A method for the dealkylation of ethylene oxide by absorption in water

Abstract

This invention discloses a method for removing formaldehyde from ethylene oxide-rich absorbent water, belonging to the field of chemical production technology. Ethylene oxide crude gas, after being cooled by a cooler, enters the quenching section at the bottom of an ethylene oxide absorption tower. The rich absorbent liquid pipeline at the bottom of the ethylene oxide absorption tower is connected to the inlet of a circulating pump, and the sodium hydroxide alkaline solution pipeline is connected to the rich absorbent liquid pipeline. The outlet of the circulating pump is connected to a tubular reactor via a delivery pipeline. The formaldehyde removal agent in the formaldehyde removal preparation tank is sent to the delivery pipeline via a formaldehyde removal agent metering pump and enters the tubular reactor for formaldehyde removal reaction. The reacted rich absorbent liquid is sent to the inlet of the quenching section cooler through the first outlet pipeline of the tubular reactor. After cooling in the quenching section cooler, it is sent to the ethylene oxide absorption tower as circulating quenching liquid through the second outlet pipeline. An online analyzer is installed on the outlet pipeline of the quenching section cooler. By adding formaldehyde removal agent and utilizing a chemical reaction, the formaldehyde content in the ethylene oxide-rich absorbent water is reduced, thereby improving the purity of the ethylene oxide product.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, specifically relating to a method for removing formaldehyde from ethylene oxide using water-rich absorption. Background Technology

[0002] Ethylene oxide, also known as ethylene oxide, is the second largest downstream product of ethylene after various types of polyethylene. It is also an important organic chemical raw material and intermediate. It can be used to produce ethylene glycol, ethanolamine, nonionic surfactants and polyether polyols. The wide application of ethylene oxide makes it an important support for many industries such as chemical, medical, energy and agriculture, and plays an irreplaceable role in promoting industrial upgrading and ensuring social needs.

[0003] The main method for producing ethylene oxide in industry is the direct oxidation of ethylene. The best catalyst for the direct oxidation of ethylene to produce ethylene oxide is a silver catalyst. Generally, the internationally leading Shell technology is used. Ethylene and oxygen undergo oxidation reaction in a tubular fixed-bed reactor containing a silver catalyst, with methane acting as a stabilizer for the ethylene oxide reaction system.

[0004] The direct oxidation of ethylene inevitably involves side reactions, producing trace amounts of formaldehyde and acetaldehyde. With the expansion and upgrading of ethylene oxide plants and the increase in load, the total amount of formaldehyde and acetaldehyde also increases. The current national standard for industrial ethylene oxide, GB / T 13098-2006, specifies that the superior grade of industrial ethylene oxide has an ethylene oxide mass fraction of ≥99.95% and an acetaldehyde mass fraction of ≤0.003%. During the production process, aldehydes are not easily separated from ethylene oxide and accumulate continuously in the refining system, resulting in seriously excessive aldehyde content, which directly affects the purity of ethylene oxide products.

[0005] The invention patent with announcement number CN103275037B discloses a method for removing aldehydes from ethylene oxide circulating water. In this method, ethylene oxide-rich circulating water is injected from the top of a stripping tower and heated by a steam reboiler, causing the ethylene oxide to evaporate from the water in gaseous form and then discharged from the top of the stripping tower. The remaining circulating water containing aldehydes is pumped to the outside of the stripping tower by a bottom pump. This method requires the addition of stripping tower equipment, which increases the investment cost and energy consumption. Furthermore, the high-temperature stripping separation effect is not good, and some ethylene oxide may be lost.

[0006] The utility model patent with publication number CN222956174U discloses an ethylene oxide absorption and formaldehyde removal system. In this system, sodium bisulfite is used as an external formaldehyde removal agent, which can effectively reduce the formaldehyde content in lean absorption water. Sodium bisulfite will react with sodium hydroxide, consuming the amount of sodium hydroxide and reducing the pH of the ethylene oxide absorption tower. At the same time, due to the salting-out effect, it will increase the risk of blockage in the salt discharge pipeline of the quench flash evaporation tower bottom, affecting the operation of the device. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a method for removing formaldehyde from ethylene oxide-rich absorbent water. By adding a formaldehyde removal agent and utilizing a chemical reaction, the formaldehyde content in the ethylene oxide-rich absorbent water is reduced, thereby improving the purity of the ethylene oxide product.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for removing formaldehyde from ethylene oxide rich in absorbent water, comprising the following steps: ethylene oxide crude gas transported by the ethylene oxide crude gas inlet pipeline is cooled by a cooler and then enters the quenching section at the bottom of the ethylene oxide absorption tower, where formaldehyde, organic acid compounds and monochloroethane decomposition products are neutralized by circulating quenching liquid in the quenching section.

