System and process method for removing aromatic hydrocarbon in sewage

Abstract

The invention relates to a system and a process method for removing aromatic hydrocarbons in sewage, in particular to removal of toluene and xylene pollutants in sewage. The process comprises 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 an adsorption system, aromatic hydrocarbons are adsorbed in an adsorbent, and effluent does not contain or contains trace aromatic hydrocarbons; when the adsorbent is regenerated after adsorption saturation, firstly, low-temperature inert gas is used for purging sewage among adsorbent particles, and then water vapor is used for regenerating the adsorbent; the regenerated tail gas is condensed and then stands, aromatic hydrocarbon and water are separated through an extraction method, and the aromatic hydrocarbon can be reused after being refined. The process has the characteristics of thorough removal of the aromatic pollutants, low regeneration energy consumption and recyclability of the aromatic pollutants.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and specifically relates to a process for removing aromatic hydrocarbons from sewage, and in particular to the treatment of sewage containing toluene and xylene. Background Art

[0002] Adsorption separation process is an efficient and flexible water pollution control technology. By selecting suitable adsorbents and optimizing operating conditions, effective removal of pollutants in water can be achieved, providing support for the sustainable use of water resources. ZSM-5 molecular sieve is a high-silicon molecular sieve with excellent performance. It is used in water pollution treatment processes because of its large specific surface area, good thermal stability and acidity. For example, high-silicon molecular sieves can be directly put into wastewater by physical adsorption, and their large specific surface area and good adsorption properties can be used to adsorb pollutants such as COD and ammonia nitrogen in the wastewater. The adsorption capacity of ZSM-5 molecular sieves for organic matter in water depends on factors such as its pore size, acidity and hydrophobicity.

[0003] Generally speaking, ZSM-5 molecular sieve has good adsorption capacity for small molecular organic substances such as methanol, ethanol, acetone, acetic acid, etc., because the molecular size of these organic substances is small and can enter the micropores of ZSM-5 molecular sieve. For macromolecular organic substances such as benzene, toluene, xylene, etc., due to their large molecular size, they usually cannot enter the micropores of ZSM-5 molecular sieve, so the adsorption capacity is poor. In addition, aromatic pollutants in water usually need to be heated at high temperature to turn them into a gaseous mixture of water and aromatics, and then treated by adsorbents. There is currently no report on the process of using adsorbents to achieve liquid adsorption separation at room temperature. In summary. It is necessary to develop an adsorption process that can completely remove aromatic pollutants in water at room temperature and realize the low-temperature energy consumption recovery and utilization of aromatics. At the same time, the adsorbent can be regenerated and reused. Summary of the invention

[0004] In order to solve the problems of high energy consumption, severe environmental pollution, and health impact caused by the incineration method in the prior art for treating wastewater containing aromatic hydrocarbons, the present invention provides a system and a process for removing aromatic hydrocarbons from wastewater.

[0005] The technical solution of the present invention is a method for removing aromatic hydrocarbons from sewage, the method comprising the following steps: S1) The wastewater containing aromatic hydrocarbons is adsorbed by an adsorbent.

[0006] S2) regenerating the adsorbent saturated with adsorption in step S1 by using a water vapor method.

[0007] S3) The regenerated adsorbent is used to repeatedly adsorb the wastewater containing aromatic hydrocarbons, and the water vapor and aromatic hydrocarbon mixture generated by the regeneration are condensed and separated.

[0008] The preparation steps of the adsorbent are as follows: treating ZSM-5 and / or β molecular sieves with a silicon-aluminum molecular ratio of ≥200 with acid, washing with water to a pH of 5-7, drying and calcining, and mixing and slurrying with a silane coupling agent at a mass ratio of 1:5-20 at 0-80°C; removing the silane coupling agent on the surface of the molecular sieve obtained by solid-liquid separation, and then subjecting the molecular sieve to rolling, drying, calcining, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent.

[0009] The silane coupling agent is selected from one or more of KH-550, KH-560 and KH-570.

