阅读说明：本技术 一种芳香化合物硝化废水中混合盐分离提纯的方法 (Method for separating and purifying mixed salt in aromatic compound nitration wastewater ) 是由 杨树斌 徐林 丁克鸿 王怡明 王丹 徐高明 王再飞 王建昌 于 2020-11-27 设计创作，主要内容包括：本发明提供一种含硝酸钠和硫酸钠的混合溶液的分离提纯方法,所述分离提纯方法结合两级纳滤和至少两级反渗透处理步骤,不仅能够有效实现溶液中硝酸钠和硫酸钠的高效分离,而且通过纳滤与反渗透同时实现了浓缩的作用,大大降低了后期浓缩和结晶的能耗,经济价值显著提高,应用前景广阔,能够较好的用于芳香化合物硝化废水中混合盐的分离提纯。(The invention provides a separation and purification method of a mixed solution containing sodium nitrate and sodium sulfate, which combines two-stage nanofiltration and at least two-stage reverse osmosis treatment steps, not only can effectively realize the high-efficiency separation of sodium nitrate and sodium sulfate in the solution, but also realizes the concentration effect through nanofiltration and reverse osmosis, greatly reduces the energy consumption of later-stage concentration and crystallization, obviously improves the economic value, has wide application prospect, and can be better used for the separation and purification of mixed salt in aromatic compound nitration wastewater.)

1. A separation and purification method of a mixed solution containing sodium nitrate and sodium sulfate is characterized by comprising the following steps:

(1) nanofiltration is carried out on a mixed solution containing sodium nitrate and sodium sulfate, and the nanofiltration total concentrated water is subjected to first concentration and first crystallization in sequence to obtain sodium sulfate;

(2) and the total produced water after nanofiltration is subjected to at least two-stage reverse osmosis treatment, and the concentrated water after the reverse osmosis treatment is subjected to second concentration and second crystallization in sequence to obtain sodium nitrate.

2. The method according to claim 1, wherein the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate in the step (1) is 0.1-5 wt%;

preferably, the content of sodium nitrate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-3 wt%.

3. The method according to claim 1 or 2, wherein the nanofiltration in step (1) comprises a first nanofiltration and a second nanofiltration;

preferably, the operating temperatures of the first nanofiltration and the second nanofiltration are respectively and independently 5-50 ℃, preferably 25-35 ℃;

preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, the operating pressure of the first nanofiltration is lower than that of the second nanofiltration;

preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, the operating pressure of the first nanofiltration is 0.2-2.0 MPa, preferably 0.6-1.0 MPa;

preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, the operating pressure of the second nanofiltration is 1.0-4.1 MPa, preferably 1.5-3.8 MPa.

4. The method according to any one of claims 1 to 3, wherein the operating pressure of the first nanofiltration is higher than that of the second nanofiltration when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2 to 5 wt%;

preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2-5 wt%, the operating pressure of the first nanofiltration is 1.0-4.1 MPa, preferably 1.5-3.8 MPa;

preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2-5 wt%, the operating pressure of the second nanofiltration is 0.2-2.0 MPa, preferably 0.6-1.0 MPa.

5. The method according to any one of claims 1 to 4, wherein the water produced by the first nanofiltration enters a second nanofiltration;

preferably, the membrane modules of the first nanofiltration and the second nanofiltration have a pore diameter of 1-10nm and a molecular weight cut-off of 150 Da;

preferably, the membrane module of the first nanofiltration is suez DK 8040;

preferably, the membrane module of the second nanofiltration is suez DK 8040.

6. A process according to any one of claims 1 to 5, wherein the concentration of sodium sulphate in the first concentrated concentrate is 40 to 80 wt%, preferably 40 to 60 wt%.

7. The method according to any one of claims 1 to 6, wherein the reverse osmosis treatment in the step (2) has two stages, namely first-stage reverse osmosis and second-stage reverse osmosis;

preferably, the operating temperature of the reverse osmosis treatment is 5-50 ℃, preferably 30-40 ℃;

preferably, the operating pressure of the primary reverse osmosis is 1.0-4.0 MPa, preferably 2.0-3.8 MPa;

preferably, the operating pressure of the secondary reverse osmosis is 3.0-8.0 MPa, preferably 4.0-7.0 MPa;

preferably, the produced water of the secondary reverse osmosis treatment is recycled to the primary reverse osmosis treatment;

preferably, the reverse osmosis membrane of the first-stage reverse osmosis is a DuPont anti-pollution brackish water membrane BW-8040;

preferably, the reverse osmosis membrane of the secondary reverse osmosis is a DuPont sea membrane SW-8040.

8. A process according to any one of claims 1 to 7, wherein the concentration of sodium nitrate in the second concentrated concentrate of step (2) is from 40 to 80 wt%, preferably from 50 to 70 wt%.

