Method for absorbing ethyl acetate waste gas by ozone catalytic auxiliary alkali liquor multistage

Abstract

The application discloses a method for absorbing ethyl acetate waste gas by using ozone catalytic auxiliary alkaline solution in multiple stages, which uses n-stage absorption towers connected in series as a treatment device for continuously absorbing ethyl acetate waste gas, and a solid acid catalyst layer is arranged in the absorption tower; ethyl acetate waste gas is mixed with ozone dilution gas to form waste gas dilution gas, the waste gas dilution gas flows from the first-stage absorption tower to the n-stage absorption tower in a continuous feeding mode, and alkaline solution is used as absorption liquid and flows from the first-stage absorption tower to the n-stage absorption tower in a continuous feeding mode; the waste gas dilution gas and the alkaline solution are countercurrently contacted and reacted in each stage of the absorption tower, the ethyl acetate is hydrolyzed to generate ethanol and acetate under the catalysis of alkali, and the ethanol is converted into acetate by reaction. In the process, the ethyl acetate content can basically reach the standard discharge (<60mg / m 3 ) after the multiple-stage spray absorption, the generated waste liquid only contains a small amount of sodium hydroxide and high-concentration acetate, and the high-purity acetate can be recovered through a simple treatment technology.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment technology, specifically relating to a method for ozone catalytic-assisted alkaline solution multi-stage absorption of ethyl acetate waste gas. Background Technology

[0002] Coating is an important processing technology for altering and improving the surface properties of materials, and it is widely used in many industrial sectors such as specialty paper processing, printing, adhesives, and cosmetics. In coating industries such as paper processing, adhesives, and cosmetics, ethyl acetate is the most commonly used solvent. With increasingly stringent environmental protection requirements, the emission standards for ethyl acetate are becoming more stringent. For example, the Volatile Organic Compounds (VOCs) emission standard DB33 / 2146-2018 stipulates an emission standard of 60 mg / m³. 3 Therefore, it is imperative to purify and treat the low-concentration ethyl acetate waste gas in the coating industry.

[0003] Currently, the main methods for treating ethyl acetate in industry include activated carbon adsorption, catalytic combustion, photocatalysis, biological filtration, and liquid-phase absorption. Liquid-phase absorption primarily involves adding surfactants to increase the saturated absorption capacity of water and using chemical absorbents (alkaline solutions) to hydrolyze ethyl acetate for absorption. Patent CN112709998A utilizes two-stage catalytic combustion chambers, placing precious metal catalysts and ordinary metal catalysts respectively, to effectively treat ethyl acetate and other waste gases. Patent CN109731433A provides a method for recovering ethyl acetate combining activated carbon adsorption and rotary adsorption, increasing the adsorption rate of medium and high concentrations of ethyl acetate to 99.5%. Patent CN111111368A employs photocatalysis to remove ethyl acetate and other organic waste gases, and uses a two-stage heat exchange method to reduce the temperature and humidity of the organic waste gases, achieving harmless treatment of the organic waste gases. Patent CN108329208A discloses a method for absorbing ethyl acetate using a highly efficient and low-loss solvent (N-methylpyrrolidone, N,N-dimethylacetamide, 1,4-butyrolactone, dioctyl phthalate, methyl nylonate).

[0004] Catalytic combustion and RTO combustion methods are mostly used for high-concentration ethyl acetate waste gas. Biological methods have not been widely used due to their large footprint and high cost, and photocatalytic methods have low conversion rates. Considering the process safety and economy of treating large volumes of low-concentration ethyl acetate waste gas in paper processing, adhesives, cosmetic workshops, etc., alkaline absorption technology is widely used due to its low cost and high absorption rate. However, ethyl acetate waste gas cannot meet emission standards after alkaline absorption alone. This is because ethyl acetate hydrolyzes under alkaline conditions to produce ethanol and sodium acetate. Ethanol is easily volatile, and after a period of alkaline absorption, the ethanol emission in the tail gas will increase, resulting in excessive VOCs emissions. Therefore, using alkaline absorption alone cannot completely purify industrial VOCs waste gas from ethyl acetate.

