Physicochemical Properties of Gases Within Catalytic Pellets

27-4 PHYSICOCHEMICAL PROPERTIES OF GASES WITHIN CATALYTIC PELLETS 

Gas-phase concentrations in the vicinity of the external surface of the catalyst are calculated using the ideal gas law. Under standard-state conditions, 1 mol of any ideal gas occupies 22.4 L. Furthermore, the ideal gas law suggests that molar density varies inversely with temperature. Hence, 

The temperature dependence of the effective intrapellet diffusion coefficient conforms to the assumption that ordinary molecular diffusion provides the dominant resistance to mass transfer in the pores, relative to Knudsen diffusion. This is valid when the pore diameter is larger than 1 tim. Gas-phase diffusivities are approximately proportional to the three-halves power of absolute temperature. Hence, 

The enthalpy change for reaction is exothermic and varies from 50 to 80 kJ/mol. The activation energy for the forward reaction varies from 25 to 27 kJ/mol. The temperature at the external surface of the pellet is constant at 350 K. The effective thermal conductivity of alumina catalysts is 1.6 x 10 J/cm s K. The chemical reaction is first-order and irreversible and the catalysts exhibit rectangular symmetry. When a(0) 1 in the mass transfer equation, simulations in 

TABLE 27-1 Numerical Results for Coupled Heat and Mass Ttansfer with First-Order Irreversible Exothermic Chemical Reaction in Porous Catalysts with Rectangular Symmetry  

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