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Process & Energy – Intensified Reaction & Separation Systems
Particle Formation by Crystallization
Herman J.M. Kramer
Intensified Reaction & Separation Systems
Process & Energy
Delft University of Technology
Leeghwaterstraat 39
2628 CB Delft
The Netherlands
Acknowledgement
JMBC Particle Technology Course: Crystallization
Crystallization
A. Crystallization: Phenomena, Process & Product Properties
Introduction Crystallization
Crystals as Product:
Crystal purity, Crystal Size Distribution, Crystal shape and crystal solid form
Crystallization kinetics
Nucleation, Crystal Growth, Attrition
Crystallization process
thermodynamics
process design
equipment
modelling optimization and control
B. Advanced crystallization topics
Polymorphism
Chiral crystallization
2
JMBC Particle Technology Course: Crystallization
Literature
Basic references
• Industrial Crystallization, fundamentals and application, A. Lewis, M.S. Seckler, H.J.M. Kramer and G.M van Rosmalen, Cambrridge University press, 2015
• Handbook of Industrial Crystallization, A.S Myerson, 2002, Butterworth- Heinemann
• Crystallization, J.W. Mullin, 2001,Butterworth & Heinemann
• Crystallization, H.J.M. Kramer, G.M. van Rosmalen, In: Encyclopedia of Separation Science, Ed. I.D. Wilson, 2000, Vol. 1, page 64-84.
3
JMBC Particle Technology Course: Crystallization
Crystallization
Crystallization Synthesis
of API Filtration
Crystalline product 99.99% pure
Solution containing impurities and dissolved synthesis product
High selectivity Mild conditions Low energy demand Particular product Slow process
4
A separation unit operation
JMBC Particle Technology Course: Crystallization
Pro’s & Con’s of Crystallization
• High distribution coefficient KA of compound to be crystallized • Low distribution coefficient KS of solvent and impurities • High selectivity α
• Pure product in one process step
99.9-100% pure
1
* *
cr
AA
A A
xK
x x (very large)
0
* *
cr
SS
S S
xK
x x (very small)
a =K
i
KS
(very large)
5
JMBC Particle Technology Course: Crystallization
Pro’s & Con’s of Crystallization
• Highly selective
• Energy efficient
• Mild conditions
• No auxiliary phase
• Solid particulate product
• Slurry handling
• Solid/liquid separation
• Complex control
• Fundamental knowledge
• Product specific designs
• Slow process:
• Growth rate ~ 10-8-10-7 m/s
99.9-100% pure
6
JMBC Particle Technology Course: Crystallization
Crystallization is more than a separation technique • Separation
• Table salt, soda, sugar • Purification
• Pharmaceuticals, caprolactam, parrafin, proteins • Concentration
• Beverages, waste water • Particulate Product Formation
• nano-scale (creams, magnetic tapes, catalysts, zeolites) • micro-scale (inhalers) • macro-scale (silicon wafers) • Pharmaceutical crystal form: organic salt, polymorphism, co-
crystals • Analysis
• Proteins
integration of separation and crystalline product formation
7
JMBC Particle Technology Course: Crystallization
Relevance of Crystallization
• About 70% of all products are solids
• After distillation the most important separation technology
• The most frequently used separation technology
• Food - Sugar, cacao butter, iced beer, sweeteners
• Pharmaceuticals - Aspirin, inhalers, antibiotics, enzymes, insuline
• Salt & derivatives - Table salt, soda
• Fine-chemicals - Pigments
• Petrochemicals - Starting material for polymers
• Electronics - Silicon wafers
• Agriculture - Fertilizer
• Waste treatment - Freeze-concentration, metal-recovery
8
JMBC Particle Technology Course: Crystallization
The Crystalline Product
Table salt
• Crystal purity >99.9%
• Crystal size distribution
• Crystal shape: cubic
• Crystal stucture • Solvates
• Polymorphs
• Chiral crystals
L [m]
f(L)
9
JMBC Particle Technology Course: Crystallization
Crystallization occurs at molecular level
step
terrace
kink
Incorporation of single molecules into the crystal lattice
Arrangement of millions of molecules into crystal lattice Interaction at surface with solvent and impurities
10 Crystallization is highly selective One step crystallizations can result in 99.9% pure products
JMBC Particle Technology Course: Crystallization
Molecular structure: the crystal unit cell
Adipic acid Monoclinic (P21/c) abc, ==90°
Aspartame Tetragonal (P41)
a=bc, ===90°
11
JMBC Particle Technology Course: Crystallization
What is a crystal?
