Method for removing sulfate ions in iron ethylenediaminetetraacetate complexing wet-process denitration liquid by solvent elution

Abstract

The invention discloses a method for removing sulfate ions in iron ethylenediaminetetraacetate complexing wet denitration liquid by solvent elution, and belongs to the field of chemical environmental protection. The method for removing the sulfate ions in the ferric ethylenediaminetetraacetate complexing wet-process denitration liquid by solvent elution comprises the following steps: regenerating the ferric ethylenediaminetetraacetate complexing circulating denitration liquid to be treated, then introducing a solvent, standing and crystallizing, and filtering, thereby obtaining the sulfate ions in the ferric ethylenediaminetetraacetate complexing wet-process denitration liquid. After crystallization is finished, filtering and distilling to obtain ferric ethylenediaminetetraacetate complexing wet-process denitration liquid without sulfate ions; adjusting the pH value of the obtained denitration liquid, and introducing the denitration liquid into a denitration process for circulating denitration; the solvent is any one of ethanol, methanol and phenol. The method can effectively solve the problem that the denitration capacity of the denitration liquid is reduced due to sulfate accumulation of the circulating denitration liquid, the process is simple and easy to implement, guarantee is provided for cyclic utilization of the complexing denitration liquid, and good economic and environment-friendly benefits can be obtained.

Description

Technical Field

[0001] The invention belongs to the field of chemical environmental protection, relates to a method for removing sulfate in the cyclic regeneration process of a divalent iron chelate complex denitration liquid in a wet denitration technology, and specifically relates to a method for removing sulfate ions in an ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution. Background Art

[0002] At present, the most widely used technologies in the field of denitrification are medium and low temperature flue gas denitrification SCR technology and high temperature flue gas denitrification SNCR technology. However, the low temperature flue gas generated by some kiln terminals cannot meet the basic requirements of SCR technology (flue gas temperature is lower than 180℃). In order to meet the requirements, the flue gas is often supplemented with heat, resulting in high denitrification costs. Among the wet denitrification technologies, the divalent iron chelate wet denitrification technology has been widely studied for its advantages such as fast NO absorption rate, large capacity and simultaneous desulfurization.

[0003] The ethylenediaminetetraacetic acid iron complex wet denitrification technology has the advantages of efficiently removing nitrogen oxides from flue gas, achieving simultaneous desulfurization, good stability, being suitable for various types of flue gas treatment, and low operating and maintenance costs. However, as denitrification proceeds, the denitrification liquid needs to be recycled and regenerated. During multiple cycles of regeneration, the accumulation of sulfate will lead to a decrease in the efficiency of the denitrification liquid.

[0004] Dissolution crystallization is an important chemical separation technology, and its principle is based on the fact that the solubility of a solute in a solvent changes with the composition of the solvent. Specifically, dissolution crystallization is a process in which one or more solvents that are miscible with the solvent but have low or poor solubility for the solute (called dissolution agents) are added to the solution to change the solubility of the original solvent for the solute, so that the solute gradually becomes supersaturated in the solution and eventually crystals are precipitated. This promotes the aggregation of solute molecules or ions to form crystal nuclei, which further grow into crystals. Dissolution crystallization technology has many advantages, such as simple operation, low equipment investment, and easy implementation of continuous production.

[0005] CN112079366A discloses a method for separating and recovering sodium nitrate and sodium sulfate from a low-temperature flue gas oxidation denitration absorption liquid, the method comprising the following steps: adding a salting-out agent to the low-temperature flue gas oxidation denitration absorption liquid, stirring to drive away the gas in the solution, and then standing, sodium sulfate crystals gradually precipitate at the bottom of the solution, and solid-liquid separation to obtain sodium sulfate crystals and sodium nitrate solution; the salting-out agent is methanol and / or ethanol, and the amount of the salting-out agent added accounts for 40-60% of the volume of the denitration absorption liquid; the sodium nitrate solution is heated, concentrated, and cooled to room temperature to obtain sodium nitrate crystals. Although the method can separate the denitration absorption liquid by crystallization to obtain sodium sulfate and sodium nitrate recovery, it no longer obtains a recyclable denitration liquid, the method cannot achieve the recycling of the denitration absorption liquid, and cannot solve the problem of reduced efficiency of the denitration liquid caused by the accumulation of sulfate during the recycling process of the denitration liquid. Summary of the invention

[0006] The technical problem to be solved by the present invention is the problem that the denitrification capacity of the denitrification liquid is reduced due to the accumulation of sulfate in the denitrification cycle regeneration process of the denitrification liquid.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] The method of removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution is as follows: the ethylenediaminetetraacetic acid iron complex circulating denitration liquid to be treated is regenerated, then a solvent is introduced and allowed to stand for crystallization, and after the crystallization is completed, the ethylenediaminetetraacetic acid iron complex wet denitration liquid with sulfate ions removed is obtained by filtering and distilling.

