The catalytic steam conversion of hydrocarbons, including methane, is one of the basic means of producing hydrogen on industrial scales. A multicomponent gas mixture of hydrogen, various hydrocarbons, the oxides of carbon, and water vapor are obtained as a result of this conversion. The composition of the mixture depends heavily on the vapor/gas ratio in the initial mixture, the pressure and the temperature.It is known that a mixture consisting primarily of the following five components corresponds to the equilibrium constants of chemical reactions at the temperatures and pressures in the converters: hydrogen, water vapor, carbon dioxide, carbon monoxide, and methane. The concentrations of other components are insignificantly low; the composition of the mixture during thermodynamic equilibrium can therefore be considered a result of three reversible chemical reactions H 2 + CO 2 = H20 +CO;4H 2 + CO. = CH 4 + 2H20;C + CO~ = 2COwith the corresponding constants of chemical equilibrium:' x2jx4,s .

The possibility is analyzed of preparing specially pure hydrogen (SPH) in a high-temperature converter-membrane equipment system drawing on model representations developed previously using heat-resistant palladium alloys. Dependences are calculated for the parameters of membrane separation of methane steam catalytic conversion products on membrane area with different ratios of C H 2 O /C CH 4 in the starting material. The high efficiency of preparing SPH is demonstrated, i.e., of the order of 1.28 m 3 per cubic meter of starting gas.Previously in membrane equipment and units for preparing specially pure hydrogen (SPH) there has mainly been use of palladium alloyed with silver distinguished by high hydrogen permeability. In Russia, the most extensively used alloy has been type V-1 [1] with the optimum combination of physical, mechanical, engineering, and operating properties. The majority of large test-industrial membrane equipment and units for producing SPH of 100-2100 m 3 /h [2] are fitted with membranes of this alloy. With membrane separation of hydrogen containing gas atmospheres that do not interact chemically, such as the products of ammonia dissociation [3] and technical-grade hydrogen after furnaces for "light" annealing of electrical engineering steels [4], use of alloy V-1 has made it possible to resolve practical problems quite effectively.In order to prepare SPH with use of natural gas as a starting material, consisting almost solely of methane, it is normal to carry out prior high-temperature vapor catalytic conversion of methane at 800-900°C with preparation of a multicomponent gas mixture (H 2 , H 2 O, CO 2 , CO, CH 4 ). Nickel applied to a porous ceramic carrier (for example Al 2 O 3 ) with a high internal surface is used as the active component of the conversion catalyst.Under conditions providing absence of carbon deposition, the ratio between the components given above for the gas phase is determined by two reversible chemical reactions:With the use of alloy V-1, direct membrane separation of methane conversion products is not sufficiently effective both with absence [5] and with presence [6] of a methane conversion catalyst in the high-pressure chamber of the membrane equipment. The reason for the low efficiency of SPH preparation from natural gas is connected with the limitation for the membrane material working temperature (600°C).

The possibility is confirmed by calculation of reducing the operating temperature of a high-temperature converter-membrane system, combined with a CH 4 conversion catalyst, from 800 to 700-600°C with an insignificant reduction in technical and economic indices, but with the additional possibility of expanding the choice of membrane and structural materials, including palladium alloy V-1 highly recommended in practice. Results of quantitative evaluation of high-temperature converter-membrane system parameters are in good agreement with published data for a membrane converter.Creation of new and improved systems for hydrogen production, including specially pure hydrogen (SPH), is an important area of contemporary hydrogen power generation and technology [1].Recently there has been an increase in interest for creating compact stationary and mobile gaseous high purity hydrogen generators for energy installations based on fuel elements (FE) with proton-conducting solid-polymer electrolyte [2]. The requirement for hydrogen purity with the use of methane as a raw material is due to the sensitivity of the FE anode material to contamination with carbon dioxide with a CO impurity content in the gas phase of more than 10 ppm [2].On the basis of analyzing possible ways for effective preparation of SPH from methane [3][4][5] it follows that most suitable for solving this problem is a system of a high-temperature converter -membrane equipment (HTC-HTME) [5]. Membrane equipment with unique productivity of 100-1050 m 3 /h [6, 7] with high permeability hydrogen-selective membranes made of alloys based on palladium has made it possible for a long time (up to ten years [6]) to provide the required hydrogen purity (99.9999 vol.%), prepared from simple chemical independently acting hydrogen-containing gas mixtures (H 2 -H 2 O, H 2 -N 2 ).Analysis of an HTC-HTME system at 800°C [5] confirmed the high efficiency of this system for SPH preparation from the most promising raw material, i.e., methane. A mixture of methane and water vapor is fed to the inlet of the HTC-HTME (Fig. 1). In a high-temperature converter in a nickel catalyst the original mixture is converted into a multicomponent hydrogen-containing gas mixture, containing H 2 , H 2 O, CO 2 , CO, and CH 4 . Under conditions providing absence of carbon deposition, the ratio between these gas phase components is determined by two chemical equilibria: CH 4 + H 2 O → ← 3H 2 + CO;(1) CO + H 2 O → ← H 2 + CO 2 .(2)

A. B. Vandyshev, L. L. Murav'ev, V. M. Makarov, and I'. B. Usova UDC 534.544:621.593Production of extra-pure hydrogen (EPH) using thin continuous metallic membranes is one of the urgent trends in hydrogen power generation and technology [ 1 ]. The membrane method of producing EPH is based on the high permeability and selectivity with respect to hydrogen of membranes formed from palladium-based alloys at 773-873 K and makes it possible to produce hydrogen with a purity of 99.9999% and higher.High-temperature membrane vessels and assemblies have come into rather widespread use in foreign [2] and domestic practice [3]. For further development of membrane equipment and the procedure used to produce EPH, it is necessary to refine model representations of the process of the membrane separation of hydrogen-containing gaseous media. Different aspects of the membrane extraction of EPH primarily from binary hydrogen-containing gaseous H2-N 2 and H2-H20 mixtures have been examined in previously proposed mathematical models [4][5][6][7][8][9]. It is interesting to develop a simple mathematical model suitable for description of laws governing the membrane separation of multicomponent hydrogen-containing gaseous mixtures, the com-0009-2355/99/0102-0003522.00 9Kluwer Academic/Plenum Publishers