Methane autothermal reforming

S adsorption Partial oxidation Low temperature Oz bleeding Autothermal reforming Methanation... 

Fig. 11 Free energy changes in the oxidative steam reforming/autothermal reforming of ethanol, acetaldehyde and methane.

CO = 25 vol.%, C02 = 12 vol.%) not containing any hydrocarbons and a low tar (200 mg Nm 3) content at 800 °C and S/C (steam over carbon ratio) = 1.5. Problems associated with pyrolysis oil gasification are similar to those of biomass gasification. Gasification of the tar fraction and conversion of methane formed are important challenges. Both require highly active and stable steam/autothermal reforming catalysts. 

Hydrogen production from carbonaceous feedstocks requires multiple catalytic reaction steps For the production of high-purity hydrogen, the reforming of fuels is followed by two water-gas shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. Steam reforming, partial oxidation and autothermal reforming of methane are well-developed processes for the production of hydro-... 

In the first part of the chapter, a state-of-the-art review and also a thermodynamic analysis of the autothermal reforming reaction are reported. The former, relevant to both chemical and engineering aspects, refers to the reaction system and the relevant catalysts investigated. The latter discusses the effect of the operating conditions on methane conversion and hydrogen yield. 

Unlike the methane steam reformer, the autothermal reformer requires no external heat source and no indirect heat exchangers. This makes autothermal reformers simpler and more compact than steam reformers, resulting in lower capital cost. In an autothermal reformer, the heat generated by the POX reaction is fully utilized to drive the SR reaction. Thus, autothermal reformers typically offer higher system efficiency than POX systems, where excess heat is not easily recovered. 

Heinzel et al. [77] compared the performance of a natural gas autothermal reformer with that of a steam reformer. The ATR reactor was loaded with a Pt catalyst on a metallic substrate followed by a fixed bed of Pt catalyst. In the start-up phase, the metallic substrate was electrically heated until the catalytic combustion of a stoichiometric methane-air mixture occurred. The reactor temperature was increased by the heat of the combustion reaction and later water was added to limit the temperature rise in the catalyst, while the air flow was reduced to sub-stoichiometric settings. With respect to the steam reformer, the behavior of the ATR reactor was more flexible regarding the start-up time and the load change, thus being more suitable for small-scale stationary applications. 

An experimental study by Lee et al. [72] reported the development and testing of a natural gas fuel processor, which incorporates a catalytic autothermal reformer, a sulfur trap and a WGS reactor. The fuel processor was successfully run over 2300 h of continuous operation. The ATR reactor gave over 40% H2 (dry basis) in the ATR reformate and 96-99.9% methane conversion over the entire test duration. 

Kikas et al. [47] operated a micro structured autothermal reformer for methane in the conventional and reverse flow mode. Owing to the reverse flow conditions, a more uniform temperature profile was achieved in the reactor (Figure 2.21). 

The ATR (Autothermal Reforming) process makes CO-enriched syngas. It combines partial oxidation with adiabatic steam-reforming and is a cost-effective option when oxygen or enriched air is available. It was developed in the late 1950 s for ammonia and methanol synthesis, and then further developed in the 1990 s by Haldor Topspe2. The difference between Steam Methane Reforming (SMR) and ATR is in how heat is provided to activate the endothermic steam reforming reaction. In SMR, the catalyst is contained in tubes that are heated by an external burner. 

The primary ways in which natural gas, mostly methane, is converted to hydrogen involve reaction with either steam (steam reforming), oxygen (partial oxidation), or both in sequence (autothermal reforming). The overall reactions are shown below ... 

Steam reforming of methane, which like CO2 reforming is endothermic, has also been combined with the exothermic partial oxidation of methane (44-47). This combination process is usually called autothermal reforming , because no heat addition is required for the reforming reaction. For example, ExxonMobil (44—46,... 

Ayabe, S., Omoto, H., Utaka, T., Kikuchi, R., Sasaki, K., Teraoka, Y., Eguchi, K. (2003). Catalytic autothermal reforming of methane and propane over supported metal catalysts. Appl. Catalysis A General 241, 261-269. 

In an autothermal reforming process, lOOOkmol/h of methane at 20°C is compressed to 10 bar, mixed with 2500 kmol/h of saturated steam and reacted with pure oxygen to give 98% conversion of the methane. The resulting products are cooled and passed over a medium-temperature shift catalyst that gives an outlet composition corresponding to equilibrium at 350°C. 

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