Tài liệu Applied pyrolysis handbook

DK3999_C000.fm Page i Thursday, October 26, 2006 6:12 AM Applied Pyrolysis Handbook Half Title Page Second Edition DK3999_C000.fm Page ii Thursday, October 26, 2006 6:12 AM DK3999_C000.fm Page iii Thursday, October 26, 2006 6:12 AM Applied Pyrolysis Handbook Title Page Second Edition edited by Thomas P. Wampler Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business DK3999_C000.fm Page iv Thursday, October 26, 2006 6:12 AM CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2007 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 1-57444-641-X (Hardcover) International Standard Book Number-13: 978-1-57444-641-8 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Applied Pyrolysis handbook / edited by Thomas Wampler. -- 2nd ed. p. cm. Includes bibliographical references and index. ISBN-13: 978-1-57444-641-8 (alk. paper) ISBN-10: 1-57444-641-X (alk. paper) 1. Pyrolysis--Handbooks, manuals, etc. I. Wampler, Thomas P., 1948- II. Title. TP156.P9A67 2006 543--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com 2006023252 DK3999_C000.fm Page v Thursday, October 26, 2006 6:12 AM Preface to the Second Edition Analytical pyrolysis is the study of molecules by applying enough thermal energy to cause bond cleavage, and then analyzing the resulting fragments by gas chromatography, mass spectrometry, or infrared spectroscopy. Pyrolysis has been employed for the analysis of organic molecules for most of this century. It was initially connected with investigations of vapor-phase hydrocarbons and later became a routine technique for analyzing fuel sources and natural and synthetic polymers. Current applications include analysis of trace evidence samples in forensic laboratories, evaluation of new composite formulations, authentication and conservation of artworks, identification of microorganisms, and the study of complex biological and ecological systems. In the time since the first edition of this book, several significant changes have occurred in the field of analytical pyrolysis. First, the introduction of autosamplers for Py-gas chromatography-mass spectromety (GC/MS) has made the technique more routine, more reproducible, and more acceptable for the analysis of complex solids. Second, the widespread availability of mass spectrometers as detectors for Py-GC has led to a better understanding of the degradation products and the processes that create them. Third, as mass spectrometry detectors have become more sensitive, the application of analytical pyrolysis to trace-level determinations has become routine, so that analysts may not only look at the matrix composition, but also investigate additives such as plasticizers, antioxidants, and stabilizers. This book is intended to be a practical guide to the application of pyrolysis techniques to various samples and sample types. To that end, general and theoretical considerations, including instrumentation and degradation mechanisms, have been consolidated in the first two chapters. The balance of the book describes the use of pyrolysis as a tool in specific fields. Synthetic polymers, forensic materials, and other samples with a long history of analysis by pyrolysis are covered. In addition, we have been pleased to see some new areas of study, such as the analysis of surfactants, antiquities, and environmental materials, and these topics are presented as well. The chapters examine the scope of work based on pyrolysis in particular fields of analysis and give specific examples of methods currently used for the examination of representative samples. This book is intended to serve as a starting point for analysts who are adding pyrolysis to their array of analytical techniques by providing concrete examples and suggesting additional reading. I thank all of the authors for their contributions. With only a few exceptions, the authors of the chapters in the first edition agreed to update the chapters they wrote, adding recent examples and references. Each is actively involved in scientific pursuits, and the time that they have taken away from their busy schedules to contribute to this project was valuable and greatly appreciated. Thomas P. Wampler DK3999_C000.fm Page vi Thursday, October 26, 2006 6:12 AM DK3999_C000.fm Page vii Thursday, October 26, 2006 6:12 AM The Editor Thomas P. Wampler has been actively engaged in the field of analytical pyrolysis for 25 years. He is director of science and technology at CDS Analytical, Inc., in Oxford, Pennsylvania. He is the author or coauthor of numerous professional papers on the use of analytical pyrolysis and other thermal sampling techniques. He received a B.S. degree (1970) in chemistry and a M.Ed. degree (1973) in natural science from the University of Delaware, Newark. DK3999_C000.fm Page viii Thursday, October 26, 2006 6:12 AM DK3999_C000.fm Page ix Thursday, October 26, 2006 6:12 AM Contributors Norbert S. Baer Conservation Center New York University New York, New York John M. Challinor Chemistry Centre (WA) East Perth, Western Australia Randolph C. Galipo University of South Carolina Columbia, South Carolina Karen Jansson CDS Analytical, Inc. Oxford, Pennsylvania C.J. Maddock Horizon Instruments Ltd. Heathfleld, East Sussex, England Stephen L. Morgan University of South Carolina Columbia, South Carolina T.O. Munson Department of Math/Science Concordia University Portland, Oregon Hajime