UNIVERSITY OF CALIFORNIA, SAN DIEGO Study of the Thermochemistry for Oxygen Production for a Solar Sulfur-Ammonia Water-Splitting Process A thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Chemical Engineering by Mimi Kai Wai Wang Committee in charge: Professor Jan Talbot, Chair Professor Richard Herz Professor Joe Goddard 2012 The Thesis of Mimi Kai Wai Wang is approved and it is acceptable in quality and form for publication on microfilm and electronically: ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Chair University of California, San Diego 2012 ! iii Dedicated to my friends and family ! iv TABLE OF CONTENTS Signature Page ................................................................................................................... iii Dedication .......................................................................................................................... iv Table of Contents .................................................................................................................v List of Figures .................................................................................................................... vi List of Tables ..................................................................................................................... ix Acknowledgements ..............................................................................................................x Abstract .............................................................................................................................. xi Introduction ..........................................................................................................................1 References ................................................................................................................4 2. Background ......................................................................................................................6 2.1 Thermochemical Cycles .....................................................................................7 2.2 Sulfur-Ammonia Cycle ......................................................................................9 2.3 Molten Sulfate Salt Chemistry and Properties .................................................13 References ..............................................................................................................18 3. Experimental Procedures ...............................................................................................21 3.1 Materials ..........................................................................................................21 3.2 Melting Tests ...................................................................................................22 3.3 Thermogravimetric and Differential Thermal Analysis ..................................23 3.4 Small Reactor Experiments ..............................................................................24 3.5 Viscosity Measurements ..................................................................................27 4. Results and Discussion ..................................................................................................31 4.1 Melting Tests ...................................................................................................31 4.2 Thermogravimetric and Differential Thermal Analysis ..................................33 4.3 Small Reactor Experiments ..............................................................................49 4.4 Viscosity Measurements ..................................................................................60 References ..............................................................................................................66 5. Conclusions ....................................................................................................................68 ! v LIST OF FIGURES Figure 2.1: Schematic of a Sulfur-Ammonia Thermochemical Cycle ..............................6 Figure 2.2: Schematic of the Oxygen Sub-Cycle ............................................................13 Figure 2.3: Experimental density data for molten K2SO4, Na2SO4, K2S2O7, and Na2S2O7 as a function of temperature ..........................................................................15 Figure 2.4: Experimental viscosity data for molten Na2SO4 as a function of temperature . .......................................................................................................................16 Figure 2.5: Calculated phase diagrams with experimental data of Na2SO4 + Na2S2O7 (top left), K2SO4 + K2S2O7 (top right), Na2SO4 + K2SO4 (bottom left), and Na2S2O7 + K2S2O7 (bottom right) systems at 0.1 MPa total pressure taken from Lindberg et al. ......................................................................................17 Figure 3.1: Set-up for melting tests with the quartz crucible inside atop a piece of ceramic (left) and photograph of K2S2O7 at room temperature (right) .........23 Figure 3.2: Schematic of custom-made quartz tube: A) entrance, B) chamber, C) thermocouple well .........................................................................................26 Figure 3.3: Custom quartz tube in the tube furnace with a thermocouple in the thermocouple well .........................................................................................27 Figure 3.4: Tube furnace, UGA200, and computer set-up for the small reactor experiments ...................................................................................................27 Figure 3.5: Schematic of a 110 mm long stainless steel tube 1.7 mm in diameter (tube A) and a 43 mm long stainless steel tube 3.2 mm in diameter (tube B) inserted through a 20 mm long rubber stopper .............................................28 Figure 3.6: Set-up for viscosity measurements with the tube furnace on its side and the quartz tube filled with salt inside ..................................................................30 Figure 4.1: TG/DTA data for (NH4)2SO4 in a platinum pan heated at 20°C/min ...........41 Figure 4.2: TG/DTA data for (NH4)2SO4 in an alumina pan heated at 20°C/min ..........42 Figure 4.3: RGA data of mass number A) 16, B) 17, and C) 18 for (NH4)2SO4 in a platinum pan heated at 20°C/min ..................................................................43 Figure 4.4: RGA data of mass number A) 40, B) 48, and C) 64 for (NH4)2SO4 in a platinum pan heated at 20°C/min ..................................................................44 ! vi Figure 4.5: RGA data of mass number A) 48, B) 64, and C) 80 for CuSO4 in a platinum pan heated at 20°C/min .................................................................................45 Figure 4.6: Normalized RGA data for (NH4)2SO4 in a platinum pan heated at 20°C/min . .......................................................................................................................46 Figure 4.7: TG/DTA data for (NH4)2SO4 in a platinum pan and a platinum lid heated at 5°C/min, held for 5 minutes at 1000°C, and cooled back to room temperature at 5°C/min .................................................................................47 Figure 4.8: TG/DTA data for (NH4)2SO4 + K2SO4 in a platinum pan and a platinum lid heated at 5°C/min ..........................................................................................48 Figure 4.9: TG/DTA data for (NH4)2SO4 + 2 K2SO4 + 8 K2S2O7 in a platinum pan and a platinum lid heated at 5°C/min, held at 1000°C for 5 minutes, and cooled back to room temperature at 5°C/min ...........................................................49 Figure 4.10: RGA data of mass number A) 16, B) 17, and C) 18 for (NH4)2SO4 + K2SO4 + 4 K2S2O7 + Na2SO4 + 4 Na2S2O7 heated in a small quartz reactor at 1°C/min from room temperature to ~700°C .................................................56 Figure 4.11: RGA data of mass number A) 48 and B) 64 for (NH4)2SO4 + K2SO4 + 4 K2S2O7 + Na2SO4 + 4 Na2S2O7 heated in a small quartz reactor at 1°C/min from room temperature to ~700°C ................................................................56 Figure 4.12: Normalized RGA data for (NH4)2SO4 + K2SO4 + 4 K2S2O7 + Na2SO4 + 4 Na2S2O7 heated in a small quartz reactor at 1°C/min from room temperature to ~700°C ......................................................................................................57 Figure 4.13: RGA data of mass number A) 16, B) 17, and C) 18 for (NH4)2SO4 + K2SO4 + 4 K2S2O7 + Na2SO4 + 4 Na2S2O7 heated in a small quartz reactor at 20°C/min from room temperature to 375°C and held for 25 minutes then heated at 20°C/min to 400°C and held for 25 minutes and heated to the following temperatures at 20°C/min and held for 60 minutes: 1) 425°C, 2) 450°C, 3) 475°C, 4) 500°C, 5) 525°C, 6) 550°C, and 7) 575°C ..................58 Figure 4.14: RGA data of mass number A) 48 and B) 64 for (NH4)2SO4 + K2SO4 + 4 K2S2O7 + Na2SO4 + 4 Na2S2O7 heated in a small quartz reactor at 20°C/min from room temperature to 375°C and held for 25 minutes then heated at ! vii 20°C/min to 400°C and held for 25 minutes and heated to the following temperatures at 20°C/min and held for 60 minutes: 1) 425°C, 2) 450°C, 3) 475°C, 4) 500°C, 5) 525°C, 6) 550°C, and 7) 575°C ...................................59 Figure 4.15: Normalized