9. A method according to any one of claims 1 to 8, characterized in that the method comprises the steps of:

(1) when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2-5 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on the mixed solution containing sodium nitrate and sodium sulfate, wherein the operating pressure of the first nanofiltration is 1.0-4.1 MPa, the operating pressure of the second nanofiltration is 0.2-2.0 MPa, the operating pressure of the first nanofiltration is higher than that of the second nanofiltration, returning the concentrated water of the second nanofiltration to the first nanofiltration, and sequentially carrying out first concentration on the concentrated water of the first nanofiltration until the concentration of sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

(2) subjecting the water produced by the second nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to second concentration until the concentration of sodium nitrate is 40-80 wt% and second crystallization to obtain sodium nitrate;

or, the method comprises the steps of:

(1) when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃, wherein the operating pressure of the first nanofiltration is 0.2-2.0 MPa, the operating pressure of the second nanofiltration is 1.0-4.1 MPa, the operating pressure of the first nanofiltration is lower than that of the second nanofiltration, the concentrated water of the first nanofiltration enters the second nanofiltration, the produced water of the second nanofiltration is circulated to the first nanofiltration, and the concentrated water of the second nanofiltration is sequentially subjected to first concentration until the concentration of sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

(2) and subjecting the water produced by the first nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to secondary concentration until the concentration of sodium nitrate is 40-80 wt% and secondary crystallization to obtain sodium nitrate.

10. A method for separating and purifying mixed salt in aromatic compound nitrification wastewater, which is characterized in that the method is carried out by adopting the method for separating and purifying the mixed solution containing sodium nitrate and sodium sulfate according to any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of separation and purification, in particular to a method for separating and purifying mixed salt in aromatic compound nitration wastewater.

Background

Aromatic compound nitration products such as nitrobenzene, m-dinitrobenzene, p/o/m-nitrochlorobenzene, 3,4-/2, 5-dichloronitrobenzene and the like are important chemical intermediates of pesticides, medicines, dyes, pigments and the like. At present, aromatic compounds are mainly produced by adopting a mixed acid process, and nitrification wastewater is generated in the process. The nitrified wastewater contains aromatic hydrocarbon and derivatives thereof, nitrified products, nitrophenol and sodium salt thereof (total phenol for short), sodium sulfate, sodium nitrate and the like, and has high toxicity, high salt content, poor biodegradability and high treatment cost. Aiming at the characteristics of nitrified wastewater, physical and chemical means such as adsorption, oxidation and other pretreatment means are generally adopted at present, so that the concentration of organic matters in the wastewater is reduced, and the biodegradability of the wastewater is improved, but the separation and purification of mixed salts in the nitrified wastewater are not considered, so that the resource waste is caused.

CN1233570C discloses a resin adsorption recovery process of nitrochlorobenzene in nitrochlorobenzene production wastewater, which adopts a styrene-divinylbenzene resin adsorption scheme to separate and recover nitrochlorobenzene in wastewater, and realizes the recovery of nitrochlorobenzene in wastewater through saturated resin steam desorption regeneration, but the resin price is higher, and the temperature of a steam desorption regeneration mode is high, so that the resin aging risk is increased.

CN111018264A discloses a process method for treating o-nitre wastewater, which adopts a scheme of combining an advanced oxidation unit, an electrodialysis unit, an evaporation unit and a biochemical unit, and can simultaneously realize the recovery of sodium sulfate, the standard discharge of water and the sludge reduction, but the process is more, and the separation and recovery of nitrate in the wastewater are not mentioned.

In 2020, Kazu east et al, Vol.40, No. 1, pp.63-65, have the technical problems of high energy consumption and great operational difficulty due to the fact that the separation of sodium sulfate, sodium chloride and sodium nitrate is realized by fractional crystallization of miscellaneous salts in high-salt wastewater, and the product reaches the industrial standard, but this scheme requires multiple times of evaporative crystallization (see "research on separation process of sodium sulfate-sodium chloride-sodium nitrate in wastewater from coal chemical industry", Vol.40, pp.1, pp.63-65).

Therefore, it is required to develop a method for recovering and treating the nitrified waste water of aromatic compounds, which can sufficiently recover the nitrate therein and alleviate the environmental pollution problem.

Disclosure of Invention

In view of the problems in the prior art, the invention provides a separation and purification method of a mixed solution containing sodium nitrate and sodium sulfate, which combines two-stage nanofiltration and at least two-stage reverse osmosis treatment steps, not only can effectively realize the high-efficiency separation of sodium nitrate and sodium sulfate in the solution, but also greatly reduces the energy consumption of later-stage concentration and crystallization, and has high economic value and wide application prospect.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a separation and purification method of a mixed solution containing sodium nitrate and sodium sulfate, the separation and purification method comprising:

(1) nanofiltration is carried out on a mixed solution containing sodium nitrate and sodium sulfate, and the nanofiltration total concentrated water is subjected to first concentration and first crystallization in sequence to obtain sodium sulfate;

(2) and the total produced water after nanofiltration is subjected to at least two-stage reverse osmosis treatment, and the concentrated water after the reverse osmosis treatment is subjected to second concentration and second crystallization in sequence to obtain sodium nitrate.

According to the method for separating and purifying the mixed solution containing the sodium nitrate and the sodium sulfate, provided by the invention, the sodium nitrate and the sodium sulfate are separated by adopting a nanofiltration mode, the sodium sulfate is concentrated, the energy consumption of later-stage sodium sulfate concentration and crystallization is reduced, the solution containing the sodium nitrate is concentrated by adopting reverse osmosis treatment subsequently, and then the solution containing the sodium nitrate is combined with second concentration and second crystallization, so that the high-purity sodium nitrate can be prepared under the condition of lower energy consumption.