A crystal is a solid
in which its building units (molecules, atoms, ions)
are packed in regularly ordered, repeated patterns
extending in all 3 dimensions
12
JMBC Particle Technology Course: Crystallization
Crystallization
Product • Purity • Size distribution • Shape • Crystal form
Process • Creation of supersaturation • Crystallization method • Batch continuous
Phenomena • Nucleation • Growth • Attrition • Agglomeration
Fundamentals (molecular
interactions)
Process design
Equipment design
13
JMBC Particle Technology Course: Crystallization
MgSO4 Crystallisation plant
14
JMBC Particle Technology Course: Crystallization
Product phenomena
Impurity effect on product quality
15
JMBC Particle Technology Course: Crystallization
Product is dependent on process conditions
Gypsum - CaSO4.2H2O
Stimulate agglomeration during process to enhance filterability
16
JMBC Particle Technology Course: Crystallization
Crystallization Process
Principle phenomena
• Primary nucleation
• Secondary nucleation
• Attrition /breakage
• Growth
• Agglomeration
17
JMBC Particle Technology Course: Crystallization
Other properties of crystal products
5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile JACS 122 (2000) 585
18
Type of polymorph
• Shape
• Color
• Solubility
• Stability
Chirality
• Bio activity
• Crystal shape: cubic
• Crystal form: anhydrate
JMBC Particle Technology Course: Crystallization
Solid Forms in Pharmaceutical Industry
1998 Product withdrawal of Norvir (ritonavir). Dissolution failure of oral capsules as a result of the appearance of a thermodynamically more stable form.
2008 Recall of Neupro (transdermal rotigotine) patches. Crystallization of a new polymorph that resembled snowflake-like crystals.
2010 Recall of the popular blood thinner Coumadin (warfarin sodium 2-propanol solvate). Variation in the 2-propanol levels, which affect the crystallinity of warfarin sodium.
Brand Name
Company API Sales [billions $]
# solid phases
Lipitor Pfizer Atorvastatin Calcium
12.5 41
Diovan Novartis Valsartan 6.0 10
Nexium AstraZeneca Esomeprazole magnesium
5.0 4
Some bestselling small molecule drugs in 2009
19
JMBC Particle Technology Course: Crystallization
Crystallization as a molecular affinity separation
• A directed spontaneous self-assembly of a 3-dimensional array of atoms, molecules or ions
• Crystallization is more than a separation technique: integration of separation and product formation
• Product quality aspects
• Purity, CSD, shape, crystal form
• Crystallization requires sold/liquid separation steps
20
JMBC Particle Technology Course: Crystallization
Main product quality characteristics
Crystal size distribution
Product quality
Crystal shape Crystal form Purity
Filterability Packing density Caking Surface area Morphology Agglomeration …
Filterability Packing density Caking Surface area …
Polymorphs Solvates Salts Color Solubility Dissolution behavior Bioavailability Stability ..
Impurity content Inclusions Agglomeration Polymorphs …
Customer demands
21
JMBC Particle Technology Course: Crystallization
Crystal form
22
JMBC Particle Technology Course: Crystallization
Free base
Metastable polymorph
Co-crystal Solvate
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
Salt
H+ A-
API Co-former Solvent Acid
stable polymorph
Composition change
Structure change
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
Crystal form
23
JMBC Particle Technology Course: Crystallization
Crystal form: Hydrates and solvates
Gypsum (CaSO4.2H2O) Anhydrite (CaSO4)
24
JMBC Particle Technology Course: Crystallization
Crystal form: Polymorphism
-form -form
L-Glutamic acid
25
JMBC Particle Technology Course: Crystallization
Crystal form: Polymorphism
CaCO3 - Calcite (lozenges) and vaterite (spheres)
26
JMBC Particle Technology Course: Crystallization
Crystal Size Distribution
27
JMBC Particle Technology Course: Crystallization
Crystal size versus particle size
A
B
C
A
B
C
Sólido irregularSólido regular
A
B C
Particle size is a broader term
28
JMBC Particle Technology Course: Crystallization
name definition
length maximal length
sieve diameter width of the minimum square aperture through which the particle will pass
volume diameter diameter of a sphere having the same volume as the crystal
surface diameter diameter of a sphere having the same surface area as the crystal
projected area diameter
diameter of a sphere having the same projected area as the crystal viewed from a fixed direction
Particle size definitions
• Each method for size measurement captures a specific feature of particle size
• Do not compare sizes measured by distinct methods !