[0009] In the above method, the obtained denitrification liquid can be introduced into the denitrification process for cyclic denitrification after adjusting the pH.

[0010] In the above method, the solvent is any one of ethanol, methanol and phenol.

[0011] Furthermore, the solvent is anhydrous ethanol.

[0012] The above-mentioned method of removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution specifically comprises the following steps:

[0013] A. Filter the ferric ethylenediaminetetraacetic acid complex circulating denitrification liquid to be treated, then add sodium sulfite, adjust the pH value, and stir and regenerate under heating conditions;

[0014] B. After the regenerated circulating denitrification liquid is cooled, anhydrous ethanol is introduced at a volume ratio of 1:1, and after sufficient stirring, it is allowed to stand for crystallization for 30 minutes;

[0015] C. After the crystallization is completed, the sodium sulfate crystal powder and the filtrate are obtained by filtration;

[0016] D. The filtrate is distilled to obtain ethanol and ethylenediaminetetraacetic acid iron complex wet denitration liquid from which sulfate ions have been removed. After adjusting the pH of the obtained denitration liquid, it is passed into the denitration process for cyclic denitration.

[0017] Furthermore, in step A of the above method, the amount of sodium sulfite added is 5 to 10 g / L.

[0018] Furthermore, in step A of the above method, the pH is adjusted to 7.0-9.0.

[0019] Furthermore, in step A of the above method, the heating temperature is controlled to be 85-100°C.

[0020] Furthermore, in step B of the above method, the regenerated circulating denitrification liquid is cooled to 20-30° C. by circulating cooling water.

[0021] Furthermore, in step B of the above method, stirring is carried out at a rotation speed of 400 r / min for 10 min.

[0022] Furthermore, in step D of the above method, the distillation temperature is 77-79°C.

[0023] Furthermore, in step D of the above method, the pH of the obtained denitrification liquid is adjusted to 7.0-7.5.

[0024] The beneficial effects of the present invention are as follows: the present invention introduces an organic solvent (ethanol, etc.) as a dissolving agent, and removes sulfate radicals in the denitrification liquid by controlling the amount of organic solvent added (the volume ratio of the organic solvent to the denitrification liquid to be treated). After filtering and separating the precipitated sodium sulfate, a simple distillation method can be used to separate the denitrification liquid from ethanol, and the added dissolving agent ethanol can be recycled, and no new wastewater is generated while removing sulfate radicals, which is economical, environmentally friendly, and has high removal efficiency.

[0025] The present invention provides a method for removing sulfate from ferrous ethylenediaminetetraacetic acid complex denitrification liquid, which can effectively solve the problem of reduced denitrification capacity of denitrification liquid due to sulfate accumulation in circulating denitrification liquid. The process of the present invention is simple and easy to implement, provides a guarantee for the recycling of complex denitrification liquid, can achieve good economic and environmental benefits, and is of great significance to the promotion of engineering application of divalent iron chelate wet denitrification technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process flow of Na2SO4 dissolution, crystallization and separation of circulating denitrification liquid in the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention can be specifically implemented in the following manner.

[0028] The method of removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution, that is, circulating denitration liquid Na2SO4 dissolution crystallization separation process, the flow diagram is as follows Figure 1 As shown, the specific steps include the following steps.

[0029] (1) After filtering the ethylenediaminetetraacetic acid iron complex circulating denitrification liquid to be regenerated, sodium sulfite (5-10 g / L) is added while controlling the pH value, and then stirring and regenerating under heating conditions of 85-100°C.

[0030] The purpose of adding sodium sulfite is to reduce the oxidized ferrous ions in the denitrification liquid and to reduce the nitroso acylates produced by the denitrification liquid gas absorption with the assistance of heating. At the same time, the sulfate ions produced after the reduction need to be further removed after reaching a certain concentration.

