Model hydrocarbon partial oxidation

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... 

The partial oxidation of methane in catalytic monoliths at short contact-times is another example with several empty routes illustrating importance of thermodynamic consistency in selection of kinetic parameters. This reaction offers a promising route for the conversion of natural gas into more useful chemicals such as synthesis gas (syngas), a mixture of hydrogen and carbon monoxide. Syngas can subsequently be converted into methanol or higher hydrocarbons. The kinetic model for partial oxidation of methane on Rh includes 19 reversible reactions with six-gas phase species and 11 adsorbed species [5]. Presence of 19 steps, one balance equation (which relates coverage of surface species) and... 

In the partial oxidation of hydrocarbons, the molecules are converted stepwise. Germain [134] remarks that a mechanism with the model of a rake applies... 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

The continental biosphere is a large source of hydrocarbons. Quantification of these sources in toms of geophysical (e.g. temperature, humidity, light levels) and biogeochemical (soil physical and chemical properties, land use) parameters is much needed for inclusion in atmospheric models. The hydrocarbon oxidation mechanisms in the atmosphere should also be better understood, so that formation of ozone, carbon monoxide, partially oxidized gaseous hydrocarbons, and organic aerosol can be better quantified. The formation of organic aerosol from hydrocarbon precursors and then-capability to serve as cloud condensation nuclei are issues which need to be studied in depth. 

The kinetics of partial oxidation, ATR, and dry reforming of liquid hydrocarbons have also been reported recently.103,155 Pacheco et al.155 developed and validated a pseudo-homogeneous mathematical model for the ATR of isooctane and the subsequent WGS reaction, based on the reaction kinetics and intraparticle mass transfer resistance. They regressed the kinetic expressions from the literature for partial oxidation and steam reforming reactions to determine the kinetics parameters for the ATR of isooctane on Pt/ceria catalyst. The rate expressions used in the reformer modeling and the parameters of these rate expressions are given in Tables 2.19 and 2.20, respectively. 

Effective cathode catalysts for partial oxidation of hydrocarbons by the method in Figure 1 were looked for using cyclohexane as a model substrate. The metal salts to be tested as electrocatalysts were added to graphite by impregnation from aqueous solutions of their metal chlorides and were dried at 373 K. The reaction products were cyclohexanol and cyclohexanone and no CO2 was produced. The active cathode catalysts contained rare earth metal cations. 

On-line analysis of the effluent gases was conducted using a gas chromatograph (Hewlett Packard model 5890 Series H), equipped with FID and TCD detectors. A DB-624 fused silica capillary column was used for the hydrocarbon separation. The carbon monoxide and carbon dioxide were separated using molecular sieves (5A) and Hayesep R columns. Tlie effluent gases were analyzed for the unconverted VOCs, partial oxidation products such as chloroform and 1,1,2-trichlorocthanc, and total oxidation products (CO and COj). The HO and Clj analysis was performed using Drager tubes. The total conversion is based on total cartoon atoms in the feed. 

Faravelli, T., Goldaniga, A., Ranzi, E., etal. (1998). Partial Oxidation of Hydrocarbons Experimental and Kinetic Modeling Study, in A. Parmaliana, D. Sanfilippo, F. Fmsteri, et al. (eds). Natural Gas Conversion V(Studies in Surface Science and Catalysis 119), Elsevier, Amsterdam, pp. 575-580. 

These calculations make it possible to estimate the yields of H2 and CO for the heavier hydrocarbons, such as propane and butane, direct kinetic calculations for which are difficult to perform because of the lack of reliable kinetic models of their oxidation under these conditions. Assmning that the dependences displayed in Fig. 12.4 hold for other hydrocarbons, one estimate the )delds of H2 and CO from propane and butane oxidation by using H C = 2.67 for propane and H C = 2.5 for butane. Thus, the main factor determining the )delds of H2 and CO in the homogeneous partial oxidation of hydrocarbons to syngas is the mixture composition. The optimal composition of the mixture and the corresponding maximum yields of the conversion products are determined by the specific conditions of the partial oxidation of the hydrocarbon. 

Ranzi, E., Dente, M., Goldaniga, A., Bozzano, G., Faravelli, T. Lumping procedures in detailed kinetic modeling of gasification, pyrolysis, partial oxidation and combustion of hydrocarbon mixtures. Prog. Energy Combust. Sci. 27,99-139 (2001)... 

Regarding the kinetics, the oxidation of o-xylene and o-tolualdehyde were compared for catalysts with different V/Ti ratios (Table 36). The ratio between partial and complete oxidation (X for o-xylene and Y for o-tolualdehyde) are influenced similarly, indicating that a change in the catalyst structure influences all the reaction steps. The oxidation of o-tolualdehyde in mixtures with o-xylene revealed that o-tolualdehyde reduces the o-xylene oxidation rate by a factor of about 2. The authors conclude that a redox model is inadequate and that hydrocarbon adsorption cannot be rate-determining. Adsorption of various products should be included, and equations of the Langmuir—Hinshelwood type are proposed. It should be noted that the observed inhibition is not necessarily caused by adsorption competition, but may also stem from different... 

Measurements of these relatively minor species will not only complete the budget of NO, but will also indicate if our understanding of the hydrocarbon oxidation schemes in the atmosphere is complete. The organic nitrates that completed the NO, budget in the example in Figure 9 arose primarily from the oxidation of the naturally emitted hydrocarbon, isoprene (2-methylbutadiene). To demonstrate the oxidation mechanisms believed to be involved in the production of multifunctional organic nitrates, a partial OH oxidation sequence for isoprene is discussed. The reaction pathways described are modeled closely to those described in reference 52 for propene. The first step in this oxidation is addition of the hydroxyl radical across a double bond. Subsequent addition of 02 results in the formation of a peroxy radical. With the two double bonds present in isoprene, there are four possible isomers, as shown in reactions 2-5 ... 

---