Method for continuously synthesizing pyruvic acid through catalytic oxidation of ethyl lactate and coupled reaction rectification

Abstract

The invention belongs to the technical field of chemical processes, and particularly relates to a method for continuously synthesizing pyruvic acid through catalytic oxidation of ethyl lactate and coupled reaction rectification. According to the method, ethyl lactate and hydrogen peroxide are used as raw materials, a titanium silicalite molecular sieve is used as a catalyst, pyridine-2-formic acid is added as an auxiliary agent, ethyl pyruvate is synthesized in a tubular reactor filled with the catalyst, then under the condition of reduced pressure, pyruvate is hydrolyzed through a continuous reactive distillation tower, and a pyruvic acid water solution is obtained at the tower bottom. According to the invention, a tubular reactor model is adopted, the side reaction of hydrogen peroxide caused by backmixing of kettle reaction is solved, meanwhile, pyridine-2-formic acid is added as an auxiliary agent, the invalid decomposition of hydrogen peroxide in the catalytic oxidation process is solved, and the utilization rate of hydrogen peroxide is improved. Reaction rectification is coupled in the ethyl pyruvate hydrolysis process, continuous hydrolysis of ethyl pyruvate is achieved, a reaction section is filled with styrene resin with sulfonic acid groups to catalyze hydrolysis of ester, the reaction rate is increased from the thermodynamic angle, ethyl alcohol is promoted to be moved out of a system in the decompression hydrolysis kinetics, the reaction time is greatly shortened, and the yield is increased. And high-efficiency, continuous and green synthesis of pyruvic acid is realized.

Description

Technical Field

[0001] This invention belongs to the field of chemical process technology, specifically relating to a method for the continuous synthesis of pyruvate by catalytic oxidation of ethyl lactate and coupled reactive distillation. Background Technology

[0002] Pyruvic acid, also known as α-oxopropionic acid, is an organic compound with the chemical formula C3H4O3 and the structure CH3COCOOH. It is an important intermediate in the sugar metabolism of all biological cells and the interconversion of various substances in the body. Because the molecule contains activated ketone and carboxyl groups, it is widely used as a basic chemical raw material in various fields such as chemistry, pharmaceuticals, food, agriculture and environmental protection. It can be prepared by chemical synthesis and biotechnology.

[0003] Currently, there are two main industrial methods for synthesizing pyruvate: chemical and biosynthesis. Biosynthesis primarily utilizes microbial fermentation to convert inexpensive carbon sources or enzymatic methods to convert other substances into pyruvate. However, the biosynthetic pyruvate production product contains other metabolites and impurities, resulting in a complex composition that requires extraction using physical and chemical methods. Enzymatic conversion typically uses lactate as a substrate to maintain bacteria or enzymes within a suitable pH range, yielding pyruvate as the product, but the substrate cost is high. Microbial fermentation uses low-cost glucose as a substrate to produce pyruvate, but the genetic stability of the microbial strains and production efficiency are low, and subsequent separation is difficult, making industrial-scale production challenging. Chemical synthesis involves oxidizing tartaric acid (or lactate ester) to pyruvate ester in the liquid or gas phase, followed by hydrolysis to obtain pyruvate. However, this method is highly polluting, costly, and lacks competitiveness.

[0004] Existing technologies, such as Chinese patent CN103570532A, use titanium-silicon molecular sieves as catalysts, hydrogen peroxide as oxidants, and alcohols or aromatic hydrocarbons as solvents, achieving a pyruvate yield of 79% at 70°C. Patent CN107930687B employs a modification process involving initial steam treatment, secondary crystallization, secondary steam treatment, and washing liquid treatment. The modified molecular sieve can efficiently catalyze the preparation of pyruvate from lactate under solvent-free conditions, achieving a pyruvate yield of over 95%. While fixed-bed processes (such as CN110054564A) achieve continuous lactate synthesis, they have high requirements for catalyst particle shape, strength, and raw material purity. Long-term operation is prone to catalyst pulverization or impurity accumulation, leading to bed blockage and increased pressure drop. Furthermore, they do not involve the hydrolysis of lactate to produce pyruvate. In all existing technologies, continuous synthesis of pyruvate has not been achieved, and raw material utilization is low.

[0005] Challenges of traditional processes for the hydrolysis of ethyl pyruvate include: Chemical equilibrium limitations: Hydrolysis is a reversible reaction. In traditional processes where the reaction proceeds first and then the separation occurs, the conversion rate of the reactants is limited by equilibrium and cannot reach a high level. Product inhibition: The generated alcohol and pyruvate inhibit catalyst activity and promote the reverse reaction (esterification). High separation energy consumption: The post-reaction mixture contains water, alcohol, pyruvate, and unreacted pyruvate esters, requiring multiple distillation columns and high energy consumption for separation.

