ELECTROCHEMICAL CELL AND PROCESS

Description

Technical field

[0001] The invention relates to electrochemical cells, particularly for carrying out electrochemical reactions involving a gaseous reactant or in which gas is suppfied for another purpose such as purging or sweeping away a product of reaction, or as a buffering agent or to inhibit unwanted reactions.

[0002] The invention is more specifically, but not exclusively, concerned with an electrochemical cell for electro-organic synthesis, for example the electrochemical oxidation of unsaturated and poly-unsaturated hydrocarbons. The electrochemical production of propylene oxide is particularly interesting, and will be discussed in greater detail by way of example.

Background art

[0003] In the electrochemical production of propylene oxide, propylene is converted to propylene halohydrin by reaction with halogen generated in situ by the anodic oxidation of the halide salt of an alkali metal in aqueous solution. The propylene halohydrin is converted to propylene oxide by reaction with the hydroxyl group at the cathode from which hydrogen is liberated. The general scheme of reaction when sodium bromide is used as the electrolyte is:

Anode

2Br^-→Br₂+2e

C₃H₈+Br₂+H₂O→C₃H₆BrOH+HBr

Cathode

2H₂0->H_Z+20H--2e

C₃H₆BrOH+OH→C₃H₈O+H₂O+Br

Overall

C₃H,+H₂0-⁺C₃H₆0+H,

[0004] In principle, only water, propylene and electrical energy are consumed in the formation of propylene oxide and hydrogen. The halide electrolyte, sodium bromide, is continuously oxidized and regenerated within the cell for further use, although losses of bromine may be caused by the formation of hypobromite and bromine gas.

[0005] The advantages of this electrochemical route, which obviates the production of waste calcium chloride encountered in the conventional chemical process, have long been recognized but attempts to implement it have not proved to be very effective.

[0006] French Patent Specification No. 1,375,973 and W. German Auslegeschrift No. 1,258,856 proposed the use of diaphragm cells in which propylene halohydrin is generated at a porous anode and passes through the diaphragm into an alkaline catholyte in a porous cathode where it is saponified to propylene oxide. However, these cells are complex and the efficiency low.

[0007] U.S. Patent Specification No. 3,394,059 proposed carrying out the halohydrin process in a non-divided cell, preferably a flowing mercury cathode cell, in which propylene was simply bubbled into the electrolyte. Again, the performance was poor and F. Beck (IUPAC XXIVth International Congress, Hamburg, 1973, Vol. 5, "Applied Electrochemistry", pages 111-136) has claimed an improved performance using a capillary gap cell. In this propylene dispersed in a dilute NaBr electrolyte is supplied through a central hole in a pile of electrode discs and flows radially outwards between the discs. The gap between the electrode discs was made small (0.2 to 0.5 mm) to enable low bromide concentrations to be handled with low ohmic losses. A current efficiency of 70% or just above and an energy consumption of 0.23-0.30 kwh/gmol propylene oxide are reported for a small capillary gap cell, but scaling up this cell for industrial production would involve difficulties.

[0008] Fleischmann et al. (Symposium on Electrochemical Engineering /, Newcastle 1971, Editor J. D. Thornton) have studied the synthesis of propylene oxide using a bipolar packed bed cell. The cell consisted of a packed bed made up of a mixture of conducting and non-conducting particles. The conducting particles become bipolar by using dilute electrolyte in the cell and applying sufficient voltage gradient between the contact electrodes so as to overcome the resistance drop in the electrolyte. Using glass coated with graphite as the conducting particles and glass beads as the non-conducting particles, all particles having a diameter of about 0.05 cm, the energy consumption of such a cell was found to be high, in the range of 2.5-3 kwh/gmol propylene oxide.

[0009] A bipolar rod flow cell was used by King et al. (Trans. Inst. Chem. Eng., 53, 1975) for the production of propylene oxide. The cell consisted of vertical rows of electrically- conductive rods, separated from one another by a small gap. The electrolyte was fed to the top rods, flowed downwards over the vertical rows and was collected from the bottom rods for recirculation. The gaseous reactant, propylene, was passed up the space between the vertical rows, in continuous contact with the electrolyte film. The current efficiency of this cell was of the order of 70% and the energy consumption is estimated in the range 0.35-0.4 kwh/gmol propylene oxide.

[0010] R. E. W. Jansson et al. have developed a bipolar electrochemical pump cell for which an energy yield below 0.2 kwh/gmol of propylene oxide is claimed (Journal of App. Electrochemistry, 7, (1977), 437-443) for trial experiments on a laboratory scale using a cathode rotating at 3000 rpm with an electrode gap of 0.25 mm. However, the structure is not easily scaled-up for industrial production.

[0011] Various other cell structures designed to provide a gas supply to the electrolyte are also known. For example, in the electrowinning of metals such as copper, it is well known to supply a gas through bubble tubes situated below the electrodes in order to agitate the electrolyte (e.g. see U.S. Patent Specification No. 3,875,041 and the earlier patents referred to therein). Another suggestion made in U.S. Patent Specification No. 3,259,049 was to provide electrolyte agitation in an electroplating tank using a hollow, flat manifold which is placed in the electrolyte, under the electrodes, and has a perforated upper surface for bubbling gas up into the electrolyte, the gas being supplied to the manifold via a gas flow tube. In contrast to the fixed bubble-tube arrangements, the entire manifold structure was made removable to facilitate periodic cleaning to remove fragments which may block the perforations in the manifold.

[0012] US Patent 3 632 497 describes cells for carrying out inter alia the electrochemical oxidation of oelfins using a monopolar array of platinized titanium anodes carried on a titanium base acting as a current feeder and having apertures for the passage of oxidizing gas via porous plates usually forming the anode walls, the electrolyte inlet and outlet being in a concrete cell cover.

