Optimizing adsorbents for heat storage applications [Elektronische Ressource] : estimation of thermodynamic limits and Monte Carlo simulations of water adsorption in nanopores = Optimierung von Adsorbentien für Wärmespeicheranwendungen / vorgelegt von Ferdinand Paul Schmidt

Ferdinand Paul Schmidt

Informations

• Publié par: albert-ludwigs-universitat_freiburg
• Publié le: 01 janvier 2004
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Optimizing Adsorbents for Heat Storage Applications:
Estimation of Thermodynamic Limits and Monte Carlo Simulations
of Water Adsorption in Nanopores
Optimierung von Adsorbentien fur¨ Warmespeicheranwendungen:¨ Abschatzung¨ der thermodynamischen
Grenzen und Monte Carlo Simulation der Wasseradsorption in Nanoporen
Inaugural Dissertation
zur
Erlangung des Doktorgrades
der
Fakultat¨ fur¨ Mathematik und Physik
der
Albert Ludwigs Universit at¨
Freiburg im Breisgau
vorgelegt von
Ferdinand Paul Schmidt
aus Verden / Aller
Juli 2004Dekan: Prof. Dr. R. Schneider
Leiter der Arbeit: Prof. Dr. J. Luther
Referent: Prof. Dr. J.
Korreferent: Prof. Dr. H. Haberland
Tag der Verkundigung¨
des Prufungser¨ gebnisses: 1. September 2004PUBLICATIONS iii
In the context of this thesis, the following articles have been published:
Peer reviewed Journal
Schmidt, F. P., J. Luther and E. D. Glandt: 2003.
Influence of Adsorbent Characteristics on the Performance of an Adsorption Heat Storage Cycle.
Industrial & Engineering Chemistry Research 42, 4910–4918
Conference contributions and other publications
Schmidt, F. P., S. K. Henninger , T. Nu´nez,˜ H. M. Henning and E. D. Glandt, 2004.
Adsorbent Optimization for Heat Storage: Estimation of Achievable Energy Densities from Analyti
cal Thermodynamic Model. Poster presentation at Fundamentals of Adsorption (FOA 8) conference,
Sedona, Arizona, May 23–28, 2004, paper # 372
Henninger, S. K., F. P. Schmidt, T. Nu´nez˜ and H. M. Henning, 2004.
Monte Carlo Investigation of the water adsorption behavior in MFI Type Zeolites for different Si/Al
ratios with regards to heat transformation applications. Poster presentation at Fundamentals of Ad
sorption (FOA 8) conference, Sedona, Arizona, May 23–28, 2004, paper # 363
Schmidt, F. P. and J. Luther, 2002.
Monte Carlo Simulation of Water Adsorption in Micropores
Freiburg Materials Research Center: Annual Report 2002, p. 67
Henning, H. M., F. P. Schmidt, S. Henninger and T. Nu´nez,˜ 2001.
Materials Research for Adsorption Heat Storage: Application of Molecular Computer Simulation.
Fraunhofer ISE: Achievements and Results – Annual Report 2001, p. 32Contents
Publications iii
1 Introduction 3
2 Thermodynamics of adsorption heat storage 9
2.1 Heat storage: State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Hot water storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.2 Phase Change Materials (PCMs) . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.3 Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.4 System concepts for adsorption heat storage . . . . . . . . . . . . . . . . . . . . . 13
2.2 General adsorption thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.1 Classification of adsorption isotherms . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Henry’s constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3 Adsorption heat storage cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4 The “Dubinin approach” to materials optimization . . . . . . . . . . . . . . . . . . . . . . 23
2.5 Statistical thermodynamics approach to adsorbent optimization . . . . . . . . . . . . . . . 26
2.5.1 Langmuir model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.2 Reference conditions for cycle modeling . . . . . . . . . . . . . . . . . . . . . . 31
2.5.3 Parametric study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.5.4 Modeling energetic heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.5.5 Lattice gas models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.5.6 Variation of temperature lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3 Experimental results and comparison with model predictions 53
3.1 Thermogravimetric measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.2 Henry’s constants of water on silica gels . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.3 Comparison with Langmuir and lattice gas models . . . . . . . . . . . . . . . . . . . . . 59
3.4 Volumetric energy densities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.5 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4 Monte Carlo Simulations: Background and models employed 71
4.1 Monte Carlo sampling techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.1.1 Random sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.1.2 Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.1.3 The Metropolis algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.1.4 The condition of detailed balance . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.1.5 Simulations in the grand canonical ensemble . . . . . . . . . . . . . . . . . . . . 78
4.1.6 Simulation of non spherical molecules . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 Molecular modeling of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.2.1 Partial charge models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.2.2 Ewald summation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.3 Tetrahedral square well (TSW) water model . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.4 How to increase Sampling Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862 CONTENTS
4.4.1 Configurational bias algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.4.2 Tests of particle exchange efficiency . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.5 Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
24.6 Force fields and zeolite modeling in Cerius /Sorption . . . . . . . . . . . . . . . . . . . . 91
4.6.1 Generation of zeolite host grids . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.6.2 Force fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5 Simulation results and comparison with experiment 97
25.1 Simulations of water in zeolites with Cerius . . . . . . . . . . . . . . . . . . . . . . . . 98
5.1.1 Water adsorption in zeolite NaX . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
5.1.2 Water in ZSM 5 . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.2 Properties of the TSW water model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5.2.1 Virial coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5.2.2 Radial distribution function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.3 From activated carbon to silica surface models . . . . . . . . . . . . . . . . . . . . . . . . 105
5.3.1 Activated carbon model used previously with TSW water . . . . . . . . . . . . . . 106
5.3.2 Previous results on adsorption properties of activated carbon model . . . . . . . . 107
5.3.3 Adaptation of slit pore model to silica gel surface structure . . . . . . . . . . . . . 109
5.3.4 Cristobalite model surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.3.5 Conclusions for modeling silica surfaces with respect to TSW water model . . . . 115
5.4 Slit pore model with amorphous silica surface . . . . . . . . . . . . . . . . . . . . . . . . 116
5.5 Adsorption properties of slit pore model . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.5.1 Reference pore and scheme of parametric study . . . . . . . . . . . . . . . . . . . 120
5.5.2 Variation of silanol surface density . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.5.3 Finite size effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
5.5.4 Variation of pore width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.6 Conclusions for heat storage and suggested model refinements . . . . . . . . . . . . . . . 130
6 Summary and Outlook 137
6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
6.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
A Adsorbents 147
A.1 Zeolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
A.1.1 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
A.1.2 Water adsorption properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
A.2 Silica Gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
A.2.1 Pore structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
A.2.2 Use of silica gels for adsorptive heat transformation . . . . . . . . . . . . . . . . . 150
A.2.3 SWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
A.3 Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
A.3.1 MCM type adsorbents . . . . . . . . . . . .