Process for treating and recycling sebacic acid production wastewater

Abstract

The invention discloses a sebacic acid production wastewater treatment and recycling process which comprises the following steps: a heat pump evaporation system comprises an evaporator, a compressor, a circulating pump and a heating heat exchanger, sebacic acid production wastewater is efficiently desalted through the heat pump evaporation system, and obtained steam enters a catalytic combustion device for catalytic combustion reaction; the final effluent is reused for an evaporation process and a crude sebacic acid washing process in the production process. Low-level heat energy of the system is recovered through the heat pump technology, evaporation energy consumption is remarkably reduced, gas-phase oxidation removal of organic matter is achieved through catalytic combustion, and secondary pollution is avoided; meanwhile, closed-loop recycling of wastewater is achieved, fresh water consumption and wastewater discharge are greatly reduced, and the comprehensive advantages of being low in operation cost, high in treatment efficiency, high in environmental friendliness and the like are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sebacic acid preparation, and particularly relates to a preparation and wastewater treatment of sebacic acid. BACKGROUND

[0002] Sebacic acid is an important long-chain dicarboxylic acid, which is widely used as a key monomer for producing nylon engineering plastics, high-temperature lubricating oil, environmentally friendly plasticizer and high-performance coating. Its industrial production usually adopts castor oil acid methyl ester alkali cleavage process, which includes: adding a predetermined amount of water, alkali and diluent into a reaction kettle, heating to a first temperature stage to evaporate water, continuing to heat to a second temperature stage, and then starting to continuously add castor oil acid methyl ester raw oil, and after the feeding is completed, the cleavage reaction is carried out at the temperature. The obtained slurry product after the reaction is completed is dissolved with hot water, and then sulfuric acid is added to the mixture to neutralize, and after standing and separating, sebacic acid monosodium salt solution and liquid paraffin are obtained. Then, sulfuric acid is added to the sebacic acid monosodium salt solution to acidify and crystallize, and sebacic acid crude product and acidification wastewater are obtained through solid-liquid separation. The wastewater in the production of sebacic acid is mainly the wastewater evaporated in the reaction and the high-concentration salt-containing organic acidification wastewater generated after the material after the reaction is dissolved, neutralized and separated from the sebacic acid crude product. In addition, a large amount of water is also needed for washing to remove the residual sulfuric acid and inorganic salt in the crude product. The acidification wastewater has the characteristics of high salt content (calculated as sodium sulfate), low pH (usually 2-4), and contains a small amount of sebacic acid and other fatty acids. In the current sebacic acid production process, 25-30 tons of wastewater are discharged for every ton of sebacic acid produced, which consumes a large amount of water and has high energy consumption.

[0003] Chinese patent CN102351682A discloses a preparation method of sebacic acid using decanoic fatty acid as a diluent. The advantage of this technology is that decanoic fatty acid is used as a reaction diluent and a recyclable byproduct, which avoids the use of phenolic substances, eliminates phenol pollution from the source, and realizes the internal circulation of byproducts, thereby reducing the raw material cost and the complexity of subsequent treatment to a certain extent. However, high-salt organic wastewater containing sodium sulfate is still generated in the preparation process of sebacic acid, and its treatment difficulty and cost are still high.

[0004] Chinese patent CN110963909A provides a method for preparing sebacic acid by castor oil cleavage without phenol, which has the innovation of using microwave cleavage technology and avoiding the use of phenolic diluent, thereby eliminating the pollution of phenol-containing wastewater from the source. However, this method still cannot avoid the generation of other high-salt organic wastewater in the production process of sebacic acid.

[0005] Chinese patent CN107326051A discloses a process for preparing high purity sebacic acid by microbial fermentation. This technology has the characteristics of green and sustainable, mild reaction conditions, environmental friendliness, low content of impurities such as decanoic acid and decanohydroxy fatty acid in the obtained product, high purity, and is suitable for the synthesis of high-end polymers such as polyamide and polyester. However, this fermentation route still has certain limitations: the fermentation process control is complex, the raw material cost is high, and the fermentation wastewater produced depends on biochemical treatment, and the environmental governance burden is still outstanding.