[0005] To simultaneously purify ethanol waste gas generated from alkaline absorption, this invention discloses a method for multi-stage alkaline absorption of ethyl acetate waste gas catalyzed by ozone. When ethyl acetate waste gas molecules enter the aqueous phase, they undergo hydrolysis under the catalytic reaction of alkali (KOH and NaOH) to produce acetic acid and ethanol. Acetic acid reacts with alkali to form non-volatile sodium acetate or potassium acetate salts, while ethanol is further oxidized by ozone in the water under the action of a catalyst, converting it into acetic acid, which then reacts with alkali to produce sodium acetate or potassium acetate salts. This process can produce more economically beneficial byproducts—sodium acetate (CH3COONa) or potassium acetate (CH3COOK). These can be crystallized and recovered, achieving resource utilization in line with the national advocacy of a circular economy and sustainable development. Summary of the Invention

[0006] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a method for ozone catalytic-assisted alkaline solution multi-stage absorption of ethyl acetate waste gas.

[0007] The technical solution adopted in this invention is as follows:

[0008] The method for ozone catalytic-assisted multi-stage absorption of ethyl acetate waste gas using alkaline solution comprises n-stage absorption towers connected in series as a continuous treatment device for ethyl acetate waste gas absorption. Each absorption tower includes, from top to bottom, a wire mesh demister layer, a spray layer, a packing layer, a solid acid catalyst layer, and a liquid storage layer. The specific treatment method includes the following steps:

[0009] 1) The ethyl acetate waste gas is mixed with ozone dilution gas to form waste gas dilution gas. The waste gas dilution gas flows from the first-stage absorption tower to the nth-stage absorption tower in a continuous feeding manner. At the same time, alkaline solution is used as the absorbent and flows from the first-stage absorption tower to the nth-stage absorption tower in a continuous feeding manner.

[0010] Each stage of the absorption tower includes the following process: the absorbent liquid is sprayed down from the spray layer at the top of the absorption tower, and the waste gas dilution gas is introduced from the gas inlet at the bottom of the absorption tower. The waste gas dilution gas rises continuously in the absorption tower and comes into full contact with the sprayed alkaline liquid through the packing layer. Ethyl acetate undergoes hydrolysis under alkaline catalysis to produce ethanol and acetate. A portion of the ethanol is oxidized to acetic acid by ozone. The unreacted ethanol flows down with the absorbent liquid to the solid acid catalyst layer. Under the solid acid catalysis, the ethanol is oxidized to acetic acid by ozone. Acetic acid reacts with the alkali to produce acetate. Finally, the absorbent liquid flows down to the storage layer.

[0011] The waste gas dilution gas discharged from the top outlet of the previous absorption tower is introduced into the bottom inlet of the adjacent next absorption tower, and the absorbent liquid in the bottom storage layer of the previous absorption tower is introduced into the spray layer inside the top of the adjacent next absorption tower for spraying.

[0012] 2) The exhaust gas discharged from the top outlet of the nth stage absorption tower meets the emission standards. The absorbent liquid in the bottom storage layer of the nth stage absorption tower, after n-stage circulation absorption, is discharged outside the tower. The solute in the absorbent liquid is mainly sodium acetate and a small amount of alkali. After subsequent treatment and purification, it can produce high-purity acetate, a more economically valuable by-product.

[0013] Furthermore, the reaction temperature in each stage of the absorption tower is controlled at 30-50℃.

[0014] Furthermore, the solid acid catalyst filling the solid acid catalyst layer is a metal oxide supported on an alumina support, namely an ABOx / Al2O3 catalyst, where AB is Mn. 2+ Cu 2+ Fe 3+ One or two of them, with ABOx load ranging from 5% to 20%.

[0015] Furthermore, the filler layer is filled with one or more of the following: wire mesh, ceramic rings, glass, PP multifaceted hollow spheres, Pall rings, stepped rings, and plastic flower ring fillers.

[0016] Furthermore, the freshly introduced alkaline solution is a NaOH aqueous solution with a mass concentration of 1-4%, and the corresponding acetate is sodium acetate.

[0017] Furthermore, the packing layer is 1000-4000mm high, and the wire mesh demister layer is 100-500mm high; the absorption tower can be a spray tower, a packed tower, a bubble tower, or other high-efficiency absorption towers, and multi-stage absorption can be carried out by combining multiple towers in series.

[0018] Furthermore, the filler layer is filled with filler particles with a particle size of 10-40 mm, and the solid acid catalyst layer is filled with solid acid catalyst particles with a particle size of 50-200 mm, preferably 80-120 mm.

[0019] Furthermore, the ozone is generated by an oxygen production system or liquid oxygen via an ozone generator. The ozone is then diluted with air and mixed with ethyl acetate waste gas. The concentration of ethyl acetate waste gas in the mixed gas is 5000 mg / m³. 3 The ozone concentration is 100–200 ppm.

