Propane oxidation, general

Nevertheless, there is a possibility to solve restricted tasks using approaches described above. In particular, the utility principle (see Section II.C) can be fruitfully utilized. For instance, such an approach was utilized by Vedeneev et al. (1997a, b) to describe the NTC behavior in propane oxidation. Generally speaking, if we are interested in the optimization of some particular product yield, we can select a block of reactions in which it is formed and further transformed and analyze it taking into account qualitative or even semi-quantitative notions about the reaction environment. 

In every case, large particles of metal are more active in oxidation than the smallest ones. CO oxidation is moderately structure-sensitive (less than one order of magnitude between metal foil and much dispersed catalysts). By contrast, propane oxidation (and in general oxidation of small alkanes) are strongly stmcture-sensitive (two orders of magnitude between large and small particles). Rate equations were also expressed as... 

Jibril, B.Y. Propane oxidative dehydrogenation over chromium oxide-based catalysts. Appl. Catal. A General 2004, 264, 193-202. 

Propane oxidation experiments were generally carried out with 0.5g catalyst at atmospheric pressure, in the tenq)erature range 400-500°C, at a space velocity of 60 ml.min gcat. The gas feed composition was 10% C3H8, 10% O2 and 80% He (total flow rate 30 ml/min). Some experiments were also performed at a lower space velocity of 36 ml.min gcat, with a reactant mixture corresponding to 17% C3Hg, 17% O2 and 66% He (total flow rate 18 ml/min). 

No new formulations seem to have been proposed for propane oxidative dehydrogenation since 1993, the year of the work cited above, and a literature computer survey indicates only 7 articles which deal with mechanisms, one mentioning catalysts containing Bi, Mo, W, V and Ti [5], and 2 rather general patents. The literature is not richer for the oxidation of propane to acrolein, with mention of the formulation Ago.oi Bio.85 V0.54 M00.45 O4.0, giving a selectivity to acrolein of 32% at a propane conversion of 52% [6], quite comparable to results obtained in 1991 by other authors [7]. Similar remarks can be made for other oxidation reactions. 

The determination of the reaction network on CS2.5H15PViMon.xWxO40 heteropoly compounds can be deduced from the effect of contact time on propane oxidation shown in Figure 3. Extrapolation of the curves at zero contact time gives informations about the sequence of the formation of the products. Generally, primary products have nonzero intercept at zero contact time, whereas secondary or higher order products appear at a positive contact time. 

For example, carbon dioxide from air or ethene nitrogen oxides from nitrogen methanol from diethyl ether. In general, carbon dioxide, carbon monoxide, ammonia, hydrogen sulfide, mercaptans, ethane, ethene, acetylene (ethyne), propane and propylene are readily removed at 25°. In mixtures of gases, the more polar ones are preferentially adsorbed). 

Some more recent processes have been developed which involve direct hydrogenation of the oil to the fatty acid and 1,2-propane diol. These high-temperature (>230 °C) and high-pressure processes generally use a copper chromium oxide catalyst. 

In the following scheme, an oxidation pathway for propane and propene is proposed. This mechanism, that could be generalized to different hansition metal oxide catalysts, implies that propene oxidation can follow the allylic oxidation way, or alternatively, the oxidation way at C2, through acetone. The latter easily gives rise to combustion, because it can give rise to enolization and C-C bond oxidative breaking. This is believed to be the main combustion way for propene over some catalysts, while for other catalysts acrolein overoxidation could... 

---