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Catalytic Impurities, Habit Catalytic Impurities, Habit Modification and Crystal Modification and Crystal
Scott Hindle – University of LeedsScott Hindle – University of Leeds Paul Smith – Unilever and SIKPaul Smith – Unilever and SIK Kevin Smith – Unilever ColworthKevin Smith – Unilever Colworth
The Importance of Catalytic The Importance of Catalytic ImpuritiesImpurities
They are generally essential to They are generally essential to crystallization – homogeneous crystallization – homogeneous nucleation is very rare in oilsnucleation is very rare in oils
The physics of crystal nucleation is The physics of crystal nucleation is very different to that of crystal very different to that of crystal growth. So an effective catalyser can growth. So an effective catalyser can also poison the growth of individual also poison the growth of individual crystal faces, dramatically altering crystal faces, dramatically altering crystal morphology and even prevent crystal morphology and even prevent growth altogether.growth altogether.
Determine the rate of increase of Determine the rate of increase of crystal material at constant crystal material at constant undercoolingundercooling
Use ultrasound velocity to determine Use ultrasound velocity to determine crystal solidscrystal solids
Obtain Gibbs free energy, upper limit Obtain Gibbs free energy, upper limit for critical nucleus size, for critical nucleus size,
The emulsion crystallization The emulsion crystallization techniquetechnique
There are great advantages to dispersing There are great advantages to dispersing material as an emulsion in a non-crystallizing material as an emulsion in a non-crystallizing continuous phase in order to study crystal continuous phase in order to study crystal nucleation. nucleation.
It permits the use of the very accurate and It permits the use of the very accurate and convenient ultrasound technique for the convenient ultrasound technique for the determination of the low quantity of solids determination of the low quantity of solids evident during the initial stages of nucleation. evident during the initial stages of nucleation.
The concentration of nuclei may be controlled The concentration of nuclei may be controlled through droplet size. through droplet size.
Isothermal crystallization studies may be Isothermal crystallization studies may be conveniently carried out this way, permitting the conveniently carried out this way, permitting the identification of nuclei, through the direct identification of nuclei, through the direct determination of the bulk melting point.determination of the bulk melting point.
Determining catalytic impuritiesDetermining catalytic impurities Emulsify oil as a hot oil-in-water emulsion in which Emulsify oil as a hot oil-in-water emulsion in which
all components of the oil are liquid.all components of the oil are liquid. Measure psd (Light scattering - dilute and Measure psd (Light scattering - dilute and
ultrasound scattering - concentrated)ultrasound scattering - concentrated) Crash cool to a given undercooling at which the Crash cool to a given undercooling at which the
rate of crystallization is appropriate for our rate of crystallization is appropriate for our measurement techniquemeasurement technique
Measure the temporal evolution of crystal solids at Measure the temporal evolution of crystal solids at constant temperature. Repeat at 4 other constant temperature. Repeat at 4 other undercooling.undercooling.
Find the best fit model (Homogeneous, Find the best fit model (Homogeneous, heterogeneous, surface, volume – 4 models in all) heterogeneous, surface, volume – 4 models in all) using psd. Determine using psd. Determine JJ, , nn, , GG and and dd5050
1450
1500
0 5 10 15 20 25Temperature (°C)
Vel
ocity
(m
/s)
Tween 20
Sodium caseinatePlot of ultrasonic velocity Plot of ultrasonic velocity against temperature for against temperature for 20.75% (v/v) WACB-in-water 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20 and emulsions (0.8% Tween 20 and 1.0% sodium caseinate) cooled 1.0% sodium caseinate) cooled at 5°C/hour.at 5°C/hour.
Plot of solids against Plot of solids against temperature for 20.75% (v/v) temperature for 20.75% (v/v) WACB-in- water emulsions WACB-in- water emulsions cooled at 5°C/hour (0.8% cooled at 5°C/hour (0.8% Tween 20 & 1.0% sodium Tween 20 & 1.0% sodium caseinate).caseinate).
