Hydrocarbons, partial oxidation

All effluents must be characterized in detail when treating agents contaminated with metals from disassembled chemical weapons (i.e., potential trace species and reaction by-products, such as nitrated hydrocarbons, partially oxidized products, and metals, must be identified) and their environmental impacts evaluated. 

In the investigation of hydrocarbon partial oxidation reactions the study of the factors that determine selectivity has been of paramount importance. In the past thirty years considerable work relevant to this topic has been carried out. However, there is yet no unified hypothesis to address this problem. In this paper we suggest that the primary reaction pathway in redox type reactions on oxides is determined by the structure of the adsorbed intermediate. When the hydrocarbon intermediate (R) is bonded through a metal oxygen bond (M-O-R) partial oxidation products are likely, but when the intermediate is bonded through a direct metal-carbon bond (M-R) total oxidation products are favored. Results on two redox systems are presented ethane oxidation on vanadium oxide and propylene oxidation on molybdenum oxide. 

Hydrocarbon Partial Oxidation Catalysts Prepared by the High-Temperature Aerosol Decomposition Process Crystal and Catalytic Chemistry... 

Moser, W. R., Hydrocarbon partial oxidation catalysts prepared by the high-temperature aerosol decomposition process, in Catalytic Selective Oxidation, ACS Symp. Ser. (S. T. Oyama and J. W. Hightower, Eds.), pp. 523,244 (1993). 

The classical oxidation example is that of SO2 to SO3, which is described in more detail below. The second class is the partial oxidation of hydrocarbons in which the desired product selectivity is significantly sensitive to both temperature and the oxygen concentration. More specifically, yield losses to carbon oxides, which result from sequential or parallel side reactions, undermine the goal of achieving high product selectivity at a reasonable hydrocarbon conversion per pass. Most hydrocarbon partial oxidation reactions have this feature. Two illustrative commercial processes include the silver-catalyzed oxidation of methanol to formaldehyde and the catalytic oxidation of monomethylforma-mide to methyl isocyanate. 

The principal constituents of most solid catalysts are metal oxides. These may be nearly inert supports, but typically they are catalytically active themselves. Within the class of metal oxides, a great range of catalytic activities is found the oxides include acids and bases, hydrogenation/dehydrogenation catalysts, hydrocarbon partial oxidation catalysts, etc. (Table 1, 14.2.1). 

Because of the extremely complicated nature of hydrocarbon partial oxidation and the consequent various equilibrium relationships that may exist between the different components of tire systems, it becomes necessary to study each of these possible relationships individually in order that a complete picture of the whole may be obtained. This has been done to some extent iu the other chapters of this book. 

A model for a similar membrane reactor, shown schematically on the top of Figure 5.15, has been developed by Harold et al [5.54] to simulate reactant and products concentrations in parallel-consecutive reaction networks. The membrane reactor compartments on either side of the membrane were assumed to be completely stirred with no pressure gradient across the membrane. The model reaction studied is of relevance to hydrocarbon partial oxidation reactions, where the intermediate oxidation product can further react with oxygen to produce the undesirable total combustion products. Here the goal is to maximize the yield of the intermediate desired product. The calculation results... 

Hydrocarbon partial oxidation reactions are highly exothermic but reaction temperatures are normally kept down to prevent by-product formation. Any energy recovered in the form of steam is usually fully utilized in the distillation train and/or other processes which are used to separate the desired product in sufficient purity from the accompanying spectrum of by-products. One process which is a net exporter of energy is the naphtha oxidation process for the manufacture of acetic (ethanoic) acid (section 12.5). The only two other processes which are significant exporters of energy are the manufacture of sulphuric acid from sulphur and the oxidation of ammonia to nitric acid. 

In methane, all four bonds to the carbon atom are C—H bonds. In carbon dioxide, its combustion product, all four bonds to the carbon are C—O bonds. Combustion is an oxidation reaction, the replacement of C—H bonds by C—O bonds. In methane, carbon is in its most reduced form, and in carbon dioxide, it is in its most oxidized form. Intermediate oxidation states of carbon are also known, in which only one, two, or three of the C—H bonds are converted to C—O bonds. It is not surprising, then, that if insufficient oxygen is available for complete combustion of a hydrocarbon, partial oxidation may occur, as illustrated in eqs. 2.5 through 2.8. 

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