Electrochemical method for pairwise synthesizing syringic acid and adiponitrile

Abstract

The invention provides an electrochemical method for pairwise synthesizing syringic acid and adiponitrile. The method comprises the following steps: 1) mixing syringaldehyde, an alkaline electrolyte, an alcohol solvent, an alkyl glycoside surfactant and water, and adding the mixture into an anode chamber of an electrolytic cell; (2) acrylonitrile, phosphate, borate, a quaternary ammonium base surfactant and water are mixed and added into a cathode chamber of the electrolytic cell; and 3) heating the electrolyte in the cathode chamber and the anode chamber of the electrolytic cell, then carrying out an electrolytic reaction, carrying out electrochemical oxidation on syringaldehyde at the anode to synthesize syringic acid, enabling hydrated hydrogen ions to enter the cathode chamber across a membrane, and synthesizing adiponitrile with acrylonitrile at the cathode. The syringic acid synthesis method is clean, environmentally friendly and low in cost, meanwhile, the problem of anode corrosion in the operation process of electrosynthesis of adiponitrile is solved, and the tail gas safety risk caused by oxygen evolution of an anode for synthesis of adiponitrile is eliminated. The method has the advantages of simple steps, high total product yield, low equipment investment, low operation risk, mild reaction conditions, less three wastes and low energy consumption, and is suitable for wide industrial application.

Description

Technical Field

[0001] This invention belongs to the field of organic electrochemical synthesis, specifically relating to an electrochemical synthesis process for the paired synthesis of syringic acid and adiponitrile. Background Technology

[0002] Eugenolic acid (4-hydroxy-3,5-dimethoxybenzoic acid) is a naturally occurring phenolic acid compound widely found in the plant kingdom. Eugenolic acid possesses strong antioxidant activity and has great potential applications in the pharmaceutical field. It has broad therapeutic applications in preventing oxidative stress-related diseases (such as cardiovascular diseases, neurodegenerative diseases, and cancer), and also exhibits antioxidant, anti-endotoxin, antibacterial, anti-inflammatory, and hepatoprotective and neuroprotective activities. In the industrial sector, eugenol derivatives, such as eugenol esters, possess tensile strength, water solubility, and anti-caries properties, and are used as components in dental adhesives. Eugenolic acid is also used as a natural and safe alternative to synthetic preservatives to extend the shelf life of food and prevent rancidity and microbial spoilage.

[0003] The main method for producing syringic acid is chemical synthesis. The main production process uses 3,4,5-trimethoxybenzoic acid, i.e. trimethyl gallate, as a raw material, and reacts it with dimethyl sulfate ((CH3O)2SO2) or iodomethane (CH3I) under alkaline conditions (such as K2CO3) to undergo a selective methylation reaction, thereby obtaining syringic acid.

[0004] CN104693022A discloses a process for synthesizing syringic acid from syringaldehyde as a raw material via anhydride esterification, hydrogen peroxide oxidation, and alkali / acid hydrolysis. This method can synthesize high-purity syringic acid, but it suffers from several drawbacks, such as demanding equipment requirements, numerous reaction steps, long reaction times leading to difficulties in subsequent separation and purification, high energy consumption, and severe environmental pollution.

[0005] CN118207263A proposes a method for preparing syringic acid through whole-cell biosynthesis, which improves the synthesis rate and yield of syringic acid by utilizing cellular metabolic pathways and enzyme systems. However, this method uses high-cost inducing agents, antibiotics, and cofactors, resulting in high production costs. Repeated centrifugation also leads to problems such as high energy consumption, large equipment investment, and long production cycles.

[0006] Current methods for synthesizing syringic acid have drawbacks such as numerous reaction steps, high energy consumption, heavy pollution, and high cost. Therefore, developing a clean, environmentally friendly, and low-cost method for synthesizing syringic acid is of great significance.

[0007] Adiponitrile (ADN), also known as 1,4-dicyanobutane, is an important organic chemical raw material. Currently, its most important use is in the production of hexamethylenediamine. Hexamethylenediamine reacts with adipic acid to produce nylon 66 salt, which is then used to produce nylon 66 fibers. Approximately 90% of the world's adiponitrile is used for the production of nylon 66 salt annually. In addition, hexamethylenediamine can also be photochemically reacted to produce HDI (1,6-diisocyanate), which is a major raw material for the production of high-grade environmentally friendly coatings—another important use of adiponitrile.

