Low-concentration DMF (Dimethyl Formamide) wastewater treatment device

Abstract

The utility model relates to the technical field of wastewater treatment, and particularly discloses a low-concentration DMF (Dimethyl Formamide) wastewater treatment device which comprises a lifting pump, a heat exchanger, an alkali adding device, a mixer, an alkaline hydrolysis tank, a gaseous membrane component, an absorption liquid storage tank, an absorption liquid circulating pump, an evaporated liquid circulating pump, a forced circulation evaporator, a separator and an MVR (Mechanical Vapor Recompression) compressor, a gaseous membrane is adopted to absorb dimethylamine generated by alkaline hydrolysis, mass transfer power is the partial pressure difference of dimethylamine gas on the two sides of the membrane, dimethylamine is transferred from the interior of membrane filaments to the exterior of the membrane filaments to be absorbed by absorption liquid and reacts with the absorption liquid to generate dimethylamine salt, and therefore the high partial pressure is always kept on the wastewater side, and the partial pressure of dimethylamine on the absorption liquid side is extremely low; the whole process is large in mass transfer power and high in removal rate, dimethylamine hydrochloride in the absorption liquid is high in concentration and small in evaporation capacity, a large amount of energy consumption is saved compared with direct rectification, DMF in the wastewater can be converted into valuable dimethylamine hydrochloride through a series of chemical reactions, and crystals can be recycled after centrifugal separation and purification.

Description

Technical Field

[0001] The utility model relates to the technical field of wastewater treatment, in particular to a low-concentration DMF wastewater treatment device. Background Art

[0002] N-Dimethylformamide (DMF), an excellent organic solvent and chemical raw material, is widely used in a variety of industries, including pharmaceuticals, pesticides, synthetic leather, and petrochemicals. DMF is toxic to living organisms and can enter the human body through the respiratory tract, skin, and digestive tract, causing severe irritation. High concentrations of DMF can damage organs such as the liver, kidneys, and lungs, and in severe cases, can even directly threaten human life. Each year, related industries generate large amounts of DMF wastewater. If allowed to be discharged recklessly, it will cause significant damage to the ecological environment and human health.

[0003] At present, for high-concentration DMF wastewater, DMF is often recovered by distillation or extraction. For low-concentration DMF wastewater (usually DMF content less than 5%), the mainstream treatment methods include adsorption, alkaline hydrolysis-stripping, Fenton oxidation, and biological methods. The biological method is mature and has low operating costs, making it the most economical means of treating DMF wastewater. However, DMF has poor biodegradability and is biotoxic, which requires high biochemical treatment requirements, low treatment load, and long treatment time. Although the adsorption method has good treatment effects, it requires a large amount of adsorbent, and after adsorption saturation, it needs to be regenerated. The failed adsorbent and regeneration liquid also need further treatment, which is complicated. The Fenton oxidation method generally has high equipment requirements and generates a large amount of solid waste during operation. It cannot recover DMF in the wastewater, resulting in waste of resources. The alkaline hydrolysis-stripping method has high energy consumption and is prone to secondary pollution during the stripping process. Therefore, it is necessary to propose a low-concentration DMF wastewater treatment device to solve the above-mentioned problems. Utility Model Content

[0004] The purpose of the utility model is to provide a low-concentration DMF wastewater treatment device, which has the advantages of strong adaptability, simple operation, good treatment effect and no secondary pollution, and can recover valuable dimethylamine salt.

[0005] To achieve the above object, the utility model provides the following technical solutions: a low-concentration DMF wastewater treatment device, comprising a lift pump, a heat exchanger, an alkali adding device, a mixer, an alkaline hydrolysis tank, a gaseous membrane assembly, an absorption liquid storage tank, an absorption liquid circulation pump, an evaporation liquid circulation pump, a forced circulation evaporator, a separator, and an MVR compressor;

