JPS6217038B2 - - Google Patents

Description

Claim 1: An electrochemical cell that is divided into an upper chamber and a lower chamber by a horizontal perforated plate, and the two chambers are communicated by a conduit that leads an electrolyte from the upper chamber to the lower chamber. The upper chamber consists of an electrode chamber with an open top having the perforated plate as a bottom wall, an electrolyte inlet/outlet provided at both ends of the electrode chamber, and a gas collection chamber above the electrode chamber, and the lower chamber collects gas through the perforated plate. An electrochemical device characterized in that it is composed of a gas supply chamber that supplies gas to an electrode chamber in an upper chamber through a hole in a plate, and a receiver section located at the bottom of the chamber for pooling the reacted electrolyte. Tank.

2. The electrochemical cell according to claim 1, wherein the electrolyte inlet and the electrolyte outlet are each formed by a weir.

3. The electrochemical cell according to claim 2, wherein the top of the electrolyte inlet weir is higher than the top of the electrolyte outlet, and the top of the electrolyte outlet weir is higher than the top of the electrode.

4. The electrochemical cell according to claim 2 or 3, wherein the weir is formed by a plate standing upright from a perforated plate.

5. A bipolar array of vertical plate-like electrodes arranged in spaced parallel relationship to form a channel between an electrolyte inlet and an electrolyte outlet. Electrochemical bath.

6. A claim in which the bipolar electrodes are placed on a perforated plate made of electrically insulating material, and the holes in the perforated plate are arranged in rows spaced approximately centrally between adjacent electrodes. The electrochemical cell according to item 5.

7. A conduit (down pipe) from the upper chamber to the lower chamber leads from the electrolyte outlet weir to the bottom of the lower chamber in order to discharge the reacted electrolyte into the pool. The electrochemical cell according to item 2.

8. The electrochemical cell of claim 7 including a riser extending downward through the upper chamber for discharging fresh electrolyte into the electrolyte inlet weir.

9 comprising an array of vertical plate-like bipolar electrodes arranged in spaced parallel relationship to form a channel between an electrolyte inlet weir and an electrolyte outlet weir, the array of electrodes being arranged on opposite sides of the upper chamber; 2. An electrochemical cell as claimed in claim 1, including a terminal electrode inserted into the side wall of the cell.

10 consisting of an upper chamber having an electrode chamber, a plurality of intermediate chambers, and a lower chamber stacked vertically, the upper chamber, the intermediate chamber, and the lower chamber being divided by horizontal perforated plates; A multi-stage electrochemical cell connected by a conduit that sequentially guides an electrolytic solution from the chamber to the intermediate chamber and from the intermediate chamber to the lower chamber, and the upper chamber and the intermediate chamber are provided with a perforated plate on the bottom wall. It consists of an electrode chamber with an open top, an electrolyte inlet/outlet provided on both sides of the electrode chamber, and a gas collection chamber above the electrode chamber, and the gas collection chamber (excluding the upper chamber)
forms a gas supply chamber to the upper chamber and the intermediate chamber above it, each perforated plate is placed above the gas supply chamber, and the lower chamber sequentially supplies gas through the holes in the perforated plate. A multi-stage electric device comprising a gas supply chamber for supplying gas to the upper intermediate chamber and the electrode chamber in the upper chamber, and a receiver section located at the bottom for pooling the reacted electrolyte. Chemical tank.

11. The multi-stage electrochemical cell according to claim 10, wherein the electrolyte inlet and outlet of the upper chamber and the intermediate chamber are formed by weirs.

12 The top of the electrolyte inlet weir of the upper chamber and the intermediate chamber is higher than the top of the electrolyte outlet, and the top of the electrolyte outlet is higher than the top of the electrode.
The multi-stage electrochemical cell according to item 1.

13. Claim 11 or 12, wherein the weir is formed by a plate standing upright from a perforated plate.
Multi-stage electrochemical cell as described in section.

14. Claims comprising a bipolar array of vertical plate-like electrodes arranged in spaced parallel relationship to form a channel between an electrolyte inlet and an electrolyte outlet of an upper chamber and an intermediate chamber. A multi-stage electrochemical cell according to scope 10.

15 The electrodes are placed on perforated plates in the upper and middle chambers, the perforated plates are made of electrically insulating material, and the holes in the perforated plates are approximately centrally spaced between each adjacent electrode. 15. The multi-stage electrochemical cell according to claim 14, which is arranged in rows spaced apart from each other.