Ohtani Nagoya Institute of Technology Nagoya, Japan T.W. Ottley Horizon Instruments Ltd. Heathfleld, East Sussex, England Alexander Shedrinsky Chemistry and Biochemistry Department Long Island University Brooklyn, New York Shin Tsuge Nagoya University Nagoya, Japan Thomas P. Wampler CDS Analytical, Inc. Oxford, Pennsylvania Bruce E. Watt University of South Carolina Columbia, South Carolina Charles Zawodny CDS Analytical, Inc. Oxford, Pennsylvania DK3999_C000.fm Page x Thursday, October 26, 2006 6:12 AM DK3999_book.fm Page xi Tuesday, October 24, 2006 7:17 AM Contents Chapter 1 Analytical Pyrolysis: An Overview .....................................................1 Thomas P. Wampler Chapter 2 Instrumentation and Analysis.............................................................27 Thomas P. Wampler Chapter 3 Pyrolysis Mass Spectrometry: Instrumentation, Techniques, and Applications .................................................................................47 C.J. Maddock and T.W. Ottley Chapter 4 Microstructure of Polyolefins ............................................................65 Shin Tsuge and Hajime Ohtani Chapter 5 Degradation Mechanisms of Condensation Polymers: Polyesters and Polyamides .................................................................81 Hajime Ohtani and Shin Tsuge Chapter 6 The Application of Analytical Pyrolysis to the Study of Cultural Materials.............................................................................105 Alexander Shedrinsky and Norbert S. Baer Chapter 7 Environmental Applications of Pyrolysis ........................................133 T.O. Munson Chapter 8 Examination of Forensic Evidence ..................................................175 John M. Challinor Chapter 9 Characterization of Microorganisms by Pyrolysis-GC, Pyrolysis-GC/MS, and Pyrolysis-MS ..............................................201 Stephen L. Morgan, Bruce E. Watt, and Randolph C. Galipo DK3999_book.fm Page xii Tuesday, October 24, 2006 7:17 AM Chapter 10 Analytical Pyrolysis of Polar Macromolecules ...............................233 Charles Zawodny and Karen Jansson Chapter 11 Characterization of Condensation Polymers by Pyrolysis-GC in the Presence of Organic Alkali ....................................................249 Hajime Ohtani and Shin Tsuge Chapter 12 Index of Sample Pyrograms ............................................................271 Thomas P. Wampler Index......................................................................................................................285 DK3999_book.fm Page 1 Tuesday, October 24, 2006 7:17 AM 1 Analytical Pyrolysis: An Overview Thomas P. Wampler CONTENTS 1.1 1.2 Introduction ......................................................................................................1 Degradation Mechanisms.................................................................................2 1.2.1 Random Scission..................................................................................2 1.2.2 Side Group Scission.............................................................................5 1.2.3 Monomer Reversion.............................................................................6 1.2.4 Relative Bond Strengths ......................................................................6 1.2.4.1 Polyolefins.............................................................................7 1.2.4.2 Vinyl Polymers .....................................................................8 1.2.4.3 Acrylates and Methacrylates ................................................8 1.3 Examples and Applications..............................................................................9 1.3.1 Forensic Materials................................................................................9 1.3.2 Fibers and Textiles .............................................................................11 1.3.3 Paper, Ink, and Photocopies...............................................................13 1.3.4 Art Materials and Museum Pieces ....................................................16 1.3.5 Synthetic Polymers ............................................................................18 1.3.6 Natural Materials and Biologicals .....................................................19 1.3.7 Paints and Coatings............................................................................22 1.3.8 Trace-Level Analyses .........................................................................22 References................................................................................................................24 1.1 INTRODUCTION Pyrolysis, simply put, is the breaking apart of chemical bonds by the use of thermal energy only. Analytical pyrolysis is the technique of studying molecules either by observing their behavior during pyrolysis or by studying the resulting molecular fragments. The analysis of these processes and fragments tells us much about the nature and identity of the original larger molecule. The production of a variety of smaller molecules from some larger original molecule has fostered the use of pyrolysis as a sample preparation technique, extending the applicability of instrumentation designed for the analysis of gaseous species to solids, especially polymeric materials. As a result, gas chromatography, mass spectrometry, and Fourier-transform infrared 