FI67095C - FOER REQUIREMENTS FOR ELECTRIC FRAMSTERING WITH SODIUM CHLORATOINES AND ELECTRICITY REQUIREMENTS FOR GENERATION - Google Patents

Description

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Canada (CA) 321399 (71) Erco Industries Limited, 2 Gibbs Road, Islington, Ontario, Canada (CA) (72) David Gerald Hatherly, Mississauga, Ontario,

Roy Ernest Wi 11 iams, Mississauga, Ontario, Canada (CA) (74) Oy Kolster Ab (54) Method for the electrolytic preparation of sodium chlorate and the implementation of the method for the electrolytic production of sodium chlorate - For the preparation of sodium chlorate and for the electrolysis of the present invention a process for preparing sodium chlorate by electrolysing sodium chloride, in which the sodium chloride feed solution is introduced into an electrolysis cell, the electrolysis products are introduced into a reactor, the sodium chlorate product is removed from the reactor, all remaining liquid is recycled to pH of the sodium chloride feed solution and

Sodium chlorate is a valuable industrial chemical and is produced by electrolysis of aqueous sodium chloride solutions. Several cell structures for electrolysis are known.

The present invention provides a process for the preparation of sodium chlorate and an electrolysis plant which are very advantageous compared with conventional methods.

The process for preparing sodium chlorate according to the invention is characterized in that one sodium chloride feed solution is introduced into several sodium chlorate-producing zones, each with several electrolytic cells connected in parallel with each other and with one reactor, the sodium chlorate product being removed from each reactor and combined to form a single chlorate.

67095

The invention also relates to a sodium chlorate production plant characterized in that it comprises a plurality of electrolysis zones, each comprising a plurality of individual electrolytic cells connected in electrical series with each other by electrical conductors and connected to a single reaction vessel. extend from the lower inlet to the upper outlet, a supply line connected in parallel with the reaction tanks of the plurality of electrolysis zones and a product line connected in parallel to the inlet of the plurality of electrolysis zones through a discharge line and a heat exchanger and a product discharge line to remove the sodium chlorate product from the mixing tank. container.

The invention is illustrated by the accompanying drawings, in which Figure 1 is a flow diagram of a multi-cell sodium chlorate production plant, Figure 2 is a perspective view of a disassembled single chlorate cell, Figure 3 is a perspective close-up view Fig. 2 taken along line 4-4, Fig. 5 is a sectional view taken along line 5-5 of Fig. 4, Fig. 6 is a sectional view taken along line 6-6 of Fig. 5, and Fig. 7 is a vertical sectional view of pipe connections with one cell connected to the reaction vessel.

Next, Fig. 1 will be described, which shows a sodium chlorate production plant 10 consisting of several cell units. The chlorate plant 10 is constructed of several separate sodium chlorate production units 12 connected in parallel with respect to flow. Two sodium chlorate production units 12 are shown in the figure, but usually there are several desired production units. 67095 si so that each unit 12 is sized to produce about 1200 tons of sodium chlorate per year.

Each chlorate unit 12 includes a reaction vessel 14 containing a solution in which chlorate formation reactions occur between electrolysis products. A plurality of non-membrane electrolytic cells 16 are connected in parallel to the tank 14 so that the solution to be electrolyzed advances from the tank 14 to each cell 16 and the electrolyzed solution circulates from each cell 16 back to the tank 14.

Each reaction vessel 14 has an inlet pipe 18 for the electrolytic saline solution and an outlet pipe 20 for the sodium chlorate solution. The reaction vessel 14 has a vent 22 for gaseous products from electrolysis.

The flow rate of brine entering each reaction vessel 14 can be manually adjusted by valve 23 to the desired temperature in the reaction vessel. A meter 25 can be fitted to the sodium chlorate solution outlet pipe 20 to monitor the temperature of the solution, and changes in the flow rate to the reaction vessel 14 can be made accordingly.

The sodium chlorate solution tubes 20 merge into a single product solution tube 21 leading to the plant's only common mixing tank 24. The sodium chlorate solution is removed from the tank 25 via line 26 as a product of plant 10. Sodium chloride make-up solution is introduced from line 28 and hydrochloric acid from line 30 into the mixing tank so as to provide the acidity required for electrolysis, e.g. a pH of about 6.8. The sodium dichromate catalyst that may be required for the electrolysis reaction may be added along with the sodium chloride solution via line 28.

The mixing tank 24 may be provided with a ventilation pipe 31, from which any gases entrained along the pipe 21 with the sodium chlorate entering the mixing tank are discharged.