Disclosure of invention

[0013] An object of the invention is to provide an electrochemical cell specifically (but not exclusively) for the production of propylene oxide and which can be designed to meet up to the following requirements better than the previously proposed cells:

1) Simplicity of the mechanical construction;

2) Good heat and mass transfer characteristics;

3) Simplicity of operation and continuous operation;

4) Good gas-liquid contact; and

5) Good mixing of anolyte and catholyte products.

[0014] According to the invention, in its simplest form, an electrochemical cell comprises electrodes disposed over a perforated generally horizontal plate, an electrolyte inlet and an electrolyte outlet spaced apart on opposite sides of the electrodes across the perforated plate, and a cell housing which is divided by the perforated plate into an upper chamber and a lower chamber. The lower chamber is a gas supply chamber from which, in use, gas passes up through perforations in the plate and bubbles through electrolyte on the plate to collect in the upper chamber.

[0015] The electrolyte inlet and electrolyte outlet of the cell are each advantageously formed by a weir. The top of the inlet weir is higher than the top of the outlet weir which in turn is higher than the top of the electrodes. Hence, by controlling the supply of fresh electrolyte to the inlet weir, the electrolyte is made to flow over the inlet weir and between the electrodes as it passes across the perforated plate, while spent or reacted electrolyte flows out over the outlet weir at a chosen rate. These weirs may be formed by upstanding plates integral with or fixed on the perforated plate.

[0016] The electrodes, advantageously a bipolar array of vertical plate-like electrodes disposed in spaced parallel relationship to provide channels between the electrolyte inlet and outlet, may rest on the perforated plate which, in this instance, will be made of electrically insulating material. The perforations in the plate can be arranged in rows each spaced about mid-way between adjacent electrodes. Perforations in the form of generally circular bores having a diameter of about 1 mm have been found satisfactory, but perforations of other form and size can be used.

[0017] The bottom of the lower chamber of the cell housing can serve as a receptacle for a pool of spent or reacted electrolyte which flows via a downcomer tube leading from the aforementioned outlet weir into the pool from which electrolyte is removed via an outlet and may be recycled. Fresh electrolyte can be supplied to the aforementioned inlet weir via an incomer tube which extends down through the upper chamber of the cell housing into the electrolyte retained by the inlet weir.

[0018] The upper and lower chambers may be formed by upper and lower sections of a box-like cell housing, these sections being separated by the aforesaid plate which is perforated only in the region under the electrodes. A rectangular enclosure for the electrodes may thus be formed by the side walls of the upper housing section fitting against upstanding plates forming the inlet and outlet weirs. These side walls can carry inset terminal electrodes of the electrode array.

[0019] The invention also concerns an electrochemical reactor formed by stacking several cells according to the invention in a column whereby the gas-collection chamber of each cell (except the top one) forms the gas-supply chamber for the cell above. In other words, the perforated plate of each cell (except the lowest one) forms the top of the gas-collection chamber of the cell below. With this arrangement, in operation, gas passes up through the cells from the bottom of the column to the top, bubbling through the electrolyte in each cell. Preferably, the electrolyte outlets and inlets of the successive cells are connected in cascade so that the electrolyte flows down the column from one cell to the next, the electrolyte flowing across the perforated plate of each cell from the inlet to the outlet and then down to the inlet of the cell below. Each cell of such a reactor can have the aforementioned preferred features of a single cell unit, such as the electrolyte inlets and outlets being formed by weirs.

[0020] Another aspect of the invention is a method of carrying out an electrochemical process or reaction using a cell according to the invention, this method comprising passing gas up through the perforations in the plate so that it bubbles into the electrolyte on the plate. Depending on the reaction, the method may be operated continuously, i.e. continuously supplying gas, electrolyte and electric current, or discontinuously, i.e. with an intermittent supply of gas, electrolyte and/or current.

[0021] Yet another aspect of the invention is a method of carrying out an electrochemical process or reaction using a reactor formed by a column of cells according to the invention, this method comprising flowing electrolyte down the column from one cell to the next and across the perforated plate of each cell, and passing gas up through the perforations in the successive plates so that the gas bubbles through the electrolyte on each plate. This method may also be operated continously or discontinuously.

[0022] The gas may be a reactant or a mixture of reactants, or may serve another purpose, for instance an inert purge gas such as nitrogen may be used to sweep away a product of reaction, or a buffering agent such as C02 or NH₃ may be used to control the pH of the electrolyte, for example to inhibit unwanted reactions.

[0023] In addition to the preparation of propylene oxide, the cell according to the invention could be used in the electro-synthesis of other products such as the formation of butylene oxide from butene.

[0024] Another important application is the electrochemical treatment of some effluent gases. Generally speaking, many applications concern the situation where one or more of the reactants is a gas and where mixing of anolyte and catholyte is advantageous or inconsequential.

Brief description of drawings

[0025] Embodiments of the invention are shown, by way of example, in the accompanying drawings, in which:

Figure 1 is a cross-section of a cell along the line I-I of Figure 2;

Figure 2 is a cross-section along the line II-II of Figure 1;

Figure 3 is a sectional view of the cell of Figures 1 and 2 along the line III-III of Figure 1;

Figure 4 is a cut-away view similar to Figure 1, of part of a column formed of several cells connected in cascade. ,

Best modes for carrying out the invention

[0026] The cell of Figures 1 to 3 comprises a generally rectangular box-like housing composed of an upper section 1 and a lower section 2. A plate 3, fixed between flanges 34 of the upper and lower sections 1, 2 divides the housing into an upper chamber 4 and a lower chamber 5. The joints between the flanges 34 and the plate 3 are sealed by gaskets 6.

