THERMALLY METASTABLE FULLERENES IN FLAMES BY TAPESH KUMAR YADAV Subnutted to the Department of Cherical Engineering in partial fulfillment of the requirements for the degree of DOCTOR OF PHELOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May 1994 1994 Massachusetts Institute of Technology All rights reserved Signature of Author j;/ I,- -, I I - IV - , I-4)eMl --------t of Chemical- Engineering March 10, 1994 Certified by Jack B. Howard I---- Thesis Supervisor Accepted by !;dence RobertETohen "" Department Committee for Graduate Students JUN 6 994 Thermally Metastable Fullerenes in Flames by Tapesh Yadav Submitted to the Department of Chemical Engineering on March 10, 1994 in partial fulfillment of the requirements for the Degree of Philosophy in Chemical Engineering. ABSTRACT Fullerenes are closed caged molecules of pure carbon. These carbon molecules are produced in abundant quantities by certain sooting processes. In particular, fullerenes are observed in large quantities in the soot produced by low pressure (100 Torr), inert environment, vaporization of pure carbon and in the soot produced by low pressure 40 Torr) laminar combustion of premixed benzene/oxygen/inert vapors. Along with the observation of large quantities of fullerenes, many more observations can be made from the soot of the two processes. One particularly significant observation is the presence of many thermally metastable fullerenes in the soot produced by flames. This thesis focuses on an experimental and modeling study of one of the many thermally metastable fullerenes. Specifically, this thesis establishes the true identity of one of the thermally metastable ftillerene produced in flames; the thesis investigates where in the flame the thermally metastable fullerene forms; the thesis reports thermochernical. properties obtained from structural modeling of the thermally metastable fullerene; and finally, the thesis reports computational chemistry based modeling of the thermochernical kinetics of the formation of the thermally metastable fullerene. The study began by experimentally investigating low pressure, premixed, laminar, flat benzene/oxygen/ inert flames. Process conditions explored ranged from pressures of 20 Toff to 100 Torr, CIO ratios from 0.91 to 1.08, inerts such as helium, argon and nitrogen, inert dilutions from 0% to 50%, and input gas velocities from 29 cm/sec to 52 cni/sec 300 K). Flame conditions that produced large quantities of the thermally metastable fullerene were identified and used to produce sufficient quantities needed to analytically establish the identity of the thermally metastable ftillerene. The thermally metastable fullerene so produced was purified from other fullerenes bv developing and using a three step preparative chromatography. The identity of the thermally metastable fullerene was established with the help of analytical high performance liquid chromatography, UV-Visible spectroscopy, electron impact mass spectrometry, ion-spray mass spectrometry, fourier transformed infra-red spectroscopy, proton nuclear magnetic resonance spectroscopy, proton coupled and proton decoupled 13C nuclear magnetic resonance spectroscopy and chemical tests. The query: where in the flame does the thermally metastable fullerene form, was examined by performing a profile analysis of the flame process. The thermochernical properties of the thermally metastable fullerene was obtained by molecular mechanics modeling and semi-empirical quantum modeling. The thermochernical kinetics of the formation of the thermally metastable fullerene was predicted using transition state theory and by identifying and modeling the transition state for the chemical transformation using a semi-empirical quantum model. The results establish that the thermally metastable fullerene observed in the flame is C6OC5H6 a Diels- Alder adduct Of C60. The profile study suggests that the adduct is not formed in the flame, but is generated by post flame chemistry. The computational chemistry results qualitatively predict the experimental observations. The method followed bv the thesis is fairly universal in nature and can be used in the study of other metastable fullerenes in particular and chemical species in general. Thesis Supervisor: Dr. Jack B. Howard, Professor of Chemical Engineering 2 Acknowledgments Ithank: • Professor Jack B. Howard for his guidance, his critiques, his suggestions and the freedom he offered me during the course of this thesis. Working with him has been one of the most productive experiences in my life. • Dr. Arthur L Lafleur for his timely guidance and his insightful comments during the analytical work of this thesis. • Professor Janos M. Bedr and Professor Adel F. Sarofim for their comments and their encouragement during the course of this thesis. • Dr. Vincent Rotello for his 'assistance in NMR and mass spectrometry work and for general discussions. • Dr. Joseph Anacleto and Dr. Robert Boyd of National Research Council, Canada and Dr. Stephen McElvany and Dr. Mark Ross of Naval Research Laboratories, Washington D. C. for the assistance with the specialized mass spectrometry required during this thesis. • The MIT's UROP team for their assistance and for their excitement in fullerenes research. In particular, the following deserve special thanks: Lorin Theiss, Mika Nystr6m, Laura Giovane, Elaine Johnson, Anna Chwang, Diana Goldenson, Albert Dietz and Michael Chung. • The MIT's combustion team for the extensive discussions about fullerenes and future. Working with them has been a wonderful experience. In particular, Kathy Brownell and Dr. Joseph Marr deserve a special mention. • Professor Klavs Jensen and Professor Daniel Blankschtein for the productive discussions on chemical engineering fundamentals; particularly, during my work as a teaching assistant to them in Chemical Reactor Engineering 10.65) and Chemical Engineering Thermodynan'dcs 10.40) respectively. • The Division of Chemical Sciences, Office of Energy Research, U.S. Department of Energy for the financial support of this research under Grant DE-FG02-84ER13282. 3 Table of Contents 1. Introduction ............................................................................................... 8 Thesis Objectives .................................................................................. 12 2. Literature Review ..................................................................................... 13 2.0 Overview ............................................................................................. 13 2.1 Fullerene Production ............................................................................ 13 2. 1 I Carbon Vaporization Processes ................................................... 13 2.1.2 The Flame Process ...................................................................... 15 2.1.3 Contrasting Fullerene Processes .................................................. 19 2.1.4 The Thermally M etastable Fullerenes ........................................... 20 2.2 Fullerene Structures and -ComputationalChemistry ............................... 21 2.2.1 Fullerene structures ..................................................................... 23 2.2.2 Computational Chemistry ............................................................ 24 2.3 Fullerene Reactions and Kinetics M odeling ........................................... 26 3. Equipment and Experimental ...................................................................... 28 3.0 Overview ............................................................................................. 28 3.1 The Synthesis ....................................................................................... 28 3 11 The Fuel and Gas Feed System .................................................... 29 3.1.2 The Burner System ..................................................................... 3 3.1.3 The Sampling System .................................................................. 33 3.1.4 The Post Run Activities ............................................................... 36 3.2 The Analysis ........................................................................................ 37 3.2.1 High Performance Liquid Chromatography .................................. 37 3.2.2 Preparative Column Chromatography .......................................... 38 3.2.3 Ultraviolet-Visible Spectroscopy ................................................. 40 3.2.4 M ass Spectrometry ...................................................................... 41 3.2.5 Fourier Transformed Infra Red Spectroscopy .............................. 42 3.2.6 Nuclear M agnetic Resonance Spectroscopy ................................. 43 3.2.7 Chemical Tests ............................................................................ 46 3.3 The Computational Chemistry Software ............................................... 46 3.3.1 The M olecular M echanics M odels ............................................... 48 3.3.2 The Semi-empirical Quantum M odels .......................................... 49 4 3.3.3 Thermochemistry ........................................................................ 49 3.4 The Experimental Strategy ................................................................... 53 3.4.1 Optimizing the Flame .................................................................. 54 3.4.2 Optimizing the Purification M ethod ............................................. 55 4. Experimental Results and Discussion .........................................................