US2860100A - Diaphragm cells - Google Patents

Description

L. J. K. KRZYSZKOWSKI DIAPHRAGM CELLS Filed May 10, 1954 8\%T FIG. I

FIG. 3

FIG. 2

IN VEN TOR.

LESZEK JAN KoNRAO KnzYszKowsK tates 1* 2,8s0,100 nIAPr-rnAoM CELLS This invention relates toelectrolytic diaphragm cells and more particularly to improvements in the diaphragm of such cells. i I

Electrolytic cells with `Vertical diaphragms suffer nom the drawback of a non-uniforrn fiow through the diaphragm caused by differences in hydrostatic pressure on either side of the diaphragm at the various levels of the cell. This isparticularly true in cells in which the anolyte and catholyte difer substantially in specific gravity, the greatest problem being present in cells that are designed to run with an empty cathode compartrnent, such as certain caustic and chlorine cells. In cells of this type the percolation rate of the electrolyte through the diaphragm from one compartment to the other may reach a value three to four times higher at the bottom than at the upper part of the cell. The present invention is particularly adapted to cells having a substantially empty cathode ,chamb'en suchas certain electrolytic cells for the production of sodium hydroxide andchlorine, though not limited thereto. The invention will, therefore, be dcscribed as applied to electrolytic` diaphragm cells Operating witl'ra 4subs'tantially liquid free cathode chamber, adapted to pfoduce sodium hydroxide and chlorine from aqueous sodium chloide solutions. A schematic sketch of a cell of this type is illustrated in Figure l of the drawings.

In chloralkali cells, the flow of brine through the diaphragm is necessary to check the migrationpof the OH ions to theanode. The migration Velocity of these ions, for example, is 0.018` ein/second at a potential drop of l v./cm. at 18 C; The percolation rate of the electrolyte through the diaphragm should, therefore, be adjusted to counteract this niiglration according to the desired density and current efiiciency of operation. In practice, fiows in excess of the figure calculatedwfromionic migration velocitiesare needed because of mechanical defects in` the diaphragm, non-streamline fiow, etc.

Due to thel different hydrostatic pressure prevailing Aat the various levels of the anolyte, the ideal flhw or percolation rate with a c'onventional diaphragm can be obtained at only one level hereinafter referred to as the neutral zone Above this level the percolation rate is too slow to counteract migration of the OH ions, while below this level` the percolation rate is sufiiciently rapid to carry substantial amounts of dissolved chlorine through the diaphragm. As a result, in the upper levels of the cell the alkaline area shifts towards the anode causing a lower current efficiency and the formation of chlorates, while near the bottom of the cell the chlorinated brine percolating to the cathode compartrnent forms hypochlorite which causes corrosion of the cell as well as reducing the current efficiency. Also, the diaphragm, which is generally made of asbestos, is in a highly alkaline meldiun'i in the upper portion of the cell and is in an acid medium in the lower portion of the cell.

Asbestos is attacked by hot alkali solutions, and asbestosV leached by sodium hydroxide is susceptible to attack by acid brine. As a result, the life of the diaphragm,

Patented Nov. ll, 1958 2 which is generally made of asbestos, is substantially` shortened. Where there are fluctuations in cell operation, i. e`. variations in voltage, variations in pressure in the chlorine and hydrogen lines, etc., the so-called neutral zone" tends to shift during operation. This subjects a portion of the asbestos diaphragm, which `has been w'eakened through leaching by alkali, to attack by theiacidbrine and the life of the diaphragm is still further shortened.

The problem of diaphragm life and uniformity of dperaton is further complicated by the fact `that asbestos paper is substantally weakened when Wet and is subject to failure because of this.

To prevent these conditions, various devices have ,been conceived. Attempts have been made to solve the problem by varying the size of the perforations in the cathod'e so that a 'substantially uniform percolation rate through the cathode is obtained. However, in order to obtain a uniform percolation rate through the cathode the removed portion of the cathode must be so small, particularly in the lower area, that a substantial amount of the hydrogen formed is prevented from escaping through the cathode.` Also, the active cathode area must be substantially less near the upper part of the cathode than near the lower part of the cathode. It has further been proposed to increase the thickness ofthe diaphragm towar'ds the bottom. However, there is substantially more material and labor required for this type `of diaphragm; `it is difiicult to obtain the proper taper, and the electrical resistance is increased proportionately to the thickriess of the diaphragm, other factors being Constant.

