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Available online at www.sciencedirect.com

Separation and Purification Technology 60 (2008) 259–263

Preparation and gas permeation of composite carbon membranes frompoly(phthalazinone ether sulfone ketone)

Bing Zhang a,b, Tonghua Wang a,∗, Yonghong Wu b, Qingling Liu a, Shili Liu a,Shouhai Zhang c, Jieshan Qiu a,∗∗

a Carbon Research Laboratory, State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Center for Nano Materials and Science,Dalian University of Technology, 158 Zhongshan Road, P.O. Box 49, Dalian, Liaoning 116012, China

b School of Petrochemical Engineering, Shenyang University of Technology (Liaoyang Campus), 30 Guanghua Street, Liaoyang, Liaoning 111003, Chinac Department of Polymer Science and Materials, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116012, China

Received 7 February 2007; received in revised form 20 August 2007; accepted 20 August 2007

bstract

Composite carbon membranes were prepared from poly(phthalazinone ether sulfone ketone) (PPESK) by incorporating with polyvinylpyrrolidonePVP) or zeolite (ZSM-5) through stabilization and pyrolysis processes. The thermal stability of composite polymeric membranes was measured byhermal gravimetric analysis. The resultant composite carbon membranes were characterized by scanning electron microscopy, X-ray diffractionnd gas permeation technique, respectively. The results illustrated that the thermal stability of composite polymeric membranes was enhanced byddition of ZSM-5 or reduced by PVP. For ZSM-5 or PVP composite carbon membranes prepared at 650 ◦C, the O2 permeability is 199.70 Barrerr 124.89 Barrer, and the O2/N2 selectivity is 10.3 or 4.2, respectively. Compared with carbon membranes from pure PPESK, the O2 permeability

f ZSM-5 or PVP composite carbon membranes increases by 18.5 or 11.6 times, together with the O2/N2 selectivity decreasing by 35.2% or 73.6%,espectively. The gas separation mechanism of composite carbon membranes is molecular sieving. Adsorption effect also plays a significant roleor CO2 permeating through ZSM-5 composite carbon membranes. 2007 Elsevier B.V. All rights reserved.

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eywords: Carbon molecular sieves; Composite membrane; Pyrolysis; Gas sep

. Introduction

Membrane-based gas separation processes offer a number ofdvantages in terms of high efficiency, low energy use and cap-tal investments. Membranes can be potentially used in variousas separation applications, such as nitrogen and oxygen enrich-ent, hydrogen recovery and acid gas removal from natural

as [1,2]. Studies have shown that large amount of organic andnorganic materials can be used as membrane materials [3–6].f these membrane materials, recently carbon membranes have

een attracted much attention due to their superior advantages,.g., high gas selectivity, excellent thermal and chemical stabil-ty [2,7]. However, up to now carbon membranes have not be

∗ Corresponding author. Fax: +86 411 88993968.∗∗ Corresponding author. Fax: +86 411 88993991.

E-mail addresses: wangth@chem.dlut.edu.cn (T. Wang),qiu@dlut.edu.cn (J. Qiu).

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383-5866/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2007.08.022

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ruly commercialized and used on large-scale because of someroblems, i.e., high-cost, poor mechanical strength, and low per-eability. In order to overcome those problems, some methods

ave been developed, including oxidation, chemical vapor depo-ition and composition [8–13]. Among them, composition (orncorporation with additives) has exhibited obvious effects toodify the gas permeation of carbon membranes. The additives

nclude organic (i.e., PEG and PVP, etc.) and inorganic materi-ls (i.e., metal, metal oxides and zeolite, etc.). Lie and HAAgg14] added metal oxides into precursor and found that the resul-ant carbon membranes containing Ag and Cu showed muchigher H2 permeability than the one containing Ca, Mg dueo the facilitated transportation effects. Shiflett and Foley [15]eported that the addition of polyethylene glycol (PEG) into therecursor polymer increased the oxygen fluxes for carbon mem-

ranes from 2.04 × 10−10 to 77.7 × 10−10 mol m−2 s−1 Pa−1,nd decreased the O2/N2 selectivity from 8.0 to 4.4. Kim etl. [12] increased the gas permeability for O2 by 28% throughntroducing thermally labile polyvinylpyrrolidone (PVP) to

