Method for converting saccharides into formic acid through vanadium-carbon wet co-catalytic oxidation

Abstract

The invention discloses a method for converting saccharides into formic acid through vanadium-carbon wet co-catalytic oxidation, and belongs to the technical field of catalysis. Carbohydrates and water are subjected to a hydrothermal reaction in an oxygen-containing atmosphere in the presence of a vanadium-based main catalyst and a carbon-based cocatalyst. According to the method, carbohydrates can be converted into formic acid in a high-selectivity manner through one-step hydrothermal reaction through catalytic oxidation, an organic solvent medium and a strong oxidant do not need to be adopted, and the method has the advantages of being high in raw material conversion rate, simple in process, high in product additional value and the like; the consumption of fossil energy can be reduced; and the problem of environmental pollution can be solved.

Description

Technical Field

[0001] This invention relates to a method for the oxidative conversion of sugars into formic acid, and particularly to a wet co-catalytic oxidation method using a vanadium-based main catalyst and a carbon-based co-catalyst to convert sugars into formic acid, belonging to the field of catalysis technology. Background Technology

[0002] Formic acid is an important chemical raw material, widely used as a food additive, preservative and bactericide in silage and animal feed, and also has applications in the dye, rubber, textile, and leather industries. Producing formic acid from biomass-derived sugars can achieve sustainable formic acid production. In recent years, with the increasing depletion of fossil fuels, the development and large-scale application of sustainable energy has become extremely important, and formic acid, as a high-quality liquid organic hydrogen carrier and an ideal fuel for fuel cells, has attracted widespread attention. Traditional formic acid production uses CH3OH and CO derived from fossil fuels, and the main production process is the hydrolysis of methyl formate. Therefore, developing green and sustainable new technologies for formic acid preparation can help achieve the "dual carbon" goal (carbon reduction, carbon emission reduction, and carbon sequestration).

[0003] Carbohydrates (glucose, cellobiose, etc.) can be obtained through biomass hydrolysis. Traditional oxidative cracking reactions of carbohydrates use stoichiometric amounts of hydrogen peroxide as an oxidant and sulfuric acid as an additive, which presents separation and reactor corrosion problems. Chinese patent (CN115304470B) discloses a method for the catalytic oxidation of glucose to formic acid in a microchannel reactor. This patented technology leverages the advantages of the microchannel reactor, such as efficient heat and mass transfer and controllable reaction process, to simultaneously increase the conversion rate of glucose and the yield of formic acid. However, the use of sulfuric acid as a co-catalyst makes separation and purification difficult. Guo et al. (FUELPROCESS TECHNOL., 2023, 242, 107662) proposed a method for the catalytic oxidation of glucose to formic acid using a Mo-modified MnOx catalyst. However, this method requires the use of the strong oxidant potassium permanganate during catalyst synthesis, and the catalyst preparation method is complex, expensive, and difficult to apply on a large scale industrially. Summary of the Invention

[0004] To achieve the above-mentioned technical objectives, the present invention aims to provide a vanadium-carbon wet co-catalytic oxidation method for converting sugars into formic acid. This method can achieve highly selective catalytic oxidative cracking of sugar raw materials into high-value-added small-molecule organic carboxylic acid—formic acid—through a one-step hydrothermal reaction, without the need for organic solvent media and strong oxidants (such as hydrogen peroxide and potassium permanganate). It features high raw material conversion rate, simple process, and high product added value. At the same time, as a renewable biomass raw material, sugars can reduce the consumption of fossil energy and help solve environmental pollution problems.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for the vanadium-carbon wet co-catalytic oxidation of sugars into formic acid. The method involves a hydrothermal reaction of sugars and water in an oxygen-containing atmosphere in the presence of a vanadium-based main catalyst and a carbon-based co-catalyst.