[0009] The bottom of the ethylene oxide absorption tower is connected to the rich absorbent pipeline and the inlet of the circulating pump. The sodium hydroxide alkali solution pipeline is connected to the rich absorbent pipeline. The outlet of the circulating pump is connected to the tubular reactor via a delivery pipeline. The formaldehyde removal agent in the formaldehyde removal preparation tank is sent to the delivery pipeline via a formaldehyde removal agent metering pump and enters the tubular reactor for formaldehyde removal reaction. The rich absorbent after reaction is sent to the inlet of the quench cooler through the first outlet pipeline of the tubular reactor. After being cooled by the quench cooler, it is sent to the ethylene oxide absorption tower as circulating quench liquid through the second outlet pipeline. An online analyzer is installed on the outlet pipeline of the quench cooler.

[0010] Further: the formaldehyde removal agent is selected from one or more of ethanolamine, hydrazine hydrate, cyclohexylamine, and ethylenediamine.

[0011] Furthermore, the ethylene oxide absorbent at the bottom of the ethylene oxide absorber contains 3%–3.5% ethylene oxide, 2.8%–3.1% ethylene glycol, 1350–1500 ppm formaldehyde, 28–31 ppm acetaldehyde, and has a pH of 7.5–8.

[0012] Furthermore, the mass concentration of the formaldehyde removal agent is 1% to 60%.

[0013] Furthermore: the mass concentration of the formaldehyde removal agent is 40% to 55%.

[0014] Furthermore, the molar ratio of formaldehyde and acetaldehyde to the formaldehyde removal agent is 1:1.1~1.6.

[0015] Furthermore, the molar ratio of formaldehyde and acetaldehyde to the formaldehyde removal agent is 1:1.2~1.3.

[0016] Furthermore: the structure of the tubular reactor is a single tube or multiple tubes connected in parallel, and the tubular reactor can be horizontal tube, vertical tube, coil tube, or multiple tubes connected in parallel.

[0017] Furthermore, the reaction temperature inside the tubular reactor is 30~44℃, and the reaction pressure is 1.2~1.5MPa.

[0018] Furthermore, the tubular reactor contains 3%–3.5% ethylene oxide, 2.8%–3.1% ethylene glycol, 1220–1340 ppm formaldehyde, 15.7–20.4 ppm acetaldehyde, and has a pH of 8.3–8.5 in its rich absorbent.

[0019] Furthermore, the temperature of the rich absorbent after being cooled by the quench section cooler is 34℃~36℃.

[0020] Furthermore: the two ends of the temperature control pipeline are connected to the first outlet pipeline and the second outlet pipeline respectively, and a temperature control valve is installed on the temperature control pipeline.

[0021] Compared with existing technologies, this invention has the following advantages: By introducing organic amines and hydrazine-based formaldehyde removal agents and combining them with the enhanced reaction of a tubular reactor, the formaldehyde removal efficiency in ethylene oxide-rich absorbent water is improved by 8.3%–11.7%, and the acetaldehyde removal efficiency is improved by 29.5%–47.6%, compared with simply adding 20% ​​sodium hydroxide solution. The organic amine / hydrazine-based formaldehyde removal agents used, such as ethanolamine, hydrazine hydrate, cyclohexylamine, and ethylenediamine, do not react with sodium hydroxide to generate inorganic salts, fundamentally eliminating the risk of blockage in the salt discharge pipeline of the quench flash evaporation tower caused by the salting-out effect. At the same time, the tubular reactor adopts a continuous flow reaction mode, and the reactants have a high flow velocity in the tube, making it less likely to generate polymer deposition, further reducing the probability of system blockage and significantly improving the operational stability and continuous production cycle of the device. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention.

