Process for producing ethylene glycol

Abstract

1. A method for producing monoethylene glycol, comprising subjecting an aqueous oxalic acid solution to a hydrogenation reaction in the presence of hydrogen and a metal-containing hydrogenation catalyst, the method being a continuous flow process in a fixed bed reactor; an aqueous oxalic acid solution and a hydrogen gas stream are fed to the fixed bed reactor; the reactor comprises a hydrogenation catalyst bed, the catalyst being a supported metal-containing hydrogenation catalyst having a total metal loading of 2.0 wt.% or more to 20.0 wt.% or less; and the hydrogenation reaction is carried out at a temperature selected from the range of 95°C or more to 125°C or less, at a hydrogen pressure selected from the range of 10 bar H2 or more to 150 bar H2 or less, with a residence time of 5 minutes to 2 hours; thereby producing monoethylene glycol with a high selectivity of 80% or more at a conversion of oxalic acid of 90% to 100%.

Description

[Technical field]

[0001] The present invention relates to a process for producing ethylene glycol which involves the hydrogenation of oxalic acid. [Background technology]

[0002] In view of the climate change problem, many efforts are being developed to reduce the amount of greenhouse gases in the atmosphere. There is increasing attention on CO2 capture, where CO2 is mainly captured from large point sources, for example, chemical or power plants, industries with significant CO2 emissions (such as steelmaking), natural gas processing, hydrogen production from fossil fuels, etc. After capture, the next step is the storage (CCS) and / or utilization (CCU) of CO2. The main difference between storage and utilization is that CCS techniques store CO2 underground so that it cannot be re-released into the atmosphere, while CCU techniques use CO2 to convert it into more valuable products such as plastics or biofuels. It is noteworthy that today, traditional fossil resources for energy generation can be replaced in a net-zero emission way (at least in theory), but this is not the case for the production of materials such as plastics or concrete. Therefore, the use of CO2 for material production is essential to ensure a low impact on natural resources and is one of the few options to achieve negative emissions (at least provided that non-fossil CO2 and renewable energies are used).

[0003] For example, CO2 can be used to produce oxalic acid (HOOCCOOH), which can then be hydrogenated to produce, for example, glycolic acid (HOCH2COOH; GA) and monoethylene glycol (HOCH2CH2OH; MEG), which are valuable chemicals for several different applications, such as the production of plastics, and GA as a preservative in food processing, and as a skin care agent in cosmetics.

[0004] However, hydrogenation of carboxylic acids, despite being an important organic reaction for the synthesis of useful and valuable chemicals, is a chemically challenging reaction due to the low reactivity and acidity of the carboxyl group. This requires, for example, the rational design of catalysts. See Tamura, M. et al. Recent Developments of Heterogeneous Catalysts for Hydrogenation of Carboxylic Acids to Their Corresponding Alcohols. Asian J. Org. Chem. 2020, 9 (2), 126-143.

[0005] Therefore, the direct reduction of carboxylic acids requires harsh conditions. However, high temperatures cannot be used because oxalic acid begins to decompose above 130°C to CO2 and formic acid, and further to methane under hydrogenation conditions. As a result, there are few technical disclosures regarding this particular reaction.

[0006] In 1955, Carnahan et al. (J.Am.Chem.Soc., 1955, 77 (14), 3766-3768, D0l:10.1021 / ja01619a025) reported that glycolic acid could be effectively reduced to monoethylene glycol at temperatures above 145 °C using ruthenium dioxide or ruthenium / carbon catalysts. However, very high pressures (650-710 atm, 700-775 atm) were required to reach yields of 80% or more. They also reported the conversion of oxalic acid dihydrate (solvent-free) at temperatures between 94 and 170 °C using ruthenium oxide catalyst at similarly high pressures (630-990 atm) and long reaction times (10.5 h), but the yield of monoethylene glycol was only 47%.

