Wastewater treatment method for co-oxidation method epoxypropane device

Abstract

The invention provides a wastewater treatment method for a co-oxidation method epoxypropane device. The wastewater treatment method comprises the following steps: S1, feeding wastewater into a peroxide decomposer, and decomposing under alkaline and high-temperature conditions to remove peroxides; s2, feeding the treated wastewater into an extraction unit, and extracting alcohol ketone in the wastewater by taking aromatic hydrocarbon as an extraction agent; s3, feeding the treated wastewater into a steam stripping tower, and introducing water vapor from the tower bottom of the steam stripping tower; s4, performing concentration treatment on organic acid sodium salt in the treated wastewater obtained at the tower bottom of the steam stripping tower by a multiple-effect evaporation unit, and reducing COD (Chemical Oxygen Demand) of the wastewater of the POSM device or the CHPPO device to 1t from-200000 mg / L through a combined process of peroxide decomposition, aromatic hydrocarbon extraction, steam stripping and multiple-effect evaporation; and the concentration is 1000 mg / L.

Description

A wastewater treatment method for a co-oxidation propylene oxide plant Technical Field

[0001] This invention relates to the field of wastewater treatment technology for co-oxidation propylene oxide plants. Specifically, it is a stepwise treatment method for the main organic compounds in wastewater from propylene oxide / styrene (POSM) plants and cumene-based propylene oxide (CHPPO) plants: alcohols and ketones (phenylethanol, acetophenone, benzyl alcohol, dimethyl benzyl alcohol, etc.), aromatics (ethylbenzene, cumene, etc.), and sodium salts of organic acids (sodium benzoate, sodium acetate, sodium formate, etc.). Through combined processes, it achieves efficient reduction of COD in wastewater, enabling the treated wastewater to meet suitable standards for biochemical treatment. Background Technology

[0002] The co-oxidation process for propylene oxide has been successfully industrialized in China, primarily through propylene oxide / styrene units (POSM units) and cumene-based propylene oxide units (CHPPO units).

[0003] POSM units generate large amounts of wastewater containing soluble organic matter during production. The main pollutants include phenylethanol (α-phenylethanol, β-phenylethanol), acetophenone, benzyl alcohol, ethylbenzene, sodium benzoate, sodium acetate, and sodium formate. CHPPO units are similar to POSM units, also generating large amounts of wastewater containing soluble organic matter during production. The main pollutants include dimethylbenzyl alcohol, acetophenone, ethylbenzene, sodium benzoate, sodium phenolate, sodium acetate, and sodium formate. This type of wastewater has a very high COD (actually measured to exceed 200,000 mg / L; without considering sodium organic acid salts, the COD is 10,000-20,000 mg / L). Direct discharge or direct entry into conventional biological treatment systems would severely exceed the treatment capacity, leading to environmental pollution or system failure.

[0004] Currently, the co-oxidation propylene oxide industry has proposed many treatment solutions for wastewater from POSM and CHPPO units. These include wet catalytic oxidation (CN112624300, CN112624300, CN113003847) and electrolytic treatment (CN119912125, CN209797659U). However, these methods have not achieved widespread application due to high energy consumption or difficulty in industrialization. Additionally, some patents have attempted to directly employ anaerobic biological treatment methods (CN104773928, CN110891904), but direct biological treatment is very difficult due to the high salt, high COD, and high peroxide content in the wastewater from co-oxidation propylene oxide units.

[0005] Wanhua's patent CN114762827 and Jiangsu Hongwei Chemical's patent CN119771302 describe catalysts or methods for removing peroxides from wastewater from propylene oxide plants, but this is only a necessary step in the treatment of this wastewater.