29
JMBC Particle Technology Course: Crystallization
Particle size: Sieving
Aperture
30
JMBC Particle Technology Course: Crystallization
0.1%2.9%
19.2%
48.0%
19.2%
9.6%
1.0%
0
0.1
0.2
0.3
0.4
0.5
0 40 100 200 400 600 20001000
L m
Particle size distributions Size range [m]
Mass
[g]
0 - 40
40 - 100
100 - 200
200 - 400
400 - 600
600 - 1000
1000 - 2000
0.1
2.9
19.2
48.0
19.2
9.6
1.0
Size range [m]
Mass fraction
[-]
Mass density distribution
<L>=362m
31
JMBC Particle Technology Course: Crystallization
Crystal Shape
32
JMBC Particle Technology Course: Crystallization
Crystal shape
33
JMBC Particle Technology Course: Crystallization
Crystal shape
Crystal shape
agglomeration
Crystal structure
Process
Phenomena
impurities
crystal form (equilibrium shape)
solvent
supersaturation
temperature
growth
nucleation
34
JMBC Particle Technology Course: Crystallization
Crystal morphology
• Morphology is determined by the slowest growing faces
slow
fast
35
JMBC Particle Technology Course: Crystallization
Crystal shape: supersaturation effect
Lysozyme
36
JMBC Particle Technology Course: Crystallization
Crystal shape
Temperature (S=1)
Supersaturation (constant T)
Thermal roughening
Kinetic roughening
37
JMBC Particle Technology Course: Crystallization
Crystal shape: solvent effect RDX crystal morphology from different solvents
Solvent can have a distinct effect on the crystal shape
38
JMBC Particle Technology Course: Crystallization
Crystal shape: impurity effect
grown in the presence of Fe(CN)4-6
NaCl crystals
Table salt
39
JMBC Particle Technology Course: Crystallization
NaCl from a fluid bed crystallizer NaCl from an Oslo crystallizer
NaCl grown in a rotating flow NaCl grown under high supersation
Crystal shape: crystallizer
40
JMBC Particle Technology Course: Crystallization
Crystal Purity
41
JMBC Particle Technology Course: Crystallization
Product purity
• Impurity incorporation in crystal lattice
• Inclusion of mother liquor
• due to impurity and growth
• due to attrition / secondary nucleation
• Impure product due to agglomeration
• Adhering mother liquor
42
JMBC Particle Technology Course: Crystallization
Crystallization kinetics
• Solubility, supersaturation and phase diagrams
• Nucleation (formation of a new crystalline phase)
• Primary nucleation
• Secondary nucleation
• Crystal growth (mass deposition on existing crystals )
• Mass transfer
• Integration of solute molecules in crystal lattice
• Agglomeration
• Collision
• Cementation
• Rupture
43
JMBC Particle Technology Course: Crystallization
Solubility, supersaturation and Phase diagrams
LZ
LC
Lever-rule: Eutectic system, constant P
Solid A + solid B
Suspension density
44
Solubility ideal system:
1 1* exp
m
Hx
R T T
Melting temperature Of pure B
Enthalpy of dissolution of B
Mole fraction of B
Be careful solubility not dependent on the properties of the solvent. Not realistic!!!
! However the temperature dependence is.
JMBC Particle Technology Course: Crystallization
Solubility, supersaturation and Phase diagrams
LZ
LC
Lever-rule: Eutectic system, constant P
Solid A + solid B
Suspension density
45
SL
akTLL ln*
eqL
eq
L
eq
SS akT ln*
eqa
akT ln
Definition supersaturation
JMBC Particle Technology Course: Crystallization
Supersaturation
eqa
akT ln
eq
eq
eqeqeq c
cc
c
c
x
x
a
alnlnln
Ideal system dilute system
low supersaturation
Dilute system
1<C/Ceq<1.1 Relative supersaturation
46
Methods to generate supersaturation • See handbooks • Important for the design of the crystallization process
JMBC Particle Technology Course: Crystallization
Suspension • Establish an equilibrium in a stirred suspension at a given T,P
between the solid and liquid phase • Filter solution of crystals to isolate liquid • Analyse the liquid phase to measure concentration at given T,P by
evaporating the solvent or by analytical techniques
How to measure solubility?