[0007] Catalytic hydrogenation of aqueous oxalic acid over a ruthenium-carbon catalyst has been reported by Santos et al. (Reaction Kinetics, Mechanism and Catalysis (2020) 131:139-151). They investigated the reduction of oxalic acid in the presence of 5 wt% Ru / C microporous catalyst in a slurry reactor at a pressure of 80 bar and a temperature range of 120-150 °C under continuous gas flow in batch mode with an operation time of 7 h. They confirmed the formation of glycolic acid, acetic acid, ethylene glycol, and volatile compounds. Although the conversion of oxalic acid reached more than 90%, the highest operation selectivity for ethylene glycol was only 16% (130 °C), in addition to 63% selectivity for glycolic acid (120 °C) and 87% selectivity for volatile products (150 °C).

[0008] WO2017134139 discloses a method for preparing glycolic acid and / or ethylene glycol, comprising at least the steps of: (a) providing an aqueous oxalic acid-containing stream having a molar ratio of water / oxalic acid greater than 5.0; (b) subjecting the aqueous oxalic acid-containing stream provided in step (a) to hydrogenation in the presence of a metal hydride catalyst and hydrogen, thereby obtaining a glycolic acid-containing stream; (c) optionally subjecting the glycolic acid-containing stream obtained in step (b) to hydrogenation in the presence of a metal hydride catalyst and hydrogen, thereby obtaining an ethylene glycol (HOCH2CH2OH)-containing stream. All examples of WO2017134139 operate in batch mode. The highest selectivity of ethylene glycol reported in the batch process of WO2017134139 was 70% at 99% conversion of oxalic acid, which was produced after a total reaction time of 18 h at 90-120 °C (followed by 6 h at 90 °C and 12 h at 120 °C) at a H2 pressure of 100-120 bar.

[0009] From the Santos publication it can be seen that at relatively high temperatures (130°C) and long operating times (7 hours), the conversion of oxalic acid is relatively high (93%), but only 16% of monoethylene glycol is produced. On the other hand, WO2017134139 teaches that at somewhat lower temperatures (90-120°C) and a very long reaction time of 18 hours, the selectivity for monoethylene glycol is very high (70%) with almost complete conversion of oxalic acid (99%). Despite the selectivity for monoethylene glycol reaching 70%, both these documents report a significant residue of material for the process, including, in particular, glycolic acid, acetic acid, ethanol, volatile substances (methane, ethane, CO, CO2), and some starting materials (oxalic acid), etc.

[0010] Other known routes to monoethylene glycol from oxalic acid require multiple steps via an oxalic acid diester as an intermediate.

[0011] Thus, although it has been known that monoethylene glycol can be prepared by the reduction of oxalic acid, commercially attractive conditions for the efficient and selective production of monoethylene glycol have not yet been reported.

[0012] There remains a need for a commercially attractive process for converting oxalic acid to monoethylene glycol that is characterized by both high conversion of the oxalic acid starting material and high yield of the desired monoethylene glycol product. It would be particularly advantageous to provide an industrially applicable continuous process for the hydrogenation of oxalic acid to selectively produce monoethylene glycol. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] WO2017134139 [Non-patent literature]

[0014] [Non-Patent Document 1] Tamura, M. et al. Recent Developments of Heterogeneous Catalysts for Hydrogenation of Carboxylic Acids to Their Corresponding Alcohols.Asian J. Org.Chem. 2020, 9 (2), 126~143 [Non-Patent Document 2] Carnahan et al. J.Am.Chem.Soc., 1955, 77 (14), 3766~3768, D0l:10.1021 / ja01619a025 [Non-Patent Document 3] Santos et al. Reaction Kinetics, Mechanism and Catalysis (2020) 131 :139~151 [Non-Patent Document 4] S. Taniguchi et al. / Applied Catalysis A: General 397 (2011) 171~173 Summary of the Invention [Means for solving the problem]

[0015] Therefore, the present invention provides a method for producing monoethylene glycol, comprising the step of subjecting an aqueous solution of oxalic acid to a hydrogenation reaction in the presence of hydrogen and a metal-containing hydrogenation catalyst, The method is a continuous flow process in a fixed bed reactor; An aqueous oxalic acid solution and a hydrogen gas stream are fed into a fixed bed reactor; the reactor comprises a hydrogenation catalyst bed, the catalyst being a supported metal-containing hydrogenation catalyst having a total metal loading of 2.0 wt. % or more and 20.0 wt. % or less; and The hydrogenation reaction is carried out at a temperature selected from the range of ≧95° C. to ≦125° C., at a hydrogen pressure selected from the range of ≧10 bar H2 to ≦150 bar H2, and with a residence time of ≧5 minutes to ≦2 hours; As a result, a method for producing monoethylene glycol with a high selectivity of 80% or more at a conversion rate of oxalic acid of 90% to 100% is provided.