[0010] In the method for removing aromatic hydrocarbons from sewage, the molecular sieve obtained by solid-liquid separation is subjected to negative pressure method to remove the silane coupling agent on the surface, and the temperature of the negative pressure removal of the silane coupling agent is 200-300°C and the pressure is -0.05--0.095 MPa.

[0011] The method for removing aromatic hydrocarbons from sewage has a high-temperature water treatment temperature of 500-800°C, a water vapor mass space velocity of 0.2-2 / h, and a treatment time of 2-12h.

[0012] In the method for removing aromatic hydrocarbons from sewage, the binder is alkyl orthosilicate and the auxiliary agent is one or more of water, methanol and ethanol.

[0013] In the method for removing aromatic hydrocarbons from sewage, the mass of the binder is 10-20% of the mass of the molecular sieve, and the amount of the auxiliary agent is 15-25% of the mass of the molecular sieve.

[0014] In the method for removing aromatic hydrocarbons from sewage, the binder is selected from one or both of methyl orthosilicate and ethyl orthosilicate.

[0015] The method for removing aromatic hydrocarbons from sewage has a drying temperature of 60-125°C, a drying time of 10-40 h, a roasting temperature of 500-600°C, and a roasting time of 5-15 h.

[0016] The present invention also provides a process system for removing aromatic hydrocarbons from sewage, comprising at least two adsorption towers filled with adsorbents, and the aromatic hydrocarbon-containing sewage pipeline and the water vapor pipeline can be connected to any one or more of the adsorption towers through valve switching.

[0017] During the operation of the process system, it is ensured that at least one adsorption tower is used for adsorption. Taking a process system including three adsorption towers as an example, the operation process of the entire process system is as follows: during the first operation, the first adsorption column enters water, and the last adsorption column discharges water; when the first adsorption column is saturated with adsorption, the first adsorption column is regenerated, the second adsorption column enters water, and the last column discharges water; when the second adsorption column is saturated with adsorption, the second adsorption column is regenerated, the third adsorption column enters water, and the first adsorption column discharges water; and so on, ensuring that at least one adsorption column is used.

[0018] The process system and the preparation steps of the adsorbent are as follows: treating ZSM-5 and / or β molecular sieves with a silicon-aluminum molecular ratio of ≥200 with acid, washing with water to a pH of 5-7, drying and calcining, and mixing and slurrying with a silane coupling agent at a mass ratio of 1:5-20 at 0-80°C; removing the silane coupling agent on the surface of the molecular sieve obtained by solid-liquid separation, and then subjecting the molecular sieve to rolling, drying, calcining, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent.

[0019] In the process system, the wastewater containing aromatic hydrocarbons enters and exits the adsorption tower in the adsorption system in a bottom-in and top-out manner, and the effluent contains no or trace amounts of aromatic hydrocarbons.

[0020] When the adsorption tower is saturated with adsorption, low-temperature inert gas is first used to purge the sewage between the adsorbent particles, and then water vapor is used to regenerate the adsorbent. The regenerated mixture of aromatic hydrocarbons and water is condensed and separated by liquid separation.

[0021] The process system has an inert gas volume space velocity of 0.5-3.0 / h, a top-in-bottom-out purge regeneration tower, a purge temperature of 0-30°C, and a purge volume of 3-5 times the regeneration tower volume.

[0022] The method described uses 120~180℃ water vapor to regenerate the adsorbent, the water vapor volume space velocity is 1.0~3.0 / h, and 5~10 times the volume of the regeneration tower is purged; the separation temperature of the mixture of aromatics and water after condensation is 30~80℃. The beneficial effects of the present invention are as follows: the process includes an adsorption system, a regeneration system, and an aromatics recovery system; the wastewater containing aromatics enters and exits in the adsorption system in sequence, the aromatics are adsorbed in the adsorbent, and the effluent contains no or trace amounts of aromatics; when the adsorbent is regenerated after adsorption saturation, the sewage between the adsorbent particles is first purged with a low-temperature inert gas, and then the adsorbent is regenerated with water vapor; the regenerated tail gas is condensed and left to stand, and the aromatics and water are separated by an extraction method, and the aromatics can be reused after being refined. The process has the characteristics of thorough removal of aromatic pollutants, low regeneration energy consumption, and recyclable aromatic pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of a process system for removing aromatic hydrocarbons from wastewater.

