Performance Investigation of Membranes Suitable for Osmotic Membrane Pressure Actuators

109 Pages·2014·4.41 MB·English

by  Gaute Tolås Trondsen

Performance Investigation of Membranes
Suitable for Osmotic Membrane Pressure
Actuators
Gaute Tolås Trondsen
Chemical Engineering and Biotechnology
Submission date: July 2014
Supervisor: May-Britt Hägg, IKP
Co-supervisor: Qiang Yu, IKP
Norwegian University of Science and Technology
Department of Chemical Engineering

Abstract
Polybenzimidazole (PBI) membrane performance having hydrocarbons mixed with the feed
water was investigated. Forward osmosis (FO) and pressure retarded osmosis (PRO)
experiments were performed with different ratios of hydrocarbons. The membranes
performed well under these conditions. The results did not conclusively indicate that there is
a relationship between the hydrocarbon ratio and the water or salt permeability. It appeared
that the contact between the water and the membrane surface is an important factor
contributing to water permeation. The results indicated that exposure to hydrocarbons
possibly increases the membrane’s salt retention. It was also found that hydrocarbons
possibly cause swelling of the membrane. This was done by measuring thickness before and
after exposure under different circumstances. In experiments conducted in PRO mode
pressure was generated on the draw side when hydrocarbons were mixed together with
water in the feed. PRO experiments using pure water in the feed were performed at different
pressure differences. The results showed no linear relationship between water flux and
pressure difference. FO experiments using pure water in the feed were carried out to test the
effect of temperature on the trans-membrane water and salt flux. It was found that both water
and salt flux increase with temperature. The PBI membrane’s thermal stability was
investigated using thermogravimetric analysis. It was heated to temperatures just short of
600 °C with very little loss of mass. The membrane morphology was characterized by SEM,
and its hydrophilic properties demonstrated by attempted contact angle measurements.
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Sammendrag
Polybenzimidasol membraners ytelse ble undersøkt med hydrokarboner blandet med
fødevannet. Eksperimenter ble utført ved vanlig osmose (FO) og trykk retardert osmose
(PRO) med forskjellige forhold av hydrokarboner og vann. Membranene presterte godt under
disse forholdene. Resultatene indikerte at det kanskje ikke var noen sammenheng mellom
hydrokarbonforholdet og vann eller salt permeabiliteten. Det viste seg imidlertid at vannets
kontakt med membranoverflaten kan være en viktig faktor som påvirker permeabiliteten i stor
grad. Resultatene tydet også på at eksponering av membranene for hydrokarboner muligens
fører til redusert salt permeabilitet. Målinger av membrantykkelsen før og etter eksponering
for hydrokarboner ble utført. Resultatet av disse målingene tydet på at hydrokarboner kan
forårsake membransvelling. Under eksperimenter utført i PRO modus ble det observert
trykkøkning i trekkløsningen når hydrokarboner var blandet inn i fødevannet. PRO
eksperimenter med rent fødevann ble utført ved forskjellige trykkforskjeller mellom trekk og
fødesiden. Resultatene tydet ikke på at det var en lineær sammenheng mellom vannfluksen
og trykkforskjellen. FO eksperimenter med rent fødevann ble utført for å undersøke effekten
av temperatur på vann og salt fluksen gjennom membranen. Resultatet tydet på at både
vann og salt fluks øker med temperaturen. PBI membranens termisk stabilitet ble undersøkt
ved hjelp av termogravimetrisk analyse. Oppvarming til temperaturer i underkant av 600 ° C
førte til lite tap av masse. Morfologi undersøkelser ble utført ved hjelp av SEM og
membranens hydrofile egenskaper ble demonstrert med kontakt-vinkelmålinger.

