Method for producing ethylene oxide

Abstract

[Problem] To provide a method for producing ethylene oxide, said method being capable of reducing the emission amount of carbon dioxide. [Solution] A method for producing ethylene oxide, said method comprising: an ethylene oxide production step 1 wherein a first mixture containing ethylene oxide is obtained by causing ethylene and oxygen to react with each other in the presence of a diluent gas; a gas-liquid separation step 2 wherein the first mixture is gas-liquid separated into a second mixture that contains ethylene, oxygen and carbon dioxide and a third mixture that contains ethylene oxide and water; a carbon dioxide separation step 3 wherein carbon dioxide is separated from the second mixture; and an electrolytic reduction step 4 wherein oxygen and a fourth mixture that contains ethylene, methane and carbon dioxide are obtained by electrolytically reducing the carbon dioxide. In the carbon dioxide separation step, carbon dioxide is separated from the fourth mixture. In the ethylene oxide production step, the second mixture and the fourth mixture, from which carbon dioxide has been removed, and the oxygen, which has been obtained in the electrolytic reduction step, are used as starting materials and a diluent gas.

Description

[Technical field]

[0001] The present invention relates to a process for producing ethylene oxide. [Background technology]

[0002] As shown in Patent Document 1, a method for producing ethylene oxide is known in which ethylene oxide is produced by catalytically oxidizing gaseous ethylene using silver as a catalyst. In this production method, a side reaction occurs in which ethylene is completely burned and carbon dioxide is produced. This side reaction occurs more easily as the conversion rate of ethylene increases. For this reason, a recycling method is often adopted for producing ethylene oxide, in which the conversion rate of ethylene is reduced, ethylene oxide is recovered from the reaction product, and the unreacted ethylene and oxygen are reused as raw materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-172272 A Summary of the Invention [Problem to be solved by the invention]

[0004] The carbon dioxide contained in the reaction product is separated from ethylene oxide, ethylene, oxygen, etc., and a part of it is recovered and used in food production, but most of it is released into the atmosphere. Since a large amount of carbon dioxide is emitted from the ethylene oxide production process, it is desirable to reduce it from the viewpoint of protecting the global environment.

[0005] In view of the above background, an object of the present invention is to provide a method for producing ethylene oxide that can reduce carbon dioxide emission. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, one aspect of the present invention is a method for producing ethylene oxide, comprising: an ethylene oxide production step (1) of reacting a raw material containing ethylene and oxygen in the presence of a diluent gas to obtain a first mixture containing ethylene oxide; a gas-liquid separation step (2) of separating the first mixture into a second mixture which is a gas component containing ethylene, oxygen, and carbon dioxide, and a third mixture which is a liquid component containing ethylene oxide and water; a carbon dioxide separation step (3) of separating carbon dioxide from the second mixture; and an electrolytic reduction step (4) of electrolytically reducing the carbon dioxide separated from the second mixture to obtain a fourth mixture containing ethylene, methane, and unreacted carbon dioxide at a cathode and to obtain oxygen at an anode, wherein the carbon dioxide separation step further separates unreacted carbon dioxide from the fourth mixture, and the ethylene oxide production step uses the second mixture and the fourth mixture from which carbon dioxide has been removed in the carbon dioxide separation step, and the oxygen obtained in the electrolytic reduction step, as at least a part of the raw material and the diluent gas.

[0007] According to this embodiment, ethylene and oxygen, which are raw materials for ethylene oxide, can be produced by utilizing carbon dioxide generated during the production of ethylene oxide. This allows a significant reduction in the amount of carbon dioxide emissions, which is a greenhouse gas. Furthermore, the cost of raw materials can be reduced in the method for producing ethylene oxide. Furthermore, methane, which is generated as a by-product when ethylene is produced from carbon dioxide, can be used as a dilution gas for reducing the oxygen concentration during the reaction of ethylene oxide, thereby reducing the cost of the dilution gas. Furthermore, the carbon dioxide separation step can be used to remove carbon dioxide from the fourth mixture generated from the cathode in the electrolytic reduction step.

[0008] In the above aspect, the fourth mixture may be mixed with the second mixture before it is treated in the carbon dioxide separation step.

[0009] According to this embodiment, the carbon dioxide separation step can be diverted to remove unreacted carbon dioxide from the fourth mixture produced in the electrolytic reduction step.

