A method and apparatus for treating 6-aminocapronitrile process wastewater

Abstract

The application provides a method and device for treating 6-aminocapronitrile process wastewater, which comprises the following steps: adding 6-aminocapronitrile process wastewater, acid and adsorbent into a distillation kettle for distillation; heating the liquid in the distillation kettle to boiling; and further heating the steam to enter a vapor permeation membrane for gas phase membrane separation; condensing the gas on the permeation side of the vapor permeation membrane to collect an aqueous phase; condensing the gas on the interception side to form an interception side component containing organic impurities; the amount of the adsorbent added accounts for 0.5-50% of the mass of the 6-aminocapronitrile process wastewater; and the pressure difference between the interception side and the permeation side of the vapor permeation membrane is between 0.05-0.3 MPa. The COD value of the aqueous phase collected on the permeation side of the vapor permeation membrane is about 1300 ppm, and the water content of the organic residual liquid at the bottom of the kettle is about 25%, thus effectively solving the problem of 6-aminocapronitrile process wastewater.

Description

Technical Field

[0001] This invention relates to the field of amine-containing wastewater treatment technology, and in particular to a method and apparatus for treating process wastewater of 6-aminohexanonitrile. Background Technology

[0002] The process route for preparing 6-aminohexanonitrile via the caprolactam method involves caprolactam undergoing ammoniation ring-opening and dehydration reactions to produce 6-aminohexanonitrile. Water is inevitably generated during the dehydration reaction. The crude 6-aminohexanonitrile product obtained after dehydration is separated by distillation. The first step is to collect wastewater rich in multi-component organic matter, approximately 0.174 tons / ton of product. A 50,000-ton production unit generates approximately 8,700 tons of process wastewater annually. The wastewater contains approximately 8% organic amine impurities and has a COD of approximately 250,000-300,000 ppm.

[0003] Currently, there are no reports on specific treatment technologies for this type of wastewater. Generally, conventional treatment methods for amine-containing wastewater before it enters biological treatment include: dilution, suitable for processes with small wastewater volumes; concentrated alkali salting-out, suitable for recovering useful components from the wastewater; incineration, suitable for wastewater with extremely high organic matter content; advanced oxidation methods such as Fenton oxidation, suitable for wastewater where organic matter is easily oxidized and degraded; adsorption or extraction, suitable for wastewater where organic matter is easily adsorbed or extracted; and distillation or rectification, suitable for wastewater where the boiling point of organic matter differs significantly from that of water and is not azeotropic.

[0004] The wastewater from the 6-aminohexanonitrile process is characterized by a moderate organic matter content of about 8%, which does not meet the requirements for incineration treatment; the organic matter composition is complex, with some azeotropically reacting with water, making separation by conventional distillation or rectification methods difficult or too energy-intensive; the wastewater has a high COD, and the efficiency of advanced oxidation of amines is also low, making it difficult to effectively reduce COD to meet the standards for biochemical treatment using conventional methods.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for treating wastewater from the 6-aminohexanonitrile process. This method employs a distillation-steam permeate membrane separation coupling approach. After steam is separated by the membrane, the COD of the water phase collected on the permeate side is significantly reduced to meet the standards for biochemical treatment. High-concentration organic impurities are collected on the interception side, and high-boiling-point organic impurities are enriched in the distillation vessel. This solves the wastewater treatment problem in the caprolactam process for preparing 6-aminohexanonitrile and eliminates environmental concerns.

[0007] The second objective of this invention is to provide an apparatus for treating process wastewater from 6-aminohexanonitrile.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] This invention provides a method for treating process wastewater from 6-aminohexanonitrile, comprising the following steps:

[0010] Wastewater from the 6-aminohexanonitrile process, acid, and adsorbent are added to a distillation kettle for distillation. The distillate is heated to boiling, and the steam is further heated before entering a vapor permeation membrane for gas-phase membrane separation. The gas on the permeate side of the vapor permeation membrane condenses and is collected as an aqueous phase, while the gas on the retentate side condenses to form a retentate-side component mainly containing organic impurities.

[0011] The amount of adsorbent added is 0.5-50% of the mass of the 6-aminohexanonitrile process wastewater.