Preferably, the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate in step (1) is 0.1 to 5 wt%, and for example, it may be 0.1 wt%, 0.7 wt%, 1.2 wt%, 1.8 wt%, 2.3 wt%, 2.9 wt%, 3.4 wt%, 4 wt%, 4.5 wt%, or 5 wt%, but is not limited to the values listed, and other values not listed in this range are also applicable.

Preferably, the content of sodium nitrate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1 to 3 wt%, and for example, may be 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.1 wt%, 1.4 wt%, 1.8 wt%, 2.1 wt%, 2.4 wt%, 2.7 wt%, or 3 wt%, but is not limited to the above-mentioned values, and other values not listed in this range are also applicable.

Preferably, the COD of the mixed solution containing sodium nitrate and sodium sulfate is 100ppm or less, and may be, for example, 20ppm, 29ppm, 38ppm, 47ppm, 56ppm, 65ppm, 74ppm, 83ppm, 92ppm or 100ppm, etc., but not limited to the values listed, and other values not listed in the range are also applicable.

Preferably, the pH of the mixed solution containing sodium nitrate and sodium sulfate is 5.0 to 8.0, and may be, for example, 5.0, 5.4, 5.7, 6, 6.4, 6.7, 7, 7.4, 7.7 or 8.0, but is not limited to the above-mentioned values, and other values not mentioned in this range are also applicable.

Preferably, the nanofiltration comprises a first nanofiltration and a second nanofiltration.

Preferably, the operating temperature of the first nanofiltration and the second nanofiltration in step (1) are independently 5 to 50 ℃, for example, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃, but not limited to the recited values, and other values not recited in the range are also applicable, preferably 25 to 35 ℃.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, the operating pressure of the first nanofiltration is lower than that of the second nanofiltration.

According to the invention, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is preferably 0.1-1 wt%, a mode of low-pressure nanofiltration and high-pressure nanofiltration is adopted, so that smooth water production can be ensured, and the normal operation of the system can be ensured.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1 to 1 wt%, the operating pressure of the first nanofiltration may be 0.2 to 2.0MPa, for example, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa, 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, or 2.0MPa, but is not limited to the above-mentioned values, and other values not mentioned in this range are also applicable, and preferably 0.6 to 1.0 MPa.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1 to 1 wt%, the operating pressure of the second nanofiltration is 1.0 to 4.1MPa, and may be, for example, 1.0MPa, 1.4MPa, 1.7MPa, 2MPa, 2.4MPa, 2.7MPa, 3MPa, 3.4MPa, 3.7MPa, 4.0MPa, or 4.1MPa, but is not limited to the above-mentioned values, and other values not listed in this range are also applicable, and 1.5 to 3.8MPa is preferable.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2-5 wt%, the operating pressure of the first nanofiltration is higher than that of the second nanofiltration.

According to the invention, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is preferably 2-5 wt%, the impact on the nanofiltration membrane can be reduced and the service life of the nanofiltration membrane can be prolonged by adopting a mode of high-pressure nanofiltration and then low-pressure nanofiltration.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2 to 5 wt%, the operating pressure of the first nanofiltration is 1.0 to 4.1MPa, and may be, for example, 1.0MPa, 1.4MPa, 1.7MPa, 2MPa, 2.4MPa, 2.7MPa, 3MPa, 3.4MPa, 3.7MPa, 4.0MPa, or 4.1MPa, and preferably 1.5 to 3.8 MPa.

Preferably, when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2 to 5 wt%, the operating pressure of the second nanofiltration is 0.2 to 2.0MPa, and may be, for example, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa, 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, or 2.0MPa, and preferably 0.6 to 1.0 MPa.

Preferably, the water produced by the first nanofiltration enters a second nanofiltration.

Preferably, the membrane modules of the first nanofiltration and the second nanofiltration have a pore diameter of 1-10 nanometers and a molecular weight cut-off of 150 Da.

In the invention, nanofiltration adopts a pressure-driven membrane separation technology, the aperture range is about a few nanometers, the separation performance is between reverse osmosis and ultrafiltration, some inorganic salts and some solvents are allowed to permeate through the membrane, and the separation of sulfate radicals and nitrate radicals in the solution can be realized.

Preferably, the membrane module of the first nanofiltration is suez DK 8040.

Preferably, the membrane module of the second nanofiltration is suez DK 8040.

Preferably, the concentration of sodium sulfate in the concentrated solution after the first concentration is 40 to 80 wt%, for example, 40 wt%, 45 wt%, 49 wt%, 54 wt%, 58 wt%, 63 wt%, 67 wt%, 72 wt%, 76 wt%, or 80 wt%, etc., but not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, preferably 40 to 60 wt%.

Preferably, the concentration comprises evaporative concentration.

Preferably, the first concentrated effluent is recovered as recycled water.

Preferably, the reverse osmosis treatment in the step (2) has two stages, namely first-stage reverse osmosis and second-stage reverse osmosis.