[0006] In summary, current treatment schemes for wastewater from co-oxidation propylene oxide plants lack a comprehensive approach tailored to the characteristics of the organic matter in the wastewater, resulting in the following shortcomings: 1. Because phenylethanol, acetophenone, benzyl alcohol, dimethyl benzyl alcohol, and other compounds form an azeotropic reaction with water, and the azeotropic temperature differs from the boiling point of water by less than 1°C, conventional single-stage stripping processes cannot remove alcohols and ketones from the wastewater. This leads to high alcohol and ketone content and high COD in the effluent, failing to meet the requirements for biochemical treatment. 2. While extraction can partially remove alcohols and ketones, single-stage extraction still cannot achieve ideal removal results and easily leads to secondary residues of ethylbenzene in the wastewater. 3. While multi-effect evaporation can remove sodium organic acid salts from the wastewater, it is ineffective in removing ethylbenzene and alcohols and ketones, resulting in COD exceeding standards in the final wastewater, making it difficult to meet the influent requirements for biochemical treatment.

[0007] Therefore, developing a combined treatment method that can efficiently remove the main pollutants in the wastewater from the co-oxidation propylene oxide unit in stages has become the key to solving the wastewater treatment problem of the POSM unit. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing co-oxidation propylene oxide plants, especially POSM and CHPPO plants, in wastewater treatment technologies, which suffer from low organic matter removal efficiency and incomplete COD reduction. This invention provides a stepwise treatment method based on pollutant properties. Through a combined process of "peroxide decomposition - aromatic hydrocarbon extraction - steam stripping - multi-effect evaporation," alcohols and ketones (phenylethanol, acetophenone, benzyl alcohol, dimethyl benzyl alcohol), aromatic hydrocarbons (ethylbenzene, isopropylbenzene), and sodium salts of organic acids (sodium benzoate, sodium phenolate, sodium formate, sodium acetate) are sequentially removed from the wastewater, resulting in a significant reduction in COD. The treated wastewater has a COD ≤ 1000 mg / L, making it suitable for subsequent biochemical treatment.

[0009] To achieve the above objectives, in a first aspect, this application provides a wastewater treatment method for a co-oxidation propylene oxide plant, comprising the following steps: S1, sending the wastewater generated from the co-oxidation propylene oxide plant into a peroxide decomposer for decomposition and removal of peroxides under alkaline and high-temperature conditions, wherein the pH value of the alkaline liquid in the decomposer is 10-14, preferably 12-13.5, and the temperature inside the decomposer is 100℃-240℃, preferably 160℃-180℃. In this step, a removal rate of >95% for organic peroxides can be achieved, and the content of organic peroxides in the treated wastewater is generally <10ppm; S2, sending the wastewater treated in step S1 into an extraction unit, using aromatics as the extractant to extract alcohols and ketones from the wastewater, wherein the volume ratio of extractant to wastewater is 0.05-10, preferably 0.1-1, and the oil phase containing alcohols and ketones generated after extraction is sent to a POSM unit or a CHPPO unit production system for recycling; S3, sending the wastewater treated in step S1 into an extraction unit for further processing. The wastewater treated in step S2 is fed into a steam stripping tower. Steam is introduced from the bottom of the tower, and the gas phase generated at the top of the tower is condensed and separated. The oil phase is returned to the POSM or CHPPO production system for recycling, while the water phase is returned to the top of the tower. This step can achieve a removal rate of ethylbenzene or cumene of >99%, and the aromatic hydrocarbon (ethylbenzene or cumene) content in the treated wastewater is generally <1ppm. In step S4, the wastewater obtained from the bottom of the steam stripping tower after step S3 is concentrated by a multi-effect evaporation unit. The gas phase distilled from the multi-effect evaporation unit is condensed and cooled to obtain wastewater for biochemical treatment. The concentrated water after multi-effect evaporation is crystallized or incinerated. This step can achieve a removal rate of ≥99% for organic acid sodium salts. The COD of the treated wastewater is reduced to <1000mg / L, meeting the requirements for biochemical treatment influent.

[0010] Optionally, the alkaline liquid in step S1 is an aqueous solution of NaOH.

[0011] Optionally, in step S1, the wastewater stays in the decomposer for >0.5h, preferably >1h.

[0012] Optionally, in step S2, ethylbenzene is used as the extractant when treating the wastewater from the POSM unit, and cumene is used as the extractant when treating the wastewater from the CHPPO unit.

