IES960072A2 - Hydrochloric acid recovery - Google Patents
Hydrochloric acid recoveryInfo
- Publication number
- IES960072A2 IES960072A2 IES960072A IES960072A2 IE S960072 A2 IES960072 A2 IE S960072A2 IE S960072 A IES960072 A IE S960072A IE S960072 A2 IES960072 A2 IE S960072A2
- Authority
- IE
- Ireland
- Prior art keywords
- scrubber
- hydrochloric acid
- fumes
- line
- ionised water
- Prior art date
Links
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 title claims abstract description 73
- 238000011084 recovery Methods 0.000 title description 4
- 239000003517 fume Substances 0.000 claims abstract description 25
- 239000008367 deionised water Substances 0.000 claims abstract description 16
- 238000000034 method Methods 0.000 claims abstract description 15
- 239000003929 acidic solution Substances 0.000 claims abstract description 12
- 238000005201 scrubbing Methods 0.000 claims abstract description 10
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 9
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 8
- 239000002253 acid Substances 0.000 claims abstract description 7
- 230000003134 recirculating effect Effects 0.000 claims abstract description 5
- 239000000243 solution Substances 0.000 claims description 14
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 239000007921 spray Substances 0.000 claims description 4
- 239000003595 mist Substances 0.000 claims description 2
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 39
- 235000011121 sodium hydroxide Nutrition 0.000 description 13
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 9
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 239000000460 chlorine Substances 0.000 description 8
- 239000005708 Sodium hypochlorite Substances 0.000 description 7
- 239000012267 brine Substances 0.000 description 7
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 7
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 6
- 229910052801 chlorine Inorganic materials 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- 239000012528 membrane Substances 0.000 description 5
- 238000003860 storage Methods 0.000 description 5
- 238000005868 electrolysis reaction Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- 229910001415 sodium ion Inorganic materials 0.000 description 4
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 4
- 238000010926 purge 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
- 230000002378 acidificating effect Effects 0.000 description 2
- 239000003518 caustics Substances 0.000 description 2
- 238000006298 dechlorination reaction Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- -1 hydroxide ions Chemical class 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 235000010265 sodium sulphite Nutrition 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 239000004743 Polypropylene Substances 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
- 239000011324 bead Substances 0.000 description 1
- 229920001429 chelating resin Polymers 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000001419 dependent effect Effects 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
- 239000012535 impurity Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 230000020477 pH reduction Effects 0.000 description 1
- 229920001155 polypropylene Polymers 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
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 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
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
Landscapes
- Treating Waste Gases (AREA)
Abstract
In order to recover acid and reduce costs in hydrochloric acid effluent treatment there is provided a method for scrubbing hydrochloric acid fumes in which de-ionised water is fed to a scrubber into which hydrochloric acid fumes are introduced, the scrubber having a recirculation line, for recirculating the weakly acidic solution formed on contact of the fumes and de-ionised water in the scrubber into the scrubber again, wherein the scrubber is provided with a by-pass line on the recirculation line, the bypass line being connectable to a hydrochloric acid synthesis furnace to allow transfer of the acidic solution to the furnace. An apparatus for carrying out the method is also described <Fig. 2>.
Description
Hydrochloric Acid Recovery
The present invention relates to an improved method and apparatus for the scrubbing of hydrochloric acid fumes, and in particular to allow recovery of the acid. The invention has particular application in the chloroalkali industry.
In the chloroalkali industry the electrolysis process uses salt and water as starting materials 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 electrolyser. 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 electrolysers 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 enriched both in sodium ions which pass through the membrane from the anode and in hydroxide ions by the cathode reaction. Hydrogen gas is
960072
- 2 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 Na++Cl (1)
-------->
CT+Cl --------> Cl2(g)+2e (2)
Cathode Reactions:
HpO Electrical Energy H++0H (3)
-------->
2e+H++H+ > H2(g) (4)
Na++0H .....—> NaOH (5)
Overall Reaction:
2NaCl + 2H20 .....—> Cl2 + Η£ (g) + 2 NaOH (6)
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
- 3 chlorine-free solution is returned to the pit saturator for re-saturation.
It can be seen from Fig. 1 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
> 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
NaOCI + 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%
960072
- 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 disadvantage with the present process is the necessity to store 36% fuming hydrochloric acid. The acid is stored in a variety of storage tanks in which fumes are generated. These fumes are scrubbed with mains water, which as a result becomes acidic. The scrubber is run with one pass through of water and the acidic water output has to be transferred to an effluent treatment plant for neutralisation. Thus a substantial portion of the acid supply in the form of fumes is wasted and the effluent treatment requires the use of caustic solution, both of which amount to a a cost to the process.
It is therefore an object of the present invention to provide an improved method and apparatus for the scrubbing of hydrochloric acid fumes, which allows recovery of a majority of the acid and has a reduced requirement for water.
