Method for recycling caprolactam waste liquid and application thereof

Abstract

The application relates to a recycling method of caprolactam waste liquid and application thereof. The method comprises the following steps: S1, treating the caprolactam waste liquid by using a low-temperature plasma technology, so that caprolactam in the caprolactam waste liquid is ring-opened to generate aminocaproic acid, and waste liquid containing aminocaproic acid is obtained; and S2, heating the waste liquid containing aminocaproic acid, adding polyether polyol, generating a polyether surfactant by using an esterification reaction of aminocaproic acid and the polyether polyol, and obtaining waste liquid containing the polyether surfactant. The application further discloses application of the waste liquid containing the polyether surfactant in preparation of water coal slurry. The method realizes efficient utilization of the caprolactam waste liquid, saves fresh water for preparation of the water coal slurry, effectively reduces the cost of the water coal slurry additive, and improves slurryability of the water coal slurry.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for recycling caprolactam waste liquid and its application. Background Technology

[0002] Caprolactam is an important organic chemical raw material, mainly used in the production of polyamide-6 chips. These chips can be further processed into nylon fibers, engineering plastics, and plastic films. Currently, caprolactam is mainly produced using the cyclohexanone-hydroxylamine route. The main process includes: the reaction of cyclohexanone and hydroxylamine to produce cyclohexanone oxime; the cyclohexanone oxime undergoes the Beckmann rearrangement reaction under fuming sulfuric acid; the resulting crude caprolactam product is then purified and impurity removed through ammonium sulfate, ammonium sulfate extraction, alkali washing, back-extraction, vertical cross-linking, and evaporation distillation processes. The media used in the rearrangement, ammonium sulfate, ammonium sulfate, alkali washing, and vertical cross-linking processes in the refining unit, such as nicotinic acid, ammonia, benzene, and alkali, can introduce organic and inorganic impurities such as 2-hydroxycyclohexanone, ammonium sulfate, sodium salts, and benzene.

[0003] The production of caprolactam generates a large amount of wastewater, primarily from refining, ion exchange, and equipment rinsing processes. Caprolactam wastewater is characterized by its large volume, poor biodegradability, reluctance to degrade, and high ammonia nitrogen concentration. It is classified as difficult-to-treat industrial organic wastewater, resulting in high treatment costs. Its pH value is between 3 and 6, and its main components include: ammonium sulfate (2-5% by mass), caprolactam (3-6% by mass), benzene (60 ppm), other organic or inorganic impurities (1-2%), and water (87-94%).

[0004] Currently, caprolactam manufacturers typically use three methods to treat wastewater from caprolactam production: concentration-incineration, concentration-extraction, and coal-water slurry preparation. In concentration-incineration, the presence of caprolactam, ammonium sulfate, and other organic and inorganic compounds in the wastewater increases nitrogen oxide and sulfide emissions during incineration. Concentration-extraction requires significant additional consumption of natural gas and steam, increasing treatment costs, and its extraction efficiency is relatively low. Preparing coal-water slurry from caprolactam wastewater involves mixing the wastewater with pulverized coal, reducing the consumption of fresh water during preparation. However, this requires the addition of large amounts of coal-water slurry additives to improve slurry consistency and reduce water separation, again increasing treatment costs.

[0005] Therefore, developing a highly efficient and low-cost method for treating caprolactam wastewater is of great significance for caprolactam companies to reduce wastewater treatment costs and for the sustainable development of the industry.

[0006] Patent CN111979000A discloses a method for preparing coal-water slurry using benzene extraction residue. Bituminous coal and anthracite are mixed uniformly at a predetermined weight ratio to prepare a blended coal. The benzene extraction residue is then mixed with an alkaline solution, and the pH is adjusted to 7.0-7.9. Gaseous ammonia generated during pH adjustment is incinerated in an ammonia flare. Finally, the blended coal, weakly alkaline benzene extraction residue, flux, and coal-water slurry additives are mixed in a predetermined ratio and then ground uniformly in a rod mill to prepare the coal-water slurry, which is then fed into a gasifier to produce synthetic ammonia. This invention patent uses caprolactam wastewater to prepare coal-water slurry, requiring the addition of additives such as naphthalene sulfonate formaldehyde condensate and sodium lignin sulfonate during the preparation process to ensure the slurry's consistency, thus increasing processing costs. Summary of the Invention