[0010] In the above aspect, in the electrolytic reduction step, a catalyst supported on the cathode may be selected so that the selectivity of ethylene at the cathode is 30% or more.

[0011] According to this embodiment, the ratio of ethylene produced during the electrolytic reduction of carbon dioxide is increased, thereby reducing the amount of methane produced, and preventing methane from becoming excessive relative to the amount required as a diluent gas.

[0012] In the above aspect, the electrolytic reduction step may use an electrolytic reduction device (10) including: a cathode gas chamber (11) to which gaseous carbon dioxide is supplied, a cathode fluid chamber (12) to which a cathode fluid is supplied, an anode fluid chamber (13) to which an anode fluid is supplied, a cathode (16) serving as a gas diffusion electrode separating the cathode gas chamber from the cathode fluid chamber, an ionically conductive partition wall (17) separating the cathode fluid chamber from the anode fluid chamber, and an anode (18) disposed in the anode fluid chamber.

[0013] According to this embodiment, it is possible to prevent the fourth mixture containing ethylene and methane and unreacted carbon dioxide produced at the cathode from being mixed with the oxygen produced at the anode, and therefore it is possible to omit the step of separating the carbon dioxide from the oxygen.

[0014] In the above aspect, the present invention may further include a carbon monoxide removal step of removing carbon monoxide from the fourth mixture generated in the electrolytic reduction step. Also, the carbon monoxide removal step may remove carbon monoxide from the fourth mixture before carbon dioxide is removed in the carbon dioxide separation step.

[0015] According to this embodiment, when the catalyst used in the ethylene oxide production step is poisoned by carbon monoxide, this can be suppressed.

[0016] In the above embodiment, the method may further include an ethylene glycol production step (6) of producing ethylene glycol from the ethylene oxide contained in the third mixture by a hydration method.

[0017] According to this embodiment, the produced ethylene oxide can be utilized to produce ethylene glycol.

[0018] In the above embodiment, in the electrolytic reduction step (4), carbon dioxide discharged from another plant may be used as part of the carbon dioxide to be electrolytically reduced.

[0019] According to this embodiment, the amounts of ethylene and methane produced can be increased, and the raw material and dilution gas can be further reduced.

[0020] In the above embodiment, in the electrolytic reduction step (4), the electrolytic reduction of carbon dioxide may be carried out using electricity generated from natural energy.

[0021] According to this embodiment, it is possible to suppress the amount of carbon dioxide discharged. Effect of the Invention

[0022] According to the above-mentioned embodiment, it is possible to provide a method for producing ethylene oxide that can reduce the amount of carbon dioxide emission. [Brief description of the drawings]

[0023] [Figure 1] Schematic diagram showing the production process of ethylene oxide and ethylene glycol [Diagram 2] Schematic diagram showing an electrolytic reduction device DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the method for producing ethylene oxide according to the present invention will be described. As shown in FIG. 1, the method for producing ethylene oxide according to the present invention includes an ethylene oxide production step 1 in which a raw material containing ethylene and oxygen is reacted in the presence of a diluent gas to obtain a first mixture containing ethylene oxide, a gas-liquid separation step 2 in which the first mixture is separated into a second mixture which is a gas component containing ethylene, oxygen, and carbon dioxide, and a third mixture which is a liquid component containing ethylene oxide and water, a carbon dioxide separation step 3 in which carbon dioxide is separated from the second mixture, and a carbon dioxide electrolytic reduction step 4 in which the carbon dioxide separated from the second mixture is electrolytically reduced to obtain a fourth mixture containing ethylene, methane, and unreacted carbon dioxide at the cathode and oxygen is obtained at the anode. The carbon dioxide separation step 3 further separates unreacted carbon dioxide from the fourth mixture. The ethylene oxide production step 1 uses the second mixture and the fourth mixture from which carbon dioxide has been removed in the carbon dioxide separation step 3, and the oxygen obtained in the electrolytic reduction step 4 as at least a part of the raw material and diluent gas.

