Method for preparing ethylene glycol based on synthesis gas staged catalysis one-step method

Abstract

The invention discloses a green process for preparing ethylene glycol by taking straw synthesis gas as a raw material through a one-step method, by designing a Cu-Co-Zr / CNTs and Pd-Mn-ZnO / SiO segmented catalytic system, CO is directly coupled and hydrogenated to generate ethylene glycol, and a by-product is innovatively converted into a reaction accelerator by using a methanol circulation technology. According to the process, the ethylene glycol yield reaches 72%, the hydrogen consumption is reduced by 42.4%, the service life of the catalyst exceeds 500 hours, and the process is suitable for chemical production under the goals of efficient conversion of biomass energy and carbon neutralization.

Description

Technical Field

[0001] The present invention belongs to the technical field of efficient conversion and catalytic synthesis of biomass resources, and particularly relates to a method for preparing ethylene glycol by a one-step catalytic synthesis with segmented syngas. The method uses straw gasification syngas as raw material, and directly prepares ethylene glycol through a segmented multiphase catalytic system, and realizes the efficient separation and recycling of by-product methanol, significantly improving the yield and process economy of ethylene glycol. Background Art

[0002] Traditional production processes of ethylene glycol mainly rely on petrochemical-based ethylene oxide hydration method or coal-based indirect methanol synthesis method, such as methanol carbonylation to dimethyl oxalate followed by hydrogenation. Existing syngas-to-ethylene glycol technologies (such as Davy process) need to use methanol as an intermediate, and have the following defects: 1) Long process: It requires multiple steps of methanol synthesis and methanol conversion, with high equipment investment and energy consumption; 2) High hydrogen consumption: Additional hydrogen needs to be supplemented for methanol preparation, and the hydrogen utilization rate in the intermediate steps is low; 3) By-product inhibition: The content of CO2 / CH4 in straw syngas is high (15 - 20%), and traditional catalysts are prone to poisoning and inactivation; 4) Methanol accumulation: By-product methanol cannot be effectively recycled, reducing the selectivity of ethylene glycol.

[0003] Based on the above defects of the existing technology, this application has been developed. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the existing technology, and provide a method for preparing ethylene glycol by a one-step catalytic synthesis with segmented syngas. This method has a short process and low hydrogen consumption, and directly prepares ethylene glycol from syngas. Through segmented catalytic design and methanol recycling strategy, it realizes the efficient conversion of straw syngas and the improvement of ethylene glycol yield.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A method for preparing ethylene glycol by a one-step catalytic synthesis with segmented syngas, which comprises the following steps: (a) Desulfurizing, dechlorinating and membrane separating the syngas (such as straw gasification syngas, etc.); (b) The syngas obtained in step (a) passes through the first catalytic bed layer, and an intermediate product containing glycolaldehyde is generated at 220 - 250 °C and 4 - 6 MPa; (c) The intermediate product obtained in step (b) enters the second catalytic bed layer and is hydrogenated to ethylene glycol at 180 - 200 °C and 2 - 3 MPa; (d) The reaction product obtained in step (c) is subjected to three-stage condensation and azeotropic distillation to separate ethylene glycol and methanol.

[0006] Specifically, in step (a), a two-stage adsorption of Fe2O3-MnO2 desulfurizer and alkaline activated carbon is adopted for desulfurization and dechlorination treatment. After the desulfurization and dechlorination treatment, the total sulfur ≤ 5 ppm and the chlorine ≤ 1 ppm.

[0007] Specifically, in step (a), the membrane separation treatment controls the H2 / CO molar ratio to be 1.2 - 1.5:1.

