CN111254455B - Device and method for decomposing chlorate generated by side reaction of anode chamber of electrolytic cell in chlor-alkali production and related acid adding process - Google Patents

Device and method for decomposing chlorate generated by side reaction of anode chamber of electrolytic cell in chlor-alkali production and related acid adding process Download PDF

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CN111254455B
CN111254455B CN202010186563.XA CN202010186563A CN111254455B CN 111254455 B CN111254455 B CN 111254455B CN 202010186563 A CN202010186563 A CN 202010186563A CN 111254455 B CN111254455 B CN 111254455B
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chlorate
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吕子红
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B7/00—Halogens; Halogen acids
    • C01B7/01—Chlorine; Hydrogen chloride
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D3/00—Halides of sodium, potassium or alkali metals in general
    • C01D3/04—Chlorides
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
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Abstract

The invention provides a device and a method for decomposing chlorate generated by side reaction in an anode chamber of an electrolytic cell in chlor-alkali production and a related acid adding process2、Cl‑、H2O, unstable gas ClO no longer exists in gas phase2Pure wet Cl2Directly into the manifold. The peracid amount in the fresh brine after the chlorate decomposition is utilized to replace the fresh brine for dechlorination and acid addition, so that the self-used hydrochloric acid and caustic soda produced by electrolysis are saved. In the actual operation of electrolysis, the decomposed chlorate can be balanced with chlorate which is a byproduct of an electric cell at any time, so that the chlorate enriched by an electrolysis system can be quickly reduced, the problems of chlorate enrichment in the electrolysis system, influence on caustic soda quality, strong corrosion to solid caustic soda equipment and the like are solved, and the technical progress of chlor-alkali electrolysis production is greatly promoted.

Description

Device and method for decomposing chlorate generated by side reaction of anode chamber of electrolytic cell in chlor-alkali production and related acid adding process
Technical Field
The invention belongs to the field of brine electrolysis production technology (containing NaOH and KOH production) in the chlor-alkali industry, and particularly relates to a production process technology for eliminating chlorate generated by side reaction in an anode chamber and converting the chlorate into reusable sodium chloride and chlorine in an ion membrane caustic soda electrolysis process.
Background
The production of caustic soda by electrolyzing saline solution by an ion membrane method is the most main production process in the existing chlor-alkali industry, a byproduct chlorate is generated in an anode chamber in the electrolysis process, and the continuous accumulation of chlorate in the saline solution not only influences the solubility of NaCl, but also increases the chlorate content in the product NaOH and reduces the quality.
Under the action of direct current, the basic chemical reaction is as follows:
2NaCl+2H2O→2NaOH+Cl2↑+H2↑；
anode chamber electricityChemical reaction: 2Cl--2e→Cl2；
Electrochemical reaction in a cathode chamber: 2H++2e→H2；
The anode chamber mainly has chemical side reactions: OH transferred from the cathode compartment-The following side reactions occur in the anode chamber;
Cl2(aqueous solution) + H2O→HClO+H++Cl-
NaOH+HClO→NaClO+H2O
2HClO+NaClO→NaClO3+2HCl
From the above intermediate chemicals, NaClO is contained in the substances generated in the anode chamber of the electrolytic cell3Is a final, stable chemical, so chlorate is reduced to recyclable NaCl and Cl2It is also difficult.
In the existing chlor-alkali industry technology, the decomposition (elimination) of chlorate has the following two methods:
mainstream method for decomposing chlorate with as-product chlor-alkali industry
According to the amount of chlorate in the dilute brine produced in the anode chamber of the electrolytic cell, a set of chlorate decomposing device is specially arranged, part of the dilute brine at the temperature of-87 ℃ which is discharged out of the electrolytic cell is continuously discharged into the chlorate decomposing cell, a proper amount of hydrochloric acid is added in proportion, the mixture is externally heated or steam is directly introduced into the chlorate reaction cell to be heated to 90-95 ℃, the reaction time is about 2.5 hours, and the mixture overflows and is discharged into a collecting tank to be dechlorinated and recycled. NaClO in reaction finishing liquid of chlorate discharging reaction tank for controlling process index33-5 g/L, HCl is less than or equal to 20g/L, chlorine generated by the reaction is diluted by adding a proper amount of air (ClO generated is prevented)2Decomposition explosion) as waste gas to be disposed of in the downstream process. The chlorate decomposition amount and the electrolytic anode chamber generation amount are in balance.
The above chlorate decomposition method has the following disadvantages:
firstly, the chlorate decomposing device has complex process configuration, and steam is directly introduced into the reaction solution to pollute the light brine;
secondly, the decomposition time is long and needs more than 2.5 hours, the decomposition rate is reduced by 50-65%, chlorate in the brine can only run beyond the standard when the current efficiency is low when the ionic membrane of the electric tank runs to the later stage, and the production and the operation of the brine and the electrolysis system are deteriorated;
the hydrochloric acid is excessive after decomposition, a certain amount of caustic soda is added for neutralizing the excessive acid after dechlorination, and compared with the stopping of a chlorate decomposition device, the consumption of caustic soda during dechlorination is much higher;
ClO is contained in chlorine gas generated when beginning to decompose at low temperature or when the amount of hydrochloric acid is insufficient2Cannot produce high-purity chlorine gas and send the chlorine gas to a downstream process, and only can add air to dilute the chlorine gas (prevent ClO from being generated)2Decomposition and explosion) as waste gas treatment, and waste chlorine treatment facilities and operation cost are increased;
the chlorate decomposition is partial decomposition and incomplete chemical reaction.
