Green preparation method of ethyl pyruvate

Abstract

The invention relates to a green preparation method of ethyl pyruvate. According to the method, ethyl lactate is taken as a raw material and is subjected to continuous gas-liquid phase oxidation in a fixed bed in the presence of oxygen-containing gas, a Mn-Cu-Co ternary oxide is loaded on a nitrogen-containing porous carbon catalyst, air calcination and CO2 atmosphere activation are matched, and pretreatment can be carried out in ethyl lactate / carrier gas so as to regulate and control the metal valence state and the oxygen vacancy structure. Water and trace lactic acid amide, glycine and alanine are introduced into the raw material solution, and optional phytic acid / phytate is combined with choline chloride to construct a weak coordination and hydrogen bond network to adjust the interface oxidability; the fixed bed is provided with double reaction zones for segmented temperature control and oxygen supply along the material flow direction. According to the method, high conversion of ethyl lactate and high selectivity of ethyl pyruvate are realized under relatively mild conditions, byproducts are few, and the stability of the catalyst is good.

Description

Technical Field

[0001] This invention relates to the technical field of ethyl pyruvate preparation, and in particular to a green method for preparing ethyl pyruvate. Background Technology

[0002] Ethyl pyruvate is an important fine chemical intermediate used in the synthesis of pharmaceutical raw materials, pesticide compounds, and other functional chemicals. Currently, there are many routes for the preparation of ethyl pyruvate, among which the traditional tartaric acid dehydration and decarboxylation method has been gradually reduced in use due to its numerous steps, low atom utilization, and high energy consumption. With the development of the lactic acid industry chain, oxidation routes using lactic acid or lactic esters as raw materials have attracted attention, as they are considered to have better raw material availability and greener processes.

[0003] Patent CN1204108C discloses a method for catalytic oxidation of ethyl lactate by mixing the gas phase with air in the presence of a silver / silica gel catalyst at approximately 250–300°C. This method avoids the use of chlorinating agents or strong oxidizing agents, but the reaction temperature is high, and ethyl lactate is prone to side reactions and coking at high temperatures, leading to a heavy equipment load and limited long-term operational stability. Patent CN106928059A discloses a technical solution for liquid-phase oxidation of ethyl lactate using strong oxidizing agents or halogenated oxidizing agents. Although oxidation can occur at relatively mild temperatures, the required oxidizing agents are corrosive or toxic, potentially producing chlorine-containing or other difficult-to-treat byproducts, resulting in high environmental pressure and safety risks, and failing to meet the demands of continuous and green industrial processes.

[0004] Therefore, the urgent problem to be solved is how to simultaneously achieve high conversion rate, high selectivity, and stable catalytic performance of ethyl lactate under continuous gas-liquid phase reaction conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a green preparation method for ethyl pyruvate. Under the conditions of continuous gas-liquid phase reaction in a fixed bed with oxygen-containing gas as oxidant, the conversion process of ethyl lactate to ethyl pyruvate is carried out within a relatively mild temperature and pressure range. At the same time, a high conversion rate is achieved while improving the selectivity of ethyl pyruvate, and the performance stability of the catalytic system is maintained during continuous operation.

[0006] To achieve the above objectives, the present invention provides a green preparation method for ethyl pyruvate, comprising the following steps: (1) The raw material liquid containing 75% to 99% ethyl lactate by mass is mixed with oxygen-containing gas and then continuously fed into a fixed bed reactor; (2) In the presence of a porous support catalyst with oxides of three metals, manganese, copper and cobalt, the reaction was carried out in a continuous gas-liquid phase contact reaction at 80℃~150℃ and 0.1MPa~1.0MPa to obtain the reaction product effluent containing ethyl pyruvate. (3) The effluent of the reaction product is separated to obtain ethyl pyruvate product.

[0007] Preferably, the porous support is a nitrogen-containing carbon material, and the molar ratio of manganese, copper and cobalt in the catalyst is 1:0.5 to 2.0:0.1 to 1.5.

[0008] This invention employs a solid catalyst with manganese, copper, and cobalt oxides as active components, supported on a nitrogen-containing carbon porous material, to selectively oxidize ethyl lactate to ethyl pyruvate through continuous gas-liquid contact. By limiting the molar ratio of manganese, copper, and cobalt, multivalent redox centers with stable oxygen vacancies can be formed on the support surface. Manganese provides the main active oxygen species, enabling reversible abstraction of ortho-hydrogen from hydroxyl groups. Copper is used to regulate the number of oxygen vacancies and electron density, increasing the regeneration rate of surface oxygen atoms. Cobalt participates in the intermetallic redox cycle, stabilizing the reaction pathway before excessively high oxidation potentials are formed. If the copper content is too low, insufficient oxygen vacancies lead to a decrease in conversion; if the copper or cobalt content is too high, excessive surface oxidation capacity will trigger carbon-carbon bond breaking, significantly reducing the selectivity of ethyl pyruvate. By limiting the range of their proportions, suitable redox conditions for the oxidation of ethyl lactate are formed, achieving optimal levels of both conversion and selectivity.

[0009] Nitrogen-containing carbon supports possess a high specific surface area and abundant microporous and mesoporous structures. Furthermore, the nitrogen-containing configurations such as pyridine nitrogen and graphitic nitrogen present in the support form stable coordination with the ternary metal oxide, resulting in a more uniform distribution of metal active centers and preventing aggregation and sintering during continuous operation. The weakly basic groups on the support surface can stabilize the active oxygen generated by the metal oxide and inhibit metal surface hydration, allowing the catalyst to maintain a high reaction rate under cyclic operating conditions.

[0010] Controlling the reaction temperature ensures that the activation energy for the surface oxidation and dehydrogenation process is met, while avoiding significant deep oxidation beyond this range. Controlling the pressure maintains the gaseous and dissolved oxygen concentrations in a state that matches the mass transfer rate, preventing deviations caused by insufficient or excessive oxygen concentration in the fixed bed.

[0011] After the reaction, the residue is separated to obtain ethyl pyruvate, while unreacted ethyl lactate is purified and reintroduced into the reaction section, improving feedstock utilization. Because the catalyst exhibits good water resistance and deactivation resistance under the aforementioned metal ratio and support conditions, the recycling process does not accumulate intermediate impurities that lead to decreased selectivity, nor does it experience activity degradation due to metal leaching. The catalyst can maintain a long service life throughout continuous operation.

[0012] In summary, by defining the combination of the chemical environment of the metal and the support, along with the operating conditions, a stable and controllable redox cycle is formed for the oxidation reaction. This combination cannot be achieved through a single metal or simple mixing; rather, it forms a multi-metal synergistic structure suitable for the oxidation of ethyl lactate under specific ratios and the action of the support. This results in significant performance advantages in terms of conversion rate, selectivity, stability, and energy consumption, demonstrating the ingenuity of the overall technical solution.

