EP0043945B1

EP0043945B1 - Electrolytic cell and process for the electrolysis of brines

Info

Publication number: EP0043945B1
Application number: EP81104813A
Authority: EP
Inventors: James Milton Ford; David Blaine Wright; John Olen Adams
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1980-07-09
Filing date: 1981-06-22
Publication date: 1985-11-21
Also published as: JPS5748306A; AU537949B2; DE3172967D1; BR8104180A; ZA814120B; CA1157808A; EP0043945A1; AU7189781A

Description

This invention relates to electrolytic cells and a process for the production of gaseous products by the electrolysis of brines. More particularly, this invention relates to the separation of gases from liquid-gas mixture produced in electrolytic cells.
Modern electrolytic cells employing metallic electrodes having electrocatalytic coatings and separated by hydraulically impermeable ion exchange membranes are operated at high current densities and narrow interelectrode gaps to generate large amounts of gas and liquid products per unit of cell volume. In the upper portion of the cells, a gas-electrolyte mixture is produced which requires separation of the gaseous product from the electrolyte. This separation can be accomplished in a gas disengager apparatus which is connected to but separated from the electrolytic cell. To be efficient, a gas disengager should effectively separate the gaseous product from the electrolyte while minimizing foam generation and optimizing the size of the disengager.
Gas disengagers employed in electrolytic cells of the prior art include those of U.S. Patent No. 1,855,732 issued to J. N. Smith, in which a mixture of water and oxygen or hydrogen contacts baffles which deflect both fluids downward onto a plurality of parallel screens through which the mixture percolates by gravity and a partial separation of the gas is achieved. The remaining gas separates when the electrolyte falls to the bottom of the disengager.
Using this apparatus permits undesired contact between the gas and the disengaged liquid which results in re-entrainment of the gas in the liquid. In addition, this apparatus requires a large container to accommodate the combination of baffles and screens, adding to the cost of gas disengagement.
U.S. Patent No. 3,855,091 issued to L. W. Pies- ter, particularly Fig. 7, to which the preamble of claim 1 refers, teaches the separation of chlorine gas from a chlorine-anolyte liquor froth by changing the momentum of the froth prior to discharging the froth into the disengager. This cell likewise maintains the separated gas in contact with the disengaged electrolyte and results in undesired re-entrainment of the gas product in the electrolyte.
There is a need for a gas disengager for electrolytic cells which efficiently separates a gas product from a gas-entrained liquid while minimizing contact between the separated gas and the disengaged electrolyte.
It is an object of the present invention to provide an electrolytic cell and process which efficiently separates gas from a gas-entrained electrolyte produced in the electrolytic cell while minimizing contact between the separated gas from the gas-disengaged electrolyte.
Another object of the present invention is to provide a cell capable of separating gas from a gas-entrained electrolyte produced in the electrolytic cell having increased cross-sectional area without increasing the size of the disengager.
These and other objects of the invention are accomplished in an electrolytic cell for the electrolysis of brines according to the preamble of claim 1 and characterized by the features included in the characterizing part of claim 1. Claims 2 and 3 show preferred embodiments of such cells.
From U.S. Patent No. 3,574,095 an electrolytic cell is known per se having a degassifier atop and being directly connected thereto, the degassifier being exemplified by a dome, the mixture from the cell being introduced tangentially thereto. U.S. Patent No. 4,052,287 furthermore discloses already an electrolytic cell wherein the degassifi- cation zone is a curved container subtending an angle of about 75°, terminating in a zone wherefrom the gas is removed from an upper, and the liquid from a lower, outlet.
Furthermore, the invention includes a process for the electrolysis of brines characterized in that it is carried out in a cell according to one of the claims 1 to 3. Claims 4 and 5 show preferred embodiments of such a process.
Other advantages of the invention will become apparent upon reading the description below and the invention will be better understood by reference to the attached drawings in which:

FIGURE 1 shows a side view of a monopolar filter press cell employing one embodiment of the disengaging means of the present invention.
FIGURE 2 illustrates an end view of the embodiment of the disengager means of FIGURE 1 taken along line 2-2.
FIGURE 3 represents a plan view of the embodiment of the disengager means of FIGURE 2.
FIGURE 4 shows an enlarged schematic view of the disengager portion of FIGURE 1.
FIGURE 5 illustrates an alternate embodiment of the disengaging means of the present invention.