0
0.2
0.4
0.6
0.8
1
6 8 10 12 14 16Temperature (°C)
Sol
ids
Sodium caseinate
Tween 20
Plot of solids against time for 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20) crystallised isothermally at 14.2, 15.0, 15.5 and 15.8°C. Heterogeneous volume particle size distribution models are fitted.
Plot of solids against time for 20.75% (v/v) WACB-in-water emulsions (0.8% Tween 20) crystallised isothermally at 14.2, 15.0, 15.5 and 15.8°C. Heterogeneous volume particle size distribution models are fitted
Determine Determine the the temperature temperature dependence dependence of the of the concentration concentration of catalytic of catalytic impuritiesimpurities
y = -0.6791x + 27.127
R2 = 0.9631
16
16.5
17
17.5
18
14 14.5 15 15.5 16
Isothermal temperature (°C)lo
g10 N
imp
(m
-3)
y = -0.1334x + 40.054
R2 = 0.951
36
36.5
37
37.5
38
38.5
39
12 14 16 18 20 22 24 26
Supercooling term (10-5 K-3)
lnJ
o (
m-3
s-1)
Cocoa butter seed crystalsCocoa butter seed crystals There are few seed crystals whose size There are few seed crystals whose size
exceeds 0.28 exceeds 0.28 m at 80 m at 80 C. C. From our isothermal crystallization From our isothermal crystallization
experiments, with between 3 x 10experiments, with between 3 x 101616 and 3 x and 3 x 10101717 seed crystals per m seed crystals per m33 of cocoa butter, of cocoa butter, we infer their average size to be less than we infer their average size to be less than 0.09 0.09 m. m.
The melting point of the nucleating layer in The melting point of the nucleating layer in the seed crystal is 14 the seed crystal is 14 ooC.C.
There is strong evidence from X-ray There is strong evidence from X-ray diffraction that it is the alpha form of POS diffraction that it is the alpha form of POS that comprises the nucleating layer in the that comprises the nucleating layer in the seed crystal.seed crystal.
Crystal growth and catalytic Crystal growth and catalytic impuritiesimpurities
Paul Smith, “The Paul Smith, “The molecular basis for molecular basis for crystal habit crystal habit modification in modification in tryglycerides”, tryglycerides”, University of Leeds University of Leeds Thesis, 1995Thesis, 1995
Chain length Chain length matchingmatching
TrilaurinTrilaurin
Trilaurin, catalytic impurities and Trilaurin, catalytic impurities and chain length matchingchain length matching
Trilaurin crystal growthTrilaurin crystal growth
ConclusionsConclusions
Catalytic impurities play a role both Catalytic impurities play a role both during nucleation and during crystal during nucleation and during crystal growthgrowth
Catalytic impurities may both catalyse Catalytic impurities may both catalyse nucleation and prevent crystal growth nucleation and prevent crystal growth of one or more crystal facetsof one or more crystal facets
Identification of catalytic impurities is Identification of catalytic impurities is one of the most important outstanding one of the most important outstanding issues in crystallisationissues in crystallisation
ReferencesReferences www.food.leeds.ac.uk/mp.htmwww.food.leeds.ac.uk/mp.htm Povey, M. J. W., Hindle, S. and Smith, K. H. (2001) Crystallization in Food Emulsions, Povey, M. J. W., Hindle, S. and Smith, K. H. (2001) Crystallization in Food Emulsions, in "Food Colloids - in "Food Colloids -
Fundamentals of Formulation" - RSC Special Publication Number 258 eds Eric Dickinson and Reinhard Fundamentals of Formulation" - RSC Special Publication Number 258 eds Eric Dickinson and Reinhard Miller, pp 152 -162Miller, pp 152 -162