The mixing tank 24 is divided from the inside into two parts by a partition 32 extending from the bottom upwards below the liquid surface.

The sodium chlorate solution coming through line 21 is led to another part below the liquid surface and the exit of the product via line 26 is connected to this, while the sodium chloride and saline supply pipes 28 and 30 lead to another part below the liquid surface. Thus, contamination of the chlorates product stream 26 with the added materials is avoided, as the chlorate solution is allowed to flow over the septum 32 and mix with the added material.

The sodium chlorate solution, to which sodium chloride has been added and which has been acidified with hydrochloric acid (hereinafter referred to as "brine"), is removed from the other part of the mixing tank 24 via a pipe 34 and passed through a suitable heat exchanger 36. The saline solution is then fed in parallel to the units 12 via respective supply pipes 18.

The heat exchanger 36 cools the solution recycled to the tube 34 to the desired temperature, e.g., about 40 ° C, while the heat generated in the cells 16 is removed and recovered with the product passing through the overflow tube 20. As described above, the temperature of this solution can be adjusted to a desired value, e.g., between about 60 and 90 ° C, by controlling the flow of brine to the cell units 12 by means of valves.

The cells 16 are electrically conductively connected to each other by flexible electrical conductors 38 so that the cells 16 can be moved to a desired position relative to each other.

Each cell 16 has a drain pipe 40 with a valve and its own flow control valve 42, by means of which individual cells or all cells can be disconnected from the solution flow and dried for maintenance.

Thus, the sodium chlorate plant 10 needs only one salt solution addition, acid addition, and heat exchange unit to serve a plurality of co-operating sodium chlorate production units 12, with the number of units 12 depending on their capacity and the total production capacity of the plant 10. The mixing tank 24 and the heat exchanger 36 are dimensioned to correspond to the total production capacity of the plant 10.

The grouping and construction of the cell unit 12 according to Figure 1 has several advantages. Thus, each individual unit 12 produces a chlorate solution of the desired concentration, which is the result of the operation of several cells 16 operating in parallel with each other. The product streams contained in the tubes 20 do not require additional electrolysis before leaving the svs-5 67095 theme. Each unit 12 is thus independent and individual operational problems can be isolated and addressed without having to interrupt the operation of other units.

Since the sodium chlorate plant 10 needs only one saline addition, acid addition and heat exchange unit, the associated equipment costs are kept to a minimum and the operating conditions of the plant 10 are made uniform in a simple manner.

When each unit 12 has a plurality of cells connected in parallel with a common reaction vessel 14, product variations caused by variations in the operation of the individual cells are minimized and equipment costs are reduced compared to the case where each cell 16 has its own reaction vessel 14.

The flexible electrical conductors connecting the cells 16 allow the cells 16 to be moved relative to each other, thus avoiding the potential difficulties associated with the cells being fixed to the bench in a fixed position relative to each other.

Next, Figures 2 to 6 will be described in detail describing the preferred structure of the chlorate cells 16 of Figure 1. The chlorate cell 16 resembles a closed box with a solution inlet end tube 50 below and a solution outlet end tube 52 on top, shown in exploded form in Figure 2. Inlet and outlet end tubes 50 and 52, which may be cathodically shielded, are mounted fixedly in place by welding them to a vertical rectangular atode wall plate 54. The inlet and outlet main tubes 50 and 52 and the cathode wall plate are made of cast steel. A plurality of thin steel cathode plates 56 protrude from the wall plate 54 perpendicular to it and in a vertical row relative to each other.

Input and ulostulopääputket 50 and 52 enclose the top and bottom of the unit and katodiseinälevy 54 and the two outermost cathode plate 56 closing the drawer three cell wall. The fourth wall of the cell box consists of an anode wall plate, which is described below.

Inlet and outlet end pipes made of cast steel allow them to be attached to the rest of the cell box by welding instead of the need for bolts or other means of attachment if the structural material were a non-corrosive polymeric material.

The use of electrodes as cell walls also simplifies the structure of the cell, in which case it is not necessary to use bolts or seals.

67095

In the cathode wall plate 54, an inner steel plate 58 is attached by blasting to the outer copper or aluminum plate 60. This two-part structure improves the electrical connections to the cell 16 and minimizes the voltage drop at the terminals connecting the cells.

The steel plate 58 has a plurality of vertical grooved cavities 62, into each of which the other edge of the cathode plate 56 is firmly inserted and welded closed.

