Partial Oxidation of Hydrocarbons to Syngas

The first report on catalytic partial oxidation of hydrocarbons to synthesis gas was published by Liander in 1929, followed by Padovani and Franchetti in 1933 and 

Prettre et al in 19467 Ni-based catalysts were used in each study, and equilibrium conversion to syngas was reported for temperatures above 850°C. Despite the promising results, the CPO reaction did not receive further attention until the late 1980s. 

Co and Fe, which are well-known catalysts for the Fischer-Tropsch reaction (in principle the reverse reaction of Eqs. 8.3 and 8.4) have also been tested as CPO catalysts. However, Co, and especially Fe, are more difficult to reduce than Ni, and in general show lower activity for the CPO reaction than Ni. CoO and Fe304 have further been reported to have signihcant activity for the complete oxidation of methane. Enger et al recently tested C0/AI2O3 catalysts for the CPO reaction and reported that the addition of promoters such as Ee, Cr, Re, Mn, W, Mo, V and Ta oxides dramatically reduced the conversion capacity of Co, while Ni promotion enhanced it.  

Vernon et al tested a series of noble metal catalysts, either Ru, Rh, Pt, Pd or Ir supported on AI2O3, or rare earth ruthenium pyrochlore materials. All materials yielded the equilibrium CPO conversion of methane to syngas at IITC and 1 atm. After the reaction, it was found that Ru had been reduced out of the pyrochlore structures. Claridge et al. studied coke formation over alumina-supported or pyrochlore-derived catalysts and reported that the coke forming rates decreased in the order Ni Pd Rh Ir, as illustrated in Fig. 8.3.  

Ceria is one of the best known oxygen storage materials and is, for example, used in three-way catalysts. Several recent works describe ceria as an oxidizer for the conversion of CH4 to syngas. Perovskite-type oxides (ABO3) represent another class of reducible oxides with the potential to be partial oxidation catalysts. In general, however, non-metal catalysts are found to have too low an activity for the CPO reaction to be commercially interesting. Therefore, studies of these classes of materials for CPO have focused on high temperature applications (above 800°C). Most recent works combine such materials with metals for use in the CPO process. 

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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. 

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