A method for the production of maltobionic acid with facilitated oxygen mass transfer

Abstract

The application discloses a method for promoting oxygen mass transfer to produce maltobionic acid, comprising the following steps: S1, dissolving maltose in water by removing ions, and adding a nitrogen-doped carbon composite catalyst with O2 adsorption; S2, pressurizing by inputting oxygen and sealing; S3, heating and oxidizing conversion; with stirring, the nitrogen-doped carbon composite catalyst continuously adsorbs O2 dissolved in the aqueous solution on the surface of the nitrogen-doped carbon composite catalyst for converting maltose into maltobionic acid; oxygen in the environment continuously dissolves into the liquid phase; S4, rapidly cooling to room temperature and discharging gas; S5, filtering the solid nitrogen-doped carbon composite catalyst, and obtaining a liquid phase material; S6, reducing pressure and concentrating, adding calcium hydroxide to the material to be neutral, adding ethanol, filtering, and obtaining calcium maltobionate; S7, purifying the obtained calcium maltobionate into maltobionic acid; the application promotes oxygen mass transfer in the liquid phase by using a metal-free catalyst, thereby improving the yield and production efficiency of maltobionic acid.

Description

Technical Field

[0001] This invention relates to the field of maltodextrin technology, and in particular to a method for promoting oxygen mass transfer to produce maltodextrin. 。 Background Technology

[0002] In maltose, the hemiacetal hydroxyl group of the glucose unit forming the glycoside is α-formed. This α-1,4-glycosidic bond with the C4 of another glucose molecule is called an α-1,4-glycosidic bond. Maltose is oxidized through fermentation to produce maltodextrin, which is widely used as a food additive and has a slightly sour taste. Maltose is a reducing sugar containing an aldehyde group (-CHO), which can be oxidized to a carboxyl group (-COOH) under certain conditions, thus producing an organic acid. Based on the natural tendency of sugars, sugars can generally be oxidized to carboxylic acids.

[0003] Maltodextrin can be prepared by chemical catalytic synthesis and microbial transformation. Chemical synthesis often produces various byproducts during oxidation, complicating separation and purification steps and resulting in relatively high production costs. Microbial fermentation transformation offers advantages such as almost no byproduct formation and high conversion rates. A common technique in microbial fermentation transformation involves the oxidation of maltose to sodium maltose via sugar oxidase and catalase. During the reaction, atmospheric air is added at a rate of 1 L / min, and the pH is maintained constant at 6.4 by continuously adding 1 M Na₂CO₃ solution. The total reaction time is approximately 17 hours, during which virtually all maltose is converted to maltodextrin. This method requires large quantities of water and Na₂CO₃ solution and has a relatively long reaction time. Summary of the Invention

[0004] The purpose of this invention is to provide a method for promoting oxygen mass transfer in the production of maltodextrin. This invention utilizes a metal-free catalyst to promote oxygen mass transfer in the liquid phase, thereby improving the yield and production efficiency of maltodextrin. 。

[0005] To solve this technical problem, the technical solution of the present invention is: a method for promoting oxygen mass transfer to produce maltodextrin, the method comprising the following steps:

[0006] S1. Dissolve maltose in deionized water, place it in a reaction vessel, and add a nitrogen-doped carbon composite catalyst with O2 adsorption properties.

[0007] S2. Introduce oxygen and pressurize, then seal.

[0008] After purification with oxygen, the reactor is filled with oxygen at a pressure of 1 MPa to 1.3 MPa.

[0009] S3, Heating and Oxidation Conversion

[0010] During the heating process, intermittent stirring is performed until the maltose conversion rate reaches 100%;

[0011] The stirring process parameters are as follows:

[0012] Stir at 500 to 600 rpm for 20 to 30 seconds; let stand for 10 to 20 seconds; repeat this cycle for 40 to 60 minutes.

[0013] The conversion temperature is 90℃ to 100℃;

[0014] With stirring, the nitrogen-doped carbon composite catalyst continuously adsorbs O2 dissolved in the aqueous solution onto the surface of the nitrogen-doped carbon composite catalyst to convert maltose into maltodextrin.