[0008] The main industrial processes for producing adiponitrile include adipic acid ammoniation dehydration, acrylonitrile electrolytic dimerization, and butadiene hydrocyanation. Among these, the adipic acid ammoniation dehydration process is complex, has high raw material costs, low product yield, and poor quality, and has been phased out abroad. While the butadiene hydrocyanation method has low raw material costs and advanced technology, hydrocyanic acid is highly toxic, posing significant potential risks. Furthermore, the reaction process is lengthy, and the technology has high barriers to entry, making its development in my country extremely difficult. Compared to the adipic acid and butadiene methods, the biggest advantage of the acrylonitrile electrolytic dimerization method is its simple reaction process and readily available, inexpensive raw materials. However, during the electrosynthesis of adiponitrile, oxygen is generated at the anode, and this oxygen strips the acrylonitrile into the explosion limit, posing a serious safety risk due to the exhaust gas. In addition, the anodes for acrylonitrile electrolysis are mainly made of carbon steel, which suffers from severe corrosion during operation, requiring frequent anode replacement within the electrolytic cell. A separate aqueous purification system is also needed to remove iron ions from the electrolyte. Developing a new electrochemical preparation method for adiponitrile that ensures safe and reliable exhaust gas, slows down electrode corrosion, reduces electrode replacement frequency, and lowers production costs is of great significance. Summary of the Invention

[0009] To address the aforementioned shortcomings in existing technologies, the present invention aims to provide an electrochemical synthesis method for the paired synthesis of syringic acid and adiponitrile. This method offers advantages such as high conversion rate and selectivity, wide availability of raw materials, simple steps, high atom economy, low electrode corrosion rate, low energy consumption, and low cost.

[0010] The electrochemical method described in this invention uses a proton exchange membrane to separate the cathode and anode chambers. Syringaldehyde is electrolyzed in the anode chamber to synthesize syringic acid, and acrylonitrile is electrolyzed in the cathode chamber to synthesize adiponitrile. This method, which uses syringaldehyde to synthesize syringic acid in a one-step process, overcomes the shortcomings of traditional methods, such as multiple reaction steps, high energy consumption, heavy pollution, and high cost. It also avoids the problems of anode corrosion and tail gas safety issues caused by oxygen evolution at the anode during adiponitrile synthesis.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] This invention provides an electrochemical method for the paired synthesis of syringic acid and adiponitrile, comprising the following steps:

[0013] 1) Mix eugenol, alkaline electrolyte, alcohol solvent, alkyl glycoside surfactant and water, and add to the anode chamber of the electrolytic cell;

[0014] 2) Mix acrylonitrile, phosphate, borate, quaternary ammonium surfactant and water, and add to the cathode chamber of the electrolytic cell;

[0015] 3) After heating the electrolyte in the anode and cathode chambers of the electrolytic cell, an electrolytic reaction is carried out. Syringaldehyde is electrochemically oxidized at the anode to synthesize syringic acid, and hydrated hydrogen ions cross the membrane into the cathode chamber, where they react with acrylonitrile to synthesize adiponitrile at the cathode.

[0016] In step 1), the mass ratio of eugenol, alkaline electrolyte, alcohol solvent, alkyl glycoside surfactant, and water is 1:2-6:5-15:0.1-0.5:5-15, preferably 1:3-5:8-10:0.2-0.4:10-15.

[0017] In step 1), the alkaline electrolyte is selected from any one or a combination of at least two of potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate, preferably potassium hydroxide and sodium hydroxide;

[0018] In step 1), the alcohol solvent is any one or a combination of at least two of methanol, ethanol, and propanol, preferably methanol and ethanol;

[0019] In step 1), the alkyl glycoside surfactant is selected from any one or a combination of at least two of octyl glucoside, decyl maltose, and lauryl glucoside, preferably decyl maltose and lauryl glucoside.

[0020] In step 2), the mass ratio of acrylonitrile, phosphate, borate, quaternary ammonium base surfactant and water is 1:3-10:0.5-2:0.1-0.5:40-80, preferably 1:5-8:1-1.5:0.2-0.4:30-50.

[0021] In step 2), the phosphate is selected from any one or a combination of at least two of dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, and sodium dihydrogen phosphate, preferably dipotassium hydrogen phosphate and disodium hydrogen phosphate.

