A method for recovering active ingredients in p-chlorobenzaldehyde wastewater

Abstract

The invention provides a method for recovering an effective ingredient in p-chlorobenzaldehyde wastewater, including the preparation, refinement and wastewater recovery process of p-chlorobenzaldehyde, wherein the preparation of p-chlorobenzaldehyde includes chlorination reaction, hydrolysis reaction and neutralization reaction, the oily substance after the neutralization reaction enters the p-chlorobenzaldehyde refining process, the wastewater after the neutralization reaction enters the recovery process, the wastewater after the p-chlorobenzaldehyde neutralization reaction is passed into an oxidation reactor in the recovery process, an active oxidant is provided in the oxidation reactor, the oxidant is instantly generated as the wastewater is passed, and the p-chlorobenzaldehyde in the wastewater is oxidized to p-chlorobenzoic acid. The wastewater of p-chlorobenzaldehyde is used for the production and preparation of p-chlorobenzoic acid, the p-chlorobenzoic acid in the wastewater is recovered, and the effective ingredient p-chlorobenzaldehyde therein is converted into p-chlorobenzoic acid simultaneously, reducing wastewater treatment pressure, reducing pollution to the environment, and avoiding waste of materials.

Description

Technical Field

[0001] The present invention relates to a post-processing process in the preparation of p-chlorobenzaldehyde, and in particular to a method for recovering effective components in p-chlorobenzaldehyde wastewater. Background Art

[0002] p-Chlorobenzaldehyde is an important pharmaceutical intermediate. It is synthesized through condensation and cyclization with mercaptopropionic acid to produce fenalol. Fenalol is a mild tranquilizer with sedative, tranquilizing, and central nervous system muscle relaxant effects. It is also used to treat symptoms such as mental stress, fear, chronic fatigue, anxiety, agitation, and irritability and insomnia caused by certain diseases. It can also be used in combination with analgesics to treat limb pain and rheumatoid arthritis. p-Chlorobenzaldehyde can also be used to synthesize drugs such as aminophenylbutyric acid. Therefore, as an important pharmaceutical intermediate, the synthesis process of p-chlorobenzaldehyde is crucial. Currently, most companies in my country primarily use the chlorination-hydrolysis method to produce p-chlorobenzaldehyde. For example, patent publication number CN109651111B discloses a method for preparing p-chlorobenzaldehyde. Although the selectivity of the substitution reaction is improved by the action of a catalyst, and the yield of p-chlorobenzaldehyde is increased by combining a hydrolysis reaction with an air-catalyzed oxidation reaction, the wastewater volume is large and difficult to treat. In addition, the wastewater contains a large amount of sodium p-chlorobenzoate. If directly treated without recovery, it is likely to pollute the environment and cause material waste.

[0003]

[0004] Generally, after neutralization and washing, the wastewater containing sodium p-chlorobenzoate is separated from the main product p-chlorobenzaldehyde. The wastewater containing sodium p-chlorobenzoate is extracted to extract a small amount of p-chlorobenzaldehyde from the wastewater. The extracted p-chlorobenzaldehyde enters the production washing process; the wastewater containing sodium p-chlorobenzoate separated from p-chlorobenzaldehyde enters the production acidification process. After acidification, sodium p-chlorobenzoate is reduced to p-chlorobenzoic acid, and the p-chlorobenzoic acid product is formed through filtration and drying processes. The mother liquor is centrifuged to remove the wastewater treatment process. This procedure extracts p-chlorobenzaldehyde from the wastewater by extraction, which requires the use of organic solvents, increases the pressure of subsequent water treatment, and is not conducive to environmental protection. In addition, the complex extraction operation can only extract a small amount of p-chlorobenzaldehyde, increasing the process cost, which is not conducive to large-scale production.

[0005] Parachlorobenzoic acid is a white powdery solid, soluble in methanol, absolute ethanol and ether, very slightly soluble in water, toluene and 95% ethanol. Parachlorobenzoic acid, as a kind of important pharmaceutical intermediate, is used for the preparation of non-steroidal anti-inflammatory analgesics, and this class medicine is generally used for alleviating pain, anti-inflammation and cooling the body. The production of parachlorobenzoic acid is generally based on parachlorotoluene as raw material, and adopts methods such as chemical reagent oxidation method, gas phase oxidation method, photochlorination hydrolysis method to produce. But these methods are more costly, and tail gas and waste water do not meet environmental protection requirements. Therefore, based on the consideration of environmental protection and cost, many enterprises combine parachlorobenzaldehyde and parachlorobenzoic acid to produce, and take the waste water of parachlorobenzaldehyde as raw material recovery and extraction parachlorobenzoic acid. For example, the patent of publication number CN109020801B discloses a kind of recovery method of byproduct parachlorobenzoic acid in the parachlorobenzaldehyde production process in the prior art. However, the prior art uses potassium permanganate or hydrogen peroxide as an oxidant to oxidize p-chlorobenzaldehyde in the wastewater into p-chlorobenzoic acid. When potassium permanganate is used to oxidize benzaldehyde, a large number of by-products, such as solid precipitates such as manganese dioxide, are produced in the reaction. The separation and treatment of these by-products may increase production costs and difficulty. When hydrogen peroxide is used as an oxidant, although it has the advantage of being green and environmentally friendly, hydrogen peroxide has relatively weak oxidizing ability and is easily decomposed, resulting in a large amount of p-chlorobenzaldehyde still existing in the oxidized product. Purification operations such as dissolution in toluene, stratification, and low-temperature precipitation treatment are required. As a result, a large amount of toluene is contained in the wastewater, which increases the pressure on wastewater treatment and is not conducive to environmental protection. Summary of the Invention