[0015] Meanwhile, oxygen in the liquid phase is continuously used to convert maltose into maltose acid, promoting the continuous dissolution of oxygen in the environment into the liquid phase;

[0016] S4. Remove the reactor and place it in an ice-water mixture to cool it rapidly to room temperature, and then release the gas from the reactor.

[0017] S5. Open the reactor and filter out the solid nitrogen-doped carbon composite catalyst to obtain liquid material.

[0018] S6. Concentrate the liquid phase material obtained in S5 under reduced pressure at 50℃ to 60℃ until the volume is 25% of the volume of the liquid phase material obtained in S5. Add calcium hydroxide until the material is neutral. Add ethanol in a volume ratio of 0.25:1 to the volume of deionized water added in S1.

[0019] Stir well, filter, and obtain calcium maltose;

[0020] S7. The obtained calcium maltose is purified and converted into maltose acid.

[0021] A further improvement is made to the preparation method of the nitrogen-doped carbon composite catalyst, which includes the following steps:

[0022] S11. Disperse carbon nanotubes in concentrated nitric acid for etching, soaking time is 6 to 12 hours; filter, wash and dry to obtain etched carbon nanotubes.

[0023] S12. Chitosan and the carbon nanotubes obtained in step one are dispersed in nitric acid solution and stirred to obtain a gel.

[0024] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0025] S13. Freeze-dry to obtain the precursor;

[0026] S14, nitrogen-doped carbon composite catalyst obtained by high-temperature calcination under nitrogen protection.

[0027] This invention prepares a nitrogen-doped carbon composite catalyst with carbon nanotubes as the framework. Electronegative nitrogen atoms are loaded onto the surface of the carbon nanotubes to form a composite with carbon, regulating the oxygen adsorption performance of the resulting product and thus promoting the effective enrichment and transport of oxygen during maltose conversion. In this invention, the carbon nanotubes serving as the framework are etched with concentrated nitric acid, introducing more carboxyl groups. When mixed with chitosan, the amino and hydroxyl groups of chitosan can form amide and ester bonds with the carboxyl groups and other oxygen-containing groups on the carbon nanotube surface. That is, a certain degree of chemical bonding occurs between chitosan and the carbon nanotubes as the framework during dispersion. In subsequent preparation processes such as mixing and calcination, the materials are uniformly and stably dispersed, which is beneficial to improving the catalytic effect of the obtained catalyst.

[0028] In preferred step S11, the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects is 11 mol / L to 14 mol / L. The use of concentrated nitric acid in this invention ensures effective etching and oxidation.

[0029] In the preferred step S12, the mass ratio of chitosan to carbon nanotubes is 1g:5g;

[0030] The ratio of chitosan to nitric acid is 1 g: (2.5 mmol to 7.5 mmol).

[0031] In this invention, a certain amount of nitric acid is added to promote the formation of chitosan gel, which helps to maintain the structure of the obtained catalyst stably during the preparation process.

[0032] In the preferred step S13

[0033] The freeze-drying temperature is -50℃ to -60℃, and the freeze-drying time is 48 hours to 72 hours.

[0034] The preferred process parameters for high-temperature calcination in step S14 are as follows:

[0035] Calcination temperature: 700℃ to 800℃;

[0036] Calcination time: 3 to 5 hours.

[0037] This invention effectively ensures that the calcination temperature and time promote effective nitrogen doping and cyclization of carbon materials. The carbon materials here include not only the carbon elements inherent in chitosan but also the framework carbon nanotubes formed by etching to increase surface defects. After calcination, nitrogen and carbon elements from chitosan and nitrates graphitize along the surface of the carbon nanotubes, effectively enhancing the adjustment of the electron distribution formed by nitrogen doping to carbon for the adsorption of small oxygen molecules. The integrity of the carbon nanotube structure effectively ensures the adsorption of large maltose molecules. Therefore, in this invention, the catalyst, due to the presence of different adsorption effects, simultaneously adsorbs oxygen and maltose molecules, promoting the conversion of maltose to maltodextrin.

[0038] In preferred step S1, the ratio of maltose to nitrogen-doped carbon composite catalyst is 1 mmol: (50 mg to 150 mg).