[0025] In the ethylene oxide production step 1, ethylene gas is catalytically oxidized with oxygen gas in the presence of a silver catalyst to obtain a first mixture containing ethylene oxide. The ethylene oxidation reactor in which the ethylene oxide production step 1 is performed may be, for example, a multi-tube reaction vessel filled with a silver catalyst. Ethylene gas and oxygen gas as raw materials, and a diluent gas are heated and then supplied to the ethylene oxidation reactor. The diluent gas is used for the purpose of reducing the oxygen concentration in the ethylene oxidation reactor and suppressing explosion. The diluent gas may be, for example, an inert gas such as methane, nitrogen, or argon. In this embodiment, methane is used as the diluent gas as an example. The first mixture obtained from the ethylene oxidation reactor contains ethylene oxide as a reaction product, unreacted ethylene and oxygen, methane as a diluent gas, water as a by-reaction product, carbon dioxide, aldehydes such as formaldehyde and acetaldehyde, and organic acids such as acetic acid.

[0026] The silver catalyst may contain an alumina carrier and silver supported on the alumina carrier. The amount of silver supported may be, for example, 15 to 35 wt %. The silver catalyst may contain a promoter such as cesium, rhenium, tungsten, or molybdenum. The reaction conditions for the ethylene oxide production step 1 may be, for example, a temperature of 230 to 270° C., a pressure of 15 to 25 bar, and a GHSV (gas hourly space velocity) of 3000 to 8000 hr -1 In order to suppress the generation of carbon dioxide and water due to the combustion of ethylene, which is a side reaction, the conversion rate of ethylene is preferably set to 8 to 15%.

[0027] In the gas-liquid separation step 2, the first mixture is cooled to a temperature higher than the freezing point of water (0°C) and lower than the boiling point of ethylene oxide (10.7°C), and then separated into a second mixture, which is a gas component, and a third mixture, which is a liquid component. The second mixture contains ethylene, oxygen, and carbon dioxide. The third mixture contains water and ethylene oxide. In addition, the third mixture also contains by-products such as acetaldehyde and acetic acid. In the gas-liquid separation step 2, a gas-liquid separator such as a knockout drum may be used.

[0028] In the carbon dioxide separation step 3, carbon dioxide is separated from the second mixture. The separation of carbon dioxide may be performed by a carbon dioxide separation device based on a known method such as a chemical adsorption method such as the Benfield method and the MDEA (methyldiethanolamine) method, a physical adsorption method such as the Selexol method and the Rectisol method, a membrane separation method, a PSA method (pressure swing adsorption), or a PTSA method (pressure temperature swing adsorption). The carbon dioxide separated from the second mixture and adsorbed to various adsorbents is separated from the adsorbents by a regeneration process and becomes a highly concentrated gaseous state.

[0029] The second mixture after the carbon dioxide is separated contains ethylene, oxygen and methane. The gas containing ethylene, oxygen and methane is returned to the ethylene oxide production step 1 and used as a raw material and diluent gas for producing ethylene oxide.

[0030] In the carbon dioxide electrolytic reduction step 4, the carbon dioxide separated from the second mixture in the carbon dioxide separation step 3 is electrolytically reduced. In the electrolytic reduction step 4, it is preferable to use an electrolytic reduction device using a gas diffusion electrode as a cathode, an electrolytic reduction device using a solid polymer membrane as a separator, or the like.

[0031] As shown in FIG. 2, the electrolytic reduction device 10 used in the electrolytic reduction step 4 may be, for example, a three-chamber electrolytic reduction device. Specifically, the electrolytic reduction device 10 may have an electrolytic cell 14 having a cathode gas chamber 11, a cathode fluid chamber 12, and an anode fluid chamber 13, which are separated from one another. The cathode gas chamber 11 and the cathode fluid chamber 12 are separated by a cathode 16 serving as a gas diffusion electrode. The cathode fluid chamber 12 and the anode fluid chamber 13 are separated by a partition wall 17 having ion conductivity. The anode 18 is disposed in the anode fluid chamber 13. The cathode gas chamber 11 is supplied with carbon dioxide gas separated in the gas-liquid separation step 2. The cathode fluid chamber 12 is supplied with cathode fluid. The anode fluid chamber 13 is supplied with anode fluid. The anode 18 and the cathode 16 are connected to a DC power source 19.