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60 B. Zhang et al. / Separation and Pur

recursor polyimide. Tin et al. [16] found that the CO2ermeability of 611 Barrer (1 Barrer = 1 × 10−10 cm3 (STP)m/cm2 s cmHg) for pure carbon membranes decreased to66 Barrer for KY type zeolite composite carbon membraneith the CO2/CH4 selectivity increasing from 61 to 124. Inur preliminary experiments, nano-sized zeolite composite car-on membranes from polyimide were prepared, of which the2 permeability was significantly increased from 2.21 Barrerf polyimide-based carbon membranes to 499.0 Barrer togetherith the satisfactory O2/N2 selectivity above 12 [17]. We think

hat the improvement of gas permeability is due to the interfa-ial gaps between carbon matrix and zeolite phase because of thehase separation effect. But, the high-cost and rigorous synthe-is conditions of nano-sized zeolite make it unsuitable to prepareeolite composite carbon membranes on large-scale. Herein, its recommended to use the commercial product micron-sizedSM-5.

Previously, a novel precursor, poly(phthalazinone ether sul-one ketone) (PPESK) was successfully developed to preparearbon membrane by us, of which the maximum gas separationactor for O2/N2 system could reach above 24 [18]. However, theas permeability of the carbon membranes is not satisfactorilyigh enough to meet the requirement for the purpose of industrialpplications. The main objective of this work is to modify theas permeation of PPESK-based carbon membranes by chargingith additives. Here, commercial products, micron-sized ZSM-5

nd PVP, were adopted as additives to prepare composite carbonembranes.

. Experimental

.1. Materials and membrane preparation

The precursor material, poly(phthalazinone ether sulfoneetone) (PPESK) with the sulfone/ketone molar ratio of/1, was provided by Dalian New Polymer Corporation ofhina. The typical chemical structure and detailed synthe-

is procedure of PPESK were described elsewhere [19].he chemical N-methyl-2-pyrrolidone (NMP) with analyti-al grade was used as solvent without any purification. Theommercial product ZSM-5 (SiO2/Al2O3 = 22.8) powder inhe particle diameter of 1.0–2.0 �m was calcined at 450 ◦Cor 3 h to remove its impurities. The molecular weight ofhemical PVP used in the experiments was in the range of0,000–70,000 g/mol. ZSM-5 and PVP were separately addednto two 15 wt% PPESK/NMP solutions and kept their con-entration at 5 and 2 wt%, respectively. Then, the two-dopedolutions were vigorously stirred for 4 h and ultrasonicallyispersed for another 2 h. The freestanding polymeric mem-ranes were formed by solvent evaporation at 100 ◦C for4 h. Carbon membranes were prepared via air stabilizationnd argon pyrolytic atmosphere according to the procedurend conditions described elsewhere [18]. The as-obtained

arbon membranes derived from pure PPESK, incorporatingith ZSM-5 or PVP were denoted as CM-t, CZ-t or CP-t

t represents the pyrolytic temperature), respectively. Carbonembranes with the thickness ca. 50 �m were stored in a des-

Adot

on Technology 60 (2008) 259–263

ccator to avoid the effects of vapor and CO2 species in their.

.2. Characterizations

Thermal degradation behavior of precursors was measured byMettler-Toledo TGA/SDTA851 thermogravimetric analyzer

n flowing nitrogen at a heating rate of 10 ◦C/min from 100 to00 ◦C.

X-ray diffraction (XRD) patterns were recorded using a/Max-2400 diffractometer (Cu K� radiation) with the diffrac-

ion angle 2θ from 5 to 60◦. The interlayer distance d002 ofamples were calculated by the well-known Bragg equation.

