US3766044A

US3766044A - Electrolytic cell system including upper and lower reacting chambers

Info

Publication number: US3766044A
Application number: US00157469A
Authority: US
Inventors: G Westerlund
Original assignee: Chemech Engineering Ltd
Current assignee: Chemech Engineering Ltd
Priority date: 1970-06-26
Filing date: 1971-06-28
Publication date: 1973-10-16
Anticipated expiration: 1990-10-16
Also published as: FI59268B; CA914610A; SE378620B; FI59268C; JPS5583757U

Abstract

An electrolytic cell assembly and system is provided which includes two or more modular units, each being provided for throughflow of electrolyte and includes a plurality of parallel alternately spaced anodes and cathodes, with the anodes and cathodes occupying less than the entire cross-sectional area of each unit. The end plates of each of the modular units are respectively an anode end plate and a cathode end plate. The electrodes project, preferably at right angles, from the end plates, but in staggered spaced-apart relation, so that each anode electrode (with the exception of the end ones) can be disposed between a pair of adjacent cathode electrodes and vice versa. The end plates are provided with either anode electrodes or cathode electrodes projecting, preferably at right angles, from one face. Between adjacent modular units are intermediate plates which, in one variant, are imperforate and act as combined anode and cathode holding and current transmitting plates. The intermediate plates are provided both with anode electrodes projecting from one face and cathode electrodes projecting from the other face. In another variant, the intermediate plates are porous to permit the throughflow of electrolyte and products of electrolysis from one modular unit to the neighboring one. The system includes means attached to each unit to bring cell products to a common upper reacting chamber, means connecting the upper reacting chamber to a common lower reacting chamber, and means connected between the lower reacting chamber and the units for introducing contents of the lower reacting chamber into each unit.

Description

nited t1? esterinnd [75] Inventor: Gothe 0. Westerllund, Vancouver,

British Columbia, Canada [73] Assignee: Chenieclt Engineering Ltd,

Vancouver, British Columbia, Canada [22] Filed: June 28, 11971 [21] Appl. No.: 157,469

[30] Foreign Application Priority Data June 26, 1970 Canada 086626 [52] US. Cl 204M268, 204/95, 204/270, 204/275 [51] int. Cl non 3/00 [58] Field of Search 204/82, 95, 256, 204/258, 268, 270, 275

[56] References Cited UNITED STATES PATENTS 3,539,486 11/1970 Fleck 204/95 1,485,461 3/1924 Knowles 204/256 2,944,957 7/1960 Keidel 204/275 3,489,667 1/1970 Colman et al. 204/268 1,219,333 3/1917 Kynaston 204/275 883,170 3/1908 Christy 204/268 FOREIGN PATENTS OR APPLICATIONS 791,699 8/1968 Canada 204/95 Primary Examiner-John H. Mack Assistant Examiner-W. I. Solomon Att0rneyCushman, Darby & Cushman [111 Winfield [451 on, in, two

[5 7] ABSTRACT 'Ah electTolyticcell assembly andsysteniis provided which includes two or more modular units, each being provided for throughflow of electrolyte and includes a plurality of parallel alternately spaced anodes and cathodes, with the anodes and cathodes occupying less than the entire cross-sectional area of each unit. The end plates of each of the modular units are respectively an anode end plate and a cathode end plate. The electrodes project, preferably at right angles, from the end plates, but in staggered spaced-apart relation, so that each anode electrode (with the exception of the end ones) can be disposed between a pair of adjacent cathode electrodes and vice versa. The end plates are provided with either anode electrodes or cathode electrodes projecting, preferably at right angles, from one face. Between adjacent modular units are intermediate plates which, in one variant, are imperforate and act as combined anode and cathode holding and current transmitting plates. The intermediate plates are provided both with anode electrodes projecting from one face and cathode electrodes projecting from the other face. In another variant, the intermediate plates are porous to permit the throughflow of electrolyte and products of electrolysis from one modular unit to the neighboring one. The system includes means attached to each unit to bring cell products to a common upper reacting chamber, means connecting the upper reacting chamber to a common lower reacting chamber, and means connected between the lower reacting chamber and the units for introducing contents of the lower reacting chamber into each unit.