[0032] The anolyte and catholyte are aqueous solutions having an electrolyte dissolved therein. The electrolyte includes potassium, sodium, lithium, or at least one of these compounds. For example, the electrolyte may include at least one of the group consisting of LiOH, NaOH, KOH, Li2CO3, Na2CO3, K2CO3, LiHCO3, NaHCO3, and KHCO3.

[0033] The cathode 16 is a gas diffusion electrode, and has a gas diffusion layer 21 and a microporous layer 22. The gas diffusion layer 21 is permeable to gas containing carbon dioxide, but suppresses the permeation of an aqueous solution containing a cathode liquid. The microporous layer 22 is permeable to both gas containing carbon dioxide and an aqueous solution containing a cathode liquid. The gas diffusion layer 21 and the microporous layer 22 are each formed in a planar shape. The gas diffusion layer 21 is disposed on the cathode gas chamber 11 side, and the microporous layer 22 is disposed on the cathode liquid chamber 12 side.

[0034] The gas diffusion layer 21 may be a porous conductive substrate such as carbon paper, carbon felt, or carbon cloth on which a water-repellent coating such as polytetrafluoroethylene is formed. The conductive substrate is connected to the negative electrode of the DC power source 19 and receives a supply of electrons. The microporous layer 22 is formed on the surface of the gas diffusion layer 21 using carbon black or the like and supports a catalyst. The catalyst may be a known carbon dioxide reduction catalyst, and includes at least one of, for example, a Group 11 element such as copper, a Group 12 element such as zinc, a Group 13 element such as gallium, a Group 14 element such as germanium, or a metal compound thereof. The metal compound includes at least one of an oxide, a sulfide, and a phosphide. The catalyst is preferably one suitable for reducing carbon dioxide to produce ethylene, and is preferably, for example, copper or a copper compound. A binder such as an ion exchange resin may be added to the microporous layer 22.

[0035] The anode 18 is made of, for example, a metal material such as titanium, nickel, molybdenum, platinum, gold, silver, copper, iron, lead, or the like, or an alloy material of these metals, a carbon-based material such as carbon, or a conductive ceramic. The shape of the anode 18 may be a flat plate, a flat plate with a plurality of openings, a mesh, or a porous body. The shape of the openings formed in the flat plate may be a circle, a diamond, a star, or the like. The flat plate may be formed in a corrugated or curved shape, and may have an uneven surface. The anode 18 supports an oxygen generating catalyst such as platinum or iridium. The anode 18 may be provided on the surface of the partition wall 17 on the anode liquid chamber 13 side.

[0036] The DC power supply 19 converts power obtained by thermal power generation, nuclear power generation, solar power generation, wind power generation, hydroelectric power generation, or the like into DC as necessary and supplies the power to the cathode 16 and the anode 18. From the viewpoint of reducing carbon dioxide emissions, it is preferable to use power obtained by solar power generation, wind power generation, hydroelectric power generation, or the like that utilizes natural energy (renewable energy) as the DC power supply 19. The DC power supply 19 applies a voltage so that the cathode 16 has a negative potential with respect to the anode 18. The DC power supply 19 may obtain the potential of the cathode 16 using a reference electrode and control the voltage applied so that the potential of the cathode 16 is within a predetermined range.

[0037] The cathode gas chamber 11 has an inlet 24 and an outlet 25. Carbon dioxide gas supplied from the carbon dioxide separation process 3 is supplied from the inlet 24 and discharged from the outlet 25. The outlet 25 of the cathode gas chamber 11 is connected to the inlet 24 via a gas circulation path 26.

[0038] The cathode fluid chamber 12 has an inlet 27 and an outlet 28. The inlet 27 and the outlet 28 of the cathode fluid chamber 12 are connected by a cathode fluid circulation path 29. Similarly, the anolyte chamber 13 has an inlet 31 and an outlet 32. The inlet 31 and the outlet 32 ​​of the anolyte chamber 13 are connected by an anolyte circulation path 33. The cathode fluid circulation path 29 is provided with a cathode side gas-liquid separator 35. The anolyte circulation path 33 is provided with an anode side gas-liquid separator 36. In addition, the cathode fluid circulation path 29 and the anolyte circulation path 33 may each be provided with an electrolyte concentration control device 37, 38 for adjusting the electrolyte concentrations of the cathode fluid and the anolyte within a predetermined range. The electrolyte concentration control devices 37, 38 preferably include sensors for detecting the electrolyte concentrations of the cathode fluid and the anolyte, an electrolyte fluid supplier for supplying new cathode fluid and anolyte of predetermined concentrations, and a drainage device for discharging a portion of the circulating cathode fluid and anolyte.

