Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-III-9COMPARISON OF IRREVERSIBLE GAS-SOLID REACTIONBEHAVIOR IN PLUG-FLOW AND GRADIENT-FREE REACTORSV.L. HartmannJSC Novomoskovsk Institute of Nitrogen IndustryKirova str. 11, Novomoskovsk, Tula region 301650, Russia, e-mail: vhart@yandex.ruPlug-flow reactors are widely used both in industry and researches. As for gradient-freereactors they are mainly intended for kinetics studies. While the description of steady-statecatalytic reactions in gradient-free reactors is widely known, that for unsteady gas-solidreactions seems not to be. Besides the case of gas-solid reaction kinetics study where thegradient-free flow may be created deliberately, following situations are also of interest. Testreactor may contain only few granules of solid reagent in a flat bed, so it is hard to expect anygradient of gaseous reagent along the gas flow. Or, the gradient of gas composition maysmooth out because of longitudinal diffusion or convection.So the model (or models) of absorbent or solid reactant behavior in a gradient-free reactormay be of interest especially in comparison with that for plug-flow reactor, particularly, theway to distinguish these types of flow mode in some reactor under study.The obvious material balance for the reaction of minor gas admixture in a gradient-freereactor can be expressed as follows:( )cin − c G= wVb R, dP dt = − wb(1)where c in – inlet gas admixture content; c – gas admixture content inside the reactor; G – totalgas volume flow rate; w b – reaction rate per unit reactor volume; V R – solid reactant volume;P – instant content of the solid reactant per unit reactor volume; t – current reaction time.Assuming irreversibility of the reaction and first order of the reaction rate with respect togas admixture content, following [1], we havewb = cfm( P), (2)function f m (P) being determined by the nature of gas-solid reaction and mass transferinvolved. Functions f m (P) (m is a model number) for various reaction models are given in ref.[2].Substituting (2) to (1), finally we get after some transformations:−( ) 1 ⎤ , ( ) ⎡ ( )1 −1ν = ⎡τac fm P0η + dη dt =− cin P0τac + fmP 0η ⎤⎣ ⎦ ⎣ ⎦−1, (3)where ν = c/c in ; τ ac = V R /G – contact time; η = P/P 0 ; P 0 – initial content of the solid reactantper unit reactor volume.319