[0012] The pressure difference between the cut-off side and the permeate side of the steam permeation membrane is between 0.05 and 0.3 MPa.

[0013] Furthermore, the acid can be an organic or inorganic acid, including but not limited to formic acid, acetic acid, citric acid, phosphoric acid, sulfuric acid, etc.; and / or

[0014] The amount of acid added is 0.5-5% of the mass of the 6-aminohexanonitrile process wastewater, preferably 0.5-1%, for example 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0015] After adding the acid, the pH value of the 6-aminohexanonitrile process wastewater is less than 7.

[0016] Furthermore, the adsorbent can be one or more selected from activated carbon, diatomaceous earth, activated alumina, etc., preferably activated carbon, which can effectively adsorb organic matter in wastewater that has low polarity and is difficult to separate from water.

[0017] The amount of adsorbent added is, for example, 0.5%, 0.8%, 1%, 2%, 5%, 10%, 15%, 20%, 30%, 40%, or 50% of the mass of the 6-aminohexanonitrile process wastewater.

[0018] Furthermore, distillation can be carried out under atmospheric or reduced pressure, with atmospheric pressure being the preferred method.

[0019] Furthermore, the steam is further heated by a heat exchanger to become superheated steam, with the superheat (temperature rise) being 5-10°C, to prevent liquefaction in the separation membrane and thus reduce membrane separation efficiency.

[0020] Furthermore, the pressure difference between the cut-off side and the permeate side of the steam permeation membrane is between 0.1 and 0.3 MPa;

[0021] Furthermore, the support of the vapor permeation membrane is ceramic, and the material of the vapor permeation membrane can be molecular sieve, organic polyol or polyimide, such as NaA type zeolite molecular sieve membrane.

[0022] Furthermore, the vapor permeation membrane can consist of multiple membranes connected in series, parallel, or in a mixed configuration, with a total membrane mass transfer area of ​​50-70 m². 2 If the area is too small, the water content of the intercepted components will be too high; if it is too high, the investment will be large and the system's cost-effectiveness will be reduced.

[0023] In a preferred embodiment, after collecting a sufficient mass of water, the distillate from the bottom of the distillation vessel is cooled by a heat exchanger and discharged as a highly enriched organic residue. This residue is then mixed with the intercepted side components, which mainly contain organic impurities, and then incinerated as hazardous waste.

[0024] This invention employs a distillation-coupled vapor permeation membrane separation scheme: wastewater with adjusted pH and added adsorbent is fed into a distillation vessel, heated to boiling, and the steam is further heated via a heat exchanger before entering the vapor permeation membrane module for gas-phase membrane separation. Some water molecules permeate, while the remaining mixed vapor containing more organic matter is retained. The permeate side collects the aqueous phase with reduced COD, while the retention side collects the organic solution containing organic impurities (retention side component). Organic residue is discharged from the bottom of the vessel. The COD value of the aqueous phase collected on the permeate side of the vapor permeation membrane is approximately 1300 ppm, and the water content of the organic residue at the bottom of the vessel is approximately 25%. The lower COD aqueous phase enters the biochemical treatment unit in the chemical industrial park. This invention effectively achieves the compliant treatment of 6-aminohexanonitrile process wastewater, eliminating environmental concerns. Using the preferred technical solution of this application, the water content of the retention side component containing organic impurities is approximately 5%, and the organic residue is treated as hazardous waste and incinerated by a qualified unit.

[0025] Another aspect of the present invention provides an apparatus for treating process wastewater of 6-aminohexanonitrile, comprising a distillation vessel and a vapor permeation membrane. The distillation vessel is provided with a feed port. The top of the distillation vessel is connected to the retentative side inlet of the vapor permeation membrane. The permeation side outlet of the vapor permeation membrane is connected to a first heat exchanger to collect the aqueous phase. The retentative side outlet of the vapor permeation membrane is connected to a second heat exchanger to collect the retentative side component mainly containing organic impurities.

[0026] Furthermore, the top of the distillation vessel is connected to the retrieval side inlet of the vapor permeation membrane via a third heat exchanger.