Preferably, the reverse osmosis treatment is performed at an operating temperature of 5 to 50 ℃, for example, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃, but not limited to the recited values, and other values not recited in the range are also applicable, preferably 30 to 40 ℃.

Preferably, the operating pressure of the primary reverse osmosis is 1.0 to 4.0MPa, and may be, for example, 1.0MPa, 1.4MPa, 1.7MPa, 2MPa, 2.4MPa, 2.7MPa, 3MPa, 3.4MPa, 3.7MPa or 4.0MPa, but is not limited to the values listed, and other values not listed in this range are also applicable, and preferably 2.0 to 3.8 MPa.

Preferably, the operating pressure of the secondary reverse osmosis is 3.0 to 8.0MPa, for example, 3.0MPa, 3.6MPa, 4.2MPa, 4.7MPa, 5.3MPa, 5.8MPa, 6.4MPa, 6.9MPa, 7.5MPa or 8.0MPa, but not limited to the values listed, and other values not listed in this range are also applicable, preferably 4.0 to 7.0 MPa.

The invention controls the pressure of two-stage reverse osmosis within the range, is more beneficial to the concentration of sodium nitrate solution, and improves the recovery rate and the purity.

Preferably, the produced water of the first-stage reverse osmosis treatment is recycled as reclaimed water.

Preferably, the produced water of the secondary reverse osmosis treatment is recycled to the primary reverse osmosis treatment.

Preferably, the reverse osmosis membrane of the first-stage reverse osmosis is a DuPont anti-pollution brackish water membrane BW-8040.

Preferably, the reverse osmosis membrane of the secondary reverse osmosis is a DuPont sea membrane SW-8040.

Preferably, the concentration of sodium nitrate in the second concentrated concentrate of step (2) is 40 to 80 wt%, for example, 40 wt%, 45 wt%, 49 wt%, 54 wt%, 58 wt%, 63 wt%, 67 wt%, 72 wt%, 76 wt%, or 80 wt%, etc., but not limited to the recited values, and other values not recited in this range are also applicable, preferably 50 to 70 wt%.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 2-5 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on the mixed solution containing sodium nitrate and sodium sulfate, wherein the operating pressure of the first nanofiltration is 1.0-4.1 MPa, the operating pressure of the second nanofiltration is 0.2-2.0 MPa, the operating pressure of the first nanofiltration is higher than that of the second nanofiltration, returning the concentrated water of the second nanofiltration to the first nanofiltration, and sequentially carrying out first concentration on the concentrated water of the first nanofiltration until the concentration of sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

(2) subjecting the water produced by the second nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to second concentration until the concentration of sodium nitrate is 40-80 wt% and second crystallization to obtain sodium nitrate;

or, the method comprises the steps of:

(1) when the content of sodium sulfate in the mixed solution containing sodium nitrate and sodium sulfate is 0.1-1 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃, wherein the operating pressure of the first nanofiltration is 0.2-2.0 MPa, the operating pressure of the second nanofiltration is 1.0-4.1 MPa, the operating pressure of the first nanofiltration is lower than that of the second nanofiltration, the concentrated water of the first nanofiltration enters the second nanofiltration, the produced water of the second nanofiltration is circulated to the first nanofiltration, and the concentrated water of the second nanofiltration is sequentially subjected to first concentration until the concentration of sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

(2) and subjecting the water produced by the first nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to secondary concentration until the concentration of sodium nitrate is 40-80 wt% and secondary crystallization to obtain sodium nitrate.

The concentration is not particularly limited in the present invention, and any method for concentration known to those skilled in the art can be used, and can be adjusted according to the actual process, for example, evaporation concentration or multi-effect evaporation concentration, etc.

In a second aspect, the invention provides a method for separating and purifying mixed salts in aromatic compound nitration wastewater, which is carried out by adopting the method for separating and purifying the mixed solution containing sodium nitrate and sodium sulfate in the first aspect.

The aromatic compound nitration wastewater mainly contains sodium nitrate and sodium sulfate, and the separation and purification method of the first aspect can be used for recovering water resources, sodium nitrate and sodium sulfate from the nitration wastewater, so that the environmental pressure is relieved, and the method has high economic benefit.

Preferably, the pretreated effluent of the pretreated aromatic compound nitration wastewater enters the first nanofiltration.

Preferably, the content of sodium sulfate in the pretreated effluent is 0.1 to 5 wt%, and may be, for example, 0.1 wt%, 0.7 wt%, 1.2 wt%, 1.8 wt%, 2.3 wt%, 2.9 wt%, 3.4 wt%, 4 wt%, 4.5 wt%, or 5 wt%, but is not limited to the values listed, and other values not listed in this range are also applicable.

Preferably, the content of sodium nitrate in the pretreated effluent is 0.1 to 3 wt%, and for example, may be 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.1 wt%, 1.4 wt%, 1.8 wt%, 2.1 wt%, 2.4 wt%, 2.7 wt%, or 3 wt%, but is not limited to the values listed, and other values not listed in this range are also applicable.

Preferably, the COD in the pretreated effluent is 100ppm or less, and may be, for example, 20ppm, 29ppm, 38ppm, 47ppm, 56ppm, 65ppm, 74ppm, 83ppm, 92ppm or 100ppm, but is not limited to the recited values, and other values not recited in the range are also applicable.