Dechlorate elimination process with capsule wall-passing LSZ reductant
On the basis of the chlorate decomposing device, facilities such as unloading, storage, a metering pump and the like are added, a prepared strong reducing agent is provided by a supplier to replace part of hydrochloric acid to decompose chlorate, and the supplier keeps secret about the components of the reducing agent but ensures that the reducing agent is harmless to brine electrolysis. The reducing agent is mixed with a certain amount of hydrochloric acid and then added into fresh brine discharged from the tank to reduce chlorate in a chlorate decomposition tank, the reduction process is an exothermic reaction, heating is not required under normal conditions, dechlorination of the solution is completed, and chlorine can be recycled to a chlorine main pipe without dilution.
The LSZ reducing agent elimination chlorate process suffers from the following disadvantages:
firstly, a chlorate decomposing device is additionally provided with storage equipment, metering pump medicament adding equipment and the like, the operation is more complicated, and the decomposing effect is not obvious when the medicaments are not uniformly mixed;
secondly, a certain amount of hydrochloric acid is still required to be added to improve the oxidability of the perchlorate, and the use amount of the hydrochloric acid can be reduced by half;
the cost of purchasing the medicine of a supplier is high, and the production cost is increased by using a large amount of outsourcing medicine;
fourthly, the components of the strong reducing agent are unclear, unclear substances are brought into a production system, the generated substances are discharged out of an electrolysis system, and certain risks exist in electrolysis production;
residual chlorate and excessive hydrochloric acid in the decomposition finished solution are incomplete chemical reaction.
In the existing chlor-alkali industrial technology, chlorate decomposition, dechlorination of light salt brine, electrolysis of the cell light salt brine in an acid mode are as follows:
first, electrolytic tank-entering light salt water acid-adding mode
During the operation of the cell, in particular during the run of the ionic membrane to the later stage, in order to neutralize the OH which has migrated back from the cathode compartment (containing the permeate NaOH)-Ion, each electrolytic cell needs to be added with a certain amount of hydrochloric acid to neutralize OH-The ions reduce the pH value, reduce the consumption of chlorine gas caused by the nascent active chlorine in the anode chamber and the side reaction thereof, and the increase of the electrolysis side reaction can increase the consumption and equipment corrosion in the aspects of dechlorination of light salt water, purification of salt water and the like.
The adding mode is as follows: 31% HCl high-purity hydrochloric acid from a 31% HCl high-purity hydrochloric acid main pipe is respectively and independently mixed with the salt water entering each electrolytic tank through a control valve and a flow meter, and then enters the electrolytic tank along with the salt water entering each electrolytic tank.
② acid adding mode for dechlorinating dilute brine
Dissolving a certain amount of active chlorine (Cl) in the dilute brine out of the tank2、ClO-NaClO) and ClO3 -Chlorine gas is precipitated from the dilute brine in a dechlorinating tower under vacuum at a pH of 1.5-2.5, and the dilute brine discharged from the dechlorinating tower is generally at a pH of 3.5-5, so that the pH of the dilute brine is adjusted to 1.5-2.5 by adding acid, and the dilute brine discharged from the dechlorinating tower needs to be dechlorinated by adding acid.
The adding mode is as follows: 31% HCl high-purity hydrochloric acid from a 31% HCl high-purity hydrochloric acid header pipe is intensively added into an anolyte header pipe at an outlet of an electrolytic cell to be uniformly mixed after passing through an automatic control valve and a flow meter, an acid adding regulating valve is controlled according to the pH value of light brine entering a dechlorinating tower, the pH value is controlled to be 1.5-2.5, and the light brine enters the dechlorinating tower through a light brine inlet header pipe of the dechlorinating tower to remove free chlorine in the light brine.
③ acid adding method for decomposing chlorate in light salt water
On a light salt water main pipe of a dechlorinating tower, a proper amount of light salt water is separated according to the height of chlorate in the light salt water, 31% HCl high-purity hydrochloric acid from a 31% HCl high-purity hydrochloric acid main pipe is added according to the proportion, steam is directly introduced into the bottom of a chlorate decomposing tank to heat and stir, after decomposition reaction is carried out for 2.5 hours, the mixture is discharged into a collecting tank to be dechlorinated in a dechlorinating tower, and the acid adding amount is adjusted by taking 3 g/L-5 g/L of chlorate in a reaction finished solution and less than or equal to 20g/L of HCl as indexes.
In conclusion, the mainstream chlorate decomposition method in the chlor-alkali industry is far from achieving the optimal process control index of chlorate decomposition.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a device and a method for decomposing chlorate generated by side reaction in an anode chamber of an electrolytic cell in chlor-alkali production and a related acid adding process, so as to improve the reaction speed and the decomposition rate of chlorate, simplify the process, reduce the consumption and prevent the byproduct chlorate from influencing the electrolytic operation.
The theoretical basis of the method for decomposing chlorate of the invention is as follows:
chemical equation for chlorate decomposition in electrolyzed weak brine:
(1)NaClO3+6HCl→NaCl+3Cl2+3H2O
(2)NaClO3+2HCl→NaCl+ClO2+1/2Cl2+H2O
which of the two above equations occurs preferentially depends on the operating conditions, but it is not possible to have only one chemical reaction, the chemical reaction of formula (1) is the most desirable in the decomposition of chlorate in electrolytic systems, and it is also sought after how to limit the occurrence of formula (2) or to minimize the occurrence of ClO2The generation is also one of the contents of the technical improvement scheme.
