A method and system for treating wastewater produced during the extraction of phenolic compounds from coal tar

Abstract

This invention relates to the field of wastewater treatment technology, and particularly to a method and system for treating wastewater generated during the extraction of phenolic compounds from coal tar. The treatment method includes: mixing wastewater with stabilized gasoline, allowing it to stand and separate to obtain an upper oil phase and a lower wastewater phase; mixing the wastewater phase with a precipitant to precipitate phosphate ions in the wastewater phase, obtaining a precipitate and a supernatant; distilling the supernatant to remove ammonia, obtaining ammonia gas and deammoniated wastewater; mixing the deammoniated wastewater with an extractant for extraction, obtaining an extract phase and a raffinate phase; distilling the raffinate phase to obtain qualified biochemical treatment influent; and reusing the recovered extractant in the extraction process. This method solves the problem that treated wastewater still fails to meet biochemical treatment standards and causes secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method and system for treating wastewater generated during the extraction of phenolic compounds from coal tar. Background Technology

[0002] The wastewater generated during the extraction of phenolic compounds from coal tar mainly includes oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate, and pyridine phosphate. Currently, the main methods for treating phenol-containing wastewater include biodegradation, solvent treatment (extraction), activated carbon adsorption, and chemical oxidation. Biodegradation is primarily suitable for low-concentration phenol-containing wastewater. In high-phenol-content wastewater, phenol and its derivatives are highly toxic to microorganisms, significantly impacting their biological activity and making it difficult for microorganisms to degrade phenolic organic matter. Extraction and activated carbon adsorption are effective for treating high-phenol-content wastewater. However, extraction has high requirements for the extraction environment and process. Phenolic wastewater is generally alkaline, while extraction requires acidic conditions, necessitating a large amount of acid. Furthermore, extraction requires sufficient temperature, easily leading to secondary pollution, and the recovery of the extractant also requires high energy consumption. Activated carbon adsorption suffers from drawbacks such as easy saturation, difficult desorption, high regeneration costs, and is also prone to secondary pollution.

[0003] Industrial wastewater containing pyridine and its derivatives as primary pollutants typically contains high concentrations of salt and ammonia nitrogen. Traditional biological treatment methods require extensive dilution, usually reducing salinity to below 0.5%, leading to increased treatment volume, energy consumption, and a large footprint for the wastewater treatment system. Furthermore, traditional biological methods have low degradation efficiency for pyridine and its derivatives, contributing to environmental pollution. While distillation concentration can effectively remove salt, pyridine and its derivatives have boiling points close to water (around 115°C), resulting in significant amounts of these substances being distilled off and difficult to remove. The distillate also contains a certain concentration of ammonia nitrogen, and treating the concentrated distillate remains challenging. Moreover, this method is costing hundreds of yuan per ton of wastewater, making it unaffordable for most companies. Phosphorus removal processes in wastewater primarily include precipitation, coagulation, adsorption, ion exchange, and biological methods, but these methods also suffer from high costs. Meanwhile, there is currently no existing technology that can simultaneously remove oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate and pyridine phosphate from wastewater so that the deammoniation wastewater meets the biochemical treatment standards and avoids secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for treating wastewater generated during the extraction of phenolic compounds from coal tar. The treatment method can simultaneously remove oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate, and pyridine phosphate from the wastewater, solving the problems of foul odor, high treatment costs, failure to meet biochemical treatment standards after treatment, and secondary pollution caused by the wastewater.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for treating wastewater generated during the extraction of phenolic compounds from coal tar, comprising the following steps:

[0007] Wastewater is mixed with stabilized gasoline and then allowed to stand for separation to obtain an upper oil phase and a lower wastewater phase; the wastewater phase contains oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate and pyridine phosphate.

[0008] The wastewater phase and the precipitant are mixed to precipitate the phosphate ions in the wastewater phase, resulting in a precipitate and a supernatant.

