DE1567621A1 - Process and device for the production of alkali chlorate by electrolysis of aqueous alkali chloride solutions - Google Patents

Description

ftVerfabren and driving for the production of alkali borate by Electrolysis of aqueous alkali boride solutions "The invention relates to a method for the production of alkali borate by electrolysis of aqueous alkali boride solutions, in which the lead electrolyte flows upwards through a lead electrolysis zone with fissure spaces between anodes and cathodes under the influence of gas bubble formation as well as preferably with a reduced flow velocity through a carbonate formation zone and from there is returned to the electrolysis zone.

It is well known that in the first reactions of this kind at the Aaode - predominantly molecular chlorine, at the cathode predominantly volumetric Wannerotoff are removed. In the gap spaces through which the electrolyser flows, the entirety of which is referred to as the electrolysis zone, there is, however, some absorption of the boiled-off bile-form chlorine with the formation of hypoblorous acid and hypoblorite. In addition to the carbon ions, unexpectedly, hydroxyl: ions and hypoblorite ions were also discharged at the anode and, on the other hand, ablorate and hypoblorite were reduced to carbonate at the cathode. Whether these secondary reactions occur, experience has shown that the current yield remains reduced. It is therefore desirable to avoid such secondary reactions as far as possible.

The formation of gas bubbles also makes some of the electrode surfaces inactive and also reduces the electrical conductivity of the electrolyte in the electrolysis zone. This results in high cell voltages and thus increased energy consumption, combined with increased heating of the lead electrolyte and the electrodes in the electrolysis zone. Dienes makes in turn disadvantageous when using Gwapbitanodeng as they can be heated as a result of their Temperaturempfindliebkeit most up tu 45 0 (3, so that only when using amodioebe said Grapbitanoden Stromdiebten may allow up to a maximum 10 Amp./da second Upon further An increase in road traffic leads to an uneconomically high grapbit consumption, which also leads to unfavorable operating conditions and an increase in the cell voltage due to the change in the gap widths.

In order to avoid these disadvantages in the electrolytic production of sodiumoblorate from sodium chloride solutions, it is known that the sodium chloride solution is bound through the gap between the electrodes at such a speed that the OH ions cannot reach the electrode. In this case, the alkali formed during electrolysis is left outside the electrode gap for a sufficient time to bind the carbonate to caustic soda and the solution obtained on these wines is left a sufficient time for the formation of carbonate. The circulating speed of the chloride solution is so great and the current strength for the electrolysis is so low that no strong development takes place and the wafer remains in the lead electrolyte solution9 until the electrolyzed solution has left the lead electrolysis zone. The thermoset flow rate of the solution through the lead electrolysis cell is controlled with the aid of a pump and a thermoset flow regulator, whereby the pump can also be used to pump the solution from one of the feeders into a container of the next feeder when the electrolytic cells are frictionally connected. The well-known Terfalren presupposes an essentially more jaminous through-flow of the metal electrodes, since with a turbulent flow the migration of the OH-ions in the rubbing on the anode can not be influenced by the measures of the known process. This known process is therefore only suitable for very low electrolyte flow rates and low lead electrolyte flow rates, which also require a relatively low anodiaobic current thief.

In order to eliminate the secondary parts caused by the use of Grepbit anodes, we asked metellinebe anodes. For example, made of platinum-plated titanium, which means that we can work with a few coarse strobe thieves and who also allow a coarse lead electrolyte temperature. Whether the bob anodiaobic thieves are thieves, the secondary reactions described at the beginning will be reduced. When using such anode tubes, the electrolysis zone remains smaller and the electrolyte volume is reduced, but intensive circulation of the lead electrolyte is necessary for a favorable efficiency yield. For this purpose, the electrolysis zones were asked to create relatively narrow gaps in the electrolysis zone and, in some cases, to increase the buoyancy effect caused by the formation of geobes, to increase gas entry and / or the arrangement of feed pumps in order to achieve electrolyte flow speeds of 0.10 m / sec. In the known processes, the absorption of the granular obliteration, which already begins in the electrolysis zone, takes place essentially next to the discharge of the lead electrolyte from the lead electrolysis zone in an overlying electrolyte. In this absorption zone, in addition to the formation of the hypoeblorite, the ebeziaobic carbonate formation takes place through the reaction of the hypoeblorite with the lower acid. This Ohloratbildung jedoeb is effected in the main in an electrolyte collecting space having the relatively large may be separated from the vorgesebe4 Elektrolyeezelle as slowly durobströmter space either part of or Blektrolysezelle and against its Hoebe Breitenabwessungen. Practical experience shows that there is only incomplete absorption of oblorates and little oblorate formation in this zone.

