A model to Unni's experiments on cyclic catalytic oxydation of SO2

Mihail, R.; Paul, Rajesh

doi:10.1016/0009-2509(79)80007-x

Cited by 11 publications

(6 citation statements)

References 6 publications

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“…Open arguments exist in the literature concerning the ability of such adsorption-desorption models to predict rate improvements and product selectivities due to periodic operation (Lynch, 1984;Amariglio and Rambeau, 1984;Jain et al, 1983;Feimer et al, 1982). The difficulty of modeling cyclic reactors, even qualitatively, is well known (Mihail and Paul, 1979;Jain et al, 1981;Imbihl et al, 1985;Salmi et al, 1986). Rate models developed from steady-state experiments do not hold for cyclic states.…”

Section: The Perturbed Equilibrium Modelmentioning

confidence: 99%

Equilibrium‐limited periodic separating reactors

Vaporciyan

Kadlec

1987

AIChE Journal

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A new unit operation is presented that utilizes a rapid feed pressure swing cycle in a bed packed with catalyst and adsorbent to effect both reaction and separation. This hybrid device combines features of a cyclic-steady-state pressure swing adsorber with those of a flowforced catalytic reactor. Feed sequences for the periodic separating reactor (PSR) are those of rapid, single-bed pressure swing adsorbers (PSA). Only the case of extremely fast reactions is considered here. A perturbed reaction-sorption equilibrium model is formulated and solved for isothermal operation for different equilibrium constants and reaction stoichiometries. The capacity and separation performance for an equilibrium-limited PSR (EPSR) can be of the same order of magnitude as PSA alone. For reactions involving a single reactant or single product, the principal component in a particular exit stream depends upon both the reaction stoichiometry and feed fraction of the process cycle. The pressure dependency of the reaction equilibrium expression is the cause of separation reversals as parameters are varied.

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Section: The Perturbed Equilibrium Modelmentioning

confidence: 99%

Equilibrium‐limited periodic separating reactors

Vaporciyan

Kadlec

1987

AIChE Journal

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“…When this state was finally achieved, this apparently false indication disappeared, revealing the cycle-invariant state to exist within the steady and quasi-steady state bounds. Another instance of this same difficulty arose in our investigation (Jain et al 1981a,b) of a model proposed by Mihail and Paul (1979) purporting to explain the resonance observed by Unii et al (1973). Of the order of 100,OOO cycles had to be calculated before the cycle invariant state was achieved.…”

Section: Discussionmentioning

confidence: 52%

“…They found that it exhibited multiple maxima wherein the rate of catalytic oxidation of CO over V205 was found to be 160% higher under certain cycling conditions, compared with the rate under non-cycling conditions. Several attempts have been made in the past to model and predict the time-average reaction rates (Abdul-Kareem, 1978;Denis and Kabel, 1970;Mihail and Paul, 1979). These involved the identification of step-by-step reaction sequences such as the adsorption of the reactants on the catalyst surface, the surface reaction between the adsorbed reactants and the product desorption, the unsteady-state mass balance for each gas phase and adsorbed species, and solving the resulting set of differential equations to calculate the transient and time-average reaction rates.…”

mentioning

confidence: 99%

Adsorption/desorption models: How useful for predicting reaction rates under cyclic operation

Jain¹,

Hudgins²,

Silveston³

1983

Can J Chem Eng

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A computational study is reported of the behaviour of three catalytic reaction models containing conventional adsorption, desorption, and surface reaction steps under conditions of forced composition cycling in a mixed reactor. The models contained varying degrees of non‐linearity. With long cycle periods, the time‐average rate of reaction asymptotically approached the quasi‐steady state. Time‐average rate behaviour was found to be bounded by the asymptotes of quasi‐steady state rate under slow cycling, and the relaxed steady state under rapid cycling. It is concluded that the approach used until now to model catalytic reactions is very likely inadequate to describe the dynamics of forced cyclic operation observed in a number of experimental systems

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“…Models proposed by other investigators of cyclic forcing of catalytic reactions (1,(12)(13)(14) assume that adsorption/desorption and surface reaction steps. These allow, therefore, only for resistance and conductance.…”

Section: Resultsmentioning

confidence: 99%

Reaction Rate Resonance in the Concentration Cycling of the Catalytic Oxidation of Carbon Monoxide

Jain

Silveston

Hudgins

1982

ACS Symposium Series

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The effect of forced concentration cycling was investigated on the oxidation of CO over industrial V2O5 catalyst. The re sulting rate, when time-averaged, exhibited frequency-dependent harmonic behavior, with multiple extrema. Some preliminary inter pretation is provided by analogy to an electrical network con taining resistance and inductance.Some experimental studies (1-7) have demonstrated the pos sibility of improving the performance of a catalytic reactor through cyclic operation. Renken et al. (4) reported an improve ment of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SO2 over V2O5 catalyst can be increased by as much as 30%. Re cently Cutlip (6) reported a thirty-fold increase in the rate of CO oxidation over Pt/alumina catalyst under forced concentration cycling at high frequencies. Abdul-Kareem et al. (7) observed large effects of the mean composition, period and the amplitude of cycling on the rate of oxidation of CO over V2O5. In this study, rate resonance was observed in the low frequency region (10 min < τ < 60 min). In the present work, the search for such a phenomenon was extended to higher frequencies (1 min < τ < 10 min), although the low frequency range was also re-examined. Sym metrical square concentration waves were used, as illustrated in Figure 1. The effects of amplitude and cycle period were investi gated. Temperature (400°C) and space velocity (80,000 h -1 ) were held constant. To identify processes which control behavior under cyclic operation, variations in rate during step-changes in gas phase concentration were studied at two temperatures: 390 and 440°C.

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A model to Unni's experiments on cyclic catalytic oxydation of SO2

Cited by 11 publications

References 6 publications

Equilibrium‐limited periodic separating reactors

Equilibrium‐limited periodic separating reactors

Adsorption/desorption models: How useful for predicting reaction rates under cyclic operation

Reaction Rate Resonance in the Concentration Cycling of the Catalytic Oxidation of Carbon Monoxide

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