A method for treating wastewater from lauryl lactam production

Abstract

The invention provides a method for treating wastewater from laurolactam production, belonging to the technical field of wastewater treatment and resource utilization. For wastewater from laurolactam production with complex organic matter types, the pH value of the wastewater from laurolactam production is first adjusted to less than 7, and then most of the organic matter is removed by coagulation and flocculation precipitation, and then the remaining organic matter is removed by adsorption of activated carbon with specific hydrophilic modification, and finally the adsorbed water is evaporated and crystallized to obtain a fertilizer-grade ammonium sulfate product. The treatment method has a simple process, good treatment effect, low treatment cost, and the obtained ammonium sulfate byproduct is of high quality.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment and resource utilization, and relates to a method for treating wastewater produced by laurolactam production. Background Art

[0002] Lauryl lactam is an important monomer for the synthesis of nylon 12 (PA12). PA12 is mainly used in the automotive industry, among which the fuel pipeline system is the most important application. Other applications are mostly industrial equipment pipelines, electronic appliances, magnetic plastics, powder coating, etc. The synthetic route of lauryl lactam is to use 1,3-butadiene as the raw material, trimerize it into cyclododecatriene, then oxidize it into epoxycyclododecadiene, then hydrogenate and reduce it to obtain cyclododecanol, then dehydrogenate it into cyclododecanone, react with hydroxylamine sulfate to obtain cyclododecanone oxime, and then carry out Beckmann rearrangement to prepare it.

[0003] During the preparation of laurolactam, cyclododecanone reacts with an aqueous solution of hydroxylamine sulfate to generate cyclododecanone oxime, and at the same time generates ammonium sulfate wastewater with a concentration of 10wt%. In addition to the main reaction, many side reactions also occur during the rearrangement reaction of cyclododecanone oxime, including hydrolysis of cyclododecanone oxime to cyclododecanone, hydrolysis of laurolactam to aminododecanoic acid, dehydration to generate nitrile substances, sulfonation to generate yellow color-producing substances, dehydration and carbonization, etc. The rearrangement reaction liquid is neutralized with ammonia water, and after standing and phase separation, an oil phase containing laurolactam and ammonium sulfate wastewater with a concentration of 34wt% are obtained. Therefore, it is necessary to treat the oximation wastewater and rearrangement wastewater to recover ammonium sulfate.

[0004] At present, the treatment methods of ammonium sulfate wastewater generated by different industries include the following methods. CN105417819B discloses a process for efficiently treating rare earth ammonium sulfate wastewater, wherein the ammonium sulfate wastewater is processed with industrial oxalic acid to remove rare earth and calcium in the solution, and the concentrated solution is heated and concentrated to a concentration of 11-13wt% by an MVR evaporator, and then the concentrated solution is transported to a five-effect evaporator to reduce the temperature of the concentrated solution to 50-55°C, and then enters a continuous crystallizer, and the slurry is centrifuged to obtain ammonium sulfate solid. This process solves the blockage problem of calcium and rare earth, and has obvious energy-saving effects, but the equipment investment is relatively high; CN103964556B discloses a method for separating calcium and magnesium ions in ammonium sulfate wastewater, wherein the ammonium sulfate wastewater is first adjusted to 7-11 with ammonia water, and then a soluble phosphate is added to the ammonium sulfate solution to produce crystalline precipitation of calcium phosphate and magnesium phosphate, and solid-liquid separation is performed to remove calcium and magnesium ions in the wastewater, but it is not suitable for the removal of organic impurities.