[0022] In step 2), the borate is selected from any one or a combination of at least two of potassium tetraborate, sodium pentaborate, sodium tetraborate, and potassium pentaborate, preferably sodium pentaborate and potassium pentaborate;

[0023] In step 2), the quaternary ammonium base surfactant is selected from any one or a combination of at least two of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, preferably tetrapropylammonium hydroxide and tetrabutylammonium hydroxide;

[0024] In step 3), the electrolysis reaction is carried out at an electrolysis temperature of 30-60℃, such as 30℃, 40℃, 50℃, or 60℃, preferably 40-50℃; and the electrolysis time is 10-40h, such as 10h, 15h, 20h, 30h, or 40h, preferably 20-30h.

[0025] In step 3), the electrolytic reaction is carried out with an electrolytic cell voltage range of 4-9V, such as 5V, 6V, 7V, 8V, or 9V, preferably 5-6V; and an electrolytic current density of 500-2000 A / m. 2 For example, 500A / m 2 1000A / m 2 1500A / m 2 2000A / m 2 500-1000A / m is preferred 2 .

[0026] In step 3), acrylonitrile can be optionally added to the cathode chamber. The acrylonitrile addition rate is related to the electrolysis current and is 1.5-2.0 g / (A*h), that is, for every 1A increase in electrolysis current, the addition rate increases by 1.5-2.0 g / h.

[0027] In step 3), after the electrolysis reaction is completed, the catholyte can be processed through phase separation, extraction, and distillation to obtain purified adiponitrile. The operations included in the post-processing are all conventional methods in the art and are not specifically required; any feasible method is acceptable. For example, the catholyte can first be separated into an oil phase, and the metal ions in the oil phase can be extracted with water. Then, the oil phase can be processed through a light phase removal tower and a heavy phase removal tower to obtain the adiponitrile product.

[0028] In step 3), after the electrolysis reaction is completed, the anolyte can undergo acidification, cooling crystallization, and water washing to obtain pure syringic acid. The post-processing steps are all conventional methods in the field and are not specifically required; any feasible method is acceptable. For example, the anolyte can be first adjusted to pH 3, cooled to 10°C to obtain crystals, and then the crystals can be washed with water until pH = 7 to obtain the syringic acid product.

[0029] In the preparation method of the present invention, the electrolysis is carried out in an electrolytic cell, which includes an anode, a cathode and a diaphragm.

[0030] The anode is selected from any one of Pt electrode, boron-doped diamond (BDD) electrode or Ti-based PbO2 electrode; the cathode is a lead electrode or a cadmium electrode; the diaphragm is one of Nafion N115, N117, NR211, and NR212.

[0031] The electrolytic cell is made of polypropylene (PP), polytetrafluoroethylene (PTFE), or titanium, preferably titanium.

[0032] This invention does not impose any restrictions on the shape and arrangement of electrodes in the electrolytic cell. All electrode shapes and cathode and anode arrangements that can achieve electrolysis are covered within the method of this invention.

[0033] This invention ensures the concentration of syringaldehyde in the anolyte region during electrolysis by introducing an appropriate amount of alkyl glycoside surfactant into the anolyte chamber, thereby accelerating the mass transfer of syringaldehyde in the anolyte region. Simultaneously, the alkyl glycoside surfactant does not decompose in the oxidizing environment of the anolyte region, effectively inhibiting the oxygen evolution reaction at the anolyte and improving the anolyte current efficiency. A diaphragm is used to separate the electrosynthesized syringic acid and adiponitrile, and an insoluble anode is used, eliminating the anolyte corrosion problem during the electrosynthetic adiponitrile process and also eliminating the tail gas safety risks associated with oxygen evolution at the adiponitrile anolyte synthesis anolyte.

[0034] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0035] The electrochemical method of this invention can synthesize syringic acid and adiponitrile in pairs, improving the system current efficiency. It has the advantages of simple steps, high overall product yield, low equipment investment, low operational risk, mild reaction conditions, less waste, and low energy consumption, and is suitable for a wide range of industrial applications. Detailed Implementation

[0036] The preparation method provided by the present invention will be further described in detail below through examples, but the present invention is not limited thereto.

