A process for the preparation of glycolic acid from electrolytic oxalic acid

Abstract

This invention relates to the field of electrochemical synthesis technology, specifically a method for producing glycolic acid by electrolysis of oxalic acid; aiming to solve the problems of high reaction temperature and high toxicity of raw materials in existing glycolic acid synthesis processes. This invention, under ambient temperature and pressure, utilizes various nano-carbon materials loaded with metal oxides as cathode materials, and water as solvent and hydrogen source, to complete the process of hydrogenating oxalic acid to glycolic acid in a membrane-containing electrolytic cell. Compared with existing glycolic acid production methods, this invention has the advantages of inexpensive and non-toxic raw materials, mild reaction conditions, low equipment cost, and no need to use H2, making it a highly promising green synthesis method for glycolic acid.

Description

Technical Field

[0001] This invention relates to the field of electrochemical synthesis technology, specifically a method for producing glycolic acid by electrolysis of oxalic acid. Background Technology

[0002] Glycolic acid is a crucial organic intermediate and fine chemical, widely used in electroplating, chemical cleaning, cosmetics, and biodegradable polymers. However, existing processes suffer from high product impurities, highly toxic raw materials, high equipment costs, and demanding production conditions, resulting in high production costs and market prices for glycolic acid. Developing new processes to produce glycolic acid under mild conditions using inexpensive, non-toxic reagents will have significant economic and environmental benefits, and is crucial for sustainable development.

[0003] Organic electrosynthesis is an emerging and powerful green synthetic method. The synthesis of glycolic acid via the electrolysis of oxalic acid is a highly promising production route. This reaction process has the advantages of inexpensive and non-toxic raw materials, mild reaction conditions, and simple production equipment.

[0004] Since the reaction takes place in a strongly acidic solution, the working electrode faces the problems of acid corrosion and a strong hydrogen evolution reaction. Previous studies have shown that some metal oxides possess the advantages of being resistant to acid corrosion and having relatively weak hydrogen evolution activity; at the same time, the positively charged center structure formed by oxygen vacancies on metal oxides is highly conducive to the adsorption of carboxyl groups.

[0005] Supported catalysts are prepared by loading catalysts onto a support. Due to the supporting and dispersing effect of the support, the catalyst's stability can be significantly improved, while its catalytic activity can be further enhanced. Nanomaterials are highly suitable as support materials for electrocatalysts due to their advantages such as good specific conductivity, large specific surface area, low cost, non-toxicity, and good stability.

[0006] Therefore, this invention utilizes a series of different metal oxides / nanocarbon materials as cathode electrocatalysts to realize the reaction process for preparing glycolic acid by electrolysis of oxalic acid. This invention has the advantages of non-toxic and inexpensive raw materials, mild reaction conditions, and simple equipment, representing a green synthetic route for glycolic acid with great potential. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing glycolic acid synthesis technologies by providing a route for producing glycolic acid through the electrolysis of oxalic acid. A series of metal oxide / nanocarbon materials were prepared as electrode materials for the reaction using a simple ultrasonic impregnation method. The reaction process has the advantages of being mild and environmentally friendly.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] The first aspect of this invention discloses a method for preparing glycolic acid by electrocatalytic hydrogenation of oxalic acid, the specific steps of which are as follows:

[0010] (1) Glycolic acid is produced by electrolyzing an aqueous electrolyte containing oxalic acid on an electrode containing a catalyst in an electrolytic cell;

[0011] (2) The water in the electrolyte is evaporated to concentrate the glycolic acid content, and glycolic acid crystals are precipitated by crystallization. The glycolic acid product is obtained by filtration, separation and vacuum drying.

[0012] Preferably, the oxalic acid concentration in the aqueous electrolyte containing oxalic acid in step (1) is 0.05–5 mol / L.

[0013] Preferably, when the concentration of oxalic acid in the electrolyte of step (1) is low, 0.1 to 5 mol / L sulfuric acid or perchloric acid is added as an additive.

[0014] Preferably, the reaction temperature in step (1) is 20–80°C.

[0015] Preferably, in step (1), the electrolytic current density in the electrolytic cell is between 5 and 500 mA / cm². 2 The total electrolysis charge is 2-8 F per mole of oxalic acid, where F is the Faraday constant.

[0016] Preferably, the catalyst in step (1) is a nano-carbon material supported on a metal oxide, and the catalyst loading is between 0.5 and 10 mg / cm³. 2 .