[0006] In view of this, the present invention aims to propose a method for recovering the active ingredients in p-chlorobenzaldehyde wastewater to solve the problems in the prior art that p-chlorobenzaldehyde wastewater is not environmentally friendly, the active ingredients are difficult to recover, and the material cost is wasted.

[0007] A method for recovering active ingredients from p-chlorobenzaldehyde wastewater includes p-chlorobenzaldehyde preparation, refining and wastewater recovery processes, wherein the p-chlorobenzaldehyde preparation includes chlorination reaction, hydrolysis reaction and neutralization reaction, the oily substance after the neutralization reaction enters the p-chlorobenzaldehyde refining process, and the wastewater after the neutralization reaction enters the recovery process, and the recovery process at least includes:

[0008] (1) oxidation reaction, the wastewater after the neutralization reaction of p-chlorobenzaldehyde is passed into an oxidation reactor, and an active oxidant is provided in the oxidation reactor. The oxidant is generated immediately as the wastewater is passed into the reactor, and the p-chlorobenzaldehyde in the wastewater is oxidized to p-chlorobenzoic acid;

[0009] (2) Acidification treatment: After the oxidation reaction, the wastewater contains p-chlorobenzoic acid and some unoxidized p-chlorobenzaldehyde. The wastewater enters the acidification kettle. Under acidic conditions, the wastewater containing p-chlorobenzoic acid and a small amount of p-chlorobenzaldehyde in the acidification kettle is further oxidized by the active oxygen oxidant to p-chlorobenzoic acid. At the same time, sodium p-chlorobenzoate in the wastewater is converted into p-chlorobenzoic acid precipitate under acidic conditions. The p-chlorobenzoic acid precipitate and the wastewater together form a reaction slurry and enter the next step;

[0010] (3) Filtration treatment: the reaction slurry in the acidification kettle enters the solid-liquid filter through a pipeline for filtration, and the filtered solid material p-chlorobenzoic acid enters the dryer through a p-chlorobenzoic acid conveyor for drying.

[0011] Furthermore, during the acidification treatment, hydrochloric acid is added to control the pH value in the acidification kettle to be between 1 and 2.

[0012] Furthermore, the dried p-chlorobenzoic acid enters a dust collector for dust removal and is then packaged to obtain a finished p-chlorobenzoic acid product, and the tail gas in the dust collector is recovered by an induced draft fan.

[0013] Furthermore, the dried tail gas of p-chlorobenzoic acid enters a circulation tower and is absorbed by alkali solution. The heat in the alkali solution is removed by a cooler. The p-chlorobenzoic acid in the tail gas reacts with the alkali solution to generate a water-soluble substance, sodium p-chlorobenzoate. The mixture of sodium p-chlorobenzoate and alkali solution is pumped into the acidification kettle of step (2).

[0014] Furthermore, an alkali solution with a mass fraction of 5-10% is circulated in the circulation tower by a pump, and the p-chlorobenzoic acid dust in the tail gas contacts and reacts with the alkali solution in the circulation tower to generate sodium p-chlorobenzoate. The concentration of the alkali solution in the circulation tower is continuously monitored. When the concentration of the alkali solution is lower than about 0.5%, the alkali solution in the circulation tower is replaced.

[0015] Furthermore, the active oxidant is prepared by reacting tetraacetylethylenediamine and sodium percarbonate.

[0016] Furthermore, the mass ratio of tetraacetylethylenediamine to sodium percarbonate is 1:1.2-1.4.

[0017] Furthermore, the drying equipment used for drying p-chlorobenzoic acid is a vacuum steam dryer.

[0018] Furthermore, an external spray structure is provided inside the oxidation reactor, the external spray structure is connected to the wastewater pipeline, a spray arm is provided on the external spray structure, and a plurality of spray arms are provided. A plurality of atomizing nozzles are provided on the spray arm, and the wastewater after the neutralization reaction of para-chlorobenzaldehyde is passed into the oxidation reactor, and the wastewater is formed into small droplets through the atomizing nozzle and sprayed into the interior of the outer reactor.

