Combined ion exchange and microfiltration

Transcription

1 Loughborough Univerity Intitutional epoitory Combined ion exchange and microfiltration Thi item wa ubmitted to Loughborough Univerity' Intitutional epoitory by the/an author. Citation: DAGOSAVAC, M.M., HOLDICH,.G. and VLADISAVLJEVIC, G., Combined ion exchange and microfiltration. DIAMOND'09 Conference Decommiioning, Immobiliation and Management of Nuclear Wate for Dipoal, 9-10 September 2009, York, UK. Additional Information: Thi conference paper wa preented at DIAMOND'09: Metadata ecord: Pleae cite the publihed verion.

2 Thi item wa ubmitted to Loughborough Intitutional epoitory ( by the author and i made available under the following Creative Common Licence condition. For the full text of thi licence, pleae go to:

3 DIAMOND 09 Conference Decommiioning, Immobiliation and Management of Nuclear Wate for Dipoal 9-10 September 2009 York, UK COMBINED ION EXCHANGE AND MICOFILTATION Marijana M. Dragoavac, ichard G. Holdich and Goran T. Vladiavljevic Department of Chemical Engineering, Loughborough Univerity ABSTACT The purpoe behind thi work i to produce polytyrene-divinylbenzene cation exchange rein particle at variou ize, maller than are conventionally available, and to ue them in a microfiltration proce; comparing the reult with conventional column operation. A a model ytem, for production of droplet uing membrane emulification, unflower oil (dicontinuou phae) and 2% Tween 20 olution (continuou phae) were ued. By increaing the hear at the membrane urface the droplet ize decreaed from 185 to 50 μm. In the eeded microfiltration proce, urface microfilter with lot without internal tortuoity were ued to minimize fouling. A filtration flux rate of 42 l m-2 h-1 wa achieved. ate of copper orption on to ion exchange rein were found to be dependent on ma tranport limitation due to aqueou film diffuion and internal particle diffuion. For prediction of copper orption a model that take into account both film and internal diffuion wa ued. Microfiltration combined with ion exchange ha the advantage of very fat kinetic, when compared to column ue, and may provide better utilization of the rein particle, depending on the internal diffuion coefficient of the tranferring pecie within the particle. INTODUCTION The reearch i focued on heavy metal cation preent in watewater from different indutrie including nuclear power plant, including: ceium (C + ), trontium (Sr 2+ ), and copper (Cu 2+ ). One of the method for removing heavy metal from watewater i treatment in ion exchange column. Column with tandard ion exchange rein have to fulfil the requirement that preure drop within the column i low o the bead ued in column are uually large (greater then 200 μm). There i a need that fine filtration, performed before the column, to enure that material will not depoit on the particle. The eaiet way to progre metal removal i to reduce the ize of particle, but maller particle lead to high preure drop, which i not practical in column ue. A Holdich et. al. reported (2006), decreaing the ion exchange bead diameter increaed the ion exchange utilization. They invetigated boron removal from water during eeded microfiltration (a hybrid proce which combine microfiltration together with ion exchange) and determined that at large particle ize the rein wa poorly utilized a only the layer cloe to the urface took ignificant concentration of boron. At the mall ize the rein wa better utilized, a the diffuion gradient within the rein bead wa teeper and boron wa more eaily tranported to the bead centre. They concluded that maller bead ize would increae the time before breakthrough and would provide better overall performance, but that mall ize may provide handling difficultie. So the bead hould be neither too mall, nor too large, and a ize of μm wa reported a a good ize. Small bead may be produced by cruhing conventional ion exchange bead, but cruhing ha two main problem: When cruhed they have wide ize ditribution, and irregular hape, Becaue of the wide ize ditribution they will need to be eparated into different fraction, thi i time conuming and doe not enure optimal performance. The project will make the ion exchange rein particle at the required ize and ue them in a microfiltration ytem. In uch a ytem ma tranfer i much fater and, once the tranfer coefficient are deduced the modelling will compare the reult with column ue. Microfiltration combined with ion exchanger may have everal potential application, e.g. adding ion exchange rein to a ytem containing activity in both water and olid phae it i poible to filter the water and upended olid through the bed of rein reulting in a ignificantly decontaminated tream. EXPEIMENTAL For production of ion exchange bead membrane emulification will be ued, and for the preliminary tet unflower oil wa ued to commiion the ytem. Conventional ion exchange rein wa ued (Dowex 50WX8) for removal of copper ion