[0006] The key to this invention lies in employing a vanadium-based main catalyst and a carbon-based co-catalyst as a synergistic catalytic system. This system exhibits high conversion rates and selectivity for the oxidation of sugars. While a single vanadium-based catalyst shows high activity for the oxidation of sugars, it exhibits low selectivity for formic acid. However, by introducing an appropriate amount of carbon-based material as a co-catalyst, it was unexpectedly discovered that while achieving high sugar conversion rates, the selectivity for formic acid could be significantly improved. This is mainly due to the introduction of carbon-based material as a high specific surface area active material. It has adsorption and dispersion effects on vanadium-based catalysts dissolved in the aqueous phase, exposing more vanadium catalytic active sites and accelerating the aggregation of substrates and intermediates on its surface. This facilitates the contact between the substrates and intermediates and the vanadium active centers on the carbon-based material surface, completing the catalytic conversion. Simultaneously, the introduction of activated carbon forms unit-point vanadium active centers on its surface, causing polyhydroxy sugars to generate formic acid through a successive breaking of C-C bonds, avoiding the generation of large amounts of oxalic acid and subsequent CO2 formation. This significantly improves the efficiency of converting substrates and intermediates into formic acid, increasing the formic acid yield from 45% to 75%.

[0007] As a preferred embodiment, the vanadium-based main catalyst comprises at least one of V₂O₅, VOSO₄, and NaVO₃. These vanadium compounds are all commercially available reagents. Under appropriate hydrothermal conditions, these vanadium-based catalysts, when used in conjunction with carbon-based co-catalysts, exhibit high levels of sugar conversion and formic acid selectivity.

[0008] As a preferred embodiment, the carbon-based cocatalyst includes at least one of graphene oxide, activated carbon, and mesoporous carbon. These carbon materials are all commercially available reagents, such as commercially available GO, AC, MC, etc. Activated carbon can also be obtained by existing preparation methods, such as glucose-based activated carbon, which is obtained through hydrothermal treatment, calcination, activation, and other steps. The preparation method of glucose-based activated carbon is illustrated as follows: (1) A glucose aqueous solution with a concentration of 0.5-1 mol / L is placed in a hydrothermal reactor, placed in an oven, heated to 170-200℃ and kept at that temperature for 6-10 h, filtered, washed, and dried to obtain glucose hydrothermal carbon Cs. (2) Cs is placed in a nitrogen tube furnace and calcined at a temperature of 500℃-1000℃ for 4-10 h to obtain Cs-Y (Y is the calcination temperature). (3) Cs-Y is mixed with KOH and / or NaOH at a mass ratio of 1 to 6, and then placed in a nitrogen tube furnace and calcined at 500℃ to 1000℃ for 4 to 10 hours to obtain Cs-YX (X is the ratio of Cs-Y to the amount of KOH and / or NaOH added). Further preferred carbon-based co-catalysts have a larger specific surface area, better dispersibility in aqueous solution, and stronger adsorption capacity, which is beneficial for promoting the oxidation reaction of sugars.

[0009] As a preferred embodiment, the amount of the vanadium-based main catalyst is 1% to 10% of the sugar mass. With the introduction of the vanadium-based main catalyst, the conversion rate of the sugar and the selectivity of formic acid both increase slightly, but the increasing trend is not significant. Therefore, the amount of the vanadium-based main catalyst is further preferably 2.5% to 7.5% of the sugar mass.

[0010] As a preferred embodiment, the amount of the carbon-based co-catalyst is 25% to 60% of the sugar mass. When the amount of vanadium-based main catalyst is constant, the conversion rate of sugar tends to increase first and then decrease with the introduction of vanadium-based main catalyst, while the selectivity of formic acid does not change much. Therefore, the amount of carbon-based co-catalyst is further preferably 45% to 55% of the sugar mass.

[0011] As a preferred embodiment, the sugar includes at least one of glucose, fructose, arabinose, xylose, sucrose, maltose, cellobiose, and starch. These sugars are all common monosaccharides, disaccharides, or polysaccharides, and are all polyhydroxy compounds rich in reducing groups.

[0012] As a preferred embodiment, the amount of water used is 20 to 50 times the mass of the sugar.

