Answer Happy

An industrial process stream contains trace amounts of CO, which have to be removed due to environmental legislation. For this, a catalyst is used that catalyses the following irreversible reaction: mol CO + 0₂ → CO₂ with -Rco = ksCco Co₂ mcatalysts There are two types of catalyst available. One is monolithic and the other is a porous spherical catalyst. The monolithic catalyst consists of several, small square parallel channels (see figure), of which the walls are non-porous. In these channels, you can assume that the gas flows in plug flow. The porous catalyst is simply fixed in a packed bed reactor, in which the reaction predominantly takes place at the internal surface of the catalyst. Also in the packed bed reactor, you can assume that the gas flows in plug flow. Additional information is given at the end of the problem. a) Show that, since the large excess of oxygen, the surface reaction can also be represented by a 1st order surface reaction with k₁= 5.71.10³ m s-1 (If you cannot find this value, continue the problem with using this value) For the monolithic reactor: b) Calculate the exit concentration of CO (in ppm) in the monolith reactor if: i) external mass transfer is neglected ii) external mass transfer is included in the calculations; what can you conclude from the comparison of the answers at 3b i) with 3b ii)? For the packed bed reactor (again use the 1st order approximation as detailed in 3a): c) Show that the internal efficiency factor in the porous particle is 21% d) Show that the conversion is strongly external diffusion limited e) Calculate the exit concentration of CO (in ppm) in the packed bed reactor f) Which of the 2 reactors should you choose if i) the reaction is very fast and ii) if the reaction is very slow?
Given: Process conditions (for both reactors) Volumetric gas flow m³s¹ (at 1.0 bar and 800 K) Inlet mole fraction of CO ppm (= 0.10 mol %) Inlet mole fraction of O₂ mol% Pressure bar Temperature K Reaction rate constant (k.) m² mol¹ s¹ Diffusion coefficient of CO (Dco) m² s.1 Diffusion coefficient of O₂ (Do₂) m² s¹¹ External mass transfer constant (kc) m s¹¹ (in the case of monolith, to the walls in the channels, in case of packed bed, from bulk catalyst surface) Monolithic Reactor: Length of channels (L) 1.0 Total number of channels 2500 Width of individual channel (a) 2.0-10¹³ m The thickness of the catalyst layer on the walls of the channels is negligible small Packed Bed Reactor: Length of Packed bed 1.0 m Porosity of bed 0.50 Internal surface area (=p SA) 50000 m²/m³catalyst particle Diameter of the catalyst 5.0-10³ m Diameter of the packed bed 0.16 m Since the catalyst is very porous, you can assume that the effective diffusion coefficient in the catalyst is equal to the molecular diffusion coefficient (De.co=Dco) 1.0-10² 1000 19 1.0 800 2.0-10³ 1.0-105 5.0-10-5 1.0-10¹³ to the