Ch'E' 427 Spring 20042005

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Ch.E. 427Spring 2004-2005

• CRYSTALLIZATION
• Group K
• Serkan Besbinar
• Çagdas Senis
• Burcu Terzioglu
• Aykut Pehlivanoglu
• Mustafa Yücel
• May 26, 2005
• Ankara

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Outline

• Introduction
• Theoretical Background
• Equipment
• Applications

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Introduction

• Crystallization The formation of solid crystals
  from a homogeneous solution. 
• In order for crystallization to take place a
  solution must be supersaturated by one of the
  following
• - Cooling temperature reduction
• - Evaporation of solvent
• - Adding a third component

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Theoretical Background

• No crystallization in the metastable zone (in
  gray)
• Crystals can form from liquid solution, liquid
  melt or vapor.
• NUCLEATION
• formation of an ordered solid phase from a
  liquid or amorphous phase

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Nucleation and Growth

• Nucleation and growth kinetics determine such
  crystal characteristics as size distribution,
  purity, and shape or habit.
• Homogeneous Nucleation occurs if the material is
  very pure. Few grains are produced. Only in labs.
• Heterogeneous Nucleation, Impurities provide
  seeds for nucleation. More uniform grains.

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Nucleation and Growth

• Primary Nucleation
• formation of first crystals, does not occur in
  the metastable region.
• Secondary Nucleation
• seed crystals are needed. Low
  supersaturation can support secondary but not
  primary nucleation.

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Crystallization of 1,4-naphthoquinone
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Why is secondary nucleation more important for
industrial crystallizers?

• Continuous crystallizers and seeded batch
  crystallizers have crystals in the magma that can
  participate in secondary nucleation mechanisms.
• The requirements for the mechanisms of secondary
  nucleation to be operative are fulfilled easily
  in most industrial crystallizers.
• Low supersaturation can support secondary but not
  primary nucleation, and most crystallizers are
  operated in a low supersaturation regime that
  improves yield and enhances product purity and
  crystal morphology.

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Equipment

• Tank Crystallizers
• Scraped Surface Crystallizers
• Forced Circulating Liquid Evaporator-Crystallizer
• Circulating Magma Vacuum Crystallizer

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• Tank Crystallizers
• Hot, saturated solutions are allowed to cool in
  open tanks.  After crystallization, the mother
  liquor is drained and the crystals are
  collected. 
• Controlling nucleation and the size of the
  crystals is difficult
• Fine chemical or pharmaceutical industries, fatty
  acids, sugar, molecular sieve zeolites
• Scraped Surface Crystallizers
• The outside is jacketed with cooling coils and an
  agitator blade gently passes close to the trough
  wall removing crystals that grow on the vessel
  wall.
• Used for relatively small scale applications
• p-Xylene, organic dyes, boric acid

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Forced Circulating Liquid Evaporator-Crystallizer

• Crystallization and evaporation occurs
  simultaneously, driving the mother liquor towards
  supersaturation
• The supersaturated liquor flows down through a
  tube, then up through a fluidized area of
  crystals and liquor where crystallization takes
  place via secondary nucleation. 
• Larger product crystals are withdrawn while the
  liquor is recycled, mixed with the feed, and
  reheated
• AgNO3, inorganic sulfites, gypsum

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Circulating Magma Vacuum Crystallizer

• Crystal/solution mixture (magma) is circulated
  out of the vessel body.  The magma is heated
  gently and mixed back into the vessel. 
• A vacuum in the vapor space causes boiling at the
  surface of the liquid.  The evaporation causes
  crystallization and the crystals are drawn off
  near the bottom of the vessel body.
• The most important one of all types in use today
• Highly preferable for the cases where solvent is
  vaporized
• Borax, KNO4, KCl, NaCl

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Applications

• 1- SEPARATION
• Sodium carbonate (soda ash) is recovered from
  brine by first contacting the brine with carbon
  dioxide to form sodium bicarbonate A high
  percentage of sodium bicarbonate is solidified.
  With the available pressure drop across filters,
  the capacity of the process is determined by the
  rate at which liquor flows through the filter
  cake. That rate is set by the crystal size
  distribution (CSD) produced in the
  crystallizer.

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Applications

• 2- CONCENTRATION
• The concentration of fruit juice requires
  removal of solvent (water) from the natural
  juice. Solvent is crystallized (frozen) in a
  relatively pure form. Significant advantages in
  product taste have been observed in the
  application of this process to concentration of
  certain fruit juices, comparing to the
  evaporation technique.

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Applications

• 3- PURIFICATION
• L-isoleucine, is separated by crystallization
  from a fermentation broth that has been filtered
  and subjected to ion exchange. The recovered
  crystals contain impurities deleterious to use of
  the product, and these crystals are, therefore,
  redissolved and recrystallized to enhance purity.

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Applications

• 4- SOLIDIFICATION
• Production in a suitable form for use and
  acceptable to the consumer also may be an
  objective of a crystallization process. A final
  crystallization may thus be called for to bring
  the product appearance into compliance with
  expectations. Also liquid sulfur that has to be
  solidified and liquid sulfur is solidified as
  pastilles to provide for a free flowing, dust
  free product.

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Applications

• 5- ANALYSIS
• It is the goal of the crystal grower to produce
  resonably large protein crystals, in which the
  molecules have sufficient long range order that
  an x-ray beam will be diffracted into a pattern
  of reflections that will ( through
  crystallographic data analysis) produce a three
  dimensional map of the molecules electron
  density. A model of the protein's known sequence
  is then fit to this density map. Thus the model
  structure is dependent completely on the data
  produced in the xray experiment and that in turn
  can only be as good as the crystals from which it
  taken.

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• 6- CDS(Crystal Size Distribution) CONTROL
• It is often important to control the CSD of
  pharmaceutical compounds, eg, in the synthesis of
  human insulin, which is made by recombinant DNA
  techniques. The most favored size distribution is
  one that is all crystals are of the same size, so
  that the rate at which the crystals dissolve and
  are taken up by the body is known and
  reproducible. Such uniformity can be achieved by
  screening or otherwise separating the desired
  size from a broader distribution or by devising a
  crystallization process that will produce insulin
  in the desired form.

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• THANK YOU FOR YOUR ATTENTION
• ANY QUESTIONS OR COMMENTS?