[0039] The ratio of maltose to deionized water is 1 mmol: 25 ml.

[0040] In this invention, the nitrogen-doped carbon composite catalyst promotes the enrichment of oxygen in the liquid phase, but the increase in yield is limited by the oxygen dissolution rate in the reactor environment.

[0041] The preferred purification and transformation steps in S7 include the following steps:

[0042] S71. Prepare an aqueous solution of calcium maltose obtained in S6, slowly add an equimolar amount of concentrated sulfuric acid while stirring, heat in a water bath at 60°C to 90°C for 1 to 3 hours, and filter out the precipitated calcium sulfate.

[0043] S72. After cooling the filtrate obtained in S71, pass it through an anion and cation exchange resin column to obtain maltodextrin.

[0044] By adopting the above technical solution, the beneficial effects of the present invention are:

[0045] In this invention, the oxidant used in the oxidation of maltose to maltose acid is oxygen supplied to the reaction vessel. However, conventional catalysts accelerate the reaction process. This invention not only utilizes a nitrogen-doped carbon composite catalyst to promote the conversion of maltose but also enriches and adsorbs oxygen in the liquid phase. The nitrogen-doped carbon composite catalyst uses carbon nanotubes as a framework, possessing a large surface area. Concentrated nitric acid is then used to etch the surface of the carbon nanotubes, increasing surface defects and oxidizing more carboxyl groups. Subsequently, a gel is formed with nitric acid and chitosan, effectively surrounding the carbon nanotubes. Nitric acid under nitrogen protection and the carbon atoms of chitosan are loaded onto the surface of the carbon nanotubes. Nitrogen and carbon atoms are adjacent in the periodic table, with similar atomic radii. The nitrogen atom has a lone pair of electrons, making it more electronegative, thus causing the adjacent carbon atom to carry a positive charge. Polarization occurred, and due to the structure of carbon nanotubes, they served as a carbon and nitrogen source to a certain extent, forming a template for the calcination of the catalyst loaded on the surface of the carbon nanotubes, thus strengthening the graphitization structure. Utilizing the adsorption properties of the carbon nanotubes themselves and the nitrogen doping adsorbing oxygen molecules to reduce the oxygen dissociation barrier, the basic sites facilitate the oxidation of aldehyde groups to carboxyl groups, thereby oxidizing oxygen to carboxyl groups from the aldehyde groups of maltose. Simultaneously, the presence of carbon nanotubes effectively adsorbs maltose molecules. Therefore, this invention utilizes the presence of different adsorption effects to achieve the simultaneous adsorption of oxygen and maltose molecules, promoting the conversion of maltose to maltodextrin. Furthermore, due to the nitrogen-doped carbon composite catalyst in the liquid phase, combined with intermittent stirring, oxygen is continuously adsorbed and consumed, ensuring that oxygen in the gas phase environment of the reactor continuously dissolves and enters the liquid phase reaction system for enrichment and consumption. This improves the limitation of reaction rate on liquid phase mass transfer, resulting in complete maltose conversion, a fast conversion rate, and stable conversion effect. Attached Figure Description

[0046] Figure 1 This is the infrared spectrum of the nitrogen-doped carbon composite catalyst precursor used in this invention. Detailed Implementation