The outermost cathode plates 56 forming the walls of the cell 16 are welded to the outer frames 64 to which the inlet and outlet end tubes 50 and 52 are also welded. Outside the outermost plates 56, protective and reinforcing plates 65 are welded to the outer frames 64.

A vertical and rectangular anode wall plate 66 parallel to the cathode wall plate 54 forms the fourth wall of the cell 16. Protruding from the anode wall plate 66 are a plurality of vertically arranged anode plates 68 parallel to and aligned with the cathode plates 56. In the anode wall plate 66, the inner titanium plate 70 is attached by blasting to the outer copper and aluminum plate 72t, as this improves the electrical connection to the anode plates and minimizes the voltage drop at the terminals between the cells. The titanium plate 70 has a plurality of vertical grooved cavities 74 into each of which the other edge of the anode plate 68 is firmly inserted and welded closed.

It is preferred that the thin anode plates 68 be made of titanium having an electrically conductive surface, e.g., a platinum group metal or an alloy thereof, or another electrically conductive coating, such as a platinum group metal oxide.

The thin anode plates 68 overlap the thin cathode plates 56 in the cell box so as to form parallel vertical flow passages 75 through which the electrolyte passes from top to bottom through the cell 16 between the electrode plates 76. apart.

As can be seen from Figures 2-6, the overlapping electrodes occupy the entire space between the side walls of the cell box and divide it into vertical flow channels 75, so that the cell box has a very large electrolysis capacity.

67095

By using spacers 76 and vertical grooves in the anode wall plate and the cathode wall plate into which the electrode plates can be inserted and welded, respectively, the space of the cell can be used as accurately as possible, since the electrode plates can be very thin, e.g. about 0.16 to 0.32 cm thick.

This structure differs significantly from previous structures in which the anode plates are bolted to the wall plate in that it limits the number of anode plates to be installed and increases the thickness of the cathode plates, which is typically about 1.27 cm to maintain the desired electrode spacing (about 0.16 to 0 , 32 cm).

An additional advantage associated with a welded anode plate structure is that a moderately high voltage drop between the bolted anode plate and the wall plate is eliminated.

When thin cathode plates are used in cell 16, cells of similar capacity but much lighter can be constructed, and in general, the flexibility of the cathodes allows the anode array to be easily overlapped with the cathode array compared to a relatively rigid cathode array with thick cathode plates and pulse.

As can be seen from the detailed drawing of Figure 3, the spacers 76 holding the electrodes in the desired position relative to each other include a one-piece portion 78 made of a substantially rigid, non-corrosive material, such as polytetrafluoroethylene. In the body 78 and a short cylindrical part or neck 80 which just exceeds the thickness of the electrode plate 56 or 68, and two knobs 82 having a diameter larger than the diameter of the cylinder part 80 and located at the ends of the cylinder part 80.

Each knob 82 has a planar inner surface 81, a planar outer surface 83 parallel thereto, a beveled edge 85, and a cylindrical portion 87 extending from the flat inner surface 81 to the beveled edge 85.

The planar inner surfaces 81 are to be opposed to the outer surfaces of the electrode plates 56 or 68 when the spacers 76 are mounted thereon, as will be described later, and the planar outer surfaces 83 are to be opposed to the adjacent electrode plates so that the desired distance is maintained. The longitudinal thickness of the knobs 82 is the same as the distance between the electrode plates.

Each knob 82 has the center of the curve on the axis of the short cylindrical part, i.e. the neck 80, so that a symmetrical structure is created.

For ease of use and manufacture, the neck 80 is cylindrical in shape, but may have a different cross-section. The neck portion 80 may be, for example, a square or a hexagon or the like.

Likewise, the shape of the knob 82 may deviate from the preferred circular cross-section described, provided that its largest cross-sectional diameter is greater than the largest cross-sectional diameter of the neck portion 80.

The knob 82 may be, for example, square, oval, hexagonal or rectangular in cross section.

The spacers 76 can be made of a substantially rigid non-corrosive material by any suitable method, such as machining, molding, or the like.

The spacers 76 are mounted as needed to secure the distance to the edge of the electrode plates 56 or 68 from the wall plates 54 or 66 by making an elongate groove 84 projecting inwardly from the edge of the electrode plate, preferably perpendicular thereto, with a vertical height slightly greater than the diameter of the cylindrical portion 80. the spacer 76 is inserted into the groove 84 so that the planar inner surfaces 81 of the knobs 82 abut the outer surfaces of the electrode plate, and the spacer 76 is prevented from closing by closing the groove 84 by turning down and inward the torsional slit 86 obtained by making a short groove 88 which is usually parallel with the groove 84 so as to create an obstacle which holds the spacer 76 firmly in place in the groove 84.

