MULTILAYERED PEI-BASED FILMS FOR CO2 ADSORPTION AND DIFFUSION A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Jing Liu May, 2013 MULTILAYERED PEI-BASED FILMS FOR CO2 ADSORPTION AND DIFFUSION Jing Liu Thesis Approved: Accepted: Advisor Dean of the College Dr. Steven S.C. Chuang Dr. Stephen Z.D. Cheng Co-Advisor or Faculty Reader Dean of the Graduate School Dr. Li Jia Dr. George R. Newkome Department Chair Date Dr. Coleen Pugh ii ABSTRACT Polyethyleneimine (PEI), composed of the amine group on the repeating unit, o o can bind CO2 at 50–75 C and dissociate it at 100–130 C. This unique characteristic allows PEI to serve as an active molecule in solid sorbents for the thermal swing and membrane processes for CO2 separation. The nature and concentration of CO2 adsorption on amine sites of PEI can be observed and investigated by Fourier Transform Infrared Spectroscopy (FTIR) 15. In-situ FTIR was used to evaluate and determine i) the CO2 adsorption on PEI layers containing 1, 8, 21 and 35wt% of water and ii) the rate of diffusion of CO2 through multiple layers of PEI partially crosslinked with glutaraldehyde (GA). Each sequential PEI layer was prepared by increasing the degree of cross-linking with GA, generating a gradient amine concentration throughout the multiple layers thickness. Initial results show an increase of CO2 adsorption at a lower concentration of water. The multiple layered amine gradients enhanced the rate of CO2 diffusion compared to a single layer of crosslinked PEI of similar thickness. The fundamental information obtained from this study will be used to fabricate multilayer PEI-based films having rapid diffusion of CO2 and enhanced CO2 capture capacity at moderate temperatures. iii ACKNOWLEDGEMENTS I would like to express my deepest appreciation to my research advisor, Professor Steven S.C. Chuang, who continually and convincingly gives me guidance, supervision and help throughout my master studies. I would like to give my high gratitude to my friends and colleagues, Mr. Mathew Isenberg, Miss. Shirin Norooz Oliaee, Miss. Uma Tumuluri, Mr. Ernesto Silva Mojica, Mr. Chris Wilfong and Mr. Nader Hedayat. I acquired many important skills including experimental skill, data analysis capacity and writing ability from them. And thank all of them for encouraging me when I felt confused or un-confident during research process. iv TABLE OF CONTENTS Page LIST OF FIGURES ............................................................................................... viii LIST OF TABLES ................................................................................................... x CHAPTER I. INTRODUCTION .................................................................................................. 1 II. LITERATURE REVIEW ........................................................................................ 3 2.1 CO2 Removal ................................................................................................. 3 2.2 CO2 membranes ............................................................................................. 4 2.2.1 Membrane Materials for CO2 Removal ............................................... 4 2.2.2 Membrane Permeation ......................................................................... 6 2.2.3 Membrane Structure............................................................................. 9 2.2.4 PEI-based membranes........................................................................ 11 2.3 Layer-by-layer assembly technology ........................................................... 14 III. EXPERIMENTAL SECTIONS ............................................................................ 18 3.1 Materials ...................................................................................................... 18 3.2 FTIR study ................................................................................................... 19 3.3 Water effects on high MW PEI films ........................................................... 20 3.3.1 H2O adsorption to PEI films .............................................................. 20 3.3.2 H2O desorption from PEI films.......................................................... 21 v 3.3.3 CO2 adsorption on PEI/H2O films ..................................................... 22 3.4 Water effects on Low MW PEI .................................................................... 22 3.5 Crosslinked PEI/GA films............................................................................ 23 3.5.1 Single layer of crosslinked PEI/GA film ........................................... 23 3.5.2 CO2 adsorption on single layer of crosslinked PEI/GA film ............. 23 3.5.3 Multilayer of crosslinked PEI/GA film .............................................. 24 3.5.4 CO2 adsorption on multilayer of crosslinked PEI/GA film ............... 25 IV. RESULTS AND DISCUSSION............................................................................ 26 4.1 Water effects on high MW PEI .................................................................... 26 4.1.1 Water adsorption to PEI film ............................................................. 26 4.1.2 Water desorption from PEI film ......................................................... 27 4.1.3 CO2 adsorption on PEI/H2O film ....................................................... 30 4.2 Water effects on low MW PEI ..................................................................... 32 4.3 Crosslinked PEI ........................................................................................... 35 4.3.1 Single layer of PEI/GA film............................................................... 35 4.3.2 CO2 adsorption on Single layer of PEI/GA film ................................ 39 4.3.3 Multilayer of crosslinked PEI/GA film .............................................. 41 4.3.4 CO2 adsorption on multilayer of crosslinked PEI/GA film ............... 44 4.3.5 CO2 diffusion through PEI-based films ............................................. 47 V. CONCLUSIONS................................................................................................... 50 REFERENCES ............................................................................................................ 51 APPENDICES……………………………………………………………………….55 vi APPENDIX A. ESTIMATION OF WATER CONTENT DURING WATER DESORPTION...................................................................................................... 56 APPENDIX B. WATER RESISTIVITY OF PEI/GA FILMS ........................... 59 APPENDIX C. LOW Mw PEI THIN FILM .................................................... 63 vii LIST OF FIGURES Figure Page 1 The multilayered PEI/GA film with amine concentration gradient ......................... 2 2 SEM photographs of cross-section of the asymmetric polyimide membranes .. 10 3 The MFI zeolite structure . ................................................................................... 13 4 The fabrication process of the PVPy/PVPh LBL membrane ............................... 16 5 The process of taking IR scan for PEI/GA films ................................................... 20 6 (a) IR Single beam spectra and (b) absorbance spectra of PEI film during the first minute water bubbling in an enclosed system. .......................................................... 27 7 (a) IR Single beam spectra and (b) absorbance spectra of PEI film during water evaportation in an ambient environment...................................................................... 28 8 Absorbance of the PEI film during water evaporation from 30oC to 200oC in the ambient condition......................................................................................................... 29 9 Absorbance of PEI/H2O spectra with different water content. .............................. 30 10 Absorbance of PEI/H2O spectra at initial state and after 5min purge.................. 31 11 Absorbance of PEI/H2O spectra after 20min CO2 flowing. ................................. 32 12 Absorbance of PEI/H2O spectra at initial state .................................................... 33 13 Absorbance of PEI/H2O spectra after 20min CO2 flowing ................................ 34 14 PEI/GA solutions after being prepared (a) 5min, (b) 24h and (c) 48h................. 36 15 Absorbance of PEI/H2O spectra in an enclosed system....................................... 37 16 The intensity ratio of NH2/CH2 and C=N/CH2 versus molar ratio of C=O/CH2 . 39 viii 17 Absorbance of cross-linked PEI spectra with CO2 flowing at 75C ..................... 40 18 Absorbance of crosslinked PEI spectra with CO2 at different temperatures. .... 40 19 Photographs of PEI/GA films before and after washing...................................... 43 20 Absorbance of PEI/GA spectra (a) before and (b) after being washed (Ph=6).... 43 21 Absorbance of PEI/GA spectra before flowing CO2............................................ 44 22 Absorbance of PEI/GA spectra after flowing 15min CO2. ................................ 45 23 The intensity ratio of C=N/CH2 for PEI/GA films .............................................. 47 24 The intensity ratio of 1573/CH2 for PEI and PEI/GA films................................. 47 25 Peak intensity of absorbance spectra at 1573cm-1 ............................................... 48 26 Temperature change versus time in the FTIR and TGA measurements. ............. 55 27 Photographs