CN114409157B - Recycling method for preparing chlor-alkali by waste salt water electrolysis - Google Patents
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Abstract
The invention discloses a method for preparing chlor-alkali by using waste salt water electrolysis, which comprises the following steps: s1, evaporating and concentrating the organic wastewater containing salt, and crystallizing the organic wastewater in a fractional manner to obtain crystalline sodium sulfate; s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater to obtain salt-containing wastewater; s3, filtering mechanical impurities in the salt-containing wastewater; s4, refining the salt-containing wastewater after the filtering treatment for the first time by using an inorganic membrane filter; s5, refining the salt-containing wastewater subjected to the first refining for the second time by utilizing chelate resin; s6, electrolyzing the second refined salt-containing wastewater by using a zero-polar-distance ionic membrane electrolytic tank to obtain alkali liquor, hydrogen and chlorine. According to the invention, the organic wastewater containing salt of diphenylmethane diisocyanate (MDI) is converted into the raw material of chlor-alkali industry through recycling treatment, so that the recycling of salt resources in the wastewater is realized, and the problem of emission pollution of the organic wastewater containing high salt is solved.
Description
Technical Field
The invention relates to the field of high-salt-content wastewater treatment, in particular to a recycling method for preparing chlor-alkali by using waste salt water electrolysis.
Background
With the rapid development of petrochemical industry and chemical industry, china gradually forms more perfect petrochemical industry, natural gas chemical industry, coal chemical industry, salt chemical industry and biochemical industry production systems. However, the production of a large amount of petrochemical and chemical products is accompanied by the generation of a large amount of chemical wastewater, and the chemical wastewater has very complex components and contains a large amount of organic matters, inorganic salts, heavy metals and the like, wherein the high-concentration salt-containing organic wastewater is particularly prominent.
At present, for the treatment of high-concentration salt-containing organic wastewater, harmless measures of dilution discharge or evaporation concentration-incineration are mainly adopted, so that the waste of salt resources is caused. Due to the lack of technical, economic feasibility and reliability, most of the wastewater is still discharged in a dilution way, especially the discharge of saline wastewater, which leads to mineralization of fresh water resources and alkalization of soil.
The organic wastewater containing salt of diphenylmethane diisocyanate (MDI) is taken as one of the high-concentration organic wastewater containing salt, has large discharge amount, serious environmental hazard and very difficult resource utilization, and is a difficult problem to be solved in the technical field of domestic and foreign green resources at present.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention aims to provide a recycling method for preparing chlor-alkali by using waste salt water electrolysis, which converts organic wastewater containing salt of diphenylmethane diisocyanate (MDI) into raw materials of chlor-alkali industry by recycling treatment, realizes recycling of salt resources in the wastewater, and solves the problem of discharge pollution of high-salt organic wastewater.
The aim of the invention is realized by the following technical scheme:
a recycling method for preparing chlor-alkali by using waste salt water to hydrolyze comprises the following steps:
s1, evaporating and concentrating the organic wastewater containing salt, and crystallizing the organic wastewater in a fractional manner to obtain crystalline sodium sulfate;
s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater to obtain salt-containing wastewater;
s3, filtering mechanical impurities in the salt-containing wastewater;
s4, refining the salt-containing wastewater after the filtering treatment for the first time by using an inorganic membrane filter;
s5, refining the salt-containing wastewater subjected to the first refining for the second time by utilizing chelate resin;
s6, electrolyzing the second refined salt-containing wastewater by using a zero-polar-distance ionic membrane electrolytic tank to obtain alkali liquor, hydrogen and chlorine.
Further, evaporating and concentrating the salt-containing organic wastewater in the step S1, and removing sodium sulfate in the salt-containing organic wastewater by fractional crystallization comprises the following steps:
carrying out pre-concentration treatment on SN1 and the organic wastewater containing salt;
SN2, carrying out water evaporation treatment on the pre-concentrated salt-containing organic wastewater to obtain sodium chloride salt crystals and concentrated solution, wherein the concentration of sodium sulfate in the concentrated solution reaches a saturated state;
SN3, cooling the concentrated solution, evaporating water to obtain sodium chloride salt crystals and a re-concentrated solution; part of the re-concentrated solution enters the step S2 for treatment;
SN4, carrying out heating water evaporation treatment on the rest re-concentrated solution to obtain crystalline sodium sulfate and residual solution, and treating the residual solution in a step SN 3.