[0007] The technical objective of this invention is to provide a method for recycling caprolactam waste liquid. In this method, the chemical components in the caprolactam waste liquid are transformed into a useful dispersant in the preparation of coal-water slurry, thereby achieving efficient utilization of caprolactam waste liquid, solving the problem of discharge and treatment of such chemical wastewater, and reducing the pollution of the environment by organic wastewater.

[0008] Another technical objective of this invention is to provide a caprolactam waste liquid recovered by the above method.

[0009] Another technical objective of this invention is to provide a method for preparing coal-water slurry, which utilizes caprolactam waste liquid recovered through the above-mentioned method, thereby saving fresh water in the preparation of coal-water slurry and eliminating the need for additional additives, thus reducing the preparation cost of coal-water slurry.

[0010] On one hand, the present invention provides a method for recycling caprolactam waste liquid, the method comprising:

[0011] S1: The caprolactam waste liquid is treated using low-temperature plasma technology, causing the caprolactam in the waste liquid to undergo ring-opening to generate aminocaproic acid, resulting in a waste liquid containing aminocaproic acid; and

[0012] S2: The waste liquid containing aminocaproic acid is heated to 50-70°C, and polyether polyol is added. The esterification reaction of aminocaproic acid and polyether polyol is used to generate polyether surfactant, thereby obtaining waste liquid containing polyether surfactant.

[0013] In a specific embodiment, in step S1, the caprolactam waste liquid comes from caprolactam refining, ion exchange, or equipment rinsing processes.

[0014] In a specific embodiment, in step S1, the caprolactam waste liquid is pumped to the plasma processor at a flow rate of 4-8 m³ / h. 3The plasma is introduced at a rate of 500-5000W per hour for 10-200 minutes. In this step, carbon dioxide or oxygen forms reactive oxygen atoms (O*) under the influence of low-temperature plasma. These reactive oxygen atoms break the C / C bonds of caprolactam in the waste liquid, generating aminocaproic acid.

[0015] In a specific implementation, in step S1, the caprolactam waste liquid is pumped to the plasma processor at a flow rate of 5 m³ / s. 3 / h, oxygen, carbon dioxide or air is introduced, plasma processing power is 3000W, plasma processing time is 60min.

[0016] In a specific embodiment, in step S2, the waste liquid containing aminocaproic acid is pumped into an esterification reactor to undergo an esterification reaction with polyether polyol. The flow rate of the waste liquid containing aminocaproic acid is 5 m³ / s. 3 The flow rate of the polyether polyol is 10 kg / h, the molecular weight of the polyether polyol is 2000 g / mol, the heating temperature is 50-60℃, and the esterification time is 0.5-3 h. In this step, the acidic environment of the wastewater is used to achieve the esterification reaction between the carboxyl groups in aminocaproic acid and the hydroxyl groups of the polyether polyol, forming a terminal amine polyether surfactant.

[0017] In a specific embodiment, in step S2, the heating temperature is 60°C and the esterification time is 1 hour.

[0018] In a specific implementation, the method further includes step S3:

[0019] Add sodium hydroxide solution to the waste liquid containing polyether surfactant obtained in step S2 and adjust the pH to 7-7.5 to obtain a dispersant suitable for preparing coal-water slurry.

[0020] On the other hand, the present invention provides a waste liquid containing polyether surfactant recovered by the above method.

[0021] In another aspect, the present invention provides an application of the above-mentioned waste liquid containing polyether surfactant in the preparation of coal-water slurry.

[0022] In another aspect, the present invention provides a method for preparing coal-water slurry, the method comprising:

[0023] The waste liquid containing polyether surfactants was mixed with dried coal powder to obtain a coal-water slurry with a solid content of 50-65% by weight.