[0013] Optionally, in step S2, the extraction process adopts multi-stage extraction, with a theoretical extraction stage of 2 to 10 stages, preferably 3 to 5 stages, and an extraction temperature of 40 to 60°C, preferably 40 to 45°C.

[0014] Optionally, in step S2, the extraction unit uses one of the following extraction devices: a vertical extraction tower, a static sieve plate tower, or other extraction towers with kinetic energy input.

[0015] Optionally, in step S2, the extraction process also includes oil-water separation after multi-stage extraction.

[0016] Optionally, in step S2, each stage of the multi-stage extraction uses fresh extractant or the extractant is extracted in a multi-stage countercurrent manner.

[0017] Optionally, in step S3, the bottom of the steam stripping tower is fed with steam from outside the tower by direct supplementation or by setting up a reboiler in the tower bottom to heat the wastewater in the tower bottom through a heat source.

[0018] Optionally, in step S3, the operating pressure of the steam stripping tower is 10~200 kPaA, preferably 20~60 kPaA.

[0019] Optionally, in step S4, the number of effects of the multi-effect evaporation unit is 2 to 6, preferably 3, which usually depends on the balance between equipment investment and heat source consumption.

[0020] Optionally, in step S4, the multi-effect evaporation unit is one of the tower-type multi-effect evaporator or the split-type multi-effect evaporator disclosed in patent CN214105842U.

[0021] Optionally, in step S4, the wastewater concentration ratio of the multi-effect evaporation unit is 2 to 20 times, preferably 3 to 10 times.

[0022] This invention provides a wastewater treatment method for a co-oxidation propylene oxide plant. Compared with existing technologies, its advantages are as follows: 1. Highly targeted and thorough pollutant removal: This invention designs step-by-step treatment steps targeting the different physicochemical properties of organic peroxides, alcohols and ketones (phenylethanol, acetophenone, benzyl alcohol, dimethyl benzyl alcohol), aromatics (ethylbenzene, isopropylbenzene), and sodium salts of organic acids (sodium benzoate, sodium phenolate, sodium acetate, sodium formate). In the removal of organic peroxides, an alkaline and high-temperature environment is used for decomposition. Under these high-temperature conditions, not only can organic peroxides be removed more thoroughly, but the content of polar components can also be significantly reduced, lowering the load on subsequent extraction operations, reducing the amount of aromatic extractant used, and decreasing the aromatic content in the aqueous phase after extraction. This provides better operating conditions for subsequent stripping operations, thereby achieving a removal rate of ≥90~99% for each pollutant and avoiding blind spots in the removal of specific pollutants by a single process; 2. Significant COD reduction effect: This invention achieves significant COD reduction through "peroxide decomposition-aromatics..." The combined process of "hydrocarbon extraction-steam stripping-multi-effect evaporation" can reduce the COD of wastewater from POSM or CHPPO units from an initial level of ~200,000 mg / L to <1,000 mg / L, achieving a COD reduction rate of 99%-99.5%. 3. It combines resource recovery and environmental protection: In this invention, the decomposition of organic peroxides in the wastewater not only removes biochemical toxins but also allows some of the generated alcohols and ketones to be recovered in the subsequent aromatic hydrocarbon extraction process. The aromatic hydrocarbon extraction process not only removes alcohols and ketones from the wastewater, reducing COD, but also recovers these alcohols and ketones for return to the propylene oxide unit, reducing material consumption. The aromatics distilled during the stripping process can also be effectively utilized, while the stripping process itself reduces COD in the wastewater. The concentrated water obtained from multi-effect evaporation can be further treated; whether crystallization or incineration is used, there will be no secondary pollutant emissions. 4. It has strong process compatibility: The method of this invention can be used in POSM and CHPPO units. It can also be used for other similar wastewater (such as wastewater from phenol-acetone units), making it easy to promote industrial application. Attached Figure Description

[0023] Figure 1 is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0026] As shown in Figure 1, a wastewater treatment method for a co-oxidation propylene oxide plant according to the present invention includes the following steps: Step 1: Decomposition of organic peroxides. Wastewater S1 (containing organic peroxides, alcohols, ketones, aromatics, and sodium salts of organic acids) generated from the co-oxidation propylene oxide plant is fed into a peroxide decomposer. The peroxides are decomposed and removed under alkaline and high-temperature conditions within the decomposer. Wastewater S2, after the peroxides are removed, flows out from the decomposer.

