A method for treating ethylene oil-containing waste lye

Abstract

The application discloses a treatment method of ethylene oil-containing waste lye, which comprises the following steps: firstly, adding an acid to the waste lye for partial neutralization, and controlling the pH value of the waste lye to be 8-9; then, adding a demulsifier to the waste lye for demulsification; and finally, removing the oil phase from the demulsified waste lye by using an extractant, and performing post-treatment on the raffinate. The waste lye treatment method is simple and easy to implement, a small amount of demulsifier can be added to demulsify the emulsified butter, the treatment effect is good, the waste lye has a low COD content, the economic efficiency is high, and the demulsified butter can be removed by extraction, and the process is simple and easy to operate.

Description

Technical Field

[0001] This invention relates to the field of waste liquid treatment, and specifically to a method for treating ethylene-containing oily alkaline waste liquid. Background Technology

[0002] Ethylene waste alkaline solution contains a high concentration of alkali (approximately 1-3 wt%), salts such as Na₂S and Na₂CO₃ (approximately 8-12 wt%), and a large amount of butter, making it a high-salt, high-oil wastewater. The butter is a mixture of aldehyde and ketone components from cracked gas undergoing condensation under alkaline conditions, as well as the condensation of butadiene, cyclopentadiene, and other dienes, and the condensation of heavy hydrocarbons. It has a relatively large molecular weight and high density, and is present in large quantities in the alkaline solution, with concentrations reaching 20,000-30,000 ppm or even higher. Even after prolonged settling and stratification, the oil content remains above 1500 ppm, contributing significantly to the COD of the discharged wastewater.

[0003] The ethylene industry has developed various methods for treating waste alkaline solutions, including persulfate acidification-stripping, CO2 neutralization, and biological treatment. However, ethylene waste alkaline solutions contain large amounts of Na2S, Na2CO3, NaOH, and grease, making it difficult to treat them completely using a single method. The industry typically uses static separation to remove some of the grease and wet oxidation to remove sulfur. 2- The ions are then neutralized to remove NaOH, turning the waste alkaline solution into saline wastewater for further treatment. During this process, the oil, water, and salt in the waste alkaline solution form an emulsion that is difficult to separate. Therefore, even after settling and separation, the oil content in the waste alkaline solution remains too high. Wet oxidation cannot completely oxidize the oil in the alkaline solution, leading to excessive oil content and COD levels in the neutralized wastewater, which adversely affects downstream water treatment systems.

[0004] Patent CN102424498A discloses a method for the comprehensive recycling of ethylene waste alkali solution. This method first extracts oil from the waste alkali using an extractant, then further removes oily suspended solids from the waste alkali solution using a hydrophobic gravity oil removal tank. An indirect steam heating stripping method is then used to distill off dissolved hydrocarbons in the waste alkali solution, crystallizing out Na2S. Lime is then added to remove Na2CO3. This method can also treat ethylene waste alkali solution, but its disadvantages include a long process, high investment costs, and the generation of H2S and some light hydrocarbon waste gas during evaporation, as well as solid waste residue requiring downstream treatment.

[0005] Existing technologies also employ chemical degreasing methods to remove oil from waste alkaline solutions. For example, CN100348512C discloses a process for treating ethylene waste alkaline solutions. This process involves adding metal ion flocculants to the waste alkaline solution to flocculate the oil, followed by centrifugal separation to remove the oil phase. However, using such metal salt flocculants to treat waste alkaline solutions generates solid waste during the process, increasing treatment costs and complexity. Other literature mentions adding organic polymeric flocculants, utilizing the adsorption of organic functional groups onto droplets to achieve oil-water separation. This method typically requires a large amount of flocculant, and the demulsification effect is often unsatisfactory, also generating solid waste.

[0006] How to create a simple, easy-to-operate waste alkali solution that can thoroughly remove oil from waste alkali solutions and achieve good treatment results is a problem that urgently needs to be solved in the industry. Summary of the Invention

[0007] To address the above problems, this invention provides a method for treating oily alkali waste liquid from ethylene, comprising the following steps:

[0008] (1) First, add acid to the waste alkaline solution to neutralize it and control its pH value to 8-9;

[0009] (2) Add a demulsifier to the waste alkaline solution to demulsify;

[0010] (3) The waste alkaline solution after demulsification is extracted with an extractant to remove the oil phase, and the raffinate is then post-treated.

