A method for preparing sorbitol from glucose using a cobalt-silver activated carbon bimetallic catalyst

Abstract

This invention belongs to the field of sorbitol preparation and discloses a method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst. Specifically, a glucose aqueous solution undergoes selective hydrogenation under the action of a CoAg / activated carbon composite catalyst to generate sorbitol. The CoAg / AC catalyst does not require high-temperature pre-reduction treatment before use. Under conditions of 140℃ and 4MPa hydrogen pressure for 4 hours, the glucose conversion rate can reach 100%, and the yield and selectivity of sorbitol can reach 93.57%. This exhibits higher catalytic activity and glucose selectivity than CoAg / Al2O3, CoAg / HY, and CoAg / HZSM-5 catalysts. Furthermore, Ag, as a promoter, can inhibit the precipitation and oxidation of Co, solving the problems existing in current catalysts and possessing industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of sorbitol preparation, specifically relating to a method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst. Background Technology

[0002] The global resource crisis is a serious problem facing human society today. Biomass-derived feedstocks have enormous potential as alternatives to fossil fuels to meet ever-increasing energy demands, and can also be used to produce value-added chemicals. Furthermore, the utilization of renewable resources will have a positive environmental impact. Lignocellulose, as one of the most abundant biomass sources, has been converted into chemicals and liquid fuels through various technologies such as rapid pyrolysis, thermal gasification, enzymatic fermentation, and chemical catalysis. Glucose can be obtained from the decomposition of cellulose or hemicellulose. Glucose is one of the most common and readily available primary biomass compounds, and glucose monomers, as a primary feedstock, provide a biorefining platform for the production of sorbitol, mannitol, fuel alcohols, or other high-value-added chemicals through chemical or biocatalytic processes. D-sorbitol is a versatile sugar alcohol widely used in pharmaceuticals, specialty foods, adhesives, textiles, and surfactants. In addition, D-sorbitol is an intermediate in vitamin C production. Industrially, sorbitol can be produced through biochemical methods, such as conventional fermentation with monocultures, or through chemical pathways, such as glucose-catalyzed hydrogenation. Fermentation methods for sorbitol include the use of strains such as *Mortrophlida* and *Lactobacillus plantarum*, but these biotechnological routes require long reaction times, resulting in low glucose conversion rates, low sorbitol yields, and high costs. Compared to fermentation, chemical methods are easier to fine-tune and refine, providing higher yields at lower costs. Therefore, research on the hydrogenation of glucose as a raw material to produce sorbitol under catalysis is of great value.

[0003] When hydrogenating glucose to sorbitol using chemical methods, noble metals (Ru, Rh, Pd, and Pt) and transition metals (Fe, Ni, Cu, and Co) can be used because these metals can provide efficient conversion. Zhang J, Lin L, Zhang J, et al. Efficient conversion of d-glucose into d-sorbitol over MCM-41 supported Ru catalyst prepared by a formaldehyde reduction process[J].CarbohydrateResearch,2011,346(11):1327-1332. The Ru / MCM-41 catalyst prepared by the impregnation-formaldehyde reduction method has high catalytic activity and sorbitol selectivity in the hydrogenation reaction of glucose. The experimental results show that at 120℃, with a catalyst dosage of 20% (based on glucose) and a reaction time of 2h, the sorbitol yield is the highest at 94.43%, and the glucose conversion rate is as high as 100%. At the same time, the catalyst recycling experiment shows that Ru / MCM-41 is a good catalyst and can be reused 3 or 4 times. Byun MY, Park D W, Lee M S. Effect of sodium propionate as a stabilizer on the catalytic activity of Pt / C catalysts for d-glucose hydrogenation [J]. Elsevier, 2020. This study investigated the preparation of Pt / C catalysts using a deposition-precipitation method with different concentrations of sodium propionate (SP) as stabilizers. Carbon black (CB), multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers (CNFs) have been used as catalyst supports. Under conditions of 5 wt% Pt, H2 pressure = 45 bar, T = 140 °C, and 5 h, 100% glucose conversion and 89% sorbitol selectivity were obtained. Noble metal catalysts such as Ru and Pt have high activity for glucose hydrogenation, but their high price limits their industrial application.

[0004] Nickel-based catalysts are the most widely used transition metal catalysts. Yamaguchi, Sho, et al., "Air-stable and reusable nickel phosphide nanoparticle catalyst for the highly selective hydrogenation of D-glucose to D-sorbitol," Green Chemistry (2021), synthesized a hydrotalcite (HT)-supported nickel phosphide nanoparticle (nano-Ni2P / HT) catalyst, which exhibited high activity for the selective hydrogenation of glucose to D-sorbitol. Under mild reaction conditions, the nano-Ni2P / HT catalyst achieved a 99% selectivity for D-sorbitol; however, phosphorus contamination limited its industrial application.

