Process for the synthesis of adiponitrile by electrooxidation of propionitrile

Abstract

The present application relates to a kind of electrochemical method for synthesizing adiponitrile with propionitrile as raw material.Adopt metal Au doped platinum group metal as anode.Propionitrile, water, supporting electrolyte, inorganic salt are mixed according to certain proportion, electrolysis reaction is carried out in diaphragmless electrolytic cell, and adiponitrile is obtained by directly refining electrolyte oil phase.The process flow is short, three wastes are less, conditions are mild, cost is extremely low, and it has extremely high industrialization prospect.

Description

Technical Field

[0001] This invention relates to an electrochemical method for synthesizing adiponitrile from propionitrile, belonging to the field of organic chemical technology. Background Technology

[0002] The electrolytic synthesis of adiponitrile from acrylonitrile has been industrialized. This process produces a large amount of propionitrile as a byproduct, and the resource utilization of propionitrile is an important source of profit growth for this process. Patent CN109988082B discloses a method for the continuous dehydrogenation preparation of acrylonitrile from propionitrile. Although this process route is simple and the subsequent separation process is short, the product acrylonitrile is a widely used petrochemical product with low price and low added value. Therefore, the conversion of propionitrile to acrylonitrile is not a superior route.

[0003] US Patent 2007 / 0161820A1 discloses a method for preparing propionic acid by hydrolysis of propionitrile. The downstream applications of propionic acid are mainly the preparation of propionate salts and their use as feed additives. In recent years, with the widespread adoption of low-cost ethylene carbonyl synthesis processes, the price of propionic acid has dropped to 7000-8000 yuan / ton. Therefore, the process of preparing propionic acid by propionitrile hydrolysis has low added value. Summary of the Invention

[0004] To address the above problems, this invention provides a method for electrolytically synthesizing adiponitrile using propionitrile as a raw material.

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

[0006] This invention provides an electrochemical method for synthesizing adiponitrile from propionitrile, comprising the following steps:

[0007] (1) Prepare an electrolyte by mixing propionitrile, water, supporting electrolyte, and inorganic salt additives in a certain proportion;

[0008] (2) A certain amount of electrolyte is introduced into the electrolytic cell, stirring is turned on, the electrolyte temperature is controlled, the anode and cathode plates are connected, and the electrolytic reaction is run in a constant current density manner.

[0009] (3) After the electrolysis reaction is completed, the reaction solution is allowed to stand to obtain an oil-water two-phase solution. The aqueous phase can be continuously reused after adding electrolyte. The oil phase is separated and purified to obtain adiponitrile.

[0010] Preferably, the supporting electrolyte in step (1) can be a quaternary ammonium base, such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyladamantylammonium hydroxide, benzyltrimethylammonium hydroxide, or ethyltrimethylammonium hydroxide; the mass content of the supporting electrolyte in the electrolyte is 0.2%-5%.

[0011] Preferably, the mass fraction of propionitrile in the electrolyte of step (1) is 1%-30%, more preferably 3%-9%.

[0012] Preferably, the inorganic salt additive in step (1) is disodium hydrogen phosphate or dipotassium hydrogen phosphate, and its content in the electrolyte is 5%-20%.

[0013] The core of this invention lies in the electrode design. If an electrode with an excessively high oxygen evolution overpotential is selected, propionitrile will undergo a degradation reaction; if the electrode's oxygen evolution overpotential is too low, the electrolysis reaction will produce more oxygen, causing hydrogen in the electrolysis tail gas to enter the explosion limit, posing a safety issue. During experiments, it was found that platinum group elements (Pt, Pd, Ir, Ru) have excellent catalytic ability for the electrolytic coupling of propionitrile to adiponitrile, but the electrodes are highly susceptible to organic poisoning. Within a short time, a large amount of organic precipitate adheres to the electrode surface, causing the reaction tank voltage to rise rapidly, and the reaction running time can only be maintained within 1 hour. To address these key issues, this invention employs a gold (Au) doping strategy during electrode preparation. It was found that gold has excellent resistance to propionitrile poisoning, the tank voltage can remain constant for 120 hours, and the reaction selectivity can be maintained above 75%.

[0014] Preferably, the cathode used in step (2) is a nickel-based electrode;

[0015] The anode is a metal-doped platinum group metal, with Au as the dopant and Pt, Pd, Ir, and Ru as the main platinum group metals, i.e., Pt-Au alloy, Pd-Au alloy, Ir-Au alloy, or Ru-Au alloy.

[0016] Preferably, the anode contains 5%-15% Au in various electrodes, based on a total molar amount of metal elements of 100%.