[0005] The types of organic matter in the wastewater from laurolactam production are complex, including non-polar organic matter such as laurolactam, cyclododecanone, and cyclododecanone oxime, as well as polar substances such as aminododecanoic acid and sulfonation products. Therefore, a treatment process suitable for wastewater from laurolactam production is developed to treat ammonium sulfate wastewater at a lower cost and make the treated ammonium sulfate meet the requirements of fertilizer-grade ammonium sulfate. Summary of the invention

[0006] The object of the present invention is to provide a method for treating wastewater produced by laurolactam production, which adopts a method combining coagulation flocculation precipitation with modified activated carbon adsorption, and can remove organic matter in wastewater produced by laurolactam production at a lower treatment cost, so that the byproduct ammonium sulfate meets the fertilizer grade quality requirements.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for treating wastewater from laurolactam production, the method comprising the following steps:

[0009] (1) After adjusting the pH value of lauryl lactam production wastewater to less than 7, a coagulant and a flocculant are sequentially added thereto for coagulation, flocculation and precipitation, and a supernatant and a sludge precipitate are obtained after standing;

[0010] (2) passing the supernatant of step (1) into an activated carbon fixed bed for adsorption to obtain adsorbed water;

[0011] The activated carbon fixed bed is filled with modified activated carbon;

[0012] (3) The adsorbed water produced in step (2) is evaporated and crystallized to obtain fertilizer-grade ammonium sulfate.

[0013] In the present invention, the inorganic matter in the laurolactam production wastewater includes but is not limited to ammonium sulfate, and the organic matter includes but is not limited to cyclododecanone, cyclododecanone oxime, laurolactam, aminododecanoic acid, aminododecanonitrile, sulfonation product or laurolactam oligomer.

[0014] In the present invention, after the sludge precipitation in step (1) is filtered, the filtrate is returned to the coagulation tank. The fertilizer-grade ammonium sulfate meets the GB / T 535-2020 standard.

[0015] The treatment method provided by the present invention is aimed at laurolactam production wastewater with complex organic matter types. The pH value of the laurolactam production wastewater is first adjusted to less than 7, and then most of the organic matter is removed by coagulation and flocculation precipitation, and then the remaining organic matter is removed by adsorption of activated carbon with specific hydrophilic modification, and finally the adsorbed water is evaporated and crystallized to obtain a fertilizer-grade ammonium sulfate product. The treatment method has a simple process, good treatment effect, low treatment cost, and the obtained ammonium sulfate byproduct is of high quality.

[0016] As a preferred technical solution of the present invention, the total organic carbon (TOC) concentration of the laurolactam production wastewater in step (1) is greater than 200 ppm, for example, it can be 210 ppm, 220 ppm, 240 ppm, 250 ppm, 260 ppm or 280 ppm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] In the present invention, the total organic carbon concentration refers to the mass concentration of total organic carbon.

[0018] The chromaticity of the laurolactam production wastewater in step (1) is greater than 100 hazen, for example, it can be 110 hazen, 120 hazen, 140 hazen, 150 hazen, 160 hazen or 180 hazen, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] In the present invention, the initial pH value of the laurolactam production wastewater is ≥8.

[0020] The temperature of the laurolactam production wastewater in step (1) is 30-40°C, for example, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C or 39°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] The pH value of the laurolactam production wastewater in step (1) is adjusted to 4-6, for example, 4.2, 4.5, 4.8, 5, 5.2 or 5.5, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 4.5-5.5.

[0022] In the present invention, the adjusting agent used in step (1) to adjust the pH comprises acid solution; and the acid solution comprises sulfuric acid.

[0023] It is worth noting that before coagulation, flocculation and sedimentation, the laurolactam production wastewater needs to be cooled to 30-40°C and the pH is adjusted to weak acidity to improve the treatment effect of coagulation, flocculation and sedimentation, thereby removing most of the organic matter therein.

[0024] As a preferred technical solution of the present invention, the coagulant in step (1) includes polyaluminium chloride (PAC) and / or polyaluminium sulfate (PAS).

[0025] In the present invention, the alkalinity of the coagulant is 30-50%, for example, it can be 32%, 35%, 38%, 40%, 42%, 45% or 48%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] After the coagulant is added in step (1), the mass concentration of the coagulant contained in the wastewater is 100-500 ppm, for example, it can be 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm or 450 ppm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 200-300 ppm.

[0027] The interval time between adding the coagulant and the flocculant in step (1) is ≥30 min, for example, it can be 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 38 min or 40 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the flocculant in step (1) includes anionic polyacrylamide.