[0011] Preferably, in step (3), the raffinate can be allowed to stand and separate into layers to remove the remaining oil phase before oxidation treatment, which can be carried out using a low-pressure wet waste alkali oxidation system.

[0012] Preferably, in step (1), the acids include, but are not limited to, sulfuric acid and hydrochloric acid.

[0013] Preferably, in step (2), the demulsifier is one or more of a polyacrylamide cationic demulsifier or a polyethanolamine demulsifier.

[0014] Preferably, the demulsifier is produced using a static mixer to disperse the demulsifier in the waste alkaline solution as particles smaller than 1 mm, thereby maximizing the mixing and dispersion effect. The demulsifier is fully in contact with the oil phase in the alkaline solution, and the amount of demulsifier added is such that the mass concentration of the demulsifier in the neutralized waste alkaline solution is 10-500 ppm.

[0015] Preferably, the temperature of the waste alkali solution in step (2) is 20-40℃.

[0016] Preferably, the extractant comprises C6-C8 hydrocarbons, and may be one or more of benzene, toluene, xylene, ethylbenzene, etc., with hydrogenated gasoline being the preferred extractant;

[0017] Preferably, the mass ratio of the extractant to the waste alkali solution is between 1:30 and 1:10.

[0018] The neutralized waste alkali solution and the demulsifier enter the extraction tower together. The extractant enters from the bottom, and the demulsifier and the neutralized waste alkali solution are mixed by a static mixer and then enter from the top of the tower. The extraction can be carried out under normal pressure, and the settling time is about 1-1.5 hours. The extracted waste gasoline is discharged from the top of the tower, and the waste alkali solution is discharged from the bottom of the tower.

[0019] The applicant discovered through research that directly adding demulsifiers to waste alkali solution results in poor demulsification due to the high concentration of alkali in the system. Even with a large amount of demulsifier, partial emulsification between the butter and waste alkali solution occurs, affecting butter separation. Adding large amounts of demulsifier can also cause the oil phase in the alkali solution to agglomerate, posing a risk of pipeline blockage in industrial applications. However, when the pH of the waste alkali solution is adjusted to the range of 8-9, its properties change. Because most hydroxide ions are neutralized, the viscosity of the waste alkali solution and the interfacial tension between the alkali solution and the butter change, making it easier for the oil phase in the alkali solution to aggregate and separate from the aqueous phase, thus facilitating separation. The demulsifier provided in this invention can more easily disrupt the emulsion state between the waste alkali solution and the butter under these conditions, resulting in more thorough separation and better demulsification. However, when the pH is lowered to 8, especially to 7.5, acidic conditions may occur in parts of the alkali solution during the neutralization process, causing hydrogen and sulfur ions to escape in the form of hydrogen sulfide, posing a risk of toxic gas leakage.

[0020] To further reduce the oil content, extraction is used to remove the butter separated after demulsification and any remaining butter droplets from the alkali solution. Through these three steps, the oil content of the waste alkali solution can be reduced to below 100 ppm, only about 20% of that achieved with traditional treatment methods.

[0021] This invention discloses a method for treating oily alkali waste liquid from ethylene plants. Using pre-neutralization, demulsification, and extraction techniques, most of the heavy oil in the alkali liquid is removed. The remaining small amount of oily substances are then treated using conventional wet alkali oxidation technology. Under low pressure, the COD of the discharged alkali waste liquid can be reduced to below 500 ppm, or even below 300 ppm, improving the COD reduction effect. The process does not generate waste gas or residue, reducing the investment cost of the alkali oxidation unit and increasing the stability and operating cycle of the entire alkali treatment system. It can extend the operating cycle of traditional ethylene plant alkali oxidation systems by 2-4 times or more.

[0022] This application also provides a method for neutralizing waste alkali solution. First, a dilute acid solution is prepared, which can be prepared by mixing demineralized water with a strong acid to achieve an acid concentration of 10%-40% by mass. The lower the acid concentration, the more stable the pH control. Then, a dilute alkali solution is prepared by mixing demineralized water with alkali to achieve a certain concentration. The alkali concentration is generally below 10% by mass; if the concentration is too high, the pH value will fluctuate greatly. The prepared dilute acid is used to titrate the waste alkali solution in a neutralization tank, and the prepared dilute alkali is used to fine-tune the pH at the end of the neutralization tank to prevent over-neutralization.