[0019] Furthermore, the temperature of the oxidation reactor is controlled at 50-60°C.

[0020] The beneficial effects of the present invention are as follows:

[0021] Under the process conditions of the present invention, with proper control, the p-chlorobenzoic acid dust recovery rate is close to 100%.

[0022] The wastewater of p-chlorobenzaldehyde is used for the production of p-chlorobenzoic acid, the p-chlorobenzoic acid in the wastewater is recovered, and the effective ingredient p-chlorobenzaldehyde is converted into p-chlorobenzoic acid, which reduces the wastewater treatment pressure, reduces the pollution to the environment, and avoids material waste.

[0023] In addition, by recycling the tail gas during the drying of 4-chlorobenzoic acid, the 4-chlorobenzoic acid dust in the tail gas is almost completely recovered and processed without causing environmental pollution; the efficient recovery and utilization of the effective ingredients in the 4-chlorobenzaldehyde wastewater is further improved, avoiding material waste.

[0024] Moreover, the active oxygen oxidant used in the present invention can have a good oxidation effect on other organic wastewater or organic tail gas containing aldehydes, and effectively remove the aldehydes in the tail gas or wastewater. For example, it can also be used to treat aldehydes in wastewater or exhaust gas of pharmaceutical intermediates such as o-chlorobenzonitrile and p-chlorobenzonitrile, and its principle is similar to that of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the p-chlorobenzaldehyde wastewater treatment process according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the process for preparing p-chlorobenzaldehyde according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the recovery of the tail gas from the drying of p-chlorobenzoic acid according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic structural diagram of an oxidation reactor according to an embodiment of the present invention;

[0029] Figure 5 Schematic diagram of the change in active oxygen concentration after the reaction of tetraacetylethylenediamine and sodium percarbonate under different conditions.

[0030] Description of reference numerals:

[0031] 100-Oxidation reactor, 1-Built-in reactor, 11-Liquid hole, 12-Internal spray structure, 13-Support plate, 14-Liquid inlet pipeline, 2-Outer reactor, 21-Wastewater pipeline, 22-External spray structure, 23-Atomizing nozzle, 24-Stirring impeller, 200-Chlorination reactor, 300-Hydrolysis reactor, 400-Neutralization reactor, 500-Alkali liquid circulation tower, 600-Acidification reactor, 700-Solid-liquid filter, 800-Dryer, 900-Dust collector DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0033] like Figures 1 to 3 As shown, a method for recovering the active ingredients in p-chlorobenzaldehyde wastewater includes the preparation, refining and wastewater recovery processes of p-chlorobenzaldehyde. The preparation of p-chlorobenzaldehyde includes chlorination reaction, hydrolysis reaction and neutralization reaction. The oily substance after the neutralization reaction enters the p-chlorobenzaldehyde refining process, and the wastewater after the neutralization reaction enters the recovery process. The recovery process includes oxidation reaction, acidification treatment, filtration treatment, drying and tail gas recovery and utilization. Specifically, the recovery process includes:

[0034] (1) Oxidation reaction: The wastewater after the neutralization reaction of p-chlorobenzaldehyde is passed into an oxidation reactor. An active oxidant is set in the oxidation reactor. The oxidant is generated immediately as the wastewater is passed into the reactor, and the p-chlorobenzaldehyde in the wastewater is oxidized into p-chlorobenzoic acid.

[0035] like Figure 4 As shown, the oxidation reactor 100 can be configured as a double-layer reactor structure, including an inner reactor 1 and an outer reactor 2, wherein the inner reactor 1 is located inside the outer reactor 2, and the two are coaxially arranged.

[0036] The built-in reactor 1 contains sodium percarbonate. A liquid-passing hole 11 is provided on the wall of the built-in reactor. An aqueous solution of tetraacetylethylenediamine is introduced into the built-in reactor through a liquid inlet pipe 14 and is evenly sprayed onto a support plate 13 inside the built-in reactor through an internal spray structure 12. The support plate 13 is configured as a porous structure. The sodium percarbonate is placed in the support plate 13. The bottom surface of the support plate 13 is configured as a hollow structure. The aqueous solution of tetraacetylethylenediamine reacts with the sodium percarbonate inside the built-in reactor to instantly generate active oxygen. Pressure is applied to the interior of the built-in reactor so that the active oxygen solution is discharged from the built-in reactor through the liquid-passing hole 11 of the built-in reactor into the outer reactor 2. The interior of the outer reactor 2 is connected to a wastewater pipe 21 near the top. The wastewater entering the outer reactor 2 through the wastewater pipe 21 is fully mixed with the active oxygen oxidant and undergoes a preliminary oxidation reaction, thereby oxidizing p-chlorobenzaldehyde to p-chlorobenzoic acid. The p-chlorobenzaldehyde and active oxygen ions that have not undergone the oxidation reaction are present in the wastewater and enter the acidification kettle together with the wastewater. The double-layer reactor structure separates tetraacetylethylenediamine and sodium percarbonate, allowing them to contact each other when needed to instantly generate peracetic acid. Peracetic acid ionizes into active oxygen ions. Compared with hydrogen peroxide, the active oxygen oxidant has stronger oxidizing properties and is beneficial to the oxidation of 4-chlorobenzaldehyde. The instantly generated oxidant can also prevent the oxidant from becoming ineffective due to long-term exposure.