Further, in the step SN1, the salt-containing organic wastewater is preheated and then subjected to pre-concentration treatment; and (3) saturated sodium chloride in the pre-concentrated salt-containing organic wastewater.
Further, clear liquid generated after sodium chloride salt crystals obtained in the step SN2 are treated by a salt cyclone separator and a centrifuge sequentially is mixed with salt-containing organic wastewater to dilute the clear liquid to obtain countercurrent brine, and sodium chloride at salt legs of the crystals in the step SN3 is washed;
the concentrated solution is precipitated and then enters into step SN3 for treatment.
Further, the countercurrent brine part is washed with sodium chloride at the salt legs of the crystallization in step SN3, and the remaining part is mixed with the sodium chloride crystals obtained in step SN 2.
Further, in step SN3, the concentrated solution is subjected to a temperature-reducing and water-evaporating treatment, and the water-evaporating treatment is performed by using a flash evaporation effect and a mechanical vapor recompression system.
Further, the pre-concentration process of step SN1, the evaporation process of moisture in SN2 and SN4 all utilize a mechanical vapor recompression system.
Further, in the step S2, the organic matters in the concentrated salt-containing organic wastewater are oxidized and decomposed, and the method comprises the following steps:
adding 3-6% sodium hypochlorite to make the concentration of sodium hypochlorite in the reaction tank be 0.8-1.2%;
adding 10% -15% sodium carbonate with the excess of 0.5-1.0 g/L;
adding 28% -35% concentration sodium hydroxide with the excess of 0.3-0.5 g/L.
Further, the filtering treatment in the step S3 is to adopt a filter to filter and separate out mechanical impurities with the particle size of more than or equal to 1 mm;
further, in the step S4, the first refining is filtered by adopting a cross-flow filtering mode of three-stage series inorganic membrane filtering units, and after the salt-containing wastewater is collected by filtering through each inorganic membrane filtering unit, sodium nitrite is added to remove free chlorine.
Due to the adoption of the technical scheme, the invention has the following advantages:
sodium sulfate and sodium chloride are obtained while the salt-containing organic wastewater is treated, so that the waste salt resource utilization of the diphenylmethane diisocyanate (MDI) salt-containing organic wastewater is realized; the investment of huge construction membrane method denitration is avoided; the salt and nitrate co-production is realized by fractional crystallization, the existing membrane method denitration device greatly influenced by TOC is replaced, and the stable operation of the denitration device is promoted.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
The drawings of the present invention are described as follows:
the flow chart of the method for preparing chlor-alkali by electrolysis of waste brine in the embodiment of fig. 1 is shown in the specification.
Detailed Description
The invention is further described below with reference to the drawings and examples.
Examples:
as shown in figure 1, the method for preparing chlor-alkali by using the waste salt water electrolysis comprises the following steps:
firstly, evaporating and concentrating the organic wastewater containing salt, and crystallizing the organic wastewater in a fractional manner to obtain crystalline sodium sulfate; the method specifically comprises the following steps:
SN1, preheating the salt-containing organic wastewater, injecting the salt-containing organic wastewater into a first falling film evaporator after preheating, and heating by utilizing recompression steam of a first mechanical steam recompression (MVR unit) system. After heating, the evaporation process starts, so that the concentration of the organic wastewater containing salt is increased, and the water is evaporated and concentrated. The concentration of sodium chloride in the pre-concentrated salt-containing organic wastewater is close to or reaches a saturated state.
SN2, injecting the pre-concentrated salt-containing organic wastewater into a second falling film evaporator, and heating by using recompression steam of a second mechanical steam recompression (MVR) unit system. Evaporating the water in the pre-concentrated salt-containing organic wastewater, crystallizing and gradually depositing sodium chloride salt crystals, enabling the concentration of sodium sulfate in the rest concentrated solution to reach a saturated state, and carrying out precipitation to separate sodium chloride salt precipitates of crystals which are not attached;
the crystalline sodium chloride crystal salt is sequentially processed by a salt hydrocyclone and a centrifuge to obtain wet salt, and clear liquid obtained by the salt hydrocyclone and the centrifuge is mixed with a small amount of salt-containing organic wastewater to obtain countercurrent brine.