[0013] As a preferred embodiment, the hydrothermal reaction conditions are: an oxygen partial pressure of 1–4 MPa in an oxygen-containing atmosphere, a temperature of 90–200°C, and a time of 0.5–12 h. The oxygen-containing gas is oxygen or air. Oxygen is a cheap and environmentally friendly oxidant. Within the selected temperature range, as the hydrothermal reaction temperature increases, the conversion rate of sugars and the selectivity of formic acid significantly improve; however, excessively high temperatures can also lead to increased side reactions. Therefore, the hydrothermal reaction temperature is further preferably 150–180°C, and the hydrothermal reaction time is further preferably 1–3 hours. Within these preferred ranges, both the conversion rate of sugars and the selectivity of formic acid reach a high level.

[0014] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0015] The process of catalytic oxidation of carbohydrates to formic acid in this invention is achieved through a one-step hydrothermal reaction, resulting in a high conversion rate of carbohydrates and a high selectivity for formic acid.

[0016] In the process of catalytic oxidation of sugars to formic acid in this invention, there is no need to use organic solvent media and strong oxidants such as hydrogen peroxide and potassium permanganate, thus avoiding the generation of waste liquid and reducing production costs.

[0017] This invention uses sugars as biomass raw materials to produce high-value-added small-molecule organic carboxylic acid—formic acid, which can reduce the consumption of fossil energy and help solve environmental pollution problems.

[0018] The process for the catalytic oxidation of carbohydrates to formic acid of the present invention has the characteristics of simple process and high added value of product, and is expected to generate significant economic value and social benefits.

[0019] The process of catalytic oxidation of sugars to formic acid in this invention uses commercial vanadium-based catalysts and carbon-based co-catalysts. The catalysts are simple to obtain and easy to produce on a large scale.

[0020] The present invention uses green and environmentally friendly oxygen or air as an oxidant in the catalytic oxidation of sugars to formic acid. It can be carried out without additional acidification, has low cost, high product purity, is easy to separate, and is conducive to large-scale production. Attached Figure Description

[0021] Figure 1 TEM image of glucose-based activated carbon Cs-700-3.

[0022] Figure 2 This is a graph of catalyst cycle data. Detailed Implementation

[0023] The following specific embodiments are intended to further illustrate the content of the present invention, but are not intended to limit the scope of protection of the claims of the present invention.

[0024] The preparation method of glucose Cs-YX in the following specific embodiments is as follows: (1) A glucose aqueous solution with a concentration of 1 mol / L is placed in a hydrothermal reactor, placed in an oven, heated to 180℃ and kept at that temperature for 8 hours, filtered, washed and dried to obtain glucose hydrothermal carbon Cs. (2) Cs is placed in a nitrogen tube furnace and calcined at a temperature of 500℃~1000℃ for 6 hours to obtain Cs-Y (Y is the calcination temperature). (3) Cs-Y is mixed with KOH in a mass ratio of 1~6, and placed in a nitrogen tube furnace again and calcined at a temperature of 500℃~1000℃ for 6 hours to obtain Cs-YX (X is the ratio of Cs-Y to KOH added).

[0025] Example 1

[0026] 200 mg glucose, 20 mg V₂O₅, 100 mg (commercially available GO, AC, or MC, or Cs-700-X), and 10 ml deionized water were placed in a 100 ml magnetically stirred stainless steel autoclave with a PTFE liner. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 90 °C and 900 rpm for 12 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 1.

[0027] Table 1. Results of glucose oxidation catalyzed by adding different carbon-based co-catalysts and V2O5.

[0028]

[0029] Table 1 shows that at a reaction temperature of 90℃, V₂O₅ alone cannot catalyze the conversion of glucose to formic acid without the addition of any carbon-based co-catalyst. V₂O₅, in synergistic catalytic oxidation with various carbon-based co-catalysts, yields a higher formic acid yield. Activated carbon exhibits the best effect, with higher glucose conversion and formic acid yield. This is attributed to the adsorption and dispersion of V₂O₅ dissolved in the aqueous phase by the carbon-based co-catalyst, coupled with the attraction of the carbon-based co-catalyst to the substrate, which promotes the contact between the V active sites on the surface of the carbon-based co-catalyst and the substrate, thus completing the catalytic conversion process.

[0030] Example 2

[0031] 200 mg glucose, 20 mg VOSO4 or NaVO3, 100 mg commercially available AC, and 10 ml deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. 2 MPa O2 was introduced into the autoclave, and the reaction was carried out at 90 °C and 900 rpm for 12 h. After the reaction was completed, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 2.