[0006] The lifting pump, heat exchanger and mixer are connected to the alkaline hydrolysis tank in sequence; the dosing port of the mixer is connected to the outlet of the alkali adding device through a pipeline; the discharge port of the alkaline hydrolysis tank is connected to the feed port of the gaseous membrane assembly through a pipeline; the absorption liquid inlet of the gaseous membrane assembly is connected to the absorption liquid outlet of the absorption liquid storage tank through an absorption liquid circulation pump; the absorption liquid outlet of the gaseous membrane assembly is connected to the absorption liquid reflux port of the absorption liquid storage tank through a pipeline; the dimethylamine salt solution outlet of the absorption liquid storage tank is connected to the feed port of a forced circulation evaporator through an evaporative liquid circulation pump; the discharge port of the forced circulation evaporator is connected to the feed port of a separator through a pipeline; the concentrated liquid outlet of the separator is connected to the feed port of the forced circulation evaporator through an evaporative liquid circulation pump; and the steam outlet of the separator is connected to the steam inlet of the forced circulation evaporator through an MVR compressor.

[0007] In order to treat wastewater, a low-concentration DMF wastewater treatment device is preferably used in the present invention. The interior of the gaseous membrane component is filled with a hydrophobic porous PTFE hollow fiber membrane, and the outer diameter / inner diameter of the membrane wire are 1mm / 0.5mm respectively. The feed port and the discharge port of the gaseous membrane component are connected to the inner side of the membrane wire of the PTFE hollow fiber membrane, and the absorption liquid inlet and the absorption liquid outlet of the gaseous membrane component are connected to the outer side of the membrane wire of the PTFE hollow fiber membrane. The channels inside and outside the membrane wire are isolated from each other, and only gas is allowed to permeate and transfer mass through the membrane pores on both sides of the membrane wire.

[0008] In order to discharge the crystals, as a low-concentration DMF wastewater treatment device of the present invention, the bottom of the separator is preferably connected to a crystal discharge outlet.

[0009] In order to discharge the condensed water in the forced circulation evaporator, as a low-concentration DMF wastewater treatment device of the present invention, the outer wall of the forced circulation evaporator is connected to a condensed water discharge pipe.

[0010] In order to discharge the wastewater in the gaseous membrane assembly, as a preferred low-concentration DMF wastewater treatment device of the present invention, the top of the gaseous membrane assembly is connected to a discharge port.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. The utility model adopts a gaseous membrane to absorb dimethylamine produced by alkaline hydrolysis. The mass transfer power is the partial pressure difference of dimethylamine gas on both sides of the membrane. Dimethylamine is transferred from the inside of the membrane to the outside of the membrane and absorbed by the absorption liquid, and reacts with the absorption liquid to produce dimethylamine salt. Therefore, the partial pressure on the wastewater side is always high, while the partial pressure of dimethylamine on the absorption liquid side is extremely low. The mass transfer power of the whole process is large and the removal rate is high.

[0013] 2. The utility model uses hydrochloric acid to absorb the dimethylamine produced by alkaline hydrolysis. The concentration of dimethylamine hydrochloride in the absorption liquid is high and the evaporation amount is small, which saves a lot of energy compared with direct distillation.

[0014] 3. The low-concentration DMF wastewater treatment device provided by the utility model reduces the dosage of reagents compared to the mainstream Fenton oxidation and alkaline hydrolysis-stripping methods, and the entire process is closed, no additional solid waste is generated, and secondary pollution caused by the volatilization of dimethylamine into the air is avoided;

[0015] 4. The low-concentration DMF wastewater treatment device provided by the utility model can convert DMF in the wastewater into valuable dimethylamine hydrochloride through a series of chemical reactions, and the crystals can be recovered after centrifugal separation and purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the overall structural diagram of the utility model;

[0017] Figure 2 This is a connection diagram of the mixer, heat exchanger and alkali adding device of the utility model;

[0018] Figure 3 This is a structural diagram of the gas membrane component of the present utility model.

