Oxidative processes for the direct conversion of coal under mild conditions Dissertation zur Erlangung des Grades eines Doktors der Naturwissenschaften Vorgelegt der Fakultät für Chemie und Biochemie der Ruhr-Universität Bochum Von Nadine Braun aus Duisburg Bochum Februar 2016 Die vorliegende Arbeit wurde in der Zeit von September 2011 bis Januar 2016 am Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr unter der Leitung von Herrn Dr. Roberto Rinaldi angefertigt. Referent: Prof. Dr. Martin Muhler Korreferent: Prof. Dr. Wolfgang Grünert Acknowledgements First of all, I would like to thank Dr. Roberto Rinaldi for giving me the opportunity to work on such a fascinating topic in his research group and the chance to develop myself on a professional and on a personal level. I wish to express my gratitude to Prof. Dr. Martin Muhler for agreeing to be the first referee. I appreciate his contribution of time, interest, valuable comments and his support during the submission of my thesis. I would also like to thank Prof. Dr. Wolfgang Grünert for agreeing to be the second referee. I wish to express my appreciation to Dr. Dirk Hollmann for his support with the EPR spectroscopy studies at the Leibniz-Institut für Katalyse e.V. in Rostock and also for the fruitful discussions during the project meetings. I am deeply thankful to Dr. Christophe Farès for the technical training at the NMR laboratories and his unconditional support and all the helpful discussions over the last two years. I would also like to thank: Dr. Bodo Zibrowius and Wolfgang Endler at the NMR department for their help with the solid- state NMR spectrometer and measurements. The SEM department, particularly Silvia Palm, for the nice aid to visualize the numerous coal samples. Udo Richter, for all his support, good scientific advices and the lab organization. André Pommerin for the introduction and advises on working with the TG analyzer. Marc-Philipp Ruby for his help with the TG-MS measurements. My present and past office mates and colleagues, Hebert, Jakob, JP, Gaetano, Michael, Zhengwen, Alex, Marco, Sarah, Tobi G., Carolina N., Tobi Z., Caro G., Mario, Kameh, Kiki, Niklas and everyone from AK Schüth and AK Rinaldi for the nice working atmosphere. Mis queridos, Jorge, Ilton and Heitor, for the inspiring discussions about chemistry and life in general, all the nice and funny lunchbreaks, our shared addiction to GoT and the sincere friendship. Annette Krappweis and Kirsten Kalischer for their support and engagement in administrative matters. I gratefully acknowledge the founding by the SusChemSys cluster and the basic founding of the MPG. Finally, I would like to thank my family and friends for all their love and encouragement. I deeply thank and dedicate this thesis to my mother for being a great source of motivation, guidance, for her patience and support during all these years. II Content 1 Introduction .............................................................................................................. 1 2 State of the art .......................................................................................................... 5 2.1 Coal ..................................................................................................................... 5 2.1.1 Coalification, coal rank and structure............................................................. 6 2.2 Coal liquefaction- State of the art ......................................................................... 9 2.2.1 Direct coal liquefaction processes ................................................................. 9 2.2.2 Indirect coal liquefaction processes ............................................................. 12 2.3 Oxidation of coal ................................................................................................ 22 2.4 Oxidations and industrial oxidants ...................................................................... 29 2.4.1 Industrial Oxidants ...................................................................................... 29 2.4.2 Mechanism proposed by several authors .................................................... 36 2.4.3 The utilization of Group 3 metals and hydrogen peroxide as oxidant ........... 39 3+ 3 Oxidative conversion of lignite mediated by [Al(H2O)6] /H2O2 ............................ 41 3.1 Introduction ........................................................................................................ 41 3.2 Lignite used for experiments .............................................................................. 41 3.3 Conversion of lignite at different temperatures ................................................... 48 3.3.1 Characterization of the product oil ............................................................... 49 3.3.2 Characterization of the obtained coal residues ............................................ 63 3.3.3 Characterization of the water-soluble products ............................................ 69 3.4 Monitoring the evolution of the conversion of lignite ........................................... 72 3.4.1 Characterization of the product oil ............................................................... 72 3.4.2 Analysis of lignite residues obtained from duration effect studies ................ 80 3.4.3 Characterization of the water-soluble products ............................................ 84 III 3.5 Conclusion ......................................................................................................... 87 4 Solvents and solvent effects on the oxidation of lignite mediated by 3+ [Al(H2O)6] /H2O2 ............................................................................................................. 88 4.1 Participation of reaction medium in the extent of coal oxidation .......................... 90 4.1.1 Ultimate analysis of the coal residue samples ............................................. 90 13 4.2 Coal oxidation experiments in methanol- C at 65 °C ......................................... 99 4.3 Hydrodeoxygenation (HDO) experiments of lignite residues obtained from reactions in methanol ................................................................................................. 104 4.4 Conclusion ....................................................................................................... 109 5 Effect of coal rank................................................................................................. 111 5.1 Analysis of obtained coal residue samples ....................................................... 111 5.2 Conclusions ..................................................................................................... 120 3+ 6 Activation of hydrogen peroxide by the [Al(H2O)6] /H2O2 system - Part I: ....... 121 3+ 6.1 EPR investigations into the [Al(H2O)6] system ................................................ 125 3+ 6.2 EPR studies of the [Al(H2O)6] /H2O2 system in organic solvents ...................... 129 6.2.1 2-Methyl-tetrahydrofuran ........................................................................... 129 6.2.2 Methanol ................................................................................................... 132 6.2.3 Comparison of 2-Methyl-tetrahydrofuran and methanol as solvents used for 3+ reactions with the [Al(H2O)6] /H2O2 system ............................................................ 134 3+ 6.3 EPR studies of the conversion of coal with Al(H2O)6] /H2O2 system in 2-Methyl- tetrahydrofuran ........................................................................................................... 135 6.3.1 Lignite ....................................................................................................... 135 6.3.2 Anthracite .................................................................................................. 138 3+ 6.3.3 EPR studies of the reaction with coal and the [Al(H2O)6) /H2O2 system in methanol ................................................................................................................. 140 3+ 6.4 EPR studies of the [Al(H2O)6] /H2O2 system formed from aluminum perchlorate ................................................................................................................. 142 IV 6.4.1 EPR investigations into the activation of hydrogen peroxide by the 3+ [Al(H2O)6] /H2O2 system formed from aluminum perchlorate ................................. 142 3+ 6.4.2 The [Al(H2O)6] /H2O2 system formed from aluminum perchlorate in the presence of tetrahydrofuran as the solvent ............................................................. 145 3+ 6.4.3 The [Al(H2O)6] /H2O2 system formed from aluminum perchlorate in the presence of coal and tetrahydrofuran as the solvent ............................................... 147 6.5 Activation of hydrogen peroxide by other nitrates ............................................. 150 6.5.1 Decomposition of hydrogen peroxide mediated by different nitrates .......... 150 6.6 EPR characterization of hydrogen peroxide activation with other metals .......... 152 6.6.1 Comparison of In(NO3)3 and Ga(NO3)3 with Al(NO3)3 as an activator for H2O2 …………………………………………………………………………………….152 6.6.2 Comparison of In(ClO4)3 and Ga(ClO4)3 with Al(ClO4)3 as an activator for H2O2 …………………………………………………………………………………….157 6.7 Conclusions EPR studies ................................................................................. 166 7 Activation of hydrogen peroxide- Part II: ...........................................................