The countercurrent brine partially washes sodium chloride deposited at the crystalline salt legs of the step, so that the temperature of sodium chloride crystals can be reduced, the centrifuge can be protected during centrifuge processing, and the size of sodium chloride crystals can be simultaneously carried out, so that the uniform salt crystal size suitable for pusher centrifuge processing is obtained. The remaining portion of the counter-current brine flows into the crystalline sodium chloride salt.
If the counter-current brine were not used to flush the crystallized sodium chloride salt, a significant amount of NaClO3 would leave the second falling film evaporator and enter the salt slurry tank and filtrate storage tank, contaminating the final sodium chloride salt and negatively affecting the sodium chloride crystallization process. On the other hand, too high a concentration of NaClO3 in the sodium chloride salt may cause serious corrosion of the apparatus and significantly increase the boiling point, resulting in a decrease in the evaporation capacity.
SN3, the concentrated solution was injected into a flash evaporator under vacuum, and the solubility of sodium sulfate was decreased with an increase in temperature over a certain temperature range, while the solubility of sodium chloride was increased with an increase in temperature (standard dissolution property). By adopting the principle, sodium chloride can be crystallized and separated out at a lower temperature, and sodium sulfate can be crystallized and separated out at a higher temperature.
Therefore, the temperature of the concentrated solution is controlled so that sodium chloride is precipitated and sodium sulfate is dissolved in the concentrated solution, specifically, the temperature is controlled to be about 50 ℃.
At the same time of utilizing flash evaporation effect, the concentrated solution is heated by utilizing a hot vapor recompression (MVR) system (the temperature is kept in a range that sodium chloride is separated out and sodium sulfate is dissolved), so that the water in the concentrated solution is evaporated, and finally, the crystallized sodium chloride and the reconcentrate are obtained.
In this step, the counter-current brine washes out sodium chloride deposited at the crystalline salt legs, functioning as in step SN 2.
The resulting re-concentrate after partial evaporation is discharged as a final effluent from the system, which contains non-crystallised compounds such as sodium chlorate, iodine, TOC etc. The discharge of iodine can reduce the influence on the ionic membrane in the subsequent electrolysis process, and is beneficial to stabilizing the operation efficiency of the ionic membrane. The discharged sodium chlorate also directly eliminates the running costs of current chlorate plants. The discharged TOC material may reduce the operating costs of the operation of the TOC removal device.
SN4, the remaining re-concentrate enters a third falling film evaporator and is heated using the re-compressed vapor of a third mechanical vapor re-compression (MVR unit). After the water is evaporated, sodium sulfate starts to crystallize, and the rest liquid is precipitated under the action of the pressure difference of the flash evaporator and then enters the flash evaporator again for treatment.
And (3) heating up and evaporating water to obtain crystalline sodium sulfate and residual liquid, and processing the residual liquid in the step SN 3.
In the first step, the steam of the MVR system is fully utilized, so that the energy consumption is effectively reduced.
Secondly, adding 3-6% sodium hypochlorite into the discharged re-concentrated solution serving as the final discharged solution in the step SN3, so that the concentration of the sodium hypochlorite in the reaction tank is 0.8-1.2%; adding 10% -15% sodium carbonate with the excess of 0.5-1.0 g/L; adding 28% -35% concentration sodium hydroxide with the excess of 0.3-0.5 g/L for treatment.
Adding sodium carbonate solution into the re-concentrated solution to react with Ca < 2+ > in the re-concentrated solution to generate insoluble calcium carbonate precipitate; adding sodium hydroxide solution into the re-concentrated solution to react with Mg2+ in the re-concentrated solution to generate insoluble Mg (OH) 2 precipitate; and (3) oxidizing and decomposing bacteria, algae and other organic matters brought by the reconcentration liquid by free chlorine in the sodium hypochlorite to finally obtain the salt-containing wastewater.
And thirdly, passing the salt-containing wastewater through a coarse filter with the aperture of 1.0mm to remove mechanical impurities.
And fourthly, sequentially passing the salt-containing wastewater for filtering mechanical impurities through three stages of inorganic membrane filtering units connected in series. The inorganic membrane filter adopts a ceramic membrane tube as a filter element, and filters and removes suspended particles in a cross-flow filtering mode, so that the contents of SS, ca2+ and Mg2+ in the brine are ensured to meet the requirements, and finally refined filtered brine is obtained.