[0027] The upper chamber 4 has an electrolyte inlet section 7, an electrode section 8 and an electrolyte outlet section 9. The inlet section 7 comprises an incomer tube 10 which passes through the top 35 of the upper section 1 and extends down to near the plate 3, between an upstanding plate 11 and three side walls 36 of the section 1. The plate 11, which is integral with the plate 3, extends across the width of the chamber 4 and forms an inlet weir which, in use, holds a pool of electrolyte at a level 12, this electrolyte being delivered via the incomer tube 10.

[0028] The electrolyte outlet section 9 comprises an outlet weir plate 13 which also extends across the width of the chamber 4, but is formed by one wall of an enlarged square end 14 of a downcomer tube 15 which passes through a hole 16 in the plate 3. The square end 14 is fitted in a corresponding square recess defined by the side walls 36 of the upper section 1 and an upstanding plate 17 integral with the plate 3. The top of the outlet weir plate 13, is lower than the top of the inlet weir plate 11 and, in use, it maintains electrolyte in the electrode section 8 at a level 18.

[0029] In the electrode section 8 are disposed seven electrodes 19 in the form of plates held in spaced parallel relationship in vertical grooves 20 in the plates 11 and 17. The electrodes 19 are disposed between two terminal electrodes 21 which are inset in the side walls 36 through which pass current leads 22. The plate 11 at one end of the spaced electrodes, and the plates 17 and 13 at the other end define, with the side walls 36 of the section 1, an electrolyte receptacle whose bottom is formed by a perforated central part of the plate 3. The perforations in the plate 3, indicated at 23, are in the form of circular holes or bores having a diameter of about 1 mm, arranged in eight rows each of seven equally-spaced holes disposed mid-way between the adjacent electrodes 19 or 19 and 21.

[0030] The upper housing section 1 also comprises, in its top 35, a gas outlet pipe 24 for the removal of gas from the upper chamber 4.

[0031] In the lower chamber 5, the downcomer tube 15 extends near to the bottom, below the level of an upstanding wall 30 which forms a trap or weir holding a pool of outgoing electrolyte at a level 31. In the bottom of the lower section 2 is an outlet pipe 32 for removing the electrolyte which has flowed over the weir wall 30. The lower housing section 2 also has a gas inlet pipe 33 for delivering gas into the lower chamber 5. Electrolyte in the bottom of the chamber 5 prevents this gas from escaping via the outlet pipe 32 or the downcomer tube 15, so that the gas passes up through the perforations 23 in the plate 3 and bubbles into the electrolyte between the electrodes 19, and 19 and 21 in the electrode section 8.

[0032] To operate the cell, the electrolyte outlet pipe 32 is connected to the incomer tube 10 by an electrolyte circulating system, and the gas outlet pipe 24 is connected to the inlet pipe 33 by a gas circulating system. The electrolyte is circulated at a chosen rate so that fresh electrolyte from the incomer tube 10 flows over the inlet weir, namely the plate 11, across the electrode section 8, i.e. through the parallel channels defined between the electrodes 19, and 19 and 21, and out over the outlet weir plate 13. The gas is also circulated at a chosen rate, which can be adjusted independently of the electrolyte flow rate. It passes from the lower chamber 5 up through the perforations 23 and bubbles through the electrolyte between the electrodes 19, and 19 and 21 into the upper or gas-collection chamber 4. When all of the flows have been set up, current is supplied to the electrodes 19 and 21. In some instances, i.e. when the gas is a reactant, current is supplied to the electrodes as the gas is supplied, and the operation is advantageously continuous, i.e. with constant electrolyte and gas flow-rates. In other instances, however, it may be advantageous to operate discontinuously, i.e. with an intermittent flow of electrolyte or gas or both, with current supply during the appropriate phase. The product of the electrochemical reaction may be taken off as a gas and removed from the gas stream before recirculating, or may be taken off dissolved in the electrolyte, in which case it is removed from the electrolyte before recycling. For the production of propylene oxide, the product will partition itself between the electrolyte and the gas phase and may therefore advantageously be removed through the gas outlet pipe 24 and separated by condensation.

Industrial applicability

[0033] A cell as shown in Figures 1 to 3 was used for the production of propylene oxide. The electrodes were plates of graphite each 6.3 cm high, 8.3 cm long and 0.3 cm thick and spaced apart by a distance of about 4 mm. The electrolyte, 5 litres of 0.1 M or 0.2M NaBr solution, was flowed at a constant rate, in the rate from about 20 to 45 cm³/sec. Propylene gas was also circulated, using a supply of fresh propylene at a constant rate in the range from about 5 to 40 cm³/sec. Before supplying a constant current (at from 1 to 2A and a constant voltage from 25 to 40V), the propylene was circulated for several minutes to remove air from the cell housing and to saturate the electrolyte solution. Operation was carried out at ambient temperature and atmospheric pressure and the pH of the electrolyte was maintained between about 11 and 12 by adding HBr solution. Gas and liquid samples were checked at 1/2 hourly intervals. In some instances, a foaming agent ("Decon", Trademark) was added with a view to promoting rapid mass transport of the reactants to the electrodes, and to increase the solubility of propylene. The results showed a high current efficiency, about 80%, and a low energy consumption, 0.2 to 0.3 kwh/gmol of propylene oxide when operating at low temperature, low current and low gas flowrate using dilute NaBr. For the epoxidation of 1-butene using the same cell, an energy consumption of 0.26 kwh/gmol of butylene oxide was achieved at a current efficiency approaching that obtained with propylene oxide. These performances may be improved by optimizing the cell dimensions and process conditions and, possibly, by operating at elevated pressures.

