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Pore size control (2)

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News and Views Pore size control (1) Pore size control (2) Workers at Kyoto Un/versity, Japan have been looking at ways to control the pore s/ze In s/I/ca-based ox/de gels. The gels, which have pro-range Interconnected pore morphologies, are prepared by the spmodal decomposition of alkoxy-der/ved gel forming solutions and it has been found that solvent exchange treatments on the wet gels can dete~mlne the pore s/ze range In the dried state. Incorporation of various water-soluble organic polymers In the hydrolysis and polycondensation of alkoxy~lmne under wa~er-rich conditions leads to the formation of gels with p~n-rAn~e Interconnected pores. The macropore structure of the gels can be regulated by changing the solubflfly of the polymers or the polymerization rate of the s/I/ca, both of which Influence the spinodal decompos/tion behavlour at the gel forming stage. Under acld-catalyzed and water-poor conditions, with addition of form~mlde, hydrolys/s of alkoxysflane results In gels which can have pore s/zes going from several nm up to the pm range. Further Information.from.. Dr Kazuki Nakanlshl, Department of lndustrlal Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606-01, Japan. In the USA, a research group hm~ been fabricating ceramic membranes with ~ored pore size and distribution by a method which entAtl~ the Incorporation of carbon fibres as a fugitive phase m the ceram/c matrl~ The fugitive carbon fibre phase Is subsequently removed by oxidation and the result Is oriented microchannels of well-controlled dimensions In the matr~ The US team has been undertaking bas/c studies on the feaslbfllty of the technlque using polyacrylomtrlle (PAN) based fibres In a Pyrex glass matrl~ The mechantsm and control of the ox/dation process for the fibre removal/s still an area that requlres work, but it bAR been confirmed that on removal the resultant mlcrochannels represent the original carbon fibre size (about 5 ~m In diameter) and shape. Mlcrochannel alze and shape can be tailored by proper fibre selection and m/crochannel orientation Porous glass membrane A porous glass membrane prepared from sodlum borosfl/cate glass containing ZrO2 and CaO -- composltion (wt%) $IO2 (53), B203 (24.5), Na20 (5.5), Ca<:) (8), ZrO2 (6),/11203 (3) -- is being character/zed at the, Government Industrial Research Institute/n Osaka, Japan. To produce the membrane the borate-rlch phase is leached by aqueous solution of 1N HNOs for 48 hours at 98 "C. The result Is a median pore diameter of 3.0--3.5 nm. Surface modification treatments are currently being e~mlned and tested for their effect on the separation of gaseous CO2 from a 50/50 m/xture of CO2 and N2. Two treatments look promising: the first Involves dlppL-.g the glass membrane In an aqueous n/trate solution of potassinm, magnes/um, silver and chromlum and a subsequent bak/ng at the decomposltion temperatures of the nltrate salts; In the second, the membrane Is dipped tn xylene and subsequently baked In a reducing atmosphere. Measurements of permeabtl/ties and CO2 separation factor were made at temperatures from 30 to 400°C. Although In general both variables decrease wlth Increased temperature there is a beneficial effect with the second treatment which maintains a good separation factor even at the higher temperatures. Further Information frorrc Dr Tetsuo Yazawa, Government Industrial Research Institute, Osaka Mkiorigaoka l-chome, Ik~da-shl, Osaka 563, Japan. Tel +81 727 51 8531. (a) Mb~ostructure of a PAN-fibre~Pyrex composite after wddativn of the carbon flbres at 793 K; (b) A higher magnylcation vtew of individual ~crochannels. Membrane Technology No. 29 3
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Page 1: Pore size control (2)

N e w s a n d V i e w s

Pore s i z e c o n t r o l (1) Pore s i z e c o n t r o l (2) Workers a t Kyoto Un/versity, J a p a n have been looking a t ways to control the pore s/ze In s /I /ca-based ox/de gels. The gels, which have pro-range Interconnected pore morphologies, a re p repa red b y the spmoda l decomposi t ion of alkoxy-der/ved gel forming solut ions and it h a s been found tha t solvent exchange t r ea tmen t s on the wet gels can dete~mlne the pore s/ze range In the dried s ta te .