Stirrer
Temperature control
JMBC Particle Technology Course: Crystallization
Alternative technique Measure saturation temperature
X
Suspension (Low T)
Clear point: The temperature at which a suspension becomes a clear solution during heating with a certain rate
Clear solution (high T)
Light Light
48
JMBC Particle Technology Course: Crystallization
Clear & Cloud Point Measurements
T
Tra
nsm
ission
Clear point, 100% transmission
Ts=42.2°C
Ts=42.3°C
1440 min = 1 day
49
JMBC Particle Technology Course: Crystallization
Crystallization kinetics
50
… …
RP
-1
mp
10
6.2
oC
=
21
.7°
RO
Y
OR
PP
bca
=
39
.4°
OP
P2
1 /c
mp
11
2.7
oC
=
46
.1°
ON
P2
1 /c
mp
11
4.8
oC
=
52
.6°
YN
P-1
=
10
4.1
°
YP
21 /c
mp
10
9.8
oC
=
10
4.7
°
N
S
HN
OO
C
NCH
3
Primary nucleation
JMBC Particle Technology Course: Crystallization
51
Primary
Nucleation
Homogeneous
Nucleation (HON)
Heterogeneous
Nucleation (HEN)
• Primary nucleation is the process of random generation
of nanoscopically small formations of a new phase that
have the ability for irreversible growth to
macroscopically large sizes.
• Primary nucleation is primarily driven by the level of
supersaturation and conditions that facilitate the
formation of a surface
Crystallization kinetics n
spherical cluster
in solution
substrate
n
cap-shaped cluster
on a substrate
JMBC Particle Technology Course: Crystallization
52
Primary nucleation
… …
RP
-1
mp
10
6.2
oC
=
21
.7°
RO
Y
OR
PP
bca
=
39
.4°
OP
P2
1 /c
mp
11
2.7
oC
=
46
.1°
ON
P2
1 /c
mp
11
4.8
oC
=
52
.6°
YN
P-1
=
10
4.1
°
YP
21 /c
mp
10
9.8
oC
=
10
4.7
°
N
S
HN
OO
C
NCH
3
Nucleation model of Szilard: nucleation is a series of bimolecular
“reactions” between molecules (monomers) and clusters.
1 2 3 … n* 1 n* n* +1 … fn1
gn1
fn
gn
fn – attachment frequency of monomers to n-sized cluster
gn – detachment frequency of monomers to n-sized cluster
JMBC Particle Technology Course: Crystallization
Nucleation work for HON
Free
energy
W(n)
0
W(n)
ΔGV
ΔGs
W*
n* 0
Cluster size n
Interfacial energy and
supersaturation ratio S
STk
vW
2
3
22
2
ln3
16*
53
2 3
3 3 2
W * 16 vJ A exp A exp
kT 3k T ln S
1. Creation of volume, ΔGV 2. Creation of surface, ΔGS 3. To form a cluster with n molecules, W (n) = ΔGV + ΔGS
JMBC Particle Technology Course: Crystallization
Homogeneous and heterogeneous nucleation
Homogeneous
AHON = 1030-1035
Heterogeneous
AHEN = 1015-1025
ef = with 0<<1
> ef
AHON > AHEN
At high S Homogeneous nucleation
dominant
At lower S Heterogeneous nucleation
dominant
Heterogeneous particles (dust particles, impurities, …) are always present
These particles affect the while also A is strongly different
54
JMBC Particle Technology Course: Crystallization
Primary nucleation rate
The number of crystals created per unit of volume and time
J in units [m-3s-1]
Arrhenius type reaction
with energy barrier W *
2 3
3 3 2
W * 16 vJ A exp A exp
kT 3k T ln S
Highly non-linear behavior towards S and
55
1.0E+03
1.0E+06
1.0E+09
1.0E+12
1.0E+15
1.0E+18
1 10 100 1000 10000 100000 1000000
S
J
[#/m3s]
Supersaturation ratio S
HON A=1030
HEN A=1020 =0.7
JMBC Particle Technology Course: Crystallization
Secondary nucleation
Attrition
• Takes place in the presence of larger crystals (parent crystals)
• Stages:
• generation of attrition fragments
• removal of fragments from parent crystal
• survival and growth of the fragments
• Is affected by hydrodynamics, design of equipment and the supersaturation and particle properties
56
JMBC Particle Technology Course: Crystallization
57
Secondary nucleation rate: power law
or j
T
hi
LN MNGkB 0
1
0
kb jspN TB k σ P M
B0 = Secondary nucleation rate [# m-3 s-1] GL = Crystal growth rate (m/s), GL = kg b
N = Impeller rotational speed [rpm] MT = Total mass of crystals per unit volume = relative supersaturation (-) Psp = specific power input Psp ~ N3
are constants related to crystallizer geometry (impeller type, number of blades, scale of operation)
kN and kN1
1 < b < 3; 0.6 < k < 0.7; j = 1 or 2
JMBC Particle Technology Course: Crystallization
Nucleation & growth in a batch process
0%
10%
20%
30%
40%
50%
0 20 40 60 80 100 120
Temperature
c [w
%]
Solubility
Metastable zone limit
start of nucleation
Unpredictable Uncontrollable
58
JMBC Particle Technology Course: Crystallization
59
Crystallization Characteristics Clear point - Upon heating there is a temperature that a suspension turns into a clear solution Cloud point - Upon cooling a solution there is a temperature that crystals will be detected Metastable Zone Width - The difference between the saturation temperature (Clear point) and cloud point is the
JMBC Particle Technology Course: Crystallization
60
Isonicotinamide in Ethanol: Metastable zone width
Why is there a difference between clear and cloud point?