[0034] As shown in Figure 4, several cells similar to that of Figures 1 to 3 can be stacked in a column with the electrolyte flow system connected in cascade. In Figure 4, the same parts are designated by the same references as before, some parts of the intermediate cells being designated by double references. The upper section 1 of the housing of the top cell and the lower section 2 of the housing of the bottom cell are exactly the same as the upper and lower sections 1 and 2 of Figures 1 and 2. However, in the reactor column, the perforated plate 3 forming the bottom of one cell also forms the top of the gas collection chamber 4 of the cell below and its perforations 23 act as the gas outlet for that chamber; the downcomer tube 15 for the discharge of electrolyte from one cell forms the incomer tube 10 of the cell below; the gas collection chamber 4 of each cell (except the top one) forms the gas supply chamber 5 for the cell above; and so forth.

[0035] In operation of this reactor column, gas is supplied at the bottom of the column, via the inlet pipe 33, passes up through the successive cells, bubbling up through the electrolyte in each electrode section 8, and is removed from the top of the column via the outlet pipe 24. Electrolyte is supplied at the top 35 of the column via the top incomer tube 10 and, as indicated by the arrow, cascades down from one cell to the next, flowing across the electrode section 8 of each cell, and is removed from the bottom of the column via the outlet pipe 32. As before, current is supplied to the electrodes of each cell and the operation may be continuous or discontinuous.

[0036] Many variations may be made to the described embodiments. Various electrode materials can be used, depending on the reaction: in particular, dimensionally-stable metal electrodes will be preferred for some reactions. Also, the electrodes need not be bipolar. In some instances, spaced parallel electrodes can be disposed transverse to the general direction of flow of electrolyte across the perforated plate. Various shapes and sizes of perforations can be provided in this plate and, instead of being disposed between the adjacent electrodes, for certain reactions these perforations could lead into porous or foraminous electrodes disposed on the perforated plate. Instead of the preferred electrolyte inlet and outlet weirs, other means could be provided to enable a flow of the electrolyte generally across the perforated plate, while maintaining a given electrolyte level.

Claims

1. An electrochemical cell, comprising electrodes disposed over a perforated generally horizontal plate, an electrolyte inlet and an electrolyte outlet spaced apart on opposite sides of the electrodes across the perforated plate, and a cell housing which is divided by the perforated plate into an upper chamber and a lower chamber, wherein the lower chamber is a gas supply chamber for passing gas via the perforations in the perforated plate through the electrolyte located above the plate in the upper chamber.

2. The electrochemical cell of Claim 1, wherein the electrolyte inlet and the electrolyte outlet are each formed by a weir.

3. The electrochemical cell of Claim 2, wherein the top of the electrolyte inlet weir is higher than the top of the electrolyte outlet weir which is higher than the top of the electrodes.

4. The electrochemical cell of Claim 2 or 3, wherein the weirs are formed by plates upstanding from the perforated plate.

5. The electrochemical cell of claim 1, comprising a bipolar array of vertical plate-like electrodes disposed in spaced parallel relationship to define channels between the electrolyte inlet and the electrolyte outlet.

6. The electrochemical cell of claim 5, wherein the bipolar electrodes rest on the perforated plate, which is made of electrically-insulating material, and wherein the perforations in the plate are arranged in rows spaced about mid-way between adjacent electrodes.

7. The electrochemical cell of claim 2, wherein a bottom part of the lower chamber forms a receptacle for a pool of reacted electrolyte, and a downcomer tube leads from the electrolyte outlet weir to the bottom part of the lower chamber, for the delivery of reacted electrolyte to the pool.

8. The electrochemical cell of claim 7, comprising an incomer tube extending down through the upper chamber, for the delivery of fresh electrolyte to the electrolyte inlet weir.

9. The electrochemical cell of claim 1, wherein the upper and lower chambers are formed by respective separate upper and lower sections of a box-like cell housing, the housing sections are separated by and secured to the periphery of the plate and the perforations are disposed in the plate only in the region under the electrodes.

10. The electrochemical cell of claim 9, wherein the upper housing section has facing side walls which fit against upstanding plates forming electrolyte inlet and outlet weirs to define a rectangular enclosure for the electrodes.

11. The electrochemical cell of claims 5 and 10, wherein the polar electrode array includes terminal electrodes inset in said facing side walls of the upper housing section.

12. The electrochemical cell of claim 1, wherein the electrodes are disposed over perforations in the perforated plate.

13. An electrochemical reactor comprising (I) a plurality of cells, each cell comprising (i) electrodes disposed over a perforated generally horizontal plate and (ii) an electrolyte inlet and (iii) an electrolyte outlet spaced apart on opposite sides of the electrodes across the perforated plate, and (II) a reactor housing in which the cells are stacked in a columnar arrangement, the perforated plates of the cells dividing the reactor housing into superimposed chambers, each perforated plate being disposed over a gas-supply chamber for passing gas up through perforations in the plate to bubble through electrolyte on the plate and collect in the chamber thereabove and which (except for that of the top cell) forms the gas-supply chamber for the cell above.

14. The electrochemical reactor of claim 13, wherein the electrolyte inlet and the electrolyte outlet of each cell are formed by weirs.

15. The electrochemical reactor of claim 14, wherein the top of the electrolyte inlet weir of each cell is higher than the top of the electrolyte outlet weir which is higher than the top of the electrodes.

16. The electrochemical reactor of claim 14 or 15, wherein the weirs are formed by plates upstanding from the perforated plates.

17. The electrochemical reactor of claim 13, wherein each cell comprises a bipolar array of vertical plate-like electrodes disposed in spaced parallel relationship to define channels between the electrolyte inlet and the electrolyte outlet of the cell.

