Method for synthesizing menadione through in-tank indirect electrooxidation of 2-methylnaphthalene

Abstract

The invention relates to a method for synthesizing menadione through in-tank indirect electrooxidation of 2-methylnaphthalene. Metal titanium is used as a substrate, a Sn-Ir-doped titanium-based PbO2 electrode is prepared by adopting a coating method and is used as an electrolytic anode, and a Pb electrode is used as a cathode. 2-methylnaphthalene, a solvent, cobaltous sulfate, sulfuric acid, ammonium sulfate, an electrocatalyst and water are prepared into anolyte according to a certain proportion, a sulfuric acid aqueous solution serves as catholyte, an oil-water two-phase reaction solution is obtained from an anode in a two-phase electrolysis mode, an oil phase is directly refined to obtain menadione, and a water phase is reused after being refined. The method is short in technological process, few in three wastes, mild in condition and extremely low in cost, and has extremely high industrialization prospects.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing menadione by in-tank indirect electrooxidation of 2-methylnaphthalene, belonging to the technical field of organic chemical industry. Background Art

[0002] Menadione is a fat-soluble vitamin drug, a key intermediate for synthesizing vitamin K3, and an important raw material for fine chemicals, with wide applications in medicine and feed additives. The existing production of menadione mainly adopts the co-production process of dichromate oxidation and by-product chromium tanning agent. This process has disadvantages such as a large amount of chromium-containing wastewater, serious pollution, and complex process. Especially, the treatment problem of chromium-containing waste liquid has been plaguing the industrial production of menadione.

[0003] The literature "Process Study on Preparation of 2-Methyl-1,4-Naphthoquinone by Oxidation of 2-Methylnaphthalene with Cr(Ⅳ)" reported the indirect electrooxidation synthesis of menadione. Although hexavalent chromium can be recycled by electrolysis, chromium salts will remain in the menadione product, and a large amount of chromium-containing wastewater will inevitably be generated during the product refining process. Summary of the Invention

[0004] The present invention provides a method for synthesizing menadione by in-tank indirect electrooxidation of 2-methylnaphthalene, that is, Co 2+ is electrolytically oxidized at the anode to generate Co 3+ , and then the Co 3+ salt directly reacts with methylnaphthalene in the electrolytic cell to generate menadione. Through the design of the electrode and electrolyte system, the yield of menadione can be increased to more than 93%, and the current efficiency can reach more than 87%. This process flow is short, with less three wastes, mild conditions, and extremely low cost, having extremely high industrialization prospects.

[0005] To achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for synthesizing menadione by in-tank indirect electrooxidation of 2-methylnaphthalene, the method comprising the following steps:

[0007] (1) Prepare an anolyte by mixing 2-methylnaphthalene, a solvent, cobalt sulfate, sulfuric acid, ammonium sulfate, an electrocatalyst, and water in a certain proportion, and use a sulfuric acid aqueous solution with the same concentration as the sulfuric acid in the anolyte as the catholyte;

[0008] (2) Feed the anolyte and the catholyte into the electrolytic cell respectively, start stirring, control the electrolyte temperature, and operate the electrolytic reaction in a constant current density mode;

[0009] (3) After the electrolytic reaction is completed, obtain an oil-water two-phase reaction solution, where the oil phase is directly refined to obtain menadione, and the water phase can be refined and reused.

[0010] Preferably, the electrocatalyst in the step (1) is at least one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogensulfate, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, etc. In the anolyte, the content of the electrocatalyst is 0.2 wt% - 5 wt%, such as 1%, 2%, 3%, 4%, etc.

[0011] Preferably, in the anolyte of the step (1), the mass fraction of 2-methylnaphthalene is 5% - 30%, preferably 9% - 23%, such as 5%, 10%, 15%, 20%, etc.

[0012] It is necessary to use a suitable solvent to completely dissolve 2-methylnaphthalene, and the solvent is, for example, non-polar solvents such as cyclohexane, n-hexane, ethylcyclohexane, n-heptane, etc.

[0013] Preferably, in the anolyte of the step (1), the mass fraction of cobalt sulfate is 1% - 40%, preferably 2% - 5%, the mass fraction of sulfuric acid is 5% - 15%, and the mass fraction of ammonium sulfate is 1% - 5%.