[0023] In the diagram: 1. Ethylene oxide absorption tower; 2. Ethylene oxide crude gas inlet pipeline; 3. Crude gas cooler; 4. Sodium hydroxide alkali solution pipeline; 5. Circulating pump; 6. Formaldehyde removal preparation tank; 7. Formaldehyde removal agent metering pump; 8. Tubular reactor; 9. Tubular reactor cross-line shut-off valve; 10. Temperature control valve; 11. Quenching section cooler; 12. Online analyzer; 13. Absorbent rich liquid pipeline; 14. Delivery pipeline; 15. First outlet pipeline; 16. Second outlet pipeline; 17. Temperature control pipeline. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate specific implementation methods of the present invention, but the protection scope of the present invention is not limited to the following embodiments. Where specific technical conditions are not specified in the embodiments, they are implemented according to conventional technical means in the art; where specific experimental data are not specified, they are executed according to conventional chemical production parameters.

[0025] A method for removing formaldehyde from ethylene oxide using water-rich absorption, characterized by the following steps: ethylene oxide crude gas transported by ethylene oxide crude gas inlet pipeline 2 is cooled by cooler 3 and then enters the quenching section at the bottom of ethylene oxide absorption tower 1, where formaldehyde, organic acid compounds and monochloroethane decomposition products are neutralized by circulating quenching liquid.

[0026] The bottom of the ethylene oxide absorption tower 1 is connected to the rich absorbent pipeline 13, which is connected to the inlet of the circulating pump 5. The absorbent at the bottom of the ethylene oxide absorption tower 1 contains 3%–3.5% ethylene oxide, 2.8%–3.1% ethylene glycol, 1350–1500 ppm formaldehyde, 28–31 ppm acetaldehyde, and has a pH of 7.5–8. The molar ratio of formaldehyde and acetaldehyde to the formaldehyde removal agent is 1:1.1–1.6. The sodium hydroxide alkaline solution pipeline 4 is connected to the rich absorbent pipeline 13. The outlet of the circulating pump 5 is connected to the tubular reactor 8 via the delivery pipeline 14. The formaldehyde removal agent in the formaldehyde removal preparation tank 6 is sent to the delivery pipeline 14 via the formaldehyde removal agent metering pump 7. The formaldehyde removal agent has a mass concentration of 1%–60% and enters the tubular reactor 8 for formaldehyde removal. The rich absorbent after the reaction is then passed through the tubular reactor. The first outlet pipeline 15 of the tubular reactor 8 is sent to the inlet of the quench section cooler 11. After cooling by the quench section cooler 11, the liquid is sent to the ethylene oxide absorption tower 1 as circulating quench liquid through the second outlet pipeline 16. An online analyzer 12 is installed on the outlet pipeline 16 of the quench section cooler 11. The tubular reactor 8 has a single tube or multiple tubes connected in parallel. The tubular reactor 8 can be a horizontal tube, vertical tube, coil tube, or multiple tubes connected in parallel. The reaction temperature in the tubular reactor 8 is 30~44℃, the reaction pressure is 1.2~1.5MPa, the mass fraction of ethylene oxide in the rich absorption liquid of the tubular reactor 8 is 3%~3.5%, the mass fraction of ethylene glycol is 2.8%~3.1%, the formaldehyde content is 1220~1340ppm, the acetaldehyde content is 15.7~20.4ppm, and the pH is 8.3~8.5.

[0027] The formaldehyde removal agent is selected from one or more of ethanolamine, hydrazine hydrate, cyclohexylamine, and ethylenediamine.

[0028] The tubular reactor 8 has a structure of single tube or multiple tubes in parallel. The tubular reactor 8 can be horizontal tube, vertical tube, coil tube, or multiple tubes in parallel. The temperature of the rich absorbent liquid after being cooled by the quench section cooler 11 is 34℃~36℃. The first outlet pipeline 15 is connected to the conveying pipeline 14 by a cross-line. A tubular reactor cross-line shut-off valve 9 is installed on the cross-line.

[0029] The temperature control pipeline 17 is connected to the first outlet pipeline 15 and the second outlet pipeline 16 at both ends, and a temperature control valve 10 is installed on the temperature control pipeline 17.