[0008] Specifically, in step (b), the first catalytic bed layer uses a Cu-Co-Zr / carbon nanotube catalyst, with the molar ratio of Cu:Co:Zr being 2 - 4:1 - 2:0.5 - 1.5 and the space velocity being 3500 - 5000 h⁻¹. Further, in step (b), the Cu-Co-Zr / carbon nanotube catalyst is prepared through steps such as carrier acidification and impregnation reduction, specifically as follows: Carrier acidification: Carbon nanotubes (CNTs) are mixed with 60 - 70% nitric acid and refluxed at 70 - 95°C for 5 - 8 hours to obtain acidified carbon nanotubes; Impregnation reduction: Impregnation with a nitrate ethanol solution and reduction with H2; specifically: Copper nitrate, cobalt nitrate, and zirconium oxynitrate are dissolved in ethanol, then impregnated on the acidified carbon nanotubes, ultrasonicated for 10 - 40 min, left standing for 10 - 14 h, and rotary evaporated; reduced in a H2 / N2 mixed gas (in the mixed gas, the volume fraction of hydrogen is 8 - 12%) at 350 - 450°C for 3 - 5 h, and tableted (porosity 65%) to obtain the product.

[0009] Specifically, in step (c), the second catalytic bed layer uses a Pd-Mn-ZnO / SiO2 catalyst, where Pd accounts for 1.2 - 1.8 wt% of the catalyst mass, the Mn / Pd molar ratio is 1.8 - 2.2:1, ZnO accounts for 4 - 6 wt% of the ZnO / SiO2 carrier mass, and the space velocity is 1000 - 3000 h⁻¹. Further, in step (c), the Pd-Mn-ZnO / SiO2 catalyst is prepared through steps such as carrier modification and co-precipitation method, specifically as follows: Carrier modification: SiO2 is loaded with 4 - 6 wt% ZnO (calcined at 500 - 600°C for 2 - 4 hours) to obtain the ZnO / SiO2 carrier; Co-precipitation method: Co-precipitation of PdCl2 and Mn(NO3)2 solution and reduction with H2 after calcination; specifically: The ZnO / SiO2 carrier is immersed in a solution containing PdCl2 and Mn(NO3)2, the pH is adjusted to 9 - 10 with ammonia water, filtered after precipitation for 1 - 3 h, calcined at 450 - 550°C for 3 - 5 h, and reduced in H2 at 250 - 350°C for 1.5 - 3 h to obtain the product.

[0010] Specifically, in step (d), after methanol dehydration, it is mixed with fresh syngas at a volume ratio of 1:2 - 4 and recycled to step (b); the recycled methanol is dehydrated using 3Å molecular sieve, and the water content of the dehydrated methanol is ≤50 ppm.

[0011] The process of the present invention reduces energy consumption by 18% through the reactive distillation coupling technology, and uses the waste heat of syngas to drive the regeneration of molecular sieve. As a preference, the overall process route of the present invention is as follows: (1) Syngas pretreatment: Desulfurization and dechlorination: Two-stage adsorption using Fe2O3-MnO2 desulfurizer and basic activated carbon, total sulfur ≤5 ppm, chlorine ≤1 ppm; H2 / CO ratio adjustment: Controlling the H2 / CO molar ratio to 1.2 - 1.5 through membrane separation; (2) Segmented catalytic reaction: The first-stage catalysis (C-C coupling): Catalyst: Cu-Co-Zr / carbon nanotubes (Cu:Co:Zr = 3:1:0.5, specific surface area >300 m² / g); Conditions: 220 - 250 °C, 4 - 6 MPa, space velocity 4000 h⁻¹, to generate glycolaldehyde intermediate (HOCH2CHO); The second-stage catalysis (selective hydrogenation): Catalyst: Pd-Mn-ZnO / SiO2 (Pd 1.2 - 1.8 wt%, Mn / Pd = 1.8 - 2.2:1, ZnO 4 - 6 wt%); Conditions: 180 - 200 °C, 2 - 3 MPa, space velocity 2000 h⁻¹, hydrogenation of glycolaldehyde to ethylene glycol (selectivity >65%); (3) Product separation and methanol recycling: Three-stage condensation: Condensing step by step from 0 °C → -20 °C → -50 °C to recover more than 99% of the liquid-phase products; Azeotropic distillation: Low-pressure distillation at 10 kPa, the methanol-water azeotrope (methanol purity 99.5%) is taken from the top of the column, and ethylene glycol is collected at the bottom of the column.

[0012] Recycling of dehydrated methanol: Adsorbed by 3Å molecular sieve, after the water content is <50 ppm, it is mixed with fresh syngas at a volume ratio of 1:3 and recycled to the first-stage reactor.

