CN113774413A

CN113774413A - Method for preparing adiponitrile by safely and efficiently electrolyzing acrylonitrile in single-phase solution

Info

Publication number: CN113774413A
Application number: CN202111165008.XA
Authority: CN
Inventors: 梁长海; 齐骥; 安紫缨; 李闯; 陈霄
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2021-12-10

Abstract

The invention belongs to the technical field of adiponitrile preparation, and discloses a method for preparing adiponitrile by safely and efficiently electrolyzing acrylonitrile in a single-phase solution, which can realize the efficient and safe electrolysis of acrylonitrile in a high-concentration acrylonitrile-containing single-phase solution. The used electrolyte is added with 2-10 wt% of cosolvent, so that the high-concentration acrylonitrile water-based electrolyte containing 4-15 wt% of acrylonitrile can exist in a single-phase mixed capacity mode, on one hand, the processing flux of a reaction system is increased by improving the solubility of acrylonitrile, on the other hand, the solution conductivity is enhanced, the energy consumption is reduced, meanwhile, the contact probability of anode oxygen of an electrolytic cell with a reactant acrylonitrile and a product adiponitrile is reduced, fire and explosion are avoided, the whole electrolytic process is safe and efficient, finally, the adiponitrile selectivity can reach 90%, and the yield can reach 85%.

Description

Method for preparing adiponitrile by safely and efficiently electrolyzing acrylonitrile in single-phase solution

Technical Field

The invention relates to the technical field of adiponitrile preparation, and particularly discloses a method for preparing adiponitrile by electrolyzing acrylonitrile in a single-phase electrolyte, which can realize efficient and safe electrolysis of acrylonitrile in a high-concentration acrylonitrile-containing single-phase solution.

Background

Adiponitrile is an important precursor of nylon 66, adiponitrile and hydrogen are added to generate hexamethylene diamine, and the hexamethylene diamine and adipic acid react to generate nylon 66 salt under a strict material ratio. Adiponitrile, an important intermediate for synthesizing nylon 66, is the most important and valuable industrial application developed by adiponitrile, belongs to a highly oligopolistic product, and has CR5 of more than 80 percent. The worldwide adiponitrile industrialization process route mainly comprises three processes of a butadiene process, an acrylonitrile electrolytic dimerization process and an adipic acid catalytic ammoniation process, and the technology mainly focuses on 5 companies of United states England (the former is DuPont textile and indoor decoration company), French Rodiya company, Germany Basff (Sorvey), Japan Asahi chemical industry and China Huafeng group (pause production). At present, the butadiene method is adopted in the world for more than 50 percent of capacity, the acrylonitrile electrolytic dimerization method also occupies a large part of market share, however, the process route is popularized in China and cannot be realized on a large scale because of the limitation of the problems of efficiency and safety.

The M.M. Baizer group patented the electrolytic synthesis of adiponitrile from acrylonitrile in 1963, disclosed a process for producing adiponitrile by electrolyzing acrylonitrile in a diaphragm type electrolytic cell, and realized the industrialization of the electrolytic synthesis of adiponitrile in 1965 by Monsanto, USA, in which "two-phase process" was abbreviated because of the separation of oil and water layers between acrylonitrile and adiponitrile. The efficiency of this process is problematic due to the low solubility of acrylonitrile in water. Through research and improvement, Asahi chemical company develops an emulsion process in 1969, increases the solubility of acrylonitrile, and realizes the electro-synthesis of adiponitrile by the hydrodimerization of acrylonitrile emulsion in an electrolytic bath. Similarly, Belgian Union Chemicals has also achieved the electrosynthesis of adiponitrile using an emulsion process in a diaphragm-free electrolytic cell. The cathode used in the method is graphite, the anode is a magnet, the adopted electrolyte is microemulsion, and sodium hexametaphosphate is added as an anticorrosive agent. Although the emulsion method improves the solubility of acrylonitrile to a certain extent, the total dissolved amount and the conductivity of the electrolyte still have room for improvement. It is worth mentioning that the electrolytic dimerization of acrylonitrile must avoid the direct contact of the products of high concentration with the oxygen generated at the anode, otherwise there will be a great safety risk of combustion and explosion.

For the two-phase method, the number of acrylonitrile molecules participating in the reaction within the whole reaction system time is insufficient due to the low solubility of acrylonitrile, and finally, the treatment efficiency of the whole reaction system needs to be improved. In the emulsion method, although the solubility of acrylonitrile can be improved to a certain extent by using emulsion or microemulsion for electrolysis, the contact efficiency between reactants and electrodes still needs to be improved, and thus, a larger promotion space is provided in terms of treatment capacity. In addition, the process needs to add a demulsification separation process, and also increases the power consumption because the conductivity of the electrolyte is lower. The invention provides a new method for synthesizing adiponitrile by electrolyzing acrylonitrile in a diaphragm-free electrolytic tank by using a single-phase miscible acrylonitrile solution instead of a two-phase solution, an emulsion or a microemulsion. Finally, on the premise of ensuring the yield of adiponitrile, the efficiency and the safety of the whole system are improved. Specific representative known techniques, and corresponding lifting spaces, are summarized as follows:

belgian patent, publication No.: BE631302, describes a process for the two-phase electrolysis of acrylonitrile to adiponitrile by subjecting the lower aqueous electrolyte solution containing the reactants to continuous electrolysis and the organic phase containing the products is removed gradually from the upper layer of the solution. Because the solubility of acrylonitrile in water is low, the treatment flux of the reaction system is low, and the equipment investment is high under the condition of the same yield.