[0029] In the present invention, the molecular weight of the anionic polyacrylamide is 1600-2000W, for example, it can be 1650W, 1700W, 1750W, 1800W, 1850W, 1900W or 1950W, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] After the flocculant is added in step (1), the mass concentration of the flocculant contained in the wastewater is 3-8 ppm, for example, it can be 3.5 ppm, 4 ppm, 4.5 ppm, 5 ppm, 5.5 ppm, 6 ppm or 7 ppm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 5 ppm.

[0031] The coagulation, flocculation and sedimentation time in step (1) is ≥ 40 min, for example, it can be 42 min, 45 min, 48 min, 50 min, 52 min, 55 min, 58 min or 60 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] As a preferred technical solution of the present invention, the supernatant in step (1) is also subjected to membrane filtration before passing into the activated carbon fixed bed.

[0033] The pore size of the filter membrane is 3-6 μm, for example, 3.5 μm, 4 μm, 4.5 μm, 5 μm or 5.5 μm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] In the present invention, in order to prevent the floating matter in the supernatant from affecting the adsorption process, it needs to be filtered through a membrane.

[0035] As a preferred technical solution of the present invention, the method for preparing the modified activated carbon in step (2) comprises: mixing the activated carbon and a persulfate solution and performing an oxidation reaction.

[0036] It is worth noting that the present invention uses persulfate oxidation to modify the activated carbon, thereby increasing the hydrophilicity of the activated carbon surface, thereby increasing the removal rate of the activated carbon for polar organic matter and non-polar organic matter in wastewater.

[0037] The activated carbon includes any one of coal charcoal, fruit shell charcoal or wood charcoal, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of coal charcoal and fruit shell charcoal, a combination of fruit shell charcoal and wood charcoal, or a combination of coal charcoal, fruit shell charcoal and wood charcoal.

[0038] The average particle size of the activated carbon is 5-20 mesh, for example, it can be 6-10 mesh, 8-12 mesh, 6-12 mesh, 10-16 mesh, 12-18 mesh, 16-20 mesh or 18-20 mesh, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 10-16 mesh.

[0039] It is worth noting that the present invention selects activated carbon within a specific particle size range to further improve the removal rate of polar organic matter and non-polar organic matter in wastewater.

[0040] The persulfate in the persulfate solution includes any one of sodium persulfate, potassium persulfate or ammonium persulfate, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of sodium persulfate and potassium persulfate, a combination of potassium persulfate and ammonium persulfate, or a combination of sodium persulfate, potassium persulfate and ammonium persulfate, etc.

[0041] The mass concentration of the persulfate solution is 1-5wt%, for example, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt% or 4.5wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 3-4wt%.

[0042] As a preferred technical solution of the present invention, the mixing method includes immersing the activated carbon in a persulfate solution.

[0043] In the present invention, the persulfate solution is used in excess.

[0044] The temperature of the oxidation reaction is 60-80°C, for example, it can be 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, 72°C, 74°C, 75°C, 76°C or 78°C, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 60-70°C.

[0045] In the present invention, the initial temperature of the persulfate solution is also 60-80°C.

[0046] The oxidation reaction time is 1-5h, for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or 4.5h, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 3-4h.

[0047] It is worth noting that by controlling the temperature and time range of the oxidation reaction, it is not only conducive to the smooth progress of the oxidation modification reaction, but also ensures that the hydrophilic groups on the surface of the activated carbon are within the required range.

[0048] In the present invention, pure water washing is also performed after the oxidation reaction to remove residual persulfate.

[0049] As a preferred technical solution of the present invention, the temperature of the activated carbon fixed bed in step (2) is 30-40°C, for example, it can be 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C or 39°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] The residence time of the activated carbon fixed bed in step (2) is 30-60 min, for example, 32 min, 35 min, 38 min, 40 min, 42 min, 45 min, 48 min, 50 min, 52 min, 55 min or 58 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] It is worth mentioning that by controlling the temperature and adsorption time of the activated carbon fixed bed, not only the adsorption efficiency is improved, but also the adsorption effect is optimized.

