US3337445A - Multicelled electrodialysis apparatus including frictionally engaging components - Google Patents

Description

g- 22, 1967 s. KATZ 3,337,445

MULTICELLED ELECTRODIALYSIS APPARATUS INCLUDING FRICTIONALLY ENGAGING COMPONENTS Filed Oct. 29, 1962 3 Sheets-Sheet l INVENTOR. S A M K ATZ ATTORNEY Aug. 22, 196'? s T-z I 3,337,445

MULTICELLED ELECTRODfALYSIS APPARATUS INCLUDING FRICTIONALLY ENGAGING COMPONENTS Filed Oct. 29, 1962 3 Sheets-Sheet 2 INVENTOR. S A M K A TZ ATTORNEY Aug. 22, 19$? 5. KATZ 3,337,445

, MULTICELLED ELECTRODIALYSIS APPARATUS INCLUDING v FRICTIONALLY ENGAGING COMPONENTS Filed Oct. 29, 1962 3 Sheets-$heet 5 iFli r INVENTOR. S A M KATZ ATTORNEY INCLUDING FRICTIONALL E PONENTS Y NGAGING COM Sam Katz, Rockville,

of America as Navy Md., assignor to the United States represented by the Secretary of the Filed Oct. 29, 1962, Ser. No. 233,976 7 Claims. (Cl. 204--301) The invention described herein may be manufactured and used by or for the Government of the United States of Arnerlca for governmental purposes without the payment of any royalties thereon or therefor. The present invention relates generally to improvements in electrodialysis apparatus and the like and more particularly to a new and improved three-cell structure for removing electrolytes from solution.

Previous apparatus for removing ions from solution often required painstaking effort to prevent leaks, electrical malfunctions and temperature gradients during operation. A water-tight arrangement of parts was obtamed by adjusting the metal frames, supports and clamps misalignment of parts or to necessary adjustments during operatron, resulting in leakages from the various joints. In addition, the presence of metal in contact with glass vessels, wh ch were dripping with moisture, caused electrical shorting with concomitant loss of electrolytic action and considerable hazard to the operator.

The present invention provides an improved apparatus for dialyzlng solutions in which ionizable materials are sub ected to an electric potential and the ions are selectlvely transported through cation-permeable and anionpermeable membranes toward the cathode and anode electrodes, respectively. The present apparatus is consrderably simplified in structure and is better suited for the treatment of small batches of solutions by reducing the numebr of external joints which are prone to leak. The apparatus is also equipped with more efficient and convenient cooling means for effective dissipation of heat. Furthermore, the invention provides an apparatus which may be assembled and operate tures, metal frames, clamps and the like; a novel coupling arrangement in the parts provides both rigidity and effect1ve seahng means for the apparatus, yet the assembled parts may be easily detached for cleaning or adjusting.

The apparatus described herein is capable of desalting solut ons containing large molecules, such as polymers protems, dyes, etc., until the resulting material is present in a system of defined composition and concentration and essentially free from small ions. Similarly, the apparatus can be employed to remove ionizable substances, such as salts and low molecular weight polyampholytes from neufor example, salts from sugars, steroids pholipids from neutral lipids.

Therefore, it is an object of the present invention to provide a simple, more efficient apparatus for electrod1alys1s that overcomes the disadvantages of the prior art.

Another object of the invention is to reduce the complexity and bulk of the conventional three-cell dialysis apparatus to provide an improved structure which is especially useful for treating relatively small amounts of material.

A further object of the invention is to provide an apparatus for desalting proteins and other substances in solution wherein polarization at the electrodes is effectively minimized.

Further objects, features and advantages will more clearly appear from the following description taken in v United States Patent (1 without supporting struc- I connection with the accompanying drawings in which:

FIG. 1 is an exploded view of a preferred embodiment of the electrodialysis apparatus;

FIG. 2 is a front view of the apparatus which includes a vibrating type stirrer;

FIG. 3 is a cross-section of an exaggerated view showing coupling structure in the cells in accordance with one embodiment of the invention;

FIG. 3a shows the coupled arrangement of cells in accordance with the embodiment of FIG. 3;

FIG. 4 is a cross section of an exaggerated view showing an alternative coupling structure in the cells; and

FIG. 4a shows the coupled arrangement of the cells shown in FIG. 4.

