A system and process for removing aromatics from wastewater
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA CATALYST HLDG CO LTD
- Filing Date
- 2024-10-23
- Publication Date
- 2026-06-26
AI Technical Summary
In existing technologies, the treatment of aromatic wastewater has problems such as high energy consumption, significant environmental pollution, and health impacts. Furthermore, at room temperature, ZSM-5 molecular sieves have poor adsorption capacity for large molecular aromatics, making it difficult to achieve low-temperature energy recovery and utilization.
Using ZSM-5 and/or β molecular sieves as adsorbents, aromatic pollutants are removed by room temperature adsorption. The adsorbent is regenerated by steam method, and combined with inert gas purging and condensation separation technology, the aromatics are recycled.
It achieves efficient removal of aromatics from water at room temperature, reduces energy consumption, allows the adsorbent to be regenerated and reused, and enables the recycling of aromatic pollutants, thus reducing environmental pollution.
Smart Images
Figure CN119330454B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of water treatment technology, specifically relating to a process for removing aromatic hydrocarbons from wastewater, and particularly to the treatment of wastewater containing toluene and xylene. Background Technology
[0002] Adsorption separation is a highly efficient and flexible water pollution treatment technology. By selecting suitable adsorbents and optimizing operating conditions, effective removal of pollutants from water can be achieved, supporting the sustainable use of water resources. ZSM-5 molecular sieve is a high-silica molecular sieve with excellent performance. Due to its large specific surface area, good thermal stability, and acidity, it is used in water pollution treatment processes. For example, high-silica molecular sieves can be directly added to wastewater through physical adsorption, utilizing their large specific surface area and good adsorption performance to adsorb pollutants such as COD and ammonia nitrogen from the wastewater. The adsorption capacity of ZSM-5 molecular sieve for organic matter in water depends on factors such as its pore size, acidity, and hydrophobicity.
[0003] Generally, ZSM-5 molecular sieves exhibit good adsorption capacity for small-molecule organic compounds such as methanol, ethanol, acetone, and acetic acid because these organic compounds have small molecular sizes and can enter the micropores of the ZSM-5 molecular sieve. However, for large-molecule organic compounds such as benzene, toluene, and xylene, their larger molecular sizes typically prevent them from entering the micropores of the ZSM-5 molecular sieve, resulting in poor adsorption capacity. Furthermore, aromatic pollutants in water usually require high-temperature heating to convert them into a mixture of water and aromatic gaseous substances before treatment with an adsorbent. Currently, no reports exist on processes using adsorbents to achieve liquid adsorption separation at room temperature. In conclusion, it is necessary to develop an adsorption process capable of completely removing aromatic pollutants from water at room temperature, achieving low-temperature energy recovery and utilization of aromatics, and enabling the adsorbent to be regenerated and reused. Summary of the Invention
[0004] In order to address the problems of high energy consumption, significant environmental pollution, and health risks associated with incineration methods in the treatment of aromatic hydrocarbon-containing wastewater in the prior art, this invention provides a system and process for removing aromatic hydrocarbons from wastewater.
[0005] The technical solution of the present invention: a method for removing aromatic hydrocarbons from wastewater, the method comprising the following steps:
[0006] S1) The aromatic wastewater is adsorbed by an adsorbent.
[0007] S2) The adsorbent that was saturated in step S1 was regenerated by steam method.
[0008] S3) The regenerated adsorbent is used to repeatedly adsorb aromatic wastewater. The water vapor and aromatic mixture generated during regeneration are condensed and separated.
[0009] The preparation steps of the adsorbent are as follows: ZSM-5 and / or β molecular sieves with a silicon-aluminum ratio ≥200 are acid-treated, washed with water to pH 5-7, dried, calcined, and then mixed with silane coupling agent at a mass ratio of 1:5-20 at 0-80℃ to form a slurry; after solid-liquid separation, the molecular sieves obtained are subjected to silane coupling agent removal from the surface and then sequentially subjected to ball rolling, drying, calcination, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent.
