A method for producing salicylic acid by comprehensive utilization of wastewater

Abstract

The invention relates to a salicylic acid production method for comprehensively utilizing wastewater, comprising the following steps: S1: reacting phenol with liquid alkali to obtain sodium phenolate; S2: introducing carbon dioxide into the sodium phenolate to carry out a carboxylation reaction, and then carrying out rearrangement isomerization to obtain sodium salicylate; and then carrying out acid precipitation to obtain a crude salicylic acid product; S3: washing and centrifuging the crude salicylic acid product to obtain a salicylic acid product and salicylic acid production wastewater; S4: subjecting the wastewater to adsorption by a resin column, wherein the adsorption effluent comprises front-end effluent and back-end effluent, and the front-end effluent is used for the carboxylation reaction and acid precipitation operation in step S2; S5: inputting the back-end effluent into an evaporation crystallization device to obtain a crude sodium sulfate product and a kettle residue, and the kettle residue is used for the carboxylation reaction and acid precipitation operation in step S2; and S6: after the resin column is saturated with adsorption, eluting and regenerating with alkali solution, and obtaining an eluent comprising a front-end eluent and a back-end eluent, wherein the front-end eluent is used for step S1, and the back-end eluent is used for preparing the alkali solution.

Description

Technical Field

[0001] The invention belongs to the technical field of salicylic acid production and wastewater utilization, and particularly relates to a salicylic acid production method that comprehensively utilizes wastewater. Background Art

[0002] Salicylic acid is an important raw material for fine chemical products such as pesticides, medicines, foods, spices, dyes and rubber additives. Currently, the main methods for synthesizing salicylic acid in industry include the phenol atmospheric pressure method, the phenol medium pressure method and the o-cresol method. Among them, the phenol medium pressure method is widely used in the field of industrial synthesis of salicylic acid due to its advantages such as low cost, high phenol single-pass conversion rate and good product quality. Due to the process characteristics of the phenol medium pressure method for producing salicylic acid, its production wastewater has the following characteristics: (1) contains a large amount of unreacted phenol raw material and unsublimed crude salicylic acid; (2) has a high salt content, mainly sodium sulfate; (3) is highly acidic, with a pH generally between 1 and 2; (4) has poor biodegradability, with a B / C ratio generally less than 0.1. Therefore, salicylic acid production wastewater is a typical high-salt, phenol-containing and difficult to biodegrade strong acidic toxic organic industrial wastewater, and contains a large amount of valuable resources. If salicylic acid production wastewater is treated using general water treatment methods, it will not only be difficult and costly, but also result in a waste of resources. Summary of the Invention

[0003] In response to the above problems, the present invention provides a salicylic acid production method that comprehensively utilizes wastewater. The method combines ultra-high cross-linked resin with low-temperature evaporation and crystallization technology, has a simple process, organically combines the wastewater treatment process with the salicylic acid production process, fully utilizes phenol, crude salicylic acid and acidity in the wastewater, avoids waste of resources, and recovers sodium sulfate. After treatment, no residual pollutants are discharged, thus achieving zero discharge of wastewater treatment.

[0004] The salicylic acid production method using comprehensive wastewater utilization comprises the following steps:

[0005] S1: Phenol reacts with liquid alkali to produce sodium phenolate;

[0006] S2: introducing carbon dioxide into the sodium phenolate obtained in step S1 to perform a carboxylation reaction to obtain sodium phenol carbonate, which is then subjected to rearrangement isomerization to obtain sodium salicylate;

[0007] Then carry out acid precipitation to obtain crude salicylic acid;

[0008] S3: washing and centrifuging the crude salicylic acid obtained in step S2 to obtain a salicylic acid product and salicylic acid production wastewater;

[0009] S4: The salicylic acid production wastewater is adsorbed by a resin column, and the adsorption effluent includes the front-end effluent and the back-end effluent. The front-end effluent is used for the carboxylation reaction and acid precipitation operation of step S2 in the next batch of salicylic acid preparation;

[0010] S5: The water effluent from the latter stage is fed into an evaporation crystallization device, and after high-temperature evaporation and cooling crystallization, a crude sodium sulfate product and a kettle residue are obtained. The kettle residue is used for the carboxylation reaction and acid precipitation operation of the next batch of salicylic acid preparation step S2;

[0011] S6: After the resin column in step S4 is saturated with adsorption, it is eluted and regenerated with alkaline solution. The obtained eluate includes a front-end eluate and a back-end eluate. The front-end eluate is used in step S1 of the next batch of salicylic acid preparation, and the back-end eluate is used to prepare alkaline solution for the next resin elution and regeneration.

