Method for improving yield of ethylene glycol
By synthesizing Cu/SiO2-NCNTs-NH2 catalyst, the problem of low yield in the process of hydrogenation of dimethyl oxalate to produce ethylene glycol is solved, and the effect of improving the yield of ethylene glycol and easy catalyst recovery is achieved.
Patent Information
- Application Number
- CN202411763392.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-03
- Publication Date
- 2025-03-04
AI Technical Summary
During the process of hydrogenation of dimethyl oxalate to produce ethylene glycol, methyl glycolate is easily adsorbed on Si-OH in the Cu/SiO2 catalyst, resulting in the cover of active sites and the generation of by-products, thereby reducing the yield of ethylene glycol.
The Cu/SiO2-NCNTs-NH2 catalyst was synthesized, and by introducing nitrogen-doped magnetic carbon nanotubes (NCNTs) into the Cu/SiO2 catalyst and grafting amino groups (-NH2), the pore structure and dispersion of active sites of the catalyst are improved, and the generation of by-products is reduced.
The hydrogenation reaction rate is increased, the generation of by-products is reduced, the selectivity and yield of ethylene glycol is improved, and the catalyst is easy to recover.
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Figure BDA0005168250880000081
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of ethylene glycol hydrogenation preparation, and in particular to a method for improving the yield of ethylene glycol. Background Art
[0002] Ethylene glycol is an extremely critical organic chemical raw material in the field of petrochemicals. It is not only used to synthesize polyethylene terephthalate (PET) with terephthalic acid, but is also widely used in the manufacture of alkyd resins, polyester fibers and polyester plastics. In addition, ethylene glycol can also be used to produce desiccant, plasticizer, surfactant, cosmetics and explosives, and is used as a solvent for dyes, inks and other products, and is also used to prepare engine antifreeze.
[0003] The traditional ethylene glycol production routes are mainly divided into petroleum-based ethylene oxide hydration and coal and natural gas-based C1 synthesis technology. C1 synthesis technology generates dimethyl oxalate (DMO) through CO oxidative coupling, and then converts dimethyl oxalate into ethylene glycol through catalytic hydrogenation. The petroleum route technology is quite mature, but it is highly dependent on petroleum resources. In view of the characteristics of my country's energy structure, that is, abundant coal resources and relatively scarce petroleum resources, C1 synthesis technology provides a feasible alternative to coal-to-ethylene glycol.
[0004] In the process of hydrogenation of dimethyl oxalate to ethylene glycol, the catalyst is the key factor. Copper-based catalysts are mostly used in the hydrogenation of dimethyl oxalate to ethylene glycol. Copper-based catalysts can selectively catalytically activate CO / C=O bonds, but the catalytic activity for CC bonds is very low, so they are proven to be good catalysts for selective hydrogenation of CO / C=O bonds. When SiO2 is used as a carrier, the dispersion of Cu species is higher and the catalytic performance is better.
[0005] However, in the process of hydrogenating dimethyl oxalate to ethylene glycol, the intermediate product methyl glycolate is first generated, and then methyl glycolate is further hydrogenated to ethylene glycol. Methyl glycolate is easily adsorbed on the silanol (Si-OH) in the Cu / SiO2 catalyst, resulting in the covering of the active sites; at the same time, Si-OH, as a basic site, will accelerate the formation of side reactions and generate by-products, resulting in a low yield of ethylene glycol. Summary of the invention
[0006] The object of the present invention is to provide a method for improving the yield of ethylene glycol, so as to solve the problem of low yield in the process of preparing ethylene glycol by hydrogenation of dimethyl oxalate.
[0007] The purpose of the present invention can be achieved by the following technical solutions:
[0008] A method for improving the yield of ethylene glycol comprises the following steps:
[0009] S1, synthesis of Cu / SiO2-NCNTs-NH2 catalyst;
[0010] S2, Cu / SiO2-NCNTs-NH2 catalyst catalyzes the hydrogenation of dimethyl oxalate to ethylene glycol;
[0011] NCNTs are nitrogen-doped magnetic carbon nanotubes.