Monopolar filter press cell 60, illustrated in FIGURE 1, comprises a plurality of interleaved anode frames 24 and cathode frames 68 compressingly held between front end plate 62 and a rear end plate 64 by a plurality of tie bolts 69. Conductor rods 20 are bolted to anode collectors 50 to which electric current is supplied through anode terminals 52. Electrolysis of the electrolyte in the anode frames 24 produces a gas-containing anolyte which enters anolyte disengager 56 through outlets 42. Within anolyte disengager 56, the gas-containing electrolyte contacts semicircular baffle 48. Semicircular baffle 48 centrifugally moves the gas-containing electrolyte to separate the gas from the electrolyte, as best seen in FIGURE 2. The product gas is removed from anolyte disengager 56 through gas outlet 58. Gas-disengaged electrolyte is returned to anolyte frames 24 along with fresh anolyte supplied through anolyte feed pipe 54 through inlets 44.
Cell 60 is supported on support legs 70 and is provided with an anolyte drain 46. Line 46 can be a valved drain line connected to the bottom member (not shown). of each of anode frame 24 by inlets 40 to allow anolyte to be drained. Alternatively, line 46 can be connected to anolyte disengager 56 in order to provide a recirculation path for disengaged anolyte liquid.
In FIGURE 2, semicircular baffle 48 is bolted to outlets 42. Semicircular baffle 48 centrifugally separates the gas from the gas-containing electrolyte from a plurality of outlets 42, as shown in FIGURE 3.
FIGURE 4 depicts anolyte disengager 56 having outlets 42 through which gas-containing anolyte is discharged against semicircular baffle 48. Disengaged liquid is removed from anolyte disengager 56 through conduit 57. Gas released is removed from anolyte disengager 56 through gas outlet 58.
Semicircular baffle 48 centrifugally separates the gas from the gas-containing electrolyte, as shown in FIGURE 2, by directing the denser liquid along the curvature of semicircular baffle 48 towards area B. The disengaged gas which collects in area A, flows along the length of semicircular baffle 48 and out the ends, as shown in FIGURE 4.
FIGURE 5 shows an alternate embodiment in which anolyte disengager 72 has two curved surfaces 74 joined along inner edges 76. Gas-containing anolyte discharged through outlet 42 is centrifugally separated along curved surfaces 74, the disengaged gas being removed through gas outlet 58.
More in detail, the novel apparatus and process of the present invention may be used with any gas-entrained electrolyte produced in an electrolytic cell including gas-entrained anolytes or gas-entrained catholytes. Suitable anolytes include alkali metal halides or alkaline earth metal halides where the halides are chloride or bromides and the entrained gas is chlorine or bromine. Also suitable as anolytes are water or alkaline solutions in which oxygen is the entrained gas. Preferred anolytes are alkali metal chlorides where the alkali metal is sodium or potassium. These anolytes are referred to as "brine" in the description and claims.
Gas-entrained catholytes include water or alkaline solutions such as metal hydroxides or alkaline earth metal hydroxides in which hydrogen is the entrained gas.
The gas-entrained electrolytes may be produced in a variety of electrolytic cells including monopolar or bipolar cells which employ liquid permeable diaphragms or ion permeable membranes as separators. Preferred electrolytic cells are filter press cells and in particular monopolar filter press cells comprising a plurality of interleaved anode frames and cathode frames which are compressingly held between two end plates by a plurality of tie bolts. The electrodes have horizontally oriented conductors which permit the construction of electrodes having a height of from about 1 to about 5 meters while maintaining a short direct current path through the cell. When used, for example, in electrolyzing alkali metal chloride brines such as sodium chloride, chlorine gas is produced in the anode frames. The chlorine gas bubbles produced rise up through the anode chamber to form in the upper portions a chlorine-entrained sodium chloride brine containing up to about 30 percent by volume of the gas. This chlorine-entrained brine passes through outlets in the top of the anode frame and through conduits of the type shown in FIGURES 1-3 into the disengager. Within the gas disengager is a gas disengaging means which, when impinged upon by the chlorine-entrained brine, imparts a centrifugal force to the fluid. This centrifugal force causes a separation by density of the chlorine gas from the liquid brine. For example, using the semicircular gas disengaging means shown in FIGURES 1-4, the denser liquid brine flows around the curved surface and down the side of the gas disengaging means while the gas remains under the curved portion, flowing along the disengaging means and being discharged at the ends of the disengaging means.
By imparting a centrifugal force to the gas-entrained electrolyte, the gas and the electrolyte are separated in a manner which minimizes contact between the separated gas and the disengaged electrolyte and eliminates or substantially prevents re-entrainment of the gas by the disengaged electrolyte.
The disengaging means may be any surface capable of imparting a centrifugal force to the gas-entrained electrolyte. For example, surfaces having a curvature of at least 45 degrees and preferably of from about 100 to about 180 degrees are suitably used.
While the embodiment of FIGURES 2 and 5 show the conduit discharging the gas-entrained electrolyte tangentially by being located adjacent to one side of the disengaging means, separation of the gas from the electrolyte may be attained, by, for example, placing the conduit so that the gas-entrained electrolyte is discharged at the center of the curved surface.
As shown in FIGURE 2, the gas disengaging means is attached, for example, by bolting to the conduits for discharging the gas-entrained electrolyte. However, the gas disengaging means may be attached to, for example, walls of the sealed container by any suitable means.
Any container such as a tank may be used as the sealed container.
The novel process for disengaging gas from a gas-entrained electrolyte of the present invention results in efficient separation of the gas from the electrolyte while minimizing contact between the gas and the gas-disengaged electrolyte which would result in re-entrainment of the gas.

Claims

1. An electrolytic cell (60) for the electrolysis of brines including at least one conduit (42) adapted to discharge a gas-entrained electrolyte upward into disengaging chamber containing disengaging means (72) comprising a member (48, 74) having a curved surface adapted to contact said gas-entrained electrolyte and to separate the gas from the electrolyte, outlets (57, 58) being provided in said disengaging chamber for said gas and the gas-disengaged electrolyte, the outlet (57) for that electrolyte being arranged below said member and the outlet (58) for the gas being arranged above the level of the electrolyte to be collected in the disengaging chamber, characterized in that
said member forms a baffle (48; 74) positioned with its curved surface above the discharge end of said conduit in such a way that the electrolyte is deflected downwards along the curved surface and the gas is collected under the top of the curved surface and guided away into an upper zone of the disengaging chamber towards the outlet (58) for the gas.

2. The electrolytic cell of claim 1 in which said baffle (48; 74) has a semicircular surface.

3. The electrolytic cell of claim 1 or claim 2 in which said baffle (48; 74) is attached to said conduit (42).

4. A process for the electrolysis of brines characterized in that it is carried out in a cell according to one of the claims 1 to 3.

5. The process of claim 4 in which said electrolyte is an alkali metal chloride brine.

6. The process of claim 5 in which said gas is chlorine and said electrolyte is sodium chloride.