Polyetheramine–polyhedral oligomeric silsesquioxane organic–inorganic hybrid membranes for CO2/H2 and CO2/N2 separation

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<ul><li><p>Journal of Membrane Science 385 386 (2011) 40 48</p><p>Contents lists available at SciVerse ScienceDirect</p><p>Journal of Membrane Science</p><p>j ourna l ho me pag e: www.elsev ier .com</p><p>Polyeth uiomembr</p><p>Mei Ling Taia Department o 11926b Department o</p><p>a r t i c l</p><p>Article history:Received 13 MReceived in reAccepted 6 SepAvailable onlin</p><p>Keywords:Carbon captureCO2-selective membranePEAPEOPOSS</p><p>ne (Pn diox</p><p> the Pons foe obse mepared</p><p>mechanical strength of the soft PEA is enhanced. A high CO2 permeability of 380 Barrer with a moderateCO2/N2 selectivity of 39.1 and a CO2/H2 selectivity of 7.0 are achieved at 35 C and 1 bar for PEA:POSS50:50 membrane. The relationship between gas transport properties and membrane composition is elu-cidated in terms of PEA/gas interaction and nanohybrid structure. Fundamental study on the effect oftemperature and pressure on the performance of the membranes were also carried out. The gas per-</p><p>1. Introdu</p><p>The typiamine absothe need toan attractivenergy efcfeature [1].membranesbe easily prrelatively lositivity towtemperaturmeric memmembrane robust enou</p><p>Over thecrystalline </p><p> CorresponE-mail add</p><p>0376-7388/$ doi:10.1016/j.meability through the membrane is found to increase at the expense of selectivity with the increase intemperature. At higher upstream gas pressure during permeation tests, improvements are observed inboth CO2 permeability and ideal CO2/H2 and CO2/N2 selectivity due to the plasticization effect of CO2. TheCO2/N2 selectivity of the membrane is found to decrease considerably under the binary mixture becauseof competitive sorption between CO2 and N2 in the membranes.</p><p> 2011 Elsevier B.V. All rights reserved.</p><p>ction</p><p>cal separation of carbon dioxide from gas mixtures usingrption is an energy-intensive process and it involves</p><p> regenerate the solvent. Membrane technology offerse alternative to amine absorption due to its higheriency, small footprint and environmental friendliness</p><p> A suitable candidate for fabricating gas separation is polymeric materials as the cost is low and it canocessed into different congurations [2]. However, thew performance of commercial polymers and the sen-ards harsh process conditions of gas streams (pressure,e, high ow rates) are some of the drawbacks of poly-branes [3,4]. This drives the researchers to developmaterials that exhibit better performance and that aregh for long-term operations.</p><p> last few years, poly(ethylene oxide) (PEO), a semi-polymer, has gained interests as a feasible material to</p><p>ding author. Tel.: +65 65166645; fax: +65 67791936.ress: chencts@nus.edu.sg (T.-S. Chung).</p><p>fabricate carbon dioxide-selective membranes for carbon diox-ide/hydrogen (CO2/H2) and carbon dioxide/nitrogen (CO2/N2)separations [514]. Its strong afnity to carbon dioxide due to thepolar ether groups present allows preferential removal of carbondioxide. However, its shortcomings such as tendency to crystallizedue to its semi-crystalline nature and weak mechanical strengthhave restricted its applications [5]. Incorporating PEO with othermonomers as copolymers or as polymer blends or crosslinking itare some of the strategies done to overcome the drawbacks of PEOand improve the gas separation performance. Okamoto and co-workers fabricated PEO-segmented copolymers with various hardsegments [6]. Peinemanns group blended different low molecularweights of poly(ethylene glycol) (PEG) with synthesized PEO-PBT(poly(butylene terephthalate)) and commercial Pebax respec-tively [7,8]. Enhancement in the gas separation performance of themembranes was observed. CO2 permeability increased by eight-fold to more than 850 Barrer for the Pebax membrane