[0013] The present invention discloses a green process for the one-step preparation of ethylene glycol from syngas. By designing a segmented catalytic system of Cu-Co-Zr / CNTs and Pd-Mn-ZnO / SiO2, the direct coupling hydrogenation of CO to produce ethylene glycol is realized, and the methanol recycling technology is innovatively used to convert by-products into reaction promoters. The ethylene glycol yield of this process reaches 78%, the hydrogen consumption is reduced by 42.4%, the catalyst life exceeds 500 hours, and it is applicable to the efficient conversion of biomass energy and chemical production under the goal of carbon neutrality.

[0014] The method for the one-step preparation of ethylene glycol based on the segmented catalysis of syngas in the present invention uses syngas as a raw material and directly prepares ethylene glycol through a segmented multiphase catalytic system, and realizes the efficient separation and recycling of by-product methanol, significantly improving the yield of ethylene glycol and process economy. This method has a short process flow and low hydrogen consumption, and directly prepares ethylene glycol by using syngas. Through segmented catalytic design and methanol recycling strategy, it realizes the efficient conversion of straw syngas and the improvement of ethylene glycol yield. Compared with the prior art, the method of the present invention has the following innovative points and beneficial effects: 1) One-step short process flow: Skipping the methanol intermediate, directly coupling hydrogenation of CO, reducing equipment investment by 30%; 2) Methanol recycling for efficiency enhancement: By-product methanol is used as a reaction promoter, and the ethylene glycol yield is increased to 78%; 3) Wide component tolerance: The activity of the catalyst remains >90% within the range of H2 / CO molar ratio of 1.2 - 1.5; 4) Low hydrogen consumption: The hydrogen utilization rate is increased to 90%, reducing hydrogen consumption by 42.4% compared with the traditional process. Description of the Drawings

[0015] Figure 1 It is the process flow chart for the one-step preparation of ethylene glycol by the segmented catalysis of syngas in the present invention; Figure 2 It is the schematic diagram of the segmented catalytic reaction path (CO → glycolaldehyde → ethylene glycol) in the process of the present invention; Figure 3 It is the influence curve of methanol recycling on the ethylene glycol yield in the process of the present invention. Detailed Embodiments

[0016] The following further details the technical solutions of the present invention in combination with embodiments, but the protection scope of the present invention is not limited thereto.

[0017] In the present invention, the used Fe2O3-MnO2 desulfurizer was purchased from Sichuan Shutai Chemical Technology Co., Ltd., and the basic activated carbon was purchased from Gongyi Fanbei Environmental Protection Technology Co., Ltd.

[0018] In the following examples, the composition of the raw material straw synthesis gas used: CO 40% - 45%, H2 30% - 35%, CO2 about 15%, CH4 about 8%, and there are also small amounts of carbon dioxide, sulfur impurities, chlorine impurities, tar, and a part of water vapor and other impurities.

[0019] Example 1: Catalyst preparation (1) The catalyst Cu-Co-Zr / carbon nanotubes used in the first-stage catalytic bed Carrier acidification: Carbon nanotubes (CNTs) are mixed with 65% nitric acid at a material-liquid ratio of 1 g:20 ml and refluxed at 95 °C for 7 hours to ensure that the CNTs are fully dispersed and acidified. After cooling to room temperature, filtration is carried out, and distilled water is used for washing until the washing liquid is close to neutral (pH = 7), and then dried at 80 - 100 °C for 12 - 24 h to obtain acidified carbon nanotubes; Impregnation reduction: Weigh 17.83 g (0.095 mol) of copper nitrate, 5.8 g (0.032 mol) of cobalt nitrate, and 3.66 g (0.016 mol) of zirconium oxynitrate and dissolve them in 200 mL of ethanol; impregnate 10 g of acidified carbon nanotubes, ultrasonicate for 30 minutes, let it stand at room temperature for 12 hours and then rotary evaporate; reduce it with a H2 / N2 mixed gas (the proportion of H2 in the mixed gas is 10%) at 400 °C for 4 hours, and then press it into tablets, that is, obtained (diameter 3 mm, specific surface area 350 m² / g).

