Oxidation catalytic partial

The production of synthesis gas based on heterogeneous catalytic reactions using 02 (air) as an oxidant is referred to as catalytic POx (CPO). Although the process is potentially able to process a wide range of hydrocarbon feedstocks, including heavy hydrocarbons, most of the information in the literature relates to the CPO of methane (or NG). The CPO of methane can be presented by the following equation  

Thermodynamic equilibrium composition of POx products obtained from CH4 02 = 2 1 (molar) mixture as a function of temperature. Pressure—atmospheric. 

Different barriers for H I O — OH reaction on Pt and Rh correlate well with the difference in H2 selectivity. 

Schematics of an oxygen membrane reactor for catalytic POx of methane. A blown up section on the left-hand side shows the details of the ceramic membrane wall explaining the mechanism of oxygen permeation across the membrane. /- is the chemical potential of oxygen and ai and re are the ionic and electronic components of the conductivity, respectively. 

The disadvantages are that fuel and oxygen must be premixed. The proportions are such that the mixture may be flammable or even explosive, particularly if small variations (e.g. as a result of pumping and vaporizing liquid fuels) are possible. 

Hydrogen production from light alcohols (e.g. methanol and ethanol) via CPO has been the subject of several recent studies. Many catalysts were proposed which showed sufficient activity and stability to be considered further for practical applications (see Sections 6.4.1 and 6.4.2). Information on the CPO of more complex oxygenated molecules is scarce in the literature. 

Successful experiences dealing with membrane applications are reported in literature, such as Galuszka et al. who observed considerable enhancement of 

CH4 conversion and CO and H2 yield, and Basile et al. who achieved a maximum methane conversion of 96% at 550 °C, both using a palladium membrane reactor. 

The retentate from the second stage is added with CO2 and enters the third CPO stage where the reactions take place at around 920 °C to reach the target feed + CO2 conversion. Effluent is sent to a CO2 removal section where CO2 is partially recycled to the third CPO stage. Hydrogen streams are cooled down to condense the steam, then compressed and partially routed to the syngas to readjust the H2/CO ratio to 2 1. 

Capturing carbon dioxide and recycling it back to process to transform it into CO by dry reforming not only will reduce the greenhouse effect, but will also enhance the production of the syngas and reduce the costs. 

CPO with no flame was practiced in the 1950s [355] at low pressure and later by Lurgi at pressure [231], The reaction was started by an 

Extensive studies of CPO reactions were carrried out by Lanny Schmidt et al. [229] [443] using a millisecond fixed-bed reactor. It was possible to produce syngas over a rhodium monolitii at residence times of milliseconds [229]. Platinum was less active than rhodium. It was shown [242] that the reaetions take place in an oxidation zone as combined surface/gas-phase reactions followed by a steam reforming zone with equilibration of the steam reforming and shift reactions. It was also possible to convert liquid hydrocarbons [164], ethanol [434] and biomass [444] in the milliseeond reactor. 

The fixed-bed CPO technology has been studied at pilot scale [41] and at pressure. When operating at 20 bar [2] [41] and O2/NG=0.56, it was possible to achieve stable conversions close to thermod5mamic equilibrium. 

The direct CPO reaction RIO in Table 1.7 appears to be the ideal solution for methanol and Fischer—Tropsch syntheses, as it provides a H2/CO molar ratio of 2 and has a low heat of reaction  

It is often considered a dream reaction with H2/CO ratios lower than two at low conversions, but industrial utilisation would imply expensive recycle of non-converted methane as also discussed for direct conversion of methane (refer to Section 1.1.2). Other studies which claim high yields at low temperatures may be misleading [105]. 

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The catalytic partial oxidation of methane into CO and H2 according to... 

The catalytic partial oxidation of methane for the production of synthesis gas is an interesting alternative to steam reforming which is currently practiced in industry [1]. Significant research efforts have been exerted worldwide in recent years to develop a viable process based on the partial oxidation route [2-9]. This process would offer many advantages over steam reforming, namely (a) the formation of a suitable H2/CO ratio for use in the Fischer-Tropsch synthesis network, (b) the requirement of less energy input due to its exothermic nature, (c) high activity and selectivity for synthesis gas formation. 

Tonkovich, A. L. Y, Zilka, J. L., Powell, M. R., Gall, C. J., The catalytic partial oxidation of methane in a micro-channel chemical reactor, in Ehrfeld, W, Rinard, I. H., Wegeng, R. S. (Eds.), Process Miniaturization 2nd International Conference on Microreaction Technology, IMRET 2, Topical Conf. Preprints, pp. 45-53, AIChE, New Orleans (1998). 

Catalytic partial oxidation of a substituted alcohol to Knoechel (1994)... 

Vaidyanathan and Doraiswamy [Chem. Eng. Sci., 23 (537), 1966] have studied the catalytic partial oxidation of benzene in a composition range where the reactions of interest all follow pseudo first-order kinetics. The pertinent stoichiometric equations are... 

Voutetakis, S. et al., Catalytic partial oxidation of methane in a spouted bed reactor, in Natural Gas Conversion V, Studies in Surface Science and Catalysis, vol. 119, Parmaliana, A. et al., Eds., Elsevier, Amsterdam, 807 1998. 

The other two main processes for conversion of methane into synthesis gas are partial oxidation and CO2 reforming. In the 1940s, Prettre et al. (3) first reported the formation of synthesis gas by the catalytic partial oxidation of CH4... 

They used a Ni-containing catalyst. In contrast to steam reforming of methane, methane partial oxidation is exothermic. However, the partial oxidation requires pure oxygen, which is produced in expensive air separation units that are responsible for up to 40% of the cost of a synthesis gas plant (2) (in contrast, the steam reforming process does not require pure oxygen). Therefore, the catalytic partial oxidation of methane did not attract much interest for nearly half a century, and steam reforming of methane remained the main commercial process for synthesis gas manufacture. 

Table 6 Catalysts for the catalytic partial oxidation of ethanol (CPOX/POE) for hydrogen production...

In addition to SMR, other technologies are used for syngas production from natural gas that involve addition of oxygen or air. The catalytic partial oxidation (CPO) reaction is given in Reaction (3) and in autothermal reforming (ATR) this reaction is combined with Reactions (1) and (2). 

Private communication with Johnson Matthey Technology Centre, Reading, England, February 2000. 17. "Catalytic Partial Oxidation Reforming of Hydrocarbon Fuels," S. Ahmed, et al., ANL, Pg. 242, Fuel Cell Seminar Abstracts, Courtesy Associates, Inc., November 1998. 

Catalytic partial oxidation of methanol can be expressed by the following equation ... 

Numerous studies have been published on catalyst material directly related to rich catalytic combustion for GTapplications [73]. However, most data are available on the catalytic partial oxidation of methane and light paraffins, which has been widely investigated as a novel route to H2 production for chemical and, mainly, energy-related applications (e.g. fuel cells). Two main types of catalysts have been studied and are reviewed below supported nickel, cobalt and iron catalysts and supported noble metal catalysts. 

Co and Fe catalysts have also been studied for the partial oxidation of methane to synthesis gas. Their potential relies on the fact that Co and Fe have higher melting and vaporizing points than Ni. Lower performances were mostly observed, however, which is probably related to the higher activity of CoO and FC2O3 for the complete oxidation of methane [121, 132, 133]. The recognized order of reactivity for partial oxidation is in fact Ni Co > Fe. However, it was observed that the performance of Co improves when a promoter is added. An extensive study of the catalytic partial oxidation of methane over CO/AI2O3 catalysts with different metals (0.1 wt% of Ni, Pt,... 

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