blendedwith 50 wt% of PEG-dimethyl ether. The CO2/N2 selectivity was31. Reijerkerk et al. also attempted to blend an additive, PDMS(poly(dimethyl siloxane))PEG, into Pebax with the aim to enhancethe membrane performance with the aid of highly permeable andexible PDMS and highly selective PEO [9]. CO2 permeability was</p><p> see front matter 2011 Elsevier B.V. All rights reserved.memsci.2011.09.008eraminepolyhedral oligomeric silsesqanes for CO2/H2 and CO2/N2 separation</p><p> Chuaa, Lu Shaob, Bee Ting Lowa, Youchang Xiaoa,f Chemical and Biomolecular Engineering, National University of Singapore, Singaporef Polymer Science and Engineering, Harbin Institute of Technology, 150001, China</p><p> e i n f o</p><p>ay 2011vised form 2 September 2011tember 2011e 28 September 2011</p><p>a b s t r a c t</p><p>In this study, composite polyetheramiwere successfully fabricated for carbotion. The organic functional groups onwith PEA. With the optimized condititicles across the membranes could bPEA:POSS 50:50, the crystallinity of thtion of the melting point to 2.6 C, com/ locate /memsci</p><p>xane organicinorganic hybrid</p><p>-Shung Chunga,</p><p>0, Singapore</p><p>EA)polyhedral oligomeric silsesquioxane (POSS) membraneside/hydrogen (CO2/H2) and carbon/nitrogen (CO2/N2) separa-OSS cage and its small particle size enhanced its compatibilityr membrane fabrication, a uniform distribution of POSS par-erved from the SEMEDX analysis. With the weight ratio ofmbranes is signicantly suppressed as observed in the reduc-</p><p> with the original PEA melting point of 37.4 C. In addition, the</p></li><li><p>M.L. Chua et al. / Journal of Membrane Science 385 386 (2011) 40 48 41</p><p>improved by ve times to 530 Barrer at 50 wt% of PDMSPEG.The increase in permeability was mainly ascribed to the increasein diffusivity due to the incorporation of PDMS. Freemans groupapplied ultraviolet light to crosslink different ratios of PEG diacry-late (PEGDAresultant sttallization oincorporatemeability [1selectivity dsilane as a cstrategy hinthe permeamethacrylahad improv5 folds andhighly permhybrid netwinherent pr</p><p>Polyhedcage-like rigbe another formance gavailable onsess good chsystems [16it to have b[17,18]. ThePEO crystalIn additionvolume andport. Simuldiametrical4.442 A, whide and nitrabove-menthat the peinclusion oin permeabcontributed</p><p>In this san organicadvantagesnately PEO which are post-combucompositiocal and mecand the effetemperatur</p><p>2. Experim</p><p>2.1. Materi</p><p>Poly(propoly(propy2000 g/molSigmaAldrits low cooligomeric Hybrid Plaepoxy-aminTetrahydrosolvent to </p><p>hemic</p><p>eivedals isSS wgenn waactio</p><p> in d gaacedfon drane</p><p> for 12. Altion.the s</p><p> and </p><p>embr</p><p>lyticteriznd vatrixd speain</p><p>n m60LAmbreasu</p><p> whs. Th</p><p> memiffrarce </p><p>4 A. T can </p><p>d sin</p><p> n is diff</p><p> thea difetricnmenres ranging from 100 C to 100 C. The ramping rate was setC/min. The rst cycle of ramping and cooling of the sample</p><p> eliminate any thermal history. The second heating curve wasr further analysis. TGA was performed on Perkin-Elmer TGAtemperature was ramped at 10 C/min from 25 C to 800 C.s used as the purging gas and the ow rate was maintained</p><p> ml/min. mechanical strength of the membranes was tested using andentor (Agilent Nanoindentor XP). A 5 mN load was placed) and PEG methyl ethyl acrylate (PEGMEA) [10]. Theructure had a hyperbranched network in which crys-f PEO was restricted. Siloxane-based monomers wered with PEO acrylates with the intention to increase per-1,12]. The CO2 permeability was enhanced while theecreased. Shao and Chung also explored the addition ofrosslinking agent to form PEO-based membranes. Thisdered the formation of crystals which in turn increasedbility of PEO [13]. Further studies by grafting PEGte (PEGMA) and blending PEG into the polymer matrixed the performance of the membranes signicantly by</p><p> 2.5 