Fluid Solid Reactions

Non-Catalytic Heterogeneous Reactions

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Non-Catalytic Reactions

▪ The reactions proceeding without any interference of any substance (catalyst)▪ For example;

* Reaction between “NH3” and “Na” to produce “NaNH2”

NH3 + Na NaNH2 + 0.5H2

Non-Catalytic Reactions

• The capturing of NOx from combustion flue gases is an other example of Non-Catalytic reactions

4NO + 4NH3 + O2 -> 4N2 + 6H2O

Heterogeneous React ions

▪ The reaction involving two or more phases▪Most common are “Combustion of Coal”, “Roasting of Sulfide Ores” and “reaction of metals with acid to produce metal oxides”▪ But our concern is with “Fluid-Solid Reactions”

Fluid-Solid Reactions▪ Fluid-Solid reactions are of much importance in Industrial aspects. ▪ In this type of reactions product may contain a fluid, a solid or both of them.▪ Fluid-Solid reactions in industry are generally Gas-Solid reactions.

Fluid-Solid Reactions

Important industrial reactions are;–Extraction of metals from their ores

Fe 3 O 4 + 4H 2 3Fe + 4H 2 O–Coal Gasification reactions

C + H 2 O CO + H 2

Reaction Mechanism▪ Fluid-Solid Reactions proceeds in two ways.–Solid particles remain unchanged in size during reaction

(When Product Contain Solid Particles)–Solid particles shrink in size during reaction

(When Product Contain Fluid Only)

Progressive Conversion Model (PCM)

▪ PCM is the case where product contain solid particles.▪ Reactant gas reacts throughout the solid particles at all times, most likely at different locations.▪ Usually the solid particles do not change in size.

Shrinking-Core Model (SCM)

▪ SCM is the case when Product contain only fluid.

▪ First outer skin of the particle react

▪ The reaction zone then converted into the solid

▪ Complete reaction leaves inert solid particle only.

Steps Involved In SCM

1.Diffusion of fluid reactant through the film surrounding the particle.

2.Penetration & diffusion through ash to unreacted core.

3.Reaction of fluid & solid.

Steps Involved In SCM

4.Diffusion of Fluid product through the ash, back to the exterior surface of solid.

5.Diffusion of product through film surrounding the particle to main body of fluid.

Rate Controlling Parameters for Fluid-Solid System

1.Temperature

2.Time

3.Particle Size

4.Ash & Film Resistance