[0037] The test methods used in the embodiments and comparative examples of this invention are as follows:

[0038] Main raw material sources

[0039] The reagents and raw materials used in the embodiments and comparative examples of this invention are sourced from the following sources. Unless otherwise specified, all other reagents and raw materials are commercially available products:

[0040] Syringaldehyde: Shanghai Aladdin Biochemical Technology Co., Ltd., purity 98%;

[0041] Octyl glucoside: Shanghai Aladdin Biochemical Technology Co., Ltd., purity 97%;

[0042] Decylmaltose: Shanghai Aladdin Biochemical Technology Co., Ltd., purity 97%;

[0043] Lauryl glucoside: Shanghai Aladdin Biochemical Technology Co., Ltd., 99% purity;

[0044] Tetramethylammonium hydroxide: Shanghai Aladdin Biochemical Technology Co., Ltd., 25% in methanol;

[0045] Tetraethylammonium hydroxide: Shanghai Aladdin Biochemical Technology Co., Ltd., 25% in methanol;

[0046] Tetrapropylammonium hydroxide: Shanghai Aladdin Biochemical Technology Co., Ltd., 25% in methanol;

[0047] Tetrabutylammonium hydroxide: Shanghai Aladdin Biochemical Technology Co., Ltd., 25% in methanol;

[0048] Potassium tetraborate: Beijing Innocare Technology Co., Ltd., AR, purity 99.5%;

[0049] Sodium pentaborate: Beijing Inokai Technology Co., Ltd., purity 99%;

[0050] Sodium tetraborate: Beijing Inokai Technology Co., Ltd., purity 99%;

[0051] Potassium pentaborate: Beijing Innocare Technology Co., Ltd., purity 97%;

[0052] Acrylonitrile: Beijing Innocare Technology Co., Ltd., purity 99%;

[0053] Dipotassium hydrogen phosphate: Beijing Innocare Technology Co., Ltd., purity 98%;

[0054] Disodium hydrogen phosphate: Beijing Innocare Technology Co., Ltd., purity 99%;

[0055] Potassium dihydrogen phosphate: Beijing Innocare Technology Co., Ltd., purity 99.5%;

[0056] Sodium dihydrogen phosphate: Beijing Inokai Technology Co., Ltd., purity 98%;

[0057] Diaphragm electrolyzer: Jiangsu Ankai Technology Co., Ltd.

[0058] Main testing methods

[0059] In the following examples, adiponitrile conversion and selectivity were determined using gas chromatography area-corrected normalization analysis. Instrument model: Shimadzu GC2010; Column: HP-INNOWAX quartz capillary column (30m×0.25mm×0.25μm); Column temperature: programmed temperature rise (initial temperature 40℃, held for 2 min, increased to 180℃ at 20℃ / min, then increased to 220℃ at 5℃ / min); Injector temperature: 310℃; FID temperature: 300℃; N2 flow rate: 1mL / min; H2 flow rate: 40mL / min; Septum purge (N2) flow rate: 3mL / min; Carrier gas (N2) flow rate: 1mL / min; Split injection, split ratio: 50; Injection volume: 0.1μL.

[0060] In the following examples, syringic acid was analyzed by liquid chromatography. The liquid chromatography used a reversed-phase C18 column (250 mm × 4.6 mm, 5 μm); the detection wavelength was 254 nm; the mobile phase was 60% methanol solution; the flow rate was 1.0 mL / min; the column temperature was 25 °C; and the injection volume was 20 μL.

[0061] In the following examples, adiponitrile and eugenol were characterized by proton NMR spectroscopy using a Brucker ARX-400 instrument.

[0062] Syringic acid selectivity = (Cyringic acid molar yield / Syringaldehyde molar consumption) * 100%

[0063] Adiponitrile selectivity = (Molar yield of adiponitrile * 2) / (Molar consumption of acrylonitrile * 100%)

[0064] Current efficiency = (Molar yield of adiponitrile + Molar yield of eugenol) * 2 * 96500 / (Electrolysis current * Electrolysis time) * 100%

[0065] Example 1

[0066] Syringic acid and adiponitrile were synthesized in pairs via electrolysis:

[0067] 1) Mix 10g eugenol, 60g potassium hydroxide, 50g propanol, 1g octyl glucoside, and 150g water, and add the mixture to the anode chamber of the diaphragm electrolyzer. The diaphragm of the electrolyzer is Nafion N115, the anode is a platinum electrode, and the cathode is a lead electrode.

[0068] 2) Take 3g of acrylonitrile, 30g of dipotassium hydrogen phosphate, 1.5g of potassium tetraborate, 1.5g of tetramethylammonium hydroxide and 240g of water, mix them and add them to the cathode chamber of the electrolytic cell.

