Hydrodynamic and disperson behaviour of an analytical silica monolith reconstructed from sub microtomographic scans using computational fluid dynamics

HYDRODYNAMIC AND DISPERSION BEHAVIOUR OF AN ANALYTICAL SILICA MONOLITH RECONSTRUCTED FROM SUB-MICROTOMOGRAPHIC SCANS USING COMPUTATIONAL FLUID DYNAMICS VIVEK VASUDEVAN NATIONAL UNIVERSITY OF SINGAPORE 2013 HYDRODYNAMIC AND DISPERSION BEHAVIOUR OF AN ANALYTICAL SILICA MONOLITH RECONSTRUCTED FROM SUB-MICROTOMOGRAPHIC SCANS USING COMPUTATIONAL FLUID DYNAMICS VIVEK VASUDEVAN (M.S., West Virginia University, U.S.A. B. Chem. Eng., University Dept. of Chemical Technology, India) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 ACKNOWLEDGEMENTS I take this opportunity to express my gratitude to many individuals who have had an influence on me and my research work. Firstly, I wish to acknowledge A/P Loh Kai-Chee and thank him for giving me an opportunity to be a part of his diverse research group. He believes in giving his students complete independence of thought, which was one of the keys factors that helped me identify my strengths and weaknesses as a researcher. I also wish to thank Dr. William Krantz for his wonderful inputs on scaling analysis and guidance on simulations from CT images. Some of the most fruitful and exciting discussions that I have had regarding research has been with the diverse group of students in Prof. Loh‘s lab. I wish to thank Dr. Cao Bin, Dr. Sudhir, Mr. Bulbul, Ms. Jia-Jia, Ms. Linh, Ms. Duong, Mr. Prashant and Dr. Xiyu for making the lab a very warm and conducive place to work in. I wish to specially thank Dr. Vignesh and Dr. Satyen Gautam for being very patient sounding boards to my research ideas. I am eternally grateful to the technical staff at the NUS High Performance Computing Centre (HPCC) for being very patient with my queries. Without them, my simulations would never have run. Special thanks to Mr. Wang Junhong (Lead HPC Specialist) at NUS-HPCC for all his time and efforts towards solving my simulation queries. I must also thank the innumerable technical and managerial support personnel at Analyze, Ansys and Fluent for helping me figure out several bottlenecks in my computational efforts. I am deeply grateful to all the lab officers, namely, Mdm Chow Pek, Mdm Alyssa Tay, Mdm Novel and Mr. Wee Siong, for their administrative support. I am thankful to NUS for providing me an opportunity to pursue research on a scholarship. ii I am ever thankful to my wife, Dr. Mrs. Karthiga Nagarajan, for being a source of support and strength and believing in my abilities. I thank my in-laws for always being there for my wife and helping her provide me with constant encouragement and support. I would not have been able to purse a higher level of education if not for my parents‘ encouragement and selflessness to send me away for higher studies. I dedicate this thesis as a small repayment for all their innumerable sacrifices for securing my future. I am grateful to the Almighty and to Karthiga for the most beautiful and precious gift, my son Aaditya, who provided me with the impetus to complete my doctoral studies and look ahead in life. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS II DECLARATION IV TABLE OF CONTENTS V SUMMARY IX LIST OF TABLES XI LIST OF FIGURES XII LIST OF ABBREVIATIONS AND SYMBOLS 1. XVII INTRODUCTION 1.1 BACKGROUND AND MOTIVATION 2. 3. 1.2 RESEARCH OBJECTIVES 11 1.3 THESIS ORGANISATION 12 LITERATURE SURVEY 14 2.1 MONOLITHS AND APPLICATIONS 14 2.2 MODELS FOR POROUS MEDIA 17 2.3 DIRECT IMAGING TECHNIQUES 19 2.4 TRANSPORT IN MODELS RECONSTRUCTED FROM 3D SCANS 20 2.5 EDDY DISPERSION 23 EXPERIMENTAL METHODS 25 3.1 APPARATUS, COLUMNS AND CHEMICALS 25 3.2 PRESSURE DROP MEASUREMENTS 26 3.3 INVERSE SIZE EXCLUSION CHROMATOGRAPHY 26 v 4. 5. 3.4 TOMOGRAPHIC SCAN 26 3.5 MERCURY POROSIMETRY 27 3.6 NON-POROUS DISPERSION 27 3.7 POROUS/NON-RETAINED DISPERSION 28 3.8 RETAINED DISPERSION 28 3.9 DISPERSION DATA ANALYSIS 29 COMPUTATIONAL METHODS 30 4.1 IMAGE ANALYSIS 30 4.2 DEVELOPMENT OF CFD MODEL 31 3.1.1 Hydrodynamics 31 3.1.2 Peak Parking Simulations 33 3.1.3 Dispersion Simulations 35 3.1.4 Retention conditions 38 MODEL VALIDATION FROM HYDRODYNAMICS AND NONPOROUS DISPERSION SIMULATIONS 42 5.1. INTRODUCTION 42 5.2. RESEARCH OBJECTIVES 46 5.3. RESEARCH APPROACH 47 5.4. RESULTS AND DISCUSSIONS 48 5.4.1 Inverse Size Exclusion Chromatography (ISEC) 48 5.4.2 Porosity Analysis 52 5.4.3 Pore and Skeleton Size Distributions 56 5.4.4 Hydrodynamic Simulations 60 5.4.5 Peak Parking Simulations 71 vi 5.4.6 Transient Dispersion Simulations 73 5.4.7 Estimation of Transcolumn Dispersion 77 5.4.8 Estimation of Transchannel and Short-Range interchannel eddy dispersion 84 5.5. CONCLUSIONS 6. 