5
10
15
20
25
30
35
40
45
50
55
60
6:00 7:12 8:24 9:36 10:48 12:00
Time (hour)
Tem
pera
ture
(oC
)
0
10
20
30
40
50
60
70
80
90
100
Tra
nsm
issiv
ity (
%)
Cloud point
Clear point
MSZWTemperature
[°C] Transmission
of light [%]
JMBC Particle Technology Course: Crystallization
Intermezzo
61
Light Source
Photochemical Effect
Non-Photochemical
Effect
Non-Photochemical
NPLIN: Used to study the fundamental of primary nucleation Facilitate primary nucleation at mild (low supersaturaton) conditions
JMBC Particle Technology Course: Crystallization
Smooth or layer growth
• growth units attach to kinks sites in the steps
• steps propagate along the crystal surface and form growth layers
• two step sources generate steps:
• Birth and Spread growth mechanism
• Spiral growth mechanism
Rough growth
• growth units attach anywhere to the rough crystal surface
• Rough growth mechanism
Crystal growth: Smooth or rough surface
62
The growth units are incorporated in an existing crystal lattice
JMBC Particle Technology Course: Crystallization
Polymorphism Dutch painter Escher
Fish form I Fish form II
63
JMBC Particle Technology Course: Crystallization
Free base
Metastable polymorph
Co-crystal Solvate
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
Salt
H+ A-
API Co-former Solvent Acid
stable polymorph
Composition change
Structure change
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
H+
A-
Crystal form
64
JMBC Particle Technology Course: Crystallization
Polymorphism: product quality
The ability of a chemical compound to crystallize into different crystalline compounds
65
JMBC Particle Technology Course: Crystallization
Polymorphism
• The number of forms known for a given compound is proportional to the time and money spent in research on that compound (McCrone, 1965)
• Currently not true anymore – although now and then a new polymorph pops up
• Succesfull research strategies have been developed to search for polymorphs
Record: 17 polymorphs J.A. Pesti, R.A. Chorvat, G.F. Huhn, Chem. Innovations 2002, Oct. 28
66
JMBC Particle Technology Course: Crystallization
Polymorphism: L-histidine
-form Orthorhombic (P21 21 21)
abc, ===90°
-form monoclinic
(P21) abc, ==90°
67
JMBC Particle Technology Course: Crystallization
Polymorphism: Ritonavir
• The HIV-1 and HIV-2 protease inhibitor Ritonavir
• In 1996 Ritonavir was introduced on the market
• In 1998 a new, more stable form appeared • The new polymorph had a 4 times lower solubility • This affected the bioavailability of the pharmaceutical • The company Abbott withdrew Ritonavir from the market
• 1 year of research effort enabled the production of the old less
stable polymorph again.