[0047] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0048] In this invention, the oxidant used in the oxidation of maltose to maltose acid is oxygen supplied to the reaction vessel. However, conventional catalysts accelerate the reaction process. This invention not only utilizes a nitrogen-doped carbon composite catalyst to promote the conversion of maltose but also enriches and adsorbs oxygen in the liquid phase. The nitrogen-doped carbon composite catalyst uses carbon nanotubes as a framework, possessing a large surface area. Concentrated nitric acid is then used to etch the surface of the carbon nanotubes, increasing surface defects and oxidizing more carboxyl groups. Subsequently, a gel is formed with nitric acid and chitosan, effectively surrounding the carbon nanotubes. Nitric acid under nitrogen protection and the carbon atoms of chitosan are loaded onto the surface of the carbon nanotubes. Nitrogen and carbon atoms are adjacent in the periodic table, with similar atomic radii. The nitrogen atom has a lone pair of electrons, making it more electronegative, thus causing the adjacent carbon atom to carry a positive charge. Polarization occurred, and due to the structure of carbon nanotubes, they served as a carbon and nitrogen source to a certain extent, forming a template for the calcination of the catalyst loaded on the surface of the carbon nanotubes, thus strengthening the graphitization structure. Utilizing the adsorption properties of the carbon nanotubes themselves and the nitrogen doping adsorbing oxygen molecules to reduce the oxygen dissociation barrier, the basic sites facilitate the oxidation of aldehyde groups to carboxyl groups, thereby oxidizing oxygen to carboxyl groups from the aldehyde groups of maltose. Simultaneously, the presence of carbon nanotubes effectively adsorbs maltose molecules. Therefore, this invention utilizes the presence of different adsorption effects to achieve the simultaneous adsorption of oxygen and maltose molecules, promoting the conversion of maltose to maltodextrin. Furthermore, due to the nitrogen-doped carbon composite catalyst in the liquid phase, combined with intermittent stirring, oxygen is continuously adsorbed and consumed, ensuring that oxygen in the gas phase environment of the reactor continuously dissolves and enters the liquid phase reaction system for enrichment and consumption. This improves the limitation of reaction rate on liquid phase mass transfer, resulting in complete maltose conversion, a fast conversion rate, and stable conversion effect.

[0049] Example 1

[0050] This embodiment discloses a method for preparing a nitrogen-doped carbon composite catalyst for oxidizing maltose to maltose acid, comprising the following steps:

[0051] S11. Disperse carbon nanotubes in concentrated nitric acid for etching, soaking time is 6 to 12 hours; filter, wash and dry to obtain etched carbon nanotubes.

[0052] In step S11, the concentration of concentrated nitric acid used to etch carbon nanotubes and increase the defects on the surface of the carbon nanotubes is 11 mol / L.

[0053] S12. Chitosan and the carbon nanotubes obtained in step one are dispersed in nitric acid solution and stirred to obtain a gel.

[0054] The mass ratio of chitosan to carbon nanotubes is 1g:5g;

[0055] The ratio of chitosan to nitric acid was 1 g: 2.5 mmol.

[0056] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0057] S13. Freeze-dry to obtain the precursor;

[0058] The freeze-drying temperature was -50℃, and the freeze-drying time was 72 hours.

[0059] S14, nitrogen-doped carbon composite catalyst obtained by high-temperature calcination under nitrogen protection.

[0060] The process parameters for high-temperature calcination in step S14 are as follows:

[0061] Calcination temperature: 700℃;

[0062] Calcination time: 5 hours.

[0063] Example 2

[0064] The main difference between this embodiment and Example 1 lies in the process parameters for each step in preparing the nitrogen-doped carbon composite catalyst, as detailed in Table 1.

[0065] Example 3

[0066] The main difference between this embodiment and Example 1 lies in the process parameters for each step in preparing the nitrogen-doped carbon composite catalyst, as detailed in Table 1.

[0067] Table 1. Process parameters for the preparation of nitrogen-doped carbon composite catalysts in Examples 1 to 3.

[0068]

[0069] The infrared spectrum of the precursor obtained in step S13 of Example 2 is as follows: Figure 1 As shown, from Figure 1 It can be seen that the freeze-dried precursor in Example 2 was prepared from chitosan, nitric acid, and carbon nanotubes. Figure 1 From this, we can know that 3453cm -1 This is a common vibrational peak for both OH and NH, at 1682 cm⁻¹. -1 The stretching vibration peak of C=O in the -CONH- group, which forms an amide bond between the amino groups of chitosan and the carboxyl groups on the surface of carbon nanotubes, is 1756 cm⁻¹. -1 This is the stretching vibration peak of C=O in the ester bond formed by the hydroxyl groups of carbon nanotubes and chitosan; 1386 cm⁻¹ -1 The NO in nitrate is a symmetric stretching vibration, through Figure 1 The characteristic peaks in the sample indicate that the precursor of Example 2 effectively loaded chitosan and nitric acid with carbon nanotubes as the framework.