4 a a tet model in the initial eeded microfiltration work. Emulification ued a Micropore Technologie Ltd. Diperion Cell, ee Figure 1. Thi device ue a 24 V DC motor to drive a paddle-blade tirrer, above the membrane urface (Figure 1). A membrane with a 10 μm pore ize wa ued. The dipered phae (unflower oil) wa injected through the membrane pore into the aqueou continuou phae. On Figure 1, for the membrane emulification follow the light grey (or yellow) line. Varian, UK). For microfiltration copper olution with concentration between 1 and 100 ppm were prepared. Ma of ion exchanger ued wa 0.1 or 1g. All microfiltration experiment were performed in the gla cell provided by Micropore Technology Ltd. UK, Figure 1. During all experiment a volume of 150ml wa maintained in the cell. A lotted nickel membrane wa fitted on the bottom of the gla cell. The membrane diameter wa.2 cm and the working area wa 8.4x10-4 m 2. Freh copper containing olution flowed into the cell (Influent) at the ame rate a permeate wa withdrawn from the cell (effluent). A peritaltic pump wa ued to induce the flow. At tart-up, the cell wa filled with ditilled water and known ma of rein wa added. A flow rate of 46 ml min -1 (42 lm -2 h -1 ) wa et. At predetermined time 10 ml of effluent ample wa collected and analyzed. If no ion exchange rein wa ued in the cell the ytem act a a CST (continuou tirred tank reactor) and can be modelled a uch. Figure 1. Equipment ued for production of droplet (light grey arrow and membrane with circular pore) and alo for microfiltration (dark grey arrow and lotted membrane) For the ion exchange tudie, all reagent ued were analytical grade chemical. Solution of copper ion with concentration between 1 and 100 ppm were made by diolving appropriate amount of Cu(NO ) 2.6H 2 0 (Sigma Aldrich, UK) in ditilled water. The ion exchange rein wa Dowex 50WX8 (trong acid cation rein containing 8% divinylbenzene) obtained from Sigma Aldrich. The mean ize and ize ditribution of Dowex 50WX wa determined by laer diffraction particle ize analyzer (LA-920, HOIBA). The mean ize wa 240 μm (Figure 2). Cumulative ma underize (%) Dowex Diameter (μm) Figure 2. Cumulative ditribution curve for Dowex 50WX Analyi of copper wa performed uing an Atomic Aborbance Spectrophotometer (Spectra AA-200 MODELLING COMBINED IX AND MICOFILTATION A ma balance for a well mixed ytem for copper can be expreed a below: dc V = F( Co C) m (1) where V i the liquid volume in the cell, C i the concentration in the olution (both in the cell and the exit), Co i the concentration in the feed to the cell, F i the feed flow rate, m i the ma of the rein in the cell and q i the average ma of copper per ma of rein. The average ma of copper per ma of rein can be obtained by integrating the local ma throughout the rein form 0 to 2 q( t) = q( r, t) r dr (2) 0 where i bead radiu and the diffuion equation for ma tranfer inide the particle i 1 = ( D r 2 ) 2 eff () t r where r i radial poition inide the particle and D eff i effective diffuion coefficient of cation inide the particle. The ma rate of cation entering the particle i m = ka( C C ) (4) where A i the urface area of the rein bead, C i the equilibrium concentration of cation at the urface of the rein and k i the ma tranfer

5 coefficient in the liquid phae. According to film theory D liq k = (5) δ where D liq i the diffuion coefficient of cation in liquid phae and δ i the film thickne (ditance over which the liquid phae diffuion take place). Froling equation i ued to evaluate k, uing Sherwood, Particle eynold and Schmi dimenionle number Sh = e lip Sc (6) k 2 Sh = D liq Sc = μ D liqu ρ ν lip 2ρ e lip = μ where μ i the dynamic liquid vicoity and ρ i liquid denity. Terminal velocity i depending on particle ize and for mall particle when Particle eynold number i maller than 0.2, terminal velocity may be calculated by Stoke law: ν lip = g 2 ( 2) ( ρ ρ ) 18μ (7) If Particle eynold number i larger than 0.2 variou correlation can be ued (Holdich 2002). For ma tranfer coefficient combination of Froling equation together with Sherwood dimenionle number can be ued. earranging the iotherm equilibrium concentration of cation at the urface of the particle can be expreed: C = b ( q q ) m q (8) The cation exchange rein ha a pherical hape, and uing pecific urface area of a phere, urface area can be expreed a following: m 6m 6m ρ = = A = (8) Vre in Ax ρ x V rein i rein particle volume, ρ i denity of the particle, A i urface area and x i diameter of the rein bead. Flux of the cation inide of the rein can be expreed a follow: ( C ) ka C = m = Aρ Deff m So the ma balance of the cation i: dc V = md r eff = F( Co C) mdeff (10) For olving of differential equation boundary condition have to be determined. At the tart cell ha freh liquid: q ( t = 0,0 r ) = 0 C ( t = 0 ) = 0 In the centre of the bead there i no cation at the centre (0). ( t 0) 0 = 0 (11) And for the full radiu of the bead () boundary condition i ( t 0) k = ( C C ) (12) Deff ρ The ytem of equation mut be olved imultaneouly in an equation olver capable of olving partial differential equation, PDESOL (Numerica, Dalla, USA) wa ued. A a tart, for model data the following were taken from Awang (2001). Table 1 Data neceary for modelling of ma tranfer during microfiltration with Dowex 50W8X 100 ion exchanger q m (mg mg -1 ) b(m g -1 ) D liq (m 2-1 ) D eff (m 2-1 ) ESULTS AND DISCUSION membrane emulification A a model ytem for production of droplet unflower oil and 2% Tween 20 olution wa ued. Figure how the influence of paddle tirrer rotation peed (i.e. hear) on droplet ize. From the figure it can be een that increaing the rotation peed decreae the droplet ize from 185 down to 50 μm. Alo hown on Figure are a few microcopic photograph of emulion at different rotation peed. d(n,0.5) / μm rpm 80 rpm d(n,0.5) at 0 L m -2 h ω / rpm Figure. Influence of rotation peed on droplet ize. combined ix and microfiltration