1 DK3999_book.fm Page 2 Tuesday, October 24, 2006 7:17 AM 2 Applied Pyrolysis Handbook, Second Edition (FT-IR) spectrometry may be used routinely for the analysis of samples such as synthetic polymers, biopolymers, composites, and complex industrial materials. The fragmentation that occurs during pyrolysis is analogous to the processes that occur during the production of a mass spectrum. Energy is put into the system, and as a result, the molecule breaks apart into stable fragments. If the energy parameters (temperature, heating rate, and time) are controlled in a reproducible way, the fragmentation is characteristic of the original molecule, based on the relative strengths of the bonds between its atoms. The same distribution of smaller molecules will be produced each time an identical sample is heated in the same manner, and the resulting fragments carry with them much information concerning the arrangement of the original macromolecule. The application of pyrolysis techniques to the study of complex molecular systems covers a wide and diversified field. Several books have been published that present theoretical as well as practical aspects of the field, including a good introductory text by Irwin1 and a compilation of gas chromatographic applications by Liebman and Levy.2 A 1989 bibliography3 lists approximately 500 papers in areas as diverse as food and environmental and geochemical analysis, an excellent review by Blazsó4 lists over 150 papers just in the analysis of polymers, and the application to microorganisms has been examined by Morgan et al.5 This chapter will include only a few representational examples of the kinds of applications being pursued, with references for further reading. Specific areas of analysis are detailed in subsequent chapters. 1.2 DEGRADATION MECHANISMS The degradation of a molecule that occurs during pyrolysis is caused by the dissociation of a chemical bond and the production of free radicals. The general processes employed to explain the behavior of these molecules are based on free radical degradation mechanisms. The way in which a molecule fragments during pyrolysis and the identity of the fragments produced depend on the types of chemical bonds involved and the stability of the resulting smaller molecules. If the subject molecule is based on a carbon chain backbone, such as that found in many synthetic polymers, it may be expected that the chain will break apart in a fairly random fashion to produce smaller molecules chemically similar to the parent molecule. Some of the larger fragments produced will preserve intact structural information snipped out of the polymer chain, and the kinds and relative abundances of these specific smaller molecules give direct evidence of macromolecular structure. The traditional degradation mechanisms generally applied to explain the pyrolytic behavior of macromolecules will now be reviewed, followed by some general comments on degradation via free radicals. 1.2.1 RANDOM SCISSION Breaking apart a long-chain molecule such as the carbon backbone of a synthetic polymer into a distribution of smaller molecules is referred to as random scission. If all of the C—C bonds are of about the same strength, there is no reason for one to break more than another, and consequently, the polymer fragments to produce a DK3999_book.fm Page 3 Tuesday, October 24, 2006 7:17 AM Analytical Pyrolysis: An Overview 3 wide array of smaller molecules. The polyolefins are good examples of materials that behave in this manner. When poly(ethylene) (shown as structure I, with hydrogen atoms left off for simplicity) is heated sufficiently to cause pyrolysis, it breaks apart into hydrocarbons, which may contain any number of carbons, including methane, ethane, propane, etc. I II —C—C—C—C—C—C— —C—C— C • • C—C— C— Chain scission produces hydrocarbons with terminal free radicals (structure II), which may be stabilized in several ways. If the free radical abstracts a hydrogen atom from a neighboring molecule, it becomes a saturated end and creates another free radical in the neighboring molecule (structure III), which may stabilize in a number of ways. The most likely of these is beta scission, which accounts for most of the polymer backbone degradation by producing an unsaturated end and a new terminal free radical. III • —C—C—C—C—C—C— Beta scission IV —C—C—C = CH2 + •C—C— This process continues, producing hydrocarbon molecules that are saturated and have one terminal double bond or a double bond at each end. When analyzed by gas chromatography, the resulting pyrolysate looks like the bottom chromatogram in Figure 1.1. Each triplet of peaks represents the diene, alkene, and alkane containing a specific number of carbons and eluting in that order. The next set of three peaks contain one more carbon, etc. It is typical to see all chain lengths from methane to compounds containing 35 to 40 carbons, limited only by the upper temperature of the gas chromatography (GC) column. When poly(propylene) is pyrolyzed, it behaves in much the same manner, producing a series of hydrocarbons that have methyl branches indicative of the structure of the original polymer. The center pyrogram in Figure 1.1 shows poly(propylene), revealing again a recurring pattern of peaks, with each group now containing three more carbons than the preceding group. Likewise, when a polymer made from a four-carbon monomer