[0019] In the figure: 1. Lifting pump; 2. Heat exchanger; 3. Alkali adding device; 4. Mixer; 5. Alkaline hydrolysis tank; 6. Gaseous membrane assembly; 7. Absorption liquid storage tank; 8. Absorption liquid circulation pump; 9. Evaporation liquid circulation pump; 10. Forced circulation evaporator; 11. Separator; 12. MVR compressor. DETAILED DESCRIPTION

[0020] See also Figures 1 to 3A low-concentration DMF wastewater treatment device includes a lifting pump 1, a heat exchanger 2, an alkali adding device 3, a mixer 4, an alkaline hydrolysis tank 5, a gaseous membrane assembly 6, an absorption liquid storage tank 7, an absorption liquid circulation pump 8, an evaporation liquid circulation pump 9, a forced circulation evaporator 10, a separator 11, and an MVR compressor 12; the lifting pump 1, the heat exchanger 2, and the mixer 4 are connected to the alkaline hydrolysis tank 5 in sequence, the dosing port of the mixer 4 is connected to the outlet of the alkali adding device 3 through a pipeline, the discharge port of the alkaline hydrolysis tank 5 is connected to the feed port of the gaseous membrane assembly 6 through a pipeline, and the absorption liquid inlet of the gaseous membrane assembly 6 is connected through the absorption liquid circulation pump 8. The absorption liquid outlet of the absorption liquid storage tank 7 is connected, the absorption liquid outlet of the gaseous membrane assembly 6 is connected to the absorption liquid reflux port of the absorption liquid storage tank 7 through a pipeline, the dimethylamine salt solution outlet of the absorption liquid storage tank 7 is connected to the feed port of the forced circulation evaporator 10 through the evaporative liquid circulation pump 9, the discharge port of the forced circulation evaporator 10 is connected to the feed port of the separator 11 through a pipeline, the concentrated liquid outlet of the separator 11 is connected to the feed port of the forced circulation evaporator 10 through the evaporative liquid circulation pump 9, and the steam outlet of the separator 11 is connected to the steam inlet of the forced circulation evaporator 10 through the MVR compressor 12.

[0021] In this embodiment, DMF wastewater enters the heat exchanger 2 by the lifting pump 1, and the wastewater temperature is raised to 60-80°C in the heat exchanger 2. The effluent from the heat exchanger 2 passes through the mixer 4, and the alkali adding device 3 adds liquid alkali to the DMF wastewater through the dosing port of the mixer 4. The molar ratio of the amount of liquid alkali added to the DMF in the wastewater is 1.2:1. The DMF wastewater and the liquid alkali are fully mixed in the mixer 4 and then enter the alkaline hydrolysis tank 5. Under the operating conditions of a relative pressure of 0.04 MPa, alkaline hydrolysis is performed for 60-120 minutes. More than 98% of the DMF in the DMF wastewater is alkaline hydrolyzed into formate and dimethylamine. The wastewater after alkaline hydrolysis enters the gaseous membrane module 6 through the feed port of the gaseous membrane module 6 and flows in the membrane wire. The absorption liquid in the absorption liquid storage tank 7 enters the gaseous membrane module 6 from the absorption liquid inlet of the gaseous membrane module 6, and then flows back to the absorption liquid storage tank 7 through the absorption liquid outlet of the gaseous membrane module 6. The absorption liquid circulates back and forth outside the membrane wire. At this time, the dimethylamine in the wastewater volatilizes from the gas-liquid interface, diffuses through the membrane pores of the hydrophobic porous PTFE hollow fiber membrane, is transferred from the membrane filaments to the outside of the membrane filaments and is absorbed by the absorption liquid, and the treated wastewater is discharged from the discharge port of the gaseous membrane assembly 6; after multiple cycles of absorption, the dimethylamine hydrochloride in the absorption liquid storage tank 7 reaches a certain concentration and is discharged from the dimethylamine salt solution outlet of the absorption liquid storage tank 7, enters the forced circulation evaporator 10 after being pressurized by the evaporating liquid circulation pump 9, and enters the separator 11 after being heated to 85°C. The operating absolute pressure in the separator 11 is 0.055MPa. Under this state, the saturated steam temperature of water is 85°C. The water vapor generated in the separator 11 is heated by the MVR compressor 12 and then refluxed to the forced circulation evaporator 10 to heat the dimethylamine hydrochloride solution. The concentrated liquid after the evaporation of the dimethylamine hydrochloride in the separator 11 is circulated to the forced circulation evaporator 10 through the evaporating liquid circulation pump 9 for multiple heat exchange evaporation until crystallization.

