Development and characterization of thermochemical materials based on salt hydrates and salt alcoholates Von der Fakultät Nachhaltigkeit der Leuphana Universität Lüneburg zur Erlangung des Grades Doktorin der Naturwissenschaften (Dr. rer. nat.) genehmigte Dissertation von Dipl.-Ing. Kathrin Korhammer geboren am 04.03.1984 in Altötting November 2018 Eingereicht am: 29.11.2018 Mündliche Verteidigung (Disputation) am: 24.02.2020 Erstbetreuer und Erstgutachter: Prof. Dr.-Ing. Wolfgang K. L. Ruck Zweitgutachter: Prof. Dr. Oliver Opel Drittgutachter: Prof. Dr. Frédéric Kuznik Die einzelnen Beiträge des kumulativen Dissertationsvorhabens sind oder werden wie folgt veröffentlicht: I Fopah Lele A, Korhammer K, Wegscheider N, Rammelberg HU, Osterland T, Ruck W. Thermal conductivity measurement of salt hydrate as porous material using calorimetric (DSC) method. 8th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (ExHFT), Lisboa, Portugal: A. Faria - Edicao Electronica Lda.; 2013. II Druske M-M, Fopah-Lele A, Korhammer K, Rammelberg HU, Wegscheider N, Ruck W, et al. Developed materials for thermal energy storage: Synthesis and characterization. Energy Procedia 2014;61:96–9. III Korhammer K, Druske M-M, Fopah-Lele A, Rammelberg HU, Wegscheider N, Opel O, et al. Sorption and thermal characterization of composite materials based on chlorides for thermal energy storage. Applied Energy 2016;162:1462–72. IV Korhammer K, Apel C, Osterland T, Ruck WKL. Reaction of calcium chloride and mag- nesium chloride and their mixed salts with ethanol for thermal energy storage. Energy Procedia 2016;91:161–71. V Korhammer K, Mihály J, Bálint S, Trif L, Vass Á, Tompos A, et al. Reversible formation of alcohol solvates and their potential use for heat storage. Journal of Thermal Analysis and Calorimetry 2019;138:11–33. VI Korhammer K, Neumann K, Opel O, Ruck WKL. Micro-scale thermodynamic and kinetic analysis of a calcium chloride methanol system for process cooling. Energy Procedia 2017;105:4363–9. VII Korhammer K, Neumann K, Opel O, Ruck WKL. Thermodynamic and kinetic study of CaCl2-CH3OH adducts for solid sorption refrigeration by TGA/DSC. Applied Energy 2018;230:1255–78. VIII Korhammer K, Opel O, Ruck WKL. Energy storage and adsorption cooling efficiency of novel composite adsorbents. To be submitted to Thermochimica Acta. Contents Nomenclature iii Abstract v Zusammenfassung vii 1. Heat storage in hydrates and alcoholates1 1.1. General introduction..............................1 1.1.1. Background and motivation......................1 1.1.2. Classification and evolution of thermal energy storage technolgoies 2 1.1.3. Current state of knowledge of thermochemical energy storage..5 1.2. General approaches and main results.....................9 1.2.1. Selection and assessment of appropriate salt hydrates and salt alcoholates................................9 1.2.2. Design of two-component composite adsorbents.......... 11 1.2.3. Thermal energy storage characteristics of the composite adsorbents designed and their parent salts.................... 13 1.2.4. Transport and kinetic phenomena observed in the composite ad- sorbents designed and their parent salts............... 15 1.2.5. Prediction of discharge/charge cycling effects on the thermal sta- bility of the TCMs tested........................ 17 1.3. General discussion............................... 18 2. Paper overview 21 3. Paper I 25 4. Paper II 31 5. Paper III 37 6. Paper IV 49 7. Paper V 61 i Contents 8. Paper VI 85 9. Paper VII 93 10. Paper VIII 119 Appendices 154 A. Final energy consumption statistics 155 B. Selective literature review on composite materials 157 C. List of materials and devices used in this study 163 D. Supplementary data on paper II and paper III 167 E. Supplementary data on paper IV 171 Bibliography 198 Acknowledgements 199 Curriculum vitae 201 Declaration of authorship 207 ii Nomenclature Latin symbols symbol description unit D diameter m dpore pore diameter m p vapor pressure Pa 2 1 SBET specific surface area m g− Tb boiling point ∘C Tm melting point ∘C 3 1 Vpore pore volume m kg− w salt content wt% Greek symbols symbol description unit 1 1 λ thermal conductivity W m− K− 3 ρb bulk density kg m− 2 ρa area density g m− 3 ρs density kg m− Abbreviations ACF activated carbon foam BC biochar DSC differential scanning calorimetry ENG expanded natural graphite compacted ENGP expanded natural graphite powder EV expanded vermiculite EV2 expanded vermiculite PCM phase change material SG silica gel TCM thermochemical material TES thermal energy storage TGA thermogravimetric analysis TG-MS thermogravimetry-mass spectrometry XRD X-ray diffraction Z13X binderless zeolite 13X ZNC zeolite natural clinoptilolite iii Abstract The geographical situation of Germany considerably