Preferably, the pH of the pretreated effluent is 5.0 to 8.0, and may be, for example, 5.0, 5.4, 5.7, 6, 6.4, 6.7, 7, 7.4, 7.7, or 8.0, but not limited to the values listed, and other values not listed in this range are also applicable.

Preferably, the mother liquor of the first crystallization is recycled to the pretreatment.

Preferably, the mother liquor of the second crystallization is recycled to the pretreatment.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) the method for separating and purifying the mixed solution containing the sodium nitrate and the sodium sulfate combines two-stage nanofiltration and at least two-stage reverse osmosis treatment, realizes the high-efficiency separation of the sodium nitrate and the sodium sulfate in the solution, greatly reduces the energy consumption of later-stage concentration and crystallization, and has high economic value;

(2) the method for separating and purifying the mixed solution containing the sodium nitrate and the sodium sulfate has the advantages that the purity and the recovery rate of the recovered sodium nitrate and the recovered sodium sulfate are high, the purity of the sodium nitrate is more than 98.5 percent, the purity of the sodium sulfate is more than 93 percent, and the requirements of national standard qualified products are met;

(3) the method for separating and purifying the mixed salt in the aromatic compound nitration wastewater provided by the invention realizes the recovery of water resources, sodium nitrate and sodium sulfate, relieves the environmental pressure and has higher economic benefit.

Drawings

FIG. 1 is a schematic flow chart of one of the methods for separating and purifying a mixed solution containing sodium nitrate and sodium sulfate according to the present invention.

Fig. 2 is a schematic flow chart of one of the methods for separating and purifying the mixed solution containing sodium nitrate and sodium sulfate according to the present invention.

FIG. 3 is a schematic flow chart of a method for separating and purifying mixed salts in the nitrified wastewater of aromatic compounds according to the present invention.

FIG. 4 is a schematic flow chart of a method for separating and purifying mixed salts in the nitrified wastewater of aromatic compounds according to the present invention.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

The flow schematic diagram of the separation and purification method of the mixed solution containing sodium nitrate and sodium sulfate provided by the invention is shown in figure 1, and the separation and purification method comprises the following steps:

(1) sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on a mixed solution containing sodium nitrate and sodium sulfate, returning concentrated water obtained by the second nanofiltration to the first nanofiltration, and sequentially carrying out first concentration on the concentrated water obtained by the first nanofiltration until the concentration of the sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

the first concentrated effluent is recycled as reclaimed water, and the first crystallization mother liquor is subjected to post-treatment or circulated to other processes;

(2) subjecting the water produced by the second nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to second concentration until the concentration of sodium nitrate is 40-80 wt% and second crystallization to obtain sodium nitrate;

the second concentrated effluent is recycled as reclaimed water, and the second crystallization mother liquor is subjected to post-treatment or circulated to other processes; the produced water of the first-stage reverse osmosis treatment is recycled as reclaimed water;

alternatively, as shown in fig. 2, the separation and purification method includes the steps of:

(1) sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on a mixed solution containing sodium nitrate and sodium sulfate, enabling concentrated water of the first nanofiltration to enter the second nanofiltration, returning produced water of the second nanofiltration to the first nanofiltration, and sequentially carrying out first concentration on the concentrated water of the second nanofiltration until the concentration of the sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

the first concentrated effluent is recycled as reclaimed water, and the first crystallization mother liquor is subjected to post-treatment or circulated to other processes;

(2) subjecting the water produced by the first nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to secondary concentration until the concentration of sodium nitrate is 40-80 wt% and secondary crystallization to obtain sodium nitrate;

the second concentrated effluent is recycled as reclaimed water, and the second crystallization mother liquor is subjected to post-treatment or circulated to other processes; and the produced water of the first-stage reverse osmosis treatment is recycled as reclaimed water.

The flow schematic diagram of the method for separating and purifying the mixed salt in the aromatic compound nitration wastewater provided by the invention is shown in fig. 3, and the separation and purification method comprises the following steps:

(1') pretreating aromatic compound nitration wastewater to obtain pretreated effluent;

(2') when the content of sodium sulfate in the pretreated effluent is 2-5 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on the pretreated effluent, returning concentrated water obtained by the second nanofiltration to the first nanofiltration, and sequentially carrying out first concentration on the concentrated water obtained by the first nanofiltration until the concentration of sodium sulfate is 40-80 wt% and first crystallization to obtain sodium sulfate;

the first concentrated effluent is recycled as reclaimed water, and the first crystallization mother liquor is recycled to pretreatment for recycling;

(3') subjecting the water produced by the second nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to secondary concentration until the concentration of sodium nitrate is 40-80 wt% and secondary crystallization to obtain sodium nitrate;

recycling the second concentrated effluent as reclaimed water, and circulating the second crystallization mother liquor to pretreatment for recycling; and the produced water of the first-stage reverse osmosis treatment is recycled as reclaimed water.