The surface morphology of composite carbon membranesas observed by a JEOL JMS-5600LV scanning electronicroscope (SEM) operating at 20 kV. Energy-dispersive X-ray

EDX) was also performed to identify the elemental compositionf membrane surface.

Single gas permeation of membranes was tested by con-entional variable volume–constant pressure method. Highlyurified gas provided by compressed gas cylinder was intro-uced to the upper side of a stainless membrane cell and theressure was regulated at 0.1 MPa by a pressure regulator. Theure gas flux at permeating side of membrane cell was moni-ored by a capillary flowmeter. The detailed test procedure waseported in our previous article [18]. The permeability, “P”, wasalculated from the following equation,

= Flux · l

A · �p

here �p, A and l are the partial pressure difference of the gascross the tested membrane, the effective permeation area andhe thickness of the tested membrane, respectively. The precisionn permeability for each membrane was found to be within therror range of ±10%.

The ideal separation factor or selectivity “α” is obtained byhe ratio of the permeation rate of two gases,

= PA

PB

here PA and PB are the permeation rate for gas A and B,espectively.

To ensure a good reproducibility of carbon membranes, theeplicative experiments were performed at least three times. Theas permeation data presented in this article are referred to theverage values.

. Results and discussion

.1. Thermal stability, morphology and microstructure

Fig. 1a and b show the thermal weight loss and differentialeight loss profiles of composite and pure PPESK membranes.

s shown in Fig. 1a, pure PPESK has three obvious thermalegradation stages. The first stage starts from the temperaturef 200–300 ◦C with the weight loss ca. 4.5 wt% that is attributedo the removal of residual solvent NMP and minor thermal degra-

B. Zhang et al. / Separation and Purification Technology 60 (2008) 259–263 261

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pStgZplpinttof silica in ZSM-5 surrounded by carbon matrix. It is reportedthat high content of silica offers the advantage of hydrophobicityand retains their adsorption capacity well even in the presenceof steam [23]. It will surely affect the gas permeating through

Fig. 1. Thermal gravimetric analysis of composite and pure polyme

ation of end or lateral groups in PPESK molecular chains. Theecond thermal weight loss stage is between 500 and 600 ◦C,uring which huge weight loss of PPESK was about 38 wt%. Inhis stage, small gases (i.e., H2S, SO2, CO, CO2 and HCN, etc.)ere released by the degradation of functional groups in mainolecular chains. When the thermal degradation temperature is

p to 600 ◦C, the weight loss rate slows down and the weight losss about 21 wt% of the total weight loss due to the rearrangementf carbon structure. Compared to pure PPESK, PVP/PPESK hasdditional one weight loss stage in the temperature range of50–450 ◦C due to the decomposition of PVP [12]. The ther-ally labile degradation of PVP in the early stage of pyrolysisould lead to the creation of large amount of micropores in theatrix. As the result, the gas permeability of PVP composite car-

on membranes would be improved. Although ZSM-5/PPESKas similar thermal degradation profile as compared to purePESK, the former presents lower thermal weight loss during

he temperature range from 255 to 446 ◦C owing to the cat-lytic degradation effect of PPESK induced by ZSM-5. As theesult of this effect, large amount of coke or aromatic compoundsould be produced on the surface of ZSM-5 and modified theore mouth of ZSM-5 [20]. The temperature at maximum ratef decomposition (Tmax) is usually regarded as the basis tovaluate the thermal stability of polymers. For Fig. 1b, the ther-al stability indicator (Tmax) of composite membranes follows

he sequence of ZSM-5/PPESK > PPESK > PVP/PPESK. Themprovement in thermal stability by adding ZSM-5 into poly-

eric membranes also can be found in literature because of theointly thermal effect [21].