[0069] 3) Heat the electrolytic cell to 50℃ to begin the electrolysis reaction. The current density of the electrolytic cell is 2000 A / m³. 2 The electrolysis potential was 9V. Acrylonitrile was added to the cathode chamber at a rate of 1.5g / (A*h). The electrolysis reaction was carried out at 50℃ for 10h, and samples were taken for testing. The catholyte was separated into an oil phase. Metal ions in the oil phase were extracted with water. Then, it was passed through a light phase removal tower at a bottom temperature of 150℃ to remove unreacted acrylonitrile and by-product propionitrile. It was then passed through a heavy phase removal tower at a bottom temperature of 210℃ to remove by-product hexanetrionitrile, thus obtaining adiponitrile product. The anolyte was acidified by adding inorganic acid to lower the pH of the system to below 4, causing syringic acid molecules to precipitate from the water in an electrically neutral form. After acidification, the system was kept at a low temperature (0-5℃) and slowly stirred for a period of time. The crystallized suspension was poured into a Buchner funnel, and a vacuum pump was turned on to filter the filter cake. The soluble impurities adsorbed in the filter cake were washed away with pre-cooled deionized water or distilled water. After the above process was completed, pure syringic acid was obtained.

[0070] The 1H NMR data of adiponitrile are as follows:

[0071] 1H NMR (600MHz, CDCl3): δ1.66 (m, 4H), 1.87 (t, 4H).

[0072] The 1H NMR data for syringic acid are as follows:

[0073] 1H NMR (600MHz, CDCl3): δ3.83 (s, 6H), 5.35 (s, 1H), 7.15 (s, 2H), 11.0 (s, 1H).

[0074] In this embodiment, the conversion rate of acrylonitrile was 81.4%, the selectivity of the synthesized adiponitrile was 90.4%, the conversion rate of syringaldehyde was 84.6%, the selectivity of the synthesized syringic acid was 97.1%, and the current efficiency was 149%.

[0075] Example 2

[0076] Syringic acid and adiponitrile were synthesized in pairs via electrolysis:

[0077] 1) Mix 10g eugenol, 30g sodium hydroxide, 80g ethanol, 4g decyl maltodextrin, and 100g water and add the mixture to the anode chamber of the diaphragm electrolyzer. The diaphragm of the electrolyzer is Nafion N117, the anode is a boron-doped diamond (BDD) electrode, and the cathode is a cadmium electrode.

[0078] 2) Take 3g of acrylonitrile, 9g of disodium hydrogen phosphate, 6g of sodium pentaborate, 0.3g of tetraethylammonium hydroxide and 120g of water, mix them and add them to the cathode chamber of the electrolytic cell.

[0079] 3) Heat the electrolytic cell to 60℃ to begin the electrolysis reaction. The current density of the electrolytic cell is 500 A / m³. 2 The electrolysis potential was 4V, and acrylonitrile was added to the cathode chamber at a rate of 2g / (A*h). The electrolysis reaction was completed after 40 hours, and samples were taken for testing. The catholyte was separated into an oil phase, and metal ions in the oil phase were extracted with water. Then, it was passed through a light phase removal tower at a bottom temperature of 150℃ to remove unreacted acrylonitrile and by-product propionitrile, and through a heavy phase removal tower at a bottom temperature of 210℃ to remove by-product hexanetrionitrile, thus obtaining adiponitrile product. The anolyte was acidified by adding inorganic acid to lower the pH of the system to below 4, causing syringic acid molecules to precipitate from the water in an electrically neutral form. After acidification, the system was kept at a low temperature (0-5℃) and slowly stirred for a period of time. The crystallized suspension was poured into a Buchner funnel, and a vacuum pump was turned on to filter the filter cake. The soluble impurities adsorbed in the filter cake were washed away with pre-cooled deionized water or distilled water. After the above process was completed, pure syringic acid was obtained.

[0080] In this embodiment, the conversion rate of acrylonitrile was 74.3%, the selectivity of the synthesized adiponitrile was 91.1%, the conversion rate of syringaldehyde was 85.7%, the selectivity of the synthesized syringic acid was 95.8%, and the current efficiency was 138%.

[0081] Example 3

[0082] Syringic acid and adiponitrile were synthesized in pairs via electrolysis:

[0083] 1) Mix 10g eugenol, 20g potassium carbonate, 150g methanol, 5g lauryl glucoside, and 50g water, and add the mixture to the anode chamber of the diaphragm electrolyzer. The diaphragm of the electrolyzer is Nafion N211, the anode is a Ti-based PbO2 electrode, and the cathode is a lead electrode.