1 Claim, 7 Drawing lFigures Patented Oct. 16, 1973 W Swain-Sham 1.

1 R0 n mM/m MM YW s A W M 0 6 Patented Oct. 16,1973 3,766,044

4 Shwmtm-Shmt 2 INVENTOR GOT/V5 0. W55 rEeLu/VD L /ATTORNEYS Patented Oct. 16, 1973 3,766,044

4 Shoots-Shoot 4 INVENTOR 50 77/5 0. W25 7-591. .u/vp

ATTORNEYS ELECTROLYTTC CELL SYSTEM llNQlLlUlDllNG UlPflEllt AND LOWER lltlEACTliNG CHAMBERS BACKGROUND OF THE INVENTION This invention relates to a modular electrolytic cell unit which is assembled as a multi-unit electrolytic cell assembly to provide a compact system for high production. It also relates to the complete electrolysis system which may be provided therefrom.

Monopolar electrolytic cells provided with metal an odes and metal cathodes for the production of alakali metal chlorates from alkali metal chlorides are now extremely well known. However, plants employing monopolar cells normally find it necessary to employ high amperage, about 20,000 to 150,000 amps, and low voltage which usually is expensive in capital cost for both power substation cost, bus bar cost and power losses by the current transmission losses. It is therefore manifest that it is desirable to provide an electric cell and system in which the voltage and amperage are optimized to provide high production for optimum capital cost.

SUMMARY OF THE INVENTION a. Aims of the Invention An object of one aspect of this invention is to provide a modular electrolytic cell assembly provided with metal electrodes in which the conventional bus bar connections between cell units may be eliminated.

An object of another aspect of this invention is to provide such an assembly which offers high production output by the use of multiple such modular units.

An object of yet another aspect of this invention is the provision of such modular units in the assembly which are electrically connected in series so that the assembly will have a voltage equal to a unit voltage times number of such modular units.

An object of yet another aspect of this invention is the provision of such a system which makes it practical to employ a rectifier power substation which is economically optimized by designing for a desirable voltage: current ratio.

An object of yet another aspect of this invention is to provide such modular units assembled in such a way as to minimize the floor area compared to conventional units of such throughput.

An object of still another aspect of this invention is to provide such modular units assembled in such a way as to minimize valving and piping requirements and to simplify control.

An object of a still further aspect of this invention is to provide such modular units assembled in such a way as to provide improved circulation of liquid due to gas lift and density differential.

b. Brief Description of Aspects of the Invention By the present invention, in its broad aspects, a modular electrolytic cell unit is provided which includes two or more modular units, each being a double openended, preferably cylindrical, chamber. in one variant of the invention, each such chamber is provided with circumferential inlet and outlet means for throughflow of electrolyte in a direction of flow parallel to, and between, adjacent, parallel alternately spaced anodes and cathodes. One end plate of the modular unit is an anode end plate and the opposite end plate is a cathode end plate. The anode end plate is disposed at, and seals, one open end, the anode end plate being provided with a plurality of spaced-apart anodes projecting from one face thereof into the chamber. Similarly, the cathode end plate is disposed at, and seals, the other open end, the cathode end plate being provided with a plurality of spaced-apart cathodes projecting from one face thereof into the chamber in staggered alternate relationship to the anode electrodes which also project into the same chamber. In this variant of the invention, if two or more such modular units are provided in lateral, side-by-side relationship, each two adjacent such units are provided with a common intermediate cathodeanode holding and current transmitting plate disposed at, and sealing, the adjacent open ends of two adjacent such cells. Such common plate is provided with a plurality of spaced-apart cathodes projecting from one face thereof into the main chamber in staggered alternate relationship to the anodes also projecting into the main chamber, and a plurality of spaced-apart anodes projecting from the other face thereof into the main chamber in staggered alternate relationship to the cathodes also projecting into the main chamber.

