Electrolyte and electrolysis method for producing adiponitrile by electrolysis of acrylonitrile

Abstract

This invention discloses an electrolyte for the electrolysis of acrylonitrile to adiponitrile, comprising acrylonitrile, a modified quaternary ammonium salt, and water. The modified quaternary ammonium salt comprises functional groups represented by formulas (a) and (b): the functional group represented by formula (b) is an alkyl group in formula (a) having 0 to 6 carbon atoms; formula (b) is an alkyl group with n carbon atoms, n = 1 to 20; the modified quaternary ammonium salt contains 2 to 4 functional groups represented by formula (a). A method for electrolyzing acrylonitrile to adiponitrile using the above electrolyte is also disclosed. The electrolyte for the electrolysis of acrylonitrile to adiponitrile of this invention contains a modified quaternary ammonium salt, thereby improving the conversion rate and selectivity of the electrolysis of acrylonitrile to adiponitrile.

Description

Technical Field

[0001] This invention relates to the field of electrochemical synthesis, specifically to an electrolyte and electrolysis method for the electrochemical synthesis of adiponitrile from acrylonitrile. Background Technology

[0002] Adiponitrile (ADN) is an important organic chemical intermediate, mainly used in the production of materials such as polyhexamethylene adipamide (Nylon 66), 1,6-hexamethylene diisocyanate (HDI), and Nylon 610. It is estimated that approximately 90% of the world's adiponitrile is used to produce Nylon 66 annually. The process involves hydrogenating adiponitrile to produce hexamethylenediamine, which is then polycondensed with adipic acid to obtain a translucent or opaque milky-white synthetic resin (Nylon 66).

[0003] Adiponitrile has high technological barriers and investment thresholds, resulting in extremely high industry concentration. Adiponitrile manufacturers all have supporting hexamethylenediamine production facilities, with most of their capacity used for the production of hexamethylenediamine and nylon 66. Only a few companies have some surplus adiponitrile products for external sale. Invista almost monopolizes the global supply of adiponitrile, leading to a tight global adiponitrile market.

[0004] Industrial production technologies for adiponitrile include adipic acid catalytic amination (ADA), acrylonitrile electrolytic dimerization (AN), and butadiene cyanidation (BD). These technologies are primarily monopolized by a few companies such as Invista, BASF, and Asahi Kasei. Currently, there are no adiponitrile production facilities in China, and the product is entirely dependent on imports.

[0005] The electrolytic dimerization of acrylonitrile was initially industrialized by Monsanto. This process uses acrylonitrile as a raw material and electrochemically dimers it to adiponitrile. The electrolytic dimerization of acrylonitrile to adiponitrile has advantages such as a short process and high product quality. However, existing processes suffer from drawbacks such as low current density and low product selectivity; therefore, there is a need to develop more efficient synthesis methods. Summary of the Invention

[0006] To overcome the above-mentioned defects, the present invention provides an electrolyte for electrolyzing acrylonitrile to produce adiponitrile and a preparation method thereof.

[0007] This invention provides an electrolyte for the electrolysis of acrylonitrile to produce adiponitrile, comprising acrylonitrile, a modified quaternary ammonium salt, and water, wherein the modified quaternary ammonium salt comprises functional groups shown in formulas (a) and (b):

[0008]

[0009] The functional group shown in formula (b) is

[0010] In formula (a), R1 to R5 are alkyl groups with 0 to 6 carbon atoms, respectively; and in formula (b), an alkyl group with n carbon atoms, where n = 1 to 20.

[0011] The modified quaternary ammonium salt contains 2 to 4 functional groups as shown in formula (a). When the modified quaternary ammonium salt contains 2 functional groups as shown in formula (a), the free ends of the 2 functional groups as shown in formula (a) are connected by the 2 free ends of the functional group as shown in formula (b1). When the modified quaternary ammonium salt contains 3 functional groups as shown in formula (a), the free ends of the 3 functional groups as shown in formula (a) are connected by the 3 free ends of the functional group as shown in formula (b2). When the modified quaternary ammonium salt contains 4 functional groups as shown in formula (a), the free ends of the 4 functional groups as shown in formula (a) are connected by the 4 free ends of the functional group as shown in formula (b3).