[0027] Furthermore, the bottom outlet of the distillation vessel is connected to a fourth heat exchanger to collect organic residue.

[0028] Furthermore, the bottom outlet of the distillation vessel is connected to a vacuum pump for collecting organic residue.

[0029] like Figure 1 As shown, the process of treating 6-aminohexanonitrile process wastewater using the above-mentioned device is as follows:

[0030] (1) Add the 6-aminohexanonitrile process wastewater into the distillation vessel 11 through the feed port 1 of the distillation vessel, and add a certain amount of organic or inorganic acid and a certain amount of adsorbent at the same time.

[0031] Organic or inorganic acids, including but not limited to formic acid, acetic acid, citric acid, phosphoric acid, sulfuric acid, etc.; and / or

[0032] The amount of acid added is 0.5-5% of the mass of the 6-aminohexanonitrile process wastewater, preferably 0.5-1%. After adding the acid, the pH value of the 6-aminohexanonitrile process wastewater is less than 7.

[0033] Furthermore, the adsorbent may be one or more selected from activated carbon, diatomaceous earth, activated alumina, etc., preferably activated carbon; and / or

[0034] The amount of adsorbent added is 0.5-50% of the mass of the 6-aminohexanonitrile process wastewater.

[0035] (2) The distillation vessel liquid is heated to boiling, and the steam is heated to superheated steam (temperature rise of 5-10℃) through the third heat exchanger 5 and enters the vapor permeation membrane 6 for gas phase membrane separation. The permeate side steam is condensed and collected through the first heat exchanger 7 to obtain the aqueous phase 2 with a significantly reduced COD. The retentate side steam is condensed through the second heat exchanger 8 to form the retentate side component 3, which mainly contains organic impurities.

[0036] Preferably, the support of the vapor permeation membrane is ceramic, and the material of the vapor permeation membrane can be molecular sieve, organic polyol or polyimide;

[0037] Preferably, the vapor permeation membrane can consist of multiple membranes connected in series, parallel, or in a mixed configuration, with a total membrane mass transfer area of ​​50-70 m². 2 .

[0038] (3) After collecting sufficient water, the bottom liquid of the distillation vessel is cooled by vacuum pump 10 and fourth heat exchanger 9 and discharged as highly enriched organic residue 4. It is then mixed with the intercepted side component 3 and treated as hazardous waste incineration.

[0039] The technical solution of the present invention has the following beneficial effects:

[0040] The COD value of the aqueous phase collected from the permeate side of the vapor permeation membrane in this invention is around 1300 ppm, and the water content of the organic residue at the bottom of the reactor is around 25%. The aqueous phase with lower COD enters the biochemical treatment unit in the chemical industrial park. In a preferred embodiment, the water content of the retrieval side component containing organic impurities collected from the retrieval side is around 5%, and the organic residue is treated as hazardous waste and incinerated by a qualified unit. Compared with distillation-coupled membrane separation, this scheme uses distillation-coupled membrane separation, which is significantly more energy-efficient. Applying this scheme effectively solves the wastewater problem of the 6-aminohexanonitrile process.

[0041] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments.

[0042] Unless otherwise expressly stated, numerical ranges throughout the application include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value. Unless otherwise expressly stated, numerical values ​​throughout the application represent approximate measures or limitations on the range of embodiments including minor deviations from a given value and having approximately the mentioned value as well as having the mentioned precise value. Except in the detailed description of the working embodiments provided at the end, all numerical values ​​of parameters (e.g., quantities or conditions) in this application (including the appended claims) should in all cases be understood to be modified by the term “approximately,” regardless of whether “approximately” actually precedes the numerical value. “Approximately” indicates that the stated numerical value allows for slight inaccuracies (some close to precision at that value; approximately or reasonably close to the value; approximate). If the inaccuracy provided by “approximately” is not understood in this common sense in the art, then “approximately” as used herein at least indicates a variation that can be produced by common methods of measuring and using these parameters. For example, “approximately” can include variations less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the apparatus for treating process wastewater of 6-aminohexanonitrile provided in one embodiment of the present invention.

