Particle formation with supercritical fluids : challenges and limitations

142 Pages·2014·7.136 MB·English

by  Türk, Michael

Supercritical Fluid Science
and Technology
Series Editor – Erdogan Kiran
Vol.1 SupercriticalFluidsandOrganometallicCompounds:FromRecoveryofTrace
MetalstoSynthesisofNanostructuredMaterials.
ByCanErkey
Vol.2 High-PressureFluidPhaseEquilibria:PhenomenologyandComputation.
ByUlrichK.DeitersandThomasKraska
Vol.3 PhaseEquilibriumEngineering.
ByEstebanBrignoleandSelvaPereda
Vol.4 IntroductiontoSupercriticalFluids:ASpreadsheet-basedApproach.
ByRichardSmith,HiroshiInomata,andCorPeters
Vol.5 HydrothermalandSupercriticalWaterProcesses
ByGerdBrunner
Supercritical Fluid Science and Technology
Volume 6
Particle Formation
with Supercritical Fluids
Challenges and Limitations
Michael Tu¨rk
Karlsruhe Institute of Technology (KIT)
Institute for Technical Thermodynamics and Refrigeration
Karlsruhe, Germany
AMSTERDAMlBOSTONlHEIDELBERGlLONDONlNEWYORKlOXFORD
PARISlSANDIEGOlSANFRANCISCOlSINGAPORElSYDNEYlTOKYO
Elsevier
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Firstedition2014
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Foreword
Particle formation with supercritical fluids is one of the early areas of appli-
cationofsupercriticalfluids.Theareaisstillveryactivewithmuchacademic
and industrial interest as it offers an effective and environmental friendly
pathway for generation of both organic and inorganic particles without
contamination or degradation. Professor Michael Tu¨rk is a world-recognized
leader inthe areawith extensiveresearch experiencespanning morethan two
decades at the Karlsruhe Institute of Technology. I am extremely pleased that
he is now sharing his vast knowledge in this volume, providing us with
valuable insights and critical perspectives on diverse materials ranging from
pharmaceutical compounds to inorganic materials and catalysts.
Chapter 1 provides a brief overview of this important field of application
that sets the stage for the remainder of the book.
Chapter 2 continues with a concise treatment of the fundamentals that
pertain to supercritical fluids and thermodynamics of mixtures with an
emphasisonthosesystems,whichinvolvesubstancesthathavelowvolatility.
Basicequationsofstatesandtheiruseinmodelingofvaporeliquidequilibria
and solubility and the descriptions of ternary systems are reviewed. High
pressure techniques, as well as particle characterization techniques, are also
briefly discussed.
Chapter3isdedicatedtothedescriptionoftheparticleformationprocesses
and treatment of the associated fundamentals involving mass, energy, and
momentum transfer. Energetics of nucleation and dynamics of phase separa-
tion, particle formation, and growth are discussed.
Chapter 4 discusses the key particle formation techniques for organic
materialsthataredissolvedinsupercriticalfluids.TheseincludeRESS(Rapid
Expansion of Supercritical Solutions) and its variations such as CORESS
(Co-precipitation during Rapid Expansion of Supercritical Solutions),
RESOLVE and RESSAS (Rapid Expansion of Supercritical Solutions into
liquid or Aqueous Solutions), and CPD (Controlled Particle Deposition).
Chapter 5 is devoted to formation of organic particles using supercritical
fluids not as a solvent, but as an antisolvent. The GAS (Gas Antisolvent
Process) and its modifications such as the SAS (Supercritical Antisolvent
Precipitation), and SAA (Supercritical Fluid-Assisted Atomization) are
described in some detail.
Chapter 6 is also devoted to formation of organic particles with extended
discussions of another process, the PGSS (Particles from Gas-Saturated
ix
x Foreword
Solutions) process that utilizes the solubility of a compressible fluid such as
CO inmaterialssuchaspolymersratherthanthesolubilityofthematerialof
2
interest in the fluid. Variations of the PGSS process are also covered. Among
these are the CPF (Concentrated Powder Formation), which is used in
generation of powders that incorporate a high level of liquid content. Other
modifications that are discussed are the CPCSP (Continuous Powder Coating
Spraying Process), the PGSS drying process for drying of aqueous solutions,
andtheDELOSprocessthatinvolvesDepressurizationofanExpandedLiquid
Organic Solution.
