NOTES. Can. J. Chem. Downloaded from by on 05/01/18

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1 NOTES A NEW TYPE OF ULTRAFILTER INTRODUCTION Most ultrafilters (2, 3, 6) have perforated or porous plates as membrane supports, use membranes of small area, and to get appreciable rates of filtration are operated at relatively high pressures. The solution, being under pressure, cannot readily be stirred and, becoming increasingly concentrated on the membrane surface, has a tendency to block the membrane pores (I). Such ultrafilters are not suitable for handling large quantities of materials. A simple and inexpensive method of supportiilg membranes which was developed by the authors for an osmometer cell and which inhibits ballooning in membranes as large as 200 sq. cm. in area is described elsewhere (4). In the present note we describe an ultrafiltration unit consisting of a number of slightly modified osmometer cells which has been used for the fractionation of ligninsulphonates (5). Since the membrane area is large, the unit may be used at relatively low pressure differentials using water aspirators. It is fully automatic, simple to construct, leakproof, and allows thorough stirring of the liquid. ULTRAFILTER CELLS Each ultrafilter cell consists mainly of two lucite dislts and two rubber rings (Fig. I). The membrane is clamped between the rubber rings, reinforced with fine-mesh stainless steel screens, and supported on both sides by two layers of tightly packed glass beads. To avoid leakage at the edges of the screens, rings of dental dam rubber are placed between them and the membrane and between them and the rubber rings, forming the body of the cell. When the unit is compressed, the dental dam penetrates into the meshes of the screen reinforcers and seals the cell effectively. The necessary parts for a typical cell are described in Table I. A simple leakproof connection between the glass parts and the lucite can be made without cement. For this purpose tygon tubing with 1.5 mm. wall thicliness and 10 mm. O.D. is placed into 8 mm. bore holes in the lucite. To introduce the tubing into the hole the end of it is cut off conically along the length and pulled into the hole by the tongue thus formed, and the tongue is then cut away. Each lucite disk is equipped with the connectors before assembling the cell. To prevent glass beads from droppiilg into the tygon tubing, a small piece of stainless steel screen is placed in the tubing. 'Holder of the Anglo-Paper Research Fellowship and of a Studentship frovz the National Researclt Council of Canada. Present address: Indz~strial Cellulose Research Ltd., Hawkesbury, Ontarzo.

2 CANADIAN JOURNAL OF CHEMISTRY. VOL. 33 FRONT VIEW SECTION ' A-A 3 ' FIG. 1. Details of the ultrafilter cell: (1) lucite dislcs, (2) rubber rings, (3) glass beads, (4) dental dam gaskets, (5) stainless steel screens, (6) membrane, (7) inlet hole. TABLE I CELL COMPONENTS 1. 2 lucite dislcs Diameter 25 cm. Thickness 1 cm. 8 holes with centers on a 23 cm. diameter circle concentric with the dislcs to accommodate the screws 2 holes with centers on the same diameter 17.5 cm. apart-bore diameter 8 mm rubber rings Inside diameter 18 cm. Outside diameter 25 cm. Thickness 0.3 to 0.32 cm. 8 holes drilled in identical positions as in the lucite for holding the screws 3. 4 dental dam gaskets Inside diameter 18 cm. Outside diameter 22 cm. Thickness about 0.03 cm stainless steel screens 5. 1 membrane Diameter 20 cm. Diameter 21 cm. 125 mesh 6. Glass beads 7. 8 screws, 8 wing nuts, 16 washers Diameter 0.28 to 0.3 cm. THE CIRCULATING PUMP Stirring in the cells is provided by circulating the solution from a reservoir. The pumping unit, shown in detail in Fig. 2, coilsists of a membrane pump (A) governed by an oscillating mercury pump (B).

3 GARDON AND MASON: ULTRAFILTER MERCURY RUBBER FIG. 2. Details of the circulating pump: (A) membrane pump, (a) stopcock, (b) inlet holes, (c) dental dam membrane, (d) valves, (B) oscillatillg mercury pump, (e) valve, (f) cork floater. The construction of the membrane pump is similar to that of the ultrafilter cells. It is made up of two lucite dislts of 12 cm. diameter, two rubber rings 5 mm. thick with 10 cm. outside diameter and 8 cm. inside diameter, and an elastic dental dam membrane dislt (c) of 10 cm. diameter clamped between the rubber rings. To accommodate the screws, both lucite disks have four holes with centers on an I1 cm. diameter circle conceiltric with the disks and two 8 mm. bore holes (b), with centers 3.75 cm. from the center of the dislt and on the same diameter, in which tygon tubing is placed in the same manner as described above. The membrane is made of two dental dam rubber sheets stuck together with silicone grease. This method of preparation gives the membrane a life of at least several months of continuous operation. The two check valves (d) are made of spherical glass joints of 12 mm. diameter. The oscillating mercury pump functions as follows. By applying vacuum in the upper chamber, mercury is sucked into it. The rising mercury raises the cork float (f) and thus opens valve (e). Consequently air enters into the upper chamber, the mercury level drops, valve (e) is closed, and a new pumping cycle starts. The lower chamber of this pump is connected with the membrane pump, and the membrane in the latter forcibly has to follow the movements of the mercury. In practice the oscillating mercury pump is put into