The decomposition speed of chlorate can be seen from the electrochemical theory: chloric acid is a strong acid, close in strength to hydrochloric and nitric acids, and chloric acid is also a strong oxidant, but the chlorate solution is only oxidizing in acidic media.
The standard electrode potentials for the chemical reactions during chlorate decomposition in acidic medium are as follows
ClO2+e→ClO2 -ψ0 1＝1.18V(a)
ClO3 -+3H++2e→HClO2+H2Oψ0 2＝1.21V(b)
ClO2+H++e→HClO2ψ0 3＝1.275V(c)
ClO3 -+6H++5e→1/2Cl2+3H2Oψ0 4＝1.47V(d)
2HClO+2H++2e→Cl2(g)ψ0 5＝1.63V(e)
HClO2+2H++2e→HClO+H2Oψ0 6＝1.84V(f)
Because of ClO in neutral media3 -Combined with metal ions and existing in the form of salt, has weak oxidizing power and ClO3 -+3H2O+6e→Cl-+6OH-Standard electrode potential of only psi0 7＝0.62V，H+The increase of the ion concentration can effectively improve the electrode potential value, H, of the chlorate+The higher the ion concentration, the stronger the chlorate oxidation ability. Chlorate decomposition consumes a considerable amount of H+Ions, H remaining after consumption+Ions, still maintaining a sufficiently high H+The ion concentration. The above six formulas all reflect that the higher the residual hydrochloric acid concentration the more complete the forward reaction. Only the formula (d) apparently occurs in the chlorate decomposition reactor all the time, and the decomposition rate can be completely 100%. Of course, other chemical reactions are also possible in the course of this, ensuring sufficient reaction temperature and H at the end of the reaction+Under the premise of ion concentration, chlorate in the dilute brine can be rapidly and completely decomposed, and ClO can not be generated in gas phase2The reaction is safer due to the existence of the catalyst.
However, the prior chlorate reaction apparatus cannot ensure the above conditions, and not only the chemical reaction is incomplete, but also other substances (ClO)2) Is generated. Therefore, the configuration of the existing production device and the control of the process index are not the most reasonable.
Therefore, by increasing and maintaining the proper amount of peracid in the fresh brine, the electrode potential value of chlorate can be effectively increased and maintained, and the oxidation strength can be maintained, thereby increasing the rate of chlorate decomposition in the fresh brine. Further, the higher the temperature, the higher the activity of ions in the dilute brine, the more oxidizing the salt, and the higher the decomposition rate.
The decomposition rate of chlorate since ClO is formed in the formula (2)2Is not completely avoidable, especially when the acid content in the solution is insufficient and the temperature is low during the chlorate decomposition, the ClO2The formation amount is relatively large, and chlorate is decomposed into Cl2The amount of (A) is low, ClO2The content in gas phase and light salt water is high. ClO in light brine2Is unstable and may contain ClO in the generating solution of the formulae (c), (f) and (e) in a dilute saline environment with a high excess of acid2Quickly reduce to Cl2And HClO,Under the condition that the reaction temperature and the reaction time (3 min-5 min) can be ensured, chlorate in the dilute brine returned to the anolyte circulating tank can be completely decomposed.
ClO in gas phase2In the case of Cl formed in chlorate reaction2、ClO2The gas, which cannot be separated and released directly, must exist in the environment of gas-liquid mixture of light brine with high over-acid content and gas ClO in the mixture2And the successive conversion of the formulae (a) and (c) into HClO in solution in the liquid phase will take place2In the liquid phase, gas ClO of the formulae (f) and (e) continues to occur2Quickly reduce to Cl2And HClO. The higher the temperature of the gas-liquid mixture and the higher the hydrochloric acid concentration, the higher the gas ClO2The more complete the reduction, the shorter the time the gas ClO is2Completely disappear in gas-liquid mixture, and then gas-liquid separation is carried out to obtain pure Cl2Can be directly incorporated into Cl2The main pipe, the light salt water containing a certain excess hydrochloric acid enters the electrolysis bath light salt water main pipe.
Therefore, it is required to rapidly increase the decomposition rate of chlorate and ensure the decomposition rate of chlorate and CL2Purity, chemical reaction (1), is the effect we ultimately pursued. In addition to a suitable increase in the reaction temperature, the current electrolytic acid addition system and chlorate decomposition process cannot be solved. Chlorate of on-the-spot operationThe decomposing device can consume a large amount of caustic soda due to too high peracid amount, only can control lower peracid amount, and can not consume more caustic soda by increasing reaction time, and finally the chlorate decomposition completion liquid controls NaClO33.5-5 g/L, HCl is less than or equal to 20 g/L. NaClO normally operates when chlorate in fresh brine is discharged from a tank3When the concentration is 10g/L, the primary decomposition rate of the chlorate decomposer is only 50-65%. Only by innovatively changing the acid using process and chlorate decomposition mode in the existing electrolysis system can the purposes of improving the chlorate decomposition speed and decomposition rate and eliminating ClO in gas phase2The purpose of (1).
In order to solve the above problems, the applicant has conducted the following experiments with respect to the rate and rate of chlorate decomposition in dilute brine:
taking a certain amount of electrolyzed fresh brine out of the cell, and analyzing NaClO in the fresh brine3Content, analysis results NaClO in light brine319.4 g/L. Taking 100mL of light saline water, adding 30mL of high-purity hydrochloric acid with the concentration of 31%, heating to boil for 1min, naturally cooling to 80 ℃ for 15s, and cooling primary water to normal temperature; analyzing NaClO in the solution after thermal decomposition3Content, analysis result is NaClO3The content is 1.3g/L, and the test is repeated 17 times, and the results are basically the same.
