Crystallization E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 519

Veröffentlichungsjahr: 2013

Beschreibung

Crystallization is a natural occurring process but also a process abundantly used in the industry. Crystallization can occur from a solution, from the melt or via deposition of material from the gas phase (desublimation). Crystals distinguish themself from liquids, gases and amorphous substances by the long-range order of its building blocks that entail the crystals to be formed of well-defined faces, and give rise to a large number of properties of the solid. Crystallization is used at some stage in nearly all process industries as a method of production, purification or recovery of solid materials. Crystallization is practiced on all scales: from the isolation of the first milligrams of a newly synthesized substance in the research laboratory to isolating products on the mulit-million tonne scale in industry. The book describes the breadth of crystallization operations, from isolation from a reaction broth to purification and finally to tailoring product properties. In the first section of the book, the basic mechanisms - nucleation, growth, attrition and agglomeration are introduced. It ensures an understanding of supersaturation, the driving force of crystallization. Furthermore, the solubility of the substance and its dependences on process conditions and the various techniques of crystallization and their possibilities and limitations are discussed. Last but not least, the first part includes an intensive treatment of polymorphism . The second part builds on the basics, exploring how crystallization processes can be developed, either batch-wise or continuous, from solution or from the melt. A discussion of the purification during crystallization serves as a link between the two sections, where practical aspects and an insight using theoretical concepts are combined. Mixing and its influence on the crystallization as well as the mutual interference of down-stream processes with the crystallization are also treated. Finally, techniques to characterize the crop are discussed. The third part of the book is dedicated to accounts of actual developments and of carried-out crystallizations. Typical pitfalls and strategies to avoid these as well as the design of robust processes are presented.