[0013] Preferably, the raw material liquid in step (1) further includes water with a mass fraction of 1-15% and a mixture of lactamide and amino acids with a mass fraction of 0.01-1.0%, wherein the mass fraction of ethyl lactate is 70-95%.

[0014] This invention introduces a certain amount of water into the feed solution and controls the ethyl lactate mass fraction within the range of 70% to 95%. This ensures that the feed solution maintains a certain polarity and an adjustable hydrogen bond network while ensuring the concentration of ethyl lactate. This facilitates the establishment of a stable interfacial adsorption state of ethyl lactate on the surface of a nitrogen-containing porous carbon support, thereby making it easier to obtain stable conversion and selectivity during continuous oxidation. Furthermore, this invention selects lactamide and short-chain glycine and alanine as auxiliary components. The mixture of lactamide and amino acids can form a low-coverage, reversibly exchanged, weakly interacting layer on the catalyst surface. These nitrogen-containing small molecules, through –NH2 or –CONH– structures, generate weak coordination, hydrogen bonding, or electrostatic interactions with metal-oxygen clusters and nitrogen-containing sites on the nitrogen-containing carbon support. This buffers the fluctuation range of the valence state of metal-oxygen species and maintains the oxidation chemical potential at the interface within a range favorable for selective oxidation. Because of its extremely low addition amount, this weakly interacting layer does not occupy the main active sites in a continuous covering manner, but rather acts as a limiter for the transient enrichment of high oxidation potential sites and strongly electrophilic adsorbed oxygen, thereby reducing the probability of C–C bond breaking and deep oxidation pathways, while maintaining the reaction channels required for α–H removal and subsequent mild re-oxidation.

[0015] The selective oxidation of ethyl lactate can proceed simultaneously with both a target pathway and a deep oxidation pathway. The target pathway primarily relies on the coupling of reversible dehydrogenation and re-oxidation, while the deep oxidation and C–C cleavage pathways are more sensitive to high-valence metal centers and strongly electrophilically adsorbed oxygen. The weak coordination and hydrogen bonding at the lactamide / amino acid interface more readily act on the aforementioned high oxidation potential-related species, causing a greater reduction in the apparent rate of the parallel deep oxidation pathway than the target pathway. This results in improved ethyl pyruvate selectivity while maintaining a high conversion rate.

[0016] Furthermore, water, lactamide / amino acids, and nitrogen-containing carbon supports collectively form a multi-point weak interaction network. This network is facilitated by -COO... - -NH3 + The synergistic effect between the lone pair electrons at the N-position and the surface hydroxyl groups makes the adsorption orientation of ethyl lactate on the catalyst surface more regular, which is conducive to directional dehydrogenation and unfavorable to non-selective cleavage. This structured adsorption state can significantly increase the formation rate of ethyl pyruvate and suppress the formation of small molecule byproducts from deep oxidation.

[0017] In addition, lactamide and amino acids are low-molecular-weight substances with moderate boiling points and easy to flow out with the products. They will not form carbon deposits on the catalyst surface, avoiding the deactivation risk caused by similar macromolecular modifiers, thus ensuring the long-term stability of the catalyst under continuous fixed bed conditions.

[0018] Preferably, the amino acids are glycine and alanine, and the molar ratio of the total molar amount of lactamide and amino acids to ethyl lactate is (1-10)×10. -3 ∶1.

[0019] When the total molar amount of lactamide and amino acids is within (1~10)×10 -3 Within a molar ratio range of 1:1, the weakly interacting components in the system are maintained within an appropriate range, allowing them to exhibit low coverage and reversible exchange regulation characteristics at the solid-liquid interface. When the molar ratio is too low, interface regulation is insufficient, high oxidation potential species are more prone to transient enrichment, and the probability of parallel pathways of deep oxidation and C–C breakage increases. When the molar ratio is too high, the residence time of the weakly interacting layer increases and may cause local site confinement, reducing the apparent rate of dehydrogenation-related steps. The aforementioned preferred range makes small molecules more inclined to form extremely thin in-situ regulation layers around local metal-oxygen clusters, limiting the generation of high valence fluctuations and strongly electrophilic adsorbed oxygen. This results in a greater suppression of the parallel pathway of deep oxidation than the target pathway, promoting higher ethyl pyruvate selectivity while maintaining high conversion rates. The carboxyl groups of glycine and alanine can partially form -COO under the reaction microenvironment. -The adsorption form of glycine and alanine creates weak electrostatic and hydrogen bonds with the –COOEt structure of the ethyl lactate molecule, resulting in a more stable configuration of ethyl lactate when adsorbed on the catalyst surface. This adsorption state reduces the probability of side reactions, particularly the formation of deeply oxidized products such as ethyl acetate. Furthermore, the low melting and boiling points of glycine and alanine prevent their accumulation during the reaction, allowing them to flow out with the products without causing carbon buildup or poisoning, thus maintaining the long-term stability of the continuous fixed-bed reaction.

[0020] Preferably, the raw material liquid in step (1) further includes a mixture of phytic acid and phytate with a mass fraction of 0.01 to 0.5% and choline chloride with a mass fraction of 0.02 to 2%.

[0021] Preferably, the molar ratio of phytic acid to choline chloride is 1:1.5 to 3.

[0022] By adopting the above technical solution, a trace deep eutectic structure with multi-coordination characteristics and a strong hydrogen bond network will be formed inside the reaction system. This will have a significant and highly synergistic regulatory effect on the surface electronic structure, metal oxygen species valence state and liquid phase adsorption configuration of the porous nitrogen-containing carbon catalytic system supported on manganese, copper and cobalt oxides. This will make the reaction pathway of selective oxidation of ethyl lactate to ethyl pyruvate more controlled and significantly reduce side reactions.

[0023] Specifically, phytic acid molecules possess multiple phosphate groups, enabling partial dissociation in the reaction solution to form polydentate, polyanionic coordination units. These coordination units can form weak, multi-site complexes with the oxide sites of Mn, Cu, and Co on nitrogen-containing carbon surfaces, buffering the valence fluctuations of metal-oxygen species. This structure suppresses the transient accumulation of highly oxidizing, high-valence metal species, thereby reducing the likelihood of attack on the C–C bonds of ethyl lactate and making the reaction more prone to α–H removal and hydroxyl dehydrogenation, thus improving the selectivity of ethyl pyruvate.