[0037] The mass ratio of tetraacetylethylenediamine to sodium percarbonate is 1:1.2-1.4.

[0038] (2) Acidification reaction: The wastewater after the oxidation reaction contains p-chlorobenzoic acid and some unoxidized p-chlorobenzaldehyde. The wastewater enters the acidification kettle, and hydrochloric acid is added to control the pH value in the acidification kettle to be between 1 and 2. The wastewater in the acidification kettle contains p-chlorobenzoic acid and a small amount of p-chlorobenzaldehyde. Under acidic conditions, the active oxygen oxidant further oxidizes the remaining p-chlorobenzaldehyde into p-chlorobenzoic acid. At the same time, the sodium p-chlorobenzoate in the wastewater is converted into p-chlorobenzoic acid precipitate under acidic conditions. The p-chlorobenzoic acid precipitate and the wastewater together form a reaction slurry and enter the next step.

[0039] (3) Filtration treatment: The reaction slurry in the acidification kettle enters the solid-liquid filter through a pipeline for filtration, and the filtered solid material p-chlorobenzoic acid enters the dryer through a p-chlorobenzoic acid conveyor for drying.

[0040] (4) Drying: The dried p-chlorobenzoic acid enters a dust collector for dust removal and is then packaged to obtain the finished p-chlorobenzoic acid product.

[0041] (5) Tail gas recovery and utilization: The tail gas of parachlorobenzoic acid after the dust collector is recovered through the induced draft fan.

[0042] The dried tail gas of p-chlorobenzoic acid enters a circulation tower and is absorbed by alkali liquor. The heat in the alkali liquor is removed by a cooler. The p-chlorobenzoic acid in the tail gas reacts with the alkali liquor to generate a water-soluble substance, sodium p-chlorobenzoate. The mixture of sodium p-chlorobenzoate and the alkali liquor is pumped into the acidifying kettle of step (2). Hydrochloric acid is added to the acidifying kettle. The sodium p-chlorobenzoate reacts with the hydrochloric acid to be reduced to p-chlorobenzoic acid. After filtering through a solid-liquid filter, the recovered p-chlorobenzoic acid is dried and recycled (the steps after entering the acidifying kettle are the same as those described above). By recycling the tail gas, the tiny p-chlorobenzoic acid particles in the tail gas during the p-chlorobenzoic acid drying process are recycled, thereby reducing environmental pollution during the p-chlorobenzoic acid drying process.

[0043] The steps of entering the circulation tower for absorption with alkali solution include collecting the p-chlorobenzoic acid dust in the tail gas and entering the circulation tower, circulating the alkali solution with a mass fraction of 5-10% in the circulation tower by a pump, and the p-chlorobenzoic acid dust in the tail gas and the alkali solution contacting and reacting with each other in the circulation tower to generate sodium p-chlorobenzoate, continuously monitoring the concentration of the alkali solution in the circulation tower, and replacing the alkali solution in the circulation tower when the concentration of the alkali solution is lower than about 0.5%, and pumping the mixture of sodium p-chlorobenzoate and the alkali solution into the acidification kettle in step (2).

[0044] The mixture of sodium p-chlorobenzoate and alkali liquor is pumped into the acidification kettle of step (2), and hydrochloric acid is added to the acidification kettle. The process steps include starting the acidification kettle stirring device, pumping the mixture of sodium p-chlorobenzoate and alkali liquor into the acidification kettle, adding hydrochloric acid dropwise, controlling the pH value of the acidification kettle to 1-2, and stopping the addition of acid until the pH value does not change after 10 minutes, indicating that the reaction is terminated, and sodium p-chlorobenzoate reacts with hydrochloric acid to form a p-chlorobenzoic acid precipitate. The p-chlorobenzoic acid precipitate and wastewater together form a reaction slurry and enter a solid-liquid filter through a pipeline for filtration. The filtered solid material p-chlorobenzoic acid enters a dryer through a p-chlorobenzoic acid conveyor for drying, thereby realizing the recycling and utilization of the tail gas.

