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CR 2: Crystallization Process Chemistry
Part 1: Crystal Habit Modification
1 DEFINING AND MEASURING CRYSTAL HABITS
1.2 Terminology and Definitions
1.3 Shape Factors
1.4 Symmetry Measurements
1.5 Crystallographic Identification
1.6 An Example
2 ROLE OF THE SOLID PHASE IN DETERMINING CRYSTAL HABIT
2.2 Equilibrium Habit
2.3 Growth Habit
2.4 F, S and K Faces and Crystal Habit
2.5 Detailed Examples of Habit Prediction using PBC Theory
2.6 The Structure of Interfaces
2.7 An Example
3 ROLE OF THE FLUID PHASE IN DETERMINING CRYSTAL HABIT
3.2 Crystal Growth Mechanisms
3.2.1 Growth Models
3.2.3 Mass transfer and bulk diffusion
3.3 Influence of Variables on Crystal Growth
3.3.3 Fluid mechanics
3.4 Adsorption Processes
4 EXPERIMENTAL TECHNIQUES AND PROBLEM SOLVING
4.2 Simple Screening Tests
4.3 Kinetic Measurements
4.3.1 Batch experiments
4.3.2 Continuous experiments
4.3.3 Face growth rates
4.4 Problem Solving
4.4.1 Process problems
4.4.2 Product control
5 INDUSTRIAL NEEDS AND FUTURE WORK
Part 2: Agglomeration during Crystallization and Precipitation
1.1 Aims and Objectives
1.2 Definition of Terms
1.3 Significance and Scope
2 PARTICLE CHARACTERISTICS
2.3 Size Distribution
2.4 Degree of Agglomeration
2.5 Co-ordination Number
2.6 Porosity and Internal Surface Area
3 CRYSTALLOGRAPHY AND PRIMARY AGGLOMERATION
3.1 Crystal Structure
3.1.1 Crystal symmetry
3.1.2 Crystal systems
3.1.3 Miller indices
3.1.4 Crystal habit
3.2 Dendrite Growth
3.3 Parallel Growth
4 COLLOID AND SURFACE SCIENCE
4.1 Particle Forces
4.2 Surface Charge
4.2.1 Electrical double layer
4.2.2 Particle interactions
4.2.3 Steric interaction
5 FLUID AND PARTICLE DYNAMICS
5.1 Brownian Motion
5.2 Couette Flow
5.3 Agitated Vessels
5.4 Fluid-Particle Interactions
6 AGGREGATION AND SECONDARY AGGLOMERATION
6.1 Population Balance
6.2 Perikinetic Aggregation
6.3 Orthokinetic Aggregation
6.3.1 Collection efficiency
6.4 Turbulence Effects
6.5 Particle Dispersion
6.5.1 Maximum aggregate size
6.6 Empirical Expressions
7 CRYSTALLIZATION AND PRECIPITATION
7.3 Downstream Effects
7.4 Troubleshooting Hints
8 CONCLUSIONS AND RECOMMENDATIONS
Part 3: Crystallization from Organic Solvents
1.3 Location within the manual structure
1.4 Document structure
1.5 Introductory comments
2 FACTORS AFFECTING THE CRYSTALLIZATION PROCESS
2.1.1 Range of solvents available
2.1.2 Solvent classification
2.1.3 Solute classification
2.1.4 Solubility in different solvents
2.1.5 The Ideal Solution Concept
2.1.6 Solute state
2.1.7 Mixed solvents
2.1.8 Examples involving the use of mixed solvent systems
2.1.9 Summary of solvent effects on solubility
2.2.1 Primary nucleation
2.2.2 Secondary Nucleation
2.2.3 Summary of solvent effects on nucleation
2.3.2 Characterisation of Crystal Faces
2.3.3 The role of the solvent in the growth mechanism
2.3.5 Solvent effect on morphology
2.3.6 Summary of solvent effects on crystal growth
2.4.1 Isolation of solvates
2.4.2 Isolation of polymorphs
2.4.3 Summary of solvent effects in determining the phase isolated
2.5 Downstream processing
2.5.2 Washing the product
2.5.4 Solvent recovery
2.5.5 Summary of solvent effects in downstream processing
2.6 Solvent - Solute Interaction Tables and Example Tables
2.6.1 Ionic solutes
2.6.2 Polar protic solutes
2.6.3 Dipolar aprotic basic solutes
2.6.4 Dipolar aprotic non-basic solutes
2.6.5 Non-polar solutes
3 EXPERIMENTAL TECHNIQUES
3.1 Introductory Comments
3.2 Solubility and Supersaturation
3.2.1 Non-specific Analytical Techniques.
3.2.2 Solute Specific Analytical Techniques.
3.2.3 Separation based analytical techniques.
3.2.4 Quick Tests.
3.3.1 Metastable Zone Width
3.3.2 Nucleation Kinetics
3.4.1 Surface or Bulk Diffusion Control?
3.4.2 Prediction and Control of Morphology
3.5 Isolated Phase
3.6 Downstream Processing
3.6.4 Solvent recovery and reuse.
4 PROCESS DEVELOPMENT AND TROUBLE SHOOTING
4.1 Introductory Remarks:
4.1.1 The Magnitude of the Problem
4.1.2 The Object of the Solvent Selection Guide
4.1.3 Limitations of the Solvent Selection Guide
4.1.4 Methodology of the Solvent Selection Guide
4.1.5 Using the Selection Guide for Process Development and Trouble Shooting
4.1.6 Practical Considerations in Solvent Selection
4.2 Using the Master Solvent - Solute Interaction Table to Select the Solvent Class.
4.2.1 Defining Product and Process Objectives
4.2.2 Preliminary Information Gathering.
4.2.3 The Table Structure
4.2.4 Completing the Table
4.3 Making the Selection
4.3.1 Process Objectives
4.3.2 Solvent 1: The Base Case
4.3.3 Solvent 2: Evaluation of the preferred alternative solvent
4.3.4 Solvent Selection: The solvent class
4.4 Solvent Selection - Fine tuning
4.4.1 Pre-selection criterion
4.4.2 Fine Tuning the Solvent Selection
4.4.3 How to change the chosen solvent property?
4.5 Concluding Comments on Solvent Selection
7 APPENDIX A : Blank "Master solvent solute interaction tables"
This Manual Volume is concerned with various topics related to the underlying chemistry and physics of the crystallization processes.
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.