[0024] Secondly, phytic acid / phytate molecules contain polyphosphate groups, providing a multi-site environment for hydrogen bonding and anion coordination; choline chloride provides quaternary ammonium cation and chloride ion pairs, which, with the participation of a small amount of water, form local structural units with high hydrogen bond density and ion association characteristics. Since ethyl lactate molecules contain ester groups and have a certain degree of polarity, the polar components in the system form limited miscibility and selective association with ethyl lactate, promoting the formation of polar enrichment domains in the host phase through dynamic aggregation of phytic acid / phytate, choline chloride, and water. These enrichment domains preferentially adsorb and locally enrich upon contact with nitrogen-containing sites, surface hydroxyl / oxygen-containing functional groups, and ternary metal-oxygen clusters on the surface of the nitrogen-containing carbon support, altering the dielectric environment, ionic strength, and proton migration behavior at the solid-liquid interface, thereby buffering the transient valence distribution and oxygen migration rate of metal-oxygen species.

[0025] Because the interfacial oxidation potential is locally softened and its fluctuations are suppressed, ethyl lactate tends to convert to ethyl pyruvate via α-H removal and mild re-oxidation, while the probability of deep oxidation and CC cleavage pathways decreases. Simultaneously, the multi-site weak complexation of phytic acid / phytate and the ionic environment of choline chloride reduce the driving force for metal species dissociation from the oxygen cluster surface, thus decreasing the tendency for metal leaching and secondary side reactions caused by leaching.

[0026] The choline cations in choline chloride can modulate the ionic strength and proton migration behavior at the interface, thereby affecting the oxygen migration rate of metal-oxygen species and the hydroxyl group reconstruction process, making the oxidative dehydrogenation step more reversible. Due to a more balanced formation and elimination of hydroxyl groups and alkoxy intermediates at the interface, the conversion of ethyl lactate to ethyl pyruvate is promoted, while the formation of ethyl acetate and further small-molecule byproducts from oxidation is significantly reduced.

[0027] Furthermore, the polyphosphate structure of phytic acid can also exert a local stabilizing effect with Mn, Cu, and Co species, reducing the leaching of metal ions and significantly decreasing metal loss during continuous operation of the fixed-bed reaction, thereby maintaining the long-term stability of the catalyst. The participation of choline chloride further enhances the stability of the interfacial microenvironment, enabling the catalyst to maintain higher activity and selectivity over longer operating periods.

[0028] Preferably, the porous supported catalyst with surface-supported manganese copper cobalt oxide used in step (2) is prepared by the following steps: (a) Loading an inorganic salt precursor containing manganese, copper and cobalt onto a porous carrier containing nitrogen-carbon material, drying it and then calcining it at 400-550°C for 2-6 hours in air atmosphere; (b) The calcined product obtained in step (a) is treated in a carbon dioxide atmosphere at 300–450 °C for 1–5 hours.

[0029] By adopting the above technical solution, step (a) involves calcining the manganese, copper, and cobalt inorganic salt precursors loaded on a nitrogen-containing carbon porous support at 400–550°C in an air atmosphere. This process transforms the precursors into metal oxides with relatively uniform crystal phases and promotes the dispersion of manganese, copper, and cobalt species on the support surface. Simultaneously, it establishes an initial metal-nitrogen interface structure with pyridine nitrogen, graphitic nitrogen, and other sites in the support, providing a foundation for subsequent structural regulation.

[0030] Secondly, in step (b), the material obtained by air calcination is further treated at 300–450°C under a carbon dioxide atmosphere. This causes a weakly acidic and basic reaction involving carbon dioxide on the catalyst surface, generating carbonate or bicarbonate surface substances. These carbonate or bicarbonate surface substances can regulate the acidity / basicity of the metal oxide surface and the distribution of oxygen vacancies, and together with the nitrogen-containing sites on the support, form an acid-base bifunctional structure, allowing ethyl lactate to obtain a more suitable adsorption configuration on the catalyst surface. Furthermore, the recalcination process under a carbon dioxide atmosphere can guide surface oxygen migration behavior, making the distribution of oxygen vacancies more uniform and forming a metal-oxygen cluster structure suitable for reversible dehydrogenation processes.

[0031] Preferably, step (c) is performed after step (b): the catalyst obtained in step (b) is pretreated in a mixture of ethyl lactate and carrier gas at 150–250°C for 1–4 hours.

[0032] In step (c), a mixture of ethyl lactate vapor and carrier gas is introduced for pretreatment, which allows some high-valence metal oxygen species on the catalyst surface to undergo controllable reduction under mild conditions and form a relatively stable low-valence combination. At the same time, a low-coverage organic interaction layer composed of ethyl lactate and its trace adsorbates is formed at the solid-liquid interface, so that the catalyst is in an interface state close to the actual reaction environment before entering the oxygen-containing reaction, thereby reducing the transient enrichment probability of high oxidation potential species in the early stage of the reaction and shortening the induction period.

[0033] Preferably, the pretreatment is performed according to the following procedure: after the catalyst is loaded into the fixed-bed reactor, it is first purged with carrier gas at 0.05-0.5 MPa for 30-60 min; then the temperature is increased to 150-250°C at 1-5°C / min and stabilized for 10-30 min; then a mixture of ethyl lactate vapor and carrier gas is introduced for pretreatment for 1-4 h, wherein the ethyl lactate vapor is generated by an evaporator, and the evaporator temperature is preferably 90-140°C to stabilize the partial pressure of ethyl lactate vapor; after the pretreatment, the carrier gas is switched to purge for 10-30 min to remove condensable components and restore a stable bed pressure drop, and then the temperature is lowered to the reaction temperature to enter the oxidation reaction. Preferably, the total space velocity of the pretreatment mixture is 500-5000 h⁻¹. -1 The total gas flow rate (based on catalyst loading volume) or (based on catalyst mass) is 50–500 mL / min·(g_cat). -1 The pretreatment level is controlled by process criteria. Once the main components of the outlet gas fluctuate by less than ±5% within 30 minutes and the bed pressure drop is stable, pretreatment continues for the set time to avoid over-reduction or over-deposition that could limit the active sites.

[0034] Preferably, in step (c), the volume fraction ratio of ethyl lactate vapor to carrier gas in the mixed gas is 1:3 to 1:15, and the carrier gas is composed of nitrogen and carbon dioxide, with carbon dioxide having a volume fraction of 20% to 80%.

[0035] Preferably, the fixed-bed reactor is provided with a first reaction zone and a second reaction zone sequentially along the material flow direction. The bed temperature of the first reaction zone is 80-110℃, and the bed temperature of the second reaction zone is 110-150℃. The fixed-bed reactor is provided with a first air inlet and a second air inlet arranged at intervals along the material flow direction. The first air inlet is located at the bottom of the reactor and is used to introduce a first stream of oxygen-containing gas into the first reaction zone. The second air inlet is located at the boundary between the first and second reaction zones and is used to supplement the second reaction zone with a second stream of oxygen-containing gas. The flow rates of the first and second air inlets are adjusted by independent mass flow controllers so that the molar ratio of oxygen to ethyl lactate in the first reaction zone is 0.2-0.8:1, and the total molar ratio of oxygen to ethyl lactate in the second reaction zone is 0.6-1.5:1. Preferably, an inert-filled isolation section and / or porous distribution component with a thickness of 10-50 mm is provided at the boundary between the two reaction zones so that the second stream of oxygen-containing gas is evenly distributed radially after entering the bed and backmixing is reduced.