[0024] Figure 2 This is a schematic diagram of the initial operation process. Figure 3 It is a schematic diagram of the process of inert gas purging regeneration tower to entrain aromatic wastewater.

[0025] Figure 4 It is a schematic diagram of the steam regeneration process.

[0026] Among them, 1, the first pipeline, 2, the second pipeline, 3, the adsorption tower, 3a, the first valve, 3b, the second valve, 3c, the third valve. DETAILED DESCRIPTION

[0027] Figure 1 A schematic diagram of the structure of a process system for removing aromatic hydrocarbons from sewage is shown. In the figure, the process system for removing aromatic hydrocarbons from sewage comprises a first pipeline 1, a second pipeline 2 and three adsorption towers 3 connected end to end in sequence, a first valve 3a is provided on the inlet pipe at the bottom of each adsorption tower 3, a second valve 3b is provided on the pipe section where the second pipeline 2 is connected to the inlet pipe of each adsorption tower 3, and a third valve 3c is provided on the pipe section where the first pipeline 1 is connected to the inlet pipe of each adsorption tower 3. Each adsorption tower 3 is also provided with an exhaust port and a liquid discharge port.

[0028] Example 1: Preparation of ZSM-5 molecular sieve and β molecular sieve According to Example 3 of the patent document with publication number 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 value of the washing liquid was 6.5, and the molecular sieve was dried at 80°C for 6 hours and calcined at 400°C for 3 hours to a dry basis of 97.2%.

[0029] With reference to Example 14 of the patent document with publication number CN117509665A (application number 202311487249.5), a high silicon-aluminum ratio Beta molecular sieve (SiO2 / Al2O3 ratio of 257.3) was synthesized, and the dry basis after calcination was 99.4%.

[0030] Example 2: Preparation of adsorbent M1 The ZSM-5 molecular sieve and β molecular sieve (mass ratio 2:1) obtained in Example 1 were mixed with KH-560 silane coupling agent of 5 times the total mass of the molecular sieve at 50°C for 2h, separated by filter pressing, and then dehydrated in a vacuum muffle furnace at 260°C and -0.07MPa for 30min to a molecular sieve dry basis of 82%.

[0031] The obtained molecular sieve is rolled using tetraethyl orthosilicate as a binder and ethanol as an auxiliary agent. The mass of the binder is 15% of the mass of the molecular sieve, and the mass of ethanol is 20% of the mass of the molecular sieve. Pour the ethanol into a spray pot and spray it evenly on the surface of the sphere several times during the rolling process. The size is 6~10 mesh. After forming, it is gradually dried at 60℃, 80℃, 100℃, and 120℃ (drying for 4 hours respectively), and roasted at 550℃ for 6 hours to 99.5% dry basis.

[0032] 50 g of the formed molecular sieve was taken and placed in a reactor at 800°C. Water vapor was introduced at a water vapor mass space velocity of 0.2 / h for 10 h. The temperature was then purged with argon and dropped to room temperature to obtain adsorbent M1.

[0033] Example 3: Preparation of adsorbent M2 The preparation process of adsorbent M2 is the same as that of Example 2, except for the steam treatment process: 50 g of the formed molecular sieve is introduced into a reactor at 600°C with a steam mass space velocity of 0.8 / h for 6 hours, and the temperature is purged with argon to obtain adsorbent M2.