[0016] With the present continuous flow process, high conversion of oxalic acid and particularly high selectivity to monoethylene glycol was found at short reaction / residence times (i.e., commercially attractive time frames).

[0017] Advantageously, this novel process provides an opportunity for the efficient industrial production of monoethylene glycol from oxalic acid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention relates to a continuous flow process for the production of monoethylene glycol from oxalic acid. Continuous flow means that, in contrast to a batch process, the process can be run without interruption and does not require frequent raw material inputs. To date, only a few prior art documents have mentioned the production of monoethylene glycol from oxalic acid, and these documents only described the process in detail in batch mode. A "batch process" refers to a process that includes a series of steps following a specific order and has a beginning and an end. In general, a continuous flow process refers to a process that is defined by the flow of reactants and products (step by step), where the process is carried out for a longer period of time, with new reactants being continuously fed and products being continuously removed. Although batch processing usually requires more energy, is more expensive, and takes longer, it is often considered the safest and most manageable way to process a particular compound. Continuous processing is efficient and cost-effective, but is not always suitable for every chemical reaction.

[0019] The presently disclosed continuous flow process is carried out in a fixed bed reactor (also called a packed bed reactor), which can be any fixed bed reactor known in the art, including, for example, a reactor that is a single cylindrical tube, but also including a multi-tube reactor, suitably filled / packed with a suitable catalyst. The catalyst bed is often in the form of pellets, and is arranged so as not to move relative to the reactor itself. The reactants, including the reactant gas, flow uniformly over the fixed catalyst bed. A preferred type of fixed bed reactor for carrying out the present process is a trickle bed reactor. Trickle bed reactors include a group of reactors in which the gas phase reactant reacts with the liquid phase reactant while flowing downward (in the direction of gravity) over a bed of solid catalyst particles. The gas phase flow can be either upward or downward depending on the type of application. Preferably, in the present process, the gas phase reactant (hydrogen gas) flows downward along with the liquid phase reactant (aqueous oxalic acid solution).

[0020] The aqueous oxalic acid solution advantageously contains oxalic acid that is ≧1.0% to ≦40% by weight, preferably ≧2.5% by weight, more preferably ≧5.0% to ≦20% by weight.

[0021] The selected temperature of the aqueous oxalic acid solution being fed (the "feed temperature") is generally the same temperature at which the hydrogenation reaction is carried out.

[0022] To increase the solubility of oxalic acid in water, certain additives may be used in the aqueous solution of oxalic acid, such as alcohols, ethers, etc. that are inert under the reaction conditions. The presence of such additives in the aqueous solution therefore affects the saturation, which means, for example, that a 100% saturated solution will contain more oxalic acid per liter than in the absence of these additives.

[0023] Suitably, the aqueous oxalic acid solution used as the feed may be or may comprise a recycle stream from the hydrogenation reaction. The recycle stream may thus comprise one or more hydrogenation (by)products, such as glycolic acid, ethylene glycol, glyoxylic acid, acetic acid, etc. Preferably, the aqueous oxalic acid solution used as the feed comprises at most 20% by weight of such hydrogenation (by)products in total.

[0024] In a presently preferred embodiment of the claimed process, the aqueous oxalic acid solution used as the feed does not contain potassium in any form, the presence of which is believed to be detrimental to the activity of the catalyst.

[0025] Suitably the fixed bed catalyst is a supported metal-containing hydrogenation catalyst having a total metal loading of from 2.0 wt% to 20.0 wt%, preferably from 3.0 wt% to 15.0 wt%, especially 12.0 wt% or less.

