Resource utilization device and process for wastewater generated in preparation of benzyl alcohol through toluene oxidation

Abstract

The invention discloses a resource utilization device and process for wastewater generated during preparation of benzyl alcohol through toluene oxidation. The resource utilization device comprises a cryogenic absorption unit, a waste heat neutralization unit, a steam stripping separation unit and a waste heat concentration unit, the method comprises the following steps: capturing organic substances in free water through cryogenic capture, carrying out phase separation and recovery, adding an alkaline solution with a certain concentration for neutralization and preheating, converting a low-molecular acidic organic phase into sodium salt, carrying out steam stripping separation, separating organic phase substances dissolved in a sodium salt wastewater solution, and concentrating to obtain concentrated sodium salt wastewater which can be used as a denitrifying bacterium nutrient solution. Inorganic salt and organic phase in the acid-base adjusting preheating kettle can be thoroughly separated by adopting the stripping tower. A circulating pump adopts a large-flow and low-lift axial flow pump for forced circulation, a second reboiler is selected as a falling film type reboiler, a heat source of the reboiler adopts external 90-DEG C hot water waste heat for heating evaporation, and the reboiler tube nest and the like can be prevented from being blocked by selecting the combination of three forms. Sodium salt wastewater concentrated by the device is sold as a denitrifying bacterium nutrient solution.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of wastewater generated by the oxidation of toluene to prepare benzyl alcohol, and specifically relates to a resource utilization device and process for wastewater generated by the oxidation of toluene to prepare benzyl alcohol. Background Art

[0002] The toluene oxidation method for preparing benzyl alcohol has the advantages of a short process flow, low production cost, and chlorine-free and high-quality benzyl alcohol products. This process uses toluene as a raw material, and under the action of a catalyst, an initiator and an auxiliary agent, it undergoes a liquid-phase oxidation reaction with oxygen in the air to generate benzyl peroxide. Subsequently, under specific conditions, the benzyl peroxide decomposes to form benzyl alcohol. In the process of producing benzyl alcohol by toluene oxidation, the oxidation tail gas will inevitably produce high COD wastewater, and the pollutants in the high COD wastewater are mainly organic substances such as small molecular organic acids, toluene, and toluene derivatives. Through analysis and testing, the COD of the wastewater is generally between 40000-50000 mg / L, and it is difficult to manage the standard discharge, which greatly increases the cost of enterprise sewage treatment.

[0003] In order to solve this problem, the present invention has developed a device and process for resource utilization of wastewater generated by oxidation of toluene to prepare benzyl alcohol. Summary of the invention

[0004] Based on the above description, the present invention provides a device and process for resource utilization of wastewater generated by the oxidation of toluene to prepare benzyl alcohol. Through the device, the wastewater can be converted into a commodity that can be directly sold as a nutrient solution for denitrifying bacteria, thereby realizing the resource utilization of wastewater. At the same time, through the device, the COD of the generated condensate can be controlled at 500-1000 mg / L, greatly reducing the cost of sewage treatment.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A resource utilization device for wastewater produced by oxidation of toluene to prepare benzyl alcohol, comprising a deep cooling absorption unit, a neutralization waste heat unit, a stripping separation unit and a waste heat concentration unit connected in sequence; The organic matter in the free water is captured by a deep cooling absorption unit, separated and recovered after phase separation, and then a certain concentration of alkaline solution is added for neutralization and preheating through a neutralization waste heat unit to convert the low molecular weight acidic organic phase into sodium salts. The organic phase substances dissolved in the sodium salt wastewater solution are separated by a steam stripping separation unit, and concentrated by a waste heat concentration unit to obtain concentrated sodium salt wastewater that can be used as a nutrient solution for denitrifying bacteria.

[0006] Based on the above technical solution, the present invention can also be improved as follows.

[0007] Furthermore, the above-mentioned resource utilization device for the wastewater generated by the oxidation of toluene to prepare benzyl alcohol, the deep cold absorption unit includes a deep cold absorption tower, an absorption liquid phase separation tank, and a high-efficiency spiral tube cooler, the bottom of the deep cold absorption tower is connected to the top of the absorption liquid phase separation tank, the bottom of the absorption liquid phase separation tank divides into a first pipe and a second pipe, the first pipe is connected to the bottom of the high-efficiency spiral tube cooler, and refluxes from the top of the high-efficiency spiral tube cooler to the upper part of the deep cold absorption tower, the second pipe enters the neutralization waste heat unit, and the absorption liquid circulation pump is connected to the pipe between the diversion point of the first pipe and the second pipe and the bottom of the absorption liquid phase separation tank.

