Homogeneous Nucleation of Carbon Dioxide (CO2) in Supersonic Nozzles DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University Kayane Kohar Dingilian, M.S. Graduate Program in Chemical Engineering The Ohio State University 2020 Dissertation Committee: Barbara E. Wyslouzil, Advisor Nicholas Brunelli Isamu Kusaka i Copyright by Kayane Kohar Dingilian 2020 ii ABSTRACT Carbon dioxide (CO2) is an important greenhouse gas that contributes to global warming. To combat the rising emissions of CO2 into the atmosphere, scientists and researchers have devised several methods of carbon capture and storage (CCS), including the use of membranes to trap CO2 molecules, valves to condense CO2 from a mixture of gases, etc. Supersonic separation is a novel method of gas-gas separation that has been used to separate natural gas from other gases. It has been suggested for and is being currently studied as a method for the removal of CO2 from flue gas before it enters the atmosphere. Supersonic separation relies on the condensation of CO2 clusters into particles large enough to be inertially separated, requiring a size of approximately 1 micrometer in diameter. In order to effectively design hardware to capture CO2 using this mechanism, we need to study and collect fundamental nucleation properties of CO2 and quantify the process under supersonic flow conditions. To this end, we studied the condensation of CO2 in two supersonic nozzles of differing expansion rates, T1 and T3, and sought to quantify the onset of nucleation, particle size distributions, and aerosol number densities. First, we confirmed that homogeneous nucleation of CO2 could not take place in nozzle T1 when expansions started from a stagnation temperature of 20°C, no heat release was observed in pressure trace measurements at 7.0 to 11 mol% CO2. Lowering the stagnation temperature to 10°C showed some evidence of heat release, but it was uncertain to what extent that was due to condensation of particles or whether the nozzle i overexpansion had caused a shock to increase the temperature and pressure of the flow. Analysis of the saturation curve suggests the nucleation event was incomplete, and lower temperatures were required for a full characterization. Second, we performed a series of pressure trace measurements (PTM) in nozzle T3 for concentrations of CO2 in Ar ranging from 0.5 to 39 mol% with a stagnation pressure of 458 Torr (61 kPa) and a stagnation temperature of 20°C. We successfully observed the complete nucleation event over that range and characterized the flow conditions at the onset of nucleation at pressures ranging from 7.45 to 793 Pa and temperatures between 66.5 and 92.3 K. We also observed a wide variety of saturations at onset, ranging from 2290 to 1.49 x 106. An arbitrary cutoff was made, denoting systems of 3.0 mol% CO2 and higher to be of “mid-high” flow rates, and for systems at 2.0 mol% CO2 and lower to be of “low” flow rates. We observed a consistent shift in onset conditions and nucleation rates at approximately 12 mol% CO2 as increases in the amount of CO2 in the system contributed to an increasingly softer and warmer expansion. We further characterized the mid-high (3.0 to 39 mol%) flow region using small angle X-ray scattering (SAXS) and a limited number of Fourier transform infrared (FTIR) spectroscopy experiments. Experimental number densities were found to be on the order of 1012 cm-3 and nucleation rates on the order of 1017 cm-3s-1. Extrapolating from these experiments into the low CO2 flow regime, we obtained similar values for estimates of the number density and nucleation rates. FTIR spectra of the system of 12 mol% CO2 showed a transition from the gas phase to the solid crystalline phase, and the spectra suggest these particles are cubic in shape. ii Third, we compared our experimental results for the onset conditions and nucleation rates with theory, choosing combinations of self-consistent nucleation theory (SCNT) or simulation-based theory (ST) and surface tension relations by Quinn or based on fitting the data to the Lielmezs-Herrick (L-H) functional form. We also applied the nonisothermal correction factor of Feder et al. to account for incomplete thermalization between the condensing clusters and the carrier gas. The values of the nonisothermal correction factor ranged from 0.015 to 0.391, resulting in nucleation rates that ranged from approximately 1018 cm-3s-1 to 1019 cm-3s-1. In general, using the Quinn surface tension expression with either nucleation theory overestimates the pressures required to initiate nucleation, and using L-H with either nucleation theory underestimates them. We found, however, that ST theory captures the temperature dependence of the experimental data slightly better than SCNT does. We also developed a protocol for ensuring that the nucleation we observed in our experiments was purely homogeneous or in the near-homogenous limit by flowing carrier gas through the nozzle for 1 hour at 90 SLM to remove any trace amounts of condensable vapors. An independent analysis of the dry traces from our