[0020] Furthermore, the ethyl acetate content in the exhaust gas discharged from the top outlet of the nth stage absorption tower is <60 mg / m³. 3 .

[0021] The method employs n absorption towers, sequentially designated as a first-stage absorption tower, a second-stage absorption tower, ..., an nth-stage absorption tower, where n is an integer from 2 to 6. Each of the n absorption towers comprises, from top to bottom, a wire mesh demister layer, a spray layer, a packing layer, a solid acid catalyst layer, and a storage layer. The solid acid catalyst layer is used to fill with solid acid catalyst, and above it is the packing layer, which is used to fill with packing material. An air inlet is located at the bottom of the tower, below the solid acid catalyst layer, and an air outlet is located at the top of the tower.

[0022] Each of the first n-1 absorption spray towers is equipped with a circulating water pump. The inlet of each circulating water pump is connected to a liquid inlet pipe. The end of the liquid inlet pipe furthest from the pump inlet is connected to the bottom of the storage layer of the preceding absorption tower near the bottom. The outlet of each circulating water pump is connected via a pipeline to a spray head in the spray layer of the subsequent absorption tower. The nth-stage absorption tower has an overflow port at the top of its storage layer, which connects to an overflow pool and a storage tank. The first-stage absorption tower has a replenishment port at the top of its storage layer.

[0023] The gas outlet of the first-stage absorption spray tower is connected to the air inlet of the second-stage absorption spray tower via a pipeline. The gas outlet of the second-stage absorption spray tower is connected to the air inlet of the third-stage absorption spray tower via a pipeline, and so on. The gas outlet of the (n-1)th-stage absorption spray tower is connected to the air inlet of the nth-stage absorption spray tower via a pipeline, and the gas outlet of the nth-stage absorption spray tower is discharged into the atmosphere.

[0024] By adopting the technical solution of the present invention, the following technical effects will be achieved:

[0025] 1. In the process of this invention, after multi-stage spray absorption, the ethyl acetate content can basically meet the discharge standards (<60mg / m³). 3The waste liquid produced contains only a small amount of sodium hydroxide and a high concentration of sodium acetate. High-purity sodium acetate can be recovered through simple treatment technology.

[0026] 2. The process technology of this invention is simple to operate, has low overall operating costs, and high safety, making it highly suitable for the treatment of ethyl acetate waste gas in various large and small coating industries. Furthermore, it produces no waste liquid discharge, aligning with the national advocacy of a circular economy and sustainable development.

[0027] 3. In this invention, the most critical factor affecting the efficiency of the absorption tower is the concentration of sodium hydroxide in the solution. Increasing the concentration of the alkaline solution is beneficial to the initial absorption rate of ethyl acetate. However, since ethyl acetate is not easily soluble in water, its reaction rate is also controlled by the mass transfer rate of ethyl acetate from the gas phase to the liquid phase. Therefore, the concentration of the alkaline solution should be controlled between 1% and 4%. Simultaneously, utilizing the property that ethanol is easily oxidized by ozone, O3 in the solid acid catalyst layer at the bottom of the contact tower will decompose under the action of the catalyst to produce more reactive free radicals, especially hydroxyl radicals (·OH). Through this characteristic, the ethanol produced by hydrolysis can be more thoroughly oxidized to acetic acid, which then reacts with the alkaline solution to form the salt sodium acetate (CH3COONa), finally yielding a high-concentration sodium acetate solution. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the ozone-catalyzed assisted alkaline solution multi-stage absorption of ethyl acetate waste gas according to the present invention.

[0029] Figure 1 In the middle: 1-Ozone generator; 2-Dilution fan; 3-First-stage absorption tower; 4-Second-stage absorption tower; 5-Third-stage absorption tower; 6-Fourth-stage absorption tower; 7-Waste liquid overflow pool; 8-Waste liquid storage tank. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1:

[0032] See Figure 1 The multi-stage catalytic coupling absorption process technology provided by this invention specifically employs a four-stage absorption process, and the device used includes four absorption towers (namely...). Figure 1 The system includes a first-stage absorption tower 3, a second-stage absorption tower 4, a third-stage absorption tower 5, and a fourth-stage absorption tower 6; three circulating water pumps; a waste liquid overflow pool 7 and a waste liquid pump; and a waste liquid storage tank 8.