[0045] In the oxidation reaction step, hydrochloric acid is added to the aqueous solution of tetraacetylethylenediamine, and the pH value of the tetraacetylethylenediamine aqueous solution is controlled to be about 4. Under this condition, the generation rate of active oxygen is faster. When wastewater is oxidized, the active oxygen generated immediately is used as an oxidant, and the oxidizing ability is strong. The aldehyde in the p-chlorobenzaldehyde wastewater can be effectively oxidized to acid, and the obtained p-chlorobenzoic acid has a higher purity. It is not necessary to use toxic substance toluene recrystallization purification, reduce harm to workers, and the wastewater does not contain toluene, reduce wastewater treatment pressure, and is beneficial to environmental protection.

[0046] An external spray structure 22 is provided inside the outer reactor 2 and is connected to the wastewater pipeline 21. A spray arm is provided on the external spray structure 22 and is arranged outside the inner reactor 1 and parallel to the wall of the inner reactor 1. Multiple spray arms can be provided and evenly distributed around the outer side of the inner reactor 1. Multiple atomizing nozzles 23 are provided on the spray arms, through which the wastewater is formed into small droplets and sprayed into the inner side of the outer reactor 2.

[0047] A stirring impeller 24 is provided at the bottom of the outer reactor 2. The stirring impeller 24 drives the active oxygen oxidant inside the outer reactor 2 to fully contact with the p-chlorobenzoic acid, thereby increasing the contact frequency between the two and further improving the oxidation reaction efficiency.

[0048] Furthermore, sodium dodecyl sulfate is added before the aqueous solution of tetraacetylethylenediamine enters the built-in reactor. Adding sodium dodecyl sulfate and tetraacetylethylenediamine together can promote the mutual mixing and dissolution of tetraacetylethylenediamine and sodium percarbonate, thereby improving the reaction efficiency and allowing the immediate generation of active oxygen ions. The mass ratio of sodium dodecyl sulfate to sodium percarbonate is 0.3% to 0.8%:1

[0049] Furthermore, to ensure the normal progress of the oxidation reaction, the temperature of the oxidation reactor needs to be controlled at 50-60°C. This temperature easily causes the decomposition of active oxygen ions, and the addition of sodium dodecyl sulfate can inhibit the decomposition of active oxygen ions. This may be because the long chain structure of sodium dodecyl sulfate occupies the space around the small molecular active oxygen ions, thereby hindering the contact and reaction of other molecules or ions with the active oxygen ions to a certain extent, thereby reducing the decomposition rate of the active oxygen ions. At the same time, since heating promotes molecular motion, it increases the probability of p-chlorobenzaldehyde coming into contact with the active oxygen ions, and the oxidation reaction gradually begins.

[0050] In order to determine the oxidation reaction time after adding sodium dodecyl sulfate, the present application explored the changes in oxidant concentration at different times when sodium dodecyl sulfate was added and when no sodium dodecyl sulfate was added, as shown in the following example: Figure 5As shown, at 50°C, comparisons were made of no sodium dodecyl sulfate added to 1 L of solution (black curve); 3 g of tetraacetylethylenediamine, 4 g of sodium percarbonate, and 0.03 g of sodium dodecyl sulfate added to 1 L of solution (blue curve); and 0.03 g of sodium dodecyl sulfate and 3 g of tetraacetylethylenediamine dissolved in 1 L of water and then slowly added to 4 g of sodium percarbonate in the form of a solution (red curve). The experimental results show that when tetraacetylethylenediamine is directly mixed with sodium percarbonate, the two can react rapidly to generate a large amount of active oxygen in a short period of time, and the active oxygen concentration quickly reaches a peak value. However, due to the early contact time and the instability of the active oxygen, the active oxygen concentration drops sharply about 20 minutes after the two are mixed, affecting its oxidation performance. When tetraacetylethylenediamine is directly mixed with sodium percarbonate and sodium dodecylsulfonate, the reaction time of the two is slightly delayed due to the effect of sodium dodecylsulfonate, and the active oxygen concentration reaches a peak value at about 25 minutes. Although the active oxygen can stably exist for a longer time than that without sodium dodecylsulfonate, the active oxygen will still decompose rapidly in a short period of time and cannot play an effective oxidation role. When the sodium dodecylsulfonate and tetraacetylethylenediamine solution is slowly added within 30 minutes, active oxygen can be rapidly generated, and the active oxygen concentration can reach a peak at about 40 minutes, and can maintain a high concentration in a stable state for a time of about 30 minutes, which can effectively improve the oxidation reaction rate. Therefore, the time is counted from the time when tetraacetylethylenediamine, sodium percarbonate and sodium laurylsulfonate begin to be mixed, and wastewater is added about 40 minutes after the mixture of tetraacetylethylenediamine, sodium percarbonate and sodium laurylsulfonate, so that the wastewater to be oxidized can quickly contact with the high concentration of active oxygen during the addition process to undergo a sufficient oxidation reaction, thereby improving the oxidation efficiency.

[0051] As part of an embodiment of the present invention, the drying equipment used for drying p-chlorobenzoic acid is a vacuum steam dryer.