Incorporat ion of var ious water-soluble organic polymers In the hydrolysis a n d polycondensat ion of alkoxy~lmne unde r wa~er-rich condit ions leads to the format ion of gels with p~n-rAn~e Interconnected pores. The macropore s t ruc tu re of the gels can be regulated by changing the solubflfly of the polymers or the polymerizat ion ra te of the s/I/ca, bo th of which Influence the spinodal decompos/ t ion behavlour at the gel forming stage. Under acld-catalyzed a n d water-poor conditions, with addit ion of form~mlde, hydrolys/s of alkoxysflane resu l t s In gels which can have pore s/zes going from several n m u p to the pm range.

Further Information.from.. Dr Kazuki Nakanlshl, Department of lndustrlal Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606-01, Japan.

In the USA, a r e sea rch group hm~ been fabricat ing ceramic m e m b r a n e s wi th ~ o r e d pore size a n d dis tr ibut ion b y a me thod which entAtl~ the Incorporat ion of ca rbon fibres a s a fugitive phase m the ceram/c m a t r l ~ The fugitive ca rbon fibre phase Is subsequen t ly removed b y oxidation and the resul t Is oriented microchanne ls of well-controlled dimensions In the m a t r ~

The US t eam h a s been under t ak ing bas/c s tudies on the feaslbfllty of the technlque us ing polyacrylomtrl le (PAN) b a s e d fibres In a Pyrex glass m a t r l ~ The m e c h a n t s m a n d control of the ox/dation process for the fibre r e m o v a l / s still a n a rea tha t requlres work, b u t it bAR b e e n conf i rmed tha t on removal the resu l t an t mlc rochanne l s represen t the original ca rbon fibre size (about 5 ~m In diameter) and shape. Mlcrochannel alze a n d s h a p e can be tailored by proper fibre selection a n d m/crochanne l orientat ion

P o r o u s g lass m e m b r a n e A porous glass m e m b r a n e p repa red f rom sodlum borosfl/cate glass containing ZrO2 and CaO - - composl t ion (wt%) $IO2 (53), B203 (24.5), Na20 (5.5), Ca<:) (8), ZrO2 (6),/11203 (3) - - is being character /zed at the, Government Industr ia l Research I n s t i t u t e / n Osaka, J apan . To p roduce the m e m b r a n e the borate- r lch p h a s e is leached by aqueous solution of 1N HNOs for 48 hou r s a t 98 "C. The resul t Is a median pore d iameter of 3.0--3.5 nm. Surface modification t r ea tmen t s a re cur ren t ly being e ~ m l n e d and tes ted for their effect on the separa t ion of gaseous CO2 from a 5 0 / 5 0 m/x ture of CO2 a n d N2.

Two t r ea tmen t s look promising: the first Involves dlppL-.g the glass m e m b r a n e In a n aqueous n/ t ra te solution of po tass inm, magnes /um, silver and ch romlum and a subsequen t bak /ng a t the decomposl t ion t empera tu re s of the nl t ra te salts; In the second, the m e m b r a n e Is d ipped tn xylene and subsequen t ly b a k e d In a reducing a tmosphere . Measu remen t s of permeabt l / t ies and CO2 separa t ion factor were m a d e a t t empera tu re s f rom 30 to 400°C.

Although In general bo th var iables decrease wlth Increased t empe ra tu r e there is a beneficial effect with the second t r ea tmen t which ma in t a in s a good separa t ion factor even a t the higher tempera tures .

Further Information frorrc Dr Tetsuo Yazawa, Government Industrial Research Institute, Osaka Mkiorigaoka l-chome, Ik~da-shl, Osaka 563, Japan. Tel +81 727 51 8531.

(a) Mb~ostructure of a PAN-fibre~Pyrex composite after wddativn of the carbon flbres at 793 K; (b) A higher magnylcation vtew of individual ~crochannels.

Membrane Technology No. 29 3

Page 2: Pore size control (2)

N e w s a n d V i e w s

could be fur ther enhanced b y designing and controlling the fibre archi tec ture dur ing composi te fabrication.

Further Information frem: Dr Eric R. Trumbauer, Center for Advanced Materials, The Pennsylvania State University, University Park, PA 16802, USA. Tel +1 814 865 6331. Fax +1 814 863 4627.

Replacing dis t i l la t ion ? A rev/ew of the p rospec t s for dismlnt ion (Chemical Engineering, December 1992, p p 86-98) is confident tha t improvemen t s in energy efficiency of dis t l l~t ion co lumns w/ll keep the compet ing separa t ion systems, including m e m b r a n e separa t ions , fighting each other for a small port /on of the separa t /ons act/vRy m the chemical p rocess indus t r /es (CPI). J / m m y H u m p h r e y and F rank Selbert note tha t d/sH11ntion current ly accoun t s for more appl /cat lons t h a n all the other processes - - extract/on, adsorpt ion, crystalll,~t~lon and m e m b r a n e - b a s e d technologies - - combined, and es t imate tha t more t h a n 95% of the energy cons umed by separa t ion p rocesses in the CPI goes for distillation.