In Chapter 7, the focus is shifted to the formation of inorganic particles
and the use of supercritical fluids as solvent, reaction, and separation media.
Formation of noble metal particles and their dispersion in porous substances
that involve SFRD (Supercritical Fluid Reactive Deposition) are treated in
detail.Thesignificanceofsupercriticalwaterasprocessandreactionmedium
in HTS (Hydrothermal Synthesis) is also discussed with emphasis on
formation of metal oxide nanoparticles.
Chapter 8 provides a critical review of modeling of particle formation in
supercritical fluids, highlighting the challenges and further needs that pertain
tothemodelingofthevariousprocessesincludingRESS,GAS,PGSS,SFRD,
and HTS.
Chapter 9 provides further perspectives on future trends and potential
developmentsalongwitharticulationsoftheneedforimprovedunderstanding
of the fundamentals and the need for development of improved experimental
tools to pave the way to new advances.
Asyoucanseefromtheforegoingdescriptions,thisbook,whichhasbeen
written by an outstanding expert, presents an elegant treatment of an exciting
fieldofutilizationofsupercriticalfluidswithhighpracticalsignificance.Itrust
you will all find this volume to be of great value in your research, teaching,
and process development activities.
Erdogan Kiran
Series Editor
Blacksburg, VA
August 2014
Preface
This book comprehensively presents and discusses the current status of
research and development of different supercritical fluid (SCF)-based particle
formationprocesses.Itisacombinationofthegeneralprinciples,adiscussion
oftheunderlyingphaseequilibria,thefluiddynamicsoftheprocesses,andthe
phaseseparationkinetics,i.e.,thenucleationtheoryrelatedtotheseprocesses.
Based on this, the underlying physical and chemical phenomena needed to
understand the different processes and the relationship between process
conditions and product properties are presented.
Furthermore, the book is intended to bridge the gap between theory and
application and to impart the scientific and engineering fundamentals of
innovative particle formation processes. This interdisciplinary “modus oper-
andi” makes it a valuable tool for chemical engineers, materials scientists,
chemists, and physicists from both academiaand industry andwillencourage
anintensivecooperationbetweenscientistsandresearchersfromdifferentbut
complementary disciplines.
Based on an initiative of the “GVC-Fachausschuss Hochdruckverfahren-
stechnik” (the German working party on High-Pressure Chemical Engineer-
ing) and after a successful proposal written under the guidance of Prof. Gerd
Brunner from the Technische Universita¨t Hamburg-Harburg, in 1995 the
“Deutsche Forschungsgemeinschaft, DFG” (German Research Foundation)
launched a research program on “Supercritical fluids as solvents and reaction
media.” At around the same time, I started working in the field of high-
pressure fluid phase equilibria and particle formation. The research program
and the colleagues involved introduced me to the broad scientific field of
SCFs. Since that time the complex high-pressure fluid phase equilibria and
SCF-based particle formation processes are the research fields that attract my
special interest. This background enables the fascinating combination of
fundamental research with process optimization and product design.
First I would like to thank the editor of the series, Erdogan Kiran from
VirginiaTech,Blacksburg,VA,whoencouragedmetowritethisbook.About
15yearsago,ImetErdoganattheAIChEannualmeetinginMiamiBeachin
1998 for the first time. Since that time, we have had a large number of
stimulating discussions about potentially new and promising research activ-
itiesandapplicationsinthefieldofSCFs.Withoutadoubtitishisdedication,
enthusiasm, and ongoing activities for promoting the exchange of knowledge
andexperienceintheexcitingfieldofsupercriticalscienceandtechnologythat
xi
xii Preface
have been an inspiration to me and a countless number of colleagues in their
research.
I would especially like to thank the large number of bachelor and master
studentswhospentendlesshoursinthelaboratories,workinginthebroadfield
of the determination of high-pressure phase equilibria data and/or the
formation of small and uniform particles with unique product properties. In
particular, the work performed by Eugenia Breininger, Moritz Knuplesch,
Boris Stehli, and Nina Teubner helped me progress in all the projects on
particle formation. To date, Armin Diefenbacher, Britta Helfgen, Peter Hils,
Gerd Upper, Ralph Lietzow, Dennis Bolten, and Maren Daschner have
completed their PhD theses and shared with me the findings they discovered.