[0017] The method for preparing the metal-doped platinum group metal anode includes the following steps:

[0018] 1) Take appropriate amounts of platinum group metal (Pt, Pd, Ir, Ru) powder and gold powder as raw materials;

[0019] 2) Mix platinum group metal powder and gold powder in a certain proportion until uniform, wherein the molar fraction of gold element is maintained at 5%-15%;

[0020] 3) Add 1%-4% polyvinyl alcohol (PVA) adhesive by weight of the powder to the mixed powder and stir evenly to form a mixture with good plasticity;

[0021] 4) The mixture is placed into a mold and pressed to obtain a platinum group metal anode with the required shape and size;

[0022] 5) Sinter the electrodes, maintaining the sintering temperature at 700-1500℃ and controlling the sintering time at 30-200min to improve the density and strength of the electrodes.

[0023] Preferably, in step (2), the electrolyte temperature needs to be controlled at 25℃-80℃, more preferably 40℃-65℃.

[0024] Preferably, in step (2), the current density needs to be controlled within the range of 100-800 A / m. 2 .

[0025] The beneficial effects of this invention are as follows:

[0026] This method has a simple process, high selectivity for adiponitrile (up to 75%), generates no waste, and the aqueous electrolyte can be recycled, making it highly promising for industrialization. Detailed Implementation

[0027] To make the technical problem to be solved and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. Furthermore, the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] I. Main raw material information for the examples and comparative examples:

[0029] Propylene: Wanhua Chemical Group Co., Ltd.;

[0030] Tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyladamantylammonium hydroxide, benzyltrimethylammonium hydroxide, ethyltrimethylammonium hydroxide: Zhejiang Kent Catalytic Materials Technology Co., Ltd.;

[0031] Platinum group metals (Pt, Pd, Ir, Ru) powders and gold powders: Beijing Zhongke Keyou Technology Co., Ltd.

[0032] Unless otherwise specified, all other raw materials are commercially available products, and all reagents are of analytical grade.

[0033] II. Analysis and testing methods used in the embodiments:

[0034] Agilent gas chromatograph (GC2010 Plus): DB-5 column 30*0.32*0.25; FID2 detector; vaporization chamber temperature 260℃, detector temperature 300℃; temperature program: 50℃ for 2 min; 5℃ / min to 80℃; then 15℃ / min to 280℃, hold for 10 min.

[0035] Taking the preparation of Pt-Au alloy anodes as an example, the electrode preparation process is introduced:

[0036] 1) Mix 9g of platinum (Pt) metal powder and 1g of gold powder evenly, wherein the molar fraction of gold element is approximately 10%;

[0037] 2) Add 2% polyvinyl alcohol (PVA) adhesive to the mixed powder and stir evenly to form a mixture with good plasticity;

[0038] 3) The mixture is placed into an electrode mold and pressed to obtain a gold-doped Pt-Au alloy anode;

[0039] 4) The electrode is sintered at a temperature of 1000℃ for 90 minutes. The electrode is then formed and ready for use.

[0040] Example 1

[0041] Take 6g propionitrile, 80g water, 12g dipotassium hydrogen phosphate and 2g trimethyladamantyl ammonium hydroxide as the supporting electrolyte and place them in an electrolytic cell. Turn on the stirring and control the electrolyte temperature at 50℃. The anode is a 4cm anode prepared by the above method. 2 The Pt-Au alloy electrode uses a nickel electrode as the cathode, and the current density is controlled at 600 A / m. 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and the lower aqueous phase were analyzed, revealing a selectivity of 76% for adiponitrile and a current efficiency of 82%.

[0042] Using the above reaction conditions, the difference lies in changing the type and concentration of the supporting electrolyte. The results are as follows:

[0043] Example Supported electrolyte categories / content % Product selectivity / % Current efficiency / % 2 Benzyltrimethylammonium hydroxide / 2% 75 78 3 Ethyltrimethylammonium hydroxide / 3% 81 83 4 Tetrapropylammonium hydroxide / 4% 82 85 5 Tetramethylammonium hydroxide / 5% 83.5 86.6

[0044] Example 6

[0045] Take 3g propionitrile, 85g water, 10g disodium hydrogen phosphate, and 2g tetramethylammonium hydroxide (TMA) as the supporting electrolyte and place them in an electrolytic cell. Turn on the stirring and control the electrolyte temperature at 65℃. The anode is a 4cm anode prepared using the above method. 2 The Pt-Au alloy electrode uses a nickel electrode as the cathode, and the current density is controlled at 800 A / m. 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, revealing a selectivity of 83% for adiponitrile and a current efficiency of 72%.