A plurality of spacers 76 are placed on each electrode plate depending on the dimensions of the electrode plates. Typically, at least three spacers 76 are required, one near the top of the electrode plate, one near the bottom, and one approximately in the middle.

9 67095

Spacers have been used in already known electrolytic cells, but they usually consist of two parts which are pressed together or otherwise connected to each other through openings made in the plates of the cell. These two-piece spacers have generally been found to be unsatisfactory, as they tend to disintegrate when the cell is assembled and thus become ineffective.

This problem is avoided by using tightly mounted one-piece spacers 76 that provide a reliable and long-lasting solution.

The insulating and sealing seal 90 surrounds the periphery of the anode wall plate 66 so that in the assembled cell box the anode becomes electrically isolated from adjacent cathodic outer frames 64. The anode plate 66 is mounted to the outer frames 64 by suitably insulated nuts and bolts 92 extending in adjacent holes.

The nut and bolt assembly 92 uses sleeves 93 and sealing rings 95 of a strength such that they can withstand the pressure required to seal the seal 90 to fluid tightness. The construction material suitable for the sealing rings 85 is e.g. melanin and the material suitable for the sleeves 93 is e.g. polypropylene.

The electrically conductive mounting plates 96 and 98 are welded to the outer surface of the cathode wall plate 54 and the anode wall plate 66. Fasteners 96 and 98 are connected to electrical wires not shown.

The cell mounting plates 100 protrude horizontally from the side walls of the cell box so that the cell box can be mounted in a vertical position in a suitable frame.

Referring now to Figure 7, there are shown pipe connections connecting the cell 16 to the tank 14. The pipe units 102 are made of a non-corrosive but electrically conductive material, such as titanium, and are divided into portions separated by suitable electrical insulators 104 so that the waste current in these pipes and the corrosion due to the potential difference between the pipes and the solution flowing in them are kept to a minimum.

10 67095

The diameter of the inlet and outlet tubes 102 is generally much smaller than in other cellular systems using bottom-up flow, resulting in a slower flow of fluid through the electrode surfaces. A typical diameter for a 35,000 amp cell is about 10 cm, while a diameter of about 20 to 25 cm has previously been used, and the flow rate is about 10 cm / s, while the speed previously used is about 40 cm / s.

It has been found that this relatively low solution flow rate has a negligible effect on oxygen evolution and inefficiency and gas lift depend more on flow conditions than retention on volume. Smaller diameter pipes also have lower capital costs and power dissipation.

The present invention thus provides a sodium cellate production system with certain advantages, a unique cell unit and the unique intermediate solution used therein. Modifications are possible within the scope of this invention.

Claims (6)

A process for preparing sodium chlorate by electrolysis of sodium chloride, in which process the sodium chloride supply solution is introduced into an electrolysis cell, electrolysis products are introduced into a reactor, a sodium chlorate product is removed from the reactor, or residual liquid is recirculated of the sodium chloride supply solution and the sodium chloride supply solution are regulated by the addition of hydrochloric acid, characterized in that a sodium chloride supply solution is introduced into several sodium chlorate-producing zones, each of which has several electrolysis cells connected to each other by sodium and one reactor. each reactor and are combined to form a single chlorate product stream. 2. A method according to claim 1, characterized in that the temperature of the sodium chlorate product solution starting from each sodium chlorate producing zone is measured and the flow rate of the sodium chloride supply solution to each such zone is individually controlled in the required manner to maintain the desired temperature in the product solution. Electrolysis plant for preparing a sodium chlorate solution by electrolysis of a sodium chloride solution by the method of claim 1, characterized in that it comprises several electrolysis zones (12), each of which comprises several individual electrolysis cells (16) connected in an electric series with each other by means of electrical conduits (36) and interconnected with a single reactor tank (14), each of which cells (16) each have multiple, relatively overlapping anodes (68) and cathodes (56) for forming electrolyte channels (75), extending from a downstream inlet port (50) to an upstream outlet port (52), a supply line (18) parallel to the reactor tanks (14) for multiple electrolysis zones ( 12) and a product line (20, 21) which is connected in parallel to the reactor tanks (14) for several electrolysis zones (12) and a mixing tank (24) connected to the product line (21), the sodium chloride solution. inlet conduit (28) and inlet conduit (30) of hydrochloric acid which are connected to the supply conduit (18) through the outlet conduit (34) and heat exchanger (36) of the ether circulation,