[0030] Examples 1-6:

[0031] The absorbent at the bottom of the ethylene oxide absorption tower contained 3.37% ethylene oxide, 2.9% ethylene glycol, 1464.56 ppm formaldehyde, 28.96 ppm acetaldehyde, and a pH of 7.61. The total aldehyde to formaldehyde removal agent was mixed in molar ratios of 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, and 1:1.6, respectively, and the reaction was carried out in a tubular reactor at a temperature of 36–40 °C and a pressure of 1.2–1.4 MPa. Upon exiting the tubular reactor, the ethylene oxide mass fraction was 3.35%, and the ethylene glycol mass fraction was 2.89%. The formaldehyde removal rate, acetaldehyde removal rate, and pH value are detailed in Table 1.

[0032] Table 1

[0033] Examples 7-12:

[0034] The absorbent at the bottom of the ethylene oxide absorption tower contained 3.49% ethylene oxide, 2.45% ethylene glycol, 1478.15 ppm formaldehyde, 27.14 ppm acetaldehyde, and a pH of 7.66. The total aldehyde to formaldehyde removal agent molar ratios were 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, and 1:1.6, respectively. The reaction was carried out in a tubular reactor at a temperature of 36–40 °C and a pressure of 1.2–1.4 MPa. Upon exiting the tubular reactor, the ethylene oxide mass fraction was 3.47%, the ethylene glycol mass fraction was 2.48%, and the formaldehyde removal rate, acetaldehyde removal rate, and pH value are detailed in Table 2.

[0035] Table 2

[0036] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing formaldehyde from ethylene oxide using water-rich absorption, characterized in that, Includes the following steps: The ethylene oxide crude gas transported by the ethylene oxide crude gas inlet pipeline (2) is cooled by the cooler (3) and then enters the quench section at the bottom of the ethylene oxide absorption tower (1). In the quench section, formaldehyde, organic acid compounds and monochloroethane decomposition products are neutralized by circulating quench liquid. The bottom of the ethylene oxide absorption tower (1) is connected to the rich absorbent pipeline (13) and the inlet of the circulating pump (5). The sodium hydroxide alkaline solution pipeline (4) is connected to the rich absorbent pipeline (13). The outlet of the circulating pump (5) is connected to the tubular reactor (8) through the delivery pipeline (14). The formaldehyde removal agent in the formaldehyde removal preparation tank (6) is sent to the delivery pipeline (14) through the formaldehyde removal agent metering pump (7) and enters the tubular reactor (8) for formaldehyde removal reaction. The rich absorbent after reaction is sent to the inlet of the quench section cooler (11) through the first outlet pipeline (15) of the tubular reactor (8). After the quench section cooler (11) is cooled, it is sent to the ethylene oxide absorption tower (1) as the circulating quench liquid through the second outlet pipeline (16). An online analyzer (12) is installed on the outlet pipeline (16) of the quench section cooler (11).

2. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that, The formaldehyde removal agent is selected from one or more of ethanolamine, hydrazine hydrate, cyclohexylamine, and ethylenediamine.

3. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that, The ethylene oxide absorption tower (1) contains 3% to 3.5% ethylene oxide, 2.8% to 3.1% ethylene glycol, 1350 to 1500 ppm formaldehyde, 28 to 31 ppm acetaldehyde, and pH 7.5 to 8 in the bottom absorbent.

4. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 2, characterized in that: The formaldehyde removal agent has a mass concentration of 1% to 60%.

5. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that, The molar ratio of formaldehyde and acetaldehyde to the formaldehyde removal agent is 1:1.1~1.

6.

6. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that: The structure of the tubular reactor (8) is a single tube or multiple tubes connected in parallel. The tubular reactor (8) can be a horizontal tube, a vertical tube, a coil tube, or a multi-tube parallel tube.

7. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that: The reaction temperature inside the tubular reactor (8) is 30~44℃ and the reaction pressure is 1.2~1.5MPa.

8. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that: The tubular reactor (8) contains 3% to 3.5% ethylene oxide, 2.8% to 3.1% ethylene glycol, 1220 to 1340 ppm formaldehyde, 15.7 to 20.4 ppm acetaldehyde, and pH 8.3 to 8.5 in its rich absorbent.

9. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that: The temperature of the rich absorbent liquid after being cooled by the quench section cooler (11) is 34℃~36℃.

10. The method for removing formaldehyde from ethylene oxide using water-rich absorption as described in claim 1, characterized in that: The first outlet pipeline (15) and the second outlet pipeline (16) are connected to the two ends of the temperature control pipeline (17) respectively, and a temperature control valve (10) is installed on the temperature control pipeline (17).

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