experiments showed that we could reproduce the background flow conditions to a maximum deviation of pressure ratio of 0.00046 and temperature of 0.307 K. Overall, we observed excellent agreement between our experiments and those of higher pressure and temperature conditions, as well as promising overlap with those at lower ones. The free energy barrier to nucleation in our experiments appears to be similar to those of other experiments in supersonic nozzles and can serve to bridge the gap between different nucleation regimes. iii To my family, who instilled and nurtured my passion for learning, And to the faculty and students, who fostered my passion for teaching others. iv ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Dr. Barbara Wyslouzil, for her guidance and mentorship of my graduate career. She helped me grow and develop as a researcher and also encouraged me to explore myself as an academic professional through participation in teaching opportunities and conferences. I truly believe I could not have found a better advisor for my graduate experience. Second, I extend my gratitude to the faculty with whom I developed my skills as a teaching assistant and lecturer at The Ohio State University – namely Dr. David Tomasko, Dr. David Wood, Dr. Jeffrey Chalmers, Dr. Andrew Tong, and Dr. Kurt Koelling. They have all provided me with opportunities to perform duties beyond those of grading and holding office hours, including providing full or abridged lectures and becoming involved in the courses at a deeper instructional level. I have gained valuable teaching experience and learned lessons that will help me as I progress in my career. Third, I would like to thank those who have served on my committees, at all levels of exams, especially Dr. Nicholas Brunelli, Dr. Isamu Kusaka, and Dr. Heather Allen, for encouraging me to think critically about my research and reflect on the greater significance of my findings. Fourth, I would like to thank my previous advisor and mentors from the California Institute of Technology, Dr. Richard Flagan and Dr. Michael Vicic, for their support beginning from my undergraduate years and extending through the years afterwards. Through them, I’ve been allowed to establish a greater network of scientists and researchers as well as pursue my academic dreams. v Fifth, I would like to thank Soenke Seifert and Randall Winans at Argonne National Laboratory for their assistance in setting up and making measurements using the beam at the Advanced Photon Source. Thank you to Martina Lippe for visiting and helping conduct experiments as well. Sixth, my appreciation goes out to my labmates, both former and present, including: Dr. Andrew Amaya, Dr. Yensil Park, Dr. Kehinde Ogunronbi, Tong Sun, Jiaqi Luo, and visiting scholar Jiang Bian. Much of my training in the experiments was performed by Andrew and Kehinde. I also had the pleasure of mentoring and training two wonderful undergraduate researchers myself – Lahari Pallerla and Gabrielle Adams. Finally, I would like to thank the Dingilian family – my father, mother, sister Armine, and brother Hovanness, for their continued presence and support. None of my efforts would have been possible without the strong backbone of my family. vi VITA October 2012 – June 2016 Bachelor of Science, Chemical Engineering California Institute of Technology Pasadena, California, USA August 2016 – December 2019 Master of Science, Chemical Engineering The Ohio State University August 2017 – May 2019 Graduate Teaching Assistant January 2020 – May 2020 The Ohio State University August 2016 – present Graduate Research Associate The Ohio State University vii PUBLICATIONS 1. K. K. Dingilian, R. Halonen, V. Tikkanen, B. Reischl, H. Vehkamäki, B. E. Wyslouzil. Homogeneous nucleation of carbon dioxide in supersonic nozzles I: experiments and classical theories. Physical Chemistry and Chemical Physics. 2020. 2. R. Halonen, V. Tikkanen, B. Reischl, K. K. Dingilian, B. E. Wyslouzil, H. Vehkamäki. Homogeneous nucleation of carbon dioxide in supersonic nozzles II: molecular dynamics simulations and properties of nucleating clusters. Physical Chemistry and Chemical Physics, submitted. FIELDS OF STUDY Major Field: Chemical Engineering Aerosol Physics Physical/Analytical Chemistry viii TABLE OF CONTENTS Abstract…………………………………………………………………………………………… i Acknowledgements…………………………………………………………………………….. v Vita………………………………………………………………………………………………. vii List of Tables……………………………………………………………………………………. xi List of Figures…………………………………………………………………………………. xiii Chapter 1: Introduction………………………………………………………………………… 1 Chapter 2: Nucleation Theory…………………………………………………………………. 7 Section 2.1: Thermodynamics of Nucleating Clusters……………………………… 8 Section 2.2: The Classical Nucleation Rate………………………………………... 12 Section 2.3: Self-Consistent Nucleation Theory…………………………………… 17 Section 2.4: The Non-Isothermal Correction Factor………………………………. 18 Chapter 3: Materials and Methods………………………………………………………….. 24 Section 3.1: Physical Properties of Ar and CO2…………………………………….24 Section 3.2: Nozzles T1 and T3……………………………………………………..