Paraffins, oxidation

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 product secondary alcohols from paraffin oxidation are converted to ethylene oxide adducts (alcohol ethoxylates) which are marketed by Japan Catalytic Chemical and BP Chemicals as SOFTANOL secondary alcohol ethoxylates. Union Carbide Chemical markets ethoxylated derivatives of the materials ia the United States under the TERGlTOL trademark (23). 

The byproduct is a stoichiometric amount of 60 wt % H2S04, which is used in the chemical industry. The wastewater (0.3 m3/100 kg active matter), which contains paraffin, oxidation products of the paraffin, alkanesulfonate, and sulfur dioxide, has a chemical oxygen demand (COD) of 1800 mg/L and is readily biodegradable (>95% after 7 days). The sulfur dioxide emission after repeated washing of the off-gas amounts to 0.5 g/100 kg active matter [6]. 

H02C(CH2) C02H it was found that beyond a certain point the increment in the rate coefficient for an increases of one in n is constant at 5.2 x 10 l.mole . sec which compares with a value of 5.73 x 10 1.mole . sec for n-paraffin oxidation (p. 293). It is clear that carboxylic acids behave as paraffins except that a slight retardation due to the inductive effect of -CO2H is apparent. Permanganate behaves in much the same way and some examples of carboxylic acid oxidation have been cited in the section on hydrocarbons. 

Secondary alcohols, produced previously in small quantities from linear paraffin oxidation, have today almost disappeared from the market. The difficulties in producing the corresponding derivatives (ethoxylates, etc.) were a major drawback for their potential development. 

Beginning in the fifties, acetic acid was predominantly obtained from paraffin oxidation, especially n-butane W. Acetic acid s chemical history has been rich and varied. 

The yield of alcohol from normal paraffin oxidation may be improved to a commercially useful level by oxidizing in the presence of boric acid. 

Fig. 63. Stability of transition-metal-substituted polyoxometalatc for oxo transfer to hydrocarbons. Values on the ordinate indicate numbers of turnovers for paraffin oxidation. shows the ranges of the numbers of turnovers. (From Ref. 320b.)...

The paraffin oxidation by immobilized Por and Pc complexes is strongly influenced by the polarity of the support. This has been studied in detail for the oxidation of cyclohexane with f-BuOOH by immobilized phthalocyanines. Thus, adsorption of the polar reaction products cyclohexanol and r-butyl alcohol competes with sorption of the cyclohexane reagent, particularly when a polar support such as a zeolite Y is used (124,134). Consequently, the activity decreases rapidly, and it can be restored only by extensive solvent extraction. In contrast, FePc on the apolar support carbon black is much less sensitive to this type of deactivation (121). 

Many catalytic reactions form a range of products rather than only a single one. In most such cases, the pathway to a co-product branches off from that to the main product after the first or a few early steps. The network then consists of cycles that have a step or pathway segment in common. Typical examples are the formation of isomeric products in paraffin oxidation and olefin hydration, hydrohalogenation, hydroformylation, and hydrocyanation, as well as paraffin by-product formation in hydroformylation. 

Even though methanol carbonylation is the favored process for new acetic acid capacity today, existing paraffin oxidation plants remain quite competitive where coproducts can be marketed successfully [2, 3]. Over half the original capacity of acetic acid plants based on paraffin oxidation remains in use today. In North America, Hoechst Celanese operates two facilities using the butane oxidation process to make acetic acid. The reported 1994 capacity at Pampa, Texas, is 250000 metric tons/year, while that at monton, Alberta, is 75 000 metric tons/year [4]. There are two plants believed to be using the naphtha oxidation process to make acetic acid BP Chemicals in Hull, England, with a capacity of 210000 metric tons/year [5] and a state complex in Armenia (in the former USSR) with a capacity reported to be 35 000 metric tons/year [6]. 

The significant reductions in acetic acid capacity based on paraffin oxidation that have occurred include those at (1) the butane oxidation plant operated by Union Carbide at Brownsville, Texas, (2) butane oxidation processes in the Netherlands and Germany, and (3) a Russian naphtha oxidation plant. 

Catalysts are not absolutely essential in paraffin oxidations but their use can have significant advantages such as shifting of the relative magnitude of the various steps of uncatalyzed reactions. Perhaps it should be noted in passing that commercial oxidations conducted in metal equipment always have some adventitious corrosion ions present, so the term an uncatalyzed reaction implies only that no catalyst was deliberately added. 

Primary and secondary alcohols appear to oxidize rapidly to the corresponding carbonyl compounds with good efficiencies [10]. The initial point of attack is predominantly on the hydrogen on the carbinol carbon atom. Tertiary alcohols do not have a hydrogen in this position and are relatively resistant to oxidation. Alcohols, like aldehydes, are usually important intermediates in paraffin oxidations [18]. They undergo subsequent oxidation somewhat less readily than aldehydes, but primary and secondary alcohols oxidize much faster than the starting paraffin(s). Quite unlike aldehydes, however, alcohols do not, in general, autoxidize readily by themselves. Moreover, the deliberate addition of alcohol to an oxidation can slow or even stop the reaction [10, 19-21]. 

Aldehydes and ketones are the major immediate precursors of acetic acid in paraffin oxidation. The reported mechanisms for the oxidations of these intermediates are somewhat involved and are not of primary concern for the present purpose. A point of interest, however, is that acylperoxy radicals, intermediates in aldehyde oxidations, are much stronger hydrogen abstractors than alkylperoxy radicals [8]. Aldehyde oxidations have been more extensively covered elsewhere [10, 18, 39, 41-43]. Acetic acid is quite resistant to further oxidation [10] and tends to be a terminal product. 

Probably because of the rate problem, the very active and highly specific copper-ion reactions apparently have not yet found useful application in paraffin oxidation processes. This further illustrates the requirement that a viable catalyst... 

Although there have been contradictory reports about the effect of water on paraffin oxidations [98, 99], there is some evidence that, above some low concentration, water can have a strong inhibiting effect [99]. This may be related to the gem-dioh ... 

The gcw-diol product would, on oxidation, produce dihydroxyalkylperoxy radicals, analogous to eq. (10) with alcohols. Such peroxy radicals decompose to produce HOO radicals [100], perhaps by a mechanism analogous to eq. (15). Aldehydes are important intermediates in most paraffin oxidations. The diversion of even a small fraction of the aldehydes into an inhibitor-producing reaction could account for the reported effect. 

Acetic acid, as noted above, is rather resistant toward oxidation in a paraffin oxidation process. It is not, however, completely inert it can be attacked by the higher valence states of catalyst ions and by the free radicals in solution. In the case of Co , an acetoxy radical is produced (eq. (34)) ... 

Properties which are specific for the compounds examined, and which make them rather unique for some peculiar reactions of paraffin oxidation are ... 

The unique possibility of tuning the redox properties (and the acidic properties as well) of heteropolycompounds by chancing the composition of the anion, or by modifying the cationic composition. Changes in composition have dramatic effects in the nature of the products obtained in paraffin oxidation, i.e. oxygenated compounds vs. olefins. 

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