Fig. 2 shows the XRD patterns of carbon membranes. Thengerprints of ZSM-5, several sharp peaks at 2θ = 7.90◦, 8.80◦,3.08◦ and 23.90◦, can be obviously found in the XRD patternsf ZSM-5 composite carbon membranes [22]. This indicateshat the crystal structure of ZSM-5 is well maintained even atigh pyrolytic temperature of 800 ◦C. Compared PVP compos-te carbon membranes with pure carbon membranes prepared athe same pyrolytic temperature, 650 or 800 ◦C, they have sim-

lar XRD profiles and close (0 0 2) diffraction peak position at2.79◦ and 24.27◦, respectively. From the (0 0 2) diffraction peakositions, the interlayer distance d002 as 0.390 and 0.366 nm arebtained by Bragg equation, suggesting that the addition of PVP

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embranes. (a) Thermal weight loss and (b) differential weight loss.

nto PPESK does not markedly change the microstructure ofesulting carbon membranes.

Fig. 3a and b give the SEM images of ZSM-5 and PVP com-osite carbon membranes prepared at 650 ◦C. Seen from theEM image of ZSM-5 composite carbon membranes (Fig. 3a),

he white spots are ZSM-5 particles that are distributed homo-eneously on the crackless membrane surface. The imbeddedSM-5 particles would exert two functions to improve the gasermeability of composite carbon membranes: one is providingarge amount of gas diffusion channels in their interior orderedorous structure; the other is engendering phase gap between thenterfaces of ZSM-5 and carbon matrix. By those diffusion chan-els and interfacial gaps, gases can be more easily permeatedhrough carbon membranes. The very sharp Si peak shown inhe inserted EDX spectrum evidently illustrates the high content

ig. 2. XRD patterns of composite and pure carbon membranes. The markedumbers correspond to the diffraction peak position of carbon membranes.

262 B. Zhang et al. / Separation and Purification Technology 60 (2008) 259–263

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ig. 3. SEM pictures for composite carbon membranes: (a) CZ-650 and (b) Cembrane surface, revealing the homogenously distribution of ZSM-5 particles

arbon membranes. In the case of PVP composite carbon mem-ranes (Fig. 3b), the membrane surface is very dense and smooth.o other element on the membrane surface was found except

or carbon shown by EDX. The microstructure of PVP compos-te carbon membranes is simply constructed by the disorderedacking of amorphous carbon.

.2. Gas permeation of composite carbon membranes

In the present study, composite carbon membranes CZ-650nd CP-650 exhibit higher H2, CO2 and O2 permeability thanure carbon membranes CM-650, as shown in Table 1. The gasermeabilities for H2, CO2 and O2 increase by 7–20 times, whilehe H2/N2, CO2/N2 and O2/N2 selectivities decrease by 77.5%,7.4%, 35.2% for CZ-650, and 88.3%, 90.4%, 73.6% for CP-50, respectively. The improvement in gas permeability for PVPomposite carbon membranes is due to the formation of largemount of pore structure by excessively thermal degradationnd low char yield of PVP during pyrolysis of PVP/PPESK. Asor ZSM-5 composite carbon membranes, the improvement inas permeability is attributed to the reduction of gas transportesistance through membranes by providing additionally micro-

orous channels in ZSM-5 and interfacial resistance [17,24].een from the above results, although the gas permeability ofarbon membranes is significantly increased, the selectivity isimultaneously decreased by incorporating additives. Therefore,

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able 1as permeability and selectivity of composite carbon membranes measured at 0.1 M

ample codes Permeability (Barrera)

H2 CO2 O2

nudsen diffusion – – –M-650b 118.40 85.00 10.80Z-650 758.10 791.50 199.70P-650 602.44 356.83 124.89M-800b 47.90 30.90 4.43Z-800 17.46 67.39 4.53P-800 36.06 24.38 6.12

a 1 Barrer = 1 × 10−10 cm3 (STP) cm/cm2 s cmHg.b Carbon membranes derived from pure PPESK reported in our previous work [18]

0. The inserted EDX images in SEM show the elemental composition on theZ-650.

he compromise between permeability and selectivity of car-on membranes should be balanced for a given application orurpose.

