Methane partial pressure

Because the volume occupied by each molecule is similar at low pressures, the concentration by volume is equal to the concentration by moles, and nmeth/Wair = 2 x 10 . Therefore, Pmeth/Fair = 2 x 10 . This means that the two are interchangeable. At one atmosphere total pressure, then, the methane partial pressure for this example... 

In methane oxidation, a positive effect of methane partial pressure was measured in a wide range of feed composition the reaction order is 0.7 in CH4 and 0.1 in O2. In propane oxidation, the rise of fuel partial pressure promotes the reaction only at low reactant/oxygen ratio at higher values, surface saturation seems to take place (Figure 9). The oxygen dependence is 0.8, suggesting stronger competition by propane for surface sites, compared to methane. 

We will assume the first bubble-point pressure value close to methane partial pressure in example 2.16, i.e. 4 MPa at temperature 40 °C. 

Methane partial pressure methane atm = 3600(methane mole frac in liquid)... 

Many of the important applications for the separation of CO2 and CH4 correspond to CO2 partial pressures well above 20 atm (e.g., cases 1-3 in the previous discussion of enhanced oil recovery applications). In such cases, competition for unrelaxed volume should be of second-order importance, since the condensable nature of CO2 causes it to dominate the microvoid environments in the polymer even in the face of substantial methane partial pressures. At high CO2 partial pressures, plasticizing behavior such as that illustrated in Fig. 20.4-4 may be observed. On the other hand, at relatively low C( pressures (20 atm) (cases 4 and S in the discussion of enhanced oil recovery applications), competition effects would be anticipated for most glassy polymers. These effects could be mask in the case of cellulose acetate because of its strong tendency to interact with CO2 and exhibit plasticization at low partial pressures. 

Benzinger, W. and Hiittinger, K.J. 1999a. Chemical vapor infiltration of pyrocarbon—lit The influence of increasing methane partial pressure at increasing total pressure on infiltration rate and degree of pore filling. Carbon 37 181-193. 

Ross and Steel (1973) studied reforming of methane over a coprecipitated nickel-alumina catalyst at temperatures between 500 and 680 C in the pressure range from 1-10 Torr. Their results supported first order dependence of the rate of disappearance of methane upon methane partial pressure together with evidence of water inhibition. Agnelli et al (1987) measured rates of reaction in a 10mm diameter reactor between 642 and 738 C. 

An important measure to prevent coking on Ni-based anodes is the insertion of an inert porous barrier layer, between the fuel flow and the anode. The barrier, composed of an oxide material with little tendency for coking, helps eliminate coking by reducing the methane partial pressure and trapping H2O and CO2 reaction products in the anode [6,26, 33, 35]. Two designs have been utilized a separate barrier layer inserted between the fuel flow and the SOFC anode and an integral barrier provided by an oxide cell support. 

In this expression, k is the reforming rate constant (mol/s), fcPcH4 is the methane partial pressure, Q is the mass action expression, and Kref is the reforming reaction rate equilibrium constant. The reaction rates of both the electrochemical reactions can be described through Faraday s law as... 

The proportionality of the reaction rate to the methane partial pressure to the first power. 

In most cases, the reoxidation rate does not limit the overall rate of the process. The high and similar activation energies of these reactions, proportionality of their rates to the methane partial pressure, and manifestations of the kinetic isotope effect with fccH4/ fccD4 > 1 confirm the validity of the assumption that the rate-limiting step in these oxidation processes is due to the cleavage of the C—H bond on the catalyst surface. 

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