[0012] According to one embodiment of the present invention, in the functional group shown in formula (a), R1 to R5 are alkyl groups having 0 to 4 carbon atoms, and in the functional group shown in formula (b), n is 4 to 6.

[0013] According to another embodiment of the present invention, the anion of the modified quaternary ammonium salt is one or more of hydroxide, hydrogen sulfate, dihydrogen phosphate, acetate, and nitrate.

[0014] According to another embodiment of the present invention, the content of the modified quaternary ammonium salt is 0.1 to 10 wt%, preferably 0.5 to 5 wt%.

[0015] According to another embodiment of the present invention, the electrolyte further contains 0.1 to 10 wt% EDTA or its sodium or potassium salt, and 0.01 to 5 wt% borax.

[0016] According to another embodiment of the present invention, the electrolyte further contains 1 to 20 wt% phosphate, wherein the phosphate is at least one selected from potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0017] According to another embodiment of the present invention, the acrylonitrile content is 3-7 wt%.

[0018] The present invention also provides a method for producing adiponitrile by electrolysis of acrylonitrile, wherein the above-mentioned electrolyte is used for the electrolysis reaction.

[0019] According to one embodiment of the present invention, the cathode of the electrolytic reaction is Cd or Pb or their alloy, and the anode is carbon steel or stainless steel.

[0020] According to another embodiment of the present invention, the reaction temperature of the electrolysis reaction is 30–70°C, and the current density is 200–5000 A / m. 2 .

[0021] The electrolyte for the electrolytic production of adiponitrile from acrylonitrile of the present invention contains a modified quaternary ammonium salt, thereby improving the conversion rate of acrylonitrile and the selectivity of adiponitrile. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments.

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The electrolyte for the electrolytic production of adiponitrile from acrylonitrile according to the present invention comprises acrylonitrile, a modified quaternary ammonium salt, and water, wherein the modified quaternary ammonium salt comprises functional groups shown in formulas (a) and (b):

[0025]

[0026] The functional group shown in equation (b) is

[0027] In formula (a), R1 to R5 are alkyl groups with 0 to 6 carbon atoms, respectively; and in formula (b), an alkyl group with n carbon atoms, where n = 1 to 20.

[0028] The modified quaternary ammonium salt contains 2 to 4 functional groups as shown in formula (a). When the modified quaternary ammonium salt contains 2 functional groups as shown in formula (a), the free ends of the 2 functional groups as shown in formula (a) are connected by the 2 free ends of the functional group as shown in formula (b1). When the modified quaternary ammonium salt contains 3 functional groups as shown in formula (a), the free ends of the 3 functional groups as shown in formula (a) are connected by the 3 free ends of the functional group as shown in formula (b2). When the modified quaternary ammonium salt contains 4 functional groups as shown in formula (a), the free ends of the 4 functional groups as shown in formula (a) are connected by the 4 free ends of the functional group as shown in formula (b3). The alkyl group in formula (b) is not limited to the form shown in the schematic diagram, but is an alkyl group composed of different carbons such as primary carbon, secondary carbon, quaternary carbon, and tertiary carbon. The alkyl group as a whole has 2 to 4 free ends, which are connected to the free ends in (a).

[0029] The functional group shown in formula (a) of the modified quaternary ammonium salt has a tetravalent N group. +The structural unit acts as an "inducer" in the electrolytic dimerization reaction of acrylonitrile, forming a hydrophobic layer on the electrode surface and increasing the solubility of acrylonitrile on the electrode surface. R1 to R5 are alkyl groups with 0 to 6 carbon atoms. When the number of carbon atoms in R1 to R5 is greater than 6, the steric hindrance is large, which is unfavorable for the formation of a hydrophobic layer on the electrode surface.

[0030] In the structure of the modified quaternary ammonium salt, the functional group shown in formula (b) serves to link multiple functional groups from formula (a) into a single molecular structure. In formula (b), n = 1 to 20. When n is greater than 20, the steric hindrance is large, which is not conducive to the formation of a hydrophobic layer on the electrode surface.

[0031] The modified quaternary ammonium salt containing formulas (a) and (b) has multiple functional groups of formula (a) linked in a single molecular structure, which enhances the induction of acrylonitrile electrolytic dimerization and increases the selectivity and conversion rate of the acrylonitrile electrolytic dimerization reaction.