The third reaction step, namely the conversion of the hypoeblorite formed to the oblorate in the oblorate formation zone, which is connected to the absorption zone, is a process which is much slower than electrolysis and absorption and thus requires a considerable volume of lead electrolyte. For this reason, after passing through the absorption zone and after removing the gaseous electrolysis products on the free surface, the electrolyte is often transferred into a lead electrolyte collecting container, in which the main conversion of the hypochlorite into the oblate takes place.

In the devices for practicing the known method in which See electrolysis zone, absorption zone and at least part of the oblorate formation zone are in a common cell trough, it cannot be avoided Part of the electrical current in the lead electrolysis zone, albeit with a lower current density, the remaining electrolytes contained in the cell permeated. The electrolysis processes, by this flow of parts are triggered "are gber, ger .pde Because of the lower current density, especially staglf "and I4t current yield losses afflicted. This adversely affects the host affinity of the production.

The object of the invention is ea, 'dan Verebren for the production of alkali chlorate of the kind described in the introduction to improve acy that one in the electrolysis zone Rise in the energy yield and one in the subsequent treatments Improvement of the reactions as well as a reduction of the power losses is achieved.

To solve this problem, the invention seeks that the electrolyte after the flow of the Blektrolyaezens with at least the same flow velocity as in the lead electrolysis zone in an ascending direction over a turning towards the lead electrolysis zone Corresponding elevations with the formation of an absorption and buoyancy zone in the oblorate formation zone is initiated.

As a result of this development, a circulating flow of the electrolyte is achieved based on the principle of a combi-pump, namely by virtue of the chimney-like effect of the buoyancy flow between the electrolysis zone and the carbonate formation zone. Durob the Hoebe the Auftrdiebeströmung, the chimney effect and that can be achieved on the Elektrolynezone repercussions in terms of the BesoBeunigung Blektrolytatrömuna eingegtell-t: worden.- The Auftriebewirkung int depends on the respective Geoblosenbildung in Blektrolysesoneg since the Gesgehalt to different specific gravities and Pressure differences over the height of the liquid column leads.

It is useful if the electrolyte is blocked by the absorption and buoyancy zone in the form of a piston flow. In this way, contrary to what is known, in the buoyancy and absorption zone, on the one hand, a high flow velocity with locally high turbulence, but on the other hand only a low level of dissipation in the flow friction is achieved. S are thus achieved in the Abeorptionazone particularly favorable conditions for the Abeorption not abeorbierten in Blektrolysezone chlorine without but the Obloratbildung is reduced, which begins in this zone. It has been shown that the formation of oblate from the hypoeblorite in a room with a thermoset flow is the fastest when there is no breakdown in the flow rate, while on the other hand a great turbulence is of particular advantage for the conversion of the chlorine contained in the form of the finest bubbles in lead electrolytes. This can also be shown theoretically without difficulty: It is known from the literature that the rate of formation of the oblorate from hypoeblorite depends on the actual concentration of the hypoeblorite ion (C109) in the volume element concerned, on the square of the molar concentration of the hypoblorite acid (HClO) and one only temperature-dependent reaction constants K and that this dependency is given by the formula: can be represented. It is also known that the concentration of hypoblorous acid in the solution does not change during the conversion process of the hypoeblorite into the chlorate, since it is constantly being reproduced and that 3 mol of hypoeblorite are used to form 1 mol of oblorate.