Povey, M. J. W. (2001), Crystallization of Oil-in-Water Emulsions, in Crystallization Processes in Fats Povey, M. J. W. (2001), Crystallization of Oil-in-Water Emulsions, in Crystallization Processes in Fats and Lipid Systems 1 , Editor N. Garti and K. Sato , Marcel Dekker, NEW YORK, Chapter and Lipid Systems 1 , Editor N. Garti and K. Sato , Marcel Dekker, NEW YORK, Chapter 7,7, pp 255-288 pp 255-288
Hindle, S., Povey, M. J. W. and Smith, K. (2000), Kinetics of Crystallization in Polydisperse n-Hindle, S., Povey, M. J. W. and Smith, K. (2000), Kinetics of Crystallization in Polydisperse n-hexadecane and Cocoa Butter Emulsions Accounting for Droplet Collision-Mediated Nucleation, hexadecane and Cocoa Butter Emulsions Accounting for Droplet Collision-Mediated Nucleation, J. Coll. J. Coll. Interface Sci. Interface Sci. 232232, 370-380, 370-380
Smith, P. R., and Povey, M. J. W. (1997), The Effect of Partial Glycerides on Trilaurin Crystallization, Smith, P. R., and Povey, M. J. W. (1997), The Effect of Partial Glycerides on Trilaurin Crystallization, J. J. Am. Oil. Chem. Soc. Am. Oil. Chem. Soc. 7474, 169-171, 169-171
Dickinson, E., Ma, J., and Povey, M. J. W. (1996), Crystallization Kinetics in Oil-In-Water Emulsions Dickinson, E., Ma, J., and Povey, M. J. W. (1996), Crystallization Kinetics in Oil-In-Water Emulsions Containing a Mixture of Solid and Liquid Droplets,Containing a Mixture of Solid and Liquid Droplets, J. Chem. Soc. -Faraday Trans. I J. Chem. Soc. -Faraday Trans. I 9292, 1213-1215, 1213-1215
Smith, P. R., Povey, M. J. W., and Cebula, D. J. (1994), The Application of Temperature Gradient Smith, P. R., Povey, M. J. W., and Cebula, D. J. (1994), The Application of Temperature Gradient Microscopy Techniques to Trilaurin Crystallisation,Microscopy Techniques to Trilaurin Crystallisation, Crystallisation and crystal growth: An Crystallisation and crystal growth: An interdisciplinary perspective.interdisciplinary perspective.
Smith, P. R., Cebula, D. J., and Povey, M. J. W. (1994), The Effect of Lauric-Based Molecules on Trilaurin Smith, P. R., Cebula, D. J., and Povey, M. J. W. (1994), The Effect of Lauric-Based Molecules on Trilaurin Crystallization, Crystallization, J. Am. Oil. Chem. Soc. J. Am. Oil. Chem. Soc. 7171, 1367-1372, 1367-1372
Povey, M. J. W. (1993), Analysis of Lipid Structure by Neutron Diffraction in Developments in the Povey, M. J. W. (1993), Analysis of Lipid Structure by Neutron Diffraction in Developments in the Analysis of Lipids Editors: J. H. P. Tyman and M. H. Gordon, RSC, Cambridge, UKAnalysis of Lipids Editors: J. H. P. Tyman and M. H. Gordon, RSC, Cambridge, UK
Coupland, J., Dickinson, E., McClements, D. J., Povey, M. J. W., and de Rancourt de Mimmerand, C. Coupland, J., Dickinson, E., McClements, D. J., Povey, M. J. W., and de Rancourt de Mimmerand, C. (1993), Crystallisation in Simple Paraffins and Monoacid Saturated Triacylglycerols Dispersed in Water, (1993), Crystallisation in Simple Paraffins and Monoacid Saturated Triacylglycerols Dispersed in Water, Food Colloids and Polymers: Stability and Mechanisms, RSCFood Colloids and Polymers: Stability and Mechanisms, RSC
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Smith, PR (1997) The Molecular Basis for Crystal Habit Modification, PhD Thesis, University of LeedsSmith, PR (1997) The Molecular Basis for Crystal Habit Modification, PhD Thesis, University of Leeds Hindle, SA (2000) Investigation of Cocoa Butter Crystallization Using Ultrasound Velocity Hindle, SA (2000) Investigation of Cocoa Butter Crystallization Using Ultrasound Velocity
Measurements, PhD Thesis, University of LeedsMeasurements, PhD Thesis, University of Leeds