[0009] The supernatant is distilled to remove ammonia, yielding ammonia gas and deammoniation wastewater, wherein the deammoniation wastewater includes oil, pyridine and pyridine derivatives, phenolic compounds and water;

[0010] The deammoniation wastewater and the extractant are mixed and extracted to obtain an extract phase and a raffinate phase. The extract phase contains the extractant, oil, pyridine and pyridine derivatives, and phenolic compounds.

[0011] After the raffinate is distilled, qualified biochemical treatment influent is obtained;

[0012] The qualified biochemically treated influent is then subjected to biochemical treatment.

[0013] Preferably, the pH value of the wastewater is 9-10;

[0014] The wastewater contains 150–300 g / L COD, 1–2 g / L oil, 50–80 g / L total phenols, 3.2–9.5 g / L ammonia nitrogen, and 0.5–15 g / L phosphate.

[0015] Preferably, the mass ratio of the wastewater to the stabilized gasoline is 1:(1-10);

[0016] The wastewater and stabilized gasoline are mixed at a temperature of 25–50°C and at atmospheric pressure.

[0017] Preferably, the precipitant comprises calcium hydroxide;

[0018] The mass ratio of the precipitant to the wastewater phase is (0.3-10):100.

[0019] Preferably, the precipitation temperature is 25–80°C and the pressure is 90–200 kPa;

[0020] The precipitation is carried out under stirring conditions, and the stirring speed is 500-3000 r / min.

[0021] Preferably, the deammoniation treatment is carried out in a deammoniation system;

[0022] The top temperature of the ammonia removal system is 135–150℃, and the pressure is 0.3–0.7 MPa.

[0023] The bottom temperature of the ammonia removal system is 148–160℃, and the pressure is 0.33–0.73 MPa.

[0024] The number of trays in the deammoniation system is 35 to 45, and the reflux ratio is 2 to 9.

[0025] Preferably, the extractant includes one or more of ester solvents, hydrocarbon solvents, ether solvents, and ketone solvents;

[0026] The mass ratio of the extractant to the deammoniation wastewater is 1:(1-10).

[0027] Preferably, the extraction is carried out in a distillation column, wherein the number of trays in the distillation column is 70 to 90;

[0028] The extraction temperature is 25–65°C, and the pressure is 90–350 kPa.

[0029] The present invention also provides a wastewater treatment system generated during the coal tar extraction of phenolic compounds process, comprising a mixing and clarification tank, a reaction settling tank, a deammoniation system, an extraction system, and a second distillation column connected in sequence by pipelines.

[0030] Preferably, the processing system further includes a first distillation column;

[0031] The outlet of the first distillation column is connected to the second distillation column and the extraction system via a three-way valve;

[0032] The second distillation column is reconnected to the extraction system via a pipeline.

[0033] This invention provides a method for treating wastewater generated during the extraction of phenolic compounds from coal tar, comprising the following steps: mixing wastewater with stabilized gasoline and allowing it to stand for separation to obtain an upper oil phase and a lower wastewater phase; the wastewater phase contains oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate, and pyridine phosphate; mixing the wastewater phase with a precipitant to precipitate phosphate ions in the wastewater phase to obtain a precipitate and a supernatant; distilling the supernatant to remove ammonia to obtain ammonia and deammoniation wastewater, the deammoniation wastewater comprising oil, pyridine and pyridine derivatives, phenolic compounds, and water; mixing the deammoniation wastewater with an extractant for extraction to obtain an extract phase and a raffinate phase, the extract phase containing the extractant, oil, pyridine and pyridine derivatives, and phenolic compounds; distilling the raffinate phase to obtain qualified biochemical treatment influent; and subjecting the qualified biochemical treatment influent to biochemical treatment. The treatment method described in this invention first uses inexpensive stable gasoline to extract wastewater, removing most of the oil, pyridine and pyridine derivatives and phenolic compounds from the wastewater; then, a precipitant is used to remove phosphate from the wastewater, followed by distillation to remove ammonia, and finally, an extractant is used to extract and remove the remaining oil, pyridine and pyridine derivatives and phenolic compounds to obtain qualified biochemically treated influent. Attached Figure Description

[0034] Figure 1 This invention relates to a wastewater treatment system for the process of extracting phenolic compounds from coal tar.