[0026] The hydrogenation catalyst preferably contains one or more metals selected from the group A metals: platinum, nickel, copper, ruthenium, rhodium and iridium, preferably ruthenium. In addition, the hydrogenation catalyst optionally also contains one other metal selected from the group B metals: tin, bismuth, palladium, rhenium, gold and antimony. Preferably, the hydrogenation catalyst contains ruthenium (group A metal), preferably one group B metal.

[0027] A highly preferred hydrogenation catalyst contains ruthenium and tin. Such ruthenium-tin catalyst can be advantageously used to suppress the formation of by-products. The molar ratio of ruthenium to tin in the catalyst is 10:1-1:10, preferably 5:1-1:5, more preferably 5:2-1:4.

[0028] A further preferred catalyst for use in this process is a three-way catalyst containing ruthenium, platinum and tin. See, for example, S. Taniguchi et al. / Applied Catalysis A: General 397 (2011) 171-173. The amount and molar ratio of ruthenium and tin in the three-way catalyst are selected as described above. The amount of platinum is preferably 1-5% by weight, more preferably 1.5-3% by weight, based on the catalyst support. A highly preferred catalyst for optimal production of monoethylene glycol from oxalic acid is Ru1Sn 0.85 Pt 0.2 % ruthenium, 5 wt. % tin, and 2 wt. % platinum. The conversion of oxalic acid is also improved when platinum is present in the catalyst.

[0029] Advantageously, the catalyst used in the present process is chloride-free, which is believed to be important for the stability of the catalyst.

[0030] Preferably, the catalyst used in the process according to the present disclosure is calcined (pretreated) at a temperature selected from 200° C. to 450° C. prior to use.

[0031] The catalyst support can be selected from any support material that does not interfere with the current hydrogenation reaction. It has been found that the conversion of oxalic acid to monoethylene glycol hardly occurs on aluminum oxide supported ruthenium catalyst. Preferably, the hydrogenation catalyst is supported on a support selected from carbon, silicon carbide, MAX-phase (Ti2Al2C), TiO2 and ZrO2, more preferably carbon or MAX-phase.

[0032] According to the present invention, highly useful reaction conditions have been found for a continuous flow process for the selective production of monoethylene glycol with high oxalic acid conversion. At temperatures of 95°C or higher and 125°C or lower, particularly 105°C or higher and 125°C or lower, a selectivity of monoethylene glycol, advantageously of at least 85%, can be obtained with an oxalic acid conversion of 90% or higher and 100% or lower, within a commercially attractive time frame.

[0033] The commercially attractive time frame in which the present continuous flow process is carried out is expressed in terms of "residence time". The term "residence time" defines the average length of time that the feed, or specifically the molecules in the feed, remain inside the reactor (here meaning inside the part containing the catalyst bed). According to the process of the present invention, a residence time of 5 minutes or more and 2 hours or less is required. Preferably, the residence time is 10 minutes or more and 1 hour or less. In a flow reactor suitable for the present hydrogenation reaction, the residence time can be changed by changing factors such as the reactor volume, the feed flow rate (both the oxalic acid solution and hydrogen gas), the length of the catalyst bed, etc. Compared to a continuous flow process, in a batch process, the residence time can be related to the reaction time, i.e., how long the vessel is held at a particular temperature in a batch process.

[0034] In the process of the present invention, it has been found that increasing the feed flow does not affect the selectivity to products. If the feed flow is very high, resulting in a very short residence time, only the conversion of oxalic acid will not proceed to completion, but still selectively form monoethylene glycol. Those skilled in the art will understand how to balance the feed flow and the most appropriate residence time at a given temperature. At relatively high temperatures, shorter residence times (and therefore higher feed flows) are required to maximize both the conversion of oxalic acid and the selectivity to the desired products.

[0035] The process is carried out at a hydrogen pressure selected from the range of ≧10 bar H2 to ≦150 bar H2, preferably at a hydrogen pressure of 20 to 100 bar H2.

[0036] The product stream of the continuous flow process according to the present disclosure is continuously removed from the process and can be directly subjected to further processing, although if necessary the product stream can also be (partially) recycled before separating the desired glycolic acid from the solution.

