Isobutene, isobutane oxidation

This activation feature identifies one class of selective oxidation catalyst namely, those that activate the substrate through rupture of the weakest C-H bond. The performance of these selective oxidation catalysts is best presented in terms of selectivity-conversion plots. Using this approach, multiple selectivity-conversion plots can be generated, such as that shown in Figure 1 for isobutene and isobutane oxidation to methacrolein.12 These plots are intended to illustrate that there exists in relation to each selective oxidation reaction an upper performance limit beyond which experimental studies have not yet progressed. 

Figure 1 Multiple selectivity-conversion plots for (A) isobutene and (B) isobutane oxidation to methacrolein12...

The former starts with propylene, and the latter with isobutane or isobutene, whose oxidation by nitrogen oxides and nitric add in x-hydroxybutyric add, an intermediate of methacrylic add production, has already led to industrial developments (Nissan) and construction (Escambia), now abandoned. 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

Fig. 3. FT-IR spectra of the adsorbed species arising from the interaction of (a) rerr-butanol and (b) isobutane over a combustion catalyst (MgCr204) at 423 K, and from rerr-butanol (373 K, c), isobutene (300 K, d) and isobutane (380 K, e) on a selective oxidation catalyst.

Figure 14.3 Different strategies for integration of isobutane (oxi)dehydrogenation to isobutene and isobutene oxidation to methacrolein and to methacrylic acid.

In the second scheme, the alkane is transformed to the olefin by oxidehydro-genation, and the outlet stream is sent to the second oxidation reactor without any intermediate separation." Isobutane and isobutene are recycled, together with oxygen, nitrogen, and carbon oxides. Finally, the third scheme differs from the first one in that hydrogen is separated from propane/propylene after the dehydrogenation step, and oxygen is preferably used instead of air in the oxidation reactor." ... 

The reaction network for isobutane selective oxidation catalyzed by POMs consists of parallel reactions for the formation of methacrolein, methacrylic acid, carbon monoxide, and carbon dioxide. Consecutive reactions occur on methacrolein, which is transformed to acetic acid, methacrylic acid, and carbon oxides. ° Methacrylic acid undergoes consecutive reactions of combustion to carbon oxides and acetic acid, but only under conditions of high isobutane conversion. Isobutene is believed to be an intermediate of isobutane transformation to methacrylic acid, but it can be isolated as a reaction product only for very low alkane conversion. ... 

Indenopyrene, see Indeno[l,2,3-crf pyrene l//-Indole, see Indole Indolene, see Indoline Inexit, see Lindane Inhibisol, see 1,1,1-Trichloroethane Insecticide 497, see Dieldrin Insecticide 4049, see Malathion Insectophene, see a-Endosulfan, p-Endosulfan Intox 8, see Chlordane Inverton 245, see 2,4,5-T lodomethane, see Methyl iodide IP, see Indeno[l,2,3-crf pyrene IP3, see Isoamyl alcohol Ipaner, see 2,4-D IPE, see Isopropyl ether IPH, see Phenol Ipersan, see Trifluralin Iphanon, see Camphor Isceon 11, see Trichlorofluoromethane Isceon 122, see Dichlorodifluoromethane Iscobrome, see Methyl bromide Iscobrome D, see Ethylene dibromide Isoacetophorone, see Isophorone a-Isoamylene, see 3-Methyl-l-butene Isoamyl ethanoate, see Isoamyl acetate Isoamylhydride, see 2-Methylbutane Isoamylol, see Isoamyl alcohol Isobac, see 2,4-Dichlorophenol Isobenzofuran-l,3-dione, see Phthalic anhydride 1,3-Isobenzofurandione, see Phthalic anhydride IsoBuAc, see Isobutyl acetate IsoBuBz, see Isobutylbenzene Isobutane, see 2-Methylpropane Isobutanol, see Isobutyl alcohol Isobutene, see 2-Methylpropene Isobutenyl methyl ketone, see Mesityl oxide Isobutyl carbinol, see Isoamyl alcohol Isobutylene, see 2-Methylpropene Isobutylethylene, see 4-Methyl-l-pentene Isobutyl ketone, see Diisobutyl ketone Isobutyl methyl ketone, see 4-Methyl-2-pentanone Isobutyltrimethylmethane, see 2,2,4-Trimethylpentane Isocumene, see Propylbenzene Isocyanatomethane, see Methyl isocyanate Isocyanic acid, methyl ester, see Methyl isocyanate Isocyanic acid, methylphenylene ester, see 2,4-Toluene-diisocyanate... 

