CH4 steam reforming

Fuel reforming is popular way for hydrogen production for fuel cell use. Hydrocarbons are used for the fuel resource. Methane (CH4) steam reforming process consists of the following two gas phase reactions with various catalysts. 

Methanol Formaldehyde Ethylene Propylene oxide Phenol 1,4-Butanediol Tetrahydrofuran Ethylene glycol Adipic acid Isocyanates Styrene Methyl methacrylate Methyl formate Two-step, via CH4 steam reforming Three-step, via methanol Cracking of naphtha Co-product with t-butyl alcohol or styrene Co-product with acetone Reppe acetylene chemistry Multi-step Hydration of ethylene oxide Multi-step Phosgene chemistry Co-product with propylene oxide Two-step, via methacrolein Three-step, via methanol... 

Fig.4. Deactivation of CH4 steam reforming catalyst (Tops e R-67). Variation of the tar conversion in exit gas with time-on-stream for different catalyst particle sizes at 740 C (space-time=0.45kg.h/kq). ...

The ratio of the CH4-to-H2 direct decomposition rate to that of the CH4 steam-reforming reaction one was not found to be different from location to location in the porous electrode. Therefore, it was considered that the supply of H2O was sufficient in the present experiment. It was probable that a sufficient amount of CH4 and H2O diffused through the porous electrode and arrived at an electrodeelectrolyte interface. The direct decomposition reaction as well as the steam-reforming reaction simultaneously occurred at a narrow interface imder the condition of the sufficient supply of electric charge to the cathode electrode. As seen in Figure 9, some carbon deposited at the narrow interface between the electrolyte and electrode. This may be because the steam-reforming reaction was slower than the protonic conductivity of electrolyte and, consequently, the direct decomposition of CH4 provided electron and H+ ion to the interface. Since the carbon deposition was localized at the interface. Therefore, there was no effect on the mass and charge transfer in the present cell system. 

Splitting process Energy required [kWh/Nm ofH2] Status Efficiency [%] Costs relative to CH4 steam reform/ Fraction of production [%] 2)... 

EXAMPLE 6 Stoichiometric Subspace for CH4 Steam Reforming in Mass Fraction Space... 

In Chapter 8, we showed how the stoichiometric subspace for the methane steam reforming reaction can be computed in concentration space. Since the reaction occurs in the gas phase, it is more appropriate to determine the stoichiometric bounds in mass fraction space. This approach is preferable as the density of the mixture is no longer required to be constant. Compute the stoichiometric subspace for the CH4 steam reforming reaction and compare it to the answer obtained in Chapter 8. Assume that a feed molar vector of Uf = [1,1, l,0,0] kmol/s is available, and that the gas mixture obeys the ideal gas assumption to simplify calculations. Assume a constant pressure and temperature of P = 101 325 Pa and T = 500 K, respectively. 

In Section 9.2.7, the stoichiometric subspace for the CH4 steam reforming reaction was computed. In reality, the system of equations given involves the CH4 reforming reaction, as well as the water-gas shift reaction. Both of these reactions are important, for instance, in Fischer-Tropsch synthesis reactors (Anderson et al., 1984 Dry, 2002). It follows that it would be useful to understand the limits of achievability for this system. 

In this section, the AR for the CH4 steam reforming and water-gas shift reaction will be investigated. This system involves two independent reactions involving five components. Ordinarily, generation of the AR for this system would involve the construction of a two-dimensional AR. For this example, the interest will also be in understanding the minimum reactor volume achievable. Reactions of all components occur in the gas phase under nonisothermal conditions. The ideal gas equation of state is hence not a suitable one for this system. Instead, the Peng-Robinson equation of state shall be employed for this purpose. 

Species Contents at Equilibrium during CH4 Steam Reforming Step... 

Robbins, E.A., Zhu, H. and Jackson, G.S. (2003) Transient modeling of combined catalytic combustion/CH4 steam reforming. Catal. Today, 83, 141-156. 

Figure 1.15 Illustration of the generalized degree of rate control Xrc and degree of catalyst control Xcc (dashed PES) for CH4 steam reforming. Xrc(CH4-TS) = 0.8, Xrc(C) = -0.26, Xcc(C) = 0.11.

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