folds, respectively [14,15]. Thus, combining witheable groups and fabricating it as an organicinorganicork seems to be a promising strategy to enhance the</p><p>operties of CO2-selective PEO.ral oligomeric silsesquioxane (POSS), a molecule withid structure of particle size ranging from 1 to 3 nm, maysuitable candidate to crosslink PEO to attain high per-as separation membranes. The functional side groups</p><p> the POSS cage structure allow POSS molecules to pos-emical reactivity and compatibility with many polymer]. Furthermore, the small particle size of POSS enablesetter dispersion at molecular level in the membranes</p><p> formation of a crosslinked network may disrupt thes arrangement and potentially reduce the crystallinity., the bulky POSS molecules may aid to increase free</p><p> the cage may provide a possible pathway for gas trans-ation results showed that the distance between two</p><p> opposite silicon atoms in each face was approximatelyich is larger than the kinetic diameter of carbon diox-ogen [19]. An attempt by Dominguez et al. to exploit thetioned advantages of POSS molecules has demonstratedrmeability of oxygen and nitrogen increased with thef POSS with polystyrene as copolymers [20]. This riseility could be attributed to the increase in free volume</p><p> by the bulky POSS molecules.tudy, we aim to explore the feasibility of fabricatinginorganic hybrid membrane combining the various</p><p> of a polyetheramine (PEA), which contains predomi-backbone, and POSS for CO2/H2 and CO2/N2 separation,the major components in the pre-combustion andstion capture of carbon dioxide respectively. Differentns of PEA and POSS are fabricated. The physiochemi-hanical properties of the membranes are characterizedcts of varying POSS composition, testing pressure ande on gas performance of the membranes are evaluated.</p><p>ental</p><p>als and membrane fabrication procedure</p><p>pylene glycol)-block-poly(ethylene glycol)-block-lene glycol) bis(2-aminopropyl ether) (PEA) with Mne (approximately 85 wt% of PEO) was purchased fromich and was chosen as the source for PEO due tost and widespread availability. Glycidyl polyhedralsilsesquioxane (POSS) cage mixture, acquired fromstics, Inc, was selected to react with PEA to forme crosslinked organicinorganic hybrid membranes.furan (THF), obtained from Merck, was used as thedissolve PEA and POSS. All the chemicals were used</p><p>Fig. 1. Cbranes.</p><p>as recmateriand POa homosolutiothe regroupstrappeand plthe Telmemb120 Cin Fig. fabricaX:Y in of PEA</p><p>2.2. M</p><p>AnacharacThe bomer mInfrareber domelectroJSM-63the mewas m1200e)sampleof theX-ray dray sou = 1.5space)</p><p>n = 2where is the</p><p>Theusing gravimenviroperatuat 10 </p><p>was toused fo7. The N2 waat 100</p><p>Thenano-ial structure of the starting materials for fabricating the hybrid mem-</p><p>. The respective chemical structure of the starting illustrated in Fig. 1. To fabricate the membrane, PEAere dissolved in THF at various compositions to prepareeous solution containing 2 wt% solid concentration. Thes then heated under reux at 60 C for 3 h to initiaten between the epoxy groups in POSS and the aminoPEA [13]. After sonicating for 10 min to remove theses, the solution was slowly casted onto a Telfon dish</p><p> in the oven at 40 C. A glass plate was used to coverish to allow slow evaporation of the solvent. The dried</p><p> was peeled off and further annealed under vacuum at2 h. The membrane preparation procedure is depictedl the membrane samples were kept in the dry box after</p><p> The ratio of PEA to POSS is represented by PEA:POSSubsequent gures, where X and Y are the weight ratioPOSS, respectively.