Oxidation of Butenes

The mixture of n-hutenes (1- and 2-hutenes) could he oxidized to different products depending on the reaction conditions and the catalyst. The three commercially important oxidation products are acetic acid, maleic anhydride, and methyl ethyl ketone. 

Due to the presence of a terminal double bond in 1-butene, oxidation of this isomer via a chlorohydrination route is similar to that used for propylene. 

Currently, the major route for obtaining acetic acid (ethanoic acid) is the carbonylation of methanol (Chapter 5). It may also be produced by the catalyzed oxidation of n-butane (Chapter 6). 

The production of acetic acid from n-butene mixture is a vapor-phase catalytic process. The oxidation reaction occurs at approximately 270°C over a titanium vanadate catalyst. A 70% acetic acid yield has been reported. The major by-products are carbon oxides (25%) and maleic anhydride (3%)  

Acetic acid may also be produced by reacting a mixture of n-butenes with acetic acid over an ion exchange resin. The formed sec-butyl acetate is then oxidized to yield three moles of acetic acid  

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Another attractive commercial route to MEK is via direct oxidation of / -butenes (34—39) in a reaction analogous to the Wacker-Hoechst process for acetaldehyde production via ethylene oxidation. In the Wacker-Hoechst process the oxidation of olefins is conducted in an aqueous solution containing palladium and copper chlorides. However, unlike acetaldehyde production, / -butene oxidation has not proved commercially successflil because chlorinated butanones and butyraldehyde by-products form which both reduce yields and compHcate product purification, and also because titanium-lined equipment is required to withstand chloride corrosion. 

With the development of techniques for preparing and isolating acyclic allylic hydroperoxides, an attempt was made to examine the behavior of butene hydroperoxide and determine which secondary products arise from it during the oxidation of butenes. Butenes were of particular interest since indirect evidence had already indicated that none of the readily identified products can be ascribed unequivocally to a hydroperoxide source (4). 

It is clear that the aldehydes produced in the oxidation of butenes arise from addition reactions as already assumed by several workers (4, 16, 17). Nothing in the present work indicates whether the aldehydeforming addition product is a peroxy alkyl (17), (Reaction 2) or an alkoxy alkyl (16) radical (Reaction 3) as has been postulated, or both. 

The possibilities for selective oxidation of butenes present a complex picture because of the various ways of introducing oxygen into the molecule and the possibilities of dehydrogenation and isomerization. Finally, there are catalysts with a capacity for producing dimerization and aro-matization. 

Economically, the oxidation of butenes is of importance mainly for the production of butadiene and maleic acid anhydride. 

Abd. El-Salaam et al. [1] have studied the catalytic activity of various bismuth molybdates for the oxidative dehydrogenation of 2,5-dihydro-furan to furan. A close correlation with the oxidation of butene to butadiene is expected and was indeed observed. 

Reaction order in olefin for oxidation of butene isomers... 

Ai and Suzuki [5,9] investigated the combination V2Os—P2Os. The acidity was measured indirectly by the activity for dehydration of isopropanol and was shown to decrease with increasing P2Os content. The activity for the oxidation of butene-1 and butadiene to maleic acid anhydride decreased accordingly. It was shown that the adsorption equilibrium constant of the olefin on the catalyst also decreased in the same way. 

In general, the oxidation of butene can be schematically represented as two interconnecting parallel pathways (Scheme 2). Path I is the selective oxidation reaction. Path II is the combustion reaction. The relative rates of the two... 

The dependence of the selectivity on the conversion at low conversions has been investigated by varying the amount of catalysts used and the flow rate of the feed. For conversions below 10%, the selectivity is slightly higher at lower conversion, although the difference is only a few percent. The areal rate (rate per unit surface area of iron oxide) of butene oxidation is slightly higher... 

It has been reported that Mo-P oxides show a good performance in oxidation of butenes to maleic anhydride [26]. On the other hand, Bordes et al. [27] have reported that U-Mo oxides with Mo-rich compositions are effective as catalysts for oxidation of butenes to maleic anhydride. These findings suggest that the functions required for oxidation of toluene are similar to those required for oxidation of butenes to maleic anhydride. However, the V-P oxides are not effective for toluene oxidation. Possibly, the consecutive oxidation of benzaldehyde cannot be suppressed with V Og-containing catalysts. Even over the Mo-P and U-Mo oxides, benzaldehyde is degraded, to a certain extent. 

Annenkova et al. (105) studied both the physicochemical and catalytic properties of the Bi-Fe-Mo oxide system. The X-ray diffraction, infrared spectroscopic, and thermographic measurements indicated that the catalysts were heterogeneous mixtures consisting principally of ferric molybdate, a-bismuth molybdate, and minor amounts of bismuth ferrite and molybdenum trioxide. The Bi-Fe-Mo oxide catalysts were more active in the oxidation of butene to butadiene and carbon dioxide than the bismuth molybdate catalysts. The addition of ferric oxide to bismuth molybdate was also found to increase the electrical conductivity of the catalyst. 

The creation of selective catalysts for such complex reactions seems to be an especially difficult problem. Nevertheless, surprisingly, selective catalysts have been developed for complex reactions, which can be exemplified by the oxidation and ammoxidation of propylene, oxidation of butene and even butane to maleic anhydride (which requires seven oxygen atoms). Such reactions are usually performed over V and Mo oxide systems [4, 6, 8-10]. High selectivity of these systems is presumably provided by a special structure of the catalyst surface that allows control... 

