Lecture 6 Kjemisk reaksjonsteknikk Chemical Reaction Engineering Review
- Slides: 27
Lecture 6 Kjemisk reaksjonsteknikk Chemical Reaction Engineering • Review of previous lectures • Pressure drop in fixed bed reactor • PFR reactor design with pressure drop (ε=0) Department of Chemical Engineering 1 - 11/26/2020
Reaction Engineering Stoichiometry Rate Laws Department of Chemical Engineering 2 Mole Balance Isothermal reactor design These topics build upon one another 2 - 11/26/2020
Reactor Mole Balances in terms of conversion Reactor Differential Algebraic Integral X Batch t CSTR Department of Chemical Engineering 3 PFR X PBR W 3 - 11/26/2020
Concentration Flow System: Gas Phase Flow System: Department of Chemical Engineering 4 4 - 11/26/2020
Pressure Drop in Packed Bed Reactors Note: Pressure drop does NOT affect liquid phase reactions Sample Question: Department of Chemical Engineering 5 Analyze the following second order gas phase reaction that occurs isothermally in a PBR: 2 A B Mole Balance: Must use the differential form of the mole balance to separate variables: Rate Law: Second order in A and 5 - 11/26/2020
Pressure Drop in Packed Bed Reactors Stoichiometry: Isothermal, T=T 0 Department of Chemical Engineering 6 Combine: Need to find (P/P 0) as a function of W (or V if you have a PFR) 6 - 11/26/2020
Pressure Drop in Packed Bed Reactors Ergun Equation: Department of Chemical Engineering 7 P pressure, Φ porosity (volume of void/total bed volume) 1 - Φ (volume of solid/total bed volume) gc conversion factor. 1. 0 for metric system Dp diameter of particle in bed μ viscosity of gas passing through the bed Z length down the packed bed u, superficial velocity ρ gas density G= ρu superficial mass velocity k. Pa m kg/m. s m m/s kg/m 3 kg/m 2, s 7 - 11/26/2020
Pressure Drop in Packed Bed Reactors Ergun Equation: Constant mass flow: Department of Chemical Engineering 8 8 - 11/26/2020
Pressure Drop in Packed Bed Reactors Variable Density Department of Chemical Engineering Let 9 9 - 11/26/2020
Pressure Drop in Packed Bed Reactors Catalyst Weight Where Ac, cross section area Department of Chemical Engineering Let 10 10 - 11/26/2020
Pressure Drop in Packed Bed Reactors We will use this form for single reactions: Department of Chemical Engineering 11 Isothermal case 11 - 11/26/2020
Pressure Drop in Packed Bed Reactors and Department of Chemical Engineering 12 or The two expressions are coupled ordinary differential equations. We can only solve them simultaneously using an ODE solver such as Polymath. For the special case of isothermal operation and epsilon = 0, we can obtain an analytical solution. Polymath will combine the mole balance, rate law and stoichiometry. 12 - 11/26/2020
PBR A B 1) Mole Balance: Department of Chemical Engineering 2) Rate Law: 13 13 - 11/26/2020
PBR Initial condition Department of Chemical Engineering 14 14 - 11/26/2020
1 P Department of Chemical Engineering 15 W 15 - 11/26/2020
2 CA 16 Department of Chemical Engineering W 16 - 11/26/2020
3 -r. A 17 Department of Chemical Engineering W 17 - 11/26/2020
4 X 18 Department of Chemical Engineering W 18 - 11/26/2020
Department of Chemical Engineering 19 19 - 11/26/2020
5 1. 0 20 Department of Chemical Engineering W 20 - 11/26/2020
Example 1: Gas Phase Reaction in PBR for δ = 0 Gas Phase Reaction in PBR with δ = 0 (Polymath Solution) A + B 2 C Repeat the previous one with equil molar feed of A and B and k. A = 1. 5 dm 9/mol 2/kg/min α = 0. 0099 kg-1 Find X at 100 kg Department of Chemical Engineering 21 21 - 11/26/2020
Example 1: Gas Phase Reaction in PBR for δ = 0 A + B 2 C Case 1: Department of Chemical Engineering Case 2: 22 22 - 11/26/2020
Example 1: Gas Phase Reaction in PBR for δ = 0 1) Mole Balance: 2) Rate Law: 3) Department of Chemical Engineering 4) 23 23 - 11/26/2020
Example 1: Gas Phase Reaction in PBR for δ = 0 5) Department of Chemical Engineering 24 24 - 11/26/2020
Example 1: Gas Phase Reaction in PBR for δ = 0 Department of Chemical Engineering 25 25 - 11/26/2020
Example A + B → 2 C Department of Chemical Engineering 26 26 - 11/26/2020
Example A + B → 2 C Department of Chemical Engineering 27 27 - 11/26/2020