[0035] Among them, 1 is a mixing and clarification tank, 2 is a reaction settling tank, 3 is a deammoniation system, 4 is an extraction system, 5 is a first distillation column and 6 is a second distillation column. Detailed Implementation

[0036] This invention provides a method for treating wastewater generated during the extraction of phenolic compounds from coal tar, comprising the following steps:

[0037] Wastewater is mixed with stabilized gasoline and then allowed to stand for separation to obtain an upper oil phase and a lower wastewater phase; the wastewater phase contains oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate and pyridine phosphate.

[0038] The wastewater phase and the precipitant are mixed to precipitate the phosphate ions in the wastewater phase, resulting in a precipitate and a supernatant.

[0039] The supernatant is distilled to remove ammonia, yielding ammonia gas and deammoniation wastewater, wherein the deammoniation wastewater includes oil, pyridine and pyridine derivatives, phenolic compounds and water;

[0040] The deammoniation wastewater and the extractant are mixed and extracted to obtain an extract phase and a raffinate phase. The extract phase contains the extractant, oil, pyridine and pyridine derivatives, and phenolic compounds.

[0041] After the raffinate is distilled, qualified biochemical treatment influent is obtained;

[0042] The qualified biochemically treated influent is then subjected to biochemical treatment.

[0043] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0044] This invention involves mixing wastewater with stabilized gasoline and then allowing it to stand for separation to obtain an upper oil phase and a lower wastewater phase. The wastewater phase contains oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate, and pyridine phosphate.

[0045] In this invention, the pH value of the wastewater is preferably 9-10; the wastewater preferably comprises 150-300 g / L COD, 1-2 g / L oil, 50-80 g / L total phenols, 9.5 g / L ammonia nitrogen, and 0.5-15 g / L phosphate. In this invention, the ammonia nitrogen includes nitrogen from pyridine and pyridine derivatives and ammonium phosphate.

[0046] In this invention, the mass ratio of wastewater to stabilized gasoline is preferably 1:(1-10), more preferably 1:(2-8), and most preferably 1:(4-6).

[0047] In this invention, the mixing is preferably carried out in a mixing and clarifying tank, and the temperature inside the mixing and clarifying tank is preferably 20-50°C, more preferably 25-40°C, and most preferably 25-30°C; the pressure is preferably atmospheric pressure. This invention does not impose any special limitations on the mixing method; any method well known to those skilled in the art can be used.

[0048] The present invention does not impose any special limitations on the static separation process. It can be carried out using a process well known to those skilled in the art, as long as the generated oil phase and the lower wastewater phase are fully separated.

[0049] In this invention, the upper oil phase is preferably sent to a storage tank area as a hydrogenation feedstock or as a feedstock for the extraction of high-value products.

[0050] After obtaining the lower wastewater phase, the present invention mixes the wastewater phase with a precipitant to precipitate the phosphate ions in the wastewater phase, thereby obtaining a precipitate and a supernatant.

[0051] In this invention, the precipitant is preferably calcium hydroxide. The mass ratio of the precipitant to the phosphate ions in the wastewater phase is preferably (0.3-10):100, more preferably (2-8):100, and most preferably (4-6):100. In this invention, the function of the precipitant is to remove phosphate ions from the wastewater and generate tricalcium phosphate precipitate.

[0052] In this invention, the precipitation temperature is preferably 25–80°C, more preferably 30–60°C, and most preferably 40–50°C; the pressure is preferably 90–200 kPa, more preferably 100–160 kPa, and most preferably 120–140 kPa; the precipitation is preferably carried out under stirring conditions, and the stirring speed is preferably 500–3000 r / min, more preferably 1000–2500 r / min, and most preferably 1500–2000 r / min. In this invention, the precipitation is preferably carried out in a precipitation reaction tank.