16 Upper chamber and middle chamber (excluding the bottom middle chamber)
12. A multi-stage electrochemical cell according to claim 11, comprising a conduit (down pipe) for discharging the electrolyte from the electrolyte outlet weir of the cell to the electrolyte inlet weir of the intermediate chamber below.

17. The multi-stage electrochemical cell of claim 16 including a riser extending downwardly through the upper chamber for discharging fresh electrolyte into the electrolyte inlet weir of the upper chamber.

18 comprising a bipolar array of vertical plate-like electrodes arranged in spaced parallel relationship in the upper chamber and the intermediate chamber to form a channel between the electrolyte inlet weir and the electrolyte outlet weir; 11. The multi-stage electrochemical cell of claim 10, wherein each electrode arrangement includes terminal electrodes inserted into opposing side walls of the respective upper and middle chambers.

TECHNICAL FIELD The present invention relates to electrochemical vessels, in particular electrochemical reactions involving gaseous reactants, or the use of gases for other purposes, such as purging or sweeping reaction products, or as a buffer or suppressing undesired reactions. This invention relates to an electrochemical cell for carrying out an electrochemical reaction.

The invention relates more particularly, but not exclusively, to an electrochemical cell for electroorganic synthesis, such as, but not limited to, the electrochemical oxidation of unsaturated and polyunsaturated hydrocarbons. The electrochemical production of propylene oxide is of particular interest and will be detailed as an example.

BACKGROUND OF THE INVENTION In the electrochemical production of propylene oxide, propylene is converted to propylene halohydrin by reaction with halogens generated in situ by anodization of halide salts of alkali metals in aqueous solution. This propylene halohydrin is converted into propylene oxide by reaction with hydroxyl groups at the cathode where hydrogen is liberated. When using sodium bromide as the electrolyte, the general diagram of the reaction is as follows: Anode 2Br ^- →Br ₂ +2e C ₃ H ₆ +Br ₂ +H ₂ O→C ₃ H ₆ BrOH+HBr Cathode 2H ₂ O→H ₂ +2OH ^- -2e C ₃ H ₆ BrOH+OH→C ₃ H ₆ O+H ₂ O+Br Total C ₃ H ₆ +H ₂ O→C ₃ H ₆ O+H _2In principle, only water, propylene, and electrical energy can be combined with propylene oxide and hydrogen. consumed in the production of The halide electrolyte, sodium bromide, is continuously oxidized and regenerated in the bath for further use, but loss of bromine may also occur due to the generation of hypobromite and bromine gas.

Although the advantages of this electrochemical route, which eliminates the production of waste calcium chloride encountered in conventional chemical methods, have long been recognized, attempts to satisfy it have proven to be very ineffective. Ta.

French Patent Specification No. 1 375 973 and West German Publication No. 1 258 856 generate propylene halohydrin in a porous anode and pass it through a membrane into an alkaline electrolyte in a porous cathode, where it is We proposed the use of a diaphragm tank to saponify propylene oxide. However, these vessels are complex and have low efficiency.

US Pat. No. 3,394,059 proposed carrying out the halohydrin process in an undivided cell, preferably a flowing mercury cathode cell, and simply whisking the propylene into the electrolyte. Again, this performance was poor, and F.Beck (IUPAC XXIVth
International Congress, Hamburg, 1973,
Vol. 5, “Applied Electrochemistry” pages 111-136) described improved performance using capillary gap baths. In this, propylene dispersed in a dilute NaBr electrolyte is fed through a central hole in the pile of electrode discs and flows radially outward between the discs. The electrode disk gap was kept small (0.2-0.5 mm) to allow handling of low concentrations of bromide with low ohmic losses.
70% or slightly higher current efficiency and
Although energy consumption of 0.23 to 0.30 kWh/gram mole of propylene oxide has been reported for small capillary gap vessels, scaling up this vessel for industrial production would be difficult.

Fleischmann et al. (Symposium on
Electrochemical Engineering I , Newcastle
(1971, Editor JDT Thornton) studied the synthesis of propylene oxide using a bipolar packed bed tank. The vessel consisted of a filled bed made from a mixture of conductive and non-conductive particles. The conductive particles become bipolar by using a dilute electrolyte in the bath and applying a sufficient voltage gradient between the contact electrodes, thereby overcoming the decrease in resistance in the electrolyte. Using glass beads coated with graphite as conductive particles and glass beads as non-conductive particles,
The energy consumption of such a bath was found to be high, 2.5 to 3 kilowatt hours/gram mole of propylene oxide, assuming a diameter of all particles of about 0.05 cm.