In another variant of the invention, two or more such modular units are provided in vertically stacked relationship. The lowermost of the units is provided with inlet means, e.g. circumferential inlet means for an introduction of electrolyte. The uppermost of the units is provided with outlet means, e.g. radial outlet means for the removal of electrolyte and both dissolved and gaseous products of electrolysis. One end plate of the modular units is an anode end plate and the other end plate is a cathode and plate. The anode end plate is disposed at, and seals, one open end, the anode end plate being provided with a plurality of spaced-apart anodes projecting from one face thereof into the chamber. Similarly, the cathode end plate is disposed at, and seals, the other open end, the cathode end plate being provided with a plurality of spaced-apart cathodes projecting from one face thereof into the chamber in staggered alternate relationship to the anode electrodes which also project into the same chamber. Each two adjacent such units are provided with a common intermediate cathode-anode holding and current transmitting plate disposed at, and sealing, the adjacent open ends of two adjacent such cells. Such common plate is provided with a plurality of spaced-apart cathodes projecting from one face thereof into the main chamber in staggered alternate relationship to the anodes also projecting into the main chamber, and a plurality of spaced-apart anodes projecting from the other face thereof into the main chamber in staggered alternate relationship to the cathodes also projecting into the main chamber. The sealing provided is between the cell units and the exterior of the cell units. The adjacent cell units are interconnected by providing communicating apertures in the common holding plates. The current leakage is controlled by the cross-sectional area and length of the apertures.

By another aspect of each of these variants of this invention, the main open-ended chamber is cylindrical. Each open end is thus provided with an angular flange and each end plate is secured to the open end by means engaging the angular flange, the means being clamped between a retaining ring and the end plate being secured to the open end, a gasket being disposed between the open end and the end plate. When more than two such units are used, each intermediate plate is disposed between adjacent modular units and simultaneously clamp the adjacent units together by spaced-apart means engaging the annular flanges, the means being clamped between a pair of spaced-apart retaining rings and the intermediate plate being secured to the open ends of the adjacent modular units, a gasket being disposed between each open end and the intermediate plate.

The invention also provides in another of its variants, the provision of any of the variants of electrolytic cell units described above in combination with a common upper reacting chamber, having liquor inlet means from the cells, a brine inlet and gas outlet, and a lower reacting chamber having a liquor outlet means to the cell, and finished product outlet. The cell assemblies direct effluent to the upper reacting chamber by gas lift and receive inlet from the lower reacting chamber. The two chambers are interconnected by a common connecting conduit, preferably through a heat exchanger. The reacting chambers are provided with sufficient conduit piping to minimize current leakage.

Preferably, the combination includes a pair of such modular unit systems, each cell in each system including: an effluent liquor riser pipe leading to an upper portion of the upper reacting chamber; a liquor infeed riser leading from a lower portion of the lower reacting chamber; and including a common connecting conduit situated between the pair of modular unit systems, the conduit being provided with heat exchanger means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an idealized side elevational view of a plurality of modular units of an aspect of this invention, assembled to provide a electrolytic cell assembly as a horizontal unit;

FIG. 2 is an idealized central vertical section of the electrolytic cell assembly of FIG. 1;

FIG. 3 is a side elevational view, rotated through 90 of the anode and cathode plates of the embodiment shown in FIG. 2;

FIG. 4 is a section along the line IVIV of FIG. 3;

FIG. 5 is an idealized central longitudinal vertical sectional view of a plurality of modular units of another variant of this invention, assembled to provide an electrolytic cell assembly as a vertical tower;

FIG. 6 is an idealized side elevational view of a complete electrolysis system embodying the electrolytic cell assembly of FIG. 1; and

