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Adsorptive crystallization of organic substances in silica aerogels from supercritical solutions [Elektronische Ressource] / vorgelegt von Babu Suresh Kumar Gorle

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153 pages
Adsorptive Crystallization of Organic Substances in Silica Aerogels from Supercritical Solutions Der Technischen Fakultät der Universität Erlangen-Nürnberg zur Erlangung des Grades DOKTOR-INGENIEUR vorgelegt von M.Sc. Babu Suresh Kumar GORLE aus Hyderabad, Indien Erlangen – 2009 Als Dissertation genehmigt von der Technischen Fakultät der Universität Erlangen-Nürnberg Tag der Einreichung: 06.04.2009 Tag der Promotion: 10.06.2009 Dekan: Professor Johannes Huber Vorsitzender: Professor Axel König 1. Berichterstatter: Professor Wolfgang Arlt 2. Berichterstatter: Professor Irina Smirnova 3. Berichterstatter: Professor Wilhelm Schwieger weiteres prüfungsberechtigtes Mitglied: Professor Peter Wellmann II Acknowledgement During my last three and half year, I worked on my PhD work at Chair of Separation and Technology, University of Erlangen. During this time, I worked in close co-operation with many people spent one quality time with lots of friends, whom I sincerely wish to acknowledge in this section. Thanks to Prof. Wolfgang Arlt for accepting me for a PhD position at his chair and for supervising my work. His critical remarks on the research work helped me to have an eye on finer details in the research work.
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Adsorptive Crystallization of Organic Substances in Silica Aerogels
from Supercritical Solutions





Der Technischen Fakultät der
Universität Erlangen-Nürnberg
zur Erlangung des Grades




DOKTOR-INGENIEUR




vorgelegt von
M.Sc. Babu Suresh Kumar GORLE
aus Hyderabad, Indien






Erlangen – 2009













Als Dissertation genehmigt von
der Technischen Fakultät der
Universität Erlangen-Nürnberg




Tag der Einreichung: 06.04.2009

Tag der Promotion: 10.06.2009

Dekan: Professor Johannes Huber
Vorsitzender: Professor Axel König
1. Berichterstatter: Professor Wolfgang Arlt
2. Berichterstatter: Professor Irina Smirnova
3. Berichterstatter: Professor Wilhelm Schwieger

weiteres prüfungsberechtigtes Mitglied: Professor Peter Wellmann
II Acknowledgement

During my last three and half year, I worked on my PhD work at Chair of Separation and
Technology, University of Erlangen. During this time, I worked in close co-operation with many
people spent one quality time with lots of friends, whom I sincerely wish to acknowledge in this
section.

Thanks to Prof. Wolfgang Arlt for accepting me for a PhD position at his chair and for
supervising my work. His critical remarks on the research work helped me to have an eye on
finer details in the research work. His popularity in the research community always helped me to
get in contact with other research groups where I need to conduct some experiments.

Special thanks to Prof. Irina Smirnova (presently Chair of Institut für Thermische
Verfahrenstechnik, Technical University of Hamburg and Harburg), who initiated this PhD
research project and guided me through my work. I am truly indebted for her continuous
inspiration, timely appreciation and encouragement which helped me to keep going during the
three and half years of my project. Her enormous abilities of generating new ideas, discussions
and explanations lead to a new direction in the present research work ‘adsorptive crystallization’
which is presented in this work.

I would like thank Prof. Mark A. McHugh for his remarks, comments, suggestion on the PhD
work during his sabbatical at the Chair of Separation and Technology, University of Erlangen.
Interacting with him has taught me how to look at finer details of the experimental data. I cherish
long discussions and explanations of various phenomena’s with him has given a new path to the
present research work.

Thanks to Prof. Axel König for his help in performing DSC experiments. Discussion with him
always helped to understand the results of DSC. I am grateful his comments and suggestions. I
am also thankful to Prof. Wilhem Schwieger for providing me the MCM41 and Zeolite samples. I
would like thank his student; Ayyapan, Sai, Abhijeet for helping me to do some TGA/MS
experiments and also sharing me their knowledge about Zeolite and MCM41 materials.
II I
I would like to thank Detlef and Martin Drescher for their great help in built the plant for my
experiments. I would like thank Edelgard for her help in analysis all my samples and preparing
aerogels. During my work with her gave me a chance to understand the German social and
culture exposure. Thanks to Petra Kiefer for help in analysis samples and making some nice
digital pictures for my work. Thanks to Petra Koch for her help in performing BET of my aerogel
samples and also placing the chemical orders for me. Thanks to Rosa, Jorge, Jose for helping me
to make DSC analyses for me.