[0010] The silane coupling agent is selected from one or more of KH-550, KH-560, and KH-570.
[0011] The method for removing aromatic hydrocarbons from wastewater involves removing silane coupling agents from the surface of a molecular sieve obtained through solid-liquid separation using a negative pressure method. The temperature for removing the silane coupling agent under negative pressure is 200~300 ℃, and the pressure is -0.05~-0.095 MPa.
[0012] The method for removing aromatics from wastewater involves a high-temperature water treatment temperature of 500-800℃, a steam mass hourly space velocity of 0.2-2 / h, and a treatment time of 2-12h.
[0013] The method for removing aromatics from wastewater uses an alkyl orthosilicate as a binder and one or more of water, methanol, and ethanol as additives during the rolling process.
[0014] The method for removing aromatics from wastewater uses a binder with a mass of 10-20% of the molecular sieve mass and an additive with a mass of 15-25% of the molecular sieve mass.
[0015] The method for removing aromatic hydrocarbons from wastewater uses a binder selected from one or both of methyl orthosilicate and ethyl orthosilicate.
[0016] The method for removing aromatics from wastewater involves drying at a temperature of 60-125℃ for 10-40 h, and calcining at a temperature of 500-600℃ for 5-15 h.
[0017] The present invention also provides a process system for removing aromatic hydrocarbons from wastewater, comprising at least two adsorption towers filled with adsorbent, wherein the aromatic hydrocarbon-containing wastewater pipeline and the water vapor pipeline are respectively connected to any one or more of the adsorption towers by valve switching.
[0018] During the operation of the aforementioned process system, the minimum number of adsorption towers used for adsorption is guaranteed to be one. Taking a process system containing three adsorption towers as an example, the entire process is as follows: During the initial operation, water is introduced into the first adsorption tower, and water is discharged from the last adsorption tower; when the first adsorption tower becomes saturated, the first adsorption tower is regenerated, water is introduced into the second adsorption tower, and water is discharged from the last tower; when the second adsorption tower becomes saturated, the second adsorption tower is regenerated, water is introduced into the third adsorption tower, and water is discharged from the first adsorption tower; and so on, ensuring that the minimum number of adsorption towers is guaranteed to be one.
[0019] The process system described herein includes the following steps for preparing the adsorbent: ZSM-5 and / or β molecular sieves with a silicon-aluminum molecular ratio ≥200 are acid-treated, washed with water to a pH of 5-7, dried, calcined, and then mixed with a silane coupling agent at a mass ratio of 1:5-20 at 0-80°C to form a slurry; the molecular sieve obtained by solid-liquid separation is then subjected to silane coupling agent removal from its surface and sequentially subjected to ball rolling, drying, calcination, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent.
[0020] In the aforementioned process system, aromatic wastewater enters and exits the adsorption tower from the bottom up, and the effluent contains little or no aromatics.
[0021] Once the adsorption tower is saturated, the wastewater between the adsorbent particles is first purged with low-temperature inert gas, and then the adsorbent is regenerated with steam. The resulting mixture of aromatics and water is condensed and separated by liquid-liquid separation.
[0022] The process system described above uses an inert gas volume hourly space velocity of 0.5~3.0 / h, a top-inlet and bottom-outlet purging regeneration tower, a purging temperature of 0~30℃, and a purging volume of 3~5 times that of the regeneration tower.
[0023] The method described uses 120-180℃ steam (bottom-in, top-out) to regenerate the adsorbent, with a steam volume hourly space velocity (VHSV) of 1.0-3.0 / h, purging 5-10 times the volume of the regeneration tower. The separation temperature of the aromatic hydrocarbon-water mixture after condensation is 30-80℃. The beneficial effects of this invention are: the process includes an adsorption system, a regeneration system, and an aromatic hydrocarbon recovery system; aromatic hydrocarbon-containing wastewater sequentially enters from the bottom and exits from the top in the adsorption system, where aromatic hydrocarbons are adsorbed in the adsorbent, resulting in effluent containing little or no aromatic hydrocarbons; when the adsorbent is saturated, during regeneration, first, a low-temperature inert gas is used to purge the wastewater between the adsorbent particles, then steam is used to regenerate the adsorbent; after condensation and settling, the aromatic hydrocarbons are separated from the water using an extraction method, and the refined aromatic hydrocarbons can be reused. This process features thorough removal of aromatic hydrocarbon pollutants, low regeneration energy consumption, and the recyclability of aromatic hydrocarbon pollutants. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of a process system for removing aromatic hydrocarbons from wastewater.