[0052] After the adsorption in step (2), the produced water is also filtered through a membrane.

[0053] The pore size of the filter membrane is 3-6 μm, for example, 3.5 μm, 4 μm, 4.5 μm, 5 μm or 5.5 μm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] In the present invention, the produced water after adsorption is filtered by a filter membrane to remove the carbon powder dropped from the granular activated carbon.

[0055] The total organic carbon concentration of the adsorbed water produced in step (2) is ≤50 ppm, for example, it can be 49 ppm, 48 ppm, 46 ppm, 45 ppm, 42 ppm, 40 ppm or 35 ppm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] The chromaticity of the adsorbed water produced in step (2) is ≤30 hazen, for example, it can be 29 hazen, 28 hazen, 26 hazen, 25 hazen, 22 hazen, 20 hazen or 15 hazen, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] As a preferred technical solution of the present invention, the evaporation crystallization in step (3) is carried out using an MVR evaporation crystallization device.

[0058] In the present invention, after the evaporation crystallization obtains the crystal slurry, it is successively subjected to a thickener, centrifugal separation and drying to obtain white fertilizer-grade ammonium sulfate.

[0059] The evaporated water obtained in the evaporative crystallization in step (3) is reused.

[0060] As a preferred technical solution of the present invention, the processing method comprises the following steps:

[0061] (1) Cooling the wastewater from laurolactam production to a temperature of 30-40°C, adjusting the pH value to 4-6, and then sequentially adding a coagulant and a flocculant to the wastewater for coagulation, flocculation and precipitation. After standing, a supernatant and a sludge precipitate are obtained, and the obtained supernatant is filtered through a filter membrane with a pore size of 3-6 μm;

[0062] The total organic carbon concentration of the laurolactam production wastewater is greater than 200 ppm and the chromaticity is greater than 100 hazen;

[0063] After the coagulant is added, the mass concentration of the coagulant in the wastewater is 100-500ppm; after the flocculant is added, the mass concentration of the flocculant in the wastewater is 3-8ppm; the interval time between the addition of the coagulant and the flocculant is ≥30min; the coagulation, flocculation and sedimentation time is ≥40min;

[0064] (2) The supernatant after filtration in step (1) is passed into an activated carbon fixed bed at a temperature of 30-40°C for adsorption and retention for 30-60 minutes, and then the produced water is filtered through a filter membrane with a pore size of 3-6 μm to obtain adsorbed produced water;

[0065] The activated carbon fixed bed is filled with modified activated carbon;

[0066] The preparation method of the modified activated carbon comprises: immersing activated carbon with an average particle size of 5-20 meshes in a persulfate solution with a mass concentration of 1-5wt%, and then performing an oxidation reaction at a temperature of 60-80°C for 1-5h;

[0067] The total organic carbon concentration of the adsorption water is ≤50ppm and the chromaticity is ≤30hazen;

[0068] (3) placing the adsorbed water produced in step (2) in an MVR evaporation and crystallization device for evaporation and crystallization to obtain fertilizer-grade ammonium sulfate.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] The treatment method provided by the present invention is aimed at laurolactam production wastewater with complex organic matter types. The laurolactam production wastewater is first cooled and the pH value is adjusted to less than 7, and then most of the organic matter is removed by coagulation and flocculation precipitation, and then the remaining organic matter is removed by adsorption of specific hydrophilic modified activated carbon, and finally the adsorbed water is evaporated and crystallized to obtain a fertilizer-grade ammonium sulfate product; wherein the TOC of the adsorbed water is ≤50ppm and the chromaticity is ≤30hazen. The treatment method has a simple process, good treatment effect, low treatment cost, and the obtained ammonium sulfate byproduct is of high quality. DETAILED DESCRIPTION

[0071] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0072] The main raw material information used in the specific implementation of the present invention is as follows:

[0073] Lauryl lactam production wastewater, generated during the preparation of lauryl lactam by Wanhua Chemical Co., Ltd.;

[0074] Sulfuric acid (mass concentration 98%), produced by Wanhua Chemical Co., Ltd.;

[0075] Potassium persulfate, sodium persulfate, and ammonium persulfate were purchased from Fujian Zhanhua Chemical Co., Ltd.;

[0076] Polyaluminium chloride (basicity 45%), polyaluminium sulfate (basicity 45%), anionic polyacrylamide (molecular weight 1800W, purchased from Shenzhen Changlong Technology Co., Ltd.;

[0077] Activated carbon (average particle size of 5-20 mesh) was purchased from Yantai General Activated Carbon Co., Ltd.

[0078] The main equipment and instrument information used in the specific implementation of the present invention is as follows:

[0079] Total organic carbon analyzer, multi N / C 3100, Jena Analytical Instruments (Beijing) Co., Ltd.;

[0080] Colorimeter, LICO690, Hach Company, USA;

[0081] pH meter, OHS-3C, Shanghai Leici Instrument Co., Ltd.

[0082] In the following examples and comparative examples, the TOC of the laurolactam production wastewater is 220 ppm and the chromaticity is 120 hazen; the amount of coagulant and flocculant added refers to the mass concentration of the coagulant / flocculant contained in the wastewater after the coagulant / flocculant is added.

[0083] Example 1

[0084] This embodiment provides a method for treating wastewater from laurolactam production, the method comprising the following steps:

[0085] (1) The wastewater from the production of lauryl lactam was cooled to a temperature of 35°C, and then the pH value was adjusted to 4 with sulfuric acid. Polyaluminium chloride was then added thereto for coagulation for 30 minutes, and then anionic polyacrylamide was added thereto for flocculation for 10 minutes. After standing, a supernatant and sludge precipitation were obtained, and the supernatant was filtered through a filter membrane with a pore size of 5 μm;

[0086] The amount of polyaluminium chloride added is 200ppm; the amount of anionic polyacrylamide added is 5ppm;

[0087] (2) The supernatant after filtration in step (1) is passed into an activated carbon fixed bed at a temperature of 35°C for adsorption and retained for 50 minutes, and then the produced water is filtered through a filter membrane with a pore size of 5 μm to obtain adsorbed produced water;

[0088] The activated carbon fixed bed is filled with modified activated carbon;

[0089] The preparation method of the modified activated carbon comprises: immersing activated carbon with an average particle size of 10-16 mesh in a potassium persulfate aqueous solution with a temperature of 70° C. and a mass concentration of 3 wt %, then performing an oxidation reaction at a temperature of 70° C. for 4 hours, and then washing with pure water;

[0090] (3) The adsorbed water produced in step (2) is placed in an MVR evaporation crystallization device for evaporation crystallization at a temperature of 100° C. and a pressure of 70 KPa. Crystal slurry is obtained at the bottom of the MVR evaporation crystallization device. The crystal slurry is sequentially passed through a thickener, centrifuged and dried to obtain white fertilizer-grade ammonium sulfate. The evaporated water is condensed and used as wash water for the Beckmann rearrangement unit of laurolactam.

[0091] Examples 2-13 and Comparative Examples 1-3

[0092] The parameters such as the wastewater cooling temperature and pH value, the type and amount of coagulant added, the amount of flocculant added, the preparation conditions of modified activated carbon (average particle size of activated carbon, type and mass concentration of persulfate, oxidation reaction temperature, oxidation reaction time) and adsorption temperature are changed as shown in Table 1-2. The other conditions are the same as those in Example 1.

[0093] Table 1 Specific parameters of the corresponding conditions in the treatment methods of Examples 1-8

[0094]

[0095] Table 2 Specific parameters of corresponding conditions in the treatment methods of Examples 9-12 and Comparative Examples 1-3

[0096]

[0097] The test results of the supernatant after filtration and the adsorption water in the above embodiments and comparative examples are shown in Table 3. The TOC and chromaticity of the supernatant after filtration and the adsorption water were tested using a total organic carbon analyzer and a colorimeter, respectively.

