CN114057337A

CN114057337A - Separation and purification method of aqueous waste solvent

Info

Publication number: CN114057337A
Application number: CN202010745003.3A
Authority: CN
Inventors: 宋力; 宋伟; 杨雷; 王宏志; 陈佳
Original assignee: SHANGHAI YIKE GREEN ENGINEERING CO LTD
Current assignee: SHANGHAI YIKE GREEN ENGINEERING CO LTD
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2022-02-18

Abstract

The invention relates to the field of water treatment, in particular to a separation and purification method of an aqueous waste solvent. The method for separating and purifying the aqueous waste solvent comprises the following steps: introducing a coagulating agent into a solvent to be treated for coagulating sedimentation treatment to provide a first liquid phase stream and wet paint slag; performing dehydration treatment on the wet paint slag to provide a second liquid-phase stream and dry paint slag; combining the first and second liquid phase streams and introducing a separation agent to perform a separation and purification process to provide an upper separation liquid and a lower separation liquid; removing the solvent from the lower layer of the separated liquid to provide a recovered pharmaceutical agent; at least part of the recovered medicament is used as a separation medicament for separation and purification treatment. The method and the system for separating and purifying the aqueous waste solvent can treat the aqueous waste solvent stably, reliably and inexpensively, can reduce hazardous waste and can realize repeated recycling of medicaments, solvents and the like in the treatment process.

Description

Separation and purification method of aqueous waste solvent

Technical Field

The invention relates to the field of water treatment, in particular to a separation and purification method of an aqueous waste solvent.

Background

The aqueous waste solvent is mainly generated in some aqueous coating production lines, such as coating production lines of automobiles, containers, engineering machinery, digital products and the like, especially in automobile coating production lines, and is one of main industries for generating the aqueous waste solvent due to large production scale and large amount of spray paint.

In the production process of automobile painting, paints with different colors need to be sprayed, an aqueous solvent is needed to clean a spray gun and a pipeline for conveying the paints between each color change, the adopted aqueous solvent is generally prepared by diluting pure solvent stock solution, the concentration of the solvent is generally about 10 percent, and the main components of the solvent comprise ethers such as ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether and ethylene glycol hexyl ether, alcohols such as isopropanol, methanol, n-butanol and the like, and other small amounts of additives. The water-based solvent after cleaning the spray gun is converted into water-based waste solvent, a large amount of cleaned paint components are contained, the solvent components are lost, and the effective concentration is reduced to 5-8% from about 10%.

If the aqueous waste solvent is used as wastewater to enter a wastewater station for treatment, the CODcr of the aqueous waste solvent is as high as 50-100 ten thousand mg/L, and even if the paint components in the wastewater are removed, the CODcr is as high as 20-30 ten thousand mg/L, so that a very large pressure is brought to a wastewater treatment system, in addition, the solvent components are completely dissolved with water, the solvent components cannot be removed by adopting a physical-chemical coagulation method, and finally, only all the solvent components enter a biochemical system, and the B/C of most of the solvent components is not higher than 1/3, so that the load and energy consumption of biochemical treatment are greatly increased, and even the risk of excessive discharge is caused. If the aqueous waste solvent is used as hazardous waste to be incinerated and disposed, the current market price is generally 3000-5000 yuan/ton, and for an automobile coating production line, the disposal cost is 300-500 ten thousand yuan/year according to 1000 tons/year of the production amount of the aqueous waste solvent, the cost is quite high, and the current green environmental protection concept of waste recycling is not met.

Therefore, at present, many manufacturers and research institutions try to develop a new wastewater treatment process for treating the aqueous waste solvent to achieve standard discharge, or treat the aqueous waste solvent to be recycled for the coating production line, so that the burden of a wastewater treatment system is reduced, high hazardous waste treatment cost is saved, the consumption of fresh solvent in a workshop is saved, and the production cost is reduced. For example, patent No. CN105174529A discloses a method for treating waste water containing butyl ether of diethylene glycol produced in a surface treatment process, which comprises oxidizing butyl ether of diethylene glycol with waste water containing nitric acid, wherein the method requires a large amount of acidic nitric acid waste water, also needs to put in PVA gel, and then needs to perform denitrification treatment, and finally can perform biochemical treatment, the process is complex, the investment is large, and an automobile plant does not have a large amount of nitric acid waste water, so the possibility of popularization and application is low; for another example, in the patent "aqueous paint waste liquid treatment system" with application number CN201620011783, a two-stage membrane is mentioned to treat aqueous paint waste liquid, but the use of the membrane to treat waste liquid with COD of hundreds of thousands mg/L inevitably causes serious pollution blockage, and in addition, the membrane treatment system is expensive in cost, which limits the popularization and application; for another example, patent No. CN201910671630, method and composition for treating and recovering a cleaning agent solvent, refers to a method of removing paint residues in a cleaning agent solvent by means of coagulation reaction and the like, and then filtering and recycling the paint residues as a cleaning agent, but the obtained regenerated cleaning agent has low concentration due to loss of solvent components, and is difficult to achieve a normal cleaning effect, so that popularization and recycling are limited.

Therefore, the development of a stable and reliable treatment process of the aqueous waste solvent, which has low equipment investment and operation cost, can reduce the amount of hazardous waste, reduce the burden of a waste water system and realize the recycling is urgently needed.

Disclosure of Invention

In view of the above-mentioned disadvantages of the prior art, the present invention aims to provide a method for separating and purifying an aqueous waste solvent, which solves the problems of the prior art.

To achieve the above and other related objects, according to one aspect of the present invention, there is provided a method for separating and purifying an aqueous waste solvent, the method comprising:

1) introducing a coagulating agent into a solvent to be treated for coagulating sedimentation treatment to provide a first liquid phase stream and wet paint slag;

2) performing dehydration treatment on the wet paint slag to provide a second liquid-phase stream and dry paint slag;

3) combining the first and second liquid phase streams and introducing a separation agent to perform a separation and purification process to provide an upper separation liquid and a lower separation liquid;

4) removing the solvent from the lower layer of the separated liquid to provide a recovered pharmaceutical agent;

at least part of the recovered medicament is used as a separation medicament for separation and purification treatment.