Japanese patent, publication No.: JP45024129B discloses a process for the preparation of adiponitrile by electrolysis of acrylonitrile in an emulsion, the adiponitrile selectivity being high. Although the emulsion method improves the solubility of acrylonitrile to a certain extent, the total dissolution amount still has room for improvement, and the conductivity of the emulsion needs to be improved to reduce energy consumption.

Chinese patent, publication No.: CN105543888A introduces a method for preparing adiponitrile by electrolyzing acrylonitrile, and reduces electrode corrosion during electrolysis by adding biquaternary ammonium salt and borax into electrolyte, so that the selectivity and current efficiency of adiponitrile reach more than 90%, and the consumption of biquaternary ammonium salt is reduced. The method is a two-phase diaphragm-free method, and the flux and safety of acrylonitrile treatment have the potential of improvement.

Disclosure of Invention

The invention provides a new method for synthesizing adiponitrile by electrolyzing acrylonitrile in a diaphragm-free electrolytic tank by using a single-phase miscible acrylonitrile solution to replace a two-phase solution, an emulsion or a microemulsion, and the efficiency and the safety of the whole system are improved on the premise of ensuring the selectivity and the yield of the adiponitrile.

In order to achieve the above object, the technical solution of the present invention:

a method for preparing adiponitrile by efficiently electrolyzing acrylonitrile in a single-phase solution comprises the following steps:

first, a basic electrolytic aqueous solution is prepared: 8 to 15 weight percent of phosphate, 0.1 to 3 weight percent of EDTA salt and 1 to 10 weight percent of borax; then, before the reaction, a reaction solution was prepared: 2 to 10 weight percent of cosolvent, 4 to 15 weight percent of acrylonitrile, 0.1 to 5 weight percent of quaternary ammonium salt and the balance of basic electrolytic aqueous solution; the pH value of the phosphate adjusting electrolyte used as the supporting electrolyte and the acid-base adjusting reagent is about 7-9.

The cosolvent is one of N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoric triamide and N-methylpyrrolidone.

The supporting electrolyte used in the present invention is sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate or potassium dihydrogen phosphate.

In the diaphragm-free electrolytic cell, usable anode materials are DSA stable anodes, iridium-tantalum coatings, ruthenium-titanium coatings and the like; the cathode material is Pb or Cd; the electrosynthesis of ADN was performed using the following electrode pairs: iridium tantalum (+) -Pb (-), iridium tantalum (+) -Cd (-), ruthenium titanium (+) -Pb (-), iridium titanium (+) -Pb (-), or ruthenium titanium (+) -Cd (-); any one of the electrode pairs and the reference electrode (saturated calomel electrode) form a three-electrode system.

By the method, ADN can be produced by electrolysis of single-phase electrolyte in a diaphragm-free electrolytic cell.

The invention has the beneficial effects that: the invention adds the cosolvent and the like into the electrolyte to form single-phase electrolyte, thereby improving the molecular concentration of acrylonitrile in a water phase in the electrolyte and increasing the treatment capacity and the reaction efficiency. In addition, the electrolyte reduces the contact degree of the reactant acrylonitrile product adiponitrile and oxygen generated by the anode, and reduces the safety risk of combustion and explosion. The method realizes the synthesis of adiponitrile by electrolyzing acrylonitrile safely and efficiently, and finally the adiponitrile selectivity can reach 90 percent and the yield can reach 85 percent.

Detailed Description

The process of the present invention is further illustrated below with reference to specific examples.

Example 1

Charging an electrolyte into a diaphragm-free electrolytic cell: the electrolyte of the aqueous solution contains 8 wt% of AN and 8 wt% of Na₂HPO4, 3 wt% disodium EDTA, 5 wt% borax, 3 wt% tetraethylammonium hydroxide and 4ml dmf, pH 7.

Adopts iridium tantalum DSA as an anode and Pb as a cathode, and the effective size of each plate is 2 x 2cm²。

Passing a current at 30 ℃ with a current density of 750 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After electrolysis for 2h, the yield y (ADN) of the product ADN was 87.91%, and the selectivity s (ADN) was 89.44%.

Example 2

The same procedure as in example 1 was followed, except that the electrolyte formulation was: containing 8 wt% of AN and 7% of K₂HPO4, 3 wt% potassium EDTA, 6 wt% borax, 4ml DMF and 3 wt% tetrabutylammonium hydroxide, the pH of the electrolyte being 8.