[0053] In this invention, the supernatant obtained after precipitation is subjected to subsequent processing, and the precipitate is preferably subjected to further purification to obtain a commercially available phosphate product (for example, when the precipitant is calcium hydroxide, tricalcium phosphate can be prepared).

[0054] After obtaining the supernatant, the present invention performs ammonia removal treatment on the supernatant by distillation to obtain ammonia gas and ammonia removal wastewater, wherein the ammonia removal wastewater includes oil, pyridine and pyridine derivatives, phenolic compounds and water.

[0055] In this invention, the ammonia removal treatment is preferably carried out in an ammonia removal system; the ammonia removal system is preferably an ammonia removal tower; the top temperature of the ammonia removal tower is preferably 35-50°C, more preferably 38-46°C, and most preferably 42-43°C; the pressure is preferably 0.3-0.7 MPa, more preferably 0.4-0.6 MPa, and most preferably 0.5 MPa; the bottom temperature of the ammonia removal tower is preferably 148-160°C, more preferably 150-158°C, and most preferably 153-156°C; the pressure is preferably 0.33-0.73 MPa, more preferably 0.4-0.7 MPa, and most preferably 0.5-0.6 MPa; the number of trays in the ammonia removal tower is preferably 35-45, more preferably 38-42; the reflux ratio is preferably 2-9, more preferably 4-6.

[0056] In this invention, the ammonia gas obtained after the deammoniation treatment is used for recovery, and the deammoniation wastewater obtained after the deammoniation treatment is subjected to further subsequent treatment.

[0057] After obtaining the deammoniation wastewater, the present invention mixes the deammoniation wastewater with an extractant for extraction to obtain an extract phase and a raffinate phase. The extract phase contains an extractant, oil, pyridine and pyridine derivatives and phenolic compounds. The extractant in the extract phase is recovered by distillation.

[0058] In this invention, the extractant preferably includes one or more of esters, hydrocarbons, ethers, and ketones; the ester is preferably butyl acetate and / or dimethyl carbonate; the hydrocarbon is preferably one or more of n-hexane, cyclohexane, and toluene; the ether is preferably diisopropyl ether and / or methyl tert-amyl ether; the ketone is preferably methyl propyl copper and / or methyl isopropyl ketone; more preferably dimethyl carbonate; when the extractant is two or more of the above-mentioned specific selections, this invention does not have any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

[0059] In this invention, the mass ratio of the extractant to the deammoniation wastewater is preferably 1:(1-10), more preferably 1:(2-8), and most preferably 1:(4-6).

[0060] In this invention, the extraction is preferably carried out in a distillation column, the number of trays of which is preferably 70-90, more preferably 75-85, and most preferably 78-82; the extraction temperature is preferably 25-65℃, more preferably 30-60℃, and most preferably 40-50℃; the pressure is preferably 90-350 kPa, more preferably 150-300 kPa, and most preferably 200-250 kPa.

[0061] In this invention, the extraction is used to remove residual oil, pyridine and pyridine derivatives and phenolic compounds from the wastewater.

[0062] After obtaining the raffinate phase, the present invention preferably recovers the extractant in the raffinate phase by distillation and reuses the recovered extractant in the extraction process; after distilling the raffinate phase, qualified biochemical treatment influent is obtained.

[0063] In this invention, the process of recovering the extractant from the extract phase by distillation is preferably carried out in a distillation column, wherein the top temperature of the distillation column is preferably 75-105°C, more preferably 80-100°C, and most preferably 85-95°C; and the bottom temperature is preferably 145-215°C, more preferably 160-200°C, and most preferably 170-180°C.

