Treatment system and method for gas containing ethylene oxide and carbon dioxide

Abstract

The invention relates to the field of ethylene oxide production, and discloses a system and a method for treating gas containing ethylene oxide and carbon dioxide. The treatment system for the gas containing ethylene oxide and carbon dioxide comprises an ethylene oxide-carbon dioxide absorption tower, a flash tank and an ethylene oxide-carbon dioxide desorption tower which are communicated with one another, the ethylene oxide-carbon dioxide absorption tower is used for synchronously absorbing ethylene oxide and carbon dioxide in the reaction rich recycle gas to obtain a rich absorbent containing ethylene oxide and carbon dioxide and reaction lean recycle gas; the flash tank is used for carrying out flash treatment on the rich absorbent to obtain light component gas and light component removal containing ethylene oxide and carbon dioxide; and the ethylene oxide-carbon dioxide desorption tower is used for synchronously desorbing ethylene oxide and carbon dioxide in the light component to obtain ethylene oxide, carbon dioxide and a lean absorbent. The system can reduce the operation difficulty of ethylene oxide production and reduce the energy consumption and material consumption level of the device.

Description

Technical Field

[0001] This invention relates to the technical field of ethylene oxide production, and more specifically to a processing system and method for ethylene oxide and carbon dioxide gas. Background Technology

[0002] Ethylene oxide (EO) is an important petrochemical product with excellent bactericidal and disinfectant effects. It is mainly used in the production of ethylene glycol, nonionic surfactants, water-reducing agents, and ethanolamine. Because carbon dioxide (CO2) is produced as a byproduct during EO production, it has also been used in recent years in the synthesis of ethylene carbonate (EC) from EO and CO2.

[0003] Industrially, EO is mainly produced through the gas-phase reaction of ethylene and oxygen in the presence of a silver catalyst. Due to the selectivity of the catalyst, the reaction also produces a large amount of CO2 and a small amount of aldehyde impurities as byproducts. Because of the safety of EO and the limitations of catalyst conversion, the reaction requires a large amount of stabilizing gas, methane or nitrogen, and only a portion of the ethylene and oxygen undergoes conversion. Therefore, the reaction product gas at the EO reactor outlet is a mixture containing EO, CO2, methane or nitrogen, ethylene, oxygen, and aldehyde impurities. To further refine and separate EO and ensure the smooth operation of the catalyst reaction, the generated EO and CO2 need to be removed promptly. Current technologies employ a two-step removal method: first, water is used as an absorbent to remove EO from the reaction-rich recycle gas in an EO absorption tower; then, the EO-free recycle gas is passed into a CO2 absorption tower to remove CO2 with a hot potassium alkali solution, and finally, the reaction-lean recycle gas is returned to the reactor inlet after being pressurized by a compressor. Both absorbents require a large amount of steam for desorption and regeneration to remove EO and CO2 before being recycled. The process suffers from problems such as complexity, high energy consumption, material loss (EO stripping generates ethylene glycol through hydration), and difficulty in removing aldehyde impurities. Furthermore, when absorbing CO2 with hot potassium hydroxide solution, a decarbonization accelerator made from vanadate (prepared from highly toxic vanadium pentoxide, V2O5) is required to promote absorption and meet the CO2 concentration requirements at the reactor inlet, posing a potential risk to the environment and personnel safety. Therefore, a low-energy, green, and environmentally friendly short-process technology is needed to simultaneously absorb and desorb EO and CO2.

[0004] Patent application CN 115724819A discloses a process route for absorbing EO using EC (ethylene carbonate) instead of water as the absorbent. Although this method reduces material consumption losses compared to water absorption, the high melting point of EC (39°C) hinders the use of an effective amount of absorbent, making it difficult to effectively reduce heat recovery losses. According to conventional methods using water, the absorption operation temperature is 20-37°C, which is too low for EC. To conduct the entire operation without any freezing issues, the process should practically be maintained at least above 50°C. This means that absorption operations using EC must be maintained at a temperature at least 13°C higher than those using water. This reduces absorption capacity, necessitating an increase in the amount of circulating absorbent, significantly weakening the reduction in heat recovery losses between absorption and stripping. Furthermore, the high freezing point of EC leads to serious problems in operation, insulation, and maintenance. For example, even when the equipment is not running, a large amount of absorbent needs to be kept heated, resulting in higher operating costs for the heating system. Furthermore, due to partial solidification caused by the heat exchange contact between EC and cooling water, the tendency for pipe blockage or decreased heat exchange efficiency is difficult to avoid. Since EC has a relatively weak CO2 absorption capacity, the CO2 absorption process is the same as water absorption, still requiring the use of a hot potassium hydroxide solution. Therefore, the entire process of EO and CO2 absorption and desorption remains a two-step removal process, with each step involving separate absorption and desorption, making it roughly equivalent in complexity to traditional water and hot potassium hydroxide absorption methods.

[0005] Patent application CN 110479037A discloses a composite absorbent comprising ionic liquid and EC to replace water for EO absorption. Although its absorption and desorption effects on EO are better than those using EC alone, the problems of EC's high freezing point and the need for hot potassium alkali solution for CO2 absorption are not solved. The entire process is also a two-step removal process, and its complexity is basically the same as that of traditional water or EC and hot potassium alkali absorption. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a processing system and method for ethylene oxide and carbon dioxide gas. This system can reduce the operational difficulty of ethylene oxide production and reduce energy and material consumption levels.

[0007] To achieve the above objectives, the first aspect of the present invention provides a treatment system for ethylene oxide and carbon dioxide gas, wherein the system comprises an ethylene oxide-carbon dioxide absorption tower, a flash tank and an ethylene oxide-carbon dioxide desorption tower connected to each other.

[0008] The ethylene oxide-carbon dioxide absorption tower is used to simultaneously absorb ethylene oxide and carbon dioxide gas in the reaction-rich circulating gas to obtain a rich absorbent containing ethylene oxide and carbon dioxide and a reaction-lean circulating gas.

