Method for resource utilization of nitroaniline wastewater
Technical Field
The invention relates to a method for treating nitroaniline wastewater, in particular to a method for recycling ammonia, ammonium chloride, nitroaniline and the like from the nitroaniline wastewater to realize resource utilization.
Background
Nitroaniline is an important chemical raw material, is an intermediate of various printing and dyeing, pesticides and pharmaceutical chemicals, can be used for producing phenylenediamine, antioxidants, preservatives and the like, and can also be used for analytical reagents.
In the domestic nitroaniline production process, nitrochlorobenzene and ammonia water are used as raw materials and are obtained by high-temperature and high-pressure ammonolysis, the reaction is finished, the temperature is reduced, the pressure is relieved, the filtration and the separation are carried out to obtain the nitroaniline and the ammonolysis waste water, and the nitroaniline is washed by water to remove ammonium chloride, so that the washing waste water is generated. The method is characterized in that about 2-6 tons of wastewater is produced by normally producing 1 ton of nitroaniline, the wastewater is dark brown due to the existence of a small amount of tar, the TOC content of the wastewater is 2000-4000 ppm, the quantitative content of the characteristic pollutant nitrochlorobenzene is 0-0.10%, the quantitative content of the nitroaniline is 0.10-0.30%, the mass concentration of ammonium chloride is 5-20%, the mass concentration of ammonia is 1-10%, and the pH value is more than 9.
Nitroaniline is more toxic than aniline, is absorbed through the skin and respiratory tract, and is a strong methemoglobin forming agent. Cyanosis can appear in hours after absorption, hemolysis is caused, liver damage can be caused by long-term large-scale contact, and the harm to the environment is large.
The method for treating the wastewater containing nitroaniline mainly comprises an adsorption method, an oxidation-reduction method, a biological method and the like, but the method has higher cost in the practical application process and is likely to generate secondary pollution, and in order to reduce the cost, a plurality of manufacturers only carry out simple treatment on the nitroaniline wastewater, and then dilute the wastewater into a biochemical pool, so that the treatment effect is poor.
Patent CN101244878A mentions a method for treating wastewater from paranitroaniline production and recycling resources, which comprises recovering part of paranitroaniline by cooling crystallization, deaminating to recover free ammonia in water, adding hydrochloric acid to adjust acid, adsorbing paranitroaniline by activated carbon fiber, and concentrating and crystallizing the adsorbed water to obtain ammonium chloride crystal. The method has the problems that after the activated carbon fiber is adsorbed and saturated, the desorption and regeneration process is complex, and 98-99% of the recovered paranitroaniline can not meet the quality requirement of national standard GB/T4840-.
Patent CN106430398A mentions a chromatography treatment method for industrial wastewater containing paranitroaniline, which adopts a macroporous adsorption resin combined chromatography with various performances to effectively adsorb the paranitroaniline in the wastewater, so that the paranitroaniline in the wastewater is effectively removed and recovered, but does not mention the problem of whether the effluent after adsorption meets the standard or not.
Patent CN109665651A mentions a processing method of p-nitroaniline waste water, and the air blow-off treatment is carried out to p-nitroaniline waste water earlier, and the waste water after the blow-off treatment enters high-efficient catalytic oxidation device to carry out oxidation treatment, and the waste water after the oxidation further adopts coagulating sedimentation to handle, and the waste water after the processing mixes with other waste water of low COD and low salinity, gets into biochemical system again and handles, and biochemical effluent discharge up to standard after the decoloration discharges. Although the scheme realizes the standard discharge of the wastewater, the paranitroaniline and the ammonium chloride in the wastewater cannot be recovered, so that the resource waste is caused.
Patent CN109020030A mentions a process for treating wastewater in chemical production of p-nitroaniline, o-nitroaniline and corresponding anilines, which comprises a material recovery section, a wastewater acidification section, a formaldehyde condensation section, a micro-electrolysis section, an oxidation section, a neutralization section and an ammonium chloride stock solution section, wherein p-nitroaniline and ammonium chloride in the wastewater are recovered. Has the problems that secondary pollutant iron mud is generated in the micro-electrolysis and oxidation processes, and the wastewater treatment cost is increased.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a scheme for resource utilization of nitroaniline wastewater, which can effectively separate organic matters, inorganic matters and water in the wastewater through a series of treatment processes, realize the recovery of nitroaniline, ammonium chloride and ammonia in the wastewater and has wide application prospect.
