Isobutane oxygenation

Figure 14.1 Triangular scheme of composition isobutane/oxygen/inert, showing the flammability area for mixtures at room temperature, and the feed composition claimed by several industrial companies.

Fig. 12. The variation with time of peroxide yield during the cool-flame oxidation of isobutane. Initial temperature = 310 C isobutane introduced = 1.44 x 10 mole. 1 isobutane oxygen = 1 2 volume of reaction vessel = 500 cm. A fcrf-butyl hydroperoxide x 10 , hydrogen peroxide. (From ref. 132).

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.

Fig. 30. Phase diagram for the propagation of two cool flames during the oxidation of isobutane at 315 °C and 220 torr. Isobutane oxygen =1 2 volume of reaction vessel = 500 cm. (From ref. 193.)...

Fig. 36. Isobutane—oxygen. Molar ratio 1 2 spherical pyrex reaction vessel, volume 500 cm. (From ref. 134.)...

Preparation of ferf-butyl hydroperoxide. Of considerable interest is the possibility of s)m-thesizing ferf-butyl hydroperoxide by the vapour-phase oxidation of hydrocarbons with a tertiary carbon atom in the presence of hydrogen bromide. For example, at 160 °C, a mixture of isobutane, oxygen, and hydrogen bromide in a proportion of 10 10 1 gives f-butyl hydroperoxide with a yield of 75% ... 

These are effective high-octane gasoline additive oxygenates. The conversion of isobutane into isopropyl, methyl ketone, or isopentane into isobutyl, methyl ketone is illustrative. In this reaction, no branched carboxylic acids (Koch products) are formed. 

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Isobutane shows the usual NTC and cool flame phenomena (78,154,157,158). As the pressure is iacreased, the expected iacrease ia oxygenated products retaining the parent carbon skeleton is observed (96). Under similar conditions, isobutane oxidizes more slowly than / -butane (159). There are stUl important unresolved questions concerning isobutane VPO (160). 

Reactions of /l-Butane. The most important industrial reactions of / -butane are vapor-phase oxidation to form maleic anhydride (qv), thermal cracking to produce ethylene (qv), Hquid-phase oxidation to produce acetic acid (qv) and oxygenated by-products, and isomerization to form isobutane. 

The oxygen released is recycled to the isobutane oxidation step. GTBA contains some methanol and acetone coproducts and is used as a blending agent for gasoline. 

Catalytic testings have been performed using the same rig and a conventional fixed-bed placed in the inner volume of the tubular membrane. The catalyst for isobutane dehydrogenation [9] was a Pt-based solid and sweep gas was used as indicated in Fig. 2. For propane oxidative dehydrogenation a V-Mg-0 mixed oxide [10] was used and the membrane separates oxygen and propane (the hydrocarbon being introduced in the inner part of the reactor). 

Schubert, C.C., Pease, R.N. (1956) The oxidation of lower paraffin hydrocarbons. I. Room temperature reaction of methane, propane, n-butane and isobutane with ozonized oxygen. J. Am. Chem. Soc. 78, 2044—2048. 

What are the three commonly used chemical ionization reagent gases (methane, isobutane, water, ammonia, methanol, hydrogen, oxygen, nitrogen, etc.). 

Since the complete oxidation of two isomeric hydrocarbons will give the same number of moles of C02 and H20, using the same moles of oxygen, we can find their heats of combustain. For butane and isobutane, the values determined experimentally are ... 

The key factor is the action of the metal on the peroxo group making one oxygen atom electrophilic. Whether or not the metal is bonded to the alkene in the intermediate is not known if so, this will depend strongly on the particular substrate and the catalyst. Later, in the discussion of the dihydroxylation reaction we will come back to this (section 14.3.2). In the example shown in Figure 14.2 the second product is t-butanol stemming from t-butylhydroperoxide (industrially prepared from isobutane and dioxygen). 