In some embodiments of the present invention, in the step 1), the content of paint residue in the solvent to be treated is 5 to 15 wt%.

In some embodiments of the present invention, in step 1), the solvent to be treated includes an organic solvent, the content of the organic solvent is 5 to 8 wt%, and the organic solvent is selected from an ether solvent and/or an alcohol solvent.

In some embodiments of the invention, in step 1), the solvent to be treated has a CODcr of 5 x 10⁵～10*10⁵mg/L。

In some embodiments of the invention, in the step 1), the coagulant includes a coagulant and/or a flocculant, the coagulant is selected from one or more of modified melamine formaldehyde resin, cationic starch, cationic quaternary ammonium salt, cationic biquaternary ammonium salt, cationic polyquaternary ammonium salt, bentonite, diatomite, soluble aluminum salt, soluble iron salt, polyaluminum chloride, polyaluminum ferric chloride, and macromolecular organic acid, the coagulant is added at a concentration of 0.3 to 3 wt%, the flocculant is selected from polyacrylamide PAM, the PAM is selected from one or more of cationic PAM, anionic PAM, and nonionic PAM, and the flocculant is added at a concentration of 5 to 30 mg/L.

In some embodiments of the invention, in the step 2), the moisture content of the wet paint slag is greater than or equal to 98 wt%, and the moisture content of the dry paint slag is less than or equal to 75 wt%.

In some embodiments of the invention, in step 3), the first and/or second liquid phase streams are further subjected to a first filtration treatment in which the pore size of the filter medium is 10-50 μm.

In some embodiments of the invention, in step 3), the separation agent is selected from ionic compounds selected from combinations of one or more of carboxylate salts, amine salts, quaternary ammonium salts, phenoxide salts, alkoxide salts, sodium salts, potassium salts, magnesium salts, calcium salts, iron salts, aluminum salts.

In some embodiments of the invention, in the step 3), the adding concentration of the separation agent is 5-30 wt%.

In some embodiments of the invention, in the step 3), the upper layer separation liquid accounts for 5-15 v/v% of the water body introduction amount, the concentration of the organic solvent in the upper layer separation liquid is 50-90 wt%, and the CODcr of the upper layer separation liquid is 15 x 10⁵～18*10⁵mg/L。

In some embodiments of the invention, in the step 3), the lower layer separation liquid accounts for 85-95 v/v% of the introduced amount of the water body, and the CODcr of the lower layer separation liquid is 3 x 10⁴～5*10⁴mg/L。

In some embodiments of the invention, in the step 3), the upper layer separation liquid is further subjected to a second filtration treatment, and the pore size of the filter medium in the second filtration treatment is 1-10 μm.

In another aspect of the present invention, there is provided a separation and purification system for an aqueous waste solvent, the system including:

the coagulating sedimentation device is used for introducing a coagulating agent into a solvent to be treated for coagulating sedimentation treatment so as to provide a first liquid phase flow and wet paint residues;

a solid-liquid separation device for performing dehydration treatment on the wet paint slag to provide a second liquid phase stream and dry paint slag, wherein the solid-liquid separation device is in fluid communication with the coagulating sedimentation device;

a separation and purification device for combining the first liquid phase stream and the second liquid phase stream and introducing a separation agent for separation and purification treatment to provide an upper layer of separation liquid and a lower layer of separation liquid, the separation and purification device being in fluid communication with the coagulating sedimentation device and the solid-liquid separation device, respectively;

a solvent removal device for removing solvent from the lower layer of separated liquid to provide a recovered reagent, at least a portion of the recovered reagent being used as a separation reagent for the separation purification process, the solvent removal device being in fluid communication with the separation purification device.

In some embodiments of the invention, further comprising a first filtration device for subjecting the first liquid phase stream and/or the second liquid phase stream to a first filtration treatment, the coagulating sedimentation device and/or the solid-liquid separation device being in fluid communication with the separation and purification device via the first filtration device;

the aperture of the filter medium in the first filter device is 10-50 μm.

In some embodiments of the present invention, the apparatus further comprises a second filtering device for performing a second filtering process on the upper layer separation liquid provided by the separation and purification process, wherein the second filtering device is in fluid communication with the separation and purification device;

the aperture of the filter medium in the second filter device is 1-10 mu m.

Drawings

Fig. 1 is a schematic structural diagram of a separation and purification system for an aqueous waste solvent according to the present invention.

FIG. 2 is a schematic view of a process flow in an embodiment of the invention.

Description of the element reference numerals

1 coagulating sedimentation device

2 separation and purification device

3 solvent removing device

4 solid-liquid separation device

5 first filtering device

6 second filter device

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments, and other advantages and effects of the present invention will be apparent to those skilled in the art from the disclosure of the present specification.

The inventor of the invention has conducted extensive research and research, and has provided a stable, reliable, and low-cost separation and purification method by combining a soluble ionic compound with a treatment method of an aqueous waste solvent, and the method can practically achieve reduction of hazardous waste, thereby completing the present invention.