[0009] The flash tank is used to flash-treat the rich absorbent to obtain light component gas and delighted component containing ethylene oxide and carbon dioxide.

[0010] The ethylene oxide-carbon dioxide desorption tower is used to simultaneously desorb ethylene oxide and carbon dioxide from light components, yielding ethylene oxide, carbon dioxide, and lean absorbent.

[0011] A second aspect of the present invention provides a method for treating a gas containing ethylene oxide and carbon dioxide, wherein the method is performed in the system described in the first aspect, and the method includes:

[0012] (A) In the presence of a lean absorbent, a reaction-rich circulating gas containing ethylene oxide and carbon dioxide is simultaneously absorbed in an ethylene oxide-carbon dioxide absorption tower to obtain a rich absorbent containing ethylene oxide and carbon dioxide and a reaction-lean circulating gas, wherein the lean absorbent contains a composite absorbent.

[0013] (B) The rich absorbent is flash-treated in a flash tank to obtain light component gas and delighted component containing ethylene oxide and carbon dioxide;

[0014] (C) The light component is simultaneously desorbed into ethylene oxide and carbon dioxide in an ethylene oxide-carbon dioxide desorption tower to obtain ethylene oxide, carbon dioxide and lean absorbent. The lean absorbent is returned to step (A) for reuse.

[0015] The system provided by this invention achieves simultaneous absorption of ethylene oxide and carbon dioxide in the same absorption tower and simultaneous desorption of ethylene oxide and carbon dioxide in the same desorption tower. This overcomes the shortcomings of the traditional two-step removal method. Compared with the prior art where ethylene oxide and carbon dioxide are absorbed and desorbed separately in their respective absorption towers and desorption towers, this system, which sets up two independent absorption and desorption tower systems for the absorption and desorption of ethylene oxide and carbon dioxide, can better achieve the simultaneous absorption and separation of ethylene oxide and carbon dioxide in the mixed gas after ethylene oxidation. This reduces the operational complexity of the ethylene oxide production unit while further reducing the energy and material consumption levels of the unit.

[0016] The method provided by this invention uses a composite absorbent capable of absorbing ethylene oxide and carbon dioxide (preferably, a composite absorbent containing propylene carbonate and / or polyethylene glycol dimethyl ether) instead of the absorbent in the prior art. Since there is no hydrolysis of ethylene oxide and no decarbonization promoter containing vanadate components is involved, the equipment has better material consumption, is safer and more environmentally friendly, and belongs to a low-energy-consumption, green and environmentally friendly short-process technology.

[0017] The method provided by this invention is a low-energy, green, and environmentally friendly short-process technology that can simultaneously achieve the absorption and desorption separation of ethylene oxide and carbon dioxide. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the processing system in the embodiment;

[0019] Figure 2 This is a schematic diagram of a proportional processing system.

[0020] Explanation of reference numerals in the attached figures

[0021] Figure 1 middle,

[0022] 1-Ethylene oxide-carbon dioxide absorption tower; 2-Flash tank;

[0023] 3-Ethylene oxide-carbon dioxide desorption tower; 4-Absorption tower inlet / outlet heat exchanger;

[0024] 5- Lean / Rich absorbent heat exchanger; 6- Desorption tower condenser;

[0025] 7-Desorption tower cryostat; 8-Desorption tower heater;

[0026] 9-Lean absorbent cooler; 10-Desorption tower reflux tank;

[0027] 11-Lean absorbent injection flash tank; 12-Carbon dioxide injector;

[0028] 13-Carbon dioxide compressor; 14-Desorption tower feed pump;

[0029] 15 - Desorption tower reflux pump; 16 - Desorption tower bottom pump;

[0030] 17 - Lean absorbent booster pump; S1 - Reaction-rich circulating gas;

[0031] S2 - Lean recycle gas; S3 - Light component gas;

[0032] S4 - Carbon dioxide; S5 - Ethylene oxide;

[0033] S6 - Lean absorbent; S7 - Rich absorbent;

[0034] U1 - Refrigerant 1; U2 - Heater;

[0035] U3-Refrigerant 2; U4-Refrigerant 3.

[0036] Figure 2 middle,

[0037] 1-Ethylene oxide absorption tower; 2-Carbon dioxide absorption tower;

[0038] 3-Ethylene oxide desorption tower; 4-Carbon dioxide desorption tower;

[0039] 5-Flash evaporator for removing light components; 6-Recirculation tank for carbon dioxide desorption tower; 7-Ethylene oxide desorption tower reflux tank; 8-Carbon dioxide desorption tower cooler; 9- Reboiler for carbon dioxide desorption tower; 10- Condenser for ethylene oxide desorption tower; 11-Ethylene oxide desorption tower bottom pump; 12-Ethylene oxide desorption tower reflux pump; 13-Carbon dioxide desorption tower reboiler pump; 14-Carbon dioxide desorption tower reflux pump;

[0040] S1 - Reaction rich in circulating gas; S2 - Reaction lean in circulating gas;

[0041] S3 - Light component gas; S4 - Carbon dioxide;

[0042] S5 - Process wastewater; S6 - Ethylene oxide aqueous solution;

[0043] S7 - Process steam; S8 - Methane stripping gas;

[0044] S9 - Water absorption by ethylene oxide-poor; S10 - Water absorption by ethylene oxide-rich;

[0045] S11 - Carbon dioxide-poor carbonate absorbent solution; S12 - Carbon dioxide-rich carbonate absorbent solution; U1 - Cooling water; U2 - Steam;

[0046] U3-low temperature water. Detailed Implementation

[0047] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0048] The first aspect of this invention provides a processing system for gases containing ethylene oxide and carbon dioxide, such as... Figure 1 As shown, the system includes an ethylene oxide-carbon dioxide absorption tower 1, a flash tank 2, and an ethylene oxide-carbon dioxide desorption tower 3 that are interconnected.