[0012] Optionally, the reaction of phenol with liquid alkali in step S1, the carboxylation reaction, rearrangement isomerization and acid precipitation in step S2, and the washing and centrifugation of the crude salicylic acid in step S3 are all carried out under the same process conditions as the existing phenol medium-pressure method for preparing aqueous hydrochloric acid.

[0013] Optionally, in step S1, the liquid caustic soda is a sodium hydroxide solution with a mass fraction of 50%, and the reaction temperature of phenol and liquid caustic soda is 105-130° C.;

[0014] In step S2, the sodium phenolate is vacuum dried and then cooled to 100° C., and then dry carbon dioxide is introduced. When the pressure in the autoclave reaches 0.7-0.8 MPa, the carbon dioxide is stopped, and sodium phenol carbonate is generated. Then, intramolecular rearrangement isomerization occurs at 130-140° C. to produce sodium salicylate.

[0015] Optionally, in step S3, the salicylic acid product can also be sublimed under reduced pressure to obtain salicylic acid product.

[0016] Optionally, in step S4, the resin filled in the resin column is selected from one of ND-800 resin, CHA-111 resin, and LS-100 resin;

[0017] The adsorption process parameters are adsorption temperature of 15-30°C and wastewater flow rate of 0.5-2BV / h.

[0018] Optionally, in step S4, the front-end effluent and the rear-end effluent flow out from the resin column in chronological order, and the front-end effluent and the rear-end effluent are determined based on the mass concentration of sodium sulfate in the adsorbed effluent. Specifically, the mass concentration of sodium sulfate in the front-end effluent is less than 12%, and the mass concentration of sodium sulfate in the rear-end effluent is not less than 12%.

[0019] As the adsorption time increases, the resin column gradually reaches saturation, the adsorption capacity for pollutants in the wastewater gradually decreases, and the pollutants in the adsorbed effluent gradually increase. The present invention only selects sodium sulfate as an indicator for measuring the adsorbed effluent. This is specially designed to match the pollutants contained in the adsorbed effluent and the eluate of the present invention to be returned to different steps of salicylic acid production. When the mass concentration of sodium sulfate in the adsorbed effluent is greater than 12%, it means that there is a lot of sodium sulfate in the effluent, and the sodium sulfate should be recovered, and the recovery meets the requirements of cost, energy consumption, etc.

[0020] The effluent from the front section is acidic and contains a small amount of sodium sulfate, very small amounts of phenol and salicylic acid, which does not affect the acid precipitation operation of sodium salicylate and can also dissolve sodium salicylate and reduce the amount of sulfuric acid used in the acid precipitation operation.

[0021] The effluent from the latter stage contains a high amount of sodium sulfate, which has recovery value. This crude sodium sulfate can be obtained through an evaporation crystallization device. After further purification, the crude sodium sulfate can be used to produce anhydrous sodium sulfate or thenardite by freeze crystallization, thereby recovering sodium sulfate from the wastewater. The residual liquid obtained from the evaporation crystallization device is acidic and contains very small amounts of sodium sulfate, phenol, and salicylic acid. This residual liquid can also be reused in the acid precipitation operation, fully utilizing the adsorbed water.

[0022] Optionally, an intermediate water pool is provided between the resin column and the evaporation crystallization device for temporarily storing the water effluent from the latter stage and playing the role of filtering and homogenizing; the water outlet of the intermediate water pool is connected to the evaporation crystallization device via a lifting pump.

[0023] Optionally, before step S5, the water effluent from the rear section is input into an intermediate water pool, accumulated, homogenized, and filtered, and then input into an evaporation crystallization device by a lift pump. The evaporation crystallization device is a conventional evaporation crystallization tower in the art.

[0024] Optionally, in step S5, the high-temperature evaporation temperature is 100-105°C, and after the water amount is reduced, it is cooled to 30-40°C for crystallization.