[0098] Table 3 TOC and chromaticity test results of the supernatant after filtration and adsorption water in the examples and comparative examples

[0099]

[0100] From Table 3, we can see that:

[0101] (1) The treatment method provided in Examples 1-3 of the present invention first cools the wastewater produced by laurolactam and adjusts the pH, then removes most of the organic matter by coagulation and flocculation precipitation, and then removes the remaining organic matter by adsorption using activated carbon modified by specific hydrophilicity, and the adsorbed water is evaporated and crystallized to obtain a fertilizer-grade ammonium sulfate product; wherein the TOC of the adsorbed water is ≤50ppm and the chromaticity is ≤30hazen;

[0102] (2) It can be seen from the comparison between Example 1, Example 4 and Comparative Example 1 that when the pH of the wastewater is adjusted to be too acidic, the coagulation and flocculation effect becomes worse due to the hydrolysis and solubility of the flocculant; when the pH of the wastewater is adjusted to be neutral, the organic matter in the ammonium sulfate wastewater exists in the form of ions and the polarity is enhanced, which makes it difficult for the organic matter to be captured and removed by the coagulant, and the coagulation and flocculation effect becomes worse;

[0103] (3) From the comparison between Example 1 and Examples 5-6, it can be seen that when the temperature of the activated carbon fixed bed is too high, the temperature increase will lead to the enhancement of the thermal motion of the molecules in the activated carbon pores, the weakening of the interaction between the molecules, the reduction of the adsorption capacity, and the deterioration of the adsorption effect; when the temperature of the activated carbon fixed bed is too low, the activated carbon has no obvious effect on the adsorption effect of organic matter;

[0104] (4) By comparing Example 1 with Examples 7-8 and Comparative Example 2, it can be seen that when the amount of coagulant added is too little or no coagulant is added, the organic matter cannot be fully destabilized, resulting in poor coagulation and flocculation effects; when the amount of coagulant added is too much, the coagulation and flocculation effects are not significantly improved, but the treatment cost will increase;

[0105] (5) From the comparison between Example 1 and Examples 9-10, it can be seen that when the concentration of the persulfate solution used for modification is too low, the amount of oxidant is insufficient, resulting in a decrease in the hydrophilic groups on the surface of the modified activated carbon, which in turn leads to a poor adsorption effect; when the concentration of the persulfate solution used for modification is too high, the effect on the hydrophilic groups on the surface of the modified activated carbon is not obvious, and the adsorption effect is not significantly improved, but the cost of the modification agent will increase;

[0106] (6) It can be seen from the comparison between Example 1 and Examples 11-13 that when the temperature of the oxidation reaction is too low, the activated carbon cannot be fully modified, resulting in fewer hydrophilic groups on the surface of the modified activated carbon, which in turn leads to poor adsorption effect; when the temperature of the oxidation reaction is too high, the oxidant decomposes due to the high temperature, and the concentration of the oxidant actually participating in the oxidation reaction decreases, resulting in a decrease in the hydrophilic groups on the surface of the modified activated carbon, which in turn leads to poor adsorption effect;

[0107] (7) From the comparison between Example 1 and Comparative Example 3, it can be seen that when pure activated carbon is used for adsorption, the adsorption effect of organic matter in wastewater becomes poor due to the poor hydrophilicity of activated carbon.

[0108] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for treating wastewater from laurolactam production, characterized in that: The processing method is carried out by the following steps: (1) After adjusting the pH value of the laurolactam production wastewater to 4-6, a coagulant and a flocculant are sequentially added thereto for coagulation, flocculation and precipitation, and a supernatant and a sludge precipitate are obtained after standing; (2) passing the supernatant of step (1) into an activated carbon fixed bed at a temperature of 30-40° C. for adsorption to obtain adsorbed water; The activated carbon fixed bed is filled with modified activated carbon; The preparation method of the modified activated carbon comprises: immersing the activated carbon in a persulfate solution with a mass concentration of 1-5wt%, and performing an oxidation reaction at a temperature of 60-80°C for 1-5h; The total organic carbon concentration of the adsorption water is ≤50ppm and the chromaticity is ≤30hazen; (3) The adsorbed water produced in step (2) is evaporated and crystallized to obtain fertilizer-grade ammonium sulfate.