[0006] Traditional reaction-separation processes are limited by chemical equilibrium in terms of reactant conversion rates, making it difficult to achieve high levels. The generated alcohols and pyruvic acids inhibit catalyst activity and promote reverse reactions (esterification), resulting in product inhibition. The post-reaction mixture contains multiple components, requiring separation through multi-tower distillation, leading to high overall energy consumption. Summary of the Invention

[0007] To overcome the problems in the prior art, the present invention aims to provide a method for the continuous synthesis of pyruvate by catalytic oxidation of ethyl lactate and coupled reactive distillation. The method provided by the present invention can improve the hydrolysis rate while removing the generated alcohol from the system, effectively reducing the occurrence of reverse reactions, and producing a product with high purity.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for the continuous synthesis of pyruvate by catalytic oxidation of ethyl lactate and coupled reactive distillation, comprising the following steps: ① The catalyst is loaded into the reactor, and ethyl lactate, hydrogen peroxide and pyridine-2-carboxylic acid are mixed evenly. After the tubular reactor is heated, the raw material liquid is continuously pumped into the reactor. After the reaction, the ethyl pyruvate solution is collected. ② The ethyl pyruvate solution is continuously fed into the reactive distillation column. After the column bottom temperature is raised, the reflux ratio is adjusted to maintain the top temperature of the column. The aqueous solution of pyruvate is continuously collected according to the liquid level in the column bottom.

[0009] Preferably, in step ①, the catalyst is TS-1; the molar ratio of ethyl lactate, hydrogen peroxide and pyridine-2-carboxylic acid is 1:1.02~1.04:0.01~0.03; the feed rate of the raw material liquid is 10~50 ml / min; most preferably, the feed rate is 20~40 ml / min.

[0010] Preferably, in step ①, the reactor is a tubular reactor; the tubular reactor is a three-stage tubular reactor module, each stage having a length of 1m and an inner diameter of 15~30mm; the three-stage tubular reactor module has three-stage temperature control, with the first stage temperature control at 50~60℃, the second stage at 60~70℃, and the third stage at 70~80℃; the back pressure maintains a certain pressure in the system, with a pressure range of 0.05~0.2MPa.

[0011] Preferably, in step ①, the continuous tubular reactor has three-stage temperature control: the first-stage temperature control is 55~60℃, the second-stage temperature control is 65~70℃, and the third-stage temperature control is 75~80℃; the inner diameter of the tubular reactor is 20mm.

[0012] Preferably, in step ②, the reactive distillation column is filled with acidic ion exchange resin; the acidic ion exchange resin is a styrene-based resin with sulfonic acid groups, and the filling method is bag-type structured packing. The catalyst filling concentration gradually decreases from top to bottom, with concentrations of 100%, 50%, 25%, and 10%, respectively.

[0013] Preferably, in step ②, the rectifying section of the reactive distillation column is 0.5~1m, the reaction section is 1~1.5m, and the column diameter is 20~40mm.

[0014] Preferably, in step ②, the reaction-distillation process is carried out under reduced pressure to remove alcohol byproducts, with a vacuum degree of 300 mbar to 500 mbar; most preferably, the vacuum degree is 300 mbar to 400 mbar; the reboiler is heated to 80 to 100°C.

[0015] Preferably, in step ②, the feed rate of the ethyl pyruvate solution is 10~50 ml / min; most preferably, the feed rate is 20~40 ml / min.

[0016] Preferably, in step ②, the reflux ratio at the top of the column is 10:2 to 10:5; most preferably, the reflux ratio at the top of the column is 10:2 to 10:3.

[0017] In some embodiments, the reactive distillation column is filled with a styrene-based resin having sulfonic acid groups, including but not limited to type 732 resin.

[0018] Ethyl lactate is oxidized with hydrogen peroxide to obtain an aqueous solution of pyruvate ester. However, pyruvate ester is easily hydrolyzed. After 1 hour, methyl pyruvate hydrolyzes by more than 30%. The hydrolyzed pyruvate is prone to side reactions with unreacted hydrogen peroxide. Therefore, the selection of the reaction model is crucial. Thus, a tubular reactor model with plug flow effect is preferred. At the same time, the molar ratio of hydrogen peroxide feed is reduced to reduce the side reactions of hydrogen peroxide.