FIG. 7 is an idealized cross-sectional view along the line VIIVII of the electrolysis system of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS a. Description of FIGS. 1 and 2 Turning now to FIGS. 1 and 2, it is seen that the multi-unit electrolytic cell system 10 includes a plurality, in this case 4, modular cell units 11. Structurally, each modular cell unit includes a cylindrical tube 12, open at each

end

13, 14 and provided with aligned circumferential liquor inlet cylindrical nozzle 15 and liquor effluent cylindrical nozzle 16. The circumferential lip adjacent opening 13 is provided with an angular and annular flange 17, while the circumferential lip adjacent opening 14 is provided with an angular and annular flange 18. An end plate 19, in this case a cathode end plate, is secured to the tube 12 at open end 13 by means of annular retaining flange 20, which has an angular surface mating angular surface of flange 17, and retaining ring 21, all being held together with suitable tension, and with liquor-tight and electrically nonconductive gasket 22 disposed at the open end 13, by means of bolt and nut combinations 23, passing through aligned apertures in retaining ring 21 and cathode end plate 19 respectively. An anode end plate is of the same structure as cathode end plate 19 and may be secured at open end 13 in a similar manner.

A combined cathode-anode intermediate plate 24 is provided between adjacent modular units 11, and the means holding the plate 24 to the adjacent units 11 also holds adjacent units 11 together. Thus, gasket 25 is placed at open end 14, an annular retaining flange 26 is placed in mating relation to flange 18, and retaining ring 27 is placed against annular retaining flange 26. Gasket 22, annular retaining flange 21, and retaining ring 23 are placed at open end 13 of the adjacent tube 12 of modular unit 11. Then the sub-assembly is assembled by means of nut and bolt combinations 28 passing through aligned apertures in retaining

rings

23, 27 and intermediate plate 24.

The main body or tube 12 of the modular electrolytic cell 11 is preferably formed of glass for several reasons, namely, that it is (i) chemically resistant: (ii) transparem; and (iii) electrically resistant. One alternative to using glass tube 12 is to use steel, but in this case, the tube 12 should be electrically connected to the cathodes for protection against corrosion. It is, of course, absolutely essential that tube 12 be electrically isolated from the anodes, e.g. by gaskets and spacers. Another alternative is to make the tubes of titanium, which is chemically resistant to the liquor and does not require cathodic protection. To avoid the need for cathodic protection, the voltage potential is controlled to under 6 volts for current flow from the container. As shown, it is preferred to have a multi-unit assembly 10 comprising many units, e.g., one plant is designed for l2 units in one assembly.

b. Description of FIGS. 2, 3 and 4 Turning now to FIGS. 2, 3 and 4, it is seen that the intermediate plate is provided with a plurality of anode plates 29 on one face 30 thereof and a plurality of cathode plates 31 on the opposite face 32 thereof. Plate 24 may be a composite plate, e.g. one side steel to provide face 32 for the cathode electrodes 31, the other side titanium with noble metal of the platinum group or its oxides coating to provide face 30 for the anode electrodes 29. Such composite plates are commercially available, e.g. from Du Pont, under the Trade Mark DETACLAD.

The electrodes may be welded to the holding plate or connected. As clearly seen in FIG. 2, the anode and

cathode electrodes

29, 31 respectively are offset to fit precisely in between each other when assembled to an adjacent unit. The interelectrode space varies between 2 and 10 mm. The end plates 19 are, of course, either an anode or a cathode, but would have the same construction features as the intermediate electrode assembly.

c. Description of FIG. 5

Another variant of the invention is shown schematically in FIG. 5. The multi-unit electrolytic cell system is a vertical tower of plurality, in this case nine, cells or compartments 111. The number of such compartments may, however, be as few as two, or as many as 50. Each shell of the cell or compartment 111 is a cylindrical tube 112 formed, for example, of plastics material, e.g. polyvinyl chloride, polystyrene, etc. or glass.