[0033] The four absorption towers have identical structures, each with an air inlet at the bottom. The tower body consists of a packing layer (filled with 25mm PP multifaceted hollow spheres) and a solid acid catalyst layer (filled with 100mm MnO2 / Al2O3 spherical solid acid catalyst with a 5% MnO2 loading). The air inlet is located below the solid acid catalyst layer. Six water spray heads are installed above the packing layer, and a 200mm wire mesh demister layer is installed above the water spray heads. An air outlet is located at the top of the tower. Each absorption tower has a 4m... 3 The first three absorption towers each have a storage layer. A circulating water pump is installed next to the storage layer of each absorption tower. The inlet of each pump is connected to an inlet pipe. The end of the inlet pipe, away from the pump inlet, connects to the bottom of the storage layer of the preceding absorption tower near the bottom. The outlet of each pump is connected via a pipeline to a spray head in the spray layer of the following absorption tower. The fourth absorption tower has an overflow port on the upper part of one side of its casing. The overflow port connects to an overflow pool and ultimately to a storage tank. The first absorption tower has a replenishment port on the upper part of its storage layer.

[0034] The specific treatment process for multi-stage absorption of ethyl acetate waste gas in this embodiment is as follows:

[0035] (1) Ethyl acetate waste gas absorption process:

[0036] a. Preparation: Use fresh alkaline solution (i.e., NaOH aqueous solution) with a feed flow rate of 1L / min and a mass concentration of 4% as the absorbent and feed it continuously from the first-stage absorption tower to the fourth-stage absorption tower.

[0037] b. High-concentration ethyl acetate waste gas is extracted from the vacuum pump, and the ozone is diluted by the dilution fan. The total discharge volume of the two mixtures is 8000 m³. 3 / h, the ethyl acetate concentration after mixing is 5000 mg / m³. 3 The ozone concentration is 150 ppm. The gas enters the first-stage absorption tower, passes through the packing layer, and comes into full contact with the alkaline solution. Ethyl acetate is continuously hydrolyzed, and ozone reacts with the ethanol produced after hydrolysis until a gas-liquid equilibrium is reached between the gaseous ethyl acetate and O3 and the liquid ethyl acetate and O3. The waste gas then enters the second, third, and fourth-stage absorption towers. The absorption efficiency of each stage is greater than 90%. After multi-stage absorption in series, the absorption efficiency of ethyl acetate is >99.9999%, and the utilization rate of O3 is >99.99%.

[0038] (2) Absorption process of the absorbent: The most critical factor affecting the efficiency of the absorption tower is the concentration of the alkaline solution in the solution. Increasing the concentration of the alkaline solution is beneficial to the initial absorption rate of ethyl acetate. However, since ethyl acetate is not easily soluble in water, its reaction rate is also controlled by the mass transfer rate of ethyl acetate from the gas phase to the liquid phase. Therefore, the concentration of the alkaline solution is controlled. At the same time, the property of ethanol being easily oxidized by ozone is utilized, especially when O3 re-contacts the solid catalyst layer at the bottom of the tower. Under the action of the catalyst, it will decompose and produce more active free radicals with stronger oxidizing power, especially hydroxyl radicals ·OH. Through this property, the ethanol produced by hydrolysis can be oxidized to acetic acid, and react with the alkaline solution to form the salt - sodium acetate (CH3COONa), finally obtaining high-concentration sodium acetate. The specific chemical reaction is as follows:

[0039]

[0040] (3) Waste liquid recycling process: During continuous operation, high-concentration sodium acetate waste liquid overflows into the overflow pool through the overflow pipe next to the four-stage tower. The high-concentration sodium acetate waste liquid can be sold as a commodity and reused in other industries after simple treatment.

[0041] Operational Results: The device of this invention treats ethyl acetate waste gas according to the above process (ozone dilution gas is mixed with high-concentration ethyl acetate waste gas, and the flow rate of the mixed waste gas is 8000 m³ / h). 3 / h, ethyl acetate concentration 5000 mg / m 3 The ozone concentration was 150 ppm. The designed tower diameter was 800 mm, the tower height was 4000 mm, the catalyst was MnO2 / Al2O3 spheres (MnO2 loading was 5%), the packing was 25 mm PP multifaceted hollow spheres, and a fresh alkaline solution (i.e., NaOH aqueous solution) with a mass concentration of 4% was used as the absorbent with a feed flow rate of 1 L / min. After stable operation under the above conditions, the absorption efficiencies of the first, second, third, and fourth stage absorption towers for ethyl acetate were 90%, 91%, 94%, and 92%, respectively. After four stages of treatment, the concentration of ethyl acetate in the tail gas was detected and the emission concentration was 20 mg / m³. 3 The levels of ozone and ethanol were almost zero when tested.