[0049] The ethylene oxide-carbon dioxide absorption tower 1 is used to simultaneously absorb ethylene oxide and carbon dioxide in the reaction-rich circulating gas S1 to obtain a rich absorbent S7 containing ethylene oxide and carbon dioxide and a reaction-lean circulating gas S2.

[0050] The flash tank 2 is used to flash treat the rich absorbent S7 to obtain light component gas and delighted components containing ethylene oxide and carbon dioxide.

[0051] The ethylene oxide-carbon dioxide desorption tower 3 is used to simultaneously desorb ethylene oxide and carbon dioxide from the light components to obtain ethylene oxide S5, carbon dioxide S4, and lean absorbent S6.

[0052] The system provided by this invention can achieve simultaneous absorption of ethylene oxide and carbon dioxide in the same absorption tower and simultaneous desorption of ethylene oxide and carbon dioxide in the same desorption tower. This overcomes the shortcomings of the traditional two-step removal method. Compared with the prior art where ethylene oxide and carbon dioxide are absorbed and desorbed separately in their respective absorption towers, this invention uses two independent absorption and desorption tower systems for ethylene oxide and carbon dioxide. This allows for better simultaneous absorption and separation of ethylene oxide and carbon dioxide in the mixed gas after ethylene oxidation. It also reduces the operational complexity of ethylene oxide production equipment and further reduces the energy and material consumption levels of the equipment.

[0053] In this invention, the rich absorbent refers to a composite absorbent that has fully absorbed EO and CO2. Based on the total amount of the composite absorbent, the total content of EO and CO2 in the composite absorbent is 2-20 wt%. This invention does not impose any particular limitation on the content of EO and CO2 in the composite absorbent, as long as the total content of the two meets the aforementioned range.

[0054] In this invention, the lean absorbent refers to the composite absorbent after desorption of EO and CO2. Based on the total amount of the composite absorbent, the total content of EO and CO2 in the composite absorbent is 0-2 wt%. This invention does not impose any particular limitation on the content of EO and CO2 in the composite absorbent, as long as the total content of the two meets the aforementioned range.

[0055] In this invention, it is understood that simultaneous absorption refers to the use of a composite absorbent in an ethylene oxide-carbon dioxide absorption tower to achieve the absorption of ethylene oxide and carbon dioxide; simultaneous desorption refers to the use of a composite absorbent in an ethylene oxide-carbon dioxide desorption tower to achieve the desorption of ethylene oxide and carbon dioxide. This invention does not impose any particular limitation on the type of composite absorbent; for example, it can be a composite absorbent containing propylene carbonate and / or polyethylene glycol dimethyl ether, as long as it can achieve the absorption of ethylene oxide and carbon dioxide. Those skilled in the art can select according to actual needs.

[0056] In this invention, preferably, the ethylene oxide-carbon dioxide absorption tower 1 is equipped with an absorption internal component. The arrangement of the absorption internal component ensures sufficient contact between the reaction-rich circulating gas and the lean absorbent, thereby maximizing the absorption of ethylene oxide and carbon dioxide.

[0057] In this invention, the specific type of absorption internal components is not particularly limited. For example, the internal components can be packed towers and / or plate towers, preferably packed towers. By selecting packed towers, the pressure drop of the reaction circulation gas can be reduced, thus saving energy consumption.

[0058] In this invention, the specific arrangement of the absorbent internal components is not particularly limited, and those skilled in the art can make adjustments according to actual needs.

[0059] In this invention, heat coupling is achieved by utilizing the heat inherent in each material, which further saves energy consumption. Preferably, the system further includes an ethylene oxide-carbon dioxide absorber inlet / outlet heat exchanger 4. The first inlet of the ethylene oxide-carbon dioxide absorber inlet / outlet heat exchanger 4 is connected to the reaction-rich circulating gas outlet of the upstream reaction unit, the first outlet of the ethylene oxide-carbon dioxide absorber inlet / outlet heat exchanger 4 is connected to the first inlet of the ethylene oxide-carbon dioxide absorber 1, the second inlet of the ethylene oxide-carbon dioxide absorber inlet / outlet heat exchanger 4 is connected to the first outlet of the ethylene oxide-carbon dioxide absorber 1, and the second outlet of the ethylene oxide-carbon dioxide absorber inlet / outlet heat exchanger 4 is connected to the inlet of the flash tank 2.

[0060] In this invention, there are no particular limitations on the arrangement of the flash tank; for example, it can be vertical and / or horizontal, with a horizontal arrangement being preferred. Installing the flash tank horizontally provides more flash space, facilitating the flash process.

[0061] In this invention, preferably, the top of the flash tank 2 is provided with a reabsorption section, which is used to absorb the flash vapor of the rich absorbent S7 to obtain light component gas S3. By setting the reabsorption section, the rich absorbent flash vapor obtained by flash evaporation in the flash tank comes into countercurrent contact with the lean absorbent from the ethylene oxide-carbon dioxide desorption tower, resulting in light component gas rich in ethylene and methane, which is returned to the upstream reaction unit for reuse.

[0062] In this invention, the specific structure of the reabsorption section is not particularly limited. For example, the reabsorption section may be provided with separation internal components, and preferably with packing material.

[0063] In this invention, preferably, the system further includes a desorption tower top condenser 6, a desorption tower reflux tank 10, and a desorption tower top cryostat 7. In this invention, the specific types of the desorption tower top condenser, desorption tower reflux tank, and desorption tower top cryostat are not particularly limited, and those skilled in the art can adjust them according to actual needs.

