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Wetting of polypropylene hollow fiber membrane contactors
East China University of Science and Technolog. (Bioenergy group)
East China University of Science and Technology.
East China University of Science and Technology.
Mälardalen University, School of Sustainable Development of Society and Technology.ORCID iD: 0000-0003-0300-0762
Show others and affiliations
2010 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 362, no 1-2, p. 444-452Article in journal (Refereed) Published
Abstract [en]

The membrane wetting by the absorbent leads to the increase of mass transfer resistance and deterioration of CO2 absorption performance during membrane gas absorption process. In this paper, polypropylene (PP) fibers were immersed in monoethanolamine (MEA), methyldiethanolamine (MDEA) and deionized (DI) water, respectively, assuming that the immersed PP fibers would undergo similar exposure conditions as those used in hollow fiber membrane contactor. The wetting evolution of PP fibers was investigated as a function of immersion time. The characterization results confirmed that the absorbent molecules diffused into the PP polymer during the exposure process, resulting in the swelling of the membrane. The absorption-swelling wetting mechanism was proposed to explain what happened during the wetting process. A 30.8° reduction in the contact angle was observed, indicating that the membrane surface hydrophobicity decreased significantly following the immersion time. Experimental results showed that the membrane surface morphology and surface roughness suffered significant and complicated changes after being immersed in the absorbents for a certain period. It was found that the absorbent with higher surface tension is in favor of fewer changes of the membrane surface morphologies. Based on the experimental results, improving the membrane surface hydrophobicity was suggested as an effective way to overcome the wetting problem.

Place, publisher, year, edition, pages
2010. Vol. 362, no 1-2, p. 444-452
Keywords [en]
Wetting; Hollow fiber membrane contactors; Polypropylene; Surface morphologies; CO2 capture
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-10361DOI: 10.1016/j.memsci.2010.06.067ISI: 000281571100049Scopus ID: 2-s2.0-77955665036OAI: oai:DiVA.org:mdh-10361DiVA, id: diva2:354580
Projects
Swedish Research Links ProgrammeAvailable from: 2013-06-17 Created: 2010-10-04 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Experimental Studies on CO2 Absorption in Hollow Fiber Membrane Contactor
Open this publication in new window or tab >>Experimental Studies on CO2 Absorption in Hollow Fiber Membrane Contactor
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Membrane gas absorption technology is considered as one of the promising alternatives to conventional techniques for CO2 separation from the flue gas of fossil fuels combustion. As a hybrid approach of chemical absorption and membrane separation, it may offer a number of important features, including operational flexibility, compact structure, linear scale up and predictable performance. The main challenge is the additional membrane mass transfer resistance, especially when this resistance increases due to the absorbent intruding into the membrane pores.

In this thesis, the experimental was set up to investigate how the operating parameters affect the absorption performance when using absorbent in hollow fiber contactor, and to obtain the optimal range of operation parameters for the designated membrane gas absorption system . During 20 days’ continuous experiment, we observed that the CO2 mass transfer rate decreases significantly following the operating time, which is attributed to the increase of membrane mass transfer resistance resulting from partial membrane wetting.

To better understand the wetting evolution mechanism, the immersion experiments were carried out to assume that the membrane fibers immersed in the absorbents would undergo similar exposure as those used in the membrane contactor. Various membrane characterization methods were used to illustrate the wetting process before and after the membrane fibers were exposed to the absorbents. The characterization results showed that the absorbent molecules diffuse into the polypropylene (PP) polymer during the contact with the membrane, resulting in the swelling of the membrane. In addition, the effects of operating parameters such as immersion time, CO2 loading, as well as absorbent type on the membrane wetting were investigated in detail. Finally, based on the analysis results, methods to smooth the membrane wetting were discussed. It was suggested that improving the hydrophobicity of PP membrane by surface modification may be an effective way to improve the membrane long-term performance.

Modification of the polypropylene membrane by depositing a rough layer of PP was carried out in order to improve the non-wettability of membrane. The comparison of long-term CO2 absorption performance by PP membranes before and after modification proves that the modified polypropylene membranes retained higher hydrophobicity than the untreated polypropylene membrane. Therefore modification is likely to be more suitable for use in membrane gas absorption contactors for CO2 separation, particularly over long operation time.

Place, publisher, year, edition, pages
Mälardalen University: Västerås, 2010
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 121
Keywords
CO2 capture; Hollow fiber membrane contactor; Membrane gas absorption; Partial wetting; Surface modification;
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-9617 (URN)978-91-86135-75-1 (ISBN)
Presentation
2010-06-04, U2-012, Mälardalen University, Högskoleplan 1, Västerås, 10:00 (English)
Opponent
Supervisors
Available from: 2010-05-24 Created: 2010-05-24 Last updated: 2014-01-22Bibliographically approved
2. Experimental Studies on CO2 Capture Using Absorbent in a Polypropylene Hollow Fiber Membrane Contactor
Open this publication in new window or tab >>Experimental Studies on CO2 Capture Using Absorbent in a Polypropylene Hollow Fiber Membrane Contactor
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, membrane gas absorption technology has been considered as one of the promising alternatives to conventional techniques for CO2 capture due to its favorable mass transfer performance. As a hybrid approach of chemical absorption and membrane separation, it exhibits a number of advantages, such as operational flexibility, compact structure, high surface-area-to-volume ratio, linear scale up, modularity and predictable performance. One of the main challenges of membrane gas absorption technology is the membrane wetting by absorbent over prolonged operating time, which may significantly decrease the mass transfer coefficients of the membrane module.