Alternatively, as shown in fig. 4, the separation and purification method includes the steps of:

(1') pretreating aromatic compound nitration wastewater to obtain pretreated effluent;

(2') when the content of sodium sulfate in the pretreated effluent is 0.1-1 wt%, sequentially carrying out first nanofiltration at 5-50 ℃ and second nanofiltration at 5-50 ℃ on the pretreated effluent, enabling concentrated water obtained by the first nanofiltration to enter the second nanofiltration, circulating produced water obtained by the second nanofiltration to the first nanofiltration, sequentially carrying out first concentration on the concentrated water obtained by the second nanofiltration until the concentration of sodium sulfate is 40-80 wt% and carrying out first crystallization to obtain sodium sulfate;

the first concentrated effluent is recycled as reclaimed water, and the first crystallization mother liquor is recycled to pretreatment for recycling;

(3') subjecting the water produced by the first nanofiltration to primary reverse osmosis treatment at the pressure of 1.0-4.0 MPa and the temperature of 5-50 ℃ and secondary reverse osmosis treatment at the pressure of 3.0-8.0 MPa and the temperature of 5-50 ℃, and sequentially subjecting the concentrated water subjected to the secondary reverse osmosis treatment to secondary concentration until the concentration of sodium nitrate is 40-80 wt% and secondary crystallization to obtain sodium nitrate;

recycling the second concentrated effluent as reclaimed water, and circulating the second crystallization mother liquor to pretreatment for recycling; and the produced water of the first-stage reverse osmosis treatment is recycled as reclaimed water.

First, an embodiment

Example 1

The embodiment provides a method for separating and purifying mixed salts in aromatic compound nitration wastewater, which comprises the following steps:

(1') pretreatment: pretreating aromatic compound nitration wastewater to obtain nitration wastewater pretreatment effluent containing sodium nitrate and sodium sulfate, wherein the composition of the effluent is as follows: 2.56 wt%, sodium nitrate: 1.04 wt%, COD: 41ppm, pH: 6.5;

(2') nanofiltration separation: the nanofiltration membrane component adopts Suez DK8040, the effluent of the nitrification wastewater pretreatment is pumped into a high-pressure first nanofiltration, the operation temperature is 35 ℃, the pressure is 3.8MPa, the appearance of the concentrated water of the first nanofiltration is colorless and transparent, and the concentrated water enters a concentration and crystallization step;

pumping concentrated water subjected to first nanofiltration into a water pump of a concentration kettle, carrying out first concentration and first crystallization under vacuum of 45kPa, wherein the temperature of the kettle at the end of concentration is 90 ℃, the first concentrated water is recycled as reclaimed water, filtering at 80-90 ℃ to obtain a white by-product sodium sulfate, and returning the first crystallization mother liquor subjected to concentration and crystallization to the pretreatment process;

the appearance of the produced water of the first nanofiltration is colorless and transparent, and the low-pressure second-stage nanofiltration is removed;

the second-stage nanofiltration is carried out at the operating temperature of 35 ℃ and the pressure of 0.8MPa to obtain concentrated water for the second-stage nanofiltration, the concentrated water is colorless and transparent in appearance and returns to the first nanofiltration, and the produced water for the second-stage nanofiltration is colorless and transparent in appearance and goes to the step (3');

(3') reverse osmosis treatment: the first-stage reverse osmosis membrane component adopts a DuPont anti-pollution brackish water membrane BW-8040, the produced water of the second-stage nanofiltration is pumped into a first-stage reverse osmosis device, the operation temperature is 30 ℃, the pressure is 3.8MPa, the appearance of the produced water of the first-stage reverse osmosis treatment is colorless and transparent and is used as reclaimed water for reuse, and the appearance of the concentrated water of the first-stage reverse osmosis treatment is colorless and transparent and enters a second-stage reverse osmosis device;

the secondary reverse osmosis membrane component adopts a DuPont sea fresh water membrane SW-8040, concentrated water of primary reverse osmosis is pumped into a secondary reverse osmosis device, the operation temperature is 35 ℃, the pressure is 6.8MPa, the appearance of produced water of the secondary reverse osmosis is colorless and transparent, the water returns to the primary reverse osmosis treatment, and concentrated water of the secondary reverse osmosis enters the concentration treatment;

pumping the second-stage reverse osmosis concentrated water into a second concentration kettle, carrying out second concentration by a water pump with vacuum of 45kPa, carrying out second concentration at the end of concentration at the kettle temperature of 92 ℃, discharging second concentrated water with colorless and transparent appearance, recycling the second concentrated water as reclaimed water, cooling the second concentration kettle material, carrying out second crystallization to 20 ℃, filtering, drying to obtain white sodium nitrate, and returning the second crystallization mother liquor to the pretreatment process, wherein the second crystallization mother liquor is pale yellow in appearance.

The composition of each effluent in this example is shown in table 1.