[0012] Further, the Cu / SiO2-NCNTs-NH2 catalyst described in S1 is prepared by the following steps:
[0013] S11. Preparation of Cu / SiO2-NCNTs:
[0014] Dissolve soluble copper salt in deionized water, add ammonia water to mix, then add urea and nitrogen-doped magnetic carbon nanotubes, and then slowly add colloidal silica with a burette under mechanical stirring; stir at 70-75°C for 3-4 hours, filter, wash with deionized water, and dry, and calcine the dried product at 340-350°C in an air atmosphere for 2-2.5 hours to obtain Cu / SiO2-NCNTs;
[0015] S12, Cu / SiO2-NCNTs grafted with amino groups to obtain Cu / SiO2-NCNTs-NH2:
[0016] Mix Cu / SiO2-NCNTs with anhydrous methanol, and add aminosilane coupling agent dropwise at 40-50°C while stirring. Heat the solution after the reaction to 80-90°C, stir and react for 5-6h, centrifuge, wash and dry the anhydrous ethanol to obtain Cu / SiO2-NCNTs-NH2.
[0017] Furthermore, the soluble copper salt in S11 is one of copper nitrate trihydrate, copper chloride dihydrate and copper acetate monohydrate.
[0018] Furthermore, the mass ratio of copper in the soluble copper salt, the mass of silicon dioxide in the colloidal silicon dioxide and the mass ratio of nitrogen-doped magnetic carbon nanotubes in S11 is 20:65-75:5-15.
[0019] Furthermore, the preparation steps of the nitrogen-doped magnetic carbon nanotubes in S11 are:
[0020] Ultrasonic dispersion of ferric chloride hexahydrate in anhydrous ethanol, and then addition of melamine for ultrasonic dispersion to obtain a uniform suspension; continuous stirring of the suspension at 70-75° C. until the ethanol is completely volatilized to obtain a precursor; drying and grinding the precursor, and then placing the precursor in an Ar-filled tubular furnace and heating it to 650° C. at 3° C. / min, and keeping the temperature for 2 hours for high-temperature calcination and pyrolysis to obtain nitrogen-doped magnetic carbon nanotubes;
[0021] The molar ratio of the ferric chloride hexahydrate to melamine is 1:2.
[0022] Furthermore, the aminosilane coupling agent in S12 is one of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane and 4-aminobutyltriethoxysilane.
[0023] Furthermore, the dosage ratio of Cu / SiO2-NCNTs and aminosilane coupling agent in S12 is 2 g:1 mmol.
[0024] Further, the step of catalytic hydrogenation of dimethyl oxalate to ethylene glycol by the Cu / SiO2-NCNTs-NH2 catalyst in S2 is:
[0025] S21, Cu / SiO2-NCNTs-NH2 catalyst activation:
[0026] The Cu / SiO2-NCNTs-NH2 catalyst was reduced in a H2 atmosphere at 300-350°C for 4-5h, and then cooled to the reaction temperature to obtain activated Cu / SiO2-NCNTs-NH2;
[0027] S22, activated Cu / SiO2-NCNTs-NH2 catalyzed hydrogenation of dimethyl oxalate:
[0028] 200-300 mg of activated Cu / SiO2-NCNTs-NH2 catalyst was loaded into a fixed bed reactor, and hydrogen was introduced into the reactor. The hydrogen pressure was set to 2.5 MPa, the reaction temperature was set to 200 °C, the hydrogen-to-ester ratio was set to 80, and the mass liquid hourly space velocity of dimethyl oxalate was set to 1-2 h -1 , catalytic hydrogenation for 2h to obtain ethylene glycol.
[0029] Furthermore, the H2 atmosphere in S21 is a H2-N2 mixed gas or a H2-Ar mixed gas with a H2 mass fraction of 5-10%.
[0030] Furthermore, the fixed bed reactor in S22 is a cylindrical reactor with a tube length of 80 cm and an inner diameter of 6 mm.
