Chemical Reaction Engineering An Introduction to Industrial Catalytic Reactors

1. Chemical Reaction EngineeringAn Introduction to Industrial Catalytic Reactors TarekMoustafa, Ph.D. November 2011 Tarek Moustafa

2. Module objectives (TPO) • To differentiate between various types of catalytic reactors • To apply the design equations: material, energy and momentum balance equations on ideal and industrial catalytic reactors Tarek Moustafa

3. Introduction • In most of chemical engineering job venues, a good understanding of industrial reactors is essential and important • The reactors are the heart of most chemical processes and all technologies starts from the reaction part and accordingly the reactor • Many types of industrial reactors are available depending on the reaction and the process involved Tarek Moustafa

4. General Classifications • Catalytic vs. non-catalytic Reactions - Catalytic reactions are more dominant in chemical industry (especially organic) - Catalytic reactions are more difficult to handle • Homogeneous vs. Heterogeneous Catalysts - Homogeneous catalysts are generally more active but a separation & recycle steps for the catalyst are essential - Heterogeneous catalysts are most widely used Tarek Moustafa

5. Introduction • Ultimate Objective: Commercial Reactor • Design and Operate: Successfully • Typical Unfortunate News • Catalyst does not perform well when scaled-up to commercial reactor • Hot spot, temperature runaway, explosion Tarek Moustafa

6. Phenomena in Commercial Reactors • Transport Phenomena • Momentum Transfer • Heat Transfer • Mass Transfer • Chemical Reactions • On Heterogeneous Catalyst Surface All Happens Simultaneously ! Tarek Moustafa

7. Types/Configurations of catalytic reactors • Fixed Bed Catalytic Reactors • Adiabatic single packed bed • Adiabatic beds in series with intermediate cooling or heating • Multi-tubular fixed bed • Radial flow bed • Reverse flow bed • Auto-thermal reactors • Fluidized Bed Reactors • Moving Bed Reactors • CSTR with jacket or coil (usually for liquid phase) Tarek Moustafa

8. Single Adiabatic bed Multitubular fixed bed Reactors’ Schematic Adiabatic beds in series or staged beds with intermediate heating or cooling Tarek Moustafa

9. T0 T Auto-thermal reactors Reverse flow reactors Radial flow bed Reactors’ Schematic Tarek Moustafa

10. Important Phenomena & Considerations • Adiabatic Packed Bed Catalytic Reactors • Simplest design • Used when reaction is associated with moderate heat generation / consumption • Multi-tubular fixed bed - Reaction is associated with high heat generation / consumption • Radial flow bed - Pressure drop is critical • Reverse flow bed - Used for endothermic reactions, to produce product and exothermic catalyst regeneration Tarek Moustafa

11. Ideal reactors • CSTR (continuous stirred tank reactor) • Composition and temperature everywhere is the same and equals that of the outlet • Infinite diffusion and sometimes called one point reactor • PFR (Plug flow reactor) - Composition and temperature changing from one point to another along the length of the reactor - No diffusion and flow is only due to bulk flow inside the reactor Tarek Moustafa

12. Process Feed Cooling/Heating fluid inlet Non-isothermal continuous-flow stirred catalytic reactor Tarek Moustafa

13. Non-isothermal continuous-flow stirred catalytic reactor – Design Equations • Material Balance W rA = FAo x • Rate Law (in case of first order reaction) rA = ko e-E/RT CA • Energy Balance Q = Fout Cp (T – Tr) - FAo Cpo (To – Tr ) + FAo x HR Q = U A (T – Tc) Tarek Moustafa

14. Example 101 An isomerization reaction is taking place in a continuous stirred catalytic reactor: A  B The reaction is first order with respect to A and the rate can be expressed as: k = 16.96*1014 e-19400/T m3/kg cat h. It is desired to feed 800 kgmole per hour of pure liquid A to the reactor. If the reactor is operated adiabatically and the inlet temperature and concentration are 140°C and 10 gmol/l respectively. What is the volume required of the catalyst to achieve 20% conversion if the catalyst bulk density is 2 g/cm3. (Hr = 21 kcal/gmole, Cp A = 32 cal/gmole K and Cp B = 36 cal/gmole K) Tarek Moustafa

15. Solution • Material Balance W rA = FAo x W rA = 800 * 0.2 • Energy Balance • Rate Law Q = Fout Cp (T – Tr) - FAo Cpo (To – Tr ) + FAo x HR 0 = 800*32.8*(T – 298) – 800*32*(413 – 298) - 800*0.2*21000 T = 538.2 K rA = ko e-E/RT CA = 16.96 1014 e-19400/538.2 *10(1-0.2) = 0.377 kgmol/kgcat h W = 424.6 kg and V = 0.2123 m3 Tarek Moustafa

16. Fs 1 T, P1 Fs 2 T, P2 Isothermal plug-flow catalytic reactor • Compositions and possibly pressure are changing along the length of the reactor • Rate is not constant inside the reactor, and is varying form one location to another Tarek Moustafa

17. Isothermal plug-flow catalytic reactor – Design Equations • Material Balance rAdW = FAodx • Rate Law Could be power form or Langmuir-Hinshelwood kinetics rA = ko e-E/RT CA /(1+KACA+KBCB) Tarek Moustafa

18. Fs 1 T1, P1 Fs 2 T2, P2 Non-isothermal plug-flow catalytic reactor • Compositions, temperature and possibly pressure are changing along the length of the reactor • Rate is not constant inside the reactor, and is varying form one location to another Tarek Moustafa

19. Momentum Balance • dP/dL = - G (1-) [150(1- ) + 1.75 G] Dp 3 Dp Non-isothermal plug-flow catalytic reactor – Design equations • Material Balance rA dW = FAo dx • Rate Law (Langmuir-Hinshelwood kinetics) rA = ko e-E/RT CA /(1+KACA+KBCB) • Energy Balance F Cp dT + rA dW  HRo - U A (T – Tc) = 0 Tarek Moustafa

20. References • Missen, R., Mims, C. and Saville, B., Introduction to chemical reaction engineering and kinetics, Wiley (1999). • Fogler, S., Elements of chemical reaction engineering, 4th ed., Prentice-Hall (2004). • Froment, G.F. and K.B. Bishoff, “Chemical reactor analysis and design”, 2nd ed., Wiley (1990). Tarek Moustafa