And fifthly, pressurizing the refined filtered brine, heating the pressurized refined filtered brine to 60+/-5 ℃ through a heat exchanger, conveying the pressurized refined filtered brine to a chelating resin tower, adsorbing Ca2+, mg2+ and other heavy metal ions in the refined filtered brine, and capturing broken resin through a resin catcher to obtain the refined brine.
And sixthly, injecting refined brine into the zero-pole-distance ion membrane electrolytic tank for electrolysis, producing qualified chlorine gas at the anode of the electrolytic tank, and producing qualified alkali liquor and hydrogen gas at the cathode.
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.
Claims (1)
1. The method for preparing chlor-alkali by using the waste salt water to hydrolyze is characterized by comprising the following steps:
s1, evaporating and concentrating the organic wastewater containing salt, and crystallizing the organic wastewater in a fractional manner to obtain crystalline sodium sulfate; the method specifically comprises the following steps: carrying out pre-concentration treatment on SN1 and the organic wastewater containing salt; SN2, carrying out water evaporation treatment on the pre-concentrated salt-containing organic wastewater to obtain sodium chloride salt crystals and concentrated solution, wherein the concentration of sodium sulfate in the concentrated solution reaches a saturated state; SN3, cooling the concentrated solution, evaporating water to obtain sodium chloride salt crystals and a re-concentrated solution; part of the re-concentrated solution enters the step S2 for treatment; SN4, carrying out heating water evaporation treatment on the rest re-concentrated solution to obtain crystalline sodium sulfate and residual solution, and treating the residual solution in a step SN 3;
s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater, and specifically comprising the following steps of: adding 3-6% sodium hypochlorite to make the concentration of sodium hypochlorite in the reaction tank be 0.8-1.2%; adding 10% -15% sodium carbonate with the excess of 0.5-1.0 g/L; adding 28% -35% sodium hydroxide with the excess of 0.3-0.5 g/L to obtain salt-containing wastewater;
s3, filtering mechanical impurities in the salt-containing wastewater;
s4, refining the salt-containing wastewater after the filtering treatment for the first time by using an inorganic membrane filter;
s5, refining the salt-containing wastewater subjected to the first refining for the second time by utilizing chelate resin;
s6, electrolyzing the second refined salt-containing wastewater by using a zero-polar-distance ionic membrane electrolytic tank to obtain alkali liquor, hydrogen and chlorine;
in the step SN1, the salt-containing organic wastewater is preheated and then subjected to pre-concentration treatment; saturated sodium chloride in the pre-concentrated salt-containing organic wastewater;
clear liquid generated after sodium chloride salt crystals obtained in the step SN2 are sequentially processed by a salt cyclone separator and a centrifuge is mixed and diluted with salt-containing organic wastewater to obtain countercurrent brine, and sodium chloride at salt legs of the crystals in the step SN3 is washed;
precipitating the concentrated solution, and then processing in a step SN 3;
the countercurrent brine part washes sodium chloride at salt legs of the crystals in the step SN3, and the rest part is mixed with sodium chloride crystals obtained in the step SN 2;
in the step SN3, cooling and water evaporation treatment is carried out on the concentrated solution, and the water evaporation treatment is carried out by utilizing a flash evaporation effect and a mechanical vapor recompression system;
the pre-concentration treatment of the step SN1, the water evaporation treatment in the SN2 and the SN4 all use a mechanical vapor recompression system;
the filtering treatment in the step S3 is to adopt a filter to filter and separate out mechanical impurities with the particle size of more than or equal to 1 mm;
in the step S4, the first refining adopts a cross-flow filtering mode of three-stage series inorganic membrane filtering units, each inorganic membrane filtering unit filters to obtain salt-containing wastewater, and sodium nitrite is added to remove free chlorine after the salt-containing wastewater is collected.
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| US20210101815A1 (en) * | 2018-02-14 | 2021-04-08 | Covestro Intellectual Property Gmbh & Co. Kg | Process for the work-up and reuse of salt-containing process water |
| CN109293089A (en) * | 2018-10-29 | 2019-02-01 | 甘肃银光聚银化工有限公司 | A kind of processing method of TDI production neutral and alkali brine waste |
| CN109292797A (en) * | 2018-11-02 | 2019-02-01 | 江苏中圣高科技产业有限公司 | A kind of brine waste sub-prime recovery method |
| CN111661886A (en) * | 2019-03-07 | 2020-09-15 | 广州市迈源科技有限公司 | MVR evaporation salt separation system |
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