[0025] Figure 2 This is a schematic diagram of the initial operation process.
[0026] Figure 3 This is a schematic diagram of the process of wastewater containing aromatic hydrocarbons carried by the inert gas purging regeneration tower.
[0027] Figure 4 This is a schematic diagram of the steam regeneration process.
[0028] Among them, 1 is the first pipeline, 2 is the second pipeline, 3 is the adsorption tower, 3a is the first valve, 3b is the second valve, and 3c is the third valve. Detailed Implementation
[0029] Figure 1 A schematic diagram of a process system for removing aromatics from wastewater is shown. The system includes a first pipeline 1, a second pipeline 2, and three adsorption towers 3 connected sequentially. Each adsorption tower 3 has a first valve 3a at its bottom inlet pipe, a second valve 3b on the section of the second pipeline 2 connecting to the inlet pipe of each adsorption tower 3, and a third valve 3c on the section of the first pipeline 1 connecting to the inlet pipe of each adsorption tower 3. Each adsorption tower 3 also has an exhaust port and a drain port.
[0030] Example 1: Preparation of ZSM-5 molecular sieve and β molecular sieve
[0031] ZSM-5 molecular sieve was synthesized according to Example 3 of patent document CN105776245A (application number 201410806365.3). The synthesized ZSM-5 molecular sieve was treated in 10% hydrochloric acid at 50°C for 1 hour, then washed with water until the pH of the washing solution was 6.5. The molecular sieve was dried at 80°C for 6 hours and calcined at 400°C for 3 hours until the dry basis was 97.2%.
[0032] Referring to Example 14 of patent document CN117509665A (application number 202311487249.5), a high silicon-to-aluminum ratio Beta molecular sieve (SiO2 / Al2O3 ratio of 257.3) was synthesized, with a dry basis of 99.4% after calcination.
[0033] Example 2: Preparation of Adsorbent M1
[0034] The ZSM-5 molecular sieve and β molecular sieve obtained in Example 1 (mass ratio 2:1) were mixed with KH-560 silane coupling agent at 5 times the total mass of the molecular sieve at 50°C for 2 hours. After pressure filtration, the mixture was dehydrated in a vacuum muffle furnace at 260°C and -0.07MPa for 30 minutes until the dry basis of the molecular sieve was 82%.
[0035] The obtained molecular sieves were rolled into balls using tetraethyl orthosilicate as a binder and ethanol as an additive. The mass of the binder was 15% of the molecular sieve mass, and the mass of the ethanol was 20% of the molecular sieve mass. Ethanol was poured into a spray bottle and sprayed evenly onto the surface of the balls multiple times during the rolling process, with a mesh size of 6-10 mesh. After molding, the balls were dried at 60℃, 80℃, 100℃, and 120℃ (for 4 hours each time), and then calcined at 550℃ for 6 hours until the dry basis content reached 99.5%.
[0036] Take 50g of the shaped molecular sieve and introduce water vapor into a reactor at 800℃. The water vapor mass hourly space velocity is 0.2 / h, and the treatment time is 10 h. After purging with argon gas to cool to room temperature, adsorbent M1 is obtained.
[0037] Example 3: Preparation of Adsorbent M2
[0038] The preparation process of adsorbent M2 is the same as in Example 2. The steam treatment process is as follows: 50g of the shaped molecular sieve is taken and steam is introduced into a reactor at 600℃. The steam mass hourly space velocity is 0.8 / h and the treatment time is 6h. The adsorbent M2 is obtained by purging with argon gas to cool to room temperature.