[0032] In optional embodiments, R1 to R5 in the functional group shown in formula (a) are alkyl groups with 0 to 4 carbon atoms, and n in the functional group shown in formula (b) is 4 to 6. Within a preferred range, tetravalent N is used. + The smaller steric hindrance exposed in the electrolyte bulk is beneficial for increasing the selectivity and conversion rate of the acrylonitrile electrolytic dimerization reaction.

[0033] In an optional embodiment, the modified quaternary ammonium salt anion (A - () can be one or more of hydroxide, hydrogen sulfate, dihydrogen phosphate, acetate, and nitrate.

[0034] In optional embodiments, the content of the modified quaternary ammonium salt is 0.1–10 wt%. When the content of the modified quaternary ammonium salt in the electrolyte is less than 0.1 wt%, the content is too low to significantly affect the conversion rate and selectivity of the acrylonitrile electrolytic dimerization reaction; when it is greater than 10 wt%, the content is too high, resulting in high usage costs. Those skilled in the art can choose any value within the above range, such as, but not limited to, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc. Preferably, the content of the modified quaternary ammonium salt in the electrolyte is 0.5–5 wt%.

[0035] In an optional embodiment, to improve electrolysis efficiency, the electrolyte may also contain 0.1 to 10 wt% of EDTA or its sodium or potassium salt, and 0.01 to 5 wt% of borax.

[0036] In optional embodiments, the electrolyte may further contain 1-20 wt% phosphate, wherein the phosphate is at least one selected from potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. The phosphate serves to adjust the pH value of the electrolyte, and an appropriate phosphate content can be selected according to actual needs to achieve the desired pH value. For example, the phosphate concentration may be, but is not limited to, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, etc.

[0037] In an optional embodiment, the acrylonitrile content is 3–7 wt%. When the acrylonitrile content in the electrolyte is less than 3 wt%, the preparation efficiency is low; and the saturated solubility of acrylonitrile in the electrolyte is 7 wt%. Therefore, an acrylonitrile content of 3–7 wt% is preferred.

[0038] The present invention also provides a method for producing adiponitrile by electrolysis of acrylonitrile, wherein the above-mentioned electrolyte is used for the electrolysis reaction.

[0039] In an optional embodiment, the cathode of the electrolytic reaction is Cd or Pb or their alloys, and the anode is carbon steel or stainless steel.

[0040] In an optional embodiment, the electrolysis reaction temperature is 30–70°C, and the current density is 200–5000 A / m. 2 Current density less than 200 A / m 2 If the current density is greater than 5000 A / m, the production efficiency will be too low, requiring investment in more electrolytic cells to achieve the same production capacity; 2 If the current generates more heat, the side reactions will increase.

[0041] After the electrolysis reaction is completed, the electrolyte is mixed with crude adiponitrile to absorb the unreacted acrylonitrile. The mixture is then separated into an oil phase and an aqueous phase containing acrylonitrile, adiponitrile and organic by-products. The oil phase is then distilled to obtain acrylonitrile, crude adiponitrile and organic by-products.

[0042] The present invention is further described below through specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments and comparative examples are commercially available.

[0043] In the following examples, all reactions were carried out in an electrolytic cell with electrode dimensions of 100mm*200mm, with the anode and cathode positioned parallel to each other and spaced 3mm apart. The electrolyte was pumped and circulated, with a linear velocity of 1m / s within the electrolytic cell. Current was applied based on the current density and electrode area, and the reaction time was calculated based on a Faraday efficiency of 100%. Electrolysis was performed using the calculated current and reaction time. After the reaction was complete, the organic matter in the electrolyte was extracted with CH2Cl2 and weighed. The composition of the organic matter was analyzed chromatographically, and the acrylonitrile conversion and adiponitrile selectivity were calculated. All pressures used were gauge pressures. The test results are shown in Table 1.