According to the present invention there is provided a method for scrubbing hydrochloric acid fumes in which de-ionised water is fed to a scrubber into which hydrochloric acid fumes are introduced, the scrubber having a recirculation line, for recirculating the weakly acidic solution formed on contact of the fumes and de-ionised water in the scrubber into the scrubber again, wherein the scrubber is provided with a by-pass line on the recirculation line, the bypass line being connectable to a hydrochloric acid synthesis furnace to allow transfer of the acidic solution to the furnace.
The invention further relates to an apparatus for scrubbing hydrochloric acid fumes comprising a scrubber having an input for hydrochloric acid fumes adjacent the base of the scrubber, an input
- 5 9600 7 2 line for de-ionised water adjacent the upper end of the scrubber, and a recirculation line for recirculating weakly acidic solution, formed in the scrubber on reaction of the fumes and water, from the base of the scrubber unit to the upper end of the scrubber, wherein the recirculation line is provided with a bypass line for transfer of the acidic solution to the hydrochloric acid synthesis furnace.
Preferably, the upper end of the scrubber is vented to atmosphere.
Preferably the de-ionised water is fed into the scrubber as a fine spray or mist.
Preferably the concentration of the weak acid solution is maintained below 5% hydrochloric acid in order to reduce emissions from the scrubber to less than 5 ppm.
The invention will now be described in greater detail with reference to the accompanying drawings in which :
Figure 1 is a diagramatic representation of the principles of operation of the electrolytic cell and
Figure 2 is a drawing of a hydrochloric acid fume scrubber in accordance with the present invention.
The hydrochloric acid fume scrubber in accordance with the present invention comprises a scrubber column (1) packed with polypropylene beads. The base of the scrubber (1) is provided with a gas inlet port (2) through which the hydrochloric acid fumes are introduced to the scrubber. The scrubber is vented to atmosphere via a vent (3) at the top of the scrubber. A fine spray of de-ionised water is introduced into the top of the scrubber via a de-ionised water inlet (4). The de-ionised water is stored in a tank (5) from which the water is pumped to the de-ionised water inlet (4) by a pump (6). As the hydrochloric acid fumes pass up through the scrubber (1) they meet the fine spray of de-ionised water travelling downwards and react to form a mildly acidic solution which falls to the bottom of the scrubber.
This acidic solution is then drained from the base of the scrubber (1) and recirculated into the top of the scrubber again via a . 960072
- 6 recirculation line (7). A bypass line (8) is taken off the recirculation line (7) and connects to the hydrochloric acid synthesis furnace in the hydrochloric acid manufacturing plant.
Introduction of this modified scrubber unit has allowed a saving of 4000 gallons of water a day from the effluent treatment plant at a cost saving of £38 per day. This amounts to a total saving of £13,780 per annum to the process.
Claims (5)
1. A method for scrubbing hydrochloric acid fumes scrubbing hydrochloric acid fumes in which de-ionised water is fed to a scrubber into which hydrochloric acid fumes are introduced, the scrubber having a recirculation line, for recirculating the weakly acidic solution formed on contact of the fumes and de-ionised water in the scrubber into the scrubber again, wherein the scrubber is provided with a by-pass line on the recirculation line, the bypass line being connectable to a hydrochloric acid synthesis furnace to allow transfer of the acidic solution to the furnace.
2. A method as claimed in claim 2 or 3 wherein the concentration of the weak acid solution is maintained below 5° hydrochloric acid in order to reduce emissions from the scrubber to less than 5 ppm.
3. An apparatus for scrubbing hydrochloric acid fumes comprising a scrubber having an input for hydrochloric acid fumes, an output line for de-ionised water adjacent the upper end of the scrubber, and a recirculation line for recirculating weakly acidic solution formed in the scrubber, from the base of the scrubber unit, wherein the recirculation line is provided with a by-pass line for transfer of the acidic solution to the hydrochloric acid manufacturing plant.
4. An apparatus as claimed in claim 3 wherein the de-ionised water is fed into the scrubber as a fine spray or mist.
5. An apparatus for scrubbing hydrochloric acid fumes substantially as described herein with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IES960072 IES69660B2 (en) | 1996-01-22 | 1996-01-22 | Hydrochloric acid recovery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IES960072 IES69660B2 (en) | 1996-01-22 | 1996-01-22 | Hydrochloric acid recovery |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| IES960072A2 true IES960072A2 (en) | 1996-10-02 |
| IES69660B2 IES69660B2 (en) | 1996-10-02 |
Family
ID=11041057
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| IES960072 IES69660B2 (en) | 1996-01-22 | 1996-01-22 | Hydrochloric acid recovery |
Country Status (1)
| Country | Link |
|---|---|
| IE (1) | IES69660B2 (en) |
-
1996
- 1996-01-22 IE IES960072 patent/IES69660B2/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| IES69660B2 (en) | 1996-10-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MM4A | Patent lapsed |