On the basis of the last statement, one can also write a carbonate formation space for d to small 'iolunelement: (2) - d (0101) 3 K (RC, 0) 2 x (010f) - dt If one applies equation (2) to a carbonate formation space of the size V, with ideal duroplastic blending, to which electrolyte solution with a hypoeblorite concentration of (0101) is added per unit of time, the hypoeblorite concentration of the Löav «in each volume element is equal to the concentration (0101) Q in discharged lead electrolyte and one obtains: The turnover U. id.M. of elypoeblorite per unit of time is I (4) U. Q [(clot). - (olot) "] id.Me * # If one assumes that with otherwise unchanged conditions in the same carbonate formation space there is an ideal piston flow, that there is no restriction in flow friction of the electrolyte solution and one replaces dt in equation (2) with the expression and integrates the equation over the entire volume VRj a. o, one obtains the expression for the concentration of the hypoeblorite in the emerging lead electrolyte If you replace the expression from equation (3) the conversion in the reaction space with ideal piston flow is obtained as follows: Equations (4) and (5) allow a comparison of the conversion of hypooblorite in the reaction space for the two flow forms for different values of the hyporablori, t concentration ratio (0101) e / (olot) as The result is recorded and proven in the fruit table the superiority of the piston flow. (010f) e sales at sales at (0101 ideal ideal Mixing piston flow 1 100% 100% 1925 100% 11098% -1950 100% 11796% 2900 100% 12694 % 3900 100% 12996% 4900 100% 12695% 5900 100% 1229 7% To carry out the method, the invention relates to a device in which an electrolysis cell is provided with gaps between anodes and cathodes, which are connected on the outlet side of the electrolyte to a collection and wafer formation area for the electrolyte, one of which is connected to the inlet side the cell connected to the return line.

According to the invention, this device is characterized in that (let the electrolyte collection and carbonate formation room separated in a manner known per se is arranged by the cell and that for connection to the cell a Steigrobr is provided, which extends from the area immediately above the column about as much as possible a height corresponding to the cell arch extends and has a transverse section9 which corresponds at most to the sum of the clear gap cross-sections.

The training can be designed in such a way that you can see that Steigrobr extends into the interior of a lead electrolyte collecting container and underneath the liquid reservoir in this container.

-In another appropriate embodiment, the Steigrobr ends above a bend of the liquid level, so that the liquid with the gene bubbles located in it initially from which Robr emerges freely. Here you go favorable ratios for the degassing of the liquid are obtained.

According to the invention, the electrolyte amalgamation and oblorate formation room is preferred at least partially than in the return line of the lead electrolyte to the lead electrolysis cell Lying Robr trained. Durob this execution can be achieved with little construction love Effort a great efficiency in the Ohloratbildungezone, -due to be an intensive one Local turbulence, but essentially no interference in the friction of the flow path can enter. It is not recommended to use the return pipe for the electrolyte at least over part of the length with a bucket drive for abfübrung the Equip process heat so that the electrolyte of the cell with an entepreobend reduced temperature is fed.

In order to meet the above-mentioned requirements in the obliterate formation zone, it is useful that the length of the robr-shaped part of the collecting tank in which the obliterate formation takes place is at least the same length as the hydraulic diameter of the cross-flow tanks. The tubular part of the collecting container is advantageously given a creine-shaped cross section, its length corresponding to at least 5 times the inner tube neaser. This redesign of the tubular part of the collecting container achieved favorable conditions for the above-mentioned formation of chlorate. To achieve extensive utilization of the electrolyte , the well-known series connection of several arrangements for electrolyte inlet duct with electrolyte cell, riser pipe and collecting container and return line can be provided, with the inputs of the subsequent electrolytic cells being connected to the electrolyte collecting containers of the preceding arrangement via overflow pipes.

Fig. 1 shows in section an example of an arrangement for carrying out the new method; FIG. 2 shows a sonicity through the sheet metal cell according to FIG. 1 along the section line AA; FIG. 3 shows the series connection of several arrangements according to FIG. 19, but in a somewhat different embodiment in a schematic Yorm; Fig. 4 gives one of the Pig. 1 different execution form of the arrangement again.