[0008] Furthermore, in the above-mentioned resource utilization device for the wastewater generated by the oxidation of toluene to prepare benzyl alcohol, the neutralization waste heat unit includes an acid-base regulating preheating kettle and a heat exchanger, the second pipeline is connected to the upper part of the acid-base regulating preheating kettle, the bottom part of the acid-base regulating preheating kettle is divided into a third pipeline and a fourth pipeline, the third pipeline is connected to the bottom of the heat exchanger, the top of the heat exchanger refluxes to the upper part of the acid-base regulating preheating kettle, the fourth pipeline is connected to the stripping separation unit, the top of the acid-base regulating preheating kettle is connected to the tail gas treatment device, and a preheating circulation pump is connected to the pipeline between the diversion point of the third pipeline and the fourth pipeline and the bottom of the acid-base regulating preheating kettle.

[0009] Furthermore, the above-mentioned resource utilization device for the wastewater generated by the oxidation of toluene to prepare benzyl alcohol, the stripping separation unit includes a stripping tower, a first reboiler, a first condenser, and a stripping tower reflux tank, the fourth pipeline is connected to the upper part of the stripping tower, the top of the stripping tower is connected to the inlet of the first condenser, the bottom outlet of the first condenser is connected to the top of the stripping tower reflux tank, the top outlet of the first condenser is connected to the tail gas treatment device, a part of the bottom of the stripping tower reflux tank is refluxed to the upper part of the stripping tower, and the other part is recovered to the toluene oxidation system, the bottom of the stripping tower is divided into a fifth pipeline and a sixth pipeline, the fifth pipeline is refluxed to the lower part of the stripping tower through the first reboiler, the sixth pipeline is connected to the waste heat stripping unit, and the pipeline between the diversion point of the fifth pipeline and the sixth pipeline and the bottom of the stripping tower is connected to a stripping tower bottom liquid circulation pump.

[0010] Furthermore, the above-mentioned resource utilization device for the waste water generated by the oxidation of toluene to prepare benzyl alcohol, the waste heat concentration unit includes a waste heat concentration tower, a second reboiler, a second condenser, and a condensate tank, the sixth pipeline is connected to the lower part of the waste heat concentration tower, the top of the waste heat concentration tower is connected to the inlet of the second condenser, the top outlet of the second condenser is connected to a vacuum pump, the bottom outlet is connected to the condensate tank, the outlet of the condensate tank is connected to a decontamination point, the bottom part of the waste heat concentration tower is divided into a seventh pipeline and an eighth pipeline, the seventh pipeline is refluxed to the lower part of the waste heat concentration tower through the second reboiler, the eighth pipeline is connected to a filling device, and a circulating pump is connected to the pipeline between the diversion point of the seventh pipeline and the eighth pipeline and the bottom of the waste heat concentration tower.

[0011] Furthermore, in the above-mentioned resource utilization device for wastewater generated by toluene oxidation to prepare benzyl alcohol, the deep cooling absorption tower is provided with multiple groups of spiral nozzles, the multiple groups of spiral nozzles are arranged in a plum blossom form, the acid-base adjustment preheating kettle adopts a ring pipe distribution form, and the lower parts of the two sets of ring pipes are evenly distributed with lower liquid holes of φ10. The spiral nozzle can be one of the existing technologies.

[0012] Furthermore, in the above-mentioned wastewater resource utilization device for preparing benzyl alcohol by oxidation of toluene, the stripping tower comprises a nozzle, a two-stage trough distributor, and a perforated plate corrugated packing. The trough distributor is a φ1200 standard trough distributor, and the model of the perforated plate corrugated packing is 250Y.

[0013] On the other hand, the present invention provides a process for resource utilization of wastewater generated by the oxidation of toluene to prepare benzyl alcohol, using the device for resource utilization of wastewater generated by the oxidation of toluene to prepare benzyl alcohol as claimed in claim 4, comprising the steps of deep cold absorption, neutralization of waste heat, stripping separation, and waste heat concentration, and the concentrated sodium salt wastewater solution in the process is directly sold as a nutrient solution for denitrifying bacteria; The cryogenic absorption comprises: using a pressure flow to transport the high-temperature mixed tail gas into the lower part of the cryogenic absorption tower, the absorption liquid enters the high-efficiency spiral tube cooler to be cooled to 7-8°C and refluxes to the cryogenic absorption tower, and is evenly distributed into the tower through the spiral nozzle of the cryogenic absorption tower, and is countercurrently contacted with the high-temperature tail gas in the regular perforated plate corrugated packing of the cryogenic absorption tower for mass transfer cooling and absorption. Under high pressure and extremely low temperature conditions, the absorption liquid controls the temperature of the entire tower to be less than 10°C, and absorbs toluene and its derivative organic matter in the tail gas; Neutralizing waste heat: pre-treating the acidic wastewater, conveying the wastewater to an acid-base regulating preheating kettle, uniformly dropping 10wt%-13wt% sodium carbonate solution into the acid-base regulating preheating kettle, generating sodium salt wastewater mainly composed of small molecule organic acid sodium salt; a part of the sodium salt wastewater in the acid-base regulating preheating kettle enters the heat exchanger through external circulation, and is preheated to 50-60° C. using the waste heat of the device, and another part of the sodium salt wastewater is conveyed to the stripping tower through a preheating circulation pump for separation of the organic phase; The stripping separation: this sodium salt wastewater falls from the upper part of the stripping tower, and contacts with the water vapor at the lower part of the stripping tower in countercurrent for mass transfer and heat transfer. The organic phase and a small amount of water vapor are condensed into the stripping tower reflux tank through the first condenser at the top of the tower. A part of the material is refluxed and recovered to the upper part of the stripping tower through the stripping tower reflux pump, and the reflux ratio is controlled at 1.4-1.7. The other part goes to the tail gas treatment device; The waste heat concentration: the dilute sodium salt wastewater from the steam stripping tower kettle is fed into the lower part of the waste heat concentration tower packing section, forced to circulate by a circulating pump, and the second reboiler is selected to heat and evaporate.