[0019] In the synthesis method provided by this invention, hydrogen peroxide is added as a catalyst. Under a continuous oxidation model of ethyl lactate and hydrogen peroxide, 2-pyridine-carboxylic acid is added as a catalyst. Its functions are: ① Formation of stable Ti complexes: These molecules possess both nitrogen atoms and carboxylate oxygen atoms capable of coordinating with Ti, forming chelate coordination with the Ti center, resulting in a very stable structure. This structure can extremely effectively inhibit the ineffective decomposition of Ti-peroxide species; ② Precise electronic and spatial regulation: They provide a highly ordered pocket for H2O2 activation, ensuring that the generated reactive oxygen species have moderate electrophilicity through precise electronic effects and spatial constraints, attacking only the α-hydroxyl groups with higher electron cloud density in the lactate ester, without attacking the carbonyl group of the already formed pyruvate ester or initiating decarboxylation; ③ Buffering effect: The carboxylate group can provide moderate buffering capacity, maintaining the optimal pH microenvironment of the reaction system and preventing side reactions caused by local over-acidity or over-alkaliness. The yield of pyruvate ester can reach over 99% (based on ethyl lactate ester) during the oxidation process.

[0020] The synthesis method provided by this invention uses reactive distillation to hydrolyze ethyl pyruvate. Without a suitable acid catalyst, the hydrolysis rate of ethyl pyruvate using the same packed column is only 50%. However, by auxiliary packing with an ion exchange resin packing layer, the hydrolysis rate of the ester is increased, and the generated ethanol and product are separated, with ethanol collected at the top of the column and pyruvate collected at the bottom. This achieves continuous hydrolysis while increasing the hydrolysis rate of ethyl pyruvate to over 99%.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for continuous synthesis of pyruvate by catalytic oxidation of ethyl lactate and coupled reactive distillation provided by the present invention uses ethyl lactate and hydrogen peroxide as the main raw materials, and obtains ethyl pyruvate under the conditions of titanium silicate molecular sieve catalyst and pyridine-2-carboxylic acid auxiliary. It is a method suitable for industrial continuous synthesis of pyruvate.

[0022] (2) This invention improves the utilization rate of hydrogen peroxide and achieves high product selectivity by adding pyridine-2-carboxylic acid as a co-catalyst through the synergistic system of H2O2 and TS-1. The yield of pyruvate reaches over 99%, and the utilization rate of hydrogen peroxide is over 97%. (3) The synthesis method provided by the present invention has a three-stage tubular reactor module with multi-stage temperature control in the oxidation stage to realize the continuous oxidation of ethyl lactate; in the reactive distillation column, acidic ion exchange resin (styrene resin with sulfonic acid group) is used to fill the reaction section, with strong acid at the front end to rapidly convert most of the reactants; weak acid at the rear end to gently complete the final conversion and suppress side reactions, which significantly improves the overall selectivity, and the hydrolysis rate of ethyl pyruvate reaches more than 99%, while realizing the continuous hydrolysis of ethyl pyruvate. Attached Figure Description

[0023] Figure 1 This is a simplified flowchart of the continuous synthesis of pyruvate according to the present invention; Figure 2 Schematic diagram of the tubular reactor used in the continuous synthesis of pyruvate in this invention; Figure 3 This is a structural diagram of the reactive distillation column used in the continuous synthesis of pyruvate in this invention. Detailed Implementation

[0024] To better understand the technical solution of the present invention, the following detailed embodiments are provided to further illustrate the above-mentioned content of the present invention. However, this should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0025] A simplified flowchart of the continuous synthesis of pyruvate in this invention is shown below. Figure 1 As shown.

[0026] Example 1 The raw materials are ethyl lactate, hydrogen peroxide, and pyridine-2-carboxylic acid (molar ratio 1:1.02:0.02). The reactor is a multi-stage tubular reactor (e.g., Figure 2 The reactor (as shown) has an inner diameter of 20 mm and is filled with TS-1 catalyst in three sections, each 1 m long. The jacket temperatures are 60℃, 70℃, and 80℃, respectively. Since the process is continuous in three stages, the residence time corresponding to the liquid holdup within each temperature range is sufficient. Feeding is performed according to the feed flow rate. The back pressure is maintained within a range of 0.15 MPa. The feed liquid is fed into the tubular reactor at a flow rate of 30 ml / min, and the discharged reaction liquid enters the synthesis liquid storage tank. After stabilizing for 1 hour, the discharged reaction liquid weighs 1791 g. Liquid phase analysis shows that the ethyl pyruvate content is 46.65% and the ethyl lactate content is 0.3%, calculating the ethyl lactate conversion rate to be 99.37% and the ethyl pyruvate yield to be 99.10%.