In this thesis, the experimental was set up to investigate the dependency of CO2 removal efficiency and mass transfer rate on various operating parameters, such as the gas and liquid flow rates, absorbent type and concentration and volume fraction CO2 at the feed gas inlet. In addition, the simultaneous removal of SO2 and CO2 was investigated to evaluate the feasibility of simultaneous desulphurization and decarbonization in the same membrane contactor. During 14 days of continuous operation, it was observed that the CO2 mass transfer rate decreased significantly following the operating time, which was attributed to partial membrane wetting.

To better understand the wetting mechanism of membrane pores during their prolonged contact with absorbents, immersion experiments for up to 90 days were carried out. Various membrane characterization methods were used to illustrate the wetting process before and after the membrane fibers were exposed to the absorbents. The characterization results showed that the absorbent molecules diffused into the polypropylene polymer during the contact with the membrane, resulting in the swelling of the membrane. In addition, the effects of operating parameters such as immersion time and absorbent type on the membrane wetting were investigated in detail. Finally, based on the analysis results, methods to smooth the membrane wetting were discussed. It was suggested that improving the hydrophobicity of polypropylene membrane by surface modification may be an effective way to improve the long-term operating performance of membrane contactors. Therefore, the polypropylene hollow fibers were modified by depositing a thin superhydrophobic coating on the membrane surface to improve their hydrophobicity. The mixture of cyclohexanone and methylethyl ketone was considered as the best non-solvent to achieve the fiber surface with good homogeneity and acceptably high hydrophobicity. In the long-period operation, the modified membrane contactor exhibited more stable and efficient performance than the untreated one. Hence, surface treatment provides a feasibility of improving the system stability for CO2 capture from the view of long-term operation.

Abstract [sv]

En av de tekniker som under senare framhållits som ett lovande alternativ till konventionell CO2-avskiljning är membran-gas-absorptionstekniken på grund av god prestanda vad gäller masstransport. Det blandade angreppssättet med både kemisk absorption och membranseparation har en rad fördelar, såsom driftflexibilitet, kompakt konstruktion, högt yt-volymsförhållande, linjär uppskalning, modularitet och förutsägbar prestanda. En av de viktigaste utmaningarna för membran-gas-absorptionstekniken är vätningen av membranet med absorbenten under långa drifttider, vilket väsentligt kan minska membranmodulens masstransportkoefficienter. 

I avhandlingen har en rad olika driftparametrars påverkan på CO2-reningsgraden och massöverföringshastigheten undersökts. Driftparametrar inkluderar gas- och vätskeflöden, typ av absorbent och koncentration och volymfraktion av CO2 vid gasinloppet. Avskiljning av SO2 och CO2 har dessutom undersökts för att utvärdera möjligheten att samtidigt, i samma membranenhet, avlägsna svavel och kol. Under 14 dagars kontinuerlig drift konstaterades det att massöverföringshastigheten för CO2 minskade avsevärt med drifttiden, vilket hänfördes till partiell vätning av membranet.  

För att bättre förstå mekanismerna för vätning av membranporer under långvarig kontakt med absorbenter genomfördes doppningsexperiment i upp till 90 dagar. Olika metoder för karakterisering av membran användes för att illustrera vätningsprocessen före och efter det att membranfibrerna exponerades för absorbenterna. Resultaten av karakteriseringen visade att absorbentmolekylerna spreds in i polypropenpolymeren under kontakten med membranet, vilket ledde till att membranet svällde. Dessutom undersöktes effekterna av driftsparametrar såsom nedsänkningstid och typ av absorbent i detalj. Slutligen, på grundval av analysresultaten, diskuterades metoder för att underlätta vätningen av membran. Att förbättra polypropylenmembranets hydrofobicitet genom modifiering av ytan föreslogs kunna vara ett effektivt sätt att förbättra den långsiktiga driftprestandan för membranenheter. Därför modifierades de ihåliga fibrerna av polyproylen med ett tunt lager av en superhydrofob beläggning på membranets yta för att förbättra hydrofobiciteten. En blandning av cyklohexanon och metyletylketon ansågs vara det bästa icke-lösningsmedlet för att få en fiber yta med god homogenitet och acceptabelt hög hydrofobicitet. Under lång driftperiod, uppvisade den modifierade membranenheten stabilare och effektivare prestanda än den obehandlade. Därför erbjuder ytbehandling en möjlighet till att förbättra systemets stabilitet för CO2-avskiljning när det gäller långsiktig drift.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2011
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 102
Keywords
CO2 capture; Simultaneous removal of CO2 and SO2; Hollow fiber membrane contactor; Membrane gas absorption; Partial wetting; Surface modification, CO2-avskiljning, samtidig avskiljning av CO2 och SO2, ihålig fiber, membran, gas absorption, vätning, ytmodifiering
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-12320 (URN)978-91-7485-023-9 (ISBN)
Public defence
2011-06-17, Lambda, Mälardalens högskola, Västerås, 10:00 (English)
Opponent
Supervisors
Projects
VR-SIDA Swedish Research Links Programme
Available from: 2011-05-27 Created: 2011-05-25 Last updated: 2014-01-22Bibliographically approved

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