The major conventional processes for the production of acetic acid include the carbonylation of methanol (originally developed by Monsanto, and now carried out by several companies, such as Celanese-ACID OPTIMIZATION, BP-CATIVA, etc.), the liquid-phase oxidation of acetaldehyde, still carried out by a few companies, and the liquid-phase oxidation of n-butane and naphtha. More recent developments include the gas-phase oxidation of ethylene, developed by Showa Denko K.K., and the liquid-phase oxidation of butenes, developed by Wacker [2a],... 

Despite the enormous importance of zeolites (molecular sieves) as catalysts in the petrochemical industry, few studies have been made of the use of zeolites exchanged with transition metal ions in oxidation reactions.6338- 634a-f van Sickle and Prest635 observed large increases in the rates of oxidation of butenes and cyclopentene in the liquid phase at 70°C catalyzed by cobalt-exchanged zeolites. However, the reactions were rather nonselective and led to substantial amounts of nonvolatile and sieve-bound products. Nevertheless, the use of transition metal-exchanged zeolites in oxidation reactions warrants further investigation. 

VO)2P207 is superior for the selective dehydrogenation of n-butane to butene to other crystalline V-P oxides, while few differences exist between the oxidation of butene and butadiene, which are considered reaction intermediates. The abstraction of methylene hydrogen from n-butane is the slowest step. Hence this step determines the overall catalytic activity." 2) Selectivity in forming anhydride from C4 and C5 alkanes, but not in selective oxidation of lower (C2 and C3) or higher (Ce-Cg) alkanes." 3) The number of surface layers involving the catalytic reactions is limited to 2-3 in contrast to Bi-Mo-O catalysts. 

The intermediates in Table 1 (with the exception of 2,5-dihydrofuran and Y-butyrolactone) have been observed in the oxidation of butenes and butadiene to maleic anhydride on the VPO catalysts [10]. 

Table 1.20 lists Arrhenius parameters for a number of secondary initiators. When acting as a secondary initiator in an autocatalytic reaction, the time to maximum rate is comparable with the half-life of the initiator. Thus the half-life of H2O2 at 60Torr (mostly N2 and O2) and 753 K is about 60 sec, consistent with the induction period shown in the oxidation of butene-2 (see later). The half-life of alkyl peroxides is much shorter, but in the high pressure rapid combustion observed in gasoline engines this rate of initiation is too slow and only radical branching is sufficiently fast to explain the observed phenomena. The formation of dihydroperoxide... 

Major yields of propene (ca. 10%) are found in the initial products from isobutene oxidation between 673 and 773 K, but effectively no propene is observed initially from the oxidations of butene-1, 2-methylbutene-2 and 2,3-dimethylbutene-2. Structurally, propene formation is possible via C3H7 radicals in all cases through the hydroxy adduct. 

Kochi s study of the copper salt-catalyzed oxidation of butenes by peresters (17) is interesting because the role of a ligand in controlling stereoselectivity was clearly demonstrated. This reaction, which involves the oxidation of allylic radicals by cupric ion, results in the formation of high yields of allylic ester in which the double bond is terminal, and it is described as occurring within a metal complex. When phenanthroline... 

The oxidation of butenes by mercuric acetate (40), involving a butenylmercury intermediate, exhibits a high degree of stereoselectivity. Apparently such stereoselectivities are a unique feature of reactions involving allylmetal intermediates. 

The lower activation energy for the reduction of tin-antimony oxides with hydrogen as compared with that for the pure oxides has been confirmed by Saia and Trifiro (47), and, contrary to other studies, the activity reported to vary with calcination temperature. Some studies (50-52) have reported an increase in activity and selectivity for the oxidation of butene with increasing antimony content and to be maximized at an antimony concentration of about 20% (50). Saia and Trifiro also reported that materials calcined at 900°C showed peaks in activity for butadiene formation at antimony to tin ratios of 0.20 and 0.90 and that selectivity to butadiene increased with antimony content to 80% for the catalyst with a ratio of 0.40. 

In cases where the oxidation state of the solid changes during the reaction, the active solid state phase present at steady state must be characterized. For example, the reduced vanadium phosphate phase forms during the oxidation of butene to maleic anhydride (28,29). And for supported catalysts such as V Oc-/TiO anatase. 

Ti02) is effective in this reaction, giving substantial yields of maleic anhydride (Figure 10) The butadiene formed does not desorb and reacts at the surface of the catalyst according to the known mechanism for the oxidation of butene to maleic anhydride The notion of interfacial effects has therefore been applied, with some success, to finding a new catalyst ... 

The production of 1,3-butadiene needs catalysts that cannot adsorb butadiene strongly. Actually, this occurs on Mg ferrite and distinguishes the behavior of this material from that of vanadia-based catalysts, that allow the oxidation of butenes to maleic anhydride and actually adsorb butadiene strongly [12]. Our data suggest that the predominant pathway to total oxidation is competitive with respect to the key alkoxide elemination step, more than successive to it, over MgFe204. 

Maleic anhydride can also be made by the air oxidation of butenes. Maleic anhydride is used in the preparation of unsaturated polyester resins. It can also be reduced to buty-rolactone and to 1,4-butanediol. It also offers a possible synthesis of phthalic anhydride by a Diels-Alder reaction with 1,3-butadiene (12.9). 

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