[0070] Example 4

[0071] This embodiment discloses a method for promoting oxygen mass transfer to produce maltodextrin, including the following steps:

[0072] S1. Dissolve maltose in deionized water, place it in a reaction vessel, and add a nitrogen-doped carbon composite catalyst with O2 adsorption properties.

[0073] The ratio of maltose to nitrogen-doped carbon composite catalyst was 1 mmol: 50 mg.

[0074] The ratio of maltose to deionized water is 1 mmol: 25 ml.

[0075] This embodiment uses the nitrogen-doped carbon composite catalyst prepared in Example 2.

[0076] The pH value of the liquid material in the reactor was adjusted to 8.

[0077] S2. Introduce oxygen and pressurize, then seal.

[0078] After purification with oxygen, the reactor is filled with oxygen at 1.1 MPa.

[0079] S3, Heating and Oxidation Conversion

[0080] During the heating process, intermittent stirring is performed until the maltose conversion rate reaches 100%;

[0081] The stirring process parameters are as follows:

[0082] Stir at 500 rpm for 20 seconds; let stand for 20 seconds; repeat this cycle for 40 minutes.

[0083] The conversion temperature is 90℃;

[0084] With stirring, the nitrogen-doped carbon composite catalyst continuously adsorbs O2 dissolved in the aqueous solution onto the surface of the nitrogen-doped carbon composite catalyst to convert maltose into maltodextrin.

[0085] Meanwhile, oxygen in the liquid phase is continuously used to convert maltose into maltose acid, promoting the continuous dissolution of oxygen in the environment into the liquid phase;

[0086] S4. Remove the reactor and place it in an ice-water mixture to cool it rapidly to room temperature, and then release the gas from the reactor.

[0087] S5. Open the reactor and filter out the solid nitrogen-doped carbon composite catalyst to obtain liquid material.

[0088] S6. Concentrate the liquid phase material obtained in S5 under reduced pressure at 50°C to a volume of 25% of the volume of the liquid phase material obtained in S5. Add calcium hydroxide until the material is neutral. Add ethanol in a volume ratio of 0.25:1 to the volume of deionized water added in S1.

[0089] Stir well, filter, and obtain calcium maltose;

[0090] S7. The obtained calcium maltose is purified and converted into maltose acid, including the following steps:

[0091] S71. Prepare an aqueous solution of calcium maltose obtained in S6, and slowly add an equimolar amount of 98% concentrated sulfuric acid while stirring. The concentrated sulfuric acid used in this example has a mass fraction of 98%. Heat the solution in a water bath at 60°C for 3 hours and filter out the precipitated calcium sulfate.

[0092] S72. After cooling the filtrate obtained in S71, pass it through an anion and cation exchange resin column to obtain maltodextrin.

[0093] Example 5

[0094] The main difference between this embodiment and embodiment 4 lies in the setting of process parameters for each step, as detailed in Table 2.

[0095] Example 6

[0096] The main difference between this embodiment and embodiment 4 lies in the setting of process parameters for each step, as detailed in Table 2.

[0097] Example 7

[0098] The main difference between this embodiment and embodiment 4 lies in the setting of process parameters for each step, as detailed in Table 2.

[0099] Comparative Example

[0100] This comparative example uses a platinum-carbon catalyst, and the specific preparation method is as follows:

[0101] The particle size is 300 mesh, and the specific surface area is 1200 m². 2 / g of activated carbon with an average pore radius of 2.5nm was refluxed in a 4% nitric acid solution for 2h, then washed with deionized water until the pH of the washing solution was 6, and dried to obtain a pretreated activated carbon carrier.

[0102] The pretreated activated carbon carrier was immersed in a 0.3% sodium dodecylbenzenesulfonate aqueous solution and stirred for 1 hour to mix it evenly and reach adsorption equilibrium, thus obtaining the modified activated carbon suspension.

[0103] Weigh platinum citrate, dilute it with deionized water to a platinum concentration of 10 g / L, and adjust the pH to 1 with hydrochloric acid while stirring to obtain a platinum precursor solution. Add the platinum precursor solution to the modified activated carbon suspension at a rate of 1000 ml / min to obtain mixture A.