[0046] Using the above reaction conditions, only the propionitrile content was changed during the experiment, and the results are as follows:

[0047]

[0048] Example 10

[0049] Take 6g propionitrile, 81.8g water, 12g dipotassium hydrogen phosphate, and 0.2g supporting electrolyte tetramethylammonium hydroxide and place them in an electrolytic cell. Turn on the stirring and control the electrolyte temperature at 40℃. The anode is a 4cm anode prepared by the above method. 2 The Pt-Au alloy electrode uses a nickel electrode as the cathode, and the current density is controlled at 100 A / m. 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, revealing a selectivity of 74.8% for adiponitrile and a current efficiency of 72%.

[0050] Example 11

[0051] Place 6g propionitrile, 85% water, 12g disodium hydrogen phosphate, and 2g tetramethylammonium hydroxide (TMA) as the supporting electrolyte in an electrolytic cell. Turn on the stirring and control the electrolyte temperature at 50℃. The anode should be 4cm thick. 2 A Pd-Au alloy electrode (10% Au molar fraction) is used, with a nickel cathode, and the current density is controlled at 600 A / m. 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, revealing a selectivity of 75% for adiponitrile and a current efficiency of 73%.

[0052] Example 12

[0053] Place 6g propionitrile, 80g water, 12g dipotassium hydrogen phosphate, and 2g tetramethylammonium hydroxide (TMA) as the supporting electrolyte in an electrolytic cell. Turn on the stirring and control the electrolyte temperature at 50℃. Use a 4cm anode. 2 A Pt-Au alloy electrode (5% Au molar fraction) is used, with a nickel cathode, and the current density is controlled at 600 A / m. 2 The reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, revealing a selectivity of 75.8% for adiponitrile and a current efficiency of 63.5%.

[0054] Using the above reaction conditions, only the molar content of Au in the anode was changed, and the results are as follows:

[0055]

[0056]

[0057] Comparative Example 1

[0058] The experimental method of Example 1 was used, except that the molar fraction of Au in the anode was reduced to 2%, and the reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, yielding an adiponitrile selectivity of 58% and a current efficiency of 45%.

[0059] Comparative Example 2

[0060] The experimental method of Example 1 was used, except that the propionitrile content in the electrolyte was reduced to 0.5%, and the reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, yielding an adiponitrile selectivity of 68.5% and a current efficiency of 34%.

[0061] Comparative Example 3

[0062] The experimental method of Example 1 was used, except that the supporting electrolyte content was reduced to 0.02%, and the reaction was stopped after 6 hours of electrolysis. The reaction solution was allowed to stand, and the upper oil phase and lower aqueous phase were analyzed, yielding an adiponitrile selectivity of 46% and a current efficiency of 42.6%.

Claims

1. An electrochemical process for the synthesis of adiponitrile starting from propionitrile, characterized in that, The method comprises the following steps: (1) preparing an electrolyte by mixing propionitrile, water, a supporting electrolyte, and an inorganic salt additive in a certain proportion; The supporting electrolyte is a quaternary ammonium base type, and the mass content of the supporting electrolyte in the electrolyte is 0.2wt%-5wt%; the mass fraction of propionitrile in the electrolyte is 1wt%-30wt%; (2) passing a certain amount of electrolyte into an electrolytic cell, starting stirring, controlling the temperature of the electrolyte, connecting the anode and cathode plates, and running the electrolysis reaction in a constant current density mode; the anode is a Au-doped platinum group metal, wherein the main platinum group metal is Pt, Pd, Ir, or Ru, and the molar fraction of the doped metal Au is 5%-15% based on the total molar amount of the metal elements being 100%; (3) after the electrolysis reaction is completed, the reaction liquid is allowed to stand to obtain oil and water two phases, the oil phase is separated, and refined adiponitrile is obtained.

2. The method of claim 1, wherein, The supporting electrolyte in step (1) is selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyladamantylammonium hydroxide, benzyltrimethylammonium hydroxide, and ethyltrimethylammonium hydroxide.

3. The method of claim 1, wherein, The inorganic salt additive in step (1) is selected from disodium hydrogen phosphate and / or dipotassium hydrogen phosphate.

4. The method according to claim 1 or 3, characterized in that, The content of the inorganic salt additive in the electrolyte is 5wt%-20wt%.

5. The method of claim 1, wherein, The temperature of the electrolyte in step (2) is 25℃-80℃.

6. The method of claim 5, wherein, The temperature of the electrolyte in step (2) is 40℃-65℃.

7. The method of claim 1, wherein, The current density in step (2) is in the range of 100-800 A / m 2 .

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