IES68307B2 - Improvements in cathodes - Google Patents
Improvements in cathodesInfo
- Publication number
- IES68307B2 IES68307B2 IES960071A IES68307B2 IE S68307 B2 IES68307 B2 IE S68307B2 IE S960071 A IES960071 A IE S960071A IE S68307 B2 IES68307 B2 IE S68307B2
- Authority
- IE
- Ireland
- Prior art keywords
- cathode
- stainless steel
- sodium
- solution
- electrolytic cell
- Prior art date
Links
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 12
- 239000010935 stainless steel Substances 0.000 claims abstract description 10
- 229910001220 stainless steel Inorganic materials 0.000 claims abstract description 10
- 239000000203 mixture Substances 0.000 claims description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 48
- 235000011121 sodium hydroxide Nutrition 0.000 description 16
- 239000000243 solution Substances 0.000 description 16
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 13
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 10
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 9
- 239000005708 Sodium hypochlorite Substances 0.000 description 9
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 7
- 239000012267 brine Substances 0.000 description 7
- 239000000460 chlorine Substances 0.000 description 7
- 238000005868 electrolysis reaction Methods 0.000 description 7
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 6
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 6
- 239000003518 caustics Substances 0.000 description 6
- 229910052801 chlorine Inorganic materials 0.000 description 6
- 239000012528 membrane Substances 0.000 description 6
- 230000003628 erosive effect Effects 0.000 description 5
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 4
- 238000003860 storage Methods 0.000 description 4
- 229910000831 Steel Inorganic materials 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 238000010926 purge Methods 0.000 description 3
- 239000010959 steel Substances 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- BZSXEZOLBIJVQK-UHFFFAOYSA-N 2-methylsulfonylbenzoic acid Chemical compound CS(=O)(=O)C1=CC=CC=C1C(O)=O BZSXEZOLBIJVQK-UHFFFAOYSA-N 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 238000006298 dechlorination reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- 235000010265 sodium sulphite Nutrition 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000010964 304L stainless steel Substances 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 241001397173 Kali <angiosperm> Species 0.000 description 1
- 229910019093 NaOCl Inorganic materials 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- XTZVWOPRWVJODK-UHFFFAOYSA-N [Si].[Mn].[C] Chemical compound [Si].[Mn].[C] XTZVWOPRWVJODK-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229920001429 chelating resin Polymers 0.000 description 1
- VNNRSPGTAMTISX-UHFFFAOYSA-N chromium nickel Chemical compound [Cr].[Ni] VNNRSPGTAMTISX-UHFFFAOYSA-N 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910000041 hydrogen chloride Inorganic materials 0.000 description 1
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- -1 hydroxide ions Chemical class 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 210000002445 nipple Anatomy 0.000 description 1
- 230000020477 pH reduction Effects 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- HFFLGKNGCAIQMO-UHFFFAOYSA-N trichloroacetaldehyde Chemical compound ClC(Cl)(Cl)C=O HFFLGKNGCAIQMO-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Landscapes
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
The invention relates to an electrolytic cell for use in for use in the chloralkali industry having a cathode comprising stainless steel having a low carbon content of between 0.028 and 0.032% by weight .
Description
The present invention relates to an electrolysis process for the manufacture of hydrochloric acid, caustic soda liquor and sodium hypochlorite. In particular the invention relates to the use of an improved cathode, having a low carbon content, in the electrolysis process, in order to reduce erosion of the cathode.
The electrolysis process uses salt and water as starting materials 10 to produce hydrochloric acid, caustic soda liquor and sodium hypochlorite. Salt is stored on a storage pad. From the pad the salt is transferred by loader to a pit saturator. Softened water and recycled spent brine are also introduced into the saturator and by drawing this liquid through the bed of salt, a saturated brine solution is obtained. The solution is then filtered and the total hardness is reduced from approximately 5 ppm to less than 20 ppb by ion exchange. The resin used in the ion exchange columns is a specialised chelating resin and requires regenerating every 10 days approximately. The softened brine enters storage from where it can then be fed to the process.
The electrolysis cells require DC current for operation and the 10 KV supply from the grid is passed through two sets of rectifiertransformers to be converted from AC to DC output.
The electrolysis cells used in the process are monopolar with two cells per electrolvser. An electrolyser consists of a titanium anode chamber with two mesh screens, two cathode chambers with stainless steel plates, two membranes separating anode screen from cathode plates and two bulkheads to sandwich the electrolyser components together.