[0064] In this invention, preferably, the inlet of the desorption tower top condenser 6 is connected to the gas phase outlet at the top of the ethylene oxide-carbon dioxide desorption tower 3, and the outlet of the desorption tower top condenser 6 is connected to the first inlet of the desorption tower reflux tank 10. The gas containing ethylene oxide and carbon dioxide at the top of the ethylene oxide-carbon dioxide desorption tower enters the desorption tower top condenser for condensation, condensing most of the ethylene oxide. The resulting ethylene oxide then enters the desorption tower reflux tank. In this invention, preferably, the condensation of ethylene oxide is carried out in the presence of a primary condenser. Preferably, the temperature of the primary condenser is 30-33°C. This invention does not particularly limit the type of primary condenser, as long as the above temperature is met. This invention does not particularly limit the source of the primary condenser. Preferably, the primary condenser is provided by refrigerant U3.

[0065] In this invention, preferably, the first outlet of the desorption tower reflux tank 10 is connected to the first inlet of the ethylene oxide-carbon dioxide desorption tower 3 and / or to the downstream ethylene oxide processing unit. By connecting the desorption tower reflux tank to both the ethylene oxide-carbon dioxide desorption tower and the downstream ethylene oxide processing unit, the liquid ethylene oxide in the desorption tower reflux tank is diverted. A portion is returned to the ethylene oxide-carbon dioxide desorption tower, while the other portion is transported as ethylene oxide S5 product to the downstream ethylene oxide processing unit for further processing.

[0066] In this invention, preferably, the desorption tower reflux tank 10 and the ethylene oxide-carbon dioxide desorption tower 3 are connected via a desorption tower reflux pump 15. Driven by the desorption tower reflux pump 15, the liquid phase of ethylene oxide is separated.

[0067] In this invention, preferably, the second outlet of the desorption tower reflux tank 10 is connected to the inlet of the desorption tower top cryogenic heater 7. Through the connection between the desorption tower reflux tank and the desorption tower top cryogenic heater, the gaseous products, after condensation in the desorption tower top condenser, enter the desorption tower top cryogenic heater for deep cooling. A small amount of ethylene oxide in the gaseous products is further condensed and then transported to the desorption tower reflux tank for subsequent processing, reducing material loss and preventing ethylene oxide from entering subsequent processes, thus improving safety. In this invention, preferably, the condensation of ethylene oxide is carried out in the presence of a secondary condenser. Preferably, the temperature of the secondary condenser is -5 to 15°C. This invention does not particularly limit the type of secondary condenser, as long as the above temperature is met. This invention does not particularly limit the source of the secondary condenser. Preferably, the secondary condenser is provided by refrigerant U4.

[0068] In this invention, preferably, the first outlet of the desorption tower top cryostat 7 is connected to the downstream carbon dioxide treatment unit. Through this connection, a portion of the uncondensed carbon dioxide gas is transported to the downstream carbon dioxide treatment unit for further processing. For example, depending on the downstream process configuration, it can be used as raw material CO2 for the reaction of EO and CO2 to produce ethylene carbonate (EO), or further refined into a product for sale.

[0069] In this invention, a portion of the uncondensed carbon dioxide gas is returned to the ethylene oxide-carbon dioxide desorption tower for use as desorption gas. Preferably, the system further includes a carbon dioxide ejector 12, the suction side of which is connected to the second outlet of the cryogenic cooler 7 at the top of the desorption tower, and the exhaust side of which is connected to the second inlet of the ethylene oxide-carbon dioxide desorption tower 3. The advantage of this preferred embodiment is that by utilizing the compressed CO2 in the desorption gas for reuse to promote the desorption process, it can effectively reduce or even eliminate the additional heat input required for the desorption process, thereby reducing desorption energy consumption.

[0070] In this invention, preferably, the desorption tower top cryostat 7 and the carbon dioxide injector 12 are connected via a carbon dioxide compressor 13. By employing this preferred embodiment, a portion of the uncondensed carbon dioxide gas is supplied to the carbon dioxide compressor, thus achieving pressurization.

[0071] In this invention, to reduce the design pressure of the lean absorbent heat exchanger between the ethylene oxide-carbon dioxide desorption tower and the ethylene oxide-carbon dioxide absorption tower, a heat exchanger is typically installed to fully utilize the heat of the desorbed lean absorbent and further reduce it to the temperature required for absorption. Preferably, the system further includes a lean / rich absorbent heat exchanger 5, the first inlet of which is connected to the first outlet of the flash tank 2, and the first outlet of which is connected to the third inlet of the ethylene oxide-carbon dioxide desorption tower 3. The lean / rich absorbent heat exchanger enables heat coupling between the materials, which helps reduce the overall energy consumption of the system.

[0072] In this invention, preferably, the lean / rich absorbent heat exchanger 5 and the flash tank 2 are connected via the desorption tower feed pump 14.

[0073] In this invention, to further enhance the desorption effect, preferably, the system further includes a lean absorbent injection flash tank 11. The inlet of the lean absorbent injection flash tank 11 is connected to the bottom liquid phase outlet of the ethylene oxide-carbon dioxide desorption tower 3, the liquid phase outlet of the lean absorbent injection flash tank 11 is connected to the second inlet of the lean / rich absorbent heat exchanger 5, and the gas phase outlet of the lean absorbent injection flash tank 11 is connected to the exhaust side of the carbon dioxide ejector 12. The advantage of this preferred embodiment is that the carbon dioxide, as the desorption gas, creates a local low pressure in the lean absorbent injection flash tank via the carbon dioxide ejector, which further releases dissolved carbon dioxide gas, which is then fed into the ethylene oxide-carbon dioxide desorption tower as the desorption gas.

[0074] In this invention, there are no particular limitations on the arrangement of the lean absorbent spray flash tank. For example, it can be vertical or horizontal, and preferably vertically integrated into the desorption tower kettle to save space.

[0075] In this invention, preferably, the carbon dioxide injector 12 is positioned at the top of the lean absorbent injection flash tank 11. The preferred embodiment described above ensures effective suction.

[0076] In this invention, preferably, the lean absorbent injection flash evaporator 11 is equipped with a baffle. The baffle enhances the suction flash evaporation effect. This invention does not impose any particular limitation on the specific arrangement of the baffle.