[0014] Furthermore, in the above-mentioned resource utilization process of the wastewater generated by the oxidation of toluene to prepare benzyl alcohol, in the neutralization waste heat step, the absorption liquid undergoes a neutralization reaction in an alkaline environment with a pH value of 7-8, the reaction residence time is 20-30 minutes, and the acid-base adjustment preheating kettle reaction pressure is 1-10 kPa (g).

[0015] Furthermore, in the above-mentioned resource utilization process of the wastewater generated by the oxidation of toluene to prepare benzyl alcohol, the stripping tower is a normal pressure stripping tower, the small molecule organic acid sodium salt solution in the bottom of the tower is heated to 100°C by a first reboiler, the heat source of the first reboiler is 0.43Mpa (g) saturated steam, and the bottom liquid circulating pump of the stripping tower is forced to circulate to prevent sodium salts from causing scaling of the reboiler.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: The high-temperature mixed tail gas enters the lower part of the deep-cold absorption tower by pressure flow, and the absorption liquid circulation pump transports the absorption liquid to the high-efficiency spiral tube cooler to cool it to 7-8°C. It is evenly distributed to the tower through the six groups of spiral nozzles of the deep-cold absorption tower. The high-temperature tail gas and the deep-cold absorption liquid are countercurrently contacted in the regular perforated plate corrugated packing of the deep-cold absorption tower for mass transfer cooling and absorption. Under high pressure and extremely low temperature conditions, the absorption liquid can control the temperature of the entire tower at <10°C, and absorb the toluene and its derivative organic matter in the tail gas. In a deep-cold environment, the solubility of organic matter in water will decrease, thereby reducing the dissolved organic matter in water, and the free organic matter can be simply separated by phase separation.

[0017] The acid-base adjustment preheating kettle adopts the form of ring pipe distribution. The lower part of the two sets of ring pipes is evenly distributed with a φ10 lower liquid hole, so that the liquid can react quickly when it contacts the liquid surface. The acid-base adjustment preheating kettle is stirred and forced to circulate by the agitator to improve the mixing degree, strengthen mass transfer and heat transfer. A part of the reaction liquid enters the heat exchanger through external circulation and is preheated to 50-60℃ using the waste heat of the device. Under this temperature condition, the reaction rate will increase. Since the temperature of the absorption liquid in the deep-cold absorption tower is too low, it can effectively improve the work efficiency after passing through the preheating unit, and the cost of using waste heat to heat up is low; the other part is extracted to the stripping tower to separate a small amount of organic matter in the sodium salt wastewater solution.

[0018] There is still a certain amount of organic matter in the sodium salt wastewater in the acid-base adjustment preheating kettle, which does not meet the requirements for the use of denitrifying bacteria nutrient solution. The use of a stripping tower can completely separate the inorganic salt and organic phase.

[0019] The circulation pump adopts a large-flow, low-lift axial flow pump for forced circulation. The second reboiler is a falling film reboiler. The reboiler heat source adopts external 90°C hot water waste heat for heating and evaporation. The combination of these three forms is mainly considered that sodium salt wastewater will crystallize and precipitate due to poor concentration control during the concentration process, which will cause blockage of reboiler tubes and other equipment.

[0020] The sodium salt wastewater solution concentrated in the bottom of the tower is directly sold as nutrient solution for denitrifying bacteria. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart of a device for resource utilization of wastewater generated by oxidizing toluene to prepare benzyl alcohol provided in an embodiment of the present invention; Figure 2 It is a structural schematic diagram of a deep cooling absorption tower of the present invention; Figure 3 It is a structural schematic diagram of the acid-base regulating preheating kettle of the present invention; Figure 4 It is a structural schematic diagram of the stripping tower of the present invention; Figure 5 It is a structural schematic diagram of the waste heat concentration tower of the present invention; Figure 6 A schematic diagram of the overall structure of a device for resource utilization of wastewater generated by oxidation of toluene to prepare benzyl alcohol provided in an embodiment of the present invention.