The electrolvsers are arranged in modules of five and connected in « series electrically so that the same load flows through each.
/ Saturated brine is pumped into the anode compartment where the sodium chloride is depleted in chloride ions by the anode reaction and in sodium ions by transport through the membrane. Chlorine gas is generated and flows from the anode with the depleted brine. To the cathode a diluted sodium hydroxide solution is circulated where it is 5 enriched both in sodium ions which pass through the membrane from the
I anode and in hydroxide ions by the cathode reaction. Hydrogen gas is generated and leaves the cathode chamber with the enriched sodium hydroxide solution.
The reactions which take place are represented by the following equations:Anode Reactions:
NaCl Electrical Energy --------> Ha +C1 (1) CT+CI' ---> Cl2(g)+2e (2) Cathode Reactions: H?0 Electrical Energy H++0H (3) ---> 2e+H++H+ ----- ---> H2(g) (4) Na +0H ---> NaOH (5) Overal1 Reaction:
2NaCl + 2H20 ......—>
(6)
Cl 2 + H2 (g) + 2 NaOH
The enriched sodium hydroxide solution is collected in a caustic circulation tank from where part is pumped directly to storage and part is diluted and recirculated back to the electrolysers. The spent brine which contains approximately 200 gpl sodium chloride is saturated with dissolved chlorine gas and undergoes dechlorination in a three stage process. The first stage involves pH reduction using hydrochloric ,.
acid. The solubility of the chlorine gas is greatly reduced at low pH values and most of the chlorine 'gasses off from the solution. The *.· second stage involves scrubbing the low pH solution with air to further reduce the levels of chlorine remaining down to less than 10 ppm.
Final dechlorination is achieved through chemical destruction using sodium sulphite. This stage is performed at pH values in the range 10 - 12 and sodium hydroxide solution is used to increase the pH. The chlorine-free solution is returned to the pit saturator for re-saturation.
It can be seen from Fig. 2 that a certain amount of hydroxide passes through the membrane from the cathode chamber to the anode.
This results in the formation of an impurity, sodium chlorate, which builds up in the brine loop. To prevent this, a small quantity of spent brine must be purged to drain, the purge rate being dependent on the rate of increase of sodium chlorate in the system. Factors affecting this include membrane condition (rips, blisters and holes), operating load and initial feed brine concentration. This purge also acts as a sulphate purge which builds up in the system through the addition of sodium sulphite.
The hydrogen gas produced in electrolysis is cooled and piped directly to the HC1 synthesis furnace. The chlorine gas is piped to both the HC1 synthesis furnace and the sodium hypochlorite system.
In the manufacture of hydrochloric acid, chlorine gas is burned in hydrogen gas to form hydrogen chloride gas according to the reaction (6).’
H2+C12 —-----> 2 HC1 (6)
The gas is then scrubbed out in de-ionised water to form hydrochloric acid. The process takes place in a graphite lined furnace which is jacketed and cooled to remove the heat of reaction. The system, for safety reasons and product quality, must be operated with excess hydrogen. As both gases are produced in the same molecular ratio, chlorine is fed continuously to the sodium hypochlorite reactor where it is reacted with sodium hydroxide according to equation (7):
Cl2 + 2 NaOH ——......> NaOCl + NaCl * H20 (7)
Sodium hypochlorite is produced batch-wise, initially with a charge of approximately 20% NaOH solution and reacting this with chlorine down to a residual sodium hydroxide content of between 0.3 and 1.0% and available chlorine content of between 14% and 15%. It is of utmost importance that the residual sodium hydroxide is kept above 0.3%
- 4 NaOH as the solution becomes highly unstable at levels below this and may even result in the release of chlorine gas.
By taking chlorine gas continuously to sodium hypochlorite manufacture, an excess of hydrogen is obtained at HC1 synthesis. The amount of chlorine to sodium hypochlorite can be varied depending on requirements for either sodium hypochlorite or hydrochloric acid. Each of the three products is pumped to dedicated storage tanks from where they can then be filled into bulk road tankers, IBC's, barrels or carboys.
A significant problem with the process was that the cathodes of the electrolysis cells became eroded rapidly. Initially the discharge nozzles for output of caustic and hydrogen gas started to leak and new nozzles were welded in place. Then the corner welds of the cathode started to leak and had to be rewelded. Eventually, it became apparent that the box frame had been eroded from 4 mm thick to paper thin and these box sections had to be replaced. Since the cathode is of a louvered design in order to promote circulation of the electrolytic solution in the cell, as the carbon coating on the cathode became worn off, the carbon blocked the louvers and reduced circulation. The erosion became so bad that leaks appeared in the cells which resulted in caustic solution at a temperature of 90°C spraying from the cell. Such leaks had to be repaired by welding, necessitating downtime in the cell.