[0006] Chinese patent CN104609640A discloses a comprehensive treatment method for sebacic acid production wastewater. The wastewater is treated by extraction, biochemical treatment, advanced treatment and evaporation desalination device in turn, and the circulating mother liquor produced by evaporation is returned to the biochemical system. This method can realize wastewater reuse, but the process is long, depends on high energy consumption evaporation concentration unit, and the extraction agent residue and biochemical sludge treatment may cause secondary pollution problems.

[0007] Chinese patent CN105084529A proposes a method for treating sebacic acid wastewater by using salt-tolerant microorganisms. By adding a composite microbial agent in the biochemical system, the microorganisms can degrade COD and volatile phenol pollutants under 3% to 15% salinity. This method improves the salt tolerance, but still has problems such as slow start of the biochemical system, complex microbial agent cultivation, limited degradation efficiency of characteristic pollutants (such as long-chain organic acids), and poor effluent stability under high salt environment, making it difficult to achieve stable reuse.

[0008] Chinese patent CN104609641A discloses an evaporation desalination pretreatment method for sebacic acid wastewater. This technology introduces a multi-stage purification step of "non-dilution biochemical + flocculation precipitation + filtration" before evaporation, aiming to improve the efficiency and stability of subsequent evaporation desalination. The condensed water and sodium sulfate salt obtained by evaporation of the pretreated wastewater can be directly reused or used as byproducts, having certain resource recycling value. However, the multi-stage pretreatment system has large equipment investment, and the biochemical unit has poor adaptability to high-salinity wastewater (special salt-tolerant bacteria are needed), and the addition of flocculants also increases the operating cost and sludge treatment burden.

[0009] The above prior art respectively tries to solve the problems in sebacic acid production and wastewater treatment from different angles: CN102351682A and CN110963909A eliminate phenol pollution from the source by replacing raw materials, CN107326051A uses biological method to improve product purity, and CN104609640A, CN105084529A and CN104609641A are committed to optimizing the wastewater treatment process. However, these technologies have obvious limitations: the first three methods cannot avoid the generation of high-salt or high-COD wastewater, and the last three treatment methods face challenges such as long process, high energy consumption, complex bacteria culture or easy secondary pollution, and none of them can achieve efficient and economic wastewater treatment and resource recycling. SUMMARY

[0010] The technical problem to be solved by the present application is to overcome the problems of high energy consumption, low efficiency, easy secondary pollution and serious water resource waste in the existing sebacic acid production process, and to provide a green sebacic acid preparation process integrating wastewater deep treatment and recycling. The process realizes efficient purification and internal circulation recycling of wastewater by heat pump coupled with catalytic combustion technology, reduces the comprehensive energy consumption and the consumption of auxiliary materials such as sulfuric acid, and achieves the synergistic improvement of economic and environmental benefits.

[0011] The technical solution adopted by the present application is as follows:

[0012] A sebacic acid production wastewater treatment and recycling process, comprising the following steps:

[0013] Step 1: The heat pump evaporation system includes an evaporator, a compressor, a circulating pump and a heating heat exchanger. The sebacic acid production wastewater is fed into the evaporator, the liquid at the bottom of the evaporator is pumped out by the circulating pump and heated by the cold channel of the heating heat exchanger before being returned to the evaporator, and the gas at the top of the evaporator is pumped out and compressed by the compressor to form a vacuum inside the evaporator;

[0014] According to the operation process of the heat pump evaporation system, the wastewater is evaporated and treated, and the desalted water vapor is discharged from the outlet of the compressor, and the salt-containing concentrated liquid is discharged from the bottom of the evaporator;

[0015] Step 2: The desalted water vapor at the outlet of the compressor is transported together with air to a catalytic combustion device, and the residual organic matter in the water is deeply degraded by catalytic combustion;

[0016] Step 3: The water vapor containing water after catalytic combustion treatment in step 2 enters the hot channel of the heating heat exchanger as a heat source to exchange heat, and the outlet water is obtained after heat exchange and cooling.

[0017] Further, the absolute pressure in the evaporator is controlled to be 70-90kPa, and the steam temperature is 90-96.8℃.