88 MODEL VALIDATION FROM NON-RETAINED AND RETAINED DISPERSION SIMULATIONS 92 6.1. INTRODUCTION 92 6.2. RESEARCH OBJECTIVES 92 6.3. RESEARCH APPROACH 93 6.4. MODEL SETUP 94 5.4.9 Porous Conditions 94 5.4.10 Non-retained conditions 96 5.4.11 Retained conditions 96 6.5. RESULTS AND DISCUSSIONS 5.4.12 Peak Parking Simulations 5.4.13 Transient Dispersion Simulations 5.4.14 Estimation of dispersion due to transcolumn velocity bias and external film mass transfer resistance 97 100 105 5.4.15 Estimation of short-range interchannel eddy dispersion 119 5.4.16 Phenomenological approach to estimate transcolumn dispersion 122 6.6. CONCLUSIONS 7. 97 127 EFFECT OF MACROPOROSITY ON DISPERSION BEHAVIOUR OF SILICA MONOLITHS 130 vii 7.1. INTRODUCTION 130 7.2. RESEARCH OBJECTIVES 132 7.3. RESEARCH APPROACH 132 7.4. GENERATION OF ARTIFICIAL MONOLITHIC MIMICS 133 7.5. RESULTS AND DISCUSSION 134 5.4.17 Pore and Skeleton Size Distributions 134 5.4.18 Hydrodynamic Simulations 137 5.4.19 Peak Parking Simulations 144 5.4.20 Dispersion simulations 146 5.4.21 Estimation of transchannel and short-range interchannel eddy dispersion 5.4.22 Estimation of dispersion due to transcolumn velocity bias and external film mass transfer resistance 8. 155 160 7.6. CONCLUSIONS 166 7.7. IMPROVEMENTS TO MORPHOLOGY 168 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK 170 8.1 CONCLUSIONS 170 8.2 NOVELTY AND IMPACT 173 8.3 ADVANTAGES AND LIMITATIONS 175 8.4 RECOMMENDATIONS FOR FUTURE WORK 177 BIBLIOGRAPHY 179 LIST OF PUBLICATIONS AND PRESENTATIONS 192 viii SUMMARY Downstream separation of mixtures in a variety of fields such as protein purification, quality control of drugs, pharmacokinetic studies, and determination of pollutants or food additives has traditionally been carried out using particulate HPLC columns where the separation efficiency increases with decreasing particle size, at the cost of higher operating pressures. Monoliths are a class of chromatographic columns cast in the form of tubes, rods or disks as a single and co-continuous block that is porous and permeable. A high external porosity resulting from a regular network of through-macropores and a mesoporous skeleton network provide a combination of low hydraulic resistance to the mobile phase and enhanced mass transfer rates of sample molecules through the column, respectively. In this research, an analysis of the transport properties of the bulk homogeneous core of a silica monolith is presented via direct numerical simulations in a topological model reconstructed from 3D nanotomographic scans. A commercially available silica monolith (Chromolith®) was scanned at three isotropic resolutions to investigate the resolution required to adequately capture the throughpore and skeleton-surface heterogeneity. Hydrodynamic behaviour of the macropore space in domains representative of the bulk porosity was analysed via computational fluid dynamics. A 30 m cubic unit cell at 190 nm scanning resolution was found to be representative of the Darcy permeability, with a ±6% deviation from experimental and reported literature data. Transcolumn eddy dispersion, reported to be the single-most dominant contributor of inefficiency in the first generation of silica monoliths, was estimated from the deviation of axial dispersion simulations under non-porous, porous/non-retained and retained simulations from experiments using ix 3. The current set of geometries has identical domain-sizes and a fairly constant skeleton heterogeneity. CT scans of several different silica monoliths in various formats are required so that a comprehensive study on the effects of varying domain-sizes, heterogeneities and porosities can be explored. 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(2010) Transport and reaction in reconstructed porous polypropylene particles: Model validation, Chemical Engineering Science, 65, 2361-2372. 191 LIST OF PUBLICATIONS AND PRESENTATIONS 1. Vasudevan, V. and Loh, K-C. (2013) Hydrodynamic and dispersion behaviour in a non-porous silica monolith through fluid dynamic study of a computational mimic reconstructed from sub-micro-tomographic scans, Journal of Chromatography A, 1274, 65-76. 2. Vasudevan, V. and Loh, K-C. Transcolumn dispersion in a computational mimic of an analytical silica monolith reconstructed from sub-microtomographic scans using computational fluid dynamics (Submitted to Separation and Purification Technology) 3. Vasudevan, V. and Loh, K-C., Theoretical investigation on the effect of external porosity on the hydrodynamic and dispersion behaviour of constant-domain silica monoliths (Under preparation) 4. A realistic 3D model of silica monoliths for CFD simulations, Poster Presentation, Graduate Students‘ Symposium, National University of Singapore, Singapore, December 2008. 5. Development Of A Realistic 3D Model Of Silica Monoliths For CFD Simulations, Oral Presentation, AIChE Annual Meeting, Philadelphia, Pennsylvania, USA, November 2008. 6. Development Of A Realistic 3D Model Of Silica Monoliths For CFD Simulations, Oral Presentation, AIChE Annual Meeting, Salt Lake City, Utah, USA, November 2007. 