[0036] By employing the above technical solution, the dehydrogenation of ethyl lactate to generate an intermediate in the first reaction zone can be carried out under relatively mild conditions, avoiding deep oxidation caused by excessive oxygen concentration. In the second reaction zone, the dehydrogenation intermediate can be further converted into ethyl pyruvate under suitable temperature and oxygen concentration.

[0037] In this invention, by sequentially employing air calcination, carbon dioxide atmosphere activation, and pretreatment with a mixture of ethyl lactate and carrier gas, a coordinated adjustment process is formed on the catalyst surface in terms of component distribution, oxygen vacancy structure, and valence state of metal oxygen species. This process matches the segmented temperature and segmented oxygen supply conditions of the first and second reaction zones set along the material flow direction in the fixed-bed reactor, enabling the entire oxidation reaction system to exhibit continuous and coordinated selective regulation behavior.

[0038] The pretreated catalyst first enters the first reaction zone in a fixed-bed reactor, where the temperature is low and the molar ratio of oxygen to ethyl lactate is low. In this zone, the low-valence metal centers and the uniform oxygen vacancy structure jointly dominate the selective α-hydrogen removal of ethyl lactate, allowing the dehydrogenation process to be completed preferentially under mild conditions, thus avoiding non-selective oxidation or cracking of the feedstock in a high-temperature, high-oxygen environment. Subsequently, the dehydrogenation intermediate enters the second reaction zone with a higher temperature and higher oxygen concentration. In this zone, the weakly oxidizing interface formed by carbon dioxide treatment and self-reduction pretreatment inhibits the deep oxidation pathway, causing the intermediate to undergo a one-step oxidation to ethyl pyruvate, rather than further conversion to ethyl acetate or small molecule gases, thereby achieving a further improvement in selectivity.

[0039] Therefore, by using air calcination, carbon dioxide modulation, ethyl lactate self-reduction pretreatment, and a fixed-bed dual-reaction zone, the formation process of the catalyst surface structure and the setting of reaction conditions are coordinated to maintain the metal valence state, oxygen vacancy structure, and adsorption configuration of the catalyst surface in a state suitable for selective oxidation, and a stable connection is achieved between the dehydrogenation and oxidation steps.

[0040] The present invention, by adopting the above technical solution, has the following beneficial effects: Under the condition of oxygen-containing gas as oxidant, a synergistic catalytic system is achieved by loading ternary oxides of manganese, copper and cobalt in a specific molar ratio onto a nitrogen-containing carbon porous support. Combined with air calcination, carbon dioxide atmosphere activation and ethyl lactate / carrier gas self-reduction pretreatment, the metal valence state and oxygen vacancy structure on the catalyst surface are regulated. Efficient and selective oxidation of ethyl lactate can be achieved under continuous gas-liquid phase reaction conditions. Thus, high conversion rate of ethyl lactate and selectivity of ethyl pyruvate are obtained simultaneously under relatively mild process conditions, reducing energy consumption and equipment load, and relying less on high temperature, high pressure or strong oxidants. The overall process is greener and safer.

[0041] Secondly, by limiting the mass fraction of ethyl lactate and the water content in the feed solution, and introducing trace amounts of lactamide, glycine, and alanine, as well as further combinations of phytic acid, phytate, and choline chloride, a multi-point weak coordination and hydrogen bond network, as well as locally deep eutectic microregions, are formed in the reaction system. This allows ethyl lactate and intermediates to be adsorbed and transformed on the catalyst surface in a manner more conducive to selective dehydrogenation and mild oxidation, significantly inhibiting carbon-carbon bond breaking and deep oxidation pathways, reducing the formation of byproducts such as ethyl acetate, and simultaneously reducing drastic fluctuations in the valence state and leaching of metal species, thus extending the stable operating time of the catalyst. The fixed-bed reactor is configured with a first reaction zone and a second reaction zone along the feed direction, with different temperatures and oxygen-to-ethyl lactate molar ratios controlled separately. This allows the dehydrogenation and further oxidation steps to proceed sequentially under suitable conditions, avoiding the risk of simultaneously bearing strong exothermic and deep oxidation risks in a single area. This helps to balance heat release and oxygen supply, improving operational stability during long-term continuous operation. Detailed Implementation

[0042] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0043] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0046] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention. Example 1

[0047] This embodiment provides a green preparation method for ethyl pyruvate, the specific steps of which are as follows: (1) 950 parts of industrial-grade ethyl lactate and 50 parts of deionized water were stirred and mixed evenly to obtain a feed solution containing 95 wt% ethyl lactate and 5 wt% water. 80 parts of catalyst were loaded into a stainless steel tubular fixed-bed reactor, and the feed solution was fed into the fixed bed at a volumetric flow rate of 0.50 mL / min. Compressed air was used as the oxygen-containing gas, entering the reactor in parallel from the bottom, with an air volumetric flow rate set to 200 mL / min. The molar ratio of oxygen in the mixed gas to the ethyl lactate entering the reactor was controlled to be approximately 2:1.

[0048] (2) Place the reactor in a constant temperature furnace, heat it to 120 °C, stabilize the pressure at 0.50 MPa, and run it continuously. After reaching a stable state, collect the reaction product effluent to obtain the reaction product effluent containing ethyl pyruvate. (3) The reaction product effluent continuously flowing from the top of the reactor is introduced into a high-efficiency condenser and condensed at 10 °C to obtain a liquid mixture. The liquid mixture is separated by an atmospheric distillation column, and the low-boiling-point component is distilled off from the top of the column. The ethyl pyruvate fraction with a purity ≥99.5 wt% is collected as the product.

[0049] The catalyst is prepared as follows: The porous carrier for the nitrogen-containing carbon material was nitrogen-doped porous carbon nanoparticle powder, product model NCP-7, supplied by Nanjing Jicang Nanotechnology Co., Ltd. This carrier is a black powdery nitrogen-doped porous carbon material with a specific surface area of ​​approximately 595 m². 2 / g, with an average pore size of approximately 7nm, a nitrogen content of approximately 3wt%, and a particle size of approximately 200nm.