[0077] In this invention, preferably, the lean absorbent injection flash tank 11 and the lean / rich absorbent heat exchanger 5 are connected via the desorption tower bottom pump 16.

[0078] In this invention, preferably, the system further includes a lean absorbent cooler 9, the first inlet of which is connected to the second outlet of the lean / rich absorbent heat exchanger 5, and the first outlet of the lean absorbent cooler 9 is connected to the reabsorption section of the flash tank 2 and / or the second inlet of the ethylene oxide-carbon dioxide absorption tower 1. After being cooled by the lean absorbent cooler, a portion enters the reabsorption section of the flash tank for reabsorption, while the other portion returns to the ethylene oxide-carbon dioxide absorption tower as lean absorbent S6 for recycling.

[0079] In this invention, preferably, the lean absorbent cooler 9 is connected to the ethylene oxide-carbon dioxide absorption tower 1 via a lean absorbent booster pump 17. In a preferred embodiment, the temperature of the lean absorbent cooler 9 is controlled by refrigerant 1U1.

[0080] In this invention, preferably, the system further includes a desorption tower heater 8 disposed at the bottom of the ethylene oxide-carbon dioxide desorption tower 3, the desorption tower heater 8 being used to control the desorption temperature. In a preferred embodiment, the temperature of the desorption tower heater 8 is controlled by a heat transfer medium U2, allowing for flexible control of the desired desorption temperature.

[0081] In this invention, the purpose of setting up each heat exchanger is to fully utilize the heat of the desorbed lean absorbent and further reduce it to the temperature required for absorption. It should be noted that there is no particular limitation on the specific setting of each heat exchanger. For example, a series pump can be preferred. In order to further save investment and space, the series pump is preferably operated by a coupling pump sharing a motor. Those skilled in the art can adjust it according to actual needs.

[0082] A second aspect of the present invention provides a method for treating a gas containing ethylene oxide and carbon dioxide, wherein the method is performed in the system described in the first aspect, and the method includes:

[0083] (A) In the presence of lean absorbent S6, reaction rich gas S1 containing ethylene oxide and carbon dioxide is simultaneously absorbed in ethylene oxide-carbon dioxide absorption tower 1 to obtain rich absorbent S7 containing ethylene oxide and carbon dioxide and reaction lean gas S2, wherein the lean absorbent S6 contains a composite absorbent.

[0084] (B) The rich absorbent S7 is flash-treated in flash tank 2 to obtain light component gas S3 and delighted component containing ethylene oxide and carbon dioxide.

[0085] (C) The light component is simultaneously desorbed into ethylene oxide and carbon dioxide in ethylene oxide-carbon dioxide desorption tower 3 to obtain ethylene oxide S5, carbon dioxide S4 and lean absorbent S6. Lean absorbent S6 is returned to step (A) for reuse.

[0086] The method provided by this invention uses a composite absorbent capable of absorbing ethylene oxide and carbon dioxide (preferably, a composite absorbent containing propylene carbonate and / or polyethylene glycol dimethyl ether) instead of the absorbent in the prior art. Since there is no hydrolysis of ethylene oxide and no decarbonization promoter containing vanadate components is involved, the equipment has better material consumption, is safer and more environmentally friendly, and belongs to a low-energy-consumption, green and environmentally friendly short-process technology.

[0087] The method provided by this invention is a low-energy, green, and environmentally friendly short-process technology that can simultaneously achieve the absorption and desorption separation of ethylene oxide and carbon dioxide.

[0088] In this invention, preferably, the reaction-rich circulating gas S1 also contains methane, ethylene, argon, and oxygen. Methane can be used as a stabilizing gas for the reaction.

[0089] In this invention, the content of each component in the reaction cycle gas S1 is not particularly limited. Preferably, in step (A), based on the total amount in the reaction-rich cycle gas S1, the concentration of ethylene oxide is 0.5-5 mol / %, and the concentration of carbon dioxide is 0.5-9.5 mol / %.

[0090] In this invention, preferably, in step (A), the temperature of the reaction-rich circulating gas S1 is 35-80°C and the pressure is 1.2-3 MPaG.

[0091] In this invention, preferably, in step (A), the composite absorbent contains acrylic acid carbonate and / or polyethanol dimethyl ether. The acrylic acid carbonate in this composite absorbent has the following advantages: First, acrylic acid carbonate has excellent absorption capacity per unit mass for both EO and CO2, comparable to or even higher than that of water and hot potassium alkali. For example, the absorption capacity of acrylic acid carbonate (PC) for EO per unit mass is about 50% higher than that of water and about 40% higher than that of ethylene carbonate (EC). Furthermore, the absorption capacity of the PC composite absorbent for CO2 per unit mass is comparable to that of a hot potassium alkali solution without added vanadate. Second, acrylic acid carbonate has a low specific heat; the specific heat of PC is 0.4 cal / g·℃, only 40% of the specific heat of water, and close to that of EC. Third, it does not react with EO, CO2, or other materials in the reaction cycle gas. First, PC is very stable for byproducts such as aldehydes and acids produced during ethylene oxidation, even more so than EC. Second, under normal operating conditions, acrylic acid carbonate has a low freezing point and stable chemical properties. Since the freezing point of PC is -49℃, which is much lower than that of water (0℃) and EC (39℃), and also much lower than the crystallization temperature of hot potassium alkali solution (about 39℃), the absorption process can be carried out at a lower temperature without worrying about freezing, thus eliminating the need for high operating costs and stringent operating conditions. Third, acrylic acid carbonate has a high boiling point and low volatilization loss during regeneration. The boiling point of PC is 239℃, which is close to that of EC and much higher than that of water (100℃), so there is almost no volatilization loss during desorption.

[0092] In this invention, preferably, in step (A), based on the total amount of the lean absorbent, the content of acrylic acid carbonate and / or polyethylene glycol dimethyl ether in the lean absorbent S6 is 30-100 wt%. In this invention, preferably, the lean absorbent S6 contains acrylic acid carbonate and polyethylene glycol dimethyl ether. This invention does not specifically limit the content of each of the acrylic acid carbonate and polyethylene glycol dimethyl ether, as long as the total amount of both is met. Those skilled in the art can adjust this according to actual needs.