[0027] A NaOH aqueous solution is injected into the decomposer to maintain a pH value of 10-14, preferably 12-13.5.

[0028] The temperature in the decomposer is 100℃~240℃, preferably 160℃~180℃.

[0029] The residence time in the decomposer of wastewater is >0.5h, preferably >1h.

[0030] This step can achieve a removal rate of over 95% for organic peroxides, and the content of organic peroxides in the treated wastewater is generally <10 ppm.

[0031] Step 2: Multi-stage extraction of aromatics (ethylbenzene or cumene) to remove alcohols and ketones (phenylethanol, acetophenone, benzyl alcohol, dimethylbenzyl alcohol). The wastewater S2 from Step 1 is fed into the extraction unit, using aromatics S3 as the extractant (ethylbenzene in the POSM unit and cumene in the CHPPO unit) to extract the alcohols and ketones from the wastewater, removing them from the water. The resulting oil phase S4 containing alcohols and ketones can be returned to the POSM or CHPPO unit production system for recycling, avoiding secondary pollution.

[0032] The theoretical extraction stages are 2 to 10, with 3 to 5 being preferred.

[0033] The extraction temperature is 40~60℃, preferably 40~45℃; the volume ratio of extractant to wastewater is 0.05~10, preferably 0.1~1; the extraction equipment can be a vertical extraction tower, which can be a static sieve plate tower or an extraction tower with other kinetic energy input.

[0034] The extraction process can also employ a multi-stage extraction + oil-water separation process, such as a static mixer + oil-water separator, or a stirred extraction tank + oil-water separator.

[0035] In multi-stage extraction, fresh extractant can be used in each stage, or a multi-stage countercurrent method can be used.

[0036] Step 3: Steam stripping to remove aromatics (ethylbenzene or cumene). The wastewater S5 from Step 2 is fed into a steam stripping tower. Steam is introduced at the bottom of the tower to evaporate the lighter azeotropic components (ethylbenzene / water, or cumene / water) from the wastewater to the top of the tower. The bottom of the tower yields an aqueous phase S7 containing only sodium organic acid salts. The organic matter and water at the top of the stripping tower are condensed and separated to remove the upper oil phase. The aqueous phase is then returned to the top of the stripping tower. The oil phase S6 at the top of the stripping tower is returned to the POSM or CHPPO production system for recycling.

[0037] The steam at the bottom of the stripping tower can be directly supplied by external steam, or a reboiler can be installed in the tower bottom to heat the wastewater in the tower bottom to generate steam.

[0038] The operating pressure of the stripping tower is 10~200 kPaA, preferably 20~60 kPaA.

[0039] This step can achieve a removal rate of over 99% for ethylbenzene or cumene, and the content of aromatic hydrocarbons (ethylbenzene or cumene) in the treated wastewater is generally <1 ppm.

[0040] Step 4: Multi-effect evaporation to remove sodium organic acids. The wastewater S7 treated in Step 3 is sent to a multi-effect evaporation unit to concentrate the sodium organic acids in the wastewater. The evaporated gas phase is condensed and cooled to obtain wastewater S8 with COD ≤ 1000 mg / L, which can be sent to a biochemical treatment plant for further treatment. The concentrated wastewater S9 after multi-effect evaporation can be further crystallized or directly sent to an incinerator for incineration.

[0041] The number of effects in a multi-effect evaporation unit is 2 to 6, preferably 3, which usually depends on the balance between equipment investment and heat source consumption.

[0042] The multi-effect evaporator can be the tower-type multi-effect evaporator disclosed in patent CN214105842U, or it can be a split-type multi-effect evaporator.

[0043] The wastewater concentration ratio of multi-effect evaporation is 2 to 20 times, preferably 3 to 10 times.

