Adsorption rates of oxygen in aqueous slurries of activated carbon

Niiyama, Hiroo; Smith, J. M.

doi:10.1002/aic.690230427

Cited by 13 publications

(9 citation statements)

References 6 publications

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“…A value of 16.4 X m3/kg at Table 3. Niiyama and Smith (1977) in their nonreaction study with oxygen obtained k, = 0.32 X m3/kgs at the slightly higher temperature of 278 K. The agreement of this value with our results is very satisfactory since the data were obtained by different investigators, in the one case from adsorption-only experiments and in the other from reaction studies. Table 3 is particularly interesting in that it is equal to the ratio of reaction rate to desorption rate, as seen from Eq.…”

Section: Combined Rate-constant Function From Zero Momentsupporting

confidence: 89%

“…From the intercepts, K L is found to be nearly the same for the two m, runs: 0.606 and 0.621 for ma = 0.209 and 0.143 X 103 kg/m3, respectively. For the same reactor, impeller, and baffle geometry, the oxygen adsorption results of Niiyama and Smith (1977) correspond to K L = 0.68 at 278 K.…”

Section: Analysis Of Moment Data For Reactionmentioning

confidence: 99%

“…The diffusivity of oxygen in water at 298 K, 2.1 X lo-9 m2/s, as given by Sherwood et al (1975), was corrected to 274.5 K by the StokeEinstein equation and used in the correlation along with a value of 1.5 X lo-' kgm/s for the viscosity of water. Niiyama and Smith (1977) determined the effective diffusivity of oxygen in the pores of the same carbon to be 2.0 x 10-9 m2/s, while Komiyama and Smith (1975) found De = 5.3 X 10-10m2/s from their reaction data; both values were for 298 K. However, this uncertainty in De does not appreciably affect the evaluation of K , and ka/K. To evaluate the rate constant function in Eq.…”

Section: Combined Rate-constant Function From Zero Momentmentioning

confidence: 99%

“…Because the carbon particles were very small, results for k, and k, are not sensitive to ks and De. Hence, values previously available (Niiyama and Smith, 1977;Furusawa and Smith, 1973) could be used without introducing significant errors.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, to evaluate k, and k, separately, K must be known. These quantities were determined in part from our data and in part from Niiyama and Smith (1977), who studied rates and equilibrium for the adsorption of oxygen in aqueous slurries of the same carbon. Higher moments would provide additional relations between the rate constants, but the accuracy of experimental values for higher moments is questionable.…”

Section: Introductionmentioning

confidence: 99%

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Separation of adsorption and surface reaction rates: Dynamic studies in a catalytic slurry reactor

Ahn¹,

McCoy²,

Smith³

1985

AIChE Journal

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Dynamic experiments provide an opportunity to determine, separately, values of the adsorption and surface reaction rates occurring in a heterogeneous, catalytic reaction. In this method it is not necessary to assume that either adsorption, surface reaction, or desorption controls the rate, in contrast to the procedure used for analyzing steady state rate data.The dynamic method is applied to experimental data for the oxidation of sulfur dioxide in a three-phase aqueous-slurry reactor using activated carbon as the catalyst. The results for 274.5 K show that both rates of reversible adsorption of oxygen and the subsequent, irreversible surface reaction affect the overall rate. Neither process can be considered to be controlling.The data required for the analysis are the zero and first moments of the response in the effluent gas to a disturbance in the feed, the adsorption equilibrium constant for oxygen, and appropriate mass transfer coefficients. SCOPEThe usual procedure-the Hougen and Watson (1947) method-for analyzing steady state rate data for heterogeneous, catalytic reactions is to assume one process to be controlling in the sequence of adsorption, surface reaction, and desorption. Without this assumption the analytical expressions for the rate become too cumbersome to use. Perhaps more important, steady state data cannot provide information about the magnitudes of rates of the individual processes.When one process is assumed to be slow, the others occur at near-equilibrium. Then the rate equation formulated by the Hougen and Watson method includes equilibrium constants for these processes. Hence, an indirect way to test the assumption of a single processs controlling the overall rate is to compare separately determined equilibrium constants, for example for adsorption, with the values for these constants that must be used in the Hougen and Watson equation to correlate the rate data. Most such comparisons have been unsuccessful, leading to the conclusion that the so-called equilibrium constants in the Hougen and Watson equations are best regarded as empirical constants. However, Kabel and Johanson (1962) and Raghavan and Doraiswamy (1977) have found satisfactory agreement between adsorption equilibrium constants determined separately and by correlating steady state rate data.As pointed out by Bennett (1967Bennett ( ,1976, dynamic experiments provide an opportunity to avoid the controlling-process assumption, since adsorption, surface reaction, and desorption can occur at different rates during the transient period. During this period adsorbed concentrations as well as fluid-phase values are changing with time. At steady state, such concentrations are constant and the rates of adsorption, surface reaction, and desorption are identical.Our objective was to develop the dynamic method for a slurry reactor and use it with experimental data to determine reaction rates for the individual processes. Solution of the equations describing reaction under dynamic conditions in the real time domain is difficult. However, s...

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Section: Combined Rate-constant Function From Zero Momentsupporting

confidence: 89%

Section: Analysis Of Moment Data For Reactionmentioning

confidence: 99%

Section: Combined Rate-constant Function From Zero Momentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Separation of adsorption and surface reaction rates: Dynamic studies in a catalytic slurry reactor

Ahn¹,

McCoy²,

Smith³

1985

AIChE Journal

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Three phase slurry reactors

1980

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This article reviews the major developments in the engineering and design of three‐phase slurry catalytic reactors. A general theoretical analysis for predicting the overall rate of reaction in a slurry reactor for various kinetics is presented, incorporating all the transport effects. Modeling of semi‐batch reactors is discussed and design procedures are indicated. Some major correlations and methods for determining gas‐liquid and liquid‐solid mass transfer coefficients and effective diffusivity in liquid filled pores are reviewed. Slurry reactors are compared with other three‐phase reactors, such as trickle bed or packed bed reactors, and relative merits are pointed out.

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Dynamic behavior of trickle-bed reactors

Ramachandran

Smith

1979

Chemical Engineering Science

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Adsorption rates of oxygen in aqueous slurries of activated carbon

Cited by 13 publications

References 6 publications

Separation of adsorption and surface reaction rates: Dynamic studies in a catalytic slurry reactor

Separation of adsorption and surface reaction rates: Dynamic studies in a catalytic slurry reactor

Three phase slurry reactors

Dynamic behavior of trickle-bed reactors

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