Ceramic Processing Research

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1 Jurnal f Ceramic Prcessing Research. Vl. 10, N. 3, pp. 359~363 (009) J O U R N A L O F Ceramic Prcessing Research H permeable nanprus SiC membrane fr an IGCC applicatin M Hyun Suh a, W-Teck Kwn a, Eun Bi Kim a, S-Ryng Kim a, Seng Yul Bae b, D Jin Chi c and Yunghee Kim a, * a Krea Institute f Ceramic Engineering and Technlgy, Krea b Hanyang University, Krea c Ynsei University, Krea Ceramic membranes having less than 1nm size pres have great ptential fr gas separatin at high temperature due t their gd thermal stability. Mrever, nanprus silicn carbide membranes have a ptential applicatin under hydrthermal cnditins at high temperatures since they are highly stable at high temperature. In this research, a nanprus SiC membrane has been develped n a prus alumina supprt using a preceramic plymer. Fr a gradual pre size distributin, γ-al O 3 interlayer was intrduced in between the nanprus SiC membrane and prus alumina supprt. The SiC membrane having a cntrlled pre size was characterized by SEM and pre size measurements. The hydrgen permeability and selectivity twards nitrgen gas f the membrane develped were mle/m s pa and 4.5, respectively. The nanprus hydrgen selective SiC membrane shws a prmising applicatin in hydrgen separatin frm cal gasificatin such as in the integrated gasificatin cmbined cycle (IGCC). Key wrds: SiC nanprus membrane, Hydrgen separatin, IGCC. Intrductin In recent years there has been cnsiderable interest in the develpment f inrganic membranes fr the separatin f hydrgen frm a mixed gas stream [1-7]. Inrganic membranes can be used under cnditins such as at high temperature and in reactive envirnments where rganic membranes are nt usable. Amngst the inrganic membranes fr the separatin f hydrgen, nanprus inrganic membranes ffer many advantages ver dense palladium membranes and in-transprt membranes. Nanprus inrganic membranes that can be used at higher pressures can be fabricated frm a variety f materials and are relatively cheaper as cmpared t palladium membranes. Thus, there have been attempts t prduce nanprus inrganic membranes f alumina, silica, zelites, silicn carbide, etc. Hwever, silica and alumina membranes shw instability at high temperatures specially in the presence f steam. The main advantage f silicn carbide is a cmbinatin f strength, thermal and chemical stability at high temperatures, especially under hydrthermal cnditins. Fr highly efficient gas separatin, the cntrl f the effective mean pre diameter is very imprtant. As a very small pre size preferably less than 1 nm is required fr hydrgen separatin, the membrane must be very thin. There are relatively few reprts discussing the cntrl f the effective mean pre diameter. Recently, sme researchers have tried t cntrl the pre size by a multi-layer *Crrespnding authr: Tel : Fax: yhkkim@kicet.re.kr cmpsite structured membrane and pyrlysis f plymer precursrs. The derived micrstructure and chemical cmpsitins f the final prduct are strngly dependent n the cmpsitin f the precursr materials used. The preparatin f ceramics frm plymeric precursrs has generated a great deal f interest because it allws the prcessing f ceramics at lw temperatures as cmpared t the high sintering temperatures required in the cnventinal pwder rutes [8-10]. Suda and cwrkers [7], used a plycarbsilane that they cured in xygen t prepare a Si-O-C membranes n α-al O 3 tubular substrates with an xygen cntent f wt%, using plystylene (PS) as the pre frmer. In this study, fr the purpse f hydrgen separatin frm CO, SiC membranes n prus alumina supprts having less than 1nm pre size have been develped by intrducing a γ-al O 3 interlayer in between the nanprus SiC membrane and prus alumina supprt fr a gradual pre size distributin. Experimental Prcedure Cating the γ-al O 3 interlayer n a prus alumina supprt A behmite slutin was btained frm Nanpre Materials C. Ltd. Krea, which was synthesized by hydrlysis fllwed by the peptizatin f aluminium sec butxide. The behmite slutin btained was spin cated and penetrated int the near surface layer f the prus alumina supprt (5 mm diameter, mm thickness). The behmite-cated prus alumina supprt was then heated at varius temperatures in the range f C fr 1 h in 359