A bipolar rod fluidized bath was developed by King et al. (Trans.Inst.
Chem.Eng.Chemical.Eng., 53, 1975) in the production of propylene oxide. The tank consisted of vertical rows of conductive rods separated from each other by small gaps. Electrolyte was fed into the top bar, flowed downwards over the vertical bar, and collected from the bottom bar for recirculation. The gaseous reactant, propylene, is passed upwardly through the space between the vertical rods in continuous contact with the film of electrolyte. The current efficiency of this tank was about 70%. Energy consumption is estimated at 0.35-0.4 kWh/gram mole of propylene oxide.

REW Jansson et al. developed a bipolar electrochemical pump cell with an energy yield of less than 0.2 kWh/gram mole of propylene oxide at 3000 rpm with an electrode gap of 0.25 mm.
(Journal of App.
Electrochemistry, 7, (1977), 437-443). However, its structure is not easy to scale up for industrial production.

Various other cell constructions designed to supply gas to the electrolyte are also known. For example, in the electrowinning of metals such as copper, it is well known to supply gas through froth tubes located below the electrodes to agitate the electrolyte (e.g., U.S. Pat. No. 3,875,041 and supra. (see patent). Another proposal, made in U.S. Pat. It was proposed to use a manifold to agitate the electrolyte in the electroplating bath by supplying gas to the manifold from a gas flow tube. In contrast to a fixed froth tube arrangement, the entire manifold structure was removed to facilitate periodic cleaning to remove debris that could block the holes in the manifold.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a tank that can be designed to better satisfy the following requirements than previously proposed tanks;
In particular, but not exclusively, to provide an electrochemical cell for the production of propylene oxide: 1. Simple mechanical construction; 2. Good heat and mass transfer properties; 3. Operation and continuous operation. 4. Good gas-liquid contact; and 5. Good anolyte and catholyte product mixing.

The electrochemical cell of the present invention has the following configuration.

"An electrochemical cell which is divided into an upper chamber and a lower chamber by a horizontal perforated plate, and the two chambers are communicated by a conduit that leads an electrolyte from the upper chamber to the lower chamber, The chamber consists of an electrode chamber with an open top having the perforated plate as a bottom wall, an electrolyte inlet/outlet provided at both ends of the electrode chamber, and a gas collection chamber above the electrode chamber, and the lower chamber collects gas through the holes of the perforated plate. The structure consists of a gas supply chamber that supplies gas to the electrode chamber in the upper chamber through the gas supply chamber, and a receiver section located at the bottom of the chamber for pooling the reacted electrolyte.

According to the invention, in its simplest form:
An electrochemical cell includes an electrode disposed on a perforated generally horizontal plate, an electrolyte inlet and an electrolyte outlet spaced across the perforated plate on either side of the electrode, and a perforated plate. It consists of a tank enclosure divided into an upper chamber and a lower chamber by a. The lower chamber contains a gas supply chamber from which, in use, gas flows upwardly through holes in the plate, foams through the electrolyte on the plate, and is collected in the upper chamber.

Advantageously, the electrolyte inlet and the electrolyte outlet of this cell are each formed by a weir. The top of the inlet weir is higher than the top of the outlet weir, and the top of the outlet weir is higher than the top of the electrode. Therefore, by regulating the supply of fresh electrolyte to the inlet weir, at a chosen rate, electrolyte flows across the inlet weir and between the electrodes, while spent or reacted electrolyte flows out the outlet. Allow it to flow over the cough. These weirs can be formed by upright plates integral with or fixed to the perforated plate.

Electrodes, preferably vertical plate-like electrodes in a bipolar array, arranged in spaced parallel relationship to form a channel between the inlet and outlet of the electrolyte,
It can be placed on a perforated plate, which in this case can be made of an electrically insulating material. The holes in the plate can be arranged in rows, each spaced approximately midway between adjacent electrodes. Although generally circular holes of 1 mm in diameter have been found to be satisfactory, other shapes and sizes of holes can be used.