[0027] Reaction-distillation column (e.g.) Figure 3 The reaction section (as shown) is filled with a gradient of 732 type sulfonated styrene resin, diluted with glass springs at proportions of 100%, 50%, 25%, and 10%. The hydrolysate feed rate is 30 ml / min, the top temperature is 60℃, the bottom temperature is 90℃, the vacuum is 400 mbar, and the reflux ratio is 10:3. Ethanol-water solution is collected from the top, and pyruvate-water solution is collected from the bottom. After stabilizing for 1 hour, the bottom product is 1330 g of reaction solution. Liquid phase analysis shows that the pyruvate content in the bottom is 47.6%, and the ethyl pyruvate content is 0.05%. The top fraction is 470 g, and the ethyl pyruvate content is 0.1%. The calculated ethyl pyruvate conversion rate is 99.86%, and the pyruvate yield is 99.49%.

[0028] The conversion rate of ethyl lactate was 99.37%, and the yield of pyruvate was 98.59% (based on ethyl lactate).

[0029] Comparative Example 1 The raw materials were ethyl lactate and hydrogen peroxide (molar ratio 1:1.02). The reactor was a multi-section tubular reactor with an inner diameter of 20 mm, and three sections were filled with TS-1 catalyst, each section being 1 m long. The jacket temperatures were 60℃, 70℃, and 80℃, respectively. The raw material solution was fed into the tubular reactor at a feed rate of 30 ml / min, and the discharged reaction solution was sent to a synthesis liquid storage tank. After stabilizing for 1 hour, the discharged reaction solution weighed 1782 g. Liquid phase analysis showed that the ethyl pyruvate content was 42.6% and the ethyl lactate content was 1.53%. The calculated conversion rate of ethyl lactate was 96.85%, and the yield of ethyl pyruvate was 89.14%.

[0030] The reaction section of the reaction-distillation column was filled with a gradient of 732 type sulfonated styrene resin, diluted with glass springs at proportions of 100%, 50%, 25%, and 10%. The hydrolysate feed rate was 30 ml / min, the top temperature was 60℃, the bottom temperature was 90℃, the vacuum was 400 mbar, and the reflux ratio was 10:3. Ethanol-water solution was collected from the top, and pyruvate-water solution was collected from the bottom. After stabilizing for 1 hour, the bottom product was 1260 g of reaction solution. Liquid phase analysis showed that the pyruvate content in the bottom was 47.6%, and the ethyl pyruvate content was 0.06%. The top fraction was 540 g, with an ethyl pyruvate content of 0.15%. The calculated ethyl pyruvate conversion rate was 99.80%, and the pyruvate yield was 99.31%.

[0031] The conversion rate of ethyl lactate was 96.85%, and the yield of pyruvate was 88.53% (based on ethyl lactate).

[0032] Comparative Example 2 The raw materials were ethyl lactate, hydrogen peroxide, and pyridine (molar ratio 1:1.02:0.02). The reactor was a multi-section tubular reactor with an inner diameter of 20 mm, loaded with TS-1 catalyst in three sections, each 1 m long, with jacket temperatures of 60℃, 70℃, and 80℃ respectively. The feed solution was fed into the tubular reactor at a flow rate of 30 ml / min, and the discharged reaction solution was sent to a synthesis liquid storage tank. After stabilizing for 1 hour, the discharged reaction solution weighed 1785.6 g. Liquid chromatography analysis showed that the ethyl pyruvate content was 39.6% and the ethyl lactate content was 1.25%, calculating the ethyl lactate conversion rate to be 97.41% and the ethyl pyruvate yield to be 83.57%.

[0033] The reaction section of the reaction-distillation column was filled with a gradient of 732 type sulfonated styrene resin, diluted with glass springs at proportions of 100%, 50%, 25%, and 10%. The hydrolysate feed rate was 30 ml / min, the top temperature was 60℃, the bottom temperature was 90℃, the vacuum was 400 mbar, and the reflux ratio was 10:3. An ethanol-water solution was collected from the top, and a pyruvate-water solution was collected from the bottom. After stabilizing for 1 hour, the bottom product was 1280 g of reaction solution. Liquid phase analysis showed that the pyruvate content in the bottom was 47.6%, and the ethyl pyruvate content was 0.05%. The top fraction was 520 g, with an ethyl pyruvate content of 0.12%. The calculated ethyl pyruvate conversion rate was 99.82%, and the pyruvate yield was 99.05%.

