Surface Area Studies of Carbon–Carbon Dioxide Reaction

Walker, P.L.; Foresti, Roberta; Wright, C. C.

doi:10.1021/ie50524a032

Cited by 56 publications

(39 citation statements)

References 4 publications

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“…Several workers [14][15][16][17] have noticed changes in the pore structure of both carbonaceous materials and iron-oxides during reduction under appropriate gaseous environments, which exert a considerable influence over the reduction rate by virtue of influencing the passage of the gases through the solid phases, as well as altering the area of solid surface available for chemical reaction with the gas phase. The area available for chemical reaction is a strong function of the relative proportion of the isolated micropores (<1 lm in diameter), which are not readily accessible to the gases and the interconnectivity of the macropores within the solid.…”

Section: Carbon-co 2 Reactionmentioning

confidence: 99%

“…The kinetics of the carbon gasification reaction by CO 2 has been studied exhaustively by several researchers in the past. [5][6][14][15][16][17][18][19] However, most of these works were hindered by mass-transport effects at the temperatures of interest. The same holds true for the estimation of rate constants of iron-oxide reduction using appropriate CO-CO 2 gas mixtures.…”

Section: Introductionmentioning

confidence: 99%

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Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

Halder

Fruehan

2008

Metall Mater Trans B

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A new ironmaking concept using iron-oxide-carbon composite pellets has been proposed, which involves the combination of a rotary hearth furnace (RHF) and an iron bath smelter. This part of the research focuses on studying the two primary chemical kinetic steps. Efforts have been made to experimentally measure the kinetics of the carbon gasification by CO 2 and wu¨stite reduction by CO by isolating them from the influence of heat-and mass-transport steps. A combined reaction model was used to interpret the experimental data and determine the rate constants. Results showed that the reduction is likely to be influenced by the chemical kinetics of both carbon oxidation and wu¨stite reduction at the temperatures of interest. Devolatilized wood-charcoal was observed to be a far more reactive form of carbon in comparison to coalchar. Sintering of the iron-oxide at the high temperatures of interest was found to exert a considerable influence on the reactivity of wu¨stite by virtue of altering the internal pore surface area available for the reaction. Sintering was found to be predominant for highly porous oxides and less of an influence on the denser ores. It was found using an indirect measurement technique that the rate constants for wu¨stite reduction were higher for the porous iron-oxide than dense hematite ore at higher temperatures (>1423 K). Such an indirect mode of measurement was used to minimize the influence of sintering of the porous oxide at these temperatures.

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Section: Carbon-co 2 Reactionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

Halder

Fruehan

2008

Metall Mater Trans B

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“…Most of the surface area is provided by the micropores and a small fraction by the macropores. There have been some studies on the change of pore characteristics and available surface area with gasification (Kawahata and Walker, 1963;Turkdogen et al, 1970;Walker et a]., 1953;Petersen et al, 1955;Hashimoto andSilveston, 1973n,b, Dutta eta]., 1977). In almost all cases, it was found that the surface area initially increased with gasification and then dropped sharply at higher conversions.…”

Section: Internal Structure and Kineticsmentioning

confidence: 99%

A single‐particle char gasification model

Srinivas

Amundson

1980

AIChE Journal

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A model is developed for the gasification of a single-char particle in an environment of water, hydrogen, carbon dioxide, carbon monoxide and methane, existing in the gasification zone of a reactor. The model, consisting of the mass and energy conservation equations, together with the Stefan-Maxwell relations includes the intraparticle effects and the change in internal surface area. It is found that the intraparticle effects and the surface area effects are significant and hence cannot be neglected, and the situation becomes more acute with increasing particle size and high temperatures. Comparisons with other models and existing empirical relations show that the model agrees well when diffusional effects are minimal, but at higher temperature and large particle size there is a significant difference. The model may be used to discriminate among various idealized models such as the homogeneous and the shrinking core model. The convective terms in the Stefan-Maxwell relations have negligible influence. The analysis can be directly used in the modeling studies of gasification reactors and will be so applied in a later paper.

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“…A number of workers (Emmett, 1941; Lamond and Marsh, 1964; Walker and Kini, 1965) have suggested the use of the saturated va our pressure po, of CO, in the liquid, rather than solid, form when app P ying the BET and Kaganer equations at 195 OK. This convention has been followed and the relevant values, computed from available data, are given in Table I In calculating the surface area from BET or Kaganer plots a value of the cross-sectional area, a, must be assigned to the adsorbate molecule at a particular temperature.…”

Section: Methodsmentioning

confidence: 99%

“…In addition, the problems associated with activated diffusion of adsorbate gas (e.g. nitrogen at 77 OK) within micropores of a solid can sometimes be overcome by the use of CO, as adsorbate at 195 O K or 298 O K (Walker and Kini, 1965). However, uncertainties exist concerning the value of the molecular area of adsorbed CO, to be used in calculations and the validity of the BET method ap lied to micro orous solids.…”

mentioning

confidence: 99%

The Determination of the Surface Area of Sepiolite From Carbon Dioxide Adsorption Isotherms

Dandy

1969

Journal of Soil Science

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Sepiolite has a microporous structure the pores of which may be Renetrated to differing extents by molecules of different gases. A study has been made of the adsorption of CO, on outgassed sepiolite (from Amboseli, Tanzania) at I93O, 209.7~~ 273.*2:, and 298.2 OK using a gravimetric method. Values of the surface area of sepiolite were calculated from BET (Brunauer, Emmett, and Teller) andKaganer plots of results, assuming molecular areas for CO, based on extrapolated liquid densities. There were only relatively small deviations from a mean value of 279 m'/g. However, the values were much lower than those previously determined by adsorption of Ns and of other gases.It is suggested that COI adsorbed at these temperatures should be assumed to be in the liquid state, but that the usual method of calculating the molecular areas of adsorbed CO, from the liquid densities at these temperatures yields values which are too low. Molecular areas of 20.8 A' at 193 O K and 23.4 A' at 209.7 OK are preferred.Isosteric heats of adsorption at different coverages were calculated from the isotherms. The results indicated heterogeneity of the surface, with decreases in the values of the heat of adsorption occurring at low coverages and in the 'monolayer region'. They compare well with values calculated from the BET equation.

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Surface Area Studies of Carbon–Carbon Dioxide Reaction

Cited by 56 publications

References 4 publications

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants

A single‐particle char gasification model

The Determination of the Surface Area of Sepiolite From Carbon Dioxide Adsorption Isotherms

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