[0084] 2) Take 3g acrylonitrile, 15g potassium dihydrogen phosphate, 3g sodium tetraborate, 0.6g tetrapropylammonium hydroxide and 90% water, mix them and add them to the cathode chamber of the electrolytic cell.

[0085] 3) Heat the electrolytic cell to 30℃ to begin the electrolysis reaction. The current density of the electrolytic cell is 1000 A / m. 2 The electrolysis potential was 6V. Acrylonitrile was added to the cathode chamber at a rate of 1.5g / (A*h). The electrolysis reaction was completed after 20 hours, and samples were taken for testing. The catholyte was separated into an oil phase. Metal ions in the oil phase were extracted with water. Then, it was passed through a light phase removal tower at a bottom temperature of 150℃ to remove unreacted acrylonitrile and by-product propionitrile. It was then passed through a heavy phase removal tower at a bottom temperature of 210℃ to remove by-product hexanetrionitrile, yielding adiponitrile product. The anolyte was acidified by adding inorganic acid to lower the pH of the system to below 4, causing syringic acid molecules to precipitate from the water in an electrically neutral form. After acidification, the system was kept at a low temperature (0-5℃) and slowly stirred for a period of time. The crystallized suspension was poured into a Buchner funnel, and a vacuum pump was turned on for filtration to obtain a filter cake. The soluble impurities adsorbed in the filter cake were washed away with pre-cooled deionized water or distilled water. After the above process was completed, pure syringic acid was obtained.

[0086] In this embodiment, the conversion rate of acrylonitrile was 77.5%, the selectivity of the synthesized adiponitrile was 89.1%, the conversion rate of syringaldehyde was 82.8%, the selectivity of the synthesized syringic acid was 96.4%, and the current efficiency was 145%.

[0087] Example 4

[0088] Syringic acid and adiponitrile were synthesized in pairs via electrolysis:

[0089] 1) Mix 10g eugenol, 50g sodium carbonate, 100g methanol, 2g octyl glucoside, and 150g water, and add the mixture to the anode chamber of the diaphragm electrolyzer. The diaphragm of the electrolyzer is Nafion N212, the anode is a platinum electrode, and the cathode is a lead electrode.

[0090] 2) Mix 3g acrylonitrile, 24g sodium dihydrogen phosphate, 4.5g potassium pentaborate, 1.2g tetrabutylammonium hydroxide and 150g water, and add them to the cathode chamber of the electrolytic cell.

[0091] 3) Heat the electrolytic cell to 40℃ to begin the electrolysis reaction. The current density of the electrolytic cell is 1000 A / m. 2 The electrolysis potential was 5V, and acrylonitrile was added to the cathode chamber at a rate of 1.5g / (A*h). The electrolysis reaction was completed after 30 hours, and samples were taken for testing. The catholyte was separated into an oil phase, and metal ions in the oil phase were extracted with water. Then, it was passed through a light phase removal tower at a bottom temperature of 150℃ to remove unreacted acrylonitrile and by-product propionitrile, and through a heavy phase removal tower at a bottom temperature of 210℃ to remove by-product hexanetrionitrile, thus obtaining adiponitrile product. The anolyte can be acidified by adding inorganic acid to lower the pH of the system to below 4, causing syringic acid molecules to precipitate from the water in an electrically neutral form. After acidification, the system was kept at a low temperature (0-5℃) and slowly stirred for a period of time. The crystallized suspension was poured into a Buchner funnel, and a vacuum pump was turned on to filter the filter cake. The soluble impurities adsorbed in the filter cake were washed away with pre-cooled deionized water or distilled water. After the above process was completed, pure syringic acid was obtained.

[0092] In this embodiment, the conversion rate of acrylonitrile was 80.2%, the selectivity of the synthesized adiponitrile was 88.8%, the conversion rate of syringaldehyde was 84.9%, the selectivity of the synthesized syringic acid was 95.3%, and the current efficiency was 139%.

[0093] Comparative Example 1

[0094] The method is the same as in Example 1, except that no octyl glucoside surfactant is added to the electrolyte, while other operations and conditions remain unchanged.