[0050] (a) Weigh 4.03 g of Mn(NO3)2·4H2O, 3.02 g of Cu(NO3)2·3H2O, and 1.46 g of Co(NO3)2·6H2O, add them to 50 g of deionized water and stir until completely dissolved to obtain a transparent mixed metal salt solution. Weigh 10.0 g of the porous nitrogen-containing carbon support from step 1 and place it in a rotary evaporator. Slowly add the metal salt solution using an equal-volume impregnation method to ensure that the total volume of the solution is approximately the same as the total pore volume of the support. While adding the solution, slowly rotate the evaporator to ensure that the solution uniformly wets the pores of the support. Let it stand at room temperature for 4 hours for impregnation. Then, slowly evaporate the water under reduced pressure in a 40°C water bath to obtain a moist precursor solid. Place the obtained moist precursor in a forced-air drying oven and dry it at 110°C for 12 hours. Then, heat it to 500°C in air at a heating rate of 2°C / min and calcine it for 4 hours. After the calcination is complete, cool it to room temperature.

[0051] (b) The calcined product obtained in step (a) is loaded into a quartz tube furnace and heated to 380°C at 5°C / min under a high-purity carbon dioxide atmosphere of 100 mL / min. The temperature is maintained for 3 h and then naturally cooled to room temperature in a carbon dioxide atmosphere to obtain the final catalyst. Example 2

[0052] The difference from Example 1 is that the catalyst is pretreated as follows before the continuous gas-liquid phase contact reaction.

[0053] The catalyst was loaded into a fixed-bed reactor and pretreated without the introduction of oxygen. Before the pretreatment began, a carrier gas (N2 / CO2 = 50 / 50, volume fraction) was introduced to replace the reactor and bed for 40 minutes to remove residual air and stabilize the bed pressure drop.

[0054] The composition and ratio of the mixed gas were determined by evaporating ethyl lactate into vapor at 120°C in a heated evaporator and mixing it with the vapor at a volume ratio of 1:5 to obtain a stable pretreatment mixed gas. The carrier gas consisted of nitrogen and carbon dioxide, with the volume fraction of carbon dioxide in the carrier gas determined to be 50%, i.e., the carrier gas ratio was N2 / CO2 = 50 / 50 (volume fraction).

[0055] Gas flow rate settings: The total flow rate of the carrier gas is set to 300 mL / min (standard conditions); the equivalent volumetric flow rate of ethyl lactate vapor after evaporation is approximately 60 mL / min (standard conditions); the final total flow rate of the mixed gas is approximately 360 mL / min.

[0056] Heating and holding conditions: The reactor was heated to 200℃ at a heating rate of 3℃ / min and held at that temperature for 15 min. The above-mentioned mixed gas was then introduced at 200℃ and maintained for 3 h. During the pretreatment, the catalyst bed temperature fluctuation did not exceed ±2℃, and the reactor operating pressure was maintained at 0.30 MPa. When the main component of the outlet gas fluctuated by less than ±5% for 30 consecutive min and the bed pressure drop stabilized, the pretreatment was considered to have entered the stable stage and continued until the set pretreatment time was completed.

[0057] After the pretreatment was completed, the gas was switched to nitrogen for 20 minutes to purge the residual condensable components. Then, the temperature was lowered to the reaction temperature and the continuous oxidation reaction was carried out according to Example 1.

[0058] Example 3 and Example 4 Example 3, based on Example 1, involves setting up a first reaction zone and a second reaction zone sequentially along the material flow direction in a fixed-bed reactor. Different temperature controls and different molar ratios of oxygen to ethyl lactate are used in the first and second reaction zones, respectively. The remaining steps are the same as in Example 1.

[0059] Example 4, based on Example 2, involves setting up a first reaction zone and a second reaction zone sequentially along the material flow direction in a fixed-bed reactor. Different temperature controls and different molar ratios of oxygen to ethyl lactate are used in the first and second reaction zones, respectively. The remaining steps are the same as in Example 3.

[0060] The fixed-bed reactor was modified into a dual-zone temperature-controlled structure with a total length of 1.5 m. The lengths of the two zones and the bed packing are as follows: First reaction zone (front 0.5 m): 25 parts catalyst; Second reaction zone (rear 1 m): 55 parts catalyst. The catalyst used was the catalyst prepared in Example 1 and pretreated in Example 2.

[0061] A first air inlet is provided at the bottom of the reactor, through which a first stream of oxygen-containing gas is introduced and supplies oxygen to the first reaction zone; a second air inlet is provided at the axial boundary between the first reaction zone and the second reaction zone, through which a second stream of oxygen-containing gas is introduced and supplements oxygen to the second reaction zone; the two air inlets are independently regulated by a mass flow controller.

[0062] An inert-filled isolation section (quartz sand, 20 mm thick) is set at the boundary between the two reaction zones to homogenize the radial distribution of the second gas stream and reduce backmixing.

[0063] The operating temperatures for the reaction zones are determined as follows: bed temperature in the first reaction zone: 100 ℃; bed temperature in the second reaction zone: 130 ℃.

[0064] The gas molar ratio in the reaction zone and the liquid feed flow rate of ethyl lactate were maintained the same as in Example 2, i.e., 0.50 mL / min; the oxygen molar flow rate in the first reaction zone was set to 3.25 mL / min (standard conditions), and the oxygen molar flow rate in the second reaction zone was set to 15.7 mL / min (standard conditions).

[0065] Examples 5 and 6 Example 5 is based on Example 1, but differs from Example 1 in that the composition of the raw material liquid used in step (1) is different. The remaining reaction steps and catalyst preparation steps are the same as in Example 1.

[0066] Example 6 is based on Example 4, except that the composition of the raw material liquid used in step (1) is different. The rest of the reaction steps and catalyst preparation steps are the same as those in Example 4.

[0067] The raw material solution includes 850 parts of ethyl lactate, 100 parts of deionized water, 2 parts of lactamide, and 3 parts of amino acid mixture (glycine and alanine mixed in a 1:1 mass ratio).

[0068] The feed solution was used in a fixed-bed reaction, and the preparation of the resulting ethyl pyruvate was performed in the same manner as in Example 1.

[0069] Examples 7 and 8 Example 7 is based on Example 1, but differs from Example 1 in that the composition of the raw material liquid used in step (1) is different. The remaining reaction steps and catalyst preparation steps are the same as in Example 1.

[0070] Example 8 is based on Example 4, but differs from Example 4 in that the composition of the raw material liquid used in step (1) is different. The remaining reaction steps and catalyst preparation steps are the same as those in Example 4.

[0071] The raw material solution includes 910 parts of ethyl lactate, 70 parts of deionized water, 0.5 parts of lactamide, and 0.4 parts of amino acid mixture (glycine and alanine mixed in a 1:1 mass ratio).

[0072] The feed solution was used in a fixed-bed reaction, and the preparation of the resulting ethyl pyruvate was performed in the same manner as in Example 1.