According to the invention, a three-cell electrodialysis apparatus, which includes a center cell. and two end electrode cells, is formed into a unified, sealed body that is singularly free of all external metallic or other connecting elements. The cells are formed of aninsulating material, preferably of a transparent composition, such as glass or Lucite, to provide direct observation of the interior. The ends of the center cell are: adapted to be inserted into and form a snug engagement with the end cells; the inclusion of heavy yielding gaskets, rubber seals or O-rings in the ends of said cells provides firm, water-tight connections in the coupled cells.

A novel seating arrangement within the cells provides improved means for retaining the membranes between the coupled cells and accordingly eliminates previous efforts for compressing the outer edges of the membranes. The membranes form sealed partitions between cells simply by inserting the center cell into end cells which contain the membranes therein, the inserted center cell establishing an effective seal around the membrane surface.

The cell arrangement in the present apparatus provides improvements in water-cooling for minimizing temperature gradients and for flushing electrode and membrane surfaces to prevent accumulation of electrolytic products and polarization effects. A cooling jacket in the center cell completely surrounds the material undergoing dialysis, while an inlet and outlet in each end cell provides a coolant against the electrode and membrane surfaces therein.

Referring now to the drawings, wherein like reference characters designate corresponding parts throughout the several views, there is shown in FIG. 1 a cylindrical threecell structure comprising a center cell 11 having a cooling jacket 12 surrounding a sample chamber 13, and end cells 14 and 15 (also designated as electrode cells) positioned on each side of the center cell. The end cells, which are also cylindrical, have been shaped at the outer ends thereof into closed hemispherical surfaces 16. The open end 17 of each electrode cell corresponds with opening 18 on each end of the center cell. The center cell is provided at each end thereof with a section of reduced diameter forming a step 19. The three-cell apparatus is coupled together by inserting the step 19 of the center cell into the open end 17 of each electrode cell.

The end cells are provided with an electrode 21, which is formed of a flat disk of platinum or other suitable electrode metal. The electrode, which is carried on the end of a platinum wire 23 sealed into a glass tube 24, is electrically connected with external terminal 22. A sealing composition 25, such as a suitable phenolic or epoxy resin, may be used to attach the external terminal onto the cell surface. The electrode cells are also provided with an inlet 26 and an outlet 27 for continuous water flow through said cells. The water inlet is positioned so that the water stream entering the cell will pass in front of the electrode to carry away electrolytic products which have a tendency to accumulate near the electrode and membrane surface which can result in polarization and reduced efiiciency. The outlet line from each electrode cell is provided with a needle valve 28 to obtain accurate regulation of water flow.

A supporting ledge 29, sealed to the inner surface of an electrode cell, serves as a seat for maintaining the membrane in a sealed position within the coupled cells. A heavy rubber gasket 31 is positioned on said ledge; 21 membrane 32 rests on said gasket and a second gasket 33 is placed over the membrane. The step 19 in the center cell is grooved on its outer surface forming a recess which retains one or more sealing rings 34. The cells are coupled together to form a snug fit by inserting the step 19 into the open end 17 of the electrode cell, the sealing rings assuring a water-tight seal.

When the three cells are coupled together, as shown in FIG. 2, the membrane area is substantially equal to the cross-section area of the sample chamber 13. The electrodes are positioned as close to the membranes as possible, allowing only sufficient space for Water to flow laterally on the electrode and membrane surfaces. Constant flow of cooling water across said surfaces prevents ion polarization and also minimizes temperature gradients.

Inlet ports 35 communicate with the sample chamber 13 by means of a short tubing 36, which passes through and outwardly from the cooling jacket, are used for introducing the sample by means of a buret and for the insertion of electrodes for pH monitoring. The bottom stem 37 extends from the sample chamber and serves as an outlet for the treated material. Inlet stem 39 and outlet stem 41 are used to circulate a suitable coolant through the cooling jacket 12.

