2. CRYSTALLIZATION:
Crystallization is important as an industrial process
because of the number of materials that are and can be
marketed are in the form of crystals.
Crystallization may be carried out from a vapor, from a
melt, or from a solution.
More than 80% of the substances used in
pharmaceuticals, fine chemicals, agrochemicals, food
and cosmetics are isolated or formulated in their solid
form.
Crystallization is in general the last chemical purification
step in the production of ingredients.
3. Crystallization is the (natural or artificial) process of
formation of solid crystals precipitating from a solution,
melt or more rarely deposited directly from a gas.
Crystallization is also a chemical solid-liquid separation
technique, in which mass transfer of a solute from the
liquid solution to a pure solid crystalline phase occurs.
Its extensive use is based on the fact that this single
operation is both a separation and a purification process
whereby a solid crystalline product can be isolated with
high purity and with relatively low capital and operating
costs.
4. Crystals
A crystal may be defined as a solid composed of atoms arranged
in an orderly, repetitive array.
Crystals are grown in many shapes, which are dependent upon
downstream processing or final product requirements
Crystal shapes can include
cubic, tetragonal, orthorhombic, hexagonal, monoclinic, triclinic
, and trigonal.
In order for crystallization to take place a solution must be
"supersaturated".
Supersaturation refers to a state in which the liquid (solvent)
contains more dissolved solids (solute) than can ordinarily be
accomodated at that temperature
The crystallization process consists of two major
events, nucleation and crystal growth.
5. Nucleation
Nucleation is the step where the solute molecules dispersed
in the solvent start to gather into clusters, on the
nanometer scale (elevating solute concentration in a small
region), that becomes stable under the current operating
conditions.
the clusters reach a critical size in order to become stable
nuclei.This is dictated by the operating conditions
(temperature, supersaturation, etc)
Total nucleation is the sum effect of two categories of
nucleation - primary and secondary.
6. Primary nucleation
Primary nucleation is the initial formation of a crystal
where there are no other crystals present or where, if
there are crystals present in the system, they do not
have any influence on the process.
This can occur in two conditions:
1. homogeneous nucleation
2. heterogeneous nucleation
7. Secondary nucleation
Secondary nucleation is the formation of nuclei
attributable to the influence of the existing
microscopic crystals in the magma.
first type of known secondary crystallization is
attributable to fluid shear, the other due to collisions
between already existing crystals with either a solid
surface of the crystallizer or with other crystals
themselves.
8. Crystal growth
Once the first small crystal, the nucleus, forms it
acts as a convergence point for molecules of solute
touching - or adjacent to - the crystal so that it
increases its own dimension in successive layers.
Growth rate is influenced by several physical
factors, such as surface tension of
solution, pressure, temperature, relative crystal
velocity in the solution.
9. Artificial methods
For crystallization to occur from a solution it must be
supersaturated
This can be achieved by various methods:
1. solution cooling,
2. addition of a second solvent to reduce the solubility of
the solute
3. chemical reaction
4. solvent evaporation
10. Applications
There are two major groups of applications for the
artificialcrystallization process:
1. crystal production and
2. purification.
11. Equipment for crystallization
Tank Crystallizers
Forced circulation crystallizer
Scraped surface crystallizers
Circulating-magma vacuum crystallizer
Oslo crystallizer
16. Whole broth processing
The concept of recovering a metabolite directly from
an unfiltered fermentation broth is of considerable
interest because of its simplicity, the reduction in
process stages and the potential cost savings.
It may also be possible to remove the desired
fermentation product continuously from a broth
during fermentation so that inhibitory effects due to
product formation and product degradation can be
minimized throughout the production phase.
18. Ion exchange resins
Ion exchange resins are polymers that are capable of exchanging
particular ions within the polymer with ions in a solution that is
passed through them
The resins are prepared as spherical beads 0.5 to 1.0 mm in diameter.
These appear solid even under the microscope, but on a molecular scale
the structure is quite open.
This means that a solution passed down a resin bed can flow through
the crosslinked polymer, bringing it into intimate contact with the
exchange sites.
19. Dialysis
Removal of soluble impurities from solution by the use
of semipermeable membrane is known as dialysis
Solutes present in a solution(broth) can pass through
a semipermeable membrane.
Cycloheximide was extracted using methylene
chloride. Methylene chloride was circulated in a
dialysis tubing loop which passed through a
fermentor.
The product yield increased by almost double by this
dialysis-solvent extraction method.
20. Resin Method
Sterile beads of an acrylic resin, as dispersed beads
or beads wrapped in ultrafiltration method, were
put in fermentors 48 hours after inoculation.
Some of the cycloheximide formed in broth was
absorbed in resin.
Recovery of antibiotic from resin is achieved by
solvents or by changing temperature.
21. Electrodialysis(ED)
Electrodialysis(ED) is a well known separation
process where ionized compounds are separated from
non ionized compounds in aqueous solutions based on
transport through ion exchange membranes in an
electric field.
Since in a fermentation broth the lactate salt is
ionized, whereas the carbohydrates and proteins and
amino acids are either non ionized or weakly ionized,
recovery and purification of lactate salts from a
fermentation broth by electrodialysis is feasible.
22. Expanded-Bed Adsorption Theory
Expanded-Bed Adsorption Theory
When the resin has packed in the column, the beads are close together (1). As the
column is fluidized, the resin beads establish a concentration gradient (2). The sample
feedlot is injected, and particulates and cell debris (green dots) move past the resin and
out of the column, while the compound of interest (red dots) interacts with the beads
(3). The column is then repacked, the flow is reversed, and the compound is eluted
from the beads (4).