[0018] Further, the catalytic combustion device is filled with metal or metal oxide catalyst, and the reaction temperature is controlled at 200-400℃.

[0019] Further, the desalted water vapor at the outlet of the compressor is first exchanged with the water vapor containing water after the treatment of the catalytic combustion device in the first heat exchanger, the desalted water vapor is heated and transported to the catalytic combustion device together with air, and the water vapor containing water after the treatment of the catalytic combustion is sequentially passed through the first heat exchanger and the heating heat exchanger.

[0020] Further, the decanoic acid production wastewater is from the following production process:

[0021] S1 mixing-evaporation-reaction process: water, NaOH and diluent liquid paraffin are added into a reaction kettle, heated to a first temperature stage to evaporate water, continuously added with methyl ricinoleate raw material oil after heating to a second temperature stage, and the cracking reaction is carried out at the temperature after the feeding is completed;

[0022] S2 dissolution process: the slurry product after the reaction of step S1 is dissolved with hot water;

[0023] S3 neutralization-layering process: sulfuric acid is added to the mixed solution of step S2 for neutralization, and the decanoic acid monosodium salt solution and liquid paraffin are obtained after standing and layering;

[0024] S4 adsorption treatment: activated carbon is added to the decanoic acid monosodium salt solution obtained in step S3, and the activated carbon is filtered after adsorption treatment for 20-40 min;

[0025] S5 acidification-filtration: sulfuric acid is added to the filtrate obtained in step S4 for acidification and crystallization, and the decanoic acid crude product and acidification wastewater are obtained after filtration;

[0026] S6 washing-drying process: the decanoic acid crude product obtained in step S5 is washed with water and dried to obtain the decanoic acid product and washing water.

[0027] Further, the water after the treatment of the catalytic combustion is used for the washing process and the evaporation process in the decanoic acid production process.

[0028] Further, the washing water generated in the washing process is used for the dissolution process of the slurry product to realize the internal recycling of water resources.

[0029] Further, the wastewater is from the wastewater evaporated in the decanoic acid production process and the acidification wastewater generated after the dissolution, neutralization and acidification separation of the decanoic acid crude product from the reacted material.

[0030] Further, the water consumption in the dissolution process is 13-18 times the weight of the methyl ricinoleate raw material.

[0031] Further, the water consumption of the washing procedure is 13-18 times of the weight of methyl ricinoleate raw material.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] (1) Achieving near-zero discharge of wastewater and resource recycling: The system can be continuously and stably operated, the effluent quality meets the recycling requirements of the production process, and the fresh water consumption can be greatly reduced to realize the closed loop of water circulation in the process.

[0034] (2) Low operating energy consumption and significant economic efficiency: The present application uses heat pump technology to efficiently recover the heat energy in the system, which is used for reheating in the evaporation and concentration section, significantly reducing the energy consumption of this unit, significantly reducing the economic cost, and greatly improving the economic feasibility of the wastewater treatment process.

[0035] (3) Small occupied area and low capital investment: The catalytic combustion unit is efficient and compact, does not need to rely on large biochemical tanks and sludge treatment facilities, and the occupied area is reduced by more than 90% compared with the biochemical method, effectively saving the civil engineering and equipment investment, and is particularly suitable for technical transformation of existing plants.

[0036] (4) The treated wastewater meets the first level standard (50mg / L) (referring to the Integrated Wastewater Discharge Standard (GB 8978-1996)), and there is no secondary pollution: The catalytic combustion process can decompose organic matter into CO2 and H2O, without the presence of extractant residues and biological sludge, avoiding secondary pollution and being environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is the main process flow diagram of the sebacic acid production wastewater treatment and recycling process of the present application;

[0038] Figure 2 is the structure diagram of the heat pump evaporation system and catalytic combustion device of the present application. DETAILED DESCRIPTION

[0039] The content of the present application is described below in combination with specific embodiments, so as to facilitate further understanding of the present application by those skilled in the art.