The gas permeability of PVP composite carbon mem-ranes decreases along with the selectivity increasing when theyrolytic temperature is elevated from 650 to 800 ◦C. This trade-ff relationship between gas permeability and selectivity againstoyroytic temperature can be found for most carbon membranesn literatures [2,7,8]. However, with increasing the pyrolyticemperature from 650 to 800 ◦C, both the permeability and selec-ivity for ZSM-5 composite carbon membranes decrease exceptor CO2/N2 selectivity. This reasons may be summarized asollows: (1) the reduction of gas permeability is due to the rear-angement of turbostratic carbon structure; (2) the decrease ofelectivity is probably ascribed to the enlargement of interfacialap between ZSM-5 and carbon matrix; (3) the increment ofO2/N2 selectivity implies that more channels in ZSM-5 takeart in gas separation and the preferential adsorption effect ofSM-5 to CO2 is markedly enhanced [25,26].

The gas permeability of PVP composite carbon membranesollows an order of H2 > CO2 > O2 > N2, which is just in accordith their kinetic diameters (H2 (0.289 nm), CO2 (0.33 nm),

2 (0.346 nm), N2 (0.364 nm)). This indicates that the gasermeation through PVP composite carbon membranes obeysolecular sieving mechanism. In the case of ZSM-5 composite

arbon membranes, the permeating gases H2, O2 and N2 also

Pa and 30 ◦C

Ideal selectivity

N2 H2/N2 CO2/N2 O2/N2

– 3.7 0.8 0.90.68 174.1 125.0 15.9

19.40 39.1 40.8 10.329.74 20.3 12.0 4.20.18 266.1 171.7 24.60.66 26.6 102.5 6.90.95 38.0 25.7 6.5

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B. Zhang et al. / Separation and Purifica

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ig. 4. Relationship between the permeability and selectivity of composite car-on membranes for O2/N2 separation at 30 ◦C.

beys molecular sieving mechanism except for CO2 that showshe highest permeability among the four tested species. Thiss undoubtedly ascribed to the preferential adsorptions of CO2olecules on the pore wall in zeolite [25,26]. It is demonstrated

hat the gas permeating mechanisms through ZSM-5 compositearbon membranes include not only molecular sieving but alsoelective-adsorption.

To evaluate the gas separation performance for polymericembrane, there is a well-known Robeson’s upper bound that isdouble logarithmic plot of selectivity against the permeabilityf gases [27]. Likewise, the upper bound for carbon membranesas also recommended by collecting large amount of gas perme-

tion data in literature [28]. Here, we try to correlate the oxygenermeability with the O2/N2 selectivity of composite carbonembranes as shown in Fig. 4. It can be found that the correla-

ion points for all composite carbon membranes prepared in theresent work fall above the Robeson’s upper bound limit that isncommon for polymeric membranes. For membranes CP-650,P-800 and CZ-800, they fall in the region between the twopper bounds, which is the normal scope for most reported car-on membranes. It is excitingly noticed that the point of CZ-650s far beyond the carbon membrane’s upper bound, illustratinghat the gas permeability of carbon membranes can be improvedy incorporating additives on the precondition of surpassing car-on membrane’s upper bound. The above results have shownhat the gas separation performance of PPESK-based carbon

embranes can be well tuned by incorporation of PVP andSM-5. However, many works are still needed to be further car-

ied out for PPESK-based composite carbon membrane, such ashe effects of PVP and ZSM-5 composition on gas separationerformances.

. Conclusions

In this study, composite carbon membranes were pre-ared from PPESK by incoporating with zeolite (ZSM-5) orolyvinylpyrrolidone (PVP). The gas permeation property foromposite carbon membranes were markedly influenced by

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tion Technology 60 (2008) 259–263 263

he thermal degradation behaviour of PVP and the gas trans-ortation property of ZSM-5. Introduction of thermally labileolymer (PVP) leads to the formation of porous structures inhe carbon membranes during pyrolysis. Addition of microp-rous molecular sieving zeolite materials (ZSM-5) reduces theransportation resistance of gases by providing additional path-ays in carbon membranes. The two additives can drastically

mprove the gas permeability of H2, CO2 and O2 by 7–20 timeslong with the reduction in the selectivity of H2/N2, CO2/N2nd O2/N2 by 35.2–90.4% for resulting composite carbon mem-ranes. The composite carbon membranes from PPESK loadingith PVP and ZSM-5 are good candidate membranes for gas

eparation.