Structurally, then, each modular cell unit or compartment 111 includes a cylindrical tube 112, open at each end 113, 1141. The circumferential lip adjacent opening 113 is provided with an angular and annular flange 117, while the circumferential lip adjacent opening 1141 is provided with an angular and annular flange 113. An end plate 119), in this case a cathode end plate, is secured to the tube 112 at open end 113 by means of annular retaining flange 120, which has an angular surface mating angular surface of flange 117, and retaining ring 121, all being held together with suitable tension, and with liquor-tight and electrically nonconductive gasket 122 disposed at the open end 1113, by means of bolt and nut combinations 123, passing through aligned apertures in retaining ring 121 and cathode end plate 119 respectively. The anode end plate 11111 is similar in structure to the cathode end plate 191 and may be secured to open end 113 in a similar fashion.

A combined cathode-anode intermediate plate 1241 is provided between adjacent modular units 111, and the means holding the plate 1241 to the adjacent units 111 also holds adjacent units 1111 together. Thus, gasket 125 is placed at open end 114, an annular retaining flange 126 is placed in mating relation to flange 113, and retaining ring 127 is placed against annular retaining flange 12b. Gasket 122, annular retaining flange 121, and retaining ring 123 are placed at open end 113 of the adjacent tube 112 of modular unit 111. Then the sub-assembly is assembled by means of nut and bolt combinations 12% passing through aligned apertures in retaining

rings

123, 127 and intermediate plate 124.

As described hereinbefore with reference to FIGS. 1 41, the main body or tube 112 of the modular electrolytic cell 111 is preferably formed of glass for several reasons, namely, that it is (i) chemically resistant; (ii) transparent; and (iii) electrically resistant. One alternative to using glass tube 11112 is to use steel, but in this case, the tube 112 should be electrically connected to the cathodes for protection against corrosion. It is, of course, absolutely essential that tube 112 be electrically isolated from the anodes, e.g. by gaskets and spacers. Another alternative is to make the tubes of titanium, which is chemically resistant to the liquor and does not require cathodic protection. To avoid the need for cathodic protection, the voltage potential is controlled to under 6 volts for current flow from the container. As shown, it is preferred to have a multi-unit assembly 110 comprising many units, e.g., one plant is designed for 12 units in one assembly.

The intermediate plate 12 1 is provided with a plurality of anode plates 129 on one face thereof and a plurality of cathode plates 131 on the opposite face thereof. Plate 121 may be a composite plate, e.g. one side steel to provide the face forthe cathode electrodes 131, the other side titanium with noble metal of the platinum group or its oxides coating to provide the face for the anode electrodes 129. Such composite plates are commercially available, e.g. from Du Pont, under the Trade Mark DlETACLAD.

The electrodes may be welded to the holding plate or connected. The anode and

cathode electrodes

129, 131 respectively are offset to fit precisely in between each other when assembled to an adjacent unit. The interelectrode space 11341 varies between 2 and mm. The

end plates 1119 are, of course, either an anode or a cathode, but would have the same construction features as the intermediate electrode assembly.

It is seen that the lowermost unit of the plurality of stacked units 111 includes a circumferential liquor inlet nozzle 11S, and the uppermost unit of plurality of stacked units 111 includes an axial product outlet 116, carrying liquor and evolved gas which is entrained and- /or occluded within the liquor.

It is also seen that the holding plates 12 1- are provided with perforations 131} thereby to channel the reactant liquor and the products of the reaction from the bottommost unit to the uppermost unit. The arrows 132 show the flow of the reactant liquor and the product through the plate 1241 or an insert in the plate 124.

It will be observed that there is a non-electrolytic space 133. Assuming the

electrodes

129, 130 do not seal tightly to the container 112, i.e. communicate with side sections and that there is a significant pressure drop for flow through the openings 1311 in the holding plate 1241, there will be a significant internal circulation between the side sections or non-electrolytic spaces 133 and the space 1341 between electrodes.