[0052] Example 1

[0053] (1) Oxidation reaction: Before the wastewater is introduced, a mixture of tetraacetylethylenediamine (10 kg), sodium percarbonate (14 kg) and sodium dodecylsulfonate (0.1 kg) is added to the oxidation reactor to control the pH value in the oxidation reactor to be around 4. The oxidation reactor is a common oxidation reactor, which is a single-layer reactor. An external spray structure 22 is provided inside the outer reactor 2. The external spray structure 22 is connected to the wastewater pipeline 21. A spray arm is provided on the external spray structure 22. The spray arm is provided with multiple spray arms, and multiple atomizing nozzles 23 are provided on the spray arm. The wastewater (2000 L) after the neutralization reaction of p-chlorobenzaldehyde is introduced into the oxidation reactor. The wastewater is formed into small droplets by the atomizing nozzle and sprayed into the inner part of the outer reactor 2. The temperature of the oxidation reactor is controlled to be 50-60°C. The time is counted from the time when the wastewater starts to be introduced. The reaction liquid and solid slurry are extracted from the bottom of the reactor to the next process every 45 minutes.

[0054] (2) Acidification reaction: The wastewater after the oxidation reaction enters the acidification kettle, and industrial hydrochloric acid is added to control the pH value in the acidification kettle to be 1-2. It is fully stirred for about 2 hours. The sodium p-chlorobenzoate in the wastewater is converted into p-chlorobenzoic acid precipitate under acidic conditions. The p-chlorobenzoic acid precipitate and the wastewater together form a reaction slurry and enter the next step.

[0055] (3) Filtration treatment: The reaction slurry in the acidification kettle enters the solid-liquid filter through a pipeline for filtration. The filtered solid material p-chlorobenzoic acid enters the dryer through a p-chlorobenzoic acid conveyor for drying. The drying temperature is set at 60°C and the drying time is about 12 hours.

[0056] (4) Drying: The dried p-chlorobenzoic acid enters a dust collector for dust removal and is then packaged to obtain 134 kg of p-chlorobenzoic acid finished product with a purity of 97.49%, wherein the content of p-chlorobenzaldehyde is 1.17%.

[0057] (5) Tail gas recovery and utilization: The tail gas in the dust collector is recovered and collected through the induced draft fan.

[0058] Example 2

[0059] (1) Oxidation reaction: Using the double-layer reactor structure of the present invention, 14 kg of sodium percarbonate was added to the built-in reactor. 2000 L of wastewater was heated to 50° C. and divided into two parts, of which about 800 L was mixed with 10 kg of tetraacetylethylenediamine and dispersed into the built-in reactor. The rest entered the outer reactor 2 through the outer spray structure 22. The temperature of the oxidation reactor was controlled at 50-60° C. The time was counted from the time the wastewater was first introduced. The reaction liquid and solid slurry were extracted from the bottom of the reactor every 45 minutes to the next process.

[0060] Steps (2) to (4) are the same as in Example 1.

[0061] 152 kg of p-chlorobenzoic acid product was obtained with a purity of 98.94%, wherein the content of p-chlorobenzaldehyde was 0.12%. The tail gas in the dust collector was recovered and collected by an induced draft fan.

[0062] Example 3 - Wastewater is introduced at the beginning

[0063] (1) Oxidation reaction: The double-layer reactor structure of the present invention is adopted. 14 kg of sodium percarbonate is fed into the built-in reactor. 2000 L of wastewater is heated to 50° C. and divided into two parts. About 800 L of the wastewater, 10 kg of tetraacetylethylenediamine, and 0.1 kg of sodium laurylsulfonate are introduced into the built-in reactor. The remaining wastewater enters the outer reactor 2 through the outer spray structure 22. The temperature of the oxidation reactor is controlled at 50-60° C. and the pH value is about 4. The time is counted from the time when the wastewater starts to be introduced. The reaction liquid and solid slurry are extracted from the bottom of the reactor every 45 minutes to the next process.

[0064] Steps (2) to (4) are the same as in Examples 1 and 2.

[0065] 164 kg of p-chlorobenzoic acid product was obtained with a purity of 99.58%, wherein the content of p-chlorobenzaldehyde was 0.02%. The tail gas in the dust collector was recovered and collected by an induced draft fan.

[0066] Example 4

[0067] (1) Oxidation reaction: Using the double-layer reactor structure of the present invention, 40 kg of sodium percarbonate was added to the built-in reactor. 2000 L of wastewater was heated to 50° C. and divided into two parts, of which about 800 L, 10 kg of tetraacetylethylenediamine and 0.1 kg of sodium laurylsulfonate were introduced into the built-in reactor. The remaining wastewater entered the outer reactor 2 through the outer spray structure 22 40 minutes after the tetraacetylethylenediamine was introduced. The temperature of the oxidation reactor was controlled at 50-60° C. and the pH value was about 4. The time was counted from the time when the wastewater was first introduced. The reaction liquid and solid slurry were extracted from the bottom of the reactor every 45 minutes to the next process.