I have now solved this problem of non-uniform percolation rate through the diaphragm, and at the same time have obtained a diaphragm of substantially increased strength `by marking on the diaphragm surface a pattern which blocks out different areas of the diaphragm, the pattern being such as to make the permeability of the diaphragm inverselyproportional tothe hydrostatic pressure head encouhtered in the cell.` The marking material used serves two purposes. It makes certain portions of the diaphragm impervious to the electrolyte and thus enables control of the percolation. It binds the asbestos fibers together so as to form a strengtheningpattern `ou the diaphragm. `T his helps to` mairitain the shape of the diaphragm when wet.

In the drawings: ,i i

Figure l is a schematic View of a chlorine cell;

Figure 2 is a section of a diaphragm showing one type of marking; and ,p w p Figure 3 is a section of a diaphragm showing a different type of marking.

Referring to the cell of Figure l, 1 is the cell casing which has an anolyte Chamber 2 and catholyte Chamber 3. Anodes 4, which are generally made of graphite, project downwardly into the cell and are surrounded by` an iron perforated cathode 5. An asbestos diaphragm 6 is placed between the anode and cathode against the cathode. The brine electrolyte is brought into the cell through inlet 7. The chlorine is removed through outlet S, the hydrogen through outlet 9, and the sodium hydroxide solution through Outlet 10.

The diaphragm as shown in Figures 2 and 3 has marked thereon a pattern which provides uninked areas which progressively increase in size from the bottom to the top. In Figure 2, the pattern consists of a series of Vertical inked lines 11, crossed by a series of horzorital inked lines 12. The Vertical lines T11 are equally spaced whereas the spacing between the horizontal lines 12 progressively increases with increased distance from the bottom. In Figure 3 the pattern is formed by Vertical lines 13. These progressively decrease in width from the bottom towards the top. For further strength horizontal lines 14 may be added. Any pattern can be used which will block out progressively larger areas of the diaphragm approaching the bottom. However, those patterns are preferred which give the greatest supporting strength to the diaphragm. Thus, the preferred patterns are formed by crossing lines, the simplest and most easily calculated being the series of rectangles shown in Figure 2.

The patterns can be drawn on the diaphragm or can be printed by any suitable printing apparatus. Since, for controlling the percolation rate it is only necessary that the design appear on one side of the asbestos diaphragm, the thickness of the paper on which the design is marked is not particularly critical. For greatest strength and life of the diaphragm, however, and for preferred operation, the design should appear on the side of the diaphragm which is facing the anode and is in direct contact with the main body of the electrolyte. The actual diaphragm may be built up of several layers of asbestos paper until a diaphragm of the desired thickness has been obtained. In such a case only one layer of asbestos paper need have the design marked thereon to obtain uniform percolation though other layers can be so marked if desired. If the layer so marked is the one nearest the anode and the surface facing the anode is marked, then the markings will help to strengthen the whole diaphragm since the asbestos Will be held between the printed lattice and cathode. In practicing the present invention it is therefore preferred that the layer closest to the anode always be marked even though other layers of the diaphragm may contain the described markings thereon.

Various methods may be used for arriving at the size of the areas on the diaphragm surface to be left open. The following, however, is the preferred method.

The percolation rate for different hydrostatic pressure heads is first obtained for the diaphragm paper which is to be used.

Hvdrostatic Pressure/inch Percolation. Rate, cc./h./dm.2 200 AP=constantg A=wO P represents the percolation rate at varying hydrostatic pressures and A the area which would be required to keep the flow rate Constant. Substituting the percolation data prevously obtained in this equation, values can be obtained for a new graph representing the areas required to keep a uniform percolation at the various levels.

In order to obtain a unit area at approximately the middle of the diaphragm, approximately 30" high, that would represent a unit, the value of the percolation rate, 200 cc., at a hydrostatic pressure head of 15" is used, as a base figure. Substituting this in the equation, one obtains the area changing factor or the relative Variation in area that must exist at the different hydrostatic pressure levels to obtain a uniform percolation.

For example, at 15" the area is represented as a unit 200 A-zTo At 7" the area must be 2.26 times that at 15"; i. e.,

If a diaphragm with rectangular markings is to be prepared the simplest method of preparation is to first assume definite dimensions for the unit area at the 15" level. A suitable choice is 1A x 1A". The diaphragm is then marked with parallel Vertical lines M1 apart giving a constant width to all areas. Now by multiplying 1A 25) by the area changing factor for any hydrostatic pressure height, the spacing between the horizontal lines for that height to give uniform percolation can readily be determined. Thus the spacing at 7'I would be .25" x 2.26 or .565".