[0014] Preferably, the anode used in the step (2) is a titanium-based PbO2 electrode doped with Sn-Ir, its substrate is a Ti mesh, and the coating is PbO2 doped with Sn-Ir;

[0015] The cathode is a lead electrode or a lead-based alloy electrode;

[0016] Preferably, based on the total mass of Sn, Ir, and PbO2 in the anode being 100%, the mass fraction of the main body PbO2 is preferably 65% - 95%; the mass fraction of the doped metal Sn is ≥2%, preferably 4% - 34%; the mass fraction of the doped metal Ir is 1% - 2.5%.

[0017] Preferably, in the step (2), it is necessary to control the electrolyte temperature to be 25°C - 95°C, preferably 55°C - 80°C.

[0018] Preferably, in the step (2), it is necessary to control the current density range to be 500 - 2000 A / m 2 .

[0019] Another aspect of the present invention provides a preparation method of a titanium-based PbO2 electrode doped with Sn-Ir.

[0020] The preparation method of the titanium-based PbO2 electrode doped with Sn-Ir includes the following steps:

[0021] 1) Take appropriate amounts of Sn, Ir, and PbO2 powders as raw materials;

[0022] 2) Mix Sn, Ir, and PbO2 evenly in a certain proportion;

[0023] 3) Add an adhesive to the mixed powder and stir evenly to form a mixture with good plasticity;

[0024] 4) Coat the mixture on a titanium mesh, put the whole into a mold for pressing, and obtain a doped Sn-Ir titanium-based PbO2 anode with the required shape and size;

[0025] 5) Sinter the electrode to obtain a doped Sn-Ir titanium-based PbO2 electrode;

[0026] Among them, the sintering temperature is maintained at 700 - 1500 °C, and the sintering time is controlled at 30 - 200 min to improve the density and strength of the electrode.

[0027] Among them, the adhesive described in step 3) can be polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), preferably polyvinyl alcohol (PVA); the dosage of the adhesive is 0.5% - 15% of the mass of the mixed powder, preferably 1% - 4%.

[0028] The core of the process of the present invention lies in the design of the electrode and the electrolyte system. For the design of the electrode, if an electrode with too high oxygen evolution overpotential is selected as the anode, the reaction of excessive oxidation and degradation of methylnaphthalene will occur, resulting in a low yield of menaquinone; if the oxygen evolution overpotential of the electrode is low, the main current efficiency of the anodic Co 2+ electrolytic oxidation to Co 3+ is too low, and the reaction of water electrolysis to generate oxygen will occur, resulting in a low space-time yield of menaquinone. The inventor found in the experiment that the doping of Sn-Ir metal has a good effect on reducing the oxygen evolution overpotential of lead dioxide. For the design of the electrolyte system, since the Co 3+ and methylnaphthalene in the tank-type process are an oil-water two-phase reaction and an appropriate amount of electrocatalyst needs to be added, the design of an electrocatalyst with a wide potential window is also crucial for improving the space-time yield of menaquinone.

[0029] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0030] (1) There is no need to use substances such as heavy metal chromium salts, ensuring the safety of the process;

[0031] (2) Using a small amount of metal cobalt salt as an intermediate medium, menaquinone is synthesized by one-step electrooxidation with a yield of more than 93%, no three wastes are generated, and the separation process is simple;

[0032] (3) The high oxygen evolution overpotential PbO2 electrode is doped with metals (Sn, Ir), the current efficiency is increased to more than 87%, and the electrolysis energy consumption is reduced. Detailed implementation mode

[0033] In order to make the technical problems to be solved and the beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. In addition, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] 1. Main raw material information of examples and comparative examples:

[0035] 2-Methylnaphthalene: Pengchen New Materials Technology Co., Ltd.;

[0036] Benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride: Beijing Inokai Co., Ltd.;

[0037] Sn, Ir, PbO2: Beijing Bailingwei Technology Co., Ltd.;

[0038] Unless otherwise specified, other raw materials were commercially available and reagents were of analytical grade.

[0039] 2. Analysis and testing methods used in the embodiments:

[0040] Agilent gas chromatograph (chromatograph model GC2010 Plus): chromatographic column DB-5 30*0.32*0.25; detector FID2; vaporization chamber temperature was 260°C, detector temperature was 300°C; program temperature rise: 50°C, 2 min; 5°C / min to 80°C; then 15°C / min to 280°C, and maintained for 10 min.