[0042] After purification, the entire ethyl acetate waste gas system can meet emission standards. Ethyl acetate can be completely recycled by converting it into sodium acetate, without any secondary pollution such as "three wastes".

[0043] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for ozone-catalyzed, alkaline-assisted multi-stage absorption of ethyl acetate waste gas, characterized in that... A series of n absorption towers connected in series are used as a continuous treatment device for ethyl acetate waste gas. Each absorption tower includes, from top to bottom, a wire mesh demister layer, a spray layer, a packing layer, a solid acid catalyst layer, and a liquid storage layer. The specific treatment method includes the following steps: 1) The ethyl acetate waste gas is mixed with ozone dilution gas to form waste gas dilution gas. The waste gas dilution gas flows from the first-stage absorption tower to the nth-stage absorption tower in a continuous feeding manner. At the same time, alkaline solution is used as the absorbent and flows from the first-stage absorption tower to the nth-stage absorption tower in a continuous feeding manner. Each stage of the absorption tower includes the following process: the absorbent liquid is sprayed down from the spray layer at the top of the absorption tower, and the waste gas dilution gas is introduced from the gas inlet at the bottom of the absorption tower. The waste gas dilution gas rises continuously in the absorption tower and comes into full contact with the sprayed alkaline liquid through the packing layer. Ethyl acetate undergoes hydrolysis under alkaline catalysis to produce ethanol and acetate. A portion of the ethanol is oxidized to acetic acid by ozone. The unreacted ethanol flows down with the absorbent liquid to the solid acid catalyst layer. Under the solid acid catalysis, the ethanol is oxidized to acetic acid by ozone. Acetic acid reacts with the alkali to produce acetate. Finally, the absorbent liquid flows down to the storage layer. The waste gas dilution gas discharged from the top outlet of the previous absorption tower is introduced into the bottom inlet of the adjacent next absorption tower, and the absorbent liquid in the bottom storage layer of the previous absorption tower is introduced into the spray layer inside the top of the adjacent next absorption tower for spraying. 2) The exhaust gas discharged from the top outlet of the nth stage absorption tower meets the emission standards. The absorbent liquid in the bottom storage layer of the nth stage absorption tower after n-stage circulation absorption is discharged outside the tower. The solute in the absorbent liquid is sodium acetate and a small amount of alkali. After subsequent treatment and purification, it can produce high-purity acetate, a more economically valuable by-product. The solid acid catalyst layer is filled with a metal oxide supported on an alumina support, namely an ABOx / Al2O3 catalyst, where AB represents Mn. 2+ Cu 2+ Fe 3+ One or two of them, with ABOx load ranging from 5% to 20%; The freshly introduced alkaline solution is a 1-4% (w / w) NaOH aqueous solution, and the corresponding acetate is sodium acetate. The n is an integer from 2 to 6; The ozone is generated by an oxygen production system or liquid oxygen via an ozone generator. The ozone is then diluted with air and mixed with ethyl acetate waste gas. The concentration of ethyl acetate waste gas in the mixed gas is 5000 mg / m³. 3 The ozone concentration is 100–200 ppm.

2. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 1, characterized in that... The reaction temperature in each stage of the absorption tower is controlled at 30-50℃.

3. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 1, characterized in that... The filler layer is filled with one or more of the following: wire mesh, ceramic rings, glass, PP multifaceted hollow spheres, Pall rings, stepped rings, and plastic flower ring fillers.

4. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 1, characterized in that... The packing layer is 1000-4000mm high, and the absorption tower is a spray tower, a packed tower or a bubble tower, which is used for multi-stage absorption in the form of multiple towers connected in series.

5. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 1, characterized in that... The filler layer is filled with filler particles with a particle size of 10~40mm, and the solid acid catalyst layer is filled with solid acid catalyst particles with a particle size of 50~200mm.

6. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 5, characterized in that... The solid acid catalyst filling layer has a particle size of 80~120mm.

7. The method for ozone-catalyzed assisted alkaline multi-stage absorption of ethyl acetate waste gas as described in claim 1, characterized in that... The ethyl acetate content in the exhaust gas discharged from the top outlet of the nth stage absorption tower is <60 mg / m³. 3 .

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