[0023] The neutralization tank can be divided into multiple zones by baffles. The first few zones are circulated with dilute acid solution to neutralize the waste alkali solution. The last zone can be connected to both dilute acid and dilute alkali solutions for fine-tuning the pH value of the waste alkali solution. The acid and alkali flow rates are automatically adjusted according to the pH value and flow control. Preferably, the neutralization tank is equipped with two baffles to divide it into three parts. The first part neutralizes and removes most of the alkali solution, with feedforward control based on the alkali concentration, flow rate, and sulfuric acid concentration. The second part neutralizes and controls the pH value to around 8-10. The third part fine-tunes the pH value, controlling it between 8-9. Each part is equipped with a stirring device. The first and second parts together account for 30-50% of the total volume of the neutralization tank, and the third part accounts for 50-70% of the total volume, which is beneficial for stabilizing the pH value of the waste alkali solution after delivery.

[0024] The waste alkali liquid treatment method of the present invention is simple and easy to implement. A small amount of demulsifier can be added to demulsify the emulsified butter. It has good effect, low COD content of waste alkali liquid, and high economic efficiency. The butter after demulsification can be removed by extraction. The process is simple and easy to operate. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the ethylene oily waste alkaline solution treatment technology of the present invention.

[0026] Among them, 1 is the acid mixing tank, 2 is the alkali mixing tank, 3 is the neutralization tank, 4 is the demulsifier tank, and 5 is the extraction tower. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0028] like Figure 1 As shown, a treatment device for ethylene oily waste alkaline solution includes: two acid mixing tanks, one alkali mixing tank, one neutralization tank, one extraction tower, one demulsifier tank, and two demulsifier metering pumps.

[0029] The specific connection method is as follows: The acid mixing tank and the alkali mixing tank are respectively connected to the neutralization tank. The neutralization tank is equipped with two baffles, dividing it into three parts. The first and second parts each account for 20% of the neutralization tank's volume, and the third part accounts for 60%. The pipelines of the acid mixing tank connect to the first, second, and third parts of the neutralization tank, respectively, and the pipelines of the alkali mixing tank connect to the third part of the neutralization tank. Each part of the neutralization tank is equipped with a stirring device. The acid mixing tank contains a mixture of demineralized water and concentrated sulfuric acid, with a sulfuric acid mass concentration of 20%. The alkali mixing tank contains a mixture of demineralized water and a strong alkali, sodium hydroxide, with a sodium hydroxide mass concentration of 5%.

[0030] The waste alkali solution is fed into a neutralization tank, passing through the first, second, and third sections in sequence. After neutralization, it is discharged from the neutralization tank at a temperature of approximately 25°C. The demulsifier in the demulsifier tank is pumped into the extraction tower. Before entering the extraction tower, the neutralized waste alkali solution and the demulsifier are mixed in a static mixer. The mixed solution of the neutralized waste alkali solution and the demulsifier is fed from the top of the extraction tower, while the extractant is fed from the bottom. The two react countercurrently to extract the solution. The top pipeline of the extraction tower is the extractant outlet, and the bottom of the tower is the waste alkali solution outlet.

[0031] The ethylene plant waste alkali solution used in this embodiment of the invention has a production capacity of 3.5 t / h. Before treatment, the oil content of the waste alkali solution when it exits the alkali washing tower is about 2000-3000 ppm, and the highest concentration has reached 20000 ppm. After being left to stand in the waste alkali storage tank (the standing time is more than 24 hours), the oil content is still as high as 1500-2000 ppm.

[0032] Example 1

[0033] The apparatus described in this application is used to treat ethylene-containing oily waste alkaline solution. After neutralization in a neutralization tank, the pH value of the waste alkaline solution is 9. A cationic polyacrylamide demulsifier provided by Nalco is added to the demulsifier tank. The amount of demulsifier added is such that the mass concentration of the demulsifier in the neutralized waste alkaline solution is 500 ppm. Hydrogenated gasoline is used for extraction. The mass flow rate ratio of the extractant to the mass flow rate of the waste alkaline solution in the extraction tower is 1:10. The residence time of the extractant is 1 hour. After treatment, the oil content of the waste alkaline solution is reduced to about 100 ppm.