[0044] This step can achieve a removal rate of ≥99% for sodium organic acids, and the COD of the wastewater after final treatment is reduced to <1000mg / L, meeting the requirements for influent in biological treatment.

[0045] Based on the physicochemical properties of the main pollutants in the wastewater from the POSM and CHPPO units, the technical principle of this invention is explained: Organic peroxides: Ethylbenzene hydrogen peroxide and cumene hydrogen peroxide are organic peroxides present in the wastewater from the POSM and CHPPO units, respectively. These peroxides, when entering the biological system, cause poisoning and death of microorganisms, and therefore must be removed. The treatment method involves high-temperature decomposition under alkaline conditions to remove the organic peroxides from the wastewater.

[0046] Phenylacetyl alcohol / acetophenone / benzyl alcohol: These are the main organic solubles in the POSM unit wastewater. They azeotropically react with water, but the azeotropic temperature is between 99 and 100°C, making them difficult to separate from water by distillation. Compared to water, phenylacetyl alcohol / acetophenone / benzyl alcohol is miscible with ethylbenzene. Therefore, ethylbenzene can be used as an extractant to separate phenylacetyl alcohol / acetophenone from water through a multi-stage extraction method. Dimethylbenzyl alcohol: This is also the main organic soluble in the CHPPO unit wastewater. Similar to the solubility properties of phenylacetyl alcohol / acetophenone / benzyl alcohol, it can also be extracted from the wastewater using aromatic hydrocarbons. Since the main aromatic stream in the CHPPO unit is cumene, cumene can be used as an extractant to separate dimethylbenzyl alcohol from water through a multi-stage extraction method. Ethylbenzene / cumene: Ethylbenzene forms an azeotropic system with water (azeotropic temperature 87.7℃, azeotropic composition ethylbenzene / water = 66 / 34), which can be separated from water by distillation, removing residual ethylbenzene from the water. Similarly, cumene forms an azeotropic system with water (azeotropic temperature 95℃, azeotropic composition isocumene / water = 56 / 44), which can also be separated from water by distillation, removing residual cumene from the water. Sodium organic acids: mainly sodium benzoate, sodium phenolate, sodium formate, and sodium acetate. These sodium salts are miscible with water and have extremely low vapor pressure in the gas phase during evaporation. Therefore, the concentration and separation effect of multi-effect evaporation can be used to retain the sodium organic acids as concentrated water, while the dilute water meets the low COD standard.

[0047] Example 1: Wastewater treatment for POSM unit The main organic matter content of the wastewater from the 270,000 / 600,000 tons / year POSM unit is as follows: ethylbenzene hydrogen peroxide 0.03%, α-phenylethanol 0.2%, β-phenylethanol 0.06%, benzyl alcohol 0.17%, ethylbenzene 0.01%, sodium organic acid salt (calculated as sodium benzoate) 5%, total COD ~200,000 mg / L.

[0048] Treatment process: Peroxide decomposition: Wastewater is fed into a peroxide decomposer, and a 30% NaOH aqueous solution is injected to control the pH value in the decomposer at ~13. The peroxide decomposer is heated to 160℃, and the wastewater retention time is 60 minutes. After decomposition, the ethylbenzene hydrogen peroxide content in the wastewater is 10 ppm, with a removal rate of ~97%.

[0049] Aromatic Extraction: Wastewater treated to remove ethylbenzene and hydrogen peroxide is fed into the aromatic extraction unit. Ethylbenzene is used as the extractant, with a volume ratio of extractant to wastewater of 0.2:1. Three-stage extraction is performed at 40℃ using a static mixer and an oil-water separator. The extraction process is a three-stage countercurrent extraction. The extracted oil is returned to the oxidation unit of the POSM unit. After extraction, the levels of phenylethanol and benzyl alcohol in the wastewater are significantly reduced: α-phenylethanol, 0.025%, β-phenylethanol, 0.008%, and benzyl alcohol, 0.058%, with a total removal rate of approximately 80%. Steam Stripping: The extracted wastewater is fed to the top of a steam stripping tower. Steam from the bottom of the tower enters from the bottom, with a supply rate of 1-2 t / h. The tower pressure is controlled at 35 kPaA, and there are 25 trays. Wastewater entering the stripping tower flows out of the tower bottom. After stripping, the ethylbenzene content in the wastewater is <1ppm, with a removal rate >99%. Multi-effect evaporation: The stripped wastewater is sent to the first effect of a triple-effect evaporator. The wastewater concentrated in the first effect enters the second effect, where the secondary steam generated continues to heat the wastewater. The wastewater concentrated in the second effect enters the third effect, where the secondary steam generated continues to heat the wastewater. The operating temperatures of the first, second, and third effects are 85℃, 72℃, and 58℃, respectively. After triple-effect evaporation, the removal rate of sodium organic acids is >99%.

