2. The second-order decomposition reaction A \rightarrow B+2 C is carried out in a tubular reactor packed with catalyst pellets 0.4 cm in diameter. The reaction is internal-diffusion-limited. Pure A

enters the reactor at a superficial velocity of 3 m/s, a temperature of 250°C, and a pressure of 500 kPa. Experiments carried out on smaller pellets where surface reaction is limiting yielded a specific reaction rate of 0.05 m^6/mol•g-cat•s.Calculate the length of bed necessary to achieve 80% conversion. Critique the numerical answer. (Ans.: L =2.8 *10-5 m) Additional information: * Effective diffusivity: 2.66 *10-8 m²/s * Pellet density: 2 106 g/m^3 * Internal surface area: 400 m^2/g * Bed porosity: 0.4