• Costs: 100 of millions of dollars
68
JMBC Particle Technology Course: Crystallization
Thermodynamic stability: solubility
c*
Temperature
enantiotropic
c*
Temperature
monotropic
The transition temperature is independent from the solvent
Tt
69
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallization
c* c
Temperature Tt
I
II
Thermodynamics: Above Tt I is obtained, below Tt II is obtained, but …
70
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallization
c* c
Temperature Tt
I
II Metastable zone widths
Adjustable by changing solvent
71
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallization
c* c
Temperature Tt
I
II
72
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallisation
+ seeds
II
I
T Ttransform
Concentr
ation
Temperature
73
JMBC Particle Technology Course: Crystallization
Solvent mediated polymorph transformation: L-glutamic acid
Supersaturation
Nucleation &
crystal growth
Unstable Polymorph
Solvent mediated polymorph
transformation
Supersaturation
Nucleation &
crystal growth
Stable Polymorph
74
JMBC Particle Technology Course: Crystallization
Solvent mediated polymorph transformation: L-glutamic acid & Raman spectroscopy
0.300
0.350
0.400
0.450
0.500
0.550
0.600
0.650
0.700
0.750
0.800
600 650 700 750 800 850
Raman Shift [cm-1]
-form fraction in crystalline phase
0%
31%
68%
97%
-form -form
Raman can detect polymorphic fraction in
crystal phase of suspension
Relative intensity
75
JMBC Particle Technology Course: Crystallization
Control & optimization of polymorph crystallization
0
20
40
60
80
100
-1 0 2 4 6 8 10
Time [hr]
-form fraction [wt%]
I II
50ºC 45ºC 40ºC
25ºC
Large effect of temperature on transformation process
76
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallization
c* c
Temperature Tt
I
II Metastable zone widths
High possibility of concomitant
polymorphism
77
JMBC Particle Technology Course: Crystallization
Concomitant polymorphism
Calcite and vaterite (CaCO3)
1,1-dicyano-4-(4-dimethylaminophenyl)-1,3-butadiene
78
JMBC Particle Technology Course: Crystallization
Kinetics in cooling crystallization: oiling out
c* c
Temperature
I
0
100%
liquid-liquid phase split
solute-rich and solute-poor phase with equal chemical potential
crystallization usually starts in the solute rich phase
Roger Davey, Chem. Comm. 2003 79
JMBC Particle Technology Course: Crystallization
Anti-solvent crystallization
• Why?
• Thermally instable API
• Removal from remaining solution after cooling crystallization
• Solubility is variable
• Be aware of local conditions
• Many process configurations
• Wide variety of particle size distributions and polymorphs
Ascorbic acid from EtOH/CO2
Acetaminophen from EtOH/CO2
80
JMBC Particle Technology Course: Crystallization
Kinetics in antisolvent crystallization
S
AS
w% antisolvent →
So
lub
ility
→
100 AS 0
Slow addition mild conditions less chance for
unwanted polymorph
81
JMBC Particle Technology Course: Crystallization
Kinetics in antisolvent crystallization
AS
S
w% antisolvent →
So
lub
ility
→
100 AS 0
Extreme supersaturations Concomitant polymorphism
82
JMBC Particle Technology Course: Crystallization
Polymorphism: Ritonavir
• The HIV-1 and HIV-2 protease inhibitor Ritonavir
• In 1996 Ritonavir was introduced on the market
• In 1998 a new, more stable form appeared • The new polymorph had a 4 times lower solubility • This affected the bioavailability of the pharmaceutical • The company Abbott withdrew Ritonavir from the market
• 1 year of research effort enabled the production of the old less
stable polymorph again.
• Costs: 100 of millions of dollars
83
JMBC Particle Technology Course: Crystallization
Kinetics in antisolvent crystallization
How to obtain the metastable form I of Ritonavir?
1. Crystallize form I a. suspension form I seeds in anti-solvent b. fed-batch addition of solution to anti-solvent
2. Inhibition of transition I => II Choice of solvent mixture inhibits transition
Ethyl-acetate/Heptane 2:1 >90% polymorph II Ethyl-acetate/Heptane 1:2 mostly polymorph I
84
JMBC Particle Technology Course: Crystallization
Conclusions
• Polymorphism is the ability of a chemical compound to form different crystalline lattices
• polymorphs differ in their physical properties and is therefore an important issue in pharmaceutical industry
• The crystallization of polymorphs is a process of nucleation and growth of both polymorphs and the possible solvent mediated transition from a metastable form to a more stable form.
• Crystallization of polymorphs is a balance between thermodynamics and kinetics
85
JMBC Particle Technology Course: Crystallization
References
• Joel Bernstein, Polymorphism in molecular crystals, Clarendon Press, Oxford, 2002
• T. Threlfall, Crystallisation of Polymorphs: Thermodynamic Insight into the Role of Solvent, Organic Process Research Development 4 (2000) 384-390
• J. Bernstein, J. Dunitz, Disappearing polymorphs, Acc. Chem. Res. 28 (1995) 193-200.