It is seen that the assembly in FIG. 5 is basically the same as the assembly of FIGS. 11 and 2 earlier described. However, it will be noted that the flow through the assembly is longitudinally therethrough. Preferably all of the liquor to the assembly is fed to the lowest unit in the assembly through inlet nozzle and liquor and gas are channelled from one unit to the other, preferably by openings 1311 in the electrode holding plates 12 1 and finally discharged to a reactor from the top unit through outlet nozzle 1116. The current leakage is controlled by cross-sectional area of the openings 1311 in the plate 1241 and the thickness of electrode holding plate 124. While not shown, the apertures 1311 may be provided with hollow cylindrical inserts for annealing the effluent liquor and product gases. Then, the current leakage would be governed by the cross-sectional area of the hollow cylindrical inserts and the length of such inserts.

The main advantages of such vertical assembly compared to the horizontal assembly include the following, namely: (1) the floor area requirement is drastically reduced; (2) one inlet for the liquor and one outlet for the product for each assembly is possible, thus minimizing valving and piping requirements and simplifying control; and (3) the assembly works essentially as a column containing a product of significantly lower density then the liquor feed; thus, the gas lift as well as the density differential cooperate in improving the circulation of liquor through the assembly.

It is also noted that the

electrodes

129, 131 do not normally cover the entire cross-sectional area of the cell container. Thus, the design incorporates internal circulation. This is an especially important feature of the design when the assembly is erected vertically, since the internal liquor circulation resulting from the gas evolution on the electrode surface provides for interchange of electrolyte between the electrodes and standardizes conditions in the cell chambers.

While not shown in detail, the vertical assembly design may be designed to make the column size sufficiently large to provide mainly by means of nonelectrolytic spaces 133 in the compartment the total desirable electrolyte volume and retention time for chemical reactions to chlorate. In this case, no external recirculation would be required. This is very desirable in some aspects since it minimizes piping requirements and provides cascade arrangement between compartments, or cells, under favourable conditions. Thus, electrolyte (brine) enters at the lowest compartment and finished product leaves at the top compartment, the retention time being provided in each and every compartment. This construction provides the conditions for conversion of hypochlorite to chlorate in each compartment. Temperature control could be maintained by, for example, installing a cooling coil in he compartments or jacketing the columns. On the other hand, with the variant of FIGS. 1 and 2, a separate cell assembly may be installed indoors and the reactors outdoors.

The electrode assembly may be fitted inside a larbe tube (e.g. a glass column) rather than dividing the column into sections. The electrode holding plates would then be placed between sections.

While the assembly has been shown vertical, it may be inclined to various degrees up to and including vertical installation, i.e., from O to 90 relative to the horizontal.

d. Description of FIGS. 6 and 7 Turning now to FIGS. 6 and 7, it is seen that a pair of multimonopolar electrolytic cell assembly and system 10 is disposed between and interconnected to an upper reaction chamber 36 and a lower reaction chamber 37 to provide an electrolysis system 35. Each outlet nozzle is connected to an effluent riser pipe 38, each riser pipe extending upwardly within upper reaction chamber 36 to terminate near the top thereof at outlet 39. Entrained and/or occluded gases formed during the electrolysis reaction are permitted to separate from the liquor 40 and to pass upwardly into a gas chamber 41 provided with a frangible cover 42 (for safety reasons) and with a gas outlet nozzle 43 leading away from the electrolysis system. Fresh brine is introduced through cylindrical inlet nozzle 44 which extends downwardly into the upper reaction chamber 36 to terminate in a submerged outlet 45.

