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What Limits the Yield of Levoglucosan During Fast Pyrolysis of Cellulose? Juan Sebastian Proano-Aviles Iowa State University

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What Limits the Yield of Levoglucosan During Fast Pyrolysis of Cellulose? Juan Sebastian Proano-Aviles Iowa State University Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2017 What limits the yield of levoglucosan during fast pyrolysis of cellulose? Juan Sebastian Proano-Aviles Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Mechanical Engineering Commons, and the Oil, Gas, and Energy Commons Recommended Citation Proano-Aviles, Juan Sebastian, "What limits the yield of levoglucosan during fast pyrolysis of cellulose?" (2017). Graduate Theses and Dissertations. 15607. https://lib.dr.iastate.edu/etd/15607 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. i What limits the yield of levoglucosan during fast pyrolysis of cellulose? by Juan Proano‐Aviles A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Co‐majors: Mechanical Engineering and Biorenewable Resources and Technology Program of Study Committee: Robert C. Brown, Major Professor Xianglan Bai James Michael Dave Raman Brent Shanks Iowa State University Ames, Iowa 2017 Copyright © Juan Proano‐Aviles, 2017. All rights reserved. ii DEDICATION I have learned that the path of the graduate student is a humbling one, and it is one of the most challenging I have encountered. I started this journey inspired and supported by each one of my compatriots so this work is dedicated to them, the Ecuadorian people. iii TABLE OF CONTENTS Page LIST OF TABLES ........................................................................................................................... v LIST OF FIGURES ........................................................................................................................ vi ACKNOWLEDGMENTS ............................................................................................................... xi ABSTRACT ................................................................................................................................. xii CHAPTER 1 INTRODUCTION ...................................................................................................... 1 CHAPTER 2 BACKGROUND ........................................................................................................ 4 Cellulose and Levoglucosan .................................................................................................. 4 Condensed Phase Degradation of Levoglucosan .................................................................. 6 Competition between evaporation and repolymerization of levoglucosan ..................... 7 Evidence of Gas Phase Degradation of Levoglucosan ......................................................... 10 Agglomeration, Coalescence and Char Formation .............................................................. 12 Cellulose Pyrolysis Mechanisms .......................................................................................... 13 Challenges to Determine Kinetic Data from Pyrolysis ........................................................ 15 Mass Transfer Limitations ............................................................................................... 17 Internal ........................................................................................................................ 17 External ....................................................................................................................... 21 Extended residence times ........................................................................................... 22 Heat Transfer Limitations ................................................................................................ 22 Relevant Methods for Kinetic Studies During Pyrolysis Reactions ..................................... 26 Efforts to measure kinetic parameters for pyrolysis of cellulose ................................... 28 Cracking and unzipping participation revealed by reaction rate curve behavior ........... 31 CHAPTER 3 METHODOLOGY ................................................................................................... 34 Materials .............................................................................................................................. 34 Apparatus ............................................................................................................................ 35 Analytical Instruments ........................................................................................................ 40 Analysis of Kinetic Data ....................................................................................................... 41 Single step, first order approximation............................................................................. 41 Isoconversional and model fitting methods .................................................................... 44 Modeling Secondary Gas‐Phase Reactions of Levoglucosan in Micropyrolysis Experiments ......................................................................................................................... 47 Modeling Early Stages of Cellulose Pyrolysis ...................................................................... 49 Cracking and unzipping initial models ............................................................................. 49 Cracking as the only depolymerization reaction ............................................................. 49 iv Cracking and unzipping model ........................................................................................ 51 Cracking and unzipping model with limited unzipping levoglucosan yields ................... 52 CHAPTER 4 RESULTS AND DISCUSSION .................................................................................. 55 Recovery of Anhydrosugars in a Furnace‐Based Micropyrolyzer ....................................... 55 Evacuation of levoglucosan from the sample holder ...................................................... 55 Degradation of levoglucosan in the gas phase ................................................................ 59 Repolymerization of Intermediate Products During Carbohydrate Pyrolysis ..................... 62 Experimental Investigation of Thermohydrolysis During Cellulose Pyrolysis ..................... 69 Experimental Methods to Measure Chemical Kinetic Constants ....................................... 71 Evaluating heat and mass transfer limitations in micropyrolyzer experiments ............. 71 Global chemical kinetics of cellulose and other carbohydrates during pyrolysis ........... 75 Kinetic data analysis ........................................................................................................ 80 Modeling Cellulose Pyrolysis ............................................................................................... 84 Cracking and unzipping initial models ............................................................................. 84 Cracking as the only depolymerization reaction ........................................................ 84 Cracking and unzipping model .................................................................................... 85 Cracking and unzipping model with limited unzipping levoglucosan yields .............. 88 CHAPTER 5 CONCLUSIONS AND FUTURE WORK .................................................................... 92 Conclusions .......................................................................................................................... 92 Future work ......................................................................................................................... 94 References .............................................................................................................................. 97 v LIST OF TABLES Page Table 1. List of materials utilized in micropyrolysis experiments during this study. Mois‐ ture content reported from thermogravimetric analysis. ...................................................... 34 Table 2. Commonly employed reaction models for curve fitting in chemical kinetic studies. .................................................................................................................................... 46 Table 3. Kinetic data utilized in calculations of degradation of levoglucosan in the gas phase. ...................................................................................................................................... 48 Table 4. Chemical kinetics data utilized in models ................................................................ 86 Table 5. Chemical kinetics data utilized in new combined model. ........................................ 90 vi LIST OF FIGURES Page Figure 1. Simplified structure of cellulose. The schematic shows the presence of the reducing‐end group (RE) and the non‐reducing‐end group (NR). ............................................ 4 Figure 2. Hydroxyl groups on D‐glucose that lead to the formation of a furanose or pyranose ring, dehydration step not shown. Adapted. ............................................................ 5 Figure 3. Relative levoglucosan intensity determined by TOF‐MS during free‐fall experiments at 400 (a), 500 (b), and 600 °C
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