The invention provides a method for separating and purifying aqueous waste solvent, which comprises the following steps:

In the method for separating and purifying the aqueous waste solvent provided by the invention, the solvent to be treated can be generally sourced from an aqueous coating line, such as a coating line (for example, an automobile coating line). In the production process of a coating line, paints with different colors are generally required to be sprayed, and each color change generally requires cleaning equipment (such as a spray gun, a pipeline for conveying the paints, and the like) by using an aqueous solvent, the aqueous solvent used in the cleaning process is generally prepared by diluting an organic solvent by using water, and the content of the organic solvent in the prepared aqueous solution is generally about 10 wt%. The organic solvent may be an alcohol solvent, an ether solvent, or the like, and the ether solvent may be specifically mentionedFor example, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol hexyl ether, etc., and specific examples of the alcohol solvent include isopropyl alcohol, methanol, n-butanol, etc. After cleaning the equipment, these aqueous solutions are converted to aqueous waste solvents (i.e., the solvent to be treated), which contain a significant amount of the cleaned paint components and a significant loss in the organic solvent concentration. The paint residual components in the solvent to be treated may generally be residual components of an aqueous paint (i.e. a coating product mainly comprising water, alcohol, ether and the like as a dispersion medium, and the solvent system of which is generally miscible with water), i.e. components other than the solvent in the aqueous paint, for example, may include a resin (i.e. a polymeric film-forming substance), a filler and the like. The content of the paint residual component may be 5 to 15 wt%, 5 to 7 wt%, 7 to 9 wt%, 9 to 11 wt%, 11 to 13 wt%, or 13 to 15 wt%. For another example, the organic solvent may be present in the solvent to be treated in an amount of 5 to 8 wt%, 5 to 5.5 wt%, 5.5 to 6 wt%, 6 to 6.5 wt%, 6.5 to 7 wt%, 7 to 7.5 wt%, or 7.5 to 8 wt%, and the solvent to be treated may have a CODcr of 5 to 10⁵～10*10⁵mg/L、5*10⁵～5.5*10⁵mg/L、5.5*10⁵～6*10⁵mg/L、6*10⁵～6.5*10⁵mg/L、6.5*10⁵～7*10⁵mg/L、7*10⁵～7.5*10⁵mg/L、7.5*10⁵～8*10⁵mg/L、8*10⁵～8.5*10⁵mg/L、8.5*10⁵～9*10⁵mg/L、9*10⁵～9.5*10⁵mg/L, or 9.5 x 10⁵～10*10⁵mg/L. The solvent to be treated may further contain a small amount of additives, for example, the additives may be ester additives (e.g., butyl acetate, etc.), amine additives (e.g., dimethylethanolamine, etc.), etc., and the content of the additives may be 0.05 to 0.5 wt%, 0.05 to 0.1 wt%, 0.1 to 0.2 wt%, 0.2 to 0.3 wt%, 0.3 to 0.4 wt%, or 0.4 to 0.5 wt%.

The method for separating and purifying the aqueous waste solvent provided by the invention can comprise the following steps: and introducing a coagulating agent into the solvent to be treated for coagulating sedimentation treatment to provide a first liquid phase stream and wet paint slag. The coagulation sedimentationPrecipitation treatment generally refers to a treatment process in which a coagulating agent is introduced into a solvent system, thereby destabilizing the precipitation of paint residual components in the solvent system and forming paint residues. In the coagulating sedimentation treatment, the coagulating agent may generally comprise a coagulant and/or a flocculant. According to the action mechanisms of different stages in the process of particle agglomeration in a water body, a coagulant refers to a medicament which mainly destabilizes colloidal particles through surface charge neutralization or double-layer compression, and a flocculant refers to a medicament which mainly generates a bridging effect among the destabilized colloidal particles and a sweeping effect in the destabilizing process. Different from biochemical sludge and materialized sludge generated in conventional wastewater treatment, paint slag generally has certain viscosity, and in order to prevent the blockage of equipment pipelines, a coagulant and/or a flocculating agent can be introduced into a treatment system, so that the viscosity of the paint slag can be reduced while the function of the coagulant is played. The coagulant used in the present application may be one or a combination of more of modified melamine formaldehyde resin, cationic starch, cationic quaternary ammonium salt, cationic diquaternary ammonium salt, cationic polyquaternary ammonium salt, bentonite, diatomaceous earth, soluble aluminum salt, soluble iron salt, polyaluminum chloride, polyferric chloride, polyaluminum ferric chloride, macromolecular organic acid, and the like. Macromolecular organic acids generally refer to organic acids having a molecular weight of 1000 or more, and may be, for example, humic acid, tannic acid, etc. In an embodiment of the invention, the flocculant may be a combination of bentonite, soluble aluminum salt, polymeric ferric chloride, and macromolecular organic acid, wherein the mass ratio of bentonite to soluble aluminum salt may be 1: 0.4-4, 1: 0.4-0.6, 1: 0.6-0.8, 1: 0.8-1, 1: 1-2, 1: 2-3, or 1: 3-4, the mass ratio of bentonite to polymeric ferric chloride may be 1: 0.6-8, 1: 0.6-0.8, 1: 0.8-1, 1: 1-2, 1: 2-4, 1: 4-6, or 1: 6-8, and the mass ratio of bentonite to macromolecular organic acid may be 1: 0.8-7, 1: 0.8-1, 1: 1-2, 1: 2-3, 1: 3-4, 1: 4-5, 1: 5-6, or 1: 6-7. The coagulant is generally used in an amount that destabilizes and coagulates the dissolved paint to form fine flocs, and that disperses uniformly in water under agitation without adhering to the container. For example, the addition concentration of the coagulant can be 0.3-3 wt% and 0.3-0.5 wt%0.5 to 0.7 wt%, 0.7 to 1 wt%, 1 to 1.5 wt%, 1.5 to 2 wt%, 2 to 2.5 wt%, or 2.5 to 3 wt%. Suitable types of flocculating agent that can be complexed with a coagulant to cause paint in a solvent system to form paint sludge will be known to those skilled in the art, for example, the flocculating agent may be selected from PAM (polyacrylamide) and the like, which may in particular be selected from a combination of one or more of cationic PAM, anionic PAM, non-ionic PAM and the like, which may have a molecular weight of 15 x 10⁵～200*10⁵、15*10⁵～20*10⁵、20*10⁵～30*10⁵、30*10⁵～50*10⁵、50*10⁵～60*10⁵、60*10⁵～80*10⁵、80*10⁵～100*10⁵、100*10⁵～150*10⁵Or 150 x 10⁵～200*10⁵Preferred PAM's may have a molecular weight of 80 x 10⁵～200*10⁵. The amount of flocculating agent used is generally such that the supernatant of the resulting solution system after treatment is clear and the sinking paint sludge flocs are large to facilitate rapid sedimentation, and the volume of the sludge layer should generally be no more than 35%, 40%, or 45% of the total solvent system. For example, the addition concentration of the flocculating agent can be 5-30 mg/L, 5-10 mg/L, 10-15 mg/L, 15-20 mg/L, 20-25 mg/L or 25-30 mg/L. In the coagulating sedimentation treatment, a coagulating agent is required to be in full contact with a solvent to be treated, so that paint components can be fully destabilized and sedimentated to form paint slag, for example, in the coagulating sedimentation treatment, a reaction system can be fully stirred, and for example, the stirring time of the reaction system in the coagulating sedimentation treatment can be 20-60 min, 20-30 min, 30-40 min, 40-50 min or 50-60 min.