• S. Gracin, Å.C. Rasmuson, Polymorphism and crystallization of p-aminobenzoic acid, Crystal growth design 4(5) (2004) 1013-1023.
• J. Bauer et al., Ritonavir: An extraordinary example of conformational polymorphism, Pharmaceutical research 18(6) (2001) 859-866.
• T. Ono, J.H. ter Horst, P.J. Jansens, Quantitative Measurement of the Polymorphic Transformation of L-Glutamic Acid Using In-Situ Raman Spectroscopy, Crystal Growth Design 4(3) (2004) 465-469.
• C.S. Towler, R.J. Davey, R.W. Lancaster, C.J. Price, Impact of molecular speciation on crystal nucleation in polymorphic systems: the conundrum of glycine and molecular “self poisioning”, J. Am. Chem. Soc. 126 (2004) 13347-13353.
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Process & Energy – Intensified Reaction & Separation Systems
Chiral separation
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JMBC Particle Technology Course: Crystallization
Chirality
“I call any geometrical figure, or group of points, chiral, and say it has chirality, if its image in a plane mirror, ideally realised, cannot be brought to coincide with itself.”
Lord Kelvin.
Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light, 1904.
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JMBC Particle Technology Course: Crystallization
Enantiomers
Enantiomers are stereoisomer pairs in a mirror-image relationship.
Enantiomer pairs possess identical physical properties, but their biological activities and
effects can be markedly different.
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JMBC Particle Technology Course: Crystallization
Amino acids
L-leucine
L-phenylalanine
L-tyrosine
L-tryptophan
All taste bitter.
D-leucine
D-phenylalanine
D-tyrosine
D-tryptophan
All taste sweet.
COOCH3
HNHOOC
NH2
CH2PhO
L COOCH3
HNHOOC
NH2
CH2PhO
D
sweet bitter
Aspartames
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JMBC Particle Technology Course: Crystallization
In the 1960s, thalidomide was administered as a mixture of two enantiomeric forms:-
NH
N
H
O
O
O O NH
N
H
O
O
O O
R-thalidomidemild sedative
S-thalidomideteratogen
Thalidomide
Causes birth defects
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JMBC Particle Technology Course: Crystallization
Chiral compounds
Racemic compound enantiopure compound
+ +
Escher 92
JMBC Particle Technology Course: Crystallization
Crystallization from a racemic mixture
Racemic compound
conglomerate
Escher 93
JMBC Particle Technology Course: Crystallization
Crystallization from a racemic mixture
• Racemic crystals (92%).
• Enantiomer pairs incorporated stoichiometrically into the unit cell.
• Resolvable only by chemical intervention.
• Conglomerates (8%).
• Mechanical mixtures of homochiral crystals of the two enantiomer forms.
• Resolvable physically by crystallization methods.
• Pseudoracemates (very few).
• Crystallize as solid solutions.
• Require chemical intervention for resolution.
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JMBC Particle Technology Course: Crystallization
Solubility
If the solubility is low, the saturation temperature is high
T
c
1/T
Lnx
JMBC Particle Technology Course: Crystallization
Clear & Cloud Point Measurements
T
Tra
nsm
ission
Clear point, 100% transmission
Ts=42.2°C
Ts=42.3°C
JMBC Particle Technology Course: Crystallization
Clear Point & Solubility
Thermodynamic Solubility point
JMBC Particle Technology Course: Crystallization
Chiral compounds
T
yR S R
S+L R+L
L
R+S
yR S R
L
RS
yR S R
S+L
L
R+L
S+RS R+RS
Conglomerate Racemic compound Solid solution
The phase diagram reflects the kind of solid state
RS+L
Binary phase diagram Co-crystal
JMBC Particle Technology Course: Crystallization
Chiral Compounds: Asparagine in Water
0
5
10
15
20
25
30
0 5 10 15 20 25 30
x R [mmol/mol]
x s
[mmol/mol]
x=25
x=15
a
40
50
60
70
80
0 0.25 0.5 0.75 1
y R [-]
T s
[°C]
x=25
x=15
b
Conglomerate
Ternary phase diagram screening
JMBC Particle Technology Course: Crystallization
Chiral Compounds: Ibuprofen in Hexane
Racemic compound
0
50
100
150
200
0 50 100 150 200
x R [mmol/mol]
x s
[mmol/mol]
x =175 c
0
10
20
30
40
50
60
0 0.25 0.5 0.75 1
y R [-]
T s
[°C]
d
Ternary phase diagram screening
JMBC Particle Technology Course: Crystallization
Chiral Compounds: Atenolol in Ethanol
Solid solution
0
10
20
30
0 10 20 30
x R [mmol/mol]
x s
[mmol/mol]
x=25
x=10
x=25
x=10
e
0
10
20
30
40
50
60
0 0.25 0.5 0.75 1
y R [-]
T s
[°C]
x=25
x=10
x =25
x =10
f
Ternary phase diagram screening
JMBC Particle Technology Course: Crystallization
Chiral Compounds
• Saturation temperature measurements can be used to identify the kind of solid state of a chiral pharmaceutical at solution crystallization conditions
• The ternary phase diagram is obtained as a bonus
Racemic Compound, Conglomerate or Solid Solution?