The bottom of the lower chamber of the cell enclosure can serve as a receptacle for the pool of spent or reacted electrolyte. This electrolyte flows through a down pipe leading from the aforementioned outlet weir to the pool, from which it can be withdrawn via the outlet and recycled. Fresh electrolyte is supplied to the aforementioned inlet weir via a riser. This tube extends downwardly through the upper chamber of the cell enclosure and into the electrolyte held by the inlet weir.

The upper and lower chambers can be formed by the upper and lower parts of the enclosure of the box-like tank, these parts being separated by the aforementioned plate, which is perforated only in the region below the electrodes. A rectangular enclosure for the electrodes can thus be formed by the side walls of the upper enclosure part, which are fitted against the upright plates forming the inlet and outlet weirs. These side walls can support plug-in terminal electrodes of the electrode array.

Further, the present invention has the following configuration consisting of multiple stages of the electrochemical baths.

"It consists of an upper chamber with an electrode chamber, a plurality of intermediate chambers, and a lower chamber stacked vertically, and the upper chamber, intermediate chamber, and lower chamber are divided by horizontal perforated plates, and the upper chamber This is a multi-stage electrochemical cell which is connected by a conduit that sequentially guides an electrolytic solution from the to the intermediate chamber and from the intermediate chamber to the lower chamber, and the upper chamber and the intermediate chamber are provided with a perforated plate on the bottom wall. It consists of an electrode chamber with an open top, an electrolyte inlet/outlet provided at both ends of the electrode chamber, and a gas collection chamber above the electrode chamber, and the electricity collection chamber (excluding the upper chamber)
forms a gas supply chamber to the upper chamber and intermediate chamber above it, each perforated plate is placed above the gas supply chamber, and the lower chamber sequentially supplies gas through the holes in the perforated plate. It is composed of a gas supply chamber for supplying gas to the upper intermediate chamber and the electrode chamber in the upper chamber, and a receiver section located at the bottom for pooling the reacted electrolyte.

With this device, in operation, gas passes from the bottom of the lower chamber through the intermediate chamber to the upper chamber, and bubbles through the electrolyte in each intermediate chamber and the upper chamber.
Preferably, the electrolyte outlets and inlets of successive cells are connected in a cascade so that the electrolyte flows from the upper chamber down each intermediate chamber and across the perforated plate of each said chamber from the inlet to the outlet; Then go down and go to the entrance to the room below. Such an upper chamber, an intermediate chamber, may have the preferred characteristics of a single electrochemical cell unit as described above, such that an inlet and an outlet for the electrolyte are formed by a weir.

Another aspect of the invention is an electrochemical method and method of carrying out a reaction using an electrochemical cell according to the invention, which method comprises passing a gas upwardly through holes in a plate;
This consists in passing gas into the electrolyte on the plate. Depending on the reaction, this method continuously
That is, it can be carried out by continuously supplying gas, electrolyte and/or electric current, or discontinuously, ie by discontinuously supplying gas, electrolyte and/or electric current.

Still another aspect of the invention is a method of carrying out an electrochemical process or reaction using the multi-stage electrochemical cell described above, which method directs the electrolyte downwardly from an upper chamber to an intermediate chamber and between each chamber. flow across the perforated plate,
The method then consists of flowing the gas upward through holes in successive plates, thereby causing the gas to bubble into the electrolyte on each plate. The method can also be carried out continuously or discontinuously.

The gas may be a reactant or a mixture of reactants, or it may serve other purposes, for example an inert purge gas such as nitrogen may be used to sweep away the products of the reaction, or CO ₂
or the PH of the electrolyte using a buffer like _NH3
can be controlled to suppress undesired reactions.

In addition to the production of propylene oxide, a vessel according to the invention could be used for the electrosynthesis of other products, for example the production of butylene oxide from butene.

Another important application is the electrochemical treatment of certain effluent gases. Generally speaking, many applications are where one or more of the reactants are gases and mixing the anolyte and catholyte is advantageous or not a problem.

BEST MODE FOR CARRYING OUT THE INVENTION The electrochemical cell shown in FIGS. 1 to 3 has an upper chamber 1 and a lower chamber 2.
It consists of a generally rectangular box-like enclosure made up of A plate 3 fixed between the flanges 34 of the upper chamber 1 and the lower chamber 2 separates the enclosure from the upper chamber 1 and the lower chamber 2.
Divide into. The joint between the flange 34 and the plate 3 is sealed by a gasket 6.