2 360 M Hyun Suh, W-Teck Kwn, Eun Bi Kim, S-Ryng Kim, Seng Yul Bae, D Jin Chi and Yunghee Kim air. The pre size was determined by nitrgen physisrptin using a Micrmeritics ASAP 010. Preparatin f nanprus SiC membrane 0% f hydridplycarbsilane (HPCS, starfiresystem C.) in cyclhexane was spin cated nt the tp f the γ-alo3 interlayer and cnverted int an amrphus SiC layer by heat treatment at 600 C with a heating rate f 10 C/min, fllwed by heat treatment at 900 C fr 1h with a heating rate f 10 C /min under an inert atmsphere. A Rigaku D/max-RINT 500 diffractmeter with Cu Kα radiatin was used fr the XRD analysis f the samples. A Hitachi, S-4100 scanning electrn micrscpe was used fr mrphlgical bservatins f SiC nanprus membranes. The pre size was determined by argn physisrptin using a Micrmeritics ASAP 010. analyzed by XRD. The diffractin peaks f the sample arund 35, 60, and 73 crrespnded t the β-sic and it is cnfirmed that hydridplycarbsilane is suitable as a SiC ceramic precursr (Fig. 1). A slutin f 5 wt.% f hydridplycarbsilane in cyclhexane was spin cated directly nt the tp f the prus alumina supprt and cnverted int an amrphus SiC layer by heat treatment at 600 C with a heating rate f 10 C/min, fllwed by heat treatment at 900 C fr 1 h with a heating rate f 10C /min under an inert atmsphere. Hwever, as shwn in Fig., hydridplycarbsilane slutin had entirely penetrated int the pres f the alumina supprt and n SiC membrane was frmed. A SiC membrane was frmed using a 0 wt.% f hydridplycarbsilane slutin, hwever mst f the Gas Separatin measurement Gas permeatin experiments were perfrmed at rm temperature using a single cmpnent hydrgen and nitrgen gas measurement apparatus. Each flw rate was measured with a sap film flw meter. The applied pressure was 6 psi (41,370 Pa) and permeance rate and selectivity were btained frm the fllwing equatins: Permeance Rate Q1 = Ai/(Pri Ppi) S t, (1) Selectivity α = QH/QN () Q: Permeance Rate (ml/m s pa), A: Permeate mle (ml), Pr: Feed Pressure (Pa), Pp: Permeate pressure (Pa) S: Membrane area (m), T: Time (secnds), i: H, N Result and Discussin In rder t examine the pyrlysis residue f hydridplycarbsilane which was used as the SiC ceramic precursr, the sample after heat treatment at 1,00 C fr 1 h under an Ar atmsphere was crushed int a pwdered frm and X-ray diffractin pattern f heat treated HPCS (hydridplycarbsilane) which is the preceramic plymer after heat treatment at 100 C fr 1 h in an argn atmsphere. Fig. 1. SEM data f a SiC membrane prepared at 900 C by a spin cating methd using a 5 wt.% preceramic precursr in cyclhexane (a) surface (b) crss sectin. Fig..

3 H permeable nanprus SiC membrane fr an IGCC applicatin 361 Variatin f average pre diameter f a γ-al O cated prus alumina supprt with different dehydrxilatin temperatures. Fig SEM data f a SiC membrane prepared at 900 C by a spin cating methd using a 0 wt.% preceramic precursr in cyclhexane (a) surface (b) crss sectin. Fig. 3. hydridplycarbsilane had penetrated int the pres f the alumina supprt (Fig. 3). This is attributed t the large pre size f the alumina supprt. In ur experiments, we utilized cmmercial α-alo3 supprts with an average pre size f 100 nm as the supprts fr the SiC membrane preparatin. T make nanprus SiC membranes having a pre size f less than 1 nm, an α-alo3 supprt with an average pre size f 100 nm was nt suitable. T achieve a gd quality nanprus membrane, it is necessary t design in a gradual pre size distributin. T btain an asymmetric pre size distributin, we intrduced a γ-alo3 interlayer in between the nanprus SiC membrane and prus alumina supprt using a behmite slutin. The average pre diameter varied in the range SEM data f a SiC membrane prepared n the tp f a γal O cated prus alumina supprt. Fig. 5. 3