[0045] Figure labels: 1-Feed port; 2-Aqueous phase; 3-Retained side component; 4-Organic residue; 5-Third heat exchanger; 6-Vapor permeation membrane; 7-First heat exchanger; 8-Second heat exchanger; 9-Fourth heat exchanger; 10-Vacuum pump; 11-Distillation vessel. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0047] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0048] The wastewater from the 6-aminohexanonitrile process originates from the wastewater generated during the dehydration of the lactone ring-opening and dehydration process.

[0049] raw material:

[0050] Activated carbon: Industrial grade wood-based powdered carbon, model W7, Shandong Nanke Activated Carbon Co., Ltd.

[0051] Device:

[0052] Distillation vessel: 250L enamel-lined vessel;

[0053] The vapor permeate membrane separator unit consists of three (stages) of membrane modules connected in parallel. Each (stage) membrane module has a ceramic support and is covered with a NaA-type zeolite molecular sieve membrane. The single-stage membrane area is 20 m². 2 Zibo Dongqiang Membrane Technology Co., Ltd.

[0054] Example

[0055] Example 1

[0056] 100 kg of 6-aminohexanonitrile process wastewater (COD value 260,000 ppm), 0.8 kg of phosphoric acid, and 1 kg of activated carbon were added to a distillation kettle and heated to boiling. The steam was superheated to 125°C through a heat exchanger and then entered a system consisting of three membranes (NaA type zeolite molecular sieve membranes, each with an area of ​​20 m²). 2 A steam permeation membrane separator unit is configured in parallel. The pressure difference between the retentate side and the permeate side of the steam permeation membrane is 0.15 MPa. The condensate phase on the permeate side and the condensate on the retentate side are collected. After 1 hour of operation, the level of the residual liquid (organic residual liquid) in the distillation vessel drops to 10% of the original level. The COD value of the aqueous phase (total water), the water content of the condensate on the retentate side, and the water content of the residual liquid in the distillation vessel are analyzed at this time.

[0057] Results: Total water mass: 89 kg, COD: 1300 ppm; total mass of retained components: 1 kg, water content: 5.2%; water content of residue in reactor: 25.1%.

[0058] Example 2

[0059] Except for the addition of 0.5 kg of phosphoric acid, the other implementation methods are the same as in Example 1.

[0060] Results: Total water mass: 88.9 kg, COD: 1295 ppm; total mass of retained components: 1.05 kg, water content: 5.1%; water content of residue in reactor: 25.2%.

[0061] Example 3

[0062] Except for the fact that the vapor permeation membrane is made of polyimide, the other implementation methods are the same as in Example 1.

[0063] Results: Total water mass: 89.2 kg, COD: 1305 ppm; total mass of retained components: 0.99 kg, water content: 5.1%; water content of residue in reactor: 24.8%.

[0064] Example 4

[0065] Except for the pressure difference of 0.05 MPa between the retentate side and the permeate side of the vapor permeation membrane, the other implementation methods are the same as in Example 1.

[0066] Results: Total water mass: 59.4 kg, COD: 1290 ppm; total mass of retained components: 30.5 kg, water content: 96%; water content of residue in reactor: 25.4%.

[0067] Example 5

[0068] In addition to using a single-stage vapor permeation membrane (molecular sieve membrane, area 20m²) 2 Except for the above, the other implementation methods are the same as in Example 1.

[0069] Results: Total water mass: 30.4 kg, COD: 1300 ppm; total mass of retained components: 59.5 kg, water content: 98%; water content of residue in reactor: 24.8%.

[0070] Comparative Example 1

[0071] Compared to Example 1, the vapor permeation membrane module is omitted and conventional distillation is used instead, while other implementation methods are the same as in Example 1.

[0072] Results: The total water mass was 90 kg, with a COD of 13,000 ppm and a residual liquid water content of 25%. The treated water did not meet the influent standards for biological treatment and could not be further treated.

[0073] Comparative Example 2

[0074] Compared with Example 1, the vapor permeation membrane module was omitted and ordinary distillation was used instead of adding acid and activated carbon. Other implementation methods were the same as in Example 1.

