CRYSTALLIZATION

Presented By: RABIA IJAZRegistration no. 2013-MS-CH-13

Crystallization basics Crystal geometry Crystal properties Solid-Liquid Phase Equilibrium Crystallization techniques Mechanism of crystallization

◦ Nucleation◦ Crystal growth

Crystal Size Distribution (CSD) Factors effecting crystallization Batch crystallization Melt crystallization Design consideration Conclusions

TOPICS TO STUDY

Crystallization 3

What is crystallization?◦ Formation of solid particles within homogeneous

phase What is the objective of crystallization?

◦ High purity◦ Good yield

What are the principles of crystallization?◦ Purity◦ Yield◦ Equilibria

Understanding Crystallization

Crystallization 4

There are seven basic crystal shapes, also called lattices. They are ◦ Cubic,◦ Trigonal◦ Triclinic◦ Orthorhombic◦ Hexagonal◦ Tetragonal◦ Monoclinic

Crystal Geometry

Crystallization 5

Crystallization 6

Anisotropic Liquid Crystal Amorphous Polymorphous

Crystal Properties

Crystallization 8

Slow Crystallization

What Happens during Crystallization?

Crystallization 9

Quick Crystallization

Continued…

Crystallization 10

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Solid-Liquid phase Equilibrium

Crystallization

12Crystallization

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Crystallization by cooling◦ It is chosen when the solubility of solute varies

with the temperature Crystallization by Evaporation

◦ It is chosen when solubility of solute is nearly independent of temperature

Crystallization Techniques

Crystallization

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Nucleation Crystal growth

Nucleation◦ formation of new crystals◦ Primary nucleation◦ Secondary nucleation

Mechanism of Crystallization

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Rate of nucleation:

R= Gas constant C= frequency factor molar volume of crystal v= no. of ions per molecule of solute

Continued…

Crystallization

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Deposition of solid material on existing crystals◦ Solid growth◦ Liquid growth◦ Vapor growth

Growth Rate:

∆L Law◦ ∆L= G ∆t

Crystal growth

Crystallization

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Important parameter of crystalline product Correct crystal size vital for economic

production Crystals produced in commercial

crystallization processes are usually small◦30 to 100 um in diameter

Population Density Function

Crystal Size Distribution (CSD)

Crystallization

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Super saturation Time Temperature Impurities in solution Rate of stirring

Factors effecting crystallization

Crystallization

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Low capacity Seed crystals added Maintain suitable level of super saturation

Batch Crystallization

Crystallization

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Separation without solvent Purify products of low thermal stability Carried out in:

◦ Suspension◦ By passing melt through cooled tubes

Melt crystallization

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Important parameters involved in design of crystallizer◦ Feed rate & state◦ Desired crystal size distribution (CSD) & yield◦ Solvent evaporation rate & heat transfer area

required◦ Crystallizer volume◦ Crystallizer dimension

Design Considerations

Crystallization

CONCLUSIONS

Crystallization

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The main point in crystallization is to achieve super saturation.

Crystal Size Distribution is main parameter. Crystal formation is start by two steps:

◦ Nucleation◦ Crystal growth

Conclusions

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 Warren L. McCabe, Julian C. Smith, Peter Harriott. Chapter # 27, Unit Operations of Chemical Engineering

Principles of mass transfer & separation processes. Binary K. Dutta, PHIlearning private limited.

Understanding crystallization & crystallizer by Ketan D. Samant, Lionly O’Young, clear waterbay technology, Inc.

http://orgchem.colorado.edu/Technique/Procedures/Crystallization/Crystallization.html

Reference

Crystallization