[0031] Beneficial effects of the present invention:
[0032] (1) The present invention prepares Cu / SiO2-NCNTs-NH2 as a catalyst to catalyze the hydrogenation of dimethyl oxalate to prepare ethylene glycol; the catalyst can increase the hydrogenation reaction rate, reduce the generation of by-products, and improve the selectivity of ethylene glycol, thereby increasing the yield of ethylene glycol and being easy to recycle.
[0033] (2) The introduction of nitrogen-doped magnetic carbon nanotubes (NCNTs) into the Cu / SiO2 catalyst can improve the pore structure of the catalyst, thereby increasing the dispersion of the active component Cu; in addition, the high electrical conductivity of NCNTs helps to quickly transfer electrons to the Cu active sites, thereby improving the electron supply efficiency of the catalytic reaction and enhancing the activation of hydrogen; thereby increasing the rate of the hydrogenation reaction and thus increasing the yield of ethylene glycol.
[0034] (3) Grafting amino groups (-NH2) onto Cu / SiO2 catalysts can passivate silanol groups (Si-OH), thereby reducing the probability that the intermediate product methyl glycolate is easily adsorbed on Si-OH in the Cu / SiO2 catalyst, resulting in the active site being covered; it also reduces the probability that Si-OH acts as a basic site and generates by-products; and -NH2 can provide electrons, increasing the electron cloud density on the surface of the active component Cu, thereby promoting the dissociation of hydrogen; therefore, grafting -NH2 onto Cu / SiO2 catalysts can increase the hydrogenation reaction rate and enhance the selectivity of ethylene glycol, thereby increasing the yield of ethylene glycol. DETAILED DESCRIPTION
[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0036] Example 1
[0037] This embodiment provides a method for improving the yield of ethylene glycol, comprising the following steps:
[0038] S1. Synthesis of Cu / SiO2-NCNTs-NH2 catalyst:
[0039] S11. Preparation of Cu / SiO2-NCNTs:
[0040] 9.06 g of copper nitrate trihydrate was dissolved in 100 mL of deionized water, stirred and ammonia water was added until the precipitate disappeared, then 6 g of urea and 0.6 g of nitrogen-doped magnetic carbon nanotubes (NCNTs) were added, and then 36 g of 25 wt% colloidal silica was slowly added dropwise with a burette under mechanical stirring; stirred at 75° C. for 3 h, filtered, washed with deionized water, and dried, and the dried product was calcined at 350° C. in an air atmosphere for 2 h to obtain Cu / SiO2-NCNTs containing 20% Cu, 75% SiO2 and 5% NCNTs, recorded as 20Cu / 75SiO2-5NCNTs;
[0041] The preparation steps of the nitrogen-doped magnetic carbon nanotubes are as follows:
[0042] 10 mL of 1 mol / L ferric chloride hexahydrate was ultrasonically dispersed in anhydrous ethanol, and then 2.5 g of melamine was added and ultrasonically dispersed to obtain a uniform suspension; the suspension was continuously stirred at 75°C until the ethanol was completely volatilized to obtain a precursor; the precursor was dried and ground, and then placed in an Ar-filled tubular furnace and heated to 650°C at 3°C / min, and kept warm for 2 hours for high-temperature calcination and pyrolysis to obtain nitrogen-doped magnetic carbon nanotubes.
[0043] S12, Cu / SiO2-NCNTs grafted with amino groups to obtain Cu / SiO2-NCNTs-NH2:
[0044] Mix 2 g of 20Cu / 75SiO2-5NCNTs with 50 mL of anhydrous methanol, and add 0.18 g of 3-aminopropyltrimethoxysilane dropwise while stirring at 40-50°C. Heat the solution after the reaction to 90°C and stir for 5 h. Centrifuge, wash and dry with anhydrous ethanol to obtain 20Cu / 75SiO2-5NCNTs-NH2.
