Fixed and Packed Bed Catalytic Reactor

Fixed vs Packed reactor

This is sort of a tower and there’s uniform packing for the given reactor length, which is our catalyst for support. This packing is provided to reinforce the mass transfer for creating the right contact between both the reactants. The reactants are applied downward to the tower then they’ll submit to the catalyst packing and from where they can change its property convert themselves into the required product. Fixed or packed bed reactor assembled is an assembly randomly.

Porous Catalyst Particle

  • The particles are porous to extend the expanse of the catalyst.
  • Reactants are transported inside the pores using molecular diffusion and adsorb to the active sites where the reaction occurs.
  • Products desorb and diffuse back to the majority.
  • Heat is transported by conduction.

 

Uses of Packed Bed Reactor

  1. The aim of a packed bed reactor is employed to extend the contact time between the two phases versus natural action.
  2. It’s employed in an apparatus, distillation process, or scrubber.
  3. It’s also accustomed store heat in chemical plants.
  4. It’s widely used with immobilized cells.

 

packed reactor
                  packed-bed-reactor

 

Enhance the Performance of the Packed Bed Reactor

To improve the performance of packed reactors there are several constructions of packed bed reactors. the foremost reactor designs are:

  1. Single bed reactor
  2. Multi bed reactor
  3. Multi-tube reactor

Single Bed Reactor

All the particles are located in an exceedingly single vessel in this reactor.

Advantages/Disadvantages

  • It is simple to construct
  • Inexpensive
  • It is applicable only if the reaction isn’t very exothermic and endothermic.

Multi Bed Reactor

In this reactor, there are several serial beds are arranged with intermediate cooling and heating stages.

Advantages/Disadvantages

  • Applicable for an exothermic reaction.

Multi-tube reactor:

If there are several tubes of small diameter full of particles in this reactor stages

Advantages/Disadvantages:

  • High surfaces are required for warmth exchanges.
  • It has excellent temperature control.
  • Applicable for an exothermic and chemical reaction.

 

Challenges/Limitations:

These are the three challenges that are visiting face in these varieties of reactors.

  1. Temperature control
  2. Pressure drop
  3. Catalyst deactivation

 

Temperature control:

The challenge challenges control has got to face are:

  • Endothermic reactions may die out.
  • Exothermic reaction may damage the reactor.
  • Selectivity control.

Pressure drop

  • The pressure drop is thanks to the friction between gas and therefore the liquid phase.
  • High-pressure drop will lead to high compression cost.
  • Some systems have a coffee tolerance for pressure drop.
  • The pressure drop is especially passionate about reactor length, particle diameter, void friction, and gas velocity.

Catalyst deactivation

  • The catalyst gets deactivated if the active sites get contaminated.

The sulfur compound deactivates the Ni-catalyst. Desulfurization is usually necessary before reform.

  • Formation of carbon deposit deactivates the catalyst. an oversized number of carbon can deposits which clog the tubes ends up in hot spots that damage the reactor.
  • Catalyst regeneration is important.

Applications

  1. Synthesis of gas production
  2. Methanol synthesis
  3. Ammonia synthesis
  4. Fischer-Tropsch synthesis
  5. Valorization of food
  6. Gas cleaning
  7. Waste treatment
  8. Nutraceutical synthesis
  9. Packed column bed distillation is employed to boost the contact between vapor and liquid rather than tray packing.

Advantages of packed bed reactor

  1. High conversion rate per unit weight of catalyst than other catalytic reactors.
  2. The reaction rate is predicated on the solid catalyst instead of the quantity of the reactor.
  3. This type of reactor has low budget items and low maintenance.
  4. The method employing a packed bed reactor operates continuously.
  5. Little decline catalyst and equipment.
  6. Simple analysis.
  7. It’s little loss or attrition.
  8. The Usually high ratio of catalysts to reactants long continuance complete reaction.

Disadvantages of packed bed reactor

  1. Large gradient or undesired thermal gradient may occur.
  2. It’s inefficient heat exchange.
  3. It’s suitable for slow or non-deactivating processes.
  4. It’s poor temperature control.
  5. Channeling may occur.
  6. Unit is also difficult to service and clean.
  7. Deformation of the reactor thanks to swelling of catalyst.
  8. The regeneration or replacement of the catalyst is difficult – stop working is required.
  9. Pore diffusional problems intrude in large pellets.

How to overcome the disadvantages:

  • Monolithic supports will overcome the issues of non-uniform flow patterns, plugging high for little pellets, and pore diffusional problems.
  • Temperature problems are overcome with:
  1. Recycle
  2. Internal and external heat exchanges
  3. Staged reactors
  4. Cold shot cooling
  5. Use of diluents
  6. Multiple tray reactor- fluid redistributed and cooled between stages and catalyst is removed which varied from tray to tray.
  7. Temperature self-regulation with competing reactions, one endothermic and one exothermic.
  8. Temperature control by selectivity and temporarily poisoning the catalyst.

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