In FIG. 1 , the electrolysis cell provided in the arrangement, which is shown in section in FIG. 2, is denoted by 1. It has a housing made of a highly conductive material, for example fluoro iron, and is provided at the top with a connection flange for the riser pipe 2 protruding into the oil collecting container 4. In addition, it is equipped with a lower flange for connecting the return line 3 , which consists of an electrically non-conductive material and which returns the lead electrolyte from the Ohloratsammelbehälters 4 to the actual lead electrolysis cell 1 .

On the side where the housing 1 of the cell has two mutually opposite rectangular flange connections 5 and 6 . The flange 5 serves to receive the cover 7, for example made of fluids, which is reamed liquid-tight by means of the bolts 8 with the interposition of a seal 9. Two rectangular cathode sheets 10 are welded to this cover, while a connection lug 11 is provided on the outside of the cover for connecting the cover 7 to the negative pole of a direct current source.

In an analogous manner, a rectangular flat cover 12, preferably made of copper, is arranged on the rectangular flat connection 6 and is plated with titanium on the side facing the lead electrolyte. Three rectangular titanium anodes 13 , platinum-plated on both sides, are welded to this cover 12. A copper tab 14 extends outward from the cover 12 for connecting the anodes to the positive pole of the direct current source. The cover 7 carrying the cathode sheets 10 is connected to the housing 1 in a current-conducting manner by means of the screw bolts 8 , so that the two housing walls parallel to the anode and cathode sheets also act as cathodes. The cover 12 carrying the anode sheets 13, on the other hand, is liquid-tight but not electrically connected to the housing by the seal 16 and insulating bolts 15.

The distance between the anode sheets 13 and the adjacent cathode sheets 10 and the housing wall is each dimensioned to be the same size and denoted by J in FIG. In the embodiment shown, six electrolysis gaps of height He and width B as well as a lead electrode spacing J are provided, the entirety of which forms the lead electrolysis zone. The total flow cross section of the electrolysis zone is therefore 6 for the cell shown. H e 0 B The part of the housing 1 located above the sheet metal electrodes and the riser pipe 2 connected to it form the absorption zone, which ends at the free sheet metal surface in the sheet metal collecting container. The riser pipe 2 is designed, for example, as a forged iron pipe lined on the inside with hard rubber. The height of the absorption zone is according to FIG. 1 Hi + H 2 + 4 # H, where Hi denotes the distance from the upper edge of the metal electrode plates to the lower opening of the metal electrolyte container 4 and H2 denotes the length of the riser pipe 2 extending into container 4, while AE reproduces the tube section from the standpipe ignition to the liquid level in the collecting container 4. The lead electrolyte, which is permeated with gas bubbles in the lead electrolysis cell, experiences a buoyancy effect in the riser pipe 2, whereby only the part of the absorption zone marked with Ei and H2 is effective for this effect.

In the buoyancy zone, the formation of chlorate already begins, but in its main phase it takes place in the lead electrolyte tank 4 through conversion of the hypochlorite formed. The sheet metal is fed back to the cell 1 through the return line 3 .

The lead electrolyte collecting container 4 can be made of wrought iron and is rubberized on the inside. In the flat connection cover a nozzle 17 is provided, through which the gas produced by the electrolysis process, consisting essentially of hydrogen, is drawn off.

The lead electrolyte tank 4 is connected to a line 19 via a connector 18 , through which fresh chloride solution is fed in from time to time or continuously. From an additional container 20 , hydrochloric acid is added in a metered amount to the supply line 21 into the return line 3 to acidify the lead electrolyte.

The amount of Auftriebezone Hi and H2 in the example is about 3.7 times the height He of Blektrolysezone. The cross section of the riser pipes 2 is only about 1/9 of the flow cross section of the electrolysis zone.

On part of the length, the return line 3 is equipped with a cooling jacket 25 , which has an inlet connection 28 and an outlet connection 29 , for the purpose of dissipating the heat generated during the Blektrolyoeprozens. The cooling water flows through the cooling jacket 29 in countercurrent to the lead electrolyte.

The circumferential Blektrolytmenge is adjusted by means of a Regulierventiles 24 in the return line 3 to the jeweils'gewünschten word and Ensen using a rotameters 23 g ". * With the return line 3, a drain valve 22 is further connected, through which discharged the Blektrolyt from the arrangement been can.