[0005] A, Ran Xi, et al. "Selective hydrogenation of glucose to sorbitol with tannic acid-based porous carbon sphere supported Ni-Ru bimetallic catalysts." Green Energy & Environment (2022). They synthesized Ni-Ru bimetallic porous carbon sphere (Ni-Ru@PCS) catalysts via a formaldehyde-assisted, metal-coordinated crosslinked sol-gel chemical method. Using the Ni:Ru 5:1@PCS catalyst to catalyze the hydrogenation of glucose to sorbitol, the fresh catalyst achieved a glucose conversion of nearly 98% and a sorbitol yield of 97% under reaction conditions of 140℃ for 3 h and 2 h, respectively. The reused catalyst showed stable performance for 4 cycles. However, the glucose conversion and sorbitol yield decreased slightly in the fifth cycle (92% glucose conversion, 91% sorbitol yield). After treating the consumed Ni-Ru 10:1@PCS catalyst at 450℃ under a 2% H2 / N2 mixed atmosphere for 2 h, the regenerated catalyst achieved a glucose conversion of 100% and a sorbitol yield of 99%. The catalytic activity of Ni-Ru10:1@PCS material decreased slightly before regeneration, which is due to the oxidation of some metal particles and the covering of some catalyst active sites by products.

[0006] Fu Y, Ding L, Singleton ML, et al. Synergistic effects altering reaction pathways: the case of glucose hydrogenation over Fe-Ni catalysts[J]. Applied Catalysis B: Environmental, 2021: 119997. Fu et al. synthesized a bimetallic FeNi / CB catalyst using the sol-gel method, achieving a 50% yield of sorbitol for the catalytic hydrogenation of glucose. After hydrogenation experiments, Fu et al. analyzed the stability of the FeNi / CB catalyst using XRD, XPS, and other characterization methods. XRD calculations showed that the average particle size of the FeNi alloy particles increased from 9.0 nm to 17.1 nm after the reaction. Furthermore, 6.5% Ni was precipitated from the FeNi alloy catalyst. The growth and precipitation of nickel particles are the main reasons for the loss of active sites and the deactivation of these catalysts.

[0007] In summary, the catalysts currently used for the hydrogenation of glucose to sorbitol mainly include noble metal catalysts and transition metal catalysts. Among noble metal catalysts, Ru-based catalysts are the most widely used, generally exhibiting higher activity than other noble metal catalysts, characterized by high activity and good stability. However, noble metals are expensive; for example, Ru metal is 1000 times more expensive than Ni metal. Therefore, from the perspective of cost for industrial applications, transition metal catalysts are more advantageous. Ni-based catalysts are representative of transition metal catalysts, offering advantages such as low cost and high activity. However, transition metal components such as Ni precipitate during glucose hydrogenation. Metal precipitation not only leads to irreversible catalyst deactivation but also contaminates the product, increasing product purification costs. Furthermore, transition metals such as Ni require high-temperature reduction to their elemental state before the reaction, but elemental metals are easily oxidized under hydrothermal conditions, thus losing activity. Therefore, to improve the quality of transition metal catalysts, the problems of metal precipitation and oxidation deactivation must be addressed. Summary of the Invention

[0008] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst (CoAg / AC).

[0009] The objective of this invention is achieved through the following technical solutions:

[0010] A method for preparing a cobalt-silver-activated carbon bimetallic catalyst, comprising the following steps:

[0011] Using water as a solvent, glucose reacts with H2 in the presence of a CoAg / AC catalyst at a temperature of 100-180℃ and a hydrogen pressure of 2-5 MPa for 2-6 hours to obtain sorbitol.

[0012] The CoAg / AC catalyst described above has the following composition and preparation process:

[0013] (1) The catalyst that provides hydrogenation catalysis is a multivalent Co oxide complex; the catalyst support is activated carbon (AC); the catalyst is prepared by equal volume impregnation-vacuum drying-nitrogen preservation calcination method, the specific steps are as follows: activated carbon support: the activated carbon is ground and the activated carbon powder with <200 mesh is sieved out by molecular sieve to obtain the activated carbon support.