In the separation and purification method, the solvent to be treated can provide a first liquid phase stream and wet paint residues after being subjected to coagulating sedimentation treatment. The first liquid phase stream is typically the supernatant obtained after the coagulating sedimentation treatment, the remainder being mainly wet paint sludge with a high water content. Generally speaking, the moisture content of the wet paint slag may be 90 wt% or more, 92 wt% or more, 94 wt% or more, 96 wt% or more, 98 wt% or more, or 99 wt% or more, and the yield may be based on the volume of the solvent to be treated20-40 v/v%, 20-25 v/v%, 25-30 v/v%, 30-35 v/v%, or 35-40 v/v%. While the organic solvent content of the first liquid phase stream (i.e., the supernatant from the separation) may typically be 5-8 wt%, 5-5.5 wt%, 5.5-6 wt%, 6-6.5 wt%, 6.5-7 wt%, 7-7.5 wt%, or 7.5-8 wt%, and the CODcr of the first liquid phase stream may typically be 2 x 10⁵～3*10⁵mg/L、2*10⁵～2.2*10⁵mg/L、2.2*10⁵～2.4*10⁵mg/L、2.4*10⁵～2.6*10⁵mg/L、2.6*10⁵～2.8*10⁵mg/L, or 2.8 x 10⁵～3*10⁵mg/L, the yield of the product can account for 60-80 v/v%, 60-65 v/v%, 65-70 v/v%, 70-75 v/v%, or 75-80 v/v% of the volume of the solvent to be treated.

The method for separating and purifying the aqueous waste solvent provided by the invention can further comprise the following steps: the wet paint slag is subjected to a dehydration treatment to provide a second liquid phase stream and dry paint slag. Due to the high water content in the wet paint slag, the wet paint slag is further subjected to a dehydration treatment to provide a second liquid phase stream and dry paint slag. The dehydration treatment generally refers to a treatment method for separating water from paint slag in wet paint slag. Suitable methods for separating the paint residue from water will be known to those skilled in the art and may be, for example, centrifuge dewatering, stack screw dewatering, plate and frame filter dewatering, oven dewatering, belt filter dewatering, vacuum dewatering, and the like. Generally, the water content of the dry paint slag has been minimized, for example, the water content of the dry paint slag may be 70 wt.% or less, 75 wt.% or less, or 80 wt.% or less. The first and second liquid phase streams obtained by separation can be combined and further subjected to subsequent separation and purification treatments.

The method for separating and purifying the aqueous waste solvent provided by the invention can further comprise the following steps: the first and second liquid phase streams are combined and introduced into a separation agent for a separation and purification process to provide an upper separation liquid and a lower separation liquid. The separation and purification treatment generally refers to a treatment method in which a separation agent is introduced into a solvent system, so that an organic solvent in the solvent system is precipitated, and the organic solvent gradually floats upwards to form an upper-lower layered solvent system due to low density, thereby realizing solvent separation. The separating agent may be an ionic compound having good solubility in a solution system, and the organic solvent in the solvent system may be precipitated by breaking the hydrogen bonding force between the organic solvent component and water by hydration of the added ionic compound using the principle of phase equilibrium, for example, the ionic compound may be one or a combination of more selected from carboxylate, amine salt, quaternary ammonium salt, phenoxide, alkoxide, sodium salt, potassium salt, magnesium salt, calcium salt, iron salt, aluminum salt, and the like. For another example, the concentration of the separating agent may be 5-30 wt%, 5-10 wt%, 10-15 wt%, 15-20 wt%, 20-25 wt%, or 25-30 wt%. In the separation and purification treatment, it is generally required to make the separation agent fully contact with the first liquid phase stream and the second liquid phase stream so as to fully separate out the organic solvent in the solvent system, for example, in the separation and purification treatment, the reaction system may be fully stirred, and for example, the stirring time of the reaction system in the separation and purification treatment may be 30 to 60min, 30 to 40min, 40 to 50min, or 50 to 60 min.

In the separation and purification method, the combined stream can provide an upper separation liquid and a lower separation liquid after being subjected to separation and purification treatment. The obtained upper layer separation liquid is mainly an organic solvent part, the upper layer separation liquid can account for 5-15 v/v%, 5-7 v/v%, 7-9 v/v%, 9-11 v/v%, 11-13 v/v%, or 13-15 v/v% of the water body introduction amount, the concentration of the organic solvent in the upper layer separation liquid can be 50-90 wt%, 50-60 wt%, 60-70 wt%, 70-80 wt%, or 80-90 wt%, and the CODcr of the upper layer separation liquid can be 15 10⁵～18*10⁵mg/L、15*10⁵～16*10⁵mg/L、16*10⁵～17*10⁵mg/L, or 17 x 10⁵～18*10⁵mg/L. The upper layer separation liquid can be further recycled as an aqueous solvent in a coating line. The obtained lower layer separation liquid mainly comprises an aqueous phase part of a separation medicament, the separation medicament used in the separation and purification treatment can be mainly contained in the lower layer separation liquid, and the lower layer separation liquid can account for 85-95 v/v%, 85-87 v/v%, 87-89 v/v%, 89 ℃ and 89 ℃ of the water body introduction amount91 v/v%, 91-93 v/v%, or 93-95 v/v%, and the lower layer separation liquid CODcr may be 3 x 10⁴～5*10⁴mg/L、3*10⁴～3.5*10⁴mg/L、3.5*10⁴～4*10⁴mg/L、4*10⁴～4.5*10⁴mg/L, or 4.5 x 10⁴～5*10⁴mg/L。