[0017] The catalyst mentioned above is specifically a nano-carbon material supported on a metal oxide. The metal oxide in the material is one or more of lead, tin, tantalum, zirconium, niobium, vanadium, chromium, titanium, and hafnium oxides. The nano-carbon material used as the support is one of activated carbon, carbon black, carbon nanotubes, graphene, porous carbon nanospheres, mesoporous carbon, or carbon nanofibers.

[0018] The second aspect of this invention discloses a method for preparing the above-mentioned nano-carbon material supported on metal oxides, comprising the following steps:

[0019] S1: Ammonium persulfate was used to oxidize the nano-carbon support to obtain nano-carbon materials with oxygen-containing functional groups on the surface; ethanol was used as a solvent to dissolve the precursor of the metal oxide to prepare a metal salt solution for later use.

[0020] S2: Mix 1g of nano-carbon material obtained in S1 with 1-20ml of metal salt solution; then, subject the mixture to ultrasonic vibration, vacuum baking and calcination at 400-500℃ for 2-5h under argon protection to obtain nano-carbon material loaded with metal oxide.

[0021] Compared with existing technologies, this invention has the advantages of high glycolic acid yield, low energy consumption, low environmental impact and mild reaction conditions, and is a highly promising glycolic acid production route. Detailed Implementation

[0022] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0023] Example 1

[0024] a. Add 2g of activated carbon to 100ml of 1mol / L ammonium persulfate solution and react at 60℃ for 3h. After the reaction is complete, collect the solid to obtain a material whose surface is functionalized with oxygen-containing groups. Weigh 23.33g of titanium tetrachloride, dissolve it in ethanol, and then make up the volume of the solution to 100ml for later use.

[0025] b. Mix 1g of the material obtained in step (a) with 5ml of the solution. Then, subject the mixture to ultrasonic vibration for 2h, vacuum baking at 60℃ for 24h, and calcination at 500℃ under an inert atmosphere for 3h to obtain titanium dioxide / activated carbon material.

[0026] c. Sonicately mix 100 mg of titanium dioxide / activated carbon material and 2.5 ml of 0.5% Nafion ethanol solution, and then apply 250 μL of the mixture to a 1 cm thick surface. 2 Electrodes are fabricated on carbon paper.

[0027] d. Add 20 mL of 0.125 mol / L sulfuric acid solution to the anode region of the electrolytic cell, and add 20 mL of a solution containing 0.125 mol / L sulfuric acid and 0.3 mol / L oxalic acid to the cathode region; then, at room temperature and pressure, apply an electrolytic charge at 45 mA / cm². 2 A constant current electrolysis was performed at a current density of 8 F (where F is the Faraday constant) per mole of oxalic acid. After the reaction, the composition of the electrolyte was analyzed by high performance liquid chromatography, and the yield of glycolic acid was calculated to be 92%.

[0028] Example 2

[0029] a. Add 2g of carbon black to 100ml of 1mol / L ammonium persulfate solution and react at 60℃ for 3h. After the reaction is complete, collect the solid to obtain a material with oxygen-containing functionalized surface. Weigh 33.92g of zirconium nitrate, dissolve it in ethanol, and then make up the volume to 100ml for later use.

[0030] b. Mix 1g of material obtained in step (a) with 5ml of solution. Then, subject the mixture to ultrasonic vibration for 2h, vacuum baking at 60℃ for 24h, and calcination at 500℃ under Ar protection for 3h in sequence to obtain zirconium dioxide / carbon black material.

[0031] c. Sonicately mix 100 mg of zirconium dioxide / carbon black material with 2.5 ml of 0.5% Nafion ethanol solution, and then apply 250 μL of the mixture to a 1 cm thick surface. 2 Electrodes are fabricated on carbon paper.

[0032] d. Add 20 mL of 0.125 mol / L sulfuric acid solution to the anode region of the electrolytic cell, and add 20 mL of a solution containing 0.125 mol / L sulfuric acid and 0.75 mol / L oxalic acid to the cathode region; bubble the cathode electrolyte with argon gas for 15 min; then, at room temperature and pressure, at 60 mA / cm². 2 A constant current electrolysis was performed at a current density of 8 F (where F is the Faraday constant) per mole of oxalic acid. After the reaction, the composition of the electrolyte was analyzed by high performance liquid chromatography, and the yield of glycolic acid was calculated to be 84%.