[0068] Steps (2) to (4) are the same as in Examples 1 and 2.

[0069] 171 kg of p-chlorobenzoic acid product was obtained with a purity of 99.69%, wherein the content of p-chlorobenzaldehyde was 0.02%. The tail gas in the dust collector was recovered and collected by an induced draft fan.

[0070] Example 5

[0071] (1) Oxidation reaction: Using the double-layer reactor structure of the present invention, 14 kg of sodium percarbonate was added to the built-in reactor. 2000 L of wastewater was heated to 50° C. and divided into two parts, of which about 800 L was introduced into the built-in reactor together with 10 kg of tetraacetylethylenediamine and 0.1 kg of sodium laurylsulfonate. The remaining wastewater entered the outer reactor 2 through the outer spray structure 22 65 minutes after the tetraacetylethylenediamine was introduced. The temperature of the oxidation reactor was controlled at 50-60° C. and the pH value was about 4. The time was counted from the time when the wastewater began to be introduced. The reaction liquid and solid slurry were extracted from the bottom of the reactor every 45 minutes to the next process.

[0072] Steps (2) to (4) are the same as in Examples 1 and 2.

[0073] 159 kg of p-chlorobenzoic acid product was obtained with a purity of 99.64%, wherein the content of p-chlorobenzaldehyde was 0.02%. The tail gas in the dust collector was recovered and collected by an induced draft fan.

[0074] Example 6

[0075] This embodiment describes the recovery and treatment of the dried tail gas of p-chlorobenzoic acid in the present invention. The sodium p-chlorobenzoate generated by the reaction of p-chlorobenzoic acid in the tail gas with alkali solution is used as part of the raw material source for the acidification process and then enters the acidification kettle for recycling, thereby completing the method for recycling p-chlorobenzoic acid dust.

[0076] Specifically include:

[0077] Steps (1) to (4) are the same as those in Example 4.

[0078] (5) Tail gas recovery: The tail gas in the dust collector is recovered through the induced draft fan.

[0079] a. The exhaust gas at approximately 95°C generated during the drying process of para-chlorobenzoic acid is collected from the dust collector. This exhaust gas contains para-chlorobenzoic acid dust (approximately 0.06%), water (approximately 0.22%), and air (approximately 99.72%). The exhaust gas is introduced into the alkali circulation tower device via a pipeline. The heat brought by the exhaust gas is removed by the circulating water in the circulating cooler, and the alkali temperature is controlled to be less than 50°C. At a temperature of 50°C and normal pressure, the para-chlorobenzoic acid in the exhaust gas reacts with approximately 6% alkali solution to form a water-soluble substance, sodium para-chlorobenzoate. The mixed solution contains sodium para-chlorobenzoate, water, and sodium hydroxide. The para-chlorobenzoic acid in the exhaust gas is intercepted and washed down. The exhaust gas from the alkali circulation tower that does not contain para-chlorobenzoic acid is introduced into the atmosphere via a pipeline.

[0080] b. When the sodium hydroxide content in the mixed liquid is less than 0.5%, 2 / 3 of the mixed liquid is pumped into the acidification kettle of the production system through a pipeline (another 6% alkali solution is added to the alkali solution circulation tower).

[0081] c. Start the stirring device of the acidification kettle, add hydrochloric acid dropwise, control the pH value of the acidification kettle to 2, and stop adding acid. If the pH value does not change after 10 minutes, the reaction is terminated and sodium p-chlorobenzoate reacts with hydrochloric acid to form p-chlorobenzoic acid precipitate.

[0082] d. The p-chlorobenzoic acid in the acidification kettle enters the solid-liquid filter through the pipeline for filtration, and the filtered p-chlorobenzoic acid enters the drying system for drying, and the mother liquor is treated with sewage.

[0083] Steps c to d are the same as (2) to (4) in Example 3, thereby recycling the useful substance p-chlorobenzoic acid in the tail gas, thereby completing the tail gas recovery process. Finally, 186 kg of finished p-chlorobenzoic acid was obtained, with a purity of 99.73%, of which the content of p-chlorobenzaldehyde was 0.02%.