[0014] (2) Preparation of salt solution: Take a certain amount of Co(NO3)2·6H2O and AgNO3 into a beaker, and dissolve them in a mixture of deionized water and anhydrous ethanol to prepare a salt solution;

[0015] (3) Equal volume impregnation: Weigh the corresponding amount of activated carbon and add it to the prepared metal salt solution so that the salt solution is just absorbed by the activated carbon. Stir with a glass rod for about 10-15 minutes, and then let the sample stand at room temperature for about 4-6 hours.

[0016] (4) Vacuum drying: Place the sample that has been left to stand in step (3) into a vacuum drying oven, first draw a vacuum, the vacuum degree is not less than 0.98 atm, heat to 60°C under vacuum conditions, dry for 12 hours, cool down and pressurize after drying, and grind into powder using an agate mortar.

[0017] (5) Nitrogen-protected roasting: The powdered sample prepared in step (4) is placed in the quartz tube of a tubular roasting furnace and heated from room temperature to 500°C at a programmed temperature of 10°C / min under a nitrogen atmosphere. The sample is then roasted at 500°C for 1-5 hours. When the temperature drops to room temperature, the sample is removed and sealed for storage.

[0018] The reaction uses water as a solvent, the glucose hydrogenation reaction temperature is 100-180℃, the hydrogen pressure is 2-5MPa, and the reaction time is 2-6h. In step (2), the volume ratio of water to ethanol is 10:1 to 5:5; the ratio of Co(NO3)2·6H2O to AgNO3 is 2:1-10:1; in steps (2) and (3), the ratio of Co(NO3)2·6H2O to the support AC is 0.5-3.5 mmol / g, and the ratio of AgNO3 to the support AC is 0.1-1 mmol / g; the prepared CoAg / AC catalyst does not require reduction pretreatment before being added to the reactor.

[0019] The present invention has the following advantages and effects compared with the prior art:

[0020] (1) The developed CoAg / AC bimetallic catalyst exhibits excellent catalytic activity in the hydrogenation reaction of glucose, and for the first time, a CoAg bimetallic catalyst was constructed for the hydrogenation of glucose to sorbitol. The Ag component can inhibit the precipitation of transition metal Co and prevent its oxidative deactivation. Moreover, the catalyst does not require reduction pretreatment and can efficiently hydrogenate glucose to sorbitol under mild conditions, significantly simplifying the catalyst preparation and maintenance process.

[0021] (2) The CoAg / AC catalyst was prepared by equal-volume impregnation-vacuum drying-nitrogen-preserving calcination. This preparation method is suitable for large-scale industrial production. The Co component used is a transition metal. Although Ag is a noble metal, its dosage is small and its price is lower than that of Ru, Pt and other noble metals. It has excellent catalytic function and moderating effect. The reaction conditions are mild, which has obvious advantages and industrial application value. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be purchased from chemical companies.

[0023] The inventive concept of this invention is to construct a CoAg bimetallic catalyst for the hydrogenation of glucose to sorbitol. Ag, as a promoter, can enhance the catalytic activity of the Co catalyst and inhibit Co precipitation. Furthermore, activated carbon support exhibits better CoAg bimetallic catalytic function than supports such as alumina and molecular sieves. Co and Ag oxides are impregnated on the activated carbon support using an equal-volume impregnation-vacuum drying-nitrogen-controlled calcination process, eliminating the need for high-temperature pre-reduction treatment, and can be used for the hydrogenation of glucose to sorbitol. This catalyst, reacting in an aqueous glucose solution at 4 MPa hydrogen pressure and 140°C for 4 hours, completely converts glucose with a sorbitol yield of 93.57%. The synthesized catalyst does not require reduction pretreatment and exhibits high catalytic activity and sorbitol selectivity under mild conditions, providing a novel and highly efficient catalyst for the hydrogenation of glucose to sorbitol.

[0024] Examples 1-5: Batch Reactions at Different Reaction Temperatures

[0025] 1. Catalyst preparation: CoAg / AC catalyst was prepared using an equal-volume impregnation-vacuum drying-nitrogen-protected calcination method. The specific steps are as follows:

[0026] A method for preparing sorbitol by hydrogenation of glucose catalyzed by a cobalt silver-activated carbon (AC) catalyst is characterized by the following steps: using water as a solvent, glucose reacts with H2 in the presence of a CoAg / AC catalyst to obtain sorbitol;

[0027] The CoAg / AC catalyst described above has the following preparation process:

[0028] (1) Activated carbon carrier: Activated carbon is ground and activated carbon powder with a molecular sieve with a mesh size of <200 is obtained to obtain activated carbon carrier;

[0029] (2) Preparation of salt solution: Take 0.5826g of Co(NO3)2·6H2O and 0.0849g of AgNO3 into a beaker and dissolve them in 0.784mL of deionized water to prepare a salt solution;

[0030] (3) Equal volume impregnation: Add 0.2 mL of anhydrous ethanol to the prepared salt solution, shake well and set aside. Weigh approximately 1 g of AC and add it to a beaker, stirring continuously with a glass rod. Let the sample stand at room temperature for 4 hours;

[0031] (4) Vacuum drying: Place the sample that has been left to stand in step (3) in a vacuum drying oven and dry it at 60°C for 12 hours. Grind it into powder using an agate mortar.

