This
Manual Volume is concerned with various topics
related to the underlying chemistry and physics
of the crystallization processes.
Volume
CR II Part 1 Crystal habit modification.
Crystal habit is an important
product quality parameter in crystallization, affecting
not only the acceptability of the product, but also
its separation and handling characteristics. Crystal
habit is controlled by many aspects of the crystallization
process. The crystals themselves have an equilibrium
habit defined by the growth characteristics of the various
crystal faces, but the interface between the crystal
and the liquor, and the state of the liquor itself will
also affect the habit. This report provides a general
introduction to crystal habit, and discusses the effects
of all these factors. A guide to the types of experimental
techniques for looking at crystal habit is given, along
with advice on solving crystal habit problems, which
is not always (or, indeed, usually) the addition of
a "habit modifier". A bibliography of published
crystal habit modification effects is also provided,
together with a list of contacts in organisations which
can provide information and services on crystal habit.
Volume
CR II Part 2 Agglomeration during crystallization
and precipitation.
This
report reviews agglomeration during crystallization
and precipitation processes. Two basic modes of crystal
agglomeration are identified viz. primary agglomeration
arising from crystal growth processes and secondary
agglomeration resulting from particle collision. The
crystallographic, colloidal and hydrodynamic background
to both these processes is considered in detail. For
the former case, geometrical analysis of primary agglomerates
is well-established but kinetic data or predictive models
are largely absent. Secondary agglomeration has been
considered in more detail of which two main types have
been identified viz. perikinetic due to Brownian motion)
and orthokinetic (due to fluid shear). The former affects
particles of colloidal dimensions while the latter affects
larger particles whose motion is sensitive to hydrodynamic
conditions.
Agglomeration
is mainly observed in precipitation processes with a
generally lower degree seen during crystallization.
Although the dominant mode of agglomeration is often
not identified explicitly, and can be difficult to do
so, secondary agglomeration is most frequently implied
in reported studies. Agglomeration can have a marked
effect on both product quality and downstream processing
as well as confounding the accurate determination of
crystal growth and nucleation kinetics in which it is
usually ignored. Agglomeration is largely determined
by the prevailing level of supersaturation with suspension
density, particle size, degree of agitation, ionic strength
and the presence of impurities being important factors
to consider for its control.
Volume
CR II Part 3 Crystallization
from organic solvents.
Although
many industrially important products are crystallized
from organic solvents most of the work published in
the open literature concerns crystallization from aqueous
solution. The objective of this report is to consider
the role of the solvent in crystallization, highlighting
differences between aqueous and non-aqueous systems
citing examples where possible.
The document
begins with an extensive review of the literature concerning
crystallization from organic solvents. This information
from the literature is combined with current theory,
and general trends are identified as a basis for predicting
the likely crystallization characteristics of individual
classes of solute from different classes of solvent.
This is
followed by a discussion of experimental procedures
appropriate for measuring important parameters which
can help characterise crystallizations from organic
solvents.
The last
chapter of the report concerns identification of solvent
related crystallization problems. The possibility of
using the solvent as a variable to improve crystallization
processes is discussed in the context of process development
and trouble-shooting. Finally a procedure to assist
in solvent selection is presented.