In the above separation and purification method, the first liquid phase stream and/or the second liquid phase stream may be subjected to a first filtration treatment before the separation and purification treatment. The first filtration treatment generally refers to a treatment process by means of a suitable filtration medium, whereby solid particulate impurities (e.g. residual paint residue particles, etc.) entrained in the first and/or second liquid phase streams are removed. The resulting stream after the first filtration treatment should generally be clear and transparent, e.g., the turbidity may be < 12NTU, < 10NTU, or < 8 NTU. For another example, the pore size of the filter medium in the first filtration treatment may be 10 to 50 μm, 10 to 15 μm, 15 to 20 μm, 20 to 25 μm, 25 to 30 μm, 30 to 35 μm, 35 to 40 μm, 40 to 45 μm, or 45 to 50 μm.

In the above separation and purification method, the upper layer separated liquid provided by the separation and purification treatment may be subjected to a second filtration treatment. The second filtration treatment generally refers to a treatment method in which solid impurities remaining in the upper layer separation liquid are removed by passing through a suitable filter medium. In the separation and purification process, with the addition of a separation agent, besides solvent components are separated and floated, some residual components (such as coagulant) in original clear liquid are separated out due to the change of a clear liquid solubility system to form floc particle impurities, and the impurities such as the impurities are directly used for a coating production line along with a solvent concentrated solution, although the cleaning quality is not influenced, the residual impurities can be sprayed on the surface of a vehicle body along with paint after paint spraying is resumed to influence the coating quality. Therefore, before recycling, the micro-flocs in the upper layer separation liquid should be filtered, for example, the pore size of the filter medium in the second filtering treatment can be 1-10 μm, 1-2 μm, 2-4 μm, 4-6 μm, 6-8 μm, or 8-10 μm.

The method for separating and purifying the aqueous waste solvent provided by the invention can further comprise the following steps: the lower layer of the separated liquid is desolventized to provide a recovered pharmaceutical agent. As described above, a large amount of separation chemicals are dissolved in the lower layer separation liquid, and after the solvent is removed from the lower layer separation liquid, the obtained solid phase is the separation chemicals, and at least part of the separation chemicals can be recycled and reused for separation and purification treatment again.

The second aspect of the present invention provides a separation and purification system for an aqueous waste solvent, which can be used in the separation and purification method for an aqueous waste solvent provided in the first aspect of the present invention. The above separation and purification system for the aqueous waste solvent may include:

the system comprises a coagulating sedimentation device 1, a first liquid phase flow and wet paint slag, wherein the coagulating sedimentation device is used for introducing a coagulating agent into a solvent to be treated for coagulating sedimentation treatment to provide a first liquid phase flow and the wet paint slag;

the solid-liquid separation device 4 is used for dehydrating the wet paint residues to provide a second liquid phase flow and dry paint residues, and the solid-liquid separation device 4 is connected with the coagulating sedimentation device 1;

a separation and purification device 2 for combining the first liquid phase stream and the second liquid phase stream and introducing a separation agent to perform separation and purification treatment to provide an upper layer separation liquid and a lower layer separation liquid, wherein the separation and purification device 2 is respectively communicated with the coagulation and precipitation device 1 and the solid-liquid separation device 4 in a fluid manner;

and a solvent removing device 3 for removing the solvent from the lower layer separated liquid to provide a recovered chemical agent, at least a part of which is used as the separated chemical agent for the separation and purification treatment, the solvent removing device being in fluid communication with the separation and purification device.

The separation and purification system provided by the invention can comprise a coagulating sedimentation device 1, wherein the coagulating sedimentation device 1 is mainly used for introducing a coagulating agent into a solvent to be treated for coagulating sedimentation treatment so as to provide a first liquid phase flow and wet paint residues. Suitable coagulating sedimentation device 1 should be known to the person skilled in the art, for example, the coagulating sedimentation device 1 may be a coagulation reaction tank. The coagulation sedimentation device 1 may further include a stirring device to sufficiently mix the reaction system, and the stirring device may be, for example, mechanical impeller stirring or aeration tube stirring. The bottom of the coagulating sedimentation device 1 can be generally conical, and a liquid outlet pipeline of the coagulating sedimentation device 1 can be generally communicated with the solid-liquid separation device 4 and is positioned at the bottom of the coagulating sedimentation device 1, so that paint residues can be conveniently gathered at the bottom of the coagulating sedimentation device and can be led out of the coagulating sedimentation device 1. The liquid outlet pipeline of the coagulating sedimentation device 1 can be generally provided with a pump body, and the applicable pump body can be specifically a pneumatic diaphragm pump, an electric diaphragm pump or a screw pump and the like.

The separation and purification system provided by the invention can further comprise a solid-liquid separation device 4, wherein the solid-liquid separation device 4 is mainly used for carrying out dehydration treatment on wet paint residues to provide a second liquid phase flow and dry paint residues, and the solid-liquid separation device 4 is in fluid communication with the coagulating sedimentation device 1. The wet paint slag obtained by the coagulating sedimentation treatment can be further introduced into a solid-liquid separation device 4 for solid-liquid separation treatment. Suitable solid-liquid separation devices 4 should be known to those skilled in the art, for example, the solid-liquid separation device 4 may be a dehydrator, specifically, a centrifugal dehydrator, a stacked screw dehydrator, a plate-and-frame filter press dehydrator, a drying dehydrator, a belt filter press dehydrator, a vacuum dehydrator, or the like.