[0044] The experimental conditions and results are calculated as follows:

[0045] Current = Electrode area × Current density;

[0046] Reaction time = (2 × mass of acrylonitrile × Faraday constant) / (molar mass of acrylonitrile × current);

[0047] Acrylonitrile conversion rate = (1 - mass of remaining acrylonitrile / mass of added acrylonitrile) × 100%;

[0048] Adiponitrile yield = (actual mass of adiponitrile received / theoretical mass of acrylonitrile completely converted to adiponitrile) × 100%;

[0049] The compounds of formulas (A) to (D) described in the examples are shown below:

[0050]

[0051] Example 1

[0052] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% of the modified quaternary ammonium salt shown in formula (B). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Pb, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0053] Example 2

[0054] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% of the modified quaternary ammonium salt shown in formula (B). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Cd, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0055] Example 3

[0056] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% of the modified quaternary ammonium salt shown in formula (C). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Cd, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0057] Example 4

[0058] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% of the modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Cd, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0059] Example 5

[0060] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 0.1 wt% of the modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Cd, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0061] Example 6

[0062] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 10 wt% of the modified quaternary ammonium salt shown in formula (D). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Cd, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0063] Comparative Example 1

[0064] The electrolyte used contains 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% tetrabutylammonium hydroxide. The pH of the electrolyte is adjusted to 8 by adding NaOH. The acrylonitrile concentration is 7 wt%. The cathode is Pb, the anode is carbon steel, and the current density is 1000 A / m. 2 .

[0065] Comparative Example 2

[0066] The electrolyte used contained 4 wt% sodium EDTA, 8 wt% sodium dihydrogen phosphate, 1 wt% borax, and 2 wt% of the modified quaternary ammonium salt shown in formula (A). The pH of the electrolyte was adjusted to 8 by adding NaOH. The acrylonitrile concentration was 7 wt%, the cathode was Pb, the anode was carbon steel, and the current density was 1000 A / m. 2 .

[0067] Table 1

[0068]

[0069]

[0070] As can be seen from the results in Table 1, the embodiments used in this invention have significantly better results.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An electrolyte for the electrolysis of acrylonitrile to adiponitrile, characterized in that, The mixture comprises acrylonitrile, a modified quaternary ammonium salt, and water, wherein the modified quaternary ammonium salt comprises functional groups represented by formulas (a) and (b): The functional group shown in formula (b) is In formula (a), R1 to R5 are alkyl groups with 0 to 6 carbon atoms, respectively; and in formula (b), an alkyl group with n carbon atoms, where n = 1 to 20. The modified quaternary ammonium salt contains 2 to 4 functional groups as shown in formula (a). When the modified quaternary ammonium salt contains 2 functional groups as shown in formula (a), the free ends of the 2 functional groups as shown in formula (a) are connected by the 2 free ends of the functional group as shown in formula (b1). When the modified quaternary ammonium salt contains 3 functional groups as shown in formula (a), the free ends of the 3 functional groups as shown in formula (a) are connected by the 3 free ends of the functional group as shown in formula (b2). When the modified quaternary ammonium salt contains 4 functional groups as shown in formula (a), the free ends of the 4 functional groups as shown in formula (a) are connected by the 4 free ends of the functional group as shown in formula (b3). The content of the modified quaternary ammonium salt is 0.1–10 wt%.

2. The electrolyte according to claim 1, characterized in that, In the functional group shown in formula (a), R1 to R5 are alkyl groups with 0 to 4 carbon atoms, and in the functional group shown in formula (b), n is 4 to 6.

3. The electrolyte according to claim 1, characterized in that, The modified quaternary ammonium salt has one or more of the following anions: hydroxide, hydrogen sulfate, dihydrogen phosphate, acetate, and nitrate.

4. The electrolyte according to claim 1, characterized in that, The content of the modified quaternary ammonium salt is 0.5–5 wt%.

5. The electrolyte according to claim 1, characterized in that, The electrolyte also contains 0.1 to 10 wt% EDTA or its sodium or potassium salt, and 0.01 to 5 wt% borax.

6. The electrolyte according to claim 1, characterized in that, The electrolyte also contains 1-20 wt% phosphate, wherein the phosphate is at least one of potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

7. The electrolyte according to claim 1, characterized in that, The acrylonitrile content is 3-7 wt%.

8. A method for producing adiponitrile by electrolysis of acrylonitrile, characterized in that, The electrolysis reaction is carried out using the electrolyte described in any one of claims 1-7.

9. The method according to claim 8, characterized in that, The cathode of the electrolytic reaction is Cd or Pb or their alloys, and the anode is carbon steel or stainless steel.

10. The method according to claim 8 or 9, characterized in that, The electrolysis reaction is carried out at a temperature of 30–70°C and a current density of 200–5000 A / m. 2 .

Images