Device and method for reducing COD (Chemical Oxygen Demand) content of wastewater of epoxypropane device

Abstract

The invention provides a device and a method for reducing the COD (Chemical Oxygen Demand) content of wastewater of an epoxypropane device. The treatment method comprises the following steps: carrying out negative pressure cyclone separation on flashed saponification wastewater to obtain a first gas phase and a first liquid phase; condensing the first gas phase to obtain a second gas phase and a second liquid phase; carrying out gas-liquid separation on the second gas phase to obtain an oil phase and a third gas phase; and mixing the second liquid phase and the oil phase, standing and separating to obtain dichloro isopropyl ether and a water phase. The COD (Chemical Oxygen Demand) content and the dichloro isopropyl ether content of the treated saponified wastewater are reduced.

Description

Technical Field

[0001] This invention belongs to the field of propylene oxide and relates to an apparatus and method for reducing the COD content of wastewater from propylene oxide plants. Background Technology

[0002] Propylene oxide (PO) is an important organic chemical intermediate widely used in the production of polyether polyols, propylene glycol, polyurethane foam, and other products, holding an irreplaceable position in industries such as construction, automotive, home appliances, and pharmaceuticals. The chlorohydrin process is a common method for producing propylene oxide.

[0003] In the chlorohydrin process for propylene oxide production, the saponification process generates a large amount of high-concentration organic wastewater (i.e., saponification wastewater). This wastewater has a high COD concentration, and dichloroisopropyl ether (a highly toxic substance) generated in the chlorohydrin reactor enters the wastewater treatment system along with the saponification wastewater. This substance has a strong inhibitory effect on biological microorganisms, leading to low wastewater treatment efficiency and posing environmental risks. Direct discharge of this substance would cause serious damage to aquatic ecosystems.

[0004] Therefore, developing an efficient, stable, and economical saponification wastewater treatment device and method to achieve simultaneous deep removal of COD and dichloroisopropyl ether is of great practical significance and application value for promoting the green upgrading of the chlorohydrin-based propylene oxide industry and reducing environmental risks. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for treating saponification wastewater during the chlorohydrin process of propylene oxide production, comprising the following steps: The saponification wastewater after flash evaporation is separated by negative pressure cyclone separation to obtain the first gas phase and the first liquid phase; The first gas phase is condensed to obtain a second gas phase and a second liquid phase; The second gas phase is subjected to gas-liquid separation to obtain an oil phase and a third gas phase; The second liquid phase and oil phase are mixed and allowed to stand for separation to obtain dichloroisopropyl ether and an aqueous phase.

[0006] According to an embodiment of the present invention, the saponification wastewater comprises: approximately 0.10wt%-0.60wt% Ca(OH)2, a COD content of 1300-1500mg / L, and a dichloroisopropyl ether content of 100mg / L.

[0007] According to an embodiment of the present invention, the operating pressure of the flash evaporation is 30-50 kPa (A), for example 30 kPa (A), 35 kPa (A), 40 kPa (A), 45 kPa (A) or 50 kPa (A).

[0008] According to an embodiment of the present invention, the negative pressure range is -80 kPa to -40 kPa, for example -75 kPa, -70 kPa, -65 kPa, -60 kPa, -55 kPa, -50 kPa or -45 kPa; if the pressure is too low, too much water phase is separated, resulting in a large amount of water evaporating into the propylene oxide product, forcing the distillation column load to increase, which in severe cases affects product quality and leads to a decrease in the purity of propylene oxide; if the pressure is too high, the organic matter is not fully volatilized, resulting in a high COD content in the wastewater.

[0009] According to an embodiment of the present invention, the negative pressure cyclone separation is carried out in a wastewater diffusion tower, and the wastewater diffusion tower is equipped with cyclone blades, i.e., a plate tower.

[0010] According to an embodiment of the present invention, the liquid level in the wastewater diffusion tower is controlled at 20-80%, for example, 25%, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%.

[0011] According to an embodiment of the present invention, the condensation operation temperature is ≤40°C, for example, 25~40°C.

[0012] According to an embodiment of the present invention, the operating conditions for gas-liquid separation are as follows: the liquid level in the gas-liquid separation tank is controlled at 20%-80%, and the pressure is controlled at ≤5KPa; for example, the liquid level is 25%, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%, and the pressure is 1KPa, 2KPa, 3KPa, or 4KPa.

[0013] According to an embodiment of the present invention, the settling and separation time is 4 hours.

[0014] According to an embodiment of the present invention, the static separation is carried out in a dichloroisopropyl ether separation tank, and the pressure is controlled at ≤5 kPa, for example 1 kPa, 2 kPa, 3 kPa or 4 kPa.