The separation and purification system provided by the invention can further comprise a separation and purification device 2, wherein the separation and purification device 2 is mainly used for combining the first liquid-phase flow and the second liquid-phase flow and introducing a separation agent to perform separation and purification treatment so as to provide an upper layer separation liquid and a lower layer separation liquid, and the separation and purification device 2 is respectively in fluid communication with the coagulating sedimentation device 1 and the solid-liquid separation device 4. The first liquid phase stream obtained from the coagulating sedimentation treatment and the second liquid phase stream obtained from the solid-liquid separation treatment can be further introduced into the separation and purification plant 2 for separation and purification treatment. Suitable separation and purification devices 2 should be known to the person skilled in the art, for example, the separation and purification device 2 may be a separation and purification tank. The separation and purification apparatus 2 may further include a stirring device to sufficiently mix the reaction system, and the stirring device may be, for example, mechanical impeller stirring or aeration tube stirring. The liquid outlet pipeline in the separation and purification device 2 can be generally communicated with the subsequent second filtering device 6 and the solvent removal device 3 and is positioned at the bottom of the device, so that the lower-layer separated liquid occupying most of water can be firstly discharged after the reaction is finished, and then the upper-layer separated liquid is discharged, and the separated collection of the two parts of separated liquid is realized. The liquid outlet pipeline of the separation and purification device 2 may be further provided with a pump body, which may be, for example, a pneumatic diaphragm pump, an electric diaphragm pump, a screw pump, a centrifugal pump, etc.

The separation and purification system provided by the invention can further comprise a solvent removal device 3, wherein the solvent removal device 3 is mainly used for removing the solvent from the lower layer separation liquid so as to provide a recovered medicament, at least part of the recovered medicament is used as the separation medicament for separation and purification treatment, and the solvent removal device is in fluid communication with the separation and purification device. The lower separated liquid obtained by the separation and purification treatment may be further introduced into a solvent removal device 3 to remove the solvent. Suitable solvent removal devices 3 should be known to the person skilled in the art, for example, the solvent removal device 3 may be an evaporator or a crystallizer, in particular an MVR evaporator, a multiple effect evaporator, a wiped film evaporator, a DTB crystallizer, an OSLO crystallizer, a horizontal crystallizer, an FC crystallizer or the like.

The separation and purification system provided by the invention can further comprise a first filtering device 5, wherein the first filtering device 5 is mainly used for performing a first filtering treatment on the first liquid-phase stream and/or the second liquid-phase stream, and the coagulating sedimentation device 1 and/or the solid-liquid separation device 4 are/is in fluid communication with the separation and purification device 2 through the first filtering device 5. The first liquid phase stream resulting from the coagulating sedimentation treatment and the second liquid phase stream resulting from the solid-liquid separation treatment may be introduced into the first filtering device 5 to be subjected to the first filtering treatment, and further introduced into the separation and purification device 2 to be subjected to the separation and purification treatment after being subjected to the filtering treatment. Suitable first filter means 5 should be known to the person skilled in the art, for example the first filter means 5 may be of the cartridge type, bag type, stainless steel filter mesh, disc filter or the like, and for example the pore size of the filter medium in the first filter means 5 may be 10-50 μm.

The separation and purification system provided by the invention can further comprise a second filtering device 6, the second filtering device 6 is mainly used for carrying out second filtering treatment on the upper layer separation liquid provided by the separation and purification treatment, and the second filtering device 6 is in fluid communication with the separation and purification device 2. The upper layer separated liquid resulting from the separation and purification treatment may be introduced into the second filtering device 6 to be subjected to the second filtering treatment. Suitable second filter means will be known to those skilled in the art, for example, the second filter means may be of the cartridge type, bag type, stainless steel filter mesh, disc filter or the like, and for example, the filter media in the second filter means may have a pore size of 1 to 10 μm.

The method and the system for separating and purifying the aqueous waste solvent can treat the aqueous waste solvent stably and reliably at low cost, can really realize the reduction of hazardous waste, can realize the repeated cyclic utilization of medicaments, solvents and the like in the treatment process, greatly reduce the treatment cost, and have good industrialization prospect.

The invention of the present application is further illustrated by the following examples, which are not intended to limit the scope of the present application.

Example 1

1000t of aqueous waste solvent is produced by a coating production line of a certain automobile manufacturing plant every year, all outward transportation is used as hazardous waste incineration disposal at present, the disposal cost is 4000 yuan/t, the annual disposal cost is about 400 ten thousand, and in order to reduce the cost, a separation and purification process of the aqueous waste solvent is adopted to implement a hazardous waste reduction project.

The main components of the water-based cleaning solvent used by the coating production line are alcohols such as ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, isopropanol and n-butanol, and other small additives, and the effective component of the solvent is 10%. The aqueous solvent passing through the cleaning spray gun is converted into aqueous waste solvent, which contains a large amount of residual paint components (6 wt%) cleaned, and the effective concentration of the solvent is reduced from 10 wt% to 6 wt%, and the CODcr of the solvent is 70 ten thousand mg/L.

Firstly, carrying out coagulating sedimentation treatment to remove paint components in the paint, wherein the volume of a prepared coagulating tank is designed according to the once-per-day treatment amount, the water-based waste solvent is generated 4t every day according to the 250-day annual production of the coating production line, in order to ensure a certain buffer amount, the volume of the coagulating tank is designed according to 5t, the bottom of a coagulating reaction tank is made into a conical shape, and a pneumatic diaphragm pump is arranged to discharge paint slag at the bottom. The paint slag pump adopts a pneumatic diaphragm pump, the wet paint slag production amount accounts for 30% of the total water inflow, and the wet paint slag amount per day is 1.2 t. The coagulation tank is provided with a mechanical impeller stirrer, and the rotating speed is not too fast or too slow, namely 80-120 revolutions per minute, so that the coagulation reaction is sufficient and the formed floc is not broken.