Any marking material may be used which is reslstant to the cell liquor, which will render the marked areas more impervious to fluid flow and which will form a strengthening pattern When marked on the diaphragm.

Among the materials that have been found suitable for this purpose are chlorinated rubber, chlorinated and chloro-sulfonated polyethylene, highly chlorinated or fluorinated hydrocarbons, polyvinyl, polyvinylidene and acrylic latexes. The following are illustrative ink formulations:

Percent Parlon 10 C. P. (chlorinated rubber, Hercules) 10 Halowax 4005 (chlorinated paraffin 70% Cl).. 40 Halowax 4003 (chlorinated parafiin 40% Cl) 5 Stabilizer A5 2 Solvent (mixture of methyl Cellosolve and acetone) 43 Exon 400 XR61 (a fluorocarbon resin) 7.0 Halowax 4005 40.0 Halowax 4003 2.0 Stabilizer A5 1.0

Solvent (mixture of methyl Cellosolve and acetone) 50.0

Diaphragms prepared in accordance with the present invention were tested in regular chlorine cell operation over substantial periods of time. The printed diaphragms used were about 2/3 the thickness of the diaphragms used in the non-test cells producing commercial chlorine. This represents a substantial saving in asbestos. The voltage of the cells with the printed diaphragms was about 8 to 10% lower than that of adjacent cells equipped with regular diaphragms. This resulted in an 8 to 10% saving on power. Yet the strength of the lye obtained from the test cells using the printed diaphragm was within the same range as that of the other cells. None of the cell contaners using the printed diaphragms showed any signs of internal corrosion and no hypochlorite was noted in the lye or excessive hydrogen in the chlorine gas produced. The cells were opened and tests were made of the lye concentration at various levels. These tests indicated that the flow rate of the cell liquod through the diaphragm Was substantially uniform.

In describing the present invention the diaphragms have been described as used with chlorine cells of the empty cathode compartment type. However, the invention is not limited to cells of this type but the marked diaphragms of the present invention may be used to ad- Vantage in any cell where non-uniform flow rate through the diaphragm, due to difierences in hydrostatic pressure, is a problem.

Having thus described my invention, I clairn:

1. In an electrolytic diaphragm cell comprising an anode, a cathode, an anolyte Chamber and a catholyte chamber, a preformed pervious diaphragm arranged substantially vertically between the anode and the cathode and having a series of impervious lines dividing the area of the diaphragm into pervious spaces which are progressively smaller from the top to the bottom of the diaphragm to produce a uniform percolation rate throughout the area of the diaphragm.

2. The diaphragm of clam 1, in which the lines form a series of rectangles that decrease in size from the top to the bottom of the diaphragm.

3. The diaphragm of claim 1, made of asbestos with the lines drawn thereon.

4. The diaphragm of claim 1, made of asbestos with the lines printed thereon.

5. The diaphragm of claim 1, in which the lines are 15 References Cited in the file of this patent UNITED STATES PATENT'S 1,299,519 Smart Apr. 8, 1919 1,357,400 Jewell Nov. 2, 1920 1,771,091 Lawaczeck July 22, 1930 1,831,406 Beckmann Nov. 10, 1931 2,228,264 Freedley Jan. 14, 1941 2,591,755 Wilson Apr. 8, 1952 UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,860,100 November 11, 1958 Leszek Jan Konrad Krzyszkowski It is hereby certfied that error appears in the prnted specification of the above numbered patent requirng correotlon and that the Sald Letters Patent should read as aorrected below.

Column 4,1ines 2 and 3, for that portion of the equation reading 2oo gggz A--8-6-226 read A- 88 2.26

line 63, for 'liquod read --1iquor--.

Signed and sefied this 31st day of S'larch 1959.

[seen] Attest: KARL H. AXLINE, ROBERT C. WATSON,

Claims (1)

1. IN AN ELECTROLYTIC DIAPHRAGM CELL COMPRISING AN ANODE, A CATHODE, AN ANOLYTE CHAMBER AND A CATHOLYTE CHAMBER, A PREFORMED PERVIOUS DIAPHROM ARRANGED SUBSTANTIALLY VERTICALLY BETWEEN THE ANODE AND THE CATHODE AND HAVING A SERIES OF IMPERVIOUS LINES DIVING THE AREA OF THE DIAPHRAGM INTO PERVIOUS SPACES WHICH ARE PROGRESSIVELY SMALLER FROM THE TOP TO THE BOTTOM OF THE DIAPHRAGM

Images