CHOICE OF REACTOR

1. CHOICE OF REACTOR REACTION TEMPERATURE • Single Irreversible or reversible Endothermic Reactions: high temperature • Single Reversible Exothermic Reaction: • continuously decreasing temperature • Multiple Reactions: Increases faster than : High temperature Increases faster than : Low temperature

2. CHOICE OF REACTOR REACTION TEMPERATURE Temperature Control • Adiabatic Operation: simplest and cheapest • Indirect Heat Transfer: jacket or coil • Cold or Hot Shots: injection of feed at intermediate points. • Heat Barrier: inert material that increases the overall heat capacity flowrate. • Quench: rapid cooling of reactor effluent.

3. CHOICE OF REACTOR REACTION PRESSURE Vapor-phase • Single Irreversible Reactions: • as high as practical • Single Reactions with decrease in the number of moles: • as high as practical • Single Reactions with increase in the number of moles: • continuously decreasing • Multiple Reactions: • choose P such Selectivity is maximized

4. CHOICE OF REACTOR REACTION PRESSURE Liquid-phase • Effect of P is less pronounced • P is chosen to: • Prevent vaporization of products • Allow vaporization as a means of removing heat • Allow selective vaporization in a rev. reaction to increase conversion.

5. CHOICE OF REACTOR CATALYSTS • HOMOGENEOUS: reaction occurs entirely in the vapor or liquid phase. • HETEROGENEOUS: catalyst is in a different phase from the reacting species. • Bulk material: a noble metal wire mesh • Supported: active material is dispersed over the surface of a porous media.

6. CHOICE OF REACTOR CATALYSTS DEGRADATION • Deterioration comes with time and produces: • Lower Reaction Rate • Lower Conversion • Can compensate by increasing temperature, but • Can degrade Selectivity • Can accelerate catalyst degradation

7. CHOICE OF REACTOR CATALYSTS DEGRADATION • Physical Loss • Surface Deposits: impede reaction • Sintering: reduce surface area • Poisoning: the poison reacts or bonds with reactant(s)

8. CHOICE OF REACTOR PRACTICAL REACTORS • Stirred-tank Reactors • Tubular Reactors • Fixed-bed Catalytic Reactors • Fixed-bed Non-catalytic Reactors • Fluidized-bed Reactors

9. CHOICE OF REACTOR Stirred-tank Reactors • Batch, semi-batch, or continuous • Batch: • variable production rates • several products in same equipment • Continuous operation: • Automatic Control is much straightforward • Can get closer to IDEAL CSTR is fluid is no too viscous.

10. CHOICE OF REACTOR Stirred-tank Reactors • Batch, semi-batch, or continuous • Batch: • variable production rates • several products in same equipment

11. CHOICE OF REACTOR Stirred-tank Reactors • Continuous operation: • Automatic Control is much straightforward • Can get closer to IDEAL CSTR is fluid is no too viscous. • Not GOOD choice for high pressure. • Not GOOD choice if reactant or products are hazardous or toxic.

12. CHOICE OF REACTOR Tubular Reactors • Bundle of tubes where the movement is in one direction only. • GOOD choice when control of residence time is critical. • GOOD choice for high pressure operation.

13. CHOICE OF REACTOR Fixed-bed Catalytic Reactors • Tubular Reactor packed with catalyst solid particles • Temperature control could be difficult due to variation along the bed. • Exothermic reactions: Local hot points can produce sintering. Use mixed of catalyst and inert solid to dilute heat.

14. CHOICE OF REACTOR Fixed-bed Non-catalytic Reactors • ~GOOD for gas-solid reactions. • Non-steady state operation. • Need to be taken off-line for regeneration • GOOD for Gas-liquid • The solid bed provides active area. • Concurrent operation is preferred if short liquid residence time is needed.