[0040] The structure diagram of the heat pump evaporation system and catalytic combustion device of the present application is as follows: Figure 2As shown, the heat pump evaporation system includes an evaporator 1, a compressor 2, a circulating pump 6 and a heating heat exchanger 4. The decanoic acid production wastewater is pumped into the evaporator 1, the liquid at the bottom of the evaporator 1 is pumped out by the circulating pump 6 and heated by the cold channel of the heating heat exchanger 4 and then returned to the evaporator 1, the gas at the top of the evaporator 1 is pumped out and compressed by the compressor 2, and a vacuum is formed in the evaporator 1. According to the operation process of the heat pump evaporation system, the wastewater is evaporated and treated, the desalted water vapor is discharged from the outlet of the compressor 2, and the concentrated liquid containing salt is discharged from the bottom of the evaporator 1.

[0041] The desalted water vapor at the outlet of the compressor 2 and the water vapor containing water treated by the catalytic combustion device are first exchanged by the first heat exchanger 3, the desalted water vapor is heated by the first heat exchanger 3, and the air is transported to the catalytic combustion device, and the water vapor containing water treated by the catalytic combustion is sequentially passed through the first heat exchanger 3 and the heating heat exchanger 4 as a heat source.

[0042] The desalted water vapor at the outlet of the compressor 2 and the air are transported to the catalytic combustion device 5, and the organic matter remaining in the water is deeply degraded by catalytic combustion. The water vapor containing water treated by the catalytic combustion is sequentially passed through the hot channel of the first heat exchanger 3 and the hot channel of the heating heat exchanger 4 as a heat source, and the water is obtained after heat exchange and cooling.

[0043] Example 1: A method for treating decanoic acid production wastewater and recycling by heat pump coupled catalytic combustion, the specific steps are as follows:

[0044] (1) Wastewater treatment: In the production process of decanoic acid, evaporation, acidification filtration and washing processes produce evaporation wastewater, acidification wastewater and washing wastewater respectively. The parameters of the three kinds of wastewater produced in the production of decanoic acid are shown in Table 1.

[0045] After the evaporation wastewater 4kg and the acidification wastewater 59kg are combined, the wastewater is pumped into the heat pump evaporation system (using steam mechanical re-compression technology (MVR)), and the concentrated acid water discharged from the bottom of the evaporator is transported to the neutralization process in the production process of decanoic acid for recycling, which can save about 1.4% of sulfuric acid. The organic light component wastewater vapor obtained by evaporation is pumped out by the compressor, and is introduced into the catalytic combustion device filled with 20g of iron-based catalyst (the active component is iron oxide, the mass fraction is 30%, and the rest is calcium sulfate). The wastewater is introduced at a rate of 60kg / h, the temperature of the catalytic combustor is controlled at 320℃, and air is introduced at a rate of 300L / h for catalytic combustion reaction. The high-temperature steam obtained by the reaction is recycled as the evaporation heat source of the wastewater. The transparent and clear high-temperature steam condensate water obtained after treatment is 53kg, the COD is less than 30mg / L, and the pH is 6.87, which reaches the first level standard of wastewater comprehensive discharge.

[0046] (2) Reuse operation: all the purified water obtained by the above treatment is reused in the reaction process and the crude product washing process in the sebacic acid production process, and about 8 kg of fresh water is supplemented in the crude product washing stage. The washing wastewater (the weight of the washing water is 15 times the weight of the crude sebacic acid oil) generated by washing the crude sebacic acid is collected, heated to 90°C, and then used to dissolve the slurry-like reaction product. The system pH is adjusted to 6 using 50% sulfuric acid. After standing and layering, sebacic acid monosodium salt solution and liquid paraffin are obtained. The separated liquid paraffin is returned to the mixing process for recycling. To the obtained sebacic acid monosodium salt solution, 1% of the total mass of activated carbon is added, and the adsorption treatment is carried out at 30°C for 30 minutes. After removing the activated carbon by filtration, the filtrate is heated to 40°C, and the pH is adjusted to 2 using 50% sulfuric acid for acidification crystallization. After filtration, washing and drying of the reaction liquid, the sebacic acid product is prepared, with a purity of 92.28% and a yield of 66.78%. See Table 2 for specific product quality indicators.

[0047] The results of Example 1 show that using treated wastewater for reuse not only does not affect the product quality of sebacic acid, but also reduces the amount of sulfuric acid used and achieves the recycling of liquid paraffin.