[0050] Treatment Results: After treatment of the wastewater from the POSM unit, the removal rates of various pollutants were as follows: ethylbenzene and hydrogen peroxide: 97%; α-phenylethanol + β-phenylethanol + benzyl alcohol: 80%; ethylbenzene: 99%; sodium organic acid salts: 99%. The composition of each pollutant was: ethylbenzene and hydrogen peroxide ~10ppm, α-phenylethanol 0.025%, β-phenylethanol 0.008%, benzyl alcohol 0.058%, ethylbenzene 0.0001%, sodium organic acid salts (calculated as sodium benzoate) <0.001%. The final COD of the wastewater was reduced to ~2000mg / L, meeting the requirements of biological treatment.

[0051] Example 2: Same as Example 1, but the ethylbenzene / water ratio in the first step of aromatic extraction was increased to 1:1, while other steps remained unchanged. After the first step was completed, the total removal rate of α-phenylethanol + β-phenylethanol + benzyl alcohol was increased to ~91%, and the COD of the treated wastewater was ~1100ppm.

[0052] Example 3: Same as Example 1, except that the equipment in the first step of aromatic extraction is replaced with a vertical static sieve plate tower with 50 trays and a theoretical number of stages (~6 stages), while other aspects remain unchanged. In the wastewater treatment extraction step, the total removal rate of α-phenylethanol + β-phenylethanol + benzyl alcohol is increased to ~92%, and the COD of the final treated wastewater is <1000ppm.

[0053] Example 4: Wastewater Treatment from a 100,000-ton / year CHPPO unit. The main organic compounds in the wastewater were: cumene hydrogen peroxide 0.028%, dimethyl benzyl alcohol 0.25%, acetophenone 0.05%, cumene 0.01%, and sodium organic acid salts (calculated as sodium benzoate) 5%. Treatment process: Peroxide decomposition: The wastewater was fed into a peroxide decomposer, and a 30% NaOH aqueous solution was injected to control the pH value in the decomposer at ~13. The peroxide decomposer was heated to 160℃, and the wastewater retention time was 90 minutes. After decomposition, the cumene hydrogen peroxide content in the wastewater was ~12 ppm, with a removal rate of ~96%.

[0054] Aromatic Extraction: Wastewater treated to remove peroxides is fed into the aromatic extraction unit, using cumene as the extractant at a volume ratio of 0.2:1 (extractant to wastewater). Three-stage extraction is performed at 40°C using a static mixer and an oil-water separator. The extraction process employs a vertical static extraction tower with 50 trays (approximately 6 theoretical stages). Cumene enters from the bottom of the tower and undergoes mass transfer with the wastewater flowing in from the top. The extracted oil is collected from the top and returned to the CHPPO unit for further recycling. The levels of dimethylbenzyl alcohol and acetophenone in the wastewater flowing from the bottom of the tower are significantly reduced: dimethylbenzyl alcohol to 0.02%, and acetophenone to 0.005%, resulting in a total removal rate of approximately 93%. Steam Stripping: The extracted wastewater is fed to the top of a steam stripping tower. Steam enters from the bottom of the tower at a supply rate of approximately 1.5 t / h, with the tower pressure controlled at 35 kPaA. The tower has 40 trays. Wastewater entering the stripping tower flows out of the tower bottom. After stripping, the cumene content in the wastewater is <1ppm, with a removal rate >99%. Multi-effect evaporation: The stripped wastewater is sent to the first effect of a triple-effect evaporator. The wastewater concentrated in the first effect enters the second effect, where the secondary steam generated continues to heat the wastewater. The wastewater concentrated in the second effect enters the third effect, where the secondary steam generated continues to heat the wastewater. The operating temperatures of the first, second, and third effects are 85℃, 72℃, and 58℃, respectively. After triple-effect evaporation, the removal rate of sodium organic acids is >99%.