To further investigate the influence of the addition of hydrochloric acid and the decomposition temperature on the decomposition rate and rate of the chloride, the following comparative test was designed:
taking a certain amount of electrolyzed fresh brine out of the cell, and analyzing NaClO in the fresh brine3Content, analysis results NaClO in light brine319.4 g/L. Taking 100mL of light saline water, adding 10mL of high-purity hydrochloric acid with the concentration of 31%, heating to boil for 1min, naturally cooling to 80 ℃ for 2.5h, and cooling primary water to normal temperature; analyzing NaClO in the solution after thermal decomposition3Content, analysis result is NaClO3The content is 9.2g/L, the test is repeated 17 times, and the results are basically the same.
Conclusion from the above experiments:
mixing dilute saline water with 31% HCl hydrochloric acid at a volume ratio of 100:30, boiling the solution, naturally cooling to 90 deg.CReaction time is only 1.25min, NaClO3The decomposition rate of the chlorate can reach 93.3 percent, and the chlorate can be completely decomposed to reach 100 percent by properly prolonging the reaction time;
secondly, the decomposition speed is high, and is 120 times faster than the mixing ratio of fresh brine and 31% HCl 10:1 of the prior chlorate decomposition device which needs 2.5 hours;
③ because the peracid content in the weak brine is high, the generation of chlorate decomposition reaction (2) can be reduced to the utmost extent, and the ClO can be eliminated completely2Is present.
As can be seen from the above analysis, the oxidation strength of chlorate is in direct proportion to the concentration of hydrochloric acid in the dilute brine, and the concentration of hydrochloric acid added in proportion to the concentration of chlorate in the dilute brine is gradually reduced along with the increase of the decomposition amount, so that the oxidation strength of chlorate is reduced until the chlorate is not decomposed, and ClO (ClO) is generated according to the formula (2) in the decomposition process2And (4) generating. Therefore, the technological indexes in the reaction finished liquid of the chlorate outlet reaction tank can only be controlled by NaClO33-5 g/L, HCl is less than or equal to 20 g/L. In addition, the reaction temperature can not reach the boiling state, chlorate is decomposed in the boiling state, the amount of the evaporated waste water containing low-concentration active chlorine is large, the treatment is difficult, the steam consumption is high, the waste water is not economical, and the process index of the reaction temperature can only be set to be 90-95 ℃. Therefore, the prior chlorate decomposition method must be replaced by a new process.
In summary, the present invention provides a method for continuously maintaining strong oxidation ability of chlorate with high excess acid and high enough reaction temperature (boiling state), thereby realizing rapid, safe and complete decomposition of chlorate in dilute brine, and indirectly solving the problems of low heat energy utilization rate, high consumption of caustic soda hydrochloride and ClO in wet chlorine2To a problem of (a).
The technical scheme adopted by the invention for solving the technical problems is as follows:
1. the invention provides a chlorate decomposition device generated by side reaction of an anode chamber of an electrolytic cell in chlor-alkali production, comprising:
the electrolytic cell is used for producing chlor-alkali, and is connected with an in-cell refined salt water pipeline and an out-cell light salt water pipeline which are connected with the electrolytic cell, and the out-cell light salt water pipeline is connected with a light salt water main pipe through an anolyte circulating cell;
the high-purity hydrochloric acid main pipe is divided into two branch pipes, the electrolysis acid adding branch pipe is led to the electrolysis tank to be led to the refined salt water pipeline, and the second branch pipe is led to the chlorate decomposition tank;
the chlorate decomposing tank is connected with the dilute brine main pipe through the dilute brine branch pipe, and chlorate decomposing finished liquid is divided into two paths after passing through the gas-liquid separator, wherein one path is used for removing chlorine from the dilute brine main pipe, and the other path is returned to the anode liquid circulating tank.
Preferably, a heat exchanger is arranged at an inlet pipeline of the chlorate decomposition tank, a cold medium inlet of the heat exchanger is connected with the anolyte circulation tank and the high-purity hydrochloric acid main pipe, a cold medium outlet corresponding to the heat exchanger is connected with an inlet of the chlorate decomposition tank, a heat medium inlet of the heat exchanger is connected with an outlet of the chlorate decomposition tank, and a heat medium outlet corresponding to the heat exchanger is connected with a gas-liquid separator.
Preferably, a steam interlayer is arranged at the chlorate decomposing tank, and steam is introduced into the steam interlayer to provide a proper temperature for chlorate decomposition.
Preferably, the dilute brine outlet pipeline enters a dilute brine header pipe through an anolyte circulating tank to a dechlorination tower.
Preferably, flow meters and adjusting valves are arranged between the dilute brine branch pipe and the chlorate decomposing tank and between the chlorate decomposing acidification branch pipe and the chlorate decomposing tank, a pH meter is arranged on the dilute brine main pipe, and the opening degree of the adjusting valve is adjusted according to the pH value, so that the proportion adjustment of the dilute brine and the hydrochloric acid entering the chlorate decomposing tank and the pH adjustment of the dilute brine main pipe are realized.