192 7. Development of a realistic 3D model of silica monoliths for CFD simulations, Poster Presentation, Graduate Students‘ Symposium, National University of Singapore, Singapore, September 2007. 8. Morphological chromatographic representation performance, of silica Poster monoliths Presentation, for simulation Graduate of Students‘ Symposium, National University of Singapore, Singapore, September 2006. 193 [...]... modelling efforts to describe the hydrodynamic and dispersion behaviour of monoliths, iii) non-invasive scanning approaches utilised to capture the morphology of porous media in several applications and iv) use of CT scans and fluid dynamics to capture hydrodynamic and dispersion characteristics of silica and polymer monoliths Chapter three details the materials used and experimental protocols followed... model of a commercially available silica monolith from sub- micron x-ray computed tomography scans and study its hydrodynamic and dispersion behaviour using a commercial computational fluid dynamics program The research work comprised the following: a) Develop a computational model to capture the inherent structural morphology in silica monoliths from non-invasive 3D scans at several resolutions and compare... provide a combination of low 1 hydraulic resistance to the mobile phase, and enhanced mass transfer rates of sample molecules through the column Silica monolithic columns have found many applications in diverse fields such as high throughput analysis of drugs and metabolites, separation of environmentally relevant substances and food additives, separation of enantiomers and separation of complex biological... motivation for modelling the hydrodynamic and dispersion characteristics of monoliths in commercially available CFD software, Ansys Fluent, using geometry reconstructed from sub- micron CT scans This chapter also lists the overall and specific objectives of the research program An extensive literature review follows in chapter two that traces i) the history of the development of monoliths and their applications... after estimation of transcolumn eddy dispersion and external film mass transfer from and , respectively 107 Figure 6.8: Experimental and simulated reduced-plate heights vs reduced-linear velocity under retained conditions Dotted line indicates fit after estimation of transcolumn eddy dispersion and external film mass transfer from and , respectively 107 Figure 6.9: Experimental and simulated... work and (B) Gritti and Guiochon (2011) 114 Figure 6.12: Experimental and simulated reduced-plate heights vs reduced-linear velocity under non-retained conditions Dotted line indicates fit after estimation of transcolumn eddy dispersion and external film mass transfer ( and ) 117 Figure 6.13: Longitudinal diffusion, stationary-phase mass transfer, transchannel and short-range interchannel... identify the transcolumn dispersion contribution – a major source of inefficiency in the current generation of silica monoliths 11 d) Study the effect of external porosity on hydrodynamic and dispersion characteristics of silica monoliths 1.3 Thesis Organisation This thesis comprises of eight chapters The first chapter briefly discusses the role of monoliths in current HPLC practices and provides an insight... inhomogeneities in the macropore network of a silica monolith at lower scanning resolutions We attempt to show that if a lower resolution is able to relate the hydrodynamic and dispersion performance of the silica monolith to its pore structure, without significant loss of accuracy and at an appreciably reduced computational expense, then detailed studies on the dispersion behaviour of the macropore network under... performance than conventional particulate columns in pressure-driven liquid chromatography (Ikegami and Tanaka, 2004) They are cast in the form of tubes, rods or disks as a single and co-continuous block that is porous and permeable An important characteristic of monoliths is their high external porosity resulting from a network of through-macropores (Miyabe and Guiochon, 2004) The regular structure of. .. description of the image analysis techniques, CFD model setup, and numerical analyses and equations employed in this work The model validation via image analyses results and hydrodynamic and non-porous dispersion studies is presented in chapter five Chapter six focuses on extending the model to simulate dispersion under porous and retained conditions with special emphasis on the transcolumn and film mass transfer . HYDRODYNAMIC AND DISPERSION BEHAVIOUR OF AN ANALYTICAL SILICA MONOLITH RECONSTRUCTED FROM SUB-MICROTOMOGRAPHIC SCANS USING COMPUTATIONAL FLUID DYNAMICS VIVEK VASUDEVAN . UNIVERSITY OF SINGAPORE 2013 HYDRODYNAMIC AND DISPERSION BEHAVIOUR OF AN ANALYTICAL SILICA MONOLITH RECONSTRUCTED FROM SUB-MICROTOMOGRAPHIC SCANS USING COMPUTATIONAL FLUID DYNAMICS . Estimation of transchannel and short-range interchannel eddy dispersion 155 5.4.22 Estimation of dispersion due to transcolumn velocity bias and external film mass transfer resistance 160 7.6.