2. The processing method according to claim 1, characterized in that: The total organic carbon concentration of the laurolactam production wastewater in step (1) is greater than 200 ppm; The chromaticity of the laurolactam production wastewater in step (1) is >100 hazen; The temperature of the laurolactam production wastewater in step (1) is 30-40°C.

3. The processing method according to claim 1, characterized in that: The coagulant in step (1) includes polyaluminium chloride and / or polyaluminium sulfate; After the coagulant is added in step (1), the mass concentration of the coagulant in the wastewater is 100-500 ppm; In step (1), the interval between adding the coagulant and the flocculant is ≥ 30 min.

4. The processing method according to claim 1, characterized in that: The flocculant in step (1) comprises anionic polyacrylamide; After the flocculant is added in step (1), the mass concentration of the flocculant in the wastewater is 3-8 ppm; The coagulation, flocculation and sedimentation time in step (1) is ≥ 40 min.

5. The processing method according to claim 1, characterized in that: The supernatant in step (1) is also filtered through a membrane before passing into the activated carbon fixed bed; The pore size of the filter membrane is 3-6 μm.

6. The processing method according to claim 1, characterized in that: The activated carbon includes any one of coal charcoal, fruit shell charcoal or wood charcoal, or a combination of at least two of them; The average particle size of the activated carbon is 5-20 mesh; The persulfate in the persulfate solution includes any one of sodium persulfate, potassium persulfate or ammonium persulfate, or a combination of at least two of them.

7. The processing method according to claim 1, characterized in that: The residence time of the activated carbon fixed bed in step (2) is 30-60 min; After the adsorption in step (2), the produced water is also filtered through a membrane; The pore size of the filter membrane is 3-6 μm.

8. The processing method according to claim 1, characterized in that: The evaporation crystallization in step (3) is carried out using an MVR evaporation crystallization device; The evaporated water obtained in the evaporative crystallization in step (3) is reused.

9. The processing method according to claim 1, characterized in that: The processing method is carried out by the following steps: (1) Cooling the wastewater from laurolactam production to a temperature of 30-40°C, adjusting the pH value to 4-6, and then sequentially adding a coagulant and a flocculant to the wastewater for coagulation, flocculation and precipitation. After standing, a supernatant and a sludge precipitate are obtained, and the obtained supernatant is filtered through a filter membrane with a pore size of 3-6 μm; The total organic carbon concentration of the laurolactam production wastewater is greater than 200 ppm and the chromaticity is greater than 100 hazen; After the coagulant is added, the mass concentration of the coagulant in the wastewater is 100-500ppm; after the flocculant is added, the mass concentration of the flocculant in the wastewater is 3-8ppm; the interval time between the addition of the coagulant and the flocculant is ≥30min; the coagulation, flocculation and sedimentation time is ≥40min; (2) The supernatant after filtration in step (1) is passed into an activated carbon fixed bed at a temperature of 30-40°C for adsorption and retention for 30-60 minutes, and then the produced water is filtered through a filter membrane with a pore size of 3-6 μm to obtain adsorbed produced water; The activated carbon fixed bed is filled with modified activated carbon; The preparation method of the modified activated carbon comprises: immersing activated carbon with an average particle size of 5-20 meshes in a persulfate solution with a mass concentration of 1-5wt%, and then performing an oxidation reaction at a temperature of 60-80°C for 1-5h; The total organic carbon concentration of the adsorption water is ≤50ppm and the chromaticity is ≤30hazen; (3) placing the adsorbed water produced in step (2) in an MVR evaporation and crystallization device for evaporation and crystallization to obtain fertilizer-grade ammonium sulfate.

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