[0020] (2) The catalyst Pd-Mn-ZnO / SiO2 used in the second-stage catalytic bed Carrier modification: Load 5 wt% ZnO on SiO2, Add the SiO2 carrier to the prepared 22.4 ml zinc nitrate solution with a concentration of 50 g / L according to the loading amount, and stir at room temperature for 3 hours to allow the zinc nitrate solution to fully impregnate the SiO2 carrier. This process can make zinc ions evenly distributed on the surface and pores of SiO2. The impregnated sample is dried overnight at 150 °C. Calcined at 550 °C for 3 hours, and after the calcination is completed, it is naturally cooled to room temperature to obtain the ZnO / SiO2 carrier with a ZnO loading of 5 wt%. Obtain the ZnO / SiO2 carrier; Coprecipitation method: Immerse 5 g of the ZnO / SiO2 carrier in an aqueous solution containing 0.15 g of PdCl2 and 0.32 g of Mn(NO3)2, adjust the pH to 9.5 with ammonia water, filter after precipitation for 2 hours, calcine at 500 °C for 4 hours, and reduce with H2 at 300 °C for 2 hours, that is, obtained.

[0021] The catalysts Cu-Co-Zr / carbon nanotubes and Pd-Mn-ZnO / SiO2 prepared in this example are used in the process of Example 2 to prepare ethylene glycol.

[0022] Example 2: Process Operations (see details in Figure 1 and Figure 2 ) Perform desulfurization and dechlorination treatment on the straw syngas: 1. Primary desulfurization and dechlorination (adsorption by Fe2O3-MnO2 desulfurizer): Load the Fe2O3-MnO2 desulfurizer inside the fixed-bed adsorption reactor. Pass the straw syngas into the reactor at a certain flow rate, and control the reaction temperature at 300 - 350 °C. Within this temperature range, the active components in the Fe2O3-MnO2 desulfurizer can chemically react with sulfur and chlorine impurities in the syngas. Taking hydrogen sulfide (H2S) as an example, the following reaction will occur: Fe2O3 + 3H2S = Fe2S3 + 3H2O. MnO2 can also react with sulfur and chlorine impurities, converting them into solid or liquid substances and adsorbing them on the surface of the desulfurizer. At the same time, to ensure the desulfurization effect, the residence time of the syngas in the reactor needs to be controlled within 30 - 60 minutes, so that most of the sulfur and chlorine impurities are effectively removed.

[0023] 2. Secondary desulfurization and dechlorination (adsorption by basic activated carbon): The syngas after primary desulfurization and dechlorination treatment enters the adsorption tower filled with basic activated carbon. Basic activated carbon has a large specific surface area and a rich pore structure, and has basic groups on its surface, which can further adsorb residual sulfur and chlorine compounds in the syngas. The temperature of the adsorption tower is maintained at room temperature (20 - 25 °C), and the syngas passes through the adsorption tower at a low flow rate, with a residence time of about 30 minutes. During this process, basic activated carbon can not only capture residual sulfur and chlorine molecules through physical adsorption, but also use its basicity to chemically react with acidic sulfur and chlorine compounds to enhance the adsorption effect. After two-stage adsorption treatment, ensure that the total sulfur content in the syngas ≤ 5 ppm and the chlorine content ≤ 1 ppm.

[0024] Membrane separation treatment: 1. Membrane module selection and installation: Select a metal palladium composite membrane module (Yiwu Ruisheng New Material Technology Co., Ltd., model Pd M-380) with high selectivity for hydrogen and carbon monoxide separation. Install the membrane module in the sealed housing of the membrane separation equipment to ensure tight connection and no gas leakage.

