Equilibrium composition steam

The principle of Le Chatelier shows that when the pressure applied to a gaseous system is increased, dre equilibrium composition will chairge in order to reduce tire number of gaseous molecules. In the case of tire steam reforming of metlrane, the partial pressures of methane and steam will increase as the pressure is increased. In the water-gas reaction, where tire number of molecules is the same on both sides of the equation, the effect of increasing... 

Table 4.3 Equilibrium composition in the steam-reforming reaetion at 900 K as afunetion of pressure (molar fraetion)...

Thus if a platinum wire is heated electrically in a flask of steam, the latter conies to the equilibrium composition 2H2O 2H2 -f" O2 at the temperature of the wire. 

Direct thermal decomposition of methane was carried out, using a thermal plasma system which is an environmentally favorable process. For comparison, thermodynamic equilibrium compositions were calculated by software program for the steam reforming and thermal decomposition. In case of thermal decomposition, high purity of the hydrogen and solidified carbon can be achieved without any contaminant. 

In this example the exit gas stream composition from a converter will be determined for a given inlet gas composition and steam ratio by assuming that in the outlet stream the gases reach chemical equilibrium. In practice the reaction is carried out over a catalyst, and the assumption that the outlet composition approaches the equilibrium composition is valid. Equilibrium constants for the reaction are readily available in the literature. 

Find the equilibrium composition when 1 mol of methane is mixed with 5 mols of steam at 1 atm. 

Fig. 7 Thermodynamic equilibrium compositions on dry basis for the steam reforming of ethanol. All species are in gas phase. Initial concentrations of CO, CH4, CH3CHO are taken as zero in the calculation.

SRE (Fig. 7) and POE (Fig. 10) reactions, a maximum yield of H2 could be attained in the OSRE reaction above 600 °C because CH4, if formed as an intermediate by ethanol decomposition could be completely converted into syngas above this temperature.7,8,10,109 The participation of reverse WGS reaction at high temperature leads to an increase in CO composition above 400 °C with a concomitant decrease in the composition of C02. Thus, at higher operating temperatures of above 600 °C, the system would produce mainly syngas rather than a mixture of H2 and C02. A comparison of equilibrium compositions of POE and OSRE reactions indicates that the presence of steam in this system increases the maximum yield of H2 from about 50% in the POE reaction (Fig. 10) to about 65% in the OSRE, and this is very close to that observed in the SRE reaction (around 70%) due to the participation of steam... 

The thermodynamics of Steam Reforming and Partial Oxidation are compared in Figure 5.18174. These graphs illustrate how the equilibrium compositions in the products streams vary (compare Table 5.9 and Table 5.21). 

In the feed Is sufficiently high so that carbon cannot be present at equilibrium, the equilibrium composition can be calculated from consideration of only Chemical Reactions I and II. Accordingly, the activities of each of the species can be calculated If the equilibrium constants, Kj and KII and value of n are known provided the activity ratio Inequalities given In Equation 1 are met. If the Inequalities of Equation 1 are not met, coke deposition Is possible. Values of the n at which the equalities of Equation 1 are met represent the minimum steam/methane ratio, n., at which no carbon deposition will take place at equilibrium. Figure 1 displays n versus temperature, T. Extending the analysis to Include Chemical Reaction III permits the calculation of the equilibrium coke laydown as a function of n and T shown In Figure 2. These curves will be used later to compare with the corresponding kinetic curves obtained experimentally. 

The equilibrium composition of the synthesis gas depends on the steam-to-gas ratio entering the reactor, the reaction temperature, the reaction pressure, and the quantity of inerts in the reaction mixture. To avoid carbon formation as indicated by reactions 22-3 and 22-4, the steam-to-gas ratio must be kept high... 

FIGURE 9.1 Change in the equilibrium composition of carbon-steam systems with pressure at 1200 K. From Parent and Katz (1948). 

Parent, J. D., and Katz, S. (1948). Equilibrium Compositions and Enthalpy Changes for the Reactions of Carbon, Oxygen, and Steam, Bulletin No. 2. Institute of Gas Technology, Chicago. 

Figure 2.9. Effect of temperature on equilibrium compositions in steam reforming of n-hexadecane S/C = 2.5, 1 atm pressure.

Figures 10 - 12 present calculated equilibrium compositions at 1100°K neglecting CHz, for the carbon-steam system with various ways of providing the needed heat. The reactants are indirectly heated for Fig. 10, heated by addition of a stoichiometric mixture of air and methane for Fig. 11, and by consumption by oxygen of some of the carbon for Fig. 12. The results for heating by an air-carbon reaction are given in Fig. 7.

Parent, J.D. Equilibrium compositions and enthalpy changes for the reactions of carbon, oxygen and steam. Inst. Gas Technol. Res. Bull. 1948, 1. 

The composition out of the reformer is based mainly on chemical equilibrium (Marsh et al., 1994, p. 165). Determine the equilibrium composition under the following conditions using Aspen Plus. (1) 750°C, 14 bar, steam/hydrogen = 3 (2) 650 C, 14 bar, steam/hydrogen = 2. 

The equilibrium composition of the product gas can be altered by choice of suitable temperature, pressure, and steam to feedstock ratio to produce a gas mixture consisting largely of methane or largely of hydrogen having varying proportions of carbon monoxide (qv). In each case, some carbon dioxide (qv)... 

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