[0084] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for recovering active ingredients in p-chlorobenzaldehyde wastewater, characterized in that: The invention comprises a process for the preparation, refining and wastewater recovery of p-chlorobenzaldehyde, wherein the preparation of p-chlorobenzaldehyde comprises a chlorination reaction, a hydrolysis reaction and a neutralization reaction, the oily substance after the neutralization reaction enters the p-chlorobenzaldehyde refining process, and the wastewater after the neutralization reaction enters the recovery process, and the recovery process at least comprises: (1) Oxidation reaction, the wastewater after the neutralization reaction of p-chlorobenzaldehyde is passed into an oxidation reactor, and an active oxygen oxidant is set in the oxidation reactor. The active oxygen oxidant is generated immediately as the wastewater is passed into the reactor, and the p-chlorobenzaldehyde in the wastewater is oxidized into p-chlorobenzoic acid; wherein the active oxygen oxidant is prepared by reacting tetraacetylethylenediamine and sodium percarbonate, and the mass ratio of tetraacetylethylenediamine to sodium percarbonate is 1:1.2~1.4; the oxidation reactor is set as a double-layer reactor structure, including an inner reactor and an outer reactor, the inner reactor is located inside the outer reactor, and the two are coaxially arranged. Sodium percarbonate is placed in the built-in reactor, and a liquid-passing hole is provided on the wall of the built-in reactor. An aqueous solution of tetraacetylethylenediamine is introduced into the built-in reactor through a liquid inlet pipe and is evenly sprayed onto a support plate inside the built-in reactor through an internal spray structure. The support plate is configured as a porous structure, and the sodium percarbonate is placed in the support plate. The bottom surface of the support plate is configured as a hollow structure. The aqueous solution of tetraacetylethylenediamine reacts with the sodium percarbonate inside the built-in reactor to instantly generate active oxygen. Pressure is applied to the interior of the built-in reactor so that the active oxygen aqueous solution is discharged from the built-in reactor through the liquid-passing hole of the built-in reactor into an outer reactor. The interior of the outer reactor is connected to a wastewater pipeline near the top. Wastewater entering the outer reactor through the wastewater pipeline is fully mixed with the active oxygen oxidant and undergoes a preliminary oxidation reaction, thereby oxidizing p-chlorobenzaldehyde to p-chlorobenzoic acid. The p-chlorobenzaldehyde and active oxygen ions that have not undergone the oxidation reaction are present in the wastewater and enter the acidification reactor together with the wastewater. (2) Acidification treatment: After the oxidation reaction, the wastewater contains p-chlorobenzoic acid and some unoxidized p-chlorobenzaldehyde. The wastewater enters the acidification kettle. Under acidic conditions, the wastewater containing p-chlorobenzoic acid and a small amount of p-chlorobenzaldehyde in the acidification kettle is further oxidized by the active oxygen oxidant to p-chlorobenzoic acid. At the same time, the sodium p-chlorobenzoate in the wastewater is converted into p-chlorobenzoic acid precipitate under acidic conditions. The p-chlorobenzoic acid precipitate and the wastewater together form a reaction slurry and enter the next process. (3) Filtration treatment: the reaction slurry in the acidification kettle enters the solid-liquid filter through the pipeline for filtration, and the filtered solid material p-chlorobenzoic acid enters the dryer through the p-chlorobenzoic acid conveyor for drying.

2. The method according to claim 1, characterized in that During acidification treatment, hydrochloric acid is added to control the pH value in the acidification kettle to be between 1 and 2.

3. The method according to claim 1, characterized in that The dried p-chlorobenzoic acid enters the dust collector for dust removal and is then packaged to obtain the p-chlorobenzoic acid product. The tail gas in the dust collector is recovered by an induced draft fan.

4. The method according to claim 3, characterized in that The dried tail gas of p-chlorobenzoic acid enters the circulation tower and is absorbed by alkali solution. The heat in the alkali solution is removed by the cooler. The p-chlorobenzoic acid in the tail gas reacts with the alkali solution to generate a water-soluble substance, sodium p-chlorobenzoate. The mixture of sodium p-chlorobenzoate and alkali solution is pumped into the acidification kettle of step (2).

5. The method according to claim 4, characterized in that The alkali solution with an initial mass fraction of 5-10% in the circulation tower is circulated by a pump. The p-chlorobenzoic acid dust in the tail gas contacts and reacts with the alkali solution in the circulation tower to generate sodium p-chlorobenzoate. The concentration of the alkali solution in the circulation tower is continuously monitored. When the concentration of the alkali solution is lower than 0.5%, the alkali solution in the circulation tower is replaced.

6. The method according to claim 1, characterized in that The drying equipment used for drying p-chlorobenzoic acid is a vacuum steam dryer.

7. The method according to claim 1, characterized in that An external spray structure is provided inside the oxidation reactor, the external spray structure is connected to the wastewater pipeline, a spray arm is provided on the external spray structure, the spray arm is provided on the outside of the built-in reactor, and the spray arm is parallel to the wall of the built-in reactor. There are multiple spray arms, and multiple atomizing nozzles are provided on the spray arms. The wastewater after the neutralization reaction of para-chlorobenzaldehyde is passed into the oxidation reactor, and the wastewater is formed into small droplets through the atomizing nozzle and sprayed into the interior of the outer reactor.

8. The method according to claim 1 or 7, characterized in that The temperature of the oxidation reactor is controlled at 50~60℃.

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