18. The electrochemical reactor of any of claims 13 to 17, comprising means for connecting the outlets and inlets of successive cells in cascade to flow electrolyte down the reactor from the electrolyte outlet of one cell to the electrolyte inlet of the cell below.

19. The electrochemical reactor of claim 17, wherein the electrodes rest on the perforated plate of the associated cell, each plate is made of electrically-insulating material and the perforations in each plate are arranged in rows spaced about mid-way between the respective adjacent electrodes.

20. The electrochemical reactor of claims 14 and 18, comprising downcomer tubes for delivering electrolyte from the electrolyte outlet weir of each cell (except the lowest one) to the electrolyte inlet weir of the cell below.

21. The electrochemical reactor of claim 20, wherein a bottom part of the lowest chamber forms a receptacle for a pool of reacted electrolyte and a further downcomer tube leads from the electrolyte outlet of the lowest cell to the bottom part of the lowest chamber, for the delivery of reacted electrolyte to the pool.

22. The electrochemical reactor of claim 21, comprising an incomer tube extending down through the top chamber, for the delivery of fresh electrolyte to the electrolyte inlet weir of the top cell.

23. The electrochemical reactor of claim 13, wherein the respective sections of the reactor housing are separated by and secured to the periphery of the respective horizontal plates, which are perforated only in the regions under the electrodes of the respective cells of the reactor.

24. The electrochemical reactor of claim 23, wherein each housing section (except the lowest one) has facing side walls which fit against upstanding plates forming electrolyte inlet and outlet weirs to define a rectangular enclosure for the electrodes of the respective cell.

25. The electrochemical reactor of claims 17 and 24, wherein each bipolar electrode array includes terminal electrodes inset in the facing side walls of the respective housing section.

26. The electrochemical reactor of any of claims 13 to 18 and 23 to 25, wherein the electrodes are disposed over perforations in the respective plate.

27. A method of carrying out an electrochemical process or reaction in the electrochemical cell of any of claims 1 to 12, which comprises passing gas from the gas-supply chamber up through perforations in the plate to bubble through electrolyte on the plate and collect in the upper chamber.

28. A method of carrying out an electrochemical process or reaction in the electrochemical reactor of any of claims 13 to 26, which comprises flowing electrolyte down the columnar reactor from one cell to the next and across the perforated plate of each cell, and passing gas up through the perforations in the successive plates so that the gas bubbles through the electrolyte on each plate.

29. The method of claim 27 or 28, wherein the gas is a reactant in the electrochemical reaction.

30. The method of claim 27 or 28, wherein the gas is propylene and the electrolyte is a halide salt of an alkali metal in aqueous solution.

Ansprüche

1. Elektrochemische Zelle mit Elektroden, die sich über eine perforierte, allgemein horizontale Platte erstrecken, einem Elektrolyteinlaß und einem Elektrolytauslaß, die im Abstand an entgegengesetzten Seiten der über die perforierte Platte verlaufenden Elektroden angeordnet sind, und einem Zellgehäuse, das durch die perforierte Platte in eine obere Kammer und eine untere Kammer unterteilt ist, wobei die untere Kammer eine Gaszufuhrkammer zur Führung von Gas durch die Perforationen in der perforierten Platte und durch den über der Platte in der oberen Kammer angeordneten Elektrolyten ist.

2. Elektrochemische Zelle nach Anspruch 1, dadurch gekennzeichnet, daß sowohl der Elektrolyteinlaß als auch der Elektrolytauslaß als ein Wehr ausgebildet ist.

3. Elektrochemische Zelle nach Anspruch 2, dadurch gekennzeichnet, daß das obere Ende des Elektrolyteinlaßwehrs höher ist als das obere Ende des Elektrolytauslaßwehrs, das seinerseits über dem oberen Ende der Elektroden liegt.

4. Elektrochemische Zelle nach Anspruch 2 oder 3, dadurch gekennzeichnet, daß die Wehre durch aufrecht auf der perforierten Platte stehende Platten gebildet werden.

5. Elektrochemische Zelle nach Anspruch 1, dadurch gekennzeichnet, daß die plattenartig ausgebildeten Elektroden bipolar in Abständen parallel so zueinander angeordnet sind, daß sie Kanäle zwischen dem Elektrolyteinlaß und dem Elektrolytauslaß begrenzen.

6. Elektrochemische Zelle nach Anspruch 5, dadurch gekennzeichnet, daß die bipolaren Elektroden auf der aus elektrisch isolierendem Material hergestellten perforierten Platte aufsitzen und die Perforationen in der Platte in Reihen, die etwa in der Mitte zwischen benachbarten Elektroden verlaufen, angeordnet sind.

7. Elektrochemische Zelle nach Anspruch 2, dadurch gekennzeichnet, daß ein Bodenteil der unteren Kammer einen Behälter zur Aufnahme eines Pools an umgesetzten Elektrolyt bildet und eine Fallrohr vom Elektrolytauslaßwehr zu diesem Bodenteil der unteren Kammer zum Ausbringen von umgesetztem Elektrolyte in den Pool führt.

8. Elektrochemische Zelle nach Anspruch 7, gekennzeichnet durch ein abwärts durch die obere Kammer verlaufendes Zufuhrrohr zur Lieferung von frischem Elektrolyt zu dem Elektrolyteinlaßwehr.

9. Elektrochemische Zelle nach Anspruch 1, dadurch gekennzeichnet, daß obere und untere Kammer als oberer und unterer Abschnitt eines kastenförmigen Zellgehäuses ausgebildet und diese Gehäuseabschnitte durch die Platte voneinander getrennt und am Umfang der Platte befestigt sind und daß die Perforationen sich nur in dem unter den Elektroden liegenden Gebiet der Platte befinden.