[0025] Optionally, in step S6, the alkaline solution is a sodium hydroxide solution with a mass fraction of 5-10%, that is, the eluent; the elution temperature is 50-70° C., and the flow rate is 0.5-1.5 BV / h.

[0026] Optionally, in step S6, the front-segment eluate and the back-segment eluate flow out of the resin column in chronological order, and the front-segment eluate and the back-segment eluate are determined based on the mass concentration of sodium salicylate and / or sodium phenolate in the eluate;

[0027] Specifically, the mass concentration of sodium salicylate in the front-stage eluent is not less than 65%, and the mass concentration of sodium salicylate in the back-stage eluent is less than 65%; or,

[0028] The mass concentration of sodium phenolate in the front-stage eluent is not less than 72%, and the mass concentration of sodium phenolate in the back-stage eluent is less than 72%.

[0029] As the elution time increases, the resin is gradually eluted and regenerated into the sodium type, and the sodium phenolate and sodium salicylate in the eluent gradually decrease. The front eluent containing high concentrations of sodium salicylate and sodium phenolate is returned to step S1 of the next batch as the solution of the reaction system; the rear eluent containing low concentrations of sodium salicylate and sodium phenolate is used to prepare the next batch of eluent and can be recycled.

[0030] The traditional resin adsorption column is a hollow tube type, with resin particles directly filled inside. It relies on the resin's own gravity to be naturally compacted, and then the liquid to be treated flows from top to bottom through the resin column. In the adsorption process, uneven water flow often occurs, and the resin bed will also have dead zones and channel flow, resulting in a decrease in resin utilization and a decrease in adsorption effect. The current conventional operation is to wait until the adsorption is completed, then pass water from bottom to top, use hydraulic impact to lift the resin layer, loosen the resin layer and then loosen it, flush out the dead zones, release the air inside, and then perform subsequent elution and regeneration. This method not only wastes time and flushing water, but also cannot solve the problem of the resin bed during the adsorption process. It can only be remedied after the adsorption is completed, which directly leads to a decrease in resin utilization and adsorption rate, and a reduction in processable materials. The present invention provides a solution. By arranging a movable intercepting net inside the resin column, it can be moved to the position of the resin layer that needs to be dredged, and fixed-point dredging can be performed. After dredging, the adsorption operation can be continued, thereby improving the utilization rate of the resin and the adsorption efficiency. This method only loosens and improves the accumulation of the resin layer by mechanical means without using hydraulic power, and can clear the blockage in time during the adsorption process, after which the adsorption operation can continue.

[0031] Optionally, the resin column is a sleeve structure, comprising an inner tube and an outer tube, the inner tube is filled with resin, and the outer tube is empty;

[0032] Several interception nets are provided in the inner tube, and several moving magnets are provided on the edge of each interception net, and the moving magnets are evenly arranged along the circumference of the interception net; several positioning magnets are provided in the outer tube, and each positioning magnet attracts a corresponding moving magnet. Each positioning magnet is connected to the driving device outside the outer tube through a connecting rod, which is used to drive the moving magnet up and down through the connecting rod and the positioning magnet, thereby driving the interception net to move to clear the resin layer and improve the accumulation of the resin layer.

[0033] Further optionally, the inner tube and outer tube are concentrically arranged, and a water inlet and an air vent are provided at the top of the inner tube, which are respectively used to input wastewater or eluent into the inner tube and output the air in the resin layer, and a water outlet is provided at the bottom of the inner tube for discharging the adsorbed water or eluent.

[0034] Further optionally, the top of the outer tube is open for passing a connecting rod, the bottom of the outer tube is fixedly connected to the outer wall of the inner tube for fixing the position of the inner tube, and the outer wall of the outer tube can be connected to the bracket to fix the resin column;

[0035] The inner tube and the outer tube are both made of transparent materials, such as acrylic, so that the condition of the resin layer in the inner tube and the movement of the positioning magnet leading the moving magnet in the outer tube can be observed in real time.

[0036] Further optionally, the interception net includes a circular frame at the edge and a plurality of mutually parallel net ropes inside, and both ends of each net rope are connected to the circular frame;

[0037] The corresponding moving magnets and positioning magnets are separated by the wall of the inner tube and attract each other. The positioning magnet controls the moving magnet, thereby controlling the movement of the interception net.