[0022] In the accompanying drawings, the components represented by the reference numerals are listed as follows: 1. Cryogenic absorption tower; 2. Absorption liquid phase separation tank; 3. Absorption liquid circulation pump; 4. High-efficiency spiral tube cooler; 5. Acid-base adjustment preheating kettle; 6. Electric motor; 7. Heat exchanger; 8. Preheating circulation pump; 9. Stripping tower; 10. First reboiler; 11. Stripping tower bottom liquid circulation pump; 12. First condenser; 13. Stripping tower reflux pump; 14. Stripping tower reflux tank; 15. Waste heat stripping tower; 16. Second reboiler; 17. Circulation pump; 18. Second condenser; 19. Condensate tank; 20. Delivery pump. DETAILED DESCRIPTION

[0023] In order to facilitate understanding of the present application, the present application will be described more comprehensively below. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0025] It should be noted that when an element is considered to be “connected to” another element, it can be directly connected to the other element or connected to the other element through an intervening element.

[0026] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0027] The present invention provides a device and a process for resource utilization of wastewater generated by the oxidation of toluene to prepare benzyl alcohol, wherein organic matter in free water is captured by deep cooling for phase separation and recovery, and then a certain concentration of alkaline solution is added for neutralization and preheating to convert a low-molecular acidic organic phase into sodium salts, and then stripping separation is performed to separate organic phase substances dissolved in the sodium salt wastewater solution, and then concentrated to obtain concentrated sodium salt wastewater that can be used as a nutrient solution for denitrifying bacteria.

[0028] Example 1 A resource utilization device for wastewater produced by oxidation of toluene to prepare benzyl alcohol, comprising a deep cooling absorption unit, a neutralization waste heat unit, a stripping separation unit and a waste heat concentration unit connected in sequence; The organic matter in the free water is captured by a deep cooling absorption unit, separated and recovered after phase separation, and then a certain concentration of alkaline solution is added for neutralization and preheating through a neutralization waste heat unit to convert the low molecular weight acidic organic phase into sodium salts. The organic phase substances dissolved in the sodium salt wastewater solution are separated by a steam stripping separation unit, and concentrated by a waste heat concentration unit to obtain concentrated sodium salt wastewater that can be used as a nutrient solution for denitrifying bacteria.

[0029] The cryogenic absorption unit includes a cryogenic absorption tower 1, an absorption liquid phase separation tank 2, and a high-efficiency spiral tube cooler 4. The bottom of the cryogenic absorption tower 1 is connected to the top of the absorption liquid phase separation tank 2. The bottom of the absorption liquid phase separation tank 2 is divided into a first pipe and a second pipe. The first pipe is connected to the bottom of the high-efficiency spiral tube cooler 4 and refluxes from the top of the high-efficiency spiral tube cooler 4 to the upper part of the cryogenic absorption tower 1. The second pipe enters the neutralization waste heat unit. The absorption liquid circulation pump 3 is connected to the pipe between the diversion point of the first pipe and the second pipe and the bottom of the absorption liquid phase separation tank 2.

[0030] The neutralization waste heat unit includes an acid-base regulating preheating kettle 5 and a heat exchanger 7. The second pipeline is connected to the upper part of the acid-base regulating preheating kettle 5. The bottom of the acid-base regulating preheating kettle 5 is divided into a third pipeline and a fourth pipeline. The third pipeline is connected to the bottom of the heat exchanger 7. The top of the heat exchanger 7 refluxes to the upper part of the acid-base regulating preheating kettle 5. The fourth pipeline is connected to the stripping separation unit. The top of the acid-base regulating preheating kettle 5 is connected to the tail gas treatment device. The preheating circulation pump 8 is connected to the pipeline between the diversion point of the third pipeline and the fourth pipeline and the bottom of the acid-base regulating preheating kettle 5.

[0031] The stripping separation unit includes a stripping tower 9, a first reboiler 10, a first condenser 12, and a stripping tower reflux tank 14. The fourth pipeline is connected to the upper part of the stripping tower 9, the top of the stripping tower 9 is connected to the inlet of the first condenser 12, the bottom outlet of the first condenser 12 is connected to the top of the stripping tower reflux tank 14, and the top outlet of the first condenser 12 is connected to the tail gas treatment device. A part of the bottom of the stripping tower reflux tank 14 is refluxed to the upper part of the stripping tower 9, and the other part is recovered to the toluene oxidation system (the system for preparing benzyl alcohol by oxidizing toluene in the prior art). The bottom of the stripping tower 9 is divided into a fifth pipeline and a sixth pipeline. The fifth pipeline is refluxed to the lower part of the stripping tower 9 through the first reboiler 10. The sixth pipeline is connected to the waste heat stripping and concentration unit. The pipeline between the diversion point of the fifth pipeline and the sixth pipeline and the bottom of the stripping tower 9 is connected to a stripping tower bottom liquid circulation pump 11.