TABLE 1

Example 2

The embodiment provides a method for separating and purifying mixed salts in aromatic compound nitration wastewater, which comprises the following steps:

(1') pretreatment: pretreating aromatic compound nitration wastewater to obtain nitration wastewater pretreatment effluent containing sodium nitrate and sodium sulfate, wherein the composition of the effluent is as follows: 0.5 wt%, sodium nitrate: 3 wt%, COD: 58ppm, pH: 7.5;

(2') nanofiltration separation: the nanofiltration membrane component adopts Suez DK8040, the effluent of the nitrification wastewater pretreatment is pumped into a first nanofiltration, the operation temperature is 25 ℃, the pressure is 1.0MPa, the appearance of the produced water of the first nanofiltration is colorless and transparent, and the step (3') is carried out;

pumping the colorless and transparent appearance of the concentrated water subjected to the first nanofiltration into a second nanofiltration device, concentrating the concentrated water subjected to the second nanofiltration device at the operating temperature of 35 ℃ and the pressure of 2.0MPa to obtain concentrated water subjected to the second nanofiltration, concentrating the concentrated water at the colorless and transparent appearance, carrying out first concentration and first crystallization by a water pump of a concentration kettle under the vacuum condition of 50kPa, wherein the temperature of the kettle at the end of concentration is 85 ℃, the first concentrated water is recycled as reclaimed water, filtering the concentrated water at the temperature of 80-85 ℃ to obtain a white byproduct sodium sulfate, and returning the first crystallization mother liquor subjected to the concentration;

(3') reverse osmosis treatment: the first-stage reverse osmosis membrane component adopts a DuPont anti-pollution brackish water membrane BW-8040, the produced water of the first nanofiltration is pumped into a first-stage reverse osmosis device, the operating temperature is 40 ℃, the pressure is 2.0MPa, the appearance of the produced water of the first-stage reverse osmosis treatment is colorless and transparent and is used as reclaimed water for reuse, and the appearance of the concentrated water of the first-stage reverse osmosis treatment is colorless and transparent and enters a second-stage reverse osmosis device;

the secondary reverse osmosis membrane component adopts a DuPont sea fresh water membrane SW-8040, concentrated water of primary reverse osmosis is pumped into a secondary reverse osmosis device, the operation temperature is 30 ℃, the pressure is 4.0MPa, the appearance of produced water of the secondary reverse osmosis is colorless and transparent, the water returns to the primary reverse osmosis treatment, and concentrated water of the secondary reverse osmosis enters the concentration treatment;

pumping the second-stage reverse osmosis concentrated water into a second concentration kettle, carrying out second concentration by a water pump with vacuum 50kPa, carrying out second concentration at the end of concentration at the kettle temperature of 95 ℃, discharging second concentrated water with colorless and transparent appearance, recycling the second concentrated water as reclaimed water, cooling the second concentration kettle material, carrying out second crystallization to 25 ℃, filtering, drying to obtain white sodium nitrate, and returning the second crystallization mother liquor to the pretreatment process, wherein the second crystallization mother liquor is pale yellow in appearance.

The composition of the effluent from each section of this example is shown in Table 2.

TABLE 2

Example 3

The embodiment provides a method for separating and purifying mixed salts in aromatic compound nitration wastewater, which comprises the following steps:

(1') pretreatment: pretreating aromatic compound nitration wastewater to obtain nitration wastewater pretreatment effluent containing sodium nitrate and sodium sulfate, wherein the composition of the effluent is as follows: 4.5 wt%, sodium nitrate: 3 wt%, COD: 70ppm, pH: 7.3;

(2') nanofiltration separation: the nanofiltration membrane component adopts Suez DK8040, the effluent of the nitrification wastewater pretreatment is pumped into a high-pressure first nanofiltration, the operation temperature is 25 ℃, the pressure is 4.1MPa, the appearance of the concentrated water of the first nanofiltration is colorless and transparent, and the concentrated water enters a concentration and crystallization step;

pumping concentrated water subjected to first nanofiltration into a water pump of a concentration kettle, carrying out first concentration and first crystallization under vacuum of 40kPa, wherein the kettle temperature at the end of concentration is 88 ℃, the first concentrated water is recycled as reclaimed water, filtering is carried out at 80-88 ℃ to obtain a white by-product sodium sulfate, and the first crystallization mother liquor subjected to concentration and crystallization is returned to the pretreatment process;

the appearance of the produced water of the first nanofiltration is colorless and transparent, and the low-pressure second-stage nanofiltration is removed;

the second-stage nanofiltration is carried out at the operating temperature of 25 ℃ and the pressure of 0.6MPa to obtain concentrated water for the second-stage nanofiltration, the concentrated water is colorless and transparent in appearance and returns to the first nanofiltration, and the produced water for the second-stage nanofiltration is colorless and transparent in appearance and goes to the step (3');

(3') reverse osmosis treatment: the first-stage reverse osmosis membrane component adopts a DuPont anti-pollution brackish water membrane BW-8040, the produced water of the second-stage nanofiltration is pumped into a first-stage reverse osmosis device, the operation temperature is 32 ℃, the pressure is 4.0MPa, the appearance of the produced water of the first-stage reverse osmosis treatment is colorless and transparent and is used as reclaimed water for reuse, and the appearance of the concentrated water of the first-stage reverse osmosis treatment is colorless and transparent and enters a second-stage reverse osmosis device;

the secondary reverse osmosis membrane component adopts a DuPont sea fresh water membrane SW-8040, concentrated water of primary reverse osmosis is pumped into a secondary reverse osmosis device, the operation temperature is 38 ℃, the pressure is 7.0MPa, the appearance of produced water of the secondary reverse osmosis is colorless and transparent, the water returns to the primary reverse osmosis treatment, and concentrated water of the secondary reverse osmosis enters the concentration treatment;

pumping the second-stage reverse osmosis concentrated water into a second concentration kettle, carrying out second concentration by a water pump with vacuum 50kPa, carrying out second concentration at the end of concentration at the kettle temperature of 95 ℃, discharging second concentrated water with colorless and transparent appearance, recycling the second concentrated water as reclaimed water, cooling the second concentration kettle material, carrying out second crystallization to 25 ℃, filtering, drying to obtain white sodium nitrate, and returning the second crystallization mother liquor to the pretreatment process, wherein the second crystallization mother liquor is pale yellow in appearance.