Isobutene is present in refinery streams. Especially C4 fractions from catalytic cracking are used. Such streams consist mainly of n-butenes, isobutene and butadiene, and generally the butadiene is first removed by extraction. For the purpose of MTBE manufacture the amount of C4 (and C3) olefins in catalytic cracking can be enhanced by adding a few percent of the shape-selective, medium-pore zeolite ZSM-5 to the FCC catalyst (see Fig. 2.23), which is based on zeolite Y (large pore). Two routes lead from n-butane to isobutene (see Fig. 2.24) the isomerization/dehydrogenation pathway (upper route) is industrially practised. Finally, isobutene is also industrially obtained by dehydration of f-butyl alcohol, formed in the Halcon process (isobutane/propene to f-butyl alcohol/ propene oxide). The latter process has been mentioned as an alternative for the SMPO process (see Section 2.7). 

As the fuel consumption increased, the alkene concentration eventually reached a kinetically controlled stationary value [43]. Since the major product at all stages in the oxidation of isobutene is acetone [42] (Fig, 4), it was possible to follow the consumption of isobutene during the oxidation of isobutane by observing the formation of acetone. It can be seen from Fig. 5 that a marked increase in the yield of acetone in the later... 

Large yields of isobutene were also found during the induction period of the oxidation of isobutane, and Zeelenberg and Bickel [53] also concluded that its mode of formation was by reactions (5) and (2). In contrast to Knox, however, they suggested that the intermediate oxygenated products are formed from homogeneous isomerization and decomposition reactions of alkylperoxy radicals. 

More recent studies by Irvine and Knox [50] on the competitive oxidation of isobutane with ethane and propane at 300 °C have also led them to conclude that at low rates of reaction of isobutane a heterogeneous component leading to isobutene does indeed occur in parallel, but independently of the homogeneous reaction under most experimental conditions used in slow oxidation studies. They have suggested, however, in agreement with Semenov, that the reaction responsible probably involves the direct reaction of oxygen with isobutane adsorbed on the surface of the reactor (see p. 263), viz. 

Baldwin and Walker [99] have pointed out that, from kinetic considerations, surface reactions of alkylperoxy radicals cannot play a significant role except at very low overall rates of reaction and conclude that it is more likely that surface destruction of relatively stable intermediates such as the alkyl hydroperoxides or hydrogen peroxide are the main cause of surface effects in hydrocarbon oxidation. Luckett and Pollard [68, 134] have provided evidence, which suggests that the surface destruction of tert-butylhydroperoxide is indeed important during the oxidation of isobutane below ca. 320 °C. Since isobutene and acetone are known products of the decomposition of tert-butylhydroperoxide, it is clear that many of the foregoing results can be explained in these terms, but if this is the predominant heterogeneous reaction the yield of acetone would be... 

Fig. 25. The variation with initial pressure of the initial percentage yield of products from the oxidation of isobutane at 310 °C. Isobutane oxygen = 1 2 volume of reaction vessel = 500 cm. isobutene , acetaldehyde O, propionaldehyde propene t>, fcrf-butyl hydroperoxide , isobutene oxide o, acetone.

The results of pyrolysis of polypropylene in air depends on the pyrolysis heating rate because the pyrolysis process competes with the oxidation [108], By heating between 120° C and 280° C in air, polypropylene is reported to generate ethene, ethane, propene, propane, isobutene, butane, isobutane, pentadiene, 2-methyl-1-pentene, 2,4-dimethyl-1-pentene, 5-methyl-1-heptene, dimethylbenzene, methanol, ethanol, 2-methyl-2-propene-1-ol, 2-methylfuran, 2,5-dimethylfuran, formaldehyde, acetaldehyde, acrolein, propanal, methacrolein, 2-methylpropanal, butanal, 2-vinylcrotonaldehyde, 3-methylpentanal, 3-methylhexanal, octanal, nonanal, decanal, ethenone, acetone, 3-buten-2-one, 2-butanone, 1-hydroxy-2-propanone, 1-cyclopropylethanone, 3-methyl-2-buten-2-one, 3-penten-2-one, 2-pentanone, 2,3-butanedione [109]. 

The r-butyl alcohol, co-product produced at the rate of 15 t/t<3) of propylene oxide, depending on whether or not a market is available, is utilized as such or dehydrated to isobutene (200°C, atmospheric pressure, titanium oxide base catalyst). If the isobutene is itself unusable, it can be hydrogenated to isobutane, which is recycled. The good antiknock properties of r-butyl alcohol currently mak/ it a highly popular additive for automotive gasolines. In addition, certain recent processes (Mitsubishi Rayon, Nippon Shokubal Oxirane) can be used to convert the r-butyl alcohol to metbacrylic acid (see Section 11.2.3.2). 

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