Experimental Investigation on Gas Separation Using Porous Membranes vorgelegt von Master-Ing. Weiqi ZHANG von der Fakultät III - Prozesswissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktorin der Ingenieurwissenschaften – Dr.-Ing. – genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr.-Ing. Felix Ziegler Berichter: Prof. Dr. Frank Behrendt Berichter: Prof. Dr.-Ing. Bernd Hillemeier Tag der wissenschaftlichen Aussprache: 03. December 2010 Berlin 2011 D 83 Ich erkläre hiermit, dass ich die vorliegende Arbeit selbständig verfasst und keine an- deren als die angegebenen Quellen und Hilfsmittel verwendet habe. Berlin, den 03. December 2010 Acknowledgment I am deeply thankful to colleagues and advisors, who helped me complete for this project, firstly to Univ.-Prof. Dr. Frank Behrendt, who gave me the opportunity to do this Ph.D., made this work possible; Prof. Dr.-Ing. Bernd Hillemeier and Prof. Dr.-Ing. Felix Ziegler, who took over the supervision of my thesis. Maria Gaggl, who helped me with the practicalities of living in Germany, and even shared with me her flat for two weeks when I first started my Ph.D.. Gregor Gluth, for making all the membranes used in this project, but also for his patience. Dr.- Ing. York Neubauer and Dr.-Ing. Nico Zobel, for their competence; if you encounter any problems, either theoretical or experimental status, you can turn to them and certainly get a reasonable answer. Horst Lochner and Uwe Röhr, who made membrane cell and many other small parts patiently for me, and helped me with all sorts of technicalities. Susanne Hoffmann who gave me lots of suggestions over operations with gas chromatograph (GC ). Fang He, Gregor Drenkelfort, Birgit Packeiser, Renhui sun, etc., my special thanks also go to for their patience and advice. I would also like to acknowledge the on going financial support provided by Federal Ministry of Food, Agriculture and Consumer Protection (BMELV), Agency for Renew- able Resources (FNR), and the scholarship from Women’s central office to finish my thesis. Last but not least, I would like to thank all the helpful persons that I have forgotten to mention by name. This thesis could not have been written without the support of my parents, my husband Jingqun Song and my friends. Contents Abstract XIII Nomenclature XV 1 Introduction 1 2 State of the Art 5 2.1 An introduction to gas separation using membranes . .5 2.2 Inorganic membranes . .6 2.2.1 Dense inorganic membranes . .7 2.2.2 Porous inorganic membranes . .8 2.3 Porous cement membranes . .9 2.4 Separation and process design . 10 2.4.1 Possible flow patterns . 10 2.4.2 Number of stages . 11 2.4.3 Known influence of operating parameters . 14 3 Experimental Setup 17 3.1 Flow chart . 17 3.2 Experimental setup . 19 3.3 Operating parameters and procedure . 26 Contents VII 4 Summary of Equations 31 4.1 Basic assumptions . 31 4.2 Gas equations . 32 4.2.1 The fundamental equations for ideal gases . 32 4.2.2 Balances . 32 4.3 Equations for transport mechanisms through porous membranes . 33 4.4 Equations for the experimental setup . 35 4.4.1 LabVIEW . 35 4.4.2 Soap film flowmeter . 36 4.4.3 Mass flow controller . 36 4.4.4 Gas chromatograph . 36 4.5 Efficiency of gas separation through membrane . 37 5 Experimental Results and Discussion 41 5.1 Controlling equipment and corresponding special procedures, calibration 41 5.1.1 Bubble flow-meter . 41 5.1.2 Data correction of mass flow controller . 42 5.1.3 Calibration of gas chromatograph (GC )............. 43 5.2 Experiments . 55 5.2.1 First set of experiments with Gaggl’s membranes . 55 5.2.2 Second set of experiments with modified cell . 62 5.2.3 Third set of experiments with tubular membrane and cell . 83 6 Summary and Outlook 91 6.1 Summary of results . 91 6.2 Observations . 92 6.3 Future work . 93 Bibliography 97 Mitteilungen 107 List of Figures 2.1 Schematic representation of membrane separation . .6 2.2 Transport mechanisms in porous membranes [1] . .9 2.3 Schematics of possible flow patterns [2,3] . 10 2.4 Flow pattern in presence of sweep gas [2] . 11 2.5 Schemes of commercial two-stage separation [2,3] . 12 2.6 Schemes of commercial three-stage separation [2,3] . 13 2.7 Novel single-stage separation with recycling [2,3] . 13 3.1 Process schematic of gas separation . 17 3.2 Process schematic of reference measurements . 18 3.3 Gas chromatographic system . 22 3.4 Chromatogram of five-component gas . 23 3.5 LabVIEW controlling system . 25 4.1 Chromatograms of two-component gas and pure standard-gases . 37 5.1 Flow rate of two-component gas at 2.4 bar . 