10. Elektrochemische Zelle nach Anspruch 9, dadurch gekennzeichnet, daß der obere Gehäuseabschnitt einander zugewandte Seitenwände, die an aufrecht stehenden, das Elektrolyteinlaßwehr und das Elektrolytauslaßwehr bildenden Platten anliegen und dadurch eine rechteckige Einfassung für die Elektroden bilden, aufweist.

11. Elektrochemische Zelle nach Anspruch 5 und 10, dadurch gekennzeichnet, daß die bipolare Elektrodenanordnung endständige Elektroden, die in die einander zugewandten Seitenwände des oberen Gehäuseabschnitts eingelassen sind, aufweist.

12. Elektrochemische Zelle nach Anspruch 1, dadurch gekennzeichnet, daß die Elektroden über Perforationen in der perforierten Platte angeordnet sind.

13. Elektrochemischer Reaktor aus (1) einer Anzahl von Zellen, von denen jede (i) über einer perforierten, allgemein horizontalen Platte angeordnet ist, (ii) einen Elektrolyteinlaß und (iii) einen Elektrolytauslaß, die in Abstand voneinander an entgegengesetzten Seiten der Elektroden über der perforierten Platte angeordnet sind, aufweist, (11) einem Reaktorgehäuse, in dem die Zellen in Säulenform übereinander gestapelt sind, wobei die perforierten Platten der Zellen den Reaktor in übereinander liegende Kammern aufteilen, jede perforierte Platte über einer Gaszufuhrkammer zur Führung von Gas durch die Perforationen in der Platte, so daß es durch den Elektrolyten perlt und sich in der Kammer darüber sammelt, angeordnet ist und (mit Ausnahme derjenigen der obersten Zelle) eine Gaszufuhrkammer für die darüberliegende Zelle bildet.

14. Elektrochemischer Reaktor nach Anspruch 13, dadurch gekennzeichnet, daß der Elektrolyteinlaß und der Elektrolytauslaß jeder Zelle durch ein Wehr gebildet wird.

15. Elektrochemischer Reaktor nach Anspruch 14, dadurch gekennzeichnet, daß das obere Ende des Elektrolyteinlaßwehrs jeder Zelle höher ist als das obere Ende des Elektrolytauslaßwehrs, das seinerseits höher ist als das obere Ende der Elektroden.

16. Elektrochemischer Reaktor nach Anspruch 14 oder 15, dadurch gekennzeichnet, daß die Wehre durch aufrecht auf den perforierten Platten stehende Platten gebildet werden.

17. Elektrochemischer Reaktor nach Anspruch 13, dadurch gekennzeichnet, daß jede Zelle eine bipolare Anordnung vertikaler, plattenartiger Elektroden, die in Abständen voneinander und parallel zueinander angeordnet sind, so daß sie Kanäle zwischen dem Elektrolyteinlaß und dem Elektrolytauslaß der Zelle bilden, aufweist.

18. Elektrochemischer Reaktor nach einem der Ansprüche 13 bis 17, gekennzeichnet durch Einrichtungen zur Verbindung der Auslässe und der Einlässe aufeinander folgender Zellen in Kaskadenform, so daß der Elektrolyt durch den Reaktor nach unten von dem Elektrolytauslaß einer Zelle zu dem Elektrolyteinlaß der darunterliegenden Zelle geführt wird.

19. Elektrochemischer Reaktor nach Anspruch 17, dadurch gekennzeichnet, daß die Elektroden auf der perforierten Platte der jeweiligen Zelle aufsitzen, jede Platte aus elektrisch isolierendem Material hergestellt ist und die Perforationen in jeder Platte in Reihen angeordnet sind, die in Abständen voneinander etwa in der Mitte zwischen je zwei einander benachbarten Elektroden verlaufen.

20. Elektrochemischer Reaktor nach Anspruch 14 und 18, gekennzeichnet durch Fallrohre zum Führen von Elektrolyte von dem Elektrolytauslaßwehr jeder Zelle (mit Ausnahme der untersten) zu dem Elektrolyteinlaßwehr der darunterliegenden Zelle.

21. Elektrochemischer Reaktor nach Anspruch 20, dadurch gekennzeichnet, daß ein Bodenteil der untersten Kammer einen Aufnahmebehälter für einen Pool von umgesetztem Elektrolyte bildet und ein weiteres Fallrohr von dem Elektrolytauslaß der untersten Zelle zum Bodenteil der untersten Kammer zum Ausbringen von umgesetztem Elektrolyt in dem Pool führt.

22. Elektrochemischer Reaktor nach Anspruch 21, gekennzeichnet durch ein Einlaßrohr, das nach unten durch die oberste Kammer führt, zur Führung von frischem Elektrolyte zu dem Elektrolyteinlaßwehr der obersten Zelle.

23. Elektrochemischer Reaktor nach Anspruch 13, dadurch gekennzeichnet, daß die einzelnen Abschnitte des Reaktorgehäuses durch die entsprechenden horizontalen Platten voneinander getrennt und am Umfang dieser Platten befestigt sind, wobei diese Platten nur in den Gebieten unter den Elektroden der entsprechenden Zellen des Reaktors perforiert sind.

24. Elektrochemischer Reaktor nach Anspruch 23, dadurch gekennzeichnet, daß jeder Gehäuseabschnitt (mit Ausnahme des untersten) einander zugekehrte Seitenwände aufweist, die an aufrechtstehenden Platten, die das Elektrolyteinlaßwehr und das Elektrolytauslaßwehr bilden, anliegen, so daß eine rechtwinklige Umfassung für die Elektroden der Zelle gebildet wird.