The upper chamber 1 has an electrolyte inlet 7, an electrode chamber 8 and an electrolyte outlet 9. The inlet 7 consists of a riser 10 which passes through the top 35 of the upper chamber 1;
In the vicinity of the plate 3, it extends downwardly between the upright plate 11 and the three side walls 36 of the upper chamber 1. The plate 11 is integral with the plate 3 and extends across the width of the upper chamber 1 and forms an inlet weir which, in use, holds a pool of electrolyte at the liquid level 12 and this weir. Electrolyte is supplied via riser 10.

The electrolyte outlet 9 consists of an outlet weir plate 13 which also extends across the width of the upper chamber 1 but is formed by one wall of the enlarged square end 14 of the down pipe 15; The downpipe 15 then passes through the hole 16 in the plate 3. The square ends 14 are fitted into corresponding square recesses defined by the side walls 36 of the upper chamber 1 and the upright plate 17 which is integral with the plate 3. The top of the outlet dam 13 is lower than the top of the inlet dam 11 and, in use, it maintains the electrolyte in the electrode chamber 8 at the liquid level 18.

Seven electrodes in the form of plates are arranged in the electrode chamber 8, and these electrodes are connected to the plates 11 and 17.
are held in spaced apart parallel relationship in vertical grooves 20 therein. The electrode 19 has two terminal electrodes 21
The terminal electrode 21 is disposed between the side wall 36
The current lead wire 22 passes through the side wall 36 of the cap. Plate 11 at one end of the electrode chamber
and the plates 17 and 13 at the other end are the side walls 3 of the upper chamber 1.
6 together form an electrolyte receiver, the bottom of which is plate 3
It is formed by a perforated central part. hole 2 in plate 3
3 is in the form of a circular hole with a diameter of about 1 mm, and each 7 is in the center between adjacent electrodes 19 or 19 and 21.
They are arranged in eight rows of equally spaced holes.

The upper chamber 1 of the enclosure also includes in its top 35 a gas outlet pipe 24 for extracting gas from the gas collection chamber 4 .

In the lower chamber 2, the down pipe 15 is located near the bottom.
The liquid level 31 extends below the level of an upright wall 30 forming a trap or weir that retains the pool of exiting electrolyte. At the bottom of the lower chamber 2 there is an outlet pipe 32 which draws off the electrolyte flowing over the weir wall 30. The lower chamber 2 also has a gas inlet pipe 33 that supplies gas into the gas supply chamber 5 . The electrolyte at the bottom of the gas supply chamber 5 prevents this gas from escaping via the outlet pipe 32 or downpipe 15, so that the gas goes up through the holes 23 in the plate 3 and into the electrode chamber 8. It foams up in the electrolyte between the electrodes 19 and 19 and 21.

To operate this electrochemical cell, the electrolyte outlet pipe 32 is connected to the downpipe 10 by an electrolyte circulation system, and the gas outlet pipe 24 is connected to the inlet pipe 33 by a gas circulation system. The electrolyte is circulated at a selected rate so that fresh electrolyte from the downcomer 10 passes over the inlet weir, i.e. plate 11, across the electrode chamber 8, i.e. between electrode 19 and between 19 and 21. It flows through defined parallel channels and exits over the outlet dam 13. Also, the gas is circulated at a selected rate, which rate can be adjusted independently of the electrolyte flow rate. The gas passes upwardly from the gas supply chamber 5 through the hole 23, bubbles through the electrode 19 and the electrolyte between 19 and 21, and enters the upper or gas collection chamber 4. Once all current is established, current is applied to electrodes 19 and 21. In some cases, i.e. when gas is the reactant,
Electric current is supplied to the electrodes when supplying gas, and operation is advantageously carried out continuously, ie with constant electrolyte and gas flow rates. However, in other cases it may be advantageous to operate discontinuously, ie with the electrolyte or gas or both flowing discontinuously and the current flowing between the appropriate phases. The products of the electrochemical reaction can be removed as a gas and extracted from the gas stream before being recycled, or they can be dissolved in an electrolyte, in which case the reaction products are electrolyzed before being recycled. Remove from liquid. For the production of propylene oxide, it may be advantageous for the product to partition itself between the electrolyte and the gas phase, and therefore to be removed from the gas outlet pipe 24 and separated by condensation.