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Acknowledgements
I would like to express my sincere gratitude to my supervisor Professor May-Britt Hägg for
her guidance and support during the last year. The contributions of members of the OMPA
project team to this work is recognized and acknowledged with special thanks to my co-
supervisor Dr. Qiang Yu for his limitless patience, guidance, support and good
companionship in the lab. I would like to give special thanks to Dr. Maria Teresa Guzman
Gutierrez and Dr. Taek-Joong Kim for their help and companionship in the lab. Thanks to the
OMPA project partners Statoil, Inflow Control, Sintef Materials and Chemistry and ITM-CNR
institute for their funding and contributions to the work. I would also like to thank Head of
Department, Professor Edd Anders Blekkan, Dep. of Chemical Engineering, for his support.
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Table of contents

Abstract ................................................................................................................................... i
Sammendrag ......................................................................................................................... iii
Acknowledgements ................................................................................................................ v
Table of contents .................................................................................................................. vii
Symbols and abbreviations .................................................................................................... x
1 Introduction .................................................................................................................... 1
1.1 The background for the thesis ................................................................................. 1
1.2 The problem of produced water in the offshore oil and gas industry ........................ 2
1.3 The power of osmosis ............................................................................................. 2
2 Theoretical background .................................................................................................. 4
2.1 Osmotic processes .................................................................................................. 4
2.2 The membrane material .......................................................................................... 8
2.3 The solubility of hydrocarbons in water .................................................................... 8
2.4 The experimental method ........................................................................................ 8
2.5 Theoretic osmotic pressure ................................................................................... 10
3 Materials and methods ..................................................................................................11
3.1 Investigation of temperature effect in forward osmosis .......................................... 11
3.1.1 Materials .........................................................................................................11
3.1.2 Method ............................................................................................................12
3.2 Evaluation of the membrane preparation method .................................................. 12
3.2.1 Materials .........................................................................................................12
3.2.2 Method ............................................................................................................12
3.3 Investigation of the effect of hydrocarbons in forward osmosis .............................. 13
3.3.1 Materials .........................................................................................................13
3.3.2 Method ............................................................................................................14
3.4 Investigation of membrane performance in PRO ................................................... 18
3.4.1 Materials .........................................................................................................18
3.4.2 Method ............................................................................................................19
3.5 The effect of hydrocarbons on the generated pressure in PRO ............................. 20
3.5.1 Materials .........................................................................................................20
3.5.2 Method ............................................................................................................21
3.6 Characterization .................................................................................................... 22
3.6.1 Investigation of the effect of hydrocarbons on the membrane thickness ..........22
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3.6.2 Thermogravimetric analysis .............................................................................22
3.6.3 Contact angle measurements ..........................................................................23
3.6.4 SEM morphology investigation ........................................................................23
4 Results ..........................................................................................................................24
4.1 Membrane thickness and area measurements ...................................................... 24
4.2 Investigation of temperature effect in forward osmosis .......................................... 24
4.3 Evaluation of the membrane preparation method .................................................. 25
4.4 Investigation of the effect of hydrocarbons in forward osmosis .............................. 27
4.5 Investigation of membrane performance in PRO ................................................... 30
4.6 The effect of hydrocarbons on the generated pressure in PRO ............................. 30
4.7 Characterization .................................................................................................... 33
4.7.1 Investigation of the effect of hydrocarbons on the membrane thickness ..........33
4.7.2 Thermogravimetric analysis .............................................................................33
4.7.3 Contact angle measurements ..........................................................................34
4.7.4 SEM micrograph of the membrane ..................................................................35
5 Discussion .....................................................................................................................36
5.1 Temperature effect on the flux ............................................................................... 36
5.2 Evaluation of the membrane preparation method .................................................. 36
5.3 The effect of hydrocarbons .................................................................................... 36
5.4 The membrane performance in PRO ..................................................................... 39
5.5 Concentration polarization and fouling................................................................... 39
5.6 Characterization .................................................................................................... 41
6 Conclusion ....................................................................................................................43
7 References ....................................................................................................................44
8 Appendix .......................................................................................................................46
A Calibration curves ..................................................................................................... 46
B Data and calculations for the temperature dependence experiments ........................ 48
B.a 23 ºC experiment with example calculations .......................................................48
B.b 42 ºC experiment ................................................................................................50
B.c 62 ºC experiment ................................................................................................51
C Data and calculations for the forward osmosis experiments ...................................... 53
C.a Membrane B reference test with example calculations ........................................53
C.b Membrane C reference test ................................................................................55
C.c Membrane D reference test ................................................................................57
C.d Membrane D 20 % HC test .................................................................................58
C.e Membrane D 50 % HC test .................................................................................59
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