[0038] When the resin layer of the inner tube has dead zones or channel flow, which is not conducive to the uniform flow of wastewater, the resin layer can be unblocked by the following methods:

[0039] (1) Determine the location that needs to be dredged by observation, and move several interception nets to the location that needs to be dredged by using a driving device and a connecting rod;

[0040] (2) In order from top to bottom or from bottom to top, the interception nets are rotated horizontally at a certain angle in sequence, so that the corresponding ropes of the interception nets adjacent to each other form a certain angle with each other. After the accumulation of the rotation angles of several interception nets stacked up and down, the overall stacked interception net composed of several interception nets becomes a crisscross and mutually inclined interception net, but the different interception nets are always parallel and do not cross;

[0041] (3) The integrally superimposed interception net moves up and down under the drive of the positioning magnet and the connecting rod, and can intercept and drive the resin above it to move up and down. At the same time, some resin particles leak through the mesh of the interception net to change the resin accumulation state at that location.

[0042] In step (1), since a single interception net only has parallel ropes inside, it cannot effectively intercept the resin, so it can move up and down in the resin layer with less resistance. Preferably, 3-4 interception nets are moved individually to the position that needs to be dredged.

[0043] Optionally, in step (2), the certain angle is 1-90°, and the intercepting nets are rotated horizontally at the certain angle in sequence. This can be done by moving and stacking several intercepting nets before rotating them, or by first rotating several intercepting nets to a preset angle and then moving and stacking the intercepting nets. The driving device is capable of rotating, thereby driving the connecting rod and the positioning magnet to rotate.

[0044] Optionally, in step (3), the changing of the resin accumulation state at that location includes but is not limited to loosening the resin layer, allowing the resin particles to naturally accumulate again, and releasing bubbles in the resin layer, and the released gas is discharged from the inner tube through the vent.

[0045] There are many forms of control methods for the positioning magnets. Optionally, the positioning magnets corresponding to the moving magnets of the same interception net are connected to the same driving device through a connecting rod, so that the same interception net moves synchronously.

[0046] Optionally, the positioning magnets corresponding to the moving magnets of the same interception net are connected to different driving devices through connecting rods and can be controlled individually, so that a single interception net can be tilted at a certain angle, such as 5-35°, which is conducive to loosening the resin layer.

[0047] Those skilled in the art can also think of other control methods not listed above, which also fall within the scope of protection of the present invention.

[0048] The method for producing salicylic acid by comprehensive utilization of wastewater according to the present invention has the following beneficial effects:

[0049] 1. Resin adsorption-desorption is used to recover salicylic acid and phenol from wastewater. Depending on the eluent situation, the front-end eluent is returned to the production process as raw material. The recovery rate of salicylic acid and phenol is close to 100%. At the same time, the back-end eluent is returned to the acid precipitation process to reduce process water consumption.

[0050] 2. After most of the sodium sulfate is recovered from the adsorption effluent, it is returned to production and then enters the resin adsorption system again after use. This is repeated, which is beneficial to the accumulation of salt in the wastewater and improves the resin adsorption efficiency;

[0051] 3. When the salt in the wastewater accumulates to a certain level, evaporation concentration and cooling crystallization are carried out to recover sodium sulfate, which not only fully recovers the by-product sodium sulfate, but also saves energy consumption of the evaporation crystallization system;

[0052] 4. All the effluent from the resin column system is reused in salicylic acid production, which not only reduces the water cost of the salicylic acid production process but also achieves zero wastewater discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the structure of the resin column in Example 7;

[0054] Figure 2 Schematic diagram of the top view of the resin column.

[0055] In the accompanying drawings, 1-inner tube, 2-outer tube, 3-interception net, 4-moving magnet, 5-positioning magnet, 6-connecting rod, 7-water inlet, 8-vent, 9-water outlet, 10-circular frame, 11-net rope. DETAILED DESCRIPTION

[0056] Example 1

[0057] This embodiment provides a method for producing salicylic acid by comprehensive utilization of wastewater, comprising the following steps:

[0058] S1: Phenol reacts with 50% by mass sodium hydroxide solution at 105°C to produce sodium phenolate;