Degassed liquor in which the reaction to chlorate has been at least partially completed passes through a common connecting conduit 46 disposed between the pair of multi-unit cell systems 10 and passes through an annular heat exchanger 47 having cooling water inlet 48 and water effluent 49. If desired, the heat exchanger may be cooling coils disposed in the lower reaction chamber 37, or any other suitable means. From the lower reacting chamber, an inlet riser pipe 50, connected to each inlet nozzle 15 of cell 11 originates at an inlet 51 near the bottom of chamber 37 and brings liquor 53 from lower reacting chamber 37 to cells 11. Finished product chlorate is withdrawn from outlet nozzle 54 at the bottom of chamber 37 and passes via outflow conduit 55 leading to chlorate storage (not shown).

During the course of the electrolysis, gases produced are in the liquor in the form of entrained or occluded bubbles. This reduces the density of the liquor to such an extent that the effluent liquor is pumped, by gas lift, up effluent riser pipes 38 and is sucked upwardly through inlet riser pipes 50. The

pipe risers

38 and 50 provide sufficient piping to minimize current leakage.

In the example where the cells 11 are used for chlorate electrolysis, the electrolyte is brine and the electrolytic products are: hypochlorite, chlorate and hydrogen gas, as well as by-product oxygen and water vapor.

Since the electrolysis is of sodium chloride brine with no diaphragm, the effluent, consisting of C1 Na, H OH, ClOH, Cl, H", and OCl' and in the form both of liquor and gaseous products, pass from effluent pipe risers 38 to upper reacting chamber 36. The level of the liquor 40 in upper reacting chamber 36 is shown by level line 52 and is higher than outlets 39 so that liquor and gaseous products are separated from one another. The upper portion of the upper reacting chamber 36 consequently acts as a degasifier. Recycle liquor passes down through upper reacting chamber 36 through common conduit 46 to lower reacting chamber 37.

The liquor velocity through upper reacting chamber 36 is reduced to such an extent that optimum separation of the entrained gases takes place without shortcircuiting through the tank, which would result from too low a liquor velocity. The velocity, on the other hand, must be sufficient to utilize the entire vessel but not too rapid to inhibit the expulsion of any further entrained and/or occluded product gases. The optimum velocity is a function of the apparent density of the liquid, which, in turn, is dependent on the amount of entrained gases and the bubble size. It has been found that a liquor velocity of about 10 ft/min. can separate substantially 100 percent of the entrapped gases.

Upper reacting chamber 36 and lower reacting chamber 37 combined are for the purpose of permitting the reaction to take place. For any selected temperature, the retention time in reacting

chambers

36, 37 is a function of the concentration of ClOH and C10" present in the liquor which in turn is directly related to the current density. Thus, it was found that to yield a current efficiency of greater than percent, with a constant recirculation of liquor and a pH ofrapproximately 6.5, the current concentration should be less than 7 amps/ litre at 80C. or less than 6 amps/litre at 60C. The current concentration (in amps/litre) is the main determining factor in calculating the reacting chamber volume. The retention time, on the other hand, is dependent on the rate of the liquor circulation, as well as on the volume of the reaction vessel.

The liquor entering the upper reacting chamber 36 may have temperatures ranging from about 45 to C., preferably between about 60 and 80C. FIGS. 6 and 7 show a heat exchanger 47 which is provided for temperature control. The reacting chamber parameters are such that there is a sufficiently long retention time of liquor in reacting

chambers

36, 37 to favour the desirable reaction NaOCl 2l-lClO NaClO +2116].

It is also important to minimize the concentration of the hypochlorite for if his too high, it will decompose and anode electrode coating wear increases. In addition, the pH should be maintained below 7.5 and preferably between about 5 and 7. At a pH of 6.8, the optimum reaction of 2 moles of HClO to 1 mole of NaOCl takes place if no dichromate is present.

Effluent from the lower reacting chamber 37 is conveyed to cells 11 through inlet pipe riser 50 to inlet nozzle 14. Gas is drawn off at outlet 43 from gas chamber 41. Gases, consisting of H2, H O (vzfpor), O COQaiid Cig may be vented as waste through outlet 43 or may be utilized.