[0104] KOH was added to mixture A until the pH of the solution reached 9. At the same time, 0.3% of methylpentanol was added to mixture A. The mixture was stirred for 2 hours to obtain a dispersion B of small and uniformly distributed precipitate particles. Hydrazine hydrate was added to dispersion B, with a platinum to hydrazine hydrate mass ratio of 1:10. The mixture was stirred and reduced at 60°C for 5 hours. After cooling and filtration, the particles were obtained. The particles were washed with deionized water until no chloride ions were present in the washing liquid. The particles were then centrifuged and dried to obtain the platinum-carbon catalyst.

[0105] The platinum-carbon catalyst in this comparative example was used in the preparation of maltodextrin. The specific preparation process parameters are shown in Table 2.

[0106] The contents of maltodextrin were determined by high performance liquid chromatography (HPLC) of the liquid materials obtained in Examples 4 to 7 and the comparative example after step S5. The specific data are shown in Table 3.

[0107] Table 2. Process parameters for the preparation process in Examples 4 to 7

[0108]

[0109] Table 3. Yields and purity of maltodextrin in Examples 4 to 7 and the comparative examples.

[0110]

[0111]

[0112] As shown in Tables 2 and 3, the present invention uses a nitrogen-doped carbon composite catalyst to promote oxygen transfer and accelerate the conversion of maltose to maltodextrin, thus shortening the conversion time compared to the comparative example. The platinum-carbon catalyst used in the comparative example is a precious metal catalyst, which is expensive, but takes a long time to achieve 100% maltose conversion. The various embodiments of the present invention can achieve rapid conversion of maltose in a relatively short time. The main reason for this is that the present invention not only utilizes a nitrogen-doped carbon composite catalyst to promote the conversion of maltose, but also utilizes the nitrogen-doped carbon composite catalyst to enrich and adsorb oxygen in the liquid phase, effectively increasing the contact probability between oxygen, maltose, and the catalyst, and promoting the conversion reaction towards the formation of maltodextrin. Under a constant oxygen pressure in the reactor, as oxygen in the liquid environment is continuously consumed, it dissolves and enters the liquid reaction environment, where it is adsorbed and enriched by the nitrogen-doped carbon composite catalyst, thus promoting the conversion of maltose to maltodextrin. Because nitrogen atoms have a lone pair of electrons, they are more electronegative, causing adjacent carbon atoms to become positively charged, i.e., polarization. Simultaneously, due to the presence of carbon nanotubes, carbon and nitrogen sources are loaded onto the surface of the carbon nanotubes to a certain extent. The presence of carbon nanotubes during catalyst calcination strengthens the graphitization structure. Utilizing the adsorption properties of carbon nanotubes and the reduction of the oxygen dissociation barrier by nitrogen doping adsorbing oxygen molecules, this invention controls the amount of nitrogen doping to effectively coordinate the loading and connection of carbon nanotubes, synergistically promoting the adsorption of oxygen and the synchronous adsorption and conversion of maltose molecules. The basic sites formed by nitrogen doping also facilitate the oxidation of aldehyde groups to carboxyl groups. Furthermore, alternating stirring and settling promotes the desorption of maltodextrin, facilitating the effective adsorption-contact-conversion-desorption of reactants on the surface of the nitrogen-doped carbon composite catalyst, thus creating a cycle.

[0113] In this invention, the nitrogen doping in the nitrogen-doped carbon composite catalyst also includes defective carbon nanotubes. Therefore, the resulting composite catalyst has a stable structure and stable catalytic effect. The solid catalysts used in Examples 4 to 7 were filtered, washed, dried, and reused 10 times. The yield and purity of maltodextrin in the tenth use are shown in Table 4.

[0114] Table 4. Yields and purity of maltodextrin in Examples 4 to 7

[0115] project yield purity Example 4 70.5％ 98.0％ Example 5 73.4％ 98.3％ Example 6 74.6％ 98.1％ Example 7 73.6％ 98.0％

[0116] As can be seen from Tables 3 and 4, the present invention improves the conversion rate of maltose by promoting oxygen mass transfer, has little impact on the catalyst, and has a stable catalytic effect.