[0064] In this invention, the distillation process of the extract phase is preferably carried out in a distillation column, wherein the top temperature of the distillation column is preferably 75-105°C, more preferably 80-100°C, and most preferably 85-95°C; and the bottom temperature is preferably 85-110°C, more preferably 90-105°C, and most preferably 95-100°C.

[0065] In this invention, the raffinate phase is distilled to obtain qualified biochemical treatment influent.

[0066] After obtaining qualified biochemically treated influent, the present invention performs biochemical treatment on the qualified biochemically treated influent.

[0067] The present invention does not impose any special limitations on the biochemical treatment process; any process well known to those skilled in the art can be used.

[0068] The present invention also provides a wastewater treatment system generated during the coal tar extraction of phenolic compounds process, comprising a mixing and clarification tank, a reaction settling tank, a deammoniation system, an extraction system, and a second distillation column connected in sequence by pipelines.

[0069] As an embodiment of the present invention, the extraction system is specifically an extraction tower;

[0070] As an embodiment of the present invention, the processing system further includes a first distillation column;

[0071] The outlet of the first distillation column is connected to the second distillation column and the extraction system via a three-way valve;

[0072] The second distillation column is reconnected to the extraction system via a pipeline.

[0073] In this invention, the preferred method of using the treatment system is as follows: wastewater and stabilized gasoline are mixed in a mixing and clarification tank, then allowed to stand for separation. The upper oil phase is separated and used as a hydrogenation feedstock. The lower wastewater phase is transported to a reaction settling tank while the precipitant is added to the reaction settling tank for precipitation, resulting in precipitate and supernatant. The precipitate is further purified to recover phosphate products. The supernatant is transported to a deammoniation system for deammoniation, resulting in ammonia and deammoniation wastewater. The ammonia is recovered. The deammoniation wastewater is transported to an extraction system while an extractant is added for extraction, resulting in an extract phase and raffinate phase. The extract phase is transported to a first distillation column for distillation to recover the extractant and high-value recoverables, including oil, pyridine and pyridine derivatives, and phenolic compounds. The recovered extract phase is reused in the extraction process, and the high-value recoverables are used for further production of fine products. The raffinate phase is transported to the first distillation column for distillation to obtain the extractant and qualified biochemical wastewater.

[0074] The following detailed description, in conjunction with embodiments, of the wastewater treatment method and system generated during the extraction of phenolic compounds from coal tar provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0075] Example 1

[0076] Wastewater generated during the extraction of phenolic compounds from coal tar has the following characteristics: pH 9, COD 186 g / L, oil 2.35 g / L, total phenols 64 g / L, ammonia nitrogen 9.5 g / L, and phosphate 9.6 g / L.

[0077] The wastewater treatment system includes a mixing and clarification tank, a reaction settling tank, a deammoniation tower, an extraction tower, a first distillation tower, a second distillation tower, and a biochemical treatment device connected in sequence by pipelines; the top outlet of the extraction tower is connected to the first distillation tower by a pipeline; the bottom outlet of the extraction tower is connected to the second distillation tower by a pipeline, and the second distillation tower is connected back to the extraction system by a pipeline;

[0078] Wastewater treatment methods:

[0079] 1 kg of wastewater and 3 kg of stabilized gasoline were mixed in a mixing and clarifying tank (temperature 25℃, pressure atmospheric pressure), and then allowed to stand for 30 min. The upper oil phase was separated and used as a hydrogenation feedstock. The resulting lower wastewater phase was transferred to a reaction settling tank, and 12 g of calcium hydroxide was added to the tank for precipitation (temperature 40℃, pressure 110 kPa, stirring speed 1500 r / min), yielding precipitate and a supernatant. The precipitate was further purified to recover tricalcium phosphate. The supernatant was then transferred to a deammoniation tower for deammoniation (top temperature 43℃, pressure 0.45 MPa; bottom temperature 152℃, pressure 0.45 MPa; number of trays in the deammoniation tower 38; reflux ratio 5), yielding ammonia and feed to the extraction tower. The ammonia was recovered. The deammoniation wastewater was then processed at a 5:1 mass ratio. Water is fed into the extraction tower while dimethyl carbonate extractant is added for extraction (extraction temperature is 30°C, pressure is atmospheric pressure, and the number of trays in the extraction tower is 75) to obtain the extract phase and the raffinate phase. The extract phase is then fed into a first distillation tower for distillation recovery (top temperature is 79°C, bottom temperature is 145°C) of the extractant and high-value recoverables, including: oil, pyridine and pyridine derivatives, and phenolic compounds. The recovered extractant is reused in the extraction process, and the high-value recoverables are used for further production of fine products. The raffinate phase is then fed into the first distillation tower for distillation (top temperature is 79°C, bottom temperature is 105°C) to obtain the extractant and qualified biochemical wastewater (pH value is 7.5, COD content is 3.5 g / L, oil content is 0.082 g / L, total phenol content is 0.5 g / L, ammonia nitrogen content is 0.038 g / L, and phosphate content is 0.0105 g / L).

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating wastewater generated during the extraction of phenolic compounds from coal tar, characterized in that, Includes the following steps: Wastewater is mixed with stabilized gasoline and then allowed to stand for separation to obtain an upper oil phase and a lower wastewater phase; the wastewater phase contains oil, pyridine and pyridine derivatives, phenolic compounds, ammonium phosphate and pyridine phosphate. The wastewater phase and the precipitant are mixed to precipitate the phosphate ions in the wastewater phase, resulting in a precipitate and a supernatant. The supernatant is distilled to remove ammonia, yielding ammonia gas and deammoniation wastewater, wherein the deammoniation wastewater includes oil, pyridine and pyridine derivatives, phenolic compounds and water; The deammoniation wastewater and the extractant are mixed and extracted to obtain an extract phase and a raffinate phase. The extract phase contains the extractant, oil, pyridine and pyridine derivatives, and phenolic compounds. The raffinate phase is then subjected to distillation to obtain qualified biochemical treatment influent; The qualified biochemically treated influent is then subjected to biochemical treatment. The pH value of the wastewater is 9-10; The wastewater contains 150-300 g / L COD, 1-2 g / L oil, 50-80 g / L total phenols, 9.5 g / L ammonia nitrogen, and 0.5-15 g / L phosphate, wherein the ammonia nitrogen includes nitrogen from pyridine and pyridine derivatives and ammonium phosphate. The extractant includes one or more of ester solvents, hydrocarbon solvents, ether solvents, and ketone solvents; The deammoniation treatment is carried out in the deammoniation system; The top temperature of the ammonia removal system is 135~150℃, and the pressure is 0.3~0.7MPa; The bottom temperature of the ammonia removal system is 148~160℃, and the pressure is 0.33~0.73MPa; The number of trays in the deammoniation system is 35-45, and the reflux ratio is 2-9.

2. The processing method as described in claim 1, characterized in that, The mass ratio of the wastewater to the stabilized gasoline is 1:(1~10). The wastewater and stabilized gasoline are mixed at a temperature of 25-50°C and a pressure of atmospheric pressure.

3. The processing method as described in claim 1, characterized in that, The precipitant includes calcium hydroxide; The mass ratio of the precipitant to the wastewater phase is (0.3~10):

100.

4. The processing method as described in claim 1 or 3, characterized in that, The precipitation temperature is 25~80℃, and the pressure is 90~200kPa; The precipitation is carried out under stirring conditions, and the stirring speed is 500~3000 r / min.

5. The processing method as described in claim 1, characterized in that, The mass ratio of the extractant to the deammoniation wastewater is 1:(1~10).

6. The processing method as described in claim 1 or 5, characterized in that, The extraction is carried out in a distillation column with 70 to 90 trays. The extraction temperature is 25~65℃ and the pressure is 90~350kPa.

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