affects the final energy consumption of the country. Thermally intensive processes are the largest consumer of energy. In contrary, the level of energy consumed by air conditioning systems and utilized on process cooling is relatively low. Thermal energy storage systems have a high potential for a sustainable energy management, as they provide an efficient integration of thermal energy from renewables and heat recovery processes through spatial and temporal decoupling. Low temperature thermochemical energy stores based on gas-solid reactions represent appealing alternative options to sensible and latent storage technologies, in particular for heating and cooling purposes. They convert heat energy provided from renewable energy and waste heat sources into chemical energy and can effectively contribute to load balancing and CO2 mitigation. Reasonable material intrinsic energy storage density and cooling power are demanded. At present, several obstacles are associated with the implementation in full-scale reactors. Notably, the mass and heat transfer must be optimized. Limitations in the heat transport and diffusions resistances are mainly related to physical stability issues, adsorption/desorption hysteresis and volume expansion and can impact the reversibility of gas-solid reactions. The aim of this thesis was to examine the energy storage and cooling efficiency of CaCl2, MgCl2, and their physical salt mixtures as adsorbents paired with water, ethanol and methanol as adsorbates for utilization in a closed, low level energy store. Two- component composite adsorbents were engineered using a representative set of different host matrices (activated carbon, binderless zeolite NaX, expanded natural graphite, expanded vermiculite, natural clinoptiolite, and silica gel). The energetic characteristics and sorption behavior of the parent salts and modified thermochemical materials were analyzed employing TGA/DSC, TG-MS, Raman spectroscopy, and XRD. Successive discharging/charging cycles were conducted to determine the cycle stability of the storage materials. The overall performance was strongly dependent on the material combination. Increase in the partial pressure of the adsorbate accelerated the overall adsorbate uptake. From energetic perspectives the CaCl2-H2O system exhibited higher energy storage densities than the CaCl2 and MgCl2 alcoholates studied. The latter were prone to irreversible decomposition. Ethyl chloride formation was observed for MgCl2 at room and elevated temperatures. TG-MS measurements confirmed the evolution of alkyl v Abstract chloride from MgCl2 ethanolates and methanolates upon heating. However, CaCl2 and its ethanolates and methanolates proved reversible and cyclable in the temperature range between 25 ∘C and 500 ∘C. All composite adsorbents achieved intermediate energy storage densities between the salt and the matrix. The use of carbonaceous matrices had a heat and mass transfer promoting effect on the reaction system CaCl2-H2O. Expanded graphite affected only moderately the adsorption/desorption of methanol onto CaCl2. CaCl2 dispersed inside zeolite 13X showed excellent adsorption kinetics towards ethanol. However, main drawback of the molecular sieve used as supporting structure was the apparent high charging temperature. Despite variations in the reactivity over thermal cycling caused by structural deterioration, composite adsorbents based on CaCl2 have a good potential as thermochemical energy storage materials for heating and cooling applications. Further research is required so that the storage media tested can meet all necessary technical requirements. vi Zusammenfassung Die geografische Lage Deutschlands bestimmt wesentlich den Endenergieverbrauch des Landes. Wärmeintensive Prozesse stellen den größten Anteil am Energieverbrauch dar. Im Vergleich dazu ist der Energiebedarf von Klimaanlagen und Kälteanwendungen verhältnismäßig niedrig. Wärmespeicher haben ein großes Potential für eine nachhaltige Energiewirtschaft, indem sie eine effiziente Integration von thermischer Energie aus erneuerbaren Energien oder Wärmerückgewinnungsprozessen durch eine räumliche und zeitliche Trennung ermöglichen. Thermochemische Niedertemperaturspeicher, die auf Gas-Feststoff Reaktionen ba- sieren, sind eine attraktive Alternative zu sensiblen und latenten Speichertechnologien, insbesondere für Kühlungs- und Heizungszwecke. Sie wandeln Wärmenergie, welche von erneuerbaren Energien oder Abwärmequellen stammt, in chemische Energie um und können somit effektiv zum Lastenausgleich und zur Reduktion von CO2 beitragen. Anforderungen sind eine angemessene materialspezifische Energiespeicherdichte und Kühlleistung. Bei der Implementierung in Pilotanlagen bestehen derzeit noch erhebliche Hindernisse. Zu optimierende