[0093] In this invention, preferably, in step (A), the temperature of the lean absorbent S6 is 5-50°C and the pressure is 1.2-3 MPaG.

[0094] In this invention, preferably, in step (A), the conditions for synchronous absorption include a pressure of 1.2-3 MPaG.

[0095] In this invention, preferably, the pressures in steps (A), (B), and (C) are decreased progressively. By controlling the operating pressure of each step progressively, the degree of desorption throughout the reaction process can be further controlled.

[0096] In this invention, the conditions for flash evaporation are not particularly limited, as long as the feeding requirements are met. For example, the pressure setting for flash evaporation can allow material from the upstream absorption tower to be fed through the pressure difference. Preferably, in step (B), the flash evaporation conditions include a pressure of 0.1-1 MPaG.

[0097] In this invention, preferably, in step (C), the total amount of the lean reaction gas S2 is based on a standard, and the concentration of ethylene oxide in the lean reaction gas S2 is less than 100 ppm, and the concentration of carbon dioxide is less than 1.2 mol / %. The advantage of using the above preferred embodiment is that the concentrations of ethylene oxide and carbon dioxide in the lean reaction gas meet the above ranges, which can satisfy the requirements of silver catalyst in downstream preparation processes (such as ethylene oxide oxidation reaction units).

[0098] In this invention, preferably, in step (C), the conditions for simultaneous desorption include: a pressure of -0.99 to 0.3 MPaG and a temperature of 80-140°C.

[0099] In a preferred embodiment of the present invention, the method further includes conveying ethylene oxide S5 to a downstream ethylene oxide processing unit for the production of products such as ethylene oxide, ethylene glycol, and ethylene carbonate (EC).

[0100] In this invention, preferably, the method further includes returning at least a portion of the carbon dioxide as desorption gas to the ethylene oxide-carbon dioxide desorption tower 3 for reuse to achieve desorption, and at least a portion of the carbon dioxide as carbon dioxide S4 product gas is transported to the downstream carbon dioxide treatment unit. For example, depending on the configuration of the downstream process, it can be used as raw material CO2 for the reaction of EO and CO2 to generate ethylene carbonate (EO) or further refined for sale as a product.

[0101] The present invention will be described in detail below through embodiments.

[0102] Example

[0103] Using the method provided by this invention, in Figure 1 The system shown processes gases containing ethylene oxide and carbon dioxide.

[0104] (A) The reaction-rich circulating gas S1 has a volumetric flow rate of 13427 kmol / hr, a molecular weight of 24.4, and its main components (mol%) are: methane 48.6%, ethylene 27.9%, argon 11.9%, oxygen 5.9%, EO 2.22%, and CO2 1.45%. The feed pressure and temperature are 2.04 MPaG and 70°C, respectively. It enters the bottom of the ethylene oxide-carbon dioxide absorption tower 1 and comes into full countercurrent contact with the lean absorbent S6 (containing methyl acrylate PC with a mass concentration of not less than 60 wt%) from the top of the ethylene oxide-carbon dioxide absorption tower 1 at a temperature of 36°C. After sufficient countercurrent contact, EO, CO2, and a small amount of light component gases are fully absorbed. The operating pressure of ethylene oxide-carbon dioxide absorption tower 1 is 2.02 MPaG. The reaction lean circulating gas S2 leaving the top of ethylene oxide-carbon dioxide absorption tower 1 has a volumetric flow rate of 13017 kmol / hr, a molecular weight of 23.9, and its main components (mol%) are: methane 50.2%, ethylene 28.8%, argon 12.3%, oxygen 6.1%, EO 10 ppm, and CO2 1.1%, with a pressure and temperature of 2.02 MPaG and 38 °C, respectively. It is returned to the upstream reaction unit (upstream treatment unit).

[0105] (B) The rich absorbent S7 from the bottom of the ethylene oxide-carbon dioxide absorption tower 1 is preheated to 55°C by the inlet / outlet heat exchanger 4 of the ethylene oxide-carbon dioxide absorption tower and enters the flash tank 2. In the reabsorption section at the top of the flash tank 2, the dissolved light component gas S3 is flashed out and returned to the front reaction system. The main components of the light component gas S3 are: methane 33.5%, ethylene 52.7%, argon 8%, oxygen 3.6%, CO2 2.2%, volumetric flow rate 17.1 kmol / hr, molecular weight 27.8, and the pressure of the flash tank 2 is controlled at 0.35 MPaG.

[0106] (C) After the light components are removed from the bottom of the flash tank 2 with rich absorbent S7, a light-removed component containing ethylene oxide and carbon dioxide is obtained. This stream is pressurized by the desorption tower feed pump 14, preheated to 75°C by the lean / rich absorbent heat exchanger 5, and then sent to the ethylene oxide-carbon dioxide desorption tower 3. The operating pressure of this tower is about 0.2 MPaG, and the tower bottom temperature is controlled at 90°C (the temperature is controlled by the heat medium U2 in the desorption tower heater 8). At the top of the tower, EO and CO2 in the stream are desorbed and then cooled in two stages by the desorption tower condenser 6 and the desorption tower cryocooler 7. The refrigerants 2U3 and 3U4 are supplied at temperatures of 32℃ and 5℃ respectively, condensing the EO. The EO is then refluxed through the desorption tower reflux tank 10 and desorption tower reflux pump 15. Most of the EO is returned to the top of the ethylene oxide-carbon dioxide desorption tower 3 as reflux, with a EO reflux rate of 65650 kg / hr (reflux ratio approximately 5:1) and a temperature of 40℃. The remaining EO is sent as product ethylene oxide S5 to the downstream ethylene oxide treatment unit, with an EO discharge rate of 13130 ​​kg / hr and a temperature of 40℃. Part of the condensed CO2 is pressurized by the carbon dioxide compressor 13, while the other part is sent as product carbon dioxide S4 to the downstream carbon dioxide treatment unit.