[0059] S2: The sodium phenolate obtained in step S1 is vacuum dried, cooled to 100° C., and then introduced into dry carbon dioxide to carry out a carboxylation reaction. When the pressure in the autoclave reaches 0.7-0.8 MPa, the carbon dioxide is stopped to obtain sodium phenol carbonate, and then rearranged and isomerized at 130-140° C. to obtain sodium salicylate;

[0060] Then, 7-8 wt% sulfuric acid was added for acid precipitation, the pH value was 1-2, cooled and filtered, and vacuum dried to obtain crude salicylic acid;

[0061] S3: washing and centrifuging the crude salicylic acid obtained in step S2 to obtain a salicylic acid product and salicylic acid production wastewater; subliming the salicylic acid product under reduced pressure to obtain a refined salicylic acid product;

[0062] S4: The salicylic acid production wastewater is adsorbed by a resin column filled with ND-800 resin, the volume ratio of the resin to the treated wastewater is 1:8, the adsorption temperature is 30°C, and the wastewater flow rate is 2 BV / h;

[0063] The adsorption effluent includes the front-end effluent and the back-end effluent. The front-end effluent is used for the carboxylation reaction and acid precipitation operation in step S2 of the next batch of salicylic acid production.

[0064] The front-end effluent and the back-end effluent flow out from the resin column in chronological order. The mass concentration of sodium sulfate in the adsorbed effluent is used as the basis for determining the front-end effluent and the back-end effluent. The mass concentration of sodium sulfate in the front-end effluent is less than 12%, and the mass concentration of sodium sulfate in the back-end effluent is not less than 12%. That is, 12% is used as the dividing line to distinguish the front-end effluent and the back-end effluent.

[0065] S5: The water effluent from the latter stage is fed into an evaporation crystallization device, and the high-temperature evaporation temperature is 100-105°C. After the water volume is reduced, the water is cooled to 30-40°C and crystallized to obtain a crude sodium sulfate product and a kettle residue. The kettle residue is used for the carboxylation reaction and acid precipitation operation in step S2 of the next batch of salicylic acid production. The evaporation crystallization device is a conventional evaporation crystallization device;

[0066] S6: After the resin column of step S4 is saturated with adsorption, it is eluted and regenerated with a sodium hydroxide solution having a mass fraction of 5-10%. The elution temperature is 50° C. and the flow rate is 1.5 BV / h. The obtained eluate includes a front-end eluate and a back-end eluate. The front-end eluate is used to prepare sodium phenolate in step S1 for the production of the next batch of salicylic acid, and the back-end eluate is used to prepare an alkaline solution for the next resin elution and regeneration.

[0067] The front-end eluate and the back-end eluate flow out from the resin column in chronological order, and the front-end eluate and the back-end eluate are determined based on the mass concentration of sodium salicylate and / or sodium phenolate in the eluate;

[0068] Specifically, the mass concentration of sodium salicylate in the front eluate is not less than 65%, and the mass concentration of sodium salicylate in the back eluate is less than 65%, that is, 65% is used as the dividing line to distinguish the front eluate from the back eluate.

[0069] The wastewater recovery rate of this embodiment is 100%, and the salicylic acid production wastewater is fully utilized.

[0070] Comparative Example 1

[0071] This comparative example provides a salicylic acid production method that comprehensively utilizes wastewater. The difference from Example 1 is that the adsorption effluent in step S4 does not distinguish between the front-end effluent and the back-end effluent, but is all directly discharged to the sewage treatment plant; the eluate in step S6 does not distinguish between the front-end eluate and the back-end eluate, but is all directly discharged to the sewage treatment plant.

[0072] The wastewater recovery rate of this comparative example is 0%, and all wastewater from salicylic acid production needs to be treated, which increases the burden of wastewater treatment.

[0073] Comparative Example 2

[0074] This comparative example provides a salicylic acid production method using comprehensive wastewater utilization. Unlike Example 1, the adsorption effluent in step S4 is not differentiated between the front-end and back-end effluents. Instead, all effluent proceeds to step S5 and is then fed into an evaporation crystallization apparatus. Because the front-end effluent contains a low sodium sulfate content, this increases the energy consumption of the evaporation crystallization apparatus.

[0075] Comparative Example 3

[0076] This comparative example provides a salicylic acid production method using comprehensive wastewater utilization. This method differs from Example 1 in that the eluent in step S6 is not differentiated between the front-end eluent and the back-end eluent; instead, the entire eluent is used to prepare the alkaline solution for the next resin elution and regeneration. The high levels of sodium phenolate and sodium salicylate in the front-end eluent affect the subsequent resin elution.

