Kinetics methane reforming

We studied methane reforming kinetics at atmospheric pressure. The utilization of circulation flow systems made it possible to use nickel foil as... 

The reactor can operate with either a liquid-phase reaction or a gas-phase reaction. In both types, temperature is very important. With a gas-phase reaction, the operating pressure is also a critical design variable because the kinetic reaction rates in most gas-phase reactions depend on partial pressures of reactants and products. For example, in ammonia synthesis (N2 + 3H2 O 2NH3), the gas-phase reactor is operated at high pressure because of LeChatelier s principle, namely that reactions with a net decrease in moles should be mn at high pressure. The same principle leads to the conclusion that the steam-methane reforming reaction to form synthesis gas (CH4 + H20 O CO + 3 H2) should be conducted at low pressure. 

A few of representative kinetic studies in recent years are discussed in this section. Gokon et al49 discussed different kinetics models employed for methane reforming studies, including the Langmuir-Hinshelwood (LH), basic (BA),... 

Table 2.4. Kinetic Constants for the Steam Methane Reforming and Water-Gas Shift Reactions10-53...

Table 2.5. Kinetic Parameters for the Steam Methane Reforming over Ni-, Pt-, and Ir-Based Supported Catalysts54-57...

Wei, J. and Iglesia, E. Isotopic and kinetic assessment of the mechanism of methane reforming and decomposition reactions on supported iridium catalysts. Physical Chemistry Chemical Physics, 2004, 6, 3754. 

Ochoa-Fernandez, E., Rusten, H.K., Jakobsen, H.A., R0nning, M., Holmen, A., and Chen, D. Sorption enhanced hydrogen production by steam methane reforming using Ii2Zr03 as sorbent Sorption kinetics and reactor simulation. Catalysis Today, 2005, 106 (1—4), 41. 

Blaylock, D.W., Ogura, T., Green, W.H., Beran, G.J.O. Computational investigation of thermochemistry and kinetics of steam methane reforming on Ni(lll) under realistic conditions. J. Phys. Chem. C 2009, 113, 4898-908. 

A. Methane Reforming.—Several of the kinetic equations in Table 4 relating to CH4 reforming include a term (1 — K jK), where K is the equilibrium constant for the reforming reaction, e.g. (5) or (6), and K is pco. Ph IPch. Ph o for example for reaction (5), pco, etc. being the actual partial pressures of the gaseous components. The term is important under conditions near equilibrium because it takes into account the back reaction, the rate of which increases as equilibrium... 

Three different versions of the basic one dimensional model were developed, two heterogeneous models and a pseudo-homogeneous model. The difference in the two heterogeneous models is the way the sorbent was installed in the reactor bed. One model version considers that Li2Zr03 and the reforming catalyst are coated on two different particles, while in the other case there is one particle with both catalytic and capture properties. The steam methane reforming and the water-gas shift reaction kinetics are taken from Xu and Proment [14], but corrected for different properties of the catalyst. 

P.3.2.3 Kinetics The reaction given by Equation 9.22a describes methane reforming with steam, whereas Equation 9.22b describes the water-gas shift reaction. The kinetic expression used for the CH4 reforming reaction shall be given by the following simple relation ... 

Kinetic study—methane reforming with CO2—heterogeneous reaction... 

In this practical experimental reports how can we determine the catalytic activity and reaction kinetics in methane reforming with CO2. A great effort has been directed to the development of active and stable catalysts for this reaction. 

Mbodji, M., Commenge, J. M., Falk, L., Di Marco, D., Rossigno, F., Prost, L., et al. (2012). Steam methane reforming reaction process intensification by using a milistructured reactor experimental setup and model validation for global kinetic rate estimation. Chemical Engineering Journal, 207, 871—884. 

Oliveira, E. L. G., Grande, C. A., Rodrigues, A. E. (2009). Steam methane reforming in a Ni/ AI2O3 catalyst kinetics and diffusional limitations in extrudates. Canadian Journal of Chemical Engineering, 87, 945—956. 

Numaguchi, K., Kikuchi, T. (1988). Intrinsic kinetics and design simulation in a complex reaction network steam-methane reforming. Chemical Engineering Science, 43, 2295-2301. 

Two reforming reactions are modeled as quasi-homogeneous gas-phase reactions the steam methane reforming reaction (SMR, subscript refl ) and the water gas shift reaction (WGSR, subscript ref2 ). Reversible kinetics are apphed to describe the rates of these reactions. Their heat of reaction is completely attributed to the gas phase. 

Hecht ES et al (2005) Methane reforming kinetics within a Ni-YSZ SOFC anode. Appl Catal A General 295 40... 

Ivers-Tiffee E, Timmermann H, Leonide A, Mentzer NH, Malzbender J (2009) Methane reforming kinetics, carbon deposition, and redox durability of Ni/8 yttria stabilized zirconia (YSZ) anodes. In Vielstich W, Yokokawa H, Gasteiger HA (eds) Handbook of fuel cells fundamental technology and applications vol 6. Advanced in electrocatalysis, materials, diagnostics and durability Part 2. Wiley, Chichester, pp 933-956... 

Numerous reaction mechanisms were investigated by Froment, and the best reaction scheme is shown in Figure 8 and Table 3 of Reference 1. Best was determined by model discrimination methods described by Froment. The kinetic expressions used for methane reforming account for adsorption of all the reacting species present (CO, H2, CH4, and H2O), as well as reaction... 

As for the one-dimensional model simulations, the kinetic model used for the conventional steam methane reforming (SMR) process was taken from Xu and Fro-ment [167]. The reaction takes place on a Ni/MgAl204 catalyst. The kinetics can be described by three reaction equations ... 

Steam methane reforming on nickel-based catalysts is the main process for industrial production of hydrogen or synthesis gas. Numerous studies have been reported on the kinetics of these reactions [1, 3, 59, 167]. Xu and Froment [167] investigated a large number of detailed mechanisms and proposed the intrinsic rate equations for the steam reforming of methane on the nickel-alumina catalyst, i.e., (4.193), (4.194) and (4.195) which have been widely used. These rate equations were thus used by... 

These three reactions are not independent because the third reaction equals the sum of the other two reactions. The reactions are catalyzed by pellets coated with nickel (M/MgAhOs) and are highly endothermic overall. The operating process conditions are typically 20-40 bar with inlet temperature of 300-650 °C and outlet temperature of 700-950 C. The kinetics, physical data, correlations and operating conditions used for the conventional steam methane reforming process are taken from Froment and Bischoff [3], De Groote and Froment [1] and Xu and Froment [19, 20]. 

Figure 11.11 shows that a dry hydrogen mole fraction above 0.84 only is reached in the first minutes. After that the hydrogen content decreases, and after 50min it is down to just above 70 %, which is close to the thermodynamic limit for steam methane reforming without C02-acceptor at these conditions. The lower dry hydrogen mole fraction in the reactor is due to the decreasing capture kinetics. The decrease in kinetics is mainly because of the dependence of fractional conversion, but also because... 

The kinetics of methane reforming over nickel cermet anodes have been fairly well established for high-temperature operation [3,20,21]. It has been found that different nickel cermet anodes can have markedly different reforming activities [3,24,26,76.91,92],... 

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