6 Starting copper concentration in the feed olution wa 1.2ppm when 0.1g of ion exchange rein wa ued and 1.5ppm when 1g of ion exchange rein wa ued. Experiment lated for For both mae of rein the experiment wa repeated and reult are preented in Figure 4. A can be een even after 5000, for both mae (0.1 and 1g), the rein wa not aturated: an approximately. contant effluent concentration wa reached which did not correpond to the inlet concentration (Co). Uing the previouly decribed model it wa determined that it would take 2.5 day to reach the inlet concentration and a few characteritic part on the modelled curve were deduced (Figure 4 A, B C and D). Copper concetration in effluent (ppm) A 1g Dowex Co=1.ppm; 0.1g Dowex Co=1.5ppm; Model for 1g ; Model for 0.1g ; B Copper concetration in effluent (ppm) Time () Figure 4. Different ma of ion exchanger. c c D D Time () From the Figure 4, it can be een that the increae of copper concentration in the effluent i very quick at the tart, and after that it reache a contant value (A-B). In order to tet the full capabilitie of the rein the concentration of influent wa increaed to 100 ppm (Figure 5). It can be een that the curve ha the expected region (A, B C and D). Thee arer explained a follow. egion A indicate a quick increae in effluent concentration and i the period when the aqueou film concentration gradient develop, hence all the ma tranfer reitance i in the aqueou film. Copper concentration in effluent (ppm) A B C D Time () Figure 5.. Different ma of ion exchanger. 0.1g of Dowex 100 CST (Model) When a uitable concentration gradient i achieved and the rein ha good internal diffuivity copper i eaily tranferred internally (region B). Internal tranfer of copper will continue until rein reitance to ma tranfer increae when copper concentration in the rein become high (region C), but at ome point the rein will become aturated (region D). CONCLUSIONS A a model ytem for production of droplet unflower oil wa injected in to 2% Tween 20 olution and droplet in the ize range between 184 and 50 μm were produced. Malik, et al. (2009) reported recently that it i poible to produce crolinked polytyrene co-divinylbenzene adorbent microphere with median diameter between 40 and 00 μm in a imilar device, and thi will be ued for future production of the ion exchange rein bead. In the eeded microfiltration proce, urface microfilter with lot without tortuoity were ued to minimize internal fouling. By uing eeded microfiltration a high filtrate flux rate 42 l m -2 h -1 wa achieved. ate of copper orption on to ion exchange rein were found to be dependent on ma tranport limitation, due to aqueou film diffuion and internal diffuion and a model uitable for it analyi (and column prediction) wa teted. Seeded microfiltration (microfiltration combined with ion exchange) may have everal potential engineering application, and may become a ueful laboratory technique for tranport property evaluation of rein particle and ytem. EFFEENCES AWANG, A..B., Seeded microfiltration of copper with modified activated carbon, PhD Thei, Loughborough Univerity. HOLDICH,.G., Fundamental of particle technology. MidlandIT, Shephed, UK. HOLDICH.G., CUMMING I.W., PENI S., Boron ma tranfer during eeded microfiltration. Chemical Engineering eearch and Deign, 84(1), pp MALIK, D., WEBB, C., HOLDICH,., AMSDEN, J., WAWICK, G., OCHE, I., WILLIAMS, D., TOCHIMCZUK, A., DALE, J. and HOENICH, N., Synthei and characterization of izeelective nanoporou polymeric adorbent for blood purification. Separation and Purification Technology, 66, pp