[0025] 2. Membrane separation operation: The desulfurized and dechlorinated straw syngas is pressurized to 3 - 5 MPa and then fed into the membrane separation device. Driven by the pressure difference, hydrogen molecules can preferentially permeate through the palladium composite membrane, while most of the carbon monoxide molecules are retained. By adjusting the temperature of the membrane separation device to 40 - 60 °C, the difference in the permeation rates of hydrogen and carbon monoxide is optimized. At the same time, according to the flow rate and composition of the syngas, the area of the membrane and the flow rate of the gas in the membrane module are precisely controlled to make the H2 / CO molar ratio in the treated syngas reach 1.2 - 1.5:1. During the membrane separation process, the composition of the inlet and outlet gases is continuously monitored, and the operating parameters are adjusted in a timely manner to ensure the stability of the membrane separation effect. This membrane separation can be achieved by using conventional techniques in the art and will not be elaborated here as it is not the innovation of this application.

[0026] After membrane separation, the composition of the raw gas (straw syngas): CO (35%), H2 (42%), CO2 (15%), CH4 (8%), H2 / CO = 1.3; The first-stage reactor (C-C coupling): The catalyst Cu-Co-Zr / carbon nanotubes is selected for the first catalytic bed layer. The reaction conditions are: 240 °C, 5 MPa, space velocity 4000 h⁻¹, CO conversion rate 82%, and glycolaldehyde selectivity 58%; The second-stage reactor (catalytic hydrogenation): The catalyst Pd-Mn-ZnO / SiO2 is selected for the second catalytic bed layer. The reaction conditions are: 190 °C, 2.5 MPa, space velocity 2000 h⁻¹, ethylene glycol selectivity 68%, and ethanol < 3%; Three-stage condensation: The high-temperature reaction products coming out of the second-stage reactor first enter the three-stage condensation system. In the first-stage condensation, the temperature is reduced to 0 °C. At this time, most of the methanol, ethanol, and part of the water vapor will condense into liquid, and this part of the liquid-phase product is collected at the bottom of the condensation device by gravity sedimentation. Then, the gas-phase product enters the second-stage condensation, and the temperature is further reduced to -20 °C. More methanol, ethanol, and a small amount of impurities with higher boiling points will continue to condense, and gas-liquid separation is carried out again to collect the liquid-phase product. Finally, the gas-phase product enters the third-stage condensation, and the temperature is reduced to -50 °C. Almost all the remaining condensable components will condense. After three-stage condensation, more than 99% of the liquid-phase product can be recovered. The uncondensed gas phase mainly consists of unreacted CO, H2, CO2, CH4, etc., which can be subjected to subsequent treatment or recycling.

[0027] Azeotropic distillation: The liquid-phase product after three-stage condensation mainly contains ethylene glycol, methanol, and a small amount of water. Since methanol and water form an azeotrope and it is difficult to completely separate them by ordinary distillation, azeotropic distillation is adopted. The liquid-phase product is fed into an azeotropic distillation column and distilled under a low pressure of 10 kPa. Inside the distillation column, the mixture is vaporized by heating, and the light components (the azeotrope of methanol and water) gradually move towards the top of the column, while the heavy components (ethylene glycol) are concentrated at the bottom of the column. The methanol purity in the methanol-water azeotrope withdrawn from the top of the column can reach over 99%, and ethylene glycol is obtained at the bottom of the column.

[0028] Methanol recycling: Methanol (99.5%) at the top of the distillation column is recycled after dehydration by molecular sieve, and the utilization rate is ≥95%.

[0029] Example 3: Verification of H2 / CO ratio adjustment Raw gas composition: CO (38%), H2 (45%), CO2 (12%), CH4 (5%) (H2 / CO = 1.18) Process conditions: The first stage: 235 °C, 5.5 MPa, space velocity 3500 h⁻¹ The second stage: 185 °C, 3.0 MPa, space velocity 2500 h⁻¹ Catalyst parameters: The first stage: Cu-Co-Zr / CNTs (specific surface area 350 m² / g) The second stage: Pd-Mn-ZnO / SiO2 (Pd 1.8 wt%); other process parameters refer to Examples 1 and 2.

[0030] Results: CO conversion rate 85%, ethylene glycol selectivity 72%, by-product methanol <2%.