[0015] According to an embodiment of the present invention, the first liquid phase is sent to a settling tank.

[0016] According to an embodiment of the present invention, the third gas phase is fed into the waste gas treatment system.

[0017] According to an embodiment of the present invention, the aqueous phase is recovered.

[0018] The present invention also provides a device for treating saponification wastewater, comprising: Flash tank, wastewater diffusion tower, condenser, gas-liquid separator, dichloroisopropyl ether separator and dichloroisopropyl ether receiving tank; The liquid phase outlet of the flash tank is connected to the feed inlet of the wastewater diffusion tower; The material inlet of the condenser is connected to the gas phase outlet of the wastewater diffusion tower, the liquid phase outlet of the condenser is connected to the material inlet of the dichloroisopropyl ether separator, and the gas phase outlet of the condenser is connected to the material inlet of the gas-liquid separator. The oil phase outlet of the gas-liquid separator is connected to the material inlet of the dichloroisopropyl ether separator. The oil phase outlet of the dichloroisopropyl ether separator is connected to the dichloroisopropyl ether receiving tank.

[0019] According to an embodiment of the present invention, the gas phase outlet of the gas-liquid separator is connected to the waste gas treatment system.

[0020] According to an embodiment of the present invention, the treatment apparatus further includes a settling tank connected to the liquid phase outlet of a wastewater diffusion tower.

[0021] According to an embodiment of the present invention, the processing apparatus further includes an aqueous phase recovery tank connected to the aqueous phase outlet of the dichloroisopropyl ether separator.

[0022] According to an embodiment of the present invention, the method for treating the saponification wastewater is carried out in the above-mentioned saponification wastewater treatment apparatus.

[0023] Beneficial effects By using a swirling flow method to allow the saponification residue to flow from the top to the bottom of the wastewater diffusion tower, the surface area for liquid phase evaporation is increased, improving evaporation efficiency and reducing equipment investment costs. At the same time, by controlling the negative pressure, the amount of water flashed out and the COD content of the wastewater in the tower bottom are precisely controlled, reducing the COD content of the saponification wastewater to 1100 mg / L and the content of dichloroisopropyl ether in the wastewater to be reduced by about 3 times. This maintains the activity of microorganisms and reduces the load on the biological treatment of wastewater.

[0024] The aqueous phase separated by condensation at the top of the wastewater diffusion tower is reused, while the oil phase (dichloroisopropyl ether) is incinerated, achieving a COD removal rate of over 10% for saponification wastewater. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a saponification wastewater treatment device; Figure label: 1-Flash tank, 2-Wastewater diffusion tower, 3-Condenser, 4-Gas-liquid separator, 5-Dichloroisopropyl ether separator, 6-Dichloroisopropyl ether receiving tank, 7-Sedimentation tank, 8-Aqueous phase recovery tank, 9-Waste gas treatment system. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0027] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0028] like Figure 1 The saponification wastewater treatment apparatus shown includes: Flash tank 1, wastewater diffusion tower 2, condenser 3, gas-liquid separator 4, dichloroisopropyl ether separator 5, dichloroisopropyl ether receiving tank 6, settling tank 7, and aqueous phase recovery tank 8; The liquid phase outlet of flash tank 1 is connected to the feed inlet of wastewater diffusion tower 2; The material inlet of condenser 3 is connected to the gas phase outlet of wastewater diffusion tower 2, the liquid phase outlet of condenser 3 is connected to the material inlet of dichloroisopropyl ether separator 5, and the gas phase outlet of condenser 3 is connected to the material inlet of gas-liquid separator 4. The oil phase outlet of the gas-liquid separator 4 is connected to the material inlet of the dichloroisopropyl ether separator 5, and the gas phase outlet of the gas-liquid separator 4 is connected to the waste gas treatment system 9. The oil phase outlet of the dichloroisopropyl ether separator 5 is connected to the dichloroisopropyl ether receiving tank 6. The settling tank 7 is connected to the liquid phase outlet of the wastewater diffusion tower 2; The aqueous phase recovery tank 8 is connected to the aqueous phase outlet of the dichloroisopropyl ether separator 5.