4 36 M Hyun Suh, W-Teck Kwn, Eun Bi Kim, S-Ryng Kim, Seng Yul Bae, D Jin Chi and Yunghee Kim f nm fr the as dried behmite slutin heated in the range f C as shwn in Fig. 4. The pre size was fund t increase with the dehydrxilatin temperature. The increase in pre size was likely due t the lss f the O-H grups (dehydrxilatin) during heating. The pre size was fund t increase linearly with temperature up t 700 C abve which it was nn-linear. The nn-linearity abve 700 C might be due t the transfrmatin f γ-alumina int δ-alumina. In the present case the transfrmatin f γ-alumina t d-alumina may ccur between C. As shwn in Fig. 5, the SEM micrstructure f a SiC membrane with a γ-al O 3 interlayer des nt shw any penetratin f the preceramic plymer int the supprt after heat treatment at 900 C under an argn atmsphere. Pre size distributin measurements shw that the sample cntains arund 1 nm sized nanpres (Fig. 6). Als nanpres existing in a SiC membrane are knwn t be able t be selectively mre permeable t H gas than CO, CO, N gases. As shwn in Table 1, the hydrgen gas permeance f a SiC membrane with a γ-al O 3 interlayer was mle/m s pa and the hydrgen selectivity tward N gas was 4.5. Hwever, the hydrgen selectivity f a SiC membrane withut a γ-al O 3 interlayer was 4.37 and this value is similar t the Kundsen diffusin selectivity fr H /N, which is 3.74 [11]. In the Knudsen flw regime, selectivity is based n the reverse square rt rati f the mlecular weights f A and B : a AB =[M B /M A ] 1/ [1]. Cnclusins Nanprus SiC membranes having less than 1 nm pre size were fabricated n prus alumina substrates. Fr a gradual pre size distributin, a γ-al O 3 interlayer was intrduced in between the nanprus SiC membrane and a prus alumina supprt. T prepare SiC nanprus membranes, 0 wt.% hydridplycarbsilane was spin cated and penetrated int the near surface layer f the prus alumina substrate. Then, the surface layer was cnverted int amrphus SiC layer by heat treatment at 900 C under an inert atmsphere. SiC cated prus alumina pssesses an asymmetric pre size distributin. There are micrpres riginating frm the prus alumina substrate and nanpres derived frm the amrphus state f SiC membranes. The hydrgen gas permeance f the SiC membrane prepared was mle/m s pa and the hydrgen selectivity tward N gas was 4.5. The nanprus hydrgen selective SiC membranes develped shw prmise fr applicatin in hydrgen separatin frm cal gasificatin such as integrated gasificatin cmbined cycle (IGCC) Fig. 6. Pre size distributin f a SiC membrane prepared n the tp f a γ-al O 3 cated prus alumina supprt. Table 1. Hydregn permeance and separatin factr f the prepared membranes Samples Applied pressure H Flw N Flw H Permeance N Permeance Separatin Factr g-al O 3 cated a-al O 3 substrate SiC cated a-al O 3 substrate SiC/g-Al O 3 cated a-al O 3 substrate 6 psi (41,370 Pa).5 SCCM 5.7 SCCM mle/m S Pa mle/m S Pa psi (41,370 Pa) 0.5 SCCM 4.7 SCCM mle/m S Pa mle/m S Pa psi (41,370 Pa) 1.7 SCCM 0.0 SCCM mle/m S Pa > mle/m S Pa > 4.5

5 H permeable nanprus SiC membrane fr an IGCC applicatin 363 References 1. Y.S. Lin, Separatin and Purificatin Technlgy, 5 (001) M.H. Zahir, K. Sat and Y. Iwamt, J. Membr. Sci. 47 (005) G.R. Gavalas, C.E. Megiris and S.W. Nam, Chem. Eng. Sci. 44 (1989) N.K. Raman, C.J. Brinker: J. Membr. Sci. 105 (1995) B.K. Sea, K. And, K. Kusakabe and S. Mrka, J. Membr. Sci. 146[1] (1998), V. Suwanmethannd, E. G, P.K.T. Liu, G. Jhnstn, M. Sahimi and T. Tstsis, Ind. Eng. Chem. Res., 39 (000), H. Suda, H. Yamauchi, Y. Uchimaru, I. Fujiwara and K. Haraya, Desalinatin, 193 (006), Y.H. Kim, S.R. Kim, K.H. Ch, S.Y. Bae and W.T. Kwn, Materials Science frum, (006), S. Yajima, Y. Hasegawa, K.Okamura and T. Matsuzawa: Nature, 73 (1973), Y.H. Kim, S.J. Jung, H.R. Kim, H.D. Kim, D.G. Shin and D.H. Riu: Adv. in Tech. Of Mat. Prc. J., 6[] (004), R.A. Wach, M. Sugimt, A. Idesaki, M. Yshikawa, Materials Science and Engineering B, 140 (007), G.Q. Lu, J.C. Diniz, da Csta, M. Duke, S. Giessler, R. Sclw, R.H. Williams, T. Kreutz, J. Cllid and Interface Science, 314 (007),