[0032] (5) Nitrogen-protected calcination: The powdered sample prepared in step (4) is placed in the quartz tube of a tubular calcination furnace and heated from room temperature to 500°C at a programmed temperature of 10°C / min under a nitrogen atmosphere. The sample is then calcined at 500°C for 2 hours. When the temperature drops to room temperature, the sample is removed and sealed for storage.

[0033] 2. Reaction Test: The performance of the CoAg / AC catalyst in the hydrogenation of glucose was tested using a batch reaction. The specific steps are as follows:

[0034] (1) Take a mechanically stirred high-pressure reactor, add 2g of glucose, 10mL of water and 200mg of CoAg / AC catalyst, tighten the reactor and check the airtightness of the device. After ensuring that the device is airtight, introduce 4MPa H2, stir at 600rpm, set the specified temperature and react for 4h.

[0035] (2) After the reaction is complete, the liquid product is collected and analyzed by high performance liquid chromatography. The catalyst is recovered by natural sedimentation and washing.

[0036] Where: Glucose conversion rate = (Amount of glucose at the beginning of the reaction - Amount of glucose at the end of the reaction) / Amount of glucose at the beginning of the reaction × 100%

[0037] Sorbitol yield = (Amount of sorbitol at the end of the reaction / Amount of glucose at the beginning of the reaction) × 100%

[0038] Sorbitol selectivity = sorbitol yield / glucose conversion rate × 100%

[0039] The chromatographic analysis conditions were as follows: a differential refractive index detector (RID) was used, 0.005 mol / L H2SO4 solution was used as the mobile phase, and the external standard method was employed.

[0040] 3. The reaction results are shown in Table 1.

[0041] Table 1 Results at different reaction temperatures

[0042]

[0043] As shown in Examples 1-5, the glucose conversion rate and sorbitol yield were low when the reaction temperature was 100°C; when the reaction temperature reached 140°C, the glucose conversion rate reached 100% and the sorbitol yield reached 93.57%. When the temperature was above 180°C, the sorbitol yield decreased significantly, indicating that sorbitol continued to decompose or isomerize at high temperatures.

[0044] Batch reactions with different reaction times in Examples 2 and 6-7

[0045] 1. Catalyst preparation: Same as the catalyst preparation process in Examples 1-5.

[0046] 2. Reaction test: The operation process is the same as the reaction test process in Examples 1-5, but the specific reaction conditions are set: different specified reaction times, 600 rpm stirring speed, 120℃ temperature, and 4 MPa H2.

[0047] 3. The reaction results are shown in Table 2.

[0048] Table 2 Results for different reaction times

[0049]

[0050] As shown in Examples 2 and 6-7, under conditions of 4 MPa H2 and 120 °C, the glucose conversion rate and sorbitol yield changed significantly from 2 to 6 hours. When the reaction time was 2 hours, glucose was not completely converted; when extended to 4 hours, the glucose conversion rate reached 98.8%, and the sorbitol yield also increased; when extended to 6 hours, the glucose conversion rate decreased significantly, and no sorbitol was generated. This may be because sorbitol underwent isomerization to sorbitol or decomposed into lower alcohols, indicating that a 4-hour reaction can promote the selective conversion of glucose to sorbitol via the CoAg / AC catalyst.

[0051] Examples 3 and 8-10: Batch reactions at different hydrogen pressures

[0052] 1. Catalyst preparation: Same as the catalyst preparation process in Examples 1-5.

[0053] 2. Reaction test: The operation process is the same as the reaction test process in Examples 1-5. The specific reaction conditions are as follows: after ensuring that the device is airtight, different specified H2 pressures are introduced, the stirring speed is 600 rpm, the temperature is set at 140℃, and the reaction time is 4 hours.

[0054] 3. The reaction results are shown in Table 3.