2. The invention also provides a method for decomposing chlorate generated by the anode chamber side reaction of the electrolytic cell in the chlor-alkali production, based on the decomposition device, the method divides corresponding light salt water from the anolyte circulating tank to a chlorate decomposition part according to the content of byproduct chlorate in the chlor-alkali production, and high-purity hydrochloric acid is intensively added to the chlorate decomposition part according to high excess acid amount to realize chlorate decomposition;
and after the chlorate decomposition is finished, returning the light salt brine with high residual hydrochloric acid to the anolyte circulating tank to replace high-purity hydrochloric acid to reduce the pH value of the circulating anolyte, conveying the circulating anolyte to each unit of electrolysis, dechlorination and chlorate decomposition through a light salt brine header pipe after the pH value of the circulating anolyte is reduced to a specified value, finely adjusting the high-purity hydrochloric acid by using the part with insufficient acid in the electrolytic tank to supplement, and not adding acid any more when the light salt brine is dechlorinated.
Preferably, after the chlorate decomposition is finished, wet chlorine is contained in the decomposition finished liquid besides the dilute brine with high excess hydrochloric acid, and the decomposition finished liquid is divided into two paths after passing through a gas-liquid separator: the light salt water with high surplus hydrochloric acid returns to the anode liquid circulating tank, and the wet chlorine gas returns to the chlorine gas main pipe.
Preferably, after completion of the chlorate decomposition, the decomposition-completed solution is cooled to below 80 ℃.
Preferably, the flow rate of the dilute brine and the addition amount of the high-purity hydrochloric acid are calculated according to the content of the chlorate in the dilute brine in a ratio of 100: and adjusting the proportion of 25-35.
Preferably, the chlorate decomposition temperature is controlled to above 90 ℃, preferably chlorate is decomposed in boiling state.
Preferably, the pH value of the dilute brine main pipe at the outlet of the anolyte circulating tank is controlled to be 1.5-2.5.
Preferably, the specified value of the pH value of the circulating anolyte is between 1.5 and 2.5.
Preferably, the pH of the circulating anolyte is reduced to a predetermined value and then fed to electrolysis, dechlorination and chlorate decomposition by an anolyte circulating pump on the dilute brine header pipe.
3. The invention also provides an acid adding process related to the chlorate byproduct in the anode chamber of the electrolytic cell in the production of the chlor-alkali, wherein hydrochloric acid is respectively and simultaneously added into the electrolytic cell, the dechlorination unit and the chlorate decomposition unit of the high-purity hydrochloric acid header pipe in the acid adding mode in the electrolytic production process, so that the problem of OH migration in the anode chamber of the electrolytic cell is separately solved-High pH value of dechlorinated light salt water, hydrochloric acid for chlorate decomposition,
combining the acid for decomposing, dechlorinating and partially electrolyzing the original chlorate, intensively adding high-purity hydrochloric acid from a chlorate decomposition place, mixing the high-purity hydrochloric acid with light brine containing byproduct chlorate added from a chlorate decomposition place to realize chlorate decomposition, returning the light brine which is higher than the residual hydrochloric acid to an anolyte circulating tank after the chlorate decomposition is finished, replacing the high-purity hydrochloric acid to reduce the pH value of the circulating anolyte, conveying the light brine to each unit for electrolyzing, dechlorinating and decomposing the chlorate through a light brine main pipe after the pH value of the circulating anolyte is reduced to a specified value, and supplementing the high-purity hydrochloric acid by the electrolytic tank by slightly adjusting the part with insufficient acid;
when the acid in the circulating fresh brine is excessive, the acid adding amount at the chlorate decomposition part is reduced, and the acid adding amount of the electric cell can be reduced to improve the pH value of the fresh brine out of the electric cell, so that the pH value of the fresh brine of the electrolytic circulating system is ensured to be at a specified value.
Compared with the prior art, the invention has the beneficial effects that:
the invention greatly improves the chlorate decomposition speed, the chlorate decomposition rate and Cl2The purity and the chlorate decomposition rate can reach 100 percent once, the chlorate decomposition rate is improved by 35 to 50 percent, the fresh brine participating in the chlorate decomposition is greatly reduced, the chlorate decomposition speed is increased by 3 to 5 minutes and can be finished, the speed is 120 times faster than that of the existing running device, and wet Cl is generated2High purity, unstable gas ClO2No longer exists, eliminates the explosion hidden trouble in the process of decomposing chlorate and is the safest method for decomposing chlorate in electrolytic dilute brine.
② the invention can realize the reverse migration of acid amount used by the electrolytic system and the cathode liquid of the electrolytic cell-Ions and permeated NaOH are in dynamic phase balance, the consumption of 31 percent HCl high-purity hydrochloric acid, caustic soda, heating steam and other substances is reduced to the maximum extent, and the separated pure and wet chlorine is not polluted any more and is directly recycled to a chlorine main pipe;
thirdly, because chlorate in the whole electrolysis process system is decomposed in time and thoroughly at one time, the saturated salt content of refined salt water, the quality of finished caustic soda, the service life of solid caustic soda equipment and the like are all improved;
fourthly, the technology simplifies complex chlorate decomposition facilities and process configuration, and the electrolysis production operation and process indexes are more optimized.
Drawings
In order to more clearly describe the working principle of the device and the method for decomposing chlorate generated by the side reaction of the anode chamber of the electrolytic cell in the production of chlor-alkali and the acid adding process involved in the invention, the following schematic diagram is further illustrated.