[0048] Comparative Example 1: Collect all the wastewater and reuse it after heat pump coupled catalytic combustion treatment

[0049] (1) Wastewater treatment: Take the same batch of sebacic acid production raw materials as in Example 1, and use fresh water for evaporation, dissolution, and crude product washing. Use 60 kg of fresh water 15 times the weight of the oil to heat to 90°C for dissolving the slurry-like reaction, adjust the pH to 6.0 with 50% sulfuric acid, and separate to obtain sebacic acid monosodium salt solution and liquid paraffin. Add 1% of the total mass of activated carbon to the sebacic acid monosodium salt solution, and adsorb at 30°C for 30 min. After filtration, the filtrate is acidified and crystallized at 40°C by adjusting the pH to 2 using 50% sulfuric acid. The crude sebacic acid is obtained by filtration, and the crude sebacic acid is washed with 60 kg of fresh water 15 times the weight of the oil. Evaporation wastewater, acidification wastewater, and washing wastewater are obtained, and the three kinds of mixed wastewater 114 kg are pumped into a heat pump evaporation system (using steam mechanical re-compression technology (MVR)) to vaporize to obtain wastewater steam containing organic light components. The wastewater is introduced into a catalytic combustion device filled with a catalyst (the catalyst composition and amount are the same as in Example 1) at a rate of 60 kg / h, the temperature of the catalytic combustor is controlled at 320°C, and air is introduced at a rate of 300 L / h for catalytic combustion reaction. The high-temperature steam obtained by the reaction is reused as a waste water vaporization heat source. The transparent and clear high-temperature steam condensate water obtained after treatment is 103 kg, with a COD less than 30 mg / L and a pH of 6.58, meeting the first-level standard for wastewater comprehensive discharge.

[0050] (2) Reuse Operation: All the purified water was reused in the evaporation, dissolution, and washing processes of sebacic acid production. 60 kg of purified water (15 times the weight of oil) was heated to 90°C to dissolve the slurry reaction product. The pH was adjusted to 6.0 with 50% sulfuric acid to separate the layers, resulting in a sebacic acid monosodium salt solution and liquid paraffin. 1% of the total mass of activated carbon was added to the sebacic acid monosodium salt solution, and adsorption was performed at 30°C for 30 min. After filtration to remove the carbon, the filtrate was heated to 40°C, and the pH was adjusted to 2 with 50% sulfuric acid for acidification and crystallization. After filtration, washing, and drying, sebacic acid was obtained with a purity of 91.61% and a yield of 66.89%.

[0051] The process also involves wastewater treatment and reuse, but the amount of wastewater treated is nearly twice that of Example 1, resulting in high energy consumption, which is more than 50% higher than that of Example 1, and it is impossible to form a closed loop for water circulation within the process.

[0052] Compare with Example 2: Collect all wastewater and reuse it after only evaporation treatment.

[0053] The difference between this comparative example and Comparative Example 1 is that the three types of mixed wastewater generated during the production process were pumped into an evaporator for desalination treatment, but the organic matter was not degraded by a catalytic combustion device. All the treated effluent was reused in the evaporation, dissolution, and washing processes of sebacic acid production.

[0054] The results showed that the purity of the sebacic acid product obtained by this process was 90.46%, and the yield was 65.93%. As shown in Table 2, when wastewater was desalinated without COD removal, the product purity did not change significantly. However, the residual organic matter in the system continuously accumulated, leading to a sustained increase in COD concentration in the reuse system. Ultimately, this resulted in a significant darkening of the sebacic acid product's color, indicating that desalination alone cannot meet the water quality reuse requirements for producing high-quality products.

[0055] Table 1. Wastewater quality during sebacic acid preparation process

[0056]

[0057] Table 2. Parameters of treated water and mass of crude sebacic acid obtained by different treatment methods.