[0039] Example 4: Preparation of Adsorbent M3
[0040] The preparation process of adsorbent M3 is the same as in Example 2. The mass ratio of ZSM-5 molecular sieve and β molecular sieve is 1:3. The steam treatment process is as follows: 50 g of the shaped molecular sieve is taken and steam is introduced into a reactor at 500 °C. The steam mass hourly space velocity is 1 / h and the treatment time is 4 h. Argon gas is used to purge and cool the temperature to room temperature to obtain adsorbent M3.
[0041] Example 5: Preparation of Adsorbent M4
[0042] The preparation process of adsorbent M4 is the same as in Example 2. The mass ratio of ZSM-5 molecular sieve to β molecular sieve is 5:1. The steam treatment process is as follows: 50g of the shaped molecular sieve is taken and steam is introduced into a reactor at 500℃. The steam mass hourly space velocity is 2 / h and the treatment time is 2h. Argon gas is used to purge and cool the temperature to room temperature to obtain adsorbent M4.
[0043] Example 6: Preparation of Adsorbent M5
[0044] The preparation process of adsorbent M5 is the same as in Example 2, except for the steam treatment process: take 50g of the shaped molecular sieve, put it into a reactor at 500℃, introduce steam, steam mass hourly space velocity 1 / h, treat for 4h, and then purge with argon to cool to room temperature to obtain adsorbent M5.
[0045] Example 7: Preparation of Adsorbent M6
[0046] The preparation process of adsorbent M6 is the same as in Example 2. The mass ratio of ZSM-5 molecular sieve and β molecular sieve is 1:5. The silane coupling agent treatment process is as follows: the molecular sieve obtained in Example 1 is mixed with 10 times the mass of KH-560 silane coupling agent at 80°C for 2 hours. After pressure filtration, it is dehydrated to 85% dry basis of molecular sieve at 260°C and -0.09MPa.
[0047] Example 8: Preparation of Adsorbent M7
[0048] The preparation process of adsorbent M7 is the same as in Example 2. The mass ratio of ZSM-5 molecular sieve and β molecular sieve is 1:1. The silane coupling agent treatment process is as follows: the molecular sieve obtained in Example 1 is mixed with 18 times the mass of KH-560 silane coupling agent at 30°C for 4 hours. After pressure filtration separation, it is dehydrated to 83% dry basis of molecular sieve at 230°C and -0.05MPa.
[0049] Example 9: Preparation of Adsorbent M8
[0050] The preparation process of adsorbent M8 is the same as in Example 2, except that ZSM-5 molecular sieve and β molecular sieve at a mass ratio of 2:1 are replaced by ZSM-5 molecular sieve.
[0051] Comparative Example 1
[0052] The ZSM-5 molecular sieve prepared in Example 1 was further calcined to 99.6% on a dry basis, and the adsorbent was designated as V1.
[0053] Test case
[0054] The above adsorbents M1~M9 were loaded into... Figure 1 In the three adsorption towers 3, each with a volume of 10L, adsorption experiments were conducted on wastewater containing 50 ppm toluene and 30 ppm paraxylene at 25℃. The aromatic wastewater was adsorbed through the adsorbent at a volume hourly space velocity (VHSV) of 2.0 / h for 24 hours before switching to the next tower. The first adsorption tower was regenerated after 24 hours of adsorption, and the second and third adsorption towers then performed adsorption. The first adsorption tower was purged with 25℃ nitrogen gas at a VHSV of 1.0 / h for 3 hours (top in, bottom out). Then, 150℃ steam was used at a VHSV of 2.0 / h for 3 hours, after which regeneration was completed and the tower was allowed to cool naturally. After the second adsorption tower became saturated, the same purging, regeneration, and natural cooling process was repeated, and the first and third adsorption towers then performed adsorption. Similarly, after the third adsorption tower became saturated, the same purging, regeneration, and natural cooling process was repeated, and the first and second adsorption towers then performed adsorption (e.g., ...). Figure 2-4 (as shown in the figure); and so on. The content of toluene and paraxylene in the wastewater effluent was detected, as shown in Table 1.