The nitroaniline in the nitroaniline wastewater can be o-nitroaniline, p-nitroaniline, o-chloro-p-nitroaniline and the like.
In order to achieve the purpose, the invention takes the paranitroaniline wastewater as an example, and adopts the technical scheme that the method comprises the following steps:
1. and (3) decoloring: pumping the paranitroaniline wastewater into a decoloring kettle, adding a certain amount of active carbon, after adsorption, passing through a filter to obtain a filter cake and decoloring filtrate, treating the filter cake as solid waste, and feeding the decoloring filtrate into the next process;
2. and (3) deamination: preheating the decolorized filtrate, then feeding the preheated filtrate into a deamination tower, controlling the temperature of the deamination tower, introducing air for deamination, trapping and absorbing the gas phase at the top of the deamination tower by using RO water produced in the step 6 to obtain dilute ammonia water, discharging the ammonia out of the deamination tower when the ammonia in the water at the bottom of the deamination tower is reduced to a certain concentration, and feeding the ammonia into a neutralization process;
3. neutralizing: pumping water at the bottom of the deamination tower into a neutralization kettle for cooling, adding hydrochloric acid for neutralization, separating out a small amount of paranitroaniline in the cooling and neutralization process, filtering to obtain paranitroaniline wet base, and feeding the neutralized filtrate into an electrodialysis process;
4. electrodialysis: the neutralized filtrate and the concentrated effluent water obtained in the step 5 are respectively conveyed to a diluting chamber and a concentrating chamber of an electrodialyzer and circulated in the electrodialyzer, under the action of an electric field, ammonium chloride in the neutralized filtrate enters the concentrated effluent water through an anion-cation membrane to obtain electrodialyzed concentrated water and electrodialyzed fresh water, and the electrodialyzed concentrated water and the electrodialyzed fresh water respectively enter the next procedure;
5. concentration and crystallization: the electrodialysis concentrated water enters a concentration and crystallization device, the concentrated effluent is reused in the step 4, and the concentrated mother liquor is crystallized to obtain white ammonium chloride;
6. and (3) concentrating by using an RO membrane: and (3) the electrodialysis fresh water enters an RO membrane concentration device, RO produced water is obtained through a reverse osmosis membrane under certain pressure and is used for ammonia absorption in the step (2), and the reverse osmosis concentrated water is reused for ammonolysis filter cake washing.
In the decoloring process in the first step, the amount of the added active carbon is 0.05-0.10% of the mass percentage of the amount of the wastewater.
In the first step of the decolorization process, the activated carbon can be selected from powder and granular activated carbon.
In the first step of the decolorization process, the filtrate obtained is transparent in brown-yellow or orange-yellow appearance.
In the second step, in the deamination process, the decolored filtrate is preheated to 80-90 ℃.
In the second step, the temperature of a deamination tower is 90-95 ℃.
In the deamination process in the second step, the mass concentration of ammonia in the water in the kettle of the deamination tower is 0.0-1.0%.
In the neutralization process in the third step, the water in the kettle of the deamination tower is reduced to 20-40 ℃;
and in the neutralization process in the third step, hydrochloric acid is added into water in the kettle of the deamination tower for neutralization to adjust the pH value to be 6-7.
In the neutralization process in the third step, water in a neutralization kettle is filtered to obtain the paranitroaniline with the normalized content of more than or equal to 99.5 percent.
In the neutralization process in the third step, water in a neutralization kettle is filtered to obtain filtrate with the quantitative content of p-nitroaniline of 0-0.10%.
In the electrodialysis process in the fourth step, the mass concentration of ammonium chloride in the concentrated water is more than or equal to 20 percent, the appearance is colorless and transparent, and the TOC is less than or equal to 200 ppm.
In the fourth step, in the electrodialysis process, the mass concentration of ammonium chloride in the fresh water is 0-0.5%.
In the fifth step, in the concentration and crystallization process, the concentrated effluent is colorless and transparent, and the COD is less than or equal to 100 ppm.