[0039] The gas circulation passage 26 is provided with a gas circulation flow rate regulator 40 for discharging a portion of the gas circulating therein. The outlet of the gas circulation flow rate regulator 40 is connected to a first gas return passage 41. The first gas return passage 41 is connected to a gas discharge passage of the cathode-side gas-liquid separator 35. The gas circulation flow rate regulator 40 regulates the flow rate and pressure of the gas circulating through the gas circulation passage 26 and the cathode gas chamber 11 by discharging the gas to the first gas return passage 41. The gas circulation flow rate regulator 40 maintains the gas pressure in the cathode gas chamber 11 at a predetermined value higher than the liquid pressure in the cathode liquid chamber 12. This prevents the cathode liquid in the cathode liquid chamber 12 from passing through the cathode 16 and flowing into the cathode gas chamber 11. A portion of the gas in the cathode gas chamber 11 passes through the cathode 16 and flows into the cathode liquid chamber 12. It is preferable that the amount of gas flowing from the cathode gas chamber 11 into the cathode liquid chamber 12 be small.

[0040] The carbon dioxide in the cathode gas chamber 11 diffuses into the gas diffusion layer 21 of the cathode 16 and is reduced in the microporous layer 22 to obtain a fourth mixture. The fourth mixture contains ethylene and methane as main products, and contains minute amounts of by-products such as hydrogen, carbon monoxide, and formic acid. Most of the fourth mixture is generated on the cathode gas chamber 11 side of the cathode 16. A part of the fourth mixture is generated on the cathode fluid chamber 12 side of the cathode 16. The fourth mixture in the cathode fluid chamber 12 is mixed with unreacted carbon dioxide that has flowed into the cathode fluid chamber 12. Similarly, the fourth mixture in the cathode gas chamber 11 is mixed with unreacted carbon dioxide.

[0041] Of the fourth mixture generated on the cathode fluid chamber 12 side of the cathode 16, ethylene, methane, and by-products hydrogen and carbon monoxide are gaseous and are separated from the cathode fluid together with unreacted carbon dioxide by the cathode-side gas-liquid separator 35 of the cathode fluid circulation path 29 and flow into the first gas return passage 41. Of the fourth mixture, formic acid is liquid and circulates through the cathode fluid circulation path 29 together with the cathode fluid and is discharged from the electrolyte concentration control device 37 together with the cathode fluid.

[0042] Of the fourth mixture generated on the cathode gas chamber 11 side of the cathode 16, ethylene, methane, and by-products hydrogen and carbon monoxide circulate through the gas circulation path 26 together with unreacted carbon dioxide, and are discharged from the gas circulation flow rate adjuster 40 to the first gas return passage 41. The fourth mixture containing ethylene, methane, and by-products hydrogen and carbon monoxide generated in the cathode liquid chamber 12 of the cathode 16, and unreacted carbon dioxide flows from the cathode-side gas-liquid separator 35 and the gas circulation flow rate adjuster 40 to the first gas return passage 41.

[0043] In the anode 18, water and hydroxide ions in the anolyte are oxidized to generate oxygen. The oxygen is in the form of gas, and is separated from the anolyte by the anode-side gas-liquid separator 36 in the anolyte circulation passage 33 and flows into the second gas return passage 42.

[0044] In the electrolytic reduction step 4, it is preferable to select a catalyst supported on the cathode 16 so that the selectivity for ethylene production at the cathode 16 is 30% or more.

