ABSTRACT High-Performance Liquid Chromatographic Methods For
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ABSTRACT High-Performance Liquid Chromatographic Methods for Quantitative Assessment of Degradation Products and Extractives in Pretreated Lignocellulose Shou-Feng Chen, Ph.D. Mentor: C. Kevin Chambliss, Ph.D. Long-term economic, national security, and environmental concerns have motivated research into renewable fuels from lignocellulosic biomass. Among energy alternatives, biomass-derived ethanol represents one of the more promising commodities for long-term sustainability of transportation fuels. Herbaceous agricultural residues, such as corn stover, represent a major source of lignocellulosic material with considerable potential for use in biomass-to-ethanol schemes. Currently, the technology for conversion of biomass to ethanol involves dilute acid pretreatment of lignocellulosic materials, followed by enzymatic hydrolysis of cellulose and fermentation of monomeric sugars to produce ethanol. However, a variety of degradation products are produced during dilute acid pretreatment of lignocellulosic biomass, which exert an inhibitory effect on downstream fermentation processes and reduce bio-ethanol conversion. Thus there is an increased demand for reliable analytical methods to advance a better understanding of lignocellulose pretreatment. Several liquid chromatographic methods are developed for a systematic analysis of various degradation products. High-performance liquid chromatography is the most widely used analytical separation technique, because of its reproducibility, sensitivity, and suitability for separating nonvolatile species, which makes the method ideal for accurate quantitative determinations. A reversed-phase HPLC method with UV detection is developed for simultaneous separation and quantitation of organic acids and neutral degradation products present in the corn stover hydrolysate. On the other hand, inorganic ions and some organic anions, which are present in the water extractive from corn stover, are separated and quantitated by a developed ion chromatographic method with conductivity detection. Sugars and alditols are also determined using high-performance anion chromatography with pulsed amperometric detection. High-Performance Liquid Chromatographic Methods for Quantitative Assessment of Degradation Products and Extractives in Pretreated Lignocellulose by Shou-Feng Chen, B.S. A Dissertation Approved by the Department of Chemistry and Biochemistry ___________________________________ David E. Pennington, Ph.D., Interim Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee ___________________________________ C. Kevin Chambliss, Ph.D., Chairperson ___________________________________ Kenneth W. Busch, Ph.D. ___________________________________ Stephen L. Gipson, Ph.D. ___________________________________ Mary Lynn Trawick, Ph.D. ___________________________________ Ian A. Gravagne, Ph.D. Accepted by the Graduate School December 2007 ___________________________________ J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2007 Shou-Feng Chen All rights reserved TABLE OF CONTENTS List of Figures............................................................................................................ vii List of Tables ............................................................................................................. ix Acknowledgments...................................................................................................... xi CHAPTER ONE – Renewable Energy from Biomass: Resource and Analytical Technology An Introduction....................................................... 1 Alternative Energy from Biomass ..................................................... 1 Projected Depletion of Earth’s Petroleum Reserves.................... 1 Environmental Impacts of Bio-ethanol........................................ 2 Biomass Resources for Ethanol Production................................. 3 Biomass Composition........................................................................ 4 Biomass Conversion.......................................................................... 5 Pretreatment Processes................................................................. 6 Dilute-Acid Pretreatment............................................................. 7 Scope of the Dissertation ................................................................... 7 Brief Description of Relevant Chromatographic Techniques............ 11 Reversed-Phase HPLC with UV Detection ................................. 12 Ion Chromatography with Conductivity Detection...................... 16 High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection.................................. 20 iii CHAPTER TWO – High-Performance Liquid Chromatography Method for Simultaneous Determination of Aliphatic, Aromatic Acid, and Neutral Degradation Products in Biomass Pretreatment Hydrolysates ...................... 25 Introduction........................................................................................ 25 Experimental: Materials and Methods............................................... 27 Chemicals and Reagents.............................................................. 27 Preparation of Standards.............................................................. 28 HPLC Analysis............................................................................ 29 Hydrolysate Sample Preparations................................................ 31 Sample Preparation and Extraction Procedures........................... 32 Extraction Efficiency ................................................................... 33 Results and Discussion...................................................................... 33 What Degradation Products are Formed?.................................... 33 Selection of Analytes................................................................... 35 Method Development and Validation.......................................... 36 Method Application..................................................................... 49 Conclusions........................................................................................ 51 CHAPTER THREE – Pseudo Reaction Kinetics of Organic Degradation Products in Dilute-Acid-Catalyze Corn Stover Pretreatment Hydrolysates................. 53 Introduction........................................................................................ 53 Experimental: Materials and Methods............................................... 57 Chemicals and Reagents.............................................................. 57 Preparation of Standards.............................................................. 58 HPLC Analysis............................................................................ 58 iv Experimental Design and Hydrolysate Preparation..................... 59 Results and Discussion...................................................................... 61 Effect of Reaction Severity on Accumulation ............................. 61 Empirical Modifications of the Severity Function....................... 63 Reaction Kinetics......................................................................... 71 Conclusions........................................................................................ 74 CHAPTER FOUR – Compositional Analysis of Water-Soluble Materials in Corn Stover .................................................... 76 Introduction........................................................................................ 76 Experimental: Materials and Methods............................................... 77 Corn Stover Feedstocks and Chemical Reagents......................... 77 Sample Preparation...................................................................... 78 Water Extraction.......................................................................... 78 Fractionation and Compositional Analysis.................................. 79 Water Fraction: Sugars and Related Alditols............................... 80 Water Fraction: Aliphatic Acids and Inorganic Anions .............. 82 Water Extract: Inorganic Cations................................................. 84 − Bicarbonate (HCO3 ) Fraction: Aromatic Acids ......................... 84 Red-Brown Fraction..................................................................... 87 Identification and Quantitation of Analytes................................. 87 Results and Discussion...................................................................... 88 Mass Balance for Water-Soluble Materials.................................. 88 Carbohydrates............................................................................... 91 v Alditols and Aliphatic Acids........................................................ 94 Aromatic Acids............................................................................. 95 Inorganic Ions............................................................................... 97 Tentative Identification of the Red-Brown Fraction .................... 97 Contributors to the Unknown Fraction of Water Extracts................. 100 APPENDICES ...................................................................................................... 102 Appendix A: Accumulated Concentrations of Individual Degradation Products Identified at Three Levels of Reaction Severity ....... 103 Appendix B: Optimization