A manner in which the cells may be coupled in accordance with the present invention is illustrated in FIGS. 3 and 3a. The center cell 11 provides a step 19 in which a rectangular groove 20 retains an O-ring of elliptical cross-section. The supporting ledge 29 which is sealed to the end cell 15 provides a seating arrangement for gasket 31, membrane 32 and a second gasket 33. When the cells are coupled together, as shown in FIG. 3a, the step 19 fits snugly into the opening of cell 15, the cylindrical end section of cell 15 forming a continuous outer surface with the center cell. The O-ring becomes compressed into a circular form within the groove and forms a four-point contact within its confined space which is an effective leak-proof arrangement. The membrane is compressed against the ledge between gasket surfaces that provides an effective seal around the ledge surface.

Additional rigidity is provided in the coupling arrangement when the step 19 is increased in length to include additional grooves. In the embodiment shown in FIGS. 4 and 4a the multiple O-ring structures, or soft rubber seals, provide increased rigidity to the coupled cells. In addition, the ledge 46 may be provided with a groove and O- ring may be included in edge 47 of the step. Upon coupling these cells, the O-ring structures retain the membrane into a tight arrangement which obviates the use of heavy rubber gaskets.

Preliminary to electrodialysis, the apparatus is tested for leaks. The sample chamber, in one test procedure, was filled with water, and distilled water from a container approximately 200 cm. above the apparatus flowed continuously through the electrode cells. The needle valves 28 were shut, thereby applying a hydrostatic head of about 200 cm. water on the unit. Another test for leaks was carried out by keeping the needle valves shut and opening the inlets 26 on both electrode cells to the atmosphere. When the contents exhibited no tendency to leak during the course of an hour or more, the apparatus was considered leak-free.

A typical and representative example of operating the present apparatus, shown in FIG. 2, will now be described with respect to the method of desalting proteins, and more specifically with the method of purifying a 2% albumin solution in 0.1 M NaCl. The apparatus was assembled by inserting a rubber gasket 31 on the supporting ledge 29 of the electrode cell and then placing a permselective membrane 32 on the rubber gasket. A second gasket 33 was then placed over the membrane and the center cell was coupled to the end cell by inserting the step into the opening thereof. An insert 42 was placed in the sample chamber 13, and the other electrode cell was then assembled and connected similarly.

The membranes used for desalting the albumin solution were commercially available permselective types. The anion-permeable membrane was of the amine type and was identified as Nepton ARl11-A; the cation-permeable membrane was of the sulfonated type and was identified as Nepton CR-6l.

In the particular apparatus which was employed for the albumin preparation, the sample chamber had a capacity of 35 ml. and each of the electrode cells had a capacity of about 15 ml. Shiny platinum electrodes which measured 28 mm. in diameter were mounted 6 mm. from the membrane surface. Inlets 26 were connected to water lines 48 equipped with make-break connectors 49, and outlets 27 were connected to drain lines (not shown). Coolant water lines were connected to inlet stem 39 and outlet stem 41 and water was then circulated through the coolant jacket of the center cell. A direct current power supply was connected to appropriate terminals, the stopcock in the sample cell was closed, 10 ml. of albumin solution was introduced in the sample chamber and processing was begun. The electrode water flow rate varied from 10 to 30 ml./min. depending on the wattage, while the coolant water flow in the center cell was about 800 ml./min.

The solution in the sample chamber must be sufficient to wet at least of the membrane during operation to prevent polarization. Membrane polarization occurs when the rate of ion transport from the solution is insufficient to compensate for the ions being removed via the membrane resulting in a zone near the membranes which is ion depleted. To meet the voltage=current demand of the solution, decomposition of water occurs, and the hydrogen ion produced is transferred through the cation-permeable membrane thus creating a zone of elevated pH. The converse occurs at the other membrane: the hydroxyl ion concentration increases near the membrane resulting in an alkaline zone.

In order to improve the liquid contact with the membranes, a hollow, plastic or glass insert 42 of appropriate volume is placed in the sample chamber to reduce the chamber volume and raise the solution to a height sufficient to wet all or most of the membrane surface. The insert bears a number of small protuberances on the outer surface to minimize surface contact with the chamber wall. In addition, the insert may be adapted to provide vibrating stirring, as shown in FIG. 2, by including a small piece of magnetic metal or magnet 43 attached to the inner wall. The insert is vibrated by means of an electromagnet 44 connected to a chopper, shown simply as block 4-5, said chopper having a frequency of about =30 c.p.m.