25. Elektrochemischer Reaktor nach Anspruch 17 und 24, dadurch gekennzeichnet, daß für jede bipolare Elektrodenanordnung eine Einlassung für die endständigen Elektroden in den einander zugewandten Seitenwänden des entsprechenden Gehäuseabschnitts vorgesehen ist.

26. Elektrochemischer Reaktor nach einem der Ansprüche 13 bis 18 und 23 bis 25, dadurch gekennzeichnet, daß die Elektroden über Perforationen in der entsprechenden Platte angeordnet sind.

27. Verfahren zur Durchführung eines elektrochemischen Verfahrens oder einer elektrochemischen Reaktion in der elektrochemischen Zelle nach einem der Ansprüche 1 bis 12, dadurch gekennzeichnet, daß man Gas von der Gaszufuhrkammer nach oben durch Perforationen in der Platte führt, so daß dieses Gas durch den Elektrolyten auf der Platte perlt und sich in der oberen Kammer sammelt.

28. Verfahren zur Durchführung eine elektrochemischen Verfahrens oder einer elektrochemischen Umsetzung in dem elektrochemischen Reaktor nach einem der Ansprüche 13 bis 26, dadurch gekennzeichnet, daß man den Elektrolyt durch den säulenförmigen Reaktor von einer Zelle zur nächsten und über die perforierte Platte jeder Zelle strömen läßt und Gas aufwärts durch die Perforationen in den aufeinanderfolgenden Platten führt, so daß das Gas durch den Elektrolyten auf jeder Platte perlt.

29. Verfahren nach Anspruch 27 oder 28, dadurch gekennzeichnet, daß das Gas ein Reaktant in der elektrochemischen Reaktion ist.

30. Verfahren nach Anspruch 27 oder 28, dadurch gekennzeichnet, daß das Gas Propylen und der Elektrolyt ein Halogenid eines Alkalimetalls in wäßriger Lösung ist.

Revendications

1. Cellule électrochimique, caractérisée en ce qu'elle comprend des électrodes disposées sur une plaque perforée généralement horizontale, une admission d'électrolyte et un échappement d'électrolyte situés à distance l'un de l'autre de part et d'ature des électrodes, d'un côté et de l'autre de la plaque perforée, et une enveloppe de cellule qui est divisée par la plaque perforée en une chambre supérieure et une chamber inférieure, la chambre inférieure étant une chambre d'alimentation en gaz à partir de laquelle le gaz traverse les perforations de la plaque perforée pour passer à travers l'électrolyte qui se trouve au-dessus de la plaque dans la chambre supérieure.

2. Cellule électrochimique selon la revendication 1, caractérisée en ce que l'admission d'électrolyte et l'échappement d'électrolyte sont constitués chacun par un déversoir.

3. Cellule électrochimique selon la revendication 2, caractérisée en ce que le haut du déversoir d'admission d'électrolyte est à un niveau plus élevé que le haut du déversoir d'échappement d'électrolyte, qui est à un niveau plus élevé que le haut des électrodes.

4. Cellule électrochimique selon la revendication 2 ou 3, caractérisée en ce que les déversoirs sont formés par des plaques qui s'étendent verticalement à partir de la plaque perforée.

5. Cellule électrochimique selon la revendication 1, caractérisée en ce qu'elle comprend une série bipolaire d'électrodes en plaque verticales, disposées parallèlement les unes aux autres de manière à délimiter des passages entre l'admission d'électrolyte l'échappement d'électrolyte.

6. Cellule électrochimique selon la revendication 5, caractérisée en ce que les électrodes bipolaires reposent sur la plaque perforée qui est faite de matière électriquement isolante, et en ce que les perforations de la plaque sont disposées en rangées espacées, situées chacune à mi-distance entre des électrodes voisines.

7. Cellule électrochimique selon la revendication 2, caractérisée en ce qu'une partie du fond de la chambre inférieure constitue un réceptacle pour un volume d'électrolyte ayant réagi et en ce qu'un tuyau descendant s'étend entre le déversoir d'échappement d'électrolyte et la partie du fond de la chambre inférieure, pour diriger l'électrolyte ayant réagi vers ledit volume.

8. Cellule électrochimique selon la revendication 7, caractérisée en ce qu'elle comprend un tuyau d'arrivée qui s'étend de haut en bas à travers la chambre supérieure, pour diriger l'électrolyte frais vers le déversoir d'admission d'électrolyte.

9. Cellule électrochimique selon la revendication 1, caractérisée en ce que les chambres supérieure et inférieure sont formées respectivement par des parties supérieure et inférieure séparées d'une enveloppe de cellule en forme de caisse, ces parties de l'enveloppe étant séparées par la périphérie de la plaque et fixées à celle-ci et les perforations n'étant pratiquées dans la plaque que dans la région sous-jacente aux électrodes.

10. Cellule électrochimique selon la revendication 9, caractérisée en ce que la partie supérieure de l'enveloppe comporte des parois latérales opposées contre lesquelles s'aboutent des plaques verticales constituant les déversoirs d'admission et d'échappement d'électrolyte, pour délimiter une enceinte rectangulaire pour les électrodes.

11. Cellule électrochimique selon la revendication 5 ou 10, caractérisée en ce que la série d'électrodes bipolaires comprend des électrodes de jonction encastrées dans lesdites parois latérales opposées de la parties supérieure de l'enveloppe.

12. Cellule électrochimique selon la revendication 1, caractérisée en ce que les électrodes sont disposées au-dessus des perforations de la plaque perforée.