[0031] Example 4: Verification of wide-component syngas adaptability Raw gas composition: CO (30%), H2 (38%), CO2 (20%), CH4 (12%) (H2 / CO = 1.27) Process conditions: The first stage: 250 °C, 6 MPa, space velocity 4000 h⁻¹ The second stage: 200 °C, 3 MPa, space velocity 2000 h⁻¹ Catalyst parameters: The first stage: Cu-Co-Zr / CNTs (specific surface area 350 m² / g) The second stage: Pd-Mn-ZnO / SiO2 (ZnO loading 6 wt%); other process parameters refer to Examples 1 and 2.

[0032] Results: CO conversion rate is 79%, ethylene glycol selectivity is 65%, and the catalyst activity remains at 92% (after running for 500 hours).

[0033] Comparative Example 1 (Traditional Davy Process) Feed gas: CO (60%), H2 (35%), CO2 (<5%) Process conditions: Methanol synthesis section: 250°C, 10 MPa; Oxalate synthesis section: 180°C, 1.5 MPa; Results: Total ethylene glycol yield is 62%, hydrogen consumption is 12.5 mol / mol EG, and catalyst life is 300 hours.

[0034] Table 1: Comparison of Key Indicators between Traditional Davy Process and the Process of the Present Invention Table 1 gives the comparison of key indicators between the traditional process and the present invention. It can be seen from the table that: 1) When preparing ethylene glycol, the hydrogen consumption is 12.5 mol / mol EG, while the process of Example 3 of the present invention is only 7.2 mol / mol EG, a reduction of 42.4%. This indicates that the present invention is more efficient in hydrogen utilization, greatly reducing hydrogen consumption. This not only reduces production costs but also meets the current requirements for efficient energy utilization and energy conservation and emission reduction, facilitating the conservation of hydrogen resources in actual production and enhancing economic and environmental benefits.

[0035] 2) The total ethylene glycol yield is significantly improved: The total ethylene glycol yield of the traditional process is 62%, while the process of Example 3 of the present invention reaches 72%, an increase of 16.1%. The significant increase in yield means that the present invention can produce more ethylene glycol products with the same raw material input.

[0036] 3) The catalyst life is greatly extended: The catalyst life of the traditional process is 300 hours, while the catalyst life of the first stage of the present invention reaches 500 hours. The longer catalyst life reduces the catalyst replacement frequency, further reducing production costs.

[0037] Figure 3 The influence curve of methanol recycle on ethylene glycol yield is given; it can be seen from Figure 3 it that: 1) The methanol recycling ratio is positively correlated with the ethylene glycol yield: as the methanol recycling ratio gradually increases from 1:5 to 1:2, the ethylene glycol yield shows an upward trend. This indicates that methanol recycling has a positive effect on increasing the ethylene glycol yield. Within the ratio range studied experimentally, an increase in the methanol recycling amount can promote the reaction in the direction of ethylene glycol formation. This may be because the recycled methanol acts as a reaction promoter, changing the chemical equilibrium of the reaction system, increasing the concentration of reactants, or participating in some intermediate reaction processes, thus increasing the amount of ethylene glycol produced.

[0038] 2) There is an optimal methanol recycling ratio range: Although the increase in the methanol recycling ratio generally improves the ethylene glycol yield, the curve slope is not constant, indicating that a higher methanol recycling ratio is not necessarily better. In actual production, too high a methanol recycling ratio may cause other problems, such as increased energy consumption, equipment load, and production costs. Based on the curve trend and actual situation, it is speculated that the methanol recycling ratio range of 1:2 - 1:4 may be more ideal for improving the ethylene glycol yield and controlling the comprehensive production cost, providing an important reference for optimizing the process operation.

[0039] 3) Methanol recycling significantly improves the process performance: It can be intuitively seen from the curve that methanol recycling has an obvious effect on increasing the ethylene glycol yield. Compared with no methanol recycling, an appropriate methanol recycling ratio can significantly increase the ethylene glycol yield, further reflecting the importance and effectiveness of the methanol recycling technology in this invention. It is one of the key factors for improving the economy of the entire process and the product yield.