[0107] The CO2, after being pressurized by the carbon dioxide compressor 13, enters the suction side of the carbon dioxide injector 12. The exhaust side of the carbon dioxide injector 12 is connected to the gas phase outlet at the top of the lean absorbent injection flash tank 11. Then, the exhaust side of the carbon dioxide injector 12 is connected to the ethylene oxide-carbon dioxide desorption tower 3. The pressurized CO2 is transported to the ethylene oxide-carbon dioxide desorption tower 3 as desorption gas for desorption gas extraction.

[0108] The bottom discharge of the ethylene oxide-carbon dioxide desorption tower 3 is fed into the lean absorbent injection flash tank 11. The CO2, which is pressurized by the carbon dioxide compressor 13, is further injected and depressurized into the lean absorbent injection flash tank 11 by the carbon dioxide injector 12 to obtain desorbed material. After being pressurized by the desorption tower bottom pump 16, the desorbed material is cooled to 70°C by the lean / rich absorbent heat exchanger 5, and then cooled to 36°C by the lean absorbent cooler 9 (the temperature is controlled by the refrigerant U1 in the lean absorbent cooler 9). One part is fed into the reabsorption section at the top of the flash tank 2, and the other part is further pressurized by the lean absorbent booster pump 17 and then circulated back to the upper part of the ethylene oxide-carbon dioxide absorption tower 1 as lean absorbent S6.

[0109] Comparative Example

[0110] According to existing technological methods, Figure 2 The system shown processes gases containing ethylene oxide and carbon dioxide:

[0111] (A) The reaction-rich circulating gas S1 (containing EO, CO2, ethylene, methane, etc.) enters the ethylene oxide absorption tower 1. After being fully countercurrently contacted by the lean ethylene oxide absorption water S9 in the ethylene oxide absorption tower 1, the EO is fully absorbed. The ethylene oxide-rich absorbent water S10, after EO absorption, exits from the bottom of the ethylene oxide absorption tower 1 and enters the ethylene oxide desorption tower 3 using pressure differential. By introducing process steam S7 into the bottom of the ethylene oxide desorption tower 3, the EO and a small amount of dissolved light components are stripped. After being condensed by the ethylene oxide desorption tower condenser 10 (the temperature of the ethylene oxide desorption tower condenser 10 is controlled by low-temperature water U3), it enters the ethylene oxide desorption tower reflux tank 7. A small portion of the liquid phase is pressurized by the ethylene oxide desorption tower reflux pump 12 and returned to the ethylene oxide desorption tower 3 as reflux. The majority of the ethylene oxide aqueous solution S6 is sent downstream for further purification. The light component gas S3 at the top of the ethylene oxide desorption tower reflux tank 7, containing ethylene, methane, etc., is recovered and returned to the front reaction system. The lean ethylene oxide absorption water S9 at the bottom of the ethylene oxide desorption tower 3, after desorption of EO, is pressurized by the bottom pump 11 of the ethylene oxide desorption tower and then recycled back to the ethylene oxide absorption tower 1 for reuse.

[0112] (B) The top gas from the ethylene oxide absorption tower 1 after EO removal enters the carbon dioxide absorption tower 2. After sufficient countercurrent contact with the lean carbon dioxide carbonate absorbent S11, CO2 is fully absorbed, and a lean reaction recycle gas S2 is obtained at the top of the tower. The carbon dioxide-rich carbonate absorbent S12 after CO2 absorption is discharged from the bottom of the carbon dioxide absorption tower 2 and enters the light component removal flash tank 5 using the pressure difference. In the presence of methane stripping gas S8, it undergoes depressurization flash evaporation. The light component gas S3 at the top of the light component removal flash tank 5, containing ethylene, methane, etc., is recovered and returned to the front reaction system. The liquid phase from the bottom of the flash evaporator 5 (for removing light components) enters the carbon dioxide desorption tower 4. Heat from the reboiler 9 (temperature controlled by steam U2) strips and regenerates the CO2. After cooling by the cooler 8 (temperature controlled by cooling water U1), the liquid enters the reflux tank 6. A small portion of the liquid phase is pressurized by the reflux pump 14 and returned to the carbon dioxide desorption tower 4 as reflux. The majority is discharged as process wastewater S5. The gaseous carbon dioxide S4 at the top of the reflux tank 6 is treated and then vented or recovered. The lean carbon dioxide carbonate absorbent S11 from the bottom of the carbon dioxide desorption tower 4, after CO2 desorption, is pressurized by the bottom pump 13 and recycled back to the carbon dioxide absorption tower 2.

[0113] As can be seen from the examples and comparative examples, the system and method provided by the present invention can achieve simultaneous absorption of ethylene oxide and carbon dioxide in the same absorption tower and simultaneous desorption of ethylene oxide and carbon dioxide in the same desorption tower. This overcomes the shortcomings of the traditional two-step removal method. Compared with the prior art in Comparative Example 1, where ethylene oxide and carbon dioxide are absorbed in their respective absorption towers and desorbed in their respective desorption towers, i.e., the absorption and desorption of ethylene oxide and carbon dioxide are set up with two independent absorption and desorption tower systems, it can better achieve the simultaneous absorption and separation of ethylene oxide and carbon dioxide in the mixed gas after ethylene oxidation. This reduces the operational complexity of the ethylene oxide production unit while further reducing the energy and material consumption of the unit.