[0037] Oxalic acid is a corrosive material. Therefore, a stainless steel reactor is not ideal for the process. Therefore, the hydrogenation reaction is advantageously carried out in a reactor with a non-metallic or inert liner such as Teflon, glass, PVC, titanium or Hastelloy. [Brief description of the drawings]

[0038] [Figure 1] Results of SFU experiments of oxalic acid reduction at different temperatures. Results of different experiments are summarized in one graph. Conversion (A), selectivity (B) and carbon balance (C) data obtained by liquid chromatography (LC). Conditions during the reaction: temperature = 50–100 °C, pressure = 60 bar, feed = aqueous oxalic acid solution (5 wt%), feed flow = 0.1 ml min-1, gas flow (H2) = 200 ml min-1. A commercial Ru / C catalyst (9.76 wt% Ru / C, 0.5 wt% water from Johnson Mattey) was used for this reaction. Carbon balance was corrected. EXAMPLES

[0039] The invention is further illustrated by the following non-limiting examples.

[0040] List of Abbreviations (M)EG = (mono)ethylene glycol OA=Oxalic acid SFU = Single Flow Unit

[0041] experiment Materials and Reagents Oxalic acid (C2H2O4) was obtained from Sigma-Aldrich®, dried and stored in a dry environment. All water used during this work was filtered using a Millipore system.

[0042] The catalyst used was 9.76 wt% ruthenium on carbon supplied by Johnson Matthey (identification number: 110005, lot number M17160) The catalyst contained 0.5% moisture.

[0043] Catalyst reduction and preparation The catalyst extrudates were ground in a ceramic mortar and sieved to obtain mesh sizes between 105 and 200 μm. The catalyst particles were transferred to a ceramic crucible and reduced in a tube furnace. In the furnace, the particles were heated with a mixture of 7% H2 in N2 at a flow rate of 100 ml min. -1 The temperature in the furnace was increased by 10°C each time until it reached 300-450°C. -1 The temperature was increased with a ramp of 0.05°C. The temperature was kept constant for 180 min. After completion of the reduction procedure, the temperature was slowly decreased and the 7% H2 / N2 mixture was flushed with a pure nitrogen flow.

[0044] Components of the Single Flow Unit (SFU) Flow chemistry experiments were carried out in a trickle-bed reactor system. This unit can be divided into different subsections. Gas flows were controlled by two mass flow controllers (MFCs) for both nitrogen and hydrogen. The nitrogen MFC had a maximum flow rate of 1000 ml. -1 While the hydrogen MFC can handle up to 200ml of flow, -1 The pressure in the reactor was controlled by a pressure indicator, which applied pressure to a back pressure regulator located after the reactor to adjust the pressure in the system. The feed section consisted of a Jasco HPLC pump. The liquid feed flow rate ranged from 0.1 to 5 ml min−1. -1 and was transported to the reactor separately from the gas stream.

[0045] The reactor used in the experiments was a 30 cm long reactor tube with a diameter of 4.6 mm. The reactor had a reactor volume of 5 ml, of which 1.82 ml was within the isothermal zone of the system, thus allowing for catalyst loading.

[0046] The system had space for eight separate exhaust sample vials to collect the effluent that passed through the reactor and was routed to the sample vials through a selector valve system. The sample vials had two needles inserted into them, one input needle from the selector valve and one output needle to relieve pressure or allow excess feed to be drained into a "flush" jerry can. The selector valve itself had 16 channels, eight of which led to the sample vials and eight that led through a manifold to a "drain" jerry can.

[0047] The system was equipped with a feed solution heating and agitation system that allowed for heating and agitation of the feed solution to create a more evenly dispersed feed solution.