[0034] Example 2

[0035] The waste alkali solution was treated using the same method as in Example 1, with the main difference being that a polyethanolamine demulsifier from Shandong Huayou Company was used, with a demulsifier mass concentration of 200 ppm. The ratio of the amount of extractant added to the mass of the waste alkali solution was 1:20, and the oil content of the alkali solution after treatment was 150 ppm.

[0036] Example 3

[0037] The waste alkali solution was treated using the same method as in Example 1, with the main difference being that the demulsifier had a mass concentration of 50 ppm, the ratio of the amount of extractant added to the mass of the waste alkali solution was 1:30, and the oil content of the alkali solution after treatment was 250 ppm.

[0038] Comparative Example 1

[0039] The waste alkali solution was not neutralized or demulsified before being directly extracted into the extraction tower. The remaining extraction conditions were the same as in Example 1. The oil content of the waste alkali solution after extraction was about 800 ppm.

[0040] Comparative Example 2

[0041] The waste alkali solution was not neutralized, and a demulsifier was directly added. The other conditions were the same as in Example 3. The oil content of the waste alkali solution did not change significantly and remained at around 1500 ppm, which was basically the same as the oil content of the untreated original alkali solution. The high concentration of demulsifier was continued to be added. When the concentration of demulsifier increased to around 800 ppm, the high concentration of demulsifier caused the large molecular oil phase in the alkali solution to aggregate, and flocculent matter began to appear in the waste alkali solution. In this example, the flocculent matter was in an aggregated form and floated on the water surface.

[0042] As can be seen from Comparative Example 2, compared with the technical solution of this application, the neutralization demulsification extraction process adopted by this patent only controls the concentration of the demulsifier to below 500ppm, which can demulsify the alkali solution without causing the butter in the alkali solution to agglomerate, making the method more economical and feasible.

Claims

1. A method for treating oily alkaline waste ethylene solution, characterized in that, Includes the following steps: (1) First, add acid to the waste alkaline solution to neutralize it and control its pH value to 9; (2) Add a demulsifier to the waste alkaline solution to demulsify; the demulsifier is one or more of a polyacrylamide cationic demulsifier or a polyethanolamine demulsifier; (3) The waste alkaline solution after demulsification is extracted with an extractant to remove the oil phase, and the raffinate is then post-treated.

2. The processing method according to claim 1, characterized in that, In step (3), the raffinate is first allowed to stand and separate into layers to remove the remaining oil phase, and then it is oxidized using a low-pressure wet alkali oxidation system.

3. The processing method according to claim 1 or 2, characterized in that, In step (1), the acids include, but are not limited to, sulfuric acid and hydrochloric acid.

4. The processing method according to claim 1, characterized in that, The amount of demulsifier added is such that the mass concentration of the demulsifier in the neutralized waste alkaline solution is 10-500 ppm.

5. The processing method according to claim 1, characterized in that, The temperature of the waste alkali solution in step (2) is 20-40℃.

6. The processing method according to claim 1, characterized in that, The extractant comprises C6-C8 hydrocarbons.

7. The processing method according to claim 6, characterized in that, The extractant is one or more of benzene, toluene, xylene, and ethylbenzene.

8. The processing method according to claim 1, characterized in that, The extractant is hydrogenated gasoline.

9. The processing method according to claim 1, characterized in that, The ratio of the amount of extractant added to the mass of waste alkali solution is 1:30-1:

10.

10. The processing method according to claim 1, characterized in that, In step (1), the neutralization method of the waste alkali solution is as follows: first, a dilute acid solution is prepared, then a dilute alkali solution is prepared. The neutralization tank is divided into multiple areas by baffles. The first few areas are circulated with dilute acid solution for neutralizing the waste alkali solution. The last area can be connected to dilute acid solution and dilute alkali solution respectively for fine-tuning the pH value of the waste alkali solution.

11. The processing method according to claim 10, characterized in that, In step (1), the neutralization tank is divided into three parts by two baffles. The first part neutralizes and removes most of the alkali solution. Feedforward control is performed based on the concentration and flow rate of the alkali solution and the concentration of sulfuric acid. The second part is set to control the pH value at 8-10. The third part is fine-tuned and controls the pH value at 9. Each part is equipped with a stirring device. The first and second parts together account for 30-50% of the total volume of the neutralization tank, and the third part accounts for 50-70% of the volume of the neutralization tank.

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