[0022] As a technical optimization solution of the present invention, the interior of the gaseous membrane component 6 is filled with a hydrophobic porous PTFE hollow fiber membrane, and the outer diameter / inner diameter of the membrane wire are 1mm / 0.5mm respectively. The feed port and the discharge port of the gaseous membrane component 6 are connected to the inner side of the membrane wire of the PTFE hollow fiber membrane, and the absorption liquid inlet and the absorption liquid outlet of the gaseous membrane component 6 are connected to the outer side of the membrane wire of the PTFE hollow fiber membrane. The channels inside and outside the membrane wire are isolated from each other, and only the gas is allowed to permeate and transfer mass through the membrane pores on both sides of the membrane wire.

[0023] In this embodiment: the absorption liquid entering the gaseous membrane component 6 circulates back and forth outside the membrane fibers. During absorption, the dimethylamine in the wastewater evaporates from the gas-liquid interface, diffuses through the membrane pores of the hydrophobic porous PTFE hollow fiber membrane, and is transferred from the inside of the membrane fibers to the outside of the membrane fibers to be absorbed by the absorption liquid.

[0024] As a technical optimization solution of the present invention, the bottom of the separator 11 is connected to a crystal discharge outlet.

[0025] In this embodiment, the crystals are discharged from the crystal discharge port at the bottom of the separator 11 , and the crystals can be recovered after centrifugal separation and purification in subsequent processes.

[0026] As a technical optimization solution of the present invention, the outer wall of the forced circulation evaporator 10 is connected to a condensed water discharge pipe.

[0027] In this embodiment, the condensed water in the forced circulation evaporator 10 can be discharged through the condensed water drain pipe.

[0028] As a technical optimization solution of the present invention, the top end of the gaseous membrane assembly 6 is connected to a discharge port.

[0029] In this embodiment, the wastewater in the gaseous membrane assembly 6 can be discharged through the discharge port.

[0030] Working principle: First, DMF wastewater enters the heat exchanger 2 through the lifting pump 1, and the wastewater temperature is raised to 60-80℃ in the heat exchanger 2. The outlet water of the heat exchanger 2 passes through the mixer 4, and the alkali adding device 3 adds liquid alkali to the DMF wastewater through the dosing port of the mixer 4 (the alkali added by the alkali adding device 3 is one of sodium hydroxide or potassium hydroxide solution). The molar ratio of the amount of liquid alkali added to the DMF in the wastewater is 1.2:1. The DMF wastewater and the liquid alkali are fully mixed in the mixer 4 and then enter the alkaline hydrolysis tank 5. Under the operating conditions of relative pressure of 0.04MPa, alkaline hydrolysis is carried out for 60-120min. More than 98% of the DMF in the DMF wastewater is hydrolyzed into formate and dimethylamine (according to the wastewater The DMF content is medium, the operating temperature in the alkaline hydrolysis tank 5 is 60-80°C, the relative pressure of the operation is 0.04MPa, and the reaction time is 60-120min. The following chemical reaction occurs in the alkaline hydrolysis tank 5: HCONH(CH3)2+OH-→HCOO-+NH(CH3)2, and the reaction produces formate and dimethylamine. Among them, dimethylamine has a low boiling point and strong volatility and can be recovered by gaseous membrane absorption. Formate has good biochemical reaction performance. After membrane absorption, the produced water is discharged from the outlet of the gaseous membrane component 6. After simple pH adjustment, it can enter the biochemical treatment system for treatment until it meets the discharge standards. The wastewater after alkaline hydrolysis enters the feed port of the gaseous membrane component 6 through the feed port The gaseous membrane component 6 flows in the membrane wire, and the absorption liquid in the absorption liquid storage tank 7 (the absorption liquid used in the absorption liquid storage tank 7 is a hydrochloric acid solution) enters the gaseous membrane component 6 from the absorption liquid inlet of the gaseous membrane component 6, and then flows back to the absorption liquid storage tank 7 through the absorption liquid outlet of the gaseous membrane component 6. The absorption liquid circulates back and forth like this outside the membrane wire. During absorption, the dimethylamine in the wastewater evaporates from the gas-liquid interface, diffuses through the membrane pores of the hydrophobic porous PTFE hollow fiber membrane, and is transferred from the inside of the membrane wire to the outside of the membrane wire to be absorbed by the absorption liquid. The treated wastewater is discharged from the discharge port of the gaseous membrane component 6; after multiple cycles of absorption, the dimethylamine hydrochloride in the absorption liquid storage tank 7 reaches a certain concentration and is discharged from the dimethylamine in the absorption liquid storage tank 7. The amine salt solution is discharged from the outlet, pressurized by the evaporating liquid circulation pump 9, and then enters the forced circulation evaporator 10. After being heated to 85°C, it enters the separator 11. The operating absolute pressure in the separator 11 is 0.055 MPa. Under this state, the saturated vapor temperature of water is 85°C. The water vapor generated in the separator 11 is heated by the MVR compressor 12 and then refluxed to the forced circulation evaporator 10 to heat the dimethylammonium hydrochloride solution. The concentrated liquid after the evaporation of the dimethylammonium hydrochloride in the separator 11 is circulated to the forced circulation evaporator 10 through the evaporating liquid circulation pump 9, and is evaporated multiple times by heat exchange until crystallization. The crystals are discharged from the crystal outlet at the bottom of the separator 11. The crystals can be recovered after centrifugal separation and purification in the subsequent process.