[0034] Example 4: Preparation of adsorbent M3 The preparation process of adsorbent M3 is the same as that of Example 2, except that the mass ratio of ZSM-5 molecular sieve to β molecular sieve is 1:3. The water vapor treatment process is as follows: 50 g of the formed molecular sieve is taken and water vapor is introduced into a reactor at 500 °C with a water vapor mass space velocity of 1 / h for a treatment time of 4 h. The adsorbent M3 is obtained by purging with argon and dropping the temperature to room temperature.

[0035] Example 5: Preparation of adsorbent M4 The preparation process of adsorbent M4 is the same as that of Example 2, except that the mass ratio of ZSM-5 molecular sieve to β molecular sieve is 5:1. The water vapor treatment process is as follows: 50 g of the formed molecular sieve is taken and water vapor is introduced into a reactor at 500°C with a water vapor mass space velocity of 2 / h for a treatment time of 2h. The adsorbent M4 is obtained by purging with argon and cooling to room temperature.

[0036] Example 6: Preparation of adsorbent M5 The preparation process of adsorbent M5 is the same as that of Example 2, except for the water vapor treatment process: 50 g of the formed molecular sieve is taken, and water vapor is introduced into a reactor at 500°C with a water vapor mass space velocity of 1 / h for 4 hours. The temperature is then purged with argon and dropped to room temperature to obtain adsorbent M5.

[0037] Example 7: Preparation of adsorbent M6 The preparation process of adsorbent M6 is the same as that of Example 2, the mass ratio of ZSM-5 molecular sieve to β molecular sieve is 1:5, and 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 2h, and after separation by pressure filtration, it is dehydrated to 85% of the molecular sieve dry basis at 260°C and -0.09MPa.

[0038] Example 8: Preparation of adsorbent M7 The preparation process of adsorbent M7 is the same as that of Example 2, the mass ratio of ZSM-5 molecular sieve to β molecular sieve is 1:1, and 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 4h, and after separation by pressure filtration, it is dehydrated to 83% of the molecular sieve dry basis at 230°C and -0.05MPa.

[0039] Example 9: Preparation of adsorbent M8 The preparation process of adsorbent M8 is the same as that of Example 2, except that ZSM-5 molecular sieve is used to replace the ZSM-5 molecular sieve and β molecular sieve in a mass ratio of 2:1.

[0040] Comparative Example 1 The ZSM-5 molecular sieve prepared in Example 1 was further calcined to 99.6% on a dry basis, and the adsorbent was numbered V1.

[0041] Test Case The above adsorbents M1~M9 are loaded into Figure 1 Among the three adsorption towers 3, the volume of a single tower is 10L, and 25℃ wastewater containing 50 ppm toluene and 30 ppm para-xylene was taken for adsorption experiments. The aromatic hydrocarbon wastewater was adsorbed by the adsorbent at a volumetric space velocity of 2.0 / h. After 24 hours of adsorption, it was switched to the next tower for feeding. The first adsorption tower was regenerated after 24 hours of adsorption, and the second and third adsorption towers were used for adsorption. The first adsorption tower used 25℃ nitrogen to purge the sewage, with a purge volumetric space velocity of 1.0 / h, and purged from top to bottom for 3 hours. Then it was switched to 150℃ water vapor with a volumetric space velocity of 2.0 / h. After purging for 3 hours, the regeneration was completed and the temperature was naturally cooled. After the second adsorption tower was saturated with adsorption, the above-mentioned purge, regeneration, and natural cooling steps were carried out, and the third adsorption tower and the first adsorption tower were used for adsorption; after the third adsorption tower was saturated with adsorption, the above-mentioned purge, regeneration, and natural cooling steps were carried out, and the first adsorption tower and the second adsorption tower were used for adsorption (such as Figure 2-4 The contents of toluene and p-xylene in the wastewater effluent were tested, as shown in Table 1.