[0045] The fourth mixture containing ethylene and methane generated at the cathode 16 in the carbon dioxide electrolytic reduction step 4 is supplied to the carbon dioxide separation step 3 through the first gas return passage 41, where the carbon dioxide is removed. The fourth mixture containing ethylene and methane may contain carbon monoxide or hydrogen. In such a case, the fourth mixture may be supplied to the carbon monoxide removal step 5 before being supplied to the carbon dioxide separation step 3, where the carbon monoxide is removed. In the carbon monoxide removal step 5, the carbon monoxide may be adsorbed using an adsorbent using, for example, zeolite. The carbon monoxide removal step 5 is not an essential component and may be omitted. The fourth mixture containing ethylene and methane may also be supplied to a hydrogen removal step before being supplied to the carbon dioxide separation step 3, where the hydrogen is removed. For example, pressure swing adsorption (PSA) or the like may be applied to the hydrogen removal step. The hydrogen removal step is not an essential component and may be omitted. The fourth mixture supplied from the first gas return passage 41 may be mixed with the second mixture supplied from the gas-liquid separation step 2 to the carbon dioxide separation step 3. As a result, the fourth mixture is returned to the ethylene oxide production step 1 together with the second mixture, carbon dioxide is removed therefrom in the gas-liquid separation step 2, and the fourth mixture is used as part of the raw material and diluent gas.

[0046] The oxygen supplied from the second gas return passage 42, i.e., the oxygen generated from the anode 18 in the electrolytic reduction step 4, is returned to the ethylene oxide production step 1 and used as part of the raw material. The oxygen generated from the anode 18 in the electrolytic reduction step 4 is preferably mixed with the second mixture and the fourth mixture from which carbon dioxide has been removed in the carbon dioxide separation step 3, and then returned to the ethylene oxide production step 1.

[0047] A sensor 51 may be provided for detecting the flow rate of each component of the gas supplied from the carbon dioxide separation step 3 and the second gas return passage 42. Furthermore, a control device (not shown) may adjust the flow rates of ethylene, oxygen, and methane supplied to the ethylene oxidation reactor of the ethylene oxide production step 1 by controlling flow rate control valves 52, 53, and 54 that control the flow rates of ethylene, oxygen, and methane newly supplied to the ethylene oxide production step 1, based on the detection value of the sensor 51.

[0048] The third mixture containing ethylene oxide and water separated from the first mixture in the gas-liquid separation step 2 is used as a raw material in the ethylene glycol production step 6. In the ethylene glycol production step 6, ethylene glycol is produced by hydrolyzing ethylene oxide in the presence of a catalyst, i.e., by a hydration method. The catalyst may be, for example, a resin catalyst such as "Amberlist" (registered trademark), "Doulit" (registered trademark), or "DOWEX" (registered trademark). In the ethylene glycol production reaction, the reaction temperature is preferably 100 to 120°C, and the reaction pressure is preferably 20 to 35 bar.

[0049] The effects of the above embodiment will be described. According to the method for producing ethylene oxide according to the embodiment, it is possible to produce ethylene and oxygen, which are raw materials for ethylene oxide, by utilizing carbon dioxide generated during the production of ethylene oxide. This makes it possible to reduce the amount of carbon dioxide emissions, which is a greenhouse gas. Furthermore, it is possible to reduce raw material costs in the method for producing ethylene oxide. Furthermore, methane, which is generated as a by-product when producing ethylene from carbon dioxide, can be used as a dilution gas for reducing the oxygen concentration during the reaction of ethylene oxide, thereby reducing the cost of the dilution gas.

[0050] In the carbon dioxide electrolytic reduction step 4, by setting the faradaic efficiency for the production of ethylene at the cathode 16 to 30% or more, it is possible to reduce the amount of methane produced during the electrolytic reduction of carbon dioxide and to prevent methane from becoming excessive relative to the amount required as a diluent gas.

[0051] Examples of the above embodiment will now be described.

[0052] Example 1 An example of the ethylene oxide production process 1 will be described. A fixed-bed type reactor was used, which was filled with about 30 cc of a catalyst in which 20 wt% of silver was supported on α-alumina and 3 wt% of rhenium was further added as a promoter. A gas containing 25 mol% ethylene, 10 mol% oxygen, and 65 mol% methane was fed at a temperature of 250°C, a pressure of 20 bar, and a GHSV of 5000 hr. -1 The reaction products obtained from the outlet of the reactor were 22.6 mol % ethylene, 3.7 mol % oxygen, 65.9 mol % methane, 2.1 mol % ethylene oxide, 2.3 mol % carbon dioxide, and 3.4 mol % water.