4 1628 CANADIAN JOURNAL OF CHEMISTRY. VOL. 33 operation first, independently of the membrane pump, and stopcock (a) is closed afterwards. The difference in level between the mercury in the lower and upper chambers should alternate between 10 and 14 cm. The diameter in both the upper and lower chambers of the oscillating mercury pump is 7 cm. and the length of the pump is 25 cm. The valve (e) is made of a 12 mm. diameter spherical glass joint. The capacity of this pumping unit is around 200 cc. per minute. OPERATION The assembled ultrafilter is shown in Fig. 3. The solution chambers of the different cells are connected in series and the solution is circulated from reservoir (C) to provide adequate stirring. LUCITE SOLUTION RUBBER r.,,..r. FIG. 3. The assembled ultrafiltration unit: (A) water reservoir, (B) constant head device, (b) solution trap, (C) solution reservoir, (D) membrane pump, (d) valves, (E) ultrafilter cells, (e) stopcocks, (F) suction flask, reservoir for ultrafiltrate, (G) glass wool filter. The volume of the liquor is kept constant by the constant head device (B). If the level in reservoir (C) drops sufficiently to expose the end of the tube (B) to the air, air will enter into the distilled water container (A) and consequently water will flow into reservoir (C). The rising level in the reservoir closes tube (B) and thus stops the water flow. Trap (b) is needed to prevent the solution from entering the distilled water container. The ultrafiltrate is fed into suction flask (F) by gravity. Keeping the residual liquor at constant volume allows good control of the process. If Vo is the volume of the residual liquor, K the volume of ultrafiltrate produced in unit time, c(t) the concentration of the component to be removed, and y c(t) its concentration in the ultrafiltrate passing through the membrane at time t (y is the partition coefficient between the solutions inside and outside

5 GARDON AND MASON: ULTRAFILTER 1629 the membrane, 0 < y < I ), the following relation may be derived for the variation of c(t) with time: - Vo dc = y K ~(t) dt, which on integration yields c(t) = c(o).e-vktlv*. By determining K, Vo, co, and several values of c(t) at different time intervals, y can be evaluated and the time necessary for the removal of any arbitrary portion of the component in question can be calculated. The rate of ultrafiltration is readily varied by changing the number of cells in the unit. 1. BECHHOLD, H. Z. physik. Chem. 60: CUMMINGS, A. P. Technique of organic chemistry. Vol Edited by A. Weissberger. Interscience Publishers, Inc., New York pp FERRY, J. D. Chem. Revs. 18: GARDON, J. L. and MASON, S. G. Can. J. Chem. 33: GARDON, J. L. and MASON, S. G. Can. J. Chem. 33: MCBAIN, J. W. Colloid science. D. C. Heath & Company, Boston pp RECEIVED JUNE 10, PULP AND PAPER RESEARCH INSTITUTE OF CANADA, AND CHEMISTRY DEPARTMENT, MCGILL UNIVERSITY, MONTREAL, QUEBEC. THE REMOVAL OF FLUORIDE ION FROM AQUEOUS SOLUTION BY MAGNESIUM OXIDE BY JOHN C. BARTLET AND ROSS A. CHAPMAN' Venltateswarlu and Karayana Rao (1, 2,3) reported that magnesium oxide taltes up fluoride ion from hot solution, basic to phenolphthalein. Light magnesiu~ll oxide was reported to remove up to 20 pgm. of fluoride per mgm. of magnesium oxide. This procedure was used to reduce the fluoride content of water (1, 2) and as an aid in the determination of fluoride in tea (3). In this laboratory, it was found that the removal of fluoride could be increased manj,fold if the original solution was acidic. Table I shows the effect TABLE I THE EFFECT OF ph ON THE TAKING UP OF FLUORIDE FROM AQUEOUS SOLUTION BY hiagnesiuhz OXIDE ph % Removal Before addition After addition of fluoride of NIgO of MgO 'Prese~zt address: World Health Organisation, Geneva, Switserland.

Agilent InfinityLab Preparative Flow Cells for MWD & DAD

Agilent InfinityLab Preparative Flow Cells for MWD & DAD Technical Note This technical note describes the preparative flow cells for the Agilent 1260 Infinity II DAD WR (G7115A) and Agilent 1260 Infinity