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

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.

CHOICE OF REACTOR REACTION PRESSURE 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 Vapor-phase

CHOICE OF REACTOR REACTION PRESSURE 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. Liquid-phase

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.

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

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

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

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.

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

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.

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.

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.

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.