[0073] Examples 9 and 10 Example 9 further adds phytic acid, a mixture of phytates and choline chloride to Example 7.

[0074] Example 10 further incorporates phytic acid, a mixture of phytates, and choline chloride, based on Example 8.

[0075] The raw material solutions of Examples 9 and 10 both included 900 parts of ethyl lactate, 70 parts of deionized water, 0.50 parts of lactamide, 0.20 parts of glycine, 0.20 parts of alanine, 2.0 parts of a mixture of phytic acid and sodium phytate (mass ratio 4:1), and 7.0 parts of choline chloride.

[0076] The remaining steps, catalyst usage, and fixed-bed reaction conditions are the same as in Example 1.

[0077] Comparative Example 1 The difference between this comparative example and Example 1 is that the catalyst is a traditional single-metal manganese-based catalyst, specifically a manganese dioxide catalyst from Hunan Minchuang Environmental Protection Technology Co., Ltd., with an MnO2 content ≥85wt%, a particle size of 1-3mm, and a specific surface area of ​​approximately 40-60m². 2 / g.

[0078] Comparative Example 2 The difference between this comparative example and Example 1 is that the catalyst is different, and the preparation method is as follows: The porous carrier for the nitrogen-containing carbon material was nitrogen-doped porous carbon nanoparticle powder, product model NCP-7, supplied by Nanjing Jicang Nanotechnology Co., Ltd. This carrier is a black powdery nitrogen-doped porous carbon material with a specific surface area of ​​approximately 595 m². ² / g, with an average pore size of approximately 7nm, a nitrogen content of approximately 3wt%, and a particle size of approximately 200nm.

[0079] (a) Weigh 4.03 g of Mn(NO3)2·4H2O and 3.02 g of Cu(NO3)2·3H2O, add them to 50 g of deionized water and stir until completely dissolved to obtain a transparent mixed metal salt solution. Weigh 10.0 g of the porous nitrogen-containing carbon support from step 1, place it in a rotary evaporator, and slowly add the metal salt solution using an equal-volume impregnation method to ensure that the total volume of the solution is approximately the same as the total pore volume of the support. While adding the solution, slowly rotate the evaporator to ensure that the solution uniformly wets the pores of the support, and let it stand at room temperature for 4 hours. Then, slowly evaporate the water under reduced pressure in a 40°C water bath to obtain a moist precursor solid. Place the obtained moist precursor in a forced-air drying oven and dry it at 110°C for 12 hours. Then, heat it to 500°C in air at a heating rate of 2°C / min and calcine it for 4 hours. After the calcination is complete, cool it to room temperature.

[0080] (b) The calcined product obtained in step (a) is loaded into a quartz tube furnace and heated to 380°C at 5°C / min under a high-purity carbon dioxide atmosphere of 100 mL / min. The temperature is maintained for 3 h and then naturally cooled to room temperature in a carbon dioxide atmosphere to obtain the final catalyst.

[0081] Comparative Example 3 The difference between this comparative example and Example 1 is that the catalyst composition is the same as in Example 1, but the catalyst preparation method is different, as follows: (a) Preparation of impregnation solution: Weigh 4.03 g of Mn(NO3)2·4H2O, 3.02 g of Cu(NO3)2·3H2O, and 1.46 g of Co(NO3)2·6H2O, and dissolve them in 50 g of deionized water to obtain a mixed metal salt solution.

[0082] (b) Selection of carrier and impregnation: The carrier selected is alumina (γ-Al2O3, BET is 200m). 2 / g, Shanghai McLean Company). Weigh 10g of γ-Al2O3 and add an equal volume of mixed impregnation solution for impregnation for 4h.

[0083] (c) Drying and calcination: Dry at 110°C for 12 hours, then heat to 450°C in air at 2°C / min and hold for 4 hours.

[0084] Comparative Example 4 The difference between this comparative example and Example 1 is that the catalyst is different. The catalyst is prepared as follows: The porous carrier for the nitrogen-containing carbon material was nitrogen-doped porous carbon nanoparticle powder, product model NCP-7, supplied by Nanjing Jicang Nanotechnology Co., Ltd. This carrier is a black powdery nitrogen-doped porous carbon material with a specific surface area of ​​approximately 595 m².2 / g, with an average pore size of approximately 7nm, a nitrogen content of approximately 3wt%, and a particle size of approximately 200nm.

[0085] (a) Weigh 4.03 g of Mn(NO3)2·4H2O, 12.08 g of Cu(NO3)2·3H2O, and 1.46 g of Co(NO3)2·6H2O, add them to 50 g of deionized water and stir until completely dissolved to obtain a transparent mixed metal salt solution. Slowly add the above mixed metal salt solution to a rotary evaporator containing 10 g of porous nitrogen-containing carbon support, and use the impregnation adsorption method to fully wet the support under slow rotation. After standing at room temperature for 4 hours, evaporate the water under reduced pressure in a 40°C water bath to obtain a moist precursor solid. Place the obtained moist precursor in a forced-air drying oven and dry at 110°C for 12 h, then heat it to 500°C in air at a heating rate of 2°C / min and calcine it for 4 h. After the calcination, cool it to room temperature.

[0086] (b) The calcined product obtained in step (a) is loaded into a quartz tube furnace and heated to 380°C at 5°C / min under a high-purity carbon dioxide atmosphere of 100 mL / min. The temperature is maintained for 3 h and then naturally cooled to room temperature in a carbon dioxide atmosphere to obtain the final catalyst. Performance testing

[0087] 1. Catalytic performance testing method: Examples 1-10 and Comparative Examples 1-4 were selected and tested under the same catalyst and fixed-bed conditions as the corresponding examples. The reactor was continuously operated under these conditions. After reaching a stable state, three product samples were continuously collected from the reactor outlet (each sample collected at 1-hour intervals), and the samples were mixed as analytical samples. Components such as ethyl lactate, ethyl pyruvate, and ethyl acetate in the samples were quantitatively analyzed using gas chromatography-flame detection (GC-FID), with n-butanol used as an internal standard. If necessary, gas chromatography-mass spectrometry (GC-MS) was used for qualitative confirmation of the main peaks. The catalytic performance of different examples and comparative examples obtained under the above method is shown in Table 1.