In all cases steam is present as the main ballast. The role of steam is to decrease the concentration of isobutane and oxygen in the recycle loop and thus keep the reactant mixture outside the flammability region. Water can be easily separated from the other components of the effluent stream, and also plays a positive role in the catalytic performance of POMs. It is also possible that the presence of water favors the surface reconstruction of the Keggin stmcture, which decomposes during the reaction at high temperature, and also promotes desorption of methacrylic acid, saving it from unselective consecutive reactions. 

Key points that limit the industrialization of the process were recently illustrated by researchers from Sumitomo. Since the selectivity to methacryhc acid plus methacrolein typically decreases with temperature as the conversion increases, this implies that the rate of production of useful products increases only until the higher conversion compensates for the fall of selectivity. As a consequence of this, the maximum productivity value is reached at a specified temperature. For instance, when a selectivity of 45% is reached at 22% isobutane conversion, with a residence time of 5.4 s, a temperature of 370°C, and a feed containing 25% isobutane, 25% oxygen, and 15% steam, a productivity equal to 0.72 mmol/h/gcat is obtained, which is one order of magnitude lower than the one needed to make the process industrially viable. However, the productivity is limited by the oxygen conversion, the maximum concentration of which is dictated by the flammability limits (see Figure 14.1), and by temperature, since the POM decomposes above 380°C. 

Possible solutions to overcome this problem are (1) decrease the residence time the decrease of conversion is more than compensated by an increase of selectivity (due to the lower extent of methacrylic acid combustion), and in overall the productivity increases (2) increase the total pressure, while simultaneously increasing both the oxygen and the isobutane partial pressure, as well as the total gas flow (so as to keep a constant contact time in the reactor). A higher pressure also implies smaller reactor volume, and hence lower investment costs. Under these circumstances, productivity as high as 6.4 mmol/h/gcat was reached, which is acceptable for industrial production. The additional heat required for the recirculation of unconverted isobutane and for increased pressure would be equalized by the higher heat generated by the reaction. 

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." ... 

POM composed of (NH4)3PMoi204o data were collected at a reaction temperature of 380°C, with an isobutane-rich feedstock (26 mol % isobutane, 13% oxygen, 12% steam, remainder helium), and a residence time of 3.6 s. At the very beginning of its lifetime, the fresh POM was completely unselective and inactive. After approximately 100 hours reaction time, it was 6.5% converted, with a selectivity to methacrylic acid of 42% and to methacrolein of 13%. The main by-product was carbon dioxide. Therefore, the equilibration time was necessary for the generation of the active and selective sites. 

The catalytic performance depends a great deal on the reaction conditions, and specifically on the isobutane-to-oxygen ratio in the feed. Usually isobutane-rich conditions are claimed to be more selective, and the reason for this is that under these conditions the operative POM is a partially reduced one, and a more reduced POM is intrinsically more selective than a fully oxidized one. High isobutane partial pressures help to improve the selectivity, avoiding further oxidation of methacrylic acid. 

NG is found to consist mainly of the lightweight alkanes, with varying quantities of carbon dioxide, carbon monoxide, hydrogen, nitrogen and oxygen, in some cases also hydrogen sulfide and possibly ammonia. A typical sample of NG when it is collected at its source contains 80% methane (CH ), 7% ethane (C Hj), 6% propane (CjHj), 4% butane and isobutane (C Hj ), and 3% pentane (CgHj ). 

Butane isomerization is usually carried out to have a source of isobutane which is often reacted with C3-C5 olefins to produce alkylate, a high octane blending gasoline [13]. An additional use for isobutane was to feed dehydrogenation units to make isobutene for methyl tert-butyl ether (MTBE) production, but since the phaseout of MTBE as an oxygenate additive for gasoline, this process has decHned in importance. Zeolitic catalysts have not yet been used industriaUy for this transformation though they have been heavily studied (Table 12.1). 

The second manufacturing method for propylene oxide is via peroxidation of propylene, called the Halcon process after the company that invented it. Oxygen is first used to oxidize isobutane to r-butyl hydroperoxide (BHP) over a molybdenum naphthenate catalyst at 90°C and 450 psi. This oxidation occurs at the preferred tertiary carbon because a tertiary alkyl radical intermediate can be formed easily. 

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