I would like thank the work shop team Matthias, Hans for their continuous help in solving my
experimental setup problems. I appreciate Matthias help and idea in solving the problems that
occurred during my work without his help it would not have been possible to continue to the
experimental work. I am also thanks full to Wolfgang Gäckel for his help in fixing all my
experimental problems.

Thanks to Reddy who was always free and ready to discuss my results and to share some private
talks. I am thankful to my German friends at the chair; Martin, Alexander, Florian, Sussa, Lissi,
Tanya, and Ulrike, the time I spent with them both in private and in the chair, who taught me the
German culture which includes beer. I am thankful to Dirk Weckesser for his help in solving my
computer problems. It was great to share small chats during coffee time with Jinglan, Bo-Hyun,
Liping, Mirjana, Ludmilla, Vladimar, Jose, and Jorge. Special thanks to Bo Hyun for correcting
formatting of my PhD thesis. Thanks to Ludmilla for her critical remarks on research work and
presentations. I would like thank the students who worked on my project during my work;
Fatima, Daniel, Muard, Katharina, Sudhanshu, Abhishek, Rustem.

Last but not least, I am thankful to my family members for their continuous telephone or personal
talks with me during my stay in Germany, without which I would not have realized my PhD
work.

Finally, I would like to thank all the people who were not mentioned above but have helped me
in some or the other way to complete my work successful.
IV
Nomenclature

-OR Alkyl group
VOC’s Volatile organic compounds
TMOS Tetramethylorthosilicate
MEOH Methanol
BET Brunauer, Emmett, and Teller
BJH Barrett Joiner Halenda
-CH Methyl 3
CHN Carbon Hydrogen and Nitrogen
T Melting temperature m
DSC Differential scanning calorimeter
CP1 Critical point of substance 1
CP2 Critical point of substance 2
UCEP Upper Critical Point End
LCEP Lower Critical Point End
SLG Solid Liquid Gas
TP2 Triple point of substance 2
TLCEP Temperature of LCEP
TUCEP Temperature of UCEP
Tmin Temperature minimum
XRD X- ray diffraction
m(p,T) mass of solute/solvent adsorbed(g)/(g) aerogel absolute
m(p,T) mass of solute/solvent adsorbed(g)/(g) aerogel excess
V Volume of basket b
V Volume of sample (aerogel) s
V Volume of adsorbed CO ads 2
b ρ Bulk density of CO or CO + solute 2 2
ρ density of adsorbed CO adsorbed 2
Δm Weight difference due to adsorbed
V solute/solvent
SANS Small angle neutron scattering
RESS Rapid Expansion form Supercritical Solutions
GAS Gas anti solvent
SAS Supercritical Anti Solvent
PGSS Particles from Gas Saturated Solutions
co-precipitation during the rapid expansion of
CO-RESS
supercritical solutions
SCF Supercritical fluids