[0032] Table 2 Results of glucose oxidation catalysis by adding AC and different V-based catalysts

[0033]

[0034] As shown in Table 2, at a reaction temperature of 90℃, the V-based catalysts VOSO4 and NaVO3, along with AC, also exhibit a similar synergistic catalytic effect to V2O5 in the oxidation of glucose. The addition of AC as a co-catalyst improves both the glucose conversion rate and the formic acid yield.

[0035] Example 3

[0036] 200 mg glucose, 20 mg V₂O₅, 100 mg (commercially available GO, AC, or MC, or Cs-700-X), and 10 ml deionized water were placed in a 100 ml magnetically stirred stainless steel autoclave with a PTFE liner. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 3.

[0037] Table 3 Results of glucose oxidation catalyzed by adding different carbon-based co-catalysts and V2O5

[0038]

[0039] Table 3 shows that at a reaction temperature of 170℃, unlike at 90℃, V₂O₅ alone achieved a glucose conversion rate of over 90%, while V₂O₅ and various carbon-based co-catalysts synergistically catalyzed the oxidation of glucose within the same timeframe all achieved conversion rates of over 90%. Unlike the results of V₂O₅ alone, the addition of carbon-based co-catalysts significantly improved the formic acid yield, with commercially available activated carbon showing the highest formic acid yield.

[0040] Example 4

[0041] 200 mg glucose, 20 mg VOSO4 or NaVO3, 100 mg commercial AC, and 10 ml deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. 2 MPa O2 was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 4.

[0042] Table 4 Results of glucose oxidation catalysis by combining AC with different V-based catalysts

[0043]

[0044] As shown in Table 4, at a reaction temperature of 170℃, the V-based catalysts VOSO4 and NaVO3, in conjunction with commercial activated carbon, achieved similar results to V2O5 in the same time period for the oxidation of glucose. Furthermore, the formic acid yield obtained by VOSO4 was almost the same as that obtained by V2O5.

[0045] Example 5

[0046] 200 mg glucose, 20 mg V₂O₅, 100 mg commercial AC, and 10 ml deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 150 °C (160 °C, 170 °C, or 180 °C) and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry (LC-MS) and high performance liquid chromatography (HPLC). The reaction results are shown in Table 5.

[0047] Table 5 Results of combined catalytic oxidation of glucose with AC and V2O5 at different temperatures.

[0048]

[0049] As shown in Table 5, the glucose conversion rate did not change significantly within the same time period as the reaction temperature increased, while the formic acid yield showed a trend of first increasing and then decreasing.

[0050] Example 6

[0051] 200 mg glucose, 20 mg V₂O₅, 100 mg commercial AC, and 10 ml deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. The autoclave was then charged with 1 MPa, 2 MPa, 3 MPa, or 4 MPa O₂, or 2 MPa air, and reacted at 170 °C and 900 rpm for 1 h. After the reaction, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 6.

[0052] Table 6. Results of combined catalytic oxidation of glucose under different pressures with added AC and V2O5.

[0053]

[0054] a: refers to the reaction under 2MPa air conditions.

[0055] As shown in Table 6, the reaction pressure affects the formic acid yield. Under the same reaction conditions except for pressure, the formic acid yield gradually increases with increasing pressure. The same 2 MPa air pressure can still oxidize glucose to formic acid.

[0056] Example 7

[0057] 200 mg glucose, 2 mg (5 mg, 10 mg, 15 mg, or 20 mg) V₂O₅, 100 mg commercial AC, and 10 ml deionized water were placed in a 100 ml magnetically stirred stainless steel autoclave with a PTFE liner. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry (LC-MS) and high performance liquid chromatography (HPLC). The reaction results are shown in Table 7.

[0058] Table 7 Results of combined catalytic oxidation of glucose with AC and different V2O5 additions

[0059]

[0060]

[0061] As shown in Table 7, a small amount of V2O5 can still achieve a glucose conversion rate of over 90% under the same conditions, and there is a trend that the formic acid yield increases with the increase of V2O5 amount.