[0033] Comparative Example 1

[0034] Sun et al. Using formaldehyde and carbon monoxide as raw materials, and acidic polyoxometalate compounds (Cs) x H 3-x PW 12 O 40 Using a catalyst, the reaction was carried out at a temperature of 50–400 °C and a pressure of 0.1–100 MPa, yielding glycolic acid in a 73% yield.

[0035] (Y. Sun, H. Wang, Z. Liu, et al. Production methods of glycolic acid [P]. CN 102099323A, 2011.)

[0036] Comparative Example 2

[0037] Chen et al. used ethylene glycol and oxygen as raw materials, and V2O5 and Al2O3 as catalysts, to react at a temperature of 120-155℃ and a pressure of 0.20-0.50 MPa, and obtained glycolic acid with a yield of 94%.

[0038] (Chen Jianhua, Shu Jiansheng, Lin Zhenyi, et al. A method for preparing glycolic acid from ethylene glycol [P]. CN 102153460A, 2011.)

[0039] Comparative Example 3

[0040] Tai et al. used chloroacetic acid and sodium hydroxide as raw materials to hydrolyze the reaction at 105℃ to obtain glycolic acid with a yield of 93%.

[0041] (Tai Yanfang, Wu Jingmei, Dong Xiongzi. Improved synthesis conditions for the hydrolysis of chloroacetic acid to glycolic acid [J]. Journal of Yunnan University for Nationalities, 2012, 21(6): 412-414.)

[0042] Comparative Example 4

[0043] Yu et al. used methyl glycolate as raw material and keggin-type phosphotungstic acid as catalyst to hydrolyze the product at 80°C, obtaining glycolic acid with a yield of 56%.

[0044] (Yu Kesheng, Geng Guangjuan, Yang Xiaozhi, et al. Preparation of glycolic acid by hydrolysis of methyl glycolate [J]. Chemical Technology and Development, 2019, 48, 1, 27-29.)

[0045] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A process for the electrocatalytic hydrogenation of oxalic acid to glycolic acid, characterized in that, The specific steps are as follows: (1) glycolic acid is prepared by electrolysis of an aqueous electrolyte containing oxalic acid on an electrode containing a catalyst in an electrolytic cell; (2) water in the electrolyte is evaporated to concentrate the content of glycolic acid, and a crystallization method is used to precipitate glycolic acid crystals, and the glycolic acid product is obtained by filtration separation and vacuum drying; The catalyst of step (1) is a nano-carbon material loaded with metal oxides, and the catalyst loading is 0.5-10 mg / cm 2 ; The metal oxide in the material is selected from titanium dioxide or zirconium dioxide; The nano-carbon material as the carrier is one of activated carbon, carbon black, carbon nanotube, graphene, porous nano-carbon sphere, mesoporous carbon, and carbon nanofiber; The preparation method of the nano-carbon material loaded with metal oxide comprises the following steps: S1: using ammonium persulfate to oxidize the nano-carbon carrier to obtain a nano-carbon material with a surface functionalized with oxygen-containing groups; using ethanol as a solvent, a metal oxide precursor is dissolved therein to prepare a metal salt solution for standby; S2: 1 g of the nano-carbon material prepared in S1 and 1-20 ml of the metal salt solution are mixed; then, the mixture is subjected to ultrasonic oscillation, vacuum baking, and baking at 400-500 ℃ under argon protection for 2-5 h in sequence to obtain a nano-carbon material loaded with metal oxide.

2. The method for preparing glycolic acid by electrocatalytic hydrogenation of oxalic acid according to claim 1, characterized in that, The concentration of oxalic acid in the aqueous electrolyte containing oxalic acid in step (1) is 0.05-5 mol / L.

3. The process for the electrocatalytic hydrogenation of oxalic acid to glycolic acid according to claim 2, characterized in that, 0.1-5 mol / L of sulfuric acid or perchloric acid is added to the electrolyte of step (1) as an additive.

4. The method for preparing glycolic acid by electrocatalytic hydrogenation of oxalic acid according to claim 1, characterized in that, The reaction temperature in step (1) is 20-80 ℃.

5. The method for preparing glycolic acid by electrocatalytic hydrogenation of oxalic acid according to claim 1, characterized in that, Step (1) The electrolytic current density of the electrolytic cell is 5-500 mA / cm 2 , and the total electrolytic electric quantity is 2-8 F per mole of oxalic acid, F being the Faraday constant.