[0053] Example 2 An example of the carbon dioxide absorption method in the carbon dioxide separation step 3 will be described. A glass gas absorption bottle was immersed in a thermostatic water bath set to a temperature of 40°C, and 50 mL of an aqueous solution containing 18.8 wt% N-methyldiethanolamine and 31.2 wt% piperazine was filled in the bottle. A mixed gas containing 20 wt% carbon dioxide and 80 wt% nitrogen was dispersed in the form of bubbles at atmospheric pressure and 0.7 L / min into the liquid to be absorbed. The carbon dioxide concentration in the gas at the inlet and outlet of the absorption liquid was measured, and the carbon dioxide absorption amount was measured from the difference in the carbon dioxide flow rate at the inlet and outlet. The saturated absorption amount was the amount at the time when the carbon dioxide concentration at the outlet of the absorption liquid coincided with the carbon dioxide concentration at the inlet. The saturated absorption amount of carbon dioxide was 115.7 g / L. Next, the liquid temperature was raised to 70°C in a few minutes in the same gas flow, and the amount and rate of carbon dioxide desorption from the liquid were measured. The amount of carbon dioxide desorption was 25.4 g / L, and the desorption rate was 2.05 g / L / min.

[0054] Example 3 An example of the carbon dioxide electrolytic reduction step 4 will be described. An electrolytic reduction device 10 having the above-mentioned cathode gas chamber 11, cathode fluid chamber 12, and anode fluid chamber 13 was used. A copper-zinc composite catalyst was used as the catalyst in the gas diffusion layer 21 of the cathode 16. The anode 18 was a titanium plate carrying an iridium oxide catalyst. A 1 M aqueous potassium bicarbonate solution was flowed at 1 mL / min as the anode fluid and cathode fluid. Carbon dioxide was flowed at 100 mL / min into the cathode gas chamber 11, and a current of 300 mA / cm was applied. 2 The current was passed for 6 hours at this temperature. Analysis of the components of the gas generated from the cathode fluid chamber 12 revealed that the ethylene selectivity was 53% at the cathode 16, the methane selectivity was 18%, and the hydrogen selectivity was 20%. Analysis of the components of the gas generated from the anode fluid chamber 13 revealed that the oxygen selectivity was 99% at the anode 18.

[0055] Example 4 Table 1 below shows the calculation results of the material balance when ethylene glycol is produced at 100 ton / hr, assuming a plant using the above-mentioned ethylene oxide production method. As shown in FIG. 1, the composition of the raw material of the ethylene oxide production process 1 newly added from outside the system is C1, the composition of the product of the ethylene glycol production process 6 is C2, the composition of the material supplied from the carbon dioxide separation process 3 to the electrolytic reduction process 4 is C3, the composition of the mixture of the second and fourth mixtures from which carbon dioxide has been removed by the carbon dioxide separation process 3 and oxygen from the electrolytic reduction process 4 is C4, the composition of the material supplied to the ethylene glycol production process 6 is C5, and the composition of the dilution gas of the ethylene oxide production process 1 newly added from outside the system is C6. As the calculation conditions of the material balance, the outlet temperature of the ethylene oxidation reactor in the ethylene oxide production process 1 was 250°C, and the outlet pressure was 20 bar. In addition, the carbon dioxide was absorbed in the carbon dioxide separation process 3 using a chemical absorption method using an aqueous solution containing 18.8 wt% N-methyldiethanolamine and 31.2 wt% piperazine. The reaction conditions in the reactor in the ethylene glycol production step 6 were a reaction temperature of 100° C. and a pressure of 25 bar. The reaction conditions in the carbon dioxide electrolytic reduction step 4 were a carbon dioxide conversion rate of 70%, an ethylene selectivity at the cathode 16 of 80%, and a methane selectivity of 20%.

[0056] [Table 1]

[0057] Although the description of the specific embodiment is finished above, the present invention is not limited to the above embodiment and can be widely modified. The second gas return passage 42 may be connected to the first gas return passage 41. In this case, the oxygen generated at the anode 18 is mixed with the fourth mixture generated at the cathode 16, and after carbon dioxide is separated in the carbon dioxide separation process 3, it is returned to the ethylene oxide production process 1.

[0058] Various known electrolytic reduction devices can be applied to the electrolytic reduction device 10. For example, the electrolytic reduction device 10 may be configured such that the cathode gas chamber 11 is omitted and the cathode 16 is disposed in the cathode liquid chamber 12. In this case, carbon dioxide gas may be blown into the cathode liquid by bubbling in the vicinity of the cathode 16. Alternatively, carbon dioxide gas may be dissolved in the cathode liquid.