13. Réacteur électrochimique, caractérisé en ce qu'il comprend' (I) plusieurs cellules, chaque cellule comportant (i) des électrodes disposées au-dessus d'une plaque perforée généralement horizontale, (ii) une admission d'électrolyte et (iii) un échappement d'électrolyte situés à distance l'un de l'autre de part et d'autre des électrodes, d'un côté et de l'autre de la plaque perforée, et (II) une enveloppe de réacteur dans laquelle les cellules sont empilées en une disposition en colonne, les plaques perforées des cellules divisant l'enveloppe de réacteur en chambres superposées, chaque plaque perforée étant disposée au-dessus d'une chambre d'alimentation en gaz à partir de laquelle le gaz traverse les perforations de la plaque pour barboter dans l'électrolyte qui se trouve au-dessus de la plaque et se rassembler dans la chambre située au-dessus qui constitue (sauf celle de la cellule du haut) la chambre d'alimentation en gaz de la cellule sus-jacente.

14. Réacteur électrochimique selon la revendication 13, caractérisé en ce que l'admission d'électrolyte et l'échappement d'électrolyte de chaque cellule sont constitués par de déversoirs.

15: Réacteur électrochimique selon la revendication 14, caractérisé en ce que le haut du déversoir d'admission d'électrolyte de chaque cellule est à un niveau plus élevé que le haut du déversoir d'échappement d'électrolyte, lequel est à un niveau plus élevé que le haut des électrodes.

16. Réacteur électrochimique selon la revendication 14, caractérisé en ce que les déversoirs sont formés par des plaques qui s'étendent verticalement à partir des plaques perforées.

17. Réacteur électrochimique selon la revendication 13, caractérisé en ce que chaque cellule comprend une série bipolaire d'électrodes en plaque verticales, disposées parallèlement à distance les unes des autres de manière à délimiter des passages entre l'admission d'électrolyte et l'échappement d'électrolyte de la cellule.

18. Réacteur électrochimique selon l'une quelconque des revendications 13 à 17, caractérisé en ce qu'il comprend des moyens pour relier en cascade les échappements et les admissions de cellules successives, afin de faire circuler l'électrolyte de haut en bas dans le réacteur, de l'échappement d'électrolyte d'une cellule à l'admission d'électrolyte de la cellule sousjacente.

19. Réacteur électrochimique selon la revendication 17, caractérisé en ce que les électrodes reposent sur la plaque perforée de la cellule à laquelle elles appartiennent, en ce que chaque plaque est faite de matière électriquement isolante et en ce que les perforations de chaque plaque sont disposées en rangées espacées, situées à peu près à mi-distance entre les électrodes voisines correspondantes.

20. Réacteur électrochimique selon la revendication 14 ou 18, caractérisé en ce qu'il comprend des tuyaux pour diriger l'électrolyte entre le déversoir d'échappement d'électrolyte de chaque cellule (à l'exception de celle du bas) et le déversoir d'admission d'électrolyte de la cellule sous-jacente.

21. Réacteur électrochimique selon la revendication 20, caractérisé en ce qu'une partie du fond de la chambre du bas constitue un réceptacle pour un volume d'électrolyte ayant réagi et en ce qu'un autre tuyau descendant s'étend entre l'échappement d'électrolyte de la cellule du bas et ladite partie du fond de la chambre du bas, pour diriger l'électrolyte ayant réagi vers ledit volume.

22. Réacteur électrochimique selon la revendication 21, caractérisé en ce qu'il comprend un tuyau d'arrivée qui s'étend de haut en bas à travers la chambre du haut, pour diriger l'électrolyte frais vers le déversoir d'admission d'électrolyte de la cellule du haut.

23. Réacteur électrochimique selon la revendication 13, caractérisé en ce que les différentes parties de l'enveloppe du réacteur sont séparées par la périphérie des plaques horizontales respective et sont fixées à celle-ci, les plaques n'étant perforées que dans les régions situées au-dessous des électrodes des cellules respectives du réacteur.

24. Réacteur électrochimique selon la revendication 23, caractérisé en ce que chaque partie de l'enveloppe (à l'exception de celle du bas) comporte des parois latérales opposées contre lesquelles s'aboutent des plaques verticales constituant les déversoirs d'admission et d'échappement d'électrolyte, pour délimiter une enceinte rectangulaire pour les électrodes de la cellule respective.

25. Réacteur électrochimique selon la revendication 17 ou 24, caractérisé en ce que chaque série d'électrodes bipolaires comprend des électrodes de jonction encastrées dans les parois latérales opposées de la partie d'enveloppe respective.

26. Réacteur électrochimique selon l'une quelconque des revendications 13 à 18 et 23 à 25, caractérisé en ce que les électrodes sont disposées au-dessus de perforations de la plaque respective.

27. Procédé d'exécution d'un traitement ou réaction électrochimique dans la cellule électrochimique selon l'une quelconque des revendications 1 à 12, caractérisé en ce qu'il comprend l'opération consistant à faire passer un gaz de bas en haut, à partir de la chambre d'alimentation en gaz, à travers les perforations de la plaque, pour qu'il barbote dans l'électrolyte sur la plaque et qu'il se rassemble dans la chambre supérieure.

28. Procédé d'exécution d'un traitement ou réaction électrochimique dans le réacteur électrochimique selon l'une quelconque des revendications 13 à 26, caractérisé en ce qu'il comprend l'opération consistant à faire s'écouler l'électrolyte de haut en bas dans le réacteur en colonne, d'une cellule à la suivante et d'un côté à l'autre de la plaque perforée de chaque cellule, et à faire passer le gaz des bas en haut à travers les perforations des plaques successives, de telle manière que le gaz barbote dans l'électrolyte sur chaque plaque.

29. Procédé selon la revendication 27 ou 28, caractérisé en ce que le gaz est un réactif dans la réaction électrochimique.

30. Procédé selon la revendication 27 ou 28, caractérisé en ce que le gaz est le propylène et l'électrolyte est un sel haloïde d'un métal alcalin en solution aqueuse.

Drawing