[0042] Table 1 Contents of toluene and p-xylene in wastewater after adsorption Adsorbent No. Toluene content in wastewater after the adsorbent is reused 10 times / ppm p-Xylene content in wastewater after the adsorbent was reused 10 times / ppm Toluene content in wastewater after the adsorbent is reused 50 times / ppm p-Xylene content in wastewater after the adsorbent was reused 50 times / 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 The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing aromatic hydrocarbons from sewage, characterized in that: The method comprises the following steps: S1) adsorbing the wastewater containing aromatic hydrocarbons through an adsorbent; S2) regenerating the adsorbent saturated with adsorption in step S1 by a water vapor method; S3) The regenerated adsorbent is used to repeatedly adsorb the wastewater containing aromatic hydrocarbons, and the water vapor and aromatic hydrocarbon mixture generated by the regeneration are condensed and separated; The preparation steps of the adsorbent are as follows: treating ZSM-5 and / or β molecular sieves with a silicon-aluminum ratio of ≥200 with acid, washing with water until the pH value is 5-7, drying and calcining, and then mixing and slurrying with a silane coupling agent at a mass ratio of 1:5-20 at 0-80° C.; removing the silane coupling agent on the surface of the molecular sieve obtained by solid-liquid separation, and then rolling, drying, calcining, 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.

2. A method for removing aromatic hydrocarbons from sewage according to claim 1, characterized in that: The molecular sieve obtained by solid-liquid separation is subjected to negative pressure method to remove the silane coupling agent on the surface. The temperature of negative pressure removal of the silane coupling agent is 200~300 ℃ and the pressure is -0.05~-0.095 MPa.

3. A method for removing aromatic hydrocarbons from sewage according to claim 1, characterized in that: The high-temperature water treatment temperature is 500~800℃, the water vapor mass space velocity is 0.2~2 / h, and the treatment time is 2~12h.

4. A method for removing aromatic hydrocarbons from sewage according to claim 1, characterized in that: The binder used in rolling the ball is alkyl orthosilicate, and the auxiliary agent is one or more of water, methanol and ethanol.

5. A method for removing aromatic hydrocarbons from sewage according to claim 4, characterized in that: The binder is selected from one or both of methyl orthosilicate and ethyl orthosilicate.

6. A process system for removing aromatic hydrocarbons from sewage, characterized in that: It comprises at least two adsorption towers filled with adsorbents, and the aromatics-containing wastewater pipeline and the water vapor pipeline can be connected to any one or more of the adsorption towers through valve switching.

7. The process system according to claim 6, characterized in that: The preparation steps of the adsorbent are as follows: treating ZSM-5 and / or β molecular sieves with a silicon-aluminum molecular ratio of ≥200 with acid, washing with water to a pH of 5-7, drying and calcining, and mixing and slurrying with a silane coupling agent at a mass ratio of 1:5-20 at 0-80°C; removing the silane coupling agent on the surface of the molecular sieve obtained by solid-liquid separation, and then subjecting the molecular sieve to rolling, drying, calcining, high-temperature water treatment, and inert gas purging and cooling to obtain the adsorbent.

8. The process system according to claim 6, characterized in that: In the adsorption system, the wastewater containing aromatic hydrocarbons enters and exits the adsorption tower in a bottom-in and top-out manner, and the effluent contains no or trace amounts of aromatic hydrocarbons; When the adsorption tower is saturated with adsorption, an inert gas at 0-40°C is first used to purge the sewage between the adsorbent particles, and then water vapor is used to regenerate the adsorbent. The regenerated mixture of aromatic hydrocarbons and water is condensed and separated by liquid separation.

9. The process system according to claim 8, characterized in that: The inert gas volume space velocity is 0.5~3.0 / h, and the regeneration tower is purged from top to bottom. The purge temperature is preferably 0~30℃, and 3~5 times the volume of the regeneration tower is purged.

10. The method according to claim 8, characterized in that: Use 120~180℃ water vapor to regenerate the adsorbent, with a water vapor volume space velocity of 1.0~3.0 / h, and purge 5~10 times the volume of the regeneration tower; The separation temperature of the mixture of aromatics and water after condensation is 30~80℃.

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