V I Table of Contents
1. Introduction and Objective of the work .....................................................................14
2. Theory ........................................................................................................................16
2.1 Silica aerogels...................................................................................................16
2.1.1 Synthesis of silica aerogels and their properties...................................17
2.1.2 General applications of silica aerogels .................................................23
2.1.3 Impregnation of bioactive, inorganic, and organic substances in aerogels 23
2.2 Methods of solute precipitation / crystallization from supercritical CO .........25 2
2.2.1 Supercritical fluids as solvent...............................................................25
2.2.2 High pressure binary mixture (CO + Solute) phase diagrams ............27 2
2.2.3 Different methods of SCF particle formation technologies..................30
2.3 Physical state (crystalline / amorphous form) of drugs in a carrier..................33
2.3.1 General stabilization methods and problems of amorphization ...........33
2.3.2 Characterization of amorphous state: relevant techniques ...................34
2.4 High pressure adsorption isotherms on adsorbents at supercritical conditions 35
2.4.1 Adsorption measurements using Magnetic Suspension Balance (MSB)35
2.4.2 Data analysis of MSB adsorption measurements .................................35
2.4.3 Analytical adsorption isotherms ...........................................................37
3. Materials and Methods...............................................................................................41
3.1 Materials 41
3.1.1 Materials used for silica aerogel synthesis ...........................................41
3.1.2 Materials used for adsorption & crystallization in aerogels .................41
3.1.3 MCM 41, Zeolite NAY, Trispor glass..................................................42
3.2 Preparation methods of silica aerogels .............................................................42
3.2.1 Sol - gel process and drying methods...................................................42
3.2.2 Methods used for hydrophobization of aerogels ..................................43
3.3 Choice of crystallization temperature...............................................................44
3.4 Experimental techniques...................................................................................44
7 Table of Contents
3.4.1 Adsorption measurements using Magnetic Suspension Balance .........45
3.4.2 Adsorption experiments using an autoclave.........................................46
3.4.3 Crystallization experiments using an autoclave ...................................47
3.4.4 Drug release experiments .....................................................................48
3.5 Characterization techniques used .....................................................................49
3.5.1 Measuring of the bulk density of aerogels............................................49
3.5.2 Nitrogen Adsorption and Desorption; BET analysis............................49
3.5.3 Elementary Analysis.............................................................................50
3.5.4 UV - Vis Spectroscopy.........................................................................50
3.5.5 Gas Chromatography (GC)...................................................................51
3.5.6 IR spectroscopy ....................................................................................51
3.5.7 Differential Scanning Calorimeter........................................................51
3.5.8 X - Ray Diffraction...............................................................................51
3.5.9 TGA / TGA - MS analysis....................................................................52
4. Results and Discussions .............................................................................................53
4.1 Properties of aerogels synthesized and other carriers used ..............................53
4.2 Adsorption and crystallization of polar solutes in silica aerogels ....................58
4.2.1 Adsorption and crystallization of benzoic acid in silica aerogels ........58
4.2.1.1 Stability of aerogels under pressure .......................................58
4.2.1.2 CO adsorption on aerogels....................................................59 2
4.2.1.3 Excess binary adsorption of CO + benzoic acid ...................62 2
4.2.1.4 Static adsorption of benzoic acid in silica aerogels................64
4.2.1.5 Crystallization of benzoic acid in silica aerogels by CO-RESS65
4.2.1.6 Effect of the aerogel properties on the crystallization process67
4.2.1.7 Crystallinity of benzoic acid in aerogels ................................70
4.2.1.8 Crystallization of benzoic acid in other porous carriers.........73
4.2.1.9 IR analysis of loaded benzoic acid .........................................74
8 Table of Contents
4.2.2 Adsorption of 1-menthol in silica aerogels...........................................76
4.2.2.1 Menthol adsorption in silica aerogels.....................................76
4.2.2.2 TGA of menthol - loaded, hydrophilic aerogels.....................82
4.2.2.3 TGA of menthol - loaded, hydrophobic aerogels...................85
4.2.2.4 IR analysis of loaded menthol ................................................87
4.2.2.5 Long - term stability of menthol at room temperature ...........88
4.3 Adsorption and crystallization of moderately polar solutes in silica aerogels .91
4.3.1 Adsorption and crystallization of naphthalene in silica aerogels .........91
4.3.1.1 Excess binary adsorption of CO + naphthalene in aerogels..91 2
4.3.1.2 Static adsorption of naphthalene in aerogels..........................92
4.3.1.3 Crystallization of naphthalene in silica aerogels by CO-RESS94
4.3.1.4 Crystallinity of naphthalene in aerogels.................................99
4.3.1.5 IR analysis of loaded naphthalene........................................101
4.3.2 Adsorption of 2-Methoxy pyrazine in silica aerogels ........................104
4.3.2.1 Methoxy pyrazine adsorption in aerogels.............................104
4.3.2.2 TGA analysis of methoxy pyrazine loaded aerogels............106
4.3.2.3 Long - term stability of methoxy pyrazine at room temperature108
4.4 Adsorption and crystallization of nonpolar solutes in silica aerogels ............110
4.4.1 Adsorption and crystallization of octacosane in silica aerogels .........110
4.4.1.1 IR analysis of loaded octacosane..........................................113
4.4.2 Adsorption of dodecane in silica aerogels..........................................115
4.5 Summarized table of loadings, physical form of loaded solutes ....................117
4.6 Extension of the method to other porous carriers: comparison of drug release profiles
119
4.6.1 Synthesis of the MCM - 41 materials.................................................119
4.6.2 Characterization of MCM41...............................................................120
4.6.3 Loading of MCM41s with Ibuprofen .................................................121
4.6.4 Release of ibuprofen from MCM41 in the phosphate buffer solution122
9 Table of Contents
5. Conclusions ..............................................................................................................125
6. Outlook.....................................................................................................................127
7. Appendix ..................................................................................................................128
7.1 GC column data ..............................................................................................128
7.2 Stability of aerogels at CO-RESS process......................................................128
7.3 Multiple additive loading................................................................................128
7.4 Benzoic acid results........................................................................................129
7.5 MSB adsorption..............................................................................................134
7.6 Menthol results ...............................................................................................136
7.7 Naphthalene results.........................................................................................137
7.8 Error Propagation ...........................................................................................139
8. References ................................................................................................................142

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