[0075] Results: The total water mass was 90 kg, with a COD of 120,000 ppm and a residual liquid water content of 60%. The treated water did not meet the influent standards for biological treatment and could not be further treated.

[0076] Comparative Example 3

[0077] Except for the absence of acid, the implementation method is the same as in Example 1.

[0078] Results: Total water mass: 88.7 kg, COD: 4505 ppm; total mass of retained components: 1.1 kg, water content: 7.1%; water content of residue in reactor: 26%.

[0079] Comparative Example 4

[0080] Except for the 0.1 kg of activated carbon, the other implementation methods are the same as in Example 1.

[0081] Results: Total water mass: 89.1 kg, COD: 5050 ppm; total mass of retained components: 1 kg, water content: 8.5%; water content of residue in reactor: 27%.

[0082] Comparative Example 5

[0083] Except for the pressure difference of 0.5 MPa between the retentate side and the permeate side of the vapor permeation membrane, the other implementation methods are the same as in Example 1.

[0084] Results: Total water mass: 89.7 kg, COD: 8100 ppm; total mass of retained components: 0.32 kg, water content: 20%; water content of residue in reactor: 25.4%.

[0085] Based on the experimental results of the above examples and comparative examples, it is evident that a large number of organic components in wastewater are difficult to separate under ordinary distillation conditions. The addition of an appropriate amount of acid can form salts with some amines, reducing or even eliminating their volatility. The addition of a certain amount of activated carbon can effectively adsorb low-polarity, volatile organic matter. A reasonable membrane contact area and pressure difference between the retrieval side and the permeation side can achieve effective retention of organic components in water vapor while maintaining a reasonable permeation rate.

[0086] Compared to distillation, distillation significantly reduces energy consumption. Coupled with vapor permeation membrane separation, it can efficiently reduce organic components in wastewater while saving energy, lowering COD to below 2000 ppm, meeting the influent standards for biological treatment. Organic matter can be significantly concentrated for treatment as hazardous organic waste. In this technical solution, the vapor permeation membrane plays a crucial role in both blocking organic matter and selectively permeating water.

[0087] In Examples 4 and 5, where the pressure difference between the retentate and permeate sides of the vapor permeation membrane is low or the membrane area is small, it is possible to reduce COD to below 2000 ppm to meet the feedwater standards for biological treatment. However, the total amount of components on the retentate side is relatively large. Moreover, due to the high water content of the retentate side components, they cannot be mixed with the residue in the reactor and require further treatment. Therefore, Examples 1-3 are more preferred embodiments in comparison.

[0088] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for treating process wastewater from 6-aminohexanonitrile, characterized in that, Includes the following steps: Wastewater from the 6-aminohexanonitrile process, acid, and adsorbent are added to a distillation kettle for distillation. The distillate is heated to boiling, and the steam is further heated before entering a vapor permeation membrane for gas-phase membrane separation. The gas on the permeate side of the vapor permeation membrane condenses and is collected as an aqueous phase, while the gas on the retentate side condenses to form a retentate-side component containing organic impurities. The acid is selected from at least one of formic acid, acetic acid, citric acid, phosphoric acid, and sulfuric acid. The amount of acid added is 0.5-5% of the mass of the 6-aminohexanonitrile process wastewater. The adsorbent is at least one selected from activated carbon, diatomaceous earth, and activated alumina. The amount of adsorbent added is 0.5-50% of the mass of the 6-aminohexanonitrile process wastewater. The pressure difference between the cut-off side and the permeate side of the steam permeation membrane is between 0.1 and 0.3 MPa. After the liquid at the bottom of the distillation vessel is cooled by a heat exchanger, the organic residue is discharged and mixed with the retrieval side component containing organic impurities before being treated as hazardous waste incineration.

2. The method according to claim 1, characterized in that, The amount of acid added is 0.5-1% of the mass of the 6-aminohexanonitrile process wastewater.

3. The method according to claim 1, characterized in that, The adsorbent is activated carbon.

4. The method according to claim 1, characterized in that, The vapor permeation membrane is made of at least one material selected from molecular sieves or polyimides; and / or The total membrane mass transfer area of ​​the vapor permeation membrane is 50-70 m². 2 .

Images