The composition of the effluent from each section of this example is shown in Table 3.

TABLE 3

Example 4

This example provides a method for separating and purifying a mixed salt in aromatic compound nitrification wastewater, which is the same as example 1 except that the operating pressure of the first nanofiltration in step (2') is 3.0MPa and the operating pressure of the second nanofiltration is 1.0 MPa.

Example 5

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 1 except that the operation pressure of the first nanofiltration in step (2') is 2.0 MPa.

Example 6

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 1 except that the operation pressure of the first nanofiltration in step (2') is 4.1 MPa.

Example 7

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 1 except that the second nanofiltration operation pressure in step (2') is 2.0 MPa.

Example 8

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 1 except that the second nanofiltration operation pressure in step (2') is 0.2 MPa.

Example 9

This example provides a method for separating and purifying a mixed salt in aromatic compound nitrification wastewater, which is the same as example 2 except that the operating pressure of the first nanofiltration in step (2') is 2.0MPa and the operating pressure of the second nanofiltration is 4.1 MPa.

Example 10

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 2 except that the operating pressure of the first nanofiltration in step (2') is 1.5 MPa.

Example 11

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 2 except that the operation pressure of the first nanofiltration in step (2') is 0.2 MPa.

Example 12

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 2 except that the operation pressure of the second nanofiltration in step (2') is 4.1 MPa.

Example 13

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 2 except that the second nanofiltration operation pressure in step (2') is 1.5 MPa.

Example 14

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 1 except that the operation pressure of the second nanofiltration in step (2') is 4.1 MPa.

Aiming at the solution with the sodium sulfate content of 2-5 wt% in the effluent of the pretreatment of the aromatic compound nitrification wastewater, in the embodiment, the operating pressure of the first nanofiltration is lower than that of the second nanofiltration, the sodium sulfate content of the produced water of the first nanofiltration is only 0.1-0.5 wt%, the feed liquid osmotic pressure is low, the impact on the nanofiltration membrane is high due to the high operating pressure of the second nanofiltration, and the service life of the nanofiltration membrane is obviously influenced.

Example 15

This example provides a method for separating and purifying mixed salts in aromatic compound nitrification wastewater, which is the same as example 2 except that the second nanofiltration operation pressure in step (2') is 0.5 MPa.

Aiming at the solution with the sodium sulfate content of 0.1-1 wt% in the effluent of the aromatic compound nitration wastewater pretreatment, in the embodiment, the operating pressure of the first nanofiltration is higher than that of the second nanofiltration, the sodium sulfate content of the concentrated water of the first nanofiltration is 2-3 wt%, the feed liquid has high osmotic pressure, and the operating pressure of the second nanofiltration is low, so that normal water production is difficult.

Second, test and results

COD: potassium dichromate titration method.

Testing the contents of sodium sulfate and sodium nitrate in the solution: and quantifying sulfate radicals and nitrate radicals by adopting ion chromatography, and converting to obtain the contents of sodium sulfate and sodium nitrate.

Sodium sulfate purity test: the method is determined by referring to the method of GB/T6009-2014.

Sodium nitrate purity test: the determination is carried out by referring to the method of GB/T4553-.

The sodium sulfate rejection rates of the first and second nanofiltration, the composition of the concentrated water of the first nanofiltration, and the composition of the prepared sodium sulfate product in the above examples are shown in table 4.

TABLE 4

The composition of the concentrate treated by the secondary reverse osmosis in the above examples, and the composition of the sodium nitrate product obtained are shown in table 5.

TABLE 5

As can be seen from tables 1-5:

it can be seen from the comprehensive examples 1-13 that the purity of the sodium sulfate obtained by separation according to the technical scheme of the invention is more than 93%, and the requirement of the GB/T6009-2014 III-type qualified product is met, and the purity of the sodium nitrate obtained by separation is more than 98.5%, and the requirement of the GB/T4553-2016-type general industrial qualified product is met.

In conclusion, the method for separating and purifying the mixed solution containing sodium nitrate and sodium sulfate combines two-stage nanofiltration and at least two-stage reverse osmosis treatment steps, not only can effectively realize the high-efficiency separation of sodium nitrate and sodium sulfate in the solution, but also realizes the concentration effect through nanofiltration and reverse osmosis, greatly reduces the energy consumption of later-stage concentration and crystallization, ensures that the purity of sodium sulfate products is more than 93 percent and the purity of sodium nitrate products is more than 98.5 percent, remarkably improves the economic value and has wide application prospect.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.