The entire arrangement rests on insulators 26 on a ceiling 27 and is supported by this.

Fig. 1 shows that the absorption zone consists essentially of the space enclosed by the riser and is provided above the Elektrol ffl one in the cell 1 and that the absorption zone at the same time forms a buoyancy zone, which in the sense of an acceleration to the flow rate of the Blektrolyten through the cell 1-einwirkt. the Ohloratbildungezone ISTG as the Ausführungebeispiel of FIG. 1 can be seen, completely provided separately from the electrolysis zone, so that the disadvantages occurring in the known can not occur due to current effects on the absorption or Ohloratbildungszone.

The device according to FIG. 1 can be operated obargenweise by filling with an alkali chloride solution at the beginning and the electrolysis process being operated until the desired degree of conversion of the chloride to carbonate is achieved, the process water consumed during batch operation being replenished with fresh chloride solution is replaced.

The arrangement can also be operated continuously by Fresh Ohloridlösung continuously fed via the line 20 and the corresponding Ohloratlösung amount is discharged by means of drain valve 22.

The arrangement according to FIG. 3 shows the series connection of three devices similar to FIG. 1 , these being continuously flowed through by the electrolyte in the main stream one after the other, but at the same time an electrolyte cycle is maintained within the individual arrangements.

In the case of the individual devices, two are in turn communicating connected massiveness columns provided in one of the electrolysis zone as well Absorption and buoyancy zone lies while in the other the The electrolyte is returned to the lead electrolysis zone.

The lead electrolysis cell is designated in FIG. 3 in the left-hand arrangement with 30 and its structure corresponds to the cell 1 according to FIGS. 1 and 2. It is connected to the poles of a direct current source via connection tabs 31 and 32, respectively. A riser pipe 33, which preferably has a circular cross-section and opens via a bend 33a into a lead electrolyte collecting container 34 above the liquid level, is in turn connected to the lead electrolysis cell 30. The cell member is discharged from the arrangement through a connecting piece 34a of the container 34. At the bottom of the container 34 there is a connector 35 which is connected to a return line 36 which returns the lead electrolyte from the collecting container 34 to the lead electrolysis cell 30 . This return line consists of non-conductive material. Over part of its length, it is again provided with a cooling jacket 37 with associated inlet and outlet nozzles 38, 39 for the coolant guided in countercurrent to the lead electrolyte.

In the return line 36 , as in the example in FIG. 1, a valve 40 for regulating the amount of circulation of the lead electrolyte is installed.

The supply of fresh Ohloridlösung takes place in the collecting container 34 via an equipped with a valve 43 feed line 41. In the Samelbehälter 34 protrudes from the bottom, an overflow pipe 45 in, which the respective amount of overflow feeds the Blektrolyten from the Sammelbebälter 34 the following arrangement, which in their equivalent in structure to the version described in the left part of FIG. 3. This is followed by yet a further arrangement, the overflow pipe 46 in a auamündet Simmelsberg container 47 for the Ohloratlösung. The entire arrangement is electrically insulated via Iaolators 48 and scaffolding supports 49 and arranged on the floor.

In the embodiment of FIG. 4, an arrangement is shown which differ from those previously described with regard to the development of the Ohloratbildungezone Devices differs.

