Oxidation of higher hydrocarbons

The oxidation of higher hydrocarbons may also be promoted by the presence of nitrogen oxides. While the interaction is more complex than for methane (Section 14.3.1.3), it also involves mainly rapid conversion of peroxides to more active radicals by reaction with nitric oxide. 

C. Chevalier, J. Warnatz and H. Melenk, Automatic Generation of Reaction Mechanisms for the Description of the Oxidation of Higher Hydrocarbons, Ber. Bunsenges. Phys. Chem. 94 (1990) 1362-1367. 

Nickel catalysts are rarely applied for the partial oxidation of higher hydrocarbons. One example is the work of Li et al. [228], which converted propane completely at 700 °C at an O/C ratio of 1.2 at a moderate weight hourly space velocity of 120 L (hgcat) . The catalyst was a hydrotalcite (Mg2.5Nio.5AlO) doped with different amounts of ruthenium. The catalyst containing 0.1 wt.% ruthenium turned out to be the most active formulation. 

L.D. (2000) High yields of synthesis gas by millisecond partial oxidation of higher hydrocarbons. Catal. Lett. 70,... 

Krummenacher, J.J., West, K.N. and Schmidt, L.D. (2003) Catalytic partial oxidation of higher hydrocarbons at millisecond contact times decane. 

A second rule is that the oxidation of higher hydrocarbons, especially on perovskites doped with noble metals for increasing activity, may be described by Langmuir-Hinshelwood kinetics, indicating that both oxygen and CH species are adsorbed on the surface sites. On the contrary, for methane, the oxidation proceeds more or less via Rideal-Eley (RD) mechanism, which is in line with the notorious difficulty of this molecule to be activated. Let us review some cases from the literature. 

Modify the Frank-Kamenetsyi model for the oxidation of higher hydrocarbons (see Sect. 3.4) assuming that initial substance bums out. Perform corresponding calculations. 

Chevalier, C., Wamatz, J., Melenk, H. Automatic generation of reaction mechanisms for description of oxidation of higher hydrocarbons. Ber. Bunsenges. Phys. Chem. 94, 1362-1367 (1990) Chinnick, S.J., Baulch, D.L., Ayscough, P.B. An expert system for hydrocarbon pyrolysis reactions. Chemometr. Intell. Lab. Syst. 5, 39-52 (1988)... 

Bacterial utilization and degradation of hydrocarbons. The oxidation of higher hydrocarbons under aerobic conditions by Micrococcus, Pseudomonas, Mycobacterium, and Nocardia is an important environmental process by which petroleum wastes are eliminated from water and soil. The initial step in the microbial oxidation of alkanes is conversion of a terminal -CH3 group to a -CO2 group followed by p-oxidation,... 

The oxidation of hydrocarbons involves the sequential formation of a number of similar reactions in which various intermediate radicals which are combinations of carbon, hydrogen and oxygen are formed. In the simplest case, the oxidation of medrane, the methyl radical CH3 plays an important part both in direct oxidation to CO(g) and in indirect oxidation duough the formation of higher hydrocarbons such as CaHe before CO is formed. The chain reactions include... 

On the basis of this principle, a process involving oxidation of unsaturated hydrocarbons and other organic compounds, more readily oxidized than alkenes, contribute substantially to solving problems in direct single-stage production of propylene and higher alkylene oxides. 

By adjusting catalyst concentration from the higher value of Hay and Blanchard to that used in this study, we can direct the oxidation of aromatic hydrocarbons to increase the yields of alcohols and aldehydes. The oxidation period for optimum conversion can readily be determined by low voltage mass spectrometry. 

Even comprehensive mechanisms, however, must be utilized with caution. The GRI-Mech fails, for instance, under pyrolysis or very fuel-rich conditions, because it does not include formation of higher hydrocarbons or aromatic species. Its predictive capabilities are also limited under conditions where the presence of nitrogen oxides enhances the fuel oxidation rate (NO f sensitized oxidation), a reaction that may affect unbumed hydrocarbon emissions from some gas-fired systems, for example, internal combustion engines. 

In the following sections we discuss the chemistry of selected Ci to C3 hydrocarbons in some detail and outline the oxidation characteristics of higher hydrocarbons. The influence of temperature regime on the dominating oxidation mechanism will be discussed as well as the promoting effect of nitrogen oxides on the oxidation rate at lower temperatures. 

Both the methyl (CH3) and the peroxide (HO2) radicals are comparably unreactive. The low reactivity of CH3 is part of the explanation that the oxidation characteristics of methane are different from those of higher hydrocarbons. 

At higher temperatures the C2 hydrocarbons (ethane, ethylene, acetylene) are oxidized along the same pathways as outlined in Section 14.3.1. The C2 radicals C2H5 and C2H3 are much more reactive than CH3, and consequently C2 hydrocarbons are more easily oxidized than methane. This is illustrated in Fig. 14.4, which shows data for oxidation of selected hydrocarbons in a flow reactor. Measurements of the outlet CO concentration, obtained in the 800 to 1500 K range under slightly fuel-rich conditions, are compared with modeling predictions [148]. 

Low- Temperature Chemistry At temperatures below those of the NTC regime, a chain-branching low-temperature oxidation mechanism dominates. The low-temperature chemistry of higher hydrocarbons is quite complex, and despite extensive research [317,... 

Lanthanide-containing porous materials have found many applications in various fields [20-22], They are known as active and selective catalysts for synthesis of higher hydrocarbons (mostly ethane and ethylene) from methane [23], which is of considerable importance for utilizing the reserves of natural gas around the World. Cerium oxide has been employed as a catalyst or as a structural promoter for supported metal oxide catalysts... 

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