[0029] Example 1 use Figure 1 The saponification wastewater treatment device shown has the following components: the flash evaporation residue in the flash tank (composition: Ca(OH)2 approximately 0.10%-0.60%, COD content 1300-1500 mg / L, dichloroisopropyl ether content 100 mg / L) is pumped to the wastewater diffusion tower via a flash bottom pump. The wastewater diffusion tower is equipped with swirl vanes, and the top pressure of the wastewater diffusion tower is controlled at -70 kPa, and the liquid level is controlled at 50%. After being swirled by the swirl vanes, a first gas phase and a first liquid phase are obtained. The first gas phase rises and enters the condenser. The gas phase outlet temperature of the condenser is ≤40℃. After condensation, a second gas phase and a second liquid phase are obtained. The second gas phase enters the gas-liquid separator. The liquid level of the gas-liquid separator is controlled at 40%, and the pressure is controlled at 2 kPa, resulting in an oil phase and a third gas phase. The third gas phase enters the waste gas treatment system. The oil phase and the second liquid phase (i.e., the aqueous phase obtained from the condenser) enter the dichloroisopropyl ether separator. The pressure inside the tank is controlled at 1 kPa. After standing separation for 4 hours, the oil phase enters the dichloroisopropyl ether receiving tank, and the aqueous phase enters the aqueous phase recovery tank. The bottom liquid of the wastewater diffusion tower is transported to the settling tank by the bottom pump of the diffusion tower.

[0030] After treatment, the COD content of the saponification wastewater was reduced to 1100 mg / L, and the dichloroisopropyl ether content was 30-40 mg / L.

[0031] Comparative Example 1 Unlike Example 1, no wastewater diffusion tower was installed. After treatment, the COD content of the wastewater was 1300 mg / L, and the dichloroisopropyl ether content was 100 mg / L.

[0032] Comparative Example 2 Unlike Example 1, no swirl vanes were installed in the wastewater diffusion tower. After treatment, the COD content of the saponification wastewater was 1250 mg / L, and the dichloroisopropyl ether content was 80 mg / L.

[0033] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating saponification wastewater in a chlorohydrination process for producing propylene oxide, characterized by, The treatment method comprises the following steps: The saponification wastewater after flash evaporation is subjected to negative pressure cyclone separation to obtain a first gas phase and a first liquid phase; The first gas phase is subjected to condensation to obtain a second gas phase and a second liquid phase; The second gas phase is subjected to gas-liquid separation to obtain an oil phase and a third gas phase; The second liquid phase and the oil phase are mixed and subjected to standing separation to obtain dichloroisopropyl ether and an aqueous phase.

2. The treatment method according to claim 1, characterized in that, The saponification wastewater comprises Ca(OH)2 0.10wt%-0.60wt%, COD content 1300mg / L~1500mg / L, and dichloroisopropyl ether content 80~120mg / L.

3. The treatment method of claim 1, wherein, The operation pressure of the flash evaporation is 30-50KPa(A).

4. The treatment method of claim 1, wherein The negative pressure range is -80KPa to -40KPa.

5. The treatment method of claim 1, wherein The negative pressure cyclone separation is performed in a wastewater diffusion tower, the wastewater diffusion tower is provided with cyclone blades, and the liquid level in the wastewater diffusion tower is controlled to be 20~80%.

6. The treatment method of claim 1, wherein The operation temperature of the condensation is ≤40℃.

7. The treatment method of claim 1, wherein The operation condition of the gas-liquid separation is that the liquid level of a gas-liquid separation tank is controlled to be 20%-80% and the pressure is controlled to be ≤5KPa.

8. The treatment method of claim 1, wherein, The standing separation time is 4h. And / or, the standing separation is performed in a dichloroisopropyl ether separation tank, and the pressure is controlled to be ≤5KPa.

9. A device for treating saponification wastewater, characterized by comprising: The treatment method of the saponification wastewater according to any one of claims 1~8 is performed in a treatment device for the saponification wastewater; The treatment device comprises: a flash evaporation tank, a wastewater diffusion tower, a condenser, a gas-liquid separation tank, a dichloroisopropyl ether separation tank, and a dichloroisopropyl ether receiving tank; the liquid phase outlet of the flash evaporation tank is connected with the feed inlet of the wastewater diffusion tower; the material inlet of the condenser is connected with the gas phase outlet of the wastewater diffusion tower, the liquid phase outlet of the condenser is connected with the material inlet of the dichloroisopropyl ether separation tank, and the gas phase outlet of the condenser is connected with the material inlet of the gas-liquid separation tank; the oil phase outlet of the gas-liquid separation tank is connected with the material inlet of the dichloroisopropyl ether separation tank; the oil phase outlet of the dichloroisopropyl ether separation tank is connected with the dichloroisopropyl ether receiving tank.

10. The processing device of claim 9, wherein, the gas phase outlet of the gas-liquid separation tank is connected with a waste gas treatment system; And / or, the treatment device further comprises a sedimentation tank connected with the liquid phase outlet of the wastewater diffusion tower; And / or, the treatment device further comprises an aqueous phase recovery tank connected with the aqueous phase outlet of the dichloroisopropyl ether separation tank.

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