Workshop 09: External and internal diffusion effects
Lecture notes for chemical reaction engineering
Solutions to these problems are uploaded at Workshop 9 solutions
P 14-9
The irreversible gas-phase reaction
\ce{ A ->[ cat ] B}
is carried out adiabatically over a packed bed of solid catalyst particles. The reaction is first order in the concentration of A on the catalyst surface
-r_{As}' = k' C_{As}
The feed consists of 50% (mole) A and 50% inerts, and enters the bed at a temperature of 300 K. The entering volumetric flow rate is 10 dm3/s (i.e., 10,000 cm3/s). The relationship between the Sherwood number and the Reynolds number is
Sh = 100 Re^{1/2}
As a first approximation, one may neglect pressure drop. The entering concentration of A is 1.0 M. Calculate the catalyst weight necessary to achieve 60% conversion of A for
isothermal operation.
adiabatic operation.
Additional information:
- Kinematic viscosity: \mu/\rho = 0.02 cm^2/s
- Particle diameter: d_p = 0.1 cm
- Superficial velocity: U =10 cm/s
- Catalyst surface area/mass of catalyst bed: a= 60 cm^2/g-cat
- Diffusivity of A: D_e = 10^{-2} cm^2/s
- Heat of reaction: \Delta H_{Rx}^{\circ} = 10,000 cal/g mol A
- Heat capacities: C_{pA} = C_{pB} = 25 cal/g mol \cdot K, C_{pS}\, \text{(solvent)} = 75 cal/g mol \cdot K
- k' (300 K) = 0.01 cm^3 /s \cdot g-cat \; \text{with}\; E = 4000 cal/mol
Citation
@online{utikar2024,
author = {Utikar, Ranjeet},
title = {Workshop 09: {External} and Internal Diffusion Effects},
date = {2024-03-24},
url = {https://cre.smilelab.dev//content/workshops/09-external-and-internal-diffusion-effects},
langid = {en}
}