FIG. 1 is a flow diagram of a prior art chlorate decomposition process of the present invention;
figure 2 is a flow diagram of the prior art chlorate decomposition process of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Example one
The invention provides an acid adding process related to chlorate as a byproduct in an anode chamber of an electrolytic cell in chlor-alkali production, which combines the acid adding mode in the electrolytic production process, and hydrochloric acid is respectively and simultaneously added into an electrolytic unit, a dechlorination unit and a chlorate decomposition unit of a high-purity hydrochloric acid main pipe, so as to independently solve the problem of OH migration in the anode chamber of the electrolytic cell-High pH value of dechlorinated light salt water, hydrochloric acid for chlorate decomposition,
combining the acid for decomposing, dechlorinating and partially electrolyzing the original chlorate, intensively adding high-purity hydrochloric acid from a chlorate decomposition place, mixing the high-purity hydrochloric acid with light brine containing byproduct chlorate added from a chlorate decomposition place to realize chlorate decomposition, returning the light brine which is higher than the residual hydrochloric acid to an anolyte circulating tank after the chlorate decomposition is finished, replacing the high-purity hydrochloric acid to reduce the pH value of the circulating anolyte, conveying the light brine to each unit for electrolyzing, dechlorinating and decomposing the chlorate through a light brine main pipe after the pH value of the circulating anolyte is reduced to a specified value, and supplementing the high-purity hydrochloric acid by the electrolytic tank by slightly adjusting the part with insufficient acid;
when the acid in the circulating fresh brine is excessive, the acid adding amount at the chlorate decomposition part is reduced, and the acid adding amount of the electric cell can be reduced to improve the pH value of the fresh brine out of the electric cell, so that the pH value of the fresh brine of the electrolytic circulating system is ensured to be at a specified value.
Solution of chlorate decomposition part:
firstly, according to the chlorate content in the dilute brine and the operation condition of the electrolytic cell, a proper amount of dilute brine is branched off. Removing the acid from the position of the dilute brine discharged from the electrolytic bath, and concentrating the direct addition of the acid into the dilute brine during chlorate decomposition, wherein the flow rates of the dilute brine and the hydrochloric acid for decomposing chlorate are 100: adding acid in a ratio of 25-35, and fine adjustment of the over-acid amount of the 31% HCl high-purity hydrochloric acid is determined by the pH value of a light salt water main pipe.
Secondly, calculating the consumed high-purity hydrochloric acid according to the content of the chlorate, if the required high-purity hydrochloric acid is higher, adding acid according to the upper limit of the acid adding amount ratio, and when the added acid is too high to exceed the pH value control index of the dilute brine main pipe, reducing the acid adding amount of the electrolytic tank and improving the pH value of the brine in the tank for control.
③ heating the acid-added dilute brine uniformly mixed, wherein the chlorate starts to decompose mainly by the chemical reaction (2) due to the lower temperature, ClO2Large amount of ClO in fresh brine2When the acid-added dilute brine is boiled by continuing the heating without stabilization, ClO in the generating solution of the formulae (c), (f) and (e) is generated in the environment of the dilute brine with a high excess acid content2Quickly reducing the acid, and existing in gas-liquid mixed high-peracid brackish water. Gas ClO in mixture2And the successive conversion of the formulae (a) and (c) into HClO in solution in the liquid phase will take place2And is continuously reduced to Cl2And HClO, with only Cl present in the final gas phase2、H2O, so far, the complete decomposition of chlorate in the light brine is completed.
Fourthly, gas-liquid separation is carried out, the solution after pyrolysis is cooled to be below 80 ℃, the vaporized water vapor returns to the light brine again, the gas-liquid mixture enters a gas-liquid separator, and pure wet Cl2Enters a chlorine main pipe from the upper part of the gas-liquid separator, and the light salt water of which the reaction finished liquid consumes a certain amount of hydrochloric acid flows into the anolyte from the outlet of the gas-liquid separator to circulateThe ring groove is used for dechlorinating the light salt brine and reducing the PH value of the light salt brine circulated by the electrolytic cell.
Example two
With reference to the attached figure 2, the invention provides a chlorate decomposition device generated by side reaction of an anode chamber of an electrolytic cell in chlor-alkali production, which comprises:
the electrolytic cell is used for producing chlor-alkali, and is connected with an in-cell refined salt water pipeline and an out-cell light salt water pipeline which are connected with the electrolytic cell, and the out-cell light salt water pipeline is connected with a light salt water main pipe through an anolyte circulating cell;
the high-purity hydrochloric acid main pipe is divided into two branch pipes, the electrolysis acid adding branch pipe is led to the electrolysis tank to be led to the refined salt water pipeline, and the second branch pipe is led to the chlorate decomposition tank;
the chlorate decomposing tank is connected with the dilute brine main pipe through the dilute brine branch pipe, and chlorate decomposing finished liquid is divided into two paths after passing through the gas-liquid separator, wherein one path is used for removing chlorine from the dilute brine main pipe, and the other path is returned to the anode liquid circulating tank.
In order to realize the full utilization of energy, a heat exchanger is arranged at the inlet pipeline of the chlorate decomposition tank, a cold medium inlet of the heat exchanger is connected with the anolyte circulating tank and the high-purity hydrochloric acid main pipe, a cold medium outlet corresponding to the heat exchanger is connected with an inlet of the chlorate decomposition tank, a heat medium inlet of the heat exchanger is connected with an outlet of the chlorate decomposition tank, and a heat medium outlet corresponding to the heat exchanger is connected with a gas-liquid separator.
Generally, the chlorate decomposition is carried out at the temperature of more than 90 ℃, in order to reach the chlorate decomposition temperature, a steam interlayer is arranged at the chlorate decomposition tank, and steam is introduced into the steam interlayer to provide a proper temperature for the chlorate decomposition.
And the fresh salt water outlet pipeline enters a fresh salt water header pipe to a dechlorination tower through an anolyte circulating tank.