[0041] Example 1

[0042] The electrode containing 75% of PbO2 component, 24% of doped Sn and 1% of doped Ir component is prepared by a coating method, which mainly includes the following steps:

[0043] 1) Mix Sn, Ir and PbO2 in a certain proportion, wherein the mass fraction of PbO2 is 75%, the mass fraction of metal Sn is 24% and the mass fraction of metal Ir is 1%;

[0044] 2) Add 2% polyvinyl alcohol adhesive to the mixed powder and stir evenly to form a mixture with good plasticity;

[0045] 3) coating the mixture on a titanium mesh, placing the entire mesh into a mold, and pressing the mesh to obtain a Sn-Ir-doped titanium-based PbO2 anode having a shape and size that meets the requirements;

[0046] 4) Sintering treatment is performed at a sintering temperature of 1200° C. and a sintering time of 90 min to obtain a titanium-based PbO2 electrode doped with Sn and Ir that meets the requirements.

[0047] Take 10 g of 2-methylnaphthalene and 30 g of cyclohexane to prepare the electrolyte oil phase. Separately, take 5 g of cobalt sulfate, 15 g of 98% concentrated sulfuric acid, 3 g of benzyltriethylammonium chloride, 37 g of deionized water, and 1.5 g of ammonium sulfate and mix them thoroughly to prepare the electrolyte aqueous phase. Place the prepared electrolyte aqueous phase and oil phase in the anode chamber of the electrolytic cell. Mix 15 g of 98% concentrated sulfuric acid with 86.5 g of deionized water thoroughly to prepare the electrolyte and place it in the cathode chamber. Start stirring, control the electrolyte temperature at 65 °C, and use an electrode with 75% PbO2 component, 24% doped Sn, and 1% doped Ir prepared by the above method at the anode, with a 4 cm 2 electrode. Use a 4 cm 2 lead electrode at the cathode, control the current density at 1500 A / m 2 , and stop the reaction after electrolysis for 6 h. Let the anode reaction solution stand still, take the upper oil phase for refining analysis to obtain menadione, and analyze that the yield of menadione is 94% and the current efficiency is 88%.

[0048] Example 2

[0049] Take 12 g of 2-methylnaphthalene and 25 g of cyclohexane to prepare the electrolyte oil phase. Separately, take 4 g of cobalt sulfate, 12 g of 98% concentrated sulfuric acid, 2 g of tetrabutylammonium bromide, 40 g of deionized water, and 1.5 g of ammonium sulfate and mix them thoroughly to prepare the electrolyte aqueous phase. Place the prepared electrolyte aqueous phase and oil phase in the anode chamber of the electrolytic cell. Mix 12 g of 98% concentrated sulfuric acid with 84.5 g of deionized water thoroughly to prepare the electrolyte and place it in the cathode chamber. Start stirring, control the electrolyte temperature at 70 °C, and use an electrode with 75% PbO2 component, 24% doped Sn, and 1% doped Ir prepared by the above method at the anode, with a 4 cm 2 electrode. Use a 4 cm 2 lead electrode at the cathode, control the current density at 1000 A / m 2 , and stop the reaction after electrolysis for 6 h. Let the reaction solution stand still, take the upper oil phase for refining analysis to obtain menadione, and analyze that the yield of menadione is 95.6% and the current efficiency is 89.5%.

[0050] Example 3

[0051] Take 15 g of 2-methylnaphthalene and 28 g of ethylcyclohexane to prepare the electrolyte oil phase. Separately, take 3 g of cobalt sulfate, 10 g of 98% concentrated sulfuric acid, 2.5 g of tetrabutylammonium chloride, 45 g of deionized water, and 3 g of ammonium sulfate and mix them thoroughly to prepare the electrolyte aqueous phase. Place the prepared electrolyte aqueous phase and oil phase in the anode chamber of the electrolytic cell. Mix 10 g of 98% concentrated sulfuric acid with 96.5 g of deionized water thoroughly to prepare the electrolyte and place it in the cathode chamber. Start stirring, control the electrolyte temperature at 90 °C, and use a 4 cm 2 electrode with 93% PbO2 component, 5% doped Sn, and 2% doped Ir at the anode. Use a 4 cm2 Lead-antimony alloy electrode, controlled current density 500A / m 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase was taken for refined analysis to obtain menadione. The yield of menadione was 97.3% and the current efficiency was 90.5%.