[0040] In summary, this invention prepares ethylene glycol by a one-step method using straw syngas as the raw material. Through the design of a segmented catalytic system of Cu-Co-Zr / CNTs and Pd-Mn-ZnO / SiO2, it realizes the direct coupling hydrogenation of CO to produce ethylene glycol, and innovatively uses the methanol recycling technology to convert by-products into reaction promoters. This process has a CO conversion rate as high as 85%, an ethylene glycol yield of 72%, a hydrogen consumption reduction of 42.4%, and a catalyst life exceeding 500 hours, and is applicable to the efficient conversion of biomass energy and chemical production under the goal of carbon neutrality.

Claims

1. A method for preparing ethylene glycol by a one-step catalytic process based on syngas in segments, characterized in that, It includes the following steps: (a) Desulfurizing and dechlorinating the syngas, and performing membrane separation treatment; (b) The syngas obtained in step (a) passes through the first-stage catalytic bed, and an intermediate product containing glycolaldehyde is generated at 220 - 250 °C and 4 - 6 MPa; (c) The intermediate product obtained in step (b) enters the second-stage catalytic bed and is hydrogenated to ethylene glycol at 180 - 200 °C and 2 - 3 MPa; (d) The reaction product obtained in step (c) is condensed and separated by azeotropic distillation to obtain ethylene glycol and methanol.

2. The method for preparing ethylene glycol by a one-step catalytic process based on syngas in sections as claimed in claim 1, wherein In step (a), a two-stage adsorption of Fe2O3-MnO2 desulfurizer and basic activated carbon is used for desulfurization and dechlorination treatment. After the desulfurization and dechlorination treatment, the total sulfur ≤ 5 ppm and the chlorine ≤ 1 ppm.

3. The method for preparing ethylene glycol by a one-step catalytic process with staged syngas as claimed in claim 1, wherein In step (a), the membrane separation treatment controls the H2 / CO molar ratio to be 1.2 - 1.5:

1.

4. The method for preparing ethylene glycol by a one-step catalytic process with syngas in sections as claimed in claim 1, wherein In step (b), the first-stage catalytic bed uses a Cu-Co-Zr / carbon nanotube catalyst, and the Cu:Co:Zr molar ratio is 2 - 4:1 - 2:0.5 - 1.5, and the space velocity is 3500 - 5000 h⁻¹.

5. The method for preparing ethylene glycol by a one-step segmented catalytic process based on syngas according to claim 4, characterized in that, In step (b), the Cu-Co-Zr / carbon nanotube catalyst is prepared through the following steps: Dissolve copper nitrate, cobalt nitrate, and zirconium oxynitrate in ethanol, then impregnate the acidified carbon nanotubes, ultrasonicate for 10 - 40 min, stand for 10 - 14 h, and perform rotary evaporation; reduce in a H2 / N2 mixed gas at 350 - 450 °C for 3 - 5 h to obtain it.

6. The method for preparing ethylene glycol by a one-step catalytic process based on syngas in a segmented manner as claimed in claim 1, wherein, In step (c), the second catalytic bed layer uses a Pd-Mn-ZnO / SiO2 catalyst, wherein Pd accounts for 1.2-1.8 wt% of the catalyst mass, the Mn / Pd molar ratio is 1.8-2.2:1, ZnO accounts for 4-6 wt% of the ZnO / SiO2 support mass, and the space velocity is 1000-3000 h -1 .

7. The method for preparing ethylene glycol by the stepwise catalytic one-step method based on syngas according to claim 6, characterized in that, In step (c), the Pd-Mn-ZnO / SiO2 catalyst is prepared through the following steps: Immerse the ZnO / SiO2 support in a solution containing PdCl2 and Mn(NO3)2, adjust the pH to 9 - 10 with ammonia water, filter after precipitation for 1 - 3 h, calcine at 450 - 550 °C for 3 - 5 h, and reduce in H2 at 250 - 350 °C for 1.5 - 3 h to obtain it.

8. The method for preparing ethylene glycol by a one-step catalytic process with staged syngas as claimed in claim 6, wherein In step (d), after methanol dehydration, it is recycled to step (b) at a volume ratio of 1:2 - 4; the methanol recycling uses 3 Å molecular sieve for dehydration, and the water content of the dehydrated methanol ≤ 50 ppm.

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