Flow meters and regulating valves are arranged between the dilute brine branch pipe and the chlorate decomposing tank and between the chlorate decomposing acidification branch pipe and the chlorate decomposing tank, a pH meter is arranged on the dilute brine main pipe, and the opening of the regulating valve is regulated and controlled according to the pH value, so that the proportion regulation of the dilute brine and the hydrochloric acid entering the chlorate decomposing tank and the pH regulation of the dilute brine main pipe are realized.
EXAMPLE III
With reference to fig. 2, the present invention provides a method for decomposing chlorate generated by an anode chamber side reaction in an electrolytic cell in chlor-alkali production, based on the decomposition apparatus of the second embodiment, the method comprises the steps of distributing corresponding weak brine from an anolyte circulation tank to a chlorate decomposition site according to the content of by-product chlorate contained in chlor-alkali production, and intensively adding high-purity hydrochloric acid at the chlorate decomposition site according to high peracid amount to realize chlorate decomposition;
and after the chlorate decomposition is finished, returning the light salt brine with high residual hydrochloric acid to the anolyte circulating tank to replace high-purity hydrochloric acid to reduce the pH value of the circulating anolyte, conveying the circulating anolyte to each unit of electrolysis, dechlorination and chlorate decomposition through a light salt brine header pipe after the pH value of the circulating anolyte is reduced to a specified value, finely adjusting the high-purity hydrochloric acid by using the part with insufficient acid in the electrolytic tank to supplement, and not adding acid any more when the light salt brine is dechlorinated.
After the chlorate is decomposed, wet chlorine is contained in the decomposed liquid except the light salt water with high excess hydrochloric acid, and the decomposed liquid is divided into two paths after passing through a gas-liquid separator: the light salt water with high surplus hydrochloric acid returns to the anode liquid circulating tank, and the wet chlorine gas returns to the chlorine gas main pipe.
After completion of the chlorate decomposition, the decomposition-completed solution is cooled to 80 ℃ or lower.
According to the content of chlorate in the weak brine, the flow rate of the weak brine and the addition amount of the high-purity hydrochloric acid are calculated according to the following ratio of 100: the ratio of 25-35 is adjusted, and can be 100: 25. 100, and (2) a step of: 30. 100, and (2) a step of: 35.
1. the temperature of the chlorate decomposition is controlled to be more than 90 ℃, preferably, the chlorate is decomposed in a boiling state and reacts for 1-1.5min, the decomposition rate of the chlorate can reach more than 93 percent, the reaction time is 1.5-10 min, and the decomposition rate of the chlorate can reach more than 99 percent.
The pH value of the dilute brine main pipe at the outlet of the anolyte circulating tank is controlled to be 1.5-2.5.
The specified value of the pH value of the circulating anolyte is between 1.5 and 2.5.
After the pH value of the circulating anolyte is reduced to a specified value, the anolyte is conveyed to electrolysis, dechlorination and chlorate decomposition through an anolyte circulating pump on a dilute brine header pipe.
When the chlorate decomposing device is operated, the chlorate decomposing device is divided into three cases:
1. in the first case, the amount of chlorate decomposed is balanced with the amount of electric tank by-products.
a. 31% HCl high-purity hydrochloric acid sent from outside the battery limits enters a 31% high-purity hydrochloric acid header pipe in the battery limits, and the header pipe is divided into two branches in an electrolysis system, wherein one branch of the electrolysis system is used for adding acid into the electrolysis tank, and the other branch is used for removing chlorate for decomposition;
b. and (3) separating a part of decomposed chlorate from the light brine in the dechlorinating tower, electrolyzing to obtain 50kg/h byproduct chlorate when 10g/L sodium chlorate exists in the light brine, and separating 5m3/h light brine according to the weight ratio of 100:30 adding 31 percent high-purity hydrochloric acid 1.5m3/h；
c. The chlorate solution is fully mixed in a chlorate decomposition tank, the chlorate decomposition solution which is uniformly mixed is heated and decomposed by the generated steam, the reaction solution gradually reaches a boiling state, and the intermediate product ClO is quickly decomposed and decomposed by the chlorate2、ClO2 -、ClO3 -Reduction of HClO to Cl2、Cl-、H2O exists in the gas-liquid mixed light salt water, a large amount of gas-state water vapor is changed into liquid state again and returns to the light salt water after being cooled to the temperature below 80 ℃, the outlet flow is adjusted, the reaction time is controlled (3 min-5 min), and the decomposition completion liquid NaClO is analyzed3If the content is 0, the product is qualified, if the product is not qualified, the discharge flow rate is controlled, and the reaction time is prolonged until chlorate is not contained;
d. gas-liquid separation, heat exchanging the high-temperature decomposition liquid with the acid-added dilute salt water from the chlorate decomposition tank, cooling to below 80 ℃, gas-liquid separation, and purifying wet Cl2The chlorine gas enters a chlorine gas header pipe, the light brine containing a certain amount of excess hydrochloric acid is discharged to a light brine outlet header pipe of the tank and then enters an anolyte circulating tank for dechlorinating the light brine and reducing the pH value of the circulating light brine, and the wet chlorine gas does not contain ClO2The product is qualified;
e. adding excessive hydrochloric acid into the decomposition finished solution, adding the solution into a circulating light salt water tank to be mixed with other light salt water for dechlorination, detecting the pH value of the solution, slightly adjusting the acid adding amount if the pH value deviates from 1.5-2.5, and increasing or reducing the pH value of the solution out of the tank if the acid adding amount of the solution into the tank is adjusted to the standard;
f. the acid adding amount of the electrolytic cell can be adjusted to a large extent, 31 percent HCl high-purity hydrochloric acid can not be added, and the acid adding proportion can be ensured to be in a specified range during the chlorate decomposition.
