Influence of gas composition

Changes in gas composition and other conditions have different impact on reduction rate of catalysts with different structures. When H2 content is increased, the exchange intensity of the diffusion in pores is increased. When a molecule moves, every component in the mixed gas independently diffuses in the speed of inverse square root proportion to the molecular weight. Therefore, under the same conditions, diffusion of H2 molecules in gas mixture (H2 and H2O) in the pores is faster than the diffusion of gaseous H2O in the opposite direction. As the result, the absolute pressure in pore rises continuously until the partial pressure gradient of H2 and H2O reaches the value of /Mh o/Mh = 300%). The diffusion equations for the two gas flows (H2 and H2O) can be established at this time, while the diffusion gradient in the pores is determined by the slowest step i.e., the diffusion of product H2O. 

CO or synthesis gas is usually used for the reduction of iron catalyst for the Fischer-Tropsch synthesis. However, a substantial amount of research results show that whether at low temperatures or at high temperatures, H2 as reducing agent is more suitable than the CO for the reduction of iron oxide. 

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Figure 8-12 Influence of Gas Composition of the Theoretical Open-Circuit Potential of...

To provide the reader with the entire scope of data and facts about this process alongside with their comprehensive analysis, the chapters 2 through 4 discuss the products of DMTM, the main parameters of the process and the influence of gas composition on its behavior. These chapters present some imique data in this resped, some from sources difficult to access or published only in Russian. 

Schulz H, Schulz A, Eder G, Heyder J. Influence of gas composition on convective and diffusive intrapulmonary gas transport. Exp Lung Res 1995 21 853-876. Svartengren M, Anderson K, Philipson K, Camner P. Human lung deposition of particles suspended in air or in helium/oxygen mixture. Exp Lung Res 1989 15 575-585. 

The catalyst activity depends not only on the chemical composition but also on the diffusion properties of the catalyst material and on the size and shape of the catalyst pellets because transport limitations through the gas boundary layer around the pellets and through the porous material reduce the overall reaction rate. The influence of gas film restrictions, which depends on the pellet size and gas velocity, is usually low in sulphuric acid converters. The effective diffusivity in the catalyst depends on the porosity, the pore size distribution, and the tortuosity of the pore system. It may be improved in the design of the carrier by e.g. increasing the porosity or the pore size, but usually such improvements will also lead to a reduction of mechanical strength. The effect of transport restrictions is normally expressed as an effectiveness factor q defined as the ratio between observed reaction rate for a catalyst pellet and the intrinsic reaction rate, i.e. the hypothetical reaction rate if bulk or surface conditions (temperature, pressure, concentrations) prevailed throughout the pellet [11], For particles with the same intrinsic reaction rate and the same pore system, the surface effectiveness factor only depends on an equivalent particle diameter given by... 

Dongre A.R., Jones J.L., Somogyi A., and Wysocki G.H. (1996), Influence of peptide composition, gas-phase basicity, and chemical modification on fragmentation efficiency evidence for the mobile proton model, J. Am. Soc. Mass Spectrom. 118, 8465-9374. 

Bowman RS, Essington ME, O Connor GA. 1981. Soil sorption of nickel Influence of solution composition. Soil Science Society of America Journal 45 860-865. 

Previous studies of direct reduction on iron ore pellets have been reviewed by Themelis(1), Bogdandy(2) and Huebler(3). Work on reduction by mixtures has been reported by Szekely(4) and Hughes et al(5). Modelling studies on countercurrent moving bed systems have been reported by Spitzer(6) for isothermal reduction in hydrogen, by Miller(7) for non-isothermal reduction in carbon monoxide and more recently by Tsay et al(8) and Kam and Hughes(9) for C0/H2 mixtures. However, since iron is known to be a catalyst for the water gas shift reaction, this reaction will influence the gas composition and therefore the extent of reduction. None of the previous analyses have considered this aspect and the objective of the present paper is to account for the overall reduction by inclusion of this reaction. 

Figure 4a. Influence of gas phase composition in a stirred cell reactor. 

The homologation of methanol has been proved to be a most promising process for the production of oxygenated Cj chemicals. A survey of the recent literature demonstrates the considerable efforts to improve yields and selectivilies of this synthesis gas reaction. The complex influence of catalyst composition and reaction conditions has been empltasizcd, and although the course of the reaction is not fully understood, recent results suggest a mechanistic pattern similar to that of methanol carbonylation. 

Levine J. R. (1987) Influence of coal composition on the generation and retention of coalbed natural gas. Proceed. 1987 Coalbed Methane Symp. 15—18. 

Whereas diffusion of gas at depth is widespread, mass flow is often localised (near the ground surface, in faults) or intermittent (volcanic emptions). Mass flow is an important consideration in the application of gas geochemistry to mineral because of its significant role in the interchange of atmospheric air and soil air, and therefore its influence on gas composition in the shallow subsurface from where most samples and measurements are taken. Lovell (1979) reviewed soil aeration in this context. 

The standard sample weight was 200 mg. of raw acceptor. The flow rate of gas was such that C02 consumed or evolved from the acceptor had no appreciable influence on gas composition. 

In contrast with exposure tests, thermogravimetric experiments are useful to study short-term kinetics regarding possible incubation times or the influence of gas phase composition. Evidence must show that the overall mass change is not influenced by reactions of the salt itself, by significant evaporation, or by reaction with the gas phase. 

M. Spiegel, Influence of gas phase composition on the hot corrosion of steels and nickel-based alloys beneath a (Ca-Na-K) sulfete mixture containing PbS04 and ZnS04, Mater. Corros. 51 (2000) 303-312. 

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