[0062] Example 8

[0063] 100 mg (200 mg, 300 mg, 400 mg, or 500 mg) of glucose, 20 mg of V₂O₅, 100 mg of commercial AC, and 10 ml of deionized water were placed in a 100 ml magnetically stirred stainless steel autoclave with a PTFE liner. 2 MPa of O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 2 hours. After the reaction was completed, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 8.

[0064] Table 8 Results of co-catalytic oxidation of glucose with AC and V2O5 at different dosages

[0065]

[0066] As shown in Table 8, when the glucose concentration is increased to 50 g / L, glucose can still be completely converted under the same conditions, yielding a 60% formic acid yield.

[0067] Example 9

[0068] 200 mg glucose, 20 mg V₂O₅, 50 mg, 100 mg or 120 mg commercial AC, and 10 ml deionized water were placed in a 100 ml magnetically stirred stainless steel autoclave with a PTFE liner. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 9.

[0069] Table 9. Results of co-catalytic oxidation of different glucosees with different amounts of AC and V2O5.

[0070]

[0071]

[0072] Example 10

[0073] 200 mg of arabinose (xylose, sucrose, fructose, maltose, cellobiose, or starch), 20 mg of V₂O₅, 100 mg of commercial AC, and 10 ml of deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. 2 MPa of O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction was complete, the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The reaction results are shown in Table 10.

[0074] Table 10 Results of co-catalytic oxidation of different sugars with added AC and V2O5.

[0075]

[0076] As shown in Table 9, the system of catalytic oxidation of glucose to formic acid by V2O5 and activated carbon has an enhancing effect on other sugars (monosaccharides, disaccharides, and polysaccharides).

[0077] Example 11

[0078] 200 mg glucose, 20 mg V₂O₅, 100 mg commercial AC, and 10 ml deionized water were placed in a 100 ml stainless steel autoclave with a PTFE liner and magnetic stirring. 2 MPa O₂ was introduced into the autoclave, and the reaction was carried out at 170 °C and 900 rpm for 1 h. After the reaction, 0.5 ml of the reaction solution was filtered through a 0.45 μm filter to remove the solid catalyst. The conversion rate of glucose and the yield of formic acid were calculated using the standard curve method with liquid chromatography-mass spectrometry and high performance liquid chromatography. The remaining reaction solution was removed by rotary evaporation, and the resulting solid was recycled. The reaction results are shown in the appendix. Figure 2 .

Claims

1. A method for the vanadium-carbon wet co-catalytic oxidation of sugars to formic acid, characterized in that: Sugars and water undergo a hydrothermal reaction in an oxygen-containing atmosphere in the presence of a vanadium-based main catalyst and a carbon-based co-catalyst.

2. The method for converting sugars into formic acid via vanadium-carbon wet co-catalytic oxidation according to claim 1, characterized in that: The vanadium-based main catalyst includes at least one of V2O5, VOSO4 and NaVO3; The carbon-based cocatalyst includes at least one of graphene oxide, activated carbon, and mesoporous carbon.

3. The method for converting sugars into formic acid via vanadium-carbon wet co-catalytic oxidation according to claim 1 or 2, characterized in that: The amount of the vanadium-based main catalyst used is 1% to 10% of the mass of the sugar.

4. A method for converting sugars into formic acid via vanadium-carbon wet co-catalytic oxidation according to claim 1 or 2, characterized in that: The amount of the carbon-based co-catalyst used is 25% to 60% of the mass of the sugar.

5. The method for converting sugars into formic acid via vanadium-carbon wet co-catalytic oxidation according to claim 1, characterized in that: The sugars include at least one of glucose, fructose, arabinose, xylose, sucrose, maltose, cellobiose, and starch.

6. The method for converting sugars into formic acid via vanadium-carbon wet co-catalytic oxidation according to claim 1, characterized in that: The amount of water used is 20 to 50 times the mass of the sugars.

7. A method for the vanadium-carbon wet co-catalytic oxidation of sugars to formic acid according to claims 1, 2, 5, 6, 3, or 4, characterized in that: The conditions for the hydrothermal reaction are: oxygen partial pressure of 1-4 MPa in an oxygen-containing atmosphere, temperature of 90-200℃, and time of 0.5-12 h.

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