In the figure, a riser pipe 50 is again provided on the outlet side of the lead electrolysis cell, which opens out via a bend 50a above prescaler rings 52 which are arranged outside the liquid column in the container 51. The lead through the riser pipe as a result of the buoyancy effect to the container 51, interspersed with gas bubbles trickles down over the distributor rings'52 'whereby the gas bubbles contained in the lead electrolyte are separated. The riser pipe 50 in turn surrounds the absorption zone, while the chlorate formation zone is formed by the container 51 and the adjoining pipe 53 . The diameter of the tube 53 is considerably larger than that of the subsequent return line 57, so that a lower flow velocity in the tube 53 occurs. The lower part of the tube 53 is in turn with a Provided cooling jacket 54 for the supply and the Räckleitung Payment means Stutsen 5 # and 56 has. From the formation of ohlorates Through the tube 53 the clectrolyte arrives via the Rft brum-ge. line 579 as prepared in cooperation with the other figures was described, back to the Blektrolzoogelle. In left = ar- works the arrangement described above in the same wines as this is already explained in connection with the other figures became. In a practical example, 2itana modes were used with a height of 50 cm used9 whereby the electrode mask stands Was 5 m. The cell was amplified with a current density of 50 dm2 operated. Immediately after the Blektrol, 7 »ezo» found a buoyancy zone of 230 cm in height. By serving could with the help of the buoyancy by the Gaeblamen in the Illek- troljeezone a lead electrolyte speed of 100 cm / nee will be held. Versuchmweine was the Blektrolytge- 0 ndiß & eit in the Blektroljeesone on 10 cia / nee droned, whereas compared to the 1 [electrolysis rate of 100 OB / sec a cell voltage increased by 0.51 volts was measured.

Claims (2)

Patent claims 1. A process for the preparation of Alkaliohlorat by electrolysis wäsariger Alkalichloridlösungeng wherein the Blektrolyt passed aufwärteströmend by a Blektrolysezone with gap spaces between Anoden'und cathode under the influence of Gaablasenbildung and is preferably returned with reduced Strömungegeaobwindigkeit by a Ohloratbildungezone and from there to Blektrolysezone, d a -duroh g e k ennzeiohnet that the Blektrolyt after passing through the Blektrolysezone is introduced having at least the same flow velocity as in the Blektrolysezone in an ascending direction via the at least Blektrolysezone appropriate height to form an absorption and Auftriebezone in the Ohloratbildungezone. 2. The method according to claim 1, d a d ur a h g e k ennzeio b net that the lead electrolyte is passed through the absorption and buoyancy zone in the form of a piston flow. 3. Device for carrying out the method according to claim 1 or 2, in which a lead electrolysis cell is provided with gaps between anodes and cathodes which are connected on the outlet side of the lead electrolyte with a collecting and Ohloratbildungeraum for the lead electrolyte, to which one is connected. the return line connected to the entry side of the cell "e" äd ur o h g e k ennzei c h u e tg that the and Ohloratbildungaraum arranged in a known manner separately from the cell and that toi &'V, erblii (Iüüg-'init the cell a riser pipe is provided, wel% üdäc # -iif.tt from the' area immediately above the column above ' Yienigütens a-cell height corresponding height extends and has a cross section, corresponding to the maximum of the sum of the clearance gap cross sections of the cell. 4. an apparatus according to claim 3, d a d uroh g e k ennzeich net, that the riser extends into the interior of the 5. Device according to claim 3, d a d ur c h g e k ennzeiohne t. That the riser pipe opens out via a bend above the liquid level in the lead electrolyte collecting space. 6. Device according to one or more of the claims 3 to 59 d a d g e k urcb ennze i o t teeth. that the Blektrolytaammel- Obloratbildungsraum and at least partially lie in the return line as the Blektrolyten to Blektrolysezelle end tube is formed. 7. The device according to one or more of claims 3 to 69 d a d uroh g e k ennze i c he t. that the return Leitungeröhr the electrolyte at least over part of the is aligned lengthways with a lead device. 8. Device »whether claim 4 to 79 d a d ur o he k 9 nn so i a h no tu that the Idinge the tubular Share at least the 5-faobe des to the Seimmel containers hydraulic »Urolmenern the flow cross sections amounts to. 9. Device = oh one or more of the claims 4 to 81p d a d ur o h gok 9 nn me 1 from n 9 t. that * the pipe grainy part, the collecting container has a circular grainy cross cut and at least a pipe length corresponding to the 5-fold has the inner tube penetration. 10. Device whether one or more of claims 3 to 9g g 0 k 0 n aa 0 1 0 ba 0 t d ur whether one behind the other Maintenance of miebrerer devices with lead electrolyte inlet Guided tour with a j "eil14er M lyso cell," riser pipe and S # elbAter novib iMe eleitung, with the inputs Each of the following Blektrolyseselle Uber overflow pipes with the SmaelboMtern of the transferring order are bound .