The coagulant comprises a coagulant and a flocculant, wherein the adopted coagulant comprises bentonite, soluble aluminum salt, polymeric ferric chloride and macromolecular organic acid, the proportioning concentration of the components is respectively 10%, 5%, 10% and 10%, and the balance is water. Selecting sodium-based bentonite, using soluble aluminum salt as aluminum sulfate and using macromolecular organic acid as humic acid; the adopted flocculating agent (PAM) is cationic PAM, the molecular weight of the cationic PAM is 1200 ten thousand, and the flocculating agent (PAM) is prepared into 0.1-0.5% diluent for use. Before the coagulant is used, a small experiment is carried out, and the adding concentration of the adopted coagulant is confirmed to be 2 percent, and the adding concentration of the flocculating agent PAM is confirmed to be 15 mg/L. By adding the coagulant, the paint dissolved in the aqueous waste solvent is destabilized and coagulated to form fine flocs, and the fine flocs are uniformly dispersed in water under the action of a mechanical impeller stirrer and do not adhere to the inside of a coagulation tank; by adding the flocculating agent PAM, the supernatant is clarified, paint slag forms large flocs and is rapidly deposited at the bottom of the tank, and the volume of a slag layer accounts for about 30%. The paint slag settled at the bottom of the coagulation tank is wet paint slag, the water content of the wet paint slag reaches more than 98 percent, the wet paint slag yield is about 300t according to the water-based waste solvent amount of 1000 t/year, and then further dehydration treatment is needed.

After coagulation treatment, the lower layer paint slag is discharged to dewatering equipment for dewatering treatment, the content of the effective solvent in the remaining supernatant is 6 percent, the CODcr is 23 ten thousand mg/L, the water amount accounts for about 70 percent of the total water inflow, and the yield of the supernatant is about 700 t/year according to the water-based waste solvent amount of 1000 t/year.

The dewatering equipment of the wet paint slag adopts a plate-and-frame filter press. The wet paint slag is conveyed to a plate-and-frame filter press from a coagulation reaction tank by a paint slag pump for dehydration treatment, the wet paint slag forms dry paint slag after the dehydration treatment, the water content of the dry paint slag is reduced from 98% to 70%, namely the reduction rate of the paint slag reaches 93.3%, and the hazardous waste disposal cost is saved. According to the fact that the wet paint slag yield is 30% of the total water inflow, the wet paint slag yield is 300 t/year, after dehydration treatment, the dry paint slag yield is 20 t/year, the paint slag decrement is 280 t/year, namely the water portion removed is 280 t/year, and the water portion and the supernatant are combined to be 980 t/year in total.

Impurities such as paint slag particles and the like may be contained in the supernatant and the wet paint slag after the coagulation reaction, so that the two streams of water are combined and then need to be filtered, and the selected filter is a bag filter with the filtering precision of 25 mu m. The filtered clear solution is clear and transparent, the turbidity is lower than 10NTU, and the clear solution enters the separation and purification treatment process.

Similar to the coagulation reaction tank, the separation and purification tank is designed in volume according to the amount of the aqueous component solvent to be treated in one batch per day, and is also designed in 5t because the water inflow amount is substantially the same as that of the coagulation reaction tank. The separating agent is prepared by compounding 3 soluble ionic compounds including quaternary ammonium salt, magnesium salt and aluminum salt, wherein the quaternary ammonium salt is dodecyl polyoxyethylene ammonium chloride, the magnesium salt is magnesium sulfate heptahydrate, the aluminum salt is aluminum trichloride, the proportion of the components is respectively 20%, 35% and 45%, and the adding concentration of the compound separating agent is 10%. The hydration of the added separating agent destroys the hydrogen bond acting force of the solvent components and water, so that the solvent components are gradually separated from the water, and simultaneously, the separating agent is gradually transferred to the water. The separation and purification tank is equipped with a mechanical impeller stirrer, and the reaction time of each batch of separation, purification and stirring is 40 min. The separation and purification tank is provided with a pneumatic diaphragm pump, after the reaction is finished, the lower layer thin liquid occupying most of the water is discharged, the upper layer thick liquid is discharged, and the upper layer thick liquid and the lower layer thin liquid need to be collected respectively.

The amount of the upper layer solvent concentrate separated by separation and purification is 98 t/year, the effective concentration of the solvent reaches 80 percent, the CODcr reaches 170 ten thousand mg/L and is far higher than about 10 percent of the freshly prepared solvent, the solvent is sent to a production line of a coating workshop for cleaning a spray gun, the requirement of the coating production line for cleaning the spray gun can be completely met, then the solvent is diluted by 5 times, the effective concentration of the solvent is 16 percent, the concentration of the solvent is still higher than about 10 percent of the freshly prepared solvent, and the spray gun is cleaned, so that the requirement of the coating production line for cleaning the spray gun is met.

The upper layer concentrated solution needs to be filtered before being reused in a coating production line so as to remove floc particle impurities formed by the residual coagulant and prevent the influence on the coating quality. Since the treated fine flocs are small, a bag filter having a filtration accuracy of 5 μm is selected.

The main components of the lower layer dilute solution are water, a dissolved separation agent and a small amount of solvent components, the CODcr of the lower layer dilute solution is reduced to 23 ten thousand mg/L and then to 5 ten thousand mg/L from 70 ten thousand mg/L of the aqueous waste solvent stock solution through coagulation treatment in the first step, and the lower layer dilute solution can be directly discharged into a wastewater treatment system for treatment. However, as a large amount of separation agents are dissolved in the lower layer of weak solution, in order to save the cost of the separation agents, an MVR evaporator and a DTB crystallizer are adopted to carry out evaporation crystallization treatment on the lower layer of weak solution, the crystals and solid matters of the obtained separation agents are 92 t/year, the separation agents required all the year are 98 t/year, and only 6 t/year of the separation agents are needed to be supplemented. The water evaporated is condensed to 888 t/year and then discharged into a wastewater treatment system for treatment.