H Cl 2ll-[Cl (producing hydrogen chloride) 2H ZH O (producing water vapor) The hydrogen chloride may be recovered as hydrochloric acid by scrubbing with water.

It is generally known that the oxygen content of the cell gas decreases with a lower pH of the electrolyte simultaneously as the chlorine losses increase. Using a combustion chamber for the recovery of chlorine losses as hydrochloric acid, the cell may be operated at a low pH and thus benefit by the resulting improved current efficiency.

Thus, it should be pointed out that the cell apparatus may be used employing forced circulation. The process system hereinabove discussed utilizes the gaseous products as a means to create a lift in the external pipe riser and thus does not require any means for forced circulation.

In the above-described assembly containing the cells llll, gases produced in the cell assemblies llll rise in the pipe riser and thus cause recirculation of liquor. Two reactors are preferred, but the cell assemblies may also be used with a system employing one reactor only. An external heat exchanger is desirable for easy maintenance and to achieve a high U-value by the higher velocity compared to a heat exchanger (or coil) which may be placed inside the upper reacting chamber 36.

Current flow is from one end of the cell assembly through first unit anode electrodes 1W via the cell electrolyte space to the cathode electrodes of the intermediate holding plate 24.1 and then into the second unit and so on until the current leaves at the opposite end of the electrode assembly.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably and intended" to be, within the full range of equivalence of the following claims.

I claim:

ll. An electrolysis assembly comprising in combination: A) a pair of multi-unit cell systems, each comprised of at least two units disposed horizontally in lateral end-to-end relationship, each such unit comprismg:

a. an open-ended main chamber including inlet ilfll means for the flow of electrolyte to, and between adjacent, parallel, alternately spaced anodes and cathodes and outlet means constructed and arranged to withdraw electrolyte along with gaseous products of electrolysis entrained and/or occluded therein from the chamber, said chamber being electrically isolated from said anodes and cathodes;

b. an anode end plate disposed at, and sealing one open end of said chamber, the anode end plate being provided with a plurality of spaced-apart anodes projecting from one face thereof into said chamber;

c. a cathode end plate disposed at, and sealing the other open end of said chamber, the cathode end plate being provided with a plurality of spacedapart cathodes projecting from one face thereof into said main chamber in staggered alternate relationship to the anodes also projecting into said chamber;

said anodes and cathodes occupying less than the entire cross-sectional area of the chamber thereby to provide at least one non-electrolysis zone within said unit, thereby to enable internal liquor circulation resulting from gases evolved on the electrode surfaces to interchange electrolyte between the electrodes and to provide substantially homogeneous conditions in the chamber; the plate between two adjacent such units being a common intermediate cathode-anode holding and current transmitting plate disposed at, and sealing the adjacent open ends of said two adjacent such units, and being provided with a plurality of spaced-apart cathodes projecting from one face thereof into one such unit in staggered alternate relationship to the anodes also projecting into said unit from the other end thereof and a plurality of spaced-apart anodes projecting from the other face thereof into the other such unit in staggered alternate relationship to the cathodes also projecting into said unit from the other end thereof;

B. a common upper reacting chamber having a liquor inlet connected to said cell system, a brine inlet and a gas outlet;

C. a common lower reacting chamber having a liquor inlet, a liquor outlet connected to said cell systems to feed said systems and a finished product outlet; and g D. a common conduit interconnecting the upper reacting chamber and the lower reacting chamber, said conduit being located between the pair of cell systems and being provided with heat exchanger means;

the circulation between cell systems, upper reacting chamber and lower reacting chamber being by means of gas lift, each unit in the cell systems including an effluent liquor riser pipe leading to a portion of the upper reacting chamber and a liquor infeed riser leading from a lower portion of the lower reacting chamber.

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