such as 1-butene is pyrolyzed, it produces yet another pattern of peaks, with oligomers differing by four carbons, as seen in the top pyrogram in Figure 1.1. The relationships of specific compounds produced in the pyrolysate to the original polymer structure have been extensively studied by Tsuge et al.,6 for example, in the case of poly(propylenes). The effects of temperature and heating rate have also been studied.7 DK3999_book.fm Page 4 Tuesday, October 24, 2006 7:17 AM 4 Applied Pyrolysis Handbook, Second Edition 10 5.00 10.00 14 15.00 20.00 25.00 30.00 35.00 40.00 FIGURE 1.1 Pyrograms of poly(1-butene) (top), poly(propylene) (center), and poly(ethylene) (bottom). DK3999_book.fm Page 5 Tuesday, October 24, 2006 7:17 AM Analytical Pyrolysis: An Overview 5 Abundance 2.5e+07 2.4e+07 2.3e+07 2.2e+07 2.1e+07 2e+07 1.9e+07 1.8e+07 1.7e+07 1.6e+07 1.5e+07 1.4e+07 1.3e+07 1.2e+07 1.1e+07 1e+07 9000000 8000000 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0 Time--> 2 1 4 3 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 FIGURE 1.2 Pyrogram of poly(vinyl chloride) at 750°C for 15 seconds. Peaks: 1 = HCl, 2 = benzene, 3 = toluene, 4 = naphthalene. 1.2.2 SIDE GROUP SCISSION When poly(vinyl chloride) (PVC) is pyrolyzed, no such oligomeric pattern occurs. Instead of undergoing random scission to produce chlorinated hydrocarbons, PVC produces aromatics, especially benzene, toluene, and naphthalene, as shown in Figure 1.2. This is the result of a two-step degradation mechanism that begins with the elimination of HCl from the polymer chain (structure V), leaving the polyunsaturated backbone shown as structure VI. V Cl H Cl H Cl H | | | | | | —C — C — C — C — C — C— — HC1 VI —C = C — C = C — C = C— Upon further heating, this unsaturated backbone produces the characteristic aromatics seen in the pyrogram. This mechanism has been well characterized, and the occurrence of chlorinated aromatics is used as an indication of polymer defect structures, as in the work of Lattimer and Kroenke.8 DK3999_book.fm Page 6 Tuesday, October 24, 2006 7:17 AM 6 Applied Pyrolysis Handbook, Second Edition 1.2.3 MONOMER REVERSION A third pyrolysis behavior is evidenced by polymers such as poly(methyl methacrylate). Because of the structure of methacrylate polymers (structure VII), the favored degradation is essentially a reversion to the monomer. VII CH3 CH3 CH3 | H | H | -C — C — C — C — C • | H | H | CO2R CO2R CO2R Beta Scission CH3 CH3 | H | —C — C — C • + | H | CO2R CO2R CH3 | CH2 = C | CO2R Monomer Monomer production is for the most part unaffected by the R group, so that poly(methyl methacrylate) will revert to methyl methacrylate, poly(ethyl methacrylate) will produce ethyl methacrylate, etc. This proceeds in copolymers as well, with the production of both monomers in roughly the original polymerization ratio. Figure 1.3 shows a pyrogram of poly(butyl methacrylate), with the butyl methacrylate monomer peak by far the predominant product. A pyrogram of a copolymer of two or more methacrylate monomers would contain a peak for each of the monomers in the polymer. 1.2.4 RELATIVE BOND STRENGTHS The question of which degradation mechanism a particular polymer will be subjected to — random scission, side group scission, monomer reversion, or a combination of these — is simplified by considering the nature of thermal degradation as a free radical process. All of the degradation products shown, as well as minor constituents, and deviations to the simplified rules are consistent with the following general statements: Pyrolysis degradation mechanisms are free radical processes and are initiated by breaking the weakest bonds first. The composition of the pyrolysate will be based on the stability of the free radicals involved and on the stabilities of the product molecules. Free radical stability follows the usual order of 3° > 2° > 1° > CH3, and intramolecular rearrangements, which produce more stable free radicals, play an important role, particularly the shift of a hydrogen atom. DK3999_book.fm Page 7 Tuesday, October 24, 2006 7:17 AM Analytical Pyrolysis: An Overview 7 Abundance 1.6e+07 1.5e+07 1.4e+07 1.3e+07 1.2e+07 1.1e+07 1e+07 9000000 8000000 7000000 6000000 5000000 4000000 3000000 2000000 1000000 0 Time--> 5.00 10.00 15.00 20.00 25.00 30.00 35.00 FIGURE 1.3 Pyrogram of poly(butyl methacrylate), showing large monomer peak (750°C for 15 seconds). A quick review of the previous degradation examples will help show how each of the above categories is in reality just one aspect of the general rule of free radical processes. 1.2.4.1 Polyolefins Poly(ethylene) and the other polyolefins contain only C—C bonds and C—H bonds. Since an average C—C bond is about 83 kcal/mole and a C—H bond 94 kcal/mole, the initiation step involves breaking the backbone of the molecule, with subsequent stabilization of the free radical. In the case of poly(ethylene), the original free radicals formed are terminal or primary. Hydrogen abstraction from a neighboring molecule creates a C—H bond (stable product) and a new, secondary free radical, which may then undergo beta scission to form an unsaturated end. In addition, transfer of a hydrogen atom from the carbon 5 removed from the free radical (via a six-membered ring) transforms a primary free radical to a secondary, increasing the free radical stability. H / -----C5 | C4 \ 1C • | 2C / C3 H \ C | C / -----C • | C \ C