Industrial Applicability An electrochemical cell as shown in Figures 1-3 was used for the production of propylene oxide. The electrodes were graphite plates, each 6.3 cm high, 8.3 cm long, and 0.3 cm thick, and were spaced approximately 4 mm apart. 0.1
An electrolyte of 5 molar or 0.2 molar NaBr solution was flowed at a constant rate ranging from about 20 to 45 cm ³ /sec.
The propylene was also circulated at a constant rate ranging from about 5 to 40 cm ³ /sec with a fresh supply of propylene. Constant current (approximately 1~2A and constant voltage 25~
Propylene was circulated for several minutes to remove air from the electrochemical cell enclosure and saturate the electrolyte solution before supplying 40 V). The operation was carried out at room temperature and atmospheric pressure, and the pH of the electrolyte was maintained between about 11 and 12 by addition of HBr solution. Gas and liquid samples were tested at 0.5 hour intervals. In some cases, a blowing agent (〓Decon'' trademark) was added to promote rapid mass transfer of the reactants to the electrodes and was seen to increase dissolution of propylene.lower temperatures, lower currents and lower gas flow rates The results showed high current efficiency, about 80%, and low energy consumption, 0.2-0.3 kWh/gram mole of propylene oxide when using dilute NaBr in the epoxidation of 1-butene using the same bath. An energy consumption of 0.26 kWh/gram mole of butylene oxide was achieved with current efficiencies approaching the values obtained with propylene oxide. These performances were achieved by optimizing the bath dimensions and process conditions. , and can be improved by operating at higher pressures if possible.

As shown in FIG. 4, upper, middle and lower chambers similar to FIGS. 1-3 can be stacked to form a multi-stage electrochemical cell with a cascaded electrolyte flow system. In FIG. 4, the same parts are designated with the same reference numerals as before, and some parts of the intermediate chamber are designated with double reference numerals. The upper chamber 1 and the lower chamber 2 are exactly the same as the upper chamber 1 and the lower chamber 2 of FIGS. 1 and 2. However, in a multi-stage electrochemical cell, the perforated plate 3 forming the bottom of the upper chamber, the middle chamber also forms the top of the gas collection chamber 4 of the lower middle chamber (except the bottom middle chamber), and The hole 23 acts as a gas outlet of the intermediate chamber; the downcomer 1 for the discharge of the electrolyte from the upper chamber, the intermediate chamber (except the lowest intermediate chamber)
5 forms the down pipe 10 of the lower intermediate chamber; the intermediate chamber gas collection chamber 4 forms the upper intermediate chamber, the gas supply chamber 5 of the upper chamber; and so on.

In operation of this multi-stage electrochemical cell, gas is supplied to the bottom of the lower chamber from the inlet pipe 33, passes upward through the continuous middle chamber and upper chamber, and bubbles in the electrolyte in each electrode chamber 8. and is extracted from the top 35 of the upper chamber via the outlet pipe 24. The electrolyte is supplied to the down pipe 1 at the top 35 of the upper chamber.
0, descends from the upper chamber to the middle chamber and the lower chamber as indicated by the arrow, flows across the electrode chambers of the upper chamber, the middle chamber, and is extracted from the bottom of the lower chamber via an outlet pipe 32. It can be done. As before,
Current is supplied to the electrodes of the upper chamber, the middle chamber, and operation can be continuous or discontinuous.

Many modifications can be made to the embodiments described above. A variety of electrode materials can be used depending on the reaction conditions; in particular, dimensionally stable metal electrodes may be preferred for some reactions. Further, the electrodes do not necessarily have to be bipolar. In some cases, parallel spaced electrodes can be arranged generally transverse to the direction in which the electrolyte flows across the perforated plate. Holes of various shapes and sizes can be formed in this plate, and for certain reactions, instead of being placed between adjacent electrodes, these holes can be placed in a porous or It can be introduced into a perforated electrode. In place of the preferred electrolyte inlet and outlet weirs, other means could be provided to create a flow of electrolyte generally across the perforated plate while maintaining a constant electrolyte level.

[Brief explanation of the drawing]

Embodiments of the invention are illustrated, by way of example, in the accompanying drawings. 1 is a cross-sectional view of the electrochemical cell along the line - of FIG. 2; FIG. 2 is a cross-sectional view of the electrochemical cell along the line - of FIG. 1; FIG.
FIG. 4 is a cross-sectional view of the cell of FIGS. 1 and 2 along the lines; FIG. 4 is a cross-sectional view of the cell of FIG. FIG.