It s eems clear tha t m e m b r a n e - b a s e d rou tes and some of the other p rocesses have the potent ial for s/gn/flcant energy savings, so what are the obstacles? The au tho r s cite the higher capital costs of al ternat ive processes relathre to ctistfllation, par t icular ly for high capaci ty applications. Also, the wholesale rep lacement of existing co lumns requires tha t existing equ ipment be scrapped, a n expensive propoaltion, a n d mla they say m e a n s tha t the newer processes will have to wait on new p lan t cons t ruc t ion and fur ther cost reductions.

Further informatWn from: Dr A.F. Selbert, Separations Technology Program, The University of Texas at Austln, Austin, TX 78712, USA. Tel +1 512 471 7063.

Envi nment monit ng s t a y One of the las t act ions of the UK's National Economic Development Council before Its demise a t the end of 1992 was to publ i sh the resu l t s of a survey of The Environmental MonUoring Business in the UK. The report , subt i t led ~what buye r s want , need and can afford', sugges ts ~hat the UK m a r k e t in air a n d water mon/tor ing s t ands a t abou t £140 m f l t o n a n d / s expected to grow at abou t 10% a year. Developments In new sensor technolog/es a re br/efly discussed, a l though the bu lk of the 37-page repor t is a m a rke t a s s e s s m e n t n |med a t compan ies supplying or cons/dering supplying this type of equipment .

Copies of the report are avaaable for £15 from: Nicola Mosley, GAMBICA, 8 Leicester Street, London WC2H 7BN, UI~ Tel +44 (0)71 437 0878. Fax +44 (0)71 437 4901.

Books Biosemmrs and CAmmlmd m ~ o ~ : P e r f o r m a n c e t h r o u g h P o l y m e r l e Mate r l s l s , I' O B d e U u n a n d a W a g 0ki.) ACS Symposium Serles No 487, 1992, 332pp, 879.95, ISBN 0-8412-2218-5

Coverage includes permselect tve m e m b r a n e s and tmmobll/zation for enzyme sys tems, electropolymerlzed thin films, polylner m e m b r a n e s on p lanar subs t ra tes , a n d hydra t /on-dependent polymer appl/cat/ons.

R e c o v e r y P r o c e s s e s for ~ Matm/a l s , J F K e n n e d y a n d J M S C a l m d (Bds) Wiley, 1993, 592 pp, 8100, ISBN 0471 93349 X

Organl~,ed tn 18 chap te r s covering all the principal downs t ream process ing opera t ions - - including m e m b r a n e separa t ions n and w/th a n introduct ion to blolog/cal p roduc t s a n d the s t a b f R y of blomolecules dur ing processing.

Wastes Mansgement Intemat /onah A D/rectory of Manufacturers and S ~ v / c e s , a ~ tiM) Wiley, 1993, 650 pp, £95, ISBN 0471 93328 7

First edlt/on of wha t is in tended to be a n annua l ly revised Directory covering all a spec t s of was te m a n a g e m e n t f rom collection to disposal m bo th I/qu/d and sol/d wastes . Entr /es will be Ested in count ry order bu t indexed to allow use r s to find and compare the al ternative solut ions available worldw/de for a par t icular problem.

for soft cont tion A new set of NIST S tanda rd Reference Mater/a/s will help in the a s s e s s m e n t of the effic/ency of processes to remove tox/c chem/cals f rom soft a t haza rdous waste sites. NIST - - the US National Inst i tute for Science a n d Technology - - a l ready provldes SRMs for water a n d air pollution, b u t the new soft s amples are the first cert/fled a t the InsUtute. Three different soft samples a re certified for basel ine, modera te and high levels of t race e lements as m o m t o r e d by the US Envi ronment Protectton Agency. The soft SRMs (2709, 2710 a n d 271 I) cost 8193 each.

Further information on all of the pollution SRMs from: NIST, Stan~o_rd Reference Mater~!~ Program, Room 205, Building 202, Gcdthersburg, MD 20899-0001, US/L Tel +1 301 975 6776. Fax +1 301 948 3 730.

4 Membrane Technology No. 29


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