Oxygen propane oxidation

Propane. The VPO of propane [74-98-6] is the classic case (66,89,131—137). The low temperature oxidation (beginning at ca 300°C) readily produces oxygenated products. A prominent NTC region is encountered on raising the temperature (see Fig. 4) and cool flames and oscillations are extensively reported as compHcated functions of composition, pressure, and temperature (see Fig. 6) (96,128,138—140). There can be a marked induction period. Product distributions for propane oxidation are given in Table 1. 

The noncatalytic oxidation of propane in the vapor phase is nonselec-tive and produces a mixture of oxygenated products. Oxidation at temperatures below 400°C produces a mixture of aldehydes (acetaldehyde and formaldehyde) and alcohols (methyl and ethyl alcohols). At higher temperatures, propylene and ethylene are obtained in addition to hydrogen peroxide. Due to the nonselectivity of this reaction, separation of the products is complex, and the process is not industrially attractive. 

Steffan RJ, K McClay, S Vainberg, CW Condee, D Zhang (1997) Biodegradation of the gasoline oxygenates methyl ferf-butyl ether, ethyl ferf-butyl ether, and amyl tcrt-butyl ether by propane-oxidizing bacteria. Appl Environ Microbiol 63 4216-4222. 

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). 

The role of adsorbed oxygen species in the mechanism of alkane transformation, on the contrary, is more questionable. The effect induced by the substitution of O2 with N2O and IR indications are in agreement with this interpretation, but, on the other hand, activated electrophilic oxygen species form on reduced sites, preferably in tetrahedral coordination (79). The partial reduction of tetrahedral V =0 with formation of tetrahedral v after propane oxidative dehydrogenation can be observed using UV-Visible diffuse reflectance, ESR and V-NMR spectroscopies. It is thus not possible to assign unequivocally the active species in propane selective activation to a tetrahedral V =0 species or to or V -0-0 species formed in the... 

A chemical equation for the combustion of propane, C3H8, is shown in exercise 67. Through this reaction are the oxygen atoms oxidized or reduced ... 

Harris and Egerton (25) reported that formaldehyde added to a 1 to 1 mixture of oxygen and propane at 300° to 340° C. increased the induction period. Satterfield and Wilson (51) ascribe formaldehyde formation in propane oxidation above 370° C. to CH3 + 02 — CH20 -f OH. 

In order to clarify the resistivity characteristics of the specimens, we obtained the relationship between an equilibrium oxygen partial pressure and the oxygen excess ratio from both theoretical calculations and measurements using the oxygen sensor. The complete propane oxidation can be described by the following reaction. 

Fig. 8.6 Calibration plot of oxygenate sensor-1 for total oxygenate compounds produced by catalytic propane oxidation the yield of each oxygenate was determined with a conventional FID gas chromatograph (reproduced by permission of Elsevier from [19]).

Fig. 8.7 shows the product distributions determined by (a) a gas sensor system and (b) gas chromatography for propane oxidation over alkali Fe Si02 (=1 0.05 100). Since little alcohol was produced, there was no large difference between the signals from oxygenate sensors 1 and 2. When we compared the oxyge-... 

Figure 6.14 Synchrotron based valence band spectra (hv = ISOeV) of clean reference binary oxides (A) and catalytic materials under reaction conditions (B). The reference oxides were recorded at elevated temperature (623-673 K) in 0.2-1 mbar oxygen to remove carbon contamination and minimize reduction. The Ml catalysts (1 Ml l, 2 Ml 2) are under propane oxidation conditions with addition of steam to the feed. 3 M050,4-type MoVW-...

Recently we found that highly redueed H3PMol2O40 which was formed by the heat-treatment of pyridinium salt can catalyze the propane oxidation to acrylic acid and acetic acid selectively [24, 25]. After activation in N2 flow at 420°C for 2hr, the catalyst of HsPMo 12040 (Py) shows reduced state of molybdenum and a new stable structure in which pyridine remains as the linkage of the secondary structure. The activated H3PMoi2O40 (Py) also gives catalytic activities in the partial oxidations of ethane and isobutane to acetic acid and methacrylic acid respectively. In this paper, we will report the oxidation results of C2-C4 alkanes and discuss the roles of reduced state and aetivation of molecular oxygen over this catalyst. 

Figure 3. Effects of 02 partial pressure on the propane oxidation over reduced H3PMol2O40(Py) at340°C. Symbols and reaction conditions except oxygen partial pressure are the same as those in Figure 2.

Fig. 1. Maximum pressure jump d(Ap)/dt (reaction rate) during homogeneous propane oxidation vs. temperature (Vedeneev et al., 1997a, b). (1) experimental (2) calculated. Reaction conditions initial pressure P0 = 200Torr propane-to-oxygen ratio = 23.

However, there are also very important limitations. As we mentioned above, even in oxidation of methane and ethane many elementary reactions are not accessible for direct and detailed investigation. When we shift from ethane to propane, not only the number of carbon atoms in the molecule increases, but also the complexity of the reaction network. In particular, one may assume that even in propane oxidation the formation of complex oxygenate intermediates, including bi-radicals and complex peroxides, may take place. Although such compounds can play a principal role in kinetically relevant steps (such as chain-branching), up to now our knowledge about such compounds is negligible. 

Thus, a preliminary analysis of olefin production pathways can be performed based on the methane-to-ethylene ratio and on temperature dependence of the (C3 = )-to-(C2 =) ratio. A more detailed elaboration can be reached from experiments with varied oxygen concentration and from the detailed analysis of the product distribution (including hydrogen formation). However, ethylene formation itself is strong evidence for the contribution of the radical route in product formation. The analysis of experimental data about product distribution during propane oxidation (Kondratenko et al, 2005) demonstrates that over rare-earth oxide catalysts radical route is prevailing in olefin formation. On the other hand, over supported Y-containing catalysts, propylene... 

The oxidation of propane to propan-l-ol by Rhodococcus rhodochrous may formally involve a reaction comparable to that for the eukaryotic oxidation of 2-nitropropane (Section 4.4.3) since one molecule of oxygen is incorporated into 2 mol of propane (Babu and Brown 1984). Details of the latter reaction suggest, however, a different mechanism for the propane oxidation. 

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