[0088] Table 1. Comparison of catalytic performance of different embodiments and comparative examples under the same conditions. sample Ethyl lactate conversion rate / % Ethyl pyruvate selectivity / % Ethyl acetate selectivity / % Total selectivity of other byproducts / % Ethyl pyruvate yield / % Example 1 92 84 10 6 77.3 Example 2 92 88 7 5 81 Example 3 93 89 6 5 82.8 Example 4 94 92 5 3 86.5 Example 5 88 90 6 4 79.2 Example 6 90 95 3 2 85.5 Example 7 93 92 5 3 85.6 Example 8 95 95 3 2 90.2 Example 9 92 95 3 2 87.4 Example 10 96 97 2 1 93.1 Comparative Example 1 95 60 25 15 57 Comparative Example 2 90 75 12 13 67.5 Comparative Example 3 85 75 15 10 63.8 Comparative Example 4 96 55 30 15 52.8 As shown in Table 1, under the same reaction temperature, pressure, and space velocity conditions, the manganese-copper-cobalt ternary metal oxide / nitrogen-containing carbon porous support catalyst used in Example 1 significantly improved the selectivity and yield of ethyl pyruvate compared to Comparative Examples 1-3. The yield of ethyl pyruvate increased from 57.0% to 77.3%–86.5%, while the selectivity of ethyl acetate and other deep oxidation products decreased significantly, verifying the synergistic effect of the combination of the ternary metal molar ratio and the nitrogen-containing carbon support in terms of conversion and selectivity in this invention. In Comparative Example 4, when the copper content was too high, even though the conversion rate of ethyl lactate remained high, the selectivity of ethyl pyruvate decreased to 55%, and the selectivity of deep oxidation byproducts increased, proving that the Mn:Cu:Co molar ratio range defined in this invention has criticality.

[0089] Compared to Example 1, Example 2 only added a self-reduction pretreatment step of ethyl lactate and carrier gas mixture before the reaction. With essentially the same conversion rate, the selectivity of ethyl pyruvate increased from 84% to 88%, and the yield increased from 77.3% to 81.0%, indicating that the pretreatment optimization of this invention can gently reduce the proportion of high-valence metal oxygen species, making the surface oxidation capacity more suitable and suppressing deep oxidation pathways. Example 3, based on Example 1, used a dual-reaction zone with segmented temperature and segmented oxygen supply. Without changing the feed solution, the selectivity increased from 84% to 89%, and the yield increased to 82.8%, verifying the role of segmented operation in regulating the selective oxidation pathway in this invention. Example 4 simultaneously employed CO2 atmosphere activation, ethyl lactate self-reduction pretreatment, and dual-reaction zone operation. Under a conversion rate of 94%, the selectivity of ethyl pyruvate increased to 92%, and the yield reached 86.5%, significantly higher than Examples 1, 2, and 3, proving that the optimized steps in this invention, when implemented in combination, have good effects.

[0090] Compared to Examples 1 and 4, Examples 5 and 6 introduced water, lactamide, and a relatively high amount of glycine / alanine mixture into the feed solution, resulting in a slight decrease in ethyl lactate conversion but a significant increase in selectivity. Examples 7 and 8 used lower doses of lactamide and glycine / alanine in the feed solution, maintaining both high conversion and high selectivity. Example 8 achieved a selectivity of 95% and a yield of 90.2% at a conversion rate of 95%. A comparison of Examples 5-8 with Examples 1 and 4 shows that the water and lactamide / amino acid content in the present invention, within a range of (1-10)×10⁻⁶, is optimal. -3 When added within the specified molar ratio range, the oxidation capacity of metal oxygen species and the adsorption state of ethyl lactate interface can be finely adjusted through weak coordination and hydrogen bonding, thereby improving the selectivity and yield of ethyl pyruvate. However, deviating from this range will lead to a decrease in conversion or an increase in byproducts.

[0091] Examples 9 and 10 further added a mixture of phytic acid / phytate and choline chloride to the raw material formulations of Examples 7 and 8, with the molar ratio controlled within the range of 1:1.5 to 3. Compared with Examples 7 and 8, which did not add phytic acid / choline, Examples 9 and 10, under similar conversion conditions, showed a further increase in the selectivity of ethyl pyruvate, while the selectivity of ethyl acetate and other byproducts continued to decrease. The yield of ethyl pyruvate in Example 10 reached 93.1%. This result verifies the mechanism by which the preferred phytic acid and phytate, along with choline chloride, synergistically regulate interfacial polarity and metal valence state, making the reaction more inclined towards the α-H removal and hydroxyl dehydrogenation pathways.

[0092] 2. Long-term stability testing: Examples 1, 2, 4, 8, and 10, as well as Comparative Examples 1 and 3, were selected for long-term continuous operation testing, with each test lasting 100 hours. During the operation, the feed flow rate, reaction temperature, pressure, and space velocity were kept constant. Product samples were collected at 10 hours and 100 hours of operation, and the conversion rate of ethyl lactate and the selectivity of ethyl pyruvate were analyzed according to the aforementioned method. The yield was calculated, and the results are shown in Table 2.

[0093] Table 2 Comparison of long-term stability under different catalysts and process conditions sample Runtime / h Ethyl lactate conversion rate / % Ethyl pyruvate selectivity / % Ethyl pyruvate yield / % Example 1 10 92 84 77.3 Example 1 100 88 80 70.4 Example 2 10 92 88 81 Example 2 100 90 86 77.4 Example 4 10 94 92 86.5 Example 4 100 92 90 82.8 Example 8 10 95 95 90.2 Example 8 100 94 94 88.4 Example 10 10 96 97 93.1 Example 10 100 95 96 91.2 Comparative Example 1 10 95 60 57 Comparative Example 1 100 80 40 32 Comparative Example 3 10 85 75 63.8 Comparative Example 3 100 78 65 50.7 As shown in Table 2, the single-metal manganese dioxide catalyst in Comparative Example 1 showed a significant decrease in ethyl lactate conversion from 95% to 80% and ethyl pyruvate selectivity from 60% to 40% after 100 hours of operation, with the yield dropping considerably from 57.0% to 32.0%, indicating severe deactivation. The ternary catalyst using γ-Al₂O₃ support in Comparative Example 3 also exhibited significant degradation, with a yield of only 50.7% after 100 hours. In contrast, Examples 1, 2, and 4 maintained high conversion and selectivity after 100 hours of operation, and the decrease in ethyl pyruvate yield was significantly smaller than that in Comparative Examples 1 and 3. This demonstrates that the combination of nitrogen-containing carbon support, air calcination, and CO₂ atmosphere activation in this invention effectively suppresses metal sintering and surface acid-base imbalance, thereby improving the catalyst's resistance to deactivation. Compared to Example 1, Example 2 showed that after introducing ethyl lactate self-reduction pretreatment, the yield at 100 h increased from 70.4% to 77.4%, indicating that the pretreatment step not only improved the initial selectivity but also had a positive effect on delaying inactivation and shortening the induction period. In Examples 8 and 10, under the conditions of pretreatment, two-reaction-divided staged operation, and the addition of lactamide, amino acids, phytic acid, and choline chloride, the yields of ethyl pyruvate remained at 88.4% and 91.2% respectively after 100 h of operation, with relatively small declines. This indicates that the combined effect of the feed solution formulation and operating conditions can maintain high conversion and selectivity during long-term operation and significantly slow down the rate of inactivation.