[0031] The reason for controlling pH is that the optimal pH range for the main active ingredient of denitrification liquid, Fe(Ⅱ)EDTA, is between 7.0 and 9.0. Within this range, divalent iron can effectively form a stable complex with the reduced ferrous ions. Especially when the pH is 7.0, the stability constant (K) of Fe(Ⅱ)EDTA is very high, reaching the order of 10^15. As the pH value decreases or increases, the stability constant decreases accordingly.

[0032] (2) After the circulating denitrification liquid is heated and regenerated, its temperature is reduced to 20-30°C by circulating cooling water, and then anhydrous ethanol is introduced at a volume ratio of 1:1, stirred at a speed of 400r / min for 10 minutes, and then allowed to stand for crystallization for 30 minutes. Among them, according to the stability of the complex of different complexing agents of the taken ferrous ion with temperature changes, the temperature range can be independently adjusted, and the selection of the solvent can be changed according to subjective opinions. For example, methanol, phenol, etc. can replace anhydrous ethanol, and the effect is approximately the same.

[0033] The reason for controlling the temperature is that temperature has a certain influence on the stability of Fe(Ⅱ)EDTA. Generally speaking, at lower temperatures, the stability of Fe(Ⅱ)EDTA is higher. As the temperature increases, the stability of the complex decreases, because high temperature may promote the oxidation of Fe(Ⅱ) and the decomposition of the complex, resulting in an increase in the free state, resulting in a decrease in the effective component content of the denitrification liquid and a small amount of ferrous iron may be precipitated as ferrous sulfate crystals.

[0034] The ethanol dissolution and sodium sulfate removal process is set up after the regeneration of the denitrification liquid because: the sodium sulfite in the regeneration process reduces iron ions and nitroso acylates to produce sulfate ions. The concentration of sulfate ions increases with the cumulative number of regenerations, and the pH of the regenerated denitrification liquid is adjusted to 7.0 to 7.5. The ferrous ions in the denitrification liquid can be fully complexed and are not prone to crystallization. While removing sulfate, the effective denitrification components are better preserved.

[0035] (3) After the solution is allowed to stand for precipitation, the denitrification liquid is filtered by suction filtration. After filtration, the sodium sulfate crystal powder crystallized out is collected, dried in a drying oven, and then weighed and sent for inspection to calculate the purity of the sodium sulfate.

[0036] Preferably, the suction filtration uses the pressure difference caused by vacuum to achieve precise and rapid filtration of the solution and solid-liquid separation. The filter membrane with suitable material and pore size is selected and installed on the filter head and sealed. After the filtration is completed, the suction bottle pipe is first removed to prevent water from being sucked back in the water tank, and then the separation and distillation operations are performed.

[0037] (4) The mixed solution of the filtered denitrified liquid and ethanol is passed into a distillation device and distilled at 77-79° C. The ethanol obtained after the distillation can be recycled. After the pH of the denitrified liquid is adjusted to 7.0-7.5, it can be passed into the denitrification process for cyclic denitrification.

[0038] Preferably, the filtrate obtained by suction filtration is poured into a distillation flask, zeolite is added to prevent violent boiling, and after the distillation device is installed, condensation water is turned on, the distillation flask is heated to evaporate ethanol, and the distillate is collected through a condenser. It is important to control the heating temperature and the collection temperature range to 77-79°C.

[0039] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0040] Example

[0041] The present invention provides three groups of Examples 1 to 3 for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid using the method of the present invention. The specific test process is as follows:

[0042] (1) First, the denitrification liquid to be regenerated is filtered to remove the suspended matter therein, and sodium sulfite is added to the obtained filtrate to control the concentration to 6 g / L and the pH value to 7.0, and then stirred and regenerated at 92°C for 20 minutes;

[0043] Detection of sulfate ion content in the denitrification liquid after regeneration:

[0044] The content of sulfate in the denitration liquid after regeneration in Example 1 is 60 g / L;

[0045] Example 2 The content of sulfate in the denitrification liquid after regeneration is 80 g / L;

[0046] Example 3 The content of sulfate in the denitrification liquid after regeneration is 60 g / L.