[0034] The conversion rate of ethyl lactate was 97.41%, and the yield of pyruvate was 82.77% (based on ethyl lactate).

[0035] Comparative Example 3 The raw materials were prepared as ethyl lactate, hydrogen peroxide, and pyridine-2-carboxylic acid (molar ratio 1:1.02:0.02). The reactor was a multi-section tubular reactor with an inner diameter of 20 mm, and three sections were filled with TS-1 catalyst, each section being 1 m long. The jacket temperatures were 60℃, 70℃, and 80℃, respectively. The raw material solution was fed into the tubular reactor at a feed rate of 30 ml / min, and the discharged reaction solution was sent to a synthesis liquid storage tank. After stabilizing for 1 hour, the discharged reaction solution weighed 1791 g. Liquid chromatography analysis showed that the ethyl pyruvate content was 46.65% and the ethyl lactate content was 0.3%, calculating the ethyl lactate conversion rate to be 99.37% and the ethyl pyruvate yield to be 99.10%.

[0036] The reaction-distillation column was filled with glass springs. The hydrolysate feed rate was 30 ml / min, the top temperature was 60℃, the bottom temperature was 90℃, the vacuum was 400 mbar, and the reflux ratio was 10:3. Ethanol-water solution was collected from the top, and pyruvate-water solution was collected from the bottom. After stabilizing for 1 hour, the bottom product was 1450 g of reaction solution. Liquid phase analysis showed that the pyruvate content in the bottom product was 23.65%, and the ethyl pyruvate content was 26.5%. The top fraction was 350 g, with an ethyl pyruvate content of 0.18%. The calculated ethyl pyruvate conversion rate was 54.16%, and the pyruvate yield was 53.89%.

[0037] The conversion rate of ethyl lactate was 99.37%, and the yield of pyruvate was 53.40% (based on ethyl lactate).

[0038] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for the continuous synthesis of pyruvate by catalytic oxidation of ethyl lactate and coupled reactive distillation, characterized in that: Includes the following steps: ① The catalyst is loaded into the reactor, and ethyl lactate, hydrogen peroxide and pyridine-2-carboxylic acid are mixed evenly. After the tubular reactor is heated, the raw material liquid is continuously pumped into the reactor. After the reaction, the ethyl pyruvate solution is collected. ② The ethyl pyruvate solution is continuously fed into the reactive distillation column. After the bottom of the column is heated, the reflux ratio is adjusted to maintain the top temperature of the column. The aqueous solution of pyruvate is continuously collected according to the bottom liquid level.

2. The method according to claim 1, characterized in that, In step ①, the catalyst is TS-1; the molar ratio of ethyl lactate, hydrogen peroxide and pyridine-2-carboxylic acid is 1:1.02~1.04:0.01~0.03; and the feed rate of the raw material liquid is 10~50 ml / min.

3. The method according to claim 1 or 2, characterized in that, In step ①, the reactor is a tubular reactor; the tubular reactor is a three-stage tubular reactor module, each stage of which is 1m long and has an inner diameter of 15~30mm; the three-stage tubular reactor module has three-stage temperature control, with the first stage temperature control at 50~60℃, the second stage at 60~70℃, and the third stage at 70~80℃; the back pressure maintains a certain pressure in the system, with a pressure range of 0.05~0.2MPa.

4. The method according to claim 1, characterized in that, In step ②, the reactive distillation column is filled with acidic ion exchange resin; the acidic ion exchange resin is a styrene-based resin with sulfonic acid groups, and the filling method is bag-type structured packing. The catalyst filling concentration gradually decreases from top to bottom, with concentrations of 100%, 50%, 25%, and 10%, respectively.

5. The method according to claim 1 or 4, characterized in that, The rectifying section of the reactive distillation column is 0.5~1m, the reaction section is 1~1.5m, and the column diameter is 20~40mm.

6. The method according to claim 1, 4, or 5, characterized in that, In step ②, the reaction-distillation process is carried out under reduced pressure to remove alcohol byproducts, with a vacuum degree of 300 mbar to 500 mbar; the reboiler is heated to 80 to 100 °C.

7. The method according to any one of claims 1, 4-6, characterized in that, In step ②, the feed rate of ethyl pyruvate solution is 10~50 ml / min.

8. The method according to any one of claims 1, 4-7, characterized in that, In step ②, the reflux ratio at the top of the tower is 10:2 to 10:5.

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