[0114] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A treatment system for gas containing ethylene oxide and carbon dioxide, characterized in that, The system includes an ethylene oxide-carbon dioxide absorption tower (1), a flash tank (2), and an ethylene oxide-carbon dioxide desorption tower (3) that are interconnected. The ethylene oxide-carbon dioxide absorption tower (1) is used to simultaneously absorb ethylene oxide and carbon dioxide in the reaction-rich circulating gas (S1) to obtain a rich absorbent (S7) containing ethylene oxide and carbon dioxide and a reaction-lean circulating gas (S2). The flash tank (2) is used to flash treat the rich absorbent (S7) to obtain light component gas (S3) and delighted components containing ethylene oxide and carbon dioxide; The ethylene oxide-carbon dioxide desorption tower (3) is used to simultaneously desorb ethylene oxide and carbon dioxide from the light components to obtain ethylene oxide (S5), carbon dioxide (S4) and lean absorbent (S6).

2. The system according to claim 1, wherein, The system also includes an ethylene oxide-carbon dioxide absorption tower inlet / outlet heat exchanger (4), the first inlet of which is connected to the reaction-rich circulating gas outlet of the upstream reaction unit, the first outlet of which is connected to the first inlet of the ethylene oxide-carbon dioxide absorption tower (1), the second inlet of which is connected to the first outlet of the ethylene oxide-carbon dioxide absorption tower (1), and the second outlet of which is connected to the inlet of the flash tank (2).

3. The system according to claim 1 or 2, wherein, The flash tank (2) is installed vertically and / or horizontally, preferably horizontally; Preferably, the top of the flash tank (2) is provided with a reabsorption section, which is used to absorb the flash vapor of the absorbent-rich (S7) to obtain light component gas (S3).

4. The system according to any one of claims 1-3, wherein, The system also includes a desorption tower top condenser (6), a desorption tower reflux tank (10), and a desorption tower top cryostat (7). The inlet of the desorption tower top condenser (6) is connected to the top gas phase outlet of the ethylene oxide-carbon dioxide desorption tower (3), and the outlet of the desorption tower top condenser (6) is connected to the first inlet of the desorption tower reflux tank (10). Preferably, the first outlet of the desorption tower reflux tank (10) is connected to the first inlet of the ethylene oxide-carbon dioxide desorption tower (3) and / or to the downstream ethylene oxide treatment unit; Preferably, the second outlet of the desorption tower reflux tank (10) is connected to the inlet of the desorption tower top cryostat (7); Preferably, the first outlet of the desorption tower top cryostat (7) is connected to the downstream carbon dioxide treatment unit.

5. The system according to claim 4, wherein, The system also includes a carbon dioxide injector (12), the suction side of which is connected to the second outlet of the desorption tower top cryostat (7), and the exhaust side of which is connected to the second inlet of the ethylene oxide-carbon dioxide desorption tower (3). Preferably, the system further includes a lean / rich absorbent heat exchanger (5), the first inlet of which is connected to the first outlet of the flash tank (2), and the first outlet of which is connected to the third inlet of the ethylene oxide-carbon dioxide desorption tower (3). Preferably, the system further includes a lean absorbent injection flash tank (11), the inlet of which is connected to the bottom liquid outlet of the ethylene oxide-carbon dioxide desorption tower (3), the liquid outlet of which is connected to the second inlet of the lean / rich absorbent heat exchanger (5), and the gas outlet of which is connected to the exhaust side of the carbon dioxide injector (12). Preferably, the system further includes a lean absorbent cooler (9), the first inlet of which is connected to the second outlet of the lean / rich absorbent heat exchanger (5), and the first outlet of the lean absorbent cooler (9) is connected to the reabsorption section of the flash tank (2) and / or the second inlet of the ethylene oxide-carbon dioxide absorption tower (1).

6. A method for treating gas containing ethylene oxide and carbon dioxide, wherein, The method is performed in the system described in any one of claims 1-5, and the method includes: (A) In the presence of lean absorbent (S6), reaction rich gas (S1) containing ethylene oxide and carbon dioxide is simultaneously absorbed in ethylene oxide-carbon dioxide absorption tower (1) to obtain rich absorbent (S7) containing ethylene oxide and carbon dioxide and reaction lean gas (S2), wherein the lean absorbent (S6) contains a composite absorbent. (B) The rich absorbent (S7) is flash-treated in a flash tank (2) to obtain light component gas S3 and delighted component containing ethylene oxide and carbon dioxide; (C) The light component is simultaneously desorbed into ethylene oxide and carbon dioxide in the ethylene oxide-carbon dioxide desorption tower (3) to obtain ethylene oxide (S5), carbon dioxide (S4) and lean absorbent (S6). The lean absorbent (S6) is returned to step (A) for reuse.

7. The method according to claim 6, wherein, In step (A), based on the total amount in the reaction-rich circulating gas (S1), the concentration of ethylene oxide is 0.5-5 mol / %, and the concentration of carbon dioxide is 0.5-9.5 mol / %. Preferably, in step (A), the temperature of the reaction-rich circulating gas (S1) is 35-80°C and the pressure is 1.2-3 MPaG; Preferably, in step (A), the composite absorbent contains acrylic acid carbonate and / or polyethylene glycol dimethyl ether; Preferably, in step (A), based on the total amount of the lean absorbent, the content of acrylic acid carbonate and / or polyethylene glycol dimethyl ether in the lean absorbent (S6) is 30-100 wt / %. Preferably, in step (A), the temperature of the lean absorbent (S6) is 5-50°C and the pressure is 1.2-3 MPaG; Preferably, in step (A), the conditions for synchronous absorption include a pressure of 1.2-3 MPaG.

8. The method according to claim 6 or 7, wherein, The pressure decreases progressively in steps (A), (B), and (C).

9. The method according to claim 6 or 7, wherein, In step (B), the flash evaporation conditions include a pressure of 0.1-1 MPaG.

10. The method according to claim 6 or 7, wherein, In step (C), the total amount of the reaction lean cycle gas (S2) is based on the following: the concentration of ethylene oxide is less than 100 ppm and the concentration of carbon dioxide is less than 1.2 mol / %. Preferably, in step (C), the conditions for simultaneous desorption include: a pressure of -0.99 MPaG to 0.3 MPaG and a temperature of 80-140°C.

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