The installation of a nickel sacrifical bushing to prevent destruction of the nipple and cathode frame, as recommended by the equipment st^pplier, proved unsuccessful in preventing erosion.
Accordingly, it is an object of the present invention to provide an electrolytic cell having a cathode which would not erode as easily as the prior art cathodes. Prior art cathodes used in the chloral kali industry are either mild steel cathodes, which have a high carbon content or nickel cathodes, nickel being very expensive. It is therefore a further object of the present invention to provide a replacement cathode having a low cost. It was a further object of the invention to provide an electrolytic cell in which no part in contact with caustic solution would erode easilv.
J
According to the present invention there is provided an electrolytic cell for the production of hydrochloric acid, caustic soda and sodium hypochlorite, having a cathode comprising stainless steel with a low carbon content of 0.028% to 0.032% by weight, preferably 0.03% by weight. Preferably this stainless steel has the following composition:
Composition (maxima) % by weight
Carbon
Silicon
Manganese
Phosporous
Sulpher
Chromium
Nickel
0.03
.00
.00
0.045
0.030
17.00-19.00
9.00-12.00
The stainless steel may suitably be grade 304L available from Amari Ireland Ltd. or The Steel Company of Ireland.
The electrolytic cell may further comprise a faceplate on the bulkhead comprising stainless steel with a low carbon content as defined above. Preferably the faceplate is provided on all surfaces of the bulkhead which come in contact with the caustic solution.
The invention will now be described in greater detail with reference to the accompanying drawings in which:Figure 1 is a schematic diagram of an electrolyser,
Figure 2 is a diagramatic representation of the principles of operation of the electrolytic cell, and
Figure 3 is a drawing of a cathode frame assembly in accordance with the present invention.
Figure 1 shows a schematic diagram of an electrolyser (1). The electrolyser (1) consists of an anode chamber (2) with two mesh screens (3) and two cathode chambers (4). Two membranes (not shown) separate the anodes (2) from the cathodes (4). Two bulkheads (δ) sandwich the electrolyser components together. The anode (2) of one electrolyser is connected to the cathode (4) of the next electrolvser in the cell room via a busbar (5). As shown in Figure 3, the cathode (4) comprises a plurality of louvers (7). The cathode chamber (4) is also provided with a feed inlet (8) and a drain (9) and two discharge ports (10) for the discharge of hydrogen gas and enriched sodium hydroxide solution.
Example
The original electrolytic cells comprising mild steel had an average life-span of three years with substantial erosion being apparent at the end of that time.
Prototype cells, using 304L stainless steel as the cathode and as a faceplate on the mild steel bulkhead were introduced. The faceplate served to convert the mild steel bulkhead into a low carbon content steel bulkhead i.e. all parts of the cell in contact with the caustic solution were now made of low carbon content steel. No evidence of erosion was detectable in these cells after 2-3 years in operation.
Claims (4)
1. An electrolytic cell for use in the chloralkali industry having a cathode comprising stainless steel having a low carbon content of between 0.028 and 0.032% by weight.
2. An electrolytic cell as claimed in Claim 1 further comprising a faceplate on the bulkhead comprising stainless steel having a low carbon content of 0.028 to 0.032% by weight.
3. An electrolytic cell as claimed in Claim 1 or Claim 2 wherein the stainless steel has a carbon content of 0.03% by weight.
4. An electrolytic cell as claimed in any preceding claim wherein the stainless steel has the composition
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IES960071 IES68307B2 (en) | 1996-01-22 | 1996-01-22 | Improvements in cathodes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IES960071 IES68307B2 (en) | 1996-01-22 | 1996-01-22 | Improvements in cathodes |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| IES960071A2 IES960071A2 (en) | 1996-06-12 |
| IES68307B2 true IES68307B2 (en) | 1996-06-12 |
Family
ID=11041056
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IES960071 IES68307B2 (en) | 1996-01-22 | 1996-01-22 | Improvements in cathodes |
Country Status (1)
| Country | Link |
|---|---|
| IE (1) | IES68307B2 (en) |
-
1996
- 1996-01-22 IE IES960071 patent/IES68307B2/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| IES960071A2 (en) | 1996-06-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MM4A | Patent lapsed |