Leseprobe

Contents

Cover

Related Titles

Title Page

Copyright

List of Contributors

Chapter 1: Crystallization: Introduction

Chapter 2: Mechanisms of Crystallization

2.1 Crystal Lattice

2.2 Nucleation of Crystals

2.3 Growth and Growth Rate of Crystals

Further Reading

Chapter 3: Solubility and Solution Equilibria in Crystallization

3.1 Phase Equilibria and Phase Diagrams: General Issues

3.2 Melt Phase Diagrams

3.3 Solution Equilibria

Acknowledgment

References

Further Reading

Chapter 4: Agglomeration During Crystallization

4.1 Mechanisms and Kinetics of Agglomeration

4.2 Parameters Influencing Agglomeration

4.3 Agglomeration During Crystallization

4.4 Mechanical Properties of Agglomerates

References

Further Reading

Chapter 5: Polymorphism of Crystalline Systems

5.1 Introduction and Definitions

5.2 Occurrence and Properties of Polymorphs and Solvates

5.3 Thermodynamics of Polymorphs of Solid-State Forms

5.4 Thermodynamics of Hydrates

5.5 Experimental Techniques to Elucidate Thermodynamics

5.6 Formation of Various Polymorphs and Solid-State Forms-Polymorph Screens

5.7 Selection of Optimal Form for Development

5.8 Symbols

Acknowledgments

References

Chapter 6: The Influence of Additives and Impurities on Crystallization

6.1 Influence of Additives and Impurities on Crystallization

6.2 Influence of Impurities: Modeling

6.3 Tailor-Made Additives

6.4 Modeling the Influence of Solvents

References

Chapter 7: Purification by Crystallization

7.1 Introduction

7.2 Mechanisms of Impurity Incorporation and Purification

References

Further Reading

Chapter 8: Characterization of Crystalline Products

8.1 Introduction

8.2 Characterization of Intrinsic Properties of a Solid

8.3 Characterization of Particle Shape and Size

8.4 Powder Flow Properties

8.5 In-Process Characterization

Acknowledgments

References

Chapter 9: Basics of Industrial Crystallization from Solution

9.1 Generation of Supersaturation in a Crystallizer

9.2 Mass and Population Balance for Growth from Suspension

9.3 Operation of a Continuous Crystallizer: Basics

9.4 Operation of a Batch Crystallizer: Basics

Chapter 10: Development of Batch Crystallizations

10.1 Setting Goals

10.2 Crystallization of Organic Moieties

10.3 Generation of Supersaturation in Batch Crystallizations

10.4 Initiation of Crystallization – Nucleation Phase

10.5 Seeded Batch Crystallizations

10.6 Crystallization Period

10.7 Scale-Up Considerations

10.8 Manipulating Particle Shape

Chapter 11: Continuous Crystallization

11.1 Concept and Design of Continuous Crystallizers

11.2 Various Continuous Crystallizers

11.3 Periphery

11.4 Special Features of the Process

11.5 Adjustment of Suspension Densities

References

Chapter 12: Precipitation

12.1 Precipitation from Solution by Mixing Two Streams

12.2 Semi-Batch Precipitations

12.3 Model of Mixing during Precipitation

12.4 Precipitations Using Supercritical Fluids

12.5 Crystal Issues

12.6 Particle Size as a Function of Operating Conditions

Chapter 13: Mixing in Crystallization Processes

13.1 Mixing in Batch and Continuous Crystallization Processes

13.2 Basic Mixing Tasks – Mixing Tasks in Crystallization

13.3 Impellers and Agitation Systems

13.4 Power Consumption of an Impeller System [2]

13.5 Blending

13.6 Suspending

13.7 Scale-Up of a Crystallization Process

References

Chapter 14: Downstream Processes

14.1 Transfer of Suspension and Filter Cake

14.2 Solid–Liquid Separation

14.3 Drying

References

Chapter 15: Melt Crystallization

15.1 Characteristics of Melt Crystallization

15.2 Processes of Melt Crystallization

15.3 Postcrystallization Treatments

15.4 Laboratory Techniques

References

Chapter 16: Examples of Realized Continuous Crystallization Processes

16.1 Choosing the Drain Point in Process Design

16.2 Example Crop Crystallization for Organic Compounds

16.3 Example Crystallization of Table Salt

16.4 Results

Chapter 17: Design Examples of Melt Crystallization

17.1 Concepts of Melt Crystallization

17.2 Outlook

References

Index

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List of Contributors

Wolfgang Beckmann

Bayer Technology Services

Crystallization

Building E41

51368 Leverkusen

Germany

Rolf Hilfiker

Solvias AG

Römerpark 2

4303 Kaiseraugst

Switzerland

Günter Hofmann

GEA Messo GmbH

Friedrich-Ebert-Str. 134

47299 Duisburg

Germany

Matthew J. Jones

AstraZeneca

Västra Mälarehamnen 9

15185 Södertälje

Sweden

Heike Lorenz

MPI für Dynamik komplexer technischer Systeme

Sandtorstr. 1

39106 Magdeburg

Germany

Christian Melches

GEA Messo GmbH

Friedrich-Ebert-Str. 134

47299 Duisburg

Germany

Bernd Nienhaus

EKATO Rühr- und Mischtechnik GmbH

Käppelemattweg 2

79650 Schopfheim

Germany

Christiane Schmidt

AstraZeneca

Västra Mälarehamnen 9

15185 Södertälje

Sweden

Torsten Stelzer

University of Halle

Zentrum für Ingenieurwissenschaften, Verfahrenstechnik

Hoher Weg 7

06099 Halle (Saale)

Germany

Joachim Ulrich

University of Halle

Zentrum für Ingenieurwissenschaften, Verfahrenstechnik

Hoher Weg 7

06099 Halle (Saale)

Germany

Dierk Wieckhusen

Novartis AG

Lichtstr. 35

4002 Basel

Switzerland

1

Crystallization: Introduction

Wolfgang Beckmann

The beauty of crystals can be found in both the naturally appearing minerals such as diamonds or quartzite crystals and the industrial products such as sugar crystals. Crystals that are bound by flat faces intersecting at well-defined angels are characteristic of the substance and give the crop a reproducible appearance. This regular appearance is due to the long-range order of the building blocks of the crystal, be it either atoms or molecules. For example, in sodium chloride, the sodium and chlorine atoms are arranged in a cubic lattice (Figure 1.1). This arrangement maximizes the attractive interactions between the building blocks and thus minimizes the energetic state. The long-range order of its building blocks makes the crystalline state distinct from the gaseous and liquid as well as the amorphous solid state. The long-range order is also the root cause of a number of well-defined properties of the crystals, so these properties can be tailored through the crystallization process.

