Catalytic Reactors

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Catalytic Reactors

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Catalytic reactors

� Packed bed reactor

�It may not be possible to use this

reactor for removing/adding heat.

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� Multi-tube fixed bed reactor

� If heat of reaction is large, each catalysttube must be small to prevent excessivetemperature within the reaction mixture.

� It can be used for high exothermic reaction.

� Multi bed reactor

� This arrangement reduces the temperature variation.

� All these reactors use relatively large size catalyst (granular, pellet, cylindrical or spherical)

for low pressure drop.

� Catalyst is stationary.

Catalytic reactors (Cont.,)

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� Fluidized bed reactors:� Suitable, when frequent catalyst regeneration is required (or) for reaction with a very high heat

effects.

� Containing fine catalyst particles (50 – 250 �m).

� The reactant gas is introduced through the bottom of the reactor at a rate such that catalyst

particles are suspended in a gas stream without being carried out .Under these conditions, the

entire bed of particles behave like a boiling liquid. This action tends to make composition of

reaction mixture and temperature uniform throughout the bed.

� FBR for a stable catalyst which does notrequire regeneration continuously.

� FBR for deactivating catalyst that requiresremoval & regeneration continuously.

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FIXED BED REACTOR FLUIDIZED BED REACTOR

�Catalyst particles are stationary andgas flows through it.

�Catalyst regeneration is a seriousproblem.

�Operation is not practically isothermal.

�No carryover of catalyst particles. So, itdoes not require recovery units.

�Cannot use very small size catalystparticles due to plugging and highpressure drop. Uses relatively large sizeparticles for low pressure drop.

�Gas approximates plug flow.

�Small diameter multi tubular units.

�Catalyst particles are suspended in thegas stream. They move about dependingupon the gas stream velocity.

�Catalyst regeneration is very easy.

�Practically isothermal operation.

�Carry over of catalyst particles. So,requires recovery units.

�Uses fine size catalyst particles (whichprovides large area of contact).

�Gas flow is far from plug flow withconsiderable by passing.

�Large diameter vessels.


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� Multi phase reactors:

� Three phases Gas, Liquid phases that contact a solid

Slurry & Trickle bed reactor


� Slurry reactor

�Catalyst (~100µm) is suspended in the liquid and gasis bubbled through the liquid.

� It may be operated in either a semi-batch (or)continuous mode.

�Only little movement between particles and fluid.

� Main advantage

� Temperature control and heat recovery are easily achieved.

� Constant overall catalytic activity can be maintained by the addition of small amount of

catalyst.

� Adv. over fixed bed reactor is similar to FBR.


� When to use� When there are both volatile and non-volatile reactants, or when a liquid solvent is

necessary with all gaseous reactants, three phase reactor is needed.

� Most disadvantage of slurry reactor

� Difficulty in retaining the catalyst in the vessel (screens and other devices placed in the

outlet lines tend to clog or otherwise be unreliable)

Slurry reactors:

Slurry reactor Fluidized bed reactor

Catalyst suspended in a liquid Suspending fluid is the reacting gas itself.


Ex: Hydrogenation of fattyacid over a supportednickel catalyst.

Ex: Polymerization of ethylene(or) propylene.(liquid: Cyclohexane)

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Solid catalyst

Gas bubbleLiquid

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� Trickle bed reactor:

� Gas and liquid flow concurrently downward over fixed bed ofcatalyst particles contained in a tubular reactor.

� Since the catalyst particle sizes in these reactors arerelatively large, intraparticle resistances will be moresignificant than for slurry reactor.

� No difficulty in retaining the large particles in the bed.


� Three phase fluidized bed reactor

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Catalytic Reactors