</p><p>ane characterizations</p><p>al tools were employed to verify the structure ande the physical properties of the fabricated membranes.ibration of the various groups of atoms in the poly-</p><p> was detected by a Perkin-Elmer Fourier Transformctrometer (FTIR-ATR) (Spectrum 2000). The wavenum-</p><p> obtained ranged from 4000 cm1 to 600 cm1. Scanningicroscope and electron dispersive X-ray analysis (JEOL) was employed to examine the distribution of POSS in</p><p>anes (SEMEDX). The density of the crosslinked networkred using a gas pycnometer (Quantachrome Ultrapycere helium was used to determine the volume of thee inter-chain spacing (d-space) and the crystallinitybranes were analyzed at room temperature by an</p><p>ctometer (Bruker D8 advanced diffractometer). The X-used was Ni-ltered Cu K rays at the wavelength ofhe dimension spacing between diffracting planes (d-be computed based on the Braggs law.</p><p> (1)</p><p>an integer, is the wavelength of the X-ray source andraction angle.rmal properties of the membranes were analyzed byferential scanning calorimeter (DSC) and a thermo-</p><p> analyzer (TGA). The membranes were tested under N2t (100 ml/min) using DSC822e (Mettler Toledo) at tem-</p></li><li><p>42 M.L. Chua et al. / Journal of Membrane Science 385 386 (2011) 40 48</p><p>er ne</p><p>on the inde30 s. The diModulus anentire procsurface to o</p><p>2.3. Measur</p><p>The solutransport mfeed gas disthe concentpermeabilitthe pure gaproduct of membrane of the downchamber (V(T). p2 is theis under vacability is BaThe permeapressure ofvaried from</p><p>P = QlA P</p><p>=</p><p>The ideathe pure gavolume andmeasure thimental set</p><p>A/B =PAPB</p><p>Based oexpressed a</p><p>electctivi</p><p> S </p><p>DADB</p><p> gas alans preity cogas sfusivabiliten reFig. 2. Fabrication procedure and the resultant polym</p><p>ntor tip and held on the surface of the membranes forsplacement of the tip was measured and the Youngsd the hardness of the membranes were derived. Theedure was repeated for 10 points on the membranebtain an average value.</p><p>ements of pure gas permeation</p><p>tion-diffusion model is often applied to explain theechanism of gases through dense membranes [21]. Thesolves into the surface of the membrane, diffuses acrossration gradient and desorbs at the other side. The gasy was obtained by taking the ratio of the product ofs ux (Q) and the thickness of the membrane (l) to thethe membrane area and the pressure drop across the(P). The pure gas ux is related to the rate of increase</p><p>ideal sity sele</p><p>P = D </p><p>A/B =</p><p>TheMicrobfeed gasolubilof the The difpermehas bestream pressure (dp/dt), the volume of the downstream) and the operating temperature of the permeation cell</p><p> upstream pressure of the feed gas. The permeate sideuum conditions before the gas tests. The unit of perme-rrer where 1 Barrer = 1010 cm3 (STP)-cm/cm2 s cm Hg.bility of H2, N2 and CO2 in this study was measured at a</p><p> 1 bar from 30 to 50 C. The upstream pressure was also 1 to 10 bar.</p><p>273 1010760</p><p>Vl</p><p>AT[p2 76/14.7](</p><p>dp</p><p>dt</p><p>)(2)</p><p>l selectivity of gas A to gas B was taken as the ratio ofs permeability of A to B, as shown in Eq. (3). A constant</p><p> variable pressure method was used in this study toe pure gas permeability and selectivity. Detailed exper-up and procedure can be found elsewhere [22].</p><p>(3)</p><p>n the solutiondiffusion model, permeability can bes a product of diffusivity and solubility. Therefore, the</p><p>S = CP</p><p>Besides 50:50 mixtubrane at 35side is undeing, the dowchromatogrpermeate cexperimentThe permeaequations</p><p>PCO2 =yCO2xCO2</p><p>PN2 =(1 1 </p><p>where yCO2ate and xCOmixture.twork (y 39, (x + z) 6).</p><p>ivity is the product of diffusivity selectivity and solubil-ty.</p><p>(4)</p><p>SASB</p><p>(5)</p><p>sorption of the membranes was determined by a Cahnce. The gain in the mass of the membranes at differentssures from 1 bar to 10 bar at 35 C was recorded and theefcient (S) was analyzed by dividing the concentrationorbed (C) by the pressure (P) as shown in Eq. (6) [23].ity coefcient was determined by taking t...</p></li></ul>


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