43 5.2 Flow rate of 2 % to 4 % . 44 5.3 Flow rate of two-component gas at different pressures . 45 5.4 GC measurements . 46 5.5 Base line of chromatogram . 46 5.6 Area of H2 in two-component gas measurements with different run times 47 5.7 Area of pure H2 measurements at different temperatures . 48 X List of Figures 5.8 GC measurements of different reference-flow rate . 50 5.9 N2 amount and flow rates in automatic injection . 51 5.10 Flow rate calculation of standard-gases . 52 5.11 Pure H2 peak area for calibration of 2M measurement . 53 5.12 Calibration curve for H2 of 2M measurement . 54 5.13 Schematic of the first idea . 55 5.14 Schematic of the first membrane cell . 56 5.15 The first membrane cell and holders . 56 5.16 Pore size distribution of the first membranes . 57 5.17 Gaskets for the first membrane cell . 58 5.18 Flow rate influence at different temperatures . 58 5.19 Gas separation with different volume flows . 59 5.20 Gas separation with different feed gases . 60 5.21 Experimental and theoretic selectivity . 61 5.22 Problem of the first membrane cell . 62 5.23 First version of the secondary membrane cell . 63 5.24 Final design of the modified membrane cell . 63 5.25 Axial section view of the modified membrane cell . 64 5.26 Pore distribution of PZ-2 . 67 5.27 Graphite gaskets around membrane . 68 5.28 Performance of membrane cells in <H2;N2> ............... 69 5.29 Influence of temperature in <H2;N2>................... 70 5.30 Influence of temperature in <2M;N2> .................. 70 5.31 Influence of equivalent water to cement ratio in <2M;N2> . 71 5.32 Influence of pore size in <2M;N2> .................... 72 5.33 Effect of different sample thickness on diffusion in <2M;N2> . 73 5.34 Membranes after heating . 74 5.35 Comparison of compositions in <5M;N2> ................ 75 List of Figures XI 5.36 Permeabilities of H2 using different feed gases . 76 5.37 Influence of pressure difference in <2M;N2>............... 76 5.38 Influence of sweeping gas in <H2;N2>................... 77 5.39 Measurements of different sweeping gases in <2M;N2> and <2M;CO> 78 5.40 Influence of adhesives . 79 5.41 SEM images of the PZ-2+MS ....................... 80 5.42 Knudsen number of H2 and CO2 ...................... 81 5.43 Diffusion coefficients of H2 ......................... 82 5.44 Schematic of transport in tubular membrane cell [1] . 83 5.45 Tubular membrane cell . 84 5.46 Heating system for tubular membrane . 84 5.47 Design of tubular membrane cells . 85 5.48 Tubular membrane and gaskets . 86 5.49 Components in permeate-gas in <2M;N2>................ 87 5.50 Separation factors of H2 to CO2 ...................... 87 5.51 Water from tubular membrane . 88 ◦ 5.52 Chromatogram in <5M;N2> at 200 C .................. 88 5.53 Large cracks after heating . 89 6.1 Process schematic of using CO2 as sweeping gas . 95 6.2 Process schematic of using steam as sweeping gas . 95 List of Tables 2.1 Applications of gas separation using membranes . .6 2.2 Classification of inorganic materials on pore size [4] . .7 2.3 Separation factor of some typical gas mixtures . 15 3.1 Operating conditions of Gas Chromatograph . 23 5.1 Flow rates of two-component gas controlled by MFC . 42 5.2 Gases compositions using N2 as reference . 48 5.3 Gases compositions using He as reference . 49 5.4 Volume flows of permeate-gases . 50 5.5 Corresponding points of standard-gases . 51 5.6 Characteristic peak area of H2 in permeate-gas and standard gases . 52 5.7 H2 concentration in permeate-gases . 53 5.8 Physical and geometrical data of the first test membranes . 56 5.9 Cement membranes . 65 5.10 Code name of cement membrane . 66 5.11 Porosity of cement membrane . 66 5.12 Permeation fluxes using PZ-2+MS in <2M;N2>............. 73 5.13 Separation factors using HOZ+MS in <5M;N2>............. 75 5.14 Separation factors using 5 mm membranes in <2M;N2> . 80 5.15 Data using PZ-2+MS (5 mm, (w/c)eq 0.25) in <2M;N2> . 81 5.16 Permeation ability using PZ-2+MS (5 mm, (w/c)eq 0.25) in <2M;N2> 82 5.17 Permeation ability using tubular-PZ-2+MS (5 mm, 0.25) in <2M;N2> 89 5.18 Permeation ability using tubular-PZ-2+MS (5 mm, 0.25) in <5M;N2> 90 Abstract Membranes have been long utilized in industry for separation of gas mixtures [5]. Thanks to their chemical, physical, and thermodynamic stability, as well as for their high durability at elevated temperatures and high permeation flux, ceramic membranes have become especially popular in the field. Cement is looked at as a valid alternative for the future, as in addition to being stable, it would bring the advantage of lower costs and longer lifespan.