[0032] The waste heat concentration unit includes a waste heat concentration tower 15, a second reboiler 16, a second condenser 18, and a condensate tank 19. The sixth pipeline is connected to the lower part of the waste heat concentration tower 15, the top of the waste heat concentration tower 15 is connected to the inlet of the second condenser 18, the top outlet of the second condenser 18 is connected to a vacuum pump, and the bottom outlet is connected to the condensate tank 19. The outlet of the condensate tank 19 is connected to a decontamination point. The bottom of the waste heat concentration tower 15 is divided into a seventh pipeline and an eighth pipeline. The seventh pipeline refluxes to the lower part of the waste heat concentration tower 15 through the second reboiler 16. The eighth pipeline is connected to a filling device. A circulating pump 17 is connected to the pipeline between the diversion point of the seventh pipeline and the eighth pipeline and the bottom of the waste heat concentration tower 15.

[0033] The cryogenic absorption tower 1 is provided with multiple groups of spiral spray heads arranged in a plum blossom pattern, and the acid-base regulating preheating kettle 5 is in the form of an annular tube distribution, and the lower parts of the two annular tubes are evenly distributed with lower liquid holes of φ10. The spiral spray heads can be any one of the existing technologies.

[0034] The stripping tower 9 includes a nozzle, a two-stage trough distributor, and a perforated plate corrugated packing. The trough distributor is a standard trough distributor of φ1200, and the model of the perforated plate corrugated packing is 250Y.

[0035] Example 2 The present invention also provides a resource utilization process for wastewater generated by toluene oxidation to prepare benzyl alcohol. The process is divided into four steps: 1. deep cold absorption, 2. neutralization preheating, 3. stripping separation, and 4. waste heat concentration.

[0036] The solution adopted by the present invention to solve the technical problem is a resource utilization process of wastewater generated by oxidizing toluene to prepare benzyl alcohol, comprising the following steps: Deep Cold Absorption: The oxidation tail gas generated in the process of producing benzyl alcohol by toluene oxidation method will contain some water vapor and organic gas, and these gases need to be processed before they can be discharged into the atmosphere. The present invention first uses pressure flow to transport the high-temperature mixed tail gas into the lower part of the deep-cold absorption tower 1, and the absorption liquid circulation pump 3 transports the absorption liquid to the high-efficiency spiral tube cooler 4 to cool it to 7-8°C, and then it is evenly distributed into the tower through six groups of spiral nozzles of the deep-cold absorption tower 1. The high-temperature tail gas and the deep-cold absorption liquid are countercurrently contacted in the regular orifice plate corrugated packing of the deep-cold absorption tower 1 for mass transfer cooling and absorption. Under high pressure and extremely low temperature conditions, the absorption liquid can control the temperature of the entire tower to less than 10°C, and absorb toluene and its derivative organic matter in the tail gas. The deep cooling absorption tower 1 uses six groups of spiral nozzles arranged in a plum blossom shape. After the acidic absorption liquid is heated to 7-8°C by the high-efficiency spiral tube heat exchanger 7, it is evenly atomized by the six groups of nozzles and instantly deep-cooled to below 10°C in countercurrent contact with the oxidation tail gas. The absorption liquid then falls to the absorption liquid phase separation tank 2 through the regular orifice plate corrugated packing. The absorbed organic matter and the acidic absorption liquid are separated into layers. The upper organic phase is recovered to the toluene oxidation system, and the lower absorption liquid enters the acid-base adjustment preheating kettle. The agitator is started by the motor 6.

[0037] When the high-temperature tail gas containing organic matter is mixed with the deep-cold absorption liquid and enters the absorption liquid phase separation tank 2 for phase separation, since the tail gas contains 70% toluene and its derivatives, the relative density of the organic phase in the mixed liquid is lighter than the absorption liquid. The free organic matter can be initially separated through a sufficient residence time (about 1 hour), and the organic matter in the upper layer overflows through the baffle of the absorption liquid phase separation tank 2 to the liquid level side of the absorption liquid phase separation tank 2 and is recovered to the toluene oxidation system. The absorption liquid is continuously circulated and absorbed, and the small molecular organic acid therein is miscible with water, and water vapor in the oxidation tail gas is continuously cooled to water, so the absorption liquid will continue to increase. At this time, the absorption liquid needs to be continuously collected externally, and this externally collected acidic absorption liquid enters the acid-base adjustment preheating kettle 5 for treatment.