[0055] Table 3 Results for different hydrogen pressures

[0056]

[0057] Examples 3 and 8-10 show that, under conditions of 140°C and 3-4.5 MPa for 4 hours, and at a hydrogen pressure of 3-4 MPa, the glucose conversion and sorbitol yield increase with increasing pressure. When the H2 pressure reaches 4.5 MPa, the conversion and yield decrease slightly. This may be because the increased concentration of dissolved hydrogen in the water leads to greater adsorption of glucose on the catalyst surface, resulting in excessive hydrogenation of glucose and a decrease in sorbitol yield. Comparison of batch reactions with different supported catalysts in Examples 1-3 is also provided.

[0058] 1. Catalyst preparation: CoAg / Al2O3, CoAg / HY, and CoAg / HZSM-5 catalysts were prepared by equal-volume impregnation-vacuum drying-nitrogen-preservative calcination method. The specific steps are as follows, except for step (3) Impregnation: Place the prepared salt solution in a beaker. Weigh 1.0g of Al2O3, HY, and HZSM-5 respectively, add them to the beaker, and stir continuously with a glass rod. Let the sample stand at room temperature for 4h;

[0059] The remaining preparation steps are the same as in Examples 1-5.

[0060] 2. Reaction test: The performance of CoAg / Al2O3, CoAg / HY, and CoAg / HZSM-5 catalysts in the hydrogenation of glucose was tested using a batch reaction method. The specific steps were the same as in Examples 1-5.

[0061] 3. The reaction results are shown in Table 4.

[0062] Table 4 Results for catalysts with different supports

[0063]

[0064] As can be seen from Comparative Examples 1-3, the CoAg bimetallic catalysts supported on Al2O3, HY, and HZSM-5 supports exhibit good conversion rates but poor selectivity. In contrast, the CoAg / AC catalysts in the above examples demonstrate high selectivity under the same reaction conditions. This indicates that CoAg / AC plays a unique role as a support in the catalytic hydrogenation of glucose to sorbitol.

[0065] The CoAg / AC bimetallic catalyst of this invention exhibits high selectivity for the hydrogenation of glucose to sorbitol. The transition metal Co is the active component, and Ag, as a promoter, can enhance the catalytic activity of the Co catalyst and inhibit Co precipitation. In addition, the activated carbon support is more effective in performing the CoAg bimetallic catalytic function than supports such as alumina and molecular sieves.

[0066] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst, characterized in that, This is achieved through the following steps: using water as a solvent, glucose reacts with H2 in the presence of a CoAg / AC catalyst to obtain sorbitol; The CoAg / AC catalyst described above has the following preparation process: (1) Activated carbon carrier: The activated carbon is ground and the activated carbon powder with a molecular sieve <200 mesh is obtained to obtain the activated carbon carrier; (2) Preparation of salt solution: Co(NO3)2·6H2O and AgNO3 were placed in a beaker and dissolved in a mixture of deionized water and anhydrous ethanol to prepare salt solution. The mass ratio of Co(NO3)2·6H2O to AgNO3 was 2:1-10:1, and the ratio of AgNO3 to carrier AC was 0.1~1 mmol / g. (3) Equal volume impregnation: Weigh the corresponding amount of activated carbon and add it to the prepared metal salt solution so that the salt solution is just absorbed by the activated carbon. Stir with a glass rod for 10-15 min and then let the sample stand at room temperature for 4-6 h. (4) Vacuum drying: Place the sample after standing in step (3) into a vacuum drying oven, first draw a vacuum, the vacuum degree is not less than 0.98 atm, heat to 60 ℃ under vacuum conditions, dry for 12 h, cool down and pressurize after drying, and grind into powder with a mortar. (5) Nitrogen-protected calcination: The powdered sample prepared in step (4) is placed in the quartz tube of a tube calcination furnace and heated from room temperature to 500 ℃ at a programmed temperature of 10 ℃ / min under a nitrogen atmosphere. The sample is then calcined at 500 ℃ for 1-5 h. When the temperature drops to room temperature, the sample is removed and sealed for storage. The hydrogenation reaction of glucose is carried out at a temperature of 100-180℃, a hydrogen pressure of 2-5 MPa, and a reaction time of 2-6 h. The prepared CoAg / AC catalyst does not require reduction pretreatment before being added to the reactor.

2. The method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst according to claim 1, characterized in that, The activated carbon in step (1) is coconut shell activated carbon.

3. The method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst according to claim 1, characterized in that, In step (2), the volume ratio of water to ethanol is 10:1 to 5:

5.

4. The method for preparing sorbitol from glucose using a cobalt-silver-activated carbon bimetallic catalyst according to claim 1, characterized in that, The ratio of Co(NO3)2·6H2O to carrier AC in steps (2) and (3) is 0.5~3.5 mmol / g.

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