[0077] Example 2

[0078] This embodiment provides a salicylic acid production method using comprehensive wastewater utilization. The difference from Example 1 is that an intermediate water tank is provided between the resin column and the evaporation crystallization device for temporarily storing the effluent from the latter stage and for filtering and homogenizing the effluent. The outlet of the intermediate water tank is connected to the evaporation crystallization device via a lift pump. Before step S5, the effluent from the latter stage is also input into the intermediate water tank, and after accumulation, homogenization, and filtration, the effluent is input into the evaporation crystallization device via the lift pump.

[0079] Example 3

[0080] This embodiment provides a method for producing salicylic acid by comprehensively utilizing wastewater. The difference from Example 1 is that the resin filled in the resin column is CHA-111 resin.

[0081] Example 4

[0082] This embodiment provides a salicylic acid production method using comprehensive wastewater utilization. The difference from Embodiment 1 is that, in step S4, the effluent from the front section and the effluent from the back section are determined based on the mass concentration of sodium sulfate in the effluent from the front section being less than 15% and the mass concentration of sodium sulfate in the effluent from the back section being not less than 15%.

[0083] Example 5

[0084] This embodiment provides a salicylic acid production method using comprehensive wastewater utilization. The difference from Embodiment 1 is that, in step S4, the effluent from the front section and the effluent from the back section are determined based on the mass concentration of sodium sulfate in the effluent from the front section being less than 11% and the mass concentration of sodium sulfate in the effluent from the back section being not less than 11%.

[0085] Example 6

[0086] This embodiment provides a salicylic acid production method using comprehensive wastewater utilization. The difference from embodiment 1 is that in step S6, the front-end eluate and the back-end eluate are determined based on 70% as the dividing line to distinguish the front-end eluate from the back-end eluate.

[0087] Example 7

[0088] This embodiment provides a method for producing salicylic acid by comprehensive utilization of wastewater. The difference from Example 1 is that: Figure 1-Figure 2 As shown, the resin column is a sleeve structure, comprising an inner tube 1 and an outer tube 2, wherein the inner tube 1 is filled with resin and the outer tube 2 is empty;

[0089] Three interception nets 3 are provided in the inner tube 1, and four movable magnets 4 are provided at the edge of each interception net 3, and the movable magnets 4 are evenly arranged along the circumference of the interception net 3; 12 positioning magnets 5 are provided in the outer tube 2, and each positioning magnet 5 attracts a corresponding movable magnet 4, and each positioning magnet 5 is connected to the driving device outside the outer tube 2 through a connecting rod 6, which is used to drive the movable magnet 4 to move up and down through the connecting rod 6 and the positioning magnet 5, thereby driving the interception net 3 to move and clear the resin layer, thereby improving the accumulation of the resin layer.

[0090] The inner tube 1 and the outer tube 2 are concentrically arranged. The top of the inner tube 1 is provided with a water inlet 7 and an air vent 8, which are respectively used to input wastewater or eluent into the inner tube 1 and output the air in the resin layer. The bottom of the inner tube 1 is provided with a water outlet 9 for discharging the adsorbed water or eluent.

[0091] The top of the outer tube 2 is open for passing the connecting rod 6. The bottom of the outer tube 2 is fixedly connected to the outer wall of the inner tube 1 to fix the position of the inner tube 1. The outer wall of the outer tube 2 is connected to the bracket to fix the resin column.

[0092] The inner tube 1 and the outer tube 2 are both made of transparent acrylic material, so that the condition of the resin layer in the inner tube 1 and the movement of the positioning magnet 5 leading the moving magnet 4 in the outer tube 2 can be observed in real time.

[0093] The interception net 3 includes a circular frame 10 at the edge and four parallel net ropes 11 inside, and both ends of each net rope 11 are connected to the circular frame 10;

[0094] The corresponding moving magnets 4 and positioning magnets 5 are separated by the wall of the inner tube 1 and attract each other. The positioning magnets 5 control the moving magnets 4 and further control the movement of the interception net 3.

[0095] The interception net 3 is a flexible and lightweight rope net structure as a whole, has a light weight, and can move under the guidance of a corresponding number of moving magnets 4.