Of course, I would also like to express my thanks to my current collabo-
rators Marlene Crone, Sabrina Mu¨ller, Simone Wolff, Sarah Reiser, and the
large number of colleagues with whom me and my current and previous
collaborators have cooperated successfully in various research projects. On
behalf of all of them I just want to mention Sabine Beuermann, Thomas
Kraska, Bettina Kraushaar-Czarnetzki, Karlheinz Schaber, Martin Wahl, and
Alfred Weber who all are or were co-applicants in various research projects
supportedbytheDFG.Theircontributionshavealwaysbeenaninspirationin
our research since they helped me to obtain new insights and therewith to
answer previously unresolved issues. I am sure that some of them will find
their tracks at one point or another in this book.
Furthermore, Marlene Crone deserves special thanks for helping me in
preparing the figures and for carefully reading and correcting mistakes in
writing.Finally,IamgratefulforthesupportoftheElsevierteam,inparticular
Susan Dennis and Derek Coleman, for all their efforts in ensuring the timely
publication of this book.
Michael Tu¨rk
Karlsruhe Institute of Technology
Karlsruhe, July 2014
Chapter 1
Introduction
1.1 SOME CONVENTIONS
At the beginning, before entering into the discussion of the various particle
formation processes and their underlying fundamentals, it is useful to intro-
duce and clarify some conventions and definitions.
It is well known that there are three common states1 of matter, namely,
solid,liquid,andgas.AccordingtothebookwrittenbyDeitersandKraska[1],
no difference is made in the notation of “gas” or “vapor” phase. Thus, the
following abbreviations are used if a phase or an aggregation state has to be
indicated in phase diagrams or equations:
S: solid phase
L: liquid phase
G: gas (gaseous) ¼ vapor phase
Throughoutthebook,nodistinctionismadebetween“solidsubstance”and
“low volatile substance”.
Phase equilibria are indicated by the combination of the different phases,
e.g.,
S ¼ L: solideliquid equilibrium, i.e., a solid and a liquid phase coexist
S ¼ G: solidegas equilibrium, i.e., a solid and a gas phase coexist
L ¼ G: liquidegas equilibrium, i.e., a liquid and a gas phase coexist
S ¼ L ¼ G: solideliquidegas equilibrium, e.g., in case of a pure sub-
stance, the three phases coexist at the triple point, whereas for binary
systems, the three phases coexist at the SeLeG, three-phase line.
In case of mixtures consisting of “n” components, component “1” is the
substancewith the highestsublimation(in case ofsolids) orvapor (in case of
liquids)pressureatagiventemperature.Fromthisfollowsthatcomponent“n”
isthesubstancewiththelowest(sublimationorvapor)pressureor,atconstant
pressure, the highest boiling temperature.
1. Sometimes the so-called “plasma state” is referred as the fourth state. Since “a plasma” is
characterizedbyionizedspecies,itisdifferentfromusualgasesandthereforenotconsidered.
ParticleFormationwithSupercriticalFluids.http://dx.doi.org/10.1016/B978-0-444-59486-0.00001-2
Copyright©2014ElsevierB.V.Allrightsreserved. 1
2 Particle Formation with Supercritical Fluids
The composition, unless mentioned otherwise the mole fraction, of the
liquid phase is characterized by x and of the gas/vapor phase by y, e.g.,
P
x1 ¼ mole fraction of component 1 in the liquid phase with xPi ¼ 1;
y1 ¼ mole fraction of component 1 in the gas/vapor phase with yi ¼ 1.
1.2 SOLID COMPOUNDS OF INTEREST
Thesupercriticalfluid(SCF)-basedparticleformationprocessespresentedand
discussedinthisbookcanbesubdividedintoeitheraphysicaltransformation
(e.g., rapid decompression, antisolvent effect) or a chemical reaction. The
materials that can be synthesized by these processes include mainly two
different types of solid substancesdpoorly water-soluble drugs and metallic
nanoparticles (NPs).