[0024] Beneficial effects

[0025] This application utilizes low-temperature plasma technology to treat caprolactam waste liquid, achieving ring-opening of caprolactam in the waste liquid. A nonionic surfactant is generated through esterification with polyether polyol under acidic conditions, replacing the original dispersant in coal-water slurry. On one hand, this achieves efficient utilization of the waste liquid, effectively solving the discharge and treatment problems of such chemical wastewater, reducing environmental pollution from organic wastewater, and saving fresh water for coal-water slurry preparation, thus possessing certain economic advantages. On the other hand, it transforms caprolactam waste liquid into a valuable resource, effectively reducing the cost of coal-water slurry additives while effectively improving the slurry-forming properties of the slurry. Attached Figure Description

[0026] Figure 1 Ring-opening reaction of caprolactam in a plasma processor under low-temperature plasma.

[0027] Figure 2 : Esterification reaction of aminocaproic acid with polyether polyol. Detailed Implementation

[0028] The technical solutions of this application are described in detail below through specific embodiments to enable those skilled in the art to better understand this application. However, the provision of these embodiments is not intended to limit the scope of this application.

[0029] Materials and Instruments

[0030] Caprolactam waste liquid mainly comes from caprolactam refining, ion exchange, and equipment rinsing processes. Its main components include: ammonium sulfate 2-5wt%, caprolactam 3-6wt%, benzene content 60ppm, other organic or inorganic impurities 1-2wt%, and water 87-94wt%.

[0031] Carbon dioxide gas: Hangzhou Oxygen Plant Group Co., Ltd.

[0032] Oxygen: Hangzhou Oxygen Plant Group Co., Ltd.

[0033] Polyether polyols: Nantong Renda Chemical Co., Ltd.

[0034] Plasma generator: 500-5000W (adjustable power), DDBD dual-dielectric (TDK) Cangzhou Muyang Environmental Protection Equipment Co., Ltd.

[0035] Example 1:

[0036] Plasma treatment process:

[0037] Low-temperature plasma technology was used to treat caprolactam waste liquid to obtain waste liquid containing aminocaproic acid. The specific operation was as follows: the waste liquid was pumped into a plasma processor (equipped with a motor, power supply, electrodes, and stirrer) at a flow rate of 5 m³ / s. 3 / h, oxygen is introduced, plasma treatment power is 3000W, and plasma treatment time is 60min. In this operation, oxygen forms active oxygen atoms O* under the action of low-temperature plasma. Utilizing the high activity of active oxygen atoms, the C-C bonds of caprolactam in the waste liquid are broken to generate aminocaproic acid (…). Figure 1 ).

[0038] Esterification process: Waste liquid containing aminocaproic acid is pumped into the esterification reactor at a flow rate of 5 m³ / h. 3 The heating temperature was 60℃, and polyether polyol was added at a flow rate of 10 kg / h. The molecular weight of the polyether polyol was 2000 g / mol, and the esterification time was 1 h. The acidic environment of the wastewater was utilized to achieve the esterification reaction between the carboxyl groups in aminocaproic acid and the hydroxyl groups in the polyether polyol. Figure 2 (The value of n in the polyol in the figure depends on the molecular weight of the polyether polyol used), forming an amine-terminated polyether surfactant.

[0039] pH adjustment process: Add 5% sodium hydroxide solution to the terminal amino polyether waste liquid generated by the esterification reaction to adjust the pH to 7-7.5.

[0040] Water-coal slurry preparation process: Take a certain amount of the aforementioned waste liquid and mix it with dried coal powder, stir for 10 minutes to obtain water-coal slurry with a solid content of 61%, and analyze the water separation rate of the water-coal slurry.

[0041] Example 2:

[0042] Water-coal slurry was prepared using the same method as in Example 1, except that air was used as the plasma gas source.

[0043] Example 3:

[0044] Water-coal slurry was prepared using the same method as in Example 1, except that carbon dioxide was used as the plasma gas source.

[0045] Example 4:

[0046] Water-coal slurry was prepared using the same method as in Example 1, except that the plasma processing power was 500W.

[0047] Example 5:

[0048] Water-coal slurry was prepared using the same method as in Example 1, except that the plasma processing power was 5000W.

