CHOICE OF REACTOR
REACTION TEMPERATURE
•Single Irreversible or reversible Endothermic Reactions:
high temperature
•Single Reversible Exothermic Reaction:
continuously decreasing temperature
•Multiple Reactions:
k1 Increases faster than k 2 : High temperature
k 2 Increases faster than k1 : 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
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
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.
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.