[0052] Comparative Example 1

[0053] The experimental method in Example 3 was used, the only difference being that the anode was 4 cm 2 The electrode contains 60% PbO2 component and 40% doped Sn component. The reaction is stopped after 6 hours of electrolysis. The reaction solution is allowed to stand, and the upper oil phase is taken for refined analysis to obtain menadione. The analysis shows that the yield of menadione is 81% and the current efficiency is 72%.

[0054] Comparative Example 2

[0055] The experimental method in Example 3 was used, except that no electrocatalyst was added. The experimental conditions were as follows:

[0056] 15 g of 2-methylnaphthalene and 28 g of ethylcyclohexane were prepared as the electrolyte oil phase, and 3 g of cobalt sulfate, 10 g of 98% concentrated sulfuric acid, 45 g of deionized water, and 3 g of ammonium sulfate were mixed to prepare the electrolyte water phase. The prepared electrolyte water phase and oil phase were placed in the anode chamber of the electrolytic cell, and 10 g of 98% concentrated sulfuric acid was mixed with 94 g of deionized water to prepare the electrolyte and placed in the cathode chamber; stirring was started, the electrolyte temperature was controlled at 90°C, and the anode was 4 cm 2 The electrode contains 93% PbO2, 5% doped Sn and 2% doped Ir. The cathode uses 4 cm 2 Lead-antimony alloy electrode, controlled current density 500A / m 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase was taken for refined analysis to obtain menadione. The yield of menadione was 73.5% and the current efficiency was 68.2%.

[0057] The present invention reduces the oxygen evolution overpotential of the electrode by doping and modifying the electrode, and improves the selectivity and current efficiency of menadione. The process is short, has little three wastes, mild conditions, extremely low cost, and has extremely high industrialization prospects.

Claims

1. A method for synthesizing menadione by indirect electro-oxidation of 2-methylnaphthalene in a tank, characterized in that, The method includes the following steps: (1) Prepare an anolyte by mixing 2-methylnaphthalene, a solvent, cobalt sulfate, sulfuric acid, ammonium sulfate, an electrocatalyst, and water in a certain proportion, and use an aqueous sulfuric acid solution with the same concentration as the sulfuric acid in the anolyte as the catholyte; (2) Pass the electrolyte into an electrolytic cell, control the temperature of the electrolyte, and operate the electrolytic reaction at a constant current density; (3) After the electrolytic reaction is completed, obtain an oil-water two-phase reaction solution, and directly refine the oil phase to obtain menadione.

2. The method according to claim 1, characterized in that The electrocatalyst in step (1) is at least one of benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogensulfate, trioctylmethylammonium chloride, and dodecyltrimethylammonium chloride; preferably, the content of the electrocatalyst in the anolyte is 0.2%-5%.

3. The method according to claim 1, wherein In the electrolyte of step (1), the mass fraction of 2-methylnaphthalene is 5%-30%, preferably 9%-23%.

4. The method according to claim 1, characterized in that In the electrolyte of step (1), the mass fraction of cobalt sulfate is 1%-40%, preferably 2%-5%.

5. The method according to claim 1, characterized in that In the electrolyte of step (1), the mass fraction of sulfuric acid is 5%-15%.

6. The method according to claim 1, wherein In the electrolyte of step (1), the mass fraction of ammonium sulfate is 1%-5%.

7. The method according to claim 1, characterized in that, In step (2), the anode used is a titanium-based PbO2 electrode doped with Sn-Ir.

8. The method according to claim 7, characterized in that, Based on the total mass of Sn, Ir, and PbO2 in the anode being 100%, the mass fraction of PbO2 is 65%-95%; the mass fraction of the doped metal Sn is ≥2%, preferably 4%-34%; the mass fraction of the doped metal Ir is 1%-2.5%.

9. The method according to any one of claims 1-8, characterized in that, In step (2), the temperature of the electrolyte is 25°C-95°C, preferably 55°C-80°C.

10. The method according to any one of claims 1-8, characterized in that, In the step (2), the current density range is 500 - 2000 A / m 2 .