[0048] Reactor Materials Oxalic acid is an excellent complexing agent and therefore could potentially leach metals from the reactor components or catalyst. To gain insight into leaching, the reaction solution after 2 hours of reaction at 65 °C with 25 wt% OA in water was analyzed by ICP-OES in a Hastelloy reactor. Strong leaching of chromium, iron, and nickel was observed, but no leaching of ruthenium from the catalyst was observed. To investigate the influence of these metals in solution, three times the amount found in the leaching experiments for Cr, Fe, and Ni was added to the starting solution. It was found that the initial reaction rate was inhibited by 10-15%. To prevent leaching, a non-metallic liner was tested for the Hastelloy reactor to prevent metal parts from coming into contact with the reaction solution. Comparing the performance of the reactor with and without Teflon and glass liners, it was found that the catalyst stability was better with the liner. To clarify the potential influence of leaching, six consecutive reactions were performed with the same solvent. For each of the six reactions, fresh reaction solution was added, but the catalyst was kept in the reactor. The Teflon liner worked best to preserve the catalytic activity as the catalyst was highly over-reduced to ethylene glycol. Metal ions (Ni, Cr, Mo) from reactor corrosion at ppm levels could have inhibited the catalyst performance, and only the Teflon liner provided sufficient protection.

[0049] Filling the reactor A stainless steel reactor 30 cm long was used for the single flow reaction. Equilibration experiments were performed on this reactor prior to this study to ensure that the isothermal zone was between 9 and 20 cm from the bottom. The inner diameter of the reactor was 4.6 mm, which corresponds to a reactor volume of 5 ml (or 1.82 ml for the isothermal zone). For each reactor loading, the maximum amount of catalyst (1.82 ml) was used to fill the isothermal zone of the reactor. The catalyst was reduced ex-situ at 350 °C in a hydrogen atmosphere, packed into the reactor bed, and pre-reduced in-situ in the flow reactor at 200 °C in a hydrogen atmosphere. The remainder of the reactor was filled with layers of silicon carbide (SiC) and quartz wool.

[0050] Installation of the reactor The stainless steel reactor was equipped with Swagelok fittings. The SFU was installed in the reactor using standard Swagelok installation procedures. Swagelok fittings are the fittings of choice here because they can hold high pressure without leaking.

[0051] analysis Liquid chromatography was performed as follows: The sample was diluted with demineralized water to 0.67 mg stock mL -1 The concentrations of oxalic acid, glycolic acid, glyoxylic acid, acetic acid, and ethylene glycol were measured using an Agilent Technologies 1260 Infinity II. A quantitative liquid phase IR measurement method was used in random order to confirm the results from the second method. Results were consistent with both methods.

[0052] Working Example The system used for these reactions is a trickle bed reactor system, which allows for unlimited continuous operation and automatic collection of eight samples per experiment without interruption. Jasco HPLC pumps create the reactant feed flows, and mass flow controllers (MFCs) control the gas (H2 or N2) flows towards the reactor. At the top of the reactor, both the feed and gas flows join, which results in downward movement of liquid and co-current movement of gas over a packed catalyst bed.

[0053] Control Experiment (1) Absence of catalyst - To rule out the possibility of the trickle bed reactor reacting with the reactant feed, control experiments were performed. In these control experiments, a similarly packed reactor was used, as described in the "Reactor Packing" section. In the control experiments, the catalyst in the isothermal zone of the system was replaced with silicon carbide. Various reactant feed flow rates (5-0.1 ml min -1 ) was considered.

[0054] Results: Nearly zero conversion of oxalic acid to observable reaction products during these reactions was observed. The slight conversion observed is within the error range of the analytical method. Liquid chromatography showed only oxalic acid. In conclusion, in the system employed, in the absence of any catalyst, oxalic acid is not converted.

[0055] (2) No hydrogen - the effect of the presence of hydrogen was investigated. Reactor following the procedure described in the "Reactor Loading" section. In this experiment, a commercial catalyst with the following characteristics (9.76 wt% Ru / C, 0.5 wt% moisture) provided by Johnson Mattey was loaded in the isothermal zone of the reactor. Instead of hydrogen flow, various nitrogen flows were investigated. The reaction conditions during this experiment were similar to the actual experimental conditions described herein where glycolic acid was obtained, with the only exception that nitrogen flow was used instead of hydrogen.

[0056] Results: In the absence of catalyst, no reaction products were obtained in this experiment, similar to the results of the control experiment. Conversions were negligible and within the error range of the LC analysis, and no conclusions regarding any possible conversions can be drawn from these data.

