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A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight

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A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight Aromatic Compounds and Cogeneration of Hydrogen A dissertation presented to the faculty of the Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirements for the degree Doctor of philosophy Mahtab Naderinasrabadi May 2020 © 2020 Mahtab Naderinasrabadi. All Rights Reserved. 2 This dissertation titled A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight Aromatic Compounds and Cogeneration of Hydrogen by MAHTAB NADERINASRABADI has been approved for the Department of Chemical and Biomolecular Engineering and the Russ College of Engineering and Technology by John Staser Associate Professor of Chemical and Biomolecular Engineering Mei Wei Dean, Russ College of Engineering and Technology 3 ABSTRACT NADERINASRABADI, MAHTAB, Ph.D., May 2020, Chemical Engineering A Continuous Electrochemical Process to Convert Lignin to Low Molecular Weight Aromatic Compounds and Cogeneration of Hydrogen Director of Dissertation: John Staser Lignin is one of the main byproducts of pulp and paper industry and biorefineries. Depolymerization of lignin can lead to producing valuable low molecular weight compounds with different functional groups, which are mainly achieved from crude oil sources. Lignin electrolysis could address issues of other lignin depolymerization methods such as complexity, lignin combustion, and low selectivity. On the other hand, lignin electrolysis can occur at significantly lower overpotentials than those required for water electrolysis, which leads to lower-voltage electrolyzer operation and as a result lower energy consumption for hydrogen production. This study includes research and experimental works on developing a continuous electrochemical process for both lignin electrolysis and hydrogen production in an electrolyzer. At the first step of this project, high surface area TiO2 or carbon-supported NiCo electrocatalysts were synthesized and applied for lignin depolymerization at room temperature and pressure. The electrocatalysts were characterized by Brunauer- Emmett-Teller (BET), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques. In addition, a three-electrode rotating disc electrode (RDE) system was used to test the performance 4 and durability of 6 electrocatalysts individually and among them 1:3NiCo/TiO2 was selected as the most effective catalyst for lignin depolymerization. In the second step, a continuous electrochemical cell with 10 cm2 electrodes, separated by an anion exchange membrane (AEM), was applied for lignin electrolysis in the anode and hydrogen generation in the cathode. The effects of temperature, lignin concentration, cell voltage, and electrolysis time on hydrogen production, oxygen evolution, lignin conversion, products with different functional groups, and energy efficiency of the electrochemical reactor were investigated. Although applying high cell voltages increases the rate of electrochemical reactions and lignin conversion, it produces inefficiencies in energy consumption by enhancing oxygen evolution reaction (OER). Several techniques including gas chromatography-mass spectroscopy (GC/MS), ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), and Raman spectroscopy were applied to analyze the lignin samples. In addition, the generalized standard addition method (GSAM) for the first time was applied for measuring lignin conversion after electrolysis. The third step of this project included scaling-up the 10 cm2 continuous 2 electrochemical cell to a 200 cm reactor and utilizing it for lignin electrolysis and H2 production on a larger scale. The results indicate that the performance of the scaled-up reactor is extremely analogous to the 10 cm2 cell. 5 DEDICATION To my mother and father, who always had confidence in me and encouraged me to go on every adventure in my life and my adviser, Dr. John Staser, for all of his guidance and supports during my Ph.D. study 6 ACKNOWLEDGMENTS We appreciatively acknowledge the financial support of this project by the US Department of Energy (DOE) under award DE-EE0007105. The project team is also thankfully acknowledging the contribution of the Center for Intelligent Chemical Instrumentation, directed by Professor Harrington, for all of their helpful guidance on lignin characterization and introducing Generalized Standard Addition Method for measuring lignin conversion. In addition, the collaboration of Hexion Company1 in collecting gel permeation chromatography (GPC) data and OH number determination is gratefully acknowledged. 1 Address: 6200 Camp Ground Rd, Louisville, KY 40216 7 TABLE OF CONTENTS Page Abstract .........................................................................................................................3 Dedication .....................................................................................................................5 Acknowledgments.........................................................................................................6 List of Tables ..............................................................................................................10 List of Figures .............................................................................................................12 Chapter 1: Introduction ...............................................................................................15 Chapter 2: Literature Review ......................................................................................18 2-1- Biomass Conversion .......................................................................................18 2-1-1- Lignocellulosic Biomass .......................................................................18 2-1-2- Bonds Within Lignocellulose Biomass and Building Units of Polymers 19 2-1-3- Functional Groups of Lignocellulose Biomass Components ................21 2-1-4- Lignin Depolymerization ......................................................................22 2-1-5- Electrochemical Oxidation of Lignin....................................................23 2-2-Hydrogen Production ......................................................................................27 2-2-1-Hydrogen Generation by Water Electrolysis .........................................27 2-2-2- Anode Electrocatalysts for Water Electrolyzers ...................................30 2-3- Hydrogen Production by Biomass Electrolysis ..............................................32 2-3-2 Electrolysis of Alcohol Solutions for Hydrogen Production .................33 2-3-3- Lignin Electrolysis for Hydrogen Production .......................................35 2-3-4-Influence of Different Parameters on Biomass Electrolysis for Hydrogen Production ........................................................................................................37 Chapter 3: Synthesis and Characterization of Nickel Cobalt Electrocatalysts ...........40 Objectives ..............................................................................................................40 3-1-Introduction .....................................................................................................40 3-2-Materials and Methods ....................................................................................42 3-2-1-Electrocatalysts Synthesis ......................................................................42 3-2-2- Electrocatalysts Physical Characterization ...........................................43 3-2-2-1-Brunauer-Emmett-Teller (BET) Method ............................................43 3-2-2-2-X-Ray Diffraction Spectroscopy (XRD) ............................................43 3-2-2-3-Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray (EDS) Spectroscopy .........................................................................................44 3-2-3-Electrochemical Characterization of Electrocatalysts ...........................44 8 3-2-3-1-Three Electrode RDE Electrochemical Cell .......................................44 3-2-3-2-Lignin Solution Preparation................................................................45 3-3-Results and Discussion ....................................................................................46 3-3-1- Physical Characterization of Electrocatalysts .......................................46 3-3-2- Electrochemical Characterization of Electrocatalysts ..........................52 3-4-Conclusion .......................................................................................................55 Chapter 4: Hydrogen ProductIon and Energy Efficiency ...........................................56 Objectives ..............................................................................................................56 4-1-Introduction .....................................................................................................56 4-2-Materials and Methods ....................................................................................58 4-2-1-Lignin Solution ......................................................................................58 4-2-2-Electrode Preparation .............................................................................58 4-2-3-Continuous Electrochemical Reactor .....................................................58 4-2-4-H2 Detection ...........................................................................................60
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