Volume
IV covers the design and modelling of crystallization
plant.
Volume
CR IV Part 1 Design of well-mixed batch crystallizers.
Batch
crystallization has the advantage of using relatively
simple and flexible equipment. Both the equipment and
the operating procedure should be designed to give the
best conditions for making the product. Before starting
to design the crystallizer, the designer must know the
required specification of the product, and obtain information
on the crystallization kinetics of the material. From
this, he can select the method of supersaturation generation
(e.g. cooling or evaporation) and hence the type of
equipment to use. The equipment can now be specified
in more detail, including vessel size, agitator/pumping
requirements, and heat exchanger duty. The operating
policy can then be specified to achieve a particular
product.
The report also considers
the use of seeding, and variable cooling and/or evaporation
rates to improve product quality.
Volume
CR IV Part 2 Design of continuous crystallizers.
This report provides guidance
on all aspects of the design of continuous solution crystallizers.
The selection of crystallizer type to fulfil specific
objectives is reviewed in the context of material constraints.
Design strategies are presented for control of product
size distribution and purity using experimentally determined
information including kinetics. The report deals with
multiple stage and well as single stage continuous crystallizers.
Volume
CR IV Part 3 Agitators
and pumps.
Agitation
plays a vital role in crystallization processes. It
affects:
- Heat transfer to cooling
or heating surfaces such as vessel walls, cooling
coils or heat exchangers.
- Mass transfer from between
crystals and solutions, between the supersaturation
generation region and the bulk contents of the vessel,
and at the molecular scale within the mother liquor.
- Suspension of solids
either as a near homogeneous slurry, or stratified
in some manner according to the crystallizer design.
- Nucleation/attrition
processes by direct physical damage to crystals and
generation of a turbulent flow field.
The report
describes the various mechanisms relating to the above
processes. Various types of agitators and pumps are
reviewed and their characteristics highlighted. A selection
guide is also presented for both in-vessel agitators
and pumps for emptying or circulation of crystallizer
contents.
Volume
CR IV Part 4 Crystallizer
Scale-up.
Volume
IV.4 provides a comprehensive review of the issues affecting
scale up and highlights pitfalls to be avoided. In the
report areas where scale-up caries a large risk are
highlighted and methods to reduce this risk are suggested
in many cases. A major strength of this report is its
breadth of coverage as such it compliments the older
SAR 22 which provides a step by step guide to the scale
up of an MSMPR crystallizer. Both reports are written
on the assumption that some bench-scale or pilot plant
crystallization trials will be performed to provide
data for the design of the full-scale equipment. The
reports discuss methods for scaling-up different aspects
of the crystallization process from measurements at
laboratory or pilot scale to full-scale plant.
For nucleation
rates, scale-up will depend on the relative importance
of the various nucleation mechanisms which occur simultaneously
within the vessel. These will, in turn, depend on such
parameters as the physical properties of the crystals
and liquor, the supersaturation levels and the vessel
geometry and agitation levels. Growth rates will depend
both on the distribution of supersaturation and on the
fluid/particle interactions. The vessel hydrodynamics
control the rate of mixing of both the liquid and solid
phases in the vessel as well as the criteria for suspension
of the crystals.
Volume
CR IV Part 5 Control
systems for crystallizers.Classification
procedures, such as fines destruction/removal or classified
product removal, can be used to control the crystal size
distribution from continuous crystallizers; they can also
eliminate problems such as cycling of the product size.
Prediction of the stability of crystal size distribution
is mathematically very complex, and this report summarizes
the impact of fines removal/destruction, residence time
control and product classification on crystal size distribution.
The various methods of implementing the control are discussed,
along with such factors as the effects of transients on
the product crystal size distribution. The preface to
the report contains a summary of the main conclusions
without going into detail, allowing easy assessment of
the likely applicability of these techniques to the crystallization
in question.
Volume
CR IV Part 6 CRYCON
1.0 - USER GUIDE. Crycon
is a continuous crystallizer dynamic simulation program
developed by SPS. The program will simulate the performance
of a continuous crystallizer, generating detailed information
on the state of the crystallizer throughout the crystallization.
Volume
CR IV Part 7 Development of a batch crystallization
process. Often
those charged with the development of a crystallization
process are not crystallization specialists. Typically
the task may fall to a development chemist whose primary
focus and principal skill lies in the area of chemical
synthesis rather than the product isolation. This document
is designed to address the needs of this specific group.
The reader is taken through the stages of generating the
first crystals of a difficult to crystallize material,
on to polymorph and solvate screening and salt form selection.
The next stage, selection of a superstauration generation
route, is handled by gathering basic solubility data of
sufficient quality to be able to identify potential starting
points and isolation points based on the possible supersaturation
generation routes of; cooling, drowning out, evaporation
and reaction (pH shift, salt formation, coupling etc).
The next stage involves a scoping crystallization in which
the metastable zone width is determined from the proposed
starting point. The scoping experiment also provides material
that can be characterised both in terms of solid-liquid
separation performance and specific properties of the
crystalline product. At each stage practical guidelines
are provided for the conduct of the simple experiments
needed to gather the key data necessary to select the
supersaturation generation technique(s) and the crystallization
conditions. These experiments are designed to be quick
and simple and to yield data of a quality sufficient to
allow the initial decisions to be made. The manual part
is written with the development of a scaleable and operable
process in mind and the impact of scale up on alternative
crystallization strategies is examined at key points throughout
the manual. A subsequent manual part is proposed for troubleshooting
batch crystallization processes.