[0031] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low-concentration DMF wastewater treatment plant, characterized in that: It comprises a lifting pump (1), a heat exchanger (2), an alkali adding device (3), a mixer (4), an alkaline hydrolysis tank (5), a gaseous membrane assembly (6), an absorption liquid storage tank (7), an absorption liquid circulation pump (8), an evaporation liquid circulation pump (9), a forced circulation evaporator (10), a separator (11), and an MVR compressor (12); The lifting pump (1), the heat exchanger (2) and the mixer (4) are connected to the alkaline hydrolysis tank (5) in sequence, the dosing port of the mixer (4) is connected to the outlet of the alkali dosing device (3) through a pipeline, the discharge port of the alkaline hydrolysis tank (5) is connected to the feed port of the gaseous membrane assembly (6) through a pipeline, the absorption liquid inlet of the gaseous membrane assembly (6) is connected to the absorption liquid outlet of the absorption liquid storage tank (7) through an absorption liquid circulation pump (8), the absorption liquid outlet of the gaseous membrane assembly (6) is connected to the absorption liquid reflux port of the absorption liquid storage tank (7) through a pipeline. The dimethylamine salt solution outlet of the absorption liquid storage tank (7) is connected to the feed port of the forced circulation evaporator (10) through an evaporative liquid circulation pump (9), the discharge port of the forced circulation evaporator (10) is connected to the feed port of the separator (11) through a pipeline, the concentrated liquid outlet of the separator (11) is connected to the feed port of the forced circulation evaporator (10) through the evaporative liquid circulation pump (9), and the steam outlet of the separator (11) is connected to the steam inlet of the forced circulation evaporator (10) through an MVR compressor (12).

2. a kind of low-concentration DMF wastewater treatment plant according to claim 1, is characterized in that: The interior of the gaseous membrane assembly (6) is filled with a hydrophobic porous PTFE hollow fiber membrane, and the outer diameter / inner diameter of the membrane wire are 1mm / 0.5mm respectively. The feed port and the discharge port of the gaseous membrane assembly (6) are connected to the inner side of the membrane wire of the PTFE hollow fiber membrane, and the absorption liquid inlet and the absorption liquid outlet of the gaseous membrane assembly (6) are connected to the outer side of the membrane wire of the PTFE hollow fiber membrane. The channels inside and outside the membrane wire are isolated from each other, and only gas is allowed to permeate and transfer mass on both sides of the membrane wire through the membrane pores.

3. a kind of low-concentration DMF wastewater treatment plant according to claim 1, is characterized in that: The bottom of the separator (11) is connected to a crystal discharge outlet.

4. a kind of low-concentration DMF wastewater treatment plant according to claim 1, is characterized in that: The outer wall of the forced circulation evaporator (10) is connected to a condensed water discharge pipe.

5. a kind of low-concentration DMF wastewater treatment plant according to claim 1, is characterized in that: The top end of the gaseous membrane assembly (6) is connected to a discharge port.

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