[0057] From control and preliminary experiments it was concluded that the conversion of oxalic acid requires the presence of a catalyst and pressurized hydrogen.

[0058] Example 1 The reduction of oxalic acid was carried out at different temperatures in the SFU. In each of these reactions, catalyst particles (size: 105-200 μm) of the same commercial catalyst from Johnson Mattey (9.76 wt% Ru / C, 0.5 wt% moisture) were loaded into the isothermal zone of the reactor. The data shown in Figure 1 are a combination of the results of different temperature effect experiments. In these experiments, 0.1 ml min -1 A reactant feed flow rate of 200 ml / min was used, which corresponds to a residence time of 1092 s in the fully liquid state (18.2 min). The hydrogen flow rate was 200 ml / min. -1 The gas / feed ratio was kept constant at 2000, which means that the gas / feed ratio of 2000 was kept constant during the experiment. Pressure = 60 bar. Feed = aqueous oxalic acid (5 wt%). The feed was not heated or stirred during the reaction, which resulted in a slightly uneven distribution of oxalic acid in the reactant feed bottle, resulting in small concentration differences. Due to this inaccuracy, the carbon balance was corrected to 96% using a correction factor to more accurately portray the actual carbon balance. Figure 1 shows that the conversion of oxalic acid increases at temperatures between 50 and 70 °C, reaches 100%, and then remains constant with further increases in temperature. Initially, oxalic acid is converted only to glycolic acid (Figure 1B, at 50 °C). At higher temperatures, the reaction rate increases, leading to the formation of ethylene glycol from glycolic acid, especially selectively above 95 °C.

Claims

1. A method for producing monoethylene glycol, comprising the step of subjecting an aqueous oxalic acid solution to a hydrogenation reaction in the presence of hydrogen and a metal-containing hydrogenation catalyst, the process is a continuous flow process in a fixed bed reactor; The aqueous oxalic acid solution and the hydrogen gas stream are fed to a fixed bed reactor; the reactor comprises a hydrogenation catalyst bed, the catalyst being a supported metal-containing hydrogenation catalyst having a total metal loading of 2.0 wt. % or more and 20.0 wt. % or less; and The hydrogenation reaction is carried out at a temperature selected from the range of 95° C. or more and 125° C. or less, and at a pressure of 10 bar or more of H 2 to 150 bar or less H 2 and a residence time of 5 minutes to 2 hours, This method allows the production of monoethylene glycol with a high selectivity of 80% or more at a conversion rate of oxalic acid of 90% to 100%.

2. 10. The process of claim 1, wherein the reactor is a trickle bed reactor.

3. The method according to claim 1 or 2, wherein the aqueous oxalic acid solution contains 1.0% by mass or more and 40% by mass or less of oxalic acid.

4. 4. The process according to any one of claims 1 to 3, wherein the hydrogenation catalyst contains one or more metals selected from Group A metals: platinum, nickel, copper, ruthenium, rhodium and iridium, and optionally one other metal selected from Group B metals: tin, bismuth, palladium, rhenium, gold and antimony.

5. 5. The process according to any one of claims 1 to 4, wherein the hydrogenation catalyst contains ruthenium as a group A metal and preferably one group B metal.

6. 6. The method of claim 5, wherein the hydrogenation catalyst contains ruthenium and tin.

7. 7. The process according to claim 6, wherein the molar ratio of ruthenium to tin in the catalyst is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 5:2 to 1:

4.

8. 8. The method according to claim 1, wherein the catalyst is a three-way catalyst containing ruthenium, tin and platinum.

9. The hydrogenation catalyst is selected from the group consisting of carbon, silicon carbide, MAX-phase (Ti 2 Al 2 C) TiO 2 and ZrO 2 9. The process according to claim 1 , wherein the catalyst is supported on a support selected from the group consisting of carbon and MAX-phase.

10. 10. The process according to any one of claims 1 to 9, wherein the hydrogenation reaction is carried out in a reactor having a non-metallic or inert liner, preferably selected from Teflon, glass, PVC, titanium and Hastelloy.

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