[0045] S2, Cu / SiO2-NCNTs-NH2 catalyst catalyzes hydrogenation of dimethyl oxalate to ethylene glycol:
[0046] S21, Cu / SiO2-NCNTs-NH2 catalyst activation:
[0047] 200 mg of 20Cu / 75SiO2-5NCNTs-NH2 catalyst was reduced in a H2-N2 mixed gas with a H2 mass fraction of 10% at 300°C for 5 h, and then cooled to the reaction temperature to obtain activated 20Cu / 75SiO2-5NCNTs-NH2;
[0048] S22, activated Cu / SiO2-NCNTs-NH2 catalyzed hydrogenation of dimethyl oxalate:
[0049] 200 mg of activated 20Cu / 75SiO2-5NCNTs-NH2 catalyst was loaded into a cylindrical reactor with a tube length of 80 cm and an inner diameter of 6 mm. Hydrogen was introduced into the reactor. The hydrogen pressure was set to 2.5 MPa, the reaction temperature was 200 °C, the hydrogen-to-ester ratio was 80, and the mass liquid hourly space velocity of dimethyl oxalate was 1 h -1 , catalytic hydrogenation for 2h to obtain ethylene glycol.
[0050] Example 2
[0051] Compared with Example 1, the difference between this example is that the "0.6g nitrogen-doped magnetic carbon nanotubes (NCNT), 36g 25wt% colloidal silica" in S11 is changed to "1.2g nitrogen-doped magnetic carbon nanotubes (NCNT), 33.6g 25wt% colloidal silica", and the catalyst prepared at this time is 20Cu / 70SiO2-10NCNTs-NH2; the other raw materials and preparation process remain the same as in Example 1.
[0052] Example 3
[0053] Compared with Example 1, the difference between this example is that the "0.6g nitrogen-doped magnetic carbon nanotubes (NCNT), 36g 25wt% colloidal silica" in S11 is changed to "1.8g nitrogen-doped magnetic carbon nanotubes (NCNT), 31.2g 25wt% colloidal silica". The catalyst prepared at this time is 20Cu / 65SiO2-15NCNTs-NH2; the other raw materials and preparation process remain the same as in Example 1.
[0054] Example 4
[0055] Compared with Example 3, this embodiment differs in that the "200 mg activated 20Cu / 65SiO2-15NCNTs-NH2 catalyst" in S22 is changed to "250 mg activated 20Cu / 65SiO2-15NCNTs-NH2 catalyst"; the remaining raw materials and preparation process remain the same as in Example 3.
[0056] Example 5
[0057] Compared with Example 3, this embodiment differs in that the "200 mg activated 20Cu / 65SiO2-15NCNTs-NH2 catalyst" in S22 is changed to "300 mg activated 20Cu / 65SiO2-15NCNTs-NH2 catalyst"; the remaining raw materials and preparation process remain the same as in Example 3.
[0058] Example 6
[0059] The difference between this embodiment and embodiment 5 is that the "mass liquid hourly space velocity of dimethyl oxalate is 1h -1 ” was changed to “The mass liquid hourly space velocity of dimethyl oxalate is 1.5h -1 "; The rest of the raw materials and preparation process remain the same as in Example 5.
[0060] Example 7
[0061] The difference between this embodiment and embodiment 5 is that the "mass liquid hourly space velocity of dimethyl oxalate is 1h -1 ” was changed to “The mass liquid hourly space velocity of dimethyl oxalate is 2h-1 "; The rest of the raw materials and preparation process remain the same as in Example 5.
[0062] Example 8
[0063] The difference between this embodiment and Example 7 is that "9.06 g of copper nitrate trihydrate" is changed to "6.39 g of copper chloride dihydrate"; the remaining raw materials and preparation process remain the same as those in Example 7.
[0064] Example 9
[0065] The difference between this embodiment and Example 7 is that "9.06 g of copper nitrate trihydrate" is changed to "7.48 g of copper acetate monohydrate"; the remaining raw materials and preparation process remain the same as those in Example 7.
[0066] Comparative Example 1
[0067] The difference between this comparative example and Example 1 is that no amino group is grafted onto the catalyst, and Cu / SiO2-NCNTs is prepared as the catalyst; the other raw materials and preparation process remain the same as those in Example 1.