[0055] Treatment Results: After treatment, the wastewater discharged from the CHPPO unit achieved the following removal rates for each pollutant: xylenebenzyl alcohol + acetophenone: 92%, cumene: 99%, and sodium organic acid salts: 99%. The composition of each pollutant was as follows: xylenebenzyl alcohol reduced to 0.02%, acetophenone: 0.005%, cumene: 0.0001%, and sodium organic acid salts (calculated as sodium benzoate) <0.001%. The final wastewater COD was <1000 mg / L, meeting the requirements for biological treatment.

[0056] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A wastewater treatment method for a co-oxidation propylene oxide plant, characterized in that, Includes the following steps: S1. Wastewater from the co-oxidation propylene oxide unit is fed into a peroxide decomposer to decompose and remove peroxides under alkaline and high-temperature conditions. The alkaline liquid in the decomposer has a pH of 10-14, and the temperature inside the decomposer is 100℃-240℃. S2. Wastewater treated in step S1 is fed into an extraction unit to extract alcohols and ketones from the wastewater using aromatics as the extractant. The volume ratio of extractant to wastewater is 0.05-10. The oil phase containing alcohols and ketones produced after extraction is sent to the POSM unit or CHPPO unit production system for recycling. S3. Wastewater treated in step S2 is fed into a steam stripping tower. Steam is introduced from the bottom of the steam stripping tower. The gas phase generated at the top of the steam stripping tower is condensed and separated. The oil phase is returned to the POSM unit or CHPPO unit production system for recycling, and the aqueous phase is returned to the top of the steam stripping tower. S4. The wastewater obtained from the bottom of the steam stripping tower after step S3 is concentrated by the multi-effect evaporation unit. The wastewater obtained after condensing and cooling the gas phase distilled by the multi-effect evaporation unit is then subjected to biochemical treatment. The concentrated water obtained after the multi-effect evaporation unit is then subjected to crystallization treatment or incineration treatment.

2. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: The alkaline liquid in step S1 is an aqueous solution of NaOH.

3. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S1, the wastewater stays in the decomposer for >0.5h.

4. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S2, ethylbenzene is used as the extractant for treating the wastewater from the POSM unit, and cumene is used as the extractant for treating the wastewater from the CHPPO unit.

5. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S2, the extraction process adopts multi-stage extraction, with a theoretical extraction stage of 2 to 10 stages and an extraction temperature of 40 to 60°C.

6. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S2, the extraction unit uses one of the following extraction devices: a vertical extraction tower, a static sieve plate tower, or an extraction tower with other kinetic energy input.

7. A wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 5, characterized in that: In step S2, the extraction process also includes oil-water separation after multi-stage extraction.

8. A wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 5, characterized in that: In step S2, each stage of the multi-stage extraction uses fresh extractant or the extractant is extracted in a multi-stage countercurrent manner.

9. A wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S3, steam is introduced into the bottom of the steam stripping tower by either directly supplementing it with external steam or by installing a reboiler in the tower bottom to heat the wastewater in the tower bottom through a heat source.

10. A wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S3, the operating pressure of the steam stripping tower is 10~200 kPaA.

11. A wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S4, the number of effects in the multi-effect evaporation unit is 2 to 6.

12. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S4, the multi-effect evaporation unit is either a tower-type multi-effect evaporator or a split-type multi-effect evaporator.

13. The wastewater treatment method for a co-oxidation propylene oxide plant as described in claim 1, characterized in that: In step S4, the wastewater concentration ratio of the multi-effect evaporation unit is 2 to 20 times.

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