[0049] Example 6:

[0050] Water-coal slurry was prepared using the same method as in Example 1, except that the molecular weight of the polyether polyol was 100 g / mol.

[0051] Example 7:

[0052] Water-coal slurry was prepared using the same method as in Example 1, except that the molecular weight of the polyether polyol was 8000 g / mol.

[0053] Example 8:

[0054] The coal-water slurry was prepared using the same method as in Example 1, except that the esterification time was 0.5 h.

[0055] Example 9:

[0056] The coal-water slurry was prepared using the same method as in Example 1, except that the esterification time was 3 hours.

[0057] Comparative Example 1

[0058] A certain amount of fresh water and sodium lignosulfonate dispersant at 3‰ of the coal powder mass were mixed with dried coal powder and stirred for 10 minutes to obtain a coal-water slurry with a solid content of 61%. The water separation rate of the coal-water slurry was analyzed.

[0059] Comparative Example 2

[0060] Water-coal slurry was prepared using the same method as in Example 1, except that the low-temperature plasma treatment step was omitted.

[0061] The data from Examples 1-9 and Comparative Examples 1-2 are summarized in Table 1 below.

[0062] Table 1

[0063]

[0064] As can be seen from the data in Table 1 above, treating the caprolactam wastewater of this application and using it as a dispersant in the preparation of coal-water slurry achieves the same or even better technical effects as using sodium lignosulfonate dispersant. This demonstrates that the method of this invention saves on the addition of fresh water in the preparation of coal-water slurry, reduces the cost of coal-water slurry additives, and also achieves resource reuse of caprolactam wastewater. Therefore, the method of this application has great potential for industrial application.

Claims

1. A method for recycling caprolactam waste liquid, the method comprising: S1: The caprolactam waste liquid is treated with low-temperature plasma technology to cause the caprolactam in the waste liquid to undergo ring-opening to generate aminocaproic acid, resulting in a waste liquid containing aminocaproic acid. as well as S2: The waste liquid containing aminocaproic acid is heated to 50-70°C, and polyether polyol is added. The esterification reaction of aminocaproic acid and polyether polyol is used to generate polyether surfactant, thereby obtaining waste liquid containing polyether surfactant.

2. The method according to claim 1, wherein, In step S1, the caprolactam waste liquid comes from caprolactam refining, ion exchange, or equipment rinsing processes.

3. The method according to claim 1, wherein, In step S1, the caprolactam waste liquid is pumped to the plasma processor at a flow rate of 4-8 m³ / h. 3 The plasma is introduced at a rate of 500-5000W per hour, with a plasma treatment power of 500-5000W and a plasma treatment time of 10-200 minutes.

4. The method according to claim 1, wherein, In step S1, the caprolactam waste liquid is pumped to the plasma processor at a flow rate of 5 m³ / s. 3 / h, oxygen, air or carbon dioxide is introduced, plasma treatment power is 3000W, plasma treatment time is 60min.

5. The method according to claim 1, wherein, In step S2, the waste liquid containing aminocaproic acid and the polyether polyol undergo an esterification reaction in an esterification reactor. The flow rate of the waste liquid containing aminocaproic acid is 5m³. 3 The flow rate of the polyether polyol is 10 kg / h, and the molecular weight of the polyether polyol is 2000 g / mol; the heating temperature is 50-60℃, and the esterification time is 0.5h-3h.

6. The method according to claim 1, wherein, In step S2, the heating temperature is 60°C and the esterification time is 1 hour.

7. The method according to claim 1, wherein, The method further includes step S3: Add sodium hydroxide solution to the waste liquid containing polyether surfactant obtained in step S2 and adjust the pH to 7-7.5 to obtain a dispersant suitable for preparing coal-water slurry.

8. A waste liquid containing a polyether surfactant recovered by the method of any one of claims 1 to 7.

9. The application of the waste liquid containing polyether surfactant as described in claim 8 in the preparation of coal-water slurry.

10. A method for preparing coal-water slurry, the method comprising: The waste liquid containing polyether surfactant as described in claim 8 is mixed with dried coal powder to obtain a coal-water slurry with a solid content of 50-65% by weight.

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