[0055] Table 1. Content of toluene and p-xylene in the wastewater after adsorption
[0056] Adsorbent number Toluene content in wastewater after 10 reuses of the adsorbent (ppm) After the adsorbent was reused 10 times, the p-xylene content in the wastewater was reduced to ppm. Toluene content in wastewater after 50 reuses of the adsorbent (ppm) After the adsorbent is reused 50 times, the p-xylene content in the wastewater is as follows (ppm). M1 3 3 4 4 M2 2 3 3 4 M3 2 3 3 4 M4 3 4 4 4 M5 2 4 3 4 M6 2 5 3 5 M7 1 3 2 3 M8 4 5 4 5 V1 6 7 10 12
[0057] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.
Claims
1. A method for removing aromatic hydrocarbons from wastewater, characterized in that, The method comprises the following steps: S1) The aromatic-containing wastewater is adsorbed by an adsorbent; S2) The adsorbent saturated in step S1 is regenerated using a steam method; S3) The regenerated adsorbent is used to repeatedly adsorb aromatic wastewater. The water vapor and aromatic mixture generated during regeneration are condensed and separated. The preparation steps of the adsorbent are as follows: ZSM-5 and / or β molecular sieves with a silicon-to-aluminum ratio ≥200 are acid-treated, washed with water to pH 5-7, dried, calcined, and then mixed with silane coupling agent at a mass ratio of 1:5-20 at 0-80℃ to form a slurry; after solid-liquid separation, the molecular sieve obtained has its surface silane coupling agent removed and is then subjected to ball rolling, drying, calcination, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent; The silane coupling agent is selected from one or more of KH-550, KH-560, and KH-570; The high-temperature water treatment temperature is 500~800℃, the water vapor mass hourly space velocity is 0.2~2 / h, and the treatment time is 2~12h.
2. The method for removing aromatics from wastewater according to claim 1, characterized in that, The molecular sieve obtained by solid-liquid separation is subjected to a negative pressure method to remove the silane coupling agent from its surface. The temperature for removing the silane coupling agent under negative pressure is 200~300℃, and the pressure is -0.05~-0.095MPa.
3. The method for removing aromatics from wastewater according to claim 1, characterized in that, The binder used in the ball rolling process is alkyl orthosilicate, and the additives are one or more of water, methanol, and ethanol.
4. The method for removing aromatics from wastewater according to claim 3, characterized in that, The adhesive is selected from one or both of methyl orthosilicate and ethyl orthosilicate.
5. A system used in the method for removing aromatics from wastewater according to any one of claims 1 to 4, characterized in that, It includes at least two adsorption towers filled with adsorbent, and the aromatic wastewater pipeline and the water vapor pipeline can be connected to any one or more of the adsorption towers by switching valves.
6. The system according to claim 5, characterized in that, Aromatic wastewater enters and exits the adsorption tower in the adsorption system using a bottom-in, top-out method, and the effluent contains no or trace amounts of aromatics. Once the adsorption tower is saturated, the wastewater between the adsorbent particles is first purged with an inert gas at 0-40°C, and then the adsorbent is regenerated with steam. The resulting mixture of aromatics and water is condensed and separated by liquid-liquid separation.
7. The system according to claim 6, characterized in that, The inert gas volume hourly space velocity is 0.5~3.0 / h, and it is purged from the top and exited from the bottom of the regeneration tower. The purging temperature is 0~30℃, and the purging volume is 3~5 times that of the regeneration tower.
8. The system according to claim 6, characterized in that, The adsorbent is regenerated using 120~180℃ steam (bottom in, top out), with a steam volume hourly space velocity of 1.0~3.0 / h, and the volume of the regeneration tower is purged by 5~10 times. The separation temperature of the mixture of aromatics and water after condensation is 30~80℃.