[0095] In this comparative example, the conversion rate of acrylonitrile was 77.9%, the selectivity of the synthesized adiponitrile was 87.5%, the conversion rate of syringaldehyde was 25.9%, the selectivity of the synthesized syringic acid was 44.8%, and the current efficiency was 89.3%.

Claims

1. An electrochemical process for the synthesis of pairs of syringic acid and adiponitrile, characterized by, The method comprises the following steps: 1) mixing syringaldehyde, alkaline electrolyte, alcohol solvent, alkyl glycoside surfactant and water, and adding them into the anode chamber of an electrolytic cell; 2) mixing acrylonitrile, phosphate, borate, quaternary ammonium base surfactant and water, and adding them into the cathode chamber of the electrolytic cell; 3) after warming the electrolyte in the anode and cathode chambers of the electrolytic cell, performing electrolysis reaction, syringaldehyde is electrochemically oxidized to synthesize syringic acid in the anode, and hydrated hydrogen ions cross the membrane to enter the cathode chamber to synthesize adiponitrile with acrylonitrile in the cathode.

2. The method of claim 1, wherein, In step 1), the alkaline electrolyte is selected from any one or a combination of at least two of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate, preferably potassium hydroxide and sodium hydroxide; and / or, in step 1), the alcohol solvent is any one or a combination of at least two of methanol, ethanol and propanol, preferably methanol and ethanol; and / or, in step 1), the alkyl glycoside surfactant is selected from any one or a combination of at least two of octyl glucoside, decyl maltoside and lauryl glucoside, preferably decyl maltoside and lauryl glucoside.

3. The method of claim 1 or 2, wherein, In step 1), the syringaldehyde, alkaline electrolyte, alcohol solvent, alkyl glycoside surfactant and water are added in a mass ratio of 1:2-6:5-15:0.1-0.5:5-15, preferably 1:3-5:8-10:0.2-0.4:10-15.

4. The method according to any one of claims 1 to 3, characterized in that, In step 2), the phosphate is selected from any one or a combination of at least two of dipotassium hydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate and sodium dihydrogen phosphate, preferably dipotassium hydrogen phosphate and disodium hydrogen phosphate; and / or, in step 2), the borate is selected from any one or a combination of at least two of potassium tetraborate, sodium pentaborate, sodium tetraborate and potassium pentaborate, preferably sodium pentaborate and potassium pentaborate; and / or, in step 2), the quaternary ammonium base surfactant is selected from any one or a combination of at least two of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide, preferably tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

5. The method according to any one of claims 1 to 4, characterized in that, In step 2), the acrylonitrile, phosphate, borate, quaternary ammonium base surfactant and water are added in a mass ratio of 1:3-10:0.5-2:0.1-0.5:40-80, preferably 1:5-8:1-1.5:0.2-0.4:30-50.

6. The method according to any one of claims 1 to 5, wherein, In step 3), the electrolysis temperature is 30-60°C, preferably 40-50°C; the electrolysis time is 10-40h, preferably 20-30h; and / or, in step 3), the electrolysis tank voltage interval is 4-9V, preferably 5-6V; the electrolysis current density is 500-2000A / m 2 , preferably 500-1000A / m 2 .

7. The method according to any one of claims 1 to 6, wherein In step 3), acrylonitrile can be optionally supplemented into the cathode chamber at a supplementing rate of 1.5-2.0 g / (A*h), i.e. the supplementing rate increases by 1.5-2.0 g / h for each increase of 1 A of electrolysis current.

8. The method according to any one of claims 1 to 7, wherein In step 3), after the electrolysis reaction is completed, the cathode liquid can be purified through phase separation, extraction, rectification and other treatment processes to obtain purified adiponitrile; and / or, in step 3), after the electrolysis reaction is completed, the anode liquid can be treated through acidification, cooling crystallization, water washing and other processes to obtain pure syringic acid.

9. The method according to any one of claims 1 to 8, wherein, The electrolysis is performed in an electrolytic cell, and the electrolytic cell comprises an anode, a cathode and a diaphragm; preferably the material of the electrolytic cell is polypropylene (PP), polytetrafluoroethylene (PTFE) or titanium, preferably titanium.

10. The method of any one of claims 1-9, wherein, The anode is selected from any one of a Pt electrode, a boron-doped diamond (BDD) electrode, or a Ti-based PbO2 electrode; the cathode is a lead electrode or a cadmium electrode; and the separator is one of Nafion N115, N117, NR211, or NR212.