In the fifth step, in the concentration and crystallization process, the mass concentration of ammonium chloride in the concentrated mother liquor is 40-60%.
In the fifth step, in the concentration and crystallization process, the content of the ammonium chloride obtained by crystallization after treatment is more than or equal to 99.0 percent.
In the sixth step, the reverse osmosis process is carried out at the operating pressure of 0.5-3.0 MPa;
in the reverse osmosis process in the sixth step, the reverse osmosis produced water is colorless and transparent, and the COD is less than or equal to 100 ppm;
in the reverse osmosis process in the sixth step, the reverse osmosis concentrated water is brown yellow or orange yellow and transparent, and the mass concentration of ammonium chloride is 0-1.0%.
Compared with the prior art, the invention has the following beneficial effects:
(1) the active carbon is used for decoloring, so that the separation and resource utilization of each component in the wastewater are facilitated;
(2) the p-nitroaniline in the wastewater can be effectively recovered, and the yield of the target product is improved;
(3) the electrodialysis process realizes the separation of ammonium chloride from organic matters in the wastewater and simultaneously concentrates the ammonium chloride, thereby avoiding the consumption of a large amount of steam by a direct concentration scheme and having low cost;
(4) the method not only realizes the recovery and resource utilization of ammonia, ammonium chloride and nitroaniline in the wastewater, but also realizes the circulation of water in an ammonolysis system, and no wastewater is discharged in the process;
(5) the method has the advantages of simple and convenient process flow, mild operation conditions, stable and reliable treatment effect, low cost, easy industrial implementation and universality in related fields.
Drawings
FIG. 1 is a flow chart of nitroaniline wastewater resource utilization.
Detailed Description
Example 1
The wastewater amount of the paranitroaniline is about 4 tons/ton paranitroaniline, the appearance is dark brown, the TOC content is 2950ppm, the paranitrochlorobenzene content is 0.02 percent, the paranitroaniline content is 0.21 percent, the mass concentration of ammonium chloride is 9.8 percent, the mass concentration of chlorine is 5.8 percent, and the pH value is more than 9.
(1) Decolorization of
Pumping the paranitroaniline wastewater into a decoloring kettle, adding powdered activated carbon accounting for 0.05 percent of the weight of the wastewater, stirring for 1 hour at the normal temperature of 25-35 ℃ after the feeding is finished, and filtering to obtain a filter cake accounting for 0.11 percent of the weight of the wastewater and decoloring filtrate. The filter cake is used as solid waste and is delivered to a professional company for treatment. The decolorized filtrate is orange yellow and transparent, the TOC content is 2773ppm, the quantitative content of p-nitrochlorobenzene is 0.02 percent, the quantitative content of p-nitroaniline is 0.20 percent, the mass concentration of ammonium chloride is 9.8 percent, the mass concentration of ammonia is 5.7 percent, and the pH value is more than 9.
(2) Deamination
Preheating the decolorized filtrate to 80-90 ℃ by a preheater, then feeding the decolorized filtrate into a deamination tower, controlling the temperature of a kettle of the deamination tower to be 90-95 ℃, introducing air, separating ammonia from wastewater in the deamination tower, absorbing the ammonia by RO (reverse osmosis) produced water in the step (6) to obtain dilute ammonia water with the mass concentration of 10.8%, introducing the dilute ammonia water to prepare concentrated ammonia water with the mass concentration of 42%, and then recycling the concentrated ammonia water for ammonolysis reaction, wherein the mass concentration of the water ammonia in the kettle of the deamination tower is 0.45%, and the pH value is more than 7.
(3) Neutralization
Pumping the deamination kettle into a neutralization kettle, cooling to 20-25 ℃, dropwise adding industrial hydrochloric acid with the mass concentration of 30% to adjust the pH value to 6-7, adjusting the acid to neutralize, wherein the chlorine mass concentration is reduced due to the temperature reduction of the wastewater, a small amount of p-nitroaniline is separated out, filtering to obtain orange-yellow p-nitroaniline wet base accounting for 0.16% of the weight of the wastewater, the normalization content of 99.90% can be combined with an ammonolysis filter cake to be treated and then sold as a p-nitroaniline finished product, the TOC content of the neutralization filtrate is 1085ppm, no p-nitrochlorobenzene is detected, the quantitative content of the p-nitroaniline is 0.07%, the mass concentration of ammonium chloride is 11.7%, and the pH value is 6-7.