[0068] Comparative Example 2
[0069] Compared with Example 1, the difference between this comparative example and Example 1 is that Cu / SiO2 is prepared for use as a catalyst, and the preparation steps are: 9.06g of copper nitrate trihydrate is dissolved in 100mL of deionized water, stirred and added with ammonia water until the precipitate disappears, then 6g of urea is added, and then 38.4g of 25wt% colloidal silica is slowly added with a burette under mechanical stirring; stirred at 75°C for 3h, filtered, washed with deionized water, and dried, and the dried product is calcined at 350°C in an air atmosphere for 2h to obtain a catalyst containing 20% Cu, 80% SiO2 and Cu / SiO2; the remaining raw materials and preparation process remain the same as those in Example 1.
[0070] Comparative Example 3
[0071] The difference between this comparative example and Example 1 is that the "nitrogen-doped magnetic carbon nanotubes" in S11 are changed to "magnetic carbon nanotubes"; the other raw materials and preparation process remain the same as those in Example 1.
[0072] The products of Examples 1 to 9 and Comparative Examples 1 to 3 were analyzed by chromatography, and the conversion rate of dimethyl oxalate and the selectivity of each product were calculated. The results are shown in Table 1.
[0073] Table 1
[0074]
[0075]
[0076] It can be seen from Table 1 that the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol in Examples 1 to 9 are relatively high, indicating that the Cu / SiO2-NCNTs-NH2 catalyst has excellent catalytic performance and can improve the yield of ethylene glycol.
[0077] Compared with Examples 1 to 3, increasing the amount of NCNTs in the catalyst is beneficial to improving the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol. The reason is that NCNTs can improve the pore structure of the catalyst, thereby improving the dispersibility of the active component Cu; in addition, the high electrical conductivity of NCNTs helps to quickly transfer electrons to the Cu active sites, thereby improving the electron supply efficiency of the catalytic reaction and enhancing the activation of hydrogen, because the activation of hydrogen requires the participation of electrons.
[0078] Compared with Example 3 to Example 5, increasing the amount of catalyst in the reaction system is beneficial to improving the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol. Compared with Example 5 to Example 7, increasing the mass liquid hourly space velocity of dimethyl oxalate is beneficial to improving the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol.
[0079] Comparison between Example 1 and Comparative Example 1 shows that when the catalyst is not grafted with amino groups and Cu / SiO2-NCNTs is used as the catalyst, the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol are lower. The reason is that grafting amino groups (-NH2) on the Cu / SiO2 catalyst can passivate the silanol groups (Si-OH); thereby reducing the probability that the intermediate product methyl glycolate is easily adsorbed on the Si-OH in the Cu / SiO2 catalyst, resulting in the active sites being covered; it also reduces the probability that Si-OH serves as a basic site and generates by-products; and -NH2 can provide electrons, increase the electron cloud density on the surface of the active component Cu, thereby promoting the dissociation of hydrogen, thereby increasing the hydrogenation reaction rate and improving the selectivity of ethylene glycol.
[0080] Comparison of Comparative Example 2 with Example 1 shows that the conversion rate of dimethyl oxalate and the selectivity of ethylene glycol obtained using the Cu / SiO2 catalyst are the lowest.
[0081] Comparing Comparative Example 3 with Example 1, it is found that nitrogen-doped magnetic carbon nanotubes have better conductivity than magnetic carbon nanotubes, can better promote the electron transfer of the reaction, better improve the electron supply efficiency of the catalytic reaction, enhance the activation of hydrogen, and thus increase the hydrogenation reaction rate.
[0082] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.
[0083] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for improving the yield of ethylene glycol, characterized in that: The following steps are involved: S1, synthesis of Cu / SiO2-NCNTs-NH2 catalyst; S2, Cu / SiO2-NCNTs-NH2 catalyst catalyzes the hydrogenation of dimethyl oxalate to ethylene glycol; NCNTs are nitrogen-doped magnetic carbon nanotubes.