The economic benefit analysis of the project year is detailed in table 1 (annual aqueous waste solvent production is 1000 t):

TABLE 1

Main economic indicators	Number of	Remarks for note
			Cost of paint slag disposal Yuan	100000	20 t/year, 5000 Yuan/t
Cost of coagulant	200000	Adding the raw materials according to the concentration of 2%, wherein the adding concentration needs 20t and 10000 Yuan/t
			Cost of flocculant	450	Adding into the mixture according to the concentration of 15mg/L, wherein the adding concentration needs 0.015t and 30000 yuan/t
Cost of separating the medicament	30000	6 t/year, 5000 Yuan/t
			Depreciation cost of equipment	150000	Investment in equipment 1500000 yuan, depreciation in 10 years
Energy consumption, yuan	125000	Mainly the charges of electricity, compressed air and the like
			Personnel operation, Yuan	100000
Saving the cost of hazardous waste disposal	4000000	According to 4000/t
			The recycling workshop saves cost and is good	3920000	98 t/year, 40000 yuan/t of saving
Total cost saving	7214550

As shown in table 1, the annual cost of the method for separating and purifying the aqueous waste solvent provided by the present application can be about 721 ten thousand yuan compared with the conventional process.

In conclusion, the present invention effectively overcomes various disadvantages of the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. A method for separating and purifying an aqueous waste solvent, the method comprising:

2. The method for separating and purifying the aqueous waste solvent according to claim 1, wherein in the step 1), the content of paint residue in the solvent to be treated is 5-15 wt%;

and/or in the step 1), the solvent to be treated comprises an organic solvent, the content of the organic solvent is 5-8 wt%, and the organic solvent is selected from an ether solvent and/or an alcohol solvent;

and/or, in the step 1), the CODcr of the solvent to be treated is 5 x 10⁵～10*10⁵mg/L。

3. The method for separating and purifying the aqueous waste solvent according to claim 1, wherein in the step 1), the coagulant comprises a coagulant and/or a flocculant, the coagulant is selected from one or more of modified melamine formaldehyde resin, cationic starch, cationic quaternary ammonium salt, cationic diquaternary ammonium salt, cationic polyquaternary ammonium salt, bentonite, diatomite, soluble aluminum salt, soluble iron salt, polyaluminum chloride, polyferric chloride, polyaluminum ferric chloride and macromolecular organic acid, the coagulant is added at a concentration of 0.3-3 wt%, the flocculant is selected from polyacrylamide PAM, the PAM is selected from one or more of cationic PAM, anionic PAM and nonionic PAM, and the flocculant is added at a concentration of 5-30 mg/L.

4. The method for separating and purifying the aqueous waste solvent according to claim 1, wherein in the step 2), the moisture content of the wet paint slag is not less than 98 wt%, and the moisture content of the dry paint slag is not more than 75 wt%.

5. The method for separating and purifying the aqueous waste solvent according to claim 1, wherein the first liquid phase stream and/or the second liquid phase stream is further subjected to a first filtering process in step 3), and the pore size of the filtering medium in the first filtering process is 10-50 μm.

6. The method for separating and purifying the aqueous waste solvent according to claim 1, wherein the separating agent in the step 3) is selected from ionic compounds selected from one or more combinations of carboxylate, amine salt, quaternary ammonium salt, phenoxide, alkoxide, sodium salt, potassium salt, magnesium salt, calcium salt, iron salt and aluminum salt;

and/or in the step 3), the adding concentration of the separating agent is 5-30 wt%;

and/or in the step 3), the upper layer separation liquid accounts for 5-15 v/v% of the water body introduction amount, the concentration of the organic solvent in the upper layer separation liquid is 50-90 wt%, and the CODcr of the upper layer separation liquid is 15 x 10⁵～18*10⁵mg/L；

And/or in the step 3), the lower layer separation liquid accounts for 85-95 v/v% of the water body introduction amount, and the CODcr of the lower layer separation liquid is 3 x 10⁴～5*10⁴mg/L。

7. The method for separating and purifying an aqueous waste solvent according to claim 1, wherein in the step 3), the upper layer separation liquid is further subjected to a second filtration treatment in which a pore diameter of a filter medium is 1 to 10 μm.

8. A system for separation and purification of an aqueous spent solvent, the system comprising:

the system comprises a coagulating sedimentation device (1) and a control system, wherein the coagulating sedimentation device is used for introducing a coagulating agent into a solvent to be treated to carry out coagulating sedimentation treatment so as to provide a first liquid phase flow and wet paint slag;

a solid-liquid separation device (4) for performing a dehydration treatment on the wet paint slag to provide a second liquid phase stream and dry paint slag, the solid-liquid separation device (4) being in fluid communication with the coagulating sedimentation device (1);

a separation and purification device (2) for combining the first liquid phase stream and the second liquid phase stream and introducing a separation agent to perform a separation and purification treatment to provide an upper layer of separation liquid and a lower layer of separation liquid, wherein the separation and purification device (2) is respectively communicated with a coagulation and precipitation device (1) and a solid-liquid separation device (4) in a fluid manner;

a solvent removal device (3) for removing solvent from the lower layer of separated liquid to provide a recovered chemical agent, at least a portion of which is used as the separated chemical agent for the separation and purification treatment, the solvent removal device (3) being in fluid communication with the separation and purification device (2).

9. The separation and purification system of aqueous waste solvent according to claim 8, further comprising a first filtering device (5) for performing a first filtering treatment on the first liquid phase stream and/or the second liquid phase stream, wherein the coagulating sedimentation device (1) and/or the solid-liquid separation device (4) is in fluid communication with the separation and purification device (2) through the first filtering device (5);

the aperture of the filter medium in the first filter device (5) is 10-50 μm.

10. The separation and purification system for aqueous waste solvent according to claim 8, further comprising a second filtering device (6) for performing a second filtering process on the supernatant fluid provided by the separation and purification process, wherein the second filtering device (6) is in fluid communication with the separation and purification device (2);

the aperture of the filter medium in the second filter device (6) is 1-10 mu m.