Figure 1.1 Arrangement of the sodium and chlorine atoms in the simple cubic lattice of sodium chloride.

A further consequence of the well-defined arrangement of the building blocks is the outer shape of the crystals; crystals are limited by flat faces that intersect under well-defined angles determined by the lattice. This can be easily observed for the large crystals of rock sugar (Figure 1.2). For a given substance, ordering is a characteristic. Consequently, the faces and their angles are characteristics of a given substance. All crystals grown under similar conditions will exhibit the same faces and partitioning of the faces.

Figure 1.2 Crystals of rock sugar with large well-developed flat faces, which intersect under certain angels characteristic of the substance; note that the apparent roughness of the faces arises not from the crystallization process, but from the downstream processes like washing.

Though the lattice is characteristic of a given substance, a large number of substances can crystallize following more than one ordering motive, leading to polymorphism. Carbon, for example, can crystallize in two different lattices, as diamond and as graphite. In diamond, the carbon atoms are arranged in two face-centered cubic lattices; in graphite, the carbon atoms are arranged in layers in which the atoms have a hexagonal symmetry (Figure 1.3). With respect to energy and stability, graphite is more stable than diamond at room temperature and ambient pressure, though the barrier for transformation is extremely high.

Figure 1.3 Carbon crystallizing in two different modifications – as graphite and as diamond – having different lattice arrangements.

A further equally important consequence of packing is the well-known purification during crystallization; only molecules of one type are incorporated, while most other molecules are rejected by the growing interface. This is for geometric as well as for energetic reasons as it is energetically favorable to incorporate a proper building block instead of an impurity molecule.

Crystallization belongs to the oldest unit operations known to mankind. Namely, the crystallization of salts can be found through the ages. Early civilizations in coastal areas used large open ponds, salines, to crystallize out the salt, which could then be easily handled, stored, transported, traded, and finally used (Figure 1.4). Salines around the seaport of Ostia are said to have facilitated the development of Roma and the Roman Empire.

Figure 1.4 Solar ponds in Venezuela (courtesy of Günter Hofmann).

However, salt obtained by evaporation of seawater had a number of drawbacks; the purity was limited, mainly due to the high content of inclusions of mother liquor that entrained impurities. Hence, industrial techniques have developed over the time for the industrial crystallization of salt, resulting in the modern continuous vacuum crystallization apparatus.

Today, crystalline products can be found in every aspect of life. Relevant product properties are determined by crystal properties and thus tailored via crystallization. Three examples are shown in Figure 1.5. Sucrose, sugar, is extracted from plants and crystallized to meet a certain particle size distribution, typically in the range of 700–800 μm, to be free of fines, which allows a free-flowing product that does not agglomerate. Finally, the process arrives at purities of >99.5% in an essentially single-step process of a seeded batch crystallization. Table salt also is required to be free flowing and not to agglomerate even in the high relative humidity environment of a kitchen. Here, additives can be employed during the crystallization, which is usually continuously operated evaporation crystallization. Finally, one of the main components of chocolate, cocoa fat has to be crystallized in a certain crystal modification or polymorph to achieve the special mouth taste of chocolate. This modification is unstable at room temperature and achieved via melt crystallization, where the crystals of the desired modification are generated and grown via a temperature program. In addition, additives can be used to stabilize the required modification. The unstable modification of the fatty acid ester can recrystallize to a more stable one, resulting in undesired changes in the appearance of the product.

Figure 1.5 Sugar, table salt, and chocolate as examples of everyday life products, where the properties of the crystalline state determine product properties and where the crystallization is tailored to meet this demand.

In a number of cases, mother liquor is the desired product of the crystallization process. The crystallization of ice from aqueous solutions can be used for freeze concentration of aqueous solutions. One example of everyday life is orange juice that can be freeze concentrated at low temperatures gently and in an energy-efficient way. The concentration of waste from effluent waters is another application.

