Tarek Moustafa1 Chemical Reaction Engineering An Introduction to Industrial Catalytic Reactors Tarek Moustafa, Ph.D. November 2011

Tarek Moustafa2 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 Moustafa3 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 Moustafa4 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 Moustafa5 Introduction Ultimate Objective: Commercial Reactor –Design and Operate:Successfully Typical Unfortunate NewsTypical Unfortunate News –Catalyst does not perform well when scaled-up to commercial reactor –Hot spot, temperature runaway, explosion runaway, explosion

Tarek Moustafa6 Phenomena in Commercial Reactors Transport Phenomena –Momentum Transfer –Heat Transfer –Mass Transfer Chemical Reactions –On Heterogeneous Catalyst Surface All Happens Simultaneously !

Tarek Moustafa7 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 Moustafa8 Reactors’ Schematic Single Adiabatic bed Adiabatic beds in series or staged beds with intermediate heating or cooling Multitubular fixed bed

Tarek Moustafa9 Reactors’ Schematic Radial flow bed Reverse flow reactors Auto-thermal reactors T T0T0

Tarek Moustafa10 Important Phenomena & Considerations Adiabatic Packed Bed Catalytic Reactors -Simplest design -Used when reaction is associated with moderate heat generation / consumption Multi-tubular fixed bed - R eaction 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 Moustafa11 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 Moustafa12 Non-isothermal continuous-flow stirred catalytic reactor Process Feed Cooling/Heating fluid inlet

Tarek Moustafa13 Non-isothermal continuous-flow stirred catalytic reactor – Design Equations Q = F out C p (T – T r ) - F Ao C po (T o – T r ) + F Ao x  H R Material Balance W r A = F Ao x Rate Law (in case of first order reaction) r A = k o e -E/RT C A Energy Balance Q = U A (T – T c )

Tarek Moustafa14 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*10 14 e /T m 3 /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/cm 3. (  H r = 21 kcal/gmole, C p A = 32 cal/gmole K and C p B = 36 cal/gmole K)

Tarek Moustafa15 Solution Q = F out C p (T – T r ) - F Ao C po (T o – T r ) + F Ao x  H R Material Balance W r A = F Ao x  W r A = 800 * 0.2 Energy Balance Rate Law 0 = 800*32.8*(T – 298) – 800*32*(413 – 298 ) - 800*0.2*21000 r A = k o e -E/RT C A = e /538.2 *10(1-0.2) = kgmol/kgcat h T = K W = kg and V = m 3

Tarek Moustafa16 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 F s 2 T, P 2 F s 1 T, P 1

Tarek Moustafa17 Isothermal plug-flow catalytic reactor – Design Equations Material Balance r A dW = F Ao dx Rate Law Could be power form or Langmuir-Hinshelwood kinetics r A = k o e -E/RT C A /(1+K A C A +K B C B )

Tarek Moustafa18 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 F s 2 T 2, P 2 F s 1 T 1, P 1

Tarek Moustafa19 Non-isothermal plug-flow catalytic reactor – Design equations F C p dT + r A dW  H R o - U A (T – T c ) = 0 Material Balance r A dW = F Ao dx Rate Law (Langmuir-Hinshelwood kinetics) r A = k o e -E/RT C A /(1+K A C A +K B C B ) Energy Balance Momentum Balance dP/dL = - G (1-  ) [150(1-  )  G]  D p  3 D p

Tarek Moustafa20 References Missen, R., Mims, C. and Saville, B., Introduction to chemical reaction engineering and kinetics, Wiley (1999). Fogler, S., Elements of chemical reaction engineering, 4 th ed., Prentice-Hall (2004). Froment, G.F. and K.B. Bishoff, “Chemical reactor analysis and design”, 2 nd ed., Wiley (1990).