[0038] Neutralization preheating: Since the pH of this part of the absorption liquid is acidic and has a certain degree of corrosiveness to equipment and human body, it needs to be pre-treated. This part of the absorption liquid needs to be transported to the acid-base adjustment preheating kettle 5, and 12.5% ​​sodium carbonate solution is uniformly added to the acid-base adjustment preheating kettle 5. Since the acid-base adjustment preheating kettle 5 adopts a ring pipe distribution form, the lower part of the two sets of ring pipes is evenly distributed with lower liquid holes of φ10, so that the absorption liquid and sodium carbonate solution can react quickly when they come into contact. The absorption liquid undergoes a neutralization reaction in an alkaline environment with a temperature range of 50-60℃ and a pH value of 7-8. The reaction residence time is 20~30min. The reaction pressure of the acid-base adjustment preheating kettle 5 is 1~10kpa (g), and sodium salt wastewater mainly composed of small molecule organic acid sodium salt is generated, where (g) represents the surface pressure; The acid-base adjustment preheating kettle 5 is stirred by the agitator therein to improve the mixing degree and strengthen the mass transfer and heat transfer. A part of the sodium salt wastewater enters the heat exchanger 7 through the external circulation and is preheated to 50-60°C using the waste heat of the device. Under this temperature condition, the reaction rate will be increased. Since the temperature of the absorption liquid in the deep-cold absorption tower 1 is too low, the work efficiency can be effectively improved after passing through the preheating unit, and the cost of heating using waste heat is low; the other part of the sodium salt wastewater is transported to the stripping tower 9 through the preheating circulation pump 8 after the pH value and temperature reach the ideal indicators to separate a small amount of organic matter in the sodium salt wastewater solution.

[0039] Stripping separation: There is still a certain amount of organic matter in the sodium salt wastewater in the acid-base adjustment preheating kettle 5, which cannot meet the use requirements of the denitrifying bacteria nutrient solution. The stripping tower 9 is now used to completely separate the inorganic salt and the organic phase. This sodium salt wastewater is evenly distributed and falls from the upper part of the stripping tower 9 through the nozzle, two-stage trough distributor, and orifice corrugated packing, and countercurrently contacts with the water vapor at the lower part of the stripping tower 9 for mass transfer and heat transfer. The organic phase and a small amount of water vapor are condensed to the stripping tower reflux tank through the first condenser 12 at the top of the tower. A part of the material is refluxed and recovered to the upper part of the stripping tower 9 through the stripping tower reflux pump 13, and the reflux ratio is controlled at 1.4-1.7, and the other part goes to the tail gas treatment device.

[0040] This tower is a normal pressure stripping tower 9. The small molecule organic acid sodium salt wastewater solution in the bottom of the tower is forced to circulate through the first reboiler 10 to heat to 100°C by the stripping tower bottom liquid circulation pump 11. The heat source of the first reboiler 10 is 0.43Mpa (g) saturated steam. The stripping tower bottom liquid circulation pump 11 is forced to circulate to prevent sodium salts from causing reboiler scaling. Because sodium salts will not be evaporated, the organic matter content in the bottom of the stripping tower 9 after stripping can be almost negligible. One stream of the stripping tower 9 bottom material is forced to circulate back to the bottom of the tower, and one stream is extracted to the waste heat concentration tower 15 for waste heat concentration.

[0041] Waste heat concentration: In the process of concentration, the waste heat concentration tower 15 adopts vacuum evaporation, and the pressure is controlled at 10Kpa(a), where (a) represents absolute pressure. The evaporated liquid at the top of the tower is condensed into the condensate tank 19 through the second condenser 18, and is transported to the sewage treatment center through the delivery pump 20. At this time, the COD of the condensate in the condensate tank 19 can be controlled at 500-1000mg / L, which greatly reduces the cost of sewage treatment.

[0042] The sodium salt wastewater from the bottom of the stripping tower 9 is relatively dilute and needs to be concentrated. The dilute sodium salt wastewater is fed from the lower part of the packing section of the waste heat concentration tower 15. The circulation pump 17 adopts a large-flow, low-lift axial flow pump for forced circulation. The second reboiler 16 is a falling film reboiler, and an external 90°C hot water waste heat is used as a heat source for heating and evaporation. The combination of these three forms is mainly selected because the sodium salt wastewater will crystallize and precipitate due to poor concentration control during the concentration process, which will cause blockage of equipment such as the reboiler tubes.

[0043] The sodium salt wastewater solution after concentration in the bottom of the tower can be directly bottled and sold as nutrient solution for denitrifying bacteria. The COD content of the bottom solution can reach 250,000 mg / L.

[0044] Denitrification experiment of concentrated sodium salt wastewater The present invention also conducts a denitrification experiment on the concentrated sodium salt wastewater obtained after the process treatment, and confirms that the concentrated sodium salt wastewater solution treated by the process of the present invention can be used as a denitrification carbon source.