Ternary phase diagram screening
S. Sukanya, J.H. ter Horst, Racemic Compound, Conglomerate, or Solid Solution: Phase Diagram Screening of Chiral Compounds,
Crystal Growth Design 10(4) (2010) 1808-1812.
JMBC Particle Technology Course: Crystallization
Phase diagram
(S)
(+) (-)
S'
s(+) + s(-) + l
s(-) + l s(+) + l
Conglomerate
(S)
(+) (-)
s(+) + s(R) + l s(-) + s(R) + l
s(R) + l s(+) + l s(-) + l
S'
Racemic crystals
S. Srisanga, J.H. ter Horst, Crystal growth design, 2010
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JMBC Particle Technology Course: Crystallization
Resolution of Conglomerates - Methods available
1. Preferential crystallization
2. Crystallization of diastereomers
3. The grinding method: Combining a racemization reaction with suspension grinding
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JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R Seed fraction
Grow S Dissolve R
Dissolve S Grow R
Grow S & R Dissolve S Nucleate & Grow R
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JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R Seed fraction
Add seeds with excess S:
Only R crystals dissolve
106
JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R
Grow S crystals,
Remove S crystals
107
JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R
Add seeds with excess R:
Only S crystals dissolve
108
JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R
Grow R crystals,
Remove R crystals
109
JMBC Particle Technology Course: Crystallization
1. Preferential crystallization - principle
Solvent
S R
Take care in avoiding Crystallization of the
Other enaniomer: Difficult!
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JMBC Particle Technology Course: Crystallization
2. Resolution of racemic crystal systems.
A single-enantiomer resolving agent can be used to form a pair of products in a diastereomeric relationship.
Example: racemic acid (±)-A-H+ and resolving base (+)-B:
(±)-A-H+ + (+)-B [(+)-A-.(+)-BH+] + [(-)-A-.(+)-BH+] ‘p’-salt ‘n’-salt
Compounds in diastereomeric relationships often exhibit significantly
different physical properties, unlike enantiomer pairs.
Selection of resolving agent is a trial-and-error exercise.
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JMBC Particle Technology Course: Crystallization
2. Resolution of racemic crystal systems.
NH3
CH3
+OOC
R
-
R = CH3, C2H5, OH
Model system
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JMBC Particle Technology Course: Crystallization
2. Resolution of racemic crystal systems
0
0.5
1
0 20 40 60
Temperature C
So
lub
ilit
y m
ol/
L
R-form
S-form
Solubilities – R = CH3
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JMBC Particle Technology Course: Crystallization
0
0.5
1
0 20 40 60
Temperature C
So
lub
ilit
y m
ol/
L
S-form
R-form
2. Resolution of racemic crystal systems
Solubilities – R = OH
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JMBC Particle Technology Course: Crystallization
3. The grinding method
conglomerate Enantiopure
W.L. Noorduin et al., J. Am. Chem. Soc. 130 (2008) 1158.
Combining a racemization reaction and suspension grinding
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JMBC Particle Technology Course: Crystallization
Chiral separation
• A conglomerate system can be separated using preferential crystallization
• A racemic compound can be separated by finding a suited resolving agent forming diastereomeric salts
• This pair of products can have distinct physical properties such as solubilities exploitable for chiral separation through crystallization
• The newly proposed grinding method combines a racemization reaction and grinding
116