At 30 ℃, the current density is 500 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After electrolysis for 2h, the yield y (ADN) of the product ADN was 86.12%, and the selectivity s (ADN) was 95.83%.

Example 3

The same procedure as in example 1 was followed, except that the electrolyte formulation was: containing 7 wt% of AN and 5 wt% of K₂HPO4, 3 wt% EDTA, 7% borax, 3.5ml DMF and 3 wt% tetrapropylammonium phosphate, the pH of the electrolyte was 7.

Adopting ruthenium titanium DSA as anode and Pb as cathode, the effective size of each plate is 4 x 4cm²。

At 35 ℃, the current density is 1000 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After 2h electrolysis, the yield y (ADN) of the product ADN was 83.3%, and the selectivity s (ADN) was 94.5%.

Example 4

The same procedure as in example 1 was followed, except that the electrolyte formulation was: containing 6 wt% of AN and 7 wt% of K₂HPO4, 2 wt% EDTA, 5 wt% borax, 3ml DMSO, and 3 wt% ethylammonium dihydrogen phosphate, and the pH of the electrolyte was 7.

Adopting DSA of ruthenium and titanium as anode and Cd as cathode, the effective size of each plate is 3 x 3cm²。

At 40 ℃, the current density is 875 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After 2h electrolysis, the yield y (ADN) of the product ADN was 73.4%, and the selectivity s (ADN) was 87%.

Example 5

The same procedure as in example 1 was followed, except that the electrolyte formulation was: containing 7 wt% of AN and 12 wt% of K₂HPO4, 1 wt% EDTA, 5 wt% borax, 3.5ml DEF, and 4 wt% tetraethylammonium hydroxide, the pH of the electrolyte was 9.

Adopting ruthenium titanium DSA as anode and Pb as cathode, the effective size of each plate is 2 x 2cm²。

Passing a current at 35 deg.C with a current density of 750 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After 2h electrolysis, the yield y (ADN) of the product ADN was 80.1%, and the selectivity s (ADN) was 90.5%.

Example 6

The same procedure as in example 1 was followed, except that the electrolyte was formulated: containing 10 wt% of AN and 10 wt% of K₂HPO4, 2 wt% EDTA, 6 wt% borax, 4.5ml DMF and 3 wt% tetraethylammonium phosphate, the pH of the electrolyte was 8.

Adopts iridium tantalum DSA as an anode and Pb as a cathode, and the effective size of each plate is 3 x 4cm²。

At 30 ℃, the current density is 700 A.m^-2The direct current of (2) is used for carrying out the electrosynthesis reaction.

After 2h electrolysis, the yield y (ADN) of the product ADN was 77.2%, and the selectivity s (ADN) was 83.58%.

Claims

1. A method for preparing adiponitrile by efficiently electrolyzing acrylonitrile in a single-phase solution is characterized by comprising the following steps: firstly, preparing a single-phase electrolyte solution, and adding a cosolvent to ensure that the single-phase electrolyte solution is transparent and uniform when the concentration of acrylonitrile reaches a higher range; the single-phase electrolyte solution comprises the following components in percentage by mass in a reaction system: 8 to 15 weight percent of phosphate, 0.1 to 3 weight percent of EDTA salt, 1 to 10 weight percent of borax, 0.1 to 5 weight percent of quaternary ammonium salt, and the balance of deionized water; then the single-phase electrolyte solution is filled into a diaphragm-free electrolytic cell, the temperature of the single-phase electrolyte solution is 25-60 ℃ during electrolysis, and the current density is 500-2000A/m²The method for preparing adiponitrile has the advantages that the single-phase electrolyte solution is transparent and uniform in the whole process, and no emulsification or phase separation exists.

2. The method of claim 1, wherein: the cosolvent is one of N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoric triamide and N-methylpyrrolidone.

3. The method according to claim 1 or 2, characterized in that: the mass fraction of the cosolvent in the system is 2-10 wt%.

4. The method according to claim 1 or 2, characterized in that: the mass fraction of the acrylonitrile in the system is 4 wt% -15 wt%.

5. The method of claim 3, wherein: the mass fraction of the acrylonitrile in the system is 4 wt% -15 wt%.

6. The method of claim 1, 2 or 5, wherein: the phosphate is one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

7. The electrolyte for preparing adiponitrile by electrolyzing acrylonitrile according to claim 3, wherein: the phosphate is one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

8. The method of claim 4, wherein: the phosphate is one of sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

9. The method of claim 1, 2, 5, 7 or 8, wherein: the anode material of the diaphragm-free electrolytic cell is an iridium tantalum coating which is coated on a titanium substrate, and the cathode material is lead or cadmium.

10. The method of claim 6, wherein: the anode material of the diaphragm-free electrolytic cell is iridium tantalum, ruthenium titanium, iridium titanium or ruthenium titanium, and the coating is coated on the titanium substrate, and the cathode material is lead or cadmium.