[0096] During the resin column adsorption process, if dead zones or channeling occur in the resin layer of the inner tube 1, which are not conducive to the uniform flow of wastewater, the resin layer can be cleared by the following methods:

[0097] (1) Determine the location that needs to be dredged by observation, and move the three interception nets 3 to the location that needs to be dredged separately and in sequence through the driving device and the connecting rod 6;

[0098] (2) From top to bottom, the interception nets 3 are rotated horizontally by 60° in sequence, so that the corresponding net ropes 11 of the upper and lower adjacent interception nets 3 are 60° to each other. After the accumulation of the rotation angles of the three interception nets 3 stacked up and down, the overall stacked interception net 3 composed of the three interception nets 3 becomes a form with a crisscross and mutually inclined cross-section, but the different interception nets 3 are always parallel and do not cross; the driving device can rotate, thereby driving the connecting rod 6 and the positioning magnet 5 to rotate;

[0099] (3) The integrally superimposed interception net 3 moves up and down driven by the positioning magnet 5 and the connecting rod 6, and can intercept and drive the resin above it to move up and down. At the same time, some resin particles leak out from the mesh of the interception net 3 to change the resin accumulation state at that location.

[0100] The changing of the resin accumulation state at that location includes but is not limited to loosening the resin layer, allowing the resin particles to naturally accumulate again, and releasing the bubbles in the resin layer, and the released gas is discharged from the inner tube 1 through the vent 8 .

[0101] The positioning magnets 5 corresponding to the moving magnets 4 of the same interception net 3 are connected to the same driving device through a connecting rod 6, so that the same interception net 3 moves synchronously.

[0102] Table 1 Comparison of adsorption effects of Examples 1, 3 and 8

[0103]

[0104] Table 2 Comparison of energy consumption of evaporation crystallization of Examples 1, 2, 4 and 5

[0105]

[0106]

[0107] Energy consumption of evaporation crystallization (kJ / kg sodium sulfate): the energy consumed to obtain 1 kg of sodium sulfate.

[0108] Table 3 Comparison of the effect of the latter eluents of Examples 1, 6 and 7 for the next resin elution

[0109] Elution time (min / L resin) Example 1 20 Example 6 25

[0110] Since the latter eluent is used for the next resin elution, the pollutants in the latter eluent have a certain impact on the pollutants adsorbed on the elution resin during the next elution.

[0111] As can be seen from the above table, the salicylic acid production method for comprehensive utilization of wastewater provided by the present invention can achieve zero discharge of salicylic acid production wastewater. According to the properties and component contents of the adsorption effluent and the eluate, reasonable recycling and reuse are carried out, thereby maximizing the wastewater treatment capacity and reducing the energy consumption for treating wastewater.

Claims

1. A method for producing salicylic acid by comprehensive utilization of wastewater, characterized in that: The following steps are involved: S1: Phenol reacts with liquid alkali to produce sodium phenolate; S2: introducing carbon dioxide into the sodium phenolate obtained in step S1 to perform a carboxylation reaction to obtain sodium phenol carbonate, which is then subjected to rearrangement isomerization to obtain sodium salicylate; and then acid precipitation is performed to obtain crude salicylic acid; S3: washing and centrifuging the crude salicylic acid obtained in step S2 to obtain a salicylic acid product and salicylic acid production wastewater; S4: The salicylic acid production wastewater is adsorbed by a resin column, and the adsorption effluent includes the front-end effluent and the back-end effluent. The front-end effluent is used for the carboxylation reaction and acid precipitation operation of step S2 in the next batch of salicylic acid preparation; S5: The water effluent from the latter stage is fed into an evaporation crystallization device, and after high-temperature evaporation and cooling crystallization, a crude sodium sulfate product and a kettle residue are obtained. The kettle residue is used for the carboxylation reaction and acid precipitation operation of the next batch of salicylic acid preparation step S2; S6: After the resin column in step S4 is saturated with adsorption, it is eluted and regenerated with alkaline solution. The obtained eluate includes a front-end eluate and a back-end eluate. The front-end eluate is used in step S1 for the next batch of salicylic acid preparation, and the back-end eluate is used to prepare alkaline solution for the next resin elution and regeneration; Before step S5, the water from the rear section is input into the intermediate water pool, and after accumulation, homogenization and filtration, it is input into the evaporation crystallization device by the lifting pump; An intermediate water pool is provided between the resin column and the evaporation crystallization device for temporarily storing the water effluent from the latter stage and playing the role of filtering and homogenizing; the outlet of the intermediate water pool is connected to the evaporation crystallization device through a lifting pump; After most of the sodium sulfate is recovered from the adsorption effluent, it is returned to production and then enters the resin adsorption system again after use. This is repeated, which is beneficial to the accumulation of salt in the wastewater and improves the resin adsorption efficiency; When the salt content in the wastewater accumulates to a mass concentration of 12%, evaporation concentration-cooling crystallization is carried out to recover sodium sulfate. This not only fully recovers the by-product sodium sulfate, but also saves energy consumption in the evaporation crystallization system.

2. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: In step S4, the resin filled in the resin column is selected from one of ND-800 resin, CHA-111 resin, and LS-100 resin.

3. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: In step S4, the adsorption process parameters are an adsorption temperature of 15-30° C. and a wastewater flow rate of 0.5-2 BV / h.

4. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: In step S4, the front-end effluent and the rear-end effluent flow out of the resin column in chronological order, and the front-end effluent and the rear-end effluent are determined based on the mass concentration of sodium sulfate in the adsorbed effluent. The mass concentration of sodium sulfate in the front-end effluent is less than 12%, and the mass concentration of sodium sulfate in the rear-end effluent is not less than 12%.

5. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: In step S6, the alkaline solution is a sodium hydroxide solution with a mass fraction of 5-10%, which is used as the eluent; the elution temperature is 50-70°C, and the flow rate is 0.5-1.5BV / h.

6. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: The front-end eluate and the back-end eluate flow out from the resin column in chronological order, and the front-end eluate and the back-end eluate are determined based on the mass concentration of sodium salicylate and / or sodium phenolate in the eluate; The mass concentration of sodium salicylate in the front-end eluent is not less than 65%, and the mass concentration of sodium salicylate in the back-end eluent is less than 65%; or, The mass concentration of sodium phenolate in the front-end eluent is not less than 72%, and the mass concentration of sodium phenolate in the back-end eluent is less than 72%.

7. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 1, characterized in that: The resin column is a sleeve structure, comprising an inner tube and an outer tube, the inner tube is filled with resin, and the outer tube is empty; Several interception nets are provided in the inner tube, and several moving magnets are provided on the edge of each interception net, and the moving magnets are evenly arranged along the circumference of the interception net; several positioning magnets are provided in the outer tube, and each positioning magnet attracts a corresponding moving magnet. Each positioning magnet is connected to the driving device outside the outer tube through a connecting rod, which is used to drive the moving magnet up and down through the connecting rod and the positioning magnet, thereby driving the interception net to move to clear the resin layer and improve the accumulation of the resin layer.

8. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 7, characterized in that: The inner tube and the outer tube are concentrically arranged, the top of the inner tube is provided with a water inlet and an air vent, and the bottom of the inner tube is provided with a water outlet; The top of the outer tube is open, and the bottom of the outer tube is fixedly connected to the outer wall of the inner tube. Both the inner tube and the outer tube are made of transparent materials; The intercepting net comprises a circular frame at the edge and a plurality of mutually parallel net ropes inside, and both ends of each net rope are connected to the circular frame.

9. The method for producing salicylic acid by comprehensive utilization of wastewater according to claim 8, characterized in that: Clear the resin layer by: (1) Determine the location that needs to be dredged by observation, and move several interception nets to the location that needs to be dredged by using the driving device and connecting rod; (2) In order from top to bottom or from bottom to top, the interception nets are rotated horizontally at a certain angle in sequence, so that the corresponding ropes of the interception nets adjacent to each other form a certain angle with each other. After the accumulation of the rotation angles of several interception nets stacked up and down, the overall stacked interception net composed of several interception nets becomes a crisscross and mutually inclined interception net, but the different interception nets are always parallel and do not cross; (3) The integrally stacked intercepting net moves up and down under the drive of the positioning magnet and the connecting rod, and can intercept and drive the resin above it to move up and down. At the same time, some resin particles leak through the mesh of the intercepting net to change the resin accumulation state at that location.

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