[0047] (2) After the circulating denitrification liquid is heated and regenerated, its temperature is lowered to 20°C, and then anhydrous ethanol is added as a dissolving agent at a volume ratio of 1:1 between the denitrification liquid and ethanol for dissolution and crystallization. The mixture is stirred at a speed of 400 r / min for 10 min, and then allowed to stand for 30 min for crystallization.

[0048] (3) The above solution is filtered through a suction filtration device, and the obtained sodium sulfate powder sample is dried in a drying oven at 120° C. for 48 hours, and the filtrate is subjected to the next distillation process;

[0049] The purity of the sodium sulfate powder obtained by weighing and testing is:

[0050] The purity of the sodium sulfate obtained in Example 1 is 92.4%;

[0051] The purity of the sodium sulfate obtained in Example 2 is 93.2%;

[0052] The purity of the sodium sulfate obtained in Example 3 is 94.6%.

[0053] (4) Pour the filtrate obtained by suction filtration into a distillation flask, add zeolite to prevent violent boiling, install the distillation device, turn on the condensation water, control the temperature to 78°C, heat the distillation flask to evaporate ethanol, collect the distillate through the condenser, until the distillation is sufficient, and obtain the denitrification liquid from which sulfate ions have been removed;

[0054] Detection of sulfate ion content in the obtained denitrification liquid:

[0055] The content of sulfate in the denitration liquid obtained in Example 1 is 15 g / L, and the sulfate removal rate is 75%;

[0056] The content of sulfate in the denitration liquid obtained in Example 2 was 17 g / L, and the sulfate removal rate was 78.8%;

[0057] The content of sulfate in the denitration liquid obtained in Example 3 is 10 g / L, and the sulfate removal rate is 83%.

[0058] (5) Add citric acid to the denitrification liquid from which sulfate ions have been removed to adjust the pH of the denitrification liquid to 7.0. After standing for a period of time, the resulting solution can enter the denitrification process:

[0059] The denitration efficiency of the denitration liquid obtained in Example 1 can be increased by about 70% compared with the untreated circulating liquid;

[0060] The denitration efficiency of the denitration liquid obtained in Example 2 can be increased by about 76% compared with the untreated circulating liquid;

[0061] The denitration efficiency of the denitration liquid obtained in Example 3 can be increased by about 79% compared with the untreated circulating liquid.

Claims

1. A method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution, characterized in that: The ferric ethylenediaminetetraacetate complex circulating denitration liquid to be treated is regenerated, and then a solvent is introduced to stand for crystallization. After the crystallization is completed, the ferric ethylenediaminetetraacetate complex wet denitration liquid with sulfate ions removed is obtained by filtering and distilling; the obtained denitration liquid can be introduced into the denitration process for circulating denitration after the pH value is adjusted; the solvent is any one of ethanol, methanol, and phenol.

2. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 1, characterized in that: The solvent is anhydrous ethanol.

3. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 2, characterized in that: The specific steps include: A. Filter the ferric ethylenediaminetetraacetic acid complex circulating denitrification liquid to be treated, then add sodium sulfite, adjust the pH value, and stir and regenerate under heating conditions; B. After the regenerated circulating denitrification liquid is cooled, anhydrous ethanol is introduced at a volume ratio of 1:1, and after sufficient stirring, it is allowed to stand for crystallization for 30 minutes; C. After the crystallization is completed, the sodium sulfate crystal powder and the filtrate are obtained by filtration; D. The filtrate is distilled to obtain ethanol and ethylenediaminetetraacetic acid iron complex wet denitration liquid from which sulfate ions have been removed. After adjusting the pH of the obtained denitration liquid, it is passed into the denitration process for cyclic denitration.

4. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step A, the amount of sodium sulfite added is 5-10 g / L.

5. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step A, the pH is adjusted to 7.0-9.

0.

6. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step A, the heating temperature is controlled to be 85-100°C.

7. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step B, the regenerated circulating denitrification liquid is cooled to 20-30° C. by circulating cooling water.

8. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step B, stirring is performed at a rotation speed of 400 r / min for 10 min.

9. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step D, the distillation temperature is 77-79°C.

10. The method for removing sulfate ions from ethylenediaminetetraacetic acid iron complex wet denitration liquid by solvent dissolution according to claim 3, characterized in that: In step D, the pH of the obtained denitrification liquid is adjusted to 7.0-7.5.

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