The application of crystallization in industry ranges from the isolation of the few milligrams of a substance newly synthesized in the laboratory – where a well-defined melting point is used to both achieve and prove a decent purity of the crop and as an identity check – to a mass crystallization carried out in very diverse industries; some products are listed with their annual production volume in Table 1.1.

Table 1.1 Examples for the annual production of crystalline products in various fields.

ProductProduced inProduction (t/a)Sodium chloride2001 in the EU38 350 000Sugar2001 in the EU15 000 000Caprolactam2002 worldwide3 500 000Ascorbic acid2009 worldwide110 000Acetylsalicylic acid2008 worldwide35 000

The equipment used in the industrial crystallization varies widely, from multipurpose batch vessels in the life science industry to highly sophisticated dedicated equipment used for some large volume products.

In the following chapters, the basic concepts of the modern understanding of crystallization will be discussed, such as the internal structure of the crystals and their growth mechanisms or the phase diagrams. Attention will be directed to the purification by crystallization and to effects of polymorphism. Next, the basic methods to carry out a crystallization, from both the solution and the melt, are discussed. Finally, the concepts of mass crystallization in continuously operated crystallizers will be shown.

2

Mechanisms of Crystallization

Wolfgang Beckmann

One of the most important features of crystals is the long-range order of their building blocks and symmetry of their arrangement. This arrangement maximizes the interaction between the building blocks, stabilizing the crystal. Most macroscopic properties of crystals, such as their shape or the purification during crystallization, are a direct consequence of this arrangement. Thus, the discussion of the mechanisms of crystallizations has first to deal with the symmetry and long-range order in crystals. In the second part, the nucleation and growth mechanisms of crystals are discussed. In both cases, a supersaturated mother phase or a deviation from saturation is necessary. The dependence of the processes on supersaturation and other parameters has to be discussed. The discussion of crystal nucleation has two goals: first, to determine the mechanisms and thus also the prerequisites for nucleation; second, to derive expressions for the dependence on supersaturation.

2.1 Crystal Lattice

2.1.1 Arrangement of Building Blocks and Symmetries

Crystallization is a phase transformation for which the free enthalpy has to be negative (Equation 2.1). The crystal will be stabilized by minimizing the enthalpy term , which is determined by the interaction of the building blocks. Interactive forces might either be van der Waals or electrostatic forces. In molecular crystals, hydrogen bonding also plays an important role.

The van der Waals forces do have a relatively short-range order, a typical potential is given by , where is the distance between the interaction bodies. The potential is shown in Figure 2.1. The interaction potential of electrostatic forces decreases via .

(2.1)

Figure 2.1 Trend of the pair interaction potential of van der Waals forces. Note that the minimum in the pair interaction at is slightly different from the equilibrium distance in a crystal. It is apparent that the interaction is mainly determined by the first nearest neighbors.

Due to the rapid decrease of the potential with distance, the nearest-neighbor interactions determine the energetics of the arrangement. Consequently, only well-defined symmetries in the arrangement of the building blocks of a crystal are allowed. This is visualized for a two-dimensional lattice by packing units with different symmetries (Figure 2.2). In part (a), objects with a two-, four-, and sixfold symmetry are packed; in part (b), the units have a five- and sixfold symmetry. The former set of objects allows packing, maximizing the pair interaction of building blocks, while the latter ones lead to suboptimal packing that is subsequently not found in crystals.

Figure 2.2 Construction of a 2D lattice by packing units with different symmetries. In part (a), objects with a two-, four-, and sixfold symmetry are packed; in part (b), the units have a five- and sixfold symmetry. While the former set of objects maximizes the interaction between building blocks, the latter ones can only be arranged in a suboptimal packing.

The considerations can be applied to the three-dimensional lattice. The packing of spheres in a plane is optimal for a hexagonal arrangement, as shown in Figure 2.3.

Figure 2.3 Optimized packing of spheres in (a) in one dimension, followed by the addition of further layers of hexagonally arranged building blocks (b and c). Here, only the case of the cubic closest packing is shown.