Claims

1. A method of facilitating oxygen mass transfer for the production of maltobionic acid, characterized by: The method comprises the following steps: S1, dissolve maltose in deionized water, place it in a reaction kettle, and add nitrogen-doped carbon composite catalyst with O2 adsorption; S2, oxygen is introduced and pressurized, and the reaction kettle is sealed; After purifying the reaction kettle with oxygen, oxygen is filled to 1Mpa to 1.3Mpa; S3, heat and oxidize; During heating, intermittent stirring is performed until the conversion rate of maltose is 100%; The stirring process parameters are as follows: Stirring at 500rpm to 600rpm for 20s to 30s, static for 10s to 20s, and repeat the above process for 40min to 60min; The conversion temperature is 90℃ to 100℃; With stirring, the nitrogen-doped carbon composite catalyst continuously adsorbs O2 dissolved in the aqueous solution on the surface of the nitrogen-doped carbon composite catalyst for the conversion of maltose to maltobionic acid; At the same time, the oxygen in the liquid phase is continuously used for the conversion of maltose to maltobionic acid, and the oxygen in the environment is continuously dissolved into the liquid phase; S4, take out the reaction kettle and place it in an ice-water mixture to quickly cool to room temperature, and discharge the gas in the reaction kettle; S5, open the reaction kettle, filter the solid nitrogen-doped carbon composite catalyst therein, and obtain a liquid phase material; S6, concentrate the liquid phase material obtained in S5 to a volume of 25% of the volume of the liquid phase material obtained in S5 at 50℃ to 60℃ under reduced pressure, add calcium hydroxide to neutralize the material, and add ethanol in a volume ratio of 0.25:1 to the deionized water added in S1; Stir well, filter, and obtain calcium maltobionate; S7, purify the obtained calcium maltobionate into maltobionic acid; The preparation method of the nitrogen-doped carbon composite catalyst comprises the following steps: S11, disperse carbon nanotubes in concentrated nitric acid for etching, soak for 6 hours to 12 hours, filter, wash, and dry to obtain etched carbon nanotubes; S12, disperse chitosan and the carbon nanotubes obtained in step one in a nitric acid solution, stir, and obtain a gel; The amino groups of chitosan and the oxygen atoms of nitrate are surrounded around the carbon nanotubes through electrostatic adsorption; S13, freeze-dry to obtain a precursor; S14, high-temperature calcination under nitrogen protection to obtain a nitrogen-doped carbon composite catalyst.

2. A method of facilitating oxygen mass transfer for production of maltobionic acid according to claim 1, characterized by: In step S11, the concentration of concentrated nitric acid used to etch the carbon nanotubes to increase the defects on the surface of the carbon nanotubes is 11mol / L to 14mol / L.

3. A method of facilitating oxygen mass transfer for production of maltobionic acid according to claim 1, wherein: In step S12, The mass ratio of chitosan to carbon nanotubes is 1g:5g; The amount ratio of chitosan to nitric acid is 1g:(2.5mmol to 7.5mmol).

4. A method of facilitating oxygen mass transfer for production of maltobionic acid according to claim 1, wherein: In step S13, The temperature for freeze-drying is -50℃ to -60℃, and the freeze-drying time is 48 hours to 72 hours.

5. A method of facilitating oxygen mass transfer for production of maltobionic acid as claimed in claim 1, wherein: The process parameters for high-temperature calcination in step S14 are as follows: Calcination temperature: 700℃ to 800℃; Calcination time: 3 hours to 5 hours.

6. The method for promoting oxygen mass transfer to produce maltobionic acid according to claim 1, wherein: In step S1, The amount ratio of maltose to nitrogen-doped carbon composite catalyst is 1mmol:(50mg to 150mg); The amount ratio of maltose to deionized water is 1mmol:25ml.

7. A method of facilitating oxygen mass transfer for production of maltobionic acid according to claim 1, wherein: The purification and conversion steps in S7 comprise the following steps: S71, the calcium maltobionate obtained in S6 is adjusted into an aqueous solution, and then equal-molar concentrated sulfuric acid is slowly added under stirring, and heated in a water bath at 60-90°C for 1-3h, and the precipitated calcium sulfate is filtered off; S72, the filtrate obtained in S71 is cooled and then passed through a cation and anion exchange column to obtain maltobionic acid.

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