2. The second case rapidly reduces the accumulation of chlorate in the electrolysis system. Due to abnormal operation of the cell or lack of chlorate decomposition over a long period of time, the amount of chlorate accumulated in the electrolysis system is relatively high and rapid reduction of chlorate is required.
a. 31% HCl high-purity hydrochloric acid sent from outside the battery limits enters a 31% high-purity hydrochloric acid header pipe in the battery limits, two branches are arranged in an electrolysis system, wherein one branch is removed from an electric tank and added with acid, and the other branch is removed from chlorate for decomposition;
b. separating out a part of decomposed chlorate from the light brine in the dechlorinating tower, electrolyzing to obtain 50kg/h byproduct chlorate when 30g/L of sodium chlorate in the light brine needs to be reduced to 5g/L, and separating out 7.5m3Per hour of light brine, 100:30 adding 31 percent high-purity hydrochloric acid 2.25m3The method has the advantages that the method can reduce 25kg/h of accumulated sodium chlorate in an electrolysis system besides 50kg/h of chlorate which is a byproduct of electrolysis, and can decompose more, and the amount of circulating light salt brine in the electrolysis system is not large, so that the process index can be quickly reached;
c. heating the uniformly mixed chlorate decomposition liquid to generate steam, heating and decomposing, gradually boiling the reaction liquid, and quickly decomposing chlorate to decompose intermediate product ClO2、ClO2 -、ClO3 -Rapid reduction of HClO to Cl in a short time2、Cl-、H2O exists in the gas-liquid mixed light salt water, a large amount of gas-state water vapor is changed into liquid state again and returns to the light salt water after being cooled to the temperature below 80 ℃, the outlet flow is adjusted, the reaction time is controlled (3 min-5 min), and the decomposition completion liquid NaClO is analyzed3If the content is 0, the product is qualified, if the product is not qualified, the discharge flow rate is controlled, and the reaction time is prolonged until chlorate is not contained;
d. gas-liquid separation, heat exchanging between high-temp. decomposition liquid and the diluted salt water from chlorate decomposing tank, cooling to below 80 deg.C, gas-liquid separation, and purifying wet Cl2Entering a chlorine main pipe, and containing a certain excess amount of dilute brine of hydrochloric acidDischarging to a light salt brine main pipe of the discharge tank, and then feeding into an anolyte circulating tank for dechlorinating the light salt brine and reducing the pH value of the circulating light salt brine, wherein the wet chlorine gas does not contain ClO2The product is qualified;
e. adding excessive hydrochloric acid into the decomposition finished solution, adding the solution into a circulating light salt water tank to be mixed with other light salt water for dechlorination, detecting the pH value of the solution, slightly adjusting the acid adding amount if the pH value deviates from 1.5-2.5, and increasing or reducing the pH value of the solution out of the tank if the acid adding amount of the solution into the tank is adjusted to the standard;
f. the adjustable range of the acid adding amount of the electrolytic cell is larger, and high-purity hydrochloric acid is not required, so that the acid adding proportion during the chlorate decomposition is ensured to be in a specified range;
g. NaClO in weak brine of electrolysis system3And recovering to the process operation index of the specific embodiment I after the requirement is met by not more than 5 g/L.
3. The content of chlorate in dilute brine in an electrolysis system is low, and when an electrolysis byproduct chlorate decomposition device is not required to be started, the content of chlorate in dilute brine in the electrolysis system can be more than 100: adding 31% HCl high-purity hydrochloric acid into 25-35 shunt fresh brine, wherein the HCl content of the fresh brine after acid addition is no more than 10% at most. And adjusting the acid adding amount, keeping the pH value of the dilute brine in the dechlorinating tower to be 1.5-2.5, normally operating the whole electrolysis system, and operating the chlorate decomposition system according to the specific embodiment one after the electrolysis byproduct chlorate reaches a certain accumulation amount.
While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all alterations and modifications as fall within the scope of the application.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
In addition to the technical features described in the specification, the technology is known to those skilled in the art.

Claims (1)

1. A method for decomposing by-product chlorate in anode chamber of electrolyzer in chlor-alkali production is characterized by that according to the content of by-product chlorate contained in chlor-alkali production said method can separate out correspondent light salt water from anolyte circulating tank to chlorate decomposition place, and at the chlorate decomposition place high-purity hydrochloric acid can be added according to high acid-excess quantity,
according to the content of chlorate in the weak brine, the flow rate of the weak brine and the addition amount of the high-purity hydrochloric acid are calculated according to the following ratio of 100: 25-35 in proportion
Adjusting;
controlling the chlorate decomposition temperature to decompose chlorate in a boiling state;
after the chlorate decomposition is finished, wet chlorine is contained in the decomposition finished liquid besides the light salt water with high excess hydrochloric acid, and the decomposition finished liquid is divided into two paths after passing through a gas-liquid separator: returning the dilute brine with high surplus hydrochloric acid to the anode liquid circulating tank, and returning wet chlorine to the chlorine header pipe; and returning the light salt brine with high excess hydrochloric acid into the anolyte circulating tank to replace high-purity hydrochloric acid to reduce the pH value of the circulating anolyte, conveying the circulating anolyte to each unit of electrolysis, dechlorination and chlorate decomposition through a light salt brine header pipe after the pH value of the circulating anolyte is reduced to a specified value, finely adjusting the high-purity hydrochloric acid by using an acid-deficient part for supplementing the electrolytic tank, and not adding acid for dechlorination of the light salt brine.
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