In carrying out the electrodialysis of protein by means of the present invention, it has been found that voltages which exceed 225 volts result in denaturation of the protein. The apparatus should be operated preferably at a potential difference of 200 volts and at a maximum power of 5 watts. When the salt content of the material decreases to 0.001 equiv/liter, the voltage is reduced to volts.

Any existing ion-exchange membranes may be used in connection with the present apparatus. The permselective membranes in the above preparation contained sulfonic radicals (cationic) or a mixture of weak and strong amine radicals (anionic) covalently bonded in a crosslinked divinylbenzene polystyrene matrix.

The desalting operation was completed in approximately 4 hours, and electrodialysis was considered complete when the salt content decreased to 1X10 N or less and the pH was constant to within i001 units for at least one hour.

It has been found that maximum efliciency is achieved by providing a large membrane area relative to the distance of ion-transport. It is highly important therefore to provide a sample chamber of relatively short length and as large a cross section area as the diameter of available membranes and electrode will permit.

The susceptibility of proteins to heat denaturation is overcome in the present apparatus by means of separate and continuous cooling means in the center and the electrode cells. Under normal operating conditions, with a power input of .5 watts or less, the temperature in the sample chamber is invariably under 25 C. For optimum results, a temperature in the range of to C. should be maintained in the solution during electrodialysis.

Experimental evidence revealed that 65% of the total heat was dissipated by the cooling jacket and the remainder of the heat was removed by the electrode water. When cooling water of 14 C. was available for the cooling jacket, the temperature of the treated solution was maintained throughout the process at 18 C.

As a result of the foregoing, it can readily be seen that the improved electrodialysis apparatus provides an improved coupling structure, improved membrane retention Within the cells and more etfective cooling and flushing provisions in the individual cell structures, thus minimizing both temperature gradients and polarization effects.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electrodialysis apparatus which comprises:

a cylindrical tubular center cell open at each end,

said center cell including a main body portion with end sections of lesser outside diameter than said main body portion,

a closed coolant chamber within said main body portion coaxial therewith,

an inlet means and an outlet means connected with said coolant chamber to permit fluid flow therethrough,

an inlet means and an outlet means passing through said main body portion through said coolant chamber to permit fluid flow into and from said center cell,

first and second end cells in axial alignment with said center cell,

each of said end cells including a closed end and a cylindrical open end section,

said cylindrical open end section having the same outer diameter as the main body of said center cell and an inner diameter substantially the same as the outer diameter of said end portion of said center cell to telescopically receive therein said end portion of said center cell with a tight fit,

a ledge on the inner surface of each of said end cells in axial alignment with said end sections of said center cell,

a cylindrical ion-permeable partition secured within each of said end cells with the outer edge thereof secured between the end of said end sections of said center cell and the ledge within each of said end cells, ll

a disk type electrode secured within each of said end cells coaxial therewith juxtaposed said ledge and said partition perpendicular to the axis of said cells,

said electrodes having a diameter less than the inner diameter of the cylindrical portion of each of said end cells to provide a spacing therebetween,

insulated electrical conductor means secured electrically to said electrode in each of said end cells and extending outwardly from the closed ends thereof, and

inlet and outlet means secured to each of said end cells for passing a coolant fluid through said end cells along the surfaces of said electrodes and the adjacent surface of said partition secured within said end cells thereby flushing said partitions and said electrodes to prevent accumulation of electrolytic products which result in polarization.

2. An electrodialysis apparatus as claimed in claim 1,

wherein,

a seal means is provided between the outer surface of the ends of said center cell and the inner surface of said end cells witln'n which the ends of said center cell telescope.

3. An electrodialysis apparatus as claimed in claim 1,

wherein,

a sealing means is positioned between the ends of said center cell and the partitions within said end cells.

4. An electrodialysis apparatus as claimed in claim 2,

wherein,

a sealing means is positioned between the ends of said center cell and the partitions within said end cells.

5. An electrodialysis apparatus as claimed in claim 4,

wherein,

a sealing means is positioned between said partition in each of said end cells and the ledge therein.

6. An electrodialysis apparatus .as claimed in claim 5,

which includes,

a non-metallic insert within said center cell spaced from the inner wall of said center cell.

7. An electrodialysis apparatus as claimed in claim 6,

wherein,

said insert is provided with a small piece of magnetizable material, and

means for inducing vibrational motion to said insert due to magnetic attraction of said small piece of magnetizable material secured to said insert.