In case of the pharmaceutical substances, the oral application is often
limited due to the drug’s aqueous solubility that results in a low dissolution
behavior and gastrointestinal permeability. Among other methods, the resul-
tant low bioavailability can be improved by increasing the particle’s specific
surfaceareabyreducingtheparticlesize(PS).Disadvantagesofconventional
micronization techniques such as milling and grinding, spray-drying, freeze-
drying, high-pressure homogenization, and milling are degradation of the
product, broad particle size distribution (PSD), and cumbersome solids
handling. In contrast thereto, SCF-based particle reduction processes can be
conducted at moderate operating conditions and are thus suitable for many
heat-labile compounds such as pharmaceuticals. According to the Fick’s law,
the mass transfer rate of a particulate solid is directly proportional to the
particle’ssurface area andtherewithparticle’ssize.Therefore, submicronand
uniformdrugparticlesshouldbecharacterizedbyanimprovedbioavailability.
This holds especially for drugs, which are classified into “Class 2, i.e., low
solubility and high permeability” of the biopharmaceutics classification
system (BCS) [2]. Examples of such poorly water-soluble drugs are carba-
mazepine, griseofulvin, ibuprofen, and naproxen.
Metallic precursors, e.g., Pt(COD)Me , Pd(HFAC) , orCu(TMHD) , have
2 2 2
beenreceivinganincreasinginterestinawiderangeofdifferentareassuchas
thepreparationofnewmaterials,e.g.,supportedmetallicNPsduetochemical
transformation of the precursor into its metal form. Noble metal NPs and,
especially, platinum (Pt) NPs have been demonstrated to be efficient as cat-
alystsforchemicalreactionssuchashydrogenation,hydration,andoxidation.
Usually these catalysts are prepared by aqueous impregnation of a porous
substrate with a metal-containing solution, followed by reductive treatment.
Drawbacksofsuchapreparationprocessarethepoorcontrolofthedeposition
processresultinginmetalparticleswithbroadsizedistribution,largevolumes
of wastewater, and an intensive drying procedure. The first leads to a lower
catalyticactivity,thesecondtoanexpensivewastedisposal,andthethirdone
Introduction Chapter j1 3
requires high temperatures and results therewith in a high-energy consump-
tion. For more details about the specific properties of organometallic pre-
cursors and the synthesis of nanostructured materials, readers are
recommended to read the book Supercritical Fluids and Organometallic
Compounds, written by Can Erkey [3].
1.3 SCOPE OF THE BOOK
Since Krukonis inspired in the late 1970s the interest in SCF-based particle
formationprocesses,alargenumberofextensiveexperimentalandtheoretical
investigationshavebeendoneinthisfield.Basedonalargenumberofresults
published in literature during 1970e2010, one can follow that particle for-
mation in SCFs is a promising alternative to conventional precipitation pro-
cesses as it allows the reduction of PS and control of morphology and PSD
without degradation or contamination of the product.
However,thenastoday,forthetransformationoflaboratory-scalefindings
to large-scale operations, it is essential to answer the question “What quan-
titativeadvantagescanbeexpectedfromusingSCFsinmaterialsynthesis?”in
a satisfactory manner. Therefore, the comparison of materials prepared using
SCFswithmaterialspreparedbyconventionaltechniquesaswellastheability
to understand and explain the principle of causes, i.e., the underlying phase
behavior and process conditions, and effect, i.e., product properties, are
essential for the progress in SCF-based processes. This holds for the broad
range of formation and processing of nanostructured materials that exhibit
promisingpropertiesforapplicationsinfieldssuchasdrugandgenedelivery,
catalysis, electronics, energy, and optics.
This book gives a survey (that can never pretend to be exhaustive!) of
published knowledge about particle and product design with a focus on the
formation of small, uniform particles with desired product properties. Thus,
one key aspect of this book is to impart the scientific and engineering fun-
damentals that will allow the reader to understand the relationship between
process conditions and the properties of the obtained particles. However, to
fulfill this challenge, fundamental knowledge about (complex) high-pressure
phase behavior, the transport properties, the fluid dynamics of the processes,
the phase separation kinetics, i.e., the nucleation theory related to these pro-
cesses and nucleation phenomena, is required.
Consequently, bridging the gap between theory and application, the book
imparts the scientific and engineering fundamentals for innovative particle
formation processes. The interdisciplinary “modus operandi” makes it a
valuable tool for chemical engineers, materials scientists, chemists, and
physicists from both academia and industry, and encourages cooperation be-
tweenscientistsandresearchersfromdifferentbutcomplementarydisciplines.
Therefore, this book is organized as follows: A brief overview of the
intention,motivation,andusefulconventionsisgiveninChapter1.Chapters2