[0045] Nitrification rate test: Two parallel experiments were set up for the nitrification rate test experiment. In each group, 0.2L activated sludge and 0.8L concentrated sodium salt wastewater solution were prepared into COD solution and placed in a 1L narrow-mouth bottle. The bottle was wrapped with tin foil and connected to an aeration device. They were marked as 1# and 2# respectively. Samples were taken and filtered to detect COD. Samples were taken every 24 hours, and the rapid digestion spectrophotometry (HJ / T399-2007) was used to detect COD for three days.

[0046] BOD5 test experiment: Five groups of BOD5 test experiments were set up. The concentrated sodium salt wastewater solution was diluted to prepare an experimental solution with a COD of 1000 mg / L in a culture container. After 5 days of culture, the COD was detected by the rapid digestion spectrophotometry method (HJ / T399-2007). The BOD5 was determined by the "Dilution and Inoculation Method for Determination of Five-Day Biochemical Oxygen Demand (BOD5) of Water Quality" (HJ505-2009), and the B / C was calculated to evaluate the biodegradability of the concentrated sodium salt wastewater solution.

[0047] Denitrification experiment: Two groups were set up in the denitrification experiment, namely the blank group and the experimental group. Take 1000mL of denitrifying bacteria liquid and add 40mL of 800mg / L standard TN solution to the blank group, add 40mL of 800mg / L standard TN solution and 0.8mL of concentrated sodium salt wastewater solution to the experimental group, and control the stirrer to rotate at 250r / min for the experiment. Sampling was performed every 1h, and the COD was detected by rapid digestion spectrophotometry (HJ / T399-2007), and the TN value was detected by alkaline potassium persulfate digestion ultraviolet spectrophotometry (HJ636-2012). The denitrifying bacteria liquid was GANDEW-MIX, purchased from Shanghai GANDEW Environmental Engineering Co., Ltd.

[0048] Nitrification rate test results:

[0049] COD and BOD5 test results after 5 days of cultivation:

[0050] Denitrification experiment results:

[0051] Experimental conclusion: The COD solutions prepared with concentrated sodium salt wastewater and activated sludge were subjected to aeration experiments, and the COD decreased rapidly. The biodegradability test results of the concentrated sodium salt wastewater solution showed that the B / C average was 0.512, and the concentrated sodium salt wastewater solution had good biodegradability. The total nitrogen content decreased by 82% in 4 hours of the denitrification experiment, and the total nitrogen decreased to within 7.0 mg / L, indicating that the concentrated sodium salt wastewater solution can be used as a denitrification carbon source.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for recycling wastewater generated by oxidation of toluene to produce benzyl alcohol, characterized in that: It includes a cryogenic absorption unit, a neutralization waste heat unit, a stripping separation unit and a waste heat concentration unit connected in sequence; The organic matter in the free water is captured by a deep cooling absorption unit, separated and recovered after phase separation, and then a certain concentration of alkaline solution is added for neutralization and preheating through a neutralization waste heat unit to convert the low molecular weight acidic organic phase into sodium salts. The organic phase substances dissolved in the sodium salt wastewater solution are separated by a steam stripping separation unit, and concentrated by a waste heat concentration unit to obtain concentrated sodium salt wastewater that can be used as a nutrient solution for denitrifying bacteria.

2. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 1, characterized in that: The cryogenic absorption unit comprises a cryogenic absorption tower (1), an absorption liquid phase separation tank (2), and a high-efficiency spiral tube cooler (4); the bottom of the cryogenic absorption tower (1) is connected to the top of the absorption liquid phase separation tank (2); a first pipeline and a second pipeline are separated from the bottom of the absorption liquid phase separation tank (2); the first pipeline is connected to the bottom of the high-efficiency spiral tube cooler (4) and refluxes from the top of the high-efficiency spiral tube cooler (4) to the upper part of the cryogenic absorption tower (1); and the second pipeline enters the neutralization waste heat unit.

3. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 2, characterized in that: The neutralization waste heat unit comprises an acid-base regulating preheating kettle (5) and a heat exchanger (7); the second pipeline is connected to the upper part of the acid-base regulating preheating kettle (5); the bottom of the acid-base regulating preheating kettle (5) is divided into a third pipeline and a fourth pipeline; the third pipeline is connected to the bottom of the heat exchanger (7); the top of the heat exchanger (7) refluxes to the upper part of the acid-base regulating preheating kettle (5); and the fourth pipeline is connected to the stripping separation unit.

4. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 3, characterized in that: The stripping separation unit comprises a stripping tower (9), a first reboiler (10), a first condenser (12), and a stripping tower reflux tank (14); the fourth pipeline is connected to the upper part of the stripping tower (9); the top of the stripping tower (9) is connected to the inlet of the first condenser (12); the bottom outlet of the first condenser (12) is connected to the top of the stripping tower reflux tank (14); the top outlet of the first condenser (12) is connected to the tail gas treatment device; a part of the bottom of the stripping tower reflux tank (14) is refluxed to the upper part of the stripping tower (9), and the other part is recovered to the toluene oxidation system; a fifth pipeline and a sixth pipeline are separated from the bottom of the stripping tower (9); the fifth pipeline is refluxed to the lower part of the stripping tower (9) through the first reboiler (10); and the sixth pipeline is connected to the waste heat stripping and concentration unit.

5. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 4, characterized in that: The waste heat concentration unit comprises a waste heat concentration tower (15), a second reboiler (16), a second condenser (18), and a condensate tank (19); the sixth pipeline is connected to the lower part of the waste heat concentration tower (15); the top of the waste heat concentration tower (15) is connected to the inlet of the second condenser (18); the top outlet of the second condenser (18) is connected to a vacuum pump; the bottom outlet is connected to the condensate tank (19); the outlet of the condensate tank (19) is connected to a decontamination location; a seventh pipeline and an eighth pipeline are separated from the bottom of the waste heat concentration tower (15); the seventh pipeline refluxes to the lower part of the waste heat concentration tower (15) through the second reboiler (16); and the eighth pipeline is connected to a filling device.

6. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 3, characterized in that: The deep-cold absorption tower (1) is provided with a plurality of groups of spiral nozzles arranged in a plum blossom pattern. The acid-base regulating preheating kettle (5) is provided in a ring tube distribution pattern, and lower liquid holes of φ10 are evenly distributed at the bottom of the two sets of ring tubes.

7. The resource utilization device for wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 4, characterized in that: The stripping tower (9) comprises a nozzle, a two-stage trough distributor, and a perforated plate corrugated packing.

8. A process for resource utilization of wastewater generated by oxidation of toluene to prepare benzyl alcohol, characterized in that: The resource utilization device for the wastewater produced by the oxidation of toluene to prepare benzyl alcohol according to claim 4 comprises the steps of deep cold absorption, neutralization of waste heat, stripping separation, and waste heat concentration. The concentrated sodium salt wastewater solution in this process is directly sold as a nutrient solution for denitrifying bacteria; The cryogenic absorption comprises: using a pressure flow to transport the high-temperature mixed tail gas into the lower part of a cryogenic absorption tower (1); the absorption liquid enters a high-efficiency spiral tube cooler (4) to be cooled to 7-8°C and refluxed to the cryogenic absorption tower (1); the absorption liquid is evenly distributed into the tower through a spiral nozzle of the cryogenic absorption tower (1); the absorption liquid and the high-temperature tail gas are countercurrently contacted in the regular perforated plate corrugated packing of the cryogenic absorption tower (1) for mass transfer, cooling and absorption; the absorption liquid controls the temperature of the entire tower to less than 10°C under high pressure and extremely low temperature conditions, and absorbs toluene and its derivative organic matter in the tail gas; The neutralization waste heat: pre-treating the acidic wastewater, conveying the wastewater to an acid-base regulating preheating kettle (5), uniformly adding 10wt%-13wt% sodium carbonate solution to the acid-base regulating preheating kettle (5) to generate sodium salt wastewater mainly composed of small molecule organic acid sodium salt; a part of the sodium salt wastewater in the acid-base regulating preheating kettle (5) enters the heat exchanger (7) through external circulation, and is preheated to 50-60° C. using the waste heat of the device, and another part of the sodium salt wastewater is conveyed to a stripping tower (9) for separation of the organic phase; The stripping separation: the sodium salt wastewater falls from the upper part of the stripping tower (9), and contacts with the water vapor at the lower part of the stripping tower (9) in countercurrent for mass transfer and heat transfer. The organic phase and a small amount of water vapor are condensed into the stripping tower reflux tank through the first condenser (12) at the top of the tower. A part of the material is refluxed and recovered to the upper part of the stripping tower (9), and the reflux ratio is controlled at 1.4-1.

7. The other part is sent to the tail gas treatment device. The waste heat concentration: the dilute sodium salt wastewater from the bottom of the stripping tower (9) is fed into the lower part of the packing section of the waste heat concentration tower (15), and the second reboiler (16) is used for heating and evaporation.

9. The process for resource utilization of wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 8, characterized in that: In the step of neutralizing the waste heat, the absorption liquid undergoes a neutralization reaction in an alkaline environment with a pH value of 7-8, the reaction residence time is 20-30 minutes, and the reaction pressure of the acid-base adjustment preheating kettle (5) is 1-10 kPa (g).

10. The process for resource utilization of wastewater generated by oxidation of toluene to prepare benzyl alcohol according to claim 8, characterized in that: The stripping tower (9) is a normal pressure stripping tower (9), and the small molecule organic acid sodium salt solution in the bottom of the tower is heated to 100° C. by a first reboiler (10), and the heat source of the first reboiler (10) is 0.43 MPa (g) saturated steam.

Images