidation, methanol or methyl acetate carbonylation, or light hydrocarbon Hquid-phase oxidation. Comparatively small amounts are generated by butane Hquid-phase oxidation, direct ethanol oxidation, and synthesis gas. Large amounts of acetic acid are recycled industrially in the production of cellulose acetate, poly(vinyl alcohol), and aspirin and in a broad array of other... 

In 1953 the Celanese Corporation of America introduced a route for the production of vinyl acetate from light petroleum gases. This involved the oxidation of butane which yields such products as acetic acid and acetone. Two derivatives of these products are acetic anhydride and acetaldehyde, which then react together to give ethylidene diacetate (Figure 14.2.)... 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

Acetic Acid. Although at the time of this writing Monsanto s Rh-catalyzed methanol carbonylation (see Section 7.2.4) is the predominant process in the manufacture of acetic acid, providing about 95% of the world s production, some acetic acid is still produced by the air oxidation of n-butane or light naphtha. n-Butane is used mainly in the United States, whereas light naphtha fractions from petroleum refining are the main feedstock in Europe. 

The low cost of light alkanes and the fact that they are generally environmentally acceptable because of their low chemical reactivity have provided incentives to use them as feedstock for chemical production. A notable example of the successful use of alkane is the production of maleic anhydride by the selective oxidation of butane instead of benzene (7). However, except for this example, no other successful processes have been reported in recent years. A potential area for alkane utilization is the conversion to unsaturated hydrocarbons. Since the current chemical industry depends heavily on the use of unsaturated hydrocarbons as starting material, if alkanes can be dehydrogenated with high yields, they could become alternate feedstock. 

In the present work, therefore, a comparative study of the production of O-heterocycles during the cool-flame combustion of three consecutive n-alkanes—viz., n-butane, n-pentane, and n-hexane—was carried out under a wide range of reaction conditions in a static system. The importance of carbon chain length, mixture composition, pressure, temperature, and time of reaction was assessed. In addition, the optimum conditions for the formation of O-heterocycles and the maximum yields of these products were determined. The results are discussed in the light of currently accepted oxidation mechanisms. 

The abundance and low cost of light alkanes have generated in recent years considerable interest in their oxidative catalytic conversion to olefins, oxygenates and nitriles in the petroleum and petrochemical industries [1-4]. Rough estimates place the annual worth of products that have undergone a catalytic oxidation step at 20-40 billion worldwide [4]. Among these, the 14-electron selective oxidation of -butane to maleic anhydride (2,5-furandione) on vanadium-phosphorus-oxide (VPO) catalysts is one of the most fascinating and unique catalytic processes [4,5] ... 

The activation of light saturated hydrocarbons becomes increasingly more difficult as the molecules become smaller, with methane reactions being the most difficult to control. On the other hand, the occurrence of non-catalysed gas phase oxidation makes selectivity control very complicted. This is a problem common to almost all oxidations, unless one of the products is extremely stable examples are unsaturated nitriles (e.g. acrylonitrile in the ammoxidation of propane) or maleic anhydride (in the oxidation of butane). There is a parallel trend in the changes of reactivity with molecular weight in catalytic and non catalytic (gas phase) oxidation. The challenge to catalysis to achieve selective reactions at lower temperature is thus equally important for all light hydrocarbons. 

Acetaldehyde, together with many other oxygenated products, has been produced industrially by the vapor phase oxidation of paraffins such as butanes and propane/butane mixtures, or more generally from a light gasoline, according to a technology developed... 

A single plant operating in Texas, based on the noncatalytic controlled oxidation of propane-butane hydrocarbons, is reported to consume over 50 million gal annually of these light hydrocarbons together with large volumes of natural gas in the production of over 300 million lb of chemicals per year. Chemical products include formaldehyde purified to resin grade by means of ion-exchaiige resins, acetic acid, methanol, propanol, isobutanol, butanol, acetaldehyde, acetone, methyl ethyl ketone, mixtures of C4-C7 ketones, mixtures of C4-C7 alcohols, and propylene and butylene oxides. Catalytic liquid-phase oxidation of propane and butane is much more specific, and major yields of acetic acid are obtained. 

Higher and light (methane, ethane, propane, normal butane and isobutane) alkanes can be easily oxidized by this system at room temperature, at 0 °C and even at -22 °C if acetonitrile (or nitromethane) is used as a solvent. Turnover numbers of 3300 have been attained and the yield of oxygenated products is 46% based on the alkane. The oxidation initially affords the corresponding alkyl hydroperoxide as the predominant product, however this compound decomposes later to produce the corresponding ketones and alcohols (see Figure X.2 [15p,q]). 

Formic acid is produced mainly by carbonylation of methanol to methyl formate followed by hydrolysis of this ester to formic acid and methanol [route (d) in Topic 5.3.3]. The applied reaction sequence represents formally the hydrolysis of carbon monoxide to formic acid. Owing to the growing worldwide interest in converting CO2 into useful chemicals, the catalytic hydrogenation of CO2 to formic acid has been investigated intensively but no commercial processes has been realized yet. Formic acid is also obtained as one of the side products in the catalytic oxidation of butane and light naphtha to acetic acid (see Section 6.15 for details). 

The oxidation of butane or naphtha is also used for the commercial production of acetic acid. The relevant processes were developed in the 1950s and 1960s, when increasing refinery capadties led to attractive prices for light hydrocarbon cuts. Not all mixtures of hydrocarbons are good feedstock for this process. The desirable ratio of methyl to methylene groups is 1 1 and the alkene content must be very low. 

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