(4) Electrodialysis
And (4) pumping the neutralized and filtered filtrate and the concentrated effluent water obtained in the step (5) into an electrodialysis thick chamber and a electrodialysis thin chamber respectively, and starting a circulating pump for circulating for about 0.5 h. The direct current power supply is turned on to regulate the voltage, and the electrodialyzer starts to work. When chloride ions in the fresh water at the outlet of the fresh water chamber are less than or equal to 1500ppm, closing the direct current power supply and the circulating pump to obtain electrodialysis fresh water with the TOC content of 1218ppm, the quantitative content of paranitroaniline of 0.07 percent, the mass concentration of ammonium chloride of 0.23 percent and the appearance of orange yellow; the electrodialysis concentrated water ammonium chloride has the mass concentration of 21.5 percent and the TOC content of 185ppm, and is colorless and transparent in appearance.
(5) Concentrated crystallization
Pumping the electrodialysis concentrated water into a concentration crystallization kettle, carrying out negative pressure to-0.090 MPa, heating to 55-58 ℃ to concentrate the effluent, and reusing the concentrate effluent in the step (4) after the concentrate effluent accounts for 60% of the electrodialysis concentrated water by weight, wherein the COD content of the concentrate effluent is 67ppm, the concentrate effluent is colorless and transparent, the concentrate effluent is cooled to 20-30 ℃ to obtain white ammonium chloride through crystallization, the content of the concentrate is 99.3% after drying, and the crystallization mother liquor is applied to next concentration crystallization.
(6) RO Membrane concentration
The electrodialysis fresh water enters an RO membrane concentration device, the pressure is 2.0MPa, the water produced by a reverse osmosis membrane accounts for 56.0 percent of the weight of the electrodialysis fresh water, the COD is 51ppm, ammonium chloride is not detected, paranitroaniline is not detected, the appearance is colorless and transparent, and the electrodialysis fresh water is used for preparing concentrated ammonia water by deamination absorption; the TOC content of the reverse osmosis membrane concentrated water is 2152ppm, the quantitative content of p-nitroaniline is 0.15%, the mass concentration of ammonium chloride is 0.53%, the appearance is orange yellow and transparent, and the reverse osmosis membrane concentrated water is reused for washing an ammonolysis filter cake.
Example 2
On the basis of example 1, the amount of powdered activated carbon was adjusted to 0.10% by weight of the wastewater, and the resulting filter cake accounted for 0.20% by weight of the wastewater, and the decolorized filtrate was orange-yellow and transparent in appearance, and had a TOC content of 2319ppm, a p-nitrochlorobenzene content of 0.01%, a p-nitroaniline content of 0.15%, an ammonium chloride mass concentration of 9.8%, a chlorine mass concentration of 5.7%, and a pH of > 9. After the deamination of the decolored filtrate is finished, neutralizing, cooling, filtering and recovering p-nitroaniline to be orange-yellow wet base, wherein the p-nitroaniline accounts for 0.10 percent of the weight of the wastewater, and the normalization content of 99.92 percent can be combined with an ammonolysis filter cake to be treated and then be sold as a p-nitroaniline finished product.
Example 3
On the basis of example 2, granular activated carbon with the weight of 0.10 percent of that of the wastewater is added to obtain a filter cake which accounts for 0.15 percent of the weight of the wastewater, the decolored filtrate is orange yellow and transparent, the TOC content is 2706ppm, the content of p-nitrochlorobenzene is 0.02 percent, the content of p-nitroaniline is 0.19 percent, the mass concentration of ammonium chloride is 9.8 percent, the mass concentration of chlorine is 5.7 percent, and the pH value is more than 9. After the deamination of the decolored filtrate is finished, neutralizing, cooling, filtering and recovering p-nitroaniline to be orange-yellow wet base, wherein the p-nitroaniline accounts for 0.16 percent of the weight of the wastewater, and the normalization content of 99.89 percent can be combined with an ammonolysis filter cake to be treated and then be sold as a p-nitroaniline finished product.
The specific embodiments of the present invention are merely provided to facilitate the understanding of the technical solutions of the present invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.