[0059] In the carbon dioxide electrolytic reduction step 4, carbon dioxide discharged from another plant may be used as part of the carbon dioxide to be electrolytically reduced, thereby increasing the amounts of ethylene and methane produced. [Explanation of symbols]

[0060] 1: Ethylene oxide production process 2: Gas-liquid separation process 3: Carbon dioxide separation process 4: Electrolytic reduction process 5: Carbon monoxide separation process 6: Ethylene glycol production process 10: Electrolytic reduction device 11: Cathode gas chamber 12: Cathode liquid chamber 13: Anode fluid chamber 14: Electrolytic cell 16: Cathode 17: Bulkhead 18: Anode 19:DC power supply 24: Entrance 25:Exit 26: Gas circulation path 27: Entrance 28: Exit 29: Cathode liquid circulation path 31: Entrance 32:Exit 33: Anode liquid circulation path 35: Cathode side gas-liquid separator 36: Anode side gas-liquid separator 37: Electrolyte concentration control device 38: Electrolyte concentration control device 40: Gas circulation flow rate control device 41: First gas return passage 51: Sensor 52: Flow control valve 53: Flow control valve 54: Flow control valve

Claims

1. A method for producing ethylene oxide, comprising the steps of: an ethylene oxide production step of reacting a raw material containing ethylene and oxygen in the presence of a diluent gas to obtain a first mixture containing ethylene oxide; a gas-liquid separation step of separating the first mixture into a second mixture which is a gas component containing ethylene, oxygen, and carbon dioxide, and a third mixture which is a liquid component containing ethylene oxide and water; a carbon dioxide separation step of separating carbon dioxide from the second mixture; and a carbon dioxide electrolytic reduction step of electrolytically reducing the carbon dioxide separated from the second mixture to obtain a fourth mixture containing ethylene, methane and unreacted carbon dioxide at the cathode and to obtain oxygen at the anode. The carbon dioxide separation step further comprises separating carbon dioxide from the fourth mixture, the ethylene oxide production step uses the second mixture and the fourth mixture from which carbon dioxide has been removed in the carbon dioxide separation step, and oxygen obtained in the electrolytic reduction step, as at least a part of the raw material and the diluent gas; The fourth mixture is mixed with the second mixture before being treated in the carbon dioxide separation step, The oxygen generated at the anode is mixed with the second mixture and the fourth mixture from which carbon dioxide has been removed in the carbon dioxide separation step, and then returned to the ethylene oxide production step.

2. 2. The method for producing ethylene oxide according to claim 1, wherein in the electrolytic reduction step, a catalyst supported on the cathode is selected so that a selectivity of the ethylene at the cathode is 30% or more.

3. 3. The method for producing ethylene oxide according to claim 1 or 2, wherein the electrolytic reduction step uses an electrolytic reduction device having: a cathode gas chamber to which gaseous carbon dioxide is supplied, a cathode fluid chamber to which a cathode fluid is supplied, an anode fluid chamber to which an anode fluid is supplied, a cathode serving as a gas diffusion electrode separating the cathode gas chamber from the cathode fluid chamber, a partition wall having ion conductivity separating the cathode fluid chamber from the anode fluid chamber, and an anode disposed in the anode fluid chamber.

4. 4. The method for producing ethylene oxide according to claim 1, further comprising a carbon monoxide removal step of removing carbon monoxide from the fourth mixture generated in the electrolytic reduction step.

5. The method for producing ethylene oxide according to claim 4, wherein the carbon monoxide removal step removes carbon monoxide from the fourth mixture before carbon dioxide is removed in the carbon dioxide separation step.

6. 6. The method for producing ethylene oxide according to claim 1, further comprising an ethylene glycol production step of producing ethylene glycol from the ethylene oxide contained in the third mixture by a hydration method.

7. The method for producing ethylene oxide according to any one of claims 1 to 6, wherein in the electrolytic reduction step, carbon dioxide discharged from another plant is used as part of the carbon dioxide to be electrolytically reduced.

8. The method for producing ethylene oxide according to any one of claims 1 to 7, wherein the electrolytic reduction step performs the electrolytic reduction of carbon dioxide using electric power generated by natural energy.

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