References Cited UNITED STATES PATENTS 869,662 10/1907 Snyder 285-336 1,926,591 9/1933 Toddesol 20430l 2,247,065 6/ 1941 Pauli et al. 204-301 2,251,083 7/ 1941 Theorell 204-301 2,438,529 3/1948 Woodling 285-351 2,516,743 7/1950 Allin 285-347 2,735,505 2/1956 Kleiman 285-336 2,752,306 6/1956 Juda 204-301 3,038,844 6/ 1962 Webb et al. 204- 3,216,911 11/ 1965 Kronenberg 204- OTHER REFERENCES Heftman: Chromotography, p. 414, 1961.

JOHN H. MACK, Primary Examiner. JOHN R. SPECK, Examiner. ATI T, K-

st n Ex e s

Claims (1)

1. AN ELECTRODIALYSIS APPARATUS WHICH COMPRISES: A CYLINDRICAL TUBULAR CENTER CELL OPEN AT EACH END, SAID CENTER CELL INCLUDING A MAIN BODY PORTION WITH END SECTIONS OF LESSER OUTSIDE DIAMETER THAN SAID MAIN BODY PORTION, A CLOSED COOLANT CHAMBER WITHIN SAID MAIN BODY PORTION COAXIAL THEREWITH, AN INLET MEANS AND AN OUTLET MEANS CONNECTED WITH SAID COOLANT CHAMBER TO PERMIT FLUID FLOW THERETHROUGH, AN INLET MEANS AND AN OUTLET MEANS PASSING THROUGH SAID MAIN BODY PORTION THROUGH SAID COOLANT CHAMBER TO PERMIT FLUID FLOW INTO AND FROM SAID CENTER CELL, FIRST AND SECOND END CELLS IN AXIAL ALIGNMENT WITH SAID CENTER CELL, EACH OF SAID END CELLS INCLUDING A CLOSED END AND A CYLINDRICAL OPEN AND SECTION, SAID CYLINDRICAL OPEN END SECTION HAVING THE SAME OUTER DIAMETER AS THE MAIN BODY OF SAID CENTER CELL AND AN INNER DIAMETER SUBSTANTIALLY THE SME AS THE OUTER DIAMETER OF SAID END PORTION OF SAID CENTER CELL TO TELECOPICALLY RECEIVE THEREIN SAID END PORITON OF SAID CENTER CELL WITH A TIGHT FIT, A LEDGE ON THE INNER SURFACE OF EACH OF SAID END CELLS IN AXIAL ALIGNMENT WITH SAID END SECTIONS OF SAID CENTER CELL, A CYLINDRICAL IION-PERMEABLE PERTITION SECURED WITHIN EACH OF SAID END CELLS WITH THE OUTER EDGE THEREOF SECURED BETWEEN THE END OF SAID END SECTIONS OF SAID CENTER CELL AND THE LEDGE WITHIN EACH OF SAID END CELLS, A DISK TYPE ELECTRODE SECURED WITHIN EACH OF SAID END CELLS COAXIAL THEREWITH JUXTAPOSED SAID LEDGE AND SAID PARTITION PERPENDICULAR TO THE AXIS OF SAID CELLS, SAID ELECTRODES HAVING A DIAMETER LESS THAN THE INNER DIAMETER OF THE CYLINDRICAL PORTION OF EACH OF SAID END CELLS TO PROVIDE A SPACING THEREBETWEEN, INSULATED ELECTRICAL CONDUCTOR MEANS SECURED ELECTRICALLY TO SAID ELECTRODE IN EACH OF SID END CELLS AND EXTENDING OUTWARDLY FROM THE CLOSED ENDS THEREOF, AND INLET AND OUTLET MEANS SECURD TO EACH OF SAID END CELLS FOR PASSING A COOLANT FLUID THROUGH SAID END CELLS ALONG THE SURFACES OF SAID ELECTRODES AND THE ADJACENT SURFACE OF SAID PARTITION SECURED WITHIN SAID END CELLS THEREBY FLUSHING SID PARTITIONS AND SAID ELECTRODES TO PREVENT ACCUMULATION OF ELECTROLYTIC PRODUCTS WHICH RESULTS IN POLARIZATION.

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