[0094] 3. Catalyst carbon deposition and metal leaching tests: The amount of carbon deposition and metal leaching were measured for catalyst samples used in Examples 1, 4, and 10, and Comparative Examples 1, 3, and 4 after the completion of the long-term stability test.

[0095] (1) Carbon deposition test method: The used catalyst was washed sequentially with anhydrous ethanol and deionized water to remove soluble salts and organic matter. After vacuum drying, samples were taken for thermogravimetric analysis (TGA). The temperature was increased to 900℃ at 10℃ / min under a nitrogen atmosphere, and the mass loss at this stage was recorded. Then, the atmosphere was switched to air, and the temperature was increased again, and the mass loss caused by residual carbon oxidation was recorded. The sum of the mass losses related to organic matter oxidation in the two stages was calculated as the carbon deposition based on the initial catalyst mass, in wt%.

[0096] (2) Metal leaching test method: collect the condensate and tower bottom material corresponding to each long-cycle test, mix and record the total volume, take a certain volume and completely digest it by acidification with nitric acid, and use inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the concentration of Mn, Cu and Co in the solution, convert it into a percentage relative to the initial metal content of the catalyst, and use it as the metal leaching amount.

[0097] The test results are listed in Table 3.

[0098] Table 3. Carbon deposition and metal leaching of catalyst after long-term operation sample Carbon deposits / wt% Mn leaching amount / % Cu leaching amount / % Co leaching amount / % Example 1 3 1.5 1 0.8 Example 4 2.2 1 0.7 0.5 Example 10 1.5 0.5 0.3 0.3 Comparative Example 1 6 4.5 — — Comparative Example 3 4.5 3 2.5 2 Comparative Example 4 5.5 3.5 4 2.5 The “—” indicates that the corresponding metal was not introduced into the catalyst system.

[0099] As shown in Table 3, the single-metal manganese dioxide catalyst used in Comparative Example 1 achieved a carbon deposition of 6.0 wt% and a Mn leaching of 4.5% after long-term operation. Comparative Examples 3 and 4, which used alumina supports or ternary catalysts with excessive copper content, also exhibited significantly higher carbon deposition and metal leaching rates than the embodiments of this invention. In contrast, the nitrogen-containing carbon supports in Examples 1 and 4, after air calcination and CO2 atmosphere activation, showed carbon deposition rates of 3.0 wt% and 2.2 wt%, respectively, with a significant reduction in metal leaching. In Example 10, after further using phytic acid / phytate and choline chloride, the carbon deposition decreased to 1.5 wt%, and the leaching rates of Mn, Cu, and Co were all controlled below 1%. This indicates that the support structure and feed solution formulation of this invention play a superior role in inhibiting carbon deposition and improving metal fixation, thus effectively supporting the results of the long-term stability test.

[0100] The above tests on catalytic performance, long-term stability, and deactivation mechanism demonstrate that this invention achieves high conversion rate, high selectivity, and high stability in the selective oxidation process of ethyl lactate to ethyl pyruvate under relatively mild conditions by limiting the molar ratio of ternary metals, combining heat treatment with air / CO2 on a nitrogen-containing porous carbon support, self-reduction pretreatment, and the joint regulation of various trace components in the feed solution.

[0101] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A green preparation method for ethyl pyruvate, characterized in that, Includes the following steps: (1) The raw material liquid containing 75% to 99% ethyl lactate by mass is mixed with oxygen-containing gas and then continuously fed into a fixed bed reactor; (2) In the presence of a porous support catalyst with oxides of three metals, manganese, copper and cobalt, the reaction was carried out in a continuous gas-liquid phase contact reaction at 80℃~150℃ and 0.1MPa~1.0MPa to obtain the reaction product effluent containing ethyl pyruvate. (3) The effluent of the reaction product is separated to obtain ethyl pyruvate product.

2. The green preparation method of ethyl pyruvate according to claim 1, characterized in that, The raw material solution in step (1) also includes water with a mass fraction of 1 to 15% and a mixture of lactic acid amide and amino acids with a mass fraction of 0.01 to 1.0%.

3. The green preparation method of ethyl pyruvate according to claim 2, characterized in that, The amino acids are glycine and alanine, and the molar ratio of the total molar amount of lactamide and amino acids to ethyl lactate is (1–10) × 10⁻⁶. -3 ∶1.

4. The green preparation method of ethyl pyruvate according to claim 1 or 2, characterized in that, The raw material solution in step (1) also includes a mixture of phytic acid and phytate with a mass fraction of 0.01 to 0.5% and choline chloride with a mass fraction of 0.02 to 2%.

5. The green preparation method of ethyl pyruvate according to claim 4, characterized in that, The molar ratio of phytic acid to choline chloride is 1:1.5 to 3.

6. The green preparation method of ethyl pyruvate according to claim 1, characterized in that, The porous supported catalyst with surface-supported manganese copper-cobalt oxide used in step (2) is prepared by the following steps: (a) Loading an inorganic salt precursor containing manganese, copper and cobalt onto a porous carrier containing nitrogen-carbon material, drying it and then calcining it at 400-550°C for 2-6 hours in air atmosphere; (b) The calcined product obtained in step (a) is treated in a carbon dioxide atmosphere at 300–450 °C for 1–5 hours.

7. The green preparation method of ethyl pyruvate according to claim 6, characterized in that, Step (c) is performed after step (b): the catalyst obtained in step (b) is pretreated in a mixture of ethyl lactate and carrier gas at 150–250 °C for 1–4 hours.

8. The green preparation method of ethyl pyruvate according to claim 7, characterized in that, In step (c), the volume fraction ratio of ethyl lactate vapor to carrier gas in the mixed gas is 1:3 to 1:15, and the carrier gas is composed of nitrogen and carbon dioxide, with carbon dioxide having a volume fraction of 20% to 80%.

9. The green preparation method of ethyl pyruvate according to claim 7, characterized in that, The fixed-bed reactor is arranged with a first reaction zone and a second reaction zone in sequence along the material flow direction. The bed temperature of the first reaction zone is 80-110℃, and the bed temperature of the second reaction zone is 110-150℃. The molar ratio of oxygen to ethyl lactate in the first reaction zone is controlled to be 0.2-0.8:1, and the total molar ratio of oxygen to ethyl lactate in the second reaction zone is 0.6-1.5:

1.

10. The green preparation method of ethyl pyruvate according to claim 1, characterized in that, The porous support is a nitrogen-containing carbon material, and the molar ratio of manganese, copper, and cobalt in the catalyst is 1:0.5 to 2.0:0.1 to 1.5.