2. A method for improving the yield of ethylene glycol according to claim 1, characterized in that: The Cu / SiO2-NCNTs-NH2 catalyst described in S1 is prepared by the following steps: S11. Preparation of Cu / SiO2-NCNTs: Dissolve soluble copper salt in deionized water, add ammonia water and mix, then add urea and nitrogen-doped magnetic carbon nanotubes, and then drop colloidal silica; stir at 70-75°C for 3-4 hours, filter, wash with deionized water, and dry, and calcine the dried product at 340-350°C in an air atmosphere for 2-2.5 hours to obtain Cu / SiO2-NCNTs; S12, Cu / SiO2-NCNTs grafted with amino groups to obtain Cu / SiO2-NCNTs-NH2: Cu / SiO2-NCNTs and anhydrous methanol are mixed, and an aminosilane coupling agent is added at 40-50°C. The solution after the reaction is heated to 80-90°C, stirred for reaction for 5-6h, and the anhydrous ethanol is centrifuged, washed, and dried to obtain Cu / SiO2-NCNTs-NH2.
3. A method for improving the yield of ethylene glycol according to claim 2, characterized in that: The soluble copper salt in S11 is one of copper nitrate trihydrate, copper chloride dihydrate and copper acetate monohydrate.
4. A method for improving the yield of ethylene glycol according to claim 2, characterized in that: The mass ratio of copper in the soluble copper salt, the mass of silicon dioxide in the colloidal silicon dioxide and the mass ratio of nitrogen-doped magnetic carbon nanotubes in S11 is 20:65-75:5-15.
5. A method for improving the yield of ethylene glycol according to claim 2, characterized in that: The preparation steps of the nitrogen-doped magnetic carbon nanotubes in S11 are: Ultrasonic dispersion of ferric chloride hexahydrate in anhydrous ethanol, and then addition of melamine for ultrasonic dispersion to obtain a uniform suspension; continuous stirring of the suspension at 70-75° C. until the ethanol is completely volatilized to obtain a precursor; drying and grinding the precursor, and then placing the precursor in an Ar-filled tubular furnace and heating it to 650° C. at 3° C. / min, and keeping the temperature for 2 hours for high-temperature calcination and pyrolysis to obtain nitrogen-doped magnetic carbon nanotubes; The molar ratio of the ferric chloride hexahydrate to melamine is 1:
2.
6. A method for improving the yield of ethylene glycol according to claim 2, characterized in that: The aminosilane coupling agent in S12 is one of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane and 4-aminobutyltriethoxysilane.
7. A method for improving the yield of ethylene glycol according to claim 2, characterized in that: The dosage ratio of Cu / SiO2-NCNTs and aminosilane coupling agent in S12 is 2g:1mmol.
8. A method for improving the yield of ethylene glycol according to claim 1, characterized in that: The steps of preparing ethylene glycol by catalytic hydrogenation of dimethyl oxalate with Cu / SiO2-NCNTs-NH2 catalyst in S2 are: S21, Cu / SiO2-NCNTs-NH2 catalyst activation: The Cu / SiO2-NCNTs-NH2 catalyst was reduced in a H2 atmosphere at 300-350°C for 4-5h, and then cooled to the reaction temperature to obtain activated Cu / SiO2-NCNTs-NH2; S22, activated Cu / SiO2-NCNTs-NH2 catalyzed hydrogenation of dimethyl oxalate: 200-300 mg of activated Cu / SiO2-NCNTs-NH2 catalyst was loaded into a fixed bed reactor, and hydrogen was introduced into the reactor. The hydrogen pressure was set to 2.5 MPa, the reaction temperature was set to 200 °C, the hydrogen-to-ester ratio was set to 80, and the mass liquid hourly space velocity of dimethyl oxalate was set to 1-2 h -1 , catalytic hydrogenation for 2h to obtain ethylene glycol.
9. A method for improving the yield of ethylene glycol according to claim 8, characterized in that: The H2 atmosphere in S21 is a H2-N2 mixed gas or a H2-Ar mixed gas with a H2 mass fraction of 5-10%.
10. A method for improving the yield of ethylene glycol according to claim 8, characterized in that: The fixed bed reactor in S22 is a cylindrical reactor with a tube length of 80 cm and an inner diameter of 6 mm.