[0058]

Claims

1. A process for treatment and reuse of sebacic acid production wastewater, characterized by, Comprise the following steps: Step 1: The heat pump evaporation system comprises an evaporator (1), a compressor (2), a circulating pump (6) and a heating heat exchanger (4), the sebacic acid production wastewater is fed into the evaporator (1), the liquid at the bottom of the evaporator (1) is pumped out by the circulating pump (6) and heated by the cold channel of the heating heat exchanger (4) and then returned to the evaporator (1), the gas at the top of the evaporator (1) is pumped out and compressed by the compressor (2), so that a vacuum is formed in the evaporator (1); According to the operation process of the heat pump evaporation system, the wastewater is evaporated and treated, the desalted water vapor is discharged from the outlet of the compressor (2), and the salt-containing concentrated liquid is discharged from the bottom of the evaporator (1); Step 2: The desalted water vapor from the outlet of the compressor (2) is transported to the catalytic combustion device (5) together with air, and the residual organic matter in the water is deeply degraded by catalytic combustion; Step 3: The water vapor containing water after catalytic combustion treatment enters the hot channel of the heating heat exchanger (4) as a heat source to exchange heat and obtain the outlet water after heat exchange and cooling.

2. The process for treatment and reuse of sebacic acid production wastewater as claimed in claim 1 wherein, The absolute pressure in the evaporator (1) is controlled to be 70-90 kPa, and the steam temperature is 90-96.8℃.

3. The process for treatment and reuse of sebacic acid production wastewater as claimed in claim 1 wherein, The catalytic combustion device is filled with metal or metal oxide catalyst, and the reaction temperature is controlled at 200-400℃.

4. The process for treatment and reuse of sebacic acid production wastewater as claimed in claim 1 wherein, The desalted water vapor from the outlet of the compressor (2) and the water vapor containing water after treatment by the catalytic combustion device are first exchanged by the first heat exchanger (3), the desalted water vapor is heated by the first heat exchanger (3), and then transported to the catalytic combustion device together with air, and the water vapor containing water after catalytic combustion treatment is sequentially passed through the first heat exchanger (3) and the heating heat exchanger (4) as a heat source.

5. The process for treatment and reuse of decanedioic acid production wastewater as claimed in claim 1 wherein, The sebacic acid production wastewater comes from the following production process: S1 mixing-evaporation-reaction process: water, NaOH and diluent liquid paraffin are added to the reaction kettle, heated to the first temperature stage to evaporate water, continuously added castor oil acid methyl ester raw oil after heating to the second temperature stage, and the cracking reaction is carried out at the temperature after the feeding is completed; S2 dissolution process: the slurry product obtained after step S1 reaction is dissolved with hot water; S3 neutralization-layering process: sulfuric acid is added to the mixture liquid of step S2 for neutralization, and sebacic acid monosodium salt solution and liquid paraffin are obtained after standing and layering; S4 adsorption treatment: activated carbon is added to the sebacic acid monosodium salt solution obtained in step S3, and the activated carbon is filtered after adsorption treatment for 20-40 min; S5 acidification-filtration: sulfuric acid is added to the filtrate obtained in step S4 for acidification and crystallization, and sebacic acid crude product and acidification wastewater are obtained by filtration; S6 washing-drying process: the sebacic acid crude product obtained in step S5 is washed with water and dried to obtain sebacic acid product and washing water.

6. A process for treating and reusing sebacic acid production wastewater as claimed in claim 5 wherein, The outlet water after catalytic combustion treatment is used for the washing process and the evaporation process in the sebacic acid production process.

7. A process for treating and reusing sebacic acid production wastewater as claimed in claim 5 wherein, The washing water generated in the washing process is used for the dissolution process of the slurry product, realizing the system internal recycling of water resources.

8. A process for treating and reusing sebacic acid production wastewater as claimed in claim 5 wherein, The wastewater is derived from the wastewater evaporated in the sebacic acid production process and the acidification wastewater generated after the reaction material is dissolved, neutralized and separated into sebacic acid crude product.

9. A process for treating and reusing sebacic acid production wastewater as claimed in claim 5 wherein, The water consumption in the dissolution process is 13-18 times the weight of the castor oil acid methyl ester raw material.

10. A process for treating and reusing sebacic acid production wastewater as claimed in claim 5 wherein, The water amount used in the washing step is 13 to 18 times the weight of the methyl ricinoleate raw material. The water amount used in the washing step is 13 to 18 times the weight of the methyl ricinoleate raw material.

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