cknowledgments

This work was financially supported by the National Natu-al Science Foundation of China (No. 20276008), the Nationalasic Research Program of China (G2003CB615806), the Pro-ram for New Century Excellent Talents in Universities of ChinaNo. NCET-04-0274).

eferences

[1] P. Pandey, R.S. Chauhan, Prog. Polym. Sci. 26 (2001) 853.[2] W.J. Koros, R. Mahajan, J. Membr. Sci. 175 (2000) 181.[3] J.W. Phair, R. Donelson, Ind. Eng. Chem. Res. 45 (2006) 5657.[4] C.E. Powell, G.G. Qiao, J. Membr. Sci. 279 (2006) 1.[5] A. Basu, J. Akhtar, M.H. Rahman, M.R. Islam, Pet. Sci. Technol. 22 (2004)

1343.[6] R.W. Baker, Ind. Eng. Chem. Res. 41 (2002) 1393.[7] K.M. Steel, W.J. Koros, Carbon 43 (2005) 1843.[8] H.B. Park, I.Y. Suh, Y.M. Lee, Chem. Mater. 14 (2002) 3034.[9] K. Haraya, H. Suda, H. Yanagishita, Chem. Commun. (1995) 1781.10] J.-I. Hayashi, M. Yamamoto, K. Kusakabe, S. Morooka, Ind. Eng. Chem.

Res. 36 (1997) 2134.11] J.-I. Hayashi, H. Mizuta, M. Yamamoto, J. Membr. Sci. 124 (1997) 243.12] Y.K. Kim, H.B. Park, Y.M. Lee, J. Membr. Sci. 243 (2004) 9.13] J.N. Barsema, N.F.A. van der Vegt, G.H. Koops, M. Wessling, Adv. Funct.

Mater. 15 (2005) 69.14] J.A. Lie, M.-B. HAAgg, Carbon 43 (2005) 2600.15] M.B. Shiflett, H.C. Foley, J. Membr. Sci. 179 (2000) 275.16] P.S. Tin, T.-S. Chung, L. Jiang, S. Kulprathipanja, Carbon 43 (2005) 2025.17] Q. Liu, T. Wang, C. Liang, B. Zhang, S. Liu, Y. Cao, J. Qiu, Chem. Mater.

18 (2006) 6283.18] B. Zhang, T. Wang, S. Zhang, J. Qiu, X. Jian, Carbon 44 (2006) 2764.19] X.G. Jian, Y. Dai, L. Zeng, R.X. Xu, J. Appl. Polym. Sci. 71 (1999) 2385.20] J.G.A.P. Filho, E.C. Gracilianoa, A.O.S. Silva, M.J.B. Souzab, A.S. Araujo,

Catal. Today 107–108 (2005) 507.21] M.J.A. Sales, S.C.L. Dias, J.A. Dias, T.A.P.F. Pimentel, Polym. Degrad.

Stab. 87 (2005) 153.22] E.L. Wu, S.L. Lawton, D.H. Olson, A.C. Rohrman Jr., G.T. Kokotailo, J.

Phys. Chem. 83 (1979) 2777.23] P.A. Barrett, T. Boix, M. Puche, D.H. Olson, E. Jordan, H. Koller, M.A.

Chamblor, Chem. Commun. (2003) 2114.24] Y. Li, T.-S. Chung, C. Cao, S. Kulprathipanja, J. Membr. Sci. 260 (2005)

45.25] A. Tavolaro, E. Drioli, Adv. Mater. 11 (1999) 975.

66 (2003) 181.27] L.M. Robeson, J. Membr. Sci. 62 (1991) 165.28] N. Nishiyama, W. Momose, Y. Engashira, K. Ueyama, J. Chem. Eng. Jpn.

36 (2003) 603.